Georgios Anagnostou

Abstract The article revisits the classic problem of tunnel face stability with special emphasis on the effect of horizontal stresses. These are important for shear resistance and thus also for the equilibrium of the potentially unstable body in front of the tunnel face, but they also present the difficulty of static indeterminacy. Starting from the computational model of Anagnostou and Kovári, an alternative model is presented, which is based on the so‐called method of slices, and is consistent with silo theory, but does not need an a priori assumption as to the distribution of horizontal stress. In addition, a simple design equation for estimating support pressure under this model is presented and the results of comparative analyses concerning the average stresses in the wedge and the effects of shear resistance at the lateral slip surfaces are shown. The analytical results obtained by the method of slices agree very well with published results of numerical analyses and physical tests. Beitrag der räumlichen Tragwirkung zur Stabilität der Tunnelbrust. Der vorliegende Artikel untersucht das klassische Problem der Stabilität der Ortsbrust unter besonderer Beachtung der Horizontalspannungen. Letztere sind zwar sehr wichtig für den Gleitwiderstand und somit auch für die Stabilität von potenziellen Bruchkörpern, können aber nicht allein aufgrund von Gleichgewichtsbetrachtungen ermittelt werden. Im Beitrag wird eine Berechnungsmethode vorgestellt, die das Berechnungsmodell nach Anagnostou und Kovári insofern verbessert, dass sie keine a priori Annahme über die Verteilung der Spannungen im keilförmigen Bruchkörper vor der Ortsbrust benötigt und auf konsistente Weise das Gleichgewicht im Keil und im darüber liegenden prismatischen Bruchkörper analysiert. Basierend auf der Lamellenmethode wird eine einfache Bemessungsformel aufgestellt und der Einfluss der horizontalen Verspannung auf den erforderlichen Stützdruck der Ortsbrust aufgezeigt. Die Modellprognosen stimmen mit veröffentlichten Ergebnissen von numerischen Spannungsanalysen sowie mit Versuchsresultaten gut überein.

This paper proposes a decentralized derivative-free dynamic state estimation method in the context of a power system with unknown inputs, to address cases when system linearization is cumbersome or impossible. The suggested algorithm tackles situations when several inputs, such as the excitation voltage, are characterized by uncertainty in terms of their status. The technique engages one generation unit only and its associated measurements, and it remains totally independent of other system wide measurements and parameters, facilitating in this way the applicability of this process on a decentralized basis. The robustness of the method is validated against different contingencies. The impact of parameter errors, process, and measurement noise on the unknown input estimation performance is discussed. This understanding is further supported through detailed studies in a realistic power system model.

The CMS detector team describes their experiment and observation of decay products from a standard model Higgs boson, allowing its mass to be determined.

In this paper we investigate the interaction between yielding supports and squeezing ground by means of spatial numerical analyses that take into account the stress history of the ground. We also present design nomograms which enable the rapid assessment of yielding supports. The idea behind yielding supports is that squeezing pressure will decrease by allowing the ground to deform. When estimating the amount of deformation required, one normally considers the characteristic line of the ground, i.e. the relationship between the ground pressure and the radial displacement of the tunnel wall under plane strain conditions. The computation of the characteristic line assumes a monotonic decrease of radial stress at the excavation boundary, while the actual tunnel excavation and subsequent support installation involve a temporary complete radial unloading of the tunnel wall. This difference, in combination with the stress path dependency of the ground behavior, is responsible for the fact that the results obtained by spatial analysis are not only quantitatively, but also qualitatively different from those obtained by plane strain analysis. More specifically, the relationship between ground pressure and deformation at the final state prevailing far behind the face is not unique, but depends on the support characteristics, because these affect the stress history of the ground surrounding the tunnel. The yield pressure of the support, i.e. its resistance during the deformation phase, therefore proves to be an extremely important parameter. The higher the yield pressure of the support, the lower will be the final ground pressure. A targeted reduction in ground pressure can be achieved not only by installing a support that is able to accommodate a larger deformation (which is a well-known principle), but also by selecting a support that yields at a higher pressure.

SUMMARY The ground response to tunnel excavation is usually described in terms of the characteristic line of the ground (also called ‘ground response curve’, GRC), which relates the support pressure to the displacement of the tunnel wall. Under heavily squeezing conditions, very large convergences may take place, sometimes exceeding 10–20% of the excavated tunnel radius, whereas most of the existing formulations for the GRC are based on the infinitesimal deformation theory. This paper presents an exact closed‐form analytical solution for the ground response around cylindrical and spherical openings unloaded from isotropic and uniform stress states, incorporating finite deformations and linearly elastic‐perfectly plastic rock behaviour obeying the Mohr–Coulomb failure criterion with a non‐associated flow rule. Additionally, the influence of out‐of‐plane stress in the case of cylindrical cavities under plane‐strain conditions is examined. The solution is presented in the form of dimensionless design charts covering the practically relevant parameter range. Finally, an application example is included with reference to a section of the Gotthard Base tunnel crossing heavily squeezing ground. The expressions derived can be used for preliminary convergence assessments and as valuable benchmarks for finite strain numerical analyses. Copyright © 2014 John Wiley & Sons, Ltd.

A study of b quark hadronisation is presented using inclusively reconstructed B hadrons in about four million hadronic Z decays recorded in 1992-2000 with the OPAL detector at LEP. The data are compared to different theoretical models, and fragmentation function parameters of these models are fitted. The average scaled energy of weakly decaying B hadrons is determined to be <xe>=0.7193+-0.0016(stat)+0.0036-0.0031(syst)

The interplay between support systems and the rock when tunneling under squeezing conditions is normally studied by means of two-dimensional analyses. The present paper shows that the underlying plane strain assumption involved in a two-dimensional analysis may lead, under certain conditions, to ground pressure and deformation values that are considerably lower than those produced by stress analyses that take into account spatial effects in the vicinity of the tunnel face. The differences are due to the stress path dependency in the elasto-plastic behavior of the ground and, more specifically, to the inability of the plane strain model to map the actual radial stress history, which involves a complete radial unloading (and, later, a re-loading) of the tunnel boundary over the unsupported span. This inherent weakness of any plane strain analysis is relevant from the design standpoint, particularly for heavily squeezing conditions that require a yielding support. For the majority of tunneling conditions and methods, however, involving as they do the completion of a stiff support within a few meters of the face, the errors introduced by the plane strain assumption are not important from a practical point of view.

This paper proposes a rigorous anomaly detection scheme, developed to spot power system operational changes which are inconsistent with the models used by operators. This novel technique relies on a state observer, with guaranteed estimation error convergence, suitable to be implemented in real time, and it has been developed to fully address this important issue in power systems. The proposed method is fitted to the highly nonlinear characteristics of the network, with the states of the nonlinear generator model being estimated by means of a linear time-varying estimation scheme. Given the reliance of the existing dynamic security assessment tools in industry on nominal power system models, the suggested methodology addresses cases when there is deviation from assumed system dynamics, enhancing operators' awareness of system operation. It is based on a decision scheme relying on analytical computation of thresholds, not involving empirical criteria which are likely to introduce inaccurate outcomes. Since false-alarms are guaranteed to be absent, the proposed technique turns out to be very useful for system monitoring and control. The effectiveness of the anomaly detection algorithm is shown through detailed realistic case studies in two power system models.

Large-scale photovoltaic (PV) integration to the network necessitates accurate modeling of PV system dynamics under solar irradiance changes and disturbances in the power system. Most of the available PV dynamic models in the literature are scope-specific, neglecting some control functions and employing simplifications. In this paper, a complete dynamic model for two-stage PV systems is presented, given in entirely state-space form and explicit equations that takes into account all power circuit dynamics and modern control functions. This is a holistic approach that considers a full range of ancillary services required by modern grid codes, supports both balanced and unbalanced grid operation, and accounts for the discontinuous conduction mode of the dc/dc converter of the system. The proposed dynamic model is evaluated and compared to other approaches based on the literature, against scenarios of irradiance variation, voltage sags, and frequency distortion. Simulation results in MATLAB/Simulink indicate high accuracy at low computational cost and complexity.

This paper presents a novel, very simple, accurate, theoretically well-founded and widely applicable relationship expressing the tunnel convergences obtained from large strain elasto-plastic analyses as a hyperbolic function solely of the corresponding small strain convergences. It can thus be used for ‘self-correcting’ small strain solutions, removing the need for large strain elasto-plastic analyses at least at the preliminary design stage and quantifying a hitherto unknown error caused by disregarding the geometric non-linearity. The proposed relationship can be proved rigorously for the plane strain rotationally symmetric ground response problem with a general elasto-plastic constitutive law with or without dilatancy and hardening. Numerical analyses of characteristic two- and three-dimensional excavation problems show that this relationship is generally applicable, irrespective of the in situ stress state and the tunnel geometry. It is therefore very useful from an engineering point of view for the design of tunnels crossing heavily squeezing ground, where the convergences may be so large (sometimes well in excess of 10% of the tunnel radius) that the usual small strain elasto-plastic analyses are deficient.

The process $\mathrm{e}^+\mathrm{e}^- \to\gamma\gamma(\gamma)$ is studied using data collected by the OPAL detector at LEP between the years 1997 and 2000. The data set corresponds to an integrated luminosity of 672.3 pb-1 at centre-of-mass energies lying between 181 GeV and 209 GeV. Total and differential cross-sections are determined and found to be in good agreement with the predictions of QED. Fits to the observed angular distributions are used to set limits on parameters from several models of physics beyond the Standard Model such as cut-off parameters, contact interactions of the type $\mathrm{e}^+\mathrm{e}^- \gamma\gamma$ , gravity in extra spatial dimensions and excited electrons. In events with three photons in the final state the mass spectrum of photon pairs is investigated. No narrow resonance $X\to\gamma\gamma$ is found and limits are placed on the product of the $\rm X \gamma$ production cross-section and branching ratio.

A search for the Standard Model Higgs boson has been performed with the OPAL detector at LEP based on the full data sample collected at s≈192–209 GeV in 1999 and 2000, corresponding to an integrated luminosity of approximately 426 pb−1. The data are examined for their consistency with the background-only hypothesis and various Higgs boson mass hypotheses. A lower bound of 109.7 GeV is obtained on the Higgs boson mass at the 95% confidence level. At higher masses, the data are consistent with both the background and the signal-plus-background hypotheses.

A search for single top quark production via flavour changing neutral currents (FCNC) was performed with data collected by the OPAL detector at the e+e− collider LEP. Approximately 600 pb−1 of data collected at s=189–209 GeV were used to search for the FCNC process e+e−→tc(u)→bWc(u). This analysis is sensitive to the leptonic and the hadronic decay modes of the W boson. No evidence for a FCNC process is observed. Upper limits at the 95% confidence level on the single top production cross-section as a function of the centre-of-mass energy are derived. Limits on the anomalous coupling parameters κγ and κZ are determined from these results.

A search for stable and long-lived massive particles of electric charge |Q/e|=1 or fractional charges of 2/3, 4/3, and 5/3 is reported using data collected by the OPAL detector at LEP, at centre-of-mass energies from 130 to 209 GeV. These particles are assumed to be pair-produced in e+e− collisions and not to interact strongly. No evidence for the production of these particles was observed. Model-independent upper limits on the production cross-section between 0.005 and 0.028 pb have been derived for scalar and spin-1/2 particles with charge ±1. Within the framework of the Constrained Minimal Supersymmetric Standard Model (CMSSM), this implies a lower limit of 98.0 (98.5) GeV on the mass of long-lived right- (left-)handed scalar muons and scalar taus. Long-lived charged heavy leptons and charginos are excluded for masses below 102.0 GeV. For particles with fractional charge ±2/3, ±4/3 and ±5/3, the upper limit on the production cross-section varies between 0.005 and 0.020 pb. All mass and cross-section limits are derived at the 95% confidence level and are valid for particles with lifetimes longer than 10−6 s.

A search for pair-produced doubly charged Higgs bosons has been performed using data samples corresponding to an integrated luminosity of about 614 pb−1 collected with the OPAL detector at LEP at centre-of-mass energies between 189 GeV and 209 GeV. No evidence for a signal has been observed. A mass limit of 98.5 GeV/c2 at the 95% confidence level has been set for the doubly charged Higgs particle in left–right symmetric models. This is the first search for doubly charged Higgs bosons at centre-of-mass energies larger than 91 GeV.

Hadronic event shape distributions from e+e- annihilation measured by the OPAL experiment at centre-of-mass energies between 91 GeV and 209 GeV are used to determine the strong coupling {\alpha}S. The results are based on QCD predictions complete to the next-to- next-to-leading order (NNLO), and on NNLO calculations matched to the resummed next-to-leading-log-approximation terms (NNLO+NLLA). The combined NNLO result from all variables and centre-of-mass energies is {\alpha}S(mZ0) = 0.1201 {\pm} 0.0008(stat.) {\pm} 0.0013(exp.) {\pm} 0.0010(had.) {\pm} 0.0024(theo.). while the combined NNLO+NLLA result is {\alpha}S(mZ0) = 0.1189 {\pm} 0.0008(stat.) {\pm} 0.0016(exp.) {\pm} 0.0010(had.) {\pm} 0.0036(theo.). The completeness of the NNLO and NNLO+NLLA results with respect to missing higher order contributions, studied by varying the renormalization scale, is improved compared to previous results based on NLO or NLO+NLLA predictions only. The observed energy dependence of {\alpha}S agrees with the QCD prediction of asymptotic freedom and excludes the absence of running.

Abstract We investigate the effects of the support pressure distribution and of the free unsupported span on the stability of the tunnel face by means of limit equilibrium computations, which are based upon the so‐called method of slices. Design equations and diagrams are introduced for the estimation of the necessary support pressure taking into account these effects assuming a linear pressure distribution. Furthermore, the errors introduced by the common assumption of support pressure uniformity are discussed for the typical distributions of face support pressure in tunnelling by slurry shields, EPB shields and compressed air shields. The error is less than 10% in the case of closed‐shield tunnelling but may be significant in the case of face reinforcement. Der Einfluss der Stützdruckverteilung und der freien Spannweite auf die Stabilität der Tunnelortsbrust. Im vorliegenden Beitrag wird untersucht, in welchem Maß sich der erforderliche Stützdruck im Vorhandensein einer freien Spannweite zwischen Ausbruchsicherung und Ortsbrust erhöht. Ferner wird der Effekt der Verteilung des Stützdrucks unter der Annahme eines linearen Verlaufs quantifiziert. Das zugrunde liegende Berechnungsmodell untersucht das Grenzgleichgewicht eines Bruchmechanismus nach der sogenannten Lamellenmethode. Die Berechnungsergebnisse werden in Form von Bemessungsformeln und Diagrammen dargestellt. Ferner wird der Fehler der gängigen vereinfachenden Annahme eines gleichmäßig verteilten Stützdrucks für typische Problemstellungen diskutiert. Der Fehler beträgt weniger als 10% im Fall von geschlossenen Schildvortrieben (Erddruck‐, Flüssigkeits‐ oder Druckluftstützung), kann aber im Fall einer Ortsbrustbewehrung sehr groß und auf der unsicheren Seite sein.

Recently, the Lambert W function has emerged as a valuable mathematical tool in photovoltaic (PV) modeling and other scientific fields. This increasing interest is because it can be used to reformulate the implicit equations of the single-diode PV model into explicit form. However, the computation of the Lambert W function itself is still not clear in the literature; some studies use the iterative built-in functions in MATLAB or other computational platforms, while others adopt their own approximation formulae. This paper takes a deeper look at the ways the Lambert W function is evaluated in PV models and carries out a comparative study to assess the most commonly used methods in terms of accuracy, computational cost, and application range. These alternatives are implemented in a modern computer and a typical microcontroller to evaluate their performance in both simulations and embedded applications. The analysis concludes that some series expansions are good options for PV modeling applications, requiring less execution time than the built-in MATLAB lambertw function and exhibiting negligible approximation error.

The amplitude of the signal collected from the PbWO4 crystals of the CMS electromagnetic calorimeter is reconstructed by a digital filtering technique. The amplitude reconstruction has been studied with test beam data recorded from a fully equipped barrel supermodule. Issues specific to data taken in the test beam are investigated, and the implementation of the method for CMS data taking is discussed.

The method of artificial ground freezing was employed to ensure stability and waterproofing of the platform and escalator tunnels in the Università station of the Naples underground. The paper presents the temperature histories monitored within the ground during the freezing process. Furthermore, the importance of the mineralogical composition of the ground is discussed and it is shown that the temperatures monitored can be interpreted numerically using the ‘Freeze' code, a thermo-hydraulic software developed at the ETH Zurich. The influence of important parameters, such as the spacing between the freeze pipes, the thermal conductivity of the ground and the time–development of cooling temperatures in the freeze pipes, is investigated and critically discussed in order to gain a better understanding of the thermal behaviour of the ground during artificial freezing with liquid nitrogen. ‘Freeze' software is a powerful tool for analysing field data for cases involving non-constant temperatures within freeze pipes.

This paper presents a finite strain theoretical analysis of the ground response around highly deformed circular tunnel cross sections that are subjected to (repeated) re-profiling in order to re-establish the desired clearance. Plane strain axially symmetric conditions are considered, with linearly elastic, perfectly or brittle plastic rock behaviour according to the non-associated Mohr–Coulomb model. On the basis of this theoretical analysis, some practical questions are addressed with respect to the ground response curve, the maximum rock pressure (as carried by a practically rigid new temporary support) and the maximum wall convergence (as expected in the presence of a light new support) after re-profiling. Finally, the paper revisits the question of the effectiveness of a pilot tunnel with respect to the ground response during enlargement of the tunnel cross section.

A search for the single production of doubly-charged Higgs bosons is performed using e+e− collision data collected by the OPAL experiment at centre-of-mass energies between 189 GeV and 209 GeV. No evidence for the existence of H±± is observed. Upper limits are derived on hee, the Yukawa coupling of the H±± to like-signed electron pairs. A 95% confidence level upper limit of hee< 0.071 is inferred for M(H±±)<160 GeV assuming that the sum of the branching fractions of the H±± to all lepton flavour combinations is 100%. Additionally, indirect constraints on hee from Bhabha scattering at centre-of-mass energies between 183 GeV and 209 GeV, where the H±± would contribute via t-channel exchange, are derived for M(H±±)<2 TeV. These are the first results both from a single production search and on constraints from Bhabha scattering reported from LEP.

Searches for a scalar top quark and a scalar bottom quark have been performed using a data sample of 438 pb−1 at centre-of-mass energies of s=192–209 GeV collected with the OPAL detector at LEP. No evidence for a signal was found. The 95% confidence level lower limit on the scalar top quark mass is 97.6 GeV if the mixing angle between the supersymmetric partners of the left- and right-handed states of the top quark is zero. When the scalar top quark decouples from the Z0 boson, the lower limit is 95.7 GeV. These limits were obtained assuming that the scalar top quark decays into a charm quark and the lightest neutralino, and that the mass difference between the scalar top quark and the lightest neutralino is larger than 10 GeV. The complementary decay mode of the scalar top quark decaying into a bottom quark, a charged lepton and a scalar neutrino has also been studied. The lower limit on the scalar top quark mass is 96.0 GeV for this decay mode, if the mass difference between the scalar top quark and the scalar neutrino is greater than 10 GeV and if the mixing angle of the scalar top quark is zero. From a search for the scalar bottom quark, a mass limit of 96.9 GeV was obtained if the mass difference between the scalar bottom quark and the lightest neutralino is larger than 10 GeV.

Anomalous quartic couplings between the electroweak gauge bosons may contribute to the $\ensuremath{\nu}\overline{\ensuremath{\nu}}\ensuremath{\gamma}\ensuremath{\gamma}$ and $q\overline{q}\ensuremath{\gamma}\ensuremath{\gamma}$ final states produced in ${e}^{+}{e}^{\ensuremath{-}}$ collisions. This analysis uses the LEP2 OPAL data sample at center-of-mass energies up to 209 GeV. Event selections identify $\ensuremath{\nu}\overline{\ensuremath{\nu}}\ensuremath{\gamma}\ensuremath{\gamma}$ and $q\overline{q}\ensuremath{\gamma}\ensuremath{\gamma}$ events in which the two photons are reconstructed within the detector acceptance. The cross section for the process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}q\overline{q}\ensuremath{\gamma}\ensuremath{\gamma}$ is measured. Averaging over all energies, the ratio of the observed ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}q\overline{q}\ensuremath{\gamma}\ensuremath{\gamma}$ cross section to the standard model expectation is $\mathrm{R}(\mathrm{data}/\mathrm{SM})=0.92\ifmmode\pm\else\textpm\fi{}0.07\ifmmode\pm\else\textpm\fi{}0.04,$ where the errors represent the statistical and systematic uncertainties respectively. The $\ensuremath{\nu}\overline{\ensuremath{\nu}}\ensuremath{\gamma}\ensuremath{\gamma}$ and $q\overline{q}\ensuremath{\gamma}\ensuremath{\gamma}$ data are used to constrain possible anomalous ${W}^{+}{W}^{\ensuremath{-}}\ensuremath{\gamma}\ensuremath{\gamma}$ and $\mathrm{ZZ}\ensuremath{\gamma}\ensuremath{\gamma}$ couplings. Combining with previous OPAL results from the ${W}^{+}{W}^{\ensuremath{-}}\ensuremath{\gamma}$ final state, the 95% confidence level limits on the anomalous coupling parameters ${a}_{0}^{\mathrm{Z}},$ ${a}_{\mathrm{c}}^{\mathrm{Z}},$ ${a}_{0}^{\mathrm{W}}$ and ${a}_{\mathrm{c}}^{\mathrm{W}}$ are found to be $\ensuremath{-}0.007 {\mathrm{GeV}}^{\ensuremath{-}2}&lt;{a}_{0}^{\mathrm{Z}}/{\ensuremath{\Lambda}}^{2}&lt;0.023 {\mathrm{GeV}}^{\ensuremath{-}2},$ $\ensuremath{-}0.029 {\mathrm{GeV}}^{\ensuremath{-}2}&lt;{a}_{\mathrm{c}}^{\mathrm{Z}}/{\ensuremath{\Lambda}}^{2}&lt;0.029 {\mathrm{GeV}}^{\ensuremath{-}2},$ $\ensuremath{-}0.020 {\mathrm{GeV}}^{\ensuremath{-}2}&lt;{a}_{0}^{\mathrm{W}}/{\ensuremath{\Lambda}}^{2}&lt;0.020 {\mathrm{GeV}}^{\ensuremath{-}2},$ $\ensuremath{-}0.052 {\mathrm{GeV}}^{\ensuremath{-}2}&lt;{a}_{\mathrm{c}}^{\mathrm{W}}/{\ensuremath{\Lambda}}^{2}&lt;0.037 {\mathrm{GeV}}^{\ensuremath{-}2},$ where $\ensuremath{\Lambda}$ is the energy scale of the new physics. Limits found when allowing two or more parameters to vary are also presented.

.Using the OPAL detector at LEP, the running of the effective QED coupling α(t) is measured for space-like momentum transfer from the angular distribution of small-angle Bhabha scattering. In an almost ideal QED framework, with very favourable experimental conditions, we obtain: \( \Delta \alpha {\left( { - 6.07\;{\text{GeV}}^{2} } \right)} - \Delta \alpha {\left( { - 1.81\;{\text{GeV}}^{2} } \right)} = {\left( {440 \pm 58 \pm 43 \pm 30} \right)} \times 10^{{ - 5}} ,\) where the first error is statistical, the second is the experimental systematic and the third is the theoretical uncertainty. This agrees with current evaluations of α(t). The null hypothesis that α remains constant within the above interval of -t is excluded with a significance above 5σ. Similarly, our results are inconsistent at the level of 3σ with the hypothesis that only leptonic loops contribute to the running. This is currently the most significant direct measurement where the running α(t) is probed differentially within the measured t range.

The response of the CMS barrel calorimeter (electromagnetic plus hadronic) to hadrons, electrons and muons over a wide momentum range from 2 to 350 GeV/c has been measured. To our knowledge, this is the widest range of momenta in which any calorimeter system has been studied. These tests, carried out at the H2 beam-line at CERN, provide a wealth of information, especially at low energies. The analysis of the differences in calorimeter response to charged pions, kaons, protons and antiprotons and a detailed discussion of the underlying phenomena are presented. We also show techniques that apply corrections to the signals from the considerably different electromagnetic (EB) and hadronic (HB) barrel calorimeters in reconstructing the energies of hadrons. Above 5 GeV/c, these corrections improve the energy resolution of the combined system where the stochastic term equals 84.7±1.6% and the constant term is 7.4±0.8%. The corrected mean response remains constant within 1.3% rms.

Summary The instantaneous response of saturated low permeability grounds to tunnel excavation is important for deformations and stability close to the tunnel face. It is characterized by zero volume change in combination with the development of excess pore pressures. In tunnelling through poor quality ground under great depth of cover and high in situ pore pressure, heavily squeezing conditions (characterized by very large convergences) may occur soon after excavation. This paper presents exact finite strain analytical solutions for the undrained ground response around cylindrical and spherical openings that are unloaded from uniform and isotropic initial stress states, on the basis of the Modified Cam Clay (MCC) model and the Mohr–Coulomb (MC) model. The solution for a Drucker–Prager material is also given as it requires only a very small modification to the MC solution. The so‐called ground response curve, that is, the relationship between the support pressure and the cavity wall displacement, is derived in closed form for the MC model. The solution for the MCC problem is semi‐analytical in that it uses the trapezium rule for the computation of a definite integral. The influence of the significant parameters of the problem on the predicted deformation behaviour is shown by means of dimensionless charts. Finally, the practical usefulness of the solutions presented is illustrated by applying them to the breccia zones of the planned Gibraltar Strait tunnel – an extreme case of weak, low permeability ground under high pore pressure. The solutions can serve as a trustworthy benchmark for numerical procedures that incorporate material and geometric nonlinearities. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Performance tests of some aspects of the CMS ECAL were carried out on modules of the "barrel" sub-system in 2002 and 2003. A brief test with high energy electron beams was made in late 2003 to validate prototypes of the new Very Front End electronics. The final versions of the monitoring and cooling systems, and of the high and low voltage regulation were used in these tests. The results are consistent with the performance targets including those for noise and overall energy resolution, required to fulfil the physics programme of CMS at the LHC.

Squeezing ground may cause a series of difficulties such as sticking of the cutter head or the shield, extensive convergences of the bored profile or destruction of the tunnel support. In very soft rock, clogging or sagging of the cutter head may also occur, and TBM bracing by the gripper plates may become impossible. These difficulties, alone or in combination with instabilities of the tunnel face and walls, may slow down or even obstruct TBM operation and, if occurring over frequent tunnel intervals or persisting over longer portions of a tunnel, may have a decisive effect on the feasibility of a TBM drive. This paper discusses the specific problems of mechanized tunneling in squeezing ground, investigates the problem of shield jamming and analyses the effects of possible countermeasures, on the basis of the results of numerical computations.(A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. Reprinted with permission from Elsevier.

This Letter describes a direct search for pair produced magnetic monopoles in e+e− collisions. The analysis is based on 62.7 pb−1 of data collected with the OPAL detector at an average centre-of-mass energy of s=206.3GeV. The monopole signal was assumed to be characterized by two back-to-back particles with an anomalously high ionization energy loss dE/dx in the tracking chambers. No evidence for production of monopoles was observed. Upper limits were obtained on the magnetic monopole pair-production cross-section (σ) in the mass range 45GeV/c2<mM<102GeV/c2. The average limit is σ<0.05pb and is essentially independent of the magnetic monopole mass. The cross-section limit is derived at the 95% confidence level and is valid for spin-1/2 magnetic monopoles.

Calibration of the relative response of the individual channels of the barrel electromagnetic calorimeter of the CMS detector was accomplished, before installation, with cosmic ray muons and test beams. One fourth of the calorimeter was exposed to a beam of high energy electrons and the relative calibration of the channels, the intercalibration, was found to be reproducible to a precision of about 0.3%. Additionally, data were collected with cosmic rays for the entire ECAL barrel during the commissioning phase. By comparing the intercalibration constants obtained with the electron beam data with those from the cosmic ray data, it is demonstrated that the latter provide an intercalibration precision of 1.5% over most of the barrel ECAL. The best intercalibration precision is expected to come from the analysis of events collected in situ during the LHC operation. Using data collected with both electrons and pion beams, several aspects of the intercalibration procedures based on electrons or neutral pions were investigated.

Abstract A search is made for charged Higgs bosons predicted by Two-Higgs-Doublet extensions of the Standard Model (2HDM) using electron-positron collision data collected by the OPAL experiment at $\sqrt{s}=189\mbox{--}209\ \mbox{GeV}$ , corresponding to an integrated luminosity of approximately 600 pb −1 . Charged Higgs bosons are assumed to be pair-produced and to decay into $\mathrm{q} \bar{\mathrm{q}}$ , τν τ or AW ± . No signal is observed. Model-independent limits on the charged Higgs-boson production cross section are derived by combining these results with previous searches at lower energies. Under the assumption $\mathrm{BR} (\mathrm{H}^{\pm} \to \tau\nu_{\tau}) + \mathrm{BR} (\mathrm{H}^{\pm} \to \mathrm{q} \bar{\mathrm{q}}) = 1$ , motivated by general 2HDM type II models, excluded areas on the $[m_{\mathrm{H}^{\pm}} , \mathrm{BR} (\mathrm {H}^{\pm} \to \tau\nu_{\tau})]$ plane are presented and charged Higgs bosons are excluded up to a mass of 76.3 GeV at 95 % confidence level, independent of the branching ratio BR(H ± → τν τ ). A scan of the 2HDM type I model parameter space is performed and limits on the Higgs-boson masses $m_{\mathrm{H}^{\pm}}$ and m A are presented for different choices of tan β .

In electric grids with large photovoltaic (PV) integration, the PV system dynamics triggered by irradiance variation is an important factor for the power system stability. Although there are models in the literature that describe these dynamics, they are usually formulated as block diagrams or flowcharts and employ implicit equations for the PV generator, thus requiring application-specific software and iterative solution algorithms. Alternatively, to provide a rigorous mathematical formulation, a state-space representation of the PV system dynamics driven by irradiance variation is presented in this paper. This is the first PV dynamic model in entirely state-space form that incorporates the maximum power point tracking function. To this end, the Lambert W function is used to express the PV generator's equations in an explicit form. Simulations are performed in MATLAB/Simulink to evaluate and compare the proposed dynamic model over the detailed switching modeling approach in terms of accuracy and computational performance.

Abstract The present work aims to improve the reliability of shield jamming and lining damage risk assessment in squeezing ground by analysing the effects of creep on the evolution of rock pressure over time. The study is based on numerical simulations of typical mechanised tunnelling processes, generally consisting of shield advance phases alternating with shorter or longer standstills for lining installation, maintenance, etc . A linear elastic—viscous plastic constitutive model based upon Perzyna’s overstress theory is employed, which considers the time-dependency of plastic deformations via a single viscosity parameter. The investigations demonstrate the following: (i) shield loading during advance increases with increasing viscosity under certain conditions, which contradicts the common perception in many existing works that creep is thoroughly favourable for shield jamming; (ii) creep is thoroughly unfavourable for shield loading during long standstills and long-term lining loading, due to the additional viscoplastic ground deformations manifested over time; (iii) the commonly adopted simplifying assumption of continuous excavation with the gross advance rate is adequate only where standstills are very short (e.g., for lining erection during the stop-and-go shield tunnelling process), but otherwise underestimates the shield loading, even in cases of regular inspection and maintenance standstills lasting only a few hours. Two application examples, the Fréjus safety gallery and the Gotthard Base tunnel, demonstrate the need to consider creep and the accuracy of modelling tunnel construction by a semi-discrete approach, where only the very short standstills for lining erection are considered via an average advance rate, but longer standstills are explicitly simulated.

A search was performed for charginos with masses close to the mass of the lightest neutralino in e+e- collisions at centre-of-mass energies of 189-209 GeV recorded by the OPAL detector at LEP. Events were selected if they had an observed high-energy photon from initial state radiation, reducing the dominant background from two-photon scattering to a negligible level. No significant excess over Standard Model expectations has been observed in the analysed data set corresponding to an integrated luminosity of 570pb-1. Upper limits were derived on the chargino pair-productin cross-section, and lower limits on the chargino mass were derived in the context of the Minimal Supersymmetric Extension of the Standard Model for the gravity and anomaly mediated Supersymmetry breaking scenarios.

Non-commutative QED would lead to deviations from the Standard Model depending on a new energy scale ΛNC and a unique direction in space defined by two angles η and ξ. In this analysis, η is defined as the angle between the unique direction and the rotation axis of the earth. The predictions of a tree level calculation for the process e+e−→γγ are evaluated for the specific orientation of the OPAL detector and compared to the measurements. Distributions of the polar and azimuthal photon angles are used to extract limits on the energy scale ΛNC depending on the model parameter η. It is shown that the time dependence of the total cross-section could be used to determine the model parameter ξ if there were a detectable signal. This is the first experimental study of non-commutative QED at an e+e− collider.

Flavour inclusive, udsc and b fragmentation functions in unbiased jets, and flavour inclusive, udsc, b and gluon fragmentation functions in biased jets are measured in e+e- annihilations from data collected at centre-of-mass energies of 91.2, and 183-209 GeV with the OPAL detector at LEP. The unbiased jets are defined by hemispheres of inclusive hadronic events, while the biased jet measurements are based on three-jet events selected with jet algorithms. Several methods are employed to extract the fragmentation functions over a wide range of scales. Possible biases are studied in the results are obtained. The fragmentation functions are compared to results from lower energy e+e- experiments and with earlier LEP measurements and are found to be consistent. Scaling violations are observed and are found to be stronger for the fragmentation functions of gluon jets than for those of quarks. The measured fragmentation functions are compared to three recent theoretical next-to-leading order calculations and to the predictions of three Monte Carlo event generators. While the Monte Carlo models are in good agreement with the data, the theoretical predictions fail to describe the full set of results, in particular the b and gluon jet measurements.

A search is performed for Higgs bosons decaying into invisible final states, produced in association with a Z0 boson in e+e− collisions at energies between 183 and 209 GeV. The search is based on data samples collected by the OPAL detector at LEP corresponding to an integrated luminosity of about 660 pb−1. The analysis aims to select events containing the hadronic decay products of the Z0 boson and large missing momentum, as expected from Higgs boson decay into a pair of stable weakly interacting neutral particles, such as the lightest neutralino in the Minimal Supersymmetric Standard Model. The same analysis is applied to a search for nearly invisible Higgs boson cascade decays into stable weakly interacting neutral particles. No excess over the expected background from Standard Model processes is observed. Limits on the production of invisibly decaying Higgs bosons produced in association with a Z0 boson are derived. Assuming a branching ratio BR(h0→invisible)=1, a lower limit of 108.2 GeV is placed on the Higgs boson mass at the 95% confidence level. Limits on the production of nearly invisibly decaying Higgs bosons are also obtained.

This paper investigates the impact of the overexcitation limiters (OELs) on the stability margin of a power system which is operating under stressed conditions. Several OEL modeling approaches are presented and the effect of their action has been examined in model power systems. It is realized that, more often than not, OEL operating status goes undetected by existing dynamic security assessment tools commonly used in the industry. It is found that the identification and accurate representation of OELs lead to significantly different transient stability margins. Unscented Kalman filtering is used to detect the OEL activation events. In the context of stressed system operation, such quantitative assessment is very useful for system control. This understanding is further reinforced through detailed studies in two model power systems.

In this paper we show how it is possible to reduce the number of significant parameters appearing in typical rock mechanics boundary value problems of rock engineering and tunneling. Further, we present methods to gain information concerning the solutions to these problems, presuming the rock mass obeys the well‐known, and in geomechanics widely used, Mohr‐Coulomb yield criterion. The system of differential equations that governs boundary value problems with a Mohr‐Coulomb elastoplastic material can be reformulated by means of simple substitutions in such a way that cohesion and Young's modulus do not explicitly appear. This makes substantial savings of computational effort possible, and contributes to a better understanding of the structure of the solution. Computational results obtained for some values of Young's modulus, cohesion, initial stresses, and boundary tractions can easily be transformed to the results for other values. The transformed equations suggest very clearly the influence of cohesion, i.e., as compared to the effect of a support pressure.

A study of W+W− events accompanied by hard photon radiation, Eγ>2.5 GeV, produced in e+e− collisions at LEP is presented. Events consistent with being two on-shell W-bosons and an isolated photon are selected from 681 pb−1 of data recorded at 180 GeV<s<209 GeV. From the sample of 187 selected W+W−γ candidates with photon energies greater than 2.5 GeV, the W+W−γ cross-section is determined at five values of s. The results are consistent with the Standard Model expectation. Averaging over all energies, the ratio of the observed cross-section to the Standard Model expectation is R(data/SM)=0.99±0.09±0.04, where the errors represent the statistical and systematic uncertainties respectively. These data provide constraints on the related O(α) systematic uncertainties on the measurement of the W-boson mass at LEP. Finally, the data are used to derive 95% confidence level upper limits on possible anomalous contributions to the W+W−γγ and W+W−Z0γ vertices: −0.020 GeV−2<a0Λ2<0.020 GeV−2,−0.053 GeV−2<acΛ2<0.037 GeV−2,−0.16 GeV−2<anΛ2<0.15 GeV−2, where Λ represents the energy scale for new physics and a0, ac and an are dimensionless coupling constants.

This paper studies the capacity of an indoor wireless system operating at 60 GHz using a physical channel model that incorporates multiple elements at both antenna terminals. The proposed channel model utilizes the geometric characteristics of the environment, the angle of arrival and angle of departure of each one of the propagation paths, the antenna elements and their spacing. The results showed that the system capacity increases significantly if SIMO, MISO or MIMO configuration is utilized instead of the basic SISO channel. The capacity decreases, as the distance between the terminals increase. In the 90% of the cases the capacity remains above 4.3 b/s/Hz, even when the receiver is 15 m away from the base station. Finally, very high data rates, can be achieved maintaining low SNR.

Squeezing in tunnelling is commonly assessed using the linearly elastic–perfectly plastic Mohr–Coulomb (MC) model. Weak rocks and fault materials, however, exhibit confining stress-dependent and strain-hardening behaviour prior to failure; in other words, the higher the confining stress and the lower the shear strain the stiffer the rock behaviour. As the MC model assumes a strain- and stress-independent Young's modulus, the selection of an appropriate ‘operational’ value, E MC , remains a major problem in tunnel studies using this model. Although E MC has a significant effect on the deformation predictions (they are inversely proportional to this value under small strain theory), there is no widely accepted or well-validated approach to its selection. This paper shows, using the results of triaxial compression tests on weak rocks and fault materials from the Gotthard base tunnel and five other projects, and performing a theoretical analysis of the ground response to tunnel excavation, that E MC can be taken as equal to the secant modulus E 50 (rather than equal to the unloading–reloading modulus) extrapolated from standard triaxial compression test results to the in situ stress level. This is particularly useful for practical purposes as it allows standard computational methods to be used with sufficient accuracy, rendering more refined models unnecessary, at least at the preliminary design stage.

This paper proposes a novel Kalman filtering based dynamic state estimation method, which addresses cases of models with a nonlinear unknown input, and it is suitable for wind turbine model state estimation. Given the complexity characterizing modern power networks, dynamic state estimation techniques applied on renewable energy based generators, such as wind turbines, enhance operators' awareness of the components comprising modern power networks. In this context, the method developed here is implemented on a doubly-fed induction generator based wind turbine, under unknown wind velocity conditions, as opposed to similar studies so far, where all model inputs are considered to be known, and this does not always reflect the reality. The proposed technique is derivative-free and it relies on the formulation of the nonlinear output measurement equations as power series. The effectiveness of the suggested algorithm is tested on a modified version of the IEEE benchmark 68-bus, 16-machine system.

Measurements of the $\tau$ lepton polarization and forward-backward polarization asymmetry near the Z $^0$ resonance using the OPAL detector are described. The measurements are based on analyses of $\tau \rightarrow{\rm e} \nu_e\nu_{\tau}, \tau\rightarrow \mu\nu_{\mu}\nu_{\tau}, \tau\rightarrow \pi\nu_{\tau}, \tau \rightarrow \rho\nu_{\tau}$ and $\tau\rightarrow{\rm a}_1\nu_{\tau}$ decays from a sample of 144,810 $\rm e^+e^-\rightarrow \tau^+\tau^-$ candidates corresponding to an integrated luminosity of 151 pb $^{-1}$ . Assuming that the $\tau$ lepton decays according to V–A theory, we measure the average $\tau$ polarization near $\sqrt{s} ={\rm M}_{\mathrm{Z}}$ to be $\langle P_{\tau}\rangle= (-14.10 \pm 0.73 \pm 0.55)\%$ and the $\tau$ polarization forward-backward asymmetry to be $\rm A_{\mathrm{pol}}^{\mathrm{FB}} = (-10.55 \pm 0.76 \pm 0.25)\%$ , where the first error is statistical and the second systematic. Taking into account the small effects of the photon propagator, photon-Z $^0$ interference and photonic radiative corrections, these results can be expressed in terms of the lepton neutral current asymmetry parameters: \begin{eqnarray} {\cal A}_{\tau} & = & 0.1456 \pm 0.0076 \pm 0.0057, \nonumber {\cal A}_{\mathrm e}& = & 0.1454 \pm 0.0108 \pm 0.0036. \nonumber \end{eqnarray} These measurements are consistent with the hypothesis of lepton universality and combine to give ${\cal A}_{\ell} = 0.1455 \pm 0.0073$ . Within the context of the Standard Model this combined result corresponds to $=0.23172 \pm 0.00092$ . Combing these results with those from the other OPAL neutral current measurements yields a value of $=0.23211 \pm 0.00068$ .

.Gluon jets with a mean energy of 22 GeV and purity of 95% are selected from hadronic Z0 decay events produced in e + e- annihilations. A subsample of these jets is identified which exhibits a large gap in the rapidity distribution of particles within the jet. After imposing the requirement of a rapidity gap, the gluon jet purity is 86%. These jets are observed to demonstrate a high degree of sensitivity to the presence of color reconnection, i.e. higher order QCD processes affecting the underlying color structure. We use our data to test three QCD models which include a simulation of color reconnection: one in the Ariadne Monte Carlo, one in the Herwig Monte Carlo, and the other by Rathsman in the Pythia Monte Carlo. We find the Rathsman and Ariadne color reconnection models can describe our gluon jet measurements only if very large values are used for the cutoff parameters which serve to terminate the parton showers, and that the description of inclusive Z0 data is significantly degraded in this case. We conclude that color reconnection as implemented by these two models is disfavored. The signal from the Herwig color reconnection model is less clear and we do not obtain a definite conclusion concerning this model. In a separate study, we follow recent theoretical suggestions and search for glueball-like objects in the leading part of the gluon jets. No clear evidence is observed for these objects.

A search is performed for production of short-lived particles in e+e−→XY, with X→γγ and Y→ff̄, for scalar X and scalar or vector Y. Model-independent limits in the range of 25–60 femtobarns are presented on σ(e+e−→XY)×B(X→γγ)×B(Y→ff̄) for centre-of-mass energies in the range 205–207 GeV. The data from all LEP centre-of-mass energies 88–209 GeV are also interpreted in the context of fermiophobic Higgs boson models, for which a lower mass limit of 105.5 GeV is obtained for a “benchmark” fermiophobic Higgs boson.

The applicability limits of the closed-form solution to the problem of ground response to tunnelling are sounded out by systematically investigating the effect of deviations from some of the important assumptions underlying the closed-form solution. The ground response curve (GRC) expresses the relationship between tunnel support pressure and the radial displacement of the tunnel boundary on the basis of a rotationally symmetric model. The assumptions underlying rotational symmetry are a circular tunnel, a hydrostatic and uniform initial stress field, an isotropic and homogeneous ground and uniformly distributed support pressure. Deviations from these assumptions generally necessitate potentially time-consuming numerical analyses. The paper revisits the classical problem of tunnel excavation in a linearly elastic, perfectly plastic ground obeying the Mohr–Coulomb yield criterion, and analyses the effects of non-uniformity and anisotropy of the initial stress field and of a non-circular tunnel geometry. The results show that the GRC also provides a reasonably accurate approximation of average tunnel convergence for a wide range of ground conditions that violate rotational symmetry.

The present paper proposes a limit equilibrium method for the stability analysis of reinforced tunnel faces in purely cohesive soils exhibiting constant or depth-dependent undrained shear strength. The method can be applied to arbitrary reinforcement layouts in relation to bolt spacing and length. The computational predictions are compared to the results of other models and numerical stress analyses in terms of the so-called load factor. Finally, design nomograms are presented that provide a rapid assessment of the stability of uniformly reinforced faces in soils with constant or depth-dependent undrained strength.

Using about 3.9 million hadronic Z decays from e+e− collisions recorded by the OPAL detector at LEP at centre-of-mass energies s≈MZ, the branching ratio for the decay D−s→τ−ν̄τ has been measured to be BR(D−s→τ−ν̄τ)=(7.0±2.1(stat)±2.0(syst))%. This result can be used to derive the decay constant of the D−s meson: fDs=(286±44(stat)±41(syst))MeV.

Elements of the spin density matrix for W bosons in e+e−→W+W−→qq̄′ℓνℓ events are measured from data recorded by the OPAL detector at LEP. This information is used to calculate polarised differential cross-sections and to search for CP-violating effects. Results are presented for W bosons produced in e+e− Collisions with centre-of-mass energies between 183 GeV and 209 GeV. The average fraction of W bosons that are longitudinally polarised is found to be (23.9±2.1±1.1)% compared to a Standard Model prediction of (23.9±0.1)%. All results are consistent with CP conservation.

During summer 2006 a fraction of the CMS silicon strip tracker was operated in a comprehensive slice test called the Magnet Test and Cosmic Challenge (MTCC). At the MTCC, cosmic rays detected in the muon chambers were used to trigger the readout of all CMS sub-detectors in the general data acquisition system and in the presence of the 4 T magnetic field produced by the CMS superconducting solenoid. This document describes the operation of the Tracker hardware and software prior, during and after data taking. The performance of the detector as resulting from the MTCC data analysis is also presented.

We search for lepton flavour violating events (eμ, eτ and μτ) that could be directly produced in e+e− annihilations, using the full available data sample collected with the OPAL detector at centre-of-mass energies between 189 GeV and 209 GeV. In general, the Standard Model expectations describe the data well for all the channels and at each s. A single eμ event is observed where according to our Monte Carlo simulations only 0.019 events are expected from Standard Model processes. We obtain the first limits on the cross-sections σ(e+e−→eμ, eτ and μτ) as a function of s at LEP2 energies.

A search for charged excited leptons decaying into a lepton and photon has been performed using approximately 680 pb-1 of e+e- collision data collected by the OPAL detector at LEP at centre-of-mass energies between 183 GeV and 209 GeV. No evidence for their existence was found. Upper limits on the product of the cross-section and the branching fraction are inferred. Using results from the search for singly produced excited leptons, upper limits on the ratio of the excited lepton coupling constant to the compositeness scale are calculated. From pair production searches, 95% confidence level lower limits on the masses of excited electrons, muons and taus are determined to be 103.2 GeV.

We present the first experimental results based on the jet boost algorithm, a technique to select unbiased samples of gluon jets in ${e}^{+}{e}^{\ensuremath{-}}$ annihilations, i.e. gluon jets free of biases introduced by event selection or jet finding criteria. Our results are derived from hadronic ${Z}^{0}$ decays observed with the OPAL detector at the LEP ${e}^{+}{e}^{\ensuremath{-}}$ collider at CERN. First, we test the boost algorithm through studies with HERWIG Monte Carlo events and find that it provides accurate measurements of the charged particle multiplicity distributions of unbiased gluon jets for jet energies larger than about 5 GeV, and of the jet particle energy spectra (fragmentation functions) for jet energies larger than about 14 GeV. Second, we apply the boost algorithm to our data to derive unbiased measurements of the gluon jet multiplicity distribution for energies between about 5 and 18 GeV, and of the gluon jet fragmentation function at 14 and 18 GeV. In conjunction with our earlier results at 40 GeV, we then test QCD calculations for the energy evolution of the distributions, specifically the mean and first two nontrivial normalized factorial moments of the multiplicity distribution, and the fragmentation function. The theoretical results are found to be in global agreement with the data, although the factorial moments are not well described for jet energies below about 14 GeV.

The hadronic structure function of the photon F2γ(x,Q2) is measured as a function of Bjorken x and of the photon virtuality Q2 using deep-inelastic scattering data taken by the OPAL detector at LEP at e+e− centre-of-mass energies from 183 to 209 GeV. Previous OPAL measurements of the x dependence of F2γ are extended to an average Q2 of 〈Q2〉=780 GeV2 using data in the kinematic range 0.15<x<0.98. The Q2 evolution of F2γ is studied for 12.1<〈Q2〉<780 GeV2 using three ranges of x. As predicted by QCD, the data show positive scaling violations in F2γ with F2γ(Q2)/α=(0.08±0.02+0.05−0.03)+(0.13±0.01+0.01−0.01)lnQ2, where Q2 is in GeV2, for the central x region 0.10–0.60. Several parameterisations of F2γ are in qualitative agreement with the measurements whereas the quark-parton model prediction fails to describe the data.

From a total data sample of 701.1 pb-1 recorded with e+e- centre-of-mass energies of $\sqrt{s} =$ 161–209 GeV with the OPAL detector at LEP, 11693 W-pair candidate events are selected. These data are used to obtain measurements of the W-pair production cross sections at 10 different centre-of-mass energies. The ratio of the measured cross sections to the standard model expectation is found to be: ${\text{data}}/{{\text{SM}}} = 1.002\pm0.011 ({\text{stat.}}) \pm0.007 ({\text{syst.}}) \pm0.005 ({\text{theory}})$ , where the uncertainties are statistical, experimental systematics and theory systematics respectively. The data are used to determine the W boson branching fractions, which are found to be consistent with lepton universality of the charged current interaction. Assuming lepton universality, the branching ratio to hadrons is determined to be 67.41±0.37(stat.)±0.23(syst.)%, from which the CKM matrix element |Vcs| is determined to be 0.969±0.017(stat.)±0.012(syst.). The differential cross section as a function of the W- production angle is measured for the qqeν and qqμν final states. The results described in this paper are consistent with the expectations from the standard model.

Hadronic final states with a hard isolated photon are studied using data taken at centre-of-mass energies around the mass of the Z boson with the OPAL detector at LEP. The strong coupling αs is extracted by comparing data and QCD predictions for event shape observables at average reduced centre-of-mass energies ranging from 24 GeV to 78 GeV, and the energy dependence of αs is studied. Our results are consistent with the running of αs as predicted by QCD and show that within the uncertainties of our analysis event shapes in hadronic Z decays with hard and isolated photon radiation can be described by QCD at reduced centre-of-mass energies. Combining all values from different event shape observables and energies gives αs(MZ)=0.1182±0.0015(stat.)±0.0101(syst.).

A study of Bose–Einstein correlations in pairs of identically charged pions produced in e+e- annihilations at the Z0 peak has been performed for the first time assuming a non-static emitting source. The results are based on the high statistics data obtained with the OPAL detector at LEP. The correlation functions have been analyzed in intervals of the average pair transverse momentum and of the pair rapidity, in order to study possible correlations between the pion production points and their momenta (position–momentum correlations). The Yano–Koonin and the Bertsch–Pratt parameterizations have been fitted to the measured correlation functions to estimate the geometrical parameters of the source as well as the velocity of the source elements with respect to the overall centre-of-mass frame. The source rapidity is found to scale approximately with the pair rapidity, and both the longitudinal and transverse source dimensions are found to decrease for increasing average pair transverse momenta.

Abstract Klassifikationen aufgrund von Indexwerten wie Q oder RMR, die sich aus der Multiplikation oder Addition verschiedener physikalischer Parameter oder gar Bewertungen ergeben, dürfen weder zur Beurteilung des Gebirgsverhaltens beim Vortrieb noch zur Festlegung der Ausbruchsicherung herangezogen werden. Ein Klassifikationssystem sollte nur jene Merkmale und Eigenschaften zum Gegenstand haben, die für die Beantwortung konkreter Fragestellungen der Planung signifikant sind. Die genannten Indexwerte erfüllen diese Bedingung nicht. Wissenschaftlich unhaltbar sind auch die verschiedentlich vorgeschlagenen Beziehungen zwischen dem so genannten GSI‐Wert und dem Gebirgs‐E‐Modul oder den Festigkeitsparametern der so genannten empirischen Hoek‐Brownschen Bruchbedingung. Letztere ist weder genauer, noch einfacher als die in der Geotechnik etablierte Mohr‐Coulombsche Bruchbedingung. Die empirische Basis der postulierten Beziehungen zwischen den Gebirgsparametern und dem GSI wurde nie veröffentlicht. Eine kritische Überprüfung dieser Beziehungen ist daher nicht möglich. On the rock mass classifications with indices in tunnelling. Classifications based on indices such as Q or RMR, which result from the multiplication or addition of various physical parameters or ratings, should not be used to estimate the rock mass behaviour or the necessary tunnel support. A classification system should take account only of the characteristics and properties that are significant when addressing specific planning issues. The mentioned indices do not fulfil this condition. The proposed relationships between the so‐called Geological Strength Index (GSI) and the rock mass parameters under the empirical Hoek‐Brown failure condition are also scientifically untenable. This failure condition is neither more accurate nor easier to handle than the familiar linear Mohr‐Coulomb condition. The proposed relationships defy scientific testing because their empirical basis has never been published and, in addition, they contain non‐measurable entities.

Correlations among hadrons with the same electric charge produced in Z0 decays are studied using the high statistics data collected from 1991 through 1995 with the OPAL detector at LEP. Normalized factorial cumulants up to fourth order are used to measure genuine particle correlations as a function of the size of phase space domains in rapidity, azimuthal angle and transverse momentum. Both all-charge and like-sign particle combinations show strong positive genuine correlations. One-dimensional cumulants initially increase rapidly with decreasing size of the phase space cells but saturate quickly. In contrast, cumulants in two- and three-dimensional domains continue to increase. The strong rise of the cumulants for all-charge multiplets is increasingly driven by that of like-sign multiplets. This points to the likely influence of Bose–Einstein correlations. Some of the recently proposed algorithms to simulate Bose–Einstein effects, implemented in the Monte Carlo model Pythia, are found to reproduce reasonably well the measured second- and higher-order correlations between particles with the same charge as well as those in all-charge particle multiplets.

The magnitude of the CKM matrix element Vub is determined by measuring the inclusive charmless semileptonic branching fraction of beauty hadrons at OPAL based on b -> Xu l nu event topology and kinematics. This analysis uses OPAL data collected between 1991 and 1995, which correspond to about four million hadronic Z decays. We measure Br(b -> Xu l) to be (1.63 +/- 0.53 +0.55/-0.62) x 10^(-3). The first uncertainty is the statistical error and the second is the systematic error. From this analysis, Vub is determined to be: |Vub| = (4.00 +/- 0.65(stat) +0.67/-0.76(sys) +/- 0.19(HQE)) x 10^(-3). The last error represents the theoretical uncertainties related to the extraction of |Vub| from Br(b -> Xu l) using the Heavy Quark Expansion.

Searches for first generation scalar and vector leptoquarks, and for squarks in R-parity violating SUSY models with the direct decay of the squark into Standard Model particles, have been performed using e+e− collisions collected with the OPAL detector at LEP at e+e− centre-of-mass energies between 189 and 209 GeV. No excess of events is found over the expectation from Standard Model background processes. Limits are computed on the leptoquark couplings for different values of the branching ratio to electron–quark final states.

The charged particle multiplicities of two- and three-jet events from the reaction e $^+$ e $^-$ $\rightarrow$ Z $^0\rightarrow hadrons$ are measured for Z $^0$ decays to light quark (uds) flavors. Using recent theoretical expressions to account for biases from event selection, results corresponding to unbiased gluon jets are extracted over a range of jet energies from about 11 to 30 GeV. We find consistency between these results and direct measurements of unbiased gluon jet multiplicity from $\Upsilon$ and Z $^0$ decays. The unbiased gluon jet data including the direct measurements are compared to corresponding results for quark jets. We perform fits based on analytic expressions for particle multiplicity in jets to determine the ratio $r\equiv\mathrm{N}_{g}/\mathrm{N}_{q}$ of multiplicities between gluon and quark jets as a function of energy. We also determine the ratio of slopes, $r^{(1)}\equiv(\mathrm{d}\mathrm{N}_{g} /\mathrm{d}y) /(\mathrm{d}\mathrm{N}_{q} /\mathrm{d}y)$ , and of curvatures, $r^{(2)}\equiv(\mathrm{d}^2\mathrm{N}_{g} /\mathrm{d}y^2) /(\mathrm{d}^2\mathrm{N}_{q} /\mathrm{d}y^2)$ , where y specifies the energy scale. At 30 GeV, we find $r=1.422\pm0.051,r^{(1)}=1.761\pm0.071$ and $r^{(2)}=1.98\pm0.13$ , where the uncertainties are the statistical and systematic terms added in quadrature. These results are in general agreement with theoretical predictions. In addition, we use the measurements of the energy dependence of ${\mathrm{N}}_{g}$ and ${\mathrm{N}}_{q}$ to determine an effective value of the ratio of QCD color factors, $C_{\mathrm A}/C_{\mathrm F}$ . Our result, $C_{\mathrm A}/C_{\mathrm F}=2.23\pm0.14 $ (total), is consistent with the QCD value of 2.25.

The τ−→μ−ν̄μντ branching ratio has been measured using data collected from 1990 to 1995 by the OPAL detector at the LEP collider. The resulting value of B(τ−→μ−ν̄μντ)=0.1734±0.0009(stat)±0.0006(syst) has been used in conjunction with other OPAL measurements to test lepton universality, yielding the coupling constant ratios gμ/ge=1.0005±0.0044 and gτ/ge=1.0031±0.0048, in good agreement with the Standard Model prediction of unity. A value for the Michel parameter η=0.004±0.037 has also been determined and used to find a limit for the mass of the charged Higgs boson, mH±>1.28tanβ, in the Minimal Supersymmetric Standard Model.

We present a determination of the LEP beam energy using “radiative return” fermion-pair events recorded at centre-of-mass energies from 183 to 209 GeV. We find no evidence of a disagreement between the OPAL data and the LEP Energy Working Group's standard calibration. Including the energy-averaged 11 MeV uncertainty in the standard determination, the beam energy we obtain from the OPAL data is higher than that obtained from the LEP calibration by 0±34(stat.)±27(syst.)MeV.

A search for the Higgsstrahlung process e+e−→hZ is described, where the neutral Higgs boson h is assumed to decay into hadronic final states. In order to be sensitive to a broad range of models, the search is performed independent of the flavour content of the Higgs boson decay. The analysis is based on e+e− collision data collected by the OPAL detector at energies between 192 and 209 GeV. The search does not reveal any significant excess over the Standard Model background prediction. Results are combined with previous searches at energies around 91 and at 189 GeV. A limit is set on the product of the cross-section and the hadronic branching ratio of the Higgs boson, as a function of the Higgs boson mass. Assuming the hZ coupling predicted by the Standard Model, and a Higgs boson decaying only into hadronic final states, a lower bound of 104 GeV/c2 is set on the mass at the 95% confidence level.

Data from e+e- annihilation into hadrons at centre-of-mass energies between 91 GeV and 209 GeV collected with the OPAL detector at LEP, are used to study the four-jet rate as a function of the Durham algorithm resolution parameter ycut. The four-jet rate is compared to next-to-leading order calculations that include the resummation of large logarithms. The strong coupling measured from the four-jet rate is alphas(Mz0)= 0.1182+-0.0003(stat.)+-0.0015(exp.)+-0.0011(had.)+-0.0012(scale)+-0.0013(mass) in agreement with the world average. Next-to-leading order fits to the D-parameter and thrust minor event-shape observables are also performed for the first time. We find consistent results, but with significantly larger theoretical uncertainties.

The inclusive branching ratio for the process b→τ−ν̄τX has been measured using hadronic Z decays collected by the OPAL experiment at LEP in the years 1992–2000. The result is: BR(b→τ−ν̄τX)=(2.78±0.18±0.51)%. This measurement is consistent with the Standard Model expectation and puts a constraint of tanβ/MH±<0.53 GeV−1 at the 95% confidence level on Type II Two Higgs Doublet Models.

The production of charm quarks is studied in deep-inelastic electron–photon scattering using data recorded by the OPAL detector at LEP at nominal e+e− centre-of-mass energies from 183 to 209 GeV. The charm quarks have been identified by full reconstruction of charged D★ mesons using their decays into D0π with the D0 observed in two decay modes with charged particle final states, Kπ and Kπππ. The cross-section σD★ for production of charged D★ in the reaction e+e−→e+e−D★X is measured in a restricted kinematical region using two bins in Bjorken x, 0.0014<x<0.1 and 0.1<x<0.87. From σD★ the charm production cross-section σ(e+e−→e+e−cc̄X) and the charm structure function of the photon F2,cγ are determined in the region 0.0014<x<0.87 and 5<Q2<100 GeV2 . For x>0.1 the perturbative QCD calculation at next-to-leading order agrees perfectly with the measured cross-section. For x<0.1 the measured cross-section is 43.8±14.3±6.3±2.8 pb with a next-to-leading order prediction of 17.0+2.9−2.3 pb.

We observe Bose–Einstein correlations in π0 pairs using back-to-back two jet hadronic events from Z0 decays in the data sample collected by the OPAL detector at LEP 1 from 1991 to 1995. Using a static Gaussian picture for the pion emitter source, we obtain the chaoticity parameter λ=0.55±0.10±0.10 and the source radius R=(0.59±0.08±0.05) fm. According to the JETSET and HERWIG Monte Carlo models, the Bose–Einstein correlations in our data sample largely connect π0s originating from the decays of different hadrons. Prompt pions formed at string break-ups or cluster decays only form a small fraction of the sample.

A measurement of the forward–backward asymmetries of e+e−→bb̄ and e+e−→cc̄ events using electrons and muons produced in semileptonic decays of bottom and charm hadrons is presented. The outputs of two neural networks designed to identify b→ℓ− and c→ℓ+ decays are used in a maximum likelihood fit to a sample of events containing one or two identified leptons. The b and c quark forward–backward asymmetries at three centre-of-mass energies s and the average B mixing parameter χ̄ are determined simultaneously in the fit. Using all data collected by OPAL near the Z resonance, the asymmetries are measured to be: AFBbb̄=(4.7±1.8±0.1)%,AFBcc̄=(−6.8±2.5±0.9)%at〈s〉=89.51 GeV,AFBbb̄=(9.72±0.42±0.15)%,AFBcc̄=(5.68±0.54±0.39)%at〈s〉=91.25 GeV,AFBbb̄=(10.3±1.5±0.2)%,AFBcc̄=(14.6±2.0±0.8)%at〈s〉=92.95 GeV. For the average B mixing parameter, a value of: χ̄=(13.12±0.49±0.42)% is obtained. In each case the first uncertainty is statistical and the second systematic. These results are combined with other OPAL measurements of the b and c forward–backward asymmetries, and used to derive a value for the effective electroweak mixing angle for leptons sin2θeffℓ of 0.23238±0.00052.

The inclusive production of charged hadrons in the collisions of quasi-real photons (e+e−→e+e−+X) has been measured using the OPAL detector at LEP. The data were taken at e+e− centre-of-mass energies from 183 to 209GeV. The differential cross-sections as a function of the transverse momentum and the pseudorapidity of the hadrons are compared to theoretical calculations of up to next-to-leading order (NLO) in the strong coupling constant αs. The data are also compared to a measurement by the L3 Collaboration, in which a large deviation from the NLO predictions is observed.

Inclusive jet production (e+e- -> e+e- +jet+X) is studied in collisions of quasi-real photons radiated by the LEP beams at e+e- centre-of-mass energies sqrt see from 189 to 209 GeV. Jets are reconstructed using the kp jet algorithm. The inclusive differential cross-section is measured as a function of the jet transverse momentum, ptjet, in the range 5 <ptjet < 40 GeV for pseudo-rapidities, etaj, in the range -1.5 < etaj < 1.5. The results are compared to predictions of perturbative QCD in next-to-leading order in the strong coupling constant.

The b quark forward–backward asymmetry has been measured using hadronic Z0 decays collected by the OPAL experiment at LEP. Z0→bb̄ decays were selected using a combination of secondary vertex and lepton tags, and the sign of the b quark charge was determined using an inclusive tag based on jet, vertex and kaon charges. The results, corrected to the quark level, are: AFBb=0.0582±0.0153±0.0012ats=89.50GeV,AFBb=0.0977±0.0036±0.0018ats=91.26GeV,AFBb=0.1221±0.0123±0.0025ats=92.91 GeV, where the first error is statistical and the second systematic in each case. Within the framework of the Standard Model, the result is interpreted as a measurement of the effective weak mixing angle for electrons of sin2θeff,eW=0.23205±0.00068.

We have measured the mean charged particle multiplicities separately for bb̄, cc̄ and light quark (uū,dd̄,ss̄) initiated events produced in e+e− annihilations at LEP. The data were recorded with the OPAL detector at eleven different energies above the Z0 peak, corresponding to the full statistics collected at LEP1.5 and LEP2. The difference in mean charged particle multiplicities for bb̄ and light quark events, δbl, measured over this energy range is consistent with an energy independent behaviour, as predicted by QCD, but is inconsistent with the prediction of a more phenomenological approach which assumes that the multiplicity accompanying the decay of a heavy quark is independent of the quark mass itself. Our results, which can be combined into the single measurement δbl=3.44±0.40(stat)±0.89(syst) at a luminosity weighted average centre-of-mass energy of 195 GeV, are also consistent with an energy independent behaviour as extrapolated from lower energy data.

QCD coherence effects are studied based on measurements of correlations of particles with either restricted transverse momenta, pT<pTcut, where pT is defined with respect to the thrust axis, or restricted absolute momenta, p≡|p|<pcut, using about four million hadronic Z decays recorded at LEP with the OPAL detector. The correlations are analyzed in terms of normalized factorial and cumulant moments. The analysis is inspired by analytical QCD calculations which, in conjunction with Local Parton–Hadron Duality (LPHD), predict that, due to colour coherence, the multiplicity distribution of particles with restricted transverse momenta should become Poissonian as pTcut decreases. The expected correlation pattern is indeed observed down to pTcut≈1GeV but not at lower transverse momenta. Furthermore, for pcut→0GeV a strong rise is observed in the data, in disagreement with theoretical expectation. The Monte Carlo models reproduce well the measurements at large pTcut and pcut but underestimate their magnitudes at the lowest momenta. The e+e− data are also compared to the measurements in deep-inelastic e+p collisions at HERA. It is shown that for soft particles, the often assumed equivalence of a single hemisphere in e+e− annihilation with the current region in the Breit frame of a deep-inelastic collision may be misleading. Our study indicates difficulties with the LPHD hypothesis when applied to many-particle inclusive observables of soft hadrons.

This paper describes a topological search for an invisibly decaying Higgs boson, H, produced via the Bjorken process (e+e-→HZ). The analysis is based on data recorded using the OPAL detector at LEP at centre-of-mass energies from 183 to 209 GeV corresponding to a total integrated luminosity of 629 pb-1. In the analysis only hadronic decays of the Z boson are considered. A scan over Higgs boson masses from 1 to 120 GeV and decay widths from 1 to 3000 GeV revealed no indication for a signal in the data. From a likelihood ratio of expected signal and standard model background we determine upper limits on cross-section times branching ratio to an invisible final state. For moderate Higgs boson decay widths, these range from about 0.07 pb (MH=60 GeV) to 0.57 pb (MH=114 GeV). For decay widths above 200 GeV the upper limits are of the order of 0.15 pb. The results can be interpreted in general scenarios predicting a large invisible decay width of the Higgs boson. As an example we interpret the results in the so-called stealthy Higgs scenario. The limits from this analysis exclude a large part of the parameter range of this scenario experimentally accessible at LEP 2.

A method to search for particles of unknown masses in events with missing energy is presented. The only assumption is the topology of the decay chain. The solvability of the event has significant mass information and can be used to extract the unknown masses. The method is tested in events with top pairs decaying leptonically with the presence of two neutrinos in the final state. Similar topologies are predicted by supersymmetric models with conserved R-parity were sparticles are produced in pairs through cascade decay chains with the presence of the lightest neutralino in the end of each chain.

Shield jamming is one of the potential problems for mechanized tunnelling through squeezing ground. The risk of jamming depends essentially on the rapidness of rock deformation and thus on the creep and consolidation rate of the ground. For given geotechnical conditions, the load exerted by the ground upon a shield during continuous excavation depends on the TBM advance rate, on the shield length, on the amount of overboring and on the coefficient of friction between the steel and the rock. During a break in operations, the ground pressure increases with time, thereby necessitating a higher thrust in order to overcome skin friction and to restart TBM. The critical duration of a standstill depends on all of the parameters mentioned above and, of course, on the available thrust. An interesting result is that a high advance rate not only reduces the risk of a shield jamming during continuous excavation, but also increases the critical duration of a subsequent standstill. Figure 1. Required total thrust force Ftot as a function of the advance rate v (ground permeability k = 10 m/s, gap between shield and ground R = 5 or 15 cm, shield length L = 10 m, skin friction coefficient  = 0.25; for other parameters: see Table 1). Figure 2. Radial pressure p acting upon the shield or lining at different times t during standstill (advance rate before standstill v = 10 m/cd, ground permeability k = 10 m/s, gap between shield and ground R = 5 or 15 cm; for other parameters: see Table 1). The same mechanisms govern the ground behaviour in the course of an excavation standstill (Section 4). If the drained conditions have not been reached already during the preceding continuous excavation (i.e. if the advance rate was high enough or the ground permeability low), consolidation will continue during the standstill period until reaching the steady state pore pressure distribution. Due to the change of the effective stresses, the ground will deform and the rock pressure will increase over time. The higher the advance rate during the preceding excavation, the more the conditions prevailing at the begin of standstill will deviate from the drained conditions and, consequently, the more time must elapse until reaching a steady state. So, rapid excavation is advantageous also with respect to a subsequent standstill, whether intended or not. 3 THRUST REQUIRED DURING EXCAVATION When tunnelling with a shielded TBM, some limited convergence can occur, due to the gap between the shield and the surrounding ground. If the convergences develop fast enough, the ground closes the gap near to the tunnel face, thereby starting to develop pressure upon the shield. If the permeability is low and the advance rate high, the gap remains open for a longer period and, consequently, the pressure acting upon the shield is lower or even zero. The thrust force required to overcome shield friction during continuous excavation in given ground conditions depends on the length of the shield L, on the amount of overboring R, on the skin friction coefficient  and on the advance rate v. A reduction in the advance rate leads as a rule to an increase in the ground pressure, and thus to further deceleration or even standstill of the machine. The available thrust force depends on the installed thrust and on the capacity of the thrusting system. Subsequently, the role of pore water pressure dissipation will be illustrated by means of a numerical example concerning a 500 m deep, O 10 m tunnel which crosses weak ground at a depth of 100 m beneath the water table. Information on the modelling assumptions and numerical procedures can be found in the Appendix. Figure 1 shows the thrust force Ftot required to overcome the friction of a 10 m long shield as a function of the advance rate v in a low-permeability ground (k = 10 m/s). The curves have been calculated by integrating the ground pressure p over the shield length L and taking into account additionally the thrust needed for the boring process (15 MN). The skin friction coefficient  was taken equal to 0.25. In the case of a normal overboring (R = 5 cm, upper curve), a continuous excavation rate of v = 10 m/cd in combination with a considerable thrust of about 90 MN would be necessary to overcome squeezing. The lower curve applies to a gap of R = 15 cm. Accordingly, the thrust requirements can be reduced considerably by a major overboring – this comes, however, at the cost of possible steering difficulties and reduced production rates. 4 THRUST NEEDED FOR RESTARTING OPERATION Generally, it is not possible to completely avoid standstills of a TBM drive. Besides the unpredictable stops due to technical problems, it has first of all to be considered that a certain time is needed for support installation (real continuous excavation is only possible with double shielded TBMs advancing in gripper mode). An important factor is also the need to carry out regular maintenance work. This causes halts in excavation but is at the same time important for reducing the risk of mechanical breakdown. In difficult ground conditions, it is important to keep standstills as short as possible. If an identified critical zone has to be crossed, exhaustive maintenance work should be accomplished in advance and the necessary logistical precautions taken to allow for continuous operation in the critical zone. Figure 2 shows, for the example discussed before, the ground pressure p acting upon the shield and lining at different times t (elapsed since the standstill began) assuming that the preceding excavation advanced by v =10 m/cd. In this numerical example, the face was considered as being unsupported. The core yields and extrudes freely, the radial stress ahead of the face decreases, additional load is transferred to the shield via arching in the longitudinal direction and, therefore, a pressure peak occurs close to the face (Fig. 2). The behaviour of the face in squeezing ground is the subject of current research. Figure 3 shows the time-development of the respective total thrust force Ftot required in order to restart excavation for a 10 m long shield. During continuous excavation the machine has to overcome sliding friction, while directly after the TBM-stop (t = 0) static friction becomes relevant. Therefore, a higher skin-friction coefficient μ was considered (0.40 instead of 0.25, Gehring 1996). In the case of a major overboring (ΔR = 15 cm), the gap between shield and ground remains open for a certain period. The ground starts to exert a pressure upon the shield only after 5 days, while reaching steady state conditions takes about 50 days. The required thrust force may increase to the level of the available thrust force after a certain period of time. Figure 4 shows the influence of ground permeability k on the critical standstill duration tcrit under the assumptions that the advance rate was v = 10 m/cd before the standstill and that the available thrust force amounts to 150 MN – a high, but still feasible value (Grandori 2006, Stahn & Grimm 2006). The higher the permeability of the ground, the shorter the critical standstill duration will be. For permeabilities higher than about k = 10 m/s and a normal overboring of ΔR = 5 cm, the critical standstill duration tcrit decreases rapidly to zero: at this permeability range, the required thrust force was close to the available one already during the previous continuous excavation that proceeded with v = 10 m/cd. However, as mentioned in Section 2, the conditions prevailing at the beginning of a standstill will depend on the advance rate during the previous TBM operation: for a given ground permeability k, the higher the advance rate v, the lower the total required thrust force Ftot will be during excavation (Fig. 1) and, therefore, the more time must elapse during a standstill in order that the required thrust reaches the available one (Fig. 5). Figure 3. Required total thrust force Ftot as a function of the standstill length t (advance rate before standstill v = 10 m/cd, ground permeability k = 10 m/s, gap between shield and ground ΔR = 5 or 15 cm, shield length L = 10 m, skin friction coefficient μ = 0.25 or 0.40 for continuous excavation or standstill, respectively; for other parameters: see Table 1). Figure 4. Critical standstill duration tcrit as a function of ground permeability k (available thrust force Ftot = 150 MN, advance rate before standstill v = 10 m/cd, gap between shield and ground ΔR = 5 or 15 cm, shield length L = 10 m, skin friction coefficient μ = 0.40; for other parameters: see Table 1). Figure 5. Critical standstill duration tcrit as a function of the advance rate v before standstill (available thrust force Ftot = 150 MN, ground permeability k = 10 m/s, gap between shield and ground ΔR = 5 or 15 cm, shield length L = 10 m, skin friction coefficient μ = 0.40; for other parameters: see Table 1).

Data collected around $\sqrt{s}=91$ GeV by the OPAL experiment at the LEP e+e− collider are used to study the mechanism of baryon formation. As the signature, the fraction of Σ− hyperons whose baryon number is compensated by the production of a $\overline{\Sigma^{-}},\overline{\Lambda}$ or $\overline{\Xi^{-}}$ antihyperon is determined. The method relies entirely on quantum number correlations of the baryons, and not rapidity correlations, making it more model independent than previous studies. Within the context of the JETSET implementation of the string hadronization model, the diquark baryon production model without the popcorn mechanism is strongly disfavored with a significance of 3.8 standard deviations including systematic uncertainties. It is shown that previous studies of the popcorn mechanism with $\Lambda \overline{\Lambda}$ and $\mathrm{p}\uppi \overline{\mathrm{p}}$ correlations are not conclusive, if parameter uncertainties are considered.

This paper analyses the data monitored during tunnel construction in the Giumello gneiss formation of the Ceneri Base Tunnel in order to find the factors that have a major influence on squeezing convergences. The observed deformations were distributed non-uniformly over the tunnel cross-section and varied along the tunnel. The Giumello gneiss formation is characterized by heterogeneity and anisotropy (faults, schistosity). Analysis of the data shows that the non-uniform distribution of the deformations in the tunnel cross-section is mainly due to the schistosity of the rock mass. The effect of rock anisotropy is, nevertheless, superposed by those of lithology and of fault zones, which also influence the distribution of the convergences.

Four-fermion final states qqbar e+e- and qqbar mu+mu- from neutral-current interactions in e+e- collisions are studied in the OPAL detector at LEP at centre-of-mass energies from 183 GeV to 209 GeV. The data analysed correspond to a total integrated luminosity of about 650 pb-1 recorded from 1997 to 2000. Corresponding to the acceptance of the OPAL detector, a signal definition is applied requiring both leptons to have a scattering angle satisfying cos0 <0.95. Further requirements are made on the invariant masses of the fermion pairs. The extracted cross-sections for the processes e+e- -> qqbar e+e- and e+e- qqbar mu+mu- are consistent with the expectations from the Standard Model.

A search for first generation scalar and vector leptoquarks (LQ) as well as for squarks ( $\tilde{\mbox{q}}$ ) in R-parity violating SUSY models with the direct decay of the $\tilde{\mbox{q}}$ into Standard Model particles has been performed using e $^+$ e $^-$ collisions collected with the OPAL detector at LEP at an e $^+$ e $^-$ centre-of-mass energy $\sqrt{s_{\rm ee}}$ of 189 GeV. The data correspond to an integrated luminosity of about 160 pb $^{-1}$ . The dominant process for this search is $\mbox{eq}\to\LQ/\tilde{\mbox{q}}\to\mbox{eq},\nu\mbox{q}$ , where a photon, which has been radiated by one of the beam electrons, serves as a source of quarks. The numbers of selected events found in the two decay channels are in agreement with the expectations from Standard Model processes. This result allows to set lower limits at the 95% confidence level on the mass of first generation scalar and vector leptoquarks, and of squarks in R-parity violating SUSY models. For Yukawa couplings $\lambda$ to fermions larger than $\sqrt{4\pi\alpha_{\rm em}}$ , the mass limits range from 121 GeV $/c^2$ to $175$ GeV $/c^2$ ( $149$ GeV $/c^2$ to $188$ GeV $/c^2$ ) depending on the branching ratio $\beta$ of the scalar (vector) leptoquark state. Furthermore, limits are set on the Yukawa couplings $\lambda$ for leptoquarks and $\lambda'_{1jk}$ for squarks, and on $\beta$ as a function of the scalar leptoquark/squark mass.

The present paper investigates the problem of the stability of the tunnel face under seepage flow conditions based upon the so-called “method of slices”. This computational model improves the limit equilibrium method of Anagnostou & Kovari (1996) by treating the equilibrium in the wedge consistently with the overlying prism and does not need an a priori assumption concerning the distribution of the vertical stresses. Assuming a simplified distribution of the hydraulic head in the ground ahead of the face, a closed-form solution is derived which can be used for assessing face stability.

On account of their low permeability, clays respond to tunnel excavation with a considerable delay.This is favourable for the interplay between ground, tunnel support and tunnelling equipment and, inter alia, also for the stability of the tunnel face.Nevertheless, even when tunnelling through practically impermeable clay deposits, the face may fail under certain conditions.The latter represents the subject of the present paper.Specifically, based upon a simple but accurate face stability model and a well-known empirical relationship, this paper provides generic answers to two important questions: which geotechnical conditions would result in an unstable face, thus necessitating, e.g., closed-mode TBM operation?and which conditions would be prohibitive in this respect, i.e. the required face support pressure would be beyond today's technical feasibility limits, so that soil improvement measures would become indispensable?

Many variants of (delegated) Proof-of-Stake blockchains have been introduced since 2016, among which Cardano, Algorand, and Tezos have been more widely adopted. Each of these blockchains has attempted to address the scalability and consumption issues of Proof-of-Work (PoW) blockchains from different angles. However, the economic incentives of these blockchains have raised the concern about the decentralisation level of key players, such as validators, and stakeholders, in those “expected to be decentralised” networks. In this work, we conduct an analysis of Cardano's activity and wealth concentration. For the first time, we perform a clustering of the addresses that belong to the same wallet based on existing heuristics for UTXO-like blockchains. Moreover, an analysis of reward distribution on Cardano is presented. The analysis results of this work disclose objective insights into the Cardano blockchain, including the rewards distribution, stake balance distribution, and wealth concentration.

The process e+ e- -> e+ e- Z/gamma* is studied with the OPAL detector at LEP at a centre of mass energy of sqrt(s) = 189 GeV. The cross-section times the branching ratio of the Z/gamma* decaying into hadrons is measured within Lorentz invariant kinematic limits to be (1.2 +/- 0.3 +/- 0.1) pb for invariant masses of the hadronic system between 5 GeV and 60 GeV and (0.7 +/- 0.2 +/- 0.1) pb for hadronic masses above 60 GeV. The differential cross-sections of the Mandelstam variables s-hat, t-hat, and u-hat are measured and compared with the predictions from the Monte Carlo generators grc4f and PYTHIA. From this, based on a factorisation ansatz, the total and differential cross-sections for the subprocess e gamma -> e Z/gamma* are derived.

A new scalar resonance, called the radion, with couplings to fermions and bosons similar to those of the Higgs boson, is predicted in the framework of Randall–Sundrum models, proposed solutions to the hierarchy problem with one extra dimension. An important distinction between the radion and the Higgs boson is that the radion would couple directly to gluon pairs, and in particular its decay products would include a significant fraction of gluon jets. The radion has the same quantum numbers as the Standard Model (SM) Higgs boson, and therefore they can mix, with the resulting mass eigenstates having properties different from those of the SM Higgs boson. Existing searches for the Higgs bosons are sensitive to the possible production and decay of radions and Higgs bosons in these models. For the first time, searches for the SM Higgs boson and flavour-independent and decay-mode independent searches for a neutral Higgs boson are used in combination to explore the parameter space of the Randall–Sundrum model. In the dataset recorded by the OPAL experiment at LEP, no evidence for radion or Higgs particle production was observed in any of those searches at centre-of-mass energies up to 209 GeV. The results are used to set limits on the radion and Higgs boson masses. For all parameters of the Randall–Sundrum model, the data exclude masses below 58 GeV for the mass eigenstate which becomes the Higgs boson in the no-mixing limit.

Measurements of Rb, the ratio of the bbbar cross-section to the qqbar cross- section in e+e- collisions, are presented. The data were collected by the OPAL experiment at LEP at centre-of-mass energies between 182 GeV and 209 GeV. Lepton, lifetime and event shape information is used to tag events containing b quarks with high efficiency. The data are compatible with the Standard Model expectation. The mean ratio of the eight measurements reported here to the Standard Model prediction is 1.055+-0.031+-0.037, where the first error is statistical and the second systematic.

Events with a final state consisting of two or more photons and large missing transverse energy have been observed in e+e− collisions at centre-of-mass energies in the range 192–209 GeV using the OPAL detector at LEP. Cross-section measurements are performed within the kinematic acceptance of the selection and compared with the expectations from the Standard Model process e+e−→νν¯γγ(γ). No evidence for new physics contributions to this final state is observed. Upper limits on σ(e+e−→XX)⋅BR2(X→Yγ) are derived for the case of stable and invisible Y. In the case of massive Y the combined limits obtained from all the data range from 10 to 60 fb, while for the special case of massless Y the range is 20 to 40 fb. The limits apply to pair production of excited neutrinos (X=ν*,Y=ν), to neutralino production (X=χ˜20,Y=χ˜10) and to supersymmetric models in which X=χ˜10 and Y=G˜ is a light gravitino.

A review is presented of searches performed by CMS experiment for new particles produced in association with or decaying to top quarks, as well as heavy top partners. The analysis presented use data collected with CMS experiment during 2012, in proton-proton collisions at a centre-of-mass energy of 8 TeV.