L. Wang

The addition of discontinuous silicon carbide (SiC) to aluminum (Al) alloys can result in a five-fold increase in the yield stress. The magnitude of the increase is obviously a function of the volume fraction and the particle size of the SiC. Previously, it was proposed that the strength increase due to SiC addition to Al alloys was the result of change in the matrix strength, i.e. an increase in dislocation density and a reduction of subgrain size. The data obtained from a series of experiments indicate that dislocation density increases with an increase in volume fraction of SiC and decreases with an increase in particle size. The subgrain size decreases as the volume fraction increases and increases as the particle size increases. There is a good correlation between the microstructural changes in the matrix and the changes in the yield stress of the composites. L'addition de carbure de silicium (SiC) discontinu à des alliages d'aluminium (Al) peut conduire à une élévation d'un facteur 5 de la lamite élastique. La grandeur de cette augmentation est évidemment fonction de la fraction volumique et de la taille des particules de SiC. On a déjà suggéré que l'augmentation de la résistance mécanique due à l'addition de SiC dans les alliages d'aluminium est le résultat d'un changement de la résistance mécanique de la matrice, c'est à dire d'une augmentation de la densité de dislocations et d'une réduction de la taille des sous-grains. Les données obtenues pour une série d'expériences indiquent que la densité de dislocations croît lorsque la fraction volumique de SiC augmente et décroît lorsque la taille des particules croît. La taille des sous-grains décroît lorsque la fraction volumique augmente et croît lorsque la taille des particules diminue. Il existe une bonne corrélation entre les changements microstructuraux dans la matrice et les variations de la lamite élastique des composites. Zugabe von diskontinuierlichem Siliziumkarbid (SiC) zu Aluminium (Al)-Legierungen kann die Flieβspannung verfünffachen. Diese Erhöhung hängt offenkundig vom Volumantiel und der Teilchengröβe des SiC ab. Früher wurde dargelegt, daβ diese Festigkeitserhöhung von einer Änderung in der Matrixfestigkeit, d.h. einem Anstieg in der Versetzungsdichte und einer Verringerung der Subkorngröβe, herrührt. Eine Reihe von erhaltenen experimentallen Ergebnissen zeigt, daβ die Versetzungsdichte mit zunehmenden Volumantiel von SiC ansteigt und mit zunehmender Teilchengröβe abnimmt. Die Subkorngröβe nimmt mit zunehmendem Volumantiel ab und mit zunehmender Teilchengröβe zu. Zwischen den Änderungen in der Mikrostruktur der Matrix und den Änderungen der Flieβspannung des Materials besteht gute Korrelation.

Tensile tests of SiC-6061 Al composites containing various volume fractions of whiskers or particles (20, 5 and 0 vol.%) showed that for samples containing a high volume fraction (20 vol.%) the fracture process was very localized, i.e. a very narrow neck. As the volume fraction of whiskers or particles decreased, the deformed region spread out. One might expect that the microstructure should correspond to the macroscale changes. In the highly deformed region the dislocation density is expected to be higher, in the less deformed regions the dislocation density should be lower, and if the deformation is very localized, then the high dislocation density should also be limited to a very narrow region. Overall, there is good agreement between the microstructure (dislocation density) change and the macroscale deformation of SiCAl composite tensile samples. The mechanism proposed to account for this change in deformation behavior as a function of volume fraction of SiC in aluminum is related to the expansion of the plastic zone (due to differences in thermal coefficients of expansion between SiC and aluminum) when the external stress is applied. Also, the localized deformation is related to localized clusters of SiC particles. There is a cooperative effect which leads to a region of very localized plastic deformation.

Quantum-mechanical fluctuations between competing phases at $T=0$ induce exotic finite-temperature collective excitations that are not described by the standard Landau Fermi liquid framework. These excitations exhibit anomalous temperature dependences, or non-Fermi liquid behavior, in the transport and thermodynamic properties in the vicinity of a quantum critical point, and are often intimately linked to the appearance of unconventional Cooper pairing as observed in strongly correlated systems including the high-$T_c$ cuprate and iron pnictide superconductors. The presence of superconductivity, however, precludes direct access to the quantum critical point, and makes it difficult to assess the role of quantum-critical fluctuations in shaping anomalous finite-temperature physical properties. Here we report temperature-field scale invariance of non-Fermi liquid thermodynamic, transport, and Hall quantities in a non-superconducting iron-pnictide, Ba(Fe$_{1/3}$Co$_{1/3}$Ni$_{1/3}$)$_{2}$As$_{2}$, indicative of quantum criticality at zero temperature and zero applied magnetic field. Beyond a linear in temperature resistivity, the hallmark signature of strong quasiparticle scattering, we find the scattering rate that obeys a universal scaling relation between temperature and applied magnetic fields down to the lowest energy scales. Together with the dominance of hole-like carriers close to the zero-temperature and zero-field limits, the scale invariance, isotropic field response, and lack of applied pressure sensitivity suggests a unique quantum critical system that does not drive a pairing instability.

Abstract The helimagnet FeP is part of a family of binary pnictide materials with the MnP-type structure, which share a nonsymmorphic crystal symmetry that preserves generic band structure characteristics through changes in elemental composition. It shows many similarities, including in its magnetic order, to isostructural CrAs and MnP, two compounds that are driven to superconductivity under applied pressure. Here we present a series of high magnetic field experiments on high-quality single crystals of FeP, showing that the resistance not only increases without saturation by up to several hundred times its zero-field value by 35 T, but that it also exhibits an anomalously linear field dependence over the entire range when the field is aligned precisely along the crystallographic c -axis. A close comparison of quantum oscillation frequencies to electronic structure calculations links this orientation to a semi-Dirac point in the band structure, which disperses linearly in a single direction in the plane perpendicular to field, a symmetry-protected feature of this entire material family. We show that the two striking features of magnetoresistance—large amplitude and linear field dependence—arise separately in this system, with the latter likely due to a combination of ordered magnetism and topological band structure.

Atomic defect color centers in solid-state systems hold immense potential to advance various quantum technologies. However, the fabrication of high-quality, densely packed defects presents a significant challenge. Herein we introduce a DNA-programmable photochemical approach for creating organic color-center quantum defects on semiconducting single-walled carbon nanotubes (SWCNTs). Key to this precision defect chemistry is the strategic substitution of thymine with halogenated uracil in DNA strands that are orderly wrapped around the nanotube. Photochemical activation of the reactive uracil initiates the formation of sp3 defects along the nanotube as deep exciton traps, with a pronounced photoluminescence shift from the nanotube band gap emission (by 191 meV for (6,5)-SWCNTs). Furthermore, by altering the DNA spacers, we achieve systematic control over the defect placements along the nanotube. This method, bridging advanced molecular chemistry with quantum materials science, marks a crucial step in crafting quantum defects for critical applications in quantum information science, imaging, and sensing.

The addition of 20 vol.% titanium diboride in particulate form (1–3 μm) to nickel aluminide (TiB2NiAl) results in a twofold increase in the high temperature strength of NiAl. There are at least two theories that have been proposed to account for the high temperature strength of discontinuous reinforced metal matrix composites. However, they cannot be adequately used as a basis to explain the observed strengthening. An investigation was undertaken of NiAl, 10vol.%TiB2NiAl and 20vol.%TiB2NiAl in the annealed condition and after deformation, allowed to cool slowly. There is a low dislocation density in the annealed samples and the dislocation density did increase slightly as a result of deformation. However, deformation did produce some intriguing dislocation arrangements; for example, it was found that there was a high dislocation density within the TiB2 in the deformed higher volume fraction composites and the dislocation density within the NiAl matrix was not uniform.

Acquisition of the customer data for product design selection using conventional customer survey techniques can be a time-consuming and costly undertaking. The aim of this paper is to overcome this limitation by using web based User-Generated Content (UGC) as an alternative to the conventional customer survey techniques. UGC refers to various public media contents created by web users including contents in online customer reviews, blogs, and social networking interactions. So far, there has not been any systematic effort in using UGC in design selection for a customer durable product. Using UGC in product design selection is not an easy task because UGC can be freely expressed and written by customers with little constraints, structure and bounds. As a result, UGC can contain a lot of noise, variability in content and even bias induced by the customers. In order to make use of UGC, this paper develops a systematic methodology for eliciting product attributes from UGC, constructing customer preference models and using these models in design selection. To demonstrate the proposed method, design selection of a smartphone using UGC is considered as an example. It is shown in the example that the proposed method can provide a reasonable estimation of customer preferences while being useful for product design selection.

The interfacial structure of a SiC/Al composite was investigated in order to determine whether a specific orientation relationship exists between the basal planes of α-SiC and Al and, also, to obtain evidence as to the possible existence of dislocations at the interface between SiC and Al. The interface was seen to be clean and free of any voids. Although some interfaces showed the appearance of a thick amorphous layer, most of the interfaces appeared to show a clean and continuous bond across the interface. The (112) Al planes were parallel to the basal planes of the α-SiC so that a specific crystallographic orientation was obtained at the interface. Dislocations were not observed at the interface (except for those in the matrix that had been generated due to the difference in the coefficients of thermal expansion).

A wide-gap-chamber experiment has been performed to study the decay of the KLO meson into π+π−πO. If the matrix element for this decay is parametrized in the form M ∝ 1 + α (mKmπ+2)(2TπO − TπOmax) the value of α from this experiment is α = −0.311 ± 0.026. The error estimated here includes uncertainties in systematic errors. The data also provide a measure of the charge asymmetry: N+ − N−N+ + N− = 0.000 ± 0.018.

A wide-gap spark chamber operated in a magnetic field has been used to measure the energy dependence of the form factor ${f}_{+}({q}^{2}) \mathrm{in} {K}_{L}^{0}\ensuremath{\rightarrow}\ensuremath{\pi}+e+\ensuremath{\nu}$ decay. Decays of ${K}_{L}^{0}$ mesons in vacuum were detected in the -30\ifmmode^\circ\else\textdegree\fi{} neutral beam of the AGS at Brookhaven National Laboratory. ${K}_{e3}^{0}$ decays were identified by electromagnetic showers produced in a lead radiator plate between the two 12-inch gaps of the chamber. The linear parameter ${\ensuremath{\lambda}}_{+}$ in the form factor ${f}_{+}({q}^{2})$ was determined to be 0.040 \ifmmode\pm\else\textpm\fi{} 0.012, where the error includes uncertainties in the corrections for systematic effects. A study of these systematic effects and the resulting errors is presented.