Yan‐Wen Tan

When electrons are confined in two-dimensional materials, quantum-mechanically enhanced transport phenomena such as the quantum Hall effect can be observed. Graphene, consisting of an isolated single atomic layer of graphite, is an ideal realization of such a two-dimensional system. However, its behaviour is expected to differ markedly from the well-studied case of quantum wells in conventional semiconductor interfaces. This difference arises from the unique electronic properties of graphene, which exhibits electron-hole degeneracy and vanishing carrier mass near the point of charge neutrality. Indeed, a distinctive half-integer quantum Hall effect has been predicted theoretically, as has the existence of a non-zero Berry's phase (a geometric quantum phase) of the electron wavefunction--a consequence of the exceptional topology of the graphene band structure. Recent advances in micromechanical extraction and fabrication techniques for graphite structures now permit such exotic two-dimensional electron systems to be probed experimentally. Here we report an experimental investigation of magneto-transport in a high-mobility single layer of graphene. Adjusting the chemical potential with the use of the electric field effect, we observe an unusual half-integer quantum Hall effect for both electron and hole carriers in graphene. The relevance of Berry's phase to these experiments is confirmed by magneto-oscillations. In addition to their purely scientific interest, these unusual quantum transport phenomena may lead to new applications in carbon-based electronic and magneto-electronic devices.

The conductivity of graphene samples with various levels of disorder is investigated for a set of specimens with mobility in the range of 1-20x10(3) cm2/V sec. Comparing the experimental data with the theoretical transport calculations based on charged impurity scattering, we estimate that the impurity concentration in the samples varies from 2-15x10(11) cm(-2). In the low carrier density limit, the conductivity exhibits values in the range of 2-12e2/h, which can be related to the residual density induced by the inhomogeneous charge distribution in the samples. The shape of the conductivity curves indicates that high mobility samples contain some short-range disorder whereas low mobility samples are dominated by long-range scatterers.

The quantum Hall (QH) effect in two-dimensional (2D) electrons and holes in high quality graphene samples is studied in strong magnetic fields up to 45 T. QH plateaus at filling factors $\nu=0,\pm 1,\pm 4$ are discovered at magnetic fields $B>$20 T, indicating the lifting of the four-fold degeneracy of the previously observed QH states at $\nu=\pm(|n|+1/2)$, where $n$ is the Landau level index. In particular, the presence of the $\nu=0, \pm 1$ QH plateaus indicates that the Landau level at the charge neutral Dirac point splits into four sublevels, lifting sublattice and spin degeneracy. The QH effect at $\nu=\pm 4$ is investigated in tilted magnetic field and can be attributed to lifting of the spin-degeneracy of the $n=1$ Landau level.

In this Communication, we report fabrication of ultrabright water-dispersible silicon nanoparticles (SiNPs) with quantum yields (QYs) up to 75% through a novelly designed chemical surface modification. A simple one-pot surface modification was developed that improves the photoluminescent QYs of SiNPs from 8% to 75% and meanwhile makes SiNPs water-dispersible. Time-correlated single photon counting and femtosecond time-resolved photoluminescence techniques demonstrate the emergence of a single and uncommonly highly emissive recombination channel across the entire NP ensemble induced by surface modification. The extended relatively long fluorescence lifetime (FLT), with a monoexponential decay, makes such surface-modified SiNPs suitable for applications involving lifetime measurements. Experimental results demonstrate that the surface-modified SiNPs can be utilized as an extraordinary nanothermometer through FLT imaging.

The quantum Hall (QH) effect in two-dimensional electron and hole gas is studied in high quality graphene samples. Graphene samples whose lateral size ∼10 μm were fabricated into mesoscopic devices for electrical transport measurement in magnetic fields. In an intermediate field range of up to 10 T, a distinctive half-integer QH effect is discovered with QH plateaus appearing at a filling factor sequence, ν=4(n+1/2), where n is the Landau level (LL) index. As the magnetic field increases to the extreme quantum limit, we observe additional QH plateaus at filling factors ν=0,±1,±4. Further detailed investigations show that the presence of the ν=0,±1 QH states indicates the n=0 LL at the charge neutral Dirac point splits into four sublevels. This lifts both the sublattice and the spin degeneracy, while the QH states at ν=±4 can be attributed to lifting of the spin degeneracy of the LLs. Above 30 T of magnetic field, the large quasiparticle gaps between the n=0 and n=±1 LLs lead to the QH effect that can be observed even at room temperature.

Abstract Despite long‐term efforts for exploring antibacterial agents or drugs, potentiating antibacterial activity and meanwhile minimizing toxicity to the environment remains a challenge. Here, it is experimentally shown that the functionality of reduced graphene oxide (rGO) through copper ions displays selective antibacterial activity that is significantly stronger than that of rGO itself and no toxicity to mammalian cells. Remarkably, this antibacterial activity is two‐orders‐of‐magnitude greater than the activity of its surrounding copper ions. It is demonstrated that rGO is functionalized through the cation–π interaction to massively adsorb copper ions to form a rGO–copper composite and result in an extremely low concentration level of surrounding copper ions (less than ≈0.5 µ m ). These copper ions on rGO are positively charged and strongly interact with negatively charged bacterial cells to selectively achieve antibacterial activity, while rGO exhibits the functionality to not only actuate rapid delivery of copper ions and massive assembly onto bacterial cells but also result in the valence shift in the copper ions from Cu 2+ into Cu + , which greatly enhances the antibacterial activity. Notably, this rGO functionality through cation–π interaction with copper ions can similarly achieve algaecidal activity but does not exert cytotoxicity against neutrally charged mammalian cells.

We determine the density-dependent electron mass m(*) in two-dimensional electron systems of GaAs/AlGaAs heterostructures by performing detailed low-temperature Shubnikov-de Haas measurements. Using very high-quality transistors with tunable electron densities we measure m(*) in single, high mobility specimens over a wide range of r(s) (6 to 0.8). Toward low densities we observe a rapid increase of m(*) by as much as 40%. For 2>r(s)>0.8 the mass values fall approximately 10% below the band mass of GaAs. Numerical calculations are in qualitative agreement with our data but differ considerably in detail.

• A dielectric barrier discharge (DBD) reactor was used for to efficiently degrade hazardous benzohydroxamic acid (BHA). • The degradation process of BHA in DBD reactor conforms to first-order kinetic equations. • For AC voltage 14.5 kV, gas flow 30 L/min, treatment time 60 min, and concentration 80 mg/L, the degradation efficiency of BHA wastewater reached the highest 98.7 %. • O 3 , H 2 O 2 , and their transformed •OH, •O 2 - were the main causes of BHA degradation. • It verifies that Industrial beneficiation wastewater usually contains Pb 2+ and Cd 2+ improved the BHA degradation by the dielectric barrier discharge technology. A dielectric barrier discharge (DBD) reactor was developed to efficiently degrade hazardous benzohydroxamic acid (BHA) in industrial beneficiation wastewater. The structural and optimum discharge parameters of the DBD reactor for BHA degradation were determined experimentally. Degradation, visual images, voltage-current waveforms, and Lissajous figures were used to evaluate the BHA abatement performance. After treatment for 40 min, 84.3 % of BHA was degraded. The energy yield attained a maximum of 0.63 mg/kWh at 13.5 kV and a gas flow rate of 30 L/min. Regardless of the energy yield, the maximum degradation of BHA was 98.7 %. The BHA decomposition is described by a first-order kinetic model. The results demonstrate that if the BHA wastewater contains Pb 2+ and Cd 2+ ions, degradation of BHA is slightly improved by DBD. The degradation mechanism of BHA in the DBD reactor was analyzed by testing the concentration changes of O 3 , H 2 O 2 in the solution and the influence of •OH, •O 2 – on the degradation. This confirmed that hydrated electrons were not an important active substance in the degradation when discharge plasma was formed in an air atmosphere. Liquid chromatography-mass spectrometry was used to identify the intermediates of the degradation reaction and predict the degradation pathway of BHA.

Much evidence has shown that reactive oxygen species (ROS) regulate several plant hormone signaling cascades, but little is known about the real-time kinetics and the underlying molecular mechanisms of the target proteins in the brassinosteroid (BR) signaling pathway. In this study, we used single-molecule techniques to investigate the true signaling timescales of the major BR signaling components BRI1-EMS-SUPPRESSOR 1 (BES1) and BRASSINOSTEROID INSENSITIVE 2 (BIN2) of Arabidopsis thaliana. The rate constants of BIN2 associating with ATP and phosphorylating BES1 were determined to be 0.7 ± 0.4 mM-1 s-1 and 2.3 ± 1.4 s-1 , respectively. Interestingly, we found that the interaction of BIN2 and BES1 was oxygen-dependent, and oxygen can directly modify BIN2. The activity of BIN2 was switched on via modification of specific cysteine (Cys) residues, including C59, C95, C99 and C162. The mutation of these Cys residues inhibited the BR signaling outputs. These findings demonstrate the power of using single-molecule techniques to study the dynamic interactions of signaling components, which is difficult to be discovered by conventional physiological and biochemical methods.

Abstract As a powerful tool for studying molecular dynamics in bioscience, single-molecule fluorescence detection provides dynamical information buried in ensemble experiments. Fluorescence in the near-infrared (NIR) is particularly useful because it offers higher signal-to-noise ratio and increased penetration depth in tissue compared with visible fluorescence. The low quantum yield of most NIR fluorophores, however, makes the detection of single-molecule fluorescence difficult. Here, we use asymmetric plasmonic nano-antenna to enhance the fluorescence intensity of AIEE1000, a typical NIR dye, by a factor up to 405. The asymmetric nano-antenna achieve such an enhancement mainly by increasing the quantum yield (to ~80%) rather than the local field, which degrades the molecules’ photostability. Our coupled-mode-theory analysis reveals that the enhancements stem from resonance-matching between antenna and molecule and, more importantly, from optimizing the coupling between the near- and far-field modes with designer asymmetric structures. Our work provides a universal scheme for engineering single-molecule fluorescence in the near-infrared regime.

The cellular compartmentation induced by self-assembly of natural proteins has recently attracted widespread attention due to its structural–functional significance. Among them, as a highly conserved metabolic enzyme and one of the potential targets for cancers and parasitic diseases in drug development, CTP synthase (CTPS) has also been reported to self-assemble into filamentous structures termed cytoophidia. To elucidate the dynamical mechanism of cytoophidium filamentation, we utilize single-molecule fluorescence imaging to observe the real-time self-assembly dynamics of CTPS and the coordinated assembly between CTPS and its interaction partner, Δ1-pyrroline-5-carboxylate synthase (P5CS). Significant differences exist in the direction of growth and extension when the two proteins self-assemble. The oligomer state distribution analysis of the CTPS minimum structural subunit under different conditions and the stoichiometry statistics of binding CTPS and P5CS by single-molecule fluorescence photobleach counting further confirm that the CTPS cytoophidia are mainly stacked with tetramers. CTPS can act as the nucleation core to induce the subsequent growth of the P5CS filaments. Our work not only provide evidence from the molecular level for the self-assembly and coordinated assembly (coassembly) of CTPS with its interaction partner P5CS in vitro but also offer new experimental perspectives for the dynamics research of coordinated regulation between other protein polymers.

Abstract In this study, a dielectric barrier discharge reactor was designed for the rapid and efficient degradation of methylparaben (MeP), an organic pollutant in wastewater. The superiority of the degradation performance against MeP was jointly evaluated by degradation, voltage-current waveform plots, kinetic curves, energy efficiency and synergy factor. The single DBD discharge performance was investigated and it was determined that the coaxial electrode structure achieves an optimal energy consumption of 0.28 g/kWh at a dielectric tube thickness of 1 mm gas gap of 2 mm peak voltage of 21 kV.The degradation rate of MeP reached 70.1% after 15 min of treatment at discharge frequency of 7.8 kHz, aeration flow rate of 8 L/min, initial MeP concentration of 30 mg/L and pH=7. The DBD synergized persulfate (PS) system conforms to first-order kinetics, with a kinetic constant increase of 0.080 min -1 over single DBD. The highest synergy factor was 2.50 at a PS addition of 15 mM, and the highest energy efficiency was 0.99 g/kWh at an initial concentration of 90 mg/L of MeP. Common inorganic anions, CO2-3 promoted degradation, SO 2- 4 inhibited degradation, Cl - and HPO2-4 had little effect. •OH, •O-2, and SO-4• all participate in the reaction, with •O-2 contributing the most. H 2 O 2 and O 3 were equally involved in degradation.The actual intermediates of the degradation process were identified by LC-MS and combined with DFT calculations to predict the MeP degradation pathway, and toxicity analysis by QSAR model.

Cellular informational and metabolic processes are propagated with specific membrane fusions governed by soluble N-ethylmaleimide sensitive factor attachment protein receptors (SNARE). SNARE protein Ykt6 is highly expressed in brain neurons and plays a critical role in the membrane-trafficking process. Studies suggested that Ykt6 undergoes a conformational change at the interface between its longin domain and the SNARE core. In this work, we study the conformational state distributions and dynamics of rat Ykt6 by means of single-molecule Förster Resonance Energy Transfer (smFRET) and Fluorescence Cross-Correlation Spectroscopy (FCCS). We observed that intramolecular conformational dynamics between longin domain and SNARE core occurred at the timescale ~200 μs. Furthermore, this dynamics can be regulated and even eliminated by the presence of lipid dodecylphoshpocholine (DPC). Our molecular dynamic (MD) simulations have shown that, the SNARE core exhibits a flexible structure while the longin domain retains relatively stable in apo state. Combining single molecule experiments and theoretical MD simulations, we are the first to provide a quantitative dynamics of Ykt6 and explain the functional conformational change from a qualitative point of view.

Neutral spin texture (ST) excitations at $\ensuremath{\nu}=1/3$ are directly observed for the first time by resonant inelastic light scattering. They are determined to involve two simultaneous spin flips. At low magnetic fields, the ST energy is below that of the magnetoroton minimum. With increasing in-plane magnetic field these mode energies cross at a critical ratio of the Zeeman and Coulomb energies of ${\ensuremath{\eta}}_{c}=0.020\ifmmode\pm\else\textpm\fi{}0.001$. Surprisingly, the intensity of the ST mode grows with temperature in the range in which the magnetoroton modes collapse. The temperature dependence is interpreted in terms of a competition between coexisting phases supporting different excitations. We consider the role of the ST excitations in activated transport at $\ensuremath{\nu}=1/3$.

Abstract Membrane fluidity, essential for cell functions, is obviously affected by copper, but the molecular mechanism is poorly understood. Here, we unexpectedly observed that a decrease in phospholipid (PL) bilayer fluidity caused by Cu 2+ was more significant than those by Zn 2+ and Ca 2+ , while a comparable reduction occurred in the last two ions. This finding disagrees with the placement in the periodic table of Cu just next to Zn and far from Ca. The physical nature was revealed to be an anomalous attraction between Cu + cations, as well as the induced motif of two phospholipids coupled by Cu-Cu bond (PL- di Cu-PL). Namely, upon Cu 2+ ion binding to a negatively charged phosphate group of lipid, Cu 2+ was reduced to Cu + . The attraction of the cations then caused one Cu + ion simultaneously binding to two lipids and another Cu + , resulting in the formation of PL- di Cu-PL structure. In contrast, this attraction cannot occur in the cases of Zn and Ca ions. Remarkably, besides lipids, the phosphate group also widely exists in other biological molecules, including DNA, RNA, ADP and ATP. Our findings thus provide a new view for understanding the biological functions of copper and the mechanism underlying copper-related diseases, as well as lipid assembly.

We determine the spin susceptibility $χ$ in the weak interaction regime of a tunable, high quality, two-dimensional electron system in a GaAs/AlGaAs heterostructure. The band structure effects, modifying mass and g-factor, are carefully taken into accounts since they become appreciable for the large electron densities of the weak interaction regime. When properly normalized, $χ$ decreases monotonically from 3 to 1.1 with increasing density over our experimental range from 0.1 to $4\times10^{11} cm^{-2}$. In the high density limit, $χ$ tends correctly towards $χ\to 1$ and compare well with recent theory.

Abstract All-inorganic cesium lead halide perovskite quantum dots have recently received much attention as promising optoelectronic materials with great luminescent properties and bright application prospect in lighting, lasing, and photodetection. Although notable progress has been achieved in lighting applications based on such media, the performance could still be improved. Here, we demonstrate that the light emission from the perovskite QDs that possess high intrinsic luminous efficiency can be greatly enhanced by using metallic thin films, a technique that was usually considered only useful for improving the emission of materials with low intrinsic quantum efficiency. Eleven-fold maximal PL enhancement is observed with respect to the emission of perovskite QDs on the bare dielectric substrate. We explore this remarkable enhancement of the light emission originating from the joint effects of enhancing the incident photonic absorption of QDs at the excitation wavelength by means of the zero-order optical asymmetric Fabry–Perot-like thin film interference and increasing the radiative rate and quantum efficiency at the emission wavelength mediated by surface plasmon polaritons. We believe that our approach is also potentially valuable for the enhancement of light emission of other fluorescent media with high intrinsic quantum efficiency.

Cryptochromes are blue light receptors that mediate circadian rhythm and magnetic sensing in various organisms. A typical cryptochrome consists of a conserved photolyase homology region domain and a varying carboxyl-terminal extension across species. The structure of the flexible carboxyl-terminal extension and how carboxyl-terminal extension participates in cryptochrome's signaling function remain mostly unknown. In this study, we uncover the potential missing link between carboxyl-terminal extension conformational changes and downstream signaling functions. Specifically, we discover that the blue-light induced opening of carboxyl-terminal extension in C. reinhardtii animal-like cryptochrome can structurally facilitate its interaction with Rhythm Of Chloroplast 15, a circadian-clock-related protein. Our finding is made possible by two technical advances. Using single-molecule Förster resonance energy transfer technique, we directly observe the displacement of carboxyl-terminal extension by about 15 Å upon blue light excitation. Combining structure prediction and solution X-ray scattering methods, we propose plausible structures of full-length cryptochrome under dark and lit conditions. The structures provide molecular basis for light active conformational changes of cryptochrome and downstream regulatory functions.

In this study, the degradation of salicylhydroxamic acid (SHA) in industrial beneficiation wastewater was investigated using dielectric barrier discharge (DBD) and La-Fe3O4-doped activated carbon (La-Fe3O4/AC). The physical and chemical properties of La-Fe3O4/AC were studied using several characterization techniques including scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The response surface methodology was used to optimize three critical experimental parameters of the catalyst: its dosage and the mass ratios of La and Fe3O4. These parameters contributed to the SHA degradation in the following decreasing order: mass ratio of La > catalyst dosage > mass ratio of Fe3O4. The SHA degradation efficiency reached 98.6%, and the synergistic factor was 2.83 at a peak-to-peak discharge voltage of 23 kV. The results showed that the DBD-La-Fe3O4/AC system improved the SHA degradation efficiency and exhibited a significant synergistic effect. Pb2+ and Cu2+ slightly increased the SHA degradation efficiency. Quenching experiments on activated substances confirmed that •OH and O2– were crucial to the degradation of SHA. The O3 and H2O2 generated by the DBD-catalyst system were absorbed by the La-Fe3O4/AC catalyst to produce more •OH. Ten main intermediates were detected in the degradation process of the DBD-catalyst system using HPLC-MS, and three degradation procedures were proposed.

A dielectric barrier Discharge (DBD) plasma catalytic system for synergistic degradation of benzohydroxamic acid (BHA) was established. A series of Er3+-BiOI samples doped with rare earth elements (Er3+) were prepared by the hydrothermal synthesis method. The characterization showed that Er3+-BiOI had a microglobular structure assembled by nanosheets, and the specific surface area of Er3+-BiOI was larger than that of pure BiOI. The degradation performance showed that in the DBD/Er3+-BiOI system, the highest BHA degradation efficiency reached 96.3 % with 4 % Er3+. Compared with the DBD-BiOI system and the single DBD system, the degradation efficiency of BHA increased by 9.1 % and 17.5 %, respectively. Meanwhile, the kinetic constants and cofactors were also the highest, at 3.36 and 2.88 times the DBD-BiOI system, respectively. The radical capture experiments showed ∙OH, ∙O2−, and cavities play a key role in the degradation of BHA, while O3, H2O2, e−, and H+ promote the degradation of BHA. The intermediates in the degradation of BHA were determined by LC-MS, and the possible degradation pathways of BHA were predicted. Finally, the degradation mechanism of BHA in the DBD/4 % Er3+-BiOI system was proposed.

Accurate cell division requires the proper assembly of high-order septin structures. In fission yeast (Schizosaccharomyces pombe), Spn1-Spn4 are assembled into a primary septin ring at the division site, and the subsequent recruitment of Mid2 to the structure results in a stable septin ring. However, not much is known about the regulation of this key process. Here, we found that deletion of Spt20, a structural subunit of the Spt-Ada-Gcn5-acetyltransferase (SAGA) transcriptional activation complex, caused a severe cell separation defect. The defect was mainly due to impaired septin ring assembly, as 80% of spt20Δ cells lost septin rings at the division sites. Spt20 regulates septin ring assembly partially through the transcriptional activation of mid2(+). Spt20 also interacted with Spn2 and Mid2 in vitro and was associated with other components of the ring in vivo. Spt20 colocalized with the septin ring, but did not separate when the septin ring split. Importantly, Spt20 regulated the stability of the septin ring and was required for the recruitment of Mid2. The transcription-dependent and -independent roles of Spt20 in septin ring assembly highlight a multifaceted regulation of one process by a SAGA subunit.

Plant-hormone-initiated signaling pathways are extremely vital for plant growth, differentiation, development, and adaptation to environmental stresses. Hormonal perception by receptors induces downstream signal transduction mechanisms that lead to plant responses. However, conventional techniques—such as genetics, biochemistry, and physiology methods—that are applied to elucidate these signaling pathways can only provide qualitative or ensemble-averaged quantitative results, and the intrinsic molecular mechanisms remain unclear. The present study developed novel methodologies based on in vitro single-molecule fluorescence assays to elucidate the complete and detailed mechanisms of plant hormone signal transduction pathways. The proposed methods are based on multicolor total internal reflection fluorescence microscopy and a flow cell model for gas environment control. The methods validate the effectiveness of single-molecule approaches for the extraction of abundant information, including oligomerization, specific gas dependence, and the interaction kinetics of different components.

Protein engineering is actively pursued in industrial and laboratory settings for high thermostability. Among the many protein engineering methods, rational design by bioinformatics provides theoretical guidance without time-consuming experimental screenings. However, most rational design methods either rely on protein tertiary structure information or have limited accuracies. We proposed a primary-sequence-based algorithm for increasing the heat resistance of a protein while maintaining its functions. Using adenylate kinase (ADK) family as a model system, this method identified a series of amino acid sites closely related to thermostability. Single- and double-point mutants constructed based on this method increase the thermal denaturation temperature of the mesophilic Escherichia coli (E. coli) ADK by 5.5 and 8.3 °C, respectively, while preserving most of the catalytic function at ambient temperatures. Additionally, the constructed mutants have improved enzymatic activity at higher temperature.

Abstract In this study, Sn 2+ solution simulation method is used to investigate the effect of Sn on pitting corrosion behavior of tin-containing ferritic stainless steel 430LX. It is found that the correlation between E pit and [Sn 2+ ] is opposite to the correlation between critical potential temperature (CPT) and [Sn 2+ ]. After potentiostatic polarization at a specific potential, the correlations become the same. The CPT experiment after a series of potentiostatic steps proves that Sn 2+ exhibits positive influence only when the pH and potential is within a certain range. All the complicated phenomena can be explained by the under-potential deposition mechanism. SnO 2 passivation film that enhances the corrosion resistance is only produced when under-potential deposition occurs.

We have studied the quantum Hall (QH) effect in two-dimensional electrons and holes in high quality graphene samples in strong magnetic fields up to 45 T. A distinctive half-integer QH effect is discovered at high magnetic fields, with QH plateaus appearing at filling factors ν = ±4(|n| + 1/2), where n is the Landau level (LL) index. This finding is consistent with theoretical predictions. In addition, in the extreme magnetic quantum limit with magnetic fields up to 45 T, we observe LL splittings in graphene at filling factors ν = 0,±1,±4. Further detailed investigation shows that the presence of the ν = 0,±1 QH states indicates the n = 0 LL at the charge neutral Dirac point splits into four sublevels, lifting both the sublattice and the spin degeneracy, while the QH states at ν = ±4 can be attributed to lifting of the spin degeneracy of the n = ±1 LLS.

Many biological molecules respond to external stimuli that can cause their conformational states to shift from one steady state to another. Single-molecule FRET (Fluorescence Resonance Energy Transfer) is of particular interest to not only define the steady-state conformational ensemble usually averaged out in the ensemble of molecules but also characterize the dynamics of biomolecules. To study steady-state transitions, i.e., non-equilibrium transitions, a data analysis methodology is necessary to analyze single-molecule FRET photon trajectories, which contain mixtures of contributions from two steady-state statuses and include non-equilibrium transitions. In this study, we introduce a novel methodology called WAVE (Wasserstein distance Analysis in steady-state Variations in smFRET) to detect and locate non-equilibrium transition positions in FRET trajectories. Our method first utilizes a combined STaSI-HMM (Stepwise Transitions with State Inference Hidden Markov Model) algorithm to convert the original FRET trajectories into discretized trajectories. We then apply Maximum Wasserstein Distance analysis to differentiate the FRET state compositions of the fitting trajectories before and after the non-equilibrium transition. Forward and backward algorithms, based on the Minimum Description Length (MDL) principle, are used to find the refined positions of the non-equilibrium transitions. This methodology allows us to observe changes in experimental conditions in chromophore-tagged biomolecules or vice versa.

We have observed very high-frequency, highly reproducible magneto-oscillations in modulation doped $\mathrm{GaAs}/\mathrm{AlGaAs}$ quantum well structures. The oscillations are periodic in an inverse magnetic field ($1/B$) and their amplitude increases with temperature up to $T\ensuremath{\sim}700\text{ }\text{ }\mathrm{mK}$. Being initially most pronounced around the filling factor $\ensuremath{\nu}=1/2$, they move towards lower $\ensuremath{\nu}$ with increasing $T$. Front and back-gating data imply that these oscillations require a coupling to a parallel conducting layer. A comparison with existing oscillation models renders no explanation.

A dielectric barrier Discharge (DBD) plasma catalytic system for synergistic degradation of benzohydroxamic acid (BHA) was established. A series of Er3+-BiOI samples doped with rare earth elements (Er3+) were prepared by the hydrothermal synthesis method. The characterization showed that Er3+-BiOI had a microglobular structure assembled by nanosheets, and the specific surface area of Er3+-BiOI was larger than that of pure BiOI. The degradation performance showed that in the DBD/Er3+-BiOI system, the highest BHA degradation efficiency reached 96.3% with 4% Er3+. Compared with the DBD-BiOI system and the single DBD system, the degradation efficiency of BHA increased by 9.1% and 17.5%, respectively. Meanwhile, the kinetic constants and cofactors were also the highest, at 3.36 and 2.88 times the DBD-BiOI system, respectively. The radical capture experiments showed ∙OH, ∙O2-, and cavities play a key role in the degradation of BHA, while O3, H2O2, e-, and H+ promote the degradation of BHA. The intermediates in the degradation of BHA were determined by LC-MS, and the possible degradation pathways of BHA were predicted. Finally, the degradation mechanism of BHA in the DBD/4% Er3+-BiOI system was proposed.

Deep Neural Networks (DNN) will emerge as a cornerstone in automotive software engineering. However, developing systems with DNNs introduces novel challenges for safety assessments. This paper reviews the state-of-the-art in verification and validation of safety-critical systems that rely on machine learning. Furthermore, we report from a workshop series on DNNs for perception with automotive experts in Sweden, confirming that ISO 26262 largely contravenes the nature of DNNs. We recommend aerospace-to-automotive knowledge transfer and systems-based safety approaches, e.g., safety cage architectures and simulated system test cases.

Fӧrster-type resonance energy transfer (FRET) with fluorescence cross-correlation spectroscopy (FCCS) is a powerful combination for observing intramolecular conformational dynamics on the micro- to millisecond timescale. Owing to its sensitivity to various physical parameters, FRET-FCCS has also been used to detect the reagent effects on proteins dynamics. However, FRET-FCCS alone cannot acquire the exact measurements of rate constants. Moreover, this technique is highly model dependent and can be unreliable when determining too many parameters at once. On the contrary, single-molecular FRET (smFRET) can measure the conformational states and their populations directly, although it is extremely challenging for probing fast dynamics under 1 ms. In this chapter, we describe how to realize sub-millisecond conformational dynamics measurements of a SNARE protein Ykt6 under lipid environments by smFRET and FRET-FCCS. This protocol includes sample preparation, microscope designs, data acquisition, and analysis methodology.

Electrochemical impedance spectroscopy (EIS) and electrochemical noise analysis (ENA) were used as combined techniques to study and evaluate the film persistency of several commercial batch treatment inhibitors which are used for protecting oil-wells, gas-wells or pipelines from CO{sub 2} corrosion. It was found that the inhibitors film deterioration was accompanied by typical changes in the EIS spectra, which could be used as indicators for monitoring inhibitor film breakdown. ENA was shown to be able to continuously follow and monitor the inhibitor film deterioration processes. The noise resistance (R{sub noise}) was confirmed to be strongly correlated to linear polarization resistance (R{sub p}) and this correlation was explained based on a concept called statistical linear polarization. The presence of the hydrocarbon phase and CO{sub 2} corrosion product scale were found to be factors which greatly affect batch treatment inhibitor film persistency.

We determined the spin susceptibility χ and the effective mass m* towards the high density limit. Using a tunable GaAs/AlGaAs heterostructure, we can vary the 2D electron density from n=1×1010cm-2 to 4×1011cm-2. From ∼5×1010cm-2 to our highest densities the mass values fall ∼10% below the band mass of GaAs. The enhancement of χ decreases monotonically from a factor of 3 to 0.88 with increasing density. It continues to follow a previously observed power law, which leads to an unphysical limit for n→∞. Band structure effects affecting mass and g-factor become appreciable for large n and, when taken into account, lead to the correct limiting behavior of χ. Numerical calculations are in qualitative agreement with our data but differ in detail.

Brassinosteroids, the steroid hormones of plants, control physiological and developmental processes through its signaling pathway. The major brassinosteroid signaling network components, from the receptor to transcription factors, have been identified in the past two decades. The development of biotechnologies has driven the identification of novel brassinosteroid signaling components, even revealing several crosstalks between brassinosteroid and other plant signaling pathways. Herein, we would like to summarize the identification and improvement of several representative brassinosteroid signaling components through the development of new technologies, including brassinosteroid-insensitive 1 (BRI1), BRI1-associated kinase 1 (BAK1), BR-insensitive 2 (BIN2), BRI1 kinase inhibitor 1 (BKI1), BRI1-suppressor 1 (BSU1), BR signaling kinases (BSKs), BRI1 ethyl methanesulfonate suppressor 1 (BES1), and brassinazole resistant 1 (BZR1). Furthermore, improvement of BR signaling knowledge, such as the function of BKI1, BES1 and its homologous through clustered regularly interspaced short palindromic repeats (CRISPR), the regulation of BIN2 through single-molecule methods, and the new in vivo interactors of BIN2 identified by proximity labeling are described. Among these technologies, recent advanced methods proximity labeling and single-molecule methods will be reviewed in detail to provide insights to brassinosteroid and other phytohormone signaling pathway studies.

Brassinosteroids (BRs) are the sixth class of plant hormones that involved in numerous plant development processes such as leaf expansion, shoot elongation and pollen tube formation. Once the signal transduction is initiated by the membrane receptor kinase BRI1 (brassinosteroid insensitive 1), the signal transmits from the cytoplasm to the nucleus and a number of genes will be regulated. The downstream signaling pathway is realized by three proteins: BIN2 (brassinosteroid insensitive 2), BES1 (BRI1 ems suppressor1) and a kind of 14-3-3s protein . BRs signaling pathway have been extensively studied via genetics, proteomics, genomics and cell biology techniques. However, these bulk methods can't follow the transduction process in situ or resolve molecular details at a rate matching the true signaling time-scale. Here we use a single molecular assay based on Total-Internally Reflected Fluorescence (TIRF) microscopy to observe the interaction of these three proteins. The result shows that BIN2 can phosphorylate BES1 on the order of seconds, and the dimeric 14-3-3s can only bind with BES1 in its phosphorylated form. In addition, we have, for the first time, found that the interaction between BIN2 and BES1 is oxygen dependent. This result may have implications on BRs signaling pathway's involvement of stress acclimation in plants.

Cellular informational and metabolic processes are propagated with specific membrane fusions governed by soluble N-ethylmaleimide sensitive factor attachment protein receptors (SNAREs). SNARE protein Ykt6 is highly expressed in brain neurons and plays a critical role in the membrane-trafficking process. Studies suggested that Ykt6 undergoes a conformational change at the interface between its longin domain and the SNARE core. In this work, we study the conformational state distributions and dynamics of rat Ykt6 by means of single-molecule Förster Resonance Energy Transfer (smFRET) and Fluorescence Cross-Correlation Spectroscopy (FCCS). We observed that intramolecular conformational dynamics between longin domain and SNARE core occurred on a timescale around 200 µs. Furthermore, this dynamics can be regulated and even eliminated by the presence of lipid dodecylphoshpocholine (DPC). Our molecular dynamics simulations have shown that, the SNARE core exhibits a flexible structure while the longin domain retains relatively stable in apo state. Combining kinetic rates of the dynamics process extracted from single molecule experiments, we are the first to explain this functional conformational change from a quantitative point of view.

This chapter contains sections titled: Introduction Converting Chemical Energy to Mechanical Work: Molecular Motors Allostery in Proteins Enzyme Catalysis Conclusions References

Ana tuketilir meyve olarak, tropikal meyve Cin’in guney kesiminde buyuk bir pazara sahiptir. Cin - ASEAN Serbest Ticaret Bolgesi “Erken Hasat Programi”na basladigindan bu yana Guneydogu Asya Milletleri Birligi’nden Cin’e yapilan tropikal meyve ithalati her yil artmaktadir. Ayni zamanda, Cin’de tropikal meyve uretiminin de buyume egilimi gostermesi Cin’de tropikal meyvelerde pazar talebinin arttigini gostermektedir. Bu nedenle, tropikal meyve potansiyel pazarinin derinlemesine analizi, kentsel ve kirsal kesimlerin tropikal meyve tuketimini etkileyen faktorlerin tartisilmasi, Cin’de tropikal meyve endustrisinin tanitimi icin buyuk pratik oneme sahiptir. Tropikal meyvelerde buyuk bir tuketime sahip Guangdong sehrinde oturanlarin tuketici davranislari konusunda yapilan anket verilerinin temel alindigi bu calismada, Guangdong sehrinde oturan kentsel ve kirsal kesimin tropikal meyve tuketirken tuketici davranislarini etkileyen ana faktorlerin analizi icin sirali cok degiskenli kesikli tercih modeli kullanilmistir. Arastirma sonuclari gelir, ekonomik gelismislik duzeyi ve egitim durumunun tropikal meyve tuketimini etkiledigini gostermektedir. Cin’in ulusal ekonomisinin hizli gelisimi ile birlikte, tropikal meyve tuketimi yakin gelecekte buyuk oranda artacaktir

Many enzymes endure sizable conformational remodeling on a timescale comparable to their catalytic cycle. In adenylate kinase (AK) from E. coli, this involves large-amplitude rearrangements of the enzyme's lid domain, which may be critical to the enzymes’ catalytic function. We applied high-resolution single-molecule FRET developed in our laboratory to follow AK's domain movements on its catalytic timescale. This was achieved by recording and analyzing data photon by photon to rigorously account for counting noise, background, and cross talks. By utilizing a maximum entropy-based approach to remove photon-counting noise, the enzyme's entire conformational distribution was quantitatively recovered without a presumed model. Armed with precise single-molecule FRET dynamics measurements and comprehensive bulk kinetic studies of the mechanism, we were able to quantitatively reconstruct the elementary steps as well as the energetic pathways along the AK's enzymatic cycle. The mechanistic roles of AK's stochastic lid dynamics were found to engage in conformation gating, shuffling of reaction pathways, and dynamical induced fit.

Enhancing fluorescence through engineering plasmonic modes in nano-structures has been actively pursued in the past decade. Such fluorescence enhancement can be achieved by two separate mechanisms: 1) the enhancement of local electromagnetic field and 2) the enhancement of spontaneous emission rate, i.e. the Purcell effect. While most experimental studies focused on local-field enhancement, the Purcell enhancement offers distinct advantages: it improves the quantum yield of the emitter and avoids the damaging effect of a strong local field. This makes the Purcell enhancement well suited for fluorescent proteins and NIR-fluorophores. Here, we engineer the plasmonic modes of asymmetric nano-antennas, and modulate the fluorescence emission rate of fluorophores. We demonstrated a useful general strategy for fluorescence enhancement using nano-antennas. Our method has the potential to be applicable to photo-sensitive molecular studies, like bio-chip sensing, DNA sequencing, single-molecule detection ⋯etc.

Improved single-molecule methods can largely increase our understanding of underlying molecular mechanism during cellular signal transduction. In contrast to conventional bulk methods, monitoring molecules one at a time can circumvent averaging effects and acquire unique information. With single-molecule techniques, quantitative characterizations can be achieved at microscopic level, especially for biochemical systems with strong heterogeneity. Here we review four fundamental single-molecule techniques including total internal reflection fluorescence imaging, single-molecule fluorescence recovery after photobleaching, single-molecule Förster resonance energy transfer, and fluorescence correlation/cross-correlation spectroscopy. These techniques are frequently employed in quantitatively investigating the molecular translocation, protein-protein interactions, aggregations, and conformational dynamics involved in the signal transduction both in vitro and in vivo . We also summarized the basic principles and implementations of these single-molecule techniques, as well as the conjunct applications extending the single-molecule measurements to multiple dimensions.

Z. Jiang, 2, ∗ Y. Zhang, H. L. Stormer, 3, 4 and P. Kim Department of Physics, Columbia University, New York, New York 10027, USA National High Magnetic Field Laboratory, Tallahassee, Florida 32310, USA Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027, USA Bell Laboratories, Alcatel-Lucent, Murray Hill, New Jersey 07974, USA (Dated: February 1, 2008)

Y.-W. Tan, J. Zhu, H. L. Stormer, L. N. Pfeiffer, K. W. Baldwin, and K. W. West Department of Physics, Columbia University, New York, New York 10027 Department of Physics, Cornell University, Ithaca, New York 14853 Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027 Bell Labs, Lucent Technologies, Murray Hill, New Jersey 07974 (Dated: November 24, 2004)

Despite long-term efforts for exploring antibacterial agents or drugs, it remains challenging how to potentiate antibacterial activity and meanwhile minimize toxicity hazards to the environment. Here, we experimentally show that the functionality of reduced graphene oxide (rGO) through copper ions displays selective antibacterial activity significantly stronger than that of rGO itself and no toxicity to mammalian cells. Remarkably, this antibacterial activity is two orders of magnitude greater than the activity of its surrounding copper ions. We demonstrate that the rGO is functionalized through the cation-${\pi}$ interaction to massively adsorb copper ions to form a rGO-copper composite in solution and result in an extremely low concentration level of surrounding copper ions (less than ~0.5 ${\mu}M$). These copper ions on rGO are positively charged and strongly interact with negatively charged bacterial cells to selectively achieve antibacterial activity, while rGO exhibits the functionality to not only actuate rapid delivery of copper ions and massive assembly onto bacterial cells but also result in the valence shift in the copper ions from Cu$^{2+}$ into Cu$^{+}$ which greatly enhances the antibacterial activity. Notably, this functionality of rGO through cation-${\pi}$ interaction with copper ions can similarly achieve algaecidal activity but does not exert cytotoxicity against neutrally charged mammalian cells. The remarkable selective antibacterial activity from the rGO functionality as well as the inherent broad-spectrum-antibacterial physical mechanism represents a significant step toward the development of a novel antibacterial material and reagent without environmental hazards for practical application.

The conventional electrochemical techniques have major limitations in studying localised corrosion and other heterogeneous electrochemical processes. This is mainly because traditional electrochemical techniques usually employ a one-piece electrode which can only detect mixed or averaged electrochemical parameters over the whole electrode surface and can not measure electrochemical parameters from a chosen location of the electrode surface. Furthermore, conventional electrochemical kinetic techniques are based on the fundamental Butler-Volmer equation which only describes the kinetics of a uniform electrochemical process. In order to overcome some of these limitations, a multi-piece electrode, namely the wire beam electrode (WBE), has been developed and used to measure electrochemical parameters from local areas of an electrode surface and to determine the kinetics of heterogeneous electrochemical processes. This paper briefly describes how the WBE was applied to study practical localised corrosion processes occurring in simulated oil and gas flowline environments and to map corrosion kinetics. Localised C02 corrosion in a synthetic brine, in a multi-phase produced water/crude oil mixture, and under a crevice, was studied. Using a WBE, in conjunction with electrochemical noise resistance measurements, localised corrosion kinetics were quantitatively and quickly determined. A corrosion rate distribution map, which correlates well with microscopic observation of corrosion depths, was produced. This research suggests that the WBE is a practical method and it will lead to the development of a series of commercial instruments and tools for industrial applications. (a) For the covering entry of this conference, please see IRRD abstract no. E200447.