Exciton swapping in a twisted graphene bilayer as a solid-state realization of a two-brane model

It is shown that exciton swapping between two graphene sheets may occur under specific conditions. A magnetically tunable optical filter is described to demonstrate this new effect. Mathematically, it is shown that two turbostratic graphene layers can be described as a "noncommutative" two-sheeted (2+1)-spacetime thanks to a formalism previously introduced for the study of braneworlds in high energy physics. The Hamiltonian of the model contains a coupling term connecting the two layers which is similar to the coupling existing between two braneworlds at a quantum level. In the present case, this term is related to a K-K' intervalley coupling. In addition, the experimental observation of this effect could be a way to assess the relevance of some theoretical concepts of the braneworld hypothesis.Comment: 15 pages, 3 figures, final version published in European Physical Journal

Conformational dynamics and internal friction in homopolymer globules: equilibrium vs. non-equilibrium simulations

We study the conformational dynamics within homopolymer globules by solvent-implicit Brownian dynamics simulations. A strong dependence of the internal chain dynamics on the Lennard-Jones cohesion strength ε and the globule size N [subscript G] is observed. We find two distinct dynamical regimes: a liquid-like regime (for ε ε[subscript s] with slow internal dynamics. The cohesion strength ε[subscript s] of this freezing transition depends on N G . Equilibrium simulations, where we investigate the diffusional chain dynamics within the globule, are compared with non-equilibrium simulations, where we unfold the globule by pulling the chain ends with prescribed velocity (encompassing low enough velocities so that the linear-response, viscous regime is reached). From both simulation protocols we derive the internal viscosity within the globule. In the liquid-like regime the internal friction increases continuously with ε and scales extensive in N [subscript G] . This suggests an internal friction scenario where the entire chain (or an extensive fraction thereof) takes part in conformational reorganization of the globular structure.American Society for Engineering Education. National Defense Science and Engineering Graduate Fellowshi

Quantum dots coordinated with conjugated organic ligands: new nanomaterials with novel photophysics

CdSe quantum dots functionalized with oligo-(phenylene vinylene) (OPV) ligands (CdSe-OPV nanostructures) represent a new class of composite nanomaterials with significantly modified photophysics relative to bulk blends or isolated components. Single-molecule spectroscopy on these species have revealed novel photophysics such as enhanced energy transfer, spectral stability, and strongly modified excited state lifetimes and blinking statistics. Here, we review the role of ligands in quantum dot applications and summarize some of our recent efforts probing energy and charge transfer in hybrid CdSe-OPV composite nanostructures

Velocity-space sensitivity of the time-of-flight neutron spectrometer at JET

The velocity-space sensitivities of fast-ion diagnostics are often described by so-called weight functions. Recently, we formulated weight functions showing the velocity-space sensitivity of the often dominant beam-target part of neutron energy spectra. These weight functions for neutron emission spectrometry (NES) are independent of the particular NES diagnostic. Here we apply these NES weight functions to the time-of-flight spectrometer TOFOR at JET. By taking the instrumental response function of TOFOR into account, we calculate time-of-flight NES weight functions that enable us to directly determine the velocity-space sensitivity of a given part of a measured time-of-flight spectrum from TOFOR

Relationship of edge localized mode burst times with divertor flux loop signal phase in JET

A phase relationship is identified between sequential edge localized modes (ELMs) occurrence times in a set of H-mode tokamak plasmas to the voltage measured in full flux azimuthal loops in the divertor region. We focus on plasmas in the Joint European Torus where a steady H-mode is sustained over several seconds, during which ELMs are observed in the Be II emission at the divertor. The ELMs analysed arise from intrinsic ELMing, in that there is no deliberate intent to control the ELMing process by external means. We use ELM timings derived from the Be II signal to perform direct time domain analysis of the full flux loop VLD2 and VLD3 signals, which provide a high cadence global measurement proportional to the voltage induced by changes in poloidal magnetic flux. Specifically, we examine how the time interval between pairs of successive ELMs is linked to the time-evolving phase of the full flux loop signals. Each ELM produces a clear early pulse in the full flux loop signals, whose peak time is used to condition our analysis. The arrival time of the following ELM, relative to this pulse, is found to fall into one of two categories: (i) prompt ELMs, which are directly paced by the initial response seen in the flux loop signals; and (ii) all other ELMs, which occur after the initial response of the full flux loop signals has decayed in amplitude. The times at which ELMs in category (ii) occur, relative to the first ELM of the pair, are clustered at times when the instantaneous phase of the full flux loop signal is close to its value at the time of the first ELM

Fault location in electric 35–10–6 kV networks according to empirical criteria in the coordinates of three symmetric components

Солдатов Валерий Александрович, д-р техн. наук, проф., заведующий кафедрой информационных технологий в электроэнергетике, Костромская государственная сельскохозяйственная академия, поселок Караваево, Костромской район, Костромская область, Россия; [email protected]. Климов Николай Александрович, канд. техн. наук, доц., доц. кафедры информационных технологий в электроэнергетике, Костромская государственная сельскохозяйственная академия, поселок Караваево, Костромской район, Костромская область, Россия; [email protected]. Яблоков Алексей Сергеевич, канд. техн. наук, доц., кафедра информационных технологий в электроэнергетике, Костромская государственная сельскохозяйственная академия, поселок Караваево, Костромской район, Костромская область, Россия; [email protected]. Valeriy A. Soldatov, Dr. Sci. (Eng.), Prof., Head of the Department of Information Technologies in Electroenergetics, Kostroma State Agricultural Academy, Karavaevo, Kostroma district, Kostroma region, Russia; [email protected]. Nikolai A. Klimov, Cand. Sci. (Eng.), Ass. Prof., Ass. Prof. of the Department of Information Technologies in Electroenergetics, Kostroma State Agricultural Academy, Karavaevo, Kostroma district, Kostroma region, Russia; [email protected]. Aleksey S. Yablokov, Cand. Sci. (Eng.), Ass. Prof., the Department of Information Technologies in Electroenergetics, Kostroma State Agricultural Academy, Karavaevo, Kostroma district, Kostroma region, Russia; [email protected].В работе исследуется метод определения места повреждения в распределительных электрических сетях 35–10–6 кВ на основе эмпирических критериев в координатах трех симметричных составляющих индивидуальных для каждого вида аварийного режима. То есть в формулах критериев использованы напряжения и токи прямой, обратной и нулевой последовательности. Сами формулы определялись по следующему принципу: если напряжения или токи увеличиваются при перемещении точки аварии вдоль длины линии, то они помещаются в числитель, а если наоборот, то в знаменатель. Для каждого критерия получен график интерполирующей функции, который хранится в памяти компьютера. При возникновении повреждения рассчитывается значение критерия и по графику находится место возникновения аварийного режима. Выявлена расчетная математическая погрешность разработанного метода при малой погрешности измерения ±0,2 %. Показано, что все погрешности составляют менее 1 %, кроме режимов однофазных замыканий на землю, когда погрешность достигает 2,6 %. Как показывают расчеты, погрешность ОМП прямо пропорциональна результирующей погрешности измерений и точности задания исходных данных. Так, при результирующей точности ±2,5 % максимальная погрешность ОМП близка к 3 %, а при точности ±5 % близка к 6 %. Существующие приборы ОМП работают с погрешностью 3–20 %, кроме того, они неспособны определить повреждения с замыканиями на землю и обрывами. Эффективность рассмотренного метода подтверждена технико-экономическими расчетами. Так, в расчете на один фидер 35, 10 и 6 кВ экономический эффект соответственно составляет 200, 150 и 110 тыс. руб. в год при сроке окупаемости около года. При применении метода на 1000 фидерах эффект составит порядка 200, 150 и 110 млн руб. в год. Таким образом, полученные критерии для определения места аварии эффективны как с технической, так и с экономической точек зрения. The paper investigates the method of detecting fault location in 35–10–6 kV electrical distribution networks based on empirical criteria in the coordinates of three symmetrical components, specific for each type of emergency mode. Voltages and currents of the direct, reverse and zero sequence are used in the formulas of the criteria. The formulas themselves were developed according to the following principle: if voltages or currents increase when the fault point moves along the length of the line, they are used as numerators, and if vice versa, the voltages or currents values are used as denominators. For each criterion, a graph of the interpolating function was obtained which is stored in the computer's memory. When a fault occurs, the value of the criterion is calculated and, according to the graph, the place of the emergency mode is found. The calculated mathematical error of the developed method is revealed with a small measurement error of ±0.2 %. It is shown that all errors are less than 1 %, except for single-phase earth fault modes, when the error reaches 2.6 %. As calculations show, the error of the fault location is directly proportional to the resulting measurement error and the accuracy of setting the initial data. So, with a resulting accuracy of ±2.5 %, the maximum error of the fault location is close to 3%, and with an accuracy of ±5 %, it is close to 6 %. Existing fault detection devices operate with an error of 3–20 %. Moreover, they are unable to detect damage with ground faults and breaks. The effectiveness of the considered method is confirmed by technical and economic calculations. So, based on one 35, 10 and 6 kV feeder, the economic effect is 200, 150 and 110 thousand rubles per year, respectively, with a payback period of about a year. When applying the method for 1000 feeders, the effect will be about 200, 150 and 110 million rubles per annum. Thus, the criteria obtained for fault location are effective from both technical and economic points of view

Experimental Determination of the Subband Electron Effective Mass in InGaAs/InAlAs HEMT-structures by the Shubnikov – de Haas Effect at Two Temperatures

AbstractThe electron effective masses m* in different dimensionally quantized subbands in InGaAs/InAlAs HEMT-structures have been measured by the Shubnikov – de Haas effect at two temperatures whose ratio was not equal to 2. The electron effective masses were found separately for the every subband. It was realized by digital bandpass filtering of the Shubnikov – de Haas oscillation to monochromatic oscillations corresponding to subbands. We obtained the dependence of m* in every subband on InAs content in quantum well

Fabrication of multi-walled carbon nanotubes–aluminum matrix composite by powder metallurgy technique

We report on fabrication of an aluminum matrix composite containing multi-walled carbon nanotubes (MWCNTs) produced by MOCVD method and functionalized via acid treatment by a H2SO4/HNO3 mixture.Specimens were prepared by spark plasma sintering (SPS) of the aluminum powder with different amounts of functionalized MWCNTs (FMWCNTs) in the range of 0.1–1 wt.%. We studied the effect of FMWCNTs amount on microstructure and mechanical properties of composites. It is shown that functionalization allows homogeneous dispersing of the MWCNTs in Al powder. The maximal increase in micro-hardness and tensile strength is registered at 0.1 wt.%. Keywords: Multi-walled carbon nanotubes, Functionalization, Spark plasma sintering, Microstructure, Micro-hardness, Tensile strengt