Methods for a Nonuniform Bose Gas

We review mathematical methods for the treatment of a system of Bose particles with nonuniform density. The use of the pseudopotential is explained, especially with respect to negative scattering lengths. It is emphasized that the delta-function potential produces no scattering in three dimensions, and should not be used in the Bogoliubov self-consistent field method, which is variational in nature. A common misuse of the Bogoliubov method at finite temperatures is pointed out. A Gaussian variational method is proposed.     

Realization of Regular-Mixed Quasi-1D Borophene Chains with Long-Range Order

The polymorphism of borophene makes it a promising system to realize tunable physical or chemical properties. Various pure borophene phases consisting of quasi-1D boron chains with different widths have been commonly obtained in experimental studies. Here, it is shown that, due to a substrate mediation effect, artificial long-range ordered phases of borophene consisting of different combinations of boron chains seamlessly joined together can be achieved on Ag(100). Scanning tunneling microscopy measurements and theoretical calculations reveal that mixed-chain phases are more stable than the pure phase, and interact only weakly with the substrate. The mixed-chain phases with various proportions of different chains can be well separated based on the crystal direction of the substrate. The successful growth of mixed-chain phases is expected to deepen the impact of substrate tailored synthesis of borophene.     

Quasi 1 and 2d Dilute Bose Gas in Magnetic Traps: Existence of Off-Diagonal Order and Anomalous Quantum Fluctuations

Current magnetic traps can be made so anisotropic that dilute Bose gases confined in these traps will occupy the lowest quantum state in the tightly confining direction, while still in the Thomas-Fermi limit in the loosely confining direction. As a result, the trapped Bose gas behaves like a quasi one or two dimensional systems. Unlike the homogeneous case, quantum phase fluctuations do not destroy macroscopic off-diagonal order of trapped Bose gases in d2 because they are suppressed by the the trapping potential. In the dilute limit, quantum fluctuations increase, remain constant, and decrease with size for 3, 2, 1 d respectively. These behaviors are due to the combination of a finite gap and the universal spectrum of the collective mode.     

The dynamics of three-mode coupling in a trapped Bose gas

ABSTRACT

Multiple mode couplings in topological coherent modes of Bose–Einstein condensate are considered, by introducing an external alternating (resonating) field in the system. This analysis is based on the analytical solutions of nonlinear Gross–Pitaevskii equation for a trapped Bose gas at nearly absolute zero temperature. The dynamics of fractional populations of the generated coherent modes are analysed, particularly for a three-level system in the limit of small to large detuning of the intermediate state. These coupled topological modes, though nonlinear, are analogous to a resonant atom and exhibit a variety of significant non-trivial phenomena (effects), like: dynamic phase transitions, interference patterns, critical phenomena, mode-locking and chaotic motion.     

Thermodynamics of an Ideal Bose Gas with a Finite Number of Particles Confined in a Three-Dimensional Quartic Trap

Within an exact canonical-ensemble treatment, we investigate the thermodynamics for a finite number of ideal bosons confined in a three-dimensional quartic trap. We calculate several physical quantities including the specific heat C _N , chemical potential μ, condensate fraction 〈n ₀〉/N, root-mean-square fluctuations δn ₀ of the condensate population, and transition temperature T _c . We discuss the particle-number dependence of T _c through proposing three T _c definitions, which are compared with ones derived in the grand canonical ensemble.     

The Finite-Size Effect on the Correlation Functions of a Bose Gas in a Trap and Vanishing of the Order Parameter in the Finite Bose Systems

No Heading The influence of finite sizes on coherent properties of 3D Bose systems is considered. It is shown that normal correlation functions of a Bose gas in a trap decays exponentially in the long-time limit and the anomalous averages understanding in the sense of quasi-averaging vanish resulting in the disappearance of the order parameter.     

放电离子化二维色谱法分析高纯氢中痕量杂质

概述了放电离子化二维色谱法测定高纯氢中微量氧、氮、一氧化碳的工作原理,探讨了样品气不同流量、不同浓度通过中心切割对峰面积产生的影响,并对实验方法的可靠性进行验证。     

调制掺杂ZnMgO/ZnO异质结构中的二维电子气

基于调制掺杂的ZnMgO/ZnO异质结构模型,通过自洽求解一维泊松-薛定谔方程,研究了掺杂浓度、空间层厚度对ZnMgO/ZnO异质界面处二维电子气(2DEG)的分布、面密度等性质的影响。结果表明:ZnO沟道中的二维电子气主要来源于极化效应诱生的电子和掺杂层转移的电子,通过改变掺杂浓度和空间层厚度可以有效地调控异质结中的二维电子气。采取的研究方法和所得结果可以为ZnO基异质结构及相关器件的构筑提供基础。     

ZnMgO/ZnO异质结构中极化对二维电子气的影响

基于 ZnMgO/ZnO 异质结构模型,从压电极化对应变弛豫度的依赖关系出发,通过自洽求解一维泊松-薛定谔方程,研究了 ZnMgO 势垒层的厚度、Mg 组分和应变弛豫度对 ZnMgO/ZnO 异质界面处二维电子气(2DEG)的分布、面密度等性质的影响,并结合极化和能带偏移对计算结果进行了分析讨论。结果表明通过改变 Mg 组分和应变弛豫度可以调节异质界面两边的极化强度不连续性,进而有效地调控异质结中的二维电子气。     

Thermal Behavior of a Stagnant Gas Confined in a Horizontal Microchannel as Described by the Dual-Phase-Lag Heat Conduction Model

The transient thermal behavior of a stagnant gas confined in a horizontal microchannel is investigated analytically under the effect of the dual-phase-lag heat conduction model. The microchannel is formed from two infinite horizontal parallel plates where the upper plate is heated isothermally and the lower one is kept adiabatic. The model that combines both the continuum approach and the possibility of slip at the boundary is adopted in this study. The effects of the Knudsen number Kn, the thermal relaxation time _q, and the thermal retardation time _T on the microchannel thermal behavior are investigated using three heat conduction models. It is found that the deviations between the predictions of the parabolic and the hyperbolic models are insignificant. On the other hand, the deviations between the parabolic and dual-phase-lag models are significant under the same operating conditions.     

Spin Relaxation in a Two-Dimensional Electron Gas in Si Quantum Wells

Electron spin resonance of two-dimensional (2D) electron gas in Si/SiGe quantum wells allows to evaluate both the longitudinal and the dephasing spin relaxation time. Diakonov–Perel (DP) relaxation, caused by Bychkov–Rashba (BR) spin orbit coupling, occurs to be the dominant mechanism in high mobility samples. For low mobility the Elliott–Yaffet mechanism dominates the longitudinal spin relaxation. When the BR effect is small, inhomogeneous broadening caused by potential fluctuations is seen. We compare spin relaxation of the 2D electron gas in Si and in GaAs quantum wells with respect to applications of these materials in spintronics.     

Order release in a workload controlled flow-shop with sequence-dependent set-up times

In this paper, we report a simulation study on the role of sequence-dependent set-up times in decision making at the order release level of a workload controlled make-to-order flow-shop. The study evaluates the potential for set-ups savings, dependent on the level of workload in the shop, for two alternative strategies, namely considering set-up times centrally, within the release decision or locally, within the dispatching decision. These strategies are compared and assessed on the basis of two main performance measures namely time in system and standard deviation of the job lateness. Results indicate that the local strategy, which has been traditionally adopted in practice and in most of the studies dealing with sequence-dependent set-up times, does not always give the best results. The release frequency and the shop workload appear critical to the selection of the strategy to adopt, strongly influencing system performance.     

Superfluid vs Ferromagnetic Behavior in a Bose Gas of Spin-1/2 Atoms

We study the thermodynamic phases of a Bose gas of spin-1/2 atoms in the Hartree-Fock approximation. Our main result is that, for repulsive or weakly attractive inter-component interaction strength, the superfluid and ferromagnetic phase transitions occur at the same temperature. For strongly attractive inter-component interaction strength, however, the ferromagnetic phase transition occurs at a higher temperature than the superfluid phase transition. We also find that the presence of a condensate acts as an effective magnetic field that polarizes the normal cloud. We finally comment on the validity of the Hartree-Fock approximation in describing different phenomena in this system.     

Order picking in a parallel-aisle warehouse with turn penalties

In many real-life routing problems, incorporating the negative effects of turns is an important, but often overlooked aspect. This is especially true for order picking in warehouses, where making the turns not only decreases the picking efficiency by reducing the speed of the vehicle, but it also results in other unquantifiable effects such as vehicle tipovers, increased congestion and increased risk of collision with pedestrians or other vehicles. In this paper, we consider the order picking problem in a parallel-aisle warehouse by taking into account the number and effect of the turns. In particular, we show that the problem of minimising the number of turns, minimising travel time under turn penalties, the biobjective problem that involves turn and travel time minimisation as separate objectives, and the triobjective problem with U-turn minimisation as a third objective can all be solved in polynomial time. Our computational results show that the algorithms we develop can generate the corresponding Pareto front very quickly, and significantly outperform heuristic approaches used in practice.     

Order allocation in purchasing management: a review of state-of-the-art studies from a supply chain perspective

Supplier selection (SS) and order allocation (OA) are strategic decisions that have a substantial effect on a company’s performance. However, order allocation is often neglected, since it results from supplier selection and is considered supplementary: little attention has been paid to its specific nature and complexity. Consequently, the authors conducted a systematic literature review specifically regarding order allocation methods. The research aimed to evaluate how often and when the issue has been dignified with an individual focus, independently of the supplier selection problem. This study conducted a comprehensive examination of the order allocation models and solutions, criteria for order quantity allocation, features of suppliers, items, planning periods, and demand most commonly considered in the literature. Finally, it aimed to discover whether supply chain configurations and trends have been considered in efforts to find a solution to the problem. The scientific contribution of this study is threefold: (i) to expand the review of scientific literature regarding order allocation models, (ii) to identify research gaps and highlight research opportunities, and (iii) to suggest a research agenda for the development of order allocation models according to the requirements of current trends in supply chain management.     

Magnetoresistance of the Two-Dimensional Electron Gas in GaN Quantum Wells in a Parallel Magnetic Field

We present results for the resistivity of the two-dimensional spin-polarized electron gas as realized in GaN quantum wells at zero temperatures. A parallel magnetic field is used to create a spin-polarized electron gas. We discuss the density dependence of the magnetoresistance for impurity scattering and interface-roughness scattering. Finite width effects of the electron gas on the magnetoresistance are described.     

长北气田某气井油管腐蚀速率增大原因

长北气田油管整体腐蚀速率缓慢,但某气井在多臂井径检测中发现,该油管局部腐蚀速率增大,远远大于整个气田的油管腐蚀速率和该井前期的腐蚀速率.进行了水质、气质组分分析、多臂井径检测和腐蚀挂片等试验,分别对腐蚀挂片的宏观形貌及腐蚀产物进行了分析,并结合油管的腐蚀程度和腐蚀情况,对该井油管腐蚀速率突然加快的原因及腐蚀机理进行了分...     

Simulation of a DC Discharge in a Transverse Supersonic Gas Flow

This study is devoted to the investigation of a dc discharge in a transverse gas flow. It is shown that the discharge may exist in several forms depending on the gas flow velocity. The standard stationary discharge similar to a discharge in still gas is realized if the displacement rate of the plasma boundary exceeds the gas flow velocity. The displacement rate of the plasma boundary in a diffusion model is defined by the relation V _f = 2 , where D _a is the ambipolar diffusion coefficient, and _i is the frontal ionization frequency. Otherwise, the discharge assumes the form of two plasma wakes formed by the cathode and anode, respectively. The surface of the plasma wakes is oriented at an angle to the flow velocity C _s (sin = V _f /C _s ). If sin is smaller than the ratio of the discharge sustaining voltage in the stationary regime U _st to the breakdown voltage U _bk , the discharge transforms into the pulse–periodic form, when the formation of a structure of the cathode and anode plasma wakes is interrupted by a new gas breakdown. A numerical simulation of the discharge properties is performed. The numerical simulation results are compared to the experimental ones.     

Order picking in parallel-aisle warehouses with multiple blocks: complexity and a graph theory-based heuristic

In this paper, we consider the order picking problem (OPP), which constitutes one of the special cases of the Steiner travelling salesperson problem and addresses the costliest operation in a warehouse. Given a list of items to be picked and their locations in the warehouse layout, the OPP aims to find the shortest route that starts from a depot point, picks all the items in the list, and returns to the depot. This paper fills two important gaps regarding the OPP. First, to the best of our knowledge, we present the first complexity results on the problem. Second, we propose a heuristic approach that makes use of its graph-theoretic properties. Computational experiments on randomly generated instances show that the heuristic not only outperforms its state-of-the-art counterparts in the literature, but it is also robust in terms of changing problem parameters.     

Friedel Oscillations in a One-Dimensional Noninteracting Electron Gas

Using the linear response theory, we studied the Friedel oscillations in a one-dimensional noninteracting electron gas in the presence of two impurities. The oscillations are strongly affected by the distance between impurities. The case of Coulomb potential for a single impurity is also considered.