Optimal transport of cold atoms by modulating the velocity of traps

This work experimentally demonstrates a new method of optimizing the transport of cold atoms via modulating the velocity profile imposed on a magnetic quadrupole trap.The trap velocity and corresponding modulation are controlled by varying the currents of two pairs of anti-Helmholtz coils.Cold 87Rb atoms are transported in a non-adiabatic regime over 22 mm in 200 ms.For the transported atoms their final-vibration amplitude dependences of modulation period number,depth,and initial phase are investigated.With modulation period n = 5,modulation depth K = 0.55,and initial phase φ = 0,cold atom clouds with more atom numbers,smaller final-vibration amplitude,and lower temperature are efficiently transported.Theoretical analysis and numerical simulation are also provided,which are in good agreement with experimental results.

Controlling the Directed Quantum Transport of Ultracold Atoms in an Optical Lattice with a Periodic Driving Field

We propose a new method to control the directed quantum transport of ultracold atoms in a one-dimensional optical lattice. In this proposal, the effective tunneling between the neighboring sites can be adjusted via coherent destruction of tunneling by tuning the phase of the external field, instead of using the driving field intensity or the frequency, thus the directed quantum transport of ultracold atoms can be coherently controlled in a nmch easier manner. Our proposal overcomes the major drawback of the method used by Creffield et al [Phys. Rev. Lett. 99 （2007） 110501], and can be implemented, in principle, in any one-dimensional optical lattice. Some potential applications of the scheme are also discussed.

Formation and Transport of Atomic Hydrogen in Hot-Filament Chemical Vapor Deposition Reactors

In this paper we focus on diamond film hot-filament chemical vapor deposition reactors where the only reactant is hydrogen so as to study the formation and transport of hydrogen atoms. Analysis of dimensionless numbers for heat and mass transfer reveals that thermal conduction and diffusion are the dominant mechanisms for gas-phase heat and mass transfer, respectively. A simplified model has been established to simulate gas-phase temperature and H concentration distributions between the filament and the substrate. Examination of the relative importance of homogeneous and heterogeneous production of H atoms indicates that filament-surface decomposition of molecular hydrogen is the dominant source of H and gas-phase reaction plays a negligible role. The filament-surface dissociation rates of H2 for various filament temperatures were calculated to match H-atom concentrations observed in the literature or derived from power consumption by filaments. Arrhenius plots of the filament-surface hydrogen dissociation rates suggest that dissociation of H2 at refractory filament surface is a catalytic process, which has a rather lower effective activation energy than homogeneous thermal dissociation. Atomic hydrogen, acting as an important heat transfer medium to heat the substrate, can freely diffuse from the filament to the substrate without recombination.

Observation of oscillations in the transport for atomic layer MoS_2

In our experiment, an atomic layer MoS2structure grown on SiO2/Si substrates is used in transport test. The voltage U14,23 oscillates and the corresponding period varies with applied current. The largest period appears at 45 μA. The oscillation periods are different when samples are under laser radiation or in darkness. We discover that under the laser irradiation, the oscillation period occurs at lower current than in the darkness case. Meanwhile, the drift velocity is estimated at ~10~7 cm/s. Besides, by studying the envelope of U14,23 versus applied current, we see a beating phenomenon at a certain current value. The beating period in darkness is larger than under laser irradiation. The difference between beating periods reveals the energy difference of electrons. Similar results are obtained by using different laser power densities and different light sources. The possible mechanism behind the oscillation period is discussed.

Single photon transport properties in coupled cavity arrays nonlocally coupled to a two-level atom in the presence of dissipation

We discuss the effects of dissipation on the behavior of single photon transport in a system of coupled cavity arrays, with the two nearest cavities nonlocally coupled to a two-level atom. The single photon transmission amplitude is solved exactly by employing the quasi-boson picture. We investigate two different situations of local and nonlocal couplings, respectively. Comparing the dissipative case with the nondissipative one reveals that the dissipation of the system increases the middle dip and lowers the peak of the single photon transmission amplitudes, broadening the line width of the transport spectrum. It should be noted that the influence of the cavity dissipation to the single photon transport spectrum is asymmet- ric. By comparing the nonlocal coupling with the local one, one can find that the enhancement of the middle dip of single photon transmission amplitudes is mostly caused by the atom dissipation and that the reduced peak is mainly caused by the cavity dissipation, no matter whether it is a nonlocal or local coupling case. Whereas in the nonlocal coupling case, when the coupling strength gets stronger, the cavity dissipation has a greater effect on the single photon transport spectrum and the atom dissipation affection becomes weak, so it can be ignored.

Spin-Dependent Transport in Carbon Nanotubes with Chromium Atoms

Method is developed for self-consistent calculation of the energy spectrum of free energy and electrical disordered crystals. Processes of electron scattering on the ionic core potential of different sort, fluctuations of charge, spin density and lattice vibrations are taken into account. Electronic states of the system are described using tight binding multiband model. The nature of the spin-dependent electron transport of carbon nanotubes with chromium atoms adsorbed on the surface is explained. The value of the spin polarization of electron transport is determined by the difference of the partial densities of states of electrons with opposite spin projection at the Fermi level and the difference between the relaxation times of electron states. The value of the spin polarization of the electric current increases with increasing of Cr atoms concentration and magnitude of the external magnetic field.

New bipartition model of neutral particle transport in the HL-2A divertor region

A new bipartition neutral transport model has been developed for simulation of the hydrogenic neutral particle transport in the vicinity of HL-2A divertor target plate.The numerical calculation results on the basis of this model are fairly consistent with the results obtained with the "multi-generation method". One possible application of this model is to provide a source term originating from neutral transport calculation for any other edge plasma transport code, for instance, B-2 code, which has been used to simulate edge plasma transport of the HL-2A divertor configuration. Especially it can be utilized to quickly classify the plasma in divertor region as high or low recycling regime.

基于极限学习机的短期交通流预测混合优化模型

交通流的动态性、不确定性和非线性等特性导致交通流难以精确预测,本文在极限学习机(Extreme Learning Machine,ELM)的基础上,通过嵌入原子搜索算法(Atom Search Optimization,ASO),构建ASO-ELM短期交通流预测混合优化模型,对比现有短期交通流预测模型,分析混合优化模型在短期交通流预测领域的表现。实验选取荷兰阿姆斯特丹市A10环形公路为路网原型,使用ASO-ELM混合模型与常见交通流预测模型进行对比实验。实验结果表明:ASO-ELM混合模型在4个数据集下的平均绝对百分比误差(Mean Absolute Percentage Error,MAPE)相较于ELM模型分别下降了4.3%、3.5%、6.9%和5.4%,均方根误差(Root Mean Squared Error,RMSE)分别下降了4.8%、4.0%、2.0%和5.2%;其次,与人工神经网络(Artificial Neural Network,ANN)相比,MAPE分别下降了9.6%、8.6%、9.8%和5.0%,RMSE也分别下降了4.5%、5.9%、2.6%和1.7%。研究成果揭示了混合优化模型在短期交通流预测领域的潜力。

金属Al诱导Si晶化的Al/Si异质薄膜的原子输运模拟

【目的】从原子层次分析金属Al诱导Si晶化的物理过程与机理。【方法】运用第一性原理计算方法,对Al/Si异质非晶薄膜在热处理过程中Si的晶化过程进行理论计算与模拟。【结果】结果表明,Al/Si异质薄膜在热处理过程中Al、Si原子发生了互扩散现象。随热处理时间的延长,膜层系统进入能量更低较为稳定的状态。Al原子逐步上移,Si原子逐步下移,在结构演变的过程中逐步实现Al/Si异质膜层的翻转。【结论】Al原子引起Si原子之间成键状态的变化,Al原子的库仑屏蔽作用使得Si—Si键的强度减弱,Al原子扩散进入Si层具有能量优势,降低了Si的晶化能垒,有利于Si原子的迁移并结晶。

费米气体通过量子点接触的输运行为简介

输运测量是研究物质状态基本性质的重要工具。其中通过量子点接触(Quantum Point Contact)的输运是介观物理学中一个非常有趣的现象。在无相互作用或弱相互作用费米系统中,电导随门电压的变化呈现出量子化的阶梯状,这一现象揭示了物质的量子特性。近年来,冷原子体系中输运的研究已成为该领域的前沿研究之一冷原子体系具有高度可操控性的特点,也存在许多新奇物态,因此可以在冷原子的输运实验中观测到许多材料物理中无法观测到的新的实验现象。本文将以综述的形式介绍冷原子费米气体通过量子点接触的输运行为的一些前沿实验进展,此外,我们也将介绍处理该体系常用的非平衡场论方法。

电子输运过程的确定论计算方法研究

电子输运过程是核辐射探测器内形成电流的关键过程之一,相应的数值模拟是先进探测器设计与分析软件急需研发的功能。由于该过程的短平均自由程和高度前向峰等特点,确定论方法比蒙特卡罗方法的计算效率更高。本文采用多群形式的Boltzmann输运方程刻画电子输运过程;从EPICS2017中的电子截面数据EEDL出发,基于核数据处理软件NECP-Atlas编写了相应的电子截面处理模块,制作了多群截面数据库;利用Bamboo-Lattice程序中基于特征线方法的中子输运计算核心,构建了确定论电子输运计算程序。利用单核素均匀问题、化合物均匀问题和化合物非均匀问题等一系列算例,通过与蒙特卡罗程序的计算结果进行详细对比,对该确定论电子输运计算程序进行了定量数值验证与分析。结果表明,该程序可以正确模拟电子输运过程,且计算效率能比蒙特卡罗程序快80倍以上。

一维双组分原子气体模型的输运性质

一维双组分原子气体模型是研究低维流体输运性质的关键模型之一,在低维输运理论及相关应用研究中发挥着重要且独特的作用.在最近10年间,厦门大学复杂系统研究组围绕该模型对低维输运理论开展了大量攻关研究,给出了热功转换效率达到热力学上限的普适条件,指出微观相互作用是达到热力学不确定性关系上限的必要条件,证明了一维系统中可存在自组织及非平衡态相变,发现耦合输运中可存在与所有热力学力都相反的反向流.本文将对这些突破性进展做一简要介绍.

超声雾化系统的雾化性能测试

研究建立了超声雾化装置,用激光粒度仪测试了雾化液滴的粒径,并研究了雾化溶液加入量、超声雾化功率、载气流量等雾化参数对超声雾化速率及管路输运损失的影响。结果表明,雾化液滴的粒径约 2.6μm。在一定加液量范围内,加液量的变化对雾化速率影响不大,雾化速率随载气流量和雾化功率的增大而增大;而管路输运损失随载气流量的增大先减小,在载气流量为800cm3/min附近达到最小后,再随载气流量的增大而增大。

槽型空心阴极放电特性的模拟

为进一步揭示槽型空心阴极放电的放电机理,利用流体-亚稳态原子传输模型模拟研究了槽型空心阴极放电等离子体参数的时空分布特性。模拟得到了不同时刻槽型空心阴极放电中电势、电子密度、电场场强和电离速率等的分布特性。结果表明槽型空心阴极放电在不同时刻处于不同的放电模式,即初始放电阶段为Townsend放电模式,此阶段以轴向放电为主;第2阶段为放电由槽外向槽内发展阶段,此阶段电场场强由轴向向径向转换;第3阶段为形成空心阴极效应放电模式阶段,此阶段逐渐形成稳定的阴极鞘层结构;第4阶段为稳定放电阶段,放电参数不随时间发生变化。研究结果为进一步分析空心阴极放电的时间发展特性提供了参考。

靶材溅射及溅射原子输运的计算机模拟

用软件SRIM及蒙特卡罗法综合模拟了靶材溅射及溅射原子输运的过程。模拟结果包括溅射原子输运到衬底时的能量、入射角和入射位置。由模拟结果知,溅射原子输运主要受P×d影响(P为真空室气压,d为靶基距),P×d愈大输运到衬底的溅射原子愈少,且能量愈小;溅射原子到达衬底时,能量集中在几电子伏范围内,且在能量很低的区域有分布峰;角度分布主要集中在垂直方向,这与从靶面出射时的分布相似,但垂直方向的分布有所减小;位置分布与从靶面出射时相比,分布范围在径向扩大、趋于均匀化,但主要在靶直径范围内。

(GaAs)_n(n=1—4)原子链电子输运性质的理论计算

本文利用密度泛函理论结合非平衡格林函数的方法,对(GaAs)_n(n=1—4)直线原子链与Au(100)-3×3两半无限电极耦合构成Au-(GaAs)_n-Au纳米结点的电子输运性质进行了第一性原理计算.在各结点拉伸过程中,对其结构进行了优化,得到各结点稳定平衡结构时Ga—As的平均键长分别为0.220,0.224,0.223,0.223 nm,平衡电导分别为2.328G_0,1.167G_0,0.639G_0,1.237G_0;通过对结点投影态密度的计算,发现电子传输主要是通过Ga,As原子中p_x与p_y电子轨道相互作用形成的π键进行的.在0—2 V的电压范围内,对于(GaAs)_n(n=1—3)的原子链的电流随电压增大而增大,I-V曲线呈线性关系,表现出类似金属导电行为;对于(GaAs)_4原子链在0.6—0.7 V,0.8—0.9 V的电压范围内却存在负微分电阻现象.

静电喷雾研究与应用综述

综述了静电喷雾研究与应用现状，主要就液体雾化、雾滴充电。

X光辐射输运多群参数数据库的建立

为便捷地求解等离子体的Ｘ光辐射的辐射输运多群方程需要建立辐射输运多群参数数据库，给出了建立辐射输运多群参数数据库的计算公式和计算方法及检验计算是否正确的校验方法。并在２０（等离子体密度）×２０（电子温度）的原始金原子物理参数的基础上建立了２０（等离子体密度）×２０（电子温度）×２０（光子温度）×２０（群数）的金辐射输运多群参数数据库。

丙磺舒等药物对双环铂肾排泄的影响及其机理

目的:比较在大鼠中丙磺舒、甲氨蝶呤、地高辛、维拉帕米等不同药物转运蛋白底物对双环铂肾排泄的影响。方法:采用原子吸收法测定大鼠尿液中铂浓度,计算4 h尿药累积排泄率。结果:合用不同转运蛋白底物后,双环铂在尿中的排泄量均有所降低,双环铂组4 h累积排泄百分率为(70.7±9.8)%,而合用丙磺舒、维拉帕米、地高辛或甲氨蝶呤后其累积排泄百分率分别下降为(28.8±4.1)%、(34.2±10.1)%、(43.6±2.8)%和(47.4±8.5)%,肾组织铂浓度则由(278.8±112.0)μg/g分别降低或升高为(179.6±122.2),(309.5±88.8),(374.4±90.1),(266.0±107.5)μg/g。结论:合用丙磺舒等药物可抑制双环铂的肾排泄速度,双环铂及其代谢物的肾排泄过程中可能有MRP2,OAT或OATP等药物转运蛋白参与。

空心阴极放电中的电势垒和电场反转

利用流体-亚稳态原子模型对柱型空心阴极放电中电场反转和电势垒进行了研究。模拟得到了稳态放电时电势、电子密度、离子密度、电场和粒子流密度等的分布特性。220 V阳极电压和133 Pa氩气下,电子和离子密度峰值位于放电单元中心处,为2.4×1010cm-3;在阴极位降区,离子密度远高于电子密度。负辉区电势高于阳极电势,放电的轴向存在电场反转现象,放电单元的中心处形成一电势垒。电子扩散流密度和电子流密度之比对电场反转的形成有重要影响。文章同时研究了阳极电压对电场反转特性的影响。结果表明,电压升高时,电子扩散流密度升高,电场反转和电势垒现象增强。模拟结果同时表明空心阴极放电模式下有利于电场反转的形成。该研究对于分析空心阴极放电中电场反转的成因有重要的参考价值。