冷原子吸收法测定土壤中总汞

本文使用自制的汞原子化装置，与原子吸收仪联用，采用冷原子吸收法测定土壤中总汞，该法快速，简便，稳定性好，用于实际样品测试，结果令人满意。     

用短程飞行时间吸收谱对铯磁光阱中冷原子温度的测量

介绍采用短程飞行时间吸收谱测量铯原子磁光阱(MOT) 中冷原子温度的基本原理及实验实现.与通常的飞行时间方法不同，采用短程飞行时间吸收谱来测量MOT 中冷原子云的温度.在MOT 区域正下方若干毫米处入射一束圆柱状共振探测光束(实验中对于h=3mm，5mm，8mm的情况均作了研究)，释放冷原子云，在其膨胀和自由下落过程中穿过探测光束，即可由光电探测器测得飞行时间吸收谱，由此推得MOT中冷原子的温度. 关键词： 磁光阱 冷原子 飞行时间 短程飞行时间 铯原子     

国内外原子吸收分光光度计产品介绍及其技术发展动向

文章对国内外原子吸收分光光度计的产品结构及特点作了较为详尽的分析：国外产品重点介绍了PE、Varian、IL、PU、岛津等公司的仪器；国内部分则重点介绍了85年前后推出的微机化产品，叙述了国内原子吸收分光光度计的发展全过程。文章还以仪器的光源、原子化系统、扣背景方式三个方面全面综述了国外原子吸收仪器的技术发展动向，对发展我国原子吸收分光光度计亦提出了个人的一此看法。     

N型四能级系统的原子吸收

研究了在较强光低饱和限制下相干光场与N型四能级原子相互作用系统中原子的吸收性质。借助于数值计算,讨论了较强光失谐、探针光强、激发能级向低能级衰减的分配系数对原子吸收的影响。结果表明,抽运场失谐使原子吸收发生横向变化,信号场失谐使原子吸收发生纵向变化;探针光强影响非线性吸收,并通过它影响原子吸收,当探针光强远小于抽运和信号光强时,原子吸收与线性吸收一致,均表现为电磁感应透明特征,当信号光强增大,非线性吸收产生了增益,原子吸收也由透明变为增益;激发能级同时向两个低能级衰减,当对应探针光的原子衰减通道的衰减分配系数趋近零时,原子吸收随该系数变化非常强烈,当该分配系数等于零时,其增益在探针场共振处趋于无穷大。     

原子吸收法测定溶液中的钯含量

采用原子吸收法分析乙醛催化剂溶液中的钯含量，使分析工作者避免接触有毒试剂，改善了工作环境，又缩短了分析时间，通过准确度与精密度试验，证明了原子吸收法准确可靠，操作简便，适应性强，适用于各种含钯溶液的钯含量分析。     

原子捕获—火焰原子吸收光度法测定火药烟晕中微量铅和锑

本文采用双缝式原子捕获石英管在火焰原子吸收分光光度计上测定火药烟晕中微量铅和锑，研究了捕获的时间及乙炔的流量等测试条件。实验表明，本文提高了原子吸收分光光度法的灵敏度，铅提高４倍，锑提高了９倍，方法的回收率铅为９８．６～１０４％，锑为９８～１１０％。     

100.8 km大动态零差相干微波光子传输链路

全同性原理要求电子波函数必须满足交换反对称性的条件，针对其对多电子系统的瞬态吸收谱产生的影响，运用Ritz变分法求出了具有全同反对称性的氦原子波函数。在此基础上，通过求解三能级模型并与不考虑电子交换作用的旧模型对比，在理论上研究了氦原子阿秒极紫外(XUV)光瞬态吸收谱。该研究突破传统所采用的单电子跃迁模型，重点考虑电子的交换作用对XUV光瞬态吸收谱的影响。研究发现该交换作用对该瞬态吸收谱的强度和吸收峰的位置等物理量都有重要的影响，该研究结果可为运用瞬态吸收谱探测原子内电子超快关联动力学提供参考。     

高纯铯中痕量磷,砷的孔雀绿—磷（砷）酸钼浮膜分离及萃取—间接原子吸收…

本文提出一种测定金属铯中痕量磷，砷的方法－孔雀绿离子试剂分离，间接原子吸收测定法，该离子是由孔雀绿和磷（砷）酸钼生成薄膜，介于水相和乙醚相之间，分离后，用甲醇溶解，并用原子吸收法测定钼来确定磷，砷的含量。     

耦合场线宽：抑制电磁诱导吸收

原子相干对吸收的相长干涉导致电磁诱导吸收，这是一类新的相干效应. 以三个电偶极跃迁构成N型链，中间跃迁作为探测跃迁的四能级系统为例，揭示耦合场线宽抑制电磁诱导吸收的强度. 这并非与电磁诱导透明系统中耦合场线宽产生或者增强吸收的情形相矛盾，线宽仍然是抑制系统的相干性. 关键词： 电磁诱导吸收 耦合场线宽 原子相干 退相干     

泡沫塑料快速富集－石墨炉原子吸收法测定化探样品中的痕量金

本文系统研究了泡沫塑料快速富集－石墨炉原子吸收法测定金的方法，对泡沫塑料富集、分离金和石墨炉原子吸收法测定金的条件均做了详细的研究。该法用于化探样品中金的测定，结果与推荐值相符。     

Complete Hamiltonian Description of Wave-Like Features in Classical and Quantum Physics

The analysis of the Helmholtz equation is shown to lead to an exact Hamiltonian system describing in terms of ray trajectories, for a stationary refractive medium, a very wide family of wave-like phenomena (including diffraction and interference) going much beyond the limits of the geometrical optics (“eikonal”) approximation, which is contained as a simple limiting case. Due to the fact, moreover, that the time independent Schrödinger equation is itself a Helmholtz-like equation, the same mathematics holding for a classical optical beam turns out to apply to a quantum particle beam moving in a stationary force field, and leads to a system of Hamiltonian equations providing exact and deterministic particle trajectories and dynamical laws, and containing the laws of Classical Mechanics in the eikonal limit.     

On comparing dynamical systems by defective conjugacy: A symbolic dynamics interpretation of commuter functions

While the field of dynamical systems has been focused on properties which are invariant to “good” change of variables, namely conjugacy, which is an equivalence relationship, when using dynamical systems methods in science and modeling, there lacks a dynamical way to compare dynamical systems, even when they are in some sense “close.” In Skufca and Bolt (2007) [7] and Skufca and Bolt (2008) [8], we introduced mathematics to support a philosophy that two dynamical systems should be compared through a change of coordinates between them, that is, a commuter between them which may fail to be a homeomorphism. The progressive degree to which the commuter fails to be a homeomorphism defines what we call a homeomorphic defect. However, at the time of publication of these papers, there were limits in the mathematical technology requiring that the transformations be one-dimensional mappings and flows which are well described, for construction of the commuters by fixed point iteration, and further, difficulties in numerically computing defects in the more complicated one-dimensional cases, and further limits to higher-dimensional problems. Therefore, here we extend the theory to allow for multivariate transformations, with construction methods separate from the fixed point iteration, and new methods to compute defect. In the course of this work, we introduce several new technical innovations in order to cope with much more general problems. We introduce assignment mappings to understand and illustrate commuters in a broader setting. We discuss the role of symbolic dynamics and coding as related to commuters as well as defect measure. Further, we discuss refinement and convergence of a nested refinement of commuter representations. This work represents a step forward in the possibility of using the commuter and defects to judge model quality in those dynamical systems for which a symbolic dynamics, and hence a generating partition may be available; while finding a generating partition is a problem in its own right, we offer this work as further perspective for interpretation of the meaning of commuters and defect measure.     

The design of a high power ultrasonic test cell using finite element modelling techniques

This paper will describe the application of a finite element (FE) code to design a test cell, in which a single transducer is used to generate acoustic cavitation. The FE model comprises a 2-D slice through the centre of the test cell and was used to evaluate the generated pressure fields as a function of frequency. Importantly, the pressure fields predicted by FE modelling are used to indicate the position of pressure peaks, or 'hot-spots', and nulls enabling the systems design engineer to visualise both the potential cavitation areas, corresponding to the 'hot-spots', and areas of low acoustic pressure. Through this design process, a rectangular test cell was constructed from perspex for use with a 40 kHz Tonpilz transducer. A series of experimental measurements was conducted to evaluate the cavitation threshold as a function of temperature and viscosity/surface tension, for different fluid load media. The results indicate the potential of the FE design approach and assist the design engineer in understanding the influence of the fluid load medium on the cell's ability to produce a strong cavitation field.     

Condensates in the Cosmos: Quantum Stabilization of the Collapse of Relativistic Degenerate Stars to Black Holes

According to prevailing theory, relativistic degenerate stars with masses beyond the Chandrasekhar and Oppenheimer–Volkoff (OV) limits cannot achieve hydrostatic equilibrium through either electron or neutron degeneracy pressure and must collapse to form stellar black holes. In such end states, all matter and energy within the Schwarzschild horizon descend into a central singularity. Avoidance of this fate is a hoped-for outcome of the quantization of gravity, an as-yet incomplete undertaking. Recent studies, however, suggest the possibility that known quantum processes may intervene to arrest complete collapse, thereby leading to equilibrium states of macroscopic size and finite density. I describe here one such process which entails pairing (or other even-numbered association) of neutrons (or constituent quarks in the event of nucleon disruption) to form a condensate of composite bosons in equilibrium with a core of degenerate fermions. This process is analogous to, but not identical with, the formation of hadron Cooper pairs that give rise to neutron superfluidity and proton superconductivity in neutron stars. Fermion condensation to composite bosons in a star otherwise destined to collapse to a black hole facilitates hydrostatic equilibrium in at least two ways: (1) removal of fermions results in a decrease in the Fermi level which stiffens the dependence of degeneracy pressure on fermion density, and (2) phase separation into a fermionic core surrounded by a self-gravitating condensate diminishes the weight which must be balanced by fermion degeneracy pressure. The outcome is neither a black hole nor a neutron star, but a novel end state, a “fermicon star,” with unusual physical properties.     

Hysteretic behavior induced by an electroacoustic feedback loop in a thermo-acousto-electric generator

An active control method of the spatial distribution of the acoustic field is applied in a thermo-acousto-electric generator. An auxiliary acoustic source is used to force the self-sustained thermoacoustic oscillation in order to control the thermoacoustic amplification. The auxiliary source consists of a loudspeaker, located inside the loop-tube close to the main ambient heat exchanger, and supplied with a delayed signal through an electric feedback loop, comprising a phase-shifter and an amplifier, connected to a reference microphone. Experiments are performed on a prototype engine working with air at a static gauge pressure of 5 bars. Experimental results demonstrate how it is possible to tune the acoustic oscillations in order to increase the global performance of the generator, compared to the case without control, as well as the existence of a hysteretic behavior induced by the electroacoustic feedback loop itself, which leads to a discrepancy between the onset heat input and the offset one.     

A new method to generate relativistic comb bunches with tunable subpicosecond spacing

We propose and analyze a scheme to produce comb bunches, i.e. a bunch consisting of micro-bunch trains, with tunable subpicosecond spacing. In the scheme, the electron beam is first deflected by a deflecting cavity which introduces a longitudinal-dependent linear transverse kick to the particles. After passing through a drift space, the transverse beam size is linearly coupled to the longitudinal position of the particle inside the beam, and a mask is placed there to tailor the beam, then the mask distribution is imprinted on the beam's longitudinal distribution. A quadrupole magnet and another deflecting cavity are used in the beam line to compensate the transverse angle due to the first deflecting cavity. Analysis shows that the number, length, and spacing of the trains can be controlled through the parameters of the deflecting cavity and the mask. Such electron bunch trains can be applied to an infrared free electron laser, a plasma-wakefield accelerator and a supper-radiance THz source.     

The 'DANTE' experiment

The selective excitation scheme known as ‘DANTE’ emerged from a confluence of several ideas for new NMR experiments, some more fanciful than others. DANTE offers a simple and effective way to restrict excitation to a very narrow frequency band, usually that of a single resonance line. Initially applied to the study of individual proton-coupled carbon-13 spin multiplets, the method has been extended to water presaturation, relaxation measurements, and chemical exchange studies. Through the imposition of a magnetic field gradient it offers a simple method to enhance resolution by restricting the effective volume of the sample. Multiple DANTE excitation (with Hadamard encoding) can speed up multidimensional spectroscopy by orders of magnitude. Applied to magnetic resonance imaging, the DANTE sequence has been used to superimpose a rectangular grid onto a cardiac image, permitting motional distortions to be monitored in real time.     

Superconductor-normal metal quantum phase transition in dissipative and non-equilibrium systems

Abstract

In physical systems, coupling to the environment gives rise to dissipation and decoherence. For nanoscopic materials, this may be a determining factor of their physical behaviour. However, even for macroscopic many-body systems, if the strength of this coupling is sufficiently strong, their ground-state properties and phase diagram may be severely modified. Also dissipation is essential to allow a system in the presence of a time-dependent perturbation to attain a steady, time-independent state. In this case, the non-equilibrium phase diagram depends on the intensity of the perturbation and on the strength of the coupling of the system to the outside world. In this paper, we investigate the effects of both dissipation and time-dependent external sources in the phase diagram of a many-body system at zero and finite temperatures. For concreteness, we consider the specific case of a superconducting layer under the action of an electric field and coupled to a metallic substrate. The former arises from a time dependent vector potential minimally coupled to the electrons in the layer. We introduce a Keldysh approach that allows to obtain the time dependence of the superconducting order parameter in an adiabatic regime. We study the phase diagram of this system as a function of the electric field, the coupling to the metallic substrate and temperature.     

Quantum speed limit for mixed states in a unitary system

Since the evolution of a mixed state in a unitary system is equivalent to the joint evolution of the eigenvectors contained in it, we could use the tool of instantaneous angular velocity for pure states to study the quantum speed limit (QSL) of a mixed state. We derive a lower bound for the evolution time of a mixed state to a target state in a unitary system, which automatically reduces to the quantum speed limit induced by the Fubini-Study metric for pure states. The computation of the QSL of a degenerate mixed state is more complicated than that of a non-degenerate mixed state, where we have to make a singular value decomposition (SVD) on the inner product between the two eigenvector matrices of the initial and target states. By combing these results, a lower bound for the evolution time of a general mixed state is presented. In order to compare the tightness among the lower bound proposed here and lower bounds reported in the references, two examples in a single-qubit system and in a single-qutrit system are studied analytically and numerically, respectively. All conclusions derived in this work are independent of the eigenvalues of the mixed state, which is in accord with the evolution properties of a quantum unitary system.