超流~3He、~4He溶液流体动力学方程——Ⅰ.超流~4He、~3He-B相溶液

我们的工作是把Landau的二流体超流理论推广到超流~3He、~4He溶液,用Lagrangian不定乘子法研究超流~4He、~3He-B相溶液和超流~4He、~3He-A相溶液的动力学性质.本文先讨论~4He、~3He-B相溶液,严格导出其流体动力学方程.     

利用手征SU(3)夸克模型研究轻双Λ超核^6_ΛΛHe,^5_ΛΛHe,^5_ΛΛH,^4_ΛΛHe,和^4_ΛΛH的结合能

在手征SU(3)夸克集团模型下, 通过共振群方法(RGM)计算了双Λ超核^6_ΛΛHe,^5_ΛΛHe,^5_ΛΛH,^4_ΛΛHe,和^4_ΛΛH的结合能. 结果表明, 假定双Λ超核具有双Λ集团和壳心核集团构成的两集团结构, 得到的^6_ΛΛHe超核的结合能与实验值基本吻合, 表明手征SU(3)夸克集团模型不仅能较好地描述重子谱、N-N和Y-N相互作用及轻Λ超核的结合能, 也能较好地描述Y-Y相互作用及双Λ超核^6_ΛΛHe,^5_ΛΛHe,^5_ΛΛH,^4_ΛΛHe,和^4_ΛΛH的结合能, 指出了它们存在的可能性.     

超流体~4He中的声

超流体们~4He是一种特殊的液体,具有量子液体性质。超流体~4He中声传播的研究是发展量子流体动力学的重要方面,为研究凝聚态物理中的许多复杂问题,如声子、旋子及其它元激发等,提供了简便而有力的途径。这也表明声波作为研究物质性质的重要手段的能力。本文为近年来,研究超流体~4He中的声的总结。     

超流^4He液滴中的单个分子及其红外光谱

按照超流的二流体模型，超流体的总密度ρ包括正常组分ρｎ和超流组分ρｓ二部分贡献，并且随温度降低ρｓ增加而ρｎ减小．为了确认上述模型的预言，１９４６年Ａｎｄｒｏｎｉｋａｓｈｖｉｌｉ完成了一个构思独特的实验．该实验装置很像是力学中测量转动惯量的扭摆，被扭...     

利用手征SU(3)夸克模型研究轻双Λ超核_(ΛΛ)~6He,_(ΛΛ)~5He, _(ΛΛ)~5H,_(ΛΛ) ~4He和_(ΛΛ)~4H的结合能

在手征SU(3)夸克集团模型下,通过共振群方法(RGM)计算了双Λ超核~6_(ΛΛ)He, ~5_(ΛΛ)He, ~5_(ΛΛ)H, ~4_(ΛΛ)He和~4_(ΛΛ)H的结合能．结果表明,假定双Λ超核具有双Λ集团和壳心核集团构成的两集团结构,得到的~6_(ΛΛ)He超核的结合能与实验值基本吻合,表明手征SU(3)夸克集团模型不仅能较好地描述重子谱、N-N和Y-N相互作用及轻Λ超核的结合能,也能较好地描述Y-Y相互作用及双Λ超核的结合能．使用相同的模型参数,计算了轻双Λ超核~5_(ΛΛ)He, ~5_(ΛΛ)H, ~4_(ΛΛ)He和~4_(ΛΛ)H的结合能,指出了它们存在的可能性．     

氦同位素原子与钠分子碰撞转动激发积分散射截面的理论计算

多体刚性椭球模型是一种比较精确的描述氦原子与钠分子碰撞的理论模型.本文用多体刚性椭球模型计算了不同能量下He的同位素原子3He,4He,7He,10He与Na2分子碰撞的转动激发积分散射截面,表明增加椭球等势面个数可以得到更准确的转动激发积分散射截面;总结出3He,4He,7He,10He-Na2碰撞体系转动激发积分散射截面随相对入射能量和体系约化质量变化的规律;讨论了相对入射能量为100meV时,相互作用势的不同区域对4He-Na2碰撞体系转动激发积分散射截面的影响情况.     

利用手征SU(3)夸克模型研究轻超核_Λ~5He,_Λ~4He和_Λ~4H的结合能

利用手征SU(3)夸克集团模型,通过共振群方法(RGM)得到非定域的YN相互作用势和Λ超子与壳心核的相互作用势,并用其计算了轻Λ超核5ΛHe,4ΛHe和4ΛH的结合能.计算结果表明,手征SU(3)夸克集团模型不仅能较好地描述Λp散射,也能较好地描述轻Λ超核的结合能.由于利用共振群方法(RGM)直接抽取的非定域YN相互作用势更为准确,因此计算得到的轻Λ超核5ΛHe,4ΛHe和4ΛH的结合能更符合实验数据,同时,这也为将来研究超核和多夸克体系确定了一套更为精确的模型参数.     

利用手征SU(3)夸克模型研究轻超核5ΛHe,4ΛHe和4ΛH的结合能

利用手征SU(3)夸克集团模型，通过共振群方法(RGM)得到了非定域的YN 相互作用势和Λ超子与壳心核的相互作用势,并计算了轻Λ超核5ΛHe,4ΛHe和4ΛH 的结合能. 计算结果表明，手征SU(3)夸克集团模型不仅能较好地描述Λp散射，也能较好地描述轻Λ超核的结合能. 由于利用共振群方法(RGM)直接抽取的非定域YN相互作用势更为准确，因此计算得到的轻Λ超核5ΛHe ,4ΛHe 和4ΛH 的结合能更符合实验数据，同时，也为将来的超核和多夸克体系确定了一套更为精确的模型参数.     

最高冷的元素——氦

正在元素周期表中,氦元素排在第二,原子核外只有一个轨道,并且被两个电子完全占据,没有额外的电子可以参与成键,属于最轻的惰性元素。氦有3He和4He两种同位素,氦气常压下的沸点是4.2 K,是最难液化的气体。液态氦在温度下降至2.18 K时,性质发生突变,成为一种超流体,能没有粘滞力地流动,热导率变得非常高,约为铜的800倍;其比热容、表面张力、压缩性都是反常的。因此在元素单质中,氦不仅是温度最低的流体,也基本不参与其他元素的化学反     

超热电子在稠密等离子体中输运的混合粒子模拟方法

相对论激光等离子体相互作用以及所产生的带电粒子束在高密度等离子体中的输运行为非常重要.该物理问题的数值模拟研究仍面临技术挑战.本文介绍一种粒子/流体混合模拟方法.该方法中超热电子采用动力学方法描述,背景冷的稠密等离子体采用简化的流体方程描述,适合于超热电子密度远小于背景电子密度,超热电子能量远大于背景电子温度.我们的三维并行混合模拟程序HEETS的模拟结果表明：背景材料的电离和电阻率模型至关重要,将严重影响高能电子输运过程的模拟.     

The two-fluid model with superfluid entropy

Summary The two-fluid model of liquid helium is generalized to the case that the superfluid fraction has a small entropy content. We present theoretical arguments in favour of such a small superfluid entropy. In the generalized two-fluid model various sound modes of He II are investigated. In a superleak carrying a persistent current the superfluid entropy leads to a new sound mode which we call sixth sound. The relation between the sixth sound and the superfluid entropy is discussed in detail.     

Hydrodynamics of superfluid helium in a single nanohole

The flow of liquid helium through a single nanohole with radius smaller than 25 nm was studied. Mass flow was induced by applying a pressure difference of up to 1.4 bar across a 50 nm thick Si(3)N(4) membrane and was measured directly by means of mass spectrometry. In liquid He I, we experimentally show that the fluid is not clamped by the short pipe with diameter-to-length ratio D/L?1, despite the small diameter of the nanohole. This viscous flow is quantitatively understood by making use of a model of flow in short pipes. In liquid He II, a two-fluid model for mass flow is used to extract the superfluid velocity in the nanohole for different pressure heads at temperatures close to the superfluid transition. These velocities compare well to existing data for the critical superflow of liquid helium in other confined systems.     

Two-fluid hydrodynamics: New aspects

Several systems described by the two-fluid model are considered. (1) For the superfluid ⁴He and ³He-⁴He mixtures, a new integral of motion is found, finite-temperature conditions for thermodynamic stability generalizing the Landau criterion for superfluidity are analyzed, and a theory of critical-velocity behavior of superflow is developed. (2) For the two-component system consisting of a lattice and a quasiparticle gas, a two-velocity elasticity theory is developed that explains linear facet growth in helium crystals. (3) For superflow in a uniform gravitational field, the hydrodynamic equations derived by invoking the equivalence principle of general relativity are used to analyze dissipative heat transfer in the Earth’s gravity field.     

Superfluid helium interferometry: an introduction

This article describes, at an introductory level, how superfluids can be used to measure absolute rotations. To make it self-contained to some degree, I first introduce briefly the two-fluid model for superfluid helium and the concept of superfluid order parameter. These ideas, which were put forward for the superfluid heliums, are now widely used, in particular for the BEC gases which are the main topic of this volume. They are presented in the somewhat different perspective of helium physics. The second part will deal with the Josephson effects, the real engine behind superfluid interferometry. These effects were predicted in the early sixties for superconductors and were promptly observed in the laboratory. It was quickly realised that they would also exist in superfluids but the search took longer and conclusive experiments were performed in the eighties only in the B-phase of superfluid ³He. How these experiments are done, and how they can be used to measure the rotation of the Earth by superfluid interferometry is surveyed in the last two sections.     

Relaxation and collective motion in superconductors: a two-fluid description

A simple, unified discussion of branch imbalance and gap relaxation in superconductors is presented. Both phenomena are treated within the framework of the ordinary Boltzmann equation, supplemented by the BCS gap equation. We show that the physics of the process commonly referred to as quasiparticle branch imbalance relaxation may be understood simply if one introduces a two-fluid model for the charge in the superconductor, and regards the process as one in which charge associated with the normal component is converted into charge associated with the superfluid. We derive in detail the exact solutions of the Boltzmann equation, which are valid near T_c, and allow for the effects of anisotropy. We discuss the comparison between relaxation rates measured in the superfluid and those obtained from normal state measurements and calculations. We then derive a set of two-fluid hydrodynamic equations based on the two-fluid model for the charge, and find that the current of charge associated with the normal component is not in general equal to the usual normal current. On the basis of these equations we derive expressions for the characteristic quasiparticle diffusion length near phase slip centers, and for the frequency of the recently observed collective mode. We compare our result with those of both microscopic and phenomenological calculations.     

Dynamics of liquid 4He in vycor

Using inelastic neutron scattering, we have observed well-defined phonon-roton ( p-r) excitations in superfluid 4He in Vycor over a wide wave-vector range, 0.3相似文献   

Energy spectra of quantum turbulence in He II and 3He-B: A unified view

Quantum turbulence in superfluid He II and in ³He-B that can be regarded as nearly isothermal, isotropic, and homogeneous is discussed within the two-fluid model. A general form of the 3D energy spectrum is proposed: at large length scales, where normal and superfluid eddies are locked together by the mutual friction force, the energy spectrum is essentially classical and includes an inertial range of a Kolmogorov K62 form. With increasing wavenumber k, the normal fluid part of the spectrum terminates due to finite viscosity, while the superfluid part of the spectral energy density changes towards k ⁻³ and then back into Kolmogorov-like k ^−5/3 again. Agreement with computer simulations and experiments is claimed if account is taken of the turbulent box size and of the energy decay rate. The text was submitted by the author in English.     

On the dynamics of superfluid vorticity in non-dissipative processes

We investigate the consequences of the possible existence of superfluid vorticity on the Landau two-fluid equations. Assuming a conservation law for superfluid circulation, we show that in non-dissipative situations, the superfluid vorticity is swept along by the normal fluid.     

Superfluid bose liquid with a suppressed BEC and an intensive pair coherent condensate as a model of 4He

One introduces a model of the superfluid state of a Bose liquid with repulsion between bosons, in which at T=0, along with a weak single-particle Bose-Einstein condensate, there exists an intensive pair coherent condensate, analogous to the Cooper condensate in a Fermi liquid with attraction between fermions. A closed system of nonlinear integral equations for the normal and anomalous self-energy parts is solved numerically, and a quasiparticle spectrum is obtained, which is in good agreement with the experimental spectrum of elementary excitations in superfluid 4He. It is shown that the roton minimum in the spectrum is associated with the negative minimum of the Fourier component of the pair interaction potential.     

Shear flow and Kelvin-Helmholtz instability in superfluids

The first realization of instabilities in the shear flow between two superfluids is examined. The interface separating the A and B phases of superfluid 3He is magnetically stabilized. With uniform rotation we create a state with discontinuous tangential velocities at the interface, supported by the difference in quantized vorticity in the two phases. This state remains stable and nondissipative to high relative velocities, but finally undergoes an instability when an interfacial mode is excited and some vortices cross the phase boundary. The measured properties of the instability are consistent with the classic Kelvin-Helmholtz theory when modified for two-fluid hydrodynamics.