The Hydrodynamic Equations of Superfluid Mixtures in Magnetic Traps

The hydrodynamics equations of binary mixtures of Bose gases, Fermi gases, and mixtures of Bose and Fermi gases in the presence of external potentials are derived. These equations can be applied to current experiments on mixtures of atomic gases confined in magnetic traps.     

Trapping Electrons in Electrostatic Traps over the Surface of 4He

We have observed trapping of electrons in an electrostatic trap formed over the surface of liquid ⁴He. These electrons are detected by a Single Electron Transistor located at the center of the trap. We can trap any desired number of electrons between 1 and ∼30. By repeatedly (∼10³–10⁴ times) putting a single electron into the trap and lowering the electrostatic barrier of the trap, we can measure the effective temperature of the electron and the time of its thermalisation after heating up by incoherent radiation. E. Rousseau’s present address: Ecole Centrale, Paris, France. D. Ponarine’s present address: Chemistry Dept., North Carolina State Univ., Raleigh, NC 27695, USA.     

Superconductivities of Quasi-One-Dimensional and Quasi-Two-Dimensional Tight-Binding Electrons in Magnetic Field

The superconductivity of the tight binding electrons in a magnetic field is studied. We can treat both cases of quasi-one-dimension and quasi-two-dimension in the same manner. We study a various kind of anisotropic superconductivity with line nodes of the energy gap by taking attractive interaction between electrons in nearest sites along each axis. The magnetic field dependence of the transition temperature is calculated for a various pairing symmetry of superconductivity. When a magnetic field is applied in the conducting plane, the transition temperature is shown to increase as the magnetic field increases. In the strong magnetic field the eigenstates approach to those in the absence of hopping between planes, resulting in no orbital frustration.     

Heating Effect in Biocompatible Magnetic Fluid

This work is devoted to the study of heating of a biocompatible magnetic fluid due to time-varying magnetic induction. The adsorption of dextran on magnetite particles was confirmed by IR spectroscopy. A considerable thickness of the surfactant layer (oleate sodium + dextran) of about 4.3 nm prevents the formation of clusters made of nanomagnetic particles as evidenced by the fact that no maxima of the ultrasound wave absorption coefficient corresponding to cluster formation have been detected. The results show that the observed heating effect may be applied in hyperthermia treatments especially in the preferable region of 500 – 800 kHz. An “H ²– law” observed for the dependence of the SAR on the square of the amplitude of the magnetic field demonstrates the presence of superparamagnetic particles in the ferrofluid. Paper presented at the Seventeenth European Conference on Thermophysical Properties, September 5-8, 2005, Bratislava, Slovak Republic.     

Magnetotransport of Q1D Electrons Through Magnetic Barriers

BallisticelectrontransportthIoughmultiplemag-neticbarriersofa2DEGhasattractedcurrentinter.st[1~3].Itiswellknownthatmagneticfieldpossesseswave-vectorfilteringpropertiesandelec-trontunnelingisinherentlytwo-dimensionalprocess.Whathappensforaquasi-one-dimensional(Q1D)electrons(a2DEGconfinedbyatransversepotential)?Inthisreport,weconsiderelectrontunnelingthIoughdoublemagneticbarriers(DMB)andthreemagneticbarriers(TMB)ofa2DEGconfinedbyaparabolicpotentialwithoscillationfrequencyn.Themagnetic-ba…     

Anisotropic Superconductivity of Quasi-Two-Dimensional Tight-Binding Electrons in a Strong Magnetic Field

Based on the mean field theory, we have investigated the transition temperature T _c (H) of anisotropic superconductivity in quasi-two-dimensional (Q2D) tight-binding electrons in a strong magnetic field, where we assume the nearest-site attractive interaction. By taking account of the quantum effect of electronic motion in a strong magnetic field parallel to the 2D conducting plane, T _c (H) of the Q2D superconductor has been shown to increase in an oscillatory manner as the magnetic field becomes large and to reach T _c (0) in a strong magnetic field limit for the spin-triplet superconductor. We get the different magnetic field dependencies from that of on-site case.     

Structuralization of Magnetic Nanoparticles Induced by Laser Heating in Magnetic Fluids

The structuralization of magnetic particles in magnetic fluids due to the thermodiffusion induced by laser light illumination was experimentally observed in two types of magnetic fluids: one based on a mineral oil with magnetite particles covered by a monolayer of oleic acid as a surfactant and the other a kerosene-based magnetic fluid sterically stabilized by a double layer consisting of oleic acid and dodecylbenzenesulphonic acid (DBS). Forced Rayleigh scattering (FRS) showed different behaviors of magnetic particle structuralization in the observed magnetic fluids. While for the case of mineral oil-based magnetic fluids, there was observed a positive thermodiffusion (S > 0), an indication of negative thermodiffusion (S < 0) was observed in magnetic fluids based on kerosene. This was also confirmed by the time-dependent decay of a grating of magnetic particles. Numerical simulation of aggregation for the case of negative thermodiffusion was confirmed by the observed aggregation after laser illumination in kerosene-based magnetic fluids and enabled an estimated value of the negative Soret constant in the magnetic fluid studied (S ≈ −10⁻² K ⁻¹).     

Microwave Study of Surface Electrons on Helium Films in a Magnetic Field

We report preliminary results of a cyclotron resonance study of surface electrons (SE) on saturated helium films covering a PMMA substrate at T > 1 K. The real and imaginary parts of the dielectric response (k,) of the SE are measured at fixed k and in B-fields up to 10 T in a 12 GHz cavity. The cyclotron resonance of the SE is determined at different helium film thicknesses d _He and at various electron densities. At small d _He we find significant anomalies in the cyclotron resonance lineshape and position. As d _He increases the lineshape becomes progressively more symmetric and its peak moves towards the cyclotron field value expected for a free electron. To fit these data we have modified the classical Drude expression, introducing two different relaxation times for the low and high B-field regions. The phenomenological formulas fit the data quite well. A systematic theoretical analysis of these results is in progress.     

影响磁性氧化铁纳米颗粒磁热疗加热效率的因素

磁性纳米颗粒作为产热介质在生物医学方面取得了广泛的应用前景.近年来,新开发的纳米颗粒细胞内疗法更是克服了常规治疗方法的副作用,使治疗效率大大提高.氧化铁纳米颗粒由于其优异的磁性能在磁热疗应用的磁性纳米颗粒中脱颖而出,但存在着在交变磁场下加热效率受限的问题.具有高加热效率受限的磁性纳米粒子是磁热疗的必要条件.本文综述了近...     

Magnetic and Luminescent Properties of Barium Fluoride Nanopowder Obtained by Electron-Beam Evaporation in Low-Pressure Gas

Mesoporous amorphous-crystalline nanopowders of BaF₂ with the specific surface area up to 34.8 m²/g were obtained using evaporation by a pulsed electron beam in vacuum. Influence of the thermal annealing of the BaF₂ nanoparticles in air at the temperatures from 200 to 900°C on the size and morphology of the particles and changes in their magnetic and luminescent properties was studied. The paramagnetic response of the BaF₂ nanopowder was found to transform to the ferromagnetic response after annealing at 900°C. The appearance and transformation of the magnetic response in nanopowders made of BaF₂, which is diamagnetic as the bulk material, are ascribed to the appearance of radiation-induced and structural defects during the synthesis process by pulsed electron-beam evaporation.     

Particularities of the Magnetic State of CuO Nanoparticles Produced by Low-Pressure Plasma Arc Discharge

Copper oxide nanoparticles were produced by direct plasmachemical synthesis in a plasma arc discharge of low pressure. The formation of CuO nanoparticles with an average size of 12 nm and narrow size distribution intervals was determined by using the x-ray diffraction analysis and TEM microscopy methods. It was defined by using a vibration magnetometer and a SQUID magnetometer, that the magnetic properties of CuO nanoparticles with such size were extremely different from the magnetic properties of bulk antiferromagnetic CuO. Structural defects caused the formation of a ferromagnetic state, remaining at least up to the room temperature. The temperature of corresponding antiferromagnetic ordering was significantly decreased (down to ～ 100 K). Meanwhile, some of the copper surface spins showed a spin-glass behavior at low temperatures.     

Heating Characteristics of Transformer Oil-Based Magnetic Fluids of Different Magnetic Particle Concentrations

The heating ability of mineral oil-based magnetic fluids with different magnetic particle concentrations is studied. The calorimetric measurements were carried out in an alternating magnetic field of 500 A · m⁻¹ to 2500 A · m⁻¹ amplitude and of 1500 kHz frequency. The revealed H ⁿ law-type dependence of the temperature increase rate, (dT/dt) _t=0, on the amplitude of the magnetic field indicates the presence of superparamagnetic and partially ferromagnetic particles in the tested samples since n > 2. The specific absorption rate (SAR) defined as the rate of energy absorption per unit mass increases with a decrease of the volume fraction of the dispersed phase. This can be explained by the formation of aggregates in the samples with a higher concentration of magnetic particles.     

稳恒强磁场热处理对钴铁氧体结构和磁性能的影响

在强磁场下对钴铁氧体纳米粉末压块进行了热处理,分析讨论了热处理温度和磁感应强度对钴铁氧体的结构和磁性能的影响.结果表明,强磁场退火有利于钴铁氧体结晶度的提高和磁性能的增强,在居里点附近550℃下磁场处理作用效果最强,磁场强度越大,作用效果越明显.     

Electrons in Magnetic Structures with Domain Walls: Accumulation of Spin, Charge, and Transport Properties

We present the results of our theoretical analysis of magnetic, electric, and transport properties of domain walls in ferromagnets. The results were obtained within the semiclassical approximation and are valid for smooth domain walls. Taking into account Coulomb interaction between electrons, we calculated spin and charge accumulation at the wall. Local conductivity due to scattering from impurities located in the region of the domain wall was also calculated.     

汽轮机低压叶片断裂原因分析

针对国产300MW汽轮机低压缸扭叶片发生断裂失效事故进行研究分析;通过对扭叶片有限元计算、叶片振型模态实测,分析该叶片各阶自振频率,其计算结果和模态实测值基本吻合,为事故分析提供理论依据;对叶片材质元素成分测试,并着重对叶片实际运行工况及承受的各种可能的激振力分析,探求导致该级扭叶片疲劳断裂的真实原因,为同类型机组的安全、可靠运行提供一种借鉴作用和分析方法.     

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 Runaway of Electrons and the Formation of Beams in Glow Discharges

Analytical methods are used to obtain the criterion defining the boundary between the beam and hydrodynamic modes of motion of electrons in uniform and nonuniform electric fields for Townsend and high-voltage glow discharges. The beam approximation is used to study the electron energy distribution function in view of electrons being produced in gas. The hydrodynamic approximation is used to obtain the criterion which characterizes the runaway of electrons and the criterion of transition to the beam mode of motion. It is demonstrated that the curve of discharge ignition on the U(pd) diagram differs significantly from the boundary line between the beam and hydrodynamic modes of motion of electrons.     

Stability of Two-Component Bose-Einstein Condensates in Traps

Static and dynamic stabilities of two-component Bose-Einstein condensates trapped in harmonic potentials are studied. Using the variational method, we obtain the static stability condition and the phase separation condition. They are expressed as functions of the particle numbers and the s-wave scattering lengths. We find that the interaction between the different species of atoms (simply, interspecies interaction) has significant effects on the stability of each condensate. The instability of the ground state is explained in terms of the lowering (softening) of the collective excitation energies. We investigate the low-lying excitations and the possibility of their softening by use of the Gaussian ansatz and the sum-rule approach.