共查询到20条相似文献,搜索用时 31 毫秒
1.
R. O. Zaitsev 《JETP Letters》2004,79(3):113-116
The concept of spin fluctuations in the Hubbard model is used for deriving a closed system of equations for the superconducting order parameter Δ and spin susceptibility. The limiting cases of low temperatures and temperatures close to the superconducting transition temperature are considered. The temperature dependences of the parameter Δ and the Knight shift are obtained. The conditions under which the second-order phase transition turns to the first-order phase transition are established. 相似文献
2.
A four-fluid model is used to investigate the structure of a dusty plasma sheath with two species of electrons, i.e., cold and hot electrons. Numerical results show that, in the presence of hot electrons, regular fluctuations are developed in the spatial profiles of the sheath potential and number densities of the plasma and dust nanoparticles. The amplitude and spatial period of the fluctuations depend on the hot electron parameters. The sheath width shows a non-monotonic dependence on the temperature and number density of the hot electrons, as well as the density and Mach number of the nanoparticles. 相似文献
3.
Sunil K. Mishra 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,78(1):65-73
We investigate slow dynamics of collection of a few noninteracting
antiferromagnetic NiO nanoparticles.
Our purpose is to enquire the role of size-dependent magnetization
fluctuations in temperature and time dependent properties of
antiferromagnetic nanoparticles. The zero-field cooled magnetization
exhibits size dependent fluctuations. We find memory effects in
field cooled magnetization, as well as aging effects in
thermoremenant magnetization of antiferromagnetic nanoparticles.
The antiferromagnetic nanoparticles show a stronger memory effect
than the corresponding effect in the ferromagnetic particles, when
the distribution of particles include very small sizes.
The situation reverses for bigger sizes. The relaxation of
the magnetization after a sudden cooling, heating and removal
of fields reiterate the memory effects. We also see a weak signature
of size-dependent magnetization fluctuations in aging effect of
antiferromagnetic nanoparticles. We find a two-step relaxation of
thermoremenant magnetization in antiferromagnetic case, which
differs qualitatively from relaxation of ferromagnetic nanoparticles. 相似文献
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5.
V. M. Samsonov D. E. Demenkov V. I. Karacharov A. G. Bembel’ 《Bulletin of the Russian Academy of Sciences: Physics》2011,75(8):1073-1077
The root-mean square fluctuations of the temperature and energetic surface tension of metallic and molecular nanoparticles
have been estimated. It is revealed that the relative value of mentioned fluctuations is not higher than several percents
even for the particles of 0.5 nm in size. We thus conclude that it is possible to apply the thermodynamic approach to nanoparticles
with fluctuating properties, and the fluctuations do not lead to nanoparticle instability and decay. 相似文献
6.
J. Sanchez E. Anabitarte 《International Journal of Infrared and Millimeter Waves》1989,10(9):1139-1152
A phase discrimination method for homodyne reflectometers applied to plasma density fluctuations is proposed and tested in the laboratory simulating the plasma fluctuations by a vibrating metallic mirror.Applicability conditions for plasma measurements are established. The method can be used in broadband operation. Application to density profile measurements is also possible. 相似文献
7.
Using Monte Carlo simulations, we study a coarse-grained model of a water layer confined in a fixed disordered matrix of hydrophobic nanoparticles at different particle concentrations c. For c=0, we find a first-order liquid-liquid phase transition (LLPT) ending in one critical point at low pressure P. For c>0, our simulations are consistent with a LLPT line ending in two critical points at low and high P. For c=25%, at high P and low temperature, we find a dramatic decrease of compressibility, thermal expansion coefficient, and specific heat. Surprisingly, the effect is present also for c as low as 2.4%. We conclude that even a small presence of hydrophobic nanoparticles can drastically suppress thermodynamic fluctuations, making the detection of the LLPT more difficult. 相似文献
8.
Caused by the interaction between the particles, structural fluctuations influence thermodynamics and order of transformation
of an ensemble of nanoparticles. A stringed thermodynamic analysis revealed that, in fluctuating ensembles, the ratio of particle
numbers in the equilibrium over the one in the non-equilibrium phase is independent of any metastable in between. Structural
transformations in such ensembles, connected to latent heat, are of infinite order. These findings are summarized in a set
of theorems ruling structural fluctuations. Finally, the consequences of fluctuations are demonstrated by an example. 相似文献
9.
利用热场动力学的方法研究了具有热噪声的相干态和压缩态中场正交分量的高阶涨落和高阶压缩.利用测量相位算符讨论了这些热化态中相位的高阶涨落.从而得到在有限温度下这些态的低阶及高阶涨落与温度的关系和压缩特性与温度的关系.由于实际的场态总是在一有限的温度下,所以讨论温度对涨落和压缩的影响是很有意义的.
关键词: 相似文献
10.
Frank J. Owens 《Journal of Physics and Chemistry of Solids》2003,64(11):2289-2292
Measurements of the orientational dependence of the ferromagnetic resonance (FMR) spectra are made on Fe3O4 nanoparticles in ferrofluids solidified in dc magnetic fields. The in field solidification locks the direction of magnetization parallel to the direction of the cooling field enabling measurements as a function of orientation with respect to the direction of magnetization in the frozen state. The g value of the FMR spectra at 77 K is 2.16 and the anisotropy constant is −1.23 J/m3. A marked reduction of the difference between the field position in the parallel and perpendicular orientation onsets on warming to 140 K well below the melting temperature of the fluid carrier and is attributed to the onset of fluctuations in the direction of the magnetization in the solid phase. The phase transition of the magnetic symmetry observed in bulk Fe3O4 occurs at much lower temperature in the nanoparticles. 相似文献
11.
The Lagrangian formalism is used to derive a system of nonlinear inhomogeneous dissipative differential equations describing the nonlinear dynamics of interrelated fluctuations of density, δρ, and temperature, δT, in a medium. With these equations, the unstable (with respect to initial conditions) phase trajectory describing parameter fluctuations in the ρ-T plane was obtained. By numerically solving the equations, we show that δρ and δT oscillate in time almost periodically, which is typical of fluctuations. 相似文献
12.
E. Popovici C. Luculescu R. Alexandrescu C. Fleaca F. Dumitrache R. Barjega M. Scarisoreanu E. Dutu A. Barbut I. Morjan E. Vasile 《Applied Surface Science》2012,258(23):9326-9332
The laser synthesis of nanoparticles starting from liquid precursors is particularly suitable as synthesis technique for obtaining nanoparticles. In the present work the laser pyrolysis is performed in a novel setup where the liquid precursor is brought with the aid of an original evaporator system to temperatures in excess of the boiling point and is finally fed into the reactor under the form of heated vapors.The process occurs in the gas phase and ensures the avoidance of the condensation. The temperature control system allows for the maintaining of the overall system temperature below the decomposition temperature and above the boiling. Temperatures up to 500 °C are assured for the mixed precursors. The control of the amount of the active substances is performed upstream, in the liquid phase. The set-up is able to offer safety conditions at the synthesis of substances with high toxicity. This experimental set-up was proposed in order to synthesize TiO2 nanoparticles from TTIP because its boiling temperature is relatively high (239 °C grades). Different analytical techniques such as EDX, TEM, XRD and HRTEM were used in order to evaluate the structural characteristics of the produced nanopowders. 相似文献
13.
采用分子动力学方法模拟了纳米金属铝在粒径为0.8-3.2 nm 时的熔点、密度和声子热导率的变化, 研究了粒径为1.6 nm的铝纳米颗粒的密度、比热和声子热导率随温度的变化. 采用原子嵌入势较好地模拟了纳米金属铝的热物性及相变行为, 根据能量-温度曲线和比热容-温度曲线对铝纳米颗粒的相变温度进行了研究, 并利用表面能理论、尺寸效应理论对铝纳米颗粒熔点的变化进行了分析. 随着纳米粒径的不断增大, 铝纳米颗粒的熔点呈递增状态, 当粒径在2.2-3.2 nm时, 熔点的增幅减缓, 但仍处于递增趋势. 随着纳米粒径的增大, 铝纳米颗粒的密度呈单调递减, 热导率则呈线性单调递增, 且热导率的变化情况符合声子理论. 随着温度的升高, 粒径为1.6 nm的铝纳米颗粒的密度、热导率均减小. 该模拟从微观原子角度对纳米材料的热物性进行了研究, 对设计基于铝纳米颗粒的相变材料具有指导意义. 相似文献
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J. Adámek I. Ďuran M. Hron J. Stöckel P. Balan R. Schrittwieser C. Ionita E. Martines M. Tichý G. Van Oost 《Czechoslovak Journal of Physics》2002,52(10):1115-1120
A new probe head, composed of two electro-emissive probes and two Langmuir probes has been designed to measure edge fluctuations in the CASTOR tokamak. In this contribution, only one Langmuir and one electron-emissive probe are used to measure the temperature and potential fluctuations and the phase angle between them. 相似文献
16.
The temperature and coverage dependence of the mean square concentration fluctuations in a small open domain of an adsorbed layer is discussed for various situations. It is shown that fluctuations decrease with increasing temperature and reach a limiting value when attractive interactions predominate, but increase and reach a limiting value when repulsive interactions predominate, if a single non-ideal two -dimensional phase exists. Deviations from ideal gas behavior are strongest at half coverage. At very low coverage (low particle concentration) and very high coverage (low hole concentration) ideal behavior is approached. If the layer consists of a two phase system, for instance a two-dimensional liquid or solid in equilibrium with a two-dimensional gas, fluctuations far below the critical temperature are dominated by fluctuations in the partition between phases. As the critical temperature is approached fluctuations first decrease because the mean concentrations in the two phases approach each other, and then increase very sharply near Tc. Detailed calculations for the single phase situation are given for several approximations: a dilute gas; a mean field approximation; a lattice gas in both the Bragg-Williams and the BethePeierls-Weiss approximations. The latter which takes some account of correlations between adsorbate particle positions seems to explain reasonably the presently available experimental observations on chemisorbed layers. 相似文献
17.
Weixing Wang Jarett C. Martin Ning Zhang Chao Ma Aijie Han Luyi Sun 《Journal of nanoparticle research》2011,13(12):6981-6990
Biogenic silica nanoparticles were synthesized using rice husks (RHs) as the raw material via controlled pyrolysis. The characterization
results showed that the morphology of the synthesized silica was highly related to the pretreatment of RHs and the pyrolysis
conditions. Particularly, potassium cations in RHs were found to catalyze the melting of silica, during which the amorphous
silica were converted to crystalline phase. Two hours of pyrolysis at 700 °C appeared to be ideal to synthesize silica nanoparticles
with a diameter of ca. 20–30 nm. Higher temperature and longer duration of pyrolysis led to undesired melting of silica nanoparticles,
while too low a temperature cannot effectively remove carbonous residues. Such amorphous silica nanoparticles with narrow
size distribution and high purity are expected to replace silica gel and fumed silica for various applications. 相似文献
18.
Igor Danilenko Tetyana Konstantinova Galina Volkova Valentina Glazunova 《Phase Transitions》2013,86(10):987-999
The aim of this study was to produce yttria-stabilized zirconia nanopowders from zirconium oxychloride and zirconium oxynitrate salts using a co-precipitation technique, and to investigate the influence of hydrostatic pressure on the phase transition in these powders. It is shown that synthesis conditions and calcination temperature have a strong influence on the nanopowder's agglomeration, as well as on the stability of the tetragonal phase to phase transition under pressure conditions. Doped zirconia nanopowders synthesized from oxynitrate salts are more agglomerated and more stable than the oxychloride-based powders. Increasing the role of interfacial energy in agglomerated nanopowders leads to an increase in the stability of the tetragonal phase in doped zirconia nanopowders systems obtained at low and high calcination temperatures. Formation of separated nanoparticles at middle calcination temperature leads to a decrease in the stability of the tetragonal phase to phase transition under hydrostatic pressure conditions. 相似文献
19.
Quantum tunneling of the magnetic moments of Ni nanoparticles with various spatial atomic structures is studied. The crossover temperature of the nanoparticle fluctuations exhibits a step when the icosahedral structure of the particles changes to the fcc structure. The rate of quantum magnetic fluctuations is determined. 相似文献
20.
For the 1D fully asymmetric exclusion model with open boundary conditions, we calculate exactly the fluctuations of the current of particles. The method used is an extension of a matrix technique developed recently to describe the equatime steady-state properties for open boundary conditions and the diffusion constant for particles on a ring. We show how the fluctuations of the current are related to non-equal-time correlations. In the thermodynamic limit, our results agree with recent results of Ferrari and Fontes obtained by working directly in the infinite system. We also show that the fluctuations of the current become singular when the system undergoes a phase transition with discontinuities along the first-order transition line. 相似文献