Current fluctuations in stochastic lattice gases

We study current fluctuations in lattice gases in the macroscopic limit extending the dynamic approach for density fluctuations developed in previous articles. More precisely, we establish a large deviation theory for the space-time fluctuations of the empirical current which include the previous results. We then estimate the probability of a fluctuation of the average current over a large time interval. It turns out that recent results by Bodineau and Derrida [Phys. Rev. Lett. 92, 180601 (2004)]] in certain cases underestimate this probability due to the occurrence of dynamical phase transitions.     

Current fluctuations in chain of nanoparticles

We have fabricated and analyzed devices where an electrode gap was bridged by a chain of citrate stabilized gold particles. The current-voltage characteristic I∼ζ(V−Vt) with voltage threshold Vt≈0 and scaling exponent ζ=0.91 is attributed to charge transport in a one-dimensional path. We observe current fluctuations in the frequency range 3-100 mHz as function of time as a result of conformational changes in the citrate molecules induced by charge transfer across the molecules.     

Current fluctuations in the multiphoton photoemissive effect

It is found theoretically that the number of photoelectrons which appear above the surface of a target having a known quantum yield as a result of the multiphoton photoemissive effect depends on both the order of the effect and the fluctuation properties of the radiation field. The mean square fluctuation in the number of photoelectrons can always be written as a sum taking into account the fluctuations of classical particles and wave fields. It is also shown that fluctuations in the photoelectric current, governed unambiguously by the order of the effect and by the statistics of the radiation field, increase rapidly with increasing order of the effect.Translated from Izvestiya VUZ. Fizika, No. 4, pp. 136–140, April, 1970.     

Current fluctuations in an interacting quantum dot

We calculate the counting statistics of electron transfer through an open quantum dot with charging interaction. A dot that is connected to leads by two single-channel quantum point contacts in an in-plane magnetic field is described by a Luttinger liquid with impurity at the Toulouse point. We find that the fluctuations of the current through this conductor exhibit distinctive interaction effects. Fluctuations saturate at high voltages, while the mean current increases linearly with the bias voltage. All cumulants higher than the second one reach at large bias a temperature independent limit.     

CoSb3纳米热电材料的制备及热传输特性

以Sb，Co为起始原料，采用固相反应法合成了CoSb3.通过高能球磨制得CoSb3纳米粉末，用放电等离子烧结(SPS)方法制备出最小平均晶粒尺寸为150nm的块体材料.研究了晶粒尺寸与热传输性能之间的关系：CoSb3化合物结构纳米化对其晶格热导率κL有显著影响，当晶粒尺寸由微米尺度减小到纳米尺度，晶格热导率κL显著降低，但对载流子热导率κc的影响不甚显著.CoSb3化合物的热导率κ随晶粒尺寸的减小而降 低主要是由于晶格热导率κL随晶粒尺寸的减小而降低所致. 关键词： 纳米 Skutterudite 制备 热传输特性     

Current fluctuations in 1D double - barrier heterostructures

A theoretical formalism to study the current-noise characteristic of one-dimensional double barrier heterostructures taking into account correlation effects is developed within the context of the Keldysh nonequilibrium Green functions. The effects of the Coulomb blockade on the characteristic curve (current versus voltage) and on the current fluctuation are studied in a selfconsistent calculation. For the static case a reduction of the full shot noise is observed. The effects of the barrier characteristics on the transport properties are also analyzed. A connection between the noise frequency spectrum and the transit time of the electron going along the structure is established.     

Current density and field fluctuations in a conducting medium

We study thermal fluctuations in a conducting medium which may be spatially non-uniform and anisotropic. The fluctuation spectra for charge and current density, and for the electromagnetic fields, are expressed in terms of the basic propagators of the macroscopic equations. The theory is based on an application of the generalized Nyquist theorem.     

CoSb_3纳米热电材料的制备及热传输特性

以Sb ,Co为起始原料 ,采用固相反应法合成了CoSb3.通过高能球磨制得CoSb3纳米粉末 ,用放电等离子烧结(SPS)方法制备出最小平均晶粒尺寸为 1 5 0nm的块体材料 .研究了晶粒尺寸与热传输性能之间的关系 :CoSb3化合物结构纳米化对其晶格热导率κL 有显著影响 ,当晶粒尺寸由微米尺度减小到纳米尺度 ,晶格热导率κL 显著降低 ,但对载流子热导率κc 的影响不甚显著 .CoSb3化合物的热导率κ随晶粒尺寸的减小而降低主要是由于晶格热导率κL 随晶粒尺寸的减小而降低所致     

Current fluctuations in nonequilibrium diffusive systems: an additivity principle

We formulate a simple additivity principle allowing one to calculate the whole distribution of current fluctuations through a large one dimensional system in contact with two reservoirs at unequal densities from the knowledge of its first two cumulants. This distribution (which in general is non-Gaussian) satisfies the Gallavotti-Cohen symmetry and generalizes the one predicted recently for the symmetric simple exclusion process. The additivity principle can be used to study more complex diffusive networks including loops.     

Current fluctuations in negistor structures based on noncrystalline Ga-Te films

The results of investigation of low-frequency (up to 10⁶ Hz) and microwave (at a frequency of 10 GHz) electric current fluctuations in negistor structures of the type of glass carbon-noncrystalline Ga_{1 ? x} Te _x film (where x = 0.75 or 0.80)-glass carbon are presented. Low-frequency current fluctuations are studied in strong electric fields up to the emergence of electric instability, while microwave fluctuations are studied after the current pinching at low current sustaining the low-resistance state. It is shown that regularities governing such fluctuations in these structures substantially differ from the corresponding regularities in selenium film negistors studies earlier. According to the results of analysis, the processes initiating electrical instability and the current pinching in these structures are not associated with manifestations of heating of charge carriers by the electric field. In addition, it is found that the filament diameter virtually remains unchanged in the range of currents sustaining the low-resistance state, while the electrical conductivity of the pinching region shows a tendency to increase with current. Possible reasons for these phenomena are considered.     

Current reversals in an inhomogeneous system with asymmetric unbiased fluctuations

We present a study of the transport of a Brownian particle moving in a periodic symmetric potential in the presence of asymmetric unbiased fluctuations. The particle is considered to move in a medium with periodic space dependent friction. By tuning the parameters of the system, the direction of the current exhibits reversals, both as a function of temperature as well as the amplitude of rocking force. We found that the mutual interplay between the opposite driving factors is the necessary term for current reversals.Received: 11 October 2003, Published online: 9 April 2004PACS: 05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion - 02.50.Ey Stochastic processes - 87.10. + e General theory and mathematical aspects     

Current fluctuations in nanopores: The effects of electrostatic and hydrodynamic interactions

Using nonequilibrium Langevin dynamics simulations of an electrolyte with explicit solvent particles, we investigate the effect of hydrodynamic interactions on the power spectrum of ionic nanopore currents. At low frequency, we find a power-law dependence of the power spectral density on the frequency, with an exponent depending on the ion density. Surprisingly, however, the exponent is not affected by the presence of the neutral solvent particles. We conclude that hydrodynamic interactions do not affect the shape of the power spectrum in the frequency range studied.     

Current fluctuations from various crystal faces of a clean tungsten field emitter

The temperature, frequency and current dependence of current fluctuations have been measured for the (310), (112) and (100) planes of a tungsten field emitter. The rms percent fluctuation of the current at 900 K was 8.7, 1.5 and 0.13% and the threshold temperature for current fluctuation was 300, 650 and 1000 K for the (310), (112) and (100) planes respectively. Based on the results reported here it is concluded that the current fluctuations arise from the generation of mobile atoms on net plane terraces.     

Gradient-driven fluctuations in microgravity

Equilibrium fluctuations of thermodynamic variables, such as density or concentration, are known to be small and typically occur at a molecular length scale. In contrast, theory predicts that non-equilibrium fluctuations grow very large both in amplitude and spatial size. On earth, the presence of gravity and buoyancy forces severely limits the development of the fluctuations. We will present the results of a 14-year long international collaboration on an experiment on non-equilibrium fluctuations in a single liquid and in a polymer solution under microgravity conditions. Non-equilibrium conditions are generated by applying a temperature gradient across millimetre-size liquid slabs. Phase modulations introduced by fluctuations are measured using a quantitative shadowgraph method, with the optical axis parallel to the temperature gradient. Thousands of images are analysed and their two-dimensional power spectra yield the fluctuation structure function S(q), once data are reduced accounting for the instrumental transfer function T(q). The mean-squared amplitude of the fluctuations exhibits an impressive power-law dependence at larger q and a crossover at low q showing that the fluctuation size is limited by the sample thickness. The shape of the structure function, its increase due to removing gravity, and its dependence on applied gradient are in reasonable agreement with available theoretical predictions.     

Local-field fluctuations in paramagnets

Equations are derived for the local-field fluctuations in a paramagnet. A comparison is made with the second moment and with the Lorentz local field.     

Minimum fluctuations in nanostructures

The properties of the Bose gas in traps have been experimentally and theoretically investigated. The main results of these investigations were discussed in L. Pitaevskii’s review. In this study, we consider excitations of low-lying levels in a disk-shaped magnetic trap. In contrast to the macrostructure, the excitation spectrum in the traps is a set of quasi-Bogolyubov modes with the gaps, which can be interpreted as a discrete breathing mode spectrum.     

Spin fluctuations in intermetallics

A review is given of investigations of the quasiparticle spectra and of the magnetic fluctuations spectra of metals with strong longitudinal magnetic susceptibilities which were performed by means of the de Haas-van Alphen effect and inelastic neutron scattering. Among the systems investigated are the incipient ferromagnets Ni₃Ga and TiBe₂, the low temperature ferromagnets Ni₃Al, YNi₃, ZrZn₂ and MnSi, the light rare earth metals including PrCu₂ which are close to antiferromagnetic instabilities at low temperatures, and the actinide heavy fermion superconductors UPt₃ and UBe₁₃. The strong renormalisation of the quasiparticle masses and the temperature dependence of the heat capacity and of the magnetic equation of state of these systems are discussed in terms of a quantitative model based on the relaxation frequency of very low lying spin fluctuations.     

Structural fluctuations in nanoparticles

Standard methods of thermodynamics are used to investigate fluctuation conditions for individual nanoparticles. This analysis leads to a theorem on fluctuations of nanoparticles in the vicinity of the phase transformation temperature stating that fluctuations are possible only between an equilibrium and a non-equilibrium phase. The basic conditions used to describe fluctuations are well suited to calculate the limits for fluctuations as function of temperature and particle size.     

Shock-timing experiments in polystyrene target

Direct-drive and indirect-drive inertial confinement fusion （ICF） targets use temporally shaped drive pulses to optimize target performance. The timing of multiple shock waves is crucial to the performance of ICF ignition targets. Velocity interferometer system for any refiector （VISAR） is the principal diagnostic tool for shock-timing experiments. We present velocity measurements from the shock waves in polystyrene targets driven by two 200-ps pulses separated by 1–2 ns. These pulses drive two shock waves that coalescence in the target. Coalescence time and transit times are observed by VISAR.