Kondo correlation and spin-flip scattering in spin-dependent transport through a quantum dot coupled to ferromagnetic leads

We investigate the linear and nonlinear dc transport through an interacting quantum dot connected to two ferromagnetic electrodes around Kondo regime with spin-flip scattering in the dot. Using a slave-boson mean field approach for the Anderson Hamiltonian having finite on-site Coulomb repulsion, we find that a spin-flip scattering always depresses the Kondo correlation at arbitrary polarization strength in both parallel and antiparallel alignment of the lead magnetization and that it effectively reinforces the tunneling related conductance in the antiparallel configuration. For systems deep in the Kondo regime, the zero-bias single Kondo peak in the differential conductance is split into two peaks by the intradot spin-flip scattering; while for systems somewhat further from the Kondo center, the spin-flip process in the dot may turn the zero-bias anomaly into a three-peak structure.Comment: 4 pages, 2 figure

Thermal conduction of carbon nanotubes using molecular dynamics

The heat flux autocorrelation functions of carbon nanotubes (CNTs) with different radius and lengths is calculated using equilibrium molecular dynamics. The thermal conductance of CNTs is also calculated using the Green-Kubo relation from the linear response theory. By pointing out the ambiguity in the cross section definition of single wall CNTs, we use the thermal conductance instead of conductivity in calculations and discussions. We find that the thermal conductance of CNTs diverges with the CNT length. After the analysis of vibrational density of states, it can be concluded that more low frequency vibration modes exist in longer CNTs, and they effectively contribute to the divergence of thermal conductance.Comment: 15 pages, 6 figures, submitted to Physical Review

Magnetic configurations of the tilted current sheets in magnetotail

In this research, the geometrical structures of tilted current sheet and tail flapping waves have been analysed based on multiple spacecraft measurements and some features of the tilted current sheets have been made clear for the first time. The geometrical features of the tilted current sheet revealed in this investigation are as follows: (1) The magnetic field lines (MFLs) in the tilted current sheet are generally plane curves and the osculating planes in which the MFLs lie are about vertical to the equatorial plane, while the normal of the tilted current sheet leans severely to the dawn or dusk side. (2) The tilted current sheet may become very thin, the half thickness of its neutral sheet is generally much less than the minimum radius of the curvature of the MFLs. (3) In the neutral sheet, the field-aligned current density becomes very large and has a maximum value at the center of the current sheet. (4) In some cases, the current density is a bifurcated one, and the two humps of the current density often superpose two peaks in the gradient of magnetic strength, indicating that the magnetic gradient drift current is possibly responsible for the formation of the two humps of the current density in some tilted current sheets. Tilted current sheets often appear along with tail current sheet flapping waves. It is found that, in the tail flapping current sheets, the minimum curvature radius of the MFLs in the current sheet is rather large with values around 1 <I>R<sub>E</sub></I>, while the neutral sheet may be very thin, with its half thickness being several tenths of <I>R<sub>E</sub></I>. During the flapping waves, the current sheet is tilted substantially, and the maximum tilt angle is generally larger than 45°. The phase velocities of these flapping waves are several tens km/s, while their periods and wavelengths are several tens of minutes, and several earth radii, respectively. These tail flapping events generally last several hours and occur during quiet periods or periods of weak magnetospheric activity

Dominant Physicochemical Properties of SF6/N2 Thermal Plasmas with a Two-temperature Chemical Kinetic Model

It's increasingly clear that the existence of thermodynamic equilibrium is an exception rather than the role in SF6/N2 thermal plasmas. We intended to investigate the dominant physicochemical properties of SF6/N2 thermal plasmas at 4  atm from 12000 K to 1000 K with considering the thermal non-equilibrium. A two-temperature chemical kinetic model containing all the available reactions is developed. The temperature difference between the electron and the heavy species is defined as a function of the electron number density. The molar fractions of species are compared to the equilibrium composition predicted by Gibbs free energy minimization. By analyzing the main reactions in the generation and loss of a dominant species, the chemistry set is simplified and characterized by a few species and reactions. Then, the dominant physicochemical properties are captured and the computing time of complicated chemical kinetic model is dramatically shortened at the same time

Utilising Tree-Based Ensemble Learning for Speaker Segmentation

Part 2: Learning-Ensemble LearningInternational audienceIn audio and speech processing, accurate detection of the changing points between multiple speakers in speech segments is an important stage for several applications such as speaker identification and tracking. Bayesian Information Criteria (BIC)-based approaches are the most traditionally used ones as they proved to be very effective for such task. The main criticism levelled against BIC-based approaches is the use of a penalty parameter in the BIC function. The use of this parameters consequently means that a fine tuning is required for each variation of the acoustic conditions. When tuned for a certain condition, the model becomes biased to the data used for training limiting the model’s generalisation ability.In this paper, we propose a BIC-based tuning-free approach for speaker segmentation through the use of ensemble-based learning. A forest of segmentation trees is constructed in which each tree is trained using a sampled version of the speech segment. During the tree construction process, a set of randomly selected points in the input sequence is examined as potential segmentation points. The point that yields the highest ΔBIC is chosen and the same process is repeated for the resultant left and right segments. The tree is constructed where each node corresponds to the highest ΔBIC with the associated point index. After building the forest and using all trees, the accumulated ΔBIC for each point is calculated and the positions of the local maximums are considered as speaker changing points. The proposed approach is tested on artificially created conversations from the TIMIT database. The approach proposed show very accurate results comparable to those achieved by the-state-of-the-art methods with a 9% (absolute) higher F1 compared with the standard ΔBIC with optimally tuned penalty parameter

Hawking radiation of Dirac particles via tunneling from Kerr black hole

We investigated Dirac Particles' Hawking radiation from event horizon of Kerr black hole in terms of the tunneling formalism. Applying WKB approximation to the general covariant Dirac equation in Kerr spacetime background, we obtain the tunneling probability for fermions and Hawking temperature of Kerr black hole. The result obtained by taking the fermion tunneling into account is consistent with the previous literatures.Comment: 7 pages, no figures, to appear in CQ

Neutron diffraction study of the magnetic order in NdMn2Ge1.6Si0.4

Here we report a detailed investigation of NdMn2Ge1.6Si0.4; this forms part of our investigation of the magnetic order across the NdMn2Ge2−xSix (x = 0–2.0) series by magnetometry, x-ray diffraction and neutron diffraction over the temperature range 6–465 K. On decreasing the temperature from 465 K, NdMn2Ge1.6Si0.4 exhibits four magnetic transitions: (i) from paramagnetism to intralayer antiferromagnetism AFl at TIntraN ~ 430 K; (ii) AFl to canted ferromagnetism Fmc at TInterC ~ 330 K; (iii) Fmc to conical magnetic ordering of the Mn sublattice Fmi at Tcc ~ 178 K and (iv) Fmi(Mn) to Fmi(Mn)+F(Nd) at TNdC ~ 72 K