Linear magnetoconductivity in an intrinsic topological Weyl semimetal

Searching for the signature of the violation of chiral charge conservation in solids has inspired a growing passion on the magneto-transport in topological semimetals. One of the open questions is how the conductivity depends on magnetic fields in a semimetal phase when the Fermi energy crosses the Weyl nodes. Here, we study both the longitudinal and transverse magnetoconductivity of a topological Weyl semimetal near the Weyl nodes with the help of a two-node model that includes all the topological semimetal properties. In the semimetal phase, the Fermi energy crosses only the 0th Landau bands in magnetic fields. For a finite potential range of impurities, it is found that both the longitudinal and transverse magnetoconductivity are positive and linear at the Weyl nodes, leading to an anisotropic and negative magnetoresistivity. The longitudinal magnetoconductivity depends on the potential range of impurities. The longitudinal conductivity remains finite at zero field, even though the density of states vanishes at the Weyl nodes. This work establishes a relation between the linear magnetoconductivity and the intrinsic topological Weyl semimetal phase.Comment: An extended version accepted by New. J. Phys. with 15 pages and 3 figure

High-field magnetoconductivity of topological semimetals with short-range potential

Weyl semimetals are three-dimensional topological states of matter, in a sense that they host paired monopoles and antimonopoles of Berry curvature in momentum space, leading to the chiral anomaly. The chiral anomaly has long been believed to give a positive magnetoconductivity or negative magnetoresistivity in strong and parallel fields. However, several recent experiments on both Weyl and Dirac topological semimetals show a negative magnetoconductivity in high fields. Here, we study the magnetoconductivity of Weyl and Dirac semimetals in the presence of short-range scattering potentials. In a strong magnetic field applied along the direction that connects two Weyl nodes, we find that the conductivity along the field direction is determined by the Fermi velocity, instead of by the Landau degeneracy. We identify three scenarios in which the high-field magnetoconductivity is negative. Our findings show that the high-field positive magnetoconductivity may not be a compelling signature of the chiral anomaly and will be helpful for interpreting the inconsistency in the recent experiments and earlier theories.Comment: An extended version accepted by Phys. Rev. B, with 11 pages and 4 figure

Edge states and integer quantum Hall effect in topological insulator thin films

The integer quantum Hall effect is a topological state of quantum matter in two dimensions, and has recently been observed in three-dimensional topological insulator thin films. Here we study the Landau levels and edge states of surface Dirac fermions in topological insulators under strong magnetic field. We examine the formation of the quantum plateaux of the Hall conductance and find two different patterns, in one pattern the filling number covers all integers while only odd integers in the other. We focus on the quantum plateau closest to zero energy and demonstrate the breakdown of the quantum spin Hall effect resulting from structure inversion asymmetry. The phase diagrams of the quantum Hall states are presented as functions of magnetic field, gate voltage and chemical potential. This work establishes an intuitive picture of the edge states to understand the integer quantum Hall effect for Dirac electrons in topological insulator thin films.Comment: 10 pages, 5 figure

High frequency switching parallel processing topology for AC uninterruptible power supply

This thesis presents the description, analysis and design of a high frequency parallel processing ac uninterruptible power supply. Compared to the standard UPS system used today, the proposed system has higher efficiency, smaller size and less weight, this is due primary to the usage of a high-frequency switching topology. The main power circuit configuration is shown to describe the steady state behaviour of the system in both ac line supply and battery backup modes of operation. A stability analysis is developed to describe the system behaviour against the load variation and the input disturbance. The detailed design of the output voltage control loop is carried out. A transient analysis is presented to describe the transition between the two operation modes of ac line supply and dc battery backup. From this analysis a fast switching transition control circuit is designed. A design procedure is illustrated to select the system components for a 300W UPS. The corresponding system performance such as efficiency is evaluated. All the theoretical results obtained in this thesis are experimentally verified

A New Method for Figuring the Number of Hidden Layer Nodes in BP Algorithm

In the field of artificial neural network, BP neural network is a multi-layer feed-forward neural network. Because it is difficult to figure the number of hidden layer nodes in a BP neural network, the theoretical basis and the existing methods for BP network hidden layer nodes are studied. Then based on traditional empirical formulas, we propose a new approach to rapidly figure the quantity of hidden layer nodes in two-layer network. That is, with the assistance of experience formulas, the horizon of unit number in hidden layer can be confirmed and its optimal value will be found in this horizon. Finally, a new formula for figuring the quantity of hidden layer codes is obtained through fitting input dimension, output dimension and the optimal value of hidden layer codes. Under some given input dimension and output dimension, efficiency and precision of BP algorithm may be improved by applying the proposed formula

PO-161 Effect of different type of exercise on mitochondrial homeostasis in rats with myocardial infarction

Objective To investigate the different effect of moderate-intensity continuous training (MCT) and high-intensity interval exercise training (HIT) on ventricular remodeling and mitochondrial homeostasis after acute myocardial infarction (AMI). Methods The AMI rat model was achieved by ligating coronary artery. The AMI and sham operation rats were randomly divided into four groups: sham operation group (Sham), AMI control group (AMI), AMI MCT group (AMI+M), and AMI HIT group (AMI+H). Animals in the AMI+M and AMI+H groups underwent 4 weeks MCT and HIT respectively. Five weeks after AMI, hemodynamic changes, mitochondrial bioenergetics, and PINK1, Beclin1, Mfn2, Drp1, Tfam, COXⅣ, PGC-1α were detected. Results Comparing with AMI group, in AMI+M and AMI+H groups, Beclin1 (146.33±18.47, 143.28±16.96.vs. 123.27±13.27, P<0.05), PINK1 (150.33±20.54, 152.28±18.34.vs. 125.27±17.67, P<0.05), Mfn2 (122.28±18.81, 117.19±17.04.vs. 46.27±6.72, P<0.01), and PGC-1α (82.15±16.58, 102.25±13.27.vs. 60.27±9.36, P<0.05~0.01) expression elevated significantly, whereas ROS generation (122.28±18.81, 117.19±17.04.vs. 46.27±6.72, P<0.01) and Drp1 expression (9.58±1.40, 10.18±1.37.vs. 15.85±1.61, P<0.05) showed dramatic decrease. In addition, in AMI+H group, +dp/dt max (6326±325.vs. 5368±271, P<0.05), -dp/dt max (-5312±246.vs. -4457±250, P<0.05), mitochondrial membrane potential (85.24±11.94.vs. 71.28±8.34, P<0.05), ATP synthesis activity (38.77±5.16.vs. 32.33±4.14, P<0.05), Tfam (95.25±12.05.vs. 78.27±12.22, P<0.05) and COXⅣ (89.25±14.06.vs. 67.27±13.71, P<0.05) expression improved significantly. Comparing with AMI+M group, in AMI+H group, +dp/dt max (6326±325.vs. 5775±310, P<0.05), -dp/dt max (-5312±246.vs. -4778±305, P<0.05), PGC-1α (102.25±13.27.vs. 82.15±16.58 1, P<0.05), Tfam (95.25±12.05.vs. 80.15±11.99, P<0.05) and COXⅣ(89.25±14.06.vs. 72.15±10.89, P<0.05) expression improved significantly. Conclusions High-intensity interval exercise training is superior to moderate-intensity continuous training for ameliorating ventricular remodeling and mitochondrial homeostasis after acute myocardial infarction

Empirical metallicity-dependent calibrations of effective temperature against colours for dwarfs and giants based on interferometric data

We present empirical metallicity-dependent calibrations of effective temperature against colours for dwarfs of luminosity classes IV and V and for giants of luminosity classes II and III, based on a collection from the literature of about two hundred nearby stars with direct effective temperature measurements of better than 2.5 per cent. The calibrations are valid for an effective temperature range 3,100 - 10,000 K for dwarfs of spectral types M5 to A0 and 3,100 - 5,700 K for giants of spectral types K5 to G5. A total of twenty-one colours for dwarfs and eighteen colours for giants of bands of four photometric systems, i.e. the Johnson ($UBVR_{\rm J}I_{\rm J}JHK$), the Cousins ($R_{\rm C}I_{\rm C}$), the Sloan Digital Sky Survey (SDSS, $gr$) and the Two Micron All Sky Survey (2MASS, $JHK_{\rm s}$), have been calibrated. Restricted by the metallicity range of the current sample, the calibrations are mainly applicable for disk stars ([Fe/H]$\,\gtrsim\,-1.0$). The normalized percentage residuals of the calibrations are typically 2.0 and 1.5 per cent for dwarfs and giants, respectively. Some systematic discrepancies at various levels are found between the current scales and those available in the literature (e.g. those based on the infrared flux method IRFM or spectroscopy). Based on the current calibrations, we have re-determined the colours of the Sun. We have also investigated the systematic errors in effective temperatures yielded by the current on-going large scale low- to intermediate-resolution stellar spectroscopic surveys. We show that the calibration of colour ($g-K_{\rm s}$) presented in the current work provides an invaluable tool for the estimation of stellar effective temperature for those on-going or upcoming surveys.Comment: 28 pages, 19 figures, 8 tables, accepted for publication in MNRA