Miracle-dz/UniFAR-FTUs huggingface dataset:
High field density-functional-theory based Monte Carlo: 4H-SiC impact ionization and velocity saturation

We present 4H-SiC electron and hole Monte Carlo transport calculations that are obtained using the density functional theory (DFT) calculated conduction and valence band density-of-states (DOS) curves. The transport properties include room temperature average electron-hole velocities, energies, and impact ionization rates as functions of applied fields, as well as mobilities. This is achieved employing detailed DFT-DOS curves, which obviate the need to consider electron-hole energy dispersion details that are generally calculated using the empirical pseudopotential method. Thus the proposed method facilitates fast computations of carrier-phonon and semiclassical field-carrier interactions, and the relevant field-dependent averages. Specifically, our calculated average electron velocities peak at 1.6×107 cm/s for 0.2 MV/cm field bias, and the simulated electron ionization coefficients match well with experimental data in the 3–5 MV/cm range. To obtain similar averages for 4H-SiC’s holes, we resolve the hol.
Wave-CISK in the Tropics

Abstract CISK (Conditional Instability of the Second Kind) is examined for internal waves where low-level convergence is due to the inviscid wave fields rather than to Ekman pumping. It is found that CISK-induced waves must give rise to mean cumulus activity (since there are no negative clouds), and it is suggested that this mean activity plays an important role in the finite-amplitude equilibration of the system. The most unstable CISK waves will be associated with very short vertical wavelengths [O(3 km)] in order to maximize (in some crude sense) subcloud convergence. Thus, the vertical scale is largely determined by the height of cloud base. The vertical scale, in turn, determines the dispersive relations between horizontal and temporal scales. It is found that there exists a wave-CISK mode which is independent of longitude, and hence independent of the mean zonal flow. Because of this independence, the period of this oscillation should form a prominent line in tropical spectra. This period turns out .
Temperature Dependence of Band Gap Change in InN and AlN

The optical band gap of InN and AlN single crystal films was measured through absorption spectra in the temperature range of 4.2 to 300 K. The samples were grown on (0001)α-Al2O3 substrates by metalorganic vapor phase epitaxy. The Varshni equation and the Bose-Einstein expression have been compared with the experimental results. The nitride III-V compound semiconductors have smaller temperature dependence of band gap change. In III-V compound semiconductors, the variation of the band gap change increases in the order of N, P and As.
Interrelations between Various Direct Simulation Methods for Solving the Boltzmann Equation

Interrelations between the five direct simulation methods of Nanbu, Belotserkovskiy and Yanitskiy, Koura, Deshpande, and Bird are examined by means of probability consideration. These methods are divided into two groups; one based on the Boltzmann equation and the other based on the Kac master equation. Nanbu's method belongs to the first group while all other methods belong to the second group. The methods of Koura, Deshpande, and Bird are modifications of that of Belotserkovskiy and Yanitskiy. Although the probability law for simulating molecular collisions is different from method to method, the mean rate of collision is essentially the same for all methods. This implies that there is no significant difference at least among macroscopic properties resulting from all methods.
Exploring an Approach for Grouping through Predicting Group Performance from Analysis of Learner Characteristics

In this paper, we present a mathematical model for forming heterogeneous groups of learners under different teaching strategies. This model requires a formulation which can effectively predict the learning performance of cooperative learning groups. Therefore, we explore the correlations between learning performance and various learner characteristics including learning motivation, learning strategy use, learning styles and gender based on real-world data. By means of analyzing learner data of 157 students in a cooperative learning course, learner attributes irrelevant to cooperative learning performance are excluded from the formulation; this sharply decreases the workload of group formation calculation. In future work, a tool will be implemented based on this adjustable mathematical model and this tool will be used in daily teaching to evaluate its effectiveness.
Asymptotic approximations for modified Bessel functions

The behavior of a q ν(x) =I ν(x)/I ν a (x), where I ν is a modified Bessel function with integral or half‐integral index ν and I ν a the leading term of its asymptotic series, is investigated for x≫1. It is shown that q ν(x) may be approximated by e ν(x) =exp(−ν2/2x), the difference r ν(x) =q ν(x)−e ν(x) being of order x −1/4. Bounds for r ν(x) depending only on x are derived for each of the two classes of ν’s and an application of these results in scattering theory is indicated.
The evolution of rotating stars. I - Method and exploratory calculations for a 7-solar-mass star

A method is developed which allows us to study the evolution of rotating stars well beyond the main-sequence stage. We consider four different cases of redistribution of angular momentum in an evolving star. Evolutionary sequences for a 7 M/sub sun/ star, rotating according to these different cases, were computed form the zero-age main sequence to the double shell source stage. Each sequence was begun with a (typical) equatorial rotational velocity of 210 km s/sup -1/. On the main sequence, the effects of rotation are of minor importance. However, as the core contracts during later stages, important effects arise in all physically plausible cases. The outer regions of the cores approach critical velocities and develop unstable angular velocity distributions. The effects of these instabilities should significantly alter the subsequent evolution. (AIP)
Quantized tracking control for a multi‐agent system with high‐order leader dynamics

This paper presents a study of a tracking control problem for a multi‐agent system with an active leader and quantized communication constraints. We first design a discrete‐time distributed estimator‐based tracking control for each follower‐agent and analyze the tracking convergence with the help of the Riccati equation and common Lyapunov function when the communication channel is perfect and the interconnection topology is time‐varying. Then a stochastic quantization strategy is applied to model the information communication in the agent coordination and the corresponding solution to the tracking control problem is also given. Finally, a numerical example is given to illustrate the tracking control algorithm.
Altered Variability and Concordance of Dynamic Resting-State fMRI Indices in Patients With Attention Deficit Hyperactivity Disorder

Objective: Attention deficit hyperactivity disorder (ADHD) is a commonly diagnosed neuropsychiatric disorder in children, which is characterized by inattention, hyperactivity and impulsivity. Using resting-state functional magnetic resonance imaging (R-fMRI), the alterations of static and dynamic characteristics of intrinsic brain activity have been identified in patients with ADHD. Yet, it remains unclear whether the concordance among indices of dynamic R-fMRI is altered in ADHD. Methods: R-fMRI scans obtained from 50 patients with ADHD and 28 healthy controls (HC) were used for the current study. We calculated the regional dynamic changes in brain activity indices using the sliding-window method and compared the differences in variability of these indices between ADHD patients and HCs. Further, the concordance among these dynamic indices was calculated and compared. Finally, the relationship between variability/concordance of these indices and ADHD-relevant clinical test scores was investigated. Results: Patients with ADHD showed decreased variability of dynamic amplitude of low-frequency fluctuation (dALFF) in the left middle frontal gyrus and increased one in right middle occipital gyrus, as compared with the HCs. Besides, ADHD patients showed decreased voxel-wise concordance in the left middle frontal gyrus. Further, lower voxel-wise concordance in ADHD’s left middle frontal gyrus was associated with more non-perseverative errors in Wisconsin Card Sorting Test, which reflects worse cognitive control. Conclusion: Our findings suggest that variability and concordance in dynamic brain activity may serve as biomarkers for the diagnosis of ADHD. Further, the decreased voxel-wise concordance is associated with deficit in cognitive control in ADHD patients.
Nationwide assessment of potential output from wind-powered generators

Abstract A method of computing power output from wind-powered generators has been developed and applied to estimate potential power output at various sites across the continental United States. The method assumes a wind-powered generator system which can be characterized by a cut-in speed V0, a rated speed V1 and a cut-out speed V2. The generator output power is assumed to be constant at the rated power Pr between V1 and V2 and to vary parabolically from zero at V0 to Pr at V1. The wind distributions at various sites have been found to vary according to a Weibull distribution between realistic values of V0 and V1. Values of the Weibull distribution parameters at approximately 135 sites across the United States have been evaluated. These results have been projected to a constant height of 30.5 m (100 ft) and 61 m (200 ft) using data determined from observed Weibull parameter height variations at several meteorological tower sites across the country. A contour map is presented for generator capacity factor .
Infrared standard stars

The results of an observational program aimed at setting up a network of faint near-infrared standards of sufficient accuracy are reported. The network covers both northern and southern hemispheres and includes standards red enough to provide at least a limited check on color transformations. The standards are set up at J (1.2 micron), H (1.6 micron), K (2.2 microns), and L (3.5 microns), and their H2O and CO molecular absorption indices are determined. The problem of color transformations between observatories is discussed briefly. All magnitudes presented are transformed to the natural system defined by the CIT observations.
Solved and Unsolved Problems in Number Theory

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Flow topology in compressible turbulent boundary layer

Abstract The flow topologies of compressible turbulent boundary layers at Mach 2 are investigated by means of direct numerical simulation (DNS) of the compressible Navier–Stokes equations, and statistical analysis of the invariants of the velocity gradient tensor. We identify a preference for an unstable focus/compressing topology in the inner layer and an unstable node/saddle/saddle (UN/S/S) topology in the outer layer. The dissipation and dissipation production originate mainly from this UN/S/S topology. The enstrophy depends mainly on an unstable focus/stretching (UFS) topology, and the enstrophy production relies on a UN/S/S topology in the inner layer and on a UFS topology in the outer layer. The compressibility effect on the statistical properties of the topologies is investigated in terms of the ‘incompressible’, compressed and expanding regions. It is found that the locally compressed region tends to be more stable and the locally expanding region tends to be more dissipative. The compressibility is mainly related to unstable focus/compressing and stable focus/stretching topologies. Moreover, the features of the average dissipation, enstrophy, dissipation production and enstrophy production of the various topologies are clarified in the locally compressed and expanding regions.
The pair annihilation process in relativistic plasmas

Exact analytical expressions are derived in the Born approximation for the pair annihilation rate and spectral emissivity from isotropic, monoenergetic electrons and positrons of arbitrary energies. The annihilation rate and spectral emissivity for arbitrary particle distribution functions are given as double integrals. The spectral emissivity is determined exactly for the case where the positrons (electrons) have a Maxwell-Boltzmann distribution, while the electrons (positrons) are at rest. A discussion is given for the more complicated case in which both the electrons and the positrons have Maxwell-Boltzmann distributions at the same temperature. Asymptotic expressions are derived for the annihilation rate, the cooling rate, and the spectral emissivity at relativistic temperatures. Useful, approximate expressions, valid at temperatures larger than 10/sup 8/ K, are given for the annihilation rate and the cooling rate.
On probabilistic safety assessment in the case of zero failures

Probabilistic safety assessment often depends on the quantification of the frequencies of failures, on the basis of zero failures in the available data. A variety of estimates for such frequencies have been suggested in the literature, mainly within the classical and Bayesian statistical frameworks, and with emphasis on the constant failure rate of an exponential distribution. In this paper, this problem is considered from the perspective of non-parametric predictive inference (NPI), where the main difference from the established approaches is the use of lower and upper probabilities, leading to lower and upper estimates for the constant exponential failure rate instead of point estimates. On the basis of zero failures observed, the lower estimate for the failure rate is zero; so interest is mostly in the upper failure rate. Such lower and upper estimates reflect the indeterminacy due to the data scarcity. The NPI-based upper estimate for the failure rate depends not only on the length of the failure-free period represented as data but also on the required or chosen length of the future period considered in the risk assessment, in a possibly surprising manner. The use of failure rate estimates in probabilistic safety assessment is discussed, and a more straightforward predictive approach is suggested.
A Residual Variance Based Discriminant Function and its Algorithm

Time series analysis is advantageous since it offers insight into the underlying dynamics and forecasts system behavior. The construction of the discriminant function is of vital importance in the time series analysis based fault diagnosis. Aiming at the problem that some of the time series analysis based fault diagnosis methods exist the weakness of higher time complexity, weaker discriminant ability and insufficient online diagnosis power, this paper proposes an approach which makes full use of the characteristics of the model and observation data to construct the discriminant function, and presents an efficient algorithm which can effectively recognize the system state by the proposed discriminant function. As compared to the related work, it has the characteristics of lower time complexity, shorter computation time and stronger distinguished ability, without the requirement of same orders of the reference model and the detected model. The fault diagnosis steps based on the proposed discriminant function and its algorithm are also suggested.
COSP: Satellite simulation software for model assessment

Errors in the simulation of clouds in general circulation models (GCMs) remain a long-standing issue in climate projections, as discussed in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report. This highlights the need for developing new analysis techniques to improve our knowledge of the physical processes at the root of these errors. The Cloud Feedback Model Intercomparison Project (CFMIP) pursues this objective, and under that framework the CFMIP Observation Simulator Package (COSP) has been developed. COSP is a flexible software tool that enables the simulation of several satellite-borne active and passive sensor observations from model variables. The flexibility of COSP and a common interface for all sensors facilitates its use in any type of numerical model, from high-resolution cloud-resolving models to the coarser-resolution GCMs assessed by the IPCC, and the scales in between used in weather forecast and regional models. The diversity of model parameterization techniques makes the comparison between model and observations difficult, as some parameterized variables (e.g., cloud fraction) do not have the same meaning in all models. The approach followed in COSP permits models to be evaluated against observations and compared against each other in a more consistent manner. This permits a more detailed diagnosis of the physical processes that govern the behavior of clouds and precipitation in numerical models. The World Climate Research Programme (WCRP) Working Group on Coupled Modelling has recommended the use of COSP in a subset of climate experiments that will be assessed by the next IPCC report. In this article we describe COSP, present some results from its application to numerical models, and discuss future work that will expand its capabilities.
Mass loss in O-type stars - Parameters which affect it

Newly determined mass loss rates are presented for sixteen O-type stars in three open clusters. Combining the data with that already in the literature, no evidence is found that the rates are different in clusters with differing galactocentric distances and compositions, at least near the sun. There is still appreciable dispersion in the relationship between the mass loss rate and the stellar luminosity. It may be that the mass loss depends additionally on the stellar mass and/or radius, but these data cannot unequivocally indicate which physical dependence is correct. Evidence is found that a stellar wind increases as a massive star evolves from the zero-age main sequence.
Dual-polarized patch antenna with high isolation for DTV applications

Abstract In this paper, the design, simulation results, and measurements of a coaxial-fed dual-polarized patch antenna with high port isolation are presented. The proposed antenna consists of two cross center-fed patch dipole antennas against a reflector as ground plane, while the patch antenna contains two pairs of X-shaped slots along the diagonals and two pairs of T-shaped slots along the centerlines. The proposed antenna achieves a -10 dB with bandwidth of 470–730 MHz and demonstrates the dual polarization in both directions. Stable radiation patterns at slanted polarization have been obtained within the band. Measurements show two linear polarizations with an isolation of more than 33 dB over the operating frequency band. The proposed antenna can be used for Digital television applications (DTV).
Consensus problems for high-dimensional multi-agent systems

As a new area of research, consensus problems for multi-agent systems have been studied extensively in the literature. It is usually assumed that all agents share a common one-dimensional state space. The authors of this study concentrate on the consensus problems of multi-agent systems in the framework of high-dimensional state space. As a basis for the analysis, a general model is first introduced by presenting two typical examples along with some necessary and sufficient conditions for the system to solve a consensus problem. Then the structures of consensus functions are investigated and some algebraic characterisations are given. Finally, a class of switched multi-agent systems are discussed and some sufficient conditions for the possession of the consensus property are provided. Several examples to illustrate the effectiveness of theoretical results are given.
Alignment of vorticity and scalar gradient with strain rate in simulated Navier-Stokes turbulence

The alignment between vorticity and eigenvectors of the strain‐rate tensor in numerical solutions of Navier–Stokes turbulence is studied. Solutions for isotropic flow and homogeneous shear flow from pseudospectral calculations using 1283 grid points have been examined. The Taylor Reynolds number is 83 or greater. In both flows there is an increased probability for the vorticity to point in the intermediate strain direction and at three‐fourths of the sample points this strain is positive (extensive). This propensity for vorticity alignment with a positive intermediate strain is a consequence of angular momentum conservation, as shown by a restricted Euler model of the coupling between strain and vorticity. Probability distributions for intermediate strain, conditioned on total strain, change from a symmetric triangular form at small strain to an asymmetric one for large strain. The most probable value of the asymmetric distribution gives strains in the ratios of 3:1: −4. The evolution of the distribution .
Multivariate Dispersion Models Generated From Gaussian Copula

In this paper a class of multivariate dispersion models generated from the multivariate Gaussian copula is presented. Being a multivariate extension of Jorgensen's (1987a) dispersion models, this class of multivariate models is parametrized by marginal position, dispersion and dependence parameters, producing a large variety of multivariate discrete and continuous models including the multivariate normal as a special case. Properties of the multivariate distributions are investigated, some of which are similar to those of the multivariate normal distribution, which makes these models potentially useful for the analysis of correlated non-normal data in a way analogous to that of multivariate normal data. As an example, we illustrate an application of the models to the regression analysis of longitudinal data, and establish an asymptotic relationship between the likelihood equation and the generalized estimating equation of Liang & Zeger (1986).
Data-Driven Model Choice in Multivariate Nonparametric Regression

The problem of choosing between different regression models, is investigated. A completely automatic model selection procedure is defined and asymptotic optimality results are shown. These results are stated in a general framework including as well nested as unnested situations, including as well i.i. d. as dependent samples, and without specifying any class of non-parametric smoothers. Because of the well-known curse of dimensionality, model selection is of particular interest in multivariate regression settings, and it will be discussed how the previous general model choice approach can be used in several different highdimensional situations.
Influence of Electron Velocity Overshoot Effect on High-Frequency Characteristics of Quantum Well Infrared Photodetectors

We have studied the transient response of AlxGa1-xAs/GaAs quantum well infrared photodetectors (QWIPs) and their high-frequency performance using a self-consistent ensemble Monte Carlo particle method. It has been shown that the photocurrent caused by the electron intersubband transitions under the influence of an ultra-short pulse of infrared radiation reveals a sharp peak followed by relatively slow decay. This is associated with the electron velocity overshoot and the electron transit time and capture effects. The velocity overshoot results in the existence of an additional plateau-like region in the QWIP frequency-dependent responsivity which can correspond to the terahertz range.