Miracle-dz/UniFAR-FTUs huggingface dataset:
Algebraic Closure of Scalar Dissipation Rate for Large Eddy Simulations of Turbulent Premixed Combustion

An a-priori analysis of the filtered reaction rate closure based on Favre-filtered scalar dissipation rate (SDR) for large eddy simulations (LES) of turbulent premixed combustion has been conducted using a direct numerical simulation (DNS) database of freely propagating statistically planar flames for a range of different values of heat release parameter τ, global Lewis number Le, and turbulent Reynolds number Ret. It has been found that an existing SDR based reaction rate closure for Reynolds averaged Navier–Stokes (RANS) simulations is also valid for LES, when the filter width is larger than the flame thickness. This RANS-based reaction rate closure has been extended here for LES, and a satisfactory performance of this LES closure is observed for the values of filter widths, τ, Le, and Ret investigated here. A-priori DNS assessment of the SDR closures based on passive scalar mixing model and a power-law has been conducted. Moreover, an existing algebraic model of Favre-averaged SDR for RANS simulations has been extended here for LES. The performances of the algebraic closures of have been assessed with respect to Favre-filtered SDR extracted from the DNS data. It has been found that the newly proposed model for , which was extended here for LES from an existing RANS-based closure, predicts both local and volume-averaged behaviors of SDR satisfactorily for a range of for flames with different values of τ, Le, and Ret. The sensitivity of sub-grid turbulent velocity fluctuation modeling on the newly developed algebraic SDR closure has also been analyzed and it has been observed that the modeling does not significantly affect the performance of the algebraic SDR model proposed in this study.
A numerical model for induction heating processes coupling electromagnetism and thermomechanics

This paper presents a mathematical and numerical model developed for coupling the various physical phenomena (electromagnetic, thermal and mechanical) taking place in axisymmetrical induction heating processes. All three electromagnetic, thermal and mechanical models are time dependent and take full account of the electromagnetic and thermal non‐linear effect especially with magnetic materials. The electromagnetic problem is discretized and solved in the workpiece, air and inductors. The heat transfer equation and the mechanical equilibrium equations are solved in the workpiece only, both using a finite element method. The mechanical model can take into account thermoelastic–plastic behaviour for the part. The model has been successfully applied to several cases of induction heating. Comparisons between numerical and experimental results show an excellent agreement. Copyright © 2003 John Wiley & Sons, Ltd.
High-power high-efficiency 0.98-/spl mu/m wavelength InGaAs-(In)GaAs(P)-InGaP broadened waveguide lasers grown by gas-source molecular beam epitaxy

We describe the design and experimental results for high-power, high-efficiency, low threshold current, 0.98-/spl mu/m wavelength, broadened waveguide (BW) aluminum-free InGaAs-(In)GaAs(P)-InGaP lasers. The decrease in the internal losses with an increase in the width of the waveguide layer for a separate-confinement heterostructure multiple-quantum-well (SCW-MQW) structure is attributed to lower free-carrier absorption due to the reduced overlap of the optical mode with the highly doped cladding regions. The BW lasers grown with both InGaAsP and GaAs waveguides show lower internal losses and similar threshold currents than those designed for an optimum optical confinement factor within the QW region. We report a record-low internal loss of 1.8/spl plusmn/0.2 cm/sup -2/ for (In)GaAs(P)-InGaP lasers grown by gas-source molecular beam epitaxy (GSMBE). The temperature dependence of internal loss suggests that optical loss from free-carrier absorption in the waveguide dominates at T>40/spl deg/C, while near room temperature, the residual loss is attributed to scattering and free-carrier absorption in the QW's. The relative insensitivity of internal loss near room temperature has enabled the use of a simplified InGaAs-GaAs-InGaP BW structure to achieve very high CW and quasi-CW (QCW) power operation. We report the highest CW output power of 6.8 W for a GaAs-InGaP laser, and the highest quasi-continuous output power of 13.3 W measured for a single 100-/spl mu/m-wide aperture, 0.8-0.98-/spl mu/m wavelength Al-free laser diode grown by GSMBE.
Characterization of non‐Gaussian rough surface scattering

Abstract In this paper, we examine the scattering properties of rough differently correlated surfaces using the IEM model. The effective correlation length of such a surface is pointed out and its effect on the backscattering behavior is discussed. It may be found from the cases considered here that the non‐Gaussian effects are very significant even with the same correlation length and height variance. This can be seen from the surface spectra where the roughness scales are distributed. Among the non‐Gaussian correlated surfaces, the exponential correlated has more small scale roughness at the high frequency components.
Single-Particle Excitations in Magnetic Insulators

In this paper, the density of states and the mobility of an extra electron or hole are calculated in the atomic limit of the Hubbard model. Both the half-filled single-band and multiple-band situations are discussed. The problem is formulated in terms of the number of paths which return to the origin leaving the spin configuration unchanged. The density of states then depends on spin configuration and we have considered the random (R) (high-temperature) and antiferromagnetic (AF) arrangements. Examination of the first five nonzero moments for the simple cubic lattice indicates that the bands are narrowed by a factor of 0.745 (AF) and 0.805 (R). However, the exact bands have tails extending out to the full free-particle width for both spin arrangements. An approximate one-particle Green's function is obtained by summing all graphs with no closed loops. Such paths give a density of states that is independent of spin arrangement and is relatively flat with a sharp square-root edge at $2{(z\ensuremath{-}1)}^{\frac{1}{2}}t$. Here $z$ is the coordination number and $t$ is the nearest-neighbor hopping integral. Within this approximation, we have calculated the mobility of an extra hole and have found typical values to be \ensuremath{\sim}1 ${\mathrm{cm}}^{2}$/V sec so that the mobility is rather small, even though the density of states has a width of order \ensuremath{\sim}1 eV. Intra-atomic exchange is shown to give a further narrowing of the band [a factor of ${(2)}^{\ensuremath{-}1/2}$ in the two-band large-intra-atomic-exchange example]. The effect of finite $\frac{t}{U}$ is considered, where $U$ is the intra-atomic Coulomb interaction, and is shown to have a strong effect on the band tail but relatively weak effects on the bulk of the band. Finally, we make a few remarks comparing our results with the observed mobilities in NiO and the relevance of intra-atomic exchange to the behavior of the dioxide and sesquioxide series.
Experimental verification on the origin of plateau-like current-voltage characteristics of resonant tunneling diodes

Current-voltage (I–V) characteristics of GaAs-based resonant tunneling diodes have been investigated in the presence of a perpendicular magnetic field. Electron resonant tunneling is strongly suppressed by the applied magnetic field, leading to peak current decreasing with increasing magnetic field. The observed plateau-like structures appear in negative differential resistance region on the I–V curves and are magnetic-field dependent. The plateau-like structures are due to the coupling between the energy levels in the emitter well and in the main quantum well.
Kinematics of the Neutral Hydrogen toward the Core of NGC 3894

We present results of high-resolution VLBA observations at 1.4 GHz of the nuclear region of the nearby elliptical galaxy NGC 3894. An angular resolution of 9 mas (1.4 h-1 pc) was obtained, with a velocity resolution of 7 km s-1 and an rms noise of 1.5 mJy beam-1 per channel. The 21 cm atomic hydrogen line is seen in absorption slightly redshifted with respect to the systemic velocity toward the core, jet, and counterjet of this source. There are four components in the gas that are spatially and/or spectrally distinct, two of which appear to be part of a single larger structure, possibly a circumnuclear torus.
Limited-Area Ensemble-Based Data Assimilation

Ensemble-baseddataassimilationis astateestimation technique thatusesshort-termensembleforecaststo estimate flow-dependent background error covariance and is best known by varying forms of ensemble Kalman filters (EnKFs). The EnKF has recently emerged as one of the primary alternatives to the variational data assimilation methods widely used in both global and limited-area numerical weather prediction models. In addition to comparing the EnKF with variational methods, this article reviews recent advances and challenges in the development and applications of the EnKF, including its hybrid with variational methods, in limited-area models that resolve weather systems from convective to meso- and regional scales.
On the motion of solids in a liquid possessing vorticity

1. The following investigations were undertaken at the suggestion of Mr. G. I. Taylor as an extension of some of his own. The equation of motion of any system of solids in a liquid which moves without vorticity were obtained by Lord Kelvin by a method based on that of ignorable co-ordinary dynamics. They are of Lagrange's type, and were afterwards obtained by various writers by an adaptation to hydro-dynamics of Lagrange's original method.
Mistake bounds and logarithmic linear-threshold learning algorithms

We consider a problem of learning from examples. In each of a sequence of trials the learner observes an instance to be classified and must respond with a prediction of its correct classification. Following the prediction the learner is told the correct response. We consider the two category case, and work for the most part with instances composed of a number of Boolean attributes or, more generally, chosen from (0, 1) $\sp{n}$. Initially, we assume that the correct response in each trial is a function of the corresponding instance, this target function being chosen from some target class of $\{0,1\}$-valued functions. We relax this assumption somewhat later. We focus on evaluation of on-line predictive performance, counting the number of mistakes made by the learner during the learning process. For certain target classes we have found algorithms for which we can prove excellent mistake bounds, using no probabilistic assumptions. In the first part of the dissertation we study the properties of such worst-case mistake bounds. In the central part of this dissertation, we present a group of linear-threshold algorithms that are particularly well suited to circumstances in which most of the attributes of the instances are irrelevant to determining the correct predictions. For target classes that can be handled by these algorithms, we show that the worst-case mistake bounds grow only logarithmically with the number of irrelevant attributes. We demonstrate that these algorithms have some measure of robustness in the face of anomalies in the training data caused, for example, by noise. We also consider the implications of on-line, worst-case mistake bounds for learning in a batch setting with probabilistic assumptions, making use of the probabilistic PAC-learning model introduced by Valiant (Va184). We present an analysis that shows that a straightforward transformation applied to mistake bounded algorithms, consisting of adding a hypothesis testing phase, produces algorithms that have asymptotically optimal PAC-learning bounds for certain target classes.
On the turbulence generated by the potential surface waves

[1] The turbulence (the random vortex motions) of the upper ocean is nourished by the energy and momentum of the surface waves (the potential motion). The statistical characteristics of the turbulence (turbulent kinetic energy, dissipation rate, and Reynolds stresses) depend on the state of the ocean surface waves. This paper discusses the possibilities of generating this turbulence using the vortex instability of the potential surface waves. The vortex component of fluctuations of velocity field and possibly the interaction between both the vortex and potential motions cause the vertical transport of the momentum. The Reynolds tensor is a linear function of the correlation tensor of vortex field. The initial small vortex perturbations always exist in the upper ocean because of the molecular viscosity influences, especially near the free surface, and the fluctuations of the seawater density. The horizontal inhomogeneities of the seawater density produce the vortex field even if the initial vorticity was zero and the initial flow was the potential flow. The evolution of the small initial vortex disturbances in the velocity field of potential linear surface waves is reduced to a coupled set of linear ordinary differential equations of the first order with periodic coefficients. The solution of this problem shows that the small initial vortex perturbations of potential linear surface waves always grow. The initial small vortex perturbations interacting with the potential surface wave produce the small-scale turbulence (Novikov's turbulence) that finally causes the viscous dissipation of the potential surface wave. The wave-induced turbulence can be considered as developed turbulence with a well distinguishable range of the turbulent wave numberskwhere turbulence obeys the Kolmogorov's self-similarity law.
Model investigation of the Raman spectra of amorphous silicon

A model for calculating the first-order Raman spectra of amorphous silicon (a-Si) without adjustable parameters is proposed. Calculations on the original 216-atom model of a-Si, generated by the algorithm of Wooten, Winer, and Weaire (WWW) are in very good agreement with experimental spectra and give further indication that the WWW cluster is a realistic model of moderately disordered a-Si. The TA-TO assignment of the low and high frequency bands is supported by direct numerical calculations of the phase quotient and the stretching character of the vibrational modes. The calculated participation ratios and correlation lengths of the vibrational modes indicate that the high-frequency TO-like modes are strongly localized on defects. The relative intensities of the TA-, LA-, and LO-like bands depend on the intermediate-range order, while that of the TO-like band mainly on the short-range order.
Supported Blow-Up and Prescribed Scalar Curvature on Sn

The author expounds the notion of supported blow-up and applies it to study the renowned Nirenberg/Kazdan-Warner problem on $S^n$. When $n \ge 5$ and under some mild conditions, he shows that blow-up at a point with positive definite Hessian has to be a supported isolated blow-up, which, when combined with a uniform volume bound, is a removable singularity. A new asymmetric condition is introduced to exclude single simple blow-up. These enable the author to obtain a general existence theorem for $n \ge 5$ with rather natural condition.
NONLINEAR INERTIAL LOADING. PART I: ACCELERATIONS IN STEEP 2-D WATER WAVES

Abstract This paper reports on a new series of laboratory observations in which both the unsteady and the convective components of the water particle acceleration arising beneath an extreme two-dimensional transient wave were determined. The waveform investigated was produced by focusing frequency components within an irregular wave train, such that a large number of zero up-crossings arise at one point in space and time. For a given underlying set of frequency components, this produces an extreme event that has the maximum wave slope and therefore also the largest horizontal water particle accelerations. Spectral analysis, based upon the water surface elevation measured at the focal location, confirms that there are significant transfers of energy into the high-frequency components. Neither a linear random wave theory nor a steady nonlinear wave theory, both of which are commonly used in design applications, are able to correctly model these frequency components. As a result, such solutions provide a poor description of the large unsteady accelerations arising close to the water surface. Furthermore, since they are also unable to model the spatial evolution of the wave group, inaccurate predictions of the convective accelerations result. In contrast, a fully nonlinear unsteady wave theory, similar to that originally proposed by Fenton & Rienecker (1980), provides a good description of the laboratory data. To assess the importance of the nonlinear accelerations the inertia forces acting on a vertical, surface-piercing, cylinder are calculated and comparisons made with the nonlinear slender body forces identified by Rainey (1989, 1995). These comparisons confirm the importance of the applied wave model and suggest that the dominant contribution to the high-frequency forcing arises due to the nonlinearity of the wave motion. These results have applications in Offshore Engineering where transient structural deflections, occurring at frequencies well above the wave frequency, have been observed in a number of deep-water structures.
Center-focus and isochronous center problems for discontinuous differential equations

The study of the center focus problem and the isochronicity problem for differential equations with a line of discontinuities is usually done by computing the whole return map as the composition of the two maps associated to the two smooth differential equations. This leads to large formulas which usually are treated with algebraic manipulators. In this paper we approach to this problem from a more theoretical point of view. The results that we obtain relate the order of degeneracy of the critical point of the discontinuous differential equations with the order of degeneracy of the two smooth component differential equations. Finally we apply them to some families of examples.
3-D FDTD Analysis of Sound Field Focused by Biconcave Acoustic Lens for Normal Incidence

Recently, the finite difference time domain (FDTD) method has been frequently used for the analysis of underwater sound propagation. There are demonstrated advantages of this FDTD method in terms of obtaining data regarding snapshots of sound pressure distribution and a series of waveforms at any point. In addition, the method facilitates the modeling of factors, such as the sound source and media into the analysis domain. In this study, a three-dimensional FDTD analysis was carried out in order to obtain the sound field focused by a biconcave acoustic lens specialized to measure the normal incidence of the spherical wave. Additionally, the results of the analysis were compared with experimental results obtained in a water tank. When the frequency of the sound source was 500 kHz, the range between the acoustic lens and the sound source was 1.78 m, and the attenuation constant was 0.5–1.0 dB/λ, the experimental results regarding the position of the focal point, the on-axis characteristics and the beam pattern were all found to agree well with the simulation results obtained by FDTD method.
The Properties of Holographic Overlap Gratings

The analysis of a holographic beam expander which can, under perfect lossless conditions, convert a plane input beam into a plane diffracted beam, with a specified diffraction efficiency and beam width expansion ratio, is presented. Using solutions of the coupled-wave differential equations of [2], the effects of average loss, and both constant and spatially dependent dephasing are studied. These solutions are also used to compare the properties of overlap gratings with Kogelnik's [1] results for infinite gratings, and to extend the analysis of [4] to lossy, dephased cases. The maximum possible diffraction efficiency of an absorption overlap grating is shown to depend on its shape and also to lie between the values for Kogelnik's reflection and transmission cases.
The Modified Gamma Size Distribution Applied to Inhomogeneous and Nonspherical Particles: Key Relationships and Conversions

AbstractThe four-parameter modified gamma distribution (MGD) is the most general mathematically convenient model for size distributions of particle types ranging from aerosols and cloud droplets or ice particles to liquid and frozen precipitation. The common three-parameter gamma distribution, the exponential distribution (e.g., Marshall–Palmer), and power-law distribution (e.g., Junge) are all special cases. Depending on the context, the particle “size” used in a given formulation may be the actual geometric diameter, the volume- or area-equivalent spherical diameter, the actual or equivalent radius, the projected or surface area, or the mass.For microphysical and radiative transfer calculations, it is often necessary to convert from one size representation to another, especially when comparing or utilizing distribution parameters obtained from a variety of sources. Furthermore, when the mass scales with Db, with b < 3, as is typical for snow and ice and other particles having a quasi-fractal structure, .
Baroclinic Instability on the Sphere: Solutions with a More Realistic Tropopause

Abstract The authors' previous study of baroclinic instability using a primitive equation model with spherical geometry is extended to include more realistic initial distributions of zonal wind and temperature in the upper troposphere and lower stratosphere. Results show little difference in the low-level structure of normal modes, but generally larger upper-level amplitudes for wavelengths close to or longer than that giving maximum linear growth rate. Near the tropopause these disturbances may extend significantly toward the equator, a result shown to be consistent with the forced barotropic response of tropical regions. Their eddy momentum fluxes exhibit some of the variability noted previously, but transfer tends to be predominantly poleward at upper levels. The upper-level heat flux is stronger relative to the momentum flux than is found in general circulation statistics.
Bayesian estimation of NIG models via Markov chain Monte Carlo methods

The normal inverse Gaussian (NIG) distribution is a promising alternative for modelling financial data since it is a continuous distribution that allows for skewness and fat tails. There is an increasing number of applications of the NIG distribution to financial problems. Due to the complicated nature of its density, estimation procedures are not simple. In this paper we propose Bayesian estimation for the parameters of the NIG distribution via an MCMC scheme based on the Gibbs sampler. Our approach makes use of the data augmentation provided by the mixture representation of the distribution. We also extend the model to allow for modelling heteroscedastic regression situations. Examples with financial and simulated data are provided. Copyright © 2004 John Wiley & Sons, Ltd.