Miracle-dz/UniFAR-FTUs huggingface dataset:
Inverse cascades of angular momentum

Most theoretical and computational studies of turbulence in Navier—Stokes fluids and/or guiding-centre plasmas have been carried out in the presence of spatially periodic boundary conditions. In view of the frequently reproduced result that two-dimensional and/or MHD decaying turbulence leads to structures comparable in length scale to a box dimension, it is natural to ask if periodic boundary conditions are an adequate representation of any physical situation. Here, we study, computationally, the decay of two-dimensional turbulence in a Navier—Stokes fluid or guiding-centre plasma in the presence of circular no-slip rigid walls. The method is wholly spectral, and relies on a Galerkin approximation by a set of functions that obey two boundary conditions at the wall radius (analogues of the Chandrasekhar— Reid functions). It is possible to explore Reynolds numbers up to the order of 1250, based on an RMS velocity and a box radius. It is found that decaying turbulence is altered significantly by the no-slip boundaries. First, strong boundary layers serve as sources of vorticity and enstrophy and enhance the early-time energy decay rate, for a given Reynolds number, well above the periodic boundary condition values. More importantly, angular momentum turns out to be an even more slowly decaying ideal invariant than energy, and to a considerable extent governs the dynamics of the decay. Angular momentum must be taken into account, for example, in order to achieve quantitative agreeement with the predicition of maximum entropy, or ‘most probable’, states. These are predicitions of conditions that are established after several eddy turnover times but before the energy has decayed away. Angular momentum will cascade to lower azimuthal mode numbers, even if absent there initially, and the angular momentum modal spectrum is eventually dominated by the lowest mode available. When no initial angular momentum is present, no behaviour that suggests the likelihood of inverse cascades is observed.
Linear Recursive Equations, Covariance Selection, and Path Analysis

Abstract By defining a reducible zero pattern and by using the concept of multiplicative models, we relate linear recursive equations that have been introduced by econometrician Herman Wold (1954) and path analysis as it was proposed by geneticist Sewall Wright (1923) to the statistical theory of covariance selection formulated by Arthur Dempster (1972). We show that a reducible zero pattern is the condition under which parameters as well as least squares estimates in recursive equations are one-to-one transformations of parameters and of maximum likelihood estimates, respectively, in a decomposable covariance selection model. As a consequence, (a) we can give a closed-form expression for the maximum likelihood estimate of a decomposable covariance matrix, (b) we can derive Wright's rule for computing implied correlations in path analysis, and (c) we can describe a search procedure for fitting recursive equations.
Kelvin–Helmholtz instability under horizontal rotation and magnetic fields

The author's previous work on the Rayleigh–Taylor instability is extended to the Kelvin–Helmholtz instability, and the maximum growth rate of a perturbation and an estimate of its upper bound is obtained for an infinite fluid layer under horizontal rotation where the density, horizontal velocity (shear) and magnetic field are continuously stratified in the direction of gravity. Conclusions are drawn about the possibility of stability for some directions of propagation of the perturbation, even in the case of unstably stratified density. It is also shown that the new terms that appear owing to the interaction of the horizontal shear flow, horizontal rotation and stratified magnetic field increase the range of values that contribute to the estimate of the maximum growth rate compared with previous work. Furthermore, a generalization of the sufficient condition for stability under horizontal rotation alone obtained by Johnson is calculated in the presence of density stratification. A new method is also given to obtain a sufficient condition for stability when a magnetic field is present in addition to rotation and density stratification.
Proton firehose instability in bi-Kappa distributed plasmas

Context. Protons or heavier ions with anisotropic velocity distributions and non-thermal departure from Maxwellian, are frequently reported in the magnetosphere and at different altitudes in the solar wind. These observations are sustained by an extended number of mechanisms of acceleration in any direction with respect to the interplanetary magnetic field. However, the observed anisotropy is not large and most probably constrained by the kinetic instabilities. Aims. An excess of parallel kinetic energy, T� /T⊥ > 1( whereand ⊥ denote directions relative to the background magnetic field) drives a proton firehose mode to grow, limiting any further increase in the anisotropy according to the observations. The effects of suprathermal populations on the principal characteristics of the proton firehose instability are investigated. Methods. For low-collisional plasmas, the dispersion approach is based on the fundamental kinetic Vlasov-Maxwell equations. The anisotropy of plasma distributions including suprathermal populations is modeled by bi-Kappa functions, and the new dispersion relations are derived in terms of the modified plasma dispersion function (for Kappa distributions), and analytical approximations of this function. Results. Growth rates of the proton firehose solutions and threshold conditions are provided in analytical forms for different plasma regimes. The proton firehose instability needs a larger anisotropy and a larger parameter β� to occur in a Kappa-distributed plasma. A precise numerical evaluation shows that the growth rates are, in general, lower and the wave frequency is only slightly affected, but the influence of suprathermal populations is essentially dependent on both the proton and electron anisotropies. Departures from the standard dispersion of a Maxwellian plasma can eventually be used to evaluate the presence of suprathermal populations in solar flares and the magnetosphere.
Asset Price Dynamics, Volatility, and Prediction

Asset Price Dynamics Volatility And Prediction Ebook. Asset Price Dynamics Volatility And Prediction Stephen. Asset Price Dynamics Volatility And Prediction. Asset Price Dynamics Volatility And Prediction By. Asset Price Dynamics Volatility And Prediction Kindle. Stephen J Taylor Asset Price Dynamics Volatility And. 0691134790 Asset Price Dynamics Volatility And. Asset Price Dynamics Volatility And Prediction. Volatility And Prediction Wolleplanet De. Leggere Asset Price Dynamics Volatility And Prediction. Asset Price Dynamics Volatility And Prediction Edition. Asset Price Dynamics Volatility And Prediction Ebook By. Asset Price Dynamics Volatility And Prediction. Asset Price Dynamics Volatility And Prediction Ebook. Asset Price Dynamics Volatility And Prediction Mehrpc De. Asset Price Dynamics Volatility And Prediction Pdf Download. Asset Price Dynamics Volatility And Prediction. Introduction To Asset Price Dynamics Volatility And. Asset Price Dynamics Volatility And Prediction Stephen. Pdf Free Download Asset Price Dynamics Volatility And
Influence of Hopper Eccentricity on Discharge of Cylindrical Mass Flow Silos with Rigid Walls

The influence of hopper eccentricity on silo discharge has always concerned researchers. Eccentric discharge brings about asymmetries in the distribution of normal pressures, the values of which are not known with precision. This study presents a three-dimensional model of the dynamic discharge of a silo with an eccentric hopper, considering the Drucker-Prager plasticity model for the behavior of stored material. The results obtained for different hopper eccentricities reveal that pressures decrease in the hopper along the generatrix of the silo above the outlet, as compared to the opposite side. An increase in normal pressures occurs at this generatrix, as compared to the diametrically opposite generatrix, in the lower part of the cylindrical wall above the silo-hopper transition.
Effect of wind-generated bubbles on fixed range acoustic attenuation in shallow water at 1–4kHz

Long-range acoustic propagation in isothermal conditions is considered, involving multiple reflections from the sea surface. If the sea is calm there is almost perfect reflection and hence little loss of acoustic energy or coherence. The effect of wind is to increase propagation loss due to rough surface scattering and the interaction with near-surface bubble clouds. Previously published measurements of wind-related attenuation in shallow water, at a fixed range of 23km, are converted to surface reflection loss by dividing the total attenuation by the expected number of surface interactions. Theoretical predictions of coherent reflection loss are compared with these measurements in the frequency range 0.9–4.0kHz and wind speeds up to 13m∕s. Apart from an unexplained seasonal dependence, it is shown that the magnitude of the predicted rough surface scattering loss is sufficient to explain the measurements if the effect of bubbles is included, and not otherwise. The bubbles are found to play an important ca.
On the Unicity Conjecture for Markoff Numbers

Abstract In 1913 Frobenius conjectured that for any positive integer m, there exists at most one pair of integers (x, y) with 0 ≤ x ≤ y ≤ m such that (x, y, m) is a solution to the Markoff equation: x 2 + y 2 + m 2 = 3xym. We show this is true if either m, 3m — 2 or 3m + 2 is prime, twice a prime or four times a prime.
On the origin of solar wind MHD turbulence: Helios data revisited

We study the fluctuations of density, magnetic and velocity fields in the frequency range from (1 day)−1 ≈ 1.2×10−5 Hz to (2.8 min)−1≈ 6×10−3 Hz, as measured by the primary Helios mission (118 days), at heliocentric distances ranging from 0.3 to 1 AU. We address the question of the existence of nonlinear cascades in the observed turbulence, possibly separate for the two “inward” and “outward” components, corresponding to opposite directions of propagation along the large-scale magnetic field. We consider energies per unit mass, not per unit volume, in order to work with variables which are not very sensitive to the heliocentric distance variations. We find that while the whole spectrum of total (kinetic plus magnetic) turbulent energy undergoes very large daily variations both in its amplitude and spectral shape the instantaneous spectrum follows a power law in the frequency range 10−4 to 6×10−3 Hz. We show that both the amplitude and the spectral index m depend on the proton temperature, in a monotonic way, so that a large temperature (thermal speed about 60 km/s) leads to a low level of turbulence with a steep, Kolmogorov-like spectrum (m ≈ −1.8), while a low temperature (thermal speed about 16 km/s) leads to a flatter spectrum (m ≈ −1.2) with a high level of turbulence. This relation is independent from heliocentric distance, at least between 0.3 and 1 AU. Decomposing the turbulent energy into two components, “outward” and “inward,” we find that the spectrum of the outward component also follows very closely the daily proton temperature variations, while the inward component's spectrum is less sensitive to the temperature but also varies with the relative level of rms proton density fluctuations. As a consequence, Alfvenic periods (in which energy is dominated by the outgoing component) occur mainly when density fluctuations are low and temperature is high, which does not contradict the classical view that they are found in the “trailing edges of high-speed streams” (Belcher and Davis, 1971). The existence of inertial ranges controlled by the level of density fluctuations is not completely new (see the numerical simulations of purely hydrodynamic turbulence by Pouquet and Passot (1987)), but the strong dependence of both turbulent energy level and spectral slope on temperature is a new, unexpected property of solar wind turbulence which remains to be explained.
Progress in high-energy-class diode laser pump sources

A new generation of diode-pumped high-energy-class solid-state laser facilities is in development that generate multijoule pulse energies at around 10 Hz. Currently deployed quasi-continuous-wave (QCW) diode lasers deliver average inpulse pump powers of around 300 W per bar. Increased power-per-bar helps to reduce the system size, complexity and cost per Joule and the increased pump brilliance also enables more efficient operation of the solid state laser itself. It has been shown in recent studies, that optimized QCW diode laser bars centered at 940…980 nm can operate with an average in-pulse power of > 1000 W per bar, triple that of commercial sources. When operated at pulsed condition of 1 ms, 10 Hz, this corresponds to > 1 J/bar. We review here the status of these high-energy-class pump sources, showing how the highest powers are enabled by using long resonators (4…6 mm) for improved cooling and robustly passivated output facets for high reliability. Results are presented for prototype passively-cooled single bar assemblies and monolithic stacked QCW arrays. We confirm that 1 J/bar is sustained for fast-axis collimated stacks with a bar pitch of 1.7 mm, with narrow lateral far field angle (< 12° with 95% power) and spectral width (< 12 nm with 95% power). Such stacks are anticipated to enable Joule/bar pump densities to be used near-term in commercial high power diode laser systems. Finally, we briefly summarize the latest status of research into bars with higher efficiencies, including studies into operation at sub-zero temperatures (-70°C), which also enables higher powers and narrower far field and spectra.
A new positivity‐preserving nonstandard finite difference scheme for the DWE

An improved positivity‐preserving nonstandard finite difference scheme for the linear damped wave equation is presented. Unlike an earlier such scheme developed by the authors, the new scheme involves three time levels and is therefore able to include the effects of the equation's relaxation coefficient. © 2005 Wiley Periodicals, Inc. Numer Methods Partial Differential, 2005
Confinement and bursty transport in a flux-driven convection model with sheared flows

Transport and confinement within the resistive-g paradigm are investigated by means of two-dimensional numerical simulations. The system is driven by a constant incoming heat flux at the inner radial boundary. Different confinement and transport states are identified, involving self-sustained sheared poloidal flows. At the onset of turbulent convection the probability distribution functions of pressure and radial velocity fluctuations measured in the centre of the plasma layer have a nearly Gaussian form. Further increasing the heat flux drive these distributions become increasingly non-Gaussian, developing exponential tails. This large-scale intermittency is ascribed to the presence of bursting in the domain averaged convective transport and the fluctuation energy integrals. The quasi-periodic bursts are separated by shear-dominated quiescent periods in which the mean flow energy decreases and the confined heat increases on diffusive timescales. The time-averaged thermal energy confined within the plasma layer shows a power law dependence and significant increase with the injected power over the range of turbulent convection investigated.
Decoder selection based on cross-entropies

The authors generalize the maximum likelihood and related optimization criteria for training and decoding with a speech recognizer. The generalizations are constructed by considering weighted linear combinations of the logarithms of the likelihoods of words, of acoustics, and of (word, acoustic) pairs. The utility of various patterns of weights are examined. <<ETX>>
Self‐Similar Strong Shocks with Radiation in a Decreasing Exponential Atmosphere

The self‐similar one‐dimensional flow behind a plane shock propagating upward into an exponentially decreasing atmosphere is considered. The flow is taken to be isothermal in view of the large radiation mean free paths associated with high altitudes and the intense radiation heat transfer accompanying the high temperatures characteristic of an accelerating shock wave. The equations of motion are formulated in Lagrangian coordinates and are integrated exactly for all values of the shock density ratio. Solutions are presented for the cases where the boundary conditions at the shock correspond to a Hugoniot shock and to a Chapman‐Jouguet shock. A significant result of the analysis is that in both of these cases the shock propagates much faster than for the case of adiabatic flow.
Influence of surface states on the two-dimensional electron gas in AlGaN/GaN heterojunction field-effect transistors

The electron transfer into the two-dimensional electron gas (2DEG) of AlGaN/GaN heterojunction field-effect transistors (HFETs) is examined theoretically using a charge-control model. The model is based on a self-consistent solution of the Poisson, Schrodinger, and charge balance equations, together with the k⋅p Hamiltonian for the valence band states. Realistic surface boundary conditions are imposed, and surface states are included using Fermi–Dirac statistics. Based on the assumption that surface donors are the underlying cause of the 2DEG, a wide range of published data on the 2DEG can be explained. For instance, the variation of the 2DEG density with the AlGaN layer thickness and mole fraction can be accounted for, along with other experimental results, such as the reduction of the 2DEG density when the HFET is capped with a GaN layer, the saturation of the 2DEG density for thick GaN caps, and the increase in the 2DEG density when the surface is passivated.
Systematic investigation of mid-term periodicity of the solar full-disk magnetic fields

The Magnetic Plage Strength Index (MPSI) and theMountWilson Sunspot Index (MWSI), which have been measured at Mount Wilson Observatory (MWO) since the 1970s and which indicate weak and strong magnetic field activity on the solar full disk, respectively, are used to systematically investigate midterm periodicities in the solar full-disk magnetic fields. Multitudinousmid-term periodicities are detected in MPSI and MWSI on timescales of 0.3 to 4.5 yr, and these periodicities are found to fluctuate around several typical periodicities within a small amplitude in different solar cycles or phases. The periodicity of 3.44 yr is found in MPSI, and the periodicities of 3.85 and 3.00 yr are detected in MWSI. Our analysis indicates that they reflect the true oscillating signals of solar magnetic field activity. The typical periodicities are 2.8, 2.3 and 1.8 yr in MPSI and MWSI, and possible mechanisms for these periodicities are discussed. A 1.3 yr periodicity is only detected in MPSI, and should be related to meridional flows on the solar surface. The typical annual periodicity of MPSI and MWSI is 1.07 yr, which is not derived from the annual variation of Earth’s heliolatitude. Several periodicities shorter than 1 yr found in MPSI and MWSI are considered to be Rieger-type periodicities.
Next-generation, high-efficiency III-V multijunction solar cells

Next-generation solar cell approaches such as AlGaInP/GaAs/GaInNAs/Ge 4-junction cells, lattice-mismatched GaInP/GaInAs/Ge, concentrator cells, and improved 3-junction device structures hold the promise of greater efficiency than even today's highly successful multijunction cells. Wide-bandgap tunnel junctions, improved heterointerfaces, and other device structure improvements have resulted in several record-efficiency GaInP/GaAs/Ge cell results. Triple-junction (3J) cells grown in this work have demonstrated 29.3% efficiency for space (AMO, 1 sun). Space concentrator 3J cells have efficiency up to 30.0% at low concentration (AMO, 7.6 suns), and terrestrial concentrator cells grown at Spectrolab and processed at NREL have reached 32.3% (AM1.5D, 440 suns).
The common physical origin of the glass transition, macromolecular entanglement and turbulence

The interface excitation (IE) on intermolecular interface is a common concept connecting the glass transition (GT), macromolecular entan-glement (ME), and turbulence. IE has an addi-tional repulsion energy and extra vacancy vol-ume that result from the two neighboring molecules with antiparallel delocalization all in, e.g., the z-axial ground state of single-molecule instantaneous polarized dipole at GT. IEs only occur in the 8 orders of 2D IE loop-flows on lo-cal x-y projection plane. Theoretical proof of the 3.4 power law of ME viscosity reveals that (i) the delocalization mode of GT and solid-liquid tran-sition is solitary wave; wave- particle duality of solitary wave is ascribed to the equal probabili-ties between appearing and disappearing of IE loop-flow in inverse cascade and cascade mode; (ii) macromolecular chain-length in ME motion corresponds to Reynolds number in hydrody-namics; both the ME motion and the turbulent flow obey the same scale law. IE is not the ex-citation of dipole energy level at GT. However, when IEs are associated with the energy levels of instantaneous polarized dipole, we predict that the coherent structure formed by multilevel 8 orders of 2D IE loop-flows is the physical ori-gin of turbulence based on the universal ran-dom delocalization transition theory.
Enhanced molecular abundances in low-mass star-forming cores

The outflow from a young stellar object interacts with the dense core in which it is embedded to create anomalously high abundances of HCO + that under high resolution show a 'butterfly' morphology. It has been suggestedthat the high HCO + abundance and its morphology arose in a photochemistry induced in the highly turbulent interface induced between the outflow and the core. In this paper we use a very large chemical network to explore the molecular nature of this interface, and demonstrate that, beside HCO + , many other molecular tracers should be anomalously enhanced in this interface and should under high resolution show the same morphology as HCO+. We predict that particularly abundant species should include H 2 S, CS, H 2 CS, SO, SO 2 , CH 3 OH, and recommend that a study for these species and their morphologies be made in star-forming cores. Such observations should help to define the fluid interaction in the interface. The range of molecules predicted here should more generally represent a chemical signature of energetic turbulent mixing of hot and cold interstellar fluids, and our models developed may be able to interpret observations to determine the nature of the fluids and their interaction.
Molecules in nearby and primordial supernovae

Abstract We present new chemical models of supernova (SN) ejecta based on a chemical kinetic approach. We focus on the formation of inorganic and organic molecules including gas phase dust precursors, and consider zero-metallicity progenitor, massive supernovae and nearby core-collapse supernovae such as SN1987A. We find that both types are forming large amounts of molecules in their ejecta at times as early as 200 days after explosion. Upper limits on the dust formation budget are derived. Our results on dust precursors do not agree with existing studies on dust condensation in SN ejecta. We conclude that PMSNe could be the first non-primodial molecule providers in the early universe, ejecting up to 34% of their progenitor mass under molecular form to the pristine, local gas.