Miracle-dz/UniFAR-FTUs huggingface dataset:
Coronal holes and high‐speed wind streams

Coronal holes are regions of unusually low density and low temperature in the solar corona. During a 9-month Skylab solar workshop, 50 participants established some of the basic properties of coronal holes and their associated high-speed wind streams using a combination of Skylab, satellite, and ground-based observations. The holes have been identified now as Bartel's M regions, i.e., sources of high-speed wind streams that produce recurrent geomagnetic variations. Throughout the Skylab period the polar caps of the sun were coronal holes, and at lower latitudes the most persistent and recurrent holes were equatorial extensions of the polar caps. The holes rotated ‘rigidly’ at the equatorial synodic rate. They formed in regions of unipolar photospheric magnetic field, and their internal magnetic fields diverged rapidly with increasing distance from the sun. The geometry of the magnetic field in the inner corona seems to control both the physical properties of the holes and the global distribution of high-speed wind streams in the heliosphere. The diverging field lines in well-established holes act as Laval nozzle which produces supersonic flow and depressed densities at low altitudes. The latitude variation of the divergence of the coronal magnetic field lines produces corresponding variations in wind speed, in agreement with interplanetary scintillation measurements and multisatellite observations. During the years of declining solar activity the global field of the corona approximates a perturbed dipole. The divergence of field lines in each hemisphere produces a high-speed wind near the poles and low-speed wind in a narrow belt that coincides with the magnetic neutral sheet. The width and magnetic polarity of recurrent wind streams, as measured near earth, has been predicted successfully on the basis of the global coronal magnetic field geometry, at least during the Skylab period. The analysis of electron density measurements within a polar hole indicates that solar wind is accelerated principally in the region between 2 and 5 Rs and that mechanical wave pressure (possibly Alfven wave) may be responsible for the acceleration of the wind. Phenomenological models for the birth and decay of coronal holes have been proposed. A global pattern of formation, with a systematic eastward drift of successive hole appearances, suggests that the diverging magnetic fields of the coronal holes arise through dynamo action in the deep convection zone. However, attempts to explain the birth and rigid rotation of holes through dynamo action have been only partially successful. More observational data exist on the solar cycle variation of wind streams than on coronal holes. The polar holes shrink, and the volume occupied by the neutral sheet may increase near solar maximum. The 11-year variation of cosmic ray intensities at the earth may result from cyclic variation of open field regions associated with coronal holes.
Simulation and Experimental Research of a Novel Vircator

A new configuration of an axially-extracted vircator with three resonant cavities is put forward and optimized by simulation with the PIC code. The output power of over 1 GW is obtained at around 4.1 GHz in the experiment, in agreement well with the PIC simulation results. The beam to wave power conversion efficiency is more than 6.6%.
Whole-body CT in polytrauma patients: The effect of arm position on abdominal image quality when using a human phantom

For a considerable number of emergency computed tomography (CT) scans, patients are unable to position their arms above their head due to traumatic injuries. The arms-down position has been shown to reduce image quality with beam-hardening artifacts in the dorsal regions of the liver, spleen, and kidneys, rendering these images non-diagnostic. The purpose of this study was to evaluate the effect of arm position on the image quality in patients undergoing whole-body CT. We acquired CT scans with various acquisition parameters at voltages of 80, 120, and 140 kVp and an increasing tube current from 200 to 400 mAs in 50 mAs increments. The image noise and the contrast assessment were considered for quantitative analyses of the CT images. The image noise (IN), the contrast-to-noise ratio (CNR), the signal-to-noise ratio (SNR), and the coefficient of variation (COV) were evaluated. Quantitative analyses of the experiments were performed with CT scans representative of five different arm positions. Results of the CT scans acquired at 120 kVp and 250 mAs showed high image quality in patients with both arms raised above the head (SNR: 12.4, CNR: 10.9, and COV: 8.1) and both arms flexed at the elbows on the chest (SNR: 11.5, CNR: 10.2, and COV: 8.8) while the image quality significantly decreased with both arms in the down position (SNR: 9.1, CNR: 7.6, and COV: 11). Both arms raised, one arm raised, and both arms flexed improved the image quality compared to arms in the down position by reducing beam-hardening and streak artifacts caused by the arms being at the side of body. This study provides optimal methods for achieving higher image quality and lower noise in abdominal CT for trauma patients.
Perturbations of optical solitons.

A perturbation theory is developed to investigate the effects of various perturbations on soliton propagation down an optical fiber. The theory is formulated within the «natural» framework of inverse scattering theory. The perturbative effects of third-order dispersion, the soliton self-frequency shift, bandwidth-limited gain, periodic modulation, and stochastic fluctuations are analyzed in detail. In each case, the analytic results presented here are in excellent agreement with simulations carried out here and elsewhere
Parameter Estimation in Credit Models Under Incomplete Information

We consider the filtering model of Frey and Schmidt (2012) stated under the real probability measure and develop a method for estimating the parameters in this framework by using time-series data of CDS index spreads and classical maximum-likelihood algorithms. The estimation-approach incorporates the Kushner-Stratonovich SDE for the dynamics of the filtering probabilities. The convenient formula for the survival probability is a prerequisite for our estimation algorithm. We apply the developed maximum-likelihood algorithms on market data for historical CDS index spreads (iTraxx Europe Main Series) in order to estimate the parameters in the nonlinear filtering model for an exchangeable credit portfolio. Several such estimations are performed as well as accompanying statistical and numerical computations.
Well-Posedness in Critical Spaces for Barotropic Viscous Fluids with Truly Not Constant Density

This paper is dedicated to the study of viscous compressible barotropic fluids in dimension N ≥ 2. We address the question of well-posedness for large data having critical Besov regularity. Our sole additional assumption is that the initial density be bounded away from zero. This improves the analysis of Danchin (2001) where the smallness of for some positive constant was needed. Our result relies on a new a priori estimate for a class of parabolic systems with variable coefficients, which is likely to be useful for the investigation of other models in fluid mechanics.
Three-dimensional ray tracing of fast magnetosonic waves

A three dimensional ray tracing of fast magnetosonic (MS) waves is first performed by using a global core density model and a field-aligned density model. Simulating results show that MS waves are primarily confined within a few degrees of the geomagnetic equator due to magnetospheric reflection. MS waves originating from different L-shells on the dayside can propagate either into or out of the plasmasphere through the plasmapause. In particular, MS waves can propagate eastward (later MLT) or westward (earlier MLT) over a broad region of MLT. The current results further reveal a variety of propagation characteristics, particularly important for the MLT distribution of MS waves.
Time analysis of aneurysm wall shear stress for both Newtonian and Casson flows from image-based CFD models

The optimal management of unruptured aneurysms is controversial, and current decision making is mainly based on aneurysm size and location. Incidentally detected unruptured aneurysms less than 5mm in diameter should be treated conservatively. However, small unruptured aneurysms also bleed. Risk factors based on the hemodynamic forces exerted over the arterial wall have been investigated using image-based computational fluid dynamic (CFD) methodologies during the last decade. Accurate estimation of wall shear stress (WSS) is required to properly study associations between flow features and aneurysm processes. Previous works showed that Newtonian and non-Newtonian (Casson) models produce similar WSS distributions and characterization, with no significant differences. Other authors showed that the WSS distribution computed from time-averaged velocity fields is significantly higher for the Newtonian model where WSS is low. In this work we reconstructed ten patient-specific CFD models from angiography images to investigate the time evolution of WSS at selected locations such as aneurysm blebs (low WSS), and the parent artery close to the aneurysm neck (high WSS). When averaging all cases it is seen that the estimation of the time-averaged WSS, the peak WSS and the minimum WSS value before the systolic peak were all higher when the Casson rheology was considered. However, none of them showed statistically significant differences. At the afferent artery Casson rheology systematically predicted higher WSS values. On the other hand, at the selected blebs either Newtonian or Casson WSS estimations are higher in some phases of the cardiac cycle. Those observations differ among individual cases.
DRIFT SHELL SPLITTING BY INTERNAL GEOMAGNETIC MULTIPOLES.

Computations on an 80–coefficient model of the earth's field illustrate the ‘topography’ of the magnetic equatorial surface (on which B · ∇B = 0) and the geometry of the drift shells of geomagnetically trapped particles. Individual terms in the spherical harmonic expansion (offset dipole coordinates) of the geomagnetic scalar potential V(γ, θ, ϕ) are either even or odd in cos θ, where θ = π/2 denotes the dipole equator. Terms that (unlike the dipole) are even in cos θ tend to ‘warp’ the equatorial surface, but do not (in first order) distort particle drift shells radially nor split the drift shells of particles having different equatorial pitch angles. Azimuthally asymmetric terms that are odd in cos θ do cause shell splitting in first order. Shell splitting at large L values (neglecting deformation of the earth's field by the solar wind) is found to be dominated by the geomagnetic octupole. At L ∼ 1, shell splitting is strongly enhanced by the South American and South African anomalies. When combined with pitch angle diffusion caused by atmospheric scattering, these results may be able to account for anomalous radial diffusion of inner zone electrons (as observed at L ≲ 1.2).
Weighted energy estimates for wave equations in exterior domains

Abstract Weighted energy estimates including the Keel, Smith and Sogge estimate is obtained for solutions of exterior problem of the wave equation in three or higher dimensional Euclidean spaces. For the solutions of the Cauchy problem, which is corresponding to the free system in scattering theory, the estimates are given by using the ideas introduced by Morawetz and summarized by Mochizuki for the Dirichlet problem in the outside of star shaped obstacles. From the estimates for the free system, the corresponding estimates for exterior domains are given if it is assumed that the local energy decays uniformly with respect to initial data, which depends on the structures of propagation of singularities.
Vanishing l1-sums of the Poisson kernel, and sums with positive coefficients

For z in D and ζ in ∂D, we denote by pz(ζ) the Poisson kernel (1 − │z│2)│1 − z̄ζ−2 for the open unit disc D. We ask for what countable sets {an:n∈ℕ} of points of D there exist complex numbers λn with by which we mean that the series converges to zero in the norm of L1(∂D).
The number of small-amplitude limit cycles of Liénard equations

We consider second order differential equations of Liénard type: Such equations have been very widely studied and arise frequently in applications. There is an extensive literature relating to the existence and uniqueness of periodic solutions: the paper of Staude[6] is a comprehensive survey. Our interest is in the number of periodic solutions of such equations.
Pseudospectral methods for Nagumo equation

In this paper we present two pseudospectral methods based on Fourier series and rational Chebyshev functions for solving the Nagumo equation. In each of the two presented methods the problem is reduced to a system of ordinary differential equations that is solved by the leapfrog difference scheme and the fourth‐order Runge–Kutta method, respectively. We compare the numerical solutions with the exact solution to validate the numerical methods. Numerically comparing of the two methods also will be considered. Copyright © 2009 John Wiley & Sons, Ltd.
Scanning probe microscope dimensional metrology at NIST

Scanning probe microscope (SPM) dimensional metrology efforts at the US National Institute of Standards and Technology (NIST) are reviewed in this paper. The main SPM instruments for realizing the International System of Units (SI) are the Molecular Measuring Machine, the calibrated atomic force microscope and the critical dimension atomic force microscope. These are optimized for long-distance measurements, three-dimensional measurements over conventional SPM distances and critical dimension or linewidth measurements, respectively. 10 mm distances have been measured with the relative standard uncertainty, uc, of 1.5 × 10−5; step heights at the 100 nm scale have been measured with the relative uc of 2.5 × 10−3 and sub-micrometer linewidths have been measured with uc = 0.8 nm.
Polarization induced hole doping in graded AlxGa1−xN (x = 0.7 ∼ 1) layer grown by molecular beam epitaxy

Polarization induced hole doping on the order of ∼1018 cm−3 is achieved in linearly graded AlxGa1−xN (x = 0.7 ∼ 1) layer grown by molecular beam epitaxy. Graded AlxGa1−xN and conventional Al0.7Ga0. 3N layers grown on AlN are beryllium (Be) doped via epitaxial growth. The hole concentration in graded AlxGa1−xN:Be (x = 0.7 ∼ 1) layers demonstrates that polarization generates hole charges from Be dopant. The Al0.7Ga0. 3N layer is not conductive owing to the absence of carriers generated from the Be dopant without the inducement of polarization. Polarization doping provides an approach to high efficiency p-type doping in high Al composition AlGaN.
Instability of rotating convection

Convection rolls in a rotating layer can become unstable to the Küppers–Lortz instability. When the horizontal boundaries are stress free and the Prandtl number is finite, this instability diverges in the limit where the perturbation rolls make a small angle with the original rolls. This divergence is resolved by taking full account of the resonant mode interactions that occur in this limit: it is necessary to include two roll modes and a large-scale mean flow in the perturbation. It is found that rolls of critical wavelength whose amplitude is of order ε are always unstable to rolls oriented at an angle of order ε2/5. However, these rolls are unstable to perturbations at an infinitesimal angle if the Taylor number is greater than 4π4. Unlike the Küppers–Lortz instability, this new instability at infinitesimal angles does not depend on the direction of rotation; it is driven by the flow along the axes of the rolls. It is this instability that dominates in the limit of rapid rotation. Numerical simulations confirm the analytical results and indicate that the instability is subcritical, leading to an attracting heteroclinic cycle. We show that the small-angle instability grows more rapidly than the skew-varicose instability.
Pseudo-Likelihood Methodology for Hierarchical Count Data

Generalized Estimating Equations (GEE) are a widespread tool for modeling correlated data, based on properly formulating a marginal regression function, combined with working assumptions about the correlation function. Should interest be placed in addition on the correlation function, then, apart from second-order GEE, pseudo-likelihood (PL) also provides an attractive alternative, especially in its pairwise form, where the covariance between each pair of the response vector is modeled as well. An elegant PL approach is formulated in this paper, based on a flexible bivariate Poisson model. The performance of the PL-method is studied, relative to GEE, using simulations. Data on repeated counts of epileptic seizures in a two-arm clinical trial are analyzed. A macro has been developed by the authors and made available on their web pages.
Characteristics of quantum well infrared photodetectors

A model is presented for the performance of quantum well infrared photodetectors (QWIPs) utilizing intersubband electron transitions and tunneling injection electrons. The dark current and the responsivity are derived as functions of the QWIP parameters, including the number of the QWs, in an analytical form. Nonlinear effects in the QWIP operation at high infrared power are considered and the threshold value of power density is estimated.
A description of turbulent wall-flow vorticity consistent with mean dynamics

Abstract A depiction of the mean and fluctuating vorticity structure in turbulent wall flows is presented and described within the context of the self-similar properties admitted by the mean dynamical equation. Data from a relatively wide range of numerical and physical experiments are used to explore and clarify the structure postulated. The mean vorticity indicator for the onset of the four-layer regime of the mean dynamics is revealed. With increasing Reynolds number, the mean vorticity is shown to segregate into two increasingly well-defined domains. Half of the mean vorticity concentrates into a near-wall region of width (relative to the overall flow width) that diminishes proportionally to the inverse square root of Reynolds number. The remainder of the mean vorticity is spread, with diminishing amplitude, over an outer domain that approaches the overall flow width at high Reynolds number. Vorticity stretching and reorientation are surmised to be the characteristic mechanisms accounting for the inner domain behaviour of both the mean and fluctuating vorticity. Vorticity dispersion via advective transport is surmised to be the characteristic mechanism in the outer domain. In this domain, the fluctuating enstrophy approaches that of the instantaneous enstrophy with increasing Reynolds number. This underpins an emerging self-similarity between the mean and r.m.s. vorticity in the domain where the mean velocity profile is logarithmic. The Reynolds number dependence of a number of properties associated with the vorticity field is explored and quantified. The study closes with brief account of the combined vortical and mean dynamical structure of turbulent wall flows.
Ocean, platform, and signal processing effects on synthetic aperture sonar performance

Abstract : Synthetic Aperture Sonar (SAS), the underwater sound application of the aperture synthesis method borrowed from Synthetic Aperture Radar (SAR), is investigated by means of ocean medium effects, platform motion effects, and signal processing effects. Synthetic aperture methods, both in radar and in sonar, allow large synthesized apertures, or equivalently synthesized arrays, to be formed from the combined use of signal processing and a small, real aperture transducer (e.g. a radar or a sonar transducer). Large synthetic apertures give rise to relatively narrow synthesized beams, which in turn allow very high resolution focused images to be formed from radar or sonar data. The target in the synthetic aperture sonar case could be the ocean bottom, and the objective could be, for example, ocean-bottom mapping or searching for a sunken vessel. Synthetic Aperture Sonar(SAS) , Synthetic aperture radar, Acoustical imaging, Radar imaging
Diffraction by an Aperture

Diffraction of a wave by an aperture of any shape in a thin screen is treated by a new method—``the geometrical theory of diffraction. '' This is an extension of geometrical optics which accounts for diffraction by introducing new rays called diffracted rays. They are produced when incident rays hit the aperture edge and they satisfy the ``law of diffraction. '' A field is associated with each ray in a quantitative way, by means of the optical principles of phase variation and energy conservation. In addition ``diffraction coefficients'' are introduced to relate the field on a diffracted ray to that on the corresponding incident ray.By this method a simple formula is obtained for the field diffracted by any aperture. It yields the field in the aperture, the diffraction pattern and the transmission cross section. Explicit formulas and numerical results are given for slits and circular apertures. The accuracy of the results increases as the wavelength decreases, but they are useful for wavelengths even as lar.
Evolution of the galactic cosmic ray electron to proton ratio: Ulysses COSPIN/KET observations

The Ulysses orbit provides a unique opportunity to study the propagation of cosmic rays in a wide range of heliographic latitudes and during different solar activity and polarity in the inner heliosphere. Around July 2000 the solar magnetic field reversed its global polarity. In late 2000, the electron to proton ratio at the rigidities of 1.2 GV and 2.5 GV, measured by the Kiel Electron Telescope aboard Ulysses, was roughly the same as in the previous solar maximum. During 2001 the ratio profile began to flatten, however after late 2001 the ratio began to increase again, leading to the conclusion that drifts are becoming increasingly important again. Comparing the Ulysses observations with the IMP and ICE measurements in the 1980s reveals a similar time profile. If solar cycle 23 would evolve similar to solar cycle 21 then the electron intensity will increase more quickly than the helium and proton intensities in 2003/2004.
Temperature dependence of tunability of Ba(SnxTi1−x)O3 ceramics

The electric field dependence of the dielectric constant (dc-tunability) as a function of temperature for a few compositions of Ba(Sn,Ti)O3 ceramics was investigated. Dense and homogeneous BaSnxTi1−xO3 ceramics (ferroelectric for x = 0.05 and x = 0.10, relaxor for x = 0.15 and 0.20) with high dielectric constant and low dielectric losses were prepared by solid state reaction. Their dc-tunability characteristics were investigated at a few temperatures from 20–120 °C, including the Curie range. The tunability data were discussed in terms of the Johnson model completed with a Langevin term that describes the “extrinsic” contribution to the nonlinear ɛ(E) dependences.
Solar Wind Scaling Law

We derive a simple, robust scaling law, which explains naturally how the well-known anticorrelation between final solar wind speed and freezing-in temperature results from the loss of radiated energy in the corona. Furthermore, if the Sun injects roughly fixed electromagnetic energy per particle, this law provides a unified theory for the source of solar wind: fast tenuous solar wind from dark coronal holes; slow dense wind from hotter, brighter regions; and bound but unstable plasma in extremely hot regions, which may be related to solar transients. The scaling law is not an extension or a new variant of previous solar wind models, but rather a requirement on all solar wind models, which should apply quite generally to magnetically driven winds. Thus, this paper reveals an underlying connection between the solar wind and its coronal source.