Miracle-dz/UniFAR-FTUs huggingface dataset:
Topology of stellar coronae

Abstract While the existence of cycles in stellar chromospheric flux has been known for some time, the nature of the corresponding coronal response has been more elusive. We describe recent results on the relationship between cyclic variations in surface magnetic flux and coronal structure and re-assess the role of prominence observations in understanding the topology of stellar coronas. We present a new paradigm for prominence support which allows for extended prominences to co-exist with a compact corona. We discuss briefly the recent results on coronal structure in high- and low-mass stars and their implications for dynamo theory.
Large-Eddy Simulations of Convective Boundary Layers over Flat and Urbanlike Surfaces

AbstractThe effects of urbanlike surfaces with a block array on the dry convective boundary layer (CBL) are numerically investigated using the parallelized large-eddy simulation model. Five cases representing a free CBL, a sheared CBL, and a strongly sheared CBL over flat surfaces, a sheared CBL over a block array, and a sheared CBL over a modeled canopy layer are simulated and compared. In the sheared CBL over a block array, mixed-layer flow is decelerated because of increased surface shear and horizontal convective rolls appear in the mixed layer. In contrast, convection cells and intermediate structures between cells and rolls occur in the free and sheared CBLs over flat surfaces, respectively. Horizontal convective rolls and the traces of block-induced turbulent eddies are detected in the spectral density fields of vertical velocity and in the vertical profiles of vertical velocity skewness in the sheared CBL over a block array. The decelerated mixed-layer flow in the sheared CBL over a block array le.
Thermal stability dependence on Tb content in TbFeCo thin film

Measurements of the time dependence of magnetization at various reversing fields and remanence coercivity in Tb/sub x/(Fe/sub 90/Co/sub 10/)/sub 100-x/ films (x = 13 /spl sim/ 31) where the compensation composition is x = 22.5, indicate that the thermal stability in transition metal-rich films is better than that in the rare earth-rich ones. There seems to be a difference in (K/sub u/V/k/sub B/T) between the TM-rich and RE-rich compositions.
Sensitivity of Tropical Cyclone Rainbands to Ice-Phase Microphysics

A high-resolution tropical cyclone model with explicit cloud microphysics has been used to investigate the dynamics and energetics of tropical cyclone rainbands. As a first step, the model rainbands have been qualitatively compared with observed rainband characteristics. The model-generated rainbands show many of the mesoscale and convective-scale features of observed tropical cyclone rainbands. Sensitivity studies of numerically simulated tropical cyclone convection to ice-phase microphysical parameters showed that the model was most sensitive to changes in the graupel fall speed parameters. Increasing the fall speeds saw graupel being confined to the convective regions and producing higher rain rates in the inner core of the storm. A greater region of stratiform precipitation was produced when the efficiency for the collection of snow and cloud ice by graupel was reduced and when the mean size of graupel was reduced. Both of these simulations resulted in a higher concentration of snow being transported into the stratiform region. Although the precipitation structure changed across the simulations, the surface rainfall rate and the fundamental dynamical variables showed little sensitivity to the parameter variations.
Experimental investigation of cylindrical converging shock waves interacting with a polygonal heavy gas cylinder

The interaction of cylindrical converging shock waves with a polygonal heavy gas cylinder is studied experimentally in a vertical annular diaphragmless shock tube. The reliability of the shock tube facility is verified in advance by capturing the cylindrical shock movements during the convergence and reflection processes using high-speed schlieren photography. Three types of air/SF6 polygonal interfaces with cross-sections of an octagon, a square and an equilateral triangle are formed by the soap film technique. A high-speed laser sheet imaging method is employed to monitor the evolution of the three polygonal interfaces subjected to the converging shock waves. In the experiments, the Mach number of the incident cylindrical shock at its first contact with each interface is maintained to be 1.35 for all three cases. The results show that the evolution of the polygonal interfaces is heavily dependent on the initial conditions, such as the interface shapes and the shock features. A theoretical model for circulation initially deposited along the air/SF6 polygonal interface is developed based on the theory of Samtaney & Zabusky (J. Fluid Mech., vol. 269, 1994, pp. 45–78). The circulation depositions along the initial interface result in the differences in flow features among the three polygonal interfaces, including the interface velocities and the perturbation growth rates. In comparison with planar shock cases, there are distinct phenomena caused by the convergence effects, including the variation of shock strength during imploding and exploding (geometric convergence), consecutive reshocks on the interface (compressibility), and special behaviours of the movement of the interface structures (phase inversion).
New analysis for the assignment of UV-visible ionic Xe laser lines

Visible and UV laser emissions from a highly ionized pulsed Xe plasma were studied in relation to the ionic assignment of the laser lines. Time-resolved spectroscopy and intensity versus pressure analysis were used to determine the ionic origin of the studied lines. The results of both methods show good agreement, and the joint coincidence is used as a criterion for ionic classification, thus imposing a stringent condition for the assignment of the lines and enhancing its reliability. The disagreement between some of our assignments and those from other authors are discussed on the basis of the results of our systematic analysis of more than 200 spontaneous lines in the region of interest. >
Cutoff frequencies of transmission lines consisting of pair of cylinders

The paper presents a method of evaluation of cutoff frequencies of higher-order modes of transmission line of parallel cylinders by transforming them into a parallel plate configuration using cotangent hyperbolic transformation. Application of the method of finite difference to the weighted Helmholtz equation leads to a set of simultaneous equations. The eigenvalues related to cutoff frequencies are determined from the characteristic equation expressed in terms of matrices obtained from the simultaneous equations. Numerical data are presented.
Limits on variations of the quark masses, QCD scale, and fine structure constant

We perform calculations of the dependence of nuclear magnetic moments on quark masses and obtain limits on the variation of the fine structure constant $\ensuremath{\alpha}$ and ${(m}_{q}/{\ensuremath{\Lambda}}_{\mathrm{QCD}})$ from recent measurements of hydrogen hyperfine (21 cm) and molecular rotational transitions in quasar absorption systems, atomic clock experiments with hyperfine transitions in H, Rb, Cs, ${\mathrm{Yb}}^{+},$ ${\mathrm{Hg}}^{+},$ and optical transition in ${\mathrm{Hg}}^{+}. $ Experiments with ${\mathrm{Cd}}^{+},$ deuterium/hydrogen, molecular ${\mathrm{SF}}_{6},$ and Zeeman transitions in ${}^{3}\mathrm{H}\mathrm{e}/\mathrm{X}\mathrm{e}$ are also discussed.
Whipping instability characterization of an electrified visco-capillary jet

The charged liquid micro-jet issued from a Taylor cone may develop a special type of non-axisymmetric instability, usually referred to in the literature as a whipping mode. This instability usually manifests itself as a series of fast and violent lashes of the charged jet, which makes its characterization in the laboratory difficult. Recently, we have found that this instability may also develop when the host medium surrounding the Taylor cone and the jet is a dielectric liquid instead of air. When the oscillations of the jet occur inside a dielectric liquid, their frequency and amplitude are much lower than those of the oscillations taking place in air. Taking advantage of this fact, we have performed a detailed experimental characterization of the whipping instability of a charged micro-jet within a dielectric liquid by recording the jet motion with a high-speed camera. Appropriate image processing yields the frequency and wavelength, among the other important characteristics, of the jet whipping as a function of the governing parameters of the experimental set-up (flow rate and applied electric field) and liquid properties. Alternatively, the results can be also written as a function of three dimensionless numbers: the capillary and electrical Bond numbers and the ratio between an electrical relaxation and residence time.
Hysteresis behavior of CoPt nanoparticles

CoPt nanoparticles embedded in nonmagnetic matrices M (M = C, BN) have been obtained by annealing multilayer precursors prepared by sputtering from Co/sub 50/Pt/sub 50/ and M targets in a tandem deposition mode onto Si substrate. The structure and microstructure development of the CoPt/C films has been studied at different annealing stages. Magnetic properties of CoPt with different particle size are investigated with respect to bilayer thickness, annealing conditions, and temperature. The possibility for high density recording media is discussed.
Alternation-based generalizations are stored in the mental grammar: Evidence from a sorting task experiment

According to constructional approaches, grammar consists of an inventory of symbolic pairings of a syntactic form with an abstract meaning. Many of such so-called constructions can be perceived as having highly similar meanings: such pairs have been discussed under the name of alternations, especially in the domain of argument structure, for example the widely documented dative alternation (e.g. John gave Mary a book vs. John gave a book to Mary). This paper explores what status such pairs of constructions can be given in construction grammar, on the basis of a sorting task experiment. Construction grammar traditionally recognizes generalizations of a c ommon syntactic form over semantically similar sentences, but the status of higherlevel generalizations of a common meaning over syntactically different forms is rarely discussed. In our study, we devised a sorting task that subjects could resolve by relying on generalizations of either of these two kinds. We find that subjects rely on alternation-based generalizations more often than purely constructional ones in their sorting behavior. We suggest these results show that generalizations of a common meaning between formally different constructions are plausible categories stored by speakers and should be given more attention in construction grammar research.
Identification of multivariable stochastic linear systems via polyspectral analysis given noisy input-output time-domain data

The problem considered is that of identification of unknown parameters of multivariable, linear "errors-in-variables" models, i.e., linear systems where measurements of both input and output of the system are noise contaminated. Attention is focused on frequency-domain approaches where the integrated polyspectrum (bispectrum or trispectrum) of the input and the integrated cross-polyspectrum, respectively, of the given time-domain input-output data are exploited. We first develop (computable) expressions for the covariance matrix of the system transfer function estimate and show that the system transfer function matrix estimate is asymptotically complex Gaussian. Then we propose and analyze a pseudo-maximum likelihood estimator of system parameters using the developed statistics of the system transfer function estimate. Finally, two simulation examples are presented.
Simulating a stochastic background of gravitational waves from neutron star formation at cosmological distances

We develop a temporal simulation of the potentially detectable gravitational wave background from neutron star formation at cosmological distances. By using a recent model for the evolving star formation rate, we investigate the statistical distribution of gravitational wave amplitudes due to supernovae that result in neutron star formation in the Einstein-de Sitter cosmology. We find that the gravitational wave amplitude distribution in our frame is highly skewed, with skewness related to the distribution of sources, and that the potentially detectable gravitational wave strain is dominated by sources at a redshift of 2-3. Time traces of the simulation, using selected waveforms, are presented graphically and are also made available as web-based audio files. The method developed can readily be extended to different cosmologies, as well as to incorporate other waveforms and source types. This type of simulation will be useful in testing and optimizing detection strategies for gravitational wave backgrounds due to various types of individually undetectable astrophysical sources.
Conjugate heat transfer during free jet impingement of a high Prandtl number fluid

This article presents the results of numerical simulation of a free jet of a high Prandtl number fluid impinging perpendicularly on a solid substrate of finite thickness containing electronics on the opposite surface. The numerical model was developed considering both solid and fluid regions and solved as a conjugate problem. The influence of different operating parameters such as jet velocity, heat flux, plate thickness, nozzle height, and plate material were investigated. Computed results were validated with available experimental data. It was found that the local Nusselt number is maximum at the center of the disk and decreases gradually with radius as the flow moves downstream. The average Nusselt number and the maximum temperature occurring in the solid varied significantly with impingement velocity, disk thickness, and thermal conductivity of the disk material.
Some observations of air flow over the sea

Wind speeds were measured over the sea at five heights up to 8 m. Though the fetch was limited, the wind profiles obtained are considered representative of flow over the sea. The wind speed varies logarithmically with height when the temperature gradient is small. Assuming that laboratory laws of flow are applicable, values of the roughness parameter z0 are deduced. It is found that z0 increases from about 0·02 cm in a wind of 5 m/sec to 0·25 cm at 9 m/sec. The relationship between wind speed and z0 however is not unique for the state of the surface is determined by other factors beside wind speed. In inversion conditions the wind-speed distribution departs from the logarithmic form a few metres above the surface. The results obtained are compared with those of some other workers. Bi-directional vanes were used to obtain gustiness measurements at the site. While the vertical gustiness is found to be of similar magnitude to that over land surfaces of comparable roughness, the cross-wind gustiness appears to be greater over the sea.
Combinatorics of oriented trees and tree-like structures

Combinatorics of oriented trees and tree-like structures Isaac Owino Okoth Department of Mathematical Sciences, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa. Dissertation: PhD (Mathematics) March 2015 In this thesis, a number of combinatorial objects are enumerated. Du and Yin as well as Shin and Zeng (by a different approach) proved an elegant formula for the number of labelled trees with respect to a given indegree sequence, where each edge is oriented from a vertex of lower label towards a vertex of higher label. We refine their result to also take the number of sources (vertices of indegree 0) or sinks (vertices of outdegree 0) into account. We find formulas for the mean and variance of the number of sinks or sources in these trees. We also obtain a differential equation and a functional equation satisfied by the generating function for these trees. Analogous results for labelled trees with two marked vertices, related to functional digraphs, are also established. We extend the work to count reachable vertices, sinks and leaf sinks in these trees. Among other results, we obtain a counting formula for the number of labelled trees on n vertices in which exactly k vertices are reachable from a given vertex v and also the average number of vertices that are reachable from a specified vertex in labelled trees of order n. In this dissertation, we also enumerate certain families of set partitions and related tree-like structures. We provide a proof for a formula that counts connected cycle-free families of k set partitions of {1, . , n} satisfying a certain coherence condition and then establish a bijection between these famiii Stellenbosch University https://scholar.sun.ac.za
Separation Control by Self-Activated Movable Flaps

Separation control is an important issue in the physiology of birdflight. Here, the adaption of the separation control mechanism by bird feathers to the requirements of engineering applications is described in detail. Self-activated movable flaps similar to artificial bird feathers represent a high-lift system for increasing the maximum lift of airfoils. Their effect on the unsteady flow around a two-dimensional airfoil configuration is investigated by a joint numerical and experimental study. First, attention is paid to the automatic opening and closing mechanism of the flap. Following this, its beneficial effect on lift is investigated for varying incidences and flap configurations. In-depth analysis of experimental and numerical results provides a detailed description of the important phenomena and the effect of self-adjusting flaps on the flow around the airfoil. In the second part of this paper, a contribution is made to verification of the applicability of unsteady Reynolds-averaged approaches using statistical turbulence models for unsteady flows with particular attention to turbulent time scales with comparison to the results of a hybrid simulation based on unsteady Reynolds-averaged Navier-Stokes equations and large-eddy simulation. Finally, flight experiments are described using an aircraft with movable flaps fitted on its laminar wing.
Directional dispersion of sporadic‐E modes between 9 and 14 MHz

Visibility function analysis of sporadic-E mode fine structure was performed on an 830 km path between 10 and 14 MHz. Angular spectra derived show resolved doublet magnetoionic components with angular separation of 4.5 to 6/sup 0/. Individual singlet components appear with 1 to 2/sup 0/ angular width. Compared to other mode fine structure data, these results indicate increased azimuth spread and multiple lines predominate on paths less than 1000 km, while longer paths more nearly conform to 1 to 2/sup 0/ core and halo distributions.
Equilibrium problems techniques in the qualitative analysis of quasi-hemivariational inequalities

In this paper, we investigate the problem of existence of solutions of quasi-hemivariational inequalities. Some concepts of semicontinuity and hemicontinuity on subsets for functions as well as for set-valued mappings are developed and applied for solving quasi-hemivariational inequalities. Generalizations of some old results on the existence of solutions of equilibrium problems are obtained and applications to quasi-hemivariational inequalities are derived.
Application of Structural Equation Models to Quality of Life

Quality of life (QOL) has become an important concept for health care. As QOL is a multidimensional concept that is best evaluated by a number of latent constructs, it is well recognized that latent variable models, such as exploratory factor analysis (EFA) and confirmatory factor analysis (CFA) are useful tools for analyzing QOL data. Recently, QOL researchers have realized the potential of structural equation modeling (SEM), which is a generalization of EFA and CFA in formulating a regression type equation in the model for studying the effects of the latent constructs to the QOL or health-related QOL. However, as the items in a QOL questionnaire are usually measured on an ordinal categorical scale, standard methods in SEM that are based on the normal distribution may produce misleading results. In this article, we propose an approach that uses a threshold specification to handle the ordinal categorical variables. Then, on the basis of observed ordinal categorical data, a maximum likelihood (ML) approach for analyzing CFA and SEM is introduced. This approach produces the ML estimates of the parameters, estimates of the scores of latent constructs, and the Bayesian information criterion for model comparison. The methodologies are illustrated with a dataset that was obtained from the WHOQOL group.
A theoretical investigation of dynamic all-optical automatic gain control in multichannel EDFA's and EDFA cascades

We present a detailed theoretical analysis of the gain dynamics of erbium-doped fiber amplifiers (EDFA's) that have been gain-clamped using a ring laser structure and of gain-stabilized EDFA chains. We examine and analyze the effects of attenuator level in the optical feedback path, switching speed, number of channels dropped or added and the choice of lasing wavelength on the stabilization of the individual EDFA. In particular, we look at the transient power excursions and relaxation oscillations experienced by surviving channels when the number of channels passing through an EDFA changes. Using this analysis as a guide, we present and compare two different approaches to chain stabilization. We highlight the robustness of each approach, show some of their limitations and advantages, and comment on the impact on multiwavelength communication systems.
The Econometrics of Learning in Financial Markets

The asymptotic behavior of the sample paths of two popular statistics that test market efficiency are investigated when markets learn to have rational expectations. Two cases are investigated, where, should markets start out at a rational expectations equilibrium, both statistics would asymptotically generate standard Brownian motions. In a first case, where agents are Bayesian and payoffs exogenous, the statistics have identical sample paths, but they are not standard Brownian motions. Whereas the finite-dimensional distributions are Gaussian, there may be a bias if agents' initial beliefs differ. A second case is considered, where payoffs are in part endogenous, yet agents consider them to be drawn from a stationary, exogenous distribution, which they attempt to learn in a frequentist way. In that case, one statistic behaves as if the economy were at a rational expectations equilibrium from the beginning on. The other statistic has sample paths with substantially non-Gaussian finite-dimensional distributions. Moreover, there is a negative bias. The behavior of the two statistics in the second case matches remarkably well the empirical results in an investigation of the prices of six foreign currency contracts over the period 1973–1990.