Miracle-dz/UniFAR-FTUs huggingface dataset:
Propagation of a light beam in an evaporating liquid-drop medium in the presence of wind refraction

An analysis is made of the self-consistent problem of a steady-state thermal self-interaction of a two-dimensional laser beam traveling in an evaporating (under the action of tie beam) liquid-drop medium in the presence of a homogeneous wind field. A nonlinear geometric-optics equation is obtained for the paths of rays in a beam with an arbitrary initial intensity distribution and an arbitrary initial divergence. The method of successive approximations is used to find the angles of nonlinear refraction of ray trajectories and of the radiation intensity profile in the medium. It is shown that a redistribution of the intensity in the light beam due to ray refraction results in considerable changes compared with a case when the refraction is ignored.
Devolving HRM and HRD to Line managers: The Case of Hilton International's UK Hotels.

This paper explores line manager responsibility for human resource management (HRM) and human resource development (HRD) in an international hotel organisation. The results identify a strong support system for line managers in relation to training and good relations with HR specialists. However, less evident is senior management support coupled with barriers in relation to philosophical understanding, time and work pressures, which are acting as inhibitors to line management’s commitment to HRM and HRD.
Crystallization kinetics of suspensions of hard colloidal spheres

The crystallization of suspensions of sterically stabilized polymer particles, with hard-sphere-like interactions, is studied by laser light scattering. Over the range of volume fractions examined, from just below melting to the glass transition, crystallization occurs by homogeneous nucleation. After the suspensions are shear melted, the intensity, position, and width of the main interlayer Bragg reflection are measured as functions of time. From these the amount of crystal, the average linear crystal dimension, the number of crystals, and the volume fraction of the crystal phase are obtained. No assumptions are made concerning the functional time dependence of nucleation or growth processes. Below the melting concentration the observed crystallization process is compatible with the classical picture of sequential nucleation and growth of isolated crystals. However, when the melting concentration is exceeded, nucleation events are correlated, nucleation is accelerated, and high nucleation rate densities suppress crystal growth. Above the melting concentration we infer, with the aid of the equations of state for the hard-sphere fluid and solid, that the first identifiable crystals are in mechanical equilibrium with the embedding fluid and, consequently, strongly compressed by it. Ensuing nucleation lags expansion of the crystal lattice.
Space-time correlation measurements in a hypersonic transitional boundary layer

An experimental investigation of the spatial structure of second-mode instability waves was carried out in the boundary layer of a 7-deg half-angle, sharp-nosed cone at an edge Mach number of 6.8. Measurements were made at Reynolds numbers of 2.3 x 10 6 to 9.1 x 10 6 based on boundary edge conditions, spanning the range from unstable laminar flow to nearly turbulent flow. Simultaneous measurements with two hot-film probes in the boundary layer comprise the primary data set. The mean boundary-layer state was measured with pitot and total temperature surveys. Correlations were taken with circumferential, streamwise, and vertical probe separations. The second-mode waves preceding transition are relatively limited in their circumferential dimension, typically less than four boundary-layer thicknesses, based on a coherence level of 20%.
NUMERICAL SCHEMES OBTAINED FROM LATTICE BOLTZMANN EQUATIONS FOR ADVECTION DIFFUSION EQUATIONS

Stability and accuracy of the numerical schemes obtained from the lattice Boltzmann equation (LBE) used for numerical solutions of two-dimensional advection-diffusion equations are presented. Three kinds of velocity models are used to determine the moving velocity of particles on a squre lattice. A system of explicit finite difference equations are derived from the LBE based on the Bhatnagar, Gross and Krook (BGK) model for individual velocity model. In order to approximate the advecting velocity field, a linear equilibrium distribution function is used for each of the moving directions. The stability regions of the schemes in the special case of the relaxation parameter ω in the LBE being set to ω=1 are found by analytically solving the eigenvalue problems of the amplification matrices corresponding to each scheme. As for the cases of general relaxation parameters, the eigenvalue problems are solved numerically. A benchmark problem is solved in order to investigate the relationship between the accuracy of the numerical schemes and the order of the Peclet number. The numerical experiments result in indicating that for the scheme based on a 9-velocity model we can find the parameters depending on the order of the given Peclet number, which generate accurate solutions in the stability region.
Validation of the Integrated Biosphere Simulator over Canadian deciduous and coniferous boreal forest stands

Data collected during the Boreal Ecosystem-Atmosphere Study (BOREAS) at four different forest stands were used to test surface energy and carbon fluxes simulated by the Integrated Biosphere Simulator (IBIS). These stands included deciduous and conifer species and were located in both the BOREAS northern and southern study areas. Two runs were made: one using the original IBIS model and the other using a version modified to consider an organic soil layer (OSL) covering the mineral soil surface. Results show that the inclusion of the OSL substantially improved the simulation of soil heat flux, as well as of temperature and moisture in the topmost soil layer. Simulations show that latent and sensible heat fluxes, and net ecosystem exchange of carbon, were not affected appreciably by the presence of a thin (10 cm or less) OSL covering the forest floor. With a thick (50 cm) OSL, however, simulation of latent heat flux and net ecosystem exchange of carbon was substantially improved. Consideration of the OSL in the model also led to better simulation of the onsets of soil thawing. Correct estimation of heat diffusion to deep soil through thick organic layers requires a parameterization that accounts for the state of the organic material decomposition. Simulations presented here also show the necessity for using detailed information on soil physical properties for better evaluation of model performance.
Radiative efficiency limits of solar cells with lateral band-gap fluctuations

The radiative recombination limit of photovoltaic power conversion under one sun terrestrial illumination is calculated for solar cells with lateral fluctuations of the band-gap energy. A simple analytical model quantifies the fluctuations by the standard deviation σEg from the mean band gap. The calculated maximum efficiency decreases by 1.7% (absolute) for σEg=50 meV and by 6.1% for σEg=100 meV with respect to a uniform band gap.
Color image encryption using singular value decomposition in discrete cosine Stockwell transform domain

In this paper, an image encryption technique using singular value decomposition (SVD) and discrete cosine Stockwell transform (DCST) is proposed. The original source image is encrypted using bands of DCST along with the SVD decomposed images. The number of bands in DCST, parameters used to mask the singular values, the way of permutation used to shuffle the values of SVD transformed images and the way of arrangement of SVD matrices are used as encryption keys. It is necessary to have correct knowledge of all the keys along with their respective values, for correct decryption of encrypted images. The robustness and the quality measurement of proposed work are analyzed by comparing it with some existing works.
Differential effects of two types of written corrective feedback ( direct focused and direct unfocused ) on the accurate use of grammatical forms by teenage EFL learners

This study examined the differential effect of two types of written corrective feedback (CF) which are direct focused CF and direct unfocused CF in improving teenage EFL learners’ grammatical accuracy in the short term and in the long term. Using one intact class in a band 3 secondary school in HK, two groups were formed: focused group (n=17) and unfocused group (n=19). During the 8-week experimental period, the students completed three tests (pre-test, post-test, delayed post-test). Based on the data from the tests, it is found out that both type of corrective feedback have a positive influence on students' accurate use of three targeted grammatical structures (i.e. Number agreement, subject-verb agreement, and propositions) both in the short term and in the long run. The difference between the effect of direct focused and direct unfocused CF remains significant in the short term while the former type largely exceeds the latter. However, with regard to the long-term mastery of the targeted linguistic forms, the two ways of giving feedback seem to have a similar effect. This finding indicated that teachers' decision on CF selection should depend on the acting time and different educational purposes.
Penumbral fine structure: Theoretical understanding

To understand the dynamic fine structure and the Evershed effect of the sunspot penumbra, we have carried out time-dependent simulations of a thin magnetic flux tube embedded in a static sunspot model (Schlichenmaier et al. 1998a,b). Here, we present new simulation results of the moving tube model which reveal flux tubes that, instead of lying horizontal in the penumbral photosphere, develop waves (photospheric serpent) that reproduce not only the inward migration of penumbral grains, but also their observed outward migration, and which exhibit downflow arches in the outer penumbra. During its evolution the flux tube exhibits quasi-steady states. These states are compared to time-independent solutions of siphon flow models, which have been used to explain the Evershed flow (Meyer & Schmidt 1968, Degenhardt 1991, Montesinos & Thomas 1997).
Autocorrelation function bias owed to a limited number of de-trended observations. Applications to autoregressive models with noise.

Analytical expressions were derived for the expectation of the autocorrelation function (ACF) corresponding to lowfrequency least squares fits and deviations from them in the case of a limited number of observations N. A vector of values of the autocovariation function may be obtained by multiplication of a N . N matrix Z (dependent on concrete basic functions used for trend determination) by a vector of the unbiased ACF. Because much computational time is needed to obtain such a matrix, its components are to be computed once for concrete N and basic functions, and then stored as a file. An algorithm is proposed for determining the contribution of the correlated signal to the ‘signal+noise’. The expressions are written for general form of the ACF, and illustrated by the application to autoregressive models. The statistical properties of the model parameters are studied. The method is applied to cataclysmic binaries AM Her and TT Ari. The precise expressions allow us to obtain reliable results and to avoid misinterpretation being possible when using the approximate methods.
Freezing of the polarization fluctuations in lead magnesium niobate relaxors

The dielectric relaxation of a solid solution of 10‐mol % lead titanate in lead magnesium niobate is found to be similar to the magnetic relaxation in spin‐glass systems.1–3 Based on this analogy, it is proposed that the relaxor ferroelectric is a polar‐glassy system which has thermally activated polarization fluctuations above a static freezing temperature. An activation energy and freezing temperature of 0.0407 eV and 291.5 K, respectively, were found by analyzing the frequency dependence of the temperature of the dielectric maximum using the Vogel–Fulcher relationship.4,5 It has also been shown that a macroscopic polarization is sustained on heating up to this freezing temperature. A coupling between nanometer scale clusters is believed to control the kinetics of the fluctuations and the development of a frustration as the system freezes into states of local equilibrium. The possibility of an orientational freezing associated with the ferroelastic nature of the nanosized polar regions in the rhombohedr.
The auroral radiating plasma cavities

The electron density profile of the nightside high latitude region has been determined from a geocentric distance 1.5 R{sub E} to 3 R{sub E} by the use of the Viking Langmuir probe. Inside this region, density depletions are observed. Most of them coincide with acceleration structure crossings. Generation of Auroral Kilometric Radiation (AKR) is observed in the strongest depletions between 1.5 and 2.5 R{sub E}. A threshold on the ratio plasma to electron gyrofrequency for AKR generation to occur is estimated at 0.14. This is in good agreement with the cyclotron maser instability theory for AKR generation.
Electron-hole trapping and self – trapping in polyethylene

An electron-hole pair, either excited optically (exciton), or injected by external fields, represents an exceedingly strong perturbation in a wide gap insulator. That is particularly true if, as in the case of polyethylene and other saturated organic molecular systems, the solid is held together by weak van der Waals forces, and can thus rather easily distort. Even in the perfect crystalline material, the question whether an electron hole pair would freely propagate, or whether it might instead generate a local distortion and become self-trapped by that, is highly relevant. We studied by ab-initio molecular dynamics simulations the behavior of an electron-hole pair in crystalline PE, and found that the pair becomes indeed self-trapped, with a trapping energy of 0.38 eV. The self-trapping is realized by the spontaneous appearance of a local distortion of the polymeric chain, consisting in a pair of trans-gauche conformational defects, 3 C2H4 units apart. Between these two defects, the chain is rotated by 120 degrees, creating a narrow inter-chain pocket, in whose neighborhood the electron and the hole become bound. The electron binding is tight, quite similarly to the free electron self-trapping state discovered in previous calculations, but the hole is only loosely bound, consistent with the lack of self-trapping for free holes. True polyethylene systems of practical use are neither crystalline nor pure. To understand the fate of an electron-hole pair in that case, we studied its behavior in polyethylene with three common chemical defects, namely: a) a grafted carbonyl (C=O); b) an intrachain vinyl double bond (C=C); c) a grafted carboxyl (COOH). Each of these cases was investigated by ab-initio simulation, and found to lead to a different result, namely we found in the three cases: a) e-h trapping, stable at the C=O graft; b) eh trapping at the intra-chain vinyl double bond, however followed by radiationless
Robust traffic sign shape recognition using geometric matching

A novel approach for recognising various traffic sign shapes in outdoor environments is presented. To reduce the influence of digital noise and extract the shape of each individual traffic sign, the external boundaries of traffic signs segmented based on colour information are simplified and decomposed through discrete curve evolution whose stop stage is determined by an arc similarity measure in tangent space. The recognition of a closed candidate shape is achieved through the direct matching with templates. An optimal enclosure is generated to minimise the geometric differences between the retrieved unclosed candidate shape and templates. The experimental results justify that the proposed algorithm is translation, rotation and scaling invariant, and gives reliable shape recognition in complex traffic scenes where clustering and partial occlusion normally occur.
Equilibrium compound distributions and stop-loss moments

A convolution representation is derived for the equilibrium or integrated tail distribution associated with a compound distribution. This result allows for the derivation of reliability properties of compound distributions, as well as an explicit analytic representation for the stop-loss premium, of interest in connection with insurance claims modelling. This result is extended to higher order equilibrium distributions, or equivalently to higher stop-loss moments. Special cases where the counting distribution is mixed Poisson or discrete phase-type are considered in some detail. An approach to handle more general counting distributions is also outlined.
Variable structure control of robotic manipulator with PID sliding surfaces

SUMMARY Dynamic behaviour of a system in sliding mode is entirely defined by the sliding surface. Customarily, the surface is selected as a hyperplane in the system’s state-space resulting in a PD-type sliding surface. This is not the only possible structure, and other designs with more complex or time-varying surfaces may provide definite advantages. Slotine and Spong1 included an integral term in the sliding surface expression that resulted in a type of PID sliding surface. However, the advantages of such a design were not elaborated in following publications of these or other researchers. In this paper we present a new design procedure and stability analysis for robotic variable structure controllers with PID-like sliding surfaces. Two versions of the controller are presented: regular and adaptive. The former is very simple and can operate with an unknown dynamic model; the only information required is a bound on one parameter. The latter provides an on-line estimation for this bound. Both controllers are robust with respect to bounded external disturbances and some unmodelled dynamic e⁄ects. The simulation results have demonstrated stability, with minimum transient responses that may be significantly faster than responses of traditional PD-manifold controllers under the same conditions. ( 1998 John Wiley & Sons, Ltd.
Geophysical model discrimination using the Akaike information criterion

A general model building procedure is developed for employing the Akaike information criterion (AIC) to select the most appropriate stochastic model to describe a specified geophysical time series. To demonstrate the effectiveness of the proposed approach to model construction, formulas for the AIC are given for many types of stochastic models and the method is successfully employed for determining the most suitable models to fit a wide variety of data sets which arise in hydrology and the natural sciences. The AIC is used to discriminate between short and long memory models when modeling annual hydrological time series. An improved constrained autoregressive model is designed for describing yearly sunspot numbers while both stationary and nonstationary linear stochastic models are entertained for modeling a tree ring series. Three types of models are considered for modeling seasonal time series and in a practical application it is shown how to select the most appropriate model to fit to a monthly river flow time series. The model building procedure is also used to select an intervention model that describes the effects of the Aswan Dam on the average annual flows of the Nile River.
The family of nested factorizations

This paper describes a family of Nested Factorization (NF) algorithms, which are used as preconditioners in the iterative solution of sparse linear systems arising in discretization of elliptic or parabolic PDE in 2D and 3D. Nested factorization differs from the widely used incomplete LU/Cholesky factorizations in that the preconditioning matrix in NF is not formed strictly from upper and lower factors. Instead, NF exploits the nested triangular structure of the original matrix by defining the preconditioner matrix as a sequence of level matrices with the diagonal matrix on the lowest level. We present the variants of NF and Generalized NF (GNF) for systems arising in regular 7-point stencil and block 7-point stencil discretizations of PDE on structured grids, respectively. We also introduce a variant of Nested Factorization named UNF, applied to matrices arising in discretization of PDE on unstructured grid. This variant is based on a special reordering technique which recovers a multi-level structure for a general sparse matrix. Numerical results presented in the paper show that nested factorization algorithms give faster convergence and require less memory than ILU-type methods for sets of test matrices.
Free oscillation in a rotating spherical shell

Free oscillations of an incompressible inviscid fluid in a rotating spherical shell are studied by means of the ray method, which is different from the conventional approach. Axisymmetric modes covering the whole sphere and asymmetric modes trapped in equatorial regions bounded by critical circles of constant latitude as well as in regions off the equator bounded by caustics are discovered. The anomalies at poles and critical circles of the ray method expansion are removed by means of uniform asymptotic expansions. The equations for the resonance frequencies of each of the various modes of oscillation are studied numerically.
Nonlinear Hadley Circulation Driven by Asymmetric Differential Heating

Abstract The dynamical state of the stratosphere influenced by radiative heating, with no internal sources or sinks of angular momentum, is examined. It is shown that there exists a nonlinear Hadley regime driven by antisymmetric (or more generally, asymmetric) thermal equilibria typical of the middle atmosphere at the solstices. This regime consists of a single mean meridional cell, equatorial easterlies and strong winter westerlies. Outside of the circulation region the flow is in thermal equilibrium. The effect of one-sided friction, acting as a drag on midlatitude westerlies only, is to expand the Hadley cell into the winter hemisphere and increase the magnitude of cross-equatorial flow. This result is possible even in the steady state when the advection of angular momentum in the tropics is made small by reducing the gradient of angular momentum in this region instead of the advecting velocity.
Polarizability of polyhedral dielectric scatterers

This paper presents numerical results for the dielectric polarizability of canonically shaped homogeneous scatterers: cube, tetrahedron, and octahedron. The method is based on solving the integral equation for the static scalar potential on the surface of the scatterer by the method of moments. Easy‐to‐use interpolation formulas are given for the polarizabilities as a function of the permittivity. © 2002 John Wiley & Sons, Inc. Microwave Opt Technol Lett 32: 60–64, 2002.
Generalized forms and gravitation

The algebra and calculus of generalized differential forms are reviewed and employed to construct a class of generalized connections and to investigate their properties. The class includes generalized connections which are flat when Einstein's vacuum field equations are satisfied. Generalized Chern-Simons action principles are formulated and it is shown that certain of these have Einstein's vacuum field equations as Euler-Lagrange equations.
Concerning the Use of the Fabry-Perot Interferometer for Wave-Number Measurement in the Infrared

Many workers have used channeled spectra produced by a Fabry-Perot interferometer to calibrate infrared spectrometers. In this paper the effects of the finite height of the spectrometer slit and the finite aperture of the condensing lens on the visibility of the spectra are discussed. The way in which maximum accuracy of calibration is to be obtained for any given experimental arrangement is indicated.