Miracle-dz/UniFAR-FTUs huggingface dataset:
A novel augmented Lagrangian‐based formulation for upper‐bound limit analysis

This paper describes a novel upper‐bound formulation of limit analysis. This formulation is an innovative variant of an existing two‐field mixed formulation based on the augmented Lagrangian method also developed by the authors. A natural approach is used to describe the deformation of each finite element. Furthermore, and in contrast to the previous formulation, two independent field approximations are now both used to define the velocity field, defined globally and at element level. It is shown that this feature allows a governing system of uncoupled linear equations to be obtained. Some numerical examples in plane strain conditions are presented in order to illustrate the current model performance. In conclusion, the potential and advantages of this new approach are discussed. Copyright © 2011 John Wiley & Sons, Ltd.
Improving predictability of time series using maximum entropy methods

We discuss how maximum entropy methods may be applied to the reconstruction of Markov processes underlying empirical time series and compare this approach to usual frequency sampling. It is shown that, in low dimension, there exists a subset of the space of stochastic matrices for which the MaxEnt method is more efficient than sampling, in the sense that shorter historical samples have to be considered to reach the same accuracy. Considering short samples is of particular interest when modelling smoothly non-stationary processes, which provides, under some conditions, a powerful forecasting tool. The method is illustrated for a discretized empirical series of exchange rates.
Bi-variate pattern spectrum

Bivariate pattern spectrum is the generalization of the concept of usual pattern spectrum. The usual pattern spectrum is the mapping from multidimensional set to 1D vector, whereas bivariate pattern spectrum is the mapping of multidimensional set to 2D vector. The introduction of bivariate pattern spectrum, based upon the geometrical concepts, has the notion to develop a shape-size descriptor, in the true sense. For defining bivariate pattern spectrum we introduce the concept of parametric and conditional parametric morphological operators. The usual binary morphological operators are the special case of parametric morphological operators.
Fiber supercontinuum sources (Invited)

We review supercontinuum generation in optical fibers for particular cases where the nonlinear spectral broadening is induced by pump radiation from fiber-format sources. Based on numerical simulations, our paper is intended to provide experimental design guidelines tailored ytterbium and erbium-based pumps around 1060 and 1550 nm, respectively. In particular, at 1060 nm, we consider conditions under which the generated spectra are phase and intensity stable, and we address the dependence of the supercontinuum coherence on the input pulse parameters and the fiber length. At 1550 nm, special attention is paid to the case of dispersion-flattened dispersion-decreasing fiber, where we revisit the underlying physics in detail and explicitly examine the use of such fiber for supercontinuum generation with pumps of peak power in the range 200-1200 W and sub-10 m fiber lengths. We show that supercontinuum generation under such conditions can be highly coherent and can be applied to nonlinear pulse compression.
A Theory of Electrons and Protons

The relativity quantum theory of an electron moving in a given electro­magnetic field, although successful in predicting the spin properties of the electron, yet involves one serious difficulty which shows that some fundamental alteration is necessary before we can regard it as an accurate description of nature. This difficulty is connected with the fact that the wave equation, which is of the form [W/ c + e / c A + ρ1 (σ, p + e / c A) + ρ3 mc ] Ψ = 0, (1) has, in addition to the wanted solutions for which the kinetic energy of the electron is positive, an equal number of unwanted solutions with negative kinetic energy for the electron, which appear to have no physical meaning. Thus if we take the case of a steady electromagnetic field, equation (1) will admit of periodic solutions of the form Ψ = u e - i E t / h , (2) where u is independent of t , representing stationary states, E being the total energy of the state, including the relativity term mc 2. There will then exist solutions (2) with negative values for E as well as those with positive values ; in fact, if we take a matrix representation of the operators ρ1σ1, ρ1σ2, ρ1σ3, ρ3 with the matrix elements all real, then the conjugate complex of any solution of (1) will be a solution of the wave equation obtained from (1) by reversal of the sign of the potentials A, and either the original wave function or its con­jugate complex must refer to a negative E.
MODIFICATIONS AND COHOMOLOGIES OF SOLVMANIFOLDS

Let G/ be a compact solvmanifold. In this paper, unifying approac hes of previous works on the subject, we develop tools for the computation of the de Rham (and Dolbeault) cohomology of various classes of compact (complex) solvmanifolds. In particular, we generalize the modification method of Witte to any subtorus of the maximal torus of the Zariski closure A(AdG(G)) of AdG(G), extending it also to the Dolbeault cohomology case.
On cnoidal waves and bores

For a train of gravity waves of finite amplitude in a frame of reference in which they are stationary, it is suggested that, in addition to the volume flow per unit span Q and the total head R, one may usefully study a third constant S, the rate of flow of horizontal momentum(corrected for pressure force, and divided by the density). The values of Q, R and S probably determine the wave-train uniquely; this is proved explicitly for long waves in a new presentation of the ‘cnoidal wave’ theory (§3). The combinations of Q, R and S which are possible in the general case are illustrated by a diagram (figure 2) in which the co-ordinates are r= R/Rc and s= S/Sc; here suffix c refers to ‘critical’ flow at the volume rate Q. There are two barriers on this diagram beyond which no stationary waves, or other steady flows, are possible; at the left-hand barrier (corresponding to uniform subcritical flows) the amplitude tends to zero; at the right-hand barrier (corresponding to uniform supercritical flows) the wave-length tends to infinity (case of the solitary wave). The diagram needs to be completed by a third barrier corresponding to ‘waves of greatest height’. This starts at the point marked Z and moves to infinity within the unshaded region without ever intersecting the left-hand barrier. The diagram may be used to determine what losses of momentum and energy a given stream can undergo, without departing from the condition of steady flow. Thus, one can determine the maximum wave resistance on a cylindrical obstacle athwart a given subcritical stream, or on a two-dimensional ‘step’ in the bed, in the absence of energy dissipation. Again, one can study the transition to a wave-train behind a bore. Such a wave-train (present in all but very strong bores) is shown to be capable of absorbing almost the whole energy which according to classical theory is liberated at the bore, although some minute residual dissipation of energy still appears to be necessary.
On the principles of fuzzy classification

In this paper we analyze the concept of fuzzy partition, starting from the classical key definition given by E.H. Ruspini (1969). Our main claim is that such a definition is too restrictive, since it assumes a particular set of classes that in practice may be reached only after a long learning process. As a consequence, some principles to be taken into account in fuzzy classification methods are discussed.
Long-term variability of the temperature time series recorded in Lisbon

As a case study for application in climate change studies, daily air temperature records in Lisbon are analysed by applying advanced statistical methodologies that take into account the dynamic nature of climate. A trend analysis based on two non-parametric tests (Spearman and Mann–Kendall) revealed the presence of statistically significant upward trends in the maximum temperatures, mainly during March. The minimum temperatures do not present significant trends, with the exception of March where a relatively weak positive trend is detected. A singular spectral analysis combined with a maximum entropy spectral analysis enables the detection of regularities in the annual mean time series of the maximum and minimum temperatures. A quasi-periodic oscillation with a peak period of about 50 years is superimposed in the linear trends. At the maximum temperature, a secondary oscillation with a peak period of nearly 20 years is also identified. No other regularities are isolated in these time series. The study is enhanced by applying an extreme value analysis to the extreme winter and summer temperatures. The generalized extreme value distribution family is shown to provide high-quality adjustments to the distributions, and a description of the temperatures related to different return periods and risks is given.
The crossover from a ferroelectric to a relaxor state in lead-free solid solutions

We investigate the gradual crossover from ferroelectric to relaxor behaviour versus substitution in lead-free ceramics. We show that the Vogel? Fulcher law in the relaxor state is the extrapolation of the ferroelectric line. To explain this extrapolation, we suggest that both the host matrix and the impurity induced clusters are triggered by the BaTiO3 soft mode correlation length. The Ti? O bond oscillations are the key mechanism.
Laboratory studies of nonlinear whistler wave processes in the Van Allen radiation belts

Important nonlinear wave-wave and wave-particle interactions that occur in the Earth's Van Allen radiation belts are investigated in a laboratory experiment. Predominantly electrostatic waves in the whistler branch are launched that propagate near the resonance cone with measured wave normal angle greater than 85°. When the pump amplitude exceeds a threshold ∼5×10−6 times the background magnetic field, wave power at frequencies below the pump frequency is observed at wave normal angles (∼55°). The scattered wave has a perpendicular wavelength that is nearly an order of magnitude larger than that of the pump wave. Occasionally, the parametric decay of a lower hybrid wave into a magnetosonic wave and a whistler wave is simultaneously observed with a threshold of δB/B0∼7×10−7.
THE ROLE OF INTERNAL DISSIPATION AND PROCESS AVERAGE TEMPERATURE IN CHILLER PERFORMANCE AND DIAGNOSTICS

The thermodynamic behavior of conventional chillers (generalized air conditioning and refrigeration systems) is acutely sensitive to internal dissipation. Previous chiller analyses have excluded entropy production in the evaporator and condenser heat exchangers, on the assumption of its being negligible. With experimental measurements from a commercial chiller, we demonstrate that heat exchanger internal dissipation is not inconsequential, and that ignoring its contribution can lead to substantial errors in chiller diagnostics and in the prediction of chiller performance curves. To evaluate the impact of this dissipation on chiller efficiency, one needs to define a proper process average temperature (PAT). In addition to discussing the fundamental significance of the correct PAT, we will show that earlier conventional definitions of PAT, where internal irreversibilities in chiller heat exchangers have been overlooked, result in inaccurate and sometimes unphysical predictions.
VLA observations of the supernova remnant Puppus A at 327 and 1515 MHz

Very Large Array radio images of Puppis A at 327 and 1515 MHz are presented. The observations were performed with the VLA in the C/D and B/C configurations, respectively. The angular resolution is about 77 arcsec x 43 arcsec. The observed radio shell shows signs of interaction between the expanding shock front and the inhomogeneous surrounding medium. An excellent correlation is found between radio and X-ray emission, mainly toward the NE border of the remnant. There is little correspondence between the optical and radio images, suggesting a different origin for the emission. A region of steeper radio spectral index is associated with the highly decelerated eastern periphery. 32 refs.
Efficient and systematic identification of MIMO bilinear state space models

We present a systematic way to identify multi-input, multioutput (MIMO) bilinear state space systems subject to white noise inputs, in the presence of process and measurement noise. The algorithm we present is based on a family of subspace identification algorithms for linear systems. It requires the linear pair (A, C) to be observable. We use subspace identification to determine the model order, to identify the linear part of the model, and to compute an initial estimate for the nonlinear part. The final estimate of the nonlinear part is computed by numerically solving a nonlinear optimization problem. A series of simulation experiments showed that the initial estimate is close to the optimum and allows convergence of the nonlinear optimization problem.
Skill of the MJO and Northern Hemisphere Blocking in GEFS Medium-Range Reforecasts

AbstractForecast characteristics of Northern Hemisphere atmospheric blocking and the Madden–Julian oscillation (MJO) were diagnosed using an extensive time series (December–February 1985–2012) of daily medium-range ensemble reforecasts based on a version of the NCEP Global Ensemble Forecast System (GEFS). For blocking, (i) interannual variability of analyzed blocking frequency was quite large, (ii) the GEFS slightly underforecasted blocking frequency at longer leads in the Euro-Atlantic sector, (iii) predictive skill of actual blocking was substantially smaller than its perfect-model skill, (iv) block onset and cessation were forecast less well than overall blocking frequency, (v) there was substantial variability of blocking skill between half-decadal periods, and (vi) the reliability of probabilistic blocking forecasts degraded with increasing lead time.For the MJO, (i) forecasts of strong Indian Ocean MJOs propagated too slowly, especially the component associated with outgoing longwave radiation (OLR),.
Geometric Study of Minkowski Differences of Plane Convex Bodies

Abstract In the Euclidean plane ${{\mathbb{R}}^{2}}$ , we define the Minkowski difference $\mathcal{K}-\mathcal{L}$ of two arbitrary convex bodies $\mathcal{K},\mathcal{L}$ as a rectifiable closed curve ${{\mathcal{H}}_{h}}\subset {{\mathbb{R}}^{2}}$ that is determined by the difference $h={{h}_{K}}-{{h}_{\mathcal{L}}}$ of their support functions. This curve ${{\mathcal{H}}_{h}}$ is called the hedgehog with support function $h$ . More generally, the object of hedgehog theory is to study the Brunn–Minkowski theory in the vector space of Minkowski differences of arbitrary convex bodies of Euclidean space ${{\mathbb{R}}^{n+1}}$ , defined as (possibly singular and self-intersecting) hypersurfaces of ${{\mathbb{R}}^{n+1}}$ . Hedgehog theory is useful for: (i) studying convex bodies by splitting them into a sum in order to reveal their structure; (ii) converting analytical problems into geometrical ones by considering certain real functions as support functions. The purpose of this paper is to give a detailed study of plane hedgehogs, which constitute the basis of the theory. In particular: (i) we study their length measures and solve the extension of the Christoffel–Minkowski problem to plane hedgehogs; (ii) we characterize support functions of plane convex bodies among support functions of plane hedgehogs and support functions of plane hedgehogs among continuous functions; (iii) we study the mixed area of hedgehogs in ${{\mathbb{R}}^{2}}$ and give an extension of the classical Minkowski inequality (and thus of the isoperimetric inequality) to hedgehogs.
Nonresponse Among Ethnic Minorities: A Multivariate Analysis

This article examines the nonresponse among ethnic minorities in the Netherlands. We have constructed a structural equation model with various response outcomes, controlling the effect of ethnicity on the response outcomes for various socio-economic and socio-demographic variables. The effect of ethnicity on response is almost entirely mediated by the degree of urbanization. We have also performed multiple group analyses to examine differences between ethnic groups in the response outcome predictors. Here again, we note that urbanization has a negative effect on the response probabilities in all the ethnic groups and in particular on the contact probabilities. This negative effect is somewhat larger, however, among sampled units with a non-Western background.
Photon bubbles - Overstability in a magnetized atmosphere

The formation of 'photon bubbles' in a convectively stable scattering atmosphere supported against gravity entirely by radiation pressure is studied by means of linear stability theory. A simple model is developed for the 2D structure of a plasma mound formed by laminar accretion onto the magnetic poles of a neutron star, in which upward photon diffusion balances downward photon advection with the plasma. It is shown that the vertical pressure and density structure is the same as in an isothermal atmosphere. Application of the stability theory to this model suggests photon bubbles would form in a polar accretion mound under the conditions expected in accretion-powered pulsars within a few tenths of a millisecond. Because long-wavelength modes have the largest rise speeds, eventual dominance by a few large bubbles is suggested, and possible connections between bubble formation and short-time variability in accretion-powered pulsars is discussed, as well as a possible connection of the photon bubble phenomenon to the rapid time variability observed in the Rapid Burster and in quasi-period oscillator sources. 31 refs.
PRECESSION AND RECIRCULATION IN TURBULENT SWIRLING ISOTHERMAL JETS

A burner with a hybrid bluff body swirl design, incorporating a central jet surrounded by a swirling annulus, is applied to the investigation of turbulent isothermal swirling jets. Nonswirling flows stabilized on this burner form only one stagnation zone on the face of the bluff body. Such a far upstream recirculation zone is typical of those formed behind solid obstructions placed in strong axial streams. The addition of swirl leads to more complex flow patterns, which may include a second recirculation zone (in more downstream axial locations), flow instabilities, and precession. Both of these effects are investigated. Laser Doppler Velocimetry is used to ascertain the presence of downstream recirculation. The seed- (alumina-) laden central jets in these flows are visualized using a combination of laser sheet forming optics and high-speed CCD camera. Postprocessing of the imaging data succeeds in resolving the precession frequency of the jet despite the variable seed density in the experiments. Precession frequency appears to be a function of swirl number as well as the Reynolds number of both the central jet and the swirling annulus.
TWO-DIMENSIONAL TRANSONIC AEROELASTIC ANALYSIS USING THIN-LAYER NAVIER–STOKES METHOD

Abstract A robust efficient upwind implicit time-marching algorithm for the two-dimensional unsteady Thin-Layer Navier–Stokes equations, employing subiterations, is presented, especially directed to the aeroelastic analysis in viscous transonic flow. The purpose of using subiterations is to accelerate steady-state convergence and to permit a large time step in time-accurate simulations, thereby reducing the computational cost, while maintaining adequate accuracy. The ability of the method is demonstrated for the cases of inherently unsteady flow due to shock-induced separation, forced vibrations with large time steps, O (10) per period, and an aeroelastic analysis of a two-degree-of-freedom airfoil.
Characterization of electron self-injection in laser wake field acceleration due to the parametric resonance

The wave-breaking processes originating from a parametric resonance in the wake of a laser pulse in the absence of pulse overfocusing are thoroughly analyzed via multidimensional particle-in-cell simulations. The processes play a key role in the electron self-injection in the laser-driven acceleration of high energy, monoenergetic electrons in plasma channels. The resonance character of the charge loading in the first, second, and third injections is shown; its effect on the electron acceleration is demonstrated.
Implicit large eddy simulation of a supersonic flat-plate boundary layer flow by weighted compact nonlinear scheme

The performance of implicit large eddy simulation (ILES) of a supersonic flat-plate turbulent boundary layer flow by weighted compact nonlinear scheme (WCNS) has been investigated. In view of features of WCNS and ILES, it was expected that ILES by WCNS could be an efficient approach to perform LES of supersonic turbulent flows. The flowfield calculated by WCNS was of lower turbulent intensity compared with an explicit LES data obtained by a numerical scheme of the same order of accuracy on a computational grid of similar resolution. It was concluded that the numerical dissipation inherent in WCNS is so large that applying WCNS to ILES of this flowfield is inefficient compared with explicit LES.
Fine Structure of Scalar Fields Mixed by Turbulence. II. Spectral Theory

Universal similarity hypotheses are proposed based on the local straining mechanisms, Kolmogoroff's local isotropy theory, and the mixing theories of Obukhov, Corrsin, and Batchelor. Three sets of similarity coordinates follow from the hypotheses depending on five fundamental parameters of turbulent mixing: e, the turbulence dissipation rate; χ, the scalar variance dissipation rate; γ, the local strain rate; ν, the kinematic viscosity; and D, the molecular diffusivity of the scalar. Transformations between coordinate systems are shown to depend only on Pr ≡ ν/D as a mapping parameter. A unified spectral array with convergence properties required by the hypotheses is produced when the similarity hypotheses are used to predict the scalar spectrum function Γ. The inertial subrange (Γ ∼ k−5/3, k is the wavenumber) of Obukhov and Corrsin and the large Pr value viscous‐convective (Γ ∼ k−1) subrange of Batchelor are reproduced. However, for small Pr values, a new inertial‐diffusive subrange arises with Γ ∼ k−3 a.
A statistical analysis of ionospheric irregularities at mid- and high latitudes

Long timeseries of the critical frequency of the F2 layer, foF2, from several mid- and high-latitude stations, are used for investigating the average behaviour of the disturbed ionospheric conditions identified by descriptive letters replacing or accompanying the ionogram scaled value. By analysing the distribution of the descriptive letters A (sporadic Es layer presence), B (absorption near fmin ), spread F appearance, G (screen by F1 layer) and R (absorption near foF2), the mean percentage occurrence of the ionospheric irregularities are calculated for four specified levels of magnetic activity according to a new magnetic activity catalogue (MAC) recently introduced for studying the dependence of the ionosphere on magnetic perturbations. After removing solar cycle effects from the statistical results obtained, it is found that the total bottomside irregularities increase with geomagnetic latitudes and represent an indicator of the ionospheric response to the magnetic activity with a time delay of the order of about 15 h according to the MAC.