Miracle-dz/UniFAR-FTUs huggingface dataset:
Stabilization of a class of underactuated mechanical systems via total energy shaping

In this paper a system of ODEs and a method for its solution are proposed for passivity-based stabilization of a class of underactuated mechanical systems. This method simplifies the PDEs imposed by the passivity-based control via interconnection and damping assignment (IDA-PBC) technique. For a class of mechanical systems satisfying some mathematical properties the PDEs are reduced to a simple set of nonlinear ODEs. A general solution for these equations in the 2-DOF case is presented, through a new parametrization of the closed loop inertia matrix. Two examples illustrate the method, achieving kinetic and potential energy shaping in a straightforward manner. The simulation analysis in comparison with recent studies highlight the advantages of these techniques.
Structural, electronic properties and heat of formation of Mg2FeH6 complex hydride: an ab initio study

In this work, the structural, energetic and electronic properties of Mg2FeH6 complex hydride have been studied using two different methods based on the density functional theory (DFT): the full potential linearized augmented plane wave plus local orbitals (FP-LAPW + lo) and the pseudo-potentials plane waves (PP-PW) methods. Based on the calculated results, the ground state of Mg2FeH6 is found to be paramagnetic (PM), which is in agreement with experimental results, and also, the optimized structural parameters including lattice constants and atomic positions are very close to the experimental and other theoretical works. For a detailed study, electronic structure calculations including those of the energy band, density of states (DOS) and charge density distribution have been performed. It is found that Mg2FeH6 hydride is a semiconductor with a direct energy gap at the X-point of about 1.87 and 2.25 eV for the FP-LAPW + lo and PW-PP methods, respectively, and the Mg atom acts as a donor to form a cation ion and the negatively charged FeH6 complex results in a mainly ionic bonding between the Mg and FeH6 complex. Other physical and energetic properties such as bulk modulus, cohesive energy and formation enthalpy of Mg2FeH6 are in good agreement with the theoretically and experimentally determined values.
The effect of interfacial layer properties on the performance of Hf-based gate stack devices

The influence of Hf-based dielectrics on the underlying SiO2 interfacial layer (IL) in high-k gate stacks is investigated. An increase in the IL dielectric constant, which correlates to an increase of the positive fixed charge density in the IL, is found to depend on the starting, pre-high-k deposition thickness of the IL. Electron energy-loss spectroscopy and electron spin resonance spectra exhibit signatures of the high-k-induced oxygen deficiency in the IL consistent with the electrical data. It is concluded that high temperature processing generates oxygen vacancies in the IL responsible for the observed trend in transistor performance.
Small time and semiclassical asymptotics for stochastic heat equations driven by Lévy noise

The paper is devoted to the study of stochastic heat equations driven by Lévy noise. Applying the WKB method, we obtain multiplicative small time and semiclassical asymptotics for the Green functions and for solutions of the Cauchy problem for the heat equation under some natural additional assumptions on their coefficients. The first step in this construction consists in solving the corresponding stochastic Hamilton-Jacobi equations which constitute the "classical part" of the semiclassical approximation. In its turn, the corresponding Hamilton-Jacobi equations can be solved via solutions of the corresponding Hamiltonian systems, which gives rise to the method of stochastic characteristics. The relevant theory of stochastic Hamiltonian systems and stochastic Hamilton-Jacobi equations was developed in our previous papers. Here we put the final rung on the ladder: stochastic Hamiltonian systems, stochastic Hamilton-Jacobi equations, stochastic heat equations.
Dynamics of velocity gradient invariants in turbulence: Restricted Euler and linear diffusion models

A complete system of dynamical equations for the invariants of the velocity gradient, the strain rate, and the rate-of-rotation tensors is deduced for an incompressible flow. The equations for the velocity gradient invariants R and Q were first deduced by Cantwell [Phys. Fluids A 4, 782 (1992)] in terms of Hij, the tensor containing the anisotropic part of the pressure Hessian and the viscous diffusion term in the velocity gradient equation. These equations are extended here for the strain rate tensor invariants, RS and QS, and for the rate-of-rotation tensor invariant, QW, using HijS and HijW, the symmetric and the skew-symmetric parts of Hij, respectively. In order to obtain a complete system, an equation for the square of the vortex stretching vector, Vi≡Sijωj, is required. The resulting dynamical system of invariants is closed using a simple model for the velocity gradient evolution: an isotropic approximation for the pressure term and a linear model for the viscous diffusion term. The local topology .
Bayesian Inference for the Generalized Exponential Distribution Based on Progressively Censored Data

Based on a progressively Type-II censored sample, Bayesian estimation of the parameters as well as Bayesian prediction of the unobserved failure times from the generalized exponential (GE) distribution are studied. Importance sampling is used to estimate the scale and shape parameters. The Gibbs and Metropolis samplers are considered for predicting times to failure of units in multiple stages. A numerical simulation study involving three data sets is presented to illustrate the methods of estimation and prediction.
Regularization and variable selection via the elastic net

Summary. We propose the elastic net, a new regularization and variable selection method. Real world data and a simulation study show that the elastic net often outperforms the lasso, while enjoying a similar sparsity of representation. In addition, the elastic net encourages a grouping effect, where strongly correlated predictors tend to be in or out of the model together. The elastic net is particularly useful when the number of predictors (p) is much bigger than the number of observations (n). By contrast, the lasso is not a very satisfactory variable selection method in the p≫n case. An algorithm called LARS‐EN is proposed for computing elastic net regularization paths efficiently, much like algorithm LARS does for the lasso.
Analysis of a time discretization for an implicit variational inequality modelling dynamic contact problems with friction

Some dynamic contact problems with friction can be formulated as an implicit variational inequality. A time discretization of such an inequality is given here, thus giving rise to a so‐called incremental solution. The convergence of the incremental solution is established, and then the limit is shown to be the unique solution of the variational inequality. This paper contains therefore not only some new results concerning the numerical aspect of some models of contact and friction but also a constructive existence result. Copyright © 2001 John Wiley & Sons, Ltd.
Trend arbitrage, bid-ask spread and market dynamics

Microstructure of market dynamics is studied through analysis of tick price data. Linear trend is introduced as a tool for such analysis. Trend arbitrage inequality is developed and tested. The inequality sets limiting relationship between trend, bid-ask spread, market reaction and average update frequency of price information. Average time of market reaction is measured from market data. This parameter is interpreted as a constant value of the stock exchange and is attributed to the latency of exchange reaction to actions of traders. This latency and cost of trade are shown to be the main limit of bid-ask spread. Data analysis also suggests some relationships between trend, bid-ask spread and average frequency of price update process.
Sequential Assignment Match Processes with Arrivals of Candidates and Offers

An infinite random stream of ordered pairs arrives sequentially in discrete time. A pair consists of a “candidate” and an “offer,” each of which is either of type I (with probability p) or of type II (with probability q = 1 – p). Offers are to be assigned to candidates, yielding a reward R > 0 if they match in type, or a smaller reward 0 ≤ r ≤ R if not. An arriving candidate resides in the system until it is assigned, whereas an arriving offer is either assigned immediately to one of the waiting candidates or lost forever. We show that the optimal long-term average reward is R, independent of the population proportion p and the “second prize” r, and that the optimal average reward policy is to assign only a match. Optimal policies for discounted and finite horizon models are also derived.
The Structure of the Super-Star Clusters in NGC 1569 from Hubble Space Telescope WFPC2 Images

We present high-resolution observations of the super-star clusters in the nearby irregular galaxy NGC 1569, obtained with the WFPC2 on board the Hubble Space Telescope. Our analysis shows that the brightest of these clusters, NGC 1569A, results from the superposition of two clusters with an angular separation of ~0. ″2. Recent ground-based spectroscopy revealed that both red supergiant and Wolf-Rayet stars are associated with NGC 1569A. According to current evolutionary models, this finding requires the coexistence of two noncoeval stellar populations within the same cluster. Our discovery that NGC 1569A is double simplifies the interpretation, since red supergiants and Wolf-Rayet stars may belong to different clusters. We derive for the three clusters half-light radii of ~1.6-1.8 pc, smaller than indicated by previous HST observations. The size, mass, and luminosity of the brightest of these superclusters confirm that these objects could be young globulars, reinforcing previous conclusions.
Numerical study of heat transfer and pressure drop for flow past inline and staggered tube bundles

Purpose – The purpose of this paper is to develop an indigenous three‐dimensional computational code and apply it to compare flow and heat transfer characteristics for inline and staggered arrangement of circular tubes in a tube bundle.Design/methodology/approach – A finite‐volume based computational code is developed to solve the momentum and energy equations for flow through a three‐dimensional rectangular channel and past built‐in tube bundles having inline and staggered arrangement. The approach is based on SIMPLE algorithm. The basic conservation equations of mass, momentum and energy are solved over a body‐fitting grid on the physical domain to obtain the flow and temperature fields.Findings – Heat transfer and pressure drop are compared for inline and staggered tube arrangements in a tube bundle over range of Reynolds numbers 300 ≤ Re ≤ 800. Results are validated suitably against those available in literature.Research implications – Tube‐fin heat exchangers with continuous fins on a tube array are .
A projection formula for the Askey-Wilson polynomials and an application

A projection formula for pn (x; a, b, c, dlq), the Askey-Wilson polynomials, is obtained by using a generalization of Askey and Wilson's q-beta integral. The result is used to find a q-analogue of the Feldheim-Vilenkin formula for ultraspherical polynomials. A q-analogue of the ultraspherical polynomials, other than the one due to Rogers, is also introduced.
Propagation and reflection of shock waves

Structure and basic properties of shock waves in gases shock wave propagation through a gas interaction of a plane shock wave with disturbances and stability of shock waves reflection of a shock wave from a smooth body of an arbitrary shape reflection of a shock wave from a concave body and shock focusing propagation of shock waves through a weakly ionized plasma.
Collisional Evolution of the Outer Asteroid Belt

We present numerical results obtained by simulations of the collisional process between outer belt asteroids and scattered planetesimals from the Uranus–Neptune zone during their accretion period. We obtained final size distributions for the Hildas dominated by the collisional process with planetesimals, and as a consequence of this result, the observed population appears to be complete or nearly complete at sizes≥10 km in radius. In the proposed scenario, the elongated shapes of the largest Hildas should not be the result of a collisional process but could be primordial. The results obtained for the Trojan asteroids, for different initial masses, show that the final size distribution is dominated by the cometesimal bombardment, but in opposition to the Hilda asteroids, the observed size distribution appears to be incomplete for r<30 km. These results make it possible to assume that the initial mass of the asteroid belt was 4–6 times that at present.
Subband structure and mobility of two-dimensional holes in strained Si/SiGe MOSFET’s

The hole mobility of $p$-type strained Si metal-oxide-semiconductor field-effect transistors (MOSFET's) fabricated on a SiGe substrate is investigated theoretically and compared with the mobility of conventional (unstrained) Si $p$-MOSFET's. Two-dimensional quantization of the holes is taken into account in terms of a self-consistent six-band $\mathbf{k}\mathbf{\ensuremath{\cdot}}\mathbf{p}$ model for the strained band structure and the confined hole subband states in the inversion channel. The hole dynamics along the inversion channel is studied in terms of ensemble Monte Carlo calculations that take into account all relevant scattering mechanisms. For a Ge concentration of $30%$ in the substrate, we predict a mobility enhancement of a factor of 2.3 compared to the unstrained $p$-type device. The calculated low-field mobility is in excellent agreement with experimental data for strained ${\mathrm{S}\mathrm{i}/\mathrm{S}\mathrm{i}}_{0.8}{\mathrm{Ge}}_{0.2}$ and for unstrained Si $p$-MOSFET's.
Local Meteoric Water Line of Northern Chile (18° S–30° S): An Application of Error-in-Variables Regression to the Oxygen and Hydrogen Stable Isotope Ratio of Precipitation

In this study, a revision of the previously published data on hydrogen (2H/1H) and oxygen (18O/16O) stable isotope ratio of precipitation in northern Chile is presented. Using the amount-weighted mean data and the combined standard deviation (related to both the weighted mean calculation and the spectrometric measurement), the equation of the local meteoric line calculated by error-in-variables regression is as follows: Northern Chile EIV-LMWL: δ2H = [(7.93 ± 0.15) δ18O] + [12.3 ± 2.1]. The slope is similar to that obtained by ordinary least square regression or other types of regression methods, whether weighted or not (e.g., reduced major axis or major axis) by the amount of precipitation. However, the error-in-variables regression is more accurate and suitable than ordinary least square regression (and other types of regression models) where statistical assumptions (i.e., no measurement errors in the x-axis) are violated. A generalized interval of δ2H = ±13.1‰ is also proposed to be used with the local meteoric line. This combines the confidence and prediction intervals around the regression line and appears to be a valid tool for distinguishing outliers or water samples with an isotope composition significantly different from local precipitation. The applicative examples for the Pampa del Tamarugal aquifer system, snow samples and the local geothermal waters are discussed.
Relative and absolute ages of Galactic globular clusters

Abstract We present a review of the latest work concerned with the relative and absolute ages of the Galactic globular clusters (GCs). Relative age-dating techniques generally divide into two types - those that measure a magnitude difference between two features in the color-magnitude diagram (i.e. Vertical Methods) and those that rely on color differences in the color-magnitude diagram (i.e. Horizontal Methods). Both types of diagnostics have been successfully applied and generally reach the same conclusions. Galactic GCs exhibit a mean age range of ~3 Gyr, smaller (or nonexistent) for metal-poor clusters and larger (as much as 6 Gyr) for metal-rich ones. Generally speaking, the inner-halo GCs are older and more uniform in age as compared with those outside of the solar circle. Furthermore, the tendency of GCs with predominantly red horizontal branches (HBs) located in the outer halo to be preferentially younger than those with bluer HBs closer to the Galactic center suggests that age is the second parameter which, in addition to metal abundance, controls the HB morphology. In particular, we present additional compelling evidence supporting this assertion using a detailed examination of new photometry for the classic second-parameter cluster pair NGC 288 and NGC 362. Moving on to the absolute ages, we note that the absolute ages of the most metal-poor Galactic GCs sets a lower limit on the age of the Universe. The preferred age indicator for absolute ages is the luminosity of the main-sequence turnoff because most theoretical models agree on the onset of hydrogen exhaustion in the cores of low-mass stars. Based on the technique of main-sequence fitting to field subdwarfs with Hipparcos parallaxes, we find an age of 11.6+1.4−1.1 Gyr for four metal-poor GCs with deep color-magnitude diagrams on a consistent photometric scale; this age is consistent with the results of a number of previous investigations.
Statistical dependence between orientation filter outputs used in a human-vision-based image code

We present an image coding scheme based on the properties of the early stages of the human visual system. The image signal is decomposed via even and odd symmetric frequency and orientation selective bandpass filters in analogy to the quadrature phase simple cell pairs in the visual cortex. The resulting analytic signal is transformed into a local amplitude and local phase representation in order to achieve a better match to its signal statistics. Both intra filter dependencies of the analytic signal and inter filter dependencies between different orientation filters are exploited by a suitable vector quantization scheme. Inter orientation filter dependencies are demonstrated by means of a statistical evaluation of the multidimensional probability density function. The results can be seen as an empirical confirmation of the suitability of vector quantization in subband coding. Instead of generating a code book by use of an conventional designalgorithm we suggest a feature specific partitioning of the multidimensional signal space matched to the properties of human vision. Using this coding scheme satisfactory image quality can be obtained with about 0. 78 bit/pixel.
Numerical solution of three‐dimensional velocity–vorticity Navier–Stokes equations by finite difference method

This paper describes the finite difference numerical procedure for solving velocity–vorticity form of the Navier–Stokes equations in three dimensions. The velocity Poisson equations are made parabolic using the false‐transient technique and are solved along with the vorticity transport equations. The parabolic velocity Poisson equations are advanced in time using the alternating direction implicit (ADI) procedure and are solved along with the continuity equation for velocities, thus ensuring a divergence‐free velocity field. The vorticity transport equations in conservative form are solved using the second‐order accurate Adams–Bashforth central difference scheme in order to assure divergence‐free vorticity field in three dimensions. The velocity and vorticity Cartesian components are discretized using a central difference scheme on a staggered grid for accuracy reasons. The application of the ADI procedure for the parabolic velocity Poisson equations along with the continuity equation results in diagonally dominant tri‐diagonal matrix equations. Thus the explicit method for the vorticity equations and the tri‐diagonal matrix algorithm for the Poisson equations combine to give a simplified numerical scheme for solving three‐dimensional problems, which otherwise requires enormous computational effort. For three‐dimensional‐driven cavity flow predictions, the present method is found to be efficient and accurate for the Reynolds number range 100⩽Re⩽2000. Copyright © 2004 John Wiley & Sons, Ltd.
Latin Americans show wide-spread Converso ancestry and the imprint of local Native ancestry on physical appearance

Historical records and genetic analyses indicate that Latin Americans trace their ancestry mainly to the admixture of Native Americans, Europeans and Sub-Saharan Africans. Using novel haplotype-based methods here we infer the sub-populations involved in admixture for over 6,500 Latin Americans and evaluate the impact of sub-continental ancestry on the physical appearance of these individuals. We find that pre-Columbian Native genetic structure is mirrored in Latin Americans and that sources of non-Native ancestry, and admixture timings, match documented migratory flows. We also detect South/East Mediterranean ancestry across Latin America, probably stemming from the clandestine colonial migration of Christian converts of non-European origin (Conversos). Furthermore, we find that Central Andean ancestry impacts on variation of facial features in Latin Americans, particularly nose morphology, possibly relating to environmental adaptation during the evolution of Native Americans.
Theory of the Star Formation Rate

Abstract This work presents a new physical model of the star formation rate (SFR), tested with a large set of numerical simulations of driven, supersonic, self-gravitating, magneto-hydrodynamic (MHD) turbulence, where collapsing cores are captured with accreting sink particles. The model depends on the relative importance of gravitational, turbulent, magnetic, and thermal energies, expressed through the virial parameter, αvir, the rms sonic Mach number, S,0, and the ratio of mean gas pressure to mean magnetic pressure, β0. The SFR is predicted to decrease with increasing αvir (stronger turbulence relative to gravity), and to depend weakly on S,0 and β0, for values typical of star forming regions (S,0≈4-20 and β0≈1-20). The star-formation simulations used to test the model result in an approximately constant SFR, after an initial transient phase. Both the value of the SFR and its dependence on the virial parameter found in the simulations agree very well with the theoretical predictions.
Chattering avoidance by second-order sliding mode control

Relying on the possibility of generating a second-order sliding motion by using, as control, the first derivative of the control signal instead of the actual control, a new solution to the problem of chattering elimination in variable structure control (VSC) is presented. Such a solution, inspired by the classical bang-bang optimal control strategy, is first depicted and expressed in terms of a control algorithm by introducing a suitable auxiliary problem involving a second-order uncertain system with unavailable velocity. Then, the applicability of the algorithm is extended, via suitable modifications, to the case of nonlinear systems with uncertainties of more general types. The proposed algorithm does not require the use of observers and differential inequalities and can be applied in practice by exploiting such commercial components as peak detectors or other approximated methods to evaluate the change of the sign of the derivative of the quantity accounting for the distance to the sliding manifold.