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Convergence of the shooting algorithm for singular optimal control problemsJun 29 2013In this article we propose a shooting algorithm for optimal control problems governed by systems that are affine in one part of the control variable. Finitely many equality constraints on the initial and final state are considered. We recall a second ... More

Singular solutions in optimal control: second order conditions and a shooting algorithmOct 28 2012Jan 07 2013In this article we study optimal control problems for systems that are affine in one part of the control variable. Finitely many equality and inequality constraints on the initial and final values of the state are considered. We investigate singular optimal ... More

A note on systems with ordinary and impulsive controlsDec 30 2013Feb 11 2015We investigate an everywhere defined notion of solution for control systems whose dynamics depend nonlinearly on the control $u$ and state $x,$ and are affine in the time derivative $\dot u.$ For this reason, the input $u,$ which is allowed to be Lebesgue ... More

On optimal control problems with impulsive commutative dynamicsNov 26 2013We consider control systems governed by nonlinear O.D.E.'s that are affine in the time-derivative du/dt of the control u. The latter is allowed to be an integrable, possibly of unbounded variation function, which gives the system an impulsive character. ... More

$\mathcal{L}^1$ limit solutions for control systemsJan 01 2014Feb 11 2015For a control Cauchy problem $$\dot x= {f}(t,x,u,v) +\sum_{\alpha=1}^m g_\alpha(x) \dot u_\alpha,\quad x(a)=\bar x, $$ on an interval $[a,b]$, we propose a notion of limit solution $x,$ verifying the following properties: i) $x$ is defined for $\mathcal{L}^1$ ... More

Optimal control of infinite dimensional bilinear systems: Application to the heat and wave equationsFeb 20 2016In this paper we consider second order optimality conditions for a bilinear optimal control problem governed by a strongly continuous semigroup operator, the control entering linearly in the cost function. We derive first and second order optimality conditions, ... More

Optimal control of infinite dimensional bilinear systems: Application to the heat and wave equationsFeb 20 2016Nov 14 2016In this paper we consider second order optimality conditions for a bilinear optimal control problem governed by a strongly continuous semigroup operator, the control entering linearly in the cost function. We derive first and second order optimality conditions, ... More

Optimal control of PDEs in a complex space setting; application to the Schrödinger equationMay 05 2016In this paper we discuss optimality conditions for abstract optimization problems over complex spaces. We then apply these results to optimal control problems with a semigroup structure. As an application we detail the case when the state equation is ... More

Necessary conditions involving Lie brackets for impulsive optimal control problemsMar 14 2019We obtain higher order necessary conditions for a minimum of a Mayer optimal control problem connected with a nonlinear, control-affine system, where the controls range on an m-dimensional Euclidean space. Since the allowed velocities are unbounded and ... More

A Higher-order Maximum Principle for Impulsive Optimal Control ProblemsMar 12 2019We consider a nonlinear control system, affine with respect to an unbounded control $u$ taking values in a closed cone of $\mathbb{R}^m$, and with drift depending on a second, ordinary control $a$, ranging on a bounded set. We provide first and higher ... More

Second order analysis of control-affine problems with scalar state constraintNov 06 2014Dec 23 2015In this article we establish new second order necessary and sufficient optimality conditions for a class of control-affine problems with a scalar control and a scalar state constraint. These optimality conditions extend to the constrained state framework ... More

Necessary conditions involving Lie brackets for impulsive optimal control problems; the commutative caseOct 16 2012In this article we study control problems with systems that are governed by ordinary differential equations whose vector fields depend linearly in the time derivatives of some components of the control. The remaining components are considered as classical ... More

Ensuring successful introduction of Wolbachia in natural populations of Aedes aegypti by means of feedback controlMar 17 2015The control of the spread of dengue fever by introduction of the intracellular parasitic bacterium Wolbachia in populations of the vector Aedes aegypti, is presently one of the most promising tools for eliminating dengue, in the absence of an efficient ... More

Effect of surfactant concentration on the responsiveness of a thermoresponsive copolymer/surfactant mixture with potential application on Smart foams formulationsJul 08 2017We studied a system formed by a mixture of a thermoresponsive negatively charged graft copolymer (Alg-g-PNIPAAm) with a brush-type structure, and an oppositely charged surfactant (DTAB), in bulk and at the air-solution interface. We performed experiments ... More

A shooting algorithm for problems with singular arcsJun 05 2012Jul 25 2013In this article we propose a shooting algorithm for a class of optimal control problems for which all control variables appear linearly. The shooting system has, in the general case, more equations than unknowns and the Gauss-Newton method is used to ... More

A Non-Existence Result for a Generalized Radial Brezis-Nirenberg ProblemJan 28 2019We develop a new method for estimating the region of the spectral parameter of a generalized Brezis--Nirenberg problem for which there are no, non trivial, smooth solutions. This new method combines the standard Rellich--Pohozaev argument with a Hardy ... More

Quadratic order conditions for bang-singular extremalsJul 01 2011Jun 29 2013This paper deals with optimal control problems for systems affine in the control variable. We consider nonnegativity constraints on the control, and finitely many equality and inequality constraints on the final state. First, we obtain second order necessary ... More

A polynomial-time relaxation of the Gromov-Hausdorff distanceOct 17 2016The Gromov-Hausdorff distance provides a metric on the set of isometry classes of compact metric spaces. Unfortunately, computing this metric directly is believed to be computationally intractable. Motivated by applications in shape matching and point-cloud ... More

Evolutionary-aided negotiation model for bilateral bargaining in Ambient Intelligence domains with complex utility functionsApr 16 2016Ambient Intelligence aims to offer personalized services and easier ways of interaction between people and systems. Since several users and systems may coexist in these environments, it is quite possible that entities with opposing preferences need to ... More

An application of John ellipsoids to the Szego kernel on unbounded convex domainsApr 05 2016We use convex geometry tools, in particular John ellipsoids, to obtain a size estimate for the Szeg\H{o} kernel on the boundary of a class of unbounded convex domains in $\mathbb{C}^n.$ Given a polynomial $b:\mathbb{R}^n \rightarrow \mathbb{R}$ satisfying ... More

The solution gap of the Brezis-Nirenberg problem on the hyperbolic spaceJul 19 2015Jan 19 2016We consider the positive solutions of the nonlinear eigenvalue problem $-\Delta_{\mathbb{H}^n} u = \lambda u + u^p, $ with $p=\frac{n+2}{n-2}$ and $u \in H_0^1(\Omega),$ where $\Omega$ is a geodesic ball of radius $\theta_1$ on $\mathbb{H}^n.$ For radial ... More

Donsker theorem for the Rosenblatt process and a binary market modelMar 03 2007In this paper, we prove a Donsker type approximation theorem for the Rosenblatt process, which is a selfsimilar stochastic process exhibiting long range dependence. By using numerical results and simulated data, we show that this approximation performs ... More

An improved bound for the non-existence of radial solutions of the Brezis-Nirenberg problem in HnJan 17 2016Jan 19 2016Using a Rellich-Pohozaev argument and Hardy's inequality, we derive an improved bound on the nonlinear eigenvalue for the non existence of radial solutions of a Brezis-Nirenberg problem, with Dirichlet boundary conditions, on a geodesic ball of Hn, for ... More

The Brezis--Nirenberg Problem on $\mathbb{S}^n$, in spaces of fractional dimensionMar 21 2015We consider the nonlinear eigenvalue problem, $$ -\Delta_{\mathbb{S}^n} u = \lambda u + |u|^{4/(n-2)} u, $$ with $u \in H_0^1(\Omega)$, where $\Omega$ is a geodesic ball in $\mathbb{S}^n$ contained in a hemisphere. In dimension 3, Bandle and Benguria ... More

The Brezis-Nirenberg problem for the Laplacian with a singular drift in $\mathbb{R}^n$ and $\mathbb{S}^n.$Mar 21 2015Feb 04 2019We consider the Brezis--Nirenberg problem for the Laplacian with a singular drift for a (geodesic) ball in both $\mathbb{R}^{n}$ and $\mathbb{S}^n$, $3 \le n \le 5$. The singular drift we consider derives from a potential which is symmetric around the ... More

Full Bayesian analysis for a class of jump-diffusion modelsAug 30 2007Feb 23 2008A new Bayesian significance test is adjusted for jump detection in a diffusion process. This is an advantageous procedure for temporal data having extreme valued outliers, like financial data, pluvial or tectonic forces records and others.

Maximum likelihood estimators and random walks in long memory modelsNov 04 2007Dec 19 2009We consider statistical models driven by Gaussian and non-Gaussian self-similar processes with long memory and we construct maximum likelihood estimators (MLE) for the drift parameter. Our approach is based on the approximation by random walks of the ... More

Deciphering the complex intermediate role of health coverage through insurance in the context of well-being by network analysisApr 19 2016Recent initiatives that overstate health insurance coverage for well-being conflict with the recognized antagonistic facts identified by the determinants of health that identify health care as an intermediate factor. By using a network of controlled interdependences ... More

Is a Brownian skew?Jan 05 2011We study the asymptotic behavior of the maximum likelihood estimator corresponding to the observation of a trajectory of a Skew Brownian motion, through a uniform time discretization. We characterize the speed of convergence and the limiting distribution ... More

Clustering subgaussian mixtures by semidefinite programmingFeb 22 2016May 10 2016We introduce a model-free relax-and-round algorithm for k-means clustering based on a semidefinite relaxation due to Peng and Wei. The algorithm interprets the SDP output as a denoised version of the original data and then rounds this output to a hard ... More

Fractional stochastic differential equation with discontinuous diffusionJul 22 2016In this paper we study a stochastic differential equation driven by a fractional Brownian motion with a discontinuous coefficient. We also give an approximation to the solution of the equation. This is a first step to define a fractional version of the ... More

A strong convergence to the Rosenblatt processSep 20 2011We give a strong approximation of Rosenblatt process via transport processes and we give the rate of convergence.

Who is Really Affected by Fraudulent Reviews? An analysis of shilling attacks on recommender systems in real-world scenariosAug 21 2018We present the results of an initial analysis conducted on a real-life setting to quantify the effect of shilling attacks on recommender systems. We focus on both algorithm performance as well as the types of users who are most affected by these attacks. ... More

Probably certifiably correct k-means clusteringSep 26 2015Apr 23 2016Recently, Bandeira [arXiv:1509.00824] introduced a new type of algorithm (the so-called probably certifiably correct algorithm) that combines fast solvers with the optimality certificates provided by convex relaxations. In this paper, we devise such an ... More

A polynomial-time relaxation of the Gromov-Hausdorff distanceOct 17 2016Oct 18 2016The Gromov-Hausdorff distance provides a metric on the set of isometry classes of compact metric spaces. Unfortunately, computing this metric directly is believed to be computationally intractable. Motivated by applications in shape matching and point-cloud ... More

Error estimates for splitting methods based on AMF-Runge-Kutta formulas for the time integration of advection diffusion reaction PDEsJan 12 2015The convergence of a family of AMF-Runge-Kutta methods (in short AMF-RK) for the time integration of evolutionary Partial Differential Equations (PDEs) of Advection Diffusion Reaction type semi-discretized in space is considered. The methods are based ... More

On the tightness of an SDP relaxation of k-meansMay 18 2015Recently, Awasthi et al. introduced an SDP relaxation of the $k$-means problem in $\mathbb R^m$. In this work, we consider a random model for the data points in which $k$ balls of unit radius are deterministically distributed throughout $\mathbb R^m$, ... More

Statistical Inference in Fractional Poisson Ornstein-Uhlenbeck ProcessDec 14 2017In this article, we study the problem of parameter estimation for a discrete Ornstein - Uhlenbeck model driven by Poisson fractional noise. Based on random walk approximation for the noise, we study least squares and maximum likelihood estimators. Thus, ... More

The Bishop-Phelps-Bollobás moduli of a Banach spaceApr 01 2013We introduce two Bishop-Phelps-Bollob\'as moduli which measure, for a given Banach space, what is the best possible Bishop-Phelps-Bollob\'as theorem in this space. We show that there is a common upper bound for these moduli for all Banach spaces and we ... More

Can we leverage rating patterns from traditional users to enhance recommendations for children?Aug 24 2018Recommender algorithms performance is often associated with the availability of sufficient historical rating data. Unfortunately, when it comes to children, this data is seldom available. In this paper, we report on an initial analysis conducted to examine ... More

Parameter estimation for random sampled Regression Model with Long Memory NoiseFeb 22 2019In this article, we present the least squares estimator for the drift parameter in a linear regression model driven by the increment of a fractional Brownian motion sampled at random times. For two different random times, Jittered and renewal process ... More

On generalized ARCH model with stationary liquidityJun 22 2018We study a generalized ARCH model with liquidity given by a general stationary process. We provide minimal assumptions that ensure the existence and uniqueness of the stationary solution. In addition, we provide consistent estimators for the model parameters ... More

Relax, no need to round: integrality of clustering formulationsAug 18 2014Apr 15 2015We study exact recovery conditions for convex relaxations of point cloud clustering problems, focusing on two of the most common optimization problems for unsupervised clustering: $k$-means and $k$-median clustering. Motivations for focusing on convex ... More

A new signal for scalar top bound state productionOct 01 1993We study the production and decay of a scalar \stst\ bound state \sigst\ at hadron supercolliders, where \st\ is the lighter stop eigenstate. If \st\ has no tree--level 2--body decays, the dominant decay modes of \sigst\ are $gg$ or, if $m_h < \mst \ll ... More

Production and Decay of Scalar Stoponium Bound StatesDec 02 1993In this paper we discuss possible signatures for the production of scalar \stst\ (stoponium) bound states \sigst\ at hadron colliders, where \st\ is the lighter scalar top eigenstate. We first study the decay of \sigst; explicit expressions are given ... More

Parton Model in Lorentz Invariant Non-Commutative SpaceMay 26 2004Aug 22 2004We consider the Lorentz invariant non-commutative QED and complete the Feynman rules for the theory up to the order $\theta^2$. In the Lorentz invariant version of the non-commutative QED the particles with fractional charges can be also considered. We ... More

Electromagnetic Response of Weyl SemimetalsMar 22 2013Jun 27 2013It has been suggested recently, based on subtle field-theoretical considerations, that the electromagnetic response of Weyl semimetals and the closely related Weyl insulators can be characterized by an axion term E.B with space and time dependent axion ... More

The Charm Quark Contribution to the Proton Structure FunctionOct 14 2006Dec 27 2006The charm quark structure function $F^c_2$ and the longitudinal structure function $F_l^p$ are directly sensitive to the gluon content of proton and therefore are crucial in understanding of proton structure function, in particular at low momentum transfer ... More

The decay of singlet scalar dark matter to unparticle and photonMay 06 2008We consider the unparticle physics introduced by Georgi and show that if the standard model is extended to include a singlet scalar as a dark matter candidate, there is a channel which leads to its decay to photon and unparticle. We calculate the decay ... More

Massive Neutrino in Non-commutative Space-timeDec 24 2007Apr 01 2008We consider the noncommutative standard model based on $SU(3)\times SU(2)\times U(1)$. We study the gauge transformation of right handed neutrino and its direct interaction with photon in the noncommutative space-time. We show that the massive Dirac neutrinos, ... More

Infinite order excitonic Bloch equations for asymmetric nanostructuresJul 04 2003We present a new exciton-based formalism for calculating the coherent response of asymmetric semiconductor multiple quantum well structures to ultra-short optical pulses valid to infinite order in the optical field and including the self-generated intraband ... More

Scalar StoponiumAug 18 1993We study the decays of a scalar \stst\ bound state \sigst, where \st\ is the lighter stop eigenstate. If \st\ has no tree--level 2--body decays, the dominant decay modes of \sigst\ are $gg$ or, if $m_h < \mst \ll \mstt$, a pair of light scalar Higgs bosons ... More

Phase boundaries of a spin-3/2 Blume-Emery-Griffiths model on a honeycomb latticeOct 11 2013The spin-3/2 Blume-Emery-Griffiths model on a honeycomb lattice is studied by Monte Carlo simulations with the goal to determine phase diagrams for a range of the model parameters and to investigate the nature of the phase transitions between the respective ... More

Flares on A-type stars: Evidence for heating of solar corona by nanoflares?Aug 11 2016We analyzed the occurrence rates of flares on stars of spectral types K, G, F, and A, observed by Kepler. We found that the histogram of occurrence frequencies of stellar flares is systematically shifted towards a high-energy tail for A-type stars compared ... More

The Formation Rates of Population III Stars and Chemical Enrichment of Halos during the Reionization EraJan 06 2009[abridged] The First Stars in the Universe form out of pristine primordial gas clouds that have been radiatively cooled to a few hundreds of degrees Kelvin either via molecular or atomic (Lyman-Alpha) hydrogen lines. This primordial mode of star formation ... More

Symmetry Adaptation Techniques in n-Photon Absorption SpectroscopyOct 27 1998We present some recent progress achieved in the application of symmetry adaptation techniques to n-photon absorption spectroscopy of rare earth ions in finite symmetry. More specifically, this work is concerned with the determination of the intensity ... More

Two-Photon Spectroscopy of Transition-Metal Ions in Cubical SymmetryOct 26 1998Symmetry adaptation techniques are applied to the determination of intensities of intra-configurational two-photon transitions for transition-metal ions in cubical symmetry. This leads to a simple model giving the polarization dependence of intensities ... More

An Alternative Basis for the Wigner-Racah Algebra of the Group SU(2)Dec 17 1997The Lie algebra of the classical group SU(2) is constructed from two quon algebras for which the deformation parameter is a common root of unity. This construction leads to (i) a not very well-known polar decomposition of the ladder generators of the ... More

Enhanced Sampling in the Well-Tempered EnsembleOct 26 2009Apr 13 2010We introduce the well-tempered ensemble (WTE) which is the biased ensemble sampled by well-tempered metadynamics when the energy is used as collective variable. WTE can be designed so as to have approximately the same average energy as the canonical ensemble ... More

Berry's Phase Induced Bose-Einstein condensation into a Vortex StateNov 23 1998The existence of a geometric phase in magnetic traps can be used to Bose condense a magnetically trapped atomic gas into a vortex state. We propose an experimental setup where a magnetic trap together with a blue detuned laser beam form a multiply connected ... More

Superconducting state in Fe-based materials and spin-fluctuation theory of pairingOct 28 2015Short review of the spin-fluctuation theory of superconductive pairing in iron-based pnictides and chalcogenides.

QCD_{1+1} with Static Quarks as Supersymmetric Quantum MechanicsFeb 09 1998We reexamine the solvable model problem of two static, fundamental quarks interacting with a SU(2) Yang-Mills field on a spatial circle, introduced by Engelhardt and Schreiber. If the quarks are at the same point, the model exhibits a quantum mechanical ... More

Massive Binary Black Holes in the Cosmic LandscapeJun 23 2009Binary black holes occupy a special place in our quest for understanding the evolution of galaxies along cosmic history. If massive black holes grow at the center of (pre-)galactic structures that experience a sequence of merger episodes, then dual black ... More

Einstein and the mystery of eternity of lifeApr 08 2009While Special and General Relativity are well known by a very large number of people, Einstein's religious convinctions are almost ignored. The paper focuses on what was his view about immortality. Einstein believed in Spinoza's view of God and in cosmic ... More

Effect of inelastic scattering on parametric pumpingAug 03 2001Pumping of charge in phase-coherent mesoscopic systems due to the out-of-phase modulation of two parameters has recently found considerable interest. We investigate the effect of inelastic processes on the adiabatically pumped current through a two terminal ... More

Hidden quantum pump effects in quantum coherent ringsFeb 27 2003Time periodic perturbations of an electron system on a ring are examined. For small frequencies periodic small amplitude perturbations give rise to side band currents which in leading order are inversely proportional to the frequency. These side band ... More

Dynamic scattering channels of a double barrier structureApr 02 2008We calculate analytically the Floquet scattering matrix for a periodically driven double-barrier structure. Our approach takes into account dynamical effects which become necessarily important when electrons propagate through a system subject to a fast ... More

Dissipation and noise in adiabatic quantum pumpsJan 16 2002We investigate the distribution function, the heat flow and the noise properties of an adiabatic quantum pump for an arbitrary relation of pump frequency $\omega$ and temperature. To achieve this we start with the scattering matrix approach for ac-transport. ... More

Remarks on the high-energy behaviour of cross-sections in weak-scale string theoriesSep 20 2001We consider the high-energy behaviour of processes involving Kaluza-Klein (KK) gravitons of weak-scale string theories. We discuss how form-factors derived within string theory modify the couplings of KK gravitons and thereby lead to an exponential fall-off ... More

Metastability in Two Dimensions and the Effective PotentialApr 12 1993We study analytically and numerically the decay of a metastable phase in (2+1)-dimensional classical scalar field theory coupled to a heat bath, which is equivalent to two-dimensional Euclidean quantum field theory at zero temperature. By a numerical ... More

New analyticity constraints on the high energy behavior of hadron-hadron cross sectionsJan 25 2006Mar 16 2006We here comment on a series of recent papers by Igi and Ishida[K. Igi and M. Ishida, Phys. Lett B 622, 286 (2005)] and Block and Halzen[M. M. Block and F. Halzen, Phys. Rev D 72, 036006 (2005)] that fit high energy $pp$ and $\bar pp$ cross section and ... More

Factorization Theorems for High Energy nn, gamma p and gamma gamma ScatteringFeb 17 2003The robustness of the factorization theorem for total cross sections, $\sigma_{nn}/\sigma_{\gamma p}=\sigma_{\gamma p}/\sigma_{\gamma\gamma}$, originally proved by Block and Kaidalov\cite{bk} for $nn$ (the even portion of $pp$ and $\pbar p$ scattering), ... More

Visualising a FuseOct 27 2010Nov 09 2010In this brief article I describe an experiment to illustrate how a fuse works. I have used this as part of lessons for my year 11 classes to demonstrate how an electrical fuse 'blows' when too high a current passes through it.

General models of Einstein gravity with a non-Newtonian weak-field limitJan 08 2009We investigate Einstein theories of gravity, coupled to a scalar field \vphi and point-like matter, which are characterized by a scalar field-dependent matter coupling function e^{H(\vphi)}. We show that under mild constraints on the form of the potential ... More

Two Loop Electroweak Bosonic Corrections to the Muon Decay LifetimeNov 04 2002Nov 19 2002A review of the calculation of the two loop bosonic corrections to $\Delta r$ is presented. Factorization and matching onto the Fermi model are discussed. An approximate formula, describing the quantity over the interesting range of Higgs boson mass values ... More

Structure and stability of Al$_2$FeJul 01 2011We employ first principles total energy and phonon calculations to address the structure and stability of Al$_2$Fe. This structure, which is reported as stable in the assessed Al-Fe phase diagram, is distinguished by an unusually low triclinic symmetry. ... More

Stability of Fe-based alloys with structure type C6Cr23Jul 23 2004Bulk metallic glass forms when liquid metal alloys solidify without crystalization. In the search for Iron-based bulk glass-forming alloys of the metal-metalloid type (Fe-B- and Fe-C-based), crystals based on the structural prototype C6Cr23 often preempt ... More

Cohesive energies of Fe-based glass-forming alloysMay 13 2004We calculate the cohesive energies of Fe-based glass-forming alloys in the B-Fe-Y-Zr quaternary system. Our {\it ab-initio} calculations fully relax atomic positions and lattice parameters yielding enthalpies of mixing at T=0K. We examine both the known ... More

Efficiently Extracting Energy from Cosmological NeutrinosJul 02 2013Aug 20 2013Detecting the extremely low-energy neutrinos that form the Cosmic Neutrino Background (CNB) presents many experimental challenges, but pursuing this elusive goal is still worthwhile because these weakly-interacting particles could provide a new window ... More

Beyond the Kolmogorov Johnson Mehl Avrami kinetics: inclusion of the spatial correlationApr 16 2003The Kolmogorov-Johnson-Mehl-Avrami model, which is a nucleation and growth poissonian process in space, has been implemented by taking into account spatial correlation among nuclei. This is achieved through a detailed study of a system of distinguishable ... More

On the stability operator for MOTS and the 'core' of Black HolesOct 13 2012Small deformations of marginally (outer) trapped surfaces are considered by using their stability operator. In the case of spherical symmetry, one can use these deformations on any marginally trapped round sphere to prove several interesting results. ... More

On the boundary of the region containing trapped surfacesDec 15 2008The boundary of the region in spacetime containing future-trapped closed surfaces is considered. In asymptotically flat spacetimes, this boundary does not need to be the event horizon nor a dynamical/trapping horizon. Some properties of this boundary ... More

The universal 'energy' operatorAug 12 2006Oct 05 2006The "positive square" of any tensor is presented in a universal and unified manner, valid in Lorentzian manifolds of arbitrary dimension, and independently of any (anti)-symmetry properties of the tensor. For rank-m tensors, the positive square has rank ... More

Trapped surfaces, horizons and exact solutions in higher dimensionsMar 30 2002May 18 2002A very simple criterion to ascertain if (D-2)-surfaces are trapped in arbitrary D-dimensional Lorentzian manifolds is given. The result is purely geometric, independent of the particular gravitational theory, of any field equations or of any other conditions. ... More

Applications of Super-Energy TensorsDec 13 1999In this contribution I intend to give a summary of the new relevant results obtained by using the general superenergy tensors. After a quick review of the definition and properties of these tensors, several of their mathematical and physical applications ... More

A New Type of Singularity TheoremDec 10 2007A new type of singularity theorem, based on spatial averages of physical quantities, is presented and discussed. Alternatively, the results inform us of when a spacetime can be singularity-free. This theorem provides a decisive observational difference ... More

Weyl Semimetal from the Honeycomb Array of Topological Insulator NanowiresNov 15 2012We show that isolated Weyl nodes can arise in a system of parallel topological insulator nano-wires arranged in a honeycomb fashion. This introduces another theoretical example of a topological semi-metal phase with more than one pair of Weyl nodes and ... More

Spin fluctuations of non-equilibrium electrons and excitons in semiconductorsNov 24 2015Effects related with deviations from thermodynamic equilibrium take a special place in the modern physics. Among those, non-equilibrium phenomena in quantum systems attract the highest interest. To date, the experimental technique of spin noise spectroscopy ... More

Spin noise of localized electrons: Interplay of hopping and hyperfine interactionMar 27 2015Apr 17 2015The theory of spin fluctuations is developed for an ensemble of localized electrons taking into account both hyperfine interaction of electron and nuclear spins and electron hopping between the sites. The analytical expression for the spin noise spectrum ... More

Effect of structure anisotropy on low temperature spin dynamics in quantum wellsFeb 07 2007Spin dynamics of two-dimensional electron gas confined in an asymmetrical quantum well is studied theoretically in the regime where the scattering frequency is comparable with the spin precession frequency due to the conduction band spin splitting. The ... More

Normal modes for metric fluctuations in a class of higher-dimensional backgroundsApr 01 1996Jan 13 1997We discuss a gauge invariant approach to the theory of cosmological perturbations in a higher-dimensonal background. We find the normal modes which diagonalize the perturbed action, for a scalar field minimally coupled to gravity, in a higher-dimensional ... More

Quantum Squeezing and Cosmological Entropy ProductionJul 20 1993The entropy growth in a cosmological process of pair production is completely determined by the associated squeezing parameter, and is insensitive to the number of particles in the initial state. The total produced entropy may represent a significant ... More

Entropy Production in the Cosmological Amplification of the Vacuum FluctuationsJan 12 1993We estimate the entropy associated to a background of squeezed cosmic gravitons, and we argue that the process of cosmological pair production from the vacuum may explain the large amount of entropy of our present universe.

The breathing-mode giant monopole resonance and the surface compressibility in the relativistic mean-field theoryNov 17 2008The breathing-mode isoscalar giant monopole resonance (GMR) is investigated using the generator coordinate method within the relativistic mean-field (RMF) theory. Employing the Lagrangian models of the nonlinear-$\sigma$ model (NL$\sigma$), the scalar-vector ... More

Scalar-vector Lagrangian without nonlinear self-interactions of bosonic fields in the relativistic mean-field theoryMay 05 2008Jul 03 2008A new Lagrangian model without nonlinear scalar self-interactions in the relativistic mean-field (RMF) theory is proposed. Introducing terms for scalar-vector interactions (SVI), we have developed a RMF Lagrangian model for finite nuclei and nuclear matter. ... More

Compressibility of Nuclear Matter from Shell Effects in NucleiApr 13 1999The compressibility of nuclear matter has received significant attention in the last decade and a variety of approaches have been employed to extract this fundamental property of matter. Recently, significant differences have emerged between the results ... More

ON THE LOW-TEMPERATURE ORDERING OF THE 3D ATIFERROMAGNETIC THREE-STATE POTTS MODELApr 24 1995The antiferromagnetic three-state Potts model on the simple-cubic lattice is studied using Monte Carlo simulations. The ordering in a medium temperature range below the critical point is investigated in detail. Two different regimes have been observed: ... More

CRITICAL EXPONENTS OF THE 3D ANTIFERROMAGNETIC THREE-STATE POTTS MODEL USING THE COHERENT-ANOMALY METHODFeb 22 1995Feb 25 1995The antiferromagnetic three-state Potts model on the simple-cubic lattice is studied using the coherent-anomaly method (CAM). The CAM analysis provides the estimates for the critical exponents which indicate the XY universality class, namely $\alpha=-0.011 ... More

Modelling sublimation and atomic layer epitaxy in the presence of competing surface reconstructionsOct 09 2000Dec 01 2000We present a solid-on-solid model of a binary AB compound, where atoms of type A in the topmost layer interact via anisotropic interactions different from those inside the bulk. Depending on temperature and particle flux, this model displays surface reconstructions ... More

Quantum Estimation by Local ObservablesJan 30 2004Jul 20 2004Quantum estimation theory provides optimal observations for various estimation problems for unknown parameters in the state of the system under investigation. However, the theory has been developed under the assumption that every observable is available ... More