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Normalizing Flows on Riemannian ManifoldsNov 07 2016Nov 09 2016We consider the problem of density estimation on Riemannian manifolds. Density estimation on manifolds has many applications in fluid-mechanics, optics and plasma physics and it appears often when dealing with angular variables (such as used in protein ... More

DRAW: A Recurrent Neural Network For Image GenerationFeb 16 2015May 20 2015This paper introduces the Deep Recurrent Attentive Writer (DRAW) neural network architecture for image generation. DRAW networks combine a novel spatial attention mechanism that mimics the foveation of the human eye, with a sequential variational auto-encoding ... More

Interaction Networks for Learning about Objects, Relations and PhysicsDec 01 2016Reasoning about objects, relations, and physics is central to human intelligence, and a key goal of artificial intelligence. Here we introduce the interaction network, a model which can reason about how objects in complex systems interact, supporting ... More

Variational Inference with Normalizing FlowsMay 21 2015Jun 14 2016The choice of approximate posterior distribution is one of the core problems in variational inference. Most applications of variational inference employ simple families of posterior approximations in order to allow for efficient inference, focusing on ... More

Variational Information Maximisation for Intrinsically Motivated Reinforcement LearningSep 29 2015The mutual information is a core statistical quantity that has applications in all areas of machine learning, whether this is in training of density models over multiple data modalities, in maximising the efficiency of noisy transmission channels, or ... More

4d Lorentzian Holst action with topological termsFeb 19 2009We study the Hamiltonian formulation of the general first order action of general relativity compatible with local Lorentz invariance and background independence. The most general simplectic structure (compatible with diffeomorphism invariance and local ... More

Variational inference for Monte Carlo objectivesFeb 22 2016Jun 01 2016Recent progress in deep latent variable models has largely been driven by the development of flexible and scalable variational inference methods. Variational training of this type involves maximizing a lower bound on the log-likelihood, using samples ... More

The theta parameter in loop quantum gravity: effects on quantum geometry and black hole entropyNov 20 2007The precise analog of the theta-quantization ambiguity of Yang-Mills theory exists for the real SU(2) connection formulation of general relativity. As in the former case theta labels representations of large gauge transformations, which are super-selection ... More

Variational Intrinsic ControlNov 22 2016In this paper we introduce a new unsupervised reinforcement learning method for discovering the set of intrinsic options available to an agent. This set is learned by maximizing the number of different states an agent can reliably reach, as measured by ... More

Learning and Querying Fast Generative Models for Reinforcement LearningFeb 08 2018A key challenge in model-based reinforcement learning (RL) is to synthesize computationally efficient and accurate environment models. We show that carefully designed generative models that learn and operate on compact state representations, so-called ... More

Stochastic Backpropagation and Approximate Inference in Deep Generative ModelsJan 16 2014May 30 2014We marry ideas from deep neural networks and approximate Bayesian inference to derive a generalised class of deep, directed generative models, endowed with a new algorithm for scalable inference and learning. Our algorithm introduces a recognition model ... More

Periodical plane puzzles with numbersJun 06 2011Consider a periodical (in two independent directions) tiling of the plane with polygons (faces). In this article we shall only give examples using squares, regular hexagons, equilateral triangles and parallelograms ("unions" of two equilateral triangles). ... More

A contribution for a mathematical classification of square tilesJun 16 2012In this article we study some geometric properties of a non-trivial square tile (a non-trivial square tile is a non-constant function on a square). Consider infinitely many copies of this single square tile and cover the plane with them, without gaps ... More

Semi-Supervised Learning with Deep Generative ModelsJun 20 2014Oct 31 2014The ever-increasing size of modern data sets combined with the difficulty of obtaining label information has made semi-supervised learning one of the problems of significant practical importance in modern data analysis. We revisit the approach to semi-supervised ... More

Energy transport and fluctuations in small conductorsOct 22 2010Dec 22 2010The Landauer-B\"uttiker formalism provides a simple and insightful way for investigating many phenomena in mesoscopic physics. By this approach we derive general formulas for the energy properties and apply them to the basic setups. Of particular interest ... More

Markov subshifts and partial representation of F_nJul 03 2001In this paper we fix a set \Lambda^* of positive elements of the free group F_n (e.g. the set of finite words occurring in a Markov subshift) as well as n partial isometries on a Hilbert space H. Based on these we define a map S:F_n --> L(H) which we ... More

Random graph model with power-law distributed triangle subgraphsDec 17 2004Apr 11 2005Clustering is well-known to play a prominent role in the description and understanding of complex networks, and a large spectrum of tools and ideas have been introduced to this end. In particular, it has been recognized that the abundance of small subgraphs ... More

Constructing a class of solutions for the Hamilton-Jacobi equation in field theorySep 12 2007A new approach leading to the formulation of the Hamilton-Jacobi equation for field theories is investigated within the framework of jet-bundles and multi-symplectic manifolds. An algorithm associating classes of solutions to given sets of boundary conditions ... More

Can We Prove Goldbach's Conjecture?Jul 21 2010Dec 26 2010In this paper we will propose a strategy to prove Goldbach's conjecture: every even integer greater than 2 can be written as the sum of two primes.

Introduction to Perl module lb2d.pm 0.1 for basic Lattice Boltzmann simulationsFeb 02 2012Feb 03 2014The Lattice Boltzmann method has been gaining acceptance for hydrodynamic problems involving complex boundaries, non-equilibrium dynamics and interfacial phenomena in multiphase or multicomponent systems. lb2d.pm is a Perl module offering a clear framework ... More

Unsupervised Learning of 3D Structure from ImagesJul 03 2016A key goal of computer vision is to recover the underlying 3D structure from 2D observations of the world. In this paper we learn strong deep generative models of 3D structures, and recover these structures from 3D and 2D images via probabilistic inference. ... More

Towards Conceptual CompressionApr 29 2016We introduce a simple recurrent variational auto-encoder architecture that significantly improves image modeling. The system represents the state-of-the-art in latent variable models for both the ImageNet and Omniglot datasets. We show that it naturally ... More

Towards Principled Unsupervised LearningNov 19 2015Dec 03 2015General unsupervised learning is a long-standing conceptual problem in machine learning. Supervised learning is successful because it can be solved by the minimization of the training error cost function. Unsupervised learning is not as successful, because ... More

One-Shot Generalization in Deep Generative ModelsMar 16 2016May 25 2016Humans have an impressive ability to reason about new concepts and experiences from just a single example. In particular, humans have an ability for one-shot generalization: an ability to encounter a new concept, understand its structure, and then be ... More

Classical Statistics and Statistical Learning in Imaging NeuroscienceMar 06 2016May 04 2016Neuroimaging research has predominantly drawn conclusions based on classical statistics, including null-hypothesis testing, t-tests, and ANOVA. Throughout recent years, statistical learning methods enjoy increasing popularity, including cross-validation, ... More

The Crossed Product by a Partial Endomorphism and the Covariance AlgebraMar 21 2005Given a local homeomorphism \sigma:U -> X where U is a clopen subset of an compact and Hausdorff topological space X, we obtain the possible transfer operators L_\rho which may occur for \al:C(X) -> C(U) given by \al(f)=f\sigma. We obtain examples of ... More

Families of Optimal Binary Non-MDS Erasure CodesSep 08 2016We introduce a definition for \emph{Families of Optimal Binary Non-MDS Erasure Codes} for $[n, k]$ codes over $GF(2)$, and propose an algorithm for finding those families by using hill climbing techniques over Balanced XOR codes. Due to the hill climbing ... More

$\mathcal{W}$-algebra constraints and topological recursion for $A_N$-singularityFeb 29 2016We derive a Bouchard--Eynard type topological recursion for the total descendant potential of $A_N$-singularity. Our argument relies on a certain twisted representation of a Heisenberg Vertex Operator Algebra (VOA) constructed via the periods of $A_N$-singularity. ... More

Response of VIRGO detectors to pre-big-bang gravitonsAug 04 2001The sensitivity achievable by a pair of VIRGO detectors to stochastic and isotropic gravitational wave backgrounds produced in pre-big-bang models is discussed in view of the development of a second VIRGO interferometer. We describe a semi-analytical ... More

Violation of the Energy Conservation Law in Lorentz-Dirac Equations for More Than One ChargeDec 30 1994An exact solution of Lorentz-Dirac equations where the energy conservation law is violated, is described herein for the case of two charges.

Interference Rate of Radiation of 2 Charges in Circular MotionDec 30 1994We present an exact formula for the computation of the interference rate of radiation in the case of two charges revolving with constant angular velocity at opposite ends of a diameter in a fixed circle. The formula is valid for arbitrary velocities of ... More

Projected Quasi-particle Perturbation theoryMay 24 2012The BCS and/or HFB theories are extended by treating the effect of four quasi-particle states perturbatively. The approach is tested on the pairing hamiltonian, showing that it combines the advantage of standard perturbation theory valid at low pairing ... More

C*-algebras Associated do Stationary Ordered Bratteli DiagramsAug 18 2011Aug 23 2011In this paper, we introduce a C*-algebra associated to any substitution (via its Bratteli diagram model). We show that this C*-algebra contains the partial crossed product C*-algebra of the corresponding Bratteli-Vershik system and show that these algebras ... More

Leavitt path algebras as partial skew group ringsFeb 13 2012We realize Leavitt path algebras as partial skew group rings and give new proofs, based on partial skew group ring theory, of the Cuntz-Krieger uniqueness theorem and simplicity criteria for Leavitt path algebras.

(M + 1)-step shift spaces that are not conjugate to M-step shift spacesMay 28 2014Jun 27 2014Recently Ott, Tomforde and Willis proposed a new approach for one sided shift spaces over infinite alphabets. In this new approach the conjugacy classes of shifts of finite type, edge shifts, and M-step shifts are distinct and the authors conjecture that ... More

A Family of Exactly Solvable Radial Quantum Systems on Space of Non-Constant Curvature with Accidental Degeneracy in the SpectrumOct 04 2010Dec 15 2010A novel family of exactly solvable quantum systems on curved space is presented. The family is the quantum version of the classical Perlick family, which comprises all maximally superintegrable 3-dimensional Hamiltonian systems with spherical symmetry. ... More

Artin algebras of finite type and finite categories of $Δ$-good modulesMay 13 2015We give an alternative proof to the fact that if the square of the infinite radical of the module category of an Artin algebra is equal to zero then the algebra is of finite type by making use of the theory of postprojective and preinjective partitions. ... More

Holographic formula for the determinant of the scattering operator in thermal AdSDec 11 2008Aug 26 2009A 'holographic formula' expressing the functional determinant of the scattering operator in an asymptotically locally anti-de Sitter(ALAdS) space has been proposed in terms of a relative functional determinant of the scalar Laplacian in the bulk. It stems ... More

Thermodynamics of small superconductors with fixed particle numberFeb 10 2012The Variation After Projection approach is applied for the first time to the pairing hamiltonian to describe the thermodynamics of small systems with fixed particle number. The minimization of the free energy is made by a direct diagonalization of the ... More

On the description of two-particle transfer in superfluid systemsOct 26 2012Oct 29 2012Exact results of pair transfer probabilities for the Richardson model with equidistant or random level spacing are presented. The results are then compared either to particle-particle random phase approximation (ppRPA) in the normal phase or quasi-particle ... More

Graph C*-algebras, branching systems and the Perron-Frobenius operatorAug 07 2009Jul 03 2014In this paper we show how to produce a large number of representations of a graph C*-algebra in the space of the bounded linear operators in $L^2(X,\mu)$. These representations are very concrete and, in the case of graphs that satisfy condition (K), we ... More

Statistical inference for time-inhomogeneous volatility modelsJun 22 2004This paper offers a new approach for estimating and forecasting the volatility of financial time series. No assumption is made about the parametric form of the processes. On the contrary, we only suppose that the volatility can be approximated by a constant ... More

The criteria of Riesz, Hardy-Littlewood et al. for the Riemann Hypothesis revisited using similar functionsJan 07 2006The original criteria of Riesz and of Hardy-Littlewood concerning the truth of the Riemann Hypothesis (RH) are revisited and further investigated in light of the recent formulations and results of Maslanka and of Baez-Duarte concerning a representation ... More

Riemann Hypothesis: a special case of the Riesz and Hardy-Littlewood wave and a numerical treatment of the Baez-Duarte coefficients up to some billions in the k-variableSep 17 2006We consider the Riesz and Hardy-Littlewood wave i.e. a ``critical function'' whose behaviour is concerned with the possible truth of the Riemann Hypothesis (RH). The function is studied numerically for the case alpha = 15/2 and beta = 4 in some range ... More

The evolution of the rest-frame J- and H-band luminosity function of galaxies to z=3.5Nov 30 2011Nov 12 2012We present the rest-frame J- and H-band luminosity function (LF) of field galaxies, based on a deep multi-wavelength composite sample from the MUSYC, FIRES and FIREWORKS survey public catalogues, covering a total area of 450 arcmin^2. The availability ... More

Stray capacitances in the watt balance operation: electrostatic forcesFeb 01 2014In a watt balance, stray capacitances exist between the coil and the magnet. Since the electric current flowing in the coil originates a difference between the coil and magnet electric-potentials, their electrostatic interactions must be taken into account. ... More

Sensitivity of wide band detectors to quintessential gravitonsMay 20 1999There are no reasons why the energy spectra of the relic gravitons, amplified by the pumping action of the background geometry, should not increase at high frequencies. A typical example of this behavior are quintessential inflationary models where the ... More

Minimal model of financial stylized factsNov 27 2010Mar 09 2011In this work we afford the statistical characterization of a linear Stochastic Volatility Model featuring Inverse Gamma stationary distribution for the instantaneous volatility. We detail the derivation of the moments of the return distribution, revealing ... More

Branching systems and representations of Cohn-Leavitt path algebras of separated graphsMar 06 2014We construct for each separated graph (E;C) a family of branching systems over a set X and show how each branching system induces a representation of the Cohn-Leavitt path algebra associated to (E;C) as homomorphisms over the module of functions in X. ... More

Unitary equivalence of representations of graph algebras and branching systemsNov 24 2009In this paper we show that, for a class of countable graphs, every representation of the associated graph algebra in a separable Hilbert space is unitarily equivalent to a representation obtained via branching systems.

Perron-Frobenius operators and representations of the Cuntz-Krieger algebras for infinite matricesAug 06 2008In this paper we extend work of Kawamura, see kawamura, for Cuntz-Krieger algebras O_A for infinite matrices A. We generalize the definition of branching systems, prove their existence for any given matrix A and show how they induce some very concrete ... More

Ultragraphs and shifts spaces over infinite alphabetsOct 15 2015Oct 16 2015In this paper we further develop the theory of one sided shift spaces over infinite alphabets, characterizing one-step shifts as edge shifts of ultragraphs and partially answering a conjecture regarding shifts of finite type (we show that there exists ... More

Discrete Conley Index for Zero-dimensional Basic SetsApr 15 2015A theorem is established where the computation of the discrete Conley index for zero dimensional basic sets is given with respect to the dynamical information contained in the associated structure matrices. A classification of the reduced homology Conley ... More

Global phase portrait of a SIS modelMay 28 2012Jun 05 2012In the qualitative theory of ordinary differential equations, we can find many papers whose objective is the classification of all the possible topological phase portraits of a given family of differential system. Most of the studies rely on systems with ... More

Sensitivity of a VIRGO pair to stochastic GW backgroundsAug 16 2000The sensitivity of a pair of VIRGO interferometers to gravitational waves backgrounds (GW) of cosmological origin is analyzed for the cases of maximal and minimal overlap of the two detectors. The improvements in the detectability prospects of scale-invariant ... More

Joining relations under discrete uncertaintyNov 01 2012In this paper we introduce and experimentally compare alternative algorithms to join uncertain relations. Different algorithms are based on specific principles, e.g., sorting, indexing, or building intermediate relational tables to apply traditional approaches. ... More

A class of adding machine and Julia setsAug 20 2015In this work we define a stochastic adding machine associated to the Fibonacci base and to a probabilities sequence $\overline{p}=(p_i)_{i\geq 1}$. We obtain a Markov chain whose states are the set of nonnegative integers. We study probabilistic properties ... More

Dynamical Casimir effect with $δ-δ^{\prime}$ mirrorsJan 22 2016Nov 01 2016We calculate the spectrum and the total rate of created particles for a real massless scalar field in $1+1$ dimensions, in the presence of a partially transparent moving mirror simulated by a Dirac $\delta-\delta^{\prime}$ point interaction. We show that, ... More

Other representations of the Riemann Zeta function and an additional reformulation of the Riemann HypothesisJul 16 2007New expansions for some functions related to the Zeta function in terms of the Pochhammer's polynomials are given (coefficients b(k), d(k), d_(k) and d__(k). In some formal limit our expansion b(k) obtained via the alternating series gives the regularized ... More

Tricritical behavior of soft nematic elastomersDec 12 2013We propose a lattice statistical model to investigate the phase diagrams and the soft responses of nematic liquid-crystal elastomers. Using suitably scaled infinite-range interactions, we obtain exact self-consistent equations for the tensor components ... More

A method for solving nonlinear differential equations: an application to $λφ^4$ modelMar 31 2014Jan 27 2015Recently, it has been great interest in the development of methods for solving nonlinear differential equations directly. Here, it is shown an algorithm based on Pad\'e approximants for solving nonlinear partial differential equations without requiring ... More

The classical Taub-Nut System: factorization, spectrum generating algebra and solution to the equations of motionNov 13 2014Jan 02 2015The formalism of SUSYQM (SUperSYmmetric Quantum Mechanics) is properly modified in such a way to be suitable for the description and the solution of a classical maximally superintegrable Hamiltonian System, the so-called Taub-Nut system, associated with ... More

Approaching Maximum Embedding Efficiency on Small Covers Using Staircase-Generator CodesAug 10 2015We introduce a new family of binary linear codes suitable for steganographic matrix embedding. The main characteristic of the codes is the staircase random block structure of the generator matrix. We propose an efficient list decoding algorithm for the ... More

Polyakov formulas for GJMS operators from AdS/CFTMar 04 2008Apr 15 2008We argue that the AdS/CFT calculational prescription for double-trace deformations leads to a holographic derivation of the conformal anomaly, and its conformal primitive, associated to the whole family of conformally covariant powers of the Laplacian ... More

Assessing the Predictive Power of Galaxy Formation Models with the Rest-Frame Optical Luminosity Functions at 2.0<z<3.3Jan 10 2008We compare recently measured rest-frame V-band luminosity functions (LFs) of galaxies at redshifts 2.0<z<3.3 to predictions of semianalytic models by De Lucia & Blaizot and Bower et al. and hydrodynamic simulations by Dave et al. The models succeed for ... More

Assessing the Predictive Power of Galaxy Formation Models: A Comparison of Predicted and Observed Rest-Frame Optical Luminosity Functions at 2.0<z<3.3May 29 2007Jan 07 2008Recent galaxy formation models successfully reproduce the local luminosity function (LF) of galaxies by invoking mechanisms to suppress star formation in low- and high-mass galaxies. As these models are optimized to fit the LF at low redshift, a crucial ... More

AdS Chern-Simons Gravity induces Conformal GravityNov 21 2013Dec 25 2013The leitmotif of this paper is the question of whether four- and higher even-dimensional Conformal Gravities do have a Chern-Simons pedigree. We show that Weyl gravity can be obtained as dimensional reduction of a five-dimensional Chern-Simons action ... More

Determinant and Weyl anomaly of Dirac operator: a holographic derivationNov 07 2011Nov 18 2011We present a holographic formula relating functional determinants: the fermion determinant in the one-loop effective action of bulk spinors in an asymptotically locally AdS background, and the determinant of the two-point function of the dual operator ... More

Partition functions and double-trace deformations in AdS/CFTFeb 20 2007Feb 19 2008We study the effect of a relevant double-trace deformation on the partition function (and conformal anomaly) of a CFT at large N and its dual picture in AdS. Three complementary previous results are brought into full agreement with each other: bulk and ... More

On the AdS Higher Spin / O(N) Vector Model Correspondence: degeneracy of the holographic imageMar 10 2006May 04 2006We explore the conjectured duality between the critical O(N) vector model and minimal bosonic massless higher spin (HS) theory in AdS. In the boundary free theory, the conformal partial wave expansion (CPWE) of the four-point function of the scalar singlet ... More

Scattering coefficients and bound states for high-energy transparent $δ-δ^{\prime}$ interactionsJul 21 2016We propose a model for energy-dependent $\delta-\delta^{\prime}$ interactions which yields scattering coefficients exhibiting full transmission for high-energy incident particles, also computing the bound solutions in one-dimension nonrelativistic quantum ... More

Polyelectrolyte intelligent gels. Design and applicationsJun 21 2012In this chapter polyelectrolyte intelligent gels are examined along three broad lines. The effects of different physical, chemical and biological stimuli on gels response are analysed and mechanisms of response are outlined. The broad range of biomedical ... More

Security for Wiretap Networks via Rank-Metric CodesDec 29 2007May 02 2008The problem of securing a network coding communication system against a wiretapper adversary is considered. The network implements linear network coding to deliver $n$ packets from source to each receiver, and the wiretapper can eavesdrop on $\mu$ arbitrarily ... More

Fast Encoding and Decoding of Gabidulin CodesJan 16 2009Apr 05 2009Gabidulin codes are the rank-metric analogs of Reed-Solomon codes and have a major role in practical error control for network coding. This paper presents new encoding and decoding algorithms for Gabidulin codes based on low-complexity normal bases. In ... More

The Theory of Quaternion Matrix DerivativesOct 01 2014A systematic theory is introduced for calculating the derivatives of quaternion matrix function with respect to quaternion matrix variables. The proposed methodology is equipped with the matrix product rule and chain rule and it is able to handle both ... More

The Sturm-Liouville problem and the Polar Representation TheoremJun 29 2010The polar representation theorem for the n-dimensional time-dependent linear Hamiltonian system with continuous coefficients, states that, given two isotropic solutions (Q1, P1) and (Q2, P2), with the identity matrix as Wronskian,the formula Q2 = rcos(f), ... More

Casimir force between $δ-δ^{\prime}$ mirrors transparent at high frequenciesJul 21 2016Nov 01 2016We investigate, in the context of a real massless scalar field in $1+1$ dimensions, models of partially reflecting mirrors simulated by Dirac $\delta-\delta^{\prime}$ point interactions. In the literature, these models do not exhibit full transparency ... More

Dependence of microwave absorption properties on ferrite volume fraction in MnZn ferrite/rubber radar absorbing materialsMay 30 2011We report the analysis of measurements of the complex magnetic permeability ($\mu_r$) and dielectric permittivity ($\epsilon_r$) spectra of a rubber radar absorbing material (RAM) with various MnZn ferrite volume fractions. The transmission/reflection ... More

Designing a robustly metallic noncenstrosymmetric ruthenate oxide with large thermopower anisotropyOct 04 2013Mar 18 2014The existence of approximately 30 noncentrosymmetric metals (NCSM) suggests a contraindication between crystal structures without inversion symmetry and metallic behavior. Those containing oxygen are especially scarce. Here we propose and demonstrate ... More

Flexible behavioral capture-recapture modellingJan 24 2014We develop some new strategies for building and fitting new flexible classes of parametric capture-recapture models for closed populations which can be used to address a better understanding of behavioural patterns. We first rely on a conditional probability ... More

A Unifying Approach to Quaternion Adaptive Filtering: Addressing the Gradient and ConvergenceOct 17 2013A novel framework for a unifying treatment of quaternion valued adaptive filtering algorithms is introduced. This is achieved based on a rigorous account of quaternion differentiability, the proposed I-gradient, and the use of augmented quaternion statistics ... More

A Self-Consistent Extrapolation Method for the Complex Permittivity and Permeability Based on Finite Frequency DataFeb 14 2014Dec 04 2014We describe a method of extrapolation based on a "truncated" Kramers-Kronig relation for the complex permittivity ($\epsilon$) and permeability ($\mu$) parameters of a material, based on finite frequency data. Considering a few assumptions, such as the ... More

The geometry of quadratic polynomial differential systems with a finite and an infinite saddle-node (A,B)Mar 06 2013The goal is to make a global study of the family QsnSN of all real quadratic polynomial differential systems which have a finite semi-elemental saddle-node and an infinite saddle-node formed by the collision of two infinite singular points. This family ... More

Global phase portraits of quadratic polynomial differential systems with a semi-elemental triple nodeDec 29 2012Planar quadratic differential systems occur in many areas of applied mathematics. Although more than one thousand papers have been written on these systems, a complete understanding of this family is still missing. Classical problems, and in particular, ... More

On the Field Dependence of the Interface Energy in Af/FM BilayersSep 23 2003In the investigations of antiferromagnetic (AF)/ ferromagnetic (FM) bilayer samples, often distinct experimental techniques yield different values for the measured exchange anisotropy field (HE). We propose that the observed discrepancy may be accounted ... More

Casimir force between $δ-δ^{\prime}$ mirrors transparent at high frequenciesJul 21 2016Aug 14 2016We investigate, in the context of a real massless scalar field in $1+1$ dimensions, models of partially reflecting mirrors simulated by Dirac $\delta-\delta^{\prime}$ point interactions. In the literature, these models do not exhibit full transparency ... More

Universal Secure Error-Correcting Schemes for Network CodingJan 19 2010This paper considers the problem of securing a linear network coding system against an adversary that is both an eavesdropper and a jammer. The network is assumed to transport n packets from source to each receiver, and the adversary is allowed to eavesdrop ... More

Adaptive Radar Detection of a Subspace Signal Embedded in Subspace Structured plus Gaussian Interference Via InvarianceAug 13 2015This paper deals with adaptive radar detection of a subspace signal competing with two sources of interference. The former is Gaussian with unknown covariance matrix and accounts for the joint presence of clutter plus thermal noise. The latter is structured ... More

Propagators and WKB-exactness in the plane wave limit of AdSxSJun 25 2004Green functions for the scalar, spinor and vector fields in a plane wave geometry arising as a Penrose limit of $AdS\times S$ are obtained. The Schwinger-DeWitt technique directly gives the results in the plane wave background, which turns out to be WKB-exact. ... More

Quaternion Gradient and HessianJun 13 2014The optimization of real scalar functions of quaternion variables, such as the mean square error or array output power, underpins many practical applications. Solutions often require the calculation of the gradient and Hessian, however, real functions ... More

Probing the nuclear obscuration in radio-galaxies with near infrared imagingDec 15 2004We present the first near-infrared (K'-band) homogeneous observations of a complete sub-sample of the 3CR radio catalogue comprising all High Excitation Galaxies (HEGs) at z<0.3. After showing that the surface brightness decomposition technique to measure ... More

A Transition in the Accretion Properties of Radio-Loud Active NucleiMar 11 2004We present evidence for the presence of a transition in the accretion properties of radio-loud sources. For a sample of radio galaxies and radio-loud quasars, selected based on their extended radio properties, the accretion rate is estimated from the ... More

Group Momentum Space and Hopf Algebra Symmetries of Point Particles Coupled to 2+1 GravityMar 12 2014Jul 24 2014We present an in-depth investigation of the ${\rm SL}(2,\mathbb{R})$ momentum space describing point particles coupled to Einstein gravity in three space-time dimensions. We introduce different sets of coordinates on the group manifold and discuss their ... More

Securing data transfer in the cloud through introducing identification packet and UDT-authentication option field: a characterizationOct 23 2010The emergence of various technologies has since pushed researchers to develop new protocols that support high density data transmissions in Wide Area Networks. Many of these protocols are TCP protocol variants, which have demonstrated better performance ... More

Fermi-surface pockets in $YBa_2Cu_3O_{6.5}$ : A comparison of ab initio techniquesJan 28 2009We study the Fermi surface of metallic, non-magnetic \textit{ortho}-II YBa$_2$Cu$_3$O$_{6.5}$ using three different density-functional-based band-structure techniques (GGA, GGA+U, PSIC). The calculated Fermi surface exhibits no pockets in GGA+U and PSIC, ... More

The Exploitation of Web Navigation Data: Ethical Issues and Alternative ScenariosDec 10 2015May 02 2016Nowadays, the users' browsing activity on the Internet is not completely private due to many entities that collect and use such data, either for legitimate or illegal goals. The implications are serious, from a person who exposes unconsciously his private ... More

Geometric control theory I: mathematical foundationsMay 16 2007May 15 2015A geometric setup for control theory is presented. The argument is developed through the study of the extremals of action functionals defined on piecewise differentiable curves, in the presence of differentiable non-holonomic constraints. Special emphasis ... More

An Algebraic Approach to Physical-Layer Network CodingMay 15 2010The problem of designing new physical-layer network coding (PNC) schemes via lattice partitions is considered. Building on a recent work by Nazer and Gastpar, who demonstrated its asymptotic gain using information-theoretic tools, we take an algebraic ... More

Sparse Network Coding with Overlapping ClassesMay 18 2009This paper presents a novel approach to network coding for distribution of large files. Instead of the usual approach of splitting packets into disjoint classes (also known as generations) we propose the use of overlapping classes. The overlapping allows ... More

Minimal Header Overhead for Random Linear Network CodingJan 24 2016The energy used to transmit a single bit of data between the devices in wireless networks is equal to the energy for performing hundreds of instructions in those devices. Thus the reduction of the data necessary to transmit, while keeping the same functionality ... More