Results for "Loukas P. Petrou"

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SqueezeJet: High-level Synthesis Accelerator Design for Deep Convolutional Neural NetworksMay 06 2018Deep convolutional neural networks have dominated the pattern recognition scene by providing much more accurate solutions in computer vision problems such as object recognition and object detection. Most of these solutions come at a huge computational ... More
Software-Defined FPGA Accelerator Design for Mobile Deep Learning ApplicationsFeb 08 2019Recently, the field of deep learning has received great attention by the scientific community and it is used to provide improved solutions to many computer vision problems. Convolutional neural networks (CNNs) have been successfully used to attack problems ... More
Expanding a robot's life: Low power object recognition via FPGA-based DCNN deploymentMar 23 2018FPGAs are commonly used to accelerate domain-specific algorithmic implementations, as they can achieve impressive performance boosts, are reprogrammable and exhibit minimal power consumption. In this work, the SqueezeNet DCNN is accelerated using an SoC ... More
A Framework of Transfer Learning in Object Detection for Embedded SystemsNov 12 2018Nov 24 2018Transfer learning is one of the subjects undergoing intense study in the area of machine learning. In object recognition and object detection there are known experiments for the transferability of parameters, but not for neural networks which are suitable ... More
Metric Map Merging using RFID Tags & Topological InformationNov 17 2017A map merging component is crucial for the proper functionality of a multi-robot system performing exploration, since it provides the means to integrate and distribute the most important information carried by the agents: the explored-covered space and ... More
Particle Acceleration in Multiple Dissipation RegionsFeb 25 2004The sharp magnetic discontinuities which naturally appear in solar magnetic flux tubes driven by turbulent photospheric motions are associated with intense currents. \citet{Par83} proposed that these currents can become unstable to a variety of microscopic ... More
Gyrokinetic electron acceleration in the force-free corona with anomalous resistivityApr 07 2006We numerically explore electron acceleration and coronal heating by dissipative electric fields. Electrons are traced in linear force-free magnetic fields extrapolated from SOHO/MDI magnetograms, endowed with anomalous resistivity ($\eta$) in localized ... More
On Fourier transforms of radial functions and distributionsDec 22 2011Feb 18 2013We find a formula that relates the Fourier transform of a radial function on $\mathbf{R}^n$ with the Fourier transform of the same function defined on $\mathbf{R}^{n+2}$. This formula enables one to explicitly calculate the Fourier transform of any radial ... More
Fractional Transport in Strongly Turbulent PlasmasJul 05 2017We analyze statistically the energization of particles in a large scale environment of strong turbulence that is fragmented into a large number of distributed current filaments. The turbulent environment is generated through strongly perturbed, 3D, resistive ... More
Formal Verification of a Programmable HypersurfaceJul 17 2018A metasurface is a surface that consists of artificial material, called metamaterial, with configurable electromagnetic properties. This paper presents work in progress on the design and formal verification of a programmable metasurface, the Hypersurface, ... More
Efficient Electrical Spin Injection from a Magnetic Metal / Tunnel Barrier Contact into a SemiconductorOct 02 2001Jan 28 2002We report electrical spin injection from a ferromagnetic metal contact into a semiconductor light emitting diode structure with an injection efficiency of 30% which persists to room temperature. The Schottky barrier formed at the Fe/AlGaAs interface provides ... More
Giant Valley Splitting in Monolayer WS2 by Magnetic Proximity EffectFeb 15 2019Lifting the valley degeneracy of monolayer transition metal dichalcogenides (TMD) would allow versatile control of the valley degree of freedom. We report a giant valley exciton splitting of 18 meV/T for monolayer WS2, using the proximity effect from ... More
Imprints of cosmic strings on the cosmological gravitational wave backgroundJun 18 2008The equation which governs the temporal evolution of a gravitational wave (GW) in curved space-time can be treated as the Schrodinger equation for a particle moving in the presence of an effective potential. When GWs propagate in an expanding Universe ... More
Fault Adaptive Routing in Metasurface Controller NetworksOct 15 2018HyperSurfaces are a merge of structurally reconfigurable metasurfaces whose electromagnetic properties can be changed via a software interface, using an embedded miniaturized network of controllers, thus enabling novel capabilities in wireless communications. ... More
$L^p$ bounds for singular integrals and maximal singular integrals with rough kernelsOct 05 1997Convolution type Calder\'on-Zygmund singular integral operators with rough kernels $\pv \Om(x)/|x|^n$ are studied. A condition on $\Om$ implying that the corresponding singular integrals and maximal singular integrals map $L^p \to L^p$ for $1<p<\nf$ is ... More
Frequency Analysis of Temporal Graph SignalsFeb 14 2016This letter extends the concept of graph-frequency to graph signals that evolve with time. Our goal is to generalize and, in fact, unify the familiar concepts from time- and graph-frequency analysis. To this end, we study a joint temporal and graph Fourier ... More
Stationary time-vertex signal processingNov 01 2016The goal of this paper is to improve learning for multivariate processes whose structure is dependent on some known graph topology. Typically, the graph information is incorporated to the learning process via a smoothness assumption postulating that the ... More
Complexity Methods Applied to Turbulence in Plasma AstrophysicsMar 01 2016In this review many of the well known tools for the analysis of Complex systems are used in order to study the global coupling of the turbulent convection zone with the solar atmosphere where the magnetic energy is dissipated explosively. Several well ... More
Approximating Spectral Clustering via Sampling: a ReviewJan 29 2019Spectral clustering refers to a family of unsupervised learning algorithms that compute a spectral embedding of the original data based on the eigenvectors of a similarity graph. This non-linear transformation of the data is both the key of these algorithms' ... More
Multilinear Calderón-Zygmund operators on Hardy spacesOct 08 2000It is shown that multilinear Calder\'on-Zygmund operators are bounded on products of Hardy spaces.
Multilinear interpolation between adjoint operatorsNov 12 2001Multilinear interpolation is a powerful tool used in obtaining strong type boundedness for a variety of operators assuming only a finite set of restricted weak-type estimates. A typical situation occurs when one knows that a multilinear operator satisfies ... More
The Marcinkiewicz multiplier condition for bilinear operatorsOct 08 2000This article is concerned with the question of whether Marcinkiewicz multipliers on $\mathbb R^{2n}$ give rise to bilinear multipliers on $\mathbb R^n\times \mathbb R^n$. We show that this is not always the case. Moreover we find necessary and sufficient ... More
The Kato-Ponce InequalityMar 21 2013In this article we develop a simplistic approach to revisit the classical Kato-Ponce inequality, which is also known as 'fractional Leibniz rule.' As a consequence, we derive the validity of this inequality even in quasi-Banach spaces $L^p$ for $p<1$ ... More
Predicting the evolution of stationary graph signalsJul 12 2016An emerging way of tackling the dimensionality issues arising in the modeling of a multivariate process is to assume that the inherent data structure can be captured by a graph. Nevertheless, though state-of-the-art graph-based methods have been successful ... More
A Note on Fault Tolerant Reachability for Directed GraphsNov 24 2015In this note we describe an application of low-high orders in fault-tolerant network design. Baswana et al. [DISC 2015] study the following reachability problem. We are given a flow graph $G = (V, A)$ with start vertex $s$, and a spanning tree $T =(V, ... More
Dominator Tree Certification and Independent Spanning TreesOct 31 2012Mar 07 2013How does one verify that the output of a complicated program is correct? One can formally prove that the program is correct, but this may be beyond the power of existing methods. Alternatively one can check that the output produced for a particular input ... More
Multilinear Fourier Multipliers with Minimal Sobolev Regularity, IApr 27 2015We find optimal conditions on $m$-linear Fourier multipliers to give rise to bounded operators from a product of Hardy spaces $H^{p_j}$, $0<p_j\le 1$, to Lebesgue spaces $L^p$. The conditions we obtain are necessary and sufficient for boundedness and ... More
The Hörmander Multiplier Theorem III: The complete bilinear case via interpolationJul 09 2016We prove the optimal version of the H\"ormander multiplier theorem concerning bilinear multiplier operators with symbols in the Sobolev space $L^r_s(\mathbb R^{2n})$, $rs>2n$, uniformly over all annuli. More precisely, given a smoothness index $s$, we ... More
Optical control of carrier wavefunction in magnetic quantum dotsJan 16 2018Spatially indirect Type-II band alignment in magnetically-doped quantum dot (QD) structures provides unexplored opportunities to control the magnetic interaction between carrier wavefunction in the QD and magnetic impurities. Unlike the extensively studied, ... More
Simplified Models for Dark Matter Searches at the LHCJun 09 2015Mar 23 2016This document outlines a set of simplified models for dark matter and its interactions with Standard Model particles. It is intended to summarize the main characteristics that these simplified models have when applied to dark matter searches at the LHC, ... More
Incremental $2$-Edge-Connectivity in Directed GraphsJul 24 2016In this paper, we initiate the study of the dynamic maintenance of $2$-edge-connectivity relationships in directed graphs. We present an algorithm that can update the $2$-edge-connected blocks of a directed graph with $n$ vertices through a sequence of ... More
A comparison of the Extrapolated Successive Overrelaxation and the Preconditioned Simultaneous Displacement methods for augmented linear systemsFeb 08 2015In this paper we study the impact of two types of preconditioning on the numerical solution of large sparse augmented linear systems. The first preconditioning matrix is the lower triangular part whereas the second is the product of the lower triangular ... More
(MS)SM-like models on smooth Calabi-Yau manifolds from all three heterotic string theoriesJul 27 2015Jan 18 2016We perform model searches on smooth Calabi-Yau compactifications for both the supersymmetric E8xE8 and SO(32) as well as for the non-supersymmetric SO(16)xSO(16) heterotic strings simultaneously. We consider line bundle backgrounds on both favorable CICYs ... More
Analytical Model of Spin-Polarized Semiconductor LasersJun 25 2008We formulate an analytical model for vertical-cavity surface-emitting lasers (VCSELs) with injection (pump) of spin-polarized electrons. Our results for two different modes of carrier recombination allow for a systematic analysis of the operational regimes ... More
Join-Reachability Problems in Directed GraphsDec 22 2010For a given collection G of directed graphs we define the join-reachability graph of G, denoted by J(G), as the directed graph that, for any pair of vertices a and b, contains a path from a to b if and only if such a path exists in all graphs of G. Our ... More
Stochastic Acceleration in Turbulent Electric Fields Generated by 3-D ReconnectionApr 10 2006Electron and proton acceleration in three-dimensional electric and magnetic fields is studied through test particle simulations. The fields are obtained by a three-dimensional magnetohydrodynamic simulation of magnetic reconnection in slab geometry. The ... More
Limits of applicability of the quasilinear approximation to the electrostatic wave-plasma interactionOct 26 2016The limitation of the Quasilinear Theory (QLT) to describe the diffusion of electrons and ions in velocity space when interacting with a spectrum of large amplitude electrostatic Langmuir, Upper and Lower hybrid waves, is analyzed. We analytically and ... More
On maximal functions for Mikhlin-Hoermander multipliersJan 08 2005Given Mikhlin-H\"ormander multipliers $m_i$, $i=1,..., N$, with uniform estimates we prove an optimal $\sqrt{\log(N+1)}$ bound in $L^p$ for the maximal function $\sup_i|\cF^{-1}[m_i\hat f]|$ and related bounds for maximal functions generated by dilations. ... More
The Fourier transform of multiradial functionsJul 31 2013We obtain an exact formula for the Fourier transform of multiradial functions, i.e., functions of the form $\Phi(x)=\phi(|x_1|, \dots, |x_m|)$, $x_i\in \mathbf R^{n_i}$, in terms of the Fourier transform of the function $\phi$ on $\mathbf R^{r_1}\times ... More
A New Framework for Strong Connectivity and 2-Connectivity in Directed GraphsNov 09 2015In this paper, we investigate some basic problems related to the strong connectivity and to the $2$-connectivity of a directed graph, by considering the effect of edge and vertex deletions on its strongly connected components. Let $G$ be a directed graph ... More
Rough Bilinear Singular IntegralsSep 21 2015Sep 22 2015We study the rough bilinear singular integral, introduced by Coifman and Meyer , $$ T_\Omega(f,g)(x)=p.v. \! \int_{\mathbb R^{n}}\! \int_{\mathbb R^{n}}\! |(y,z)|^{-2n} \Omega((y,z)/|(y,z)|)f(x-y)g(x-z) dydz, $$ when $\Omega $ is a function in $L^q(\mathbb ... More
A remark on an endpoint Kato-Ponce inequalityNov 18 2013This note introduces bilinear estimates intended as a step towards an $L^\infty$-endpoint Kato-Ponce inequality. In particular, a bilinear version of the classical Gagliardo-Nirenberg interpolation inequalities for a product of functions is proved.
Radiation hardness qualification of PbWO4 scintillation crystals for the CMS Electromagnetic CalorimeterDec 22 2009Ensuring the radiation hardness of PbWO4 crystals was one of the main priorities during the construction of the electromagnetic calorimeter of the CMS experiment at CERN. The production on an industrial scale of radiation hard crystals and their certification ... More
Full-waveform inversion in three-dimensional PML-truncated elastic mediaApr 30 2015We are concerned with high-fidelity subsurface imaging of the soil, which commonly arises in geotechnical site characterization and geophysical explorations. Specifically, we attempt to image the spatial distribution of the Lame parameters in semi-infinite, ... More
Waves and instabilities in an anisotropic universeOct 19 2001The excitation of low frequency plasma waves in an expanding anisotropic cosmological model which contains a magnetic field frozen into the matter and pointing in the longitudinal direction is discussed. Using the exact equations governing finite-amplitude ... More
L^p bounds for a maximal dyadic sum operatorDec 11 2002We prove $L^p$ bounds in the range $1<p<\infty$ for a maximal dyadic sum operator on $\rn$. This maximal operator provides a discrete multidimensional model of Carleson's operator. Its boundedness is obtained by a simple twist of the proof of Carleson's ... More
The Hörmander multiplier theorem, II: The bilinear local $L^2$ caseJul 09 2016We use wavelets of tensor product type to obtain the boundedness of bilinear multiplier operators on $\mathbb R^n\times \mathbb R^n$ associated with H\"ormander multipliers on $\mathbb R^{2n}$ with minimal smoothness. We focus on the local $L^2$ case ... More
Impulsive electron acceleration by Gravitational WavesDec 05 2003We investigate the non-linear interaction of a strong Gravitational Wave with the plasma during the collapse of a massive magnetized star to form a black hole, or during the merging of neutron star binaries (central engine). We found that under certain ... More
Certain Multi(sub)linear square functionsApr 14 2015Let $d\ge 1, \ell\in\Z^d$, $m\in \mathbb Z^+$ and $\theta_i$, $i=1,\dots,m $ are fixed, distinct and nonzero real numbers. We show that the $m$-(sub)linear version below of the Ratnakumar and Shrivastava \cite{RS1} Littlewood-Paley square function $$T(f_1,\dots ... More
Recent Advances in Understanding Particle Acceleration Processes in Solar FlaresOct 11 2011Oct 23 2011We review basic theoretical concepts in particle acceleration, with particular emphasis on processes likely to occur in regions of magnetic reconnection. Several new developments are discussed, including detailed studies of reconnection in three-dimensional ... More
Carrier-Dopant Exchange Interactions in Mn-doped PbS Colloidal Quantum DotsAug 03 2012Carrier-dopant exchange interactions in Mn-doped PbS colloidal quantum dots were studied by circularly polarized magneto-photoluminescence. Mn substitutional doping leads to paramagnetic behavior down to 5 K. While undoped quantum dots show negative circular ... More
2-Vertex Connectivity in Directed GraphsSep 22 2014Feb 19 2015We complement our study of 2-connectivity in directed graphs, by considering the computation of the following 2-vertex-connectivity relations: We say that two vertices v and w are 2-vertex-connected if there are two internally vertex-disjoint paths from ... More
Anomalous biased diffusion in networksAug 01 2013We study diffusion with a bias towards a target node in networks. This problem is relevant to efficient routing strategies in emerging communication networks like optical networks. Bias is represented by a probability $p$ of the packet/particle to travel ... More
Spinner: Scalable Graph Partitioning in the CloudApr 15 2014Feb 02 2015Several organizations, like social networks, store and routinely analyze large graphs as part of their daily operation. Such graphs are typically distributed across multiple servers, and graph partitioning is critical for efficient graph management. Existing ... More
On Low-High Orders of Directed Graphs: Incremental Algorithms and ApplicationsAug 23 2016A flow graph $G=(V,E,s)$ is a directed graph with a distinguished start vertex $s$. The dominator tree $D$ of $G$ is a tree rooted at $s$, such that a vertex $v$ is an ancestor of a vertex $w$ if and only if all paths from $s$ to $w$ include $v$. The ... More
Particle Acceleration and Heating by Turbulent ReconnectionApr 18 2016Jul 21 2016Turbulent flows in the solar wind, large scale current sheets, multiple current sheets, and shock waves lead to the formation of environments in which a dense network of current sheets is established and sustains "turbulent reconnection". We constructed ... More
Self-consistent modeling of the dynamic evolution of magnetic island growth in the presence of stabilizing ECCDSep 18 2013The most promising technique for the control of neoclassical tearing modes in tokamak experiments is the compensation of the missing bootstrap current with electron-cyclotron current drive. In this frame, the dynamics of magnetic islands has been studied ... More
Calabi-Yau compactifications of non-supersymmetric heterotic string theoryJul 22 2015Jan 18 2016Phenomenological explorations of heterotic strings have conventionally focused primarily on the E8xE8 theory. We consider smooth compactifications of all three ten-dimensional heterotic theories to exhibit the many similarities between the non-supersymmetric ... More
Efficiency of message transmission using biased random walks in complex networks in the presence of trapsJun 10 2014We study the problem of a particle/message that travels as a biased random walk towards a target node in a network in the presence of traps. The bias is represented as the probability $p$ of the particle to travel along the shortest path to the target ... More
2-Edge Connectivity in Directed GraphsJul 11 2014Jul 31 2014Edge and vertex connectivity are fundamental concepts in graph theory. While they have been thoroughly studied in the case of undirected graphs, surprisingly not much has been investigated for directed graphs. In this paper we study $2$-edge connectivity ... More
The multilinear strong maximal functionFeb 06 2010Mar 08 2011A multivariable version of the strong maximal function is introduced and a sharp distributional estimate for this operator in the spirit of the Jessen, Marcinkiewicz, and Zygmund theorem is obtained. Conditions that characterize the boundedness of this ... More
Compensating strong coupling with large chargeOct 14 2016Oct 25 2016We study some (conformal) field theories with global symmetries in the sector where the value of the global charge $Q$ is large. We find (as expected) that the low energy excitations of this sector are described by the general form of Goldstone's theorem ... More
Online Balanced RepartitioningNov 06 2015Jul 18 2016This paper initiates the study of deterministic algorithms for collocating frequently communicating nodes in a distributed networked systems in an online fashion. In particular, we introduce the Balanced RePartitioning (BRP) problem: Given an arbitrary ... More
Multilinear Fourier Multipliers with Minimal Sobolev Regularity, IIApr 27 2015Apr 28 2015We provide characterizations for boundedness of multilinear Fourier operators on Hardy-Lebesgue spaces with symbols locally in Sobolev spaces. Let $H^q(\mathbb R^n)$ denote the Hardy space when $0<q\le 1$ and the Lebesgue space $L^q(\mathbb R^n)$ when ... More
Multilinear generalized Radon transforms and point configurationsApr 19 2012Aug 19 2013We study multilinear generalized Radon transforms using a graph-theoretic paradigm that includes the widely studied linear case. These provide a general mechanism to study Falconer-type problems involving $(k+1)$-point configurations in geometric measure ... More
Maximal functions associated with Fourier multipliers of Mikhlin-H"ormander typeNov 28 2003Mar 09 2004We show that maximal operators formed by dilations of Mikhlin-H"ormander multipliers are typically not bounded on $L^p(R^d)$. We also give rather weak conditions in terms of the decay of such multipliers under which $L^p$ boundedness of the maximal operators ... More
High-dimensional approximate $r$-netsJul 16 2016The construction of $r$-nets offers a powerful tool in computational and metric geometry. We focus on high-dimensional spaces and present a new randomized algorithm which efficiently computes approximate $r$-nets with respect to Euclidean distance. For ... More
Normal and Anomalous Diffusion: A TutorialMay 05 2008The purpose of this tutorial is to introduce the main concepts behind normal and anomalous diffusion. Starting from simple, but well known experiments, a series of mathematical modeling tools are introduced, and the relation between them is made clear. ... More
Gravito-magnetic instabilities in anisotropically expanding fluidsJun 26 2008Gravitational instabilities in a magnetized Friedman - Robertson - Walker (FRW) Universe, in which the magnetic field was assumed to be too weak to destroy the isotropy of the model, are known and have been studied in the past. Accordingly, it became ... More
Multicommutators and Multiplier TheoremsNov 25 2015May 12 2016For all $k,n\in \mathbb N$, we obtain the boundedness of the $n$th dimensional Calder\'on-Coifman-Journ\'e-type multicommutator $\mathscr{C}_k^{(n)}(f,a_1,\dots, a_k)(x),$ given by \[\mathrm{p.v.}\int_{\mathbb R^{nk}} \!\! f(x-y_1-\cdots -y_k) \! \bigg(\! ... More
Compensating strong coupling with large chargeOct 14 2016We study (conformal) field theories with global symmetries in the sector where the value of the global charge $Q$ is large. We find (as expected) that the low energy excitations of this sector are described by the general form of Goldstone's theorem in ... More
Non-supersymmetric heterotic model buildingJul 23 2014Oct 17 2014We investigate orbifold and smooth Calabi-Yau compactifications of the non-supersymmetric heterotic SO(16)xSO(16) string. We focus on such Calabi-Yau backgrounds in order to recycle commonly employed techniques, like index theorems and cohomology theory, ... More
Towards stationary time-vertex signal processingJun 22 2016Graph-based methods for signal processing have shown promise for the analysis of data exhibiting irregular structure, such as those found in social, transportation, and sensor networks. Yet, though these systems are often dynamic, state-of-the-art methods ... More
Finding Dominators via Disjoint Set UnionOct 08 2013The problem of finding dominators in a directed graph has many important applications, notably in global optimization of computer code. Although linear and near-linear-time algorithms exist, they use sophisticated data structures. We develop an algorithm ... More
An Experimental Study of Dynamic DominatorsApr 10 2016Motivated by recent applications of dominator computations, we consider the problem of dynamically maintaining the dominators of flow graphs through a sequence of insertions and deletions of edges. Our main theoretical contribution is a simple incremental ... More
The bilinear Bochner-Riesz problemDec 17 2012Apr 03 2013Motivated by the problem of spherical summability of products of Fourier series, we study the boundedness of the bilinear Bochner-Riesz multipliers $(1-|\xi|^2-|\eta|^2)^\delta_+$ and we make some advances in this investigation. We obtain an optimal result ... More
Autoregressive Moving Average Graph FilteringFeb 14 2016Sep 21 2016One of the cornerstones of the field of signal processing on graphs are graph filters, direct analogues of classical filters, but intended for signals defined on graphs. This work brings forth new insights on the distributed graph filtering problem. We ... More
The Hörmander multiplier theorem I: The Linear CaseJul 09 2016We discuss $L^p(\mathbb R^n)$ boundedness for Fourier multiplier operators that satisfy the hypotheses of the H\"ormander multiplier theorem in terms of an optimal condition that relates the distance $|\frac 1p-\frac12|$ to the smoothness $s$ of the associated ... More
A self-organized criticality model for ion temperature gradient (ITG) mode driven turbulence in confined plasmaJul 05 2010Jul 09 2010A new Self-Organized Criticality (SOC) model is introduced in the form of a Cellular Automaton (CA) for ion temperature gradient (ITG) mode driven turbulence in fusion plasmas. Main characteristics of the model are that it is constructed in terms of the ... More
Approximating the Smallest Spanning Subgraph for 2-Edge-Connectivity in Directed GraphsSep 09 2015Let $G$ be a strongly connected directed graph. We consider the following three problems, where we wish to compute the smallest strongly connected spanning subgraph of $G$ that maintains respectively: the $2$-edge-connected blocks of $G$ (\textsf{2EC-B}); ... More
The Effect of Coherent Structures on Stochastic Acceleration in MHD TurbulenceSep 23 2005We investigate the influence of coherent structures on particle acceleration in the strongly turbulent solar corona. By randomizing the Fourier phases of a pseudo-spectral simulation of isotropic MHD turbulence (Re $\sim 300$), and tracing collisionless ... More
Statistical Properties of Dissipative MHD AcceleratorsMar 07 2005We use exact orbit integration to investigate particle acceleration in a Gauss field proxy of magnetohydrodynamic (MHD) turbulence. Regions where the electric current exceeds a critical threshold are declared to be `dissipative' and endowed with super-Dreicer ... More
Internal Transitions of Two-Dimensional Charged Magneto-Excitons X-: Theory and ExperimentJul 08 1999Internal spin-singlet and spin-triplet transitions of charged excitons X- in magnetic fields in quantum wells have been studied experimentally and theoretically. The allowed X- transitions are photoionizing and exhibit a characteristic double-peak structure, ... More
Gamma spectroscopic measurements using the PID350 pixelated CdTe radiation detectorNov 15 2010Spectroscopic measurements are presented using the PID350 pixelated gamma radiation detectors. A high-speed data acquisition system has been developed in order to reduce the data loss during the data reading in case of a high flux of photons. A data analysis ... More
Interaction of an electron gas with photoexcited electron-hole pairs in modulation-doped GaAs and CdTe quantum wellsJun 14 2001Sep 04 2001The nature of the correlated electron gas and its response to photo-injected electron-hole pairs in nominally undoped and modulation-doped multiple quantum-well (MQW) structures was studied by experiment and theory, revealing a new type of optically-active ... More
Analysis of the Transport Process Providing Spin Injection through an Fe/AlGaAs Schottky BarrierFeb 11 2003Electron spin polarizations of 32% are obtained in a GaAs quantum well via electrical injection through a reverse-biased Fe/AlGaAs Schottky contact. An analysis of the transport data using the Rowell criteria demonstrates that single step tunneling is ... More
Robust Magnetic Polarons in Type-II (Zn,Mn)Te Quantum DotsDec 01 2009We present evidence of magnetic ordering in type-II (Zn, Mn) Te quantum dots. This ordering is attributed to the formation of bound magnetic polarons caused by the exchange interaction between the strongly localized holes and Mn within the dots. In our ... More
Electrical Spin Pumping of Quantum Dots at Room TemperatureJan 31 2005We report electrical control of the spin polarization of InAs/GaAs self-assembled quantum dots (QDs) at room temperature. This is achieved by electrical injection of spin-polarized electrons from an Fe Schottky contact. The circular polarization of the ... More
Data Structures for Mergeable TreesNov 11 2007Motivated by an application in computational topology, we consider a novel variant of the problem of efficiently maintaining dynamic rooted trees. This variant requires merging two paths in a single operation. In contrast to the standard problem, in which ... More
Linear-Time Pointer-Machine Algorithms for Path-Evaluation Problems on Trees and GraphsJul 15 2002Nov 14 2006We present algorithms that run in linear time on pointer machines for a collection of problems, each of which either directly or indirectly requires the evaluation of a function defined on paths in a tree. These problems previously had linear-time algorithms ... More
Evaluation of Compton scattering sequence reconstruction algorithms for a portable position sensitive radioactivity detector based on pixelated Cd(Zn)Te crystalsNov 11 2010We present extensive simulation studies on the performance of algorithms for the Compton sequence reconstruction used for the development of a portable spectroscopic instrument (COCAE), with the capability to localize and identify radioactive sources, ... More
Infinite number of MSSMs from heterotic line bundles?Jun 02 2015Jun 30 2015We consider heterotic E8xE8 supergravity compactified on smooth Calabi-Yau manifolds with line bundle gauge backgrounds. Infinite sets of models that satisfy the Bianchi identities and flux quantization conditions can be constructed by letting their background ... More
Charge multiplets and masses for E(11)May 28 2008Oct 30 2008The particle, string and membrane charge multiplets are derived in detail from the decomposition of the l1 (charge) representation of E(11) in three, four, five, six, seven and eight spacetime dimensions. A tension formula relating weights of the l1 (charge) ... More
Internal transitions of negatively charged magneto-excitons and many body effects in a two-dimensional electron gasAug 21 2001Dec 18 2001Spin-singlet and spin-triplet internal transitions of quasi-two-dimensional, negatively charged magneto-excitons (X-) and their evolution with excess electron density have been studied in GaAs/AlGaAs quantum-wells by optically detected resonance (ODR) ... More
Coherent Aharonov Bohm oscillations in type-II (ZnMn)Te quantum dotsMar 17 2008The magneto-photoluminescence of type-II (ZnMn)Te quantum dots is presented. As a result of the type-II band alignment Aharonov-Bohm (AB) oscillations in the photoluminescence intensity are evident, confirming previous predictions for the suitability ... More
Reduction Of Spin Injection Efficiency by Interface Spin ScatteringOct 26 2001We report the first experimental demonstration that interface microstructure limits diffusive electrical spin injection efficiency across heteroepitaxial interfaces. A theoretical treatment shows that the suppression of spin injection due to interface ... More
Magneto-optical imaging of thin magnetic films using spins in diamondAug 10 2015Imaging the fields of magnetic materials provides crucial insight into the physical and chemical processes surrounding magnetism, and has been a key ingredient in the spectacular development of magnetic data storage. Existing approaches using the magneto-optic ... More
Quantum magnetic resonance microscopyFeb 14 2017Magnetic resonance spectroscopy is universally regarded as one of the most important tools in chemical and bio-medical research. However, sensitivity limitations typically restrict imaging resolution to length scales greater than 10 \mu m. Here we bring ... More
Eddington-inspired Born-Infeld gravity: astrophysical and cosmological constraintsJan 12 2012In this letter we compute stringent astrophysical and cosmological constraints on a recently proposed Eddington-inspired Born-Infeld theory of gravity. We find, using a generalized version of the Zel'dovich approximation, that in this theory a pressureless ... More
Prospects for GeV-TeV detection of short gamma-ray bursts with extended emissionDec 02 2013Apr 21 2014We discuss the GeV to TeV photon emission of gamma-ray bursts (GRBs) within the refreshed shock and the continuous injection scenarios, motivated by the observation of extended emission in a substantial fraction of short GRBs. In the first model we assume ... More