Results for "Felix A. Pollock"

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An introduction to operational quantum dynamicsAug 02 2017In the summer of 2016, physicists gathered in Torun, Poland for the 48th annual Symposium on Mathematical Physics. This Symposium was special; it celebrated the 40th anniversary of the discovery of the Gorini-Kossakowski-Sudarshan-Lindblad master equation, ... More
Exploiting the causal tensor network structure of quantum processes to efficiently simulate non-Markovian path integralsFeb 01 2019In the path integral formulation of the evolution of an open quantum system coupled to a Gaussian, non-interacting environment, the dynamical contribution of the latter is encoded in an object called the influence functional. Here, we relate the influence ... More
CP divisibility does not mean MarkovianityJan 16 2019In the classical domain, it is well-known that divisibility does not imply that a stochastic process is Markovian. However, for quantum processes, divisibility is often considered to be synonymous with Markovianity. We show that completely positive (CP) ... More
Kolmogorov extension theorem for general (quantum) stochastic processesDec 07 2017In classical physics, the Kolmogorov extension theorem provides the foundation for the definition and investigation of stochastic processes. In its original form, it does not hold in quantum mechanics. More generally, it does not hold in any theory -- ... More
Non-Markovian quantum control as coherent stochastic trajectoriesFeb 09 2018Feb 12 2018We develop a notion of stochastic quantum trajectories. First, we construct a basis set of trajectories, called elementary trajectories, and go on to show that any quantum dynamical process, including those that are non-Markovian, can be expressed as ... More
Energy-efficient quantum frequency estimationDec 21 2017Jun 13 2018The problem of estimating the frequency of a two-level atom in a noisy environment is studied. Our interest is to minimise both the energetic cost of the protocol and the statistical uncertainty of the estimate. In particular, we prepare a probe in a ... More
A multi-site variational master equation approach to dissipative energy transferDec 22 2012Jul 23 2013Unitary transformations can allow one to study open quantum systems in situations for which standard, weak-coupling type approximations are not valid. We develop here an extension of the variational (polaron) transformation approach to open system dynamics, ... More
Entanglement, non-Markovianity, and causal non-separabilityNov 11 2017Quantum mechanics, in principle, allows for processes with indefinite causal order. However, most of these causal anomalies have not yet been detected experimentally. We show that every such process can be simulated experimentally by means of non-Markovian ... More
Complete framework for efficient characterisation of non-Markovian processesDec 02 2015Oct 18 2016A non-Markovian process is one that retains 'memory' of its past. A systematic understanding of these processes is necessary to fully describe and harness a vast range of complex phenomena; however, no such general characterisation currently exists. This ... More
Divisible quantum dynamics satisfies temporal Tsirelson's boundOct 15 2015We show that divisibility of qubit quantum processes implies temporal Tsirelson's bound. We also prove that the classical bound of the temporal Bell's inequality holds for dynamics that can be described by entanglement-breaking channels---a more general ... More
Operational Markov condition for quantum processesJan 30 2018We derive a necessary and sufficient condition for a quantum process to be Markovian which coincides with the classical one in the relevant limit. Our condition unifies all previously known definitions for quantum Markov processes by accounting for all ... More
Pseudo-time regularization for PDE with solution-dependent diffusionNov 12 2016Nov 27 2016This work unifies pseudo-time and inexact regularization techniques for nonmonotone classes of partial differential equations, into a regularized pseudo-time framework. Convergence of the residual at the predicted rate is investigated through the idea ... More
Stabilized and inexact adaptive methods for capturing internal layers in quasilinear PDEJul 24 2015Feb 14 2016A method is developed within an adaptive framework to solve quasilinear diffusion problems with internal and possibly boundary layers starting from a coarse mesh. The solution process is assumed to start on a mesh where the problem is badly resolved, ... More
An improved method for solving quasilinear convection diffusion problems on a coarse meshFeb 09 2015A method is developed for solving quasilinear convection diffusion problems starting on a coarse mesh where the data and solution-dependent coefficients are unresolved, the problem is unstable and approximation properties do not hold. The Newton-like ... More
Reconstructing open quantum system dynamics with limited controlOct 07 2016The dynamics of an open quantum system can be fully described and tomographically reconstructed if the experimenter has complete control over the system of interest. Most real-world experiments do not fulfill this assumption, and the amount of control ... More
Emergence of a fluctuation relation for heat in typical open quantum processesOct 28 2015In a generalisation of the Landauer erasure protocol, we study bounds on the heat generated in typical open quantum processes. We derive a fluctuation relation for this heat, implying that it is almost always positive when either the system or reservoir ... More
Coherent measurements in quantum metrologySep 12 2012Feb 19 2015It is well known that a quantum correlated probe can yield better precision in estimating an unknown parameter than classically possible. However, how such a quantum probe should be measured remains somewhat elusive. We examine the role of measurements ... More
Exotic Signals of Vectorlike QuarksDec 06 2016Vectorlike fermions are an important target for hadron collider searches. We show that the vectorlike quarks may predominantly decay via higher-dimensional operators into a quark plus a couple of other Standard Model fermions. Pair production of vectorlike ... More
An ultraluminous supersoft source with a 4 hour modulation in NGC 4631Jul 06 2007Context. Supersoft X-ray sources (SSSs) are characterised by very low temperatures (< 100 eV). Classical SSSs have bolometric luminosities in the range of 10^36-10^38 erg/s and are modelled with steady nuclear burning of hydrogen on the surfaces of white ... More
HD148937: a multiwavelength study of the third Galactic member of the Of?p classMar 05 2008Three Galactic O-type stars belong to the rare class of Of?p objects: HD108, HD191612, and HD148937. The first two stars show a wealth of phenomena, including magnetic fields and strong X-ray emission, light variability, and dramatic periodic spectral ... More
The X-ray Lightcurve of WR 140Jan 07 2011WR 140 is a canonical massive "colliding wind" binary system in which periodically-varying X-ray emission is produced by the collision between the wind of the WC7 and O4-5 star components in the space between the two stars. We have obtained X-ray observations ... More
Planets and X-rays: a radiation dietSep 18 2011According to theory, high energy emission from the coronae of cool stars can severely erode the atmosphere of orbiting planets. To test the long term effects of the erosion we study a large sample of planet-hosting stars observed in X-rays. The results ... More
A Wolf-Rayet/black-hole X-ray binary candidate in NGC 300Nov 14 2006Context. Wolf Rayet/black hole binaries are believed to exist as a later evolutionary product of high-mass X-ray binaries. Hundreds of such binaries may exist in galaxies, but only a few of them are close enough to be observed as X-ray binaries. Only ... More
The Conspicuous Absence of X-ray Emission from Carbon-Enriched Wolf-Rayet StarsMar 03 2003The carbon-rich WC5 star WR 114 was not detected during a 15.9 ksec XMM-Newton observation, implying an upper limit to the X-ray luminosity of Lx < 2.5*10^{30} erg/s and to the X-ray to bolometric luminosity ratio of Lx/Lbol < 4*10^{-9}. This confirms ... More
Using a biased qubit to probe complex systemsJul 17 2015Sep 15 2016Complex mesoscopic systems play increasingly important roles in modern science -- from understanding biological functions at the molecular level, to designing solid-state information processing devices. The operation of these systems typically depends ... More
Dissipation enhanced vibrational sensing in an olfactory molecular switchMar 25 2014Feb 11 2015Motivated by a proposed olfactory mechanism based on a vibrationally-activated molecular switch, we study electron transport within a donor-acceptor pair that is coupled to a vibrational mode and embedded in a surrounding environment. We derive a polaron ... More
Optimal representation of the bath response function & fast calculation of influence functional coefficients in open quantum systems with BATHFIT 1May 21 2012May 27 2012Today's most popular techniques for accurately calculating the dynamics of the reduced density operator in an open quantum system, either require, or gain great computational benefits, from representing the bath response function a(t) in the form a(t)={\Sigma}_k^K ... More
Analytic influence functionals for numerical Feynman integrals in most open quantum systemsMar 20 2012Fully analytic formulas, which do not involve any numerical integration, are derived for the discretized influence functionals of a very extensive assortment of spectral distributions. For Feynman integrals derived using the Trotter splitting and Strang ... More
How does interference fall?Oct 07 2016We study how single- and double-slit interference patterns fall in the presence of gravity. First, we demonstrate that universality of free fall still holds in this case, i.e., interference patterns fall just like classical objects. Next, we explore lowest ... More
The energy landscape of a superconducting double dotMar 26 2014We consider the energetics of a superconducting double dot, comprising two superconducting islands coupled in series via a Josephson junction. The periodicity of the stability diagram is governed by the competition between the charging energy and the ... More
Splitting a single Cooper-pair with microwave lightApr 18 2013Mar 28 2014We measure an aluminum superconducting double quantum dot and find that its electrical impedance, specifically its quantum capacitance, depends on whether or not it contains a single broken Cooper pair. In this way we are able to observe, in real time, ... More
A matrix analysis approach to discrete comparison principles for nonmonotone PDENov 20 2017Mar 16 2018We consider a linear algebra approach to establishing a discrete comparison principle for a nonmonotone class of quasilinear elliptic partial differential equations. In the absence of a lower order term, we require local conditions on the mesh to establish ... More
Discrete comparison principles for quasilinear elliptic PDEAug 07 2017Oct 31 2017Comparison principles are developed for discrete quasilinear elliptic partial differential equations. We consider the analysis of a class of nonmonotone Leray-Lions problems featuring both nonlinear solution and gradient dependence in the principal coefficient, ... More
Uniqueness of discrete solutions of nonmonotone PDEs without a globally fine mesh conditionApr 14 2017Jun 08 2017Uniqueness of the finite element solution for nonmonotone quasilinear problems of elliptic type is established in one and two dimensions. In each case, we prove a comparison theorem based on locally bounding the variation of the discrete so- lution over ... More
Estimation of the XUV radiation onto close planets and their evaporationMay 03 2011Context: The current distribution of planet mass vs. incident stellar X-ray flux supports the idea that photoevaporation of the atmosphere may take place in close-in planets. Integrated effects have to be accounted for. A proper calculation of the mass ... More
SNR 1E 0102.2-7219 as an X-ray Calibration Standard in the 0.5-1.0 keV Bandpass and Its Application to the CCD Instruments aboard Chandra, Suzaku, Swift and XMM-NewtonJul 11 2016We desire a simple comparison of the absolute effective areas of the current generation of CCD instruments onboard the following observatories: Chandra ACIS-S3, XMM-Newton (EPIC-MOS and EPIC-pn), Suzaku XIS, and Swift XRT and a straightforward comparison ... More
A scenario of planet erosion by coronal radiationFeb 09 2010Aug 10 2010Context: According to theory, high-energy emission from the coronae of cool stars can severely erode the atmospheres of orbiting planets. No observational tests of the long term effects of erosion have yet been made. Aims: To analyze the current distribution ... More
The EXOSAT medium-energy slew survey catalogJul 30 1998We present a catalog of X-ray sources observed during slew maneuvers by the Medium Energy Detector Array onboard the EXOSAT Observatory. The EXOSAT Medium Energy slew-survey catalog (EXMS) provides a unique record of the 1--8 keV X-ray sky between 1983 ... More
Variational Density Matrix Method for Warm Condensed Matter and Application to Dense HydrogenOct 08 1999A new variational principle for optimizing thermal density matrices is introduced. As a first application, the variational many body density matrix is written as a determinant of one body density matrices, which are approximated by Gaussians with the ... More
The Orbital Period of the Wolf-Rayet Binary IC 10 X-1; Dynamic Evidence that the Compact Object is a Black HoleSep 18 2007IC 10 X-1 is a bright (Lx=10^38 ergs/s) variable X-ray source in the local group starburst galaxy IC 10. The most plausible optical counterpart is a luminous Wolf-Rayet star, making IC 10 X-1 a rare example of a Wolf-Rayet X-ray binary. In this paper, ... More
Weighing Melnick 34: the most massive binary system knownJan 15 2019Here we confirm Melnick 34, an X-ray bright star in the 30 Doradus region of the Large Magellanic Cloud, as an SB2 binary comprising WN5h+WN5h components. We present orbital solutions using 26 epochs of VLT/UVES spectra and 22 epochs of archival Gemini/GMOS ... More
Rigorous spatial statistics for gaze patterns in scene viewing: Effects of repeated viewingApr 06 2017Scene viewing is used to study attentional selection in complex but still controlled environments. One of the main observations on eye movements during scene viewing is the inhomogeneous distribution of fixation locations: While some parts of an image ... More
High-Resolution X-ray Imaging of the Colliding Wind Shock in WR147Apr 12 2002We analyze new high-resolution Chandra X-ray images of the Wolf-Rayet binary system WR147. This system contains a WN8 star with an early-type companion located 0.6'' to its north, and is the only known early-type binary with a separation on the sky large ... More
Breakdown by a magnetic field of the superconducting fluctuations in the normal state in Pb_{1-x}In_x alloysDec 26 2003The effects induced on the magnetization by coherent fluctuating Cooper pairs in the normal state have been measured in Pb_{1-x}In_x alloys up to high magnetic fields, of amplitudes above Hc2(0), the upper critical field extrapolated to T=0K. Our results ... More
A Simple Test of the Equivalence Principle(s) for Quantum SuperpositionsNov 10 2015We propose a simple experimental test of the quantum equivalence principle introduced by Zych and Brukner [arXiv:1502.00971], which generalises the Einstein equivalence principle to superpositions of internal energy states. We consider a harmonically-trapped ... More
On the limits to mobility in InAs quantum wells with nearly lattice-matched barriersOct 12 2016Oct 13 2016The growth and the density dependence of the low temperature mobility of a series of two-dimensional electron systems confined to un-intentionally doped, low extended defect density InAs quantum wells with Al$_{1-x}$Ga$_{x}$Sb barriers are reported. The ... More
Suzaku monitoring of the Wolf-Rayet binary WR140 around periastron passage: An approach for quantifying the wind parametersSep 28 2015Suzaku observations of the Wolf-Rayet binary WR 140 (WC7pd+O5.5fc) were made at four different times around periastron passage in 2009 January. The spectra changed in shape and flux with the phase. As periastron approached, the column density of the low-energy ... More
Theory of the Franck-Condon blockade regimeJun 20 2006Dec 01 2006Strong coupling of electronic and vibrational degrees of freedom entails a low-bias suppression of the current through single-molecule devices, termed Franck-Condon blockade. In the limit of slow vibrational relaxation, transport in the Franck-Condon-blockade ... More
Gamma-ray flares from red giant/jet interactions in AGNMay 28 2010Sep 03 2010Non-blazar AGN have been recently established as a class of gamma-ray sources. M87, a nearby representative of this class, show fast TeV variability on timescales of a few days. We suggest a scenario of flare gamma-ray emission in non-blazar AGN based ... More
Operators in Machine Learning: Response Properties in Chemical SpaceJul 23 2018Aug 23 2018The role of response operators is well established in quantum mechanics. We investigate their use for universal quantum machine learning models of response properties in molecules. After introducing a theoretical basis, we present and discuss numerical ... More
Dominance analysis of linear complementarity systemsFeb 01 2018Apr 12 2018The paper extends the concepts of dominance and p-dissipativity to the non-smooth family of linear complementarity systems. Dominance generalizes incremental stability whereas p-dissipativity generalizes incremental passivity. The generalization aims ... More
Interpretation of the flares of M87 at TeV energies in the cloud-jet interaction scenarioFeb 27 2012Jun 27 2012Active galactic nuclei with misaligned jets have been recently established as a class of high-energy gamma-ray sources. M87, a nearby representative of this class, shows fast TeV variability on timescales less than one day. We present calculations performed ... More
An information-theoretic on-line update principle for perception-action couplingApr 16 2018Inspired by findings of sensorimotor coupling in humans and animals, there has recently been a growing interest in the interaction between action and perception in robotic systems [Bogh et al., 2016]. Here we consider perception and action as two serial ... More
Tracing dense and diffuse neutral hydrogen in the halo of the Milky WayNov 25 2016Nov 28 2016We have combined observations of Galactic high-velocity HI from two surveys: a very sensitive survey from the Green Bank 140ft Telescope with limited sky coverage, and the less sensitive but complete Galactic All Sky Survey from the 64m Parkes Radio Telescope. ... More
Differentially passive circuits that switch and oscillateApr 12 2018The concept of passivity is central to analyze circuits as interconnections of passive components. We illustrate that when used differentially, the same concept leads to an interconnection theory for electrical circuits that switch and oscillate as interconnections ... More
Induced Cycles in GraphsJun 03 2014The maximum cardinality of an induced $2$-regular subgraph of a graph $G$ is denoted by $c_{\rm ind}(G)$. We prove that if $G$ is an $r$-regular graph of order $n$, then $c_{\rm ind}(G) \geq \frac{n}{2(r-1)} + \frac{1}{(r-1)(r-2)}$ and we prove that if ... More
Sensitive 21cm Observations of Neutral Hydrogen in the Local Group near M31Jul 19 2015Dec 16 2015Very sensitive 21cm HI measurements have been made at several locations around the Local Group galaxy M31 using the Green Bank Telescope (GBT) at an angular resolution of 9.1', with a 5$\sigma$ detection level of $\rm{N_{HI} = 3.9 \times 10^{17}~cm^{-2}}$ ... More
The need for a local source of UHE CR nucleiJul 11 2011Feb 13 2012Recent results of the Pierre Auger (Auger) fluorescence detectors indicate an increasingly heavy composition of ultra-high energy (UHE) cosmic rays (CRs). Assuming that this trend continues up to the highest energies observed by the Auger surface detectors ... More
Failure of feedback as a putative common mechanism of spreading depolarizations in migraine and strokeMar 16 2008The stability of cortical function depends critically on proper regulation. Under conditions of migraine and stroke a breakdown of transmembrane chemical gradients can spread through cortical tissue. A concomitant component of this emergent spatio-temporal ... More
Plasma Waves as a Benchmark ProblemNov 03 2016A large number of wave modes exist in a magnetized plasma. Their properties are determined by the interaction of particles and waves. In a simulation code, the correct treatment of field quantities and particle behavior is essential to correctly reproduce ... More
Essentially No Barriers in Neural Network Energy LandscapeMar 02 2018Jun 25 2018Training neural networks involves finding minima of a high-dimensional non-convex loss function. Knowledge of the structure of this energy landscape is sparse. Relaxing from linear interpolations, we construct continuous paths between minima of recent ... More
Classical Dimers on Penrose TilingsFeb 07 2019We study the classical dimer model on rhombic Penrose tilings, whose edges and vertices may be identified with those of a bipartite graph. We find that Penrose tilings do not admit perfect matchings (defect-free dimer coverings). Instead, their maximum ... More
Dominance analysis of linear complementarity systemsFeb 01 2018The paper extends the concepts of dominance and p-dissipativity to the non-smooth family of linear complementarity systems. Dominance generalizes incremental stability whereas p-dissipativity generalizes incremental passivity. The generalization aims ... More
On Recovery Guarantees for One-Bit Compressed Sensing on ManifoldsJul 17 2018This paper studies the problem of recovering a signal from one-bit compressed sensing measurements under a manifold model; that is, assuming that the signal lies on or near a manifold of low intrinsic dimension. We provide a convex recovery method based ... More
Monte Carlo FusionJan 01 2019This paper proposes a new theory and methodology to tackle the problem of unifying distributed analyses and inferences on shared parameters from multiple sources, into a single coherent inference. This surprisingly challenging problem arises in many settings ... More
Upper-division student difficulties with Separation of VariablesJul 14 2015Separation of variables can be a powerful technique for solving many of the partial differential equations that arise in physics contexts. Upper-division physics students encounter this technique in multiple topical areas including electrostatics and ... More
Validation and analysis of the coupled multiple response Colorado upper-division electrostatics (CUE) diagnosticJul 14 2015Standardized conceptual assessment represents a widely-used tool for educational researchers interested in student learning within the standard undergraduate physics curriculum. For example, these assessments are often used to measure student learning ... More
Upper-division student difficulties with the Dirac delta functionJan 29 2015The Dirac delta function is a standard mathematical tool that appears repeatedly in the undergraduate physics curriculum in multiple topical areas including electrostatics, and quantum mechanics. While Dirac delta functions are often introduced in order ... More
A new paradigm for the X-ray emission of O stars from XMM-Newton observations of the O9.7 supergiant zeta OrionisDec 18 2006XMM-Newton observations of the O supergiant zeta Orionis (O9.7 Ib) extend knowledge of its high-resolution spectrum beyond the CVI line at 33.7 Angstroms and suggest a new framework for the interpretation of the X-ray spectra of single hot stars. All ... More
Calibration and in orbit performance of the reflection grating spectrometer onboard XMM-NewtonOct 20 2014Context: XMM-Newton was launched on 10 December 1999 and has been operational since early 2000. One of the instruments onboard XMM-Newton is the reflection grating spectrometer (RGS). Two identical RGS instruments are available, with each RGS combining ... More
Spectral Aspects of the Evolution of Gamma-Ray BurstsOct 12 1999A review on the spectral and temporal properties of gamma-ray bursts is given. Special attention is paid to the spectral evolution of their continuum emission and its connection to the time evolution of the intensity. Efforts on systematizing these observations ... More
Smoothly Broken Power Law Spectra of Gamma-Ray BurstsNov 30 1998A five-parameter expression for a smoothly broken power law is presented. It is used to fit Gamma-Ray Burst (GRB) spectra observed by BATSE. The function is compared to previously used four-parameter functions, such as a sharply broken power law and the ... More
Chip-firing may be much faster than you thinkNov 06 2014Nov 24 2014A new bound (Theorem \ref{thm:main}) for the duration of the chip-firing game with $N$ chips on a $n$-vertex graph is obtained, by a careful analysis of the pseudo-inverse of the discrete Laplacian matrix of the graph. This new bound is expressed in terms ... More
On taut singularities in arbitrary characteristicsMar 25 2013Over $\C$, Henry Laufer classified all taut surface singularities. We adapt and extent his transcendental methods to positive characteristic. With this we show that if a normal surface singularity is taut over $\C$, then the normal surface singularities ... More
Tautological relations in moduli spaces of weighted pointed curvesJun 27 2013Sep 29 2015Pandharipande-Pixton have used the geometry of the moduli space of stable quotients to produce relations between tautological Chow classes on the moduli space $M_g$ of smooth genus g curves. We study a natural extension of their methods to the boundary ... More
Embeddings of decomposition spacesMay 31 2016Feb 15 2018Many smoothness spaces in harmonic analysis are decomposition spaces. In this paper we ask: Given two decomposition spaces, is there an embedding between the two? A decomposition space $\mathcal{D}(\mathcal{Q}, L^p, Y)$ can be described using : a covering ... More
Explicit Methods for Radical Function Fields over Finite FieldsNov 30 2009We develop explicit formulas and algorithms for arithmetic in radical function fields K/k(x) over finite constant fields. First, we classify which places of k(x) whose local integral bases have an easy monogenic form, and give explicit formulas for these ... More
Increasing Positive Monoids of Ordered Fields Are FF-monoidsOct 27 2016Given an ambient ordered field $K$, a positive monoid is a countably generated additive submonoid of the nonnegative cone of $K$. In this paper, we first generalize a few atomic features exhibited by Puiseux monoids of the field of rational numbers to ... More
On monotonicity-preserving perturbations of $M$-matricesAug 04 2013We obtain an explicit analytical sufficient condition on $E$ that ensures the monotonicity of the matrix $M+E$, where $M$ is an $M$-matrix.
Isometry groups of Lorentzian manifolds of finite volume and The local geometry of compact homogeneous Lorentz spacesJun 27 2011Oct 06 2011Based on the work of Adams and Stuck as well as on the work of Zeghib, we classify the Lie groups which can act isometrically and locally effectively on Lorentzian manifolds of finite volume. In the case that the corresponding Lie algebra contains a direct ... More
The X-ray Lightcurve of the Supermassive star eta Carinae, 1996--2014Jul 28 2015Eta Carinae is the nearest example of a supermassive, superluminous, unstable star. Mass loss from the system is critical in shaping its circumstellar medium and in determining its ultimate fate. Eta Car currently loses mass via a dense, slow stellar ... More
Local U(2,2) Symmetry in Relativistic Quantum MechanicsMar 11 1997Feb 07 2007Local gauge freedom in relativistic quantum mechanics is derived from a measurement principle for space and time. For the Dirac equation, one obtains local U(2,2) gauge transformations acting on the spinor index of the wave functions. This local U(2,2) ... More
Hidden Charm Spectroscopy from TevatronMay 03 2011The observation of a narrow structure near the J/psi phi threshold in exclusive B+ to J/psi phi K+ decays produced in p-pbar collisions at sqrt(s) = 1.96 TeV is reported. A signal of 19 +- 6(stat) +- 3(syst) events, with statistical significance of 5.0 ... More
Node Theorem for Matrix Schroedinger OperatorsJun 14 1996Mar 12 1997In this paper we study the ground states of a matrix Schroedinger operator, that is an operator of the type (-Laplace) + V acting on m-component wave functions in R^n. We prove in generalization of the classical node theorem that the ground states of ... More
Electron-phonon interaction in Fe-based superconductors: Coupling of magnetic moments with phonons in LaFeAsO$_{1-x}$F$_{x}$Sep 24 2010The coupling of Fe magnetic moments in LaFeAsO$_{1-x}$F$_{x}$ with the As $A_{1g}$ phonon is calculated. We present first principles calculations of the atomic and electronic structure of LaFeAsO as a function of electron doping. We perform calculations ... More
Stacked polytopes and tight triangulations of manifoldsNov 26 2009Mar 03 2011Tightness of a triangulated manifold is a topological condition, roughly meaning that any simplexwise linear embedding of the triangulation into euclidean space is "as convex as possible". It can thus be understood as a generalization of the concept of ... More
Relations in the Tautological Ring and Frobenius Manifolds near the DiscriminantMay 13 2015Sep 29 2015For generically semisimple cohomological field theories pole cancellation in the Givental-Teleman classification implies relations between classes in the tautological ring of the moduli space of curves. For the theory of the $A_2$-singularity these are ... More
Comparing tautological relations from the equivariant Gromov-Witten theory of projective spaces and spin structuresJul 17 2014Sep 29 2015Pandharipande-Pixton-Zvonkine's proof of Pixton's generalized Faber-Zagier relations in the tautological ring of $\overline M_{g, n}$ has started the study of tautological relations from semisimple cohomological field theories. In this article we compare ... More
Ehrhart f*-coefficients of polytopal complexes are non-negative integersFeb 13 2012Mar 06 2012The Ehrhart polynomial $L_P$ of an integral polytope $P$ counts the number of integer points in integral dilates of $P$. Ehrhart polynomials of polytopes are often described in terms of their Ehrhart $h^*$-vector (aka Ehrhart $\delta$-vector), which is ... More
Minimal Stable Sets in TournamentsMar 14 2008Sep 20 2010We propose a systematic methodology for defining tournament solutions as extensions of maximality. The central concepts of this methodology are maximal qualified subsets and minimal stable sets. We thus obtain an infinite hierarchy of tournament solutions, ... More
A Bernstein Theorem for Minimal Maps with Small Second Fundamental FormNov 27 2017We consider minimal maps $f:M\to N$ between Riemannian manifolds $(M,\mathrm{g}_M)$ and $(N,\mathrm{g}_N)$, where $M$ is compact and where the sectional curvatures satisfy $\sec_N\le \sigma\le \sec_M$ for some $\sigma>0$. Under certain assumptions on ... More
Definition of the Dirac Sea in the Presence of External FieldsMay 02 1997Jan 06 2009It is shown that the Dirac sea can be uniquely defined for the Dirac equation with general interaction, if we impose a causality condition on the Dirac sea. We derive an explicit formula for the Dirac sea in terms of a power series in the bosonic potentials. ... More
Relative entropies and their use in quantum information theoryNov 27 2016This dissertation investigates relative entropies, also called generalized divergences, and how they can be used to characterize information-theoretic tasks in quantum information theory. The main goal is to further refine characterizations of the optimal ... More
Measurement of Spin Correlation coefficients in \vec p \vec p --> d pi^+Dec 16 1999The spin correlation coefficent combinations A_{xx}+A_{yy} and A_{xx}-A_{yy}, the spin correlation coefficients A_{xz} and A_{zz}, and the analyzing power were measured for \vec p \vec p --> d pi^+ between center-of-mass angles 25 deg \leq \theta \leq ... More
Spin correlations in $\vec{p}\vec{p}\to pnπ^{+}$ pion production near thresholdAug 20 2001A first measurement of longitudinal as well as transverse spin correlation coefficients for the reaction $\vec{p}\vec{p}\to pn\pi^+$ was made using a polarized proton target and a polarized proton beam. We report kinematically complete measurements for ... More
Initial singlet and triplet spin state contributions to pp -> pp pi0Aug 31 1999The PINTEX facility at the IUCF Cooler ring, dedicated to the study of spin dependence in nucleon-nucleon interactions, has been used to measure polarization observables of the reaction pp -> pp pi0 at beam energies between 325 and 400 MeV. The stored ... More
Measurement of Partial-Wave Contributions in pp --> pp pi^0Jul 26 1999Jul 27 1999We report a measurement of the spin-dependent total cross section ratios delta_sigma_T/sigma_tot and delta_sigma_L/sigma_tot of the pp --> pp pi^0 reaction between 325 MeV and 400 MeV. The experiment was carried out with a polarized internal target in ... More
Multiple Asteroid Systems: Dimensions and Thermal Properties from Spitzer Space Telescope and Ground-Based ObservationsApr 19 2016Photometric lightcurves were also obtained for 14 of them during the Spitzer observations to provide the context of the observations and reliable estimates of their absolute magnitudes. The extracted mid-IR spectra were analyzed using a modified standard ... More
A Molecular Mass Gradient is the Key Parameter of the Genetc Code OrganizationJul 21 2009The structure of the genetic code is discussed in formal terms. A rectangular table of the code ("the code matrix"), whose properties reveal its arithmetical content tagged with the information symbols in several notations. New parameters used to analyze ... More
Vacuum Birefringence as a Vacuum Emission ProcessOct 12 2015We argue that the phenomenon of vacuum birefringence in strong inhomogeneous electromagnetic fields can be most efficiently analyzed in terms of a vacuum emission process. In this contribution, we exemplarily stick to the case of vacuum birefringence ... More