Results for "Sjoert Van Velzen"

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Black hole masses of tidal disruption event host galaxies IIFeb 11 2019We present new medium resolution, optical long-slit spectra of a sample of 6 UV/optical and 15 X-ray selected tidal disruption event candidate host galaxies. We measure emission line ratios from the optical spectra, finding that the large majority of ... More
On the mass and luminosity functions of tidal disruption flares: rate suppression due to black hole event horizonsJul 11 2017Jan 10 2018The tidal disruption of a star by a massive black hole is expected to yield a luminous flare of thermal emission. About two dozen of these stellar tidal disruption flares (TDFs) may have been detected in optical transient surveys. However, explaining ... More
The contribution of spin to jet-disk coupling in black holesAug 06 2013The spin of supermassive black holes could power jets from active galactic nuclei (AGN), although direct observational evidence for this conjecture is sparse. The accretion disk luminosity and jet power, on the other hand, have long been observed to follow ... More
Analytical Results for a Small Multiple-layer Parking SystemJun 05 2013in this article a multilayer parking system of size n=3 is studied. We prove that the asymptotic limit of the particle density in the center approaches a maximum of 1/2 in higher layers. This means a significant increase of capacity compared to the first ... More
Discovery of a time lag between the soft X-ray and radio emission of the tidal disruption flare ASASSN-14li: Evidence for linear disk-jet couplingSep 09 2017Mar 16 2018The tidal disruption of a star by a supermassive black hole can result in transient radio emission. The electrons producing these synchrotron radio flares could either be accelerated inside a relativistic jet or externally by shocks resulting from an ... More
The rate of stellar tidal disruption flares from SDSS dataOct 03 2012We report an observational estimate of the rate of stellar tidal disruption flares (TDFs), based on our (successful) search for these events in archival Sloan Digital Sky Survey (SDSS) multi-epoch imaging data. Our pipeline took advantage of the excellent ... More
Measurement of the rate of stellar tidal disruption flaresJul 24 2014Aug 26 2014We report an observational estimate of the rate of stellar tidal disruption flares (TDFs) in inactive galaxies, based on a successful search for these events among transients in galaxies using archival SDSS multi-epoch imaging data (Stripe 82). This search ... More
An enhanced rate of tidal disruptions in the centrally overdense E+A galaxy NGC 3156Apr 07 2016Dec 29 2016Time domain optical surveys have discovered roughly a dozen candidate stellar tidal disruption flares in the last five years, and future surveys like the {\it Large Synoptic Survey Telescope} will likely find hundreds to thousands more. These tidal disruption ... More
Radio jets from stellar tidal disruptionsApr 20 2011Jul 13 2011A star that passes too close to a massive black hole will be torn apart by tidal forces. The flare of photons emitted during the accretion of the stellar debris is predicted to be observable and candidates of such events have been observed at optical ... More
An enhanced rate of tidal disruptions in the centrally overdense E+A galaxy NGC 3156Apr 07 2016Time domain optical surveys have discovered roughly a dozen candidate stellar tidal disruption flares in the last five years, and future surveys like the {\it Large Synoptic Survey Telescope} will find hundreds to thousands more. These tidal disruption ... More
Nature and evolution of powerful radio galaxies and their link with the quasar luminosity functionNov 11 2014Current wide-area radio surveys are dominated by active galactic nuclei, yet many of these sources have no identified optical counterparts. Here we investigate whether one can constrain the nature and properties of these sources, using Fanaroff-Riley ... More
A New Class of Changing-Look LINERsApr 24 2019We report the discovery of six active galactic nuclei (AGN) caught "turning on" during the first nine months of the Zwicky Transient Facility (ZTF) survey. The host galaxies were classified as LINERs by weak narrow forbidden line emission in their archival ... More
Constraints on off-axis jets from stellar tidal disruption flaresSep 28 2012Mar 04 2013Many decades of observations of active galactic nuclei and X-ray binaries have shown that relativistic jets are ubiquitous when compact objects accrete. One could therefore anticipate the launch of a jet after a star is disrupted and accreted by a massive ... More
Science with an ngVLA: Tidal disruption eventsOct 15 2018The tidal disruption and subsequent accretion of a star by a supermassive black hole can be used as a laboratory to study the physics of relativistic jets. The ngVLA is the only planned instrument that can both discover and characterize a large number ... More
The first tidal disruption flare in ZTF: from photometric selection to multi-wavelength characterizationSep 07 2018Feb 07 2019We present Zwicky Transient Facility (ZTF) observations of the tidal disruption flare AT2018zr/PS18kh reported by Holoien et al. and detected during ZTF commissioning. The ZTF light curve of the tidal disruption event (TDE) samples the rise-to-peak exceptionally ... More
A Smart and Colorful Cadence for the LSST Wide Fast Deep Survey: Maximizing TDE ScienceDec 17 2018Tidal disruption events (TDEs) are rare, 10^(-7)/yr/Mpc^3 (Hung et al. 2018), yet the large survey volume of LSST implies a very large detection rate of 200/yr/(1000 deg^2) (van Velzen et al. 2011), a factor of 250 increase in the detection capability ... More
Sensitive Radio Survey of Obscured Quasar CandidatesMar 23 2016We study the radio properties of moderately obscured quasars over a range of redshifts to understand the role of radio activity in accretion using the Jansky Very Large Array (JVLA) at 6.0GHz and 1.4GHz. Our z~2.5 sample consists of optically-selected ... More
Stellar Tidal Disruption Events in General RelativityJan 30 2018A tidal disruption event (TDE) ensues when a star passes too close to the supermassive black hole (SMBH) in a galactic center and is ripped apart by the tidal field of the SMBH. The gaseous debris produced in a TDE can power a bright electromagnetic flare ... More
Radio galaxies of the local universe: all-sky catalog, luminosity functions, and clusteringMay 31 2012Jul 20 2012To understand the feedback of black holes on their environment or the acceleration of ultra-high energy cosmic rays in the present cosmic epoch, a systematic, all-sky inventory of radio galaxies in the local universe is needed. Here we present the first ... More
Discovery of transient infrared emission from dust heated by stellar tidal disruption flaresMay 13 2016Sep 13 2016Stars that pass within the Roche radius of a supermassive black hole will be tidally disrupted, yielding a sudden injection of gas close to the black hole horizon which produces an electromagnetic flare. A few dozen of these flares have been discovered ... More
Megahertz peaked-spectrum sources in the Boötes field I - a route towards finding high-redshift AGN?Mar 30 2015We present a 324.5MHz image of the NOAO Bo\"otes field that was made using Very Large Array (VLA) P-band observations. The image has a resolution of 5.6x5.1arcsec, a radius of $2.05^\circ$ and a central noise of ~0.2mJy\beam. Both the resolution and noise ... More
Optical/UV-to-X-Ray Echoes from the Tidal Disruption Flare ASASSN-14liMar 21 2017We carried out the first multi-wavelength (optical/UV and X-ray) photometric reverberation mapping of a tidal disruption flare (TDF) ASASSN-14li. We find that its X-ray variations are correlated with and lag the optical/UV fluctuations by 32$\pm$4 days. ... More
Gaia transient detection efficiency: hunting for nuclear transientsOct 27 2015We present a study of the detectability of transient events associated with galaxies for the Gaia European Space Agency astrometric mission. We simulated the on-board detections, and on-ground processing for a mock galaxy catalogue to establish the properties ... More
Late-time UV observations of tidal disruption flares reveal unobscured, compact accretion disksAug 31 2018The origin of thermal optical and UV emission from stellar tidal disruption flares (TDFs) remains an open question. We present Hubble Space Telescope far-UV (FUV) observations of eight optical/UV selected TDFs 5-10 years post-peak. Six sources are cleanly ... More
Black hole masses of tidal disruption event host galaxiesJun 27 2017The mass of the central black hole in a galaxy that hosted a tidal disruption event (TDE) is an important parameter in understanding its energetics and dynamics. We present the first homogeneously measured black hole masses of a complete sample of 12 ... More
Optical discovery of probable stellar tidal disruption flaresSep 08 2010Sep 13 2011Using archival SDSS multi-epoch imaging data (Stripe 82), we have searched for the tidal disruption of stars by super-massive black holes in non-active galaxies. Two candidate tidal disruption events (TDEs) are identified. They have optical black-body ... More
The Zwicky Transient Facility: Science ObjectivesFeb 05 2019The Zwicky Transient Facility (ZTF), a public-private enterprise, is a new time domain survey employing a dedicated camera on the Palomar 48-inch Schmidt telescope with a 47 deg$^2$ field of view and 8 second readout time. It is well positioned in the ... More
What are the megahertz peaked-spectrum sources?Apr 01 2016Megahertz peaked-spectrum (MPS) sources have spectra that peak at frequencies below 1 GHz in the observer's frame and are believed to be radio-loud active galactic nuclei (AGN). We recently presented a new method to search for high-redshift AGN by identifying ... More
The Zwicky Transient Facility: System Overview, Performance, and First ResultsFeb 05 2019The Zwicky Transient Facility (ZTF) is a new optical time-domain survey that uses the Palomar 48-inch Schmidt telescope. A custom-built wide-field camera provides a 47 deg$^2$ field of view and 8 second readout time, yielding more than an order of magnitude ... More
Radio spectra of bright compact sources at z>4.5Jan 23 2017Jan 25 2017High-redshift quasars are important to study galaxy and active galactic nuclei (AGN) evolution, test cosmological models, and study supermassive black hole growth. Optical searches for high-redshift sources have been very successful, but radio searches ... More
Multiple-Layer Parking with ScreeningAug 20 2015In this article a multilayer parking system with screening of size n=3 is studied with a focus on the time-dependent particle density. We prove that the asymptotic limit of the particle density increases from an average density of 1/3 on the first layer ... More
Evidence for rapid disk formation and reprocessing in the X-ray bright tidal disruption event AT 2018fykMar 28 2019We present optical spectroscopic and Swift UVOT/XRT observations of the X-ray and UV/optical bright tidal disruption event (TDE) AT 2018fyk/ASASSN-18ul discovered by ASAS-SN. The Swift lightcurve is atypical for a TDE, entering a plateau after $\sim$40 ... More
A radio jet from the optical and x-ray bright stellar tidal disruption flare ASASSN-14liNov 27 2015Jan 15 2016The tidal disruption of a star by a supermassive black hole leads to a short-lived thermal flare. Despite extensive searches, radio follow-up observations of known thermal stellar tidal disruption flares (TDFs) have not yet produced a conclusive detection. ... More
Discovery of Highly Blueshifted Broad Balmer and Metastable Helium Absorption Lines in a Tidal Disruption EventMar 13 2019We report the discovery of non-stellar hydrogen Balmer and metastable helium absorption lines accompanying a transient, high-velocity (0.05$c$) broad absorption line (BAL) system in the optical spectra of the tidal disruption event (TDE) AT2018zr ($z=0.071$). ... More
Energy Estimation of Cosmic Rays with the Engineering Radio Array of the Pierre Auger ObservatoryAug 18 2015Jun 20 2016The Auger Engineering Radio Array (AERA) is part of the Pierre Auger Observatory and is used to detect the radio emission of cosmic-ray air showers. These observations are compared to the data of the surface detector stations of the Observatory, which ... More
Measurement of the Radiation Energy in the Radio Signal of Extensive Air Showers as a Universal Estimator of Cosmic-Ray EnergyMay 09 2016Jun 21 2016We measure the energy emitted by extensive air showers in the form of radio emission in the frequency range from 30 to 80 MHz. Exploiting the accurate energy scale of the Pierre Auger Observatory, we obtain a radiation energy of 15.8 \pm 0.7 (stat) \pm ... More
Measurement of the cosmic ray spectrum above $4{\times}10^{18}$ eV using inclined events detected with the Pierre Auger ObservatoryMar 26 2015Nov 24 2015A measurement of the cosmic-ray spectrum for energies exceeding $4{\times}10^{18}$ eV is presented, which is based on the analysis of showers with zenith angles greater than $60^{\circ}$ detected with the Pierre Auger Observatory between 1 January 2004 ... More
An improved limit to the diffuse flux of ultra-high energy neutrinos from the Pierre Auger ObservatoryApr 21 2015Nov 24 2015Neutrinos in the cosmic ray flux with energies near 1 EeV and above are detectable with the Surface Detector array of the Pierre Auger Observatory. We report here on searches through Auger data from 1 January 2004 until 20 June 2013. No neutrino candidates ... More
SKA as a powerful hunter of jetted Tidal Disruption EventsJan 19 2015Observational consequences of the tidal disruption of stars by supermassive black holes (SMBHs) can enable us to discover quiescent SMBHs and constrain their mass function. Moreover, observing jetted TDEs (from previously non-active galaxies) provides ... More
A double radio relic in the merging galaxy cluster ZwCl 0008.8+5215Feb 10 2011Some merging galaxy clusters host diffuse elongated radio sources, also called radio relics. It is proposed that these radio relics trace shock waves in the intracluster medium created during a cluster merger event. Within the shock waves particles are ... More
Machine Learning for the Zwicky Transient FacilityFeb 05 2019The Zwicky Transient Facility is a large optical survey in multiple filters producing hundreds of thousands of transient alerts per night. We describe here various machine learning (ML) implementations and plans to make the maximal use of the large data ... More
The Magnetic Field and Polarization Properties of Radio Galaxies in Different Accretion StatesApr 25 2015We use the integrated polarized radio emission at 1.4 GHz ($\Pi_{\rm 1.4\,GHz}$) from a large sample of AGN (796 sources at redshifts $z<0.7$) to study the large-scale magnetic field properties of radio galaxies in relation to the host galaxy accretion ... More
Wide-field LOFAR imaging of the field around the double-double radio galaxy B1834+620: A fresh view on a restarted AGN and doubeltjesOct 02 2015The existence of double-double radio galaxies (DDRGs) is evidence for recurrent jet activity in AGN, as expected from standard accretion models. A detailed study of these rare sources provides new perspectives for investigating the AGN duty cycle, AGN-galaxy ... More
The Very Large Array Low-frequency Sky Survey Redux (VLSSr)Apr 02 2014We present the results of a recent re-reduction of the data from the Very Large Array (VLA) Low-frequency Sky Survey (VLSS). We used the VLSS catalog as a sky model to correct the ionospheric distortions in the data and create a new set of sky maps and ... More
A number theoretic question arising in the geometry of plane curves and in billiard dynamicsMar 25 2011We prove that if $\rho\neq1/2$ is a rational number between zero and one, then there is no integer $n>1$ such that $$ n\tan(\pi\rho)=\tan(n\pi\rho). $$ This has interpretations both in the theory of bicycle curves and that of mathematical billiards.
Weakly nonlocal irreversible thermodynamics - the Guyer-Krumhansl and the Cahn-Hilliard equationsJun 27 2001Oct 18 2001Examples of irreversible thermodynamic theory of nonlocal phenomena are given, based on generalized entropy current. Thermodynamic currents and forces are identified to derive the Guyer-Krumhansl and Cahn-Hilliard equations. In the latter case Gurtin's ... More
Weakly nonlocal irreversible thermodynamics - the Ginzburg-Landau equationNov 16 2001Dec 12 2001The variational approach to weakly nonlocal thermodynamic theories is critically revisited in the light of modern nonequilibrium thermodynamics. The example of Ginzburg-Landau equation is investigated in detail.
Direct Prediction of Cardiovascular Mortality from Low-dose Chest CT using Deep LearningOct 04 2018Cardiovascular disease (CVD) is a leading cause of death in the lung cancer screening population. Chest CT scans made in lung cancer screening are suitable for identification of participants at risk of CVD. Existing methods analyzing CT images from lung ... More
A Parallel-pulling Protocol for Free-Energy EvaluationMay 24 2011Feb 14 2012Jarzynski's equality (JE) allows us to compute free energy differences from distributions of work. In molecular dynamics simulations, the traditional way of constructing work distributions is to perform as many pulling simulations as possible. But reliable ... More
Singular vectors under random perturbationApr 12 2010Computing the first few singular vectors of a large matrix is a problem that frequently comes up in statistics and numerical analysis. Given the presence of noise, exact calculation is hard to achieve, and the following problem is of importance: \vskip2mm ... More
A simple SVD algorithm for finding hidden partitionsApr 15 2014Finding a hidden partition in a random environment is a general and important problem, which contains as subproblems many famous questions, such as finding a hidden clique, finding a hidden coloring, finding a hidden bipartition etc. In this paper, we ... More
Sum-product estimates via directed expandersMay 04 2007Let $\F_q$ be a finite field of order $q$ and $P$ be a polynomial in $\F_q[x_1, x_2]$. For a set $A \subset \F_q$, define $P(A):=\{P(x_1, x_2) | x_i \in A \}$. Using certain constructions of expanders, we characterize all polynomials $P$ for which the ... More
A structural approach to subset-sum problemsApr 20 2008We discuss a structural approach to subset-sum problems in additive combinatorics. The core of this approach are Freiman-type structural theorems, many of which will be presented through the paper. These results have applications in various areas, such ... More
Long-term radio and X-ray evolution of the tidal disruption event ASASSN-14liJan 09 2018We report on late time radio and X-ray observations of the tidal disruption event candidate ASASSN-14li, covering the first 1000 days of the decay phase. For the first $\sim200$ days the radio and X-ray emission fade in concert. This phase is better fit ... More
The Palomar Transient Factory Sky2Night programmeFeb 11 2019We present results of the Sky2Night project: a systematic, unbiased search for fast optical transients with the Palomar Transient Factory. We have observed 407 deg$^2$ in $R$-band for 8 nights at a cadence of 2 hours. During the entire duration of the ... More
Consistent nonparametric Bayesian inference for discretely observed scalar diffusionsJan 31 2013We study Bayes procedures for the problem of nonparametric drift estimation for one-dimensional, ergodic diffusion models from discrete-time, low-frequency data. We give conditions for posterior consistency and verify these conditions for concrete priors, ... More
Calibration of Phone Likelihoods in Automatic Speech RecognitionJun 14 2016In this paper we study the probabilistic properties of the posteriors in a speech recognition system that uses a deep neural network (DNN) for acoustic modeling. We do this by reducing Kaldi's DNN shared pdf-id posteriors to phone likelihoods, and using ... More
Bochner integrals in ordered vector spacesApr 21 2016We present a natural way to cover an Archimedean directed ordered vector space $E$ by Banach spaces and extend the notion of Bochner integrability to functions with values in $E$. The resulting set of integrable functions is an Archimedean directed ordered ... More
Integrals for functions with values in a partially ordered vector spaceMay 22 2015We consider integration of functions with values in a partially ordered vector space, and two notions of extension of the space of integrable functions. Applying both extensions to the space of real valued simple functions on a measure space leads to ... More
Status and prospects for $CPT$ and Lorentz invariance violation searches in neutral meson mixingJul 04 2014Feb 02 2015An overview of current experimental bounds on $CPT$ violation in neutral meson mixing is given. New values for the $CPT$ asymmetry in the $B^0$ and $B_s^0$ systems are deduced from published BaBar, Belle and LHCb results. With dedicated analyses, LHCb ... More
Galileons from Lovelock actionsFeb 02 2011Feb 10 2011We demonstrate how, for an arbitrary number of dimensions, the Galileon actions and their covariant generalizations can be obtained through a standard Kaluza-Klein compactification of higher-dimensional Lovelock gravity. In this setup, the dilaton takes ... More
Thin Spectrum States in SuperconductorsApr 27 2007We show that finite size superconductors have a spectrum of states at extremely low energy, i.e. inside the superconducting gap. The presence of this {\it thin spectrum} is a generic feature and related to the fact that in a superconductor the global ... More
Spontaneous Symmetry Breaking in Quantum MechanicsSep 21 2006We present a clear and mathematically simple procedure explaining spontaneous symmetry breaking in quantum mechanical systems. The procedure is applicable to a wide range of models and can be easily used to explain the existence of a symmetry broken state ... More
Dynamics on the SU(2) fundamental domainNov 24 1994For SU(2) gauge theory on the three-sphere we focus on a subspace of modes of the gauge field that contains the tunnelling paths and the sphalerons and on which the energy functional is degenerate to second order in the fields. The ultimate goal is to ... More
Front propagation techniques to calculate the largest Lyapunov exponent of dilute hard disk gasesJan 22 2002Jul 02 2002A kinetic approach is adopted to describe the exponential growth of a small deviation of the initial phase space point, measured by the largest Lyapunov exponent, for a dilute system of hard disks, both in equilibrium and in a uniform shear flow. We derive ... More
Forecasting Financial Extremes: A Network Degree Measure of Super-exponential GrowthMay 15 2015Investors in stock market are usually greedy during bull markets and scared during bear markets. The greed or fear spreads across investors quickly. This is known as the herding effect, and often leads to a fast movement of stock prices. During such market ... More
The occurrence of planets and other substellar bodies around white dwarfs using K2Nov 27 2017The majority of stars both host planetary systems and evolve into a white dwarf (WD). To understand their post-main-sequence (PMS) planetary system evolution, we present a search for transiting/eclipsing planets and other Substellar Bodies (SBs) around ... More
Optical probes of electron correlations in solidsJul 21 2008Classically the interaction between light and matter is given by the Maxwell relations. These are briefly reviewed and will be used as a basis to discuss several techniques that are used in optical spectroscopy. We then discuss the quantum mechanical ... More
Limit to manipulation of qubits due to spontaneous symmetry breakingJun 07 2006We consider a two-spin qubit that is subject to the orderparameter field of a symmetry broken manipulation device. It is shown that the thin spectrum of the manipulation device limits the coherence of the qubit.
Orbital-Peierls State in NaTiSi2O6Dec 22 2005Dec 23 2005Does the quasi one-dimensional titanium pyroxene NaTiSi2O6 exhibit the novel {\it orbital-Peierls} state? We calculate its groundstate properties by three methods: Monte Carlo simulations, a spin-orbital decoupling scheme and a mapping onto a classical ... More
Convection in rotating annuli: Ginzburg-Landau equations with tunable coefficientsSep 12 1996The coefficients of the complex Ginzburg-Landau equations that describe weakly nonlinear convection in a large rotating annulus are calculated for a range of Prandtl numbers $\sigma$. For fluids with $\sigma \approx 0.15$, we show that the rotation rate ... More
Theory of indirect resonant inelastic X-ray scatteringNov 19 2003We express the cross section for indirect resonant inelastic X-ray scattering in terms of an intrinsic dynamic correlation function of the system that is studied with this technique. The cross section is a linear combination of the charge response function ... More
Remarks on Frink's metrization technique and applicationsJul 07 2015Apr 26 2016In this paper, we give a simple counterexample to show again the limit of Frink's construction. As applications, we answer two conjectures posed by Berinde and Choban, calculate the induced metric from given $b$-metrics, and prove that the generalized ... More
Monodromy calculatons of fourth order equations of Calabi-Yau typeDec 30 2004Mar 20 2005This paper contains a preliminary study of the monodromy of certain fourth order differential equations, that were called of Calabi-Yau type in math.NT/0402386. Some of these equations can be interpreted as the Picard-Fuchs equations of a Calabi-Yau manifold ... More
The supermassive black hole coincident with the luminous transient ASASSN-15lhOct 03 2017Nov 18 2017The progenitors of astronomical transients are linked to a specific stellar population and galactic environment, and observing their host galaxies hence constrains the physical nature of the transient itself. Here, we use imaging from the Hubble Space ... More
Shock Waves in Weakly Compressed Granular MediaApr 23 2013We experimentally probe nonlinear wave propagation in weakly compressed granular media, and observe a crossover from quasi-linear sound waves at low impact, to shock waves at high impact. We show that this crossover grows with the confining pressure $P_0$, ... More
Schrodinger-Newton equation as a possible generator of quantum state reductionMar 31 2008Apr 02 2008It has been suggested by Diosi and Penrose that the occurrence of quantum state reduction in macroscopic objects is related to a manifestation of gravitational effects in quantum mechanics. Although within Penrose's framework the dynamics of the quantum ... More
Query Data With Fuzzy Information In Object-Oriented Databases An Approach Interval ValuesOct 16 2016In this paper, we propose methods of handling attributive values of object classes in object oriented database with fuzzy information and uncertainty based on quantitatively semantics based hedge algebraic. In this approach we consider to attributive ... More
Arithmetical conservation resultsJun 19 2017In this paper we present a proof of Goodman's Theorem, a classical result in the metamathematics of constructivism, which states that the addition of the axiom of choice to Heyting arithmetic in finite types does not increase the collection of provable ... More
Towards Practical, Precise and Parametric Energy Analysis of IT Controlled SystemsApr 20 2017Energy consumption analysis of IT-controlled systems can play a major role in minimising the overall energy consumption of such IT systems, during the development phase, or for optimisation in the field. Recently, a precise energy analysis was developed, ... More
Establishing Visible Interferometer System Responses: Resolved and Unresolved CalibratorsAug 11 2005The propagation of errors through the uniform disk visibility function is examined. Implications of those errors upon measures of absolute visibility through optical and near-infrared interferometers are considered within the context of using calibration ... More
Answers to Kirk-Shahzad's questions on strong $b$-metric spacesMar 27 2015Apr 02 2015In this paper, two open questions on strong $b$-metric spaces posed by Kirk and Shahzad [11, Chapter 12] are investigated. A counter-example is constructed to give a negative answer to the first question, and a theorem on the completion of a strong $b$-metric ... More
Simulating quantum computers with probabilistic methodsNov 09 2009Apr 12 2010We investigate the boundary between classical and quantum computational power. This work consists of two parts. First we develop new classical simulation algorithms that are centered on sampling methods. Using these techniques we generate new classes ... More
Second order QCD contributions to polarized spacelike and timelike processesJan 16 1998We will give an outline of the computation of the QCD corrections to the spin structure function g_1(x,Q^2) and the spin fragmentation function g_1^H(x,Q^2) which are measured in deep inelastic electron-proton scattering and in electron-positron annihilation ... More
Charm Production in Deep Inelastic Lepton-Hadron ScatteringAug 25 1997A review is given of the QCD corrections to charm quark production in deep inelastic electron-proton scattering. An outline of the computation of the virtual photon-parton subprocesses, from which one obtains the heavy quark coefficient functions, is ... More
Beware of the pseudogapFeb 19 2011In the pseudogap phase of a high-temperature cuprate superconductor, conflicting evidence from different experiments points to a competing state or a precursor-to-superconductivity state. One single experiment now determines that both states exist.
Surfaces of Revolution with Constant Gaussian Curvature in Four-SpaceMay 10 2012Sep 22 2012In this paper, we show that the constant property of the Gaussian curvature of surfaces of revolution in both $\mathbb R^4$ and $\mathbb R_1^4$ depend only on the radius of rotation. We then give necessary and sufficient conditions for the Gaussian curvature ... More
Exponential extinction time of the contact process on rank-one inhomogeneous random graphsFeb 05 2016We show that the contact process on the rank-one inhomogeneous random graphs and Erdos-R{\'e}nyi graphs with mean degree large enough survives a time exponential in the size of these graphs for any positive infection rate. In addition, a metastable result ... More
Introduction to the thermodynamic Bethe ansatzJun 09 2016Jul 24 2016We give a pedagogical introduction to the thermodynamic Bethe ansatz, a method that allows us to describe the thermodynamics of integrable models whose spectrum is found via the (asymptotic) Bethe ansatz. We set the stage by deriving the Fermi-Dirac distribution ... More
Collisions in piecewise flat gravity in 3+1 dimensionsFeb 19 2010We consider the (3+1)-dimensional locally finite gravity model proposed by 't Hooft. In particular we revisit the problem of resolving collisions of string defects. We provide a new geometric description of the configurations of strings using piecewise ... More
Cosmic Strings and Structure FormationOct 26 1998We discuss structure formation in cosmic string theories. Emphasis is laid on the properties of the peculiar velocity field, non-gaussian features and clusters of galaxies. It is found that the predicted peculiar velocity field is quiet ($v<150$ km/s ... More
The Brandeis Dice Problem and Statistical MechanicsAug 28 2014Jaynes invented the Brandeis Dice Problem as a simple illustration of the MaxEnt (Maximum Entropy) procedure that he had demonstrated to work so well in Statistical Mechanics. I construct here two alternative solutions to his toy problem. One, like Jaynes' ... More
The volume conjecture for augmented knotted trivalent graphsMay 01 2008Feb 05 2009We propose to generalize the volume conjecture to knotted trivalent graphs and we prove the conjecture for all augmented knotted trivalent graphs. As a corollary we find that for any link L there is a link containing L for which the volume conjecture ... More
Parameter estimation of a Levy copula of a discretely observed bivariate compound Poisson process with an application to operational risk modellingDec 01 2012A method is developed to estimate the parameters of a Levy copula of a discretely observed bivariate compound Poisson process without knowledge of common shocks. The method is tested in a small sample simulation study. Also, the method is applied to a ... More
Properties of neutron starsMar 20 2004I review attempts made to determine the properties of neutron stars. I focus on constraints on the maximum mass that a neutron star can have, and on attempts to measure neutron-star radii. So far, there appears to be only one neutron star for which there ... More
Constraints on the equation of state of ultra-dense matter from observations of neutron starsOct 15 2001I discuss constraints on the equation of state of matter at supra-nuclear densities that can be derived from observations of neutron stars. I focus on recent work on Vela X-1, which may well be substantially more massive than the canonical 1.4 solar masses, ... More
Neutron Star Mass DeterminationsJan 06 2000I review attempts made to determine the properties of neutron stars. The focus is on the maximum mass that a neutron star can have, or, conversely, the minimum mass required for the formation of a black hole. There appears to be only one neutron star ... More
Unique White Dwarfs Accompanying Recycled PulsarsNov 07 1996I introduce the two classes of pulsar, white-dwarf binaries, and describe for each what we have learned from a specific system, PSR J1012+5307 and PSR B0655+64, respectively, summarising what has been done, presenting new results, and discussing what ... More
Twisted Toroidal Lie AlgebrasJun 14 2001Using $n$ finite order automorphisms on a simple complex Lie algebra we construct twisted $n$-toroidal Lie algebras. Thus obtaining Lie algebras wich have a rootspace decomposition. For the case $n=2$ we list certain simple Lie algebras and their automorphisms, ... More