# Leonid Gurvits - Joint Institute for VLBI in Europe

## Contact Details

NameLeonid Gurvits |
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AffiliationJoint Institute for VLBI in Europe |
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Location |
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## Pubs By Year |
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## External Links |
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## Pub CategoriesMathematics - Combinatorics (12) Cosmology and Nongalactic Astrophysics (9) High Energy Astrophysical Phenomena (7) Quantum Physics (7) Instrumentation and Methods for Astrophysics (7) Astrophysics of Galaxies (6) Mathematics - Optimization and Control (6) Computer Science - Computational Complexity (5) Computer Science - Information Theory (2) Mathematics - Information Theory (2) Mathematics - Algebraic Geometry (2) Earth and Planetary Astrophysics (2) Mathematics - Mathematical Physics (2) Mathematical Physics (2) Statistics - Theory (1) Astrophysics (1) Computer Science - Computational Geometry (1) Mathematics - Statistics (1) Solar and Stellar Astrophysics (1) Computer Science - Data Structures and Algorithms (1) Mathematics - Classical Analysis and ODEs (1) Mathematics - Commutative Algebra (1) Computer Science - Computer Science and Game Theory (1) Quantitative Biology - Populations and Evolution (1) |

## Publications Authored By Leonid Gurvits

Radio-loud high-redshift quasars (HRQs), although only a few of them are known to date, are crucial for the studies of the growth of supermassive black holes (SMBHs) and the evolution of active galactic nuclei (AGN) at early cosmological epochs. Radio jets offer direct evidence of SMBHs, and their radio structures can be studied with the highest angular resolution using Very Long Baseline Interferometry (VLBI). Here we report on the observations of three HRQs (J0131-0321, J0906+6930, J1026+2542) at z>5 using the Korean VLBI Network and VLBI Exploration of Radio Astrometry Arrays (together known as KaVA) with the purpose of studying their pc-scale jet properties. Read More

**Authors:**Rocco Coppejans

^{1}, Sándor Frey

^{2}, Dávid Cseh

^{3}, Cornelia Müller

^{4}, Zsolt Paragi

^{5}, Heino Falcke

^{6}, Krisztina É. Gabányi

^{7}, Leonid I. Gurvits

^{8}, Tao An

^{9}, Oleg Titov

^{10}

**Affiliations:**

^{1}Department of Astrophysics/IMAPP, Radboud University, The Netherlands,

^{2}FÖMI Satellite Geodetic Observatory, Hungary,

^{3}Department of Astrophysics/IMAPP, Radboud University, The Netherlands,

^{4}Department of Astrophysics/IMAPP, Radboud University, The Netherlands,

^{5}Joint Institute for VLBI ERIC, The Netherlands,

^{6}Department of Astrophysics/IMAPP, Radboud University, The Netherlands,

^{7}FÖMI Satellite Geodetic Observatory, Hungary,

^{8}Joint Institute for VLBI ERIC, The Netherlands,

^{9}Shanghai Astronomical Observatory, Chinese Academy of Sciences, P. R. China,

^{10}Geoscience Australia, Australia

High-redshift radio-loud quasars are used to, among other things, test the predictions of cosmological models, set constraints on black hole growth in the early universe and understand galaxy evolution. Prior to this paper, 20 extragalactic radio sources at redshifts above 4.5 have been imaged with very long baseline interferometry (VLBI). Read More

The celebrated Brascamp-Lieb (BL) inequalities (and their extensions) are an important mathematical tool, unifying and generalizing numerous inequalities in analysis, convex geometry and information theory. While their structural theory is very well understood, far less is known about computing their main parameters. We give polynomial time algorithms to compute feasibility of BL-datum, the optimal BL-constant and a weak separation oracle for the BL-polytope. Read More

A bright optical flare was detected in the high-redshift ($z=2.133$) quasar CGRaBS J0809+5341 on 2014 April 13. The absolute magnitude of the object reached $-30. Read More

**Authors:**Dmitry A. Duev, Sergei V. Pogrebenko, Giuseppe Cimò, Guifré Molera Calvés, Tatiana M. Bocanegra Bahamón, Leonid I. Gurvits, Mark M. Kettenis, Joseph Kania, Valeriu Tudose, Pascal Rosenblatt, Jean-Charles Marty, Valery Lainey, Pablo de Vicente, Jonathan Quick, Marisa Nickola, Alexander Neidhardt, Gerhard Kronschnabl, Christian Plötz, Rüdiger Haas, Michael Lindqvist, Andrea Orlati, Alexander V. Ipatov, Mikhail A. Kharinov, Andrey G. Mikhailov, Jim Lovell, Jamie McCallum, Jamie Stevens, Sergei A. Gulyaev, Tim Natush, Stuart Weston, Weihua Wang, Bo Xia, Wenjun Yang, Long-Fei Hao, Juha Kallunki, Olivier Witasse

The closest ever fly-by of the Martian moon Phobos, performed by the European Space Agency's Mars Express spacecraft, gives a unique opportunity to sharpen and test the Planetary Radio Interferometry and Doppler Experiments (PRIDE) technique in the interest of studying planet - satellite systems. The aim of this work is to demonstrate a technique of providing high precision positional and Doppler measurements of planetary spacecraft using the Mars Express spacecraft. The technique will be used in the framework of Planetary Radio Interferometry and Doppler Experiments in various planetary missions, in particular in fly-by mode. Read More

**Authors:**Rocco Coppejans

^{1}, David Cseh

^{2}, Sjoert van Velzen

^{3}, Heino Falcke

^{4}, Huib T. Intema

^{5}, Zsolt Paragi

^{6}, Cornelia Muller

^{7}, Wendy L. Williams

^{8}, Sandor Frey

^{9}, Leonid I. Gurvits

^{10}, Elmar G. Kording

^{11}

**Affiliations:**

^{1}Department of Astrophysics/IMAPP, Radboud University Nijmegen,

^{2}Department of Astrophysics/IMAPP, Radboud University Nijmegen,

^{3}Department of Physics and Astronomy, The Johns Hopkins University,

^{4}Department of Astrophysics/IMAPP, Radboud University Nijmegen,

^{5}Leiden Observatory, Leiden University,

^{6}Joint Institute for VLBI ERIC,

^{7}Department of Astrophysics/IMAPP, Radboud University Nijmegen,

^{8}School of Physics, Astronomy and Mathematics, University of Hertfordshire,

^{9}FOMI Satellite Geodetic Observatory,

^{10}Joint Institute for VLBI ERIC,

^{11}Department of Astrophysics/IMAPP, Radboud University Nijmegen

Megahertz 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 unusually compact MPS sources. In this paper, we present European VLBI Network (EVN) observations of 11 MPS sources which we use to determine their sizes and investigate the nature of the sources with ~10 mas resolution. Read More

**Authors:**Michael D. Johnson

^{1}, Yuri Y. Kovalev

^{2}, Carl R. Gwinn

^{3}, Leonid I. Gurvits

^{4}, Ramesh Narayan

^{5}, Jean-Pierre Macquart

^{6}, David L. Jauncey

^{7}, Peter A. Voitsik

^{8}, James M. Anderson

^{9}, Kirill V. Sokolovsky

^{10}, Mikhail M. Lisakov

^{11}

**Affiliations:**

^{1}Harvard-Smithsonian CfA,

^{2}ASC Lebedev, MPIfR,

^{3}UCSB,

^{4}JIVE, Delft U,

^{5}Harvard-Smithsonian CfA,

^{6}ICRAR/Curtin, CAASTRO,

^{7}CSIRO, ANU Canberra,

^{8}ASC Lebedev,

^{9}Helmholtz-Zentrum Potsdam, MPIfR,

^{10}ASC Lebedev, SAI MSU,

^{11}ASC Lebedev

Earth-space interferometry with RadioAstron provides the highest direct angular resolution ever achieved in astronomy at any wavelength. RadioAstron detections of the classic quasar 3C273 on interferometric baselines up to 171,000 km suggest brightness temperatures exceeding expected limits from the "inverse-Compton catastrophe" by two orders of magnitude. We show that at 18 cm, these estimates most probably arise from refractive substructure introduced by scattering in the interstellar medium. Read More

Many physical parameters that can be estimated from space mission tracking data influence both the translational dynamics and proper time rates of observers. These different proper time rates cause a variability of the time transfer observable beyond that caused by their translational (and rotational) dynamics. With the near-future implementation of (interplanetary) transponder laser ranging, these effects will become increasingly important, requiring a re-evaluation of the common data analysis practice of using a priori time ephemerides, which is the goal of this paper. Read More

In this paper we present a deterministic polynomial time algorithm for testing if a symbolic matrix in non-commuting variables over $\mathbb{Q}$ is invertible or not. The analogous question for commuting variables is the celebrated polynomial identity testing (PIT) for symbolic determinants. In contrast to the commutative case, which has an efficient probabilistic algorithm, the best previous algorithm for the non-commutative setting required exponential time (whether or not randomization is allowed). Read More

**Authors:**Ivan Agudo, Markus Boettcher, Heino Falcke, Markos Georganopoulos, Gabriele Ghisellini, Gabriele Giovannini, Marcello Giroletti, Jose L. Gomez, Leonid Gurvits, Robert Laing, Matthew Lister, Jose-Maria Marti, Eileen T. Meyer, Yosuke Mizuno, Shane O'Sullivan, Paolo Padovani, Zsolt Paragi, Manel Perucho, Dominik Schleicher, Lukasz Stawarz, Nektarios Vlahakis, John Wardle

Relativistic jets in active galactic nuclei (AGN) are among the most powerful astrophysical objects discovered to date. Indeed, jetted AGN studies have been considered a prominent science case for SKA, and were included in several different chapters of the previous SKA Science Book (Carilli & Rawlings 2004). Most of the fundamental questions about the physics of relativistic jets still remain unanswered, and await high-sensitivity radio instruments such as SKA to solve them. Read More

**Authors:**Zsolt Paragi, Leith Godfrey, Cormac Reynolds, Maria Rioja, Adam Deller, Bo Zhang, Leonid Gurvits, Michael Bietenholz, Arpad Szomoru, Hayley Bignall, Paul Boven, Patrick Charlot, Richard Dodson, Sandor Frey, Michael Garrett, Hiroshi Imai, Andrei Lobanov, Mark Reid, Eduardo Ros, Huib van Langevelde, J. Anton Zensus, Xing Wu Zheng, Antxon Alberdi, Ivan Agudo, Tao An, Megan Argo, Rob Beswick, Andy D. Biggs, Andreas Brunthaler, Robert M. Campbell, Giuseppe Cimo, Francisco Colomer, Stephane Corbel, John Conway, David Cseh, Roger Deane, Heino Falcke, Krisztina Gabanyi, Marcin Gawronski, Michael Gaylard, Gabriele Giovannini, Marcello Giroletti, Ciriaco Goddi, Sharmila Goedhart, Jose L. Gomez, Alastair Gunn, Taehyun Jung, Preeti Kharb, Hans-Rainer Klockner, Elmar Kording, Yurii Yu. Kovalev, Magdalena Kunert-Bajraszewska, Michael Lindqvist, Matt Lister, Franco Mantovani, Ivan Marti-Vidal, Mar Mezcua, John McKean, Enno Middelberg, James Miller-Jones, Javier Moldon, Tom Muxlow, Tim O'Brien, Miguel Pérez-Torres, Sergei Pogrebenko, Jonathan Quick, Anthony P. Rushton, Richard Schilizzi, Oleg Smirnov, Bong Won Sohn, Gabriele Surcis, Greg Taylor, Steven Tingay, Valeriu Tudose, Alexander van der Horst, Joeri van Leeuwen, Tiziana Venturi, Rene Vermeulen, Wouter Vlemmings, Aletha de Witt, Olaf Wucknitz, Jun Yang

Adding VLBI capability to the SKA arrays will greatly broaden the science of the SKA, and is feasible within the current specifications. SKA-VLBI can be initially implemented by providing phased-array outputs for SKA1-MID and SKA1-SUR and using these extremely sensitive stations with other radio telescopes, and in SKA2 by realising a distributed configuration providing baselines up to thousands of km, merging it with existing VLBI networks. The motivation for and the possible realization of SKA-VLBI is described in this paper. Read More

**Authors:**Andrew P. V. Siemion, James Benford, Jin Cheng-Jin, Jayanth Chennamangalam, James Cordes, David R. DeBoer, Heino Falcke, Mike Garrett, Simon Garrington, Leonid Gurvits, Melvin Hoare, Eric J. Korpela, Joseph Lazio, David Messerschmitt, Ian S. Morrison, Tim O'Brien, Zsolt Paragi, Alan Penny, Laura Spitler, Jill Tarter, Dan Werthimer

The vast collecting area of the Square Kilometre Array (SKA), harnessed by sensitive receivers, flexible digital electronics and increased computational capacity, could permit the most sensitive and exhaustive search for technologically-produced radio emission from advanced extraterrestrial intelligence (SETI) ever performed. For example, SKA1-MID will be capable of detecting a source roughly analogous to terrestrial high-power radars (e.g. Read More

The accuracy of orbit determination has a strong impact on the scientific output of the Space VLBI mission RadioAstron. The aim of this work is to improve the RadioAstron orbit reconstruction by means of sophisticated dynamical modelling of its motion in combination with multi-station Doppler tracking of the RadioAstron spacecraft. The improved orbital solution is demonstrated using Doppler measurements of the RadioAstron downlink signal and by correlating VLBI observations made by RadioAstron with ground-based telescopes using the enhanced orbit determination data. Read More

A brief review of VLBI structures in extremely high-redshift AGN (revised/edited). Read More

We give new lower and upper bounds on the permanent of a doubly stochastic matrix. Combined with previous work, this improves on the deterministic approximation factor for the permanent. We also give a combinatorial application of the lower bound, proving S. Read More

**Authors:**Jun Yang

^{1}, Yonghua Xu

^{2}, Zhixuan Li

^{3}, Zsolt Paragi

^{4}, Robert M. Campbell

^{5}, Leonid Gurvits

^{6}, Zhiqiang Shen

^{7}, Xiaoyu Hong

^{8}, Bo Xia

^{9}

**Affiliations:**

^{1}JIVE, Netherlands,

^{2}YNAO, P.R. China,

^{3}YNAO,

^{4}JIVE,

^{5}JIVE,

^{6}JIVE,

^{7}SHAO, P.R. China,

^{8}SHAO,

^{9}SHAO

**Category:**High Energy Astrophysical Phenomena

The X-ray transient MAXI J1836-194 is a newly-identified Galactic black hole binary candidate. As most X-ray transients, it was discovered at the beginning of an X-ray outburst. After the initial canonical X-ray hard state, the outburst evolved into a hard intermediate state and then went back to the hard state. Read More

We examine a two-person game we call Will-Testing in which the strategy space for both players is a real number. It has no equilibrium. When an infinitely large set of players plays this in all possible pairings, there is an equilibrium for the distribution of strategies which requires all players to use different strategies. Read More

We present the results of several multi-station Very Long Baseline Interferometry (VLBI) experiments conducted with the ESA spacecraft Venus Express as a target. To determine the true capabilities of VLBI tracking for future planetary missions in the solar system, it is necessary to demonstrate the accuracy of the method for existing operational spacecraft. We describe the software pipeline for the processing of phase referencing near-field VLBI observations and present results of the ESA Venus Express spacecraft observing campaign conducted in 2010-2011. Read More

Global VLBI (EVN+VLBA) polarization observations at 5 and 8.4 GHz of ten high redshift (z > 3) quasars are presented. The core and jet brightness temperatures are found through modelling the self-calibrated uv-data with Gaussian components, which provide reliable estimates of the flux density and size of individual components. Read More

**Authors:**Leonid Gurvits

Let $A \in \Omega_n$ be doubly-stochastic $n \times n$ matrix. Alexander Schrijver proved in 1998 the following remarkable inequality per(\widetilde{A}) \geq \prod_{1 \leq i,j \leq n} (1- A(i,j)); \widetilde{A}(i,j) =: A(i,j)(1-A(i,j)), 1 \leq i,j \leq n. We use the above Shrijver's inequality to prove the following lower bound: \frac{per(A)}{F(A)} \geq 1; F(A) =: \prod_{1 \leq i,j \leq n} (1- A(i,j))^{1- A(i,j)}. Read More

This paper has been withdrawn by the author as one of the coauthors needs institutional permission. Read More

Context. The high-redshift (z = 4.72) blazar J1430+4204 produced a major radio outburst in 2005. Read More

The high-redshift (z=4.72) blazar J1430+4204 produced an exceptional radio outburst in 2006. We analyzed 15-GHz radio interferometric images obtained with the Very Long Baseline Array (VLBA) before and after the outburst, to search for possible structural changes on milli-arcsecond angular scales and to determine physical parameters of the source. Read More

An upper bound on the ergodic capacity of {\bf MIMO} channels was introduced recently in arXiv:0903.1952. This upper bound amounts to the maximization on the simplex of some multilinear polynomial $p(\lambda_1,. Read More

We study multivariate entire functions and polynomials with non-negative coefficients. A class of {\bf Strongly Log-Concave} entire functions, generalizing {\it Minkowski} volume polynomials, is introduced: an entire function $f$ in $m$ variables is called {\bf Strongly Log-Concave} if the function $(\partial x_1)^{c_1}.. Read More

R. Pemantle conjectured, and T.M. Read More

Let $p$ be a homogeneous polynomial of degree $n$ in $n$ variables, $p(z_1,... Read More

Let ${\bf K} = (K_1, ... Read More

**Affiliations:**

^{1}Shanghai Astronomical Observatory of the Chinese Academy of Sciences,

^{2}Joint Institute for VLBI in Europe,

^{3}Max-Planck-Institut fur Radioastronomie,

^{4}FOMI Satellite Geodetic Observatory,

^{5}Shanghai Astronomical Observatory of the Chinese Academy of Sciences

**Category:**Astrophysics

Based on the VLBI Space Observatory Programme (VSOP) observations at 1.6 and 5 GHz, we find that the luminous high-redshift (z=3.215) quasar PKS 1402+044 (J1405+0415) has a pronounced 'core--jet' structure. Read More

We derive here the Friedland-Tverberg inequality for positive hyperbolic polynomials. This inequality is applied to give lower bounds for the number of matchings in $r$-regular bipartite graphs. It is shown that some of these bounds are asymptotically sharp. Read More

Let $p(x_1,... Read More

Consider a homogeneous polynomial $p(z_1,... Read More

We show that for an m-qubit quantum system, there is a ball of radius asymptotically approaching kappa 2^{-gamma m} in Frobenius norm, centered at the identity matrix, of separable (unentangled) positive semidefinite matrices, for an exponent gamma = (1/2)((ln 3/ln 2) - 1), roughly .29248125. This is much smaller in magnitude than the best previously known exponent, from our earlier work, of 1/2. Read More

It is proved that the roots of combinations of matrix polynomials with real roots can be recast as eigenvalues of combinations of real symmetric matrices, under certain hypotheses. The proof is based on recent solution of the Lax conjecture. Several applications and corollaries, in particular concerning hyperbolic matrix polynomials, are presented. Read More

We prove that the mixed discriminant of doubly stochastic $n$-tuples of semidefinite hermitian $n \times n$ matrices is bounded below by $\frac{n!}{n^{n}}$ and that this bound is uniquely attained at the $n$-tuple $(\frac{1}{n} I,... Read More

Let $p(x_1,... Read More

The main topic of this paper is various "hyperbolic" generalizations of the Edmonds-Rado theorem on the rank of intersection of two matroids. We prove several results in this direction and pose a few questions. We also give generalizations of the Obreschkoff theorem and recent results of J. Read More

This paper continues research initiated in quant-ph/0201022 . The main subject here is the so-called Edmonds' problem of deciding if a given linear subspace of square matrices contains a nonsingular matrix . We present a deterministic polynomial time algorithm to solve this problem for linear subspaces satisfying a special matroids motivated property, called in the paper the Edmonds-Rado property . Read More

We show that for an m-partite quantum system, there is a ball of radius 2^{-(m/2-1)} in Frobenius norm, centered at the identity matrix, of separable (unentangled) positive semidefinite matrices. This can be used to derive an epsilon below which mixtures of epsilon of any density matrix with 1 - epsilon of the maximally mixed state will be separable. The epsilon thus obtained is exponentially better (in the number of systems) than existing results. Read More

For finite-dimensional bipartite quantum systems, we find the exact size of the largest balls, in spectral $l_p$ norms for $1 \le p \le \infty$, of separable (unentangled) matrices around the identity matrix. This implies a simple and intutively meaningful geometrical sufficient condition for separability of bipartite density matrices: that their purity $\tr \rho^2$ not be too large. Theoretical and experimental applications of these results include algorithmic problems such as computing whether or not a state is entangled, and practical ones such as obtaining information about the existence or nature of entanglement in states reached by NMR quantum computation implementations or other experimental situations. Read More

Classical matching theory can be defined in terms of matrices with nonnegative entries. The notion of Positive operator, central in Quantum Theory, is a natural generalization of matrices with nonnegative entries. Based on this point of view, we introduce a definition of perfect Quantum (operator) matching . Read More