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  • Open Access English
    Authors: 
    Ivano Baronchelli; G. Rodighiero; Harry I. Teplitz; Claudia Scarlata; Alberto Franceschini; S. Berta; Laia Barrufet; Mattia Vaccari; Matteo Bonato; Laure Ciesla; +15 more
    Publisher: HAL CCSD
    Countries: France, Italy, United States
    Project: EC | HELP (607254)

    For a sample of star forming galaxies in the redshift interval 0.15$<$z$<$0.3, we study how both the relative strength of the AGN infra-red emission, compared to that due to the star formation (SF), and the numerical fraction of AGNs, change as a function of the total stellar mass of the hosting galaxy group (M$^{*}_{\mathrm{group}}$), between $10^{10.25}$ and $10^{11.9}$M$_{\odot}$. Using a multi-component SED fitting analysis, we separate the contribution of stars, AGN torus and star formation to the total emission at different wavelengths. This technique is applied to a new multi-wavelength data-set in the SIMES field (23 not redundant photometric bands), spanning the wavelength range from the UV (GALEX) to the far-IR (Herschel) and including crucial AKARI and WISE mid-IR observations (4.5 \mu m$<\lambda<$24 \mu m), where the BH thermal emission is stronger. This new photometric catalog, that includes our best photo-z estimates, is released through the NASA/IPAC Infrared Science Archive (IRSA). Groups are identified through a friends of friends algorithm ($\sim$62% purity, $\sim$51% completeness). We identified a total of 45 galaxies requiring an AGN emission component, 35 of which in groups and 10 in the field. We find BHAR$\propto ($M$^{*}_{\mathrm{group}})^{1.21\pm0.27}$ and (BHAR/SFR)$\propto ($M$^{*}_{\mathrm{group}})^{1.04\pm0.24}$ while, in the same range of M$^{*}_{\mathrm{group}}$, we do not observe any sensible change in the numerical fraction of AGNs. Our results indicate that the nuclear activity (i.e. the BHAR and the BHAR/SFR ratio) is enhanced when galaxies are located in more massive and richer groups. Comment: 31 pages, 23 figures

  • Open Access
    Authors: 
    Adi Shafir; David Andelman;
    Publisher: Royal Society of Chemistry (RSC)

    We study the contribution of polyelectrolytes in solution to the bending moduli of charged membranes. Using the Helfrich free energy, and within the mean-field theory, we calculate the dependence of the bending moduli on the electrostatics and short-range interactions between the membrane and the polyelectrolyte chains. The most significant effect is seen for strong short-range interactions and low amounts of added salt where a substantial increase in the bending moduli of order $1 k_BT$ is obtained. From short-range repulsive membranes, the polyelectrolyte contribution to the bending moduli is small, of order $0.1 k_BT$ up to at most $1 k_BT$. For weak short-range attraction, the increase in membrane rigidity is smaller and of less significance. It may even become negative for large enough amounts of added salt. Our numerical results are obtained by solving the adsorption problem in spherical and cylindrical geometries. In some cases the bending moduli are shown to follow simple scaling laws. 16 pages, 6 figures

  • Publication . Article . Other literature type . Preprint . 2019
    Open Access
    Authors: 
    Igarashi, Ayumi; Izsak, Rani; Elkind, Edith;
    Publisher: Association for the Advancement of Artificial Intelligence (AAAI)
    Country: United Kingdom
    Project: EC | ACCORD (639945)

    Cooperative games provide a framework to study cooperation among self-interested agents. They offer a number of solution concepts describing how the outcome of the cooperation should be shared among the players. Unfortunately, computational problems associated with many of these solution concepts tend to be intractable---NP-hard or worse. In this paper, we incorporate complexity measures recently proposed by Feige and Izsak (2013), called dependency degree and supermodular degree, into the complexity analysis of cooperative games. We show that many computational problems for cooperative games become tractable for games whose dependency degree or supermodular degree are bounded. In particular, we prove that simple games admit efficient algorithms for various solution concepts when the supermodular degree is small; further, we show that computing the Shapley value is always in FPT with respect to the dependency degree. Finally, we note that, while determining the dependency among players is computationally hard, there are efficient algorithms for special classes of games. 10 pages, full version of accepted AAAI-18 paper

  • Publication . Article . Preprint . 2017
    Open Access English
    Authors: 
    Kyle Kawagoe; Greg Huber; Marc Pradas; Michael Wilkinson; Alain Pumir; Eli Ben-Naim;

    We investigate statistical properties of trails formed by a random process incorporating aggregation, fragmentation, and diffusion. In this stochastic process, which takes place in one spatial dimension, two neighboring trails may combine to form a larger one and also, one trail may split into two. In addition, trails move diffusively. The model is defined by two parameters which quantify the fragmentation rate and the fragment size. In the long-time limit, the system reaches a steady state, and our focus is the limiting distribution of trail weights. We find that the density of trail weight has power-law tail $P(w) \sim w^{-\gamma}$ for small weight $w$. We obtain the exponent $\gamma$ analytically, and find that it varies continuously with the two model parameters. The exponent $\gamma$ can be positive or negative, so that in one range of parameters small-weight tails are abundant, and in the complementary range, they are rare. Comment: 8 pages, 8 figures

  • Publication . Preprint . Conference object . Article . 2019
    Open Access
    Authors: 
    Yichao Yan; Qiang Zhang; Bingbing Ni; Wendong Zhang; Minghao Xu; Xiaokang Yang;
    Publisher: IEEE

    Person re-identification has achieved great progress with deep convolutional neural networks. However, most previous methods focus on learning individual appearance feature embedding, and it is hard for the models to handle difficult situations with different illumination, large pose variance and occlusion. In this work, we take a step further and consider employing context information for person search. For a probe-gallery pair, we first propose a contextual instance expansion module, which employs a relative attention module to search and filter useful context information in the scene. We also build a graph learning framework to effectively employ context pairs to update target similarity. These two modules are built on top of a joint detection and instance feature learning framework, which improves the discriminativeness of the learned features. The proposed framework achieves state-of-the-art performance on two widely used person search datasets. To appear in CVPR 2019

  • Open Access
    Authors: 
    Liam Connor; J. van Leeuwen; L. C. Oostrum; Emily Petroff; Yogesh Maan; Elizabeth A. K. Adams; Jisk Attema; J. E. Bast; Oliver M. Boersma; H. Dénes; +31 more
    Publisher: Oxford University Press (OUP)
    Country: Netherlands
    Project: NWO | ARTS - the Apertif Radio ... (10066), EC | RadioNet (730562), EC | ALERT (617199), NWO | Microporous membranes fro... (5831), NWO | ARGOThe Apertif Radio – G... (31150)

    ABSTRACT We report the detection of a bright fast radio burst, FRB 191108, with Apertif on the Westerbork Synthesis Radio Telescope. The interferometer allows us to localize the FRB to a narrow 5 arcsec × 7 arcmin ellipse by employing both multibeam information within the Apertif phased-array feed beam pattern, and across different tied-array beams. The resulting sightline passes close to Local Group galaxy M33, with an impact parameter of only 18 kpc with respect to the core. It also traverses the much larger circumgalactic medium (CGM) of M31, the Andromeda Galaxy. We find that the shared plasma of the Local Group galaxies could contribute ∼10 per cent of its dispersion measure of 588 pc cm−3. FRB 191108 has a Faraday rotation measure (RM) of +474 $\pm \, 3$ rad m−2, which is too large to be explained by either the Milky Way or the intergalactic medium. Based on the more moderate RMs of other extragalactic sources that traverse the halo of M33, we conclude that the dense magnetized plasma resides in the host galaxy. The FRB exhibits frequency structure on two scales, one that is consistent with quenched Galactic scintillation and broader spectral structure with Δν ≈ 40 MHz. If the latter is due to scattering in the shared M33/M31 CGM, our results constrain the Local Group plasma environment. We found no accompanying persistent radio sources in the Apertif imaging survey data.

  • Open Access English
    Authors: 
    M. D. Petrović; Goran Gligorić; Aleksandra Maluckov; Lj. Hadžievski; Boris A. Malomed;
    Country: Serbia
    Project: MESTD | Photonics of micro and na... (45010)

    Existence, stability and dynamics of soliton complexes, centered at the site of a single transverse link connecting two parallel 2D (two-dimensional) lattices, are investigated. The system with the on-site cubic self-focusing nonlinearity is modeled by the pair of discrete nonlinear Schr\"{o}dinger equations linearly coupled at the single site. Symmetric, antisymmetric and asymmetric complexes are constructed by means of the variational approximation (VA) and numerical methods. The VA demonstrates that the antisymmetric soliton complexes exist in the entire parameter space, while the symmetric and asymmetric modes can be found below a critical value of the coupling parameter. Numerical results confirm these predictions. The symmetric complexes are destabilized via a supercritical symmetry-breaking pitchfork bifurcation, which gives rise to stable asymmetric modes. The antisymmetric complexes are subject to oscillatory and exponentially instabilities in narrow parametric regions. In bistability areas, stable antisymmetric solitons coexist with either symmetric or asymmetric ones. Comment: 9 figures

  • Open Access English
    Authors: 
    Sodin, Mikhail;

    We answer negatively to the question posed by Aleksandrov concerning analytic functions of Smirnov's class in the unit disk with pure imaginary boundary values. We also find new sufficient conditions for representations of functions of Smirnov's class by the Schwartz and Cauchy integrals. These conditions extend a previous result of Aleksandrov. 10 pages, to appear in Mat. fizika, analiz, geometriya (Kharkov)

  • Open Access
    Authors: 
    M. Magliocchetti; Jasjeet Singh Bagla; Steve Maddox; O. Lahav;
    Publisher: Oxford University Press (OUP)

    We study the observed evolution of galaxy clustering as a function of redshift. We find that the clustering of galaxies decreases as we go from observations of the local Universe to $z \sim 2$. On the other hand, clustering of the Lyman break galaxies at $z \sim 3$ is very strong, comparable to the clustering of present day galaxies. However there are three major factors to take into account while comparing clustering measurements coming from various surveys: the so-called ``scale-dependence'' effect, due to measurements being made at different scales; the ``type-selection'' effect introduced by the fact that different galaxy surveys select different populations which do not have the same clustering amplitudes; and the Malmquist bias. We correct for the first two effects and discuss the implications of Malmquist bias on the interpretation of the data at different $z$. Then we compare the observed galaxy clustering with models for the evolution of clustering in some fixed cosmologies. Correcting for the scale-dependence effect significantly reduces the discrepancies amongst different measurements. We interpret the observed clustering signal at high redshift as coming from objects which are highly biased with respect to the underlying distribution of mass; this is not the case for $z\simlt 2$ where measurements are compatible with the assumption of a much lower biasing level which only shows a weak dependence on $z$. Finally we propose a model-independent test that can be used to place a lower limit on the density parameter $\Omega_0$. Comment: 12 pages, 5 figures, as accepter by MNRAS

  • Open Access English
    Authors: 
    Rapaport, Ariel;
    Project: EC | FRACTALSANDMETRICNT (306494)

    We show there exists a constant $0

Advanced search in
Research products
arrow_drop_down
Searching FieldsTerms
Any field
arrow_drop_down
includes
arrow_drop_down
Include:
33,765 Research products, page 1 of 3,377
  • Open Access English
    Authors: 
    Ivano Baronchelli; G. Rodighiero; Harry I. Teplitz; Claudia Scarlata; Alberto Franceschini; S. Berta; Laia Barrufet; Mattia Vaccari; Matteo Bonato; Laure Ciesla; +15 more
    Publisher: HAL CCSD
    Countries: France, Italy, United States
    Project: EC | HELP (607254)

    For a sample of star forming galaxies in the redshift interval 0.15$<$z$<$0.3, we study how both the relative strength of the AGN infra-red emission, compared to that due to the star formation (SF), and the numerical fraction of AGNs, change as a function of the total stellar mass of the hosting galaxy group (M$^{*}_{\mathrm{group}}$), between $10^{10.25}$ and $10^{11.9}$M$_{\odot}$. Using a multi-component SED fitting analysis, we separate the contribution of stars, AGN torus and star formation to the total emission at different wavelengths. This technique is applied to a new multi-wavelength data-set in the SIMES field (23 not redundant photometric bands), spanning the wavelength range from the UV (GALEX) to the far-IR (Herschel) and including crucial AKARI and WISE mid-IR observations (4.5 \mu m$<\lambda<$24 \mu m), where the BH thermal emission is stronger. This new photometric catalog, that includes our best photo-z estimates, is released through the NASA/IPAC Infrared Science Archive (IRSA). Groups are identified through a friends of friends algorithm ($\sim$62% purity, $\sim$51% completeness). We identified a total of 45 galaxies requiring an AGN emission component, 35 of which in groups and 10 in the field. We find BHAR$\propto ($M$^{*}_{\mathrm{group}})^{1.21\pm0.27}$ and (BHAR/SFR)$\propto ($M$^{*}_{\mathrm{group}})^{1.04\pm0.24}$ while, in the same range of M$^{*}_{\mathrm{group}}$, we do not observe any sensible change in the numerical fraction of AGNs. Our results indicate that the nuclear activity (i.e. the BHAR and the BHAR/SFR ratio) is enhanced when galaxies are located in more massive and richer groups. Comment: 31 pages, 23 figures

  • Open Access
    Authors: 
    Adi Shafir; David Andelman;
    Publisher: Royal Society of Chemistry (RSC)

    We study the contribution of polyelectrolytes in solution to the bending moduli of charged membranes. Using the Helfrich free energy, and within the mean-field theory, we calculate the dependence of the bending moduli on the electrostatics and short-range interactions between the membrane and the polyelectrolyte chains. The most significant effect is seen for strong short-range interactions and low amounts of added salt where a substantial increase in the bending moduli of order $1 k_BT$ is obtained. From short-range repulsive membranes, the polyelectrolyte contribution to the bending moduli is small, of order $0.1 k_BT$ up to at most $1 k_BT$. For weak short-range attraction, the increase in membrane rigidity is smaller and of less significance. It may even become negative for large enough amounts of added salt. Our numerical results are obtained by solving the adsorption problem in spherical and cylindrical geometries. In some cases the bending moduli are shown to follow simple scaling laws. 16 pages, 6 figures

  • Publication . Article . Other literature type . Preprint . 2019
    Open Access
    Authors: 
    Igarashi, Ayumi; Izsak, Rani; Elkind, Edith;
    Publisher: Association for the Advancement of Artificial Intelligence (AAAI)
    Country: United Kingdom
    Project: EC | ACCORD (639945)

    Cooperative games provide a framework to study cooperation among self-interested agents. They offer a number of solution concepts describing how the outcome of the cooperation should be shared among the players. Unfortunately, computational problems associated with many of these solution concepts tend to be intractable---NP-hard or worse. In this paper, we incorporate complexity measures recently proposed by Feige and Izsak (2013), called dependency degree and supermodular degree, into the complexity analysis of cooperative games. We show that many computational problems for cooperative games become tractable for games whose dependency degree or supermodular degree are bounded. In particular, we prove that simple games admit efficient algorithms for various solution concepts when the supermodular degree is small; further, we show that computing the Shapley value is always in FPT with respect to the dependency degree. Finally, we note that, while determining the dependency among players is computationally hard, there are efficient algorithms for special classes of games. 10 pages, full version of accepted AAAI-18 paper

  • Publication . Article . Preprint . 2017
    Open Access English
    Authors: 
    Kyle Kawagoe; Greg Huber; Marc Pradas; Michael Wilkinson; Alain Pumir; Eli Ben-Naim;

    We investigate statistical properties of trails formed by a random process incorporating aggregation, fragmentation, and diffusion. In this stochastic process, which takes place in one spatial dimension, two neighboring trails may combine to form a larger one and also, one trail may split into two. In addition, trails move diffusively. The model is defined by two parameters which quantify the fragmentation rate and the fragment size. In the long-time limit, the system reaches a steady state, and our focus is the limiting distribution of trail weights. We find that the density of trail weight has power-law tail $P(w) \sim w^{-\gamma}$ for small weight $w$. We obtain the exponent $\gamma$ analytically, and find that it varies continuously with the two model parameters. The exponent $\gamma$ can be positive or negative, so that in one range of parameters small-weight tails are abundant, and in the complementary range, they are rare. Comment: 8 pages, 8 figures

  • Publication . Preprint . Conference object . Article . 2019
    Open Access
    Authors: 
    Yichao Yan; Qiang Zhang; Bingbing Ni; Wendong Zhang; Minghao Xu; Xiaokang Yang;
    Publisher: IEEE

    Person re-identification has achieved great progress with deep convolutional neural networks. However, most previous methods focus on learning individual appearance feature embedding, and it is hard for the models to handle difficult situations with different illumination, large pose variance and occlusion. In this work, we take a step further and consider employing context information for person search. For a probe-gallery pair, we first propose a contextual instance expansion module, which employs a relative attention module to search and filter useful context information in the scene. We also build a graph learning framework to effectively employ context pairs to update target similarity. These two modules are built on top of a joint detection and instance feature learning framework, which improves the discriminativeness of the learned features. The proposed framework achieves state-of-the-art performance on two widely used person search datasets. To appear in CVPR 2019

  • Open Access
    Authors: 
    Liam Connor; J. van Leeuwen; L. C. Oostrum; Emily Petroff; Yogesh Maan; Elizabeth A. K. Adams; Jisk Attema; J. E. Bast; Oliver M. Boersma; H. Dénes; +31 more
    Publisher: Oxford University Press (OUP)
    Country: Netherlands
    Project: NWO | ARTS - the Apertif Radio ... (10066), EC | RadioNet (730562), EC | ALERT (617199), NWO | Microporous membranes fro... (5831), NWO | ARGOThe Apertif Radio – G... (31150)

    ABSTRACT We report the detection of a bright fast radio burst, FRB 191108, with Apertif on the Westerbork Synthesis Radio Telescope. The interferometer allows us to localize the FRB to a narrow 5 arcsec × 7 arcmin ellipse by employing both multibeam information within the Apertif phased-array feed beam pattern, and across different tied-array beams. The resulting sightline passes close to Local Group galaxy M33, with an impact parameter of only 18 kpc with respect to the core. It also traverses the much larger circumgalactic medium (CGM) of M31, the Andromeda Galaxy. We find that the shared plasma of the Local Group galaxies could contribute ∼10 per cent of its dispersion measure of 588 pc cm−3. FRB 191108 has a Faraday rotation measure (RM) of +474 $\pm \, 3$ rad m−2, which is too large to be explained by either the Milky Way or the intergalactic medium. Based on the more moderate RMs of other extragalactic sources that traverse the halo of M33, we conclude that the dense magnetized plasma resides in the host galaxy. The FRB exhibits frequency structure on two scales, one that is consistent with quenched Galactic scintillation and broader spectral structure with Δν ≈ 40 MHz. If the latter is due to scattering in the shared M33/M31 CGM, our results constrain the Local Group plasma environment. We found no accompanying persistent radio sources in the Apertif imaging survey data.

  • Open Access English
    Authors: 
    M. D. Petrović; Goran Gligorić; Aleksandra Maluckov; Lj. Hadžievski; Boris A. Malomed;
    Country: Serbia
    Project: MESTD | Photonics of micro and na... (45010)

    Existence, stability and dynamics of soliton complexes, centered at the site of a single transverse link connecting two parallel 2D (two-dimensional) lattices, are investigated. The system with the on-site cubic self-focusing nonlinearity is modeled by the pair of discrete nonlinear Schr\"{o}dinger equations linearly coupled at the single site. Symmetric, antisymmetric and asymmetric complexes are constructed by means of the variational approximation (VA) and numerical methods. The VA demonstrates that the antisymmetric soliton complexes exist in the entire parameter space, while the symmetric and asymmetric modes can be found below a critical value of the coupling parameter. Numerical results confirm these predictions. The symmetric complexes are destabilized via a supercritical symmetry-breaking pitchfork bifurcation, which gives rise to stable asymmetric modes. The antisymmetric complexes are subject to oscillatory and exponentially instabilities in narrow parametric regions. In bistability areas, stable antisymmetric solitons coexist with either symmetric or asymmetric ones. Comment: 9 figures

  • Open Access English
    Authors: 
    Sodin, Mikhail;

    We answer negatively to the question posed by Aleksandrov concerning analytic functions of Smirnov's class in the unit disk with pure imaginary boundary values. We also find new sufficient conditions for representations of functions of Smirnov's class by the Schwartz and Cauchy integrals. These conditions extend a previous result of Aleksandrov. 10 pages, to appear in Mat. fizika, analiz, geometriya (Kharkov)

  • Open Access
    Authors: 
    M. Magliocchetti; Jasjeet Singh Bagla; Steve Maddox; O. Lahav;
    Publisher: Oxford University Press (OUP)

    We study the observed evolution of galaxy clustering as a function of redshift. We find that the clustering of galaxies decreases as we go from observations of the local Universe to $z \sim 2$. On the other hand, clustering of the Lyman break galaxies at $z \sim 3$ is very strong, comparable to the clustering of present day galaxies. However there are three major factors to take into account while comparing clustering measurements coming from various surveys: the so-called ``scale-dependence'' effect, due to measurements being made at different scales; the ``type-selection'' effect introduced by the fact that different galaxy surveys select different populations which do not have the same clustering amplitudes; and the Malmquist bias. We correct for the first two effects and discuss the implications of Malmquist bias on the interpretation of the data at different $z$. Then we compare the observed galaxy clustering with models for the evolution of clustering in some fixed cosmologies. Correcting for the scale-dependence effect significantly reduces the discrepancies amongst different measurements. We interpret the observed clustering signal at high redshift as coming from objects which are highly biased with respect to the underlying distribution of mass; this is not the case for $z\simlt 2$ where measurements are compatible with the assumption of a much lower biasing level which only shows a weak dependence on $z$. Finally we propose a model-independent test that can be used to place a lower limit on the density parameter $\Omega_0$. Comment: 12 pages, 5 figures, as accepter by MNRAS

  • Open Access English
    Authors: 
    Rapaport, Ariel;
    Project: EC | FRACTALSANDMETRICNT (306494)

    We show there exists a constant $0

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