@article{17758, abstract = {Krstic has carried out the first quantum mechanical calculations near threshold for the charge transfer (CT) process H^+ + H_2(X ^1Sigma_g^+, nu=0, J=0) --> H(1s) + H_2^+. These results are relevant for models of primordial galaxy and first star formation that require reliable atomic and molecular data for obtaining the early universe hydrogen chemistry. Using the results of Krstic, we calculate the relevant CT rate coefficient for temperatures between 100 and 30,000 K. We also present a simple fit which can be readily implemented into early universe chemical models. Additionally, we explore how the range of previously published data for this reaction translates into uncertainties in the predicted gas temperature and H_2 relative abundance in a collapsing primordial gas cloud. Our new data significantly reduce these cosmological uncertainties that are due to the uncertainties in the previously published CT rate coefficients.}, author = {Savin, Daniel Wolf and Krsti, Predrag S. and Haiman, Zoltán and Stancil, Phillip C.}, issn = {0004-637X}, journal = {The Astrophysical Journal}, number = {2}, pages = {L167--L170}, publisher = {American Astronomical Society}, title = {{Rate Coefficient for H+ + H2(X1Σg+, ν = 0, J = 0) → H(1s) + H2+ Charge Transfer and Some Cosmological Implications}}, doi = {10.1086/421108}, volume = {606}, year = {2004}, } @article{17763, abstract = {Recent studies have suggested that during their coalescence, binary supermassive black holes (SMBHs) experience typical gravitational recoil velocities that may be as large as ≳100 km s^-1. These velocities exceed the escape velocity vesc from typical dark matter (DM) halos at high redshift (z ≳ 6), and therefore put constraints on scenarios in which early SMBHs grow at the centers of DM halos. Here we quantify these constraints for the most distant known SMBH, with an inferred mass in excess of 10^9 M☉, powering the bright quasar SDSS J1148+5251 discovered in the Sloan Digital Sky Survey at z = 6.43. We assume that this SMBH grew via a combination of accretion and mergers between preexisting seed BHs in individual progenitor halos, and that mergers between progenitors with vesc < vkick disrupt the BH growth process. Our results suggest that under these assumptions, the z ≈ 6 SMBHs had a phase during which they gained mass vary rapidly. In particular, typical z ≈ 3 quasars with luminosities similar to that of SDSS J1148+5251 have recently been inferred to have an average radiative efficiency of epsilon ≈ 20%. The growth rate of the SMBH in SDSS J1148+5251 must have significantly exceeded the Eddington accretion rate with this efficiency.}, author = {Haiman, Zoltán}, issn = {0004-637X}, journal = {The Astrophysical Journal}, number = {1}, pages = {36--40}, publisher = {American Astronomical Society}, title = {{Constraints from gravitational recoil on the growth of supermassive black holes at high redshift}}, doi = {10.1086/422910}, volume = {613}, year = {2004}, } @article{17770, abstract = {We show that the abundance and redshift distribution (𝑑⁢𝑁/𝑑⁢𝑧) of galaxy clusters in future high-yield cluster surveys, combined with the spatial power spectrum [𝑃𝑐⁡(𝑘)] of the same clusters, can place significant constraints on the evolution of the dark energy equation of state, 𝑤=𝑤⁡(𝑎). We evaluate the expected errors on 𝑤𝑎=−𝑑⁢𝑤/𝑑⁢𝑎 and other cosmological parameters using a Fisher matrix approach, and simultaneously including cluster structure evolution parameters in our analysis. We study three different types of forthcoming surveys that will identify clusters based on their x-ray emission (such as DUO, the Dark Universe Observatory), their Sunyaev-Zel'dovich (SZ) decrement (such as SPT, the South Pole Telescope), or their weak-lensing shear (such as LSST, the Large Synoptic Survey Telescope). We find that combining the cluster abundance and power spectrum significantly enhances constraints from either method alone. We show that the weak-lensing survey can deliver a constraint as tight as 𝛥⁢𝑤𝑎∼0.1 on the evolution of the dark energy equation of state, and that the x-ray and SZ surveys each yield 𝛥⁢𝑤𝑎∼0.4 separately, or 𝛥⁢𝑤𝑎∼0.2 when these two surveys are combined. For the x-ray and SZ surveys, constraints on dark energy parameters are improved by a factor of 2 by combining the cluster data with cosmic microwave background anisotropy measurements by Planck, but degrade by a factor of 2 if the survey is required to solve simultaneously for cosmological and cluster structure evolution parameters. The constraint on 𝑤𝑎 from the weak-lensing survey is improved by ∼25% with the addition of Planck data.}, author = {Wang, Sheng and Khoury, Justin and Haiman, Zoltán and May, Morgan}, issn = {1550-7998}, journal = {Physical Review D}, number = {12}, publisher = {American Physical Society}, title = {{Constraining the evolution of dark energy with a combination of galaxy cluster observables}}, doi = {10.1103/physrevd.70.123008}, volume = {70}, year = {2004}, } @article{17775, abstract = {We discuss a simple model for the growth of supermassive black holes (BHs) at the center of spheroidal stellar systems. In particular, we assess the hypotheses that (1) star formation in spheroids and BH fueling are proportional to one another, and (2) the BH accretion luminosity stays near the Eddington limit during luminous quasar phases. With the aid of this simple model, we are able to interpret many properties of the QSO luminosity function, including the puzzling steep decline of the characteristic luminosity from redshift z=2 to to z=0: indeed the residual star formation in spheroidal systems is today limited to a small number of bulges, characterized by stellar velocity dispersions a factor of 2-3 smaller those of the elliptical galaxies hosting QSOs at z > 2. A simple consequence of our hypotheses is that the redshift evolution of the QSO emissivity and of the star formation history in spheroids should be roughly parallel. We find this result to be broadly consistent with our knowledge of the evolution of both the global star formation rate, and of the evolution of the QSO emissivity, but we identify interesting discrepancies at both low and high redshifts, to which we offer tentative solutions. Finally, our hypotheses allow us to present a robust method to derive the duty cycle of QSO activity, based on the observed QSO luminosity function, and on the present-day relation between the masses of supermassive BHs and those of their spheroidal host stellar systems. The duty cycle is found to be substantially less than unity, with characteristic values in the range (3-6)x10^(-3), and we compute that the average bolometric radiative efficiency is epsilon=0.07. Finally, we find that the growth in mass of individual black holes at high redshift (z>2) can be dominated by mergers, and is therefore not necessarily limited by accretion.}, author = {Haiman, Zoltán and Ciotti, Luca and Ostriker, Jeremiah P.}, issn = {0004-637X}, journal = {The Astrophysical Journal}, number = {2}, pages = {763--773}, publisher = {American Astronomical Society}, title = {{Reasoning from fossils: Learning from the local black hole population about the evolution of quasars}}, doi = {10.1086/383022}, volume = {606}, year = {2004}, } @article{17790, abstract = {Over the last few years, the Sloan Digital Sky Survey (SDSS) has discovered several hundred quasars with redshift between 4.0 and 6.4. Including the effects of magnification bias, one expects a priori that an appreciable fraction of these objects are gravitationally lensed. We have used the Advanced Camera for Surveys on the Hubble Space Telescope to carry out a snapshot imaging survey of high-redshift SDSS quasars to search for gravitationally split lenses. This paper, the first in a series reporting the results of the survey, describes snapshot observations of four quasars at z = 5.74, 5.82, 5.99, and 6.30, respectively. We find that none of these objects has a lensed companion within 5 mag with a separation larger than 0farcs3; within 2.5 mag we can rule out companions within 0farcs1. Based on the nondetection of strong lensing in these four systems, we constrain the z ∼ 6 luminosity function to a slope of β > -4.63 (3 σ), assuming a break in the quasar luminosity function at M = -24.1. We discuss the implications of this constraint on the ionizing background due to quasars in the early universe. Given that these quasars are not highly magnified, estimates of the masses of their central engines by the Eddington argument must be taken seriously, possibly challenging models of black hole formation.}, author = {Richards, Gordon T. and Strauss, Michael A. and Pindor, Bartosz and Haiman, Zoltán and Fan, Xiaohui and Eisenstein, Daniel and Schneider, Donald P. and Bahcall, Neta A. and Brinkmann, J. and Brunner, Robert}, issn = {0004-6256}, journal = {The Astronomical Journal}, number = {3}, pages = {1305--1312}, publisher = {American Astronomical Society}, title = {{A snapshot survey for gravitational lenses among z ≥ 4.0 quasars. I. The z >5.7 sample}}, doi = {10.1086/381906}, volume = {127}, year = {2004}, } @article{17792, abstract = {Which came first, the stars and gas that make up a galaxy, or the giant black hole at its centre? Observations of a distant galaxy, caught as it forms, could help solve this chicken-and-egg problem.}, author = {Haiman, Zoltán}, issn = {0028-0836}, journal = {Nature}, number = {7003}, pages = {979--980}, publisher = {Springer Science and Business Media LLC}, title = {{Caught in the act?}}, doi = {10.1038/430979a}, volume = {430}, year = {2004}, } @article{17806, abstract = {A population of black holes (BHs) at high redshifts (z ≳ 6) that contributes significantly to the ionization of the intergalactic medium (IGM) would be accompanied by the copious production of hard (≳10 keV) X-ray photons. The resulting hard X-ray background would redshift and be observed as a present-day soft X-ray background (SXB). Under the hypothesis that BHs are the main producers of reionizing photons in the high-redshift universe, we calculate their contribution to the present-day SXB. We find that accreting BHs with a hard spectrum (be it luminous quasars or their lower mass "miniquasar" counterparts) could not fully reionize the universe without saturating the unresolved component of the 0.5-2 keV SXB at the ≥2 σ level. Distant miniquasars that produce enough X-rays to only partially ionize the IGM to a level of at most xe ~ 50% saturate the unresolved SXB by ≲1 σ. Improved determinations of the unresolved component of the SXB can provide a powerful constraint on the contribution of accreting BHs to partial or full reionization.}, author = {Dijkstra, Mark and Haiman, Zoltán and Loeb, Abraham}, issn = {1538-4357}, journal = {The Astrophysical Journal}, number = {2}, pages = {646--654}, publisher = {American Astronomical Society}, title = {{A limit from the X‐ray background on the contribution of quasars to reionization}}, doi = {10.1086/422167}, volume = {613}, year = {2004}, } @article{17812, abstract = {A remarkable result of the Wilkinson Microwave Anisotropy Probe (WMAP) observations is that the universe was significantly reionized at large redshifts. The standard explanation is that massive stars formed early and reionized the universe around redshift z ≈ 17. Here we explore an alternative possibility in which the universe was reionized in two steps. An early boost of reionization is provided by a decaying sterile neutrino whose decay products, relativistic electrons, result in partial ionization of the smooth gas. We demonstrate that a neutrino with a mass of mν ~ 200 MeV and a decay time of t ~ 4 × 1015 s can account for the electron scattering optical depth τ ≈ 0.16 measured by WMAP without violating existing astrophysical limits on the cosmic microwave and gamma-ray backgrounds. Reionization is then completed by subsequent star formation at lower redshifts. This scenario alleviates constraints on structure formation models with reduced small-scale power, such as those with a running or tilted scalar index, or warm dark matter models.}, author = {Hansen, Steen H. and Haiman, Zoltán}, issn = {1538-4357}, journal = {The Astrophysical Journal}, number = {1}, pages = {26--31}, publisher = {American Astronomical Society}, title = {{Do we need stars to reionize the universe at high redshifts? Early reionization by decaying heavy sterile neutrinos}}, doi = {10.1086/379636}, volume = {600}, year = {2004}, } @inproceedings{18331, abstract = {Recently, a 3D face recognition approach based on geometric invariant signatures, has been proposed. The key idea is a representation of the facial surface, invariant to isometric deformations, such as those resulting from facial expressions. One important stage in the construction of the geometric invariants involves in measuring geodesic distances on triangulated surfaces, which is carried out by the fast marching on triangulated domains algorithm. Proposed here is a method that uses only the metric tensor of the surface for geodesic distance computation. That is, the explicit integration of the surface in 3D from its gradients is not needed for the recognition task. It enables the use of simple and cost-efficient 3D acquisition techniques such as photometric stereo. Avoiding the explicit surface reconstruction stage saves computational time and reduces numerical errors.}, author = {Bronstein, Alexander and Bronstein, Michael M. and Spira, Alon and Kimmel, Ron}, booktitle = {8th European Conference on Computer Vision}, isbn = {9783540219835}, issn = {1611-3349}, location = {Prageu, Czech Republic}, pages = {225–237}, publisher = {Springer Nature}, title = {{Face recognition from facial surface metric}}, doi = {10.1007/978-3-540-24671-8_18}, volume = {3022}, year = {2004}, } @inproceedings{18332, abstract = {Presented here is a generalization of the modified relative Newton method, recently proposed in [1] for quasi-maximum likelihood blind source separation. Special structure of the Hessian matrix allows to perform block-coordinate Newton descent, which significantly reduces the algorithm computational complexity and boosts its performance. Simulations based on artificial and real data show that the separation quality using the proposed algorithm outperforms other accepted blind source separation methods.}, author = {Bronstein, Alexander and Bronstein, Michael M. and Zibulevsky, Michael}, booktitle = {5th International Conference on Independent Component Analysis and Blind Signal Separation}, isbn = {9783540230564}, issn = {1611-3349}, location = {Granada, Spain}, pages = {406–413}, publisher = {Springer Nature}, title = {{Blind source separation using the block-coordinate relative Newton method}}, doi = {10.1007/978-3-540-30110-3_52}, volume = {3195}, year = {2004}, } @inproceedings{18333, abstract = {The relative Newton algorithm, previously proposed for quasi maximum likelihood blind source separation and blind deconvolution of one-dimensional signals is generalized for blind deconvolution of images. Smooth approximation of the absolute value is used in modelling the log probability density function, which is suitable for sparse sources. We propose a method of sparsification, which allows blind deconvolution of sources with arbitrary distribution, and show how to find optimal sparsifying transformations by training.}, author = {Bronstein, Alexander and Bronstein, Michael M. and Zibulevsky, Michael and Zeevi, Yehoshua Y.}, booktitle = {5th International Conference on Independent Component Analysis and Blind Signal Separation}, isbn = {9783540230564}, issn = {1611-3349}, location = {Granada, Spain}, pages = {500--507}, publisher = {Springer Nature}, title = {{Optimal sparse representations for blind deconvolution of images}}, doi = {10.1007/978-3-540-30110-3_64}, volume = {3195}, year = {2004}, } @inproceedings{18334, abstract = {We propose a relative optimization framework for quasi maximum likelihood blind deconvolution and the relative Newton method as its particular instance. Special Hessian structure allows its fast approximate construction and inversion with complexity comparable to that of gradient methods. The use of rational IIR restoration kernels provides a richer family of filters than the traditionally used FIR kernels. Smoothed absolute value and the smoothed deadzone functions allow accurate and robust deconvolution of super- and sub-Gaussian sources, respectively. Simulation results demonstrate the efficiency of the proposed methods.}, author = {Bronstein, Alexander and Bronstein, Michael M. and Zibulevsky, Michael}, booktitle = {5th International Conference on Independent Component Analysis and Blind Signal Separation}, isbn = {9783540230564}, issn = {1611-3349}, location = {Granada, Spain}, pages = {554–561}, publisher = {Springer Nature}, title = {{Blind deconvolution using the relative Newton method}}, doi = {10.1007/978-3-540-30110-3_71}, volume = {3195}, year = {2004}, } @inproceedings{18335, abstract = {Blind deconvolution is considered as a problem of quasi maximum likelihood (QML) estimation of the restoration kernel. Simple closed-form expressions for the asymptotic estimation error are derived. The asymptotic performance bounds coincide with the Cramér-Rao bounds, when the true ML estimator is used. Conditions for asymptotic stability of the QML estimator are derived. Special cases when the estimator is super-efficient are discussed.}, author = {Bronstein, Alexander and Bronstein, Michael M. and Zibulevsky, Michael and Zeevi, Yehoshua Y.}, booktitle = {Proceedings of the 5th International Conference on Independent Component Analysis and Blind Signal Separation}, isbn = {9783540230564}, issn = {0302-9743}, location = {Granada, Spain}, pages = {677–684}, publisher = {Springer Nature}, title = {{QML blind deconvolution: Asymptotic analysis}}, doi = {10.1007/978-3-540-30110-3_86}, volume = {3195}, year = {2004}, } @article{18368, abstract = {Presented here is a block-coordinate version of the relative Newton method, recently proposed for quasi-maximum likelihood blind source separation. Special structure of the Hessian matrix allows performing block-coordinate Newton descent efficiently. Simulations show that typically our method converges in near constant number of iterations (order of 10) independently of the problem size.}, author = {Bronstein, Alexander and Bronstein, Michael M and Zibulevsky, Michael}, issn = {0165-1684}, journal = {Signal Processing}, number = {8}, pages = {1447--1459}, publisher = {Elsevier}, title = {{Blind source separation using block-coordinate relative Newton method}}, doi = {10.1016/j.sigpro.2004.05.019}, volume = {84}, year = {2004}, } @inproceedings{18396, abstract = {We discuss the synthesis between the 3D and the 2D data in three-dimensional face recognition. We show how to compensate for the illumination and racial expressions using the 3D facial geometry and present the approach of canonical images, which allows us to incorporate geometric information into standard face recognition approaches.}, author = {Bronstein, Alexander and Bronstein, M.M. and Gordon, E. and Kimmel, R.}, booktitle = {2004 International Conference on Image Processing}, isbn = {0780385543}, issn = {1522-4880}, location = {Singapore, Singapore}, publisher = {IEEE}, title = {{Fusion of 2D and 3D data in three-dimensional face recognition}}, doi = {10.1109/icip.2004.1418696}, year = {2004}, } @article{3990, abstract = {The writhing number measures the global geometry of a closed space curve or knot. We show that this measure is related to the average winding number of its Gauss map. Using this relationship, we give an algorithm for computing the writhing number for a polygonal knot with n edges in time roughly proportional to n(1.6). We also implement a different, simple algorithm and provide experimental evidence for its practical efficiency.}, author = {Agarwal, Pankaj and Edelsbrunner, Herbert and Wang, Yusu}, issn = {01795376}, journal = {Discrete & Computational Geometry}, number = {1}, pages = {37 -- 53}, publisher = {Springer Nature}, title = {{Computing the writhing number of a polygonal knot}}, doi = {10.1007/s00454-004-2864-x}, volume = {32}, year = {2004}, } @article{3984, abstract = {We combine topological and geometric methods to construct a multiresolution representation for a function over a two-dimensional domain. In a preprocessing stage, we create the Morse-Smale complex of the function and progressively simplify its topology by cancelling pairs of critical points. Based on a simple notion of dependency among these cancellations, we construct a hierarchical data structure supporting traversal and reconstruction operations similarly to traditional geometry-based representations. We use this data structure to extract topologically valid approximations that satisfy error bounds provided at runtime.}, author = {Bremer, Peer and Edelsbrunner, Herbert and Hamann, Bernd and Pascucci, Valerio}, issn = {1941-0506}, journal = {IEEE Transactions on Visualization and Computer Graphics}, number = {4}, pages = {385 -- 396}, publisher = {IEEE}, title = {{A topological hierarchy for functions on triangulated surfaces}}, doi = {10.1109/TVCG.2004.3}, volume = {10}, year = {2004}, } @article{3985, abstract = {Given a Morse function f over a 2-manifold with or without boundary, the Reeb graph is obtained by contracting the connected components of the level sets to points. We prove tight upper and lower bounds on the number of loops in the Reeb graph that depend on the genus, the number of boundary components, and whether or not the 2-manifold is orientable. We also give an algorithm that constructs the Reeb graph in time O(n log n), where n is the number of edges in the triangulation used to represent the 2-manifold and the Morse function.}, author = {Cole Mclaughlin, Kree and Edelsbrunner, Herbert and Harer, John and Natarajan, Vijay and Pascucci, Valerio}, journal = {Discrete & Computational Geometry}, number = {2}, pages = {231 -- 244}, publisher = {Springer Nature}, title = {{Loops in Reeb graphs of 2-manifolds}}, doi = {10.1007/s00454-004-1122-6}, volume = {32}, year = {2004}, } @article{3141, abstract = {The two actin-related subunits of the Arp2/3 complex, Arp2 and Arp3, are proposed to form a pseudo actin dimer that nucleates actin polymerization. However, in the crystal structure of the inactive complex, they are too far apart to form such a nucleus. Here, we show using EM that yeast and bovine Arp2/3 complexes exist in a distribution among open, intermediate and closed conformations. The crystal structure docks well into the open conformation. The activator WASp binds at the cleft between Arp2 and Arp3, and all WASp-bound complexes are closed. The inhibitor coronin binds near the p35 subunit, and all coronin-bound complexes are open. Activating and loss-of-function mutations in the p35 subunit skew conformational distribution in opposite directions, closed and open, respectively. We conclude that WASp stabilizes p35-dependent closure of the complex, holding Arp2 and Arp3 closer together to nucleate an actin filament.}, author = {Rodal, Avital and Sokolova, Olga and Robins, Deborah and Daugherty, Karen and Hippenmeyer, Simon and Riezman, Howard and Grigorieff, Nikolaus and Goode, Bruce}, issn = {1545-9985}, journal = {Nature Structural and Molecular Biology}, number = {1}, pages = {26 -- 31}, publisher = {Nature Publishing Group}, title = {{Conformational changes in the Arp2 3 complex leading to actin nucleation}}, doi = {10.1038/nsmb870}, volume = {12}, year = {2004}, }