Showing papers by "International School for Advanced Studies published in 2000"
TL;DR: In this article, the authors considered height-integrated equations of an advection-dominated accretion flow (ADAF), assuming that there is no mass outflow, and obtained a self-similar solution in which the rotational velocity and sound speed scale as R-1/2, where R is the radius.
Abstract: We consider height-integrated equations of an advection-dominated accretion flow (ADAF), assuming that there is no mass outflow. We include convection through a mixing-length formalism. We seek self-similar solutions in which the rotational velocity and sound speed scale as R-1/2, where R is the radius, and consider two limiting prescriptions for the transport of angular momentum by convection. In one limit, the transport occurs down the angular velocity gradient, so convection moves angular momentum outward. In the other, the transport is down the specific angular momentum gradient, so convection moves angular momentum inward. We also consider general prescriptions that lie in between the two limits. When convection moves angular momentum outward, we recover the usual self-similar solution for ADAFs in which the mass density scales as ρ ∝ R-3/2. When convection moves angular momentum inward, the result depends on the viscosity coefficient α. If α > αcrit1 ~ 0.05, we once again find the standard ADAF solution. For α < αcrit2 ~ αcrit1, however, we find a nonaccreting solution in which ρ ∝ R-1/2. We refer to this as a "convective envelope" solution or a "convection-dominated accretion flow." Two-dimensional numerical simulations of ADAFs with values of α 0.03 have been reported by several authors. The simulated ADAFs exhibit convection. By virtue of their axisymmetry, convection in these simulations moves angular momentum inward, as we confirm by computing the Reynolds stress. The simulations give ρ ∝ R-1/2, in good agreement with the convective envelope solution. The R-1/2 density profile is not a consequence of mass outflow. The relevance of these axisymmetric low-α simulations to real accretion flows is uncertain.
431 citations
TL;DR: In this article, the authors investigate the structure of dark matter halos by means of the kinematics of a very large sample of spiral galaxies of all luminosities, and they find that the Burkert profile proposed to describe the dark matter halo density distribution of dwarf galaxies also provides an excellent mass model for the dark halos around disk systems up to 100 times more massive.
Abstract: We investigate the structure of dark matter halos by means of the kinematics of a very large sample of spiral galaxies of all luminosities. The observed rotation curves show a universal profile which is the sum of an exponential thin disk term and a spherical halo term with a flat density core. We find that the Burkert profile proposed to describe the dark matter halo density distribution of dwarf galaxies also provides an excellent mass model for the dark halos around disk systems up to 100 times more massive. Moreover, we find that spiral dark matter core densities ρ0 and core radii r0 lie in the same scaling relation ρ0 = 4.5 × 10-2(r0/kpc)-2/3 M☉ pc-3 of dwarf galaxies with core radii up to 10 times smaller. At the highest masses ρ0 decreases with r0 faster than the - power law, implying a lack of objects with disk masses greater than 1011 M☉ and central densities greater than 1.5 × 10-2(r0/kpc)-3 M☉ pc-3 that can be explained by the existence of a maximum mass of about 2 × 1012 M☉ for a halo hosting a spiral galaxy.
421 citations
TL;DR: In this paper, the authors present the 21-cm rotation curve of the nearby galaxy M33 out to a galactocentric distance of 16 kpc (13 disk scale-lengths).
Abstract: We present the 21-cm rotation curve of the nearby galaxy M33 out to a galactocentric distance of 16 kpc (13 disk scale-lengths). The rotation curve keeps rising out to the last measured point and implies a dark halo mass larger than 5 10^{10} solar masses. The stellar and gaseous disks provide virtually equal contributions to the galaxy gravitational potential at large galactocentric radii but no obvious correlation is found between the radial distribution of dark matter and the distribution of stars or gas. Results of the best fit to the mass distribution in M33 picture a dark halo which controls the gravitational potential from 3 kpc outward, with a matter density which decreases radially as R^{-1.3}. The density profile is consistent with the theoretical predictions for structure formation in hierarchical clustering cold dark matter models but mass concentrations are lower than those expected in the standard cosmogony.
346 citations
TL;DR: These results reconcile melting temperature estimates based on sound velocity shock wave data with those based on diamond anvil cell experiments.
Abstract: The bulk properties of iron at the pressure and temperature conditions of Earth's core were determined by a method that combines first-principles and classical molecular dynamic simulations. The theory indicates that (i) the iron melting temperature at inner-core boundary (ICB) pressure (330 gigapascals) is 5400 (±400) kelvin; (ii) liquid iron at ICB conditions is about 6% denser than Earth's outer core; and (iii) the shear modulus of solid iron close to its melting line is 140 gigapascals, consistent with the seismic value for the inner core. These results reconcile melting temperature estimates based on sound velocity shock wave data with those based on diamond anvil cell experiments.
337 citations
TL;DR: A method for making libraries so large that the complete diversity cannot be accessed using traditional phage technology is described, which found that infecting Cre recombinase–expressing bacteria by such a primary library at a high multiplicity of infection results in the entry of many different phagemid into the cell.
Abstract: The creation of large phage antibody libraries has become an important goal in selecting antibodies against any antigen. Here we describe a method for making libraries so large that the complete diversity cannot be accessed using traditional phage technology. This involves the creation of a primary phage scFv library in a phagemid vector containing two nonhomologous lox sites. Contrary to the current dogma, we found that infecting Cre recombinase-expressing bacteria by such a primary library at a high multiplicity of infection results in the entry of many different phagemid into the cell. Exchange of Vh and Vl genes between such phagemids creates many new V h/Vl combinations, all of which are functional. On the basis of the observed recombination, the library is calculated to have a diversity of 3x1011. A library created using this method was validated by the selection of high affinity antibodies against a large number of different protein antigens.
332 citations
TL;DR: The phenotype of aged anti-NGF transgenic mice are analyzed and it is demonstrated that these mice acquire an age-dependent neurodegenerative pathology including amyloid plaques, insoluble and hyperphosphorylated τ, and neurofibrillary tangles in cortical and hippocampus neurons.
Abstract: Neurotrophin nerve growth factor (NGF) has been suggested to be involved in age-related neurodegenerative diseases, but no transgenic model is currently available to study this concept. We have obtained transgenic mice expressing a neutralizing anti-NGF recombinant antibody, in which the levels of antibodies are three orders of magnitude higher in adult than in newborn mice [F.R., S. C., A.C., E. Di Daniel, J. Franzot, S. Gonfloni, G. Rossi, N. B. & A. C. (2000) J. Neurosci., 20, 2589–2601]. In this paper, we analyze the phenotype of aged anti-NGF transgenic mice and demonstrate that these mice acquire an age-dependent neurodegenerative pathology including amyloid plaques, insoluble and hyperphosphorylated τ, and neurofibrillary tangles in cortical and hippocampal neurons. Aged anti-NGF mice also display extensive neuronal loss throughout the cortex, cholinergic deficit in the basal forebrain, and behavioral deficits. The overall picture is strikingly reminiscent of human Alzheimer's disease. Aged anti-NGF mice represent, to our knowledge, the most comprehensive animal model for this severe neurodegenerative disease. Also, these results demonstrate that, in mice, a deficit in the signaling and/or transport of NGF leads to neurodegeneration.
294 citations
TL;DR: In this paper, an ab initio study of the thermoelastic properties of MgO over a wide range of pressure and temperature is presented. But this work is restricted to the case where the thermodynamic potentials within the quasiharmonic approximation and several derived quantities of physical interest are derived.
Abstract: We present an ab initio study of the thermoelastic properties of MgO over a wide range of pressure and temperature. Phonon dispersions for equilibrium and strained configurations are obtained from density-functional perturbation theory. They are used to calculate thermodynamical potentials within the quasiharmonic approximation and several derived quantities of physical interest without further approximations. These include the temperature dependence of individual elastic constants at high pressures. Extensive and successful comparisons with experimental data demonstrate that the quasiharmonic approximation combined with ab initio phonon calculations provides an important theoretical approach for exploring thermodynamical properties of materials over a considerable pressure-temperature regime.
279 citations
TL;DR: The phase diagram of the Axelrod's model for social influence is studied and a nonequilibrium phase transition separating an ordered (culturally polarized) phase from a disordered ( Culturally fragmented) one is uncovered.
Abstract: We present extensive numerical simulations of the Axelrod's model for social influence, aimed at understanding the formation of cultural domains. This is a nonequilibrium model with short range interactions and a remarkably rich dynamical behavior. We study the phase diagram of the model and uncover a nonequilibrium phase transition separating an ordered (culturally polarized) phase from a disordered (culturally fragmented) one. The nature of the phase transition can be continuous or discontinuous depending on the model parameters. At the transition, the size of cultural regions is power-law distributed.
278 citations
TL;DR: In this article, the authors show that the X-ray emission from large scale extragalactic jets is likely to be due to inverse Compton scattering of relativistic particles off seed photons of both the cosmic microwave background field and the blazar nucleus, and that this scenario satisfactorily accounts for the spectral energy distribution detected by Chandra from the jet and core of PKS 0637-752.
Abstract: X-ray emission from large scale extragalactic jets is likely to be due to inverse Compton scattering of relativistic particles off seed photons of both the cosmic microwave background field and the blazar nucleus. The first process dominates the observed high energy emission of large scale jets if the plasma is moving at highly relativistic speeds and if the jet is aligned with the line of sight, i.e. in powerful flat radio spectrum quasars. The second process is relevant when the plasma is moving at mildly bulk relativistic speeds, and can dominate the high energy emission in misaligned sources, i.e. in radio-galaxies. We show that this scenario satisfactorily accounts for the spectral energy distribution detected by Chandra from the jet and core of PKS 0637-752.
273 citations
TL;DR: This problem is a mathematical idealization of situations commonly encountered in biology, chemistry and physics, involving the optimal structure of folded polymeric chains, and finds that, in cases where boundary effects are not dominant, helices with a particular pitch-radius ratio are selected.
Abstract: Optimal geometrical arrangements, such as the stacking of atoms, are of relevance in diverse disciplines. A classic problem is the determination of the optimal arrangement of spheres in three dimensions in order to achieve the highest packing fraction; only recently has it been proved that the answer for infinite systems is a face-centred-cubic lattice. This simply stated problem has had a profound impact in many areas, ranging from the crystallization and melting of atomic systems, to optimal packing of objects and the sub-division of space. Here we study an analogous problem--that of determining the optimal shapes of closely packed compact strings. This problem is a mathematical idealization of situations commonly encountered in biology, chemistry and physics, involving the optimal structure of folded polymeric chains. We find that, in cases where boundary effects are not dominant, helices with a particular pitch-radius ratio are selected. Interestingly, the same geometry is observed in helices in naturally occurring proteins.
265 citations
TL;DR: In this article, the authors performed 3D numerical simulations for the merger of equal mass binary neutron stars in full general relativity and found that the final product depends sensitively on the initial compactness parameter of the neutron stars.
Abstract: We perform 3D numerical simulations for the merger of equal mass binary neutron stars in full general relativity We adopt a $\ensuremath{\Gamma}$-law equation of state in the form $P=(\ensuremath{\Gamma}\ensuremath{-}1)\ensuremath{\rho}\ensuremath{\varepsilon}$ where P, $\ensuremath{\rho},$ $\ensuremath{\varepsilon}$ and $\ensuremath{\Gamma}$ are the pressure, rest mass density, specific internal energy, and the adiabatic constant with $\ensuremath{\Gamma}=2$ As initial conditions, we adopt models of corotational and irrotational binary neutron stars in a quasiequilibrium state which are obtained using the conformal flatness approximation for the three geometry as well as the assumption that a helicoidal Killing vector exists In this paper, we pay particular attention to the final product of the coalescence We find that the final product depends sensitively on the initial compactness parameter of the neutron stars: In a merger between sufficiently compact neutron stars, a black hole is formed in a dynamical time scale As the compactness is decreased, the formation time scale becomes longer and longer It is also found that a differentially rotating massive neutron star is formed instead of a black hole for less compact binary cases, in which the rest mass of each star is less than 70--80 % of the maximum allowed mass of a spherical star In the case of black hole formation, we roughly evaluate the mass of the disk around the black hole For the merger of corotational binaries, a disk of mass $\ensuremath{\sim}005\ensuremath{-}{01M}_{*}$ may be formed, where ${M}_{*}$ is the total rest mass of the system On the other hand, for the merger of irrotational binaries, the disk mass appears to be very small: $l{001M}_{*}$
TL;DR: It is shown that the stationary state of the system is described by the ground state of a disordered spin model which is exactly solvable within the simple replica symmetric ansatz.
Abstract: We study analytically a simple game theoretical model of heterogeneous interacting agents. We show that the stationary state of the system is described by the ground state of a disordered spin model which is exactly solvable within the simple replica symmetric ansatz. Such a stationary state differs from the Nash equilibrium where each agent maximizes her own utility. The latter turns out to be characterized by a replica symmetry broken structure. Numerical results fully agree with our analytical findings.
TL;DR: The results demonstrate that the decreased availability of NGF in the adult causes phenotypic effects via processes that are at least partially distinct from early developmental effects of N GF deprivation.
Abstract: The disruption of the nerve growth factor (NGF) gene in transgenic mice leads to a lethal phenotype (Crowley et al., 1994) and hinders the study of NGF functions in the adult. In this study the phenotypic knockout of NGF in adult mice was achieved by expressing transgenic anti-NGF antibodies, under the control of the human cytomegalovirus promoter. In adult mice, antibody levels are 2000-fold higher than in newborns. Classical NGF targets, including sympathetic and sensory neurons, are severely affected. In the CNS, basal forebrain and hippocampal cholinergic neurons are not affected in the early postnatal period, whereas they are greatly reduced in the adult (55 and 62% reduction, respectively). Adult mice show a reduced ability in spatial learning behavioral tasks. Adult, but not neonatal, transgenic mice further show a new phenotype at the level of peripheral tissues, such as apoptosis in the spleen and dystrophy of skeletal muscles. The analysis of this novel comprehensive transgenic model settles the controversial issue regarding the NGF dependence of cholinergic neurons in adult animals and reveals new NGF functions in adult non-neuronal tissues. The results demonstrate that the decreased availability of NGF in the adult causes phenotypic effects via processes that are at least partially distinct from early developmental effects of NGF deprivation.
TL;DR: In this paper, the authors derived a component-field expansion of the Green-Schwarz action for the type IIA string, in an arbitrary background of massless NS-NS and R-R bosonic fields, up to quadratic order in the fermionic coordinates θ using the usual derivation of Buscher T-duality rules.
TL;DR: Results proved that the human tissue transglutaminase-based ELISA represents a cost-effective strategy for identifying both symptomatic and atypical forms of celiac disease and could mean that intestinal biopsy need no longer be the gold standard for diagnosing this clinical condition.
TL;DR: In this article, the authors studied the global analytic properties of a particular family of Painleve VI equations with the parameters β=γ=0, δ=1/2 and 2α=(2μ-1)2 with arbitrary μ, 2μ≠∈ℤ.
Abstract: We study the global analytic properties of the solutions of a particular family of Painleve VI equations with the parameters β=γ=0, δ=1/2 and 2α=(2μ-1)2 with arbitrary μ, 2μ≠∈ℤ. We introduce a class of solutions having critical behaviour of algebraic type, and completely compute the structure of the analytic continuation of these solutions in terms of an auxiliary reflection group in the three dimensional space. The analytic continuation is given in terms of an action of the braid group on the triples of generators of the reflection group. We show that the finite orbits of this action correspond to the algebraic solutions of our Painleve VI equation and use this result to classify all of them. We prove that the algebraic solutions of our Painleve VI equation are in one-to-one correspondence with the regular polyhedra or star-polyhedra in the three dimensional space.
TL;DR: In this article, the authors present a systematic numerical study of axisymmetric flows around black holes, which have no radiative cooling and are treated in the framework of the viscous hydrodynamic approximation.
Abstract: We present a systematic numerical study of two-dimensional axisymmetric accretion flows around black holes. The flows have no radiative cooling and are treated in the framework of the viscous hydrodynamic approximation. The models calculated in this study cover the large range of the relevant parameter space. There are four types of flows, determined by the values of the viscosity parameter α and the adiabatic index γ: convective flows, large-scale circulations, pure inflows, and bipolar outflows. Thermal conduction introduces significant changes to the solutions but does not create a new flow type. Convective accretion flows and flows with large-scale circulations have significant outward-directed energy fluxes, which have important implications for the spectra and luminosities of accreting black holes.
Imperial College London1, International School for Advanced Studies2, University of Edinburgh3, Spanish National Research Council4, Cardiff University5, University of Cantabria6, Max Planck Society7, California Institute of Technology8, University of Padua9, National and Kapodistrian University of Athens10, University of Turku11, Roma Tre University12, Danish Space Research Institute13, Niels Bohr Institute14, University of Helsinki15, Institut d'Astrophysique de Paris16, University of Paris17
TL;DR: The European Large Area ISO Survey (ELAIS) as mentioned in this paper was the largest single Open Time project conducted by ISO, mapping an area of 12deg^2 at 15μm and at 90μm with ISOPHOT.
Abstract: We describe the European Large Area ISO Survey (ELAIS). ELAIS was the largest single Open Time project conducted by ISO, mapping an area of 12deg^2 at 15μm with ISOCAM and at 90μm with ISOPHOT. Secondary surveys in other ISO bands were undertaken by the ELAIS team within the fields of the primary survey, with 6deg^2 being covered at 6.7μm and 1deg^2 at 175μm. This paper discusses the goals of the project and the techniques employed in its construction, as well as presenting details of the observations carried out, the data from which are now in the public domain. We outline the ELAIS `preliminary analysis' which led to the detection of over 1000 sources from the 15 and 90-μm surveys (the majority selected at 15μm with a flux limit of ~3mJy), to be fed into a ground-based follow-up campaign, as well as a programme of photometric observations of detected sources using both ISOCAM and ISOPHOT. We detail how the ELAIS survey complements other ISO surveys in terms of depth and areal coverage, and show that the extensive multi-wavelength coverage of the ELAIS fields resulting from our concerted and on-going follow-up programme has made these regions amongst the best studied areas of their size in the entire sky, and, therefore, natural targets for future surveys. This paper accompanies the release of extremely reliable subsets of the `preliminary analysis' products. Subsequent papers in this series will give further details of our data reduction techniques, reliability and completeness estimates and present the 15- and 90-μm number counts from the `preliminary analysis', while a further series of papers will discuss in detail the results from the ELAIS `final analysis', as well as from the follow-up programme.
TL;DR: The results clearly indicate that a proportion of glutamatergic synaptic connections are presynaptically rather than postsynaptically silent in the neonatal hippocampus, and this cannot exclude that "latent AMPA receptors" can become functional after activity-dependent processes.
Abstract: At early developmental stages, silent synapses have been commonly found in different brain areas. These synapses are called silent because they do not respond at rest but are functional at positive membrane potentials. A widely accepted interpretation is that N-methyl-d-aspartate (NMDA) but not α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors are functionally expressed on the subsynaptic membrane. Here we show that, in both CA3 and CA1 hippocampal regions, AMPA-mediated synaptic responses can be detected already at early stages of postnatal development. However, some synapses appear silent because of a very low probability of glutamate release. They can be converted into functional ones by factors that enhance release probability such as paired-pulse stimulation, increasing the temperature or cyclothiazide (CTZ), a drug that blocks AMPA receptor desensitization and increases transmitter release. Conversely, conducting synapses can be switched off by increasing the frequency of stimulation. Although we cannot exclude that “latent AMPA receptors” can become functional after activity-dependent processes, our results clearly indicate that, in the neonatal hippocampus, a proportion of glutamatergic synaptic connections are presynaptically rather than postsynaptically silent.
TL;DR: In this paper, candidate superconformal N = 2 gauge theories that realize the AdS/CFT correspondence with M-theory compactified on the homogeneous Sasakian 7 -manifolds M 7 were classified long ago.
TL;DR: In this article, the role of different types of agents: producers, speculators as well as noise traders are studied using the minority game model, and the central issue here is the information flow: producers feed in the information whereas speculators make it away.
Abstract: Using the minority game model we study a broad spectrum of problems of market mechanism. We study the role of different types of agents: producers, speculators as well as noise traders. The central issue here is the information flow: producers feed in the information whereas speculators make it away. How well each agent fares in the common game depends on the market conditions, as well as their sophistication. Sometimes there is much to gain with little effort, sometimes great effort virtually brings no more incremental gain. Market impact is also shown to play an important role, a strategy should be judged when it is actually used in play for its quality. Though the minority game is an extremely simplified market model, it allows to ask, analyze and answer many questions which arise in real markets.
TL;DR: In this article, van Paradijs et al. showed that the gamma-ray burst emission is not produced by relativistic electrons emittingsynchrotron and inverse Compton radiation.
Abstract: If the emission of gamma–ray bursts were due to the synchrotron process in the stan-dard internal shock scenario, then the typical observed spectrum should have a slopeF ν ∝ν −1/2 , which strongly conflicts with the much harder spectra observed. Thisdirectly follows from the cooling time being much shorter than the dynamical time.Particle re–acceleration, deviations from equipartition, fastly changing magnetic fieldsand adiabatic losses are found to be inadequate to account for this discrepancy. Wealso find that in the internal shock scenario the relativistic inverse Compton scatteringis always as important as the synchrotron process, and faces the same problems. Thisindicates that the burst emission is not produced by relativistic electrons emittingsynchrotron and inverse Compton radiation.Key words: gamma rays: bursts — X–rays: general — radiation mechanisms: non–thermal 1 INTRODUCTIONSince the observational breakthrough by BeppoSAX (Costaet al. 1997; van Paradijs et al. 1997) the physics of gamma–ray bursts (GRB) has started to be disclosed. The huge en-ergy and power releases required by their cosmological dis-tances support the fireball scenario (Cavallo & Rees 1978;Rees & M´esz´aros 1992; M´esz´aros & Rees 1993), whose evo-lution and behavior is (unfortunately) largely independentof their origin.We do not know yet in any detail how the GRB event isrelated to the afterglow emission, but in the most acceptedpicture of formation of and emission from internal/externalshocks (Rees & M´esz´aros 1992; Rees & M´esz´aros 1994; Sari& Piran 1997), the former is due to collisions of pairs ofrelativistic shells (internal shocks), while the latter is gen-erated by the collisionless shocks produced by shells inter-acting with the interstellar medium (external shocks). Theshort spikes (t
TL;DR: In this article, a general version of the nonlinear Schrodinger equation with a 3-tensor position-dependent mass and arbitrary nonlinearity is considered, and it is shown that at low momenta linearized excitations of the phase of the condensate wavefunction obey a (3+1)-dimensional d'Alembertian equation coupling to a generic effective metric that is generic, and depends algebraically on the background field.
Abstract: We analyze prospects for the use of Bose-Einstein condensates as condensed-matter systems suitable for generating a generic ``effective metric'', and for mimicking kinematic aspects of general relativity. We extend the analysis due to Garay et al, [gr-qc/0002015, gr-qc/0005131]. Taking a long term view, we ask what the ultimate limits of such a system might be. To this end, we consider a very general version of the nonlinear Schrodinger equation (with a 3-tensor position-dependent mass and arbitrary nonlinearity). Such equations can be used for example in discussing Bose-Einstein condensates in heterogeneous and highly nonlinear systems. We demonstrate that at low momenta linearized excitations of the phase of the condensate wavefunction obey a (3+1)-dimensional d'Alembertian equation coupling to a (3+1)-dimensional Lorentzian-signature ``effective metric'' that is generic, and depends algebraically on the background field. Thus at low momenta this system serves as an analog for the curved spacetime of general relativity. In contrast at high momenta we demonstrate how to use the eikonal approximation to extract a well-controlled Bogoliubov-like dispersion relation, and (perhaps unexpectedly) recover non-relativistic Newtonian physics at high momenta. Bose-Einstein condensates appear to be an extremely promising analog system for probing kinematic aspects of general relativity.
TL;DR: In this article, a class of conformally flat and asymptotically anti-de Sitter geometries involving profiles of scalar fields is studied from the point of view of gauged supergravity.
Abstract: A class of conformally flat and asymptotically anti--de Sitter geometries involving profiles of scalar fields is studied from the point of view of gauged supergravity. The scalars involved in the solutions parametrize the SL(N,R)/SO(N) submanifold of the full scalar coset of the gauged supergravity, and are described by a symmetric potential with a universal form. These geometries descend via consistent truncation from distributions of D3-branes, M2-branes, or M5-branes in ten or eleven dimensions. We exhibit analogous solutions asymptotic to AdS{sub 6} which descend from the D4-D8-brane system. We obtain the related six-dimensional theory by consistent reduction from massive type IIA supergravity. All our geometries correspond to states in the Coulomb branch of the dual conformal field theories. We analyze linear fluctuations of minimally coupled scalars and find both discrete and continuous spectra, but always bounded below.
TL;DR: In this article, the gluino-induced contributions to the decay b → s were investigated in supersymmetric frameworks with generic sources of flavour violation, and it was shown that, when QCD corrections are taken into account, the relevant operator basis of the Standard Model effective Hamiltonian gets enlarged to
Abstract: The gluino-induced contributions to the decay b → s are investigated in supersymmetric frameworks with generic sources of flavour violation. It is shown that, when QCD corrections are taken into account, the relevant operator basis of the Standard Model effective Hamiltonian gets enlarged to
TL;DR: In this article, the authors investigated the dependence of the local space density of spiral galaxies on luminosity, scale size, and surface brightness, and they derived bivariate space density distributions in these quantities from a sample of about 1000 Sb-Sdm spiral galaxies, corrected for selection effects in luminosity.
Abstract: We investigate the dependence of the local space density of spiral galaxies on luminosity, scale size, and surface brightness. We derive bivariate space density distributions in these quantities from a sample of about 1000 Sb-Sdm spiral galaxies, corrected for selection effects in luminosity and surface brightness. The structural parameters of the galaxies were corrected for internal extinction using a description depending on galaxy surface brightness. We find that the bivariate space density distribution of spiral galaxies in the (luminosity, scale size)-plane is well described by a Schechter luminosity function in the luminosity dimension and a log-normal scale-size distribution at a given luminosity. This parameterization of the scale-size distribution was motivated by a simple model for the formation of disks within dark matter halos, with halos acquiring their angular momenta through tidal torques from neighboring objects and the disk specific angular momentum being proportional to that of the parent halo. However, the fractional width of the scale-size distribution at a given luminosity is narrower than what one would expect from using the distribution of angular momenta of halos measured in N-body simulations of hierarchical clustering. We present several possible explanations for the narrowness of the observed distribution. Using our bivariate distribution, we find that determinations of the local luminosity function of spiral galaxies should not be strongly affected by the bias against low surface brightness galaxies, even when the galaxies are selected from photographic plates. This may not be true for studies at high redshift, where (1 + z)4 surface brightness dimming would cause a significant selection bias against lower surface brightness galaxies, if the galaxy population did not evolve with redshift.
TL;DR: In this paper, the authors investigated the dependence of the local space density of spiral galaxies on luminosity, scalesize and surface brightness, and they derived bivariate space density distributions in these quantities from a sample of about 1000 Sb-Sdm spiral galaxies, corrected for selection effects in luminosity and surfaces brightness.
Abstract: We investigate the dependence of the local space density of spiral galaxies on luminosity, scalesize and surface brightness. We derive bivariate space density distributions in these quantities from a sample of about 1000 Sb-Sdm spiral galaxies, corrected for selection effects in luminosity and surface brightness. The structural parameters of the galaxies were corrected for internal extinction using a description depending on galaxy surface brightness. We find that the bivariate space density distribution of spiral galaxies in the (luminosity, scalesize)-plane is well described by a Schechter luminosity function in the luminosity dimension and a log-normal scale size distribution at a given luminosity. This parameterization of the scalesize distribution was motivated by a simple model for the formation of disks within dark matter halos, with halos acquiring their angular momenta through tidal torques from neighboring objects, and the disk specific angular momentum being proportional to that of the parent halo. However, the fractional width of the scalesize distribution at a given luminosity is narrower than what one would expect from using the distribution of angular momenta of halos measured in N-body simulations. We present several possible explanations for the narrowness of the observed distribution. Using our bivariate distribution, we find that determinations of the local luminosity function of spiral galaxies should not be strongly affected by the bias against low surface brightness galaxies, even when the galaxies are selected from photographic plates. This may not be true for studies at high redshift, where (1+z)^4 surface brightness dimming can cause a significant selection bias against lower surface brightness galaxies.
TL;DR: A genuine and somehow unexpected "plaquette resonating valence bond," with spontaneously broken translation symmetry and no broken rotation symmetry, comes out from the numerical simulations as the most plausible ground state for J(2)/J(1) approximately 0.5.
Abstract: We investigate the nonmagnetic phase of the spin-half frustrated Heisenberg antiferromagnet on the square lattice using exact diagonalization (up to 36 sites) and quantum Monte Carlo techniques (up to 144 sites). The spin gap and the susceptibilities for the most important crystal symmetry breaking operators are computed. A genuine and somehow unexpected "plaquette resonating valence bond," with spontaneously broken translation symmetry and no broken rotation symmetry, comes out from our numerical simulations as the most plausible ground state for J(2)/J(1) approximately 0.5.
TL;DR: The Nearby Optical Galaxy (NOG) sample as mentioned in this paper is a complete, distance-limited (cz ≤ 6000 km s-1) and magnitude-limited sample of ~7000 optical galaxies.
Abstract: In this paper we describe the Nearby Optical Galaxy (NOG) sample, which is a complete, distance-limited (cz ≤ 6000 km s-1) and magnitude-limited (B ≤ 14) sample of ~7000 optical galaxies. The sample covers (8.27 sr) of the sky (|b| > 20°) and appears to have a good completeness in redshift (97%). We select the sample on the basis of homogenized corrected total blue magnitudes in order to minimize systematic effects in galaxy sampling. We identify the groups in this sample by means of both the hierarchical and the percolation "friends-of-friends" methods. The resulting catalogs of loose groups appear to be similar and are among the largest catalogs of groups currently available. Most of the NOG galaxies (~60%) are found to be members of galaxy pairs (~580 pairs for a total of ~15% of objects) or groups with at least three members (~500 groups for a total of ~45% of objects). About 40% of galaxies are left ungrouped (field galaxies). We illustrate the main features of the NOG galaxy distribution. Compared to previous optical and IRAS galaxy samples, the NOG provides a denser sampling of the galaxy distribution in the nearby universe. Given its large sky coverage, the identification of groups, and its high-density sampling, the NOG is suited to the analysis of the galaxy density field of the nearby universe, especially on small scales.
TL;DR: An experiment that would demonstrate the dc and ac Josephson effects in two weakly linked Bose-Einstein condensates is proposed, considering a time-dependent barrier, moving adiabatically across the trapping potential.
Abstract: We propose an experiment that would demonstrate the dc and ac Josephson effects in two weakly linked Bose-Einstein condensates. We consider a time-dependent barrier, moving adiabatically across the trapping potential. The phase dynamics are governed by a "driven-pendulum" equation, as in current-driven superconducting Josephson junctions. At a critical velocity of the barrier (proportional to the critical tunneling current), there is a sharp transition between the dc and ac regimes. The signature is a sudden jump of a large fraction of the relative condensate population. Analytical results are compared with a numerical integration of the Gross-Pitaevskii equation, in an experimentally realistic situation.