16,525 research outputs found
Bivariate galaxy luminosity functions in the Sloan Digital Sky Survey
Bivariate luminosity functions (LFs) are computed for galaxies in the New York Value-Added Galaxy Catalogue, based on the Sloan Digital Sky Survey Data Release 4. The galaxy properties investigated are the morphological type, inverse concentration index, Sérsic index, absolute effective surface brightness (SB), reference frame colours, absolute radius, eClass spectral type, stellar mass and galaxy environment. The morphological sample is flux limited to galaxies with r < 15.9 and consists of 37 047 classifications to an rms accuracy of ± half a class in the sequence E, S0, Sa, Sb, Sc, Sd, Im. These were assigned by an artificial neural network, based on a training set of 645 eyeball classifications. The other samples use r < 17.77 with a median redshift of z∼ 0.08, and a limiting redshift of z < 0.15 to minimize the effects of evolution. Other cuts, for example in axis ratio, are made to minimize biases. A wealth of detail is seen, with clear variations between the LFs according to absolute magnitude and the second parameter. They are consistent with an early-type, bright, concentrated, red population and a late-type, faint, less concentrated, blue, star-forming population. This bimodality suggests two major underlying physical processes, which in agreement with previous authors we hypothesize to be merger and accretion, associated with the properties of bulges and discs, respectively. The bivariate luminosity–SB distribution is fit with the Chołoniewski function (a Schechter function in absolute magnitude and Gaussian in SB). The fit is found to be poor, as might be expected if there are two underlying processes
Hydrogen Transport and the Spatial Requirements of Renewable Energy
Unlike oil and coal, which are compressed forms of energy, renewable energy requires unusually large land areas. This article calculates the consequences of a switch to hydrogen-cell vehicles powered by electricity from wind turbines. It then re-does the calculation for three other green energy sources : wave power ; biofuels ; solar energy. We argue that policy-makers and social scientists need to understand the significant spatial demands of a move to a carbon-free society.Renewable energy ; wind power ; land use ; energy efficiency ; wind turbines ; transport ; environmental ; solar ; biomass ; wave
Updated analysis of NN elastic scattering to 3 GeV
A partial-wave analysis of NN elastic scattering data has been updated to
include a number of recent measurements. Experiments carried out at the Cooler
Synchrotron (COSY) by the EDDA Collaboration have had a significant impact
above 1 GeV. Results are discussed in terms of the partial-wave and
direct-reconstruction amplitudes.Comment: 16 pages, 14 figures, 2 tables; Fig 10 error corrected; Accepted for
publication in Physical Review
Singularity theory study of overdetermination in models for L-H transitions
Two dynamical models that have been proposed to describe transitions between
low and high confinement states (L-H transitions) in confined plasmas are
analysed using singularity theory and stability theory. It is shown that the
stationary-state bifurcation sets have qualitative properties identical to
standard normal forms for the pitchfork and transcritical bifurcations. The
analysis yields the codimension of the highest-order singularities, from which
we find that the unperturbed systems are overdetermined bifurcation problems
and derive appropriate universal unfoldings. Questions of mutual equivalence
and the character of the state transitions are addressed.Comment: Latex (Revtex) source + 13 small postscript figures. Revised versio
High temperature polyimide foams for shuttle upper surface thermal insulation
Polyimide foams developed by Monsanto Company were examined for use as upper surface space shuttle thermal insulation. It was found that postcured polyimide foams having a density of 64 kg/cu m (4 lb/cu ft) had acceptable physical properties up to and exceeding 700 K (800 F). Physical tests included cyclic heating and cooling in vacuum, weight and dimensional stability, mechanical strength and impact resistance, acoustic loading and thermal conductivity. Molding and newly developed postcuring procedures were defined
Transverse Ward-Takahashi Identity, Anomaly and Schwinger-Dyson Equation
Based on the path integral formalism, we rederive and extend the transverse
Ward-Takahashi identities (which were first derived by Yasushi Takahashi) for
the vector and the axial vector currents and simultaneously discuss the
possible anomaly for them. Subsequently, we propose a new scheme for writing
down and solving the Schwinger-Dyson equation in which the the transverse
Ward-Takahashi identity together with the usual (longitudinal) Ward-Takahashi
identity are applied to specify the fermion-boson vertex function. Especially,
in two dimensional Abelian gauge theory, we show that this scheme leads to the
exact and closed Schwinger-Dyson equation for the fermion propagator in the
chiral limit (when the bare fermion mass is zero) and that the Schwinger-Dyson
equation can be exactly solved.Comment: 22 pages, latex, no figure
Progress on neural parton distributions
We give a status report on the determination of a set of parton distributions
based on neural networks. In particular, we summarize the determination of the
nonsinglet quark distribution up to NNLO, we compare it with results obtained
using other approaches, and we discuss its use for a determination of
.Comment: 4 pages, 2 figs, uses dis2007.cls, to appear in the DIS 2007 workshop
proceeding
Recent progress on NNPDF for LHC
We present recent results of the NNPDF collaboration on a full DIS analysis
of Parton Distribution Functions (PDFs). Our method is based on the idea of
combining a Monte Carlo sampling of the probability measure in the space of
PDFs with the use of neural networks as unbiased universal interpolating
functions. The general structure of the project and the features of the fit are
described and compared to those of the traditional approaches.Comment: 4 pages, 6 figures, contribution for the proceedings of the
conference "Rencontres de Moriond, QCD and High Energy Interactions
The impact of heavy quark mass effects in the NNPDF global analysis
We discuss the implementation of the FONLL general-mass scheme for heavy
quarks in deep-inelastic scattering in the FastKernel framework, used in the
NNPDF series of global PDF analysis. We present the general features of FONLL
and benchmark the accuracy of its implementation in FastKernel comparing with
the Les Houches heavy quark benchmark tables. We then show preliminary results
of the NNPDF2.1 analysis, in which heavy quark mass effects are included
following the FONLL-A GM scheme.Comment: 5 pages, 3 figures; to appear in the proceedings of DIS 2010, Firenz
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