3,277 research outputs found
The PSCz Galaxy Power Spectrum Compared to N-Body Simulations
By comparing the PSCz galaxy power spectrum with haloes from nested and
phased N-body simulations, we try to understand how IRAS infrared-selected
galaxies populate dark-matter haloes. We pay special attention to the way we
identify haloes in the simulations.Comment: 2 pages, 1 figure, to appear in "The IGM/Galaxy Connection: The
Distribution of Baryons at z=0," eds. J.L. Rosenberg and M.E. Putma
Changes in sulfhydryl groups of honeybee glyceraldehyde phosphate dehydrogenase associated with generation of the intermediate plateau in its saturation kinetics
Honeybee and rabbit muscle GPDH were studied to obtain information at the chemical level regarding anomolous saturation kinetics of the honeybee enzyme. Results demonstrate that the enzyme's sulfhydryl groups are implicated in the process. Measured by DTNB titration, native honeybee GPDH has one less active SH than the native rabbit muscle enzyme and displays changes in overall sulfhydryl reactivity after preincubation with G-3-P or G-3-P plus NAD+. The total DTNB reactive sulfhydryls of rabbit muscle GPDH are not changed by preincubation with NAD+ or G-3-P; honeybee GPDH, under certain conductions of preincubation with these ligands, shows a decrease of two total DTNB reactive SH groups. This difference has been confirmed by an independent experiment in which the two enzymes were carboxymethylated with C-14 bromoacetic acid
A Mass Matrix for Atmospheric, Solar, and LSND Neutrino Oscillations
We construct a mass matrix for the four neutrino flavors, three active and
one sterile, needed to fit oscillations in all three neutrino experiments:
atmospheric, solar, and LSND, simultaneously. It organizes the neutrinos into
two doublets whose central values are about 1 eV apart, and whose splittings
are of the order of 10^(-3) eV. Atmospheric neutrino oscillations are described
as maximal mixing within the upper doublet, and solar as the same within the
lower doublet. Then LSND is a weak transition from one doublet to the other. We
comment on the Majorana versus Dirac nature of the active neutrinos and show
that our mass matrix can be derived from an S_2 x S_2 permutation symmetry plus
an equal splitting rule.Comment: 4 pages, 0 figures, minor text change
Liquid-liquid coexistence in the phase diagram of a fluid confined in fractal porous materials
Multicanonical ensemble sampling simulations have been performed to calculate
the phase diagram of a Lennard-Jones fluid embedded in a fractal random matrix
generated through diffusion limited cluster aggregation. The study of the
system at increasing size and constant porosity shows that the results are
independent from the matrix realization but not from the size effects. A
gas-liquid transition shifted with respect to bulk is found. On growing the
size of the system on the high density side of the gas-liquid coexistence curve
it appears a second coexistence region between two liquid phases. These two
phases are characterized by a different behaviour of the local density inside
the interconnected porous structure at the same temperature and chemical
potential.Comment: 5 pages, 4 figures. To be published in Europhys. Letter
Laser driven launch vehicles for continuous access to space
The availability of megawatt laser systems in the next century will make laser launch systems from ground to orbit feasible and useful. Systems studies indicate launch capabilities of 1 ton payload per gigawatt laser power. Recent research in ground to orbit laser propulsion has emphasized laser supported detonation wave thrusters driven by repetitively pulsed infrared lasers. In this propulsion concept each laser repetition cycle consists of two pulses. A lower energy first pulse is used to vaporize a small amount of solid propellant and then after a brief expansion period, a second and higher energy laser pulse is used to drive a detonation wave through the expanded vapor. The results are reported of numerical studies comparing the detonation wave properties of various candidate propellants, and the simulation of thruster performance under realistic conditions. Experimental measurements designed to test the theoretical predictions are also presented. Measurements are discussed of radiance and opacity in absorption waves, and mass loss and momentum transfer. These data are interpreted in terms of specific impulse and energy conversion efficiency
Large amplitude dynamics of micro/nanomechanical resonators actuated with electrostatic pulses
International audienceIn the field of resonant NEMS design, it is a common misconception that large-amplitude motion, and thus large signal-to-noise ratio, can only be achieved at the risk of oscillator instability. In the present paper, we show that very simple closed-loop control schemes can be used to achieve stable largeamplitude motion of a resonant structure, even when jump resonance (caused by electrostatic softening or Duffing hardening) is present in its frequency response. We focus on the case of a resonant accelerometer sensing cell, consisting in a nonlinear clamped-clamped beam with electrostatic actuation and detection, maintained in an oscillation state with pulses of electrostatic force that are delivered whenever the detected signal (the position of the beam) crosses zero. We show that the proposed feedback scheme ensures the stability of the motion of the beam much beyond the critical Duffing amplitude and that, if the parameters of the beam are correctly chosen, one can achieve almost full-gap travel range without incurring electrostatic pull-in. These results are illustrated and validated with transient simulations of the nonlinear closed-loop system
Exploring microstructural changes associated with oxidation in Ni-YSZ SOFC electrodes using high resolution X-ray computed tomography
State of the art solid oxide fuel cell (SOFC) anodes are typically Ni based, one of the primary drawbacks of these electrodes is their significant dimensional change upon oxidation. As commercial SOFCs may typically be expected to undergo numerous redox cycles in their operating lifetime, it is important to understand the associated microstructural degradation process. Here we present a methodology for the use of synchrotron based X-ray nano-computed tomography to explore the step-wise oxidation of the Ni phase in a Ni–YSZ composite material. This non-destructive technique demonstrates the potential to track microstructural evolution on a grain-by-grain basis in three dimensions
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