2,329 research outputs found
The evolution of the bi-modal colour distribution of galaxies in SDSS groups
We analyse colour distributions for several samples of galaxies in
groups drawn from the Fourth Data Release of the Sloan Digital Sky Survey. For
all luminosity ranges and environments considered the colour distributions are
well described by the sum of two Gaussian functions. We find that the fraction
of galaxies in the red sequence is an increasing function of group virial mass.
We also study the evolution of the galaxy colour distributions at low redshift,
in the field and in groups for galaxies brighter than
, finding significant evidence of recent evolution in the
population of galaxies in groups. The fraction of red galaxies monotonically
increases with decreasing redshift, this effect implies a much stronger
evolution of galaxies in groups than in the field.Comment: 7 pages, 6 figures, submited to MNRAS after minor revisio
Cu/Ag EAM Potential Optimized for Heteroepitaxial Diffusion from ab initio Data
A binary embedded-atom method (EAM) potential is optimized for Cu on Ag(111)
by fitting to ab initio data. The fitting database consists of DFT calculations
of Cu monomers and dimers on Ag(111), specifically their relative energies,
adatom heights, and dimer separations. We start from the Mishin Cu-Ag EAM
potential and first modify the Cu-Ag pair potential to match the FCC/HCP site
energy difference then include Cu-Cu pair potential optimization for the entire
database. The optimized EAM potential reproduce DFT monomer and dimer relative
energies and geometries correctly. In trimer calculations, the potential
produces the DFT relative energy between FCC and HCP trimers, though a
different ground state is predicted. We use the optimized potential to
calculate diffusion barriers for Cu monomers, dimers, and trimers. The
predicted monomer barrier is the same as DFT, while experimental barriers for
monomers and dimers are both lower than predicted here. We attribute the
difference with experiment to the overestimation of surface adsorption energies
by DFT and a simple correction is presented. Our results show that the
optimized Cu-Ag EAM can be applied in the study of larger Cu islands on
Ag(111).Comment: 15 pages, 7 figure
Assessing molecular outflows and turbulence in the protostellar cluster Serpens South
Molecular outflows driven by protostellar cluster members likely impact their
surroundings and contribute to turbulence, affecting subsequent star formation.
The very young Serpens South cluster consists of a particularly high density
and fraction of protostars, yielding a relevant case study for protostellar
outflows and their impact on the cluster environment. We combined CO
observations of this region using the Combined Array for Research in
Millimeter-wave Astronomy (CARMA) and the Institut de Radioastronomie
Millim\'{e}trique (IRAM) 30 m single dish telescope. The combined map allows us
to probe CO outflows within the central, most active region at size scales of
0.01 pc to 0.8 pc. We account for effects of line opacity and excitation
temperature variations by incorporating CO and CO data for the
and transitions (using Atacama Pathfinder Experiment and
Caltech Submillimeter Observatory observations for the higher CO transitions),
and we calculate mass, momentum, and energy of the molecular outflows in this
region. The outflow mass loss rate, force, and luminosity, compared with
diagnostics of turbulence and gravity, suggest that outflows drive a sufficient
amount of energy to sustain turbulence, but not enough energy to substantially
counter the gravitational potential energy and disrupt the clump. Further, we
compare Serpens South with the slightly more evolved cluster NGC 1333, and we
propose an empirical scenario for outflow-cluster interaction at different
evolutionary stages.Comment: 26 pages, 15 figures, accepted for publication in the Astrophysical
Journa
Geometric quantization of mechanical systems with time-dependent parameters
Quantum systems with adiabatic classical parameters are widely studied, e.g.,
in the modern holonomic quantum computation. We here provide complete geometric
quantization of a Hamiltonian system with time-dependent parameters, without
the adiabatic assumption. A Hamiltonian of such a system is affine in the
temporal derivative of parameter functions. This leads to the geometric Berry
factor phenomena.Comment: 20 page
Dynamics of two coupled chaotic systems driven by external signals
Setting-up a controlled or synchronized state in a space-time chaotic structure targeting an unstable periodic orbit is a key feature of many problems in high dimensional physical, electronics,
biological and ecological systems (among others). Formerly, we have shown numerically and experimentally that phase synchronization [M.G. Rosenblum, A.S. Pikovsky, J. Kurths, Phys. Rev. Lett. 78, 4193 (1997)] can be achieved in time dependent hydrodynamic flows [D. Maza, A. Vallone, H.L. Mancini, S. Boccaletti, Phys. Rev. Lett. 85, 5567 (2000)]. In that case the flow was generated in a small container
with inhomogeneous heating in order to have a single roll structure produced by a BÂŽenard-Marangoni instability [E.L. Koshmieder, BÂŽenard Cells and Taylor Vortices (Cambridge University Press, 1993)]. Phase
synchronization was achieved by a small amplitude signal injected at a subharmonic frequency obtained from the measured Fourier temperature spectrum. In this work, we analyze numerically the effects of driving
two previously synchronized chaotic oscillators by an external signal. The numerical system represents a convective experiment in a small container with square symmetry, where boundary layer instabilities are coupled by a common flow. This work is an attempt to control this situation and overcome some difficulties to select useful frequency values for the driving force, analyzing the influence of different harmonic injection signals on the synchronization in a system composed by two identical chaotic Takens-Bogdanov equations
(TBA and TBB) bidirectionally coupled
Complexity control in a synchronized complex system
We numerically analyze the problem of how to drive a synchronized state in a complex system to other state with diferent complexity, keeping synchronization. The complex system used is obtained by synchronizing two identical chaotic Takens-Bogdanov sub-systems specially coupled to recover in the global system the symmetries of each oscillator. The global state is adjusted to have an initial synchronized hyperchaotic state (with two positive Lyapunov exponents). This work is an attempt, using small amplitude external signals, to drive the global system to other complex state keeping the synchronized state. The method used to overcome the problems that we had to select a useful frequency value for the driving signal will be discussed, together with a possible experiment in a thermo-convective flow for validating the results obtained
Method of Metallurgically Bonding Articles and Article Therefor
An article suitable for laser-welded metallurgical bonding, the article having a first part having a lower surface, and a second part having an upper surface is disclosed. The lower surface of the first part is disposed at the upper surface of the second part to provide for a faying surface thereat. The faying surface has a plurality of channels with a depth equal to or greater than about 1 micron and equal to or less than about 1000 microns. The article is suitable for laser-welded metallurgical bonding at the faying surface. The plurality of channels has a repetitive pattern of channels arranged along a path of the faying surface in a direction of the metallurgical bonding action
Method of Metallurgically Bonding Articles and Article Therefor
An article suitable for arc-welded metallurgical bonding having a first part having a lower surface, and a second part having an upper surface is disclosed. The lower surface of the first part is disposed at the upper surface of the second part to provide for a faying surface thereat. The faying surface has a plurality of channels with a depth equal to or greater than about 1 micron and equal to or less than about 1000 microns. The article is suitable for arc-welded metallurgical bonding at the faying surface. The plurality of channels has a repetitive pattern of channels arranged along a path of the faying surface in a direction of the metallurgical bonding action
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