44,773 research outputs found
Anomalous aging phenomena caused by drift velocities
We demonstrate via several examples that a uniform drift velocity gives rise
to anomalous aging, characterized by a specific form for the two-time
correlation functions, in a variety of statistical-mechanical systems far from
equilibrium. Our first example concerns the oscillatory phase observed recently
in a model of competitive learning. Further examples, where the proposed theory
is exact, include the voter model and the Ohta-Jasnow-Kawasaki theory for
domain growth in any dimension, and a theory for the smoothing of sandpile
surfaces.Comment: 7 pages, 3 figures. To appear in Europhysics Letter
Some calculations on the ground and lowest-triplet state of the helium isoelectronic sequence with the nucleus in motion
The method described in the preceding paper for the solution of two-electron atoms, which was used to calculate the 1 1S and 2 3S states of helium and heliumlike atoms within the fixed-nucleus approximation, has been applied to the case where all three particles are in relative motion. The solutions in the present case automatically include the effects of the mass polarization term and are compared with the results obtained for the term by using first-order perturbation theory with the fixed-nucleus wave functions. The input data for a particular atom consist of the atomic number, as before, but now the corresponding mass of the nucleus must be given also. Nonrelativistic energies with the nuclear mass included in the calculation have been obtained for the 1 1S and 2 3S states for Z ranging from 1 to 10. The energy with the nucleus in motion can be expressed only to eight significant figures (SF's) given the accuracy with which the relevant physical constants are known at present. All the results given here are computed as if these constants were known to ten SF's so that errors not incurred due to rounding. Convergence of the energies to ten SF's for both the singlet and triplet state was reached with a matrix of size 444 for Z values from 2 to 10. Convergence for the H- ion was a little slower
Simulations of Dust in Interacting Galaxies
A new Monte-Carlo radiative-transfer code, Sunrise, is used to study the
effects of dust in N-body/hydrodynamic simulations of interacting galaxies.
Dust has a profound effect on the appearance of the simulated galaxies. At peak
luminosities, about 90% of the bolometric luminosity is absorbed, and the dust
obscuration scales with luminosity in such a way that the brightness at
UV/visual wavelengths remains roughly constant. A general relationship between
the fraction of energy absorbed and the ratio of bolometric luminosity to
baryonic mass is found. Comparing to observations, the simulations are found to
follow a relation similar to the observed IRX-Beta relation found by Meurer et
al (1999) when similar luminosity objects are considered. The
highest-luminosity simulated galaxies depart from this relation and occupy the
region where local (U)LIRGs are found. This agreement is contingent on the
presence of Milky-Way-like dust, while SMC-like dust results in far too red a
UV continuum slope to match observations. The simulations are used to study the
performance of star-formation indicators in the presence of dust. The
far-infrared luminosity is found to be reliable. In contrast, the H-alpha and
far-UV luminosity suffer severely from dust attenuation, and dust corrections
can only partially remedy the situation.Comment: 4 pages, 5 figures, to appear in the proceedings of the conference
"The Spectral Energy Distribution of Gas-Rich Galaxies", eds. C.C. Popescu &
R.J. Tuffs (Heidelberg, October 2004
Smooth rationally connected threefolds contain all smooth curves
We show that if X is a smooth rationally connected threefold and C is a
smooth projective curve then C can be embedded in X. Furthermore, a version of
this property characterises rationally connected varieties of dimension at
least 3. We give some details about the toric case.Comment: Version 1 was called "Any smooth toric threefold contains all
curves". This version is completely rewritten and proves a much stronger
result, following suggestions of Janos Kolla
An investigation of the plastic fracture of high strength steels
Three generally recognized stages of plastic fracture in high strength steels are considered in detail. These stages consist of void initiation, void growth, and void coalescence. A brief review of the existing literature on plastic fracture is included along with an outline of the experimental approach used in the investigation
Models of competitive learning: complex dynamics, intermittent conversions and oscillatory coarsening
We present two models of competitive learning, which are respectively
interfacial and cooperative learning. This learning is outcome-related, so that
spatially and temporally local environments influence the conversion of a given
site between one of two different types. We focus here on the behavior of the
models at coexistence, which yields new critical behavior and the existence of
a phase involving a novel type of coarsening which is oscillatory in nature.Comment: 23 pages, 11 figures. To appear in Phys. Rev.
Molecular Carbon Chains and Rings in TMC-1
We present mapping results in several rotational transitions of HC3N, C6H,
both cyclic and linear C3H2 and C3H, towards the cyanopolyyne peak of the
filamentary dense cloud TMC-1 using the IRAM 30m and MPIfR 100m telescopes. The
spatial distribution of the cumulene carbon chain propadienylidene H2C3
(hereafter l-C3H2) is found to deviate significantly from the distributions of
the cyclic isomer c-C3H2, HC3N, and C6H which in turn look very similar. The
cyclic over linear abundance ratio of C3H2 increases by a factor of 3 across
the filament, with a value of 28 at the cyanopolyyne peak. This abundance ratio
is an order of magnitude larger than the range (3 to 5) we observed in the
diffuse interstellar medium. The cyclic over linear abundance ratio of C3H also
varies by ~2.5 in TMC-1, reaching a maximum value (13) close to the
cyanopolyyne peak. These behaviors might be related to competitive processes
between ion-neutral and neutral-neutral reactions for cyclic and linear
species.Comment: Accepted for publication in The Astrophysical Journal, part I. 24
pages, including 4 tables, 7 figures, and figure caption
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