42,947 research outputs found
Connecting the Micro-dynamics to the Emergent Macro-variables: Self-Organized Criticality and Absorbing Phase Transitions in the Deterministic Lattice Gas
We reinvestigate the Deterministic Lattice Gas introduced as a paradigmatic
model of the 1/f spectra (Phys. Rev. Lett. V26, 3103 (1990)) arising according
to the Self-Organized Criticality scenario. We demonstrate that the density
fluctuations exhibit an unexpected dependence on systems size and relate the
finding to effective Langevin equations. The low density behavior is controlled
by the critical properties of the gas at the absorbing state phase transition.
We also show that the Deterministic Lattice Gas is in the Manna universality
class of absorbing state phase transitions. This is in contrast to expectations
in the literature which suggested that the entirely deterministic nature of the
dynamics would put the model in a different universality class. To our
knowledge this is the first fully deterministic member of the Manna
universality class.Comment: 8 pages, 12 figures. Changes in the new version: Reference list has
been correcte
Tracking and data systems support for the Helios project. Volume 3: DSN support of Project Helios May 1976 - June 1977
Spacecraft extended mission coverage does not generally carry a high priority, but Helios was fortunate in that a combination of separated viewperiods and unique utilization of the STDN Goldstone antenna have provided a considerable amount of additional science data return, particularly at key times such a perihelion and/or solar occultation
Young Binary Stars and Associated Disks
The typical product of the star formation process is a binary star. Binaries
have provided the first dynamical measures of the masses of pre-main-sequence
(PMS) stars, providing support for the calibrations of PMS evolutionary tracks.
Surprisingly, in some star-forming regions PMS binary frequencies are higher
than among main-sequence solar-type stars. The difference in PMS and
main-sequence binary frequencies is apparently not an evolutionary effect;
recent attention has focussed on correlations between binary frequency and
stellar density or cloud temperatures. Accretion disks are common among young
binary stars. Binaries with separations between 1 AU and 100 AU have
substantially less submillimeter emission than closer or wider binaries,
suggesting that they have truncated their disks. Evidence of dynamical clearing
has been seen in several binaries. Remarkably, PMS binaries of all separations
show evidence of circumstellar disks and continued accretion. This suggests
that the circumstellar disks are replenished from circumbinary disks or
envelopes. The frequent presence of disks suggests that planet formation can
occur in binary environments, and formation of planets in wide binaries is
already established by their discovery. Circumbinary disk masses around very
short period binaries are ample to form planetary systems such as our own. The
nature of planetary systems among the most common binaries, with separations
between 10 AU and 100 AU, is less clear given the observed reduction in disk
mass, though they may have disk masses adequate for the formation of
terrestrial-like planets.Comment: 32 pages, including 6 Postscript figures (TeX, uses psfig.sty); to
appear in "Protostars & Planets IV". Gif figures with captions and high-res
Postscript color figure available at
http://hven.swarthmore.edu/~jensen/preprints/ppiv.htm
Charge Transport Transitions and Scaling in Disordered Arrays of Metallic Dots
We examine the charge transport through disordered arrays of metallic dots
using numerical simulations. We find power law scaling in the current-voltage
curves for arrays containing no voids, while for void-filled arrays charge
bottlenecks form and a single scaling is absent, in agreement with recent
experiments. In the void-free case we also show that the scaling exponent
depends on the effective dimensionality of the system. For increasing applied
drives we find a transition from 2D disordered filamentary flow near threshold
to a 1D smectic flow which can be identified experimentally using
characteristics in the transport curves and conduction noise.Comment: 4 pages, 4 postscript figure
Strongly interacting confined quantum systems in one dimension
In one dimension, the study of magnetism dates back to the dawn of quantum
mechanics when Bethe solved the famous Heisenberg model that describes quantum
behaviour in magnetic systems. In the last decade, one-dimensional systems have
become a forefront area of research driven by the realization of the
Tonks-Girardeau gas using cold atomic gases. Here we prove that one-dimensional
fermionic and bosonic systems with strong short-range interactions are solvable
in arbitrary confining geometries by introducing a new energy-functional
technique and obtaining the full spectrum of energies and eigenstates. As a
first application, we calculate spatial correlations and show how both ferro-
and anti-ferromagnetic states are present already for small system sizes that
are prepared and studied in current experiments. Our work demonstrates the
enormous potential for quantum manipulation of magnetic correlations at the
microscopic scale.Comment: 11 pages, 2 figures, including methods, final versio
Fractional energy states of strongly-interacting bosons in one dimension
We study two-component bosonic systems with strong inter-species and
vanishing intra-species interactions. A new class of exact eigenstates is found
with energies that are {\it not} sums of the single-particle energies with wave
functions that have the characteristic feature that they vanish over extended
regions of coordinate space. This is demonstrated in an analytically solvable
model for three equal mass particles, two of which are identical bosons, which
is exact in the strongly-interacting limit. We numerically verify our results
by presenting the first application of the stochastic variational method to
this kind of system. We also demonstrate that the limit where both inter- and
intra-component interactions become strong must be treated with extreme care as
these limits do not commute. Moreover, we argue that such states are generic
also for general multi-component systems with more than three particles. The
states can be probed using the same techniques that have recently been used for
fermionic few-body systems in quasi-1D.Comment: 6 pages, 4 figures, published versio
Interdependence of magnetism and superconductivity in the borocarbide TmNi2B2C
We have discovered a new antiferromagnetic phase in TmNi2B2C by neutron
diffraction. The ordering vector is Q_A = (0.48,0,0) and the phase appears
above a critical in-plane magnetic field of 0.9 T. The field was applied in
order to test the assumption that the zero-field magnetic structure at Q_F =
(0.094,0.094,0) would change into a c-axis ferromagnet if superconductivity
were destroyed. We present theoretical calculations which show that two effects
are important: A suppression of the ferromagnetic component of the RKKY
exchange interaction in the superconducting phase, and a reduction of the
superconducting condensation energy due to the periodic modulation of the
moments at the wave vector Q_A
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