2,932 research outputs found
Vertical Migration, Orientation, Aggregation, and Fecundity of the Freshwater Mussel Lampsilis Siliquoidea
Author Institution: Department of Zoology, Miami UniversityThe decline in freshwater mussels makes it imperative that more information be gathered on their population status, behavior, and habitat requirements. We examined vertical migration, aggregation, and reproductive potential of captive and field populations of Lampsilis siliquoidea. Both captive populations and a field population exhibited vertical migration. This movement was strongly correlated with day length, and somewhat less strongly correlated with water temperature. While captive mussels tended to orient their siphons into the current, no pattern of orientation was detected in the field population. The field population was significantly aggregated in the fall and winter. The spatial patterning of captive mussels was random in the fall and winter, but this result may have been an artifact of the small size of the artificial streams. Weather conditions prevented data collection in the spring and, therefore, no conclusions could be drawn about the relationship between aggregation and glochidia release. The average number of glochidia (parasitic larvae) produced by individuals across a limited size range was not correlated with any maternal or marsupial properties. These results are useful for implementing qualitative sampling methods under optimum conditions and for information on the reproductive potential of Lampsilis siliquoidea
Formal Verification of an Iterative Low-Power x86 Floating-Point Multiplier with Redundant Feedback
We present the formal verification of a low-power x86 floating-point
multiplier. The multiplier operates iteratively and feeds back intermediate
results in redundant representation. It supports x87 and SSE instructions in
various precisions and can block the issuing of new instructions. The design
has been optimized for low-power operation and has not been constrained by the
formal verification effort. Additional improvements for the implementation were
identified through formal verification. The formal verification of the design
also incorporates the implementation of clock-gating and control logic. The
core of the verification effort was based on ACL2 theorem proving.
Additionally, model checking has been used to verify some properties of the
floating-point scheduler that are relevant for the correct operation of the
unit.Comment: In Proceedings ACL2 2011, arXiv:1110.447
Stacking Entropy of Hard Sphere Crystals
Classical hard spheres crystallize at equilibrium at high enough density.
Crystals made up of stackings of 2-dimensional hexagonal close-packed layers
(e.g. fcc, hcp, etc.) differ in entropy by only about per sphere
(all configurations are degenerate in energy). To readily resolve and study
these small entropy differences, we have implemented two different
multicanonical Monte Carlo algorithms that allow direct equilibration between
crystals with different stacking sequences. Recent work had demonstrated that
the fcc stacking has higher entropy than the hcp stacking. We have studied
other stackings to demonstrate that the fcc stacking does indeed have the
highest entropy of ALL possible stackings. The entropic interactions we could
detect involve three, four and (although with less statistical certainty) five
consecutive layers of spheres. These interlayer entropic interactions fall off
in strength with increasing distance, as expected; this fall-off appears to be
much slower near the melting density than at the maximum (close-packing)
density. At maximum density the entropy difference between fcc and hcp
stackings is per sphere, which is roughly 30% higher
than the same quantity measured near the melting transition.Comment: 15 page
Winter wheat, 1994
"July 1994.""Publication costs paid by Missouri Seed Improvement Association."The objective of the Missouri Winter Wheat Performance Tests is to provide wheat growers in Missouri with a reliable, unbiased, up-to-date source of information that will permit valid comparisons among improved wheat varieties. This information should help Missouri wheat growers select varieties best suited to their particular area and growing conditions. This report summarizes soft and hard winter wheat variety trials conducted throughout Missouri during the 1993-94 cropping season
Transition-Event Durations in One Dimensional Activated Processes
Despite their importance in activated processes, transition-event durations
-- which are much shorter than first passage times -- have not received a
complete theoretical treatment. We therefore study the distribution of
durations of transition events over a barrier in a one-dimensional system
undergoing over-damped Langevin dynamics.Comment: 39 pages, 11 figure
Superpotential de-sequestering in string models
Non-perturbative superpotential cross-couplings between visible sector matter
and K\"ahler moduli can lead to significant flavour-changing neutral currents
in compactifications of type IIB string theory. Here, we compute corrections to
Yukawa couplings in orbifold models with chiral matter localised on D3-branes
and non-perturbative effects on distant D7-branes. By evaluating a threshold
correction to the D7-brane gauge coupling, we determine conditions under which
the non-perturbative corrections to the Yukawa couplings appear. The flavour
structure of the induced Yukawa coupling generically fails to be aligned with
the tree-flavour structure. We check our results by also evaluating a
correlation function of two D7-brane gauginos and a D3-brane Yukawa coupling.
Finally, by calculating a string amplitude between n hidden scalars and visible
matter we show how non-vanishing vacuum expectation values of distant D7-brane
scalars, if present, may correct visible Yukawa couplings with a flavour
structure that differs from the tree-level flavour structure.Comment: 37 pages + appendices, 8 figure
Entropy and the variational principle for actions of sofic groups
Recently Lewis Bowen introduced a notion of entropy for measure-preserving
actions of a countable sofic group on a standard probability space admitting a
generating partition with finite entropy. By applying an operator algebra
perspective we develop a more general approach to sofic entropy which produces
both measure and topological dynamical invariants, and we establish the
variational principle in this context. In the case of residually finite groups
we use the variational principle to compute the topological entropy of
principal algebraic actions whose defining group ring element is invertible in
the full group C*-algebra.Comment: 44 pages; minor changes; to appear in Invent. Mat
Sub-Subgiants in the Old Open Cluster M67?
We report the discovery of two spectroscopic binaries in the field of the old
open cluster M67 -- S1063 and S1113 -- whose positions in the color-magnitude
diagram place them approximately 1 mag below the subgiant branch. A ROSAT study
of M67 independently discovered these stars to be X-ray sources. Both have
proper-motion membership probabilities greater than 97%; precise center-of-mass
velocities are consistent with the cluster mean radial velocity. S1063 is also
projected within one core radius of the cluster center. S1063 is a single-lined
binary with a period of 18.396 days and an orbital eccentricity of 0.206. S1113
is a double-lined system with a circular orbit having a period of 2.823094
days. The primary stars of both binaries are subgiants. The secondary of S1113
is likely a 0.9 Mo main-sequence star, which implies a 1.3 Mo primary star. We
have been unable to explain securely the low apparent luminosities of the
primary stars; neither binary contain stars presently limited in radius by
their Roche lobes. We speculate that S1063 and S1113 may be the products of
close stellar encounters involving binaries in the cluster environment, and may
define alternative stellar evolutionary tracks associated with mass-transfer
episodes, mergers, and/or dynamical stellar exchanges
Reconstruction of cell surface densities of ion pumps, exchangers, and channels from mRNA expression, conductance kinetics, whole-cell calcium, and current-clamp voltage recordings, with an application to human uterine smooth muscle cells
Uterine smooth muscle cells remain quiescent throughout most of gestation, only generating spontaneous action potentials immediately prior to, and during, labor. This study presents a method that combines transcriptomics with biophysical recordings to characterise the conductance repertoire of these cells, the ‘conductance repertoire’ being the total complement of ion channels and transporters expressed by an electrically active cell. Transcriptomic analysis provides a set of potential electrogenic entities, of which the conductance repertoire is a subset. Each entity within the conductance repertoire was modeled independently and its gating parameter values were fixed using the available biophysical data. The only remaining free parameters were the surface densities for each entity. We characterise the space of combinations of surface densities (density vectors) consistent with experimentally observed membrane potential and calcium waveforms. This yields insights on the functional redundancy of the system as well as its behavioral versatility. Our approach couples high-throughput transcriptomic data with physiological behaviors in health and disease, and provides a formal method to link genotype to phenotype in excitable systems. We accurately predict current densities and chart functional redundancy. For example, we find that to evoke the observed voltage waveform, the BK channel is functionally redundant whereas hERG is essential. Furthermore, our analysis suggests that activation of calcium-activated chloride conductances by intracellular calcium release is the key factor underlying spontaneous depolarisations
Phase transitions in the steady state behavior of mechanically perturbed spin glasses and ferromagnets
We analyze the steady state regime of systems interpolating between spin
glasses and ferromagnets under a tapping dynamics recently introduced by
analogy with the dynamics of mechanically perturbed granular media. A crossover
from a second order to first order ferromagnetic transition as a function of
the spin coupling distribution is found. The flat measure over blocked states
introduced by Edwards for granular media is used to explain this scenario.
Annealed calculations of the Edwards entropy are shown to qualitatively explain
the nature of the phase transitions. A Monte-Carlo construction of the Edwards
measure confirms that this explanation is also quantitatively accurate
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