10,881 research outputs found
Hard Discs on the Hyperbolic Plane
We examine a simple hard disc fluid with no long range interactions on the
two dimensional space of constant negative Gaussian curvature, the hyperbolic
plane. This geometry provides a natural mechanism by which global crystalline
order is frustrated, allowing us to construct a tractable model of disordered
monodisperse hard discs. We extend free area theory and the virial expansion to
this regime, deriving the equation of state for the system, and compare its
predictions with simulation near an isostatic packing in the curved space.Comment: 4 pages, 3 figures, included, final versio
Entanglement and the Thermodynamic Arrow of Time
We discuss quantum entanglement in the context of the thermodynamic arrow of
time. We review the role of correlations in entropy-decreasing events and prove
that the occurrence of a transformation between two thermodynamic states
constitutes a new type of entanglement witness, one not defined as a separating
plane in state space between separable and entangled states, but as a physical
process dependent on the local initial properties of the states. Extending work
by Partovi, we consider a general entangled multipartite system that allows
large reversals of the thermodynamic arrow of time. We describe a hierarchy of
arrows that arises from the different correlations allowed in a quantum state
and examine these features in the context of Maxwell's Demon. We examine in
detail the case of three qubits, and also propose some simple experimental
demonstrations possible with small numbers of qubits.Comment: 10 pages with 9 figure
Historical Arctic Logbooks Provide Insights into Past Diets and Climatic Responses of Cod
Gadus morhua (Atlantic cod) stocks in the Barents Sea are currently at levels not seen since the 1950s. Causes for the population increase last century, and understanding of whether such large numbers will be maintained in the future, are unclear. To explore this, we digitised and interrogated historical cod catch and diet datasets from the Barents Sea. Seventeen years of catch data and 12 years of prey data spanning 1930–1959 cover unexplored spatial and temporal ranges, and importantly capture the end of a previous warm period, when temperatures were similar to those currently being experienced. This study aimed to evaluate cod catch per unit effort and prey frequency in relation to spatial, temporal and environmental variables. There was substantial spatio-temporal heterogeneity in catches through the time series. The highest catches were generally in the 1930s and 1940s, although at some localities more cod were recorded late in the 1950s. Generalized Additive Models showed that environmental, spatial and temporal variables are all valuable descriptors of cod catches, with the highest occurring from 15–45°E longitude and 73–77°N latitude, at bottom temperatures between 2 and 4°C and at depths between 150 and 250 m. Cod diets were highly variable during the study period, with frequent changes in the relative frequencies of different prey species, particularly Mallotus villosus (capelin). Environmental variables were particularly good at describing the importance of capelin and Clupea harengus (herring) in the diet. These new analyses support existing knowledge about how the ecology of the region is controlled by climatic variability. When viewed in combination with more recent data, these historical relationships will be valuable in forecasting the future of Barents Sea fisheries, and in understanding how environments and ecosystems may respond
Hamiltonian Derivations of the Generalized Jarzynski Equalities under Feedback Control
In the presence of feedback control by "Maxwell's demon," the second law of
thermodynamics and the nonequilibrium equalities such as the Jarzynski equality
need to be generalized. In this paper, we derive the generalized Jarzynski
equalities for classical Hamiltonian dynamics based on the Liouville's theorem,
which is the same approach as the original proof of the Jarzynski equality
[Phys. Rev. Lett. 78, 2690 (1997)]. The obtained equalities lead to the
generalizations of the second law of thermodynamics for the Hamiltonian systems
in the presence of feedback control.Comment: Proceedings of "STATPHYS - Kolkata VII", November 26-30, 2010,
Kolkata, Indi
The binary fraction of planetary nebula central stars I. A high-precision, I-band excess search
In an attempt to determine how many planetary nebulae derive from binary
interactions, we have started a project to measure their unbiased binary
fraction. This number, when compared to the binary fraction of the presumed
parent population can give a first handle on the origin of planetary nebulae.
By detecting 27 bona fide central stars in the I band we have found that 30% of
our sample have an I band excess between one and a few sigmas, possibly
denoting companions brighter than M3-4V and with separations smaller than
approximately 1000 AU. By accounting for the undetectable companions, we
determine a de-biased binary fraction of 67-78% for all companions at all
separations. We compare this number to a main sequence binary fraction of
(50+/-4)% determined for spectral types F6V-G2V, appropriate if the progenitors
of today's PN central star population is indeed the F6V-G2V stars. The error on
our estimate could be between 10 and 30%. We conclude that the central star
binary fraction may be larger than expected from the putative parent
population. Using the more sensitive J band of a subset of 11 central stars,
the binary fraction is 54% for companions brighter than approximately M5-6V and
with separations smaller than about 900 AU. De-biassing this number we obtain a
binary fraction of 100-107%. The two numbers should be the same and the
discrepancy is likely due to small number statistics.
We also present an accurately vetted compilation of observed main sequence
star magnitudes, colours and masses, which can serve as a reference for future
studies. We also present synthetic colours of hot stars as a function of
temperature (20-170kK) and gravity (log g= 6-8) for Solar and PG1159
compositions.Comment: 22 pages, 6 figures, 12 tables, accepted by MNRA
Teff Grass Response to Nitrogen Fertilization
Teff, a warm season annual grass native to Africa, is gaining popularity as a forage crop in the United States. Little information regarding nitrogen fertilization is available for teff grass production. This field experiment was conducted to evaluate teff grass response to varying nitrogen fertilization rates under dryland conditions. There was no yield response to increasing nitrogen rate or nitrogen source applied
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