5,938 research outputs found
Ignition of thermally sensitive explosives between a contact surface and a shock
The dynamics of ignition between a contact surface and a shock wave is investigated using a
one-step reaction model with Arrhenius kinetics. Both large activation energy asymptotics and
high-resolution finite activation energy numerical simulations are employed. Emphasis is on comparing
and contrasting the solutions with those of the ignition process between a piston and a shock,
considered previously. The large activation energy asymptotic solutions are found to be qualitatively
different from the piston driven shock case, in that thermal runaway first occurs ahead of
the contact surface, and both forward and backward moving reaction waves emerge. These waves
take the form of quasi-steady weak detonations that may later transition into strong detonation
waves. For the finite activation energies considered in the numerical simulations, the results are
qualitatively different to the asymptotic predictions in that no backward weak detonation wave
forms, and there is only a weak dependence of the evolutionary events on the acoustic impedance
of the contact surface. The above conclusions are relevant to gas phase equation of state models.
However, when a large polytropic index more representative of condensed phase explosives is used,
the large activation energy asymptotic and finite activation energy numerical results are found to
be in quantitative agreement
Thermodynamic entropy of a many body energy eigenstate
It is argued that a typical many body energy eigenstate has a well defined
thermodynamic entropy and that individual eigenstates possess thermodynamic
characteristics analogous to those of generic isolated systems. We examine
large systems with eigenstate energies equivalent to finite temperatures. When
quasi-static evolution of a system is adiabatic (in the quantum mechanical
sense), two coupled subsystems can transfer heat from one subsystem to another
yet remain in an energy eigenstate. To explicitly construct the entropy from
the wave function, degrees of freedom are divided into two unequal parts. It is
argued that the entanglement entropy between these two subsystems is the
thermodynamic entropy per degree of freedom for the smaller subsystem. This is
done by tracing over the larger subsystem to obtain a density matrix, and
calculating the diagonal and off-diagonal contributions to the entanglement
entropy.Comment: 18 page
Strong nonlocality: A trade-off between states and measurements
Measurements on entangled quantum states can produce outcomes that are
nonlocally correlated. But according to Tsirelson's theorem, there is a
quantitative limit on quantum nonlocality. It is interesting to explore what
would happen if Tsirelson's bound were violated. To this end, we consider a
model that allows arbitrary nonlocal correlations, colloquially referred to as
"box world". We show that while box world allows more highly entangled states
than quantum theory, measurements in box world are rather limited. As a
consequence there is no entanglement swapping, teleportation or dense coding.Comment: 11 pages, 2 figures, very minor change
Genetic consequences of multiple translocations of the banded hare-qallaby in Western Australia
Many Australian mammal species now only occur on islands and fenced mainland havens free from invasive predators. The range of one species, the banded hare-wallaby (Lagostrophus fasciatus), had contracted to two offshore islands in Western Australia. To improve survival, four conservation translocations have been attempted with mixed success, and all occurred in the absence of genetic information. Here, we genotyped seven polymorphic microsatellite markers in two source (Bernier Island and Dorre Island), two historic captive, and two translocated L. fasciatus populations to determine the impact of multiple translocations on genetic diversity. Subsequently, we used population viability analysis (PVA) and gene retention modelling to determine scenarios that will maximise demographic resilience and genetic richness of two new populations that are currently being established. One translocated population (Wadderin) has undergone a genetic bottleneck and lost 8.1% of its source population’s allelic diversity, while the other (Faure Island) may be inbred. We show that founder number is a key parameter when establishing new L. fasciatus populations and 100 founders should lead to high survival probabilities. Our modelling predicts that during periodic droughts, the recovery of source populations will be slower post-harvest, while 75% more animals—about 60 individuals—are required to retain adequate allelic diversity in the translocated population. Our approach demonstrates how genetic data coupled with simulations of stochastic environmental events can address central questions in translocation programmes
Late Quaternary Marine and Terrestrial Environments, Northwestern Baffin Island, Northwest Territories
Paleoenvironmental data were analyzed from terrestrial, lake, and marine sediments collected near Arctic Bay, Baffin Island, N.W.T. Eighteen new radiocarbon dates provide chronological control, superseding earlier results. Spuriously old dates were obtained from both sandy peats and low-organic lake sediments. The most reliable dates were from marine shells and foraminifera. They indicate that déglaciation was underway by 9000 BP rather than 16,000 BP. Over the period of the record, the local environment was characterized by a high arctic pollen assemblage dominated by grass, sedge, and willow; a middle Holocene warm period is indicated by increased willow, herb, and moss values. Sea-ice conditions were severe enough to inhibit the growth of diatoms until ca. 6300 BP and ice proximal and deglacial conditions prevailed in the fiords until ca. 6000 BP. Diatom productivity increased between 3000 BP and 2500 BP, suggesting warmer surface waters and less sea ice. After 2000 BP diatom accumulation decreased sharply, due to a cooling of climate. The foraminifera indicate a major change in bottom water conditions ca. 4000 BP as the benthic species shift from a calcareous to an arenaceous assemblage.On a procédé à l'analyse des données paléoenvironnementales tirées de sédiments terrestres, marins et lacustres, près de Arctic Bay. Dix-huit nouvelles dates au radiocarbone ont permis d'établir une nouvelle chronologie. Les dates les plus anciennes, et les moins fiables, ont été obtenus dans des tourbes sableuses et des sédiments lacustres à basse teneur organique. Les dates les plus sûres proviennent de coquillages marins et des foraminifères. Elles indiquent que la déglaciation était en cours dès 9000 BP plutôt qu'à 16 000 BP. Pendant la période relevée, l'environnement dans le haut Arctique était caractérisé au niveau local par un assemblage pollinique dominé par l'herbe, le carex et le saule; à l'Holocène moyen, les valeurs croissantes du saule, de l'herbe et de la mousse reflètent une période chaude. La densité de la glace marine était assez forte pour empêcher la croissance des diatomées jusqu'à 6300 BP; la déglaciation s'est poursuivie jusque vers 6000 BP dans les fjords. La reproduction des diatomées a augmenté entre 3000 et 2500 BP en raison de températures de surface plus chaudes et une diminution des glaces marines. Après 2000 BP, l'accumulation des diatomées a décru abruptement en raison d'un refroidissement climatique. Les foraminifères démontrent un changement important survenu dans l'état des eaux profondes vers 4000 BP puisqu'il y a eu remplacement des espèces benthoniques à test calcaire par des espèces à test agglutiné.Man hat Palâoumweltdaten von Erd-, See- und Meeres-Sedimenten analysiert, die man in der Nâhe der Arctic Bay, lnsel Baffin, Nordwest-Territorien gesammelt hat. Achtzehn neue Radiocarbondaten liefern eine chronologische Kontrolle und ersetzen so fruhere Resultate. Faische alte Daten hat man sowohi aus sandigem Ton1 wie auch aus Seesedimenten mit niedrigem organischem Gehalt gewonnen. Die zuver-làssigsten Daten stammen von Meeres-muscheln und Foraminiferen. Sie zeigen, dass die Enteisung urn 9000 v.u.Z. und nicht um 16,000 v.u.Z. im Gange war. Liber den Zeitraum des Belegs charakterisierte sich die lokale Umwelt durch eine Pollen-Zusammensetzung der hohen Arktis, die von Gras, Schilfgras und Weide beherrscht war; auf eine warme Période wâhrend des mittleren Holozàns weisen zunehmende Weiden-, Gras- und Mooswerte. Die Meereseisbedingungen waren streng genug, um das Wachstum von Diatomeen bis etwa 6300 v.u.Z. zu verhindern und Proximaleis und Enteisungsbedingungen herrschten in den Fjords bis etwa 6000 v.u.Z. vor. Die Reproduktion von Diatomeen nahm zwischen 3000 v.u.Z. und 2500 v.u.Z. zu, was auf wàrmeres Oberflàchenwasser und weniger Meereseis schliessen làsst. Nach 2000 v.u.Z. nahm die Diatomeen-Akkumulation wegen einer Klimaabkuhlung plôtzlich ab. Die Foraminiferen zeigen einen betràchtlichen Wechsel der Bedingungen im tiefen Wasser um etwa 4000 v.u.Z., wenn die benthonischen Spezies von einer kalkartigen zu einer sandigen Zusammensetzung ubergehen
"Pudding mold" band drives large thermopower in NaCoO
In the present study, we pin down the origin of the coexistence of the large
thermopower and the large conductivity in NaCoO. It is revealed that
not just the density of states (DOS), the effective mass, nor the band width,
but the peculiar {\it shape} of the band referred to as the "pudding
mold" type, which consists of a dispersive portion and a somewhat flat portion,
is playing an important role in this phenomenon. The present study provides a
new guiding principle for designing good thermoelectric materials.Comment: 5 page
Practical Implementations of Twirl Operations
Twirl operations, which convert impure singlet states into Werner states,
play an important role in many schemes for entanglement purification. In this
paper we describe strategies for implementing twirl operations, with an
emphasis on methods suitable for ensemble quantum information processors such
as nuclear magnetic resonance (NMR) quantum computers. We implement our twirl
operation on a general two-spin mixed state using liquid state NMR techniques,
demonstrating that we can obtain the singlet Werner state with high fidelity.Comment: 6 pages RevTex4 including 2 figures (fig 1 low quality to save space
A violation of the uncertainty principle implies a violation of the second law of thermodynamics
Uncertainty relations state that there exist certain incompatible
measurements, to which the outcomes cannot be simultaneously predicted. While
the exact incompatibility of quantum measurements dictated by such uncertainty
relations can be inferred from the mathematical formalism of quantum theory,
the question remains whether there is any more fundamental reason for the
uncertainty relations to have this exact form. What, if any, would be the
operational consequences if we were able to go beyond any of these uncertainty
relations? We give a strong argument that justifies uncertainty relations in
quantum theory by showing that violating them implies that it is also possible
to violate the second law of thermodynamics. More precisely, we show that
violating the uncertainty relations in quantum mechanics leads to a
thermodynamic cycle with positive net work gain, which is very unlikely to
exist in nature.Comment: 8 pages, revte
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