750 research outputs found
Bounds from Primordial Black Holes with a Near Critical Collapse Initial Mass Function
Recent numerical evidence suggests that a mass spectrum of primordial black
holes (PBHs) is produced as a consequence of near critical gravitational
collapse. Assuming that these holes formed from the initial density
perturbations seeded by inflation, we calculate model independent upper bounds
on the mass variance at the reheating temperature by requiring the mass density
not exceed the critical density and the photon emission not exceed current
diffuse gamma-ray measurements. We then translate these results into bounds on
the spectral index n by utilizing the COBE data to normalize the mass variance
at large scales, assuming a constant power law, then scaling this result to the
reheating temperature. We find that our bounds on n differ substantially
(\delta n > 0.05) from those calculated using initial mass functions derived
under the assumption that the black hole mass is proportional to the horizon
mass at the collapse epoch. We also find a change in the shape of the diffuse
gamma-ray spectrum which results from the Hawking radiation. Finally, we study
the impact of a nonzero cosmological constant and find that the bounds on n are
strengthened considerably if the universe is indeed vacuum-energy dominated
today.Comment: 24 pages, REVTeX, 5 figures; minor typos fixed, two refs added,
version to be published in PR
Grassmann Variables and the Jaynes-Cummings Model
This paper shows that phase space methods using a positive P type
distribution function involving both c-number variables (for the cavity mode)
and Grassmann variables (for the two level atom) can be used to treat the
Jaynes-Cummings model. Although it is a Grassmann function, the distribution
function is equivalent to six c-number functions of the two bosonic variables.
Experimental quantities are given as bosonic phase space integrals involving
the six functions. A Fokker-Planck equation involving both left and right
Grassmann differentiation can be obtained for the distribution function, and is
equivalent to six coupled equations for the six c-number functions.
The approach used involves choosing the canonical form of the (non-unique)
positive P distribution function, where the correspondence rules for bosonic
operators are non-standard and hence the Fokker-Planck equation is also
unusual. Initial conditions, such as for initially uncorrelated states, are
used to determine the initial distribution function. Transformations to new
bosonic variables rotating at the cavity frequency enables the six coupled
equations for the new c-number functions (also equivalent to the canonical
Grassmann distribution function) to be solved analytically, based on an ansatz
from a 1980 paper by Stenholm. It is then shown that the distribution function
is the same as that determined from the well-known solution based on coupled
equations for state vector amplitudes of atomic and n-photon product states.
The treatment of the simple two fermion mode Jaynes-Cummings model is a
useful test case for the future development of phase space Grassmann
distribution functional methods for multi-mode fermionic applications in
quantum-atom optics.Comment: 57 pages, 0 figures. Version
Evolution of genomes, host shifts and the geographic spread of SARS-CoV and related coronaviruses
Severe acute respiratory syndrome (SARS) is a novel human illness caused by a previously unrecognized coronavirus (CoV) termed SARS-CoV. There are conflicting reports on the animal reservoir of SARS-CoV. Many of the groups that argue carnivores are the original reservoir of SARS-CoV use a phylogeny to support their argument. However, the phylogenies in these studies often lack outgroup and rooting criteria necessary to determine the origins of SARS-CoV. Recently, SARS-CoV has been isolated from various species of Chiroptera from China (e.g., Rhinolophus sinicus) thus leading to reconsideration of the original reservoir of SARS-CoV. We evaluated the hypothesis that SARS-CoV isolated from Chiroptera are the original zoonotic source for SARS-CoV by sampling SARS-CoV and non-SARS-CoV from diverse hosts including Chiroptera, carnivores, artiodactyls and humans. Regardless of alignment parameters, optimality criteria, or isolate sampling, the resulting phylogenies clearly show that the SARS-CoV was transmitted to small carnivores well after the epidemic of SARS in humans that began in late 2002. The SARS-CoV isolates from small carnivores in Shenzhen markets form a terminal clade that emerged recently from within the radiation of human SARS-CoV. There is evidence of subsequent exchange of SARS-CoV between humans and carnivores. In addition SARS-CoV was transmitted independently from humans to farmed pigs (Sus scrofa). The position of SARS-CoV isolates from Chiroptera are basal to the SARS-CoV clade isolated from humans and carnivores. Although sequence data indicate that Chiroptera are a good candidate for the original reservoir of SARS-CoV, the structural biology of the spike protein of SARS-CoV isolated from Chiroptera suggests that these viruses are not able to interact with the human variant of the receptor of SARS-CoV, angiotensin-converting enzyme 2 (ACE2). In SARS-CoV study, both visually and statistically, labile genomic fragments and, putative key mutations of the spike protein that may be associated with host shifts. We display host shifts and candidate mutations on trees projected in virtual globes depicting the spread of SARS-CoV. These results suggest that more sampling of coronaviruses from diverse hosts, especially Chiroptera, carnivores and primates, will be required to understand the genomic and biochemical evolution of coronaviruses, including SARS-CoV.Fil: Janies, Daniel. Ohio State University; Estados UnidosFil: Habib, Farhat. Ohio State University; Estados UnidosFil: Alexandrov, Boyan. Ohio State University; Estados UnidosFil: Hill, Andrew. University of Colorado; Estados UnidosFil: Pol, Diego. Museo PaleontolĂłgico Egidio Feruglio; Argentina. Ohio State University; Estados Unidos. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentin
Fabrication and modal characterisation of large-area polymer membranes for acoustic MEMS devices
Low-dimensional representations of exact coherent states of the Navier-Stokes equations from the resolvent model of wall turbulence
We report that many exact invariant solutions of the Navier-Stokes equations for both pipe and channel flows are well represented by just few modes of the model of McKeon & Sharma J. Fl. Mech. 658, 356 (2010). This model provides modes that act as a basis to decompose the velocity field, ordered by their amplitude of response to forcing arising from the interaction between scales. The model was originally derived from the Navier-Stokes equations to represent turbulent flows and has been used to explain coherent structure and to predict turbulent statistics. This establishes a surprising new link between the two distinct approaches to understanding turbulence
Examining Associations Between Funtional Brain Activation and Behavior in Adolescents With a History of Prenatal Drug Exposure
Sixteen years of social and ecological dynamics reveal challenges and opportunities for adaptive management in sustaining the commons
Efforts to confront the challenges of environmental change and uncertainty include attempts to adaptively manage socialâecological systems. However, critical questions remain about whether adaptive management can lead to sustainable outcomes for both ecosystems and society. Here, we make a contribution to these efforts by presenting a 16-y analysis of ecological outcomes and perceived livelihood impacts from adaptive coral reef management in Papua New Guinea. The adaptive management system we studied was a customary rotational fisheries closure system (akin to fallow agriculture), which helped to increase the biomass of reef fish and make fish less wary (more catchable) relative to openly fished areas. However, over time the amount of fish in openly fished reefs slowly declined. We found that, overall, resource users tended to have positive perceptions about this system, but there were negative perceptions when fishing was being prohibited. We also highlight some of the key traits of this adaptive management system, including 1) strong social cohesion, whereby leaders played a critical role in knowledge exchange; 2) high levels of compliance, which was facilitated via a âcarrot-and-stickâ approach that publicly rewarded good behavior and punished deviant behavior; and 3) high levels of participation by community actors
Multicanonical Multigrid Monte Carlo
To further improve the performance of Monte Carlo simulations of first-order
phase transitions we propose to combine the multicanonical approach with
multigrid techniques. We report tests of this proposition for the
-dimensional field theory in two different situations. First, we
study quantum tunneling for in the continuum limit, and second, we
investigate first-order phase transitions for in the infinite volume
limit. Compared with standard multicanonical simulations we obtain improvement
factors of several resp. of about one order of magnitude.Comment: 12 pages LaTex, 1 PS figure appended. FU-Berlin preprint FUB-HEP 9/9
Phase space theory of Bose-Einstein condensates and time-dependent modes
A phase space theory approach for treating dynamical behaviour of
Bose-Einstein condensates applicable to situations such as interferometry with
BEC in time-dependent double well potentials is presented. Time-dependent mode
functions are used, chosen so that one, two,.. highly occupied modes describe
well the physics of interacting condensate bosons in time dependent potentials
at well below the transition temperature. Time dependent mode annihilation,
creation operators are represented by time dependent phase variables, but time
independent total field annihilation, creation operators are represented by
time independent field functions. Two situations are treated, one (mode theory)
is where specific mode annihilation, creation operators and their related phase
variables and distribution functions are dealt with, the other (field theory)
is where only field creation, annihilation operators and their related field
functions and distribution functionals are involved. The paper focuses on the
hybrid approach, where the modes are divided up between condensate (highly
occupied) modes and non-condensate (sparsely occupied) modes. It is found that
there are extra terms in the Ito stochastic equations both for the stochastic
phases and stochastic fields, involving coupling coefficients defined via
overlap integrals between mode functions and their time derivatives. For the
hybrid approach both the Fokker-Planck and functional Fokker-Planck equations
differ from those derived via the correspondence rules, the drift vectors are
unchanged but the diffusion matrices contain additional terms involving the
coupling coefficients. Results are also presented for the combined approach
where all the modes are treated as one set.Comment: 83 pages. 0 figures. Version 3. Details to Appendices, typos
corrected, field theory treatment highlighted. To be published in Annals of
Physic
Singular regional brightening events on Titan as seen by Cassini/VIMS
Titan, the largest satellite of Saturn, is the only satellite in the solar system with a dense atmosphere. The close and continuous observations of Titan by the Cassini spacecraft, in orbit around Saturn since July 2004, bring us evidences that Titan tropo-sphere and low stratosphere experience an exotic, but complete meteorological cycle similar to the Earth hy-drological cycle, with hydrocarbons evaporation, con-densation in clouds, and rainfall. Cassini monitoring campaigns also demonstrate that Titanâs cloud cover-age and climate vary with latitude. Titanâs tropics, with globally weak meteorological activity and widespread dune fields, seem to be slightly more arid than the poles, where extensive and numerous liquid reservoirs and sustained cloud activity were discovered.
Only a few tropospheric clouds have been observed at Titanâs tropics during the southern summer [2-4]. As equinox was approaching (in August 2009), they oc-curred more frequently and appeared to grow in strength and size [5-7]
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