524 research outputs found
Resonant nonlinear spectroscopy in strong fields
A method is presented to describe multiple resonant nonlinear spectra in the presence of strong laser fields. The Liouville equation for the d. operator of the mol. system is transformed to a time-independent linear equation system. This can be easily solved rigorously by numerical methods or, after partitioning into a strong-field part and a perturbation, the soln. can be obtained anal. by a novel perturbative approach. The results account for power broadening. Rabi splitting of signals, and power-induced extra resonances, the latter being related to the pure dephasing-induced resonances in the weak-field limit. The method can be applied to a large no. of multiple resonant nonlinear spectroscopies, esp. CARS, CSRS, coherent Rayleigh scattering and sum- or difference-frequency generation
Modeling parasite dynamics on farmed salmon for precautionary conservation management of wild salmon
Conservation management of wild fish may include fish health management in sympatric populations of domesticated fish in aquaculture. We developed a mathematical model for the population dynamics of parasitic sea lice (Lepeophtheirus salmonis) on domesticated populations of Atlantic salmon (Salmo salar) in the Broughton Archipelago region of British Columbia. The model was fit to a seven-year dataset of monthly sea louse counts on farms in the area to estimate population growth rates in relation to abiotic factors (temperature and salinity), local host density (measured as cohort surface area), and the use of a parasiticide, emamectin benzoate, on farms. We then used the model to evaluate management scenarios in relation to policy guidelines that seek to keep motile louse abundance below an average three per farmed salmon during the March-June juvenile wild Pacific salmon (Oncorhynchus spp.) migration. Abiotic factors mediated the duration of effectiveness of parasiticide treatments, and results suggest treatment of farmed salmon conducted in January or early February minimized average louse abundance per farmed salmon during the juvenile wild salmon migration. Adapting the management of parasites on farmed salmon according to migrations of wild salmon may therefore provide a precautionary approach to conserving wild salmon populations in salmon farming regions
Interior of a Schwarzschild black hole revisited
The Schwarzschild solution has played a fundamental conceptual role in
general relativity, and beyond, for instance, regarding event horizons,
spacetime singularities and aspects of quantum field theory in curved
spacetimes. However, one still encounters the existence of misconceptions and a
certain ambiguity inherent in the Schwarzschild solution in the literature. By
taking into account the point of view of an observer in the interior of the
event horizon, one verifies that new conceptual difficulties arise. In this
work, besides providing a very brief pedagogical review, we further analyze the
interior Schwarzschild black hole solution. Firstly, by deducing the interior
metric by considering time-dependent metric coefficients, the interior region
is analyzed without the prejudices inherited from the exterior geometry. We
also pay close attention to several respective cosmological interpretations,
and briefly address some of the difficulties associated to spacetime
singularities. Secondly, we deduce the conserved quantities of null and
timelike geodesics, and discuss several particular cases in some detail.
Thirdly, we examine the Eddington-Finkelstein and Kruskal coordinates directly
from the interior solution. In concluding, it is important to emphasize that
the interior structure of realistic black holes has not been satisfactorily
determined, and is still open to considerable debate.Comment: 15 pages, 7 figures, Revtex4. V2: Version to appear in Foundations of
Physic
Multipole Amplitudes of Pion Photoproduction on Nucleons up to 2GeV within Dispersion Relations and Unitary Isobar Model
Two approaches for analysis of pion photo- and electroproduction on nucleons
in the resonance energy region are checked at using the results of
GWU(VPI) partial-wave analysis of photoproduction data. The approaches are
based on dispersion relations and unitary isobar model. Within dispersion
relations good description of photoproduction multipoles is obtained up to
. Within unitary isobar model, modified with increasing energy by
incorporation of Regge poles, and with unified Breit-Wigner parametrization of
resonance contributions, good description of photoproduction multipoles is
obtained up to .Comment: 23 pages, LaTe
Different Modes of Retrovirus Restriction by Human APOBEC3A and APOBEC3G In Vivo
The apolipoprotein B editing complex 3 (A3) cytidine deaminases are among the most highly evolutionarily selected retroviral restriction factors, both in terms of gene copy number and sequence diversity. Primate genomes encode seven A3 genes, and while A3F and 3G are widely recognized as important in the restriction of HIV, the role of the other genes, particularly A3A, is not as clear. Indeed, since human cells can express multiple A3 genes, and because of the lack of an experimentally tractable model, it is difficult to dissect the individual contribution of each gene to virus restriction in vivo. To overcome this problem, we generated human A3A and A3G transgenic mice on a mouse A3 knockout background. Using these mice, we demonstrate that both A3A and A3G restrict infection by murine retroviruses but by different mechanisms: A3G was packaged into virions and caused extensive deamination of the retrovirus genomes while A3A was not packaged and instead restricted infection when expressed in target cells. Additionally, we show that a murine leukemia virus engineered to express HIV Vif overcame the A3G-mediated restriction, thereby creating a novel model for studying the interaction between these proteins. We have thus developed an in vivo system for understanding how human A3 proteins use different modes of restriction, as well as a means for testing therapies that disrupt HIV Vif-A3G interactions
A new approach to social behavior simulation: the mask model
This paper proposes a new perspective, based on the concept of social masks, for the simulation of a realistic NPC (Non-Player Character) behavior. The Mask Model goal is to support AI techniques for autonomous agents by encouraging or discouraging behaviors according to the social environment and by providing knowledge about possible reactions to the agent actions. In this approach, the NPC tendencies are controlled by the interactions of three overlapping mask layers: self- perception layer, social layer and interpersonal layer. The masks mould the tendencies, the feelings and the ethics of a NPC. By changing the links between characters and masks, a wide variety of different behaviors and story-lines may arise. The paper present an algorithm for the selection of the actions and an example implementation
An Experimental Investigation of Colonel Blotto Games
"This article examines behavior in the two-player, constant-sum Colonel Blotto game with asymmetric resources in which players maximize the expected number of battlefields won. The experimental results support all major theoretical predictions. In the auction treatment, where winning a battlefield is deterministic, disadvantaged players use a 'guerilla warfare' strategy which stochastically allocates zero resources to a subset of battlefields. Advantaged players employ a 'stochastic complete coverage' strategy, allocating random, but positive, resource levels across the battlefields. In the lottery treatment, where winning a battlefield is probabilistic, both players divide their resources equally across all battlefields." (author's abstract)"Dieser Artikel untersucht das Verhalten von Individuen in einem 'constant-sum Colonel Blotto'-Spiel zwischen zwei Spielern, bei dem die Spieler mit unterschiedlichen Ressourcen ausgestattet sind und die erwartete Anzahl gewonnener Schlachtfelder maximieren. Die experimentellen Ergebnisse bestätigen alle wichtigen theoretischen Vorhersagen. Im Durchgang, in dem wie in einer Auktion der Sieg in einem Schlachtfeld deterministisch ist, wenden die Spieler, die sich im Nachteil befinden, eine 'Guerillataktik' an, und verteilen ihre Ressourcen stochastisch auf eine Teilmenge der Schlachtfelder. Spieler mit einem Vorteil verwenden eine Strategie der 'stochastischen vollständigen Abdeckung', indem sie zufällig eine positive Ressourcenmenge auf allen Schlachtfeldern positionieren. Im Durchgang, in dem sich der Gewinn eines Schlachtfeldes probabilistisch wie in einer Lotterie bestimmt, teilen beide Spieler ihre Ressourcen gleichmäßig auf alle Schlachtfelder auf." (Autorenreferat
Semi-Analytic Stellar Structure in Scalar-Tensor Gravity
Precision tests of gravity can be used to constrain the properties of
hypothetical very light scalar fields, but these tests depend crucially on how
macroscopic astrophysical objects couple to the new scalar field. We develop
quasi-analytic methods for solving the equations of stellar structure using
scalar-tensor gravity, with the goal of seeing how stellar properties depend on
assumptions made about the scalar coupling at a microscopic level. We
illustrate these methods by applying them to Brans-Dicke scalars, and their
generalization in which the scalar-matter coupling is a weak function of the
scalar field. The four observable parameters that characterize the fields
external to a spherically symmetric star (the stellar radius, R, mass, M,
scalar `charge', Q, and the scalar's asymptotic value, phi_infty) are subject
to two relations because of the matching to the interior solution, generalizing
the usual mass-radius, M(R), relation of General Relativity. We identify how
these relations depend on the microscopic scalar couplings, agreeing with
earlier workers when comparisons are possible. Explicit analytical solutions
are obtained for the instructive toy model of constant-density stars, whose
properties we compare to more realistic equations of state for neutron star
models.Comment: 39 pages, 9 figure
Sea lice infestations on juvenile chum and pink salmon in the Broughton Archipelago, Canada, from 2003 to 2012
Juvenile pink salmon Oncorhynchus gorbuscha and chum salmon O. keta were sampled by beach or purse seine to assess levels of sea lice infestation in the Knight Inlet and Broughton Archipelago regions of coastal British Columbia, Canada, during the months of March to July from 2003 to 2012. Beach seine data were analyzed for sea lice infestation that was de - scribed in terms of prevalence, abundance, intensity, and intensity per unit length. The median annual prevalence for chum was 30%, ranging from 14% (in 2008 and 2009) to 73% (in 2004), while for pink salmon, the median was 27% and ranged from 10% (in 2011) to 68% (in 2004). Annual abundance varied from 0.2 to 5 sea lice per fish with a median of 0.47 for chum and from 0.1 to 3 lice (median 0.42) for pink salmon. Annual infestation followed broadly similar trends for both chum and pink salmon. However, the abundance and intensity of Lepeophtheirus salmonis and Caligus clemensi, the 2 main sea lice species of interest, were significantly greater on chum than on pink salmon in around half of the years studied. Logistic regression with random effect was used to model prevalence of sea lice infestation for the combined beach and purse seine data. The model suggested inter-annual variation as well as a spatial clustering effect on the prevalence of sea lice infestation in both chum and pink salmon. Fish length had an effect on prevalence, although the nature of this effect differed according to host species
Cold Gas in Cluster Cores
I review the literature's census of the cold gas in clusters of galaxies.
Cold gas here is defined as the gas that is cooler than X-ray emitting
temperatures (~10^7 K) and is not in stars. I present new Spitzer IRAC and MIPS
observations of Abell 2597 (PI: Sparks) that reveal significant amounts of warm
dust and star formation at the level of 5 solar masses per year. This rate is
inconsistent with the mass cooling rate of 20 +/- 5 solar masses per year
inferred from a FUSE [OVI] detection.Comment: 10 pages, conference proceeding
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