Quantum lattice gases and their invariants

The one particle sector of the simplest one dimensional quantum lattice gas automaton has been observed to simulate both the (relativistic) Dirac and (nonrelativistic) Schroedinger equations, in different continuum limits. By analyzing the discrete analogues of plane waves in this sector we find conserved quantities corresponding to energy and momentum. We show that the Klein paradox obtains so that in some regimes the model must be considered to be relativistic and the negative energy modes interpreted as positive energy modes of antiparticles. With a formally similar approach--the Bethe ansatz--we find the evolution eigenfunctions in the two particle sector of the quantum lattice gas automaton and conclude by discussing consequences of these calculations and their extension to more particles, additional velocities, and higher dimensions.Comment: 19 pages, plain TeX, 11 PostScript figures included with epsf.tex (ignore the under/overfull \vbox error messages

Effects of forest fragmentation on the vertical stratification of neotropical bats

Vertical stratification is a key component of the biological complexity of rainforests. Understanding community- and species-level responses to disturbance across forest strata is paramount for evidence-based conservation and management. However, even for bats, known to extensively explore multiple layers of the complex three-dimensional forest space, studies are biased towards understory-based surveys and only few assessments of vertical stratification were done in fragmented landscapes. Using both ground and canopy mist-nets, we investigated how the vertical structure of bat assemblages is influenced by forest fragmentation in the experimentally fragmented landscape of the Biological Dynamics of Forest Fragments Project, Central Amazon, Brazil. Over a three year-period, we captured 3077 individuals of 46 species in continuous forest (CF) and in 1, 10 and 100 ha forest fragments. In both CF and forest fragments, the upper forest strata sustained more diverse bat assemblages than the equivalent understory layer, and the midstory layers had significantly higher bat abundance in fragments than in CF. Artibeus lituratus and Rhinophylla pumilio exhibited significant shifts in their vertical stratification patterns between CF and fragments (e.g. R. pumilio was more associated with the upper strata in fragments than in CF). Altogether, our study suggests that fragmentation modulates the vertical stratification of bat assemblages

Wavelets: mathematics and applications

The notion of wavelets is defined. It is briefly described {\it what} are wavelets, {\it how} to use them, {\it when} we do need them, {\it why} they are preferred and {\it where} they have been applied. Then one proceeds to the multiresolution analysis and fast wavelet transform as a standard procedure for dealing with discrete wavelets. It is shown which specific features of signals (functions) can be revealed by this analysis, but can not be found by other methods (e.g., by the Fourier expansion). Finally, some examples of practical application are given (in particular, to analysis of multiparticle production}. Rigorous proofs of mathematical statements are omitted, and the reader is referred to the corresponding literature.Comment: 16 pages, 5 figures, Latex, Phys. Atom. Nuc

Late-Time Convection in the Collapse of a 23 Solar Mass Star

The results of a 3-dimensional SNSPH simulation of the core collapse of a 23 solar mass star are presented. This simulation did not launch an explosion until over 600ms after collapse, allowing an ideal opportunity to study the evolution and structure of the convection below the accretion shock to late times. This late-time convection allows us to study several of the recent claims in the literature about the role of convection: is it dominated by an l=1 mode driven by vortical-acoustic (or other) instability, does it produce strong neutron star kicks, and, finally, is it the key to a new explosion mechanism? The convective region buffets the neutron star, imparting a 150-200 km/s kick. Because the l=1 mode does not dominate the convection, the neutron star does not achieve large (>450 km/s) velocities. Finally, the neutron star in this simulation moves, but does not develop strong oscillations, the energy source for a recently proposed supernova engine. We discuss the implications these results have on supernovae, hypernovae (and gamma-ray bursts), and stellar-massed black holes.Comment: 31 pages (including 13 figures), submitted to Ap

Spectral Models of Convection-Dominated Accretion Flows

For small values of the dimensionless viscosity parameter, namely $\alpha\lesssim 0.1$, the dynamics of non-radiating accretion flows is dominated by convection; convection strongly suppresses the accretion of matter onto the central object and transports a luminosity $\sim 10^{-3}-10^{-2} \dot M c^2$ from small to large radii in the flow. A fraction of this convective luminosity is likely to be radiated at large radii via thermal bremsstrahlung emission. We show that this leads to a correlation between the frequency of maximal bremsstrahlung emission and the luminosity of the source, $\nu_{\rm peak} \propto L^{2/3}$. Accreting black holes with X-ray luminosities $10^{-4} L_{Edd}\gtrsim L_X(0.5-10{\rm keV}) \gtrsim 10^{-7}L_{Edd}$ are expected to have hard X-ray spectra, with photon indices $\Gamma\sim2$, and sources with $L_X\lesssim 10^{-9}L_{Edd}$ are expected to have soft spectra, with $\Gamma\sim3.5$. This is testable with {\it Chandra} and {\it XMM}.Comment: final version accepted by ApJ; significant modifications from previous versio

Oscillatory pairing of fermions in spin-split traps

As a means of realizing oscillatory pairing between fermions, we study superfluid pairing between two fermion "spin" species that are confined to adjustable spin-dependent trapping potentials. Focusing on the one-dimensional limit, we find that with increasing separation between the spin-dependent traps the fermions exhibit distinct phases, including a fully paired phase, a spin-imbalanced phase with oscillatory pairing, and an unpaired fully spin-polarized phase. We obtain the phase diagram of fermions in such a spin-split trap and discuss signatures of these phases in cold-atom experiments.Comment: 5 pages, 5 figures, RevTe

Analytic invariant charge and the lattice static quark-antiquark potential

A recently developed model for the QCD analytic invariant charge is compared with quenched lattice simulation data on the static quark-antiquark potential. By employing this strong running coupling one is able to obtain the confining quark-antiquark potential in the framework of the one-gluon exchange model. To achieve this objective a technique for evaluating the integrals of a required form is developed. Special attention is paid here to removing the divergences encountered the calculations. All this enables one to examine the asymptotic behavior of the potential at both small and large distances with high accuracy. An explicit expression for the quark-antiquark potential, which interpolates between these asymptotics, and satisfies the concavity condition, is proposed. The derived potential coincides with the perturbative results at small distances, and it is in a good agreement with the lattice data in the nonperturbative physically-relevant region. An estimation of the parameter $\Lambda_{QCD}$ is obtained for the case of pure gluodynamics. It is found to be consistent with all the previous estimations of $\Lambda_{QCD}$ in the framework of approach in hand.Comment: LaTeX2e, 10 pages with 3 EPS figure

The cost effectiveness of integrated care for people living with HIV including antiretroviral treatment in a primary health care centre in Bujumbura, Burundi

The incremental cost effectiveness of an integrated care package (i.e., medical care including antiretroviral therapy (ART) and other services such as psychological and social support) for people living with HIV/AIDS was calculated in a not-for-profit primary health care centre in Bujumbura run by Society of Women against AIDS-Burundi (SWAA-Burundi), an African non-governmental organisation (NGO). Results are expressed as cost-effectiveness ratio 2007, constant US$per disability-adjusted life year (DALY) averted. Unit costs are estimated from the NGO's accounting data and activity reports, healthcare utilisation is estimated from the medical records of a cohort of 149 patients. Effectiveness is modelled on the survival of this cohort, using standard calculation methods. The incremental cost of integrated care for people living with HIV/AIDS in the Bujumbura health centre of SWAA-Burundi is 258 US$ per DALY averted. The package of care provided by SWAA-Burundi is therefore a very cost-effective intervention in comparison with other interventions against HIV/AIDS that include ART. It is however, less cost effective than other types of interventions against HIV/AIDS, such as preventive activities