Heavy-quark energy loss and thermalization in a strongly coupled SYM plasma

Using the AdS/CFT correspondence, we compute the radiative energy loss of a slowly decelerating heavy quark with mass M moving through a supersymmetric Yang Mills (SYM) plasma at temperature T at large t'Hooft coupling \lambda. The calculation is carried out in terms of perturbation in \sqrt{\lambda}T/M, and the rate of the energy loss is computed up to second order. We explain the physical meaning of each correction and estimate the thermalization time of a heavy quark moving in a strongly-coupled plasma.Comment: 14 pages, 1 figur

Temporal simulations and stability analyses of elastic splitter plates interacting with cylinder wake flow

Instabilities developing in a configuration constituted by an elastic plate clamped behind a rigid cylinder are analysed in this paper. The interaction between the wake flow generated by the cylinder with the elastic plate leads to self-developing vortex-induced vibrations. Depending of the stiffness of the elastic plate, the plate may oscillate about a non-deviated or a deviated mean transverse position. After having presented non-linear results computed with time-marching simulations, the instabilities are analysed in terms of a fully coupled fluid-structure eigenvalue analysis. We show that the linear stability analysis is able to predict the unstable regions, and provide a good prediction of the unstable vibration frequencies. The mean deviation is characterized by a steady divergence mode in the eigenvalue spectrum, while unstable, unsteady vortex-induced vibration modes show lock-in phenomena

Deorbit Maneuver and Targeting Strategy for Unmanned Mars Landers

Several deorbit maneuver strategies for unmanned Mars soft landers are evaluated in terms of propulsive efficiency, targeting capability, communication link geometry, and sensitivity to system uncertainties. These strategies include (1) minimum deorbit impulse, (2) minimum entry condition uncertainties, (3) minimum variation in the lander antenna aspect angle during entry, (4) minimum communication range from the lander to the orbiting spacecraft during entry. The selected maneuver strategy is a combination of the above which restricts orbiter lead angles to the range between 0 deg and -10 deg. The analysis covers a range of elliptical orbits with periapsis altitudes of 500 to 2500 KM and apoapsis altitudes of 10,000 to 20,000 KM. The nominal orbit which is selected in order to best satisfy all mission considerations is 1300 KM by 12,500 KM (hp x hA) . Mission considerations include orbit orientation of the orbiting spacecraft for planet surface mapping, landing site location between 15 to 30 degrees from the terminator for entry TV imaging, and orbit characteristics which insure a 50-year orbit lifetime and non-occultation of either the Sun or Star Canopus for 30 days after encounter. These constraints, coupled with the uncertainties introduced by trans-Mars navigation uncertainty and orbit insertion maneuver uncertainties, are used in the definition of minimum targeting flexibility required to land at a preselected location (latitude and longitude) and the regions of Mars which can be selected for landing. The selection of a landing site after surveillance from orbit where as much targeting flexibility as possible is desired is also considered. Two aspects of the error analysis are considered. The first deals with the range of orbits relative to a preselected nominal which might be experienced. The sources leading to this range uncertainty include cruise navigation, orbit insertion maneuver, and orbit trim maneuver. The deorbit maneuver strategy must be capable of compensating for these orbit uncertainties if a preselected landing site is to be acquired

Biogeographical patterns of endolithic infestation in an invasive and an indigenous intertidal marine ecosystem engineer

By altering the phenotypic properties of their hosts, endolithic parasites can modulate the engineering processes of marine ecosystem engineers. Here, we assessed the biogeographical patterns of species assemblages, prevalence and impact of endolithic parasitism in two mussel species that act as important ecosystem engineers in the southern African intertidal habitat, Perna perna and Mytilus galloprovincialis. We conducted large-scale surveys across three biogeographic regions along the South African coast: the subtropical east coast, dominated by the indigenous mussel, P. perna, the warm temperate south coast, where this species coexists with the invasive Mediterranean mussel, M. galloprovincialis, and the cool temperate west coast dominated by M. galloprovincialis. Infestation increased with mussel size, and in the case of M. galloprovincialis we found a significantly higher infestation in the cool temperate bioregion than the warm temperate region. For P. perna, the prevalence of infestation was higher on the warm temperate than the subtropical region, though the difference was marginally non-significant. On the south coast, there was no significant difference in infestation prevalence between species. Endolith-induced mortality rates through shell collapse mirrored the patterns for prevalence. For P. perna, endolith species assemblages revealed clear grouping by bioregions. Our findings indicate that biogeography affects cyanobacteria species composition, but differences between biogeographic regions in their effects are driven by environmental conditions.Agência financiadora Número do subsídio Fundacao para a Ciencia e Tecnologia (FCT-MEC, Portugal) UID/Multi/04326/2019 IF/01413/2014/CP1217/CT0004 South African Research Chairs Initiative (SARChI) of the Department of Science and Technology National Research Foundationinfo:eu-repo/semantics/publishedVersio

Next-to-leading BFKL phenomenology of forward-jet cross sections at HERA

We show that the forward-jet measurements performed at HERA allow for a detailed study of corrections due to next-to-leading logarithms (NLL) in the Balitsky-Fadin-Kuraev-Lipatov (BFKL) approach. While the description of the d\sigma/dx data shows small sensitivity to NLL-BFKL corrections, these can be tested by the triple differential cross section d\sigma/dxdk_T^2dQ^2 recently measured. These data can be successfully described using a renormalization-group improved NLL kernel while the standard next-to-leading-order QCD or leading-logarithm BFKL approaches fail to describe the same data in the whole kinematic range. We present a detailed analysis of the NLL scheme and renormalization-scale dependences and also discuss the photon impact factors.Comment: 15 pages, 9 figures, new title, NLL-BFKL saddle-point approximation replaced by exact integratio

Nonequilibrium evolution of volatility in origination and extinction explains fat-tailed fluctuations in Phanerozoic biodiversity

Fluctuations in biodiversity, large and small, pervade the fossil record, yet we do not understand the processes generating them. Here, we extend theory from nonequilibrium statistical physics to describe the fat-tailed form of fluctuations in Phanerozoic marine invertebrate richness. Using this theory, known as superstatistics, we show that heterogeneous rates of origination and extinction between clades and conserved rates within clades account for this fat-tailed form. We identify orders and families as the taxonomic levels at which clades experience interclade heterogeneity and within-clade homogeneity of rates, indicating that families are subsystems in local statistical equilibrium, while the entire system is not. The separation of timescales between within-clade background rates and the origin of major innovations producing new orders and families allows within-clade dynamics to reach equilibrium, while between-clade dynamics do not. The distribution of different dynamics across clades is consistent with niche conservatism and pulsed exploration of adaptive landscapes.Fil: Rominger, Andrew J.. No especifíca;Fil: Fuentes, Miguel Angel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Filosóficas. - Sociedad Argentina de Análisis Filosófico. Instituto de Investigaciones Filosóficas; Argentina. Universidad San Sebastián; ChileFil: Marquet, Pablo A.. Pontificia Universidad Católica de Chile; Chile. Instituto de Ecología y Biodiversidad; Chile. Universidad Nacional Autónoma de México; Méxic

Twenty-four (24) man-hour test of Alvin's environmental system

ALVIN's specifications call for a 48 man-hour environmental system capability. To check this, a 24 man-hour test was run as follows: Two successive test periods of six (6) hours each with a two (2) man crew inside the pressure hull. The break after six {6) hours was solely to change the crew. It was felt that this 24 man-hour exercise would be adequate to judge the system's 48 man-hour capability, particularly since one cannister of LiOH was used, and the submarine will normally carry two {2)