Optimal Prandtl number for heat transfer in rotating Rayleigh-Benard convection

Numerical data for the heat transfer as a function of the Prandtl (Pr) and Rossby (Ro) numbers in turbulent rotating Rayleigh-Benard convection are presented for Rayleigh number Ra = 10^8. When Ro is fixed the heat transfer enhancement with respect to the non-rotating value shows a maximum as function of Pr. This maximum is due to the reduced efficiency of Ekman pumping when Pr becomes too small or too large. When Pr becomes small, i.e. for large thermal diffusivity, the heat that is carried by the vertical vortices spreads out in the middle of the cell, and Ekman pumping thus becomes less efficient. For higher Pr the thermal boundary layers (BLs) are thinner than the kinetic BLs and therefore the Ekman vortices do not reach the thermal BL. This means that the fluid that is sucked into the vertical vortices is colder than for lower Pr which limits the efficiency of the upwards heat transfer.Comment: 5 pages, 6 figure

Boundary layer structure in turbulent thermal convection and its consequences for the required numerical resolution

Results on the Prandtl-Blasius type kinetic and thermal boundary layer thicknesses in turbulent Rayleigh-B\'enard convection in a broad range of Prandtl numbers are presented. By solving the laminar Prandtl-Blasius boundary layer equations, we calculate the ratio of the thermal and kinetic boundary layer thicknesses, which depends on the Prandtl number Pr only. It is approximated as $0.588Pr^{-1/2}$ for $Pr\ll Pr^*$ and as $0.982 Pr^{-1/3}$ for $Pr^*\ll\Pr$, with $Pr^*= 0.046$. Comparison of the Prandtl--Blasius velocity boundary layer thickness with that evaluated in the direct numerical simulations by Stevens, Verzicco, and Lohse (J. Fluid Mech. 643, 495 (2010)) gives very good agreement. Based on the Prandtl--Blasius type considerations, we derive a lower-bound estimate for the minimum number of the computational mesh nodes, required to conduct accurate numerical simulations of moderately high (boundary layer dominated) turbulent Rayleigh-B\'enard convection, in the thermal and kinetic boundary layers close to bottom and top plates. It is shown that the number of required nodes within each boundary layer depends on Nu and Pr and grows with the Rayleigh number Ra not slower than \sim\Ra^{0.15}. This estimate agrees excellently with empirical results, which were based on the convergence of the Nusselt number in numerical simulations

Collpas: Activity hotspots for frugivorous bats (Phyllostomidae) in the Peruvian Amazon

In the SE Peruvian Amazon, large numbers of frugivorous bats regularly visit natural forest clearings known locally as collpas (which are also referred to as clay licks or mineral licks). Bats arrive at collpas to drink water that has accumulated in depressions created by larger geophagous mammals that consume exposed soil. Although collpa visitation is common, little is known about its causes and its ecological implications for the bat community. We compared patterns of use of collpas and non-collpa forest sites by bats in SE Peru. We mist netted bats at collpas and non-collpa sites during the dry season and compared abundance, species richness, species composition, sex ratio, and reproductive condition. More species were captured at collpas than at non-collpa sites, and collpas were visited almost exclusively by frugivores. Overall, bat-capture frequency and combined frugivorous bat-capture frequency were higher at collpas than at non-collpa sites, although some species of frugivorous bats were captured more frequently at non-collpa sites than at collpas (e.g., Carollia spp.). Irrespective of capture site, more female bats were pregnant or lactating than not, but there was a distinct female sex bias in bats that visited collpas: 70 percent of bats captured at collpas were female, whereas 44 percent of bats captured away from collpas were female. These patterns suggest that collpas may provide important resources for frugivorous bats in SE Peru, just as they are thought to provide important resources to the vertebrates that consume collpa soils. Accordingly, collpas are important conservation targets in the region. © 2008 The Author(s)

Identification of the active site of legumain links it to caspases, clostripain and gingipains in a new clan of cysteine endopeptidases

AbstractWe show by site-directed mutagenesis that the catalytic residues of mammalian legumain, a recently discovered lysosomal asparaginycysteine endopeptidase, form a catalytic dyad in the motif His-Gly-spacer-Ala-Cys. We note that the same motif is present in the caspases, aspartate-specific endopeptidases central to the process of apoptosis in animal cells, and also in the families of clostripain and gingipain which are arginyl/lysyl endopeptidases of pathogenic bacteria. We propose that the four families have similar protein folds, are evolutionarily related in clan CD, and have common characteristics including substrate specificities dominated by the interactions of the S1 subsite

Pronghorn Habitat Suitability in the Texas Panhandle

Habitat quality is an important factor that can greatly affect wildlife populations. Pronghorn (Antilocapra americana) habitat in the Texas Panhandle, USA has been lost through growth of human settlements and agricultural lands. We determined the most pertinent environmental variables affecting habitat selection using multiple methods, including a search of peer-reviewed literature, expert opinion ranking, and habitat suitability modeling. We determined quality and extent of pronghorn habitat in the Texas Panhandle using the MAXENT modeling environment to build a presence-only habitat suitability model based on global positioning system (GPS) locations collected via aerial surveys. Our habitat suitability model indicated that woodlands, agricultural land, and summer precipitation had the greatest contributions to the overall model. Areas with greatest habitat suitability are associated with high pronghorn population densities, particularly in the northwestern corner of the Panhandle. This probabilistic model may serve as a useful tool for pronghorn conservation primarily because it provides insight into what factors are most predictive of their presence, which areas are most suitable for pronghorn, and as a simple, replicable process to identify and evaluate pronghorn habitat

Community structure, abundance, and morphology

. 2000. Community structure, abundance, and morphology. -Oikos 88: 48 -56. The role of interspecific competition in structuring communities has been a highly debated issue for the last two decades. The nonrandom nature of morphological patterns within communities has been at the center of this controversy. Null models addressing community-wide dispersions in morphology have produced equivocal results and may be based on assumptions that are too restrictive (e.g., competitive exclusion or displacement). If morphological distinctiveness allows species to escape competitive pressures and exhibit higher densities, then a positive relationship should exist between morphological dissimilarity and abundance. We develop a suite of models that evaluates patterns in abundance that are associated with the morphological proximity of a species to other competitors. We evaluated the relationship between morphological distance and abundance from a variety of morphological perspectives, from those representing strictly diffuse interactions to those representing only interactions between a species and its nearest neighbor in morphological space. These models were sufficiently powerful to detect positive associations between abundance and morphological differences in a nocturnal desert rodent guild for which the effects of competition on structure are well established. Models such as these may be more useful than traditional models evaluating morphological dispersions for many reasons. They do not require that communities reach equilibrium before competitive interactions give rise to deterministic structure. They do not suffer from limitations of potentially inaccurate faunal pools or from phylogenetic constraints. Lastly, they may be used as a diagnostic tool in comparative studies to determine the degree to which competitive interactions structure communities

A Taxonomy for the Evaluation of Computer Documentation

The evaluation of software documentation is a key issue in the more general framework of evaluating products of a software development process. The research described in this report focuses on (1) a general taxonomy of document characteristics that support an assessment of documentation adequacy, and (2) the refining of the general evaluation taxonomy to a specific application, namely, the Automated Design Description System (ADDS)