Cross-Newell equations for hexagons and triangles

The Cross-Newell equations for hexagons and triangles are derived for general real gradient systems, and are found to be in flux-divergence form. Specific examples of complex governing equations that give rise to hexagons and triangles and which have Lyapunov functionals are also considered, and explicit forms of the Cross-Newell equations are found in these cases. The general nongradient case is also discussed; in contrast with the gradient case, the equations are not flux-divergent. In all cases, the phase stability boundaries and modes of instability for general distorted hexagons and triangles can be recovered from the Cross-Newell equations.Comment: 24 pages, 1 figur

NAM-SCA: A Nonhydrostatic anelastic model with segmentally constant approximations

International audienceAn atmospheric convective system may be modeled as an ensemble of discrete plume elements. A representation of decomposited plumes provides the basis for mass-flux convective parameterization. A dry version of such a prototype model is constructed in a two-dimensional horizontally periodic domain. Each discrete plume element is approximated by a horizontally homogeneous segment such that the whole system is given by segmentally constant approximations (SCA) in the horizontal direction for each vertical level in a nonhydrostatic anelastic model (NAM). The distribution of constant segments is highly inhomogeneous in space and evolves with time in a highly adaptive manner. The basic modeling strategy from a physical point of view is to activate new segments vertically upward with time when a convective plume is growing and to deactivate segments when a plume event is over. The difference in physical values crossing segment interfaces is used as a criterion for numerically implementing this strategy. Whenever a large difference is found, the given interface is stretched vertically by subdividing an existing segment into two. In turn, when a segment interface difference is found below the threshold, the given interface is removed, thereby merging the two segments into one. This nonhydrostatic anelastic model with segmentally constant approximations (NAM-SCA) is tested on an idealized atmospheric convective boundary layer. It successfully simulates the evolution of convective plumes with a relatively limited number of segments (i.e., high compression) and with a much scarcer distribution of segments over nonplume environments (i.e., extremely inhomogeneous distribution of segments). Overall, this method compresses the size of the model up to 5 times compared to a standard NAM with homogeneous grid distribution without substantially sacrificing numerical accuracy. © 2010 American Meteorological Society

Heavy Metal Contamination and Potential Ecological Risks in Surface Sediments along Dar es Salaam Harbour Channel

Investigation of heavy metal contamination along Dar es Salaam harbour channel was carried out in order to determine their current concentrations, sources and potential ecological risks to benthic biota. Sampling was carried out from January to May 2019 and samples analysed using ICP-OES and C-H-N-S analyser. Analysis of heavy metal relationships showed that, Cu, Zn, Cr, As, Ni, Co, Fe, Cd had strong relationships with each other, while Pb only related to Zn. Principal component analysis partitioned metals into two groups; PC1: Ni, Cr, Fe, Co, As, Cu, Cd, and Zn explaining 73.6% variance and PC2: Pb, Zn, and Cd with 13.7% variance. Similarly, Cd, Pb and Zn had severe to very high enrichments (Cd > Pb > Zn) showing serious anthropogenic contamination of these metals in sediments along Dar es Salaam harbour channel. Degree of contamination and potential ecological risks varied from low, moderate, to high; indicating that sediments were considerably contaminated with heavy metals. Levels of contamination varied in space and according to the type of heavy metal Higher contamination and ecological risks were revealed at the harbour area probably due to the observed high concentrations of Cd, Pb and Zn. Monitoring of metals should be emphasized in order to control contaminants release into this area from their sources. Keywords: Dar es Salaam harbour channel, Heavy metals, Contamination, Sediments, Degree of contamination, Ecological risk

Diet Specialization by the Scarlet Kingsnake, Lampropeltis elapsoides (Colubridae)

Based on 34 natural prey items, Lampropeltis elapsoides eats primarily elongate squamates (97%), especially skinks (74%) and colubroid snakes (15%). N o ontogenetic or geographic variation is evident; prey items are swallowed headfirst and average 19% of predator mass. The diet substantially overlaps that of juveniles of some other lampropeltines, including sympatric L. triangulum, but is unusually narrow compared to adults of most other species

Diet Specialization by the Scarlet Kingsnake, Lampropeltis elapsoides (Colubridae)

Based on 34 natural prey items, Lampropeltis elapsoides eats primarily elongate squamates (97%), especially skinks (74%) and colubroid snakes (15%). N o ontogenetic or geographic variation is evident; prey items are swallowed headfirst and average 19% of predator mass. The diet substantially overlaps that of juveniles of some other lampropeltines, including sympatric L. triangulum, but is unusually narrow compared to adults of most other species

Infection of zebrafish embryos with intracellular bacterial pathogens

Zebrafish (Danio rerio) embryos are increasingly used as a model for studying the function of the vertebrate innate immune system in host-pathogen interactions (1). The major cell types of the innate immune system, macrophages and neutrophils, develop during the first days of embryogenesis prior to the maturation of lymphocytes that are required for adaptive immune responses. The ease of obtaining large numbers of embryos, their accessibility due to external development, the optical transparency of embryonic and larval stages, a wide range of genetic tools, extensive mutant resources and collections of transgenic reporter lines, all add to the versatility of the zebrafish model. Salmonella enterica serovar Typhimurium (S. typhimurium) and Mycobacterium marinum can reside intracellularly in macrophages and are frequently used to study host-pathogen interactions in zebrafish embryos. The infection processes of these two bacterial pathogens are interesting to compare because S. typhimurium infection is acute and lethal within one day, whereas M. marinum infection is chronic and can be imaged up to the larval stage (2, 3). The site of micro-injection of bacteria into the embryo (Figure 1) determines whether the infection will rapidly become systemic or will initially remain localized. A rapid systemic infection can be established by micro-injecting bacteria directly into the blood circulation via the caudal vein at the posterior blood island or via the Duct of Cuvier, a wide circulation channel on the yolk sac connecting the heart to the trunk vasculature. At 1 dpf, when embryos at this stage have phagocytically active macrophages but neutrophils have not yet matured, injecting into the blood island is preferred. For injections at 2-3 dpf, when embryos also have developed functional (myeloperoxidase-producing) neutrophils, the Duct of Cuvier is preferred as the injection site. To study directed migration of myeloid cells towards local infections, bacteria can be injected into the tail muscle, otic vesicle, or hindbrain ventricle (4-6). In addition, the notochord, a structure that appears to be normally inaccessible to myeloid cells, is highly susceptible to local infection (7). A useful alternative for high-throughput applications is the injection of bacteria into the yolk of embryos within the first hours after fertilization (8). Combining fluorescent bacteria and transgenic zebrafish lines with fluorescent macrophages or neutrophils creates ideal circumstances for multi-color imaging of host-pathogen interactions. This video article will describe detailed protocols for intravenous and local infection of zebrafish embryos with S. typhimurium or M. marinum bacteria and for subsequent fluorescence imaging of the interaction with cells of the innate immune system

Liquid Xenon Detectors for Positron Emission Tomography

PET is a functional imaging technique based on detection of annihilation photons following beta decay producing positrons. In this paper, we present the concept of a new PET system for preclinical applications consisting of a ring of twelve time projection chambers filled with liquid xenon viewed by avalanche photodiodes. Simultaneous measurement of ionization charge and scintillation light leads to a significant improvement to spatial resolution, image quality, and sensitivity. Simulated performance shows that an energy resolution of <10% (FWHM) and a sensitivity of 15% are achievable. First tests with a prototype TPC indicate position resolution <1 mm (FWHM).Comment: Paper presented at the International Nuclear Physics Conference, Vancouver, Canada, 201