Fractional Stokes-Einstein and Debye-Stokes-Einstein relations in a network forming liquid

We study the breakdown of the Stokes-Einstein (SE) and Debye-Stokes-Einstein (DSE) relations for translational and rotational motion in a prototypical model of a network-forming liquid, the ST2 model of water. We find that the emergence of ``fractional'' SE and DSE relations at low temperature is ubiquitous in this system, with exponents that vary little over a range of distinct physical regimes. We also show that the same fractional SE relation is obeyed by both mobile and immobile dynamical heterogeneities of the liquid

Dynamical Behavior Near a Liquid-Liquid Phase Transition in Simulations of Supercooled Water

We examine the behavior of the diffusion coefficient of the ST2 model of water over a broad region of the phase diagram via molecular dynamics simulations. The ST2 model has an accessible liquid-liquid transition between low-density and high-density phases, making the model an ideal candidate to explore the impacts of the liquid-liquid transition on dynamics. We locate characteristic dynamical loci in the phase diagram and compare them with the previously investigated thermodynamic loci. The low-density liquid phase shows a crossover from non-Arrhenius to Arrhenius behavior, signaling the onset of a crossover from fragile-to-strong behavior. We explain this crossover in terms of the asymptotic approach of the low-density liquid to a random tetrahedral network, and show that the temperature dependence of the diffusion coefficient over a wide temperature range can be simply related to the concentration of defects in the network. Our findings thus confirm that the low-density phase of ST2 water is a well-defined metastable liquid.Comment: 21 pages, 9 figure

High floc strength with aged polyelectrolytes

The ageing of powdered polyelectrolyte solutions has shown that while the viscosity of these solutions decreases rapidly with time, the flocculation performance and the strength of the flocs produced does not alter over periods >200 days. This was shown for polyacrylamides of cationic, anionic and non-ionic charge. The use of tap or deionized water did not adversely affect the results unless a biocide capable of associating with the polyelectrolyte was added. These results contradict the common belief that solutions made with powdered polyelectrolytes should not be stored for long periods of time as their performance decreases after being stored for several days. The results indicate that powdered polyelectrolyte solutions are suitable for intermittent process operations, such as sewer overflow treatment and that dosing and handling of the solutions can be made easier by ageing of the solutions

Using the Rosat Catalogue to find Counterparts for Unidentified Objects in the 1st Fermi/LAT Catalogue

There are a total of 1451 gamma-ray emitting objects in the Fermi Large Area Telescope First Source Catalogue. The point source location accuracy of typically a few arcminutes has allowed the counterparts for many of these sources to be found at other wavelengths, but even so there are 630 which are described as having no plausible counterpart at 80% confidence. In order to help identify the unknown objects, we have cross-correlated the positions of these sources with the Rosat All Sky Survey Bright Source Catalogue. In this way, for Fermi sources which have a possible counterpart in soft X-rays, we can use the, much smaller, Rosat error box to search for identifications. We find a strong correlation between the two samples and calculate that there are about 60 sources with a Rosat counterpart. Using the Rosat error boxes we provide tentative associations for half of them, demonstrate that the majority of these are either blazars or blazar candidates and give evidence that most belong to the BL Lac class. Given that they are X-ray selected and most are high synchrotron peaked objects, which indicates the presence of high energy electrons, these sources are also good candidates for TeV emission, and therefore good probes of the extragalactic background light.Comment: 9 pages, 1 figure; Accepted for publication in MNRA

Concentrations of Polychlorinated Biphenyls (PCB’s), Chlorinated Pesticides, and Heavy Metals and Other Elements in Tissues of Belugas, Delphinapterus leucas, from Cook Inlet

Tissues from Cook Inlet beluga whales, Delphinapterus leucas, that were collected as part of the Alaska Marine Mammal Tissue Archival Project were analyzed for polychlorinated biphenyls (PCB’s), chlorinated pesticides, and heavy metals and other elements. Concentrations of total PCB’s (ΣPCB’s), total DDT (ΣDDT), chlordane compounds, hexachlorobenzene (HCB), dieldrin, mirex, toxaphene, and hexachlorocyclohexane (HCH) measured in Cook Inlet beluga blubber were compared with those reported for belugas from two Arctic Alaska locations (Point Hope and Point Lay), Greenland, Arctic Canada, and the highly contaminated stock from the St. Lawrence estuary in eastern Canada. The Arctic and Cook Inlet belugas had much lower concentrations (ΣPCB’s and ΣDDT were an order of magnitude lower) than those found in animals from the St. Lawrence estuary. The Cook Inlet belugas had the lowest concentrations of all (ΣPCB’s aver-aged 1.49 ± 0.70 and 0.79 ± 0.56 mg/kg wet mass, and ΣDDT averaged 1.35 ± 0.73 and 0.59 ± 0.45 mg/kg in males and females, respectively). Concentrations in the blubber of the Cook Inlet males were significantly lower than those found in the males of the Arctic Alaska belugas (ΣPCB’s and ΣDDT were about half). The lower levels in the Cook Inlet animals might be due to differences in contaminant sources, food web differences, or different age distributions among the animals sampled. Cook Inlet males had higher mean and median concentrations than did females, a result attributable to the transfer of these compounds from mother to calf during pregnancy and during lactation. Liver concentrations of cadmium and mercury were lower in the Cook Inlet belugas (most cadmium values were <1 mg/kg and mercury values were 0.704–11.42 mg/kg wet mass), but copper levels were significantly higher in the Cook Inlet animals (3.97–123.8 mg/kg wet mass) than in Arctic Alaska animals and similar to those reported for belugas from Hudson Bay. Although total mercury levels were the lowest in the Cook Inlet population, methylmercury concentrations were similar among all three groups of the Alaska animals examined (0.34–2.11 mg/kg wet mass). As has been reported for the Point Hope and Point Lay belugas, hepatic concentrations of silver were r

Protein/Protein Interactions in the Mammalian Heme Degradation Pathway: Heme Oxygenase-2, Cytochrome P450 Reductase, and Biliverdin Reductase

Heme oxygenase (HO) catalyzes the rate-limiting step in the O2- dependent degradation of heme to biliverdin, CO, and iron with electrons delivered from NADPH via cytochrome P450 reductase (CPR). Biliverdin reductase (BVR) then catalyzes conversion of bili­verdin to bilirubin. We describe mutagenesis combined with kinetic, spectroscopic (fluorescence and NMR), surface plasmon resonance, cross-linking, gel filtration, and analytical ultracentrifugation studies aimed at evaluating interactions of HO-2 with CPR and BVR. Based on these results, we propose a model in which HO-2 and CPR form a dynamic ensemble of complex(es) that precede formation of the productive electron transfer complex. The 1H-15N TROSY NMR spectrum of HO-2 reveals specific residues, including Leu-201, near the heme face of HO-2 that are affected by the addition of CPR, im­plicating these residues at the HO/CPR interface. Alanine substitu­tions at HO-2 residues Leu-201 and Lys-169 cause a respective 3- and 22-fold increase in Km values for CPR, consistent with a role for these residues in CPR binding. Sedimentation velocity experiments confirm the transient nature of the HO-2·CPR complex (Kd = 15.1 μm). Our results also indicate that HO-2 and BVR form a very weak complex that is only captured by cross-linking. For example, under conditions where CPR affects the 1H-15N TROSY NMR spectrum of HO-2, BVR has no effect. Fluorescence quenching experiments also suggest that BVR binds HO-2 weakly, if at all, and that the previously reported high affinity of BVR for HO is artifactual, resulting from the effects of free heme (dissociated from HO) on BVR fluorescenc

Protein/Protein Interactions in the Mammalian Heme Degradation Pathway: Heme Oxygenase-2, Cytochrome P450 Reductase, and Biliverdin Reductase

Heme oxygenase (HO) catalyzes the rate-limiting step in the O2- dependent degradation of heme to biliverdin, CO, and iron with electrons delivered from NADPH via cytochrome P450 reductase (CPR). Biliverdin reductase (BVR) then catalyzes conversion of bili­verdin to bilirubin. We describe mutagenesis combined with kinetic, spectroscopic (fluorescence and NMR), surface plasmon resonance, cross-linking, gel filtration, and analytical ultracentrifugation studies aimed at evaluating interactions of HO-2 with CPR and BVR. Based on these results, we propose a model in which HO-2 and CPR form a dynamic ensemble of complex(es) that precede formation of the productive electron transfer complex. The 1H-15N TROSY NMR spectrum of HO-2 reveals specific residues, including Leu-201, near the heme face of HO-2 that are affected by the addition of CPR, im­plicating these residues at the HO/CPR interface. Alanine substitu­tions at HO-2 residues Leu-201 and Lys-169 cause a respective 3- and 22-fold increase in Km values for CPR, consistent with a role for these residues in CPR binding. Sedimentation velocity experiments confirm the transient nature of the HO-2·CPR complex (Kd = 15.1 μm). Our results also indicate that HO-2 and BVR form a very weak complex that is only captured by cross-linking. For example, under conditions where CPR affects the 1H-15N TROSY NMR spectrum of HO-2, BVR has no effect. Fluorescence quenching experiments also suggest that BVR binds HO-2 weakly, if at all, and that the previously reported high affinity of BVR for HO is artifactual, resulting from the effects of free heme (dissociated from HO) on BVR fluorescenc

GMRT observations of the field of INTEGRAL X-ray sources- II (newly discovered hard X-ray sources)

We have conducted low-frequency radio observations with the Giant Metrewave Radio Telescope (GMRT) of 40 new hard X-ray sources discovered by the INTEGRAL satellite. This survey was conducted in order, to study radio emissions from these sources, to provide precise position and to identify new microquasar candidates. From our observations we find that 24 of the X-ray sources have radio candidates within the INTEGRAL error circle. Based on the radio morphology, variability and information available from different wavelengths, we categorize them as seventeen Galactic sources (4 unresolved, 7 extended, 6 extended sources in diffuse region) and seven extragalactic sources (2 unresolved, 5 extended). Detailed account for seventeen of these sources was presented in earlier paper. Based on the radio data for the remaining sources at 0.61 GHz, and the available information from NVSS, DSS, 2MASS and NED, we have identified possible radio counterparts for the hard X-ray sources. The three unresolved sources, viz IGR J17303$-$0601, IGR J17464$-$3213, and IGR J18406$-$0539 are discussed in detail. These sources have been identified as X-ray binaries with compact central engine and variable in X-ray and in the radio, and are most likely microquasar candidates. The remaining fourteen sources have extended radio morphology and are either diffuse Galactic regions or extragalactic in origin.Comment: 9 pages, 7 figures, submitted to A&A. submitted to A&

Avian malaria is absent in juvenile colonial herons (Ardeidae) but not Culex pipiens mosquitoes in the Camargue, Southern France

Apicomplexan blood parasites Plasmodium and Haemoproteus (together termed “Avian malaria”) and Leucocytozoon are widespread, diverse vector-transmitted blood parasites of birds, and conditions associated with colonial nesting in herons (Ardeidae) and other waterbirds appear perfect for their transmission. Despite studies in other locations reporting high prevalence of parasites in juvenile herons, juvenile Little Egrets (Egretta garzetta) previously tested in the Camargue, Southern France, had a total absence of malaria parasites. This study tested the hypotheses that this absence was due to insufficient sensitivity of the tests of infection; an absence of infective vectors; or testing birds too early in their lives. Blood was sampled from juveniles of four species shortly before fledging: Little Egret (n = 40), Cattle Egret (Bubulcus ibis; n = 40), Black-crowned Night-Heron (Nycticorax nycticorax, n = 40), and Squacco Heron (Ardeola ralloides; n = 40). Sensitive nested-Polymerase Chain Reaction was used to test for the presence of parasites in both birds and host-seeking female mosquitoes captured around the colonies. No malaria infection was found of in any of the heron species. Four different lineages of Plasmodium were detected in pooled samples of female Culex pipiens mosquitoes, including two in potentially infective mosquitoes. These results confirm that the absence of malaria parasites previously demonstrated in Little Egret is not due to methodological limitations. Although the prevalence of infection in mosquitoes was low, conditions within the colonies were suitable for transmission of Plasmodium. These colonial heron species may have evolved strategies for resisting malaria infection through physiological or behavioral mechanisms