A low power photoemission source for electrons on liquid helium

Electrons on the surface of liquid helium are a widely studied system that may also provide a promising method to implement a quantum computer. One experimental challenge in these studies is to generate electrons on the helium surface in a reliable manner without heating the cryo-system. An electron source relying on photoemission from a zinc film has been previously described using a high power continuous light source that heated the low temperature system. This work has been reproduced more compactly by using a low power pulsed lamp that avoids any heating. About 5e3 electrons are collected on 1 cm^2 of helium surface for every pulse of light. A time-resolved experiment suggests that electrons are either emitted over or tunnel through the 1eV barrier formed by the thin superfluid helium film on the zinc surface. No evidence of trapping or bubble formation is seen.Comment: 9 pages, 3 figures, submitted to J. Low Temp. Phy

Stability-activity tradeoffs constrain the adaptive evolution of RubisCO

A well-known case of evolutionary adaptation is that of ribulose-1,5-bisphosphate carboxylase (RubisCO), the enzyme responsible for fixation of CO2 during photosynthesis. Although the majority of plants use the ancestral C3 photosynthetic pathway, many flowering plants have evolved a derived pathway named C4 photosynthesis. The latter concentrates CO2, and C4 RubisCOs consequently have lower specificity for, and faster turnover of, CO2. The C4 forms result from convergent evolution in multiple clades, with substitutions at a small number of sites under positive selection. To understand the physical constraints on these evolutionary changes, we reconstructed in silico ancestral sequences and 3D structures of RubisCO from a large group of related C3 and C4 species. We were able to precisely track their past evolutionary trajectories, identify mutations on each branch of the phylogeny, and evaluate their stability effect. We show that RubisCO evolution has been constrained by stability-activity tradeoffs similar in character to those previously identified in laboratory-based experiments. The C4 properties require a subset of several ancestral destabilizing mutations, which from their location in the structure are inferred to mainly be involved in enhancing conformational flexibility of the open-closed transition in the catalytic cycle. These mutations are near, but not in, the active site or at intersubunit interfaces. The C3 to C4 transition is preceded by a sustained period in which stability of the enzyme is increased, creating the capacity to accept the functionally necessary destabilizing mutations, and is immediately followed by compensatory mutations that restore global stability

Comparative analysis of haematological parameters in HIV patients with co-infections of hepatitis B & C, and HIV-negative patients in Rivers State, Nigeria

Background: Human immunodeficiency virus (HIV) has continued to be a threat to global health with several deaths recorded despite the introduction of highly active antiretroviral therapy (HAART). Co-infection of hepatitis B and C is now one of the leading causes of death among HIV-infected patients due to some haematological abnormalities and immunological impairment. This study was conducted to compare some haematological parameters of HIV-infectedpatients with hepatitis B and C co-infections from three hospitals in Rivers State, Nigeria Methodology: This was a comparative cross-sectional study of randomly recruited HIV-patients from antiretroviral therapy (ART) clinic and HIV-negative patients from medical out-patient department (MOPD) of three different hospitals in Rivers State, Nigeria. Socio-demographic information of each participant was obtained with a structured questionnaire. Four millilitres of blood were collected from each participant by venipuncture; 2 ml each were dispensed into ethylene diamine tetra acetic acid (EDTA) and plain bottles for estimation of full blood count (FBC), cluster of differentiation 4 (CD4), HIV, hepatitis B virus (HBV) and hepatitis C virus (HCV) serology. Results: A total of 375 participants (M:F ratio 1:1.5, age range 10-69 years) comprising 150 HIV patients on ART, 135 ART-naive HIV patients, and 90 HIV-negative patients (control) were recruited. Comparison of haematological parameters among HIV-negative (control), HIV-infected, and HIV/HBV/HCV, HIV/HCV and HIV/HBV co-infected patients showed significant increase (p<0.05) in mean lymphocyte count (%) of 36.69±13.25, 42.02±12.75, 46.53±8.36, 47.64±14.35, and 49.61±5.81, and a significant decrease (p<0.05) in mean neutrophil count (%) of 54.43±13.52, 46.33±13.04, 44.23±9.30, 41.66±12.94 and 40.86±7.56 respectively. The mean platelet count (109/L) in HIV-negative control, HIV-infected, and HIV/HCV, HIV/HBV and HIV/HBV/HCV co-infected patients showed significant decrease (p<0.05) of 235.25±109.52, 229.26±104.70, 152.25±56.64, 138.69±56.25, and 130.33±79.51, as well as a significant decrease in CD4 cell counts (cells/µl) of 803.40±211.24, 619.67±334.13, 590.63±312.20, 550.15±311.72, and 406.49±261.75 respectively. Conclusion: Alterations in the haematological parameters can lead to serious complications in HIV individuals coinfected with HBV and/or HCV. Therefore, HBV and HCV screening for every HIV-infected patient should be made mandatory in Nigeria.   French title: Analyse comparative des paramètres hématologiques chez les patients séropositifs co-infectés par les hépatites B et C et chez les patients séronégatifs dans l'État de Rivers, au Nigeria Contexte: Le virus de l'immunodéficience humaine (VIH) a continué d'être une menace pour la santé mondiale avec plusieurs décès enregistrés malgré l'introduction de la thérapie antirétrovirale hautement active (HAART). La coinfection par l'hépatite B et l'hépatite C est aujourd'hui l'une des principales causes de décès chez les patients infectés par le VIH en raison de certaines anomalies hématologiques et d'une déficience immunologique. Cette étude a été menée pour comparer certains paramètres hématologiques de patients infectés par le VIH avec des co-infections par l'hépatite B et C dans trois hôpitaux de l'État de Rivers, au Nigéria. Méthodologie: Il s'agissait d'une étude transversale comparative de patients séropositifs recrutés au hasard dans une clinique de traitement antirétroviral (TAR) et de patients séronégatifs du service médical ambulatoire (MOPD) de trois hôpitaux différents dans l'État de Rivers, au Nigeria. Les informations socio-démographiques de chaque participant ont été obtenues à l'aide d'un questionnaire structuré. Quatre millilitres de sang ont été prélevés sur chaque participant par ponction veineuse; 2 ml chacun ont été distribués dans des flacons d'acide éthylène diamine tétra acétique (EDTA) et simples pour l'estimation de la formule sanguine complète (FBC), du groupe de différenciation 4 (CD4), du VIH, du virus de l'hépatite B (VHB) et du virus de l'hépatite C (VHC) sérologie. Résultats: Un total de 375 participants (rapport M: F 1: 1,5; tranche d'âge de 10 à 69 ans) comprenant 150 patients séropositifs sous TAR, 135 patients séropositifs naïfs de TAR et 90 séronégatifs (contrôle) ont été recrutés. La comparaison des paramètres hématologiques chez les patients séronégatifs pour le VIH (contrôle), infectés par le VIH et co-infectés par le VIH/VHB/VHC, le VIH/VHC et le VIH/VHB a montré une augmentation significative (p<0,05) du nombre moyen de lymphocytes (%) des 36,69±13,25, 42,02±12,75, 46,53±8,36, 47,64±14,35 et 49,61±5,81, et une diminution significative (p<0,05) du nombre moyen de neutrophiles (%) de 54,43±13,52, 46,33±13,04, 44,23±9,30, 41,66±12,94 et 40,86±7,56 respectivement. La numération plaquettaire moyenne (109/L) chez les patients témoins séronégatifs, infectés par le VIH et co-infectés par le VIH/VHC, le VIH/VHB et le VIH/VHB/VHC a montré une diminution significative (p<0,05) de 235,25±109,52, 229,26±104,70, 152,25±56,64, 138,69±56,25 et 130,33±79,51, ainsi qu'une diminution significative du nombre de cellules CD4 (cellules/µl) de 803,40±211,24, 619,67±334,13, 590,63±312 550.15±311,72 et 406,49±261,75 respectivement. Conclusion: Des altérations des paramètres hématologiques peuvent entraîner de graves complications chez les personnes VIH co-infectées par le VHB et/ou le VHC. Par conséquent, le dépistage du VHB et du VHC pour chaque patient infecté par le VIH devrait être rendu obligatoire au Nigeri

First records of Hyalomma rufipes and Ixodes neitzi (Acari: Ixodidae) found on large carnivores in South Africa

Ixodid ticks (Acari: Ixodidae) are important disease vectors for large carnivores, but the composition of the tick communities that parasitize carnivores is poorly understood. We collected ticks from leopards (Panthera pardus) and brown hyenas (Hyaena brunnea) in the Soutpansberg Mountains, South Africa, to determine which species feed on these carnivores. We identified a total of eight tick species belonging to six genera, and recorded Ixodes neitzi and Hyalomma rufipes on P. pardus for the first time

Assessing carbon dioxide storage integrity of an extensive saline aquifer formation: East Irish Sea Basin, UK

Accurately determining the contemporary pore pressure and in situ stress conditions is critical to the safe planning and development of subsurface operations such as CO2 storage. According to the UK storage capacity atlas, CO2STORED (Bentham et al. 2014), the East Irish Sea Basin (EISB) has a significant storage capacity of nearly 4 Gt (P50) within saline aquifer parts of the Triassic-aged Ormskirk Sandstone Formation (OSF). The OSF is present over a significant part of the EISB, and where buried deeply enough to be considered for CO2 storage is overlain by the Mercia Mudstone Group (MMG), a thick sequence comprising up to 3200 m of interbedded mudstones, siltstones and evaporites. As a result of Tertiary inversion, the Jurassic and younger succession is absent over most of the basin, and so the MMG represents the vast majority of the overburden succession. The presence of numerous gas accumulations, including the Morecambe South Gas Field with its ~400 m gas column, is testament to the sealing capacity of the MMG. Where halite formations within the MMG directly overly the OSF, the sealing capacity of the MMG is significantly increased

Water surface height determination with a GPS wave glider: a demonstration in Loch Ness, Scotland

A geodetic GPS receiver has been installed on a Wave Glider, an unmanned water surface vehicle. Using kinematic precise point positioning (PPP) GPS, which operates globally without directly requiring reference stations, surface heights are measured with ~0.05-m precision. The GPS Wave Glider was tested in Loch Ness, Scotland, by measuring the gradient of the loch’s surface height. The experiment took place under mild weather, with virtually no wind setup along the loch and a wave field made mostly of ripples and wavelets. Under these conditions, the loch’s surface height gradient should be approximately equal to the geoid slope. The PPP surface height gradient and that of the Earth Gravitational Model 2008 geoid heights do indeed agree on average along the loch (0.03 m km−1). Also detected are 1) ~0.05-m-sized height changes due to daily water pumping for hydroelectricity generation and 2) high-frequency (0.25–0.5 Hz) oscillations caused by surface waves. The PPP heights compare favorably (~0.02-m standard deviation) with relative carrier phase–based GPS processing. This suggests that GPS Wave Gliders have the potential to autonomously determine centimeter-precise water surface heights globally for lake modeling, and also for applications such as ocean modeling and geoid/mean dynamic topography determination, at least for benign surface states such as those encountered during the reported experiment