154 research outputs found
Towards a better understanding on agglomeration mechanisms and thermodynamic properties of TiO2 nanoparticles interacting with natural organic matter
Interaction between engineered nanoparticles and natural organic matter is
investigated by measuring the exchanged heat during binding process with
isothermal titration calorimetry. TiO2 anatase nanoparticles and alginate are
used as engineered nanoparticles and natural organic matter to get an insight
into the thermodynamic association properties and mechanisms of adsorption and
agglomeration. Changes of enthalpy, entropy and total free energy, reaction
stoichiometry and affinity binding constant are determined or calculated at a
pH value where the TiO2 nanoparticles surface charge is positive and the
alginate exhibits a negative structural charge. Our results indicate that
strong TiO2-alginate interactions are essentially entropy driven and
enthalpically favorable with exothermic binding reactions. The reaction
stoichiometry and entropy gain are also found dependent on the mixing order.
Finally correlation is established between the binding enthalpy, the reaction
stoichiometry and the zeta potential values determined by electrophoretic
mobility measurements. From these results two types of agglomeration mechanisms
are proposed depending on the mixing order. Addition of alginate in TiO2
dispersions is found to form agglomerates due to polymer bridging whereas
addition of TiO2 in alginate promotes a more individually coating of the
nanoparticles.Comment: 30 pages, 6 figures, 11 figures in S
Experiencias controladas realizadas con distintas cocinas solares
Se presentan los resultados de distintas experiencias controladas, realizadas tanto en el Laboratorio de Secado y CocciĂłn de Alimentos (LSCA), del INENCO, como al aire libre, usándose distintas formas de calentamiento bajo radiaciĂłn de un litro de agua contenido en una olla de aluminio. Se calentĂł y comparĂł su comportamiento tĂ©rmico en diecisĂ©is sistemas diferentes, desde la simple olla de aluminio hasta diferentes modelos de cocinas solares.AsociaciĂłn Argentina de EnergĂas Renovables y Medio Ambiente (ASADES
Uso de braseros a leña en comedores infantiles de la ciudad de Salta
Se presenta el estado de situaciĂłn actual de veintisĂ©is braseros a leña optimizados que fueran transferidos gratuitamente durante los años 1994 y 1995 a dieciocho comedores infantiles de la Ciudad de Salta. Para realizar este estudio se visitaron los comedores a fin de conocer in-situ el estado de uso de las estufas y el empleo que tuvieron desde que fueron entregadas. TambiĂ©n se estudiĂł la situaciĂłn general de los comedores mediante un cuestionario elaborado por el Instituto de InvestigaciĂłn Brace. Se resumen las informaciones obtenidas a partir del mismo.AsociaciĂłn Argentina de EnergĂas Renovables y Medio Ambiente (ASADES
Long-range/short-range separation of the electron-electron interaction in density functional theory
By splitting the Coulomb interaction into long-range and short-range
components, we decompose the energy of a quantum electronic system into
long-range and short-range contributions. We show that the long-range part of
the energy can be efficiently calculated by traditional wave function methods,
while the short-range part can be handled by a density functional. The analysis
of this functional with respect to the range of the associated interaction
reveals that, in the limit of a very short-range interaction, the short-range
exchange-correlation energy can be expressed as a simple local functional of
the on-top pair density and its first derivatives. This provides an explanation
for the accuracy of the local density approximation (LDA) for the short-range
functional. Moreover, this analysis leads also to new simple approximations for
the short-range exchange and correlation energies improving the LDA.Comment: 18 pages, 14 figures, to be published in Phys. Rev.
Archaeal Diversity and CO 2
Groundwater environments provide habitats for diverse microbial communities, and although Archaea usually represent a minor fraction of communities, they are involved in key biogeochemical cycles. We analysed the archaeal diversity within a mixed carbonate-rock/siliciclastic-rock aquifer system, vertically from surface soils to subsurface groundwater including aquifer and aquitard rocks. Archaeal diversity was also characterized along a monitoring well transect that spanned surface land uses from forest/woodland to grassland and cropland. Sequencing of 16S rRNA genes showed that only a few surface soil-inhabiting Archaea were present in the groundwater suggesting a restricted input from the surface. Dominant groups in the groundwater belonged to the marine group I (MG-I) Thaumarchaeota and the Woesearchaeota. Most of the groups detected in the aquitard and aquifer rock samples belonged to either cultured or predicted lithoautotrophs (e.g., Thaumarchaeota or Hadesarchaea). Furthermore, to target autotrophs, a series of 13CO2 stable isotope-probing experiments were conducted using filter pieces obtained after filtration of 10,000 L of groundwater to concentrate cells. These incubations identified the SAGMCG Thaumarchaeota and Bathyarchaeota as groundwater autotrophs. Overall, the results suggest that the majority of Archaea on rocks are fixing CO2, while archaeal autotrophy seems to be limited in the groundwater
Group B streptococcal carriage, serotype distribution and antibiotic susceptibilities in pregnant women at the time of delivery in a refugee population on the Thai-Myanmar border
<p>Abstract</p> <p>Background</p> <p>Group B Streptococcus (GBS) is the leading cause of neonatal sepsis in the developed world. Little is known about its epidemiology in the developing world, where the majority of deaths from neonatal infections occur. Maternal carriage of GBS is a prerequisite for the development of early onset GBS neonatal sepsis but there is a paucity of carriage data published from the developing world, in particular South East Asia.</p> <p>Methods</p> <p>We undertook a cross sectional study over a 13 month period in a remote South East Asian setting on the Thai-Myanmar border. During labour, 549 mothers had a combined vaginal rectal swab taken for GBS culture. All swabs underwent both conventional culture as well as PCR for GBS detection. Cultured GBS isolates were serotyped by latex agglutination, those that were negative or had a weak positive reaction and those that were PCR positive but culture negative were additionally tested using multiplex PCR based on the detection of GBS capsular polysaccharide genes.</p> <p>Results</p> <p>The GBS carriage rate was 12.0% (95% CI: 9.4-15.0), with 8.6% positive by both culture and PCR and an additional 3.5% positive by PCR alone. Serotypes, Ia, Ib, II, III, IV, V, VI and VII were identified, with II the predominant serotype. All GBS isolates were susceptible to penicillin, ceftriaxone and vancomycin and 43/47 (91.5%) were susceptible to erythromycin and clindamycin.</p> <p>Conclusions</p> <p>GBS carriage is not uncommon in pregnant women living on the Thai-Myanmar border with a large range of serotypes represented.</p
A three year descriptive study of early onset neonatal sepsis in a refugee population on the Thailand Myanmar border.
BACKGROUND: Each year an estimated four million neonates die, the majority in the first week of life. One of the major causes of death is sepsis. Proving the incidence and aetiology of neonatal sepsis is difficult, particularly in resource poor settings where the majority of the deaths occur. METHODS: We conducted a three year observational study of clinically diagnosed early onset (<7 days of age) neonatal sepsis (EONS) in infants born to mothers following antenatal care at the Shoklo Malaria Research Unit clinic in Maela camp for displaced persons on the Thailand-Myanmar border. Episodes of EONS were identified using a clinical case definition. Conventional and molecular microbiological techniques were employed in order to determine underlying aetiology. RESULTS: From April 2009 until April 2012, 187 infants had clinical signs of EONS, giving an incidence rate of 44.8 per 1000 live births (95% CI 38.7-51.5). One blood culture was positive for Escherichia coli, E. coli was detected in the cerebrospinal fluid specimen in this infant, and in an additional two infants, by PCR. Therefore, the incidence of bacteriologically proven EONS was 0.7 per 1000 live births (95% CI 0.1-2.1). No infants enrolled in study died as a direct result of EONS. CONCLUSION: A low incidence of bacteriologically proven EONS was seen in this study, despite a high incidence of clinically diagnosed EONS. The use of molecular diagnostics and nonspecific markers of infection need to be studied in resource poor settings to improve the diagnosis of EONS and rationalise antibiotic use
Viral entry and escape from antibody-mediated neutralization influence hepatitis C virus reinfection in liver transplantation
End-stage liver disease caused by chronic hepatitis C virus (HCV) infection is a leading cause for liver transplantation (LT). Due to viral evasion from host immune responses and the absence of preventive antiviral strategies, reinfection of the graft is universal. The mechanisms by which the virus evades host immunity to reinfect the liver graft are unknown. In a longitudinal analysis of six HCV-infected patients undergoing LT, we demonstrate that HCV variants reinfecting the liver graft were characterized by efficient entry and poor neutralization by antibodies present in pretransplant serum compared with variants not detected after transplantation. Monoclonal antibodies directed against HCV envelope glycoproteins or a cellular entry factor efficiently cross-neutralized infection of human hepatocytes by patient-derived viral isolates that were resistant to autologous host-neutralizing responses. These findings provide significant insights into the molecular mechanisms of viral evasion during HCV reinfection and suggest that viral entry is a viable target for prevention of HCV reinfection of the liver graft
Scavenger receptor class B type I is a key host factor for hepatitis C virus infection required for an entry step closely linked to CD81.
International audienceHepatitis C virus (HCV) is a major cause of chronic hepatitis worldwide. Scavenger receptor class B type I (SR-BI) has been shown to bind HCV envelope glycoprotein E2, participate in entry of HCV pseudotype particles, and modulate HCV infection. However, the functional role of SR-BI for productive HCV infection remains unclear. In this study, we investigated the role of SR-BI as an entry factor for infection of human hepatoma cells using cell culture-derived HCV (HCVcc). Anti-SR-BI antibodies directed against epitopes of the human SR-BI extracellular loop specifically inhibited HCVcc infection in a dose-dependent manner. Down-regulation of SR-BI expression by SR-BI-specific short interfering RNAs (siRNAs) markedly reduced the susceptibility of human hepatoma cells to HCVcc infection. Kinetic studies demonstrated that SR-BI acts predominately after binding of HCV at an entry step occurring at a similar time point as CD81-HCV interaction. Although the addition of high-density lipoprotein (HDL) enhanced the efficiency of HCVcc infection, anti-SR-BI antibodies and SR-BI-specific siRNA efficiently inhibited HCV infection independent of lipoprotein. Conclusion: Our data suggest that SR-BI (i) represents a key host factor for HCV entry, (ii) is implicated in the same HCV entry pathway as CD81, and (iii) targets an entry step closely linked to HCV-CD81 interaction
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