93 research outputs found
Very high energy gamma rays from millisecond pulsars
No full textIn this paper we concentrate on the emission of TeV γ - rays from radio pulsars. It will be shown that the polar gap model fails to explain the observed TeV flux levels: The X-ray luminosity should exceed the TeV luminosity if the latter originates from the polar gap regions. The outer gap model of Cheng, Ho and Ruderman provides a consistent picture of TeV γ - ray emission: The total gap power is converted to TeV γ - rays by means of the inverse Compton scattering of primary electrons on the abundant soft IR flux in and around the gap. A fraction exp(-f- 1 2) escapes photon-photon absorption and may be observable Here f (∼ 0.1 for Vela and Vela-like pulsars) is the fraction of the open magnetosphere occupied by the gap. The remaining power is used for the gap sustaining mechanism. As the pulsar grows older, f → 1 and the TeV power increases and becomes comparable to the spindown power. This is the so-called "post Vela-like" stage. The model is applied to millisecond pulsars which are all Vela- and post Vela-like. The luminosity estimates are consistent with the TeV observations - despite the experimental uncertainties and theoretical assumptions. © 1990.link_to_subscribed_fulltex
Partitioning coefficients and solubilities of Cu, Pb and V in selected south African soil horizons
No full textDissertation (MSc)--University of Pretoria, 2014.In the past, contaminated soil as a source for water contamination has been largely
neglected from the South African legislation. Inconsistent evaluation and remediation
of contaminated sites have resulted in many sources of water contamination not
being sufficiently addressed. The Draft National Norms and Standards for the
Remediation of Contaminated Land and Soil Quality (GN 233 of 2012) (henceforth
Norms and Standards) was published for comments and suggestions in August
2012. A number of uncertainties have been identified that may impact on the
successful implementation of the Framework and the Norms and Standards.
Some of the issues are related specifically to the setting of soil screening values
(SSV) for protection of water resources. There is no particular method specified to
determine the soluble fraction of contaminants in soil. In a phase 1 assessment
SSVs are used to judge whether constituents present in the soils are at
concentrations high enough to pose a potential risk to the receiving environment.
With the determination of the SSV a known water quality standard is converted to a
total concentration by making use of a dilution factor and partitioning coefficient (Kd).
The proposed Kd values in the Framework are surrounded by uncertainties and
information regarding Kd values for South African soils are limited. In addition, the
Framework does not take into account the natural background concentration of soils
to differentiate between anthropogenic and natural contamination.
Setting appropriate extraction method plays the key role for an objective and
standardised initial assessment of soluble concentrations in the soil. Similarly, the
selection of appropriate Kd values based on soil properties minimizes the
uncertainties during the estimation of SSV. Appropriate screening of contaminated
land is imperative to the registration of contaminated land and has significant
implications for industry, government and the environment. The aims of this study were: a) to assess fast and simple analytical methodologies
which can be performed by a commercial laboratory to mimic the standard saturated
paste extraction method to determine soluble metal concentration in soils, b) to
determine Kd values for selected South African soils in 10 soil horizons, and c) to determine baseline concentration ranges for selected soluble contaminants to assist
in the setting of appropriate soil screening values for the protection of water
resources. The study will test the hypothesis that a 1:2.5 (soil:water ratio) water
extraction could better mimic the standard saturated paste extraction than the 1:20
ratio, commonly used in USA. The 1:2.5 ratio can be done by most commercial
laboratories and gives a better indication of the pore water quality.
To assess analytical methods, four extraction methods (1:2.5, 1:5, 1:10 and 1:20
soil:water) were tested against the standard saturated paste extraction using three
trace metals (Cu, Pb and V). These three metals were selected based on reactivity
and environmental abundance. Lead and Cu are B type metals which complex
readily with organic material and are generally more environmentally toxic.
Anthropogenic activities are increasing enrichment of B type metals in the
environment. Vanadate is an A type metal and is redox sensitive. Its association with
the Bushveld complex was the reason for its inclusion in this study. The baseline
soluble concentrations of Cu, Pb, and V were determined for selected 100 South
African soils using the extraction method selected above. The Kd values of Cu, Pb,
and V were determined for selected 10 soil horizons (1:1 clay dominated A horizon,
Vertic soil dominated by 2:1 clay minerals, Yellow oxidic / Plinthic (Soft plinthic B
horizon), low clay red oxidic B horizon, red oxidic B horizon, plinthic B horizon,
gleyed horizon (G horizon), melanic A horizon, orthic A horizon with high organic
content (OC) and E-horizon) using a batch method. For each constituent three
different metal concentrations were added to each of the soil horizons. After
extraction the concentration in the solution was used to determine the amount of
metal sorbed to the soil.
Considering the standard saturated paste extract as a bench mark, the 1:2.5
soil:water ratio extraction gave more representative soil pore water quality for Cu, Pb
and V in the low to medium concentrations. Therefore, the hypothesis was accepted.
It was also apparent that the Kd values selected for the Framework are not
representative of typical South African soils. The Kd values for Cu range between
12.7 and 19044 L kg-1. These values exceeded the value of 10 L kg-1 provided by the
Framework in all soils. For V the Kd values (10.5 – 865 L kg-1) in all soils were lower than the value of 1000 L kg-1 specified in the Framework. For Pb, the Kd of 100 L kg-1
as indicated in the Framework is not representative of soils found in South Africa.
For Pb, low clay content, weathered soils have lower Kd values, whereas higher clay
content soils have Kd values up to 4 orders of magnitude higher than the Kd in the
Framework. Therefore, due to the large variability in Kd values, a single value cannot
be used for all soil types.
To conclude, the 1:2.5 soil:water ratio was found to be more representative to the
soil pore content especially in the low to medium solute concentrations. The study
also showed that a single Kd value cannot be used across soil types. The Kd values
currently used in the Framework have low representativity of the South African soils.
In the meantime, the Kd values for Cu, Pb, and V generated from this study for
selected South African soil horizons could be used by the framework. There is,
however, a need to develop local Kd values of contaminants across soil types.lk2014Plant Production and Soil ScienceMScUnrestricte
Síntese de cristais líquidos funcionalizados contendo o heterociclo 1,3,4-oxadiazol
No full textTese (doutorado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas, Programa de Pós-Graduação em Química, Florianópolis, 2013.Neste trabalho são descritas a síntese, a caracterização e os estudos das propriedades ópticas, térmicas, elétricas e organizacionais de novos materiais líquido-cristalinos funcionalizados e derivados do heterociclo 1,3,4-oxadiazol 2,5-dissubstituído. Quatro projetos foram desenvolvidos, os quais diferem na funcionalização e forma dos cristais líquidos (CLs), totalizando 59 produtos finais. 1) CLs iônicos: um estudo sistemático permitiu demonstrar que variações estruturais afetam simultaneamente e de forma variada as propriedades térmicas e fotofísicas estudadas; 2) CLs discóticos: os compostos apresentaram mesofase Colhex e fluorescência na região do azul (370-400 nm), com rendimentos quânticos dependentes da estrutura; 3) CLs curvados contendo o grupo 2-octinoiloxi almejando a obtenção de mesofases nemáticas biaxiais: a substituição do anel benzênico pela ligação C?C gerou um abaixamento do ponto de fusão dos materiais e os produtos apresentaram a predominância da mesofase N com a presença de clusters cibotáticos do tipo SmC; 4) CLs curvados contendo grupos segregantes almejando mesofases esméticas polares: os compostos apresentaram um interessante polimorfismo, exibindo uma predominância de mesofases Colob e SmC. Medidas eletroópticas confirmaram um ordenamento ferro e/ou antiferroelétrico para alguns materiais.Abstract : In this doctoral thesis are described the synthesis, characterization and study of the optical, thermal, electrical and organizational properties of new functionalized liquid crystalline materials of 2,5-disubstituted 1,3,4-oxadiazole derivatives. The synthesized compounds had their structure and purity confirmed by IR spectroscopy, 1H, 13C and 29Si NMR, melting point and elemental analysis (CHN) techniques. Subsequently, the thermal and liquid crystalline properties were investigated by POM, DSC, TGA, XRD and electro-optical measurements. In parallel, the photophysical properties of some compounds were studied in solution and in film by UV-vis absorption and emission spectroscopy. In this thesis, four different projects have been developed, which differ in the functionalization type and in the shape of liquid crystals: 1) 29 ionic and non-ionic calamitic molecules with several structural modifications were synthesized. This allowed a detailed systematic study of the effect of structural modifications on the thermal, liquid-crystalline and photophysical properties of these materials. It was shown that every parameter studied affected simultaneously and in a different way these properties; 2) 12 flat molecules with structural variations were synthesized in order to obtain fluorescent and columnar mesophase forming materials. Generally the compounds showed mesophase Colhex and fluorescence in the blue region (370-400 nm) with quantum yields dependent on the structure. In a general way, the compounds showed a Colhex mesophase and blue fluorescence (370-400 nm), with quantum yield dependent on the structure; 3) 10 bent-core molecules with reduced rigid center and smaller aliphatic chains were synthesized in order to obtain biaxial nematic mesophases. Furthermore, the 2-octinoiloxi group was used to study the effect of the substitution of a benzene ring by one C=C triple bond. The molecules showed predominance of a nematic mesomorphism with the presence of SmC cybotactic clusters. The results also showed that the substitution of a benzene ring by a C=C bond resulted in the lowering of the materials melting point, which also caused a shortening of the mesomorphic behavior range; 4) 8 bent-core molecules with slightly elongated rigid center, larger aliphatic chains and containing segregating groups were prepared aiming polar smectic mesophases. The compounds exhibited an interesting polymorphism, showing a predominance of Colob and SmC mesophases. Electro-optic measurements confirmed ferro and/or antiferroeletric order for some materials, which depend on the molecular structure and temperature analyzed
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The Origins of Lactase Persistence in Europe
No full textLactase persistence (LP) is common among people of European ancestry, but with the exception of some African, Middle Eastern and southern Asian groups, is rare or absent elsewhere in the world. Lactase gene haplotype conservation around a polymorphism strongly associated with LP in Europeans (-13,910 C/T) indicates that the derived allele is recent in origin and has been subject to strong positive selection. Furthermore, ancient DNA work has shown that the -13,910*T (derived) allele was very rare or absent in early Neolithic central Europeans. It is unlikely that LP would provide a selective advantage without a supply of fresh milk, and this has lead to a gene-culture coevolutionary model where lactase persistence is only favoured in cultures practicing dairying, and dairying is more favoured in lactase persistent populations. We have developed a flexible demic computer simulation model to explore the spread of lactase persistence, dairying, other subsistence practices and unlinked genetic markers in Europe and western Asia's geographic space. Using data on -13,910*T allele frequency and farming arrival dates across Europe, and approximate Bayesian computation to estimate parameters of interest, we infer that the -13,910*T allele first underwent selection among dairying farmers around 7,500 years ago in a region between the central Balkans and central Europe, possibly in association with the dissemination of the Neolithic Linearbandkeramik culture over Central Europe. Furthermore, our results suggest that natural selection favouring a lactase persistence allele was not higher in northern latitudes through an increased requirement for dietary vitamin D. Our results provide a coherent and spatially explicit picture of the coevolution of lactase persistence and dairying in Europe
Efectos del consumo de Omegas 6 y 3 sobre los niveles de ácido araquidónico y su asociación con la adicción a la comida en adultos obesos: Un estudio piloto
No full textThe obesity is considered the 21st century pandemic and its prevalence in the world is increasing, this pattern is observed in Colombia according to the results of the ENSIN 2010 and 2015. This disease is caused by an energy imbalance lead by a low energy expenditure in sedentary individuals and overconsumption of high energy foods, which can be considered as an addictive like behavior in specific conditions determined in the Yale food addiction scale.
The neurobiological and behavioral changes exhibited in obese people with food addiction can be associated to the activity of the endocannabinoid system in the central nervous system, given the fact that obese population have high rates of consumption of food rich in linoleic acid or 6 omega, which derivative form, the arachidonic acid is the main precursor of endocannabinoids, compounds that have increased plasmatic levels in obese people. The main purpose of this study is to determine the association between plasmatic levels of arachidonic acid and diagnostic criteria of food addiction in
obese adults after inducing changes in the essential fatty acids intake. This thesis consists in a prospective quasi-experimental with clinical trial model, non-randomized, single-blind, crossover pilot study, conducted in obese adults whom were offered two nutritional treatments of obesity, one of these with a decrease in the omega 6 consumption and an increase in the omega 3 intake. The main findings indicate a positive correlation between arachidonic acid plasmatic levels and the scoring in the food addiction scale in individuals exposed to the experimental nutritional treatment. These results are held by the statistically significant decrease in plasmatic levels of arachidonic acid, the score in the food addiction scale, the body weight and the triglycerides
plasma concentration found in the participants who had received the intervention that modified the consumption of essential fatty acids. Other variables such as body fat percentage and plasmatic levels of total cholesterol, HDL and LDL did not exhibit expected behaviors according to the literature, so it is thought that the time of exposure to interventions was not enough in order to get significant changes in suchLa obesidad es considerada la pandemia del siglo XXI y sus prevalencias en el mundo van en aumento, lo cual coincide con el patrón reportado en Colombia por la ENSIN 2010 y 2015. Esta enfermedad tiene lugar cuando se genera un desbalance energético producto de un bajo gasto de energía en individuos inactivos físicamente con un consumo excesivo de alimentos ricos en energía, el cual puede considerarse como una conducta adictiva en condiciones específicas determinadas en la escala de adicción a la comida de Yale.
Los diferentes cambios neurobiológicos y conductuales evidenciados en individuos obesos con adicción a la comida pueden estar asociados a la actividad del sistema endocannabinoide en el sistema nervioso central, debido a que los alimentos con un mayor consumo por parte de la población obesa tienen un alto aporte de Omega 6, a partir del que se produce el ácido araquidónico, que a su vez es el principal precursor de los cannabinoides endógenos, compuestos que suelen encontrarse aumentados a nivel plasmático en personas con obesidad. De manera que el objetivo general del estudio consiste en establecer una relación entre niveles plasmáticos de ácido araquidónico y la presencia de criterios de la adicción a la comida en adultos obesos tras efectuar cambios a nivel de la ingesta dietaría de alimentos fuente de Omegas 6 y alimentos fuente de 3.
La presente tesis consiste en un estudio piloto cuasiexperimental prospectivo con modelo de ensayo clínico, no aleatorizado, simple ciego, cruzado en dos tiempos, efectuado en adultos obesos a quienes les son ofrecidos dos tratamientos nutricionales para el manejo de la obesidad, uno de estos con una disminución en el consumo de Omega 6 y un aumento en el aporte de Omega 3, encontrando una correlación positiva entre los niveles plasmáticos de ácido araquidónico y el puntaje en la escala de adicción a la comida en individuos tras su exposición al tratamiento experimental. Tales hallazgos se soportan en la disminución estadísticamente significativa de los niveles plasmáticos de ácido araquidónico, el puntaje en la escala de adicción a la comida, el peso corporal y las concentraciones plasmáticas de triglicéridos en los participantes que habían recibido la intervención dietaría con modificación en el consumo de ácidos grasos esenciales. Otras variables como el porcentaje de grasa corporal y los niveles plasmáticos de colesterol total, HDL y LDL no presentaron comportamientos esperados según la literatura, por lo que se piensa que el tiempo de exposición a las intervenciones no fue suficiente en orden de obtener cambios significativos en estas.Línea de Investigación: Compuestos Bioactivos y su Impacto en la SaludMaestrí
A new population of very high energy gamma-ray sources in the Milky Way
No full textVery high energy γ-rays probe the long-standing mystery of the origin of cosmic rays. Produced in the interactions of accelerated particles in astrophysical objects, they can be used to image cosmic particle accelerators. A first sensitive survey of the inner part of the Milky Way with the High Energy Stereoscopic System (HESS) reveals a population of eight previously unknown firmly detected sources of very high energy γ-rays. At least two have no known radio or x-ray counterpart and may be representative of a new class of “dark” nucleonic cosmic ray sources.F. Aharonian, A. G. Akhperjanian, K. M. Aye, A. R. Bazer-Bachi, M. Beilicke, W. Benbow, D. Berge, P. Berghaus, K. Bernlöhr, C. Boisson, O. Bolz, C. Borgmeier, I. Braun, F. Breitling, A. M. Brown, J. Bussons Gordo, P. M. Chadwick, L. M. Chounet, R. Cornils, L. Costamante, B. Degrange, A. Djannati-Ataï, L. O'C. Drury, G. Dubus, T. Ergin, P. Espigat, F. Feinstein, P. Fleury, G. Fontaine, S. Funk, Y. A. Gallant, B. Giebels, S. Gillessen, P. Goret, C. Hadjichristidis, M. Hauser, G. Heinzelmann, G. Henri, G. Hermann, J. A. Hinton, W. Hofmann, M. Holleran, D. Horns, O. C. de Jager, I. Jung, B. Khélifi, Nu. Komin, A. Konopelko, I. J. Latham, R. Le Gallou, A. Lemière, M. Lemoine, N. Leroy, T. Lohse, A. Marcowith, C. Masterson, T. J. L. McComb, M. de Naurois, S. J. Nolan, A. Noutsos, K. J. Orford, J. L. Osborne, M. Ouchrif, M. Panter, G. Pelletier, S. Pita, G. Pühlhofer, M. Punch, B. C. Raubenheimer, M. Raue, J. Raux, S. M. Rayner, I. Redondo, A. Reimer, O. Reimer, J. Ripken, L. Rob, L. Rolland, G. Rowell, V. Sahakian, L. Saugé, S. Schlenker, R. Schlickeiser, C. Schuster, U. Schwanke, M. Siewert, H. Sol, R. Steenkamp, C. Stegmann, J.-P. Tavernet, R. Terrier, C. G. Théoret, M. Tluczykont, D. J. van der Walt, G. Vasileiadis, C. Venter, P. Vincent, B. Visser, H. J. Völk, S. J. Wagne
Carga mecánica como regulador de la osteogénesis en células madre mesenquimales humanas
No full textEl papel de la estimulación mecánica en la diferenciación de las células madre mesenquimales humanas (CMMHs) es una alternativa terapéutica para aplicaciones en ingeniería tisular. Este estudio evaluó el efecto de cargas mecánicas sobre la diferenciación de las CMMHs, y los mecanismos celulares que intervienen en el proceso de mecanotransducción. Las CMMHs se sembraron en frascos de cultivo de 75cm2 y fueron expuestas a tensión uniaxial de deformación de 500, 1000, 1500 y 2000 micro strains (μH), con una intensidad de 9 ciclos/minuto por 3 horas durante 4 días consecutivos. Se evaluó la actividad transcripcional de los factores de transcripción Runx2 y Sox9 y de los genes de Osteocalcina (OC), Colágeno tipo 1 (Col-1) y Fosfatasa Alcalina (ALP). Después de la exposición al estímulo, los marcadores osteogénicos Col-1, OC, y ALP se expresaron temporalmente; y los factores de transcripción Runx2 y Sox9 disminuyeron la expresión con respecto a las células de grupo control (sin estímulo), sugiriendo que el estímulo mecánico indujo la diferenciación de las células CMMHs a linaje osteoblástico. La identificación de los genes que traducen los estímulos mecánicos en las CMMHs y modulan la diferenciación osteogénica, tienen proyección directa en medicina regenerativa a través del desarrollo y perfeccionamiento del enfoque de ingeniería de tejidos funcionales
OC-0052: Late toxicity in the randomized phase III Dutch Hypofractionation Trial for prostate cancer patients (HYPRO)
No full textAdditional file 7 of Biogeographical survey of soil microbiomes across sub-Saharan Africa: structure, drivers, and predicted climate-driven changes
No full textAdditional file 7. Figure S7. MIROC6 model predictions for mean annual temperature (oC) (A) and mean annual precipitation (mm) (B) under too different GH emission scenarios (SSP126 and SSP585), predicted for 2040-2060 and 2080-2100 temporal windows. The predicted datasets are grouped according to country, as indicated by the vertical dashed lines
Additional file 7 of Biogeographical survey of soil microbiomes across sub-Saharan Africa: structure, drivers, and predicted climate-driven changes
No full textAdditional file 7. Figure S7. MIROC6 model predictions for mean annual temperature (oC) (A) and mean annual precipitation (mm) (B) under too different GH emission scenarios (SSP126 and SSP585), predicted for 2040-2060 and 2080-2100 temporal windows. The predicted datasets are grouped according to country, as indicated by the vertical dashed lines
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