295 research outputs found
O impacto do homem na estrutura de uma espécie: Portugal, um paradigma
A bacia do Mediterrâneo é caracterizada pelo tradicional desaparecimento da floresta devido à acção do Homem e o impacto humano tem tido influência na alteração da diversidade genética. O pinheiro bravo ocorre em populações fragmentadas na região oeste da bacia do Mediterrâneo e a sua área de distribuição tem sido alterada nos últimos séculos devido a intensa florestação, em particular no SW de França e no Noroeste da Península Ibérica e, também, devido ao comportamento invasivo desta espécie em áreas perturbadas do ponto de vista ecológico. Nesta apresentação pretendemos sintetizar e discutir o resultado de estudos que utilizaram técnicas moleculares para revelar a diversidade do pinheiro bravo e, também, o impacto humano na sua estrutura genética; que é demonstrado paradigmaticamente em Portugal.
Os parâmetros genéticos estimados com base em microsatélites do cloroplasto (cpSSR) revelaram que a diversidade genética é muito elevada ao nível da distribuição da espécie. Observou-se uma clara e significativa diferenciação entre grupos de populações de diferente origem geográfica (Portugal, França, Itália, Espanha e Marrocos). Pelo contrário, o grau de divergência dentro dos países é geralmente muito baixo ou próximo de zero, o que indica uma variação homogénea dentro dos grupos. A presença de diferenciação entre grupos de populações de diferentes áreas reflecte a existência de diferentes refúgios durante o Quaternário. Em França, o padrão haplotípico sugere uma mistura de material proveniente de diferentes origens. Só foram encontrados 3 mitótipos, usando marcadores mitocondriais, marcador de herança maternal, o que proporciona uma imagem clara de áreas colonizadas a partir dos diferentes refúgios; nem uma só população possui uma composição mista.
Uma análise filogenética feita com base em isoenzimas mostrou que a estrutura geográfica do pinheiro bravo na Península Ibérica (PI) é muito elevada. As populações de Noroeste formam um grupo e as de Sudeste outro. Observou-se níveis elevados de diversidade nas populações de Este e Sul e uma redução importante da variabilidade em populações da região Noroeste da PI. No entanto, pode ter existido em Portugal um refúgio, pois o pinheiro bravo pode ter sobrevivido durante a última glaciação em zonas abrigadas e de baixa altitude junto ao Oceano Atlântico, o que parece também ser evidente devido a descobertas de pólen e carvão fóssil.
A distribuição da variação genética do pinheiro bravo em Portugal, observada através de cpSSR indica que a diferenciação entre populações é baixa e que a diversidade existe principalmente dentro das populações. Não se observa nenhum padrão geográfico, mas as evidências existentes de uma forte influência antrópica antropogénica associada a um fluxo genético extensivo poderiam explicar esse resultado
Host-associated biotypes within West African populations of the whitefly Bemisia tabaci (Genn.), (Hom., Aleyrodidae)
Finite Number of States, de Sitter Space and Quantum Groups at Roots of Unity
This paper explores the use of a deformation by a root of unity as a tool to
build models with a finite number of states for applications to quantum
gravity. The initial motivation for this work was cosmological breaking of
supersymmetry. We explain why the project was unsuccessful. What is left are
some observations on supersymmetry for q-bosons, an analogy between black holes
in de Sitter and properties of quantum groups, and an observation on a
noncommutative quantum mechanics model with two degrees of freedom, depending
on one parameter. When this parameter is positive, the spectrum has a finite
number of states; when it is negative or zero, the spectrum has an infinite
number of states. This exhibits a desirable feature of quantum physics in de
Sitter space, albeit in a very simple, non-gravitational context.Comment: 25 pages, 5 figure
A record-linkage study of the development of hepatocellular carcinoma in persons with hepatitis C infection in Scotland
We investigated trends in first time hospital admissions and deaths attributable to hepatocellular carcinoma (HCC) in a large population based cohort of 22 073 individuals diagnosed with hepatitis C viral (HCV) infection through laboratory testing in Scotland in 1991 2006. We identified new cases of HCC through record linkage to the national inpatient hospital discharge database and deaths registry. A total of 172 persons diagnosed with HCV were admitted to hospital or died with first time mention of HCC. Hepatocellular carcinoma incidence increased between 1996 and 2006 (average annual change of 6.1, 95% confidence interval (CI):0.9 11.6%, P¼0.021). The adjusted relative risk of HCC was greater for males (hazard ratio¼2.7, 95% CI: 1.7 4.2), for those aged 60 years or older (hazard ratio ¼2.7, 95% CI: 1.9 4.1) compared with 50 59 years, and for those with a previous alcohol related hospital admission (hazard ratio¼2.5, 95% CI: 1.7 3.7). The risk of individuals diagnosed with HCV developing HCC was greatlyincreased compared with the general Scottish population (standardised incidence ratio¼127, 95% CI: 102 156). Owing to the advancing age of the Scottish HCV diagnosed population, the annual number of HCC cases is projected to increase, with a consequent increasing burden on the public healthcare system
Recombinant human activated protein C improves endotoxemia-induced endothelial dysfunction: a blood-free model in isolated mouse arteries
Recombinant human activated protein C (rhAPC) is one of the treatment panels for improving vascular dysfunction in septic patients. In a previous study, we reported that rhAPC treatment in rat endotoxemia improved vascular reactivity, although the mechanisms involved are still under debate. In the present study, we hypothesized that rhAPC may improve arterial dysfunction through its nonanticoagulant properties. Ten hours after injection of LPS in mice (50 mg/kg ip), aortic rings and mesenteric arteries were isolated and incubated with or without rhAPC for 12 h. Aortic rings were mounted in a myograph, after which arterial contractility and endothelium-dependent relaxation were measured in the presence or absence of nitric oxide synthase or cyclooxygenase inhibitors. Flow (shear stress)-mediated dilation with or without the above inhibitors was also measured in mesenteric resistance arteries. Protein expression was assessed by Western blotting. Lipopolysaccharide (LPS) reduced aortic contractility to KCl and phenylephrine as well as dilation to acetylcholine. LPS also reduced flow-mediated dilation in mesenteric arteries. In rhAPC-treated aorta and mesenteric arteries, contractility and endothelial responsiveness to vasodilator drug and shear stress were improved. rhAPC treatment also improved LPS-induced endothelial dysfunction; this effect was associated with an increase in the phosphorylated form of endothelial nitric oxide synthase and protein kinase B as well as cyclooxygenase vasodilatory pathways, thus suggesting that these pathways, together with the decrease in nuclear factor-κB activation and inducible nitric oxide synthase expression in the vascular wall, are implicated in the endothelial effect of rhAPC. In conclusion, ex vivo application of rhAPC improves arterial contractility and endothelial dysfunction resulting from endotoxemia in mice. This finding provides important insights into the mechanism underlying rhAPC-induced improvements on arterial dysfunction during septic shock
There's no place like home: seedling mortality contributes to the habitat specialisation of tree species across Amazonia
Understanding the mechanisms generating species distributions remains a challenge, especially in hyperdiverse tropical forests. We evaluated the role of rainfall variation, soil gradients and herbivory on seedling mortality, and how variation in seedling performance along these gradients contributes to habitat specialisation. In a 4-year experiment, replicated at the two extremes of the Amazon basin, we reciprocally transplanted 4638 tree seedlings of 41 habitat-specialist species from seven phylogenetic lineages among the three most important forest habitats of lowland Amazonia. Rainfall variation, flooding and soil gradients strongly influenced seedling mortality, whereas herbivory had negligible impact. Seedling mortality varied strongly among habitats, consistent with predictions for habitat specialists in most lineages. This suggests that seedling performance is a primary determinant of the habitat associations of adult trees across Amazonia. It further suggests that tree diversity, currently mostly harboured in terra firme forests, may be strongly impacted by the predicted climate changes in Amazonia
Realizations for Kepler and Oscillator Potentials and q-Canonical Transformations
The realizations of the Lie algebra corresponding to the dynamical symmetry
group SO(2,1) of the Kepler and oscillator potentials are q-deformed. The
q-canonical transformation connecting two realizations is given and a general
definition for q-canonical transformation is deduced. q-Schr\"{o}dinger
equation for a Kepler like potential is obtained from the q-oscillator
Schr\"{o}dinger equation. Energy spectrum and the ground state wave function
are calculated.Comment: 12 pages, Latex twice, (Comparison with the other approaches and some
refs. added. The version which will appear in J. Phys. A
Risk Factors for Hepatitis C Virus Transmission to Health Care Workers after Occupational Exposure: A European Case-Control Study
Background. Additional studies are required to identify risk factors for hepatitis C virus (HCV) transmission to health care workers after occupational exposure to HCV. Methods. We conducted a matched case-control study in 5 European countries from 1 January 1991 through 31 December 2002. Case patients were health care workers who experienced seroconversion after percutaneous or mucocutaneous exposure to HCV. Control subjects were HCV-exposed health care workers who did not experience seroconversion and were matched with case patients for center and period of exposure. Results. Sixty case patients and 204 control subjects were included in the study. All case patients were exposed to HCV-infected fluids through percutaneous injuries. The 37 case patients for whom information was available were exposed to viremic source patients. As risk factors for HCV infection, multivariate analysis identified needle placement in a source patient's vein or artery (odds ratio [OR], 100.1; 95% confidence interval [CI], 7.3-1365.7), deep injury (OR, 155.2; 95% CI, 7.1-3417.2), and sex of the health care worker (OR for male vs. female, 3.1; 95% CI, 1.0-10.0). Source patient HCV load was not introduced in the multivariate model. In unmatched univariate analysis, the risk of HCV transmission increased 11-fold for health care workers exposed to source patients with a viral load >6 log10 copies/mL (95% CI, 1.1-114.1), compared with exposures to source patients with a viral load ⩽4 log10 copies/mL. Conclusion. In this study, HCV occupational transmission was found to occur after percutaneous exposures. The risk of HCV transmission after percutaneous exposure increased with deep injuries and procedures involving hollow-bore needle placement in the source patient's vein or artery. These results highlight the need for widespread adoption of needlestick-prevention devices in health care settings, together with other preventive measure
Time quantization and q-deformations
We extend to quantum mechanics the technique of stochastic subordination, by
means of which one can express any semi-martingale as a time-changed Brownian
motion. As examples, we considered two versions of the q-deformed Harmonic
oscillator in both ordinary and imaginary time and show how these various cases
can be understood as different patterns of time quantization rules.Comment: 4 pages, 2 figure
Unified -deformation of one-parametric q-deformed oscillator algebras
We define a generalized -deformed oscillator
algebra and study the number of its characteristics. We describe the structure
function of deformation, analyze the classification of irreducible
representations and discuss the asymptotic spectrum behaviour of the
Hamiltonian. For a special choice of the deformation parameters we construct
the deformed oscillator with discrete spectrum of its "quantized coordinate"
operator. We establish its connection with the (generalized) discrete Hermite I
polynomials
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