544 research outputs found
Was macht âguteâ BiologielehrkrĂ€fte aus?:Befragungen von Lehrenden in der Didaktik der Biologie und Biologie-Lehramtsstudierenden an deutschen Hochschulen
Im Projekt âOptimierung der Biologie-Lehramtsausbildung in gemeinsamer Anstrengung (OBLigAt)â kommen Vorstellungen und Standpunkte von Biologie-Fachleitern, Biologiedidaktik-Dozenten an den Hochschulen, Biologie-Lehramtsstudierenden und -Referendaren zur Verbesserung der Ausbildung zum Ausdruck. Es werden die Ergebnisse von 79 Hochschuldozenten in der Didaktik der Biologie und von 442 Biologie-Lehramtsstudenten vorgestellt. Nach ihrer Meinung werden in den fachdidaktischen Studienanteilen viele Aspekte, die zu gutem Unterricht fĂŒhren sollen, gut bis befriedigend behandelt. GrundsĂ€tzlich werden hierbei die Bedeutung der BerĂŒcksichtigung von SchĂŒlervorstellungen erkannt sowie personale und diagnostische Kompetenzen ausgebildet. Diskrepanzen zwischen der Schwerpunktsetzung der Dozenten und den Vorstellungen der Studierenden liegen in der Forderung der Studierenden nach mehr praktischen Aspekten, die sich unmittelbar fĂŒr den Unterricht umsetzen lassen. Eine theoretische Fundierung als Basis der Unterrichtsgestaltung rĂŒckt eher fĂŒr Dozenten in den Vordergrund. Insgesamt ist die Kooperation zwischen Fachwissenschaft, Didaktik und PĂ€dagogik zu optimieren. Die Ergebnisse bieten Ansatzpunkte, die Ausbildung im Sinne des Projekts OBLigAt zu verbessern
Instability of the Time Dependent Horava-Witten Model
We consider scalar perturbations in the time-dependent Ho\u{r}ava-Witten
Model in order to probe its stability. We show that during the non-singular
epoque the model evolves without instabilities until it encounters the
curvature singularity where a big crunch is supposed to occur. We compute the
frequencies of the scalar field oscillation during the stable period and show
how the oscillations can be used to prove the presence of such a singularity.Comment: 12 pages, 4 figures. References added. Some comments clarified.
Accepted in Phys. Rev.
Late-time tails, entropy aspects, and stability of black holes with anisotropic fluids
In this work we consider black holes surrounded by anisotropic fluids in four
dimensions. We first study the causal structure of these solutions showing some
similarities and differences with Reissner-Nordstr\"om-de Sitter black holes.
In addition, we consider scalar perturbations on this background geometry and
compute the corresponding quasinormal modes. Moreover, we discuss the late-time
behavior of the perturbations finding an interesting new feature, i.e., the
presence of a subdominant power-law tail term. Likewise, we compute the
Bekenstein entropy bound and the first semiclassical correction to the black
hole entropy using the brick wall method, showing their universality. Finally,
we also discuss the thermodynamical stability of the model.Comment: 23 pages, 4 figure
Shortcuts in a Nonlinear Dynamical Braneworld in Six Dimensions
We consider a dynamical brane world in a six-dimensional spacetime containing
a singularity. Using the Israel conditions we study the motion of a 4-brane
embedded in this setup. We analyse the brane behaviour when its position is
perturbed about a fixed point and solve the full nonlinear dynamics in the
several possible scenarios. We also investigate the possible gravitational
shortcuts and calculate the delay between graviton and photon signals and the
ratio of the corresponding subtended horizons.Comment: 26 pages, 9 figures. References and discussion added. Title changed
to match the version accepted in Class. and Quant. Gra
Stability Analysis and Area Spectrum of 3-Dimensional Lifshitz Black Holes
In this work, we probe the stability of a three-dimensional Lifshitz
black hole by using scalar and spinorial perturbations. We found an analytical
expression for the quasinormal frequencies of the scalar probe field, which
perfectly agree with the behavior of the quasinormal modes obtained
numerically. The results for the numerical analysis of the spinorial
perturbations reinforce the conclusion of the scalar analysis, i.e., the model
is stable under scalar and spinor perturbations. As an application we found the
area spectrum of the Lifshitz black hole, which turns out to be equally spaced.Comment: 23 pages, 6 figures. References added. Version to appear in Phys.
Rev.
Perturbations of Gauss-Bonnet Black Strings in Codimension-2 Braneworlds
We derive the Lichnerowicz equation in the presence of the Gauss-Bonnet term.
Using the modified Lichnerowicz equation we study the metric perturbations of
Gauss-Bonnet black strings in Codimension-2 Braneworlds.Comment: 26 pages, no figures, clarifying comments and one reference added, to
be published in JHE
HIV seroconcordance among heterosexual couples in rural KwaZulu-Natal, South Africa: a population-based analysis
Introduction
High levels of HIV seroconcordance at the population level reduce the potential for effective HIV transmission. However, the level of HIV seroconcordance is largely unknown among heterosexual couples in subâSaharan Africa. We aimed to quantify the population level HIV seroconcordance in stable heterosexual couples in rural South Africa.
Methods
We followed adults (â„15 years old) using a populationâbased, longitudinal and open surveillance system in KwaZuluâNatal, South Africa, from 2003 to 2016. Sexual partnerships and HIV status were confirmed via household surveys and annual HIV surveillance. We calculated the proportions of HIV seroconcordance and serodiscordance in stable sexual partnerships and compared them to the expected proportions under the assumption of random mixing using individualâbased microsimulation models. Among unpartnered individuals, we estimated the incidence rates and hazard of sexual partnership formation with HIVâpositive or HIVânegative partners by participants' own timeâvarying HIV status. Competing risks survival regressions were fitted adjusting for sociodemographic and clinical factors. We also calculated Newman's assortativity coefficients.
Results
A total of 18,341 HIVânegative and 11,361 HIVâpositive individuals contributed 154,469 personâyears (PY) of followâup. Overall, 28% of the participants were in stable sexual partnerships. Of the 677 newly formed stable sexual partnerships, 7.7% (95% CI: 5.8 to 10.0) were HIVâpositive seroconcordant (i.e. both individuals in the partnership were HIVâpositive), which was three times higher than the expected proportion (2.3%) in microsimulation models based on random mixing. The incidence rates of sexual partnership formation were 0.54/1000PY with HIVâpositive, 1.12/1000PY with HIVânegative and 2.65/1000PY with unknown serostatus partners. HIVâpositive individuals had 2.39 (95% CI: 1.43 to 3.99) times higher hazard of forming a sexual partnership with an HIVâpositive partner than did HIVânegative individuals after adjusting for age, oppositeâsex HIV prevalence (by 5âyears age groups), HIV prevalence in the surrounding community, ART coverage and other sociodemographic factors. Similarly, forming a sexual partnership with an HIVânegative partner was 1.47 (95% CI: 1.01 to 2.14) times higher in HIVânegative individuals in the adjusted model. Newman's coefficient also showed that assortativity by participant and partner HIV status was moderate (r = 0.35).
Conclusions
A high degree of population level HIV seroconcordance (both positive and negative) was observed at the time of forming new sexual partnerships. Understanding factors driving these patterns may help the development of strategies to bring the HIV epidemic under control
El control financiero del estado
Tesis (Contador Auditor)El trabajo que procederemos a desarrollar
pretende determinar los aspectos fundamentales del sistema de
Control Financiero del Estado, dando a conocer una metodologĂa
que contemple los aspectos legales contables y administrativos
que se aplican en la fiscalizaciĂłn que ejerce la
contralorĂa General de la RepĂșblica, en el sector pĂșblico
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