309 research outputs found
An alternative singularity-free cosmological scenario from cusp geometries
We study an alternative geometrical approach on the problem of classical
cosmological singularity. It is based on a generalized function which consists of a cusped coupled isosurface.
Such a geometry is computed and discussed into the context of Friedmann
singularity-free cosmology where a pre-big bang scenario is considered.
Assuming that the mechanism of cusp formation is described by non-linear
oscillations of a pre-big bang extended very high energy density field (), we show that the action under the gravitational
field follows a tautochrone of revolution, understood here as the primary
projected geometry that alternatively replaces the Friedmann singularity in the
standard big bang theory. As shown here this new approach allows us to
interpret the nature of both matter and dark energy from first geometric
principles.Comment: Proceedings of Sixth International School on Field Theory and
Gravitation-2012 - by American Institute of Physic
Value-at-Risk and Tsallis statistics: risk analysis of the aerospace sector
In this study, we analyze the aerospace stocks prices in order to
characterize the sector behavior. The data analyzed cover the period from
January 1987 to April 1999. We present a new index for the aerospace sector and
we investigate the statistical characteristics of this index. Our results show
that this index is well described by Tsallis distribution. We explore this
result and modify the standard Value-at-Risk (VaR), financial risk assessment
methodology in order to reflect an asset which obeys Tsallis non-extensive
statistics.Comment: 10 pages, 4 figures, 1 table, to appear in Physica
Constraints on feedback processes during the formation of early-type galaxies
Galaxies are found to obey scaling relations between a number of observables.
These relations follow different trends at the low- and the high-mass ends. The
processes driving the curvature of scaling relations remain uncertain. In this
letter, we focus on the specific family of early-type galaxies, deriving the
star formation histories of a complete sample of visually classified galaxies
from SDSS-DR7 over the redshift range 0.01<z<0.025, covering a stellar mass
interval from 10^9 to 3 x 10^11 Msun. Our sample features the characteristic
"knee" in the surface brightness vs. mass distribution at Mstar~3 x 10^10 Msun.
We find a clear difference between the age and metallicity distributions of the
stellar populations above and beyond this knee, which suggests a sudden
transition from a constant, highly efficient mode of star formation in
high-mass galaxies, gradually decreasing towards the low-mass end of the
sample. At fixed mass, our early-type sample is more efficient in building up
the stellar content at early times in comparison to the general population of
galaxies, with half of the stars already in place by redshift z~2 for all
masses. The metallicity-age trend in low-mass galaxies is not compatible with
infall of metal-poor gas, suggesting instead an outflow-driven relation.Comment: 12 pages,3 figures, accepted for publication in ApJ
Echo-g outputs of the 1000hpa zonal wind and temperature fields over southern South America for the last millennium
Durante el último milenio han ocurrido importantes variaciones climáticas. Luego de la Anomalía Climática Medieval tuvo lugar un prolongado período de generalizadas condiciones frías llamado Pequeña Edad de Hielo seguido por el actual Calentamiento Global . Con el Modelo de Circulación General ECHO-G se produjeron escenarios transientes que simulan las anomalías mensuales del período 1000 a 1990 AD. En este trabajo primeramente se analiza la capacidad del ECHO-G de reproducir los campos de temperatura y componente zonal del viento, ambos en el nivel de 1000hPa, en la región del cono sur de Sudamérica utilizando como referencia el re-análisis NCEP/NCAR para el período 1961-1990 testeando las diferencias de los valores medios y los desvíos estándar para la temperatura y la componente zonal del viento. En el centro norte del país el modelo ECHO-G simula temperaturas superiores a las del re-análisis NCEP-NCAR. Sin embargo, las diferencias entre el modelo y el re-análisis son menores en la Patagonia y particularmente despreciables en la región del Lago Cardiel. Por lo cual las simulaciones de los últimos 1000 años pueden ser utilizadas para analizar la variabilidad paleoclimática de esa región. Los patrones de anomalías para los Mínimos solares de Maünder y Dalton obtenidos con el ECHO-G respecto al período 1961-1990 resultan similares pero más intensos en el caso del Mínimo de Maünder. Las láminas alternantes claras y oscuras (ritmitas anuales o varves) de los testigos sedimentarios del Lago Cardiel en Patagonia central han sido previamente interpretadas como el resultado de la intensidad de los vientos regionales. En el trabajo además se comparara los espesores de dichas láminas con los valores de la componente zonal del viento y la temperatura en 1000hPa para el período comprendido entre los años 1000 a 1990 AD. Las series filtradas con promedios móviles de 80 años, que realzarían el efecto del ciclo de Gleissberg y otras periodicidades solares de menor frecuencia, sugieren relación inversa principalmente entre la componente zonal del viento y los espesores de las láminas oscuras. Esta inferencia es confirmada mediante los espectros de onditas de coherencia entre ambas series. Este primer resultado indicaría que la serie de espesores de láminas oscuras podría ser utilizada como proxy dato de la intensidad de la componente zonal del viento sobre la Patagonia.Important climatic variations have occurred during the last millennium. After the Medieval Warming period, a long period of cold conditions, called Little Ice Age , took place, being followed by the current Global Warming . Transient scenarios have been developed using the General Circulation Model ECHO-G to simulate the monthly anomalies for the period 1000-1990 AD. Firstly, the research analyses the ability of ECHO-G model to reproduce the temperature and zonal wind component at 1000hPa over southern South America in the period 1961-1990 to contrast the outputs with the NCEP/NCAR Reanalysis data. The difference of means and standard deviations has been tested for both temperature and zonal wind. In central-north Argentina, ECHO-G simulates higher temperatures than the NCEP/NCAR Reanalysis. However, the differences between model and reanalysis are smaller in the Patagonia region, especially close to the Cardiel Lake. Hence, extended simulations for the last millennium can be used to analyse paleoclimatic variations in such region. Although anomaly patterns between Maünder and Dalton solar Minimums are similar with respect to the 1960-1990 period, their amplitudes are higher for the Maünder Minimum. The alternating light and dark laminae (annual rythmites or varves) from the Cardiel Lake sediments in central Patagonia were previously interpreted as the result of regional wind intensity variations. In this work their thickness time series has been compared with the local zonal wind component and temperature time series at 1000hPa in the period 1000 AD and 1990 AD. A centered 80-years moving average has been applied to these time series to enhance the effect of the Gleissberg solar cycle and other lower frequency periodicities. The results show a reverse relationship between the zonal wind component and the thickness of the dark laminae. Such an inference is confirmed employing Coherence Wavelet Spectrum between the time series. The latter indicates that the thickness of the dark laminae can be used as a proxy for the strengthening of the zonal wind component over Patagonia.Fil: Maenza, Reinaldo Agustín. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Compagnucci, Rosa Hilda. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ariztegui, Daniel. Universidad de Ginebra; Suiz
Uso de materiais alternativos em experimentos de química, na 1ª série do ensino médio, em uma escola da comunidade Vão de Almas
Trabalho de Conclusão de Curso (graduação)—Universidade de Brasília, Faculdade UnB Planaltina (FUP), 2018.Este trabalho está relacionado à experimentação no ensino de Química na
Escola do Campo, na perspectiva de interligar os conteúdos ministrados em sala
de aula com o conhecimento já adquirido pelos educandos, de maneira
educativa, com o objetivo de motivá-los a aprenderem a Química fazendo uso de
materiais alternativos, onde o conhecimento científico vem como forma de
aprimorar seus conhecimentos prévios visando uma melhor forma de ministrar as
aulas. Sendo que os materiais utilizados pelas escolas do campo não despertam
no educando o interesse em aprender o conteúdo de forma efetiva. Nesta
monografia busca-se mostrar a importância das atividades experimentais, com o
uso de recursos alternativos, no processo de ensino aprendizagem dos
educandos do campo.This work is related to the experimentation in teaching chemistry at the school of the
field, in order to interconnect the content taught in the classroom with the knowledge
acquired by students, educational way, aiming to motivate them to learn Chemistry,
making use of alternative materials, where scientific knowledge comes as a way to
improve their previous knowledge, seeking a better way to teach the classes. And the
materials used by schools in the field does not awaken the interest of the student in
learning content effectively in this monograph, we seek to show the importance of
experimental activities, with the use of alternative resources, in the process of
teaching-aprendizage
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