14,527 research outputs found
False Vacuum Transitions - Analytical Solutions and Decay Rate Values
In this work we show a class of oscillating configurations for the evolution
of the domain walls in Euclidean space. The solutions are obtained
analytically. Phase transitions are achieved from the associated fluctuation
determinant, by the decay rates of the false vacuum.Comment: 6 pages, improved to match the final version to appear in EP
Chemical Evolution of the Galaxy Based on the Oscillatory Star Formation History
We model the star formation history (SFH) and the chemical evolution of the
Galactic disk by combining an infall model and a limit-cycle model of the
interstellar medium (ISM). Recent observations have shown that the SFH of the
Galactic disk violently variates or oscillates. We model the oscillatory SFH
based on the limit-cycle behavior of the fractional masses of three components
of the ISM. The observed period of the oscillation ( Gyr) is reproduced
within the natural parameter range. This means that we can interpret the
oscillatory SFH as the limit-cycle behavior of the ISM. We then test the
chemical evolution of stars and gas in the framework of the limit-cycle model,
since the oscillatory behavior of the SFH may cause an oscillatory evolution of
the metallicity. We find however that the oscillatory behavior of metallicity
is not prominent because the metallicity reflects the past integrated SFH. This
indicates that the metallicity cannot be used to distinguish an oscillatory SFH
from one without oscillations.Comment: 21 pages LaTeX, to appear in Ap
Uso da técnica da solarização como alternativa para o preparo do solo ou substrato para produção de mudas isentas de patógenos de solo.
O preparo de um solo ou substrato para o plantio de mudas sadias é extremamente importante, pois devem estar isentos de fitonematóides, pragas, doenças fúngicas e/ou bacterianas ou de sementes de plantas daninhas. Da mesma forma, o preparo desse substrato deve seguir a correta metodologia, de forma modo a preservar a população de micro-organismos benéficos vivos que garantirão a qualidade dos materiais que devam ser decompostos, fornecendo substâncias as quais que poderão aumentar a resistência das plantas a doenças e pragas, bem como auxiliar no controle biológico dessas pragas. Uso da técnica da solarização como alternativa para o preparo do solo.A esterilização dos solos ou substratos pode ser feita por produtos químicos. Porém, em sua maioria, esses produtos fumigantes têm sido banidos do mercado não somente em conseqüência às restrições ambientais, mas, também, à exigência do consumidor, por produtos de qualidade e sem riscos de contaminação por resíduos químicos. A desinfestação dos solos ou substratos por meio de produtos químicos, principalmente com defensivos de amplo espectro de ação, pode afetar a população de micro-organismos benéficos à cultura, bem como apresentar problemas quanto ao custo, eficiência e trazer contaminações ao ambiente e ao aplicador. Ademais, seu uso pode promover a seleção de patógenos cada vez mais resistentes a esses produtos químicos aplicados, bem como o envelhecimento da terra.bitstream/item/25503/1/cartilharitzinger.pd
HST Survey of Clusters in Nearby Galaxies. II. Statistical Analysis of Cluster Populations
We present a statistical system that can be used in the study of cluster
populations. The basis of our approach is the construction of synthetic cluster
color-magnitude-radius diagrams (CMRDs), which we compare with the observed
data using a maximum likelihood calculation. This approach permits a relatively
easy incorporation of incompleteness (a function of not only magnitude and
color, but also radius), photometry errors and biases, and a variety of other
complex effects into the calculation, instead of the more common procedure of
attempting to correct for those effects.
We then apply this procedure to our NGC 3627 data from Paper I. We find that
we are able to successfully model the observed CMRD and constrain a number of
parameters of the cluster population. We measure a power law mass function
slope of alpha = -1.50 +/- 0.07, and a distribution of core radii centered at
r_c = 1.53 +/- 0.15 pc. Although the extinction distribution is less
constrained, we measured a value for the mean extinction consistent with that
determined in Paper I from the Cepheids.Comment: 21 pages, 3 figures accepted for publication by A
The Dog on the Ship: The "Canis Major Dwarf Galaxy" as an Outlying Part of the Argo Star System
Overdensities in the distribution of low latitude, 2MASS giant stars are
revealed by systematically peeling away from sky maps the bulk of the giant
stars conforming to ``isotropic'' density laws generally accounting for known
Milky Way components. This procedure, combined with a higher resolution
treatment of the sky density of both giants and dust allows us to probe to
lower Galactic latitudes than previous 2MASS giant star studies. While the
results show the swath of excess giants previously associated with the
Monoceros ring system in the second and third Galactic quadrants at distances
of 6-20 kpc, we also find a several times larger overdensity of giants in the
same distance range concentrated in the direction of the ancient constellation
Argo. Isodensity contours of the large structure suggest that it is highly
elongated and inclined by about 3 deg to the disk, although details of the
structure -- including the actual location of highest density, overall extent,
true shape -- and its origin, remain unknown because only a fraction of it lies
outside highly dust-obscured, low latitude regions. Nevertheless, our results
suggest that the 2MASS M giant overdensity previously claimed to represent the
core of a dwarf galaxy in Canis Major (l ~ 240 deg) is an artifact of a dust
extinction window opening to the overall density rise to the more significant
Argo structure centered at larger longitude (l ~ 290 +- 10 deg, b ~ -4 +- 2
deg).Comment: 4 pages, 4 figure
Water, urea, sodium, chloride, and potassium transport in the in vitro isolated perfused papillary collecting duct
The collecting ducts are formed in the renal cortex by the connection of several nephrons. They descend within the medullary rays of the cortex, penetrate the outer medulla, and in the inner medulla successively fuse together. Based on these topographical considerations, we can recognize three segments of the collecting duct system: the cortical collecting tubule, the outer medullary collecting duct, and the papillary collecting duct. In this review, we call papillary collecting duct (PCD) that part of the collecting duct system that extends from the junction of outer medulla and inner medulla to the area cribosa. The collecting ducts in the outer medullary zone rarely have branches; however, such branches present in the inner zone have hampered study by micropuncture and microcatheterization techniques. The cortical collecting tubule (CCT) contains two types of cells, principal and intercalated cells, whereas in most animals the PCD contains only principal cells [1]. The general ultrastructure of the PCD cell seems simpler than that of the cortical collecting tubule, suggesting that the PCD is less specialized and less metabolically active than other nephron segments [2]. However, the accumulated data reveal a remarkable reabsorptive capacity for water and sodium by the PCD [3–6], thus indicating that this final part of the nephron plays an important role in the regulation of salt and water balance
A BGG-type resolution for tensor modules over general linear superalgebra
We construct a Bernstein-Gelfand-Gelfand type resolution in terms of direct
sums of Kac modules for the finite-dimensional irreducible tensor
representations of the general linear superalgebra. As a consequence it follows
that the unique maximal submodule of a corresponding reducible Kac module is
generated by its proper singular vector.Comment: 11pages, LaTeX forma
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