1,431 research outputs found
Motion of buoyant particles and coarsening of solid-liquid mixtures in a random acceleration field
Flow induced by a random acceleration field (g-jitter) is considered in two
related situations that are of interest for microgravity fluid experiments: the
random motion of an isolated buoyant particle and coarsening of a solid-liquid
mixture. We start by analyzing in detail actual accelerometer data gathered
during a recent microgravity mission, and obtain the values of the parameters
defining a previously introduced stochastic model of this acceleration field.
We then study the motion of a solid particle suspended in an incompressible
fluid that is subjected to such random accelerations. The displacement of the
particle is shown to have a diffusive component if the correlation time of the
stochastic acceleration is finite or zero, and mean squared velocities and
effective diffusion coefficients are obtained explicitly. Finally, the effect
of g-jitter on coarsening of a solid-liquid mixture is considered. Corrections
due to the induced fluid motion are calculated, and estimates are given for
coarsening of Sn-rich particles in a Sn-Pb eutectic fluid, experiment to be
conducted in microgravity in the near future.Comment: 25 pages, 4 figures (included). Also at
http://www.scri.fsu.edu/~vinals/ross2.p
Quadratic vector fields with a weak focus of third order
We study phase portraits of quadratic vector fields with a weak focus of third order at the origin. We show numerically the existence of at least 20 different global phase portraits for such vector fields coming from exactly 16 different local phase portraits available for these vector fields. Among these 20 phase portraits, 17 have no limit cycles and three have at least one limit cycle
Como aumentar a fertilidade do seu rebanho ovino e reduzir a mortalidade de cordeiros.
Com o aumento do rebanho tipo carne nas últimas décadas, a fertilidade das ovelhas tornou-se um aspecto ainda mais importante no desempenho econômico da produção ovina.bitstream/item/63675/1/CT-54-2006.pd
O uso da avaliação da condição corporal visando máxima eficiência produtiva dos ovinos.
A avaliação subjetiva do nível nutricional dos ovinos pode ser feita de forma bastante simples através do uso de escores da composição corporal, denominado de avaliação da condição corporal (CC).bitstream/item/55774/1/CT-57-2006.pd
Alternativa hormonal para o preparo de rufiões ovinos.
Rufiões são utilizados na implementação de várias biotécnicas reprodutivas em ovinos, como por exemplo, para detecção de cios na inseminação artificial, indução de ovulação fora da estação reprodutiva (efeito macho) e determinação da eficácia do acasalamento, pela taxa de não retorno ao cio, ao final da tempo.bitstream/item/63500/1/CO56-2006.pd
Alternativas para aumentar a fertilidade pós-parto de bovinos de corte em sistemas extensivos de criação.
Situação atual; Causas principais; Medidas de baixo custo que podem ser tomadas para melhorar a taxa reprodutiva do rodeio; Ajustes na lotação animal; Diagnóstico de gestação; Manejo nutricional; Avaliação da condição corporal; Seleção por fertilidade; O designe; Duração do período de acasalamento; Formação de grupos de vacas em função da data do parto; Efeito touro; Recomendações.bitstream/item/63411/1/ct22-1999.pd
Um sistema de registro simples para um manejo reprodutivo mais eficiente do rebanho leiteiro.
bitstream/item/55729/1/CR-31-circular-tecnica-rebanho-leiteiro-embrapa.pd
The escape problem under stochastic volatility: the Heston model
We solve the escape problem for the Heston random diffusion model. We obtain
exact expressions for the survival probability (which ammounts to solving the
complete escape problem) as well as for the mean exit time. We also average the
volatility in order to work out the problem for the return alone regardless
volatility. We look over these results in terms of the dimensionless normal
level of volatility --a ratio of the three parameters that appear in the Heston
model-- and analyze their form in several assymptotic limits. Thus, for
instance, we show that the mean exit time grows quadratically with large spans
while for small spans the growth is systematically slower depending on the
value of the normal level. We compare our results with those of the Wiener
process and show that the assumption of stochastic volatility, in an apparent
paradoxical way, increases survival and prolongs the escape time.Comment: 29 pages, 12 figure
Option pricing under stochastic volatility: the exponential Ornstein-Uhlenbeck model
We study the pricing problem for a European call option when the volatility
of the underlying asset is random and follows the exponential
Ornstein-Uhlenbeck model. The random diffusion model proposed is a
two-dimensional market process that takes a log-Brownian motion to describe
price dynamics and an Ornstein-Uhlenbeck subordinated process describing the
randomness of the log-volatility. We derive an approximate option price that is
valid when (i) the fluctuations of the volatility are larger than its normal
level, (ii) the volatility presents a slow driving force toward its normal
level and, finally, (iii) the market price of risk is a linear function of the
log-volatility. We study the resulting European call price and its implied
volatility for a range of parameters consistent with daily Dow Jones Index
data.Comment: 26 pages, 6 colored figure
Contribució a la flora dels macromicets de l'illa de Mallorca
Com a resultat de les prospeccions micològiques realitzades a Mallorca entre els anys 1983 i 1990, donem a conèixer un catàleg de 218 taxons (8 Ascomycetes i 210 Basidiomycetes), dels quals creiem que 74 corresponen a citacions noves per a l'illa. En destaquem, entre d'altres: Cordyceps militaris (L.) Link, Daldinia vernicosa (Schw.) Ces. et de Not., Dichomitus campestris (Quél.) Domanski et Ori., Agaricus lanipes (Moell. et Schaeff.) Sing., Amanita boudieri Barla, Clitocybe lituus (Fr.) Metr., Hygrocybe reai Mre., Inocybe tenebrosa Quél., Leucopaxillus tricolor (Peck) Kühn, i Russula seperina Dupain
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