304 research outputs found
The Portevin-Le Chatelier effect in the Continuous Time Random Walk framework
We present a continuous time random walk model for the Portevin-Le Chatelier
(PLC) effect. From our result it is shown that the dynamics of the PLC band can
be explained in terms of the Levy Walk
Estrogens increase expression of bone morphogenetic protein 8b in brown adipose tissue of mice
Background: In mammals, white adipose tissue (WAT) stores fat and brown adipose tissue (BAT) dissipates fat to produce heat. Several studies showed that females have more active BAT. Members of the bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) families are expressed in BAT and are involved in BAT activity. We hypothesized that differential expression of BMPs and FGFs might contribute to sex differences in BAT activity. Methods: We investigated the expression of BMPs and FGFs in BAT of male and female C57BL/6J mice upon gonadectomy, cold exposure, and exposure to sex steroids. Results: Of the FGF family, BAT Fgf1, Fgf9, Fgf18, and Fgf21 expression was induced upon cold exposure, but only Fgf1 expression was obviously different between the sexes: females had 2.5-fold lower BAT Fgf1 than males. Cold exposure induced BAT Bmp4 and Bmp8b expression, but only Bmp8b differed between the sexes: females had 35-fold higher BAT Bmp8b than males. Ovariectomy almost completely blunted BAT Bmp8b expression, while orchidectomy had no effect. Male mice and ovariectomized female mice treated with diethylstilbestrol (DES) had approximately 350-fold and approximately 36-fold higher BAT Bmp8b expression, respectively. Ninety-day and 7-day treatment of female mice with dihydrotestosterone (DHT) decreased BAT Bmp8b expression by approximately fivefold and approximately fourfold, respectively. Finally, treatment of primary murine brown adipocytes with DES did not result in changes in Bmp8b expression. Conclusions: BAT Bmp8b expression in mice is positively regulated by presence of ovaries and estrogens such as DES
Multifractal burst in the spatio-temporal dynamics of jerky flow
The collective behavior of dislocations in jerky flow is studied in Al-Mg
polycrystalline samples subjected to constant strain rate tests. Complementary
dynamical, statistical and multifractal analyses are carried out on the
stress-time series recorded during jerky flow to characterize the distinct
spatio-temporal dynamical regimes. It is shown that the hopping type B and the
propagating type A bands correspond to chaotic and self-organized critical
states respectively. The crossover between these types of bands is identified
by a large spread in the multifractal spectrum. These results are interpreted
on the basis of competing scales and mechanisms.Comment: 4 pages, 6 figures To be published in Phys. Rev. Lett. (2001
Relaxation oscillations and negative strain rate sensitivity in the Portevin - Le Chatelier effect
A characteristic feature of the Portevin - Le Chatelier effect or the jerky
flow is the stick-slip nature of stress-strain curves which is believed to
result from the negative strain rate dependence of the flow stress. The latter
is assumed to result from the competition of a few relevant time scales
controlling the dynamics of jerky flow. We address the issue of time scales and
its connection to the negative strain rate sensitivity of the flow stress
within the framework of a model for the jerky flow which is known to reproduce
several experimentally observed features including the negative strain rate
sensitivity of the flow stress. We attempt to understand the above issues by
analyzing the geometry of the slow manifold underlying the relaxational
oscillations in the model. We show that the nature of the relaxational
oscillations is a result of the atypical bent geometry of the slow manifold.
The analysis of the slow manifold structure helps us to understand the time
scales operating in different regions of the slow manifold. Using this
information we are able to establish connection with the strain rate
sensitivity of the flow stress. The analysis also helps us to provide a proper
dynamical interpretation for the negative branch of the strain rate
sensitivity.Comment: 7 figures, To appear in Phys. Rev.
Recurrence analysis of the Portevin-Le Chatelier effect
Tensile tests were carried out by deforming polycrystalline samples of
Al-2.5%Mg alloy at room temperature in a wide range of strain rates where the
Portevin-Le Chatelier (PLC) effect was observed. The experimental stress-time
series data have been analyzed using the recurrence analysis technique based on
the Recurrence Plot (RP) and the Recurrence Quantification Analysis (RQA) to
study the change in the dynamical behavior of the PLC effect with the imposed
strain rate. Our study revealed that the RQA is able to detect the unique
crossover phenomenon in the PLC dynamics.Comment: 17 pages, 3 figure
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