Initial Growth Rate (initial + growth_rate)

Distribution by Scientific Domains

Selected Abstracts

The influence of stratospheric potential vorticity on baroclinic instability

L. A. Smy
Abstract This article examines the dynamical coupling between the stratosphere and troposphere by considering the effect of direct perturbations to stratospheric potential vorticity on the evolution of midlatitude baroclinic instability in a simple extension of an Eady model. A simulation in which stratospheric potential vorticity is exactly zero is used as a control case, and both zonally symmetric and asymmetric perturbations to the stratospheric potential vorticity are then considered, the former representative of a strong polar vortex, the latter representative of the stratospheric state following a major sudden warming. Both types of stratospheric perturbation result in significant changes to the synoptic-scale evolution of surface temperature, as well as to zonally and globally averaged tropospheric quantities. In the case of a zonally symmetric perturbation, the linear growth rate of all unstable modes decreases with increasing perturbation amplitude. Initial growth rates in cases with significant asymmetric perturbations are also weaker than those of the control case, but final eddy kinetic energy values are much larger due to the growth of low zonal wavenumbers triggered by the initial stratospheric perturbation. A comparison of the zonally symmetric and asymmetric perturbations gives some insight into the possible influence of pre- or post-sudden-warming conditions on tropospheric evolution. Copyright © 2009 Royal Meteorological Society [source]

Catalytic decomposition of methane over supported Ni catalysts with different particle sizes

Sun Yunfei
Abstract Methane decomposition on ,-Al2O3 -supported Ni catalysts, as a method for the production of carbon nanofibers (CNFs) and CO-free hydrogen, has been investigated to show the effect of catalyst particle size on the rate and yield of CNFs formation. The catalysts were prepared by deposition,precipitation with different calcination temperature ranging from 725 to 1025 K so as to have different initial particle sizes. The results show that catalysts with smaller initial particle sizes had higher initial growth rate but experienced fast deactivation. The lifetime of the catalyst, ending at the inflection point on the rate curve of CNFs growth, could well represent the yield of CNFs of the catalyst, and the maximal yield of CNFs was achieved on the Ni catalysts calcinated at 823 K and with a particle size of around 56 nm. However, the diameters of the grown CNFs were not directly related to the initial size of the catalysts, because of particle sintering and breaking during catalyst reduction or CNFs formation. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source]

Effect of the plant peptide regulator, phytosulfokine-,, on the growth and Taxol production from Taxus sp. suspension cultures

Beum Jun Kim
Abstract Phytosulfokine-, (PSK-,) is a small plant peptide (5 amino acids) that displays characteristics typically associated with animal peptide hormones. PSK-, was originally isolated based on its mitogenic activity with plant cultures; it has been reported to increase production of tropane alkaloids from Atropa belladonna, although its general influence on secondary metabolite production is unknown. The studies reported in this article were initiated to evaluate the effects of PSK-, supplementation on production of TaxolÔ (paclitaxel) from plant cell cultures of Taxus sp. particularly when methyl jasmonate (MeJA) is added as an elicitor of secondary metabolism. The response to PSK-, supplementation was cell line dependent. Taxus cuspidata P93AF showed no statistically significant response to PSK-, supplementation while Taxus canadensis C93AD and T. cuspidata PO93X displayed a concentration-dependent response (up to 100 nM PSK-, added in first 24 h of culture) with a decrease in initial growth rate, an increase in cell density (dry weight/fresh weight), and increased Taxol production. More remarkably with T. canadensis (C93AD), a very strong synergistic response of PSK-, (100 nM) and methyl jasmonate (MeJA, 100 µM) elicitation was observed, resulting in Taxol level of 35.3,±,2.1 mg/L or 1.83,±,0.02 mg Taxol/g dry cell weight achieved at day 21, a level of approximately 10-fold higher than for either treatment by itself. Although the level of Taxol production achieved is not remarkable, this synergistic treatment was able to partially revive taxane production in cultures that have lost productivity due to extended time (over 10 years) in continuous subculture. © 2006 Wiley Periodicals, Inc. [source]

Lumbar ontogenetic growth and sexual dimorphism in modern humans

Elías Valverde
To detect and differentiate between possible heterochronic processes in the ontogenetic growth pattern of the human lumbar region, in relationship with sexual dimorphism. We measured the growth trajectories of average length and width, length/width ratio, posterior projected surface area, and bone mineral density using dual energy X-ray absorptiometry, in a sample group of 1718 modern humans. These growth patterns were analyzed using the Gompertz model. In adult lumbar region, only surface area and width were significantly higher in men. Regarding the ontogenetic growth pattern leading to the dimorphic states, all values obtained for women were significantly higher than those obtained for men. Maximum initial growth rates occurred for surface area and density in women. Width scaled faster than length in both sexes. The lumbar region followed patterns similar to those of other skeletal elements when compared with a previous classification of growth patterns in the human skeleton; however, in this study, the growth rate was slower. With regard to the effect of dimorphism, sexual differences in growth rate accounted for only a small proportion of the variation in lumbar length, mineral density, and surface area. Nevertheless, these sexual differences played an important role in the increase of the length/width ratio, which was reflected in the ages at which sexual dimorphism developed. The sexual dimorphism found in the lumbar region of human adults is not caused by any heterochronic process. The lower values of bone mineral density in adult women could explain the origin of some pathologies related. Am. J. Hum. Biol. 22:596,603, 2010. © 2010 Wiley-Liss, Inc. [source]