Home About us Contact
|
Home About us Contact | ||
|
|
||
Initial Velocity (initial + velocity)
Selected AbstractsA Mu-class glutathione S -transferase from gills of the marine shrimp Litopenaeus vannamei: Purification and characterizationJOURNAL OF BIOCHEMICAL AND MOLECULAR TOXICOLOGY, Issue 2 2007Carmen A. Contreras-Vergara Abstract Glutathione S -transferases (GSTs) are a family of detoxifying enzymes that catalyze the conjugation of glutathione (GSH) to electrophiles, thereby increasing the solubility of GSH and aiding its excretion from the cell. In this study, a glutatione S -transferase from the gills of the marine shrimp Litopenaeus vannamei was purified by affinity chromatography using a glutathione,agarose affinity column. GST was purified to homogeneity as judged by reducing SDS-PAGE and zymograms. This enzyme is a homodimer composed of ,25-kDa subunits and identified as a Mu-class GST based on its activity against 1-chloro-2,4-dinitrobenzene (CDNB) and internal peptide sequence. The specific activity of purified GST was 440.12 ,mol/(min mg), and the Km values for CDNB and GSH are very similar (390 and 335 ,M, respectively). The intersecting pattern of the initial velocities of this enzyme in the Lineweaver,Burke plot is consistent with a sequential steady-state kinetic mechanism. The high specific activity of shrimp GST may be related to a highly effective detoxification mechanism necessary in gills since they are exposed to the external and frequently contaminated environment. © 2007 Wiley Periodicals, Inc. J Biochem Mol Toxicol 21:62,67, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.20162 [source] Surface abundances of light elements for a large sample of early B-type stars , III.MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2004An analysis of helium lines in spectra of 102 stars ABSTRACT Non-local thermodynamic equilibrium analysis of He i lines in spectra of 102 B stars is implemented in order to derive the helium abundance He/H, the microturbulent parameter Vt and the projected rotation velocity v sin i. A simultaneous determination of He/H and Vt for the stars is effected by analysing equivalent widths of the 4471- and 4922-Å lines primarily as indicators of He/H and the 4713-, 5016-, 5876- and 6678-Å lines primarily as indicators of Vt. The rotation velocities v sin i are found from profiles of the same lines. It is shown that, when Vt > 7 km s,1, the Vt(He i) values determined from He i lines are systematically overestimated as compared with the Vt(O ii, N ii) values derived from O ii and N ii lines. This discrepancy is especially appreciable for hot evolved B giants with Vt(He i) = 16,23 km s,1 and may indicate a failure of classical model atmospheres to represent the strong He i lines for these stars. Two programme stars, HR 1512 and 7651, are found to be helium-weak stars. The remaining 100 stars are divided into three groups according to their masses M. The microturbulent parameter Vt(He i) is low for all stars of group A (M= 4.1,6.9 M,) and for all stars with the relative ages t/tMS < 0.8 of group B (M= 7.0,11.2 M,). Their Vt(He i) values are within the 0 to 5 km s,1 range, as a rule; the mean value is Vt= 1.7 km s,1. Only evolved giants of group B, which are close to the termination of the main-sequence (MS) evolutionary phase (t/tMS > 0.8), show Vt(He i) up to 11 km s,1. The helium abundance He/H is correlated with the relative age t/tMS in both groups; the averaged He/H enhancement during the MS phase is 26 per cent. For group C, containing the most massive stars (M= 12.4,18.8 M,), the Vt(He i) values display a correlation with t/tMS, varying from 4 to 23 km s,1. The He/H determination for hot evolved B giants of the group with Vt(He i) > 15 km s,1 depends on a choice between the Vt(He i) and Vt(O ii, N ii) scales. The mean He/H enrichment by 67 per cent during the MS phase is found, if the abundances He/H are based on the Vt(O ii, N ii) scale; however, two evolved giants with especially high v sin i, HR 7446 and 7993, show the He/H enhancement by about a factor of 2.5. When using the same Vt scale, we found a trend of He/H with projected rotational velocities v sin i; a large dispersion for v sin i > 150 km s,1 can result from differences in masses M. A comparison with the stellar model computations with rotationally induced mixing shows that the observed helium enrichment during the MS phase can be explained by rotation with initial velocities 250,400 km s,1. The He/H distribution on M and v sin i based on the Vt(O ii, N ii) scale seems to be in better agreement with the theory than one based on the Vt(He i) scale. The mean value He/H = 0.10 derived for stars in the zero age main sequence (ZAMS) vicinity can be adopted as the typical initial helium abundance for early B stars in the solar neighbourhood. [source] Hydrogen cyanide release during feeding of generalist and specialist lepidopteran larvae on a cyanogenic plant, Passiflora capsularisPHYSIOLOGICAL ENTOMOLOGY, Issue 4 2006MIGUEL E. ALONSO AMELOT Abstract The hydrogen cyanide-based interaction of a strongly cyanogenic plant, Passiflora capsularis, and larvae of two insect herbivores, a generalist (Spodoptera frugiperda) and a specialist (Heliconius erato), is examined in terms of the combined kinetics of the feeding process and the simultaneous hydrogen cyanide (HCN) liberation, as compared with the natural kinetics of hydrogen cyanide evolution by plant-leaf tissue. There are marked differences in acceptance of P. capsularis by third-instar larvae of specialist and generalist species. The former, H. erato, display a parsimonious ingestion rate of 0.74 ± 0.15 mg (fresh weight) min,1 comprising 18% active feeding time, whereas S. frugiperda larvae show a more erratic and restrained feeding involving 4% of the time at 0.45 ± 0.14 mg min,1. These S. frugiperda larvae ingest 124.4 ± 8.3 mg (fw) of the non-cyanogeneic Spinacia oleracea leaves in 24 h compared with only 74.7 ± 20.1 mg of P. capsularis in the same period. The total hydrogen cyanide released naturally from wild specimens of P. capsularis plants is in the range 326,3901 ,g g,1. Hydrogen cyanide evolution from macerated P. capsularis leaves takes place along a hyperbolic function with time and initial velocities of cyanide evolution are a linear function of total hydrogen cyanide. When feeding on P. capsularis leaves, H. erato releases only a minor fraction relative to total hydrogen cyanide (0.09%) and to the anticipated cyanide from the initial velocity (7%). By contrast, S. frugiperda evokes 5.8-fold more than the anticipated hydrogen cyanide release from the plant. The findings are interpreted as diverging strategies by generalist and specialist insects in the utilization of hydrogen cyanide in cyanogenic plants. [source] In vitro activation of the corticosteroid ciclesonide in animal nasal mucosal homogenatesBIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 2 2007H. Sato Abstract Ciclesonide, a new corticosteroid for allergic rhinitis, is administered as an inactive parent compound that is converted by esterases to the pharmacologically active metabolite, desisobutyryl-ciclesonide (des-CIC). This study investigated the in vitro activation of ciclesonide in nasal mucosa of multiple animal species. Nasal mucosal homogenates from rats, guinea-pigs, rabbits and dogs were incubated with ciclesonide 0.5 µmol/l (0.271 µg/ml) or 5 µmol/l (2.71 µg/ml) for up to 120 min. Concentrations of ciclesonide and des-CIC were measured by high-performance liquid chromatography with tandem mass spectrometry. Ciclesonide was metabolized to des-CIC in nasal mucosal homogenates of each species. The initial velocities of des-CIC formation ranged from 0.0038 to 0.0150 nmol/min/mg protein and 0.0319 to 0.0983 nmol/min/mg protein in nasal mucosal homogenates incubated with ciclesonide 0.5 µmol/l and 5 µmol/l, respectively. Furthermore, the initial velocities of ciclesonide metabolism ranged from 0.0032 to 0.0142 nmol/min/mg protein and 0.0445 to 0.1316 nmol/min/mg protein in nasal mucosal homogenates incubated with ciclesonide 0.5 µmol/l and 5 µmol/l, respectively. This study confirms that ciclesonide is converted to des-CIC in nasal mucosal homogenates without any marked differences among animal species. Copyright © 2007 John Wiley & Sons, Ltd. [source] Fluid Model of a Sheath Formed in Front of an Electron Emitting Electrode Immersed in a Plasma with Two Electron TemperaturesCONTRIBUTIONS TO PLASMA PHYSICS, Issue 2 2005T. Gyergyek Abstract The formation of a sheath in front of a negatively biased electrode (collector) that emits electrons is studied by a one-dimensional fluid model. Electron and ion emission coefficients are introduced in the model. It is assumed that the electrode is immersed in a plasma that contains energetic electrons. The electron velocity distribution function is assumed to be a sum of two Maxwellian distributions with two different temperatures, while the ions and the emitted electrons are assumed to be monoenergetic. The condition for zero electric field at the collector is derived. Using this equation the dependence of electron and ion critical emission coefficients on various parameters - like the ratio between the hot and cool electron density, the ratio between hot and cool electron temperature and the initial velocity of secondary electrons - is calculated for a floating collector. A modification of the Bohm criterion due to the presence of hot and emitted electrons is also given. The transition between space charge limited and temperature limited electron emission for a current-carrying collector is also analyzed. The critical potential, where this transition occurs, is calculated as a function of several parameters like the Richardson emission current, the ratio between the hot and cool electron density, the ratio between hot and cool electron temperature and the initial velocity of secondary electrons. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Net spinning caddisflies as stream ecosystem engineers: the influence of Hydropsyche on benthic substrate stabilityFUNCTIONAL ECOLOGY, Issue 3 2004B. J. CARDINALE Summary 1Organisms that physically modify or create habitat (ecosystem engineers) can have a profound influence on community and ecosystem dynamics. 2Here evidence is presented that one of the most abundant and widely distributed lotic insects could act as an ecosystem engineer in streams by increasing the stability of benthic substrates during flooding. 3Natural densities of larval net spinning caddisflies (Hydropsychidae) were established in stream channels that had standardized physical properties. The mobility of three particle sizes were measured during simulated flooding and the fraction of particles eroded compared with that of control streams. 4Larvae increased the initial velocity required to erode sediments by 10,30%. At velocities sufficient to scour 87% of particles from control channels, 57,100% remained stable in channels colonized by larvae. 5Assuming larvae have similar effects in natural streams, caddisflies could be expected to increase the recurrence interval of a substrate scouring flood from 1·67 year to 2·41 year, corresponding to a 17% decrease in the probability of bed scour per year. 6Our study suggests these insects could play an important role in generating the spatial ,refuges' that moderate the resistance of lotic communities to flooding. It is argued that, as has occurred in marine systems, a better understanding of how freshwater organisms engineer their physical environment has much potential to complement our historical focus on the abiotic forces that constrain populations and communities. [source] Direct computation of thermodynamic properties of chemically reacting air with consideration to CFDINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 4 2003Joe IannelliArticle first published online: 2 SEP 200 Abstract This paper details a two-equation procedure to calculate exactly mass and mole fractions, pressure, temperature, specific heats, speed of sound and the thermodynamic and jacobian partial derivatives of pressure and temperature for a five-species chemically reacting equilibrium air. The procedure generates these thermodynamic properties using as independent variables either pressure and temperature or density and internal energy, for CFD applications. An original element in this procedure consists in the exact physically meaningful solution of the mass-fraction and mass-action equations. Air-equivalent molecular masses for oxygen and nitrogen are then developed to account, within a mixture of only oxygen and nitrogen, for the presence of carbon dioxide, argon and the other noble gases within atmospheric air. The mathematical formulation also introduces a versatile system non-dimensionalization that makes the procedure uniformly applicable to flows ranging from shock-tube flows with zero initial velocity to aerothermodynamic flows with supersonic/hypersonic free-stream Mach numbers. Over a temperature range of more than 10000 K and pressure and density ranges corresponding to an increase in altitude in standard atmosphere of 30000 m above sea level, the predicted distributions of mole fractions, constant-volume specific heat, and speed of sound for the model five species agree with independently published results, and all the calculated thermodynamic properties, including their partial derivatives, remain continuous, smooth, and physically meaningful. Copyright © 2003 John Wiley & Sons, Ltd. [source] Some characteristics of sperm motility in European hake (Merluccius merluccius, L., 1758)JOURNAL OF APPLIED ICHTHYOLOGY, Issue 5 2010A.-L. Groison Summary The objective of this paper is to characterize some of the sperm motility parameters in European hake (Merluccius merluccius), which is considered to be a species with aquaculture potential. The total ATP, ADP and AMP concentrations were determined using high-performance liquid chromatography on hake sperm samples collected during the winter-early spring in the Bay of Biscay (France) (n = 22) and on hake sperm samples collected during the summer-early autumn in waters off Western Norway (n = 5). The Adenylate Energy Charge (AEC) was deduced from these data. Computer Assisted Sperm Analysis (CASA) was used to measure a series of parameters characterizing the motility and the sperm swimming performances. Changes in salinity of the swimming medium affected all the measured motility parameters. The sperm velocity and the straightness of the movement were at maximum when sperm was activated with 100% filtrated sea water (100 SW) but decreased sharply later. When sperm was activated in filtrated sea water (50% diluted with distilled water: 50 SW) the values of these parameters increased (with a lower percentage of active cells) during the first 2.5 min and thereafter decreased slowly. In 50 SW, the initial velocity was lowered but the swimming period lasting 4.5 times longer than in 100 SW (but with a lower percentage of actively swimming cells). Initial sperm motility (percentage of swimming cells) in 100 SW was affected by sperm storage duration. Undiluted sperm could be stored at 4°C for 5 days and still show 13 ± 7% motility; the velocity and straightness of the movement were at maximum at the earliest period of measurement (0.5,1 day of storage) and then decreased gradually to reach their minima after 4 days of storage. Further, both the AEC and ATP content decreased with storage time, with the AEC decreasing from 0.78 ± 0.07 (mean ± SD) at stripping time to 0.20 ± 0.09 after 2 days of storage. Over the same period ATP content decreased from 85 ± 80 to 5 ± 4 nanomoles 10,9 spermatozoa, these data presenting a high variability. [source] Kinetics and thermodynamics of glucoamylase inhibition by lactate during fermentable sugar production from food wasteJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 5 2010Xiao Qiang Wang Abstract BACKGROUND: Glucoamylase hydrolysis is a key step in the bioconversion of food waste with complicated composition. This work investigated the effect of lactate on glucoamylase from Aspergillus niger UV-60, and inhibition mechanisms of glucoamylase by lactate during food waste hydrolysis. RESULTS: For 125 min hydrolysis of food waste (10%, dry basis), reducing sugars produced in the absence of lactate were 15%, 26% and 56% more than those produced in the presence of 24 g L,1 lactate at 60, 50 and 40 °C, respectively. Kinetic study showed that the type of glucoamylase inhibition by lactate was competitive, and Km (Michaelis-Menten constent), Vmax (maximum initial velocity), KI (inhibition constant) were 103.2 g L,1, 5.0 g L,1 min,1, 100.6 g L,1, respectively, for food waste hydrolysis at 60 °C and pH 4.6. Lactate also accelerated glucoamylase denaturation significantly. Activation energy of denaturation without inhibitor was 61% greater than that of denaturation with inhibitor (24 g L,1 lactate). Half-lives (t1/2) without inhibitor were 7.6, 2.7, 2.6, 1.7 and 1.2 times longer than those with inhibitor at temperature 40, 45, 50, 55 and 60 °C, respectively. CONCLUSION: These results are helpful to process optimization of saccharification and bioconversion of food waste. Copyright © 2010 Society of Chemical Industry [source] Entry dynamics and acoustics/infrasonic/seismic analysis for the Neuschwanstein meteorite fallMETEORITICS & PLANETARY SCIENCE, Issue 10 2004D. O. REVELLE This includes ground-based photographic and radiometer data as well as infrasound and seismic data from this very significant bolide event (Spurný et al. 2002, 2003). We have also used these data to model the entry of Neuschwanstein, including the expected dynamics, energetics, panchromatic luminosity, and associated fragmentation effects. In addition, we have calculated the differential efficiency of acoustical waves for Neuschwanstein and used these values to compare against the efficiency calculated using available ground-based infrasound data. This new numerical technique has allowed the source height to be determined independent of ray tracing solutions. We have also carried out theoretical ray tracing for a moving point source (not strictly a cylindrical line emission) and for an infinite speed line source. In addition, we have determined the ray turning heights as a function of the source height for both initially upward and downward propagating rays, independent of the explicit ray tracing (detailed propagation path) programs. These results all agree on the origins of the acoustic emission and explicit source heights for Neuschwanstein for the strongest infrasonic signals. Calculated source energies using more than four different independent approaches agree that Neuschwanstein was certainly <500 kg in initial mass, given the initial velocity of 20.95 km/s, resulting in an initial source energy ,0.0157-0.0276 kt TNT equivalent (4.185 times 1012 J). Local source energies at the calculated infrasonic/seismic source altitudes are up to two orders of magnitude smaller than this initial source energy. [source] Hydrogen cyanide release during feeding of generalist and specialist lepidopteran larvae on a cyanogenic plant, Passiflora capsularisPHYSIOLOGICAL ENTOMOLOGY, Issue 4 2006MIGUEL E. ALONSO AMELOT Abstract The hydrogen cyanide-based interaction of a strongly cyanogenic plant, Passiflora capsularis, and larvae of two insect herbivores, a generalist (Spodoptera frugiperda) and a specialist (Heliconius erato), is examined in terms of the combined kinetics of the feeding process and the simultaneous hydrogen cyanide (HCN) liberation, as compared with the natural kinetics of hydrogen cyanide evolution by plant-leaf tissue. There are marked differences in acceptance of P. capsularis by third-instar larvae of specialist and generalist species. The former, H. erato, display a parsimonious ingestion rate of 0.74 ± 0.15 mg (fresh weight) min,1 comprising 18% active feeding time, whereas S. frugiperda larvae show a more erratic and restrained feeding involving 4% of the time at 0.45 ± 0.14 mg min,1. These S. frugiperda larvae ingest 124.4 ± 8.3 mg (fw) of the non-cyanogeneic Spinacia oleracea leaves in 24 h compared with only 74.7 ± 20.1 mg of P. capsularis in the same period. The total hydrogen cyanide released naturally from wild specimens of P. capsularis plants is in the range 326,3901 ,g g,1. Hydrogen cyanide evolution from macerated P. capsularis leaves takes place along a hyperbolic function with time and initial velocities of cyanide evolution are a linear function of total hydrogen cyanide. When feeding on P. capsularis leaves, H. erato releases only a minor fraction relative to total hydrogen cyanide (0.09%) and to the anticipated cyanide from the initial velocity (7%). By contrast, S. frugiperda evokes 5.8-fold more than the anticipated hydrogen cyanide release from the plant. The findings are interpreted as diverging strategies by generalist and specialist insects in the utilization of hydrogen cyanide in cyanogenic plants. [source] Global well-posedness for compressible Navier-Stokes equations with highly oscillating initial velocityCOMMUNICATIONS ON PURE & APPLIED MATHEMATICS, Issue 9 2010Qionglei Chen In this paper, we prove global well-posedness for compressible Navier-Stokes equations in the critical functional framework with the initial data close to a stable equilibrium. This result allows us to construct global solutions for the highly oscillating initial velocity. The proof relies on a new estimate for the hyperbolic/parabolic system with convection terms. © 2010 Wiley Periodicals, Inc. [source] | ||||||||||||||||