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Crucial Parameter (crucial + parameter)
Selected AbstractsInvestigation of the Influence of Overvoltage, Auxiliary Glow Current and Relaxation Time on the Electrical Breakdown Time Delay Distributions in NeonCONTRIBUTIONS TO PLASMA PHYSICS, Issue 2 2005. A. Maluckov Abstract Results of the statistical analysis of the electrical breakdown time delay for neon-filled tube at 13.3 mbar are presented in this paper. Experimental distributions of the breakdown time delay were established on the basis of 200 successive and independent measurements, for different overvoltages, relaxation times and auxiliary glows. Obtained experimental distributions deviate from usual exponential distribution. Breakdown time delay distributions are numerically generated, usingMonte-Carlo method, as the compositions of the two independent random variables with an exponential and a Gaussian distribution. Theoretical breakdown time delay distribution is obtained from the convolution of the exponential and Gaussian distribution. Performed analysis shows that the crucial parameter that determines the complex structure of time delay is the overvoltage and if it is of the order of few percentage, then distribution of time delay must be treated as an convolution of two random variables. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Estimating the price elasticity of expenditure for prescription drugs in the presence of non-linear price schedules: an illustration from Quebec, CanadaHEALTH ECONOMICS, Issue 9 2005Paul Contoyannis Abstract The price elasticity of demand for prescription drugs is a crucial parameter of interest in designing pharmaceutical benefit plans. Estimating the elasticity using micro-data, however, is challenging because insurance coverage that includes deductibles, co-insurance provisions and maximum expenditure limits create a non-linear price schedule, making price endogenous (a function of drug consumption). In this paper we exploit an exogenous change in cost-sharing within the Quebec (Canada) public Pharmacare program to estimate the price elasticity of expenditure for drugs using IV methods. This approach corrects for the endogeneity of price and incorporates the concept of a ,rational' consumer who factors into consumption decisions the price they expect to face at the margin given their expected needs. The IV method is adapted from an approach developed in the public finance literature used to estimate income responses to changes in tax schedules. The instrument is based on the price an individual would face under the new cost-sharing policy if their consumption remained at the pre-policy level. Our preferred specification leads to expenditure elasticities that are in the low range of previous estimates (between ,0.12 and ,0.16). Naïve OLS estimates are between 1 and 4 times these magnitudes. Copyright © 2005 John Wiley & Sons, Ltd. [source] Rapid Synthesis and MALDI-ToF Characterization of Poly(ethylene oxide) Multiarm Star PolymersMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 1 2010Maria Doycheva Abstract Multiarm PEO star polymers with a purely aliphatic polyether structure have been synthesized using hyperbranched polyglycerol (PG) with different molecular weights as a multifunctional initiator. Different degrees of deprotonation of the initiator were studied with respect to molecular weight control. The results show that the degree of deprotonation is a crucial parameter for the synthesis of well-defined polymers with controlled molecular weights. Partial deprotonation of the PG hydroxyl groups (5,8%) was proven to represent an optimum for the synthesis of star polymers with molecular masses close to the theoretical values. Molecular weights of the stars ranged between 9,000 and 30,000,g,·,mol,1. MALDI-ToF spectra confirmed that the PEO arms in the star polymers possess homogeneous lengths. [source] TEM horn optimized for transient radiationMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 3 2001Ivor L. Morrow Abstract Theory and measurements are presented to show that careful shaping of antenna metalization can be used to design TEM horn antennas for ultra-wideband applications involving high-fidelity impulsive electromagnetic fields. The effect on the radiated pulse, spectral bandwidth, and transfer function is discussed. A numerical time-domain formulation is described to compute the impulsive radiated far-field waveform, and some experimental results are included to indicate the usefulness of the technique. The ringing action of the antenna is recognized as the crucial parameter constraining the usefulness of the design. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 30: 161,164, 2001. [source] Polarization effects and phase equilibria in high-energy-density polyvinylidene-fluoride-based polymersACTA CRYSTALLOGRAPHICA SECTION A, Issue 5 2010V. Ranjan Using first-principles calculations, the phase diagrams of polyvinylidene fluoride (PVDF) and its copolymers under an applied electric field are studied and phase transitions between their nonpolar , and polar , phases are discussed. The results show that the degree of copolymerization is a crucial parameter controlling the structural phase transition. In particular, for tetrafluoroethylene (TeFE) concentration above 12%, PVDF,TeFE is stabilized in the , phase, whereas the , phase is stable for lower concentrations. As larger electric fields are applied, domains with smaller concentrations ( 12%) undergo a transition from the , to the , phase until a breakdown field of ~600,MV,m,1 is reached. These structural phase transitions can be exploited for efficient storage of electrical energy. [source] Characterization of microcrystalline Si films deposited at low temperatures with high rates by atmospheric-pressure plasma CVDPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3-4 2010K. Ouchi Abstract Low-temperature and high-rate depositions of hydrogenated microcrystalline silicon (,c -Si:H) films are investigated using stable plasma excited at atmospheric pressure (AP) by supplying 150-MHz very high-frequency (VHF) power. VHF power density, H2/SiH4 ratio and plasma gap are varied as parameters under a fixed substrate temperature (Tsub) of 220 ,C. Increasing VHF power density and H2/SiH4 ratio is primarily important for the sufficient decomposition of source gas molecules, improving both deposition rate and film property. In addition, the plasma gap is found to be another crucial parameter in the deposition process using AP-VHF plasma. Numerical analyses on the temperature distribution around the plasma region have revealed that the steady-state surface temperature of the glass substrate becomes approximately 100 ,C higher than the back surface temperature (Tsub), which is caused by the moderate surface heating effect of the AP-VHF plasma. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] High-level production and covalent immobilization of Providencia rettgeri penicillin G acylase (PAC) from recombinant Pichia pastoris for the development of a novel and stable biocatalyst of industrial applicabilityBIOTECHNOLOGY & BIOENGINEERING, Issue 2 2006Lidija Senerovic Abstract A complete, integrated process for the production of an innovative formulation of penicillin G acylase from Providencia rettgeri(rPACP.rett)of industrial applicability is reported. In order to improve the yield of rPAC, the clone LN5.5, carrying four copies of pac gene integrated into the genome of Pichia pastoris, was constructed. The proteinase activity of the recombinant strain was reduced by knockout of the PEP4 gene encoding for proteinase A, resulting in an increased rPACP.rett activity of approximately 40% (3.8 U/mL vs. 2.7U/mL produced by LN5.5 in flask). A high cell density fermentation process was established with a 5-day methanol induction phase and a final PAC activity of up to 27 U/mL. A single step rPACP.rett purification was also developed with an enzyme activity yield of approximately 95%. The novel features of the rPACP.rett expressed in P.pastoris were fully exploited and emphasized through the covalent immobilization of rPACP.rett. The enzyme wasimmobilized on a series of structurally correlated methacrylic polymers, specifically designed and produced for optimizing rPACP.rett performances in both hydrolytic and synthetic processes. Polymers presenting aminic functionalities were the most efficient, leading to formulations with higher activity and stability (half time stability >3 years and specific activity ranging from 237 to 477 U/g dry based on benzylpenicillin hydrolysis). The efficiency of the immobilized rPACP.rett was finally evaluated by studying the kinetically controlled synthesis of ,-lactam antibiotics (cephalexin) and estimating the synthesis/hydrolysis ratio (S/H), which is a crucial parameter for the feasibility of the process. © 2005 Wiley Periodicals, Inc. [source] Calcium-Induced Membrane Microdomains Trigger Plant Phospholipase D ActivityCHEMBIOCHEM, Issue 17 2008Konstantin Kuppe Abstract Plant ,-type phospholipase D proteins are calcium-dependent, lipolytic enzymes. The morphology of the aggregates of their phospholipid substrate fundamentally defines the interaction between the enzyme and the surface. Here we demonstrate that the Ca2+ -induced generation of membrane microdomains dramatically activates ,-type phospholipase D from white cabbage. 500-fold stimulation was observed upon incorporation of 10 mol,% 1-palmitoyl-2-oleoyl- sn -glycero-3-phosphate (POPA) into 1-palmitoyl-2-oleoyl- sn -glycero-3-phosphocholine (POPC) vesicles in the presence of Ca2+ ions. Enhanced association of PLD,2 with phospholipid surfaces containing anionic components was indicated by lag phase analysis and film balance measurements. Differential scanning calorimetry showed that the POPA-specific activation correlates with the phase behavior of the POPC/POPA vesicles in the presence of Ca2+ ions. We conclude from the results that the Ca2+ -induced formation of POPA microdomains is the crucial parameter that facilitates the binding of PLD to the phospholipid surface and suggest that this effect serves as a cellular switch for controlling PLD activity. [source] Competition for light and nitrogen among grassland species: a simulation analysisFUNCTIONAL ECOLOGY, Issue 2 2001Schippers P. Abstract 1.,A plant competition model to analyse the competition among perennial grassland species was developed. It was used to find out whether complex perennial competition processes could be simulated accurately on the basis of ecophysiological principles; what crucial parameters and processes determine succession; and how spatial heterogeneity affects interspecies competition for light and nitrogen. 2.,Simulation results were compared with results of a 2-year replacement experiment involving Holcus lanatus, Anthoxanthum odoratum and Festuca ovina. Sensitivity analyses were performed to evaluate the importance of processes and parameters. 3.,The model's sensitivity to plant height, specific leaf area and turnover and the large interspecific differences indicated that these were key determinants of competition between species. Festuca's low shoot turnover enabled it to survive the winter better and gave it an advantage in spring; this resulted in an unexpected recovery after winter in the second year. 4.,Spatially explicit simulations showed that species patchiness reduced competitive asymmetry, especially under nutrient-poor conditions. 5.,The model's ability to simulate complex perennial competition processes as observed in the experiment indicates its potential for analysing vegetation processes related to succession. [source] Syzygium cumini leaf and seed extract mediated biosynthesis of silver nanoparticles and their characterizationJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 10 2010Vineet Kumar Abstract BACKGROUND: Plant mediated synthesis of metallic nanoparticles has been studied and reported, however, to date, the biomolecules involved in the synthesis of metallic nanoparticles have not been characterized. This study was therefore undertaken to characterize the biomolecules of Syzygium cumini involved in the synthesis of silver nanoparticles. RESULTS: Synthesis kinetics and morphological characterization of silver nanoparticles (SNP) synthesized using leaf extract (LE) and seed extract (SE) as well as their polar (water) fractions from Syzygium cumini were compared. The polyphenols content and high performance liquid chromatography (HPLC) profile of different fractions revealed good correlation between size and synthesis rate of SNP. SE contains more polyphenols and biochemical constituents than LE and therefore, showed higher synthesis rate and bigger sized SNP. To analyse the nature of biomolecules involved in the synthesis of SNP, LE and SE were fractionated on a polarity basis by solvent,solvent partitioning. Only the water fractions of LE and SE showed potential for SNP synthesis. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) analysis of SNP indicated that all fractions catalyze the synthesis of spherical nanoparticles. The average size of SNP synthesized by LE, leaf water fraction, SE and seed water fraction were 30, 29, 92, and 73 nm respectively. CONCLUSION: Results suggest that only highly polar soluble constituents are responsible for SNP synthesis. The size of SNP was found to be directly correlated with the amount of polyphenols as well as surfactants present in the reaction solution. Thus, the amount of polyphenols could be one of the crucial parameters determining the size and distribution of SNP. Copyright © 2010 Society of Chemical Industry [source] STUDY OF FACTORS INFLUENCING PROTEIN ESTERIFICATION USING ,-LACTOGLOBULIN AS A MODELJOURNAL OF FOOD BIOCHEMISTRY, Issue 5 2000MAHMOUD SITOHY ABSTRACT ,-Lactoglobulin was esterified with different alcohols (methanol, ethanol, n-propanol and iso-propanol) over various conditions of acidity, protein concentration, water content, time and temperature. The resulting products were simply recovered by centrifugation of the reaction mixture at the end of the reaction. Yield of esterification was markedly dependent on the concentration of the acid, of the protein, the water content and the type of alcohol used. Using ethanol andpropanol required 5 and 10% water, respectively to reach a maximum esterification degree. Concentrations of acid and protein were the crucial parameters. Protein concentration (4 or 5%) together with an adequate H+/COOH molar ratio, not only enhance the yield of esterification with ethanol but also increase the rate of this reaction. The results may be applicable to choosing the reaction conditions for the preparation of other esterified proteins. The conditions described in this study increase esterification reaction rate compared to that under conditions used traditionally. [source] Transesterification for biodiesel production catalyzed by combined lipases: Optimization and kineticsAICHE JOURNAL, Issue 6 2010Yun Liu Abstract Preparation of biodiesel from waste cooking oil catalyzed by combined lipases in tert -butanol medium was investigated. Several crucial parameters affecting biodiesel yield were optimized by response surface methodology, such as dosage of combined lipases of Novozym 435 and Lipozyme TLIM, weight ratio of Novozym 435 to Lipozyme TLIM, amount of tert -butanol, reaction temperature, and molar ratio of oil to methanol. Under the optimized conditions, the highest biodiesel yield was up to 83.5% The proposed model on biodiesel yield had a satisfactory coefficient of R2 (= 94.02%), and was experimentally verified. The combined lipases exhibited high-operational stability. After 30 cycles (300 h) successively, the activity of combined lipases maintained 85% of its original activity. A reaction kinetic model was proposed to describe the system and deduced to be a pseudo-first-order reaction, and the calculated activation energy was 51.71 kJ/mol. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Comparison of two capillary electrophoresis online stacking modes by analysis of polycyclic aromatic hydrocarbons in airborne particulatesJOURNAL OF SEPARATION SCIENCE, JSS, Issue 13 2006Guan-Qun Song Abstract Naphthalene, fluorene, pyrene, anthracene, phenanthrene, and chrysene were successfully separated by CD-modified MEKC (CD-MEKC) using 20 mM borate (pH 9.0) containing 90 mM SDS and 75 mM ,-CD. Two online stacking methods, i. e., sweeping and field-enhanced sample injection (FESI), were explored to enhance the detection sensitivity. The influences of some crucial parameters in sweeping and FESI procedures were investigated. For FESI method, a plug of water and low-conductivity sample matrix was used to increase the stacking efficiency. Compared with the sweeping method, FESI can increase the sensitivity in the range of 10,20-fold. The proposed method was used for the analysis of polycyclic aromatic hydrocarbons in airborne particulates. [source] | ||||||||||||||||