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  • ENERGY PRODUCTION AND CONVERSION  (5)
  • PHYSICAL SCIENCES  (4)
  • extent of absorption  (2)
  • 1
    ISSN: 1573-904X
    Keywords: Bioequivalence ; highly variable drugs ; extent of absorption ; rate of absorption ; Monte Carlo simulations ; single-dose ; multiple-dose bioequivalence trial
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. Evaluating of the effects of high intrasubject variability in clearance (CL) and volume of distribution (V), on 90% confidence intervals (CIs) for AUC (Area Under the concentration Curve) in single and multiple-dose bioequivalence studies. The main methodology was Monte Carlo simulation, and we also used deterministic simulation, and examination of clinical trials. The results are compared with those previously observed for Cmax (maximum concentration.) Methods. The time course of drug concentration in plasma was simulated using a one-compartment model with log-normal statistical distributions of intersubject and intrasubject variabilities in the pharmacokinetic parameters. Both immediate-release and prolonged-release products were simulated using several levels of intrasubject variability in single-dose and multiple-dose studies. Simulations of 2000 clinical bioequivalence trials per condition (138 conditions) with 30 subjects in each crossover trial were carried out. Simulated data were compared with data from actual bioequivalence trials. Results. The current simulations for AUC show similar probabilities of failure for single-dose and multiple-dose bioequivalence studies, even with differences in the rate of absorption or fraction absorbed. AUC values from prolonged-release scenario studies are more sensitive to changes in the first order absorption rate constant ka, and to variability in CL and V than AUC from studies of immediate-release studies. Conclusions. We showed that multiple-dose designs for highly variable drugs do not always reduce intrasubject variability in either AUC or Cmax, although the behavior of AUC differs from Cmax. Single dose AUC to the last quantifiable concentration was more reliable than either single dose AUC extrapolated to infinity, or multiple dose AUC during a steady-state interval. Multiple-dose designs may not be the best solution for assessing bioequivalence of highly variable drugs.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-904X
    Keywords: pharmacokinetics ; bioequivalence ; extent of absorption ; power analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The determination of the area under the concentration–time curve (AUC) is the method most commonly used by regulatory agencies to assess extent of drug absorption after single-dose administration of oral products. Using simulations, several approaches toward measuring the actual area, in whole or part, were tested. In addition, the performance of the peak concentration (C max), usually taken as a measure of the rate of absorption was assessed evaluating extent. Model scenarios for drugs with typical mean characteristics and statistical distributions were investigated. Using different kinetic models of disposition, the time course of the drug concentration in plasma was simulated. Intraindividual and interindividual variability and assay error were modeled using Monte Carlo techniques. The accuracy, precision, and ease of use of the various measures of extent were evaluated, and statistical power analyses were performed. Among the measures tested, the most reliable were the AUC computed up to the time of the last quantifiable concentration, without extrapolation, and C max. However, being also sensitive to rate, C max as a measure of extent is of limited potential.
    Type of Medium: Electronic Resource
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  • 3
    Publication Date: 2019-06-28
    Description: The thermodynamic cycle appropriate to an AMTEC (alkali metal thermal-to-electric converter) cell is discussed for both liquid- and vapor-fed modes of operation, under the assumption that all processes can be performed reversibly. In the liquid-fed mode, the reversible efficiency is greater than 89.6 percent of Carnot efficiency for heat input and rejection temperatures (900-1300 K and 400-800 K, respectively) typical of practical devices. Vapor-fed cells can approach the efficiency of liquid-fed cells. Quantitative estimates confirm that the efficiency is insensitive to either the work required to pressurize the sodium liquid or the details of the state changes associated with cooling the low pressure sodium gas to the heat rejection temperature.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: In: IECEC '92; Proceedings of the 27th Intersociety Energy Conversion Engineering Conference, San Diego, CA, Aug. 3-7, 1992. Vol. 3 (A93-25851 09-44); p. 3.123-3.127.
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  • 4
    Publication Date: 2019-08-28
    Description: The alkali metal thermoelectric converted (AMTEC) converts heat to electrical power without moving parts. Attention is presently given to two AMTEC devices that have been optimized for conversion efficiencies of the order of 30 percent or more at 1100 K, in conjunction with high volumetric power densities. A 'tube-bundle' AMTEC configuration yields a peak power of 426 W/l; a flat-plate AMTEC system yields 2.4 W/l.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: In: Space nuclear power systems; Proceedings of the 8th Symposium, Albuquerque, NM, Jan. 6-10, 1991. Pt. 1 (A93-13751 03-20); p. 472-481.
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  • 5
    Publication Date: 2019-07-13
    Description: Proposed silicon carbide variable-potential insulated-gate field-effect transistor specially designed for use in measuring concentrations of hydrocarbon gases. Devices like this prove useful numerous automotive, industrial, aeronautical, and environmental monitoring applications.
    Keywords: PHYSICAL SCIENCES
    Type: NPO-19428 , NASA Tech Briefs (ISSN 0145-319X); 20; 3; P. 55
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  • 6
    Publication Date: 2019-07-12
    Description: Organic liquid in cathode extends working life. Rechargeable solid-electrolyte electrochemical cell includes novel mixture of organic and inorganic materials in liquid cathode. Operates at temperature about 120 to 170 degrees C lower than sodium/sulfur cells. Offers energy density comparable to that of sodium/sulfur cells - about 10 Wh/kg - and suited to such applications as military systems and electric vehicles.
    Keywords: PHYSICAL SCIENCES
    Type: NPO-17604 , NASA Tech Briefs (ISSN 0145-319X); 14; 4; P. 51
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  • 7
    Publication Date: 2019-07-12
    Description: Vapor-exposure test cell (VETC) designed to be used in testing thin-film electrodes on solid electrolytes electrochemically at high temperature. Use of VETC much simpler and less expensive than testing alkali-metal thermal-to-electric converter (AMTEC) fuel cell, electrolysis cell, or other entire device containing solid electrolyte and electrodes of material and configuration to be characterized.
    Keywords: PHYSICAL SCIENCES
    Type: NPO-18620 , NASA Tech Briefs (ISSN 0145-319X); 17; 9; P. 80
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  • 8
    Publication Date: 2019-07-12
    Description: Size and weight reduced; operating lifetime increased. Developmental alkali-metal thermal-to-electric converter (AMTEC) in which cells fed from common supply of high-pressure sodium vapor and connected electrically in series. No liquid sodium makes contact with any part of AMTEC cells. Sodium vapor supplied to solid electrolyte of each cell through porous metal anode on upstream side. Proposed design reduces need for high-temperature feedthroughs in that cells internally connected. Power withdrawn through feedthrough at lower temperature without significant thermal loss.
    Keywords: PHYSICAL SCIENCES
    Type: NPO-18667 , NASA Tech Briefs (ISSN 0145-319X); 17; 9; P. 78
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  • 9
    Publication Date: 2019-07-13
    Description: Experimental studies are being conducted at JPL to identify long life, high area power density electrodes for AMTEC. Power versus time measurements are being made in a demountable electrode test cell and, for longer term experiments, a self-contained recirculating cell. The experimental apparatus and procedures are described in detail. The results show that thin film molybdenum electrodes can be designed to produce power near 0.5 W/sq cm for over two hundred hours. Also, platinum/tungsten electrodes exhibit power densities that are stable near 0.5 W/sq cm. If the performance of these electrodes is verified for longer periods (thousands of hours), then practical AMTEC systems will be possible.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: IECEC ''87; Aug 10, 1987 - Aug 14, 1987; Philadelphia, PA; United States
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  • 10
    Publication Date: 2019-08-27
    Description: A detailed electrochemical model of the alkali metal thermoelectric converter (AMTEC) electrode and current collector grid has been developed recently. Comparative evaluations of the resulting differences in model predictions reveal that the new detailed model predicts up to 50 percent higher electrode power densities at condenser operating temperatures above 600 K. The new model, with experimentally determined parameters, was used to recalculate the projected system performance of previously reported 1- and 100-kWe AMTEC space power systems that had incorporated earlier electrolyte/electrode models. It was found that when the detailed model was used to determine the electrode power densities, enhanced specific power and efficiencies are predicted.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: In: Space nuclear power systems 1989; Proceedings of the 6th Symposium, Albuquerque, NM, Jan. 8-12, 1989. Vol. 2 (A93-20752 06-20); p. 373-378.
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