Determined Values (determine + value)

Distribution by Scientific Domains


Selected Abstracts


Competition among zinc, manganese, and cadmium uptake in the freshwater alga Scenedesmus vacuolatus

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2007
Stefanie Töpperwien
Abstract In the present study, Zn and Mn competition with Cd uptake was investigated in the freshwater alga Scenedesmus vacuolatus. Scenedesmus vacuolatus was exposed to experimental media with Cd and either Zn or Mn in short-term experiments; long-term experiments were undertaken to investigate the effect of growth on Cd accumulation. Cadmium accumulation in S. vacuolatus could be detected at very low exposure concentrations (free Cd2+, 2 × 10,14 to 1 × 10,11 M), and uptake was proportional to the free-Cd2+ concentration. Zinc was an effective competitive inhibitor of Cd uptake when the Zn2+ to Cd2+ ratio was greater than 14 in the exposure medium, whereas Mn competed with Cd for uptake above a Mn2+ to Cd2+ ratio of greater than 10,000. Binding constants for Cd and Zn affinity to the transport sites were determined (KZn and KCd). Values for KZn were slightly higher (log K = 9.4,9.8) than values for KCd (log K = 8.9,9.8). In contrast, Cd seemed not to compete with the Mn-binding sites for uptake over the Mn concentration range from 1 × 10,10 to 1 × 10,8 M. Determined values for the binding constants of Zn and Cd show that a simple model can be applied to predict Cd uptake at known Zn and Cd concentrations. The environmental implications of these results are discussed with respect to potential Cd toxicity for aquatic organisms. [source]


Trading options before Black-Scholes: a study of the market in late seventeenth-century London1

ECONOMIC HISTORY REVIEW, Issue 2009
ANNE L. MURPHY
This article uses data from the ledgers of the financial broker Charles Blunt to explore the market in equity options that emerged in London during the stock market boom of the early 1690s. Blunt's ledgers provide a unique opportunity to observe the workings of an early modern derivatives market. They reveal a broadly based and highly active trade in options. The market functioned well, determined value using agreed criteria, and was utilized by a diverse range of individuals to facilitate both risk-seeking and risk-averse investment strategies. [source]


Load-flow conditions for hvdc transmission in synchronous networks

EUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 2 2000
J. Warnking
The basic purpose for HVDC (high-voltage direct current) transmission is to transmit a determined value of electrical power from one electrical node to another. If there is an AC system in parallel to an HVDC transmission, the load flow via this parallel AC system can be controlled directly. Since HVDC systems offer possibilities to perform fast load-flow control, they can also be used for improving stability. In this paper load-flow calculations of a simplified network are presented. First a comparison between HVDC transmission operating in asynchronous resp. synchronous networks is shown. Synchronous network means that the HVDC transmission works in parallel to an AC system at the same voltage level. It is shown how voltage at the point of installation and how the load angle are influenced due to the synchronous operation. A special regard is drawn to the losses of the transmission. Conditions for minimum total losses are presented. Informer calculations loads are involved. It is shown how they influence the minimum total losses. [source]


Kinetics of PME/Pi in pig kidneys during cold ischemia

NMR IN BIOMEDICINE, Issue 7 2007
Dominik von Elverfeldt
Abstract Quality assessment of renal grafts via 31P magnetic resonance spectroscopy (MRS) has been investigated since 1986. As ATP concentrations decay rapidly during cold ischemia, the ratio of phosphomonoesters (PME) to inorganic phosphate (PiO) within the organ (PME/PiO) is commonly used as a quality marker and is considered to be the most reliable parameter. MRS did not lead to any delay in the transplantation procedure since it was performed during the time necessary for immunological matching (cross-match). Differences in the time period until transplantation call for extrapolation of the measured ratio to the end of cold ischemia before correlating with graft performance after transplantation. Therefore, quantitative determination of PME/PiO kinetics is essential. As a model for metabolite decay in human renal grafts, pig kidneys obtained from a slaughterhouse were monitored for up to 80,h via 31P MRS at 2,T. By employing chemical shift imaging (CSI) with a spatial resolution of approximately 1,×,1,×,4,cm3, it was possible to reduce partial volume effects significantly. The improved spectral resolution gained through CSI enabled reliable PME/PiO ratios to be determined only from those voxels containing renal tissue. Spectra were fitted automatically using the magnetic resonance user interface (MRUI), with prior knowledge obtained from unlocalized spectra when necessary. A monoexponential time dependence of PME/PiO for histidine,tryptophane,alpha-ketoglutarate (HTK)-perfused kidneys during cold ischemia was observed, and the determined value of the decay constant , was 0.0099,±,0.0012,h,1. In University of Wisconsin solution (UW)-perfused kidneys, an , of 0.0183,±,0.0053,h,1 was determined. Determination of the decay constant enables a usable extrapolation of PME/PiO for quality assessment of UW perfusion and a reliable extrapolation for HTK-perfused human renal grafts. Copyright © 2007 John Wiley & Sons, Ltd. [source]


FEM-Simulation of Real and Artificial Microstructures of Mo-Si-B Alloys for Elastic Properties and Comparison with Analytical Methods,

ADVANCED ENGINEERING MATERIALS, Issue 10 2007
G. Biragoni
Various three phase microstructures of Mo-Si-B alloys were simulated in tensile loading conditions using a 2D finite element method to predict the elastic properties of the composite material. Voronoi structures with the same areal fraction of phases as the real microstructures have been generated and simulated similarly. Also, with these Voronoi structures a variation of grain or phase sizes, respectively, was carried out for different compositions in order to study on the elastic properties of the composite. Finally, a comparison was made over the whole temperature range between the above numerical methods, classical analytical approaches and experimentally determined values for Young's modulus E, shear modulus G and Poisson's ratio ,. [source]


Kinetics of the gas-phase reaction of n -C6,C10 aldehydes with the nitrate radical

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 3 2003
Jun Noda
Rate coefficients for gas-phase reaction between nitrate radicals and the n -C6,C10 aldehydes have been determined by a relative rate technique. All experiments were carried out at 297 ± 2 K, 1020 ± 10 mbar and using synthetic air or nitrogen as the bath gas. The experiments were made with a collapsible sampling bag as reaction chamber, employing solid-phase micro extraction for sampling and gas chromatography/flame ionization detection for analysis of the reaction mixtures. One limited set of experiments was carried out using a glass reactor and long-path FTIR spectroscopy. The results show good agreement between the different techniques and conditions employed as well as with previous studies (where available). With butanal as reference compound, the determined values (in units of 10,14 cm3 molecule,1 s,1) for each of the aldehydes were as follows: hexanal, 1.7 ± 0.1; heptanal, 2.1 ± 0.3; octanal, 1.5 ± 0.2; nonanal, 1.8 ± 0.2; and decanal, 2.2 ± 0.4. With propene as reference compound, the determined rate coefficients were as follows: heptanal, 1.9 ± 0.2; octanal, 2.0 ± 0.3; and nonanal, 2.2 ± 0.3. With 1-butene as reference compound, the rate coefficients for hexanal and heptanal were 1.6 ± 0.2 and 1.8 ± 0.1, respectively. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 35: 120,129, 2003 [source]


Prediction of steady-state skin permeabilities of polar and nonpolar permeants across excised pig skin based on measurements of transient diffusion: Characterization of hydration effects on the skin porous pathway

JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 8 2002
Hua Tang
Abstract The applicability of a two-parameter Fickian diffusion model for predicting the skin steady-state permeability based on measurements of the transient transport of permeants across the skin was tested. Using five model permeants possessing different physicochemical properties and pig skin as the model membrane, the skin permeabilities predicted by the two-parameter Fickian diffusion model were compared with the measured skin permeabilities. Results show that the transient skin permeation profiles of the hydrophobic permeants, estradiol, testosterone, and dolichol, across split-thickness pig skin can be modeled adequately by the two-parameter Fickian diffusion model (with constant parameter values), and therefore, that this model can be utilized to shorten the experimental time required to determine the skin permeabilities of these compounds. However, the skin permeabilities of the highly hydrophilic permeants, mannitol and sucrose, predicted by the two-parameter Fickian diffusion model (with constant parameter values) were significantly lower than the experimentally determined values, indicating that the dominant skin pathway of polar permeants within the excised pig skin undergoes significant structural changes during the in vitro diffusion cell studies. Although the skin permeability values determined experimentally using the traditional steady-state method normally correspond to a highly hydrated skin sample, the two-parameter Fickian diffusion model enables an estimation of the skin permeability of the skin membrane at its less-hydrated state (a condition more representative of in vivo and clinical situations). Using the two-parameter Fickian diffusion model and a recently developed skin porous-pathway theory, the effects of skin hydration on the skin porous pathway within the excised pig skin were characterized. Specifically, we found that hydration leads to induction of new pores/reduction of the tortuosity of existing pores within the excised pig skin during the 48 h diffusion cell studies conducted, while the skin average pore radii remain relatively constant (,26 Å) for up to 48 h. © 2002 Wiley-Liss Inc. and the American Pharmaceutical Association J Pharm Sci 91:1891,1907, 2002 [source]


Pharmacokinetics and allometric scaling of levormeloxifene, a selective oestrogen receptor modulator

BIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 3 2003
O. Østerberg
Abstract The pharmacokinetics of a new selective oestrogen receptor modulator levormeloxifene was investigated in mice, rats, cynomolgus monkeys and humans by compartmental pharmacokinetics. Levormeloxifene was administered as an oral solution in all studies. Allometric scaling was used to predict human pharmacokinetic parameters and the performance of the approach was evaluated. Mean values of clearance confounded by F(CL/F) were 0.073, 0.29, 3.18 and 2.4 l/h in mice, rats, monkeys and humans, respectively. Values of distribution volume at steady state confounded by F(Vss/F) were 0.073 and 7.5 l in mice and rats. In monkeys, values of the central volume F(Vc/F) and volume at steady state F(Vss/F) were 28.9 and 57.9 l, respectively. In humans, values of Vc/F and Vss/F were 106 and 587 l, respectively. Predicted CL/F and Vss/F showed a linear relationship when plotted vs BW on a log,log scale; for CL/F, r was 0.95,0.98 and for Vss/F, r was 0.99. Using allometric scaling the predicted human Vss/F deviated 3-fold from the experimentally determined values. Observed values of CL/F deviated 21,25 fold from the predicted, the latter depending on the scaling method. Confidence intervals for the predicted parameters showed major lack of precision for all the allometric scaling methods. Copyright © 2003 John Wiley & Sons, Ltd. [source]