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Thermoluminescence dating of a set of 29 pottery sherds excavated at the neolithic sites of El Kadada and El Ghaba (near Shendi, Central Sudan) was carried out at Bordeaux University. The archaeological dose was measured using the fine grain technique. The annual dose was determined by analytical techniques (neutron activation analysis, ICP spectrometry, XRF, low background gamma spectrometry) and by “on-site” measurements of the environmental radioactivity (gammametry). The crystalline inclusions of the samples were characterized by optical microscopy and cathodoluminescence: the TL minerals mainly consist of quartz and K-feldspar crystals. In some cases, radioactive inclusions of zircons and monazites are observed. The TL and the radiocarbon dates show a good agreement, verifying the validity of the radiocarbon ages which were suspected to be too old because of the nature of the dated material (shells). Taking into account all the chronological data, it is shown that El Ghaba and El Ghaba necropolis were used respectively within the 4800-3300 B.C. and 4200-3000 B.C. date-ranges for neolithic cultures, the occupation of El Kadada starting five or six centuries later than El Ghaba. 相似文献
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D. E. Barraco R. Guibert V. H. Hamity H. Vucetich 《General Relativity and Gravitation》1996,28(3):339-345
A brief review of a first order theory with a quadratic LagrangianL=R+0R2 is presented. It is shown that a test particle follows a geodesic of the metric connection. The theory behaves in the Newtonian limit as the Newtonian theory with a correction which is proportional to the matter density at the field point. This behavior can be produced by a Yukawa potential with an atomic scale characteristic range and a coupling constant proportional to 1/
2. This type of potential is not excluded by the present experimental data. 相似文献
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Xavier Cameleyre Alain Bouchu Alain Guibert Didier Combes 《Applied biochemistry and biotechnology》1997,62(1):61-69
The synthesis of L-tyrosine fructosyl ester, from fructose and L-tyrosine methyl ester, was carried out by a transesterification
reaction catalyzed by α-chymotrypsin in water without cosolvent. The effect of fructose concentration and temperature for
the transesterification reaction were determined on both specific activities and product yield. The influence of the presence
of fructose has been studied regarding α-chymotrypsin and L-tyrosine fructosyl ester stabilities. It appeared that an increase
of temperature enhanced enzyme activity but slumped the product yield because of the very weak stability of tyrosine fructosyl
ester. 相似文献
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The objective of this study is to investigate 3-pentanone fluorescence experiments in a constant volume vessel at high temperature
and high pressure to underline the influent parameters in conditions close to those encountered in internal combustion engines.
To obtain quantitative analysis, measured fluorescence signals must be corrected by considering the influence of preponderant
parameters such as temperature, pressure and gas composition. Quantitative dependences of fluorescence on thermodynamic parameters
are measured and compared with the predictions of a photophysical model, which combines the effects of temperature, pressure,
excitation wavelength on fluorescence quantum yield. The increase of 3-pentanone fluorescence with pressure is due to the
vibrational relaxation of energy levels. The fluorescence decreases with increasing temperature, except at low temperature
where the fluorescence increase is due to an activation of intersystem crossing between triplet toward singlet levels. The
influences of thermodynamic parameters are based on an increase of the non-radiative decay rate with the vibrational energy
level of excited electronic state and the important collisions to remove the excess vibrational energy. Experimental and calculated
results show a satisfactory agreement.
PACS 33.20; 33.50; 34.90 相似文献
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The ammonium removal efficiency (ARE) and cell viability was investigated in freshly isolated rat hepatocytes exposed to increasing ammonium loads (0.1-2.0 mM). No difference was observed in both ARE and cell viability at the different ammonium concentrations tested. Storage of hepatocytes at 0 degrees C for 72 hours inhibited ammonium removal and urea synthesis. Rewarming of cells at 37 degrees C for 120 min was followed by an ARE fully comparable to freshly isolated hepatocytes. These data indicated that cold preservation of rat hepatocytes for 3 days in UW followed by a rewarming is associated with normal ammonium detoxification efficiency. 相似文献
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We devised a simple method for determining the cryoprotectant agents 1,4-butanediol or 2,3-butanediol in isolated rat hepatocytes. After extraction of of hepatocytes with water (containing internal standard - ethylene glycol 1.25 mg/mL) the diol content was analyzed by gas chromatography. The method shows a linear response in the range 0.125 to 2.50 mg/mL for 1,4-butanediol and 0.25 to 3.75 mg/mL for 2,3-butanediol. The accuracy and precision of the method were evaluated and the coefficients of variation were found to be within = 6.0 %. The recoveries from hepatocyte samples containing 0.50, 1.00 and 2.00 mg/mL were 91.0 to 108 % for 1,4-butanediol and 80.6 to 100.3 % for 2,3-butanediol, respectively. This method allowed the determination of the intracellular concentration of diols in hepatocytes preserved for up to 120 hours at - 4 (C in UW solution + 8 % w/v 1,4-butanediol (or 2,3-butanediol). 相似文献
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