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41.
利用复合靶共溅射法制备了半磁性半导体 Pb1- x Cox Se 薄膜.研究了薄膜的成分结构以及电阻率温度特性和磁化率温度特性间的关系.结果表明:由于 Co 离子介入, Pb1- x Cox Se 发生了由金属特性向半导体特性的转变,在充分低的温度下,并伴有磁相转变.磁相转变温度与磁性离子浓度相关,磁化率的相对变化幅度与磁性离子浓度有关 相似文献
42.
P. Guinebault C. Dubruc A. Haddouche C. Colafranceschi G. Bianchetti 《Chromatographia》1988,26(1):377-382
Summary In order to follow levels of S-Carboxymethyl-L-cysteine in biological fluids for a period as long as three half-lives after drug administration during pharmacokinetic studies, an improved method for its determination had to be developed. Like the previous one, this method uses a protein precipitation step followed by an O-Phthalaldehyde derivatization step and then an HPLC on-line clean-up. This latter was obtained by means of a switching valve system, including a Nucleosil CN 5 m (3 cm × 4.6 mm i.d.) precolumn and a Spherisorb ODS 5 m (15 cm×4.6 mm i.d.) analytical column. The sensitivity limit was improved to 0.1 g/ml in plasma samples and 0.2 g/ml in urine samples.This method was applied in studies comparing single (0.75 g) and repeated (0.75 g tid) oral administration of the drug to 30 elderly patients and 20 healthy volunteers. Results showed that the half-life was 40% longer in elderly patients than in healthy volunteers, and that area under the plasma concentration versus time curve (AUC) values in elderly patients were twice those obtained with young subjects. 相似文献
43.
Elasticity of various poly(hydroxybutyrate) (PHB) molecules of regular and irregular conformational structure was examined by the molecular mechanics (MM) calculations. Force - distance functions and the Young's moduli E were computed by stretching of PHB molecules. Unwinding of the 2(1) helical conformation H is characterized at small deformations by the Young's modulus E = 1.8 GPa. The H form is transformed on stretching into the highly extended twisted form E, similar to the beta-structure observed earlier by X-ray fiber diffraction. The computations revealed that in contrast to paraffins, the planar all-trans structure of undeformed PHB is bent. Hence, a PHB molecule attains the maximum contour length in highly straightened, but slightly twisted conformations. A dependence of the single-chain moduli of regular and disordered conformations on the chain extension ratio x was found. The computed data were used to analyze elastic response of tie (bridging) molecules in the interlamellar (IL) region of a semi-crystalline PHB. A modification of the chain length distribution function of tie molecules tau(N) due to secondary crystallization of PHB was conjectured. The resulting narrow distribution tau(N) comprises the taut tie molecules of higher chain moduli prone to overstressing. The molecular model outlined is in line with the macroscopically observed increase in the modulus and brittleness of PHB with storage time. 相似文献
44.
A simple and extractionless HPLC method using fluorescence detection was developed for the determination of rosiglitazone in human plasma. After deproteinization using perchloric acid the plasma samples were directly injected onto the HPLC system. The mobile phase was composed of acetonitrile (52%) and 20 mm ammonium acetate (48%, pH 7.5), and analysis was run at a flow rate of 0.2 mL/min with the detector operating at 247 nm for excitation wavelength and at 367 nm for emission wavelength, respectively. The method has a mean recovery of 97%, while the intra-day and inter-day precisions were all less than 7%. This method is simple, specific, sensitive and requires only a small plasma volume with short analytical time, and is suitable for the determination of plasma rosiglitazone in routine measurements for pharmacokinetic studies. 相似文献
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46.
The distribution of the distance between two (or more) successive occurrences of a specific word in a random sequence of letters is known under different models. In this paper, a more general problem is studied: the distribution of the distance between two (or more) successive occurrences of any word of a given set under a Markov model for the sequence. The generating function and a recurrence for obtaining the probabilities are given. These results are applied to study the distribution of the "CHI" motif in the genome sequence of Haemophilus influenzae. 相似文献
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49.
P. Karvonen T. Sonoda I. D. Moore J. Billowes A. Jokinen T. Kessler H. Penttilä A. Popov B. Tordoff J. Äystö 《The European physical journal. Special topics》2007,150(1):283-284
The ion guide technique was developed in Jyv?skyl? during the early 1980's. In the ion guide the reaction recoil products
are stopped and thermalized in high purity helium gas where they remain ionic due to high ionization potential of helium atoms.
Different designs of ion guide exist for light-ion induced fusion reactions, for heavy-ion induced fusion and for proton induced
fission. Although the IGISOL method is fast and universal it is chemically unselective and in many cases relatively inefficient.
In order to address these deficiencies in the technique, a new laser ion source project, FURIOS (Fast Universal Resonant laser
Ion
Source), commenced in 2004. In addition, resonance ionization spectroscopy has been tested off – line within a sextupole ion
beam
guide. 相似文献
50.
An integrated solid-phase spectrophotometry/flow injection analysis (FIA) method is proposed for the determination of the
synthetic colorant matter Ponceau 4R (P4R) in the presence of its unsulfonated derivative 2-hydroxy-1-[(naphthalenyl)azo]
naphthalene (N2N). The procedure is based on the measurement of P4R at λ = 508, followed by retention and preconcentration
of the low level concentration of N2N on a C18 silica gel minicolumn and subsequent measurement of the absorbance of N2N at λ = 508 nm after its elution. The applicable
concentration range, the detection and the relative standard were the following: for P4R, from 0.30 to 20.0 mg/L; 0.052 mg/L
1.1%; and for N2N, between 0.020 to 3.0 mg/L 0.003 mg/L and 1.1%. The method was applied to the determination of small amounts
of N2N present in P4R in food and cosmetic products. Percentages of recovery between 95 and 105% were obtained in all instances.
The method was applied satisfactorily to the determination of the compounds P4R and N2N in samples of sweets and cosmetic
products when compared to results offered by a HPLC reference method.
Received April 5, 2001. Revision July 25, 2001. 相似文献