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排序方式: 共有621条查询结果,搜索用时 15 毫秒
1.
Al.Th. Kermanidis D.G. Stamatelos G.N. Labeas Sp.G. Pantelakis 《Theoretical and Applied Fracture Mechanics》2006,45(2):148-158
The synergetic effect of corrosion and corrosion induced hydrogen embrittlement damage processes which occur at local scale has been found to result in a dramatic macroscopic tensile ductility loss of the 2024 aluminum alloy. In the present work, the tensile behaviour of corroded 2024 T351 specimens has been estimated on the basis of FE analysis by taking into account the local material properties in the damaged areas. A parametric study is involved to account for the effect of thickness in the results. Calculated tensile properties obtained with the analysis agree well with experimental data. 相似文献
2.
V. D. Fedotov N. P. Obuchov R. A. Zadikhanov J. Spěváček J. Straka 《Applied magnetic resonance》1993,4(4):491-511
The combined analysis of1H and13C NMR relaxation data in solid lysozyme and some typical homopolypeptides was carried out by using “model-free” approach. Three types of relaxation transitions (γ’, γ and β) were revealed in the temperature range investigated. The microdynamical parameters of these motions were determined. From the comparison of these parameters with those of selected synthetic polymers it follows that the molecular motions in proteins and synthetic polymers are of the same nature. All these motions show pronounced anisotropic character. In the investigated temperature range no molecular motions corresponding to α-relaxation (liquid-like) transition were revealed. The hydration effects on parameters of the motions in proteins were considered. The most pronounced effect takes place for β-transition. The effect of Brownian rotation of protein molecule in solution on measured correlation function of local motions was also discussed. 相似文献
3.
Th. Lagouri Sp. Dedoussis M. Chardalas A. Liolios 《Journal of Radioanalytical and Nuclear Chemistry》1996,211(1):181-185
Positron lifetime and Doppler broadening of the annihilation line measurements were performed in highT
c
superconducting samples YBa2Cu3Cd
x
O
y
,x=0, 0.05 and 6.9<y<7, as a function of temperature in the region of 14–300 K. It was found that the positron lifetime and theS parameter values are lower in the Cd doped sample than those in the undoped one. It was also observed that the positron annihilation parameters show similar temperature dependence for the undoped and Cd doped samples. We conclude that the Cd doping in highT
c
superconductor YBa2Cu3Cd
x
O
y
, 6.9<y<7 fills defects associated with oxygen vacancies probably in oxygen deficient regions which can trap positrons. 相似文献
4.
Summary The problem is considered of orthogonal 1 fitting of discrete data. Local best approximations are characterized and the question of the robustness of these solutions is considered. An algorithm for the problem is presented, along with numerical results of its application to some data sets. 相似文献
5.
Nils G. A. Ekelund Christer Sundqvist Peter H. Quail Richard D. Vierstra 《Photochemistry and photobiology》1985,41(2):221-223
Abstract— From light-induced changes in linear dichroism, we have calculated the rotation of the long-wavelength-absorbing transition moment that occurs during phototransformation of 124-kilodalton Avena sativa phytochrome. Phytochrome was purified to homogeneity and immobilized onto Sepharose beads covalently coated with antibodies against A. sativa phytochrome. Changes in linear dichroism were induced by plane-polarized red or far-red light and measured by the absorbance differences at 660 and 730 nm using a dual-wavelength spectrophotometer equipped with polarizing filters in the measuring beams. From such measurements, we calculate a rotation angle of 31o (or 149o ) during photoconversion of Pr to Pfr and 30o (or 150o ) during photoconversion of Pfr to Pr. These values are similar to the value of 32o (or 148o ) reported earlier for the rotation of the transition moment of "large" A. sativa phytochrome (∽ 120 kilodalton) isolated under conditions that did not preclude post homogenization proteolysis of the 124 kilodalton molecule. 相似文献
6.
Christer Albano William Dunn Ulf Edlund Erik Johansson Bo Nordén Michael Sjöström Svante Wold 《Analytica chimica acta》1978,103(4):429-443
Problems of pattern recognition in chemistry and other subjects can be divided conveniently into four different types depending on the level of scope of the problem.(1) Classification into one of a number of defined classes. As an example blood samples taken from persons known to be either controls or welders are considered. The problem is whether trace element concentrations in these samples contain information on whether or not a person is a welder.(2) Level 1 plus the possibility that an object is an outlier, i.e. does not belong to any of the defined classes. As an example, the üse of 13C-n.m.r. data to decide whether 2-substituted norbornanes have the exo or endo structure is discussed. (2A) Level 2, asymmetric. This situation occurs when one class does not have a systematic structure, but another class is homogeneous and can be described by a level 2 model. This occurs in the classification of materials or compounds as good or bad, active or inactive, and in binary classifications. As an example the use of trace element data to classify steel samples as having good or poor properties of strength is discussed.(3) Level 2 plus the ability to relate the variables measured to external properties of continuous character. As an example, the classification of a series of chemical compounds as β -receptor blockers, β -receptor stimulants, or neither, on the basis of their structural variables is discussed. In addition, relations between these structural variables and the measured biological activity are sought within each of the two classes.(4) Level 3 with the difference that several external property variables in the objects are measured. It may be desirable to use variables of the objects both for classification and for relations to several property variables: such examples are numerous in analytical chemistry. 相似文献
7.
Fourier transform infrared reflection-absorption spectroscopy (FT-IRAS) has been used to study the orientation and coordination of glycine, L-phenylalanine and L-histidine on gold and copper surfaces. It was found that glycine and L-histidine were weakly adsorbed (physisorbed) in the zwitterionic form on gold. The surface chemical bonding of L-histidine and L-phenylalanine to copper were chemical rather than physical by nature. Conclusive evidence was obtained for coordination to copper through both the amino-nitrogen and carboxylate-oxygen atoms. 相似文献
8.
V. Spěváček 《Tetrahedron》1973,29(15):2285-2291
Reaction mechanism of halogen exchange between arylhalogenide and halogenide anion is studied in a case when the aromatic core is inactivated with respect to the SNAr substitution by other substituents. The exchange of iodine between o-iodobenzoic acid and 131I labelled NaI serves as a modelling reaction. The reaction was found to proceed heterogeneously on a glass surface. In the case of a rapid course of the surface reaction the reaction mechanism is more complicated and the equation derived by McKay cannot be applied for expressing the time dependence of the degree of isotopic exchange. Reaction mechanism was proposed for this reaction and compared with experimental data. 相似文献
9.
Boron-doped diamond (BDD) electrodes were used to investigate the possibility of detecting aniline by linear-sweep cathodic stripping voltammetry. It was found that the dimeric species (p-aminodiphenylamine and benzidine) formed by anodic oxidation of aniline during the accumulation period are involved in electrochemically reversible redox processes and, in acidic media, the shape of the stripping voltammetric response is suitable for aniline detection in the micromolar concentration range. The low background current of conductive diamond is an advantage compared to other electrode materials and allows a detection limit of 1 μM. Weak adsorption properties and the extreme electrochemical stability are additional advantages of BDD and it was found that, even after long-time measurements, the electrode surface can regain its initial activity by an anodic polarization in the potential region of water decomposition. 相似文献
10.
Habermann W John P Matschiner H Spähn H 《Analytical and bioanalytical chemistry》1996,356(3-4):182-186
Redox electrodes made of passivated metals of the subgroups IV to VI of the periodic system with a surface coating of n-conducting metal oxides, generated by oxidizing agents or anodic oxidation, are well suited for measuring the concentration of oxidizing agents. Neither oxygen nor reducing agents affect the measurements. There is a correlation between the mean conductivity of the passive layer and its selectivity. The aged n-conducting passive layers permit reproducible potential settings, and the occurring changes in potential are greater than what is to be expected according to the Nernst equation. The potentiometric measuring of nitrosyl ions and chlorine is used as an example to demonstrate the selectivity of these electrodes. 相似文献