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991.
992.
The computation of boundary stresses by Boundary Element Method (BEM) is usually performed either by expressing the boundary tractions in a local co-ordinate system, calculating the remaining stresses by shape function differentiation and inserting into Hooke's law or recently also by solving the hypersingular integral equation for the stresses. While direct solution of the hypersingular integral equation, the so-called Somigliana stress identity, has been shown to be more reliable, the interpretation and numerical treatment of the hypersingularity causes a number of problems. In this paper, the limiting procedure in taking the load point to the boundary is carried out by leaving the boundary smooth and the contributions of all different types of singularities to the boundary integral equation are studied in detail. The hypersingular integral in the arising boundary integral equation is then reduced to a strongly singular one by considering a traction free rigid body motion. For the numerical treatment, an algorithm for multidimensional Cauchy Principal Value (CPV) integrals is extended that is applicable for the calculation of boundary stresses. Moreover, the shape of the surrounding of the singular point is studied in detail. A numerical example of elastostatics confirms the validity of the proposed method.  相似文献   
993.
994.
995.
The authors examined the subtype structure of smokers classified in the precontemplation stage of change within the transtheoretical model. From a general practice-based sample of 1,499 daily smoking patients from Germany (participation rate 80%), they used a subgroup of 929 smokers who were classified in the precontemplation stage and applied latent class analysis, using the pros and cons of nonsmoking and smoking cessation self-efficacy as the defining variables. Cross-sectional validation of the emerging classes was based on smoking behavior and processes of change variables. For longitudinal validation, generalized estimation equation analyses were used on motivational and abstinence criteria from 6-, 12-, 18-, and 24-month follow-ups. A 4-class model best represented the data. Three subtypes (labeled progressive, immotive, and disengaged pessimistic) were similar to clusters identified in U.S. studies. The 4th (disengaged optimistic), by contrast, was reminiscent of a type that had previously only emerged in a Dutch study. Cross-sectional and longitudinal validation results confirmed the distinctiveness and predictive power of the classes. The findings highlight the importance of tailoring interventions for smoking behavior change to the needs of different subgroups of precontemplating smokers. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
996.
The ultrafast dynamics of site-specific hydrogen bonds between an organic chromophore serving as hydrogen acceptor and a hydrogen-donating species in solution is studied by femtosecond vibrational spectroscopy. This new method gives specific insight into microscopic structural changes of hydrogen bonds initiated by electronic excitation of the chromophore. We study H-bonded complexes of coumarin 102 with the solvent CHCl3, and with phenol. Upon electronic excitation, the intermolecular hydrogen bond between proton donor and acceptor is cleaved within 200 fs, followed by a slower reorientation dynamics of the donor molecules extending into the picosecond regime. For CHCl3, this slower rearrangement is interpreted in terms of polar solvation. In complexes consisting of a coumarin molecule and two phenol moieties, the slower dynamics is related to geometry changes of the phenol–phenol hydrogen bond. The consequences of those results for a microscopic picture of polar solvation are discussed.  相似文献   
997.
Mal d 2, a thaumatin-like protein from apple was previously described to react to almost 75% of the apple allergic patient sera. Based on the molecular structure of this protein, the present study focused on the conformational stability of Mal d 2 in relation to in vitro IgE-binding under different physico-chemical conditions and proteolysis. The structural integrity of Mal d 2 was monitored using SDS–PAGE, Western blotting using polyclonal antibodies and human sera, fluorescence spectrometry and circular dichroism. Results confirmed the stability of Mal d 2. However, Mal d 2 was reactive to human serum IgEs mainly after reduction of disulphide bridges fixing the α-helical domain II. Contrary to previous assumptions, the current findings suggest that the allergenic epitopes of Mal d 2 are hidden inside the protein structure and none of the rigorous conditions applied in industrial juice processing or digestive proteolysis enhance or reduce the binding to IgE molecules.  相似文献   
998.
Lipoxidation in almond-derived products was investigated using the chemiluminescence (CL) and thiobarbituric acid-reactive substances (TBARS) methods to detect the first and later reaction products, respectively. The effects of light during storage at 5 °C, 22 °C and 40 °C were studied, as well as the effects of combined heat/water activity treatments in the 60–120 °C and 0.38–0.72 range. During storage, light was found to enhance the CL and TBARS values, and specific responses were observed in almond paste and the final Calisson product. During the heating of almond paste, as the initial water activity (aw) increased, the CL rate constants increased during heating to 60 °C and 80 °C, but interestingly, these values decreased during further heating to 120 °C, whereas the maximum TBARS rate constants occurred at aw 0.57 at all the heating temperatures tested. The activation energies, based on the CL and TBARS values, decreased specifically when the aw increased from 0.38 to 0.72, giving overall values ranging from110 kJ mol−1 to 60 kJ mol−1. Likewise, in the same water activity range, the temperature-dependent rate constant enhancing factor (Q10) decreased from 3.3 to 1.6.  相似文献   
999.
1000.
The main objective of this work is to detect any associative or synergistic effects between TiO2 and activated carbon in 4-chlorophenol photodegradation. Different activated carbons (AC) were prepared from Tabebuia pentaphyla wood by means of physical activation with CO2 or by extensive carbonization under N2 flow at temperatures from 450 °C up to 1000 °C during 1 h. Results indicate a clear correlation between photocatalytic activities of titania with texture and surface chemistry of AC. Kinetic results of 4-chlorophenol photodegradation indicate that for most of mixed TiO2 and AC solids a synergistic effect between both solids is observed. Surface nano-aggregation of TiO2 on AC was observed by scanning electronic microscopy and dispersion of TiO2 nanoparticles was improved as a function of more basic surface pH of AC. In conclusion, an increase of electronic density in carbon support clearly introduces an enhancement in titania's photoactivity for 4CP photodegradation. This beneficial effect indicates that it is possible to obtain clean water in a much shorter period of time by employing some selected AC in conjunction with TiO2.  相似文献   
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