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排序方式: 共有112条查询结果,搜索用时 15 毫秒
1.
In this paper, we consider the classical finite mixture model, which is an effective tool for modeling lifetime distributions for random samples from heterogeneous populations. We discuss new results on stochastic comparison for two finite mixtures when each of them is drawn from one of the following semiparametric families, i.e., proportional hazards, accelerated lifetime and proportional reversed hazards. 相似文献
2.
Sibel Akgün Gülsüm Ekici Nilüfer Mutlu Necati Beşirli Baki Hazer 《Journal of Polymer Research》2007,14(3):215-221
Modification of chitosan by grafting of vinyl butyrate was carried out in homogeneous phase using potassium persulfate as
redox initator and 1.5% acetic acid as solvent. The percent grafting and grafting efficiency were analysed and the high grafting
efficiency up to 94% was observed. The effects of reaction variables such as monomer concentration, initiator concentration,
temperature and reaction time were investigated. It was observed that the solubility of chitosan was markedly reduced after
grafting with vinyl butyrate. The grafted product is insoluble in common organic solvents as well in dilute organic and inorganic
acids. Characterization of the graft copolymers were carried out by using Fourier Transform Infrared Spectroscopy (FTIR),
Differential Scanning Calorimetry (DSC) and Scanning Electron Microscopy (SEM) technics. Characteristic signal of carbonyl
group was observed at 1,731 cm−1 which belongs to the poly vinyl butyrate segments in the graft copolymer. The melting transition of the chitosan main chain
in the copolymer shifted to 124°C from its original value 101°C. In addition to these, we have also studied topology of the
graft copolymer and the SEM micrograph showed continuous homogenous matrix which means there is no phase separation. 相似文献
3.
In this paper, regression analyses (RA) are presented for the neutronic calculation of ThO2 mixed 244CmO2 fuel with different neutronic parameters for various coolants, natural lithium, Li20Sn80 and Flinabe, respectively. The tritium breeding ratio (TBR), energy multiplication factor (M), total fission rate (Σf) and 232Th(n, γ) reaction is computed by XSDRNPM. In addition, this numerical results are estimated by RA depends on neutronic parameters and the empirical equations for neutronic performance are acquired. The results obtained by using XSDRNPM and the results of the RA, obtained empirical equations, are compared. The empirical equations indicate that RA can successfully be used for the prediction of the neutronic performance parameters in the hybrid reactor with a high degree of accuracy. In addition, correlation matrix is calculated to determined statistical relationships between variables TBR, M, Σf, and 232Th(n, γ). 相似文献
4.
Georgy A. Tskhondiya Nil N. Beklemishev 《International Journal of Material Forming》2012,5(2):157-162
A certain pulse of electric current combined with plastic deformation is a powerful tool for improving the formability of hard-to-deform metal alloys. In recent years, much research has indicated that the current not only improves macro-mechanical properties but also influences microstructural-level phenomena such as recrystallization, local phase transformation, grain refinement, and even amorphous nanocrystallization. Despite the huge experimental dataset, virtually no focus has been placed on phenomenon??s computing. In this fashion, present paper concerned with the continuum-level numerical analysis of the pulse impact on the stress field during plastic deformation. Computation conducted herein has shown that a high density electric current pulsing weakens the stress field during plastic deformation. Ultimate results of the study should be useful in developing the novel metal processing technology. 相似文献
5.
Ethylene epoxidation was studied as a function of oxygen coverage; for three different surfaces (111), (100) and (110) of three different IB metals using periodical DFT calculations. Oxygen coverage dependence was tested for 11, 25 and 33?% surface oxygen on Ag(111) surface. Calculations showed that increasing oxygen amount increased the exothermicity of the reaction while lowering the activation barriers. At studied oxygen ratios ethylene oxide and acetaldehyde formations proceed through OMC intermediate. In agreement with earlier studies, predicted selectivity is independent of surface structure. Generally the activation barriers for aldehyde formation are lower than those for epoxide formation on the studied surfaces. On copper surfaces the high stability of the precursor intermediates caused high activation barriers for the product formations. Also, epoxide formation is endothermic with respect to pre-oxygenated copper surfaces. On the other hand gold surfaces showed the smallest activation barriers for the product formations. Ag surfaces did not show conclusive differences for the activation barriers for epoxide versus aldehyde formation, which is in agreement with the ~50?% EO selectivity of the un-promoted metallic silver. 相似文献
6.
Akin Mustafa Günsel Armağan Bilgiçli Ahmet T. Tüzün Burak Arabaci Gulnur Şaki Neslihan Yarasir M. Nilüfer 《Protection of Metals and Physical Chemistry of Surfaces》2020,56(3):609-618
Protection of Metals and Physical Chemistry of Surfaces - Corrosion inhibition effects of water-soluble peripheral substituted cobalt, copper and zinc metallophthalocyanines (CoPc (1), CuPc (2) and... 相似文献
7.
Research has shown that most reported foodborne outbreaks are caused by food prepared and consumed at home, thus emphasizing the importance of consumer food safety knowledge. In this study, 2,000 randomly selected residents from ?anakkale, Turkey, participated in face-to-face interviews to assess their food safety perceptions and practices. Questions covered the attention given to expiration dates, safety certificates, and food additives during shopping; consumption of high-risk foods; safe food handling; storage knowledge; and their source of food safety knowledge. Statistical analyses were done to clarify the differences according to three main aspects: gender, age, and educational level. Results showed that women and middle-aged respondents were significantly more careful during shopping and more interested in food safety issues than men and younger individuals. A significant relationship was found between gender and consumption of high-risk foods, with men consuming more of these foods than women. Furthermore, high-risk foods were more frequently consumed by young participants than by older participants, with more highly educated consumers shopping more consciously. Although most respondents appeared to know proper food handling and storage practices, almost all participants lacked some information on some issues. In order to remove these deficiencies, a brochure was prepared and distributed to people in various parts of the city. In addition, public seminars were organized. However, to ensure that this information results in positive attitude and behavioral changes, seminars should be repeated at specific intervals, and education procedures and processes should be controlled regularly. 相似文献
8.
A compact active inductor circuit is proposed. The circuit is based on the gyrator-C approach with both transconductance stages
realized by MOS transistors in common-source configuration. The circuit has minimal number of transistors, is suitable for
low voltage operation, offers a wide inductive band, high quality factor and low power dissipation. Simulation results are
provided for a 0.13 μm CMOS process with 1.2 V supply voltage. 相似文献
9.
In this study, the lead concentrations of chewing gum samples having different compositions were determined by solid sampling electrothermal atomic absorption spectrometry. In order to optimise the experimental conditions, the effects of pyrolysis temperature, atomization temperature, sample amount and sample thermal pre-treatment, on the analyte sensitivity were investigated. The samples were ashed at 400 °C for 2 h prior to directly determined by SS-ETAAS applying 600 °C of pyrolysis and 1600 °C of atomization temperatures without to add a modifier, acid and/or surfactant. The relationship between sample mass and integrated absorbance was linear up to 1.2 mg of sample; for higher sample mass the relationship was no longer linear, irrespective of the lead content. In addition, the thermally treated chewing gum samples were digested using concentrated HNO3. The lead concentrations found by the two methods in 27 different kinds of samples were not significantly different at 95% confidence level. The proposed solid sampling technique was fast, simple, the risks of contamination and analyte loss were low. Detection limit (3σ) for lead was 0.017 ng/g. 相似文献
10.
Mridula Biswas Kannakaje Shashidhara Prasanta Kumar Ojha Tapas Kumar Chongdar Nil Ratan Bandyopadhyay 《Journal of the American Ceramic Society》2008,91(3):934-937
Nanocrystalline yittria-stabilized zirconia (YSZ) compounds with yittria concentration varying between 8 and 12 mol% have been synthesized by gel combustion method followed by heat treatment at 550°C. The YSZs are found to posses stable face centered cubic structure at room temperature by X-ray diffractometry. The lattice parameter ' a ' showed an increasing trend with increasing concentration of yittria. The crystallite size estimated by Scherrer method was in the range of 7–10 nm. Band gap studies showed an increasing trend with increasing yittria concentration and are found to be consistent with respective lattice parameters following the tight binding approximation or linear combination of atomic orbitals approximation. 相似文献