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Poly(carbonates) derived from diphenols that contain Si or Ge and bisphenol A bis(chloroformate) have been synthesized using phase-transfer conditions. The products were characterized by spectroscopic methods. Two phase-transfer catalysts and three molar ratios of NaOH/diphenol were used. The results were evaluated by the yields of product and their inherent viscosities. The data were compared with materials obtained without the catalyst and showed that the new synthetic technique was effective for the synthesis of these types of poly(carbonates). An increase in the concentration of NaOH and the phase-transfer catalysts increased the yields and inh values compared to those obtained with stoichiometric quantities of NaOH. It is proposed that the differences in electronegativities of the heteroatoms in the diphenols are responsible for this behaviour.  相似文献   
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We studied the effects of sodium nitroprusside, a nitric oxide donor, on the chemosensory responses to cyanide and nicotine in the cat carotid body. In situ, sodium nitroprusside infusion reduced the cyanide-evoked responses in a dose-dependent manner. In vitro, Tyrode containing nitroprusside reversibly reduced the cyanide- (by 59%) and nicotine-induced (by 45%) chemosensory responses. The present results suggest that chemosensory responses induced by cyanide and nicotine are reduced by increased nitric oxide content, similarly to the hypoxic chemosensory responses.  相似文献   
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Today in reliability analysis, the most used distribution to describe the behavior of devices is the Weibull distribution. Nonetheless, the Weibull distribution does not provide an excellent fit to lifetime datasets that exhibit bathtub shaped or upside‐down bathtub shaped (unimodal) failure rates, which are often encountered in the performance of products such as electronic devices (ED). In this paper, a reliability model based on the exponentiated Weibull distribution and the inverse power law model is proposed, this new model provides a better approach to model the performance and fit of the lifetimes of electronic devices. A case study based on the lifetime of a surface‐mounted electrolytic capacitor is presented in this paper. Besides, it was found that the estimation of the proposed model differs from the Weibull classical model and that affects the mean time to failure (MTTF) of the capacitor under analysis.  相似文献   
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One of the most important bases for designing robust closed-loop controllers applied to induction motor with high performance is establishing its mathematical model and state observers, as well as the parameter identification with high accuracy. In this paper, a step-by-step mathematical model of the squirrel-cage induction motor is described at αβ coordinate frame where the parameters are defined in detailed form; the rotor flux linkages and load torque are estimated via an asymptotic observer; the induction motor parameter identification is performed via a data acquisition board, applying dynamic and steady-state tests. Inductances of the induction motor model are calculated using the proposed relationships between the magnetically coupled circuit and equivalent circuit model. The mathematical model, state observers, and parameter identification procedure of squirrel-cage induction motor are validated via comparison of simulation signals with their corresponding real-time signals. This validation is made experimentally by a steady-state test, where load conditions are changed via a dynamometer which is belt coupled with the squirrel-cage induction motor.  相似文献   
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This paper examines strengths and weaknesses of companies in the context of the value chain as a way to assess a manufacturing firm. For doing this, the executives of 20 companies were interviewed and asked about the strengths and weaknesses they thought their companies had. The responses were classified according to the elements of the value chain and new sub-classifications were created. In this way, it was possible to discover the main concerns the executives had about their company and to see if there were some comonality in their responses. It was found that the main concerns were in the areas of Production and Sales, as opposed to Finances, Human Resources, Technology and Procurement. As a result, a proposition is made about the use of this value chain and its dimensions as a way for rapid internal assessment of a manufacturing firm. A case study is presented in which the developed tool was implemented. An internal analysis of a company was undertaken in few hours.  相似文献   
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Commercial transparent glass has received attention in relation to its use as a gamma radiation detector. This kind of material presents a strong post-irradiation thermal decay at room temperature, which is a problem for high dose dosimetry purposes. This effect may be avoided by taking measurements always at the same time after irradiation of the glass samples. However, in this work effort has been given to this material characteristic, submitting the glass samples to different thermal treatments. The best results were obtained with a post-irradiation treatment at 130 degrees C during 10 min. This procedure seems to destroy the unstable entities responsible for the initial strong decay of the sample response, showing acceptable stability as a function of room temperature storage time.  相似文献   
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Today, in reliability analysis, the most used distribution to describe the behavior of electronic products under voltage profiles is the Weibull distribution. Nevertheless, the Weibull distribution does not provide a good fit to lifetime datasets that exhibit bathtub‐shaped or upside‐down bathtub–shaped (unimodal) failure rates, which are often encountered in the reliability analysis of electronic devices. In this paper, a reliability model based on the beta‐Weibull distribution and the inverse power law is proposed. This new model provides a better approach to model the performance and fit of the lifetimes of electronic devices. To estimate the parameters of the proposed model, a Bayesian analysis is used. A case study based on the lifetime of a surface mounted electrolytic capacitor is presented, the results showed that the estimation of the proposed model differs from the inverse power law–Weibull and that it affects directly the mean time to failure, the failure rate, the behavior, and the performance of the capacitor under analysis.  相似文献   
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