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排序方式: 共有1579条查询结果,搜索用时 15 毫秒
1.
Plastic encapsulated microcircuits (PEMs) are increasingly being used in applications requiring operation at temperatures lower than the manufacturer’s recommended minimum temperature, which is 0°C for commercial grade components and −40°C for industrial and automotive grade components. To characterize the susceptibility of PEMs to delamination at these extreme low temperatures, packages with different geometries, encapsulated in both biphenyl and novolac molding compounds, were subjected to up to 500 thermal cycles with minimum temperatures in the range −40 to −65°C in both the moisture saturated and baked conditions. Scanning acoustic microscopy revealed there was a negligible increase in delamination at the die-to-encapsulant interface after thermal cycling for the 84 lead PQFPs encapsulated in novolac and for both 84 lead PQFPs and 14 lead PDIPs encapsulated in biphenyl molding compound. Only the 14 lead novolac PDIPs exhibited increased delamination. Moisture exposure had a significant effect on the creation of additional delamination. 相似文献
2.
We have studied the synthesis conditions and crystal structures for one-phase intermetallic alloys Ni5Zr, Ni7Zr2, and NiZr. We used the continuous weighing method to study the oxidation kinetics in air for the alloy Ni7Zr2 in the range 500-1000°C. We have shown that the oxidation process is described mainly by a parabolic law. The kinetic isotherms for the change in mass suggest that over time, the rate constant for parabolic oxidation K p decreases due to improvement in the protective properties of the scale. The temperature dependence of the oxidation rate suggests a change in the oxidation mechanism for T > 800°C, due to changes in the defect structure of the ZrO2 lattice. 相似文献
3.
Valentina I. Simagina Pavel A. Storozhenko Olga V. Netskina Oksana V. Komova Galina V. Odegova Yury V. Larichev Arcady V. Ishchenko Anna M. Ozerova 《Catalysis Today》2008,138(3-4):253
Catalytic hydrolysis of NaBH4 and NH3BH3 has been studied. It was shown that the nature of the support and the active component of the catalyst affect the H2 generation rate. Despite similar sizes of rhodium particles formed on the surface of different supports (γ-Al2O3, TiO2, carbon), their reactivity is different. Rh/TiO2 with low rhodium concentration (1 wt.%) is the most active catalyst both in the hydrolysis of NaBH4 and NH3BH3. The obtained results show that the rhodium chloride interaction with titania determines the reactivity of rhodium particles formed under action of NaBH4 medium. TEM, DRS UV–vis and XPS were used to characterize the catalysts. 相似文献
4.
AR Santos JC Nery NC Duppre ME Gallo JT Filho PN Suffys WM Degrave 《Canadian Metallurgical Quarterly》1997,46(2):170-172
A case is described in which a pericardial branch of a nongrafted left internal mammary artery communicated directly with the distal left anterior descending artery, following saphenous vein bypass grafting. This type of collateralization following coronary artery bypass surgery seems to be very rare, and perhaps could protect the myocardium from severe ischemia. 相似文献
5.
6.
Emilio Marengo Valentina Longo Elisa Robotti Marco Bobba Fabio Gosetti Orfeo Zerbinati Silvana Di Martino 《应用聚合物科学杂志》2008,109(6):3975-3982
Principal component regression (PCR), partial least squares (PLS), StepWise ordinary least squares regression (OLS), and back‐propagation artificial neural network (BP‐ANN) are applied here for the determination of the propylene concentration of a set of 83 production samples of ethylene–propylene copolymers from their infrared spectra. The set of available samples was split into (a) a training set, for models calculation; (b) a test set, for selecting the correct number of latent variables in PCR and PLS and the end point of the training phase of BP‐ANN; (c) a production set, for evaluating the predictive ability of the models. The predictive ability of the models is thus evaluated by genuine predictions. The model obtained by StepWise OLS turned out to be the best one, both in fitting and prediction. The study of the breakdown number of samples to be included in the training set showed that at least 52 experiments are necessary to build a reliable and predictive calibration model. It can be concluded that FTIR spectroscopy and OLS can be properly employed for monitoring the synthesis or the final product of ethylene–propylene copolymers, by predicting the concentration of propylene directly along the process line. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
7.
Paustovskii Alexander V. Alfintseva Raisa A. Kurinnaya Tatyana V. Pogorelaya Valentina V. Kirilenko Stepan N. 《Powder Metallurgy and Metal Ceramics》2004,43(5-6):251-257
The main parameters of electrospark alloying of steel 45 with anodes made from Ni – Cr – Al – Y alloys have been investigated. The anodes were fabricated by casting and hot pressing. The highest values of the mass transfer coefficient were observed in the case of electrospark alloying with hot-pressed alloys. Microstructure and x-ray phase analyses of electrospark coatings revealed the presence of solid solutions based on nickel, iron, chromium as well as intermetallic compounds. Coatings obtained by electrospark alloying with hot-pressed alloy are more wear-resistant than are coatings obtained by alloying with cast alloys. 相似文献
8.
The possibility of using the IEC flickermeter for the assessment of the limits of low frequency interharmonic voltages is critically analyzed. The response of flickermeters to interharmonic components is analytically investigated, obtaining approximation formulas for the calculation of Pst in the presence of couples of components at frequencies that are symmetric with reference to the fundamental and in the presence of one or more single components. The instrument characteristics and limitations are also highlighted, using the results obtained from a numerical implementation of the IEC flickermeter. Finally, the general problem of the limits of low frequency interharmonic voltages is discussed and practical solutions are proposed. 相似文献
9.
A Di Lieto G De Rosa G Albano F Gallo M Pontillo R Micalef A Colucci A Paladini 《Canadian Metallurgical Quarterly》1996,23(4):220-228
Clinical and pathological changes of the mammary gland have been studied in 64 women affected by symptomatic Benign Breast Disease (BBD) coexisting with endometriosis or uterine leiomyomata. These patients were rendered hypoestrogenic by subcutaneous administration of the LH-RH analogue Goserelin depot [D-ser (tBu)6 Aza-Gly10-GnRH (ICI118630)] performed every 28 days, for six months. They were evaluated clinically and ultrasonographically before and after treatment to find possible changes of BBD as well as of endometriosis or uterine leiomyomata. Mammary biopsies were performed before and after treatment in all the patients to study the changes of EGF-R expression. Results showed that clinical improvement is accompanied with a reduction of EGF-R expression. 相似文献
10.