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141.
The synthesis of thermal-shock-resistant materials from the system Ta2O5WO3 was investigated. Ta2WO8 had a very low unit-cell thermal expansion coefficient (+0.5 X 10–6° C–1). Ta30W2O81 also had a relatively low coefficient (+4.0 X 10–6 ° C–1) and a thermal durability over 1600° C. The thermal expansion curves of these polycrystalline ceramics were lowered because of microcracks caused by the large thermal expansion anisotropy of the crystal axes and were accompanied by hysteresis loops. The densification of Ta2WO8 ceramic was promoted by the addition of some metal oxides, and the strong ceramic of Ta30W2O81 was obtained by controlling grain growth. 相似文献
142.
Microbial sensor for preliminary screening of mutagens utilizing a phage induction test 总被引:1,自引:0,他引:1
For the preliminary screening of mutagens, a novel microbial sensor system was developed utilizing a phage induction test. Escherichia coli lysogenic strain GY5027 and nonlysogenic strain GY5026 were used in this study. The number of living cells was determined by measuring the respiration of cells immobilized onto an oxygen electrode. The injection of a mutagen, such as AF-2 and MNNG, caused the phage induction in the lysogenic strain, resulting in the decreased respiration of only the lysogenic strain immobilized onto the oxygen electrode but not of nonlysogenic strain. The rate of current increase correlated well with the concentration of mutagens. The sensor responses to the antibiotics and bactericides were definitely different from those of mutagens. Therefore, utilization of this microbial sensor system makes possible the estimation of a substrate's mutagenicity. 相似文献
143.
A model of the electronic structure of graphite-like carbon films, describing the semiconductor properties of this material, is presented. Spectra of optical constants of microcrystalline carbon films in the region λ = 0.4–8.0 μm were studied by the spectral ellipsometry and IR reflection methods. A number of distinctive features of the spectra, associated with both the appearance of C---C- and C---Hn-type bonds and direct energy gaps, were found. Analysis of the optical data using the proposed model makes possible a common interpretation of our results and literature data. Values of a parameter Θ, which is an averaged qualitative parameter of structural distortions within carbon microcrystallites as compared with crystalline graphite, are determined from comparison of theoretical results and experimental data. 相似文献
144.
Institute of Strength Problems, Academy of Sciences of the Ukrainian SSR, Kiev. Sumy Branch, Khar'kov Polytechnic Institute. Translated from Problemy Prochnosti, No. 8, pp. 102–104, August, 1989. 相似文献
145.
146.
V. Vassilev S. Thijs P. L. Segura P. Wambacq P. Leroux G. Groeseneken M. I. Natarajan H. E. Maes M. Steyaert 《Microelectronics Reliability》2005,45(2):255-268
This paper describes an approach to design ESD protection for integrated low noise amplifier (LNA) circuits used in narrowband transceiver front-ends. The RF constraints on the implementation of ESD protection devices are relaxed by co-designing the RF and the ESD blocks, considering them as one single circuit to optimise. The method is applied for the design of 0.25 μm CMOS LNA. Circuit protection levels higher than 3 kV HBM stress are achieved using conventional highly capacitive ggNMOS snapback devices. The methodology can be extended to other RF-CMOS circuits requiring ESD protection by merging the ESD devices in the functionality of the corresponding matching blocks. 相似文献
147.
I Kabelkova-Jancarkova 《Water science and technology》2006,54(6-7):331-338
This paper presents the assessment of the efficiency of the main biological nitrogen transformation processes in a shallow well-oxygenated river and conditions under which they are active and stabilise. The process dynamics was studied with the help of mathematical modelling of 2 years on-line data series measured in a reach of the Toess River, Switzerland. The algal nitrogen uptake was very stable and unaffected by most but frequent flood events. Daylight photosynthetic nitrogen uptake stabilised at 6 mgN mstreambed(-2) h(-1) (15 degrees C), dark uptake on storage products at rates of 0.5-2.5 mgN mstreambed(-2) h(-1). Nitrogen uptake by heterotrophic bacteria in the hyporheic zone was relatively constant at a level of 1.5-3.5 mgN mstreambed(-2) h(-1). Streambed nitrification could establish only during periods with average an daily concentration of at least 0.3 g(NH4-N) m(-3) in river water for several weeks. The maximum nitrification rate was 35 mgN mstreambed(-2) h(-1) for 3 g(NH4-N) m(-3). The effects of reduced nitrification in the WWTP and of river banks shading on a sudden ammonium peak were simulated. A river reach endangered by ammonium spills should be kept open to sun to favour ammonium uptake by algae. In-stream nitrification reduces ammonium peaks efficiently but leads to toxic nitrite concentrations. 相似文献
148.
X-ray diffraction analysis shows that the transformation during heat treatment from amorphous to crystalline phases of bismuth-borate glass samples takes place in sequences. After a short heat treatment, 5 min at 550 °C, a layered structure with a preferred orientation of crystallites on the surface is observed. After a long heat treatment, 8 h at the same temperature, normal polycrystalline bulk samples are obtained. 相似文献
149.
I. A. Ovid’ko 《Journal of Materials Science》2007,42(5):1694-1708
An overview of experimental study, computer simulations and theoretical models of fracture of nanocrystalline materials is
presented. The key experimentally detected facts on ductile and brittle fracture processes are discussed. Special attention
is paid to computer simulations and theoretical models of nucleation and growth of nanocracks and nanopores in deformed nanocrystalline
materials. Also, we discuss mechanisms for fracture suppression in such materials showing good ductility or superplasticity. 相似文献
150.
Christian P. Romero Jonathan I. Avila Edgardo Cisternas Guerau B. Cabrera Alejandro L. Cabrera Kristiaan Temst Margriet J. Van Bael 《Journal of Materials Science》2007,42(18):7667-7672
Hydrogen desorption curves were obtained from a sample composed of a square arrangement of Co dots with average diameter of
4.4 μm, separated by a distance of 11.6 μm. A macroscopic sample of Co dots grown on a 2.5 × 2.5 cm Si substrate was made
by standard lithographic techniques and used in these experiments. Thermal programmed desorption (TPD) was performed under
ultra-high vacuum conditions. Hydrogen TPD curves were obtained from a 1 × 1 cm Co dots samples displaying a maximum of intensity
at 425 K. Hydrogen TPD curve was also obtained from 1 cm× 1 cm samples of Co films and Co foils for comparison. The hydrogen
TPD curves have decreasing intensity from the Co foils to the Co dots and finally to the Co films. This indicates that there
are more sites for hydrogen adsorption on the Co dots than in the Co films. This is a surprising result because there is approximately
8.7 times less Co atoms exposed in the Co dots that in the Co film sample. A desorption energy of 27 kcal/mol was obtained
for the Co dots suggesting that hydrogen is adsorbed on an hcp hollow site of the Co dot crystalline structure. 相似文献