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951.
Functionally graded materials (FGM) have been widely used in many industries such as aerospace, energy and electronics. In this experimental study of fabricating FGM, an approach was developed to prepare AI/Si FGM using power ultrasonic separation method. Material sample with continuously changing composition and performance/properties was successfully produced. Results showed that the microstructure of the FGM sample transited, from its top to bottom, from the hypereutectic structure with a large quantity of primary Si gradually to the eutectic, and finally to the hypoeutectic with numerous primary AI dendrites. The distribution of primary Si and microhardness of the FGM sample also presented graded characteristics, resulting that the wear resistance of the FGM sample decreased from top to bottom. Preliminary discussion was made on the mechanism of the formation of AI/Si FGM. 相似文献
952.
基于单片机8089的超声波电源控制技术的研究 总被引:1,自引:0,他引:1
针对目前大功率超声波电源采用模拟控制电路存在精度低、动态响应慢、参数整定不方便等缺点,采用单片机8089组成智能控制的超声波电源系统。提出了基于SPWM技术的双闭环控制策略和应用单片机实现软锁相的工作原理和软件思想,使整个超声波电源实现了低损耗、高功率因数,优化了电路的整体性能。 相似文献
953.
虽然电子辐照会使P-N结中的自由载流子浓度减少,P-N结宽度增加,但其反向漏电流也随之增加,最终使P-N结反向击穿电压略有下降;对晶体管和晶闸管,由于辐照使其电流放大系数下降,最终其反向击穿电压却略有增加。 相似文献
954.
D. X. Xu G. D. Shen M. Willander J. Knall M. -A. Hasan G. V. Hansson 《Journal of Electronic Materials》1990,19(10):1033-1041
Different Si homojunction and strained Si1-xGex/Si heterojunction diodes and bipolar transistors have been fabricated by Si-MBE. The effect of annealing on Si homojunction
diodes and transistors are studied. It is found that annealing generally improves the Si device performance, such as the ideality
factor and breakdown characteristics. The influence of60Co γ irradiation on the Si1-xGex/Si diode performances are investigated by studying the temperature dependence of their electrical characteristics, and the
results are correlated with the quality of the MBE-films. γ irradiation causes a drop in material conductivity due to the
generation of atom-displacement defects in the whole volume of the wafers and increases the defect density at hetero-interfaces.
The forward I-V curves of Si1-xGex/Si devices may shift towards lower or higher voltages, depending on the film quality and the irradiation dose. The increase
of defect density in strained Si1-xGex/Si films appears to occur easier for the films with lower quality. Electrical measurements and calculations show that the
defect-associated tunneling process is important in current transport for these MBE grown Si homojunction and strained Si1-xGex/Si heterojunction devices, which have initially medium film quality or have been treated by irradiation. 相似文献
955.
In the rat, variations in maternal care affect the development of stable individual differences in anxiety-related behavior. Here, it was asked whether such experience-dependent differences can be detected already during early life. As a measure for anxiety in pups, isolation-induced ultrasonic vocalizations were used, and their dependency on different maternal behaviors, namely licking, retrieval behavior, and responsiveness to playback of pup calls, was tested. Consistent with reported differences of adult rats with high or low levels of maternal care experienced, the rarely licked offspring appeared to be more anxious, since they emitted more calls when separated from their mother and litter. Based on these findings, it was examined whether infant calling can be used as a predictor of adult anxiety-related behavior. Results show that infant call emission was negatively correlated with immobility and calling during fear conditioning. These relationships seem to be mediated at least partly by maternal care. In total, measuring ultrasonic vocalizations can provide information about an affective trait of infant and adult rats, which gives the opportunity to study the development of emotionality from early life onward. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
956.
957.
Improving hole exit quality in rotary ultrasonic machining of ceramic matrix composites using a compound step-taper drill 总被引:1,自引:0,他引:1
《Ceramics International》2016,42(12):13387-13394
Mechanical-machining-induced tearing defects at hole exits restrict the application of C/SiC composites. Rotary ultrasonic machining (RUM) is suitable for hole manufacture in brittle composites, providing reduced tearing size as compared with conventional grinding. Even so, substantial tearing defects at the hole exit remain with RUM. In this study, a novel compound step-taper diamond core drill for RUM of C/SiC was developed to further improve the hole exit quality. Contrastive machining tests were conducted to evaluate the effectiveness of the new type drill. Experimental results show that the compound drill can help reduce the tearing size by 30% on average. Results of variance analysis indicate that there is little dependency of tearing size on processing variables with the compound drill, whereas the common drill shows substantial dependence. Detailed observation of the thrust force reveals that the tearing size reduction using the compound drill is due to the reprocessing effects of its taper face. In the reprocessing process of the taper face, the thrust force gradually decreases at the hole exit. Increasing the ultrasonic amplitude can help further improve the hole exit quality when using our compound drill. 相似文献
958.
Burgdorf Jeffrey; Kroes Roger A.; Moskal Joseph R.; Pfaus James G.; Brudzynski Stefan M.; Panksepp Jaak 《Canadian Metallurgical Quarterly》2008,122(4):357
Rats (Rattus norvegicus) emit a variety of ultrasonic vocalizations throughout their lifespan that reflect different forms of emotional arousal and accompanying affective states. In this study, high frequency recordings of ultrasonic vocalizations were made during mating, aggression, and both conspecific and heterospecific (dubbed "tickling") rough-and-tumble play behavior. We found that frequency modulated 50-kHz calls (trills and step calls) were positively correlated with positively valenced appetitive behavior during mating, play, and aggression. These calls were also positively correlated with the reward value of these social encounters. However, constant frequency (i.e., flat) 50-kHz calls were not related to appetitive behaviors or reward. In contrast, 22-kHz calls were positively related to aversive/withdrawal behaviors during mating, play, and aggression. Finally, we found that rats self-administered playback of frequency modulated 50-kHz trill calls and avoided playback of 22-kHz calls. Playback of flat 50-kHz calls or tape hiss was neutral. These results suggest that frequency modulated 50-kHz calls index a positively valenced, appetitive, social-emotional state in rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
959.
Evaluation of gamma rays influence on some biochemical and microbiological aspects in black truffles
Filomena Nazzaro Florinda Fratianni Gianluca Picariello Raffaele Coppola Anna Reale Aldo Di Luccia 《Food chemistry》2007,103(2):344-354
The effects of two gamma-ray doses (1.5 kGy and 2.0 kGy) on some biochemical aspects and on the microbiological profile of black truffles was monitored, immediately after treatment and after 30 days of storage at 4 °C. Electrophoretic and chromatographic analyses of proteins and peptides, just like monitoring of polyphenol content, peroxides formation and microbial profile, allowed for the first time a better understanding of the mechanisms responsible for biochemical alterations and bacterial pattern in black truffles during their storage. Treatment at 1.5 kGy appeared to better preserve the characteristics of the fresh product. In 2.0 kGy-samples, the protein profile was characterised by a 20 kDa-polypeptide, which could be considered as an useful marker of the irradiation treatment and of the storage time of the product. MALDI-TOF mass spectrometry analysis did not permit a correct identification from tryptic peptides in databases, although the nano-ES/MS/MS analyses performed on the 10 kDa tryptic digest peptides showed an amino acidic sequence entirely contained in a protein of filamentous fungus Neurospora crassa. 相似文献
960.
Without organic solvent or catalyst, polyaspartic acid (PASP) was synthesized from maleic anhydride (MA) and ammonia (AN) under microwave irradiation. The influences of the molar ratio of maleic anhydride to ammonia and the microwave output power and irradiation time on product yield were investigated. Also, the function of microwave in the process was simply addressed. The results showed that when the molar ratio of MA/AN was 1.2, the output power was 900 W, the irradiation time was 3.5 min, and the product yield was highest and its inhibition performance on calcium carbonate was as good as the polymer synthesized by conventional pyrocondensation polymerization. The main function of microwave was its heat effect. Characterization of the product was carried out by IR, 1HNMR, and 13CNMR spectra and the results showed that the product was PASP. The microwave‐assisted synthesis process of PASP has many advantages, including quicker reaction rate, high purity, lower cost, and little pollution. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103:358–364, 2007 相似文献