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961.
Philippe Nika Yannick Bailly Michel De Labachelerie Jean Claude Jeannot Jacques De Lallee 《Nanoscale and Microscale Thermophysical Engineering》2013,17(4):301-325
The miniaturization of refrigerating systems represents a very current scientific and technical challenge to improve the performances of numerous electronic components. This work presents a global approach to the problem and suggests studying the cooling by means of small channels filled with an oscillating gas: the double inlet pulse tube refrigerator (DIPTR). A great level of miniaturization based on the technology of carving silicon is exposed. This study proposes to apply an electric analogy for modeling both hydrodynamic and thermal phenomena. Considering the complexity of the theoretical problem including mechanical, thermal, thermodynamical, and acoustic considerations, the authors take care to summarize the main governing equations in a particular form so any scientific engineer could understand the DIPTR principle. 相似文献
962.
Hydrogenated amorphous silicon films were grown on to thermally oxidized silicon wafers by Radio Frequency magnetron sputtering, and SiNx and Al2O3 capping layers were used to control the residual thermal stress. After annealing, a comparison of the silicon films with and without capping layers indicates that tensile stress induced by the capping layer enhances the crystallinity of the annealed amorphous silicon film. The stress is due to the mismatch between the coefficients of thermal expansion for the capping layer and amorphous silicon film. These results highlight the potential of thermal stress as a means to alter the crystallization in thin film architectures and suggest that even larger effects can be obtained with suitable choices of capping layer chemistry. 相似文献
963.
Emmanuel Nonnet Nicolas Lequeux Philippe Boch Sally L. Colston Paul Barnes 《Journal of the American Ceramic Society》2001,84(3):583-587
In situ Young's modulus measurements and synchrotron radiation-energy dispersive diffraction have been used to study changes in high-alumina castables subjected to heat treatment from room temperature to 1600°C. Particular attention was paid to the hydrate "conversion" process and the effects of high temperature. 相似文献
964.
The primary ultrafine carbon powders were prepared by sol–gel supercritical fluid drying method using different starting materials. After heat-treatment at 1100 and 2600°C, respectively, the ultrafine carbon powders were obtained. The properties of primary ultrafine carbon powders and their annealed products were characterized by TEM, XRD, Raman spectra and nitrogen adsorption. The results reveal that starting materials have influence on the structure of ultrafine carbon powders. 相似文献
965.
Angle-dispersive X-ray diffraction and Raman scattering measurements were carried out to follow the crystal-to-crystal transformation occurring in PbZr 0.52 Ti 0.48 O 3 ceramic powders with either increasing hydrostatic pressure or decreasing temperature. A low-temperature monoclinic phase was confirmed to exist below 298 K. External pressures of several GPa were found to fundamentally alter the structural and polar properties of PZT near the MPB and novel phase transitions were found to occur at close to 5GPa at 298 K, 7.5 GPa at 154 K and 9 GPa at 44 K. Whereas X-ray diffraction data indicated no deviation from the cubic symmetry above these pressures at each given temperatures, the unusually strong and persistent Raman signals, similar to relaxor-specific spectral signatures, indicated the presence of symmetry-breaking disorder in this phase. Based on these results, an updated version of the Pressure-Temperature phase diagram is proposed. 相似文献
966.
In order to explore the lowest attainable refrigeration temperature and improve cooling performance at temperatures around 20 K for a single-stage G-M type pulse tube cryocooler (PTC), numerical and experimental studies were performed. The National Institute of Standards and Technology (NIST) numerical model known as REGEN was applied to the simulation of a G-M type PTC for the first time. Based on the calculation results, a single-stage G-M type PTC was designed, fabricated and tested. The performance improvement of the regenerator in the temperature range of 10-80 K was investigated. The calculations predicted a lowest temperature of 10 K. A lowest temperature of 10.6 K was achieved experimentally with an input power of 7.5 kW, which is the lowest temperature ever achieved by a single-stage PTC. Further more, the cryocooler can provide a cooling power of 20 W at 20.6 K and 39.5 W at 30 K, respectively. 相似文献
967.
Anna Fischer Manuel Schmitz Barbara Aichmayer Peter Fratzl Damien Faivre 《Journal of the Royal Society Interface》2011,8(60):1011-1018
Magnetosome biomineralization and chain formation in magnetotactic bacteria are two processes that are highly controlled at the cellular level in order to form cellular magnetic dipoles. However, even if the magnetosome chains are well characterized, controversial results about the microstructure of magnetosomes were obtained and its possible influence in the formation of the magnetic dipole is to be specified. For the first time, the microstructure of intracellular magnetosomes was investigated using high-resolution synchrotron X-ray diffraction. Significant differences in the lattice parameter were found between intracellular magnetosomes from cultured magnetotactic bacteria and isolated ones. Through comparison with abiotic control materials of similar size, we show that this difference can be associated with different oxidation states and that the biogenic nanomagnetite is stoichiometric, i.e. structurally pure whereas isolated magnetosomes are slightly oxidized. The hierarchical structuring of the magnetosome chain thus starts with the formation of structurally pure magnetite nanoparticles that in turn might influence the magnetic property of the magnetosome chains. 相似文献
968.
969.
热电材料,是一种能实现电能与热能交互转变的材料,可用于温差发电、热电制冷等。到目前为止,所研究的热电材料一般都为固体材料或者高温条件下的液态金属,尚未见文献在电解质溶液热电性能方面有过报道。相关的研究表明,低维度纳米多孔化结构可能成为提高材料热电性能的重要途径,为此,进行了以碳纳米管(canbon nanotubes,CNTs)堆积床为骨架,在其中注入电解质溶液的试验研究,发现其表观塞贝克系数(Seebeck,S)可提高一个数量级,而导电系数在碳纳米管体积分数较小的情况下几乎保持不变,从而可能使热电材料的热电优值ηZT(themoelectric figure of merit,ZT)再提高1~2个数量级,而ηZT直接决定热电设备的转换效率。 相似文献
970.