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排序方式: 共有10000条查询结果,搜索用时 140 毫秒
871.
Igor Studart Medeiros Erika R. M. Andreeta Antonio C. Hernandes 《Journal of Materials Science》2007,42(11):3874-3877
872.
Mamiko Hori Cécile Pagnoux Jean-François Baumard Masayuki Nogami 《Journal of Materials Science》2007,42(1):80-86
A new method is proposed to produce gold nanoparticles (GNP) by in situ reduction of a gold salt dissolved in water. The reducing
agent used is Tiron instead of the citrate anion most often mentioned in literature. The influence of various parameters has
been investigated, such as the content of Tiron with respect to that of the precursor of gold HAuCl4, or the initial pH of the solution after mixing of reactants. It is shown that Tiron also exerts a positive influence as
a dispersant, which impedes agglomeration of gold nanoparticles. The typical average size of GNP synthesized in the present
work is close to 7 nm. 相似文献
873.
C. B. Winkelmann E. Collin Yu. M. Bunkov H. Godfrin 《Journal of Low Temperature Physics》2004,135(1-2):3-14
We report systematic measurements of the response of a Vibrating Wire Resonator (VWR) in normal and superfluid liquid 3He. Special attention has been paid to the hydrodynamic regime of the superfluid B-phase, where the response parameters of the VWR do not follow a simple law. We show that a simple interpolation between the region where first order slip-corrections can be applied and the ballistic regime is insufficient. Measuring an empirical effective viscosity, we propose a temperature calibration method which allows the use of VWRs as a secondary thermometer at intermediate and high pressures in the temperature range 0.2 T c < T < 50 mK. 相似文献
874.
A. Hernández O. Arés C. Hart D. Domínguez H. Pastoriza A. Butera 《Journal of Low Temperature Physics》2004,135(1-2):119-122
The response of mesoscopic superconductors to an ac magnetic field is investigated both experimentally and with numerical simulations. We study small square samples with dimensions of the order of the penetration depth. We obtain the ac susceptibitity χ=χ′+iχ″ at microwave frequencies as a function of the dc magnetic field H dc. We find that the dissipation, given by x″, has a non monotonous behavior in mesoscopic samples. In the numerical simulations we obtain that the dissipation increases before the penetration of vortices and then it decreases abruptly after vortices have entered, the sample. This is verified experimentally, where we find that χ″ has strong oscillations as a function of H dc in small squares of Pb. 相似文献
875.
M. F. Laguna P. S. Cornaglia C. A. Balseiro 《Journal of Low Temperature Physics》2004,135(1-2):127-130
We model a vortex system in a sample with bulk pinning and superficial pinning generated by a magnetic decoration. We perform a sequence of finite temperature numerical experiments in which external forces are applied to obtain, a dynamically ordered vortex lattice. We analyze the final structures and the behavior of the total energy of the system. 相似文献
876.
Neutron-irradiated quartz crystal is one of the interesting materials for the study of the glassy dynamics. The temperature and frequency dependence of the sound velocity in amorphous materials at temperatures above the low-temperature maximum is not well understood. In this paper we present the results of our measurements of the variation of the ultrasound velocity (270 – 650 MHz) in neutron-irradiated quartz crystals with different irradiation doses in temperature range 5 - 35 K. We have found that the temperature dependence of the ultrasound velocity is linear in the sample with a dose < 10 19 n/cm2 and is sublinear in samples with a dose > 10 19 n/cm2 . We discuss our results in the framework of the different theoretical approaches. PACS numbers: 61.43. j, 62.65.+k, 63. 相似文献
877.
OH– and OD– defects are known to form rotational tunneling systems in KCl host crystals. We have studied the complex dielectric susceptibility of KCl doped with different concentrations of OH– and OD– in a wide range of frequencies and temperatures. Our main result is that there is a transition from coherent single ion tunneling at low defect concentration to an incoherent tunneling motion at high defect concentrations. In addition, we have studied the thermally activated motion of pairwise coupled hydroxide ions in an attempt to obtain information on the microscopic configurations of the different pairs contributing to the dielectric loss. PACS numbers: 61.72.Ji, 77.22-d, 78.30.Ly 相似文献
878.
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