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11.
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R. Ravinder Reddy M. Muralidhar V. Hari Babu P. Venugopal Reddy 《Physica C: Superconductivity and its Applications》1994,220(3-4):367-372
Bi-Pb and Bi-Pb-Ag superconducting composites have been prepared by the solid state reaction method. After the usual characterization, ultrasonic longitudinal velocity and attenuation studies have been undertaken over a temperature range 80–300 K by the pulse transmission technique. In contrast to normal solids, the ultrasonic velocities of both the samples in the temperature range 200-100 K are found to decrease with decreasing temperature (softening), followed by a velocity maximum. The samples are also found to exhibit longitudinal attenuation peaks at TEMPERATURES = 260, 160 and 120 K. An attempt has also been made to verify whether the Wachtman's equations can theoretically explain the low-temperature behaviour of the Young's modulus of these materials. A qualitative explanation for both the phenomena of softening of velocity as well as the occurrence of attenuation peaks is given. 相似文献
13.
dc ionic conductivity measurements were made on single crystals of Pb(NO3)2 doped with monovalent Na+ and K+ in the temperature range of 100–400°C. In the extrinsic region the conductivity was found to decrease with Na+ having a smaller ionic size, and to increase with K+ with larger ionic size compared to the host Pb ion. Conductivity is attributed to the mobility of anti-Frenkel defects as in the case of PbF2. Dielectric loss measurements were made on the Pb(NO3)2: K+ system in the frequency range of 300 Hz to 20 kHz at different temperatures. Impurity vacancy pairs of the type K+-(NO-3)V are found to be responsible for the observed dielectric loss peaks. The maximum peak frequency is found to increase with temperature. 相似文献
14.
Effects of uncertainties in the domain on the solution of Dirichlet boundary value problems 总被引:1,自引:0,他引:1
Summary. A domain with possibly non-Lipschitz boundary is defined as a limit of monotonically expanding or shrinking domains with
Lipschitz boundary. A uniquely solvable Dirichlet boundary value problem (DBVP) is defined on each of the Lipschitz domains
and the limit of these solutions is investigated. The limit function also solves a DBVP on the limit domain but the problem
can depend on the sequences of domains if the limit domain is unstable with respect to the DBVP. The core of the paper consists
in estimates of the difference between the respective solutions of the DBVP on two close domains, one of which is Lipschitz
and the other can be unstable. Estimates for starshaped as well as rather general domains are derived. Their numerical evaluation
is possible and can be done in different ways.
Received October 16, 2001 / Revised version received January 16, 2002 / Published online: April 17, 2002
RID="*"
ID="*" The research was funded partially by the National Science Foundation under the grants NSF–Czech Rep. INT-9724783 and
NSF DMS-9802367
RID="**"
ID="**" Support for Jan Chleboun coming from the Grant Agency of the Czech Republic through grant 201/98/0528 is appreciated 相似文献
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Summary We consider the finite element approximation of the 2D elasticity problem when the Poisson ratiov is close to 0.5. It is well-known that the performance of certain commonly used finite elements deteriorates asv0, a phenomenon calledlocking. We analyze this phenomenon and characterize the strength of the locking androbustness of varioush-version schemes using triangular and rectangular elements. We prove that thep-andh-p versions are free of locking with respect to the error in the energy norm. A generalization of our theory to the 3D problem is also discussed.The work of this author was supported in part by the Office of Naval Research under Naval Research Grant N00014-90-J-1030The work of this author was supported in part by the Air Force Office of Scientific Research, Air Force Systems Command, U.S. Air Force, under grant AFOSR 89-0252 相似文献
18.
Jinyuan Liu Deming Shu Yujie Wang Suresh Narayanan Ali Mashayekhi Jun Qian Jin Wang 《Journal of synchrotron radiation》2007,14(1):138-143
The development of a sagittally focusing double‐multilayer monochromator is reported, which produces a spatially extended wide‐bandpass X‐ray beam from an intense synchrotron bending‐magnet source at the Advanced Photon Source, for ultrafast X‐ray radiography and tomography applications. This monochromator consists of two W/B4C multilayers with a 25 Å period coated on Si single‐crystal substrates. The second multilayer is mounted on a sagittally focusing bender, which can dynamically change the bending radius of the multilayer in order to condense and focus the beam to various points along the beamline. With this new apparatus, it becomes possible to adjust the X‐ray beam size to best match the area detector size and the object size to facilitate more efficient data collection using ultrafast X‐ray radiography and tomography. 相似文献
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Suresh Chandra 《Pramana》1980,14(1):41-46
The effect of dielectronic recombination as an excitation process in the intensity of solar x-ray lines of calcium ions is
investigated. It is found that x-ray line intensities are enhanced by 15% to 88% with the inclusion of dielectronic recombination
as an excitation mechanism. 相似文献