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排序方式: 共有91条查询结果,搜索用时 15 毫秒
1.
M. Gutmann P. Allenspach F. Fauth A. Furrer A. Hewat S. Rosenkranz 《Journal of Low Temperature Physics》1996,105(5-6):1487-1492
Samples of the electron-doped superconductor precursor Nd2-x-yCexLayCuO4 with 0x0.2 and y=0.5, I have been synthesized with a sol-gel method. While the as-prepared samples are in the normal state, oxygen reduction results in superconducting samples. The dependence of Tc upon Ce-doping x and oxygen content (4-) was determined in detail. It turned out that the internal pressure exerted by the La ions results in an extended superconducting range in x and compared to Nd2-xCexCuO4- Elastic neutron scattering was used to investigate the dependence of structural features upon doping. Upon oxygen reduction a non-isotropic shrinking of the unit cell (lattice parameter a increases, c decreases) and indications for interstitial oxygen were found. The local electronic surrounding of the Nd ions was observed via the crystal-field splitting by inelastic neutron scattering and turned out to be inhomogeneous. Such electronic inhomogeneities were previously measured for other high-Tc superconductors. 相似文献
2.
A. Mirmelstein V. Bobrovskii N. Golosova A. Podlesnyak A. Furrer 《Journal of Superconductivity》2002,15(5):367-372
Recent inelastic neutron scattering measurements revealed the crystal-field (CF) spectra of the overdoped R1 – y
CayBa2Cu3O7 (R = Ho, Er; 0 < y < 0.25) high-T
c superconductors to consist of two spectral components associated with the optimally doped and the overdoped domains. Increase of the Ca concentration does not affect the local charge density of domains, but changes the spectral weight of the components. In the sense of this two-phase picture, which was established earlier for the underdoped region, there is a smooth crossover between the under- and overdoped parts of the phase diagram. The charge origin of the observed superposition effect is confirmed by the systematic analysis of the concentration dependences of the CF parameters for both Ho- and Er-based compounds. Therefore, the local charge inhomogeneity in the CuO2 planes of high-T
c cuprates is a characteristic feature of the doping process, which depends neither on the way to introduce doping nor on the doping level. 相似文献
3.
Furrer S. Dahlhaus D. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2007,53(6):2028-2043
Multiple-antenna concepts for wireless communication systems promise high spectral efficiencies and improved error rate performance by proper exploitation of the randomness in multipath propagation. In this paper, we investigate the impact of channel uncertainty caused by channel estimation errors on the capacity of Rayleigh and Ricean block-fading channels. We consider a training-based multiple-antenna system that reserves a portion of time to sound the channel. The training symbols are used to estimate the channel state information (CSI) at the receiver by means of an arbitrary linear estimation filter. No CSI is assumed at the transmitter. Our analysis is based on an equivalent system model for training-based multiple-antenna systems which specifies the channel by the estimated (and hence, known) channel coefficients and an uncorrelated, data-dependent, multiplicative noise. This model includes the special cases of perfect CSI and no CSI. We present new upper and lower bounds on the maximum instantaneous mutual information to compute ergodic and outage capacities, and extend previous results to arbitrary (and possibly mismatched) linear channel estimators and to correlated Ricean fading. Several numerical results for single- and multiple-antenna systems with estimated CSI are included as illustration. 相似文献
4.
Ni-based superalloys for turbine discs 总被引:4,自引:0,他引:4
Superalloys have been developed for specific, specialized properties and applications. One of the main applications for nickel-based superalloys is gas-turbine-engine disc components for land-based power generation and aircraft propulsion. Turbine engines create harsh environments for materials due to the high operating temperatures and stress levels. Hence, as described in this article, many alloys used in the high-temperature turbine sections of these engines are very complex and highly optimized. 相似文献
5.
The corrosion behavior of glassy Mg70Al15Ga15 was investigated in 0.1 M NaCl solutions of various pH values. Potentiodynamic polarization measurements confirm a pronounced passivity for 4 ≤ pH ≤ 12. Corrosion currents in neutral solutions are found to be as low as 10?6 A/cm2. Optical microscopy and Auger electron spectroscopy were performed on samples immersed under open-circuit conditions in neutral, acidic and alkaline 0.1 M NaCl solutions to observe their time-dependent passive film formation. A significant incorporation of aluminum in the surface layers was found. The alloys show an unusual stability against dissolution in chloride-containing solutions, raising expectations of a highly corrosion-resistant Mg-based alloy. The time-dependent limitations of this stability are discussed in context with the surface films observed. 相似文献
6.
David Furrer John Schirra 《JOM Journal of the Minerals, Metals and Materials Society》2011,63(4):42-48
Over the past twenty years, integrated computational materials engineering (ICME) has emerged as a key engineering field with
great promise. Models simulating materials-related phenomena have been developed and are being validated for industrial application.
The integration of computational methods into material, process and component design has been a challenge, however, in part
due to the complexities in the development of an ICME “supply-chain” that supports, sustains and delivers this emerging technology.
ICME touches many disciplines, which results in a requirement for many types of computational-based technology organizations
to be involved to provide tools that can be rapidly developed, validated, deployed and maintained for industrial applications.
The need for, and the current state of an ICME supply-chain along with development and future requirements for the continued
pace of introduction of ICME into industrial design practices will be reviewed within this article. 相似文献
7.
O Planz S Ehl E Furrer E Horvath MA Bründler H Hengartner RM Zinkernagel 《Canadian Metallurgical Quarterly》1997,94(13):6874-6879
This study demonstrates that neutralizing-antibody-producing B cells, CD4(+) T cells, and interferons (IFNs) are of key importance in virus control both in adoptive immunotherapy of persistent infection and in the late phase of acute infection with the WE strain of lymphocytic choriomeningitis virus (LCMV). We report the following results. (i) Clearance of LCMV-WE from C57BL/6 carrier mice by adoptive transfer of memory spleen cells requires B cells and CD4(+) T cells but not necessarily CD8(+) T cells. (ii) At the doses examined, CD8(+) T cells contribute to the initial reduction of viral titers but are alone not sufficient to clear the virus because they are exhausted. (iii) In the presence of functional IFN-gamma, virus clearance correlates well with the generation of neutralizing antibodies in the treated carrier mice. (iv) In the absence of receptors for IFN-gamma, virus clearance is not achieved. (v) Adoptive immunotherapy of mice persistently infected with a distinct virus isolate, LCMV-Armstrong, revealed only low levels of neutralizing antibodies; in this case, CD8(+) T cells were needed for virus clearance in addition to B and CD4(+) T cells. (vi) After low dose infection of C57BL/6 mice with LCMV-WE, virus is eliminated below detectable levels by CD8(+) T cells, but long-term (>2 months) virus control is usually not achieved in the absence of B cells or CD4(+) T cells; reappearance of the virus is paralleled either by exhaustion of virus-specific cytotoxic T lymphocytes or lethal immunopathology. These findings are of importance for adoptive immunotherapy strategies against persistent virus infections in humans. 相似文献
8.
S. Rosenkranz U. Staub A. Furrer R. Osborn P. Lacorre V. Trounov 《Journal of Alloys and Compounds》1997,250(1-2):577-580
We determined the energy splitting of the 7F1 multiplet of Eu3+ in EuNiO3 using inelastic neutron scattering. We were able to retrieve accurate values for the second order crystalline electric field parameters, which will allow a more reliable determination of the crystalline electric field potential in the RNiO3 (R=rare earth) series. This is essential for a possible observation of a charge transfer, which is proposed by one of the models describing the observed metal-to-insulator transition in these compounds. 相似文献
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