排序方式: 共有218条查询结果,搜索用时 31 毫秒
51.
D.H. Wei K.L. You Y.D. Yao Y. Liou T.S. Chin C.C. Yu 《Journal of magnetism and magnetic materials》2006
Ultrathin Ag (0.5 nm) pinning layers (APLs) were symmetrically inserted into [Fe/Pt] bilayers to introduce controllable defects on the interfaces between Ag and Fe/Pt multilayers. The highest coercivity 7700 Oe and remanent squareness 0.95 were obtained with five APLs. The large enhancement in coercivity (75% increment compared with that without APL) is due to the relative uniform defects that introduced pinning effects on the interfaces between the APLs and Fe/Pt multilayers. According to the distribution of angule- dependent coercivity of Fe/Pt multilayers without and with APLs, a tendency is suggested of weakened domain-wall motion while enhanced rotation of reverse domain mode. 相似文献
52.
K. Kundu B.C. Gupta 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(1):23-33
We study the formation of stationary localized states using the discrete nonlinear Schr?dinger equation in a Cayley tree with
connectivity K. Two cases, namely, a dimeric power law nonlinear impurity and a fully nonlinear system are considered. We introduce a transformation
which reduces the Cayley tree into an one dimensional chain with a bond defect. The hopping matrix element between the impurity
sites is reduced by . The transformed system is also shown to yield tight binding Green's function of the Cayley tree. The dimeric ansatz is used
to find the reduced Hamiltonian of the system. Stationary localized states are found from the fixed point equations of the
Hamiltonian of the reduced dynamical system. We discuss the existence of different kinds of localized states. We have also
analyzed the formation of localized states in one dimensional system with a bond defect and nonlinearity which does not correspond
to a Cayley tree. Stability of the states is discussed and stability diagram is presented for few cases. In all cases the
total phase diagram for localized states have been presented.
Received: 18 September 1997 / Revised: 31 October and 17 november 1997 / Accepted: 19 November 1997 相似文献
53.
Pedro de Vries Kristel Michielsen Hans De Raedt 《Zeitschrift für Physik B Condensed Matter》1994,95(4):475-479
It is shown that the single-particle self-energy of the one and two-dimensional simplified Hubbard model exhibits different behavior characterized by Fermi-liquid, non-Fermi-liquid quasiparticle, or non-quasiparticle excitations, as a function of the strength of the on-site Coulomb repulsionU, temperature, and electron filling. For half-filled lattices, results for the optical conductivity indicate that the d.c. conductivity is zero for all temperatures andU>0. 相似文献
54.
F. Marin F. Minardi F. S. Pavone M. Inguscio G. W. F. Drake 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1995,32(4):285-293
The hyperfine structure of the3He 1s 3p
3
P state and the3He-4He isotope shift is determined by high precision measurements of the 1s2s
3
S
1-1s 3p
3
p
3
P
J
transition frequencies near 389 nm. A direct frequency measurement is made without the need for wavelength calibration by tuning a single laser to the atomic frequency, and using a novel heterodyne method to observe beat frequencies with a stable reference laser. A fit to a theoretical model of hyperfine structure is used to determine the hyperfine shifts. Additional off-diagonal mixing effects are investigated to resolve a possible systematic discrepancy in the hyperfine intervals. The final isotope shift without hyperfine structure of 42184308±165 kHz is used to deduce an rms nuclear charge radius for3He of 1.956±0.042 fm. This is in good agreement with other values obtained from atomic isotope shift measurements, and a recent theoretical value of 1.958±0.006 fm. The present result helps to resolve substantial differences in the3He nuclear radius derived from electron-nuclear scattering measurements, and it provides a significant test of the nuclear three-body problem. 相似文献
55.
Tatsuya Hattori Riadh Sahnoun Hideyuki Tsuboi Akira Endou Momoji Kubo Akira Miyamoto 《Applied Surface Science》2008,254(23):7929-7932
We developed a novel computational method to investigate the influences of the microstructure of the polymer electrolyte fuel cell cathode catalyst layer on the overpotential characteristic toward its optimization. Three-dimensional cathode catalyst layer models were constructed by applying three-dimensional porous structure simulator and developed simulator was used to study the overpotential characteristics. Our results showed that the overpotential decreased as decrease of the standard deviation of the ionomer thickness distribution due to the increase of number of active sites. 相似文献
56.
The artificial control of grain-boundary resistance and its contribution to magnetic and magneto-transport properties in [Co(3 nm)/Bi(2.5 nm)/Co(3 nm)]Ir20Mn80(12 nm) thin films that exhibit exchange bias is studied. Transverse magnetoresistance (MR) loops exhibit a negative MR in thin films grown by magnetron sputtering on Si/SiNx(100 nm) substrates. This negative MR effect is of the giant-MR (GMR) type, although its magnitude is less than 1%. A considerable exchange bias (EB) effect is observed only at lower temperatures, where both, GMR and isothermal magnetization loops exhibit a shift of −600 Oe at 5 K. 相似文献
57.
Igor Tikhonenkov 《Optics Communications》2006,264(2):321-325
We study the collective association dynamics of a cold Fermi gas of 2N atoms in M atomic modes into a single molecular bosonic mode. When the atomic translational motion is slow compared to the atom-molecule conversion rate, the many-body fermionic problem for 2M amplitudes is effectively reduced to a dynamical system of min{N, M} + 1 amplitudes, making the solution no more complex than the solution of a two-mode Bose-Einstein condensate and allowing realistic calculations with up to 104 particles. The many-body dynamics is shown to be formally similar to the dynamics of the bosonic system under the mapping of boson particles to fermion holes, producing collective enhancement effects due to many-particle constructive interference. 相似文献
58.
M.W.C. Dharma-wardana 《Solid State Communications》2003,127(12):783-788
The uniform electron fluid is the reference model for density functional calculations. Even for this system, many-body perturbation theory, and related methods become questionable when the density parameter rs exceeds unity. Hence, quantum Monte Carlo (QMC) simulation has been almost the only applicable method. We review a new approach, which uses a mapping of the quantum fluid to a classical Coulomb fluid, based on density-functional concepts. It is applicable at finite temperatures and arbitrary spin polarizations as well, and correctly recovers even the logarithmic terms in the exchange and correlations energies close to T=0. We show by detailed comparison with available QMC data that the method yields accurate pair-distribution functions, spin-dependent energies, static local-field factors, Landau parameter-based quantities like m∗ and g∗, for strongly coupled electron fluids. 相似文献
59.
A.N. Semenov M. Rubinstein 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(1):87-94
The effect of excluded-volume interactions on the reptation dynamics of long polymer chains is considered theoretically. It
is shown that interactions give rise to an exponential increase of the reptation time, , if polymer chains are long enough: , where is the number of monomers per entanglement. We propose a novel dynamical mechanism of activated reptation implying that neighboring
chains exchange conformations of their terminal fragments. It is shown that the exchange mechanism is compatible with the
equilibrium polymer chain statistics and that it provides a bridge between the previous theories.
Received: 25 July 1997 / Accepted: 8 October 1997 相似文献
60.