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排序方式: 共有148条查询结果,搜索用时 15 毫秒
41.
42.
Wilkins SB Spencer PD Hatton PD Collins SP Roper MD Prabhakaran D Boothroyd AT 《Physical review letters》2003,91(16):167205
We report the first direct resonant soft x-ray scattering observations of orbital ordering. We have studied the low temperature phase of La0.5Sr1.5MnO4, a compound that displays charge and orbital ordering. Previous claims of orbital ordering in such materials have relied on observations at the manganese K edge. These claims have been questioned in several theoretical studies. Instead we have employed resonant soft x-ray scattering at the manganese L(III) and L(II) edges which probes the orbital ordering directly. Energy scans at constant wave vector are compared to theoretical predictions and suggest that at all temperatures there are two separate contributions to the scattering: direct orbital ordering and strong cooperative Jahn-Teller distortions of the Mn3+ ions. 相似文献
43.
Helme LM Boothroyd AT Coldea R Prabhakaran D Tennant DA Hiess A Kulda J 《Physical review letters》2005,94(15):157206
We report polarized- and unpolarized-neutron scattering measurements of magnetic excitations in single-crystal Na0.75CoO2. The data confirm ferromagnetic correlations within the cobalt layers and reveal antiferromagnetic correlations perpendicular to the layers, consistent with an A-type antiferromagnetic ordering. The magnetic modes propagating perpendicular to the layers are sharp, and reach a maximum energy of approximately 12 meV. From a minimal spin-wave model, containing only nearest-neighbor Heisenberg exchange interactions, we estimate the interlayer and intralayer exchange constants to be 12.2+/-0.5 meV and -6+/-2 meV, respectively. We conclude that the magnetic fluctuations in Na0.75CoO2 are highly three dimensional. 相似文献
44.
P. D.?Spencer M. E.?Ghazi S. B.?Wilkins P. D.?HattonEmail author S. D.?Brown D.?Prabhakaran A. T.?Boothroyd 《The European Physical Journal B - Condensed Matter and Complex Systems》2005,46(1):27-32
We present high resolution X-ray measurements
characterising the charge stripe order state in the
La2-xSrxNiO4 system with x = 0.20, 0.225 and 0.25. We
find that in the x = 0.20, 0.225 and 0.25 systems the charge
stripe order exists in a charge stripe glass characterised by
weak, poorly correlated incommensurate charge stripes in contrast
to the strong well correlated charge stripes in the commensurate
x = 1/3 system. No stabilisation of the charge order was
observed at the next possible commensurate value of ε= 0.25. A comparison with high energy X-ray measurements suggested
that the charge order may exist in a charge stripe glass in the
bulk in the doping region x = 0.20 - 0.33. Finally at low
temperature there was an initial increase in the intensity and
correlation not observed with neutron measurements and it appears
to be an effect that X-rays are sensitive to but neutrons are not. 相似文献
45.
46.
The φ meson productions in Au+Au and/or Pb+Pb collisions at AGS, SPS,
RHIC, and LHC energies have been studied systematically with a hadron and
string cascade model LUCIAE. After considering the energy dependence of the
model parameter α in string fragmentation function and adjusting it
to the experimental data of charged multiplicity to a certain extent,
the model predictions for φ meson yield, rapidity, and
transverse mass distributions are compatible with the experimental data at
AGS, SPS and RHIC energies. A calculation for Pb+Pb collisions at LHC energy
is given as well. The obtained fractional variable in string fragmentation
function shows a saturation in energy dependence. It is discussed that the
saturation of fractional variable in string fragmentation function might be a
qualitative representation of the energy dependence of nuclear transparency. 相似文献
47.
The energy and centrality dependencies of charged particle pseudorapidity density in relativistic nuclearcollisions were studied using a hadron and string cascade model, JPCIAE. Both the relativistic p+p experimental dataand the PHOBOS and PHENIX Au+Au data at RHIC energy could be fairly reproduced within the framework ofJPCIAE model and without retuning the model parameters. The predictions for Pb + Pb collisions at the LHC energywere also given. We computed the participant nucleon distributions using different methods. It was found that thenumber of participant nucleons is not a well defined variable both experimentally and theoretically. Thus it may beinappropriate to use the charged particle pseudorapidity density per participant pair .as a function of the number ofparticipant nucleons for distinguishing various theoretical models. 相似文献
48.
49.
50.
GUY BOUCHITTÉ IRENE FONSECA GIOVANNI LEONI LUÍSA MASCARENHAS 《Archive for Rational Mechanics and Analysis》2002,165(3):187-242
An integral representation formula for a class of functionals defined on and in (the space of special functions of bounded variation) is obtained without requiring the regularity conditions usually imposed
in the literature. The approach is based on the general results of [10] and on a Poincaré-Wirtinger type inequality introduced
by DE GIORGI, CARRIERO & LEACI [25]. Applications to relaxation problems and dimension-reduction problems in brittle thin
films are presented.
(Accepted May 8, 2002) Published online October 18, 2002
Communicated by L. Ambrosio 相似文献