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排序方式: 共有246条查询结果,搜索用时 15 毫秒
71.
R F B Serpa E F O de Jesus M J Anjos L F de Oliveira L A Marins M G T do Carmo J D Corrêa Junior M S Rocha R T Lopes A M B Martinez 《Analytical sciences》2008,24(7):839-842
Knowledge about the spatial distribution and the local concentration of trace elements in tissues is of great importance, since trace elements are involved in many biological functions of living organisms. However, there are few methods available to measure the spatial (two (three)-dimensional) elemental distribution in animal brain. X-ray microfluorescence with synchrotron radiation is a multielemental mapping technique, which was used in this work to determine the topographic of iron, zinc and copper in coronal sections of female Wistar rats of different ages. Young (14 days old) and middle-aged (20 months old) rats (n = 8) were analyzed. The measurements were carried out at the XRF beam line at the Synchrotron Light National Laboratory (Campinas, Brazil). Two-dimensional scanning was performed in order to study the tendency of elemental concentration variation. The acquisition time for each pixel was 10 s/step and the step size was 300 microm/step in both directions. It was observed that the iron distribution was more conspicuous in the cortical area, thalamus and bellow the thalamus. On the other hand, the zinc distribution was more pronounced in the hippocampus. The iron, copper and zinc levels increased with advancing age. Therefore, this study reinforces the idea that these elements are involved in the chemical mechanisms of the brain that induce some neurological diseases, since they are also present in high levels in specific areas of the brain, such as the hippocampus and the substantia nigra of patients with these disorders. 相似文献
72.
O.?RojasEmail author S. M.?de Souza E. V.?Corrêa Silva M. T.?Thomaz 《The European Physical Journal B - Condensed Matter and Complex Systems》2005,46(3):385-398
The thermodynamics of the spin-S anisotropic quantum XXZ chain
with arbitrary value of S and unitary norm,
in the high-temperature regime, is
reported. The single-ion anisotropy term
and the interaction with an external magnetic field in
the z-direction are taken
into account. We obtain, for arbitrary value of S, the
β-expansion of the Helmholtz free energy of
the model up to order β6 and show that it actually
depends on
. Its classical limit
is obtained by simply taking S→∞.
At h=0 and D=0, our high temperature expansion of the
classical model coincides with Joyce’s exact solution [11].
We study, in the high temperature region, some thermodynamic quantities
such as the specific heat and the magnetic susceptibility as
functions of spin and verify
for which values of S those thermodynamic functions behave classically.
Their finite temperature behavior is inferred from interpolation of
their high- and low-temperature behavior,
and shown to be in good agreement with numerical results.
The finite temperature behavior is shown for higher values of spin. 相似文献
73.
Higham LJ Kelly PG Corr DM Müller-Bunz H Walker BJ Gilheany DG 《Chemical communications (Cambridge, England)》2004,(6):684-685
The Ramirez ylide undergoes electrophilic substitution with acetylenedicarboxylates to form Z and E adducts. The latter can react by cycloaddition with another equivalent of the alkyne to provide a new route to novel tetra-substituted azulenes, which show interesting bond localisation and crystal packing effects. 相似文献
74.
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
75.
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
76.
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79.
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
80.
用酶促聚合和原子转移自由基聚合相结合的"一锅法"合成了聚甲基丙烯酸正丁酯嵌段聚10-羟基癸酸[PBMA-b-P(10-HD)],通过核磁共振(1H NMR)、傅里叶红外光谱(FTIR)和凝胶渗透色谱(GPC)对其结构以及分子量与其分子量分布进行了表征,并通过动态光散射仪(DLS)和原子力显微镜(AFM)对聚合物在水溶液中的性质进行了研究.所得嵌段聚合物纳米粒子呈球形结构,平均直径为135 nm左右. 相似文献