In this paper we describe a detailed neutron diffraction investigation of the
crystal and magnetic structure of two layered CMR manganites
La1·2Sr1·8Mn2O7
(x = 0·4) and
La1·4Sr1·6Mn2O7
(x = 0·3). In ...these materials of reduced
dimensionality compared to the 3D perovskites, we find competing effects
between charge-lattice and spin degrees of freedom. These effects can be
investigated by studying the behaviour of crystal and magnetic structure as a
function of temperature, composition and hydrostatic pressure. We find
opposite lattice responses to the onset of charge delocalisation and magnetic
ordering in these two layered compounds. Below the insulator-to-metal
transition (TIM), the lattice response suggests that charge is transferred to
d3z2-r2
orbitals in
La1·2Sr1·8Mn2O7
and to
dx2-y2
orbitals in
La1·4Sr1·6Mn2O7.
We argue that these changes are too large to be due to chemical differences.
Instead we suggest that the orbital configuration of the Mn ion below TIM is
sensitive to electronic doping. In
La1·2Sr1·8Mn2O7
we find that the lattice response at TIM to be driven by lattice displacements
that relax below TIM, consistent with polaronic degrees of freedom. We also
note that the competition between super- and double-exchange to be significant
in reduced dimensions. This is manifested in the change in the sign of the
apical Mn-O bond compressibilities above and below TIM. Finally, we describe
the magnetic structure of these two different layered manganites. We find that
electronic doping also results in significant changes to the ordered
arrangement of Mn spins. Interestingly the magnetism in reduced dimensions in
these materials can be varied from relative simple structures that show
ferromagnetic inter-bilayer coupling as observed in
La1·2Sr1·8Mn2O7
to structures with antiferromagnetic inter-bilayer coupling as found in
La1·4Sr1·6Mn2O7.
YBaCo{sub 4}O{sub 7} belongs to a new class of geometrically frustrated magnets like the pyrochlores, in which Co spins occupy corners of tetrahedra. The structure can be viewed as an alternating ...stacking of Kagome and triangular layers. Exactly half of the triangular units of the Kagome plane are capped by Co ions to form columns running perpendicular to the Kagome sheets. Neutron powder diffraction reveals a broad temperature range of diffuse magnetic scattering, followed by long-range magnetic ordering below 110 K. A unique low-temperature magnetic structure simultaneously satisfies an S=0 arrangement in the uncapped triangular units and antiferromagnetic coupling along the columns. A spin reorientation above 30 K tracks the relative strengths of the in-plane and out-of-plane interactions.
Circadian Rhythm in Human Epidermis Radaelli, Adriano; Tadini, Gianluca; Carandente, Franca
Journal of investigative dermatology
80, Številka:
6
Journal Article
We have studied the antiangiogenetic effects of hydrocortisone and protamine given intra-arterially. The cornea of male, Sprague-Dawley rats were cauterized with silver nitrate. The following ...treatments were given: 30 micrograms hydrocortisone topical (t.p.), b.i.d., 50 mg/kg/day intraperitoneally (i.p.) or intra-arterially (i.a.), 10 mg/kg/day protamine i.p. or i.a. Saline was administered to the control groups. In separate experiments we also evaluated the anti-inflammatory effects of hydrocortisone, i.p., on the cauterized corneas. Five days after cauterization, the animals were killed, exsanguinated and India ink was injected to show the network of neovessels. The percentage area of the cornea covered by neovessels was measured morphometrically and evaluated statistically. Hydrocortisone t.p. (-84%), i.a. (-60%) and protamine i.a. (-44%) significantly inhibited angiogenesis in the cauterized cornea. Either drugs, i.p., had any antiangiogenetic effects, but hydrocortisone significantly reduced cell infiltration of the corneas. The results suggest that locoregional administration of antiangiogenetic drugs might be clinically useful.
We analyzed the programming dynamics in phase-change memory (PCM) cells. The chalcogenide phase-change mechanism and phase distribution in the programmed cell is studied by both experiments and a ...numerical model, which self-consistently addresses the electrical-thermal conduction phase transition. We show that the reset-set transition is strongly coupled to the electronic switching in the amorphous phase, thus supporting the need for a self-consistent electrothermal-phase transition model to correctly account for all experimental evidences.
This study was designed to determine whether prostaglandins can stimulate the repair of human duodenal epithelium. Ten healthy volunteers were given 50 ml 40% ethanol through an endoscope onto the ...duodenal mucosa 1-7 cm from the pyloric sphincter; 3 min later, misoprostol (200 micrograms) or inert vehicle (5 ml) was given locally in the same way. One and 5 h later, endoscopy was repeated to evaluate the damage. The conditions of the mucosa were evaluated by endoscopy and by scanning and transmission electron microscopy in biopsies taken at time 0 and 3 min, 1 and 5 h after ethanol. The study was double-blind with a cross-over balanced design. Three minutes after ethanol administration, the duodenal mucosa showed hyperemia with hemorrhagic lesions. Under the electron microscope, the lesions were caused by vascular engorgement or red blood cell extravasation into the submucosa; the epithelium underlining lesions showed loss of superficial cells and damage to the upper layer of the mucosa. One hour after ethanol, there was a striking difference between the two treatment groups, with a substantial recovery of the duodenal epithelium in the misoprostol-treated volunteers. Although spontaneous recovery was evident in the control group, there was also a significant difference at 5 h. Our results suggest that prostaglandins are able to stimulate the recovery of the duodenal epithelium after acute damage.
This study was undertaken to examine the influence of hospitalization on the nutritional status of cancer patients. We examined 126 patients consecutively admitted to the Istituto Nazionale Tumori of ...Milan. At admission, all patients underwent standard evaluations, including actual weight, percentage weight loss, arm circumference, triceps skinfold, serum proteins, serum albumin, total iron binding capacity, cholinesterase and peripheral lymphocytes. Finally, from all patients a 24-h dietary recall was obtained, in order to calculate calorie and protein intake. All the patients underwent another evaluation after 1 week of hospitalization; after 2 weeks only 37 of them were evaluated again, since some were operated, some were treated with radio-chemotherapy, some were discharged or had died. Results showed that after one week of hospitalization some variables were significantly altered, such as arm circumference in male patients, serum proteins, cholinesterase, total iron binding capacity, peripheral lymphocytes, calorie and protein intake. A significant weight loss was seen after 2 weeks. The reduced calorie and protein assumption was correlated with depletion of some of the nutritional variables (body weight, arm circumference in males, total iron binding capacity, serum albumin, cholinesterase, lymphocytes). Our data show that hospitalization plays an important role in deterioration of nutritional status in our patient population, and this problem is generally overlooked by the clinicians primarily involved in the care of cancer patients.
Para melhor conhecer o conteúdo da assistência ambulatórial em Assistência Primária à Saúde, procedeu-se a um estudo com uma amostra de 4.319 atendimentos, representando 7% da população atendida de ...março de 1985 a março de 1986. O estudo foi realizado na Unidade Sanitária Murialdo (SSMA), localizada na Vila São José, na periferia de Porto Alegre, RS (Brasil). O sexo feminino ocupou 67% do total de atendimentos. A composição etária esteve mais significativamente representada por crianças até 10 anos (37%) e mulheres em idade fértil (21%). As vinte primeiras razões de encontro corresponderam a 63% do total, e a razão principal de procura do serviço foi para renovação de receitas e pedido de medicamentos (9,3%). De todos os diagnósticos do estudo, os vinte primeiros correponderam a 61%, sendo que hipertensão arterial sistêmica (8,8%), infecções de vias aéreas superiores (7,8%) e imunizações (5,5%) foram os mais freqüentes. O procedimento mais realizado foi fornecer, prescrever ou administrar medicação. Foram encaminhadas 7,3% do total das pessoas atendidas, mais da metade (5,0%) para profissionais do próprio serviço e apenas 0,6% foram encaminhadas para hospitalização. Estes dados, acrescidos daqueles de pesquisas que captaram os aspectos de morbi-mortalidade não facilmente obtidos em estudos de demanda, poderiam servir para orientar o planejamento dos serviços sanitários e treinamento de pessoal.
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