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21.
da Costa D.B. Yacoub M.D. Filho J.C.S.S. Fraidenraich G. Mendes J.R. 《Communications Letters, IEEE》2006,10(1):13-15
This paper provides simple, exact, new closed-form expressions for the generalized phase crossing rate of Nakagami-m fading channels. Sample numerical results obtained by simulation are presented that validate the formulations developed here. A special case of this formulation is the Rayleigh case, whose result agrees with that obtained elsewhere in the literature. In passing, several new closed-form results concerning the statistics of the envelope, its in-phase and quadrature components, phase, and their time derivatives are obtained. 相似文献
22.
Platelet aggregation is known to be inhibited by ethanol, and this has been suggested to be one of the attenuating effects
of ethanol in cardiovascular disease. Recent studies have implicated an inhibition of phospholipase A2 induced arachidonic acid release, since the production of prostanoids that are formed from arachidonic acid and are involved
in the aggregation process has been shown to be diminished by ethanol. Phospholipase A2 is found in platelets in both a cytosolic form, from where it may translocate to the plasma membrane to release arachidonic
acid, and in a secretory form which is released extracellularly upon activition. In the present study, the effect of ethanol
on the secretion of phospholipase A2 and on its activity was determined. It was found that ethanol inhibited trast, the activity of the cytosolic form of phospholipase
A2 was inhibited by ethanol. 相似文献
23.
Ramon R. Costa Liu Hsu 《International Journal of Adaptive Control and Signal Processing》1992,6(1):19-33
A variable structure model reference adaptive controller (VS-MRAC) using only input and output measurements was recently proposed and shown to be globally asymptotically stable with superior transient behaviour and disturbance rejection properties. In this paper a singular perturbation approach is used in order to establish the robustness of the controller in the presence of unmodelled dynamics (parasitics) and disturbances. We develop a new Lyapunov-based technique to analyse the overall system and show that for sufficiently small parasitics the system remains stable and the output error is small in some sense. 相似文献
24.
This study sought to describe the changes in mortality among infants under one year of age in different areas of the city of Salvador, Bahia, during the period 1980-1988. This was done using estimates of variation in two indicators: proportional infant mortality and the coefficient of infant mortality. Values for the first indicator were separated into low, intermediate, high, and very high quartiles for 1980 and then calculated again using 1988 data. The second indicator was derived from the estimated number of live births using the rate of 33.4/1,000 inhabitants for 1980 and 31.4/1,000 for the years thereafter. The results showed that infant mortality in that age group had declined over the period, but that at the end of the period inequalities persisted in the distribution of infant deaths, which confirmed that conditions remained adverse for certain segments of the population. 相似文献
25.
26.
MJ Prado AL Nicastri PL Costa T Rockman IL Tersariol HB Nader RT Barros EB Prado 《Canadian Metallurgical Quarterly》1997,30(7):865-872
The aim of the present study was to evaluate renal and liver distribution of two monoclonal immunoglobulin light chains. The chains were purified individually from the urine of patients with multiple myeloma and characterized as lambda light chains with a molecular mass of 28 kDa. They were named BJg (high amount of galactose residues exposed) and BJs (sialic acid residues exposed) on the basis of carbohydrate content. A scintigraphic study was performed on male Wistar rats weighing 250 g for 60 min after i.v. administration of 1 mg of each protein (7.4 MBq), as the intact proteins and also after carbohydrate oxidation. Images were obtained with a Siemens gamma camera with a high-resolution collimator and processed with a MicroDelta system. Hepatic and renal distribution were established and are reported as percent of injected dose. Liver uptake of BJg was significantly higher than liver uptake of BJs (94.3 vs 81.4%) (P < 0.05). This contributed to its greater removal from the intravascular compartment, and consequently lower kidney accumulation of BJg in comparison to BJs (5.7 vs 18.6%) (P < 0.05). After carbohydrate oxidation, there was a decrease in hepatic accumulation of both proteins and consequently a higher renal overload. The tissue distribution of periodate-treated BJg was similar to that of native BJs: 82.7 vs 81.4% in the liver and 17.3 vs 18.6% in the kidneys. These observations indicate the important role of sugar residues of Bence Jones proteins for their recognition by specific membrane receptors, which leads to differential tissue accumulation and possible toxicity. 相似文献
27.
C. N. Elias C. S. Da Costa Viana 《Journal of Materials Engineering and Performance》1992,1(6):751-754
In the present work, the composition of H- 13 tool steel was modified with respect to the vanadium content to include an addition
of niobium to obtain improved austenite grain size control without altering the tempering response of the steel. Optical metallography
and transmission electron microscopy (TEM) observation of extraction replicas showed that the new steel had a smaller austenite
grain size and a finer carbide size distribution than the vanadium steel, which indicates a higher potential toughness. 相似文献
28.
O. L. V. Costa 《Systems & Control Letters》1991,17(1)
Mean-square stability for discrete systems requires that uniform convergence is preserved between input and state correlation sequences. Such a convergence preserving property holds for an infinite-dimensional bilinear system if and only if the associate Lyapunov equation has a unique strictly positive solution. 相似文献
29.
Summary Polymer composites have recently received a considerable amount of scientific and technological interest, because their properties
can be properly controlled, choosing the adequate doped particles, their size and concentrations, and the synthesis conditions.
In this work we report the synthesis and characterization of a polystyrene (PS) matrix doped with different concentrations
of iron nanoparticles.
X-ray diffraction and transmission electron microscopy were used to characterize the structure of the samples. The behaviour
of the d.c. electrical conductivity (σdc) and the complex permittivity (ε*=ε′-iε′′) as a function of frequency (100 Hz–10 MHz) reflects the important effect of the iron nanoparticles concentration in the
sample properties. A percolation threshold in the conductivity was observed at a critical concentration of iron nanoparticles.
A noticeable increase in the saturation magnetization and coercivity is observed with the rise of the iron nanoparticles concentration,
being thisbehaviour also noticed in the remanent magnetization. A rise of the initial a.c. susceptibility with the iron concentration
is also observed. 相似文献
30.
The objective of this paper is to present an analysis on the scale‐up procedure of two‐dimensional spouted beds. The task was carried out with three different beds measuring 0.15, 0.30 and 0.80 in width. The conditions of scale‐up were studied through geometrical similitude analysis. Some parameters of scale were adimensionalised, tested and validated in order to propose relationships capable of predicting values of dependent properties. Those relationships should be followed in a prototype of an equipment of industrial scale. The study permitted the development of correlations to predict values of maximum pressure drop, minimum spout velocity and maximum height of spouting. 相似文献