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31.
In this paper, we present a method for blind separation of co-channel BPSK signals arriving at an antenna array. This method consists of two parts: the maximum likelihood constellation estimation and assignment. We show that at high SNR, the maximum likelihood constellation estimation is well approximated by the smallest distance clustering algorithm, which we proposed earlier on heuristic grounds. We observe that both these methods for estimating the constellation vectors perform very well at high SNR and nearly attain Cramer-Rao bounds. Using this fact and noting that the assignment algorithm causes negligible error at high SNR, we derive upper bounds on the probability of bit error for the above method at high SNR. These upper bounds fall very rapidly with increasing SNR, showing that our constellation estimation-assignment approach is very efficient. Simulation results are given to demonstrate the usefulness of the bounds 相似文献
32.
We performed simultaneous fasting and fed antroduodenal manometry and EGG in 25 children with functional bowel disorders. Three patients (12%) had an uninterpretable EGG. The manometric studies showed severe neuropathy in six patients; milder neuropathic changes in five patients; postprandial hypomotility in one patient; myopathy in four patients, and normal motility in the remaining six patients. The percentage of tachygastria time (frequency > 3.5 cycles/min) was higher in the patiens with mild (44.1 +/- 15.8%) and severe (48 +/- 19.1%) neuropathy than in the patients with myopathy (20 +/- 16.2%, P < 0.05) or with normal motility (23 +/- 13.3%, P < 0.05). There was a considerable overlap in the percentage of tachygastria and total arrhythmia time among the different study groups. The ratio of post- to preprandial power was significantly higher (2.5 +/- 0.07) in children with normal motility than in the other patients groups. Every child with total arrhythmia time < 35% and a ratio of post- to preprandial power > 2.4 had normal manometry. In summary, EGG differentiated groups of children with normal manometry from others with neuropathic or myopathic changes, but in a minority of patients the study was not interpretable and there was overlap in EGG results between children with normal and abnormal manometry. 相似文献
33.
Aggregation of IgE cell surface receptors on MMC-34 cells, a murine mast cell line, induces the synthesis and secretion of prostaglandin D2 (PGD2). Synthesis and secretion of PGD2 in activated MMC-34 cells occurs in two stages, an early phase that is complete within 30 min after activation and a late phase that reaches a maximum about 6 h after activation. The early and late phases of PGD2 generation are mediated by prostaglandin synthase 1 (PGS1) and prostaglandin synthase 2 (PGS2), respectively. Arachidonic acid, the substrate for both PGS1 and PGS2, is released from membrane phospholipids by the activation of phospholipases. We now demonstrate that in activated mast cells (i) secretory phospholipase A2 (PLA2) mediates the release of arachidonic acid for early, PGS1-dependent synthesis of PGD2; (ii) secretory PLA2 does not play a role in the late, PGS2-dependent synthesis of PGD2; (iii) cytoplasmic PLA2 mediates the release of arachidonic acid for late, PGS2-dependent synthesis of PGD2; and (iv) a cytoplasmic PLA2-dependent step precedes secretory PLA2 activation and is necessary for optimal PGD2 production by the secretory PLA2/PGS1-dependent early pathway. 相似文献
34.
EG Mdurvwa JI Alak GE Pimentel-Smith HS Gakou S Kolavala H Abdelrahman PG Reddy 《Canadian Metallurgical Quarterly》1997,43(7):1039-1044
The LP-BM5 murine leukemia virus causes acquired immunodeficiency syndrome in C57BL/6J mice (MAIDS), similar to that of AIDS in humans. The objective of this study was to determine the effect of LP-BM5 viral infection on cellular activation and membrane integrity of splenocytes. Oxidative burst in splenocytes in response to exposure to PMA (20 microg/ml) was significantly higher (p<.02) in infected than in control mice at two weeks post-infection using luminol-enhanced chemiluminescence. By 13 weeks post-infection superoxide anion production in infected mice was significantly lower when compared to controls coinciding with decreased proliferative response to mitogens. The extent of cell membrane damage as indicated by lactic dehydrogenase (LDH) activity in serum was significantly higher in infected than in control mice (p<.001). The results from this study suggests that LP-BM5 virus causes an initial stimulation of cellular activity followed by a decreased cell activation characterized by decreased proliferation of splenocytes and decreased oxygen radical production. Decreased cell membrane integrity indicated by increased LDH activity may partly be responsible for these changes. 相似文献
35.
In executing tasks involving intelligent information processing, the human brain performs better than the digital computer. The human brain derives its power from a large number [O(1011)] of neurons which are interconnected by a dense interconnection network [O(105) connections per neuron]. Artificial neural network (ANN) paradigms adopt the structure of the brain to try to emulate the intelligent information processing methods of the brain. ANN techniques are being employed to solve problems in areas such as pattern recognition, and robotic processing. Simulation of ANNs involves implementation of large number of neurons and a massive interconnection network. In this paper, we discuss various simulation models of ANNs and their implementation on distributed memory systems. Our investigations reveal that communication-efficient networks of distributed memory systems perform better than other topologies in implementing ANNs. 相似文献
36.
Reddy K. Pavan S. 《IEEE transactions on circuits and systems. I, Regular papers》2007,54(10):2184-2194
We examine noise due to clock jitter in single-loop low-pass continuous-time delta-sigma (Delta Sigma) modulators (CT-DSMs) employing nonreturn to zero (NRZ) feedback digital-to-analog converters (DACs). Using the discrete-time version of the Bode sensitivity integral, we derive a lower bound on jitter noise and its relationship to the noise transfer function (NTF) of the modulator. We show that NTFs with optimized zeros result in lower jitter noise than those with all zeros at the origin. We give intuition to a recent observation (arrived through numerical optimization) that NTFs with peaking in their passbands have lower jitter noise than maximally flat NTFs. We propose a design procedure that minimizes the sum of the quantization and jitter noise. The arguments regarding Delta Sigma analog-to-digital converters are extended to Delta Sigma DACs and measurement results are presented. 相似文献
37.
38.
K. T. Ramakrishna Reddy R. W. Miles 《Journal of Materials Science: Materials in Electronics》2003,14(9):529-532
Small-area polycrystalline CuGa
x
In1–x
Se2-based solar cells produced in the laboratory have been reported with efficiencies up to 18.8%. This success at achieving high-efficiency devices has stimulated a parallel research effort to produce large-area modules based on the use of CuGa
x
In1–x
Se2 with reduced cost of production. One method that has potential to achieve these objectives is chemical spray pyrolysis. Preliminary studies have resulted in devices with efficiencies of 4–5%. Further improvements toward implementing higher-efficiency devices are expected to result from a better understanding of the physical and chemical properties of the chalcopyrite layers produced. In this work we have investigated, for the first time, the properties of these layers using X-ray photoelectron spectroscopy (XPS) to identify the secondary phases and residual impurities present. The layers studied were for In/Ga mole ratios of x=0, 0.2, 0.4, 0.6, 0.8, and 1.0 in CuGa
x
In1–x
Se2. The layers were also profiled by sputter etching away the surface of the layers and repeating the XPS measurements. The effects of annealing the layers in air, vacuum, and selenium vapor were also investigated. 相似文献
39.
We present a systematic, empirical design technique to obtain optimum broadband impedance, axial-ratio (AR) and gain bandwidths for a singly-fed electromagnetically coupled patch antenna for circular polarization. Our investigation has also revealed tradeoffs amongst obtainable AR, impedance bandwidth and AR bandwidth. Using two design examples at different frequency bands and for different senses of circular polarization, we have demonstrated the effectiveness of the proposed knowledge-based tuning method. We have obtained at C-band measured values of impedance bandwidth (VSWR/spl les/2) equal to 43%, 3-dB AR bandwidth of 8%, AR of less than 0.3 dB and a mean gain level of 7 dB. For the Ku-band element, a 40% impedance bandwidth and a 17.3% of 3-dB AR bandwidth have been obtained with a peak gain of 7.2 dBic. 相似文献
40.
Animesh Chakrabarti Man Mohan Sharma 《Journal of the American Oil Chemists' Society》1992,69(12):1251-1253
Anhydrous esterification of myristic acid with propylene was carried out in the temperature range of 110–145°C and pressure
from 190–195 psig in the presence of Amberlyst-15 (cation exchange resin) and Filtrol-24 (acid-treated clay) as catalysts.
The product ester, isopropyl myristate finds use in cosmetic and topical medicinal preparations where good absorption through
the skin is desired. Filtrol-24 is the catalyst of choice, and the recommended operating temperature is 130°C with a pressure
of 190 psig. 相似文献