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991.
I Martinez de la Fuente L Martinez J Veguillas JM Aguirregabiria 《Canadian Metallurgical Quarterly》1996,71(5):2375-2379
The numerical study of a glycolytic model formed by a system of three delay differential equations reveals a quasiperiodicity route to chaos. When the delay changes in our biochemical system, we can observe the emergence of a strange attractor that replaces a previous torus. This behavior happens both under a constant input flux and when the frequency of the periodic substrate input flux changes. The results obtained under periodic input flux are in agreement with experimental observations. 相似文献
992.
JM Kates 《Canadian Metallurgical Quarterly》1994,37(2):449-464
Sinusoidal modeling is a new procedure for representing the speech signal. In this approach, the signal is divided into overlapping segments, the Fourier transform computed for each segment, and a set of desired spectral peaks is identified. The speech is then resynthesized using sinusoids that have the frequency, amplitude, and phase of the selected peaks, with the remaining spectral information being discarded. Using a limited number of sinusoids to reproduce speech in a background of multi-talker speech babble results in a speech signal that has an improved signal-to-noise ratio and enhanced spectral contrast. The more intense spectral components, assumed to be primarily the desired speech, are reproduced, whereas the less intense components, assumed to be primarily background noise, are not. To test the effectiveness of this processing approach as a noise suppression technique, both consonant recognition and perceived speech intelligibility were determined in quiet and in noise for a group of subjects with normal hearing as the number of sinusoids used to represent isolated speech tokens was varied. The results show that reducing the number of sinusoids used to represent the speech causes reduced consonant recognition and perceived intelligibility both in quiet and in noise, and suggests that similar results would be expected for listeners with hearing impairments. 相似文献
993.
An 11-month-old girl had massive rectal bleeding. A midabdominal mass was palpated. Ultrasound scan showed a large cystic mass with diffusely echogenic contents; Tc-99M radionuclide scan confirmed a duplication. Exploratory surgery and pathology examination showed a gastric duplication with formation of a fistula into the transverse colon with a colonic ulcer and hemorrhage. This combination of findings is presented as a rare cause of lower gastrointestinal hemorrhage in infancy. 相似文献
994.
995.
The arabidopsis ACT7 actin gene is expressed in rapidly developing tissues and responds to several external stimuli 总被引:1,自引:0,他引:1
JM McDowell YQ An S Huang EC McKinney RB Meagher 《Canadian Metallurgical Quarterly》1996,111(3):699-711
ACT7 encodes one of the six distinct and ancient subclasses of actin protein in the complex Arabidopsis actin gene family. We determined the sequence and structure of the Arabidopsis thaliana ACT7 actin gene and investigated its tissue-specific expression and regulation. The ACT7 mRNA levels varied by 128-fold among several different tissues and organs. The highest levels of aCT7 mRNA were found in rapidly expanding vegetative organs, the lowest in pollen. A translational fusion with the 5' end of ACT 7 (1.9 kb) joined to the beta-glucuronidase reporter gene was strongly and preferentially expressed in all young, developing vegetative tissues of transgenic Arabidopsis plants. ACT7 was the only Arabidopsis actin gene strongly expressed in the hypocotyl and seed coat. Although no beta-glucuronidase expression was seen in developing ovules or immature seeds, strong expression was seen in dry seeds and immediately after imbibition in the entire seedling. ACT7 was the only Arabidopsis actin gene to respond strongly to auxin, other hormone treatments, light regime, and wounding, and may be the primary actin gene responding to external stimuli. The ACT7 promoter sequence contains a remarkable number of motifs with sequence similarity to putative phytohormone response elements. 相似文献
996.
997.
998.
In preeclampsia, a factor in the maternal circulation alters endothelial function via a reduction in nitric oxide synthesis. We measured the in vitro effects of 2% plasma from women with preeclampsia, compared with 2% plasma from normotensive pregnant women, on cultured endothelial cell nitrite production and nitric oxide synthase activity. On finding differential effects, we measured the effects on cellular viability (assessed by lactate dehydrogenase levels) and performed a time course study. Endothelial cell nitrite production was found to be higher after exposure to plasma from the preeclamptic group than the normotensive pregnant group. The effects of long-term exposure (120 hours) were similar to those of short-term exposure (24 hours). In addition, nitric oxide synthase activity was significantly greater after exposure to preeclamptic plasma than after exposure to normotensive pregnant plasma. No differential effect on cellular viability was found. Contrary to our hypothesis, exposure of endothelial cells to preeclamptic plasma resulted in increased nitric oxide production and nitric oxide synthase activity. 相似文献
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1000.