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排序方式: 共有436条查询结果,搜索用时 234 毫秒
41.
Bunch J.R. Le Borne R.C. Proudler I.K. 《Vision, Image and Signal Processing, IEE Proceedings -》1998,145(1):1-5
The numerical performance of lattice-based adaptive signal processing algorithms is shown to involve the conditioning of a 2×2 matrix whose off-diagonal elements contain reflection coefficients. Degraded algorithmic performance for the a posteriori recursive least squares lattice (RLSL) is shown to be attributed to the ill-conditioning of this matrix, Theoretical results are given which may be used to separate the conditioning of the underlying problem from issues concerning algorithmic stability. Although the results are not restricted to the all-pole case, for simplicity the authors make use of this well understood example since the condition number of the autocorrelation matrix will become arbitrarily close to singularity as the poles of an all-pole filter approach the unit circle. For a second-order prediction problem, four case studies of varying conditioning are provided which demonstrate the appropriateness of the theoretical bounds which analytically describe the sensitivity to perturbations in the residual update recursions. The paper illustrates the use of numerical linear algebra analysis techniques to better understand the numerical performance of algorithms in signal processing as well as emphasising that numerical performance is a function of the problem's conditioning as well as algorithmic stability 相似文献
42.
EM De Vries DO Ricke TN De Vries A Hartmann H Blaszyk D Liao T Soussi JS Kovach SS Sommer 《Canadian Metallurgical Quarterly》1996,7(3):202-213
Germline and somatic mutations in the p53 and APC genes contribute to neoplasia. The patterns of these and other acquired mutations in cancers reflect environmental mutagens and endogenous factors that contribute to carcinogenesis. Herein, we describe a database of almost 2,300 mutations in the p53 and APC genes published until September 1, 1993. In addition to cataloging the mutations, multiple fields of information have been added to facilitate future molecular epidemiological analyses of human cancer. The accuracy of the database has been checked by the present authors and, by soliciting feedback from the original corresponding authors. The strengths and limitations of the primary literature are discussed. 相似文献
43.
Although pneumatic dilatation (PD) has been an established treatment for achalasia for decades, there is limited information on its long-term clinical efficacy. We have followed up the clinical status of patients having PD with a 30- or 35-mm balloon by one of us (D.O.C.) over a 25-year period. Of 144 patients whose initial records were available for review, 31 could not be contacted. Of the remaining 113 patients, 72 (64%) responded to a questionnaire assessing swallowing status and patient satisfaction, and this forms the basis of this report. There were 32 men and 40 women, with mean age 46 years (range: 17-78); mean length of follow-up since PD was 6.5 years (range: 10 months to 25 years). Success was primarily defined by the need for no additional therapy for achalasia other than one or two PD's. PD was effective long-term treatment in 61/72 patients (85%); only four of these required a second PD over this time interval. There was no significant difference in any of the following parameters between patients with a treatment success or failure: age, sex, size of pneumatic dilator, and duration of symptoms prior to PD. Response was significantly better (P < 0.05) in patients having no prior dilatation (43/47; 91%) than in those in whom another physician had performed prior dilatation (18/25; 72%). In response to the question of whether they would select PD again, 68 patients (94%) responded positively. In conclusion, pneumatic dilatation performed using a consistent technique by an experienced physician is effective long-term therapy for achalasia patients of all ages. Most patients require only one dilatation. 相似文献
44.
L Lang L Aloj DO Kiesewetter E Jagoda JT Lee CH Paik JA Carrasquillo WC Eckelman 《Canadian Metallurgical Quarterly》1996,23(6):669-672
We have developed three biochemical probes to determine if they are sensitive probes of early biochemical change in a tumor. All three probes appear to have the appropriate properties for in vivo imaging, but must now be evaluated as probes for the sensitive detection of changes in early malignant disease. 相似文献
45.
C Wu C Miyagawa DO Kennedy Y Yano S Otani I Matsui-Yuasa 《Canadian Metallurgical Quarterly》1997,103(3):213-224
Taurine (2-aminoethanesulfonic acid) is known to protect hepatocyte injury induced by hydrazine or carbon tetrachloride. We investigated whether cellular polyamines are involved in the protective mechanism of taurine in the hepatocyte injury caused by hydrazine or carbon tetrachloride. The agents decreased cellular polyamine concentrations, but the treatment with taurine prevented this decrease. The protection of taurine against hepatic injury was not observed in hepatocytes treated with alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase which is a key enzyme in polyamine biosynthesis. The protection of taurine was recovered by the addition of polyamines to DFMO-treated hepatocytes. These results suggest that cellular polyamines play an important role in the protection of taurine in hydrazine or carbon tetrachloride-induced hepatocyte injury. 相似文献
46.
KH Baratz DT Gray DO Hodge LC Butterfield DM Ilstrup 《Canadian Metallurgical Quarterly》1997,115(11):1441-1446
Management of Q-wave acute myocardial infarction (AMI) has been shown to differ between the United States and Canada, with more catheterization and revascularization procedures performed in the United States, but with little or no apparent difference in clinical outcomes. No previous studies have evaluated management differences for the acute coronary syndromes of unstable angina pectoris and non-Q-wave AMI. We therefore compared treatments and outcomes between 14 United States and 4 Canadian tertiary care centers participating in an observational registry of all consecutive admissions for unstable angina or non-Q-wave AMI between 1990 and 1993. A random, stratified sample was selected for detailed assessment and follow-up. There were 1,733 patients enrolled in United States centers and 642 in Canadian ones. In United States centers patients were less likely to receive intravenous nitroglycerin, heparin, beta blockers, calcium antagonists, or > or = 2 anti-ischemic agents. Coronary arteriography during index hospitalization was equally frequent in both countries (63.4% vs 66.9%, p = 0.781), but at 6 weeks and 1 year coronary arteriography was slightly less frequent in the United States patients. Revascularization by coronary angioplasty or bypass surgery was equivalent at 6 weeks and 1 year; however, there were trends toward less angioplasty and more bypass surgery in the United States than in Canada. Patients at United States centers stayed in the hospital fewer days than patients at Canadian centers (mean 8.2 vs 12.1 days, p <0.001). Death or AMI by 6 weeks was not different (4.8% vs 4.4%, p = 0.633), nor was it different at 1 year (10.0% vs 10.2%, p = 0.836). The combined outcome of death, AMI, or recurrent ischemia was more common in United States than in Canadian patients at 6 weeks (18.4% vs 13.9%, p = 0.004). Our findings indicate that United States physicians and hospitals did not consistently utilize more resources and were not more aggressive than their Canadian counterparts when treating acute coronary syndromes during this period. 相似文献
47.
With the rabies vaccine presently available for preexposure prophylaxis, 20% of all individuals do not have seroconversion following routine immunizations, and 5% are allergic to this vaccine. Two experimental rabies vaccines of cell culture origin offering greater purity and potency were evaluated by means of a double-blind experiment. Thirty-one volunteers who did not have seroconversion or who were allergic to duck embryo rabies vaccine received rabies vaccine produced in either human diploid cell culture (WI-38), or hamster kidney-cell culture. All volunteers had seroconversion within 14 days of receiving a single injection of other experimental vaccine. Clinical side effects were only minor. 相似文献
48.
Ömer N. DOĞAN G. M. Michal H. -W. Kwon 《Metallurgical and Materials Transactions A》1992,23(8):2121-2129
The growth behavior of austenite grains in the presence of A1N precipitates varies with the temperature and time of anneal.
To study this behavior, two iron alloys, (in weight percent) a 0.1 carbon base chemistry with 0.03A1/0.01N and 0.09A1/0.04N,
respectively, were annealed between 1000 °C and 1200 °C for times of up to 180 minutes. Using optical microscopy, as many
as 1000 austenite grains per heat-treatment condition were measured. Conditions of sup- pressed, abnormal, and uniform grain
growth were observed. Using an extraction replica tech- nique, the size, shape, and distribution of the A1N particles were
determined using transmission electron microscopy (TEM). The largest grain boundary curvatures calculated, using the Hellman-
Hillert pinning model, were in close agreement with independent calculations of curvatures using the grain size data. The
largest grains in the lognormal size distribution of austenite grains were found to be the ones with the potential to grow
to abnormally large sizes. 相似文献
49.
DO Lewis 《Canadian Metallurgical Quarterly》1976,6(4):198-213
On the basis of previously reported findings that a high percentage of court-referred children suffered from serious psychopathology other than sociopathy, attention is called to some essential, though often overlooked, elements of diagnostic evaluation of delinquents. Emphasis is on a meticulous history, including careful attention to the significances of family histories of serious psychiatric and/or neurological disorders. The importance of a detailed perinatal and medical history, with emphasis on determining a possible history of significant insult to the central nervous system, is stressed. A systematic mental status evaluation is strongly recommended. Techniques for assessing the existence of significant hallucinatory and delusional experiences in children are suggested. The uses of psychological and neurological evaluations to augment the psychiatric are discussed. The poor social situation from which many delinquents come as well as the obvious intrafamilial psychodynamic factors influencing delinquent behavior are recognized as frequent impediments to the search for less obvious psychotic and/or organic vulnerabilities in the juvenile offender. Case histories of several children who had previously been dismissed as merely sociopathic, illustrate the thesis of the paper. 相似文献
50.