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991.
Andrzej Banaszuk Andrzej Święch John Hauser 《Mathematics of Control, Signals, and Systems (MCSS)》1996,9(3):207-241
We study the problem of approximating one-dimensional nonintegrable codistributions by integrable ones and apply the resulting
approximations to approximate feedback linearization of single-input systems. The approach derived in this paper allows a
linearizable nonlinear system to be found that is close to the given system in a least-squares (L
2) sense. A linearly controllable single-input affine nonlinear system is feedback linearizable if and only if its characteristic
distribution is involutive (hence integrable) or, equivalently, any characteristic one-form (a one-form that annihilates the
characteristic distribution) is integrable. We study the problem of finding (least-squares approximate) integrating factors
that make a fixed characteristic one-form close to being exact in anL
2 sense. A given one-form can be decomposed into exact and inexact parts using the Hodge decomposition. We derive an upper
bound on the size of the inexact part of a scaled characteristic one-form and show that a least-squares integrating factor
provides the minimum value for this upper bound. We also consider higher-order approximate integrating factors that scale
a nonintegrable one-form in a way that the scaled form is closer to being integrable inL
2 together with some derivatives and derive similar bounds for the inexact part. This allows a linearizable nonlinear system
that is close to the given system in a least-squares (L
2) sense together with some derivatives to be found. The Sobolev embedding techniques allow us to obtain an upper bound on
the uniform (L
∞) distance between the nonlinear system and its linearizable approximation.
This research was supported in part by NSF under Grant PYI ECS-9396296, by AFOSR under Grant AFOSR F49620-94-1-0183, and by
a grant from the Hughes Aircraft Company. 相似文献
992.
M Villarini M Moretti E Damiani L Greci AM Santroni D Fedeli G Falcioni 《Canadian Metallurgical Quarterly》1998,24(7-8):1310-1315
Because previous literature reports have demonstrated that nucleated trout erythrocytes in conditions of oxidative stress are subjected to both membrane damage and a decrease in the enzymatic defense systems (glutathione peroxidase), which in turn lead to hemolysis, the present study was undertaken to determine whether DNA may be affected too, prior to the hemolytic event. Impairment of DNA in stressed trout erythrocytes was assessed using the comet assay--a rapid and sensitive, single-cell gel electrophoresis technique used to detect primary DNA damage in individual cells. In addition, indolinic and quinolinic nitroxide radicals were included in the study to determine their efficacy as antioxidants against free-radical-induced DNA damage. The parameters, tail length, tail intensity, and tail moment, used as an index of DNA damage, have shown that trout erythrocytes exposed to oxidative stress experience DNA damage prior to hemolysis and that the nitroxides significantly prevent this damage. This result provides further information about the potential use of these compounds as antioxidants in biological systems. 相似文献
993.
P Peretti-Viton D Taieb JM Viton A Flori X Muracciole V Benguigui G Salamon 《Canadian Metallurgical Quarterly》1998,40(12):783-787
Our purpose was to compare prospectively the sensitivity of contrast-enhanced magnetisation transfer (MT) MRI and gradient-echo (GE) T1-weighted images in metastatic disease of the brain. We studied 52 patients with brain metastases, using conventional T1-weighted GE and MT spin-echo (SE) images after the same standard dose of gadolinium. Axial 5-mm reconstructions of GE data were compared with 5-mm MT images in the same plane. Metastases were counted independently by two neuroradiologists. In 12 patients (23%) MT imaging showed more metastases than GE images (P = 0.03). We detected 68 more metastases with the former technique. 相似文献
994.
D Meletzus P Rudnick N Doetsch A Green C Kennedy 《Canadian Metallurgical Quarterly》1998,180(12):3260-3264
To determine whether in Azotobacter vinelandii the PII protein influences the regulation of nif gene expression in response to fluxes in the ammonium supply, the gene encoding PII was isolated and characterized. Its deduced translation product was highly similar to PII proteins from other organisms, with the greatest degree of relatedness being exhibited to the Escherichia coli glnK gene product. A gene designated amtB was found downstream of and was contranscribed with glnK as in E. coli. The AmtB protein is similar to functionally characterized ammonium transport proteins from a few other eukaryotes and one other prokaryote. glnK and amtB comprise an operon. Attempts to isolate a stable glnK mutant strain were unsuccessful, suggesting that glnK, like glnA, is an essential gene in A. vinelandii. amtB mutants were isolated, and although growth on limiting amounts of ammonium was similar in the mutant and wild-type strains, the mutants were unable to transport [14C]methylammonium. 相似文献
995.
BACKGROUND: To maintain good exposure during major video-assisted thoracic surgery it is necessary to deflate completely the ipsilateral lung. However, little is known about the effects of one-lung ventilation (OLV) on pulmonary function in newborn patients. METHODS: Ten neonatal domestic pigs with a mean age of 6+/-0.6 days were intubated and ventilated in pressure-controlled mode (inspired oxygen fraction=1.0). One-lung ventilation was maintained for 120 minutes. Serial measurements of hemodynamics and gas exchange were done before, during, and until 90 minutes after OLV. Pulmonary function testing was performed before and after OLV for each lung separately. RESULTS: With the inspired oxygen fraction set at 1.0, arterial oxygen saturation remained stable at 100% during OLV. Venous admixture and alveolar-arterial oxygen tension gradient increased slightly from the baseline value of 2.6% +/-0.3% to 3.8%+/-0.3% during OLV (mean+/-standard error of the mean; p=0.02), and from 358+/-28 to 407+/-18 mm Hg (not significant), respectively. Both values returned to baseline during the subsequent ventilation of both lungs. Static compliance and resistance of the ventilated lung did not change. Compliance of the collapsed lung decreased after reexpansion from 0.42+/-0.07 to 0.29+/-0.06 mL x cm H2O(-1) x kg(-1), p=0.008). Resistance remained unchanged (0.22+/-0.02 versus 0.25+/-0.05 cm H2O x L(-1) x s(-1); not significant). CONCLUSIONS: There were only minor effects on pulmonary function during and after OLV in the neonatal piglet. Alterations in gas exchange during OLV were minimal. Prolonged collapse of the lung with subsequent reexpansion was associated with a slight decrease in compliance, indicating some mild lung injury. 相似文献
996.
Berninger Virginia W.; Vaughan Katherine; Abbott Robert D.; Brooks Allison; Abbott Sylvia P.; Rogan Laura; Reed Elizabeth; Graham Steve 《Canadian Metallurgical Quarterly》1998,90(4):587
Poor spellers in 2nd grade (n?=?128) participated in 24 20-min sessions that included (a) direct instruction in the alphabet principle (most frequent phoneme-spelling connections); (b) modeling of different approaches, singly and in combination, for developing connections between spoken and written words for 48 words ordered by sound-spelling predictability; and (c) practice in composing. Results of this multilayered intervention showed that (a) more than 1 way of developing sound-spelling connections is effective in teaching spelling but that after training in the alphabet principle, combining whole word and onset-rime training is most effective in achieving transfer of the alphabet principle across word contexts; (b) functional spelling units of not only a single letter but also 2 or more letters are important in beginning spelling; and (c) training in spelling transfers to composition and word recognition. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
997.
A clinical case control study to identify prognostic factors present at hospital admission associated with early sequelae and fatal outcome of acute Japanese encephalitis (JE) was carried out in Gusi county, Henan Province, central China from June to September 1991. A total of 70 patients with laboratory-confirmed acute JE were studied, of whom 3 cases died and 33 cases had neurological or psychiatric sequelae at the end of three months follow-up. The results showed that acute JE at younger age, with higher body temperature, high white cell count in CSF, and deep coma present at hospital admission were markers for unfavorable outcomes (sequelae or fatal). A history of the vaccination was not correlated with the early sequelae and fatal outcome of the disease. The paper suggests that early diagnosis and treatment and universal JE vaccination for all susceptible populations are keys for decreasing incidence of sequelae and fatal outcome of acute JE. 相似文献
998.
S Karacagil A Holmberg A Narbani I Eriksson D Bergqvist 《Canadian Metallurgical Quarterly》1996,12(3):337-341
Faecal samples from asymptomatic dairy cows and calves from a farm on the Island Falster, Denmark, were examined by a sucrose gradient flotation technique. Giardia cysts were found in 7.6% of the 92 samples, and estimated cyst excretion rates ranged from 50-200 cysts per gram faeces. Given that Giardia has the potential to cause clinical disease in cattle and to be transmitted to other animal species and humans, finding the parasite in cattle may be of major epidemiological significance. Future work should focus on elucidating the pathogenicity, transmission patterns and the genetic structure of Giardia populations in cattle in Denmark. 相似文献
999.
N Ferrara G Longobardi N Guerra A Nicolino D Acanfora G Furgi L Odierna R Rosiello F Rengo 《Canadian Metallurgical Quarterly》1996,34(1-2):37-41
We prospectively studied 10 patients with stable exertional ischaemia, selected from a larger group of patients referred for suspected coronary artery disease or to detect residual ischaemia after myocardial infarction, to evaluate pharmacokinetic changes during chronic treatment with gallopamil and its correlation with clinical efficacy in patients with coronary artery disease. Our study consisted of a 1-week run-in single-blind placebo treatment and a 4-week single-blind gallopamil treatment. At the end of the run-in period patients underwent two different exercise tests, the first 2 hours and the second 7 hours after placebo administration. During active treatment all patients underwent two different exercise tests, the first 2 hours and the second 7 hours after gallopamil (50 mg) administration on the 1st and 28th days of gallopamil therapy. On the same days in eight of the patients we evaluated gallopamil pharmacokinetic changes. Our data revealed a rapid increase of unchanged gallopamil and its metabolite (norgallopamil) in the plasma, and a peak concentration of these substances about 2 hour after oral administration on both the 1st and 28th day of observation. Moreover, our results demonstrated an increase between the first and 28th day of treatment in peak concentration of unchanged gallopamil in the plasma, and of AUC 0-infinity and AUC o-c values during chronic treatment with gallopamil. Our clinical data showed an improvement in exercise results during gallopamil therapy related to increased concentration of the drug. 相似文献
1000.