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101.
Westbrook P.S. Nicholson J.W. Feder K.S. Yablon A.D. 《Lightwave Technology, Journal of》2005,23(1):13-18
We demonstrate that UV exposure of highly nonlinear, germano-silicate fibers can significantly broaden the infrared supercontinuum generated by femtosecond pulses in these fibers. Both simulations and measurements of the fiber chromatic dispersion show that UV-induced refractive index changes increase the waveguide dispersion by up to 5 ps/(nm-km) at 1570 nm and shift the dispersion zero by over 100 nm. We examine fibers with a range of UV exposure levels and show that the short wavelength edge of the supercontinuum can be continuously changed by more than 100 nm. We also show that the long wavelength edge is extended beyond that of the unexposed fiber. The resulting continuum spans from 0.85 to 2.6 /spl mu/m. Cutback measurements show that the supercontinuum in the exposed fiber is generated in as little as 1 cm of fiber. A nonlinear Schro/spl uml/dinger equation (NLSE) model of the supercontinuum generation in the nonlinear fiber shows that the short wavelength behavior of the continuum is primarily controlled by changes in the fiber dispersion caused by the UV-induced change in refractive index of the fiber core. 相似文献
102.
Universal prediction 总被引:1,自引:0,他引:1
Merhav N. Feder M. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1998,44(6):2124-2147
This paper consists of an overview on universal prediction from an information-theoretic perspective. Special attention is given to the notion of probability assignment under the self-information loss function, which is directly related to the theory of universal data compression. Both the probabilistic setting and the deterministic setting of the universal prediction problem are described with emphasis on the analogy and the differences between results in the two settings 相似文献
103.
GL Burke DE Bild JE Hilner AR Folsom LE Wagenknecht S Sidney 《Canadian Metallurgical Quarterly》1996,1(4):327-335
Copper/zinc (Cu/ZnSOD) and manganese (MnSOD) superoxide dismutases which catalyze the dismutation of toxic superoxide anion, O(2-)-, to O2 and H2O2, play a major role in protecting cells from toxicity of oxidative stress. However, cells overexpressing either form of the enzyme show signs of toxicity, suggesting that too much SOD may be injurious to the cell. To elucidate the possible mechanism of this cytotoxicity, the effect of SOD on DNA and RNA strand scission was studied. High purity preparations of Cu/ZnSOD and MnSOD were tested in an in vitro assay in which DNA cleavage was measured by conversion of phage phi X174 supercoiled double-stranded DNA to open circular and linear forms. Both types of SOD were able to induce DNA strand scission generating single- and double-strand breaks in a process that required oxygen and the presence of fully active enzyme. The DNA strand scission could be prevented by specific anti-SOD antibodies added directly or used for immunodepletion of SOD. Requirement for oxygen and the effect of Fe(II) and Fe(III) ions suggest that cleavage of DNA may be in part mediated by hydroxyl radicals formed in Fenton-type reactions where enzyme-bound transition metals serve as a catalyst by first being reduced by superoxide and then oxidized by H2O2. Another mechanism was probably operative in this system, since in the presence of magnesium DNA cleavage by SOD was oxygen independent and not affected by sodium cyanide. It is postulated that SOD, by having a similar structure to the active center of zinc-containing nucleases, is capable of exhibiting non-specific nuclease activity causing hydrolysis of the phosphodiester bonds of DNA and RNA. Both types of SOD were shown to effectively cleave RNA. These findings may help explain the origin of pathology of certain hereditary diseases genetically linked to Cu/ZnSOD gene. 相似文献
104.
Collision-induced signal enhancement (CISE), a new technique to enhance the MSn capabilities of the quadrupole ion trap, is demonstrated. CISE is based on the chemistry, i.e., the dissociation pathways, of the analyte examined. Polysaccharides up to hexamers are used to demonstrate the capabilities of CISE to enhance signal in two distinct functional modes. Mode 1 CISE is designed to enhance the signal of an ion desired for MSn analysis. Mode 2 CISE is designed to enhance structurally significant product ions in an MS/MS spectrum. Two different approaches can be utilized to effect the two functional modes of CISE. Both approaches use conventional resonant excitation techniques to effect dissociation, which is performed nonanalytically, i.e., without isolation of the ions to be dissociated. The two approaches are (1) single-frequency resonance excitation, and (2) broad-band wave form resonant excitation. Experimental results for Mode 1 CISE analysis demonstrate up to a 17.3-fold signal increase for the single-frequency approach and 5.3-fold using broad-band excitation. Mode 2 CISE analysis shows up to a 16.3-fold increase in signal strength with single-frequency excitation and 3.3-fold using broad-band excitation. 相似文献
105.
After a brief presentation of the development of free walking interpreted as learning dynamical equilibrium, the problem of sensory integration in the process of walking development is discussed. A critical review of the role of vision in the development of posturo-locomotor task is presented, along with recent test results on the development of the vestibular system. A final section presents the development of head stabilization and coordination as a necessary means to assist sensory integration. It is suggested that if sensory information is necessary to enhance posturo-locomotor skills, a good mastery of walking is in turn necessary to increase the efficiency of sensory integration. 相似文献
106.
107.
GL Kay GW Sun A Aoki CA Prejean 《Canadian Metallurgical Quarterly》1995,60(6):1640-50; discussion 1651
BACKGROUND: Preoperative ejection fraction (EF) has been shown to adversely affect postoperative hospital mortality and morbidity for patients undergoing isolated coronary artery bypass grafting. METHODS: To investigate influence of EF on isolated coronary artery bypass grafting outcomes (overall hospital mortality, hospital cardiac mortality, hospital morbidity, and hospital costs), data were reviewed from 1,354 consecutive patients who underwent isolated coronary artery bypass grafting between January 1, 1990, and April 30, 1992, at a single nonprofit hospital. Overall hospital mortality was 4.06% (cardiac, 2.36%). Hospital morbidity was 14.25% (including mortality). Hospital costs (not charges) averaged $16,673 per patient. To explore the impact of preoperative EF, EF was stratified into regular intervals. Each interval was then compared with regard to hospital mortality, morbidity, and average costs. A new statistical tool, discharge analysis, was developed to analyze the cost data. This was necessary because previous efforts at cost analysis have used tools inappropriate for real world cost data. RESULTS: The statistical analysis showed that patients with EF of 0.40 or greater had the best outcomes (lowest mortality, morbidity, and cost). Once the EF is 0.40 or greater the EF does not carry further predictive value. At EF less than 0.40, patients with EF less than 0.30 have a poorer outcome than patients with EF of 0.30 to 0.39. CONCLUSIONS: (1) Ejection fraction is a valid predictor of mortality, morbidity and resource utilization based on statistical analysis. (2) Patients can be broadly grouped as having EF greater than 0.40, less than 0.30, or from 0.30 to 0.39 with regard to clinical and cost outcomes. (3) Postoperative length of stay is not predicted by risk-adjusted EF. (4) A new tool, discharge analysis, is presented to facilitate cost analysis. 相似文献
108.
GL Solomon 《Canadian Metallurgical Quarterly》1994,102(8):632-635
109.
H Lin ML Bondy LA Langford KR Hess GL Delclos X Wu W Chan MA Pershouse WK Yung PA Steck 《Canadian Metallurgical Quarterly》1998,4(10):2447-2454
The frequency of loss of heterozygosity (LOH) around MMAC/PTEN and DMBT1 loci and survival analyses based on the LOH status were assessed in 110 patients with different histological groups of gliomas. Twenty-six of the patients had anaplastic oligodendrogliomas, 31 had anaplastic astrocytomas, and 53 had glioblastomas multiforme (GM). At the DMBT1 locus, LOH was observed very frequently in all three histological groups, with no significant difference in the frequency of LOH among the three histological groups. At the MMAC/PTEN locus, patients with GM exhibited a significantly increased frequency of LOH (72%) compared with patients with anaplastic astrocytomas (29%) or anaplastic oligodendrogliomas (31%) (P < 0.0001). Kaplan-Meier survival plots showed that patients with LOH at the MMAC/PTEN locus had a significantly worse prognosis than did patients without LOH at the MMAC/PTEN locus [hazard ratio (LOH versus non-LOH), 2.65; 95% confidence interval (CI), 1.69-4.46; P < 0.0001]. Cox proportional hazards regression analysis, adjusted for age at surgery and histological grades (GM and non-GM), showed that LOH at the MMAC/PTEN locus was a significant predictor of shorter survival [hazard ratio (LOH versus non-LOH), 2.01; 95% CI, 1.1-3.5; P = 0.018). Our analysis failed to indicate a similar association between the frequency of LOH at the DMBT1 locus and patient survival [hazard ratio (LOH versus non-LOH), 2; 95% CI, 0.37-3.13; P = 0.2]. These results suggest that the DMBT1 gene may be involved early in the oncogenesis of gliomas, whereas alterations in the MMAC/PTEN gene may be a late event in the oncogenesis related to progression of gliomas and provide a significant prognostic marker for patient survival. 相似文献
110.