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51.
Reliability analyses of multi-component systems can often be refined by combining Markov-chain models for detailed component characterizations with fault-tree evaluation techniques for describing over-all system behavior. A difficulty encountered in the application of this combined approach is that component maintenance policies can induce statistical dependence among component failures. Thereby, straightforward evaluation of overall system characteristics based upon the assumption of statistically independent component failures can lead to erroneous conclusions. This paper examines the effect of dependent component failures, as induced by the component maintenance policies, on system performance; and it demonstrates that for certain types of maintenance policies (when component maintenance is independent of the condition of the other system components), meaningful results can be obtained by assuming the independence of component failures. The feasibility of the proposed approach is illustrated through a maintenance scheduling problem in nuclear engineering practice. 相似文献
52.
M Takagi D Delia L Chessa S Iwata T Shigeta Y Kanke K Goi M Asada M Eguchi C Kodama S Mizutani 《Canadian Metallurgical Quarterly》1998,58(21):4923-4929
We examined the regulation of apoptosis, radiosensitivity, and spindle checkpoint in response to DNA-damaging agents in ataxia telangiectasia (AT)-derived lymphoblastoid cell lines (AT-LCLs), which lack AT mutated (ATM) protein expression. In addition to the previous findings that AT-LCLs are defective in regulation of cell cycle at the G1, S, and G2-M checkpoints in response to X-ray irradiation (X-IR) and are highly sensitive to X-IR (J. Biol. Chem., 271: 20486-20493, 1996), we showed for the first time that AT-LCLs were defective in X-IR-associated spindle checkpoint control. The cells were also resistant to early apoptosis as much as LCLs derived from patients with Li-Fraumeni syndrome (LFS-LCLs). Terminal deoxynucleotidyl transferase-mediated nick end labeling assay of LCLs, however, demonstrated a significant increase in apoptotic cells among AT-LCLs cultured over a longer period after X-IR. These findings were in contrast to those of LFS-LCL, which showed very little increase in terminal deoxynucleotidyl transferase-mediated nick end labeling-positive population, even in cells with hyperploidy. Thus, although early apoptosis and cell cycle controls in response to DNA damage are disrupted in both ATM and p53 mutations, cells from AT patients are much more susceptible to late-onset apoptosis than those of LFS. These differences may depend on the level of accumulation of DNA damage and/or threshold that triggers late-onset cell death in ATM or p53 mutations. Our findings allow a better understanding of the role of ATM in p53-dependent and independent signal transduction pathways in response to DNA damaging agents. 相似文献
53.
54.
Detailed cystoscopic grading of ureteral orifices has proved unnecessary in our experience for determining the prognosis of moderate, primary reflux in girls. Medially placed orifices strongly predict spontaneous resolution with preventive medication, while radiographic pyelonephritic scarring and/or grade III reflux strongly predict failure to resolve. While laterally placed ureteral orifices and low volume reflux suggest a need for operation, they are prognostically less useful, particularly when those with grade III reflux are excluded. Cystitis cystica and unrelated anomalies seem to be associated with the ultimate need for operation but are of uncertain significance. 相似文献
55.
56.
Weighted residual methods (WRM) afford a viable approach to the numerical solution of differential equations. Application of WRM results in the transformation of differential equations into systems of algebraic equations in the modal coefficients. This suggests that WRM can be used as a tool for reducing optimal control problems to mathematical programming problems. Thereby, the optimal control problem is replaced by the minimization of a cost function of static coefficients subject to algebraic constraints. The motivation for this approach lies in the profusion of sophisticated computational algorithms and digital computer codes for the solution of mathematical programming problems. In this note the solution of optimal control problems as mathematical programming problems via WRM is illustrated. The example presented indicates that reasonable accuracy is obtained for modest computational effort. While the simplest types of modes-polynomials and piecewise constants-are employed in this note, the ideas delineated can be applied in conjunction with cubic splines for the generation of computational algorithms of enhanced efficiency. 相似文献
57.
Raluca C. Cretu Delia M. Gligor Laura Muresan Ionel Catalin Popescu Liana M. Muresan 《Journal of Applied Electrochemistry》2006,36(12):1327-1332
Prussian Blue-modified graphite electrodes (G/PB) with electrocatalytic activity toward H2O2 reduction were obtained by PB potentiostatic electrodeposition from a mixture containing 2.5 mm FeCl3 + 2.5 mm K3[Fe(CN)6] + 0.1 m KCl + 0.1 m HCl. From cyclic voltammetric measurements, performed in KCl aqueous solutions of different concentrations (5 × 10−2–1 m), the rate constant for the heterogeneous electron transfer (k
s) was estimated by using the Laviron treatment. The highest ks value (10.7 s−1) was found for 1 m KCl solution. The differences between the electrochemical parameters of the voltammetric response, as well as the shift of the formal potential, observed in the presence of Cl− and NO3− compared to those observed in the presence of SO42− ions, points to the involvement of anions in the redox reactions of PB. The G/PB electrodes showed a good electrochemical stability proved by a low deactivation rate constant (0.8 × 10−12 mol cm2 s−1). The electrocatalytic efficiency, estimated as the ratio
, was found to be 3.6 (at an applied potential of 0 mV vs. SCE; Γ = 5 × 10−8 mol cm−2) for a H2O2 concentration of 5 mm, thus indicating G/PB electrodes as possible H2O2 sensors. 相似文献
58.
Delia Rodríguez de Llera González Ana Rusu Mohammed Ismail 《Analog Integrated Circuits and Signal Processing》2009,61(1):35-46
This paper introduces a multi-agent behavioral-based optimization algorithm for system level radio design. Making multi-standard
wireless communication receivers that meet their specs while keeping the requirements of the individual blocks as relaxed
as possible is the goal of this algorithm. In order to achieve this goal a “divide and conquer” approach is proposed. Different
agents focus on different objectives that are pursued in parallel. Agents adopt different behaviors depending on the status
of the environment and their interaction with other agents. Agents are cooperative by default as they try to meet their spec
without making changes that affect other agents. However, more aggressive behaviors that lead to global changes can be adopted
when needed. The interaction between these simple entities yields an emergent behavior able to deal smoothly with the complexity
of the problem at hand. 相似文献
59.
Eric W. Neuman William G. Fahrenholtz Gregory E. Hilmas 《International Journal of Applied Ceramic Technology》2019,16(5):1715-1722
ZrB2 ceramics were prepared by in-situ reaction hot pressing of ZrH2 and B. Additions of carbon and excess boron were used to react with and remove the residual oxygen present in the starting powders. Additions of tungsten were utilized to make a ZrB2-4 mol%W ceramic, while a change in the B/C ratio was used to produce a ZrB2-10 vol% ZrC ceramic. All three compositions reached near full density. The baseline ZrB2 and ZrB2–ZrC composition contained a residual oxide phase and ZrC inclusions, while the W-doped composition contained residual carbon and a phase that contained tungsten and boron. All three compositions exhibited similar values for flexure strength (~520 MPa), Vickers hardness (~15 GPa), and elastic modulus (~500 to 540 GPa). Fracture toughness was about 2.6 MPa m1/2 for the W-doped ZrB2 compared to about 3.8 MPa m½ for the ZrB2 and ZrB2–ZrC ceramics. This decrease in fracture toughness was accompanied by an observed absence of crack deflection in the W-doped ZrB2 compared with the other compositions. The study demonstrated that reaction-hot-pressing can be used to fabricate ZrB2 based ceramics containing solid solution additives or second phases with comparable mechanical properties. 相似文献
60.
A sulfated-β-cyclodextrin (s-β-CD) modified reduced flow micellar electrokinetic chromatography (RF-MEKC) method was developed and validated for the determination of catechins in green tea. The optimal electrolyte consisted of 0.2% triethylamine, 50 mmol/L SDS and 0.8% s-β-CD (pH = 2.9), allowing baseline separation of five catechins in 4 min. The samples and standards were injected at 0.6 psi for 5 s under constant voltage of −30 kV. Sample preparation simply involved extraction of 2 g of tea with 200 mL water at 95 °C under constant stirring for 5 min. The method demonstrated excellent performance, with limits of detection (LOD) and quantification (LOQ) of 0.02–0.1 and 0.1–0.5 μg/mL, respectively, and recovery percentages of 94–101%. The method was applied to six samples of Brazilian green tea infusions. Epigallocatechin gallate (23.4–112.4 μg/mL) was the major component, followed by epigallocatechin (18.4–78.9 μg/mL), epicatechin gallate (5.6–29.6 μg/mL), epicatechin (4.6–14.5 μg/mL) and catechin (3.2–8.2 μg/mL). 相似文献