Optimal policies in a two-unit standby system with two types of repairmen

This paper is concerned with a two identical unit cold standby system. There is a facility of having two types of repairmen. The “regular” repairman is always kept with the system with the known fact that he might not be able to do some complex repairs within some tolerable “patience” time, while a perfect “expert” repairman is called only in need. On the completion of this tolerable time or on the system failure whichever is earlier, the expert repairman is called on to do the job. We use semi-Markov processes and numerical methods, we discuss optimum policies for calling the expert, maximizing the profit and plot the graphs.     

Finite element solution for beams using an element averaging technique

The article investigates the error in the computation of natural frequency through finite element models of the structures when elements of unequal length are chosen and then goes on to suggest an averaging technique for unequal length elements, with different structural properties. Using the element averaging technique, a typical structure has been analysed for its natural frequencies and the results are described.     

Raised cosine function for image restoration

In this paper, a new set of raised cosine functions is proposed. These functions have all the useful properties of the spline functions with the additional advantage of continuous infinite derivatives as against only a finite number of derivatives in case of the spline functions. Because of this property they exhibit a smoother behaviour. The property of smoothness, coupled with convolution, makes the raised cosine functions readily applicable to the image restoragtion problem, where the degradation is through a shift invariant blurring function. The results confirm the superior behaviour of these functions in comparison to spline functions.     

Comparison of two unit cold standby reliability models with three types of repair facilities

This paper develops three models for cold standby redundant systems, consisting of two identical units. These models are different in the sense that different types of repairmen are employed. In model 1, the repairman is always with the system. In model 2, he comes immediately at the failure of a unit, while in model 3, he takes some random time in reaching the system.Profit is evaluated in each case. Comparison of these profits is done in two parts. Part 1 considers the comparison of different models. In part 2 comparison is done by taking different criteria for evaluating the profit for the same model. Computer programs for these comparisons are also given (in the Appendix).     

Transcatheter closure of patent ductus arteriosus in children weighing < 10 kg with Gianturco coils using the balloon occlusion technique

An extractive membrane bioreactor (EMB) is described that used an undefined anaerobic culture to dechlorinate tetrachloroethene (C2Cl4) reductively in a synthetic wastewater. Comparable reactors described in the literature use set-ups where the bacteria are in direct contact with the wastewater, and thus would require the addition of significant quantities of nutrients to the wastewater stream in practical application. In the EMB, a silicone rubber membrane separates the microbial culture from the wastewater stream, so that addition of nutrients can be minimised. The EMB was operated continuously for 48 days and dechlorinated 359 micromol C2Cl4 (1 biomedium -1 day -1) on average. Lactate was fed as an electron donor and C2Cl4 dechlorination was verified by chloride measurements. Particular attention was paid to the reduction of transmembrane C2Cl4 flux caused by a membrane-attached biofilm. Following a start-up period, the reactor operation was stable and remained largely unaffected by biofilm thickness and oxygen contamination from the wastewater.     

Molecular cloning of novel genes for polycyclic aromatic hydrocarbon degradation from Comamonas testosteroni GZ39

Three strains of Comamonas testosteroni were isolated from river sediment for the ability to degrade phenanthrene; two of the strains also grew on naphthalene, and one strain also grew on anthracene. The homology of the genes for polycyclic aromatic hydrocarbon degradation in these strains to the classical genes (nah) for naphthalene degradation from Pseudomonas putida NCIB 9816-4 was determined. The three C. testosteroni strains showed no homology to the nah gene probe even under low-stringency conditions. The genes for naphthalene and phenanthrene degradation were cloned from one of the three C. testosteroni strains. Two cosmid clones expressing polycyclic aromatic hydrocarbon dioxygenase activity were identified from a library prepared with genomic DNA from C. testosteroni GZ39. The genes coding for the first two enzymes in the catabolic pathway, phenanthrene dioxygenase and cis-phenanthrene dihydrodiol dehydrogenase, were localized to a 5.4-kb NcoI-PstI fragment by subcloning and gene expression experiments. Further subcloning and analysis revealed a novel organization of the genes, with the gene for cis-phenanthrene dihydrodiol dehydrogenase located between the genes for the individual phenanthrene dioxygenase components. A Southern blot with the cloned genes from C. testosteroni GZ39 confirmed that these genes are distinct from those found in P. putida NCIB 9816-4. Southern blots also demonstrated that C. testosteroni GZ38A possesses genes for phenanthrene degradation that are similar to those cloned from C. testosteroni GZ39. However, C. testosteroni GZ42 possesses genes for phenanthrene degradation that are not homologous to those cloned from C. testosteroni GZ39. This suggests that there are at least two different sets of genes for the degradation of phenanthrene among the three C. testosteroni strains.     

Effect of coupling interval and pacing cycle length on morphology of paced ventricular complexes. Implications for pace mapping

BACKGROUND: Ventricular pace mapping is performed by comparing the QRS morphology of ventricular paced complexes to that of a template arrhythmia, either a premature ventricular depolarization or a QRS complex during ventricular tachycardia. The objective of this study was to evaluate the effect of coupling interval and pacing cycle length on QRS morphology. METHODS AND RESULTS: The study population consisted of 20 patients (mean age, 38 +/- 16 years) undergoing a clinically indicated electrophysiology procedure. In the first 10 patients, the effect of coupling interval on the morphology of single paced ventricular complexes was evaluated visually and by signal processing techniques. Visually apparent differences in QRS morphology occurred in a mean of 4/12 electrocardiographic leads with a change in coupling interval of > or = 100 ms. In the next 10 patients, the QRS complex morphology during ventricular overdrive pacing at cycle lengths of 600 and 300 ms was found to differ significantly in a mean of 4/12 leads. The QRS morphology during overdrive pacing differed significantly from that of a single paced complex whenever the pacing cycle length differed from the coupling interval of the single paced complex by > 80 ms. CONCLUSIONS: The morphology of single paced QRS complexes may vary, depending on coupling interval, and the QRS morphology during overdrive pacing is affected by the pacing cycle length. During ventricular pace mapping, the coupling interval or cycle length of the template arrhythmia should be matched during pacing. If not, rate-dependent changes in QRS morphology that are independent of the pacing site may confound the results of pace mapping.     

Formation of silicon reentrant cavity heat sinks using anisotropicetching and direct wafer bonding

A novel silicon reentrant cavity heat sink for enhanced liquid cooling of silicon multichip substances has been fabricated using a two-step anisotropic etching process followed by silicon direct wafer bonding. Cavity mouth openings ranging from 8 to 500 μm have been batch fabricated with the two-step process. The reentrant cavities suppress the temperature overshoot normally associated with the transition between the free convection and nucleate boiling regimes of liquid immersion cooling. Nucleate boiling has been observed to occur at heater fluxes below 2 W/cm² for both increasing and decreasing heat flux conditions. Specific thermal contact resistances (heater fluid) of less than 0.6 K-cm²/W have been measured in Freon-22, R-113, and FC-72     

An Algorithmic Approach to the Identification of Rigid Domains in Proteins

Many proteins undergo conformational changes to perform their functions. A simple mechanism of conformational change in proteins is a rigid domain motion, in which two parts of a structure move rigidly with respect to each other. The identification of rigid domains is therefore useful in understanding the structure-function relationship of proteins. Many algorithms, including those in [16], [22], [13], [10], and [19], have been developed to identify rigid domains. In this paper we complement these works by proposing a mathematical definition of a rigid domain. We argue that our definition more accurately captures the intuitive notion of rigid domain in the previous work, than the quantitative definition of a rigid domain introduced by Nichols et al. [19]. Furthermore, our definition admits a practical approximation algorithm. We can prove theoretical guarantee on the quality of the output of our algorithm. We implement a randomized version of our algorithm, and demonstrate its effectiveness on several known protein complexes.     

Synthesis and characterization of methacrylic acid–ethyl acrylate copolymers

Copolymerization of methacrylic acid (MAA) and ethyl acrylate (EA) was performed in aqueous medium in the presence of an emulsifier with MAA as the major component (53.7–82.3 mol %). Emulsion stability was studied as a function of concentration and the nature of the emulsifier (ionic or nonionic). Copolymers were characterized using IR and ¹H-NMR spectroscopy. ¹³C-NMR spectra of MAA–EA copolymers have been discussed in terms of their triad monomer sequence distributions. Reactivity ratios of the MAA–EA pair were determined using a nonlinear least-square errors in variables method. Partition of the monomers in aqueous and organic phases was studied using a gas chromatographic technique. A two-loci polymerization mechanism was proposed on the basis of this partition behavior and the calculated composition of the oligomeric radicals formed in the initial stages of polymerization. © 1994 John Wiley & Sons, Inc.