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101.
In this paper we present an exact method for computing the Weibull renewal function and its derivative for application in maintenance optimization. The computational method provides a solid extension to previous work by which an approximation to the renewal function was used in a Bayesian approach to determine optimal replacement times. In the maintenance scenario, under the assumption an item is replaced by a new one upon failure, the underlying process between planned replacement times is a renewal process. The Bayesian approach takes into account failure and survival information at each planned replacement stage to update the optimal time until the next planned replacement. To provide a simple approach to carry out in practice, we limit the decision process to a one‐step optimization problem in the sequential decision problem. We make the Weibull assumption for the lifetime distribution of an item and calculate accurately the renewal function and its derivative. A method for finding zeros of a function is adapted to the maintenance optimization problem, making use of the availability of the derivative of the renewal function. Furthermore, we develop the maximum likelihood estimate version of the Bayesian approach and illustrate it with simulated examples. The maintenance algorithm retains the adaptive concept of the Bayesian methodology but reduces the computational need. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
102.
Tarnopolsky AZ Fletcher NH Hollenberg LC Lange BD Smith J Wolfe J 《The Journal of the Acoustical Society of America》2006,119(2):1194-1204
The didjeridu, or yidaki, is a simple tube about 1.5 m long, played with the lips, as in a tuba, but mostly producing just a tonal, rhythmic drone sound. The acoustic impedance spectra of performers' vocal tracts were measured while they played and compared with the radiated sound spectra. When the tongue is close to the hard palate, the vocal tract impedance has several maxima in the range 1-3 kHz. These maxima, if sufficiently large, produce minima in the spectral envelope of the sound because the corresponding frequency components of acoustic current in the flow entering the instrument are small. In the ranges between the impedance maxima, the lower impedance of the tract allows relatively large acoustic current components that correspond to strong formants in the radiated sound. Broad, weak formants can also be observed when groups of even or odd harmonics coincide with bore resonances. Schlieren photographs of the jet entering the instrument and high speed video images of the player's lips show that the lips are closed for about half of each cycle, thus generating high levels of upper harmonics of the lip frequency. Examples of the spectra of "circular breathing" and combined playing and vocalization are shown. 相似文献
103.
Let O be a closed geodesic polygon in S~2 . Maps from O into S~2 are said to satisfy tangent boundary conditions if the edges of O are mapped into the geodesics which contain them. Taking O to be an octant of S 2,we compute the infimum Dirichlet energy E(H) for continuous maps satisfying tangent boundary conditions of arbitrary homotopy type H . The expression for E (H ) involves a topological invariant - the spelling length - associated with the (non-abelian) fundamental group of the n-times punctured two-sphere, π 1 (S 2 ? {s 1 , ··· , s n }, ?). The lower bound for E(H) is obtained from combinatorial group theory arguments, while the upper bound is obtained by constructing explicit representa- tives which, on all but an arbitrarily small subset of O, are alternatively locally conformal or anticonformal. For conformal and anticonformal classes (classes containing wholly con- formal and anticonformal representatives respectively), the expression for E (H ) reduces to a previous result involving the degrees of a set of regular values s 1 , ··· , s n in the target S 2 space. These degrees may be viewed as invariants associated with the abelianization of π 1 (S 2 ? {s 1 , ··· , s n }, *). For nonconformal classes, however, E(H) may be strictly greater than the abelian bound. This stems from the fact that, for nonconformal maps, the number of preimages of certain regular values may necessarily be strictly greater than the absolute value of their degrees.This work is motivated by the theoretical modelling of nematic liquid crystals in confined polyhedral geometries. The results imply new lower and upper bounds for the Dirichlet energy (one-constant Oseen-Frank energy) of reflection-symmetric tangent unit- vector fields in a rectangular prism. 相似文献
104.
Chae PS Gotfryd K Pacyna J Miercke LJ Rasmussen SG Robbins RA Rana RR Loland CJ Kobilka B Stroud R Byrne B Gether U Gellman SH 《Journal of the American Chemical Society》2010,132(47):16750-16752
We describe a new type of synthetic amphiphile that is intended to support biochemical characterization of intrinsic membrane proteins. Members of this new family displayed favorable behavior with four of five membrane proteins tested, and these amphiphiles formed relatively small micelles. 相似文献
105.
Pacchiano F Aggarwal M Avvaru BS Robbins AH Scozzafava A McKenna R Supuran CT 《Chemical communications (Cambridge, England)》2010,46(44):8371-8373
4-Substituted-ureido benzenesulfonamides showing inhibitory activity against carbonic anhydrase (CA, EC 4.2.1.1) II between 3.3-226 nM were crystallized in complex with the enzyme. Hydrophobic interactions between the scaffold of the inhibitors in different hydrophobic pockets of the enzyme were observed, explaining the diverse inhibitory range of these derivatives. 相似文献
106.
J. Barritt R. T. Mease F. Garelli B. Saladini M. Harris H. A. Neville W. C. Fritz . Phillips A. P. Mathews A. Itkina Plechan H. Pauly E. Mönch M. C. Marsh A. P. Sakoschtschikow R. Smith J. Ph. Peper T. Dokkum S. N. Schoorl D. A. Clibbens B. P. Ridge F. RSiefert H. Wolff und K. Lindner 《Fresenius' Journal of Analytical Chemistry》1936,105(5-6):222-240
Ohne Zusammenfassung 相似文献
107.
Neville Compton 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(23):6522-6524
108.
Development of a quantitative high-performance liquid chromatography-photodiode array detection measurement system for phenolic acids 总被引:2,自引:0,他引:2
A quantitative high-performance liquid chromatography-photodiode array detection method separating 16 phenolic acids was achieved. Six columns and several mobile phases were investigated. Resolution was achieved with a high-purity silica Phenomenex Luna C18 column (150 mm x 4.6 mm, 5 microm) and a binary gradient consisting of CH3OH-water (with 0.1% formic acid) and flow rate set at 0.7 ml/min. Acids were detected and quantitation performed at wavelength representing the lowest energy lambda(max) for individual acids. Extraction procedure from wine was optimized and yields ranged from 79 to 87% based on internal standard recovery. To confirm our quantitative results, identical samples were analyzed both in-house and by a collaborating laboratory. Correlation of two data sets generated linear regression equations that approached unity (0.93-0.98) and R2 values ranging from 0.990 to 0.999. 相似文献
109.
Proteomics reveal a link between the endoplasmic reticulum and lipid secretory mechanisms in mammary epithelial cells 总被引:6,自引:0,他引:6
The synthesis and secretion of lipids by mammary epithelial cells is a highly ordered process that involves several distinct steps. Triacylglycerols are synthesized in the endoplasmic reticulum and incorporated into microlipid droplets which coalesce into cytoplasmic lipid droplets. These are vectorially transported to the apical plasma membrane where they are secreted into the milk surrounded by a membrane bilayer. The origin of this membrane as well as the mechanism by which cytoplasmic lipid droplets form and become surrounded by membrane is poorly understood. Proteomic analysis of the protein composition of milk fat globules and cytoplasmic lipid droplet has revealed that the endoplasmic reticulum is not only involved in the synthesis of the lipid but also potentially contributes to the membrane component of milk fat globules. The proteins identified suggest possible mechanisms of multiple steps during this process. Completion of the proteome of milk fat globule membranes and cytoplasmic lipid droplets will provide the necessary reporter molecules to follow and dissect the mechanisms of the sorting and ultimate secretion of cytoplasmic lipid droplets. 相似文献
110.
Prem C. Srivastava Roland K. Robbins F. Takusagawa H. M. Berman 《Journal of heterocyclic chemistry》1981,18(8):1659-1662
2′-Deoxy-D-ribonucleoside analogs of biologically active 2-β-D-ribofuranosylthiazole-4-carboxamide were synthesized and the structure of the β anomer was determined by X-ray crystallography and ′1H nmr. 2′-Methylene protons of α- and β-deoxyribonucleosides were observed to exhibit characteristic patterns in the 1H nmr which was used to distinguish between the two anomers. The method could be used to determine the anomeric configuration of both N- and C-2′-deoxyribonucleosides. 相似文献