Optimal repair-cost limit for a consumer following expiry of a warranty

This paper develops a methodology for obtaining the optimalrepair-cost limit for the repair-replace decision that a consumerfaces on the expiry of a product warranty, where the producthas been minimally repaired on failure during the warranty.Three cases are considered; (i) an exponentially distributedtime to failure with an arbitrary repair-cost distribution,(ii) an exponentially distributed time to failure with a uniformrepair-cost distribution, and (iii) a Weibull-distributed timeto failure with a beta-distributed repair cost. Numerical optimizationsare performed for the third case, and conclusions drawn as tothe sensitivity of the optimal repair-cost limit on the parametervalues of the distributions involved.     

MODEL FOR THE RATIONALIZATION OF MAGNETIC FIELD EFFECTS IN VIVO. APPLICATION OF THE RADICAL-PAIR MECHANISM TO BIOLOGICAL SYSTEMS

Abstract: A model for magnetic field effects in biological systems is proposed. This model employs the basic concepts of the radical pair mechanism, and predicts that magnetic fields will increase the average radical concentration, lengthen their lifetime and enhance the probability of radical reactions with cellular components. The relevance of these effects in relation to cancer initiation, promotion and progression is discussed.     

Availability measures for components maintained by repair-replacement policies

A renewal-reward process model is given for a component maintainedby a general repair-replacement policy. The point availabilityof the component at time t and its expected operating time overthe interval (0, t) are defined in terms of a pair of relatedintegral equations. These two equations are then solved numericallyto obtain values of the two measures for the policy of repairplus replacement at age .     

A collapsing bubble in a fluid: a statistical mechanical approach

The first non-equilibrium statistical mechanical theory is presented for the mechanical and thermal behaviour of the collapse of a microsropically small bubble in a liquid. First the number density and temperature space-time profiles for the special case of weakly interacting particles, the perfect gas model, are obtained. This is then generalized to a model in which the motion of the molecules is characterized by a single finite diffusion constant. The results for the collapse of a small bubble in a typical fluid are compared with those recently obtained through computer simulation. The agreement with the simulation is remarkably good for the perfect gas model; very high temperatures, sufficient for sonoluminescence, appear in a simple and natural way. An unexpected conclusion is that the perfect gas model agrees better with computer simulation than the model characterized by a single bulk diffusion constant. This may be because the collapse of the bubble is controlled by the leading shell of the fluid where the fluid density is low.     

Low field CIDNP of amino acids and proteins: characterization of transient radicals and NMR sensitivity enhancement

A new method for measuring and exploiting the magnetic field dependence of chemically induced dynamic nuclear polarization (CIDNP) is described. A solution of an amino acid or protein together with a flavin photosensitizer is irradiated with laser light at a position in the bore of a superconducting NMR magnet where the field is between 0.1 T and 7.0 T. The polarized sample is then transferred by rapid injection into an NMR tube at the centre of the magnet (at 9.4 T), where the spectrum is recorded. The observed ¹H CIDNP field dependence of tyrosine agrees well with the diffusion model of the radical pair mechanism. The field dependence of histidine, tryptophan and methionine CIDNP allows the g values of the transient radicals responsible for the polarization to be determined. Experiments in which amino acids compete for the photoexcited flavin indicate that methionine residues could be used as probes of surface accessibility, especially if the polarization is generated in low fields (～ 0.7 T) and detected in high fields (≥ 9.4 T). Possible extensions of the technique to study protein folding and the structures of partially denatured states of proteins are discussed.     

OPTIMAL DISCOUNTING IN CONTROL PROBLEMS THAT SPAN MULTIPLE GENERATIONS

ABSTRACT. The principal contribution of this paper is the linking together of separate control problems across multiple generations using the bequest motive, intergenerational altruism, rational expectations, and solution boundary conditions. We demonstrate that discounting at the market rate of interest is an endogenous characteristic of a general equilibrium, optimal control problem that spans multiple generations. Within the confines of our model, we prove that it is optimal to discount at the market rate of interest the social benefits to distant generations from immediate clean up at toxic waste sites if the current generation that bears the cleanup cost is perfectly altruistic towards future generations. Also, we show that this result holds for alternative assumptions regarding pure time preference. Moreover, the result holds regardless of whether selfish interim generations attempt to undo the provisions made for distant generations. In our distortion‐free deterministic model, the evidence for intergenerational discounting at the market rate of interest is compelling.     

Best Chebyshev approximation from families of ordinary differential equations

Within the framework of the Meinardus and Schwedt theory ofnonlinear Chebyshev approximation we consider the approximationof functions and data by approximants generated from the solutionof parameter dependent initial value problems in ordinary differentialequations. New results are obtained for the uniqueness and characterizationof best approximations in terms of properties of the differentialequation. Some examples of new approximating families are givenalong with computed best approximations.     

选择一条最新的HDMI线材——YARBO AUDIOPHILE(雅堡)26AWG HDMI 1.3b

现在的AV发烧友越来越多,发烧过程中碰到的问题也有不少,像我这样单是为了搭配不同AV器材已经伤透脑筋,要想挑一条高品质的HDMI传输线更是难上加难了,我所担心的是质量不好的HDMI线可能会损坏机器,还有就是生怕刚买回来的好线没过多久又因为格式的升级而遭淘汰。而就在此时,专业的线材制造商YARBO(雅堡)快速而又前瞻地开发生产出了目前业界高规格的HDMI传输线材。     

Synthesis, Structure and Alkali Metal Ion Binding Properties of a Podand Polyether Derived from Calix[4]arene, 5,11,17,23-tetra-tert-butyl-25,27-di(phenylmethoxy)-26,28-di(2‘-methoxyethoxy)-calix[4]arene

The ligand 5,11,17,23-tetra-t-butyl-25,27-di(phenylmethoxy)-26,28-di(2-methoxy-ethoxy)calix[4]arene,designed as an analogue of some calixcrown speciesin order to evaluate possible origins of their selectivity in alkali metal ion binding, has been synthesised and structurally characterised by X-ray crystallography. The crystals are monoclinic, P21/n, a = 15.940(6), b = 19.388(5), c = 20.020(5) Å, = 109.10(2) deg., Z = 4, conventional R on |F| being 0.073 for 3454 independent, observed (I > 3(I)) reflections. 1H-NMR studies in 1:1 CD3CN/CDCl3solvent have shown that the ligand exerts a strong preference for the lighteralkali metal ions (Li+ and Na+) contrary to the binding behaviour of knowncalixcrowns. This may reflect interactions restricted to the lower rim donor atoms without concomitant interaction with the calixarene -electrons, perhaps because the latter interactions are substituted by those with the benzyl group -electrons.     

Integrating Molecular Modeling with Semiempirical Quantum Mechanical Calculations into the Upper-Level Inorganic Chemistry Course

The analysis of chemical bonding and reactivity from the perspective of molecular orbital theory is challenging for students at the undergraduate level. In an attempt to improve the instruction of this material in my upper-level inorganic chemistry course I developed a series of computational experiments using a molecular modeling program that can perform semiempirical quantum mechanical calculations. These exercises explore the chemistry of molecular systems through an analysis of the variation in the attractive and repulsive forces in the system as a function of structure or composition. The exercises challenge the analysis skills of the students by requiring them to consider how two or more factors contribute to the properties of the system. Examples of exercises that demonstrate different types of computational experiments are given. These sample exercises examine the structure of simple molecules, the reactivity of Lewis acids, and the bonding in transition metal complexes.