Competing first passage percolation on random graphs with finite variance degrees

We study the growth of two competing infection types on graphs generated by the configuration model with a given degree sequence. Starting from two vertices chosen uniformly at random, the infection types spread via the edges in the graph in that an uninfected vertex becomes type 1 (2) infected at rate λ₁ (λ₂) times the number of nearest neighbors of type 1 (2). Assuming (essentially) that the degree of a randomly chosen vertex has finite second moment, we show that if λ₁ = λ₂, then the fraction of vertices that are ultimately infected by type 1 converges to a continuous random variable V ∈ (0,1), as the number of vertices tends to infinity. Both infection types hence occupy a positive (random) fraction of the vertices. If λ₁ ≠ λ₂, on the other hand, then the type with the larger intensity occupies all but a vanishing fraction of the vertices. Our results apply also to a uniformly chosen simple graph with the given degree sequence.     

The kinetic Potts chain and related potts models with competing interactions

We consider a general kinetic model for a chain of three-state Potts spins. From the time-evolution operator we infer points in two-dimensional Potts systems where certain spin correlations have one-dimensional character and the model is exactly solvable. This occurs in square lattice models with different kinds of competing interactions.     

Stationary nonequilibrium states in the Ising model with locally competing temperatures

We study kinetic one- and two-dimensional Ising models whose transition probabilities occur according to two (or more) locally competing temperatures. The model is solved analytically and studied numerically on different assumptions to reveal a variety of stationary nonequilibrium states and phase transitions; we also investigate the system relaxation in some typical cases.     

Magnetic field effects on surgical ligation clips

Magnetic forces exerted on surgical clips and the magnetic resonance imaging distortion they create in phantoms and rabbits at magnetic field strengths of 1.5 Tesla were investigated. Results are reported for both ligation and aneurysm clips manufactured from three types of stainless steel as well as titanium, tantalum and niobium metals. Paramagnetism and eddy currents were measured in a customized moving Gouy balance. Direct measurements of other magnetic forces were carried out in a 1.5T MRI system. The titanium and tantalum clips showed the least interaction with the magnetic field, both in terms of forces exerted and the observed image distortion with the larger clips generating the larger interactions. The strongest field distortions and attractive forces occurred with 17-7PH stainless steel clips. These interactions were ferromagnetic in origin and of sufficient strength to present significant risk to patients having this type of clip present during an MRI scan.     

Optimum inspection under competing risks with proportional hazards

In this work, we present an inspection policy so as to detect the failures of a single‐unit system subject to N latent causes of failure when the time and cause of failure are independent. It is supposed that inspections may fail and give an erroneous result. The optimum inspection time which minimizes cost per unit of time for an infinite time span is discussed. Copyright © 2002 John Wiley & Sons, Ltd.     

On harvesting two competing populations

The problem of harvesting two competing populations is formulated in an optimal control setting. The maximum sustained rent (MSR) solution is introduced and is shown to be not only totally singular, but also to play a central role in solutions to the harvesting problem. It is further shown that nonsingular extremal subarcs must in general approach and leave the MSR along partially singular curves. A numerical example is introduced to demonstrate this phenomenon. In the case where the populations are driven onto the MSR in minimum time, however, the optimal control is shown to be bang-bang with at most one switch.The author is indebted to Professor D. H. Jacobson and Dr. D. H. Martin for helpful discussions during the preparation of this paper.     

Potential hazards and health assessment associated with different water uses in the main industrial cities of Egypt

Deterioration of water quality has become an ecological threat in many industrial areas worldwide due to unmanaged anthropogenic activities. Contaminants therein find out their ways to drinking water-pipes via broken or leak old- pipes. The current study aims at evaluating the suitability of tap water, collected from the main-ten-industrial cities of Egypt, for drinking purposes. Shallow and deep ground waters were also sampled from the same locations. This is one of the few research projects that are interested in quantifying the acrylamide in drinking water. The obtained results indicate that concentrations of COD, BOD, Fe, Mn, Ni, Pb, Cd, Zn and Hg were within the permissible levels in tap water while surpassed these levels in both shallow and deep ground waters. Acrylamide levels did not exceed the acceptable levels in all water samples (drinking, surface and deep ground waters). Overall, no potential risks were associated with the oral ingestion of tap water in all studied locations for both adults and children (all hazard quotient (HQ) values, defined as exposure intake dose of contaminants relative to the maximum permissible daily intake dose were below “1″). However, inorganic pollutants that exist in ground waters may cause undesirable dermal impacts when used for irrigating the green areas in these cities (used for picnics and as playgrounds). In this context, most HQ values associated with ground water dermal contact were above “1”. Specifically, Mn, Ni, Pb and Cd hazards exist for children (HQ > 1) while Ni, Pb and Cd toxicity detected for adults. This result; therefore, highlights the indirect negative impacts of industrialization on human health.     

物流服务水平影响竞争产品需求的协调机制

考虑一个由两个竞争性制造商、一个第三方物流服务商以及一个零售商组成的供应链系统,其中制造商生产的产品互为替代品,产品的物流分销职能由第三方物流服务商承担,并且产品市场需求依赖于第三方物流服务商提供的服务水平.为了有效地激励第三方物流服务商提高服务水平,设计了物流服务成本共担机制,分析了分散式成本共享机制和集中式成本共享机制对供应链绩效以及成员的利润影响.研究结果表明在一定条件下物流服务成本共担机制能有效改进供应链绩效.