Derandomized graph products

Berman and Schnitger gave a randomized reduction from approximating MAX-SNP problems within constant factors arbitrarily close to 1 to approximating clique within a factor ofn (for some ). This reduction was further studied by Blum, who gave it the namerandomized graph products. We show that this reduction can be made deterministic (derandomized), using random walks on expander graphs. The main technical contribution of this paper is in proving a lower bound for the probability that all steps of a random walk stay within a specified set of vertices of a graph. (Previous work was mainly concerned with upper bounds for this probability.) This lower bound extends also to the case where different sets of vertices are specified for different time steps of the walk.     

Buffer Management for Colored Packets with Deadlines

We consider buffer management of unit packets with deadlines for a multi-port device with reconfiguration overhead. The goal is to maximize the throughput of the device, i.e., the number of packets delivered by their deadline. For a single port or with free reconfiguration, the problem reduces to the well-known packets scheduling problem, where the celebrated earliest-deadline-first (EDF) strategy is optimal 1-competitive. However, EDF is not 1-competitive when there is a reconfiguration overhead. We design an online algorithm that achieves a competitive ratio of 1−o(1) when the ratio between the minimum laxity of the packets and the number of ports tends to infinity. This is one of the rare cases where one can design an almost 1-competitive algorithm. One ingredient of our analysis, which may be interesting on its own right, is a perturbation theorem on EDF for the classical packets scheduling problem. Specifically, we show that a small perturbation in the release and deadline times cannot significantly degrade the optimal throughput. This implies that EDF is robust in the sense that its throughput is close to the optimum even when the deadlines are not precisely known.     

A Preemptive Algorithm for Maximizing Disjoint Paths on Trees

We consider the on-line version of the maximum vertex disjoint path problem when the underlying network is a tree. In this problem, a sequence of requests arrives in an on-line fashion, where every request is a path in the tree. The on-line algorithm may accept a request only if it does not share a vertex with a previously accepted request. The goal is to maximize the number of accepted requests. It is known that no on-line algorithm can have a competitive ratio better than Ω(log n) for this problem, even if the algorithm is randomized and the tree is simply a line. Obviously, it is desirable to beat the logarithmic lower bound. Adler and Azar (Proc. of the 10th ACM-SIAM Symposium on Discrete Algorithm, pp. 1–10, 1999) showed that if preemption is allowed (namely, previously accepted requests may be discarded, but once a request is discarded it can no longer be accepted), then there is a randomized on-line algorithm that achieves constant competitive ratio on the line. In the current work we present a randomized on-line algorithm with preemption that has constant competitive ratio on any tree. Our results carry over to the related problem of maximizing the number of accepted paths subject to a capacity constraint on vertices (in the disjoint path problem this capacity is 1). Moreover, if the available capacity is at least 4, randomization is not needed and our on-line algorithm becomes deterministic.     

Viscosity virtual sensor to control combustion in fossil fuel power plants

Thermo-electrical power plants utilize fossil fuel oil to transform the calorific power of fuel into electric power. An optimal combustion in the boiler requires the fuel oil to be in its best conditions. One of fuel's most important properties to consider is viscosity. Viscosity has influence on the optimal combustion between fuel and air. Hardware viscosity meters for fuel oils are expensive and unreliable to operate in power plant conditions. Chemical laboratory measures viscosity accurately with special apparatus, but they cannot be used in a real time process. This paper describes the development of a virtual sensor that estimates fuel oil viscosity in the combustion process of a power plant. A virtual sensor or soft sensor is a computer program that estimates the value of a certain variable based on related measurements and a model of the process where the variable participates. In this project, a probabilistic model is constructed using automatic learning algorithms with historical data and experts' advice. The learning and validation experiments are described and discussed. The virtual sensor is installed in the Tuxpan Power Plant in Veracruz, Mexico.     

Dermatophytes isolated in our clinics. 5-year-study in Zaragoza

BACKGROUND: This review summarizes the different species of dermatophytes isolates in our laboratory between 1991 and 1995. We describe the clinical forms and establish the distribution over this period of time. METHODS: Retrospective survey of samples from outpatients of the Dermatology Service in Miguel Servet Hospital where mycologic cultures are required. The extraction of samples is made by scrapes with a carpet or scalpel and they are cultured on Saboureaud agar with chloramphenicol and dermatophytes agar for 3 weeks. All plates were incubated at 28 degrees C. The identification of isolated strains is made by means of morphologic and physiologic criteria; the doubtful strains were identified in national referral center of Majadahonda CNMVISS. RESULTS: 4004 samples were analyzed from 3934 patients and 543 strains of dermatophytes were isolated. The frequencies were as follow: Microsporum canis (44%), Trichophyton mentagrophytes (31.4%), Trichophyton rubrum (18.6%), Epidermophyton floccosum (2.6%), Microsporum gypseum (1.4%), Trichophyton tonsurans (0.7%), Trichophyton verrucosum (0.7%), Trichophyton violaceum (0.2%) y Microsporum audouinii (0.2%). The most frequently observed dermatophytoses were Tinea corporis (54.8%), followed by Tinea unguium (12.6%), Tinea capitis (12.5%), Tinea pedis (8.3%), Tinea manuum (6.3%), Tinea cruris (4.7%) and Tinea barbae (0.7%). CONCLUSIONS: The zoophylic species are the most prevalent in our area and we have observed a raise of Microsporum canis in recent years. It is important to perform mycologic survey in every suspected lesion in older to determinate the true incidence of human dermatophytoses.     

Prediction of Magnetic Susceptibilities in Diamagnetic Binary Fluid Mixtures

A model is proposed to predict magnetic susceptibilities in diamagnetic binary fluid mixtures. The model predictions are compared to experimental information for nine binary systems including polar and non-polar compounds. The predictions are also compared to the results obtained from the traditional Boyer-Donzelot equation. For all systems analyzed, the model predicted magnetic susceptibilities closer to the experimental values than those predicted from the Boyer-Donzelot equation. The deviations from the experimental values decrease when the binary system exhibits a positive excess magnetic susceptibility.     

ANION EFFECT ON SELECTIVITY IN SOLVENT EXTRACTION OF ALKALI METAL SALTS BY CROWN ETHERS

ABSTRACT

The influence of the co-extracted anion upon competitive solvent extraction of five alkali metal cations from aqueous solutions into organic diluents by the cis-syn-cis and cis-anti-cis isomers of dicyclohexano-18-crown-6 has been assessed. The anions are bromide, chloride, iodide, nitrate, perchlorate, and thiocyanate and the organic diluents are chloroform and 1-octanol. The extraction efficiency is markedly influenced by the identity of the anion and exhibits some correlation with the inverse of the hydration enthalpy of the anion. Although potassium is the best extracted cation with all anions, the selectivities for potassium over lithium, sodium, rubidium, and cesium are strongly affected by anion variation in chloroform, but not in 1-octanol. The selectivity ordering in chloroform does not correlate with the hydration enthalpy or softness parameter for the anion. Instead it appears to result from variation of the dimensional structure and the availability of specific binding sites in the anion.     

Colistin Resistance in Aeromonas spp.

The increase in the use of antimicrobials such as colistin for the treatment of infectious diseases has led to the appearance of Aeromonas strains resistant to this drug. However, resistance to colistin not only occurs in the clinical area but has also been determined in Aeromonas isolates from the environment or animals, which has been determined by the detection of mcr genes that confer a resistance mechanism to colistin. The variants mcr-1, mcr-3, and mcr-5 have been detected in the genus Aeromonas in animal, environmental, and human fluids samples. In this article, an overview of the resistance to colistin in Aeromonas is shown, as well as the generalities of this molecule and the recommended methods to determine colistin resistance to be used in some of the genus Aeromonas.