Sharing delay costs in stochastic scheduling problems with delays

An important problem in project management is determining ways to distribute amongst activities the costs that are incurred when a project is delayed because some activities end later than expected. In this study, we address this problem in stochastic projects, where the durations of activities are unknown but their corresponding probability distributions are known. We propose and characterise an allocation rule based on the Shapley value, illustrate its behaviour by using examples, and analyse features of its calculation for large problems

Influencia del tiempo de gelificación sobre las propiedades estructurales, vibracionales y eléctricas del compósito PEG0.2/V2O5

Se estudiaron las propiedades estructurales, vibracionales y eléctricas de películas V2O5·nH2O y PEG0.2/V2O5 en función del tiempo de gelificación. Las películas fueron sinterizadas por sol-gel mediante la ruta del pentóxido de vanadio sobre sustratos de vidrio previamente tratados. La caracterización se llevo a cabo mediante Difracción de Rayos-X, Espectroscopía Raman y el método de las cuatro puntas convencional de van der Pauw. Los resultados indican que el aumento en el tiempo de gelificación del sol precursor (V2O5.nH2O) incrementa la calidad cristalina, el grado de hidratación, y la concentración de iones V5+ en las películas. En el compósito híbrido (PEG0.2/V2O5) los iones VO2+ actúan como enlazantes entre las cadenas poliméricas haciéndolas más compactas, lo cual facilita la movilidad de los portadores de carga eléctrica entre los iones vanadios. Los resultados mostraron una transición de fase semiconductormetal alrededor de 34°C, una transición óptica del tipo indirecta (para V2O5·nH2O) y una transición vítrea alrededor de Tg=-69°C.Structural, vibrational and electrical properties of V2O5·nH2O and PEG0.2/V2O5 films as a function of gelation time were studied. The films were sintered by sol-gel using vanadium pentoxide route on glass substrates previously treated. Films were characterized by X-Ray Diffraction, Raman Spectroscopy and the four-point van der Pauw conventional method. The results indicated that when the gelation time of the precursor (V2O5·nH2O) is increased, the crystalline quality, the degree of hydration, and V5+ ion concentration are increased. In the hybrid composite (PEG0.2/V2O5), VO2+ ions act as bonding between the polymer chains, making them more compact to facilitate the mobility of electric charge carriers between vanadium ions. The results showed a semiconductor-metal transition about 34°C, an indirect optical transition (V2O5·nH2O) and a vitreous transition around Tg=-69°C.Fil: Londoño Calderon, Cesar Leandro. Universidad Nacional de Colombia; Colombia. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Jurado, J. F.. Universidad Nacional de Colombia; ColombiaFil: Vargas Hernández, C.. Universidad Nacional de Colombia; Colombi

Critical Repetition Rates for Perceptual Segregation of Time-Varying Auditory, Visual and Vibrotactile Stimulation

What sound quality has led to exclude infrasound from sound in the conventional hearing range? We examined whether temporal segregation of pressure pulses is a distinctive property and evaluated this perceptual limit via an adaptive psychophysical procedure for pure tones and carriers of different envelopes. Further, to examine across-domain similarity and individual covariation of this limit, here called the critical segregation rate (CSR), it was also measured for various periodic visual and vibrotactile stimuli. Results showed that sequential auditory or vibrotactile stimuli separated by at least ~80‒90 ms (~11‒12-Hz repetition rates), will be perceived as perceptually segregated from one another. While this limit did not statistically differ between these two modalities, it was significantly lower than the ~150 ms necessary to perceptually segregate successive visual stimuli. For the three sensory modalities, stimulus periodicity was the main factor determining the CSR, which apparently reflects neural recovery times of the different sensory systems. Among all experimental conditions, significant within- and across-modality individual CSR correlations were observed, despite the visual CSR (mean: 6.8 Hz) being significantly lower than that of both other modalities. The auditory CSR was found to be significantly lower than the frequency above which sinusoids start to elicit a tonal quality (19 Hz; recently published for the same subjects). Returning to our initial question, the latter suggests that the cessation of tonal quality — not the segregation of pressure fluctuations — is the perceptual quality that has led to exclude infrasound (sound with frequencies < 20 Hz) from the conventional hearing range

Transient effects in fission evidenced from new experimental signatures

A new experimental approach is introduced to investigate the relaxation of the nuclear deformation degrees of freedom. Highly excited fissioning systems with compact shapes and low angular momenta are produced in peripheral relativistic heavy-ion collisions. Both fission fragments are identified in atomic number. Fission cross sections and fission-fragment element distributions are determined as a function of the fissioning element. From the comparison of these new observables with a nuclear-reaction code a value for the transient time is deduced.Comment: 6 pages, 2 figures, background information at http://www-w2k.gsi.de/kschmidt

Manifestation of transient effects in fission induced by relativistic heavy-ion collisions

We examine the manifestation of transient effects in fission by analysing experimental data where fission is induced by peripheral heavy-ion collisions at relativistic energies. Available total nuclear fission cross sections of 238U at 1 A GeV on gold and uranium targets are compared with a nuclear-reaction code, where transient effects in fission are modelled using different approximations to the numerical time-dependent fission-decay width: a new analytical description based on the solution of the Fokker-Planck equation and two widely used but less realistic descriptions, a step function and an exponential-like function. The experimental data are only reproduced when transient effects are considered. The deduced value of the dissipation strength depends strongly on the approximation applied for the time-dependent fission-decay width and is estimated to be of the order of 2x10**21 s**(-1). A careful analysis sheds severe doubts on the use of the exponential-like in-growth function largely used in the past. Finally, we discuss which should be the characteristics of experimental observables to be most sensitive to transient effects in fissionComment: 18 pages, 2 figures, background information on http://www-w2k.gsi.de/kschmidt

Comparative study of tributyltin toxicity on two bacteria of the genus Bacillus

Tributyltin is a potent biocide mainly used in marine antifouling paints. Owing to its widespread distribution in coast areas and its high toxicity to aquatic organisms, the use of this compound is generally restricted and under government regulation. Despite of that, it persists in the aquatic environment. Organotins used in industry have also been detected in terrestrial environments. The persistence and high lipophilicity explain bioaccumulation. The role of bacteria in recycling organic matter prompted us to study the interaction of tributyltin with two ubiquitous bacilli, B. stearothermophilus and B. subtilis, proposed as biological indicators of pollutants with ecological impact. These bacteria have been used as suitable models for the study of toxicity mechanisms of unselective lipophilic compounds (e.g., DDT and endosulfan). Drug effects on growth parameters, oxygen consumption and membrane organization were assessed. Bacteria growth in a liquid complex medium was disturbed by concentrations of TBT as low as 25 nM (8 [mu]g L-1), close to the concentration in polluted environments. The respiratory activity is affected by TBT in both microorganisms. Membrane organization, assessed by fluorescence polarization of two fluidity probes, 1,6-diphenyl-1,3,5-hexatriene (DPH) and a propionic acid derivative (DPH-PA), was also perturbed by the xenobiotic. Alterations on growth, oxygen consumption and physical properties of membrane lipids are stronger in B. stearothermophilus as compared to B. subtilis. A putative relationship between growth inhibition and respiratory activity impairment induced by TBT and its effects on the physical behaviour of bacterial membrane lipids is suggested.http://www.sciencedirect.com/science/article/B6TCP-4GSJR3R-9/1/18e0ee5c8ce4e887466d84b850ad8ec

Toxicity of methoprene as assessed by the use of a model microorganism

Methoprene is an insect juvenile growth hormone mimic, commonly used as a pesticide. Although widely used for the control of several pests, toxic effects on organisms of different phyla have been reported. These events triggered studies to clarify the mechanisms of toxicity of this insecticide putatively involved in ecological issues. Here we show the effect of methoprene on the normal cell growth and viability of a strain of the thermophilic eubacterium Bacillus stearothermophilus, previously used as a model for toxicological evaluation of other environment pollutants. Respiration studies were also carried out attempting to identify a putative target for the cytotoxic action of methoprene. Cell growth was affected and a decrease of the number of viable cells was observed as a result of the addition of methoprene to the growth medium, an effect reverted by the presence of Ca2+. Methoprene also inhibited the redox flow of B. stearothermophilus protoplasts before the cytochrome oxidase segment, an effect further studied by individually assessing the enzymatic activities of the respiratory complexes. This study suggests that methoprene membrane interaction and perturbation of cell bioenergetics may underlie the mechanism of toxicity of this compound in non-target organisms.http://www.sciencedirect.com/science/article/B6TCP-4GSJXGW-4/1/788f9fd7d4f3a4f1ae5d498a5674dcc