Ermakov Systems with Multiplicative Noise

Using the Euler-Maruyama numerical method, we present calculations of the Ermakov-Lewis invariant and the dynamic, geometric, and total phases for several cases of stochastic parametric oscillators, including the simplest case of the stochastic harmonic oscillator. The results are compared with the corresponding numerical noiseless cases to evaluate the effect of the noise. Besides, the noiseless cases are analytic and their analytic solutions are briefly presented. The Ermakov-Lewis invariant is not affected by the multiplicative noise in the three particular examples presented in this work, whereas there is a shift effect in the case of the phasesComment: 12 pages, 4 figures, 22 reference

Persistence of viable but non-culturable bacteria during the production and distribution of drinking water

The direct measurement of in situ respiring bacteria using 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) shows that, especially for Gram-negative bacteria, large numbers of viable but non-culturable (VBNC) bacteria are present in finished water from a conventional water treatment plant, and the regrowth of bacteria along distribution networks can be seen rapidly by using this very sensitive technique. The level of bacterial inactivation with chlorine is much less important than has been previously supposed (based on experiments with non-injured laboratory strains of bacteria and classical culture techniques). Threshold values of VBNC bacteria leaving water treatment plants or regrowing along distribution systems have to be determined for better control of coliform regrowth and health- risks associated with the consumption of drinking water

The rabbit as an animal model for the study of ovulation-inducing factor

Ovulation–inducing factor (OIF) is a seminal plasma protein that has been found in the ejaculate of different species. Evidence suggests that OIF and its function may be conserved among species. Our general objective was to develop a rabbit model for the study of OIF in seminal plasma. In the first study, we conducted two experiments to validate the use of ultrasound biomicroscopy as a method for assessing ovarian structures in rabbits, and to develop a method that permits serial noninvasive repetitive ultrasound evaluation of ovarian structures in vivo in rabbits. In Experiment 1, the number and size of follicles ≥ 0.6 mm and corpora lutea (CL) detected by ultrasound biomicroscopy (UBM) ex situ were correlated with those detected by histology in each pair of ovaries from 4 female New Zealand White rabbits (5-5.5 months old) given an ovulation-inducing treatment. In Experiment 2, we translocated the ovaries of female New Zealand white rabbits (n=12; 5 months old) to a subcutaneous position in order to develop a method that permits serial UBM evaluation of ovarian structures in vivo in rabbits. Results showed strong correlations (P < 0.05) between UBM and histology in all the ovarian variables evaluated in Experiment 1, and also showed that ovarian structures are easily identified using UBM in vivo in the rabbits submitted to the surgical approach performed in Experiment 2. In the second study, we conducted two experiments to test the hypothesis that llama and rabbit seminal plasma elicits a surge of LH release and is responsible for inducing ovulation in rabbits. In Experiment 1, we compared the effect of an intramuscular administration of saline, GnRH, llama or rabbit seminal plasma in female New Zealand White rabbits (n=4-6 per group, 5.5 months old) that were group-housed. In Experiment 2, we compared the effects of the same treatments in rabbits (n=5-7 per group, 5.5 months old) that were individually caged. Ovulation and CL formation occurred in most rabbits regardless of the treatment given when animals were group housed, while rabbits given similar treatment but individually housed did not ovulate. In the GnRH group, a surge in plasma LH concentrations was observed in all the rabbits, followed by CL formation and an increase in plasma progesterone concentrations. In summary, we developed a rabbit model for the study of OIF, where ovarian structures can be evaluated in vivo by UBM. Results did not support the hypothesis that OIF in seminal plasma elicits ovulation in rabbits. Further studies are needed to determine the effects of dose and route of administration of seminal plasma in rabbits

Isotropization of Bianchi type models and a new FRW solution in Brans-Dicke theory

Using scaled variables we are able to integrate an equation valid for isotropic and anisotropic Bianchi type I, V, IX models in Brans-Dicke (BD) theory. We analyze known and new solutions for these models in relation with the possibility that anisotropic models asymptotically isotropize, and/or possess inflationary properties. In particular, a new solution of curve ($k\neq0$) Friedmann-Robertson-Walker (FRW) cosmologies in Brans-Dicke theory is analyzed.Comment: 15 pages, 4 postscript figures, to appear in Gen. Rel. Grav., special issue dedicated in honour of Prof. H. Dehne

Impact and application of electron shuttles on the redox (bio)transformation of contaminants : a review

During the last two decades, extensive research has explored the catalytic effects of different organic molecules with redox mediating properties on the anaerobic (bio)transformation of a wide variety of organic and inorganic compounds. The accumulated evidence points at a major role of electron shuttles in the redox conversion of several distinct contaminants, both by chemical and biological mechanisms. Many microorganisms are capable of reducing redox mediators linked to the anaerobic oxidation of organic and inorganic substrates. Electron shuttles can also be chemically reduced by electron donors commonly found in anaerobic environments (e.g. sulfide and ferrous iron). Reduced electron shuttles can transfer electrons to several distinct electron-withdrawing compounds, such as azo dyes, polyhalogenated compounds, nitroaromatics and oxidized metalloids, among others. Moreover, reduced molecules with redox properties can support the microbial reduction of electron acceptors, such as nitrate, arsenate and perchlorate. The aim of this review paper is to summarize the results of reductive (bio)transformation processes catalyzed by electron shuttles and to indicate which aspects should be further investigated to enhance the applicability of redox mediators on the (bio)transformation of contaminants.F.P. van der Zee thanks the Portuguese Fundaicao para a Ciencia e a Tecnologia for financial support (Grant SFRH/BPD/39086/2007). F. J. Cervantes greatly acknowledges a grant from Council of Science and Technology of Mexico (Grant SEP-CONACYT-C02-55045)

Simple Pendulum Revisited

We describe a 8085 microprocessor interface developed to make reliable time period measurements. The time period of each oscillation of a simple pendulum was measured using this interface. The variation of the time period with increasing oscillation was studied for the simple harmonic motion (SHM) and for large angle initial displacements (non-SHM). The results underlines the importance of the precautions which the students are asked to take while performing the pendulum experiment.Comment: 17 pages with 10 figure