A probabilistic method for the design of power grounding systems

An improved multivariable, probabilistic method for the safety analysis of power grounding systems is presented. The application of this method is demonstrated in four examples. The first three examples illustrate the practical evaluation of one new and two existing substation grounding grids when the substation is connected to an overhead distribution system. The fourth example ascertains the relative impact of a difference between the S curve of IEC Publication 479 and Dalziel's equation for the allowable body current used in ANSI/IEEE Std 80-1986 on the validity of an exposure model based on the requirements of Std 80. In this example, the statistical data on ground faults have been taken from actual system records. Further possible refinements of the exposure model are discussed     

Investigation of the basic creep of concrete by acoustic emission

The physical origins of the basic creep of concrete are still poorly understood even though some researchers have proposed hypotheses concrening the physical mechanisms that govern this delayed behaviour of concrete. A very complete summing up of these hypotheses was produced, in the past, by, Neville; he shows that none of them, provides a satisfactory explanation of the bulk of basic creep. More recently, Rossi has proposed a new hypothesis, which has been the subject of several articles. This article concerns the use of the acoustic emission technique as a ‘tool’ to provide information on the pertinence of the physical hypothesis advanced by Rossi. The counting of the total number of acoustic events together with a frequency analysis of the acoustic emission signals indicate that there is a strong correlation between the basic creep of concrete and the creation of microcracks in the material.     

Effect of Molybdenum on the Structure and on the Crystallization of SiO2–Na2O–CaO–B2O3 Glasses

Crystallization of the poorly durable Na₂MoO₄ phase able to incorporate radioactive cesium must be avoided in SiO₂–Al₂O₃–B₂O₃–Na₂O–CaO glasses developed for the immobilization of Mo-rich nuclear wastes. Increasing amounts of B₂O₃ and MoO₃ were added to a SiO₂–Na₂O–CaO glass, and crystallization tendency was studied. Na₂MoO₄ crystallization tendency decreased with the increase of B₂O₃ concentration whereas the tendency of CaMoO₄ to crystallize increased due to preferential charge compensation of BO₄⁻ entities by Na⁺ ions. ²⁹Si MAS NMR showed that molybdenum acts as a reticulating agent in glass structure. Trivalent actinides surrogate (Nd³⁺) were shown to enter into CaMoO₄ crystals formed in glasses.     

Generating relational database transactions from eb 3 attribute definitions

eb ³ is a trace-based formal language created for the specification of information systems. In eb ³, each entity and association attribute is independently defined by a recursive function on the valid traces of external events. This paper describes an algorithm that generates, for each external event, a transaction that updates the value of affected attributes in their relational database representation. The benefits are twofold: eb ³ attribute specifications are automatically translated into executable programs, eliminating system design and implementation steps; the construction of information systems is streamlined, because eb ³ specifications are simpler and shorter to write than corresponding traditional specifications, design and implementations. In particular, the paper shows that simple eb ³ constructs can replace complex SQL queries which are typically difficult to write.

Energetics and Structure of Polymer‐Derived Si–(B–)O–C Glasses: Effect of the Boron Content and Pyrolysis Temperature

The structure and properties of polymer‐derived Si–(B–)O–C glasses have been shown to be significantly influenced by the boron content and pyrolysis temperature. This work determined the impact of these two parameters on the thermodynamic stability of these glasses. High‐temperature oxide melt solution calorimetry was performed on a series of amorphous samples, with varying boron contents (0–7.7 at.%), obtained by pyrolysis of precursors made by a sol–gel technique. Thermodynamic analysis of the calorimetric results demonstrated that at a constant pyrolysis temperature, adding boron makes the materials energetically less stable. While the B‐containing glasses pyrolyzed at 1000°C were energetically less stable than the competitive crystalline components, increasing the pyrolysis temperature to 1200°C led to their enthalpic stability. ²⁹Si and ¹¹B MAS nuclear magnetic resonance (NMR) spectroscopy measurements on selected samples confirmed a decrease in the concentrations of mixed Si‐centered SO_iC_4?i and B‐centered BO_jC_3?j bonds at the expense of formation of SiO₄ and B(OSi)₃ species (indicating a tendency toward phase separation) when the boron content and pyrolysis temperature increased. In light of the findings from calorimetry and NMR spectroscopy, we propose a structure–energetic relationship in Si–(B–)O–C glasses.     

Modification of haloperidol-induced pattern of c-fos expression by serotonin agonists

Acute challenge with clozapine and haloperidol produce different anatomical patterns of c-fos expression in the forebrain. The pharmacological profile of atypical antipsychotics suggests that serotonin might contribute to the unique therapeutic benefits of these drugs. In order to test this possibility, we examined the abilities of 5-HT1A and 5-HT2A/2c agonists to modify the pattern of c-fos expression induced by haloperidol and clozapine. Various groups of rats were pretreated with either saline, DOI, 8-OH-DPAT, and 8-OH-DPAT + DOI 30 min prior to haloperidol or clozapine administration. Rats were killed 90 min after antipsychotic administration. In saline-pretreated rats, haloperidol produced intense Fos-LI in all four striatal quadrants while the effect of clozapine was restricted to the medial part of the striatum. Prior administration of 8-OH-DPAT significantly reduced haloperidol-induced Fos-LI in all four striatal quadrants while DOI and 8-OHDPAT + DOI significantly reduced Fos-LI only in dorso- and ventrolateral quadrants. In the nucleus accumbens, haloperidol induced intense Fos-LI in the core and the shell regions whereas clozapine induced c-fos expression only in the shell. Pretreatment with 8-OHDPAT in haloperidol treated rats reduced Fos-LI in the core region yielding to a c-fos pattern similar to that induced by clozapine. In the prefrontal cortex of saline-pretreated rats, haloperidol produced a moderate c-fos expression compared with the intense expression produced by clozapine. Pretreatment with serotonin agonists before haloperidol brought the number of FOS-positive neurons to the same level as in clozapine treated rats. These results show the ability of 5-HT agonists to transform the typical pattern of c-fos expression induced by haloperidol into a pattern resembling that of clozapine.     

Escherichia coli and Lactobacillus plantarum responses to osmotic stress

Artificial insemination using cryopreserved semen is a common management tool of the contemporary livestock producer. However, cryopreservation is detrimental to sperm function and fertility, killing some 50% of the spermatozoa during the process. Prediction of cryopreservation damage from prefreeze samples remains elusive. Computer-automated sperm head morphometry was used in this study to determine the effects of cryopreservation on bovine sperm head morphometry. Semen was collected from 18 bulls and was divided. One portion was extended to 200 x 10(6) sperm/ml and a microscope slide was prepared, while the remaining portion was cryopreserved in a Triscitrate-yolk extender. After thawing, the cryopreserved samples were prepared on microscope slides. All slides were air dried and were stained with hematoxylin and rose bengal. The morphometric dimensions for length, width, width/length, area, and perimeter for a minimum of 200 sperm heads were analyzed from each slide by computer-aided sperm head morphometry analysis, and the mean measurements were recorded. Bull sperm heads were significantly (P < 0.01) smaller in cryopreserved spermatozoa than in the companion extended samples for length (8.56+/-0.07 vs. 8.63+/-0.08 microm), width (4.39+/-0.05 vs. 4.48+/-0.05 microm), area (28.42+/-0.07 vs. 29.14+/-0.08 microm), and perimeter (23.33+/-0.21 vs. 23.70+/-0.23 microm) for all bulls. Width/length was also different (0.513 vs. 0.519). In addition, differences (P < 0.05) were found within 14 of 18 bulls for at least four of the morphometric parameters. The percent change in measures after cryopreservation were correlated (P < or = 0.05) to the variability of the extended sample. Variations in sperm head measurements were lower (P < or = 0.05) in extended samples of the four bulls in which no changes occurred than in extended samples of the remaining 14 bulls. These data suggest that the variability in sperm head measurements of individual bulls, or ejaculates, may be an indicator of sperm cryosurvivability.     

Modulated Structures Induced by Phase Transformations

Abstract

Modulated structures can be found in organic, inorganic and even quasicrystalline structures. They are generally detected by diffraction from the presence of satellites surrounding the Bragg reflections. Their positions may vary continuously with temperature or pressure so that the phase can be considered as incommensurately modulated. Incommensurate phases usually transform to a periodic high symmetry phase by increasing temperature and to a commensurate lock-in phase by lowering the temperature. Their domain of stability varies with temperature, pressure and with the type of compound. Examples have been identified where the interval of equilibrium vary from a few tenths to a few hundreds of degrees. Recent progress in the field of incommensurate structure analysis has been greatly favoured by the superspace group approach which is now almost exclusively applied. In many cases, the resolution of the modulated phases by diffraction methods has contributed towards the understanding of the phase changes. In addition, microscopic models for the transition mechanisms have been developed to understand small organic systems. The methods of molecular dynamics have been able to explain the formation of various sequences of commensurate and incommensurate phases observed experimentally.