The Hot-Spot Phenomenon and its Countermeasures in Bipolar Power Transistors by Analytical Electro-Thermal Simulation

This communication deals with a theoretical study of the hot spot onset (HSO) in cellular bipolar power transistors. This well-known phenomenon consists of a current crowding within few cells occurring for high power conditions, which significantly decreases the forward safe operating area (FSOA) of the device. The study was performed on a virtual sample by means of a fast, fully analytical electro-thermal simulator operating in the steady state regime and under the condition of imposed input base current. The purpose was to study the dependence of the phenomenon on several thermal and geometrical factors and to test suitable countermeasures able to impinge this phenomenon at higher biases or to completely eliminate it. The power threshold of HSO and its localization within the silicon die were observed as a function of the electrical bias conditions as for instance the collector voltage, the equivalent thermal resistance of the assembling structure underlying the silicon die, the value of the ballasting resistances purposely added in the emitter metal interconnections and the thickness of the copper heat spreader placed on the die top just to the aim of making more uniform the temperature of the silicon surface.Comment: Submitted on behalf of TIMA Editions (http://irevues.inist.fr/tima-editions

Evaluation of Monilinia fructicola on apricot fruits

Monilinia fructicola has been a quarantine pathogen in Europe until 2014; however, the disease risk remains large for Prunus species, because of the continuing spreading around Europe. In order to assess the impact of this fungus on apricot fruits, differences in variety susceptibility need to be evaluated

Factors regulating the production of STX-2 in Escherichia coli O157:H7

The severity of Escherichia coli O157:H7 disease is due in part to a major virulence factor produced by the microbe, the shiga-like toxin 2 (Stx-2). Antibiotic treatment to reduce pathogen numbers is controversial, as it is thought that antibiotics may increase the levels of Stx-2 released from the pathogen. Currently, recommended treatment for E. coli O157:H7 is palliative The purpose of this study was to examine three critical factors potentially important to disease outcomes, and to determine their effect on expression of the stx2 gene and on release of Stx-2 from the pathogen. Those factors selected for study were: (i) various classes of antibiotics; (ii) probiotic microorganisms; and (iii) carbon source variation together with cAMP. Stx-2 was assessed using MTT cytotoxicity assays and ELISA analysis, while the expression of stx2 was assessed using real time PCR. It was determined that antibiotics that affect microbial DNA increased stx2 expression and Stx-2 production, and this was linked to an upregulation in the SOS DNA repair response. A link was also observed between the upregulation of stx2 and those antibiotics that disrupt cell membrane integrity. However, these antibiotics did not increase the overall levels of Stx-2 released from E. coli O157:H7. The probiotic microorganisms Lactobacillus casei and L. plantarum were found to decrease both stx2 expression and Stx-2 release when grown in co-culture with E. coli O157:H7 at greater or equal numbers to the pathogen. This reduction in Stx-2 was at least in part attributable to organic acids produced by the probiotics, but other unknown factors produced by the lactobacilli cannot be excluded. Finally, it was determined that growth of the pathogen in glucose-supplemented media yielded significantly more stx2 expression and Stx-2 production than growth in glycerol-supplemented media. This observation was confirmed by a decrease in stx2 expression and Stx-2 production when exogenous cAMP was added to culture media. The examination of these three factors led to a clearer understanding of the intricacies involved in the regulation of stx2, and has demonstrated how such an apparently diverse group of external factors are interlinked through several complex mechanisms

Reversals in nature and the nature of reversals

The asymmetric shape of reversals of the Earth's magnetic field indicates a possible connection with relaxation oscillations as they were early discussed by van der Pol. A simple mean-field dynamo model with a spherically symmetric $\alpha$ coefficient is analysed with view on this similarity, and a comparison of the time series and the phase space trajectories with those of paleomagnetic measurements is carried out. For highly supercritical dynamos a very good agreement with the data is achieved. Deviations of numerical reversal sequences from Poisson statistics are analysed and compared with paleomagnetic data. The role of the inner core is discussed in a spectral theoretical context and arguments and numerical evidence is compiled that the growth of the inner core might be important for the long term changes of the reversal rate and the occurrence of superchrons.Comment: 24 pages, 12 figure

Different methods of evaluation of Monilinia laxa on apricot flowers and branches

- Organic apricot production is currently not profitable. - The main obstacle to sustainable profitability is brown rot caused by the fungus Monilinia laxa (Aderh. & Ruhl). - In the current apricot germplasm no source of total resistance has been shown, but some varieties are expressing interesting levels of tolerance. - A good evaluation of the M. laxa symptoms is essential for a precise diagnosis of the infection and to appreciate differences between tolerant and susceptible varieties and genotypes

Influence of turbulence on the dynamo threshold

We use direct and stochastic numerical simulations of the magnetohydrodynamic equations to explore the influence of turbulence on the dynamo threshold. In the spirit of the Kraichnan-Kazantsev model, we model the turbulence by a noise, with given amplitude, injection scale and correlation time. The addition of a stochastic noise to the mean velocity significantly alters the dynamo threshold. When the noise is at small (resp. large) scale, the dynamo threshold is decreased (resp. increased). For a large scale noise, a finite correlation time reinforces this effect

Il Casentino: tradizioni etnofarmacobotaniche nei comuni di Poppi e Bibbiena (Arezzo - Toscana)

The Casentino area: ethnopharmacobotanical traditions in the towns of Poppi and Bibbiena (Arezzo-Tuscany). The results refer an ethnopharmacobotanical study carried out in the territories of Poppi and Bibbiena in the Casentino area. There are 89 plants used in folk medicine; some of them are not known to scientific medicine (Asplenium trichomanes L., Fagus sylvatica L., Malva sylvestris L., Nerium oleander L. and Tamus communis L.)

Study of Water Speed Sensitivity in a Multifunctional Thick-film Sensor by Analytical Thermal Simulations and Experiments

The present paper deals with an application of the analytical thermal simulator DJOSER. It consist of the characterization of a water speed sensor realized in hybrid technology. The capability of the thermal solver to manage the convection heat exchange and the effects of the passivating layers make the simulation work easy and fast.Comment: Submitted on behalf of TIMA Editions (http://irevues.inist.fr/tima-editions