Dynamics of incomplete ionized dopants and their impact on4H/6H-SiC devices

The influence of incomplete ionization of dopants in 4H/6H-SiC on transient device behavior has been investigated numerically based on a self-consistent solution of the coupled system of Poisson's equation, the continuity equations of electrons and holes, and balance equations for each donor or acceptor level. If the rise time of a reverse bias pulse is equal or smaller than the characteristic ionization time constant, a dynamically enlarged extension of depletion regions is obtained which can result in a dynamic punchthrough (PT) within back-to-back junction configurations. The respective time constants of nitrogen (N), aluminum (Al), and boron (B) mere measured as functions of temperature in 4H- and 6H-SiC using thermal admittance spectroscopy (AS) and deep level transient spectroscopy (DLTS). At room temperature, for instance, we obtained 60 ps/2 ps, 300 ps/10 ps, and 100 ns/100 ns for N (cubic site), Al, and B in 4H/6H-SiC, respectively. As the time constants of N and Al are small, transient incomplete ionization turns out to be negligible, at least within today's high-power device operation areas. Boron, on the other hand, influences significantly the dynamic device characteristics. In order to demonstrate the implications of these effects, numerical device simulations of a 6H-SiC double-implanted MOSFET and a 4H-SiC thyristor were performed. These simulations allow a detailed analysis of the transient device behavior and the onset of dynamic PT which strongly depends on temperature, structure parameters, and the external excitation     

Acoustic emission for detecting deterioration of capacitors under aging

There is continuous pressure on production cost reduction of foil-based capacitors, widely used in domestic appliance. Therefore, investigation of the deterioration mechanisms within capacitors is important to reduce their production costs at maintained reliability. These mechanisms were observed in two capacitors batches of classes Y2 (27 nF) and X2 (470 nF). An acoustic emission signal was observed when the capacitors were polarized by excessive voltage. This signal is induced by partial discharges that can lead to capacitor destruction. Next, the capacitors were aged at elevated temperature and also in presence of excessive polarization. We conclude that the acoustic emission signal can predict deterioration of dielectric insulation resistance in capacitors of class Y2. The observed destruction of capacitor of class X2 is caused mainly by detachment of the sprayed metalized contacts that is induced by overheating during partial discharges sparking.     

Upward vs downward injection of droplets for the optimization of a radiative shield

A numerical and experimental study of a spray has been carried out at the laboratory scale, focusing on the comparison between downward and upward injection situations. The simulation has been carried out thanks to a dedicated numerical code addressing the two-phase flow with an Eulerian–Lagrangian approach, and treating the radiative transfer with a Monte Carlo method. The experimental setup involves a FTIR spectrometer and an IR camera, both characterizing simultaneously the spectral attenuation through the spray when irradiated by a blackbody. Numerical results and experimental data both show a better ability of the spray to attenuate radiation when injected upward. The residence time of droplets is highly increased when they are injected upward. This results in an increased attenuation ability of the spray. A gain by a factor 3 or more is possible regarding the attenuation of radiation if water is injected upward. This observation has to be considered with care however because of a possible poor stability of the spray. The influence of an air flow affecting the spray dynamics has also been investigated numerically, tests being done with a 2 m/s air flow. The droplet motion is strongly altered and the radiation attenuation is affected. In the upward injection case the deformation of the spray may be so strong in its upper part that the attenuation tends to zero because droplets are carried away.     

Reducts of propositional theories,satisfiability relations,and generalizations of semantics of logic programs

Over the years, the stable-model semantics has gained a position of the correct (two-valued) interpretation of default negation in programs. However, for programs with aggregates (constraints), the stable-model semantics, in its broadly accepted generalization stemming from the work by Pearce, Ferraris and Lifschitz, has a competitor: the semantics proposed by Faber, Leone and Pfeifer, which seems to be essentially different. Our goal is to explain the relationship between the two semantics. Pearce, Ferraris and Lifschitz's extension of the stable-model semantics is best viewed in the setting of arbitrary propositional theories. We propose here an extension of the Faber–Leone–Pfeifer semantics, or FLP semantics, for short, to the full propositional language, which reveals both common threads and differences between the FLP and stable-model semantics. We use our characterizations of FLP-stable models to derive corresponding results on strong equivalence and on normal forms of theories under the FLP semantics. We apply a similar approach to define supported models for arbitrary propositional theories, and to study their properties.     

Thermo-reversible sol–gel transition of TiO2 nanoparticles with surface modified by p-toluene sulfonic acid

In this paper an unprecedent thermo-reversible sol–gel transition for titania nanoparticles dispersed in a solution of p-toluene sulfonic acid (PTSH) in isopropanol is reported. The sol formed by the thermo-hydrolysis at 60 °C of titanium tetraisopropoxide (Ti(OⁱPr)₄) reversibly changes into a turbid gel upon cooling to room temperature. Turbidimetric measurements performed for samples containing different nominal acidity ratios (A = [PTSH]/[Ti]) have evidenced that the gel transformation temperature increases from 20 to 35 °C as the [PTSH]/[Ti] ratio increases from 0.2 to 2.0. SAXS results indicate that the thermo-reversible gelation is associated to a reversible aggregation of a monodisperse set of titania nanoparticles with average gyration radius of ≈2 nm. From the different PTSH species evidenced by Raman spectroscopy and TG/DTA of dried gels we proposed that the thermo-reversible gelation in this systems is induced by the formation of a supramolecular network, in which the protonated surface of nanoparticles is interconnected through cooperative hydrogen bonds between –SO₃ groups of p-toluene sulfonic acid.     

When cognitive exertion does not yield cognitive gain: Toward an informational explanation of learned helplessness.

This study tested a new information-processing explanation of learned helplessness that proposes that an uncontrollable situation produces helplessness symptoms because it is a source of inconsistent, self-contradictory task information during problem-solving attempts. The flow of such information makes hypothesis-testing activity futile. Prolonged and inefficient activity of this kind leads in turn to the emergence of a state of cognitive exhaustion, with accompanying performance deficits. In 3 experiments, Ss underwent informational helplessness training (IHT): They were sequentially exposed to inconsistent task information during discrimination problems. As predicted, IHT was associated with subjective symptoms of irreducible uncertainty and resulted in (a) performance deterioration on subsequent avoidance learning, (b) heightened negative mood, and (c) subjective symptoms of cognitive exhaustion. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Intratumoral microdistribution of [131I]MB-1 in patients with B-cell lymphoma following radioimmunotherapy

Leprechaunism is a rare autosomal recessive disorder characterized by marked intrauterine and postnatal growth retardation, severe insulin resistance, and altered glucose homeostasis. This syndrome is related to mutations in the insulin receptor (IR) gene that impair the transmission of the insulin signal by several mechanisms. There is no effective therapy and patients usually die within the first months of life. Here we report the prenatal diagnosis of leprechaunism in two unrelated families in which affected children were compound heterozygotes with two different deficient IR alleles. In family Par-1, the disease IR alleles carried a missense mutation located in exon 18 (Arg1092-->Trp) and exon 20 (Glu1179-->Lys). In family Als, a 3-basepair deletion causing the loss of Asn281 in exon 3 and a major deletion of exons 10-13 were present in the maternal and paternal mutant IR alleles, respectively. Prenatal diagnosis was made in each family by a specific approach combining denaturing gradient gel electrophoresis (DGGE) and Southern blotting. This methodology allowed us to correctly predict the genotype of the two fetuses at the IR locus.     

Rigorous modal analysis of structures containing inhomogeneous dielectric cylinders

The orthogonal expansion method and modified iterative scattering procedure is proposed to analyze structures containing asymmetrically located, partial-height, or multilayered inhomogeneous dielectric posts. The analysis is based on a novel concept called the hybrid impedance matrix (HIM), which describes the relation between the total scattered electric and magnetic fields obtained from all posts. As a result, the HIM can be easily applied to match it with other known incident fields and finds applications in closed (waveguide junctions, resonators) and open structures (posts in free space for plane-wave excitation). Additionally, a procedure for constructing eigenmode functions describing field components in the inhomogeneous dielectric cylinders is presented. The proposed method has been extensively verified for a rectangular waveguide junction by a finite-difference time-domain software package, as well as our own measurements and, in both cases, very good agreement can be observed.     

The polypyrimidine tract binding protein (PTB) requirement for internal initiation of translation of cardiovirus RNAs is conditional rather than absolute

Picornavirus RNAs are translated by an unusual mechanism of internal ribosome entry that requires a substantial segment of the viral 5'-untranslated region, generally known as the internal ribosome entry segment (IRES), and in some circumstances may require cellular trans-acting proteins, particularly polypyrimidine tract binding protein (PTB). It is shown here that for encephalomyocarditis virus (EMCV), the PTB dependence of IRES function in vitro is determined partly by the nature of the reporter cistron, and more especially by the size of an A-rich bulge in the IRES. With a wild-type EMCV IRES (which has a bulge of 6 As), translation is effectively independent of PTB provided the IRES is driving the synthesis of EMCV viral polyprotein. With an enlarged (7A) bulge and heterologous reporters, translation is highly dependent on PTB. Intermediate levels of PTB dependence are seen with a 7A bulge IRES driving viral polyprotein synthesis or a wild-type (6A) bulge IRES linked to a heterologous reporter. None of these parameters influenced the binding of PTB to the high-affinity site in the IRES. These results argue that PTB is not an essential and universal internal initiation factor, but, rather, that when it is required, its binding to the IRES helps to maintain the appropriate higher-order structure and to reverse distortions caused, for example, by an enlarged A-rich bulge.