An Advancement in Transistor Second Breakdown Performance Using Molybdenum Metalization

Transistor second breakdown failures usually appear as collector-emitter short circuits. Microscopic examination of these devices shows that the contact metalization has undergone physical change. Cross sectioning shows that the short circuit is the result of the contact metal melting and alloying into the device. If it is assumed that second breakdown itself is not destructive but leads to the melting and alloying of the contact metalization, then a high temperature metal should be superior to aluminum for withstanding hot spots. This paper describes the experimental results of transistors having molybdenum-aluminum metalization compared to devices with only aluminum contacts. The results indicate that devices with molybdenum, when driven into second breakdown, will outlive aluminum units with respect to current by a factor of three.     

Conformal nanocoating of zirconia nanoparticles by atomic layer deposition in a fluidized bed reactor

Primary zirconia nanoparticles were conformally coated with alumina ultrathin films using atomic layer deposition (ALD) in a fluidized bed reactor. Alternating doses of trimethylaluminium and water vapour were performed to deposit Al(2)O(3) nanolayers on the surface of 26?nm zirconia nanoparticles. Transmission Fourier transform infrared spectroscopy was performed ex situ. Bulk Al(2)O(3) vibrational modes were observed for coated particles after 50 and 70?cycles. Coated nanoparticles were also examined with transmission electron microscopy, high-resolution field emission scanning electron microscopy and energy dispersive spectroscopy. Analysis revealed highly conformal and uniform alumina nanofilms throughout the surface of zirconia nanoparticles. The particle size distribution and surface area of the nanoparticles are not affected by the coating process. Primary nanoparticles are coated individually despite their high aggregation tendency during fluidization. The dynamic aggregation behaviour of zirconia nanoparticles in the fluidized bed plays a key role in the individual coating of nanoparticles.     

A numerical method for nonlinear complex modes with application to active–passive damped sandwich structures

In this paper, a numerical method is proposed for determining complex vibrations modes of sandwich structures with piezoelectric and viscoelastic layers. Based on homotopy and asymptotic numerical techniques, this method leads to the damping properties calculation (loss factor and natural frequency per mode) of the hybrid sandwich structure. The numerical results of the loss factor and natural frequency are compared to those obtained from analytical beam model and from numerical studies the modal strain energy method.     

Electronic structure and optical properties of complex hydrides LiBH4 and NaAlH4 compounds

The properties of the complex hydrides LiBH₄ and NaAlH₄ such as structural, electronic, and optical properties were calculated using the augmented plane wave plus local orbitals (APW + lo) method. The three phases α, β, and γ of LiBH₄ and NaAlH₄ hydrides are studied, the β‐phase is transformed at the high‐pressure to γ phase for the compound LiBH₄ with the generalized gradient approximation (GGA) with a 16% volume decrease. However, NaAlH₄ compound did not show any phase transition. The interaction between the boron (aluminum) atoms and the hydrogen atoms in the [AlH₄]^? ([BH₄]^? ) complexes is strongly covalent, and between the complexes [AlH₄]^? and the lithium Li⁺ cations for the LiBH₄ compound and between the complexes [AlH₄]^? and the sodium Na⁺ cations for the NaAlH₄ compound, the bond is ionic. For the most stable phases of the two complex hydrides, different optical parameters have been calculated as a function of the photon energy. The plasma frequency ω_p is calculated from the mean peak of the energy loss function. Therefore, by way of example, the plasma energy ?ω_p of its peak position is 13.23 (12.93) eV for α‐NaAlH₄ (α‐LiBH₄).     

Discrete kinetic theory for 2D modeling of a moving crowd: Application to the evacuation of a non-connected bounded domain

This paper concerns the mathematical modeling of the motion of a crowd in a non connected bounded domain, based on kinetic and stochastic game theories. The proposed model is a mesoscopic probabilistic approach that retains features obtained from both micro- and macro-scale representations; pedestrian interactions with various obstacles being managed from a probabilistic perspective. A proof of the existence and uniqueness of the proposed mathematical model’s solution is given for large times. A numerical resolution scheme based on the splitting method is implemented and then applied to crowd evacuation in a non connected bounded domain with one rectangular obstacle. The evacuation time of the room is then calculated by our technique, according to the dimensions and position of a square-shaped obstacle, and finally compared to the time obtained by a deterministic approach by means of randomly varying some of its parameters.     

Computational representation and analysis of emotion dynamics

Multimedia Tools and Applications - Human emotions are dynamic in nature. The intensity with which they are felt changes over time, and they have a natural timescale of expression, from onset to...     

Tackling Complexity in High Performance Computing Applications

We present a software framework that supports the specification of user-definable configuration options in HPC applications independently of the application code itself. Such options include model parameter values, the selection of numerical algorithm, target platform etc. and additional constraints that prevent invalid combinations of options from being made. Such constraints, which are capable of describing complex cross-domain dependencies, are often crucial to the correct functioning of the application and are typically either completely absent from the code or a hard to recover from it. The framework uses a combination of functional workflows and constraint solvers. Application workflows are built from a combination of functional components: higher-order co-ordination forms and first-order data processing components which can be either concrete or abstract, i.e. without a specified implementation at the outset. A repository provides alternative implementations for these abstract components. A constraint solver, written in Prolog, guides a user in making valid choices of parameters, implementations, machines etc. for any given context. Partial designs can be stored and shared providing a systematic means of handling application use and maintenance. We describe our methodology and illustrate its application in two classes of application: a data intensive commercial video transcoding example and a numerically intensive incompressible Navier–Stokes solver.     

Rheological characterization of polypropylene/poly(ethylene-<Emphasis Type="Italic">co</Emphasis>-propylene) in-reactor blends synthesized under different polymerization conditions

In-reactor blends of polypropylene/poly(ethylene-co-propylene) with complex microstructure, synthesized through different polymerization procedures; two-step (one homopolymerization and one copolymerization under high ethylene concentration) and three-step (with an additional copolymerization step under low ethylene concentration), were characterized by rheological measurements. The effects of a change in the polymerization process on the types and amounts of block copolymers in the blends were evaluated using small amplitude oscillation rheometry in the linear viscoelastic region. The Palierne model in its complete form was employed to model the rheological behavior of the blends. For this analysis the reactor products were separated into xylene cold insoluble (XCI) and xylene cold soluble fractions. Besides, another two copolymer fractions at 80 and 100 °C, which are crystallizable copolymer fractions and contain block copolymers rich in polyethylene and polypropylene, respectively, were separated from XCI fraction by xylene using temperature gradient elution fractionation method. Considering all copolymer fractions as dispersed and the remained fraction (mostly polypropylene) as matrix phase, it was shown that the rheological properties of the blends could not be predicted by Palierne model. It was found that only by considering part of block copolymer fractions having long polypropylene sequences along with polypropylene homopolymer as one phase, the rheological properties of the blends could be predicted by Palierne model. By rheological modeling, it was confirmed that the amounts of copolymers with long polypropylene sequences which are miscible with the matrix are higher in the case of three-step blends and also the elasticity of three-step polymerized blends is higher than two-step polymerized blends.     

Modified preparation of HDPE/clay nanocomposite by in situ polymerization using a metallocene catalyst

In this study, preparation of high-density polyethylene (HDPE)/clay nanocomposite by in situ polymerization of ethylene using a zirconocene catalyst (bis-(cyclopentadienyl) zirconium dichloride (Cp₂ZrCl₂)) was investigated. To obtain higher efficiency, nanoclay particles (Na-montmorillonite) were modified by ammonia (NH₃), NH₃/methylaluminoxane (MAO), NH₃/dodecylamine (DDA), and NH₃/MAO/DDA systems. The results showed that the activity of the catalyst supported on the nanoclay particles modified by NH₃/MAO (762 g_p/mmol (Zr) t [atm]) was higher than that of the one supported on the unmodified nanoclay as well as the other prepared modified nanoclay-supported catalyst systems. The catalyst activities versus MAO concentration in NH₃/MAO treatment system and versus DDA concentration in NH₃/DDA system showed a maximum. Unexpectedly, a very low catalyst activity (180 g_p/mmol(Zr) t [atm]) was obtained using NH₃/MAO/DDA system. X-ray diffraction patterns showed that the HDPE/clay nanocomposites prepared by NH₃/MAO/DDA treatment system had less intercalated structure. Fourier transform infrared (FTIR) spectroscopy confirmed that water molecules of the nanoclay particles were reduced by NH₃ modification. DSC results revealed that crystallinity of the HDPE/clay nanocomposites increased with the modification of the nanoclay particles. The maximum degree of crystallinity of 80.8% was obtained for HDPE/clay nanocomposites prepared by the nanoclay modified by NH₃. In addition, nanoclay modification with NH₃, NH₃/MAO, and NH₃/DDA systems resulted in higher thermal decomposition temperature (~30 °C higher than 480 °C of the unmodified one). Such increase was not observed for the NH₃/MAO/DDA treatment system. Dynamic mechanical analysis showed an increase in the elastic modulus of the nanocomposite samples prepared by modified nanoclay particles, as well. Meanwhile, modification of the nanoclay particles by NH₃ led to the highest elastic behavior compared to the other modification systems. It was about 4.6 GPa which was 28% higher than the elastic modulus of the nanocomposite prepared by unmodified nanoclay particles.