Breaking free of electrical constraints

Photonic interconnections provide a viable means to overcome the fundamental limitations imposed upon computer system topologies by electrical signaling. Direct board-to-board (or assembly-to-assembly) signaling, without need of a backplane, provides multiple points of connectivity between adjacent electronic complexes while obviating the need to route all board-level signals to and through a central connector choke point. Optical busses can permit full-speed signaling between multiple chips, memory units, or processing units without requiring an active control plane. One-to-many and all-to-all photonic broadcasts greatly simplify multi-processor and multi-core system design.     

Improved morphology for epitaxial growth on 4° off-axis 4H-SiC substrates

A process optimization of the growth of silicon carbide (SiC) epilayers on 4° off-axis 4H-SiC substrates is reported. Process parameters such as growth temperature, C/Si ratio and temperature ramp-up conditions are optimized for the standard non-chlorinated growth in order to grow smooth epilayers without step bunching and triangular defects. The growth of 6-μm-thick n-type-doped epitaxial layers on 75-mm-diameter wafers is demonstrated as well as that of 20-μm-thick layer. The optimized process was then transferred to a chloride-based process and a growth rate of 28 μm/h was achieved without morphology degradation. A low growth temperature and a low C/Si ratio are the key parameters to reduce both the step bunching and the formation of triangular defects.     

Jet quenching and elliptic flow

In jet quenching, a hard QCD parton, before fragmenting into a jet of hadrons, deposits a fraction of its energy in the medium, leading to suppressed production of high-pT$p_T$ hadrons. Assuming that the deposited energy quickly thermalizes, we simulate the subsequent hydrodynamic evolution of the QGP fluid. Explicit simulation of Au + Au collision with and without a quenching jet indicate that elliptic flow is greatly reduced in a jet event. The result can be used to identify the jet events in heavy ion collisions.     

Effect of the oxidation process on SiO2/4H-SiC interface electrical characteristics

In this work we have compared the SiO₂/SiC interface electrical characteristics for three different oxidations processes (dry oxygen, water-containing oxygen and water-containing nitrogen atmospheres). MOS structures were fabricated on 8° off-axis 4H-SiC(0 0 0 1) n- and p-type epi-wafers. Electrical characteristics were obtained by I-V measurements, high-frequency capacitance-voltage (C-V) and ac conductance (G-ω) methods. Comparing the results, one observes remarkable differences between samples which underwent different oxidation routes. Among the MOS structures analyzed, the sample which underwent wet oxidation with oxygen as carrier gas presented the higher dielectric strength and lower values of interface states density.     

Etchability of Latent Fission Fragment Tracks in CR-39

We report the chemical etching behaviour of the CR-39 polymer detector exposed to fission fragments of 252Cf describing etchability of latent tracks, which are like nanocylinders. The fission fragment exposed detectors were etched in 1-7 N NaOH water solutions at temperatures 50-80℃ for 45 min in the case of track length and 180 min in the case of track diameter measurements. The reduced etch rate S （called here etchability） is determined using experimental results for all etching conditions and the etching conditions with the highest reduced etch are obtained. Physics and energetics of bulk and track etching are discussed. Possible effects causing spurious changes in determination of activation energy of etching are investigated.     

Crystal field and molecular structure in solid C60

The crystal field in the orientationally disordered phase of C₉₀-fullerite is derived from an intermolecular potential model, which takes into account the geometric difference between double bonds and single bonds. The molecules are modelled as rigid bodies, atoms and single bonds are treated as single interaction centers, while double bonds are described by a distribution of interaction centers along the bond. The crystal field is expanded in terms of cubic rotator functions. The calculated expansion coefficients are compared with empirical values derived from diffraction data. The angular dependence of the crystal field, resulting from an anticlockwise rotation of the molecule around the [111] axis, exhibits an absolute and a secondary minimum at angles of 98° and 38° respectively. The self interaction of the molecule in a deformable lattice is investigated.     

Saturation intensity for ultrashort-pulse X-ray laser schemes

Analytic expressions are obtained for the saturation intensity in X-ray laser schemes based on short-pulse high-intensity drivers. For field-ionized plasma schemes, the specific mean saturation intensityJ _sat is time independent and depends only on atomic transition probabilities, level degeneracies, and transition energies. The analytic expression is found to be in good agreement with a detailed numerical calculation. Integrating over space and frequency gives a saturation intensityI _sat of order 2 × 10¹¹ W/cm² for lasing in Li-like Ne at 98 . The low input energy requirements for this scheme (< 1 J), associated with using a confocal geometry, give energy efficiencies of order 10^–6 and greater. For inner-shell photo-ionization schemes, an accurate expression for a time-dependent saturation intensity is obtained. This scheme is calculated to have high saturation intensities,I _sat 10¹³ W/cm², at short wavelengths (5–15 ). The requirement of a line focus geometry leads to higher input energies (5 J) and the short duration of lasing (50 fs) results in lower energy efficiencies ( 10^–7). Repetition rates are important in determining appropriate applications for both schemes.     

Acylpyrazolone ligands: Synthesis, structures, metal coordination chemistry and applications

This review summarizes the literature on 4-acyl-5-pyrazolone ligands, their synthesis, characterization and coordination chemistry toward main group, transition, lanthanide and actinide metals and relevant applications of their metal complexes.     

NMR and pressure correlated analysis of metabolic changes in soft-X-rays irradiated yeast cells

An NMR technique for the identification of the energy related molecules, AMP, ADP and ATP, is suitably taylored to follow up the dynamics of the glycolitic metabolism in a suspension of yeast cells. Such a technique proves to be efficient to investigate soft X-ray radiation damage as complementary to other physical and chemical assessment. Received: 13 October 1998 / Accepted: 30 October 1998     

Relativistic calculation of Lβ2 satellite spectra of W and Au

Lβ₂ X-ray satellite spectra of tungsten and gold are calculated using the Multi-Configuration Dirac-Fock energies and compared with recent experimental data. New calculations of L₁-L₃M₅ Coster-Kronig transition energies for tungsten are presented, confirming the origin of the Lβ₂ visible satellites reported by two experimental groups. We found the value 5.09 eV for the average energy of the L₁-L₃M₅ Coster-Kronig transition in tungsten. The Lβ₂ satellite spectrum of tungsten was calculated in the framework of a statistical model, which makes use of Racah's algebra. A detailed calculation of the Lβ₂ and Lβ₁₅ satellite spectra was performed for gold.