Elliptic Flow from a Transversally Thermalized Fireball

The agreement of elliptic flow data at RHIC at central rapidity with the hydrodynamic model has led to the conclusion of very rapid thermalization. This conclusion is based on the intuitive argument that hydrodynamics, which assumes instantaneous local thermalization, produces the largest possible elliptic flow values and that the data seem to saturate this limit. We here investigate the question whether incompletely thermalized viscous systems may actually produce more elliptic flow than ideal hydrodynamics. Motivated by the extremely fast primordial longitudinal expansion of the reaction zone, we investigate a toy model which exhibits thermalization only in the transverse directions but undergoes collisionless free-streaming expansion in the longitudinal direction. For collisions at RHIC energies, elliptic flow results from the model are compared with those from hydrodynamics. With the final particle yield and \kt-distribution fixed, the transversally thermalized model is shown not to be able to produce the measured amount of elliptic flow. This investigation provides further support for very rapid local kinetic equilibration at RHIC. It also yields interesting novel results for the elliptic flow of massless particles such as direct photons.Comment: revtex4, 15 pages + 10 embedded EPS figure

Coherent transport in Nb/delta-doped-GaAs hybrid microstructures

Coherent transport in Nb/GaAs superconductor-semiconductor microstructures is presented. The structures fabrication procedure is based on delta-doped layers grown by molecular-beam-epitaxy near the GaAs surface, followed by an As cap layer to protect the active semiconductor layers during ex situ transfer. The superconductor is then sputter deposited in situ after thermal desorption of the protective layer. Two types of structures in particular will be discussed, i.e., a reference junction and the engineered one that contains an additional insulating AlGaAs barrier inserted during the growth in the semiconductor. This latter configuration may give rise to controlled interference effects and realizes the model introduced by de Gennes and Saint-James in 1963. While both structures show reflectionless tunneling-dominated transport, only the engineered junction shows additionally a low-temperature single marked resonance peaks superimposed to the characteristic Andreev-dominated subgap conductance. The analysis of coherent magnetotransport in both microstructures is successfully performed within the random matrix theory of Andreev transport and ballistic effects are included by directly solving the Bogoliubov-de Gennes equations. The impact of junction morphology on reflectionless tunneling and the application of the employed fabrication technique to the realization of complex semiconductor-superconductor systems are furthermore discussed.Comment: 9 pages, 8 figures, invited review paper, to be published in Mod. Phys. Lett.

Melt-growth dynamics in CdTe crystals

We use a new, quantum-mechanics-based bond-order potential (BOP) to reveal melt-growth dynamics and fine-scale defect formation mechanisms in CdTe crystals. Previous molecular dynamics simulations of semiconductors have shown qualitatively incorrect behavior due to the lack of an interatomic potential capable of predicting both crystalline growth and property trends of many transitional structures encountered during the melt $\rightarrow$ crystal transformation. Here we demonstrate successful molecular dynamics simulations of melt-growth in CdTe using a BOP that significantly improves over other potentials on property trends of different phases. Our simulations result in a detailed understanding of defect formation during the melt-growth process. Equally important, we show that the new BOP enables defect formation mechanisms to be studied at a scale level comparable to empirical molecular dynamics simulation methods with a fidelity level approaching quantum-mechanical method

Heavy Quarkonia and Quark Drip Lines in Quark-Gluon Plasma

Using the potential model and thermodynamical quantities obtained in lattice gauge calculations, we determine the spontaneous dissociation temperatures of color-singlet quarkonia and the `quark drip lines' which separate the region of bound $Q\bar Q$ states from the unbound region. The dissociation temperatures of $J/\psi$ and $\chi_b$ in quenched QCD are found to be 1.62$T_c$ and $1.18T_c$ respectively, in good agreement with spectral function analyses. The dissociation temperature of $J/\psi$ in full QCD with 2 flavors is found to be 1.42$T_c$. For possible bound quarkonium states with light quarks, the characteristics of the quark drip lines severely limit the stable region close to the phase transition temperature. Bound color-singlet quarkonia with light quarks may exist very near the phase transition temperature if their effective quark mass is of the order of 300-400 MeV and higher.Comment: 8 pages, 2 figures, in LaTex, invited talk presented at the International Conference on Strangeness in Quark Matter, UCLA, March 26-31, 200

The universal functorial equivariant Lefschetz invariant

We introduce the universal functorial equivariant Lefschetz invariant for endomorphisms of finite proper G-CW-complexes, where G is a discrete group. We use K_0 of the category of "phi-endomorphisms of finitely generated free RPi(G,X)-modules". We derive results about fixed points of equivariant endomorphisms of cocompact proper smooth G-manifolds.Comment: 33 pages; shortened version of the author's PhD thesis, supervised by Wolfgang Lueck, Westfaelische Wilhelms-Universitaet Muenster, 200

Void Formation Study of Flip Chip in Package Using No-Flow Underfill

©2008 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or distribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.DOI: 10.1109/TEPM.2008.2002951The advanced flip chip in package (FCIP) process using no-flow underfill material for high I/O density and fine-pitch interconnect applications presents challenges for an assembly process that must achieve high electrical interconnect yield and high reliability performance. With respect to high reliability, the voids formed in the underfill between solder bumps or inside the solder bumps during the no-flow underfill assembly process of FCIP devices have been typically considered one of the critical concerns affecting assembly yield and reliability performance. In this paper, the plausible causes of underfill void formation in FCIP using no-flow underfill were investigated through systematic experimentation with different types of test vehicles. For instance, the effects of process conditions, material properties, and chemical reaction between the solder bumps and no-flow underfill materials on the void formation behaviors were investigated in advanced FCIP assemblies. In this investigation, the chemical reaction between solder and underfill during the solder wetting and underfill cure process has been found to be one of the most significant factors for void formation in high I/O and fine-pitch FCIP assembly using no-flow underfill materials

Fully nonlinear excitations of non-Abelian plasma

We investigate fully nonlinear, non-Abelian excitations of quark-antiquark plasma, using relativistic fluid theory in cold plasma approximation. There are mainly three important nonlinearities, coming from various sources such as non-Abelian interactions of Yang-Mills (YM) fields, Wong's color dynamics and plasma nonlinearity, in our model. By neglecting nonlinearities due to plasma and color dynamics we get back the earlier results of Blaizot {\it et. al.}, Phys. Rev. Lett. 72, 3317 (1994). Similarly, by neglecting YM fields nonlinearity and plasma nonlinearity, it reduces to the model of Gupta {\it et. al.}, Phys. Lett. B498, 223 (2005). Thus we have the most general non-Abelian mode of quark-gluon plasma (QGP). Further, our model resembles the problem of propagation of laser beam through relativistic plasma, Physica 9D, 96 (1983). in the absence of all non-Abelian interactions.Comment: 8 pages, 2 figures, articl

Topo-Geometric Filtration Scheme for Geometric Active Contours and Level Sets: Application to Cerebrovascular Segmentation

One of the main problems of the existing methods for the segmentation of cerebral vasculature is the appearance in the segmentation result of wrong topological artefacts such as the kissing vessels. In this paper, a new approach for the detection and correction of such errors is presented. The proposed technique combines robust topological information given by Persistent Homology with complementary geometrical information of the vascular tree. The method was evaluated on 20 images depicting cerebral arteries. Detection and correction success rates were 81.80% and 68.77%, respectively

Today's problems with the evaluation methods of full lightning impulse parameters as described in IEC 60060-1

In this paper the present problems with the evaluation methods for lightning impulse parameters, as defined in IEC 60060-1, are described. Also the current practice of evaluation in many laboratories world-wide, that is obtained by a questionnaire, is presented. Some of the work performed up the present time and the initial conclusions are reported, then some recommendations are made for future work