Thermalization and the chromo-Weibel instability

Despite the apparent success of ideal hydrodynamics in describing the elliptic flow data which have been produced at Brookhaven National Lab's Relativistic Heavy Ion Collider, one lingering question remains: is the use of ideal hydrodynamics at times t < 1 fm/c justified? In order to justify its use a method for rapidly producing isotropic thermal matter at RHIC energies is required. One of the chief obstacles to early isotropization/thermalization is the rapid longitudinal expansion of the matter during the earliest times after the initial nuclear impact. As a result of this expansion the parton distribution functions become locally anisotropic in momentum space. In contrast to locally isotropic plasmas anisotropic plasmas have a spectrum of soft unstable modes which are characterized by exponential growth of transverse chromo-magnetic/-electric fields at short times. This instability is the QCD analogue of the Weibel instability of QED. Parametrically the chromo-Weibel instability provides the fastest method for generation of soft background fields and dominates the short-time dynamics of the system.Comment: 8 pages, 4 figures, Invited plenary talk given at the 19th International Conference on Ultrarelativistic Nucleus-Nucleus Collisions: Quark Matter 2006 (QM 2006), Shanghai, China, 14-20 Nov 200

Influence of wear algorithm formulation on computational-experimental corroboration

Experimental wear testing is well-established as an important part of the TKR design process. Recently, in-silico models have proved their value to corroborate long-term in-vitro results on a much shorter timescale [1]. Both FE-based models &amp; multi-body dynamics can be used to predict contact pressures, sliding distances and cross-shear (CS). The precise mechanisms of wear are not sufficiently understood to permit analytical calculations, and so empirical formulations are used to estimate wear depths &amp; volumes.Most early simulations were based on a modified Archard/Lancaster formulation; more recently a number of alternative formulations for cross shear have been proposed; it is unclear which is the most robust or accurate for the widest range of activities. The aim of this study was to develop and corroborate a fast in-silico wear model, and use this to compare different wear formulations

Colour Coherence in Photon Induced Reactions

Colour coherence in hard photoproduction is considered using the Monte Carlo event generators PYTHIA and HERWIG. Significant effects in the parton shower are found using multijet observables for direct and resolved photon induced reactions. The particle flow in the interjet region of direct processes shows a strong influence of string fragmentation effects.Comment: 6 pages, LaTeX, 6 eps figures included, to appear in the proceedings of the workshop "Future Physics at HERA

Spatially Resolved [FeII] 1.64 \mu m Emission in NGC 5135. Clues for Understanding the Origin of the Hard X-rays in Luminous Infrared Galaxies

Spatially resolved near-IR and X-ray imaging of the central region of the Luminous Infrared Galaxy NGC 5135 is presented. The kinematical signatures of strong outflows are detected in the [FeII]1.64 \mu m emission line in a compact region at 0.9 kpc from the nucleus. The derived mechanical energy release is consistent with a supernova rate of 0.05-0.1 yr$^{-1}$. The apex of the outflowing gas spatially coincides with the strongest [FeII] emission peak and with the dominant component of the extranuclear hard X-ray emission. All these features provide evidence for a plausible direct physical link between supernova-driven outflows and the hard X-ray emitting gas in a LIRG. This result is consistent with model predictions of starbursts concentrated in small volumes and with high thermalization efficiencies. A single high-mass X-ray binary (HMXB) as the major source of the hard X-ray emission although not favoured, cannot be ruled out. Outside the AGN, the hard X-ray emission in NGC 5135 appears to be dominated by the hot ISM produced by supernova explosions in a compact star-forming region, and not by the emission due to HMXB. If this scenario is common to U/LIRGs, the hard X-rays would only trace the most compact (< 100 pc) regions with high supernova and star formation densities, therefore a lower limit to their integrated star formation. The SFR derived in NGC 5135 based on its hard X-ray luminosity is a factor of two and four lower than the values obtained from the 24 \mu m and soft X-ray luminosities, respectively.Comment: Accepted for Publication in ApJ, 18 pages, 2 figure

QGP collective effects and jet transport

We present numerical simulations of the SU(2) Boltzmann-Vlasov equation including both hard elastic particle collisions and soft interactions mediated by classical Yang-Mills fields. We provide an estimate of the coupling of jets to a hot isotropic plasma, which is independent of infrared cutoffs. In addition, we investigate jet propagation in anisotropic plasmas, as created in heavy-ion collisions. The broadening of jets is found to be stronger along the beam line than in azimuth due to the creation of field configurations with B_t>E_t and E_z>B_z via plasma instabilities.Comment: 4 pages, 5 figures. Presented at the 20th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions: Quark Matter 2008 (QM2008), Jaipur, India, 4-10 Feb 200