The applicability of causal dissipative hydrodynamics to relativistic heavy ion collisions

We utilize nonequilibrium covariant transport theory to determine the region of validity of causal Israel-Stewart dissipative hydrodynamics (IS) and Navier-Stokes theory (NS) for relativistic heavy ion physics applications. A massless ideal gas with 2->2 interactions is considered in a 0+1D Bjorken scenario, appropriate for the early longitudinal expansion stage of the collision. In the scale invariant case of a constant shear viscosity to entropy density ratio eta/s ~ const, we find that Israel-Stewart theory is 10% accurate in calculating dissipative effects if initially the expansion timescale exceeds half the transport mean free path tau0/lambda0 > ~2. The same accuracy with Navier-Stokes requires three times larger tau0/lambda0 > ~6. For dynamics driven by a constant cross section, on the other hand, about 50% larger tau0/lambda0 > ~3 (IS) and ~9 (NS) are needed. For typical applications at RHIC energies s_{NN}**(1/2) ~ 100-200 GeV, these limits imply that even the Israel-Stewart approach becomes marginal when eta/s > ~0.15. In addition, we find that the 'naive' approximation to Israel-Stewart theory, which neglects products of gradients and dissipative quantities, has an even smaller range of applicability than Navier-Stokes. We also obtain analytic Israel-Stewart and Navier-Stokes solutions in 0+1D, and present further tests for numerical dissipative hydrodynamics codes in 1+1, 2+1, and 3+1D based on generalized conservation laws.Comment: 30 pages, 26 EPS figures, revtex stylefil

Product Development from Veneer-Mill Residues: An Application of the Taguchi's Method

The raw material used for decorative (face) veneer manufacturing consists mainly of hardwood logs, the highest in quality harvested for industrial purposes. Besides the common sawmill residuals, the clipping operation in the process produces quite long, strand-type vestiges, and large end-clipping cutoffs. During the course of the research project presented in this article, structural composite materials were designed and formulated using these clipping residues as principal furnish materials. A robust statistical product development technique, the Taguchi's method, helped to identify the effect of component factors on the expected mechanical properties of these novel products.Results of three-factor/three-level analyses indicated that there is a linear positive correlation between target density and performance attributes (MOE and MOR). Increasing the content of end-clippings up to 25% resulted in decline of strength and stiffness. However, when the ratio was over 1 to 4, this trend proved to be negligible. Resin solid content within the selected range had no significant control over the examined panel properties

A low-power, radiation-hard gigabit serializer for use in the CMS electromagnetic calorimeter

An integrated fiber-optic bit serializer and VCSEL driver has been constructed in radiation-hard complementary heterostructure GaAs FET (CHFET) technology. The serializer, which converts 20 parallel inputs into a high-speed serial output, consumes 60 mW at nominal supply voltage when operating at the Large Hadron Collider word rate of 40 MHz (0.8-GB/s serial rate). The integrated driver directly drives a VCSEL and provides 10-mA switched current and 5 mA of prebias. The complete digital optical link thus consumes 90 mW. (6 refs)

Monolithic Pixel Sensors in Deep-Submicron SOI Technology

Monolithic pixel sensors for charged particle detection and imaging applications have been designed and fabricated using commercially available, deep-submicron Silicon-On-Insulator (SOI) processes, which insulate a thin layer of integrated full CMOS electronics from a high-resistivity substrate by means of a buried oxide. The substrate is contacted from the electronics layer through vias etched in the buried oxide, allowing pixel implanting and reverse biasing. This paper summarizes the performances achieved with a first prototype manufactured in the OKI 0.15 micrometer FD-SOI process, featuring analog and digital pixels on a 10 micrometer pitch. The design and preliminary results on the analog section of a second prototype manufactured in the OKI 0.20 micrometer FD-SOI process are briefly discussed.Comment: Proceedings of the PIXEL 2008 International Workshop, FNAL, Batavia, IL, 23-26 September 2008. Submitted to JINST - Journal of Instrumentatio