Elliptic flow measurements at RHIC suggest that quark gluon plasma flows with very little viscosity compared to weak coupling expectations, challenging theorists to explain why this fluid is so nearly "perfect". It is therefore vital to find quantitative experimental information on the viscosity of the plasma. We propose that measurements of transverse momentum fluctuations can be used to determine the shear viscosity. We use current data to estimate the viscosity-to-entropy ratio in the range from 0.08 to 0.3, and discuss how future measurements can reduce this uncertainty. Measurements of elliptic and radial flow at RHIC are described by viscosity-free hydrodynamics, indicating that the quark-gluon system produced in these collisions is a nearly perfect liquid [1,2,3,4]. In particular, the strong suppression of flow due to shear viscosity predicted by weak-coupling transport calculations is not observed [2]. This result is exciting because a small viscosity relative to the entropy density of the system may indicate that the system is more strongly coupled than expected: The collisional shear viscosity is proportional to the mean free path, which is shorter when the coupling is stronger. But is the viscosity really small? Hirano et al. point out that color glass condensate formation may produce more elliptic flow than considered in refs. [1,2], requiring a larger viscosity for agreement with data [5].We seek an experimental probe of viscosity that is independent of elliptic flow. To that end, we propose that transverse momentum correlation measurements can be used to extract information on the kinematic viscosity,where η is the shear viscosity, s is the entropy density and T is the temperature. This ratio characterizes the strength of the viscous force relative to the fluid's inertia and, consequently, determines the effect of η on the flow [3]. We argue that viscous diffusion broadens the rapidity dependence of transverse momentum correlations, and then show how these correlations can be extracted from measurements of event-by-event p t fluctuations. A number of experiments have studied transverse momentum fluctuations at SPS and RHIC [6,7]. Interestingly, the STAR collaboration reports a 60% increase of the relative rapidity width for p t fluctuations when centrality is increased [8]. While the STAR analysis differs from the one we propose, model assumptions provide a tantalizing hint that the viscosity is small.Any experimental information on the kinematic viscosity of high energy density matter is vital for understanding the strongly interacting quark gluon plasma. Theorists had long anticipated a large collisional viscosity based on weak coupling QCD [9] and hadronic computations [10], with values of η/s roughly of order unity for both phases near the crossover temperature ∼ 170 MeV. Supersymmetic Yang Mills calculations give the significantly smaller ratio η/s = 1/4π in the strong coupling limit [11]. Lattice QCD calculations of the shear viscosity will eventually settle the question of the size of the vi...

In patients chronically infected with hepatitis C virus (HCV) genotype 4, the optimum duration of therapy and the predictors of sustained virologic response (SVR) have not been adequately determined. In this study, 358 patients with chronic hepatitis C genotype 4 were randomly assigned to pegylated interferon (PEG-IFN) alpha-2b (1.5 g/kg/week) plus oral ribavirin (10.6 mg/kg/day) for a fixed duration of 48 weeks (control group, n ‫؍‬ 50) or for a variable duration (n ‫؍‬ 318). In the variable-duration group, patients with undetectable HCV RNA at week 4 were treated for 24 weeks (group A, n ‫؍‬ 69), patients with undetectable HCV RNA at week 12 were treated for 36 weeks (group B, n ‫؍‬ 79), and the rest of the patients were treated for 48 weeks (group C, n ‫؍‬ 160). The primary endpoint was SVR (undetectable HCV RNA 24 weeks after treatment cessation). Groups A-C and the control group had SVR rates of 86%, 76%, 56%, and 58%, respectively. After the study was controlled for predictors, a low baseline histologic grade and stage were associated with SVR (P < 0.029) in all groups. In addition, among patients in group C, older age (P ‫؍‬ 0.04), a higher baseline body mass index (P ‫؍‬ 0.013), and low baseline HCV RNA (P < 0.001) were also associated with SVR attainment. The incidence of adverse events and the rate of discontinuation were higher in patients in the variable-duration and fixed-duration groups treated for 48 weeks. Conclusion: In patients with chronic hepatitis C genotype 4 and undetectable HCV RNA at weeks 4 and 12, treatment with PEG-IFN alpha-2b and ribavirin for 24 weeks and 36 weeks, respectively, is sufficient. (HEPATOLOGY

We use the ultra-relativistic quantum molecular dynamic UrQMD version 2.2 to study forward backward fluctuations and compare our results with the published data by the PHOBOS.Comment: 4 pages, 6 figures, poster presented at Strong & Electroweak Matter (SEWM2006), BNL, United States, May 10-13 200

No abstract

Path tracking is one of the most important aspects of autonomous vehicles. The current research focuses on designing path-tracking controllers taking into account the stability of the yaw and the nonholonomic constraints of the vehicle. In most cases, the lateral controller design relies on identifying a path reference point, the one with the shortest distance to the vehicle giving the current state of the vehicle. That restricts the controller’s ability to handle sudden changes of the trajectory heading angle. The present article proposes a new approach that imitates human behavior while driving. It is based on a discrete prediction model that anticipates the future states of the vehicle, allowing the use of the control algorithm in future predicted states augmented with the current controller output. The performance of the proposed approach is verified through several simulations on V-REP simulator with different types of maneuvers (double lane change, hook road, S road, and curved road) and a wide range of velocities. Predictive Stanley controller was used compared to the original Stanley controller. The obtained results of the proposed control approach show the advantage and the performance of the technique in terms of minimizing the lateral error and ensuring yaw stability by an average of 53% and 22%, respectively.