Asymmetric response of a jammed plastic bead raft

Fluctuation-dissipation relations have received significant attention as a potential method for defining an effective temperature in nonequilibrium systems. The successful development of an effective temperature would be an important step in the application of statistical mechanics principles to systems driven far from equilibrium. Many of the systems of interest are sufficiently dense that they are close to the jamming transition, a point at which interesting correlations develop. Here we study the response function in a driven system of plastic beads as a function of the density in order to elucidate the impact of the jamming transition on the use of fluctuation-dissipation relations. The focus is on measuring the response function for applied shear stress. We find that even when the amplitude of the applied stress leads to a linear response in the strain, the time scale of the response is dependent on the direction of the applied stress

Direct observation of twist mode in electroconvection in I52

I report on the direct observation of a uniform twist mode of the director field in electroconvection in I52. Recent theoretical work suggests that such a uniform twist mode of the director field is responsible for a number of secondary bifurcations in both electroconvection and thermal convection in nematics. I show here evidence that the proposed mechanisms are consistent with being the source of the previously reported SO2 state of electroconvection in I52. The same mechanisms also contribute to a tertiary Hopf bifurcation that I observe in electroconvection in I52. There are quantitative differences between the experiment and calculations that only include the twist mode. These differences suggest that a complete description must include effects described by the weak-electrolyte model of electroconvection

Fluorescence quenching of peptidyl tryptophan by external quenchers

Fluorescence quenching data have been collected on several small peptides (1-4) residues which contain tryptophan. These data have been analyzed by a variety of methods. The classical Stern-Volmer equation is utilized to obtain Stern-Volmer plots of fluorescence quenching data. Substantial upward curvature is observed in the Stern-Volmer plots of all the peptides studied. Data were also analyzed via the modified Stern-Volmer static quenching model. Although this model could explain the deviation from simple Stern-Volmer behavior found in SV plots, the parameters used by the model were often physically “unrealistic”: Therefore, another form of data analysis was used. The newly proposed Peak dynamic quenching model was tested. This model could explain the deviation from simple Stern-Volmer behavior in a physically tangible manner. A value for quenching efficiency E is derived from the Peak model. Finally, charge effects and ionic strength effects on fluorescence quenching are investigated. Some very interesting ionic strength effects have been found in the quenching data of several peptides. In the case of +TGG- vs. acrylamide, there appears to be a cation effect on quenching

Barriers to Higher Education: Underrepresented Minorities\u27 Access to UCI

Ever since the removal of Affirmative Action in California from Proposition 209, the UC system has struggled with increasing the enrollment numbers of underrepresented minorities on their campuses. In response to this, many of the UC schools are adopting different policies to help counteract the negative effects of Proposition 209. This paper examines the effects of Proposition 209 on the underrepresented minority population in the UC system, specifically focusing on the University of California, Irvine (UCI). The areas of focus for addressing the issues of Proposition 209 at UCI are outreach programs, admissions policies, and recruitment programs. This paper examines different policy options that other universities have utilized in each of these areas, and if it would be feasible for these policies to be adopted at UCI. The area the UCI is weakest in is recruitment, and it is also the area in which it is most feasible to implement change