Reversible gelation and dynamical arrest of dipolar colloids

We use molecular dynamics simulations of a simple model to show that dispersions of slightly elongated colloidal particles with long-range dipolar interactions, like ferrofluids, can form a physical (reversible) gel at low volume fractions. On cooling, the particles first self-assemble into a transient percolating network of cross-linked chains, which, at much lower temperatures, then undergoes a kinetic transition to a dynamically arrested state with broken ergodicity. This transition from a transient to a frozen gel is characterised by dynamical signatures reminiscent of jamming in much denser dispersions.Comment: 6 pages, 7 figure

Structural trends in clusters of quadrupolar spheres

The influence of quadrupolar interactions on the structure of small clusters is investigated by adding a point quadrupole of variable strength to the Lennard-Jones potential. Competition arises between sheet-like arrangements of the particles, favoured by the quadrupoles, and compact structures, favoured by the isotropic Lennard-Jones attraction. Putative global potential energy minima are obtained for clusters of up to 25 particles using the basin-hopping algorithm. A number of structural motifs and growth sequences emerge, including star-like structures, tubes, shells and sheets. The results are discussed in the context of colloidal self-assembly.Comment: 8 pages, 6 figure

Color Transparency at COMPASS energies

Pionic quasielastic knockout of protons from nuclei at 200 GeV show very large effects of color transparency as -t increases from 0 to several GeV^2. Similar effects are expected for quasielastic photoproduction of vector mesons.Comment: 9 pages, 4 figure

Experimental Characterization of Roughness and Flow Injection Effects in a High Reynolds Number Turbulent Channel

A turbulent channel flow was used to study the scaling of the combined effects of roughness and flow injection on the mean flow and turbulence statistics of turbulent plane Poiseuille flow. It was found that the additional momentum injected through the rough surface acted primarily to enhance the roughness effects and, with respect to the mean flow, blowing produced similar mean flow effects as increasing the roughness height. This was not found to hold for the turbulence statistics, as a departure from Townsend’s hypothesis was seen. Instead, the resulting outer-scaled streamwise Reynolds stress for cases with roughness and blowing deviated significantly from the roughness only condition well throughout the inner and outer layers. Investigation into this phenomena indicated that suppression of the large-scale motions due to blowing may have been contributing to this deviation

The Clean Air Act Amendments of 1990 and an Unbridled Spending Power: Will They Survive on the Supreme Court\u27s Road to Substantive Federalism

The question remains as to how far the Supreme Court will go in its refortification of the Tenth Amendment. This Note explores emerging federalism trends and evaluates the CAA in light of a stronger state sovereignty that is appearing on the constitutional horizon. Parts II and III examine the CAAA and the constitutional problems engendered by the Act. Part IV examines current Tenth Amendment and Spending Clause jurisprudence, and illustrates that the CAAA is a classic example of how Congress has been able to circumvent the Tenth Amendment with its Spending power. Part V presents a new view of federalism that is materializing in Commerce Clause and Eleventh Amendment doctrine, and extends that theory to the Tenth Amendment in the hope of finding a substantive bar on Congress\u27s excessive use of the Spending power. Part VI calls for a restructuring of the CAAA to promote its high objectives, and concludes that unless the Act falls in line with the substantive federalism trend, its objectives will not be fulfilled

Structural relaxation in Morse clusters: Energy landscapes

We perform a comprehensive survey of the potential energy landscapes of 13-atom Morse clusters, and describe how they can be characterized and visualized. Our aim is to detail how the global features of the funnel-like surface change with the range of the potential, and to relate these changes to the dynamics of structural relaxation. We find that the landscape becomes rougher and less steep as the range of the potential decreases, and that relaxation paths to the global minimum become more complicated.Comment: 21 pages, 3 tables, 5 figure