Anomalous crystalline ordering of particles in a viscoelastic fluid under high shear

Addition of particles to a viscoelastic suspension dramatically alters the properties of the mixture, particularly when it is sheared or otherwise processed. Shear-induced stretching of the polymers results in elastic stress that causes a substantial increase in measured viscosity with increasing shear, and an attractive interaction between particles, leading to their chaining. At even higher shear rates, the flow becomes unstable, even in the absence of particles. This instability makes it very difficult to determine the properties of a particle suspension. Here we use a fully immersed parallel plate geometry to measure the high-shear-rate behavior of a suspension of particles in a viscoelastic fluid. We find an unexpected separation of the particles within the suspension resulting in the formation of a layer of particles in the center of the cell. Remarkably, monodisperse particles form a crystalline layer which dramatically alters the shear instability. By combining measurements of the velocity field and torque fluctuations, we show that this solid layer disrupts the flow instability and introduces a new, single-frequency component to the torque fluctuations that reflects a dominant velocity pattern in the flow. These results highlight the interplay between particles and a suspending viscoelastic fluid at very high shear rates.Comment: SI Videos and future data sharing are available at https://doi.org/10.7910/DVN/K0XZ6

Persistence with Statins and Onset of Rheumatoid Arthritis: A Population-Based Cohort Study

In a retrospective cohort study, Gabriel Chodick and colleagues find a significant association between persistence with statin therapy and reduced risk of developing rheumatoid arthritis, but only a modest decrease in risk of osteoarthritis

Molecular mechanism for 3:1 subunit stoichiometry of rod cyclic nucleotide-gated ion channels

Molecular determinants of ion channel tetramerization are well characterized, but those involved in heteromeric channel assembly are less clearly understood. The heteromeric composition of native channels is often precisely controlled. Cyclic nucleotide-gated (CNG) channels from rod photoreceptors exhibit a 3:1 stoichiometry of CNGA1 and CNGB1 subunits that tunes the channels for their specialized role in phototransduction. Here we show, using electrophysiology, fluorescence, biochemistry, and X-ray crystallography, that the mechanism for this controlled assembly is the formation of a parallel 3-helix coiled-coil domain of the carboxy-terminal leucine zipper region of CNGA1 subunits, constraining the channel to contain three CNGA1 subunits, followed by preferential incorporation of a single CNGB1 subunit. Deletion of the carboxy-terminal leucine zipper domain relaxed the constraint and permitted multiple CNGB1 subunits in the channel. The X-ray crystal structures of the parallel 3-helix coiled-coil domains of CNGA1 and CNGA3 subunits were similar, suggesting that a similar mechanism controls the stoichiometry of cone CNG channels

Ethnicity and sexuality

This paper explores the connections between ethnicity and sexuality. Racial, ethnic, and national boundaries are also sexual boundaries. The borderlands dividing racial, ethnic, and national identities and communities constitute ethnosexual frontiers, erotic intersections that are heavily patrolled, policed, and protected, yet regularly are penetrated by individuals forging sexual links with ethnic "others." Normative heterosexuality is a central component of racial, ethnic, and nationalist ideologies; both adherence to and deviation from approved sexual identities and behaviors define and reinforce racial, ethnic, and nationalist regimes. To illustrate the ethnicity/sexuality nexus and to show the utility of revealing this intimate bond for understanding ethnic relations, I review constructionist models of ethnicity and sexuality in the social sciences and humanities, and I discuss ethnosexual boundary processes in several historical and contemporary settings: the sexual policing of nationalism, sexual aspects of US-American Indian relations, and the sexualization of the black-white color line