Three-dimensional large-strain tensile deformation of neat and calcium carbonate-filled high-density polyethylene

The large-strain tensile deformation of high-density polyethylene and high-density polyethylene filled with two volume fractions (f) of calcium carbonate particles is studied via an optical method. Digital image correlation is used to determine the local displacement gradients and full-field displacements during uniaxial tension tests on specimens of rectangular cross-section. A novel technique measures simultaneously, with a single camera, the deformation in all three dimensions. Full-field strain contours, macroscopic true stress-true strain behavior, and local volumetric strains are reduced from the raw test data. The true stress-true strain data shows an increase in modulus, but a decrease in yield stress and subsequent strain hardening, with increasing f. These results are strong evidence of particle debonding and are corroborated by an increase in volumetric strain with increasing f.     

The nuclear freeze resolution: A question of empowerment.

The American Psychological Association has done little to empower the nuclear freeze resolution (NFR) adopted in 1982. The general debate on the issues of advocacy, competency, and ethics should be suspended so that the issues associated specifically with the NFR can be resolved. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Social Media and Political Change: Capacity,Constraint, and Consequence

This introductory essay highlights the key findings, methodological tool kit, and production process of this Special Issue. We argue that communication researchers are uniquely positioned to analyze the relationships between social media and political change in careful and nuanced ways, in terms of both causes and consequences. Finally, we offer a working definition of social media, based on the diverse and considered uses of the term by the contributors to the collection. Social media consists of (a) the information infrastructure and tools used to produce and distribute content that has individual value but reflects shared values; (b) the content that takes the digital form of personal messages, news, ideas, that becomes cultural products; and (c) the people, organizations, and industries that produce and consume both the tools and the content.     

Stimulation of large-conductance Ca2+-activated K+ channels by Evans blue in cultured endothelial cells of human umbilical veins

The effect of Evans blue (EB) on large-conductance Ca2+-activated K+ (BKCa) channels was investigated in cultured endothelial cells of human umbilical veins. In whole-cell configuration, EB (50 microM) reversibly increased the amplitude of K+ outward currents (IK). When the patch pipettes were filled with 10 mM EGTA, its stimulatory effect on IK was unaltered. Further application of EB in the presence of suramin, a blocker of P2-purinergic receptor, or AOPCP, an inhibitor of 5'-nucleotidase, still increased IK. However, charybdotoxin (100 nM) suppressed EB-induced increase in IK. In inside-out configuration, bath application of EB (50 microM) did not change single channel conductance but significantly increased the activity of BKCa channels. The EB-induced increase in the activity of BKCa channels was independent on internal Ca2+. EB (50 microM) shifted the activation curve of BKCa channels to less positive membrane potentials by approximately 20 mV. The change in the kinetic behavior of BKCa channels caused by EB in these cells is due to an increase in mean open time and a decrease in mean closed time. These results indicate that EB can stimulate the activity of BKCa channel in endothelial cells. This effect is unrelated to its blockade of P2-purinergic receptors or inhibition of 5'-nucleotidase. The direct stimulation of these ionic channels by EB may contribute to its effect on capillary permeability.     

Enzymatic characteristics of recombinant medium isozyme of 2'-5' oligoadenylate synthetase

P69 is an isozyme of the medium size class of human 2'-5' oligoadenylate synthetases. In this study, recombinant P69 was expressed and used for enzymological and structural investigations. Bacterially expressed P69 was inactive whereas the same protein expressed in insect cells was highly active. Whether this difference could be due to differential post-translational modifications of the protein was investigated. Mutations of appropriate residues showed that myristoylation of the protein was not necessary for enzyme activity. In contrast, inhibition of glycosylation of P69, by tunicamycin treatment of the insect cells, produced an enzymatically inactive protein. Recombinant P69 produced in insect cells was purified by affinity chromatography. It was a dimeric glycoprotein, very stable and completely dependent on double stranded (ds) RNA for activity. The enzyme catalyzed the non-processive synthesis of 2'-5'-linked oligoadenylate products containing up to 30 residues. 2'-O-Methylated dsRNA was incapable of activating P69 and a 25-base pair dsRNA was as effective as larger dsRNA. This expression system will be useful for large scale production of P69 and its mutants for structural studies.