Inhibition of adenosine deaminase by erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA) mimics the effect of inescapable shock on escape learning in rats.

Three experiments examined the role of adenosine neuroregulation in the production of shuttle-escape deficits caused by prior exposure to inescapable electric shock in rats (learned helplessness). Intracerebroventricular administration of erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA), a selective adenosine deaminase inhibitor, mimicked the effect of earlier inescapable shock at a dose of 2.5 μM in previously restrained rats. Performance deficits produced by EHNA or by earlier exposure to inescapable shock were reversed by intraperitoneal injection of 10 mg/kg caffeine, an adenosine receptor antagonist. Finally, preexposure to an ineffective number of shocks interacted in synergy with an ineffective pretest dose (1.0 μM) of EHNA to maximize shuttle-escape latencies. These data implicate endogenous adenosine neuroregulation as a proximate mechanism in learned helplessness and conservation-withdrawal. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Team productivity and contradiction of management policy commitments.

What is the relationship between management consistency of policy and team productivity? "A simulated small industrial plant was the setting for an experiment in which a team of Ss worked together on a manufacturing problem. Their assigned task was to produce different kinds of toys at a profit… . Twenty four-man teams were divided into ten consecutive team pairs, each member of a pair being subjected either to (a) a condition under which the team's expectations of management were contradicted by subsequent events or (b) a condition under which the team's expectations were confirmed. The hypothesis that team productivity would be greater under the confirmation condition was supported by the data. Some theoretical implications of the experiment were suggested." (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of calcium chelators on physical changes in casein micelles in concentrated micellar casein solutions

The effect of calcium chelators on physical changes of casein micelles in concentrated micellar casein solutions was investigated by measuring calcium-ion activity, viscosity and turbidity, and performing ultracentrifugation. The highest viscosities were measured on addition of sodium hexametaphosphate (SHMP), because it cross-linked the caseins. For the weak calcium chelator disodium uridine monophosphate (Na₂UMP), physical changes in the solutions were negligible. Disodium hydrogen phosphate (Na₂HPO₄), trisodium citrate (TSC), and sodium phytate (SP) caused similar increases in viscosity, but had different effects on turbidity. The increase in viscosity was attributed to swelling of the casein micelles (i.e., increased voluminosity) at decreasing calcium-ion activity. The major decrease in turbidity was due to dissociation of the casein micelles. The extent of micellar dissociation was dependent on the type and concentration of calcium chelator. It seems that the micelles were dissociated in the order of SHMP ≥ SP > TSC > Na₂HPO₄ > Na₂UMP.     

The equilibrium moisture content of tung fruit and its components at different relative humidities

Summary The equilibrium moisture contents at 25°C. were determined for the whole tung fruit, the outer hull, the inner hull, shell, kernels, and seed of the fruit, and on the cake from continuous screw presses at nine different relative humidities. The relative humidities were maintained by enclosing saturated solutions of different salts in desiccators in a room maintained at constant temperature. One of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, U. S. Department of Agriculture.     

Minimization of focused ion beam damage in nanostructured polymer thin films

Focused ion beam (FIB) instruments have proven to be an invaluable tool for transmission electron microscopy (TEM) sample preparation. FIBs enable relatively easy and site-specific cross-sectioning of different classes of materials. However, damage mechanisms due to ion bombardment and possible beam heating effects in materials limit the usefulness of FIBs. Materials with adequate heat conductivity do not suffer from beam heating during FIB preparation, and artifacts in materials such as metals and ceramics are primarily limited to defect generation and Ga implantation. However, in materials such as polymers or biological structures, where heat conductivity is low, beam heating can also be a problem. In order to examine FIB damage in polymers we have undertaken a systematic study by exposing sections of a PS-b-PMMA block copolymer to the ion beam at varying beam currents and sample temperatures. The sections were then examined by TEM and scanning electron microscopy (SEM) and analyzed using electron energy loss spectroscopy (EELS). Our empirical results show beam heating in polymers due to FIB preparation can be limited by maintaining a low beam current (≤100 pA) during milling.     

Ultrahigh stress and strain in hierarchically structured hollow nanoparticles

Nanocrystalline materials offer very high strength but are typically limited in their strain to failure, and efforts to improve deformability in these materials are usually found to be at the expense of strength. Using a combination of quantitative in situ compression in a transmission electron microscope and finite-element analysis, we show that the mechanical properties of nanoparticles can be directly measured and interpreted on an individual basis. We find that nanocrystalline CdS synthesized into a spherical shell geometry is capable of withstanding extreme stresses (approaching the ideal shear strength of CdS). This unusual strength enables the spherical shells to exhibit considerable deformation to failure (up to 20% of the sphere's diameter). By taking into account the structural hierarchy intrinsic to novel nanocrystalline materials such as this, we show it is possible to achieve and characterize the ultrahigh stresses and strains that exist within a single nanoparticle during deformation.     

The Effect of Size on the Deformation Twinning Behavior in Hexagonal Close-Packed Ti and Mg

In hexagonal close-packed (HCP) structural materials, the limited activation of different slip mechanisms results in alternative deformation mechanisms, such as twinning, which become relevant to plasticity. As external/internal dimension refinement affects operative mechanisms and is commonly used to tune the mechanical properties of materials, understanding the effect of size on deformation twinning in HCP materials is a critical issue for improving their strength and ductility. Recent in situ and ex situ small-scale testing experiments have generated insights into size effects on twinning by deforming single-crystal systems with different sizes. In this article, we review some of the recent results in this field, including studies of the size-related deformation twinning behavior in Ti, Mg, and their alloys. The effect of size on deformation twinning in these systems is remarkable, resulting in a significant change in the mechanical properties of the materials. Deformation twinning can be restricted by the size effect in certain size regimes and materials but also can be promoted by the presence of surfaces at extremely small scales. The correlation of these two effects in two different HCP materials is discussed.     

The HP1a disordered C terminus and chromo shadow domain cooperate to select target peptide partners

Drosophila melanogaster heterochromatin protein 1a (HP1a) is essential for compacted heterochromatin structure and the associated gene silencing. Its chromo shadow domain (CSD) is well known for binding to peptides that contain a PXVXL motif. Heterochromatin protein 2 (HP2) is a non-histone chromosomal protein that associates with HP1a in the pericentric heterochromatin, telomeres, and the fourth chromosome. Using NMR spectroscopy, fluorescence polarization, and site-directed mutagenesis, we identified an LCVKI motif in HP2 that binds to the HP1a CSD. The binding affinity of the HP2 fragment is approximately two orders of magnitude higher than that of peptides from PIWI (with a PRVKV motif), AF10 (with a PLVVL motif), or CG15356 (with LYPLL and LSIVA motifs). To delineate differential interactions of the HP1a CSD, we characterized its structure, backbone dynamics, and dimerization constant. We found that the dimerization constant is bracketed by the affinities of HP2 and PIWI, which dock to the same HP1a homodimer surface. This suggests that HP2, but not PIWI, interaction can drive the homodimerization of HP1a. Interestingly, the integrity of the disordered C-terminal extension (CTE) of HP1a is essential for discriminatory binding, whereas swapping the PXVXL motifs does not confer specificity. Serine phosphorylation at the peptide binding surface of the CSD is thought to regulate heterochromatin assembly. Glutamic acid substitution at these sites destabilizes HP1a dimers, but improves the interaction with both binding partners. Our studies underscore the importance of CSD dimerization and cooperation with the CTE in forming distinct complexes of HP1a.