Synthesis and structure–property relationships of UV-curable urethane prepolymers with hard–soft–hard blocks

UV-curable urethane prepolymers derived from diisocyanates, rigid diols, and polypropylene glycols of different molecular weights and end-capped with 2-hydroxylethyl methacrylate were prepared by stepwise addition reactions. These prepolymers have the common structure, HEMA-hard segment-soft segment-hard segment-HEMA. As the weight ratio of soft segment to hard segment and thus the rigidity varied, the cured films from these prepolymers exhibited a wide range of mechanical and other key properties such as oxygen permeability.     

Irregular growth of AlSb in solid aluminum-solid antimony diffusion couples

An investigation was made of the growth of the intermediate phase aluminum antimonide (AlSb) in solid aluminum-solid antimony diffusion couples, AlSb being the only intermediate phase present in the equilibrum phase diagram. Most diffusion couples were assembled from polycrystalline aluminum and antimony, but a few were made from single crystals; the diffusion couple surfaces were prepared in a variety of ways and the couples were isothermally annealed at temperatures between 450° and 615°C. It was found in all cases that AlSb nucleates at the original interface and after sufficient time coalesces into a highly irregular layer, irrespective of the details of the surface treatment. In several cases in which limited nucleation of AlSb took place, the morphology of the crystals was such as to suggest that the observed anisotropic growth was related to the zinc-blende crystal structure of the AlSb. Formerly Graduate Student, Department of Physical and Engineering Metallurgy, Polytechnic Institute of Brooklyn, Brooklyn, N. Y. Formerly Graduate Student, Department of Physical and Engineering Metallurgy, Polytechnic Institute of Brooklyn.     

Fixed versus flexible MMPI diagnostic rules.

The question of whether fixed (i.e., conventional) or flexible (i.e., Bayesian) rules should be used in diagnosis has received much attention in the clinical literature. Recently, Grove (1985) presented empirical evidence suggesting that flexible rules may not be "worth the expense of their use" (p. 263). The present article attempts to demonstrate the consequences on total misdiagnosis rates of using conventional rather than flexible rules when the MMPI is used as the diagnostic instrument. The principal conclusion is that when the base rate and separation of distributions of normal and abnormal scores are in the ranges of values examined in Grove's (1985) Monte Carlo study, Grove's comments about the negligibility of misdiagnosis rate differences for fixed versus flexible rules appear to be applicable to the Minnesota Multiphasic Personality Inventory (MMPI) but that, as the base rate increases and as the separation of distributions of normal and abnormal scores decreases outside of these ranges, the difference in the misdiagnosis rates for Bayesian versus conventional rules becomes increasingly nonnegligible. Furthermore, these total misdiagnosis rate differences appear to be particularly large when the separations of normal and abnormal groups' MMPI T-score distributions are in the ranges most often encountered in the clinical literature. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Separation of seed by-products by an AC electric field

A method for separating constituents of the by-products derived from agricultural processes offers the possibility of recovering their valuable components. Partial sorting by a unique electric field enriches the protein concentration in sunflower-seed meal and cottonseed meal by removing objectionable components such as hulls or gossypol. Enrichment is accomplished by the dynamic forces from an electric field that is created by a set of parallel electrodes encased in a plastic panel and connected to an AC power supply. When the panel is activated, particles on its surface become charged, levitated and transported. When a mixture of particles contacts the panel, a difference in the charge is imparted to the components, opposite directions of transportation occur, and, then, the particles separate. The separation, or sorting, offers an additional possibility for upgrading agricultural products. Properties measured for these products and their separated components are charge, charge-to-mass ratio, size, size distribution, shape, moisture, nitrogen and gossypol. This new and direct method of separating components seems independent of their size and shape, yet it is probably dependent on the charge-to-mass ratio. The single-stage separation is an analytical tool that might become an engineering process. The electric panel of the contact type contains, transports and refines materials—all without a cup, conveyor or filter touching the sample. Its promise and versatility warrant considering the panel by itself and in conjunction with other processes.     

A transient precursor of the HIV-1 protease. Isolation, characterization, and kinetics of maturation

Recently, the mechanism of autoprocessing of the protease (PR) of the human immunodeficiency virus type 1 from the model polyprotein, MBP-DeltaTF-PR-DeltaPol, which contains the protease linked to short native flanking sequences (DeltaTF and DeltaPol) fused to the maltose binding protein (MBP) of Escherichia coli, was reported (Louis, J. M., Nashed, N. T., Parris, K. D., Kimmel, A. R., and Jerina, D. M. (1994) Proc. Natl. Acad. Sci. U. S. A. 91, 7970-7974). According to this mechanism, intramolecular cleavage of the N-terminal strands of the dimeric MBP-DeltaTF-PR-DeltaPol protein leads to the formation of the PR-DeltaPol intermediate, which is subsequently converted to the mature protease by cleavage of the C-terminal strands. We now report the purification and characterization of the PR-DeltaPol intermediate and the kinetics of its processing to the mature protease. Unlike the MBP-DeltaTF-PR-DeltaPol precursor, PR-DeltaPol has proteolytic activity similar to that of the mature enzyme at pH 5.0. The pH rate profile for kcat/Km is similar to that of the mature protease above pH 4.0. Although the PR-DeltaPol is more sensitive than the mature protease toward denaturing reagents, both the enzymatic activity and the intrinsic fluorescence of PR-DeltaPol are linearly dependent on the protein concentration, indicating that the protein is largely in its dimeric form above 10 nM. In contrast to the first-order kinetics observed for the proteolytic reaction at the N terminus of the protease, the proteolytic reaction at the C terminus of the protease is second order in protein concentration. These results are discussed in terms of a mechanism in which the C-terminally located DeltaPol peptide chains are cleaved intermolecularly to release the mature protease.     

Age-related differences in timing with breaks.

Two groups of participants differing in age were compared on a time production task during which timing was temporarily interrupted. Produced intervals lengthened with increasing delay before the break occurrence, and the effect was more pronounced in older than in younger adults. A reaction time response to the signal beginning the break period was required also. Older participants responded more slowly to this signal, but they benefited to a greater extent from a lengthening of the time preceding its presentation. These results suggest that performance of older participants is affected by attention sharing and preparation involved in timing with breaks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perception and generalization of frequency contours by a bottlenose dolphin (Tursiops truncatus).

A single adult female bottlenose dolphin was tested in a series of perceptual studies. On each trial, 4 sine-wave tones were presented that contained a falling frequency contour or some other contour. There were several frequency-transposed exemplars of each contour type in each experiment. The dolphin discriminated contours at a level significantly greater than chance in all experiments. In the 1st 2 experiments, the dolphin demonstrated only modest transfer to novel stimuli and a sensitivity to the absolute frequency of stimuli. In the 3rd experiment, there was no effect of the absolute frequency of stimuli; in the 4th experiment, the dolphin successfully transferred the discrimination to novel stimuli drawn from the octave above the previously heard range. These results demonstrate dolphins' capability to perceive frequency contours, which may underlie the recognition of conspecific whistles. (PsycINFO Database Record (c) 2010 APA, all rights reserved)