Effect of molecular architecture on microstructural characteristics in some polysiloxaneimide multiblock copolymers

Efforts to correlate molecular characteristics with microstructural dimensions in microphase-separated diblock and triblock copolymers have been very successful, resulting in relationships that can be utilized to design materials with a specific microstructure and, consequently, with particular thermomechanical properties. However, similar efforts in the arena of multiblock copolymers have not been nearly as extensive, despite the increasing interest and diversity of this class of materials. In the present work, energy-filtered electron microscopy (EFEM) and small-angle neutron scattering (SANS) are used in a complementary fashion to probe the phase behavior of a series of three polysiloxaneimide (PSI) multiblock copolymers with different molecular architectures. Despite their relatively short segment lengths, all three materials exhibit signs of microphase separation at ambient temperature. SANS data are obtained from chemically unaltered materials and are subsequently interpreted with the Teubner-Strey model for microemulsions. Resultant microstructural dimensions are in good agreement with those measured from EFEM micrographs. Additional insight into the intramolecular sequencing of each copolymer is obtained from scaling relationships.     

Individual differences in anterior brain asymmetry and fundamental dimensions of emotion.

Assessed whether individual differences in anterior brain asymmetry are linked to differences in basic dimensions of emotion. In each of 2 experimental sessions, separated by 3 wks, resting EEG activity was recorded from female adults during 8 60-sec baselines. Mean alpha power asymmetry across both sessions was extracted in mid-frontal and anterior temporal sites. Across both regions, groups demonstrating stable and extreme relative left anterior activation reported increased generalized positive affect (PAF) and decreased generalized negative affect (NAF) compared with groups demonstrating stable and extreme relative right anterior activation. Additional correlational analyses revealed robust relations between anterior asymmetry and PAF and NAF, particularly among Ss who demonstrated stable patterns of EEG activation over time. Anterior asymmetry was unrelated to individual differences in generalized reactivity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Densification of plasma deposited silicon nitride films by hydrogen dilution

The effects of hydrogen dilution on the bonding characteristics, composition, and properties of SiN films deposited from a SiH₄/NH₃ mixture by r.f. plasma enhanced chemical vapor deposition were studied. The addition of relatively small amounts of hydrogen increased the Si/N ratio resulting in a corresponding increase in the Si---H/N---H bonding ratio. At higher hydrogen dilutions, the Si/N ratio decreased towards stoichiometric with significant changes in the hydrogen bonding characteristics. Changes in the physical properties are discussed in terms of the measured changes in bonding structure. Changes normally associated with changes in bulk film density were found to be well correlated to the Si---N bond density. The effects of substrate temperature and NH₃/SiH₄ ratio on films deposited under conditions of high hydrogen dilution were similar to those widely reported in the literature for plasma-enhanced chemical vapor deposition films deposited without hydrogen. Films deposited by remote plasma using hydrogen as the excitation exhibited high Si---N bond densities and low hydrogen. Experiments are planned to clarify the mechanism responsible for the observed changes in film properties.     

Local Structure of Alkaline-Earth Boroaluminate Crystals and Glasses: II, 11B and 27Al MAS NMR Spectroscopy of Alkaline-Earth Boroaluminate Glasses

¹¹B and ²⁷Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectra of alkaline-earth boroaluminate glasses show that the structure of these glasses are far more complicated than previously thought. The relative concentrations of 3- and 4-coordinated boron vary as found by previous investigators using continuous-wave NMR methods, but the ²⁷Al NMR spectra indicate the presence of Al in 4-, 5-, and 6-fold coordination, in contrast to previous assignments. Analysis of the data based on local charge balance considerations provides a qualitative model that correctly predicts compositional variations of the NMR peak intensities and ²⁷Al chemical shifts for a wide range of boroaluminate glass compositions.     

Use of Explosives on The Moon

The utilization of explosives for excavation on the lunar surface is under serious consideration as a part of the design for construction of temporary and permanent bases. An excavation research program has shown that small‐scale explosives blasting in a lunar‐soil simulant will greatly reduce the digging forces required for scoop and dragline excavators. Some crater‐blasting parameters were determined for the lunar soil simulant at one Earth gravity and at 10 Earth gravities using a centrifuge. The size of the craters produced at 10 Earth gs matched those formed at one earth g by scaling according to the weight of the explosive. These data can be applied to explosive‐excavation problems such as habitat construction, burial of nuclear power sources, and the rapid construction of shelters remote from the main base to shield against solar‐flare activity.     

Stereological estimation of the total volume of MR visible brain lesions in patients with multiple sclerosis

Point counting represents a convenient and efficient technique for estimating the area of transects through multiple sclerosis (MS) lesions on magnetic resonance (MR) images obtained for sections through the brain. When sectioning has been performed according to the Cavalieri method, unbiased estimates of the total volume of MR-visible MS plaques can be obtained with a precision of 3–5% in 5–10 min.     

Efficient generation of a reshaped human mAb specific for the {alpha} toxin of Clostridium perfringens

We have used the technique of antibody reshaping to producea humanized antibody specific for the a toxin of Clostridiumperfringens. The starting antibody was from a mouse hybridomafrom which variable (V) region nucleo-tide sequences were determined.The complementarity-determining regions (CDRs) from these Vregions were then inserted into human heavy and light chainV region genes with human constant region gene fragments subsequentlyadded. The insertion of CDRs alone into human frameworks didnot produce a functional reshaped antibody and modificationsto the V region framework were required. With minor frameworkmodifications, the affinity of the original murine mAb was restoredand even exceeded. Where affinity was increased, an alteredbinding profile to overlapping peptides was observed. Computermodelling of the reshaped heavy chain V regions suggested thatamino acids adjacent to CDRs can either contribute to, or distort,CDR loop conformation and must be adjusted to achieve high bindingaffinity.