Formulation/cure technology for ultrahigh molecular weight silphenylene-siloxane polymers

Molecular weights above one million were achieved for methylvinylsilphenylene-siloxane terpolymers using a two-stage polymerization technique which was successfully scaled up to 200 grams. The resulting polymer was vulcanized by two different formulations and compared to an identically formulated commercial methylvinyl silicone on the basis of ultimate strength, Young's modulus, percent elongation at failure, and tear strength. Relative thermal/oxidative stabilities of the elastomers were assessed by gradient and isothermal thermogravimetric analyses performed in both air and nitrogen. The experimental elastomer exhibited enhanced thermal/oxidative stability and possed equivalent or superior mechanical properties. The effect of variations in prepolymer molecular weight on mechanical properties was also investigated

The relationship between phonological and morphological deficits in Broca's aphasia: further evidence from errors in verb inflection

A previous study of 10 patients with Broca’s aphasia demonstrated that the advantage for producing the past tense of irregular over regular verbs exhibited by these patients was eliminated when the two sets of past-tense forms were matched for phonological complexity (Bird, Lambon Ralph, Seidenberg, McClelland, & Patterson, 2003). The interpretation given was that a generalised phonological impairment was central to the patients’ language deficits, including their poor performance on regular past tense verbs. The current paper provides further evidence in favour of this hypothesis, on the basis of a detailed analysis of the errors produced by these same 10 patients in reading, repetition, and sentence completion for a large number of regular, irregular, and nonce verbs. The patients’ predominant error types in all tasks and for all verb types were close and distant phonologically related responses. The balance between close and distant errors varied along three continua: the severity of the patient (more distant errors produced by the more severely impaired patients); the difficulty of the task (more distant errors in sentence completion > reading > repetition); the difficulty of the item (more distant errors for novel word forms than real verbs). A position analysis for these phonologically related errors revealed that vowels were most likely to be preserved and that consonant onsets and offsets were equally likely to be incorrect. Critically, the patients’ errors exhibited a strong tendency to simplify the phonological form of the target. These results are consistent with the notion that the patients’ relatively greater difficulty with regular past tenses reflects a phonological impairment that is sensitive to the complexity of spoken forms

What's up prof? Current issues in the visual effects & post-production industry

We interviewed creative professionals at a number of London visual effects and post-production houses. We report on the key issues raised in those interviews: desirable new technologies, infrastructure challenges, personnel and process management

What underlies the neuropsychological pattern of irregular>regular past-tense verb production?

The disadvantage in producing the past tense of regular relative to irregular verbs shown by some patients with non-fluent aphasia has been alternatively attributed (a) to the failure of a specific rule-based morphological mechanism, or (b) to a more generalised phonological impairment that penalises regular verbs more than irregular owing to the on-average greater phonological complexity of regular past-tense forms. Guided by the second of these two accounts, the current study was designed to identify more specific aspects of phonological deficit that might be associated with the pattern of irregular > regular past-tense production. Non-fluent aphasic patients (N = 8) were tested on past-tense verb production tasks and assessed with regard to the impact of three main manipulations in other word-production tasks: (i) insertion of a delay between stimulus and response in repetition; (ii) presence/ number of consonant clusters in a target word in repetition; (iii) position of stress within a bi-syllabic word in repetition and picture naming. The performance of all patients deteriorated in delayed repetition; but the patients with the largest discrepancy between regular and irregular past-tense production showed greater sensitivity to the other two manipulations. The phonological nature of the factors that correlated with verb-inflection performance emphasises the role of a phonological deficit in the observed pattern of irregular > regular

Characterization of an Inhibitor of Neuronal Plasminogen Activator Released by Heart Cells

A basic understanding of growth cone dynamics and developmental events involving growth cones requires an understanding of the function and regulation of molecules associated with and released by growth cones. Rat sympathetic neurons in culture release a urokinase-like plasminogen activator from their distal processes and/or growth cones (Pittman, 1985a). When sympathetic neurons are grown in cocultures with heart cells, however, plasminogen activator activity is not detected. The absence of plasminogen activator activity in cocultures of sympathetic neurons and heart cells appears to be due to the release of an inhibitor of plasminogen activator by heart cells. This inhibitor has a molecular weight of approximately 50 kDa in the presence of SDS and apparent molecular weights of approximately 50 and greater than 2000 kDa under native conditions. A significant fraction of the large- molecular-weight form of the inhibitor is converted to the smaller form following treatment with heparinase. Extremely stable complexes of 68 and 80 kDa are formed between the heart inhibitor and the plasminogen activator, urokinase, such that the complexes withstand boiling in SDS/mercaptoethanol. The data are consistent with the formation of an 80 kDa urokinase-inhibitor complex in the presence of heparan sulfate proteoglycan and a 68 kDa complex in the absence of heparan sulfate proteoglycan. A highly purified preparation of the heart inhibitor produces a 2- to 3-fold increase in neurite outgrowth from sympathetic neurons. These data indicate that the activity of the plasminogen activator released by sympathetic neurons can be regulated by a normal target tissue and that this regulation may result in increased neurite outgrowth from the neurons

Ultra-high molecular weight silphenylene-siloxane polymers

Silphenylene-siloxane copolymers with molecular weights above one million were prepared using a two stage polymerization technique. The technique was successfully scaled up to produce 50 grams of this high polymer in a single run. The reactive monomer approach was also investigated using the following aminosilanes: bis(dimethylamino)dimethylsilane, N,N-bis(pyrrolidinyl)dimethylsilane and N,N-bis(gamma-butyrolactam)dimethylsilane). Thermal analyses were performed in both air and nitrogen. The experimental polymers decomposed at 540 to 562 C, as opposed to 408 to 426 C for commercial silicones. Differential scanning calorimetry showed a glass transition (Tg) at -50 to -55 C for the silphenylene-siloxane copolymer while the commercial silicones had Tg's at -96 to -112 C

Melanophore migration and survival during zebrafish adult pigment stripe development require the immunoglobulin superfamily adhesion molecule Igsf11.

The zebrafish adult pigment pattern has emerged as a useful model for understanding the development and evolution of adult form as well as pattern-forming mechanisms more generally. In this species, a series of horizontal melanophore stripes arises during the larval-to-adult transformation, but the genetic and cellular bases for stripe formation remain largely unknown. Here, we show that the seurat mutant phenotype, consisting of an irregular spotted pattern, arises from lesions in the gene encoding Immunoglobulin superfamily member 11 (Igsf11). We find that Igsf11 is expressed by melanophores and their precursors, and we demonstrate by cell transplantation and genetic rescue that igsf11 functions autonomously to this lineage in promoting adult stripe development. Further analyses of cell behaviors in vitro, in vivo, and in explant cultures ex vivo demonstrate that Igsf11 mediates adhesive interactions and that mutants for igsf11 exhibit defects in both the migration and survival of melanophores and their precursors. These findings identify the first in vivo requirements for igsf11 as well as the first instance of an immunoglobulin superfamily member functioning in pigment cell development and patterning. Our results provide new insights into adult pigment pattern morphogenesis and how cellular interactions mediate pattern formation