Influence of molecular weight and molecular weight distribution on the tensile properties of amorphous polymers

Tensile property data for polystyrene samples of varying polydispersity are correlated with various parametric measures of molecular weight. Traditional measures of molecular weight, such as M?_n, M?_w, and M?_z, are shown to be unable to account for the variation of tensile properties with molecular weight. However, a new molecular weight parameter, termed the failure property parameter, is able to provide a single relationship between tensile strength and the parameter for both the broad and narrow distribution polymers. The form of this parameter is consistent with its having origins in the view that it is the entanglement network in an amorphous polymer that provides the observed strength properties. Specifically for polystyrene, the failure property parameter results indicate that material below 60,000 molecular weight does not contribute to polymer strength. Although the results of this investigation are specifically for polystyrene, the arguments used to develop the failure property parameter are not dependent on polymer chemical structure. Consequently, we believe that both the concepts and definition of this new parameter are applicable to all amorphous polymers.     

Solid-State Electrodes for Multichannel Multiplexed Intracortical Neuronal Recording

Thin-film arrays of extracellular recording electrodes have been developed for use in studies of information processing in neural structures and eventual use in closed-loop control of neural prostheses. These probes consist of a silicon substrate which supports an array of thin-film conductors. The conductors are insulated above and below with deposited dielectrics. The electrode sites are defined by openings in the upper dielectric layer and are inlaid with gold to form low-impedance recording surfaces. The probes are typically 15 pim in thickness with shank widths as narrow as 20 ?m. The probe fabrication process is compatible with the inclusion of signal processing circuitry directly on the probe substrate. A 12 channel on-chip signal processor design with per-channel gain of 100, bandwidth of 100 Hz-6 kHz, multiplexed output, and recording-site impedance check capability is described. The probes have adequate strength to penetrate the gerbil pia-arachnoid layer and have recorded single neuron activity of over 500 ?V peak-to-peak from tip, side, and mid-carrier sites. Signal-to-noise ratios as high as 10:1 have been achieved. An equivalent circuit model for the conducting leads, the recording site, and the electrode-electrolyte interface is described. Development of biocompatible insulation and encapsulation materials for long-term implantation of active probes is underway.     

Systematic Bivariate Analysis of AM Field Strength Measurement Data

A systematic method for analyzing AM field strength measurement data to establish inverse distance field strength and ground conductivity zones is presented. The technique uses a simple bivariate error minimization routine to find the combination of radiation and conductivity which most closely matches the measurement data out to three kilometers. The balance of the conductivity zones are determined by a running average which again seeks minimum error when compared to digitized versions of the FCC groundwave propagation curves. An extension of the technique allows such net conductivities along a radial to be converted to equivalent "M3 map" conductivities. The mathematical algorithms provide unique and repeatable results, and are readily adapted for use in computer programs.     

An economic input-output analysis for urban stormwater quality planning

A new approach using input-output techniques is proposed for the analysis of urban stormwater pollution caused by urban land development. The input-output model provides projections of sectoral outputs within an urban region. By defining land as an input to production, these output projections may be translated into projections of commercial and industrial land development. Furthermore, the closed version of the input-output model is used to project residential land development as a function of projected wage income. The pollutant generation in urban stormwater is related to the quantity of each category of land development by a pollutant coefficient matrix. Thus, the model can be used to predict the impact of various economic growth scenarios on pollution loadings in runoff water. This will help planners in assessing the environmental costs of various scenarios, and in preparing for remedial actions. A numerical example is provided to illustrate the applications of the model.     

Formation of phenazine from azobenzene over H-ZSM5: Reaction control by a molecular constrained environment

Azobenzene undergoes a unique reaction in the channels of H-ZSM5 zeolite at 593–673 K to give phenazine which is mainly retained within the zeolite. The yield of phenazine is increased by the addition to the reaction carrier gas of oxygen (1% vol.) which probably functions as a hydrogen acceptor. No reaction occurs when low acidity silicalite is used. On H-USY zeolite the yield of phenazine is low and the main product is a black, insoluble material which is probably polymeric. Benzo(c)cinnoline which is a known dehydrocyclization product from azobenzene under strongly acidic reaction conditions is never more than a trace product using H-ZSM5 or H-USY. A reaction scheme is proposed involving homolysis of the N ~ N bond in protonated trans-azobenzene, forming two radicals which, in a H-ZSM5 channel, are constrained in their mutual orientation so as to lead to the formation of phenazine.     

High-gain free electron lasers using induction linear accelerators

High-power free electron lasers (FEL's) can be realized using induction linear accelerators as the source of the electron beam. These accelerators are currently capable of producing intense currents (10²-10⁴A) at moderately high energy (1-50 MeV). Experiments using a 500 A, 3.3 MeV beam have produced 80 MW of radiation at 34.6 GHz and are in good agreement with theoretical analysis. Future experiments include a high-gain, high-efficiency FEL operating at 10.6 μm using a 50 MeV beam.     

Dietary patterns vs. dietary recommendations: Identifying the gaps for complex carbohydrate

Dietary guidelines of the U.S. and Canada recommend that 55% of dietary calories of individuals should come from carbohydrates, especially complex carbohydrates. However, they generally fail to describe how much should come from complex carbohydrates. Undoubtedly, this is because of confusion about the composition of complex carbohydrate foods and incomplete knowledge of the health benefits of all components of grain products. With the intent of shifting dietary food selection to increase carbohydrate consumption above the current 46% of calories, food guides recommend 5 to 12 servings per day from grain products. Current estimated intake for adults is between four to five servings of grain products, of which less than one is from whole grain, in an average 2000‐kcal adult diet. To follow the advice of the U.S. Food Guide Pyramid, which suggests half the bread (grains) group should be whole‐grain products, adult Americans should increase their intake of whole‐grain products four‐ to fivefold and double their intake of total grain products.     

Isolation of (copper, zinc-) thioneins from pig liver

Serum samples of 403 asymptomatic blood donors carrying hepatitis B surface antigen (HB5Ag) were concentrated threefold and tested for e antigen and antibody to e antigen (anti-e) by immunodiffusion. Hepatitis B antigen (HBAg)-associated deoxyribonucleic acid (DNA) polymerase activity was specifically determined by the difference in incorporation of [methyl-3H]thymidine 5' -triphosphate into DNA by an aliquot of centrifuged serum samples after it had been treated either with normal rabbit serum or with rabbit antibody to HBSAg. All of 58 serum samples containing e antigen revealed HBAg-associated DNA polymerase activity, whereas none of 96 samples containing anti-e did. In the remaining 249 samples in which neither e antigen nor anti-e was found, 62 showed specific DNA polymerase activity, although at lower levels than the samples containing e antigen.     

Respiratory abnormalities and ventilatory capacity in a Papua New Guinea Island community

Several molecular forms of human glucose-6-phosphate dehydrogenase (D-glucose-6-phosphate:NADP+ 1-oxidoreductase, EC 1.1.1.49) corresponding to different stages of post-synthetic modifications have been purified from human leukocytes. The various enzyme forms were different in their specific activity, their kinetic properties and their isoelectrofusing pattern. The molecular weight of the subunits of the different forms was not modified. The changes in the electrofocusing pattern were not due to modifications of the N-terminal ends, the oxidation of thiol groups or the non-covalent fixation of an acid molecule upon the enzyme. Carboxypeptidase B cleaved a C-terminal lysine from the different enzyme forms and shifted the isoelectric point of the different enzyme active bands towards the acid pH. The different enzyme forms studied here seemed to result from the action upon 'native glucose-6-phosphate dehydrogenase' of 'modifying factors' especially abundant in some leukemic granulocytes. The modifying factors did not seem to be consumed during the 'modification' of glucose-6-phosphate dehydrogenase. Moreover, the storage for one year of unmodified enzyme resulted in changes in its electrofocusing pattern similar to those quickly induced by the 'modifying factors'. Consequently it appears that the modifying factors are catalysts of the modification of special residues of glucose-6-phosphate dehydrogenase. The hypothesis that this modification involves the deamination of asparagine or glutamine residues is put forward.