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  • Polymer and Materials Science  (17)
  • 82.65  (2)
  • Autoreceptors  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Energy accommodation and reactivity of O2 on tungsten (1977)
    Springer
    Applied physics 14 (1977), S. 141-147 
    Details
    ISSN: 1432-0630
    Keywords: 82.65
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract We have determined by direct molecular beam velocity measurements that translational energy accommodation of O2 molecules scattered from a hot polycrystalline tungsten target is inefficient at high surface temperatures. Translational energy accommodation is inefficient whether the surface is clean or covered with oxygen to a varying extent, even though in the latter case the scattering is diffuse. On a clean tungsten surface the scattering of the O2 was approximately specular and the reaction probability of O2 was constant and greater than 90% over the temperature range 1000K to 2800 K. It was shown by simultaneous helium scattering that atomic surface roughness of an oxygen chemilayer, rather than trapping, is a major cause of the observed diffuse scattering of oxygen. At the lowest surface temperature of 1000 K, with an oxygen chemilayer present, the velocity of the most probable number density of the scattered O2 was lower than in the incoming beam or than that expected for complete equilibration with the surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00883081
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  • 2
    Electronic Resource
    Electronic Resource
    Mechanism and speed of initial step of oxygen chemisorption-O2 on W (1977)
    Springer
    Applied physics 14 (1977), S. 411-413 
    Details
    ISSN: 1432-0630
    Keywords: 82.65
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract A direct first step in the mechanism for the initial oxidation of a polycrystalline tungsten surface, the catalyzed dissociation of O2 on it, or the formation of WO X by O2 at intermediate temperatures is shown to occur in ∼10−13 s. Molecular beam experiments demonstrated that the reactivity was greater than 90%, the unreacted O2 was substantially unaccommodated in translational energy to the surface temperature, and the reaction probability was nearly independent of surface temperature from 2800 to 415 K although there was a small increase at 415 K. The general conditions when no molecular surface precursor state contributes to the surface reactivity are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00883448
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  • 3
    Electronic Resource
    Electronic Resource
    Effect of chronic administration of the selective serotonin (5-HT) uptake inhibitor citalopram on extracellular 5-HT and apparent autoreceptor sensitivity in rat forebrain in vivo (1995)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 352 (1995), S. 597-606 
    Details
    ISSN: 1432-1912
    Keywords: Key words Microdialysis ; 5-HT release ; Chronic antidepressant ; Citalopram ; 5-HT reuptake inhibitor ; Tolerance ; Autoreceptors ; Frontal cortex ; Dorsal hippocampus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Rats were administered the selective serotonin (5-HT) uptake blocker citalopram or saline for 14 days to determine if prolonged treatment would lead to changes in extracellular 5-HT or autoreceptor sensitivity. One day after drug withdrawal, dialysis probes were implanted in the frontal cortex and dorsal hippocampus. Dialysis experiments were carried out using chloral hydrate anesthetized rats. The experimental protocol comprised the administration of three consecutive drug challenges: (1) After stable baseline levels were obtained, citalopram was infused through the dialysis probes to locally block uptake in the forebrain. (2) Subsequently, a 5-HT1B receptor agonist (RU24969 or CP93,129) was infused through the probe to test for changes in terminal autoreceptor sensitivity. (3) Last, citalopram was administered systemically to test the effect of indirect activation of somatodendritic autoreceptors. Under these conditions, with uptake already blocked locally in the forebrain, systemic citalopram produces a decrease in extracellular 5-HT, an effect that can be inhibited by pretreatment with antagonists of 5-HT1A receptors. The results indicate that during local infusion of citalopram extracellular 5-HT was significantly higher in the dorsal hippocampus of the chronic citalopram as compared to saline treatment group. This difference persisted throughout the full time course of the experiment. However, the decreases in 5-HT levels produced by local infusion of a 5-HT1B receptor agonist or after systemic citalopram administration were not significantly different between the chronic citalopram and saline treated groups. There were no significant differences between chronic citalopram and saline treated animals in frontal cortex. These results suggest that prolonged inhibition of 5-HT uptake may produce a selective change in the regulation of release from median raphe 5-HT neurons, but this change could not be clearly linked to a change in nerve terminal or somatodendritic autoreceptor sensitivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00171317
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  • 4
    Electronic Resource
    Electronic Resource
    Effect of chronic administration of the selective serotonin (5-HT) uptake inhibitor citalopram on extracellular 5-HT and apparent autoreceptor sensitivity in rat forebrain in vivo (1995)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 352 (1995), S. 597-606 
    Details
    ISSN: 1432-1912
    Keywords: Microdialysis ; 5-HT release ; Chronic antidepressant ; Citalopram ; 5-HT reuptake inhibitor ; Tolerance ; Autoreceptors ; Frontal cortex Dorsal hippocampus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Rats were administered the selective serotonin (5-HT) uptake blocker citalopram or saline for 14 days to determine if prolonged treatment would lead to changes in extracellular 5-HT or autoreceptor sensitivity. One day after drug withdrawal, dialysis probes were implanted in the frontal cortex and dorsal hippocampus. Dialysis experiments were carried out using chloral hydrate anesthetized rats. The experimental protocol comprised the administration of three consecutive drug challenges: (1) After stable baseline levels were obtained, citalopram was infused through the dialysis probes to locally block uptake in the forebrain. (2) Subsequently, a 5-HT1B receptor agonist (RU24969 or CP93,129) was infused through the probe to test for changes in terminal autoreceptor sensitivity. (3) Last, citalopram was administered systemically to test the effect of indirect activation of somatodendritic autoreceptors. Under these conditions, with uptake already blocked locally in the forebrain, systemic citalopram produces a decrease in extracellular 5-HT, an effect that can be inhibited by pretreatment with antagonists of 5-HT1A receptors. The results indicate that during local infusion of citalopram extracellular 5-HT was significantly higher in the dorsal hippocampus of the chronic citalopram as compared to saline treatment group. This difference persisted throughout the full time course of the experiment. However, the decreases in 5-HT levels produced by local infusion of a 5-HT1B receptor agonist or after systemic citalopram administration were not significantly different between the chronic citalopram and saline treated groups. There were no significant differences between chronic citalopram and saline treated animals in frontal cortex. These results suggest that prolonged inhibition of 5-HT uptake may produce a selective change in the regulation of release from median raphe 5-HT neurons, but this change could not be clearly linked to a change in nerve terminal or somatodendritic autoreceptor sensitivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00171317
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  • 5
    Electronic Resource
    Electronic Resource
    Site-specific drug delivery to the lung (1992)
    New York, NY : Wiley-Blackwell
    Polymers for Advanced Technologies 3 (1992), S. 323-329 
    Details
    ISSN: 1042-7147
    Keywords: Polyanhydrides ; Pulmonary neoplasms ; Mice ; Chemotherapy ; Cisplatin ; BCNU ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Investigations were undertaken to determine whether anti-cancer drugs introduced locally into the lung using bioerodible polyanhydride microspheres as carriers would demonstrate both efficacy and reduced toxicity.BCNU (carmustine) and CDDP (cisplatin), loaded in polyanhydride microspheres, were administered to mice bearing either of two tumors selected for their affinity for the lung: the B16F10 melanoma and the recently established GL26F4 glioma. Following intravenous inoculation of these tumor cells, the number of metastatic foci formed in the lung follows a predictable time course and can readily be determined. Comparisons were made between the efficacy of microspheres introduced into the lung by intratracheal intubation (IT) and of those administered by intraperitoneal injection (IP). Administration of microspheres loaded either with BCNU or cisplatin reduced the detectable metastatic foci by 25-90% depending on the tumor load, both when administered IP and IT.Toxicity was assessed by flow cytometric analysis of bone marrow cellularity as well as by determination of mortality rates. Intratracheal administration of either cisplatin or BCNU reduced the deleterious systemic effects observed when the drug was administered by IP injection. This was seen at high drug levels, where significant mortality occurred only in animals given drug injections IP; and at lower levels where IP injection led to a reduction of bone marrow blast cells, while IT administration caused no detectable effect on marrow cellularity.Since local delivery of BCNU or cisplatin through bioerodible polyanhydride microspheres induces significantly less systemic damage while demonstrating efficacy equal to or exceeding that of IP injection, this mode of drug delivery warrants further and more detailed exploration. Moreover, the method may be applicable to the treatment of other chronic pulmonary pathologies.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pat.1992.220030607
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  • 6
    Electronic Resource
    Electronic Resource
    Mechanical and thermal properties of dragline silk from the spider Nephila clavipes (1994)
    New York, NY : Wiley-Blackwell
    Polymers for Advanced Technologies 5 (1994), S. 401-410 
    Details
    ISSN: 1042-7147
    Keywords: Silk ; Mechanical ; Spider ; Silkworm ; Thermal ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Dragline silk from the spider, Nephila clavipes, was characterized by thermal analysis (TGA, DSC, DMA), computational modeling, scanning electron microscopy and by quasi-static as well as high rates of strain. Thermal stability to about 230°C was observed by TGA, two transitions by DMA, -75°C, representative of localized motion in the amorphous domain, and a main chain motion associated with partial melt at 210°C. Tensile tests indicated average initial modulus, ultimate tensile strength and ultimate tensile strain of 22 GPa, 1.1 GPa and 9%, respectively. The corresponding properties of the best fibers tested were 60 GPa, 2.9 GPa and 11%, respectively. High strain rates (〉50,000%/sec) indicated similar mechanical properties to the average values indicated above. Microscopy showed compressive and tensile strains to failure of 34%. Computational modeling yielded a crystal modulus of 200 GPa.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pat.1994.220050801
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  • 7
    Electronic Resource
    Electronic Resource
    Sorption of water by nylon 66 and kevlar 29. Equilibria and kineticsThis work performed at Sandia National Laboratories supported by the U.S. Dept. of Energy under Contract Number DEAC04-76DP00789. (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 42 (1991), S. 2417-2427 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The sorption of water by nylon 66 and Kevlar 29 fabrics was studied over a range of 20-98% relative humidities at 27°C. Equilibrium and rate relationships were developed from the data in this study and from nylon 66 and nylon 6 data of other studies involving fiber and film. The ratio of sorbed moisture to amide concentration is, on average and at high relative humidities, one water molecule per amide unit. The nylon equilibrium data show that there exist threshold relative humidities above and below which sorption properties differ. One threshold is correlated with the glass transition. Another is identified in the glassy state of nylon 6 in which moisture is tightly bound. The equilibrium constant values are highest and the moisture is most tightly bound at very low humidities, and the values are lowest in the plastic region at high humidities. NMR, DSC, and mechanical property data from others are correlated with the sorption discontinuities observed in this study. Rate data indicate that sorption is a diffusion-controlled process.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1991.070420907
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  • 8
    Electronic Resource
    Electronic Resource
    Light scattering of acetylated lignin (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 45 (1992), S. 407-415 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Organosolv lignin was fractionated on a Sephadex G 75 column with 0.1M aqueous NaOH resulting in 14 fractions. These fractions were acetylated and a high-molecular-weight fraction (F3) was investigated by means of combined static and dynamic light scattering (LS) in solvents acetone, tetrahydrofuran (THF), and trifluoroethanol (TFE). The measurements were found to be reproducible, and recycling of lignin by freeze drying caused slight but unessential changes in solution properties. Depending on the solvent used, weight average molecular weights Mw between two and ten million were found. By contrast, Mn of the fractions, measured by vapor pressure osmometry (VPO), was in the range of a few thousands only. Analysis of the angular dependence in static LS by means of a Casassa-Holtzer plot and the fractal dimensions showed the presence of chain stiffness, most distinct in TFE. Also, the dynamic light scattering results in TFE are typical for semiflexible chains, while in THF, and to some extent in acetone, the dynamic measurements including viscosity suggest the presence of spherical structures. These findings are being explained by large lignin clusters that consist of stiff subunits.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1992.070450305
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  • 9
    Electronic Resource
    Electronic Resource
    Preparation and stress-strain properties of SBS and SIS block polymers made with dilithium initiators (1972)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 16 (1972), S. 163-173 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: ABA-type block polymers of styrene (monomer A) and isoprene or butadiene were prepared using two commercially available dilithium adducts of isoprene as initiators. One (DiLi-1) was predominantly dilithio diisoprene and contained a small amount of dimethyl ether (ether/Li 〉 1.0). The second (DiLi-1 C.E.) was a higher molecular weight version of DiLi-1, containing about seven isoprene units per molecule. It contained only a trace of dimethyl ether (ether/Li 〈 0.1). Polymers were made by charging all of the monomers at the start of the reaction. The diene polymerized first, incorporating some styrene. When the diene was consumed, the difunctional polymer chains then added a block of nearly pure polystyrene at each end. Thus an ABA-type polymer was synthesized in one step. These polymers show the usual behavior of pseudo-vulcanized elastomers. Their stress-strain curves are given. The SBS polymers had the higher tensile strengths. None had tensile strengths as high as SBS or SIS polymers made with n- or sec-butyllithium. It was shown that the diene blocks contain appreciable amounts of styrene. This leads to more compatibility between the A and B blocks; it also shortens the styrene blocks compared to the theoretical lengths of “pure” blocks. Both effects can lead to loss of tensile strength. Microstructures of the diene homopolymers made with these initiators are also given.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1972.070160115
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  • 10
    Electronic Resource
    Electronic Resource
    Impact modification of engineering thermoplastics (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 53 (1994), S. 527-541 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Impact modification was studied for a variety of engineering thermoplastics to determine if notched Izod data obtained at various temperatures and modifier concentrations could be correlated with particle size or surface-to-surface interparticle distance of the modifier. Elastomers evaluated were characteristic of those used in commercial blend systems for those polymers, and both functionalized and nonfunctionalized materials were studied. For the single matrix polymer/elastomer-modified blend systems studied [poly(phenylene sulfide) (PPS), polyoxymethylene (POM), poly(butylene terephthalate) (PBT)], elastomer interparticle distance provides a better correlation to brittle-tough transition temperature than does particle size, as predicted by the Wu model. In POM, the dispersion morphology of the samples used was not adequate to achieve the critical interparticle distance required for supertoughening at room temperature. In this study, the critical interparticle distance has been shown to depend on the degree of crystallinity (PPS) and the modulus of the impact modifier relative to the matrix (PBT). Actual adhesion of the polymer to the matrix (variation of functionality levels) was not found to have a strong influence (PBT). In POM, the increase in impact at the brittle-tough transition was dependent on the molecular weight of the base resin. This is examined with respect to the ratio of the molecular weight (Mn) to the entanglement molecular weight (Me), which determines the critical molecular weight necessary to achieve useful physical properties. In polyester (PET)/polycarbonate (PC)/elastomer blends, the molecular weight of the primary matrix resin (PET) determined impact properties within the molecular weight range of the resin studied. This was again related to the Mn/Me ratio for PET and PC. © 1994 John Wiley & Sons, Inc.
    Additional Material: 24 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1994.070530507
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