Dynamic Compressibility of Poly (Vinyl Acetate) and Its Relation to Free Volume

The complex bulk compliance (dynamic compressibility) of a commercial sample of poly (vinyl acetate), AYAT, was measured at frequencies from 50 to 1,000 cycles per second, temperatures from 0 to 100 °C, and static hydrostatic stresses from 0 to 981 bars (gage pressure) using an alternating hydrostatic stress generated and detected by piezoelectric transducers mounted in an essentially noncompliant cavity with dimensions small in comparison to a wavelength. The above temperature range was more than sufficient to cover the dispersion region in which an inflection in the storage compliance and a maximum in the loss compliance were observed. The data were reduced to functions of reduced variables using the WLF Equations extended to include static pressure with the “universal” WLF Constants and dT/dP = 0.020 °C/bar. The difference in limiting compliances at zero and infinite frequencies was larger than that predicted from the dT/dP shift using the free volume concept. A discussion is presented on possible processes that might contribute to an excessive value between limiting compliances.     

The nature of 'overexchanged' copper and platinum on zeolites

The uptake of platinum and copper tetra-ammine (PTA and CTA, [(NH(3))(4)Pt](2+) and [(NH(3))(4)Cu](2+)) into zeolites was compared over silica and three zeolites (Y, MOR and MFI) with different points of zero charge and aluminium content. Adsorption was determined as a function of pH at several metal concentrations, and pH shifts relative to metal free control experiments were carefully monitored. The uptake of both metal ammine complexes onto silica is well described by electrostatic adsorption. We suggest that the metal cations interact with zeolites by two mechanisms, ion exchange at the Al exchange sites and electrostatic adsorption at silanol groups. The former is the dominant mechanism at low to mid pH, and the latter at high pH. This effect is most clearly manifested in zeolites with low aluminium content such as ZSM5; electrostatic adsorption at high pH in ZSM5 yields metal loadings much in excess of the ion exchange capacity and so gives rise to 'overexchange'. Differences between PTA and CTA can be explained by the weaker stability of the CTA complex and its response to the decrease in local pH near the adsorption plane of low PZC zeolites. This change in local pH near oxide surfaces is characteristic of electrostatic adsorption. As the local pH decreases, the CTA ion is probably converted to a dimerized copper complex, perhaps Cu(2)(OH)(2)(2+). A portion of the released ammonia is protonated, increasing the solution pH. In high PZC, high aluminium zeolites with high ion exchange capacity, there is relatively little contribution from electrostatic adsorption.     

Focal hyperemia on RBC blood-flow imaging. A scintigraphic marker of arterioportal venous shunting in hepatic cavernous hemangiomas?

PURPOSE: To investigate the significance of increased perfusion associated with some hepatic hemangiomata during radionuclide blood volume imaging. METHODS: Immediate dynamic planar projections and delayed SPECT imaging of a hepatic lesion were obtained after the administration of Tc-99m-labeled RBC. Scintigraphic data were compared with X-ray CT, contrast angiography and postresection histopathology. RESULTS: A surgically proven, cavernous hemangioma with typical findings on delayed radionuclide blood-pool imaging showed markedly increased perfusion by scintigraphy. This correlated with arterioportal venous shunting (AVPS) on contrast angiography. CONCLUSION: Increased perfusion on radionuclide blood-volume imaging of hepatic hemangiomata may be a scintigraphic marker of AVPS. This may serve to identify patients with increased risk for spontaneous rupture or may identify them for the development of portal hypertension.     

Social work outreach to homeless people and the need to address issues of self-esteem

Contribution of leucocytes to formation and lysis of arterial (platelet) thrombi was investigated. Secretory products of polymorphonuclear leucocytes (PMNs) during phagocytosis and cell lysates were prepared from eight volunteers. Platelet-rich thrombi were formed in flowing native human blood either by shear-stress or by collagen fibre, by haemostatometry. Tested in eight volunteers, PMN products significantly enhanced both thrombotic reactions and induced lysis of these thrombi. A specific inhibitor of leucocyte proteases (eglin c) inhibited platelet reaction to shear-stress and collagen and spontaneous thrombolysis. Our findings provide further evidence for the prothrombotic and potent thrombolytic effect of leucocytes associated with an arterial thrombus.     

Modeling original divergent responses: An initial investigation.

Investigated the effects of a videotaped model on children's verbal originality. 92 4th and 5th graders were randomly assigned to 4 groups. Group I viewed a filmed model who described highly original uses for tin cans, while Group II observed the same model describing unoriginal uses (unoriginal uses film). Group III read a booklet specifically designed to train children's idea production. Group IV was an untreated control group. On fluency and originality scores from the unusual uses test from the Torrance Tests of Creative Thinking, Form A, both film groups performed significantly better than the other groups. Further, Group I scored significantly higher than Group II. Interestingly, females performed best after viewing the unoriginal uses film, while males performed best after the original uses film. Viewing a videotaped model led to significant increases in both quantity and quality of divergent productions. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Synthesis, characterization, and optical properties of ordered arrays of III-nitride nanocrystals

A new approach involving self-assembling block copolymer micellar templates and gas-phase reactions to synthesize arrays of monodisperse III-nitrides nanocrystals in the size range of 1-5 nm with uniform spacings between the nanoparticles is demonstrated. The photoluminescence emission spectra revealed the GaN nanocrystals are in the quantum-confined regime. This method not only offers great promise for the controlled synthesis of arrays of ternary III-nitride nanocrystals but may also enable doping in binary nitrides.     

Scanning transmission x-ray microscopy of polymer nanoparticles: probing morphology on sub-10 nm length scales

Water-processable nanoparticle dispersions of semiconducting polymers offer an attractive approach to the fabrication of organic electronic devices since they offer: (1) control of nanoscale morphology and (2) environmentally friendly fabrication. Although the nature of phase segregation in these polymer nanoparticles is critical to device performance, to date there have been no techniques available to directly determine their intra-particle structure, which consequently has been poorly understood. Here, we present scanning transmission x-ray microscopy (STXM) compositional maps for nanoparticles fabricated from poly(9,9-dioctyl-fluorene-2,7-diyl-co-bis-N, N'-(4-butylphenyl)-bis-N, N'-phenyl-1,4-phenylenedi-amine) (PFB) and poly(9,9-dioctylfluorene-2,7-diyl-co-benzothiadiazole) (F8BT) 1:1 blend mixtures. The images show distinct phase segregation within the nanoparticles. The compositional data reveals that, within these nanoparticles, PFB and F8BT segregate into a core-shell morphology, with an F8BT-rich core and a PFB-rich shell. Structural modelling demonstrates that the STXM technique is capable of quantifying morphological features on a sub-10 nm length scale; below the spot size of the incident focused x-ray beam. These results have important implications for the development of water-based 'solar paints' fabricated from microemulsions of semiconducting polymers.     

Virus-templated self-assembled single-walled carbon nanotubes for highly efficient electron collection in photovoltaic devices

The performance of photovoltaic devices could be improved by using rationally designed nanocomposites with high electron mobility to efficiently collect photo-generated electrons. Single-walled carbon nanotubes exhibit very high electron mobility, but the incorporation of such nanotubes into nanocomposites to create efficient photovoltaic devices is challenging. Here, we report the synthesis of single-walled carbon nanotube-TiO(2) nanocrystal core-shell nanocomposites using a genetically engineered M13 virus as a template. By using the nanocomposites as photoanodes in dye-sensitized solar cells, we demonstrate that even small fractions of nanotubes improve the power conversion efficiency by increasing the electron collection efficiency. We also show that both the electronic type and degree of bundling of the nanotubes in the nanotube/TiO(2) complex are critical factors in determining device performance. With our approach, we achieve a power conversion efficiency in the dye-sensitized solar cells of 10.6%.     

Development of Transient Recombinant Expression and Affinity Chromatography Systems for Human Fibrinogen

Fibrin forms the structural scaffold of blood clots and has great potential for biomaterial applications. Creating recombinant expression systems of fibrinogen, fibrin’s soluble precursor, would advance the ability to construct mutational libraries that would enable structure–function studies of fibrinogen and expand the utility of fibrin as a biomaterial. Despite these needs, recombinant fibrinogen expression systems, thus far, have relied on the time-consuming creation of stable cell lines. Here we present tests of a transient fibrinogen expression system that can rapidly generate yields of 8–12 mg/L using suspension HEK Expi293^TM cells. We report results from two different plasmid systems encoding the fibrinogen cDNAs and two different transfection reagents. In addition, we describe a novel, affinity-based approach to purifying fibrinogen from complex media such as human plasma. We show that using a high-affinity peptide which mimics fibrin’s knob ‘A’ sequence enables the purification of 50–75% of fibrinogen present in plasma. Having robust expression and purification systems of fibrinogen will enable future studies of basic fibrin(ogen) biology, while paving the way for the ubiquitous use of fibrin as a biomaterial.