Gait function in spastic hemiparetic patients walking barefoot, with firm shoes, and with ankle-foot orthosis

Cortical spreading depression is a wave of electrical and biochemical changes that spreads across the cerebral cortex. It has been hypothesized to be an important underlying cause of the visual disturbances occurring during the migraine aura, but this is difficult to test in animals or humans. We created a computational model of cortical spreading depression and found that during the wave of biochemical changes the spatial pattern of neural activity broke up into irregular patterns of lines and small patches of highly activated elements. The corresponding visual disturbances that would be produced by these patterns of neural activity resemble the hallucinations reported during the migraine aura, providing strong support for the cortical spreading depression hypothesis of migraine. The model also makes the testable prediction that these hallucinations move at an exponentially increasing speed across the visual field.     

Broadband dielectric spectroscopy studies of glassy‐state relaxations in annealed poly(2,5‐benzimidazole)

A broadband dielectric spectroscopic (BDS) study of poly(2,5‐benzimidazole) revealed three sub‐glass relaxations and the manner in which the time scales of these local molecular motions shift with annealing temperature and time. Also issuing from the BDS studies was a trend in the degree of connectivity of charge migration pathways and conductivity with annealing temperature and time. These studies were complemented with dynamic mechanical analysis, which showed the same relaxations, and solid state ¹H and ¹³C NMR studies that showed hydrogen bonding group mobility versus temperature. Wide angle X‐ray diffraction investigations indicated an increase in chain‐packing efficiency that was used to rationalize the BDS and NMR results. Copyright © 2011 Society of Chemical Industry     

Viscoelastic properties and morphology of sulfonated poly(styrene-b-ethylene/butylene-b-styrene) block copolymers (sBCP), and sBCP/[silicate] nanostructured materials

Self-assembled organic/inorganic hybrid materials were created via domain targeted sol-gel reactions of tetraethylorthosilicate in solution with sulfonated poly(styrene-b-[ethylene-co-butylene]-b-styrene) (sSEBS) copolymers. Dynamic mechanical analyses (DMA) of these hybrid materials suggest that the silicate component preferentially incorporates within the sulfonated polystyrene (PS) domains. An irreversible order-order transition (OOT) for unmodified SEBS, sSEBS, and the organic/inorganic hybrids was identified using DMA in shear mode. The OOT temperature increases with sulfonation as well as by adding a silicate phase by the sol-gel process. The DMA results imply a morphological shift with sulfonation, and reflect modified interactions within and between phases. Atomic force microscopy (AFM) indicated a shift from hexagonally packed cylinders in unmodified SEBS to a lamellar morphology in the sulfonated materials, but silicate incorporation did not affect the morphology or domain dimensions. The latter result is evidence for sol-gel polymerization templating in a self-assembly process. The phase-separated morphology is stable up to the degradation temperature of the polymer and thermogravimetric analysis revealed that the degradation temperature is unaffected by silicate incorporation. Small angle X-ray scattering data are in harmony with the structures revealed by AFM in terms of degree of order and scale of features. These results are largely rationalized in terms of chain mobility restrictions due to hydrogen-bonding interactions between different sulfonated PS blocks, an increase in the PS-ethylene/butylene block mixing parameter, increased interfacial surface tension and chain restrictions posed by inserted silicate nanostructures in the case of the hybrid materials.     

Efficiency of plasticization of PVC by higher-order di-alkyl phthalates and survey of mathematical models for prediction of polymer/diluent blend Tg's

Presently, a suitable theory to predict the T_g vs. composition relationship for a given polymer-plasticizer blend, based on detailed molecular structure and molecular energitics considerations, is not available. In particular, the plasticizer efficiency parameter, k, which is uniquely defined at low-to-moderate diluent concentrations, and is an essential variable in the Mauritz-Storey theory of the diffusion of large molecules in amorphous polymers in the rubbery state, must always be determined by experiment. In this work, k was determined by DSC for PVC that was plasticized over a range of concentrations with a number of higher branched and linear di-alkyl phthalates. The results will be used in our plasticizer diffusion theory as well as provide guidance in the future development of a general mathematical model for predicting k. It was seen that k decreased with increasing molecular weight for both the linear and branched phthalates. For a given molecular weight, the branched phthalates have higher k values than the linear structures. These results have been rationalized in terms of the additional free volume created by the inefficiency of packing polymer chains about these large penetrant molecules. The DSC scans also implied an increasing degree of microstructural heterogeneity with increasing plasticizer concentration. Finally, relationships between plasticizer diffusion coefficient in the rubbery state and the plasticized T_g were established for low-to-moderate diluent concentration for three of the plasticizers studied by utilizing experimental diffusion data from our earlier work on these systems.     

A theory for the diffusion of large molecules in amorphous polymers above Tg

A general theory of diffusion of large molecules in rubbery amorphous polymers is of interest for the scientific understanding and with regard to material design and process optimization. A broadly applicable model would be useful in developing controlled transport of plasticizers and other additives through polymeric substances. A diffusion model is presented which has been developed for large molecular penetrants above the T_g of the amorphous polymer allowing for required increase in redistribution of the free volume of the polymer structure, as well as the penetrant size and shape. Applicability of the model is demonstrated by comparing theoretically developed diffusion curves for DNOP and DNDP in PVC vs. their weight fractions at 82°C and 91°C. These theoretically derived plots are compared with experimental D vs. w₁ curves for these systems generated at lower temperature.     

Rare malposition of a subclavian vein catheter

Deviation of a left subclavian vein catheter into the azygos vein occurred in a patient with cancer of the colon. On the p.a.-projection, the catheter seemed to be kinked in the vena cava. In the lateral view, the malposition in the azygos vein could be detected and was visualised by giving a bolus of contrast medium. By retracting the catheter under fluoroscopic control the proper position could be achieved. The importance of the lateral-view chest x-ray is discussed.     

Determination of the bond strength of treated wood strands embedded in a cement matrix by means of a pull-out test

Effects of chemical treatment of wood on the bonding strength of Norway spruce strands (Picea abies Karst.) embedded in a??cement matrix were investigated by means of a??pull-out test. Strands of varying thickness were used whereas a??strong influence of thickness on bonding strength could be observed. Using thick strands (800?μm) showed negative effect on bonding strength which is due to the swelling effect. The treatment of thin strands (400?μm) showed that using wet strands (～?90% moisture content) leads to the best results compared to untreated dry (12%) strands. By addition of setting accelerators (ammonium chloride) bonding strength of wet strands was even improved. Furthermore, effects of hot water and sodium hydroxide extraction as well as sodium silicate treatment were examined.     

Nafion®/(SiO2, ORMOSIL,and dimethylsiloxane) hybrids via in situ sol–gel reactions: Characterization of fundamental properties

Nafion®/SiO₂, Nafion®/[ OR ganically MO dified SIL icate (ORMOSIL)] and Nafion®/dimethylsiloxane hybrids were created via in situ sol–gel reactions for tetraethoxysilane, diethoxydimethylsilane, and their mixtures. Differential scanning calorimetry studies showed a broad endotherm for unfilled Nafion®-H⁺ at T_α ≈ 215°C that shifts upward for the Q : D = 1 : 0 (mol : mol) [Q = Si(O_1/2)₄, D = (O_1/2)₂Si(CH₃)₂] hybrid, then shifts downward with decreasing Q : D. This endotherm likely arises from release of H₂O molecules bound to ≡Si—OH groups and condensation reactions among silanol groups. The decrease in T_α is rationalized in terms of an increasing fraction of flexible D units that disrupt hydrophilic Q structures. T_m shifts to lower temperatures with decreasing Q : D, and it is suggested that main chains are restricted by side chains embedded in silicon oxide nanoparticles, but D unit insertion causes side chains to be anchored less strongly. Thermal gravimetric analysis indicates that the first mass loss step for Nafion®-H⁺ shifts to higher temperatures as D : Q increases; an increase in D unit fraction inhibits Q unit degradation by evolved HF. A dynamic mechanical transition at T_α may arise from side chain motions, and the increase in T_α in passing from unfilled Nafio®-H⁺ to the 1 : 0 hybrid is due to side chain immobilization by their entrapment in silicon oxide domains. The progression 0 : 1 → 1 : 2 → 1 : 1 → 2 : 1 generates increasing mechanical tensile strength and decreasing ductility; strength enhancement might be due to entanglements between ORMOSIL and pure silicon oxide phases and side chains. Liquid sorption experiments quantified the affinity of these hybrids for solvents of varying polarity. A dielectric relaxation for the 0 : 1 hybrid at about 1.5 kHz might be related to side chain mobility. A weaker relaxation in the range 10⁴–10⁵ Hz exists for the 0 : 1 and 1 : 1 hybrids and Nafion®-H⁺, but not for the 1 : 0 hybrid that exhibits the behavior ε′ ∼ f⁻ⁿ over a broad frequency (f) range, suggestive of intercluster proton hopping. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:747–763, 1998     

Studies of the aging of nafion®/silicate nanocomposites using 29Si solid state NMR spectroscopy

Sol‐gel reactions of tetraethylorthosilicate were conducted within the nanophase‐separated morphology of Nafion® films to yield Nafion®/silicate nanocomposites. The chemical aging of silicate phase molecular structure when the nanocomposites were exposed to (1) ambient air, (2) applied heat, (3) liquid water, (4) methanol reflux, and (5) heated sulfuric acid was explored by means of ²⁹Si solid state NMR spectroscopy. In particular, the characteristic chemical shifts and relative Intensities of peaks that identify Q_n = (HO)_4‐n Si(OSi)_n molecular subunits in silicate structures were determined for samples exposed to these aging conditions. Shifts in the Q peak distribution reflected the evolution of degree of Si atom coordination about SiO₄ units. The coordination states are always Q₄ and Q₃ although a small Q₂ population is occasionally present. Thus, a significant degree of silicate phase coordination can develop despite constraints posed by the Nafion® medium. Percent Q₄ increases in all cases but then reaches a maximum after which it decreases, the greatest de‐polymerization being for samples aged in water. The greatest increase in Q₄ relative to the un‐aged control occurred for samples heated at 100°C. Exposure to ambient air produced changes in Q₄ that were small, but not insignificant. While the initial increase in Si atom substitution around SiO₄ units can be rationalized in terms of gradual condensation reactions between residual SiOH groups, accompanied by the liberation of water molecules and their removal from the site of the reaction, the eventual decrease in coordination is not currently understood.