Low frequency ac conduction and dielectric relaxation behavior of solution grown and uniaxially stretched poly(vinylidene fluoride) films

The measurements of ac conductivity [σ_m(ω)], dielectric constant [?′(ω)] and loss [?″(ω)] have been performed on solution grown (thickness ∼85 μm) and uniaxially stretched (thickness ∼25, 45 and 80 μm) films of poly(vinylidene fluoride) (PVDF) in the frequency range 0.1 kHz-10 MHz and in the temperature range 77-400 K. The σ_m(ω) can be described by the relation σ(ω) = Aω^s, where s is close to unity and decreases with increase in temperature. Three relaxations, observed in the present investigation, have been designated as the α_c-, the α_a- and the β-relaxations appearing from high temperature side to the low temperature side. The α_c-relaxation could not be observed in the case of uniaxially stretched poly(vinylidene fluoride) films. The α_c- and α_a-relaxations are associated with the molecular motions in the crystalline regions and micro-Brownian motion in the amorphous regions of the main polymer chain, respectively, whereas the β-relaxation is attributed to the rotation of side group dipoles or to the local oscillations of the frozen main polymer chain.     

An integration–theoretical analysis of cultural and developmental differences in attribution of performance.

R. Singh et al (see record 1980-32377-001) proposed that American and Indian college students differ in their beliefs on how motivation and ability determine performance. Americans follow a multiplying rule, which implies that effort will be more effective with persons of high than of low ability. In contrast, Indians follow an equal-weight averaging, which implies that effort will be equally effective with persons of low and high ability. The present study tested this cultural-difference hypothesis using 120 Ss from 5 age groups: children 6–7, 8–9, 10–11, and 12–23 yrs old and college students 17–29 yrs old. As predicted, the Ss averaged information about past performance, motivation, and ability when predicting student performance. There was no support for the American finding that Performance?=?Motivation?×?Ability. Developmental differences appeared at the level of integrational capacity. These results illustrate the potential power of information integration theory for cross-cultural and cross-age comparisons in social perception and cognition. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Electrical switching in single crystal VO2

I–V characteristics of single crystal vanadium dioxide has been measured using a constant current source in the ambient temperature region 220–325°K. The temperature of the crystal surface has also been measured. It is observed that the switching voltage (V_th) increases but the current at switching (I_th) decreases with decreasing temperature, giving a temperature independent threshold power (V_th × I_th). At switching, the temperature of the crystal surface increases only by 3–6°K above ambient for different ambient temperatures. These results can be qualitatively explained by assuming that a filament (channel) is formed before switching. The switching occurs when the temperature of this filament of finite width approaches the semiconductor-metal transition temperature. The initial width of the channel at switching decreases with decreasing temperature and at a given ambient temperature the channel width increases with increasing current in the post breakdown region.     

Preparation and comparative characterization of keratin–chitosan and keratin–gelatin composite scaffolds for tissue engineering applications

We report fabrication of three dimensional scaffolds with well interconnected matrix of high porosity using keratin, chitosan and gelatin for tissue engineering and other biomedical applications. Scaffolds were fabricated using porous Keratin–Gelatin (KG), Keratin–Chitosan (KC) composites. The morphology of both KG and KC was investigated using SEM. The scaffolds showed high porosity with interconnected pores in the range of 20–100 μm. They were further tested by FTIR, DSC, CD, tensile strength measurement, water uptake and swelling behavior. In vitro cell adhesion and cell proliferation tests were carried out to study the biocompatibility behavior and their application as an artificial skin substitute. Both KG and KC composite scaffolds showed similar properties and patterns for cell proliferation. Due to rapid degradation of gelatin in KG, we found that it has limited application as compared to KC scaffold. We conclude that KC scaffold owing to its slow degradation and antibacterial properties would be a better substrate for tissue engineering and other biomedical application.     

Effect of thermal annealing on surface morphology and physical properties of poly(3-octylthiophene) films

An unusual morphology observed in poly(3-octylthiophene) (P3OT) films, solution grown at room temperature, which is previously shown by highly regioregular-poly(3-alkylthiophenes) (rr-P3ATs), is reported. Upon thermal annealing a rare well-arranged corrugated-rod-type (CRT) morphology, comes up gradually. It is observed by soft-heat treatment of pristine P3OT films, which is not reported for any members of polythiophenes family. This novel CRT morphology, observed by scanning electron microscopy (SEM), is supported by photoluminescence (PL) quenching, red shift of λ_max (π-π* absorption) in UV-vis spectra, and increase in conductivity. These improvements in physical properties are perhaps due to the increase in the planarity and 3D-π-π stacking of polymer chains by gradual soft-thermal annealing. It is worthwhile to mention here that the P3OT synthesized for the present investigation, with changed polymerization parameters, is comparable with its rr-P3ATs counterparts. The improvement in the quality of P3OT may induce self-assembling nature in former which results due to increased π-π interactions.