Investigation on enhancement of electrical,dielectric and ion transport properties of nanoclay-based blend polymer nanocomposites

Polymer Bulletin - An intercalated blend polymer nanocomposite (PNC) films based on blend (PEO–PVC), LiPF6 as salt and modified montmorillonite (MMMT) as nanoclay are prepared via solution...     

High strain rate mechanical behavior of epoxy under compressive loading: Experimental and modeling studies

Investigations on high strain rate behavior of epoxy LY 556 under compressive loading are presented. Compressive Split Hopkinson Pressure Bar (SHPB) apparatus was used for the experimental investigations. The studies are presented in the strain rate range of 683-1890 per second. It was generally observed that the compressive strength is enhanced at high strain rate loading compared with that at quasi-static loading. During SHPB testing of the specimens, it was observed that the peak force obtained from the strain gauge mounted on the transmitter bar is lower than the peak force obtained from the strain gauge mounted on the incident bar. Further, an analytical method is presented based on variable rate power law for the prediction of compressive strength at high strain rate loading for epoxy LY 556. Using the analytical method, high strain rate compressive stress-strain behavior is presented up to strain rate of 10,000 per second.     

Dynamic Electromechanical Hydrogel Matrices for Stem Cell Culture

Hydrogels have numerous biomedical applications including synthetic matrices for cell culture and tissue engineering. Here we report the development of hydrogel based multifunctional matrices that not only provide three‐dimensional structural support to the embedded cells but also can simultaneously provide potentially beneficial dynamic mechanical and electrical cues to the cells. A unique aspect of these matrices is that they undergo reversible, anisotropic bending dynamics in an electric field. The direction and magnitude of this bending can be tuned through the hydrogel crosslink density while maintaining the same electric potential gradient, allowing control over the mechanical strain imparted to the cells in a three‐dimensional environment. The conceptual design of these hydrogels was motivated through theoretical modeling of the osmotic pressure changes occurring at the gel‐solution interfaces in an electric field. These electro‐mechanical matrices support survival, proliferation, and differentiation of stem cells. Thus, these new three‐dimensional in vitro synthetic matrices, which mimic multiple aspects of the native cellular environment, take us one step closer to in vivo systems.     

Finite elements formulated by the weighted discrete least squares method

By use of the least squares error criterion, an alternate finite element formulation is presented. The method is based on the discrete or element-wise minimization of square and weighted differential equation residuals which are expressed in terms of element nodal quantities. In order to overcome the stringent inter-element continuity requirement, a major stumbling block, on the element trial functions two practical schemes are proposed. One is the reduction of the original governing differential equation to a system of equivalent first order differential equations; the other is a method of smoothing discontinous trial functions. The latter essentially relaxes the continuity requirement and yields efficient non-conforming finite elements. This paper also demonstrates the use of constant weights which significantly improves the rates of convergence. Several numerical examples illustrate the proposed method. From these examples, it may be concluded that the use of constant weights and the relaxation of the inter-element continuity requirement are two indispensable features of the weighted discrete least square method.     

Changes in free nucleotides,nucleosides and bases during Preparation of Pre-Cooked dehydrated minced meats

Changes in free nucleotides, nucleosides and bases during preparation of pre-cooked dehydrated minced meats from goat and sheep are reported. Major changes took place during cooking stage only; the changes during dehydration were relatively minor. Addition of EDTA at 500 ppm level significantly reduced the rate of dephosphorylation during curing process. Concentration of free nucleotides and related compounds were very low in commercially prepared accelerated freeze dried meat chunks.     

Parietal cell antibodies in iron deficiency anaemia

The present studies were designed to estimate fetal weight on the basis of the thesis that the factors which determine body weight include the fetal bone and the amount of fetal soft tissue, i.e., fetal corpulence. Scalp thickness on the fetogram in the vertex presentation was measured, and the ratio of the minimal femur diameter to the thickness of soft tissue on the extensor side in the same region was calculated as an index of fetal corpulence. The scalp thickness and the ratio obtained proved to be highly correlated with fetal weight.     

Comprehensive experimental and theoretical study of fluid flow and heat transfer in a microscopic evaporating meniscus in a miniature heat exchanger

The complex physicochemical phenomena occurring in the contact line region of an evaporating meniscus are described using a unique combination of high-resolution experimental data and three complementary models. The following were used: (1) high-resolution experimental liquid profile data (thickness, slope, curvature and curvature gradient) to obtain the pressure gradient in the evaporating pentane meniscus in a vertical constrained vapor bubble (VCVB); (2) macroscopic outside surface temperature profile data; (3) a finite element model to obtain the two-dimensional heat conduction profile in the solid substrate wall (macro-model) and the solid–liquid interfacial temperature profile in the evaporating meniscus region; (4) a continuum fluid-dynamics model (micro-model) to obtain the liquid–vapor interfacial temperature, mass flow rate, Marangoni stresses, and evaporative heat flux profiles along the length of the evaporating meniscus; and (5) the Kelvin–Clapeyron model to obtain the vapor temperature profile (liquid–vapor interfacial temperature jump) in the evaporating meniscus region.The retarded dispersion constant and high-resolution thickness, slope, curvature and curvature gradient profiles were obtained from the experimental reflectivity profiles. There was a substantial increase in the measured curvature in the transition region, where the evaporation rate and flux are a maximum. To obtain numerical closure between the three complementary models, the continuum fluid dynamics model (micro-model) required slip at the solid–liquid interface to support the observed high mass flow rates in the evaporating pentane meniscus. Mass flow rates due to Marangoni stresses, capillary pressure and disjoining pressure are compared. Depending on the liquid thickness, Marangoni stresses can either enhance or hinder fluid flow towards the contact line for the evaporating pure pentane meniscus. Due to the high heat removal rate by the evaporating pentane meniscus in the transition region, dips in the vapor, liquid–vapor and solid–liquid interface temperature were obtained. The results demonstrate and describe the sensitivity and complexity of the phase change process in micro-regions.     

An impression of coffee carbohydrates

Coffee is one of the most popular beverages in the world. It is consumed for its refreshing and stimulating properties. Carbohydrates are the major constituents of coffee beans and serve various functions like binding of aroma, stabilization of foam, formation of sedimentation, and increased viscosity of the extract. The principal low molecular weight carbohydrate is sucrose and no evidence of other simple oligosaccharides has been found. Polysaccharide fraction from green coffee is dominated by arabinogalactan, galactomannan, and cellulose. The polysaccharide content is reduced during roasting due to degradation to low molecular weight carbohydrates (viz., mono and oligosaccharide) and become more extractable. Various methods that can be employed to extract the carbohydrate from roasted coffee are sequential extraction, acid hydroloysis, hot water extraction, enzymatic extraction etc. Carbohydrates from coffee can be quantitatively determined by liquid chromatography, high performance anion exchange chromatography, size exclusion chromatography, and high performance liquid chromatography. Besides improving the organoleptic quality of the coffee beverage, carbohydrates also possess various biological activities such as lowering colon cancer risk. Besides their sheer mass, a variety of evidences testify to the important contribution that the polysaccharide content makes to the character of the final brew. Although a number of chemical and enzymatic methods have been devised to isolate and quantify the carbohydrates of R&G coffee, till date hot water extraction is the only method which can be accepted as a most feasible process and hence, there is wide scope of further research for the efficient and economically viable technology for extraction of carbohydrates from coffee.