A general mathematical formulation for finite-difference solution of mixed-boundary-value problems of anisotropic materials

This paper presents a general mathematical model, especially suitable for finite-difference analysis of stresses and displacements of the plane elastic problems of solid mechanics. The present formulation covers the problems of anisotropic, orthotropic and isotropic materials, in which the problem is formulated in terms of a single potential function, defined in terms of the displacement components. In addition, the formulation contains a new scheme of reduction of unknowns to be solved for a particular problem. Compared to the conventional computational approaches, the present scheme gets solution of higher accuracy and in extremely shorter time. The application of the present scheme is demonstrated here through a classical problem of solid mechanics, and the results are compared with the available solutions in the literature.     

Drug-induced pseudotumor cerebri

Pseudotumor Cerebri (PTC) is an uncommon disorder whose etiology is largely unknown, although its association with steroid withdrawal, hypervitaminosis A, and the use of the tetracycline group of drugs has been well documented. We report here a case in which a patient on chronic divalproex therapy for a seizure disorder developed PTC. Changing his antiepileptic medication from divalproate to topiramate effected a remission of PTC symptoms while maintaining his seizure-free status. It is recommended that physicians treating epilepsy, vascular headaches, or mood disorders with divalproate consider the diagnosis of PTC when their patients complain of new onset of headaches or an increase in frequency or severity of existing headaches--especially those associated with a visual disturbance--to prevent permanent visual loss.     

Stress-Induced Birefringence Characteristics of Polymer Optical Rib Waveguides

We report the detailed numerical investigation of stress-induced material birefringence in polymer rib waveguide for the design of nonbirefringent waveguide devices. To accurately simulate the stress-induced effects we propose a more realistic model in the finite element analysis which considers the stresses induced over the entire sequential fabrication process. It is observed that the birefringence is nonuniform, and it is different for different etch depth and core width. The maximum birefringence in the core layer is observed near the lower cladding which decreases to zero toward the top surface. The influence of this material anisotropy on the modal birefringence is analyzed also for different rib structures. We found the stress effects on the modal birefringence to be largely affected by etch depth, while core width has small effect. It is also found that the deeply etched core has better birefringence stability. Finally, an accurate design of the zero-birefringence waveguide is illustrated by taking the stress effects into account, and the results are compared with experimental data. Excellent agreement between calculated and experimental results confirms the potential application of this work to aid in the design of polarization-insensitive waveguide devices.     

Performance improvement of low bandgap polymer bulk heterojunction solar cells by incorporating P3HT

This work demonstrates a significant improvement of device performance by incorporating the polymer poly(3-hexylthiophene-2,5-diyl) (P3HT) into a low bandgap polymer poly[2,1,3-benzothiadiazole-4,7-diyl[4,4-bis(2-ethylhexyl)-4H-cyclopenta [2,1-b:3,4-b′]dithiophene-siloe 2,6-diyl]] (Si-PCPDTBT) and [6,6]-phenyl C71 butyric acid methyl ester (PC₇₁BM) host system, to form a ternary blend bulk heterojunction solar cell. The P3HT concentration was varied from 1 to 5 wt% in the host system. P3HT functions as a morphology control agent in this ternary system. A small weight percentage of P3HT can enhance the light absorption, polymer phase separation, exciton separation and charge carrier mobilities. These results are supported by UV–vis spectroscopy, X-ray diffraction, photoluminescence analysis and other characterisation methods. The highest average power conversion efficiency improvement of 10% was achieved by adding 1 wt% P3HT to the host system. This study reveals a promising way to achieve high efficiency solar cells using a low bandgap polymer.     

A Group Based Replication Mechanism to Reduce the Wastage of Processing Cycles in Volunteer Computing

Volunteer Computing is an exciting discipline for high throughput applications but due to inherent resource volatility, several issues arises such as tasks failure due to host / CPU unavailability, results validation etc. Replication is a solution to most of these problems but excessive replication can cause wastage of precious processing cycles. In this paper, we have extended our work of group based scheduling mechanism by proposing three replication policies i.e. proactive, reactive and hybrid used for Silver, Platinum and Gold groups respectively. The measures used for making the volunteer grouping are: collective impact of CPU & RAM, spot checking and task completion history. We evaluated the proposed mechanism over a network of 900 nodes having varied resources and behavior. The results are promising and show that the wastage of processing cycles can greatly be reduced by applying the suitable replication policies for each group.     

Transfer rate measurement of lysozyme by liquid-liquid extraction using reverse micelles with dense CO2

Lysozyme was extracted from aqueous solution into i-octane using reverse micelles in the presence of pressurized CO₂. A squat vessel with two independent stirrers was used to measure the mass transfer of the lysozyme across a planar interface. Mass transfer coefficient, k _L of the lysozyme from the aqueous to the organic phase was measured at selected ionic strengths, pH, sodium bis(2-ethylhexyl) sulfosuccinate (AOT) surfactant concentrations, temperatures and pressurized CO₂. The mass transfer rate of lysozyme was higher in high temperature (318 K) and pressure (20MPa). pH of 9 in aqueous phase showed highest mass transfer rate of lysozyme. The application of pressurized CO2 markedly increased the mass transfer rate of lysozyme comparing to conventional non-pressurized system.     

Evaluation of Antioxidant Properties and Mineral Composition of Purslane (Portulaca oleracea L.) at Different Growth Stages

The main objective of this research was to appraise the changes in mineral content and antioxidant attributes of Portulaca oleracea over different growth stages. The antioxidant activity was measured using 1,1-diphenyl-2-picrylhydrazyl (DPPH), ferric-reducing antioxidant power (FRAP) assays. The iodine titration method was used to determine the ascorbic acid content (AAC). DPPH scavenging (IC(50)) capacity ranged from 1.30 ± 0.04 to 1.71 ± 0.04 mg/mL, while the ascorbic acid equivalent antioxidant activity (AEAC) values were 229.5 ± 7.9 to 319.3 ± 8.7 mg AA/100 g, total phenol content (TPC) varied from 174.5 ± 8.5 to 348.5 ± 7.9 mg GAE/100 g. AAC 60.5 ± 2.1 to 86.5 ± 3.9 mg/100 g and FRAP 1.8 ± 0.1 to 4.3 ± 0.1 mg GAE/g. There was good correlation between the results of TPC and AEAC, and between IC(50) and FRAP assays (r(2) > 0.9). The concentrations of Ca, Mg, K, Fe and Zn increased with plant maturity. Calcium (Ca) was negatively correlated with sodium (Na) and chloride (Cl), but positively correlated with magnesium (Mg), potassium (K), iron (Fe) and zinc (Zn). Portulaca olerecea cultivars could be used as a source of minerals and antioxidants, especially for functional food and nutraceutical applications.     

Interfacial interaction and mechanical properties of chitin whisker–poly(vinyl alcohol) gel‐spun nanocomposite fibers

Nanocomposite fibers were prepared from chitin whiskers (ChWs) as the reinforcing phase and poly(vinyl alcohol) (PVA) as the matrix. Colloidal suspensions of ChWs, obtained by acid hydrolysis of chitin from crab shell, were thoroughly mixed with aqueous PVA. The homogeneous PVA–ChW suspensions were gel‐spun into a methanol coagulating bath. Wide‐angle X‐ray diffraction patterns evidenced the orientation of ChWs along the fiber axis. From differential scanning calorimetry, the crystallinity of the PVA component was found to increase with ChW loading due to the possible dragging of PVA chains adhering to ChWs during vertical extrusion. The non‐isothermal crystallization peak of PVA was observed to shift to lower temperature with ChW loading indicating interfacial interactions between PVA and ChW. Further interaction between PVA and ChW was evidenced by the shifting of the Fourier transform infrared bands of PVA to lower wavenumber and the dynamic tan δ peak, corresponding to α‐relaxation of PVA, shifting to higher temperature. The interaction of ChWs with the matrix PVA yielded a significant enhancement in the mechanical properties of the nanocomposites. Copyright © 2012 Society of Chemical Industry