The use of intense femtosecond laser pulses for the fragmentation of chitosan

The use of ultrashort laser pulses for the fragmentation of chitosan was investigated. Femtosecond Ti-saphire laser pulses were focused into a flask containing 1.0% chitosan in 0.1 M acetic acid. The effects of the pulse energy (between 0.1 and 0.82 mJ) and the focal length on the laser-induced fragmentation were followed by viscometry and size exclusion chromatography. The chemical structure and degree of acetylation of chitosan and its fragments were studied using elemental analysis, IR and ¹H NMR spectroscopy. The experimental results showed that (i) Ti-saphire laser irradiation induced chain scission in the chitosan macromolecules, (ii) the chemical structure, including the degree of acetylation, did not change significantly upon laser irradiation, (iii) the number of chain scission dependence on laser energy suggests that fragmentation was a two-photon process, and (iv) at constant pulse energy, the molecular weight dropped to a minimum as a function of the focal length (between 45 and 330 mm), indicating that the efficiency of fragmentation was very sensitive to the geometry of the laser beam.     

Chaos and localization in coupled quartic oscillators

We discuss some of the models for eigenfunction localization in Hamiltonian systems. In particular, we review some of our work on classical parametric scaling of orbits and identification of localized states in a two-dimensional quartic oscillator system which is deep in the classically chaotic region. We show that visual methods are a necessary complement to quantitative methods based on information entropies. Our preliminary results indicate that the periodic orbit stability determines the degree of localization in a class of states, even when the stable regions are of negligible measure.     

La0.65Sr0.35CoO3-δ (LSC 6535) as a cathode material — A study on chemical reactivity of LSC with Y2Zr2O7 pyrochlore based electrolyte for ITSOFC(LSC 6535) as a cathode material — A study on chemical reactivity of LSC with Y2Zr2O7 pyrochlore based electrolyte for ITSOFC

A reduction in the operating temperature in SOFC can decrease materials degradation for long term operation. The efficiency of energy conversion and durability of performance mainly depend on the electro catalytic activity of the cathode and its thermo-chemical compatibility with the oxide ion conducting solid electrolyte. In this work, La_0.65Sr_0.35CoO_3-δ (LSC 6535), a mixed conducting stable perovskite oxide prepared by glycine nitrate route is systematically characterized. Circular pellets were fabricated and subjected to sintering at different temperatures ranging from 1073–1773 K. the sintering behaviour of LSC and LSC-YZ composite were investigated to obtain information on the densification, shrinkage in volume after heat treatment. The thermo-chemical compatibility of this cathode material with YZ is also brought out. Complex impedance spectroscopy was used for determining the conductivity and electrical behaviour. The component diffusion coefficient and mobility of ions were calculated from conductivity values. A brief discussion is made on its suitability for application as electro catalytic materials under ITSOFC operating conditions.     

Accuracy of trace formulas

Using quantum maps, we study the accuracy of semiclassical trace formulas. The role of chaos in improving the semiclassical accuracy in some systems is demonstrated quantitatively. However, our study of the standard map cautions that this may not be most general. While studying a sawtooth map we demonstrate the rather remarkable fact that at the level of the time one trace even in the presence of fixed points on singularities the trace formula may be exact, and in any case has no logarithmic divergences observed for the quantum bakers map. As a byproduct we introduce fantastic periodic curves akin to curlicues.     

Application of response surface methodology in the optimisation of a growth medium for enhanced natural preservative bacteriocin production by a probiotic bacterium

In this study, a statistics-based experimental design was utilised for the optimisation of a growth medium which possibly enhanced bacteriocin production by Streptococcus phocae PI80. Carbon, nitrogen sources and a bio-surfactant were first screened using a one variable at a time technique and scored for increasing yield production. The selected variables were further statistically optimised using response surface methodology with a central composite design. The high- and low-level limits of the selected variables were determined, and a set of 34 experimental runs were performed. The concentration of each medium ingredient influenced the bacteriocin activity to about 22,500?AU?mL?1. The carbon and nitrogen sources were identified as significant factors in restraining the bacteriocin activity produced by S. phocae PI80. The statistics-based experimental design was found to be very efficient in optimising the media components in a number of experimental runs, with a three-fold increase in bacteriocin activity compared to the un-optimised medium. The optimum medium composition was found to be sodium succinate (10.0?g?L?1), yeast extract (4.0?g?L?1), glucose (9.0?g?L?1), NaCl (10.0?g?L?1), Tween 80 (6.0?g?L?1) and K?HPO? (1.0?g?L?1). This optimised medium is two-fold more cost effective than the commercial Lactobacillus MRS medium.     

A Hierarchically Ordered Mesoporous-Carbon-Supported Iron Sulfide Anode for High-Rate Na-Ion Storage

Sodium-ion batteries (SIBs) are promising alternatives to lithium-based energy storage devices for large-scale applications, but conventional lithium-ion battery anode materials do not provide adequate reversible Na-ion storage. In contrast, conversion-based transition metal sulfides have high theoretical capacities and are suitable anode materials for SIBs. Iron sulfide (FeS) is environmentally benign and inexpensive but suffers from low conductivity and sluggish Na-ion diffusion kinetics. In addition, significant volume changes during the sodiation of FeS destroy the electrode structure and shorten the cycle life. Herein, we report the rational design of the FeS/carbon composite, specifically FeS encapsulated within a hierarchically ordered mesoporous carbon prepared via nanocasting using a SBA-15 template with stable cycle life. We evaluated the Na-ion storage properties and found that the parallel 2D mesoporous channels in the resultant FeS/carbon composite enhanced the conductivity, buffered the volume changes, and prevented unwanted side reactions. Further, high-rate Na-ion storage (363.4 mAh g⁻¹ after 500 cycles at 2 A g⁻¹, 132.5 mAh g⁻¹ at 20 A g⁻¹) was achieved, better than that of the bare FeS electrode, indicating the benefit of structural confinement for rapid ion transfer, and demonstrating the excellent electrochemical performance of this anode material at high rates.     

Growth and Characterization of Pure and Thiourea-Doped L-Alanine Single Crystals for NLO Devices

We successfully grow single crystals of pure and thiourea-doped glycyl-L-alanine hydrochloride (GLAH and TU-GLAH) from aqueous solutions by the slow evaporation technique. We study the effect of thiourea dopant on the crystal properties. Single-crystal X-ray techniques confirm the crystal structure and change in the lattice-parameter values for the doped crystals. We analyze the doped crystals quantitatively by energy-dispersive X-ray analysis (EDAX) and confirm the presence of thiourea in the pure samples. We obtain the second-harmonic generations for the grown crystals using a Nd:YAG laser. We determine values of the work hardening coefficient from the microhardness study. We measure the values of the dielectric constant and dielectric losses in order to understand the electrical phenomena taking place in pure and TU-GLAH crystals.     

Statistical Modeling of a Pharmacokinetic System

Abstract

The aim of the article is to investigate the drug concentration behavior in a three-compartment open pharmacokinetic model which describes the disposition of an antibiotic drug used in Lyme disease, coumermycin A ₁.

We study a system of random differential equations representing this model. The three rate constants that are used in the system of differential equations are simulated using the trivariate truncated normal probability distribution. The initial values of the rate constants that are used in the simulation are calculated from the pharmacokinetic profile of coumermycin A ₁ determined in four human subjects based on the serum level data obtained from the report of a clinical study. The extensive numerical solutions for the system of random differential equations under different combinations of the covariance structure and the initial conditions are developed.

Numerical comparisons of the deterministic characterizations of the drug concentration as a function of time of the individual compartments to study the effect of various combinations of the covariance structure and the initial conditions on these characterizations are presented. A similar comparison between the deterministic and the stochastic characterizations is also presented.     

Synthesis and characterization of benzo[c]thiophene analogs incorporating benzo[b]thiophene/1-hexylindole/benzo[b]furan

Synthesis of 1,3-disubstituted benzo[c]thiophene analogs incorporating heterocycles such as benzo[b]thiophene/1-hexylindole/benzo[b]furan and thiophene units is described. Optical and electrochemical studies of the benzo[c]thiophene analogs are also reported.