Rheological properties of the liquid crystalline poly(γ-benzyl α, L-glutamate) gels in benzyl alcohol

We have determined the degree of stiffness of a poly(γ-benzyl α, L-glutamate) (PBLG) chain in benzyl alcohol by measuring the intrinsic viscosities of dilute Solutions with differing molecular weights. Viscoelastic properties in oscillatory shear flow have been studied and the dependence of the loss and storage moduli on temperature, composition, and frequency are reported. We have also studied the transient shear stress relaxation behavior of the PBLG gel at different temperatures and concentrations. A comparison has been made between these gels and a classical poly(dimethyl siloxane) (PDMS) network, as well as, typical glassy polymers. Shear creep and recovery measurements have been made for this system. Some extensional step strain experiments using lubricated squeezing have been investigated. Tensile experiments have been made to determine stress-strain relationship during elongation. Preliminary experiments using the impulse approach to viscoelasticity further indicate the high elastic contribution in the gel.     

CLUSTER THEORY FOR THE CONCENTRATION DEPENDENT TRANSLATIONAL SELF-FRICTION COEFFICIENT OF ROD-LIKE MACROMOLECULES IN SUSPENSIONS

A general theory of the concentration dependence of the self-friction coefficient of rod-like macromoiecules is presented based on multiple scattering ideas.Using the Riseman-Kirkweed model for Dolvmer, exdHEit farmyls are derived by taking both the hydrodynamic and the direct potential interactions between the solute molecules into account. Ana1vtical resullts are obdantned For the leading concentration dependence of the translational self-friction coefficient under theta conditions.     

Molecular modelling of nucleation in polymers

We have investigated the molecular mechanisms of primordial stages of polymer crystallization from solutions using Langevin dynamics simulations and theoretical models. The key feature that distinguishes polymers from small molecules at early stages of nucleation is that, in the case of polymers, a single chain can participate in several nuclei. This results in entropic frustration, leading to spontaneously selected temporary finite structures during nucleation. The experimental observation of finite lamellar thickness (much smaller than extended chain dimension) has been historically attributed to kinetic origins. Our simulations and an exactly solvable model to account for chain entropy show that the finite lamellar thickness is actually the equilibrium result. The growth at the lamellar growth front is found in our simulations to be dominated by chain adsorption and highly cooperative dynamics of all chains. Our results contradict the conventional assumptions and theories of polymer crystallization.     

Studies on Furan Polymer Concrete

Good mechanical properties and excellent chemical resistance of polymer concretes make them cost effective material of construction for civil engineering applications. These properties of polymer concretes are dependant upon the type of polymeric binder and the filler materials used. In the present investigation, a series of polymer concretes based on furan resin have been prepared using an aggregate mix proportion having minimum void content. Density, water absorption and microstructure were studied for different combinations designed on the basis of mixture design concept of design of experiments. The effects of variables on the properties were discussed.     

Li diffusion in epitaxial (11 $$\bar 2$$ 0) ZnO thin films

Zinc oxide (ZnO) possesses many interesting properties, such as a wide energy bandgap, large photoconductivity, and high excitonic binding energy. Chemical-vapor-deposition-grown ZnO films generally show n-type conductivity. A compensation doping process is needed to achieve piezoelectric ZnO, which is needed for surface acoustic wave (SAW), bulk acoustic wave, and micro-electromechanical system devices. In this work, a gas-phase diffusion process is developed to achieve piezoelectric (11 0) ZnO films. Comparative x-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements confirmed that high crystal quality and good surface morphology were preserved after diffusion. Photoluminescence (PL) measurements show a broad band emission with a peak wavelength at ∼580 nm, which is associated with Li doping. The SAW, including both Rayleigh-wave and Love-wave modes, is achieved along different directions in piezoelectric (11 0) ZnO films grown on an r-plane sapphire substrate.     

Yama: a scalable generational garbage collector for Java in multiprocessor systems

The current state-of-the-art generational garbage collector pauses all the program threads when it performs young and old generation garbage collection. As the number of program threads increases, the delay due to garbage collection also increases, thus restricting the scalability of the collector. In order to improve the scalability and reduce the pause time, an on-the-fly generational garbage collector called Yama is proposed for multiprocessor systems. This uses the on-the-fly deferred reference counting in the young generation and the DLG (Doligez Leroy Gonthier) on-the-fly mark and sweep garbage collector in the old generation. We have proposed and experimented with two novel variations of the on-the-fly deferred reference counting called Chitragupt1 and Chitragupt2 in the young generation. Yama does not pause all the application threads simultaneously. An adaptive tenuring policy based on object reference count and survival rate is also proposed. Yama has been implemented in the IBM Jikes RVM (research virtual machine). The above claims are supported with experimental results for standard benchmark programs. The results show that Yama has an extremely low pause time in both the young and the old generation. The pause time reduction results in better response times for the user programs.     

Facile one‐pot hydrothermal synthesis of stable and biocompatible fluorescent carbon dots from lemon grass herb

Luminescent carbon‐based nanomaterials hold great promise due to their stable photo‐physical behaviour, biocompatibility and lower toxicity. This work involves economic and facile one‐pot green synthesis of water‐soluble nanostructures from lemon grass (LGNS) [Cymbopogon citratus (DC) Stapf] as carbon source. High‐resolution transmission electron microscopy confirmed the formation of LGNS with lattice spacing of 0.23 nm matching low‐dimensional graphitic structures. The strong absorption exhibited at 278 nm could be attributed to л‐states of sp² /sp³ hybridisation in carbon nanostructures. Fluorescence spectroscopy of LGNS exhibited strong excitation‐dependent emission properties over a broad range of wavelengths from 300 to 600 nm. Quantitatively, these LGNS were estimated to have quantum yield of 23.3%. Biomass derived LGNS could be potentially exploited for wide variety of applications like bioimaging, up‐conversion, drug delivery and optoelectronic devices. To this extent, synthesised LGNS were used to image yeast cells via multicolour/multi‐excitation fluorescence imaging.Inspec keywords: fluorescence, carbon, nanofabrication, photoluminescence, toxicology, transmission electron microscopy, cellular biophysics, biomedical optical imaging, nanomedicine, biomedical materials, microorganisms, liquid phase depositionOther keywords: one‐pot hydrothermal synthesis, biocompatible fluorescent carbon dots, lemon grass herb, luminescent carbon‐based nanomaterials, stable photophysical behaviour, toxicity, water‐soluble nanostructures, carbon source, high‐resolution transmission electron microscopy, low‐dimensional graphitic structures, hybridisation, carbon nanostructures, fluorescence spectroscopy, excitation‐dependent emission properties, biomass derived LGNS, bioimaging, drug delivery, optoelectronic devices, yeast cell image, multicolour‐multiexcitation fluorescence imaging, C     

Existence of Solutions and Approximate Controllability of Fractional Nonlocal Neutral Impulsive Stochastic Differential Equations of Order 1 &lt; <Emphasis Type="Italic">q</Emphasis> &lt; 2 with Infinite Delay and Poisson Jumps

In this paper, we study the existence of mild solutions and the approximate controllability of nonlinear fractional nonlocal neutral impulsive stochastic differential equations of order 1 < q < 2 with infinite delay and Poisson jumps in which the initial value belong to the abstract phase space C _h . The existence of mild solutions is derived with the help of Sadovskii’s fixed point theorem. The approximate controllability of the nonlinear fractional nonlocal neutral impulsive stochastic differential systems of order 1 < q < 2 with infinite delay and Poisson jumps is discussed under the assumption that the corresponding linear system is approximately controllable. Moreover, the approximate controllability of the above control system is established by using Lebesgue dominated convergence theorem. An example is provided to illustrate the theory.     

Study of coupled heat and mass transfer during absorption of hydrogen in MmNi<Subscript>4·6</Subscript>Al<Subscript>0·4</Subscript> based hydrogen storage device

A two-dimensional numerical analysis of coupled heat and mass transfer processes in a cylindrical metal hydride reactor containing MmNi_4·6Al_0·4 is presented. To understand the hydrogen absorption mechanism the governing equations for energy, momentum and mass conservation and reaction kinetic equations are solved simultaneously using the finite volume method (FVM). Performance studies on MmNi_4·6Al_0·4 based hydrogen storage device are carried out by varying the hydrogen supply pressure, absorption (cooling fluid) temperature, overall heat transfer coefficient and hydride bed thickness. Effect of convection terms in the energy equation on hydrogen storage performance is found to be negligible. The results obtained from the computer simulation showed good agreement with the available experimental data. At the supply conditions of 30 bar and 298 K, MmNi_4·6Al_0·4 stores about 1·28 wt%, which is very close to the experimental value of 1·3 wt%. Overall high heat transfer coefficients are found to reduce the absorption time significantly.     

Study of heat and mass transfer in MmNi4.6Al0.4 during desorption of hydrogen

In this paper, a numerical investigation of two-dimensional coupled heat and mass transfer during desorption of hydrogen in a cylindrical metal hydride reactor containing MmNi_6.4Al_0.4 is presented. By considering the variation in heat transfer fluid temperature along the axial direction (variable wall temperature boundary condition), the changes in hydride bed temperature at different axial locations are presented. The effect of variable wall temperature boundary condition on hydrogen desorption rate for different hot fluid temperatures and hydride bed thicknesses is investigated. The rate of hydrogen desorption at different hot fluid temperatures showed good agreement with the experimental data reported in the literature. As the desorption progresses, the change in heat transfer fluid temperature along the axial direction is found to decrease with time and becomes unchanged at the end of the process. The effect of variable wall temperature boundary condition on desorption time is found to be significant for the hydride bed thicknesses of about 7.5 mm and more. For a given bed thickness of 17.5 mm, the maximum difference in desorption time between variable wall and constant wall temperature convective boundary conditions is about 375 s at 303 K.