Thiacalixarene Appended Azo-based Supramolecular Systems: Self-assembly and Photo Tuning Reversible Liquid Crystalline Properties

Four new azo-based supramolecular materials containing thiacalixarene core substituted by variable alkoxy groups ( TFA₁ – TFA₄ ) have been designed and synthesized for the mesomorphic and photoswitching properties. The liquid crystalline behavior were accomplished by using DSC, POM, and XRD studies. All azo-based thiacalixarene based materials with short and higher chain length display columnar hexagonal mesophase with broad temperature range. The thermal behavior of all the materials was investigated by DSC and TGA study. The structural and conformational study of the lower rim functionalized materials was confirmed by using different techniques. These thiacalixarene moulded liquid crystalline compounds shows columnar self-assembly type behavior and higher thermal stability. The introduction of bi-substituted azo-ester network towards the lower rim of thiacalixarene core has impact on the electron delocalization and liquid crystalline properties. The photoswitching properties suggested cis and trans azo-isomerization under radiation of UV light and higher thermal back relaxation time. The mesogenic behaviour of compound TFA₂ and TFA₄ were demolished by the influence of cis and trans isomerization. The structure-property correlation is studied to understand the variation in mesogenic properties with the substitution of variable alkoxy side chain.     

Electrons, phonons and superconductivity in C16 structured Zr2Fe

Inelastic neutron scattering and low-temperature specific heat measurements are reported for a polycrystalline sample of Zr₂Fe. Lattice dynamical calculation of the phonon spectrum, along with first-principles LMTO electronic structure calculations have been used for deriving the specific heat parameters, the electron–phonon coupling constant and the superconducting transition temperature. The results are in fair agreement with the experimental data.     

Computation of two‐dimensional flows past ram‐air parachutes

Computational results for flow past a two‐dimensional model of a ram‐air parachute with leading edge cut are presented. Both laminar (Re=10⁴) and turbulent (Re=10⁶) flows are computed. A well‐proven stabilized finite element method (FEM), which has been applied to various flow problems earlier, is utilized to solve the incompressible Navier–Stokes equations in the primitive variables formulation. The Baldwin–Lomax model is employed for turbulence closure. Turbulent flow computations past a Clarck‐Y airfoil without a leading edge cut, for α=7.5°, result in an attached flow. The leading edge cut causes the flow to become unsteady and leads to a significant loss in lift and an increase in drag. The flow inside the parafoil cell remains almost stagnant, resulting in a high value of pressure, which is responsible for giving the parafoil its shape. The value of the lift‐to‐drag ratio obtained with the present computations is in good agreement with those reported in the literature. The effect of the size and location of the leading edge cut is studied. It is found that the flow on the upper surface of the parafoil is fairly insensitive to the configuration of the cut. However, the flow quality on the lower surface improves as the leading edge cut becomes smaller. The lift‐to‐drag ratio for various configurations of the leading edge cut varies between 3.4 and 5.8. It is observed that even though the time histories of the aerodynamic coefficients from the laminar and turbulent flow computations are quite different, their time‐averaged values are quite similar. Copyright © 2001 John Wiley & Sons, Ltd.     

Quantum chemical computation by DFT application of NLO molecule 2-aminopyridinium <Emphasis Type="Italic">p</Emphasis>-toluenesulphonate

We investigate the face-to-face collision between multisolitons in spin-1/2 quantum plasma. It is studied in the framework of the model proposed by Marklund et al in Phys. Rev. E 76, 067401 (2007). This study is done with the help of the extended Poincare–Lighthill–Kno (PLK) method. The extended PLK method is also used to obtain two Korteweg–de Vries (KdV) equations and the phase shifts and trajectories during the head-on collision of multisolitons. The collision-induced phase shifts (trajectory changes) are also obtained. The effects of the Zeeman energy, total mass density of the charged plasma particles, speed of the wave and the ratio of the sound speed to Alfvén speed on the phase shifts are studied. It is observed that the phase shifts are significantly affected by all these parameters.     

Vibrational Dynamics,Phonon Dispersion and Specific Heat in Gas Permeable Poly(4-Methyl-2-Pentyne)

Poly(4-methyl-2-pentyne) (PMP) is an amorphous glassy disubstituted acetylene based polymer. The excellent gas-separation and mechanical properties of these polymers have stipulated their use as membrane material for vapor and gas separation. PMP is among the hydrocarbon disubstituted polyacetylenes which have been synthesized to date. This polymer combines excellent gas and vapor permeability with good resistance to organic solvents. As was shown recently, PMP offers promise in the manufacture of nanocomposite membranes for the separation of various hydrocarbon mixtures. It is also of importance as its monomer, 4-methyl- 2-pentyne, can be easily derived from commercial compounds, 4-methyl-2-pentene or methyl isobutyl ketone, produced on a large scale. It is known that PMP exists in cis and trans configurations. Synthetic conditions, e.g., the used catalyst, temperature, solvent etc., of substituted polyacetylenes decide percentage of different configurations (cis or trans). Different geometries of macromolecules can influence the supramolecular structure of the polymer, which primarily defines its properties, such as solubility, permeability, sorption, etc. Qualitative assignments of few bands of IR spectra are reported earlier. We present here, complete normal mode analysis and dispersion curves for PMP using Wilson GF matrix method modified by Higgs using Urey-Bradley force field. Dispersion curves for PMP are drawn and salient features are discussed. Predicted values of specific heat via density-of-states are also reported.     

US Coast Guard air station location with respect to distress calls: A spatial statistics and optimization based methodology

We study the problem of suitably locating US Coast Guard air stations to respond to emergency distress calls. Our goal is to identify robust locations in the presence of uncertainty in distress call locations. Our analysis differs from the literature primarily in the way we model this uncertainty. In our optimization and simulation based methodology, we develop a statistical model and demonstrate our procedure using a real data set of distress calls. In addition to guiding strategic decisions of placement of various stations, our methodology is also able to provide guidance on how the resources should be allocated across stations.     

Adsorption of Safranin-T from wastewater using waste materials- activated carbon and activated rice husks

Textile effluents are major industrial polluters because of high color content, about 15% unfixed dyes and salts. The present paper is aimed to investigate and develop cheap adsorption methods for color removal from wastewater using waste materials activated carbon and activated rice husk-as adsorbents. The method was employed for the removal of Safranin-T and the influence of various factors such as adsorbent dose, adsorbate concentration, particle size, temperature, contact time, and pH was studied. The adsorption of the dye over both the adsorbents was found to follow Langmuir and Freundlich adsorption isotherm models. Based on these models, different useful thermodynamic parameters have been evaluated for both the adsorption processes. The adsorption of Safranin-T over activated carbon and activated rice husks follows first-order kinetics and the rate constants for the adsorption processes decrease with increase in temperature.     

Sequestration of amitriptyline by liposomes

We study the uptake of amitriptyline, which is a common cause of overdose-related fatalities, in aqueous solutions by 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) liposomes and liposomes composed of a mixture of DMPC and 1,2-dioleoyl-sn-glycero-3-[phospho-rac(1-glycerol)] (DOPG) lipids. The effect of drug concentration, liposomal charge, pH, salt, and protein presence on the drug uptake is investigated using two different methodologies, a precipitation and a centrifugation method. Furthermore, the time scale of the drug uptake is studied through qualitative observations at high pH and through conductivity measurements at neutral pH and found to be <5 s. The results of the quantitative studies show that the fractional drug uptake decreases with increasing drug concentration, and for a given concentration it increases with the pH and decreases in the presence of salt. We find that a larger amount of drug is sequestered by negatively charged liposomes (those containing DOPG) than liposomes with no net charge (DMPC). We speculate that the mechanism of drug uptake is due to both electrostatic interactions as well as hydrophobic effects. The fractional uptake by DMPC:DOPG in a 70:30 ratio is as high as 95% in water and about 90% in physiological buffer. The fractional uptake is also measured in presence of 2% (w/w) bovine serum albumin (BSA), which is approximately the protein concentration in the intercellular fluid. In presence of protein the fractional uptakes by 70:30 DMPC:DOPG liposomes and 50:50 DMPC:DOPG liposomes are 82 and 90%, respectively, at 125 muM drug amitriptyline. In the absence of liposomes, 67% of the drug is taken up by the protein in a 2% (w/w) BSA, 125 muM amitriptyline solution. Thus, addition of 50:50 DMPC:DOPG liposomes reduces the free drug concentration by a factor of about 3.5, making them attractive candidates for drug detoxification.     

Influence of physical and chemical heterogeneity shape on thin film rupture

It is known that the breakup times for thin liquid films on solid surfaces can be substantially smaller if the surface is heterogeneous, either chemically or physically. In this paper we explore issues related to the effect of the shape of the physical and chemical heterogeneities on the breakup time and the thinning behavior. We consider two shapes, sinusoidal and exponential, for both physical and chemical gradients and compare the breakup times for these two different forms of gradients. Furthermore, the wavelength of the sinusoidal gradients and the length scale of the exponential gradients are varied and the effects of these on the breakup times and the film evolution are determined. For the sinusoidal gradients, we also obtain analytical results for shape evolution that are valid at short times and for small amplitude perturbation of the physical/chemical heterogeneities. The fastest growing modes are determined for spinodal breakup and also for both shapes (sinusoidal and exponential) of physical and chemical heterogeneities. The breakup times for the fastest growing modes from the linear and the nonlinear studies are compared for spinodal breakup and these results are also compared with those for both chemical and physical heterogeneities, of both sinusoidal and exponential shapes. Results show that the presence of heterogeneities, in general, accelerates the breakup of the film. In the linear regime, the growth rates are the same for the chemical and physical heterogeneities and spinodal breakup, and the effect of the heterogeneities is manifested as increased amplitude of initial perturbation. The effect of the chemical and physical heterogeneities dominate the film dynamics at early times, becoming less important at later times. The growth rates and equivalently the breakup times for the films on heterogeneous surfaces depend on the length scale over which physical/chemical gradients occur, and as the length scale approaches zero, which implies that the gradients become very steep, the effect of the heterogeneities on the breakup times becomes small.     

In-line fiber optic structures for environmental sensing applications

Fiber optic sensors based on the interaction of surface plasmons or evanescent waves with the surrounding environment are usually obtained by tapering an optical fiber, which significantly weakens the structure, or by use of just the end of the optical fiber. A fiber optic structure that maintains the structural integrity of the optical fiber with a long environmental interaction length is presented. Graded-index optical fiber elements are used as lenses, and a coreless optical fiber acts as the environmental interaction area. These elements are fused by an optical fiber splicer and result in a continuous fiber optic sensing system.