Surfactant lipids containing aromatic units produce vesicular membranes with high thermal stability

Six new vesicle-forming, cationic surfactant lipids are synthesized. Four of them contain 'flat' aromatic units at different locations of hydrophobic segments. In order to estimate the influence of aromatic units in the lipid monomer two other surfactant lipids of related structure with n-butyloxy units in the places of aromatic groups were also prepared. Transmission electron microscopy confirmed the vesicular membrane formation from these newly synthesized lipids. DSC or temperature-dependent keto-enol tautomerism of benzoylacetanilide-doped vesicles reveal a remarkable increase in the thermal stability of the membranes formed from aromatic surfactant lipids in contradistinction to their counterparts that contain n-butyloxy units. The enhanced thermal stability originates presumably as a consequence of inter-monomer stacking.

Direct Evaluation Of Transient Stability Improvement With Static Var Compensators Using A Structure Preserving Energy Function

The ability of Static Var Compensators (SVCs) to rapidly and continuously control reactive power in response to changing system conditions can result in the improvement of system stability and also increase the power transfer in the transmission system. This paper concerns the application of strategically located SVCs to enhance the transient stability limits and the direct evaluation of the effect of these SVCs on transient stability using a Structure Preserving Energy Function (SPEF). The SVC control system can be modelled from the steady- state control characteristic to accurately simulate its effect on transient stability. Treating the SVC as a voltage-dependent reactive power load leads to the derivation of a path-independent SPEF for the SVC. Case studies on a 10-machine test system using multiple SVCs illustrate the effects of SVCs on transient stability and its accurate prediction.

Intraloop and Interloop Interactions in the Folded-G Quartet Structure of Oxytricha Telomeric Sesquence

The antiparallel intramolecular G quartet structure for the 3.5 copy Oxytricha telomeric sequence d(G(4)T(4))(3)G4 has been established using a combination of spectroscopic and chemical probing methods. In the presence of Naf ions, this sequence exhibits a circular dichroism spectrum with a positive band at 295 nm and a negative band around 265 nm, characteristic of an antiparallel G quartet structure. Further, we show that d(G(4)T(4))(3)G(4) adopts an antiparallel intramolecular G quartet structure even in K+ unlike d(G(4)T(4)G(4)). KMnO4 probing experiments indicated the existence of intra and interloop interactions in the Na+ induced structure. We have found that K+ not only increases the thermal stability of,G quartet structure but also binds to the loop region and disrupts stacking and interloop interactions. Biological consequences of such cation-dependent conformational micro-heterogeneity in the loop region of G quartet structures is also discussed.

Airborne measurements of aerosol scattering properties above the MABL over Bay of Bengal during W_ICARB - characteristics and spatial gradients

Realizing the importance of aerosol characterization and addressing its spatio-temporal heterogeneities over Bay of Bengal (BoB), campaign mode observations of aerosol parameters were carried out using simultaneous cruise, aircraft and land-based measurements during the Winter Integrated Campaign for Aerosols gases and Radiation Budget (W_ICARB). Under this, airborne measurements of total and hemispheric backscatter coefficients were made over several regions of coastal India and eastern BoB using a three wavelength integrating nephelometer. The measurements include high resolution multi-level (ML) sorties for altitude profiles and bi-level (BL) sorties for spatial gradients within and above the Marine Atmospheric Boundary Layer (MABL) over BoB. The vertical profiles of the scattering coefficients are investigated in light of the information on the vertical structure of the atmospheric stability, which was derived from the collocated GPS (Global Positioning System) aided radiosonde ascents. In general, the altitude profiles revealed that the scattering coefficient remained steady in the convectively well-mixed regions and dropped off above the MABL. This decrease was quite rapid off the Indian mainland, while it was more gradual in the eastern BoB. Investigation on horizontal gradients revealed that the scattering coefficients over northern BoB are 3 to 4 times higher compared to that of central BoB within and above the MABL. A north-south gradient in scattering coefficients is observed over Port Blair in the eastern BoB, with values decreasing from south to north, which is attributed to the similar gradient in the surface wind speed, which can be replicated in the sea salt abundance. The gradients are parameterized using best-fit analytical functions.

Similarity solution of unsteady boundary layer equations with a magnetic field

The unsteady laminar incompressible boundary layer flow of an electrically conducting fluid in the stagnation region of two-dimensional and axisymmetric bodies with an applied magnetic field has been studied. The boundary layer equations which are parabolic partial differential equations with three independent variables have been reduced to a system of ordinary differential equations by using suitable transformations and then solved numerically using a shooting method. Here, we have obtained new solutions which are solutions of both the boundary layer and Navier-Stokes equations.

The effect of temperature on the surface tension and adsorption functions of the Fe-S-O melts - an analysis based on interaction parameters

The present investigation analyses the thermodynamic behaviour of the surfaces and adsorption as a function of temperature and composition in the Fe-S-O melts based on the Butler's equations. The calculated-values of the surface tensions exhibit an elevation or depression depending on the type of the added solute at a concentration which coincides with that already present in the system. Generally, the desorption of the solutes as a function of temperature results in an initial increase followed by a decrease in the values of the surface tension. The observations are analyzed based on the surface interaction parameters which are derived in the present research.

Relaxation behavior of twin nonlinear optical chromophores: Effect of the spacer length

A new series of twin nonlinear optical (NLO) molecules, having two 4-nitrophenol chromophores that are linked via a flexible polymethylene spacer of varying length [(CH2)(n), n = 1-12], were synthesized. Powder second harmonic generation measurements of these twin samples indicated a pronounced odd-even oscillation, with the odd twins exhibiting a high SHG value while the even ones gave no measurable SH signal. This behavior reflects the crystal packing preferences in such twin NLO systems that have odd and even numbers of atoms linking them - the even ones appear to prefer a centrosymmetric packing arrangement. The orientational/disordering dynamics of these twin NLO molecules, doped in a polymer (poly(methyl methacrylate)) matrix, has also been studied using SHG in electric field poled samples. Interestingly, the maximum attainable SH signal, chi((2)), in, the poled samples also showed an odd-even oscillation; the odd ones again having a higher value of chi((2)) This unprecedented odd-even oscillation in such molecularly doped systems is rationalized as being due to the intrinsically greater ease of a parallel alignment of the two chromophores in the twins with an odd spacer than in those with an even one. Further, the temporal stability of the SHG intensity at 70 degrees C, after the removal of the applied corona, was also studied. The relaxation of all the twin chromophores followed a biexponential decay; the characteristic relaxation time (tau(2)) for the slow decay component suggests that while the twin with a single methylene unit relaxes relatively slowly, the relaxation is significantly faster in cases where n = 2 and 3. In the twins with even longer spacer segments, the relaxation again becomes slower and reaches a saturation value. The observed minimum appears to reflect the interplay of two competing factors that affect the chromophore alignment in such twin systems, namely, the electrostatic repulsion between neighboring oriented dipoles and the intrinsic flexibility of the spacer.

Stability of non-parabolic flow in a flexible tube

Flows with velocity profiles very different from the parabolic velocity profile can occur in the entrance region of a tube as well as in tubes with converging/diverging cross-sections. In this paper, asymptotic and numerical studies are undertaken to analyse the temporal stability of such 'non-parabolic' flows in a flexible tube in the limit of high Reynolds numbers. Two specific cases are considered: (i) developing flow in a flexible tube; (ii) flow in a slightly converging flexible tube. Though the mean velocity profile contains both axial and radial components, the flow is assumed to be locally parallel in the stability analysis. The fluid is Newtonian and incompressible, while the flexible wall is modelled as a viscoelastic solid. A high Reynolds number asymptotic analysis shows that the non-parabolic velocity profiles can become unstable in the inviscid limit. This inviscid instability is qualitatively different from that observed in previous studies on the stability of parabolic flow in a flexible tube, and from the instability of developing flow in a rigid tube. The results of the asymptotic analysis are extended numerically to the moderate Reynolds number regime. The numerical results reveal that the developing flow could be unstable at much lower Reynolds numbers than the parabolic flow, and hence this instability can be important in destabilizing the fluid flow through flexible tubes at moderate and high Reynolds number. For flow in a slightly converging tube, even small deviations from the parabolic profile are found to be sufficient for the present instability mechanism to be operative. The dominant non-parallel effects are incorporated using an asymptotic analysis, and this indicates that non-parallel effects do not significantly affect the neutral stability curves. The viscosity of the wall medium is found to have a stabilizing effect on this instability.

The destabilization of human GCAP1 by a proline to leucine mutation might cause cone-rod dystrophy

Guanylate cyclase activating protein-1 (GCAP1) is required for activation of retinal guanylate cyclase-1 (RetGC1), which is essential for recovery of photoreceptor cells to the dark state. In this paper, experimentally derived observations are reported that help in explaining why a proline→leucine mutation at position 50 of human GCAP1 results in cone–rod dystrophy in a family carrying this mutation. The primary amino acid sequence of wild-type GCAP1 was mutated using site-directed mutagenesis to give a leucine at position 50. In addition, serine replaced a glutamic acid residue at position 6 to promote N‐terminal myristoylation, yielding the construct GCAP1 E6S/P50L. The enzyme was over-expressed in Escherichia coli cells, isolated and purified before being used in assays with RetGC1, characterized by circular dichroism (CD) spectroscopy, and investigated for protease resistance and thermal stability. Assays of cyclic guanosine monophosphate (cGMP) synthesis from guanosine triphosphate by RetGC1 in the presence of E6S/P50L showed that E6S/P50L could activate RetGC1 and displayed similar calcium sensitivity to wild-type GCAP1. In addition, E6S/P50L and wild-type GCAP1 possess similar CD spectra. However, there was a marked increase in the susceptibility to protease degradation and also a reduction in the thermal stability of E6S/P50L as observed by both the cGMP assay and CD spectroscopy. It is therefore suggested that although GCAP1 E6S/P50L has a similar activity and calcium dependency profile to the wild-type GCAP1, its lower stability could reduce its cellular concentration, which would in turn alter [Ca2+] and result in death of cells.

Reliability Based Design Optimization for Internal Stability of Reinforced Soil Structures Using Pseudo‐Static Method

Seismic design of reinforced soil structures involves many uncertainties that arise from the backfill soil properties and tensile strength of the reinforcement which is not addressed in current design guidelines. This paper highlights the significance of variability in the internal stability assessment of reinforced soil structures. Reliability analysis is applied to estimate probability of failure and pseudo‐static approach has been used for the calculation of the tensile strength and length of the reinforcement needed to maintain the internal stability against tension and pullout failures. Logarithmic spiral failure surface has been considered in conjunction with the limit equilibrium method. Two modes of failure namely, tension failure and pullout failure have been considered. The influence of variations of the backfill soil friction angle, the tensile strength of reinforcement, horizontal seismic acceleration on the reliability index against tension failure and pullout failure of reinforced earth structure have been discussed.

A new beam finite element for the analysis of functionally graded materials

A new beam element is developed to study the thermoelastic behavior of functionally graded beam structures. The element is based on the first-order shear deformation theory and it accounts for varying elastic and thermal properties along its thickness. The exact solution of static part of the governing differential equations is used to construct interpolating polynomials for the element formulation. Consequently, the stiffness matrix has super-convergent property and the element is free of shear locking. Both exponential and power-law variations of material property distribution are used to examine different stress variations. Static, free vibration and wave propagation problems are considered to highlight the behavioral difference of functionally graded material beam with pure metal or pure ceramic beams. (C) 2003 Elsevier Science Ltd. All rights reserved.

K(2)O(2): The most stable oxide of K

We have analyzed the stability of various oxides of K and find that K(2)O(2) is the most stable one. The additional stability is traced to the presence of oxygen dimers in K(2)O(2) which interact to form molecular orbitals. Other oxides such as KO(2) and KO(3) which also have dimers/trimers of oxygens are found to be less stable. This is traced to the shorter O-O bonds that one finds in them which gives rise to a significant coulomb repulsion between the electrons on the oxygen atoms making up the dimer/trimer, making them less stable.

Theoretical Studies on the Structure and Bonding of Metallacyclocumulenes, -cyclopentynes, and -cycloallenes

In this paper, we compare the electronic structure of the hafnacycloallene complex Cp(2)HfC(4)Rr'(2)R `' (5Hf), which was previously described by Erker et al., with those of the titanium, zirconium, and hafnium complexes Cp(2)M(eta(4)-RHC(4)HR) (3M; i.e. metallacyclopent-2,3,4-trienes, metallacyclocumulenes) and Cp(2)M(eta(2)-R(2)C(4)R(2)) (4M; i.e. 1-metallacyclopent-3-ynes) using density functional theory (BP86/LANL2DZ) calculations. Moreover, the eta(3)-phenylallenyl zirconocene complex 7Zr, which was synthesized by Wojcicki et al., is included for the comparison. These calculations and extended Huckel calculations show that the bonding in complex 5Hf is remarkably similar to that of complexes 4M and 7Zr. An analysis of the structural parameters and bonding reveals that the unique interaction of the internal carbon atoms along with the terminal carbon atoms with the bent-metallocene moiety is the reason for the unusual stability of these metallacycles. The molecular orbital analysis further suggests that complex 5Hf can react with another metal fragment to give the bimetallic complexes 9 and 10. The electronic structures of complexes 3M, 4M, 5Hf, and 7Zr have been comparatively studied to get a general understanding of the bonding in these metallacycles.

Unsteady free convection flow over an infinite vertical porous plate due to the combined effects of thermal and mass diffusion, magnetic field and Hall currents

The unsteady free convection flow over an infinite vertical porous plate, which moves with time-dependent velocity in an ambient fluid, has been studied. The effects of the magnetic field and Hall current are included in the analysis. The buoyancy forces arise due to both the thermal and mass diffusion. The partial differential equations governing the flow have been solved numerically using both the implicit finite difference scheme and the difference-differential method. For the steady case, analytical solutions have also been obtained. The effect of time variation on the skin friction, heat transfer and mass transfer is very significant. Suction increases the skin friction coefficient in the primary flow, and also the Nusselt and Sherwood numbers, but the skin friction coefficient in the secondary flow is reduced. The effect of injection is opposite to that of suction. The buoyancy force, injection and the Hall parameter induce an overshoot in the velocity profiles in the primary flow which changes the velocity gradient from a negative to a positive value, but the magnetic field and suction reduce this velocity overshoot.

Synchronizing and Damping Torques Analysis of Nonlinear Voltage Regulators

This paper makes an attempt to assess the benefits of replacing a conventional generator excitation system (AVR + PSS) with a nonlinear voltage regulator using the concepts of synchronizing and damping torque components in a single machine infinite bus (SMIB) system. In recent years, there has been considerable interest in designing nonlinear excitation controllers, which are expected to give better dynamic performance over a wider range of system and operating conditions. The performance of these controllers is often justified by simulation studies on few test cases which may not adequately represent the diverse operating conditions of a typical power system. The performance of two such nonlinear controllers which are designed based on feedback linearization and include automatic voltage regulation with good dynamic performance have been analyzed using an SMIB model. Linearizing the nonlinear control laws along with the SMIB system equations, a Heffron Phillip's type of a model has been derived. Concepts of synchronizing and damping torque components have been used to show that such controllers can impair the small signal stability under certain operating conditions. This paper shows the possibility of negative damping contribution due to nonlinear voltage regulators and gives a new insight on understanding the physical impact of complex nonlinear control laws on power system dynamics.