Structure and rheology of fiber-laden membranes via integration of nematodynamics and membranodynamics

This paper presents a study of the structure and dynamics of rigid fiber-laden deformable curved fluid membranes based on an viscoelastic model that integrates the statics of anisotropic membranes, the planar nematodynamics of fibers and the dynamics of isotropic membranes. Fiber-laden membranes arise frequently in biological systems, such as the plant cell wall and in protein–lipid bilayers. Based on the membrane's force and torque balance equations and the fiber's balance of molecular fields, a viscoelastic anisotropic model that provides the governing equations for the membrane's velocity and curvature and the fiber structure (fiber orientation and order) is found. A Helmholtz free energy that incorporates the tension/bending/and torsion membrane elasticity, the Landau–de Gennes fiber ordering, and fiber order-membrane curvature interactions is used to derive elastic moments, torques, and stresses. The corresponding viscous stresses and moments include the Boussinesq–Scriven contributions as well as bending, torsion, and rotational dissipation. A spectral decomposition leads to the main viscoelastic material functions for anisotropic fluid membranes. Applications of the rheological model to cylindrical growth and cylindrical axial stretching show that competing curvo-phobic, curvo-philic interactions under extensional flow predict transitions between axial and azimuthal fiber arrangements, of interest to cellulose fiber orientation in plant morphogenesis.     

Enhanced electrochemical detection of ketorolac tromethamine at polypyrrole modified glassy carbon electrode.

A glassy carbon electrode modified with a coating of polypyrrole (Ppy) exhibited an attractive performance for the detection and determination of a non-steroidal and non-narcotic analgesic compound, ketorolac tromethamine (KT). Cyclic voltammetry, differential pulse and square wave voltammetry were used in a combined way to identify the electrochemical characteristics and to optimize the conditions for detection. For calibrating and estimating KT, square-wave voltammetry was mainly used. The drug shows a well-defined peak at -1.40 V vs. Ag/AgCl in the acetate buffer (pH 5.5). The existence of Ppy on the surface of the electrode gives higher electrochemical active sites at the electrode for the detection of KT and preconcentrate KT by adsorption. The square-wave stripping voltammetric response depends on the excitation signal and the accumulation time. The calibration curve is linear in the range 1 x 10(-11) to 1 x 10(-7) M with a detection limit of 1.0 x 10(-12) M. Applicability to serum samples was also demonstrated. A detection limit of 1.0 ng ml for serum was observed. Square-wave voltammetry shows superior performance over UV spectroscopy and other techniques.     

Experimental Investigation of the Effect of Flow Arrangements on the Performance of a Micro-Channel Heat Sink

Abstract

An experimental study is carried out to investigate the effect of entrance and exit conditions that prevail due to different flow arrangements on the thermal performance of a copper micro-channel heat sink. Three flow arrangements—U-type, S-type, and P-type—were considered for the analysis with a test piece having inlet and outlet plenum dimensions of 10 mm × 30 mm × 2.5 mm with an array of parallel micro-channels having an individual width of 330 μm and a uniform channel depth of 2.5 mm. Performance evaluations for different flow conditions at inlet and outlet plenums were made by maintaining constant heat supply at 125 W, 225 W, and 375 W with varying Reynolds number ranging from 224 to 1,121. Nusselt number and pressure drop were computed by measuring temperature difference and pressure drop across the inlet and outlet plenum for various test combinations. Maximum heat transfer was observed for the U-type flow arrangement, followed by the P-type and S-type; maximum pressure drop was noted for the S-type flow arrangement, followed by the U-type and P-type arrangements for a constant Reynolds number. A detailed analysis of the experimental results indicate that from a pressure drop point of view, the P-type flow arrangement is preferred, whereas from the heat transfer point of view, the U-type is found to be a better option.     

Electrochemical impedance spectroscopic studies on aging-dependent electrochemical degradation of p-toluene sulfonic acid-doped polypyrrole thin film

The conducting polymer polypyrrole thin film was galvanostatically polymerized on stainless steel substrate for the supercapacitor electrode. The electrochemical stability of the electrode was monitored each 30 days of aging up to 90 days. The FTIR analysis showed an increase in intensity of the absorption peaks, especially high growth of the carbonyl peaks after 90 days of aging. The electrochemical capacitance degradation of the electrode was studied using cyclic voltammetric and galvanostatic charge/discharge analysis in 1 M Na₂SO₄ electrolyte, which showed ~?53% of fading in the initial specific capacitance value after 90 days. Further, the electrochemical degradation of polypyrrole electrodes was analyzed in detail using electrochemical impedance spectroscopy. The analysis showed a large increase in the internal resistance and low-power deliverability of the electrode with respect to aging as the main reasons for the degradation of specific capacitance of the polypyrrole electrode.     

Sensitized Near-Infrared Luminescence From NdIII, YbIII and ErIII Complexes by Energy-Transfer From Ruthenium 1,3-Bis([1,10]Phenanthroline-[5,6-d]-Imidazol-2 -yl)Benzene

The luminescent ruthenium 1,3 -bis([1,10]phenanthroline-[5,6 -d]- imidazol-2 -yl)benzene (bpibH₂) complex, a potentially useful bridging ligand with a vacant diimine site, has been used as ‘metallo ligand’ to make heterodinuclear d–f complexes by attachment of a {Ln(dik)₃} fragment (dik?=?1,3-diketonate) at the vacant site. When Ln?=?Nd, Yb, or Er the lanthanide centre has low-energy f–f excited states capable of accepting energy from the ³MLCT excited state of the Ru(II) centre, there is quenching in the ³MLCT luminescence of the Ru(II) centre, that affords sensitized lanthanide(III) based luminescence in the near-IR region. Nd(III) was found to be the most effective at quenching the ³MLCT luminescence of the ruthenium component because of the high density of f–f excited states of the appropriate energy which make it as effective energy-acceptor compared to Er and Yb complexes.     

A convenient synthesis of enantiomerically pure (R)-mexiletine using hydrolytic kinetic resolution method

Enantiopure (R)-mexiletine was prepared in a simple and practical way using hydrolytic kinetic resolution method of terminal epoxide by Jacobsen’s catalyst. High enantiomeric purity (98% ee) was achieved and the method is well amenable to industrial scale-up.     

Vapour phase alkylation of ethylbenzene with t -butyl alcohol over mesoporous Al-MCM-41 molecular sieves

The alkylation of ethylbenzene witht-butyl alcohol was studied over Al-MCM-41 (Si/Al = 50 and 90) and Al, Mg-MCM-41 (Si/(Al+Mg) = 50) in the vapour phase from 200 to 400°C. The products werep-t-butylethylbenzene (p-t-BEB),p-t- butylvinylbenzene (p-t-BVB) andm-t-butylethylbenzene (m-t-BEB). Ethylbenzene conversion decreased with increase in temperature and increase in the ethylbenzene content of the feed. The reaction between the freely diffusing ethylbenzene in the channel and thet-butyl cations remaining as charge compensating ions yieldedp-t- BEB.p-t-BVB, an unexpected product in this investigation, was produced by dehydrogenation ofp-t-BEB over alumina particles present in the channels of the molecular sieves. Adsorption of ethylbenzene on Br?nsted acid sites and its subsequent reaction with very closely adsorbedt-butyl cations proved to be necessary to obtainm-t-BEB. Thoughm-t-BEB was obtained, the correspondingm-t-butylvinylbenzene was not observed in this study. Study of time durations indicated rapid and slow catalyst deactivation at lower and higher streams respectively.     

Synthesis, stereochemistry, and antimicrobial activity of 2,6-diaryl-3-(arylthio)piperidin-4-ones

A series of novel 2,6-diaryl-3-(arylthio)piperidin-4-ones have been synthesized by reaction of arylthioacetones, substituted aromatic aldehydes, and methylamine/ammonium acetate and their structures elucidated by (1)H, (13)C, and 2D NMR (H, H-COSY, C, H-COSY, HMBC, and NOESY) spectroscopy. The NMR data reveal that all these piperidones exist in chair conformation with the 2,6-diaryl groups equatorially oriented, while the arylthio group prefers to be in either an equatorial or axial orientation depending on whether the substituent in the 2,6-diaryl rings is present in 4- or 2-position, respectively. In the case of NH-2,6-diaryl-3-(arylthio)piperidin-4-ones with o-substituted 2,6-diaryl groups, the arylthio group prefers the axial orientation presumably in a bid to minimize the steric and/or electronic repulsion. The arylthiopiperidin-4-ones exhibit significant antibacterial activity against Staphylococcus aureus, Vibrio cholerae, Salmonella typhi, and Escherichia coli and antifungal activity against Candida albicans and Aspergillus niger.     

Formation of Pt-Ru nanoparticles in ethylene glycol solution: an in situ X-ray absorption spectroscopy study

The chemical state and formation mechanism of Pt-Ru nanoparticles (NPs) synthesized by using ethylene glycol (EG) as a reducing agent and their stability have been examined by in situ X-ray absorption spectroscopy (XAS) at the Pt LIII and Ru K edges. It appears that the reduction of Pt(IV) and Ru(III) precursor salts by EG is not a straightforward reaction but involves different intermediate steps. The pH control of the reaction mixture containing Pt(IV) and Ru(III) precursor salts in EG to 11 led to the reduction of Pt(IV) to Pt(II) corresponding to [PtCl4](2-) whereas Ru(III)Cl3 is changed to the [Ru(OH)6](3-) species. Refluxing the mixture containing [PtCl4](2-) and [Ru(OH)6](3-) species at 160 degrees C for 0.5 h produces Pt-Ru NPs as indicated by the presence of Pt and Ru in the first coordination shell of the respective metals. No change in XAS structural parameters is found when the reaction time is further increased, indicating that the Pt-Ru NPs formed are extremely stable and less prone to aggregation. XAS structural parameters suggest a Pt-rich core and a Ru-rich shell structure for the final Pt-Ru NPs. Due to the inherent advantages of the EG reduction method, the atomic distribution and alloying extent of Pt and Ru in the Pt-Ru NPs synthesized by the EG method are higher than those of the Pt-Ru/C NPs synthesized by a modified Watanabe method.