Integral equation formulation for buoyancy-driven convection problems

An integral equation formulation for buoyancy-driven convection problems is developed and illustrated. Buoyancy-driven convection in a bounded cylindrical geometry with a free surface is studied for a range of aspect ratios and Nusselt numbers. The critical Rayleigh number, the nature of the cellular motion, and the heat transfer enhancement are computed using linear theory. Green's functions are used to convert the linear problem into linear Fredholm integral equations. Theorems are proved which establish the properties of the eigenvalues and eigenfunctions of the linear integral operator which appears in these equations.     

Permanently oriented antibody immobilization for digoxin determination with a flow-through fluoroimmunosensor

This paper reports a new flow-through fluoroimmunosensor, the function of which is based on antibodies immobilized on an inmunoreactor of controlled-pore glass (CPG), for determination of digoxin, used in the treatment of congestive heart failure and artery disease. The immunosensor has a detection limit of 1.20 microg L(-1) and provides high reproducibility (RSD=4.5% for a concentration of 0.0025 mg L(-1), and RSD=6.7% for 0.01 mg L(-1)). The optimum working concentration range was found to be 1.2 x 10(-3)-4.0 x 10(-2) mg L(-1). The lifetime of the immunosensor was about 50 immunoassays; if stored unused its lifetime can be extended to three months. A sample speed of about 10-12 samples per hour can be attained. Possible interference from substances with structures similar to digoxin (morphine, heroin, tebaine, codeine, pentazocine and narcotine) was investigated. No cross-reactivity was seen at the highest digoxin: interferent ratio studied (1:100). The proposed fluoroimmunosensor was successfully used to determine digoxin concentrations in human serum samples.     

Solvatochromic Effect on the Photophysical Properties of Two Coumarins

The absorption and emission spectra of two coumarins namely 7, 8 benzo-4-azidomethyl coumarin (C₁) and 6-methoxy-4-azidomethyl coumarin (C₂) have been recorded at room temperature in solvents of different polarities. The ground state dipole moments (μ _g ) of two coumarins were determined experimentally by Guggenheim method. The exited state (μ _e ) dipole moments were estimated from Lippert’s, Bakhshievs and Chamma-Viallet’s equations by using the variation of Stoke’s shift with the solvent dielectric constant and refractive index. The ground and excited state dipole moments were calculated by means of solvatochromic shift method and also the excited state dipole moments are determined in combination with ground state dipole moments. It was observed that dipole moments of excited state were higher than those of the ground state, indicating a substantial redistribution of the π-electron densities in a more polar excited state for two coumarins.     

Study of Fluorescence Quenching on Novel Coumarin Derivatives by Aniline in Different Solvents

The steady-state fluorescence quenching of novel coumarin derivatives; 4-(2, 6-dibromo-4-methyl-phenoxymethyl)-benzo[h]chromen-2-one [DMB] and 6-methoxy-4-p-tolyoxymethyl-chromen-2-one [TMC] has been studied in toluene, benzene, dioxane, acetonitrile and tetrahydrofuran [THF] using aniline as a quencher at room temperature with a view to understanding the role of diffusion in the quenching mechanism. The probability of quenching per encounter (p) is calculated in all the solvents. Further, an activation energy for quenching (E _a) was estimated using the values of p and the literature values of activation energy for diffusion (E _d). The magnitudes of these parameters indicate that the fluorescence quenching of these molecules by aniline is not solely due to the material diffusion but there is also a contribution of an activation energy.     

Human Neuroepithelial Cells Express NMDA Receptors

L-glutamate, an excitatory neurotransmitter, binds to both ionotropic and metabotropic glutamate receptors. In certain parts of the brain the BBB contains two normally impermeable barriers: 1) cerebral endothelial barrier and 2) cerebral epithelial barrier. Human cerebral endothelial cells express NMDA receptors; however, to date, human cerebral epithelial cells (neuroepithelial cells) have not been shown to express NMDA receptor message or protein. In this study, human hypothalamic sections were examined for NMDA receptors (NMDAR) expression via immunohistochemistry and murine neuroepithelial cell line (V1) were examined for NMDAR via RT-PCR and Western analysis. We found that human cerebral epithelium express protein and cultured mouse neuroepithelial cells express both mRNA and protein for the NMDA receptor. These findings may have important consequences for neuroepithelial responses during excitotoxicity and in disease.     

Effect of Solvent Polarity on Fluorescence Quenching of New Indole Derivatives by CCl4

ABSTRACT

The fluorescence quenching of solutes 3-[5′-methyl-3′-phenylindol-2′-yl]-s-triazolo [3,4-b] [1,3,4] thiadiazol-6(5H)-thione (MPITTT) and 3-phenyl-2,5-bis-[thiosemicarbazido] indole (PbisTI) by carbon tetrachloride (CCl₄) in dioxane and acetonitrile mixtures has been studied at room temperature by steady-state fluorescence measurements. The positive deviation from linearity has been observed in the Stern–Volmer (S-V) plots for both fluorophores in different composition of mixed solvents even at moderate CCl₄ concentration (0.10 mol dm^?3). Various quenching parameters of the quenching processes have been determined using the extended S-V equation and have been found to be dependent on the solvent polarity. Further, with the use of the finite sink approximation model, it is concluded that the bimolecular quenching reactions are diffusion limited, and the distance parameter R′ and mutual diffusion coefficient D are estimated independently.