Photophysics of norharmane in solution phase: From homogeneous to microheterogeneous environments

The photobehavior of norharmane (9H-pyrido[3,4-b]-indole) (NHM), one of the vastly used skeleton of drugs in therapeutic applications, has recently been the subject of increasing interest due to the finding of their phototoxic and photocarcinogenic properties. Its absorption and fluorescence behavior from different prototropic species show remarkable sensitivity towards the polarity, viscosity and local pH, exhibited by various microheterogeneous bio and biomimetic environments like micelles, reverse micelles, proteins, etc. The significant results obtained for NHM in homogeneous and a series of microheterogeneous environments is reviewed in this account. Much attention has been given to the properties of the excited states, location and biodistribution of NHM in different biological environments. The results can help in understanding the photophysics of the probe in biological environments and in assessing the correlation between different prototropic forms and biological activity.     

Spectral Degeneracies in the Totally Asymmetric Exclusion Process

We study the spectrum of the Markov matrix of the totally asymmetric exclusion process (TASEP) on a one-dimensional periodic lattice at arbitrary filling. Although the system does not possess obvious symmetries except translation invariance, the spectrum presents many multiplets with degeneracies of high order when the size of the lattice and the number of particles obey some simple arithmetic rules. This behaviour is explained by a hidden symmetry property of the Bethe Ansatz. Assuming a one-to-one correspondence between the solutions of the Bethe equations and the eigenmodes of the Markov matrix, we derive combinatorial formulae for the orders of degeneracy and the number of multiplets. These results are confirmed by exact diagonalisations of small size systems. This unexpected structure of the TASEP spectrum suggests the existence of an underlying large invariance group.     

Comparative vibrational spectroscopic study of 1,3-diacetylbenzene and 2,6-diacetylpyridine aided with density functional calculation

Comparative studies of the Raman and infrared spectra of 1,3-diacetylbenzene and 2,6-diacetylpyridine have been made. The spectra are interpreted with the aid of normal mode analysis following full structure optimization based on the density functional method using different levels of theories and various basis sets combination. The unscaled DFT LSDA frequencies approximate the experimental ones in much more uniform fashion than B3LYP or B3PW91 theories do. Nevertheless the use of overall scale factor leads to further significant improvement with less than 2% error. The scaled B3PW91 6-31G result is best, even though LSDA 6-311G frequencies are superior to the B3PW91 ones before scaling. While making complete assignments of vibrational wavenumbers on the basis of potential energy distribution, some interesting observation in the vibrational spectra of these two molecules have been noticed. Instances of Fermi resonances between fundamentals and some combination modes of vibration have also been ascertained. Following the quantum chemical calculation optimized geometries of the both molecules are predicted. The theoretical global minimum energy calculation helps to find the structural symmetries of the molecules.     

Polymer-stabilized colloidal gold: a convenient method for the synthesis of nanoparticles by a UV-irradiation approach

This study describes a simple and convenient method for the preparation of polymer-stabilized colloidal gold by means of an ultra-violet (UV) irradiation technique. Methoxy polyethylene glycol (MPEG) acts as the reducing agent in the presence of the UV irradiation towards gold ions and also acts as the stabilizer of gold particles. The gradual broadening of the UV-visible spectra of the stabilized gold system reflects the formation of larger particles with a longer period of exposure to the UV radiation. PACS 87.20.Dd; 81.16.Hc; 81.07.-b; 78.67.-n; 82.35.Np     

Validated scale-up procedure to predict blockage condition for fluidized dense-phase pneumatic conveying systems

This paper presents results of an ongoing investigation into modelling fluidized dense-phase pneumatic conveying of powders. For the reliable design of dense-phase pneumatic conveying systems, an accurate estimation of the blockage boundary condition or the minimum transport velocity requirement is of sig- nificant importance. The existing empirical models for fine powder conveying in fluidized dense-phase mode are either based on only a particular pipeline and product or have not been tested for their accuracy under a wide range of scale-up conditions. In this paper, a validated test design procedure has been devel- oped to accurately scale-up the blockage boundary with the help of a modelling format that employs solids loading ratio and Froude number at pipe inlet conditions using conveying data of two different samples of fly ash, electro-static precipitation （ESP） dust and cement （particle densities： 2197-3637 kgJm3; loose poured bulk densities： 634-1070kg/m3; median size： 7-30 l~m）. The developed models （in power func- tion format） have been used to predict the blockage boundary for larger diameter and longer pipelines （e.g. models based on 69 mm I.D. ~ 168 m long pipe have been scaled up to 105 mm I.D. and 554 m length）. The predicted blockage boundaries for the scale-up conditions were found to provide better accuracy compared to the existing models.     

Noise-induced reentrant transition of the stochastic Duffing oscillator

We derive the exact bifurcation diagram of the Duffing oscillator with parametric noise thanks to the analytical study of the associated Lyapunov exponent. When the fixed point is unstable for the underlying deterministic dynamics, we show that the system undergoes a noise-induced reentrant transition in a given range of parameters. The fixed point is stabilised when the amplitude of the noise belongs to a well-defined interval. Noisy oscillations are found outside that range, i.e., for both weaker and stronger noise.Received: 20 February 2004, Published online: 20 April 2004PACS: 05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion - 05.10.Gg Stochastic analysis methods (Fokker-Planck, Langevin, etc.) - 05.45.-a Nonlinear dynamics and nonlinear dynamical systems     

Emission characteristics of phenyl isocyanate and parachlorophenyl isocyanate in polar media

The fluorescence and phosphorescence quantum yields (Φ_Γ and Φ_Π) and observed triplet decay time (τ_P) of phenyl isocyanate and its chloro derivative, parachlorophenyl isocyanate have been measured in the polar solvent ethanol. Kinetic parameters for the energy depletion process have been generated K_P the triplet-singlet transition probability is much more sensitive to Cl substitution than K_ISC the intersystem crossing rate.     

Polarization properties of phase gratings recorded in a Bi12SiO20 crystal

Due to the co-existence of optical activity and linear birefringence in a Bi₁₂SiO₂₀ crystal, a phase gratting induced in this medium has many interesting and unusual properties. We study the ellipticity and orientation of the directly transmitted and diffracted beams as a function of the read-beam vector orientation. In image processing experiments the signal to noise ratio can be increased significantly by appropriately choosing the read-beam orientation such that the strong direct beam is linearly polarized and can be eliminated with the help of a polarizer.     

Nonequilibrium fluctuations and mechanochemical couplings of a molecular motor

We investigate theoretically the violations of Einstein and Onsager relations and the thermodynamic efficiency for a single processive motor operating far from equilibrium using an extension of the two-state model introduced by Kafri et al. [Biophys. J. 86, 3373 (2004)10.1529/biophysj.103.036152]. With the aid of the Fluctuation Theorem, we analyze the general features of these violations and this efficiency and link them to mechanochemical couplings of motors. In particular, an analysis of the experimental data of kinesin using our framework leads to interesting predictions that may serve as a guide for future experiments.