Optimal time advancing dispersion relation preserving schemes

In this paper we examine the constrained optimization of explicit Runge–Kutta (RK) schemes coupled with central spatial discretization schemes to solve the one-dimensional convection equation. The constraints are defined with respect to the correct error propagation equation which goes beyond the traditional von Neumann analysis   developed in Sengupta et al. [T.K. Sengupta, A. Dipankar, P. Sagaut, Error dynamics: beyond von Neumann analysis, J. Comput. Phys. 226 (2007) 1211–1218]. The efficiency of these optimal schemes is demonstrated for the one-dimensional convection problem and also by solving the Navier–Stokes equations for a two-dimensional lid-driven cavity (LDC) problem. For the LDC problem, results for Re=1000$\mathit{Re}=1000$ are compared with results using spectral methods in Botella and Peyret [O. Botella, R. Peyret, Benchmark spectral results on the lid-driven cavity flow, Comput. Fluids 27 (1998) 421–433] to calibrate the method in solving the steady state problem. We also report the results of the same flow at Re=10,000$\mathit{Re}=10\text{,}000$ and compare them with some recent results to establish the correctness and accuracy of the scheme for solving unsteady flow problems. Finally, we also compare our results for a wave-packet propagation problem with another method developed for computational aeroacoustics.     

Stimulated and spontaneous optical generation of electron spin coherence in charged GaAs quantum dots

We report on the coherent optical excitation of electron spin polarization in the ground state of charged GaAs quantum dots via an intermediate charged exciton (trion) state. Coherent optical fields are used for the creation and detection of the Raman spin coherence between the spin ground states of the charged quantum dot. The measured spin decoherence time, which is likely limited by the nature of the spin ensemble, approaches 10 ns at zero field. We also show that the Raman spin coherence in the quantum beats is caused not only by the usual stimulated Raman interaction but also by simultaneous spontaneous radiative decay of either excited trion state to a coherent combination of the two spin states.     

Die gas-chromatographische Abtrennung und Bestimmung der Milchs?ure

Ohne Zusammenfassung     

Studies on biodegradability of copolymers of lactic acid, terephthalic acid and ethylene glycol

The copolymers were synthesized by the condensation of lactic acid, terephthalic acid and ethylene glycol. Synthesized copolymers were characterized for various properties such as acid value, hydroxyl value and number average molecular weight, etc. The copolymers were analyzed by FTIR. Copolymers were biodegraded by different fungal species such as Aspergillus sp., Mucor sp., Alternaria sp. and Rhizopus sp., etc. The extent of biodegradation was examined by weight loss and scanning electron microscopy. Biodegradation of copolymer with greater amount of lactic acid was faster than the biodegradation of copolymer with lesser amount of lactic acid.     

A Jeffrey-fluid model of blood flow in tubes with stenosis

In this paper, we discuss the two-layered Jeffrey-fluid model with mild stenosis in narrow tubes. The blood flow in narrow arteries is treated as a two-fluid model with the suspension of erythrocytes, leukocytes, etc., as a Jeffrey fluid, which is a non-Newtonian fluid, in the core region and plasma, a Newtonian fluid, in the peripheral region. An analytical solution has been obtained for the velocity in the core and peripheral region, volume flow rate, resistance to flow, and wall-shear stress. The effect of Jeffrey-fluid parameters, like the height of stenosis, viscosity, etc., on volume flow rate, resistance to flow (impedance), and wall-shear stress has been discussed graphically. Through the present study, it is found that the wall-shear stress and resistance to flow increases with the increase in height of stenosis and decreases with the increase in the ratio of relaxation time. It is also found that the velocity decreases with an increase in stenosis height in both the core and the peripheral region. A previous result has been also verified.     

Metal complexes with tropolones

A review of the analytical applications of tropolone and its derivatives.     

Statistical Optimization for Succinic Acid Production from E. Coli in a Cost-Effective Medium

Response surface methodology (RSM) was employed for optimization of medium components and cultural parameters in cost effective cane molasses based medium for attaining high yield of succinic acid. The important factors obtained by “one-variable-at-a-time-approach” (cane molasses, corn steep liquor, sodium carbonate, and inoculum density) were further optimized by RSM. The optimum values of the parameters obtained through RSM (cane molasses 12.5%, corn steep liquor 7.5%, and sodium carbonate 25 mM) led to almost double yield of succinic acid (15.2 g/l in 36 h) as against “one-variable-at-a-time-approach” (7.1 g/l in 36 h) in 500-ml anaerobic bottles containing 300-ml cane molasses based medium. Subsequently, in 10-l bioreactor succinic acid production from Escherichia coli was further improved to 26.2 g/l in 30 h under conditions optimized through RSM. This fermentation-derived succinic acid will definitely help in replacing existing environmentally hazardous and cost-intensive chemical methods for the production of succinic acid.     

Photoisomerization dynamics of 3,3'-diethyloxadicarbocyanine iodide in ionic liquids: breakdown of hydrodynamic Kramers model

Photoisomerization dynamics of 3,3'-diethyloxadicarbocyanine iodide (DODCI) has been examined in a series of 1-alkyl-3-methylimidazolium (alkyl = methyl, ethyl, propyl, butyl, and hexyl) bis(trifluoromethylsulfonyl)imides by measuring its fluorescence lifetimes and quantum yields. This study has essentially been undertaken to find out whether the process of photoisomerization of DODCI in ionic liquids is different compared to that observed in conventional solvents such as alcohols. Activation energy of the reaction has been attained with the aid of isoviscosity plots and was found to be 22 ± 3 kJ mol(-1), which is a factor of two higher compared to that obtained in alcohols. The significantly higher activation energy obtained in bis(trifluoromethylsulfonyl)imides compared to alcohols is probably due to the highly ordered nature of the ionic liquids, which hinders the twisting process. Kramers theory has been applied to understand the reduced isomerization rate constants in terms of solvent friction. As in case of alcohols, the isomerization data could not be explained by the Kramers model. However, a power law relation, which is a phenomenological functional form, could mimic the observed trend.