Infrared laser multiple photon dissociation of thiophene in gas phase

Infrared laser multiple photon excitation/dissociation of Thiophene (Th) was studied as a function of Th pressure, laser pulse energy, pulse duration and added buffer gas. While the excitation process was probed via optoacoustic technique, the stable reaction products were analyzed by IR spectroscopy and mass spectrometry. Although C₂H₂ and CH₃CCH were the major hydrocarbon products under all experimental conditions, the distribution of these, as well as higher hydrocarbons of lower yield, was found to be very much dependent upon the experimental conditions. The laser induced reaction under dielectric breakdown conditions with either high substrate pressure or laser energy produced significant amount of CS₂ and unidentified polymer as well. We propose a mechanism involving breakage of the C–S bond in Th to form an unstable 1,5-diradical which further decomposed via different channels. However, at higher substrate pressures, radical-Th reactions complicated the overall chemistry of the system. Evidences for collisional energy-pooling and rotational hole-filling were also obtained.     

Selective ir laser chemistry of CDF3 in natural fluoroform

Selective decomposition of CDF₃ at natural abundance level (150ppm) in fluoroform has been achieved by infra-red multiple-photon excitation at moderate substrate pressure using 100 ns FWHM CO₂ laser pulses. Effects of energy fluence, number of laser pulses, buffer gas pressure and substrate pressure on decomposition yield and bulk selectivity are reported and discussed.     

PHOTOIONIZATION OF CRYSTAL VIOLET IN AQUEOUS SOLUTION

Abstract— Laser flash photolysis studies were carried out on a triphenylmethane dye, crystal violet (CV⁺), at 248 nm in aqueous solutions. The results show that CV⁺ undergoes photoionization and the resulting transients CV^-2+, hydrated electrons (e^-_aq) and CV⁺ radical formed by the reaction of e^-_aq with CV⁺ have been characterized. Studies using suitable scavengers were done to support the characterization of the transient species. Laser intensity effects show that the ionization is biphotonic. Two mechanisms are proposed to explain the observed photoionization involving higher excited singlet state and/ or another long-lived excited state of the dye.     

A method to carry out shape optimization with a large number of design variables

A new method for shape optimization with relatively large number of design variables is proposed. It is well known that gradient‐based methods converge to a local optimum. As a result, utilization of a richer design space does not necessarily lead to a better design. This is demonstrated via the design of an airfoil for maximum lift for Re = 1000 and α = 4° flow. The airfoil is represented by fourth‐order non‐uniform rational B‐splines, and the control points are used as design variables. Starting with a NACA0012 airfoil, it is found that the optimal airfoil obtained with 13 control points has far superior aerodynamic performance than the ones obtained with 39 and 61 control points. For effective utilization of a richer design space, it is proposed that the number of design variables be increased gradually. The method is demonstrated by designing high lift airfoils for Re = 1000 and 1 × 10⁴. The objective function is the maximization of the time‐averaged lift coefficient for α = 4°. The optimization cycle with 27 control points is initiated with the optimal airfoil obtained with 13 control points. The process is continued with gradual increase in the number of design variables. Beyond a certain number of control points, the optimization leads to a spontaneous appearance of corrugations on the upper surface of the airfoil. The corrugations are responsible for the generation of small vortices that add to the suction on the upper surface of the airfoil and lead to enhanced lift. A stabilized finite element method is used to solve the unsteady flow and adjoint equations. Copyright © 2012 John Wiley & Sons, Ltd.     

Summands of finite group algebras

Czechoslovak Mathematical Journal - We study the inverse problem of the determination of a group algebra from the knowledge of its Wedderburn decomposition. We show that a certain class of matrix...     

Determination of Alendronate Sodium by Box-Behnken Statistical Design

Spectrophotometric and LC methods have been developed and validated for the analysis of alendronate sodium in tablet dosage forms. Methods were based on reaction of the primary amino group of alendronate with ninhydrin reagent in methanolic solution of sodium bicarbonate. The condensed product exhibited UV absorption maximum at 569 nm whereas neither the reagents nor the analyte had any UV absorption. A Box-Behnken statistical design was employed to study the effect of independent variables, ninhydrin (X ₁ ), NaHCO₃ (X ₂ ) and drug concentration (X ₃ ) on dependent variable, absorption via spectrophotometer. From the point prediction tool of design software, it was observed that ninhydrin (0.26%) and NaHCO₃ (0.048 mol L^?1) produced maximum absorption. These optimized parameters were then selected for method validation. The methods obeyed Beer’s law over a selected concentration range with good correlation co-efficient (>0.99). The limit of detection and limit of quantification were 4.5 and 13.75 μg mL^?1 by spectroscopy, and 87 and 263 ng mL^?1 by LC, respectively. Accuracy, precision and % recovery were satisfactory for the proposed method. The method was highly feasible and reproducible for determination of alendronate sodium in bulk powder and pharmaceutical dosage form.