The cyclic CO2 trimer: observation of a parallel band and determination of an intermolecular out-of-plane torsional frequency

A new parallel (DeltaK=0) band of the cyclic CO(2) trimer is observed at 2364 cm(-1). The trimers are generated in a pulsed supersonic expansion from a slit-jet nozzle and probed with a tunable infrared diode laser. The band is assigned as a combination of an intramolecular CO(2) monomer nu(3) stretch and an intermolecular out-of-plane torsion, giving a torsional frequency of 12-13 cm(-1). The band is surprisingly strong and completely unperturbed, providing a rare and near perfect example for a parallel band of a symmetric top molecule with C(3h) symmetry and zero nuclear spins.     

Measurement and revised analysis of the torsional combination band of the nonpolar N2O dimer at 2249 cm(-1)

The high-resolution infrared spectrum of the weakly-bound dimer (N(2)O)(2) is studied using a rapid-scan tunable-diode laser spectrometer to probe a pulsed supersonic jet expansion. An observed band with c-type rotational structure is assigned as a combination of the intramolecular N(2)O nu(1) stretching vibration and the intermolecular out-of-plane dimer torsional vibration, with a vibrational origin at 2249.360 cm(-1). The resulting torsional frequency for the nonpolar N(2)O dimer is about 21.5 cm(-1). The present rotational analysis is completely different from that reported previously for the same band [Hecker et al., Phys. Chem. Chem. Phys., 2003, 5, 2333], which gave a band origin some 1.53 cm(-1) lower.     

A simplified model of oscillating electrolytes

Unstable electrophoretic transport leading to oscillations in concentration profiles occur in certain electrolyte systems known as oscillating electrolytes whose eigenmobilities are complex valued. The study of the nonlinear behavior of such systems is of great interest but is constrained due to a high degree of complexity in the governing equations. Here we present a simplified model of unstable electrophoretic transport in a binary system that reduces the governing equations to two partial differential equations only and does away with other equations that characterize acid–base dissociation reactions and electroneutrality. We present analytical expressions for electromigration fluxes and validate the model with full nonlinear simulations. The model exhibits similar nonlinear behavior as the actual unstable electrophoretic system under various initial disturbances. For comparison, we also show that similar modeling for a stable system predicts concentration profiles that quantitatively agree with its nonoscillating dynamics. Moreover, the unique feature of electromigration flux in oscillating electrolytes that unfolds from the modeling led us to find an elegant explanation of the instability mechanism. Our theory gives a qualitative understanding of the existence and growth of large oscillation patterns in oscillating electrolytes.     

Flow through an oscillating rectangular duct for generalized Maxwell fluid with fractional derivatives

The velocity field and the associated shear stresses corresponding to the unsteady flow of generalized Maxwell fluid on oscillating rectangular duct have been determined by means of double finite Fourier sine and Laplace transforms. These solutions are also presented as a sum of the steady-state and transient solutions. The solutions corresponding to Maxwell fluids, performing the same motion, appear as limiting cases of the solutions obtained here. In the absence of w, namely the frequency, and making α → 1, all solutions that have been determined reduce to those corresponding to the Rayleigh Stokes problem on oscillating rectangular duct for Maxwell fluids. Finally, some graphical representations confirm the above assertions.     

Generalized Monotone Mapping with an Application for Solving a Variational Inclusion Problem

The aim of this paper is to define a generalized monotone mapping, which is the sum of symmetric cocoercive mapping and symmetric monotone mapping. The resolvent operator associated with generalized monotone mapping is defined and some of its properties are shown. We solve a variational inclusion problem using these new concepts. For illustration, some examples are given.     

Intuitionistic fuzzy linear regression analysis

Linear regression analysis in an intuitionistic fuzzy environment using intuitionistic fuzzy linear models with symmetric triangular intuitionistic fuzzy number (STriIFN) coefficients is introduced. The goal of this regression is to find the coefficients of a proposed model for all given input–output data sets. The coefficients of an intuitionistic fuzzy regression (IFR) model are found by solving a linear programming problem (LPP). The objective function of the LPP is to minimize the total fuzziness of the IFR model which is related to the width of IF coefficients. An illustrative example is also presented to depict the solution procedure of the IFR problem by using STriIFNs.     

Microextraction of Rosmarinic Acid Using CMK-3 Nanoporous Carbon in a Packed Syringe

CMK-3 nanoporous carbon was prepared and used as an efficient sorbent for microextraction in packed syringe of rosmarinic acid in Rosmarinus officinalis L. (rosemary). In the proposed method, only 2 mg of the nanoporous material, inserted between a syringe’s barrel and needle, was sufficient for the extraction with minimum consumption of organic solvents. Sample preparation was performed on the packed bed using a laboratory-made programmable apparatus. The apparatus was designed and used for automation of the conditioning, sampling, washing and elution steps of the method, and increasing the reproducibility of the experiments. For optimization of the experimental parameters, a central composite design method was used. Under the optimized conditions (i.e., number of adsorption cycles 14 times, number of elution cycles ten times and volume of elution 100 μL), an extraction recovery of 90 (±4.5) % was obtained for rosmarinic acid. The same packing bed could be used for at least 80 extractions without significant changes in its properties. The efficiency of the nanoporous sorbent was found to be superior to that of activated carbon, by a factor of about 17. The proposed method was successfully applied to the extraction of three rosemary samples before analysis by HPLC.     

Inhibitor effect of sodium benzoate on the corrosion behavior of nanocrystalline pure iron metal in near-neutral aqueous solutions

Nanocrystalline iron coating was produced on carbon steel surface by pulse electrodeposition using citric acid bath. The grain size of a nanocrystalline surface was analyzed by X-ray diffractometry and scanning electron microscopy. The electrochemical behavior of nanocrystalline iron coating in the presence of sodium benzoate was evaluated in 30 mg l^-1 NaCl + 70 mg l^-1 Na₂SO₄ aqueous solution using potentiodynamic polarization curves and electrochemical impedance spectroscopy. The results were compared with that of the coarse-grained iron surface. The thermodynamic properties of the inhibitor adsorption were also determined. The results indicated that corrosion inhibition of sodium benzoate in near-neutral aqueous solution was increased as the grain size of iron was decreased from micro- to nanocrystalline surface. This was reported in terms of excess free energy of nanocrystalline surface.     

Eigenfrequencies of symmetric planar frames with semi-rigid joints using weighted graphs

The main aim of this paper is to extend the recently developed methods for calculating the free vibration analysis of planar symmetric frames to include the effect of semi-rigidity of the joints. This is achieved by decomposing a symmetric weighted graph model into two submodels and using canonical forms in such a manner that the union of the eigenvalues of the submodels result in the eigenvalues of the entire model. Thus the eigenfrequencies of the frame is obtained in an efficient manner. Here, only the free vibration of frames with linear behavior is studied.     

Spectrophotometric determination of diphenhydramine hydrochloride in pharmaceutical preparations and biological fluids via ion-pair formation

A simple, sensitive and accurate spectrophotometric method has been described for the assay of diphenhydramine hydrochloride (DPH) in raw material and in biological samples. The method is based on extraction of DPH into dichloromethane as ion-pair complexes with patent blue (PB), eriochrome black T (EBT), methyl orange (MO) and bromocresol purple (BCP) in acidic medium. The coloured species exhibited absorption maxima at 632, 514, 428 and 414 nm for PB, EBT, MO and BCP, with molar absorptivity values of 1.32 × 10⁵, 2.36 × 10⁴, 3.68 × 10⁴ and 3.07 × 10⁴ l mol^?1 cm^?1, respectively. The reaction conditions were optimized to obtain the maximum colour intensity. Beer’s law was obeyed with a good correlation coefficient (0.9982–0.9993) in the concentration ranges 0.5–3, 2.0–16, 2.0–10 and 1.0–10 μg ml^?1 for PB, EBT, MO and BCP methods, respectively. The composition ratio of the ion-association complexes was found to be 1:1 in all cases as established by Job’s method. The conditional stability constant (K_f) and the free energy changes (ΔG°) were determined for all complexes formed. The proposed method was successfully applied for the determination of DPH in tablets and human urine with good accuracy and precision. Statistical comparison of the results with those obtained by the official method showed good agreement and indicated no significant difference in accuracy and precision.