Thermodynamic Modeling of Nitric Acid Speciation Using eUNIQUAC Activity Coefficient Model

Journal of Solution Chemistry - The speciation of nitric acid was modeled using eUNIQUAC activity coefficient model and the thermodynamic dissociation constant was estimated by solving the...     

Box–Behnken Design-Based Development and Validation of a Reverse-Phase HPLC Analytical Method for the Estimation of Paclitaxel in Cationic Liposomes

Chromatographia - Stability-indicating reverse-phase HPLC analytical method for the quantification of Paclitaxel (PTX) in the bulk and cationic liposomes was developed. The optimized method was...     

Investigation of chemical space networks using graph measures and random matrix theory

Journal of Mathematical Chemistry - Large collections of molecules (chemical libraries) are nowadays routinely screened in the process of designing drugs for specific ailments. Chemical and...     

β-Cyclodextrin-based chiral nanocomposite for thin-layer chromatographic detection of enantiomers of fluoxetine

Enantioselective analysis or separation is very essential for improved therapeutic effects of drugs as the pure enantiomeric drug formulations display potential benefits over racemates. In this work, we carried out (i) the synthesis of a nanocomposite of β-cyclodextrin and 3D graphene (G/β-CD NC), and (ii) its application for the detection of fluoxetine enantiomers [(RS)-FLX)] using a thin-layer chromatographic method. The synthesized nanocomposite was introduced into silica gel slurry while preparation of thin-layer plates. The separation conditions were optimized by altering pH, temperature, and mobile phase composition. The method is simple and easy to be optimized, and it can therefore be exploited to assess and monitor routine work of enantiomeric purity of drug enantiomers. The average precision (as measured by RSD) was in the region of 1.35‒1.65% for the enantiomers of (RS)-FLX. The measured limit of detection and limit of quantification for (RS)-FLX enantiomers were 1.8 and 5.4 mg mL^‒1, respectively.

     

Traction data analysis in reference to a unique zero condition

The lack of a unique definition for the zero condition leads to innumerable zero conditions resulting in different amounts of net traction at the same value of slip. In this paper, an attempt has been made to discuss various aspects of different zero conditions and finally result in a unique definition of the zero condition. Based on this definition, a traction prediction model using mobility number approach has been developed to evaluate the performance of tractor tyres in sandy clay loam soils.     

Nonlinear Longitudinal Vibrations of Transversally Polarized Piezoceramics: Experiments and Modeling

Nonlinear behavior of piezoceramics at strong electric fields is a well-known phenomenon and is described by various hysteresis curves. On the other hand, nonlinear vibration behavior of piezoceramics at weak electric fields has recently been attracting considerable attention. Ultrasonic motors (USM) utilize the piezoceramics at relatively weak electric fields near the resonance. The consistent efforts to improve the performance of these motors has led to a detailed investigation of their nonlinear behavior. Typical nonlinear dynamic effects can be observed, even if only the stator is experimentally investigated. At weak electric fields, the vibration behavior of piezoceramics is usually described by constitutive relations linearized around an operating point. However, in experiments at weak electric fields with longitudinal vibrations of piezoceramic rods, a typical nonlinear vibration behavior similar to that of the USM-stator is observed at near-resonance frequency excitations. The observed behavior is that of a softening Duffing-oscillator, including jump phenomena and multiple stable amplitude responses at the same excitation frequency and voltage. Other observed phenomena are the decrease of normalized amplitude responses with increasing excitation voltage and the presence of superharmonics in spectra. In this paper, we have attempted to model the nonlinear behavior using higher order (quadratic and cubic) conservative and dissipative terms in the constitutive equations. Hamilton's principle and the Ritz method is used to obtain the equation of motion that is solved using perturbation techniques. Using this solution, nonlinear parameters can be fitted from the experimental data. As an alternative approach, the partial differential equation is directly solved using perturbation techniques. The results of these two different approaches are compared.     

Studies on freejets from radially lobed nozzles

The freejet characteristics of radially lobed nozzles were studied experimentally. Schlieren photographs of the freejets revealed that the lobes of the nozzles gave rise to alternate expansion-compression regions. For two of the lobed nozzles the potential core was reduced by a factor of three relative to the conical nozzle tested. The jet spread and the shear layer thickness of the lobed nozzles were considerably higher than those for the conical nozzle. The jet width and the shear layer thickness were higher in the major plane; however, the shear layer growth rate was higher in the minor plane of the lobed nozzles. Jet axial thrust measurements revealed a thrust loss of 14% for two of the lobed nozzles tested.     

Axisymmetric free vibrations of infinite thermoelastic plate

The propagation of axisymmetric free vibrations in an infinite homogeneous isotropic micropolar thermoelastic plate without energy dissipation subjected to stress free and rigidly fixed boundary conditions is investigated. The secular equations for homogeneous isotropic micropolar thermoelastic plate without energy dissipation in closed form for symmetric and skew symmetric wave modes of propagation are derived. The different regions of secular equations are obtained. At short wavelength limits, the secular equations for symmetric and skew symmetric modes of wave propagation in a stress free insulated and isothermal plate reduce to Rayleigh surface wave frequency equation. The results for thermoelastic, micropolar elastic and elastic materials are obtained as particular cases from the derived secular equations. The amplitudes of displacement components, microrotation and temperature distribution are also computed during the symmetric and skew symmetric motion of the plate. The dispersion curves for symmetric and skew symmetric modes and amplitudes of displacement components, microrotation and temperature distribution in case of fundamental symmetric and skew symmetric modes are presented graphically. The analytical and numerical results are found to be in close agreement.     

Kinetics and Mechanism of Cetyltrimethylammonium Bromide Catalyzed N-Bromosuccinimide Oxidation of D-Mannose in Acidic Medium

The kinetics and mechanism of N-bromosuccinimide (NBS) oxidation of D-mannose in the absence and presence of cetyltrimethylammonium bromide (CTAB) in acidic media have been studied under the condition [D-mannose]_T ? [NBS]_T at 40°C. Under the kinetic conditions, both the slower uncatalyzed and faster catalyzed paths go on. Both the paths show the fractional and first order dependence on [D-mannose] and [NBS]_T, respectively. The rate decreased with increase in acidity. Neither succinimide (NHS) nor Hg(II) influenced the reaction rate. Activation parameters of the reactions were determined by studying the reaction at different temperatures (30–50°C). The influence of salts on the reaction rate was also studied. CTAB accelerates the reactions and the observed effects have been explained by considering the hydrophobic and electrostatic interaction between the surfactants and reactants. In the reaction, approximately 1 mole of NBS oxidized one mole of D-mannose. A reaction scheme of the oxidation of D-mannose by NBS was found to be in consistent with the rate law and the reaction stoichiometry.     

Induced G phase through intermolecular hydrogen bonding: X. Crystallization kinetics study on two structural isomers

A comparative systematic crystallization kinetics study has been carried out on two distinct novel liquid crystalline isomers, DBA:R:DBA and DBA:H:DBA (where DBA = p-n-decyloxybenzoic acid, R = resorcinol and H = hydroquinone) using differential scanning calorimetry. The kinetics experiment is performed from the crystal G phase (kinetophase), which is a common induced phase in both compounds. The molecular mechanism and dimensionality of crystal growth are studied from the Avrami exponent n while the characteristic crystallization time (t ^*) at each crystallization temperature is deduced from the individual plots of log t vs. Δ H.