Simultaneous Determination of Acetylsalicylic Acid and Caffeine in Pharmaceutical Formulation by First Derivative Synchronous Fluorimetric Method

A sensitive, rapid, and specific assay has been developed for the simultaneous determination of acetylsalicylic acid and caffeine in commercial tablets based on their natural fluorescence. The mixture of these drugs was resolved by first derivative synchronous fluorimetric technique using two scans. At Δλ=106 nm, using first derivative synchronous scanning, only acetylsalicylic acid yields a detectable signal at 316 nm (peak to zero method) which is unaffected by caffeine. At Δλ=30 nm, the signal of caffeine at 288 nm (peak to zero method) is not affected by acetylsalicylic acid. The range of application is between 0.021 and 41.62 μg ml⁻¹ (correlation coefficient, R=0.9995) for acetylsalicylic acid and between 0.4486 and 44.86 μg ml⁻¹ (correlation coefficient, R=0.99786) for caffeine. The recovery range of 98.40–102% for acetylsalicylic acid and 90–100.5% for caffeine from their synthetic mixture was reported. Overall recovery of both compounds about 97–99% for acetylsalicylic acid and 97–98% for caffeine was obtained from real sample analysis. The detection limits are 0.0013 μg ml⁻¹ and 0.0306 μg ml⁻¹ for acetylsalicylic acid and caffeine, respectively. The relative standard deviation (n=10) for 20 μg ml⁻¹ of acetylsalicylic acid is 2.75% and for 2.2 μg ml⁻¹of caffeine is 1.7%.     

Field-induced phase transitions and reversible field-induced inversion of chirality in tilted smectic phases of bent-core mesogens

Three homologous achiral five-ring bent-core mesogens are presented where 4-chlororesorcinol is the central core and the aromatic rings are linked by ester groups. These compounds form smectic phases with a tilted arrangement of the molecules (tilt angle ≈ 45^°). On cooling the isotropic liquid this phase adopts a fan-like texture which shows for two homologues at relatively high electric fields ( 25-35V μm^-1) an antiferroelectric electro-optical response based on the collective rotation of the molecules around their long axes. At lower temperature the application of a sufficiently high electric field leads to a continuous transition into a non-birefringent texture which exhibits randomly distributed domains of opposite handedness. These domains can be reversibly switched into a state of opposite chirality by reversal of the field polarity. This switching is bistable and shows a current response typical for a ferroelectric ground state. The possible mechanism of the field-induced phase transition, of the ferroelectric switching and of the field-induced inversion of the chirality is discussed on the base of XRD, ¹³C- and ¹H-NMR investigations, dielectric and electro-optical measurements.     

Hall effect on MHD free convection boundary layer flow past a vertical flat plate

Effects of Hall current on MHD free convection boundary layer flow of a viscous incompressible electrically conducting fluid past a heated vertical flat plate of finite dimension in the presence of a uniform transverse magnetic field have been studied. An exact solution of the governing equations describing the flow has been obtained. The velocity field, induced magnetic field and bulk temperature distributions in the boundary layer flow have been discussed. It is found that the velocity components increase with an increase in Hall parameter. It is noticed that the induced magnetic field components are radically influenced by the Hall parameter. It is also found that the magnitude of bulk temperature in the x-direction decreases with an increase in either Hall parameter or magnetic parameter. On the other hand, the magnitude of the bulk temperature in the z-direction increases with an increase in Hall parameter whereas it decreases with an increase in magnetic parameter.     

Hybrid phase synchronization between identical and nonidentical three-dimensional chaotic systems using the active control method

In this article, the active control method is used to investigate the hybrid phase synchronization between two identical Rikitake and Windmi systems, and also between two nonidentical systems taking Rikitake as the driving system and Windmi system as the response system. Based on the Lyapunov stability theory, the sufficient conditions for achieving the hybrid phase synchronization of two chaotic systems are derived. The active control method is found to be very effective and convenient to achieve hybrid phase chaos synchronization of the identical and nonidentical chaotic systems. Numerical simulation results which are carried out using the Runge–Kutta method show its feasibility and effectiveness for the synchronization of dynamical chaotic systems.     

Master-slave chaos synchronization via optimal fractional order PI λ D μ controller with bacterial foraging algorithm

Chaos synchronization in a master-slave configuration has been studied in this paper with a fractional order (FO) Proportional-Integral-Derivative (PID) controller using an intelligent Bacterial Foraging Optimization (BFO) algorithm. A?comparative study has been made to highlight the advantage of using a fractional order PI ^?? D ^?? controller over the conventional PID controller for chaos synchronization using two Lu systems as a representative example. Simulation results are presented to show the effectiveness of the proposed chaos synchronization technique over the existing methodologies.     

Numerical simulation and PIV study of compressible vortex ring evolution

Formation and evolution of a compressible vortex ring generated at the open end of a short driver section shock tube has been simulated numerically for pressure ratios (PR) of 3 and 7 in the present study. Numerical study of compressible vortex rings is essential to understand the complicated flow structure and acoustic characteristics of many high Mach number impulsive jets where simultaneously velocity, density and pressure fields are needed. The flow development, incident shock formation, shock diffraction, vortex ring formation and its evolution are simulated using the AUSM+ scheme. The main focus of the present study is to evaluate the time resolved vorticity field of the vortex ring and the shock/expansion waves in the starting jet for short driver section shock tubes—a scenario where little data are available in existing literature. An embedded shock and a vortex induced shock are observed for PR =  7. However the vortex ring remains shock free, compact and unaffected by the trailing jet for PR =  3. Numerical shadowgraph shows the evolution of embedded shock and shock/expansion waves along with their interactions. The velocity and vorticity fields obtained from simulation are validated with the particle image velocimetry results and these data match closely. The translational velocity of the vortex ring, velocity across the vortex and the centre line velocity of the jet obtained from simulation also agree well with the experimental results.     

Forced convection heat transfer from an equilateral triangular cylinder at low Reynolds numbers

An unsteady two-dimensional numerical simulation is performed to investigate the forced convection heat transfer for flow past a long heated equilateral triangular cylinder in an unconfined medium for the low Reynolds number laminar regime. The Reynolds number considered in this study ranges from 50 to 250 with three different values of Prandtl number (Pr?=?0.71, 7 and 100). Fictitious confining boundaries are chosen on the lateral sides of the computational domain that makes the blockage ratio β?=?5?% in order to make the problem computationally feasible. An unstructured triangular mesh is used for the computational domain discretization and the simulation is carried out with the commercial CFD solver Fluent. The flow and heat transfer characteristics are analyzed with the streamline and isotherm patterns at various Reynolds numbers. The dimensionless frequency of vortex shedding (Strouhal number), drag coefficient and Nusselt numbers are presented and discussed. The results obtained are in good agreement with the available results in the literature.     

Impact of thermal radiation on MHD slip flow over a flat plate with variable fluid properties

The influence of partial slip, thermal radiation and temperature dependent fluid properties on the hydro-magnetic fluid flow and heat transfer over a flat plate with convective surface heat flux at the boundary and non-uniform heat source/sink is studied. The transverse magnetic field is assumed as a function of the distance from the origin. Also it is assumed that the fluid viscosity and the thermal conductivity vary as an inverse function and linear function of temperature respectively. Using the similarity transformation, the governing system of non-linear partial differential equations are transformed into similarity non-linear ordinary differential equations and are solved numerically using symbolic software MATHEMATICA 7.0. The numerical values obtained within the boundary layer for the dimensionless velocity, temperature, skin friction coefficient and the Nusselt number are presented through graphs and tables for several sets of values of the parameters. The effects of various physical parameters on the flow and heat transfer characteristics are discussed from the physical point of view.     

Scattered waves and motions of marine vessels advancing in a seaway

The steady forward motion of a marine vessel modifies the incident and scattered waves as well as its dynamic characteristics in a seaway. Small amplitude assumptions of the surface waves and vessel dynamic responses lead to linearization of the potential flow problem and its solution in the frequency domain. The mathematical formulation adopts a translating coordinate system at the vessel forward speed. The free surface boundary condition accounts for the modification of the uniform current around the vessel and a new radiation condition takes into account the Doppler shift of the scattered waves. A boundary element model, based on the Rankine source distribution, describes the steady and oscillatory flows around the vessel. Stokes’ theorem allows evaluation of the surface integrals involving the so-called m-terms due to oscillation of the vessel in a current. Through a numerical experiment with a Wigley hull form, we establish the convergence of the numerical model, verify the radiation condition, and examine the scattered wave patterns for a full range of forward speeds. Previous laboratory data provides validation of the computed hydrodynamic coefficients and dynamic response as well as the potential flow model for general seakeeping applications.     

Evaluating the effect of different test parameters on the tensile mechanical properties of single crystal silver nanowires using molecular dynamics simulation

Nanowires show amazing mechanical properties with respect to their bulk counterpart owing to their very high specific surface and/or interface area and, thus, are widely studied among several researchers. But it is difficult to study the mechanical properties of nanowires at atomistic level, and computational tools provide the required solution. Molecular dynamics simulation studies were carried out in this work to evaluate the mechanical properties of single crystal silver nanowire subjected to tensile deformation under varying wire diameter (4–14 nm), test temperature (100–500 K), and strain velocity (1–6 Å/ps). The simulation were carried out in analogous to real experiment, and the engineering stress and strain were calculated from the simulation result of load and displacement data. The mechanical properties like yield strength and Young’s modulus were calculated from the engineering stress-strain curve. The effect of different test parameters like wire diameter, equilibration temperature, and strain velocity on the mechanical properties were also thoroughly investigated. The result shows that single crystal silver nanowire shows excellent mechanical properties and, thus, can be used as a reinforcing agent to develop ultra-high strength advanced materials for defense and aerospace applications.