Young’s modulus of silicon nitride used in scanning force microscope cantilevers

The Young’s modulus and Poisson’s ratio of high-quality silicon nitride films with 800 nm thickness, grown on silicon substrates by low-pressure chemical vapor deposition, were determined by measuring the dispersion of laser-induced surface acoustic waves. The Young’s modulus was also measured by mechanical tuning of commercially available silicon nitride cantilevers, manufactured from the same material, using the tapping mode of a scanning force microscope. For this experiment, an expression for the oscillation frequencies of two-media beam systems is derived. Both methods yield a Young’s modulus of 280–290 GPa for amorphous silicon nitride, which is substantially higher than previously reported (E5146 GPa). For Poisson’s ratio, a value of n 50.20 was obtained. These values are relevant for the determination of the spring constant of the cantilever and the effective tip–sample stiffness

Studies on the dynamics and rheology of dilute suspensions of Brownian particles in simple shear flow under the action of an external force

We present a novel approach to computing the orientation moments and rheological properties of a dilute suspension of spheroids in a simple shear flow at arbitrary Peclct number based on a generalised Langevin equation method. This method differs from the diffusion equation method which is commonly used to model similar systems in that the actual equations of motion for the orientations of the individual particles are used in the computations, instead of a solution of the diffusion equation of the system. It also differs from the method of 'Brownian dynamics simulations' in that the equations used for the simulations are deterministic differential equations even in the presence of noise, and not stochastic differential equations as in Brownian dynamics simulations. One advantage of the present approach over the Fokker-Planck equation formalism is that it employs a common strategy that can be applied across a wide range of shear and diffusion parameters. Also, since deterministic differential equations are easier to simulate than stochastic differential equations, the Langevin equation method presented in this work is more efficient and less computationally intensive than Brownian dynamics simulations.We derive the Langevin equations governing the orientations of the particles in the suspension and evolve a procedure for obtaining the equation of motion for any orientation moment. A computational technique is described for simulating the orientation moments dynamically from a set of time-averaged Langevin equations, which can be used to obtain the moments when the governing equations are harder to solve analytically. The results obtained using this method are in good agreement with those available in the literature.The above computational method is also used to investigate the effect of rotational Brownian motion on the rheology of the suspension under the action of an external force field. The force field is assumed to be either constant or periodic. In the case of con- I stant external fields earlier results in the literature are reproduced, while for the case of periodic forcing certain parametric regimes corresponding to weak Brownian diffusion are identified where the rheological parameters evolve chaotically and settle onto a low dimensional attractor. The response of the system to variations in the magnitude and orientation of the force field and strength of diffusion is also analyzed through numerical experiments. It is also demonstrated that the aperiodic behaviour exhibited by the system could not have been picked up by the diffusion equation approach as presently used in the literature.The main contributions of this work include the preparation of the basic framework for applying the Langevin method to standard flow problems, quantification of rotary Brownian effects by using the new method, the paired-moment scheme for computing the moments and its use in solving an otherwise intractable problem especially in the limit of small Brownian motion where the problem becomes singular, and a demonstration of how systems governed by a Fokker-Planck equation can be explored for possible chaotic behaviour.

Studies in molecular mechanics using spectroscopic data exact force field and bond in homogeneity

This thesis deals with some studies in molecular mechanic using spectroscopic data. It includes an improvement in the parameter technique for the evaluation of exact force fields, the introduction of a new and simple algebraic method for the force field calculation and a study of asymmetric variation of bonding forces along a bond.

Studies in molecular dynamics: new criteria for evaluation of intramolecular force fields

The present thesis deals with some studies in molecular dynamics using spectroscopic data. Two new approximation procedures the variable method and the average bonding energy criterion have been developed for a reliable calculation of molecular force fields and applied to several molecular species belonging to the xy2 type.

Prevalence and distribution of Salmonella serotypes in marketed broiler chickens and processing environment in Coimbatore City of southern India

Broiler chicken is gaining popularity among the consumers of India. Since poultry is recognised as a leading food vehicle for Salmonella contamination, the prevalence and distribution of Salmonella serotypes in broiler chickens and processing environments of retail outlets has been studied. In the present study 214 samples of broiler chicken and 311 environmental samples from cage were analysed for the presence of Salmonella. Of the various body parts of live chicken analysed prevalence varied from 1.4% in cloacca to 6.9% in crop region. Environmental samples from the cage showed higher prevalence of Salmonella ranging from0 to 16.67%. Apart from Salmonella enteritidis, which was the predominant Salmonella serotype in the chickens as well as in the environmental samples, other serotypes such as S. bareilly, S. cerro, S. mbandaka and S. moladewere also encountered. The results of the research calls for strict hygiene standards for retail broiler chicken processing outlets

The incidence ,Antibiotic resistence and survival of salmonella and escherichia coli isolated from broiler chicken retail outlets

The incidence of salmonella and escherichia coli in chicken retail outlets in a residential area of coimbatore, Tamilnadu India was studied with the view that accessories may be a source of cross contamination.Accessories like cages,knives ,chopping boards weighing balance trays and the hands of butcher were examined.A toatal of 14 salmonella as well as 31 E.coli were isolated from different sources. The incidence of E.coli was higher than that of Salmonella.The highest incidence of Salmonella was found in chopping boards and the maximum level of E.Coli was detected in cages.