Saurabh K. Yadav

In vitro chloramphenicol detection in a Haemophilus influenza model using an aptamer-polymer based electrochemical biosensor.

A sensitive and selective electrochemical biosensor is developed for the determination of chloramphenicol (CAP) exploring its direct electron transfer processes in in-vitro model and pharmaceutical samples. This biosensor exploits a selective binding of CAP with aptamer, immobilized onto the poly-(4-amino-3-hydroxynapthalene sulfonic acid) (p-AHNSA) modified edge plane pyrolytic graphite. The electrochemical reduction of CAP was observed in a well-defined peak. A quartz crystal microbalance (QCM) study is performed to confirm the interaction between the polymer film and the aptamer. Cyclic voltammetry (CV) and square wave voltammetry (SWV) were used to detect CAP. The in-vitro CAP detection is performed using the bacterial strain of Haemophilus influenza. A significant accumulation of CAP by the drug sensitive H. influenza strain is observed for the first time in this study using a biosensor. Various parameters affecting the CAP detection in standard solution and in in vitro detection are optimized. The detection of CAP is linear in the range of 0.1-2500 nM with the detection limit and sensitivity of 0.02 nM and 0.102 µA/nM, respectively. CAP is also detected in the presence of other common antibiotics and proteins present in the real sample matrix, and negligible interference is observed.

A review on determination of steroids in biological samples exploiting nanobio-electroanalytical methods

The applications of nanomaterial modified sensors, molecularly imprinting polymer based, aptamer based, and immunosensors have been described in the determination of steroids using electroanalytical techniques. After a brief description of the steroids and assays in biological fluids, the principles of electrochemical detection with the advantages and the limitations of the various sensors are presented. The nanomaterial modified sensors catalyze the oxidation/reduction of steroids and are suitable for sensing them in environmental samples and biological fluids. The determination of steroids based on their reduction has been found more useful in comparison to oxidation as the common metabolites present in the biological fluids do not undergo reduction in the usual potential window and hence, do not interfere in the determination. The sensors based on immunosensors and aptamers were found more sensitive and selective for steroid determination. Conducting polymer modified bio-sensors and microchip devices are suggested as possible future prospects for the ultra sensitive and simultaneous determination of steroids and their metabolites in various samples.

A simple and efficient XFEM approach for 3-D cracks simulations

In this work, a simple and efficient XFEM approach has been presented to solve 3-D crack problems in linear elastic materials. In XFEM, displacement approximation is enriched by additional functions using the concept of partition of unity. In the proposed approach, a crack front is divided into a number of piecewise curve segments to avoid an iterative solution. A nearest point on the crack front from an arbitrary (Gauss) point is obtained for each crack segment. In crack front elements, the level set functions are approximated by higher order shape functions which assure the accurate modeling of the crack front. The values of stress intensity factors are obtained from XFEM solution by domain based interaction integral approach. Many benchmark crack problems are solved by the proposed XFEM approach. A convergence study has been conducted for few test problems. The results obtained by proposed XFEM approach are compared with the analytical/reference solutions.

AuNPs-poly-DAN modified pyrolytic graphite sensor for the determination of Cefpodoxime Proxetil in biological fluids.

A sensitive and selective electrochemical method for Cefpodoxime Proxetil (CP) determination has been developed by incorporating gold nanoparticles (AuNPs) onto the poly-1,5-diaminonapthalene layer (p-DAN) coated pyrolytic graphite. The modified sensor was characterized by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The sensor exhibited an effective catalytic response towards oxidation of CP with excellent reproducibility and stability. The peak current of CP was found to be linear in the range of 0.1-12 μM and detection limit and sensitivity of 39 nM (S/N=3) and 4.621 μA μM(-1), respectively, were observed. The method was successfully applied for the determination of CP in pharmaceutical formulations and human urine samples. The common metabolites present in human urine such as uric acid, ascorbic acid, xanthine and hypoxanthine did not interfere in the determination. A comparison of the results obtained by using developed method with high performance liquid chromatography (HPLC) indicated a good agreement. The method is simple, sensitive, rapid and precise and is useful for the routine determination of CP in pharmaceutical dosages and biological samples.

Carbon nanotube embedded poly 1,5-diaminonapthalene modified pyrolytic graphite sensor for the determination of sulfacetamide in pharmaceutical formulations

An electrochemically conductive single-walled carbon nanotube (SWCNT) embedded poly 1,5-diaminonapthalene (DAN) modified sensor has been developed for the determination of sulfacetamide (SFA). The surface morphology of the modified sensor has been characterized by FE-SEM, which revealed good dispersion of the carbon nanotube in polymer matrix. SFA was quantified using square wave voltammetry in phosphate buffer of pH 7.2, which acted as supporting electrolyte during analysis. The modified sensor exhibited an effective catalytic response towards the oxidation of SFA with excellent reproducibility and stability. The peak current of SFA was found to be linear in the concentration range of 0.005-1.5 mM and detection limit and sensitivity of 0.11 μM (S/N=3) and 23.977 µA mM(-1), respectively were observed. The analytical utility of method was checked by determining the SFA in various pharmacological dosage forms. The results obtained from the voltammetry were validated by comparing the results with those obtained from HPLC. The proposed method is sensitive, simple, rapid and reliable and is useful for the routine analysis of SFA in pharmaceutical laboratories.

Performance of Hydrostatic Textured Thrust Bearing with Supply Holes Operating with Non-Newtonian Lubricant

ABSTRACT The present article proposes a technique to improve the performance of textured hydrostatic thrust bearings with the use of oil supply holes. The article provides a comparison between smooth and surface-textured hydrostatic thrust bearings. To get an accurate prediction of the caviation regime, the Jakobsson-Floberg-Olsson (JFO) mass conservation algorithm has been used instead of the Reynolds boundary conditions. It has been observed that surface texture results in a significant decrease in friction power loss along with an improvement in other performance parameters. The study also reveals that the location of the supply hole for the lubricant system significantly affects the bearing performance.

Performance of hydrostatic circular thrust pad bearing operating with Rabinowitsch fluid model

Polymer-based additives such as poly isobutylene are blended with lubricating oil to enhance the lubricating performance of the base oil. The Rabinowitsch fluid model effectively describes the influence of polymer additives on the lubricating performance of a non-Newtonian (pseudoplastic) lubricant. This article deals with the analysis of a capillary compensated hydrostatic circular thrust pad bearing using Rabinowitsch fluid model. For a circular recess hydrostatic thrust bearing operating with pseudoplastic lubricant, the closed form expressions for load-carrying capacity, lubricant flow rate, fluid film stiffness coefficient and damping coefficient have been obtained using a small perturbation method. The close form solutions for different performance characteristic parameters have been compared with the results obtained from finite element method formulation. The numerically simulated results indicate that pseudoplastic parameter significantly affects the parameters of the bearing performance characteristics such as pocket pressure, lubricant flow rate, fluid film stiffness coefficient and damping coefficient. The value of the fluid film stiffness coefficient gets substantially increased with the pseudoplastic parameter whereas the value of damping coefficient gets reduced. The analytical results presented in this study can be used to obtain an optimum performance of a hydrostatic circular thrust pad bearing.

A direct numerical approach to compute the nonlinear rotordynamic coefficient of the noncircular gas journal bearing

Gas bearings are extensively used in several industrial applications to support the rotating load at high speed due to its favorable characteristics. The numerical computation of the gas film damping and stiffness coefficients is a difficult task due to nonlinearity in the Reynolds equation for compressible lubricant. In the present work, a numerical method based on the finite element method is developed for the direct computation of gas film damping and stiffness coefficients. In this method, a double partial differential equation approach has been used to compute the dynamic characteristics. Further, the numerical results presented shows that the bearing ellipticity ratio significantly affects the nonlinear trajectory of the journal.

Finite element analysis of tilted thrust pad bearings of various recesses shapes considering thrust pad flexibility

The performance characteristics of capillary compensated tilted pad hydrostatic bearing operating with Newtonian lubricant and cubic law lubricant are studied numerically considering the flexibility of pad. The two-dimensional Reynolds equation coupled with three-dimensional equilibrium equations governing the deformation of thrust pad has been solved by using finite element method. The results indicate the influence of tilt parameter and bearing deformation on bearing performance characteristics parameters. In the analysis, four different types of recess shapes such as rectangular, circular, elliptical, and square have been chosen for the analysis. The results show that the consideration of bearing pad deformation significantly increases the value of fluid-film stiffness coefficient and decreases the value of fluid-film damping coefficient. The fluid-film pressure distributions also compared for circular, elliptical, square, and rectangular bearing.

Harmonic XFEM Simulation of 3-D Cracks

Fracture mechanics is widely used nowadays to study and analyze the failure of components/structures. Several failures in structures are related to fracture mechanics. When failure due to fracture occurs, they are mostly unpredicted, quick, and disastrous in nature. Therefore, it becomes necessary for us to pay attention to minimize the failure when designing and analyzing modern-day structures. The stress intensity factors are extracted from the HXFEM solution by volume-based interaction integral approach using the curvilinear coordinate system and are compared against the standard XFEM and the analytical result available in the literature. In this volume-based interaction integral approach, the volume is virtually extended and integrated by applying Gauss divergence theorem. The numerical results are obtained for edge and penny crack problems.