We report here on studies of reorientation of human red blood cells (RBCs) in an optical trap. We have measured the time required, tre, for the plane of the RBC entering the optical trap to undergo a 90-deg rotation to acquire an edge on orientation with respect to the beam direction. This has been studied as a function of laser power, P, at the trap center. The variation of tre with increasing P shows an initial sharp decrease followed by a much smaller rate of further decrease. We find that this experimentally measured variation is not in complete agreement with the variation predicted by a theoretical model where the RBC is treated as a perfectly rigid circular disk-like body. We argue that this deviation arises due to deformation of the RBC. We further reason that this feature is dominated by the elastic behavior of the RBC membrane. We compare the studies carried out on normal RBCs with RBCs where varying conditions of membrane stiffness are expected. We propose that the value of energy used for maximum deformation possible during a reorientation process is an indicator of the membrane elasticity of the system under study.

Tasar silk is a variety of non-mulberry silk indigenous to the Indian subcontinent. We present the measured frequencydependent viscoelastic moduli of Tasar regenerated silk fibroin (RSF) solution using optical tweezers at two concentrations (0.16% and 0.25% w/v) and extend these measurements to the low frequency regime using a video microscopy technique. We extend the investigation on the rheological behavior of Tasar RSF for four more RSF concentrations, viz., 0.50%, 1.00%, 2.50% and 5.00% using video microscopy. In all the RSF samples, both storage and loss moduli are found to increase with frequency. At lower frequencies the loss modulus is more than the storage modulus and exhibit similar behavior until a crossover frequency beyond which the storage modulus exceeds the loss modulus at all frequencies. The relaxation time which is inversely related to the crossover frequency is found to rise sharply at 5% w/v, indicating the onset of gelation in the sample. These results are examined in relation to the viscoelastic parameters of mulberry silk, wherein the larger crossover frequencies at the same higher concentrations indicate relaxation times that are an order of magnitude smaller than those measured for Tasar RSF.

This paper presents the process of developing an aerodynamics package and a suspension system for a Formula SAE race car, with the help of computational methods for the aerodynamics design and analytical methods for the suspension design. Aerodynamics package involving Front and Rear wings and a suspension system involving a strut activated damper with double wishbones is developed. Vehicle parameters such as wheelbase, track width, etc. and the geometry for the front and rear wings are specified by conducting a review of the SAE rule book. 2D CFD simulations are performed on a wide range of high lift low Reynolds number Airfoils at various geometric configurations to select an airfoil configuration with best performance characteristics. 3D models of front and rear wings are made from the data obtained from 2D simulations to conduct 3D simulations of the wings and the entire assembly of the car with and without the wings. A kinematic analysis is performed on the suspension system since it plays a very important role in the dynamics of the vehicle. Data obtained from the aero simulations and suspension analysis is analyzed in a lap time simulator to predict and compare the performance and lap times of the car with and without the aerodynamic package.

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