K. K. Singh

In-plane displacement measurement using objective speckles in photorefractive two-beam coupling : effect of multiple exposures

Abstract A technique is proposed for the real-time measurement of in-plane displacement utilizing objective speckles and two-beam coupling in a photorefractive BaTiO 3 crystal. Speckles generated by a diffuse object in free-space geometry are used as the signal in two-beam coupling. The set-up is such that the phase shift between the refractive index grating and the interference grating is + π 2 (amplification mode). Due to the in-plane displacement, Youngs fringes are obtained with a bright speckle background as a result of the signal amplification and beam fanning. The slow process of two-beam coupling amplification in a BaTiO 3 crystal is exploited for recording multiple exposures. This method of recording multiple exposures provides a simple and convenient way of analyzing the rigid body motions with enhanced accuracy by sharpening the fringes and with acceptable contrast. Theory has been developed to obtain the intensity distribution in the fringes formed in real time at the observation plane. Experiments have been conducted to show the validity of the theoretical results. Good agreement is established between the theory and the experiments.

Cutaneous reactions due to antihypertensive drugs

Out of a total of 1147 patients on antihypertensive drugs, 23 (2.04%) developed adverse cutaneous drug reactions (ACDR). The commonest antihypertensive drug group causing ACDR was beta-blockers of which atenolol was the commonest culprit. The second most common group was calcium channel blockers with amlodipine as the commonest offender. The most common patterns of ACDR observed included urticaria followed by lichenoid drug eruption (LDE). We noted 2 new patterns of reactions; (i) one patient developed brownish blue pigmentation of nails while on atenolol for 3 years, which resolved in 4 months after withdrawal and (ii) another patient on amlodipine for 8 years developed Schambergs like purpuric pigmentation, which resolved on withdrawal of drug within 3 months. These findings have not been reported in the literature earlier. This study is presented for paucity of Indian data on ACDR due to antihypertensive drugs, and remarkable advancement in area of cardiovascular and antihypertensive pharmacology and a large number of population taking antihypertensive drugs.

Design and performance analysis of bi-directional TWDM OFDM-PON with wavelength reuse scheme

The proposed work demonstrates an architecture for bi-directional Hybrid Passive Optical Network. It employs OFDM signals at 25 Gbps for downstream transmission. Utilization of wavelength reuse scheme with NRZ modulation to carry upstream traffic at 10 Gbps helps in reducing the cost of ONU. Power budget and BER analysis of the system is done for downstream transmission and the concept of upstream re-modulation has been discussed. The performance analysis is based on received power, eye diagram and constellation diagram.

The Identification of Displacement Vector in Double-Exposure Speckle Photography of the Out-of-Plane Motion

A technique is proposed for identifying the sign of the out-of-plane displacement in double-exposure speckle photography, thus resolving the ambiguity existing with respect to the sign of the displacement. Our method is based on the introduction of a known in-plane displacement of the object or the recording plane between the two exposures. This results in shifting the point of null speckle displacement in a direction depending upon the direction of the out-of-plane displacement. The magnitude of the displacement can be evaluated from the measurements made on the fringes obtained after shifting the speckle gram at the filtering stage in a direction opposite to that of the shift of the point of null speckle displacement. Experiments have been conducted to implement the proposed technique for determining the magnitude as well as the direction of the out-of-plane displacement.