arXiv subjects

A. Krishnan

Publications and source records attributed to A. Krishnan.

6 recordsLinked to original sources

arXiv2018

On-chip label-free plasmonic based imaging microscopy for microfluidics

In this work, we demonstrated on-chip label-free imaging microscopy using real and Fourier Plane (FP) microscopic dark field images of Surface Plasmons (SP), excited on engineered 1D and 2D low aspect ratio periodic plasmonic nanostructures. The periodic plasmonic nanostructures with period almost equal to resonance wavelength, were engineered to exhibit transmission resonances as transmission peaks in visible spectrum at normal incidence, without using extraordinary optical transmission phenomena. The plasmonic nanostructures exhibited a polarization rotation of 90 degree mediated by differential phase retardation in the SP mode due to Transverse Electric and Magnetic components. This was used to develop a dark field on-chip plasmonic polarization microscope for imaging SP excitation in real and Fourier planes. After successful integration of these plasmonic nanostructures with SU- 8 based microfluidic channels, a real-time monitoring of label free on chip sensing was demonstrated. Label-free on-chip imaging for interface of colorless miscible and immiscible analytes flowing on plasmonic nanostructures in the microfluidic channels were performed using color-selective filtering nature of plasmonic nanostructures. Since the imaging is realized on a chip and does not need any complicated and bulky arrangement, it will be well suited for on-chip point of care diagnostics.

physics.app-ph↗

arXiv2010

A New Variable Threshold and Dynamic Step Size Based Active Noise Control System for Improving Performance

Several approaches have been introduced in literature for active noise control (ANC) systems. Since FxLMS algorithm appears to be the best choice as a controller filter, researchers tend to improve performance of ANC systems by enhancing and modifying this algorithm. In this paper, modification is done in the existing FxLMS algorithm that provides a new structure for improving the tracking performance and convergence rate. The secondary signal y(n) is dynamic thresholded by Wavelet transform to improve tracking. The convergence rate is improved by dynamically varying the step size of the error signal.

cs.OH↗

arXiv2010

Saturation Throughput Analysis of IEEE 802.11b Wireless Local Area Networks under High Interference Considering Capture Effects

Distributed contention based Medium Access Control (MAC) protocols are the fundamental components for IEEE 802.11 based Wireless Local Area Networks (WLANs). Contention windows (CW) change dynamically to adapt to the current contention level, Upon each packet collision, a station doubles its CW to reduce further collision of packets. IEEE 802.11 Distributed Coordination Function (DCF) suffers from a common problem in erroneous channel. They cannot distinguish noise lost packets from collision lost packets. In both situations a station does not receive its ACK and doubles the CW to reduce further packet collisions. This increases backoff overhead unnecessarily in addition to the noise lost packets, reduces the throughput significantly. Furthermore, the aggregate throughput of a practical WLAN strongly depends on the channel conditions. In real radio environment, the received signal power at the access point from a station is subjected to deterministic path loss, shadowing and fast multipath fading. In this paper, we propose a new saturation throughput analysis for IEEE 802.11 DCF considering erroneous channel and capture effects. To alleviate the low performance of IEEE 802.11 DCF, we introduce a mechanism that greatly outperforms under noisy environment with low network traffic and compare their performances to the existing standards. We extend the multidimensional Markov chain model initially proposed by Bianchi(3) to characterize the behavior of DCF in order to account both real channel conditions and capture effects, especially in a high interference radio environment.

cs.NI↗

arXiv2009

Multiple Cross-Layer Design Based Complete Architecture for Mobile Adhoc Networks

Different cross layer design for mobile adhoc network focuses on different optimization purpose, different Quality of Service (QoS) metric and the functions like delay, priority handling, security, etc. Existing cross layer designs provide individual solution for congestion control, fault tolerance, power conservation, energy minimization and flow control and the major drawback is of high cost and overhead. In this paper, we propose to design multiple cross layer design based architecture to provide a combined solution for link failure management, power conservation, congestion control and admission control. By simulation results, we show that the average end to end delay, average energy consumption and the packet loss are considerably reduced with the increase in high throughput and good delivery ratio.

cs.NI↗

arXiv2009

Photogrammetric Measurements of a 12-metre Preloaded Parabolic Dish Antenna

A 12-metre Preloaded Parabolic Dish antenna, in which the backup structure is formed by preloading its radial and circumferential members, has been designed, built and commissioned by the Raman Research Institute, Bangalore. This paper reports the first-ever photogrammetric measurements of gravity-induced deformation in the primary reflector of an antenna built using this novel concept of preloading the backup structure. Our experience will be of relevance to radio astronomy and deep space network applications that require building lightweight and economical steerable parabolic antennas.

astro-ph.IM↗

arXiv2001

Efficient Switching and Domain Interlocking Observed in Polyaxial Ferroelectrics

We present in-situ transmission electron microscopy observations of domain wall motion in thin freestanding potassium niobate single-crystals. We observe that not all domains of a given polarization orientation are equally switchable in applied electric fields. Tilted and curved 90 degree domain walls are common and display field-induced mobility, whereas untilted domain boundaries resist such motion. The sensitivity of the domain wall response to field direction suggests that electrostatic energy contributions play a crucial role in the observed switching properties. We can explain our results in terms of the polarization charges and the resulting depolarization fields associated with angled domain walls. A phenomenological Landau-Ginzburg analysis of a tilted domain boundary indicates that such electrostatic effects reduce its local switching barrier, thereby enhancing its field-induced mobility compared to that of its untilted counterpart. Consequently not all domain walls are equally mobile. Furthermore the switching efficiency of a particular domain is determined by its allowed final states, as defined by its neighbors. Switching will be inhibited if the relative energetics are unfavorable, and we call this phenomenon domain interlocking. Any increase in density of such field-resistant wall configurations with cycle time represents an inherent contribution to ferroelectric fatigue. Uniaxial ferroelectrics, with polarizations parallel to the field, should not support such interlocked domains.

cond-mat.mtrl-sci↗