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A Simulation Tool for Ultrasonic Inspection
Krishnamurthy, Adarsh,Mohan, K.V.,Karthikeyan, Soumya,Krishnamurthy, C.V.,Balasubramaniam, Krishnan The Korean Society for Nondestructive Testing 2006 한국비파괴검사학회지 Vol.26 No.3
A simulation program SIMULTSONIC is under development at CNDE to help determine and/or help optimize ultrasonic probe locations for inspection of complex components. SIMULTSONIC provides a ray-trace based assessment for immersion and contact modes of inspection. The code written in Visual C++ operating in Microsoft Windows environment provides an interactive user interface. In this paper, a description of the various features of SIMULTSONIC is given followed by examples illustrating the capability of SIMULTSONIC to deal with inspection of canonical objects such as pipes. In particular, the use of SIMULTSONIC in the inspection of very thin-walled pipes (with 450 urn wall thickness) is described. Ray trace based assessment was done using SIMULTSONIC to determine the standoff distance and the angle of oblique incidence for an immersion mode focused transducer. A 3-cycle Hanning window pulse was chosen for simulations. Experiments were carried out to validate the simulations. The A-scans and the associated B-Scan images obtained through simulations show good correlation with experimental results, both with the arrival time of the signal as well as with the signal amplitudes.
Morphology and topography of the parietal emissary foramina in South Indians: an anatomical study
B. V. Murlimanju,Vasudha V. Saralaya,M. S. Somesh,Latha V. Prabhu,Ashwin Krishnamurthy,Ganesh Kumar Chettiar,Mangala M. Pai 대한해부학회 2015 Anatomy & Cell Biology Vol.48 No.4
The objectives of the present study were to study the prevalence of the parietal emissary vein in adult South Indian population and to study the distance of foramen from the sagittal suture. There were 58 adult human skulls in the present study which were available at the anatomy department of our institution. The study included 116 parietal bones which have been observed macroscopically for the number, prevalence and topography of the emissary foramen. The emissary foramen was present in 83 parietal bones (71.5%) of the present study. It was present at the junction between the middle 1/3 and posterior 1/3 region of the parietal bone. The foramen was observed solitary in 73 parietal bones (62.9%), double in 8 bones (6.9%), and triple in 2 parietal bones (1.7%). The foramen was not observed in 33 parietal bones (28.4%). The bilateral absence of parietal emissary foramen was seen in 7 skulls (12.1%). It was absent unilaterally in 19 skulls (32.7%). The accessory foramina were seen in only 8 skulls (13.8%). The mean distance of the foramen from the sagittal suture was 6.7±2.9 mm and 6.8±2.8 mm on the right and left sides respectively. The prevalence of parietal emissary vein in the present study was 71.5%. The present study has observed important data about the morphology and morphometry of the parietal emissary vein in South Indian population. The identification of parietal emissary veins and accessory veins is important in the operation room to prevent the blood loss.
Muralidharan, Ajith,Balasubramaniam, Krishnan,Krishnamurthy, C.V. Techno-Press 2008 Smart Structures and Systems, An International Jou Vol.4 No.4
An array based, outward monitoring, ultrasonic guided wave based SHM technique using a single transmitter and multiple receivers (STMR), with a small footprint is discussed here. The previous implementation of such SHM arrays used a phase-reconstruction algorithm (that is similar to the beam-steering algorithm) for the imaging of reflectors. These algorithms were found to have a limitation during the imaging of defects/reflectors that are present in the "near-field" of the array. Here, the "near-field" is defined to be approximately 3-4 times the diameter of the compact array. This limitation is caused by approximations in the beam-steering reconstruction algorithm. In this paper, a migration-based reconstruction algorithm, with dispersion correction in the frequency domain, is discussed. Simulation and experimental studies are used to demonstrate that this algorithm improves the reconstruction in the "near-field" without decreasing the ability to reconstruct defects in the "far-field" in both isotropic and anisotropic plates.
A Distributed and Scalable Time Slot Allocation Protocol for Wireless Sensor Networks
Chih-Kuang Lin,Zadorozhny, Vladimir I,Krishnamurthy, Prashant V,Ho-Hyun Park,Chan-Gun Lee IEEE 2011 IEEE TRANSACTIONS ON MOBILE COMPUTING Vol.10 No.4
<P>There are performance deficiencies that hamper the deployment of Wireless Sensor Networks (WSNs) in critical monitoring applications. Such applications are characterized by considerable network load generated as a result of sensing some characteristics of the monitored system. Excessive packet collisions lead to packet losses and retransmissions, resulting in significant overhead costs and latency. In order to address this issue, we introduce a distributed and scalable scheduling access scheme that mitigates high data loss in data-intensive sensor networks and can also handle some mobility. Our approach alleviates transmission collisions by employing virtual grids that adopt Latin Squares characteristics to time slot assignments. We show that our algorithm derives conflict-free time slot allocation schedules without incurring global overhead in scheduling. Furthermore, we verify the effectiveness of our protocol by simulation experiments. The results demonstrate that our technique can efficiently handle sensor mobility with acceptable data loss, low packet delay, and low overhead.</P>
Characterization of Interference in OFDMA Small-Cell Networks
Yoon, Jongwon,Arslan, Mustafa Y.,Sundaresan, Karthikeyan,Krishnamurthy, Srikanth V.,Banerjee, Suman IEEE 2018 IEEE Transactions on Vehicular Technology VT Vol.67 No.9
<P>The increase in mobile Internet access is pushing mobile network operators toward deploying smaller cells (<I> femtocells</I>) and sophisticated air interface technologies, Orthogonal Frequency Division Multiple Access (OFDMA). The expected high density of deployment and uncoordinated operations of femtocells, however, make interference management both critical and extremely challenging. A significant challenge stems from the fact that femtocells have to use the same synchronous access technology as traditional macrocells. Given this, understanding the impact of the multitude of design choices (originally tailored to well-planned macrocellular networks) on interference management forms an essential first step toward designing efficient solutions for next-generation femtocell networks. This in turn is the focus of our paper. With the help of extensive measurements from our femtocell testbed, we characterize the impact of various system design choices on interference in OFDMA femtocell deployments. The design choices that we examine are categorized across three broad dimensions: 1) <I>resource isolation</I> at the logical (MAC) level across femtocells, 2) <I>resource mapping</I> through sub-channelization at the physical (PHY) level within each femtocell, and 3) <I>synchronization</I> (or lack thereof) between interfering cells. Based on the insights from our measurement study, we discuss several implications on the choice of system design features for multicell operations. We also provide guidelines for the design of efficient interference management solutions for femtocell networks.</P>