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Effect of strain path change on the texture evolution after cold rolling and recrystallization of Nickel-40 wt. %Cobalt alloy
No full textEffect of change in strain path during rolling and its role in the development of crystallographic texture after deformation and then after recrystallization has been studied for Ni-40wt%Co which is a medium stacking fault energy (SFE) material. Results indicate that textures developed after unidirectional rolling and multi-step cross-rolling are quite different which also leads to different texture evolution after recrystallization. Microstructure of both UDR and cross rolled sample shows band type of feature within the grain having lesser band density for cross rolled samples. After recrystallization unidirectionally rolled sample shows bimodal whereas cross rolled sample shows equiaxed grain size distribution. But all the samples show large fraction of annealing twins. It has been shown that in all cases formation of annealing twins have large influence on the texture transition after recrystallization
A bilateral relationship between stable profiles of pinned-pinned bistable shallow arches
No full textArch-profiles in the two force-free stable equilibrium states of shallow bistable arches are related to each other. We derive a two-way, i.e., bilateral, relationship between stress-free initial profile and stressed toggled profile so that pinned-pinned bistable arches of arbitrary profiles can be efficiently analyzed and designed. The derivation relies on representing the initial and toggled profiles with two sets of mode weights corresponding to the buckling mode shapes of a pinned-pinned column. Furthermore, we prove that the fundamental mode weights should be non-zero for an arch to be bistable. The following corollaries arise from the aforementioned relation: (1) symmetry in initial and toggled profiles remains unchanged: (2) all the mode weights other than the fundamental mode weight have the same sign in both stable states; (3) magnitudes of corrugations in stable force-free arch-profiles are approximately equal. Derivations and proofs of the principal relationship and its corollaries as well as examples of analysis and design of bistable arches of arbitrary arch-profiles are presented in the paper. (C) 2018 Elsevier Ltd. All rights reserved
Mathematical modeling of optical MEMS differential pressure sensor using waveguide Bragg gratings embedded in Mach Zehnder interferometer
No full textThis paper presents theoretical analysis of a silicon based micro-machined differential pressure sensor using a square shaped clamped diaphragm and surface relief waveguide Bragg gratings embedded in a Mach Zehnder interferometer (MZI). Each of the arms of the MZI has one surface relief Bragg grating embedded in it. Each grating is mounted at the edge of a micro-machined diaphragm so as to obtain maximum stress. Coupled mode theory has been used to design the directional coupler to equally couple the light into both of the arms of MZI and also to design and analyse the shifts in the wavelengths of the Bragg gratings due to applied pressures. The wavelength shift difference of the two gratings gives the differential pressure sensitivity and also eliminates the noise due to temperature variation. Simulation results indicate that the differential pressure measurement sensitivity is 0.2 pm/Pa
Contributions of network topological structures to the mechanical properties of PDMS elastomers
No full textSilicone elastomers (poly dimethyl siloxane, PDMS) are widely used in the fabrication of MEMS devices and in mechanobiological studies. Mechanical properties of the elastomers may be varied by changing the crosslinking density and physical entanglements in the networks. Other factors like dangling chains and uncrosslinked sol fractions also influence the network mechanics. We investigated the role of crosslinks, entanglements and sol fraction in the mechanical properties of PDMS prepared with different ratios of base to crosslinker. Results from compression tests show greater elastic modulus for the highly crosslinked networks. We removed uncrosslinked sol, altered the entanglement density with xylene extraction, and used data from mechanical tests to assess predictions from the Frenkel-Flory-Rehner model. These studies show that the polymer-solvent interaction parameter, x, varied linearly with the equilibrium volume fraction. Dynamic mechanical analyses of extracted PDMS samples showed that crosslinking density, solvent presence, and sol fraction affect their overall viscoelasticity properties. We also compared experimental data with scaling laws and demonstrate that trapped entanglements in the networks contribute to the mechanical properties of PDMS. Finally, we show from these studies that swelling behaviors of PDMS in xylene follow affine deformation
Shock interactions in hypersonic flows outside the sonic circle in front of a blunt body
No full textThe problem of shock-shock interaction between a planar oblique shock wave and a bow shock wave is undertaken by considering a wedge and a hemispherical body in a hypersonic flow. The interaction patterns, as classified by Edney, namely Type-I, Type-II, Type-V, and Type-VI, which appear when a planar oblique shock wave interacts the bow shock wave outside the sonic circle are presented. The experiments are conducted at Mach number of 5.62, with air as test gas, in the short duration Hypersonic Shock Tunnel - 2 (HST-2) at Indian Institute of Science, Bangalore. Schlieren visualization is used to capture and identify the shock interaction patterns. Time evolution of the flow using the schlieren images is correlated with the pitot pressure signal to mark the flow establishment and useful test time in the tunnel, during which measurements are taken. Surface convective heat transfer rates are measured using Platinum thin film technique to quantify the heat transfer rates on the surface of a blunt body in the presence of these shock interactions
Acceptable trip distance for walking in mass religious gatherings-A case study of world's largest human gathering Kumbh Mela in Ujjain, India
No full textThe optimum location of various facilities in mass religious gatherings, which are of common occurrence in countries like India, is affected by characteristics of walking that include the acceptable trip distance and the accessibility of various facilities based on this acceptable tripdistance. An understanding of this acceptable trip distance would help in developing various planning strategies that could promote the sustainable mode of walking in such mass religious gatherings, and thereby also possibly improving crowd control and management. Aptly, the present study focuses on analysing the various socioeconomic factors that affect the walking behaviour of people in mass religious gatherings and also develops a formula to calculate the acceptable walking distance.Kumbh Mela which is considered as the world's largest gathering was the case study for this research. The data was collected during Kumbh Mela 2016 held in Ujjain, India during 22nd April to 21st May 2016. The study found trip purpose having a greater influence on traveller's decision to walk. The results revealed that primary activities including `offering prayer' have a greater acceptable trip time/distance than secondary activities like `having food'. Further, the study also elicited the highest acceptable time for `holy dip' among all primary activities
High Power, Tunable, Continuous-Wave Fiber Lasers in the L-Band Using Cascaded Raman Amplifiers
No full textWe demonstrate a high power, all-fiber, and tunable laser source that can operate in the L-band region. A low power, tunable input laser is amplified with a recently proposed, high efficiency, sixth-order cascaded Raman amplifier. The proposed system is scalable and overcomes the limitations of Erbium and Erbium-Ytterbium co-doped fiber lasers for power scaling. A tunable Erbium-Ytterbium co-doped fiber ring laser generating similar to 0.5 W of power and tunable in 1560-1590 nm wavelength range is utilized as the seed source. The output from the seed laser is amplified to similar to 24 W using sixth-order cascaded Raman amplification. A high power Yb laser operating at 1117 nm is used as the pump laser for driving the Raman conversions. The operating wavelength of the demonstrated laser in the eye-safe, atmospherically transparent region enables high power free-space applications. In addition, this source enables other interesting applications, such as high power supercontinuum generation with conventional silica fibers
Efficient Realization of Householder Transform Through Algorithm-Architecture Co-Design for Acceleration of QR Factorization
No full textQR factorization is a ubiquitous operation in many engineering and scientific applications. In this paper, we present efficient realization of Householder Transform (HT) based QR factorization through algorithm-architecture co-design where we achieve performance improvement of 3-90x in-terms of Gflops/watt over state-of-the-art multicore, General Purpose Graphics Processing Units (GPGPUs), Field Programmable Gate Arrays (FPGAs), and ClearSpeed CSX700. Theoretical and experimental analysis of classical HT is performed for opportunities to exhibit higher degree of parallelism where parallelism is quantified as a number of parallel operations per level in the Directed Acyclic Graph (DAG) of the transform. Based on theoretical analysis of classical HT, an opportunity to re-arrange computations in the classical HT is identified that results in Modified HT (MHT) where it is shown that MHT exhibits 1.33x times higher parallelism than classical HT. Experiments in off-the-shelf multicore and General Purpose Graphics Processing Units (GPGPUs) for HT and MHT suggest that MHT is capable of achieving slightly better or equal performance compared to classical HT based QR factorization realizations in the optimized software packages for Dense Linear Algebra (DLA). We implement MHT on a customized platform for Dense Linear Algebra (DLA) and show that MHT achieves 1.3x better performance than native implementation of classical HT on the same accelerator. For custom realization of HT and MHT based QR factorization, we also identify macro operations in the DAGs of HT and MHT that are realized on a Reconfigurable Data-path (RDP). We also observe that due to re-arrangement in the computations in MHT, custom realization of MHT is capable of achieving 12 percent better performance improvement over multicore and GPGPUs than the performance improvement reported by General Matrix Multiplication (GEMM) over highly tuned DLA software packages for multicore and GPGPUs which is counter-intuitive
Tailoring Thin-Film Piezoelectrics for Crash Sensing
No full textCrash sensing and its assessment play a pivotal role in autonomous vehicles for preventing fatal casualties. Existing crash sensors are severely bottlenecked by sluggish response time, rigid mechanical components, and space constraints. Miniaturized sensors embedded with custom-tailored nanomaterials upholds potential to overcome these limitations. In this article, piezoelectric Zinc-Oxide thin film as a crash sensing layer is integrated onto a flexible metal-alloy cantilever. Material characterization studies are conducted to confirm piezoelectric property of sputtered ZnO film. The piezoelectric d(31) coefficient value of ZnO film was 7.2 pm V-1. The ZnO sensing element is firmly mounted on a scaled car model and used in a crash sensing experimental set-up. A comprehensive theoretical analysis for two different real scenarios (nearly elastic and nearly inelastic collision) of crash events followed by experimental study is discussed. The crash sensor's output exhibits a linear relationship with magnitude of impact forces experienced at crash events. The response time of ZnO crash sensor is 18.2 ms, and it exhibits a sensitivity of 28.7 mV N-1. The developed crash sensor has potential to replace bulk material sensors owing to its faster response time, high sensitivity, and compactness as the demand for crash sensors in next-generation automobile industries is progressively growing
Sol-Gel Synthesis of Mesoporous alpha-Co(OH)(2) and Its Electrochemical Performance Evaluation
No full textMesoporous structures of alpha-Co(OH)(2) have been selectively synthesized by a simple one-pot sol-gel process using propylene oxide as gelation agent. Synthesized material is investigated for its crystal structure (crystallinity, phase), morphology (shape, size, surface area, porosity), and electrochemical performance. The specific capacity of the as-synthesized alpha-Co(OH)(2) is 430 C/g, when the electrodes underwent charge/discharge cycling in 6 M potassium hydroxide at 1 A/g specific current. Enthrallingly, capacity retentions of up to 86 and 80% were found over 2000 and 3000 cycles, respectively, at a relatively high specific current of 10 A/g. The as-synthesized material is studied as full cells or complete devices, wherein it delivered capacities of about 80 and 25 C/g in symmetric and asymmetric modes, respectively, at a current of 1 A/g. High capacity is ascribed to the uniform porous nature of the material with considerable surface area. With an extraordinary cycle life and charge-storage capacity, the material prepared is an able contender for supercapacitor electrodes