Effect of hinged leaflets on vortex pair generation

We experimentally study the effect of having hinged leaflets at the jet exit on the formation of a two-dimensional counter-rotating vortex pair. A piston-cylinder mechanism is used to generate a starting jet from a high-aspect-ratio channel into a quiescent medium. For a rigid exit, with no leaflets at the channel exit, the measurements at a central plane show that the trailing jet in the present case is never detached from the vortex pair, and keeps feeding into the latter, unlike in the axisymmetric case. Passive flexibility is introduced in the form of rigid leaflets or flaps that are hinged at the exit of the channel, with the flaps initially parallel to the channel walls. The experimental arrangement closely approximates the limiting case of a free-to-rotate rigid flap with negligible structural stiffness, damping and flap inertia, as these limiting structural properties permit the largest flap openings. Using this arrangement, we start the flow and measure the flap kinematics and the vorticity fields for different flap lengths and piston velocity programs. The typical motion of the flaps involves a rapid opening and a subsequent more gradual return to its initial position, both of which occur when the piston is still moving. The initial opening of the flaps can be attributed to an excess pressure that develops in the channel when the flow starts, due to the acceleration that has to be imparted to the fluid slug between the flaps. In the case with flaps, two additional pairs of vortices are formed because of the motion of the flaps, leading to the ejection of a total of up to three vortex pairs from the hinged exit. The flaps' length (L-f) is found to significantly affect flap motions when plotted using the conventional time scale L/d, where L is the piston stroke and d is the channel width. However, with a newly defined time scale based on the flap length (L/L-f), we find a good collapse of all the measured flap motions irrespective of flap length and piston velocity for an impulsively started piston motion. The maximum opening angle in all these impulsive velocity program cases, irrespective of the flap length, is found to be close to 15 degrees. Even though the flap kinematics collapses well with L/L-f, there are differences in the distribution of the ejected vorticity even for the same L/L-f. Such a redistribution of vorticity can lead to important changes in the overall properties of the flow, and it gives us a better understanding of the importance of exit flexibility in such flows.

Effect of steady rotation on low Reynolds number vortex shedding behind a circular cylinder

In this paper control of oblique vortex shedding in the wake behind a straight circular cylinder is explored experimentally and computationally. Towards this, steady rotation of the cylinder about its axis is used as a control device. Some limited studies are also performed with a stepped circular cylinder, where at the step the flow is inevitably three-dimensional irrespective of the rotation rate. When there is no rotation, the vortex shedding pattern is three dimensional as described in many previous studies. With a non-zero rotation rate, it is demonstrated experimentally as well as numerically that the shedding pattern becomes more and more two-dimensional. At sufficiently high rotation rates, the vortex shedding is completely suppressed.

Effect of FIB milling on MEMS SOI cantilevers

Stress induced by Focused Ion Beam (FIB) milling of cantilevers fabricated on silicon-on-insulator (SOI) wafer has been studied. Milling induces stress gradients ranging from -10MPa/μm to -120MPa/μm, depending on the location of cantilevers from the point of milling. Simulations were done to estimate the stress in the milled cantilevers.

Effect of Net-Fluence on waveguide formation in ultrafast laser inscribed chalcogenide glass

Waveguides were fabricated on GeGaSEr chalcogenide glass using ultrafast laser inscription method. The thermal diffusion model is discussed for understanding the light matter interaction and shown the effect of net-fluence in waveguide formation on chalcogenide glass. (C) 2012 Optical Society of America

Effect of SST Variation on ITCZ in APE Simulations

The effect of meridional variation of sea surface temperature (SST) on tropical atmospheric circulation is analyzed using Aqua-planet Experiment (APE) simulations. The meridional SST gradient around the narrow SST peak in CONTROL simulation favours a strong and single equatorial Intertropical Convergence Zone (ITCZ, defined by the maximum of zonally averaged total precipitation) in all APE models. In contrast, flat equatorial SST peak (FLAT simulation) favours split/double ITCZs flanking the SST maximum, in the majority of the APE models. Although there is reasonable agreement for SST sensitivity of ITCZ among the APE models in CONTROL, there exists disparity among them in FLAT case. Similarly, while the total and convective precipitation responses are consistent among the models, the large-scale precipitation response shows considerable inter-model variations in FLAT case. The APE intercomparison indicates that the occurrence and positioning of the ITCZ are primarily related to boundary layer moisture convergence as a response to the meridional variation of SST. Furthermore, the meridional gradient of tropospheric temperature is found to be an important factor that can influence the positioning of ITCZ. FLAT SST distribution is found to be similar to the observed distribution over the Indian region during summer season. Models that yield double ITCZs in this case simulate an easterly jet over the equatorial region (similar to 15 degrees equatorward of the ITCZ). This is analogous to the Tropical Easterly Jet (TEJ), which is a unique feature observed over the Indian region during summer monsoon season, with its core at 12 degrees N, equatorward of the seasonal convergence zone centered along 25 degrees N. In these models, positive meridional temperature gradient and the associated easterly shear in the atmosphere strengthened by moisture convergence penetrate up to the upper troposphere, with which TEJ is in thermal wind balance.

The effect of environmental coupling on tunneling of quasiparticles in Josephson junctions

We study quasiparticle tunneling in Josephson tunnel junctions embedded in an electromagnetic environment. We identify tunneling processes that transfer electrical charge and couple to the environment in a way similar to that of normal electrons, and processes that mix electrons and holes and are thus creating charge superpositions. The latter are sensitive to the phase difference between the superconductors and are thus limited by phase diffusion even at zero temperature. We show that the environmental coupling is suppressed in many environments, thus leading to lower quasiparticle decay rates and better superconductor qubit coherence than previously expected. Our approach is nonperturbative in the environmental coupling strength.

Effect of analyte concentration on the laser-induced plasma temperature and electron density in liquid matrix

In the present work, we report spectroscopic studies of laser-induced plasmas produced by focusing the second harmonic (532nm) of a Nd:YAG laser onto the laminar flow of a liquid containing chromium. The plasma temperature is determined from the coupled Saha-Boltzmann plot and the electron density is evaluated from the Stark broadening of an ionic line of chromium Cr(II)] at 267.7nm. Our results reveal a decrease in plasma temperature with an increase in Cr concentration up to a certain concentration level; after that, it becomes approximately constant, while the electron density increases with an increase in analyte (Cr) concentration in liquid matrix.

Effect of substituent position on optical properties of boron-dipyrromethane isomers

Three isomeric meso-SiMe3C6H4 substituted BODIPYs have been synthesized and their optical properties studied. The constitutional isomers show similar absorption properties but vastly different emissive properties as a result of their different conformational flexibility. Fluorine-19 NMR study is used to unravel the conformational state of the BODIPY isomers at a molecular level. (C) 2013 Elsevier B. V. All rights reserved.

Effect Of Mo Doping On The Electrical Properties Of VO2 Phase

Solution combustion synthesis technique was adopted to synthesize V2O5, and Mo doped phases, The as-synthesized V2O5, has been reduced by a novel reduction technique to form VO2 typephase. The monophasic nature of the samples as revealed by XRD data and systematic shift in peak position indicated solid solubility up to 2 at % of Mo in VO2 lattice. The crystallite size was found to similar to 40 nm. Particle size measurement carried out using Transmission electron microscope ( TEM) agreed with XRD experiments. Scanning electron microscope revealed the morphology of the particles to be plate like and bimodal. Variation in the metal- insulator transition temperature as a function of doping was investigated by 4-probe electrical resistivity measurement on sintered ceramics.

Effect of size reduction on magnetic ordering in Bi0.2Sr0.8MnO3

We present a comparative study of the temperature dependent magnetic properties and electron paramagnetic resonance parameters of nano and bulk samples of Bi0.2Sr0.8MnO3 (BSMO). Bulk BSMO is known to have a high T-N similar to 260K and robust charge ordering (T-CO similar to 360 K). We confirm that the bulk sample shows an antiferromagnetic transition around similar to 260K and a spin-glass transition similar to 40 K. For the nano sample, we see a clear ferromagnetic transition at around similar to 120 K. We conclude that spin glass state, which is present due to the co-existence of antiferromagnetic and ferromagnetic states in the bulk sample, is suppressed in the nano sample and ferromagnetism is induced instead. (C) 2014 AIP Publishing LLC.

Effect of fluid medium on mechanical behavior of carbon nanotube foam

This study reports the constitutive response and energy absorption capabilities of fluid-impregnated carbon nanotube (CNT) foams under compressive loading as a function of fluid viscosity and loading rates. At all strain rates tested, we observe two characteristic regimes: below a critical value, increasing fluid viscosity increases the load bearing and energy absorption capacities; after a critical value of the fluid's viscosity, we observe a rapid decrease in the systems' mechanical performance. For a given fluid viscosity, the load bearing capacity of the structure slightly decreases with strain rate. A phenomenological model, accounting for fluid-CNT interaction, is developed to explain the observed mechanical behavior. (C) 2014 AIP Publishing LLC.

Effect of Reflux Time on Nanoparticle Shape

In the present work, Pt nanoparticles were produced from a reaction mixture containing a trace amount of cobalt carbonyl salt acting as a shape inducer. Nanoparticle shape evolution during reaction mixture reflux was monitored by characterizing particles extracted from the reaction mixture at different times. It was observed that 5 min of reflux produced spherical nanoparticles, 30 min of reflux produced cube shaped nanoparticles, and 60 min of reflux produced truncated octahedron morphology nanoparticles. It is illustrated that during nanoparticle synthesis the reflux process can provide energy needed for shape transformation from a metastable cube morphology to a truncated octahedron morphology which is thermodynamically the most stable geometry for fcc crystals. An optimization of the reaction reflux is thus needed for isolating metastable shapes.

Effect of amplitude correlations on coherence in the local field potential

Neural activity across the brain shows both spatial and temporal correlations at multiple scales, and understanding these correlations is a key step toward understanding cortical processing. Correlation in the local field potential (LFP) recorded from two brain areas is often characterized by computing the coherence, which is generally taken to reflect the degree of phase consistency across trials between two sites. Coherence, however, depends on two factors-phase consistency as well as amplitude covariation across trials-but the spatial structure of amplitude correlations across sites and its contribution to coherence are not well characterized. We recorded LFP from an array of microelectrodes chronically implanted in the primary visual cortex of monkeys and studied correlations in amplitude across electrodes as a function of interelectrode distance. We found that amplitude correlations showed a similar trend as coherence as a function of frequency and interelectrode distance. Importantly, even when phases were completely randomized between two electrodes, amplitude correlations introduced significant coherence. To quantify the contributions of phase consistency and amplitude correlations to coherence, we simulated pairs of sinusoids with varying phase consistency and amplitude correlations. These simulations confirmed that amplitude correlations can significantly bias coherence measurements, resulting in either over-or underestimation of true phase coherence. Our results highlight the importance of accounting for the correlations in amplitude while using coherence to study phase relationships across sites and frequencies.

Effect of Process Deviations on Performance of Piezoresistive Pressure Sensors

Diaphragm thickness and the corresponding piezoresistor locations change due to over or under etching in bulk micromachined piezoresistive pressure sensor which intern influences the device performance. In the present work, variation of sensitivity and nonlinearity of a micro electro mechanical system low pressure sensor is investigated. The sensor is modeled using finite element method to analyze the variation of sensitivity and nonlinearity with diaphragm thickness. To verify the simulated results, the sensors with different diaphragm thicknesses are fabricated. The models are verified by comparing the calculated results with experimental data. This study is potentially useful for the researchers as most of the times the diaphragm is either over-etched or under-etched due to inherent variation in wafer thickness and involving manual operations.

Effect of contact stresses on shape recovery of NiTiCu thin films

Permanent plastic deformation induced by mechanical contacts affects the shape recovery of shape memory alloys. To understand the shape recovery of NiTiCu thin films subjected to local contact stresses, systematic investigations are carried out by inducing varying levels of contact stresses using nanoindentation. The resulting indents are located precisely for imaging using a predetermined array consisting of different sized indents. Morphology and topography of these indents before and after shape recovery are characterized using Scanning Electron Microscope and Atomic Force Microscope quantitatively. Shape recovery is found to be dependent on the contact stresses at the low loads while the recovery ratio remains constant at 0.13 for higher loads. Shape recovery is found to occur mainly in depth direction of the indent, while far field residual stresses play very little role in the recovery. (C) 2014 Elsevier B.V. All rights reserved.