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Evaluation of electrochemical impedance and biocorrosion characteristics of as-cast and T4 heat treated AZ91 Mg-alloys in Ringer's solution
No full textThe present study aims at understanding the electrochemical impedance and biocorrosion characteristics of AZ91 Mg-alloy in Ringer's solution. As-cast AZ91 Mg-alloy was subjected to T4 heat treatment in a way to homogenize its microstructure by dissolving most of the beta-Mg17Al12 phase at the vicinity of grain boundaries. The electrochemical impedance and biocorrosion performances of these two different microstructures (as-cast and T4 heat treated AZ91 Mg-alloys) in Ringer solution were evaluated by electrochemical impendence spectroscopy, potentiodynamic polarization and weight loss method. EIS spectra showed that both microstructures exhibit similar dynamic response as a function of the immersion time; however, the value of impedance and maximum phase angle are about 50% higher in as-cast AZ91 Mg-alloy as compared to that of homogenized AZ91 Mg-alloy. Weight loss measurement indicated that corrosion resistance of as-cast AZ91 was significantly better than that of homogenized AZ91. Microstructural and XRD analysis revealed that as-cast AZ91 contains a passive film of MgCO3 and CaCO3 precipitates with near spherical morphologies, whereas homogenized AZ91 comprised mainly unstable Mg(OH)(2) film featured by irregular plate-like morphologies. (C) 2019 Published by Elsevier B.V. on behalf of Chongqing University
Leakage Current Patterns Observed in Polymeric Insulators Rotating Subjected to Wheel and Dip Test
No full textPresent paper discusses the behavior of leakage current flowing through silicone rubber based polymeric insulators. These insulators are investigated experimentally using rotating wheel and dip test arrangement which is designed as per IEC/TR 62730. The test specimen used in the present study has creepage length of 725 mm and four of such specimens are employed on rotating wheel. These specimens rotate through contaminants and touches high voltages in a specific cycle that runs for 1000 hours. During the experimentation, leakage current is captured and recorded. This leakage current represents an interesting behavior which is reported in the present work. Further, to analyze the leakage current pattern, Fourier transform is employed to observe the changes in the specific frequency components. It is reported that the variation of power frequency component is exponentially decaying whereas the variation of third harmonics follows a double exponential pattern. The MATLAB curve fitting tool is used to determine the parameters that confines the changes
High-Power, Independently Wavelength, Power, and Linewidth Tunable Ytterbium Fiber Laser
No full textWe report a high-power, independently tunable wavelength, linewidth, and power, continuous-wave Ytterbium-doped fiber laser. Our system is based on a simple master oscillator power amplifier configuration, which decouples the output power from the output wavelength and linewidth. We demonstrate a continuously tunable laser system that can generate any output power level up to and beyond 100 W, wavelength from 1050 to 1100 nm, and linewidth tuning of 2.5 times from 0.4 to 1 nm completely independent of each other
The potential for concentrator photovoltaics: A feasibility study in India
No full textIndia has aggressive plans for scaling up photovoltaic installations in the coming decades. Currently fixed tilt, flat plate crystalline silicon (c-Si) technology sets the standard for cost and performance and is both robust and relatively easy to deploy. Concentrator photovoltaics (CPV) systems have a different cost structure; using solar cells with the highest efficiencies, system efficiencies greater than 30% are possible, but the system is also more sensitive to meteorological conditions. India has a complex and varied atmosphere that prevents a straightforward comparison of technologies, and hence, in this paper, we use a computer model to simulate the power output from CPV systems located in locations in India where the Aerosol Robotic Network (AERONET) stations are based and additionally, in Bangalore where we have a CPV test station. We quantify the increased intermittency suffered by CPV systems that arises from the larger dynamic range in direct beam irradiance over global irradiance. Nevertheless, by calculating the target system costs required to attain a competitive levelized cost of electricity (LCOE), we find that CPV systems in some, but not all locations have the opportunity to compete against dual-axis tracked and inclined c-Si based PV in Indi
Trapping and sorting active particles: Motility-induced condensation and smectic defects
No full textWe present an experimental realization of the collective trapping phase transition Kaiser et al., Phys. Rev. Lett. 108, 268307 (2012)], using motile polar granular rods in the presence of a V-shaped obstacle. We offer a theory of this transition based on the interplay of motility-induced condensation and liquid-crystalline ordering and show that trapping occurs when persistent influx overcomes the collective expulsion of smectic defect structures. In agreement with the theory, our experiments find that a trap fills to the brim when the trap angle theta is below a threshold theta(c), while all particles escape for theta > theta(c). Our simulations support a further prediction, that B e goes down with increasing rotational noise. We exploit the sensitivity of trapping to the persistence of directed motion to sort particles based on the statistical properties of their activity
Phenothiazines and phenoxazines: as electron transfer mediators for ferritin iron release
No full textIntracellular ferritin stores iron as ferrihydrite and releases it for various cellular metabolic activities. The reductive approach, one of the possible mechanisms of iron mobilization from ferritin nanocages, requires electron transfer (ET) from reducing agent(s) to the protein encapsulated iron. In vitro, the rate of ET from the physiological reducing agent, NADH, to mineralized ferritin is very slow resulting in a smaller amount of iron release. Therefore, medically relevant phenothiazine (TH/MB/MG/TDB) and phenoxazine (BCB/CRV/NB) dyes were used as ET mediators to facilitate the electron relay and to evaluate their iron releasing ability from ferritin. These dyes have earlier been exploited as ET mediators during electrocatalysis and in the treatment of methemoglobinemia. With the exception of MG, the midpoint potentials (E-1/2) and NADH oxidizing abilities of these dyes dictated by their structure and the reaction conditions along with the dye-ferritin interaction govern the kinetics of reductive iron mobilization. A greater amount of iron release was observed in the case of TH, BCB and CRV. In comparison to neutral pH, acidic pH altered E-1/2 and protein conformation leading to enhanced iron mobilization, whereas dissolved O-2 and the photosensitizing effect of dyes were found to have a negligible impact. In analogy to in vitro, the acidic environment of the lysosome may bring about similar changes in the reducing agents/dye mediators/ferritin to facilitate the iron release process in vivo. Following Marcus theory, our current observations suggest that the dyes with E-1/2 values well separated from those of the reducing agents and ferritin's mineral core can be exploited to facilitate iron release during iron overload conditions
Steady-shear response of magnetorheological fluid containing coral-shaped yttrium-iron-garnet particles
No full textThe steady-state magneto-mechanical response of a magnetorheological fluid (MRF), prepared by dispersing 40 wt % of magnetically soft, light-weight coral-network-shaped yttrium iron garnet (YIG; Y3Fe5O12) powder in silicone oil (140 cSt) is studied as a function of shear rate, under different applied magnetic fields (B). The results show that the yield strength (tau(Y)) and viscosity (eta) of the MRF increase with B, and are strongly influenced by the physical parameters of the particles such as morphology and saturation magnetization. The low density of the YIG-particles, leading to higher volume fraction for equal mass loading, results in a higher viscosity in the absence of a magnetic field, in comparison to that of conventional metallic Fe-particle-based MRFs. Due to this, there is a relatively smaller increase in tau(Y) and eta when the magnetic field is switched on. The YIG-particles-based MRF has the advantages of high chemical stability, thermo-oxidative resistance and low-cost
Strength of Mechanical Memories is Maximal at the Yield Point of a Soft Glass
No full textWe show experimentally that both single and multiple mechanical memories can be encoded in an amorphous bubble raft, a prototypical soft glass, subject to an oscillatory strain. In line with recent numerical results, we find that multiple memories can be formed sans external noise. By systematically investigating memory formation for a range of training strain amplitudes spanning yield, we find clear signatures of memory even beyond yielding. Most strikingly, the extent to which the system recollects memory is largest for training amplitudes near the yield strain and is a direct consequence of the spatial extent over which the system reorganizes during the encoding process. Our study further suggests that the evolution of force networks on training plays a decisive role in memory formation in jammed packings
Revisiting Effectiveness of Energy Conserving Opportunistic Transmission Schemes in Energy Harvesting Wireless Sensor Networks
No full textOpportunistic transmission schemes improve the lifetime of conventional wireless sensor networks (WSNs) by reducing the number of transmissions. However, this comes at the expense of performance since fewer measurements are available. We show that in energy harvesting (EH) WSNs, in which the sensor nodes harvest energy from the environment, this trade-off is fundamentally different. For a general model in which the nodes experience independent and non-identical fading and the EH process at a node is stationary and ergodic, we present lower bounds on the mean squared error (MSE) for two important classes of channel-based opportunistic transmission schemes, namely, censoring and ordered transmissions. For the latter, we present two novel variants that arise depending on whether the energy in the battery of an EH sensor node is accounted for before ordering or not. For censoring, the lower bound leads to an insightful and explicit characterization of the optimum censoring threshold for each node. For ordered transmissions, it helps determine the optimal number of nodes that should be selected to transmit. We find that the ordered transmission schemes can outperform the censoring scheme. We also propose a hybrid scheme that combines the best features of the above schemes for EH WSNs
Thermal Conductivity Enhancement in MoS2 under Extreme Strain
No full textBecause of their weak interlayer bonding, van der Waals (vdW) solids are very sensitive to external stimuli such as strain. Experimental studies of strain tuning of thermal properties in vdW solids have not yet been reported. Under similar to 9% cross-plane compressive strain created by hydrostatic pressure in a diamond anvil cell, we observed an increase of cross-plane thermal conductivity in bulk MoS2 from 3.5 to about 25 W m(-1) K-1, measured with a picosecond transient thermoreflectance technique. First-principles calculations and coherent phonon spectroscopy experiments reveal that this drastic change arises from the strain-enhanced interlayer interaction, heavily modified phonon dispersions, and decrease in phonon lifetimes due to the unbundling effect along the cross-plane direction. The contribution from the change of electronic thermal conductivity is negligible. Our results suggest possible parallel tuning of structural, thermal, and electrical properties of vdW solids with strain in multiphysics devices