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Observation of Electro-Optic Pockels Effect at the Amorphous TiO2 and Metal Interface
No full textThe Pockels effect is theoretically forbidden in centrosymmetric media. However, centrosymmetry is broken at the interface and second-order nonlinear effects such as the Pockels effect can be detected. In this work, we report the experimental observation of the Pockels effect at the interface of two isotropic solids, amorphous sol-gel spin-coated TiO2 and polycrystalline magnetron-sputtered metal. A micronthick voltage-driven Fabry-Perot resonator is designed using these materials to experimentally detect the optical response of their interface to an applied electric field. Using the experimental data, nonlinear two-dimensional susceptibility. chi((2))(2D)(omega; omega, 0) for the interface is obtained with two different theoretical approaches and found to be 3.5 +/- 1.9 x 10(7) pm(2)/V. The order of magnitude is similar to a recent report of. chi((2))(surface)(2 omega; omega, omega) similar to 10(6) pm(2)/V for the silicon-air interface obtained from surface second-harmonic generation measurements. Isotropy usually prohibits the design of thin-film active photonic components, such as electro-optic modulators, using amorphous materials which can be deposited by simple sol-gel spin coating or sputtering. Our demonstration of the Pockels effect at the TiO2 and metal interface presents it as a new electro-optic material with potential applications for integrated active plasmonic devices
Antiproliferative and Antioxidative Bioactive Compounds in Extracts of Marine-Derived Endophytic Fungus Talaromyces purpureogenus
No full textEndophytic fungi are now recognized as sources of pharmacologically beneficial, novel bioactive compounds. This study was carried out to evaluate antiproliferative and antioxidative potential of a seaweed endophytic fungus Talaromyces purpureogenus. Extracts with different solvents of the fungus grown on different liquid media were assayed for the antiproliferative and antioxidative activities. Tested 6 cancer cell lines, the highest antiproliferative activity was observed in ethyl acetate extract of total culture grown in Potato Dextrose Broth for 28 days in a dose-dependent manner. The highest antioxidative activity was observed in hexane extract of fungal culture grown in Malt Extract Broth for 21 days. Analyzed for secondary metabolites, the extract revealed the presence of phenolics, alkaloids, flavonoids, steroids and terpenoids. Further, Gas Chromatography Mass Spectroscopy (GCMS) analysis of the extract revealed the presence of several compounds including 3-nitropropanoic acid, 4H-pyran-4-one 5-hydroxy-2-(hydroxymethyl), hexadecanoic acid, and octadecanoic acid, known to be cytotoxic or antioxidative. Among different cell lines tested, HeLa cells were the most vulnerable to the treatment of the fungal extract with an IC50 value of 101 +/- 1 mu g/mL. The extract showed no significant cytotoxicity to the normal human embryonic kidney cell line (HEK 293 T) in the MTT assay. The ethyl acetate extract induced membrane damage and mitochondrial depolarization and thereby apoptosis and cytotoxicity in HeLa cells. The study marks marine-derived endophytes as potential sources for discovery of novel drugs
Compact broadband low-loss taper for coupling to a silicon nitride photonic wire
No full textWe demonstrate an ultra-compact waveguide taper on a silicon nitride platform. The proposed taper provides a coupling efficiency of 95% at a length of 19.5 mu m in comparison to the standard linear taper of length 50 mu m, which connects a 10 mu m wide waveguide to a 1 mu m wide photonic wire. The taper has a spectral response > 75% spanning over 800 nm and resilience to fabrication variations; +/- 200 nm change in taper and end waveguide width varies transmission by <5%. We experimentally demonstrate taper insertion loss of <0.1 dB/transition for a taper as short as 19.5 mu m, and reduce the footprint of the photonic device by 50.8% compared to the standard adiabatic taper. To the best of our knowledge, the proposed taper is the shortest waveguide taper ever reported in silicon nitride. (C) 2018 Optical Society of Americ
A Reduction in Particle Size Generally Causes Body-Centered-Cubic Metals to Expand but Face-Centered-Cubic Metals to Contract
No full textFrom a careful analysis of existing data as well as new measurements, we show that the size dependence of the lattice parameters in metal nanoparticles with face-centered cubic (fcc) and body-centered cubic (bcc) symmetries display opposite trends: nanoparticles with fcc structure generally contract with decreasing particle size, while those with bcc structure expand. We present a microscopic explanation for this apparently puzzling behavior based on first-principles simulations. Our results, obtained from a comparison of density functional theory calculations with experimental data, indicate that the nanoparticles are capped by a surface monolayer of oxygen atoms, which is routinely detected by surface-sensitive techniques. The bcc- and fcc-based nanoparticles respond in contrasting fashion to the presence of the oxygen capping layer, and this dictates whether the corresponding lattice parameter would increase or decrease with size reduction. The metal oxygen bonds at the surface, being shorter and stronger than typical metal metal bonds, pull the surface metal atoms outward. This outward movement of surface atoms influences the core regions to a larger extent in the relatively open bcc geometry, producing a rather large overall expansion of the cluster, compared to the bulk. In case of fcc clusters, on the other hand, the outward movement of surface metal atoms does not percolate too far inside, resulting in either a smaller net expansion or contraction of the cluster depending on the extent of surface oxygen coverage. Our study therefore provides a convincing physicochemical basis for the correlation between the underlying geometry and the nature of change of the lattice parameters under size reduction
A Very High Resolution Stacked Multilevel Inverter Topology for Adjustable Speed Drives
No full textThis paper proposes a novel 49-level stacked inverter topology for drives. The 49 levels are achieved by stacking three 17-level inverters. Each of the 17-level inverter is developed by cascading a flying capacitor (FC) inverter with three capacitor-fed H-bridges. The device count can be reduced by making the FC and the three cascaded H-bridges common to the dc link in each phase using selector switches in between them. The selector switches need to operate at fundamental frequency only. Also, the devices need to block very low voltages. Hence, MOSFETs can be used. This topology requires three dc sources, each of Vdc/6 only, which can be replaced with stacked batteries for electric vehicle applications. The reduction in the dc voltage requirement is achieved by using a normal symmetric six-phase induction motor with parallel connection of the opposite phase windings. All the floating capacitors in the topology can be balanced irrespective of any modulation index or load power factor. Due to the high number of voltage levels, nearest level control can be used instead of pulse width modulation, which reduces the switching losses. The dv/dt during the inverter operation is also less. Detailed experimental results at different speeds of operation and during transients ensure that the novel topology can be a viable option for high-power adjustable speed drives
Implementing statistical modeling approach towards development of ultrafine grained bioceramics: Case of ZrO2-toughened Al2O3
No full textThe application of statistical modeling approach with the predictive capability of sinter density and grain size is perceived as a central theme in the development of next generation ceramics. Such computationally intensive method can be equally significant, if the predicted process conditions can be adapted experimentally to develop complex shaped ceramics with variable sizes. In the first ever attempt to address such issues for the ceramics, we have, in the present work, considered a range of factors and levels from relevant process variables (sintering temperature, sintering time) and material variables (sinter-aid addition and reinforcement content) as input parameters to formulate data-driven, high throughput analytical assays by response surface method (RSM). Using ZrO2 toughened Al2O3 (ZTA) as a model system, the adopted RSM approach has been used to quantitatively predict independent and interactive role of process and material variables on sinter density and grain size
Signature of exchange bias and magneto-electric coupling in BiFeO3/SrRuO3 heterostructure
No full textThe magnetic interaction between BiFeO3 and SrRuO3 layers in a heterostructure grown on (001) oriented SrTiO3 substrate is investigated. A two-step magnetization reversal was observed in M-H hysteresis loop measurement of the heterostructure at 10 K. The first step in the hysteresis loop is associated with the switching of the free SrRuO3 moments whereas the second step arises from the switching of the pinned moments. The total amount of the pinned SrRuO3 moment was observed to decrease with increasing thickness of the BiFeO3 layer. The presence of exchange bias effect in the heterostructure was confirmed by the field cooled M-H measurements where only the second step of hysteresis loop was observed to shift along the field axis. The coercivity of the second step of hysteresis loop decreases with increasing temperature and merges with that of the first step above 100 K which infers the desertion of the pinned magnetic moments. Temperature dependent capacitance measurement shows a kink at the ferromagnetic transition temperature of SrRuO3 and a pronounced dip was observed in the second derivative of capacitance with respect to temperature, indicating a strong magneto-electric coupling between the two layers. (C) 2017 Elsevier B.V. All rights reserved
Environmentally friendly functional fluids from renewable and sustainable sources-A review
No full textUse of animal and plant based oils for lubrication dates back to history. Discovery of petroleum and subsequent improvements in the refining technologies replaced them with mineral oil based lubricants. Mineral oil is a fast depleting resource and is also considered as an environmental pollutant. Impact of mineral oil based lubricants and restrictive environmental regulations have increased interest in lubricants derived from natural resources. Vegetable oils being renewable, non-toxic and biodegradable have become the primary choice for environmentally sensitive and total loss lubricant applications ranging from hydraulic oils to grease. This study covers the technical viabilities associated with vegetable oil based lubricants in different applications. In the first part of this review eco labeling, environmental regulations, source, composition and availability of vegetable oils are discussed. In the later part of review, performance evaluation of vegetable oils in different applications is covered. It has been noticed that straight vegetable oils have performed satisfactorily in metal forming; metal working, hydraulic applications and have shown promising performance as greases and engine oils. It was also observed that the selection of lubricant is based on price, then on performance, and lastly on environmental consideration. This would change only with the legislative pressure on restricting the use of petroleum based products and economic incentives for biobased lubricants in environmentally sensitive applications
A novel sample loading method and protocol for monitoring sample fractionation for high precision Ca stable isotope ratio measurements using double-spike TIMS
No full textThe external reproducibility (2 sigma(SD)) of Ca stable isotope ratio measurements (delta Ca-44/40) using double-spike thermal ionization mass spectrometry (TIMS) shows a large range from <0.1 parts per thousand to 0.5 parts per thousand. We demonstrate that using a Ca-43-Ca-48 double spike, which allows simultaneous measurements of delta Ca-44/40 and delta Ca-44/42, and analyses at moderate signal strengths (Ca-40 ranging from 6 to 10 V), high precision delta Ca-44/40 (external reproducibility better than +/- 0.08 parts per thousand, 2 sigma(SD)) as well as delta Ca-44/42 can be obtained if samples and standards are analyzed under similar fractionation conditions. To monitor the fractionation conditions, the usage of a parameter beta is proposed, which measures the deviation of the Ca-43/Ca-48 ratio of the sample-double spike mixture from that of the pure double spike. A novel, low-cost sample loading technique using a combination of Re and Ta filaments and a Ta2O5 activator is presented which results in a steady signal. We report the delta Ca-44/40 and delta Ca-44/42 values, calculated w.r.t. NIST SRM 915a and reported as deviations in parts per mil (parts per thousand), of NIST standards SRM 915a (0.01, -0. 02) and SRM 915b (0.73, 0.32), NASS 6 (seawater, 1.80, 0.89), USGS silicate rock standards BHVO-2 (0.86, 0.47) and BCR-2 (0.89, 0.48), Geological Survey of Japan carbonate standards JCp-1 (coral, 0.85, 0.45) and JCt-1 (clam shell, 0.83, 0.46) and ECRM 752-1 (limestone, alternative name BCS-CRM 393) (0.83, 0.46) from the Bureau of Analyzed Samples Ltd. UK. The Ca stable isotopic compositions of JCt-1 and ECRM 752-1 are reported for the first time
MiRNomics Reveals Breast Cancer Cells Cultured on 3D Scaffolds Better Mimic Tumors in Vivo than Conventional 2D Culture
No full textTissue-engineering-based three-dimensional (3D) models offer several advantages over conventional two-dimensional (2D) cultures and can mimic tissues in vivo. Although studies have 3D scaffolds. The changes in the expression of several known microRNAs were similar to the changes reported in highly invasive cancers and their profiles highly correlated with 3D culture better mimics the tissue in vivo with novel insights into the roles of miRNAs in modulating metastatic progression