205 research outputs found
High quality ferromagnetic 0 and pi Josephson tunnel junctions
We fabricated high quality \Nb/\Al_2\O_3/\Ni_{0.6}\Cu_{0.4}/\Nb
superconductor-insulator-ferromagnet-superconductor Josephson tunnel junctions.
Depending on the thickness of the ferromagnetic \Ni_{0.6}\Cu_{0.4} layer and
on the ambient temperature, the junctions were in the 0 or ground state.
All junctions have homogeneous interfaces showing almost perfect Fraunhofer
patterns. The \Al_2\O_3 tunnel barrier allows to achieve rather low damping,
which is desired for many experiments especially in the quantum domain. The
McCumber parameter increases exponentially with decreasing
temperature and reaches at . The critical
current density in the state was up to at , resulting in a Josephson penetration depth as low as
. Experimentally determined junction parameters are well
described by theory taking into account spin-flip scattering in the
\Ni_{0.6}\Cu_{0.4} layer and different transparencies of the interfaces.Comment: Changed content and Corrected typo
Far-from-equilibrium Ostwald ripening in electrostatically driven granular powders
We report the first experimental study of cluster size distributions in
electrostatically driven granular submonolayers. The cluster size distribution
in this far-from-equilibrium process exhibits dynamic scaling behavior
characteristic of the (nearly equilibrium) Ostwald ripening, controlled by the
attachment and detachment of the "gas" particles. The scaled size distribution,
however, is different from the classical Wagner distribution obtained in the
limit of a vanishingly small area fraction of the clusters. A much better
agreement is found with the theory of Conti et al. [Phys. Rev. E 65, 046117
(2002)] which accounts for the cluster merger.Comment: 5 pages, to appear in PR
Velocity Distributions of Granular Gases with Drag and with Long-Range Interactions
We study velocity statistics of electrostatically driven granular gases. For
two different experiments: (i) non-magnetic particles in a viscous fluid and
(ii) magnetic particles in air, the velocity distribution is non-Maxwellian,
and its high-energy tail is exponential, P(v) ~ exp(-|v|). This behavior is
consistent with kinetic theory of driven dissipative particles. For particles
immersed in a fluid, viscous damping is responsible for the exponential tail,
while for magnetic particles, long-range interactions cause the exponential
tail. We conclude that velocity statistics of dissipative gases are sensitive
to the fluid environment and to the form of the particle interaction.Comment: 4 pages, 3 figure
ACE as a Mechanosensor to Shear Stress Influences the Control of Its Own Regulation via Phosphorylation of Cytoplasmic Ser1270
Objectives: We tested whether angiotensin converting enzyme (ACE) and phosphorylation of Ser(1270) are involved in shear-stress (SS)-induced downregulation of the enzyme. Methods and Results: Western blotting analysis showed that SS (18 h, 15 dyn/cm(2)) decreases ACE expression and phosphorylation as well as p-JNK inhibition in human primary endothelial cells (EC). CHO cells expressing wild-type ACE (wt-ACE) also displayed SS-induced decrease in ACE and p-JNK. Moreover, SS decreased ACE promoter activity in wt-ACE, but had no effect in wild type CHO or CHO expressing ACE without either the extra-or the intracellular domains, and decreased less in CHO expressing a mutated ACE at Ser(1270) compared to wt-ACE (13 vs. 40%, respectively). The JNK inhibitor (SP600125, 18 h), in absence of SS, also decreased ACE promoter activity in wt-ACE. Finally, SS-induced inhibition of ACE expression and phosphorylation in EC was counteracted by simultaneous exposure to an ACE inhibitor. Conclusions: ACE displays a key role on its own downregulation in response to SS. This response requires both the extra- and the intracellular domains and ACE Ser(1270), consistent with the idea that the extracellular domain behaves as a mechanosensor while the cytoplasmic domain elicits the downstream intracellular signaling by phosphorylation on Ser(1270).Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)[01/00009-0]Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)[03/14115-2]Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)[06/52053-7]Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq)[480120/2007-2
Tunneling electroresistance effect in ferroelectric tunnel junctions at the nanoscale
Stable and switchable polarization of ferroelectric materials opens a
possibility to electrically control their functional behavior. A particularly
promising approach is to employ ferroelectric tunnel junctions where the
polarization reversal in a ferroelectric barrier changes the tunneling current
across the junction. Here, we demonstrate the reproducible tunneling
electroresistance effect using a combination of Piezoresponse Force Microscopy
(PFM) and Conducting Atomic Force Microscopy (C-AFM) techniques on
nanometer-thick epitaxial BaTiO3 single crystal thin films on SrRuO3 bottom
electrodes. Correlation between ferroelectric and electronic transport
properties is established by the direct nanoscale visualization and control of
polarization and tunneling current in BaTiO3 films. The obtained results show a
change in resistance by about two orders of magnitude upon polarization
reversal on a lateral scale of 20 nm at room temperature. These results are
promising for employing ferroelectric tunnel junctions in non-volatile memory
and logic devices, not involving charge as a state variable.Comment: 18 pages, 4 figure
A subgrain‐size piezometer calibrated for EBSD
We calibrate a subgrain‐size piezometer using electron backscatter diffraction (EBSD) data collected from experimentally deformed samples of olivine and quartz. Systematic analyses of angular and spatial resolution test the suitability of each dataset for inclusion in calibration of the subgrain‐size piezometer. To identify subgrain boundaries, we consider a range of critical misorientation angles and conclude that a 1° threshold provides the optimal piezometric calibration. The mean line‐intercept length, equivalent to the subgrain‐size, is found to be inversely proportional to the von Mises equivalent stress for datasets both with and without the Holyoke and Kronenberg (2010) correction. These new piezometers provide stress estimates from EBSD analyses of polymineralic rocks without the need to discriminate between relict and recrystallised grains and therefore greatly increase the range of rocks that may be used to constrain geodynamic models
Nanotechnology for catalysis and solar energy conversion
This roadmap on Nanotechnology for Catalysis and Solar Energy Conversion focuses on the application of nanotechnology in addressing the current challenges of energy conversion: 'high efficiency, stability, safety, and the potential for low-cost/scalable manufacturing' to quote from the contributed article by Nathan Lewis. This roadmap focuses on solar-to-fuel conversion, solar water splitting, solar photovoltaics and bio-catalysis. It includes dye-sensitized solar cells (DSSCs), perovskite solar cells, and organic photovoltaics. Smart engineering of colloidal quantum materials and nanostructured electrodes will improve solar-to-fuel conversion efficiency, as described in the articles by Waiskopf and Banin and Meyer. Semiconductor nanoparticles will also improve solar energy conversion efficiency, as discussed by Boschloo et al in their article on DSSCs. Perovskite solar cells have advanced rapidly in recent years, including new ideas on 2D and 3D hybrid halide perovskites, as described by Spanopoulos et al 'Next generation' solar cells using multiple exciton generation (MEG) from hot carriers, described in the article by Nozik and Beard, could lead to remarkable improvement in photovoltaic efficiency by using quantization effects in semiconductor nanostructures (quantum dots, wires or wells). These challenges will not be met without simultaneous improvement in nanoscale characterization methods. Terahertz spectroscopy, discussed in the article by Milot et al is one example of a method that is overcoming the difficulties associated with nanoscale materials characterization by avoiding electrical contacts to nanoparticles, allowing characterization during device operation, and enabling characterization of a single nanoparticle. Besides experimental advances, computational science is also meeting the challenges of nanomaterials synthesis. The article by Kohlstedt and Schatz discusses the computational frameworks being used to predict structure–property relationships in materials and devices, including machine learning methods, with an emphasis on organic photovoltaics. The contribution by Megarity and Armstrong presents the 'electrochemical leaf' for improvements in electrochemistry and beyond. In addition, biohybrid approaches can take advantage of efficient and specific enzyme catalysts. These articles present the nanoscience and technology at the forefront of renewable energy development that will have significant benefits to society
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