1,806 research outputs found

    Constraining Scatter in the Stellar Mass--Halo Mass Relation for Haloes Less Massive than the Milky Way

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    Most galaxies are hosted by massive, invisible dark matter haloes, yet little is known about the scatter in the stellar mass--halo mass relation for galaxies with host halo masses Mh1011MM_{h}\le 10^{11}M_{\odot}. Using mock catalogues based on dark matter simulations, we find that two observable signatures are sensitive to scatter in the stellar mass--halo mass relation even at these mass scales; i.e., conditional stellar mass functions and velocity distribution functions for neighbouring galaxies. We compute these observables for 179,373 galaxies in the Sloan Digital Sky Survey (SDSS) with stellar masses M>109MM_{\ast} > 10^9 M_{\odot} and redshifts 0.01 <z<< z < 0.307. We then compare to mock observations generated from the Bolshoi-Planck\textit{Bolshoi-Planck} dark matter simulation for stellar mass--halo mass scatters ranging from 0 to 0.6 dex. The observed results are consistent with simulated results for most values of scatter (<<0.6 dex), and SDSS statistics are insufficient to provide firm constraints. However, this method could provide much tighter constraints on stellar mass--halo mass scatter in the future if applied to larger data sets, especially the anticipated Dark Energy Spectroscopic Instrument Bright Galaxy Survey. Constraining the value of scatter could have important implications for galaxy formation and evolution.Comment: 11 pages, 1 table, 9 main body figures, 9 appendix figure

    Water-Driven Micromotors

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    We demonstrate the first example of a water-driven bubble-propelled micromotor that eliminates the requirement for the common hydrogen peroxide fuel. The new water-driven Janus micromotor is composed of a partially coated Al–Ga binary alloy microsphere prepared via microcontact mixing of aluminum microparticles and liquid gallium. The ejection of hydrogen bubbles from the exposed Al–Ga alloy hemisphere side, upon its contact with water, provides a powerful directional propulsion thrust. Such spontaneous generation of hydrogen bubbles reflects the rapid reaction between the aluminum alloy and water. The resulting water-driven spherical motors can move at remarkable speeds of 3 mm s^(–1) (i.e., 150 body length s^(–1)), while exerting large forces exceeding 500 pN. Factors influencing the efficiency of the aluminum–water reaction and the resulting propulsion behavior and motor lifetime, including the ionic strength and environmental pH, are investigated. The resulting water-propelled Al–Ga/Ti motors move efficiently in different biological media (e.g., human serum) and hold considerable promise for diverse biomedical or industrial applications

    Catalytic Iridium-Based Janus Micromotors Powered by Ultralow Levels of Chemical Fuels

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    We describe catalytic micromotors powered by remarkably low concentrations of chemical fuel, down to the 0.0000001% level. These Janus micromotors rely on an iridium hemispheric layer for the catalytic decomposition of hydrazine in connection to SiO_2 spherical particles. The micromotors are self-propelled at a very high speed (of ∼20 body lengths s^(–1)) in a 0.001% hydrazine solution due to osmotic effects. Such a low fuel concentration represents a 10 000-fold decrease in the level required for common catalytic nanomotors. The attractive propulsion performance, efficient catalytic energy-harvesting, environmentally triggered swarming behavior, and magnetic control of the new Janus micromotors hold considerable promise for diverse practical applications

    Highly Efficient Light-Driven TiO_2–Au Janus Micromotors

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    A highly efficient light-driven photocatalytic TiO_2–Au Janus micromotor with wireless steering and velocity control is described. Unlike chemically propelled micromotors which commonly require the addition of surfactants or toxic chemical fuels, the fuel-free Janus micromotor (diameter ∼1.0 μm) can be powered in pure water under an extremely low ultraviolet light intensity (2.5 × 10^(–3) W/cm^2), and with 40 × 10^(–3) W/cm^2, they can reach a high speed of 25 body length/s, which is comparable to common Pt-based chemically induced self-electrophoretic Janus micromotors. The photocatalytic propulsion can be switched on and off by incident light modulation. In addition, the speed of the photocatalytic TiO_2–Au Janus micromotor can be accelerated by increasing the light intensity or by adding low concentrations of chemical fuel H_2O_2 (i.e., 0.1%). The attractive fuel-free propulsion performance, fast movement triggering response, low light energy requirement, and precise motion control of the TiO_2–Au Janus photocatalytic micromotor hold considerable promise for diverse practical applications

    PYR/PYL/RCAR abscisic acid receptors regulate K<sup>+</sup> and Cl<sup>-</sup> channels through reactive oxygen species-mediated activation of Ca<sup>2+</sup> channels at the plasma membrane of intact Arabidopsis guard cells.

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    The discovery of the START family of abscisic acid (ABA) receptors places these proteins at the front of a protein kinase/phosphatase signal cascade that promotes stomatal closure. The connection of these receptors to Ca&lt;sup&gt;2+&lt;/sup&gt; signals evoked by ABA has proven more difficult to resolve, although it has been implicated by studies of the pyrbactin-insensitive &lt;i&gt;pyr1/pyl1/pyl2/pyl4&lt;/i&gt; quadruple mutant. One difficulty is that flux through plasma membrane Ca&lt;sup&gt;2+&lt;/sup&gt; channels and Ca&lt;sup&gt;2+&lt;/sup&gt; release from endomembrane stores coordinately elevate cytosolic free Ca&lt;sup&gt;2+&lt;/sup&gt; concentration ([Ca&lt;sup&gt;2+&lt;/sup&gt;]&lt;sub&gt;i&lt;/sub&gt;) in guard cells, and both processes are facilitated by ABA. Here, we describe a method for recording Ca&lt;sup&gt;2+&lt;/sup&gt; channels at the plasma membrane of intact guard cells of Arabidopsis (Arabidopsis thaliana). We have used this method to resolve the loss of ABA-evoked Ca&lt;sup&gt;2+&lt;/sup&gt; channel activity at the plasma membrane in the &lt;i&gt;pyr1/pyl1/pyl2/pyl4&lt;/i&gt; mutant and show the consequent suppression of [Ca&lt;sup&gt;2+&lt;/sup&gt;]&lt;sub&gt;i&lt;/sub&gt; increases in vivo. The basal activity of Ca&lt;sup&gt;2+&lt;/sup&gt; channels was not affected in the mutant; raising the concentration of Ca&lt;sup&gt;2+&lt;/sup&gt; outside was sufficient to promote Ca&lt;sup&gt;2+&lt;/sup&gt; entry, to inactivate current carried by inward-rectifying K&lt;sup&gt;+&lt;/sup&gt; channels and to activate current carried by the anion channels, both of which are sensitive to [Ca&lt;sup&gt;2+&lt;/sup&gt;]&lt;sub&gt;i&lt;/sub&gt; elevations. However, the ABA-dependent increase in reactive oxygen species (ROS) was impaired. Adding the ROS hydrogen peroxide was sufficient to activate the Ca&lt;sup&gt;2+&lt;/sup&gt; channels and trigger stomatal closure in the mutant. These results offer direct evidence of PYR/PYL/RCAR receptor coupling to the activation by ABA of plasma membrane Ca&lt;sup&gt;2+&lt;/sup&gt; channels through ROS, thus affecting [Ca&lt;sup&gt;2+&lt;/sup&gt;]&lt;sub&gt;i&lt;/sub&gt; and its regulation of stomatal closure

    Water-Driven Micromotors

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    We demonstrate the first example of a water-driven bubble-propelled micromotor that eliminates the requirement for the common hydrogen peroxide fuel. The new water-driven Janus micromotor is composed of a partially coated Al–Ga binary alloy microsphere prepared via microcontact mixing of aluminum microparticles and liquid gallium. The ejection of hydrogen bubbles from the exposed Al–Ga alloy hemisphere side, upon its contact with water, provides a powerful directional propulsion thrust. Such spontaneous generation of hydrogen bubbles reflects the rapid reaction between the aluminum alloy and water. The resulting water-driven spherical motors can move at remarkable speeds of 3 mm s^(–1) (i.e., 150 body length s^(–1)), while exerting large forces exceeding 500 pN. Factors influencing the efficiency of the aluminum–water reaction and the resulting propulsion behavior and motor lifetime, including the ionic strength and environmental pH, are investigated. The resulting water-propelled Al–Ga/Ti motors move efficiently in different biological media (e.g., human serum) and hold considerable promise for diverse biomedical or industrial applications

    (6R,7R)-3-Hydroxymethyl-7-(2-phenyl­acetamido)-3-cephem-4-carboxylic acid lactone

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    In the title compound {systematic name: N-[(4R,5R)-3,11-dioxo-10-oxa-6-thia-2-aza­tricyclo­[6.3.0.02,5]undec-1(8)-en-4-yl]-2-phenyl­acetamide}, C16H14N2O4S, the four- and five-membered rings adopt planar conformations (with r.m.s. deviations of 0.0349 and 0.0108 Å respectively) while the six-membered ring adopts a half-chair, or envelope-like, conformation with the S atom in the flap position. In the crystal, mol­ecules are linked by N—H⋯O hydrogen bonds

    Topological (Sliced) Doping of a 3D Peierls System: Predicted Structure of Doped BaBiO3

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    At hole concentrations below x=0.4, Ba_(1-x)K_xBiO_3 is non-metallic. At x=0, pure BaBiO3 is a Peierls insulator. Very dilute holes create bipolaronic point defects in the Peierls order parameter. Here we find that the Rice-Sneddon version of Peierls theory predicts that more concentrated holes should form stacking faults (two-dimensional topological defects, called slices) in the Peierls order parameter. However, the long-range Coulomb interaction, left out of the Rice-Sneddon model, destabilizes slices in favor of point bipolarons at low concentrations, leaving a window near 30% doping where the sliced state is marginally stable.Comment: 6 pages with 5 embedded postscript figure

    Diethyl 2,3-dihydro­thieno[3,4-b]-1,4-dioxine-5,7-dicarboxyl­ate

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    The title compound, C12H14O6S, is a dicarboxylic acid diethyl ester of 3,4-ethyl­enedioxy­thio­phene, which is a component of electrically conductive poly(3,4-ethyl­enedioxy­thio­phene) (PEDOT). The ethyl­ene group is disordered over two sites with occupancy factors 0.64 and 0.36. Both the carbonyl groups are coplanar with the thio­phene ring. The mol­ecules form centrosymmetric dimers with an R 2 2(12) coupling by inter­molecular C—H⋯O hydrogen bonds [3.333 (5) Å] at the ethoxy­carbonyl groups. The dimer units are arranged to form a ribbon-like mol­ecular sheet
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