368 research outputs found
The color gradients of spiral disks in the Sloan Digital Sky Survey
We investigate the radial color gradients of galactic disks using a sample of
about 20,000 face-on spiral galaxies selected from the fourth data release of
the Sloan Digital Sky Survey (SDSS-DR4). We combine galaxies with similar
concentration, size and luminosity to construct composite galaxies, and then
measure their color profiles by stacking the azimuthally averaged radial color
profiles of all the member galaxies. Except for the smallest galaxies (R_{50}<3
kpc), almost all galaxies show negative disk color gradients with mean g-r
gradient G_{gr}=-0.006 mag kpc^{-1} and r-z gradient G_{rz}=-0.018 mag
kpc^{-1}. The disk color gradients are independent of the morphological types
of galaxies and strongly dependent on the disk surface brightness \mu_{d}, with
lower surface brightness galactic disks having steeper color gradients. We
quantify the intrinsic correlation between color gradients and surface
brightness as G_{gr}=-0.011\mu_{d}+0.233 and G_{rz}=-0.015\mu_{d}+0.324. These
quantified correlations provide tight observational constraints on the
formation and evolution models of spiral galaxies.Comment: 20 pages, 5 figures, Accepted for publication in RAA (Research in
Astronomy and Astrophysics
A simulation study on the measurement of D0-D0bar mixing parameter y at BES-III
We established a method on measuring the \dzdzb mixing parameter for
BESIII experiment at the BEPCII collider. In this method, the doubly
tagged events, with one decays to
CP-eigenstates and the other decays semileptonically, are used to
reconstruct the signals. Since this analysis requires good separation,
a likelihood approach, which combines the , time of flight and the
electromagnetic shower detectors information, is used for particle
identification. We estimate the sensitivity of the measurement of to be
0.007 based on a fully simulated MC sample.Comment: 6 pages, 7 figure
In situ interface engineering for probing the limit of quantum dot photovoltaic devices.
Quantum dot (QD) photovoltaic devices are attractive for their low-cost synthesis, tunable band gap and potentially high power conversion efficiency (PCE). However, the experimentally achieved efficiency to date remains far from ideal. Here, we report an in-situ fabrication and investigation of single TiO2-nanowire/CdSe-QD heterojunction solar cell (QDHSC) using a custom-designed photoelectric transmission electron microscope (TEM) holder. A mobile counter electrode is used to precisely tune the interface area for in situ photoelectrical measurements, which reveals a strong interface area dependent PCE. Theoretical simulations show that the simplified single nanowire solar cell structure can minimize the interface area and associated charge scattering to enable an efficient charge collection. Additionally, the optical antenna effect of nanowire-based QDHSCs can further enhance the absorption and boost the PCE. This study establishes a robust 'nanolab' platform in a TEM for in situ photoelectrical studies and provides valuable insight into the interfacial effects in nanoscale solar cells
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Coherent Spin and Quasiparticle Dynamics in Solution-Processed Layered 2D Lead Halide Perovskites.
Layered 2D halide perovskites with their alternating organic and inorganic atomic layers that form a self-assembled quantum well system are analogues of the purely inorganic 2D transition metal dichalcogenides. Within their periodic structures lie a hotbed of photophysical phenomena such as dielectric confinement effect, optical Stark effect, strong exciton-photon coupling, etc. Detailed understanding into the strong light-matter interactions in these hybrid organic-inorganic semiconductor systems remains modest. Herein, the intricate coherent interplay of exciton, spin, and phonon dynamics in (C6H5C2H4NH3)2PbI4 thin films using transient optical spectroscopy is explicated. New insights into the hotly debated origins of transient spectral features, relaxation pathways, ultrafast spin relaxation via exchange interaction, and strong coherent exciton-phonon coupling are revealed from the detailed phenomenological modeling. Importantly, this work unravels the complex interplay of spin-quasiparticle interactions in these layered 2D halide perovskites with large spin-orbit coupling
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