67,337 research outputs found
The Effects of Halo Assembly Bias on Self-Calibration in Galaxy Cluster Surveys
Self-calibration techniques for analyzing galaxy cluster counts utilize the
abundance and the clustering amplitude of dark matter halos. These properties
simultaneously constrain cosmological parameters and the cluster
observable-mass relation. It was recently discovered that the clustering
amplitude of halos depends not only on the halo mass, but also on various
secondary variables, such as the halo formation time and the concentration;
these dependences are collectively termed assembly bias. Applying modified
Fisher matrix formalism, we explore whether these secondary variables have a
significant impact on the study of dark energy properties using the
self-calibration technique in current (SDSS) and the near future (DES, SPT, and
LSST) cluster surveys. The impact of the secondary dependence is determined by
(1) the scatter in the observable-mass relation and (2) the correlation between
observable and secondary variables. We find that for optical surveys, the
secondary dependence does not significantly influence an SDSS-like survey;
however, it may affect a DES-like survey (given the high scatter currently
expected from optical clusters) and an LSST-like survey (even for low scatter
values and low correlations). For an SZ survey such as SPT, the impact of
secondary dependence is insignificant if the scatter is 20% or lower but can be
enhanced by the potential high scatter values introduced by a highly correlated
background. Accurate modeling of the assembly bias is necessary for cluster
self-calibration in the era of precision cosmology.Comment: 13 pages, 5 figures, replaced to match published versio
A Sino-German 6cm polarisation survey of the Galactic plane IX. HII regions
Large-scale radio continuum surveys provide data to get insights into the
physical properties of radio sources. HII regions are prominent radio sources
produced by thermal emission of ionised gas around young massive stars. We
identify and analyse HII regions in the Sino-German 6cm polarisation survey of
the Galactic plane. Objects with flat radio continuum spectra together with
infrared and/or Halpha emission were identified as HII regions. For HII regions
with small apparent sizes, we cross-matched the 6cm small-diameter source
catalogue with the radio HII region catalogue compiled by Paladini and the
infrared HII region catalogue based on the WISE data. Extended HII regions were
identified by eye by overlaying the Paladini and the WISE HII regions onto the
6cm survey images for coincidences. The TT-plot method was employed for
spectral index verification. A total of 401 HII regions were identified and
their flux densities were determined with the Sino-German 6cm survey data. In
the surveyed area, 76 pairs of sources are found to be duplicated in the
Paladini HII region catalogue, mainly due to the non-distinction of previous
observations with different angular resolutions, and 78 objects in their
catalogue are misclassified as HII regions, being actually planetary nebulae,
supernova remnants or extragalactic sources that have steep spectra. More than
30 HII regions and HII region candidates from our 6cm survey data, especially
extended ones, do not have counterparts in the WISE HII region catalogue, of
which 9 are identified for the first time. Based on the newly derived radio
continuum spectra and the evidence of infrared emission, the previously
identified SNRs G11.1-1.0, G20.4+0.1 and G16.4-0.5 are believed to be HII
regions.Comment: version after some minor corrections and language editing, full Table
2 - 5 will appear in CDS, accepted for publication in A&
Probabilistic teleportation of unknown two-particle state via POVM
We propose a scheme for probabilistic teleportation of unknown two-particle
state with partly entangled four-particle state via POVM. In this scheme the
teleportation of unknown two-particle state can be realized with certain
probability by performing two Bell state measurements, a proper POVM and a
unitary transformation.Comment: 5 pages, no figur
Photo and electroluminescence behavior of Tb(ACAC)3phen complex used as emissive layer on organic light emitting diodes
This work shows the luminescence properties of a rare-earth organic complex, the Tb(ACAC)3phen. The results show the 5D4 -> 7F3,4,5,6 transitions with no influence of any ligand emission. The photoluminescence excitation spectrum is tentatively interpreted by the ligands absorption. An OLED was made by thermal evaporation (total thickness of 1200 Ă
) using TPD and Alq3 as hole and electron transport layers, respectively. The light emission reproduces the photoluminescence spectrum of the terbium complex at room temperature, with CIE (x,y) color coordinates of (0.28, 0.55). No presence of any bands from the ligands was observed. The potential use of this compound in efficient devices is discussed
Bimodal Distribution of Sulfuric Acid Aerosols in the Upper Haze of Venus
The upper haze (UH) of Venus is variable on the order of days and it is
populated by two particle modes. We use a 1D microphysics and vertical
transport model based on the Community Aerosol and Radiation Model for
Atmospheres to evaluate whether interaction of upwelled cloud particles and
sulfuric acid particles nucleated in situ on meteoric dust are able to generate
the two size modes and whether their observed variability are due to cloud top
vertical transient winds. Nucleation of photochemically produced sulfuric acid
onto polysulfur condensation nuclei generates mode 1 cloud droplets that then
diffuse upwards into the UH. Droplets generated in the UH from nucleation of
sulfuric acid onto meteoric dust coagulate with the upwelled cloud particles
and cannot reproduce the observed bimodal size distribution. The mass transport
enabled by cloud top transient winds are able to generate a bimodal size
distribution in a time scale consistent with observations. Sedimentation and
convection in the middle and lower clouds causes the formation of large mode 2
and mode 3 particles. Evaporation of these particles below the clouds creates a
local sulfuric acid vapor maximum that causes upwelling of sulfuric acid back
into the clouds. If the polysulfur condensation nuclei are small and their
production rate is high, coagulation of small droplets onto larger droplets in
the middle cloud may result in sulfuric acid "rain" below the clouds once every
few Earth months. Reduction of the polysulfur condensation nuclei production
rate destroys this oscillation and reduces the mode 1 particle abundance in the
middle cloud by two orders of magnitude, though it better reproduces the
sulfur-to-sulfuric-acid mass ratio in the cloud and haze droplets. In general
we find satisfactory agreement between our results and observations, though
improvements could be made by incorporating sulfur microphysics.Comment: 62 pages, 18 figures, 1 table. Accepted for publication in Icaru
Pycortex: an interactive surface visualizer for fMRI.
Surface visualizations of fMRI provide a comprehensive view of cortical activity. However, surface visualizations are difficult to generate and most common visualization techniques rely on unnecessary interpolation which limits the fidelity of the resulting maps. Furthermore, it is difficult to understand the relationship between flattened cortical surfaces and the underlying 3D anatomy using tools available currently. To address these problems we have developed pycortex, a Python toolbox for interactive surface mapping and visualization. Pycortex exploits the power of modern graphics cards to sample volumetric data on a per-pixel basis, allowing dense and accurate mapping of the voxel grid across the surface. Anatomical and functional information can be projected onto the cortical surface. The surface can be inflated and flattened interactively, aiding interpretation of the correspondence between the anatomical surface and the flattened cortical sheet. The output of pycortex can be viewed using WebGL, a technology compatible with modern web browsers. This allows complex fMRI surface maps to be distributed broadly online without requiring installation of complex software
Phase-Dependent Spontaneous Spin Polarization and Bifurcation Delay in Coupled Two-Component Bose-Einstein Condensates
The spontaneous spin polarization and bifurcation delay in two-component
Bose-Einstein condensates coupled with laser or/and radio-frequency pulses are
investigated. We find that the bifurcation and the spontaneous spin
polarization are determined by both physical parameters and relative phase
between two condensates. Through bifurcations, the system enters into the
spontaneous spin polarization regime from the Rabi regime. We also find that
bifurcation delay appears when the parameter is swept through a static
bifurcation point. This bifurcation delay is responsible for metastability
leading to hysteresis.Comment: Improved version for cond-mat/021157
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