4,690 research outputs found
Exploring Photometric Redshifts as an Optimization Problem: An Ensemble MCMC and Simulated Annealing-Driven Template-Fitting Approach
Using a grid of million elements () adapted from
COSMOS photometric redshift (photo-z) searches, we investigate the general
properties of template-based photo-z likelihood surfaces. We find these
surfaces are filled with numerous local minima and large degeneracies that
generally confound rapid but "greedy" optimization schemes, even with
additional stochastic sampling methods. In order to robustly and efficiently
explore these surfaces, we develop BAD-Z [Brisk Annealing-Driven Redshifts
(Z)], which combines ensemble Markov Chain Monte Carlo (MCMC) sampling with
simulated annealing to sample arbitrarily large, pre-generated grids in
approximately constant time. Using a mock catalog of 384,662 objects, we show
BAD-Z samples times more efficiently compared to a brute-force
counterpart while maintaining similar levels of accuracy. Our results represent
first steps toward designing template-fitting photo-z approaches limited mainly
by memory constraints rather than computation time.Comment: 14 pages, 8 figures; submitted to MNRAS; comments welcom
APP Expression in Primary Neuronal Cell Cultures fromP6 Mice during in vitro Differentiation
Primary neuronal cell cultures from P6 mice were investigated in order to study amyloid protein precursor (APP) gene expression in differentiating neurons. Cerebellar granule cells which strongly express APP 695 allowed the identification of three distinct isoforms of neuronal APP 695. The high-molecular-weight form of APP 695 is sialylated. The expression pattern of neuronal APP 695 changes during in vitro differentiation. Sialylated forms become more abundant upon longer cultivation time. The secreted forms of sialylated, neuronal APP 695 are shown to comigrate with APP isolated from cerebrospinal fluid. We suggest that the different sialylation states of APP 695 may reflect the modulation of cell-cell and cell-substrate interactions during in vitro differentiation and regeneration
The 2MASS Tully-Fisher Survey : Mapping the Mass in the Universe
The 2MASS Tully-Fisher Survey (2MTF) aims to measure Tully-Fisher (TF)
distances for all bright inclined spirals in the 2MASS Redshift Survey (2MRS)
using high quality HI widths and 2MASS photometry. Compared with previous
peculiar velocity surveys, the 2MTF survey provides more accurate width
measurements and more uniform sky coverage, combining observations with the
Green Bank, Arecibo and Parkes telescopes. With this new redshift-independent
distance database, we will significantly improve our understanding of the mass
distribution in the local universe.Comment: 4 pages, 3 figures, IAU Symposium 289 proceedin
Calcium potassium tris(oxalato-O-1, O-2)-chromate(III) pentahydrate
The Cr-III atom in CaK[Cr(C2O4)(3)].5H(2)O, has a regular octahedral geometry with three oxalato groups completing the coordination, Both the calcium and potassium cations are coordinated to the O atom of the oxalate group
The effect of surgical approach on the histology of the femoral head following resurfacing of the hip : analysis of retrieval specimens
Objectives: We aimed to determine the effect of surgical approach on the histology of the femoral head following resurfacing of the hip.
Methods: We performed a histological assessment of the bone under the femoral component taken from retrieval specimens of patients having revision surgery following resurfacing of the hip. We compared the number of empty lacunae in specimens from patients who had originally had a posterior surgical approach with the number in patients having alternative surgical approaches.
Results: We found a statistically significant increase in the percentage of empty lacunae in retrieval specimens from patients who had the posterior approach compared with other surgical approaches (p < 0.001).
Conclusions: This indicates that the vascular compromise that occurs during the posterior surgical approach does have long-term effects on the bone of the femoral head, even if it does not cause overt avascular necrosis
Groups of Galaxies in the Two Micron All-Sky Redshift Survey
We present the results of applying a percolation algorithm to the initial
release of the Two Micron All-Sky Survey Extended Source Catalog, using
subsequently measured redshifts for almost all of the galaxies with K < 11.25
mag. This group catalog is based on the first near-IR all-sky flux-limited
survey that is complete to |b| = 5 deg. We explore the dependence of the
clustering on the length and velocity scales involved. The paper describes a
group catalog, complete to a limiting redshift of 10,000 km/s, created by
maximizing the number of groups containing 3 or more members. A second catalog
is also presented, created by requiring a minimum density contrast of 80 to
identify groups. We identify known nearby clusters in the catalogs and contrast
the groups identified in the two catalogs. We examine and compare the
properties of the determined groups and verify that the results are consistent
with the UZC-SSRS2 and northern CfA redshift survey group catalogs. The all-sky
nature of the catalog will allow the development of a flow-field model based on
the density field inferred from the estimated cluster masses.Comment: Accepted for publication in ApJ (29 pages including 13 figures). A
version with high-resolution figures is available at
http://www.cfa.harvard.edu/~acrook/preprints
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