896 research outputs found
Decoding the spectra of SDSS early-type galaxies: New indicators of age and recent star formation
(Abridged) We apply Principal Component Analysis (PCA) to a sample of
early-type galaxies from the Sloan Digital Sky Survey (SDSS) in order to infer
differences in their star formation histories. Out of the first few principal
components (PC), we study four which give information about stellar populations
and velocity dispersion. We construct two parameters (eta and zeta) as linear
combinations of PC1 and PC2. We find zeta to be most sensitive to recent
episodes of star formation, and eta to be strongly dependent on the average age
of the stellar populations. The distribution of the eta component of the
composites appear to be indistinguishable between high and low density regions,
whereas the distribution of zeta parameters have a significant skew towards
lower values for galaxies in low density regions. This result suggests that
galaxies in lower density environments are less likely to present weak episodes
of recent star formation. In contrast, a significant number of galaxies from
our high density subsample -- which includes clusters (both outer regions and
centres) and groups -- underwent small but detectable recent star formation at
high metallicity, in agreement with recent estimates targeting elliptical
galaxies in Hickson Compact Groups and in the field (Ferreras et al.).Comment: 19 pages, 12 figures. Accepted for publication in MNRA
Stocator: A High Performance Object Store Connector for Spark
We present Stocator, a high performance object store connector for Apache
Spark, that takes advantage of object store semantics. Previous connectors have
assumed file system semantics, in particular, achieving fault tolerance and
allowing speculative execution by creating temporary files to avoid
interference between worker threads executing the same task and then renaming
these files. Rename is not a native object store operation; not only is it not
atomic, but it is implemented using a costly copy operation and a delete.
Instead our connector leverages the inherent atomicity of object creation, and
by avoiding the rename paradigm it greatly decreases the number of operations
on the object store as well as enabling a much simpler approach to dealing with
the eventually consistent semantics typical of object stores. We have
implemented Stocator and shared it in open source. Performance testing shows
that it is as much as 18 times faster for write intensive workloads and
performs as much as 30 times fewer operations on the object store than the
legacy Hadoop connectors, reducing costs both for the client and the object
storage service provider
The Impact of College Education on Geographic Mobility: Identifying Education Using Multiple Components of Vietnam Draft Risk
We examine whether higher education is a causal determinant of geographic mobility using variation in college attainment induced by draft-avoidance behavior during the Vietnam War. We use national and state-level induction risk to identify both educational attainment and veteran status among cohorts of affected men observed in the 1980 Census. Our 2SLS estimates imply that the additional years of higher education significantly increased the likelihood that affected men resided outside their birth states later in life. Most estimates suggest a causal impact of higher education on migration that is larger in magnitude but not significantly different from OLS. Our large reduced-form estimates for the effect of induction risk on out-of-state migration also imply that the Vietnam War led to substantial geographic churning in the national labor market. We conclude that the causal impact of college completion on subsequent mobility is large and provide evidence on a range of mechanisms that may be responsible for the relationship between college education and mobility.
Naturalized and simplified gauge mediation
Following recent developments in model building we construct a simple,
natural and controllable model of gauge-mediated supersymmetry breaking.Comment: 8 pages, minor change
Algebraic analysis of quantum search with pure and mixed states
An algebraic analysis of Grover's quantum search algorithm is presented for
the case in which the initial state is an arbitrary pure quantum state of n
qubits. This approach reveals the geometrical structure of the quantum search
process, which turns out to be confined to a four-dimensional subspace of the
Hilbert space. This work unifies and generalizes earlier results on the time
evolution of the amplitudes during the quantum search, the optimal number of
iterations and the success probability. Furthermore, it enables a direct
generalization to the case in which the initial state is a mixed state,
providing an exact formula for the success probability.Comment: 13 page
Excess Clustering on Large Scales in the MegaZ DR7 Photometric Redshift Survey
We observe a large excess of power in the statistical clustering of luminous red galaxies in the photometric SDSS galaxy sample called MegaZ DR7. This is seen over the lowest multipoles in the angular power spectra C-l in four equally spaced redshift bins between 0: 45 <= z <= 0: 65. However, it is most prominent in the highest redshift band at similar to 4 sigma and it emerges at an effective scale k less than or similar to 0: 01 h Mpc(-1). Given that MegaZ DR7 is the largest cosmic volume galaxy survey to date (3.3(Gpch(-1))(3)) this implies an anomaly on the largest physical scales probed by galaxies. Alternatively, this signature could be a consequence of it appearing at the most systematically susceptible redshift. There are several explanations for this excess power that range from systematics to new physics. We test the survey, data, and excess power, as well as possible origins
Scanning tunneling spectroscopy characterization of the pseudogap and the x = 1/8 anomaly in La2-xSrxCuO4 thin films
Using scanning tunneling spectroscopy we examined the local density of states
of thin c-axis La2-xSrxCuO4 films, over wide doping and temperature ranges. We
found that the pseudogap exists only at doping levels lower than optimal. For x
= 0.12, close to the 'anomalous' x = 1/8 doping level, a zero bias conductance
peak was the dominant spectral feature, instead of the excepted V- shaped
(c-axis tunneling) gap structure. We have established that this surprising
effect cannot be explained by tunneling into (110) facets. Possible origins for
this unique behavior are discussed.Comment: 15 pages, 6 figure
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