14,402 research outputs found
On data skewness, stragglers, and MapReduce progress indicators
We tackle the problem of predicting the performance of MapReduce
applications, designing accurate progress indicators that keep programmers
informed on the percentage of completed computation time during the execution
of a job. Through extensive experiments, we show that state-of-the-art progress
indicators (including the one provided by Hadoop) can be seriously harmed by
data skewness, load unbalancing, and straggling tasks. This is mainly due to
their implicit assumption that the running time depends linearly on the input
size. We thus design a novel profile-guided progress indicator, called
NearestFit, that operates without the linear hypothesis assumption and exploits
a careful combination of nearest neighbor regression and statistical curve
fitting techniques. Our theoretical progress model requires fine-grained
profile data, that can be very difficult to manage in practice. To overcome
this issue, we resort to computing accurate approximations for some of the
quantities used in our model through space- and time-efficient data streaming
algorithms. We implemented NearestFit on top of Hadoop 2.6.0. An extensive
empirical assessment over the Amazon EC2 platform on a variety of real-world
benchmarks shows that NearestFit is practical w.r.t. space and time overheads
and that its accuracy is generally very good, even in scenarios where
competitors incur non-negligible errors and wide prediction fluctuations.
Overall, NearestFit significantly improves the current state-of-art on progress
analysis for MapReduce
Deep VLT spectroscopy of the z=2.49 Radio Galaxy MRC 2104-242: Evidence for a metallicity gradient in its extended emission line region
We present spectroscopic observations of the rest-frame UV line emission
around radio galaxy MRC 2104-242 at z=2.49, obtained with FORS1 on VLT Antu.
The morphology of the halo is dominated by two spatially resolved regions. Lya
is extended by >12 arcsec along the radio axis, CIV and HeII are extended by ~8
arcsec. The overall spectrum is typical for that of high redshift radio
galaxies. The most striking spatial variation is that NV is present in the
spectrum of the region associated with the center of the galaxy hosting the
radio source, the northern region, while absent in the southern region.
Assuming that the gas is photoionized by a hidden quasar, the difference in NV
emission can be explained by a metallicity gradient within the halo. This is
consistent with a scenario in which the gas is associated with a massive
cooling flow or originates from the debris of the merging of two or more
galaxies.Comment: Accepted for publication in A&A Letter
Multidisciplinary fieldwork training in a professional geoscience environment: Quaternary mapping, landscape literacy and hazard identification
This report was produced to describe the Quaternary geology of north-east England and how it
can be interpreted and mapped. It is based on previous manuals for Quaternary geology mapping
training produced by the British Geological Survey. It gives insight into the glacial and
periglacial processes of the Yorkshire coast and the Vale of York
Strain monitoring of tapestries: results of a three-year research project
The outcomes of an interdisciplinary research project between conservators and engineers investigating the strain experienced by different areas of a tapestry are described. Two techniques were used: full-field monitoring using digital image correlation (DIC) and point measurements using optical fibre sensors. Results showed that it is possible to quantify the global strain across a discrete area of a tapestry using DIC; optical fibre and other sensors were used to validate the DIC. Strain maps created by the DIC depict areas of high and low strain and can be overlaid on images of the tapestry, creating a useful visual tool for conservators, custodians and the general public. DIC identifies areas of high strain not obvious to the naked eye. The equipment can be used in situ in a historic house. In addition the work demonstrated the close relationship between relative humidity and strain
Drawing Planar Graphs with a Prescribed Inner Face
Given a plane graph (i.e., a planar graph with a fixed planar embedding)
and a simple cycle in whose vertices are mapped to a convex polygon, we
consider the question whether this drawing can be extended to a planar
straight-line drawing of . We characterize when this is possible in terms of
simple necessary conditions, which we prove to be sufficient. This also leads
to a linear-time testing algorithm. If a drawing extension exists, it can be
computed in the same running time
Connected and disconnected quark contributions to hadron spin
By introducing an external spin operator to the fermion action, the quark
spin fractions of hadrons are determined from the linear response of the hadron
energies using the Feynman-Hellmann (FH) theorem. At our SU(3)-flavour
symmetric point, we find that the connected quark spin fractions are
universally in the range 55-70\% for vector mesons and octet and decuplet
baryons. There is an indication that the amount of spin suppression is quite
sensitive to the strength of SU(3) breaking. We also present first preliminary
results applying the FH technique to calculations of quark-line disconnected
contributions to hadronic matrix elements of axial and tensor operators. At the
SU(3)-flavour symmetric point we find a small negative contribution to the
nucleon spin from disconnected quark diagrams, while the corresponding tensor
matrix elements are consistent with zero.Comment: 7 pages, 5 figures, 32nd International Symposium on Lattice Field
Theor
Different esterase activities of exponential and plateau phases of EMT6 cells monitored by flow cytofluorimetry.
The reaction rates of enzymes hydrolysing fluorescein diacetate have been studied in populations of intact tissue-culture EMT6, cells using flow cytofluorimetric techniques. It was found that the activity of these enzymes increased in plateau phases and that this correlated inversely with plating efficiency. Highly abnormal substrate-dependent reaction velocity kinetics were found in 14-, 21-, 28- and 35-day cultures
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