5,544 research outputs found
Failure of conductance quantization in two-dimensional topological insulators due to non-magnetic impurities
Despite topological protection and the absence of magnetic impurities,
two-dimensional topological insulators display quantized conductance only in
surprisingly short channels, which can be as short as 100 nm for atomically
thin materials. We show that the combined action of short-range nonmagnetic
impurities located near the edges and on site electron-electron interactions
effectively creates noncollinear magnetic scatterers, and, hence, results in
strong backscattering. The mechanism causes deviations from quantization even
at zero temperature and for a modest strength of electron-electron
interactions. Our theory provides a straightforward conceptual framework to
explain experimental results, especially those in atomically thin crystals,
plagued with short-range edge disorder.Comment: 8 pages, 9 figures, 5 appendice
Rotation-invariant observables in parity-violating decays of vector particles to fermion pairs
The di-fermion angular distribution observed in decays of inclusively
produced vector particles is characterized by two frame-independent
observables, reflecting the average spin-alignment of the produced particle and
the magnitude of parity violation in the decay. The existence of these
observables derives from the rotational properties of angular momentum
eigenstates and is a completely general result, valid for any J=1 state and
independent of the production process. Rotation-invariant formulations of
polarization and of the decay parity-asymmetry can provide more significant
measurements than the commonly used frame-dependent definitions, also improving
the quality of the comparisons between the measurements and the theoretical
calculations.Comment: To be published in Phys. Rev.
Enhancing Job Scheduling of an Atmospheric Intensive Data Application
Nowadays, e-Science applications involve great deal of data to have more accurate analysis. One of its application domains is the Radio Occultation which manages satellite data. Grid Processing Management is a physical infrastructure geographically distributed based on Grid Computing, that is implemented for the overall processing Radio Occultation analysis. After a brief description of algorithms adopted to characterize atmospheric profiles, the paper presents an improvement of job scheduling in order to decrease processing time and optimize resource utilization. Extension of grid computing capacity is implemented by virtual machines in existing physical Grid in order to satisfy temporary job requests. Also scheduling plays an important role in the infrastructure that is handled by a couple of schedulers which are developed to manage data automaticall
Quarkonium production in the LHC era: a polarized perspective
Polarization measurements are usually considered as the most difficult
challenge for the QCD description of quarkonium production. In fact, global
data fits for the determination of the non-perturbative parameters of
bound-state formation traditionally exclude polarization observables and use
them as a posteriori verifications of the predictions, with perplexing results.
With a change of perspective, we move polarization data to the centre of the
study, advocating that they actually provide the strongest fundamental
indications about the production mechanisms, even before we explicitly consider
perturbative calculations.
Considering psi(2S) and Y(3S) measurements from LHC experiments and
state-of-the-art NLO short-distance calculations in the framework of
non-relativistic QCD factorization (NRQCD), we perform a search for a kinematic
domain where the polarizations can be correctly reproduced together with the
cross sections, by systematically scanning the phase space and accurately
treating the experimental uncertainties. This strategy provides a
straightforward solution to the "quarkonium polarization puzzle" and reassuring
signs that the theoretical framework is reliable. At the same time, the results
expose unexpected hierarchies in the non-perturbative NRQCD parameters, that
open new paths towards the understanding of bound-state formation in QCD.Comment: Submitted to Phys. Lett.
Role of final state interactions in the B meson decay into two pions
We estimate final state interactions in the B-meson decays into two pions by
the Regge model. We consider Pomeron exchange and the leading Regge
trajectories that can relate intermediate particles to the final state. In some
cases, most notably B => pi^0 pi^0 and B => pi^+ pi^-, the effect is relevant
and produces a better agreement between theory and experiment.Comment: 8 pages, 6 figure
Model-independent constraints on the shape parameters of dilepton angular distributions
The coefficients determining the dilepton decay angular distribution of
vector particles obey certain positivity constraints and a rotation-invariant
identity. These relations are a direct consequence of the covariance properties
of angular momentum eigenstates and are independent of the production
mechanism. The Lam-Tung relation can be derived as a particular case, simply
recognizing that the Drell-Yan dilepton is always produced transversely
polarized with respect to one or more quantization axes. The dilepton angular
distribution continues to be characterized by a frame-independent identity also
when the Lam-Tung relation is violated. Moreover, the violation can be easily
characterized by measuring a one-dimensional distribution depending on one
shape coefficient.Comment: 7 page
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
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