10,616 research outputs found
A Note on the least squarefree number in an arithmetic progression
We prove an asymptotic formula for squarefree in arithmetic progressions with
squarefree moduli, improving previous results by Prachar. The main tool is an
estimate for counting solutions of a congruence inside a box that goes beyond
what can be obtained by using the Weil bound.Comment: 6 pages, no figure
Microseismic study of the interandine valley between Latacunga and Cuayllabamba
The present state of two active volcanoes and the principal active seismic faults in a 100 km area from Quito to Toacaso, Ecuador was studied. A brief seismic history of the region is reviewed
Studying the interaction between microquasar jets and their environments
In high-mass microquasars (HMMQ), strong interactions between jets and
stellar winds at binary system scales could occur. In order to explore this
possibility, we have performed numerical 2-dimensional simulations of jets
crossing the dense stellar material to study how the jet will be affected by
these interactions. We find that the jet head generates strong shocks in the
wind. These shocks reduce the jet advance speed, and compress and heat up jet
and wind material. In addition, strong recollimation shocks can occur where
pressure balance between the jet side and the surrounding medium is reached.
All this, altogether with jet bending, could lead to the destruction of jets
with power . The conditions around the outflow shocks
would be convenient for accelerating particles up to TeV energies. These
accelerated particles could emit via synchrotron and inverse Compton (IC)
scattering if they were leptons, and via hadronic processes in case they were
hadrons.Comment: 4 pages. Contribution to the proceedings of High Energy Phenomena in
Relativistic Outflows, held in Dublin, Ireland, September 24-28, 200
Hawking Radiation in String Theory and the String Phase of Black Holes
The quantum string emission by Black Holes is computed in the framework of
the `string analogue model' (or thermodynamical approach), which is well suited
to combine QFT and string theory in curved backgrounds (particulary here, as
black holes and strings posses intrinsic thermal features and temperatures).
The QFT-Hawking temperature T_H is upper bounded by the string temperature T_S
in the black hole background. The black hole emission spectrum is an incomplete
gamma function of (T_H - T_S). For T_H << T_S, it yields the QFT-Hawking
emission. For T_H \to T_S, it shows highly massive string states dominate the
emission and undergo a typical string phase transition to a microscopic
`minimal' black hole of mass M_{\min} or radius r_{\min} (inversely
proportional to T_S) and string temperature T_S. The semiclassical QFT black
hole (of mass M and temperature T_H) and the string black hole (of mass M_{min}
and temperature T_S) are mapped one into another by a `Dual' transform which
links classical/QFT and quantum string regimes. The string back reaction effect
(selfconsistent black hole solution of the semiclassical Einstein equations
with mass M_+ (radius r_+) and temperature T_+) is computed. Both, the QFT and
string black hole regimes are well defined and bounded: r_{min} leq r_+ \leq
r_S, M_{min} \leq M_+ \leq M, T_H \leq T_+ \leq T_S. The string `minimal' black
hole has a life time tau_{min} \simeq \frac{k_B c}{G \hbar} T^{-3}_S.Comment: LaTex, 31 pages, no figure
AutoParallel: A Python module for automatic parallelization and distributed execution of affine loop nests
The last improvements in programming languages, programming models, and
frameworks have focused on abstracting the users from many programming issues.
Among others, recent programming frameworks include simpler syntax, automatic
memory management and garbage collection, which simplifies code re-usage
through library packages, and easily configurable tools for deployment. For
instance, Python has risen to the top of the list of the programming languages
due to the simplicity of its syntax, while still achieving a good performance
even being an interpreted language. Moreover, the community has helped to
develop a large number of libraries and modules, tuning them to obtain great
performance.
However, there is still room for improvement when preventing users from
dealing directly with distributed and parallel computing issues. This paper
proposes and evaluates AutoParallel, a Python module to automatically find an
appropriate task-based parallelization of affine loop nests to execute them in
parallel in a distributed computing infrastructure. This parallelization can
also include the building of data blocks to increase task granularity in order
to achieve a good execution performance. Moreover, AutoParallel is based on
sequential programming and only contains a small annotation in the form of a
Python decorator so that anyone with little programming skills can scale up an
application to hundreds of cores.Comment: Accepted to the 8th Workshop on Python for High-Performance and
Scientific Computing (PyHPC 2018
- …