43,983 research outputs found
Saber: window-based hybrid stream processing for heterogeneous architectures
Modern servers have become heterogeneous, often combining multicore CPUs with many-core GPGPUs. Such heterogeneous architectures have the potential to improve the performance of data-intensive stream processing applications, but they are not supported by current relational stream processing engines. For an engine to exploit a heterogeneous architecture, it must execute streaming SQL queries with sufficient data-parallelism to fully utilise all available heterogeneous processors, and decide how to use each in the most effective way. It must do this while respecting the semantics of streaming SQL queries, in particular with regard to window handling. We describe SABER, a hybrid high-performance relational stream processing engine for CPUs and GPGPUs. SABER executes windowbased streaming SQL queries in a data-parallel fashion using all available CPU and GPGPU cores. Instead of statically assigning query operators to heterogeneous processors, SABER employs a new adaptive heterogeneous lookahead scheduling strategy, which increases the share of queries executing on the processor that yields the highest performance. To hide data movement costs, SABER pipelines the transfer of stream data between different memory types and the CPU/GPGPU. Our experimental comparison against state-ofthe-art engines shows that SABER increases processing throughput while maintaining low latency for a wide range of streaming SQL queries with small and large windows sizes
Puzzles in quarkonium hadronic transitions with two pion emission
The anomalously large rates of some hadronic transitions from quarkonium are
studied using QCD multipole expansion (QCDME) in the framework of a constituent
quark model which has been successful in describing hadronic phenomenology. The
hybrid intermediate states needed in the QCDME method are calculated in a
natural extension of our constituent quark model based on the Quark Confining
String (QCS) scheme. Some of the anomalies are explained due to the presence of
an hybrid state with a mass near the mass of the decaying resonance whereas
other are justified by the presence of molecular components in the wave
function. Some unexpected results are pointed out.Comment: Conference proceedings of the XI Quark Confinement and the Hadron
Spectrum (CONFINEMENT XI). Saint Petersburg (Russia) from 8 to 12 September
201
Optimal detection of changepoints with a linear computational cost
We consider the problem of detecting multiple changepoints in large data
sets. Our focus is on applications where the number of changepoints will
increase as we collect more data: for example in genetics as we analyse larger
regions of the genome, or in finance as we observe time-series over longer
periods. We consider the common approach of detecting changepoints through
minimising a cost function over possible numbers and locations of changepoints.
This includes several established procedures for detecting changing points,
such as penalised likelihood and minimum description length. We introduce a new
method for finding the minimum of such cost functions and hence the optimal
number and location of changepoints that has a computational cost which, under
mild conditions, is linear in the number of observations. This compares
favourably with existing methods for the same problem whose computational cost
can be quadratic or even cubic. In simulation studies we show that our new
method can be orders of magnitude faster than these alternative exact methods.
We also compare with the Binary Segmentation algorithm for identifying
changepoints, showing that the exactness of our approach can lead to
substantial improvements in the accuracy of the inferred segmentation of the
data.Comment: 25 pages, 4 figures, To appear in Journal of the American Statistical
Associatio
Dual regimes of ion migration in high repetition rate femtosecond laser inscribed waveguides
Ion migration in high repetition rate femtosecond laser inscribed waveguides
is currently being reported in different optical glasses. For the first time we
discuss and experimentally demonstrate the presence of two regimes of ion
migration found in laser written waveguides. Regime-I, corresponds to the
initial waveguide formation mainly via light element migration (in our case
atomic weight < 31u), whereas regime-II majorly corresponds to the movement of
heavy elements. This behavior brings attention to a problem which has never
been analyzed before and that affects laser written active waveguides in which
active ions migrate changing their local spectroscopic properties. The
migration of active ions may in fact detune the pre-designed optimal values of
active photonic devices. This paper experimentally evidences this problem and
provides solutions to avert it.Comment: 4 pages, 5 figure
The Cosmic Near Infrared Background: Remnant Light from Early Stars
The redshifted ultraviolet light from early stars at z ~ 10 contributes to
the cosmic near infrared background. We present detailed calculations of its
spectrum with various assumptions about metallicity and mass spectrum of early
stars. We show that if the near infrared background has a stellar origin,
metal-free stars are not the only explanation of the excess near infrared
background; stars with metals (e.g. Z=1/50 Z_sun) can produce the same amount
of background intensity as the metal-free stars. We quantitatively show that
the predicted average intensity at 1-2 microns is essentially determined by the
efficiency of nuclear burning in stars, which is not very sensitive to
metallicity. We predict \nu I_\nu / \dot{\rho}_* ~ 4-8 nW m^-2 sr^-1, where
\dot{\rho_*} is the mean star formation rate at z=7-15 (in units of M_sun yr^-1
Mpc^-3) for stars more massive than 5 M_sun. On the other hand, since we have
very little knowledge about the form of mass spectrum of early stars,
uncertainty in the average intensity due to the mass spectrum could be large.
An accurate determination of the near infrared background allows us to probe
formation history of early stars, which is difficult to constrain by other
means. While the star formation rate at z=7-15 inferred from the current data
is significantly higher than the local rate at z<5, it does not rule out the
stellar origin of the cosmic near infrared background. In addition, we show
that a reasonable initial mass function, coupled with this star formation rate,
does not over-produce metals in the universe in most cases, and may produce as
little as less than 1 % of the metals observed in the universe today.Comment: 37 pages, 7 figures, (v2) Changes to abstract to emphasize that the
excess near infrared background can solely be explained by stars with
significant metals. (Metal-free stars are not necessarily needed.) (v3)
Expanded discussion on the metallicity constraint. Accepted for publication
in Ap
Constraints on Lorentz Invariance Violation using INTEGRAL/IBIS observations of GRB041219A
One of the experimental tests of Lorentz invariance violation is to measure
the helicity dependence of the propagation velocity of photons originating in
distant cosmological obejcts. Using a recent determination of the distance of
the Gamma-Ray Burst GRB 041219A, for which a high degree of polarization is
observed in the prompt emission, we are able to improve by 4 orders of
magnitude the existing constraint on Lorentz invariance violation, arising from
the phenomenon of vacuum birefringence.Comment: 5 pages, 3 figures, accepted for publication as a Rapid Communication
in Physical Review
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