4,751 research outputs found
Wavelets Applied to the Detection of Point Sources of UHECRs
In this work we analyze the effect of smoothing maps containing arrival
directions of cosmic rays with a gaussian kernel and kernels of the mexican hat
wavelets of orders 1, 2 and 3. The analysis is performed by calculating the
amplification of the signal-to-noise ratio for several anisotropy patterns
(noise) and different number of events coming from a simulated source (signal)
for an ideal detector capable of observing the full sky with equal probability.
We extend this analysis for a virtual detector located within the array of
detectors of the Pierre Auger Observatory, considering an acceptance law.Comment: 9 pages, 8 figures. Proceedings of the Young Researchers Meeting,
2010. Available in:
http://www.ifi.unicamp.br/physicae/ojs-2.1.1/index.php/physicae/article/view/191;
Physicae, Proceedings of the Young Researchers Meeting, Vol 1, 201
Iodide-ion transport in methylammonium lead iodide perovskite: Some surprising aspects
Methylammonium lead iodide, CH3NH3PbI3 (= MAPbI3), is a hybrid organic–inorganic perovskite that exhibits excellent photovoltaic properties. In comparison with traditional photovoltaic materials, such as Si or CIGS, MAPbI3 is evidently characterised by one or more highly mobile constituent ions. In photovoltaic devices based on MAPbI3, ion mobility is deemed to be responsible for current–voltage hysteresis, a huge low-frequency dielectric response, and long-term instability. Despite enormous interest in ion transport, debate surrounds almost every aspect. This is evident in the excessive scatter in activation enthalpies reported in the literature for ion conduction in MAPbI3 (see Fig. 1).
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Performance of the smallest-variance-first rule in appointment sequencing
A classic problem in appointment scheduling with applications in healthcare concerns the determination of the patients' arrival times that minimize a cost function that is a weighted sum of mean waiting times and mean idle times. One aspect of this problem is the sequencing problem, which focuses on ordering the patients. We assess the performance of the smallest-variance-first (SVF) rule, which sequences patients in order of increasing variance of their service durations. Although it is known that SVF is not always optimal, it has been widely observed that it performs well in practice and simulation. We provide a theoretical justification for this observation by proving, in various settings, quantitative worstcase bounds on the ratio between the cost incurred by the SVF rule and the minimum attainable cost. We also show that, in great generality, SVF is asymptotically optimal, that is, the ratio approaches one as the number of patients grows large. Although evaluating policies by considering an approximation ratio is a standard approach in many algorithmic settings, our results appear to be the first of this type in the appointment-scheduling literature
HT Camelopardalis: The simplest intermediate polar spin pulse
The intermediate polar HT Cam is unusual in that it shows no evidence for
dense absorption in its spectrum. We analyse an XMM-Newton observation of this
star, which confirms the absence of absorption and shows that the X-ray
spin-pulse is energy independent. The modulation arises solely from occultation
effects and can be reproduced by a simple geometrical model in which the lower
accretion footprint is fainter than the upper one.
We suggest that the lack of opacity in the accretion columns of HT Cam, and
also of EX Hya and V1025 Cen, results from a low accretion rate owing to their
being below the cataclysmic variable period gap.Comment: 5 pages, 6 figures, accepted for publication in MNRA
Two Galaxy Clusters: A3565 and A3560
We report 102 new redshifts and magnitudes for a sample of galaxies to RF ~
15.5 mag in a 2.17 deg x 2.17 deg region centered on the galaxy IC 4296, the
most luminous member of the A3565 cluster. Up to the limiting magnitude we find
29 cluster members, and measure a velocity dispersion of 228 km/s. The
estimated total mass for this system is ~ 3.0 x h**-1 10**13 Msun (where h =
H0/100 km/s/Mpc), and its dynamical properties are quite typical of poor
clusters presenting X-ray emission. We also find that galaxies with absorption
lines are more concentrated towards the center of the cluster, while systems
with emission lines are mainly located in the outer parts. The small velocity
dispersion of the cluster, coupled to the known presence of an interacting pair
of galaxies, and the large extent of the brightest cluster galaxy, could
indicate that galaxy formation through mergers may still be underway in this
system. The surveyed region also contains galaxies belonging to the Shapley
Concentration cluster A3560. Within 30 arc min of the cluster center, we detect
32 galaxies, for which we measure a velocity dispersion of 588 km/s and a mass
of ~2 x h**-1 10**14 Msun. However, because our sample is restricted to
galaxies brighter than M*, these values should be considered only as rough
estimates.Comment: 33 pages, including 6 tables and 9 postscript figures. Uses AAS Latex
macros. Postscript file and ASCII versions of Tables 4 and 6 are available at
http://www.dan.on.br/other_surveys/a3565.html. Scheduled for September 1999
issue of The Astronomical Journa
Climate related sea-level variations over the past two millennia
Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of National Academy of Sciences for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences of the United States of America 108 (2011): 11017-11022, doi:10.1073/pnas.1015619108.We present new sea-level reconstructions for the past 2100 years based on salt-marsh
sedimentary sequences from the US Atlantic coast. The data from North Carolina reveal
four phases of persistent sea-level change after correction for glacial isostatic adjustment.
Sea level was stable from at least BC 100 until AD 950. It then increased for 400 years at
a rate of 0.6 mm/yr, followed by a further period of stable, or slightly falling, sea level
that persisted until the late 19th century. Since then, sea level has risen at an average rate
of 2.1 mm/yr, representing the steepest, century-scale increase of the past two millennia.
This rate was initiated between AD 1865 and 1892. Using an extended semi-empirical
modeling approach, we show that these sea-level changes are consistent with global
temperature for at least the past millennium.Research was supported by NSF grants (EAR-0951686) to BPH and JPD. ACK thanks a
NOSAMS internship, UPenn paleontology stipend and grants from GSA and NAMS.
North Carolina sea-level research was funded by NOAA (NA05NOS4781182), USGS
(02ERAG0044) and NSF (EAR-0717364) grants to BPH with S. Culver and R. Corbett
(East Carolina University). JPD (EAR-0309129) and MEM (ATM-0542356)
acknowledge NSF support. MV acknowledges Academy of Finland Project 123113 and
COST Action ES0701
Quantum Symmetries and Strong Haagerup Inequalities
In this paper, we consider families of operators in
a tracial C-probability space , whose joint
-distribution is invariant under free complexification and the action of
the hyperoctahedral quantum groups . We prove a strong
form of Haagerup's inequality for the non-self-adjoint operator algebra
generated by , which generalizes the
strong Haagerup inequalities for -free R-diagonal families obtained by
Kemp-Speicher \cite{KeSp}. As an application of our result, we show that
always has the metric approximation property (MAP). We also apply
our techniques to study the reduced C-algebra of the free unitary
quantum group . We show that the non-self-adjoint subalgebra generated by the matrix elements of the fundamental corepresentation of
has the MAP. Additionally, we prove a strong Haagerup inequality for
, which improves on the estimates given by Vergnioux's property
RD \cite{Ve}
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