6,943 research outputs found
Beta-decay properties of neutron-rich Ca, Ti, and Cr isotopes
Beta-decay properties of neutron-rich Ca, Ti, and Cr isotopes are studied
within a deformed proton-neutron quasiparticle random-phase approximation. The
underlying mean field is described self-consistently from deformed Skyrme
Hartree-Fock calculations with pairing correlations. Residual spin-isospin
interactions in the particle-hole and particle-particle channels are also
included in the formalism. The energy distributions of the Gamow-Teller
strength, the beta-decay feedings, the beta-decay half-lives, and the
beta-delayed neutron emission probabilities are discussed and compared with
other theoretical results, as well as with the available experimental
information. The evolution of these nuclear beta-decay properties is
investigated in isotopic chains in a search for structural changes. A reliable
estimate of the beta-decay properties in this mass region is a valuable
information for evaluating decay rates in astrophysical scenarios.Comment: 11 pages, 12 figure
Issues in management of artificial intelligence based projects
Now that Artificial Intelligence (AI) is gaining acceptance, it is important to examine some of the obstacles that still stand in the way of its progress. Ironically, many of these obstacles are related to management and are aggravated by the very characteristcs that make AI useful. The purpose of this paper is to heighten awareness of management issues in AI development and to focus attention on their resolution
Improving Link Reliability through Network Coding in Cooperative Cellular Networks
The paper proposes a XOR-based network coded cooperation protocol for the uplink transmission of relay assisted cellular networks and an algorithm for selection and assignment of the relay nodes. The performances of the cooperation protocol are expressed in terms of network decoder outage probability and Block Error Rate of the cooperating users. These performance indicators are analyzed theoretically and by computer simulations. The relay nodes assignment is based on the optimization, according to several criteria, of the graph that describes the cooperation cluster formed after an initial selection of the relay nodes. The graph optimization is performed using Genetic Algorithms adapted to the topology of the cooperation cluster and the optimization criteria considered
Main-Belt Asteroids in the K2 Engineering Field of View
Unlike NASA's original Kepler Discovery Mission, the renewed K2 Mission will
stare at the plane of the Ecliptic, observing each field for approximately 75
days. This will bring new opportunities and challenges, in particular the
presence of a large number of main-belt asteroids that will contaminate the
photometry. The large pixel size makes K2 data susceptible to the effect of
apparent minor planet encounters. Here we investigate the effects of asteroid
encounters on photometric precision using a sub-sample of the K2 Engineering
data taken in February, 2014. We show examples of asteroid contamination to
facilitate their recognition and distinguish these events from other error
sources. We conclude that main-belt asteroids will have considerable effects on
K2 photometry of a large number of photometric targets during the Mission, that
will have to be taken into account. These results will be readily applicable
for future space photometric missions applying large-format CCDs, such as TESS
and PLATO.Comment: accepted for publication in AJ, 6 page
Discovery of the spectroscopic binary nature of six southern Cepheids
We present the analysis of photometric and spectroscopic data of six bright
Galactic Cepheids: GH Carinae, V419 Centauri, V898 Centauri, AD Puppis, AY
Sagittarii, and ST Velorum. Based on new radial velocity data (in some cases
supplemented with earlier data available in the literature), these Cepheids
have been found to be members in spectroscopic binary systems. V898 Cen turned
out to have one of the largest orbital radial velocity amplitude (> 40 km/s)
among the known binary Cepheids. The data are insufficient to determine the
orbital periods nor other orbital elements for these new spectroscopic
binaries.
These discoveries corroborate the statement on the high frequency of
occurrence of binaries among the classical Cepheids, a fact to be taken into
account when calibrating the period-luminosity relationship for Cepheids.
We have also compiled all available photometric data that revealed that the
pulsation period of AD Pup, the longest period Cepheid in this sample, is
continuously increasing with Delta P = 0.004567 d/century, likely to be caused
by stellar evolution. The wave-like pattern superimposed on the parabolic O-C
graph of AD Pup may well be caused by the light-time effect in the binary
system. ST Vel also pulsates with a continuously increasing period. The other
four Cepheids are characterised with stable pulsation periods in the last half
century.Comment: accepted by the MNRAS, 11 pages, 16 figures, 18 tables, a part of the
data can be downloaded from the online version of this articl
The 106Cd(α, α)106Cd elastic scattering in a wide energy range for γ process studies
Date of Acceptance: 15/04/2015Alpha elastic scattering angular distributions of the 106Cd(α, α)106Cd reaction were measured at three energies around the Coulomb barrier to provide a sensitive test for the α + nucleus optical potential parameter sets. Furthermore, the new high precision angular distributions, together with the data available from the literature were used to study the energy dependence of the locally optimized α + nucleus optical potential in a wide energy region ranging from ELab=27.0MeV down to 16.1 MeV.The potentials under study are a basic prerequisite for the prediction of α-induced reaction cross sections and thus, for the calculation of stellar reaction rates used for the astrophysical γ process. Therefore, statistical model predictions using as input the optical potentials discussed in the present work are compared to the available 106Cd + alpha cross section data.Peer reviewe
The impact of main belt asteroids on infrared--submillimetre photometry and source counts
> Among the components of the infrared and submillimetre sky background,
the closest layer is the thermal emission of dust particles and minor bodies in
the Solar System. This contribution is especially important for current and
future infrared and submillimetre space instruments --like those of Spitzer,
Akari and Herschel -- and must be characterised by a reliable statistical
model. > We describe the impact of the thermal emission of main belt
asteroids on the 5...1000um photometry and source counts, for the current and
future spaceborne and ground-based instruments, in general, as well as for
specific dates and sky positions. > We used the statistical asteroid model
(SAM) to calculate the positions of main belt asteroids down to a size of 1km,
and calculated their infrared and submillimetre brightness using the standard
thermal model. Fluctuation powers, confusion noise values and number counts
were derived from the fluxes of individual asteroids. > We have constructed
a large database of infrared and submillimetre fluxes for SAM asteroids with a
temporal resolution of 5 days, covering the time span January 1, 2000 --
December 31, 2012. Asteroid fluctuation powers and number counts derived from
this database can be obtained for a specific observation setup via our public
web-interface. > Current space instruments working in the mid-infrared
regime (Akari and Spitzer Space Telescopes) are affected by asteroid confusion
noise in some specific areas of the sky, while the photometry of space infrared
and submillimetre instruments in the near future (e.g. Herschel and Planck
Space Observatories) will not be affected by asteroids. Faint main belt
asteroids might also be responsible for most of the zodiacal emission
fluctuations near the ecliptic.Comment: accepted for publication in Astronomy & Astrophysics; Additional
material (appendices) and the related web-interface can be found at:
"http://kisag.konkoly.hu/solarsystem/irsam.html
Dense cores in the dark cloud complex LDN1188
We present a molecular line emission study of the LDN1188 dark cloud complex
located in Cepheus. In this work we focused on the densest parts of the cloud
and on the close neighbourhood of infrared point sources. We made ammonia
mapping with the Effelsberg 100-m radio telescope and identified 3 dense cores.
CS(1--0), CS(2--1) and HCO(1--0) measurements performed with the Onsala
20\,m telescope revealed the distribution of dense molecular material. The
molecular line measurements were supplemented by mapping the dust emission at
1.2\,mm in some selected directions using the IRAM 30\,m telescope. With these
data we could work out a likely evolutionary sequence in this dark clould
complex.Comment: YouResAstro2012 conference presentation; accepted to Astronomishen
Nachrichten (25-July-2013
Investigation of alpha-nuclear potential families from elastic scattering experiments
In this work we present the continuation of the reported analysis [1] of the experimentally measured angular distributions of the reaction Cd-106(alpha, alpha)Cd-106 at several different energies around the Coulomb barrier. The difficulties that arise in the study of Cd-106-alpha-nuclear potential and the so called Family Problem are addressed
- …