59,024 research outputs found
Description of Four-Body Breakup Reaction with the Method of Continuum-Discretized Coupled-Channels
We present a method for smoothing discrete breakup -matrix elements
calculated by the method of continuum-discretized coupled-channels (CDCC). This
smoothing method makes it possible to apply CDCC to four-body breakup
reactions. The reliability of the smoothing method is confirmed for two cases,
Ni(, ) at 80 MeV and the transition of He. We apply
CDCC with the smoothing method to He breakup reaction at 22.5 MeV.
Multi-step breakup processes are found to be important.Comment: 19 pages, 7 figures, published in Progress of Theoretical Physic
Mobile application platform heterogeneity: Android vs Windows phone vs iOS vs Firefox OS
Modern smartphones have a rich spectrum of increasingly sophisticated features, opening opportunities for software-led innovation. Of the large number of platforms to develop new software on, in this paper we look closely at three platforms identified as market leaders for the smartphone market by Gartner Group in 2013 and one platform, Firefox OS, representing a new paradigm for operating systems based on web technologies. We compare the platforms in several different categories, such as software architecture, application development, platform capabilities and constraints, and, finally, developer support. Using the implementation of a mobile version of the tic-tac-toe game on all the four platforms, we seek to investigate strengths, weaknesses and challenges of mobile application development on these platforms. Big differences are highlighted when inspecting community environments, hardware abilities and platform maturity. These inevitably impact upon developer choices when deciding on mobile platform development strategies
Every Cloud Has a Push Data Lining: Incorporating Cloud Services in a Context-Aware Application
We investigated context-awareness by utilising multiple sources of context in a mobile device setting. In our experiment we developed a system consisting of a mobile client, running on the Android platform, integrated with a cloud-based service. These components were integrated using pushmessaging technology.One of the key featureswas the automatic adaptation of smartphones in accordance with implicit user needs. The novelty of our approach consists in the use of multiple sources of context input to the system, which included the use of calendar data and web based user configuration tool, as well as that of an external, cloud-based, configuration file storing user interface preferences which, pushed at log-on time irrespective of access device, frees the user from having to manually configure its interface.The systemwas evaluated via two rounds of user evaluations (n = 50 users), the feedback of which was generally positive and demonstrated the viability of using cloud-based services to provide an enhanced context-aware user experience
Evolvability and genetic constraint in Dalechampia blossoms: components of variance and measures of evolvability
The SiRi Particle-Telescope System
A silicon particle-telescope system for light-ion nuclear reactions is
described. In particular, the system is designed to be optimized for level
density and gamma-ray strength function measurements with the so-called Oslo
method. Eight trapezoidal modules are mounted at 5 cm distance from the target,
covering 8 forward angles between theta = 40 and 54 degrees. The thin front dE
detectors (130 micrometer) are segmented into eight pads, determining the
reaction angle for the outgoing charged ejectile. Guard rings on the thick back
E detectors (1550 micrometer) guarantee low leakage current at high depletion
voltage.Comment: 6 pages, 8 figure
Moving Multi-Channel Systems in a Finite Volume with Application to Proton-Proton Fusion
The spectrum of a system with multiple channels composed of two hadrons with
nonzero total momentum is determined in a finite cubic volume with periodic
boundary conditions using effective field theory methods. The results presented
are accurate up to exponentially suppressed corrections in the volume due to
the finite range of hadronic interactions. The formalism allows one to
determine the phase shifts and mixing parameters of pipi-KK isosinglet coupled
channels directly from Lattice Quantum Chromodynamics. We show that the
extension to more than two channels is straightforward and present the result
for three channels. From the energy quantization condition, the volume
dependence of electroweak matrix elements of two-hadron processes is extracted.
In the non-relativistic case, we pay close attention to processes that mix the
1S0-3S1 two-nucleon states, e.g. proton-proton fusion (pp -> d+ e^+ + nu_e),
and show how to determine the transition amplitude of such processes directly
from lattice QCD.Comment: 20 pages, 3 figure
Consequences of inter-population crosses on developmental stability and canalization of floral traits in Dalechampia scandens (Euphorbiaceae)
An Elemental Assay of Very, Extremely, and Ultra Metal-Poor Stars
We present a high-resolution elemental-abundance analysis for a sample of 23
very metal-poor (VMP; [Fe/H] < -2.0) stars, 12 of which are extremely
metal-poor (EMP; [Fe/H] < -3.0), and 4 of which are ultra metal-poor (UMP;
[Fe/H] < -4.0). These stars were targeted to explore differences in the
abundance ratios for elements that constrain the possible astrophysical sites
of element production, including Li, C, N, O, the alpha-elements, the iron-peak
elements, and a number of neutron-capture elements. This sample substantially
increases the number of known carbon-enhanced metal-poor (CEMP) and
nitrogen-enhanced metal-poor (NEMP) stars -- our program stars include eight
that are considered "normal" metal-poor stars, six CEMP-no stars, five CEMP-s
stars, two CEMP-r stars, and two CEMP-r/s stars. One of the CEMP- stars and
one of the CEMP-r/s stars are possible NEMP stars. We detect lithium for three
of the six CEMP-no stars, all of which are Li-depleted with respect to the
Spite plateau. The majority of the CEMP stars have [C/N] > 0. The stars with
[C/N] < 0 suggest a larger degree of mixing; the few CEMP-no stars that exhibit
this signature are only found at [Fe/H] < -3.4, a metallicity below which we
also find the CEMP-no stars with large enhancements in Na, Mg, and Al. We
confirm the existence of two plateaus in the absolute carbon abundances of CEMP
stars, as suggested by Spite et al. We also present evidence for a "floor" in
the absolute Ba abundances of CEMP-no stars at A(Ba)~ -2.0.Comment: 20 pages, 16 figures, Accepted for publication in Ap
PCA detection and denoising of Zeeman signatures in stellar polarised spectra
Our main objective is to develop a denoising strategy to increase the signal
to noise ratio of individual spectral lines of stellar spectropolarimetric
observations.
We use a multivariate statistics technique called Principal Component
Analysis. The cross-product matrix of the observations is diagonalized to
obtain the eigenvectors in which the original observations can be developed.
This basis is such that the first eigenvectors contain the greatest variance.
Assuming that the noise is uncorrelated a denoising is possible by
reconstructing the data with a truncated basis. We propose a method to identify
the number of eigenvectors for an efficient noise filtering.
Numerical simulations are used to demonstrate that an important increase of
the signal to noise ratio per spectral line is possible using PCA denoising
techniques. It can be also applied for detection of magnetic fields in stellar
atmospheres. We analyze the relation between PCA and commonly used well-known
techniques like line addition and least-squares deconvolution. Moreover, PCA is
very robust and easy to compute.Comment: accepted to be published in A&
Abundances and kinematics of carbon-enhanced metal-poor stars in the Galactic halo*; A new classification scheme based on Sr and Ba
Carbon-enhanced metal-poor (CEMP) stars span a wide range of stellar
populations, from bona fide second-generation stars to later forming stars that
provide excellent probes of, e.g., binary mass transfer. Here we analyse 11
metal-poor stars of which 10 are CEMP stars. Based on high signal-to-noise
(SNR) X-Shooter spectra, we derive abundances of 20 elements (C, N, O, Na, Mg,
Ca, Sc, Ti, Cr, Mn, Fe, Ni, Sr, Y, Ba, La, Ce, Pr, Nd, Eu). From the high SNR
spectra, we trace the chemical contribution of the rare earth elements (REE)
from various production sites, finding a preference for metal-poor low-mass AGB
stars of 1.5Mo in CEMP-s stars, while CEMP-r/s stars may indicate a more
massive AGB contribution (2-5Mo). A contribution from the r-process - possibly
from neutron star mergers (NSM), is also detectable in the REE abundances,
especially in the CEMP-r/s. Combining spectra with Gaia DR2 astrometric data
indicates that all but one star in our sample (and most literature stars)
belong to the Galactic halo. They exhibit a median orbital eccentricity of 0.7,
and are found on both pro- and retrograde orbits. The orbital parameters of
CEMP-no and CEMP4s stars are remarkably similar in the 98 stars we study. A
special CEMP-no star, with very low Sr and Ba content, possesses the most
eccentric orbit among the stars in our sample, passing close to the Galactic
centre. Finally, we propose an improved scheme to sub-classify the CEMP stars,
making use of the SrBa ratio, which can also be used to separate very
metal-poor stars from CEMP stars in 93 stars in the metallicity range
[Fe/H]. The Sr/Ba ratio can also be used for distinguishing
CEMP-s,-r/s and -no stars. The Sr/Ba ratio is also a powerful astro-nuclear
indicator, as AGB stars exhibit very different Sr/Ba ratios, compared to fast
rotating massive stars and NSM, and it is fairly unbiased by NLTE and 3D
corrections.(abridged)Comment: 15 pages, 4 pages appendix, 11 figures, accepted for publication in
A&
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