4,042 research outputs found
RFQD - a Decelerating Radio Frequency Quadrupole for the CERN Antiproton Facility
The RFQD is designed to decelerate antiprotons of momentum 100 MeV/c (kinetic
energy 5.33MeV)down to a kinetic energy variable between ~10 keV and 120 keV.
Inside the RFQ body, at ground potential, the rf structure of the four-rod type
is mounted on insulating supports. It can be biased between plus/minus 60 kV dc
to achieve the continuous adjustment of output energy required by the ASACUSA
experiment at the CERN Antiproton Decelerator AD. The different parts of the
system are described and the present status reported
Fraction of clear skies above astronomical sites: a new analysis from the GOES12 satellite
Comparing the number of clear nights (cloud free) available for astronomical
observations is a critical task because it should be based on homogeneous
methodologies. Current data are mainly based on different judgements based on
observer logbooks or on different instruments. In this paper we present a new
homogeneous methodology on very different astronomical sites for modern optical
astronomy, in order to quantify the available night time fraction. The data are
extracted from night time GOES12 satellite infrared images and compared with
ground based conditions when available. In this analysis we introduce a wider
average matrix and 3-Bands correlation in order to reduce the noise and to
distinguish between clear and stable nights. Temporal data are used for the
classification. In the time interval 2007-2008 we found that the percentage of
the satellite clear nights is 88% at Paranal, 76% at La Silla, 72.5% at La
Palma, 59% at Mt. Graham and 86.5% at Tolonchar. The correlation analysis of
the three GOES12 infrared bands B3, B4 and B6 indicates that the fraction of
the stable nights is lower by 2% to 20% depending on the site
Sorting strategies for the arc quadrupoles of the LHC
The variation in the field gradient of the LHC arc quadrupoles can not be corrected by the dedicated trim quadrupole circuits. This may result to a beta function beating larger than the one accepted by the machine budget. In this respect, sorting strategies for the installation of these magnets were implemented in order to eliminate this effect, as locally as possible. Special care was taken for quadrupoles whose warm measurements showed large gradient errors due to an excessive magnetic permeability. The figures of merit used in the sorting and the results obtained for all 8 sectors of the LHC are detailed. The global optics function beating foreseen, as computed by analytical estimates are finally presented
First operating experience with the CERN decelerating RFQ for antiprotons
The RFQD decelerates antiprotons from a momentum of 100 MeV/c (kinetic energy 5.31 MeV) down to a kinetic energy variable between ~10 keV and 120 keV. A novel feature is the implementation of a floating internal RF structure, mounted on HV insulators, to allow continuous post-deceleration or acceleration by a DC bias. A description of the system is given, followed by reports on the first operating experience with the ASACUSA experiment, dedicated performance measurements and consolidation progress
Influence of Topological Edge States on the Properties of Al/Bi2Se3/Al Hybrid Josephson Devices
In superconductor-topological insulator-superconductor hybrid junctions, the
barrier edge states are expected to be protected against backscattering, to
generate unconventional proximity effects, and, possibly, to signal the
presence of Majorana fermions. The standards of proximity modes for these types
of structures have to be settled for a neat identification of possible new
entities. Through a systematic and complete set of measurements of the
Josephson properties we find evidence of ballistic transport in coplanar
Al-Bi2Se3-Al junctions that we attribute to a coherent transport through the
topological edge state. The shunting effect of the bulk only influences the
normal transport. This behavior, which can be considered to some extent
universal, is fairly independent of the specific features of superconducting
electrodes. A comparative study of Shubnikov - de Haas oscillations and
Scanning Tunneling Spectroscopy gave an experimental signature compatible with
a two dimensional electron transport channel with a Dirac dispersion relation.
A reduction of the size of the Bi2Se3 flakes to the nanoscale is an unavoidable
step to drive Josephson junctions in the proper regime to detect possible
distinctive features of Majorana fermions.Comment: 11 pages, 14 figure
Weak lensing observations of potentially X-ray underluminous galaxy clusters
Optically selected clusters of galaxies display a relation between their
optical mass estimates and their X-ray luminosities Lx that has a large
scatter. A substantial fraction of optically selected clusters have Lx
estimates or upper limits significantly below the values expected from the
Lx-mass relation established for X-ray selected clusters, i.e., these clusters
are X-ray underluminous for their mass. We attempt to confirm or falsify the
X-ray underluminous nature of two clusters, Abell 315 and Abell 1456, by using
weak gravitational lensing as a third and independent measure of the clusters'
masses. We obtained optical wide-field imaging data and selected background
galaxies using their colors and measured the shear exerted by the tidal field
of the foreground galaxy clusters. We then fitted parametrized models to our
shear catalogs. After accounting for projections of large-scale structure and
halo triaxiality, we find that A 315 is significantly X-ray underluminous for
its mass, while no significant lensing signal was detected for A 1456. We
re-evaluate earlier kinematic and X-ray analyses of these two clusters and
discuss the nature of the X-ray underluminous cluster A 315 and why A 1456 was
probably erroneously identified as being X-ray underluminous.Comment: Accepted for publication in A&A, included comments from language
editor, added two reference
Dynamical charge density fluctuations pervading the phase diagram of a Cu-based high-Tc superconductor
Charge density waves are a common occurrence in all families of high critical
temperature superconducting cuprates. Although consistently observed in the
underdoped region of the phase diagram and at relatively low temperatures, it
is still unclear to what extent they influence the unusual properties of these
systems. Using resonant x-ray scattering we carefully determined the
temperature dependence of charge density modulations in
(Y,Nd)BaCuO for three doping levels. We discovered
short-range dynamical charge density fluctuations besides the previously known
quasi-critical charge density waves. They persist up to well above the
pseudogap temperature T*, are characterized by energies of few meV and pervade
a large area of the phase diagram, so that they can play a key role in shaping
the peculiar normal-state properties of cuprates.Comment: 34 pages, 4 figures, 11 supplementary figure
CAPTIONALS: A computer aided testing environment for the verification and validation of communication protocols
This paper covers the verification and protocol validation for distributed computer and communication systems using a computer aided testing approach. Validation and verification make up the so-called process of conformance testing. Protocol applications which pass conformance testing are then checked to see whether they can operate together. This is referred to as interoperability testing. A new comprehensive approach to protocol testing is presented which address: (1) modeling for inter-layer representation for compatibility between conformance and interoperability testing; (2) computational improvement to current testing methods by using the proposed model inclusive of formulation of new qualitative and quantitative measures and time-dependent behavior; (3) analysis and evaluation of protocol behavior for interactive testing without extensive simulation
Planetary Science Goals for the Spitzer Warm Era
The overarching goal of planetary astronomy is to deduce how the present collection of objects found in our Solar System were formed from the original material present in the proto-solar nebula. As over two hundred exo-planetary systems are now known, and multitudes more are expected, the Solar System represents the closest and best system which we can study, and the only one in which we can clearly resolve individual bodies other than planets. In this White Paper we demonstrate how to use Spitzer Space Telescope InfraRed Array Camera Channels 1 and 2 (3.6 and 4.5 ”m) imaging photometry with large dedicated surveys to advance our knowledge of Solar System formation and evolution. There are a number of vital, key projects to be pursued using dedicated large programs that have not been pursued during the five years of Spitzer cold operations. We present a number of the largest and most important projects here; more will certainly be proposed once the warm era has begun, including important observations of newly discovered objects
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