8,087 research outputs found
The evolved circumbinary disk of AC Her: a radiative transfer, interferometric and mineralogical study
We aim to constrain the structure of the circumstellar material around the
post-AGB binary and RV Tauri pulsator AC Her. We want to constrain the spatial
distribution of the amorphous as well as of the crystalline dust. We present
very high-quality mid-IR interferometric data that were obtained with
MIDI/VLTI. We analyse the MIDI data and the full SED, using the MCMax radiative
transfer code, to find a good structure model of AC Her's circumbinary disk. We
include a grain size distribution and midplane settling of dust
self-consistently. The spatial distribution of crystalline forsterite in the
disk is investigated with the mid-IR features, the 69~m band and the
11.3~m signatures in the interferometric data. All the data are well
fitted. The inclination and position angle of the disk are well determined at
i=50+-8 and PA=305+-10. We firmly establish that the inner disk radius is about
an order of magnitude larger than the dust sublimation radius. Significant
grain growth has occurred, with mm-sized grains being settled to the midplane
of the disk. A large dust mass is needed to fit the sub-mm fluxes. By assuming
{\alpha}=0.01, a good fit is obtained with a small grain size power law index
of 3.25, combined with a small gas/dust ratio <10. The resulting gas mass is
compatible with recent estimates employing direct gas diagnostics. The spatial
distribution of the forsterite is different from the amorphous dust, as more
warm forsterite is needed in the surface layers of the inner disk. The disk in
AC Her is very evolved, with its small gas/dust ratio and large inner hole.
Mid-IR interferometry offers unique constraints, complementary to mid-IR
features, for studying the mineralogy in disks. A better uv coverage is needed
to constrain in detail the distribution of the crystalline forsterite in AC
Her, but we find strong similarities with the protoplanetary disk HD100546.Comment: update with final version published in A&
Predictions for double spin asymmetry A_{LT} in Semi Inclusive DIS
In the leading order of QCD parton model of Semi Inclusive Deep Inelastic
Scattering (SIDIS) the double spin asymmetry arises due to the
longitudinal polarization of quarks in the transversely polarized nucleon. The
corresponding weighted distribution function can be
related to ordinary helicity distribution measured in DIS. Using
recent parameterizations for (un)polarized distribution and fragmentation
functions we calculated asymmetry on transversely polarized proton and
deuteron targets for different types hadron production. The predictions are
given for COMPASS, HERMES and JLab energies. The role of Lorentz invariance
relations and positivity constraints are discussed.Comment: The new conventional definition of asymmetry is adopted -- the factor
two is added. The figures are rescaled by factor tw
Measuring the Magnetic Flux Density in the CMS Steel Yoke
The Compact Muon Solenoid (CMS) is a general purpose detector, designed to
run at the highest luminosity at the CERN Large Hadron Collider (LHC). Its
distinctive features include a 4 T superconducting solenoid with 6-m-diameter
by 12.5-m-length free bore, enclosed inside a 10000-ton return yoke made of
construction steel. The return yoke consists of five dodecagonal three-layered
barrel wheels and four end-cap disks at each end comprised of steel blocks up
to 620 mm thick, which serve as the absorber plates of the muon detection
system. Accurate characterization of the magnetic field everywhere in the CMS
detector is required. To measure the field in and around the steel, a system of
22 flux-loops and 82 3-D Hall sensors is installed on the return yoke blocks.
Fast discharges of the solenoid (190 s time-constant) made during the CMS
magnet surface commissioning test at the solenoid central fields of 2.64, 3.16,
3.68 and 4.01 T were used to induce voltages in the flux-loops. The voltages
are measured on-line and integrated off-line to obtain the magnetic flux in the
steel yoke close to the muon chambers at full excitations of the solenoid. The
3-D Hall sensors installed on the steel-air interfaces give supplementary
information on the components of magnetic field and permit to estimate the
remanent field in steel to be added to the magnetic flux density obtained by
the voltages integration. A TOSCA 3-D model of the CMS magnet is developed to
describe the magnetic field everywhere outside the tracking volume measured
with the field-mapping machine. The results of the measurements and
calculations are presented, compared and discussed.Comment: 9 pages, 7 figures, 16 references, presented at the III International
Conference on Superconductivity and Magnetism (ICSM-2012), Kumburgaz,
Istanbul, Turkey, 29 April - 4 May 201
Measuring the Magnetic Flux Density with Flux Loops and Hall Probes in the CMS Magnet Flux Return Yoke
The Compact Muon Solenoid (CMS) is a general purpose detector, designed to
run at the highest luminosity at the CERN Large Hadron Collider (LHC). Its
distinctive features include a 4 T superconducting solenoid with 6-m-diameter
by 12.5-m-length free bore, enclosed inside a 10,000-ton return yoke made of
construction steel. The flux return yoke consists of five dodecagonal
three-layered barrel wheels and four end-cap disks at each end comprised of
steel blocks up to 620 mm thick, which serve as the absorber plates of the muon
detection system. To measure the field in and around the steel, a system of 22
flux loops and 82 3-D Hall sensors is installed on the return yoke blocks. A
TOSCA 3-D model of the CMS magnet is developed to describe the magnetic field
everywhere outside the tracking volume that was measured with the field-mapping
machine. The voltages induced in the flux loops by the magnetic flux changing
during the CMS magnet standard ramps down are measured with six 16-bit DAQ
modules. The off-line integration of the induced voltages reconstructs the
magnetic flux density in the yoke steel blocks at the operational magnet
current of 18.164 kA. The results of the flux loop measurements during three
magnet ramps down are presented and discussed.Comment: 3 pages, 6 figures, presented at the IEEE Nuclear Science Symposium
2016 (NSS) in Strasbourg, France on November 3, 2016. arXiv admin note: text
overlap with arXiv:1605.0877
Flux Loop Measurements of the Magnetic Flux Density in the CMS Magnet Yoke
The Compact Muon Solenoid (CMS) is a general purpose detector, designed to
run at the highest luminosity at the CERN Large Hadron Collider (LHC). Its
distinctive features include a 4 T superconducting solenoid with 6-m-diameter
by 12.5-m-length free bore, enclosed inside a 10,000-ton return yoke made of
construction steel. The return yoke consists of five dodecagonal three-layered
barrel wheels and four end-cap disks at each end comprised of steel blocks up
to 620 mm thick, which serve as the absorber plates of the muon detection
system. To measure the field in and around the steel, a system of 22 flux loops
and 82 3-D Hall sensors is installed on the return yoke blocks. A TOSCA 3-D
model of the CMS magnet is developed to describe the magnetic field everywhere
outside the tracking volume measured with the field-mapping machine. The first
attempt is made to measure the magnetic flux density in the steel blocks of the
CMS magnet yoke using the standard magnet discharge with the current ramp down
speed of 1.5 A/s.Comment: 7 pages, 5 figures, presented at ISCM2016 - 5th International
Conference on Superconductivity and Magnetism on April 28, 2016 at Fethiye,
Turke
Ultrasound attenuation and a P-B-T phase diagram of superfluid 3He in 98% aerogel
Longitudinal sound attenuation measurements in superfluid 3He in 98% aerogel
were conducted at pressures between 14 and 33 bar and in magnetic fields up to
4.44 kG. The temperature dependence of the ultrasound attenuation in the A-like
phase was determined for the entire superfluid region exploiting the field
induced meta-stable A-like phase at the highest field. In the lower field, the
A-B transition in aerogel was identified by a smooth jump in attenuation on
both cooling and warming. Based on the transitions observed on warming, a phase
diagram as a function of pressure (P), temperature (T) and magnetic field (B)
is constructed. We find that the A-B phase boundary in aerogel recedes in a
drastically different manner than in bulk in response to an increasing magnetic
field. The implications of the observed phase diagram are discussed.Comment: 9 pages, 13 figures, accepted to PR
Validation of the CMS Magnetic Field Map
The Compact Muon Solenoid (CMS) is a general purpose detector, designed to
run at the highest luminosity at the CERN Large Hadron Collider (LHC). Its
distinctive features include a 4 T superconducting solenoid with 6-m-diameter
by 12.5-m-length free bore, enclosed inside a 10,000-ton return yoke made of
construction steel. The return yoke consists of five dodecagonal three-layered
barrel wheels and four end-cap disks at each end comprised of steel blocks up
to 620 mm thick, which serve as the absorber plates of the muon detection
system. To measure the field in and around the steel, a system of 22 flux loops
and 82 3-D Hall sensors is installed on the return yoke blocks. A TOSCA 3-D
model of the CMS magnet is developed to describe the magnetic field everywhere
outside the tracking volume measured with the field-mapping machine. The
magnetic field description is compared with the measurements and discussed.Comment: 7 pages, 5 figures, presented at 4th International Conference on
Superconductivity and Magnetism 2014, April 27 - May 2, 2014, Antalya,
Turkey. arXiv admin note: substantial text overlap with arXiv:1605.08778;
text overlap with arXiv:1212.165
Low velocity quantum reflection of Bose-Einstein condensates
We studied quantum reflection of Bose-Einstein condensates at normal
incidence on a square array of silicon pillars. For incident velocities of
2.5-26 mm/s observations agreed with theoretical predictions that the
Casimir-Polder potential of a reduced density surface would reflect slow atoms
with much higher probability. At low velocities (0.5-2.5 mm/s), we observed
that the reflection probability saturated around 60% rather than increasing
towards unity. We present a simple model which explains this reduced
reflectivity as resulting from the combined effects of the Casimir-Polder plus
mean field potential and predicts the observed saturation. Furthermore, at low
incident velocities, the reflected condensates show collective excitations.Comment: 4 figure
Sivers and Boer-Mulders functions in Light-Cone Quark Models
Results for the naive-time-reversal-odd quark distributions in a light-cone
quark model are presented. The final-state interaction effects are generated
via single-gluon exchange mechanism. The formalism of light-cone wave functions
is used to derive general expressions in terms of overlap of wave-function
amplitudes describing the different orbital angular momentum components of the
nucleon. In particular, the model predictions show a dominant contribution from
S- and P-wave interference in the Sivers function and a significant
contribution also from the interference of P and D waves in the Boer-Mulders
function. The favourable comparison with existing phenomenological
parametrizations motivates further applications to describe azimuthal
asymmetries in hadronic reactions.Comment: references and explanations added; version to appear in Phys. Rev.
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