7,926 research outputs found
The extended hypergeometric class of L\'evy processes
With a view to computing fluctuation identities related to stable processes,
we review and extend the class of hypergeometric L\'evy processes explored in
Kuznetsov and Pardo (arXiv:1012.0817). We give the Wiener-Hopf factorisation of
a process in the extended class, and characterise its exponential functional.
Finally, we give three concrete examples arising from transformations of stable
processes.Comment: 22 page
Fibrational induction meets effects
This paper provides several induction rules that can be used to prove properties of effectful data types. Our results are semantic in nature and build upon Hermida and Jacobs’ fibrational formulation of induction for polynomial data types and its extension to all inductive data types by Ghani, Johann, and Fumex. An effectful data type μ(TF) is built from a functor F that describes data, and a monad T that computes effects. Our main contribution is to derive induction rules that are generic over all functors F and monads T such that μ(TF) exists. Along the way, we also derive a principle of definition by structural recursion for effectful data types that is similarly generic. Our induction rule is also generic over the kinds of properties to be proved: like the work on which we build, we work in a general fibrational setting and so can accommodate very general notions of properties, rather than just those of particular syntactic forms. We give examples exploiting the generality of our results, and show how our results specialize to those in the literature, particularly those of Filinski and Støvring
Multiple Charge State Beam Acceleration at Atlas
A test of the acceleration of multiple charge-state uranium beams was
performed at the ATLAS accelerator. A 238U+26 beam was accelerated in the ATLAS
PII linac to 286 MeV (~1.2 MeV/u) and stripped in a carbon foil located 0.5 m
from the entrance of the ATLAS Booster section. A 58Ni9+ 'guide' beam from the
tandem injector was used to tune the Booster for 238U+38. All charge states
from the stripping were injected into the booster and accelerated. Up to 94% of
the beam was accelerated through the Booster linac, with losses mostly in the
lower charge states. The measured beam properties of each charge state and a
comparison to numerical simulations are reported in this paper.Comment: LINAC2000, MOD0
Observational evidence of the formation of cyanopolyynes in CRL618 through the polimerization of HCN
The abundance ratio of consecutive members of the cyanopolyynes family has
been explored in CRL618 using data acquired in a complete line survey covering
the frequency range 81-356 GHz. The Jup range explored for the different
molecules is the following: 1 to 4 for HCN and HNC, 9 to 39 for HC3N, 31 to 133
for HC5N, and 72 to 85 for HC7N (not detected beyond Jup=85). The lowest
vibrationally excited state of HC7N (nu_15 at 62 cm^-1) has been tentatively
detected. Data analysis has been performed by extending our previous
geometrical and radiative transfer model of the slowly expanding envelope (SEE)
surrounding the compact central continuum source of CRL 618, that was
established from the study of rotational lines in several vibrationally excited
states of HC_3N. The new lines analyzed here require to model the high velocity
wind (HVW) component and the colder circumstellar gas, remnant of the AGB phase
of CRL618. The derived HC3N/HC5N and HC5N/HC7N abundance ratios from this set
of uniformly calibrated lines are between 3 and 6 in the different regions,
similar to standard values in the CSM and ISM, and consistent with previous
estimates obtained from ISO observations and chemical models. However, the
abundance ratios of HC3N, HC5N and HC7N with respect to HCN are at least two
orders of magnitude larger than those typical for AGB C-rich stars, such as
IRC+10216. This fact indicates that, in the short transition toward the
Planetary Nebula phase, HCN is quickly reprocessed into longer cyanopolyyne
chains. A similar behavior was previously found in this object for the
polyacetylenic chains (C(2n)H2).Comment: 8 figures, accepted in ApJ main journa
New Stellar Cross Sections and The "Karlsruhe Astrophysical Database of Nucleosynthesis in Stars"
Since April 2005 a regularly updated stellar neutron cross section
compilation is available online at http://nuclear-astrophysics.fzk.de/kadonis.
This online-database is called the "Karlsruhe Astrophysical Database of
Nucleosynthesis in Stars" project and is based on the previous Bao et al.
compilation from the year 2000. The present version \textsc{KADoNiS} v0.2
(January 2007) includes recommended cross sections for 280 isotopes between
H and Po and 75 semi-empirical estimates for isotopes without
experimental information. Concerning stellar cross sections of the
32 stable, proton-rich isotopes produced by the process experimental
information is only available for 20 isotopes, but 9 of them have rather large
uncertainties of 9%. The first part of a systematic study of stellar
cross sections of the -process isotopes Se, Sr,
Pd, Te, Ba, Ba, Dy, and Hf is
presented. In another application \textsc{KADoNiS} v0.2 was used for an
modification of a reaction library of Basel university. With this modified
library -process network calculations were carried out and compared to
previous results.Comment: Proceedings "International Conference on Nuclear Data for Science and
Technology 2007", Nice/ Franc
Upgrade of the ATLAS 10 GHz ECRIS
A major renovation of the ATLAS 10 GHz ECRIS, which began operations in 1987, is in the planning and acquisition phase. The old two-stage source will be converted to a single stage design including a high gradient magnetic field, electron donor disk, large radial ports, and flexible modular design. Eight solenoid coils taken from the existing ECR will produce the axial mirror. The individual coils will be encased in an iron yoke that optimizes the magnetic field. Computer modeling of the field profile yields a minimum field along the axis of 3.0 kG with mirror ratios of 4.4 and 2.9. An open hexapole configuration consisting of Nd-Fe-B bars enclosed in an austenitic stainless steel housing will be placed in an aluminium plasma chamber that will be water cooled along the poles of the hexapole. The hexapole field at the chamber wall, 4 cm in radius, is expected to be 9.3 kG along the magnet poles and 5.7 kG along the center of the pole gaps, which are 2.4 cm wide. A 3D model produced from individual 2D field profiles was used to check the end effects of the hexapole. Based on the models this new field configuration is capable of supporting a second ECR resonance zone at 14 GHz, which may be implemented at a later date
High-Sensitivity Measurement of 3He-4He Isotopic Ratios for Ultracold Neutron Experiments
Research efforts ranging from studies of solid helium to searches for a
neutron electric dipole moment require isotopically purified helium with a
ratio of 3He to 4He at levels below that which can be measured using
traditional mass spectroscopy techniques. We demonstrate an approach to such a
measurement using accelerator mass spectroscopy, reaching the 10e-14 level of
sensitivity, several orders of magnitude more sensitive than other techniques.
Measurements of 3He/4He in samples relevant to the measurement of the neutron
lifetime indicate the need for substantial corrections. We also argue that
there is a clear path forward to sensitivity increases of at least another
order of magnitude.Comment: 11 pages, 10 figure
Finite Difference Synthetic Acoustic Logs
Synthetic seismograms of elastic wave propagation in a fluid-filled borehole were generated using both the finite difference technique and the discrete wavenumber summation technique. The latter is known to be accurate for both body and surface (guided) waves. The finite difference grid has absorbing boundaries on two sides and axes of symmetry on the remaining two sides. A grid size no less than 10 points per wavelength was used. The far absorbing boundary was located at a distance of five to 10 radii from the borehole. Two types of solid-liquid interfaces were investigated: 1) a velocity gradient using the heterogeneous formulation, and 2) a sharp boundary using a second order Taylor expansion of the displacements. The results from the finite difference modeling were compared with the synthetic seismograms generated by the
discrete wavenumber summation method. No comparison the heterogeneous formulation and the discrete wavenumber method has been made. The second order approximation to the solid-liquid interface produced seismograms that compared 'well with the discrete wavenumber seismograms. A detailed comparison between the seismograms generated by the two methods showed that the body waves (refracted P and S waves) are identical. while the guided waves showed a slight difference in both phase and amplitude. These
differences are believed to be due to the approximations introduced in the
fluid-solid interface, the absorbing boundary at the edge of the grid, and the
grid and time step sizes involved. Owing. to the fact that they are interface
waves, the guided waves, especially the higher modes, are much more sensitive
to the above mentioned approximations
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