4,182 research outputs found
Spin effects in deeply virtual Compton scattering
We consider the azimuthal angle dependence in the cross section of the hard
leptoproduction of a photon on a nucleon target. We show that this dependence
allows to define observables that isolate the twist-two and twist-three sectors
in the deeply virtual Compton scattering amplitude. All twist-two and
twist-three Compton form factors can be extracted from measurements of the
charge odd part of the polarized cross section and give access to all
generalized parton distributions.Comment: 6 pages, LaTeX, 1 figure, Talk given at IX International Workshop on
Deep Inelastic Scattering Bologna, 27 April - 1 May 200
Time comparison via OTS-2
The time comparisons carried out via OTS-2 between the Technical University Graz (Austria) and the Van Swinden Laboratory Delft (Netherlands) are discussed. The method is based on the use of the synchronization pulse in the TV-frame of the daily evening broadcasting of a French TV-program to Northern Africa. Corrections, as a consequence of changes in the position of the satellite coordinates are applied weekly after reception of satellite coordinates. A description of the method is given as well as some of the particular techniques used in both the participating laboratories. Preliminary results are presented
Doubly-differential cross section calculations for -shell vacancy production in lithium by fast O ion impact
Inner-shell vacancy production for the O-Li collision system at 1.5
MeV/amu is studied theoretically. The theory combines single-electron
amplitudes for each electron in the system to extract multielectron information
about the collision process. Doubly-differential cross sections obtained in
this way are then compared with the recent experimental data by LaForge et al.
[J. Phys. B 46, 031001 (2013)] yielding good resemblance, especially for low
outgoing electron energy. A careful analysis of the processes that contribute
to inner-shell vacancy production shows that the improvement of the results as
compared to single-active-electron calculations can be attributed to the
leading role of two-electron excitation-ionization processes
Generalized Parton Distributions of ^3He
A realistic microscopic calculation of the unpolarized quark Generalized
Parton Distribution (GPD) of the nucleus is presented. In
Impulse Approximation, is obtained as a convolution between the GPD of
the internal nucleon and the non-diagonal spectral function, describing
properly Fermi motion and binding effects. The proposed scheme is valid at low
values of , the momentum transfer to the target, the most relevant
kinematical region for the coherent channel of hard exclusive processes. The
obtained formula has the correct forward limit, corresponding to the standard
deep inelastic nuclear parton distributions, and first moment, giving the
charge form factor of . Nuclear effects, evaluated by a modern realistic
potential, are found to be larger than in the forward case. In particular, they
increase with increasing the momentum transfer when the asymmetry of the
process is kept fixed, and they increase with the asymmetry at fixed momentum
transfer. Another relevant feature of the obtained results is that the nuclear
GPD cannot be factorized into a -dependent and a
-independent term, as suggested in prescriptions proposed for finite
nuclei. The size of nuclear effects reaches 8 % even in the most important part
of the kinematical range under scrutiny. The relevance of the obtained results
to study the feasibility of experiments is addressed.Comment: 23 pages, 8 figures; Discussion in section II enlarged; discussion in
section IV shortened. Final version accepted by Phys. Rev.
Analysis of CO<sub>2</sub> leakage through "low-permeability" faults from natural reservoirs in the Colorado Plateau, southern Utah
The numerous CO2 reservoirs in the Colorado Plateau region of the United States are
natural analogues for potential geologic CO2 sequestration repositories. To better
understand the risk of leakage from reservoirs used for long-term underground CO2
storage, we examine evidence for CO2 migration along two normal faults from a
reservoir in east-central Utah. CO2 -charged springs, geysers, and a hydrocarbon seep
are localised along these faults. These include natural springs that have been active for
long periods of time, and springs that were induced by recent drilling. The CO2 -charged
spring waters have deposited travertine mounds and carbonate veins. The faults cut
siltstones, shales, and sandstones and the fault rocks are fine-grained, clay-rich gouge,
generally thought to be barriers to fluid flow. The geologic and geochemical data are
consistent with these faults being conduits for CO2 to the surface. Consequently, the
injection of CO2 into faulted geologic reservoirs, including faults with clay gouge, must
be carefully designed and monitored to avoid slow seepage or fast rupture to the
biosphere
Robust and efficient people detection with 3-D range data using shape matching
Information about the location of a person is a necessity for Human-Robot Interaction (HRI) as it enables the robot to make human aware decisions and facilitates the extraction of further useful information; such as low-level gestures and gaze. This paper presents a robust method for person detection with 3-D range data using shape matching. Projections of the 3-D data onto 2-D planes are exploited to effectively and efficiently represent the data for scene segmentation and shape extraction. Fourier descriptors (FD) are used to describe the shapes and are subsequently classified with a Support Vector Machine (SVM). A database of 25 people was collected and used to test this approach. The results show that the computationally efficient shape features can be used to robustly detect the location of people
Recommended from our members
Modelling the wintertime response to upper tropospheric and lower stratospheric ozone anomalies over the North Atlantic and Europe
During boreal winter months, mean longitude-dependent ozone changes in the upper troposphere and lower stratosphere are mainly used by different ozone transport by planetary waves. The response to radiative perturbation induced by these ozone changes near the tropopause on the circulation is unclear. This response is investigated with the ECHAM4 general circulation model in a sensitivity study. In the simulation two different mean January realizations of the ozone field are implemented in ECHAM4. Both ozone fields are estimated on the basis of the observed mean January planetary wave structure of the 1980s. The first field represents a 14-year average (reference, 1979-1992) and the second one represents the mean ozone field change (anomaly, 1988-92) in boreal extra-tropics during the end of the 1980s. The model runs were carried out pairwise, with identical initial conditions for both ozone fields. Five statistically independent experiments were performed, forced with the observed sea surface temperatures for the period 1988 to 1992. The results support the hypothesis that the zonally asymmetric ozone changes of the 80s triggered a systematic alteration of the circulation over the North Atlantic - European region. It is suggested that this feedback process is important for the understanding of the decadal coupling between troposphere and stratosphere, as well as between subtropics and extra-tropics in winter
Structure and transport in multi-orbital Kondo systems
We consider Kondo impurity systems with multiple local orbitals, such as rare
earth ions in a metallic host or multi--level quantum dots coupled to metallic
leads. It is shown that the multiplet structure of the local orbitals leads to
multiple Kondo peaks above the Fermi energy , and to ``shadow'' peaks
below . We use a slave boson mean field theory, which recovers the strong
coupling Fermi liquid fixed point, to calculate the Kondo peak positions,
widths, and heights analytically at T=0, and NCA calculations to fit the
temperature dependence of high--resolution photoemission spectra of Ce
compounds. In addition, an approximate conductance quantization for transport
through multi--level quantum dots or single--atom transistors in the Kondo
regime due to a generalized Friedel sum rule is demonstrated.Comment: 4 pages, 3 figures. Invited article, 23rd International Conference on
Low Temperature Physics LT23, Hiroshima, Japan 200
- …