Harmonics of the AC susceptibility as probes to differentiate the various creep models

We measured the temperature dependence of the 1st and the 3rd harmonics of the AC magnetic susceptibility on some type II superconducting samples at different AC field amplitudes, hAC. In order to interpret the measurements, we computed the harmonics of the AC susceptibility as function of the temperature T, by integrating the non-linear diffusion equation for the magnetic field with different creep models, namely the vortex glass-collective creep (single-vortex, small bundle and large bundle) and Kim-Anderson model. We also computed them by using a non-linear phenomenological I-V characteristics, including a power law dependence of the pinning potential on hAC. Our experimental results were compared with the numerically computed ones, by the analysis of the Cole-Cole plots. This method results more sensitive than the separate component analysis, giving the possibility to obtain detailed information about the contribution of the flux dynamic regimes in the magnetic response of the analysed samples.Comment: 9 pages, 6 figures, submitted to Physica

Pion Generalized Parton Distributions within a fully covariant constituent quark model

We extend the investigation of the Generalized Parton Distribution for a charged pion within a fully covariant constituent quark model, in two respects: (i) calculating the tensor distribution and (ii) adding the treatment of the evolution, needed for achieving a meaningful comparison with both the experimental parton distribution and the lattice evaluation of the so-called generalized form factors. Distinct features of our phenomenological covariant quark model are: (i) a 4D Ansatz for the pion Bethe-Salpeter amplitude, to be used in the Mandelstam formula for matrix elements of the relevant current operators, and (ii) only two parameters, namely a quark mass assumed to hold $m_q=~220$ MeV and a free parameter fixed through the value of the pion decay constant. The possibility of increasing the dynamical content of our covariant constituent quark model is briefly discussed in the context of the Nakanishi integral representation of the Bethe-Salpeter amplitude.Comment: Pages 20, figure 11 and table 8. Minor changes. To be published in EPJ

Neutron electromagnetic form factors and inclusive scattering of polarized electrons by polarized 3^{3}He and 3^{3}H targets

The electromagnetic inclusive responses of polarized $^{3}$He and $^{3}$H are thoroughly investigated at the quasielastic peak for squared momentum transfers up to $2 (GeV/c)^2$, within the plane wave impulse approximation. Great emphasys is put on the effects in the bound-state due to different two- and three-body nuclear forces, and to the Coulomb interaction as well. A careful analysis of the polarized responses allows to select possible experiments for minimizing the model dependence in the extraction of the neutron electromagnetic form factors. In particular, the relevant role played by the proton in the transverse-longitudinal response of polarized $^{3}$He, at low momentum transfer, can be utilized for obtaining valuable information on the proton contribution to the total polarized response and eventually on the neutron charge form factor.Comment: 27 pages, Latex, 9 Postscript figures. To appear in Phys. Rev. C (July '97

Weak decays of medium and heavy Lambda-hypernuclei

We have made a new evaluation of the Lambda decay width in nuclear matter within the Propagator Method. Through the Local Density Approximation it is possible to obtain results in finite nuclei. We have also studied the dependence of the widths on the N-N and Lambda-N short range correlations. Using reasonable values for the parameters that control these correlations, as well as realistic nuclear densities and Lambda wave functions, we reproduce, for the first time, the experimental non-mesonic widths in a wide range of mass numbers (from medium to heavy hypernuclei).Comment: 22 pages, including 5 figure

The ionizing sources of luminous compact HII regions in the RCW106 and RCW122 clouds

Given the rarity of young O star candidates, compact HII regions embedded in dense molecular cores continue to serve as potential sites to peer into the details of high-mass star formation. To uncover the ionizing sources of the most luminous and compact HII regions embedded in the RCW106 and RCW122 giant molecular clouds, known to be relatively nearby (2-4 kpc) and isolated, thus providing an opportunity to examine spatial scales of a few hundred to a thousand AU in size. High spatial resolution (0.3"), mid-infrared spectra (R=350), including the fine structure lines [ArIII] and [NeII], were obtained for four luminous compact HII regions, embedded inside the dense cores within the RCW106 and RCW122 molecular cloud complexes. At this resolution, these targets reveal point-like sources surrounded by nebulosity of different morphologies, uncovering details at spatial dimensions of <1000AU. The point-like sources display [ArIII] and [NeII] lines - the ratios of which are used to estimate the temperature of the embedded sources. The derived temperatures are indicative of mid-late O type objects for all the sources with [ArIII] emission. Previously known characteristics of these targets from the literature, including evidence of disk or accretion suggest that the identified sources may grow more to become early-type O stars by the end of the star formation process

Efficient all-optical production of large 6^6Li quantum gases using D1_1 gray-molasses cooling

We use a gray molasses operating on the D$_1$ atomic transition to produce degenerate quantum gases of $^{6}$Li with a large number of atoms. This sub-Doppler cooling phase allows us to lower the initial temperature of 10$^9$ atoms from 500 to 40 $\mu$K in 2 ms. We observe that D$_1$ cooling remains effective into a high-intensity infrared dipole trap where two-state mixtures are evaporated to reach the degenerate regime. We produce molecular Bose-Einstein condensates of up to 5$\times$10$^{5}$ molecules and weakly-interacting degenerate Fermi gases of $7\times$10$^{5}$ atoms at $T/T_{F}<0.1$ with a typical experimental duty cycle of 11 seconds.Comment: 5 pages, 3 figure

Status Report of the Measurement Service for the CERN Accelerator Logging

The LHC (Large Hadron Collider) Logging service is aimed to satisfy the requirement of capturing and storing any relevant accelerator data to track its variation over time. This service is presently operational on the whole CERN accelerator complex, from ion and proton sources to LHC, and has become a critical component of the CERN control systems. The focus is given to the measurement part of this service, which is responsible for the data acquisition and preparation (processing, filtering, concentration) prior to its storage in database and file systems. Incoming data is often processed by a concentration layer, the processes that transform data of multiple devices into single values according to well defined rules and then publish them further on, to the LHC Logging among others. The paper describes the architecture and presents the solutions to the very challenging requirements imposed by the LHC in terms of overall performance and reliability. The efficiency of the data acquisition and filtering as well as the flexible software design are highlighted