25,674 research outputs found
Phi meson mass and decay width in nuclear matter
The meson spectrum, which in vacuum is dominated by its coupling to
the system, is modified in nuclear matter. Following a model based
on chiral SU(3) dynamics we calculate the meson selfenergy in nuclear
matter considering the and in-medium properties. For the latter
we use the results of previous calculations which account for and wave
kaon-nucleon interactions based on the lowest order meson-baryon chiral
effective Lagrangian, and this leads to a dressing of the kaon propagators in
the medium. In addition, a set of vertex corrections is evaluated to fulfill
gauge invariance, which involves contact couplings of the meson to
wave and wave kaon-baryon vertices. Within this scheme the mass shift
and decay width of the meson in nuclear matter are studied.Comment: 19 pages, 10 figures in EPS format, revtex4; One section modified,
some references update
Transport properties of bottomed mesons in a hot mesonic gas
In this work we evaluate the B-meson drag and diffusion coefficients in a hot
medium constituted of light mesons (pions, kaons and eta mesons). We treat the
B-meson and B*-meson interaction with pseudo-Goldstone bosons in chiral
perturbation theory at next-to-leading order within the constraints from heavy
quark symmetry, and employ standard unitarization techniques of NLO amplitudes
in order to account for dynamically generated resonances (leading to a more
efficient heavy-flavor diffusion) and thus reach higher temperatures. We
estimate individual meson contributions from the gas to the transport
coefficients and perform a comparison with other findings in literature. We
report a bottom relaxation length of about 80 fm at a temperature of 150 MeV
and for typical momenta of 1 GeV, at which our approach is reliable. Compared
to a charm relaxation length of 40 fm in the same conditions, we conclude that
the B mesons provide a cleaner probe of the early stages of a heavy-ion
collision.Comment: 14 pages, 16 figures, 3 tables. Version published in Phys.Rev.D87,
034019 (2013). Only minor improvements with respect to v1: corrected typos,
further clarifications and updated reference
Effect of Q&P Process on 0.15C-MnSi Steels
The present study is focused on analyzing the effect of Mn amount on two experimental steel compositions, specially designed for Q&P (Quenching and Partitioning), 0.15C-2.5Mn-1.5Si and 0.15C-3Mn-1.5Si without significant contribution of Al. Two-Step Q&P thermal treatments were performed at laboratory scale in a quenching dilatometer Bähr DIL805A/D. The fractions of retained austenite were evaluated by X-ray diffraction techniques. The mechanical properties of the Q&P samples were evaluated, a strong dependence of strength, uniform elongation and strain hardening values on process parameters has been found. Higher uniform elongation were related to higher residual austenite contents. The 0.15C-3Mn-1.5Si steel showed systematically the largest mechanical values with respect to the 0.15C-2.5Mn-1.5Si steel.Peer ReviewedPostprint (published version
2GHz MIMO channel model from experimental outdoor data analysis in UMTS
The key objective of this work was to obtain a MIMO model for a line of sight (LOS) channel component as well as the covariance matrix for a non-LOS deployment. A maximum likelihood criteria is applied to obtain a LOS spatial signature vector and a NLOS covariance matrix derived from channel measurements taken in the 2 GHz UMTS spectrum for an urban deployment in Bristol (UK). Different user equipment deployments were considered to represent both LOS and NLOS, as well as static and dynamic (motion) situations. The parameters of interest were estimated from these data and the fitness model was satisfactorily evaluated in all cases. Further, the Kronecker product between transmitter and receiver matrices was evaluated in order to simplify the model, for both, LOS and NLOS cases, including polarization diversity cases.The key objective of this work was to obtain a MIMO model for a line of sight (LOS) channel component as well as the covariance matrix for a non-LOS deployment. A maximum likelihood criteria is applied to obtain a LOS spatial signature vector and a NLOS covariance matrix derived from channel measurements taken in the 2 GHz UMTS spectrum for an urban deployment in Bristol (UK). Different user equipment deployments were considered to represent both LOS and NLOS, as well as static and dynamic (motion) situations. The parameters of interest were estimated from these data and the fitness model was satisfactorily evaluated in all cases. Further, the Kronecker product between transmitter and receiver matrices was evaluated in order to simplify the model, for both, LOS and NLOS cases, including polarization diversity cases
Dynamic recrystallization mechanisms and twining evolution during hot deformation of Inconel 718
The hot deformation behavior of an IN718 superalloy was studied by isothermal compression tests under the deformation temperature range of 950–1100 °C and strain rate range of 0.001–1 s-1 up to true strains of 0.05, 0.2, 0.4 and 0.7. Electron backscattered diffraction (EBSD) technique was employed to investigate systematically the effects of strain, strain rate and deformation temperature on the subgrain structures, local and cumulative misorientations and twinning phenomena. The results showed that the occurrence of dynamic recrystallization (DRX) is promoted by increasing strain and deformation temperature and decreasing strain rate. The microstructural changes showed that discontinuous dynamic recrystallization (DDRX), characterized by grain boundary bulging, is the dominant nucleation mechanism in the early stages of deformation in which DRX nucleation occurs by twining behind the bulged areas. Twin boundaries of nuclei lost their ¿3 character with further deformation. However, many simple and multiple twins can be also regenerated during the growth of grains. The results showed that continuous dynamic recrystallization (CDRX) is promoted at higher strains and large strain rates, and lower temperatures, indicating that under certain conditions both DDRX and CDRX can occur simultaneously during the hot deformation of IN718.Peer ReviewedPostprint (author's final draft
Rotating Superconductors and the London Moment: Thermodynamics versus Microscopics
Comparing various microscopic theories of rotating superconductors to the
conclusions of thermodynamic considerations, we traced their marked difference
to the question of how some thermodynamic quantities (the electrostatic and
chemical potentials) are related to more microscopic ones: The electron's the
work function, mean-field potential and Fermi energy -- certainly a question of
general import.
After the correct identification is established, the relativistic correction
for the London Moment is shown to vanish, with the obvious contribution from
the Fermi velocity being compensated by other contributions such as
electrostatics and interactions.Comment: 23 pages 4 fi
Fidelity Between Unitary Operators and the Generation of Gates Robust Against Off-Resonance Perturbations
We perform a functional expansion of the fidelity between two unitary
matrices in order to find the necessary conditions for the robust
implementation of a target gate. Comparison of these conditions with those
obtained from the Magnus expansion and Dyson series shows that they are
equivalent in first order. By exploiting techniques from robust design
optimization, we account for issues of experimental feasibility by introducing
an additional criterion to the search for control pulses. This search is
accomplished by exploring the competition between the multiple objectives in
the implementation of the NOT gate by means of evolutionary multi-objective
optimization
- …