3,894 research outputs found
Fragmentation functions of mesons in the Field-Feynman model
The fragmentation functions of the pion with distinction between
, , and are studied in the
Field-Feynman recursive model, by taking into account the flavor structure in
the excitation of quark-antiquark pairs by the initial quarks. The obtained
analytical results are compatible with available empirical results. The
framework is also extended to predict the fragmentation functions of the kaon
with distinction between , ,
, and . This work gives a significant
modification of the original model, and the predictions can be tested by future
experiments on the fragmentation functions of the kaon.Comment: 6 Latex pages, 10 figures, to appear in EPJ
Port-Access cardiac surgery: from a learning process to the standard.
Background: Port-Access™ surgery has been one of the
most innovative and controversial methods in the spectrum
of minimally invasive techniques for cardiac operations and
has been widely used for the treatment of several cardiac diseases.
The technique was introduced in our center to evaluate
its efficacy in reproducing standardized results without an
additional risk.
Methods: Endovascular cardiopulmonary bypass (CPB)
through femoral access and endoluminal aortic occlusion
were used in 129 patients for a variety of surgical procedures,
all of which were video-assisted. A minimal (4-6 cm) anterior
thoracotomy through the fourth intercostal space was used in
all cases as the surgical approach.
Results: More than 96% of the planned cases concluded
as true Port-Access™ procedures. Mean CBP and crossclamp
times were 87.2 min. ± 51.2 (range of 10-457) and
54.9 min. ± 30.6 (range of 10-190), respectively. Hospital
mortality for the overall group was 1.5%, and mitral valve
surgery had a 2.2% hospital death rate. The incidence of early
neurological events was 0.7%. Mean extubation time, ICU
stay, and total length of hospital stay were 5 hours ± 6 hrs.
(range of 2-32), 12 hours ± 11.8 hrs. (range of 5-78), and
7 days ± 7.03 days (range of 1-72), respectively.
Conclusions: Our experience indicates that the Port-
Access™ technique is safe and permits reproduction of standardized
results with the use of a very limited surgical
approach. We are convinced that this is a superior procedure
for certain types of surgery, including isolated primary or
redo mitral surgery, repair of a variety of atrial septal defects
(ASDs), and atrial tumors. It is especially useful in high-risk
patients, such as elderly patients or those requiring reoperation.
Simplification of the procedure is nevertheless desirable
in order to further reduce the time of operation and to
address other drawbacks
Logics for Rough Concept Analysis
Taking an algebraic perspective on the basic structures of Rough Concept
Analysis as the starting point, in this paper we introduce some varieties of
lattices expanded with normal modal operators which can be regarded as the
natural rough algebra counterparts of certain subclasses of rough formal
contexts, and introduce proper display calculi for the logics associated with
these varieties which are sound, complete, conservative and with uniform cut
elimination and subformula property. These calculi modularly extend the
multi-type calculi for rough algebras to a `nondistributive' (i.e. general
lattice-based) setting
Scaling of Anisotropic Flow and Momentum-Space Densities for Light Particles in Intermediate Energy Heavy Ion Collisions
Anisotropic flows ( and ) of light nuclear clusters are studied by
Isospin-Dependent Quantum Molecular Dynamics model for the system of Kr
+ Sn at intermediate energy and large impact parameters.
Number-of-nucleon scaling of the elliptic flow () are demonstrated for the
light fragments up to = 4, and the ratio of shows a constant
value of 1/2. In addition, the momentum-space densities of different clusters
are also surveyed as functions of transverse momentum, in-plane transverse
momentum and azimuth angle relative to the reaction plane. The results can be
essentially described by momentum-space power law. All the above phenomena
indicate that there exists a number-of-nucleon scaling for both anisotropic
flow and momentum-space densities for light clusters, which can be understood
by the coalescence mechanism in nucleonic degree of freedom for the cluster
formation.Comment: 8 pages, 3 figures; to be published in Physics Letters
Scaling of anisotropy flows in intermediate energy heavy ion collisions
Anisotropic flows (, and ) of light nuclear clusters are
studied by a nucleonic transport model in intermediate energy heavy ion
collisions. The number-of-nucleon scalings of the directed flow () and
elliptic flow () are demonstrated for light nuclear clusters. Moreover,
the ratios of of nuclear clusters show a constant value of 1/2
regardless of the transverse momentum. The above phenomena can be understood by
the coalescence mechanism in nucleonic level and are worthy to be explored in
experiments.Comment: Invited talk at "IX International Conference on Nucleus-Nucleus
Collisions", Rio de Janeiro, Aug 28- Sept 1, 2006; to appear on the
proceeding issue in Nuclear Physics
Collective modes of asymmetric nuclear matter in Quantum HadroDynamics
We discuss a fully relativistic Landau Fermi liquid theory based on the
Quantum Hadro-Dynamics () effective field picture of Nuclear Matter
({\it NM}).
From the linearized kinetic equations we get the dispersion relations of the
propagating collective modes. We focus our attention on the dynamical effects
of the interplay between scalar and vector channel contributions. A beautiful
``mirror'' structure in the form of the dynamical response in the
isoscalar/isovector degree of freedom is revealed, with a complete parallelism
in the role respectively played by the compressibility and the symmetry energy.
All that strongly supports the introduction of an explicit coupling to the
scalar-isovector channel of the nucleon-nucleon interaction. In particular we
study the influence of this coupling (to a -meson-like effective field)
on the collective response of asymmetric nuclear matter (). Interesting
contributions are found on the propagation of isovector-like modes at normal
density and on an expected smooth transition to isoscalar-like oscillations at
high baryon density. Important ``chemical'' effects on the neutron-proton
structure of the mode are shown. For dilute we have the isospin
distillation mechanism of the unstable isoscalar-like oscillations, while at
high baryon density we predict an almost pure neutron wave structure of the
propagating sounds.Comment: 18 pages (LATEX), 8 Postscript figures, uses "epsfig
On the Lorentz structure of the symmetry energy
We investigate in detail the density dependence of the symmetry energy in a
relativistic description by decomposing the iso-vector mean field into
contributions with different Lorentz covariant properties. We find important
effects of the iso-vector, scalar channel (i.e. -meson like) on the
high density behavior of the symmetry energy. Applications to static properties
of finite nuclei and to dynamic situations of heavy ion collisions are explored
and related to each other. The nuclear structure studies show only moderate
effects originating from the virtual meson. At variance, in heavy ion
collisions one finds important contributions on the reaction dynamics arising
from the different Lorentz structure of the high density symmetry energy when a
scalar iso-vector field is introduced. Particularly interesting is the
related neutron/proton effective mass splitting for nucleon transport effects
and for resonance and particle production around the threshold. We show that
the -like channel turns out to be essential for the production of
pions, when comparing with experimental data, in particular for high momentum
selections.Comment: 30 pages, 12 figures (.eps
Determination of the natural frequencies of a prototype Kaplan turbine
The natural frequencies of a turbine can be calculated from numerical methods. By comparing these natural frequencies with excitation sources, one can know the danger of a resonance and a possible failure in a component of the turbine. Therefore, it is often very important to have an accurate numerical model of the turbine to determine these natural frequencies. There are not many publications on the determination of the natural frequencies of reduced-scale models of Kaplan turbines. More papers exist for pump turbines or Francis turbines. For real Kaplan turbines, very few experiments can be found to determine mode shapes and natural frequencies. In this paper a Kaplan turbine of 37MW (maximum power), 12.5m (maximum head) and 50 m3 /s (maximum flowrate) was tested. The turbine was equipped to determine the natural frequencies of the runner in air. For this purpose, one accelerometer in each blade of the runner was installed and a total of 16 impacts were done in each blade. Frequencies and mode shapes were obtained. In parallel, a numerical model was obtained. Numerical and experimental results were compared and an accurate numerical model is presented. With this numerical model the natural frequencies of the runner in water were calculated.This research activity is framed within the context of the XFLEX HYDRO project. The project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 857832. No. 857832).Peer ReviewedPostprint (published version
Inclusive B-Meson Production in e^+ e^- and p p-bar Collisions
We provide nonperturbative fragmentation functions for B mesons, both at
leading and next-to-leading order in the MS-bar factorization scheme with five
massless quark flavors. They are determined by fitting the fractional energy
distribution of B mesons inclusively produced in e^+ e^- annihilation at CERN
LEP1. Theoretical predictions for the inclusive production of B mesons with
high transverse momenta in p p-bar scattering obtained with these fragmentation
functions nicely agree, both in shape and normalization, with data recently
taken at the Fermilab Tevatron.Comment: 20 pages (Latex), 6 figures (Postscript
Asymmetric nuclear matter in a Hartree-Fock approach to non-linear QHD
The Equation of State (EOS) for asymmetric nuclear matter is discussed
starting from a phenomenological hadronic field theory of Serot-Walecka type
including exchange terms. In a model with self interactions of the scalar
sigma-meson we show that the Fock terms naturally lead to isospin effects in
the nuclear EOS. These effects are quite large and dominate over the
contribution due to isovector mesons. We obtain a potential symmetry term of
"stiff" type, i.e. increasing with baryon density and an interesting behaviour
of neutron/proton effective masses of relevance for transport properties of
asymmetric dense matter.Comment: 12 pages (LATEX), 3 Postscript figures, revised versio
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