1,260 research outputs found
Estudio comparativo de diferentes técnicas de implantación de stents en bifurcaciones coronarias
ResumenEl objetivo de este trabajo es el análisis comparativo de los cambios hemodinámicos locales producidos en una bifurcación coronaria por el implante de stents mediante 3 técnicas diferentes: stent simple en la arteria principal, stent simple en la arteria principal con orificio de comunicación con la arteria secundaria para el paso de un balón de inflado («kissing») y «culotte». Para ello se ha utilizado la geometría ideal de una bifurcación coronaria a 45 y 90°.En primer lugar se simularon los modelos en régimen estacionario mediante el código comercial ANSYS Fluent, y a continuación se validaron con las medidas experimentales tomadas en el laboratorio mediante velocimetría de imagen de partículas (particle image velocimetry [PIV]). Una vez obtenida una buena concordancia de resultados entre ambos estudios en régimen permanente, se abordó el flujo pulsátil. Los parámetros que se consideraron para comparar las diferentes técnicas en este régimen fueron los esfuerzos cortantes y la caída de presión promediados en el tiempo, así como el índice de esfuerzos cortantes oscilatorios (oscillatory shear index [OSI]). Las conclusiones finales fueron que el stent simple presenta los peores resultados, en términos de caída de presión, y la técnica «kissing», los mejores. Esto sería aplicable a los stents liberadores de fármacos, donde la reestenosis no es tan crucial como el restablecimiento del flujo sanguíneo. En cuanto al criterio basado en el valor menor de los esfuerzos cortantes (<0,4Pa) y un OSI elevado (>0,1), la técnica «culotte» presenta el peor comportamiento. Esto sería aplicable a los stents sin recubrimiento, en que la mejor opción sería el stent simple.AbstractThe objective of this work is to analyze the local hemodynamic changes caused in a coronary bifurcation by three different stenting techniques: simple stenting of the main vessel, simple stenting of the main vessel with kissing balloon in the side branch and culotte. To carry out this study an idealized geometry of a coronary bifurcation is used, and two bifurcation angles, 45° and 90°, are chosen as representative of the wide variety of real configurations. Both numerical simulations and experimental measurements are performed. First, steady simulations are carried out with the commercial code ANSYS Fluent, then, experimental measurements with PIV (Particle Image Velocimetry), obtained in the laboratory, are used to validate the numerical simulations. The steady computational simulations show a good overall agreement with the experimental data. Second, pulsatile flow is considered to take into account the transient effects. The time averaged wall shear stress, oscillatory shear index (OSI) and pressure drop obtained numerically are used to compare the behavior of the stenting techniques. As conclusions obtained, simple stenting technique shows the worst results in terms of pressure drop, and kissing the best ones. This criterion could be applied for DES (Drug Eluting Stents) where the restenosis is not as critical as the reestablishment of the blood flow. But considering the regions of low wall shear stress (<0.4Pa) and elevated OSI (>0.1), the culotte procedure shows the worst performance and the simple stent, the best. This could be applied to BMS (Bare Metal Stents)
Pulsatile flow in coronary bifurcations for different stenting techniques
The objective of this work is to analyze the local hem
odynamic changes caused in a coronary bifurcation by three different stenting techniques: simple stenting of the main vessel, simple stenting of the main vessel with kissing balloon in the side branch and culotte. To carry out this study an idealized geometry of a coronary bifurcation is
used, and two bifurcation angles, 45º and 90º, are chosen as representative of the wide variety of re
al configurations. In order to quantify the influence of the stenting technique on the local blood flow, both numeri-
cal simulations and experimental measurements are performed. First, steady simulations are carried out with the commercial code ANSYS-Fluent, and then, experimental measurements with PIV (Particle Image Velocimetry) obtained
in the laboratory are used to validate the numerical simulation. The steady computational simulations show a good overall agreement with the experimental data. Second, pulsatile flow is considered to take into account the tran-
sient effects. The time averaged wall shear stress, scillatory shear index and pressure drop obtained numerically are used to compare the behavior of the stenting techniques
Structure near ++ threshold in the in-flight He reaction
To search for an S= -1 di-baryonic state which decays to , the reaction was studied at 1.0 GeV/.
Unobserved neutrons were kinematically identified from the missing mass
of the reaction in order to have a large
acceptance for the final state. The observed events,
distributed widely over the kinematically allowed region of the Dalitz plot,
establish that the major component comes from a three nucleon absorption
process. A concentration of events at a specific neutron kinetic energy was
observed in a region of low momentum transfer to the . To account
for the observed peak structure, the simplest S-wave pole was assumed to exist
in the reaction channel, having Breit-Wigner form in energy and with a Gaussian
form-factor. A minimum method was applied to deduce its mass
2355 (stat.) (syst.) MeV/c, and decay-width
110 (stat.) (syst.) MeV/c,
respectively. The form factor parameter 400 MeV/ implies that the
range of interaction is about 0.5Comment: 12pages, 8 figure
Hemodynamic performance of different stent strategies for coronary bifurcations. Evaluation with a mathematical model
Purpose: Best percutaneous treatment strategy for lesions in coronary bifurcations is an ongoing subject of debate. There is limited data that analyses the effect of the different bifurcation strategies on coronary flow. Our aim is to evaluate the influence of different bifurcation stenting strategies on hemodynamic parameters, both in the main vessel (MV) and side branch (SB)
Measurement of the strong interaction induced shift and width of the 1s state of kaonic deuterium at J-PARC
The antikaon-nucleon interaction close to threshold provides crucial
information on the interplay between spontaneous and explicit chiral symmetry
breaking in low-energy QCD. In this context the importance of kaonic deuterium
X-ray spectroscopy has been well recognized, but no experimental results have
yet been obtained due to the difficulty of the measurement. We propose to
measure the shift and width of the kaonic deuterium 1s state with an accuracy
of 60 eV and 140 eV respectively at J-PARC. These results together with the
kaonic hydrogen data (KpX at KEK, DEAR and SIDDHARTA at DAFNE) will then permit
the determination of values of both the isospin I=0 and I=1 antikaon-nucleon
scattering lengths and will provide the most stringent constraints on the
antikaon-nucleon interaction, promising a breakthrough. Refined Monte Carlo
studies were performed, including the investigation of background suppression
factors for the described setup. These studies have demonstrated the
feasibility of determining the shift and width of the kaonic deuterium atom 1s
state with the desired accuracy of 60 eV and 140 eV.Comment: 12 pages, 9 figure
Determination of scattering lengths from measurement of atom lifetime
The DIRAC experiment at CERN has achieved a sizeable production of
atoms and has significantly improved the precision on its lifetime
determination. From a sample of 21227 atomic pairs, a 4% measurement of the
S-wave scattering length difference
has been attained, providing an important test of Chiral Perturbation Theory.Comment: 6 pages, 6 figure
Pole position of measured in reactions
We measured a set of , , and
invariant mass spectra below and above the mass
threshold in -induced reactions on deuteron. We deduced the -wave
and scattering
amplitudes in the isospin 0 channel in the framework of a and
coupled channel. We find that a resonance pole corresponding to
is located at 1417.7(fitting
errors)(systematic errors) + (fitting
errors)(systematic errors)] MeV/, closer to the
mass threshold than the value determined by the Particle Data Group.Comment: 8 pages, 5 figure
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