Effective range function below threshold

We demonstrate that the kernel of the Lippmann-Schwinger equation, associated with interactions consisting of a sum of the Coulomb plus a short range nuclear potential, below threshold becomes degenerate. Taking advantage of this fact, we present a simple method of calculating the effective range function for negative energies. This may be useful in practice since the effective range expansion extrapolated to threshold allows to extract low-energy scattering parameters: the Coulomb-modified scattering length and the effective range.Comment: 14 pages, 1 figur

A New Measurement of the 1S0 Neutron-Neutron Scattering Length using the Neutron-Proton Scattering Length as a Standard

The present paper reports high-accuracy cross-section data for the 2H(n,nnp) reaction in the neutron-proton (np) and neutron-neutron (nn) final-state-interaction (FSI) regions at an incident mean neutron energy of 13.0 MeV. These data were analyzed with rigorous three-nucleon calculations to determine the 1S0 np and nn scattering lengths, a_np and a_nn. Our results are a_nn = -18.7 +/- 0.6 fm and a_np = -23.5 +/- 0.8 fm. Since our value for a_np obtained from neutron-deuteron (nd) breakup agrees with that from free np scattering, we conclude that our investigation of the nn FSI done simultaneously and under identical conditions gives the correct value for a_nn. Our value for a_nn is in agreement with that obtained in pion-deuteron capture measurements but disagrees with values obtained from earlier nd breakup studies.Comment: 4 pages and 3 figure

Relación cartográfica entre variables hidrológicas y de degradación por pérdida de suelo superficial: sitio piloto A° Estacas, Entre Ríos

El aumento del área agrícola en el norte de la provincia de Entre Ríos resulta de la pérdida del bosque nativo. Este cambio del uso del suelo impacta los servicios ecosistémicos que brindan las cuencas hidrográficas, e incrementa el riesgo de degradación y pérdida de suelo por erosión. Actualmente el límite de pérdida de suelo utilizado para diseñar prácticas de sistematización de tierras es 15 Mg.ha-1.año-1, valor tres veces mayor al umbral para una producción sustentable. Este trabajo relaciona la cartografía de variables hidro­lógicas y pérdida de suelos para localizar y caracterizar áreas vulnerables a la erosión hídrica, como herra­mientas de ordenamiento territorial de cuencas. Se usaron los parámetros de curva número (CN), índice to­pográfico (TCI) y la ecuación USLE. Se trabajó en un entorno SIG en la cuenca del A° Estacas, con resolución espacial de 30 metros. Las imágenes fueron referenciadas al sistema POSGAR 2007 – FAJA 5. Como datos de entrada se utilizó: MDE ALOS PALSAR, carta de suelos de la provincia a escala 1:100.000, precipitación media anual, e imágenes Landsat 8. Se realizaron estadísticas por composición de mapas, gráficos de densidad por Kernel y ajuste por estimadores de máxima verosimilitud. Se observó que la pérdida de suelo se incrementa directamente con la generación de escurrimiento (CN), e inversamente con la probabilidad de encharcamiento (TCI). La cartografía generada verificó que reducir el umbral de pérdida de suelo a 3 Mg.ha-1.año-1 es factible como límite para una producción sustentable en la cuenca, independientemente del uso de suelo. Se definieron sectores que requieren una rápida acción correctiva, donde las pérdidas de suelo superan las 15 Mg.ha-1.año-1. Además, se identificaron áreas vulnerables entre 5 y 15 Mg.ha-1.año-1, tanto bajo uso agrícola como ganadero, donde se necesita revisar la intervención.Expansion of agricultural land use in the north of Entre Ríos province diminishes land occupied by native forests. At watershed scale, this change in land use impacts the provision of ecosystem services and increases soil´s degradation and water erosion. Current limit of soil loss for design of terraces is 15 Mg.ha-1. yr-1, three times larger than FAO threshold for sustainable agricultural production. In this work the mapping of hydrological variables and soil loss is combined to determine and characterize vulnerable areas to soil water erosion, as tools for watershed land use planning. The parameters of curve number (CN), topographic index (TCI) and the USLE equation were used. Work was carried out in a GIS environment in the A° Estacas watershed, with a spatial resolution of 30 meters. The images were referenced to the POSGAR 2007 - FAJA 5 system. The input data used were: ALOS PALSAR DEM, soil map of the province at a scale of 1:100,000, average annual precipitation, and Landsat 8 images. Statistical methods included univariate analyses, Kernel density distribution, and máximum likelihood. Soil loss increased directly with runoff generation (CN), and inversely with the probability of waterlogging (TCI). The generated mapping verified that regardless of land use, it is feasible to reduce the soil loss threshold for sustainable production in the basin to 3 Mg.ha-1. yr-1. The proposed mapping defined areas requiring rapid corrective actions, where estimated soil losses exceeded 15 Mg.ha-1.yr-1. In addition, the mapping allowed to localize vulnerable areas within the watershed, with soil loss between 5 and 15 Mg.ha-1.yr-1, under agricultural and livestock use, where their intervention should be reviewed.EEA ParanáFil: Pighini, Ramiro Joaquin. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Wingeyer, Ana. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Paraná; ArgentinaFil: Rodríguez, Leticia B. Universidad Nacional del Litoral. Facultad de Ingeniería y Ciencias Hídricas. Centro de Estudios Hidro-ambientales; ArgentinaFil: Wilson, Marcelo G. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Paraná; ArgentinaFil: Gabioud, Emmanuel. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Paraná; ArgentinaFil: Van Opstal, Natalia. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Paraná; Argentin

The three-nucleon bound state using realistic potential models

The bound states of $^3$H and $^3$He have been calculated using the Argonne $v_{18}$ plus the Urbana three-nucleon potential. The isospin $T=3/2$ state have been included in the calculations as well as the $n$-$p$ mass difference. The $^3$H-$^3$He mass difference has been evaluated through the charge dependent terms explicitly included in the two-body potential. The calculations have been performed using two different methods: the solution of the Faddeev equations in momentum space and the expansion on the correlated hyperspherical harmonic basis. The results are in agreement within 0.1% and can be used as benchmark tests. Results for the CD-Bonn interaction are also presented. It is shown that the $^3$H and $^3$He binding energy difference can be predicted model independently.Comment: 5 pages REVTeX 4, 1 figures, 6 table

The nucleon-nucleon interaction

We review the major progress of the past decade concerning our understanding of the nucleon-nucleon interaction. The focus is on the low-energy region (below pion production threshold), but a brief outlook towards higher energies is also given. The items discussed include charge-dependence, the precise value of the $\pi NN$ coupling constant, phase shift analysis and high-precision NN data and potentials. We also address the issue of a proper theory of nuclear forces. Finally, we summarize the essential open questions that future research should be devoted to.Comment: 42 pages, 12 figures, iopart.cls style; Topical Review prepared for J. Phys. G: Nucl. Part. Phy

An accurate nucleon-nucleon potential with charge-independence breaking

We present a new high-quality nucleon-nucleon potential with explicit charge dependence and charge asymmetry, which we designate Argonne $v_{18}$. The model has a charge-independent part with fourteen operator components that is an updated version of the Argonne $v_{14}$ potential. Three additional charge-dependent and one charge-asymmetric operators are added, along with a complete electromagnetic interaction. The potential has been fit directly to the Nijmegen $pp$ and $np$ scattering data base, low-energy $nn$ scattering parameters, and deuteron binding energy. With 40 adjustable parameters it gives a $\chi^{2}$ per datum of 1.09 for 4301 $pp$ and $np$ data in the range 0--350 MeV.Comment: 36 pages, PHY-7742-TH-9