17,515 research outputs found
Anatomy of three-body decay II. Decay mechanism and resonance structure
We use the hyperspherical adiabatic expansion method to discuss the the two
mechanisms of sequential and direct three-body decay. Both short-range and
Coulomb interactions are included. Resonances are assumed initially populated
by a process independent of the subsequent decay. The lowest adiabatic
potentials describe the resonances rather accurately at distances smaller than
the outer turning point of the confining barrier. We illustrate with realistic
examples of nuclei from neutron (He) and proton (Ne) driplines as
well as excited states of beta-stable nuclei (C).Comment: To be published in Nuclear Physics
Can on-farm bioenergy production make organic farming more sustainable? - A model for energy balance, nitrogen losses, and green house gas emissions in a 1000 ha energy catchment with organic dairy farming and integrated bioenergy production
Can biogas and bioethanol production make organic farming more sustainable?
- Results from a model for the fossil energy balance, Nitrogen losses, and greenhouse gas emissions in a 1000 ha energy catchment with organic dairy farming and integrated biogas and bioethanol production.
Dalgaard T1, Pugesgaard S1, Jørgensen U1, Olesen JE1, Møller HB1 and Jensen ES2
1) Dept. Agroecology and Environment. Faculty of Agricultural Sciences (DJF), University of Aarhus. DK-8830 Tjele. Denmark. Contact: [email protected]
2) Biosystems Department, Risø DTU, The National Laboratory for Sustainable Energy, The Technical University of Denmark DK-4000 Roskilde, Denmark
The vision of organic farming systems, independent of fossil energy resources, with significantly lower nutrient losses, and no net contribution to the greenhouse gas emissions might be fulfilled via the integration of biogas production. This is an important hypothesis investigated in the www.bioconcens.elr.dk/uk/ research project.
This poster illustrates preliminary results from a model for the fossil energy balance, Nitrogen losses, and greenhouse gas emissions in a 1000 ha energy catchment with organic dairy farming and integrated biogas production in Denmark. The model will draw on results from previous models (e.g the farmGHG model), and includes a number of organic dairy farm type components, including information on livestock production, housing, manure storage, manure and fodder import/export, crop rotations, yield levels, and soil types. In addition, a biogas plant model component evaluates effects of the inclusion of variable amounts of manures and crop residues from the specified farm types, into the biogas energy production.
The model is intended to result in an overall catchment balance for the following three types of indicators: 1) the fossil energy use – i.e. the net fossil energy use minus the bioenergy production, 2) losses of Nitrogen in the form of nitrates, ammonia and nitrous oxide, and 3) the emission of the three main greenhouse gasses from agriculture: carbon dioxide, nitrous oxide and methane, measured in carbon dioxide equivalents. Moreover, these indicator values are specified for each of the farm types included in the model, and for the biogas plant component. Finally, selected model results are discussed in relation to the overall hypothesis of the research project, and it is discussed how the integration of biogas production in organic farming, can help to improve the self-sufficiency in Nitrogen, and thereby reduce the import of nutrients to the organic farming systems
Structure and decay at rapid proton capture waiting points
We investigate the region of the nuclear chart around from a
three-body perspective, where we compute reaction rates for the radiative
capture of two protons. One key quantity is here the photon dissociation cross
section for the inverse process where two protons are liberated from the
borromean nucleus by photon bombardment. We find a number of peaks at low
photon energy in this cross section where each peak is located at the energy
corresponding to population of a three-body resonance. Thus, for these energies
the decay or capture processes proceed through these resonances. However, the
next step in the dissociation process still has the option of following several
paths, that is either sequential decay by emission of one proton at a time with
an intermediate two-body resonance as stepping stone, or direct decay into the
continuum of both protons simultaneously. The astrophysical reaction rate is
obtained by folding of the cross section as function of energy with the
occupation probability for a Maxwell-Boltzmann temperature distribution. The
reaction rate is then a function of temperature, and of course depending on the
underlying three-body bound state and resonance structures. We show that a very
simple formula at low temperature reproduces the elaborate numerically computed
reaction rate.Comment: 4 pages, 3 figures, conference proceedings, publishe
alpha particle momentum distributions from 12C decaying resonances
The computed particle momentum distributions from the decay of
low-lying C resonances are shown. The wave function of the decaying
fragments is computed by means of the complex scaled hyperspherical adiabatic
expansion method. The large-distance part of the wave functions is crucial and
has to be accurately calculated. We discuss energy distributions, angular
distributions and Dalitz plots for the , and states of
C.Comment: 6 pages, 4 figures. Proceedings of the SOTANCP2008 conference held in
Strasbourg in May 200
A combined mean-field and three-body model tested on the O-nucleus
We combine few- and many-body degrees of freedom in a model applicable to
both bound and continuum states and adaptable to different subfields of
physics. We formulate a self-consistent three-body model for a core-nucleus
surrounded by two valence nucleons. We treat the core in the mean-field
approximation and use the same effective Skyrme interaction between both core
and valence nucleons. We apply the model to O where we reproduce the
known experimental data as well as phenomenological models with more
parameters. The decay of the ground state is found to proceed directly into the
continuum without effect of the virtual sequential decay through the well
reproduced -resonance of O.Comment: 5 pages, 5 figures, under revie
Combining few-body cluster structures with many-body mean-field methods
Nuclear cluster physics implicitly assumes a distinction between groups of
degrees-of-freedom, that is the (frozen) intrinsic and (explicitly treated)
relative cluster motion. We formulate a realistic and practical method to
describe the coupled motion of these two sets of degrees-of-freedom. We derive
a coupled set of differential equations for the system using the
phenomenologically adjusted effective in-medium Skyrme type of nucleon-nucleon
interaction. We select a two-nucleon plus core system where the mean-field
approximation corresponding to the Skyrme interaction is used for the core. A
hyperspherical adiabatic expansion of the Faddeev equations is used for the
relative cluster motion. We shall specifically compare both the structure and
the decay mechanism found from the traditional three-body calculations with the
result using the new boundary condition provided by the full microscopic
structure at small distance. The extended Hilbert space guaranties an improved
wave function compared to both mean-field and three-body solutions. We shall
investigate the structures and decay mechanism of C (C+n+n). In
conclusion, we have developed a method combining nuclear few- and many-body
techniques without losing the descriptive power of each approximation at
medium-to-large distances and small distances respectively. The coupled set of
equations are solved self-consistently, and both structure and dynamic
evolution are studied.Comment: 4 pages, 3 figures, conference proceedings, publishe
Emergence of clusters: Halos, Efimov states, and experimental signals
We investigate emergence of halos and Efimov states in nuclei by use of a
newly designed model which combines self-consistent mean-field and three-body
descriptions. Recent interest in neutron heavy calcium isotopes makes Ca
(Ca+n+n) an ideal realistic candidate on the neutron dripline, and we
use it as a representative example that illustrates our broadly applicable
conclusions. By smooth variation of the interactions we simulate the crossover
from well-bound systems to structures beyond the threshold of binding, and find
that halo-configurations emerge from the mean-field structure for three-body
binding energy less than keV. Strong evidence is provided that Efimov
states cannot exist in nuclei. The structure that bears the most resemblance to
an Efimov state is a giant halo extending beyond the neutron-core scattering
length. We show that the observable large-distance decay properties of the wave
function can differ substantially from the bulk part at short distances, and
that this evolution can be traced with our combination of few- and many-body
formalisms. This connection is vital for interpretation of measurements such as
those where an initial state is populated in a reaction or by a beta-decay.Comment: 5 pages, 5 figures, under revie
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