49,199 research outputs found
Challenges in modelling dissolved organic matter dynamics in agricultural soil using DAISY
Because dissolved organic matter (DOM) plays an important role is terrestrial C-,N-and P-balances and transport of these three components to aquatic environments, there is a need to include it in models. This paper presents the concept of the newly developed DOM modules implemented in the DAISY model with focus on the quantification of DOM sorption/desorption and microbial-driven DOM turnover. The kinetics of DOM sorption/desorption is described by the deviation of the actual DOM concentration in solution from the equilibrium concentration, Ceq. The Ceq is soil specific and estimated from pedotransfer functions taking into account the soil content of organic matter, Al and Fe oxides. The turnover of several organic matter pools including one DOM pool are described by first-order kinetics.
The DOM module was tested at field scale for three soil treatments applied after cultivating grass–clover swards. Suction cups were installed at depths 30, 60 and 90 cm and soil solution was sampled for quantification of dissolved organic C (DOC) and dissolved organic N (DON). In the topsoil, the observed fluctuations in DOC were successfully simulated when the sorption/desorption rate coefficient k was low. In the subsoil, the observed concentrations of DOC were steadier and the best simulations were obtained using a high k. The model shows that DOC and DON concentrations are levelled out in the subsoils due to soil buffering. The steady concentration levels were based on the Ceq for each horizon and the kinetic concept for sorption/desorption of DOC appeared aviable approach. If Ceq was successfully estimated by the pedotransfer function it was possible to simulate the DOC concentration in the subsoil. In spite of difficulties in describing the DOC dynamics of the topsoil, the DOM module simulates the subsoil concentration level of DOC well, and also — but with more uncertainty — the DON concentration level
Pulsar Kicks With Modified URCA and Electrons in Landau Levels
We derive the energy asymmetry given the proto-neutron star during the time
when the neutrino sphere is near the surface of the proto-neutron star, using
the modified URCA process. The electrons produced with the anti-neutrinos are
in Landau levels due to the strong magnetic field, and this leads to asymmetry
in the neutrino momentum, and a pulsar kick. The magnetic field must be strong
enough for a large fraction of the eletrons to be in the lowest Landau level,
however, there is no direct dependence of our pulsar velocity on the strength
of the magnetic field. Our main prediction is that the large pulsar kicks start
at about 10 s and last for about 10 s, with the corresponding neutrinos
correlated in the direction of the magnetic field. We predict a pulsar velocity
of 1.03 km/s, which reaches 1000 km/s if T
K.Comment: 11 pages, 6 figure
On the frequency and remnants of Hypernovae
Under the hypothesis that some fraction of massive stellar core collapses
give rise to unusually energetic events, termed hypernovae, I examine the
required rates assuming some fraction of such events yield gamma ray bursts. I
then discuss evidence from studies of pulsars and r-process nucleosynthesis
that independently suggests the existence of a class of unusually energetic
events. Finally I describe a scenario which links these different lines of
evidence as supporting the hypernova hypothesis.Comment: TeX, To appear in ApJ Letter
Effective-range approach and scaling laws for electromagnetic strength in neutron-halo nuclei
We study low-lying multipole strength in neutron-halo nuclei. The strength
depends only on a few low-energy constants: the neutron separation energy, the
asymptotic normalization coefficient of the bound state wave function, and the
scattering length that contains the information on the interaction in the
continuum. The shape of the transition probability shows a characteristic
dependence on few scaling parameters and the angular momenta. The total E1
strength is related to the root-mean-square radius of the neutron wave function
in the ground state and shows corresponding scaling properties. We apply our
approach to the E1 strength distribution of 11Be.Comment: 4 pages, 1 figure (modified), additional table, extended discussion
of example, accepted for publication in Phys. Rev. Let
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