2,697 research outputs found
Full two-electron calculations of antiproton collisions with molecular hydrogen
Total cross sections for single ionization and excitation of molecular
hydrogen by antiproton impact are presented over a wide range of impact energy
from 1 keV to 6.5 MeV. A nonpertubative time-dependent close-coupling method is
applied to fully treat the correlated dynamics of the electrons. Good agreement
is obtained between the present calculations and experimental measurements of
single-ionization cross sections at high energies, whereas some discrepancies
with the experiment are found around the maximum. The importance of the
molecular geometry and a full two-electron description is demonstrated. The
present findings provide benchmark results which might be useful for the
development of molecular models.Comment: 4 pages, 3 figure
Collisions of antiprotons with hydrogen molecular ions
Time-dependent close-coupling calculations of the ionization and excitation
cross section for antiproton collisions with molecular hydrogen ions are
performed in an impact-energy range from 0.5 keV to 10 MeV. The
Born-Oppenheimer and Franck-Condon approximations as well as the impact
parameter method are applied in order to describe the target molecule and the
collision process. It is shown that three perpendicular orientations of the
molecular axis with respect to the trajectory are sufficient to accurately
reproduce the ionization cross section calculated by [Sakimoto, Phys. Rev. A
71, 062704 (2005)] reducing the numerical effort drastically. The
independent-event model is employed to approximate the cross section for double
ionization and H+ production in antiproton collisions with H2.Comment: 12 pages, 5 figures, 4 table
Stopping power of antiprotons in H, H2, and He targets
The stopping power of antiprotons in atomic and molecular hydrogen as well as
helium was calculated in an impact-energy range from 1 keV to 6.4 MeV. In the
case of H2 and He the targets were described with a single-active electron
model centered on the target. The collision process was treated with the
close-coupling formulation of the impact-parameter method. An extensive
comparison of the present results with theoretical and experimental literature
data was performed in order to evaluate which of the partly disagreeing
theoretical and experimental data are most reliable. Furthermore, the size of
the corrections to the first-order stopping number, the average energy
transferred to the target electrons, and the relative importance of the
excitation and the ionization process for the energy loss of the projectile was
determined. Finally, the stopping power of the H, H2, and He targets were
directly compared revealing specific similarities and differences of the three
targets.Comment: v1: 12 pages, 8 figures, and 1 table v2: 15 pages, 9 figures, and 2
tables; extended discussion on IPM in Method; influence of double ionization
on stopping power discussed in Result
Break-down of the single-active-electron approximation for one-photon ionization of the B state of H exposed to intense laser fields
Ionization, excitation, and de-excitation to the ground state is studied
theoretically for the first excited singlet state B of H
exposed to intense laser fields with photon energies in between about 3 eV and
13 eV. A parallel orientation of a linear polarized laser and the molecular
axis is considered. Within the dipole and the fixed-nuclei approximations the
time-dependent Schr\"odinger equation describing the electronic motion is
solved in full dimensionality and compared to simpler models. A dramatic
break-down of the single-active-electron approximation is found and explained
to be due to the inadequate description of the final continuum states.Comment: 9 pages, 4 figure
Accurate photoionisation cross section for He at non-resonant photon energies
The total single-photon ionisation cross section was calculated for helium
atoms in their ground state. Using a full configuration-interaction approach
the photoionisation cross section was extracted from the complex-scaled
resolvent. In the energy range from ionisation threshold to 59\,eV our results
agree with an earlier -spline based calculation in which the continuum is
box discretised within a relative error of in the non-resonant part of
the spectrum. Above the \He^{++} threshold our results agree on the other
hand very well to a recent Floquet calculation. Thus our calculation confirms
the previously reported deviations from the experimental reference data outside
the claimed error estimate. In order to extend the calculated spectrum to very
high energies, an analytical hydrogenic-type model tail is introduced that
should become asymptotically exact for infinite photon energies. Its
universality is investigated considering also H, Li, and HeH. With
the aid of the tail corrections to the dipole approximation are estimated.Comment: 20 pages, 7 figures, 2 table
Frustrated collisions and unconventional pairing on a quantum superlattice
We solve the problem of scattering and binding of two spin-1/2 fermions on a
one-dimensional superlattice with a period of twice the lattice spacing
analytically. We find the exact bound states and the scattering states,
consisting of a generalized Bethe ansatz augmented with an extra scattering
product due to "asymptotic" degeneracy. If a Bloch band is doubly occupied, the
extra wave can be a bound state in the continuum corresponding to a
single-particle interband transition. In all other cases, it corresponds to a
quasi-momentum changing, frustrated collision.Comment: 4 pages, 2 figure
The energetics of a collapsing meridional overturning circulation
A well-studied example of natural climate variability is the impact of large freshwater input to the polar oceans, simulating glacial melt release or an amplification of the hydrological cycle. Such forcing can reduce, or entirely eliminate, the formatio
Energetics of multidecadal Atlantic Ocean variability
Oscillatory behavior of the Atlantic meridional overturning circulation (MOC) is thought to underlie Atlantic multidecadal climate variability. While the energy sources and sinks driving the mean MOC have received intense scrutiny over the last decade, the governing energetics of the modes of variability of the MOC have not been addressed to the same degree. This paper examines the energy conversion processes associated with this variability in an idealized North Atlantic Ocean model. In this model, the multidecadal variability arises through an instability associated with a so-called thermal Rossby mode, which involves westward propagation of temperature anomalies. Applying the available potential energy (APE) framework from stratified turbulence to the idealized ocean model simulations, the authors study the multidecadal variability from an energetics viewpoint. The analysis explains how the propagation of the temperature anomalies leads to changes in APE, which are subsequently converted into the kinetic energy changes associated with variations in the MOC. Thus, changes in the rate of generation of APE by surface buoyancy forcing provide the kinetic energy to sustain the multidecadal mode of variability
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