18,363 research outputs found
Broadening of HO rotational lines by collision with He atoms at low temperature
We report pressure broadening coefficients for the 21 electric-dipole
transitions between the eight lowest rotational levels of ortho-HO and
para-HO molecules by collisions with He at temperatures from 20 to 120 K.
These coefficients are derived from recently published experimental
state-to-state rate coefficients for HO:He inelastic collisions, plus an
elastic contribution from close coupling calculations. The resulting
coefficients are compared to the available experimental data. Mostly due to the
elastic contribution, the pressure broadening coefficients differ much from
line to line, and increase markedly at low temperature. The present results are
meant as a guide for future experiments and astrophysical observations.Comment: 2 figures, 2 table
Strain balanced quantum posts
Quantum posts are assembled by epitaxial growth of closely spaced quantum dot
layers, modulating the composition of a semiconductor alloy, typically InGaAs.
In contrast with most self-assembled nanostructures, the height of quantum
posts can be controlled with nanometer precision, up to a maximum value limited
by the accumulated stress due to the lattice mismatch. Here we present a strain
compensation technique based on the controlled incorporation of phosphorous,
which substantially increases the maximum attainable quantum post height. The
luminescence from the resulting nanostructures presents giant linear
polarization anisotropy.Comment: Submitted to Applied Physics Letters (7th March 2011). 4 pages, 4
figure
N-Delta(1232) axial form factors from weak pion production
The N-Delta axial form factors are determined from neutrino induced pion
production ANL & BNL data by using a state of the art theoretical model, which
accounts both for background mechanisms and deuteron effects. We find
violations of the off diagonal Goldberger-Treiman relation at the level of 2
sigma which might have an impact in background calculations for T2K and
MiniBooNE low energy neutrino oscillation precision experiments.Comment: 4 pages, 1 figur
Dynamics of Coherent States in Regular and Chaotic Regimes of the Non-integrable Dicke Model
The quantum dynamics of initial coherent states is studied in the Dicke model
and correlated with the dynamics, regular or chaotic, of their classical limit.
Analytical expressions for the survival probability, i.e. the probability of
finding the system in its initial state at time , are provided in the
regular regions of the model. The results for regular regimes are compared with
those of the chaotic ones. It is found that initial coherent states in regular
regions have a much longer equilibration time than those located in chaotic
regions. The properties of the distributions for the initial coherent states in
the Hamiltonian eigenbasis are also studied. It is found that for regular
states the components with no negligible contribution are organized in
sequences of energy levels distributed according to Gaussian functions. In the
case of chaotic coherent states, the energy components do not have a simple
structure and the number of participating energy levels is larger than in the
regular cases.Comment: Contribution to the proceedings of the Escuela Latinoamericana de
F\'isica (ELAF) Marcos Moshinsky 2017. (9 pages, 4 figures
Reversible Graphene decoupling by NaCl photo-dissociation
We describe the reversible intercalation of Na under graphene on Ir(111) by
photo-dissociation of a previously adsorbed NaCl overlayer. After room
temperature evaporation, NaCl adsorbs on top of graphene forming a bilayer.
With a combination of electron diffraction and photoemission techniques we
demonstrate that the NaCl overlayer dissociates upon a short exposure to an
X-ray beam. As a result, chlorine desorbs while sodium intercalates under the
graphene, inducing an electronic decoupling from the underlying metal. Low
energy electron diffraction shows the disappearance of the moir\'e pattern when
Na intercalates between graphene and iridium. Analysis of the Na 2p core-level
by X-ray photoelectron spectroscopy shows a chemical change from NaCl to
metallic buried Na at the graphene/Ir interface. The intercalation-decoupling
process leads to a n-doped graphene due to the charge transfer from the Na, as
revealed by constant energy angle resolved X-ray photoemission maps. Moreover,
the process is reversible by a mild annealing of the samples without damaging
the graphene
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