2,195 research outputs found
Quantum effects in linear and non-linear transport of T-shaped ballistic junction
We report low-temperature transport measurements of three-terminal T-shaped
device patterned from GaAs/AlGaAs heterostructure. We demonstrate the mode
branching and bend resistance effects predicted by numerical modeling for
linear conductance data. We show also that the backscattering at the junction
area depends on the wave function parity. We find evidence that in a non-linear
transport regime the voltage of floating electrode always increases as a
function of push-pull polarization. Such anomalous effect occurs for the
symmetric device, provided the applied voltage is less than the Fermi energy in
equilibrium
More on the Narrowing of Impact Broadened Radio Recombination Lines at High Principal Quantum Number
Recently Alexander and Gulyaev have suggested that the apparent decrease in
impact broadening of radio recombination lines seen at high principal quantum
number n may be a product of the data reduction process, possibly resulting
from the presence of noise on the telescope spectra that is not present on the
calculated comparison spectra. This is an interesting proposal. However, there
are serious problems with their analysis that need to be pointed out. Perhaps
the most important of these is the fact that for principal quantum numbers
below n = 200, where the widths are not in question, their processed generated
profile widths do not fit the widths of the processed lines obtained at the
telescope. After processing, the halfwidths of the generated and telescope
profiles must agree below n = 200 if we are to believe that the processed
generated linewidths above n = 200 are meaningful. Theirs do not. Furthermore,
we find that after applying the linewidth reduction factors found by Alexander
and Gulyaev for their noise added profiles to our generated profiles to
simulate their noise adding effect, the processed widths we obtain still do not
come close to explaining the narrowing seen in the telescope lines for n values
in the range 200 < n < 250. It is concluded that what is needed to solve this
mystery is a completely new approach using a different observing technique
instead of simply a further manipulation of the frequency-switched data.Comment: Six pages with 4 figures. Accepted for publication in Astrophysics
and Space Scienc
Advancing Science with VGI: Reproducibility and Replicability of Recent Studies using VGI
In scientific research, reproducibility and replicability are requirements to ensure the advancement of our
body of knowledge.
T
his holds true also for VGI
-
related research and studies. However, the
characteristics
of VGI suggest particular difficulties in
ensuring
reproducibility and replicability
. In this
paper,
we aim to examine the current situation in VGI
-
related research
,
and identify strategies to ensure
realization of its full potential. To do so, we first
investigate
the different aspects of reprod
ucibility and
replicability
and their impact on
VGI
-
related research
. These impacts are different depending on the
objectives
of the study. Therefore
, we examine the
study
focus of VGI
-
related research to assess the
current body of research
and structure o
ur assessment
. Th
is work is
based
on a rigorous review of the
elements of reproducibility and a systematic mapping and analysis
of
58
papers on the use of VGI in the
crisis management field. Results of our investigation show that reproducibility issues related to data are
a
serious
concern
, while reproducibility issues related to analysis methods and processes face fewer
challenges. Howe
ver, since most studies still focus on
analyzing
the source data, reproducibility and
replicability are
still an unsolved problem
in VGI
-
related research. Therefore, we
show initiative
s
tackling
the problem, and
finally formulate strategies to improve the
situatio
Influence of the single-particle Zeeman energy on the quantum Hall ferromagnet at high filling factors
In a recent paper [B. A. Piot et al., Phys. Rev. B 72, 245325 (2005)], we
have shown that the lifting of the electron spin degeneracy in the integer
quantum Hall effect at high filling factors should be interpreted as a
magnetic-field-induced Stoner transition. In this work, we extend the analysis
to investigate the influence of the single-particle Zeeman energy on the
quantum Hall ferromagnet at high filling factors. The single-particle Zeeman
energy is tuned through the application of an additional in-plane magnetic
field. Both the evolution of the spin polarization of the system and the
critical magnetic field for spin splitting are well described as a function of
the tilt angle of the sample in the magnetic field.Comment: Published in Phys. Rev.
Exact solution of the Zeeman effect in single-electron systems
Contrary to popular belief, the Zeeman effect can be treated exactly in
single-electron systems, for arbitrary magnetic field strengths, as long as the
term quadratic in the magnetic field can be ignored. These formulas were
actually derived already around 1927 by Darwin, using the classical picture of
angular momentum, and presented in their proper quantum-mechanical form in 1933
by Bethe, although without any proof. The expressions have since been more or
less lost from the literature; instead, the conventional treatment nowadays is
to present only the approximations for weak and strong fields, respectively.
However, in fusion research and other plasma physics applications, the magnetic
fields applied to control the shape and position of the plasma span the entire
region from weak to strong fields, and there is a need for a unified treatment.
In this paper we present the detailed quantum-mechanical derivation of the
exact eigenenergies and eigenstates of hydrogen-like atoms and ions in a static
magnetic field. Notably, these formulas are not much more complicated than the
better-known approximations. Moreover, the derivation allows the value of the
electron spin gyromagnetic ratio to be different from 2. For
completeness, we then review the details of dipole transitions between two
hydrogenic levels, and calculate the corresponding Zeeman spectrum. The various
approximations made in the derivation are also discussed in details.Comment: 18 pages, 4 figures. Submitted to Physica Script
Quark spin coupling in baryons - revisited
A direct connection can be made between mixing angles in negative parity
baryons and the spin coupling of constituent quarks. The mixing angles do not
depend on spectral data. These angles are recalculated for gluon exchange and
pion exchange between quarks. For pion exchange the results of Glozman and
Riska are corrected. The experimental data on mixing are very similar to those
derived from gluon exchange but substantially different from the values
obtained for pion exchange.Comment: 10 pages, RevTex; a sign error is corrected, spin-orbit results are
include
Electronic structure and vertical transport in random dimer GaAs-Al_xGa_(1-x)As superlattices
We report a systematic study of several GaAs-AlxGa1-xAs semiconductor superlattices grown by molecular-beam epitaxy specifically designed to explore the existence of extended states in random dimer superlattices. We have confirmed our previous results [V. Bellani et al., Phys. Rev. Lett. 82, 2159 (1999)] with much additional evidence that allows us to lay claim to a clear-cut experimental verification of the presence of extended states in random dimer superlattices due to the short-range correlations (dimers) that inhibit the localization effects of the disorder
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