11,138 research outputs found
Coexistence of bulk and surface states probed by Shubnikov-de Haas oscillations in BiSe with high charge-carrier density
Topological insulators are ideally represented as having an insulating bulk
with topologically protected, spin-textured surface states. However, it is
increasingly becoming clear that these surface transport channels can be
accompanied by a finite conducting bulk, as well as additional topologically
trivial surface states. To investigate these parallel conduction transport
channels, we studied Shubnikov-de Haas oscillations in BiSe thin films,
in high magnetic fields up to 30 T so as to access channels with a lower
mobility. We identify a clear Zeeman-split bulk contribution to the
oscillations from a comparison between the charge-carrier densities extracted
from the magnetoresistance and the oscillations. Furthermore, our analyses
indicate the presence of a two-dimensional state and signatures of additional
states the origin of which cannot be conclusively determined. Our findings
underpin the necessity of theoretical studies on the origin of and the
interplay between these parallel conduction channels for a careful analysis of
the material's performance.Comment: Manuscript including supplemental materia
Ab Initio Molecular Dynamics Study of Aqueous Solvation of Ethanol and Ethylene
The structure and dynamics of aqueous solvation of ethanol and ethylene are
studied by DFT-based Car-Parrinello molecular dynamics. We did not find an
enhancement of the structure of the hydrogen bonded network of hydrating water
molecules. Both ethanol and ethylene can easily be accommodated in the
hydrogen-bonded network of water molecules without altering its structure. This
is supports the conclusion from recent neutron diffraction experiments that
there is no hydrophobic hydration around small hydrophobic groups. Analysis of
the electronic charge distribution using Wannier functions shows that the
dipole moment of ethanol increases from 1.8 D to 3.1 D upon solvation, while
the apolar ethylene molecule attains an average dipole moment of 0.5 D. For
ethylene, we identified configurations with -H bonded water molecules,
that have rare four-fold hydrogen-bonded water coordination, yielding
instantaneous dipole moments of ethylene of up to 1 D. The results provide
valuable information for the improvement of empirical force fields, and point
out that for an accurate description of the aqueous solvation of ethanol, and
even of the apolar ethylene, polarizable force fields are required.Comment: 15 pages, 10 figures, 4 tables, revtex4, submitted to J. Chem. Phy
Analytical Expression for the RKKY Interaction in Doped Graphene
We obtain an analytical expression for the Ruderman-Kittel-Kasuya-Yosida
(RKKY) interaction in electron or hole doped graphene for linear Dirac
bands. The results agree very well with the numerical calculations for the full
tight-binding band structure in the regime where the linear band structure is
valid. The analytical result, expressed in terms of the Meijer G-function,
consists of a product of two oscillatory terms, one coming from the
interference between the two Dirac cones and the second coming from the finite
size of the Fermi surface. For large distances, the Meijer G-function behaves
as a sinusoidal term, leading to the result for moments located on the same sublattice. The
dependence, which is the same for the standard two-dimensional electron gas, is
universal irrespective of the sublattice location and the distance direction of
the two moments except when (undoped case), where it reverts to the
dependence. These results correct several inconsistencies found in the
literature.Comment: 5 pages, 5 figure
De gedragsbeïnvloedende en vrijheidsbeperkende maatregel als instrument in de strijd voor de maatschappelijke (schijn)veiligheid
The European economic community and economic assosiation
I am grateful to the Afrika-Seminaar of the Potchefstroom University for inviting me to give a talk on the European Economic Community and the Association of the Overseas Countries and Territories
Teaching Signal Processing to the Medical Profession
Knowledge of signal processing is very important for medical students. A medical signal may be used for monitoring, constructing an image, or for extracting the numerical quantity of a parameter. This information forms a basis for medical decisions. However, the processing of the signal may lead to distortion and an incorrect interpretation. The present article describes an educational practical for first year medical students. It uses the electrocardiogram, which can be obtained easily, as a convenient example of a medical signal. The practical was developed at the VU University Amsterdam and summarizes the elementary concepts of signal processing
Fish to 2020: supply and demand in changing global markets
Using a state-of-the art computer model of global supply and demand for food and feed commodities, this book projects the likely changes in the fisheries sector over the next two decades. As prices for most food commodities fall, fish prices are expected to rise, reflecting demand for fish that outpaces the ability of the world to supply it. The model shows that developing countries will consume and produce a much greater share of the world's fish in the future, and trade in fisheries commodities will also increase. The authors show the causes and implications of these and other changes, and argue for specific actions and policies that can improve outcomes for the poor and for the environment.Supply balance, Trade, Aquaculture, Fishery management, Economic analysis, Environmental factors, Developing countries
Laser radiation pressure slowing of a molecular beam
There is substantial interest in producing samples of ultracold molecules for
possible applications in quantum computation, quantum simulation of condensed
matter systems, precision measurements, controlled chemistry, and high
precision spectroscopy. A crucial step to obtaining large samples of ultracold,
trapped molecules is developing a means to bridge the gap between typical
molecular source velocities (~150-600 m/s) and velocities for which trap
loading or confinement is possible (~5-20 m/s). Here we show deceleration of a
beam of neutral strontium monofluoride (SrF) molecules using radiative force.
Under certain conditions, the deceleration results in a substantial flux of
molecules with velocities <50 m/s. The observed slowing, from ~140 m/s,
corresponds to scattering ~10000 photons. We also observe longitudinal velocity
compression under different conditions. Combined with molecular laser cooling
techniques, this lays the groundwork to create slow and cold molecular beams
suitable for trap loading.Comment: 7 pages, 7 figures. Supplementary material updated
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