2,212 research outputs found
Wave function mapping in graphene quantum dots with soft confinement
Using low-temperature scanning tunneling spectroscopy, we map the local
density of states (LDOS) of graphene quantum dots supported on Ir(111). Due to
a band gap in the projected Ir band structure around the graphene K point, the
electronic properties of the QDs are dominantly graphene-like. Indeed, we
compare the results favorably with tight binding calculations on the honeycomb
lattice based on parameters derived from density functional theory. We find
that the interaction with the substrate near the edge of the island gradually
opens a gap in the Dirac cone, which implies soft-wall confinement.
Interestingly, this confinement results in highly symmetric wave functions.
Further influences of the substrate are given by the known moir{\'e} potential
and a 10% penetration of an Ir surface resonanceComment: 7 pages, 11 figures, DFT calculations directly showing the origin of
soft confinment, correct identification of the state penetrating from Ir(111)
into graphen
Low-Prandtl-number B\'enard-Marangoni convection in a vertical magnetic field
The effect of a homogeneous magnetic field on surface-tension-driven
B\'{e}nard convection is studied by means of direct numerical simulations. The
flow is computed in a rectangular domain with periodic horizontal boundary
conditions and the free-slip condition on the bottom wall using a
pseudospectral Fourier-Chebyshev discretization. Deformations of the free
surface are neglected. Two- and three-dimensional flows are computed for either
vanishing or small Prandtl number, which are typical of liquid metals. The main
focus of the paper is on a qualitative comparison of the flow states with the
non-magnetic case, and on the effects associated with the possible
near-cancellation of the nonlinear and pressure terms in the momentum equations
for two-dimensional rolls. In the three-dimensional case, the transition from a
stationary hexagonal pattern at the onset of convection to three-dimensional
time-dependent convection is explored by a series of simulations at zero
Prandtl number.Comment: 26 pages, 9 figure
Exact solutions to the focusing nonlinear Schrodinger equation
A method is given to construct globally analytic (in space and time) exact
solutions to the focusing cubic nonlinear Schrodinger equation on the line. An
explicit formula and its equivalents are presented to express such exact
solutions in a compact form in terms of matrix exponentials. Such exact
solutions can alternatively be written explicitly as algebraic combinations of
exponential, trigonometric, and polynomial functions of the spatial and
temporal coordinates.Comment: 60 pages, 18 figure
Principle of Maximum Entropy Applied to Rayleigh-B\'enard Convection
A statistical-mechanical investigation is performed on Rayleigh-B\'enard
convection of a dilute classical gas starting from the Boltzmann equation. We
first present a microscopic derivation of basic hydrodynamic equations and an
expression of entropy appropriate for the convection. This includes an
alternative justification for the Oberbeck-Boussinesq approximation. We then
calculate entropy change through the convective transition choosing mechanical
quantities as independent variables. Above the critical Rayleigh number, the
system is found to evolve from the heat-conducting uniform state towards the
convective roll state with monotonic increase of entropy on the average. Thus,
the principle of maximum entropy proposed for nonequilibrium steady states in a
preceding paper is indeed obeyed in this prototype example. The principle also
provides a natural explanation for the enhancement of the Nusselt number in
convection.Comment: 13 pages, 4 figures; typos corrected; Eq. (66a) corrected to remove a
double counting for ; Figs. 1-4 replace
The energy budget in Rayleigh-Benard convection
It is shown using three series of Rayleigh number simulations of varying
aspect ratio AR and Prandtl number Pr that the normalized dissipation at the
wall, while significantly greater than 1, approaches a constant dependent upon
AR and Pr. It is also found that the peak velocity, not the mean square
velocity, obeys the experimental scaling of Ra^{0.5}. The scaling of the mean
square velocity is closer to Ra^{0.46}, which is shown to be consistent with
experimental measurements and the numerical results for the scaling of Nu and
the temperature if there are strong correlations between the velocity and
temperature.Comment: 5 pages, 3 figures, new version 13 Mar, 200
Do mutual funds have consistency in their performance?
Using a comprehensive data set of 714 Chinese mutual funds from 2004 to 2015, the study investigates these funds’ performance persistence by using the Capital Asset Pricing model, the Fama-French three-factor model and the Carhart Four-factor model. For persistence analysis, we categorize mutual funds into eight octiles based on their one year lagged performance and then observe their performance for the subsequent
12 months. We also apply Cross-Product Ratio technique to assess the performance
persistence in these Chinese funds. The study finds no significant evidence of persis- tence in the performance of the mutual funds. Winner (loser) funds do not continue to be winner (loser) funds in the subsequent time period. These findings suggest that future performance of funds cannot be predicted based on their past performance.info:eu-repo/semantics/publishedVersio
Geophysical studies with laser-beam detectors of gravitational waves
The existing high technology laser-beam detectors of gravitational waves may
find very useful applications in an unexpected area - geophysics. To make
possible the detection of weak gravitational waves in the region of high
frequencies of astrophysical interest, ~ 30 - 10^3 Hz, control systems of laser
interferometers must permanently monitor, record and compensate much larger
external interventions that take place in the region of low frequencies of
geophysical interest, ~ 10^{-5} - 3 X 10^{-3} Hz. Such phenomena as tidal
perturbations of land and gravity, normal mode oscillations of Earth,
oscillations of the inner core of Earth, etc. will inevitably affect the
performance of the interferometers and, therefore, the information about them
will be stored in the data of control systems. We specifically identify the
low-frequency information contained in distances between the interferometer
mirrors (deformation of Earth) and angles between the mirrors' suspensions
(deviations of local gravity vectors and plumb lines). We show that the access
to the angular information may require some modest amendments to the optical
scheme of the interferometers, and we suggest the ways of doing that. The
detailed evaluation of environmental and instrumental noises indicates that
they will not prevent, even if only marginally, the detection of interesting
geophysical phenomena. Gravitational-wave instruments seem to be capable of
reaching, as a by-product of their continuous operation, very ambitious
geophysical goals, such as observation of the Earth's inner core oscillations.Comment: 29 pages including 8 figures, modifications and clarifications in
response to referees' comments, to be published in Class. Quant. Gra
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