34,485 research outputs found
Density oscillations in trapped dipolar condensates
We investigated the ground state wave function and free expansion of a
trapped dipolar condensate. We find that dipolar interaction may induce both
biconcave and dumbbell density profiles in, respectively, the pancake- and
cigar-shaped traps. On the parameter plane of the interaction strengths, the
density oscillation occurs only when the interaction parameters fall into
certain isolated areas. The relation between the positions of these areas and
the trap geometry is explored. By studying the free expansion of the condensate
with density oscillation, we show that the density oscillation is detectable
from the time-of-flight image.Comment: 7 pages, 9 figure
Hole maximum density droplets of an antidot in strong magnetic fields
We investigate a quantum antidot in the integer quantum Hall regime (the
filling factor is two) by using a Hartree-Fock approach and by transforming the
electron antidot into a system which confines holes via an electron-hole
transformation. We find that its ground state is the maximum density droplet of
holes in certain parameter ranges. The competition between electron-electron
interactions and the confinement potential governs the properties of the hole
droplet such as its spin configuration. The ground-state transitions between
the droplets with different spin configurations occur as magnetic field varies.
For a bell-shape antidot containing about 300 holes, the features of the
transitions are in good agreement with the predictions of a recently proposed
capacitive interaction model for antidots as well as recent experimental
observations. We show this agreement by obtaining the parameters of the
capacitive interaction model from the Hartree-Fock results. An inverse
parabolic antidot is also studied. Its ground-state transitions, however,
display different magnetic-field dependence from that of a bell-shape antidot.
Our study demonstrates that the shape of antidot potential affects its physical
properties significantly.Comment: 12 pages, 11 figure
Time-resolved measurement of single pulse femtosecond laser-induced periodic surface structure formation
Time-resolved diffraction microscopy technique has been used to observe the
formation of laser-induced periodic surface structures (LIPSS) from the
interaction of a single femtosecond laser pulse (pump) with a nano-scale groove
mechanically formed on a single-crystal Cu substrate. The interaction dynamics
(0-1200 ps) was captured by diffracting a time-delayed, frequency-doubled pulse
from nascent LIPSS formation induced by the pump with an infinity-conjugate
microscopy setup. The LIPSS ripples are observed to form sequentially outward
from the groove edge, with the first one forming after 50 ps. A 1-D analytical
model of electron heating and surface plasmon polariton (SPP) excitation
induced by the interaction of incoming laser pulse with the groove edge
qualitatively explains the time-evloution of LIPSS formation.Comment: 4 pages, 5 figure
Local Dielectric Measurements of BaTiO3-CoFe2O4 Nano-composites Through Microwave Microscopy
We report on linear and non-linear dielectric property measurements of BaTiO3
- CoFe2O4 (BTO-CFO) ferroelectro-magnetic nano-composites and pure BaTiO3 and
CoFe2O4 samples with Scanning Near Field Microwave Microscopy. The permittivity
scanning image with spatial resolution on the micro-meter scale shows that the
nano-composites have very uniform quality with an effective dielectric constant
\epsilon_r = 140 +/- 6.4 at 3.8 GHz and room temperature. The temperature
dependence of dielectric permittivity shows that the Curie temperature of pure
BTO was shifted by the clamping effect of the MgO substrate, whereas the Curie
temperature shift of the BTO ferroelectric phase in BTO-CFO composites is less
pronounced, and if it exists at all, would be mainly caused by the CFO.
Non-linear dielectric measurements of BTO-CFO show good ferroelectric
properties from BTO.Comment: 6 pages, 6 figures, to be published in the Journal of Materials
Researc
Prediction of the Size Distributions of Methanol-Ethanol Clusters Detected in VUV Laser/Time-of-flight Mass Spectrometry
The size distributions and geometries of vapor clusters equilibrated with methanol−ethanol (Me−Et) liquid mixtures were recently studied by vacuum ultraviolet (VUV) laser time-of-flight (TOF) mass spectrometry and density functional theory (DFT) calculations (Liu, Y.; Consta, S.; Ogeer, F.; Shi, Y. J.; Lipson, R. H. Can. J. Chem. 2007, 85, 843−852). On the basis of the mass spectra recorded, it was concluded that the formation of neutral tetramers is particularly prominent. Here we develop grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) frameworks to compute cluster size distributions in vapor mixtures that allow a direct comparison with experimental mass spectra. Using the all-atom optimized potential for liquid simulations (OPLS-AA) force field, we systematically examined the neutral cluster size distributions as functions of pressure and temperature. These neutral cluster distributions were then used to derive ionized cluster distributions to compare directly with the experiments. The simulations suggest that supersaturation at 12 to 16 times the equilibrium vapor pressure at 298 K or supercooling at temperature 240 to 260 K at the equilibrium vapor pressure can lead to the relatively abundant tetramer population observed in the experiments. Our simulations capture the most distinct features observed in the experimental TOF mass spectra: Et3H+ at m/z = 139 in the vapor corresponding to 10:90% Me−Et liquid mixture and Me3H+ at m/z = 97 in the vapors corresponding to 50:50% and 90:10% Me−Et liquid mixtures. The hybrid GCMC scheme developed in this work extends the capability of studying the size distributions of neat clusters to mixed species and provides a useful tool for studying environmentally important systems such as atmospheric aerosols
Interface enhancement of Gilbert damping from first-principles
The enhancement of Gilbert damping observed for Ni80Fe20 (Py) films in
contact with the non-magnetic metals Cu, Pd, Ta and Pt, is quantitatively
reproduced using first-principles scattering theory. The "spin-pumping" theory
that qualitatively explains its dependence on the Py thickness is generalized
to include a number of factors known to be important for spin transport through
interfaces. Determining the parameters in this theory from first-principles
shows that interface spin-flipping makes an essential contribution to the
damping enhancement. Without it, a much shorter spin-flip diffusion length for
Pt would be needed than the value we calculate independently
An alternative non-Markovianity measure by divisibility of dynamical map
Identifying non-Markovianity with non-divisibility, we propose a measure for
non-Markovinity of quantum process. Three examples are presented to illustrate
the non-Markovianity, measure for non-Markovianity is calculated and discussed.
Comparison with other measures of non-Markovianity is made. Our
non-Markovianity measure has the merit that no optimization procedure is
required and it is finite for any quantum process, which greatly enhances the
practical relevance of the proposed measure.Comment: 6 pages, 3 figue
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