30,070 research outputs found
Experimental investigation of piloted flameholders
Four configurations of piloted flameholders were tested. The range of flame stabilization, flame propagation, pressure oscillation during ignition, and pressure drop of the configurations were determined. Some tests showed a very strong effect of inlet flow velocity profile and flameholder geometry on flame stabilization. These tests led to the following conclusions. (1) The use of a piloted flameholder in the turbofan augmentor may minimize the peak pressure rise during ignition. At the present experimental conditions, delta P/P asterisk over 2 is less than 10 percent; therefore, the use of a piloted flameholder is a good method to realize soft ignition. (2) The geometry of the piloted flameholder and the amount of fuel injected into the flameholder have a strong effect on the pressure oscillation during ignition of the fuel-air mixture in the secondary zone. (3) Compared with the V-gutter flameholder with holes in its wall, the V-gutter flameholder without holes not only has advantages such as simple structure and good rigidity but offers a wide combustion stability limit and a high capability of igniting the fuel-air mixture of the secondary zone
Gate-controllable spin-battery
We propose a gate-controllable spin-battery for spin current. The
spin-battery consists of a lateral double quantum dot under a uniform magnetic
field. A finite DC spin-current is driven out of the device by controlling a
set of gate voltages. Spin-current can also be delivered in the absence of
charge-current. The proposed device should be realizable using present
technology at low temperature.Comment: 3 pages, 3 figures, accepted by Appl. Phys. Let
Quantum Information Approach to Bose-Einstein Condensate in a Tilted Double-Well System
We study the ground state properties of bosons in a tilted double-well
system. We use fidelity susceptibility to identify the possible ground state
transitions under different tilt values. For a very small tilt (for example
), two transitions are found. For a moderate tilt (for example
), only one transition is found. For a large tilt (for example
), no transition is found. We explain this by analyzing the spectrum
of the ground state. The quantum discord and total correlation of the ground
state under different tilts are also calculated to indicate those transitions.
In the transition region, both quantities have peaks decaying exponentially
with particle number . This means for a finite-size system the transition
region cannot be explained by the mean-field theory, but in the large- limit
it can be.Comment: 5 pages, 5 figures, slightly different from the published versio
Indirect exchange of magnetic impurities in zigzag graphene ribbon
We use quantum Monte Carlo method to study the indirect coupling between two
magnetic impurities on the zigzag edge of graphene ribbon, with respect to the
chemical potential . We find that the spin-spin correlation between two
adatoms located on the nearest sites in the zigzag edge are drastically
suppressed around the zero-energy. As we switch the system away from
half-filling, the antiferromagnetic correlation is first enhanced and then
decreased. If the two adatoms are adsorbed on the sites belonging to the same
sublattice, we find similar behavior of spin-spin correlation except for a
crossover from ferromagnetic to antiferromagentic correlation in the vicinity
of zero-energy. We also calculated the weight of different components of
d-electron wave function and local magnet moment for various values of
parameters, and all the results are consistent with those of spin-spin
correlation between two magnetic impurities.Comment: 3 pages, 4 figures, conference proceedin
Nuclear /EC decays in covariant density functional theory and the impact of isoscalar proton-neutron pairing
Self-consistent proton-neutron quasiparticle random phase approximation based
on the spherical nonlinear point-coupling relativistic Hartree-Bogoliubov
theory is established and used to investigate the /EC-decay half-lives
of neutron-deficient Ar, Ca, Ti, Fe, Ni, Zn, Cd, and Sn isotopes. The isoscalar
proton-neutron pairing is found to play an important role in reducing the decay
half-lives, which is consistent with the same mechanism in the decays
of neutron-rich nuclei. The experimental /EC-decay half-lives can be
well reproduced by a universal isoscalar proton-neutron pairing strength.Comment: 12 pages, 4 figure
An Astrometric Approach to Measuring the Color of an Object
The color of a star is a critical feature to reflect its physical property
such as the temperature. The color index is usually obtained via absolute
photometry, which is demanding for weather conditions and instruments. In this
work, we present an astrometric method to measure the catalog-matched color
index of an object based on the effect of differential color refraction (DCR).
Specifically, we can observe an object using only one filter or alternately
using two different filters. Through the difference of the DCR effect compared
with reference stars, the catalog-matched color index of an object can be
conveniently derived. Hence, we can perform DCR calibration and obtain its
accurate and precise positions even if observed with Null filter during a large
range of zenith distances, by which the limiting magnitude and observational
efficiency of the telescope can be significantly improved. This method takes
advantage of the DCR effect and builds a link between astrometry and
photometry. In practice, we measure the color indices and positions of Himalia
(the sixth satellite of Jupiter) using 857 CCD frames over 8 nights by two
telescopes. Totally, the mean color index BP-RP (Gaia photometric system) of
Himalia is 0.750 \pm 0.004 magnitude. Through the rotational phased color index
analysis, we find two places with their color indices exceeding the mean \pm 3
\sigma.Comment: 10 pages, 5 figures, 4 table
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