24,257 research outputs found
Interaction of a vortex induced by a rotating cylinder with a plane
In this article,we study theoretically and numerically the interaction of a
vortex induced by a rotating cylinder with a perpendicular plane. We show the
existence of weak solutions to the swirling vortex models by using the Hopf
extension method, and by an elegant contradiction argument, respectively. We
demonstrate numerically that the model could produce phenomena of swirling
vortex including boundary layer pumping and two-celled vortex that are observed
in potential line vortex interacting with a plane and in a tornado
The observed spiral structure of the Milky Way
The spiral structure of the Milky Way is not yet well determined. The keys to
understanding this structure are to increase the number of reliable spiral
tracers and to determine their distances as accurately as possible. HII
regions, giant molecular clouds (GMCs), and 6.7-GHz methanol masers are closely
related to high mass star formation, and hence they are excellent spiral
tracers. We update the catalogs of Galactic HII regions, GMCs, and 6.7-GHz
methanol masers, and then outline the spiral structure of the Milky Way. We
collected data for more than 2500 known HII regions, 1300 GMCs, and 900 6.7-GHz
methanol masers. If the photometric or trigonometric distance was not yet
available, we determined the kinematic distance using a Galaxy rotation curve
with the current IAU standard, = 8.5 kpc and = 220 km
s, and the most recent updated values of = 8.3 kpc and
= 239 km s, after we modified the velocities of tracers with the adopted
solar motions. With the weight factors based on the excitation parameters of
HII regions or the masses of GMCs, we get the distributions of these spiral
tracers. The distribution of tracers shows at least four segments of arms in
the first Galactic quadrant, and three segments in the fourth quadrant. The
Perseus Arm and the Local Arm are also delineated by many bright HII regions.
The arm segments traced by massive star forming regions and GMCs are able to
match the HI arms in the outer Galaxy. We found that the models of three-arm
and four-arm logarithmic spirals are able to connect most spiral tracers. A
model of polynomial-logarithmic spirals is also proposed, which not only
delineates the tracer distribution, but also matches the observed tangential
directions.Comment: 22 Pages, 16 Figures, 7 Tables, updated to match the published
versio
Tunable Fano-Kondo resonance in side-coupled double quantum dot system
We study the interference between the Fano and Kondo effects in a
side-coupled double-quantum- dot system where one of the quantum dots couples
to conduction electron bath while the other dot only side-couples to the first
dot via antiferromagnetic (AF) spin exchange coupling. We apply both the
perturbative renormalization group (RG) and numerical renormalization group
(NRG) approaches to study the effect of AF coupling on the Fano lineshape in
the conduction leads. With particle-hole symmetry, the AF exchange coupling
competes with the Kondo effect and leads to a local spin-singlet ground state
for arbitrary small coupling, so called "two-stage Kondo effect". As a result,
via NRG we find the spectral properties of the Fano lineshape in the tunneling
density of states (TDOS) of conduction electron leads shows double dip-peak
features at the energy scale around the Kondo temperature and the one much
below it, corresponding to the two-stage Kondo effect; it also shows an
universal scaling behavior at very low energies. We find the qualitative
agreement between the NRG and the perturbative RG approach. Relevance of our
work to the experiments is discussed.Comment: 7 pages, 7 figure
Purchasing Power Parity and Country Characteristics: Evidence from Time Series Analysis
This paper investigates the relationships between country characteristics and the validity of PPP. We use three alternative time series methods to test for the stationarity of real exchange rates for each of the 72 countries over the period from 1976 to 2005. Our result shows that the evidence of PPP exhibits geographic difference. It is most likely to find stationary real exchange rates for European countries, whereas it is least likely to obtain the result of supporting PPP for Asian countries. We then use a probit regression model to examine if county characteristics are related to the validity of PPP. The probit regression result reveals that the validity of PPP decreases with inflation rate and increases with nominal exchange rate volatility.Purchasing power parity, Country characteristics, Unit root tests
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