37,037 research outputs found
The spatial distribution of quasi-biennial oscillations in the high-latitude solar activity
Quasi-biennial oscillations (QBOs) are considered as a fundamental mode of
solar magnetic activity at low latitudes (). However, the
evolutionary aspect and the hemispheric distribution of solar QBOs at high
latitudes () are rarely studied. Here, a relatively novel
time-frequency analysis technique, named the synchrosqueezed wavelet transform,
is applied to extract the main components of the polar faculae in the northern
and southern hemispheres for the time interval from August 1951 to December
1998. It is found as the following: (1) Apart from the 22-year Hale cycle, the
17-year extended activity cycle, and the 11-year Schwabe cycle, the QBOs have
been estimated as a prominent timescale of solar magnetic activity at high
latitudes; (2) the QBOs of the polar faculae are coherent in the two
hemispheres, but the temporal (phase) and the spatial (amplitude) variations of
solar QBOs occur unevenly on both hemispheres; and (3) for the 11-year period
mode, the northern hemisphere begins three months earlier than that in the
southern one. Moreover, the spatial and temporal distributions of the
hemispheric QBOs differ from those of the 11-year Schwabe cycle mode in the two
hemispheres. Our findings could be helpful to improve our knowledge on the
physical origin of the spatial distribution of solar QBOs at high latitudes,
and could also provide more constraints on solar dynamo models introduced to
characterize the different components of the solar magnetic activity cycle.Comment: MNRA
Spinor Bose-Einstein Condensates of Rotating Polar Molecules
We propose a scheme to realize a pseudospin- model of the
bialkali polar molecules with the spin states corresponding
to two sublevels of the first excited rotational level. We show that the
effective dipole-dipole interaction between two spin- molecules couples
the rotational and orbital angular momenta and is highly tunable via a
microwave field. We also investigate the ground state properties of a
spin- molecular condensate. A variety of nontrivial quantum phases,
including the doubly-quantized vortex states, are discovered. Our scheme can
also be used to create spin- model of polar molecules. Thus, we show that
the ultracold gases of bialkali polar molecules provide a unique platform for
studying the spinor condensates of rotating molecules.Comment: 5 pages plus 5 page supplemental material, 4 figure
quantum interference in bosonic and fermionic matter-wave amplification
We investigate the quantum interference effects in two types of matter-wave
mixing experiments: one with initial matter waves prepared in independent Fock
states (type I) and the other with each individual particle prepared in a same
coherent superposition of states (type II). In the type I experiment, a
symmetric wavefunction of bosons leads to constructive quantum interference and
shows final state stimulation, while an anti-symmetric wavefunction of fermions
results in destructive quantum interference and inhibited matter wave mixing.
In the type II experiment, a coherent superposition state leads to constructive
quantum interference and enhanced matter wave mixing for both bosons and
fermions, independent of their quantum statistics.Comment: 4 pages, 2 figure
Real-Reward Testing for Probabilistic Processes (Extended Abstract)
We introduce a notion of real-valued reward testing for probabilistic
processes by extending the traditional nonnegative-reward testing with negative
rewards. In this richer testing framework, the may and must preorders turn out
to be inverses. We show that for convergent processes with finitely many states
and transitions, but not in the presence of divergence, the real-reward
must-testing preorder coincides with the nonnegative-reward must-testing
preorder. To prove this coincidence we characterise the usual resolution-based
testing in terms of the weak transitions of processes, without having to
involve policies, adversaries, schedulers, resolutions, or similar structures
that are external to the process under investigation. This requires
establishing the continuity of our function for calculating testing outcomes.Comment: In Proceedings QAPL 2011, arXiv:1107.074
Nitric Oxide in Climatological Global Energy Budget During 1982-2013
Over the past decades, temperature and density of the upper atmosphere show
negative trends and decrease of the upper atmospheric temperature is attributed
to the declining neutral density. Specifically, nitric oxide (NO) and carbon
dioxide (CO2) govern thermospheric cooling at 5.3 and 15 micron, respectively.
While a lot of efforts have focused on the CO2 effects on the long-term trends,
relatively less attention has been paid to the impacts by NO, which responds to
solar and geomagnetic activities dynamically. In this study, we investigate the
role of NO in climatological global energy budget for the recent three solar
cycles using the Global Ionosphere Thermosphere Model. From 1982 to 2013, the
F10.7 and Ap indices showed a decadal decrease of ~8% and ~20%, respectively.
By imposing temporal-varying F10.7 and Ap values in the simulations, we find a
decadal change of -0.28x1011 W or -17.3% in total NO cooling power, which
agrees well with that (-0.34x1011 W or -17.2%) from the empirical Thermosphere
Climate Index derived from the TIMED/SABER data. Neutral density decreases by
10-20% at 200-450km and Tex decreases by 25.3 K per decade. The deduced-decadal
change of NO cooling reaches ~25% of the sum of total heating at ~130 km and
its significance decreases with altitude.Comment: 3 figures, submitted to Geophysical Research Letter
The asymmetric structure of the Galactic halo
Using the stellar photometry catalogue based on the latest data release (DR4)
of the Sloan Digital Sky Survey (SDSS), a study of the Galactic structure using
star counts is carried out for selected areas of the sky. The sample areas are
selected along a circle at a Galactic latitude of +60, and 10 strips of
high Galactic latitude along different longitudes. Direct statistics of the
data show that the surface densities of from to
are systematically higher than those of from
to , defining a region of overdensity (in the direction of Virgo)
and another one of underdensity (in the direction of Ursa Major) with respect
to an axisymmetric model. It is shown by comparing the results from star counts
in the colour that the density deviations are due to an asymmetry of
the stellar density in the halo. Theoretical models for the surface density
profile are built and star counts are performed using a triaxial halo of which
the parameters are constrained by observational data. Two possible reasons for
the asymmetric structure are discussed.Comment: 17 pages, 7 figures, 5 tables, MNRAS accepte
Enhanced magnetic ordering in Sm metal under extreme pressure
The dependence of the magnetic ordering temperature To of Sm metal was
determined through four-point electrical resistivity measurements to pressures
as high as 150 GPa. A strong increase in To with pressure is observed above 85
GPa. In this pressure range Sm ions alloyed in dilute concentration with
superconducting Y exhibit giant Kondo pair breaking. Taken together, these
results suggest that for pressures above 85 GPa Sm is in a highly correlated
electron state, like a Kondo lattice, with an unusually high value of To. A
detailed comparison is made with similar results obtained earlier on Nd, Tb and
Dy and their dilute magnetic alloys with superconducting Y
Tunable topological phases with fermionic atoms in a one-dimensional flux lattice
We present a simple scheme for implementing a one-dimensional (1D)
magnetic-flux lattice of ultracold fermionic spin- atoms. The resulting
tight-binding model supports gapped and gapless topological phases, and chiral
currents for Meissner and vortex phases. Its single-particle spectra exhibit
topological flat bands at small flux, and the flatness sensitively depends on
hopping strength. An effective -wave interaction arises in a -wave paired
superfluid. Treating atomic internal states as forming a synthetic dimension
and balancing the interplay of magnetic flux and Zeeman field, our model
describes a tunable topological Fermi superfluid, which paves the way towards
experimental explorations of non-Abelian topological matter in 1D atomic
quantum gases.Comment: 6 pages, 4 figure
Invariant measures and long time behaviour for the Benjamin-Ono equation III
We complete the program developed in our previous works aiming to construct
an infinite sequence of invariant measures of gaussian type associated with the
conservation laws of the Benjamin-Ono equation
The time series forecasting: from the aspect of network
Forecasting can estimate the statement of events according to the historical
data and it is considerably important in many disciplines. At present, time
series models have been utilized to solve forecasting problems in various
domains. In general, researchers use curve fitting and parameter estimation
methods (moment estimation, maximum likelihood estimation and least square
method) to forecast. In this paper, a new sight is given to the forecasting and
a completely different method is proposed to forecast time series. Inspired by
the visibility graph and link prediction, this letter converts time series into
network and then finds the nodes which are mostly likelihood to link with the
predicted node. Finally, the predicted value will be obtained according to the
state of the link. The TAIEX data set is used in the case study to illustrate
that the proposed method is effectiveness. Compared with ARIMA model, the
proposed shows a good forecasting performance when there is a small amount of
data
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