15,950 research outputs found
Subtropical middle atmosphere dynamics observed by the Chung Li radar
The Chung Li Radar (24.91 N; 121.24 E) has been operating since 1986. A five beam observational configuration was used on a regular basis to study the various dynamics processes in the atmosphere-lower stratosphere height region. Due to its geographical location, the annual Typhoon and Mei-Yu seasons provide good opportunities to study the various interesting dynamic processes such as instabilities, generation of gravity waves, wave mean field interaction, etc. Three dimensional air motions due to these fronts are presented. Special cases of gravity wave generation, propagation and their effects on the turbulent layers are discussed
Negative reflections of electromagnetic waves in chiral media
We investigate the reflection properties of electromagnetic/optical waves in
isotropic chiral media. When the chiral parameter is strong enough, we show
that an unusual \emph{negative reflection} occurs at the interface of the
chiral medium and a perfectly conducting plane, where the incident wave and one
of reflected eigenwaves lie in the same side of the boundary normal. Using such
a property, we further demonstrate that such a conducting plane can be used for
focusing in the strong chiral medium. The related equations under paraxial
optics approximation are deduced. In a special case of chiral medium, the
chiral nihility, one of the bi-reflections disappears and only single reflected
eigenwave exists, which goes exactly opposite to the incident wave. Hence the
incident and reflected electric fields will cancel each other to yield a zero
total electric field. In another word, any electromagnetic waves entering the
chiral nihility with perfectly conducting plane will disappear.Comment: 5 pages, 5 figure
On the use of colour reflectivity plots to monitor the structure of the troposphere and stratosphere
The radar reflectivity, defined as the range squared corrected power of VHF radar echoes, can be used to monitor and study the temporal development of inversion layer, frontal boundaries and convective turbulence. From typical featurs of upward or downward motion of reflectivity structures, the advection/convection of cold and warm air can be predicted. High resolution color plots appear to be useful to trace and to study the life history of these structures, particularly their persistency, descent and ascent. These displays allow an immediate determination of the tropopause height as well as the determination of the tropopause structure. The life history of warm fronts, cold fronts, and occlusions can be traced, and these reflectivity plots allow detection of even very weak events which cannot be seen in the traditional meteorological data sets. The life history of convective turbulence, particular evolving from the planetary boundary layer, can be tracked quite easily. Its development into strong convection reaching the middle troposphere can be followed and predicted
Simulation of January 1-7, 1978 events
The solar wind disturbances of January 1 to 7, 1978 are reconstructed by a modeling method. First, the interplanetary magnetic field (IMF) background pattern, including a corotating shock, is reproduced using the Stanford source surface map. Then, two solar flares with their onset times on January 1, 0717 UT at S17 deg E10 deg and 2147 UT S17 deg E32 deg, respectively, are selected to generate two interplanetary transient shocks. It is shown that these two shocks interacted with the corotating shock, resulting in a series of interplanetary events observed by four spacecraft, Helios 1 and 2, IMP-8 (Interplanetary Monitoring Platform 8), and Voyager 2. Results show that these three shock waves interact and coalesce in interplanetary space such that Helios 2 and Voyager 2 observed only one shock and Helios 1 and IMP-8 observed two shocks. All shocks observed by the four spacecraft, except the corotating shock at Helios 1, are either a transient shock or a shock which is formed from coalescing of the transient shocks with the corotating shock. The method is useful in reconstructing a very complicated chain of interplanetary events observed by a number of spacecraft
The first operation and results of the Chung-Li VHF radar
The Chung-Li Very High Frequency (VHF) radar is used in the dual-mode operations, applying Doppler beam-swinging as well as the spaced-antenna-drift method. The design of the VHF radar is examined. Results of performance tests are discussed
Exciton gas transport through nano-constrictions
An indirect exciton is a bound state of an electron and a hole in spatially
separated layers. Two-dimensional indirect excitons can be created optically in
heterostructures containing double quantum wells or atomically thin
semiconductors. We study theoretically transmission of such bosonic
quasiparticles through nano-constrictions. We show that quantum transport
phenomena, e.g., conductance quantization, single-slit diffraction, two-slit
interference, and the Talbot effect, are experimentally realizable in systems
of indirect excitons. We discuss similarities and differences between these
phenomena and their counterparts in electronic devices.Comment: (v2) Updated title, text, and references; 12 pages, 9 figure
Exclusive Lambda_b -> Lambda l^+ l^- decay in two Higgs doublet model
Rare Lambda_b -> Lambda l^+ l^- decay is investigated in framework of general
two Higgs doublet model, in which a new source of CP violation exists (model
III). The polarization parameter, CP asymmetry and decay width are calculated.
It is shown that CP asymmetry is a very sensitive tool for establishing model
III.Comment: 16 pages, 3 figures, LaTeX formatte
On the Classical Algebra
We consider the classical \w42 algebra from the integrable system viewpoint.
The integrable evolution equations associated with the \w42 algebra are
constructed and the Miura maps , consequently modifications, are presented.
Modifying the Miura maps, we give a free field realization the classical \w42
algebra. We also construct the Toda type integrable systems for it.Comment: 14 pages, latex, no figure
Kinetic pinning and biological antifreezes
Biological antifreezes protect cold-water organisms from freezing. An example
are the antifreeze proteins (AFPs) that attach to the surface of ice crystals
and arrest growth. The mechanism for growth arrest has not been heretofore
understood in a quantitative way. We present a complete theory based on a
kinetic model. We use the `stones on a pillow' picture. Our theory of the
suppression of the freezing point as a function of the concentration of the AFP
is quantitatively accurate. It gives a correct description of the dependence of
the freezing point suppression on the geometry of the protein, and might lead
to advances in design of synthetic AFPs.Comment: 4 pages, 4 figure
Electronic Structure of KFeSe from First Principles Calculations
Electronic structure and magnetic properties for iron-selenide KFeSe
are studied by first-principles calculations. The ground state is stripe-like
antiferromagnetic with calculated 2.26 magnetic moment on Fe atoms; and
the , coupling strengths are calculated to be 0.038 eV and 0.029 eV.
The states around are dominated by the Fe-3d orbitals which hybridize
noticeably to the Se-4p orbitals. While the band structure of KFeSe is
similar to a heavily electron-doped BaFeAs or FeSe system, the Fermi
surface of KFeSe is much closer to \fs11 system since the electron
sheets around is symmetric with respect to - exchange. These
features, as well as the absence of Fermi surface nesting, suggest that the
parental KFeSe could be regarded as an electron over-doped 11 system
with possible local moment magnetism.Comment: accepted by Chinese Physics Letter, to appear as Chinese Physics
Letter, Vol 28, page 057402 (2011
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