6,431 research outputs found
Eddy turbulence, the double mesopause, and the double layer of atomic oxygen
In this study, we consider the impact of eddy turbulence on temperature and
atomic oxygen distribution when the peak of the temperature occurs in the
upper mesosphere. A previous paper (Vlasov and Kelley, 2010) considered the
simultaneous impact of eddy turbulence on temperature and atomic oxygen
density and showed that eddy turbulence provides an effective mechanism to
explain the cold summer and warm winter mesopause observed at high
latitudes. Also, the prevalent role of eddy turbulence in this case removes
the strong contradiction between seasonal variations of the O density
distribution and the impact of upward/downward motion corresponding to
adiabatic cooling/heating of oxygen atoms. Classically, there is a single
minimum in the temperature profile marking the location of the mesopause.
But often, a local maximum in the temperature is observed in the height
range of 85–100 km, creating the appearance of a double mesopause (Bills
and Gardner, 1993; Yu and She, 1995; Gusev et al., 2006). Our results show
that the relative temperature maximum in the upper mesosphere (and thus the
double mesopause) can result from heating by eddy turbulence. According to
our model, there is a close connection between the extra temperature peak in
the mesosphere and the oxygen atom density distribution. The main feature of
the O density height profile produced by eddy turbulence in our model is a
double peak instead of a single peak of O density. A rocket experiment
called TOMEX confirms these results (Hecht et al., 2004). Applying our model
to the results of the TOMEX rocket campaign gives good agreement with both
the temperature and oxygen profiles observed. Climatology of the midlatitude
mesopause and green line emission shows that the double mesopause and the
double layers of the green line emission, corresponding to the double O
density height profile, are mainly observed in spring and fall (Yu and She,
1995; Liu and Shepherd, 2006). Further observations of the oxygen atom
densities and the double mesopause would improve our understanding of the
impact of turbulence on critical mesospheric parameters
Mode mixing in asymmetric double trench photonic crystal waveguides
e investigate both experimentally and theoretically the waveguiding
properties of a novel double trench waveguide where a conventional single-mode
strip waveguide is embedded in a two dimensional photonic crystal (PhC) slab
formed in silicon on insulator (SOI) wafers. We demonstrate that the bandwidth
for relatively low-loss (50dB/cm) waveguiding is significantly expanded to
250nm covering almost all the photonic band gap owing to nearly linear
dispersion of the TE-like waveguiding mode. The flat transmission spectrum
however is interrupted by numerous narrow stop bands. We found that these stop
bands can be attributed to anti-crossing between TE-like (positive parity) and
TM-like (negative parity) modes. This effect is a direct result of the strong
asymmetry of the waveguides that have an upper cladding of air and lower
cladding of oxide. To our knowledge this is the first demonstration of the
effects of cladding asymmetry on the transmission characteristics of the PhC
slab waveguides.Comment: 7 pages, 6 figure
Geolocation applications of the Gonets LEO messaging satellites
Geostationary satellites carry a majority of the international telecommunications traffic not carried by transoceanic cable. However, because the radio path links to and from geostationary satellites total at least 70,000 km and because of inherent on-board spacecraft power limitations, earth stations used in conjunction with geostationary satellites are usually large and expensive. This limits their installation to areas with a well-developed industrial and economic infrastructure. This reality helps perpetuate a chicken egg dilemma for the developing countries and isolated regions. Economic integration with the developed world requires being 'networked'. But for many developing entities, even the initial price of entry exceeds their modest resources. Exclusion from the global information highways virtually assures retardation of economic growth for developing nations, remote and isolated areas. Very Small Aperture Terminal (VSAT) earth stations are often thought of as a solution for networking developing regions. But economic considerations often forecloses this option. If VSAT size and cost is to be minimized, powerful spot beams from the satellite need to be focused on relatively small regions. This is not often feasible because of the high cost of the satellite itself. To dedicate a high power spot beam to a small region is usually not economically feasible
Eddy turbulence parameters inferred from radar observations at Jicamarca
Significant electron density striations, neutral temperatures 27 K above nominal, and intense wind shear were observed in the E-region ionosphere over the Jicamarca Radio Observatory during an unusual event on 26 July 2005 (Hysell et al., 2007). In this paper, these results are used to estimate eddy turbulence parameters and their effects. Models for the thermal balance in the mesosphere/lower thermosphere and the charged particle density in the E region are developed here. The thermal balance model includes eddy conduction and viscous dissipation of turbulent energy as well as cooling by infrared radiation. The production and recombination of ions and electrons in the E region, together with the production and transport of nitric oxide, are included in the plasma density model. Good agreement between the model results and the experimental data is obtained for an eddy diffusion coefficient of about 1&times;10<sup>3</sup> m<sup>2</sup>/s at its peak, which occurs at an altitude of 107 km. This eddy turbulence results in a local maximum of the temperature in the upper mesosphere/lower thermosphere and could correspond either to an unusually high mesopause or to a double mesosphere. Although complicated by plasma dynamic effects and ongoing controversy, our interpretation of Farley-Buneman wave phase velocity (Hysell et al., 2007) is consistent with a low Brunt-Väisälä frequency in the region of interest. Nitric oxide transport due to eddy diffusion from the lower thermosphere to the mesosphere causes electron density changes in the E region whereas NO density modulation due to irregularities in the eddy diffusion coefficient creates variability in the electron density
Vlasov Equation In Magnetic Field
The linearized Vlasov equation for a plasma system in a uniform magnetic
field and the corresponding linear Vlasov operator are studied. The spectrum
and the corresponding eigenfunctions of the Vlasov operator are found. The
spectrum of this operator consists of two parts: one is continuous and real;
the other is discrete and complex. Interestingly, the real eigenvalues are
infinitely degenerate, which causes difficulty solving this initial value
problem by using the conventional eigenfunction expansion method. Finally, the
Vlasov equation is solved by the resolvent method.Comment: 15 page
Quantum gates and quantum algorithms with Clifford algebra technique
We use our Clifford algebra technique, that is nilpotents and projectors
which are binomials of the Clifford algebra objects with the
property , for representing quantum
gates and quantum algorithms needed in quantum computers in an elegant way. We
identify -qubits with spinor representations of the group SO(1,3) for a
system of spinors. Representations are expressed in terms of products of
projectors and nilpotents. An algorithm for extracting a particular information
out of a general superposition of qubit states is presented. It
reproduces for a particular choice of the initial state the Grover's algorithm.Comment: 9 pages, revte
Estimates of eddy turbulence consistent with seasonal variations of atomic oxygen and its possible role in the seasonal cycle of mesopause temperature
According to current understanding, adiabatic cooling and heating
induced by the meridional circulation driven by gravity waves is the major
process for the cold summer and warm winter polar upper mesosphere. However,
our calculations show that the upward/downward motion needed for adiabatic
cooling/heating of the summer/winter polar mesopause simultaneously induces
a seasonal variation in both the O maximum density and the altitude of the
[O] peak that is opposite to the observed variables generalized by the
MSISE-90 model. It is usually accepted that eddy turbulence can produce the
[O] seasonal variations. Using this approach, we can infer the eddy
diffusion coefficient for the different seasons. Taking these results and
experimental data on the eddy diffusion coefficient, we consider in detail
and estimate the heating and cooling caused by eddy turbulence in the summer
and winter polar upper mesosphere. The seasonal variations of these
processes are similar to the seasonal variations of the temperature and
mesopause. These results lead to the conclusion that heating/cooling by eddy
turbulence is an important component in the energy budget and that adiabatic
cooling/heating induced by upward/downward motion cannot dominate in the
mesopause region. Our study shows that the impact of the dynamic process,
induced by gravity waves, on [O] distributions must be included in models of
thermal balance in the upper mesosphere and lower thermosphere (MLT) for a
consistent description because (a) the [O] distribution is very sensitive to
dynamic processes, and (b) atomic oxygen plays a very important role in
chemical heating and infrared cooling in the MLT. To our knowledge, this is
the first attempt to consider this aspect of the problem
Faraday rotation, stochastic magnetic fields and CMB maps
The high- and low-frequency descriptions of the pre-decoupling plasma are
deduced from the Vlasov-Landau treatment generalized to curved space-times and
in the presence of the relativistic fluctuations of the geometry. It is
demonstrated that the interplay between one-fluid and two-fluid treatments is
mandatory for a complete and reliable calculation of the polarization
observables. The Einstein-Boltzmann hierarchy is generalized to handle the
dispersive propagation of the electromagnetic disturbances in the
pre-decoupling plasma. Given the improved physical and numerical framework, the
polarization observables are computed within the magnetized CDM
paradigm (mCDM). In particular, the Faraday-induced B-mode is
consistently estimated by taking into account the effects of the magnetic
fields on the initial conditions of the Boltzmann hierarchy, on the dynamical
equations and on the dispersion relations. The complete calculations of the
angular power spectra constitutes the first step for the derivation of
magnetized maps of the CMB temperature and polarization which are here obtained
for the first time and within the minimal mCDM model. The obtained
results set the ground for direct experimental scrutiny of large-scale
magnetism via the low and high frequency instruments of the Planck explorer
satellite.Comment: 53 pages, 15 included figure
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