4,412 research outputs found
MIMO Spatial Diversity Communications - Signal Processing and Channel Capacity
This paper derives an equivalent discrete channel model for MIMO spatial diversity communications generally considering multidimensional spatial branch symbols and arbitrary path delays. This model is subsequently used for the information capacity evaluation under various special cases
Dominant particle-hole contributions to the phonon dynamics in the spinless one-dimensional Holstein model
In the spinless Holstein model at half-filling the coupling of electrons to
phonons is responsible for a phase transition from a metallic state at small
coupling to a Peierls distorted insulated state when the electron-phonon
coupling exceeds a critical value. For the adiabatic case of small phonon
frequencies, the transition is accompanied by a phonon softening at the
Brillouin zone boundary whereas a hardening of the phonon mode occurs in the
anti-adiabatic case. The phonon dynamics studied in this letter do not only
reveal the expected renormalization of the phonon modes but also show
remarkable additional contributions due to electronic particle-hole
excitations.Comment: 7 pages, 4 figures and 1 table included; v2: discussion of Luttinger
liquid parameters adde
The green corona data: 1947-1976, revisited
Re-examining a continuous monthly data set for the
green-line corona brightness, covering February 1947 to September 1976, we have found that practically no delay exists between the trends of the green-line coronal intensity in the equatorial and middle-latitude belts at the beginning of solar activity cycle No. 20, while a
previous cycle (No. 19) shows a sudden increase in the corona intensity brightness at middle latitudes followed by a delayed one at the equatorial belts, supporting recent
findings on even-odd solar cycle differences observed in the half-yearly green corona database (1943-1993). The north-south asymmetry in the hemispheric solar activity is
not involved in this phenomenon
Surges and Si IV bursts in the solar atmosphere. Understanding IRIS and SST observations through RMHD experiments
Surges often appear as a result of the emergence of magnetized plasma from
the solar interior. Traditionally, they are observed in chromospheric lines
such as H 6563 \AA and Ca II 8542 \AA. However, whether there is a
response to the surge appearance and evolution in the Si IV lines or, in fact,
in many other transition region lines has not been studied. In this paper we
analyze a simultaneous episode of an H surge and a Si IV burst that
occurred on 2016 September 03 in active region AR12585. To that end, we use
coordinated observations from the Interface Region Imaging Spectrograph (IRIS)
and the Swedish 1-m Solar Telescope (SST). For the first time, we report
emission of Si IV within the surge, finding profiles that are brighter and
broader than the average. Furthermore, the brightest Si IV patches within the
domain of the surge are located mainly near its footpoints. To understand the
relation between the surges and the emission in transition region lines like Si
IV, we have carried out 2.5D radiative MHD (RMHD) experiments of magnetic flux
emergence episodes using the Bifrost code and including the non-equilibrium
ionization of silicon. Through spectral synthesis we explain several features
of the observations. We show that the presence of Si IV emission patches within
the surge, their location near the surge footpoints and various observed
spectral features are a natural consequence of the emergence of magnetized
plasma from the interior to the atmosphere and the ensuing reconnection
processes.Comment: 13 pages, 8 figures. The Astrophysical Journal (Accepted
The stellar atmosphere simulation code Bifrost
Context: Numerical simulations of stellar convection and photospheres have
been developed to the point where detailed shapes of observed spectral lines
can be explained. Stellar atmospheres are very complex, and very different
physical regimes are present in the convection zone, photosphere, chromosphere,
transition region and corona. To understand the details of the atmosphere it is
necessary to simulate the whole atmosphere since the different layers interact
strongly. These physical regimes are very diverse and it takes a highly
efficient massively parallel numerical code to solve the associated equations.
Aims: The design, implementation and validation of the massively parallel
numerical code Bifrost for simulating stellar atmospheres from the convection
zone to the corona.
Methods: The code is subjected to a number of validation tests, among them
the Sod shock tube test, the Orzag-Tang colliding shock test, boundary
condition tests and tests of how the code treats magnetic field advection,
chromospheric radiation, radiative transfer in an isothermal scattering
atmosphere, hydrogen ionization and thermal conduction.
Results: Bifrost completes the tests with good results and shows near linear
efficiency scaling to thousands of computing cores
Landscape phage, phage display, stripped phage, biosensors, detection, affinity reagent, nanotechnology, Salmonella typhimurium, Bacillus anthracis
Filamentous phage, such as fd used in this study, are thread-shaped bacterial
viruses. Their outer coat is a tube formed by thousands equal copies of the
major coat protein pVIII. We constructed libraries of random peptides fused to
all pVIII domains and selected phages that act as probes specific for a panel
of test antigens and biological threat agents. Because the viral carrier is
infective, phage borne bio-selective probes can be cloned individually and
propagated indefinitely without needs of their chemical synthesis or
reconstructing. We demonstrated the feasibility of using landscape phages and
their stripped fusion proteins as new bioselective materials that combine
unique characteristics of affinity reagents and self assembling membrane
proteins. Biorecognition layers fabricated from phage-derived probes bind
biological agents and generate detectable signals. The performance of
phage-derived materials as biorecognition films was illustrated by detection of
streptavidin-coated beads, Bacillus anthracis spores and Salmonella typhimurium
cells. With further refinement, the phage-derived analytical platforms for
detecting and monitoring of numerous threat agents may be developed, since the
biodetector films may be obtained from landscape phages selected against any
bacteria, virus or toxin. As elements of field-use detectors, they are superior
to antibodies, since they are inexpensive, highly specific and strong binders,
resistant to high temperatures and environmental stresses.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
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