8,396 research outputs found
Nonreciprocal Phase Gradient Metasurface: Principle and Transistor Implementation
We introduce the concept of nonreciprocal nongyrotropic phase gradient
metasurfaces. Such metasurfaces are based on bianisotropic phase shifting unit
cells, with the required nonreciprocal and nongyrotropic characteristics.
Moreover, we present a transistor-based implementation of a nonreciprocal phase
shifting subwavelength unit cell. Finally, we demonstrate the concept with a
simulation of a 6-port spatial circulator application
Angle-Independent Nongyrotropic Metasurfaces
We derive a general condition for angle-independent bianisotropic
nongyrotropic metasurfaces and present two applications corresponding to
particular cases: an angle-independent absorber/amplifier and an
angle-independent spatial gyrator
Adapting to Unknown Smoothness by Aggregation of Thresholded Wavelet Estimators
We study the performances of an adaptive procedure based on a convex
combination, with data-driven weights, of term-by-term thresholded wavelet
estimators. For the bounded regression model, with random uniform design, and
the nonparametric density model, we show that the resulting estimator is
optimal in the minimax sense over all Besov balls under the risk, without
any logarithm factor
Diversity in the outcome of dust radial drift in protoplanetary discs
The growth of dust particles into planet embryos needs to circumvent the
radial-drift barrier, i.e. the accretion of dust particles onto the central
star by radial migration. The outcome of the dust radial migration is governed
by simple criteria between the dust-to-gas ratio and the exponents p and q of
the surface density and temperature power laws. The transfer of radiation
provides an additional constraint between these quantities because the disc
thermal structure is fixed by the dust spatial distribution. To assess which
discs are primarily affected by the radial-drift barrier, we used the radiative
transfer code MCFOST to compute the temperature structure of a wide range of
disc models, stressing the particular effects of grain size distributions and
vertical settling.
We find that the outcome of the dust migration process is very sensitive to
the physical conditions within the disc. For high dust-to-gas ratios (> 0.01)
or flattened disc structures (H/R < 0.05), growing dust grains can efficiently
decouple from the gas, leading to a high concentration of grains at a critical
radius of a few AU. Decoupling of grains can occur at a large fraction (> 0.1)
of the initial radius, for a dust-to-gas ratio greater than ~ 0.05. The exact
value of the required dust-to-gas ratio for dust to stop its migration is
strongly dependent on the disc temperature structure. Non growing dust grains
are accreted for discs with flat surface density profiles (p<0.7) while they
always remain in the disc if the surface density is steep enough (p>1.2). Both
the presence of large grains and vertical settling tend to favour the accretion
of non growing dust grains onto the central object, but it slows down the
migration of growing dust grains. All the disc configurations are found to have
favourable temperature profiles over most of the disc to retain their
planetesimals.Comment: 9 pages, 8 figures, accepted for publications in A&A, corrected typo
Transmissive Suppressed-Order Diffraction Grating (SODG)
We present a novel type of Suppressed-Order Diffraction Grating(SODG). An
SODG is a diffraction grating whose diffraction orders have all been suppressed
except one that is selected to provide electromagnetic deflection. The proposed
SODG is a transmissive grating that exhibits high-efficiency refraction-like
deflection for all angles, including large angles that are generally
challenging to achieve, while featuring a deeply subwavelength thickness, as
required in the microwave regime. We first present the design rationale and
guidelines, and next demonstrate such a 10.5 GHz SODG that reaches an
efficiency of 90% at 70 degrees
Study of the Angular Spectrum of a Bianisotropic Refractive Metasurface at a Dielectric Interface
We present an initial study of the angular spectrum of a bianisotropic
refractive metasurface at an interface between two dielectric media. In this
study, we report on the existence of three distinct angular regions: a)~a
rotated transmission cone, b)~a modified total internal reflection region, and
c)~a new total retro-reflection region
Partial Sums Generation Architecture for Successive Cancellation Decoding of Polar Codes
Polar codes are a new family of error correction codes for which efficient
hardware architectures have to be defined for the encoder and the decoder.
Polar codes are decoded using the successive cancellation decoding algorithm
that includes partial sums computations. We take advantage of the recursive
structure of polar codes to introduce an efficient partial sums computation
unit that can also implements the encoder. The proposed architecture is
synthesized for several codelengths in 65nm ASIC technology. The area of the
resulting design is reduced up to 26% and the maximum working frequency is
improved by ~25%.Comment: Submitted to IEEE Workshop on Signal Processing Systems (SiPS)(26
April 2012). Accepted (28 June 2013
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