8,061 research outputs found
An Upper Bound to Zero-Delay Rate Distortion via Kalman Filtering for Vector Gaussian Sources
We deal with zero-delay source coding of a vector Gaussian autoregressive
(AR) source subject to an average mean squared error (MSE) fidelity criterion.
Toward this end, we consider the nonanticipative rate distortion function
(NRDF) which is a lower bound to the causal and zero-delay rate distortion
function (RDF). We use the realization scheme with feedback proposed in [1] to
model the corresponding optimal "test-channel" of the NRDF, when considering
vector Gaussian AR(1) sources subject to an average MSE distortion. We give
conditions on the vector Gaussian AR(1) source to ensure asymptotic
stationarity of the realization scheme (bounded performance). Then, we encode
the vector innovations due to Kalman filtering via lattice quantization with
subtractive dither and memoryless entropy coding. This coding scheme provides a
tight upper bound to the zero-delay Gaussian RDF. We extend this result to
vector Gaussian AR sources of any finite order. Further, we show that for
infinite dimensional vector Gaussian AR sources of any finite order, the NRDF
coincides with the zero-delay RDF. Our theoretical framework is corroborated
with a simulation example.Comment: 7 pages, 6 figures, accepted for publication in IEEE Information
Theory Workshop (ITW
Low-damping transmission of spin waves through YIG/Pt-based layered structures for spin-orbit-torque applications
We show that in YIG-Pt bi-layers, which are widely used in experiments on the
spin transfer torque and spin Hall effects, the spin-wave amplitude
significantly decreases in comparison to a single YIG film due to the
excitation of microwave eddy currents in a Pt coat. By introducing a novel
excitation geometry, where the Pt layer faces the ground plane of a microstrip
line structure, we suppressed the excitation of the eddy currents in the Pt
layer and, thus, achieved a large increase in the transmission of the
Damon-Eshbach surface spin wave. At the same time, no visible influence of an
external dc current applied to the Pt layer on the spin-wave amplitude in the
YIG-Pt bi-layer was observed in our experiments with YIG films of micrometer
thickness
Constrained Dynamics of Tachyon Field in FRWL Spacetime
In this paper we continue study of tachyon scalar field described by a
Dirac-Born-Infeld (DBI) type action with constraints in the cosmological
context. The proposed extension of the system introducing an auxiliary field in
the minisuperspace framework is discussed. A new equivalent set of constraints
is constructed, satisfying the usual regularity conditions.Comment: 10 pages, to be published in the Special Issue of the Facta
Universitatis Series: Physics, Chemistry and Technology devoted to the
SEENET-MTP Balkan Workshop BSW2019 (3-14 June 2018, Nis, Serbia
The shape of Fe K line emitted from relativistic accretion disc around AGN black holes
The relativistically broadened Fe K line, originating from the
accretion disc in a vicinity of a super massive black hole, is observed in only
less than 50\% of type 1 Active Galactic Nuclei (AGN). In this study we
investigate could this lack of detections be explained by the effects of
certain parameters of the accretion disc and black hole, such as the
inclination, the inner and outer radius of disc and emissivity index. In order
to determine how these parameters affect the Fe K line shape, we
simulated about 60,000 Fe K line profiles emitted from the
relativistic disc.
Based on simulated line profiles, we conclude that the lack of the Fe
K line detection in type 1 AGN could, be caused by the specific
emitting disc parameters, but also by the limits in the spectral resolution and
sensitivity of the X-ray detectors.Comment: Based on the talk presented Balkan Workshop BW2018 (10-14 June 2018,
Ni\v{s}, Serbia), accepted for publishing in International Journal of Modern
Physics A, 8 figures, 1 table, 15 page
Spectroscopic Measurements of the Far-Ultraviolet Dust Attenuation Curve at z~3
We present the first measurements of the shape of the far-ultraviolet
(far-UV; lambda=950-1500 A) dust attenuation curve at high redshift (z~3). Our
analysis employs rest-frame UV spectra of 933 galaxies at z~3, 121 of which
have very deep spectroscopic observations (>7 hrs) at lambda=850-1300 A, with
the Low Resolution Imaging Spectrograph on the Keck Telescope. By using an
iterative approach in which we calculate the ratios of composite spectra in
different bins of continuum color excess, E(B-V), we derive a dust curve that
implies a lower attenuation in the far-UV for a given E(B-V) than those
obtained with standard attenuation curves. We demonstrate that the UV composite
spectra of z~3 galaxies can be modeled well by assuming our new attenuation
curve, a high covering fraction of HI, and absorption from the Lyman-Werner
bands of H2 with a small (<20%) covering fraction. The low covering fraction of
H2 relative to that of the HI and dust suggests that most of the dust in the
ISM of typical galaxies at z~3 is unrelated to the catalysis of H2, and is
associated with other phases of the ISM (i.e., the ionized and neutral gas).
The far-UV dust curve implies a factor of ~2 lower dust attenuation of Lyman
continuum (ionizing) photons relative to those inferred from the most commonly
assumed attenuation curves for L* galaxies at z~3. Our results may be utilized
to assess the degree to which ionizing photons are attenuated in HII regions
or, more generally, in the ionized or low column density (N(HI)<10^17.2 cm^-2)
neutral ISM of high-redshift galaxies.Comment: 12 pages, 1 table, 8 figures, accepted to the Astrophysical Journa
Main memory in HPC: do we need more, or could we live with less?
An important aspect of High-Performance Computing (HPC) system design is the choice of main memory capacity. This choice becomes increasingly important now that 3D-stacked memories are entering the market. Compared with conventional Dual In-line Memory Modules (DIMMs), 3D memory chiplets provide better performance and energy efficiency but lower memory capacities. Therefore, the adoption of 3D-stacked memories in the HPC domain depends on whether we can find use cases that require much less memory than is available now.
This study analyzes the memory capacity requirements of important HPC benchmarks and applications. We find that the High-Performance Conjugate Gradients (HPCG) benchmark could be an important success story for 3D-stacked memories in HPC, but High-Performance Linpack (HPL) is likely to be constrained by 3D memory capacity. The study also emphasizes that the analysis of memory footprints of production HPC applications is complex and that it requires an understanding of application scalability and target category, i.e., whether the users target capability or capacity computing. The results show that most of the HPC applications under study have per-core memory footprints in the range of hundreds of megabytes, but we also detect applications and use cases that require gigabytes per core. Overall, the study identifies the HPC applications and use cases with memory footprints that could be provided by 3D-stacked memory chiplets, making a first step toward adoption of this novel technology in the HPC domain.This work was supported by the Collaboration Agreement between Samsung Electronics Co., Ltd. and BSC, Spanish Government through Severo Ochoa programme (SEV-2015-0493), by the Spanish Ministry of Science and Technology through TIN2015-65316-P project and by the Generalitat de Catalunya (contracts 2014-SGR-1051 and 2014-SGR-1272). This work has also received funding from the European Union’s Horizon
2020 research and innovation programme under ExaNoDe project (grant agreement No 671578). Darko Zivanovic holds the Severo Ochoa grant (SVP-2014-068501) of the Ministry of Economy and Competitiveness
of Spain. The authors thank Harald Servat from BSC and Vladimir Marjanovi´c from High Performance Computing Center Stuttgart for their technical support.Postprint (published version
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