Search results for "BAND"
showing 10 items of 2610 documents
Tunable antenna system for plug&play satellite avionics: Prototyping and test
2014
In the framework of an ESA program, a new architecture for plug&play compact antenna systems in the X band has been investigated and experimentally verified by many prototypes. The proposed antenna system takes inspiration from the LEGO building toys: the basic component of the new architecture is a 2.7cm-cube complex module that integrates a three-dimensional local network and a programmable mechanism based on the bonding-wire technology to select one among three polarization options. Elemental blocks can be augmented by accessories to shape the beam and may be used in array configuration over boards provided with cluster-level beamforming networks. Measurements have been performed for bot…
Enable concurrent transmissions with beamforming for broadband wireless access in CSMA/CA-based WLANs
2014
In CSMA/CA based wireless local networks, two stations are not allowed to transmit at the same time due to interference generated to each other, resulting in degraded throughput. Concurrent transmission, which enables simultaneous transmission of two or more stations under certain conditions, is able to overcome this problem, leading to enhanced channel utilization efficiency. Different from earlier work on this topic which focuses on omni-direction concurrent transmission, we introduce in this paper beamforming into a co-channel concurrent transmission scheme and investigate the benefits of concurrency with beamforming. The circumstances for concurrent transmission and frame scheduling are…
Visual category representations in the infant brain
2021
SUMMARYVisual categorization is a human core cognitive capacity1,2that depends on the development of visual category representations in the infant brain3–7. However, the exact nature of infant visual category representations and their relationship to the corresponding adult form remains unknown8. Our results clarify the nature of visual category representations from electroencephalography (EEG) data in 6- to 8-month-old infants and their developmental trajectory towards adult maturity in the key characteristics of temporal dynamics2,9, representational format10–12, and spectral properties13,14. Temporal dynamics change from slowly emerging, developing representations in infants to quickly e…
Genetic analysis of early lamb survival in extensively reared lambs
2005
In sheep production, lamb survival is an important economic trait (Conington et al., 2004). Therefore, this trait has been studied by many scientists, especially in countries with an extensive husbandry system. In the United Kingdom, the number of lambs dying before weaning has been estimated ranging from 5 to 40% (Eales et al., 1983).
Advancing cyanobacteria biomass estimation from hyperspectral observations: Demonstrations with HICO and PRISMA imagery
2021
Retrieval of the phycocyanin concentration (PC), a characteristic pigment of, and proxy for, cyanobacteria biomass, from hyperspectral satellite remote sensing measurements is challenging due to uncertainties in the remote sensing reflectance (?R) resulting from atmospheric correction and instrument radiometric noise. Although several individual algorithms have been proven to capture local variations in cyanobacteria biomass in specific regions, their performance has not been assessed on hyperspectral images from satellite sensors. Our work leverages a machine-learning model, Mixture Density Networks (MDNs), trained on a large (N = 939) dataset of collocated in situ chlorophyll-a concentrat…
Surface soil moisture retrieval using L-band SMAP SAR data and its validation
2016
Surface soil moisture was retrieved globally by systematically correcting for the effects of vegetation and soil surface roughness. The retrieval is enabled by employing physical-models of radar forward scattering for individual vegetation types to account for vegetation scattering and absorption, and by constraining the surface roughness effect using time-series observations. The L-band SMAP multi-polarized (HH/VV/HV) σ° data acquired globally every three days were used from mid-April to early July, 2015. Assessment was conducted over 13 rigorously-chosen core validation sites covering a wide range of biomass types, biomass amount, and soil conditions. The soil moisture retrieval reached a…
The NHXM observatory
2011
Exploration of the X-ray sky has established X-ray astronomy as a fundamental astrophysical discipline. While our knowledge of the sky below 10 keV has increased dramatically (∼8 orders of magnitude) by use of grazing incidence optics, we still await a similar improvement above 10 keV, where to date only collimated instruments have been used. Also ripe for exploration is the field of X-ray polarimetry, an unused fundamental tool to understand the physics and morphology of X-ray sources. Here we present a novel mission, the New Hard X-ray Mission (NHXM) that brings together for the first time simultaneous high-sensitivity, hard-X-ray imaging, broadband spectroscopy and polarimetry. NHXM will…
Performance Analysis of STBC-OFDM Systems in Temporally or Spatially Correlated Fading Channels
2010
This paper analyzes the performance of space-time block coded orthogonal frequency division multiplexing (OFDM) systems. In our analysis, we abandon the usually made assumption of quasi-static channel conditions. Instead of this, we consider the more general and realistic case that the channel envelope changes during two consecutive transmission time slots. In addition, we take the spatial correlation between sub-channels into account. We first present a general formal expression for the bit error probability (BEP), from which we find analytical solutions for the BEP not only for temporally fading channels but also for spatially correlated channels. The knowledge of the obtained analytical …
Structural symmetry breaking in octupolar tetrastyrylpyrazines and their dipole moments in equilibrium ground and Franck-Condon excited state
2018
Abstract From electrooptical absorption measurements (EOAM) follows that the dipole moment of octupolar tetrastyrylpyrazines in the equilibrium ground state is large and that the change of dipole moments upon transition to the excited Franck–Condon state is significant. Obtained results unambiguously testify to structural symmetry breaking in the studied octupolar tetrastyrylpyrazines. Molecular mechanics and semi-empirical calculations evidence that tetrastyrylpyrazines have non-planar configurations. The non-planar geometry of the molecules causes large μg values and significant change of dipole moment Δaμ after excitation. Due to large μg and Δaμ values the maxima of the first absorption…
Effect of pressure on structural properties and energy band gaps of γ-InSe
2003
We have investigated theoretically the effect of hydrostatic pressure on interatomic bond lengths and energy band gaps of γ-InSe. Total energy calculations were performed using the linear augmented plane wave (LAPW) method, taking into account scalar relativistic corrections as well as spin-orbit coupling. Internal structural parameters were optimized for different pressures by adopting as input the unit cell parameters known from experiment. Our theoretical results for the nearest-neighbor In-Se bond length are in excellent agreement with a recent experimental determination from high-pressure EXAFS measurements. The covalent In-In bond is found to be more compressible than the partially io…