14,472 research outputs found
HighâSpeed Data Transmission Subsystem of the SEOSAR/PAZ Satellite
This paper analyzes a digital interface and bus system modeling and optimization of the SEOSAR/PAZ Earth Observation satellite. The important part of the satellite is an Xâband Synthetic Aperture Radar instrument that integrates 384 Transmit/Receive Modules located in 12 antenna panels 7.5 m away from the central processor and controlled by a synchronous 10 Mbps bidirectional serial protocol. This type of midârange pointâtoâmultipoint transmission is affected by bit errors due to crosstalk, transmission line attenuation and impedance mismatches. The highâspeed data communication network has been designed to optimize the transmission by using a simulation model of the data distribution system which takes into account the worstâcase scenario and by developing a labâscaled prototype which exhibits BER of 10-11 for an interfering signal of 10 Vpp. The result is a pointâtoâmultipoint bidirectional transmission network optimized in both directions with optimal values of loads and equalization resistors. This highâspeed data transmission subsystem provides a compact design through a simple solution
CMOS-3D smart imager architectures for feature detection
This paper reports a multi-layered smart image sensor architecture for feature extraction based on detection of interest points. The architecture is conceived for 3-D integrated circuit technologies consisting of two layers (tiers) plus memory. The top tier includes sensing and processing circuitry aimed to perform Gaussian filtering and generate Gaussian pyramids in fully concurrent way. The circuitry in this tier operates in mixed-signal domain. It embeds in-pixel correlated double sampling, a switched-capacitor network for Gaussian pyramid generation, analog memories and a comparator for in-pixel analog-to-digital conversion. This tier can be further split into two for improved resolution; one containing the sensors and another containing a capacitor per sensor plus the mixed-signal processing circuitry. Regarding the bottom tier, it embeds digital circuitry entitled for the calculation of Harris, Hessian, and difference-of-Gaussian detectors. The overall system can hence be configured by the user to detect interest points by using the algorithm out of these three better suited to practical applications. The paper describes the different kind of algorithms featured and the circuitry employed at top and bottom tiers. The Gaussian pyramid is implemented with a switched-capacitor network in less than 50 ÎŒs, outperforming more conventional solutions.Xunta de Galicia 10PXIB206037PRMinisterio de Ciencia e InnovaciĂłn TEC2009-12686, IPT-2011-1625-430000Office of Naval Research N00014111031
Magnetic transitions in Pr2NiO4 single crystal
The magnetic properties of a stoichiometric Pr2NiO4 single crystal have been examined by means of the temperature dependence of the complex ac susceptibility and the isothermal magnetization in fields up to 200 kOe at T=4.2 K. Three separate phases have been identified and their anisotropic character has been analyzed. A collinear antiferromagnetic phase appears first between TN = 325 K and Tc1 = 115 K, where the Pr ions are polarized by an internal magnetic field. At Tc1 a first modification of the magnetic structure occurs in parallel with a structural phase transition (Bmab to P42/ncm). This magnetic transition has a firstâorder character and involves both the outâofâplane and the inâplane spin components (magnetic modes gx and gxcyfz, respectively). A second magnetic transition having also a firstâorder character is also clearly identified at Tc2 = 90 K which corresponds to a spin reorientation process (gxcyfz to cxgyaz magnetic modes). It should be noted as well that the outâofâphase component of Ïac shows a peak around 30 K which reflects the coexistence of both magnetic configurations in a wide temperature interval. Finally, two fieldâinduced transitions have been observed at 4.2 K when the field is directed along the c axis. We propose that the highâfield anomaly arises from a metamagnetic transition of the weak ferromagnetic component, similarly to La2CuO4
BOREAS: Detecting Planetary Subsurface Water
Direct detection of water on planets beyond Earth has always been a primary goal for space exploration. Our âBoreasâ project focuses on the integration of a student-designed S-Band Radar-based water detection system, which is capable of ice penetration. For improved reliability, the system is equipped with an automatic attitude determination and control subsystem. The Boreas project aims to design, test, and fabricate a small-scale radar capable of seeing through substantial layers of ice or other material covering a given body of water. Our orbiting radar will be able to orient itself to the planet during flyby and maintain nadir orientation as the sensing subsystem takes in subsurface data. This design was inspired by Jupiterâs moon Europa, which is known to harbor subsurface high-salinity oceans and further motivated by the recent exciting discovery of liquid water on Mars. The opportunities for application of the Boreas orbiter are numerous
Measurements of thermodynamic and transport properties of EuC: a low-temperature analogue of EuO
EuC is a ferromagnet with a Curie-temperature of K. It
is semiconducting with the particularity that the resistivity drops by about 5
orders of magnitude on cooling through , which is therefore called a
metal-insulator transition. In this paper we study the magnetization, specific
heat, thermal expansion, and the resistivity around this ferromagnetic
transition on high-quality EuC samples. At we observe well defined
anomalies in the specific heat and thermal expansion data.
The magnetic contributions of and can satisfactorily be
described within a mean-field theory, taking into account the magnetization
data. In zero magnetic field the magnetic contributions of the specific heat
and thermal expansion fulfill a Gr\"uneisen-scaling, which is not preserved in
finite fields. From an estimation of the pressure dependence of via
Ehrenfest's relation, we expect a considerable increase of under applied
pressure due to a strong spin-lattice coupling. Furthermore the influence of
weak off stoichiometries in EuC was studied. It is
found that strongly affects the resistivity, but hardly changes the
transition temperature. In all these aspects, the behavior of EuC strongly
resembles that of EuO.Comment: 7 pages, 6 figure
Chiral properties of hematite ({\alpha}-Fe2O3) inferred from resonant Bragg diffraction using circularly polarized x-rays
Chiral properties of the two phases - collinear motif (below Morin transition
temperature, TM=250 K) and canted motif (above TM) - of magnetically ordered
hematite ({\alpha}-Fe2O3) have been identified in single crystal resonant x-ray
Bragg diffraction, using circular polarized incident x-rays tuned near the iron
K-edge. Magneto-electric multipoles, including an anapole, fully characterize
the high-temperature canted phase, whereas the low-temperature collinear phase
supports both parity-odd and parity-even multipoles that are time-odd. Orbital
angular momentum accompanies the collinear motif, while it is conspicuously
absent with the canted motif. Intensities have been successfully confronted
with analytic expressions derived from an atomic model fully compliant with
chemical and magnetic structures. Values of Fe atomic multipoles previously
derived from independent experimental data, are shown to be completely
trustworthy
Charge delocalization and hyperpolarizability in ionic liquids
In this work the role that charge delocalization plays in the non-linear
optical response of ionic liquids is evaluated. The first hyperpolarizability
for the non-linear process of second harmonic generation (SHG) and second
hyperpolarizability for the non-linear process of electro-optical Kerr-Effect
(EOKE) of a large number of ionic liquid forming ions were estimated by means
of density functional theory calculations. The results point to that both
charge delocalization and molecular geometry are the key features that govern
their hyperpolarizabilities. Our findings show that some of the most commonly
used anions in ionic liquids are expected to present strong non-linear
responses while common cations present a much more limited performance.
However, this limitation can be overcome by a proper tailoring of cations to
present charge delocalization over large molecular regions. The hypothesis of
additivity of hyperpolarizabilities in ionic liquids is tested and exploited to
obtain a map of second and third order non-linear susceptibilities of 1496 ion
combinations. This map is intended to be a guide for future works on the
hyperpolarizability of ILsComment: 12 pages, 6 figures, 4 tables, supplementary data associated with
this article can be found, in the online version, at
https://doi.org/10.1016/j.molliq.2021.11815
Bacteria with Phosphate Solubilizing Capacity Alter Mycorrhizal Fungal Growth Both Inside and Outside the Root and in the Presence of Native Microbial Communities.
Arbuscular mycorrhizal fungi (AMF) and phosphate solubilizing Pseudomonas bacteria (PSB) could potentially interact synergistically because PSB solubilize phosphate into a form that AMF can absorb and transport to the plant. However, very little is known about the interactions between these two groups of microorganisms and how they influence the growth of each other. We tested whether different strains of bacteria, that have the capacity to solubilize phosphate, are able to grow along AMF hyphae and differentially influence the growth of AMF both outside the roots of carrot in in vitro conditions and inside the roots of potato in the presence of a microbial community. We found strong effects of AMF on the growth of the different bacterial strains. Different bacterial strains also had very strong effects on the growth of AMF extraradical hyphae outside the roots of carrot and on colonization of potato roots by AMF. The differential effects on colonization occurred in the presence of a microbial community. Our results show that these two important groups of rhizosphere microorganisms indeed interact with each other. Such interactions could potentially lead to synergistic effects between the two groups but this could depend on whether the bacteria truly solubilize phosphate in the rhizosphere in the presence of microbial communities
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