181 research outputs found

    Tropospheric gravity waves observed by three closely spaced ST radars

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    Clear-air radar experiments were carried out on the southern coast of France during the (ALPEX) Alpine experiment program vertically directed stratosphere-troposphere-radars were set up with spacings of about 5 to 6 km. The temporal and spectral characteristics of the vertical velocity fluctuations were examined. The horizontal and vertical properties of gravity waves in the lower atmosphere were analyzed. The techniques used and the first results from this wave study are described

    Peer-to-Peer Cooperative Positioning Part I: GNSS Aided Acquisition

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    To improve the performance of GNSS receivers in hostile environments, we consider a Cooperative Positioning approach, where receivers exchange data and information with their neighbors. We focus on unstructured P2P networks, without a control or fusion center. We show that a significant reduction of the acquisition time can indeed by achieved when GNSS aiding quantities like Doppler, satellite Carrierto-Noise ratio and secondary code delay are provided by some aiding peers. The approach is clearly similar to that of Assisted GNSS, but does not require a fixed infrastructure and may better take into account the local environment. Since, in the near future, multi-standard devices will be more and more inter-connected, GNSS Cooperative Positioning may soon become an alternative or a complement to fixed augmentation system

    Analysis of cubic permutation polynomials for turbo codes

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    Quadratic permutation polynomials (QPPs) have been widely studied and used as interleavers in turbo codes. However, less attention has been given to cubic permutation polynomials (CPPs). This paper proves a theorem which states sufficient and necessary conditions for a cubic permutation polynomial to be a null permutation polynomial. The result is used to reduce the search complexity of CPP interleavers for short lengths (multiples of 8, between 40 and 352), by improving the distance spectrum over the set of polynomials with the largest spreading factor. The comparison with QPP interleavers is made in terms of search complexity and upper bounds of the bit error rate (BER) and frame error rate (FER) for AWGN and for independent fading Rayleigh channels. Cubic permutation polynomials leading to better performance than quadratic permutation polynomials are found for some lengths.Comment: accepted for publication to Wireless Personal Communications (19 pages, 4 figures, 5 tables). The final publication is available at springerlink.co

    Fieldlike and antidamping spin-orbit torques in as-grown and annealed Ta/CoFeB/MgO layers

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    We present a comprehensive study of the current-induced spin-orbit torques in perpendicularly magnetized Ta/CoFeB/MgO layers. The samples were annealed in steps up to 300 degrees C and characterized using x-ray absorption spectroscopy, transmission electron microscopy, resistivity, and Hall effect measurements. By performing adiabatic harmonic Hall voltage measurements, we show that the transverse (field-like) and longitudinal (antidamping-like) spin-orbit torques are composed of constant and magnetization-dependent contributions, both of which vary strongly with annealing. Such variations correlate with changes of the saturation magnetization and magnetic anisotropy and are assigned to chemical and structural modifications of the layers. The relative variation of the constant and anisotropic torque terms as a function of annealing temperature is opposite for the field-like and antidamping torques. Measurements of the switching probability using sub-{\mu}s current pulses show that the critical current increases with the magnetic anisotropy of the layers, whereas the switching efficiency, measured as the ratio of magnetic anisotropy energy and pulse energy, decreases. The optimal annealing temperature to achieve maximum magnetic anisotropy, saturation magnetization, and switching efficiency is determined to be between 240 degrees and 270 degrees C

    SOT-MRAM 300mm integration for low power and ultrafast embedded memories

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    We demonstrate for the first time full-scale integration of top-pinned perpendicular MTJ on 300 mm wafer using CMOS-compatible processes for spin-orbit torque (SOT)-MRAM architectures. We show that 62 nm devices with a W-based SOT underlayer have very large endurance (> 5x10^10), sub-ns switching time of 210 ps, and operate with power as low as 300 pJ.Comment: presented at VLSI2018 session C8-

    Mesomechanical analysis of concrete under loading that generates rotation of cracking

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    Willam®s test has been often used to compare constitutive models which take into account induced anisotropy due to damage and cracking. This numerical test emulates the continuous rotation of the principal stress and deformation directions, with secondary cracks forming at inclined directions while original primary cracks aligned with the axes tend to close. However, a realistic verification of this type of behavior is limited by the absence of experimental results in the literature of concrete and other quasi brittle materials, which can be explained in part due to the complexity of practical difficulties in this kind of lab test. As a first way to cover this gap, this paper presents numerical results of a concrete meso-structural model under imposed deformations at the boundary similar to the Willam’s test. The results presented include the evolution of average stress components over the sample, cracking state, etc. Generally speaking, the results obtained agree well with the predictions of advanced continuum-type anisotropic models, although some specific aspects are pointed out that would deserve further detailed study and discussion

    Taxonomic and non-taxonomic responses of benthic macroinvertebrates to metal toxicity in tropical reservoirs: The case of cantareira complex, SĂŁo Paulo, Brazil

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    Benthic macroinvertebrates are organisms that are recognized as water quality bio-indicators. A wide variety of indices and metrics have been shown to respond to a variety of anthropogenic impacts, usually under a general condition of environmental impairment. The absence of a clear distinction in the relations between specific pollutants and biotic variables is very common and can lead to biased interpretation of biomonitoring. The aims of this research were to test taxonomic and non-taxonomic responses to specific environmental conditions instead to general conditions. For this purpose, we estimated the theoretical toxicity by comparing toxicity values published by EPA with metal concentrations in water and sediments. Then we tested the responses of biological variables to toxicity and other environmental conditions using the linear mixed effects models approach. We generated 32 models considering 24 different biological metrics and indices that were grouped in five levels. Taxonomic and abundance metrics were best predictor than functional or tolerance-based indexes. The strongest model was that which considered subfamily taxonomic resolution responding to Al_w and Cr_s.Fil: de Souza, Frederico Guilherme. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Cetra, MaurĂ­cio. Universidade Federal do SĂŁo Carlos; BrasilFil: Marchese Garello, Mercedes Rosa. Consejo Nacional de Investigaciones CientĂ­ficas y TĂ©cnicas. Centro CientĂ­fico TecnolĂłgico Conicet - Santa Fe. Instituto Nacional de LimnologĂ­a. Universidad Nacional del Litoral. Instituto Nacional de LimnologĂ­a; ArgentinaFil: LĂłpez DovĂĄl, JĂșlio CĂ©sar. Universidade de Sao Paulo; BrasilFil: Rosa, AndrĂ© H.. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: PompĂȘo, Marcelo L. M.. Universidade de Sao Paulo; BrasilFil: Moschini Carlos, Viviane. Universidade Estadual Paulista Julio de Mesquita Filho; Brasi
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