2,973 research outputs found
Deep mantle structure and the postperovskite phase transition
Seismologists have known for many years that the lowermost mantle of the Earth is complex. Models based on observed seismic phases sampling this region include relatively sharp horizontal discontinuities with strong zones of anisotropy, nearly vertical contrasts in structure, and small pockets of ultralow velocity zones (ULVZs). This diversity of structures is beginning to be understood in terms of geodynamics and mineral physics, with dense partial melts causing the ULVZs and a postperovskite solidâsolid phase transition producing regional layering, with the possibility of large-scale variations in chemistry. This strong heterogeneity has significant implications on heat transport out of core, the evolution of the magnetic field, and magnetic field polarity reversals
Description and performance of a digital mobile satellite terminal
A major goal of the Mobile Satellite Experiment (MSAT-X) program at the Jet Propulsion Lab (JPL) is the development of an advanced digital terminal for use in land mobile satellite communication. The terminal has been developed to minimize the risk of applying advanced technologies to future commercial mobile satellite systems (MSS). Testing with existing L band satellites was performed in fixed, land mobile and aeronautical mobile environments. JPL's development and tests of its mobile terminal have demonstrated the viability of narrowband digital voice communications in a land mobile environment through geostationary satellites. This paper provides a consolidated description of the terminal architecture and the performance of its individual elements
Modeling near-field tsunami observations to improve finite-fault slip models for the 11 March 2011 Tohoku earthquake
The massive tsunami generated by the 11 March 2011 Tohoku earthquake (M_w 9.0) was widely recorded by GPS buoys, wave gauges, and ocean bottom pressure sensors around the source. Numerous inversions for finite-fault slip time histories have been performed using seismic and/or geodetic observations, yielding generally consistent patterns of large co-seismic slip offshore near the hypocenter and/or up-dip near the trench, where estimated peak slip is ~60 m. Modeling the tsunami generation and near-field wave processes using two detailed rupture models obtained from either teleseismic P waves or high-rate GPS recordings in Japan allows evaluation of how well the finite-fault models account for the regional tsunami data. By determining sensitivity of the tsunami calculations to rupture model features, we determine model modifications that improve the fit to the diverse tsunami data while retaining the fit to the seismic and geodetic observations
An aeronautical mobile satellite experiment
The various activities and findings of a NASA/FAA/COMSAT/INMARSAT collaborative aeronautical mobile satellite experiment are detailed. The primary objective of the experiment was to demonstrate and evaluate an advanced digital mobile satellite terminal developed at the Jet Propulsion Laboratory under the NASA Mobile Satellite Program. The experiment was a significant milestone for NASA/JPL, since it was the first test of the mobile terminal in a true mobile satellite environment. The results were also of interest to the general mobile satellite community because of the advanced nature of the technologies employed in the terminal
El apagĂłn analĂłgico: costos polĂticos, econĂłmicos y sociales
El apagĂłn analĂłgico concluyĂł en MĂ©xico el 31 de diciembre de 2015. Durante el proceso se mezclaron intereses polĂticos y econĂłmicos de diversa Ăndole que lo dificultaron significativamente. Este texto describe y analiza esa discusiĂłn, que fue mĂĄs allĂĄ de lo tĂ©cnico, implicĂł presiones, exigencias y deliberaciones de los distintos actores del sector. Se afirma que en la transiciĂłn digital, lejos de democratizar o pluralizar el espectro radioelĂ©ctrico, el estado ha defendido ciegamente ciertos intereses comerciales y empresariales.ITESO, A.C
Automatic identification of gait events using an instrumented sock
Background: textile-based transducers are an emerging technology in which piezo-resistive properties of materials
are used to measure an applied strain. By incorporating these sensors into a sock, this technology offers the
potential to detect critical events during the stance phase of the gait cycle. This could prove useful in several
applications, such as functional electrical stimulation (FES) systems to assist gait.
Methods: we investigated the output of a knitted resistive strain sensor during walking and sought to determine
the degree of similarity between the sensor output and the ankle angle in the sagittal plane. In addition, we
investigated whether it would be possible to predict three key gait events, heel strike, heel lift and toe off, with a
relatively straight-forward algorithm. This worked by predicting gait events to occur at fixed time offsets from
specific peaks in the sensor signal.
Results: our results showed that, for all subjects, the sensor output exhibited the same general characteristics as
the ankle joint angle. However, there were large between-subjects differences in the degree of similarity between
the two curves. Despite this variability, it was possible to accurately predict gait events using a simple algorithm.
This algorithm displayed high levels of trial-to-trial repeatability.
Conclusions: this study demonstrates the potential of using textile-based transducers in future devices that provide active gait assistance
Medios, acumulaciĂłn y poder
ArtĂculo que nos habla de los medios electrĂłnicos de comunicaciĂłn en MĂ©xico, mostrĂĄndolos en cuatro esferas: legislaciĂłn, permisos y convergencia digital, la polĂ©mica licitaciĂłn 21 y el derecho al acceso a la informaciĂłn.ITESO, A.C
Kinetics of natural aging in Al-Mg-Si alloys studied by positron annihilation lifetime spectroscopy
The process of natural aging in pure ternary Al-Mg-Si alloys was studied by
positron annihilation lifetime spectroscopy in real time in order to clarify
the sequence and kinetics of clustering and precipitation. It was found that
natural aging takes place in at least five stages in these alloys, four of
which were directly observed. This is interpreted as the result of complex
interactions between vacancies and solute atoms or clusters. One of the early
stages of positron lifetime evolution coincides with a clustering process
observed by differential scanning calorimetry (DSC) and involves the formation
of a positron trap with \sim 0.200 ns lifetime. In later stages, a positron
trap with a higher lifetime develops in coincidence with the DSC signal of a
second clustering reaction. Mg governs both the kinetics and the lifetime
change in this stage. Within the first 10 min after quenching, a period of
nearly constant positron lifetime was found for those Mg-rich alloys that later
show an insufficient hardness response to artificial aging, the so-called
"negative effect." The various processes observed could be described by two
effective activation energies that were found by varying the aging temperature
from 10 to 37\degree C.Comment: arXiv admin note: same as v2, to correct mistaken v
Combined trellis coding and feedforward processing for MSS applications
The idea of using a multiple (more than two) symbol observation interval to improve error probability performance is applied to differential detection of trellis coded MPSK over a mobile satellite (fading) channel. Results are obtained via computer simulation. It is shown that only a slight increase (e.g., one symbol) in the length of the observation interval will provide a significant improvement in bit error probability performance both in AWGN and fading environments
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