17,520 research outputs found
Prototyping and Experimentation of a Closed-Loop Wireless Power Transmission with Channel Acquisition and Waveform Optimization
A systematic design of adaptive waveform for Wireless Power Transfer (WPT)
has recently been proposed and shown through simulations to lead to significant
performance benefits compared to traditional non-adaptive and heuristic
waveforms. In this study, we design the first prototype of a closed-loop
wireless power transfer system with adaptive waveform optimization based on
Channel State Information acquisition. The prototype consists of three
important blocks, namely the channel estimator, the waveform optimizer, and the
energy harvester. Software Defined Radio (SDR) prototyping tools are used to
implement a wireless power transmitter and a channel estimator, and a voltage
doubler rectenna is designed to work as an energy harvester. A channel adaptive
waveform with 8 sinewaves is shown through experiments to improve the average
harvested DC power at the rectenna output by 9.8% to 36.8% over a non-adaptive
design with the same number of sinewaves.Comment: accepted for publication in IEEE WPTC 201
Signal and System Design for Wireless Power Transfer : Prototype, Experiment and Validation
A new line of research on communications and signals design for Wireless
Power Transfer (WPT) has recently emerged in the communication literature.
Promising signal strategies to maximize the power transfer efficiency of WPT
rely on (energy) beamforming, waveform, modulation and transmit diversity, and
a combination thereof. To a great extent, the study of those strategies has so
far been limited to theoretical performance analysis. In this paper, we study
the real over-the-air performance of all the aforementioned signal strategies
for WPT. To that end, we have designed, prototyped and experimented an
innovative radiative WPT architecture based on Software-Defined Radio (SDR)
that can operate in open-loop and closed-loop (with channel acquisition at the
transmitter) modes. The prototype consists of three important blocks, namely
the channel estimator, the signal generator, and the energy harvester. The
experiments have been conducted in a variety of deployments, including
frequency flat and frequency selective channels, under static and mobility
conditions. Experiments highlight that a channeladaptive WPT architecture based
on joint beamforming and waveform design offers significant performance
improvements in harvested DC power over conventional
single-antenna/multiantenna continuous wave systems. The experimental results
fully validate the observations predicted from the theoretical signal designs
and confirm the crucial and beneficial role played by the energy harvester
nonlinearity.Comment: Accepted to IEEE Transactions on Wireless Communication
Research and Development at U.S. Research Universities: An Analysis of Scope Economies
This paper investigates the presence and sources of economies of scope in R&D production at U.S. research universities. The analysis evaluates the tradeoffs or synergies arising between traditional university research outputs (articles and doctorates) and a more recent and burgeoning output: academic patents. Using a shortage function, we propose a decomposition of economies of scope (decomposition which includes complementarity effects and scale effects). R&D input and output data from 92 public and private research universities are used to obtain non-parametric estimates of scope economies. The results show significant variations in economies of scope and sources by size and type of university.Research and Development/Tech Change/Emerging Technologies,
Crystal growth and annealing study of fragile, non-bulk superconductivity in YFeGe
We investigated the occurrence and nature of superconductivity in single
crystals of YFeGe grown out of Sn flux by employing x-ray diffraction,
electrical resistivity, and specific heat measurements. We found that the
residual resistivity ratio (RRR) of single crystals can be greatly improved,
reaching as high as 60, by decanting the crystals from the molten Sn at
350C and/or by annealing at temperatures between 550C and
600C. We found that samples with RRR 34 showed resistive
signatures of superconductivity with the onset of the superconducting
transition K. RRR values vary between 35 and 65 with, on
average, no systematic change in value, indicating that systematic
changes in RRR do not lead to comparable changes in . Specific heat
measurements on samples that showed clear resistive signatures of a
superconducting transition did not show any signature of a superconducting
phase transition, which suggests that the superconductivity observed in this
compound is either some sort of filamentary, strain stabilized
superconductivity associated with small amounts of stressed YFeGe
(perhaps at twin boundaries or dislocations) or is a second crystallographic
phase present at levels below detection capability of conventional powder x-ray
techniques.Comment: 8 pages, 11 figure
TECHNICAL CHANGE AND EFFICIENCY AT US LAND GRANT UNIVERSITIES: IS THERE ANY FAT LEFT TO CUT?
This work uses non-parametric efficiency analysis and a unique panel data set to analyze efficiency and technical change at US universities from 1981-1998 with a special emphasis on Land Grant institutions. The analysis demonstrates that Land Grants are on average more efficient than their counterparts. While in the 1980s they had higher levels of technological change, in the 1990s that declined to levels similar to other types of universities. Identifying factors influencing efficiency and technological progress in university production provides key insights into the future of the Land Grant system.Research and Development/Tech Change/Emerging Technologies, Teaching/Communication/Extension/Profession,
Virtual Exploration of Underwater Archaeological Sites : Visualization and Interaction in Mixed Reality Environments
This paper describes the ongoing developments in Photogrammetry and Mixed Reality for the Venus European project (Virtual ExploratioN of Underwater Sites, http://www.venus-project.eu). The main goal of the project is to provide archaeologists and the general public with virtual and augmented reality tools for exploring and studying deep underwater archaeological sites out of reach of divers. These sites have to be reconstructed in terms of environment (seabed) and content (artifacts) by performing bathymetric and photogrammetric surveys on the real site and matching points between geolocalized pictures. The base idea behind using Mixed Reality techniques is to offer archaeologists and general public new insights on the reconstructed archaeological sites allowing archaeologists to study directly from within the virtual site and allowing the general public to immersively explore a realistic reconstruction of the sites. Both activities are based on the same VR engine but drastically differ in the way they present information. General public activities emphasize the visually and auditory realistic aspect of the reconstruction while archaeologists activities emphasize functional aspects focused on the cargo study rather than realism which leads to the development of two parallel VR demonstrators. This paper will focus on several key points developed for the reconstruction process as well as both VR demonstrators (archaeological and general public) issues. The ?rst developed key point concerns the densi?cation of seabed points obtained through photogrammetry in order to obtain high quality terrain reproduction. The second point concerns the development of the Virtual and Augmented Reality (VR/AR) demonstrators for archaeologists designed to exploit the results of the photogrammetric reconstruction. And the third point concerns the development of the VR demonstrator for general public aimed at creating awareness of both the artifacts that were found and of the process with which they were discovered by recreating the dive process from ship to seabed
The influence of orbital rotation on the energy of closed-shell wavefunctions
The orbital dependence of closed-shell wavefunction energies is investigated by performing doubly-occupied configuration interaction (DOCI) calculations, representing the most general class of these wavefunctions. Different local minima are examined for planar hydrogen clusters containing two, four, and six electrons applying (spin) symmetry-broken restricted, unrestricted, and generalised orbitals with real and complex coefficients. Contrary to Hartree-Fock (HF), restricted DOCI is found to properly break bonds and thus unrestricted orbitals, while providing a quantitative improvement of the energy, are not needed to enforce a qualitatively correct bond dissociation. For the beryllium atom and the BH diatomic, the lowest possible HF energy requests symmetry-broken generalised orbitals, whereas accurate results for DOCI can be obtained within a restricted formalism. Complex orbital coefficients are shown to increase the accuracy of HF and DOCI results in certain cases. The computationally inexpensive AP1roG geminal wavefunction is proven to agree very well with all DOCI results of this study
Structure of shock compressed model basaltic glass: Insights from O K-edge X-ray Raman scattering and high-resolution ^(27)Al NMR spectroscopy
The detailed atomic structures of shock compressed basaltic glasses are not well understood. Here, we explore the structures of shock compressed silicate glass with a diopside–anorthite eutectic composition (Di_(64)An_(36)), a common Fe-free model basaltic composition, using oxygen K-edge X-ray Raman scattering and high- resolution ^(27)Al solid-state NMR spectroscopy and report previously unknown details of shock-induced changes in the atomic configurations. A topologically driven densification of the Di_(64)An_(36) glass is indicated by the increase in oxygen K-edge energy for the glass upon shock compression. The first experimental evidence of the increase in the fraction of highly coordinated Al in shock compressed glass is found in the ^(27)Al NMR spectra. This unambiguous evidence of shock-induced changes in Al coordination environments provides atomistic insights into shock compression in basaltic glasses and allows us to microscopically constrain the magnitude of impact events or relevant processes involving natural basalts on Earth and planetary surfaces
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