152 research outputs found
The structure of intercalated water in superconducting NaCoO1.37DO: Implications for the superconducting phase diagram
We have used electron and neutron powder diffraction to elucidate the
structural properties of superconducting \NaD. Our measurements show that our
superconducting sample exhbits a number of supercells ranging from
to , but the most predominant one, observed also in the neutron
data, is a double hexagonal cell with dimensions \dhx. Rietveld analysis
reveals that \deut\space is inserted between CoO sheets as to form a
layered network of NaO triangular prisms. Our model removes the need to
invoke a 5K superconducting point compound and suggests that a solid solution
of Na is possible within a constant amount of water .Comment: 4 pages, 3 figure
Gyro-Chirality Effect of Bianisotropic Substrate On the operational of Rectangular Microstrip Patch Antenna
yesIn this paper, the gyrotropic bi-anisotropy of the chiral medium in substrate
constitutive parameters (ξc and ηc) of a rectangular microstrip patch antenna is introduced in
order to observe its effects on the complex resonant frequency, half-power bandwidth and
input impedance. Numerical calculations and analysis based on the dominant mode are
carried out to show that the latter is directly related to the former. This paper is based on the
Moment Method as full-wave spectral domain approach using sinusoidal basis functions. Two
new results, namely the appearance of the difference (ξc-ηc) and sum (ξc+ηc) of the two
magneto-electric elements are obtained in the electric transverse components and Green
tensor expressions, respectively. These new results can be considered as a generalisation form of the previously published work
Revised superconducting phase diagram of hole doped Na(HO)CoOHO
We have studied the superconducting phase diagram of \NaH\space as a function
of electronic doping, characterizing our samples both in terms of Na content
and the Co valence state. Our findings are consistent with a recent report
that intercalation of \oxp\space ions into NaCoO, together with
water, act as an additional dopant indicating that Na sub-stochiometry alone
does not control the electronic doping of these materials. We find a
superconducting phase diagram where optimal \Tc\space is achieved through a Co
valence range of 3.24 - 3.35, while \Tc\space decreases for materials with a
higher Co valence. The critical role of dimensionality in achieving
superconductivity is highlighted by similarly doped non-superconducting
anhydrous samples, differing from the superconducting hydrate only in
inter-layer spacing. The increase of the interlayer separation between
CoO sheets as Co valence is varied into the optimal \Tc\space region is
further evidence for this criticality.Comment: Paper updated on 29/10/2004, 4 pages, 4 figures. Physical Review
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Horn Antennas Loaded with Metamaterial for UWB Applications
YesIn this paper, a conical horn antenna has been designed for Ultra-Wideband ap-plications by loading its section with a metamaterial. The work aims first to compare results obtained by the wavelet-moment method to a simulation performed using HFSS. Secondly the conical horn is loaded with a very thin layer of metamaterial to enhance the radiation pattern and the bandwidth performance of the conical horn antenna and reduce the size of the antenna. The operating bandwidth of the proposed antenna is in the range of 10{13 GHz. The results obtained from HFSS and moment method are in good agreement.Electronics and Telecommunication
Offset Aperture-Coupled Double-Cylinder Dielectric Resonator Antenna with Extended Wideband
YesA compact dielectric resonator antenna for ultra-wideband vehicular communication applications is proposed. Two cylindrical dielectric resonators are asymmetrically located with respect to the center of an offset rectangular coupling aperture, through which they are fed. Optimizing the design parameters results in an impedance bandwidth of 21%, covering the range from 5.9 to 7.32 GHz in the lower-band and a 53% relative bandwidth from 8.72 to 15 GHz in the upper-band. The maximum achieved gain is 12 dBi. Design details of the proposed antenna and the results of both simulations and experiment are presented and discussed
Theoretical Study of the Input Impedance and Electromagnetic Field Distribution of a Dipole Antenna Printed on an Electrical/Magnetic Uniaxial Anisotropic Substrate
The present work considers the investigation of the effects of both electrical and magnetic uniaxial anisotropies on the input impedance, resonant length, and fields distribution of a dipole printed on an anisotropic grounded substrate. In this study, the associated integral equation, based on the derivation of the Green's functions in the spectral domain, is numerically solved employing the method of moments. In order to validate the computing method and the evaluated calculation code, numerical results are compared with available data in the literature treating particular cases of electrical uniaxial anisotropy; reasonable agreements are reported. Novel results of the magnetic uniaxial anisotropy effects on the input impedance and the evaluated electromagnetic field are presented and discussed. This work will serve as a stepping stone for further works for a better understanding of the electromagnetic field behavior in complex anisotropic and bi-anisotropic media
Elucidating the optical, electronic, and photoelectrochemical properties of p type copper vanadate p Cu5V2O10 photocathodes
Evaluation of Copper Vanadate beta Cu2V2O7 as a Photoanode Material for Photoelectrochemical Water Oxidation
Impedance Bandwidth Improvement of a Planar Antenna Based on Metamaterial-Inspired T-Matching Network
In this paper a metamaterial-inspired T-matching network is directly imbedded inside the feedline of a microstrip antenna to realize optimum power transfer between the front-end of an RF wireless transceiver and the antenna. The proposed T-matching network, which is composed of an arrangement of series capacitor, shunt inductor, series capacitor, exhibits left-handed metamaterial characteristics. The matching network is first theoretically modelled to gain insight of its limitations. It was then implemented directly in the 50-Ω feedline to a standard circular patch antenna, which is an unconventional methodology. The antenna’s performance was verified through measurements. With the proposed technique there is 2.7 dBi improvement in the antenna’s radiation gain and 12% increase in the efficiency at the center frequency, and this is achieved over a significantly wider frequency range by a factor of approximately twenty. Moreover, there is good correlation between the theoretical model, method of moments simulation, and the measurement results
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