4,147 research outputs found
Compact, Frequency-Reconfigurable Filtenna with Sharply Defined Wideband and Continuously Tunable Narrowband States
© 1963-2012 IEEE. A compact, frequency-reconfigurable filtenna with sharp out-of-band rejection in both its wideband and continuously tunable narrowband states is presented. It is intended for use in cognitive radio applications. The wideband state is the sensing state and operationally covers 2.35-4.98 GHz. The narrowband states are intended to cover communications within the 3.05-4.39 GHz range, which completely covers the Worldwide Interoperability for Microwave Access (WiMAX) band and the satellite communications C-band. A p-i-n diode is employed to switch between these wide and narrowband operational states. Two varactor diodes are used to shift the operational frequencies continuously among the narrowband states. The filtenna consists of a funnel-shaped monopole augmented with a reconfigurable filter; it has a compact electrical size: 0.235λLL × 0.392λL , where the wavelength λL corresponds to the lower bound of its operational frequencies. The measured reflection coefficients, radiation patterns, and realized gains for both operational states are in good agreement with their simulated values
Stability Analysis for Nonlinear Impulsive Control System with Uncertainty Factors.
Considering the limitation of machine and technology, we study the stability for nonlinear impulsive control system with some uncertainty factors, such as the bounded gain error and the parameter uncertainty. A new sufficient condition for this system is established based on the generalized Cauchy-Schwarz inequality in this paper. Compared with some existing results, the proposed method is more practically applicable. The effectiveness of the proposed method is shown by a numerical example
Reconfigurable Intelligent Surface Assisted MEC Offloading in NOMA-Enabled IoT Networks
Integrating mobile edge computing (MEC) into the Internet of Things (IoT) enables resource-limited mobile terminals to offload part or all of the computation-intensive applications to nearby edge servers. On the other hand, by introducing reconfigurable intelligent surface (RIS), it can enhance the offloading capability of MEC, such that enabling low latency and high throughput. To enhance the task offloading, we investigate the MEC non-orthogonal multiple access (MEC-NOMA) network framework for mobile edge computation offloading with the assistance of a RIS. Different from conventional communication systems, we aim at allowing multiple IoT devices to share the same channel in tasks offloading process. Specifically, the joint consideration of channel assignments, beamwidth allocation, offloading rate and power control is formulated as a multi-objective optimization problem (MOP), which includes minimizing the offloading delay of computing-oriented IoT devices (CP-IDs) and maximizing the transmission rate of communication-oriented IoT devices (CM-IDs). Since the resulting problem is non-convex, we employ ϵ-constraint approach to transform the MOP into the single-objective optimization problems (SOP), and then the RIS-assisted channel assignment algorithm is developed to tackle the fractional objective function. Simulation results corroborate the benefits of our strategy, which can outperforms the other benchmark schemes
Quantum entangled Sagnac interferometer
SU(1,1) interferometer (SUI) is a novel type of interferometer that uses
directly entangled quantum fields for sensing phase change. For rotational
sensing, Sagnac geometry is usually adopted. However, because SUI depends on
the phase sum of the two arms, traditional Sagnac geometry, when applied to
SUI, will result in null signal. In this paper, we modify the traditional
Sagnac interferometer by nesting SU(1,1) interferometers inside. We show that
the rotational signal comes from two parts labeled as "classical" and
"quantum", respectively, and the quantum part, where quantum entangled fields
are used for sensing, has rotational signal enhanced by a factor related to the
gain of the SUI.Comment: 5 pages, 3 figure
Short- and medium-range orders in Al90Tb10 glass and their relation to the structures of competing crystalline phases
Molecular dynamics simulations using an interatomic potential developed by
artificial neural network deep machine learning are performed to study the
local structural order in Al90Tb10 metallic glass. We show that more than 80%
of the Tb-centered clusters in Al90Tb10 glass have short-range order (SRO) with
their 17 first coordination shell atoms stacked in a '3661' or '15551'
sequence. Medium-range order (MRO) in Bergman-type packing extended out to the
second and third coordination shells is also clearly observed. Analysis of the
network formed by the '3661' and '15551' clusters show that ~82% of such SRO
units share their faces or vertexes, while only ~6% of neighboring SRO pairs
are interpenetrating. Such a network topology is consistent with the
Bergman-type MRO around the Tb-centers. Moreover, crystal structure searches
using genetic algorithm and the neural network interatomic potential reveal
several low-energy metastable crystalline structures in the composition range
close to Al90Tb10. Some of these crystalline structures have the '3661' SRO
while others have the '15551' SRO. While the crystalline structures with the
'3661' SRO also exhibit the MRO very similar to that observed in the glass, the
ones with the '15551' SRO have very different atomic packing in the second and
third shells around the Tb centers from that of the Bergman-type MRO observed
in the glassy phase
Development of Interatomic Potential for Al-Tb Alloy by Deep Neural Network Learning Method
An interatomic potential for Al-Tb alloy around the composition of Al90Tb10
was developed using the deep neural network (DNN) learning method. The atomic
configurations and the corresponding total potential energies and forces on
each atom obtained from ab initio molecular dynamics (AIMD) simulations are
collected to train a DNN model to construct the interatomic potential for Al-Tb
alloy. We show the obtained DNN model can well reproduce the energies and
forces calculated by AIMD. Molecular dynamics (MD) simulations using the DNN
interatomic potential also accurately describe the structural properties of
Al90Tb10 liquid, such as the partial pair correlation functions (PPCFs) and the
bond angle distributions, in comparison with the results from AIMD.
Furthermore, the developed DNN interatomic potential predicts the formation
energies of crystalline phases of Al-Tb system with the accuracy comparable to
ab initio calculations. The structure factor of Al90Tb10 metallic glass
obtained by MD simulation using the developed DNN interatomic potential is also
in good agreement with the experimental X-ray diffraction data
Fabrication and superconductivity of NaxTaS2 crystals
In this paper we report the growth and superconductivity of
crystals. The structural data deduced from X-ray diffraction pattern shows that
the sample has the same structure as . A series of crystals with
different superconducting transition temperatures () ranging from 2.5 K to
4.4 K were obtained. It is found that the rises with the increase of
content determined by Energy-Dispersive x-ray microanalysis(EDX) of Scanning
Electron Microscope (SEM) on these crystals. Compared with the resistivity
curve of un-intercalated sample ( = 0.8 K, 70
K), no signal of charge density wave (CDW) was observed in samples
and . However, in some samples with lower
, the CDW appears again at about 65 K. Comparison between the anisotropic
resistivity indicates that the anisotropy becomes smaller in samples with more
intercalation (albeit a weak semiconducting behavior along c-axis) and
thus higher . It is thus concluded that there is a competition between the
superconductivity and the CDW. With the increase of sodium content, the rise of
in is caused mainly by the suppression to the CDW in
, and the conventional rigid band model for layered dichalcogenide
may be inadequate to explain the changes induced by the slight intercalation of
sodium in .Comment: 8 pages, 13 figures, To appear in Physical Review
Structural study on hole-doped superconductors Pr1-xSrxFeAsO
The structural details in Pr1-xSrxFeAsO (1111) superconducting system are
analyzed using data obtained from synchrotron X-ray diffraction and the
structural parameters are carefully studied as the system is moving from
non-superconducting to hole-doped superconducting with the Sr concentration.
Superconductivity emerges when the Sr doping amount reaches 0.221. The linear
increase of the lattice constants proves that Sr is successfully introduced
into the system and its concentration can accurately be determined by the
electron density analyses. The evolution of structural parameters with Sr
concentration in Pr1-xSrxFeAsO and their comparison to other similar structural
parameters of the related Fe-based superconductors suggest that the interlayer
space between the conducting As-Fe-As layer and the insulating Pr-O-Pr layer is
important for improving Tc in the hole-doped (1111) superconductors, which
seems to be different from electron-doped systems.Comment: 17 pages, 7 figures, 1 tabl
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