17 research outputs found
Intelligent Omni-Surfaces Aided Wireless Communications: Does the Reciprocity Hold?
Intelligent omni-surfaces (IOS) have attracted great attention recently due
to its potential to achieve full-dimensional communications by simultaneously
reflecting and refracting signals toward both sides of the surface. However, it
still remains an open question whether the reciprocity holds between the uplink
and downlink channels in the IOS-aided wireless communications. In this work,
we first present a physics-compliant IOS related channel model, based on which
the channel reciprocity is investigated. We then demonstrate the
angle-dependent electromagnetic response of the IOS element in terms of both
incident and departure angles. This serves as the key feature of IOS that
drives our analytical results on beam non-reciprocity. Finally, simulation and
experimental results are provided to verify our theoretical analyses.Comment: 5 pages, 6 figure
Intelligent Omni-Surfaces: Reflection-Refraction Circuit Model, Full-Dimensional Beamforming, and System Implementation
The intelligent omni-surface (IOS) is a dynamic metasurface that has recently
been proposed to achieve full-dimensional communications by realizing the dual
function of anomalous reflection and anomalous refraction. Existing research
works provide only simplified models for the reflection and refraction
responses of the IOS, which do not explicitly depend on the physical structure
of the IOS and the angle of incidence of the electromagnetic (EM) wave.
Therefore, the available reflection-refraction models are insufficient to
characterize the performance of full-dimensional communications. In this paper,
we propose a complete and detailed circuit-based reflection-refraction model
for the IOS, which is formulated in terms of the physical structure and
equivalent circuits of the IOS elements, as well as we validate it against
full-wave EM simulations. Based on the proposed circuit-based model for the
IOS, we analyze the asymmetry between the reflection and transmission
coefficients. Moreover, the proposed circuit-based model is utilized for
optimizing the hybrid beamforming of IOS-assisted networks and hence improving
the system performance. To verify the circuit-based model, the theoretical
findings, and to evaluate the performance of full-dimensional beamforming, we
implement a prototype of IOS and deploy an IOS-assisted wireless communication
testbed to experimentally measure the beam patterns and to quantify the
achievable rate. The obtained experimental results validate the theoretical
findings and the accuracy of the proposed circuit-based reflection-refraction
model for IOSs.Comment: 33 pages, 20 figure
Intelligent Omni-Surfaces for Full-Dimensional Wireless Communications: Principle, Technology, and Implementation
The recent development of metasurfaces has motivated their potential use for
improving the performance of wireless communication networks by manipulating
the propagation environment through nearly-passive sub-wavelength scattering
elements arranged on a surface. However, most studies of this technology focus
on reflective metasurfaces, i.e., the surface reflects the incident signals
towards receivers located on the same side of the transmitter, which restricts
the coverage to one side of the surface. In this article, we introduce the
concept of intelligent omni-surface (IOS), which is able to serve mobile users
on both sides of the surface to achieve full-dimensional communications by
jointly engineering its reflective and refractive properties. The working
principle of the IOS is introduced and a novel hybrid beamforming scheme is
proposed for IOS-based wireless communications. Moreover, we present a
prototype of IOS-based wireless communications and report experimental results.
Furthermore, potential applications of the IOS to wireless communications
together with relevant research challenges are discussed
Influence of a Scanning Radial Magnetic Field on Macroparticle Reduction of Arc Ion-Plated Films
Cathode spot motion influences the physical characteristics of arc plasma and the related macroparticles (MPs) in resultant films; these MPs limit the application of arc ion plating (AIP). In this paper, a scanning radial magnetic field (SRMF) was applied to the cathode surface to control the cathode spot motion and reduce the MP contamination in the deposited films. It was shown that film surface morphologies prepared using SRMF were better than those using a static radial magnetic field (RMF). The improvement was greater with increased scanning range and frequency. Using SRMF, cathode spot motion was confined to a spiral trajectory on the cathode surface and the spots moved over a large area and at a fast-moving velocity. Both the large moving area and the fast velocity decreased the temperature on the cathode surface and thus reduced the emission of the MPs
Mechanism of chromium poisoning the conventional cathode material for solid oxide fuel cells
Chromium poisoning the La0.875Sr0.125MnO3 (LSM) cathode for solid oxide fuel cells is a critical issue that can strongly affect the stability. In this study, we evaluate the temperature distribution in a SOFC based on a 3D model and then combine conductivity test and material computation to reveal the effects of chromium in SUS430 stainless steels on LSM conductivities. The starch concentration in LSM pellets and the applied pressure on the contact with interconnect materials show close relationships with the chromium poisoning behavior. The density functional theory (DFT) computing results indicate that chromium atoms preferably adsorb on the MnO2-terminated and La (Sr)-O-terminated (001) surfaces. The resulting conclusions are expected to deeply understand mechanism of chromium deactivating conventional cathodes at some typical operational conditions, and offer crucial information to optimize the structure to avoid the poisoning effect
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Overcoming the difficulties of predicting conformational polymorph energetics in molecular crystals via correlated wavefunction methods.
Molecular crystal structure prediction is increasingly being applied to study the solid form landscapes of larger, more flexible pharmaceutical molecules. Despite many successes in crystal structure prediction, van der Waals-inclusive density functional theory (DFT) methods exhibit serious failures predicting the polymorph stabilities for a number of systems exhibiting conformational polymorphism, where changes in intramolecular conformation lead to different intermolecular crystal packings. Here, the stabilities of the conformational polymorphs of o-acetamidobenzamide, ROY, and oxalyl dihydrazide are examined in detail. DFT functionals that have previously been very successful in crystal structure prediction perform poorly in all three systems, due primarily to the poor intramolecular conformational energies, but also due to the intermolecular description in oxalyl dihydrazide. In all three cases, a fragment-based dispersion-corrected second-order Møller-Plesset perturbation theory (MP2D) treatment of the crystals overcomes these difficulties and predicts conformational polymorph stabilities in good agreement with experiment. These results highlight the need for methods which go beyond current-generation DFT functionals to make crystal polymorph stability predictions truly reliable