Fading Research Articles

ZnFe2O4, a Green and High-Capacity Anode Material for Lithium-Ion Batteries: A Review

Ferrites, a broad class of ceramic oxides, possess intriguing physico-chemical properties, mainly due to their unique structural features, that, during these last 50–60 years, made them the materials of choice for many different applications. They are, indeed, applied as inductors, high-frequency materials, for electric field suppression, as catalysts and sensors, in nanomedicine for magneto-fluid hyperthermia and magnetic resonance imaging, and, more recently, in electrochemistry. In particular, ZnFe2O4 and its solid solutions are drawing scientists’ attention for the application as anode materials for lithium-ion batteries (LIBs). The main reasons are found in the low cost, abundance, and environmental friendliness of both Zn and Fe precursors, high surface-to-volume ratio, relatively short path for Li-ion diffusion, low working voltage of about 1.5 V for lithium extraction, and the high theoretical specific capacity (1072 mAh g−1). However, some drawbacks are represented by fast capacity fading and poor rate capability, resulting from a low electronic conductivity, severe agglomeration, and large volume change during lithiation/delithiation processes. In this review, the main synthesis methods of spinels will be briefly discussed before presenting the most recent and promising electrochemical results on ZnFe2O4 obtained with peculiar morphologies/architectures or as composites, which represent the focus of this review.

Game Theory for Anti-Jamming Strategy in Multichannel Slow Fading IoT Networks

The open nature of the wireless communication medium renders it vulnerable to jamming attacks by malicious users. To detect their presence and to avoid such attacks, several techniques are present in the literature. Most of these techniques aim to reduce the effect of the jamming signals by increasing the transmission power or by using complex coordination schemes. However, the implementation of such power consuming techniques might be challenging or not feasible in limited resources Internet-of-Things (IoT) devices. Therefore, a defending strategy against jamming attacks in health monitoring IoT networks is proposed in this article. This strategy operates in orthogonal frequency-division multiplexing channels and takes into consideration the effect of slow fading channels in the strategy design. Specifically, the jamming combating problem is formulated as a Colonel Blotto game where the equilibrium defines the minimization of the worst case jamming effect on the IoT sensors communications. Then, the optimal power allocation strategy for all the potential jammer power ranges is derived by investigating the Nash equilibrium of the game. This proposed strategy is shown to be efficient in combating jamming attacks while minimizing the IoT sensors power consumption.

The Impact of Vertical Salinity Gradient on Non-Line-of-Sight Underwater Optical Wireless Communication

The non-line-of-sight (NLOS) underwater communication can offer a viable route in signal propagation and coverage, thus mitigating the pointing, acquisition, and tracking difficulties in line-of-sight optical communication. However, implementing the NLOS link is non-trivial. While the NLOS technique relies on light scattering, i.e., channel turbulence can facilitate NLOS communication, the associated path-loss (PL) can be significant. Signal fading can degrade link robustness, which arises due to ocean water temperature and salinity fluctuation and gradients. To evaluate the robustness of NLOS in natural waters, we systematically measure the link metrics, such as the bit error ratio, PL, and signal-to-noise ratio (SNR), of water bodies of uniform and nonuniform vertical salinity ranging from 30–40‰ (part-per-thousand). We found that salinity-induced turbulence can establish NLOS communication with PL reduction of 2.35 dB/m and SNR increase by 32.5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> for dynamic water. Furthermore, a strong correlation was obtained between the strength of signal fluctuations and the received SNR. Finally, we obtained a Gaussian distribution of the statistical scintillation behavior. These results demonstrated the benefit of using the NLOS regime for underwater wireless sensor networks for aiding designers and engineers.

Synthesis and optical properties of novel Gd3+-doped BaZn2(PO4)2 glass-ceramics for radiation detection applications

45P2O5–15BaO–25ZnO–15B2O3 glasses doped with different concentrations (0 mol%, 0.1 mol%, 0.25 mol%, 0.5 mol%, and 0.75 mol%) of Gd3+ were prepared by a melt-quenching method and treated to fabricate glass-ceramics containing BaZn2(PO4)2 crystals by controllable crystallization. The structural, optical, and dosimetric properties were investigated. FTIR spectra indicate that the glasses are composed of [PO4], [BO3], and [BO4] basic structural units. The XRD pattern analysis indicates that the samples contain BaZn2(PO4)2 crystals. In the photoluminescence (PL) spectra, two emission bands are observed at 307 and 313 nm due to the 6P5/2→8S7/2 and 6P7/2→8S7/2 transitions of Gd3+, respectively. The OSL dosimetric properties of glass-ceramics were studied further under beta radiation of 90Sr. The optimal Gd3+ doping concentration of 0.5 mol% was determined. The fading of the OSL signal shows that the CW-OSL signal of Gd3+-doped BaZn2(PO4)2 glass-ceramics decays by about 58.95% within 120 h, and the intensity remains stable thereafter. The thermoluminescence (TL) curve has three peaks at 164, 240, and 344 °C. Minimum detectable dose (MDD) of the 0.5 mol% Gd3+-doped BaZn2(PO4)2 glass-ceramics was calculated as 0.675 mGy. The samples also exhibit good signal reusability and a broad linear dose-response range (0.3–500 Gy). Results show the excellent dosimetric properties of Gd3+-doped BaZn2(PO4)2 glass-ceramics and their potential application in radiation dosimetry.

Performance analysis of massive multiple input multiple output for high speed railway

This paper analytically reviews the performance of massive multiple input multiple output (MIMO) system for communication in highly mobility scenarios like high speed Railways. As popularity of high speed train increasing day by day, high data rate wireless communication system for high speed train is extremely required. 5G wireless communication systems must be designed to meet the requirement of high speed broadband services at speed of around 500 km/h, which is the expected speed achievable by HSR systems, at a data rate of 180 Mbps or higher. Significant challenges of high mobility communications are fast time-varying fading, channel estimation errors, doppler diversity, carrier frequency offset, inter carrier interference, high penetration loss and fast and frequent handovers. Therefore, crucial requirement to design high mobility communication channel models or systems prevails. Recently, massive MIMO techniques have been proposed to significantly improve the performance of wireless networks for upcoming 5G technology. Massive MIMO provide high throughput and high energy efficiency in wireless communication channel. In this paper, key findings, challenges and requirements to provide high speed wireless communication onboard the high speed train is pointed out after thorough literature review. In last, future research scope to bridge the research gap by designing efficient channel model by using massive MIMO and other optimization method is mentioned.

Ultra-Stable Lithium-Sulfur Batteries Using Nickel Phosphide@Carbon Fabric Interlayer

Lithium-sulfur batteries (LSB) are highly promising candidates for next generation energy storage devices due to their high theoretical capacity and the low cost of sulfur. However, dissolution of lithium polysulfides (LPS) into electrolyte causes undesirable effects, resulting in loss of active materials, low Coulombic efficiency, and fast capacity fading. To address these issues, designed interlayers are inserted between a separator and S cathode to evaluate the effect of blocking of long chain LPS and catalytic conversion of LPS to Li2S2/Li2S on battery performance. In order to amplify the effect of interlayer, the Ni2P nanoparticles are electrochemically deposited on carbon fabric (CF) which exhibit excellent adsorption and conversion effect of LPS. A cell fabricated with the Ni2P@CF interlayer allows remarkable improvement in the capacity decay of 0.04% per cycle at 1C for 1000 cycles and outstanding high rate capability. The cell delivered a capacity retention of 64% employing a current density of 8 C.

An Organic Cathode Material S‐3Q@MWCNT with Monoelectrochemical Conversion Phase for Highly Reversible Lithium Batteries

Monoelectrochemical Conversions Multielectrochemical phase conversion is usually involved in a fast capacity fading during charge–discharge processes. In article number 2100108 by Minghua Wang, Hanping Zhang, and co-workers, an organic sulfur material S-3Q@MWCNT exhibits monoelectrochemical phase conversion with an enhanced cycling performance. The finding that the chemical matching point and the electrochemical matching point are consistent with each other is also presented.

Review: Liner Notes for the Revolution: The Intellectual Life of Black Feminist Sound, by Daphne A. Brooks

Review: <i>Liner Notes for the Revolution: The Intellectual Life of Black Feminist Sound</i>, by Daphne A. Brooks

The Electrochemical Performance of δ-MnO2 Cathode Material for Aqueous Zinc-Ion Batteries: The Role of Current Collector

Electrochemical properties of δ-MnO2-based cathode materials were studied in dependence on current collector used for electrode casting (stainless steel mesh, carbon paper and titanium foil) by galvanostatic charge/discharge measurements and cyclic voltammetry. It was shown that δ-MnO2-based electrodes cast on carbon paper demonstrate the most stable electrochemical performance in comparison with two other current collectors. This can be explained by corrosion of steel and passivation of titanium in mild aqueous electrolytes. Detailed study of carbon paper as current collector shows that pressing of electrodes leads to decreasing the porosity and fast capacity fading.

A Strategic Approach to Use Upcycled Si Nanomaterials for Stable Operation of Lithium-Ion Batteries.

Silicon, as a promising next-generation anode material, has drawn special attention from industries due to its high theoretical capacity (around 3600 mAh g−1) in comparison with conventional electrodes, e.g., graphite. However, the fast capacity fading resulted by a large volume change hinders the pragmatic use of Si anodes for lithium ion batteries. In this work, we propose an efficient strategy to improve the cyclability of upcycled Si nanomaterials through a simple battery operation protocol. When the utilization degree of Si electrodes was decreased, the electrode deformation was significantly alleviated. This directly led to an excellent electrochemical performance over 100 cycles. In addition, the average charge (delithation) voltage was shifted to a lower voltage, when the utilization degree of electrodes was controlled. These results demonstrated that our strategic approach would be an effective way to enhance the electrochemical performance of Si anodes and improve the cost-effectiveness of scaling-up the decent nanostructured Si material.

Amplitude compensation using homodyne detection for inverse synthetic aperture LADAR.

Inverse synthetic aperture LADAR (ISAL), based on an electro-optic in-phase and quadrature (I/Q) modulator, and homodyne detection, has high pulse repetition frequency, simple structure, and minimum intra-pulse phase errors. Homodyne detection can implement the de-chirp operation in the optical domain, while the output amplitude is susceptible to light intensity. However, the modulated optical signal amplitude fading, induced by radio frequency devices and the I/Q modulator, is quite tricky to measure and be compensated for. In this work, the effect of amplitude distortion on the ISAL system is analyzed. A simple and effective compensation method (based on homodyne detection) is proposed, followed by some experiments. The improvement of homodyne signal power to the compensated signal compared with non-compensated signal was about 1 dB (26%), and the image quality of our ISAL system along range direction was also improved by using the proposed method. Moreover, the image of an extended target was acquired via our ISAL system with 500 mW transmitting power at a distance of 1.1 km.

Characterization and Investigation of Nonlinear Behaviour of Radio Refractivity during the Rainy and Dry Seasons in the Coastal Region of Nigeria

&#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; The transmission and receiving of good quality of signals globally has been impaired due to the internal activities of the troposphere linked to the nonlinear behaviour of the meteorological parameters. This paper focusses on characterizing and investigating the nonlinear behaviour of radio refractivity during the rainy and dry seasons in the coastal region of Nigeria using temperature, pressure and relative humidity data collected over a period of two years by the Centre for Atmospheric Research, National Space Research and Development Agency (NASRDA) from Lagos state. Data obtained were analyzed by False Nearest Neighbour (FNN) and Recurrence Quantification Analysis (RQA). The results show that recurrence techniques are able to identify the periods where there are high predictability and low predictability. The investigation of nonlinear effects of meteorological parameters and the hydrometeors on the troposphere help to avoid fading of radio signals along with the radio communication links.&#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D;

Chemomechanically Stable Ultrahigh-Ni Single-Crystalline Cathodes with Improved Oxygen Retention and Delayed Phase Degradations.

The pressing demand in electrical vehicle (EV) markets for high-energy-density lithium-ion batteries (LIBs) requires further increasing the Ni content in high-Ni and low-Co cathodes. However, the commercialization of high-Ni cathodes is hindered by their intrinsic chemomechanical instabilities and fast capacity fade. The emerging single-crystalline strategy offers a promising solution, yet the operation and degradation mechanism of single-crystalline cathodes remain elusive, especially in the extremely challenging ultrahigh-Ni (Ni > 90%) regime whereby the phase transformation, oxygen loss, and mechanical instability are exacerbated with increased Ni content. Herein, we decipher the atomic-scale stabilization mechanism controlling the enhanced cycling performance of an ultrahigh-Ni single-crystalline cathode. We find that the charge/discharge inhomogeneity, the intergranular cracking, and oxygen-loss-related phase degradations that are prominent in ultrahigh-Ni polycrystalline cathodes are considerably suppressed in their single-crystalline counterparts, leading to improved chemomechanical and cycling stabilities of the single-crystalline cathodes. Our work offers important guidance for designing next-generation single-crystalline cathodes for high-capacity, long-life LIBs.

Fast Fading Channel Estimation for OFDM Systems with Complexity Reduction

Channel estimation plays a significant role in the Inter-carrier interference (ISI) mitigation and symbol detection in Orthogonal frequency division multiplexing (OFDM) systems. As the speed of mobile terminal increases, the channel changes rapidly, causing fast fading which will degrade the system performance. In this paper, a low complexity fast fading channel estimation method suited for scattered pilot OFDM systems is proposed. This method is characterized by estimating channel matrix directly in the frequency domain, which can significantly reduce the channel estimation complexity with good system performance. Simulation results verify its superiority over the existing estimation methods.

Electrochemically incorporated Cu nanoparticles in NaVO3 with enhanced sodium-ion battery performance

Sodium-ion batteries (SIBs) are believed to be the promising low-cost candidates as compared to lithium-ion batteries (LIBs). Particularly, layered metal oxides show great potential as electrode materials with high capacity for SIB. However, the layered metal oxides undergo irreversible structural changes and suffer from low conductivity during charge and discharge, leading to sluggish electrochemical processes and fast capacity fading. To overcome these weaknesses, we electrochemically in-situ incorporate copper nanoparticles in NaVO 3 host material during battery cycling processes, giving rise to fast electron transfer in the material matrix. The resultant copper-incorporated NaVO 3 is demonstrated to have significantly increased performance for SIBs, which exhibits excellent reversible capacity, high coulombic efficiency, large capacity retention and outstanding rate capability. From ex-situ microscopy and spectroscopy characterizations, we show the evidence of the electrochemically formed Cu nanoparticles. This strategy also provides a general method to form homogeneous metal incorporation and improve the electrochemical properties for low-conductivity electrode materials. • Cu nanoparticles were electrochemically in-situ incorporated into NaVO 3 networks. • The Cu nanoparticles give rise to the enhanced conductivity of the electrode. • Detailed characterizations and the reaction mechanism were elucidated. • The product exhibited superior cycling performance as Na-ion battery electrode.

Adaptive Transmission With Frequency-Domain Precoding and Linear Equalization Over Fast Fading Channels

In this paper, the emerging orthogonal time frequency space (OTFS) modulation is firstly restructured as a precoded orthogonal frequency division multiplexing (OFDM) system, so that the well-established frequency-domain approach can be applied to perform signal in fast fading channels. Then a frequency-domain minimum mean squared error (MMSE) equalizer for OTFS is introduced and its performance is analyzed based on the eigenvalue decomposition of the channel matrix. Inspired by the frequency-domain precoding structure, an adaptive transmission scheme with frequency-domain precoding matrix composed of the eigenvectors of the channel matrix is proposed to improve the system performance under MMSE equalization, and its optimized performance is derived with simple expression. Finally, considering two extreme channel conditions, the lower and upper bounds for the diversity performance of the adaptive transmission scheme are derived. Simulation results show that the proposed adaptive transmission achieves significantly better performance for short signal frames and can work well with imperfect channel state information (CSI). The derived performance bounds can serve as benchmarks for OTFS and other precoded OFDM systems.

Lyapunov-Guided Deep Reinforcement Learning for Stable Online Computation Offloading in Mobile-Edge Computing Networks

Opportunistic computation offloading is an effective method to improve the computation performance of mobile-edge computing (MEC) networks under dynamic edge environment. In this paper, we consider a multi-user MEC network with time-varying wireless channels and stochastic user task data arrivals in sequential time frames. In particular, we aim to design an online computation offloading algorithm to maximize the network data processing capability subject to the long-term data queue stability and average power constraints. The online algorithm is practical in the sense that the decisions for each time frame are made without the assumption of knowing the future realizations of random channel conditions and data arrivals. We formulate the problem as a multi-stage stochastic mixed integer non-linear programming (MINLP) problem that jointly determines the binary offloading (each user computes the task either locally or at the edge server) and system resource allocation decisions in sequential time frames. To address the coupling in the decisions of different time frames, we propose a novel framework, named LyDROO, that combines the advantages of Lyapunov optimization and deep reinforcement learning (DRL). Specifically, LyDROO first applies Lyapunov optimization to decouple the multi-stage stochastic MINLP into deterministic per-frame MINLP subproblems. By doing so, it guarantees to satisfy all the long-term constraints by solving the per-frame subproblems that are much smaller in size. Then, LyDROO integrates model-based optimization and model-free DRL to solve the per-frame MINLP problems with very low computational complexity. Simulation results show that under various network setups, the proposed LyDROO achieves optimal computation performance while stabilizing all queues in the system. Besides, it induces very low computation time that is particularly suitable for real-time implementation in fast fading environments.

Wireless Covert Communications Aided by Distributed Cooperative Jamming Over Slow Fading Channels

In this paper, we study covert communications between a pair of legitimate transmitter-receiver against a watchful warden over slow fading channels. There coexist multiple friendly helper nodes who are willing to protect the covert communication from being detected by the warden. We propose an uncoordinated jammer selection scheme where those helpers whose instantaneous channel gains to the legitimate receiver fall below a pre-established selection threshold will be chosen as jammers radiating jamming signals to defeat the warden. By doing so, the detection accuracy of the warden is expected to be severely degraded while the desired covert communication is rarely affected. We then jointly design the optimal selection threshold and message transmission rate for maximizing covert throughput under the premise that the detection error of the warden exceeds a certain level. Numerical results are presented to validate our theoretical analyses. It is shown that the multi-jammer assisted covert communication outperforms the conventional single-jammer method in terms of covert throughput, and the maximal covert throughput improves significantly as the total number of helpers increases, which demonstrates the validity and superiority of our proposed scheme.

Boosters appear effective, but are they always needed?

High efficacy rates of the mRNA vaccines against symptomatic COVID-19, reported from clinical trials, kindled hope that they would prevent all infections caused by SARS-CoV-2. Currently approved vaccines provide high levels of protection against serious illness, but do not confer mucosal immunity to resist entry of the virus into the respiratory tract. When mostly mild breakthrough infections were reported from different countries,1–3 concern arose that individuals with a fast fading immune response to the standard vaccination schedule might experience serious illness if infected.

Towards a fast and stable filter for RSSI-based handoff algorithms in dense indoor WLANs

In dense indoor wireless networks, handoffs occur frequently. The criteria to trigger handoffs are not defined by the IEEE 802.11 standard, thus being specific to each manufacturer’s implementation. Current handoff implementations typically use RSSI (Received Signal Strength Indicator) as a performance metric and commonly cause association instability in dense environments, a well-known problem referred to as the ping-pong effect. In this paper, we present a deep analysis of RSSI traces collected in dense indoor environments using the FIBRE testbed. Based on that, we conclude that the RSSI time series presents deep fast fades that occur frequently in bursts of small sizes, which can cause ping-pongs. Motivated by this behavior, we propose a new and simple filtering mechanism called Maximum which targets to eliminate these valleys in the RSSI time series. In a nutshell, this filter chooses the maximum RSSI value from a sliding window containing the last few RSSI samples of the series. We conduct simulations based on real RSSI traces from static and mobile scenarios to evaluate Maximum with respect to other filtering mechanisms found in the literature. Additionally, we present a simplified model of the behavior of Maximum that allows us to study the probability of unwanted handoffs as a function of the RSSI of the available access points. Our analysis reveals that Maximum is able to offer a better tradeoff between handoff triggering delay and stability in mobile scenarios, while also performing well in static scenarios, effectively avoiding the occurrence of ping-pongs in most cases.