Detect to Learn: Structure Learning with Attention and Decision Feedback for MIMO-OFDM Receive Processing

The limited over-the-air (OTA) pilot symbols in multiple-input-multiple-output orthogonal-frequency-division-multiplexing (MIMO-OFDM) systems presents a major challenge for detecting transmitted data symbols at the receiver, especially for machine learning-based approaches. While it is crucial to explore effective ways to exploit pilots, one can also take advantage of the data symbols to improve detection performance. Thus, this paper introduces an online attention-based approach, namely RC-AttStructNet-DF, that can efficiently utilize pilot symbols and be dynamically updated with the detected payload data using the decision feedback (DF) mechanism. Reservoir computing (RC) is employed in the time domain network to facilitate efficient online training. The frequency domain network adopts the novel 2D multi-head attention (MHA) module to capture the time and frequency correlations, and the structural-based StructNet to facilitate the DF mechanism. The attention loss is designed to learn the frequency domain network. The DF mechanism further enhances detection performance by dynamically tracking the channel changes through detected data symbols. The effectiveness of the RC-AttStructNet-DF approach is demonstrated through extensive experiments in MIMO-OFDM and massive MIMO-OFDM systems with different modulation orders and under various scenarios.Comment: Accepted to IEEE Transactions on Communication

On the positive effect of UVC light during the removal of benzothiazoles by photoelectro-Fenton with UVA light

Benzothiazole (BTH) and 2-hydroxybenzothiazole (2-OH-BTH) are ubiquitous pollutants in aquatic ecosystems. This article reports their photoelectro-Fenton (PEF) treatment, either alone or mixed, in sulfate medium at pH 3.0 using an IrO2-based/air diffusion cell that generates H2O2 under UVA and/or UVC irradiation. UVC-PEF was more effective than UVA-PEF to remove the target pollutants, which suggests a positive impact of OH formed via Fenton's reaction and photo-induced homolysis of H2O2 in the former method. In addition, BTH disappeared more quickly than 2-OH BTH. Full-time UVA-/UVC-PEF outperformed UVC-PEF and UVA-PEF to mineralize the mixtures, although requiring a much higher energy consumption. The evolution of generated H2O2 and homogeneous OH confirmed the positive contribution of UVC photolysis in UVA-PEF. Part-time use of UVC radiation in UVA-PEF yielded a similar total organic carbon removal, with much lower energy consumption. BTH was oxidized to 2-OH-BTH, which was subsequently transformed into other five heteroaromatics

Learning to Estimate: A Real-Time Online Learning Framework for MIMO-OFDM Channel Estimation

In this paper we introduce StructNet-CE, a novel real-time online learning framework for MIMO-OFDM channel estimation, which only utilizes over-the-air (OTA) pilot symbols for online training and converges within one OFDM subframe. The design of StructNet-CE leverages the structure information in the MIMO-OFDM system, including the repetitive structure of modulation constellation and the invariant property of symbol classification to inter-stream interference. The embedded structure information enables StructNet-CE to conduct channel estimation with a binary classification task and accurately learn channel coefficients with as few as two pilot OFDM symbols. Experiments show that the channel estimation performance is significantly improved with the incorporation of structure knowledge. StructNet-CE is compatible and readily applicable to current and future wireless networks, demonstrating the effectiveness and importance of combining machine learning techniques with domain knowledge for wireless communication systems

Bifurcation in a Discrete Competition System

A new difference system is induced from a differential competition system by different discrete methods. We give theoretical analysis for local bifurcation of the fixed points and derive the conditions under which the local bifurcations such as flip occur at the fixed points. Furthermore, one- and two-dimensional diffusion systems are given when diffusion terms are added. We provide the Turing instability conditions by linearization method and inner product technique for the diffusion system with periodic boundary conditions. A series of numerical simulations are performed that not only verify the theoretical analysis, but also display some interesting dynamics

Mesoporous WO3 Nanofibers With Crystalline Framework for High-Performance Acetone Sensing

Semiconducting metal oxides with abundant active sites are regarded as promising candidates for environmental monitoring and breath analysis because of their excellent gas sensing performance and stability. Herein, mesoporous WO3 nanofibers with a crystalline framework and uniform pore size is successfully synthesized in an aqueous phase using an electrospinning method, with ammonium metatungstate as the tungsten sources, and SiO2 nanoparticles and polyvinylpyrrolidone as the sacrificial templates. The obtained mesoporous WO3 nanofibers exhibit a controllable pore size of 26.3–42.2 nm, specific surface area of 24.1–34.4 m2g−1, and a pore volume of 0.15–0.24 cm3g−1. This unique hierarchical structure, with uniform mesopores and interconnected channels, could facilitate the diffusion and transportation of gas molecules in the framework. Gas sensors, based on mesoporous WO3 nanofibers, exhibit an excellent performance in acetone sensing with a low limit of detection (<1 ppm), short response-recovery time (24 s/27 s), a linear relationship in a broad range, and good selectivity

p16 Mutation Spectrum in the Premalignant Condition Barrett's Esophagus

Background: Mutation, promoter hypermethylation and loss of heterozygosity involving the tumor suppressor gene p16 (CDKN2a/INK4a) have been detected in a wide variety of human cancers, but much less is known concerning the frequency and spectrum of p16 mutations in premalignant conditions. Methods and Findings: We have determined the p16 mutation spectrum for a cohort of 304 patients with Barrett’s esophagus, a premalignant condition that predisposes to the development of esophageal adenocarcinoma. Forty seven mutations were detected by sequencing of p16 exon 2 in 44 BE patients (14.5%) with a mutation spectrum consistent with that caused by oxidative damage and chronic inflammation. The percentage of patients with p16 mutations increased with increasing histologic grade. In addition, samples from 3 out of 19 patients (15.8%) who underwent esophagectomy were found to have mutations. Conclusions: The results of this study suggest the environment of the esophagus in BE patients can both generate an

The Performance of Dynamic-static Spectrum Access Based on Markov Transfer Model

This study presented a non-synchronized random access mechanism that supports dynamic-static spectrum. Generally, the authorized users of two networks (network A and network B) with different frequency bands communicate with each other by using static spectrum. When congestion happened, spectrum holes in their networks can be detected by the opposite networks and then utilized to communicate. Based on queuing theory and Markov transfer model, a user behavior characterized by dynamic-static spectrum access was proposed, and the feasibility of this theoretical model was validated through analog simulation. Thereafter, the theoretical parameters of system performance, like blocking possibility, forced drop-call possibility, and throughput, were measured and compared between dynamic-static mode and unconjugated mode

Organohydrogel‐Based Soft SEMG Electrodes for Algorithm‐Assisted Gesture Recognition

Abstract Epidermal electronics that can monitor physiological signals such as surface electromyogram (sEMG) signals attract widespread attentions in personalized healthcare, human–machine interfaces (HMI) and virtual/augmented reality (AR/VR). However, conventional electromyographic electrodes suffer from skin discomfort, susceptibility to motion artifact interference, and short service lifetime. Here, an organohydrogel‐based sEMG electrode endows with high conductivity, low modulus and long‐term stability is developed by doping partially reduced graphene oxide (pRGO) into highly cross‐linked organohydrogel network. The as‐fabricated polyacrylamide/sodium alginate/tannic acid/partially reduced graphene oxide (PAM/SA/TA/pRGO) organohydrogel possesses farewell conductivity (4.22 S m−1) while preserving tissue‐like compliance (Young's modulus ≈32 KPa), excellent stretchability (≈600%), high adhesion as well as superior anti‐drying properties. In addition, a stretchable sEMG electrode for long‐term reliable service is fabricated via immobilizing the organohydrogel electrodes onto a flexible very high bond (VHB) substrate. As a result, the integrated electrodes show high signal‐to‐noise ratio (SNR) (35.15 db) comparable to that of the commercial electrodes. Furthermore, with assistance of deep learning, the proposed sEMG electrodes obtain high identification accuracy of 97.11% in distinguishing sophisticated gestures. This system can be further exploited for real‐time tele‐operations and offers broad prospects in human–machine immersive interactive application

Energy Dissipation and Stress Equilibrium Behavior of Granite under Dynamic Impact

Stress equilibrium time is an important index to judge the homogeneity of rocks. In order to study the relationship between stress equilibrium time and crushing energy consumption before rock destruction, Hopkinson tests were conducted on granite specimens with different length-to-diameter ratios. In this paper, by studying the size and strain rate effects of rocks, five different sizes of granite specimens with different aspect ratios were prepared and Hopkinson impact tests were conducted under four strain rate conditions. Data analysis and processing using the three-wave method to investigate the stress uniformity of granite specimens under impact loading. The energy balance factor was introduced to compare and analyze the stress equilibrium time of five kinds of long-diameter granite specimens, and it was found that the stress equilibrium time of rocks with the same length–diameter ratio decreased with the increase of loading strain rate, while the granite specimens with length–diameter ratio of 0.8 showed a better stress equilibrium time. In order to better find the aspect ratio and loading strain rate that can crush better and maintain a long equilibrium time, the energy consumption of rock crushing is further analyzed. The energy dissipation of granite specimens with loading strain rate of 156.8 s−1 and 253.2 s−1 was found to be more concentrated, and the energy dissipation rate was stable at about 48%. Subsequently, the relationship between stress equilibrium time and energy dissipation was established, and it was proved that the fastest growing time period of the energy dissipation curve was approximately equal to the rock stress equilibrium time, while the length-to-diameter ratio of the granite specimen that could better maintain the stress uniformity before rock crushing was 0.8 and the loading strain rate was 156.8 s−1

Energy Dissipation and Stress Equilibrium Behavior of Granite under Dynamic Impact

Stress equilibrium time is an important index to judge the homogeneity of rocks. In order to study the relationship between stress equilibrium time and crushing energy consumption before rock destruction, Hopkinson tests were conducted on granite specimens with different length-to-diameter ratios. In this paper, by studying the size and strain rate effects of rocks, five different sizes of granite specimens with different aspect ratios were prepared and Hopkinson impact tests were conducted under four strain rate conditions. Data analysis and processing using the three-wave method to investigate the stress uniformity of granite specimens under impact loading. The energy balance factor was introduced to compare and analyze the stress equilibrium time of five kinds of long-diameter granite specimens, and it was found that the stress equilibrium time of rocks with the same length–diameter ratio decreased with the increase of loading strain rate, while the granite specimens with length–diameter ratio of 0.8 showed a better stress equilibrium time. In order to better find the aspect ratio and loading strain rate that can crush better and maintain a long equilibrium time, the energy consumption of rock crushing is further analyzed. The energy dissipation of granite specimens with loading strain rate of 156.8 s−1 and 253.2 s−1 was found to be more concentrated, and the energy dissipation rate was stable at about 48%. Subsequently, the relationship between stress equilibrium time and energy dissipation was established, and it was proved that the fastest growing time period of the energy dissipation curve was approximately equal to the rock stress equilibrium time, while the length-to-diameter ratio of the granite specimen that could better maintain the stress uniformity before rock crushing was 0.8 and the loading strain rate was 156.8 s−1