•TCA, LTCA and dynamic analysis is used to complete the 3-D modification.•A parabolic modification along helix direction is described in axial modification.•The results show good vibration reduction ...effect by using the proposed method.
Vibration and noise of gear meshing come from the dynamic working conditions, therefore, combining gear modification and dynamic characteristic analysis may offer reliable basis for the modification. Compared with profile modification and axial modification, 3-D modification is more comprehensive. The existing problems in current gear modification includes: (1) The ideal force under static or quasi-static conditions is used to replace the transient dynamic meshing force, so the effect of modification is not obvious in the middle and high speed gear transmission. (2) Though the modification is completed according to the dynamic performance, the dynamic characteristic analysis is not well combined with the gear meshing performance. Tooth contact analysis (TCA) and loaded tooth contact analysis (LTCA) can simulate the meshing process of gear and provide precise tooth surface geometric analysis data for later dynamic characteristic analysis. Therefore, combining TCA technology, LTCA technology and dynamic performance of gear, a 3-D modification method for reducing vibration of helical gear is proposed. Two application examples are given and good vibration reduction effects have been obtained. The biggest highlight of the paper is to use TCA technology, LTCA technology and dynamic characteristic analysis of gear to complete the 3-D modification of helical gear.
A long debate on the charge identity and the associated mechanisms occurring in contact‐electrification (CE) (or triboelectrification) has persisted for many decades, while a conclusive model has not ...yet been reached for explaining this phenomenon known for more than 2600 years! Here, a new method is reported to quantitatively investigate real‐time charge transfer in CE via triboelectric nanogenerator as a function of temperature, which reveals that electron transfer is the dominant process for CE between two inorganic solids. A study on the surface charge density evolution with time at various high temperatures is consistent with the electron thermionic emission theory for triboelectric pairs composed of Ti–SiO2 and Ti–Al2O3. Moreover, it is found that a potential barrier exists at the surface that prevents the charges generated by CE from flowing back to the solid where they are escaping from the surface after the contacting. This pinpoints the main reason why the charges generated in CE are readily retained by the material as electrostatic charges for hours at room temperature. Furthermore, an electron‐cloud–potential‐well model is proposed based on the electron‐emission‐dominatedcharge‐transfer mechanism, which can be generally applied to explain all types of CE in conventional materials.
Real‐time charge transfer in contact electrification (CE) is investigated quantitatively as a function of temperature via a triboelectric nanogenerator, revealing that electron transfer is the dominant process for CE between two inorganic solids. An electron‐cloud–potential‐well model is proposed for understanding all types of CE in conventional materials.
The development of transition‐metal‐oxides (TMOs)‐based bifunctional catalysts toward efficient overall water splitting through delicate control of composition and structure is a challenging task. ...Herein, the rational design and controllable fabrication of unique heterostructured inter‐doped ruthenium–cobalt oxide (Ru–Co)Ox hollow nanosheet arrays on carbon cloth is reported. Benefiting from the desirable compositional and structural advantages of more exposed active sites, optimized electronic structure, and interfacial synergy effect, the (Ru–Co)Ox nanoarrays exhibited outstanding performance as a bifunctional catalyst. Particularly, the catalyst showed a remarkable hydrogen evolution reaction (HER) activity with an overpotential of 44.1 mV at 10 mA cm−2 and a small Tafel slope of 23.5 mV dec−1, as well as an excellent oxygen evolution reaction (OER) activity with an overpotential of 171.2 mV at 10 mA cm−2. As a result, a very low cell voltage of 1.488 V was needed at 10 mA cm−2 for alkaline overall water splitting.
Unique ruthenium–cobalt oxide (Ru–Co)Ox hollow nanosheet arrays with an inter‐doped heterostructure are prepared on carbon cloth via a facile MOF template‐based strategy. The (Ru–Co)Ox nanoarrays exhibit excellent catalytic activity for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), indicating an outstanding bifunctional electrocatalyst for alkaline overall water splitting.
Traditional ultra-dense wireless networks are recommended as a complement for cellular networks and are deployed in partial areas, such as hotspot and indoor scenarios. Based on the massive ...multiple-input multi-output antennas and the millimeter wave communication technologies, the 5G ultra-dense cellular network is proposed to deploy in overall cellular scenarios. Moreover, a distribution network architecture is presented for 5G ultra-dense cellular networks. Furthermore, the backhaul network capacity and the backhaul energy efficiency of ultra-dense cellular networks are investigated to answer an important question, that is, how much densification can be deployed for 5G ultra-dense cellular networks. Simulation results reveal that there exist densification limits for 5G ultra-dense cellular networks with backhaul network capacity and backhaul energy efficiency constraints.
The fifth generation (5G) mobile communication systems will be in use around 2020. The aim of 5G systems is to provide anywhere and anytime connectivity for anyone and anything. Several new ...technologies are being researched for 5G systems, such as massive multiple-input multiple-output communications, vehicle-to-vehicle communications, high-speed train communications, and millimeter wave communications. Each of these technologies introduces new propagation properties and sets specific requirements on 5G channel modeling. Considering the fact that channel models are indispensable for system design and performance evaluation, accurate and efficient channel models covering various 5G technologies and scenarios are urgently needed. This paper first summarizes the requirements of the 5G channel modeling, and then provides an extensive review of the recent channel measurements and models. Finally, future research directions for channel measurements and modeling are provided.
Optical wireless communications (OWCs) refer to wireless communication technologies which utilize optical carriers in infrared, visible light, or ultraviolet bands of electromagnetic spectrum. For ...the sake of an OWC link design and performance evaluation, a comprehensive understanding and an accurate prediction of link behavior are indispensable. Therefore, accurate and efficient channel models are crucial for the OWC link design. This paper first provides a brief history of OWCs. It also considers OWC channel scenarios and their utilization trade-off in terms of optical carrier, range, mobility, and power efficiency. Furthermore, the main optical channel characteristics that affect the OWC link performance are investigated. A comprehensive overview of the most important OWCs channel measurement campaigns and channel models, primarily for wireless infrared communications and visible light communications, are presented. OWCs channel models are further compared in terms of computation speed, complexity, and accuracy. The survey considers indoor, outdoor, underground, and underwater communication environments. Finally, future research directions in OWCs channel measurements and models are addressed.
Co-infection has been reported in patients with severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome, but there is limited knowledge on co-infection among patients with ...coronavirus disease 2019 (COVID-19). The prevalence of co-infection was variable among COVID-19 patients in different studies, however, it could be up to 50% among non-survivors. Co-pathogens included bacteria, such as Streptococcus pneumoniae, Staphylococcus aureus, Klebsiella pneumoniae, Mycoplasma pneumoniae, Chlamydia pneumonia, Legionella pneumophila and Acinetobacter baumannii; Candida species and Aspergillus flavus; and viruses such as influenza, coronavirus, rhinovirus/enterovirus, parainfluenza, metapneumovirus, influenza B virus, and human immunodeficiency virus. Influenza A was one of the most common co-infective viruses, which may have caused initial false-negative results of real-time reverse-transcriptase polymerase chain reaction for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Laboratory and imaging findings alone cannot help distinguish co-infection from SARS-CoV-2 infection. Newly developed syndromic multiplex panels that incorporate SARS-CoV-2 may facilitate the early detection of co-infection among COVID-19 patients. By contrast, clinicians cannot rule out SARS-CoV-2 infection by ruling in other respiratory pathogens through old syndromic multiplex panels at this stage of the COVID-19 pandemic. Therefore, clinicians must have a high index of suspicion for coinfection among COVID-19 patients. Clinicians can neither rule out other co-infections caused by respiratory pathogens by diagnosing SARS-CoV-2 infection nor rule out COVID-19 by detection of non-SARS-CoV-2 respiratory pathogens. After recognizing the possible pathogens causing co-infection among COVID-19 patients, appropriate antimicrobial agents can be recommended.
Cellulose‐based triboelectric nanogenerators (TENGs) have gained increasing attention. In this study, a novel method is demonstrated to synthesize cellulose‐based aerogels and such aerogels are used ...to fabricate TENGs that can serve as mechanical energy harvesters and self‐powered sensors. The cellulose II aerogel is fabricated via a dissolution–regeneration process in a green inorganic molten salt hydrate solvent (lithium bromide trihydrate), where. The as‐fabricated cellulose II aerogel exhibits an interconnected open‐pore 3D network structure, higher degree of flexibility, high porosity, and a high surface area of 221.3 m2 g−1. Given its architectural merits, the cellulose II aerogel‐based TENG presents an excellent mechanical response sensitivity and high electrical output performance. By blending with other natural polysaccharides, i.e., chitosan and alginic acid, electron‐donating and electron‐withdrawing groups are introduced into the composite cellulose II aerogels, which significantly improves the triboelectric performance of the TENG. The cellulose II aerogel‐based TENG is demonstrated to light up light‐emitting diodes, charge commercial capacitors, power a calculator, and monitor human motions. This study demonstrates the facile fabrication of cellulose II aerogel and its application in TENG, which leads to a high‐performance and eco‐friendly energy harvesting and self‐powered system.
Cellulose II aerogels, with the features of high flexibility, porosity, and surface area, are integrated with triboelectric nanogenerators to yield green, sustainable energy harvesting, and sensing devices. By blending other natural polysaccharides to introduce electron‐donating and electron‐withdrawing groups, the performance of the cellulose II aerogel‐based triboelectric nanogenerators can be significantly improved and used for mechanical energy harvesting and motion monitoring.
Smoking prevalence has decreased significantly among US adolescents and young adults in the past 20 years. It is possible that adolescent and young adult smokers were moving from core to peripheral ...positions in social networks and thus less influential as suggested in previous research on adult smokers. We construct five sample datasets to test these hypotheses but none of them receives much support. When the proportion of smokers is relatively higher in two sample datasets, smokers tended to be at more marginal network positions than nonsmokers, both smokers and nonsmoker could exert peer influence, and the magnitude of peer influence from smokers was even greater than that from nonsmokers. When smoking was less frequent in the other three sample datasets, smokers and nonsmokers were at random network positions and no peer influence on smoking behavior was detected. Therefore, core/periphery network positions are still the key linking smoking prevalence and peer influence among US adolescents and young adults but operating through a different mechanism from their adult counterparts. When scientists design and conduct prevention programs against adolescent and young adult smoking behavior, core/periphery network positions, smoking prevalence, and peer influence should all be taken into consideration.
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