In order to optimize the current-control performance of the permanent-magnet synchronous motor (PMSM) system with model parameter mismatch and one-step control delay, an improved deadbeat predictive ...current control (DPCC) algorithm for the PMSM drive systems is proposed in this paper. First, the performance of the conventional predictive current control, when parameter mismatch exist, is analyzed, and then a stator current and disturbance observer (SCDO) based on sliding-mode exponential reaching law, which is able to simultaneously predict future value of stator current and track system disturbance caused by parameter mismatch in real time, is proposed. Based on this SCDO, prediction currents are used for replacing the sampled current in DPCC to compensate one-step delay, and estimated parameter disturbances are considered as the feedforward value to compensate the voltage reference calculated by deadbeat predictive current controller. Thus, a composite control method combining the DPCC part and current prediction and feedforward compensation part based on SCDO, called DPCC + SCDO method, is developed. Moreover, based on conventional exponential reaching law, a novel sliding-mode exponential reaching law is proposed to further improve the performance of the DPCC + SCDO method. Simulation and experimental results both show the validity of the proposed current control approach.
The surge of patients in the pandemic of COVID‐19 caused by the novel coronavirus SARS‐CoV‐2 may overwhelm the medical systems of many countries. Mask‐wearing and handwashing can slow the spread of ...the virus, but currently, masks are in shortage in many countries, and timely handwashing is often impossible. In this study, the efficacy of three types of masks and instant hand wiping was evaluated using the avian influenza virus to mock the coronavirus. Virus quantification was performed using real‐time reverse transcription‐polymerase chain reaction. Previous studies on mask‐wearing were reviewed. The results showed that instant hand wiping using a wet towel soaked in water containing 1.00% soap powder, 0.05% active chlorine, or 0.25% active chlorine from sodium hypochlorite removed 98.36%, 96.62%, and 99.98% of the virus from hands, respectively. N95 masks, medical masks, and homemade masks made of four‐layer kitchen paper and one‐layer cloth could block 99.98%, 97.14%, and 95.15% of the virus in aerosols. Medical mask‐wearing which was supported by many studies was opposed by other studies possibly due to erroneous judgment. With these data, we propose the approach of mask‐wearing plus instant hand hygiene (MIH) to slow the exponential spread of the virus. This MIH approach has been supported by the experiences of seven countries in fighting against COVID‐19. Collectively, a simple approach to slow the exponential spread of SARS‐CoV‐2 was proposed with the support of experiments, literature review, and control experiences.
A 3D host can effectively mitigate the dendritic growth of a zinc (Zn)‐metal anode. However, the increased electrode/electrolyte reaction area using the 3D substrate accelerates the passivation and ...corrosion at the anode interface, ultimately degrading the electrochemical performance. Here, an oriented freezing process is used to create a flexible MXene/graphene scaffold. Based on the abundant zincophilic traits and micropores in the structure, Zn is densely encapsulated inside the host by the electrodeposition process. During cycling, the composite anode endows an in situ solid electrolyte interface with zinc fluoride at the electrode/electrolyte interface due to inherent fluorine terminations in MXene, efficiently inhibiting the dendritic growth. Furthermore, the design wherein bulk Zn is distributed in a 3D microscale manner suppresses hydrogen evolution reactions (3.8 mmol h−1 cm−2) and passivation, through in/ex situ tests. As a result, in a symmetrical cell test, the electrode has a long‐cycling life of over 1000 h at 10 mA cm−2. After continuous single folding followed by double folding, a quasi‐solid‐state foldable cell with the composite anode and a LiMn2O4 cathode (60% depth of discharge) maintains high‐capacity retention of over 91%. This research presents a revolutionary encapsulating idea for aqueous Zn‐ion batteries, as well as foldable investigation.
A composite anode of metallic zinc (Zn) in graphene–MXene aerogel is prepared for Zn‐ion batteries. The Zn metal is completely encapsulated inside the host in a 3D microscale manner, which suppresses the side reactions and regulates the Zn deposition. Meanwhile, the aerogel, with excellent flexibility, achieves stable electrochemical performance for foldable Zn‐ion batteries.
Featured with unique mechanical, electronic and chemical properties, nitrogen‐doped carbon materials have become the research hotspot of energy storage. As electrode materials in supercapacitors ...(SCs), N‐doped carbons have demonstrated intriguing flexibility and superb performances in a wide electrochemical window, equipped with versatile properties as both cathodes and anodes for constructing high voltage devices. Compared with limited doping level, N‐rich and porous carbon materials (NPCs) are of great desire to release the restricted properties of N species and obtain high specific capacitances (>600 F g−1), pushing the energy density towards the battery level without scarifying the capacitor‐level power ability. In this Research News we firstly discuss the key factors influencing the performance of NPC electrodes to disclose related charge storage mechanisms. In addition, the trade‐off among N‐content, porous structure and electrical conductivity is involved as well as electrochemical behaviors in different electrolytes. Also, various progressive developments are highlighted systematically ranging from asymmetric to symmetric and hybrid configurations, covering both aqueous and non‐aqueous systems. Finally, some stubborn and unsolved problems are summarized, with prospective research guidelines on NPC‐based SCs.
Nitrogen‐rich porous carbons (NPCs) have brought new breakthroughs to supercapacitors (SCs) due to their unique physic‐chemical properties, and progressively pushed the energy density towards the battery level while keeping capacitor‐level power output, realizing high energy‐power integration to bridge the gap among current systems. Further, charge storage fundamentals in NPCs and progressive developments of NPC‐based SC configurations are highlighted systematically.
An elaborate and pervasive set of practices, calledguanxi, underlies everyday social relationships in contemporary China. Obtaining and changing job assignments, buying certain foods and consumer ...items, getting into good hospitals, buying train tickets, obtaining housing, even doing business-all such tasks call for the skillful and strategic giving of gifts and cultivating of obligation, indebtedness, and reciprocity. Mayfair Mei-hui Yang's close scrutiny of this phenomenon serves as a window to view facets of a much broader and more complex cultural, historical, and political formation. Using rich and varied ethnographic examples ofguanxistemming from her fieldwork in China in the 1980s and 1990s, the author shows how this "gift economy" operates in the larger context of the socialist state redistributive economy.
The coronavirus disease 2019 pandemic caused by the novel coronavirus SARS‐CoV‐2 (severe acute respiratory syndrome coronavirus 2) has claimed many lives worldwide. Wearing medical masks (MMs) or N95 ...masks (N95Ms namely N95 respirators) can slow the virus spread and reduce the infection risk. Reuse of these masks can minimize waste, protect the environment, and help solve the current imminent shortage of masks. Disinfection of used masks is needed for their reuse with safety, but improper decontamination can damage the blocking structure of masks. In this study, we demonstrated using the avian coronavirus of infectious bronchitis virus to mimic SARS‐CoV‐2 that MMs and N95Ms retained their blocking efficacy even after being steamed on boiling water for 2 hours. We also demonstrated that three brands of MMs blocked over 99% viruses in aerosols. The avian coronavirus was completely inactivated after being steamed for 5 minutes. Altogether, this study suggested that MMs are adequate for use on most social occasions and both MMs and N95Ms can be reused for a few days with steam decontamination between use.
Highlights
Reuse of medical masks and N95 respirators is highly needed.
The masks have excellent efficacy in blocking coronaviruses in aerosols.
The masks should be decontaminated for reuse.
The masks maintain their blocking efficacy after being steamed on boiling water.
The steam measure can inactivate coronaviruses completely.
Metallic zinc (Zn) having low cost, high capacity, environmentally friendly features is considered to be an attractive anode material for aqueous energy storage devices. However, dendritic growth and ...severe side reactions restrict the development of Zn‐metal anodes. Numerous 3D hosts are extensively explored to settle these issues, whereas the accessible prestoring of Zn metal into structured electrodes is challenging. Here, a thermal infusion strategy is first reported to create a stable composite Zn‐based anode. Upon this melting–wetting–cooling process, the metallic Zn is densely and firmly encapsulated in the 3D skeleton, efficiently inhibiting the dendritic growth. Meanwhile, through in/ex situ tests, the formation of ZnO layer on the metallic Zn surface inhibits the hydrogen evolution reactions (1.8 mmol h−1 cm−2) and passivation during cycling. Consequently, the electrode enables a long‐cycling life of over 1000 cycles at 10 mA cm−2 in a symmetrical cell. The pouch cells pairing this novel anode and LiMn2O4 cathode maintain over 94 mAh g−1 capacity retention after 300 cycles. This research presents an innovative Zn anode structure and extendable prestoring metallic Zn method for aqueous Zn‐ion batteries.
A facile thermal infusion approach is used to construct the multilevel electrode structure based on the porous Cu host for Zn metal anodes. The composite anode regulates the Zn deposition and inhibits the side reactions due to the in situ Cu–Zn solid solution and ZnO layer, thus achieving long‐cycling aqueous Zn‐ion batteries.
Cooling heat transfer of supercritical CO2 in horizontal straight tubes with wall is numerically investigated by using FLUENT. The results show that almost all models are able to present the trend of ...heat transfer qualitatively, and the stand k-ε with enhanced wall treatment model shows the best agreement with the experimental data, followed by LB low Re turbulence model. Then further studies are discussed on velocity, temperature and turbulence distributions. The parameters which are defined as the criterion of buoyancy effect on convection heat transfer are introduced to judge the condition of the fluid. The relationships among the inlet temperature, outlet temperature, the mass flow rate, the heat flux and the diameter are discussed and the difference between the cooling and heating of CO2 are compared.
A series of stable radical 2D metal‐organic frameworks has been assembled. (m‐TTFTB)3 (m‐Tetrathiafulvalene‐tetrabenzoate) trimer building blocks are beneficial for the stability of the radicals due ...to delocalization of the unpaired electron. Hexanuclear rare‐earth‐cluster‐based 1D chains further enhance the stability of the frameworks. The radical state of the middle TTF in the trimer has been observed by the change of central C−C and C−S bond distances and the configuration of the TTF by single‐crystal X‐ray diffraction. The radical characteristics are also confirmed by electron paramagnetic resonance, UV/Vis–NIR absorption, and X‐ray photoelectron spectroscopy experiments. Stability tests showed that the radicals are stable even in solutions and under acid/base environments (pH 1–12). Owing to efficient light absorption due to intramolecular charge transfer, low thermal conductivity, and outstanding stability, the radical 2D Dy‐MOF shows excellent photothermal properties, an increase of 34.7 °C within 240 s under one‐sun illumination.
The incorporation of TTF radical trimers and RE6 cluster SBUs result in a stable 2D radical MOF that is stable under harsh conditions including aqueous acid/base solutions. Exhibiting the characteristics of light absorption and excellent stability, the radical Dy‐MOF shows excellent photothermal conversion with an increase in temperature of 34.7 °C upon irradiation by one unit of sunlight within 240 s.
•The h fluctuates from top to bottom along the flow direction.•The h increases with the p, R, d increases.•The h is insensitive when p, R, d further increases.•The gravity has no obvious effect on ...the h.•The effect of the buoyancy force is weaker than that of the centrifugal force.
The cooling heat transfer of supercritical CO2 is simulated numerically in the horizontal helically coiled tube using RNG k–ε turbulence model. The parameters of the tube are: inner diameter of 4mm, a length of 2000mm, a pitch of 10mm, radius of helically coiled tube of 20mm, curvature of 0.1. It is found that the heat transfer coefficient fluctuates from top to bottom along the flow direction. On this basis, the effect of the pitch p, tube diameter of helically coiled tube d, radius of helically coiled tube R on the heat transfer coefficient (h) are studied. The results show that the h increases as the p, d, R increases and is insensitive when the p, d, R further increases to higher values. The change condition of the pressure is different with the p, d, R increasing. At the same time the contours show that the effect of the buoyancy force on h is weaker than that of the centrifugal force. A quantitative analysis is carried on to study the effect of gravity based on the setting conditions and the results shows that the effect of gravity can be ignorable on the heat transfer coefficient. The change condition of Rig is consistent with that of Gr/Re2.7 in judging the scope of the buoyancy force. The change condition of Ric/Rig indicates that the gravitational buoyancy force is more important than the centrifugal buoyancy force on the heat transfer coefficient under the setting conditions.
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