On the electron sheath theory and its applications in plasma–surface interactions

In this work,an improved understanding of electron sheath theory is provided using both fluid and kinetic approaches while elaborating on their implications for plasma–surface interactions.A fluid model is proposed considering the electron presheath structure,avoiding the singularity in electron sheath Child–Langmuir law which overestimates the sheath potential.Subsequently,a kinetic model of electron sheath is established,showing considerably different sheath proflles in respect to the fluid model due to non-Maxwellian electron velocity distribution function and flnite ion temperature.The kinetic model is then further generalized and involves a more realistic truncated ion velocity distribution function.It is demonstrated that such a distribution function yields a super-thermal electron sheath whose entering velocity at the sheath edge is greater than the Bohm criterion prediction.Furthermore,an attempt is made to describe the electron presheath–sheath coupling within the kinetic framework,showing a necessary compromise between a realistic sheath entrance and the inclusion of kinetic effects.Finally,the secondary electron emissions induced by sheath-accelerated plasma electrons in an electron sheath are analysed and the influence of backscattering is discussed.

The Beneficial Effect of Enriched Environment on Pathogenesis of Alzheimer’s Disease

Alzheimer’s disease (AD) is a common neurodegenerative disease, its main clinical symptoms are the progressive decline of cognitive and memory functions. Enriched Environment (EE) achieves the goal of improving brain cognitive reserve by enhancing the multi-directional stimulation on movement, sensory and cognitive systems of animals. And EE can regulate the levels of various trophic factors in the brain, promote synaptic regeneration and enhance neural plasticity to reduce the loss of neurons induced by inflammation. At present, there is still no effective treatment for AD and the clinical intervention drug is expensive. So it is essential to actively explore non-drug treatment. This review will explain the effects of EE on learning ability, memory ability and mental behavior in AD, and provide a new direction for the treatment and rehabilitation of AD.

Therapeutic Potential of FGF21 in Alzheimer’s Disease

Alzheimer’s disease (AD) is the most common form of dementia which mostly affects persons younger than 65 years old. Mounting findings showed that amyloid-β(Aβ) peptides, oxidative stress, neuroinflammation and insulin resistance may play central role in the pathogenesis of AD. There are very many methods to slow it through affecting these aforementioned factors. However, more efficient prevention of the progression of AD is still ambiguous. Fibroblast growth factor 21 (FGF21) is an endocrine hormone that is expressed by several organs. It increases insulin sensitivity and regulates lipid metabolism and energy homeostasis. Emerging evidence demonstrates that FGF21 has potential effects in the brain involving metabolic regulation, neuroprotection and cognition. Hence, we hypothesize that FGF21 may be a protective factor in AD by attenuating Aβ generation, inflammation, oxidative stress, and insulin resistance. Our hypothesis will shed new light on the understanding of pathogenesis of AD and help to find a new way to prevent the genesis and progress of AD.

Mechanism of capture section affecting an intake for atmosphere-breathing electric propulsion

Atmosphere-Breathing Electric Propulsion(ABEP)can compensate for lost momentum of spacecraft operating in Very Low Earth Orbit(VLEO)which has been widely concerned due to its excellent commercial potential.It is a key technology to improve the capture efficiency of intakes,which collect and compress the atmosphere for ABEP.In this paper,the mechanism of the capture section affecting capture efficiency is investigated by Test Particle Monte Carlo(TPMC)simulations with 3D intake models.The inner surface smoothness and average collision number are determined to be key factors affecting capture efficiency,and a negative effect growth model is accordingly established.When the inner surface smoothness is less than 0.2,the highest capture efficiency and its corresponding average collision number interval are independent of the capture section’s geometry and its mesh size.When the inner surface smoothness is higher than 0.2,the capture efficiency will decrease by installing any capture section.Based on the present results,the manufacturing process and material selection are suggested to be prioritized during the intake geometry design in engineering projects.Then,the highest capture efficiency can be achieved by adjusting the length and mesh size of the capture section.

无中和器离子推力器的发展现状、关键技术及展望

离子推力器具有高比冲和高效率等优势,是目前应用最广泛的电推力器之一,但亦存在着系统结构复杂、关键部件繁多等缺点.无中和器离子推力器可以消除对中和器的依赖,实现离子推进系统结构的简化,从而减小推力器体积和重量并提高系统可靠性.本文首先归纳了传统离子推力器的原理、优势及限制,引出了无中和器离子推力器的概念,对其基本原理、技术优势及分类进行了介绍;随后从等离子体源的束流自中和技术出发,总结了无中和器离子推力器的发展现状;结合空间应用需求以及无中和器离子推力器的工作特点,分析了无中和器离子推力器的关键技术,提出应将工质选择、等离子体机理研究、磁过滤装置和栅极系统设计以及栅极射频电压灵活调控方法这四方面作为其研究重点,同时应该发展并完善新的推力器参数测量方法,进一步明确无中和器离子推力器的工作特性.

Formation mechanism of streamer discharges in liquids:a review

Streamer discharges in liquids have received lots of attention with respect to their considerable applications invarious disciplines. Much effort has been spent to understand the basis of streamer ignition and propagation in dielectricliquids, but a comprehensive mechanism is far from conclusive. In this review, based on an introduction to the streamerphysics and experimentally observed characteristics in various liquids, the authors emphasise on the current status ofstreamer discharge ignition mechanisms and present their understanding for each theory.

Particle simulation of grid system for krypton ion thrusters

The transport processes of plasmas in grid systems of krypton（Kr） ion thrusters at different acceleration voltages were simulated with a 3 D-PIC model, and the result was compared with xenon（Xe） ion thrusters. The variation of the screen grid transparency, the accelerator grid current ratio and the divergence loss were explored. It is found that the screen grid transparency increases with the acceleration voltage and decreases with the beam current, while the accelerator grid current ratio and divergence loss decrease first and then increase with the beam current. This result is the same with Xe ion thrusters. Simulation results also show that Kr ion thrusters have more advantages than Xe ion thrusters, such as higher screen grid transparency, smaller accelerator grid current ratio, larger cut-off current threshold, and better divergence loss characteristic. These advantages mean that Kr ion thrusters have the ability of operating in a wide range of current. Through comprehensive analyses, it can be concluded that using Kr as propellant is very suitable for a multimode ion thruster design.

Streamer‐to‐precursor transition in N_(2)-SF_(6)mixtures under positive repetitive submicrosecond pulses

The evolution of discharge dynamics in N_(2)-SF_(6)mixtures under long‐term repetitive submicrosecond pulses is investigated based on pulse‐sequence resolved electrical and optical diagnostics.The effects of gas pressure,pulse repetition frequency(PRF),and SF6 concentration on discharge evolutions are determined.The number of applied pulses before breakdown is shown to non‐linearly decrease with increasing PRF for all included gas pressures and SF6 concentrations.A higher SF6 concentration is favourable for increasing relative insulation capability under repetitive pulses.Unexpected complexities of discharge evolutions under repetitive pulses are reported for the first time for the discharge mechanism transition when a strong electronegative gas is introduced.A pulse‐to‐pulse progressive streamer(first discharge)‐to‐precursor(before breakdown)transition is observed in an N_(2)-SF_(6)mixture under positive repetitive pulses and is less dependent on gas pressure than traditional scenarios.The formation of a precursor section is jointly supported by electrical and optical signatures.The discharge mechanism transition and the detour phenomenon under repetitive pulses are discussed based on the effects of space charges on the spatial distribution of the electric field strength.

A naked-eye colorimetric sensor for chloroform

A phenoxazine based molecule termed SP has been synthesized and used as selective sensor for halogenated solvents. This molecule shows selective fast response towards halogenated solvent via naked-eye detectable chromism. SP shows colorless solution when dissolved in most solvents initially but changes to blue color in chloroform under UV irradiation(λ = 365 nm) within 5 s. The luminescence spectra of SP in halogenated solvent show a large bathochromic shift(> 100 nm) with 60-fold enhanced emission intensity compared to that in halogen-free solvents. It is also worth mentioning that the photoinduced reaction between SP molecule and the halogenated solvents occurred. Based on the detailed NMR, fluorescence and mass spectra, the possible radical reaction mechanism was proposed.Different from the majority of solvatochromic sensors that based on the polarity of solvents for detection of halogenated solvents, our sensor system worked in a special