共查询到20条相似文献，搜索用时 31 毫秒
1.
2.
William J. Hooper 《Journal of The Franklin Institute》1926,201(3):311-331
The experiments of several previous investigators were repeated in substance with apparatus designed to make it possible to distinguish between ionization and certain spurious factors which have made questionable much of the existing evidence relating to ionization by positive-ion impact. A great many current-potential measurements and curves were obtained at different gas pressures and with a variety of electrical arrangements. The data and curves thus obtained present direct evidence (a) that the previously so-called “ionization current” is due to a secondary electron emission from the platinum walls of the ionization chamber, (b) that this secondary electron emission is produced by the impact of the positive ions with these metal walls, (c) that either there is no ionization in hydrogen gas by the impact of the positive ions accelerated by potential differences up to 925 volts, or that if this phenomenon exists, as is indicated by visual and spectroscopic evidence, its effects are so small at relatively low pressures (.012 mm.) that it is completely masked by secondary phenomena which make its detection by the ordinary direct methods problematic, and (d) that it seems possible that at relatively high gas pressures (considerably above .012 mm.), ionization by positive ions might be an important factor with accelerating potential differences between the ends of their M.F.P. well within this same range of voltages. 相似文献
3.
变革性纳米产业制造技术聚焦纳米绿色印刷与器件制造技术项目研究团队 《中国科学院院刊》2016,31(9):1112-1119
发展纳米制造技术是从纳米材料到器件规模化制造与应用发展的核心内容。传统的印刷技术主要是基于感光和刻蚀工艺,造成严重的环境污染和资源浪费。绿色印刷是一种增材制造技术,可以从源头大幅度降低能耗和减少环境污染。开发绿色印刷制造技术对我国相关产业的可持续发展具有重要的战略意义。同时,绿色印刷制造与传统微纳加工方法的结合,为器件的制造与集成提供了新的可能途径与方法,可望对产业制造技术产生变革性影响。文章介绍了纳米绿色印刷与器件制造技术项目的研究背景、项目目标与实施概况,以及已经取得的创新成果。 相似文献
4.
Domain walls (DWs) in ferroelectrics are atomically sharp and can be created, erased, and reconfigured within the same physical volume of ferroelectric matrix by external electric fields. They possess a myriad of novel properties and functionalities that are absent in the bulk of the domains, and thus could become an essential element in next-generation nanodevices based on ferroelectrics. The knowledge about the structure and properties of ferroelectric DWs not only advances the fundamental understanding of ferroelectrics, but also provides guidance for the design of ferroelectric-based devices. In this article, we provide a review of structures and properties of DWs in one of the most widely studied ferroelectric systems, BiFeO3 thin films. We correlate their conductivity and photovoltaic properties to the atomic-scale structure and dynamic behaviors of DWs. 相似文献
5.
Most metal–organic frameworks (MOFs) hardly maintain their physical and chemical properties after exposure to alkaline aqueous solutions, thus precluding their use as potential electrode materials for electrochemical energy storage devices. Here, we present the design and synthesis of a highly alkaline-stable metal oxide@MOF composite, Co3O4 nanocube@Co-MOF (Co3O4@Co-MOF), via a controllable and facile one-pot hydrothermal method under highly alkaline conditions. The obtained composite possesses exceptional alkaline stability, retaining its original structure in 3.0 M KOH for at least 15 days. Benefitting from the exceptional alkaline stability, unique structure, and larger surface area, the Co3O4@Co-MOF composite shows a specific capacitance as high as 1020 F g−1 at 0.5 A g−1 and a high cycling stability with only 3.3% decay after 5000 cycles at 5 A g−1. The as-constructed solid-state flexible device exhibits a maximum energy density of 21.6 mWh cm−3. 相似文献
6.
基于系统动力学方法和联合国政府间气候变化专门委员会(IPCC)排放因子法,对上海市 2000—2019 年的化石能源 CO2排放进行定量核算,构建上海市化石能源 CO2排放系统动力学模型,并模拟基础排放、低排放、高排放 3 种情景下的未来 CO2排放变化。研究发现：(1)根据 2000—2019 年统计数据,上海市化石能源的 CO2排放从 2003 年开始攀升,到 2010 年开始趋于平稳增长,其中增长最快的阶段为 2004—2007 年,增长了 32.7%;(2)上海市生产总值(GDP)年增长,2050 年低排放情景较基础情景下降 25%,高排放情景较基础情景上升 33%;(3)2020—2050 年低排放情景的能源消费量呈下降趋势,基础情景与高排放情景的能源消费量呈先增后降趋势,分别在 2029 年、2037 年达到峰值,但能源强度从高到低为低排放情景、基础情景、高排放情景,主要是由于 GDP 增长问题导致;(4)基础情景与低排放情景的 CO2排放在 2030 年达到峰值,... 相似文献
7.
Zhiqiang Wang Da Wang Zheyi Zou Tao Song Dixing Ni Zhenzhu Li Xuecheng Shao Wanjian Yin Yanchao Wang Wenwei Luo Musheng Wu Maxim Avdeev Bo Xu Siqi Shi Chuying Ouyang Liquan Chen 《国家科学评论(英文版)》2020,7(11):1768
Designing new cathodes with high capacity and moderate potential is the key to breaking the energy density ceiling imposed by current intercalation chemistry on rechargeable batteries. The carbonaceous materials provide high capacities but their low potentials limit their application to anodes. Here, we show that Fermi level tuning by p-type doping can be an effective way of dramatically raising electrode potential. We demonstrate that Li(Na)BCF2/Li(Na)B2C2F2 exhibit such change in Fermi level, enabling them to accommodate Li+(Na+) with capacities of 290–400 (250–320) mAh g−1 at potentials of 3.4–3.7 (2.7–2.9) V, delivering ultrahigh energy densities of 1000–1500 Wh kg−1. This work presents a new strategy in tuning electrode potential through electronic band structure engineering. 相似文献
8.
Because of their low cost, natural abundance, environmental benignity, plentiful polymorphs, good chemical stability and excellent optical properties, TiO2 materials are of great importance in the areas of physics, chemistry and material science. Much effort has been devoted to the synthesis of TiO2 nanomaterials for various applications. Among them, mesoporous TiO2 materials, especially with hierarchically porous structures, show great potential owing to their extraordinarily high surface areas, large pore volumes, tunable pore structures and morphologies, and nanoscale effects. This review aims to provide an overview of the synthesis and applications of hierarchically mesoporous TiO2 materials. In the first section, the general synthetic strategies for hierarchically mesoporous TiO2 materials are reviewed. After that, we summarize the architectures of hierarchically mesoporous TiO2 materials, including nanofibers, nanosheets, microparticles, films, spheres, core-shell and multi-level structures. At the same time, the corresponding mechanisms and the key factors for the controllable synthesis are highlighted. Following this, the applications of hierarchically mesoporous TiO2 materials in terms of energy storage and environmental protection, including photocatalytic degradation of pollutants, photocatalytic fuel generation, photoelectrochemical water splitting, catalyst support, lithium-ion batteries and sodium-ion batteries, are discussed. Finally, we outline the challenges and future directions of research and development in this area. 相似文献
9.
青海省清洁能源发电潜力及价值分析 总被引：2，自引：0，他引：2
随着科技进步,清洁能源的开发利用成为缓解资源短缺、改善生态环境的重要途径,对清洁能源潜力进行量化评估,有助于有关部门制定合理的开发利用决策。本文基于模型模拟和空间分析等方法,对青海省水电势能、太阳能、风能、生物质能、地热能5种主要清洁能源的发电潜力及价值进行评估,得到了青海省主要清洁能源发电潜力的时空分布格局和数量统计特征。结果表明：①从时间上看,2000—2018年清洁能源发电潜力呈逐年增加趋势,空间分布格局变化不大,发电潜力较稳定。从空间上看,青海省西部清洁能源发电潜力相对较高,东部较低;州（市）尺度上,玉树州、海西州处于清洁能源发电潜力高值区,西宁市处于低值区;生态功能区尺度上,三江源地区处于清洁能源发电潜力高值区,祁连山地区处于低值区。②从清洁能源结构来看,青海省水电资源潜力最为丰富,2000—2018年水电势能平均发电潜力达到2338.41亿kW·h,其次是生物质能、地热能、太阳能和风能,且在实际应用中清洁能源在能源消费中的比重逐渐增大。③2000—2018年青海省清洁能源潜力平均价值为1887.75亿元,未来可获得的清洁能源的经济价值将随着中国碳市场的发展和清洁能源开发利用强度的增大而逐渐增长。本文为青海省相关部门了解省内清洁能源的现状和未来开发利用前景,制定清洁能源开发利用政策提供了重要依据。 相似文献
10.
The six-membered ring (SMR) is a common structure unit for numerous material systems. These materials include, but are not limited to, the typical two-dimensional materials such as graphene, h-BN, and transition metal dichalcogenides, as well as three-dimensional materials such as beryllium, magnesium, MgB2 and Bi2Se3. Although many of these materials have already become ‘stars’ in materials science and condensed-matter physics, little attention has been paid to the roles of the SMR unit across a wide range of compositions and structures. In this article, we systematically analyze these materials with respect to their very basic SMR structural unit, which has been found to play a deterministic role in the occurrence of many intriguing properties and phenomena, such as Dirac electronic and phononic spectra, superconductivity and topology. As a result, we have defined this group of materials as SMR inorganic materials, opening up a new perspective on materials research and development. With their unique properties, SMR materials deserve wide attention and in-depth investigation from materials design, new physical discoveries to target-wizard applications. It is expected that SMR materials will find niche applications in next-generation information technology, renewable energy, space, etc. 相似文献
11.
《Information processing & management》2002,38(1):37-54
When accessing an information retrieval system, it has long been said that undergraduates who are in an exploratory stage of researching their essay topic should use a high recall search strategy; what prevents them from doing so is the information overload factor associated with showing the undergraduate a long list of citations. One method of overcoming information overload is summarizing and visualizing the citation list. This paper examines five summarization and visualization schemes for presenting information retrieval (IR) citation output, then discusses whether these schemes are appropriate for undergraduates and other domain novice users. We ask and answer four questions: (1) What is the message these schemes try to communicate and (2) is this message appropriate for domain novice users like undergraduates? (3) How do these schemes communicate their message and (4) is how they communicate the message appropriate for a domain novice? We conclude that (i) the most appropriate message for information space visualizations for domain novice users is associative thinking, and (ii) the message should be communicated with a standardized look that remains relatively constant over time so that the shape and form of the visualization can become familiar and thus useful to students as they navigate their way through the information space produced by a high recall search strategy. 相似文献
12.
Yingying Hu Shiyao Bian John Grotberg Marcel Filoche Joshua White Shuichi Takayama James B. Grotberg 《Biomicrofluidics》2015,9(4)
Fluid dynamics of mucus plug rupture is important to understand mucus clearance in lung airways and potential effects of mucus plug rupture on epithelial cells at lung airway walls. We established a microfluidic model to study mucus plug rupture in a collapsed airway of the 12th generation. Mucus plugs were simulated using Carbopol 940 (C940) gels at concentrations of 0.15%, 0.2%, 0.25%, and 0.3%, which have non-Newtonian properties close to healthy and diseased lung mucus. The airway was modeled with a polydimethylsiloxane microfluidic channel. Plug motion was driven by pressurized air. Global strain rates and shear stress were defined to quantitatively describe plug deformation and rupture. Results show that a plug needs to overcome yield stress before deformation and rupture. The plug takes relatively long time to yield at the high Bingham number. Plug length shortening is the more significant deformation than shearing at gel concentration higher than 0.15%. Although strain rates increase dramatically at rupture, the transient shear stress drops due to the shear-thinning effect of the C940 gels. Dimensionless time-averaged shear stress, Txy, linearly increases from 3.7 to 5.6 times the Bingham number as the Bingham number varies from 0.018 to 0.1. The dimensionless time-averaged shear rate simply equals to Txy/2. In dimension, shear stress magnitude is about one order lower than the pressure drop, and one order higher than yield stress. Mucus with high yield stress leads to high shear stress, and therefore would be more likely to cause epithelial cell damage. Crackling sounds produced with plug rupture might be more detectable for gels with higher concentration. 相似文献
13.
Xujie Lü Constantinos Stoumpos Qingyang Hu Xuedan Ma Dongzhou Zhang Songhao Guo Justin Hoffman Kejun Bu Xiaofeng Guo Yingqi Wang Cheng Ji Haijie Chen Hongwu Xu Quanxi Jia Wenge Yang Mercouri G Kanatzidis Ho-Kwang Mao 《国家科学评论(英文版)》2021,8(9)
Metal halide perovskites possess unique atomic and electronic configurations that endow them with high defect tolerance and enable high-performance photovoltaics and optoelectronics. Perovskite light-emitting diodes have achieved an external quantum efficiency of over 20%. Despite tremendous progress, fundamental questions remain, such as how structural distortion affects the optical properties. Addressing their relationships is considerably challenging due to the scarcity of effective diagnostic tools during structural and property tuning as well as the limited tunability achievable by conventional methods. Here, using pressure and chemical methods to regulate the metal off-centering distortion, we demonstrate the giant tunability of photoluminescence (PL) in both the intensity (>20 times) and wavelength (>180 nm/GPa) in the highly distorted halide perovskites [CH3NH3GeI3, HC(NH2)2GeI3, and CsGeI3]. Using advanced in situ high-pressure probes and first-principles calculations, we quantitatively reveal a universal relationship whereby regulating the level of off-centering distortion towards 0.2 leads to the best PL performance in the halide perovskites. By applying this principle, intense PL can still be induced by substituting CH3NH3+ with Cs+ to control the distortion in (CH3NH3)1-xCsxGeI3, where the chemical substitution plays a similar role as external pressure. The compression of a fully substituted sample of CsGeI3 further tunes the distortion to the optimal value at 0.7 GPa, which maximizes the emission with a 10-fold enhancement. This work not only demonstrates a quantitative relationship between structural distortion and PL property of the halide perovskites but also illustrates the use of knowledge gained from high-pressure research to achieve the desired properties by ambient methods. 相似文献
14.
我国农业生产用能与农业产出具有明显的区域差异性,本文根据我国各省份1990年-2008年农业生产用能和农业产值数据,把我国划分为四类区域,并构筑面板数据模型进行相关研究。结果表明,各地区农业生产用能与农业经济增长均存在协整关系,模型分析进一步定量揭示各地区间农业生产用能与农业产出增长之间关系的差异,以及分区内部各省份之间也存在差异;详述了区域经济发展水平与农业经济增长关系的密切程度,以及继续增加农业投入与农业经济持续增长出现差异的原因。最后指出,在农业现代化普及地区,重点是提高农业物资利用效率和实施合理的种植结构,而在农业现代化中等及欠发达地区,应注重农业物资投入及效率提高。 相似文献
15.
近年来,中国多个地区相继出现了能源“四荒”问题,说明区域能源安全仍然是中国发展中一个重要的问题。本文从能源供应、使用、经济与环境安全四方面,构建了相应的指标体系,利用熵值法确定指标权重,克服了传统赋权法的主观性,与TOPSIS法相结合,对中国区域能源安全进行评价。结果表明：中国区域能源安全性普遍处于中低水平。能源安全值高于全国平均水平的只有山西、新疆、内蒙古等9个省份,仅占研究省份的30%,其余21个省份普遍低于全国能源安全平均值。中国能源安全性大致呈现“由西北向东南”逐渐降低的特点。西北地区能源储量丰富,能源消耗量相对较低,能源安全值偏高;东部及中部地区能源储量较为匮乏,并且能源消耗量巨大,导致能源安全值偏低。最后,提出了相应的政策建议。 相似文献
16.
为对我国矿产资源空间分布的不均衡性进行定量化的测度和比较,进一步明晰不同种类的矿产资源的空间分布特征,进而为政府进行差别化管理和精细化管理提供支撑,本文采用基尼系数和洛仑兹曲线相结合的方法,以矿种在省域空间的地均查明资源储量作为指标,对我国28种重要矿产资源的空间分布状况进行定量分析,并按不均衡程度将28种矿产划分为4类,结论显示：总体上看,我国矿产资源的空间分布均具有明显的不均衡性,有15种矿产的空间分布不均衡程度相对较高,而不均衡程度相对较低和极高的矿种较少,共6种,不均衡程度相对中等的矿种有7种。从矿类上看,3种能源矿产的空间分布不均衡程度都相对较高,金属矿产基本属于相对中等和相对较高,共有13种,所选取的10种非金属矿产在四种分类中均有,根据分析结论,进一步提出将矿种的空间分布不均衡性作为矿产资源分类管理的空间要素。 相似文献
17.
经济发展与水资源和能源密不可分,研究水和能源两种资源在宏观经济系统各部门之间的流通特征,挖掘其内在规律,对地区水与能源的高效及可持续利用至关重要。本文以长江经济带为例,运用复杂网络理论创建资源网络模型,从水资源-能源的双重节约和双向节约的新视角发掘资源网络特征。结果表明：①长江经济带水-能源相关要素资源网络具备小世界性及无标度性,网络中关键部门的变化将显著影响整个网络。②江苏的化学产品业、金属冶炼和延加工业、建筑业等部门因具备较大点强度而对长江经济带的水-能源的双重节约作用显著。江苏的化学产品业、金属冶炼和延加工业、电气机械和器材业以及湖北和湖南的电力、热力的生产和供应等部门的节水带来的节能效应和节能带来的节水效应可快速传播至其他部门,对水-能源双向节约作用显著。③研究区内各省市资源流通量大体与经济发展水平呈正相关,江苏、湖南和湖北地区资源流通量较大,云南、贵州和重庆资源流通量相对较小。④对重庆（交通运输、仓储和邮政业）→重庆（租赁和商务服务业）、重庆（建筑业）→重庆（其他服务业）、四川（建筑业）→四川（其他服务业）3条贸易路径中的部门进行合理的资源调控可以显著影响整个网络的资源流通量,从而实现资源节约。本文探究地区水-能源网络特征,旨在为资源高效利用提供有益参考。 相似文献
18.
Sainan Mu Qirong Liu Pinit Kidkhunthod Xiaolong Zhou Wenlou Wang Yongbing Tang 《国家科学评论(英文版)》2021,8(7)
Sodium-based dual-ion batteries (Na-DIBs) show a promising potential for large-scale energy storage applications due to the merits of environmental friendliness and low cost. However, Na-DIBs are generally subject to poor rate capability and cycling stability for the lack of suitable anodes to accommodate large Na+ ions. Herein, we propose a molecular grafting strategy to in situ synthesize tin pyrophosphate nanodots implanted in N-doped carbon matrix (SnP2O7@N-C), which exhibits a high fraction of active SnP2O7 up to 95.6 wt% and a low content of N-doped carbon (4.4 wt%) as the conductive framework. As a result, this anode delivers a high specific capacity ∼400 mAh g−1 at 0.1 A g−1, excellent rate capability up to 5.0 A g−1 and excellent cycling stability with a capacity retention of 92% after 1200 cycles under a current density of 1.5 A g−1. Further, pairing this anode with an environmentally friendly KS6 graphite cathode yields a SnP2O7@N-C||KS6 Na-DIB, exhibiting an excellent rate capability up to 30 C, good fast-charge/slow-discharge performance and long-term cycling life with a capacity retention of ∼96% after 1000 cycles at 20 C. This study provides a feasible strategy to develop high-performance anodes with high-fraction active materials for Na-based energy storage applications. 相似文献
19.
Pankaj Abrol Ashok Verma H. S. Hooda 《Indian journal of clinical biochemistry : IJCB》2001,16(2):221-223
Thyroid hormonal status was measured in 80 malnourished children of different grades (I–IV) of protein energy malnutrition
(PEM). Serum levels of tri-iodo thyronine (T3), thyroxine (T4) and thyroid stimulating hormone (TSH) were measured by radioimmunoassay. The results were compared with 20 healthy, age
and sex matched controls. Levels of T3 and T4 were significantly low in PEM cases whereas TSH levels were similar in PEM cases when compared to controls. 相似文献
20.
Chi Zhang Junyang Tan Yikun Pan Xingke Cai Xiaolong Zou Hui-Ming Cheng Bilu Liu 《国家科学评论(英文版)》2020,7(2):324
The scalable and high-efficiency production of 2D materials is a prerequisite to their commercial use. Currently, only graphene and graphene oxide can be produced on a ton scale, and the inability to produce other 2D materials on such a large scale hinders their technological applications. Here we report a grinding exfoliation method that uses micro-particles as force intermediates to resolve applied compressive forces into a multitude of small shear forces, inducing the highly efficient exfoliation of layer materials. The method, referred to as intermediate-assisted grinding exfoliation (iMAGE), can be used for the large-scale production of many 2D materials. As an example, we have exfoliated bulk h-BN into 2D h-BN with large flake sizes, high quality and structural integrity, with a high exfoliation yield of 67%, a high production rate of 0.3 g h−1 and a low energy consumption of 3.01 × 106 J g−1. The production rate and energy consumption are one to two orders of magnitude better than previous results. Besides h-BN, this iMAGE technology has been used to exfoliate various layer materials such as graphite, black phosphorus, transition metal dichalcogenides, and metal oxides, proving its universality. Molybdenite concentrate, a natural low-cost and abundant mineral, was used as a demo for the large-scale exfoliation production of 2D MoS2 flakes. Our work indicates the huge potential of the iMAGE method to produce large amounts of various 2D materials, which paves the way for their commercial application. 相似文献