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Electrospinning is a process that creates nanofibers through an electrically charged jet of polymer solution or melt. This technique is applicable to virtually every soluble or fusible polymer and is capable of spinning fibers in a variety of shapes and sizes with a wide range of properties to be used in a broad range of biomedical and industrial applications. Electrospinning requires a very simple and economical setup but is an intricate process that depends on several molecular, processing, and technical parameters. This article reviews information on the three stages of the electrospinning process (i.e., jet initiation, elongation, and solidification). Some of the unique properties of the electrospun structures have also been highlighted. This article also illustrates some recent innovations to modify the electrospinning process. The use of electrospun scaffolds in the field of tissue engineering and regenerative medicine has also been described. 相似文献
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基于专利数据的化纤机械技术发展现状与趋势分析 总被引：2，自引：0，他引：2
[目的/意义]为揭示我国化纤机械发展趋势,为化纤机械确定行业发展方向提供参考。[方法/过程]应用专利分析方法,通过技术原创国家/地区、主要专利权人分布、技术侧重和技术关联性展示了化纤机械发展现状,通过文献计量方法描述化纤机械技术热点演化路径、专利申请趋势和技术发展趋势。[结果/结论]分析结果表明化纤机械技术处于成熟向衰退阶段转化,技术热点词集中在纤维、纺丝、纤维素、电纺、纳米、静电等方面,数字化、智能化、绿色环保是今后化纤机械研发的重点方向。 相似文献
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湖南省耕地经营协调度时空演变 总被引：1，自引：0，他引：1
揭示区域耕地经营格局特征有助于从区域层面解读耕地经营模式特点,切实有效提出区域耕地利用转型的重点和发展方向。本研究基于“集约-规模-产能”三要素提出耕地经营协调度评价模型,并借助协调度函数和探索性空间数据分析方法揭示湖南省县域耕地经营格局演变特征。结果表明：①1990—2014年间,湖南省县域耕地经营协调水平整体较高,且空间格局差异明显：“长株潭”丘陵区集约指数较高,洞庭湖平原区规模指数较高,主要市辖区及其周边县域产能指数较高;②受不同地理区位和社会经济影响,湖南省县域耕地经营要素时空集聚特征存在明显差异:空间维度上,耕地经营协调度由“大集聚”向“小集聚”分布转变;时间维度上,规模指数自相关性较强且分布较集中,产能指数自相关性较弱且分布较分散;③从“投入-规模-产出”过程看,平原区呈现“高-高-高”特征,丘陵区表现“高-低-低”特征,山地区则为“低-低-低”特征。结合耕地经营格局时空演化特征成因,建议湖南各县域因地制宜地采用以粮食作物为主的集约经营模式,以经济作物为主的复合经营模式和特色作物经营模式。 相似文献
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Guoyin Chen Gang Wang Xinrong Tan Kai Hou Qingshuo Meng Peng Zhao Shun Wang Jiayi Zhang Zhan Zhou Tao Chen Yanhua Cheng Benjamin S Hsiao Elsa Reichmanis Meifang Zhu 《国家科学评论(英文版)》2021,8(9)
Hydrogel optical light-guides have received substantial interest for applications such as deep-tissue biosensors, optogenetic stimulation and photomedicine due to their biocompatibility, (micro)structure control and tissue-like Young''s modulus. However, despite recent developments, large-scale fabrication with a continuous synthetic methodology, which could produce core-sheath hydrogel fibers with the desired optical and mechanical properties suitable for deep-tissue applications, has yet to be achieved. In this study, we report a versatile concept of integrated light-triggered dynamic wet spinning capable of continuously producing core-sheath hydrogel optical fibers with tunable fiber diameters, and mechanical and optical propagation properties. Furthermore, this concept also exhibited versatility for various kinds of core-sheath functional fibers. The wet spinning synthetic procedure and fabrication process were optimized with the rational design of the core/sheath material interface compatibility [core = poly(ethylene glycol diacrylate-co-acrylamide); sheath = Ca-alginate], optical transparency, refractive index and spinning solution viscosity. The resulting hydrogel optical fibers exhibited desirable low optical attenuation (0.18 ± 0.01 dB cm−1 with 650 nm laser light), excellent biocompatibility and tissue-like Young''s modulus (<2.60 MPa). The optical waveguide hydrogel fibers were successfully employed for deep-tissue cancer therapy and brain optogenetic stimulation, confirming that they could serve as an efficient versatile tool for diverse deep-tissue therapy and brain optogenetic applications. 相似文献
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The recent development of microfluidic “lab on a chip” devices requires the need to continuously separate submicron particles. Here, we present a PDMS microfluidic device with sidewall conducting PDMS (AgPDMS) composite electrodes capable of separating submicron particles in hydrodynamic flow. In particular, the device can service dual functions. First, the AgPDMS composite electrodes embedded in a sidewall of the device channel allow for performing AC-dielectrophoretic (DEP) characterization through direct microscopic observation of particle behavior. Characterization experiments are carried out for numerous parameters including particle size, medium conductivity, and AC field frequency to reveal important dielectrophoresis DEP information in terms of the crossover frequency and positive/negative DEP behavior under specific frequencies. Second, the device offers an advantage that sidewall AgPDMS composite electrodes can produce strong DEP effects throughout the entire channel height, and thus the robustness of the on-chip particle separation is demonstrated for continuous separation in a flowing mixture of 0.5 and 5 μm particles with 100% separation efficiency. 相似文献
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Huai-Ling Gao Ran Zhao Chen Cui Yin-Bo Zhu Si-Ming Chen Zhao Pan Yu-Feng Meng Shao-Meng Wen Chuang Liu Heng-An Wu Shu-Hong Yu 《国家科学评论(英文版)》2020,7(1):73
Bio-sourced nanocellulosic materials are promising candidates for spinning high-performance sustainable macrofibers for advanced applications. Various strategies have been pursued to gain nanocellulose-based macrofibers with improved strength. However, nearly all of them have been achieved at the expense of their elongation and toughness. Inspired by the widely existed hierarchical helical and nanocomposite structural features in biosynthesized fibers exhibiting exceptional combinations of strength and toughness, we report a design strategy to make nanocellulose-based macrofibers with similar characteristics. By combining a facile wet-spinning process with a subsequent multiple wet-twisting procedure, we successfully obtain biomimetic hierarchical helical nanocomposite macrofibers based on bacterial cellulose nanofibers, realizing impressive improvement in their tensile strength, elongation and toughness simultaneously. The achievement certifies the validity of the bioinspired hierarchical helical and nanocomposite structural design proposed here. This bioinspired design strategy provides a potential platform for further optimizing or creating many more strong and tough nanocomposite fiber materials for diverse applications. 相似文献
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由于信息不对称、风险管理缺位,导致中国企业海外耕地投资项目失败的案例持续出现,损害了参与主体各方的利益。“走出去”企业如何通过耕地投资项目实现与东道国长期合作已经成为中国推动海外农业资源保障国家粮食安全面临的关键问题。基于不同参与主体在海外耕地投资过程中的有限理性行为,构建中国企业、东道国政府和东道国土地所有者三方演化博弈模型,并以西安爱菊粮油工业集团为例进行数值分析。结果表明：①中国企业、东道国政府、东道国土地所有者三方演化博弈模型存在4个演化稳定点可达到稳定状态,分别对应三方主体不同的策略选择;②中国企业在进行“独立经营”或“合作经营”的策略选择时,往往对东道国政府和东道国土地所有者策略选择的反应更为迅速,演化路径更为敏感,而东道国政府实现均衡状态所需的时间最为漫长,演化路径最为平稳,策略选择受到中国企业与东道国土地所有者的影响较小;③东道国政府的“损失厌恶”心理往往使其在制定有利于中国企业政策的“高支持”策略时犹豫而缓慢,在制定不利于中国企业策略的“低支持”策略时坚定且迅速,这对于中国企业海外耕地投资的稳定性与长期性提出了较高的要求;④中国企业在海外耕地投资过程中离不开东道国政府的支持,当中国企业选择“独立经营”策略时,受东道国政府“高支持”策略的影响较小,而选择“合作经营”策略时,受东道国政府“高支持”策略的影响较大,此时需要考虑东道国政府策略选择的倾向性与可能性。最后,为中国企业营造稳定的海外耕地投资环境提出建议。 相似文献
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草原有“地球的皮肤”之称,中国是草原资源大国,探索研究草原资产负债表的编制与应用,对于量化草原生态服务价值、加强草原资源科学管理以及推进领导干部自然资源资产离任审计工作具有理论与现实指导意义。但目前草原资源资产负债表编制尚未形成统一的规范标准。本文基于对已有自然资源核算体系以及自然资源资产负债表编制方法的梳理,立足于草原资源特性,对草原资源资产负债表编制中报表体系的核算内容、草原资源资产和负债的价值量计算方法进行了分析,同时设计出草原资源资产负债表样表。在此基础上,以内蒙古呼伦贝尔草原数据为例,编制出草原资源资产负债表。通过草原资源资产负债表得出,2017年呼伦贝尔草原资源资产为9735219.80万元,负债为50101.60万元,所有者权益为9685118.20万元。本文方法和案例可为构建草原资源资产负债表编制体系、编制草原资源资产负债表提供参考范式。 相似文献
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非自愿性移民的农业安置模式正面临安置效果和安置效率的“双低困局”,传统“以土为本、以农为主”的移民安置方式亟待改革创新。农业安置模式的现实困境,不仅体现为人地关系的局部紧张,同时也表现为农户土地投入意愿与行为的变化。本文基于感知价值理论,利用多群组SEM的分析方法,对湖南渫水皂市水利枢纽工程移民安置区原住民与移民两类农户主体的土地投入行为进行了实证研究。结果发现：①移民安置区农户的土地投入行为决策是经济、心理和情境因素共同作用的结果,其行为逻辑符合“认知层次→认知权衡→感知价值→行为意愿→行为响应”的路径范式;②原住民与移民两类农户主体的土地投入行为决策影响因素的效应值存在显著差异,原住民农户的土地投入行为是对土地投入“利弊权衡”后的“客观理性”决策,而移民农户的土地投入行为则更多的表现出“风险厌恶”的“主观理性”倾向。 相似文献
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Anita R. Bijoor S. Sudha T. Venkatesh 《Indian journal of clinical biochemistry : IJCB》2012,27(2):147-151
Lead is found in small but appreciable quantities in air, soil drinking water and food. Exposure to such amounts of lead does not cause acute lead toxicity, but produces subtle effects, particularly in children. The CDC advocates “safe” or “acceptable” levels of blood lead up to 10 μg/dl, while OSHA declares blood lead levels up to 40 μg/dl as “safe” or “acceptable” in the occupationally exposed. The objective of the study was to see if blood levels considered “safe” can cause changes in the biogenic neurotransmitters in the developing brain which may cause neurobehavioral defects like hyperactivity and other cognitive disorders. Albino Wistar rats were divided into the control and lead-treated groups. The control group was given unleaded water, while the lead-treated group was fed with 50 ppm lead acetate in drinking water. On day 45 the animals were subjected to a passive avoidance test, their blood analysed for ZPP and lead. They were then sacrificed and the neurotransmitters—Norepinephrine (NE) and its metabolite—methoxyhydroxyphenylglycol (MHPG) estimated in the brain areas associated with learning and memory—the frontal cortex, hippocampus and the striatum by HPLC-ECD. Our results showed significant increases in blood lead, NE and MHPG, while ZPP increase was insignificant. The rats showed neurobehavioral abnormalities as assessed by the passive avoidance test. We concluded that low blood levels of lead cannot be considered “safe” or “acceptable” as it causes neurotransmitter alterations. Increased NE turnover is implicated in hyperactivity disorders such as ADHD and Tourette syndrome. 相似文献
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Vincent Labrot Michael Schindler Pierre Guillot Annie Colin Mathieu Joanicot 《Biomicrofluidics》2009,3(1)
The overall traffic of droplets in a network of microfluidic channels is strongly influenced by the liquid properties of the moving droplets. In particular, the effective hydrodynamic resistance of individual droplets plays a key role in their global behavior. Here we propose two simple and low-cost experimental methods for measuring this parameter by analyzing the dynamics of a regular sequence of droplets injected into an “asymmetric loop” network. The choice of a droplet taking either route through the loop is influenced by the presence of previous droplets that modulate the hydrodynamic resistance of the branches they are sitting in. We propose to extract the effective resistance of a droplet from easily observable time series, namely, from the choices the droplets make at junctions and from the interdroplet distances. This becomes possible when utilizing a recently proposed theoretical model based on a number of simplifying assumptions. Here we present several sets of measurements of the hydrodynamic resistance of droplets, expressed in terms of a “resistance length.” The aim is twofold: (1) to reveal its dependence on a number of parameters, such as the viscosity, the volume of droplets, their velocity as well as the spacing between them. At the same time (2), by using a standard measurement technique, we compare the limitations of the proposed methods. As an important result of this comparison, we obtain the range of validity of the simplifying assumptions made in the theoretical model. 相似文献
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居民是城市生活垃圾分类回收系统中的关键主体之一,其分类回收参与率的高低直接关系到整个城市垃圾分类工作的成败。为分析居民垃圾分类行为决策机制,本文以苏州市为案例,对其中心城区居民开展实地问卷调查,并运用结构方程统计分析方法,探讨影响居民生活垃圾分类行为的主要因素和作用路径。研究结果表明：居民生活垃圾分类行为主要由4个主观因素和7个外部情境因素共同作用的结果,且外部条件因素的综合影响是个体主观因素的近2倍,其中,“环境设施和服务”潜变量相关因素对居民行为的综合影响最大,公共宣传教育、回收设施便利性、分类设施便利性、参与意愿和环保意识为对居民垃圾生活处理行为影响最显著的前5个因素。为进一步加快推进中国城市生活垃圾分类工作,建议加强城市生活垃圾分类回收配套设施规划建设,广泛开展垃圾分类回收宣传教育,完善相关法律法规并建立有效的激励约束机制。 相似文献
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“同地同权同价”是构建城乡统一建设用地市场的重要目标,然而长期以来农村宅基地使用权的价值认知局限、流转障碍凸显、市场难以形成,使得农民宅基地财产权利显化困难,流转价格和功能价值存在较大偏离,相较于城市居住用地价格更是差距巨大。基于此,本文选取了287个北京郊区宅基地流转案例和534个北京城市居住用地交易案例,构建了宅基地使用权多元价值分段偏离测度框架,运用多功能价值评估与深度置信网络分析,测度了宅基地使用权实际流转价格、功能价值和城乡同权价值的“三元价值”和“两级偏离”。结果表明：①北京市农村宅基地使用权功能价值较流转价格平均高出8748.08元/m2,平均价值偏离度为63.14%,表现出了一定的“区域递减”空间分布特征,产生原因在于宅基地的功能和资格权的认知偏差,以及供需匹配度、市场完善度、政策外部性等诸多因素的综合影响;②农村宅基地使用权城乡同权价值较功能价值平均高出 27192.81元/m2,平均偏离度为68.32%,呈现出显著的“中心扩散”空间分布特征,主要原因在于城乡居住用地产权的完整度、明晰度和稳定度差异。因此,本文提出未来宅基地财产权利显化和价值充分盘活应该分两步进行,首先完善宅基地的“农村二级市场”,逐步纠正农民对宅基地的功能认知和增强资格权价值显化;其次对标城市居住用地构建“城乡统一市场”,通过不断完善宅基地产权权能,推进宅基地完整价值的进一步显化,推进实现城乡统一建设用地市场相对协调的“同地同权同价”。 相似文献
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耕地经营规模对农户亲环境行为的影响 总被引：1，自引：0，他引：1
本文根据农户亲环境行为实施的动态优化模型理论分析了耕地经营规模对农户亲环境行为实施的可能影响,并利用山东省549户农户1417块地块的样本数据,运用Oprobit模型和Probit模型,从家庭层面和地块层面分别实证检验了耕地经营总规模和地块经营规模对农户亲环境行为实施的影响及其差异,以期为制定治理农业面源污染、提升农业可持续发展能力等相关政策提供科学依据。研究结果表明：农户耕地经营总规模和地块经营规模与农户总体亲环境行为实施之间均存在稳健的倒“U”型关系;但上述关系因地块属性不同而呈现差异,自家地的地块经营规模与农户总体亲环境行为实施呈倒“U”型关系;而转入地的地块经营规模与农户总体亲环境行为实施呈“U”型关系。最后,提出政府应积极推进农地流转,促使农户耕地连片规模经营中应注意其适度性,以及加强规范农地流转程序和管理等建议。 相似文献
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结构调整与经济波动是经济学研究的重要内容,厘清结构调整与经济波动的关系对深入推进供给侧结构性改革具有重要意义。本文从产业结构视角分析了中国海洋渔业经济波动的引发动力,并采用动态面板模型检验判断了海洋渔业产业结构演进是熨平还是放大了海洋渔业经济波动。结果显示：①海洋渔业产业结构演进能引起海洋渔业经济波动,不同海洋渔业产业结构形态影响海洋渔业经济波动的差异明显;②海洋渔业产业结构高级化、加工系数影响海洋渔业经济波动的“杠杆效应”明显,且高级化的放大效果更加显著;③海洋渔业产业结构合理化、软化与养捕结构对海洋渔业经济波动影响的“熨平效应”显著,且合理化的抑制效果要高于养捕结构,但低于产业结构软化。为平稳推进海洋渔业供给侧结构性改革,本文认为在推进产业结构高级化过程中,要注重产业结构合理化、软化对海洋渔业经济波动的熨平作用。 相似文献
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探究贫困地区农户宅基地退出行为的影响路径对于实施宅基地退出政策具有重要的理论意义与现实意义。本文基于家庭生命周期视角,根据计划行为理论,结合全国农村宅基地改革试点县中唯一的贫困县——安徽省金寨县333份农户的微观调研数据,运用结构方程模型,探讨了贫困地区农户宅基地退出行为的影响路径,并对比分析了不同类型家庭宅基地退出行为影响路径的差异。结果表明：①贫困地区农户宅基地退出行为基本遵循计划行为理论,影响路径包括“行为态度→退出意愿→退出行为”和“主观规范→退出意愿→退出行为”,且主观规范是主导因素,行为态度次之,农户宅基地退出意愿显著正向影响其退出行为。②不同类型家庭宅基地退出行为的影响路径不同,其中抚幼养老型家庭和养老型家庭的影响路径与样本总体路径一致,包括“行为态度→退出意愿→退出行为”和“主观规范→退出意愿→退出行为”;抚幼型家庭的影响路径仅有“主观规范→退出意愿→退出行为”,且其主观规范对退出意愿的影响强于养老型家庭和抚幼养老型家庭。提出了针对不同类型家庭实施不同的农户宅基地退出激励政策,有效利用农户的社会网络,健全宅基地退出后的配套政策,以及严格落实宅基地退出补偿资金的信息公开和按时支付制度等建议。 相似文献
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In this paper a method of electrospinning conducting and nonconducting biphasic Janus nanofibers using microfluidic polydimethylsiloxane (PDMS)-based manifolds is described. Key benefits of using microfluidic devices for nanofiber synthesis include rapid prototyping, ease of fabrication, and the ability to spin multiple Janus fibers in parallel through arrays of individual microchannels. Biphasic Janus nanofibers of polyvinylpyrrolidone (PVP)+polypyrrole (PPy)∕PVP nanofibers with an average diameter of 250 nm were successfully fabricated using elastomeric microfluidic devices. Fiber characterization and confirmation of the Janus morphology was subsequently carried out using a combination of scanning electron microscopy, energy dispersion spectroscopy, and transmission electron microscopy. 相似文献
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自然资源法律概念是自然资源法学研究的基础.深圳"鹦鹉案"和江西"鹦鹉案"出现的"类案不同判"现象凸显了自然资源法律概念缺失的司法流弊.目前,学界对自然资源法律概念的阐释主要移植了自然资源的科学概念,并依据自然资源的客观性和主观性,分别形成了"状态论"和"行为论"的阐释路径,而这两条阐释路径都难以做到逻辑自洽.自然资源法... 相似文献