Vibration Damping of Carbon Nanotube Assembly Materials

Vibration reduction is of great importance in various engineering applications, and a material that exhibits good vibration damping along with high strength and modulus has become more and more vital. Owing to the superior mechanical property of carbon nanotube (CNT), new types of vibration damping material can be developed. This paper presents recent advancements, including our progresses, in the development of high-damping macroscopic CNT assembly materials, such as forests, gels, films, and fibers. In these assemblies, structural deformation of CNTs, zipping and unzipping at CNT connection nodes, strengthening and welding of the nodes, and sliding between CNTs or CNT bundles are playing important roles in determining the viscoelasticity, and elasticity as well. Towards the damping enhancement, strategies for micro-structure and interface design are also discussed

Wide-Range Tunable Dynamic Property of Carbon Nanotube-Based Fibers

Carbon nanotube (CNT) fiber is formed by assembling millions of individual tubes. The assembly feature provides the fiber with rich interface structures and thus various ways of energy dissipation, as reflected by the non-zero loss tangent (>0.028--0.045) at low vibration frequencies. A fiber containing entangled CNTs possesses higher loss tangents than a fiber spun from aligned CNTs. Liquid densification and polymer infiltration, the two common ways to increase the interfacial friction and thus the fiber's tensile strength and modulus, are found to efficiently reduce the damping coefficient. This is because the sliding tendency between CNT bundles can also be well suppressed by the high packing density and the formation of covalent polymer cross-links within the fiber. The CNT/bismaleimide composite fiber exhibited the smallest loss tangent, nearly as the same as that of carbon fibers. At a higher level of the assembly structure, namely a multi-ply CNT yarn, the inter-fiber friction and sliding tendency obviously influence the yarn's damping performance, and the loss tangent can be tuned within a wide range, as similar to carbon fibers, nylon yarns, or cotton yarns. The wide-range tunable dynamic properties allow new applications ranging from high quality factor materials to dissipative systems

Bio-Inspired Aggregation Control of Carbon Nanotubes for Ultra-Strong Composites

High performance nanocomposites require well dispersion and high alignment of the nanometer-sized components, at a high mass or volume fraction as well. However, the road towards such composite structure is severely hindered due to the easy aggregation of these nanometer-sized components. Here we demonstrate a big step to approach the ideal composite structure for carbon nanotube (CNT) where all the CNTs were highly packed, aligned, and unaggregated, with the impregnated polymers acting as interfacial adhesions and mortars to build up the composite structure. The strategy was based on a bio-inspired aggregation control to limit the CNT aggregation to be sub 20--50 nm, a dimension determined by the CNT growth. After being stretched with full structural relaxation in a multi-step way, the CNT/polymer (bismaleimide) composite yielded super-high tensile strengths up to 6.27--6.94 GPa, more than 100% higher than those of carbon fiber/epoxy composites, and toughnesses up to 117--192 MPa. We anticipate that the present study can be generalized for developing multifunctional and smart nanocomposites where all the surfaces of nanometer-sized components can take part in shear transfer of mechanical, thermal, and electrical signals

浆细胞样树突状细胞在宿主抵御隐球菌肺部感染中的作用及机制研究进展

肺隐球菌病是由隐球菌感染引起的常见真菌病,由于症状的非特异性,临床上诊断较为困难。作为条件致病性真菌感染,肺隐球菌病的结局主要与宿主免疫力有关。目前肺隐球菌病免疫学发病机制研究主要局限在T细胞和巨噬细胞。近年研究表明,作为树突状细胞亚群之一的浆细胞样树突细胞,由于其激活后可以产生大量的I型干扰素并活化相关的T细胞,所以在机体抵抗病毒和细菌免疫中发挥着重要的作用。但是浆细胞样树突细胞在真菌病,尤其是在隐球菌病的发生发展中发挥的作用尚不明确。本文将介绍肺隐球菌病的临床表现、诊治及T细胞和巨噬细胞在肺隐球菌病中的免疫机制,并通过介绍肺隐球菌病和浆细胞样树突细胞及二者之间已有报道的联系,初步阐述浆细胞样树突细胞在肺隐球菌病免疫学发病机制中的相关作用。国家自然科学基金(31770161);;上海市科学技术委员会基金(14DZ2272900);;国家卫生部基金(2018ZX10101003);;上海市科委技术标准专项(16DZ0500401)~

血管内皮生长因子表达与肝癌患者临床病理特征及预后的关系研究

目的:研究肝细胞肝癌(HCC)组织中血管内皮生长因子(VEGF)表达与患者临床病理特征及预后的关系。方法:采用免疫组织化学染色法检测79例在广西医科大学附属肿瘤医院行肝癌根治性切除术的HCC患者癌组织中VEGF的表达情况,分析VEGF表达与树突状细胞(DC)浸润程度、肿瘤大小、癌栓、包膜、血清AFP水平及术后肝外转移的关系,随访患者术后生存情况及肿瘤复发情况。结果:79例HCC患者中,VEGF低表达43例(54.4%),高表达36例(45.6%)。VEGF表达与DC浸润程度、肿瘤直径及血清AFP水平有关(P0.05)。VEGF高表达组2年内复发率为83.3%(30/36),明显高于VEGF低表达组的60.5%(26/43),差异有统计学意义(P0.05)。结论:VEGF与癌组织DC浸润程度、肿瘤直径及血清AFP水平有关,其在HCC组织中高表达可能增加肝癌术后短期复发风险,可作为肝癌早期复发预警指标

潜在变量、宏观变量与动态利率期限结构——基于DRA模型的实证分析

本文从金融-宏观经济学视角出发,运用DRA模型研究了潜在变量、宏观变量与利率期限结构之间的动态关系。通过脉冲响应函数分析了潜在变量与宏观变量之间的相互冲击效应的大小,以及潜在变量、宏观变量对收益率曲线冲击的影响,借助于方差分解量化了潜在变量、宏观变量冲击对收益率曲线预测误差的贡献率,并利用似然比检验,发现中国的收益率曲线与宏观变量之间存在双向的互动关系,但收益率曲线对未来宏观变量的影响更强

Characteristics of inorganic ions and organic components in PM_(2.5) from biomass burning

为探讨生物质在明火和阴燃两种不同条件下PM_(2.5)及主要成分的排放差异,选取了7种具有代表性的生物质样品(小麦、水稻、马尾松叶、马尾松枝、杂; 草、玉米、棉花)进行了燃烧实验,并对PM_(2.5)样品中的7种主要水溶性离子(Na~+、NH_4~+; 、K~+、Ca~(2+)、Cl~-、NO_3~- 、SO_4~(2-))及有机碳(OC) 、元素碳(EC) 、水溶性有机碳(WSOC); 、有机酸和左旋葡聚糖(LG)等有机成分进行了分析.结果表明,明火和阴燃条件下PM_(2.5)的排放因子分别为2.82~ 7.74; mg·g~(-1)和3.24~ 22.56; mg·g~(-1),阴燃时的排放因子偏高,不同燃料类型也存在一定差异.燃烧排放PM_(2.5)中水溶性离子以Cl~-为最高,占总离子的比例为72; %~; 94%,且与NH_4~+存在显著正相关关系,水溶性离子整体表现为明火条件下的浓度显著高于阴燃条件下的浓度.受阴燃条件下氧气不足的影响,PM_(2; .5)中有机组分的浓度表现为阴燃高于明火,进而导致阴燃时PM_(2.5)的排放因子增加.水稻秸秆燃烧烟尘中3种来源特征比值(LG/PM_(2.5; )、LG/OC和LG/WSOC)仅为小麦和玉米秸秆燃烧排放相应比值均值的0.34、0.24和0.27倍,表明在不同农作物的收获季节采用上述特征比; 值进行生物质燃烧来源估算时,应区别对待.Seven kinds of biomass samples including masson pine needles and; branches,wheat,rice,grass,maize and cotton straw were burned under; flaming and smoldering conditions to investigate the emission factors of; PM_(2.5) and its associated major components including organic carbon; (OC), elemental carbon,water soluble ions,water soluble organ carbon; (WSOC),organic acids and levoglucosan (LG). The results showed that the; emission factors were in the range of 2.82 ~ 7.74 mg·g~(-1) and 3.24 ~; 22.56 mg·g~(-1) for PM_(2.5) from biomass burning in flaming and; smoldering conditions, respectively. The difference between the two; burning conditions varied in different kinds of biomass fuel. The; profiles of water soluble ions in PM_(2.5) were all dominated by; Cl~-,accounting for 72%~ 94% of the total water soluble ions.; Significant positive correlations were only observed between Cl~-and; NH_4~+. The concentrations of water soluble ions were generally higher; in flaming PM_(2.5) than those in smoldering PM_(2.5). The organic; components showed much higher levels in smoldering PM_(2.5) with respect; to those in flaming PM_(2.5) because of incomplete burning. The higher; emission factors of PM_(2.5) under smoldering conditions were mainly due; to the higher emission factors of organic species. Three source; characteristic ratios including LG/PM_(2.5),LG/OC and LG/WSOC in rice; straw burning PM_(2.5) were only 0.34,0.24 and 0.27 times of the mean; ratios in wheat and maize straw burning PM_(2.5),respectively.; Thus,different characteristic ratios are required to estimate biomass; burning contribution in different biomass burning seasons.国家自然科学基金; 国家重点研发计划; 福建省自然科学基金计划项