共查询到20条相似文献，搜索用时 31 毫秒
1.
Wang F Zhang Y Tian C Girit C Zettl A Crommie M Shen YR 《Science (New York, N.Y.)》2008,320(5873):206-209
Two-dimensional graphene monolayers and bilayers exhibit fascinating electrical transport behaviors. Using infrared spectroscopy, we find that they also have strong interband transitions and that their optical transitions can be substantially modified through electrical gating, much like electrical transport in field-effect transistors. This gate dependence of interband transitions adds a valuable dimension for optically probing graphene band structure. For a graphene monolayer, it yields directly the linear band dispersion of Dirac fermions, whereas in a bilayer, it reveals a dominating van Hove singularity arising from interlayer coupling. The strong and layer-dependent optical transitions of graphene and the tunability by simple electrical gating hold promise for new applications in infrared optics and optoelectronics. 相似文献
2.
Laser scribing of high-performance and flexible graphene-based electrochemical capacitors 总被引：1，自引：0，他引：1
Although electrochemical capacitors (ECs), also known as supercapacitors or ultracapacitors, charge and discharge faster than batteries, they are still limited by low energy densities and slow rate capabilities. We used a standard LightScribe DVD optical drive to do the direct laser reduction of graphite oxide films to graphene. The produced films are mechanically robust, show high electrical conductivity (1738 siemens per meter) and specific surface area (1520 square meters per gram), and can thus be used directly as EC electrodes without the need for binders or current collectors, as is the case for conventional ECs. Devices made with these electrodes exhibit ultrahigh energy density values in different electrolytes while maintaining the high power density and excellent cycle stability of ECs. Moreover, these ECs maintain excellent electrochemical attributes under high mechanical stress and thus hold promise for high-power, flexible electronics. 相似文献
3.
Dimiev A Kosynkin DV Sinitskii A Slesarev A Sun Z Tour JM 《Science (New York, N.Y.)》2011,331(6021):1168-1172
The patterning of graphene is useful in fabricating electronic devices, but existing methods do not allow control of the number of layers of graphene that are removed. We show that sputter-coating graphene and graphene-like materials with zinc and dissolving the latter with dilute acid removes one graphene layer and leaves the lower layers intact. The method works with the four different types of graphene and graphene-like materials: graphene oxide, chemically converted graphene, chemical vapor-deposited graphene, and micromechanically cleaved ("clear-tape") graphene. On the basis of our data, the top graphene layer is damaged by the sputtering process, and the acid treatment removes the damaged layer of carbon. When used with predesigned zinc patterns, this method can be viewed as lithography that etches the sample with single-atomic-layer resolution. 相似文献
4.
Rutter GM Crain JN Guisinger NP Li T First PN Stroscio JA 《Science (New York, N.Y.)》2007,317(5835):219-222
A single sheet of carbon, graphene, exhibits unexpected electronic properties that arise from quantum state symmetries, which restrict the scattering of its charge carriers. Understanding the role of defects in the transport properties of graphene is central to realizing future electronics based on carbon. Scanning tunneling spectroscopy was used to measure quasiparticle interference patterns in epitaxial graphene grown on SiC(0001). Energy-resolved maps of the local density of states reveal modulations on two different length scales, reflecting both intravalley and intervalley scattering. Although such scattering in graphene can be suppressed because of the symmetries of the Dirac quasiparticles, we show that, when its source is atomic-scale lattice defects, wave functions of different symmetries can mix. 相似文献
5.
基于红外探测的地面林火目标自动检测与追踪系统设计 总被引：1，自引：0，他引：1
针对红外林火图像的特点,从实际应用的角度出发,在FPGA+DSP构建的硬件平台上,实现了森林灰度图像的正确采集和进行有无火点的判断,并提出了图像边缘检测和自适应阈值相结合提取林火目标的方法,达到了林火目标的自动检测;然后利用通信协议和算法控制云台转动,使热像仪的光学系统主光轴始终对准最大灰度值点,达到追踪的效果.在多种... 相似文献
6.
[目的]研究微生物生物量的测定方法。[方法]离心收集蓝细菌,用去离子水清洗后,超声破碎蓝细菌,将破碎后的蓝细菌用去离子水稀释至不同浓度,测定不同浓度破碎后的蓝细菌菌液的电导率值。同时测定蓝细菌的细胞干重及吸光度值。[结果]完全破碎后的蓝细菌菌液的电导率值与细胞干重存在良好的线性关系,线性系数r=0.999 4;蓝细菌的吸光度值与细胞干重也存在良好的线性关系,线性系数r=0.998。[结论]电导率法和吸光度法均能很好地反映蓝细菌的生物量,电导率法的方便程度和可靠性均可以与吸光度法相比较。 相似文献
7.
Amelinckx S Bernaerts D Zhang XB Van Tendeloo G Van Landuyt J 《Science (New York, N.Y.)》1995,267(5202):1334-1338
A model that postulates a mixture of scroll-shaped and concentric, cylindrical graphene sheets is proposed to explain the microstructure of graphite multishell nanotubes grown by arc discharge. The model is consistent with the observed occurrence of a relatively small number of different chiral angles within the same tubule. The model explains clustering in a natural way and is consistent with the observation of asymmetric (0002) lattice fringe patterns and with the occurrence of singular fringe spacings larger than c/2 (c is the c parameter of graphite) in such patterns. Anisotropic thermal contraction accounts for the 2 to 3 percent increase in the c parameter of nanotubes, compared with bulk graphite, but is too small to explain the singular fringe spacings. The model also explains the formation of multishell closure domes. Nucleation is attributed to the initial formation of a fullerene "dome." 相似文献
8.
为了建立厚朴Magnolia officinalis药材品质快速有效的评价方法,采用近红外反射光谱技术测定厚朴酚及和厚朴酚的质量分数。通过在全波长条件下,运用不同数学预处理、光谱散射校正和统计方法对来发展定标回归方程,其中统计方法包括偏最小二乘法(PLS)、修正的偏最小二乘法回归分析法(MPLS)和主成分回归法(PCR)。在对比分析的基础上,得到最佳的数学方法为"3,6,6,1"组合,光谱散射校正方法为SNV D或SNV,统计方法为MPLS,厚朴酚类物质的定标决定系数RSQ均达到了0.97以上。该定标模型的外部独立检验相关系数也均达0.95以上。用近红外反射光谱技术测定厚朴药材酚类物质质量分数具有与化学法相近的准确性,可在实践中应用。图2表5参11 相似文献
9.
针对农业物联网应用层通信间孤岛效应的问题,采用工作流引擎和消息转发模式方法对农业物联网集成通信平台集成进行研究.在分析物联网平台和云计算程序设计的基础上,提出基于消息中间件的工作流引擎模型应用于农业物联网的集成通信平台.试验结果表明:通过扩充POP3、SMTP、XMPP等通信协议,将多种通信协议进行转换实现端到端的互联互通,解决了在一定时间域内不同地点、不同设备在不同协议状态下与物联网信息平台间云计算的应用层通信.同时对云计算并行模式的2种消息并行程序设计方法进行了对比,在数据量达到104帧的请求压力测试下,主从模式优于对等模式. 相似文献
10.
采用自由基诱导法制备蛋白质—枸杞叶黄酮复合物，通过紫外光谱、荧光光谱、傅里叶变换红外光谱、电镜等方法表征5种蛋白质（醇溶蛋白、大豆蛋白、酪蛋白、牛血清蛋白和乳清蛋白）与枸杞叶黄酮共价结合前后蛋白质结构的变化并进行了抗氧化性的分析。结果表明，5种蛋白质都与枸杞叶黄酮发生了不同程度地相互作用，并使蛋白质的结构发生改变。枸杞叶黄酮与蛋白质共价结合，导致蛋白质荧光淬灭，改变了酪氨酸或色氨酸数量。傅里叶变换红外光谱中酰胺A带、Ⅰ带、Ⅱ带的特征峰发生偏移，表明蛋白质在共价复合枸杞叶黄酮后二级结构发生了改变。扫描电镜直观显示了共价复合物微观结构的变化，可形成球状、片状、棒状或不规则颗粒状。综合比较发现，醇溶蛋白、乳清蛋白与枸杞叶黄酮结合能力较强，对蛋白质的二级结构影响较大，且体外抗氧化活性较强。研究结果为进一步分析枸杞叶黄酮与蛋白质共价复合物的性质以及枸杞叶黄酮类化合物作为天然抗氧化剂的应用提供理论基础。 相似文献
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A synthetic pathway is described to construct "in bulk" two-dimensional (2D) polymers shaped as molecular sheets. A chiral oligomeric precursor is used that contains two reactive sites, a polymerizable group at one terminus and a reactive stereogenic center near the middle of the molecule. The bulk reaction yields bilayer 2D polymers of molecular weight in the order of millions and a monodisperse thickness of 50.2 angstroms. The 2D molecular objects form through molecular recognition by the oligomers, which self-organize into layers that place the reactive groups within specific planes. The oligomers become catenated by two different stitching reactions involving the reactive sites. At room temperature, stacks of these molecular objects can organize as single crystals and at higher temperatures melt into smectic liquid crystals. Nonlinear optical experiments reveal that solid films containing the 2D polymers form structures that are thermally and temporally more stable than those containing analogous 1D polymers. This observation suggests that the transformation of common polymers from a 1D to a 2D architecture may produce generations of organic materials with improved properties. 相似文献
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中国农业科技成果转化交易率长期以来处于较低状态,其主要原因,一是成果转化的信息严重不对称,二是成果转化的机制不完善,三是成果转化的支撑体系不健全。为此,笔者提出了建设“全国农业科技成果转化交易服务平台”的设想。平台由资源汇集展示服务、政策支持服务、科技成果交易评估服务、科技成果交易服务、产学研合作服务、中小试服务、科技投融资服务、科技成果管理等8个子服务平台构成,其性质是一个为农业科技成果转化交易双方和向交易双方提供服务的第三方提供政策、技术、人才、资金等一系列的支持和帮助的公益服务系统。为保障平台的顺利建设与运营,建议出台组织、机制、政策、人才等4个方面的政策措施。 相似文献
15.
We fabricated transferable gallium nitride (GaN) thin films and light-emitting diodes (LEDs) using graphene-layered sheets. Heteroepitaxial nitride thin films were grown on graphene layers by using high-density, vertically aligned zinc oxide nanowalls as an intermediate layer. The nitride thin films on graphene layers show excellent optical characteristics at room temperature, such as stimulated emission. As one of the examples for device applications, LEDs that emit strong electroluminescence emission under room illumination were fabricated. Furthermore, the layered structure of a graphene substrate made it possible to easily transfer GaN thin films and GaN-based LEDs onto foreign substrates such as glass, metal, or plastic. 相似文献
16.
Miao F Wijeratne S Zhang Y Coskun UC Bao W Lau CN 《Science (New York, N.Y.)》2007,317(5844):1530-1533
As an emergent electronic material and model system for condensed-matter physics, graphene and its electrical transport properties have become a subject of intense focus. By performing low-temperature transport spectroscopy on single-layer and bilayer graphene, we observe ballistic propagation and quantum interference of multiply reflected waves of charges from normal electrodes and multiple Andreev reflections from superconducting electrodes, thereby realizing quantum billiards in which scattering only occurs at the boundaries. In contrast to the conductivity of conventional two-dimensional materials, graphene's conductivity at the Dirac point is geometry-dependent because of conduction via evanescent modes, approaching the theoretical value 4e(2)/pih (where e is the electron charge and h is Planck's constant) only for short and wide devices. These distinctive transport properties have important implications for understanding chaotic quantum systems and implementing nanoelectronic devices, such as ballistic transistors. 相似文献
17.
Virus particles and murine leukemia virus complement-fixing antigen in neoplastic and nonneoplastic cell lines 总被引：9，自引：0，他引：9
W T Hall W F Andresen K K Sanford V J Evans J W Hartley 《Science (New York, N.Y.)》1967,156(771):85-88
Twenty-seven lines of murine tissue cultures derived from 12 different cell pools and grown on various media were examined with the electron microscope for morphologically detectable virus particles. They were also tested for complement-fixing mouse leukemia virus antigens and for recoverable virus. A 100-percent correlation between results obtained by these two methods is reported.An additional 19 lines from 8 different cell pools were examined for either virus particles or complement-fixing antigens. All lines were assayed for neoplastic transformation. Seven cell pools gave rise to lines showing evidence of contamination with leukemia virus. Since most of these lines had also undergone "spontaneous" neoplastic transformation in vitro, this virus cannot be excluded as a possible cause of the neoplastic change, or of influencing it. The remaining cell pools gave rise to lines with no evidence of contamination with leukemia virus;but most of these lines also underwent similar transformation. These results suggest that "spontaneous" neoplastic transformation can occur in the absence of detectable mouse leukemia virus. 相似文献
18.
上海半城市化区域自然景观生态格局优化设计的途径 总被引：4，自引：0，他引：4
半城市化现象是城市化过程中的必然阶段,上海半城市化现象具有特殊性和示范性,上海半城市化区域自然景观格局的研究途径是:以上海半城市化区域时空演变的特征和机理探索为基础,以上海半城市化区域生态景观格局优化和生态功能空间重构为目标,综合运用3S技术、土地时空演变模型分析技术、景观动态格局与生态过程关系分析技术和生态格局优化模式设计技术等方法,包括:1、上海半城市化区域空间识别,从结构、变化、景观和体制4个层面确定上海半城市化区域的范围和主要类型;2、上海半城市化区域自然景观时空演变动态及驱动力分析:综合运用土地演变的多个分析模型,探究自然景观时空演变过程和驱动力机制;3、上海半城市化区域自然景观格局与生态过程关系研究:分析上海半城市化空间扩展与自然景观生态过程之间的关系,构建上海半城市化空间拓展的生态机制;4、上海半城市化区域自然景观生态格局优化设计:综合自然景观中各类土地覆被类型的生态功能和社会、经济功能,综合分析各类生态要素,研究样区内的生态功能区、生态敏感区、生态邻里、生态要素配置的类型划分和分析,研究上海半城市化区域自然景观生态格局优化设计。 相似文献
19.
Chen Feng Kissel David E. West Larry T. Adkins W. Clark Rex Rickman Doug Luvall J. C. 《Precision Agriculture》2004,5(1):7-26
The surface soil clay concentration is a useful soil property to map soils, interpret soil properties, and guide irrigation, fertilizer, and agricultural chemical applications. The objective of this study was to determine whether surface soil clay concentrations could be predicted from remotely sensed imagery of bare surface soil or from soil electrical conductivity for a 115 ha field located in Crisp County, Georgia. The soil clay concentrations were determined for soil samples taken at 28 field locations. Three different data sources–an aerial color photograph image, two infrared bands from an ATLAS data set, and the electrical conductivity of the surface soil layer were used in the research. Principal components analysis was applied to the color photograph image, whereas the ratio of two infrared bands was applied to the ATLAS data set. Filtering was applied to both resulting images. The distribution of soil electrical conductivity was derived from the measured soil electrical conductivity data by spatial analysis. Statistical relationships between soil clay concentrations and the principal component 3, the ratio of two ATLAS infrared bands, and the soil electrical conductivity were analyzed, and three linear equations were derived with r
2 values 0.83, 0.52, and 0.78, respectively. The distribution of the soil clay concentrations was derived based on these three equations. Six levels of soil clay concentrations were classified in these three methods, and the advantages and disadvantages were discussed. The predicted and measured soil clay concentrations, based on additional soil samples from 30 field locations, were compared using linear regression (r
2=0.76, 0.45, and 0.77 for the three methods). The overall accuracy for these methods were 84%, 66%, and 76%, respectively. The principal components method had the highest accuracy in our research, while the result for the depressional areas is the best from the ratio method. 相似文献
20.
Yang H Heo J Park S Song HJ Seo DH Byun KE Kim P Yoo I Chung HJ Kim K 《Science (New York, N.Y.)》2012,336(6085):1140-1143
Despite several years of research into graphene electronics, sufficient on/off current ratio I(on)/I(off) in graphene transistors with conventional device structures has been impossible to obtain. We report on a three-terminal active device, a graphene variable-barrier "barristor" (GB), in which the key is an atomically sharp interface between graphene and hydrogenated silicon. Large modulation on the device current (on/off ratio of 10(5)) is achieved by adjusting the gate voltage to control the graphene-silicon Schottky barrier. The absence of Fermi-level pinning at the interface allows the barrier's height to be tuned to 0.2 electron volt by adjusting graphene's work function, which results in large shifts of diode threshold voltages. Fabricating GBs on respective 150-mm wafers and combining complementary p- and n-type GBs, we demonstrate inverter and half-adder logic circuits. 相似文献