首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 625 毫秒
1.
We present spatial coherence measurements of extreme ultraviolet (EUV) light generated through the process of high-harmonic up-conversion of a femtosecond laser. With a phase-matched hollow-fiber geometry, the generated beam was found to exhibit essentially full spatial coherence. The coherence of this laser-like EUV source was shown by recording Gabor holograms of small objects. This work demonstrates the capability to perform EUV holography with a tabletop experimental setup. Such an EUV source, with low divergence and high spatial coherence, can be used for experiments involving high-precision metrology, inspection of optical components for EUV lithography, and microscopy and holography with nanometer resolution. Furthermore, the short time duration of the EUV radiation (a few femtoseconds) will enable EUV microscopy and holography to be performed with ultrahigh time resolution.  相似文献   

2.
We introduce a spectroscopic method that determines nonlinear quantum mechanical response functions beyond the optical diffraction limit and allows direct imaging of nanoscale coherence. In established coherent two-dimensional (2D) spectroscopy, four-wave-mixing responses are measured using three ingoing waves and one outgoing wave; thus, the method is diffraction-limited in spatial resolution. In coherent 2D nanoscopy, we use four ingoing waves and detect the final state via photoemission electron microscopy, which has 50-nanometer spatial resolution. We recorded local nanospectra from a corrugated silver surface and observed subwavelength 2D line shape variations. Plasmonic phase coherence of localized excitations persisted for about 100 femtoseconds and exhibited coherent beats. The observations are best explained by a model in which coupled oscillators lead to Fano-like resonances in the hybridized dark- and bright-mode response.  相似文献   

3.
中国农业现代化评价及其空间格局演化   总被引：1，自引：0，他引：1  
从投入、产出、生产服务3维度构建农业现代化评价指标体系,基于2000—2016年省域面板数据,采用熵权法实证分析了中国农业现代化时空演化规律与空间溢出效应。结果表明,2000—2016年中国整体层面的农业现代化发展水平呈上升趋势,并呈现出东高西低、北高南低的空间分异特征,分化为以黄淮海平原为核心的高值区和以西南山区为核心的低值区。农业现代化存在显著的空间集聚趋势与正向空间溢出效应,局域空间集聚方式以高-高集聚和低-低集聚型为主。应制定差异化的农业现代化发展提升策略,重点推动山区农业现代化水平的提升,并充分发挥地理上的空间溢出与辐射带动效用。  相似文献   

4.
We report the observation of neural processing that occurs within 265 milliseconds after outcome stimuli that inform human participants about gains and losses in a gambling task. A negative-polarity event-related brain potential, probably generated by a medial-frontal region in or near the anterior cingulate cortex, was greater in amplitude when a participant's choice between two alternatives resulted in a loss than when it resulted in a gain. The sensitivity to losses was not simply a reflection of detecting an error; gains did not elicit the medial-frontal activity when the alternative choice would have yielded a greater gain, and losses elicited the activity even when the alternative choice would have yielded a greater loss. Choices made after losses were riskier and were associated with greater loss-related activity than choices made after gains. It follows that medial-frontal computations may contribute to mental states that participate in higher level decisions, including economic choices.  相似文献   

5.
农业高质量发展是乡村产业振兴的重要表征。广东省特色高效农业走在全国前列，以广东省为例量化评估农业高质量发展水平，可为各地诊断农业发展问题、监测农业高质量进展、支撑完善支持政策提供参考依据。本研究从高效化、绿色化和稳产化3方面构建了农业高质量发展评价模型，借助空间自相关分析方法、双变量空间关联性分析法分析了广东省农业高质量发展空间集聚特征与影响因素。研究发现，广东省农业高质量发展指数呈现“平原区>丘陵区>山地区”的特征，在空间上形成“平原区显著高高集聚、山地丘陵区显著低低集聚”的格局，高效化、绿色化和稳产化3个维度均呈现显著的正向集聚性，且空间集聚格局相似。农业高质量发展水平主要受到人均地区生产总值、高程等因素的影响，凸显农业高质量发展是一个因地制宜、循序渐进的过程，各地需立足本地资源禀赋、产业发展特色与地区经济发展水平综合施策。  相似文献   

6.
饲料中蛋白·钙·磷水平对生长期固始白鹅日增重的影响   总被引：2，自引：0，他引：2  
[目的]研究饲粮蛋白质、钙、磷添加水平对生长期固始白鹅日增重的影响。[方法]将270只生长期固始白鹅随机分成9组,每组10只,各设3个重复,其饲粮采用蛋白水平为12.4%~14.5%、14.5%~15.5%、15.5%~17.4%,钙水平为0.7%、0.8%、0.9%,磷水平为0.30%~0.39%、0.40%~0.41%、0.50%~0.52%采用3因素3水平正交设计,比较每组日增重。[结果]结果表明:不同蛋白质水平对生长期固始白鹅日增重影响极显著(P<0.01),以15.2%(第4组)和15.5%(第5组)蛋白水平增重速度最快,料重比最低;高钙低磷(第5组)水平对日增重影响同样极显著(P<0.01),但不如蛋白水平影响大;中低钙水平对生长期固始白鹅日增重影响差异不显著(P>0.05)。[结论]生长期固始白鹅饲粮适宜的蛋白质添加水平为15.2%~15.5%。  相似文献   

7.
We used the band structure of a mesoscopic Josephson junction to construct low-noise amplifiers. By taking advantage of the quantum dynamics of a Josephson junction, i.e., the interplay of interlevel transitions and the Coulomb blockade of Cooper pairs, we created transistor-like devices, Bloch oscillating transistors, with considerable current gain and high-input impedance. In these transistors, the correlated supercurrent of Cooper pairs is controlled by a small base current made up of single electrons. Our devices reached current and power gains on the order of 30 and 5, respectively. The noise temperature was estimated to be around 1 kelvin, but noise temperatures of less than 0.1 kelvin can be realistically achieved. These devices provide quantum-electronic building blocks that will be useful at low temperatures in low-noise circuit applications with an intermediate impedance level.  相似文献   

8.
马尾松种子园单亲本子代测定   总被引：7，自引：2，他引：7  
通过对漳平五一林场3年生159个家系马尾松种子园单亲本子代测定林的生长调查研究,来判定亲本的优劣,估算遗传力等主要参数,计算出选择后的遗传增益,结果表明:用家系内优良单株的子代造林,其增益是家系间和家系内选择增益之和,3年生时树高增益为21.2%,说明进行家系选择是提高林木产量的重要途径.  相似文献   

9.
We combined coherent nonlinear optical spectroscopy with nano-electron volt energy resolution and low-temperature near-field microscopy with subwavelength resolution (相似文献   

10.
复合酶制剂对肉鸡生产性能的影响   总被引：2，自引：1，他引：1  
研究复合酶制剂的不同添加水平对肉鸡日增重、料重比和成活率的影响。选用1日龄艾维茵肉鸡360只,随机分为4组,每组3个重复,每个重复30只。对照组饲喂基础日粮,试验Ⅰ,Ⅱ,Ⅲ组分别在基础日粮的基础上添加0.05%,0.10%和0.15%复合酶制剂。试验期为42 d。结果表明:与对照组相比,试验Ⅰ,Ⅱ,Ⅲ组的日增重分别提高5.96%,9.17%,4.30%,料重比分别降低7.08%,11.32%,4.25%,差异显著(P<0.05),成活率分别提高4.88%,6.07%,6.07%。各试验组鸡在日增重、饲料转化率、成活率方面显著优于对照组,以试验Ⅱ组效果最佳。  相似文献   

11.
Secular sea level trends extracted from tide gauge records of appropriately long duration demonstrate that global sea level may be rising at a rate in excess of 1 millimeter per year. However, because global coverage of the oceans by the tide gauge network is highly nonuniform and the tide gauge data reveal considerable spatial variability, there has been a well-founded reluctance to interpret the observed secular sea level rise as representing a signal of global scale that might be related to the greenhouse effect. When the tide gauge data are filtered so as to remove the contribution of ongoing glacial isostatic adjustment to the local sea level trend at each location, then the individual tide gauge records reveal sharply reduced geographic scatter and suggest that there is a globally coherent signal of strength 2.4 +/- 0.90 millimeters per year that is active in the system. This signal could constitute an indication of global climate warming.  相似文献   

12.
Understanding and controlling the complex environment of solid-state quantum bits is a central challenge in spintronics and quantum information science. Coherent manipulation of an individual electron spin associated with a nitrogen-vacancy center in diamond was used to gain insight into its local environment. We show that this environment is effectively separated into a set of individual proximal 13C nuclear spins, which are coupled coherently to the electron spin, and the remainder of the 13C nuclear spins, which cause the loss of coherence. The proximal nuclear spins can be addressed and coupled individually because of quantum back-action from the electron, which modifies their energy levels and magnetic moments, effectively distinguishing them from the rest of the nuclei. These results open the door to coherent manipulation of individual isolated nuclear spins in a solid-state environment even at room temperature.  相似文献   

13.
运用地理统计学和Illumina 16S rRNA基因测序等手段,研究广西环江木论国家自然保护区25 hm~2喀斯特常绿落叶阔叶林土壤主要门级微生物类群的空间分布。结果表明:广西环江木论国家自然保护区喀斯特森林土壤中优势菌门为变形菌门(Protebacteria,34.5%)、放线菌门(Actinobacteria,30.7%)和酸杆菌门(Acidobacteria,12.2%);土壤细菌类群显示空间相关性的自相关范围为44.4～841.4m,其中大部分细菌类群的变程在研究区域范围(500 m)内;在研究区内,变形菌门的相对丰度从北到南逐渐升高,而放线菌门和厚壁菌门(Firmicutes)的相对丰度则从北到南逐渐降低,绿弯菌门(Chloroflexi)、酸杆菌门、奇古菌门(Thaumarchaeota)、拟杆菌门(Bacteroidetes)、芽单胞菌门(Gemmatimonadetes)、疣微菌门(Verrucomicrobia)的相对丰度呈斑片状分布,硝化螺旋菌门(Nitrospirae)的相对丰度呈单峰型分布,WS3(Latescibacteria)的相对丰度则呈间歇性的低值条带和高值条带状分布。可见,喀斯特土壤主要微生物类群相对丰度呈现不同的空间分布格局。  相似文献   

14.
运用空间自相关、空间马尔科夫链方法对1987~2014年内蒙古自治区县域农业比重数据的时空分布及时空演变特征进行了研究。结果表明:1内蒙古自治区农业比重空间自相关性强且空间聚集现象明显;2农业比重存在区域趋同趋势,“低”水平县域趋同趋势有所加强,“高”水平县域趋同趋势有所减弱;3县域自身及其邻域同时向上转移的地区主要集中在蒙东以及蒙西的乌兰察布且呈收缩态势,县域自身或邻域有一方或双方均向下转移的区域绝大多数位于蒙西;4农业比重水平转移显著受到时间和区域背景的制约,区域趋同趋势在时间和空间上表现出不稳定与不独立的特征;51987~2001年,农业比重低水平地区和高水平地区的区域背景对水平转移均起到了负面影响;2001~2014年,农业比重低水平地区的区域背景对水平转移起到了负面影响,而高水平的区域背景则产生了正面影响。这为内蒙古自治区不同时期、不同区域的区域趋同趋势存在及差异提供了空间上的解释。  相似文献   

15.
Radar imaging and altimetry data from the Magellan mission have revealed a diversity of deformational features at a variety of spatial scales on the Venus surface. The plains record a superposition of different episodes of deformation and volcanism; strain is both areally distributed and concentrated into zones of extension and shortening. The common coherence of strain patterns over hundreds of kilometers implies that many features in the plains reflect a crustal response to mantle dynamic processes. Ridge belts and mountain belts represent successive degrees of lithospheric shortening and crustal thickening; the mountain belts also show widespread evidence for extension and collapse both during and following crustal compression. Venus displays two geometrical patterns of concentrated lithospheric extension: quasi-circular coronae and broad rises with linear rift zones; both are sites of significant volcanism. No long, large-offset strike-slip faults have been observed, although limited local horizontal shear is accommodated across many zones of crustal shortening. In general, tectonic features on Venus are unlike those in Earth's oceanic regions in that strain typically is distributed across broad zones that are one to a few hundred kilometers wide, and separated by stronger and less deformed blocks hundreds of kilometers in width, as in actively deforming continental regions on Earth.  相似文献   

16.
甘肃省农业现代化水平时空格局与影响因素   总被引：1，自引：1，他引：0  
采用多指标综合测评法、空间自相关和地理加权回归模型等方法,在构建农业现代化水平评价指标体系的基础上,分析2002—2016年甘肃省农业现代化水平时空分异特征及影响因素。结果表明:1)甘肃省农业现代化水平总体空间分异显著,呈北高南低、西高东低空间特征,且具有较高的稳定性;2)农业现代化水平空间集聚趋势明显,空间自相关引起的结构分异显著,河西地区为高水平集聚区,陇南地区为低水平集聚区,空间关联效应不断增强,并持续表现出空间稳定性特征;3)人均农机化财政支出、公路密度和第一产业固定资产投资总额和城乡居民人均储蓄存款是甘肃省农业现代化水平空间格局演变的重要影响因素。因此,可以从加大财政支农力度、优化财政支农结构和建立农村资金的回流导入机制等方面促进甘肃省农业现代化均衡快速发展。  相似文献   

17.
Mass changes of the Greenland Ice Sheet resolved by drainage system regions were derived from a local mass concentration analysis of NASA-Deutsches Zentrum für Luftund Raumfahrt Gravity Recovery and Climate Experiment (GRACE mission) observations. From 2003 to 2005, the ice sheet lost 101 +/- 16 gigaton/year, with a gain of 54 gigaton/year above 2000 meters and a loss of 155 gigaton/year at lower elevations. The lower elevations show a large seasonal cycle, with mass losses during summer melting followed by gains from fall through spring. The overall rate of loss reflects a considerable change in trend (-113 +/- 17 gigaton/year) from a near balance during the 1990s but is smaller than some other recent estimates.  相似文献   

18.
选用15头体重为35kg左右的长大二元杂交猪,考查饲喂褪黑激素(MT)对生长猪生产性能和饲料养分消化率的影响。试验设两个水平MT添加组[低MT组1·5mg/(kg·d),高MT组3·0mg/(kg·d)]和1个对照组,每组5个重复,每个重复1头猪。结果为,高MT组猪平均日增重和日采食量比对照组分别下降11·31%(P<0·01)和13·53%(P<0·01),料肉比(F/G)有下降趋势,但差异还未达到显著水平。低MT组日增重和采食量与对照组没有显著差异,但饲料转化率显著提高,料肉比(F/G)较对照组下降了5·85%(P<0·05)。与对照组相比,两个MT水平组对饲料消化能和总有机养分表观消化率均没有显著影响,而降低粗脂肪表观消化率,其中高MT组比对照组降低了6·19(P<0·05),低MT组比对照组降低了5·27%(P=0·056)。高MT组降低粗蛋白的表观消化率,而低MT组则提高蛋白质的表观消化率,高MT组与低MT组差异达到显著水平。本试验表明,饲喂低水平的MT可提高生长猪的饲料利用率。  相似文献   

19.
Learning curves in manufacturing   总被引：3，自引：0，他引：3  
Large increases in productivity are typically realized as organizations gain experience in production. These "learning curves" have been found in many organizations. Organizations vary considerably in the rates at which they learn. Some organizations show remarkable productivity gains, whereas others show little or no learning. Reasons for the variation observed in organizational learning curves include organizational "forgetting," employee turnover, transfer of knowledge from other products and other organizations, and economies of scale.  相似文献   

20.
This study examines the food flow in Tianjin, divided into three areas (urban, suburban, and rural), as a case study to gain a better understanding of local and regional food flows and ecosystem performance. The study has the following objectives: (1) to evaluate the capacity for self-sufficiency within Tianjin’s administrative boundary by estimating a self-sufficiency ratio (SSR) using statistical data at both the city and local scales, (2) to estimate food flow at the city scale from field surveys of the local markets and statistics provided by the local government, and (3) to examine the real flows of the two primary types of arable crops (cereal grains and vegetables) at the local level by conducting semi-structured household interviews. The results of this study show that Tianjin has experienced a rapid increase of self-sufficiency capacity since the 1980s, and it appears to have the capacity to support the citizens within its borders. Rural areas have had a surplus in all of the studied food categories since the 1980s, and suburban areas have a history of high estimated SSR for vegetables, poultry, and fish. However, a low degree of locally sourced product flow was observed in this study. Most of the local cereal crops were consumed in the agricultural production areas, but 70?% of the vegetables produced in the rural areas flowed outside of Tianjin and did not support Tianjin local consumption. To reduce its vulnerability to food security issues and to promote a more environmentally desirable local food system, Tianjin needs to recognize the high productivity of its local ecosystem and reduce its dependence on other remote ecosystems for its food needs. A stronger relationship between urban and rural areas should also be established.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号