共查询到20条相似文献，搜索用时 31 毫秒
1.
中国股票市场多标度行为的实证分析 总被引：13，自引：0，他引：13
本文研究了中国股票市场指数时间序列的多标度行为，对不同时间跨度的指数增量序列与利益率序列、广义累积绝对收益序列的标准差进行了标度分析，分析表明标准差与时间跨度满足幂律关系，且幂指数不是唯一的，具有多标度的特征，并把计算的标度指数用于刻画估计波动率的分析。 相似文献
2.
本文将边界序列的多尺度描述和傅里叶描述符结合起来,得到闭合边界的多尺度傅里叶描述符。该方法先将边界序列呈现到不同的尺度空间,然后进行傅里叶变换,得到了不同尺度空间的傅里叶描述符。分类实验表明,该方法提取的特征具有较好的分类特性。 相似文献
3.
The chaos characteristics of melt index have been first explored, and the Hilbert–Huang transform method and time delay embedding method are applied to multiscale dynamic analysis on the time series of the melt index (MI) in the propylene polymerization industry. The research results show that the embedding delay is 2, the embedding dimension is 5, the correlation dimension D2 is 1.57, and the maximum Lyapunov exponent is 0.143 for the melt index series, which provide clear evidence of chaotic multiscale features in the propylene polymerization process. Three intrinsic mode functions (IMFs) are decomposed from the melt index time series; the presence of non-integer fractal correlation dimension and positive finite maximum Lyapunov exponent are found in some IMF components. The PP melt index series are divided into two chaotic signals, a determined signal and a random signal respectively, and its complexity is therefore reduced. Furthermore, the coupling of subscale structures of the propylene polymerization is explored with the dimension of interaction dynamics and a robust algorithm for detecting interdependence. It is found that IMF(2) is the main driver in the coupling system of IMF(1)and IMF(2). All these provide a guideline for studying propylene polymerization process with chaotic multiscale theory and may offer more candidate tools to model and control propylene polymerization system in the future. 相似文献
4.
Nakano T Itoyama T Yoshida K Sawada Y Ikeda S Fukuda T Matsuda T Negoro M Arai F 《Biomicrofluidics》2010,4(4):46505
We proposed and fabricated multiscale transparent arteriole and capillary vessel models with circular cross sections of 10-500 μm using photolithography. The circularities of the fabricated 10, 50, and 500 μm diameter microchannels were 84.0%, 61.5%, and 82.3%, respectively. Next, we connected these different models to realize a circulation type blood vessel model simulating arteriole networks. We proposed a novel connection method using an intermediate connector made of wax, which we used to connect these models to make a circulation model. In flow experiments, the fabricated models showed no leakage and circulation models with seamless connections were achieved. 相似文献
5.
Contourlet变换是一种基于图像的几何性变换,通过各向异性实现了图像的多尺度多方向性分解,它能够有效地表示图像中的轮廓和纹理。利用这些特性,提出了基于Contourlet域的盲水印算法。实验证明,该算法很好地协调了透明性与鲁棒性;并且实现了盲检测。 相似文献
6.
超级计算能力是国家科技竞争力乃至综合国力的重要标志,也是经济社会发展、国防和国家安全的重要支撑。特别是在网络化、大数据、云计算和虚拟现实迅猛发展的背景下,超级计算不但是科技发展的利器,正引发科研模式的根本变革,也将成为重要的社会基础设施,并最终深刻地改变我们的生产和生活方式。但目前超级计算正面临应用效率低、能耗高、稳定性差和难以应用等严峻挑战。基于在复杂系统多尺度模拟方面多年的探索和积累,文章提出,按照计算对象、模型、软件与硬件的逻辑和结构一致的原理优化计算机体系结构,缓解和克服商品化通用硬件系统开发中的难点,可能是突破这些瓶颈的一条具有普遍意义的途径。 相似文献
7.
Analyzing review sentiments and product images by parallel deep nets for personalized recommendation
《Information processing & management》2023,60(1):103166
Recommendation is an effective marketing tool widely used in the e-commerce business, and can be made based on ratings predicted from the rating data of purchased items. To improve the accuracy of rating prediction, user reviews or product images have been used separately as side information to learn the latent features of users (items). In this study, we developed a hybrid approach to analyze both user sentiments from review texts and user preferences from item images to make item recommendations more personalized for users. The hybrid model consists of two parallel modules to perform a procedure named the multiscale semantic and visual analyses (MSVA). The first module is designated to conduct semantic analysis on review documents in various aspects with word-aware and scale-aware attention mechanisms, while the second module is assigned to extract visual features with block-aware and visual-aware attention mechanisms. The MSVA model was trained, validated and tested using Amazon Product Data containing sampled reviews varying from 492,970 to 1 million records across 22 different domains. Three state-of-the-art recommendation models were used as the baselines for performance comparisons. Averagely, MSVA reduced the mean squared error (MSE) of predicted ratings by 6.00%, 3.14% and 3.25% as opposed to the three baselines. It was demonstrated that combining semantic and visual analyses enhanced MSVA's performance across a wide variety of products, and the multiscale scheme used in both the review and visual modules of MSVA made significant contributions to the rating prediction. 相似文献
8.
科学合理地选择空间区位划定基本农田对提高耕地保护效率,实现粮食生产稳定发展,具有重要的现实意义。文章以武汉城市圈为例,在确保耕地质量的前提下,考虑耕地的空间稳定性及其尺度内的水平作用和尺度之间的垂直作用,运用EB修正的空间自相关分析方法和空间叠加分析方法,从市级、区县、乡镇三个尺度开展基本农田空间区位选择研究。研究结果显示,建设占用耕地是影响基本农田空间稳定性的重要因素,存在单尺度内的空间聚集和分散以及不同尺度之间的作用等特征。根据不同尺度的LISA图发现,LH类型区耕地的建设用地需求高,空间稳定性差,容易发生非农转化;而LL类型区耕地的建设用地需求低,耕地空间稳定性好,不易发生非农转化。将研究区划分为高风险、中等风险、较低风险、低风险四个区域,其中较低风险区和低风险区可作为基本农田的较适宜和适宜划定区域,主要集中连片分布在黄梅县刘佐乡、孝昌县花园镇、汉川市田二河镇、蔡甸区永安街道等,该结果与单尺度研究结果存在差异。 相似文献
9.
Ke Li Yingfeng Li Xinyu Wang Mengkui Cui Bolin An Jiahua Pu Jintao Liu Boyang Zhang Guijun Ma Chao Zhong 《国家科学评论(英文版)》2021,8(8)
Marine diatoms construct their hierarchically ordered, three-dimensional (3D) external structures called frustules through precise biomineralization processes. Recapitulating the remarkable architectures and functions of diatom frustules in artificial materials is a major challenge that has important technological implications for hierarchically ordered composites. Here, we report the construction of highly ordered, mineralized composites based on fabrication of complex self-supporting porous structures—made of genetically engineered amyloid fusion proteins and the natural polysaccharide chitin—and performing in situ multiscale protein-mediated mineralization with diverse inorganic materials, including SiO2, TiO2 and Ga2O3. Subsequently, using sugar cubes as templates, we demonstrate that 3D fabricated porous structures can become colonized by engineered bacteria and can be functionalized with highly photoreactive minerals, thereby enabling co-localization of the photocatalytic units with a bacteria-based hydrogenase reaction for a successful semi-solid artificial photosynthesis system for hydrogen evolution. Our study thus highlights the power of coupling genetically engineered proteins and polysaccharides with biofabrication techniques to generate hierarchically organized mineralized porous structures inspired by nature. 相似文献
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11.
【目的】对影响开放式同行评议实践的相关因素进行实证研究,发掘开放式同行评议的关键影响因素。【方法】以Directory of Open Access Journals (DOAJ)中开放式同行评议期刊为研究对象,通过网络爬取相关数据。采用变量分类赋值的方式,对影响开放式同行评议的相关定性因素进行量化分析。采用多重对应分析图展示开放式同行评议相关影响因素及其不同类别的内在关联;采用最优尺度回归模型揭示相关影响因素对开放评议类型的影响程度。【结果】开放评议类型与评议专家身份的公开类别具有极密切的关联,评议专家身份对开放评议类型有显著正向影响,且重要性程度值非常高。【结论】评议专家身份是否公开成为开放式同行评议实践模式的关键影响因素,透明性同行评议是当前开放评议行之有效的实践模式。 相似文献
12.
《Journal of The Franklin Institute》2023,360(6):4427-4455
Deep learning-based object detection algorithms have been widely used and are effective in autonomous driving. But their performance degrades dramatically under low-light conditions. The existing mitigation approach for low-light object detection uses image enhancement preprocessing to improve detection performance with limited success. In addition, this preprocessing approach incurs extra computation costs, consumes more resources, and makes it more challenging to implement the algorithm on embedded platforms. This paper proposes a novel object detection network in low-light conditions for embedded platforms. The new system consists of two innovative modules, including a lightweight low-light enhancement network DS-PyLENet and an anchor-free lightweight object detector CFEDet. DS-PyLENet is a three-level pyramid network configured with depthwise separable convolution residual blocks (DSCRBs) and multiscale DSCRBs. The CFEDet is configured with an improved EfficientNet backbone network with Coordinate Attention (CA) and vanilla MBconv, i.e., CA-fused EfficientNet, an improved Path Aggregation Network (PAN) fusion module, and an anchor-free Global Focal Loss (GFL) detection head. Two evaluation metrics, relative recall ratios, are proposed to depict the effectiveness of image enhancement on object detection more intuitively. The new model is demonstrated to be superior to the assembled model of EnlightenGAN and YOLOv5n in terms of detection accuracy and speed on GPU and embedded platforms. The testing results of the new model reveal that 83.5% mAP is achieved on the Exdark dataset and 67.4% mAP on the DarkFace dataset. The running rates of GTX 1080Ti and NVIDIA Jetson Xavier NX are 22 FPS and 2.6 FPS, respectively. The recall of CFEDet with DS-PyLENet increased to 22.1% and significantly improved over 18% with Zero-DCE and 17.2% with EnlightenGAN. 相似文献
13.
[目的/意义]受开放科学运动影响所形成的各类大规模开放学术图谱,作为一种高质量、良结构化的科研领域大数据集,为研究前沿分析创造了新的研究条件。在该数据下构建研究前沿分析的思路与框架,将有效实现数据驱动的知识发现,辅助科技情报分析和决策。[方法/过程]对研究前沿及其分析方法进行了文献回顾,并探讨了研究前沿分析面临的主要问题。进一步,对开放学术图谱进行了调研,进而构建了基于大规模开放学术图谱进行研究前沿分析的总体框架。[结果/结论]所构建的研究前沿分析框架,提出了基于大规模开放学术图谱进行研究前沿分析的详细步骤,能够基于开放学术图谱实现对研究主题的全面、快速、准确分析,为实现研究前沿的跨时空动态分析、多尺度演化分析及多因素多维分析提供可供参考的思路。 相似文献
14.
中国科学院黄土高原地球关键带与地表通量野外观测研究站（以下简称“黄土高原关键带站”）立足黄土高原，面向黄河中游，开展季风区地球关键带和地表通量的长期定位观测和数据积累，在科学上为世界地球关键带科学作出突出贡献，在服务国家需求上为黄河流域生态保护和高质量发展等国家战略提供有力的科技支撑。黄土高原关键带站提出了黄土关键带形成演化的“季风控制论”，重建了地质历史时期黄土高原植被、温度和降水的变化，查明了黄土关键带形成演化的气候背景；重建了过去500年温度、降水等气候要素序列，揭示了黄土高原干旱、高温等极端气候事件发生的诱因及特点；系统开展了黄土高原生态系统过程与服务研究，揭示了黄土高原关键带土地利用格局与生态过程的作用机理，阐明了不同生态系统服务的形成与相互作用机制，提出了面向可持续发展的黄土高原关键带类型划分的指标体系和方法框架；深入开展了黄土高原多尺度水土过程及其对重大生态工程的响应研究，阐明了黄土高原和黄河流域过去60年径流输沙和水沙关系的时空尺度特征与驱动机制，揭示了土壤水分与区域气候、土壤和植被的相互关系，定量评估了黄土高原生物和工程治理措施的环境效应；为黄土高原综合治理、生态保护和经济社会可持续发展提供决策咨询。 相似文献
15.
Hesham Khalifa Sherif A El-Safty Abdullah Reda Mohamed A Shenashen Alaa I Eid 《国家科学评论(英文版)》2020,7(5):863
We report on low-cost fabrication and high-energy density of full-cell lithium-ion battery (LIB) models. Super-hierarchical electrode architectures of Li2SiO3/TiO2@nano-carbon anode (LSO.TO@nano-C) and high-voltage olivine LiMnPO4@nano-carbon cathode (LMPO@nano-C) are designed for half- and full-system LIB-CR2032 coin cell models. On the basis of primary architecture-power-driven LIB geometrics, the structure keys including three-dimensional (3D) modeling superhierarchy, multiscale micro/nano architectures and anisotropic surface heterogeneity affect the buildup design of anode/cathode LIB electrodes. Such hierarchical electrode surface topologies enable continuous in-/out-flow rates and fast transport pathways of Li+-ions during charge/discharge cycles. The stacked layer configurations of pouch LIB-types lead to excellent charge/discharge rate, and energy density of 237.6 Wh kg−1. As the most promising LIB-configurations, the high specific energy density of hierarchical pouch battery systems may improve energy storage for long-driving range of electric vehicles. Indeed, the anisotropic alignments of hierarchical electrode architectures in the large-scale LIBs provide proof of excellent capacity storage and outstanding durability and cyclability. The full-system LIB-CR2032 coin cell models maintain high specific capacity of ∼89.8% within a long-term life period of 2000 cycles, and average Coulombic efficiency of 99.8% at 1C rate for future configuration of LIB manufacturing and commercialization challenges. 相似文献
16.
Ruichao Pang Pengfei Tian Hongliang Jiang Minghui Zhu Xiaozhi Su Yu Wang Xiaoling Yang Yihua Zhu Li Song Chunzhong Li 《国家科学评论(英文版)》2021,8(7)
Unveiling the structural evolution and working mechanism of catalysts under realistic operating conditions is crucial for the design of efficient electrocatalysts for CO2 electroreduction, yet remains highly challenging. Here, by virtue of operando structural measurements at multiscale levels, it is identified under CO2 electroreduction conditions that an as-prepared CeO2/BiOCl precatalyst gradually evolves into CeOx/Bi interface structure with enriched Ce3+ species, which serves as the real catalytically active phase. The derived CeOx/Bi interface structure compared to pure Bi counterpart delivers substantially enhanced performance with a formate Faradaic efficiency approaching 90% for 24 hours in a wide potential window. The formate Faradaic efficiency can be further increased by using isotope D2O instead of H2O. Density functional theory calculations suggest that the regenerative CeOx/Bi interfacial sites can not only promote water activation to increase local *H species for CO2 protonation appropriately, but also stabilize the key intermediate *OCHO in formate pathway. 相似文献
17.
为提高《电子工艺学》课程的教学效果,对《电子工艺学》课程教学进行了改革探索,提出了构建以“实践”为基础的教学模式、实施一体化教学、循序渐进加强技能培养、利用现代多媒体技术、加大实践考核比重等改革方法,同时也提出了存在问题及需改进之处。 相似文献
18.
数字图书馆建设之我见 总被引：2，自引：0，他引：2
本文首先从数字图书馆的提出入手，结合数字图书馆建设的状况，对数字图书馆的特征进行了分析；随后，指出目前数字图书馆建设中存在着四个方面的问题；针对这些问题，我们认为，数字图书馆系统的建设必须着重考虑和研究两方面的问题，即系统的框架结构和六方面的具体实现技术。 相似文献
19.
有许多因素对企业创业过程产生影响,因此,要取得企业创业的成功就必须注意抓核心要素。在回顾现有文献的基础上,本文认为,在转型期,中国企业创业有三个核心要素:机会、创业能力和创业文化。 相似文献
20.
《Information processing & management》2022,59(2):102868
With the continuous development of intelligent transportation systems, vehicle-related fields have emerged a research boom in detection, tracking, and retrieval. Vehicle re-identification aims to judge whether a specific vehicle appears in a video stream, which is a popular research direction. Previous researches have proven that the transformer is an efficient method in computer vision, which treats a visual image as a series of patch sequences. However, an efficient vehicle re-identification should consider the image feature and the attribute feature simultaneously. In this work, we propose a vehicle attribute transformer (VAT) for vehicle re-identification. First, we consider color and model as the most intuitive attributes of the vehicle, the vehicle color and model are relatively stable and easy to distinguish. Therefore, the color feature and the model feature are embedded in a transformer. Second, we consider that the shooting angle of each image may be different, so we encode the viewpoint of the vehicle image as another additional attribute. Besides, different attributes are supposed to have different importance. Based on this, we design a multi-attribute adaptive aggregation network, which can compare different attributes and assign different weights to the corresponding features. Finally, to optimize the proposed transformer network, we design a multi-sample dispersion triplet (MDT) loss. Not only the hardest samples based on hard mining strategy, but also some extra positive samples and negative samples are considered in this loss. The dispersion of multi-sample is utilized to dynamically adjust the loss, which can guide the network to learn more optimized division for feature space. Extensive experiments on popular vehicle re-identification datasets verify that the proposed method can achieve state-of-the-art performance. 相似文献