Spectral Methods For Hamiltonian Systems And Their Applications

Hamiltonian systems typically arise as models of conservative physical systems and have many applications. Our main emphasis is using spectral methods to preserve both symplectic structure and energy up to machine error in long time. An engery error estimation is given for a type of Hamiltonian systems with polynomial nonlinear part, which is numerical verified by solving a Henon-Heiles systems. Three interesting applications are presented : the first one is the N-body problems. The second one is approximation for Weyl\u27s Law and the third one is simulating quantum cooling in an optomechanical system to study the dissipative dynamics. Moreover, nonsmooth Hamiltonian systems problems are discussed for the limitation of this method which motivates our future work

Value Creation of E-commerce Platform Firms in Competitive Dynamics: From a Resource Orchestration Perspective

This study examines the rules of resource combination for e-commerce platform firms value creation in competitive dynamics. Based on the resource orchestration view and competitive dynamics theory, we suggest a configurational analytic framework that departs from the standard linear paradigm to examine how configurations of digital strategic action formed by digital resources creates value through the effect that competitors hard to respond to. In line with this approach, we use fuzzy-set qualitative comparative analysis (fsQCA) to news data from Chinese online tourism industry. Our findings suggest equifinal pathways to gain the effect that is hard to be responded and the specific boundary conditions of our propositions that determine what way digital technologies and partnership resources orchestrate in e-commerce platform firms’ creating value. We discuss implications for theory and practice

A YOLOv7 incorporating the Adan optimizer based corn pests identification method

Major pests of corn insects include corn borer, armyworm, bollworm, aphid, and corn leaf mites. Timely and accurate detection of these pests is crucial for effective pests control and scientific decision making. However, existing methods for identification based on traditional machine learning and neural networks are limited by high model training costs and low recognition accuracy. To address these problems, we proposed a YOLOv7 maize pests identification method incorporating the Adan optimizer. First, we selected three major corn pests, corn borer, armyworm and bollworm as research objects. Then, we collected and constructed a corn pests dataset by using data augmentation to address the problem of scarce corn pests data. Second, we chose the YOLOv7 network as the detection model, and we proposed to replace the original optimizer of YOLOv7 with the Adan optimizer for its high computational cost. The Adan optimizer can efficiently sense the surrounding gradient information in advance, allowing the model to escape sharp local minima. Thus, the robustness and accuracy of the model can be improved while significantly reducing the computing power. Finally, we did ablation experiments and compared the experiments with traditional methods and other common object detection networks. Theoretical analysis and experimental result show that the model incorporating with Adan optimizer only requires 1/2-2/3 of the computing power of the original network to obtain performance beyond that of the original network. The mAP@[.5:.95] (mean Average Precision) of the improved network reaches 96.69% and the precision reaches 99.95%. Meanwhile, the mAP@[.5:.95] was improved by 2.79%-11.83% compared to the original YOLOv7 and 41.98%-60.61% compared to other common object detection models. In complex natural scenes, our proposed method is not only time-efficient and has higher recognition accuracy, reaching the level of SOTA

Dynamic Modeling of a Flexible-Link Flexible-Joint System with Tip Mass Considering Stiffening Effect

This paper presents the dynamic model of a flexible-link, flexible-joint manipulator system with a considerable stiffening effect of the flexible link. A gripper, along with tip mass, is attached at one end of the flexible link. By employing the extended Hamilton’s principle, a nonlinear governing equation of motion is derived along with several boundary constraints. Under the assumption of small deformation in free vibration, a simplified motion equation is deduced to determine the natural frequencies of the mechanical system. Four parameters of the system are selected to carry out the sensitivity study on frequency. The results show that the second frequency mainly depends on the mass of tip payload. Moreover, the third frequency is significantly affected by the moment inertia of tip payload. Regarding the constant angular motion, the finite element method is adopted to analyze the dynamic model by considering the stiffening effect. The frequency results are obtained which show a higher stiffness of the Single Flexible-link Flexible-joint (SFF) system with the angular velocity increasing. The influence of three factors (i.e., payload mass, length of the flexible link, and angular velocity) on the fundamental natural frequencies are discussed, which show instinct characteristics of the flexible manipulator system

A Dataset of Late 1990s and Early 2000s Web Banner Ads on Chinese-and English-language Web Pages

This dataset contains information about 22,915 banner advertisement images appearing on Chinese- and English-language web pages in the late 1990s and early 2000s archived on the Wayback Machine. For each ad image, the dataset provides information about the image’s format and size, archived URLs of the image file, archived web pages the image appeared in, and, if available, web pages the image was linked to. The dataset also provides text data obtained from the images using optical character recognition (OCR). This dataset is useful for researchers in visual culture, history, media studies, and business and marketing

E-commerce Platform Resources, Sequences of Digital Strategic Actions and Competitive Advantage: An Empirical Study from Online Tourism Industry

This study examines the effects of digital strategic actions sequences on business value in long-term competitive dynamics. Based on the competitive dynamics theory and configurational perspective, we first use fuzzy-set qualitative comparative analysis to analyze the news data of Chinese online tourism industry, and find out the corresponding configurations of digital strategic actions. Then, we use panel regression to explore the relationship between the unpredictability and complexity of digital strategic actions sequences and competitive performance in the continuous competitive interaction, and find the inverted U-shaped relationship between them. Finally, we discuss implications for theory and practice

Modified stress intensity factor equations for semi-elliptical surface cracks in finite thickness and width plates

Weld defects and severe variation of shape near the welds cause high stress concentration at weld toes or weld roots. This high stress concentration reduces fatigue lives of welded structures. A stress intensity factor (SIF) which includes this effect increases the accuracy of fatigue lives prediction. A magnification factor is commonly used to multiply the SIF of semi-elliptical surface cracks to account for the stress concentration effect in welded connections. Yamada and Hirt model is one of these methods. Comparison between Yamada & Hirt SIF equations and Newman & Raju SIF equations are applied to SIF of semi-elliptical surface cracks. The results suggest that Yamada & Hirt SIF equations are valid when the crack aspect ratio is less than 0.6. New empirical SIF equations are developed based on Yamada & Hirt SIF equations. The newly derived SIF equations are verified by comparing with experimental data