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25 results on '"Lv, Qifeng"'

3. Do the Navier-Stokes equations embody all physics in a flow of Newtonian fluids?

Author

Lv, Qifeng and Wang, Sijing

Subjects
Physics - Fluid Dynamics
Abstract

The Navier-Stokes equations are the governing equations of fluid flows. They are deemed to embody all physics in a flow of Newtonian fluids like water, especially when we assume the fluid is incompressible. Fluid flows are usually described in the Eulerian perspective wherein we focus on the fluid's quantities at a fixed point in space as time processes, rather than the motion of each individual particle. The latter perspective is indeed the Lagrangian perspective which is widely used in solid mechanics like elasticity. Thus, the Navier-Stokes equations should be and indeed they are always used in the Eulerian perspective. Here we show the right-hand sides of the Navier-Stokes equations were derived not in the Eulerian perspective but rather in the Lagrangian perspective, because the strain rates used in the derivation were the Lagrangian Cauchy strain rates. Thus, for describing fluid flows in the Eulerian perspective, the Navier-Stokes equations may lost some physics. To make it sure, we put the Cauchy strain into the material derivative, and then derive the Eulerian Cauchy strain rates. We find the difference between the Eulerian and the Lagrangian Cauchy strain rates is significant when in a turbulent flow. Therefore, On the basis of the Eulerian Cauchy strain rates, we derive a new set of governing equations for the flow of Newtonian fluids. The newly derived governing equations are fully in the Eulerian perspective. We believe they are the real equations that Navier, Cauchy, Poisson and Stokes intended to find for the viscous flow of Newtonian fluids., Comment: A conference paper of American Physical Society 67th Annual DFD Meeting

Published
2014

8. sj-pdf-1-scm-10.1177_00369330231178910 - Supplemental material for Diagnostic accuracy of cervical elastography for predicting preterm delivery: Systematic review and meta-analysis

Author

Sun, Hui, Lv, Qifeng, Liu, Tingting, Zhang, Nan, and Shi, Fengfeng

Subjects
Medicine
Abstract

Supplemental material, sj-pdf-1-scm-10.1177_00369330231178910 for Diagnostic accuracy of cervical elastography for predicting preterm delivery: Systematic review and meta-analysis by Hui Sun, Qifeng Lv, Tingting Liu, Nan Zhang and Fengfeng Shi in Scottish Medical Journal

Published
2023
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18. Provérbios com animais em chinês e português: estudo contrastivo

Author

Lv Qifeng, Barroso, Henrique, and Universidade do Minho

Subjects
Estudo contrastivo, Linguistic characteristics, Provérbios com animais em chinês e português, Cultural values, Caraterísticas linguísticas, Contrastive study, Humanidades::Outras Humanidades, Chinese and Portuguese proverbs with animals, Outras Humanidades [Humanidades], Valores culturais
Abstract

Dissertação de mestrado em Estudos Interculturais Português/Chinês (área de especialização em Tradução, Formação e Comunicação Empresarial), Como uma forma especial da linguagem, os provérbios desempenham um papel importante na nossa vida quotidiana. Eles não só transmitem conhecimentos coletivos e ideias filosóficas, obtidos pela experiência de vida e pela produção dos que nos antecederam, como são também uma cristalização da sabedoria. No contexto do Mestrado em Estudos Interculturais Português-Chinês, tive a oportunidade de aprofundar os meus conhecimentos sobre os provérbios em português e chinês. Ao longo da leitura e exploração dos documentos referentes aos provérbios em português e chinês, tendo em conta que no universo dos provérbios os que se referem a animais são mais comuns e têm uma relação mais próxima com a vida do dia a dia da população, o trabalho fará incidir o foco no estudo contrastivo sobre os provérbios com animais em português e chinês, nomeadamente a investigação das diferenças e semelhanças linguísticas e culturais neles refletidas, com o objetivo de obviar a “confusão” e as interpretações menos adequadas, aumentar a eficácia da comunicação e melhorar a capacidade de utilização da língua., As a special form of language, proverbs play an important role in our daily lives. They not only convey collective knowledge and philosophical ideas obtained by the experience of life and the production of those that preceded us, but they are also a crystallization of wisdom. In the context of the Master in Intercultural Studies Portuguese-Chinese, I had the opportunity to deepen my knowledge about the proverbs in Portuguese and Chinese. Throughout the reading and exploration of the documents referring to the proverbs in Portuguese and Chinese, taking into account that in the universe of proverbs the ones that refer to animals are more common and have a closer relation with the daily life of the population, the focus will be on the contrastive study of Chinese and Portuguese proverbs with animals, namely the investigation of differences and similarities in the linguistic and cultural aspects reflected in them, in order to avoid confusion and less adequate interpretations, improve the skills of communication and the ability to use the language.

Published
2018

21. An improved elastic-tubes model for the correlation of permeability and stress with correction for the Klinkenberg effect

Author

Lv, Qifeng, Chen, Zhiqiang, and Wang, Moran

Abstract

The correlation of permeability and stress is crucial for correctly predicting the coupled process of fluid flow and solid deformation in geophysical systems. Especially in ultra-low-permeability rocks with nanopores, the apparent permeability becomes sensitive to the properties of fluid and solid. This work presents an improved tubes model, where the correlation of permeability and stress is derived with the Klinkenberg effect correction. Both the in-situ stress effect and the Klinkenberg effect have been carefully considered in current correction of permeability prediction based on Darcy's law. The experimental data can be fitted well by the new model, and the Klinkenberg effect of gas flow in the tight porous media is successfully captured. The predictive ability of the current model has been examined as well and the results are acceptable.

Published
2024
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24. Coordinated optimal control of active power of wind farms considering wake effect

Author

Shen, Yu, Xiao, Tannan, Lv, Qifeng, Zhang, Xuemin, Zhang, Yangfan, Wang, Yimei, and Wu, Jinfang

Abstract

In a large-scale wind farm, under the influence of the wake effect, the single-machine maximum power extraction control strategy would not be able to function at the ideal optimal value. It is important to study the coordinated operation strategy of the wind farm under the wake effect to improve the output power of wind farms and improve the economic benefit. In this paper, a practical wake model called the PARK model is used and a wake superposition model based on energy balance is derived. Based on these models, an optimization problem is formulated to maximize the output power of the wind farm considering the wake effect. Taking the Horns Rev offshore wind farm as an example, the stochastic points method, particle swarm optimization, and the pattern search algorithm are implemented and compared with the single-machine maximum power extraction algorithm. Test results show that the particle swarm optimization and the pattern search algorithm have better performance. The output power of the wind farm increases by about 10 percent. The particle swarm optimization requires less computation while the pattern search algorithm obtains better and more practical results. Finally, the pattern search algorithm is used to improve economic benefits under different wind conditions.

Published
2021
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25. The Specificity and Accuracy of Echocardiography in Diagnosing Acute Heart Failure: A Systematic Review and Meta-Analysis.

Author

Lv Q, Tang G, Zhang N, Yu D, and Sun H

Abstract

Objective: This meta-analysis evaluates the diagnostic value of echocardiography for Acute Heart Failure (AHF) and its utility in urgent clinical situations, emphasizing its significance for accurate and timely diagnosis in critical care., Methods: Relevant studies from databases like PubMed and Embase were selected using terms such as 'Ultrasound' and 'acute heart failure'. Inclusion criteria focused on studies evaluating echocardiographic diagnosis in adult patients presenting with symptoms suggestive of AHF. Quality assessment was performed using RevMan 5.3 and QUADAS. Key metrics like sensitivity, specificity, and likelihood ratios were analyzed using STATA 15.1. The types of echocardiography assessed included transthoracic and focused cardiac ultrasound., Results: Eighteen articles were included, indicating echocardiography's high sensitivity (0.92) and specificity (0.96) in diagnosing AHF. The combined positive likelihood ratio of 23.2 suggests that patients with AHF are over 23 times more likely to have a positive echocardiography result than those without AHF, greatly influencing clinical decision-making toward confirming the diagnosis. The AUC of the SROC curve was 0.98, indicating excellent overall accuracy., Conclusion: Echocardiography is highly accurate in diagnosing AHF, underscored by its critical role in early treatment decisions and potential integration into standard care protocols, thereby preventing adverse outcomes and improving patient management.

Published
2024

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