34 research outputs found
L'étude du principe de moindre action pour systèmes mécaniques dissipatifs, et la probabilité de chemins du mouvement mécanique aléatoire
No full textThe present thesis is devoted to the study of path probability of random motion on the basis of an extension of Hamiltonian/Lagrangian mechanics to stochastic dynamics. The path probability is first investigated by numerical simulation for Gaussian stochastic motion of non dissipative systems. This ideal dynamical model implies that, apart from the Gaussian random forces, the system is only subject to conservative forces. This model can be applied to underdamped real random motion in the presence of friction force when the dissipated energy is negligible with respect to the variation of the potential energy. We find that the path probability decreases exponentially with increasing action, i.e., P(A) ~ eˉγA, where γ is a constant characterizing the sensitivity of the action dependence of the path probability, the action is given by A = ∫T0 Ldt, a time integral of the Lagrangian L = K–V over a fixed time period T, K is the kinetic energy and V is the potential energy. This result is a confirmation of the existence of a classical analogue of the Feynman factor eiA/ħ for the path integral formalism of quantum mechanics of Hamiltonian systems. The above result is then extended to real random motion with dissipation. For this purpose, the least action principle has to be generalized to damped motion of mechanical systems with a unique well defined Lagrangian function which must have the usual simple connection to Hamiltonian. This has been done with the help of the following Lagrangian L = K – V – Ed, where Ed is the dissipated energy. By variational calculus and numerical simulation, we proved that the action A = ∫T0 Ldt is stationary for the optimal paths determined by Newtonian equation. More precisely, the stationarity is a minimum for underdamped motion, a maximum for overdamped motion and an inflexion for the intermediate case. On this basis, we studied the path probability of Gaussian stochastic motion of dissipative systems. It is found that the path probability still depends exponentially on Lagrangian action for the underdamped motion, but depends exponentially on kinetic action A = ∫T0 Kdt for the overdamped motion.La présente thèse est consacrée à l’étude de la probabilité du chemin d’un mouvement aléatoire sur la base d’une extension de la mécanique Hamiltonienne/Lagrangienne à la dynamique stochastique. La probabilité d’un chemin est d’abord étudiée par simulation numérique dans le cas du mouvement stochastique Gaussien des systèmes non dissipatifs. Ce modèle dynamique idéal implique que, outre les forces aléatoires Gaussiennes, le système est seulement soumis à des forces conservatrices. Ce modèle peut être appliqué à un mouvement aléatoire réel de régime pseudo-périodique en présence d’une force de frottement lorsque l’énergie dissipée est négligeable par rapport à la variation de l’énergie potentielle. Nous constatons que la probabilité de chemin décroît exponentiellement lorsque le son action augmente, c’est à dire, P(A) ~ eˉγA, où γ est une constante caractérisant la sensibilité de la dépendance de l’action à la probabilité de chemin, l’action est calculée par la formule A = ∫T0 Ldt, intégrale temporelle du Lagrangien. L = K–V sur une période de temps fixe T, K est l’énergie cinétique et V est l’énergie potentielle. Ce résultat est une confirmation de l’existence d’un analogue classique du facteur de Feynman eiA/ħ pour le formalisme intégral de chemin de la mécanique quantique des systèmes Hamiltoniens. Le résultat ci-dessus est ensuite étendu au mouvement aléatoire réel avec dissipation. A cet effet, le principe de moindre action doit être généralisé au mouvement amorti de systèmes mécaniques ayant une fonction unique de Lagrange bien définie qui doit avoir la simple connexion habituelle au Hamiltonien. Cela a été fait avec l’aide du Lagrangien suivant L = K − V − Ed, où Ed est l’énergie dissipée. Par le calcul variationnel et la simulation numérique, nous avons prouvé que l’action A = ∫T0 Ldt est stationnaire pour les chemins optimaux déterminés par l’équation newtonienne. Plus précisément, la stationnarité est un minimum pour les mouvements de régime pseudo-périodique, un maximum pour les mouvements d’amortissement apériodique et une inflexion dans le cas intermédiaire. Sur cette base, nous avons étudié la probabilité du chemin du mouvement stochastique Gaussien des systèmes dissipatifs. On constate que la probabilité du chemin dépend toujours de façon exponentielle de l’action Lagrangien pour les mouvements de régime pseudo-périodique, mais dépend toujours de façon exponentielle de l’action cinétique A = ∫T0 Kdt pour régime apériodique
Mammotome-assisted removal with minimal incision of large juvenile fibroadenoma of breast
No full textThe Importance of Resident's Attitude Towards Service Quality in Travel Choice of Public Transit
No full textAbstractUnderstanding residents’ attitude towards service quality is essential, because residents’ conception of service quality is seen as an important role in travel choice intention. This paper explored the relationships between attitude towards public transit service quality and travel choice intention, and introduced the measuring method of attitude in terms of satisfaction and attention. The hypotheses that attitude reflected by attention and satisfaction had an effect on travel choice intention, while attention also influenced satisfaction, were proposed. Using data obtained from the 2011 public transit stated preference survey in the city of Tongling, factor analysis combined an exploratory factor analysis (EFA) and a confirmatory factor analysis was adopted to select key factors of service indicators. Then a structural equation model was established to test the conceptualized relationship model. The findings show the influence of residents’ attitude towards service quality on travel choice intention is significant, especially residents’ attention to travel time. The implications of the findings in residents’ travel behavior analysis and service quality improvement of public transit in some small-medium cities as Tongling are discussed
L'étude du principe de moindre action pour systèmes mécaniques dissipatifs, et la probabilité de chemins du mouvement mécanique aléatoire
No full textLa présente thèse est consacrée à l étude de la probabilité du chemin d un mouvement aléatoire sur la base d une extension de la mécanique Hamiltonienne/Lagrangienne à la dynamique stochastique. La probabilité d un chemin est d abord étudiée par simulation numérique dans le cas du mouvement stochastique Gaussien des systèmes non dissipatifs. Ce modèle dynamique idéal implique que, outre les forces aléatoires Gaussiennes, le système est seulement soumis à des forces conservatrices. Ce modèle peut être appliqué à un mouvement aléatoire réel de régime pseudo-périodique en présence d une force de frottement lorsque l énergie dissipée est négligeable par rapport à la variation de l énergie potentielle. Nous constatons que la probabilité de chemin décroît exponentiellement lorsque le son action augmente, c est à dire, P(A) ~ e gA, où g est une constante caractérisant la sensibilité de la dépendance de l action à la probabilité de chemin, l action est calculée par la formule A = ST0 Ldt, intégrale temporelle du Lagrangien. L = K V sur une période de temps fixe T, K est l énergie cinétique et V est l énergie potentielle. Ce résultat est une confirmation de l existence d un analogue classique du facteur de Feynman eiA/ pour le formalisme intégral de chemin de la mécanique quantique des systèmes Hamiltoniens. Le résultat ci-dessus est ensuite étendu au mouvement aléatoire réel avec dissipation. A cet effet, le principe de moindre action doit être généralisé au mouvement amorti de systèmes mécaniques ayant une fonction unique de Lagrange bien définie qui doit avoir la simple connexion habituelle au Hamiltonien. Cela a été fait avec l aide du Lagrangien suivant L = K V Ed, où Ed est l énergie dissipée. Par le calcul variationnel et la simulation numérique, nous avons prouvé que l action A = ST0 Ldt est stationnaire pour les chemins optimaux déterminés par l équation newtonienne. Plus précisément, la stationnarité est un minimum pour les mouvements de régime pseudo-périodique, un maximum pour les mouvements d amortissement apériodique et une inflexion dans le cas intermédiaire. Sur cette base, nous avons étudié la probabilité du chemin du mouvement stochastique Gaussien des systèmes dissipatifs. On constate que la probabilité du chemin dépend toujours de façon exponentielle de l action Lagrangien pour les mouvements de régime pseudo-périodique, mais dépend toujours de façon exponentielle de l action cinétique A = ST0 Kdt pour régime apériodique.The present thesis is devoted to the study of path probability of random motion on the basis of an extension of Hamiltonian/Lagrangian mechanics to stochastic dynamics. The path probability is first investigated by numerical simulation for Gaussian stochastic motion of non dissipative systems. This ideal dynamical model implies that, apart from the Gaussian random forces, the system is only subject to conservative forces. This model can be applied to underdamped real random motion in the presence of friction force when the dissipated energy is negligible with respect to the variation of the potential energy. We find that the path probability decreases exponentially with increasing action, i.e., P(A) ~ e gA, where g is a constant characterizing the sensitivity of the action dependence of the path probability, the action is given by A = ST0 Ldt, a time integral of the Lagrangian L = K V over a fixed time period T, K is the kinetic energy and V is the potential energy. This result is a confirmation of the existence of a classical analogue of the Feynman factor eiA/ for the path integral formalism of quantum mechanics of Hamiltonian systems. The above result is then extended to real random motion with dissipation. For this purpose, the least action principle has to be generalized to damped motion of mechanical systems with a unique well defined Lagrangian function which must have the usual simple connection to Hamiltonian. This has been done with the help of the following Lagrangian L = K V Ed, where Ed is the dissipated energy. By variational calculus and numerical simulation, we proved that the action A = ST0 Ldt is stationary for the optimal paths determined by Newtonian equation. More precisely, the stationarity is a minimum for underdamped motion, a maximum for overdamped motion and an inflexion for the intermediate case. On this basis, we studied the path probability of Gaussian stochastic motion of dissipative systems. It is found that the path probability still depends exponentially on Lagrangian action for the underdamped motion, but depends exponentially on kinetic action A = ST0 Kdt for the overdamped motion.LE MANS-BU Sciences (721812109) / SudocSudocFranceF
Force Analysis of Circular Diaphragm Wall Based on Circular Cylindrical Shell Theory
No full textIn order to make up for the shortcomings of existing theory calculation methods for circular diaphragm walls, an alternative calculation method was developed with a clear concept based on the circular cylindrical shell theory and superposition principle in elasticity and named the circular cylindrical shell theory calculation method (CCSTCM). We took the north anchorage circular foundation pit of G3 Tongling Yangtze River Highway and Railway Bridge as an example and calculated and analyzed it by the proposed CCSTCM, finite element numerical simulation method (FENSM) and site monitoring. As a result, we obtained the radial displacement, circumferential stress and vertical bending moment of the circular diaphragm wall, and then summarized their regularities. By researching the results of the CCSTCM (TCR), the results of the FENSM (NSR) and the results of the site monitoring (SMR), the following conclusions could be drawn: the numerical calculation model established was reasonable; the variation trends of the data curves of the TCR were highly similar to those of the NSR and SMR; and the TCR were slightly larger than the NSR but slightly smaller than the SMR, and closer to the SMR in general. Finally, the proposed CCSTCM was proven to be correct and applicable and could be used in similar circular diaphragm wall projects
Effective strategies for indoor particulate air pollution control
No full textPh.D.It is crucial to reduce indoor exposure to particulate air pollution of indoor and outdoor origin, which is a dominant risk factor to damage occupants’ health. This thesis aims to explore the effective strategies for controlling indoor exposure to particulate air pollution in residential buildings with natural ventilation.This study firstly used the time-resolved indoor and outdoor PM₂.₅ (particulate matter with aerodynamic equivalent diameter less than 2.5 μm) concentrations and the window opening/closing behavior to differentiate the indoor exposure to PM₂.₅ of indoor and outdoor origin for naturally ventilated buildings. A statistical algorithm of change point analysis, the physical mechanism of PM₂.₅ mass balance and window behavior characteristics were combined to process the data and recognize the indoor PM₂.₅ sources. To verify the method, a set of experiments were conducted in a small-scale test rig.Besides, this study then applied the differentiation method to real building case for further validation. The real-time indoor PM₂.₅ concentrations and windows behavior in an apartment located in Tianjin, China, were monitored for a whole year. The indoor emissions and their contributions to the total exposure to PM₂.₅ were analyzed in the apartment.With the indoor emissions being correctly identified, people can take effective strategies to control indoor exposure to PM₂.₅ of both indoor and outdoor origin. An opening window can introduce fresh air and dilute indoor emissions. Besides, air filtration technology can be used to further reduce indoor exposure to particulate air pollution. Therefore, this study systematically reviewed nanofiber filter media in the literature. It was found that nanofiber filters have a relatively low pressure drop and high particle removal efficiency compared with conventional fibrous filters.Coating nanofiber filter on window screen could provide clean fresh air in the naturally ventilated residence. This study fabricated nanofiber window screens and measured the PM₂.₅ removal efficiency and pressure drop under various window opening angles. The measured data validated the proposed model for predicting the pressure drop. Then, the modelling results of a natural ventilation case showed that the nanofiber window screen can reduce indoor PM₂.₅ of outdoor origin and the ventilation rate was improved when compared with infiltration only.To facility the usage of nanofiber filter media, this study experimentally developed a semi-empirical model between the pressure drop and solid particle loading mass for nanofiber filters under various face velocities. Then the assessment of the long-term performance indicated that of an air cleaner equipped with a nanofiber filter could effectively control indoor PM₂.₅, but the lifetime of the nanofiber filter was shorter than that of traditional HEPA filters.Apart from solid particles, PM₂.₅ contains amounts of liquid aerosols. Thus, this study investigated the long-term filtration performance by conducting experiments to understand the evolution of wetting liquid aerosols, taking incense particles as an example, on nanofiber filter media and the influence of loading mass on PM₂.₅ removal efficiency and pressure drop. Using the experimental data, the method for establishing empirical equations for pressure drop and PM₂.₅ removal efficiency in terms of loading mass were developed.減少室內暴露於室內和室外空氣中的微粒污染至關重要，這是損害人體健康的主要風險因素。本論文旨在探索有效的策略，用以控制自然通風住宅中的顆粒污染物室内暴露量。本論文首先使用室內和室外PM₂.₅（空气动力学当量直徑小於2.5 μm的顆粒物）濃度和窗戶的開/關行為，來解析自然通風下的室內暴露於室內发生的和室外渗入的PM₂.₅。結合了轉變點分析的統計方法，PM₂.₅質量平衡的物理模型和开窗行為來識別室內PM₂.₅散發源。並且進行了系統的實驗驗證該方法。此外，本論文將該方法應用於實際建築以進一步驗證。對位於中國天津的一間公寓室內PM₂.₅濃度和窗戶行為進行整年實時監測。分析了公寓中室內发生源對室內PM₂.₅總暴露量的貢獻。通過正確識別室內PM₂.₅散發源，人們可以採取有效策略來控制室內PM₂.₅。在此基礎上，空氣過濾技術可用於進一步減少室內顆粒污染物的暴露程度。首先，本研究系統地回顧了文獻中的納米纖維濾料。發現與常規纖維過濾器相比，納米纖維過濾器具有相對較低的壓降和較高的PM₂.₅去除效率。把納米薄膜塗在窗紗上可為自然通風的住所提供乾淨的新鮮空氣。本論文製造了納米纖維窗紗，並測量了在不同窗戶打開角度下的PM₂.₅去除效率和壓降。實測數據驗證了所提出的預測壓降的模型。然後，自然通風案例的模擬結果表明，納米纖維窗紗可以有效地減少室外的室內PM₂.₅，並且與僅滲透（所有窗戶關閉）相比，通風量得到了提高。為了落實納米纖維過濾器的使用，本研究通過實測建立了與面風速相關的納米纖維過濾器的壓降與固體顆粒負載質量的半經驗模型。對配備納米纖維過濾器的空氣淨化器的長期性能的表明它可以有效地控制室內PM₂.₅，但是納米纖維過濾器的壽命比傳統的HEPA過濾器短。除固體顆粒外，PM₂.₅還包含一定量的液態氣溶膠。因此，本研究通過實驗以了解親水的液態氣溶膠的演變（以熏香液態顆粒為例）對納米纖維濾料的影響及負載質量對PM₂.₅去除效率和壓降的影響。利用實驗數據，本論文提出了建立壓降和PM₂.₅去除效率隨負載質量變化的經驗方程的方法。Xia, Tongling.Thesis Ph.D. Chinese University of Hong Kong 2021.Includes bibliographical references (leaves 163-175).Abstracts also in Chinese.Title from PDF title page (viewed on April 1, 2022)
Casimir effect of an ideal Bose gas trapped in a generic power-law potential
No full textThe Casimir effect of an ideal Bose gas trapped in a generic power-law potential and confined between two slabs with Dirichlet, Neumann, and periodic boundary conditions is investigated systematically, based on the grand potential of the ideal Bose gas, the Casimir potential and force are calculated. The scaling function is obtained and discussed. The special cases of free and harmonic potentials are also discussed. It is found that when T T-c, the Casimir force is an exponential decay function; and when T >> T-c, the Casimir force vanishes. Copyright (C) EPLA, 2012Specialized Research Fund for the Doctoral Program of Higher Education [20100121110024]; National Natural Science Foundation, People's Republic of China [11175148]; Region des Pays de la Loire in France [2007-6088, 2009-09333
Safety Analysis of Tunnel in Gob of High Steep Thick Coal Seam (I) - 2-D Numerical Simulation for Response
No full textTaking Wusongshan Tunnel in Tongling City as an example, two-dimensional numerical simulation of new large span highway tunnel directly through gob of steep coal seam were carried out to study the response of surrounding rock induced by mining. The actual location and scale of the ground fissure consistent well with the simulation results, which verified the analysis. The results showed that, different from those in gob of horizontal or gently inclined coal seam, the response of surrounding rock in gob of steep coal seam have the following characteristics: (1) shallow mining affects significantly on the values of settlement of earth surface and the tunnel, and deep mining on the scope; (2) in the shallow layer, a small scale coal being reserved or being effective filled after excavation can benefit greatly to the safety of structure and stability of the surrounding rock; (3) sharper uneven settlement would occour at the floor than the roof of coal seam, which can threaten the tunnel structure and should attract more special attention; (4) for this project, deep faults affect the safety of structure of tunnel and stability of surrounding rock also. Based on these results, treament plan were developed of Wusongshan Tunnel, which can also be refered for other similar projects.</jats:p
Safety Analysis of Tunnel in Gob of High Steep Thick Coal Seam (II) - 3-D Numerical Simulation for Mechanics of Initial and Secondary Support Structure
No full textTaking Wusongshan Tunnel in Tongling City as an example, three-dimensional numerical simulation of new large span highway tunnel built directly through gob of steep coal seam is carried out to study the response of tunnel structure induced by mining. The results showed that, (1) Though immediately backfilling after extraction can prevent the tunnel structure from impact of mining below the tunnel, it is still necessary to forbid extraction below the tunnel consildering the duration time of the extraciton and backfilling activity. (2) Considering the long-term settlement of gob of steep coal seam, net height of the tunnel should be enlarged 50cm to ensure enough space for operation. (3) The tensile and pressive stress of the support structure in the bottom and roof section of the gob are obviously high than other, so comperihencive measures should be taken to reinforce the structure, especially to increase the tensile strength in axial direction. (4) Fortification intensity can be reduced but the fortification should be enlarged if the continuous reinforcement by steel bar is used at the radial construction joints. Based on these results, treatment plan were developed for Wusongshan Tunnel, which can also be refered for other similar projects.</jats:p
