Effective Theories and Infinite Idealizations: A Challenge for Scientific Realism

Williams and J. Fraser have recently argued that effective field theory methods enable scientific realists to make more reliable ontological commitments in Quantum Field Theory (QFT) than those commonly made. In this paper, I show that the interpretative relevance of these methods extends beyond the specific context of QFT by identifying common structural features shared by effective theories across physics. In particular, I argue that effective theories are best characterized by the fact that they contain intrinsic empirical limitations, and I extract from their structure one central interpretative constraint for making more reliable ontological commitments in different subfields of physics. While this is in principle good news, this constraint still raises a challenge for scientific realists in some contexts, and I bring the point home by focusing on Williams's and J. Fraser's defense of selective realism in QFT

Constantes d'Erdös-Turán

The Erdös-Turán inequality measures the distance from uniform distribution of any given sequence on the torus as a function of an arbitrary parameter and two constants, $c_1$ and $c_2$. We show that $c_1\geq 1$ and $c_2\geq 2/\pi$, and we provide a set of admissible pairs $(c_1;c_2)$ that are numerically close to the hypothetical optimum $(1;2/\pi)$, including $(1;0.653)$ and $(1.1435;2/\pi)$

ON THE DIGITS OF SUMSETS

Let A, B be large subsets of {1,. .. , N }. We study the number of pairs (a, b) ∈ A × B such that the sum of binary digits of a + b is fixed

Multi-resolution Modeling of Dynamic Signal Control on Urban Streets

Dynamic signal control provides significant benefits in terms of travel time, travel time reliability, and other performance measures of transportation systems. The goal of this research is to develop and evaluate a methodology to support the planning for operations of dynamic signal control utilizing a multi-resolution analysis approach. The multi-resolution analysis modeling combines analysis, modeling, and simulation (AMS) tools to support the assessment of the impacts of dynamic traffic signal control. Dynamic signal control strategies are effective in relieving congestions during non-typical days, such as those with high demands, incidents with different attributes, and adverse weather conditions. This research recognizes the need to model the impacts of dynamic signal controls for different days representing, different demand and incident levels. Methods are identified to calibrate the utilized tools for the patterns during different days based on demands and incident conditions utilizing combinations of real-world data with different levels of details. A significant challenge addressed in this study is to ensure that the mesoscopic simulation-based dynamic traffic assignment (DTA) models produces turning movement volumes at signalized intersections with sufficient accuracy for the purpose of the analysis. Although, an important aspect when modeling incident responsive signal control is to determine the capacity impacts of incidents considering the interaction between the drop in capacity below demands at the midblock urban street segment location and the upstream and downstream signalized intersection operations. A new model is developed to estimate the drop in capacity at the incident location by considering the downstream signal control queue spillback effects. A second model is developed to estimate the reduction in the upstream intersection capacity due to the drop in capacity at the midblock incident location as estimated by the first model. These developed models are used as part of a mesoscopic simulation-based DTA modeling to set the capacity during incident conditions, when such modeling is used to estimate the diversion during incidents. To supplement the DTA-based analysis, regression models are developed to estimate the diversion rate due to urban street incidents based on real-world data. These regression models are combined with the DTA model to estimate the volume at the incident location and alternative routes. The volumes with different demands and incident levels, resulting from DTA modeling are imported to a microscopic simulation model for more detailed analysis of dynamic signal control. The microscopic model shows that the implementation of special signal plans during incidents and different demand levels can improve mobility measures

Representation and Realism in the Age of Effective Theories

Philosophers traditionally engage with metaphysical questions at the frontiers of physics by treating theories as putatively fundamental and complete. While this interpretative strategy sits uneasily with the limited success of past theories, it breaks down with the failure of our best current theories, Quantum Field Theories (QFTs), to consistently describe the world on the smallest scales. My dissertation examines how physicists' reconceptualization of successful theories as effective theories affects the epistemological and semantic foundations of the interpretative practice in physics. Chapter 1 offers a detailed analysis of renormalization theory, the set of methods that underwrite physicists' construction of empirically successful QFTs. Chapter 2 demonstrates that effective theories are not merely the only candidates left for scientific realists in QFT but also worth interpreting in realist terms. Chapter 3 shows that effective theories stand as a challenge for traditional approaches to scientific representation and realism in physics. I suggest that indexing truth to physical scales is the most promising way to account for the success of effective theories in realist terms. Chapter 4 develops the referential component of this proposal by taking a detour through the problem of referential failure across theory-change. I argue that to reliably assess referential success before theory-change, we need to index reference-fixing to the limited physical contexts where a given theory is empirically reliable

Apports de l'électromagnétisme dans les procédés d'élaboration des matériaux : quelques applications nouvelles

The contribution of electromagnetism in the development of new metallurgical process is studied for two applications: the inductive cold crucible and the direct casting of thin metal strips. From theoretical and experimental analysis, the results obtained are:- The determination of the optimal conditions for obtaining, by using continuous casting cold crucible, superalloy ingots presenting a high percentage of equiaxed grains;- The highlighting of settling possibilities of nonmetallic inclusions in nickel base superalloys by taking advantage of the mechanical effects induced in the molten material in a cold crucible levitation;- The design of a casting device to withdraw metal from the bottom of pocket type cold crucibles.Work on the direct casting is firstly based on an analysis of stabilization phenomena by AC or DC magnetic fields of free surfaces of metals. The results confirm and complement previous studies that did not include a finite conductivity in the metal. Mercury with experiments confirmed the stabilizing effect predicted by the analysis in the case of a continuous magnetic field. The presence of an alternating magnetic field is taken into account for the calculation of the shape of the free surface. In addition, a simulation of the direct casting with a water model has enabled a precise analysis of hydrodynamic instabilities. A visualization method exploiting the PVD technic gives the characteristics of various regimes. These results are used to design the inductors which can improve the quality of elaborated strips. Experiments performed on aluminum show the beneficial effect of the magnetic field.L’apport de l’électromagnétisme dans les procédés d’élaboration est étudié pour deux applications : le creuset froid inductif et la coulée directe de bandes métalliques minces. Les résultats obtenus à partir de l’analyse théorique et expérimentale sont : -La détermination des conditions optimales permettant l’obtention par coulée continue en creuset froid de lingots de superalliage présentant un pourcentage élevé de grains équiaxes ;-La mise en évidence des possibilités de décantation des inclusions non métalliques présentes dans les superalliages base nickel par mise à profit des effets mécanique induits dans le matériau fondu en creuset froid de lévitation ;-La conception d’un dispositif de coulée contrôlée par le fond des creusets froids de type poche. Le travail relatif à la coulée directe s’appuie tout d’abord sur une analyse des phénomènes de stabilisation par des champs magnétiques alternatifs ou continus sur des surfaces libres de métaux. Les résultats obtenus confortent et complètent les études antérieures qui ne tenaient pas compte d’une conductivité finie dans le métal. Des expériences avec mercure ont confirmé l’effet stabilisant prédit par l’analyse dans le cas d’un champ magnétique continu. La présence d’un champ magnétique alternatif est prise en compte pour le calcul de la forme de la surface libre. En outre, une simulation de la coulée directe par une maquette en eau a permis une analyse précise des instabilités hydrodynamiques. Une méthode de visualisation exploitant la technique Images de Particules a donné les caractéristiques des différents régimes. Ces différents résultats ont permis de concevoir des inducteurs capables d’améliorer la qualité des bandes formées. Les expériences réalisées sur aluminium montrent l’effet bénéfique du champ magnétique

Renormalization Scrutinized

In this paper, I propose a general framework for understanding renormalization by drawing on the distinction between effective and continuum Quantum Field Theories (QFTs), and offer a comprehensive account of perturbative renormalization on this basis. My central claim is that the effective approach to renormalization provides a more physically perspicuous, conceptually coherent and widely applicable framework to construct perturbative QFTs than the continuum approach. I also show how a careful comparison between the two approaches: (i) helps to dispel the mystery surrounding the success of the renormalization procedure; (ii) clarifies the various notions of renormalizability; and (iii) gives reasons to temper Butterfield and Bouatta's claim that some continuum QFTs are ripe for metaphysical inquiry (Butterfield and Bouatta, 2014)

Drawing Scales Apart: The Origins of Wilson's Conception of Effective Field Theories

This article traces the origins of Kenneth Wilson's conception of effective field theories (EFTs) in the 1960s. I argue that what really made the difference in Wilson's path to his first prototype of EFT are his long-standing pragmatic aspirations and methodological commitments. Wilson's primary interest was to work on mathematically interesting physical problems and he thought that progress could be made by treating them as if they could be analyzed in principle by a sufficiently powerful computer. The first point explains why he had no qualms about twisting the structure of field theories; the second why he divided the state-space of a toy model field theory into continuous slices by following a standard divide-and-conquer algorithmic strategy instead of working directly with a fully discretized and finite theory. I also show how Wilson's prototype bears the mark of these aspirations and commitments and clear up a few striking ironies along the way