A mathematical modelling study of an athlete's sprint time when towing a weighted sled

This is the author's accepted manuscript. The final publication is available at Springer via http://dx.doi.org/10.1007/s12283-013-0114-2.This study used a mathematical model to examine the effects of the sled, the running surface, and the athlete on sprint time when towing a weighted sled. Simulations showed that ratio scaling is an appropriate method of normalising the weight of the sled for athletes of different body size. The relationship between sprint time and the weight of the sled was almost linear, as long as the sled was not excessively heavy. The athlete’s sprint time and rate of increase in sprint time were greater on running surfaces with a greater coefficient of friction, and on any given running surface an athlete with a greater power-to-weight ratio had a lower rate of increase in sprint time. The angle of the tow cord did not have a substantial effect on an athlete’s sprint time. This greater understanding should help coaches set the training intensity experienced by an athlete when performing a sled-towing exercise

Cauchy's infinitesimals, his sum theorem, and foundational paradigms

Cauchy's sum theorem is a prototype of what is today a basic result on the convergence of a series of functions in undergraduate analysis. We seek to interpret Cauchy's proof, and discuss the related epistemological questions involved in comparing distinct interpretive paradigms. Cauchy's proof is often interpreted in the modern framework of a Weierstrassian paradigm. We analyze Cauchy's proof closely and show that it finds closer proxies in a different modern framework. Keywords: Cauchy's infinitesimal; sum theorem; quantifier alternation; uniform convergence; foundational paradigms.Comment: 42 pages; to appear in Foundations of Scienc

Comparison of effective dose and lifetime risk of cancer Incidence of CT attenuation correction acquisitions and radiopharmaceutical administration for myocardial perfusion imaging

Objective: To measure the organ dose and calculate effective dose from CT attenuation correction (CTAC) acquisitions from four commonly used gamma camera single photon emission CT/CT systems. Methods: CTAC dosimetry data was collected using thermoluminescent dosemeters on GE Healthcare's Infinia™ Hawkeye™ (GE Healthcare, Buckinghamshire, UK) four- and single-slice systems, Siemens Symbia™ T6 (Siemens Healthcare, Erlangen, Germany) and the Philips Precedence (Philips Healthcare, Amsterdam, Netherlands). Organ and effective dose from the administration of 99mTc-tetrofosmin and 99mTc-sestamibi were calculated using International Commission of Radiological Protection reports 80 and 106. Using these data, the lifetime biological risk was calculated. Results: The Siemens Symbia gave the lowest CTAC dose (1.8mSv) followed by the GE Infinia Hawkeye single- slice (1.9mSv), GE Infinia Hawkeye four-slice (2.5mSv) and Philips Precedence v. 3.0. Doses were significantly lower than the calculated doses from radiopharmaceutical administration (11 and 14mSv for 99mTc-tetrofosmin and 99mTc-sestamibi, respectively). Overall lifetime biological risks were lower, which suggests that using CTAC data posed minimal risk to the patient. Comparison of data for breast tissue demonstrated a higher risk than that from the radiopharmaceutical administration. Conclusion: CTAC doses were confirmed to be much lower than those from radiopharmaceutical administration. The localized nature of the CTAC exposure compared to the radiopharmaceutical biological distribution indicated dose and risk to the breast to be higher. Advances in knowledge: This research proved that CTAC is a comparatively low-dose acquisition. However, it has been shown that there is increased risk for breast tissue especially in the younger patients. As per legislation, justification is required and CTAC should only be used in situations that demonstrate sufficient net benefit

Bridging knowing and proving in mathematics An essay from a didactical perspective

Text of a talk at the conference "Explanation and Proof in Mathematics: Philosophical and Educational Perspective" held in Essen in November 2006International audienceThe learning of mathematics starts early but remains far from any theoretical considerations: pupils' mathematical knowledge is first rooted in pragmatic evidence or conforms to procedures taught. However, learners develop a knowledge which they can apply in significant problem situations, and which is amenable to falsification and argumentation. They can validate what they claim to be true but using means generally not conforming to mathematical standards. Here, I analyze how this situation underlies the epistemological and didactical complexities of teaching mathematical proof. I show that the evolution of the learners' understanding of what counts as proof in mathematics implies an evolution of their knowing of mathematical concepts. The key didactical point is not to persuade learners to accept a new formalism but to have them understand how mathematical proof and statements are tightly related within a common framework; that is, a mathematical theory. I address this aim by modeling the learners' way of knowing in terms of a dynamic, homeostatic system. I discuss the roles of different semiotic systems, of the types of actions the learners perform and of the controls they implement in constructing or validating knowledge. Particularly with modern technological aids, this model provides a basis designing didactical situations to help learners bridge the gap between pragmatics and theory

Studying the influence of a solid shell on lava dome growth and evolution using the level set method

A finite element formulation of the level set method, a technique to trace flow fronts and interfaces without element distortion, is presented to model the evolution of the free surface of a spreading flow for a highly viscous medium on a horizontal surface. As an example for this class of problem we consider the evolution of an axisymmetric lava dome. Equilibrium configurations of lava domes have been modelled analytically as brittle shells enclosing pressurized magma. The existence of the brittle shell may be viewed as a direct consequence of the strong temperature dependence of the viscosity. The temperature dependence leads to the formation of a thin predominantly elastic-plastic boundary layer along the free surface and acts as a constraint for the shape and flow of the lava dome. In our model, we adopt Iverson's assumption that the thin boundary layer behaves like an ideal plastic membrane shell enclosing the ductile interior of the lava dome. The effect of the membrane shell is then formally identical to a surface tension-like boundary condition for the normal stress at the free surface. The interior of the dome is modelled as a Newtonian fluid and the axisymmetry equations of motion are formulated in a Eulerian framework. We show that the level set is an effective tool to trace and model deforming interfaces for the example of the free surface of a lava dome. We demonstrate that Iverson's equilibrium dome shapes are indeed steady states of a transient model. We also show how interface conditions in the form of surface tension involving higher order spatial derivative (curvature) can be considered within a standard finite element framework

Tool Embodiment Is Reflected in Movement Multifractal Nonlinearity

Recent advances in neuroscience have linked dynamical systems theory to cognition. The main contention is that extended cognition relies on a unitary brain-body-tool system showing the expected signatures of interaction-dominance reflected in a multifractal behavior. This might be particularly relevant when it comes to understanding how the brain is able to embody a tool to perform a task. Here we applied the multifractal formalism to the dynamics of hand movement while one was performing a computer task (the herding task) using a mouse or its own hand as a tool to move an object on the screen. We applied a focus-based multifractal detrended fluctuation analysis to acceleration time series. Then, multifractal nonlinearity was assessed by comparing original series to a finite set of surrogates obtained after Iterated Amplitude Adjusted Fourier transformation, a method that removes nonlinear multiscale dependencies while preserving the linear structure of the time series. Both hand and mouse task execution demonstrated multifractal nonlinearity, a typical form of across-scales interactivity in cognitive control. In addition, a wider multifractal spectrum was observed in mouse condition, which might highlight a richer set of interactions when the cognitive system is extended to the embodied mouse. We conclude that the emergence of multifractal nonlinearity from a brain-body-tool system pleads for recent theories of radical tool embodiment. Multifractal nonlinearity may be a promising metric to appreciate how physical objects—but also virtual tools and potentially prosthetics—are efficiently embodied by the brain

La ética del psicoanálisis

Este trabajo se ocupa de la ética del psicoanálisis que, aún sin estar formulada como concepto en S. Freud, se desprende del modo en que trabaja, de la teoría que elabora y del método que diseña como adecuado a los fines que persigue. En cada concepto se considera tanto el aporte freudiano, cuanto el trabajo que a partir de ese punto realiza J. Lacan. Este último, se sirve de las contribuciones de ciencias nuevas y de los avances de otras ya consolidadas, los toma y usa con libertad para construir niveles nuevos de formalización de conceptos. Colabora así, en impedir que el psicoanálisis quede reducido a una teoría que repita conceptos paralizados por sentidos sancionados de una vez y para siempre, y a una práctica que sea aplicación mecánica de rituales. De este modo, se exponen las características de una ética solidaria a la función deseo del analista y las implicaciones que tiene para analista y analizante. El psicoanalista debe asumir la responsabilidad de dirigir la cura operando en una posición y discurso que son los que corresponden para abordar al sujeto que, en psicoanálisis, no es óntico sino ético. En torno a este eje se jalonan los otros temas de este trabajo, el saber a-subjetivo del inconsciente, la verdad en relación con lo contingente y lo necesario y la producción del objeto a con relación a la alienación y la separación. J. Lacan no permanece estéril, sometido a la sombra de un ideal sin falta, ni reniega de lo que hereda, tiene por S. Freud un amor hereje , toma con respeto y reconocimiento los dones que recibe del padre del psicoanálisis, pero no teme avanzar más allá de él. Asume por esto, las consecuencias de sus actos, así como S. Freud asumió las consecuencias de los suyos.This work deals with the ethics of psychoanalysis which, although was not explicitly elaborated as a concept by Freud, follows from his working style, the theory he develops and the method he designs as appropiate to accomplish his purposes. For each concept that is discussed both the freudian thought as the takens of Lacan about it, are considered. This author uses the contributions of new sciences as well as advances in already consolidated ones, and elaborates upon them freely to construct new levels of concept formalization. Thus he contributes to avoid the reduction of psychoanalysis to a theory that reiterates concepts, staled by meanings sanctioned once and for all, and to a practice which applies sterotyped rituals. In this way, the characteristics of an ethic which corresponds to the “analyst’s wish” function are delineated, as well as its implications for both analyst and analysand. The psychoanalyst must take responsbility for guiding the cure by taken a stand and a discourse appropiate to approach the subject who, in psychoanalysis, is ethic, non ontic. Around this axis, the other topics of this work are vertebrated, the a- subjective knowledge of the unconscious, the truth related to the contingent and the necessary and the production of the a object as it relates to alienation and separation. Lacan does not remain barren, bowing at the shadow of a faultless ideal, nor does he renegates of his inheritance. He has a ‘heretic love’ for Freud; he takes with respect and recognition the gifts he recibes from psycoanalysis’s father, but is not afraid to go beyond him. He assumes for this the consequenses of his acts, as Freud assumed the consequences of his.Fil: Arsac, Silvia Els

Corrigendum: Frequency-Specific Fractal Analysis of Postural Control Accounts for Control Strategies

International audienc

Highlighting the History of French Radio Astronomy. 4. Early Solar Research at the École Normale Supérieure, Marcoussis and Nancay

The first tentative steps in solar radio astronomy took place during the 1940s and early 1950s as physicists and engineers in a number of countries used recycled World War II equipment to investigate the flux levels and polarisation of solar bursts and emission from the quiet Sun, and sought to understand the connection between this emission and optical features in the solar photosphere and chromosphere. There was also an abiding interest in the terrestrial effects of this solar radio emission. Among these solar pioneers were French radio astronomers from the École Normale Supérieure in Paris. In this paper we review the early solar observations made by them from Paris, Marcoussis and Nançay prior to the construction of a number of innovative multi-element solar interferometers at the Nançay field station in the mid-1950s

Improved Energy Supply Regulation in Chronic Hypoxic Mouse Counteracts Hypoxia-Induced Altered Cardiac Energetics

Hypoxic states of the cardiovacular system are undoubtedly associated with the most frequent diseases of modern time. Therefore, understanding hypoxic resistance encountered after physiological adaptation such as chronic hypoxia, is crucial to better deal with hypoxic insult. In this study, we examine the role of energetic modifications induced by chronic hypoxia (CH) in the higher tolerance to oxygen deprivation.P-NMR), and to describe the integrated changes in cardiac energetics regulation by using Modular Control Analysis (MoCA). Oxygen reduction induced a concomitant decrease in RPP (−46%) and in [PCr] (−23%) in Control hearts while CH hearts energetics was unchanged. MoCA demonstrated that this adaptation to hypoxia is the direct consequence of the higher responsiveness (elasticity) of ATP production of CH hearts compared with Controls (−1.88±0.38 vs −0.89±0.41, p<0.01) measured under low oxygen perfusion. This higher elasticity induces an improved response of energy supply to cellular energy demand. The result is the conservation of a healthy control pattern of contraction in CH hearts, whereas Control hearts are severely controlled by energy supply.As suggested by the present study, the mechanisms responsible for this increase in elasticity and the consequent improved ability of CH heart metabolism to respond to oxygen deprivation could participate to limit the damages induced by hypoxia