Information and flux in a feedback controlled Brownian ratchet

We study a feedback control version of the flashing Brownian ratchet, in which the application of the flashing potential depends on the state of the particles to be controlled. Taking the view that the ratchet acts as a Maxwell's demon, we study the relationship that exists between the performance of the demon as a rectifier of random motion and the amount of information gathered by the demon through measurements. In the context of a simple measurement model, we derive analytic expressions for the flux induced by the feedback ratchet when acting on one particle and a few particles, and compare these results with those obtained with its open-loop version, which operates without information. Our main finding is that the flux in the feedback case has an upper bound proportional to the square-root of the information. Our results provide a quantitative analysis of the value of information in feedback ratchets, as well as an effective description of imperfect or noisy feedback ratchets that are relevant for experimental applications.Comment: LaTeX, 13 pages, 2 figure

Transport reversal in a delayed feedback ratchet

Feedback flashing ratchets are thermal rectifiers that use information on the state of the system to operate the switching on and off of a periodic potential. They can induce directed transport even with symmetric potentials thanks to the asymmetry of the feedback protocol. We investigate here the dynamics of a feedback flashing ratchet when the asymmetry of the ratchet potential and of the feedback protocol favor transport in opposite directions. The introduction of a time delay in the control strategy allows one to nontrivially tune the relative relevance of the competing asymmetries leading to an interesting dynamics. We show that the competition between the asymmetries leads to a current reversal for large delays. For small ensembles of particles current reversal appears as the consequence of the emergence of an open-loop like dynamical regime, while for large ensembles of particles it can be understood as a consequence of the stabilization of quasiperiodic solutions. We also comment on the experimental feasibility of these feedback ratchets and their potential applications.Comment: LaTeX, 7 pages, 6 figure

Unaccustomed Exercise Causes Rhabdomyolysis

Cross Fit TM is a relatively new strength and conditioning program defined as “constantly varied, functional movements, performed at a high intensity”. The goal of the program is to increase “work capacity across broad time and modal domains” [1]. Even though this training modality has been criticized by the main stream media for “high risk of injury” most of these claims have been anecdotal, as recent evidence suggest this training modality is not any more “dangerous” than other exercise programs [2]. One of the biggest criticisms of this training modality has been its association with Rhabdomyolysis, a condition that results in the breakdown of muscle tissue and can result in death [3,4]. However, these claims have not been substantiated by any study looking at the incidence of injury due to Cross Fit participation [2,5,6]

A Comparison of Commonly Used Accelerometer Based Activity Monitors in Controlled and Free-Living Environment

This dissertation was designed to determine the effects of body mass index (BMI) and walking speed on activity monitor outputs. A secondary purpose was to compare the activity monitors’ performance in a free-living environment. In the first experiment, 71 participants wore three waist-mounted activity monitors (Actical, ActiGraph, and NL-2000) and an ankle-mounted device (StepWatch 3) while walking on a treadmill (40, 67 and 94 m/min). The tilt angle of each device was measured. The Actical recorded 26% higher activity counts (P \u3c 0.01) in obese persons with a tilt \u3c10 degrees, compared to normal weight persons. The ActiGraph was unaffected by BMI or tilt angle. In the second experiment, the steps recorded by the devices were compared to actual steps. Speed had the greatest influence on the accuracy these devices. At 40 m/min, the ActiGraph was the least accurate device for normal weight (38%), overweight (46%) and obese (48%) individuals. The Actical, NL-2000 and StepWatch averaged 65%, 73% and 99% of steps taken, respectively. Lastly, several generations of the ActiGraph (7164, GT1M, and GT3X), and other research grade activity monitors (Actical; ActivPAL; and Digi-Walker) were compared to a criterion measure of steps. Fifty-six participants performed treadmill walking (40, 54, 67, 80 and 94 m/min) and wore the devices for 24-hours under free-living conditions. BMI did not affect step count accuracy during treadmill walking. The StepWatch, PAL, and the AG7164 were the most accurate across all speeds; the other devices were only accurate at the faster speeds. In the free-living environment, all devices recorded about 75% of StepWatch-determined steps, except the AG7164 (99%). Based on these findings, we conclude that BMI does not affect the output of these activity monitors. However, waist-borne activity monitors are highly susceptible to under-counting steps at walking speeds below 67 m/min, or stepping rates below 100 steps/min. An activity monitor worn on the ankle is less susceptible to these speed effects and provides the greatest accuracy for step counting

Prevalence and Incidence Rates Are Not the Same: Letter to the Editor

I recently became aware of an article by Weisenthal et al,2 “Injury Rate and Patterns Among CrossFit Athletes,” published in the April 2014 issue of your journal. Considering this is a topic of interest to me, I read the article with great expectations and detail. I commend the authors for their fantastic job, both in their methodology as well as in their interpretation of their findings. They truly did a great job explaining their definition of what constituted an injury, which has been lacking in several studies, as well as providing great recommendations for the “safe” participation in this training modality. However, considering how controversial this topic has become among health care professionals, fitness enthusiasts, and the mainstream media, it is important to point out a major flaw of this study, which is significant. In addition, it is also important for anyone else reading the article to understand the limitations of the data provided and their interpretation

Inductive Sensor for measuring partial discharges in electrical machines

The research group 'Diagnosis of Electrical Machines and Insulation Materials (DIAMAT) of the University Carlos III of Madrid, has developed an inductive sensor that can detect and measure partial discharge that are characteristic in electrical machines (its analysis allows to estimate the aging degree of the internal insulation)

La condición "técnica" del ser humano

A l'heure d'analyser l'accomplissement technologique et ses répercussions actuelles, il est nécessaire de s'attarder a une étape préliminaire: la propre condition technique de l'être humain, c'est-a-dire, l'affirmation d'une capacité technique radicale et intrinseque qui lui est propre et qui, a la fois, configure et donne forme et sens au monde environnant. Cet essai présente un bref survol sur ce sujet là, dans la perspective philosophique . Cinq auteurs sont traités dans ce le travail: J. Ortega y Gasset, M. Heidegger, X. Zubiri, L. Munford y J. Ellul.When one comes to analize the technological act and its contemporary repercussions, one must return to an earlier moment: the inherently technical condition of the human being,that is to say, the affirmation of a radical and intrinsic technical capacity which is his/her own and which shapes him/her at the same times as it gives form and meaning to the surrounding world. This article presents a brief survey of how this issue has been analized from the philosophical perspective, particularly important in this case. It focuses on five authors: J. Ortega y Gasset, M. Heidegger, X. Zubiri, L. Mumford and J. Ellul.Publicad

Miranda de Avilés, el más antiguo alfar (documentalmente) de todo el Principado

En número dedicado a: El Principado de de Asturia

Agricultura familiar para el desarrollo rural argentino.

Analizamos elementos del debate reciente sobre la institucionalidad del modelo rural argentino, en relación con la construcción colectiva del “Plan Estratégico Agroalimentario y Agroindustrial, Participativo y Federal 2010-2016”. Nuestra participación en la mesa de agricultura familiar del plan permite reflexionar sobre el rol de este sector en la construcción de un modelo nacional de desarrollo rural. Los agricultores familiares constituyen actores productivos que representan un sector en permanente disputa por territorios y con históricas desventajas en el mercado, urgidos de múltiples acciones simultáneas y cuyas demandas necesitan un desarrollo rural integral. Frente al alcance de las transformaciones que ha implicado el modelo de agronegocios, proponemos incorporar la agricultura familiar a un modelo de país, destacando su rol multifuncional en pie de igualdad con los otros actores del sistema agroalimentario, para reducir asimetrías con el sector de agronegocios, reconociendo el fundamental rol del Estado como regulador