Inferring Microscopic Kinetic Rates from Stationary State Distributions.

We present a principled approach for estimating the matrix of microscopic transition probabilities among states of a Markov process, given only its stationary state population distribution and a single average global kinetic observable. We adapt Maximum Caliber, a variational principle in which the path entropy is maximized over the distribution of all possible trajectories, subject to basic kinetic constraints and some average dynamical observables. We illustrate the method by computing the solvation dynamics of water molecules from molecular dynamics trajectories

Fundamental Properties of Intensity, Form, and Motion Perception in the Visual Nervous Systems of Calliphora phaenicia and Musca domestica

Several classes of interneurons in the optic lobes and brain of the insects, Musca domestica and Calliphora phaenicia, have been studied in detail. Visual stimuli have been categorized on the basis of the properties of intensity, form, and motion. Response characteristics of the classes of neural units are described with respect to these three classes of visual stimuli. While those units that detect motion in select directions have a tonic response, form detection units have a phasic response only. Through correlation of the responses of these classes with visual stimuli, it is shown that these units integrate the responses of other units which have very small visual fields. The small-field units are presumed to integrate the output of a small group of adjacent retinula cells and to respond differentially to intensity, form, and motion. It is shown that the response of both form and motion detection units is independent of the direction of pattern intensity gradation. As a consequence of this independence, it is further shown that failure to detect motion properly must start at a spatial wavelength four times the effective sampling station spacing rather than twice as has been predicted previously

On induced birefringence in viscoelastic materials

Describing induced birefringence in viscoelastic materials based on constitutive assumptions for stress and dielectric propertie

Le paradoxe de la qualité académique : implications pour les universités et les politiques publiques

Cet article traite de mécanismes d’assurance de la qualité dans le système d’enseignement supérieur et propose une interprétation du peu d’engagement des professeurs dans les processus d’analyse de la qualité des cursus universitaires et de l’expérience d’apprentissage des étudiants. L’institution universitaire valorise les performances individuelles en enseignement et en recherche et non les efforts coopératifs des départements universitaires pour assurer la qualité de l’offre de formation. C’est donc un paradoxe de la qualité académique que l’on compare à celui du célèbre roman Catch 22. À la suite des évaluations des mécanismes d’assurance de la qualité et pour résoudre le paradoxe de la qualité académique, on propose une démarche basée sur les principes de l’organisation apprenante.This article presents a discussion of mechanisms for assuring the quality of higher education and proposes one interpretation of the lack of commitment by professors in the process of quality analysis of university programs and of students’ learning experiences. As an institution, the university values individual performance in teaching and research and not the cooperative efforts of university departments in assuring the quality of the training program. This paradox of academic quality can be compared with that of the well-known novel Catch 22. Following an evaluation of the mechanisms used to assure quality and to respond to the paradox of academic quality, the author proposes a procedure based on the principles of the learning organization.Este artículo discute sobre los mecanismos para asegurar la calidad académica en el sistema de enseñanza superior y propone una interpretación sobre la poca implicación de los profesores en el proceso de análisis y en la calidad de los cursos universitarios tanto como en la experiencia de aprendizaje de los estudiantes. La institución universitaria valoriza los desempeños individuales en la enseñanza y en la investigación y no los esfuerzos cooperativos que llevan a cabo los departamentos universitarios afin de asegurar la calidad en la oferta de la formación. Hay, entonces, una paradoja en la calidad académica que puede compararse a aquella de la célebre novela Catch 22. Siguiendo con las evaluaciones de los mecanismos para asegurar la calidad académica y para resolver la paradoja de la calidad académica, se propone un proceso de evaluación basado en los principios de la organización aprendiente.In diesem Beitrag werden die Mechanismen aufzeigt, die der Qualitätskontinuität im Hochschulsystem zu Grunde liegen. Darüber hinaus wird die Frage diskutiert, warum die Lehrenden der Qualitätsanalyse von Universitätscurricula sowie dem Lernverhalten der Studenten so wenig Interesse entgegen-bringen. Die Institution valorisiert vor allem die individuellen Lehr- und Forschungsleistungen, nicht aber die gemeinschaftlichen Bemühungen der Fachbereiche um die Qualität der Studienprogramme. Diese Situation stellt einen Paradox dar, der mit einem berühmten literarischen Paradox, wie ihn der Roman Catch 22 thematisiert, verglichen wird. Im Anschluss an die kritische Auseinandersetzung mit den Qualitätsmechanismen und dem Paradox akademischer Lehrqualität wird eine Problemlösung vorgeschlagen, die auf dem Prinzip der Lernorganisation („l’organisation apprenante“) beruht

Airflow Model Testing to Determine the Distribution of Hot Gas Flow and O/F Ratio Across the Space Shuttle Main Engine Main Injector Assembly

Engine 0209, the certification engine for the new Phase 2+ Hot Gas Manifold (HGM), showed severe deterioration of the Main Combustion Chamber (MCC) liner during hot fire tests. One theory on the cause of the damage held that uneven local distribution of the fuel rich hot gas flow through the main injector assembly was producing regions of high oxidizer/fuel (O/F) ratio near the wall of the MCC liner. Airflow testing was proposed to measure the local hot gas flow rates through individual injector elements. The airflow tests were conducted using full scale, geometrically correct models of both the current Phase 2 and the new Phase 2+ HGMs. Different main injector flow shield configurations were tested for each HGM to ascertain their effect on the pressure levels and distribution of hot gas flow. Instrumentation located on the primary faceplate of the main injector measured hot gas flow through selected injector elements. These data were combined with information from the current space shuttle main engine (SSME) power balances to produce maps of pressure, hot gas flow rate, and O/F ratio near the main injector primary plate. The O/F distributions were compared for the different injector and HGM configurations