Biomedical subjects

Marc Durand

Publications and source records attributed to Marc Durand.

9 recordsLinked to original sources

PubMed2007

Situated analysis of elite trampolinists' problems in competition using retrospective interviews.

The aims of this study were to identify and analyse elite athletes' problems in competition. A situated cognition approach placed the emphasis on athletes' actions (i.e. cognitions and behaviours), which were considered to emerge from couplings with selected elements of the context. Fifty-two exercises performed by 10 elite trampolinists were analysed. Field observations, structured interviews, and self-confrontation interviews were conducted and transcribed, and used together with behavioural descriptions derived from video recordings. Performance problems were selected from these reports and from the major infringements of trampoline rules. Qualitative analysis identified the meaningful units of action and their semiotic components for each problem. Four categories of problem were identified and noted to appear either separately or jointly while performing: (a) finding the best moment to begin the performance; (b) finding and maintaining the best mode of involvement to end the performance; (c) recovering normal sensory-motor capacity to perform; and (d) solving problems quickly and definitively while performing. The results suggest that the study of action -- situation couplings in sports, as well as of their constantly evolving dynamics, not only reveals elite athletes' psychological activity, but is vital to a deeper understanding of these couplings.

Adolescent↗

PubMed2006

Relaxation time of the topological T1 process in a two-dimensional foam.

The elementary topological T1 process in a two-dimensional foam corresponds to the flip of one film with respect to the geometrical constraints, and is a process by which the structure of an out-of-equilibrium foam evolves. We study both experimentally and theoretically the T1 dynamics in a dry two-dimensional foam. The dynamics is controlled by the surface viscoelastic properties of the films (surface shear plus dilatational viscosity, mu_{s}+kappa, and Gibbs elasticity ), and is independent of the shear viscosity of the bulk liquid. Moreover, the dynamics of the T1 process provides a tool for measuring the surface rheological properties: we obtained =32+/-8 mN/m and mu_{s}+kappa=1.3+/-0.7 mPa.m.s for sodium dodecyl sulfate, and =65+/-12 mN/m and mu_{s}+kappa=31+/-12 mPa.m.s for bovine serum albumin, in good agreement with literature values.

Journal Article↗

PubMed2006

In vitro experiments and numerical simulations of airflow in realistic nasal airway geometry.

Pressure-flow relationships measured in human plastinated specimen of both nasal cavities and maxillary sinuses were compared to those obtained by numerical airflow simulations in a numerical three-dimensional reconstruction issued from CT scans of the plastinated specimen. For experiments, flow rates up to 1,500 ml/s were tested using three different gases: HeO(2), Air, and SF(6). Numerical inspiratory airflow simulations were performed for flow rates up to 353 ml/s in both the nostrils using a finite-volume-based method under steady-state conditions with CFD software using a laminar model. The good agreement between measured and numerically computed total pressure drops observed up to a flow rate of 250 ml/s is an important step to validate the ability of CFD software to describe flow in a physiologically realistic binasal model. The major total pressure drop was localized in the nasal valve region. Airflow was found to be predominant in the inferior median part of nasal cavities. Two main vortices were observed downstream from the nasal valve and toward the olfactory region. In the future, CFD software will be a useful tool for the clinician by providing a better understanding of the complexity of three-dimensional breathing flow in the nasal cavities allowing more appropriate management of the patient's symptoms.

Computer Simulation↗

PubMed2006

Architecture of optimal transport networks.

We analyze the structure of networks minimizing the global resistance to flow (or dissipative energy) with respect to two different constraints: fixed total channel volume and fixed total channel surface area. First, we show that channels must be straight and have uniform cross-sectional areas in such optimal networks. We then establish a relation between the cross-sectional areas of adjoining channels at each junction. Indeed, this relation is a generalization of Murray's law, originally established in the context of local optimization. We establish a relation too between angles and cross-sectional areas of adjoining channels at each junction, which can be represented as a vectorial force balance equation, where the force weight depends on the channel cross-sectional area. A scaling law between the minimal resistance value and the total volume or surface area value is also derived from the analysis. Furthermore, we show that no more than three or four channels meet at each junction of optimal bidimensional networks, depending on the flow profile (e.g., Poiseuille-like or pluglike) and the considered constraint (fixed volume or surface area). In particular, we show that sources are directly connected to wells, without intermediate junctions, for minimal resistance networks preserving the total channel volume in case of plug flow regime. Finally, all these results are compared with the structure of natural networks.

Journal Article↗

PubMed2005

Optimizing the bulk modulus of low-density cellular networks.

We present an alternative derivation of upper-bounds for the bulk modulus of both two-dimensional and three-dimensional cellular materials. For two-dimensional materials, we recover exactly the expression of the Hashin-Shtrikman (HS) upper-bound in the low-density limit, while for three-dimensional materials we even improve the HS bound. Furthermore, we establish necessary and sufficient conditions on the cellular structure for maximizing the bulk modulus, for a given solid volume fraction. The conditions are found to be exactly those under which the electrical (or thermal) conductivity of the material reaches its maximal value as well. These results provide a set of straightforward criteria allowing us to address the design of optimized cellular materials, and shed light on recent studies of structures with both maximal bulk modulus and maximal conductivity. Finally, we discuss the specific case of spring networks, and analyze the compatibility of the criteria presented here with the geometrical constraints caused by minimization of surface energy in a real foam.

Journal Article↗

PubMed2004

Optimizing transport in a homogeneous network.

Many situations in physics, biology, and engineering consist of the transport of some physical quantity through a network of narrow channels. The ability of a network to transport such a quantity in every direction can be described by the average conductivity associated with it. When the flow through each channel is conserved and derives from a potential function, we show that there exists an upper bound of the average conductivity and explicitly give the expression for this upper bound as a function of the channel permeability and channel length distributions. Moreover, we express the necessary and sufficient conditions on the network structure to maximize the average conductivity. These conditions are found to be independent of the connectivity of the vertices.

Journal Article↗

PubMed2004

Elite athletes' differentiated action in trampolining: a qualitative and situated analysis of different levels of performance using retrospective interviews.

Using a situated cognition approach, this study analyzed elite athletes' actions, i.e., behaviors link to cognitions, during competitive trampoline performances, which are evaluated from a succession of 10 acrobatic movements characterized by flight time and fall risk. 27 exercises performed by 10 elite athletes were ranked poor, average, or good and analyzed. Self-confrontation interviews were conducted and transcribed in relation with behavioral descriptions derived from video recordings. Qualitative analysis was performed to identify units of meaningful action and their components. The succession of units describing the stream of actions was used to identify differentiated organization of trampolinists' performances. Three patterns, corresponding to performance levels, were distinguished by (a) an increasing number of meaningful actions occurring at the same time, (b) a reduction in actions of waiting, and (c) the emergence of new actions aimed at interaction with the situation. These results suggest that differentiation in performance level is linked with meaningful actions modified through interaction with the context.

Adult↗

PubMed2003

Structure of expert players' activity during competitive interaction in table tennis.

This study analyzed the activity of expert table tennis players during a match, in reference to course of action theory (Theureau, 1992). Matches were videotaped, and the players' verbalizations as they viewed the tapes were collected a posteriori. The data was analyzed by (a) transcribing the players' actions and verbalizations, (b) decomposing their activity into elementary units of meaning, and (c) grouping the elementary units into larger sets. The results showed that the matches began with an inquiry into the specific features of the opponent's play. This was followed by reproducing the actions identified as effective during the inquiry. The results are discussed in relation to the role of training in expert performance.

Adult↗

PubMed2002

Concomitant chemoradiotherapy in pyriform sinus carcinoma.

OBJECTIVES: To test the effectiveness of concurrent chemoradiotherapy in patients with pyriform sinus carcinoma and to demonstrate the feasibility of an organ preservation approach. DESIGN: Clinical trial phase 2. SETTING: University Hospital Center, St-Etienne, France. PATIENTS: The study population comprised 46 male patients with resectable stage III and IV pyriform sinus carcinoma. METHODS: Two successive chemoradiation regimens were investigated. In protocol 1 (24 patients), carboplatin was given on days 1 through 5 and 28 through 33, with an area under the curve dose of 5 mg/mL for 1 minute per day and bifractionated radiotherapy (160 rad [1.6 Gy]/fraction) delivered on days 1 through 16 and 28 through 38. A treatment break was planned on days 16 through 27. In protocol 2 (22 patients), chemotherapy was given with the same dose of carboplatin on days 1 and 21, and fluorouracil (750 mg/m(2) per day) on days 1 through 7 and 21 through 28. Radiotherapy with a single fraction of 180 rad (1.8 Gy)/d was delivered during the first 2 weeks and then 150 rad (1.5 Gy) twice a day during the next 3 weeks. MAIN OUTCOME MEASURES: Patients were evaluated for tumor response, toxic reactions, and organ preservation and survival rates. Statistical analysis of disease-free survival and overall survival was performed using the Kaplan-Meier method. RESULTS: A complete response was noted in 21 (88%) of the 24 patients following protocol 1 and 16 (73%) of the 22 patients following protocol 2. After 2 years of follow up, 16 patients (67%) (protocol 1) and 12 patients (55%) (protocol 2) retained their larynx without evidence of disease. During therapy, 15 patients (63%) (protocol 1) and 19 patients (86%) (protocol 2) required unplanned hospitalization for toxic effects. The overall survival and disease-free survival rates at 2 years were 58% (protocol 1) vs 53% (protocol 2) and 39% (protocol 1) vs 41% (protocol 2) (P =.80), respectively. CONCLUSION: Concomitant chemotherapy and bifractionated radiotherapy, although toxic, leads to good locoregional control and therefore to a significant level of laryngeal preservation.

Adult↗