Functional MRI with active, fully implanted, deep brain stimulation systems: Safety and experimental confounds

We investigated safety issues and potential experimental confounds when performing functional magnetic resonance imaging (fMRI) investigations in human subjects with fully implanted, active, deep brain stimulation (DBS) systems. Measurements of temperature and induced voltage were performed in an in vitro arrangement simulating bilateral DBS during magnetic resonance imaging (MRI) using head transmit coils in both 1.5 and 3.0 T MRI systems. For MRI sequences typical of an fMRI study with coil-averaged specific absorption rates (SARs) less than 0.4 W/kg, no MRI-induced temperature change greater than the measurement sensitivity (0.1 °C) was detected at 1.5 T, and at 3 T temperature elevations were less than 0.5 °C, i.e. within safe limits. For the purposes of demonstration, MRI pulse sequences with SARs of 1.45 W/kg and 2.34 W/kg (at 1.5 T and 3 T, respectively) were prescribed and elicited temperature increases (> 1 °C) greater than those considered safe for human subjects. Temperature increases were independent of the presence or absence of active stimulator pulsing. At both field strengths during echo planar MRI, the perturbations of DBS equipment performance were sufficiently slight, and temperature increases sufficiently low to suggest that thermal or electromagnetically mediated experimental confounds to fMRI with DBS are unlikely. We conclude that fMRI studies performed in subjects with subcutaneously implanted DBS units can be both safe and free from DBS-specific experimental confounds. Furthermore, fMRI in subjects with fully implanted rather than externalised DBS stimulator units may offer a significant safety advantage. Further studies are required to determine the safety of MRI with DBS for other MRI systems, transmit coil configurations and DBS arrangements

Intèrêt et faisabilité de la simulation aux grandes échelles dans les moteurs automobiles.

Avec la sévérisation des normes environnementales, les constructeurs automobiles sont amenés à développer des moteurs consommant et polluant moins. Ces nouveaux moteurs fonctionnent avec des stratégies de combustion de plus en plus complexes, qui nécessitent une maîtrise très fine du mélange air/carburant et de l'aérodynamique interne. Les outils d'aide à la conception utilisés jusqu'alors, comme les bancs d'essai moteur ou les calculs 3D RANS, ne permettent plus de répondre à toutes les problématiques rencontrées lors du développement de ces moteurs. Dans ce contexte, la simulation aux grandes échelles (LES) constitue un outil très prometteur pour la mise au point des moteurs modernes car elle permet d'accéder aux instationnarités de l'écoulement. Ce travail de thèse a consisté à appliquer la simulation aux grandes échelles dans les moteurs automobiles, en montrant son intérêt, et, en développant des méthodologies de calcul. Dans un premier temps, des calculs sont réalisés dans des bancs volutes stationnaires afin de déterminer leur perméabilité (ou perte de charge) et leur nombre de swirl. Plusieurs bancs volutes sont ainsi étudiés par difficulté croissante au niveau de leur géométrie et de l'écoulement les traversant. Les résultats LES pour chaque géométrie montrent un accord satisfaisant avec les mesures expérimentales correspondantes. La LES a permis pour la géométrie la plus complexe d'analyser finement la typologie de l'écoulement, engendrée par deux conduits de forme particulière et son évolution avec la levée de soupape. Dans un deuxième temps, un modèle d'allumage (ADEL) est couplé au modèle de combustion turbulente TFLES. Ce dernier est ensuite adapté au contexte moteur. Le développement de ces deux modèles a permis de simuler la phase d'initiation et de propagation d'une flamme dans un moteur à essence à injection indirecte. Quatre cycles du même moteur sont ensuite enchaînés. Chacun d'eux est viable d'après les mesures expérimentales, mais chaque cycle diffère des autres. Les variabilités cycliques sont ensuite analysées en terme de mélange, d'aérodynamique interne, de combustion et de rendements

Characterization of Terrain-Induced Turbulence by Large-Eddy Simulation for Air Safety Considerations in Airport Siting

Topography-induced turbulence poses a potential hazard for aviation safety, in particular during the final approach and landing. In this context, it is essential to assure that the impact of topography-induced turbulence on the flight paths during take-off and landing is minimized already during the design and planning phase. As an example of the siting and planning of a potential new airport in complex terrain, this study investigates the distribution of terrain-induced boundary layer turbulence in the vicinity of the current Lofoten airport at Leknes (LKN). For that purpose, large-eddy simulations (LES) have been performed with the PAralellized Large-eddy Simulation Model (PALM) on a 40×45×4km3 computational domain around LKN. An initial parametric sensitivity study resulted in a grid spacing of 50 m and an overall simulation time of 12 h for our individual model runs. A suite of 32 model simulations for 16 different wind directions and two geostrophic wind speeds of 10 ms−1 and 20 ms−1 , was then performed and analysed. A turbulence risk analysis along idealized flight trajectories shows that the high-risk conditions are substantially determined by the wind conditions and their interaction with the topography. With respect to wind speed, the results indicate that for a geostrophic flow below 10 ms−1 , the risk of aviation critical, terrain-induced boundary layer turbulence (BLT), is rather low in the vicinity of LKN. At 20 ms−1 the situation has completely changed, as for 14 out of 16 investigated wind directions the 9 m2 s−2 aviation critical threshold of turbulent kinetic energy per unit air mass (TKE) is exceeded. In the northwesterly wind scenarios, the largest areas with critical turbulence in the vicinity of LKN are observed.publishedVersio

Early Illustrations of Geste Antagoniste in Cervical and Generalized Dystonia

Background: Geste antagoniste, or sensory trick, is a voluntary maneuver that temporarily reduces the severity of dystonic postures or movements. We present a historical review of early reports and illustrations of geste antagoniste. Results: In 1894, Brissaud described this phenomenon in Paris in patients with torticollis. He noted that a violent muscular contraction could be reversed by a minor voluntary action. He considered the improvement obtained by what he called “simple mannerisms, childish behaviour or fake pathological movements” was proof of the psychogenic origin of what he named mental torticollis. This concept was supported by photographical illustrations of the patients. The term geste antagoniste was used by Brissaud’s pupils, Meige and Feindel, in their 1902 monograph on movement disorders. Other reports and illustrations of this sign were published in Europe between 1894 and 1906. Although not mentioned explicitly, geste antagoniste was also illustrated in a case report of generalized dystonia in Oppenheim’s 1911 seminal description of dystonia musculorum deformans in Berlin. Discussion: Brissaud-Meige’s misinterpretation of the geste antagoniste unfortunately anchored the psychogenic origin of dystonia for decades. In New York, Herz brought dystonia back into the realm of organic neurology in 1944. Thereafter, it was given prominence by other authors, notably Fahn and Marsden in the 1970–1980s. Nowadays, neurologists routinely investigate for geste antagoniste when a dystonic syndrome is suspected, because it provides a further argument in favor of dystonia. The term alleviating maneuver was proposed in 2014 to replace sensory trick or geste antagoniste. This major sign is now part of the motor phenomenology of the 2013 Movement Disorder Society’s classification of dystonia

Complementarity of wind measurements from co-located X-band weather radar and Doppler lidar

Accurate wind profile measurements are important for applications ranging from aviation to numerical weather prediction. The spatial pattern of winds can be obtained with ground-based remote sensing instruments, such as weather radars and Doppler lidars. As the return signal in weather radars is mostly due to hydrometeors or insects, and in Doppler lidars due to aerosols, the instruments provide wind measurements in different weather conditions. However, the effect of various weather conditions on the measurement capabilities of these instruments has not been previously extensively quantified. Here we present results from a 7-month measurement campaign that took place in Vantaa, Finland, where a co-located Vaisala WRS400 X-band weather radar and WindCube 400S Doppler lidar were employed continuously to perform wind measurements. Both instruments measured plan position indicator (PPI) scans at 2.0 degrees elevation from the horizontal. Direct comparison of radial Doppler velocities from both instruments showed good agreement with R-2 = 0.96. We then examined the effect of horizontal visibility, cloud base height, and precipitation intensity on the measurement availability of each instrument. The Doppler lidar displayed good availability in clear air situations and the X-band radar in precipitation. Both instruments exhibited high availability in clear air conditions in summer when insects were present. The complementary performance in the measurement availability of the two instruments means that their combination substantially increases the spatial coverage of wind observations across a wide range of weather conditions.Peer reviewe

On-line motor control in patients with Parkinson's disease

Recent models based, in part on a study of Huntington's disease, suggest that the basal ganglia are involved in on-line movement guidance. Two experiments were conducted to investigate this idea. First, we studied advanced Parkinson's disease patients performing a reaching task known to depend on on-line guidance. The task was to ‘look and point' in the dark at visual targets displayed in the peripheral visual field. In some trials, the target location was slightly modified during saccadic gaze displacement (when vision is suppressed). In both patient and control groups, the target jump induced a gradual modification of the movement which diverged smoothly from its original path to reach the new target location. No deficit was found in the patients, except for an increased latency to respond to the target jump (Parkinson's disease: 243 ms; controls: 166 ms). A computational simulation indicated that this response slowing was likely to be a by-product of bradykinesia. The unexpected inconsistency between this result and previous reports was investigated in a second experiment. We hypothesized that the relevant factor was the characteristics of the corrections to be performed. To test this prediction, we investigated a task requiring corrections of the same type as investigated in Huntington's disease, namely large, consciously detected errors induced by large target jumps at hand movement onset. In contrast with the smooth adjustments observed in the first experiment, the subjects responded to the target jump by generating a discrete corrective sub-movement. While this iterative response was relatively rapid in the control subjects (220 ms), Parkinson's disease patients exhibited either dramatically late (>730 ms) or totally absent on-line corrections. When on-line corrections were absent, the initial motor response was completed before a second corrective response was initiated (the latency of the corrective response was the same as the latency of the initial response). Considered together, these results suggest that basal ganglia dependent circuits are not critical for feedback loops involving a smooth modulation of the ongoing command. These circuits may rather contribute to the generation of discrete corrective sub-movements. This deficit is in line with the general impairment of sequential and simultaneous actions in patients with basal ganglia disorder

Développer la recherche d’information et l’autorégulation collective en classe renversée : l’apport des tests d’autoévaluation

fr Ultime déclinaison de la classe inversée, la classe renversée (Cailliez et Hénin, 2017) se présente comme un dispositif audacieux visant à rendre les étudiants plus actifs et à les responsabiliser mais n’ayant, à notre connaissance, pas encore fait l’objet de travaux de recherche. Si ce dispositif semble intéressant sur le plan de la créativité et de la mise en activité, il induit un engagement cognitif élevé qui pourrait compromettre l’apprentissage et exige que les étudiants soient capables de réguler leur motivation collectivement au sein du groupe. Selon Roediger et Karpicke (2006), les tests d’autoévaluation pourraient soutenir l’apprentissage des étudiants sur le plan cognitif et métacognitif. Il reste à voir si des effets se produiront en matière de régulation de la motivation. Dans le cadre d’une recherche exploratoire, notre classe renversée a été mise en place dans un cours de Culture numérique de Diplôme Universitaire de Technologie (DUT) Information-Communication auprès d’étudiants de première année. Ce cours vise à sensibiliser les étudiants aux enjeux de la culture numérique tout en les initiant à la méthodologie de la recherche d’information qui, comme nous le verrons, est cruciale en classe renversée. Un autre enjeu important est l’autorégulation collective étant donné que les étudiants doivent élaborer une production commune par petits groupes (Cosnefroy et Jézégou, 2013; Järvela et Järvenoja, 2011). Dans cette double perspective, nous avons ajouté au dispositif deux types de tests à visée formative : les uns étaient composés de questions à choix multiples (QCM), d’autres contenaient des questions à réponse libre (QRL). Nos résultats indiquent des corrélations entre les QCM et les gains de certains apprentissages et entre les QRL et les performances des étudiants mesurées lors l’évaluation finale. Aussi, il semblerait que les tests par QRL incitent les étudiants à mettre en place des stratégies d’autorégulation collective.en A kind of flipped class, literally called « reversed classroom » (Cailliez et Hénin, 2017) is a promising instructional design which focusses on creativity and « hands on » activities. However, we know little about the learning gains that might occur in this environment. In our view, these gains are unlikely to happen unless some help is provided to manage the high cognitive load and support students’ self-regulated learning. Roediger et Karpicke (2006) suggest that self-assessments support cognitive and metacognitive learning strategies. Could they help students develop a socially constructed self-regulated learning? This paper presents an experiment that took place in a Digital Culture course of DUT Information-Communication with first-year students, in order to sensitize students to digital literacy and to develop their informational literacy skills. Another issue is the social challenges that students have to face as this class expects them to work in collaborative learning groups : in this context, students will have to regulate their motivation together and achieve socially constructed self-regulated learning (Cosnefroy et Jézégou, 2013; Järvela et Järvenoja, 2011). Two types of self-assessment tests were implemented : classical multiple-choice tests and free-recall tests. Our results show that correlations occur between multiple-choice tests and learning gains whereas free-recall tests are correlated to performance. Also, these free-recall tests indirectly lead to collective self-regulatory learning strategies among students

Evaluating modelled winds over an urban area using ground-based Doppler lidar observations

Wind information in urban areas is essential for many applications related to air pollution, urban climate and planning, safety of drone-related operations, and assessment of urban wind energy potential. These applications require accurate wind forecasts, and obtaining this information in an urban environment is challenging as the morphology of a city varies from street to street, altering the wind flow. Remote sensing techniques such as Doppler lidars (light detection and ranging) provide a unique opportunity for wind forecast verification as they can provide both the vertical profile of the horizontal wind and the spatial variation in the horizontal domain at high resolution. In this study, the performance of numerical weather prediction (NWP) models, analysis systems, and large-eddy simulation (LES) models have been analysed by comparing the modelled winds against Doppler lidar observations under various atmospheric conditions and from season to season, in the coastal environment of Helsinki, Finland. The long-term mean vertical profile of the modelled horizontal wind shows good agreement with observations; the NWP model and the analysis systems selected here exhibit different strengths and weaknesses depending on the atmospheric conditions but no significant diurnal variation in performance. However, both the model and analysis systems show differences in their spatially-averaged bias when investigating different wind directions. LES verification shows that these models can potentially provide winds down to street level, given pre-computed scenarios of atmospheric conditions. For Helsinki, the observed winds are stronger during winter than summer, and, on average, higher wind speeds were observed at the urban site than the sub-urban site.Peer reviewe