Children’s Use of a ‘Time Line’ to Indicate When Events Occurred

Children who allege abuse are often asked to provide temporal information such as when the events occurred. Yet, young children often have difficulty recalling temporal information due to their limited knowledge of temporal patterns and linguistic capabilities. As time is an abstract concept (we cannot see it), some investigators have begun to use ‘time-lines’ or pictorial representations of time to aid children. Yet, there is no published research testing whether children are able to use time-lines and whether they can provide adequate temporal information using them. We tested whether children could indicate the time-of-day of events using a pictorial time-line and then compared their responses to their parents’. Seven- to 8-year-olds were most consistent with parental estimates while 4-year-olds were least consistent. Responses from the 5- to 6-year-olds depended on the temporal task. Guessing and using general knowledge to estimate the time-of-day were ruled out, and so children were genuinely drawing on episodic memory when making time-line judgments. Thus, there was a developmental progression in children’s use of physical representations to communicate abstract information. These results are promising for the use of the time-line in forensic settings but much more research is needed

VI.— On manufactured sea-water for the aquarium

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Efficacité d'un seuil artificiel sur l'oxygénation de l'eau et l'élimination de CH4 contenu dans l'eau évacuée par la barrage hydroélectrique de Petit Saut (Guyane française)

Quelques mois après le début de la mise en eau du barrage de Petit Saut, la mise en service normale de l'usine conduisait à une désoxygénation de l'eau du tronçon de rivière aval, le rendant incompatible avec la vie aquatique. La solution retenue a été la construction d'un seuil, afin d'apporter de l'oxygène et d'éliminer les gaz réducteurs produits au fond de la retenue, notamment le méthane, consommateur potentiel d'oxygène dissous.Un seuil métallique à deux lames déversantes successives a été construit ; sa configuration prend en compte les principaux critères physiques jouant un rôle significatif sur l'oxygénation de l'eau (hauteur de chute, épaisseur de la lame déversante, le dimensionnement du bassin de réception des chutes, la présence de dispositifs favorisant l'éclatement de la lame d'eau). Placé dans le canal de fuite de l'usine, à une centaine de mètres à l'aval du barrage principal, il est à l'abri des crues et ne crée pas d'obstacle supplémentaire en rivière.L'article chiffre l'effet d'aération de ce seuil pour les deux gaz O2 et CH4 dans deux configurations : celles consécutives à l'abaissement partiel de la chute amont réalisé en deux étapes. Après décembre 2001, pour le débit moyen turbiné (près de 200 m3 /s), l'efficacité d'aération du seuil a baissé de près de 10 % (gain de 80 % en oxygène dissous et élimination de 70 % et 75 % du méthane dissous). Après février 2003, pour un débit de 100 m3/s, 75 % du déficit amont en oxygène dissous est comblé et près de 70 % du méthane dissous éliminé.From the moment tropical reservoirs are impounded, climatic conditions cause rapid (within several weeks) and marked thermal stratification, especially during the dry season. This phenomenon is further exacerbated by the chemical and biochemical processes taking place in the reservoir due to the decomposition of submerged organic matter. In dense tropical forests, the overhead biomass is estimated at roughly 170 t(C)/ha, and the carbon contained in the soil is also not negligible since it is on the order of 100 t(C)/ha. The degree of biodegradability of the different compounds in the flooded biomass is variable, ranging from a few weeks for bacteria to several centuries for tree trunks.The studies carried out at Petit Saut (French Guiana) show that, immediately after impoundment, only the epilimnion (a few dozen centimetres thick) was oxygenated whereas the hypolimnion was characterized by complete anoxia and a very high methane content (about 15 mg/L). Water quality in the river downstream from the reservoir was of course strongly linked to variations in the water quality in the reservoir as well as to its operating mode. The waters passing through the turbines, coming from the bottom layers, were anoxic and loaded with fixed or volatile reducing compounds (e.g., CH4, H2 S), and were responsible for a high immediate or progressive oxygen demand. At Petit Saut, despite an inflow of good quality water, there has been a progressive deoxygenation in the river downstream due to the high methane content (roughly 8 mg/L) of the turbined water. Thus, 40 km downstream from the dam, the oxygen content was less than 2 mg/L and therefore incompatible with most aquatic life. To solve this problem, it was necessary to build an aerating weir capable of reoxygenating the turbined waters and, more importantly, eliminating reducing gases such as methane at the same time. The function of the overflow weir was to entrain air bubbles into the water and to give these bubbles a sufficiently long immersion time to ensure that they dissolve. At the time of its installation, only three examples of oxygenating weirs existed in the entire world, all located in the United States. The weir configuration was tested using a physical model to qualitatively examine the form of the flow both across the weir and downstream from it. The degree to which air bubbles were entrained in the water was also tested, but not the question of evaluating the flux of gaseous exchanges between the air and the water.The system that was finally designed by EDF, in October 1994, was a metallic weir with two consecutive falls, the configuration of which respected the main physical criteria that play a significant role in the oxygenation of water, i.e.:- the height of the falls (roughly 5.40 m, depending on the flow rate);- the thickness of the water stream, the function of which is to entrain air bubbles and keep them in the water for a sufficiently long period of time for the oxygen to dissolve (between 12 and 25 seconds, depending on the flow rate); - the dimensions of the receiving basin of the first waterfall where the air bubbles are held (5 hexagonal alveoli); and- systems to promote the fragmentation of the flow. This structure was placed in the tailrace channel of the plant, approximately 100 m downstream from the main dam. This location protected it from floods and did not create an extra obstacle in the river. In addition, it allowed the water to be re-oxygenated as soon as it left the reservoir.The efficiency of the two waterfalls of the Petit Saut re-aerating weir was tested at two different turbine flow rates: 80 m3 /s and 230 m3 /s. In 1996, the results of the measurements showed that for a flow rate of 230 m3 /s, upstream of the weir the concentrations of CH4 were around 5 mg/L and dissolved oxygen was 0.8 mg/L. Downstream from the weir CH4 concentrations were 1.3 mg/L and dissolved oxygen concentrations were 6.8 mg/L. The dissolved methane elimination rate was approximately 75 per cent. At a flow rate of 80 m3/s, upstream of the weir the concentration of CH4 was 5.5 mg/L and the dissolved oxygen concentration was 0.7 mg/L. Downstream from the weir concentrations of CH4 and dissolved oxygen were 1.0 mg/L and 7.1 mg/L, respectively. The dissolved methane elimination rate was around 80%. The efficiency of the re-oxygenation was always greater than 90%. These data prove that the efficiency of the Petit Saut weir installation was higher when the turbine flow rate was lower. This could be due to a greater waterfall height, the better entrainment of air bubbles per unit volume and/or a longer air bubble residence time in the downstream flow.Between December 2001 and February 2003, for a flow rate of 200 m3 /s, the efficiency of the weir decreased by 10%, with the dissolved methane elimination rate at around 70-75%. The level of re-oxygenation was around 80%. Since February 2003, for a flow rate of 100 m3 /s, the efficiency of the weir has decreased by 10%, the dissolved methane elimination rate was around 70% and the level of re-oxygenation was around 75%.On a local scale, the effect on the quality of the river water has been very positive, as aquatic life has been maintained. Without the weir, the methane contained in the turbined water would have been progressively transformed, along the course of the river, into carbon dioxide. In the absence of significant additions of good quality water and without the weir, a large part of the course of the river would have a dissolved oxygen content of less than 2 mg/L, the critical threshold for the maintenance of aquatic life.At present time, the results of the current ecological survey are used to support studies on biogeochemical processes

Linear modal instabilities of hypersonic flow over an elliptic cone

Steady laminar flow over a rounded-tip 2 : 1 elliptic cone of 0.86 m length at zero angle of attack and yaw has been computed at Mach number 7.45 and unit Reynolds number Re′ = 1.015 × 107 m−1. The flow conditions are selected to match the planned flight of the Hypersonic Flight Research Experimentation HIFiRE-5 test geometry at an altitude of 21.8 km. Spatial linear BiGlobal modal instability analysis of this flow has been performed at selected streamwise locations on planes normal to the cone symmetry axis, resolving the entire flow domain in a coupled manner while exploiting flow symmetries. Four amplified classes of linear eigenmodes have been unravelled. The shear layer formed near the cone minor-axis centreline gives rise to amplified symmetric and antisymmetric centreline instability modes, classified as shear-layer instabilities. At the attachment line formed along the major axis of the cone, both symmetric and antisymmetric instabilities are also discovered and identified as boundary-layer second Mack modes. In both cases of centreline and attachment-line modes, symmetric instabilities are found to be more unstable than their antisymmetric counterparts. Furthermore, spatial BiGlobal analysis is used for the first time to resolve oblique second modes and cross-flow instabilities in the boundary layer between the major- and minor-axis meridians. Contrary to predictions for the incompressible regime for swept infinite wing flow, the cross-flow instabilities are not found to be linked to the attachment-line instabilities. In fact, cross-flow modes peak along most of the surface of the cone, but vanish towards the attachment line. On the other hand, the leading oblique second modes peak near the leading edge and their associated frequencies are in the range of the attachment-line instability frequencies. Consequently, the attachment-line instabilities are observed to be related to oblique second modes at the major-axis meridian. The linear amplification of centreline and attachment-line instability modes is found to be strong enough to lead to laminar–turbulent flow transition within the length of the test object. The predictions of global linear theory are compared with those of local instability analysis, also performed here under the assumption of locally parallel flow, where use of this assumption is permissible. Fair agreement is obtained for symmetric centreline and symmetric attachment-line modes, while for all other classes of linear disturbances use of the proposed global analysis methodology is warranted for accurate linear instability predictions

Time--Splitting Schemes and Measure Source Terms for a Quasilinear Relaxing System

Several singular limits are investigated in the context of a $2 \times 2$ system arising for instance in the modeling of chromatographic processes. In particular, we focus on the case where the relaxation term and a $L^2$ projection operator are concentrated on a discrete lattice by means of Dirac measures. This formulation allows to study more easily some time-splitting numerical schemes

An Asymptotic Preserving Scheme for the Euler equations in a strong magnetic field

This paper is concerned with the numerical approximation of the isothermal Euler equations for charged particles subject to the Lorentz force. When the magnetic field is large, the so-called drift-fluid approximation is obtained. In this limit, the parallel motion relative to the magnetic field direction splits from perpendicular motion and is given implicitly by the constraint of zero total force along the magnetic field lines. In this paper, we provide a well-posed elliptic equation for the parallel velocity which in turn allows us to construct an Asymptotic-Preserving (AP) scheme for the Euler-Lorentz system. This scheme gives rise to both a consistent approximation of the Euler-Lorentz model when epsilon is finite and a consistent approximation of the drift limit when epsilon tends to 0. Above all, it does not require any constraint on the space and time steps related to the small value of epsilon. Numerical results are presented, which confirm the AP character of the scheme and its Asymptotic Stability

CRITICAL SPEED AND CRITICAL STROKE RATE COULD BE USEFUL PHYSIOLOGICAL AND TECHNICAL CRITERIA FOR COACHES TO MONITOR ENDURANCE PERFORMANCE IN COMPETITIVE SWIMMERS

The purposes of this study were to determine whether the concepts of critical swimming speed (CSS) and critical stroke rate (CSR) could be reliable and used by coaches in order to control and monitor endurance performance in competitive swimmers. The results of this study conducted with well-trained swimmers showed that CSS could be determined easily from two common distances and more accurately from 200- and 400-m tests after a correction of minus 1.4 %. Moreover, CSS was well correlated with swimming velocity corresponding to 4 mmol.l-1 of blood lactate concentration and could avoid using lactate testing. Furthermore, the concept of a critical stroke rate defined as ‘the stroke rate value, which can be theoretically maintained continuously indefinitely without exhaustion’ and expressed, as the slope of the regression line between the number of stroke cycles and time seemed to be reliable. Coaches, in order to set not only aerobic training loads but also to control swimming technique, could easily use CSS and CSR