The Scheldt estuary revisited: occurrence and behaviour of particulate polychlorinated biphenyls and polycyclic aromatic hydrocarbons

Temporal and spatial variations in particulate PolyChlorinated Biphenyl (PCB) and Polycyclic Aromatic Hydrocarbons (PAH) concentrations were studied in the Scheldt estuary during a one-year period (May 1995-June 1996). This sampling campaign was arecurrence of a campaign held almost a decade ago. Both PCB and PAH concentrations in the Scheldt river were substantially lower in the 90's, but the Scheldt is still one of the most severely polluted rivers in the North Sea area. The annual input into the estuary was approximately 40 kg for total PCBs (sum of 8 congeners) and 3300 kg for total PAHs (19 compounds). The fraction transported to the North Sea is relatively small: 10-20 %.In the most recent sampling campaign the behaviour of particulate PCBs and PAHs found earlier was confirmed: as a result of the mixing of riverine with marine particulates the concentrations of the micropollutants generally decrease with increasing salinities, The quicker restoration of dissolved oxygen in the upper estuary gave rise to a more intense degradation of organic matter, and, probably as a result of cometabolism, degradation of low molecuiar weight PAH. Typical calculated half lives were 260 days for pyrene and 390 for fluoranthene

Analysis, Test and Simulation of Landing System Touchdown Dynamics

Future exploration missions pose demanding requirements towards the access by vehicles to scientifically interesting sites on planetary surfaces. These stem particularly from the need of more flexibility in site selection, improved payload to vehicle mass ratios and higher mission success probabilities. The Landing Technology group of the DLR Institute of Space Systems is focusing on the development and verification of experimental and analytical methods for the investigation of the touchdown dynamics of landing system, its capabilities the embedding into the landing site assessment. Core element for the experimental investigation is the Landing & Mobility Test Facility (LAMA), which allows touchdown testing under Earth gravity and under a reduced gravitational environment using an active off-loading device. The test article for investigation of legged landing systems is a modular Lander Engineering Model (LEM) designed by the Astrium ST (Bremen), representing today's European mission scenarios to the Moon and Mars such as the ESA Lunar Lander or the ESA Mars Precision Lander. Another test object recently under retesting is the Rosetta lander Philae representing a touch down system concept developed for small body landings. Usually not all relevant environmental properties of the target landing site can be provided in one single and complete test, any verification approach has to be supported by adequate numerical analyses. Thus, another key topic for the verification of the touchdown performance of a landing system is the accurate analytical and numerical representation of the flight system, its touchdown conditions and the landing site. In this area the research focuses on the development of high fidelity engineering simulations of the vehicle-to-terrain/soil interaction. The landing site characterization and assessment focuses on the development of landing site assessment methods and tools and to provide terrain models for engineering simulations (both touchdown dynamics and/or hazard detection& avoidance simulations). In return landing system performance limits are mapped onto cartographic landing site representations to support the landing safety assessment. This poster outlines the test facility, simulation and analysis tools developed by the working group and used in recent landing missions

DEVELOPMENT OF A CLASSIFICATION SYSTEM ON ANKLE-JOINT STIFFNESS

AIM OF THE PROJECT Aim of the project is to develop a classification system for the ankle stiffness in sideward rotations of the fool. MOTIVATION In a previous study (1) a classification system for (running) shoes has been developed on the aspects stability and shock absorption based on a mechanical test protocol. If corresponding features can be quantified for the (lower) legs of the runner, running shoes can be more carefully selected. For example, a runner with less stiff ankles may need shoes which have high stabilizing properties, whereas runners with stable ankles may ask for (more) shock absorbency of their shoes. Consequently, classification systems may contribute to the reduction and /or prevention of running-related injuries. In the present project we have focused ourselves on the stiffness of the ankle. Method: An apparatus has been constructed to quantify the resistance of the foot against sideward rotations. The foot of a person to be tested in a sitting position is placed on a platform and fixed by a special technique. The lower leg is kept in vertical position by straps. The leg is allowed to rotate and translate to some extent around and along the vertical axis of the lower leg. By rotating the platform, the foot can be moved through plantar/dorsal flexion, abduction/adduction and inward/outward rotation. In the first two planes of motion discrete positions of the foot are prescribed while the inward/outward motion is imposed in a motor-driven way. The axes of rotation can be adjusted to individual differences. The axial load on the lower leg can be varied in discrete steps. In this project, the moment of force (M) as a function of rotation (Φ) is measured during inversion/aversion cycle in two positions of the foot, viz. neutral position (0 degrees flexion, 0 degrees adduction) and flexed position (20 degrees plantar flexion, 10 degrees adduction) without axial loading of the tibia. At present, the left ankles of a group of 14 volunteers without ankle complaints and 6 with ankle complaints are measured. Results and Discussion:Based on the specific and reproducible non-linear M- Φ relationship several parameters are deduced such as primary stiffness, mobility, and secondary stiffness for aversion and inversion. One of the results is that in both foot positions the primary stiffness shows to be linear related to the mobility ( a higher stiffness results in a lower mobility.) In the flexed position the primary stiffness is less than in neutral foot position. Using the primary stiffness results of the “sound” group in the flexed foot position a starting classification is made in terms of “stiff”, “neutral”, and “lax”. Depiction of the results of the “injured” ankles in this classification shows that most of these ankles belong to the “lax” category. Biomechanical and epidemiological studies are necessary to evaluate the ultimate effects of combinated foot/shoe classifications

The teaching practice of Building on MOSTs

This research report is based on work supported by the U.S. National Science Foundation (NSF) under Grant Nos. DRL-1720410, DRL-1720566, and DRL-1720613

The time course of exogenous and endogenous control of covert attention

Studies of eye-movements and manual response have established that rapid overt selection is largely exogenously driven toward salient stimuli, whereas slower selection is largely endogenously driven to relevant objects. We use the N2pc, an event-related potential index of covert attention, to demonstrate that this time course reflects an underlying pattern in the deployment of covert attention. We find that shifts of attention that occur soon after the onset of a visual search array are directed toward salient, task-irrelevant visual stimuli and are associated with slow responses to the target. In contrast, slower shifts are target-directed and are associated with fast responses. The time course of exogenous and endogenous control provides a framework in which some inconsistent results in the capture literature might be reconciled; capture may occur when attention is rapidly deployed

Salience-based selection: attentional capture by distractors less salient than the target

Current accounts of attentional capture predict the most salient stimulus to be invariably selected first. However, existing salience and visual search models assume noise in the map computation or selection process. Consequently, they predict the first selection to be stochastically dependent on salience, implying that attention could even be captured first by the second most salient (instead of the most salient) stimulus in the field. Yet, capture by less salient distractors has not been reported and salience-based selection accounts claim that the distractor has to be more salient in order to capture attention. We tested this prediction using an empirical and modeling approach of the visual search distractor paradigm. For the empirical part, we manipulated salience of target and distractor parametrically and measured reaction time interference when a distractor was present compared to absent. Reaction time interference was strongly correlated with distractor salience relative to the target. Moreover, even distractors less salient than the target captured attention, as measured by reaction time interference and oculomotor capture. In the modeling part, we simulated first selection in the distractor paradigm using behavioral measures of salience and considering the time course of selection including noise. We were able to replicate the result pattern we obtained in the empirical part. We conclude that each salience value follows a specific selection time distribution and attentional capture occurs when the selection time distributions of target and distractor overlap. Hence, selection is stochastic in nature and attentional capture occurs with a certain probability depending on relative salience