48 research outputs found
Does the topographic threshold concept explain the initiation points of sunken lanes in the European loess belt?
No full textSunken lanes or ‘road gullies’ are a common geomorphic feature in the European loess belt. These landforms are usually created by various processes over time (water erosion, mass movements and traffic). They are important for ecology and biodiversity, for recreation and transport, as well as from a hydrological and geomorphological perspective (e.g. by enhancing the runoff and sediment connectivity of the landscape). Nonetheless, little is known about their origin and evolution. The formation of sunken lanes is typically only understood in qualitative terms, while no studies so far have provided a quantitative analysis of their initiation conditions. To address this research gap and to improve our geomorphic understanding of this landform, we investigated to what extent sunken lanes can be treated and described as a gully erosion process. More specifically, we explored to what extent their position in the landscape and their characteristics can be explained by the topographic slope-area (SA) threshold that typically controls gully initiation: S=kA^b, with k and b empirical constants. Based on field surveys and LIDAR data analyses, we determined the slope gradient of the soil surface (S) and contributing area (A) for 132 representative sunken lane heads in the Belgian loess belt and collected data on several other characteristics (position of initiation and sedimentation points, width, depth and length of each sunken lane). Our results show a very large scatter on the S and A values. Moreover, the morphological characteristics of sunken lanes (e.g. width and length) showed no clear relation with these values. However, a very weak SA-threshold relation with a low b-exponent (-0.016) and a low k-coefficient (0.022) could be identified. Overall, our results show that the formation of sunken lanes is not in line with the topographic threshold conditions that govern the initiation of gullies across different environments. The low k-coefficient and the lack of a strong correlation between initiation slope and contributing area point towards an overall higher susceptibility to the formation of sunken lanes than the formation of gullies. This supports the conclusion that not only concentrated flow detachment and transport, but especially human activities (mainly traffic erosion) play a major role in the initiation and development of sunken lanes.sponsorship: S. De Geeter received a scholarship from the University of Liege. (University of Liege)status: Published onlin
Soil erosion and sediment yield in Africa: Processes and factors
No full textAfrica experiences diverse and often intense soil erosion processes, yet the interplay between these processes and observed sediment yield (SY) at catchment scales is insufficiently understood. Building on previous continental- scale assessments, this study integrates a newly verified database of measured SY at 425 river outlets with, model-based estimates of Rill and Sheet Erosion (RSE), Landslide Mobilization Rates (LMR), and Gully Head Susceptibility (GHS). Our approach addresses a key gap in earlier work, which primarily relied on environmental predictors without explicitly quantifying the contribution of multiple geomorphic processes. Our results indicate that the mean observed SY is 6.07 t center dot ha-1 center dot yr- 1, whereas modelled RSE and LMR average 9.42 t center dot ha- 1 center dot yr- 1 and 1.51 t center dot ha- 1 center dot yr- 1, respectively. Although direct estimates of gully erosion were not available, the moderate to strong correlations between SY and both LMR (r = 0.47) and GHS (r = 0.57) underscore the importance of gullies and landslides in delivering sediment to catchment outlets. In contrast, RSE shows a weaker relationship with measured SY, suggesting that traditional RUSLE-type models may substantially over- or underestimate total sediment yield if they neglect gully erosion, landslides, and in-channel deposition processes. This study contributes novel insights into continental-scale sediment dynamics by explicitly linking observed SY to distinct geomorphic processes. Our findings highlight the need for integrated modeling frameworks that account for rill and sheet erosion, landslides, and gully erosion in order to enhance the accuracy of sediment yield predictions. Such approaches are vital for guiding land management and soil conservation strategies across Africa's diverse biophysical and climatic regions
Implementing radiation hardened sensors for computer aided teleoperation in a nuclear environment
No full textA comparison of decision making criteria and optimization methods for active robotic sensing
No full textThis work presents a comparison of decision making criteria and optimization methods for active sensing in robotics. Active sensing incorporates the following aspects: (i ) where to position sensors, and (ii ) how to make decisions for next actions, in order to maximize information gain and minimize costs. We concentrate on the second aspect: “Where should the robot move at the next time step?”. Pros and cons of the most often used statistical decision making strategies are discussed. Simulation results from a new multisine approach for active sensing of a nonholonomic mobile robot are given
When Beauty Hides a Beast
No full textWe present a 43-year old female patient, admitted to the intensive care unit, recovering from a Bentall procedure because of a supra-coronary aneurysm and unicuspid aortic valve. Few hours following surgery,a marked lactic acidosis, hypoxemia and increased central venous pressure developed. Pulmonary angio-CT was performed to exclude pulmonary embolism. Because of severe peripheral vasoconstriction, iodine contrast could only be administered through a narrow lumen central venous catheter, which limited the maximum flow rate to 1.5 ml/s. Images were performed with triggering in the pulmonary trunk. Review of the images showed no evidence for pulmonary embolism. Despite the low flow rate, a clear enhancement of the pulmonary artery was observed (up to 460 HU) (Fig. 1). Such an enhancement of the pulmonary artery is normally only achieved when injecting contrast at a flow rate of 4-5 ml/s. These perfect images, obtained at a low contrast flow rate in fact indicate severely impaired right ventricular function
BMIPP imaging to assess functional outcome in patients with acute and chronic left ventricular dysfunction
No full textAssessment of myocardial viability is an important clinical issue for patient management during the acute and chronic stages of myocardial infarction. BMIPP (15-(p-iodophenyl)-3-(R,S)-methyl pentadecanoic acid) is a free fatty acid analogue which is trapped in the myocardium, thus permitting for metabolic imaging with single photon emission computerized tomography (SPECT). Less BMIPP than flow tracers that may be observed in the areas of infarction, may reflect the metabolic shift from fatty acid to glucose utilization in ischaemic myocardium. In this sense, the combined imaging of BMIPP and a flow tracer with SPECT may provide similar and important information as fluoro-18 deoxyglucose (FDG) and positron emission tomography (PET) regarding the assessment of myocardial viability. The purpose of this article is to review the clinical impact of BMIPP in patients with acute and with chronic left ventricular dysfunction for the identification of jeopardized but viable myocardium and the prediction of the functional outcome.SCOPUS: re.jinfo:eu-repo/semantics/publishe
Active sensing of a nonholonomic wheeled mobile robot
No full textThis paper focuses on active sensing of nonholonomic wheeled mobile robots (WMRs). Active sensing solves the following problem: given a current knowledge about the robot state and the environment, how to select the next sensing action or sequence of actions. A vehicle is moving autonomously through a static environment gathering information from sensors. The sensor data are used to generate the robot actions in order to move around a reference trajectory with preset initial starting and desired goal configurations and imposed constraints. The paper presents a method for the determination of optimal trajectories based on optimization techniques. A suitable performance criterion is formulated to characterize the uncertainty and the extraction of information from sensor data. Finally results from experiments are given
Pathologic features after radical perineal prostatectomy in potential candidates for active monitoring
No full textGated myocardial perfusion tomography versus gated blood pool tomography for the calculation of left ventricular volumes and ejection fraction
No full textLeft ventricular (LV) volume, and not only ejection fraction (EF), is a crucial parameter for assessing the severity of cardiac disease and determining the patient's prognosis. The purpose of this study was to compare LV volumes and EF computed automatically from gated blood pool tomography (gBPT), using QUBE, and from gated myocardial perfusion tomography (gMPT), using QGS, in the same patients with a known history of myocardial infarction. The effects of the extent and severity of the myocardial perfusion defects were investigated. Thirty-seven patients were injected in a random sequence with 740 MBq of technetium-99m human serum albumin and 925 MBq of Tc-99m-tetrofosmin, within an interval of 2 days. gBPT and gMPT were acquired on the same triple-head gamma camera using the following acquisition parameters: 360degrees step-and shoot rotation, 32 stops (96 projections), 30 s per stop, 64x64 matrix (pixel size 5.8 mm), 8 time bins (75% forward/backward framing). Projection data were reconstructed by filtered back-projection using a Butterworth filter. LV volumes calculated from gBPT correlated well with LV volumes measured on gMPT (r=0.93 for end-diastolic volume and 0.95 for end-systolic volume). Volumes above 200 ml, however, were substantially higher with gMPT than with gBPT. These discrepancies were related to the severity, but not the extent, of the perfusion defects. There was also good agreement between gBPT and gMPT for the LVEF (r=0.91). On the Bland-Altman plot, no trend but a systematic error of 5.57% and a random error of 6.85% could be found. For the LVEF, the differences between the gated tomographic techniques were related neither to the extent nor to the severity of the perfusion defects. In conclusion, LV volumes and EF computed on gMPT correlated well with those measured on gBPT. Discrepancies were observed for large volumes presumably because of inaccuracies of gMPT in patients with severe perfusion defects
Tracking contact transitions during force-controlled compliant motion using an interacting multiple model estimator
No full textThis work concerns both monitoring of contact transitions and estimation of the unknown first-order geometric parameters during force-controlled motions. The robotic system is required to move an object among a sequence of contact configurations with the environment, under partial knowledge of geometric parameters (positions and orientations) of the manipulated objects and of the environment itself. An example of a compliant motion task with multiple contacts is considered, that of moving a cube into a corner. It is shown that by describing the contact configurations with different models, and by using the multiple model approach it is possible: i) to detect effectively at each moment the current contact configuration and ii) to estimate accurately the unknown parameters. The reciprocity constraints between ideal reaction forces and velocities are used as measurement equations. An Interacting Multiple Model (IMM) estimator is implemented and its performance is evaluated based on experimental data
