Mass transport in gravity waves on a sloping bottom

Summary of the graduation work published at the ICCE: In the present investigation the influence of bottom slope on mass transport by progressive waves was investigated, both theoretically and experimentally. Theoretical considerations based on linear wave theory show the greatest influence of the slope on the bottom drift velocities for relatively long waves and steep slopes. The numerical values, however, remain rather small (influence less than 20%). In addition, the experiments show that the bottom drift velocities are more determined by the local parameters than by the magnitude of the bottom slope in the cases examined. Considering the net bottom velocities, the discrepancy between the horizontal bottom theory (Longuet-Higgins) and experimental results is considerable. Taking into account the first harmonic of the local wave form and the small slope effect for relatively small depths in horizontal bottom theory does show, however, the same tendency as the experimental results.Hydraulic EngineeringCivil Engineering and Geoscience

Mass transport in gravity waves on a sloping bottom

In the present investigation the influence of bottom slope on mass transport by progressive waves was investigated both theoretically and experimentally. Theoretical considerations based on lineair wave theory show the greatest influence of the slope on the bottom drift velocities for relatively long waves and steep slopes. The numerical values, however remain rather small (influence less than 20%). In addition the experiments show that. in the cases examined. the bottom drift velocities are more determined by the local parameters than by the magnitude of the bottom slope. Considering the net bottom velocities. the discrepancy between the horizontal bottom theory (Longuet - Higgins) and experimental results is considerable. Taking into account the first harmonic of the local wave form and the small slope effect in horizontal bottom theory does show however the same tendency as the experimental results for relatively small depths.Civil Engineering and Geoscience

Security at the End of the Tunnel: The Anatomy of VPN Mental Models Among Experts and Non-Experts in a Corporate Context

With the worldwide COVID-19 pandemic in 2020 and 2021 necessitating working from home, corporate Virtual Private Networks (VPNs) have become an important item securing the continued operation of companies around the globe. However, due to their different use case, corporate VPNs and how users interact with them differ from public VPNs, which are now commonly used by end-users. In this paper, we present a first explorative study of eleven experts' and seven non-experts' mental models in the context of corporate VPNs. We find a partial alignment of these models in the high-level technical understanding while diverging in important parameters of how, when, and why VPNs are being used. While, in general, experts have a deeper technical understanding of VPN technology, we also observe that even they sometimes hold false beliefs on security aspects of VPNs. In summary, we show that the mental models of corporate VPNs differ from those for related security technology, e.g., HTTPS. Our findings allow us to draft recommendations for practitioners to encourage a secure use of VPN technology (through training interventions, better communication, and system design changes in terms of device management). Furthermore, we identify avenues for future research, e.g., into experts' knowledge and balancing privacy and security between system operators and users.Information and Communication Technolog

Bumblebees land rapidly and robustly using a sophisticated modular flight control strategy

When approaching a landing surface, many flying animals use visual feedback to control their landing. Here, we studied how foraging bumblebees (Bombus terrestris) use radial optic expansion cues to control in-flight decelerations during landing. By analyzing the flight dynamics of 4,672 landing maneuvers, we showed that landing bumblebees exhibit a series of deceleration bouts, unlike landing honeybees that continuously decelerate. During each bout, the bumblebee keeps its relative rate of optical expansion constant, and from one bout to the next, the bumblebee tends to shift to a higher, constant relative rate of expansion. This modular landing strategy is relatively fast compared to the strategy described for honeybees and results in approach dynamics that is strikingly similar to that of pigeons and hummingbirds. The here discovered modular landing strategy of bumblebees helps explaining why these important pollinators in nature and horticulture can forage effectively in challenging conditions; moreover, it has potential for bio-inspired landing strategies in flying robots.OLD Production & DeliveryControl & Simulatio

Sensitivity of dose-volume indices to computation settings in high-dose-rate prostate brachytherapy treatment plan evaluation

Purpose: To investigate the variation in computed dose-volume (DV) indices for high-dose-rate (HDR) prostate brachytherapy that can result from typical differences in computation settings in treatment planning systems (TPSs). Methods: Five factors were taken into account: number of dose-calculation points, radioactive source description, interpolation between delineated contours, intersections between delineated organ contours, and organ shape at the top and bottom contour using either full or partial slice thickness. Using in-house developed software, the DV indices of the treatment plans of 26 patients were calculated with different settings, and compared to a baseline setting that closely followed the default settings of the TPS used in our medical center. Studied organs were prostate and seminal vesicles, denoted as targets, and bladder, rectum, and urethra, denoted as organs at risk (OARs), which were delineated on MRI scans with a 3.3 mm slice thickness. Results: When sampling a fixed number of points in each organ, in order to achieve a width of the 95% confidence interval over all patients of the DV indices of 1% or less, only 32,000 points had to be sampled per target, but 256,000 points had to be sampled per OAR. For the remaining factors, DV indices changed up to 0.4% for rectum, 1.3% for urethra, and 2.6% for prostate. DV indices of the bladder changed especially if the high-dose-region was (partly) located at the most caudal contour, up to 8.5%, and DV indices of the vesicles changed especially if there were few delineated contours, up to 9.8%, both due to the use of full slice thickness for the top and bottom contour. Conclusions: The values of DV indices used in prostate HDR brachytherapy treatment planning are influenced by the computation settings in a TPS, especially at the most caudal part of the bladder, as well as in the seminal vesicles.Algorithmic