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A dynamic landslide model for early warnings in Colombia's roads
Get PDFLandslides pose a critical threat to Colombia’s Andean region, where steep topography and intense rainfall events frequently disrupt road infrastructure. Although data-driven models are widely used for landslide susceptibility, they often focus on static conditioning factors without fully capturing the temporal dimension essential for early warning. Integrating space and time into a single model remains challenging due to data heterogeneity, incomplete inventories, and the complexity of rainfall triggers. In this study, we address these gaps by developing a space-time data-driven landslide model tailored for an Early Warning System (EWS) that targets roadblocks.We address this challenge by combining multiple landslide inventories, satellite rainfall estimates (CHIRPS), and 15-day ensemble rainfall forecasts (CHIRPS-GEFS), the project aims to provide forecasted landslide probabilities. The workflow is structured into three phases. First, a landslide inventory is compiled by harmonizing multiple datasets—each varying in quality, completeness, and spatial-temporal granularity. We address inconsistencies across institutional, academic, and regional inventories to derive a consolidated database of over 17,000 rainfall-induced landslides. Second, with this inventory, we extract data on static and dynamic predictors such as slope steepness, geology, land cover, and rainfall. Using generalized additive models (GAMs), we estimate daily landslide probabilities at a spatial resolution suitable for critical road segments. We compare short-term (1–3 days) to medium-term (up to 15 days) forecasting accuracy to assess model performance. Third, results are translated into spatial dynamic probability thresholds. These thresholds are designed to alert authorities about imminent or escalating risks of landslide-induced roadblocks.Preliminary tests indicate that this type of space-time model is particularly suitable for integrating forecast-based rainfall data and testing multi-day lead times. The final outcome is a prototype EWS component where probabilistic landslide alerts are updated daily, contributing to risk-informed decision-making for road infrastructure management in Colombia. This contribution discusses the methods, preliminary results, and future steps
Ultrasound-based Velocity Vector Imaging in the Carotid Bifurcation:Repeatability and an In Vivo Comparison With 4-D Flow MRI
Get PDFObjective: Ultrasound-based velocity vector imaging (US-VVI) is a promising technique to gain insight into complex blood flow patterns that play an important role in atherosclerosis. However, in vivo validation of the 2-D velocity vector fields in the carotid bifurcation, using an adaptive velocity compounding method, is lacking. Its performance was validated in vivo against 4-D flow magnetic resonance imaging (MRI). Furthermore, the repeatability of US-VVI was determined.Methods: High frame rate US-VVI, which was repeated three times, and 4-D flow MRI data were acquired of the carotid bifurcation of 20 healthy volunteers. A semiautomatic registration of all US-VVI (n = 60) and 4-D flow MRI data was performed. The 2-D velocity vector fields were compared using cosine similarity and the root-mean-square error of the velocity magnitude. Temporal velocity profiles from the common carotid artery and internal carotid artery were compared. The interobserver and intraobserver agreement of US-VVI was determined for peak systolic velocities and end-diastolic velocities.Results: The registration was successful in 83% of cases. The 2-D velocity vector fields matched well between modalities, which is supported by high cosine similarities and low root-mean-square error of the velocity magnitudes. Temporal profiles showed high resemblance, with similarity indices of 0.87 and 0.80, and mean peak systolic velocity differences of 0.91 and 7.9 cm/s in the common carotid artery and internal carotid artery, respectively. Good repeatability of US-VVI was shown with a highest bias and standard deviation of 1.7 and 11.7 cm/s, respectively.Conclusion: Good agreements were found of both vector angles and velocity magnitudes between US-VVI and 4-D flow MRI. Given the high spatiotemporal resolution, US-VVI enables the capture of small recirculating regions of short duration that are missed by 4-D flow MRI.</p
Unifying Theory of Scaling in Drop Impact:Forces and Maximum Spreading Diameter
Get PDFThe dynamics of drop impact on a rigid surface strongly depends on the droplet's velocity, its size, and its material properties. The main characteristics are the droplet's force exerted on the surface and its maximal spreading radius. The crucial question is how do they depend on the (dimensionless) control parameters, which are the Weber number We (nondimensionalized kinetic energy) and the Ohnesorge number Oh (dimensionless viscosity). Here, we perform direct numerical simulations over the huge parameter range 1≤We≤103 and 10-3≤Oh≤102 and in particular develop a unifying theoretical approach, which is inspired by the Grossmann-Lohse theory for wall-bounded turbulence [Grossmann and Lohse, J. Fluid Mech. 407, 27 (2000)JFLSA70022-112010.1017/S0022112099007545; Phys. Rev. Lett. 86, 3316 (2001)PRLTAO0031-900710.1103/PhysRevLett.86.3316]. The key idea is to split the energy dissipation rate into the different phases of the impact process, in which different physical mechanisms dominate. The theory can consistently and quantitatively account for the We and Oh dependences of the maximal impact force and the maximal spreading diameter over the huge parameter space. It also clarifies why viscous dissipation plays a significant role during impact, even for low-viscosity droplets (low Oh), in contrast to what had been assumed in some prior theories.</p
The role of digital mobility skills in the uptake of shared modes at mobility hubs
Get PDFThe popularity of shared mobility services (such as bike or e-scooter sharing) and mobility hubs is increasing in cities worldwide, with the potential to improve accessibility for all. With the expanding role of shared mobility, travellers must rely on smartphones that are typically needed to use them, and not having the ability to use a smartphone could lead to digital inequality. However, the impact of digital mobility skills on the uptake of shared mobility has hardly been studied. This paper examines the determinants of digital mobility skills and their impacts on the uptake of different forms of shared mobility at mobility hubs. The results of a large-scale survey (N = 2515) across four different cities in Europe were analysed using statistical analyses, showing that lower digital mobility skills are related to other vulnerable-to-exclusion characteristics such as higher age, lower educational level, and unemployment. Furthermore, the uptake of shared modes at mobility hubs is much lower for people with low digital mobility skills, as they face additional barriers to using these services. These results reveal how the growth of app-driven shared mobility services can increase accessibility inequalities
A Comparative Analysis of Early Departure Buttons in Coordinated Control of EV Charging
Get PDFThe increasing adoption of electric vehicles (EVs) necessitates the efficient management of large EV parking facilities to prevent them from exceeding grid capacity and to improve the overall user experience. This paper introduces a data-driven approach for coordinated control of EV charging in an office parking facility, integrating Early Departure Buttons (EDB) into the system. These buttons provide a binary option for users to indicate an earlier departure than a predefined time. We employ the EDB data to improve departure time estimations and to address issues where EVs receive no or only very low energy. We utilize three datasets originating from different geographical locations. One dataset displays a user pattern where users leave shortly after completing their charging, unlike the other datasets which follow typical working hours. Our simulations show that the unique user pattern significantly increases fairness among users, and integrating EDBs improves fairness for the other datasets to levels similar to those of quick station turnover.</p
Iterative deconvolution of acoustic source maps:Accuracy, speed and extension to the third dimension
Get PDFThe presented research aims to advance iterative deconvolution methods for aeronautical testing in wind tunnels, a crucial tool for the evaluation of aeroacoustic performance of new aircraft concepts or components. The investigation focuses on acoustic imaging techniques and addresses signal distortion, deconvolution methods, and source location algorithms.A comparison between the exact solution and the approximate ray solution for sound transmission through shear layers, reveals that uncertainties are negligible in most common situations. A random phase screen approach was used to model signal distortions in relation to time delay statistics, furthermore establishing a relation between scattering frequency and wave orientation. This approach was validated through wind tunnel noise measurements, demonstrating high accuracy.The acoustic deconvolution problem was analysed, and splitting methods were generally found to be robust solvers, neither amplifying nor attenuating the singular components. However, accidentally introduced high spatial frequency singular components are retained in the converged solution. The simultaneous JOR and randomised ART relaxation schemes result in minimal distortion and introduction of singular components in the solution .A highly efficient deconvolution algorithm, MAID, was developed, that employs acceleration methods based on multilevel matrix multiplication, solution of an equivalent problem, and domain truncation. Using the principles of computed tomography, a three-dimensional acoustic source location algorithm, ALTRE, was developed, which was successfully demonstrated through validation with both synthetic and experimental data sets.In conclusion, significant contributions were made in the assessment of aeroacoustic measurement uncertainties and the developed deconvolution algorithms. MAID and ALTRE, offer improved capabilities for noise assessment and source location in wind tunnels.<br/
FORCETRACKER:A versatile tool for standardized assessment of tissue contractile properties in 3D Heart-on-Chip platforms
Get PDFEngineered heart tissues (EHTs) have shown great potential in recapitulating tissue organization, functions, and cell-cell interactions of the human heart in vitro. Currently, multiple EHT platforms are used by both industry and academia for different applications, such as drug discovery, disease modelling, and fundamental research. The tissues’ contractile force, one of the main hallmarks of tissue function and maturation level of cardiomyocytes, can be read out from EHT platforms by optically tracking the movement of elastic pillars induced by the contractile tissues. However, existing optical tracking algorithms which focus on calculating the contractile force are customized and platform-specific, often not available to the broad research community, and thus hamper head-to-head comparison of the model output. Therefore, there is the need for robust, standardized and platform-independent software for tissues’ force assessment. To meet this need, we developed ForceTracker: a standalone and computationally efficient software for analyzing contractile properties of tissues in different EHT platforms. The software uses a shape-detection algorithm to single out and track the movement of pillars’ tips for the most common shapes of EHT platforms. In this way, we can obtain information about tissues’ contractile performance. ForceTracker is coded in Python and uses a multi-threading approach for time-efficient analysis of large data sets in multiple formats. The software efficiency to analyze circular and rectangular pillar shapes is successfully tested by analyzing different format videos from two EHT platforms, developed by different research groups. We demonstrate robust and reproducible performance of the software in the analysis of tissues over time and in various conditions. ForceTracker’s detection and tracking shows low sensitivity to common incidental defects, such as alteration of tissue shape or air bubbles. Detection accuracy is determined via comparison with manual measurements using the software ImageJ. We developed ForceTracker as a tool for standardized analysis of contractile performance in EHT platforms to facilitate research on disease modeling and drug discovery in academia and industry.</p
Interfacial hydrogen evolution reaction from Ouzo-effect-generated bulk nano/micro droplets of liquid organic hydrogen carriers
Get PDFHypothesis: Organosilanes as liquid organic hydrogen carriers (LOHCs) offer a promising solution for the safe storage and transport of hydrogen gas as a clean energy source. However, the dehydrogenation reaction of organosilanes in the presence of water faces the challenge of sluggish kinetics in conventional bulk reactions. Dispersing organosilanes as stable nanodroplets in basic water offers a potential strategy to increase the interfacial area, thereby enhancing H2 production efficiency. Experiments: Organosilane nanodroplets were generated through spontaneous emulsification via the Ouzo effect in a ternary organosilane-water-acetone system. The reaction between the organosilane nano/microdroplets and the alkaline aqueous phase led to H2 generation. This study investigates how the composition and size distribution of these droplets influence H2 production yield. To gain deeper insight into the reaction mechanisms, single reacting microdroplets were analyzed using side-view imaging and confocal microscopy. Findings: Organosilane nano/microdroplets formed from the Ouzo effect in the presence of a co-solvent. H2 formation yields from interfacial reactions of these droplets reached up to 25%, whereas single reacting microdroplets achieved a maximum yield of 3.5%. This study demonstrates that spontaneous emulsification in ternary mixture using the Ouzo effect can enhance reaction kinetics and product yields. Furthermore, detailed insights into the behavior of H2 bubbles, from their nucleation within a microdroplet to their growth and eventual detachment, were obtained through the analysis of single reacting microdroplets.</p