Controlling Droplet Marangoni Flows to Improve Microscopy-Based TB Diagnosis

In developing countries, the most common diagnostic method for tuberculosis (TB) is microscopic examination sputum smears. Current assessment requires time-intensive inspection across the microscope slide area, and this contributes to its poor diagnostic sensitivity of ≈50%. Spatially concentrating TB bacteria in a smaller area is one potential approach to improve visual detection and potentially increase sensitivity. We hypothesized that a combination of magnetic concentration and induced droplet Marangoni flow would spatially concentrate Mycobacterium tuberculosis on the slide surface by preferential deposition of beads and TB–bead complexes in the center of an evaporating droplet. To this end, slide substrate and droplet solvent thermal conductivities and solvent surface tension, variables known to impact microfluidic flow patterns in evaporating droplets, were varied to select the most appropriate slide surface coating. Optimization in a model system used goniometry, optical coherence tomography, and microscope images of the final deposition pattern to observe the droplet flows and maximize central deposition of 1 μm fluorescent polystyrene particles and 200 nm nanoparticles (NPs) in 2 μL droplets. Rain-X® polysiloxane glass coating was identified as the best substrate material, with a PBS-Tween droplet solvent. The use of smaller, 200 nm magnetic NPs instead of larger 1 μm beads allowed for bright field imaging of bacteria. Using these optimized components, we compared standard smear methods to the Marangoni-based spatial concentration system, which was paired with magnetic enrichment using iron oxide NPs, isolating M. bovis BCG (BCG) from samples containing 0 and 103 to 106 bacilli/mL. Compared to standard smear preparation, paired analysis demonstrated a combined volumetric and spatial sample enrichment of 100-fold. With further refinement, this magnetic/Marangoni flow concentration approach is expected to improve whole-pathogen microscopy-based diagnosis of TB and other infectious diseases.

Resolving pre-collapse slope motion at the February 2021 Chamoli rock-ice avalanche via feature tracking of optical satellite imagery

<p>On the 7<sup>th</sup> of February 2021, a large rock-ice avalanche triggered a debris flow in Chamoli district, Uttarakhand, India, resulting in over 200 dead or missing and widespread infrastructure damage. The rock-ice avalanche originated from a steep, glacierized north-facing slope with a history of instability, most recently a 2016 ice avalanche. In this work, we assess whether the slope exhibited any precursory displacement prior to collapse. We evaluate monthly slope motion over the 2015 and 2021 period through feature tracking of high-resolution optical satellite imagery from Sentinel-2 (10 m Ground Sampling Distance) and PlanetScope (3-4 m Ground Sampling Distance). Assessing slope displacement of the underlying rock is complicated by the presence of glaciers over a portion of the collapse area, which display surface displacements due to internal ice deformation. We overcome this through tracking the motion over ice-free portions of the slide area, and evaluating the spatial pattern of velocity changes in glaciated areas. Preliminary results show that the rock-ice avalanche bloc slipped over 10 m in the 5 years prior to collapse, with particularly rapid slip occurring in the summer of 2017 and 2018. These results provide insight into the precursory conditions of the deadly rock-ice avalanche, and highlight the potential of high-resolution optical satellite image feature tracking for monitoring the stability of high-risk slopes.</p>

Investigation and mitigation of a failure at the Taxiarches canal of Mornos aqueduct

The sudden soil fracture and failure at the Taxiarches canal of Mornos Aqueduct of the Athens Water Supply and Sewerage Company (EYDAP SA), took place approximately 540m after the exit of Elikonas tunnel and resulted in failure and displacement of the canal segments along an 80m long section. Due to the failure the water supply was interrupted and two extensive gullies, spaced 75m apart, were created by the water outflow. The water discharge resulted in subsoil erosion and transportation of vast masses of geomaterial and two of the canal segments downhill. The debris flow destroyed part of Prodromos-Saranti Road, swapping along olive cultivations and causing extensive damage to Saranti settlement. The failure of the canal occurred in an area of steep morphology, at the front of an overthrust, within tectonic breccia and calcareous-clayey material of chaotic structure and reduced mechanical properties, vulnerable to erosion. The boundaries of the main fracture were defined by the thrust geometry. Τhe study of permanent remedial measures included excavation of a cut in the natural slope on the uphill side of the failure, construction of a bypass pipe founded on bedrock and of an anchored pile wall with pre-stressed anchors on the downhill side of the new pipe, excavation and removal of the temporary fill and finally construction of a reinforced fill for rehabilitation of the slide area.

Stability and Reinforcement of Subgrade Slope of Weathered Rock Considering the Effect of Seepage

Taking the slope of K178+500-K178+550 of Beian-Heihe expressway as example, based on the steady saturated-unsaturated seepage theory and simplified the seepage force of groundwater into equivalent nodal load, then using the strength reduction finite element method to analysis the stability and potential slide area of roadbed slope which has no engineering measures; the interaction between slide-resistant pile and weathered rock can be reasonably considered by using the contact surface element, the result shows that, the safety factor of roadbed slope can be improved and the shearing strength of roadbed slope can be evenly dispersed by the reinforcement measure. The result can be used for the stability evaluation and reinforcement of subgrade slope of weathered rock area.