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•Current sonochemical methods using stochastic cavitation are inefficient.•Nanostructured photocatalyst as sonophotocatalyst for site-controlled cavitation.•Site-controlled cavitation ...activates sonophotocatalyst at lower acoustic pressures.•Reaction kinetics show model dye degradation 1000-fold faster than other methods.•Sonophotocatalyst demonstrates an efficient, sustainable avenue for sonochemistry.
Current sonochemical methods rely on spatially uncontrolled cavitation for radical species generation to promote chemical reactions. To improve radical generation, sonosensitizers have been demonstrated to be activated by cavitation-based light emission (sonoluminescence). Unfortunately, this process remains relatively inefficient compared to direct photocatalysis, due to the physical separation between cavitation event and sonosensitizing agent. In this study, we have synthesized nanostructured titanium dioxide particles to couple the source for cavitation within a photocatalytic site to create a sonophotocatalyst. In doing so, we demonstrate that site-controlled cavitation from the nanoparticles using pulsed ultrasound at reduced acoustic powers resulted in the sonochemical degradation methylene blue at rates nearly three orders of magnitude faster than other titanium dioxide-based nanoparticles by conventional methods. Sonochemical degradation was directly proportional to the measured cavitation produced by these sonophotocatalysts. Our work suggests that simple nanostructuring of current sonosensitizers to enable on-site cavitation greatly enhances sonochemical reaction rates.
The dynamics of debris flows are fundamentally governed by the interaction between the solid and fluid phases. However, current approaches used to estimate impact load treat debris flow as an ...equivalent fluid without considering solid–fluid interaction separately from other factors. In this study, a series of centrifuge tests was carried out to investigate the influence of interaction between solid and fluid phases on single-surge debris flow impact on a rigid barrier. The effect of solid–fluid interaction was studied by varying the solid fraction of the flows. A model rigid barrier was instrumented to capture induced bending moment and impact pressure. Test results demonstrate that the transition from a pile-up mechanism to a run-up mechanism is governed by the solid fraction and thus the grain contact stresses. The rigid barrier design for the impact with a pile-up mechanism is mainly dominated by the static load. Contrary to the hydrodynamic approach, which assumes that the frontal impact is the most critical, the frontal impact of a run-up mechanism contributes less than 25% of the total force impulse. The consideration of static loading leads to the development of a new impact model with a triangular distribution of the impact pressure.
Natural terrain landslides are mainly triggered by rainstorms in Hong Kong, which pose great threats to life and property. To mitigate landslide risk, building a prediction model which could provide ...information on both spatial and temporal probabilities of landslide occurrence is essential but challenging. In this paper, real-time rainfall conditions are incorporated into landslide prediction through a unique rainstorm-based database of reported landslides. Other landslide controlling factors related to topography, geology, and land cover are also considered. Five machine learning methods, including logistic regression, random forest, adaboost tree, support vector machine, and multilayer perceptron, are utilized and compared. Validated against historical rainstorms, the machine learning powered landslide prediction model could reasonably forecast the occurrence of landslides in a spatiotemporal context. Moreover, the effects of different rainstorm characteristics in terms of distinct rainfall spatial distribution and intensity on landslide susceptibility could also be captured by this model. For the landslide controlling factors investigated, rolling rainfall factors are proven to play a more important role than antecedent rainfall factors for landslide prediction. Among the five machine learning methods, the random forest model yields the most promising results in terms of all performance indicators (i.e., classification accuracy, recall, precision, area under curve, and overall accuracy).
Microbubbles used as contrast agents for ultrasound imaging, vectors for targeted drug delivery and vehicles for metabolic gas transport require better size control for improved performance. ...Mechanical agitation is the only method currently available to produce microbubbles in sufficient yields for biomedical applications, but the emulsions tend to be polydisperse. Herein, we describe a study to generate lipid-coated, perfluorobutane-filled microbubbles and isolate their size fractions based on migration in a centrifugal field. Polydispersity of the freshly sonicated suspension was characterized by particle sizing and counting through light obscuration/scattering and electrical impedance sensing, fluorescence and bright-field microscopy and flow cytometry. We found that the size distribution was multimodal. Smaller microbubbles were more abundant. Differential centrifugation was used to successfully isolate the 1–2 and 4–5 μm diameter fractions. Isolated microbubbles were stable over two days. After two weeks, however, more dilute suspensions (<1 vol%) were susceptible to Ostwald ripening. For example, 4–5 μm microbubbles disintegrated into 1–2 μm microbubbles. This latter observation indicated the existence of an optimally stable diameter in the 1–2 μm range for these lipid-coated microbubbles. Overall, differential centrifugation provided a rapid and robust means for size selection and reduced polydispersity of lipid-coated microbubbles.
Polydispersity of lipid-coated microbubbles produced by acoustic emulsification was measured. Differential centrifugation allowed isolation of select size subpopulations, which were stable for several days.
Microbubbles occur naturally in the oceans and are used in many industrial and biomedical applications. Here, a theoretical and experimental study was undertaken to determine the fate of a ...microbubble suddenly suspended in a medium with several gas species as in, for example, the injection of an ultrasound contrast agent into the bloodstream. The model expands on Epstein and Plesset’s analysis to include any number of gases. An experimental system was developed which isolates the microbubble in a permeable hollow fiber submerged in a perfusion chamber, allowing rapid exchange of the external aqueous medium. Experimental verification of the model was performed with individual sulfur hexafluoride (SF6) microbubbles coated with the soluble surfactant, sodium dodecyl sulfate (SDS). SDS-coated microbubbles suddenly placed in an air-saturated medium initially grew with the influx of O2 and N2 and then dissolved under Laplace pressure. SF6-filled microbubbles coated with the highly insoluble lipid, dibehenoylphosphatidylcholine, were found to exhibit significantly different behavior owing to a dynamic surface tension. The initial growth phase was diminished, possibly owing to a shell “breakup” tension that exceeded the pure gas/liquid surface tension. Three dissolution regimes were observed: (1) an initial rapid dissolution to the initial diameter followed by (2) steady dissolution with monolayer collapse and finally (3) stabilization below 10 μm diameter. Results indicated that the lipid shell becomes increasingly rigid as the microbubble dissolves, which has important implications on microbubble size distribution, stability, and acoustic properties.
Isoprene is a significant source of atmospheric organic aerosol; however, the oxidation pathways that lead to secondary organic aerosol (SOA) have remained elusive. Here, we identify the role of two ...key reactive intermediates, epoxydiols of isoprene (IEPOX = β-IEPOX + δ-IEPOX) and methacryloylperoxynitrate (MPAN), which are formed during isoprene oxidation under low- and high-NOx conditions, respectively. Isoprene low-NOx SOA is enhanced in the presence of acidified sulfate seed aerosol (mass yield 28.6%) over that in the presence of neutral aerosol (mass yield 1.3%). Increased uptake of IEPOX by acid-catalyzed particle-phase reactions is shown to explain this enhancement. Under high-NOx conditions, isoprene SOA formation occurs through oxidation of its second-generation product, MPAN. The similarity of the composition of SOA formed from the photooxidation of MPAN to that formed from isoprene and methacrolein demonstrates the role of MPAN in the formation of isoprene high-NOx SOA. Reactions of IEPOX and MPAN in the presence of anthropogenic pollutants (i.e., acidic aerosol produced from the oxidation of SO₂ and NO₂, respectively) could be a substantial source of "missing urban SOA" not included in current atmospheric models.
Structural countermeasures such as rigid and flexible barriers are commonly installed in mountainous regions to intercept mass-wasting processes. Without sufficient and reliable comparable physical ...data, the study of impact mechanisms remains difficult and not well understood. In this study, a newly developed flexible model barrier together with a rigid barrier are used to simulate either dry granular or viscous liquid impacts on these model barriers in a geotechnical centrifuge. The novel flexible barrier is made of four instrumented cables controlled by spring mechanisms to replicate a bilinear prototype loading response. Tests revealed that regardless of barrier type, both dry granular and viscous flows could have similar frontal dynamic impact coefficients around unity. Compared with the kinetic energy of flow mass (∼10 MJ), only 249 kJ of flexible barrier energy capacity was mobilized. This implies that debris-resisting barriers may only be required to intercept the dynamic flow front as the subsequent flow energy may mainly be dissipated through internal shearing. Attributing to the large deformation of the flexible barrier, the granular static load acting on the flexible barrier could be 39% lower than that on the rigid barrier, resulting in an active failure mode and a lower earth pressure.
Early warning systems have often been considered an effective risk mitigation tools for landslides. In 1977, the Geotechnical Engineering Office (GEO) of Hong Kong government established the world’s ...first territorial-wide early warning system for landslide disaster. The Landslip Warning System (LWS) has then been continuously enhanced and upgraded in response to the enrichment of rainfall and landslide database, advancement in instrumentation techniques and change in public perception of landslide risk over the last 40 years. This article consolidates the extensive experience of Hong Kong in using the landslip early warning system (LEWS) as a landslide risk management tool. A comprehensive review on the development process of the rainfall-landslide prediction models is presented. The landslide prediction model evolved from a rainfall duration-intensity model (late 1970) to a simple rainfall threshold model (middle 1980 to late 1990), then to a rainfall-landslide density model (early 2000) and rainfall-landslide frequency model (middle 2000s onward). Through regular review and update of the prediction model taking into account the availability of more recent data and activities that alter landslide risks, the performance of prediction model could be enhanced. The number of rain gauges expanded from 20 to 92 to support the operation of different generations of LWS. The GEO is currently adopting internet of thing (IOT) and cloud computing technology to enhance the resilience of the LWS, especially during extreme weather condition.
Landslide debris is a common occurrence in mountainous regions around the world that can potentially result in disastrous consequences to downstream facilities. Flow-impeding structures are often ...constructed along the flow path to impede this hazardous phenomenon. Baffles are a type of flow-impeding structure regularly installed using empirical and prescriptive design methods as the interaction mechanism and the influence of baffle configuration on flow impedance is not well understood. A series of flume experiments were carried out to investigate flows characterizing landslide debris impacting an array of baffles using dry uniform sand. The influence of baffle height, row number, and spacing between successive rows was examined. Photoconductive sensors were used to estimate flow velocity, laser sensors were installed to measure flow depth profiles, and high-speed cameras were used to capture flow kinematics. Experimental results reveal that baffles can be categorized relative to the approach flow depth (h) and increasing the baffle height from 0.75h to 1.5h leads to a 40% increase in upstream flow depths from backwater effects, more effective development of subcritical conditions, and additional energy losses of up to 9%. Increasing the number of rows of 1.5h baffles from a single row to a three-row staggered array results in up to 72% additional energy loss. The energy loss is attributed to the deflection of granular jets and additional backwater effects. Increasing the row spacing from 50 to 100 mm results in up to a 14% increase in energy loss.
Multiple debris-resisting barriers have been commonly used worldwide to mitigate debris flows in drainage lines. However, a well-developed methodology to assess the mobility of debris flows with ...consideration of the obstruction of the barriers does not exist. A free-field debris-flow condition that omits the presence of multiple debris-resisting barriers is commonly considered in design, although the effects of the barriers could be critical in determining the dynamics of the landslide debris including debris velocity and debris thickness. This paper proposes a staged debris mobility analysis that accounts for the effects of multiple debris-resisting barriers. The staged analysis adopts solutions of a depth-averaged debris mobility model. The input parameters of the analysis have been established from field data and laboratory test results. Rigorous numerical simulations of debris flows intercepted by multiple debris-resisting barriers have also been undertaken using the three-dimensional finite element program LS-DYNA to provide results for benchmarking the output of the staged analysis.
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