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ABSTRACT Anthropogenic reshaping of landscapes can increase landslide activity. One example of heavily modified, landslide-prone landscapes is the Appalachian region, which hosts weak geologic strata, steep slopes, a humid climate, geologically recent river incision, and large-scale landscape modifications resulting from surface mining. Surface mining conducted before the Surface Mine Control and Reclamation Act (SMCRA) of 1977 did not require reclamation to approximate original contour, so remnant highwalls and mine benches are common throughout Appalachia. This study investigated the occurrence of slope instability and failure beneath pre-law mine benches in the northern coalfields of West Virginia. Mine bench features were manually digitized based on interpretation of high-spatial-resolution digital terrain data and aerial orthophotography, and ancillary geospatial data (i.e., mine permit boundary and disturbance extent data sets). A subset of mine bench features, stratified by coal seam, was randomly selected for slope stability analysis. The lower margins of the randomly selected mine benches were differentiated into segments with and without evidence of slope failure or instability. Results suggest that local topographic slope and aspect were not strong determinants of slope instability beneath mine benches. However, the coal seam or unit that was mined was an important determining factor. The Pittsburgh seam, and to a lesser extent the Redstone seam, had a larger proportion of their lower margins showing evidence of slope failure than did other seams. This study highlights that local-scale geology controls the geomorphic response to human landscape modifications and suggests that proactive reclamation of surface coal mines might reduce slope-failure geohazards. 

Abstract We propose and unify classes of different models for information propagation over graphs. In a first class, propagation is modelled as a wave, which emanates from a set ofknownnodes at an initial time, to all otherunknownnodes at later times with an ordering determined by the arrival time of the information wave front. A second class of models is based on the notion of a travel time along paths between nodes. The time of information propagation from an initialknownset of nodes to a node is defined as the minimum of a generalised travel time over subsets of all admissible paths. A final class is given by imposing a local equation of an eikonal form at eachunknownnode, with boundary conditions at theknownnodes. The solution value of the local equation at a node is coupled to those of neighbouring nodes with lower values. We provide precise formulations of the model classes and prove equivalences between them. Finally, we apply the front propagation models on graphs to semi-supervised learning via label propagation and information propagation on trust networks. 

Abstract BackgroundThe increasing size, severity, and frequency of wildfires is one of the most rapid ways climate warming could alter the structure and function of high-latitude ecosystems. Historically, boreal forests in western North America had fire return intervals (FRI) of 70–130 years, but shortened FRIs are becoming increasingly common under extreme weather conditions. Here, we quantified pre-fire and post-fire C pools and C losses and assessed post-fire seedling regeneration in long (> 70 years), intermediate (30–70 years), and short (< 30 years) FRIs, and triple (three fires in < 70 years) burns. As boreal forests store a significant portion of the global terrestrial carbon (C) pool, understanding the impacts of shortened FRIs on these ecosystems is critical for predicting the global C balance and feedbacks to climate. ResultsUsing a spatially extensive dataset of 555 plots from 31 separate fires in Interior Alaska, our study demonstrates that shortened FRIs decrease the C storage capacity of boreal forests through loss of legacy C and regeneration failure. Total wildfire C emissions were similar among FRI classes, ranging from 2.5 to 3.5 kg C m⁻². However, shortened FRIs lost proportionally more of their pre-fire C pools, resulting in substantially lower post-fire C pools than long FRIs. Shortened FRIs also resulted in the combustion of legacy C, defined as C that escaped combustion in one or more previous fires. We found that post-fire successional trajectories were impacted by FRI, with ~ 65% of short FRIs and triple burns experiencing regeneration failure. ConclusionsOur study highlights the structural and functional vulnerability of boreal forests to increasing fire frequency. Shortened FRIs and the combustion of legacy C can shift boreal ecosystems from a net C sink or neutral to a net C source to the atmosphere and increase the risk of transitions to non-forested states. These changes could have profound implications for the boreal C-climate feedback and underscore the need for adaptive management strategies that prioritize the structural and functional resilience of boreal forest ecosystems to expected increases in fire frequency. 

The interplay between electronic and lattice degrees of freedom in the insulator-to-metal transition (IMT) in rare-earth nickelates is a long-standing question. In the present work, broadband ultrafast transient reflectivity (TR) spectroscopy is applied to study the photoinduced IMT in ${\mathrm{NdNiO}}_3$. Both coherent and incoherent terms of the TR signal show discontinuous behavior around the same pump fluence value. A drastic drop in the sample reflectivity appearing at $\sim 100$fs timescale in the high excitation density regime indicates the closing of the gap across the IMT. In this regime, coherent phonons associated with the low-temperature crystal phase are not observed even at early time delays, indicating an ultrafast transformation of the lattice potential. A detailed analysis of the coherent phonons indicates a strong coupling between some phonon modes, electronic excitations, and possibly the magnetic order. In this study, we provide insights into the ultrafast dynamics of rare-earth nickelates. 

Abstract. The rain produced by thunderstorms has been observed to coincide spatially and temporally with enhanced near-surface concentrations of warm-temperature ice nucleating particles (INPs) of biological origin. However, the air in rainy regions is evaporatively cooled and negatively buoyant, and so it is unclear if it is entrained into its parent storms. Despite bioaerosols being highly ice-nucleation active, the microphysical influence that rain-aerosolized bioaerosols exert on storm processes is therefore not well-understood. We use the RAMS cloud-resolving model to simulate high-resolution archetypal representations of three deep convective storm morphologies: isolated deep convection, a squall line, and a supercell. We measure the degree of entrainment of rainy and non-rainy surface air into its parent storm using passive tracers, as well as calculating measures of each storm’s characteristics that influence the timing and degree of this entrainment. We find different degrees of entrainment between storm morphologies and between rainy and non-rainy surface air, with the squall line and supercell entraining significantly more rainy air than the isolated convective storm for all but the lightest rain. These differences owe to variation between the storms in their degrees of entrainment of surface air, their proportions of entrained surface air that originate in rainy regions, and their amount of rain produced per updraft mass. This study finds a specific and previously unrecognized source of air potentially containing highly ice-active aerosols which is entrained to varying degrees in different convective storm morphologies, and which is likely to exert different microphysical impacts on each type of storm.