Predicting shallow landslide size and location across a natural landscape: Application of a spectral clustering search algorithm

Predicting shallow landslide size and location across landscapes is important for understanding landscape form and evolution and for hazard identification. We test a recently‐developed model that couples a search algorithm with 3D slope‐stability analysis that predicts these two key attributes in an intensively studied landscape with a ten‐year landslide inventory. We use process‐based sub‐models to estimate soil depth, root strength, and pore pressure for a sequence of landslide‐triggering rainstorms. We parameterize sub‐models with field measurements independently of the slope stability model, without calibrating predictions to observations. The model generally reproduces observed landslide size and location distributions, overlaps 65% of observed landslides, and of these predicts size to within factors of 2 and 1.5 in 55% and 28% of cases, respectively. Five percent of the landscape is predicted unstable, compared to 2% recorded landslide area. Missed landslides are not due to the search algorithm but to the formulation and parameterization of the model and inaccuracy of observed landslide maps. Our model does not improve location prediction relative to infinite‐slope methods but predicts landslide size, improves process representation, and reduces reliance on effective parameters. Increasing rainfall intensity or root cohesion generally increases landslide size and shifts locations down hollow axes while increasing cohesion restricts unstable locations to areas with deepest soils. Our findings suggest that shallow landslide abundance, location, and size are ultimately controlled by co‐varying topographic, material, and hydrologic properties. Estimating the spatio‐temporal patterns of root strength, pore pressure, and soil depth, across a landscape may be the greatest remaining challenge

Single electron magneto-conductivity of a nondegenerate 2D electron system in a quantizing magnetic field

We study transport properties of a non-degenerate two-dimensional system of non-interacting electrons in the presence of a quantizing magnetic field and a short-range disorder potential. We show that the low-frequency magnetoconductivity displays a strongly asymmetric peak at a nonzero frequency. The shape of the peak is restored from the calculated 14 spectral moments, the asymptotic form of its high-frequency tail, and the scaling behavior of the conductivity for omega -> 0. We also calculate 10 spectral moments of the cyclotron resonance absorption peak and restore the corresponding (non-singular) frequency dependence using the continuous fraction expansion. Both expansions converge rapidly with increasing number of included moments, and give numerically accurate results throughout the region of interest. We discuss the possibility of experimental observation of the predicted effects for electrons on helium.Comment: RevTeX 3.0, 14 pages, 8 eps figures included with eps

A spectral clustering search algorithm for predicting shallow landslide size and location

The potential hazard and geomorphic significance of shallow landslides depend on their location and size. Commonly applied one-dimensional stability models do not include lateral resistances and cannot predict landslide size. Multi-dimensional models must be applied to specific geometries, which are not known a priori, and testing all possible geometries is computationally prohibitive. We present an efficient deterministic search algorithm based on spectral graph theory and couple it with a multi-dimensional stability model to predict discrete landslides in applications at scales broader than a single hillslope using gridded spatial data. The algorithm is general, assuming only that instability results when driving forces acting on a cluster of cells exceed the resisting forces on its margins, and that clusters behave as rigid blocks with a failure plane at the soil-bedrock interface. This algorithm recovers pre-defined clusters of unstable cells of varying shape and size on a synthetic landscape, predicts the size, location, and shape of an observed shallow landslide using field-measured physical parameters, and is robust to modest changes in input parameters. The search algorithm identifies patches of potential instability within large areas of stable landscape. Within these patches will be many different combinations of cells with a Factor of Safety less than one, suggesting that subtle variations in local conditions (e.g. pore pressure, root strength) may determine the ultimate form and exact location at a specific site. Nonetheless, the tests presented here suggest that the search algorithm enables the prediction of shallow landslide size as well as location across landscapes

Restriction Endonucleases that Bridge and Excise Two Recognition Sites from DNA

Most restriction endonucleases bridge two target sites before cleaving DNA: examples include all of the translocating Type I and Type III systems, and many Type II nucleases acting at their sites. A subset of Type II enzymes, the IIB systems, recognise bipartite sequences, like Type I sites, but cut specified phosphodiester bonds near their sites, like Type IIS enzymes. However, they make two double-strand breaks, one either side of the site, to release the recognition sequence on a short DNA fragment; 34 bp long in the case of the archetype, BcgI. It has been suggested that BcgI needs to interact with two recognition sites to cleave DNA but whether this is a general requirement for Type IIB enzymes had yet to be established. Ten Type IIB nucleases were tested against DNA substrates with one or two copies of the requisite sequences. With one exception, they all bridged two sites before cutting the DNA, usually in concerted reactions at both sites. The sites were ideally positioned in cis rather than in trans and were bridged through 3-D space, like Type II enzymes, rather than along the 1-D contour of the DNA, as seen with Type I enzymes. The standard mode of action for the restriction enzymes that excise their recognition sites from DNA thus involves concurrent action at two DNA sites