The Support Vector Machine (SVM) is an increasingly popular learning procedure based on statistical learning theory, and involves a training phase in which the model is trained by a training dataset ...of associated input and target output values. The trained model is then used to evaluate a separate set of testing data. There are two main ideas underlying the SVM for discriminant-type problems. The first is an optimum linear separating hyperplane that separates the data patterns. The second is the use of kernel functions to convert the original non-linear data patterns into the format that is linearly separable in a high-dimensional feature space. In this paper, an overview of the SVM, both one-class and two-class SVM methods, is first presented followed by its use in landslide susceptibility mapping. A study area was selected from the natural terrain of Hong Kong, and slope angle, slope aspect, elevation, profile curvature of slope, lithology, vegetation cover and topographic wetness index (TWI) were used as environmental parameters which influence the occurrence of landslides. One-class and two-class SVM models were trained and then used to map landslide susceptibility respectively. The resulting susceptibility maps obtained by the methods were compared to that obtained by the logistic regression (LR) method. It is concluded that two-class SVM possesses better prediction efficiency than logistic regression and one-class SVM. However, one-class SVM, which only requires failed cases, has an advantage over the other two methods as only “failed” case information is usually available in landslide susceptibility mapping.
Observations in psychiatric in-patient settings are used to reduce suicide, self-harm, violence and absconding risk. The study aims were to describe the characteristics of in-patients who died by ...suicide under observation and examine their service-related antecedents.
A national consecutive case series in England and Wales (2006-2012) was examined.
There were 113 suicides by in-patients under observation, an average of 16 per year. Most were under intermittent observation. Five deaths occurred while patients were under constant observation. Patient deaths were linked with the use of less experienced staff or staff unfamiliar with the patient, deviation from procedures and absconding.
We identified key elements of observation that could improve safety, including only using experienced and skilled staff for the intervention and using observation levels determined by clinical need not resources.
Because the construction of dams and hydro-electric power stations of Liujiaxia and Yanguoxia across the Yellow River in West Gansu Province, North-West China, inhabitants in the reservoir areas were ...resettled in Heifangtai Loess Platform. Irrigation thus started in 1968. Perched water table was significantly raised and resulted in many loess flow failures in the past 30 years. This type of landslide was often featured by long runout distance, high speed and recurrence. Laboratory tests along ICU and CSD stress paths were performed. It is shown that the loess has a strong strain-softening behavior and instability can occur in drained condition before undrained liquefaction. The failure mechanism of loess flow can be interpreted as the following process: with increasing perched water table, collapse in loess was first triggered in drained condition and led to undrained loading to adjacent soil in the lower saturated part of the loess platform. Under gravity loading applied by upper dry loess, undrained flow failure mobilized, eventually.
A full-scale field experiment involving artificial rainfall has been conducted in an instrumented loess cut slope in an expressway in a loess plateau, Northwest China. Instrumentations including soil ...moisture probes, tensiometers, piezometers, vacuum sensors, water level sensors, and rain gauge were installed in the slope. After monitoring for about 2 years, artificial rainfall was induced at the site in April 2007. This paper presents the results from soil moisture probes, tensiometers, and water levels to reveal the surface infiltration process in an unsaturated soil. The results show that the top 0.7 m in loess is an active zone under the process of infiltration and evaporation, when subjected to a maximum rainfall intensity of 40 mm/day. The depth of the “wetting front” during the wet season was limited to the top 2 m of soil. During high rainfall intensity of 120 mm/day, the depth of the “wetting front” is about 3 m. Based on the variation of volumetric water content and matric suction in soil, a method to analyze the rainfall infiltration is proposed. By means of Gravity-Predominant Flow (GPF) concept, the infiltration rate is analyzed in the deeper soil. The results explain well the observations that loess slopes could be stable in the wet season, but it may tend to slide about 3–6 months later in the dry season. The surface infiltration has a very limited effect on the permanent groundwater table, which is at a greater depth.
In recent years, Heifangtai Plateau in Gansu Province, China, has received significant attention as a loess region in which landslides frequently occur. This study aims to examine the soil behavior ...and failure mechanism(s) of loess slopes subjected to water infiltration. High-quality samples were retrieved behind the failure plane of a landslide in Heifangtai. Three sets of stress path tests were conducted to mimic the process of loess slope failures; these tests include undrained compression on anisotropically consolidated saturated samples, drained shear by decreasing mean effective stress at constant axial load on saturated samples, and wetting by decreasing matric suction at constant axial load on unsaturated samples. Loess behavior was evaluated in terms of shear strength, deformation upon shearing, critical state, state parameter, and soil water characteristic curve. Three major observations were drawn from the test results. First, the anisotropically consolidated saturated loess exhibits a noticeable strain-softening behavior upon undrained compression. The peak shear strength is mobilized at less than 1% axial strain. The ultimate shear strength is only 20–30% of the peak value. Second, when subjected to shear by decreasing mean effective stress at constant axial load, the saturated loess exhibits sudden failure when the confining stress is low. At higher stresses, the soil exhibits progressive failure. Third, unsaturated loess deforms progressively when subjected to a reduction in matric suction (i.e., wetting) at constant axial load. The failure mechanisms of the loess slopes are discussed based on the experimental findings.
•The failure mechanisms of loess slopes are examined by performing stress path tests.•The behavior of anisotropically consolidated saturated loess is presented.•The failure of saturated soil is mimicked by rising pore pressure at constant load.•The failure of unsaturated soil is mimicked by reducing suction at constant load.•The soil–water characteristic curves of loess are presented.
As it is not uncommon that irrigation has triggered landslides in the Chinese Loess Plateau, a full-scale field testing in a typical cracked plateau in Heifangtai, Gansu Province of China to simulate ...such phenomenon was conducted. In the study, piezometers were installed to measure the groundwater, and crackmeters as well as inclinometers were used to measure the slope movement. Water was pumped from the nearby source daily to simulate the irrigation process. There was a sharp increase of pore pressure in the undisturbed loess below the crack when the inclinometer registered considerable movement due to the inflow of water via the crack. Such increase in pore pressure also dissipated rapidly. Eventually, the irrigation water daylighted at the major cracks from the face of the plateau leading to local failures. The results show that cracks have significant effects on the flow of the irrigation water into the ground. The rapid rise in the local pore water pressure had reduced the stability of the slope.
► A full-scale field testing in a typical cracked plateau was for first time conducted. ► It was observed that the cracks had penetrated through the plateau edge and extended to slope face, which exerted a control on the inflow and drainage of irrigation water. ► It was concluded that to trigger large scale landslides such as the commonly-occurring loess flow failures at Heifangtai, a rise of groundwater would be necessary.
Team member turnover presents significant risks to the performance of information systems development (ISD) projects. While prior studies have identified various antecedents of turnover with the ...general objective of reducing its occurrence, turnover cannot be completely prevented in practice. This study examines practices for mitigating the negative impact of turnover when it occurs. Since ISD is knowledge intensive and turnover typically involves knowledge degradation, this study focuses on key practices for reducing such knowledge degradation, i.e., job enlargement, use of electronic knowledge repositories, and succession planning. Our model for explaining the effects of the practices, based on the human capital and organizational forgetting theories, is tested through a survey of 138 project managers of ISD teams experiencing turnover. The results indicate that the use of electronic knowledge repositories and succession planning reduce the negative effect of turnover on the project performance. In contrast, job enlargement does not have a significant mitigating effect. This study contributes to research by looking beyond the antecedents and prevention of turnover to understand how it can be managed effectively. The findings also offer pragmatic suggestions for alleviating the detrimental effects of team member turnover on the ISD project performance.
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