Limit state design framework for geosynthetic-reinforced soil structures

Conventional design of geosynthetic-reinforced soil structures is divided into two categories, walls and slopes, based on the batter of its facing system. Internal stability, characterized as sufficient reinforcement anchoring and strength, is performed using earth pressure-based design criteria for reinforced walls while reinforced slopes are founded on limit equilibrium (LE) slope stability analyses. LE analyses are also used to assess the global or compound stability of both types of structures, accounting for the geometry of the reinforced, retained and foundation soils. The application of LE-based methods typically results in determination of a slip surface corresponding to the lowest attained Safety Factor (SF), known as the Factor of Safety (Fs); however, it yields little information about reinforcement loading or connection load. In this study, use of the analyzed spatial distribution of SF known as a Safety Map, is modified to attain a prescribed constant Fs at any location in the reinforced soil mass. This modified framework, implemented through an iterative, top-down procedure of LE slope stability analyses originating from the crest of a reinforced structure and exiting at progressively lower elevations on the facing, enables the determination of a Tension Map that illustrates the required distribution of reinforcement tension to attain a prescribed limit state of equilibrium. This tension map is directly constrained by a pullout capacity envelope at both the rear and front of each reinforcement layer, providing a unified, LE-based approach towards assessing an optimal selection of mutually dependent strength and layout of the reinforcement. To illustrate the utility of the Limit State framework, a series of instructive examples are presented. The results demonstrate the effects of facing elements, closely-spaced reinforcements, secondary reinforcement layers, and is compared to conventional design approaches.     

Molecular circuits for associative learning in single-celled organisms

We demonstrate how a single-celled organism could undertake associative learning. Although to date only one previous study has found experimental evidence for such learning, there is no reason in principle why it should not occur. We propose a gene regulatory network that is capable of associative learning between any pre-specified set of chemical signals, in a Hebbian manner, within a single cell. A mathematical model is developed, and simulations show a clear learned response. A preliminary design for implementing this model using plasmids within Escherichia coli is presented, along with an alternative approach, based on double-phosphorylated protein kinases.     

From Raster to Vectors: Extracting Visual Information from Line Drawings

Vectorisation of raster line images is a relatively mature subject in the document analysis and recognition field, but it is far from being perfect as yet. We survey the methods and algorithms developed to-date for the vectorisation of document images, and classify them into six categories: Hough transform-based, thinning-based, contour-based, run-graph-based, mesh-pattern-based, and sparse-pixel-based. The purpose of the survey is to provide researchers with a comprehensive overview of this technique, to enable a judicious decision while selecting a vectorisation algorithm for a system under development or a newly developed vectorisation algorithm. Received: 10 November 1998?Received in revised form: 7 January 1999?Accepted: 7 January 1999     

Development and validation of safety climate scales for mobile remote workers using utility/electrical workers as exemplar

Purpose

The objective of this study was to develop and test the reliability and validity of a new scale designed for measuring safety climate among mobile remote workers, using utility/electrical workers as exemplar. The new scale employs perceived safety priority as the metric of safety climate and a multi-level framework, separating the measurement of organization- and group-level safety climate items into two sub-scales. The question of the emergence of shared perceptions among remote workers was also examined.

Method

For the initial survey development, several items were adopted from a generic safety climate scale and new industry-specific items were generated based on an extensive literature review, expert judgment, 15-day field observations, and 38 in-depth individual interviews with subject matter experts (i.e., utility industry electrical workers, trainers and supervisors of electrical workers). The items were revised after 45 cognitive interviews and a pre-test with 139 additional utility/electrical workers. The revised scale was subsequently implemented with a total of 2421 workers at two large US electric utility companies (1560 participants for the pilot company and 861 for the second company). Both exploratory (EFA) and confirmatory factor analyses (CFA) were adopted to finalize the items and to ensure construct validity. Reliability of the scale was tested based on Cronbach's α. Homogeneity tests examined whether utility/electrical workers’ safety climate perceptions were shared within the same supervisor group. This was followed by an analysis of the criterion-related validity, which linked the safety climate scores to self-reports of safety behavior and injury outcomes (i.e., recordable incidents, missing days due to work-related injuries, vehicle accidents, and near misses).

Results

Six dimensions (Safety pro-activity, General training, Trucks and equipment, Field orientation, Financial Investment, and Schedule flexibility) with 29 items were extracted from the EFA to measure the organization-level safety climate. Three dimensions (Supervisory care, Participation encouragement, and Safety straight talk) with 19 items were extracted to measure the group-level safety climate. Acceptable ranges of internal consistency statistics for the sub-scales were observed. Whether or not to aggregate these multi-dimensions of safety climate into a single higher-order construct (overall safety climate) was discussed. CFAs confirmed the construct validity of the developed safety climate scale for utility/electrical workers. Homogeneity tests showed that utility/electrical workers’ safety climate perceptions were shared within the same supervisor group. Both the organization- and group-level safety climate scores showed a statistically significant relationship with workers’ self-reported safety behaviors and injury outcomes.

Implications

A valid and reliable instrument to measure the essential elements of safety climate for utility/electrical workers in the remote working situation has been introduced. The scale can provide an in-depth understanding of safety climate based on its key dimensions and show where improvements can be made at both group and organization levels. As such, it may also offer a valuable starting point for future safety interventions.     

Learning equilibrium as a generalization of learning to optimize

We argue that learning equilibrium is an appropriate generalization to multi-agent systems of the concept of learning to optimize in single-agent setting. We further define and discuss the concept of weak learning equilibrium.     

Evo-devo of Child Growth: The Role of Weaning in the Transition from Infancy to Childhood

Homo sapiens are unique in having a life history phase of childhood, which follows infancy, as defined by breastfeeding. This review uses evolutionary life history theory in understanding child growth in a broad evolutionary perspective, using the data and theory of evolutionary predictive adaptive growth-related strategies for transition from infancy to childhood. We have previously shown that a delayed infancy–childhood transition has a lifelong impact on stature. Feeding practices during infancy are fundamental elements of nutrition as they program for future growth and body composition. A relationship between the duration of breastfeeding and the nature of weaning has been suggested as a possible cause for later obesity and growth patterns. This review highlights the role that breast milk feeding and variations in the weaning age have on transition to childhood, growth, and body composition.