Sociality Affects REM Sleep Episode Duration Under Controlled Laboratory Conditions in the Rock Hyrax, Procavia capensis.

The rock hyrax, Procavia capensis, is a highly social, diurnal mammal. In the current study several physiologically measurable parameters of sleep, as well as the accompanying behavior, were recorded continuously from five rock hyraxes, for 72 h under solitary (experimental animal alone in the recording chamber), and social conditions (experimental animal with 1 or 2 additional, non-implanted animals in the recording chamber). The results revealed no significant differences between solitary and social conditions for total sleep times, number of episodes, episode duration or slow wave activity (SWA) for all states examined. The only significant difference observed between social and solitary conditions was the average duration of rapid eye movement (REM) sleep episodes. REM sleep episode duration was on average 20 s and 40 s longer under social conditions daily and during the dark period, respectively. It is hypothesized that the increase in REM sleep episode duration under social conditions could possibly be attributed to improved thermoregulation strategies, however considering the limited sample size and design of the current study further investigations are needed to confirm this finding. Whether the conclusions and the observations made in this study can be generalized to all naturally socially sleeping mammals remains an open question

High performance interior point methods for three-dimensional finite element limit analysis

The ability to obtain rigorous upper and lower bounds on collapse loads of various structures makes finite element limit analysis an attractive design tool. The increasingly high cost of computing those bounds, however, has limited its application on problems in three dimensions. This work reports on a high-performance homogeneous self-dual primal-dual interior point method developed for three-dimensional finite element limit analysis. This implementation achieves convergence times over 4.5× faster than the leading commercial solver across a set of three-dimensional finite element limit analysis test problems, making investigation of three dimensional limit loads viable. A comparison between a range of iterative linear solvers and direct methods used to determine the search direction is also provided, demonstrating the superiority of direct methods for this application. The components of the interior point solver considered include the elimination of and options for handling remaining free variables, multifrontal and supernodal Cholesky comparison for computing the search direction, differences between approximate minimum degree [1] and nested dissection [13] orderings, dealing with dense columns and fixed variables, and accelerating the linear system solver through parallelization. Each of these areas resulted in an improvement on at least one of the problems in the test set, with many achieving gains across the whole set. The serial implementation achieved runtime performance 1.7× faster than the commercial solver Mosek [5]. Compared with the parallel version of Mosek, the use of parallel BLAS routines in the supernodal solver saw a 1.9× speedup, and with a modified version of the GPU-enabled CHOLMOD [11] and a single NVIDIA Tesla K20c this speedup increased to 4.65×

Computation of bounds for anchor problems in limit analysis and decomposition techniques

Numerical techniques for the computation of strict bounds in limit analyses have been developed for more than thirty years. The efficiency of these techniques have been substantially improved in the last ten years, and have been successfully applied to academic problems, foundations and excavations. We here extend the theoretical background to problems with anchors, interface conditions, and joints. Those extensions are relevant for the analysis of retaining and anchored walls, which we study in this work. The analysis of three-dimensional domains remains as yet very scarce. From the computational standpoint, the memory requirements and CPU time are exceedingly prohibitive when mesh adaptivity is employed. For this reason, we also present here the application of decomposition techniques to the optimisation problem of limit analysis. We discuss the performance of different methodologies adopted in the literature for general optimisation problems, such as primal and dual decomposition, and suggest some strategies that are suitable for the parallelisation of large three-dimensional problems. The propo sed decomposition techniques are tested against representative problems.Peer ReviewedPreprin

Three dimensional lower bound solutions for the stability of plate anchors in sand

Soil anchors are commonly used as foundation systems for structures that require uplift or lateral resistance. These types of structures include transmission towers, sheet pile walls and buried pipelines. Although anchors are typically complex in shape (e.g. drag or helical anchors), many previous analyses idealise the anchor as a continuous strip under plane strain conditions. This assumption provides numerical advantages and the problem can solved in two dimensions. In contrast to recent numerical studies, this paper applies three dimensional numerical limit analysis and axi-symetrical displacement finite element analysis to evaluate the effect of anchor shape on the pullout capacity of horizontal anchors in sand. The anchor is idealised as either square or circular in shape. Results are presented in the familiar form of breakout factors based on various anchor shapes and embedment depths, and are also compared with existing numerical and empirical solutions

Computer modeling of historical processes by means of fractal geometry

"This article is dedicated to application of theory and methodology of fractal geometry in historical research. The article represents the concrete historic issue mathematical model, specifically: the dynamics of the conscience and social environment modernization. On the basis of this model a computer program, which generates fractal images of attractors, attractor basins, and phase transformations of the social systems studied subject to user-entered numerical indicators of certain factors, has been developed. The article represents the principal approaches to the qualitative interpretation of the fractal images obtained." (author's abstract

Foundation Failure Case Histories Reexamined Using Modern Geomechanics

Case histories have played an important role in guiding development of geotechnical engineering during a time when theory was not sophisticated enough to model even simple problems with an acceptable level of rigor. As the discipline transitions from overwhelming reliance on empiricism to a greater reliance on science, it is useful to reexamine the best known case histories as a general check on modern methods of analysis. In the engineering of foundations in clay, three case histories the collapses of the Transcona and Fargo grain elevators and the near collapse of the leaning tower of Pisa stand out. We will see that limit analysis, which is a method of analysis based on two theorems from plasticity theory that allow bounding the collapse load from above and below, produces collapse load estimates that match closely the estimated collapse loads for the two failed grain elevators. It does so without giving the analyst much latitude in selection of input parameters, not requiring the elaborate assumptions needed when attempts are made to use an excessively simplified theory to analyze a real problem. We will also show, using the problem of a leaning tower, how resort to a complete analysis of a boundary-value problem, using a method like the finite element method, is sometimes required in determining the critical ultimate limit state

Stability of anchored sheet wall in cohesive-frictional soils by FE limit analysis

This study extends the limit analysis techniques used for the computation of strict bounds of the load factors in solids to stability problems with interfaces, anchors and joints. The cases considered include the pull-out capacity of multibelled anchors and the stability of retaining walls for multiple conditions at the anchor/soil and wall/soil interfaces. Three types of wall supports are examined: free standing wall, simply supported wall and anchored wall. The results obtained are compared against available experimental and numerical data. The conclusion drawn confirms the validity of numerical limit analysis for the computation of accurate bounds on limit loads and capturing failure modes of structures with multiple inclusions of complex interface and support conditions

Computational limit analysis for anchors and retaining walls

The computation of the bearing capacity of engineering structures commonly relays on results obtained for simple academic examples. Recent developments in computational limit analysis have allowed engineers to compute bounds of the bearing capacity of arbitrary geometries. We here extend these formulations to problems with practical interest such as retaining walls, anchors, or excavations with particular interface conditions. These situations require the special treatment of the contact conditions between different materials, or the modelling of joints and anchors. We demonstrate the potential of the resulting tool with some practical examples

LEARNERS’ INTERACTIONS IN MASSIVE OPEN ONLINE COURSES: ANALYSIS AND INTERPRETATION

The research is devoted to the study of data on learners’ interactions in massive open online courses. Based on the logs of online-learning platforms, the following research was made: a comparison of the behaviour of motivated and unmotivated learners regarding of video lectures, identification of the most valuable for the successful completion of the course activities of learners, creating a model of going through time-limited assignments and identification of cheating approach based on this model. The following conclusions were made: motivated and unmotivated learners watch video lectures in different ways, motivated learners appeared to be 14 times more active, the most interesting and most viewable videos were revealed. When identifying the most valuable theoretical materials influencing the successful completion of the course, the following results were obtained: some of the videos have a strong influence on the successful completion of the final assignment. Some of the videos appeared to have weak effect, they can be interpreted as non-obligatory. Ungraded tests have a positive but moderate effect on learners’ success, while communication via discussion forum has no effect at all. In addition, a model of going through time-limited assignments was built using the average passing time of reliable learners, the approach for identifying cheating with examples is presented in the study