A Mathematical Analysis of the Subsidence in the Long Beach - San Pedro Area

This report presents the significant results from a mathematical study of the subsidence in the Long Beach area. The work, begun in December 1949 at the request of Mr. M.D. Hughes, Chief Petroleum Engineer, the Petroleum Division of the Long Beach Harbor Department, has been in progress for two years. During this period a large volume of physical data pertinent to the subsidence phenomena has been made available and analyzed. Additional tests suggested by the mathematical analysis have been instigated by the Petroleum Division so that a well integrated program of research has been brought to bear upon this problem

Variation in Reported Human Head Tissue Electrical Conductivity Values

Electromagnetic source characterisation requires accurate volume conductor models representing head geometry and the electrical conductivity field. Head tissue conductivity is often assumed from previous literature, however, despite extensive research, measurements are inconsistent. A meta-analysis of reported human head electrical conductivity values was therefore conducted to determine significant variation and subsequent influential factors. Of 3121 identified publications spanning three databases, 56 papers were included in data extraction. Conductivity values were categorised according to tissue type, and recorded alongside methodology, measurement condition, current frequency, tissue temperature, participant pathology and age. We found variation in electrical conductivity of the whole-skull, the spongiform layer of the skull, isotropic, perpendicularly- and parallelly-oriented white matter (WM) and the brain-to-skull-conductivity ratio (BSCR) could be significantly attributed to a combination of differences in methodology and demographics. This large variation should be acknowledged, and care should be taken when creating volume conductor models, ideally constructing them on an individual basis, rather than assuming them from the literature. When personalised models are unavailable, it is suggested weighted average means from the current meta-analysis are used. Assigning conductivity as: 0.41 S/m for the scalp, 0.02 S/m for the whole skull, or when better modelled as a three-layer skull 0.048 S/m for the spongiform layer, 0.007 S/m for the inner compact and 0.005 S/m for the outer compact, as well as 1.71 S/m for the CSF, 0.47 S/m for the grey matter, 0.22 S/m for WM and 50.4 for the BSCR

Numerical modelling of hot polymer-coated steel pipeline joints in bending

A numerical method to analyse the effect of the application of polymer coatings on the bending resistance of steel pipeline joints is presented. Experiments were conducted to investigate the influence of the thickness of polymer field joint coatings and the cooldown time provided after applying the coatings on the behaviour of pipeline joints when being bent during reeling operations. Temperature readings were obtained from thermocouples inside the polymer field joint coating during the application process, and pipeline ovality measurements were taken during mechanical testing. Thermal modelling of the coating application procedure was developed using COMSOL Multiphysics modelling software; this model is validated against the thermocouple readings, while a mechanical model simulating the pipe being bent to a reel developed in Abaqus finite element modelling software is described. The temperature outputs, areas of stress concentration and pipe ovalities obtained from the experiments are shown to be predicted accurately by the numerical models. After successful validation of the numerical models, a parametric study assessing the influence of field joint coating thickness and cooldown times is described, whose results are used to find an optimal solution to reduce the cooldown time required prior to bending the pipe without buckling

Dielectric-Recovery Characteristic of Power Arcs in Large Air Gaps

A satisfactory test technique has been developed for studying the rates of dielectric recovery of large air gaps and other types of power-system insulation. This permits the accurate control of the fault conditions so that all practical types of fault currents can be studied. These are: (1) very high magnitude short-duration surges typical of lightning currents; (2) currents of power-system frequencies; and (3) intermediate duration currents such as those which might result from high-frequency current zeros produced by natural system oscillations. Results are presented showing the rate of dielectric recovery of 3-, 6-, and 11-inch standard rod gaps for power frequency fault currents up to 700 amperes. Electrode cooling effects were found important at 3-inch gap spacings but not at six inches or above. The 11-inch gap data are proportionately higher than the 6-inch data indicating that the results can be extrapolated. The data show that for arcs of a few cycles actual duration has little effect on rate of recovery. A range of current magnitudes from 50 to 700 amperes causes only about a 2-to-1 variation in rate of recovery. For the normal ratios of transmission-line insulation level to operating voltage (about four to one) minimum delay times of from 0.025 second for 100-ampere faults to 0.05 second for 700 ampere faults are required before the recovery voltage reaches the magnitude of the normal applied voltage. Time intervals of 0.05 to 0

Application of the California Institute of Technology Electric Analog Computer to Nonlinear Mechanics and Servomechanisms

This paper describes the non-linear elements and circuit techniques used with the California Institute of Technology electric analog computer. Their application to nonlinear mechanical vibratory systems and nonlinear servomotors is discussed in detail. These techniques have been found to be generally suitable for representing single valued nonlinear functions of a dependent variable. Nonlinear springs, spring loaded backlash, and nonlinear damping factors can be readily simulated as well as saturation effects and other single valued non-linearities in servomotors. Methods of analysis are illustrated for several typical problems including a nonlinear rotating mechanical system and an autopilot employing a solenoid-operated rate and position limited hydraulic motor. Numerous servos of this type have now been studied and correlation of computer solutions with actual servo test data have shown in every case that the mathematical equations presented here accurately describe this type of motor

Electronic Techniques Applied to Analogue Methods of Computation

This paper describes in detail the electronic devices and principles that have been developed for the California Institute of Technology (CIT) electric analogue computer. This is a general-purpose, large-scale computer applicable to a wide range of linear and nonlinear ordinary algebraic or differential equations and linear and nonlinear partial differential equations. In addition to the basic principles of the computer, a detailed discussion is given of those elements considered to be of particular interest. These include the devices for generating the arbitrary functions of the independent variable (the excitation functions), the amplifiers for producing active linear elements such as negative impedances and for representing the nonsymmetrical terms of the matrix specifying the differential equations, the multipliers for producing arbitrary functions of the dependent variables (nonlinear elements). Performance data on these devices are presented, together with analogies and solutions of representative types of problems

From clean to diffusive mesoscopic systems: A semiclassical approach to the magnetic susceptibility

We study disorder-induced spectral correlations and their effect on the magnetic susceptibility of mesoscopic quantum systems in the non-diffusive regime. By combining a diagrammatic perturbative approach with semiclassical techniques we perform impurity averaging for non-translational invariant systems. This allows us to study the crossover from clean to diffusive systems. As an application we consider the susceptibility of non-interacting electrons in a ballistic microstructure in the presence of weak disorder. We present numerical results for a square billiard and approximate analytic results for generic chaotic geometries. We show that for the elastic mean free path $\ell$ larger than the system size, there are two distinct regimes of behaviour depending on the relative magnitudes of $\ell$ and an inelastic scattering length.Comment: 7 pages, Latex-type, EuroMacr, 4 Postscript figures, to appear in Europhys. Lett. 199

Resources and student achievement – evidence from a Swedish policy reform

This paper utilizes a policy change to estimate the effect of teacher density on student performance. We find that an increase in teacher density has a positive effect on student achievement. The baseline estimate – obtained by using the grade point average as the outcome variable – implies that resource increases corresponding to the class-size reduction in the STAR-experiment (i.e., a reduction of 7 students) improves performance by 2.6 percentile ranks (or 0.08 standard deviations). When we use test score data for men, potentially a more objective measure of student performance, the effect of resources appears to be twice the size of the baseline estimate.Student performance; teacher/student ratio; policy reform; differences-in-differences

Building Engagement in Facebook: A Case Study with Utah State University Extension Sustainability

In order to stay relevant in an online world, Extension must properly use social networking platforms to effectively reach diverse audiences regarding agricultural and natural resource issues. However, few studies have focused on how Extension uses Facebook to effectively accomplish its goal. This study’s purpose was to explore how Utah State University Extension Sustainability uses Facebook to engage followers. The researchers conducted a quantitative content analysis of 504 messages posted to the USU Extension Sustainability Facebook page. Graphics and links were the most common post characteristics used by the organization. Text-only posts and posts containing videos were utilized the least. Food was the most common area of sustainability discussed on the page. Posts containing videos, shared content, or that tagged other Facebook pages in messages experienced statistically significantly higher user engagement than posts without those characteristics. Posts containing hashtags experienced statistically significantly lower engagement. Neutral sentiment appeared in the majority of posts. Additionally, information seeking was the most dominant communicative function among the posts. Neither the type of sentiment nor communicative functions were significantly connected to engagement. Future research should determine changes in knowledge, attitudes, intentions, and behavior as a result of exposure to, and engagement with, the Facebook page. Additionally, a qualitative study determining consumers’ attitudes toward Facebook content can provide a deeper understanding of the audience’s thought processes and content preferences. Page administrators should craft engaging content that builds community among followers