Fitting Linear Mixed-Effects Models using lme4

Maximum likelihood or restricted maximum likelihood (REML) estimates of the parameters in linear mixed-effects models can be determined using the lmer function in the lme4 package for R. As for most model-fitting functions in R, the model is described in an lmer call by a formula, in this case including both fixed- and random-effects terms. The formula and data together determine a numerical representation of the model from which the profiled deviance or the profiled REML criterion can be evaluated as a function of some of the model parameters. The appropriate criterion is optimized, using one of the constrained optimization functions in R, to provide the parameter estimates. We describe the structure of the model, the steps in evaluating the profiled deviance or REML criterion, and the structure of classes or types that represents such a model. Sufficient detail is included to allow specialization of these structures by users who wish to write functions to fit specialized linear mixed models, such as models incorporating pedigrees or smoothing splines, that are not easily expressible in the formula language used by lmer.Comment: 51 pages, including R code, and an appendi

Experimental and analytical study of an open cathode polymer electrolyte membrane fuel cell.

In this thesis four different fuel cell designs were simulated with consideration for electrochemical effects, reactant species transport, and heat transfer. Simulation results include the mass fraction of hydrogen, oxygen, and water, temperature gradient, pressure gradient, and velocity profile. One of the fuel cell designs was experimentally tested using two different membrane electrolyte assemblies; one high performance and the other high durability. The polarization curve resulting from simulation compares well with the polarization curve produced by experimental work. A 16 cell fuel cell stack was simulated with consideration for stack compression. The same fuel cell stack was tested experimentally for compression using pressure sensitive films. Compression testing was performed in order to find areas of low compression and high compression. Low compression regions lead to high contact resistance which degrades the performance of the fuel cell. High compression regions can cause damage to the thin and brittle membrane electrolyte assemblies. A good correlation was found between the compression pattern resulting from simulation and experimental work

Advanced materials for block copolymer lithography

textThe multi-billion dollar per year lithography industry relies on the fusion of chemistry, materials science, and engineering to produce technological innovations that enable continual improvements in the speed and storage density of microelectronic devices. A critical prerequisite to improving the computers of today relies on the ability to economically and controllably form thin film structures with dimensions on the order of tens of nanometers. One class of materials that potentially meets these requirements is block copolymers since they can self-assemble into structures with characteristic dimensions circa three to hundreds of nanometers. The different aspects of the block copolymer lithographic process are the subject of this dissertation. A variety of interrelated material requirements virtually necessitate the synthesis of block copolymers specifically designed for lithographic applications. Key properties for the ideal block copolymer include etch resistance to facilitate thin film processing, a large interaction parameter to enable the formation of high resolution structures, and thin film orientation control. The unifying theme for the materials synthesized herein is the presence of silicon in one block, which imparts oxygen etch resistance to just that domain. A collection of silicon-containing block copolymers was synthesized and characterized, many of which readily form features on approximately the length scale required for next-generation microelectronic devices. The most important thin film processing step biases the orientation of block copolymer domains perpendicular to the substrate by control of interfacial interactions. Both solvent and thermal annealing techniques were extensively studied to achieve orientation control. Ultimately, a dual top and bottom surface functionalization strategy was developed that utilizes a new class of "top coats" and cross-linkable substrate surface treatments. Perpendicular block copolymer features can now be produced quickly with a process amenable to existing manufacturing technology, which was previously impossible. The development of etching recipes and pattern transfer processes confirmed the through-film nature of the features and the efficacy of both the block copolymer design and the top coat process.Chemistr

Immediate postoperative management and complications on the intensive care unit

The postoperative management of patients immediately after liver transplantation requires knowledge of this complex surgery and the physiology that accompanies liver failure. A multidisciplinary approach to the care of these patients is essential in order to reduce postoperative complications and preserve function in the transplanted organ. By their nature, patients undergoing liver transplantation have complicated medical problems before surgery which must be borne in mind when managing them after surgery. Haemorrhage, haemodynamic instability, acute renal failure, hepatic artery thrombosis and primary graft non-function are some of the complications that clinicians must be prepared for in the first days after transplantation. Pre-empting complications and acting rapidly to overt them is likely to have a considerable positive impact in these patients

Child’s addition in the Stern–Brocot tree

AbstractWe use child’s addition and cross-differencing to discover significant relationships for diagonals, paths and branches within the Stern–Brocot tree and the Stern–Brocot sequence. This allows us to develop results for continued fraction summation under child’s addition

Point-light biological motion perception activates human premotor cortex

Motion cues can be surprisingly powerful in defining objects and events. Specifically, a handful of point-lights attached to the joints of a human actor will evoke a vivid percept of action when the body is in motion. The perception of point-light biological motion activates posterior cortical areas of the brain. On the other hand, observation of others' actions is known to also evoke activity in motor and premotor areas in frontal cortex. In the present study, we investigated whether point-light biological motion animations would lead to activity in frontal cortex as well. We performed a human functional magnetic resonance imaging study on a high-field-strength magnet and used a number of methods to increase signal, as well as cortical surface-based analysis methods. Areas that responded selectively to point-light biological motion were found in lateral and inferior temporal cortex and in inferior frontal cortex. The robust responses we observed in frontal areas indicate that these stimuli can also recruit action observation networks, although they are very simplified and characterize actions by motion cues alone. The finding that even point-light animations evoke activity in frontal regions suggests that the motor system of the observer may be recruited to "fill in" these simplified displays

The Norse waterways of West Mainland Orkney, Scotland

This study was funded by BA/Leverhulme Small Research Grants 2017-18 Round.Norse place-names for farms, individual landscape features and general landscape areas are ubiquitous throughout the Orkney Islands. These have an origin during the mediaeval period AD790–1350 when Orkney was ruled by Scandinavian earls. The oldest referenced maps for the parish of Harray (West Mainland, Orkney) suggests that in the past significant waterways crossed wetlands extending between the Loch of Harray and Houseby in an area associated with the earldom power base at Birsay. Subsequent drainage projects, changes in climate and sea level have since resulted in the loss of the waterways. An investigation of the wetlands using geophysical and geological analysis provided a reconstruction of the palaeo-environments. Comparison with place-names of significance allowed interpretation of possible routeways along navigable waters by shallow-draught Viking-Age vessels. The results allow for re-drawing the map of Norse Orkney and postulation of produce transfer corridors from estates in the south to the power centre at Birsay.PostprintPeer reviewe