Plastic load evaluation for a fixed tube sheet heat exchanger subject to proportional loading

The plastic load of pressurised components can be calculated based on both the twice elastic slope and tangent methods. Both methods are problematic since they rely on parameters that are localised and therefore have a strong dependency on the gradient of the stress–strain diagram in the plastic region. The criterion of curvature of plastic work is a suitable replacement for the above techniques. This method calculates total plastic work done on the structure and relates its change to the curvature of the load-plastic work plot. In this work the plastic load has been calculated for a fixed tube sheet exchanger according to curvature criteria using various hardening scenarios. Plastic loads calculated by other methods also have been reported. It has been indicated that tube sheet thickness calculated according to the classical ASME procedure can be significantly reduced when based on the curvature criteria

Deformation and failure of welded steels used in offshore constructions

Hydrocarbons are the most common form of energy used to date. The activities involving exploration and exploitation of large oil and gas fields are constantly in operation and have extended to such hostile environments as the North Sea. This enforces much greater demands on the materials which are used, and the need for enhancing the endurance of the existing ones which must continue parallel to the explorations. Due to their ease in fabrication, relatively high mechanical properties and low costs, steels are the most widely favoured material for the construction of offshore platforms. The most critical part of an offshore structure prone to failure are the welded nodal joints, particulary those which are used within the vicinity of the splash zones. This is an area of high complex stress concentrations, varying mechanical and metallurgical properties in addition to severe North Sea environmental conditions. The main are of this work has been concerned with the durability studies of this type of steel, based on the concept of the worst case analysis, consisting of combinations of welds of varying qualities, various degrees of stress concentrations and the environmental conditions of stress corrosion and hydrogen embrittlement. The experiments have been designed to reveal significance of defects as sites of crack initiation in the welded steels and the extent to which stress corrosion and hydrogen embrittlement will limit their durability. This has been done for various heat treatments and in some experiments deformation has been forced through the welded zone of the specimens to reveal the mechanical properties of the welds themselves to provide data for finite element simulations. A comparison of the results of these simulations with the actual deformation and fracture behaviour has been done to reveal the extent to which both mechanical and metallurgical factors control behaviour of the steels in the hostile environments of high stress, corrosion, and hydrogen embrittlement at their surface

A Semiparametric Bayesian Model for Detecting Synchrony Among Multiple Neurons

We propose a scalable semiparametric Bayesian model to capture dependencies among multiple neurons by detecting their co-firing (possibly with some lag time) patterns over time. After discretizing time so there is at most one spike at each interval, the resulting sequence of 1's (spike) and 0's (silence) for each neuron is modeled using the logistic function of a continuous latent variable with a Gaussian process prior. For multiple neurons, the corresponding marginal distributions are coupled to their joint probability distribution using a parametric copula model. The advantages of our approach are as follows: the nonparametric component (i.e., the Gaussian process model) provides a flexible framework for modeling the underlying firing rates; the parametric component (i.e., the copula model) allows us to make inference regarding both contemporaneous and lagged relationships among neurons; using the copula model, we construct multivariate probabilistic models by separating the modeling of univariate marginal distributions from the modeling of dependence structure among variables; our method is easy to implement using a computationally efficient sampling algorithm that can be easily extended to high dimensional problems. Using simulated data, we show that our approach could correctly capture temporal dependencies in firing rates and identify synchronous neurons. We also apply our model to spike train data obtained from prefrontal cortical areas in rat's brain

Synthetic and Natural Polymers Recycled to Make Matter with New Functionality and Aesthetics

This practice-led research will be accompanied by a dissertation which describes the research process and discusses the research questions and outcomes generated by the practice process. From an initial stage of laboratory and workshop experimentation with recycling High Density Polyethylene (HDPE) and General Purpose Polystyrene (GPPS), to a conclusion which brings experimental design practice to serve the needs of a specific user group, this research aims to show that the role of the designer in material-based research is multiple and complex. The significance of emotional experience is discovered to be of central importance to both material experimentation and the design for a specific user group. The initial context of sustainability becomes reframed through work with a community of residents, staff and relatives associated with a care home for the aged. From addressing the needs of a twenty- first century demographic challenge the designer finds complex meaning in the ecological, ethical and political agendas of sustainability. I employed a range of research methods in this project and conclude that qualitative research practice demands the integration of technical skills, sociological enquiry and an investigation into the ‘tacit knowledge’ of craftsmanship. I investigated the design potential of combining traditional craft and industrial technology to address the challenge of a future society and through this research into recycling plastics, polymers, textiles and other materials propose that material and meaning are closely interrelated. In my work the relationship between the visible traces of tactile sense and the presence of the hand is explored as a sign of ‘contact’ and transmission of emotion. The encasement and display of fibre, textile and personal objects in the plastic tiles is deployed as a medium of interior architecture with the potential to represent the meaning of the experience of end-of-life wellbeing. In this way the designer can make materials which encapsulate the sense of transition, departure, memory, presence and continuity for the old, their relatives and carers. Considering the principle of ‘Emotionally Durable Design’, this research finds new uses for old material

Racheting assessment of a fixed tube sheet heat exchanger subject to in-phase pressure and temperature cycles

An investigation of the cyclic elastic-plastic response of an Olefin plant heat exchanger subject to cyclic thermal and pressure loading is presented. Design by Analysis procedures for assessment of shakedown and ratcheting are considered, based on elastic and inelastic analysis methods. The heat exchanger tube sheet thickness is non-standard as it is considerably less than that required by conventional design by formula rules. Ratcheting assessment performed using elastic and stress linearization indicates that shakedown occurs under the specified loading when the non-linear component of the through thickness stress is categorized as peak stress. In practice, the presence of the peak stress will cause local reverse plasticity or plastic shakedown in the component. In non-linear analysis with an elastic-perfectly plastic material model the vessel exhibits incremental plastic strain accumulation for 10 full load cycles, with no indication that the configuration will adapt to steady state elastic or plastic action; i.e. elastic shakedown or plastic shakedown. However, the strain increments are small and would not lead to the development of a global plastic collapse or gross plastic deformation during the specified life of the vessel. Cyclic analysis based on a strain hardening material model indicates that the vessel will adapt to plastic shakedown after 6 load cycles. This indicates that the stress categorization and linearization assumptions made in the elastic analysis are valid for this configuration

An Urgent Plea for More Graduate Programs in Statistics Education

Lately, much has been written about the importance of amplifying statistics-related content in the K-12 curricula. This can be viewed in parallel or as an addendum to the existing mathematics curricula in the United States. Nevertheless, a key component of this debate is the lack of robust and cutting-edge academic programs in statistics education. In this piece, we emphasize the urgent need for investing in creating strong statistics education programs, which would significantly contribute to nurturing quantitative literacy as well as preparing a more informed citizenry in the 21st century

What orthopaedic surgery residents need to know about the hand and wrist?

<p>Abstract</p> <p>Background</p> <p>To develop a Core Curriculum for Orthopaedic Surgery; and to conduct a national survey to assess the importance of curriculum items as judged by orthopaedic surgeons with primary affiliation non-academic. Attention for this manuscript was focused on determining the importance of topics pertaining to adult hand and wrist reconstruction.</p> <p>Methods</p> <p>A 281-item questionnaire was developed and consisted of three sections: 1) Validated Musculoskeletal Core Curriculum; 2) Royal College of Physician and Surgeons of Canada (RCPSC) Specialty Objectives and; 3) A procedure list. A random group of 131 [out of 156] orthopaedic surgeons completed the questionnaire. Data were analyzed descriptively and quantitatively using histograms, a Modified Hotel ling's T²-statistic <abbrgrp><abbr bid="B1">1</abbr></abbrgrp> with p-value determined by a permutation test, and the Benjamini-Hochberg/Yekutieli procedure</p> <p>Results</p> <p>131/156 (84%) orthopaedic surgeons participated in this study. 27/32 items received an average mean score of at least 3.0/4.0 by all respondents thus suggesting that 84% of the items are either "probably important" or "important" to know by the end of residency (SD range 0.007–0.228). The Benjamini-Hochberg procedure demonstrated that for 80% of the 32 × 31/2 = 496 possible pairs of hand and wrist questions did not appear to demonstrate the same distribution of ratings given that one question was different from that of another question.</p> <p>Conclusion</p> <p>This study demonstrates with reliable statistical evidence, agreement on the importance of 27/32 items pertaining to hand and wrist reconstruction is included in a Core Curriculum for Orthopaedic Surgery. Residency training programs need ensure that educational opportunities focusing on the ability to perform with proficiency procedures pertaining to the hand and wrist is taught and evaluated in their respective programs.</p

A Point-process Response Model for Spike Trains from Single Neurons in Neural Circuits under Optogenetic Stimulation

Optogenetics is a new tool to study neuronal circuits that have been genetically modified to allow stimulation by flashes of light. We study recordings from single neurons within neural circuits under optogenetic stimulation. The data from these experiments present a statistical challenge of modeling a high frequency point process (neuronal spikes) while the input is another high frequency point process (light flashes). We further develop a generalized linear model approach to model the relationships between two point processes, employing additive point-process response functions. The resulting model, Point-process Responses for Optogenetics (PRO), provides explicit nonlinear transformations to link the input point process with the output one. Such response functions may provide important and interpretable scientific insights into the properties of the biophysical process that governs neural spiking in response to optogenetic stimulation. We validate and compare the PRO model using a real dataset and simulations, and our model yields a superior area-under-the- curve value as high as 93% for predicting every future spike. For our experiment on the recurrent layer V circuit in the prefrontal cortex, the PRO model provides evidence that neurons integrate their inputs in a sophisticated manner. Another use of the model is that it enables understanding how neural circuits are altered under various disease conditions and/or experimental conditions by comparing the PRO parameters.Comment: 24 pages, 7 figures. R package pro implementing the proposed method is available on CRAN at https://CRAN.R-project.org/package=pro . Published by Statistics in Medicine at http://onlinelibrary.wiley.com/doi/10.1002/sim.6742/ful