Automated tissue analysis from computerized axial tomographic scans

A computerized off-line analysis has been developed to study brain tissue properties from scans performed with an EMI 1005 headscanner. Except for the operator's identifying the inter-hemispheric fissure, the analysis is fully automated. It subdivides the brain area into 80 subdivisions, arranged into four bands parallel to the calvarial contour. The program computes the values of the mean and the standard deviation for each subdivision, each band, and each hemisphere as well as for the whole calvaria. This arrangement facilitates the assessment of asymmetries of brain tissue. We found that a 3 × 3 smoothing filtration decreased the standard deviation by about a factor of 1.5 to 3 and the mean values of CT numbers for the subdivisions by about 2 to 3%.     

Automated modeling for structural analysis

The numerical computations required for structural analysis are well defined and easy to automate. If structural analysis is to be automated fully, however, the modeling process, as well as the numerical computations, must be automated. This paper outlines a procedure for the automation of the entire modeling and analysis sequence.Structural analysis is considered as one of several planning, design, and analysis applications to be included in a computerintegrated design system. An essential ingredient of such a system is a central data base that supports all applications. A data base using a hierarchicalcomponent-connection concept is first described. A procedure is then outlined by which a modeler program can extract analysis models from this data base. Whereas the central data base describes the structure in terms of its components and connections, the analysis model is in terms of nodes, elements, substructures, slaving constraints, and so on. The features required in a structural analysis program to analyze the resulting model are also described. This program follows well-established principles, but is substantially different in its arhitecture from conventional analysis programs.A simple frame building is used as an example. However, the procedure is believed to be applicable to structures of a variety of types.     

Recent advances in computerized aerospace structural analysis and design

This paper presents accomplishments at the Boeing Commercial Airplane Company in the areas of (1) large problem solutions, (2) practical structural design automation and (3) a hypothesis for stable crack growth.A turbine blade (3200 nodes 350 elements, 9500 freedoms, 15 million words of storage) and a sports stadium (3400 nodes, 9600 elements, 20,000 freedoms, 70 million words of storage) are presented in terms of problem definition, strategy of approach, data management and computer resources.The Boeing automated strength design capability in the ATLAS System is discussed in terms of user specified constraints on the automated strength resizing and local optimization, strength criteria, user control and convergence criteria. Cost and weight data are presented from large aircraft design studies (20,000 design variables).A new concept of crack stability based on non-linear stress/strain analysis is presented. Stable crack growth is modeled by a suitable failure criterion in the stress analysis procedure. A crack is extended by a simultaneous unloading of the newly created crack surface and the loading of the uncracked region. Test comparisons and numerical experiments support a new hypothesis based on material strength characteristics, plastic zone size/history and the residual plastic strains.     

Formulations and solution procedures for nonlinear structural analysis

This paper presents a survey of the formulations and solution procedures for nonlinear static and dynamic structural analysis. The formulations covered include the pseudo force method, the total Lagrangian method, the updated Lagrangian method, and the convected coordinate method. The relationship of each principle to the basic principle of virtual work is presented. For static analysis, the solution by direct minimization of the total potential, Newton-Raphson and modified Newton-Raphson, and the first and second order self correcting method are reviewed and put in proper perspective. It is concluded that the most efficient methods for static problems are the modified Newton-Raphson and the first order self correcting methods. For dynamic nonlinear analysis, a new method based on modal analysis using the pseudo force method is presented. Numerical results for the highly nonlinear dynamic response of a shallow cap (λ = 6) under a step load at the apex shows the method to be 5 times faster than the Houbolt solution procedure. Other methods surveyed include the Newmark β method, the Wilson method, central differences, and the stiffly stable solution procedure of Park.     

Automated structural design and analysis of advanced composite wing models

The design of a composite wind tunnel model has demonstrated the ability to tailor the response of a composite structure to provide desired static and dynamic characteristics. This was possible because the strength and stiffness properties of composite structures can be controlled through selection of materials and lamination patterns. To take maximum advantage of the capability, efficient computer procedures are being developed for the design and analysis of composite structures. A finite element procedure and a direct Rayleigh-Ritz procedure, specialized for the preliminary analysis of wing-type structure, are discussed. The use and accuracy of these procedures have been demonstrated on a low cost, low risk basis in the design and analysis of a composite wind tunnel model and in test-theory correlation for static and dynamic response. Material selection, intermediate design decisions, fabrication, testing for natural modes and frequencies, and testing for influence coefficients for the wind tunnel model are discussed.     

Automated gaze-based mind wandering detection during computerized learning in classrooms

We investigate the use of commercial off-the-shelf (COTS) eye-trackers to automatically detect mind wandering—a phenomenon involving a shift in attention from task-related to task-unrelated thoughts—during computerized learning. Study 1 (N?=?135 high-school students) tested the feasibility of COTS eye tracking while students learn biology with an intelligent tutoring system called GuruTutor in their classroom. We could successfully track eye gaze in 75% (both eyes tracked) and 95% (one eye tracked) of the cases for 85% of the sessions where gaze was successfully recorded. In Study 2, we used this data to build automated student-independent detectors of mind wandering, obtaining accuracies (mind wandering F₁?=?0.59) substantially better than chance (F₁?=?0.24). Study 3 investigated context-generalizability of mind wandering detectors, finding that models trained on data collected in a controlled laboratory more successfully generalized to the classroom than the reverse. Study 4 investigated gaze- and video- based mind wandering detection, finding that gaze-based detection was superior and multimodal detection yielded an improvement in limited circumstances. We tested live mind wandering detection on a new sample of 39 students in Study 5 and found that detection accuracy (mind wandering F₁?=?0.40) was considerably above chance (F1?=?0.24), albeit lower than offline detection accuracy from Study 1 (F₁?=?0.59), a finding attributable to handling of missing data. We discuss our next steps towards developing gaze-based attention-aware learning technologies to increase engagement and learning by combating mind wandering in classroom contexts.

     

Design and evaluation of computerized operating procedures in nuclear power plants

A small-scale virtual system has been developed in this study to enhance operators' understanding and operating performance. For this, a computerized graphical interface based on Dynamic Work Causality Equation (DWCE) has been designed to transform the operating procedure into a flowchart. Furthermore, the Programmable Logic Controller (PLC) was installed to connect the signboard (proposed system) with the computerized graphical interface. An experiment was conducted to verify the effect of computerized graphic interface, indicating that the computerized system significantly decreases learning time and improves operational performance.     

Design and evaluation of computerized operating procedures in nuclear power plants

A small-scale virtual system has been developed in this study to enhance operators' understanding and operating performance. For this, a computerized graphical interface based on Dynamic Work Causality Equation (DWCE) has been designed to transform the operating procedure into a flowchart. Furthermore, the Programmable Logic Controller (PLC) was installed to connect the signboard (proposed system) with the computerized graphical interface. An experiment was conducted to verify the effect of computerized graphic interface, indicating that the computerized system significantly decreases learning time and improves operational performance.     

Automated structural analysis of SCR‐style software requirements specifications using PVS

The importance of effective requirements analysis techniques cannot be overemphasized when developing software requiring high levels of assurance. Requirements analysis can be largely classified as either structural or functional. The former investigates whether definitions and uses of variables and functions are consistent, while the latter addresses whether requirements accurately reflect users' needs. Verification of structural properties for large and complex software requirements is often repetitive, especially if requirements are subject to frequent changes. While inspection has been successfully applied to many industrial applications, the authors found inspection to be ineffective when reviewing requirements to find errors violating structural properties. Moreover, current tools used in requirements engineering provide only limited support in automatically enforcing structural correctness of the requirements. Such experience has motivated research to automate straightforward but tedious activities. This paper demonstrates that a theorem prover, PVS (Prototype Verification System), is useful in automatically verifying structural correctness of software requirements specifications written in SCR (Software Cost Reduction)‐style. Requirements are automatically translated into a semantically equivalent PVS specification. Users need not be experts in formal methods or power users of PVS. Structural properties to be proved are expressed in PVS theorems, and the PVS proof commands are used to carry out the proof automatically. Since these properties are application independent, the same verification procedure can be applied to requirements of various software systems. Copyright © 2001 John Wiley & Sons, Ltd.     

Automated structural synthesis for nondeterministic loads

Optimal design of structural systems subjected to probabilistic loads is posed as a standard nonlinear programming problem. The salient complexities of the problem are identified and solution strategies are proposed. Realistic design constraints pertaining to structural integrity of the optimized design are formulated. Structural fatigue is examined from the standpoint of crack propagation rates. The optimization system consists of a sequence of finite element subroutines interfaced with a feasible directions optimization algorithm through the COMMAND language on a VAX 11-750 computer. Representative numerical results are presented.     

Post-optimal procedures for structural optimization

Structural optimization is a very well established design tool in several engineering fields when the problem is formulated with a single objective function and the feasible design region turns out to be convex. Nevertheless, many real problems lead to more complex formulations, sometimes because more than one local minima exist, or because more than one objective function must be included in the formulation. For such cases two procedures intended to enhance the capabilities of design optimization, namely, one approach to global optimization and a recent procedure to obtain sensitivity analysis in multiobjective optimization, are presented in the paper.     

A note on three numerical procedures to solve Volterra integro-differential equations in structural analysis

In this paper, three numerical methods to solve Volterra integro-differential equations containing rational functions are discussed. The first one is the Differential Quadrature Method and, to the best knowledge of the author, it has never been applied to this kind of problem; the second one is a new version of the Iterative Differential Quadrature method, a method proposed by the author some years ago to solve problems in space–time domains, revised herein for the single space variable problem; the third one is a numerical Picard-like method, proposed herein to combine successive approximations with numerical integration. Stability and convergence of the second and the third method are discussed. The three methods have been applied to solve a real world problem in the field of the structural engineering and the numerical results compared.     

Efficient optimum seismic design of reinforced concrete frames with nonlinear structural analysis procedures

Performance-based seismic design offers enhanced control of structural damage for different levels of earthquake hazard. Nevertheless, the number of studies dealing with the optimum performance-based seismic design of reinforced concrete frames is rather limited. This observation can be attributed to the need for nonlinear structural analysis procedures to calculate seismic demands. Nonlinear analysis of reinforced concrete frames is accompanied by high computational costs and requires a priori knowledge of steel reinforcement. To address this issue, previous studies on optimum performance-based seismic design of reinforced concrete frames use independent design variables to represent steel reinforcement in the optimization problem. This approach drives to a great number of design variables, which magnifies exponentially the search space undermining the ability of the optimization algorithms to reach the optimum solutions. This study presents a computationally efficient procedure tailored to the optimum performance-based seismic design of reinforced concrete frames. The novel feature of the proposed approach is that it employs a deformation-based, iterative procedure for the design of steel reinforcement of reinforced concrete frames to meet their performance objectives given the cross-sectional dimensions of the structural members. In this manner, only the cross-sectional dimensions of structural members need to be addressed by the optimization algorithms as independent design variables. The developed solution strategy is applied to the optimum seismic design of reinforced concrete frames using pushover and nonlinear response-history analysis and it is found that it outperforms previous solution approaches.