Use Of Analytical Models Research Articles

Small-Angle X-Ray Scattering to Characterize Nanostructures in Inorganic and Hybrid Materials Chemistry

With the improved control of the nanostructure and the handling of multicomponent systems in sol–gel chemistry, the research interest in this field increased significantly in the past decade. For the characterization of the nanostructure of inorganic–organic hybrid materials, small-angle X-ray scattering has proven to be one of the most important techniques. By using X-rays from synchrotron radiation sources, even the structural development during processing can be followed in-situ. This short note reviews some analytical evaluation procedures used to study hybrid materials. While numerical simulation tools are nowadays available to obtain detailed fits of scattering curves, the use of analytical models is still very useful if the evaluation and interpretation of the obtained parameters is straightforward.

Microstructure-based modeling of the deformation behavior of particle reinforced metal matrix composites

A review is provided of the use of analytical models and two dimensional (2D) and three dimensional (3D) microstructure based FEM models to accurately predict the properties of particle reinforced composite materials. It is shown that analytical models do not account for the microstructural factors that influence the mechanical behavior of the material. 2D models do capture the anisotropy in deformation behavior induced by anisotropy in particle orientation. The experimentally-observed dependence of Young's modulus and tensile strength is confirmed by the 2D microstructure-based numerical model. However, because of the 2D stress state, a realistic comparison to actual experimental values is not possible. A serial sectioning process can be used to reproduce and visualize the 3D microstructure of particle reinforced metal matrix composites. The 3D microstructure-based FEM accurately represents the alignment, aspect ratio, and distribution of the particles. Comparison with single particle and multiparticle models of simple shape (spherical and ellipsoidal) shows that the 3D microstructure-based approach is more accurate in simulating and understanding material behavior.

Nonlinear reaction‐diffusion models of self‐organization and deterministic chaos: Theory and possible applications to description of electrical cardiac activity and cardiovascular circulation

The paper shows that analytical dynamic models coupled with the available signal processing methods could be used for describing the self‐organization and chaos degree in the heartbeats propagation and pressure pulses in ventricular at ejection phase. We proposed a unit analytical approach that could be associated with real ECG and pressure pulses signal processing. Our findings confirm that the real‐time computer monitoring of the main cardiovascular parameters obtained by the use of analytical models and verified by signal processing of real clinical data may be considered as available method for measuring and controlling self‐organization and chaos degree in pulse propagation.

SAFETY AND RELIABILITY ANALYSIS OF PROTECTION SYSTEMS FOR POWER SYSTEMS

This paper addresses the problem of risk analysis of protection systems and protection scheme of transmission grid. According to IEC 61508, a hybrid model has been developed supporting the analysis of protection systems. The use of analytic models in risk analysis of the elements of system protection scheme allows evaluating the security level associated to different protection strategies and supports the identification of specific ICT criticalities.

Ken Sevcik on Performance Evaluation

Ken Sevcik is Professor of Computer Science at the University of Toronto. He received his B.S. in 1966 from Stanford University and his PhD in 1971 from the University of Chicago. Sevcik joined the faculty at the University of Toronto in 1971, and was Chair of the Department from 1990 to 1992. He also served as Director of the Computer Systems Research Institute (CSRI). His research interests are in the use of analytic models for performance analysis of resource allocation, scheduling and file structures in computer systems, computer networks, and distributed data management systems.

Ken Sevcik on Performance Evaluation

Ken Sevcik is Professor of Computer Science at the University of Toronto. He received his B.S. in 1966 from Stanford University and his PhD in 1971 from the University of Chicago. Sevcik joined the faculty at the University of Toronto in 1971, and was Chair of the Department from 1990 to 1992. He also served as Director of the Computer Systems Research Institute (CSRI). His research interests are in the use of analytic models for performance analysis of resource allocation, scheduling and file structures in computer systems, computer networks, and distributed data management systems.

A dynamic model for the ideal-free distribution as a partial differential equation

One of the major approaches to understanding spatial effects in ecology and population dynamics is the use of analytic models. Some types of analytic models for spatial effects, such as dispersal models based on partial differential equations or integral kernels, can capture transient behavior and can be easily extended to incorporate population dynamics. Others, such as the ideal-free distribution or the species–area relationship derived from island biogeography theory, only provide equilibrium descriptions of the distribution of organisms or species but do not describe dynamic processes. The goal of this paper is to formulate a class of models based on partial differential equations whose equilibria are solutions to a version of the ideal-free distribution set in continuous space. One motivation is to formulate a dynamic version of the ideal-free distribution which can be compared with or incorporated into other sorts of dynamic models such as reaction–diffusion systems. Another motivation is to show how the global predictions of the ideal-free distribution can arise from simple assumptions about local dispersal behavior. The main results are derivations of partial differential equations using ideas related to Fick's law for diffusion, and alternatively by taking a continuum limit of a discrete model, and a verification that under appropriate hypotheses the solutions to those partial differential equations approach equilibria that satisfy the ideal-free distribution.

Analytical models for low-power rectenna design

The design of a low-cost rectenna for low-power applications is presented. The rectenna is designed with the use of analytical models and closed-form analytical expressions. This allows for a fast design of the rectenna system. To acquire a small-area rectenna, a layered design is proposed. Measurements indicate the validity range of the analytical models.

Component-Based Approach in the Development of a Knowledge-Based Planning Support System (KBPSS). Part 1: The Architecture of KBPSS

Urban planners need to have a flexible, interactive, and intelligent computer-based tool to support their use of analytical models and to structure their planning process. Existing spatial information systems have not developed appropriate procedures and mechanisms to enable easy construction and manipulation of models within their system environment, and to allow various information resources to be shared by different application systems and platforms. Recent research and development of planning support systems (PSS) provide a range of interesting concepts and frameworks that can be adopted by system developers to design a multifunctional and planning-specific decision support system to meet the multifaceted needs of the planning process. In this paper we aim to go beyond the current approaches of PSS and spatial decision support systems (SDSS) in designing a knowledge-based PSS (KBPSS) that uses the component-based software development (CBSD) approach. We introduce the features of CBSD and its technical advantages in the design of a multifunctional PSS. An architecture of a component-based KBPSS is subsequently proposed which incorporates four essential component systems: MapObjects GIS, Database Manager database management system, ModelObjects model-management system, and KBSAgents knowledge-based system. The first two components are based on proprietary components systems and can be easily adapted into the KBPSS environment. The ModelObjects and KBSAgents components were developed by the authors. Based on these components and their associated information layers, two application subsystems are constructed: a Model and Knowledge Development System and an Intelligent Model Selection System. These application systems can be used to assist users and model developers to build new models or to select predefined models from an existing model library for their problems. In order to implement these functions, we propose and define a number of procedures and techniques for component communication and model and knowledge development.

Productivity Preservation Through Hydraulic Propped Fractures in the Eldfisk North Sea Chalk Field

Summary The Eldfisk oil field is a high-porosity, low-permeability reservoir of soft chalk in the Norwegian North Sea. Commercial oil production from the Eldfisk field is dependent on well stimulations. To date, pseudolimited-entry acid stimulation (PLEAS) has been the standard completion technique. This technique initiates relatively high (5,000 BOPD) individual-well oil-production rates. Over time, however, many of the Eldfisk wells have experienced rapidly declining oil production characterized by wellbore skin increase and fracture closure. Solids production and casing collapse have also been problematic. In late 1997, an alternative completion technique involving four hydraulic propped-fracture stages was successfully executed in an Eldfisk horizontal well. This paper presents a simple methodology to evaluate sustained productivity enhancement of propped fractures vs. acid stimulations in soft chalk formations based on the use of analytical modeling in combination with empirical production-data analysis.

Use of pharmacoeconomics in prescribing research. Part 5: modelling--beyond clinical trials.

This paper provides an overview of modelling in the economic evaluation of pharmaceuticals, reflecting the increasing use of models in analyses prepared for reimbursement applications to national and local drug formularies. The paper seeks to demystify the most commonly encountered modelling techniques (extrapolation, decision analysis, Markov modelling and Monte Carlo simulation), and to provide guidance in assessing the quality of submitted or published modelled economic evaluations.

Enterprise-wide analytical solutions for distribution planning

Today's retail business leaders use enterprise-wide decision support tools to guide market expansion strategy and optimisation of existing networks. In particular, distribution planning models are deployed to guide site selection, determine store formats and optimise store networks. These models, however, require the integration of an array of transaction, customer and demographic market data. Once combined, special methods are required to meet the unique assumptions of geospatial analysis and to handle data collected at different levels of aggregation. This paper reviews the use of analytical models within distribution planning systems. A typical distribution planning system is described. Technology, data and analytical components are detailed. Then five key applications are described for retail and banking.

Physical model for enhanced interface-trap formation at low dose rates

We describe a model for enhanced interface-trap formation at low dose rates due to space-charge effects in the base oxides of bipolar devices. The use of analytical models allows one to reduce significantly the number of free parameters of the theory and to elucidate the main physical mechanisms that are responsible for interface-trap and oxide-trap formation processes. We found that the hole trapping in the oxide cannot be responsible for all the enhanced low-dose-rate sensitivity (ELDRS) effects in SiO/sub 2/, and the contribution of protons is also essential. The dynamics of interface-trap formation are defined by the relation between the proton mobility (transport time of the protons across the oxide) and the time required for positive-charge buildup near the interface due to trapped holes. The analytically estimated and numerically calculated interface-trap densities were found to be in very good agreement with available experimental data.

Successful treatment of sublexical reading deficits in a child with dyslexia of the mixed type

The application of cognitive neuropsychological theories to the design and implementation of treatment programmes remains relatively unexplored, especially in children. In addition, cognitive neuropsychological treatment programmes for dyslexia to date have focused on specific dyslexias such as phonological and surface dyslexia and have ignored the large subgroup of children with severe and multiple impairments of the reading system, those with mixed dyslexia. This study evaluates a sublexical treatment programme designed for a child with dyslexia of the mixed type. The treatment approach is based on sublexical treatment programmes that have been reported in cases of adult acquired dyslexia (Berndt & Mitchum, 1994; De Partz, 1986; Nickels, 1992). The focus of treatment is on nonword reading and includes training in grapheme parsing, grapheme-to-phoneme knowledge, and phoneme blending. Treatment outcome is measured through extensive pre- and post-treatment assessment of sublexical and lexical processing, semantics, and general phonology. The treatment design enables an objective assessment of treatment efficacy, stability of treatment effects over time and generalisability of the treatment to untreated stimuli and related language processes. The study illustrates the validity of the use of models and methods derived from work with adults with acquired impairments to paediatrics, and the usefulness of analytical models in cases of severe mixed dyslexia.

Assessing the costs of compliance: the Kyoto Protocol

AbstractAfter the political agreement at the Bonn climate talks, the Kyoto Protocol is now ready for ratification. Key policy questions surrounding the ultimate implementation of the Kyoto Protocol and any follow‐up international agreement on climate protection require quantitative assessment, i.e. the use of analytical models that mimic the potential economic impacts of alternative emission reduction policies. In this paper, we assess the costs of compliance with the Kyoto Protocol. The simulation results reveal why the USA has withdrawn from the Kyoto Protocol, while several other Annex B countries have pushed for an implicit relaxation of their Kyoto targets. International trade in emissions significantly reduces the total costs of compliance with Kyoto. We also explore the robustness of results with respect to changes in the values of key elasticities as well as other major assumptions, such as the baseline growth path or the scope of the abatement coalition (Kyoto with and without the USA). The sensitivity analysis helps to create an understanding of key assumptions that determine the quantitative model results and the policy conclusions to be drawn. Copyright © 2002 John Wiley & Sons, Ltd. and ERP Environment

Analytical analysis of finite cache penalty and cycles per instruction of a multiprocessor memory hierarchy using miss rates and queuing theory

Advances in technology have provided a continuing improvement in processor speed and capacity of attached main memory. The increasing gap between main memory and processor cycle times has required increasingly more levels of caching to prevent performance degradation. The net result is that the inherent delay of a memory hierarchy associated with any computing system is becoming the major performance-determining factor and has inspired many types of analysis methods. While an accurate performance-evaluation tool requires the use of trace-driven simulators, good approximations and significant insight can be obtained by the use of analytical models to evaluate finite cache penalties based on miss rates (or miss ratios) and queuing theory combined with empirical relations between various levels of a memory hierarchy. Such tools make it possible to readily determine trends in performance vs. changes in input parameters. This paper describes such an analysis approach--one which has been implemented in a spreadsheet and used successfully to perform early engineering tradeoffs for many uniprocessor and multiprocessor memory hierarchies.

Optimal extraction of optical coefficients from scattering media

An analysis is presented of the accuracy with which the optical coefficients of scattering media may be measured. The results have application for comparing performance of different optical arrangements and optimising experimental configurations. The analysis is applicable to distributed data such as temporal, spatial or angular intensities from which measurables are obtained. The relationship between optical coefficients and these measurables may be obtained through use of analytical models or Monte Carlo simulations. The measured distributions are characterised here by first and second normalised moments, and applied to the case of measuring the spatial distribution of intensity transmitted through a slab of scattering media. The analysis is used to establish the optimum slab thickness for extraction of the absorption coefficient.

Laboratory measurement of sampled infrared imaging system performance

An infrared imager (often referred to as a FLIR, from the term forward looking infrared) can be characterized in terms of sensitivity, resolution and human performance. Sensitivity, resolution and human performance have been classically described by the following measurable parameters: noise equivalent temperature difference (NETD), modulation transfer function (MTF) and minimum resolvable temperature difference (MRTD or MRT). These are laboratory measurable quantities that can be used to verify the performance of an infrared system. These laboratory measurements are used to evaluate expected design performance and to periodically test an imager during its life cycle. These quantities are predictable in sensor design through the use of analytical models. Both model estimates and laboratory measurements can be used in a target acquisition model to determine the field performance (probability of detection, recognition or identification) of the imager. Sensitivity, resolution, and human performance are influenced by sampling artifacts that must be characterized. First, sensitivity is no longer sufficiently described by a single-valued NETD. The 3-D noise methodology, inhomogeneity equivalent temperature difference (IETD), and correctability are noise figures that have been developed over the past decade to more adequately describe both temporal and fixed pattern noise associated with focal plane arrays. Undersampled imaging systems are not shift-invariant. The shift-invariance condition, in particular, is compromised by under-sampling so that sensor performance becomes a function of phase (relative position between the image and the detector array). Resolution depends on the target-to-imager phase, so the MTF measurement may reveal sampling artifacts that give large MTF variations with target to sensor position. Finally, the human-performance parameter is perhaps most affected by undersampling. MRT can be strongly dependent on phase, where dramatic differences in measured MRT are attributed to different phase shifts. MRT is normally measured at optimum phase, yet the authors don't feel that static MRT measured with either optimum or unknown phase relationships correlate well with field performance. In the same way, it is not clear how to write field acquisition calculations based on MRT values measured past the half-sample (Nyquist) rate. A dynamic MRT method has been developed and measured which uses motion to provide enhanced sampling.

Case study modeling of turbulent and mesoscale fluxes over the BOREAS region

Results from aircraft and surface observations provided evidence for the existence of mesoscale circulations over the Boreal Ecosystem‐Atmosphere Study (BOREAS) domain. Using an integrated approach that included the use of analytical modeling, numerical modeling, and data analysis, we have found that there are substantial contributions to the total budgets of heat over the BOREAS domain generated by mesoscale circulations. This effect is largest when the synoptic flow is relatively weak, yet it is present under less favorable conditions, as shown by the case study presented here. While further analysis is warranted to document this effect, the existence of mesoscale flow is not surprising, since it is related to the presence of landscape patches, including lakes, which are of a size on the order of the local Rossby radius and which have spatial differences in maximum sensible heat flux of about 300 W m−2. We have also analyzed the vertical temperature profile simulated in our case study as well as high‐resolution soundings and we have found vertical profiles of temperature change above the boundary layer height, which we attribute in part to mesoscale contributions. Our conclusion is that in regions with organized landscapes, such as BOREAS, even with relatively strong synoptic winds, dynamical scaling criteria should be used to assess whether mesoscale effects should be parameterized or explicitly resolved in numerical models of the atmosphere.

Effect of capacity concentration on highway corridor performance

This paper investigates, through use of analytical models, the effects of capacity concentration on highway corridor performance. It concludes that when highways operate at a fixed total capacity, decreasing the highway spacing can increase the average travel time because highways will become more congested. When highways operate below capacity, decreasing the spacing is usually beneficial as it tends to reduce trip length when accessing highways, and allows a greater percentage of travel to be completed on highways instead of arterials.