bluuebunny/crossref_metadata_2025 huggingface dataset:
Fabrication of Polycaprolactone Bone Tissue Engineering Scaffolds Using Selective Laser Sintering
Authors: Partee Brock , Hollister Scott J. , Das Suman
Published: April 2008

Tissue engineering combines principles of the life sciences and engineering to replace and repair damaged human tissue. Present practice generally requires the use of porous, bioresorbable scaffolds to serve as temporary 3D templates to guide cell attachment, differentiation, proliferation, and subsequent regenerate tissue formation. Such scaffolds are anticipated to play an important role in allowing physicians to simultaneously reconstruct and regenerate damaged human tissue such as bone, cartilage, ligament and tendon. Recent research strongly suggests the choice of scaffold material and its internal porous architecture significantly influence regenerate tissue structure and function. However, a lack of versatile biomaterials processing and fabrication methods capable of meeting the complex geometric and compositional requirements of tissue engineering scaffolds has slowed progress towards fully testing these promising findings. It is widely accepted that layered manufacturing methods such as selective laser sintering (SLS) have the potential to fulfill these needs. Our research aims to investigate the viability of using SLS to fabricate tissue engineering scaffolds composed of polycaprolactone (PCL), one of the most widely investigated biocompatible, bioresorbable materials for tissue engineering applications. In this work, we report our recent progress on porous scaffold design and fabrication, optimal SLS processing parameter development using systematic factorial design of experiments, and structural characterization via optical microscopy.
Kagome-Based High Authority Shape Morphing Structure
Authors: dos Santos e Lucato S. L. , McMeeking R. M. , Evans A. G.
Published: April 2008

A concept for a high authority shape morphing plate is described and demonstrated. The design incorporates an active back-plane comprising a Kagome truss, capable of changing the shape of a solid face, connected to the back-plane by means of a tetrahedral truss core. The two shape deformations to be demonstrated consist of hinging and twisting. The design is performed by a combination of analytic estimation and numerical simulation, guided by previous assessments of the Kagome configuration. It is shown that, while the structure is capable of sustaining large passive loads at low weight, the demonstrable authority is actuator-limited. An optimization based on a genetic algorithm has been used to determine the best placement of a limited number of actuators in the structure for a given set of target shapes. The force capability of the actuators and failure threshold loads of the structure were ascertained in the optimization. Possible applications of such multi-shape morphing structures include ailerons and mirrors.
A Theoretical Study of the Turbine Flowmeters With Magnetic Bearing
Authors: Sun Lijun , Zhang Tao
Published: April 2008

A novel structure of the turbine flow meter with magnetic bearing is put forward. The analysis of the structure of the turbine flowmeter with magnetic bearing and the theoretical calculation of the characteristics of the magnetic bearing are shown. It is found that there is difference between the axial force and the radial stiffness of the axially magnetized radial magnetic bearing and those of the radially magnetized one, as the shape, the dimensions and the intensity of magnetization are same. The universal model, which ignores the effects of the curvature on the accuracy of the calculation and deals with the magnetic rings as infinite long line magnets, is only suitable for the case of all the magnetic ring section dimensions are very small in comparison with the ring radius, and those are less than or equal to the gap between the two rings. The numerical integral model is accurate, which is based on the method of equivalent charges of magnetism and the direction of magnetization. The preliminary discussion of the problems occurred during the development of the turbine meter is shown also.
A Comprehensive Evaluation of NHTSA Rollover Test Data for Use in Computational Model Validation
Authors: Martin Mark R. , Allen Kerry
Published: April 2008

Increased computational power and new software have brought occupant motion simulation into the mainstream for vehicle accident reconstructionists. Using programs available today, investigators are able to achieve numerical results that match actual physical results with a high degree of accuracy. It should therefore be possible to validate the performance of a software simulation using instrument data collected from a real vehicle test. For valid results, however, one must have valid data upon which to base the simulation. We attempted to validate MADYMO occupant motion simulation software by using data from the National Highway Traffic Safety Administration (NHTSA) vehicle crash test database for vehicle rollovers. In the course of our work, we discovered flaws in the NHTSA database that rendered it useless for both validating and disputing a computational simulation. These flaws included data that did not match the descriptions of vehicle travel in the written reports, entire channels of missing data, and others. NHTSA crash tests are often cited as reliable sources of data in vehicle crash situations. While not disputing the limited scientific value of these tests, this paper documents the problems with NHTSA test reports and concludes that the data contained therein can be unintentionally misleading and of little value for computational model validation of rollover simulations. This paper also presents testing improvement procedures that should allow a greater correlation of computational and testing data.
Nonlinear Dynamics and Stability of Circular Cylindrical Shells
Authors: Pellicano F. , Catellani G. , Amabili M.
Published: April 2008

The nonlinear dynamic response of an imperfect circular cylindrical shell under combined static and dynamic axial load is analyzed. A suitable expansion of the radial displacement, able to describe both buckling and dynamic behaviors is developed; the effect of geometric imperfections is accounted for. The response of the shell subjected to a sinusoidal axial excitation at its ends, giving rise to a parametric excitation, is considered. The effect of the imperfections on the critical value of the dynamic load, that causes the loss of stability of the system, is analyzed. Interesting nonlinear dynamic phenomena are observed: direct resonance with softening behavior and parametric instability with period doubling response.
Treating Uncertainties in Multibody Dynamic Systems Using a Polynomial Chaos Spectral Decomposition
Authors: Sandu Corina , Sandu Adrian , Chan Brendan J. , Ahmadian Mehdi
Published: April 2008

This study addresses the critical need for computational tools to model complex nonlinear multibody dynamic systems in the presence of parametric and external uncertainty. Polynomial chaos has been used extensively to model uncertainties in structural mechanics and in fluids, but to our knowledge they have yet to be applied to multibody dynamic simulations. We show that the method can be applied to quantify uncertainties in time domain and frequency domain.
Function Based Risk Assessment and Failure Prediction for Unmanned Space Missions
Authors: Uder Scott J. , Stone Robert B. , Tumer Irem Y.
Published: April 2008

A strong need has emerged in the aerospace industry for a well-founded and effective failure prevention technique or process that can be employed during the conceptual design of high-risk aerospace systems. In this paper, we describe a methodology to support risk assessment and failure prevention during the earliest stages of spacecraft design and mission planning. The three-step procedure, an extension of the Function-Failure Design method, utilizes detailed information from existing subsystems and systematically abstracts this information to a level that can be used during conceptual design. During this process, we address the issue concerning the level at which systems containing a combination of electrical and mechanical components should be functionally modeled. The complete method is described in general before being applied to two major unmanned spacecraft subsystems.
Changes in Viscoelastic Properties of Brain Tissue Due to Traumatic Injury
Authors: Darvish Kurosh , Stone James
Published: April 2008

In this study, changes in viscoelastic material properties of brain tissue due to traumatic axonal injury (TAI) were investigated. The impact acceleration model was used to generate diffuse axonal injury in rat brain. TAI in the corticospinal (CSpT) tract in the brain stem was quantified using amyloid precursor protein immunostaining. Material properties along the CSpT were determined using an indentation technique. The results showed that the number of injured axons at the pyramidal decussation (PDx) was approximated 10 times higher than in the ponto-medullary junction (PmJ). The instantaneous elastic response was reduced approximately 70% at PDx compared to 40% at PmJ and the relaxation was uniformly reduced approximately 30%, which were attributed to the effect of injury on tissue properties. Application of a visco-elastic-plastic model that changes due to TAI can significantly alter the results of computational models of brain injury.
Tuned Damping of an Air-Mounted Isolation System
Authors: Kashani Reza , Mirza Kazim
Published: April 2008

Air mounts can provide the highest degree of isolation of any type vibration isolator. Soft-mounting, and thus high level of low-frequency isolation, with system natural frequency as low as 1 Hz can be achieved. Due to their construction, air mounts have negligible damping. Although, this almost undamped nature of air mounts enhances the high-frequency isolation, provisions should be made to address the lack of isolation resulting in excessive body displacements around the resonant frequencies, especially when the system is exposed to shock inputs. While the addition of viscous damping to the air mount is proposed in the literature but it is not recommended in most applications. This is because it deteriorates the mount’s high-frequency isolation performance. Instead, it would be highly desirable to add tuned damping to the mounted system at its resonant frequency (ies). The challenge in doing so, is realizing a damper tunable to a very low frequency and yet not be prohibitively large. A novel tuned damping mechanism is proposed in this paper. It adds damping to an air mount only at the resonant frequency (ies), via a bi-fluid Helmholtz resonator. In an illustrative example the mechanics and mathematics (modeling) of a one and three degree of freedom air mounted systems equipped with a tuned damper, as well as the tuning of such damper are discussed. The example also demonstrates the effectiveness of the air mount with the tuned damper.
Design and Control of a Hydraulic Human Power Amplifier
Authors: Li Perry Y.
Published: April 2008

This paper describes the design of and some preliminary control results for a hydraulically actuated human power amplifier. The system is in the form of an oar, with its reach and pitch degrees of freedom being hydraulically assisted. A robust PI force controller is proposed so that the hydraulic actuator force tracks a scaled copy of the force exerted by the human. Nonlinearities and uncertainties in the compression spring, as well as parametric uncertainties are taken into account. The passivity property of the closed loop system is also analyzed. The controller has been tested in simulations and experimentally. It is shown to be effective when pushing against an object, and in assisting in bearing static loads.
Performance Optimization of a Coal Preparation Plant Using Genetic Algorithms
Authors: Gupta Vishal , Mohanty Manoj K. , Mahajan Ajay , Biswal Surendra K.
Published: April 2008

A coal preparation plant typically has multiple cleaning circuits based on size of coal particles. The traditional way of optimizing the plant output and meeting the product constraints such as ash, sulfur and moisture content is to equalize the average product quality from each circuit. The present study includes multiple incremental product quality approach to optimize the clean coal recovery while satisfying the product constraints. The plant output was optimized at the given constraints of 7.5% ash and 1.3% sulfur. It was observed that utilizing incremental product quality process gives 2.13% higher yield which can generate additional revenue of $4,260,000 per annum than that obtained by using the equal average product quality approach in this particular case. This paper introduces a novel approach for optimizing plant output using Genetic Algorithms (GA) while satisfying the multiple quality constraints. The same plant product constraints were used for GA based analysis. The results showed that using GA as an optimization process gives 2.23% higher yield that will result in additional revenue generation of $4,460,000 per annum than average product quality approach. The GA serves as an alternative process to optimize the coal processing plant yield with multiple quality constraints.
Filtration Model of Aerosol Particles by Fibrous Filters
Authors: Zhong Wen , Pan Ning
Published: April 2008

Aerosol filtration by fibrous filters is one of the most common methods of separating and removing particles in micro and sub-micro size ranges. The statistical genesis of this process can be regarded as the interactions and the resulting equilibrium among particle and fiber cells that comprise the system. Therefore a statistical mechanics approach, the Ising’s model, combined with Monte Carlo simulation, is employed in studying the process of the aerosol filtration through fibrous filters. The process is modeled as consisting of numerous cell state exchanges driven by the difference of system energy after and before a particle moves from one cell to the other and/or deposits on a fiber cell. With the use of a simpler binary algorithm, this approach is capable of realistically simulating the complicated mechanisms involved in the filtration process. For verification, simulations are carried out for the behaviors of aerosol particles of different sizes through isotropic fiber filters with various volume fractions. Simulation results are in good agreements with reported experimental data.
Forced Convection in a Microchannel Heat Sink Using Carbon Nanotubes for Heat Transfer Enhancement
Authors: Jakaboski Blake E. , Joshi Yogendra , Rightley Michael
Published: April 2008

A new type of microchannel heat sink has been developed and evaluated in this study. The device consists of silicon microchannels on whose bottom surfaces multi-walled carbon nanotubes are grown. The objective of the study is to investigate the effect of carbon nanotubes on the heat transfer characteristics. The heat sink size is 15 mm × 15 mm × 0.675 mm. It contains two microchannel designs. One consists of eight channels of cross section 682 μm × 50 μm; the other has six channels of cross section 942 μm × 50 μm. The heat sink is incorporated in an open loop flow facility, with water as the coolant. Six different configurations are compared. Two have no nanotubes, two have closely spaced nanotube, while the last two designs have widely spaced nanotubes. The tests utilize an infrared camera as well as thermocouples placed in the flow for characterization. The heat transfer characteristics are compared for the different cases.
Mechanical Behaviors of Woven Fabrics
Authors: Sun Huiyu , Pan Ning
Published: April 2008

This paper introducing some recent research progress consists of two parts: the shear deformation analysis and Poisson’s ratios for woven fabrics. The analytical methods of the shear moduli and Poisson’s ratios for woven fabrics will enable more rigorous studies on such important issues of fabric bending and draping behaviors. A new mechanical model is proposed in this paper to evaluate the shearing properties for woven fabrics during the initial slip region. Compared to the existing mechanical models for fabric shear, this model involves not only bending but also torsion of curved yarns. Analytical results show that this model provides better agreement with the experiments for both the initial shear modulus and the slipping angle than the existing models. Furthermore, another mechanical model for a woven fabric made of extensible yarns is developed to calculate the fabric Poisson’s ratios. Theoretical results are compared with the available experimental data. A thorough examination on the influences of various mechanical properties of yarns and structural parameters of fabrics on the Poisson’s ratios of a woven fabric is given.
Fuzzy Validation and Fusion for Wireless Sensor Networks
Authors: Wen Yao-Jung , Agogino Alice M. , Goebel Kai
Published: April 2008

Miniaturized, distributed, networked sensors — called motes — promise to be smaller, less expensive and more versatile than other sensing alternatives. While these motes may have less individual reliability, high accuracy for the overall system is still desirable. Sensor validation and fusion algorithms provide a mechanism to extract pertinent information from massively sensed data and identify incipient sensor failures. Fuzzy approaches have proven to be effective and robust in challenging sensor validation and fusion applications. The algorithm developed in this paper — called mote-FVF (fuzzy validation and fusion) — uses a fuzzy approach to define the correlation among sensor readings, assign a confidence value to each of them, and perform a fused weighted average. A sensor network implementing mote-FVF for monitoring the illuminance in a dimmable fluorescent lighting environment empirically demonstrates the timely response of the algorithm to sudden changes in normal operating conditions while correctly isolating faulty sensor readings.
Numerical Simulation of Unsteady-Flow Processes in Wave Rotors
Authors: Frackowiak Martin , Iancu Florin , Potrzebowski Adam , Akbari Pezhman , Mu¨ller Norbert , Piechna Janusz
Published: April 2008

The wave rotor (pressure exchanger) is a device working based on a relatively simple idea of operation, but is challenging in its technical realization and difficult to simulate numerically. It has been common practice to create and use specialized codes for simulating the wave rotor operation. The current work presents an attempt of developing 2D and 3D models of radial and axial wave rotors using the commercial software package FLUENT. In this study geometrical models are used for the device casing and rotor cells. The application of carefully chosen initial and boundary conditions enabled the realization of relative motion of the rotor model. The vast information about the unsteady processes occurring during simulation are visualized. It occurs that such type of models are useful for the final test of devices, after the geometry was optimized by the use of specialized but much simpler 1D codes.
Numerical Analysis of the Biomechanical Characteristics and Impact Response of the Human Chest
Authors: Kimpara Hideyuki , Iwamoto Masami , Watanabe Isao , Miki Kazuo , Lee Jong B. , Yang King H. , King Albert I.
Published: April 2008

The mass density, Young’s modulus (E), tangent modulus (Et) and yield stress (σy) of the human ribs, sternum, internal organs and muscles play important roles when determining impact responses of the chest associated with pendulum impact. A series of parametric studies was conducted using a commercially available three-dimensional finite element (FE) model, Total HUman Model for Safety (THUMS) of the whole human body, to determine the effect of changing these material properties on the impact force, chest deflection, and the number of rib fractures and fractured ribs. Results from this parametric study indicate that the initial chest stiffness was mainly influenced by the mass density of the muscles covering the torso. The number of rib fractures and fractured ribs were primarily determined by E, Et and σy of the ribcage and sternum. Similarly, the E, Et and σy of the ribcage, which is defined as the bony skeleton of the chest, and sternum and E of the internal organs contributed to the maximum chest deflection in frontal impact, while the maximum chest deflection for lateral impact was mainly affected by the E, Et and σy of the ribcage.
Development of a Measuring System for the Measurement of Motions Errors of a Linear Stage
Authors: Jywe Wen-Yuh , Liu Chien-Hung , Tzeng Sheng-Chung , Chou Po , Lin Chu-Wei
Published: April 2008

A high precision six-degree-of-freedom measuring system is developed in this paper for the motion measurement of a linear stage. It integrates a miniature dual-beam fiber coupled laser interferometer with the multiple optical paths and quadrant detectors to be capable of measuring six-degree-of-freedom motion errors. The proposed measuring method provides rapid performance, simplicity of setup, and pre-process verification of a linear positioning stage. The experimental setup and algorithm for the error verification are presented in the paper. The measuring range of the proposed measuring system is ±40μm for straightness and 40 arc sec for pitch, roll and yaw. Within the range of ±40μm and 40 arc sec, it has been found that the system’s resolution and accuracy of measuring straightness error components are about 0.04 μm and ±0.06 μm, respectively. The resolution and accuracy of measuring pitch and yaw angular error components are about 0.06 arc sec and ±0.8 arc sec, respectively. The resolution and accuracy of measuring roll angular error are about 0.05 arc sec and ±0.07 arc sec, respectively.
Developing a Virtual Model of a Second Order System to Simulation Real Laboratory Measurement Problems
Authors: Avitabile Peter , Van Zandt Tracy
Published: April 2008

Most of the student’s educational exposure is to well behaved, deterministic problems with known results. Most courses expose students to material in compartmentized modules (chapters of a book) with exercises/problems (at the end of the chapter) where the majority of the material is readily found in the compartmentized module. Unfortunately, real world problems never fit this simple mold. Laboratory is the perfect place for students to become exposed to real world problems and solutions to those problems. Laboratory is the perfect place to put all the student’s knowledge of basic STEM material to the test. However, many times the real world measurement is much more complicated than the textbook problems and students often struggle with methods and procedures to solve a given problem (with no answer at the back of the book). This is true for a mechanical measurement of a simple second order mass, spring, dashpot system which is measured with displacement and acceleration instruments in an existing mechanical engineering laboratory exercise. The measurement is plagued with measurement errors, drift, bias, digital data acquisition amplitude/quantization errors, etc. In order to understand the basic underlying measurement and associated “problems” with the measurement, a simple simulation model was developed. The simulation model allows the students to define a basic second order system and then add different types of “problems” (drift, bias, quantization, noise, etc) to the measurement to see their effects. The simulation module further allows the student to “cleanse” the distorted data using common measurement tools such as coupling, filtering, smoothing, etc. to understand the effects of processing the data. The simulation model is built using Simulink/MATLAB and allows a simple GUI to modify the model, the “problems” added to the data and the “cleansing” of the data, to obtain a better understanding of the problem and tools to process the data. The simulation model is presented and discussed in the paper. Several data sets are presented to illustrate the simulation module.
Dynamic Analysis of Constrained Mechanical Systems Considering Their Statistical Properties
Authors: Choi Dong Hwan , Lee Se Jung , Yoo Hong Hee
Published: April 2008

A method of dynamic analysis and reliability analysis of constrained mechanical systems considering their statistical properties is presented in this paper. Statistical properties, which result from manufacturing tolerances, can be represented by means or variances and standard deviations. The statistical characteristics of dynamic responses of mechanical systems with tolerances are obtained by two ways: the analytic method and the Monte Carlo method. The former necessitates sensitivity information. In this paper, a direct differentiation method is used to find the sensitivities of mechanical systems. The first order variance is considered in tolerance analysis. To verify the accuracy of the proposed method, three numerical examples are solved and the results obtained by using the proposed analytic method are compared to those obtained by the Monte Carlo simulation.
Analysis of Gear Noise and Dynamic Transmission Error Measurements
Authors: Henriksson Mats
Published: April 2008

Measurements of dynamic transmission error (DTE) and noise have been performed on a truck gearbox. The DTE is related to the dynamic properties of the complete gear system. To investigate the coupling between noise and DTE, the correlation between noise and DTE is calculated for fixed speeds, as the torque is increased. The highest correlation is found for the low split gear pair, which is located closest to the gearbox housing. When the correlation is low, one of the reasons can be a resonance of the shafts, although not all resonances effect the correlation between noise and DTE. The DTE is also compared to calculated static TE for the gear teeth. Both the DTE and noise for the fifth gear increases as the torque is increased. The calculated static TE shows the opposite trend and decreases as the torque is increased.
Effect of Plunger Design on the Constricting Forces in an Adjustable Systemic to Pulmonary Artery Shunt
Authors: Thuramalla Naveen V. , Douglas William I. , Rachakonda Prem , Jacob Jamey D. , Knapp Charles F.
Published: April 2008

Hypoplastic left heart syndrome (HLHS) is a leading cause of cardiac death among newborns, in which the entire left side of the heart is underdeveloped and unable to support the blood circulation. It is the most common type of single ventricle physiology (SVP) and an important need for an adjustable systemic to pulmonary artery (SPA) shunt. In order to achieve full range control of blood flow between the systemic and pulmonary circulation, an adjustable SPA shunt is being developed. SPA shunts are generally made from FDA approved polytetrafluroethylene (PTFE). A screw-plunger mechanism is being used to cause the desired constriction in the pressurized shunt. It is necessary to optimize the design of the plunger, in order to vary the cross-section of the shunt with minimum forces required. An in vitro set up consisting of a hydraulic circuit to have a constant inlet pressure to the shunt throughout the process and a certain post shunt pressure initially, plunger attached to the force gauge mounted on a stand to cause constriction and measure forces, a mounting stand to hold the shunt and its casing, a flow meter and pressure transducers, is used to determine the effect of various plunger tip shapes. It was observed that wider the plunger, lesser is the force required to cause the same reduction in flow. Flow-displacement-force variations for each plunger tip used are also presented. Results from this study will be used to determine the torque required to drive the screw plunger mechanism to cause the desired constriction.
Deflection Control of a Corner-Supported Plate Using Segmented In-Plane Actuators
Authors: Sumali Hartono , Massad Jordan E. , Chaplya Pavel M. , Martin Jeffrey W.
Published: April 2008

This paper describes an array of in-plane piezoelectric actuator segments laminated onto a corner-supported substrate to create a thin bimorph for reflector applications. An electric field distribution over the actuator segments causes the segments to expand or contract, thereby effecting plate deflection. To achieve a desired bimorph shape, the shape is first expressed as a two-dimensional series expansion. Then, using coefficients from the series expansion, an inverse problem is solved that determines the electric field distribution realizing the desired plate shape. A static example is presented where the desired deflection shape is a paraboloid.
A Novel Micropump for Electronics Cooling
Authors: Singhal Vishal , Garimella Suresh V.
Published: April 2008

A novel micropump design for electronics cooling applications capable of integration into microchannel heat sinks is presented. The pumping action is due to the combined action of Coulomb forces due to induction electrohydrodynamics (EHD) and a vibrating diaphragm with nozzle-diffuser elements for flow rectification. A comprehensive numerical model of the micropump accounting for transient charge transport and vibrating diaphragm deformation is developed. Each component of the model is validated by comparing to analytical, numerical or experimental results from the literature. It is shown that the flow rate achieved by the micropump with combined action of EHD and vibrating diaphragm can be higher than the sum of flow rates achieved from the action of the EHD and the vibrating diaphragm, independent of each other.
Rapid Prediction of BGA Board Level Reliability Due to PWB Flexure
Authors: Zhang Chuntao
Published: April 2008

BGA interconnect fatigue failure due to printed wiring board (PWB) flexure has been one of the top board-level reliability issues in portable electronic devices as products become smaller and lighter. Although much effort has been expended in the past to investigate the effect of package design on component bending reliability, the effects of PWB structural parameters such as board support and component location on board-level reliability have not been well studied. As a result, data and information currently available for design assistance are limited. In this study, a methodology was developed to systematically characterize the component board level reliability due to PWB flexure. Response surfaces and correction factors were generated based on the systematic characterization with respect to the board structural parameters and other influential factors, and implemented in a software tool, permitting rapid reliability prediction of BGA board level reliability at the earliest stage of product development process to reduce cycle time.
Analysis of Medication Error Reports
Authors: Whitney Paul , Young Jonathan , Santell John , Hicks Rodney , Posse Christian , Fecht Barbara
Published: April 2008

In medicine, as in many areas of research and society, technological innovation and the shift from paper based information to electronic records has created a climate of ever increasing availability of raw data. There has been a corresponding lag in our abilities to analyze this mass of data, and traditional forms and expressions of statistical analysis do not allow researchers and practitioners to interact with data in the most productive way. This is true in the emerging area of patient safety improvement. Traditionally, a majority of the analysis of error and incident reports are approached as data comparisons, and starts with a specific question which needs to be answered. Newer data analysis tools have been developed which allow the researcher to not only ask specific questions but also to “mine” data: approach an area of interest without preconceived questions, and explore the information dynamically, allowing questions to be formulated based on patterns brought up by the data itself. Additionally, the “types” of information objects that can be the objects of data analysis have been extended to include text [8][9]. Since 1991, United States Pharmacopeia (USP) has been collecting data on medication errors through voluntary reporting programs. USP’s MEDMARXsm reporting program is the largest national medication error database and currently contains well over 600,000 records. USP conducts an annual quantitative analysis of data derived from “pick-lists” (i.e., items selected from a list of items) without an in-depth analysis of free-text fields. In this paper, the application of text analysis and data analysis tools used by Battelle to analyze the medication error reports already analyzed in the traditional way by USP is described. New insights and findings were revealed including the value of language normalization and the distribution of error incidents by day of the week. The motivation for this effort is to gain additional insight into the nature of medication errors to support improvements in medication safety.
Local Exergy Cost Theory
Authors: Rangel V. H. , Uson S. , Valero A. , Cortes C.
Published: April 2008

The Exergy Cost Theory (ECT) is a technique extensively applied to optimizing, diagnosing and designing energy systems. But, despite of its wide applications it has its limitations. Such limitations have to do partly with the application to discrete systems solely and partly with the cost allocation problem. Thus in the present paper we go a step further in the scope of the ECT and propose to enlarge its applicability to continuous systems. Essentially, this is carried through by taking the concept of the exergy cost to a microscopic point of view. To put it another words, the exergy costs are connected to the law of continuum physics so that all phenomenological effects can be taken into account. This new formalism may be called as Local Exergy Cost Theory (LECT). The LECT method departs from the hypothesis that unit exergy costs for distinct exergy fluxes, e.g. heat, work, etc., are given the same cost in absence of external evaluations. From this new approach, it will be possible to model an space-time function of the unit exergy cost, k* ((r), t), besides it will be helpful in providing the rules of cost allocation with physical grounds otherwise to propose new ones. Theoretical aspects of this method are succinctly explained throughout the paper. Most importantly, in order to show the practical bias of the theory a series of proposed examples which are outlined are provided. By and large, results show that the unit exergy cost locally yielded contains a lot of useful information as, for instance, precise pinpointing of the points where exergy is destroyed and what is most importantly, the costs at those points. Lastly, by means of the LECT we can build up exergy cost maps for a particular system.
Fault Adaptive Formation Control of Mobile Robots
Authors: Halder Bibhrajit , Zhang Zhen , Sarkar Nilanjan
Published: April 2008

A supervisory control framework for a team of mobile robots to accomplish a given task in the presence of system faults is presented in this paper. The supervisor, which contains the upper-level switching logic, coordinates a set of lower-level controllers to accomplish a task. The stability analysis of both the lower-level controllers and the internal dynamics associated with them are presented. A switching scheme that satisfies the input constraints and guarantees the stability of the overall system is developed. Results from a leader-follower task with a two-robot team are presented. In this task, the follower becomes the leader when the leader develops a fault by using three lower-level controllers and a switching logic that guarantees stability of the entire operation.
Transmural LV Systolic Wall Thickening Gradients and Models of Heart Wall Mechanics
Authors: Cheng Allen , Langer Frank , Rodriguez Filiberto , Criscione John C. , Daughters George T. , Miller D. Craig , Ingels Neil B.
Published: April 2008

We implanted arrays of radiopaque markers to measure lateral equatorial wall transmural strains and global and regional LV geometry in 7 sheep. Without intervening procedures, one and eight weeks after surgery, 4-D datasets from stereo radiographic studies were processed to yield transmural strains from each heart. In accordance with previous theoretical predictions and experimental results, we hypothesized that systolic radial strain (i.e., wall thickening) would exhibit a transmural gradient, increasing from subepicardium to subendocardium, and, as previous work suggested that this was a fundamental mechanism, this gradient would be observed at both the one- and eight-week studies. The one-week studies yielded the expected gradient. This gradient, however, was not present in the eight-week studies, although LV shape and hemodynamics were virtually identical to their one-week values. We discuss the implications of these findings to mechanistic theories of heart wall mechanics.
Design of a Nonlinear Position Regulator for Cooperating Hydraulic Manipulators Handling a Rigid Object
Authors: Zeng Hairong , Sepehri Nariman
Published: April 2008

In this paper, a nonlinear control scheme is developed for performing a cooperative task by hydraulic manipulators. The goal is to design a controller that allows two or more hydraulic robots to coordinately regulate an object’s position/orientation while maintaining desired internal forces on the object and sharing load. First the dynamic model of the whole system, including hydraulic functions, is derived. Then, a controller is designed, augmented by an on-line updating law to eliminate the steady-state error due to lack of knowledge about the weight of the object. Extended Lyapunov’s second method is used for stability analysis of the control system. The stability of the system is guaranteed by constructing a smooth Lyapunov function. Simulations are performed to substantiate the controller developed.
Investigation of an Active Stressing Technique for Delaying Fracture During Laser Cutting of Alumina
Authors: Akarapu R. , Segall A. E.
Published: April 2008

During a variety of high-speed laser cutting operations, full work-piece support is not always practical or possible. As a result, costly premature fractures and associated damage such as chips, burrs, and cracks (ranging from the micro- all the way to the macro-scale) can result. In most instances, the resulting stresses are primarily mechanical in nature and arise from the bending and/or twisting moments from the still attached scrap. Even if the scrap weight remains relatively constant (as is usually the case), mixed-mode fracture is all but inevitable since the remaining (supporting) section is continuously diminishing as the cut progresses. Given the predominantly mechanical, and therefore predictable nature of the resulting stresses, it is conceivable that intentionally induced compressive stresses due to an off-focus laser might be used to control (or at least, delay) such fractures. In this paper, the possibility of using a tailored laser-heating scenario ahead of a progressing cut to “actively” induce compressive thermal-stresses to control fracture, during cutting of cantilevered plate, was investigated. A numerical simulation of this active stressing approach was achieved by using a customized finite-element formulation that was previously employed to model dual-beam laser machining. During the complex 3-D simulations, probabilistic fracture mechanics was used to quantify the influence of the induced compressive stresses on the time and nature of the fracture. The effect of important parameters such as laser beam diameter, incident power density, positioning of the laser with respect to cut, as well as timing were then studied with respect to the goal of reducing and/or delaying the likelihood of fracture.
Bondgraph Based Approach to Passive Teleoperation of a Hydraulic Backhoe
Authors: Krishnaswamy Kailash , Li Perry Y.
Published: April 2008

Human operated, hydraulic actuated machines are widely used in many high-power applications. Improving productivity, safety and task quality (eg. force feedback to the operator in a teleoperated scenario) has been the focus of past research. In addressing these issues, our research proposes and experimentally demonstrates a control technique that renders a hydraulic machine (teleoperated backhoe in this case) as a two-port, co-ordinated, passive machine. The passive teleoperated backhoe is driven by a human operator at one-port and interacts with the environment at the other. It guarantees interaction stability and safety with the human / work environment as the latter are usually passive. In previous work, a passive teleoperation algorithm was proposed for multi degree of freedom teleoperation of a hydraulic backhoe approximated by its kinematic behavior. The approximation led to severe performance deterioration under certain operating conditions. In this paper, a bondgraph based passive teleoperation architecture is proposed for the non-linear dynamic modeled backhoe. Passive control is designed in two stages. In the first stage, bondgraph based system inversion ideas are used to determine a coordination control law. In the second stage, a desired locked system (desired dynamics of the coordinated teleoperator) is defined and an appropriate control law is determined to ensure the passivity property of the locked teleoperator. The proposed passive control law is experimentally verified for its bilateral energy transfer ability and performance enhancements.
Organ Culture System for Mechanobiology Studies of the Intervertebral Disc
Authors: Lee Cynthia R. , Alini Mauro , Iatridis James C.
Published: April 2008

The development of in vitro models is critical for furthering understanding of the intervertebral disc and the development of disc regeneration/tissue engineering. An in vitro culture system targeted towards mechano-biology studies of the intervertebral disc (IVD) was built and validated using bovine coccygeal discs. Discs were maintained in culture for up to one week with and without vertebral endplates. Water content and glycosaminoglycan content were found to be stable and cells were metabolically active when cultured under a 5kg static load.
Calculation of Direct Exchange Areas Using Finite Volume Method and Direct Integration
Authors: Tian Weixue , Chu K. S.
Published: April 2008

Direct integration of direct exchange areas (DEA) usually suffers from singularity problems for neighboring zones, which render numerical integration difficult. While calculation of DEA using other methods, for example, finite volume method (FVM) or monte carlo scheme, require extremely large computational resources and suffer from other problems when two zones are optically far away. In this study, we combine one of the direct integration techniques, mid-point integration, and the finite volume method. Volume-volume DEA of zones of an infinitely long rectangular enclosure with various optical thickness have been calculated using this hybrid method. Comparison with exact solution shows that the maximum error for calculated DEA using the current method is within 5% when the optical thickness of each zone is within 0.1.
Non-Equilibrium Thermodynamics and Formation of Nanoparticles in Femtosecond Laser Ablation
Authors: Cheng Changrui , Xu Xianfan
Published: April 2008

High intensity femtosecond laser ablation processes are computed by molecular dynamics (MD) simulations. The procedure of MD modeling and related numerical techniques are introduced. The volumetric phase separation is illustrated. The emphasis is to understand the thermodynamic state of a material which is heated with an extremely high heating rate, and the formation of particles with nanometer size in the laser-ablated plume. It is revealed that nanoparticles are originated from expansion of a supercritical fluid in a reduced temperature and pressure environment. The parameters of the nanoparticles (temperature, size and velocity) are shown. The results will help to understand femtosecond laser materials processing and applications where nanoparticles are of interest.
Asymptotic Impact Control of Hydraulic Actuators With Friction
Authors: Sekhavat P. , Sepehri N. , Wu Q.
Published: April 2008

The focus of this work is stabilization of hydraulic actuators during the transition from free motion to constraint motion and regulating the intermediate impacts that could drive the system unstable. In our past research, we introduced Lyapunov-based nonlinear control schemes capable of fulfilling the above goal by resting the implement on the surface of the environment before starting the sustained-contact motion. The hydraulic actuator’s stick-slip friction effect was, however, either not included in the analysis or not compensated by the control action. In this paper, the application of our previously introduced friction compensating position control scheme is extended to impact regulation of a hydraulic actuator. Theoretical solution and stability analyses as well as actual experiments prove that such control scheme is also effective for asymptotic impact control (with no position steady-state error) of hydraulic actuators in the presence of actuator’s dry friction.
Observer Backstepping Neuro-Fuzzy Control Design for a Type of Nonlinear System
Authors: Chatlatanagulchai Withit , Meckl Peter H.
Published: April 2008

This paper presents a control system design for a type of time-varying nonlinear system. The control system comprises neuro-fuzzy system identifier, Luenberger observer, backstepping controller and variable structure controller. We use adaptive neuro-fuzzy inference system to identify the plant in real time without the need of underlying mathematical model. However, some knowledge about the plant structure and upper bounds is required. With the use of observer, the control system can be designed from plant output and input alone while plant states are assumed unmeasurable. Controller is designed based on backstepping scheme and uncertainties from the plant identification and state estimation processes are handled by variable structure controller. Under some important assumptions, the control system is proved to be able to track a smooth desired trajectory with uniformly ultimately bounded tracking error. A simulation based on one-link flexible-joint robot manipulator is provided.
Modeling Liquid Spray Evaporation in Heated Porous Media With a Local Thermal Non-Equilibrium Model
Authors: Periasamy Chendhil , Sankara Chinthamony Sathish K. , Gollahalli S. R.
Published: April 2008

The situations such as rapid evaporation, and significant heat generation/convective heat transfer, typically encountered in liquid-fueled porous media combustors, warrant the use of local thermal non-equilibrium models. Knowledge of fuel vaporization and mixing is important to understand the combustion characteristics. In this paper, a two-energy equation model is presented to account for the non-equilibrium between the solid and liquid phases. In this approach, two energy equations for solid and gas phases were solved. Kerosene fuel, issued from an air-blast atomizer, was injected on to a heated porous medium. Governing equations were applied on a 2-D axisymmetric, computational domain of 20.3 cm × 2.5 cm. Computer simulations were conducted using a commercial code Fluent 6.0. Heat transfer from combustion porous medium was simulated by setting a volumetric heat source in the porous region. Accordingly, the peak temperatures in porous media varied from 473 K to 590 K. Axial temperature profiles within the porous media were obtained with equilibrium and non-equilibrium models. Results indicated that the equilibrium models slightly underpredicted the peak temperature. Using non-equilibrium models, radial profiles of kerosene vapor concentration were obtained at different axial locations and the results showed that the thermal effects of the porous medium dominated in the evaporation process. Numerical results were also compared with available data and the agreement was found to be good.