bluuebunny/crossref_metadata_2025 huggingface dataset:
Analytical Models for Time-Resolved Fluorescence Spectroscopy in Tissues
Authors: Sadoqi Mostafa , Riseborough Peter , Kumar Sunil
Published: November 2021

Laser induced fluorescence is a rapidly growing technique for the characterization of scattering material, most notably in in-vivo biomedical testing. Most previous applications have relied on the measurements of the steady-state emission spectrum, with subsequent analysis of the spectrum for relative concentrations of potential fluorophores. Only recently a few investigators have explored the use of the fluorescence lifetimes as a diagnostic tool by taking advantage of the perturbation of the lifetime by multiple scattering of the excitation and emission light in the tissue.

We have developed a model to study the fluorescence signal generated by a fluorophore distributed in a scattering medium. This model is based on two coupled transient transfer phenomena: the transport of the pulsed source laser, and the induced transient fluorescence excited by the laser. The two are coupled through the source term for the induced fluorescence field. Whereas previous research focused mainly on the fluorescence properties of various dyes, compounds, and materials, only recently have such transport questions been addressed by researchers. In addition, the studies that have been done in the literature have taken the optical properties of the tissue to be the same at the excitation and emission wavelengths. We have presented analytical and numerical solutions for finite, infinite, cylindrical and spherical geometries.
Source Terms in Thermal Therapy: A Parametric Study
Authors: Bhowmick Sankha , Bischof John C.
Published: November 2021

Interstitial thermal therapy heats tissues to temperatures exceeding 50°C for a period of seconds to minutes. This technique is currently being investigated as an autonomous therapeutic option for the treatment of benign and malignant diseases at different sites in the body including the prostate, uterine fibroid, kidney and liver (Diller and Ryan, 1998). Some of the interstitial heating techniques that are being studied are microwave, ultrasound (US) and laser. The predominant mechanism of heating associated with each of these techniques appears to be different, i.e. microwave heating is dielectric, US is by mechanical vibration and lasers through photon absorption. Clearly, the thermal distribution in the heated tissue is intrinsically dependent on the mechanism of heating. Since accurate characterization of heat deposition in the tissue is imperative for successful thermal therapy treatments, a broader understanding of the parameters governing the heating or source term(s) is needed.
Nonlinear Thermal and Mechanical Analysis in the Vibration of a Printed Wiring Board
Authors: He Xiaoling , Fulton Robert
Published: November 2021

Nonlinear laminate theory is applied and extended for the printed wiring board dynamic analysis. Equations of motion for the isotropic laminates are derived for vibration response analysis of the simply supported printed wiring board under mechanical and thermal loads. Temperature variation in spatial domain is taken into consideration. The effect of the temperature variation on the response character is analyzed and demonstrated by means of numerical results. Modal analysis is made to predict the vibration behavior in terms of deflection and stresses. Lamina stresses are used for failure prediction.
Wafer Level Underfill Processing
Authors: Nguyen Luu , Quentin Christopher , Nguyen Phuong
Published: November 2021

Underfill materials play a major role in the reliability of flip chip packages. These adhesives have been the subject of much research and development in the last few years, and much improvement in material performance has been obtained. However, the assembly method still remains unchanged, with the underfill being dispensed at the individual die level after flip chip reflow. Even with the arrival of “no-flow” underfills, assembly still requires depositing the underfill material onto the flip chip site prior to positioning the flip chip die. Processing underfill at the wafer level brings in a new paradigm shift to the area of flip chip packaging. Precoating the wafer with the underfill will create significant savings in both time and money. The application cycle time of the wafer level process becomes equivalent to a single dispensing operation for all the good dies on the wafer.

This paper will present results obtained with screen printing used as the application method for the wafer level process. An experimental underfill was printed onto un-bumped silicon wafers and cured, and the resultant films were analyzed. Process conditions affecting film thickness and surface roughness were evaluated. Preliminary results with bumped wafers are also discussed.
Parametric Design and Reliability Analysis of WIT Wafer Level Packaging
Authors: Lin Y. T. , Tang P. J. , Chiang K. N.
Published: November 2021

The demands of electronic packages toward lower profile, lighter weight, and higher density of I/O lead to rapid expansion in the field of flip chip, chip scale package (CSP) and wafer level packaging (WLP) technologies. The urgent needs of high I/O density and good reliability characteristic lead to the evolution of the ultra high-density type of non-solder interconnection such as the wire interconnect technology (WIT). The new technology using copper posts to replace the solder bumps as interconnections shown a great improvement in the reliability life. Moreover, this type of wafer level package could achieve higher I/O density, as well as ultra fine pitch. This research will focus on the reliability analysis of the WIT package structures in material selection and structural design, etc. This research will use finite element method to analyze the physical behavior of packaging structures under thermal cycling condition to compare the reliability characteristics of conventional wafer level package and WIT packages. Parametric studies of specific parameters will be performed, and the plastic and temperature dependent material properties will be applied to all of the models.
Micro-Mechanics of Creep-Fatigue Damage in Pb-Sn Solder Due to Thermal Cycling
Authors: Sharma Pradeep , Dasgupta Abhijit
Published: November 2021

This paper presents a micro-mechanistic approach for modeling fatigue damage initiation due to cyclic creep in eutectic Pb-Sn solder. Damage mechanics due to cyclic creep is modeled with void nucleation, void growth and void coalescence model based on micro-structural stress fields. Micro-structural stress states are estimated under viscoplastic phenomena like grain boundary sliding and its blocking at 2nd phase particles, and diffusional creep relaxation. A conceptual framework is provided to quantify the creep-fatigue damage due to thermo-mechanical cycling. Some parametric studies are provided to better illustrate the utility of the developed model.
Applications of World Wide Web in Teaching Large Scale Machinery Diagnostics
Authors: Shoureshi Rahmat , Terry Benjamin
Published: November 2021

As industrial competition intensifies, more emphasis is placed on increased productivity and reduction of cost. In every industry, a major component of manufacturing cost is associated with operation and maintenance expenses. Thus, there has been a significant interest expressed by industry in the development of means and methodologies for the reduction of operation and maintenance expenses.

Unfortunately, most engineering students go through an engineering curriculum that does not contain any formal courses or training on monitoring and diagnostics. Issues such as cost of operation, technical manpower, maintenance, safety, availability of space, etc. are examples of important factors that prevent universities from establishing such facilities.

This paper presents a new concept that overcomes such barriers and difficulties and introduces an engineering health monitoring and diagnostic curriculum by means of an integrated effort between academia and industry. The resulting real and virtual experimental facilities and curriculum in the area of health monitoring and on-line diagnostics are presented and described.
An Apparatus for Visualizing Frequency Response
Authors: Layton Richard A. , Pai Devdas
Published: November 2021

A second-order, mass-spring-damper apparatus was developed to help students visualize amplification, resonance, attenuation, and phase angle in mechanical systems. The apparatus was developed as a design project involving both graduate and undergraduate students. A prototype of the apparatus is complete and work is underway to correct design deficiencies and produce an improved apparatus. This paper describes the work in progress to develop a final apparatus for student use.
Signal Distortion Compensation of Linear Time-Invariant Measurement System
Authors: Wang Changting , Gao Robert X.
Published: November 2021

Non-distortion is an important aspect in precision measurement, calibration and signal processing. In this paper, the distortion error of a linear time-invariant measurement system is derived for periodical and non-periodical signal inputs, using Fourier Series and Fourier Transformation. The signal distortion is measured by the error-to-signal energy ratio. A charge amplifier circuit has been analyzed as an example, which shows that the distortion of an LTI system can not be simply neglected if precision measurement is required. Direct compensation and adaptive control methods have been discussed to reduce the LTI system distortion. The applications of these two methods to the charge amplifier design are discussed, which demonstrated good results.
A Simple Method for In Situ Determination of Linear Thermal Expansion Coefficients of Thin Films
Authors: Pan Chi Hsiang
Published: November 2021

This work presents a simple method for determination of linear thermal expansion coefficients (LTEC) of thin films with a compact microstructure. The microstructure comprises of a pair of cantilever beams with different lengths connected by a short tip. By heating the microstructure, the thermal strain causes two beams to deflect each other, thereby magnifying the deflection, which is measured by the tip directly under an optical microscope with the specimen placed in a heating stage. An analytical model is derived to relate the measured displacement to thermal strain, therefore, LTEC of thin films can be calculated. The analytical model is free from any correction factor. Furthermore, the accuracy of LTEC measurement is significantly enhanced because the measured displacement is independent of some physical values, namely the Young’s modulus, Poisson’s ratios and thickness of the substrate and the thin film, and the LTEC of the substrate. Finite element model is also used to support the analytical model and to perform nonlinear analysis. Experimental results with SiO2 films as well as undoped LPCVD polysilicon films are used herein to demonstrate the effectiveness of the proposed method.
Cartesian Versus Joint Space Command Shaping for a Ship Boom Crane
Authors: Agostini Michael J. , Parker Gordon G. , Groom Kenneth , Robinett Rush D. , Leban Frank
Published: November 2021

This paper presents a command shaping control method for suppressing operator induced payload swing in rotary, ship-based, boom cranes. The crane configuration studied consists of a payload mass that swings on the end of a spherical pendulum of varying lift-line length (hoisting). The lift-line is attached to a boom capable of elevation (luffing). The boom can rotate about an axis perpendicular to the ship’s deck (slewing). Positioning of the payload is accomplished through luff, slew, and hoist commands issued in real-time by an operator. A Cartesian space command shaping method is developed and compared to a previously documented joint space approach. Although both methods are appropriate for low rate crane maneuvers, the Cartesian method provides better performance under the tested operating conditions. Simulation results are presented to compare their performance.
Development of a Vision Based Orientation Sensor
Authors: Garner Harry , Lee Kok-Meng
Published: November 2021

The development of a vision based orientation sensor for the measurement of the orientation of a spherical body is presented. A specially designed grid pattern used to encode absolute orientation information onto a spherical surface in terms of latitude and longitude angles is discussed. A novel algorithm for the analysis of images of this grid pattern based on tracking along the grid lines is also developed that is designed to overcome limitations of other traditional image analysis techniques in terms of speed and accuracy. A procedure for recovering the absolute orientation of a spherical surface encoded with the special grid pattern using the line tracking algorithm, camera calibration, and Horn’s (1987) technique is also presented. Finally, experimental results of this procedure applied to a sequence of images are presented and discussed.
Experimental Study of a Neural Generalized Predictive Force Control for a Hydraulic Actuator
Authors: He S. , Sepehri N.
Published: November 2021

In this paper, multilayer feedforward neural networks (NNs) are used for modeling and force control of a hydraulic actuator. The predictability of the instantaneous linearized neural model is examined and is used along with the generalized predictive control (GPC) algorithm to control the force exerted on the environment. Experimental results show that the neural-based generalized predictive control can handle different contact environments despite high nonlinearity and uncertainty in the hydraulic functions.
A New Control Approach to Nonlinear Systems Undergoing Changes in a System Parameter
Authors: Nho Hyuk C. , Meckl Peter
Published: November 2021

Conventional model-based computed torque control fails to produce good trajectory tracking performance in the presence of payload uncertainty and modeling error. The problem is how to provide accurate dynamics information to the controller. A new control architecture that incorporates a neural network, fuzzy logic and a simple proportional-derivative (PD) controller is proposed to control an articulated robot carrying a variable payload. A feedforward (multilayer) neural network is trained off-line to capture the nonlinear inverse dynamics of the system. The network is placed in the feedforward path to minimize tracking error. The network receives the same input signals as conventional computed torque as well as the payload mass estimate, which comes from a fuzzy logic mass estimator. The fuzzy logic, trained off-line to optimize the membership function, is developed to estimate the changing payload mass. The fuzzy logic estimator is based on joint acceleration error to improve the speed of detection and estimation of payload mass change. The effectiveness of the proposed architecture is demonstrated by experiment on a two-link planar manipulator with changing payload mass. Experiment results show that this control architecture achieves excellent tracking performance in the presence of payload uncertainty. The results of the control architecture are also compared with those of a model-based control architecture. This approach can be employed in any nonlinear mechanical system with a sudden change in a parameter.
Aggregation of a Class of Large-Scale, Interconnected, Nonlinear Dynamical Systems
Authors: Darbha Swaroop , Rajagopal K. R.
Published: November 2021

In a previous paper, we discussed the characteristics of a “meaningful” average of a collection of dynamical systems, and introduced as well as contructed a “meaningful” average that is not usually what is meant by an “ensemble” average. We also addressed the associated issue of the existence and construction of such an average for a class of interconnected, linear, time invariant dynamical systems. In this paper, we consider the issue of the construction of a meaningful average for a collection of a class of nonlinear dynamical systems. The construction of the meaningful average will involve integrating a nonlinear differential equation, of the same order as that of any member of the systems in the collection. Such an “average” dynamical system is not only attractive from a computational perspective, but also represents the macroscopic behavior of the interconnected dynamical systems. An average dynamical system can be used in the analysis and design of hierarchical systems.
H∞ Synthesis of Nonlinear Feedback Systems in a Volterra Representation
Authors: Glass John W. , Franchek Matthew A.
Published: November 2021

Presented in this paper is a procedure for selecting the H∞ performance weights for a class of nonlinear feedback systems modeled by a truncated Volterra series. The performance weight selection addresses the trade-offs between closed loop performance and closed loop stability. The class of feedback systems consider regulating systems subject to step disturbances. The methodology is based on two recent results concerning closed loop stability for this class of nonlinear feedback systems [1]. These stability conditions can be formulated as an H∞ problem where the performance weights are systematically identified. This proposed synthesis procedure is applied to the idle speed control of a Ford 4.6L V-8 fuel injection engine. Through this application, the design trade-off between closed loop performance and stability is illustrated. A performance trade-off curve is then used to synthesize controller for the regulation system.
Power Feedback Control in Cylindrical Traverse Grinding
Authors: Hecker Rogelio L. , Liang Steven Y.
Published: November 2021

This paper describes the design of a power controller in cylindrical traverse grinding (CTG), where the power consumed by the grinding wheel is controlled by regulation of the traverse velocity.

A mathematical model relating the power to the traverse velocity was developed and quantified with machining data. The controller design was based on the power-velocity model developed and it was tuned to fulfill time response specifications including settling time and overshoot. An inner velocity loop was also designed and implemented inside the power close loop to guaranty a stable power response.

The controller was implemented and tested on an open architecture cylindrical grinding machine. The results show that the controlled system response can be regulated to meet the requirements of time specifications, over a wide range of cutting depth and input power reference.
Open Systems Formulation and Gaining Insight Using Lagrangian Bond Graphs
Authors: Redfield Robin C.
Published: November 2021

Models of a small-scale water rocket are developed as an example of open system modeling by both the bond graph approach and a more classical method. One goal of the development is to determine the benefits of the bond graph approach into affording insight into the system dynamics. Both modeling approaches yield equivalent differential equations as they should, while the bond graph approach yields significantly more insight into the system dynamics. If a modeling goal is to simply find the system equations and predict behavior, the classical approach may be more expeditious. If insight and ease of model modification are desired, the bond graph technique is probably the better choice. But then you have to learn it!
Design of Compliant Mechanical Amplifiers for Piezoceramic Stack Actuators Considering Stiffness Properties
Authors: Frecker Mary , Canfield Shawn
Published: November 2021

A topology optimization method for design of compliant mechanical amplifiers for piezoceramic stack actuators is presented. Previously the optimization was done assuming that the stack actuator provided a constant unit load to the compliant mechanism. However, it is well known that the best actuator performance occurs when the stiffness of the stack is considered and matches the stiffness of the surrounding coupling structure. In this paper an improved formulation is presented where the piezoelectric properties and stiffness of the stack are included along with an external spring representing a resisting load the actuator is working against. The optimization problem formulation, finite element implementation, solution algorithm are discussed. Two design examples are presented which illustrate the effect of the stiffness of the external spring and the size of the design domain on the topology of the solution.
Piezo Driven Mechanisms With Flexural Joints
Authors: Koster M. P.
Published: November 2021

The properties of flexures and piezo actuators in mechanisms perfectly fit. Piezo actuators in general are applied where accuracy is emphasized. Flexural joints take care that high accuracy is maintained throughout the mechanism. Flexures are known to have their limitations in terms of rotation and displacement. Piezo actuators generate relatively small displacements. Despite the limitations of fexible joints and of piezo actuators, piezo driven, flexural mechanisms were realized, capable of large displacements and high accuracy.
A Mesoscale Mechanism for Adaptive Mobile Manipulation
Authors: Voyles Richard M.
Published: November 2021

A novel, centimeter-scale crawling robot is described. Intended for military and civilian surveillance and search-and-rescue applications, the robot must be small, rugged, and lightweight with robust, reconfigurable capabilities. As a result, a dual-use design employing two arms for both manipulation and locomotion was conceived. The robot consists of two, three-degree-of-freedom arms that can stow completely inside the 75 mm diameter cylindrical body for ballistic deployment. This paper describes the mechanism and design motivation as well as three novel locomotion gaits and a fourth conventional gait. An outline for gait adaptation is suggested for future work.
The Effects of Real and Computer Generated Friction on Human Performance in a Targeting Task
Authors: Richard Christopher , Cutkosky Mark
Published: November 2021

We present the results of haptic interaction with real and virtual Coulomb friction. Tests were conducted to explore the effects of various types of friction on human performance in a Fitts-style targeting task. The results indicate that haptically rendered friction affects subject performance in a manner quite similar to that of real physical friction. Furthermore, moderate low-stiction friction tends to improve subject performance both in terms of speed and accuracy. High-stiction friction, however, degrades subjects performance, especially in terms of speed.
Analysis of Bonded Shrink Fitted Joints Under Push-Off Forces: The Effect of Joint Size on the Joint Strength
Authors: Sawa Toshiyuki , Yoneno Masahiro , Matsunami Yasuo
Published: November 2021

Shrink fitted joints have been widely used in mechanical structures. Recently, joints combining shrink fitted with an anaerobic adhesive have been developed in order to increase the joint strength. This joint is named the bonded shrink fitted joint. In this paper, push-off tests were carried out to measure the joint strength of bonded shrink fitted joints. In addition, the strength of the shrink fitted joints without the anaerobic adhesive was also measured. In the experiments, the effect of shrinking allowance, the outer diameter of the shafts, and the engagement length on the joint strength are examined. In addition, the size effect of joints is also examined in the experiments taking into account the surface roughness, and the roundness. The stress distribution of the joints subjected to a push-off load is analyzed using axisymmetrical theory of elasticity as a four-body contact problem. Using the stress distribution, the joint strength is estimated. The experimental results are in a fairly good agreement with the numerical results. It is found that the push-off strength of the bonded shrink fitted joints is greater than that of the shrink fitted joint.
Ductile Damage Evolution Under Different Strain Rate Conditions
Authors: Bonora Nicola , Gentile Domenico , Milella Pietro Paolo , Newaz Golam , Iacoviello Francesco
Published: November 2021

Failure of ductile metals is always controlled at microstructural level by the formation and growth of microcavities that nucleate from inclusions embedded in the ductile matrix, also at high deformation rate. Many damage models have been proposed to describe both evolutions of these cavities under the action of increasing plastic deformation, and the associated effects on the material behavior. Basically, two classes of damage models are currently available: the Gurson’s type model and continuum damage mechanics (CDM). In the framework of CDM, Bonora (1997) proposed a non-linear damage model for ductile failure that overcome the main limitations presented by others formulations: the model is material independent and its validity under multiaxial state of stress conditions has been verified for a number of class of metals, (Bonora, 1998, Bonora and Newaz, 1997). In addition, this model has the main feature to require a limited number of physically based parameters that can be easily identified with ad hoc tensile tests. In this paper, for the first time, the effect of the strain rate on ductile damage evolution has been studied in a quantitative manner evaluating the material loss of stiffness under dynamic loading. Damage measurements on SA537 Cl 1 steel have been performed according to the multiple strain gauge technique on hourglass shaped rectangular tensile specimen. Dynamic effect was introduced performing the test at different imposed displacement rates. An extensive scanning electron microscopy analysis has been performed in order to correlate damage effects with the microstructure morphological modification as a function of the applied deformation rate.
Computational Approach for Adhesively Bonded Composite Joints
Authors: Anwar Iqbal , Newaz Golam
Published: November 2021

A computational intensive study was performed to assess an efficient way to model adhesively bonded glass fiber reinforced composite joints in automotive applications. Three different finite element modeling techniques had been implemented. First, adhesive was represented by 1D-spring elements. Spring stiffness was calculated from adhesive property. This model is inadequate to assess stresses developed in the adhesive layer directly. So adhesive was modeled with 2D elements for better assessment of state of stress in the adhesive and the substrate. Both the model provide limit load, but crack initiation and failure of the bond can not be captured. The third approach adopted was the nodal failure model. In the nodal failure model, to understand the failure of adhesively bonded joints, bond strength had been specified to the interface nodes of the composite substrate. Combined failure criteria had been used. Cracks propagated and interface debonded when interface stress exceeded the failure limit. Finite element model results compared well with the experimental data. This modeling approach was later adopted for dynamic modeling of adhesively bonded joints, which shows promise.
Finite Shear Behaviour of Brain Tissue Under Impact Loading
Authors: Brands Dave W. A. , Bovendeerd Peter H. M. , Peters Gerrit W. M.
Published: November 2021

A method is presented for determining the dynamic shear behaviour of brain tissue using a rotational plate-plate rheometer in a strain and frequency range representative for impact conditions. The non-linear strain behaviour was characterised using shear stress relaxation experiments and expressed in terms of a damping function. Results were corrected for the non-homogeneous strain field applied. Brain tissue was found to exhibit shear softening (45% at 20% strain) that could be fitted with a second order Mooney-Rivlin model. The time dependent behaviour of brain tissue seems to be independent of the strain level. It was characterised up to 1000 Hz by small strain oscillatory shear experiments and application of the Time Temperature Superpositioning principle. The data presented can be used to fit a non-linear material model for brain tissue under shear loading for frequencies up to 1000Hz and strains up to 20%.
Influence of Stent Design on Intraaneurysmal Flow: A PIV Study
Authors: Livescu V. , Lieber B. B. , Hopkins L. N. , Wakhloo A. K.
Published: November 2021

Interaction between stents and flow inside a sidewall aneurysm model was investigated using Particle Image Velocimetry (PIV). Three spring-like stents having the same porosity but different filament diameter were placed inside the parent vessel that harbored the aneurysm traversing the aneurysmal neck. The flow field inside the aneurysm was investigated before and after placement of the stents. The flow through model was pulsatile and the hemodynamic conditions were representative for those found in human intracranial and extracranial cerebral arteries. Flow patterns inside the aneurysm were significantly altered after stent placement. To facilitate comparison among all cases, the circulation inside the aneurysm was obtained as the surface integral of the distributed vorticity. The results show that the strength of the circulation is substantially diminished for all stented cases. However, the temporal distribution of the circulation through the cardiac cycle is similar for the three stents considered. Further, the mean circulation over one cardiac cycle was obtained for each case as the integral of the absolute value of the temporal distribution. The mean circulation reveals that noteworthy differences in intraaneurysmal hemodynamics do exist among the filament diameters considered.
Biomechanics as a Tool for Study of Cardiovascular Disease: Will We Predict Cardiovascular Disease With Engineering Precision?
Authors: Schmid-Schönbein Geert W.
Published: November 2021

With the impending completion of the human genome sequence, biology will join the ranks of physics, mathematics, and chemistry as an exact basic science. This fact will be reflected in the choice of the curriculum for many academic disciplines, but especially for Bioengineering. Bioengineering, and specifically Biomechanics, will integrate these disciplines and serve as the platform for expanding analysis as well as creation and design of new approaches in Biology and Medicine. Not only is mechanics determined by biology but also biology is controlled by mechanics. Thus, biomechanics is becoming an integral part of medical research. One of the most interesting aspects of biomechanics is its application to problems related to disease (1).
Mechano/Transduction, Cellular Communication and Fluid Flow in Tissue Engineering
Authors: Weinbaum Sheldon
Published: November 2021

The growth of cellular constructs in tissue scaffolds depends on the delivery of nutrients and growth factors as well as the substrate on which they are grown. Micropatterning techniques have also made it possible to grow cells on a wide variety of substrates with greatly different topography which significantly alter cellular contact and communication. Fluid flow is critical not only in this delivery of nutrients and growth factors, but also in the interaction of the cell’s cytoskeleton with its attachment matrix. Similarly, fluid flow is known to play an important role in cell to cell communication via its regulatory effect on various gap junction proteins of the connexon family. The mechano/transduction and cell to cell signaling mechanisms will be examined for both cells with a smooth topography, such as vascular endothelium cells which are involved in angiogenesis and cells with cell processes and microvilli whose tethering attachments and protrusions interact with fluid flow in a different manner.
Molecular Mechanics and Cell Biology: Growing Cells on Soft Materials
Authors: Ju Yo-El , Janmey Paul A. , Flanagan Lisa A.
Published: November 2021

The vast majority of studies of cell growth and movement in vitro are done on rigid glass or plastic surfaces laminated with a molecular layer of specific adhesion proteins. Such studies have revealed a wealth of information about the functions of soluble and surface-bound ligands as well as the structure and components of the cytoskeletal machinery. However, the morphology, motility, and metabolic states of such cells do not often resemble the situation in vivo, where, for example, the materials to which cells attach are much softer. Recent developments in synthesis and characterization of polymer gels that allow quantitative studies of cell function have revealed that mechanical effects may be as important an aspect of cell regulation as the specific molecular stimuli traditionally studied. Designing chemically defined surfaces that permit cells to grow on materials with viscoelastic properties that resemble those of normal tissues is a step to elucidating the influence of mechanics on cell growth and structure.
A Mathematical Model of a Retinal Oscillator
Authors: Rand Richard H. , Wirkus Erika T. , Li Tong , Howland Howard C.
Published: November 2021

Circadian rhythms in vertebrates (including man) have been conjectured to help control changes in sensitivity of visual systems (which must operate over some 10 orders of magnitude in the course of night and day), by anticipating the changes in light intensity which occur at dusk and dawn (Cahill and Besharse, 1995). Diurnal rhythms in melatonin and dopamine in the retina have been shown to be affected both by a circadian oscillator as well as by changes in local light levels (Cahill and Besharse, 1995). In an experiment conducted in the laboratory of one of the authors (HCH), the growth of the eyes of baby chicks in their first two weeks of life has been shown to be strongly affected by exposure to 20 hours or more of light per day (Li et al., 2000). A descriptive model of the nature of the biochemistry of retinal dynamics has been presented (Morgan and Boelen, 1996). In this work we offer a mathematical model of the retinal oscillator based on the descriptive model given in (Morgan and Boelen, 1996). Using this model we simulate the experiment described in (Li et al., 2000).
On the Calculation of Fluid Shear Stresses at the Wall of Dilated Large Arteries: Part I—Application to 2D Axisymmetric Computational Models
Authors: Finol Ender A. , Amon Cristina H.
Published: November 2021

A procedure for calculating fluid shear stresses at the wall of two-dimensional axisymmetric models of dilated large arteries is presented. The procedure is applied to a model of a double-aneurysm abdominal aorta under pulsatile flow conditions for a time-average Reynolds number Rem = 680. The method is extended to three-dimensional artery models in Part II of this paper.
Development of Interactive Modeling System for the Computational Biomechanics Simulation Using Medical Imaging Data
Authors: Hayasaka Tomoaki , Himeno Ryutaro , Fukuyama Keisuke , Liu Hao , Yamaguchi Takami
Published: November 2021

Computational mechanics has been recognized as a powerful tool for cardiovascular disease research, vascular surgery planning and medical device design. The accurate and efficient construction of anatomic models is a critical element in the application of these computational methods. We developed an interactive modeling system for the computational biomechanics simulation using medical imaging data such as MRI or CT. The novel aspect of this modeling system is that the operator can modify the model which is rendered over the reference volumetric images. Therefore efficient modeling can be done with help of the heuristic knowledge of the operator.
Fluid-Structure Interactions Abdominal Aortic Aneurysm Models Under the Pulsatile Flow Condition
Authors: Kwon Chi-Ho , Lee Ki-Won , Kim Young-Ho
Published: November 2021

Fluid-structure interaction studies were performed on various abdominal aortic aneurysm (AAA) models under the pulsatile flow condition. Eight aneurysm models were made with four different dilatation sizes and two different wall thickness. Stresses and deformations of the aneurysm wall were significantly affected by the dilatation size as well as the wall thickness. The change in wall thickness increased with the more dilated aneurysm. In spite of considerable radial deformations, axial deformations of the aneurysm wall were dominant. The present study showed the strong possibility to understand fluid-structure interactions in the human cardiovascular system.
Comparison Between a Quasilinear and a Nonlinear Viscoelastic Model for Brain Tissue
Authors: Darvish Kurosh K. , Crandall Jeff R.
Published: November 2021

The nonlinearity of the viscoelastic behavior of brain tissue was studied. Two nonlinear constitutive models were developed using the experimental results of forced vibrations on bovine brain samples, namely a quasilinear viscoelastic model and a multiple hereditary integral model. The latter was found to be superior especially at higher frequencies (above 27 Hz).
Determination of Mechanical and Fluid-Species Transport Properties for Soft Tissues
Authors: Rigby Paul H. , Morgan Nathaniel R. , Simon Bruce R. , Williams Stuart K.
Published: November 2021

A series of experiments have been developed in order to determine some of the mechanical and fluid-species transport properties of rabbit carotid arteries. The properties to be determined in this study are mechanical parameters, water permeability, and species diffusion parameters for the intima and media.
Sensitivity of Modeling Parameters in Proximal Femur Analyses
Authors: Wang Eric L. , Jiang Yanyao , Fan Lixia , Greer Brian
Published: November 2021

Hip fracture risk can be quantified using a factor of risk (Hayes et al., 1996): (1) Φ = Applied load / Fracture load

The structural capacity, the denominator, can be affected by many parameters including femoral geometry, material properties, load locations, loading direction, loading rate, and frictional resistance.
Mechanisms of Creep-Induced Failure in Cylindrical Cortical Bone Specimens due to Radial Loading
Authors: Brown Christopher U. , Parsamian Gagik P. , Norman Timothy L. , Kish Vincent L. , Gruen Thomas A. , Blaha J. David
Published: November 2021

Damage mechanisms in human femoral cortical bone due to a constant radial load were studied in cylindrical specimens. Characterizing this damage is important for understanding its role in press-fit total hip arthroplasty. Cylindrical bone specimens were loaded at a constant internal pressure until failure. Sections were removed for microscopic observations. More microcracks were observed near the endosteal surface, as compared to the outer surface, and were located within the bone matrix and ended at a cement line. Tensile hoop and compressive radial stresses tend to open microcracks in the hoop direction resulting in cracks oriented in the radial direction.
Application of CFD in Designing Spacers: A Novel Approach
Authors: Jalili Vahid , Patel Mayur K. , Bailey Christopher
Published: November 2021

The aim of this paper is to report on a novel approach used in designing spacer (a biomedical device used to aid inhalation of the drug). The Computational Fluid Dynamics (CFD) technique has been around for some years, but to date has not been used in designing spacers. In the present study the commercial CFD engines used were FLUENT-5.1.1 and PHOENICS. The study covered a large area taking into account various parameter changes such as the inlet boundary condition i.e. changing the velocity at inlet, varying the jet angle at entry to the spacer and the actual length of the spacer. The results were possible were compared to the experimental data available and generally the comparison was good. The findings from this research have highlighted, that there is an optimum size of 6cm and inlet velocity of 30m/s which result in an increased efficiency. It was also found that there is an optimum time of 0.4 sec. For which the highest drug concentration appears to be present.
Branch Flow Effects in the Human Right Coronary Artery Trunk
Authors: Myers Jerry G. , Ojha M. , Johnston K. Wayne , Ethier C. Ross
Published: November 2021

Formation of atherosclerotic plaque in the human right coronary artery (RCA) has, in part, been linked to local hemodynamic factors (Ojha et al., 2000). Thus, there is considerable motivation to accurately characterize hemodynamic patterns in the RCA. Patient-specific geometric characteristics, such as curvature and arterial calibre, have been shown to significantly affect velocity and wall shear stress (WSS) patterns within the RCA trunk (Myers et al., 2000). However it is unclear how flow into arterial branches influences these hemodynamic patterns. In investigating this factor, we computed velocity and WSS distributions in a realistic model of a human right coronary artery (RCA) that included four branches.
Wall Shear Stress and Gradient at Anterior Communicating Artery in Pulsating Flow
Authors: Yamaguchi Ryuhei , Kudo Susumu , Yamanobe Hiroyuki , Nakajima Mikio , Ujiie Hiroshi
Published: November 2021

The aneurysm in the cerebral artery is apt to initiate around the “Circle of Willis”. The anterior communicating artery (ACoA), which composes one of major part of the circle of Willis, is the most predilection artery of the aneurysm. This artery is characterized by a singular geometry. At this artery, two proximal anterior cerebral arteries (A1, confluence) join facing each other. Just at this artery, the flow bifurcates two distal anterior cerebral arteries (A2, bifurcation). Namely, this artery has a function as a bypass channel. Therefore, the flow around the anterior communicating artery would be very unstable. The aneurysm arises around the apex of this artery where the confluent flow collides.
Driving Simulation of Electric Wheelchair on Snowy Roads
Authors: Tadano S. , Uchiyama K. , Tsukada A. , Takahashi H. , Ukai T.
Published: November 2021

An appropriate wheelchair is greatly desired for outdoor use during the winter season in a snowy region. To develope the electric wheelchair, three types of electric wheelchair were tested for their drivability on an icy road, a snow-covered road and an indoor floor. In addition, computational method was proposed to simulate the drivability of a wheelchair on the snowy road condition.
Statistical Modeling of Microstructural Effects on Fatigue Behavior of α/β Titanium Alloys
Authors: Soboyejo A. B. O. , Shademan S. , Sinha V. , Soboyejo W. O.
Published: November 2021

This paper presents the results of combined experimental and theoretical studies of the effects of colony microstructure on fatigue crack growth in Ti-6Al-4V. Colony microstructures with controlled lath widths and colony sizes are produced by controlled cooling from the β phase field. For colony microstructures with approximately 20 vol% of β phase, the fatigue crack growth rates are shown to decrease with increasing α lath and colony size. A new statistical multiparameter modeling methodology framework is proposed for the assessment of the combined effects of mechanical and microstructural random variables on the fatigue crack growth rate. Excellent statistical correlation has been observed between the theoretical model and experimental data. The implications of the results are also discussed for the estimation of fatigue life.
Life Prediction: The Need for a Mechanistically Based Probability Approach
Authors: Harlow D. Gary , Wei Robert P.
Published: November 2021

Concerns with life assessment and management for existing engineered systems and aging infrastructure worldwide have increased the emphasis on the development of methods for reliability and durability predictions. Increasingly it is being recognized that the traditional statistically and empirically based methods are inadequate. These methods are appropriate for interpolations, but their usefulness for extrapolation is limited. Effective predictors, i.e., those that provide precise estimates beyond the range of conditions employed in the development of supporting data and assessments of risk, must be based upon mechanistic models that capture the functional dependence on all the key external and internal variables. This type of modeling, to reflect typical industrial applications, requires multidisciplinary research that addresses the chemical and micromechanical processes that control damage evolution in materials and quantifies the stochastic aspects of these processes. The purpose of this paper is to demonstrate the use and applicability of the mechanistically based probability methodology and to provide a framework from which other applications can be addressed. The approach is illustrated through mechanistically based probability modeling of corrosion and corrosion fatigue of aluminum alloys and creep crack growth in high strength steels.
Contact Damage of Model Dental Multilayers: Experiments and Finite Element Simulations
Authors: Soboyejo W. O. , Wang R. , Katsube N. , Seghi R. , Pagedas C. , Skraba P. , Mumm D. , Evans A. G.
Published: November 2021

This paper presents an overview of recent studies of contact damage in multilayered structures with equivalent elastic properties to bonded dentin/crown structures. Following a brief review of restored tooth structures, prior work on the development of model dental multilayered structures is reviewed. The review examines the two sides of the current debate on the applicability of Hertzian indentation tests to real clinical scenarios. In particular, the potential effects of indentation ball size are identified as some of the reasons for the “apparent” discrepancies in the literature. An experimental framework is then presented for the exploration of the effects of ball size on contact damage mechanisms in dental multilayers. The observed cracking patterns at the onset of crack nucleation are shown to be associated with principal stress contours computed using elastic-plastic finite element models. The statistical variations in the crack nucleation loads are shown to be well described by Weibull (weakest link) statistics. The implications of the results are discussed for the design of dental multilayers that are more resistant to crack nucleation and propagation.
Corrosion and Wear Behavior of Al 2024 Alloy Coated With Intrinsically Conductive Polymers, ICPs
Authors: Shah Kunal , Iroh Jude O. , Akundy G. , Zhu Yanrong , Popoola O.
Published: November 2021

The Corrosion behavior of aluminum alloys coated with intrinsically conducting polymers, ICPs, such as polyaniline, polypyrrole and their composites has been determined. The corrosion rate of the coated substrates is significantly reduced in the presence of the ICP coating. However, the corrosion resistance of the coated Al was found to be strongly dependent on the electrochemical processing variables such as the applied current density, pH and the deposition time. Both low current densities, i 3/4 2 mA/cm2 and high current densities, i > 6 mA/cm2, resulted in high corrosion currents and low corrosion rates. Also the ICP coatings deposited at very short and very long deposition times, respectively, show decreased corrosion performance. In our presentation, we will discuss the effects of electrochemical processing variables on the surface structure and corrosion performance of ICPs coated Al.
Mathematical Modeling of High Velocity Oxygen Fuel Thermal Spraying: An Overview
Authors: Cheng D. , Trapaga G. , McKelliget J. W. , Lavernia E. J.
Published: November 2021

High velocity oxygen fuel (HVOF) thermal spraying is a versatile technique widely used for the manufacture of coatings from various materials system. The physical, mechanical, and chemical characteristics of a coating are critically influenced by the operating parameters used to obtain maximum coating performance while minimizing experimentation. In this paper, modeling of HVOF thermal spray processes is reviewed, paying particular attention to combustion, gas/particle dynamics, particle impingement, and coating formation.