bluuebunny/crossref_metadata_2025 huggingface dataset:
Biomechanics and Painful Injuries: Tissue and CNS Responses for Nerve Root Mechanical Injuries
Authors: Winkelstein Beth A. , Hubbard Raymond D. , DeLeo Joyce A.
Published: May 2008

Pain affects as many as 50 million Americans, with annual costs estimated as high as $90 billion. Unfortunately, the mechanism of injuries leading to persistent pain syndromes remain largely uncharacterized. A common painful injury results due from mechanical loading of nerve roots, which can occur for spinal injuries in both the low back and neck. Relationships have been demonstrated between tissue compression and behavioral hypersensitivity responses in animal models, with differential patterns of sensitivity depending on the nature of the mechanical insult (Colburn et al., 1999). Mechanical allodynia (MA) is an increased behavioral sensitivity to a non-noxious stimulus and is observed in the dermatome of the injured tissue. It can be measured by the frequency of paw withdrawals elicited by stimulation with normally non-noxious von Frey filaments. Allodynia is a clinical measure of sensitivity and, therefore, provides a useful gauge of nociceptive responses. Animal studies have shown that compression of neural structures initiates a variety of physiologic responses, including decreased electrical activity, increased edema formation, and increased endoneurial pressure in the region of compression (Lundborg et al., 1983; Olmarker et al., 1989, 1990; Pedowitz et al., 1992). While these studies document physiologic changes immediately following injury, they do not describe the temporal nature of these changes following tissue loading as they relate to pain behaviors. Moreover, despite this evidence of edema formation and increased endoneurial pressure locally in the nerve roots, no study has simultaneously documented local changes in nerve root geometry following compressive injury and how these changes may be linked to the onset and/or maintenance of pain-associated behaviors. Therefore, this study examines injury biomechanics for pain-behaviors in a radiculopathy (nerve root injury) model and temporally characterizes the local geometric changes in the nerve root for a series of postsurgical time points following compressive injury. While these results indicate that compression magnitude clearly modulates pain responses, the local nerve root swelling does not appear to directly drive behavioral changes. This suggests a complicated physiology for injury which likely contributes to the manifestation of pain. Findings are also presented for preliminary investigations into tissue rebound/recovery responses for varied mechanical insult magnitudes to begin to understand potential injury mechanisms leading to pain.
Computational Analysis of WSS Conditions and Critical Blood Particle Localization in a Human Carotid Artery Bifurcation
Authors: Longest P. W. , Kleinstreuer C. , Hyun S.
Published: May 2008

Early intimal thickening (IT) in the carotid artery bifurcation has been associated with multiple hemodynamic and biophysical factors including low wall shear stress (WSS) and high oscillatory shear index (OSI) (Ku et al., 1995), as well as abnormal intramural stress and strain. While WSS conditions have been widely shown to affect vascular biology and arterial wall self-regulation, the near-wall localization of critical blood particles, such as monocytes and platelets, also plays a significant role in atherosclerotic lesion formation and general IT (Ross, 1993). In this study, we hypothesize that locations of elevated monocyte and platelet interactions with reactive or activated vascular surfaces, due to injury or endothelial dysfunction, are highly susceptible to IT initialization and progression in the carotid artery bifurcation (CAB). To assess the potential role of platelet-and monocyte-wall interactions, as well as other WSS-based hemodynamic wall parameters (HWPs), experimentally validated particle-hemodynamic simulations have been conducted for a representative CAB geometry. Areas of significant particle interactions with the vascular surface have been identified by a validated near-wall residence time (NWRT) model for monocytes and platelets, which encapsulates regions of near-wall particle stasis and/or elevated concentrations. Actual early intimal thickening has been assumed consistent with the observations of Masawa et al. (1994a & b) (Fig. 1).
Superoxide Radical Transport Through Nanoheterogeneous Biosensor Film
Authors: Song Hongwei , Ilegbusi Olusegun J.
Published: May 2008

A mathematical model is developed to describe the transport phenomena and electrochemical reaction kinetics during amperometric measurement of superoxide radical concentration using ZnO-polymer nanocomposite sensor. This model assumes a logarithmic normal distribution for the nanoparticles immobilized in the polymer matrix and an empirical relation for the diffusion coefficient of superoxide radicals as a function of pore volume fraction. A kinetic with secondary order rate constant is used to represent the electrochemical reactions of electron transfer from the superoxide radicals to nanoparticles. The predicted results include the effect of diffusion coefficient on concentration and electrical conductivity.
A Three Dimensional Forward Dynamic Model of a Human Knee for Determining Ligament Forces
Authors: Webb Joshua D. , Gonzalez Roger V.
Published: May 2008

A three-dimensional musculoskeltal model of the human knee is being developed to investigate the forces placed on the four major knee ligaments as a result of muscle contraction. This computational knee model includes the femur, tibia, and patella, seven major muscles, four knee ligaments, and the patellar tendon. A constrained forward dynamic simulation is performed by using EMG data to estimate muscle forces. The ligament forces estimated by the model are verified by means of a robotic-cadaver experimental setup in which the knee flexion angle of a cadaver specimen was controlled by a robot. Estimated muscle forces were dynamically applied to the cadaver knee as it was flexed/extended through a specified range of motion. The ligament strain calculated by the model is compared to the strain measured experimentally and to values found in literature to verify the accuracy of the model.
Quasi-Static Transduction Characterization of Galfenol
Authors: Kellogg Rick A. , Flatau Alison , Clark Arthur E. , Wun-Fogle Marilyn , Lograsso Thomas
Published: May 2008

The objective of the work presented is characterization of the magnetoelastic transduction properties of single crystal and textured polycrystalline Fe-Ga alloys (Galfenol) under controlled mechanical, magnetic and thermal conditions. Polycrystalline samples of interest include a directionally solidified specimen, which possesses a favorable saturation magnetostriction output, and an extruded specimen, whose magnetostriction properties were significantly reduced by annealing. A brief discussion of the thermally controlled transducer used for the magnetic testing is presented first. Thereafter, the single crystal response to major-loop cyclic magnetic fields under different temperature and stress conditions, as well as its response to minor-loop cyclic magnetic fields and major-loop cyclic stress is examined. Next, the magnetic and magnetostrictive responses to major-loop cyclic magnetic field conditions are compared for the directionally solidified, extruded and single crystal specimens. The paper concludes with a magnetic characterization summary of the different Fe-Ga alloys examined.
Basal to Near Hyperemic Pulsatile Flow in a Deployed Coronary Stent
Authors: Holcomb Matthew D. , Slusher Steven T. , Rajamohan Divakar , Back Lloyd H. , Jog Milind , Banerjee Rupak K.
Published: May 2008

The present study focuses on developing basal to near hyperemic flow through the entrance region of a deployed stent in a coronary artery segment. Stents that are presently available in market differ significantly in design. Hence, there is a need to optimize its design such that the magnitude of wall shear stress is within physiologic limit, thus minimizing the patho-physiological effects. For near hyperemic flow, the analysis showed a 20 fold increase in the positive values of wall shear stress at the stent wires exposed to the blood flow. Further, at the void next to the entrance, the wall shear stress was an order of magnitude lower than the values typically observed in similar downstream regions.
Modelling Strengthening Mechanisms in Solids Using Dislocation Dynamics
Authors: Khraishi Tariq A. , Yan Lincan , Shen Yu-Lin
Published: May 2008

The mechanical properties of crystalline solids are inherently a function of their microstructure which in turn is governed by processing of the material. Although advances in understanding the structure-property relationships have been achieved, more basic research to expand the knowledge base is certainly needed. Recent work on exploring the strengthening effect of particles and grain-boundaries in a crystalline solid, using the fundamental approach of dislocation dynamics, is presented. Whenever appropriate, comparisons to experimental findings or theoretical models are made. The work demonstrates the power and limitations of such simulation methodology. In particular some basic physics of the interaction between dislocations and these microstructural features are revealed.
Model Development for Integrated Hybrid Electric Vehicle Dynamic Stability Systems
Authors: Anstrom Joel R.
Published: May 2008

This study expanded an existing full car dynamic model (HVOSM.VD2) to enable simulation of electric, hybrid electric, and fuel cell vehicles with integrated vehicle stability systems. A prototype range extending series hybrid vehicle was constructed with independent front wheel drives. A hybrid vehicle stability assist (VSA) algorithm was developed to perform proportional control of yaw rate through left/right distribution of front motor torques while simultaneously blending anti-lock braking and traction control with electric drive within hybrid system power limits. The new model, Hybrid Electric Vehicle Dynamic Environment, Virtual (HEVDEV), was used to simulate the hybrid VSA safety system in the prototype. Skid pad testing was performed to validate HEVDEV simulations of steady state turning behavior and develop hybrid VSA control parameters. Further simulations predicted successful hybrid VSA performance during step-steer and braking-in-a-turn dynamic maneuvers. Conclusions were made about hybrid VSA and vehicle component specifications.
Metallic Microactuators Based on Sacrificial Layer SU8 Release
Authors: Enikov Eniko T. , Lazarov Kalin V.
Published: May 2008

Thermal micro-actuators are a promising solution to the need for large-displacement, low-power MEMS actuators. Potential applications of these devices are micro-relays, tunable impedance RF networks, and miniature medical instrumentation. In this paper the development of thermal microactuators based on SU8 is described. A polymeric sacrificial layer allows the removal of the SU8 mold to occur without the use of harsh etching conditions. In addition to silicon non-traditional for MEMS substrates such as RF-printed circuit boards have also been successfully utilized to fabricate the devices. The PCB-based devices exhibited similar characteristics, thus opening the possibility of integrating RF MEMS directly on PCBs. The actuators were benchmarked with respect to power consumption, stroke, and response time. The fabricated nickel actuators are shown to be robust with displacements in the range of 76 micrometers using 80 mW of power. Actual cooling transients were captured using a two-step constant-current excitation method. It is further demonstrated through analytical models that the thermal cooling times limit the bandwidth of these devices below 1KHz. Several commercially relevant applications of the developed actuators are also discussed. One such application is a vibro-tactile display for disabled individuals.
Measurement System for BGA Coplanarity
Authors: Qiu Yu , Sun Changku , Ye Shenghua , Kang Yilan
Published: May 2008

This paper presents a line-structured laser scanning system for measuring the coplanrity of BGA chip leads. The corresponding methematics model of the system is gived. And also a study of optical image splitting and splicing technique is constructed and used to improve the resolution of the system. Furthemore, a contact-datum-plane assessment method is established to evaluate the coplanarity of BGA chip leads. The experimental studies on a 20 × 20 array of BGA chip is carryed out, the inaccuracy error of the measurement system is 2σ= 0.033μm.
A Finite Element Analysis for Stiffness of Fixture Units
Authors: Zheng Y. , Rong Y. , Hou Z.
Published: May 2008

This paper presents a systematic finite element model to predict the fixture unit stiffness by introducing nonlinear contact elements on the contact surface between fixture components. The contact element includes three independent springs: two in tangential directions and one in the normal direction of the contact surface. Strong nonlinearity is caused by possible separation and sliding between two fixture components. The problem is formulated by the penalty function method and is solved by the Newton-Raphson procedure. The model was validated by two cases of analysis of a linear cantilever beam and a simple fixture unit with two components. Results are in agreement with the corresponding analytical solution of beams and the previous experiment results for fixture in the literature.
A Study of Bridged Delaminations in High Temperature Laminates Under Heat Flux Loading
Authors: Siegmund Thomas , Hattiangadi Ashwin
Published: May 2008

High temperature ceramic matrix composites (CMCs) are material considered in many applications where high heat fluxes constitute a significant contribution to loading. The laminates can fulfill their function as thermal protection layers only if they stay intact, i.e. without internal delaminations or spalling, such that the heat flux remains undisturbed by such events. Crack bridging is an important effect in CMCs, and its implication to CMC laminates under thermal loading is investigated.
Modeling and Analysis of Crack Growth in SnPb and SnAgCu Solder Joints in PBGA Packages: Part I — Crack Initiation
Authors: Kim Donghyun , Mawer Andrew , Masada Glenn Y. , Moon Tess J.
Published: May 2008

Solder joints in electronic packages deform by creep and undergo a microstructural evolution process that includes grain coarsening, voiding, microcracking, and macrocracking. This paper describes an FEM model of the crack initiation process of SnPb and SnAgCu solder joints in 357 plastic ball grid array packages for different aging conditions and simulated under 0–100°C accelerated thermal cycling tests. The simulations show that 1) cracks initiate at the package interface first, and then at the opposite side of the board interface; 2) secondary cracks initiate at the opposite end of the primary crack at the joint interfaces; 3) no secondary cracks occur at the package interface of ages SnPb joints, since compressive stresses oppose void formation; and 4) it takes longer to initiate cracks in SnAgCu joints than SnPb joints. The damage process in the solder joints was simulated from grain coarsening, voiding, to microcracking, with SnAgCu joints not undergoing grain coarsening due to their stable microstructure. The model results were consistent with experimental results in the number and location of cracks in the joints.
Modeling and Analysis of Crack Growth in SnPb and SnAgCu Solder Joints in PBGA Packages: Part II — Crack Propagation
Authors: Kim Donghyun , Mawer Andrew , Masada Glenn Y. , Moon Tess J.
Published: May 2008

Part II of this paper describes an experimental and analytical study of crack propagation in SnPb and SnAgCu solder joints in 357-PBGA packages exposed to 30-minute thermal cycles of 0 to 100°C. Experimental results show that cracks propagate faster at the package interface than at the board interface; secondary cracks from at the package interface, but grow much slower than the primary cracks; and crack growth rates in SnPb joints are about 50% larger than in SnAgCu joints. A crack propagation model, developed using the fracture mechanics approach, calculates the energy release rate at the crack tip. Using this rate and experimental crack length data, crack propagation rates were computed. Simulation results show the effects of solder type and aging conditions on crack propagation rates and the effects of the number of cracks in a joint on crack propagation life.
On the Stability Analysis of the Human Spine
Authors: El-Rich M. , Shirazi-Adl A.
Published: May 2008

The stability of the human spine in compression has attracted a considerable amount of attention in recent years. The passive ligamentous thoracolumbar and lumbar spines are known to exhibit large displacements or hypermobility (i.e., instability in an imperfect column) under compression loads <100N. Since such compression loads are only a small fraction of those supported by the spine even in regular daily activities, let aside the manual material handling tasks, the question arises as to how the spine is stablized in vivo? Various stabilizing mechanisms have been proposed and investigated; wrapping loading [Shirazi-Adl and Parnianpour, 2000], postural adaptations [Shirazi-Adl and parnianpor, 1999], intra-abdominal pressure [Cholewicki et al, 1999] and muscle activation/coactivation [Bergmark, 1989; Crisco and Panjabi, 1991]. In this work, a novel kinematics-based methad [Shirazi-Adl et al., 2002] is first applied to compute muscle forces and internal loads in standing postures under gravity with or without 200N loads held either on sides or close to the body in front. The stability of the system under given loads and prescribed postures is sudsequently examined using both linear bucking analysis based on the deformed configurations and nonlinear analysis while employing a liner stiffness-force relationship for muscules [Bergmark, 1989; Crico and Panjabi, 1991]. The relative accuracy of foregoing methods in stability analysis of some sample structures is also investigated. Moreover, the effect of co-activity on stability of the spine in neutral postures is studied.
An Analytical Evaluation of the Transient Dynamics of Semiactive Dampers
Authors: Ahmadian Mehdi , Vahdati Nader
Published: May 2008

This paper provides an analytical evaluation of semiactive dampers, which have been more increasingly used for vehicle applications in the recent years, when transient dynamics are present. Although much research has been performed on various aspects of semiactive dampers, the vast majority of past studies have been performed for the steay sate aspects of such dampes. This study will extend the results of those studies, by providing an evaluation of semiactive dampers when they are subjected to a transient dynamics, such as a step input. The performance of a semiactive damper with two commonly used control methods—namely, skyhook control and hybrid control—is evaluated analytically, using a single suspension model. In addition to evaluating such metrics as the peak response and settling time of the spring body, this analysis will include an evaluation of the work performed by semiactive dampers. A comparison with passive suspensions shows that the semiactive suspensions that are considered here could improve various aspects of vehicle ride comfort and handling, within the limitation of a single suspension model. Field-testing of the semiactive dampers discussed here would, of course, provide more conclusive evidence on their benefits for controlling vehicle transient dynamics.
Secondary Fluids for GAX Absorption Heat Pump
Authors: Anand G. , Panchal C. B. , Erickson D. C.
Published: May 2008

The gas-fired Generator-Absorber heat eXchanger (GAX) heat pump is being considered for space conditioning in residential and light commercial applications. In order to meet the national building codes for ammonia absorption heat pumps, a secondary fluid is used to interface with the air-coils. Proper choice of a secondary fluid maximizes the economic advantage of the GAX heat pump. The secondary fluid transfers the heating and cooling loads from the absorption heat pump to and from outdoor and indoor air-coils. The physical properties of secondary fluids influence the heat transfer performance in the heat-exchange equipment and hence the effective lift, thereby determining the cycle coefficient of performance (COP). Additionally, the pumping power for each fluid varies depending on the density and viscosity at operating temperatures. The variation in cycle COP and pumping power as a result of fluid properties is ultimately manifested as changes in electric and natural-gas cost. An analysis was carried out to evaluate six secondary fluids for a GAX absorption heat pump. A performance model was developed to simulate the secondary-fluid flow loops and the absorption heat pump. The utility costs for heating and cooling were determined for a typical building. The effects of ambient conditions and local utility rates were determined by modeling the annual utility costs in four cities: Atlanta, Chicago, Los Angeles, and New York. These four cities provided wide variations in heating and cooling requirements, and utility rates for natural gas and electricity. The results from this study provide a basis for selecting secondary fluids for heat pumping in different locations.
Advances in Recuperator Technology for Gas Turbine Systems
Authors: Muley Arun , Sunde´n Bengt
Published: May 2008

For high-speed micro gas turbine plants for electrical power and heat generation, a recuperator is needed to obtain a high thermal efficiency. The recuperator receives heat from the exhaust gas and preheats the compressor discharge air before it enters the combustion chamber. Such plants contribute to an ecological and environmentally friendly energy production. This paper considers recent advances in recuperator technology. Recent investigations have shown that with prime surfaces like corrugated wavy channels ones, it would be possible to attain high heat exchanger effectiveness without added weight penalty. However, with efficient heat transfer surfaces, the inlet/outlet manifolds design also become more important for the overall performance of the recuperator. Usually customers require recuperator with high effectiveness and low total pressure drop (within certain design requirements). Also, a request on compactness is commonly at hand. All these matters make recuperator an interesting and challenging device for thermal science investigation. A brief introduction and literature review is presented followed by discussion of recuperator thermal-hydraulic performance modeling and testing. Also surface selection procedure to achieve good balance between heat transfer and pressure drop is described. Other important topics such as material aspect and fabrication methods are also delineated.
Mitigation of Biodynamic Response to Vibratory and Blast-Induced Shock Loads Using Magnetorheological Seat Suspensions
Authors: Choi Young-Tai , Wereley Norman M.
Published: May 2008

This study investigates biodynamic response mitigation to three different excitations of sinusoidal and random vibrations and shock load using a magnetorheological (MR) seat suspension. In doing so, an MR seat suspension model for military vehicles, with a detailed lumped parameter model of the human body, was developed. The lumped parameter model of the human body consists of four parts: pelvis, upper torso, viscera and head. From the model, the governing equation of motion of the MR seat suspension considering the human body was derived. Based on this equation, a semi-active nonlinear optimal control algorithm appropriate for the MR seat suspension was developed. The simulated control performance of the MR seat suspension was evaluated under three different excitations of sinusoidal and random vibration and tremendous shock load due to a mine explosion. In addition, the mitigation of injuries to humans due to such shock load was also evaluated and compared with the passive seat suspension using a passive hydraulic damper.
Experimental Observations of the Deformation Characteristics in Layered Structures
Authors: Bastawros Ashraf , Antoniou Antonia
Published: May 2008

A novel experimental configuration is devised to measure the evolution of the deformation field and the corresponding toughness evolution within soft metallic films constrained by hard layers. The experimental configuration provides pure shear state within the constrained film. The material system utilized was comprised of a ductile layer of Tin based solder, encapsulated within relatively hard copper shoulders. Different Tin-Lead compositions are tested with grain size approaching the film thickness. The in-plane strain distribution within the film layer is measured by a microscopic digital image correlation system. The toughness evolution within such highly gradient deformation field is monitored qualitatively through a 2D surface scan with a nano-indentor. The measurements showed a highly inhomogeneous deformation field within the film with discreet shear bands of concentrated strain. The localized shear bands showed long-range correlations of the order of 3–4 the grain size. A size-dependent macroscopic response on the layer thickness is observed. However, the corresponding film thickness is approximately 100–1000 times larger than those predicted by non-local continuum theories and discreet dislocation.
Nanodiamond Coating for Field Emission Filaments
Authors: Kvit A. V. , Zhirnov V. V. , Tyler T. , Hren J. J.
Published: May 2008

Nanodiamond is very important for autoemission applications because it allows investigators to reduce electric field for electron emission current generation. Moreover, we can also consider nanodiamonds as “bricks” for new method of diamond coating growth. In this paper we describe the formation and investigation of nanodiamond-based coating on Mo needles. Manipulation of nanodiamond particles with high electric fields allows us to prepare systems of isolated diamond quantum dots on a conductive surface. Localization of an isolated single-crystalline diamond particle ∼5 nm in size on the «tip of a needle» presents an unique opportunity for studies of correlations between the structural and emission properties of individual diamond nanoparticles. Combinations of TEM observations, field emission measurements, and repeated diamond depositions on the same emitter provided a direct comparison of the effects of various amounts of nanodiamond particles on the emission properties of a coated metal field emitter. By utilizing Z-contrast and EELS technique we investigated distribution of nitrogen impurity inside individual nanoparticle and aging effect (increasing of s p2 fraction on the surface of nanodiamond with time).
Thin YSZ Electrolyte Film Depositions on Dense and Porous Substrates
Authors: Xu Zhigang , Hilton Corydon , Watkins Bobby , Yarmolenko Sergey , Sankar Jag
Published: May 2008

Yttria stabilized zirconia (YSZ) thin films have been processed on polished silicon and porous strontium-doped lanthanum manganite (LSM) substrates by liquid fuel combustion chemical vapor deposition from combustion of an aerosol jet. The aerosol jet consists of Y- and Zr- containing metalorganics dissolved in toluene and high-purity oxygen. The morphology and thickness of the deposited films have been analyzed with scanning electron microscope. On the polished silicon substrates, thin and uniform films have been obtained. The grain growth rate is of the first order of the deposition time. The film growth rate was greatly enhanced by utilizing higher precursor concentrations, proper substrate temperature and the effect of thermophoresis. However, when the porous substrate is being coated, a more complex deposition process takes place. The initial deposition seems to be favored on the surface protrusions. Therefore, the covered areas serve as nucleation sites and the grains start to grow, giving rise to larger particles and rougher surface than the films on polished silicon. To enhance the pore-sealing rate, some pre-treatments and post-treatment have been used. Moreover, deposition parameters towards fast pore sealing have been investigated. Thin and continuous films with the film thickness less than 3 μm have been obtained.
A Structural-Acoustic Vehicle System Model for Noise and Vibration Analysis
Authors: Sung Shung H. , Nefske Donald J. , Feldmaier Douglas A. , Doggett Spencer J.
Published: May 2008

A structural-acoustic finite-element model of a sedan-type automotive vehicle is developed and experimentally evaluated for predicting vehicle interior noise and structural vibration. The vehicle system model is developed from finite-element models of the major structural subsystems, which include the trimmed body, front suspension, rear suspension, powertrain and exhaust system. An acoustic finite-element model of the passenger compartment cavity is coupled with the vehicle system model to predict the interior noise response. The predicted interior noise and structural vibration by the vehicle system model are compared with the measured responses for shaker excitation at the axle to 200 Hz. The comparisons demonstrate the accuracy of the structural-acoustic vehicle system model, and they indicate where modeling improvements are required.
Multi-Scale Analysis of Deformation and Failure of Superplastic Materials
Authors: Khraisheh Marwan , Thuramalla Naveen , Abu-Farha Fadi , Deshmukh Pushkarraj
Published: May 2008

The superplastic deformation is modeled within the continuum theory of viscoplasticity with an anisotropic yield function and a microstructure-based overstress function. Grain growth and cavitation are incorporated in the model and their effects on the superplastic flow stress are investigated. In addition, a new multi-scale stability criterion for superplastic deformation taking into account both geometrical (macroscopic) and microstructural features including grain growth and cavitation is presented. The new stability criterion is based on Hart’s stability criterion and is obtained by combining a modified microstructure-based constitute model for superplastic deformation with grain and cavitation evolution equations. The effects of void fraction, grain size, and strain rate sensitivity on the stability of superplastic deformation are examined. Variable strain rate optimum forming paths are derived from the stability criterion and optimum pressure profiles for superplastic blow forming are generated using FE analysis.
An Intelligent Numerical Simulation Environment on Component-Based Models: Part II
Authors: Deng Weiwen , Gu Edward Y. L.
Published: May 2008

An object-oriented simulation technology is first investigated, as a natural extension to the independent component computation (ICC) method under sequential computation environment, proposed in Part I. The intelligence, represented by an embedded expert system, is introduced. A systematic method and structure for establishing an intelligent numerical simulation environment is presented. A Windows-based software, Solver for Windows, has been developed to implement and verify the concepts presented in this paper.
A Study Into LDPE as an Undersurfacing Material for Injury Prevention and Risk Minimisation in Children’s Playgrounds
Authors: Eager David
Published: May 2008

Low Density Polyethylene (LDPE) closed-cell foam is used extensively as an impact absorbing material for injury prevention and risk minimisation in a variety of applications, including children’s playground undersurfacing, padding for trampoline frames, and other fall zones. This paper presents and analyses the data from numerous impact tests performed on samples of LDPE of select different product thicknesses (10, 20, 30 and 40 mm), nominal Relative Densities (30, 45, 60 and 75 kg/m3) and drops or free height of fall (100 mm steps in heights from 300 to 2100 mm). The impact absorption properties of LDPE are characterized using the Australian and New Zealand Standard AS/NZS 4422: Playground Surfacing — Specifications, Requirements and Test Method. The gmax and HIC results are presented both graphically and numerically. This paper also discusses uses and limitations of LDPE with particular emphasis on injury prevention and risk minimisation.
Validity of the Use of Generic Failure Frequencies in a QRA
Authors: Beerens Herlinde I. , de Haag P. A. M. Uijt , Post J. G. , Ale B. J. M.
Published: May 2008

In QRA calculations the frequency of an accident scenario is assessed by a generic failure frequency approach, defined in the Dutch Purple Book. In this paper we will examine the origin of certain failure frequencies in the Purple Book. The credibility and validity of the failure frequencies are reviewed here by means of a literature search. A study to revise and update these failure frequencies has been initiated.
The Migration of DNA Into a DNA-Crosslinked Gel Using Electrophoresis
Authors: Lin David C. , Langrana Noshir A. , Yurke Bernard
Published: May 2008

DNA-crosslinked polyacrylamide gels are polymeric electrolytes by virtue of the fact that DNA is negatively charged in an aqueous solution. As such, their mechanical properties can be altered by electrophoretic and electro-osmotic effects. Hybridization of single-stranded DNA with single-stranded sections of the crosslinks provides a novel means of altering gel mechanical properties. As a step toward exploring this means of altering gel mechanical properties, we report here on a study of the use of electrophoresis to introduce single stranded DNA into DNA crosslinked gels. Changes in elastic properties of the gel, before and after electrophoresis, were measured.
Modeling Elderly Eye Injuries in Automobile Crashes
Authors: Stitzel Joel D. , Hansen Gail A. , Duma Stefan M.
Published: May 2008

Eye injuries have been shown to be greater in the elderly population as a possible cause of this greater incidence. Three separate impact scenarios simulating a foam particle (30 m/s), a streering wheel (15 m/s), and an air bag (67 m/s), were applied to a finite element eye model in order to reveal the effects of aging on the eye when subjected to blunt trauma. The lens stiffness of the model was varied according to human lens stiffness values determined for each age group. The computational eye model demonstrated that increased risk was associated with the increasing stiffness of the lens, producing up to a 120% larger stress in the ciliary body.
Effective Stress Intensity Factor in Mode III Crack Growth in Round Shafts
Authors: Vaziri A. , Nayeb-Hashemi H.
Published: May 2008

Turbine-generator shafts are often subjected to a complex transient torsional loading. Such transient torques may initiate and propagate a circumferential crack in the shafts. Mode III crack growth in turbo-generator shafts often results in a fracture surface morphology resembling a factory roof. The interactions of the mutual fracture surfaces result in a pressure, and a frictional stress field between fracture surfaces when the shaft is subjected to torsion. This interaction reduces the effective Mode III stress intensity factor. The effective stress intensity factor in circumferentially cracked round shafts is evaluated for a wide range of applied torsional loadings by considering a pressure distribution in the mating fracture surfaces. The pressure between fracture surfaces results from climbing the rought surfaces respect to each other. The pressure profile not only depends on the fracture surface roughness (height and width (wavelength) of the peak and valleys), but also depends on the magnitude of the applied Mode III stress intensity factor. The results show that the asperity interactions significantly reduce the effective Mode III stress intensity factor. However, the crack surfaces interaction diminishes beyond a critical applied Mode III stress intensity factor. The critical stress intensity factor depends on the asperities height and wavelength. The results of these analyses are used to find the effective stress intensity factor in various Mode III fatigue crack growth experiments. The results show that Mode III crack growth rate is related to the effective stress intensity factor in a form of the Paris law.
Simulation of Brisk and Fast Phase-Contrast Magnetic Resonance Imaging by Computational Fluid Dynamics
Authors: Hershey Bradley L. , Doyle Mark , Kortright Eduardo , Anayiotos Andreas
Published: May 2008

Cardiac synchronized magnetic resonance imaging of flowfields has suffered due to the relatively long acquisition times required. We developed a rapid MRI approach, BRISK PCA (Block Regional Interpolation Scheme for k-space Phase Contrast Angiography) which was simulated here using data generated by computational fluid dynamics to investigate the role of interpolation and segmentation on the accuracy and efficiency of the method. BRISK differs from other sparse sampling schemes in that the sampling rate is a function of the position in k-space and interpolation is used to generate data points not directly acquired. Combined with conventional segementation, this allows more efficient use of time, resulting in rapid acquisitions with good spatial and temporal resolution. FAST (Fourier AcquiSition in Time) is a similar sparse sampling strategy that varies the segmentation factor, rather than the sampling rate, as a function of k-space position. BRISK and FAST can be performed in nearly equally scan times. However, deviation from ideal in the FAST data was highly dependant on the starting phase of the flow waveform, while BRISK was immune to such variation. Simulations showed that BRISK (up to segmentation factor 5) and FAST 5 retained excellent axial-velocity accuracy, but the accuracy of FAST was variable and dependent on waveform characteristics.
Dexterous Trajectory Tracking Control of a Mobile Robot
Authors: Zhang Zheng , Ji Meng , Sarkar Nilanjan
Published: May 2008

A departure from the traditional trajectory tracking control technique of a mobile robot is presented here in order to accommodate sudden changes in the reference trajectory. It is expected that in a dynamic, uncretain environment the robot may need to make sudden changes in its navigation strategy that may necessitate such an approach. In this work, a hybrid control framework is developed that first determines a suitable control strategy for a particular subtask and then implements it by means of choosing the specific controller. A supervisor is used to determine the suitable control strategy. The swiching stability among a set of trajectory tracking controllers is analyzed. Extensive simulation results demonstrate the efficacy of the proposed control technique.
Extensional Properties of Coating Colors at High Strain Rates
Authors: Arzate Alfa , Ascanio Gabriel , Carreau Pierre J. , Tanguy Philippe A.
Published: May 2008

Paper coating fluids also called colors are concentrated aqueous suspensions composed mainly of mineral pigments, thickeners, binders and dispersing agents. They are applied onto moving paper web for improving the optical and printing properties. Roll coating is one of the most used technologies for paper coating, however jet coating is currently a promising technology for high-speed processes. Coating colors are submitted to high strain rates in both roll or jet coaters, therefore the extensional viscosity plays a major role in the process. An orifice flowmeter was used for measuring the extensional properties of complex rheology fluids such as coating colors. The principle of this flowmeter is based on the relationship between pressure drop and the flow rate of fluid passing through a small orifice. The flowmeter was firstly calibrated in terms of a dimensionless Euler number as a function of the Reynolds number with Newtonian fluids. The calibration curve was then used to determine the apparent extensional viscosity of coating colors. Results of extensional properties of paper coating colors are presented and compared to shear viscosity. The ratio of extensional to shear viscosity (Trouton ratio) for some coating colors was shown to exceed considerably the theoretical value of 3 expected for Newtonian fluids.
Effect of Surfactant Additives on Centrifugal Pump Performance
Authors: Ogata Satoshi , Watanabe Keizo , Kimura Asano
Published: May 2008

Performance of a centrifugal pump when handling surfactant solutions was measured experimentally. The effects of the concentration and temperature of surfactant solutions on pump performance were investigated. It was clarified that the pump efficiency with surfactant solutions was higher than that with tap water, and increased with an increase of surfactant concentration. The value of maximum flow rate of the pump also increased. The total pump head increased with an increase in the surfactant concentration, however, the shaft power decreased with a decrease in the rotational speed of the impeller. The pump efficiency is dependent on the surfactant temperature, and there is an optimal temperature which maximizes the efficiency.
Embedded Ultrasonics With Piezoelectric Wafer Active Sensors for Structural Health Monitoring of Thin-Wall Structures
Authors: Giurgiutiu Victor
Published: May 2008

The capability of embedded piezoelectric water active sensors (PWAS) to perform in-situ ultrasonic nondestructive evaluation (NDE) is explored. Laboratory tests are used to prove that PWAS can satisfactorily perform Lamb wave transmission and reception. Subsequently, pulse-echo method for crack detection in an aircraft panel is illustrated. For large area scanning, a PWAS phased array is used to create the embedded ultrasonics structural radar (EUSR). In conclusion, opportunities for implementation into structural health monitoring applications and further research needs are discussed.
An Adaptive Semiactive Control Algorithm for Vehicle Suspension Systems
Authors: Song Xubin , Ahmadian Mehdi , Southward Steve
Published: May 2008

In general, a vehicle suspension system can be characterized as a nonlinear dynamic system that is subjected to unknown vibration sources, dependent on road roughness and vehicle speed. In this paper, we will present a nonlinear-model-based adaptive semiactive control algorithm developed for nonlinear systems exposed to broadband non-stationary random vibration sources that are assumed to be unknown or not measurable. If there exist unknown and/or varying parameters of the dynamic system such as mass and stiffness, then the adaptive algorithm can include a recursive least square (RLS) method for on-line system identification. Since the adaptive algorithm is developed for semiactive systems, stability is guaranteed based on the fact that the system is energy conservative. The convergence of the adaptive system, however is not guaranteed, and is investigated through a numerical approach for a specific case. The simulation results for a magneto-rheological seat suspension system with the suggested adaptive control are presented. The results are compared with low-damping and high-damping cases, as well æ other configurations of skyhook control, in order to show the extent of the procurement that can be expected with the suggested adaptive skyhook control provides a better broadbandk performance for the suspension, as compared to the other damping configurations that are included here.
LQG-Based Robustifying Flight Control System
Authors: Griffin D. , Kelkar A. G.
Published: May 2008

This paper presents a robust controller design for an automatic flight control system (AFCS) for a fighter aircraft model with eight inputs and seven outputs. The controller is designed based on McFarlane-Glover robustifying technique using a simple baseline LQG design. Controllers designed purely based on traditional LQG techniques are known to have no guaranteed robustness margins. The McFarlane-Glover technique can be used to enhance the stability robustness of the baseline LQG design using a two-step design process. In the first step, an LQG controller is designed which is optimized only for performance without any consideration to robustness. In the second step, the performance optimized LQG design is rendered robust using McFarlane-Glover procedure. The robustifying procedure uses a coprime factor uncertainty model and H∞ optimization. An important advantage of this procedure is that no problem dependent uncertainty modelling or weight selection is required in the second step of the process. The robustifying procedure also yields the quantitative estimate of the robustness.
Stability Behavior of Single-Phase Natural Circulation Loop
Authors: Moussavian Seyed Khalil , Misale Mario , D’Auria Francesco , Salehi Mahmoud
Published: May 2008

The circulating fluid in natural circulation loops would absorb heat from the hot zone (source) and will transport it to the cold zone (sink) without using of any mechanical pumps or other devices. The fluid density differences in hot and cold zones would lead buoyancy force which is introduced as the body force for the loop. By introducing the one-dimensional conservation equations; mass, momentum and energy in the loop and applying the perturbation method, or linear stability theory, would help us to study the stability of the rectangular natural circulation loop. The conservation equations in transient form were solved using the finite difference method. The results obtained from the linear and nonlinear stability studies would be compared with the experimental data of DITEC loop (LOOP#1) obtained at the University of Genova and with other suitable data in the literature.
Characterization of the Thermo-Oxidative Stability of Filled Thermoplastic Polyetherimide
Authors: Harinath V. A. , Lou Jianzhong , Sankar Jag , Uitenham Leonard
Published: May 2008

Selected fillers were incorporated to prepare polytherimide composite. The influence of fillers on the thermo-oxidative stability of the composite was studied by thermogravimetric analysis. The results showed that at optical filler loading and characteristics, the polymer composite became superior in its thermo-oxidative stability that is very promising in widening the window of service temperature of polyimides for extremely high temperature conditions where most polymeric composites fail. The findings should prove useful in developing high-temperature polymer composites for aerospace and electronics applications.
Mathematical Expression for the Prediction of Penetration in Butt Joints for Duplex Stainless Steel SAF-2205
Authors: Payares Mari´a Carolina , Almenara Minerva Dorta
Published: May 2008

In order to understand the mechanism of weld bead formation, a relationship between arc welding parameters and weld bead geometry must be established. This relationship is also necessary to forecast penetration variables allowing to optimize welding parameters for particular applications. Specifically in duplex stainles steel SAF-2205 welding, the influence of arc current, arc voltage and welding speed on the penetration have been empirically studied. In this research, using a multiple linear regression method, the statistical analyses produced twelve (12) potential function dependent of these welding parameters that determines the weld bead geometry in butt joints of DSS SAF 2205 using GAs Metal Arc Welding process. the mathematical model gave as a result, a very approximate contour of the weld bead geometry between the established ranges of welding parameters used. Also, the influence of these variables on the weld panetration is studied, providing with new evidence in stainless steel welding.
A Techno-Economic Analysis for MCFC Cogeneration System
Authors: Leal Elisaˆngela Martins
Published: May 2008

In this paper, a methodology for the study of a fuel cell cogeneration system and applied to a university campus is developed. The cogeneration system consists of a molten carbonate fuel cell associated to an absorption refrigeration system. The electrical and cold-water demands of the campus are about 1,000 kW and 1,840 kW (at 7°C), respectively. The energy, exergy and economic analyses are presented. This system uses natural gas as the fuel and operates on electric party. In conclusion, the fuel cell cogeneration system may have an excellent opportunity to strengthen the decentralized energy production in the Brazilian tertiary sector.