bluuebunny/crossref_metadata_2025 huggingface dataset:
Coordinate Control of Energy-Saving Programmable Valves
Authors: Liu Song , Yao Bin
Published: May 2008

The energy-saving programmable valve, a unique combination of five independent cartridge valves, not only decouples the control of meter-in and meter-out flows but also provides the ability of precisely controlling cross-port flows for energy-saving purpose. Our previous works have already shown that the tremendous control flexibility gained by the proposed hardware re-configuration enables one not only to achieve precision control of the cylinder motion but also to decrease the energy usage significantly through actively utilizing the potential and kinetic energy of the load in accomplishing certain tasks such as smooth stopping. However, the control of such an essentially multi-input valve system to achieve the above objectives is far from trivial. In our previous works, a constant off-side pressure was assumed in the controller design for simplicity. This assumption may not be realistic in certain circumstances where the off-side pressure may vary from the assumed constant pressure significantly, especially right after the change of working mode. As a result, though the controller design is simplified, larger tracking error results during the transients. This paper presents an improved way to coordinately control the five independent valves by incorporating the off-side pressure dynamics into the controller design. The Adaptive Robust Control technique is applied to guarantee the stability and tracking performance in the presence of large system parameter variations and disturbances. Simulation and experimental results are shown to verify the much improved control performance of the presented coordinate control strategy.
Genetic Algorithm for the Reconstruction of Bragg Grating Sensor Strain Distribution
Authors: Gill Apninder , Peters Kara , Studer Michel
Published: May 2008

Optical fiber Bragg gratings are unique among embedded strain sensors due to their potential to measure strain distributions with a spatial resolution of a few nanometers over gage lengths of a few centimeters. This article presents a genetic algorithm for the interrogation of optical fiber Bragg grating strain sensors. The method calculates the period distribution along the Bragg grating which can then be directly related to the axial strain distribution. The period distribution is determined from the output intensity spectrum of the grating via a T-matrix approach. The genetic algorithm inversion method presented requires only intensity information and reconstructs non-linear and discontinuous distributions well, including regions with significant gradients. The method is demonstrated through example reconstructions of Bragg grating sensor simulated data. The development of this algorithm will permit the use of Bragg grating sensors for damage identification in regions close to localized damages where strong strain non-linearities occur.
Evaluation of Turbulence Closure Schemes for Stratified Two Phase Flow
Authors: Banerjee R. , Isaac K. M.
Published: May 2008

Three turbulence closure schemes: standard k-ε, RNG k-ε and RSM models have been studied and evaluated for stratified two-phase flows. The flow was modeled using the VOF multiphase model. Four case studies were used to evaluate the turbulence schemes. The first three consisted of a straight channel and have been modeled as two-dimensional problems. The fourth is a three-dimensional meandering channel flow. The results have been compared with available experimental data. All the cases were studied using the commercial CFD package FLUENT.
Development of Plate-Type Heat Exchanger for Exhaust Gas Heat Recovery System
Authors: Park Hyunjae , Bowman Anthony , Stansfield Tod , Huibregtse Brian
Published: May 2008

In this paper, an exhaust gas heat recuperation unit for use with a boiler is developed to improve the overall thermal efficiency of integral system. The heat recuperation unit includes a plate-type heat exchanger for exhaust gas heat recovery for exchanging heat between an exhaust gas and combustion air. A proto-type heat exchanger is designed and manufactured with a series of exhaust gas plates stacked alternatively with, and parallel to, a series of air plates. Each of the exhaust gas plates and air plates contain ridges to form a substantially sinusoidal path for directing the respective gas therealong. The combustion air flown in a countercurrent to the exhaust gas to facilitate maximum heat transfer. The heat exchanger is connected to exhaust gas inlet and outlet conduits and combustion air inlet and outlet conduits. Proper number of plates for the heat exchanger is selected to obtain laminar flow through plate flow channels, producing a low gas pressure drop in each channel. Using the proto-type heat exchanger, experimental work was primarily performed to measure temperature and pressure changes of exhaust gas and combustion air at various boiler firing conditions. These test results are compared with those obtained from numerical (CFD) and analytical works. The approximate analytical model developed in this work is used to investigate the effects of exchanger design parameters on the system performance, and eventually to develop the exchanger design curves for the optimal selection of exchanger design values.
Thermodynamics of Continuous Systems
Authors: Geskin E. S.
Published: May 2008

The formalism of the classical thermodynamics, for example Gibbs equations, is routinely and successfully applied to the highly non-equilibrium processes in dynamic systems. Such applications are based on the local equilibrium hypothesis. The presented paper discusses the conditions of the application of this hypothesis. It is shown that the local equilibrium hypothesis is applicable with no limitations to continuous systems. This application is validated by the solution of the Boltzmann equation. This solution was obtained by Enskog, Chapman and Bogolubov. From the Boltzmann equation follows that regardless of the initial state of the system the duration of its approach to the local equilibrium conditions by far less than the time scale of the evolution of the macro properties of the continuous media. This result shows that the local equilibrium is the intrinsic property of this media. Thus it is possible to apply the formalism of the non-equilibrium thermodynamics (the generalized variables, forces and fluxes) to description of the continuous system with no limitations. The derivation of the Carnot theorem is presented to show the effectiveness of such an application.
A New Thermoeconomic Method for the Location of Causes of Malfunctions in Energy Systems
Authors: Toffolo Andrea , Lazzaretto Andrea
Published: May 2008

Diagnosis procedures primarily aim at locating the control volumes where anomalies occurred. This is not a simple task, since the effects of anomalies generally propagate through the whole system and affect the behavior of several components. Some components may therefore present a reduced efficiency, although they are not sources of operation anomalies, due to non flat efficiency curves. These induced effects are a big obstacle in the use of thermoeconomic techniques for the search of the origin of the anomalies. On the other hand, the real cause of the alteration of component behavior is the modification of its characteristic curve, due to degradation or failures. According to this concept, a new approach, based on an indicator measuring the alteration of the characteristic curve of the component affected by the operation anomaly, is proposed and applied to a test case power plant.
Biomechanical Analysis of Side Release and Top Release Seat Belt Buckles
Authors: Sances Anthony , Kumaresan Srirangam , Clarke Richard
Published: May 2008

Various articles suggest that the maximum release force for buckle according to Federal Motor Vehicle Safety Standards (FMVSS) 109 of 133 N is beyond the capability of a large percentage of our population [1, 2]. Inversion studies with a large male in a three-point production belt showed he could not open a side release buckle [3]. Numerous articles and patents reference the potential for entrapment of inverted occupants unable to release the seat belt buckle [4–11]. Various articles and patents discuss the problems associated with entrapment of individuals in fires, water or emergency situations or where the occupant is deprived of oxygen due to positional asphyxia [12]. While the use of seat belts has increased markedly over the years [13], investigations indicate that rollover accidents showed fatally injured occupants in their seats which were entrapped in their vehicle. The forces to release the buckles under full load of the inverted occupants were beyond the physical capacities of the occupants involved. Canadian motor vehicle safety standard 209 (CMVSS 209) requires that a buckle must release with a force of 133 N to the button with a restraining loop force of 666 N. About 80 % of driver’s could not release a buckle that requires 133 N of force on the button [1]. Females could exert about 80 N with their fingers when opening child restraint buckles [14]. Females were generally found to have about half the physical capacity to open buckles compared to males. The maximum buckle release force of 133 N is not found in literature. Dreyfuss in his book indicates various forces for females and males [15]. European standards require that latch plate be ejected, therefore side release buckles are not allowed.
Teleoperated and Automatic Nanomanipulation Systems Using Atomic Force Microscope Probes
Authors: Sitti Metin
Published: May 2008

Nanomanipulation as a new emerging area enable to change, interact and control the nanoscale phenomenon precisely. In this paper, teleoperated and automatic control strategies for Atomic Force Microscope (AFM) probe based nanomanipulation applications are introduced. Teleoperated touching to silicon surfaces at the nanoscale is realized using a scaled bilateral force-reflecting servo type teleoperation control with a custom-made 1 d.o.f. haptic device and AFM system. 1-D nanoforce sensing on the operator’s finger is achieved during vertical or horizontal motion of the AFM probe tip on surfaces. Then, automatic constant height and force control strategies are introduced for pushing nanoparticles and indenting soft surfaces. 14nm radius gold nanoparticles are successfully positioned with few nanometers resolution, and wax surface is indented with a conical AFM tip. Finally, major nanoscale control challenges are reported.
Numerical Simulation of On-Chip Injection Process With Spatial Gradients of Electrical Conductivity
Authors: Ren Liqing , Li Dongqing
Published: May 2008

The systematic design and precise control of the microfluidic dispenser (crossing microchannels etched into a plastic of glass plate) is key to the performance of many lab-on-a-chip devices. The fundamental understanding of the complicated electrokinetic phenomena in microfluidic dispensers therefore is necessary. In the literature, a few theoretical models studying the transport phenomena in similar crossing microchannels didn’t consider the spatial gradients of conductivity due to its complexity. A new theoretical model was developed in this paper to simulate the transport phenomena in a microfluidic dispenser with the consideration of a large range of spatial gradient of electric conductivity. This developed model was used to simulate the potential field, flow field, and concentration field of the injection processes where the conductivity of the sample-carrying buffer differs significantly from that of the driving buffer. The transport phenomena are found to be very sensitive to the conductivity difference between the sample-carrying buffer and the driving buffer. The developed model can be employed to find the optimal voltages for controlling the dispensed sample size and to provide guidance for designing such a microfluidic dispenser in lab-on-a-chip devices.
Characterizing Gaseous Flow in Submicron Chromatography Columns
Authors: Wong C. Channy
Published: May 2008

Enormous interest exists to develop the next generation of an integrated microsystem for chemical and biological analysis (μChemLab™) and to further reduce the volume of the system. One approach is to scale down the size of critical components and to explore any pumping mechanism that can minimize the power requirement. Since the majority of the pumping requirement is to overcome the wall resistance in the gas chromatography (GC) column, our attention is to study the gas flow in this GC column. As the column dimension decreases, the gaseous flow will go from a continuum regime into a non-continuum regime; i.e., slip, transition, and free molecular regimes. Thus it is very important to well characterize the gaseous flow in submicron columns and to understand its flow behavior. Specifically, in this study, our focus is to investigate the effects of viscosity, rarefaction, and compressibility as the column dimension decreases. Both theoretical predictions and experimental results will be presented.
Analytical Approaches to Address Homeland Security Issues
Authors: Holter Gregory M. , Young Jonathan
Published: May 2008

Homeland security concerns arising since September 11, 2001, have captured national attention and sparked a number of responses at all levels of government. As events have unfolded and the nature of the situation has become better understood within the US, the need for effective planning and response has resulted in the identification of significant analytical challenges. These challenges relate to a number of different needs, including the following: • estimating the probability and the potential impact of various threats, • identifying the need for and effectiveness of specific counter-measures, and • assessing the combined results of interacting activities and events. Analytical approaches traditionally used for safety engineering and risk analysis, coupled with analytical approaches borrowed from other systems analysis disciplines, can be usefully adapted to help meet these challenges. This paper identifies and discusses several illustrative examples of the analytical challenges currently being faced with respect to homeland security. Linkages are then examined between these specific challenges and traditional analytical approaches from a variety of disciplines, including safety engineering and risk analysis. Since effective cooperation among responsible agencies and organizations has been identified as an issue of concern and is essential to achieve an effective homeland security strategy and response capability, issues relating to multiple interacting activities are specifically highlighted.
Investigation of the Cooling Jets Used in the Blown Film Manufacturing Process
Authors: Gao Nan , Li Leonard S. Z. , Ewing Dan
Published: May 2008

The flow field of a dual-lip air ring used in the blow film manufacturing process was studied experimentally. The static pressure distributions on a model bubble was measured using manometers while the fluctuating pressure was measured using microphones. The flow field caused by the air ring was measured using single and cross-wire probes. It was found that the pressure distribution below the forming cone was determined by the lower jet velocity. The flow and the pressure distribution on the bubble above the forming cone was determined by the ratio of the upper and the lower jet velocities where two jets interact and by the upper jet after the upper jet attached to the bubble.
Characterization of the Time-Dependent Rheological Behavior of Fluids for Electronics Packaging
Authors: Chen X. B. , Zhang W. J. , Schoenau G. , Surgenor B. W.
Published: May 2008

To effectively control the dispensing process by which fluids are delivered onto substrates in electronics packaging, one of the key issues is to understand and characterize the flow behavior of the fluids being dispensed. However, this task has proven to be a demanding one as the fluids used for electronics packaging usually exhibit the time-dependent rheological behavior, which has not been well documented in the literature. In this paper, the characterization of time-dependent rheological behavior of fluids is studied. In particular, a model using the structural theory is proposed and applied to the characterization of the decay and recovery of fluid behavior, which are typically encountered in a dispensing process. Experiments are conducted to validate the proposed model.
A Study on a Long Range Nano-Precision Positioning System
Authors: Chen Jau-Liang , Chang Hsu-Yang , Wu Chiang-Sung
Published: May 2008

In this paper a nano-precision positioning system with 1mm travel length, which is composed by a voice coil motor (VCM), flexural stage, an inverted lever, and laser interferometer as positioning sensor, was established. The flexural stage was designed by using genetic algorithm. Because the output force of the VCM is too small, an inverted lever was used to enlarge the output force. A robust controller was designed by using N-times feed-forward control role together with PID control. Three different experiments were conducted: (1) fixed point test; (2) stepping test; and (3) ramp tracking test. From the experiment results, it was found that the bias was equal 0.013 nm with standard deviation (1σ) equals to 3.024 nm, for fixed-point control. While for stepping test, the bias was within 0.2 nm and 1σ value less than 4.5 nm with settling time within 0.17 to 0.71 second. For ramp tracking test, the bias was less than 0.02 nm and 1σ value less than 3.5 nm. Finally, it was found that the smallest step for this positioning system is 10 nm, and can travel 1 mm with bias equal to 0.251 nm, 1σ equals to 3.698 nm.
3D Electrothermal Simulation of Heterostructure Thin Film Micro-Coolers
Authors: Zhang Yan , Vashaee Daryoosh , Christofferson James , Shakouri Ali , Zeng Gehong , LaBounty Chris , Piprek J. , Croke Ed
Published: May 2008

A 3D electrothermal model is used to simulate and optimize Si/SiGe superlattice heterostructure micro-coolers. The model considers thermoelectric/thermionic cooling, heat conduction and Joule heating. It also includes non-ideal effects, such as contact resistance between metal and semiconductor, substrate/heatsink thermal resistance, the side contact resistance. The simulated results match very well with the experimental cooling curves for various device sizes ranging from 60×60μm2 up to 150×150μm2. It is found that the key factor limiting maximum cooling is metal semiconductor contact resistance. The maximum cooling could be doubled if we remove the metal-semiconductor contact resistance. The thin film Si/SiGe superlattice micro-coolers can provide cooling power density over 500 W/cm2 as compared with a few W/cm2 of bulk Bi2Te3 themoelectric coolers. This micro-cooler experimentally demonstrated a maximum cooling of 4.5°C at room temperature and 7°C of cooling at 100°C ambient temperature. It is a promising candidate for microprocessor spot cooling.
A Domain Evolution Model for the Ferroelastic Hysteresis of Piezoceramic Materials
Authors: Narayanan V. , Lu X. , Hanagud S.
Published: May 2008

In this paper, we model the thermo-ferroelastic hysteresis phenomena under large mechanical loading by using internal state variables that are associated with a statistical description of microstructural domain characterization. This work is to extend our previous work [1, 2] to include the ferroelastic effects. Under large mechanical loading, the total bulk strain includes the mechanical strain and the bulk piezoelectric strain. The piezoelectric strain is the accompanying strain with the evolution of the domain network, which is described by a domain orientation distribution function. In ferroelastic hysteresis, the domain evolution, which is mainly contributed by 90° domain switching, is delineated by the evolution of the associated domain distribution function and further simplified by the evolution of the associated internal state variables that are the parameters of the domain distribution function. For the mechanical field, the mechanical strain is divided into two parts- the elastic strain and the inelastic strain. The inelastic strain is the corresponding internal variable to describe the inelastic behavior under large mechanical loading. Therefore, the remnant strain contains two parts: the remnant piezoelectric strain and remnant inelastic strain. The dissipation and the associated temperature increase per unit cycle in the ferroelastic hysteresis are studied.
Numerical Simulation on Transient Electrophoretic Motion of a Circular Particle in a T-Shaped Slit Microchannel
Authors: Ye Chunzhen , Li Dongqing
Published: May 2008

This paper considers the electrophoretic motion of a circular particle in a T-shaped slit microchannel, where the size of the channel is close to that of the particle. During the process, the electric field (i.e., the gradient of the electric potential) changes with the particle motion, which in return influences the flow field and the particle motion. Therefore, the electric field, the flow field and the particle motion are coupled together, and this is an unsteady process. The objective is to obtain a fundamental understanding of the characteristics of the particle motion in the complicated T-shaped junction region. Such influences on the electric field and the particle motion are investigated as the applied electric potentials, the geometry of the channel and the size of the particle. In the theoretical analysis, the liquid phase is divided into the inner region and the outer region. The inner region consists of the electrical double layers and the outer region consists of the remainder of the liquid. Under the assumption of thin electrical double layer, a mathematical model governing the inner region, the outer region and the particle motion is developed. A direct numerical simulation method using the finite element method is employed. In this method, a continuous hydrodynamic model is adopted. By this model, both the liquid phase in the outer region and the particle phase are governed by the same momentum equations. ALE method is used to track the surface of the particle at each time step. The numerical results show that the electric field is influenced by the applied electric potentials, the geometry of the channel and the particle suspension, and that the particle motion is mainly dominated by the local electric field. It is also found that the magnitude of the particle motion is dependent on its own size in the same channel.
Static Deflection Behavior of a Piezoelectric Forceps
Authors: Susanto Ken , Yang Bingen
Published: May 2008

A model is described for predicting quasi-static behavior of a piezoelectric forceps actuator (PFA), which consists of two slightly curved composite beams with bonded piezoelectric layers. The PFA is an innovative medical device that is potentially useful for minimum invasive surgery. The PFA model is compared to the deflection measurements made by a curvature sensor in experiments. This model, with a slight modification, can also be applied to other types of piezoelectric actuators with curved structural components.
Evaluation of the Economic, Energy, and Environmental Characteristics of a Combined Heat, Power, and Hydrogen System
Authors: Ellis Michael W.
Published: May 2008

A combined heat, power, and hydrogen (HPH) system consists of a hydrogen production and distribution system that provides hydrogen fuel for vehicles and for fuel cell heat and power systems that meet the energy needs of nearby buildings. This paper describes the analysis of a proposed HPH system that serves a laboratory and the vehicle fleet of an adjacent industrial facility. In the proposed system, hydrogen from a natural gas fuel processor is compressed, stored, and used to fuel fleet vehicles. The hydrogen is also supplied to a building fuel cell system that provides both electricity and hot water for space heating and water heating during peak electrical demand periods. The analysis is based on historical data for vehicle mileage and electricity use, estimates of hot water use for the laboratory, and local utility rates. This data is used in conjunction with a model of system performance and an operating strategy based on the net marginal value of hydrogen for each resource (heat, power, and hydrogen vehicle refueling) to determine the economic and environmental impact of the HPH system. Results show that if the primary goal is vehicle refueling, adding a stationary fuel cell system to create a combined HPH system makes small fleet sizes economical and increases the economic value of the refueling station at all fleet sizes. If the primary goal is to provide building heat and power, adding a vehicle refueling capability increases the economic value provided the fleet size is relatively large. The results also confirm that for the current utility rates at the proposed site, the stationary system should be operated in a peak shaving mode with relatively few operating hours. Finally, the results indicate that application of the HPH system leads to reductions in primary energy use and reductions in emissions of carbon dioxide and oxides of nitrogen in both stationary and vehicular applications. Sulfur dioxide emissions are reduced for stationary applications but increased for vehicular applications. Overall, the HPH system represents a promising approach to facilitate the introduction of both fuel cells and a hydrogen infrastructure.
Recursive Kinematics and Inverse Dynamics for Parallel Manipulators
Authors: Khan Waseem A. , Krovi Venkat N. , Saha Subir K. , Angeles Jorge
Published: May 2008

We examine here the modular and recursive formulation of the inverse dynamics of parallel architecture mainpulators. The concept of the decoupled natural orthogonal complement (DeNOC) is combined with the spatial parallelism of the robots of interest to develop an inverse dynamics algorithm which is both recursive and modular.
Mechatronics Laboratory at UMES: A Platform to Promote Synergy in Education and Research Across Disciplinary Boundaries
Authors: Nagchaudhuri Abhijit , Saishyam Shinivas , Wood John , Stockus Anthony
Published: May 2008

Mechatronics is the synergistic integration of mechanics, instrumentation and control, software engineering and information technology. As such it integrates well with not only the modern evolution of mechanical engineering curricula but has wide and growing manifestation in the new generation of industrial products as well as children’s toys. The present set-up of the laboratory consists of an industrial SCARA (Selective Compliance Articulated Robot Arm) robot equipped with machine vision capability for guidance, inspection and recognition associated with robotic manipulation of parts. An open loop stable vibration control platform, an open loop unstable inverted pendulum and a dual water tank system interfaced with appropriate sensors and actuators provide capabilities for learning both analog and digital control of systems belonging to the solid mechanics and fluid mechanics fields. Modern software tools that include graphical programming capability using Simulink and compilation via Real time Windows Target, Real time Workshop (all from Mathworks) and Visual C++ (Microsoft) allow for developing and executing variety of control algorithms on these systems. Capabilities for remote operation of these systems over the internet have also been implemented. The laboratory facilities provide education and research capability at the interfaces of traditional disciplinary boundaries. The laboratory is also equipped with LEGO MINDSTORM and LEGO DACTA products as well as the MIT Handyboard for exploration of mechatronics and robotics activities for prospective engineers and K-12 students.
Active Stability of the Glenohumeral Joint Decreases in the Apprehension Position
Authors: Labriola Joanne E. , Jolly John T. , McMahon Patrick J. , Debski Richard E.
Published: May 2008

Muscle forces that compress the glenohumeral joint during midranges of motion may lead to increased translational forces in endrange positions, such as the apprehension position, where symptoms of anterior instability occur. The objective of this study was to quantify active stability provided by eight shoulder muscles in mid-range and end-range positions through muscle force vector analysis. Lines of action were derived from a standard geometric model and muscle force magnitudes were estimated with electromyography-based techniques. Resultant muscle force vectors were calculated by summing individual muscle force vectors. Compared to mid-range positions, lines of action of resultant force vectors were more anteriorly-directed in end-range positions. The deviation angle in the anterior direction was greatest (35°) and, consequently, stability was lowest in the apprehension position. Based on a sensitivity analysis, lines of action of resultant force vectors vary up to 6° within the population. In the apprehension position, muscle forces may promote anterior humeral head translation, predisposing the glenohumeral joint to anterior instability when other joint stabilizers are not functioning normally.
Feed Forward Multiple-Input Active Noise Control Systems
Authors: Ohadi A. R. , Mehdigholi H. , Esmailzadeh E.
Published: May 2008

The use of adaptive feedforward controllers has proven to be a very successful strategy for controlling noise and vibration in a variety of applications. One reason is that the feedforward controller is an open loop controller, which can be designed to cancel the undesired noise in one position with any accuracy. However, the feedforward controller requires an input signal, called a reference signal, correlated to the noise source. As a consequence, a single reference controller can only reduce noise radiated from a single noise source. In many applications, there is a need to attenuate noise produced by several noise sources. In this paper, three different structures, single, modulating and individual controllers, for multiple input feedforward controllers have been studied and some design aspects are investigated.
Determination of In-Vivo Elastic Properties of Soft Tissue Using Magnetic Resonance Elastography
Authors: Kennedy Francis E. , Doyley Marvin M. , Van Houten Elijah E. W. , Weaver John B. , Paulsen Keith D.
Published: May 2008

In-vivo measurement of the elastic properties of soft tissue have been made using a variety of direct techniques, such as indentation probes and rotary shear actuators, but they are unable to access much of the soft tissue of interest. Indirect ultrasonic methods for imaging elastic properties of soft tissue were first introduced about 15 years ago, see Ophir (1991). Although the results of ultrasonic elastography studies have been quite promising, they may not be suited for applications requiring accurate quantification of soft tissue properties. An alternative to ultrasound, magnetic resonance imaging, has the advantage of enabling precise measurement of all three components of tissue displacement. The reconstruction of elastic properties from the imaged displacement field is called magnetic resonance elastography (MRE), and is the subject of this paper.
An Alternative Method for Determining the Neutral Zone of Spinal Motion Segment Units
Authors: Sarver Joseph J. , Elliott Dawn M.
Published: May 2008

In-vitro mechanical testing of spinal motion segments has the potential to provide insight into mechanisms of intervertebral disc degeneration as well as a means for evaluating treatments. We describe a novel tri-linear method for quantifying the non-linear load-displacement behavior which is robust across different spinal levels, and quantifies stiffness at low-loads, which has not been included by previous threshold based methods. Mechanical data from in-vitro compression/tension testing of rodent motion segments is used to compare our tri-linear method with a threshold based method, and demonstrates that our method is insensitive to spinal level as well as provides constitutive information for low-load behavior.
Hypoxia-Induced Changes in the Mechanical Properties of the Mouse Pulmonary Artery
Authors: Kobs Ryan W. , Muvarak Nidal E. , Chesler Naomi C.
Published: May 2008

Hypobaric hypoxia produces pulmonary hypertension in mice which causes pulmonary vascular remodeling. To study the biomechanics of this process, mice were exposed to hypoxia for 0-(control), 10-, and 15-days. Using a pressurized arteriograph system, mechanical properties of the main pulmonary artery were measured and compared to the biological changes in the vessel wall measured histologically. 10- and 15-day hypoxic vessels were significantly stiffer when compared to 0-day vessels. This stiffness correlated with greater elastin and collagen content in the vessel wall.
Disc Nucleus Cellular Response to Dynamic Pressures at Critical Frequencies: A Pig Model
Authors: Merryman W. David , Loveless Kristen , Kasra Mehran
Published: May 2008

Disc degeneration is a multifactor phenomenon. It has been found that intervertebral disc (IVD) cells respond to such factors as pH, osmotic pressure, genetic factors, and mechanical loading (Guilak, 1999). During daily activities the human intervertebral disc is exposed to oscillatory hydrostatic loads that produce pressures >2MPa in vivo (Nachemson, 1964 and 1979). It is known that dynamic loads with critical frequencies close to that of the in vivo human spine resonant frequency (4–5 Hz) have a destructive effect on disc tissue properties (Pope, 1993). Whether this destructive effect is purely mechanical, due to loading magnification, or biological, affecting cell metabolism, is unknown. Previous work (Merryman, 2002) showed that there was no significant effect upon monolayer IVD cells loaded at 15Hz, while lower frequencies (1 and 8Hz) altered collagen synthesis compared to control. To address this issue, we developed a mechanically active culture system capable of delivering a wide range of loading frequencies and amplitudes of hydrostatic pressure to cultures of disc cells. Nucleus pulposus cells of pig discs were isolated and suspended in alginate beads. Alginate cultures were divided into 6 groups; five groups were exposed to cyclic pressures of frequencies 1, 3, 5, 8, and 10Hz with the same amplitude of 1MPa, and group 6 was the control group (no loading). Cultures of different groups were loaded for 3 days (30 minutes daily) in a hydraulic chamber filled with culture media. The effect of loading frequency on collagen metabolism among different groups was compared by measuring incorporated [3H]-proline into collagen for medium and total extracts. The results indicated a poor synthesis rate and more degradation near the 5Hz frequency.
Patellar Maltracking: No Longer Just a 2D Problem
Authors: Rebmann Andrea J. , Boden Barry P. , Sheehan Frances T.
Published: May 2008

In order to correctly diagnose and treat pathological knee joint mechanics we must be able to non-invasively quantify the 3D in vivo kinematics of this joint. Unfortunately, the majority of clinical diagnoses, for this joint, are based upon static 2D imaging. This is due to the fact that currently there is a scarcity of noninvasive measurement techniques that acquire 3D in vivo data dynamically. Thus, in vivo patellofemoral (PF) kinematic measurements typically compress a 3D time-dependent joint attitude to a static 2D representation. The purpose of this study was to investigate if patellar maltracking is limited to two dimensions, as assumed clinically, or if it is a complete six-degree of freedom problem. To do this, we quantified the 3D patellofemoral and tibiofemoral (TF) kinematics in both healthy individuals and those with suspected patellofemoral maltracking using fast-phase contrast magnetic resonance imaging, a technique developed in our previous work. Our data suggest that variations in kinematics were not confined to the standard axial plane measures (e.g. patellar tilt, patellar subluxation), but variations are exhibited in all six degrees of freedom. Therefore, future clinical diagnoses and interventions along with future research will be most effective if the measures used are broadened to include all six-degrees of freedom.
Design of a Passive Leg Orthosis for Human Gait Correction
Authors: Fattah Abbas , Agrawal Sunil K. , Fitzgibbons John
Published: May 2008

This paper presents the design of a passive leg orthosis for gait correction of human subjects. During normal walk, the joints of a human leg, namely, the hip, knee, and ankle satisfy certain functional relationships. During post stroke and other neural disorders, the gait deviates substantially from this normal gait. Hence, there is a need to design rehabilitation machines for gait training. Our design targets the sagittal plane motion of the leg, i.e., it considers the hip and knee flexion and extension motions. The paper describes the details of the cam design and results of a demonstration prototype.
Design and Development of Passive and Active Force Feedback Systems Using Magnetorheological Fluids
Authors: Rov Anthony M. , Neelakantan Vijay A. , Washington Gregory N.
Published: May 2008

Recently, haptic devices have been in use to increase the effectiveness of human-machine interfaces. On the forefront of this technology are passive, force-feedback controllers that resist or even limit motion. This motion control can be the result of a manipulator coming into contact with an object in either the virtual or physical world. Thus, an end-user can get both visual and tactile feedback on system operations. Furthermore, an active force-feedback controller can not only resist motion, but also create a reactive force that the user can sense. This active force-feedback is essential for delicate operations, such as telerobotic surgery, where a doctor needs to feel the difference between a spongy muscle and a hard bone. However, such haptic devices need to be simple and fast, so that they will not interfere with the existing system dynamics. A promising solution employs magnetorheological (MR) fluids in an active force-feedback controller. MR fluids feature a rheological change that is brought about when micron-sized particles within the fluid are exposed to a magnetic field. This change happens within milliseconds and can be used to create resistance quickly and easily. MR fluids can also be combined in a motor driven clutch mechanism to provide active resistance to the user with a force proportional to what the manipulator is experiencing. This paper will show the model development, design, construction, and control implementation of passive and active force-feedback devices.
Stress-Induced Mechanotransduction: Some Preliminaries
Authors: Kaazempur-Mofrad Mohammad R. , Mack Peter J. , Karcher Helene , Golji Javad , Kamm Roger G.
Published: May 2008

Mechanical stimuli affect nearly every aspect of cellular function, yet the underlying mechanisms of transduction of force into biochemical signals are not clearly understood. One hypothesis is that forces transmitted via individual proteins, either at the site of cell adhesion to its surroundings or within the stress-bearing members of the cytoskeleton, cause conformational changes that change their binding affinity to other intracellular molecules. This altered equilibrium state can subsequently initiate biochemical signaling cascades of produce immediate structural changes. This paper addresses the distribution of forces within the cell resulting from specific mechanical stimuli, computed using a 3-D multi compartment, continuum, viscoelastic finite element model, and uses these to estimate the forces transmitted by individual proteins and protein complexes. These levels of force are compared to those known to produce conformational changes in cytoskeletal proteins, as speculated from magnetocytometry observations and computed by molecular dynamics.
The Compliant A-Arm Suspension
Authors: Allred Timothy , Howell Larry L. , Magleby Spencer P. , Todd Robert H.
Published: May 2008

The use compliant mechanisms in a suspension system has been demonstrated with leaf spring mechanisms. In this research a novel compliant configuration called the Compliant A-Arm (C-A-Arm) suspension is selected for in-depth study. Closed-from equations are derived for linear small-deflection stiffness equations. Large deflections are analyzed using finite element analysis. A pseudo-rigid-body model is developed to approximate mechanism deflections and stiffness for large deflections. The results suggest that the C-A-Arm configuration may be a viable suspension alternative for future commercial application. In addition, this configuration offers a number of performance variables that could be the basis for an active control system. This paper represents a necessary first step in modeling this new configuration.
Analysis of Finger PIP Implants
Authors: Stone James J.-S. , Yu Hongrong , Linscheid Ronald L. , Cooney William P. , An Kai-Nan
Published: May 2008

Total joint arthroplasty (TJA) is implemented primarily for the relief of pain, and secondarily for achieving better function by increasing the joint’s strength and motion. In order to keep health costs low, it is desirable that the TJA achieves and maintains a long-term and secure fixation of the implanted components. Unfortunately, clinical follow-up shows that the prosthetic finger implant components have long-term complications including bone resorption, wear, loosening, and failure of the implant components. Although the mechanism of complications is not fully understood, it is well known that the wear and failure of prostheses are highly related to the mechanical forces or stresses of implant components. It is therefore desirable that reliable 3-D computational finite element analysis (FEA) models can be developed and used for the stress analysis of implants. In this study, the finger proximal interphalangeal (PIP) prosthetic components were analyzed using a nonlinear finite element method. Implant components under different joint flexion angles as well as different forces were studied. The stress distribution on the contact surface of the implant component was obtained. The developed FEA models can be used to examine the contact situations (contact stress, contact region, and stress distribution), which are critical to the wear and potential failure of the implant components. Based on FEA results, the design of the current finger PIP implants can be improved for optimum performance and a long-term fixation.
Fabrication and Design of Multifunctional Energetic Structures Using Gradient Architectures
Authors: Bruck Hugh A. , Gallant Frederick M. , Gowrisankaran Swami
Published: May 2008

The use of gradient architectures for multifunctional energetic structures is investigated using Twin Screw Extrusion (TSE) processing technology that has been configured for fabricating graded materials. It is demonstrated that polymer composites with both radial and axial gradients can be produced using this technology. A concurrent design effort is also undertaken to determine the optimal gradient architecture for a multifunctional energetic structure using the properties of the TSE processed energetic materials in structural and ballistic performance analyses. As an example case, a cylindrical propellant grain with a single perforation and a radial gradient is analyzed. It is determined that the maximum thrust can be increased by 40% and the total impulse can be increased by 73% using a gradient architecture that varies linearly from a normalized radius of 0.82 to 1.
Experimental Measurement of Boundary Layer Flow With Suction Into a Honeycomb Panel
Authors: Keffler John , Ortega Alfonso , Bouldin Bruce
Published: May 2008

Experiments were conducted in a low speed laboratory wind tunnel in order to characterize boundary layer flow that is subjected to suction as it flows over a honeycomb section of the wall. The problem arises in the design of filtered inlets to engines in aerodynamic applications. The honeycomb was baselined in a traditional orientation normal to the flow direction. The overall total and static pressure drops and the downstream velocity field were measured using pressure probes and wall static taps upstream and downstream of the honeycomb. The wind tunnel was then re-configured so that the main wind tunnel flow resembled an infinite free-stream approaching the honeycomb inlet at 90° from the normal. It was determined that the radius of curvature of the flow stream entering the honeycomb is small in the upstream region of the honeycomb, and increases monotonically in the flow direction. This inviscid effect causes a drop in the static pressure in the upstream region of the honeycomb followed by a gradual recovery of the static pressure in the flow direction. The local mass flow ingested through the honeycomb consequently is low in the forward section and increases monotonically in the flow direction. In addition to this inviscid mechanism, we observe non-uniformity of the pressure loss coefficient over the honeycomb panel, which is attributed to viscous mechanisms. The total pressure loss coefficient, K, is found to vary from a value of roughly 1.2, for grazing angle of 5° in the forward section of the honeycomb, to 0.9, for a flow approaching from the direction normal to the inlet. It is hypothesized that the increased total pressure loss for the grazing flow is due to stagnation and flow separation at the inlet of each honeycomb passage.
Optimum Range Thermal Design With Computational Fluid Dynamics
Authors: Tekriwal Prabhat
Published: May 2008

A typical cooking range design requires that UL temperature requirements be met on outside surfaces for consumer safety. Another important consumer preference is that the range oven cavity be large in capacity so that it provides more cooking flexibility to consumers. These two requirements are in conflict with each other from design standpoint. CFD (Computational Fluid Dynamics) has proven to be a good design tool in balancing these opposing requirements and providing a optimum design without having to experiment with several design options and prototyping. The width of the air-wash that is used to cool the cooking range door through natural convection has been optimized with the aid of computational fluid dynamics. Increasing the air-wash width helps reduce the door surface temperature up to certain point, beyond which no gains in temperature reduction are realized.
Dynamic Stress-Strain Response and Failure Behavior of PMMA
Authors: Moy Paul , Weerasooriya Tusit , Chen Wayne , Hsieh Alex
Published: May 2008

Strain rate response of PMMA was investigated under uniaxial compression at different rates of strain ranging from 0.0001/sec to about 4300/sec. High rate experiments (greater than 1/sec rates) were conducted using a split-Hopkinson Pressure bar (SHPB) with pulse-shaping to impose the compressive loading of the specimen at constant strain rate under dynamic stress equilibrium. At strain rates 1/s and below, intrinsic softening occurred after the initial yield and then followed by the strain hardening. However, at 1/s strain rate, material started to soften further due to thermal softening dominating over strain hardening. For higher strain rates (greater than 1/s), PMMA failed before, during or immediately after the yield depending on the rate of loading. For these high rates, strain to failure decreases with the increase in the strain rates whereas failure stress (except at very high rates where failure occurred before yielding) and modulus increase with increasing strain rate.