bluuebunny/crossref_metadata_2025 huggingface dataset:
Restraint System Performance and Injury Potential to Belted Occupants in Automobile Rollover Crashes
Authors: Meyer Steven E. , Forrest Steven , Herbst Brian
Published: April 2008

It has long been recognized within the automotive safety community and by numerous biomechanical research studies that providing effective occupant protection in automotive rollover crashes requires effective occupant restraint. Effective occupant restraint includes, at the most basic level, preventing occupant ejection and providing sufficient control of occupant kinematics through the rollover event to prevent potentially injurious contacts with interior vehicle components. This paper examines both laboratory and real-world accident analysis of restraint performance in rollover-type environments. This includes studies involving static and dynamic testing with human surrogates and anthropometric test devices (ATDs). Additionally, the effects of rollover roof deformation on the restraint systems ability to control or affect occupant kinematics, when those restraint systems are anchored to the dynamically deforming structural components of the vehicle, are examined. Finally, various production and alternative restraint system designs are considered and discussed relative to their ability to control occupant kinematics and their influence on belted occupants' injury potential in the rollover crash mode. This paper will focus on the effect of seat belt looseness, or slack, and its relationship to occupant excursion during a rollover. Literature is referenced establishing that increased occupant excursion produces increased injury potential in rollovers, both by increasing the likelihood of injurious contacts with interior vehicle components as well as an increased risk of full and partial ejection. Four complete vehicle inversion studies (spit tests) are conducted with live surrogate occupants in production vehicle restraint systems. These studies document occupant excursions under a 1G inverted environment with various amounts of seat belt slack in production restraint systems as well as comparison tests using various alternative restraint configurations. Additionally three complete vehicle inverted drop tests are conducted in which the vehicles' roof structures and the upper torso belt anchors (D-ring) are instrumented to document their displacement while producing typical real-world type roof structure damage. The effect of this restraint anchor deformation is then examined relative to the occupant excursions evaluated in the spit tests. Lastly, a complete dolly rollover test conducted on a contemporary production mini van with production restrained anthropometric test devices (ATDs) is examined with a focus on the restraint system's geometry alterations and effectiveness through the multiple roll/roof contact events.
Effect of Inertia on the Stability of Film Casting of Viscoelastic Fluids
Authors: German R. , Khayat R. E.
Published: April 2008

The influence of inertia on the stability of isothermal film casting of viscoelastic fluids is examined using a Phan-Thien and Tanner rheological model. The linear stability analysis for two-dimensional disturbances is carried out. The numerical results indicate that the flow can have single or double critical draw ratio depending on the model parameter. While in the former case the flow is stable below and unstable above a critical draw ratio, in the latter case the flow is stable below the lower and above the upper critical draw ratio and unstable between the two values. The inertia is found to have a stabilizing effect on the flow. It is also found that there is a region of Deborah number, where the inertia has a stronger stabilizing effect on stability of flow than elsewhere.
Assessing Rollover Protection Through the Deformable Occupant Compartment Impact Tester (DOCIT)
Authors: Herbst Brian , Meyer Steven E. , Forrest Stephen , Ward Carley
Published: April 2008

Occupant kinematics during rollover or inverted impacts has been the subject of significant research. Controlled experiments have utilized complete vehicles, partial vehicles and seat/restraints systems attached to various platforms. Previous experiments, which included the element of a deforming roof, have required the destruction of a complete vehicle. The Deformable Occupant Compartment Impact Tester (DOCIT) was developed to incorporate functions similar to previously research devices, but has a roof capable of deforming under impact, which can be reset without the destruction of a vehicle. The DOCIT is designed to simulate an occupant compartment including a roof, seat, restraint system in which an Anthropometric Test Device (ATD) is placed and subjected to a repeatable inverted impact environment. Two test series are reviewed, in which baseline tests that based upon real-world rollover accidents are compared with alternate design systems under the same impact environments.
Heat Transfer in Internal Flows of Non-Linear Fluids: A Review
Authors: Siginer Dennis A. , Letelier Mario F.
Published: April 2008

A survey of the developments in heat transfer studies of non-linear inelastic as well as elastic fluids in tubes is given. Experimental findings concerning heat transfer enhancement characteristics of viscoelastic aqueous polymer solutions are very significant. Specifically, it is reported that heat transfer results for viscoelastic aqueous polymer solutions are drastically higher than those found for water in laminar flow in rectangular ducts. A number of investigators suggested that the high experimental heat transfer values were due to secondary flows resulting from the elasticity of the fluids. In this context recent results concerning the fully developed thermal field in constant pressure gradient driven laminar flow of a class of viscoelastic fluids characterized by single mode, non-affine constitutive equations in straight pipes of arbitrary contour ∂D is reviewed. Heat transfer enhancement due to shear-thinning is identified together with the enhancement due to the inherent elasticity of the fluid. The latter is the result of secondary flows in the cross-section. Increasingly large enhancements are computed with increasing elasticity of the fluid as compared to its Newtonian counterpart. Large enhancements are possible even with dilute fluids. Isotherms for the temperature field are presented and discussed for several non-circular contours such as the ellipse and the equilateral triangle together with heat transfer behavior in terms of the Nusselt number Nu.
Continuous Particle Cross Over in Microfluidic Channels for Continuous Biosensing
Authors: Yang Sung , U¨ndar Akif , Zahn Jeffrey D.
Published: April 2008

A novel concept for continuous biosensing is introduced. Continuous biosensing is achieved by the mechanism named "Particle Cross Over" within microfluidic channels. The functionality of the device is demonstrated by quantifying the binding events of biotin to streptavidin coated beads. The device is designed to have precisely controlled flow structures which allow cytometric beads to pass from one flow region to another without mixing the carrier and sample fluids. The mean and standard deviation of the cytometric bead pixel intensities are 43.52 and 19.39, respectively for 1 μg/ml of biotinylated Fluorescein IsoThioCyanate concentration with a binding time of 0.464 seconds and shows a Gaussian distribution. It is expected that the particle cross over mechanism introduced in this report will be very useful mechanism for applications in continuous biosensing.
New Approach to the Inspection of Cooling Holes in Aero-Engines
Authors: Shetty Devdas , Eppes Tom , Nazaryan Nikolai , Kondo Jun , Campana Claudio
Published: April 2008

The need for improved thermal efficiency of jet engines has led to changes in the design of combustor turbine blades. Modern turbine stage inlet temperatures now exceed the melting point temperatures of turbine blade materials. Super alloys, based on nickel, have been developed for use as blades, guide vanes, afterburners etc. To combat and avert blade failure caused by excessive operating temperatures, film cooling has been incorporated into blade design. In film cooling, cool air is bled from the compressor stage, ducted into internal chambers of the turbine blades, and discharged through small holes in the blade walls. This provides a thin, cool, insulating blanket along the external surface of the turbine blade. Large numbers of shaped holes have allowed designers to maximize the cooling effect. This paper explores a new design for measuring the presence and depth of blind holes in turbine blade. In the paper, we examine the inspection techniques currently in use and present a novel optical technique as an alternative. To precisely control the location of the holes on the turbine blade, an XYZ inspection stage is employed. Using a small collimating tube, a micro-beam illuminates each hole in a pre-programmed fashion. Depending on the level of reflected intensity and when it occurs, the presence of a hole bottom is determined. The optical inspection system consists of a laser, motorized micropositioning stage, collimating tubes, data acquisition software and a customized fixture for manipulating the samples.
Physical Properties of Confined Silicon Structures Using EDIP
Authors: Pascual-Gutie´rrez Jose´ , Murthy Jayathi Y. , Viskanta Raymond
Published: April 2008

Physically confined structures such as thin films and nanowires are becoming increasingly important in the energy and electronics sectors. This has resulted from the ability to tailor nanostructures to yield physical properties that are significantly different from bulk. The main focus of this work is to examine how physical confinement in one and two dimensions affects the phonon wave vector spectrum within the first Brillouin zone of silicon thin films and silicon nanowires. Dispersion curves as well as density of states (DOS) are obtained using the dynamical matrix approach and a harmonic approximation to the three-body environmentally-dependent interatomic potential (EDIP). It is also shown how these changes in the phonon spectrum for both films and wires affect the volumetric specific heat with respect to bulk. The simulations are carried out assuming ideal free-standing boundary conditions. It is shown that confinement effects on the phonon specific heat are only important below 5 mm for both silicon films and wires.
The Effect of Viscous Dissipation on Two-Dimensional Microchannel Heat Transfer
Authors: van Rij Jennifer , Ameel Tim , Harman Todd
Published: April 2008

Microchannel convective heat transfer characteristics in the slip flow regime are numerically evaluated for two-dimensional, steady state, laminar, constant wall heat flux and constant wall temperature flows. The effects of Knudsen number, accommodation coefficients, viscous dissipation, pressure work, second-order slip boundary conditions, axial conduction, and thermally/hydrodynamically developing flow are considered. The effects of these parameters on microchannel convective heat transfer are compared through the Nusselt number. Numerical values for the Nusselt number are obtained using a continuum based three-dimensional, unsteady, compressible computational fluid dynamics algorithm that has been modified with slip boundary conditions. Numerical results are verified using analytic solutions for thermally and hydrodynamically fully developed flows. The resulting analytical and numerical Nusselt numbers are given as a function of Knudsen number, the first- and second-order velocity slip and temperature jump coefficients, the Peclet number, and the Brinkman number. Excellent agreement between numerical and analytical data is demonstrated. Viscous dissipation, pressure work, second-order slip terms, and axial conduction are all shown to have significant effects on Nusselt numbers in the slip flow regime.
Torque-Angle Formulation of Threaded Fastener Tightening
Authors: Nassar Sayed A. , Yang Xianjie
Published: April 2008

In this paper, the evolution equations of the bearing and thread friction coefficients are proposed based on mechanical behavior of the bolted joint assembly. The formulation of the torque-tension relationship during tightening and loosening is experimentally validated. The study shows excellent correlation between the proposed model and the experimental results for the breakaway torque values in both the tightening and loosening directions. Evaluation of the torque-angle control of the tightening process is made, and a modified torque-angle control approach is proposed. The effect of friction coefficients on the error in the clamping force prediction is analyzed.
Metal Line Interconnects Produced by Means of Printable Copper Precursor Solutions
Authors: Tiwari Manish , Megaridis Constantine , Majumder Prodyut , Takoudis Christos , Belot John , Xu Mindi , McAndrew James , Chamcharas Roy
Published: April 2008

Patterned metal films are essential to a wide range of applications, from printed circuits and thin film displays in large area electronics, to electrodes in biomedical implants. Current fabrication techniques are usually photolithographic, and rely on either patterning a blanket metal film or patterning a planar substrate into which the metal is deposited, followed by polishing away excess metal (the "Damascene" process). However, photolithographic techniques are expensive and more suitable for relatively small substrates. Conventional printing techniques such as inkjet, flexographic, offset and screen printing for both printable metal films and emergent organic elements, have lower resolution, but offer advantages of flexibility, overall cost savings, scalability to large substrates or those with complex topologies. In addition, these methods have environmental benefits [1].
Effect of Coating and Lubrication on the Vibration-Induced Loosening of Threaded Fasteners
Authors: Housari Basil A. , Nassar Sayed A.
Published: April 2008

This study provides an experimental and theoretical investigation of the effect of the bearing friction coefficient and the thread friction on the self-loosening of threaded fasteners that are subjected to cyclic transverse service loads. Coating and lubrication affect the thread and the underhead friction of the fastener, which affects the loosening rate when it is subjected to transverse loads. A mathematical model was developed to evaluate the self-loosening behavior in threaded fasteners when subjected to cyclic transverse loads. An experimental procedure and test set up are designed in order to collect real-time data on the rate of preload loss per cycle as well as the rotational angle of the bolt head during its gradual loosening. The values of the coefficients of friction under the bolt head and between the threads were changed in the mathematical model to monitor their effect on the loosening rate. Experimentally, the friction coefficients are modified by changing the coating or the lubrication applied to the fasteners. One coating and one solid film lubricant are used, namely, phosphate and oil coating and Olefin and Molydisulfide lubricated bolts. The theoretical and experimental results are presented and discussed.
Stability of the Droplet in Magnetic Levitation Mechanism
Authors: Huo Y. , Li B. Q.
Published: April 2008

This paper presents a numerical study of 3-D movement of a conducting spherical droplet in magnetic levitation mechanism. At present, we not only investigate vertical and horizontal movements of the magnetically levitated droplet, but also self-rotation of the droplet. The hybrid 3-D boundary element method (BEM) and finite element method (FEM) with edge elements are used to calculate electromagnetic fields, Lorentz force, and torques with respect to vertical and horizontal axis. By this method, finite elements are used to discretize the spherical droplet region, while boundary elements are applied to free space outside the droplet. The finite element and boundary element regions are then coupled through interface boundary conditions. The coupling of FEM/BEM is solved iteratively. The computed results agree excellently with available analytical and numerical solutions. Furthermore, the complex 3-D movement of the magnetically levitated droplet is solved and analyzed by using the current FE/BE model.
Modeling Dielectrophoretic Force Induced Bubble Motion in Micro-Channels
Authors: Wang Shimin , Bryan James
Published: April 2008

Using electrostatic forces to control bubble motion in meso to micro-scale channels filled with dielectric liquid is a promising and experimentally validated approach. In this study, dielectrophoretic force induced bubble motion in micro-channels is investigated in terms of a simple model, which has been verified by comparing with experimental data for bubble motion in meso-scale channels. Dielectrophoretic force, pressure drop across a gas bubble, viscous friction at channel wall, and inertial force related to fluid acceleration or deceleration when applied electrostatic field changes with position and time are parameterized and included explicitly in the model. For wide ranges of considered model parameters, including fluid properties, channel and electrode geometry, and applied electric field as well, modeling predictions for dynamic bubble motion in micro-channels are obtained and compared with the counterpart in meso-channel case. The results of this study show that with the channel size decreasing from meso-scale to micro-scale, the effect of inertial force becomes less important and negligible, while the pressure drop across the bubble increases significantly. In addition, it is demonstrated that the fringing field of the planar electrodes becomes more important and must be considered at micro-scale.
Layup Optimization for Maximum Buckling Load Considering Bounded Uncertainty
Authors: Kim Tae-Uk , Hwang In Hee , Shim JaeYeul
Published: April 2008

Optimal design of composite laminates with uncertain in-plane loadings and material properties is considered. The stacking sequence is designed to have maximum buckling load based on anti-optimization approach. To consider the above-mentioned uncertain properties, the convex modeling, interval analysis and Monte Carlo simulation techniques are used in calculating objective function. For the stacking sequence optimization, it is used the modified genetic algorithm which handles the discrete ply angles and the constraints easily. Numerical results are given for rectangular laminates of various aspect ratios. The optimal solutions from the deterministic and the stochastic cases are obtained and it is demonstrated the importance of considering uncertainty. The buckling load carried by a deterministic design is much less than the one carried by a design uncertainty considered when both are subjected to uncertain loads. Also, it is examined the effects of the method for considering uncertainty on the optimization process in the light of computational efficiency and reliability of solutions obtained.
Study on Copper Cold Plate Designs for Electronics Liquid Cooling System
Authors: Feng Yi. , Wang Y. , Huang C. Y.
Published: April 2008

The increasing power consumption of microelectronic systems and the dense layout of semiconductor components leave very limited design spaces with tight constraints for the thermal solution. Conventional thermal management approaches, such as extrusion, fold-fin, and heat pipe heat sinks, are somehow reaching their performance limits, due to the geometry constraints. Currently, more studies have been carried out on the liquid cooling technologies, as the flexible tubing connection of liquid cooling system makes both the accommodation in constrained design space and the simultaneous cooling of multi heating sources feasible. To significantly improve the thermal performance of a liquid cooling system, heat exchangers with more liquid-side heat transfer area with acceptable flow pressure drop are expected. This paper focuses on the performance of seven designs of source heat exchanger (cold plate). The presented cold plates are all made in pure copper material using wire cutting, soldering, brazing, or sintering process. Enhanced heat transfer surfaces such as micro channel and cooper mesh are investigated. Detailed experiments have been conducted to understand the performance of these seven cooper cold plates. The same radiators, fan, and water pump were connected with each cooper cold plate to investigate the overall thermal performance of liquid cooling system. Water temperature readings at the inlets and outlets of radiators, pump, and colder plate have been taken to interpret the thermal resistance distribution along the cooling loop.
Effect of Film Thickness and Laser Energy Density on the Structural Characteristics of Laser-Annealed Polycrystalline Gallium Arsenide Films
Authors: Cheng Gary J. , Pirzada Daniel , Trivedi Pankaj , Field David
Published: April 2008

Scanning electron microscopy and high-resolution electron backscatter diffraction (EBSD) have been used to study the texture and microstructure evolution during the crystallization of initially amorphous GaAs thin films. A KrF excimer laser, with 30 ns pulse duration was used for crystallization of a-GaAs grown on SiO2 Substrate using molecular beam epitaxy (MBE) technique. The effect of laser energy density and film thickness on grain morphology has been studied. The integrated information on grain size distribution, preferred orientation, and nature of grain boundaries provides useful information to postulate the mechanism of grain-growth and likely role of different contributing parameters in the evolution of final texture under the highly transient processing conditions prevailing during the short laser irradiation. The results show that for thick films the laser crystallization results in a weak <111> fiber texture. While for a thinner films the grains have a strong <001> texture that strengthens with a decrease in film thickness and increase in laser energy density.
A New Slip Model for Gas Lubrication
Authors: Shen Sheng , Crone Robert M. , Chen Gang , Anaya-Dufresne Manuel
Published: April 2008

In this paper, a new slip boundary condition is derived using the solution of the Boltzmann equation. The physical mechanisms of velocity slip in rarefied gas flow are discussed and emphasized. The Poiseuille flow rates predicted by the new slip model show better agreements with those calculated from the existing slip models such as 1st, 2nd, and 1.5th slip order. Based on the new slip model, a new modified Reynolds equation is also proposed to predict the pressure field in gas lubrication problem.
Small Thermoelectric Energy Source Using Various Fuels
Authors: Sodano Henry A. , Kneeland Philip
Published: April 2008

Over the past decade society's dependence on wireless electronics has grown substantially. Because these electronics are wireless they must carry their own power source, which in most cases is the electrochemical battery. Batteries can be problematic as a power source due to their limited lifespan. This raises significant issues for emergency and military applications, in which the function of the electronic device is crucial. In order to avoid these problems the amount of research being devoted to the development of small power sources has been growing rapidly. Here we propose the development of a small power source that can be used for the generation of electrical energy over a small duration of time. The energy source will used thermoelectric modules to convert thermal gradients to electrical energy. Several methods of generating the thermal gradient will be studied including a small butane flame equivalent to a pocket lighter, the rapid oxidation of magnesium that is commonly used in military MRE rations and lastly the slow oxidation of iron typically found in disposable pocket warmers. The efficiency and power output of each source will be identified and used to show the duration at which a mobile phone could be used.
Sound of Single Vapor Bubbles
Authors: Lee Ho Sung , Higgs Danny M.
Published: April 2008

The recent preliminary acoustic measurements of single vapor bubbles on a heated platinum wire, combined with high-speed digital photography, provided significant information for the vapor bubble dynamics such as growth, departure, collapse or coalescence with a previous bubble. Furthermore, under a given condition, the numerous consecutive single bubbles consistently showed almost identical waveforms, even at different times. This surprising result indicates that the phenomenon is not a chaotic process, but an orderly mathematical process. The deceleration of a growing bubble following the rapid initial growth was apparently detected by the acoustic emissions as a negative acoustic pressure. This is believed to be a new observation and not seen in gas bubbles. Some successive bubbles clearly underwent the spherical harmonics and compared well with a series of photographs. These results are in contrast with the previous indeterminate measurements on the sound intensity and frequency in boiling in the literature. The information for vapor bubble dynamics will be supplementary to the gas bubble dynamics such as cavitation, sonoluminescence, etc. Visual observations will be valuable for the mathematicians who study the spherical harmonics analytically. Also, the technique and information may be applicable to the fields of science and engineering associated with vapor bubbles motion including boiling.
Mechanical Characterization of Graphite Platelet Nanocomposites Through Molecular Mechanics and Continuum Modeling
Authors: Cho J. , Luo J. J. , Daniel I. M.
Published: April 2008

Mechanical properties of nanocomposites consisting of epoxy substrate reinforced by randomly oriented graphite platelets are studied with Mori-Tanaka method in collaboration with molecular mechanics. Elastic constants of graphite nanoplatelets which are the inclusion phase of the micromechanical model are calculated based on their molecular force field. The calculated elastic constants are well compared with the both experimental data and other theoretical predictions in literatures. The results from Mori-Tanaka's method based on the graphite modulus calculation from molecular mechanics are found that nanocomposite moduli have strong dependence on the aspect ratios of reinforcing particles, but no direct size dependence. The predicted nanocomposite moduli compare favorably with modulus measurement of several graphite particles of various aspect ratios and sizes. The experimental data also shows that particle sizes have very weak effect on nanocomposite moduli.
Micromechanics of Hydrogen Transport and Embrittlement in Pipeline Steels
Authors: Dadfarnia Mohsen , Sofronis Petros , Robertson Ian , Somerday Brian P. , Muralidharan Govindarajan , Stalheim Douglas
Published: April 2008

The technology of large scale hydrogen transmission from central production facilities to refueling stations and stationary power sites is at present undeveloped. Among the problems which confront the implementation of this technology is the deleterious effect of hydrogen on structural material properties, in particular at gas pressure of 1000 psi which is the desirable transmission pressure suggested by economic studies for efficient transport. To understand the mechanisms of hydrogen embrittlement our approach integrates mechanical property testing, TEM observations, and finite element modeling. In this work a hydrogen transport methodology for the calculation of hydrogen accumulation ahead of a crack tip in a pipeline steel is outlined. The approach accounts for stress-driven transient diffusion of hydrogen and trapping at microstructural defects whose density evolves dynamically with deformation. The results are analyzed to correlate the level of load in terms of the applied stress intensity factor with the time after which hydrogen transport takes place under steady state conditions. The transient and steady state hydrogen concentration profiles are used to assess the hydrogen effect on the mechanisms of fracture as they depend on material microstructure.
Unsteady Confined Swirling Flow of Polymer Solutions
Authors: Tamano S. , Itoh M.
Published: April 2008

The unsteady swirling flow of an aqueous polymer solution due to a rotating disc in a cylindrical casing was investigated using flow visualization and particle image velocimetry (PIV) system. As the aqueous polymer solution, polyacrylamide (PAA) solutions whose concentrations were 0.025, 0.1, 0.2, 0.5, 0.8 and 1.0 wt% were used. We found a new phenomenon of vortex shedding in which the ring vortex formed near the center of rotating disc was periodically shed away from the rotating disc in the unsteady flow regime. It was found that the fluid within the ring vortex formed near the rotating disc rotates with semi-rigid rotation, where the angular velocity of ring vortex was about 0.9 times that of the rotating disc. A high shear layer existed at the boundary between the ring vortex and the outer large-scale secondary flow. Just after the ring vortex was shed, the surrounding large-scale secondary flow rushed into near the rotating axis, so that the strong axial flow was observed near the rotating axis.
Hybrid Wave/Mode Active Vibration Control of a Timoshenko Beam
Authors: Mei C.
Published: April 2008

A hybrid approach to active vibration control is described in this paper. It combines elements of both wave and mode approaches to active control and is an attempt to improve on the performance of these approaches individually. In the proposed hybrid approach, wave control is first applied at one or more points in the structure. It is designed on the basis of the local behavior of the structure and is intended to absorb vibrational energy, especially at higher frequencies. Then modal control is applied, being designed on the basis of the modified global equations of motion of the structure-plus-wave-controller. These are now normally non-self-adjoint. Because the higher order modes are relatively well damped, hybrid control improves the model accuracy and the robustness of the system and gives better broadband vibration attenuation performance. Hybrid wave/mode active vibration control is described with specific reference to the control of bending vibrations in a Timoshenko beam. The particular case considered is that of collocated, point force/sensor feedback wave control combined with modal control designed using pole placement. Numerical results are presented.
Numerical Analysis of Ludwig-Soret Effect of One Binary Mixture and Two Ternary Mixtures in an Al2O3 Porous Cavity
Authors: Jaber T. J. , Saghir M. Z.
Published: April 2008

A cavity of 10 mm in width, 10 mm in height, and 32.1 mm in horizontal length filled with Al2O3 porous medium designed in Pau project to investigate thermal diffusion phenomena, or Ludwig-Soret effect. A lateral heating condition was applied with 10 °C at the left wall and 50 °C at the right wall. The thermosolutal convection of a binary mixture of water-ethanol at 75.0 MPa pressure, a ternary mixture with methane, n-butane, and n-dodecan at 35.0 MPa pressure, and a ternary mixture of n-dodecane, isobutylbenzene, and tetrahydonaphthalene at atmosphere pressure inside the Al2O3 porous medium cavity were numerically investigated. The thermal conductivity and the permeability of Al2O3 porous medium on the Ludwig-Soret effect were analyzed, the former had little influence, but the later had strong impact on the compositional separation at the steady state of thermosolutal convection, which were analyzed globally with separation ratio. The distributions of component mole fraction(s) on the horizontal and vertical lines in the center of the porous cavity were also shown to study the details of the compositional separation at the steady state of thermosolutal convection. Recommendations are made for the experimental design based on the results of numerical analysis
Imaging of Turbulent Buoyant Jet Mixing
Authors: Helmer David B. , Su Lester K.
Published: April 2008

This paper presents quantitative imaging measurements of jet fluid mole fraction fields in turbulent buoyant jets of helium issuing into air. The measurements use planar laser Rayleigh scattering. Signal levels are low, necessitating a novel approach to background subtraction in the signal processing. The jet flows considered are classified as momentum-driven, meaning that buoyancy effects are presumed to be confined to the small scales of the flow. We focus here on the near-nozzle, developing region of the jet, which is of particular interest to flows with combustion. The results suggest that buoyancy affects the details of the evolution of the mixing field even while the mean field maintains scaling properties consistent with non-buoyant jets. Specifically, the mean jet fluid mole fraction profiles show a sharper jet/ambient fluid interface relative to non-buoyant jets. The mole fraction fluctuations within the jet are also weaker than those reported in non-buoyant jets. These results will inform ongoing efforts to model the mixing process in flows with density differences, such as combustion systems.
The impact of respiratory motion and treatment technique on stereotactic body radiation therapy for liver cancer
Authors: Wu Q. Jackie , Thongphiew Danthai , Wang Zhiheng , Chankong Vira , Yin Fang‐Fang
Published: April 2008

Stereotactic body radiation therapy (SBRT), which delivers a much higher fractional dose than conventional treatment in only a few fractions, is an effective treatment for liver metastases. For patients who are treated under free‐breathing conditions, however, respiration‐induced tumor motion in the liver is a concern. Limited clinical information is available related to the impact of tumor motion and treatment technique on the dosimetric consequences. This study evaluated the dosimetric deviations between planned and delivered SBRT dose in the presence of tumor motion for three delivery techniques: three‐dimensional conformal static beams (3DCRT), dynamic conformal arc (DARC), and intensity‐modulated radiation therapy (IMRT). Five cases treated with SBRT for liver metastases were included in the study, with tumor motions ranging from 0.5 to 1.75 cm. For each case, three different treatment plans were developed using 3DCRT, DARC, and IMRT. The gantry/multileaf collimator (MLC) motion in the DARC plans and the MLC motion in the IMRT plans were synchronized to the patient's respiratory motion. Retrospectively sorted four‐dimensional computed tomography image sets were used to determine patient‐organ motion and to calculate the dose delivered during each respiratory phase. Deformable registration, using thin‐plate‐spline models, was performed to encode the tumor motion and deformation and to register the dose‐per‐phase to the reference phase images. The different dose distributions resulting from the different delivery techniques and motion ranges were compared to assess the effect of organ motion on dose delivery. Voxel dose variations occurred mostly in the high gradient regions, typically between the target volume and normal tissues, with a maximum variation up to . The greatest CTV variation of all the plans was seen in the IMRT technique with the largest motion range (D99: , D95: , and D90: ). The greatest variation for all 3DCRT plans was less than for D95. Dose variations for DARC fell between the 3DCRT and IMRT techniques. The dose volume histogram variations for normal organs were negligible. Therefore, the IMRT technique may be a preferable treatment choice in cases where the target volume and critical organs are in close proximity, or when normal organ protection is a high priority, provided that motion effect for the target volume can be managed.
Split‐focused ultrasound transducer with multidirectional heating for breast tumor thermal surgery
Authors: Cheng Tze‐Yuan , Ju Kuen‐Cheng , Ho Cheng‐Shiao , Chen Yung‐Yaw , Chang Hsu , Lin Win‐Li
Published: April 2008

This study investigated the feasibility of using a split‐focused ultrasound transducer to perform thermal surgery on breast tumors, based on a multidirectional heating scheme. The transducer is a square section of a sphere with a radius of . The transducer was tilted such that its acoustic beam was 45° relative to the rib surface, and its focal zone was arranged by a shift of away from the center of the planning target volume. The multifocus switching technique was employed to enhance the heating efficiency. When a single transducer was used, the transducer sonicated from a certain position for a given duration, and then rotated sequentially to continue the heating. Computer simulations and in vitro phantom experiments have been studied for this heating system. Both simulation and experimental results demonstrated that the system based on a multidirectional heating scheme is capable of generating a proper thermal lesion within . Meanwhile, from the simulation results, the rib heating was effectively alleviated by tilting the transducer to induce the total reflection at the muscle/bone interface. While using multiple ultrasound transducers, an appropriate arrangement was designed to have the same configuration of acoustic beams as is used for a single‐transducer strategy. The simulation results from the four‐transducer strategy indicated that the heating results could be further improved. This study revealed that it is very promising to have an appropriate arrangement of a single split‐focused ultrasound transducer with mechanical rotation, or to have multiple split‐focused transducers that use multidirectional heating for breast tumor thermal therapy.
Quantification of breast arterial calcification using full field digital mammography
Authors: Molloi Sabee , Xu Tong , Ducote Justin , Iribarren Carlos
Published: April 2008

Breast arterial calcification is commonly detected on some mammograms. Previous studies indicate that breast arterial calcification is evidence of general atherosclerotic vascular disease and it may be a useful marker of coronary artery disease. It can potentially be a useful tool for assessment of coronary artery disease in women since mammography is widely used as a screening tool for early detection of breast cancer. However, there are currently no available techniques for quantification of calcium mass using mammography. The purpose of this study was to determine whether it is possible to quantify breast arterial calcium mass using standard digital mammography. An anthropomorphic breast phantom along with a vessel calcification phantom was imaged using a full field digital mammography system. Densitometry was used to quantify calcium mass. A calcium calibration measurement was performed at each phantom thickness and beam energy. The known and measured calcium mass on 5 and 9 cm thickness phantoms were related by ( and ) and ( and ), respectively. The results indicate that accurate calcium mass measurements can be made without correction for scatter glare as long as careful calcium calibration is made for each breast thickness. The results also indicate that composition variations and differences of approximately 1 cm between calibration phantom and breast thickness introduce only minimal error in calcium measurement. The uncertainty in magnification is expected to cause up to and error in calcium mass for 5 and 9 cm breast thicknesses, respectively. In conclusion, a densitometry technique for quantification of breast arterial calcium mass was validated using standard full field digital mammography. The results demonstrated the feasibility and potential utility of the densitometry technique for accurate quantification of breast arterial calcium mass using standard digital mammography.
Anniversary Paper: Fifty years of AAPM involvement in radiation dosimetry
Authors: Ibbott G. , Ma C.‐M. , Rogers D. W. O. , Seltzer S. M. , Williamson J. F.
Published: April 2008

This article reviews the involvement of the AAPM in various aspects of radiation dosimetry over its50 year history, emphasizing the especially important role that external beam dosimetry played in the early formation of the organization. Topics covered include the AAPM's involvement with external beam and x‐ray dosimetry protocols, brachytherapy dosimetry, primary standards laboratories, accredited dosimetry chains, and audits for machine calibrations through the Radiological Physics Center.
Laser range scanning for image‐guided neurosurgery: Investigation of image‐to‐physical space registrations
Authors: Cao Aize , Thompson R. C. , Dumpuri P. , Dawant B. M. , Galloway R. L. , Ding S. , Miga M. I.
Published: April 2008

In this article a comprehensive set of registration methods is utilized to provide image‐to‐physical space registration for image‐guided neurosurgery in a clinical study. Central to all methods is the use of textured point clouds as provided by laser range scanning technology. The objective is to perform a systematic comparison of registration methods that include both extracranial (skin marker point‐based registration (PBR), and face‐based surface registration) and intracranial methods (feature PBR, cortical vessel‐contour registration, a combined geometry/intensity surface registration method, and a constrained form of that method to improve robustness). The platform facilitates the selection of discrete soft‐tissue landmarks that appear on the patient's intraoperative cortical surface and the preoperative gadolinium‐enhanced magnetic resonance (MR) image volume, i.e., true corresponding novel targets. In an 11 patient study, data were taken to allow statistical comparison among registration methods within the context of registration error. The results indicate that intraoperative face‐based surface registration is statistically equivalent to traditional skin marker registration. The four intracranial registration methods were investigated and the results demonstrated a target registration error of , , , and , for feature PBR, cortical vessel‐contour registration, unconstrained geometric/intensity registration, and constrained geometric/intensity registration, respectively. When analyzing the results on a per case basis, the constrained geometric/intensity registration performed best, followed by feature PBR, and finally cortical vessel‐contour registration. Interestingly, the best target registration errors are similar to targeting errors reported using bone‐implanted markers within the context of rigid targets. The experience in this study as with others is that brain shift can compromise extracranial registration methods from the earliest stages. Based on the results reported here, organ‐based approaches to registration would improve this, especially for shallow lesions.
Improved classifier for computer‐aided polyp detection in CT Colonography by nonlinear dimensionality reduction
Authors: Wang Shijun , Yao Jianhua , Summers Ronald M.
Published: April 2008

Computer‐aided detection (CAD) has been shown to be feasible for polyp detection on computed tomography (CT) scans. After initial detection, the dataset of colonic polyp candidates has large‐scale and high dimensional characteristics. In this article, we propose a nonlinear dimensionality reduction method based on diffusion map and locally linear embedding (DMLLE) for large‐scale datasets. By selecting partial data as landmarks, we first map these points into a low dimensional embedding space using the diffusion map. The embedded landmarks can be viewed as a skeleton of whole data in the low dimensional space. Then by using the locally linear embedding algorithm, nonlandmark samples are mapped into the same low dimensional space according to their nearest landmark samples. The local geometry is preserved in both the original high dimensional space and the embedding space. In addition, DMLLE provides a faithful representation of the original high dimensional data at coarse and fine scales. Thus, it can capture the intrinsic distance relationship between samples and reduce the influence of noisy features, two aspects that are crucial to achieving high classifier performance. We applied the proposed DMLLE method to a colonic polyp dataset of 175 269 polyp candidates with 155 features. Visual inspection shows that true polyps with similar shapes are mapped to close vicinity in the low dimensional space. We compared the performance of a support vector machine (SVM) classifier in the low dimensional embedding space with that in the original high dimensional space, SVM with principal component analysis dimensionality reduction and SVM committee using feature selection technology. Free‐response receiver operating characteristic analysis shows that by using our DMLLE dimensionality reduction method, SVM achieves higher sensitivity with a lower false positive rate compared with other methods. Forpolyps (193 true polyps contained in test set), when the number of false positives per patient is 9, SVM with DMLLE improves the average sensitivity from 70% to 83% compared with that of an SVM committee classifier which is a state‐of‐the‐art method for colonic polyp detection.
Adsorption of metallic radionuclides on plastic phantom walls
Authors: Park Mi‐Ae , Mahmood Ashfaq , Zimmerman Robert E. , Limpa‐Amara Naengnoi , Makrigiorgos G. Mike , Moore Stephen C.
Published: April 2008

Metal radionuclide solutions at neutral adhere to plastic containers. Adsorption of radionuclides on the walls of phantoms leads to a nonuniform activity distribution, which could adversely affect imaging studies, as well as phantom‐based validations of absorbed dose calculations used in radioimmunotherapy, requiring accurate knowledge of the underlying activity distribution. In the work reported here, the authors determined the degree of metal chelation required to minimize metallic radionuclide oxide formation and adsorption on phantom walls in order to yield more reliable experimental data for validating image‐based dosimetry. Using hollow spherical plastic phantoms, the authors evaluated three different radionuclides, I‐131, In‐111, and Y‐90, in solutions containing three different concentrations of the chelator, ethylenediaminetetraacetate (EDTA). Adsorption to plastic walls was determined using imaging and/or by counting aliquots of solutions. Reconstructed images and measurements of I‐131 activity showed that it was uniformly distributed within all spheres; however, images of In‐111 in EDTA indicated that the activity concentration near the wall was much higher than that in the middle of the sphere. The decrease in activity concentration near the center of the spheres was . Y‐90 in EDTA behaved similarly; the activity concentration of Y‐90 decreased by . For an In‐111 or Y‐90 radioactivity concentration of 0.74 MBq/mL, a EDTA solution was required to achieve a uniform distribution, suggesting that, under our experimental conditions, EDTA molecules were required for each radiometal atom to prevent precipitation and adsorption on poly(methylmethacrylate). For certain radiometals, e.g., In‐111 or Y‐90, adequate chelation is essential to achieve uniform activity concentration values and homogeneous distribution within the phantom compartments.