bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimal Tolerance Allocation for a Sliding Vane Compressor
Authors: Huang Yuan Mao , Shiau Ching-Shin
Published: December 2005

An optimization model has been built with consideration of the required reliability, the minimum machining cost, and quality loss. The normal and the lognormal distributions of tolerances that depend on the production types of components are used in the reliability model. Cost tolerance data obtained from Bjørke are used to calculate the machining cost. The asymmetric quadratic quality loss model is used to calculate quality loss caused by the deviation and the mean-shift of distributions. Tolerance allocation of a sliding vane rotary compressor is optimized for the required reliability, the minimum cost and quality loss, and optimum tolerances of components are recommended. The results show that high accuracies of the slot length, the vane thickness, and the slot width are required. Hence, their tolerances are smaller than other components. The effects of the correlation coefficient of the bottom cover plate and the top cover plate and the correlation coefficient of the front cover plate and the rear cover plate to total cost are insignificant. Further, the cost of quality loss is reduced when the weighting ratio of the quality loss function weighting coefficient to the machining cost function weighting coefficient is increased. The total cost is increased because tight tolerance allocation increases the machining cost.
A Full Kinematic Model of Thread-Starting for Assembly Automation Analysis
Authors: Wiedmann Stephen , Sturges Bob
Published: December 2005

This work addresses the geometry of threaded fastener insertion at a detailed level in order to determine the nature of contact between a bolt and nut during the initial phases of thread mating. The assembly problem was modeled as a constrained three-dimensional analysis to gain an understanding about how contacts between the bolt and nut change during the thread starting counterclockwise motion. We introduce a fully detailed thread profile model which is parametrically adaptable to all practical thread forms. From this geometric representation, we derive contact state maps graphically represented as axial discs. From these maps we show the phase relationship of the bolt and nut in the critical thread-starting process. This model is based on the premise that an unspecified active or passive device will be employed for correcting alignment errors. The model serves to visualize the contact conditions which could lead to wedging and jamming events, and provides one component for such analyses.
An EFG-FE Coupling Method for Microscale Adhesive Contacts
Authors: Liu Tianxiang , Liu Geng , Xie Qin , Wang Q. Jane
Published: December 2005

An elastic adhesive contact model based on the element-free Galerkin-finite element (EFG-FE) coupling method is presented in this paper. The model is first validated though comparison to theoretical solutions. A numerical simulation of the adhesive contact between a microelastic cylinder and a rigid half-space is then conducted. The adhesive contact characteristics of three metals (Al, Cu, and Fe) are studied at different Tabor parameters. The relationships of the applied load and contact half-width of the adhesive contacts are analyzed. Contact pressures, stress contours and deformed profiles of different cylinder sizes and applied loads are illustrated and discussed. The results are compared to published solutions, and good agreements are observed.
On the Role of Enduring Contact in Powder Lubrication
Authors: Jang J. Y. , Khonsari M. M.
Published: December 2005

This paper is devoted to a study of the enduring contact between granules of powder lubricants in an effort to better understand the flow characteristics of powder lubricants. Appropriate formulation of the governing equations is reported that can be used for prediction of the flow velocity, pseudo temperature, and volume fraction distribution of powders for a wide range of operating speeds. A set of parametric simulations and a limiting analytical solution is presented for predicting the behavior of a powder lubricant under low operating speeds when the enduring contact tends to dominate the kinetic regime. The limiting solution shows that below a certain sliding speed the volume fraction remains unchanged due to the effect of the enduring contact. It is also shown that below this limiting speed the enduring contact plays a major role and should not be neglected.
Three-Dimensional Dry/Wet Contact Analysis of Multilayered Elastic/Plastic Solids With Rough Surfaces
Authors: Cai Shaobiao , Bhushan Bharat
Published: December 2005

Friction/stiction and wear are among the main issues in microelectromechanical systems (MEMS/NEMS) devices having contact interfaces. Relevant parameters, i.e., layers thickness, need to be optimized. The contact analyses of multilayered structure under both dry and wet conditions are necessary to optimize these parameters. This study presents a first attempt to perform three-dimensional contact analysis of multilayered solids with rough surfaces in both dry and wet conditions. The surface displacements and contact pressure distributions are obtained based on variational principle with fast Fourier transform scheme. The effective hardness is modeled and plays a role when the local displacement meets the maximum displacement criterion. Simulations are performed to obtain the contact pressures, fractional total contact area, fractional plastic contact area, surface/subsurface stresses. Relative meniscus forces are obtained with the presence of an ultrathin liquid film for different loads and layers properties. These contact statistics and meniscus forces are analyzed to study the effects of layer-to-substrate ratios of stiffness and hardness, and the layers thickness of rough, two-layered elastic/plastic solids. The methods to decrease friction/stiction and wear are investigated, and the optimum layer parameters are identified.
Effects of Mobile and Bonded Molecules of Molecularly Thin Lubricant Film on the Vibrational Stability of a Sliding Ball
Authors: Tanaka Kentaro , Kawaguchi Masahiro , Kato Takahisa , Iwamoto Katsumi
Published: December 2005

Lubrication by an extremely thin film has become very important in micromachines, magnetic recording disks, and so on. Molecularly thin perfluoropolyether (PFPE) films are considered a good lubricant for these micro devices. When the thickness of the PFPE film is thinned to several nanometers, it is possible to assume that the film consists of mobile and bonded molecules. In this paper, we investigated the role of these molecules from the viewpoint of the vibrational stability of the sliding ball with the disk surface. From experiments by the ball on disk type tribotester, it is found that both mobile and bonded molecules exist on the disk surface, the bouncing vibration of the sliding ball can be reduced wide load range. In the case where only mobile or only bonded molecules exists, there is little effect on the bouncing vibration.
A More General Mobility Criterion for Parallel Platforms
Authors: Rico J. M. , Aguilera L. D. , Gallardo J. , Rodriguez R. , Orozco H. , Barrera J. M.
Published: December 2005

This contribution presents a more general mobility criterion applicable to parallel platforms, unlike previously employed mobility criteria based on the well-known Kutzbach-Grübler criterion that often fails to provide the correct number of degrees of freedom of parallel manipulators, the mobility criterion introduced in this contribution provides the correct number of degrees of freedom for a wider class of parallel manipulators. Furthermore, the analysis provides insight into why the criteria based on the Kutzbach-Grübler criterion often fails. Moreover, the recently developed criterion computes the passive degrees of freedom in parallel platforms and the mobility of some classes of kinematically defficient parallel platforms. Finally, it is important to note that this criterion is based on an analysis of the subalgebras of the Lie algebra, se(3), also known as screw algebra, of the Euclidean group, SE(3). Moreover, it should be emphasized that, unlike other attempts to develop a criterion, the criterion developed in this contribution does not require any consideration of reciprocal screws. As is common in many areas of kinematics, the criterion presented here can be also obtained by an analysis of the subgroups of the Euclidean group.
Enumeration of Contact Geometries for Kinematic Registration Using Tactile Sensing Fixtures
Authors: Nederbragt Walter W. , Ravani Bahram
Published: December 2005

This paper uses group theory for enumeration of contacts between geometric elements necessary for kinematic registration or part referencing in robotics. The results are applied to type synthesis of tactile sensing mechanical fixtures. Kinematic registration is an important step in robot calibration and in data driven automation. Although the scope of the paper is limited to geometric contacts involving points, lines, planar surfaces, cylindrical surfaces, and spherical surfaces, the techniques developed are general and can be applied to other geometric features and non-tactile sensing elements used in robotic calibration and part referencing.
Identification of the Workspace Boundary Of a General 3-R Manipulator
Authors: Ottaviano Erika , Husty Manfred , Ceccarelli Marco
Published: December 2005

In this paper an algebraic formulation is presented for the boundary workspace of 3-R manipulators in Cartesian Space. It is shown that the cross-section boundary curve can be described by a 16th order polynomial as function of radial and axial reaches. The cross-section boundary curve and workspace boundary surface are fully cyclic. Geometric singularities of the curve are identified and characterized. Numerical examples are presented to show the usefulness of the proposed investigation and to classify the design characteristics.
The Kinetostatic Optimization of Robotic Manipulators: The Inverse and the Direct Problems
Authors: Khan Waseem A. , Angeles Jorge
Published: December 2005

The design of a robotic manipulator begins with the dimensioning of its various links to meet performance specifications. However, a methodology for the determination of the manipulator architecture, i.e., the fundamental geometry of the links, regardless of their shapes, is still lacking. Attempts have been made to apply the classical paradigms of linkage synthesis for motion generation, as in the Burmester Theory. The problem with this approach is that it relies on a specific task, described in the form of a discrete set of end-effector poses, which kills the very purpose of using robots, namely, their adaptability to a family of tasks. Another approach relies on the minimization of a condition number of the Jacobian matrix over the architectural parameters and the posture variables of the manipulator. This approach is not trouble-free either, for the matrices involved can have entries that bear different units, the matrix singular values thus being of disparate dimensions, which prevents the evaluation of any version of the condition number. As a means to cope with dimensional inhomogeneity, the concept of characteristic length was put forth. However, this concept has been slow in finding acceptance within the robotics community, probably because it lacks a direct geometric interpretation. In this paper the concept is revisited and put forward from a different point of view. In this vein, the concept of homogeneous space is introduced in order to relieve the designer from the concept of characteristic length. Within this space the link lengths are obtained as ratios, their optimum values as well as those of all angles involved being obtained by minimizing a condition number of the dimensionally homogeneous Jacobian. Further, a comparison between the condition number based on the two-norm and that based on the Frobenius norm is provided, where it is shown that the use of the Frobenius norm is more suitable for design purposes. Formulation of the inverse problem—obtaining link lengths—and the direct problem—obtaining the characteristic length of a given manipulator—are described. Finally a geometric interpretation of the characteristic length is provided. The application of the concept to the design and kinetostatic performance evaluation of serial robots is illustrated with examples.
Extension of Graph Theory to the Duality Between Static Systems and Mechanisms
Authors: Shai Offer , Pennock Gordon R.
Published: December 2005

This paper is a study of the duality between the statics of a variety of structures and the kinematics of mechanisms. To provide insight into this duality, two new graph representations are introduced; namely, the flow line graph representation and the potential line graph representation. The paper also discusses the duality that exists between these two representations. Then the duality between a static pillar system and a planar linkage is investigated by using the flow line graph representation for the pillar system and the potential line graph representation for the linkage. A compound planetary gear train is shown to be dual to the special case of a statically determinate beam and the duality between a serial robot and a platform-type robot, such as the Stewart platform, is explained. To show that the approach presented here can also be applied to more general robotic manipulators, the paper includes a two-platform robot and the dual spatial linkage. The dual transformation is then used to check the stability of a static system and the stationary, or locked, positions of a linkage. The paper shows that two novel platform systems, comprised of concentric spherical platforms inter-connected by rigid rods, are dual to a spherical six-bar linkage. The dual transformation, as presented in this paper, does not require the formulation and solution of the governing equations of the system under investigation. This is an original contribution to the literature and provides an alternative technique to the synthesis of structures and mechanisms. To simplify the design process, the synthesis problem can be transformed from the given system to the dual system in a straightforward manner.
Synthesis of Planar Parallel Mechanisms While Considering Workspace, Dexterity, Stiffness and Singularity Avoidance
Authors: Arsenault Marc , Boudreau Roger
Published: December 2005

It is a generally well-known fact that the design of parallel mechanisms while optimizing performance is quite difficult. In this paper, a reliable synthesis method capable of optimally selecting the geometrical parameters of planar parallel mechanisms is presented. Three different architectures are considered and a genetic algorithm is used to perform the optimization. The performance of each mechanism is evaluated according to four different criteria: workspace, singular configurations, dexterity, and stiffness. In order to make the synthesis method as realistic as possible, mechanical constraints affecting the angular rotation of the 2-RP̱R and 3-RP̱R mechanisms’ passive revolute joints are considered. Moreover, since the conventional methods for computing the dexterity and the stiffness index are not valid for the 3-RP̱R and 3-ṞRR mechanisms, an alternative computation method is used.
Dynamic Performance Limitations Due to Yielding in Cable-Driven Robotic Manipulators
Authors: Yin Xiaolei , Bowling Alan P.
Published: December 2005

This paper presents a method for characterizing the performance limitations imposed by the yielding of the cables in systems with cable-driven transmissions. The method involves developing a rigid-body model of the system, where the cable tensions are considered as reaction forces. The kinematic coupling between links in the mechanism due to the use of cables is also considered. Here, the limitations on dynamic performance caused by cable yielding are added to the limitations caused by the bounds on actuator torque capacity, in order to give a more comprehensive description of the system’s capabilities. A two degrees-of-freedom planar mechanism is analyzed in order to illustrate the methodology.
An Assessment of the Greenwood-Williamson and Other Asperities Models, With Special Reference to Electrical Conductance
Authors: Ciavarella M. , Leoci F.
Published: December 2005

Although in principle simple and neat results are obtained with the classical Greenwood-Williamson (GW) model (linearity of real contact area and conductance with load), the definition of asperity as local maxima of the surface leads to uncertain results for multiscale surfaces, as suspected already by Greenwood in a recent self-assessment of his theory [Greenwood, J. A., and Wu, J.J., 2001, “Surface roughness and contact: an apology,” Meccanica 36(6), pp. 617–630]. Quoting the conclusions in the latter paper “The introduction by Greenwood and Williamson in 1966 of the definition of a ‘peak’ as a point higher than its neighbours on a profile sampled at a finite sampling interval was, in retrospect, a mistake, although it is possible that it was a necessary mistake”. Greenwood and Wu suggest that an alternative definition of asperity captures the mechanics of the contact more correctly, that of Aramaki-Majumbdar-Bhushan (AMB). Here, numerical experiments confirm that with a Weierstrass series fractal profile (taken as a 2D slice of a true fractal surface but then used to define a set of circular asperities), load and conductance for numerically measured asperities defined “à la Greenwood-Williamson” (3PP, 3-point peaks) differ significantly from the results obtained with the Aramaki-Majumbdar-Bhushan definition of asperity. The AMB definition, which is based on the bearing area intersection best parabola fitting, gives finite limits for all quantities and varies very little with small scale terms, and tends to coincide with the 3PP method only at unrealistically large fractal dimensions D, or at unrealistically large separations. However, it remains unclear how the AMB results compare with the proper treatment of the problem when interaction effects are fully taken into account.
An Elimination Procedure for Solving the Geometric Design of Spatial 3R Manipulators
Authors: Lee Eric , Mavroidis Constantinos
Published: December 2005

In this paper, the geometric design problem of serial-link robot manipulators with three revolute (R) joints when three precision points are specified is solved using an algebraic elimination method for the first time. Three spatial positions and orientations are defined and the dimensions of the geometric parameters of the 3R manipulator are computed so that the manipulator will be able to place its end-effector at these three prespecified locations. In this problem, six of the design parameters are set as free choices and their values are selected arbitrarily. For the specific case studied in this paper, a 12 deg single variable polynomial is calculated that has eight roots that are the design solutions and the other four roots are extraneous solutions.
Analytical Target Setting: An Enterprise Context in Optimal Product Design
Authors: Cooper Adam B. , Georgiopoulos Panayotis , Kim Harrison M. , Papalambros Panos Y.
Published: December 2005

In this article the process of rigorously setting supersystem targets in an enterprise context is explored as a model-based approach termed “analytical target setting.” Engineering design decisions have more value and lasting impact if they are made in the context of the enterprise that produces the designed product. Setting targets that the designer must meet is often done at a high level within the enterprise, however, with inadequate consideration of the engineering design embodiment and associated cost. For complex artifacts produced by compartmentalized hierarchical enterprises, the challenge of linking the target setting rationale with the product instantiation is particularly demanding. The previously developed analytical target cascading process addresses the problem of translating top level design targets into design targets for all systems in a multilevel hierarchically structured product, so that local targets are consistent with each other and top targets can be met as closely as possible. The effectiveness of linking analytical target setting and target cascading is demonstrated in a hybrid electric automotive truck vehicle example. The manufacturer introduces a new product (hybrid electric truck) in the market under uncertainty in fuel prices during the life cycle of the vehicle. The example demonstrates a clear interaction between the enterprise decision making and the engineering product development.
Film Condensation of R-134a on Tube Arrays With Plain and Enhanced Surfaces: Part II—Empirical Prediction of Inundation Effects
Authors: Gstoehl D. , Thome J. R.
Published: December 2005

New predictive methods for R-134a condensing on vertical arrays of horizontal tubes are proposed based on visual observations revealing that condensate is slung off the array of tubes sideways and significantly affects condensate inundation and thus the heat transfer process. For two types of three-dimensional (3D) enhanced tubes, the Turbo-CSL and the Gewa-C, the local heat flux is correlated as a function of condensation temperature difference, the film Reynolds number, the tube spacing, and liquid slinging effect. The measured heat transfer data of the plain tube were well described by an existing asymptotic model based on heat transfer coefficients for the laminar wavy flow and turbulent flow regimes or, alternatively, by a new model proposed here based on liquid slinging. For the 26fpi low finned tube, the effect of inundation was found to be negligible and single-tube methods were found to be adequate.
Estimation
of Time-Varying Inlet Temperature and Heat Flux in Turbulent Circular Pipe
Flow
Authors: Chen Cha’o-Kuang , Wu Li-Wen , Yang Yue-Tzu
Published: December 2005

This study addresses the conjugate heat transfer problem of hydrodynamically developed turbulent flow in a circular pipe. An inverse method is used to estimate the time-varying inlet temperature and the outer-wall heat flux simultaneously on the basis of temperature measurements taken at two different locations within the pipe flow. The present approach rearranges the matrix forms of the governing differential equations and then applies a whole domain estimation with the function specification method and the linear least-squares-error method to determine the two boundary conditions of the pipe flow. The dimensionless temperature data obtained from the direct problem are used to simulate the temperature measurements. The influence of temperature measurement errors upon the precision of the estimated results is investigated. The proposed method provides several advantages compared to traditional methods: (1) it yields a solution within a single computational iteration, (2) no prior information is required regarding the functional form of the quantities of interest, (3) no initial guesses of the unknown parameter values are required, and (4) the inverse problem can be solved in a linear domain. This study also considers the influence of the location of the temperature measurement sensors upon the accuracy of the calculated results. The numerical results confirm that the proposed method provides an efficient, robust, and accurate means of estimating the inlet temperature and outer-wall heat flux simultaneously in turbulent pipe flow.
Laminar Flow and Heat Transfer in the Entrance Region of Trapezoidal
Channels With Constant Wall Temperature
Authors: Renksizbulut Metin , Niazmand Hamid
Published: December 2005

Simultaneously developing three-dimensional laminar flow and heat transfer in the entrance region of trapezoidal channels have been investigated using numerical methods in the Reynolds number range from 10 to 1000. The principal and secondary velocity fields, the temperature field, and all associated heat and momentum exchange parameters have been examined. The present results for the fully developed flow region of the channels compare well with the available literature. In the entrance region, it is observed that the axial velocity profiles develop overshoots near the walls and particularly at the channel corners. It is shown that boundary-layer type of approximations, which lead to Reynolds-number-independent Poiseuille and Nusselt numbers, can be used for Reynolds numbers over 50 and after a few hydraulic diameters from the channel inlet. It is also shown that hydrodynamic entrance lengths calculated with methods based on fully developed flow data are grossly in error. New correlations are proposed for the entrance length, and for the friction and heat transfer coefficients.
Computation of the Logarithmic Mean Temperature Difference
Authors: Gomiz Antonio
Published: December 2005

The original formula for the computation of the logarithmic mean temperature difference in finite precision floating-point arithmetic may suffer from serious round-off problems when both temperature differences are very close to each other. An alternative, mathematically equivalent, yet simple formula showing better numerical properties is presented.
Active Thermal Control
of Distributed Parameter Systems Excited at Multiple
Frequencies
Authors: Richter Christoph
C. , Lienhard John
        H.
Published: December 2005

In testing packaged high-power integrated circuits, active thermal control is useful in providing die-level temperature stability. A time-varying heat load is applied to the surface of the package to compensate for the time-varying test power sequence applied to the die. An earlier study determined the proper control heat load for a single-frequency sinusoidal variation in die power subject to a finite allowed temperature variation on the die. Actual test power sequences contain many frequencies at various phase angles, each contributing to the temperature variation of the die. In the present study, we develop a method of controlling multiple frequency test sequences subject to a finite temperature tolerance. It is shown that the total control power may be minimized assigning temperature tolerances to the highest frequencies in the test power sequence.
Viscous Fluid Displacement by the Growing Bubble
Authors: Kendoush Abdullah Abbas
Published: December 2005

Equations were derived for the forces experienced by the growing bubble in displacing the liquid radially. The derivation was based on integrating the viscous dissipation function over the entire surface of the bubble. The resulted equations were applicable to bubbles in boiling and in cavitation. The derived equations were validated by applying them to the heterogeneous nucleation and growth of bubbles from cavities in pool boiling and in cavitation. The derived equations approached asymptotically the familiar equation of heterogeneous nucleation and growth of bubbles.
Immobilization effect of air‐injected blanket (AIB) for abdomen fixation
Authors: Ko Young Eun , Suh Yelin , Ahn Seung Do , Lee Sang‐wook , Shin Seong Soo , Kim Jong Hoon , Choi Eun Kyung , Yi Byong Yong
Published: December 2005

A new device for reducing the amplitude of breathing motion by pressing a patient's abdomen using an air‐injected blanket (AIB) for external beam radiation treatments has been designed and tested. The blanket has two layers sealed in all four sides similar to an empty pillow made of urethane. The blanket is spread over the patient's abdomen with both ends of the blanket fixed to the sides of the treatment couch or a baseboard. The inner side, or patient side, of the blanket is thinner and expands more than the outer side. When inflated, the blanket balloons and effectively puts an even pressure on the patient's abdomen. Fluoroscopic observation was performed to verify the usefulness of AIB for patients with lung, breast cancer, or abdominal cancers. Internal organ movement due to breathing was monitored and measured with and without AIB. With the help of AIB, the average range of diaphragm motion was reduced from in the anterior‐to‐posterior direction and from in the superior‐to‐inferior direction. The motion range in the right‐to‐left direction was negligible, for it was less than . These initial testing demonstrated that AIB is useful for reducing patients’ breathing motion in the thoracic and abdominal regions comfortably and consistently.
Simultaneous optimization of sequential IMRT plans
Authors: Popple Richard A. , Prellop Perri B. , Spencer Sharon A. , De Los Santos Jennifer F. , Duan Jun , Fiveash John B. , Brezovich Ivan A.
Published: December 2005

Radiotherapy often comprises two phases, in which irradiation of a volume at risk for microscopic disease is followed by a sequential dose escalation to a smaller volume either at a higher risk for microscopic disease or containing only gross disease. This technique is difficult to implement with intensity modulated radiotherapy, as the tolerance doses of critical structures must be respected over the sum of the two plans. Techniques that include an integrated boost have been proposed to address this problem. However, clinical experience with such techniques is limited, and many clinicians are uncomfortable prescribing nonconventional fractionation schemes. To solve this problem, we developed an optimization technique that simultaneously generates sequential initial and boost IMRT plans. We have developed an optimization tool that uses a commercial treatment planning system (TPS) and a high level programming language for technical computing. The tool uses the TPS to calculate the dose deposition coefficients (DDCs) for optimization. The DDCs were imported into external software and the treatment ports duplicated to create the boost plan. The initial, boost, and tolerance doses were specified and used to construct cost functions. The initial and boost plans were optimized simultaneously using a gradient search technique. Following optimization, the fluence maps were exported to the TPS for dose calculation. Seven patients treated using sequential techniques were selected from our clinical database. The initial and boost plans used to treat these patients were developed independently of each other by dividing the tolerance doses proportionally between the initial and boost plans and then iteratively optimizing the plans until a summation that met the treatment goals was obtained. We used the simultaneous optimization technique to generate plans that met the original planning goals. The coverage of the initial and boost target volumes in the simultaneously optimized plans was equivalent to the independently optimized plans actually used for treatment. Tolerance doses of the critical structures were respected for the plan sum; however, the dose to critical structures for the individual initial and boost plans was different between the simultaneously optimized and the independently optimized plans. In conclusion, we have demonstrated a method for optimization of initial and boost plans that treat volume reductions using the same dose per fraction. The method is efficient, as it avoids the iterative approach necessitated by currently available TPSs, and is generalizable to more than two treatment phases. Comparison with clinical plans developed independently suggests that current manual techniques for planning sequential treatments may be suboptimal.
An evaluation of the TSE MR sequence for time efficient data acquisition in polymer gel dosimetry of applications involving high doses and steep dose gradients
Authors: Baras P. , Seimenis I. , Sandilos P. , Vlahos L. , Bieganski T. , Georgiou E. , Pantelis E. , Papagiannis P. , Sakelliou L.
Published: December 2005

The use of magnetic resonance imaging as a readout method for polymer gel dosimetry commonly involves long imaging sessions, particularly when high spatial resolution is required in all three dimensions, for the investigation of dose distributions with steep dose gradients and stringent dose delivery specifications. In this work, a volume selective turbo spin echo (TSE) pulse sequence is compared to the established Carr‐Purcell‐Meiboom‐Gill (CPMG) multiecho acquisition with regard to providing accurate dosimetric results in significantly reduced imaging times. Polyethylene glycol diacrylate based (PABIG) gels were irradiated and subsequently scanned to obtain R2 relaxation rate measurements, using a CPMG multiecho sequence and a dual echo TSE utilizing an acceleration (turbo) factor of 64. R2 values, plotted against corresponding Monte Carlo dose calculations, provided calibration data of PABIG gels dose response over a wide dose range. A linear R2 versus dose relationship was demonstrated for both sequences with TSE results presenting reduced dose sensitivity. Although TSE data were found to deviate from linearity at lower doses compared to CPMG data, a relatively wide dynamic dose range of response extending up to approximately 100 Gy was observed for both sequences. The TSE and CPMG sequences were evaluated with a brachytherapy irradiation using a high dose rate source and a gamma knife stereotactic radiosurgery irradiation with a single 4 mm collimator helmet shot. Dosimetric results obtained with the TSE and CPMG are shown to compare equally well with the expected dose distributions for these irradiations. The 60‐fold scan time reduction achieved with TSE implies that this sequence could prove to be a useful tool for the introduction of polymer gel dosimetry in clinical radiation therapy applications involving high doses and steep dose gradients.
Energy dependence of response of new high sensitivity radiochromic films for megavoltage and kilovoltage radiation energies
Authors: Chiu‐Tsao Sou‐Tung , Ho Yunsil , Shankar Ravi , Wang Lin , Harrison Louis B.
Published: December 2005

The purpose of this paper is to evaluate the energy dependence of the response of two new high sensitivity models of radiochromic films EBT and XR‐QA. We determined the dose response curves of these films for four different radiation sources, namely, photon beams , , , and . The first type (EBT) is designed for intensity modulated radiation therapy (IMRT) dosimetry, and the second type (XR‐QA) is designed for kilovoltage dosimetry. All films were scanned using red and green light sources in a charge‐coupled device‐based densitometer. The dose response curves [net optical density (NOD) versus dose] were plotted and compared for different radiation energies and light sources. Contrary to the early GAFCHROMIC film types (such as models XR, HS, MD55‐2, and HD810), the net optical densities of both EBT and XR‐QA were higher with a green than those with a red light source due to the different absorption spectrum of the new radiochromic emulsion. Both film types yield measurable optical densities for doses below . EBT film response is nearly independent of radiation energy, within the uncertainty of measurement. The NOD values of EBT film at 1 and are 0.13 and 0.25 for green, and 0.1 and 0.17 for red, respectively. In contrast, the XR‐QA film sensitivity varies with radiation energy. The doses required to produce NOD of 0.5 are 6.9, 5.4, 0.7, and with green light and 19, 13, 1.7, and with red light, for , , , and , respectively. EBT film was found to have minimal photon energy dependence of response for the energies tested and is suitable for dosimetry of radiation with a wide energy spectrum, including primary and scattered radiation. XR‐QA film is promising for kilovoltage sources with a narrow energy spectra. The new high sensitivity radiochromic films are promising tools in radiation dosimetry.
Development of high quantum efficiency, flat panel, thick detectors for megavoltage x‐ray imaging: An experimental study of a single‐pixel prototype
Authors: Mei X. , Pang G.
Published: December 2005

Our overall goal is to develop a new generation of electronic portal imaging devices (EPIDs) with a quantum efficiency (QE) more than an order of magnitude higher and a spatial resolution equivalent to that of EPIDs currently used for portal imaging. A novel design of such a high QE flat‐panel based EPID was introduced recently and its feasibility was investigated theoretically [see Pang and Rowlands, Med. Phys. 31, 3004 (2004)]. In this work, we constructed a prototype single‐pixel detector based on the novel design. Some fundamental imaging properties including the QE, spatial resolution, and sensitivity of the prototype detector were measured with a 6 MV beam. It has been shown that the experimental results agree well with theoretical predictions and further development based on the novel design including the construction of a prototype area detector is warranted.
Exact BPF and FBP algorithms for nonstandard saddle curves
Authors: Yu Hengyong , Zhao Shiying , Ye Yangbo , Wang Ge
Published: December 2005

A hot topic in cone‐beam CT research is exact cone‐beam reconstruction from a general scanning trajectory. Particularly, a nonstandard saddle curve attracts attention, as this construct allows the continuous periodic scanning of a volume‐of‐interest (VOI). Here we evaluate two algorithms for reconstruction from data collected along a nonstandard saddle curve, which are in the filtered backprojection (FBP) and backprojection filtration (BPF) formats, respectively. Both the algorithms are implemented in a chord‐based coordinate system. Then, a rebinning procedure is utilized to transform the reconstructed results into the natural coordinate system. The simulation results demonstrate that the FBP algorithm produces better image quality than the BPF algorithm, while both the algorithms exhibit similar noise characteristics.
Improving IMRT quality control efficiency using an amorphous silicon electronic portal imager
Authors: Budgell G. J. , Zhang Q. , Trouncer R. J. , Mackay R. I.
Published: December 2005

An amorphous silicon electronic portal imaging device (EPID) has been investigated to determine its usefulness and efficiency for performing linear accelerator quality control checks specific to step and shoot intensity modulated radiation therapy (IMRT). Several dosimetric parameters were measured using the EPID: dose linearity and segment to segment reproducibility of low dose segments, and delivery accuracy of fractions of monitor units. Results were compared to ion chamber measurements. Low dose beam flatness and symmetry were tested by overlaying low dose beam profiles onto the profile from a stable high‐dose exposure and visually checking for differences. Beam flatness and symmetry were also calculated and plotted against dose. Start‐up reproducibility was tested by overlaying profiles from twenty successive two monitor unit segments. A method for checking the MLC leaf calibration was also tested, designed to be used on a daily or weekly basis, which consisted of summing the images from a series of matched fields. Daily images were co‐registered with, then subtracted from, a reference image. A threshold image showing dose differences corresponding to positional errors was generated and the number of pixels with such dose differences used as numerical parameter to which a tolerance can be applied. The EPID was found to be a sensitive relative dosemeter, able to resolve dose differences of . However, at low absolute doses a reproducible dosimetric nonlinearity of up to 7% due to image lag/ghosting effects was measured. It was concluded that although the EPID is suitable to measure segment to segment reproducibility and fractional monitor unit delivery accuracy, it is still less useful than an ion chamber as a tool for dosimetric checks. The symmetry/flatness test proved to be an efficient method of checking low dose profiles, much faster than any of the alternative methods. The MLC test was found to be extremely sensitive to sudden changes in MLC calibration but works best with a composite reference image consisting of an average of five successive days’ images. When used in this way it proved an effective and efficient daily check of MLC calibration. Overall, the amorphous silicon EPID was found to be a suitable device for IMRT QC although it is not recommended for dosimetric tests. Automatic procedures for low monitor unit profile analysis and MLC leaf positioning yield considerable time‐savings over traditional film techniques.
Intra‐ and interfractional patient motion for a variety of immobilization devices
Authors: Engelsman Martijn , Rosenthal Stanley J. , Michaud Susan L. , Adams Judith A. , Schneider Robert J. , Bradley Stephen G. , Flanz Jacob B. , Kooy Hanne M.
Published: December 2005

The magnitude of inter‐ and intrafractional patient motion has been assessed for a broad set of immobilization devices. Data was analyzed for the three ordinal directions—left–right , sup–inf , and ant–post —and the combined spatial displacement. We have defined “rigid” and “nonrigid” immobilization devices depending on whether they could be rigidly and reproducibly connected to the treatment couch or not. The mean spatial displacement for intrafractional motion for rigid devices is 1.3 mm compared to 1.9 mm for nonrigid devices. The modified Gill–Thomas–Cosman frame performed best at controlling intrafractional patient motion, with a 95% probability of observing a three‐dimensional (3D) vector length of motion of less than 1.8 mm, but could not be evaluated for interfractional motion. All other rigid and nonrigid immobilization devices had a of more than 3 mm for intrafractional patient motion. Interfractional patient motion was only evaluated for the rigid devices. The mean total interfractional displacement was at least 3.0 mm for these devices while was at least 6.0 mm.
Evaluation of a diode array for QA measurements on a helical tomotherapy unit
Authors: Langen K. M. , Meeks S. L. , Poole D. O. , Wagner T. H. , Willoughby T. R. , Zeidan O. A. , Kupelian P. A. , Ruchala K. J. , Olivera G. H.
Published: December 2005

A helical tomotherapy system is used in our clinic to deliver intensity‐modulated radiation therapy (IMRT) treatments. Since this machine is designed to deliver IMRT treatments, the traditional field flatness requirements are no longer applicable. This allows the unit to operate without a field flatness filter and consequently the 400 mm wide fan beam is highly inhomogeneous in intensity. The shape of this beam profile is mapped during machine commissioning and for quality assurance purposes the shape of the beam profile needs to be monitored. The use of a commercial diode array for quality assurance measurements is investigated. Central axis beam profiles were acquired at different depths using solid water built‐up material. These profiles were compared with ion chamber scans taken in a water tank to test the accuracy of the diode array measurements. The sensitivity of the diode array to variations in the beam profile was checked. Over a seven week period, beam profiles were repeatedly measured. The observed variations are compared with those observed with an on‐board beam profile monitor. The diode measurements were in agreement with the ion chamber scans. In the high dose, low gradient region the average ratio between the diode and ion chamber readings was ( standard deviation). In the penumbra region the agreement was poorer but all diodes passed the distance to agreement (DTA) requirement of 2 mm. The trend in the beam profile variations that was measured with the diode array device was in agreement with the on‐board monitor. While the calculated amount of variation differs between the devices, both were sensitive to subtle variations in the beam profile. The diode array is a valuable tool to quickly and accurately monitor the beam profile on a helical tomotherapy unit.
Target motion measurement without implanted markers and its validation by comparison with manually obtained data
Authors: Vences Lucia , Wulf Jörn , Vordermark Dirk , Sauer Otto , Berlinger Kajetan , Roth Michael
Published: December 2005

For an effective radiotherapy the exact tumor location must be determined. The localization has to take into account patient's setup position as well as internal organ motion. Among the different localization methods, the use of a computer tomography (CT) scanner in the therapy room has been proposed recently. Achieving a CT with the patient on the therapy couch, a patient's treatment position is captured. We present a method to locate tumor considering internal organ motion and displacements due to respiration. We tested the method with prostate and lung patients. The method found the most probable tumor position as well as, for high‐mobility tumors located in the lung, its trajectory during the respiratory cycle. The results of this novel method were validated by comparison with manually determined target position.
Cooling of an ideal gas by rapid expansion
Authors: Zimba Jason
Published: December 2005

We consider an ideal gas expansion in which the piston moves at speeds comparable to or greater than the average particle speed. We obtain a limiting expression for the small temperature change that results from this process. This example can help students enrich their understanding of the kinetic theory of gases and the meaning of temperature. Sample questions are included.
Why is the Sun so large?
Authors: Mullan D. J.
Published: December 2005

Although detailed models of the internal structure of the Sun require extensive calculations, the concept of the de Broglie wavelength is sufficient to allow students to obtain a reliable expression for certain parameters of a hydrogen-burning star. We use Coulomb’s Law and the de Broglie wavelength of a proton to demonstrate that the ratio of mass to radius for a star on the main sequence can be expressed as a simple combination of the gravitational constant, Planck’s constant, and the charge of a proton. Further application of the de Broglie wavelength to electrons allows us to derive a lower limit on the radius and mass of a hydrogen-burning star.
Perturbation of a classical oscillator: A variation on a theme of Huygens
Authors: Gil Salvador , Gregorio Daniel E. Di
Published: December 2005

The motion of a particle in different potentials is investigated theoretically and experimentally. The dependence of the period of oscillation on the amplitude is studied for pendula associated with some of these potentials. A technique is proposed to modify the trajectory of a pendulum bob so that it moves along a predetermined curve, and a simple and low cost experiment to study the relation between the period and amplitude for different potentials is discussed. We report on the motion of several pendula whose periods decrease with increasing amplitude. In particular, we study the effects of a perturbation of the form z4 on the frequency of oscillation of a simple harmonic oscillator. Our results agree with the expectation that any perturbation of a simple harmonic oscillator destroys its isochronism.
The fall and bounce of pencils and other elongated objects
Authors: Cross Rod
Published: December 2005

If an inclined pencil is released from rest with its bottom end resting on a table, the bottom end will slide forward or backward or it will remain at rest at the start of the fall, then slide backward for a short period before sliding forward. The magnitude and direction of the displacement of the bottom end of the pencil depends on the initial angle of inclination, the coefficient of friction, and on the length and mass distribution of the pencil. The same ground reaction forces play a similar role in the fall of trees and chimneys, the bounce of a football and any other elongated object, and in activities such as walking and running. When an elongated object is thrown obliquely to the ground, the object can bounce either forward or backward depending on the angle of inclination at impact. Spherical objects bounce away from the thrower. The difference arises because the horizontal friction force is determined not only by the normal reaction force, but also by the line of action of the normal reaction force relative to the center of mass.
A generalized Helmholtz theorem for time-varying vector fields
Authors: Davis Artice M.
Published: December 2005

This paper develops a generalized Helmholtz theorem for an arbitrary localized time-varying vector function F⃗(r⃗,t) and shows that the mathematical relations commonly referred to as Maxwell’s equations can be derived from that theorem alone.