bluuebunny/crossref_metadata_2025 huggingface dataset:
Book Reviews
Authors: RIDOUT M. S.
Published: June 2003

Visualizing Statistical Models and Concepts

(R. W. Farebrother)    C. B. Borkowf

Statistical Consulting

(J. Cabrera and A. McDougall)    A. Cowling

Data Monitoring Committees in Clinical Trials: A Practical Perspective

(S. S. Ellenberg, T. R. Fleming, and D. L. DeMets)    B. Freidlin

Combined Survey Sampling Inference: Weighing Basu's Elephants

(K. Brewer)    Y. G. Berger

Visualising Categorical Data

(M. Friendly)    R. J. Marshall

Estimating Animal Abundance: Closed Populations

(D. L. Borchers, S. T. Buckland, and W. Zucchini)    A. Chao

Likelihood, Bayesian, and MCMC Methods in Quantitative Genetics

(D. Sorensen and D. Gianola)    J. Whittaker

Block Designs: A Randomization Approach, Volumes I and II

(T. Caliński and S. Kageyama)    G. M. Clarke

Computational Statistics Handbook with Matlab

(W. L. Martinez and A. R. Martinez)    P. K. Dunn

Spatial Cluster Modelling

(A. B. Lawson and D. G. T. Denison, eds.)    D. Allard

Elements of Computational Statistics

(J. E. Gentle)    D. M. Smith

Brief Reports by the Editor

A First Course in Linear Model Theory

(N. Ravishanker and D. K. Dey)

Statistical Inference, 2nd edition

(P. H. Garthwaite, I. T. Jolliffe, and B. Jones)

Statistical Analysis of Designed Experiments, 2nd edition

(H. Toutenburg)

Logistic Regression: A Self‐Learning Text, 2nd edition

(D. G. Kleinbaum and M. Klein)

American Series in Mathematical and Management Sciences, Volume 47. USA‐II, Forum for Interdisciplinary Mathematics Proceedings on Statistics, Combinatorics, and Related Areas, Volume II of Proceedings of the University of South Alabama (U.S.A.) Conference (Mobile, Alabama, U.S.A., December 1999)

(S. N. Mishra, ed.)
Variances Are Not Always Nuisance Parameters
Authors: Carroll Raymond J.
Published: June 2003

Summary In classical problems, e.g., comparing two populations, fitting a regression surface, etc., variability is a nuisance parameter. The term “nuisance parameter” is meant here in both the technical and the practical sense. However, there are many instances where understanding the structure of variability is just as central as understanding the mean structure. The purpose of this article is to review a few of these problems. I focus in particular on two issues: (a) the determination of the validity of an assay; and (b) the issue of the power for detecting health effects from nutrient intakes when the latter are measured by food frequency questionnaires. I will also briefly mention the problems of variance structure in generalized linear mixed models, robust parameter design in quality technology, and the signal in microarrays. In these and other problems, treating variance structure as a nuisance instead of a central part of the modeling effort not only leads to inefficient estimation of means, but also to misleading conclusions.
Experimental Measurements of Velocity, Potential, and Temperature Distributions in Liquid Aluminum During Electromagnetic Stirring
Authors: Bakhtiyarov S. I. , Overfelt R. A. , Meir A. J. , Schmidt P. G.
Published: June 2003

An experimental technique has been developed to measure both axial and transverse velocities and temperature distribution in molten aluminum. Couette flow of liquid aluminum, lead, tin, and low melting alloy in cylindrical container was chosen for calibration of the experimental technique and the magnetic probe. Velocity and temperature profiles for liquid aluminum rotating in cylindrical container at different angular velocities are obtained for two different values of the depth. We determined that the velocity values increase with magnetic induction.
Hybrid Analysis Method for Reliability-Based Design Optimization
Authors: Youn Byeng D. , Choi Kyung K. , Park Young H.
Published: June 2003

Reliability-based design optimization (RBDO) involves evaluation of probabilistic constraints, which can be done in two different ways, the reliability index approach (RIA) and the performance measure approach (PMA). It has been reported in the literature that RIA yields instability for some problems but PMA is robust and efficient in identifying a probabilistic failure mode in the optimization process. However, several examples of numerical tests of PMA have also shown instability and inefficiency in the RBDO process if the advanced mean value (AMV) method, which is a numerical tool for probabilistic constraint evaluation in PMA, is used, since it behaves poorly for a concave performance function, even though it is effective for a convex performance function. To overcome difficulties of the AMV method, the conjugate mean value (CMV) method is proposed in this paper for the concave performance function in PMA. However, since the CMV method exhibits the slow rate of convergence for the convex function, it is selectively used for concave-type constraints. That is, once the type of the performance function is identified, either the AMV method or the CMV method can be adaptively used for PMA during the RBDO iteration to evaluate probabilistic constraints effectively. This is referred to as the hybrid mean value (HMV) method. The enhanced PMA with the HMV method is compared to RIA for effective evaluation of probabilistic constraints in the RBDO process. It is shown that PMA with a spherical equality constraint is easier to solve than RIA with a complicated equality constraint in estimating the probabilistic constraint in the RBDO process.
Adaptive Response Surface Method Using Inherited Latin Hypercube Design Points
Authors: Wang G. Gary
Published: June 2003

This paper addresses the difficulty of the previously developed Adaptive Response Surface Method (ARSM) for high-dimensional design problems. ARSM was developed to search for the global design optimum for computation-intensive design problems. This method utilizes Central Composite Design (CCD), which results in an exponentially increasing number of required design experiments. In addition, ARSM generates a complete new set of CCD points in a gradually reduced design space. These two factors greatly undermine the efficiency of ARSM. In this work, Latin Hypercube Design (LHD) is utilized to generate saturated design experiments. Because of the use of LHD, historical design experiments can be inherited in later iterations. As a result, ARSM only requires a limited number of design experiments even for high-dimensional design problems. The improved ARSM is tested using a group of standard test problems and then applied to an engineering design problem. In both testing and design application, significant improvement in the efficiency of ARSM is realized. The improved ARSM demonstrates strong potential to be a practical global optimization tool for computation-intensive design problems. Inheriting LHD points, as a general sampling strategy, can be integrated into other approximation-based design optimization methodologies.
Use of the Finite Element Absolute Nodal Coordinate Formulation in Modeling Slope Discontinuity
Authors: Shabana Ahmed A. , Mikkola Aki M.
Published: June 2003

A large rigid body rotation of a finite element can be described by rotating the axes of the element coordinate system or by keeping the axes unchanged and change the slopes or the position vector gradients. In the first method, the definition of the local element parameters (spatial coordinates) changes with respect to a body or a global coordinate system. The use of this method will always lead to a nonlinear mass matrix and non-zero centrifugal and Coriolis forces. The second method, in which the axes of the element coordinate system do not rotate with respect to the body or the global coordinate system, leads to a constant mass matrix and zero centrifugal and Coriolis forces when the absolute nodal coordinate formulation is used. This important property remains in effect even in the case of flexible bodies with slope discontinuities. The concept employed to accomplish this goal resembles the concept of the intermediate element coordinate system previously adopted in the finite element floating frame of reference formulation. It is shown in this paper that the absolute nodal coordinate formulation that leads to exact representation of the rigid body dynamics can be effectively used in the analysis of complex structures with slope discontinuities. The analysis presented in this paper also demonstrates that objectivity is not an issue when the absolute nodal coordinate formulation is used due to the fact that this formulation automatically accounts for the proper coordinate transformations.
Optimal Internal Structure of Volumes Cooled by Single-Phase Forced and Natural Convection
Authors: Bejan Adrian
Published: June 2003

This article is a principle-based review of a growing body of fundamental research that documents the opportunity for optimizing geometrically the cooling of spaces (e.g., electronics packages) that generate heat volumetrically. The chief result of geometric optimization is the identification of an optimal internal structure—optimal spacings between components (e.g., plates and fins), optimal sizes and aspect ratios for cooling channels, and optimal frequencies for pulsating flows. The origin of these optimal geometric features—the construction of the system—lies in the global effort to use every infinitesimal volume to the maximum, i.e., to pack the volume not only with the most heat generating components, but also with the ‘most’ coolant, in such a way that every fluid packet is engaged effectively in cooling. The optimal aspect ratio for ducts with forced and natural convection corresponds to the special geometry and flow conditions where boundary layers meet just as the coolant exits the channel. This “constructal” design principle is illustrated by several classes of examples: laminar forced and natural convection, and various internal arrangements (parallel plates, staggered plates, cylinders in cross flow, square pins with impinging flow). General trends (scaling laws) of optimal geometric form are revealed by the optimal-structure results, this, in spite of the diversity of the optimized configurations.
Blast Wave Reflection From Wedges
Authors: Igra O. , Hu G. , Falcovitz J. , Heilig W.
Published: June 2003

While a lot of attention was given to shock wave reflections from wedges during the past four decades, only little work was published regarding the similar case of blast wave reflection from wedges. In the present paper this subject is studied experimentally and theoretically/numerically. The obtained results show that the geometry of the reflected wave pattern is similar in the two cases when both incident waves have the same initial pressure jump across their fronts. However, different reflected pressure signatures (history) are observed in these two cases. The pressures obtained behind a reflected shock wave are always higher than those obtained behind the corresponding similar blast wave. In the present case differences as high as 17% were observed.
Thermal Spreading Resistance of Eccentric Heat Sources on Rectangular Flux Channels
Authors: Muzychka Y. S. , Culham J. R. , Yovanovich M. M.
Published: June 2003

A general solution, based on the separation of variables method for thermal spreading resistances of eccentric heat sources on a rectangular flux channel is presented. Solutions are obtained for both isotropic and compound flux channels. The general solution can also be used to model any number of discrete heat sources on a compound or isotropic flux channel using superposition. Several special cases involving single and multiple heat sources are presented.
On the Use of Point Source Solutions for Forced Air Cooling of Electronic Components—Part II: Conjugate Forced Convection From a Discrete Rectangular Source on a Thin Conducting Plate
Authors: Ortega Alfonso , Ramanathan Shankar
Published: June 2003

A model for uniform parallel flow over the surface of a rectangular source of heat on a conducting plate is used to demonstrate the use of analytic Green’s functions to formulate the conjugate problem. The Green’s functions are solutions to the temperature field that arises from a point source of heat on the surface. They provide a relationship between the local heat flux and surface temperature on the plate, effectively serving the same role as the heat transfer coefficient. By coupling the pointwise Green’s function to a finite element discretization of the thin plate, the surface temperature and convective heat flux distributions on the heat source and its substrate are found by a non-iterative procedure. A parametric study shows that at high Peclet numbers, the heat transfer from the source approaches the behavior of an infinite two-dimensional source of heat. The average Nusselt numbers for rectangular sources of different aspect ratios are found to be insensitive to source aspect ratio at high Peclet numbers. Board conduction reduces the average Nusselt numbers over the source when it is defined in terms of the freestream temperature. New correlations for the source Nusselt number as a function of flow Peclet number and board conductivity are presented.
Choosing Working Fluid for Two-Phase Thermosyphon Systems for Cooling of Electronics
Authors: Palm Bjo¨rn , Khodabandeh Rahmatollah
Published: June 2003

The heat fluxes from electronic components are steadily increasing and have now, in some applications, reached levels where air-cooling is no longer sufficient. One alternative solution, which has received much attention during the last decade, is to use heat pipes or thermosyphons for transferring or spreading the dissipated heat. In this paper two-phase thermosyphon loops are discussed. Especially, the choice of fluid and its influence on the design and performance is treated. The discussion is supported by results from simulations concerning heat transfer and pressure drop. In general it is found that high-pressure fluids will give better performance and more compact designs as high-pressure results in higher boiling heat transfer coefficients and smaller necessary tube diameter.
Finite Element Thermal Analysis of Bone Cement for Joint Replacements
Authors: Li Chaodi , Kotha Shiva , Huang Chen-Hsi , Mason James , Yakimicki Don , Hawkins Michael
Published: June 2003

A finite element technique was developed to investigate the thermal behavior of bone cement in joint replacement procedures. Thermal tests were designed and performed to provide the parameters in a kinetic model of bone cement exothermic polymerization. The kinetic model was then coupled with an energy balance equation using a finite element formulation to predict the temperature history and polymerization development in the bone-cement-prosthesis system. Based on the temperature history, the possibility of the thermal bone necrosis was then evaluated. As a demonstration, the effect of cement mantle thickness on the thermal behavior of the system was investigated. The temperature profiles in the bone-cement-prosthesis system have shown that the thicker the cement, the higher the peak temperature in the bone. In the 7 mm thick cement case, a peak temperature of over 55°C was predicted. These high temperatures occurred in a small region near the bone/cement interface. No damage was predicted in the 3 mm and 5 mm cement mantle thickness cases. Although thermal damage was predicted in the bone for the 7 mm mantle thickness case, the amount of thermal necrosis predicted was minimal. If more cement is used in the surgical procedure, more heat will be generated and the potential for thermal bone damage may rise. The systems should be carefully selected to reduce thermal tissue damage when more cement is used. The methodology developed in this paper provides a numerical tool for the quantitative simulation of the thermal behavior of bone-cement-prosthesis designs.
Elastic Singularity Interacting With Various Types of Interfaces
Authors: Choi S. T. , Earmme Y. Y.
Published: June 2003

The elastic solution for a singularity in an anisotropic trimaterial with perfectly bonded interfaces was obtained in the previous work by Choi and Earmme. The term “trimaterial” denotes an infinite body composed of three dissimilar materials bonded along two parallel interfaces. It is shown in this paper that when the interfaces of an anisotropic trimaterial are one of the following types: (i) perfectly bonded, (ii) rigid, (iii) separated, (iv) separated without slip, and (v) slipping interfaces, the elastic solution for a singularity in the trimaterial has the same form as that for a singularity in a trimaterial with perfectly bonded interfaces, but with the bimaterial matrices properly altered.
Effects of Wall Motion and Compliance on Flow Patterns in the Ascending Aorta
Authors: Jin Suo , Oshinski John , Giddens Don P.
Published: June 2003

Helical flows have been observed in the ascending aorta in vivo, and geometric curvature has been suggested to be a major contributing factor. We employed magnetic resonance imaging (MRI) and velocity mapping to develop a computational model to examine the effects of curvature and also wall compliance and movement upon flow patterns. In the computational model, MRI-derived geometry and velocities were imposed as boundary conditions, which included both radial expansion-contraction and translational motion of the wall. The computed results were in agreement with the MR data only when full wall motion was included in the model, suggesting that the flow patterns observed in the ascending aorta arise not only from geometric curvature of the arch but also from the motion of the aorta resulting from its attachment to the beating heart.
Evaluation of the transmitted exposure through lead equivalent aprons used in a radiology department, including the contribution from backscatter
Authors: Christodoulou Emmanuel G. , Goodsitt Mitchell M. , Larson Sandra C. , Darner Katie L. , Satti Jahangir , Chan Heang‐Ping
Published: June 2003

A study was conducted to evaluate the radiation transmission through lead equivalent aprons that are used in a radiology department. A large area beam (poor geometry) was employed for the transmission measurements, and backscatter was simulated by placing of Lucite behind each apron. Separate ionization chambers were used to measure the incident and transmitted x‐ray beams. Transmission measurements were made at 70 kVp and 100 kVp through aprons and protective shields from eight different vendors that were marked 0.25 mm and 0.5 mm lead equivalent. Transmissions through 0.254 mm and 0.508 mm of pure lead were also measured and were compared with the transmissions through the lead equivalent materials. In addition, the area densities of the aprons were measured to compare radiation transmission with respect to the weights of the aprons. At 70 kVp, the transmission through 0.254 mm of pure lead was 5.4% and the transmissions through the 0.25 mm lead equivalent materials were 4.3% to 10.2% with a mean value of 7.1% and a standard deviation (s.d.) of 1.4%. At 100 kVp, the values were 15% for 0.254 mm pure lead and 12.3% to 20.7% (mean 16.8%, s.d. 2.1%) for the 0.25 mm lead equivalent materials. The transmission through the 0.508 mm pure lead sample was 0.9% at 70 kVp, and the corresponding transmissions through the 0.5 mm lead equivalent materials were 0.6% to 1.6% (mean 1.0%, s.d. 0.2%). At 100 kVp, the transmission through the 0.508 mm lead sample was 5% and those through the 0.5 mm lead equivalent materials were 3.5% to 6.7% (mean 4.9%, s.d. 0.7%). The radiation transmissions at 70 kVp, through two “lead‐free” 0.5 mm lead equivalent aprons, were 1.7% and 1.9% and at 100 kVp the transmissions were 6.1% and 6.8%, respectively. This study indicates that there is a need to establish methods for acceptance testing of aprons and a need to establish acceptance limits for the x‐ray transmission of aprons at specific kVp values. There is also a need for the establishment of appropriate methods and frequencies of routine quality assurance testing of radiation protection aprons.
Evaluation of mechanical precision and alignment uncertainties for an integrated CT/LINAC system
Authors: Court Laurence , Rosen Isaac , Mohan Radhe , Dong Lei
Published: June 2003

A new integrated CT/LINAC combination, in which the CT scanner is inside the radiation therapy treatment room and the same patient couch is used for CT scanning and treatment (after a 180‐degree couch rotation), should allow for accurate correction of interfractional setup errors. The purpose of this study was to evaluate the sources of uncertainties, and to measure the overall precision of this system. The following sources of uncertainty were identified: (1) the patient couch position on the LINAC side after a rotation, (2) the patient couch position on the CT side after a rotation, (3) the patient couch position as indicated by its digital readout, (4) the difference in couch sag between the CT and LINAC positions, (5) the precision of the CT coordinates, (6) the identification of fiducial markers from CT images, (7) the alignment of contours with structures in the CT images, and (8) the alignment with setup lasers. The largest single uncertainties (one standard deviation or 1 SD) were found in couch position on the CT side after a rotation (0.5 mm in the RL direction) and the alignment of contours with the CT images (0.4 mm in the SI direction). All other sources of uncertainty are less than 0.3 mm (1 SD). The overall precision of two setup protocols was investigated in a controlled phantom study. A protocol that relies heavily on the mechanical integrity of the system, and assumes a fixed relationship between the LINAC isocenter and the CT images, gave a predicted precision (1 SD) of 0.6, 0.7, and 0.6 mm in the SI, RL and AP directions, respectively. The second protocol reduces reliance on the mechanical precision of the total system, particularly the patient couch, by using radio‐opaque fiducial markers to transfer the isocenter information from the LINAC side to the CT images. This protocol gave a slightly improved predicted precision of 0.5, 0.4, and 0.4 mm in the SI, RL and AP directions, respectively. The distribution of phantom position after CT‐based correction confirmed these results. Knowledge of the individual sources of uncertainty will allow alternative setup protocols to be evaluated in the future without the need for significant additional measurements.
Focal spot motion of linear accelerators and its effect on portal image analysis
Authors: Sonke Jan‐Jakob , Brand Bob , van Herk Marcel
Published: June 2003

The focal spot of a linear accelerator is often considered to have a fully stable position. In practice, however, the beam control loop of a linear accelerator needs to stabilize after the beam is turned on. As a result, some motion of the focal spot might occur during the start‐up phase of irradiation. When acquiring portal images, this motion will affect the projected position of anatomy and field edges, especially when low exposures are used. In this paper, the motion of the focal spot and the effect of this motion on portal image analysis are quantified. A slightly tilted narrow slit phantom was placed at the isocenter of several linear accelerators and images were acquired (3.5 frames per second) by means of an amorphous silicon flat panel imager positioned ∼0.7 m below the isocenter. The motion of the focal spot was determined by converting the tilted slit images to subpixel accurate line spread functions. The error in portal image analysis due to focal spot motion was estimated by a subtraction of the relative displacement of the projected slit from the relative displacement of the field edges. It was found that the motion of the focal spot depends on the control system and design of the accelerator. The shift of the focal spot at the start of irradiation ranges between 0.05–0.7 mm in the gun‐target (GT) direction. In the left–right (AB) direction the shift is generally smaller. The resulting error in portal image analysis due to focal spot motion ranges between 0.05–1.1 mm for a dose corresponding to two monitor units (MUs). For 20 MUs, the effect of the focal spot motion reduces to 0.01–0.3 mm. The error in portal image analysis due to focal spot motion can be reduced by reducing the applied dose rate.
A method for the reconstruction of four‐dimensional synchronized CT scans acquired during free breathing
Authors: Low Daniel A. , Nystrom Michelle , Kalinin Eugene , Parikh Parag , Dempsey James F. , Bradley Jeffrey D. , Mutic Sasa , Wahab Sasha H. , Islam Tareque , Christensen Gary , Politte David G. , Whiting Bruce R.
Published: June 2003

Breathing motion is a significant source of error in radiotherapy treatment planning for the thorax and upper abdomen. Accounting for breathing motion has a profound effect on the size of conformal radiation portals employed in these sites. Breathing motion also causes artifacts and distortions in treatment planning computed tomography (CT) scans acquired during free breathing and also causes a breakdown of the assumption of the superposition of radiation portals in intensity‐modulated radiation therapy, possibly leading to significant dose delivery errors. Proposed voluntary and involuntary breath‐hold techniques have the potential for reducing or eliminating the effects of breathing motion, however, they are limited in practice, by the fact that many lung cancer patients cannot tolerate holding their breath. We present an alternative solution to accounting for breathing motion in radiotherapy treatment planning, where multislice CT scans are collected simultaneously with digital spirometry over many free breathing cycles to create a four‐dimensional (4‐D) image set, where tidal lung volume is the additional dimension. An analysis of this 4‐D data leads to methods for digital‐spirometry, based elimination or accounting of breathing motion artifacts in radiotherapy treatment planning for free breathing patients. The 4‐D image set is generated by sorting free‐breathing multislice CT scans according to user‐defined tidal‐volume bins. A multislice CT scanner is operated in the ciné mode, acquiring 15 scans per couch position, while the patient undergoes simultaneous digital‐spirometry measurements. The spirometry is used to retrospectively sort the CT scans by their correlated tidal lung volume within the patient's normal breathing cycle. This method has been prototyped using data from three lung cancer patients. The actual tidal lung volumes agreed with the specified bin volumes within standard deviations ranging between 22 and 33 An analysis of sagittal and coronal images demonstrated relatively small (<1 cm) motion artifacts along the diaphragm, even for tidal volumes where the rate of breathing motion is greatest. While still under development, this technology has the potential for revolutionizing the radiotherapy treatment planning for the thorax and upper abdomen.
MAGIC‐type polymer gel for three‐dimensional dosimetry: Intensity‐modulated radiation therapy verification
Authors: Gustavsson Helen , Karlsson Anna , Bäck Sven Å. J. , Olsson Lars E. , Haraldsson Pia , Engström Per , Nyström Håkan
Published: June 2003

A new type of polymer gel dosimeter, which responds well to absorbed dose even when manufactured in the presence of normal levels of oxygen, was recently described by Fong et al. [Phys. Med. Biol. 46, 3105–3113 (2001)] and referred to by the acronym MAGIC. The aim of this study was to investigate the feasibility of using this new type of gel for intensity‐modulated radiation therapy (IMRT) verification. Gel manufacturing was carried out in room atmosphere under normal levels of oxygen. IMRT inverse treatment planning was performed using the Helios software. The gel was irradiated using a linear accelerator equipped with a dynamic multileaf collimator, and intensity modulation was achieved using sliding window technique. The response to absorbed dose was evaluated using magnetic resonance imaging. Measured and calculated dose distributions were compared with regard to in‐plane isodoses and dose volume histograms. In addition, the spatial and dosimetric accuracy was evaluated using the gamma formalism. Good agreement between calculated and measured data was obtained. In the isocenter plane, the 70% and 90% isodoses acquired using the different methods are mostly within 2 mm, with up to 3 mm disagreement at isolated points. For the planning target volume (PTV), the calculated mean relative dose was (1 SD) and the measured relative mean dose was Corresponding data for an organ at risk was and respectively. The gamma criterion (3 mm spatial/3% dose deviation) was fulfilled for 94% of the pixels in the target region. Discrepancies were found in hot spots the upper and lower parts of the PTV, where the measured dose was up to 11% higher than calculated. This was attributed to sub optimal scatter kernels used in the treatment planning system dose calculations. Our results indicate great potential for IMRT verification using MAGIC‐type polymer gel.
Benchmarking beam alignment for a clinical helical tomotherapy device
Authors: Balog John , Mackie T. R. , Pearson D. , Hui Susanta , Paliwal Bhudatt , Jeraj Robert
Published: June 2003

A clinical helical tomotherapy treatment machine has been installed at the University of Wisconsin Comprehensive Cancer Center. Beam alignment has been finalized and accepted by UW staff. Helical tomotherapy will soon be clinically available to other sites. Clinical physicists who expect to work with this machine will need to be familiar with its unique dosimetric characteristics, and those related to the geometrical beam configuration and its verification are described here. A series of alignment tests and the results are presented. Helical tomotherapy utilizes an array of post‐patient xenon‐filled megavoltage radiation detectors. These detectors have proved capable of performing some alignment verification tests. That is particularly advantageous because those tests can then be automated and easily performed on an ongoing basis.
A new look at CT dose measurement: Beyond CTDI
Authors: Dixon Robert L.
Published: June 2003

Equations are derived for generating accumulated dose distributions and the dose line integral in a cylindrical dosimetry phantom for a helical CT scan series from the single slice dose profiles using convolution methods. This exposition will better clarify the nature of the dose distribution in helical CT, as well as providing the medical physicist with a better understanding of the physics involved in dose delivery and the measurement process. Also addressed is the concern that as radiation beam widths for multi‐slice scanners get wider, the current methodology based on the measurement of the integral of the single slice profile using a 10 cm long ion chamber may no longer be adequate. It is shown that this measurement would underestimate the equilibrium dose and dose line integral by about 20% in the center of the body phantom, and by about 10% in the center of the head phantom for a 20 mm nominal beam width in a multi‐slice scanner. Rather than making the ion chamber even longer to collect the broad scatter tails of the single slice profile, an alternative to the CTDI method is suggested which involves using a small volume ion chamber, and scanning a length of phantom long enough to establish dose equilibrium at the location of the chamber. With a modern CT scanner, such a scan length can be covered in 15 s or less with a helical or axial series, so this method is not significantly more time‐consuming than the long chamber method. The method is demonstrated experimentally herein.
A new framework of image reconstruction from fan beam projections
Authors: Chen Guang‐Hong
Published: June 2003

In this paper, we present a unified framework to reconstruct images for both fan beam and cone beam projections. The important feature of our theoretical framework is that it does not depend on the classical concept of the Radon transform at all. This property allows us to directly generalize the ideas and techniques developed in this paper to the cone beam reconstruction problem. In this paper, we extract such a framework from developing a new image reconstruction scheme from fan beam projections. Our new scheme also provides us new understanding of fan beam reconstruction problem. Our main results for the fan beam reconstruction are the following: First, we derive a general reconstruction scheme, in which the data sufficiency condition is transparently revealed by the reconstruction formula. Specifically, the data sufficiency condition for an accurate reconstruction of a region of interest (ROI) is that all the lines passing through the ROI must intersect the source trajectory at least once. Second, we further simplify the general reconstruction scheme by following three major steps of our new framework: (i) using symmetries of intermediate function; (ii) handling the data redundancy; (iii) changing discrete summation over the possible focal points into an integral along the source trajectory. After these steps, we obtain a new filtered backprojection algorithm. The key characteristic of this new algorithm is to take derivative of measured data with respect to the trajectory parameter. In practice, we can trade this derivative to some other continuous functions. In the configuration of a circular source trajectory with a third generation arc/collinear detector, we demonstrate how to remove the undesirable derivative of measured projection data. It results in a new algorithm for the sequential reconstruction of a ROI with a general normalized weighting function.
Flow of sand and a variable mass Atwood machine
Authors: Flores José , Solovey Guillermo , Gil Salvador
Published: June 2003

We discuss a simple and inexpensive apparatus that lets us measure the instantaneous flow rate of granular media, such as sand, in real time. The measurements allow us to elucidate the phenomenological laws that govern the flow of granular media through an aperture. We use this apparatus to construct a variable mass system and study the motion of an Atwood machine with one weight changing in time in a controlled manner. The study illustrates Newton’s second law for variable mass systems and lets us investigate the dependence of the flow rate on acceleration.
Asteroid impact and eccentricity of Earth’s orbit
Authors: Mohazzabi Pirooz , Luecke James A.
Published: June 2003

We obtain a simple equation that accurately describes the eccentricity that an asteroid or comet impact can cause in the Earth’s nearly circular orbit about the Sun. It is found that the present eccentricity of the Earth could not have been caused or significantly altered by an asteroid or comet impact in the near past, nor could it be significantly altered by the impact of any asteroid or comet known to astronomers today.
Impact Ejecta Layer from the Mid-Devonian: Possible Connection to Global Mass Extinctions
Authors: Ellwood Brooks B. , Benoist Stephen L. , Hassani Ahmed El , Wheeler Christopher , Crick Rex E.
Published: June 2003

We have found evidence for a bolide impacting Earth in the mid-Devonian (∼380 million years ago), including high concentrations of shocked quartz, Ni, Cr, As, V, and Co anomalies; a large negative carbon isotope shift (–9 per mil); and microspherules and microcrysts at Jebel Mech Irdane in the Anti Atlas desert near Rissani, Morocco. This impact is important because it is coincident with a major global extinction event (Kacák/
otomari
event), suggesting a possible cause-and-effect relation between the impact and the extinction. The result may represent the extinction of as many as 40% of all living marine animal genera.
Transcription Start Regions in the Human Genome Are Favored Targets for MLV Integration
Authors: Wu Xiaolin , Li Yuan , Crise Bruce , Burgess Shawn M.
Published: June 2003

Factors contributing to retroviral integration have been intractable because past studies have not precisely located genomic sites of proviruses in sufficient numbers for significant analysis. In this study, 903 murine leukemia virus (MLV) and 379 human immunodeficiency virus–1 (HIV-1) integrations in the human genome were mapped. The data showed that MLV preferred integration near the start of transcriptional units (either upstream or downstream) whereas HIV-1 preferred integration anywhere in the transcriptional unit but not upstream of the transcriptional start. Defining different integration site preferences for retroviruses will have important ramifications for gene therapy and may aid in our understanding of the factors directing the integration process.
Interference of Quantized Transition-State Pathways in the H + D
2
→ D + HD Chemical Reaction
Authors: Dai Dongxu , Wang Chia C. , Harich Steven A. , Wang Xiuyan , Yang Xueming , Der Chao Sheng , Skodje Rex T.
Published: June 2003

The collision-energy dependence of the state-resolved differential cross section at a specific backward-scattering angle for the reaction H + D
2
→ D + HD is measured with the D-atom Rydberg “tagging” time-of-flight technique. The reaction was modeled theoretically with converged quantum scattering calculations that provided physical interpretation of the observations. Oscillations in the differential cross sections in the backward-scattering direction are clearly observed and are attributed to the transition-state structures that originate from the interferences of different quantized transition-state pathways.
A Live Attenuated Equine Infectious Anemia Virus Proviral Vaccine with a Modified
S2
Gene Provides Protection from Detectable Infection by Intravenous Virulent Virus Challenge of Experimentally Inoculated Horses
Authors: Li Feng , Craigo Jodi K. , Howe Laryssa , Steckbeck Jonathan D. , Cook Sheila , Issel Charles , Montelaro Ronald C.
Published: June 2003

Previous evaluations of inactivated whole-virus and envelope subunit vaccines to equine infectious anemia virus (EIAV) have revealed a broad spectrum of efficacy ranging from highly type-specific protection to severe enhancement of viral replication and disease in experimentally immunized equids. Among experimental animal lentivirus vaccines, immunizations with live attenuated viral strains have proven most effective, but the vaccine efficacy has been shown to be highly dependent on the nature and severity of the vaccine virus attenuation. We describe here for the first time the characterization of an experimental attenuated proviral vaccine, EIAV
UK
ΔS2, based on inactivation of the
S2
accessory gene to down regulate in vivo replication without affecting in vitro growth properties. The results of these studies demonstrated that immunization with EIAV
UK
ΔS2 elicited mature virus-specific immune responses by 6 months and that this vaccine immunity provided protection from disease and detectable infection by intravenous challenge with a reference virulent biological clone, EIAV
PV
. This level of protection was observed in each of the six experimental horses challenged with the reference virulent EIAV
PV
by using a low-dose multiple-exposure protocol (three administrations of 10 median horse infectious doses [HID
50
], intravenous) designed to mimic field exposures and in all three experimentally immunized ponies challenged intravenously with a single inoculation of 3,000 HID
50
. In contrast, naïve equids subjected to the low- or high-dose challenge develop a detectable infection of challenge virus and acute disease within several weeks. Thus, these data demonstrate that the EIAV
S2
gene provides an optimal site for modification to achieve the necessary balance between attenuation to suppress virulence and replication potential to sufficiently drive host immune responses to produce vaccine immunity to viral exposure.
High-Frequency Genetic Recombination and Reactivation of Orthopoxviruses from DNA Fragments Transfected into Leporipoxvirus-Infected Cells
Authors: Yao Xiao-Dan , Evans David H.
Published: June 2003

Poxvirus DNA is not infectious because establishing an infection requires the activities of enzymes packaged in the virion. This barrier can be overcome by transfecting virus DNA into cells previously infected with another poxvirus, since the resident virus can provide the
trans
-acting systems needed to reactivate transfected DNA. In this study we show that cells infected with a leporipoxvirus, Shope fibroma virus (SFV), can reactivate vaccinia virus DNA. Similar heterologous packaging systems which used fowlpox-infected cells to reactivate vaccinia virus have been described, but SFV-infected cells promoted a far more efficient reaction that can produce virus titers exceeding 10
6
PFU/μg of transfected DNA. SFV-promoted reactions also exploit the hyperrecombinogenic systems previously characterized in SFV-infected cells, and these coupled recombination and reactivation reactions could be used to delete nonessential regions of the vaccinia virus genome and to reconstruct vaccinia virus from overlapping DNA fragments. SFV-catalyzed recombination reactions need only two 18- to 20-bp homologies to target PCR amplicons to restriction enzyme-cut vaccinia virus vectors, and this reaction feature was used to rapidly clone and express a gene encoding fluorescent green protein without the need for plaque purification or selectable markers. The ability of SFV-infected cells to reactivate fragments of vaccinia virus was ultimately limited by the number of recombinational exchanges required and one cannot reconstruct vaccinia virus from multiple PCR fragments spanning essential portions of the genome. These observations suggest that recombination is an integral part of poxvirus reactivation reactions and provide a useful new technique for altering the structure of poxvirus genomes.
p21Waf1/Cip1/Sdi1Prevents Apoptosis as Well as Stimulates Growth in Cells Transformed or Immortalized by Human T-Cell Leukemia Virus Type 1-Encoded Tax
Authors: Kawata Sanae , Ariumi Yasuo , Shimotohno Kunitada
Published: June 2003

Human T-cell leukemia virus type 1 (HTLV-1) Tax regulates the expression of virally encoded genes, as well as various endogenous host genes intrans. Tax-mediated regulation of gene expression is important for the immortalization of normal human T lymphocytes and the transformation of fibroblast cells, such as Rat-1 cells. Tax has the ability to transactivate p21Waf1/Cip1/Sdi1, resulting in high expression levels in HTLV-1-immortalized cells. Since p21 expression is suppressed due to methylation of the promoter region in Rat-l cell line, p21 may not be critical for the transformation of this cell line by Tax. To further understand the role of p21 for the proliferation of Tax-transformed Rat-1 cells, we examined the effect of ectopic expression of p21 in these cells. Here, we observed that p21 expression enhanced the transformation of this cell line via at least two mechanisms: (i) the enhancement of NF-κB activation and/or CREB signaling and (ii) the excitation of antiapoptotic machinery. To analyze the role of p21 that is overexpressed in HTLV-1-immortalized lymphocytes, p21 expression was suppressed by using an antisense oligonucleotide specific for p21 mRNA; these cells then became sensitive to apoptotic induction. These results suggest that p21 plays an important role in the proliferation of Tax-expressing cells through the regulation of at least two independent mechanisms.
Viability of Poliovirus/Rhinovirus VPg Chimeric Viruses and Identification of an Amino Acid Residue in the VPg Gene Critical for Viral RNA Replication
Authors: Cheney I. Wayne , Naim Suhaila , Shim Jae Hoon , Reinhardt Meghan , Pai Bharati , Wu Jim Z. , Hong Zhi , Zhong Weidong
Published: June 2003

Picornaviral RNA replication utilizes a small virus-encoded protein, termed 3B or VPg, as a primer to initiate RNA synthesis. This priming step requires uridylylation of the VPg peptide by the viral polymerase protein 3D
pol
, in conjunction with other viral or host cofactors. In this study, we compared the viral specificity in 3D
pol
-catalyzed uridylylation reactions between poliovirus (PV) and human rhinovirus 16 (HRV16). It was found that HRV16 3D
pol
was able to uridylylate PV VPg as efficiently as its own VPg, but PV 3D
pol
could not uridylylate HRV16 VPg. Two chimeric viruses, PV containing HRV16 VPg (PV/R16-VPg) and HRV16 containing PV VPg (R16/PV-VPg), were constructed and tested for replication capability in H1-HeLa cells. Interestingly, only PV/R16-VPg chimeric RNA produced infectious virus particles upon transfection. No viral RNA replication or cytopathic effect was observed in cells transfected with R16/PV-VPg chimeric RNA, despite the ability of HRV16 3D
pol
to uridylylate PV VPg in vitro. Sequencing analysis of virion RNA isolated from the virus particles generated by PV/R16-VPg chimeric RNA identified a single residue mutation in the VPg peptide (Glu
6
to Val). Reverse genetics confirmed that this mutation was highly compensatory in enhancing replication of the chimeric viral RNA. PV/R16-VPg RNA carrying this mutation replicated with similar kinetics and magnitude to wild-type PV RNA. This cell culture-induced mutation in HRV16 VPg moderately increased its uridylylation by PV 3D
pol
in vitro, suggesting that it might be involved in other function(s) in addition to the direct uridylylation reaction. This study demonstrated the use of chimeric viruses to characterize viral specificity and compatibility in vivo between PV and HRV16 and to identify critical amino acid residue(s) for viral RNA replication.
Coexistence of Two Distinct Secretion Mutations (P5T and I97L) in Hepatitis B Virus Core Produces a Wild-Type Pattern of Secretion
Authors: Chua Pong Kian , Wen Yu-Mei , Shih Chiaho
Published: June 2003

Unlike a Tokyo isolate of hepatitis B virus variants, we found a Shanghai isolate that secretes few virions with an immature genome despite its core I97L mutation. Core mutations P5T and I97L were found to be mutually compensatory in offsetting their respective distinct effects on virion secretion.
Replication-Competent Hybrids between Murine Leukemia Virus and Foamy Virus
Authors: Shikova-Lekova Evelina , Lindemann Dirk , Pietschmann Thomas , Juretzek Thomas , Rudolph Wolfram , Herchenröder Ottmar , Gelderblom Hans R. , Rethwilm Axel
Published: June 2003

Replication-competent chimeric retroviruses constructed of members of the two subfamilies of
Retroviridae
, orthoretroviruses and spumaretroviruses, specifically murine leukemia viruses (MuLV) bearing hybrid MuLV-foamy virus (FV) envelope (
env
) genes, were characterized. All viruses had the cytoplasmic tail of the MuLV transmembrane protein. In ESL-1, a truncated MuLV leader peptide (LP) was fused to the complete extracellular portion of FV Env, and ESL-2 to -4 contained the complete MuLV-LP followed by N-terminally truncated FV Env decreasing in size. ESL-1 to -4 had an extended host cell range compared to MuLV, induced a cytopathology reminiscent of FVs, and exhibited an ultrastructure that combined the features of the condensed core of MuLV with the prominent surface knobs of FVs. Replication of ESL-2 to -4 resulted in the acquisition of a stop codon at the N terminus of the chimeric Env proteins. This mutation rendered the MuLV-LP nonfunctional and indicated that the truncated FV-LP was sufficient to direct Env synthesis into the secretory pathway. Compared to the parental viruses, the chimeras replicated with only moderate cell-free titers.