bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhancement and Desire: Japanese Qualms about Where Biotechnology is Taking Us
Authors: LaFleur William R.
Published: March 2008

In what follows, I draw on things I have found in Japanese discussions of bioethics in order to clarify some aspects of the ethics of biotechnological enhancement. In doing so it will, I hope, become evident that what we might call a “religious” component is in Japan somewhat differently construed than in the contexts with which we are more likely to be familiar in North America. And in the end an attempt will be made here to show that the materials considered give us all – not just the Japanese – reasons for going forward with biological enhancement technologies only on condition that extreme caution be exercised. The fast-moving, oncoming traffic in this domain ought to be forced, these materials suggest, to come up to a caution-demanding signal – not a green light but one that is unambiguously amber. Caution and perhaps even a full stop appear to be in order.
Hormone Therapy, Dilemmas, Medical Decisions
Authors: Schulkin Jay
Published: March 2008

The question of why women, in consultation with their physicians, should choose hormone therapy (HT) in response to menopause represents a renewed controversy at the beginning of the new century. Conflicting messages regarding the health risks and benefits of HT have been conveyed in the mainstream media, especially information in the media regarding the results of large-scale studies of the health impact of hormone therapy. Women who have been on one or another of the hormone replacement regimes have been forced to reconsider continuing on HT. Doctors who suggest these hormones to their patients are somewhat confused, as are perimenopausal women who are considering HT. Pharmaceutical companies that produce these compounds are worried, and public health officials are on the defensive.

Media coverage of HT research has been extensive. In particular, two large-scale studies, one here in the U.S. (the Women's Health Initiative, or WHI) and the other in Great Britain, have recently cast a negative light on the use of hormone therapy, after years of routine prescription of HT for menopausal women.
Recent Developments in Health Law
Authors: Lee Won Bok , Shachar Carmel , Chang Peter
Published: March 2008

In May of 2006, the Abigail Alliance for Better Access to Development Drugs (Abigail) appeared to have won a victory when a divided panel of the Court of Appeals for the District of Columbia Circuit (D.C. Circuit) ruled that “terminally ill, mentally competent adult patients” had a constitutionally protected right to access investigational medications. This victory was short lived, however. On August 7, 2007, the D.C. Circuit sitting en banc reversed this earlier decision, marking a setback in Abigail's campaign for removal of the regulatory barriers that currently prevent terminally ill patients from gaining early access to investigational drugs (i.e., experimental drugs). This loss represents a big blow for Abigail's cause, because there is no guarantee that they will have another day in court, and attaining their goal through other branches of the government remains uncertain.
Assessing Laws and Legal Authorities for Public Health Emergency Legal Preparedness
Authors: Kamoie Brian , Pestronk Robert M. , Baldridge Peter , Fidler David , Devlin Leah , Mensah George A. , Doney Michael
Published: March 2008

Public health legal preparedness begins with effective legal authorities, and law provides a key foundation for public health practice in the United States. Laws not only create public health agencies and fund them, but also authorize and impose duties upon government to protect the public's health while preserving individual liberties. As a result, law is an essential tool in public health practice and is one element of public health infrastructure, as it defines the systems and relationships within which public health practitioners operate.

For purposes of this paper, law can be defined as a rule of conduct derived from federal or state constitutions, statutes, local laws, judicial opinions, administrative rules and regulations, international codes, or other pronouncements by entities authorized to prescribe conduct in a legally binding manner. Public health legal preparedness, a subset of public health preparedness, is defined as attainment of legal benchmarks within a public health system.
Improving Cross-Sectoral and Cross-Jurisdictional Coordination for Public Health Emergency Legal Preparedness
Authors: Bullard Cheryl H. , Hogan Rick D. , Penn Matthew S. , Ferris Janet , Cleland John , Stier Daniel , Davis Ronald M. , Allan Susan , Van de Putte Leticia , Caine Virginia , Besser Richard E. , Gravely Steven
Published: March 2008

This paper is one of the four interrelated action agenda papers resulting from the National Summit on Public Health Legal Preparedness (Summit) convened in June 2007 by the Centers for Disease Control and Prevention (CDC) and multi-disciplinary partners. Each of the action agenda papers deals with one of the four core elements of public health legal preparedness: laws and legal authorities; competency in using those laws; coordination of law-based public health actions; and information. Options presented in this paper are for consideration by policy makers and practitioners — in all jurisdictions and all relevant sectors and disciplines — with responsibilities for all-hazards emergency preparedness.

Advancing and protecting the public's health depends upon the coordination of actions by many, diverse partners. For effective public health preparedness, there must be effective coordination of legal tools and law-based strategies across local, state, tribal, and federal jurisdictions, and also across sectors such as public health, health care, emergency management, education, law enforcement, community design, and academia.
History of the Care of Displaced Children in Korea
Authors: Kim Jung‐Woo , Henderson Terry
Published: March 2008

The present article explores the current nature and history of welfare provision for displaced children in Korea. It examines the early examples of care and the perspectives on the issue from scholars, lawmakers, religion and society as a whole. This provides an understanding of the background and, especially, the cultural roots of existing care. A history of what may be considered the first modern displaced child welfare provision is also given with analysis of how Christian and local approaches and perceptions integrated. This was to form the basis for present‐day transitional displaced child welfare in Korea. For this reason, the article examines the provision in a paradigm which looks at the provision as responses to Western influences. Features of congregate care, domestic/international adoptions, foster care and youth‐headed households are examined. The authors conclude that global forces will continue to be influential and recommends that religious institutions which have thus far provided crucial contributions to the foundation of care should continue to play key roles with the government’s facilitation. The need for wide participation from society and coordination from the government to manage systems, develop strategies and build consensus is highlighted.
Distribution of virF/lcrF‐positive Yersinia pseudotuberculosis Serotype O:3 at Farm Level
Authors: Niskanen T. , Laukkanen R. , Fredriksson‐Ahomaa M. , Korkeala H.
Published: March 2008

The distribution and persistence of pathogenic, virF/lcrF‐positive Yersinia pseudotuberculosis were investigated in pigs and in the pig house environment during rearing to determine possible contamination routes of early infections. Based on Y. pseudotuberculosis‐positive tonsils of slaughter pigs in our previous study, Y. pseudotuberculosis‐positive animals were traced back to the farms. Eight farms were visited from 6–10 months later, and a total of 155 pooled and six individual faecal samples from pigs and 116 pooled environmental samples were collected for analysis by different culture methods. Four of the eight farms were found to be Y. pseudotuberculosis‐positive. All positive faecal samples were obtained from fattening pigs, with prevalence varying from 5% to 71% on positive farms. Sows, boars and suckling piglets were Y. pseudotuberculosis‐negative on all farms. Most Y. pseudotuberculosis‐positive farms (three of four) were on a one‐site production system, which had a higher prevalence of Y. pseudotuberculosis (5–26%) among fattening pigs than the all‐in, all‐out system (1–5%). All Y. pseudotuberculosis isolates belonged to serotype O:3 and carried the virF/lcrF gene on the virulence plasmid. Biotypes 2 and 3 were involved, the latter in one isolate and not being previously reported in pigs. Altogether 53 isolates from 16 positive samples were characterized with pulsed‐field gel electrophoresis (PFGE). Using SpeI, NotI and XbaI enzymes, four, three and two different PFGE patterns were obtained respectively. A total of nine different genotypes were identified when the profiles of the enzymes were combined. The most common genotypes were gIV, found on three, and gXII, found on two of the four Y. pseudotuberculosis‐positive farms. The same genotypes previously detected in pig tonsils were present in pig faeces from the same farm, indicating that some Y. pseudotuberculosis strains can persist in the pig house environment.
Reduced Reaction Mechanisms for Methane and Syngas Combustion in Gas Turbines
Authors: Slavinskaya N. , Braun-Unkhoff M. , Frank P.
Published: March 2008

Two reduced reaction mechanisms were established that predict reliably for pressures up to about 20bar the heat release for different syngas mixtures including initial concentrations of methane. The mechanisms were validated on the base of laminar flame speed data covering a wide range of preheat temperature, pressure, and fuel-air mixtures. Additionally, a global reduced mechanism for syngas, which comprises only two steps, was developed and validated, too. This global reduced and validated mechanism can be incorporated into CFD codes for modeling turbulent combustion in stationary gas turbines.
Development of a Torsional Behavior Powertrain Model for Multiple Misfire Detection
Authors: Ponti Fabrizio
Published: March 2008

Many methodologies have been developed in the past for misfire detection purposes based on the analysis of the instantaneous engine speed. The missing combustion is usually detected, thanks to the sudden engine speed decrease that takes place after a misfire event. Misfire detection and, in particular, cylinder isolation are nevertheless still a challenging issue for engines with a high number of cylinders, for engine operating conditions at low load or high engine speed, and for multiple misfire events. When a misfire event takes place, a torsional vibration is excited and shows up in the instantaneous engine speed wave form. If a multiple misfire occurs, this torsional vibration is excited more than once in a very short time interval. The interaction between these successive vibrations can generate false alarms or misdetection, and an increased complexity when dealing with cylinder isolation. This paper presents the development of a powertrain torsional behavior model in order to identify the effects of a misfire event on the instantaneous engine speed signal. The identified wave form has then been used to filter out the torsional vibration effects in order to enlighten the missing combustions even in the case of multiple misfire events. The model response is also used to speed up the setup process for the detection algorithm employed, thus evaluating, before running specific experimental tests on a test bench facility, the values for the threshold and the optimal setup of the procedure. The proposed algorithm is developed in this paper for an SI L4 engine; its application to other engine configurations is possible, as is also discussed in this paper.
A Coal-Fired Power Plant With Zero-Atmospheric Emissions
Authors: Martinez-Frias Joel , Aceves Salvador M. , Ray Smith J. , Brandt Harry
Published: March 2008

This paper presents the thermodynamic and cost analysis of a coal-based zero-atmospheric emissions electric power plant. The approach involves an oxygen-blown coal gasification unit. The resulting synthetic gas (syngas) is combusted with oxygen in a gas generator to produce the working fluid for the turbines. The combustion produces a gas mixture composed almost entirely of steam and carbon dioxide. These gases drive multiple turbines to produce electricity. The turbine discharge gases pass to a condenser where water is captured. A stream of carbon dioxide then results that can be used for enhanced oil recovery or for sequestration. The term zero emission steam technology is used to describe this technology. We present the analysis of a 400MW electric power plant. The power plant has a net thermal efficiency of 39%. This efficiency is based on the lower heating value of the coal, and includes the energy necessary for coal gasification, air separation, and for carbon dioxide separation and sequestration. This paper also presents an analysis of the cost of electricity and the cost of conditioning carbon dioxide for sequestration. Electricity cost is compared for three different gasification processes (Texaco, Shell, and Koppers-Totzek) and two types of coals (Illinois 6 and Wyodak). COE ranges from 5.95¢∕kWhto6.15¢∕kWh, indicating a 3.4% sensitivity to the gasification processes considered and the coal types used.
A Wireless Microwave Telemetry Data Transfer Technique for Reciprocating and Rotating Components
Authors: Miers Scott A. , Barna Glen L. , Anderson Carl L. , Blough Jason R. , Inal M. Koray , Ciatti Stephen A.
Published: March 2008

Wireless microwave telemetry addresses the difficult issue of obtaining transducer outputs from reciprocating and rotating components through the use of advanced electronic components. This eliminates the requirements of a direct link between the transducer and the acquisition system. Accuracy of the transducer signal is maintained through the use of a double frequency modulation technique which provides temperature stability and a 20 point calibration of the complete system. Multiple transmitters can be used for larger applications and multiple antennas can be used to improve the signal strength and reduce the possibility of dropouts. Examples of automotive torque converter and piston temperature measurements are provided, showing the effectiveness of the wireless measuring technique.
The Effect of Liquid-Fuel Preparation on Gas Turbine Emissions
Authors: Nakamura Sosuke , McDonell Vince , Samuelsen Scott
Published: March 2008

The emissions of liquid-fuel fired gas turbine engines are strongly affected by the fuel preparation process that includes atomization, evaporation, and mixing. In the present paper, the effects of fuel atomization and evaporation on emissions from an industrial gas turbine engine were investigated. In the engine studied, the fuel injector consists of a coaxial plain jet airblast atomizer and a premixer which consists of a cylindrical tube with four mixing holes and swirler slits. The goal of this device is to establish a fully vaporized, homogeneous fuel/air mixture for introduction into the combustion chamber and the reaction zone. In the present study, experiments were conducted at atmospheric pressure and room temperature as well as at actual engine conditions (0.34MPa, 740K) both with and without the premixer. Measurements included visualization, droplet size, and velocity. By conducting tests with and without the premixing section, the effect of the mixing holes and swirler slit design on atomization and evaporation was isolated. The results were also compared with engine data and the relationship between premixer performance and emissions was evaluated. By comparing the results of tests over a range of pressures, the viability of two scaling methods was evaluated with the conclusion that spray angle correlates with fuel to atomizing air momentum ratio. For the injector studied, however, the conditions resulting in superior atomization and vaporization did not translate into superior emissions performance. This suggests that, while atomization and the evaporation of the fuel are important in the fuel preparation process, they are of secondary importance to the fuel/air mixing prior to, and in the early stages of the reaction in, governing emissions.
Thermodynamic Performance Assessment of Gas Turbine Trigeneration System for Combined Heat Cold and Power Production
Authors: Khaliq Abdul , Kumar Rajesh
Published: March 2008

The thermodynamic performance of the combustion gas turbine trigeneration system has been studied based on first law as well as second law analysis. The effects of overall pressure ratio and process heat pressure on fuel utilization efficiency, electrical to thermal energy ratio, second law efficiency, and exergy destruction in each component are examined. Results for gas turbine cycle, cogeneration cycle, and trigeneration cycle are compared. Thermodynamic analysis indicates that maximum exergy is destroyed during the combustion and steam generation process, which represents over 80% of the total exergy destruction in the overall system. The first law efficiency, electrical to thermal energy ratio, and second law efficiency of trigeneration system, cogeneration system, and gas turbine cycle significantly varies with the change in overall pressure ratio but the change in process heat pressure shows small variations in these parameters. Results clearly show that performance evaluation of the trigeneration system based on first law analysis alone is not adequate and hence more meaningful evaluation must include second law analysis.
Performance Trends of an Air-Cooled Steam Condenser Under Windy Conditions
Authors: van Rooyen J. A. , Kröger D. G.
Published: March 2008

Air-cooled steam condensers (ACSCs) are increasingly employed to reject heat in modern power plants. Unfortunately, these cooling systems become less effective under windy conditions and when ambient temperatures are high. A better understanding of the fundamental air flow patterns about and through such ACSCs is essential if their performance is to be improved under these conditions. The present numerical study models the air flow field about and through a particular ACSC. The performance of the fans is modeled with the aid of a novel numerical approach known as the “actuator disc model.” Distorted air flow patterns that significantly reduce fan performance in certain areas and recirculatory flows that entrain hot plume air are found to be the reasons for poor ACSC performance. It is found that the reduction in fan performance is the main reason for the poor ACSC performance while recirculation of hot plume air only reduces performance by a small amount.
Engine Design and Operational Impacts on Particulate Matter Precursor Emissions
Authors: Lukachko Stephen P. , Waitz Ian A. , Miake-Lye Richard C. , Brown Robert C.
Published: March 2008

Aircraft emissions of trace sulfur and nitrogen oxides contribute to the generation of fine volatile particulate matter (PM). Resultant changes to ambient PM concentrations and radiative properties of the atmosphere may be important sources of aviation-related environmental impacts. This paper addresses engine design and operational impacts on aerosol precursor emissions of SOx and NOy species. Volatile PM formed from these species in the environment surrounding an aircraft is dependent on intraengine oxidation processes occurring both within and downstream of the combustor. This study examines the complex response of trace chemistry to the temporal and spatial evolution of temperature and pressure along this entire intraengine path after combustion through the aft combustor, turbine, and exhaust nozzle. Low-order and higher-fidelity tools are applied to model the interaction of chemical and fluid mechanical processes, identify important parameters, and assess uncertainties. The analysis suggests that intraengine processing is inefficient. For in-service engine types in the large commercial aviation fleet, mean conversion efficiency (ε) is estimated to be 2.8–6.5% for sulfate precursors and 0.3–5.7% for nitrate precursors at the engine exit plane. These ranges reflect technological differences within the fleet, a variation in oxidative activity with operating mode, and modeling uncertainty stemming from variance in rate parameters and initial conditions. Assuming that sulfur-derived volatile PM is most likely, these results suggest emission indices of 0.06–0.13g∕kg fuel, assuming particles nucleated as 2H2SO4∙H2O for a fuel sulfur content of 500ppm.
Combined Effects of Overheating and Soot-Blower Erosion on Reheater Tubing in a Gas-Fired Large Capacity Boiler
Authors: Hosny Nasr M.
Published: March 2008

In a large capacity tangentially fired boiler, the final reheater tubing sustained abnormal oxidation and localized excessive metal wastage in a short time of the unit operation. The root causes of the problem are identified by test data analysis. The test data indicated that the reheater tubing metal temperatures in the affected areas exceeded the recommended limit of the metal oxidation temperature due to higher than expected local gas temperatures and velocities. A soot-blower facing the overheated portion of the reheater leading tubes accelerated the process of metal wastage by periodically removing the oxide layer. The configuration of the boiler internals upstream of the reheater section is found to be the main cause of the localized overheating. Side-to-side gas flow/temperature stratification due to tangential firing contributed to a lesser degree to the problem. The results and conclusions presented in this paper should be a beneficial guide to the designer of large capacity boilers.
Laboratory Studies of the Flow Field Characteristics of Low-Swirl Injectors for Adaptation to Fuel-Flexible Turbines
Authors: Cheng R. K. , Littlejohn D. , Nazeer W. A. , Smith K. O.
Published: March 2008

The low-swirl injector (LSI) is a simple and cost-effective lean premixed combustion method for natural-gas turbines to achieve ultralow emissions (<5 ppm NOx and CO) without invoking tight control of mixture stoichiometry, elaborate active tip cooling, or costly materials and catalysts. To gain an understanding of how this flame stabilization mechanism remains robust throughout a large range of Reynolds numbers, laboratory experiments were performed to characterize the flowfield of natural-gas flames at simulated partial load conditions. Also studied was a flame using simulated landfill gas of 50% natural gas and 50% CO2. Using particle image velocimetry, the nonreacting and reacting flowfields were measured at five bulk flow velocities. The results show that the LSI flowfield exhibits similarity features. From the velocity data, an analytical expression for the flame position as function of the flowfield characteristics and turbulent flame speed has been deduced. It shows that the similarity feature coupled with a linear dependency of the turbulent flame speed with bulk flow velocity enables the flame to remain relatively stationary throughout the load range. This expression can be the basis for an analytical model for designing LSIs that operate on alternate gaseous fuels such as slower burning biomass gases or faster burning coal-based syngases.
Empirical Tuning of an On-Board Gas Turbine Engine Model for Real-Time Module Performance Estimation
Authors: Volponi Al , Brotherton Tom , Luppold Rob
Published: March 2008

A practical consideration for implementing a real-time on-board engine component performance tracking system is the development of high fidelity engine models capable of providing a reference level from which performance changes can be trended. Real-time engine models made their advent as state variable models in the mid-1980s, which utilized a piecewise linear model that granted a reasonable representation of the engine during steady state operation and mild transients. Increased processor speeds over the next decade allowed more complex models to be considered, that were a combination of linear and nonlinear physics-based elements. While the latter provided greater fidelity over both transient operation and the engine operational flight envelope, these models could be further improved to provide the high level of accuracy required for long-term performance tracking, as well as address the issue of engine-to-engine variation. Over time, these models may deviate enough from the actual engine being monitored, as a result of improvements made during an engine’s life cycle such as hardware modifications, bleed and stator vane schedule alterations, cooling flow adjustments, and the like, that the module performance estimations are inaccurate and often misleading. The process described in this paper will address these shortcomings while maintaining the execution speed required for real-time implementation.
Heat-Transfer Analysis of High Porosity Open-Cell Metal Foam
Authors: Ghosh Indranil
Published: March 2008

Forced convection heat transfer in high porosity metal foam, either attached to an isothermal surface or confined between two isothermal plates, has been analyzed, assuming a repetitive simple cubic structure for the foam matrix. The model, in the microscopic level takes account of the forced convective heat transfer coupled with heat conduction through the foam fibers. Analytical expressions have been derived for the gas-solid temperature difference, total heat transfer through the foam, and efficiency of foam as an extended surface. The resulting expressions have strong resemblance with those of the conventional finned surface. The effect of porosity and foam density on the heat transfer in metallic foam has been established through parametric studies. Significant heat-transfer augmentation due to cross connections in metal struts has been noticed.
Ballistic Impact of Dry Woven Fabric Composites: A Review
Authors: Tabiei Ala , Nilakantan Gaurav
Published: March 2008

This paper reviews the topic of ballistic impact of dry woven fabric composites. It highlights previous work done in modeling the fabrics and the theory involved. Attention is also given to experimental testing, ballistic penetration resistence, projectile characteristics, and failure modes in yarns and fabric. Concepts to further enhance the ballistic penetration resistance of woven fabrics are discussed. This paper serves as an effective source of literature for those interested in conducting research into this topic. Altogether, 176 references have been cited to allow further investigation.
Optimal and Robust Control of Fluid Flows: Some Theoretical and Computational Aspects
Authors: Medjo T. Tachim , Temam R. , Ziane M.
Published: March 2008

In this article, we review from the mathematical and numerical points of view some of the recent progresses in the area of flow control.
Seed‐based transrectal ultrasound‐fluoroscopy registration method for intraoperative dosimetry analysis of prostate brachytherapy
Authors: Tutar Ismail B. , Gong Lixin , Narayanan Sreeram , Pathak Sayan D. , Cho Paul S. , Wallner Kent , Kim Yongmin
Published: March 2008

Prostate brachytherapy is an effective treatment option for early‐stage prostate cancer. During a prostate brachytherapy procedure, transrectal ultrasound (TRUS) and fluoroscopy imaging modalities complement each other by providing good visualization of soft tissue and implanted seeds, respectively. Therefore, the registration of these two imaging modalities, which are readily available in the operating room, could facilitate intraoperative dosimetry, thus enabling physicians to implant additional seeds into the underdosed portions of the prostate while the patient is still on the operating table. It is desirable to register TRUS and fluoroscopy images by using the seeds as fiducial markers. Although the locations of all the implanted seeds can be reconstructed from three fluoroscopy images, only a fraction of these seeds can be located in TRUS images. It is challenging to register the TRUS and fluoroscopy images by using the identified seeds, since the correspondence between them is unknown. Furthermore, misdetection of nonseed structures as seeds can lead to the inclusion of spurious points in the data set. We developed a new method called iterative optimal assignment (IOA) to overcome these challenges in TRUS‐fluoroscopy registration. By using the Hungarian method in an optimization framework, IOA computes a set of transformation parameters that yield the one‐to‐one correspondence with minimum cost. We have evaluated our registration method at varying noise levels, seed detection rates, and number of spurious points using data collected from 25 patients. We have found that IOA can perform registration with an average root mean square error of about even when the seed detection rate is only 10%. We believe that IOA can offer a robust solution to seed‐based TRUS‐fluoroscopy registration, thus making intraoperative dosimetry possible.
The x‐ray light valve: A potentially low‐cost, digital radiographic imaging system‐concept and implementation considerations
Authors: Webster Christie Ann , Koprinarov Ivaylo , Germann Stephen , Rowlands J. A.
Published: March 2008

New x‐ray radiographic systems based on large‐area flat‐panel technology have revolutionized our capability to produce digital x‐ray images. However, these imagers are extraordinarily expensive compared to the systems they are replacing. Hence, there is a need for a low‐cost digital imaging system for general applications in radiology. A novel potentially low‐cost radiographic imaging system based on established technologies is proposed—the X‐Ray Light Valve (XLV). This is a potentially high‐quality digital x‐ray detector made of a photoconducting layer and a liquid‐crystal cell, physically coupled in a sandwich structure. Upon exposure to x rays, charge is collected on the surface of the photoconductor. This causes a change in the optical properties of the liquid‐crystal cell and a visible image is generated. Subsequently, it is digitized by a scanned optical imager. The image formation is based on controlled modulation of light from an external source. The operation and practical implementation of the XLV system are described. The potential performance of the complete system and issues related to sensitivity, spatial resolution, noise, and speed are discussed. The feasibility of clinical use of an XLV device based on amorphous selenium as the photoconductor and a reflective electrically controlled birefringence cell is analyzed. The results of our analysis indicate that the XLV can potentially be adapted to a wide variety of radiographic tasks.
A practical global distortion correction method for an image intensifier based x‐ray fluoroscopy system
Authors: Gutiérrez Luis F. , Ozturk Cengizhan , McVeigh Elliot R. , Lederman Robert J.
Published: March 2008

X‐ray images acquired on systems with image intensifiers (II) exhibit characteristic distortion which is due to both external and internal factors. The distortion is dependent on the orientation of the II, a fact particularly relevant to II's mounted on C arms which have several degrees of freedom of motion. Previous descriptions of distortion correction strategies have relied on a dense sampling of the C‐arm orientation space, and as such have been limited mostly to a single arc of the primary angle, . We present a new method which smooths the trajectories of the segmented vertices of the grid phantom as a function of prior to solving the two‐dimensional warping problem. It also shows that the same residual errors of distortion correction could be achieved without fitting the trajectories of the grid vertices, but instead applying the previously described global method of distortion correction, followed by directly smoothing the values of the polynomial coefficients as functions of the C‐arm orientation parameters. When this technique was applied to a series of test images at arbitrary , the root‐mean‐square (RMS) residual error was . The new method was extended to three degrees of freedom of the C‐arm motion: the primary angle, ; the secondary angle, ; and the source‐to‐intensifier distance, . Only 75 images were used to characterize the distortion for the following ranges: , ; , ; , . When evaluated on a series of test images acquired at arbitrary , the RMS residual error was . This method is targeted at applications such as guidance of catheter‐based interventions and treatment planning for brachytherapy, which require distortion‐corrected images over a large range of C‐arm orientations.
Dosimetric characterization of Ir‐192 LDR elongated sources
Authors: van der Laarse R. , Granero D. , Pérez‐Calatayud J. , Meigooni Ali. S. , Ballester F.
Published: March 2008

Ir‐192 wires have been used in low‐dose‐rate brachytherapy for many years. Commercially available treatment planning systems approximate the dose rate distribution of the straight or curved wires applying the superposition principle using one of the following methods: (i) The wire is modeled as a set of point sources, (ii) the wire is modeled as a set of small straight segment wires, (iii) the values of the parameters and functions of the American Association of Physicists in Medicine (AAPM) Task Group 43 protocol are obtained for wire lengths between 3 and assuming some simplifications. The dose rate distributions obtained using these methods for linear wires of different lengths and U‐shaped wires present significant deviations compared to those obtained by Monte Carlo. In the present study we propose a new method to model wires of any length and shape, named the Two Lengths based Segmented method. This method uses the formalism stated in the AAPM Task Group 43 protocol for two straight wires only, 0.5 and , to obtain the dose rate distribution around wires of any length (down to and up to ) improving on the results of the aforementioned ones. This method can easily be applied to dose calculations around other wires, such as Pd‐103 ones.
4D‐CT lung motion estimation with deformable registration: Quantification of motion nonlinearity and hysteresis
Authors: Boldea Vlad , Sharp Gregory C. , Jiang Steve B. , Sarrut David
Published: March 2008

In this article, our goal is twofold. First, we propose and compare two methods which process deformable registration to estimate patient specific lung and tumor displacements and deformation during free breathing from four‐dimensional computed tomography (4D‐CT) data. Second, we propose techniques to quantify the physiological parameters of motion nonlinearity and hysteresis. A Fréchet distance‐based criterion is introduced to measure the motion hysteresis. Experiments were conducted with 4D‐CT data of five patients treated in radiotherapy for non‐small cell lung cancer. The accuracy of deformation fields assessed against expert‐selected landmarks was found to be within image voxel tolerance. The second method gave slightly better results in terms of accuracy and consistency, although the differences were not statistically significant between the two methods. Lung motion nonlinearity and hysteresis are patient specific, and vary across regions within the lung during respiration. For all patients, motion between end‐exhale and end‐inhale was well approximated with a straight line trajectory for the majority of lung points. Hysteresis was found to be globally correlated with trajectory length. The main limitation to the proposed method is that intensity‐based deformable registration is dependent on image quality and image resolution. Another limitation is the absence of gold standard which makes the validation of the computed motion difficult. However, the proposed tools provide patient specific motion information which, in radiotherapy for example, can ease the definition of precise internal margins. In the future, the integration of physiological information from multiple patients could help to create a general lung atlas with different clinical applications.
The x‐ray light valve: A potentially low‐cost, digital radiographic imaging system—a liquid crystal cell design for chest radiography
Authors: Szeto Timothy C. , Webster Christie Ann , Koprinarov Ivaylo , Rowlands J. A.
Published: March 2008

Digital x‐ray radiographic systems are desirable as they offer high quality images which can be processed, transferred, and stored without secondary steps. However, current clinical systems are extraordinarily expensive in comparison to film‐based systems. Thus, there is a need for an economical digital imaging system for general radiology. The x‐ray light valve (XLV) is a novel digital x‐ray detector concept with the potential for high image quality and low cost. The XLV is comprised of a photoconductive detector layer and liquid crystal (LC) cell physically coupled in a sandwich structure. Upon exposure to x rays, charge is collected at the surface of the photoconductor, causing a change in the reflective properties of the LC cell. The visible image so formed can subsequently be digitized with an optical scanner. By choosing the properties of the LC cell in combination with the appropriate photoconductor thickness and bias potentials, the XLV can be optimized for various diagnostic imaging tasks. Specifically for chest radiography, we identified three potentially practical reflective cell designs by selecting from those commonly used in LC display technology. The relationship between reflectance and x‐ray exposure (i.e., the characteristic curve) was determined for all three cells using a theoretical model. The results indicate that the reflective electrically controlled birefringence (r‐ECB) cell is the preferred choice for chest radiography, provided that the characteristic curve can be shifted towards lower exposures. The feasibility of the shift of the characteristic curve is shown experimentally. The experimental results thus demonstrate that an XLV based on the r‐ECB cell design exhibits a characteristic curve suitable for chest radiography.
The effective point of measurement of ionization chambers and the build‐up anomaly in MV x‐ray beams
Authors: McEwen M. R. , Kawrakow I. , Ross C. K.
Published: March 2008

A precision experimental investigation of the effective point of measurement (EPOM) of ion chambers in megavoltage beams has been carried out. A one‐dimensional scanning phantom system was developed with an overall accuracy in the positioning of a chamber of better than . Depth‐dose data were acquired for a beam from an Elekta Precise linac (field sizes of and ) for measurement depths in the range . The results confirmed the Monte Carlo calculations of an earlier theoretical investigation by Kawrakow [Med. Phys. 33, 1829–1839 (2006)] that the standard shift for cylindrical chambers, recommended in dosimetry protocols of (where is the internal radius of the cavity), is incorrect. A wide range of ion chambers were investigated and it was found that errors of up to could occur for certain chamber designs (although typical errors for common chambers were around ). A comparison between measurements and Monte Carlo simulations showed that once the correct EPOM is used, the details of the linac geometry are correct, and the parameters of the electron beam striking the bremsstrahlung target have been adequately determined, the EGSnrc Monte Carlo package is capable of reproducing the experimental data to or better. The investigation also confirmed that for the highest accuracy depth‐dose curves in megavoltage photon beams one should use a well‐guarded parallel‐plate ion chamber. Three chamber designs were tested here and found to be satisfactory—the Scanditronix‐Wellhöfer NACP‐02, PTW Roos and Exradin All.
Breast MRI: Fundamentals and Technical Aspects
Authors: Hendee William R.
Published: March 2008

Breast MRI: Fundamentals and Technical Aspects Hendrick R. Edward Springer Science+Business Media LLC, New York, 2008, $69.95. ISBN: 978‐0‐387‐73506‐1, 251 and xvi pp. (hardcover).
An Oncogene-Induced DNA Damage Model for Cancer Development
Authors: Halazonetis Thanos D. , Gorgoulis Vassilis G. , Bartek Jiri
Published: March 2008

Of all types of DNA damage, DNA double-strand breaks (DSBs) pose the greatest challenge to cells. One might have, therefore, anticipated that a sizable number of DNA DSBs would be incompatible with cell proliferation. Yet recent experimental findings suggest that, in both precancerous lesions and cancers, activated oncogenes induce stalling and collapse of DNA replication forks, which in turn leads to formation of DNA DSBs. This continuous formation of DNA DSBs may contribute to the genomic instability that characterizes the vast majority of human cancers. In addition, in precancerous lesions, these DNA DSBs activate
p53
, which, by inducing apoptosis or senescence, raises a barrier to tumor progression. Breach of this barrier by various mechanisms, most notably by
p53
mutations, that impair the DNA damage response pathway allows cancers to develop. Thus, oncogene-induced DNA damage may explain two key features of cancer: genomic instability and the high frequency of
p53
mutations.
Dimethylsulfoniopropionate as a Foraging Cue for Reef Fishes
Authors: DeBose Jennifer L. , Lema Sean C. , Nevitt Gabrielle A.
Published: March 2008

Coral reefs resemble islands of productive habitats where fishes aggregate, forage, and spawn. Although it has been suggested that some reef fishes use biogenic chemicals as aggregation cues, specific chemicals have not been identified. Dimethylsulfoniopropionate (DMSP), a secondary metabolite of many marine algal species, is released during foraging by higher-order consumers. DMSP has been studied intensively for its role in oceanic sulfur cycles and global climate regulation, but its ecological importance to marine fishes is unknown. We present evidence that planktivorous reef fishes will aggregate to experimental deployments of DMSP over coral reef habitats in the wild.
Comment on "Early Archaean Microorganisms Preferred Elemental Sulfur, Not Sulfate"
Authors: Bao Huiming , Sun Tao , Kohl Issaku , Peng Yongbo
Published: March 2008

Philippot
et al
. (Reports, 14 September 2007, p. 1534) interpreted multiple–sulfur isotopic compositions of ∼3.5-billion-year-old marine sulfide deposits as evidence that early Archaean microorganisms were not sulfate reducers but instead metabolized elemental sulfur. However, their data can be better explained by a scenario involving poor mixing of photochemical and surface sulfide sources.
The Dust Halo of Saturn's Largest Icy Moon, Rhea
Authors: Jones G. H. , Roussos E. , Krupp N. , Beckmann U. , Coates A. J. , Crary F. , Dandouras I. , Dikarev V. , Dougherty M. K. , Garnier P. , Hansen C. J. , Hendrix A. R. , Hospodarsky G. B. , Johnson R. E. , Kempf S. , Khurana K. K. , Krimigis S. M. , Krüger H. , Kurth W. S. , Lagg A. , McAndrews H. J. , Mitchell D. G. , Paranicas C. , Postberg F. , Russell C. T. , Saur J. , Seiß M. , Spahn F. , Srama R. , Strobel D. F. , Tokar R. , Wahlund J.-E. , Wilson R. J. , Woch J. , Young D.
Published: March 2008

Saturn's moon Rhea had been considered massive enough to retain a thin, externally generated atmosphere capable of locally affecting Saturn's magnetosphere. The Cassini spacecraft's in situ observations reveal that energetic electrons are depleted in the moon's vicinity. The absence of a substantial exosphere implies that Rhea's magnetospheric interaction region, rather than being exclusively induced by sputtered gas and its products, likely contains solid material that can absorb magnetospheric particles. Combined observations from several instruments suggest that this material is in the form of grains and boulders up to several decimetres in size and orbits Rhea as an equatorial debris disk. Within this disk may reside denser, discrete rings or arcs of material.
Long-Term Sea-Level Fluctuations Driven by Ocean Basin Dynamics
Authors: Müller R. Dietmar , Sdrolias Maria , Gaina Carmen , Steinberger Bernhard , Heine Christian
Published: March 2008

Earth's long-term sea-level history is characterized by widespread continental flooding in the Cretaceous period (∼145 to 65 million years ago), followed by gradual regression of inland seas. However, published estimates of the Late Cretaceous sea-level high differ by half an order of magnitude, from ∼40 to ∼250 meters above the present level. The low estimate is based on the stratigraphy of the New Jersey margin. By assimilating marine geophysical data into reconstructions of ancient ocean basins, we model a Late Cretaceous sea level that is 170 (85 to 270) meters higher than it is today. We use a mantle convection model to suggest that New Jersey subsided by 105 to 180 meters in the past 70 million years because of North America's westward passage over the subducted Farallon plate. This mechanism reconciles New Jersey margin–based sea-level estimates with ocean basin reconstructions.
Stimuli-Responsive Polymer Nanocomposites Inspired by the Sea Cucumber Dermis
Authors: Capadona Jeffrey R. , Shanmuganathan Kadhiravan , Tyler Dustin J. , Rowan Stuart J. , Weder Christoph
Published: March 2008

Sea cucumbers, like other echinoderms, have the ability to rapidly and reversibly alter the stiffness of their inner dermis. It has been proposed that the modulus of this tissue is controlled by regulating the interactions among collagen fibrils, which reinforce a low-modulus matrix. We report on a family of polymer nanocomposites, which mimic this architecture and display similar chemoresponsive mechanic adaptability. Materials based on a rubbery host polymer and rigid cellulose nanofibers exhibit a reversible reduction by a factor of 40 of the tensile modulus, for example, from 800 to 20 megapascals (MPa), upon exposure to a chemical regulator that mediates nanofiber interactions. Using a host polymer with a thermal transition in the regime of interest, we demonstrated even larger modulus changes (4200 to 1.6 MPa) upon exposure to emulated physiological conditions.
Fiber-Optical Analog of the Event Horizon
Authors: Philbin Thomas G. , Kuklewicz Chris , Robertson Scott , Hill Stephen , König Friedrich , Leonhardt Ulf
Published: March 2008

The physics at the event horizon resembles the behavior of waves in moving media. Horizons are formed where the local speed of the medium exceeds the wave velocity. We used ultrashort pulses in microstructured optical fibers to demonstrate the formation of an artificial event horizon in optics. We observed a classical optical effect: the blue-shifting of light at a white-hole horizon. We also showed by theoretical calculations that such a system is capable of probing the quantum effects of horizons, in particular Hawking radiation.
Pyrazinamide Resistance and
pncA
Gene Mutations in
Mycobacterium tuberculosis
Authors: Juréen Pontus , Werngren Jim , Toro Juan-Carlos , Hoffner Sven
Published: March 2008

Thirty-four pyrazinamide-resistant and 37 pyrazinamide-susceptible
Mycobacterium tuberculosis
complex strains were analyzed for
pncA
gene mutations. None of the sensitive strains had any mutations, apart from silent mutations, whereas all but one resistant strain showed
pncA
mutations. By using sequencing as a means of early resistance detection, the inconsistency of phenotypic pyrazinamide assays can be circumvented.