bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement and calculation of the dose at large distances from brachytherapy sources: Cs‐137, Ir‐192, and Co‐60
Authors: Venselaar J. L. M. , van der Giessen P. H. , Dries W. J. F.
Published: March 2003

In a small number of special cases it may be necessary to estimate the radiation dose to organs far away from the target volume of a patient receiving radiotherapy, e.g., the dose to the gonads or to the fetus of a pregnant patient. Previously, for external beam radiotherapy a model was developed, which enabled this estimation with acceptable accuracy for the range of photon beam energies from cobalt‐60 to 25 MV, independent of the make of the treatment machines, for generally used techniques and for a wide range of distances from the beam axis and field sizes [Van der Giessen and Hurkmans, Int. J. Radiat. Oncol. Biol. Phys. 27, 717–724 (1993); van der Giessen, ibid. 30, 1239–1246 (1994); to appear in Int. J. Radiat. Oncol. Biol. Phys.]. In this paper, results of measurements and Monte Carlo calculations are reported for evaluation of the dose at large distances from some brachytherapy sources. This has resulted in information on the behavior of the tissue attenuation factor T(r) for commonly used sources: Co‐60, Ir‐192, and Cs‐137, in the range of distances up to 60 cm from the source. The influence of the size of the phantom was investigated. A mathematical model, described earlier by Kornelsen and Young, proved to yield the best fit to the results [Br. J. Radiol. 54, 136 (1981)]. Parameters for this model are derived for these isotopes. A few experiments in a Rando Alderson phantom are presented to support the measurements and the calculations.
Evaluation of NCRP Report No. 49 assumptions on workloads and use factors in diagnostic radiology facilities
Authors: Simpkin Douglas J.
Published: March 2003

A survey of modern medical institutions has been performed to measure the workload and primary beam use factors used in diagnostic x‐ray installations in comparison to those suggested in Report 49 of the NCRP. Seven types of radiology installations were investigated, namely general radiographic rooms, general fluoroscopic and radiographic rooms (fluoroscopic and radiographic tubes surveyed separately), chest radiographic rooms, mammographic suites, and cardiac and peripheral angiographic suites. The radiologic technique (kVp and mAs) for each exposure performed on a total of 2396 patients was recorded either manually or by a commercially‐available invasive electronic sensing system. Additionally, the direction of the primary beam during the exposure was recorded. The kVp distribution of the workload data was determined and normalized per patient for each of the seven types of installations. The total average workload per patient surveyed in each type of installation is 2.5, 13, 1.5, 0.22, 6.7, 160, and 64 mA min per patient for the above installation types. For general radiographic rooms the primary beam was directed at the floor for 69% of the total workload, with the remaining 21.5%, 6.5%, and 1.6% of the workload directed toward three walls. When multiplied by the average number of patients examined weekly in each type of installation, the mean weekly workloads observed are 270, 230, 35, 44, 320, 3100, and 1400 mA min for the above‐listed types of installations. Additionally, a significant fraction of the observed workloads occur at potentials much less than the kVp values typically assumed for radiation shielding.
Measured electron energy and angular distributions from clinical accelerators
Authors: Deasy J. O. , Almond P. R. , McEllistrem M. T.
Published: March 2003

Electron energy spectra and angular distributions, including angular spreads, were measured using magnetic spectrometer techniques, at isocenter, for two clinical linear accelerators: one scanning beam machine, which achieves field flatness by scanning a pencil beam over the desired field at the patient plane, and one scattering foil machine, which disperses the electrons through a graded‐thickness scattering foil. All measurements were made at isocenter (in the patient plane), in air, 1 m from the nominal accelerator source. The energy measurements were confined to electrons traveling along the central axis; any widely scattered electrons were effectively neglected. The energy spectra of the scanning beam machine are all of nearly Gaussian shape and energy full‐width‐at‐half‐maximum intensity (FWHM) of about 5% of the peak mean energy (denoted . The energy spectra of the scattering foil machine have a variety of forms as a function of energy, including even spectra with double peaks, and spectra which changed with time. The FWHM values ranged from 9%–22% of . The angular spread measurements, at isocenter, yielded mrad‐MeV for the scanning beam machine, and 346 mrad‐MeV for the scattering foil machine, where denotes the standard deviation of the plane‐projected angular distribution. These angular spreads are 30%–40% smaller than angular spreads reported by others on a very similar machine using the penumbra method. Possible causes of this discrepancy are discussed.
A Fourier based algorithm for tracking SPAMM tags in gated magnetic resonance cardiac images
Authors: Zhang Shuqing , Douglas Margaret A. , Yaroslavsky Leonid , Summers Ronald M. , Dilsizian Vasken , Fananapazir Lameh , Bacharach Stephen L.
Published: March 2003

A method is described for automatically tracking spatial modulation of magnetization tag lines on gated cardiac images. The method differs from previously reported methods in that it uses Fourier based spatial frequency and phase information to separately track horizontal and vertical tag lines. Use of global information from the frequency spectrum of an entire set of tag lines was hypothesized to result in a robust algorithm with decreased sensitivity to noise. The method was validated in several ways: first, actual tagged cardiac images at end diastole were deformed known amounts, and the algorithm's predictions compared to the known deformations. Second, tagged, gated images of the thigh muscle (assumed to have similar signal to noise characteristics as cardiac images, but to not deform with time) were created. Again the algorithmic predictions could be compared to the known (zero magnitude) deformations and to thigh images which had been artificially deformed. Finally, actual cardiac tagged images were acquired, and comparisons made between manual, visual, determinations of tag line locations, and those predicted by the algorithm. At 0.5 T, the mean bias of the method was <0.34 mm even at large deformations and at late (noisy) times. The standard deviation of the method, estimated from the tagged thigh images, was <0.7 mm even at late times. The method may be expected to have even lower error at higher field strengths.
Charge transport and storage in the radiation‐charged electret ionization chamber
Authors: MacDonald Brennan A.
Published: March 2003

Numerical calculations of time‐dependent charge distributions are presented and compared with distributions measured on radiation‐charged electrets made of thin polymer films, which are charged and discharged in a radiation‐charged electret ionization chamber (REIC) through the application of ionizing radiation. The chamber resembles a parallel plate ionization chamber, and has a thin film of polymer covering the collector and guard‐ring electrodes. Calculations are performed by solving Laplace's equation for the true geometry of the charging/discharging set‐up, then applying estimates of ion‐density distributions generated from known scattering distributions and/or simpler approximations. Measurements of radiation induced conductivity (RIC) are presented and fitted to an empirically derived analytical model, and the effects of RIC on the operation of a radiation dosimeter based on the electret are investigated and discussed. Short‐term and long‐term charge decay from the electret is measured and fitted to a previously developed model. The effects of post‐charging heat treatment of the radiation‐charged electret are presented and discussed. Last, the dosimetric characteristics of the REIC are considered in light of those physical aspects investigated here.
Understanding the relative sensitivity of radiographic screens to scattered radiation
Authors: Yip Kwok L. , Whiting Bruce R. , Kocher Thomas E. , Trauernicht David P. , Van Metter Richard L.
Published: March 2003

This study compared the relative response of various screen‐film and computed radiography (CR) systems to diagnostic radiation exposure. An analytic model was developed to calculate the total energy deposition within the depth of screen and the readout signal generated from this energy for the x‐ray detection system. The model was used to predict the relative sensitivity of several screen‐film and CR systems to scattered radiation as a function of various parameters, such as x‐ray spectra, phantom thickness, phosphor composition, screen thickness, screen configuration (single front screen, single back screen, screen pair), and readout conditions. In addition, measurements of the scatter degradation factor (SDF) for different screen systems by using the beam stop technique with water phantoms were made to verify the model results. Theoretically calculated values of SDF were in good agreement with experimental data. These results are consistent with the common observation that rare‐earth screens generally produce better image quality than calcium tungstate screens and the CR screen.
Active energy selective image detector for dual‐energy computed radiography
Authors: Alvarez Robert E.
Published: March 2003

A new energy selective detector for dual energy computed radiography has been developed that combines many of the advantages of x‐ray tube voltage switching and single exposure double screen detectors. The new active detector utilizes electro‐optical modulation of the response of the storage phosphor screens to allow dual exposure acquisition with no motion of the screens. Electro‐optical modulation can be done rapidly so the detector can acquire the voltage switched images in a short enough time to minimize patient motion artifacts. Voltage switching produces effective detected energy spectra that result in much lower noise for a given patient dose than the effective spectra of double screen detectors. In this paper the new concept is described, optimal voltages and filter materials are determined by computer simulations, and the active detector performance is compared to other energy selective detectors. The new detector provides over 30 times better signal to noise ratio squared (SNR2) for the same dose and over five times better SNR2 for the same x‐ray tube loading than a double screen detector. The effects of incomplete erasure of the x‐ray exposures are determined quantitatively. With achievable erasing fractions, the SNR2 is over 20 times better for the same dose and over three times better for constant tube loading than a double screen detector. The active detector is also compared to mechanical screen switching. Mechanical switching provides somewhat better SNR2 for the same dose, approximately 1.1 times the active detector SNR2 at optimal x‐ray tube voltages. The performance is compared with highly absorbing back screens. If these are used in both the active and passive detectors, both detectors' quality factors increase, but the advantage of the active detector over the passive detector decreases with large back screen thicknesses.
On the accuracy of the Fokker–Planck and Fermi pencil beam equations for charged particle transport
Authors: Börgers Christoph , Larsen Edward W.
Published: March 2003

Electron beam dose calculations are often based on pencil beam formulas such as the Fermi–Eyges formula. The Fermi–Eyges formula gives an exact solution of the Fermi equation. The Fermi equation can be derived from a more fundamental mathematical model, the linear Boltzmann equation, in two steps. First, the linear Boltzmann equation is approximated by the Fokker–Planck equation. Second, the Fokker–Planck equation is approximated by the Fermi equation. In this paper, we study these approximations. We use a simplified model problem, but choose parameter values closely resembling those relevant in electron beam therapy. Our main conclusions are: (1) The inaccuracy of the Fokker–Planck approximation is primarily due to neglect of large‐angle scattering. (2) When computing an approximate solution to the Fokker–Planck equation by Monte Carlo simulation of a transport process, one should let the polar scattering angle be deterministic. (3) At shallow depths, the discrepancy between the linear Boltzmann and Fokker–Planck equations is far more important than that between the Fokker–Planck and Fermi equations. The first of these conclusions is certainly not new, but we state and justify it more rigorously than in previous work.
Dependence of overall correction factor of a cylindrical ionization chamber on field size and depth in medium‐energy x‐ray beams
Authors: Seuntjens Jan , Verhaegen Frank
Published: March 2003

In this paper we examine the depth and field size dependence of the overall correction factor kch for in‐phantom dose determinations in orthovoltage x‐ray beams. The overall correction factor is considered to be composed of three contributions, i.e., (1) a contribution from the angular dependence of the chamber response free‐in‐air, derived based on the measured directional response of the NE2571 for different energies combined with Monte Carlo calculations; (2) a displacement effect; and (3) a stem effect, both calculated using the Monte Carlo method for different field sizes and depths. The results show a variation of, at most, 2.2% at the lowest photon energies (29.8‐keV average photon energy) when going from 2 cm to 5 cm for a small circular 20‐cm2 field. In the medium‐energy range (≥100 kV), variations are limited to, at most, 1.5% for 120 kV–150 kV when comparing the most extreme variations in field size and depth (i.e., 2‐cm depth; 20‐cm2 area compared to 5 cm depth; 200‐cm2 area). Depth variations most importantly affect the overall correction factor by hardening of the photon fluence spectrum, whereas field diameter variations affect the factor by increase or decrease of contributions of photon scattering. The work shows that taking into account the uncertainties adopted in the recent review of data and methods recommended in the IAEA code of practice, the dependence of the overall correction factor on depth and field size is insignificant for the radiation qualities between 100 kV (HVL 0.17‐mm Cu, average energy: 52 keV) and 280 kV (HVL 3.41‐mm Cu, average energy: 144 keV).
A curved crystal spectrometer for energy calibration and spectral characterization of mammographic x‐ray sources
Authors: Hudson Lawrence T. , Deslattes Richard D. , Henins Albert , Chantler Christopher T. , Kessler Ernest G. , Schweppe John E.
Published: March 2003

Clinical efficacy of diagnostic radiology for mammographic examinations is critically dependent on source characteristics, detection efficiency, image resolution, and applied high voltage. In this report we focus on means for evaluation of source‐dependent issues including noninvasive determination of the applied high voltage, and characterization of intrinsic spectral distributions which in turn reflect the effects of added filtration and target and window contamination. It is shown that a particular form of x‐ray curved crystal spectrometry with electronic imaging can serve to determine all relevant parameters within the confines of a standard clinical exposure.
Plate scatter correction for improved performance in dual‐energy imaging
Authors: Hinshaw Dean A. , Dobbins James T.
Published: March 2003

We have developed a method for correcting for the scatter produced by the computed radiography plates in single‐shot dual‐energy imaging. In our technique, which uses a series of four computed radiography plates (the middle two plates act as a filter), the back plate can have scatter fractions as high as 30% due to the scatter from the first three plates. We use the deconvolution method to correct for this scatter, as the scatter medium is uniform and isotropic with a constant air gap. The ratio of the modulation transfer function (MTF) of a standard computed radiography plate to that of a dual‐energy plate gives us the correction factor we need to scale the Fourier transforms of our images, thus compensating for the reduced response of the system due to scatter. We also investigated the effect of having an air gap between the back dual‐energy plate and the first three plates. Our measurements show that this degrades the signal‐to‐noise response of the back plate slightly at low spatial frequencies. We also used independent scatter fraction measurements to verify the validity of our MTF measurements. Applying the correction to a back plate image improves the fine detail contrast by approximately 30%.
Assessing radiation and light field congruence with a video based electronic portal imaging device
Authors: Luchka K. , Chen D. , Shalev S. , Gluhchev G. , Rajapakshe R.
Published: March 2003

Projected light fields are used on treatment simulators and teletherapy treatment units to delineate the size and position of the radiation beam. Any discrepancy between these fields will lead to a systematic field placement error, with possibly serious implications with regard to the accuracy of the delivered dose distribution in the patient. Conventionally, film has been used for regular quality control tests of light and radiation field congruence, but this is a time consuming method and is not suitable for daily checks. A new method is described that uses a specially designed test phantom, a video‐based electronic portal imaging device, and a personal computer to test for radiation and light field congruence on treatment accelerators. This method consists of aligning the test phantom in the light field of a treatment linac and acquiring an electronic portal image. A computer program then automatically analyzes the image and determines the degree of congruence between the two fields. The final result of the test is a go, warning, or no go decision depending on the extent of misalignment between the light and radiation fields. Two algorithms were tested for reproducibility (<0.4 mm), sensitivity to noise (<0.2 mm), and positional accuracy (<0.4 mm) and are shown to give results comparable to the conventional film method. Daily testing of field congruence over a period of 84 days demonstrated differences in the results determined by the two algorithms of less than 0.1±0.2 mm (standard deviation) at 6 MV and 0.22±0.13 mm at 23 MV. Routine testing is possible as the effort and time required are minimal, and the test can be performed during daily routine start‐up procedures.
Implications of 3‐dimensional target shape and motion in aperture design
Authors: Fontenla Ernesto , Pelizzari Charles A. , Chen George T. Y.
Published: March 2003

To determine the shape of a radiation beam aperture a margin is typically applied to the clinical target volume (CTV) to yield the planning target volume (PTV), and the aperture is then determined from the projection of the PTV onto the aperture plane. This margin accounts for setup variability and organ motion originating from respiration or other physiologic processes. The use of either a uniform margin, or alternatively one which takes into account only the expected magnitude and direction of target motion, fails to account for the three‐dimensional nature of the target; such a method neglects the volumetric effect of target shape on the fractional target volume irradiated when the target shifts partially out of the aperture. A mathematical framework is developed to analyze and illustrate the consequences of irradiating an irregular target shape in the presence of target motion. The effect of target shape on volume coverage is demonstrated for selected cases involving conventional BEV aperture design techniques. The volumetric implications of target shape are considered from two complementary points of view. The first involves transformation into a “displacement space,” which isolates the volumetric effect of the shape of the target allowing it to be studied independently of the probability distribution of target motion. The second point of view combines the effects of the 3D target shape and the probability distribution of motion in a manner independent of beam direction to yield a 3D “target distribution.” The two points of view represent distinct starting points for computation of the expected value of fractional target volume coverage in the presence of target motion. In certain cases it may be beneficial to (1) employ “target distributions” for the target and normal tissues in place of the conventional static PTV and, (2) include the aperture shape, on equal footing with parameters such as beam weights and energies, into a quantitative optimization process explicitly accounting for uncertainties in the position of the target volume and critical structures.
A source model for efficient brachytherapy computations with Monte Carlo
Authors: Weaver Keith , Hartmann Siantar Christine , Chandler William , White Roger M.
Published: March 2003

Monte Carlo techniques have the potential for producing accurate brachytherapy dose distributions in heterogeneous finite geometries. However, for routine clinical use, computational speed must be adequate. A fast, all‐particle, CT‐based Monte Carlo code called PEREGRINE is being developed at Lawrence Livermore National Laboratory for radiation treatment planning. As one feature, the code will produce accurate dose distributions from brachytherapy sources in heterogeneous geometries. For efficiency, brachytherapy sources in this model are treated as points or line segments. Radiation is emitted with the proper energy spectrum and (perhaps anisotropic) angular distribution. In particular, for anisotropic emission the polar angle is determined by a random‐number driven empirical function constructed from a source's measured or precomputed fluence emission pattern. Source model parameters are presented for iodine and iridium sources. While designed for the PEREGRINE program, this source model can be used in any Monte Carlo code.
An improved shift‐invariant artificial neural network for computerized detection of clustered microcalcifications in digital mammograms
Authors: Zhang Wei , Doi Kunio , Giger Maryellen L. , Nishikawa Robert M. , Schmidt Robert A.
Published: March 2003

A shift‐invariant artificial neutral network (SIANN) has been applied to eliminate the false‐positive detections reported by a rule‐based computer aided‐diagnosis (CAD) scheme developed in our laboratory. Regions of interest (ROIs) were selected around the centers of the rule‐based CAD detections and analyzed by the SIANN. In our previous study, background‐trend correction and pixel‐value normalization were used as the preprocessing of the ROIs prior to the SIANN. A ROI is classified as a positive ROI, if the total number of microcalcifications detected in the ROI is greater than a certain number. In this study, modifications were made to improve the performance of the SIANN. First, the preprocessing is removed because the result of the background‐trend correction is affected by the size of ROIs. Second, image‐feature analysis is employed to the output of the SIANN in an effort to eliminate some of the false detections by the SIANN. In order to train the SIANN to detect microcalcifications and also to extract image features of microcalcifications, the zero‐mean‐weight constraint and training‐free‐zone techniques have been developed. A cross‐validation training method was also applied to avoid the overtraining problem. The performance of the SIANN was evaluated by means of ROC analysis using a database of 39 mammograms for training and 50 different mammograms for testing. The analysis yielded an average area under the ROC curve (AZ) of 0.90 for the testing set. Approximately 62% of false‐positive clusters detected by the rule‐based scheme were eliminated without any loss of the true‐positive clusters by using the improved SIANN with image feature analysis techniques.
K‐characteristic photon absorption from intensifying screens and other materials: Theoretical calculations and measurements
Authors: McLean Donald , Gray Joel E.
Published: March 2003

When an extended object is irradiated with primary x rays, K‐characteristic radiation is produced throughout the object. At a given location, the ratio of the K‐characteristic radiation received to the primary radiation is not well understood. Knowledge of this ratio is important in the consideration of image detector design, as K‐characteristic radiation generated within or proximal to the imaging detector may be considered as secondary radiation and as a specialized form of scatter to primary ratio, will reduce image contrast. This article models the production of K‐characteristic radiation and calculates the K‐characteristic to primary exposure and absorbed energy ratios for a number of sample materials, geometries, and detector types. Calculations have been experimentally verified for tin and gadolinium oxysulphide sample materials in some geometries using an ionization chamber detector. It was found from calculation that the magnitude of the K/p exposure and absorbed energy ratio were closely related to the ratio of the field size to the detector‐to‐sample distance when the detector‐to‐sample distances are small compared to the source‐to‐detector distance. It was also found that the K/p exposure and absorbed energy ratios were maximal and constant when the field size to detector‐to‐sample ratio was greater than 20:1 for an intensifying screen detector and greater than 100:1 for ionization chamber measurements. Calculation, also confirmed experimentally, indicated that significant ratios of K/p absorbed energy could be detected using intensifying screens proximal to fluorescing sample material.
Three‐dimensional reconstruction of arteriovenous malformations from multiple stereotactic angiograms
Authors: Yeung Daniel , Chen Naidy , Ferguson Robert D. G. , Lee Laurance I. , Kun Larry E.
Published: March 2003

Stereotactic angiography is the preferred imaging modality in the radiosurgical treatment of arteriovenous malformations (AVM). A major limitation of this technique is the inability to determine the three‐dimensional shape and the volume of the AVM. We developed a technique for reconstructing the AVM from multiple stereotactic angiograms. The fiducial marks and the identified target area are digitized for each view. The 2‐D target area is then stereotactically backprojected into a 3‐D volume. The spatial boundary of the target volume is defined by superimposing the backprojections from each of the views. In feasibility studies with a phantom, this technique accurately reconstructed complex 3‐D structures, depicting fine details as small as 1 mm. Clinical studies in two patients indicated that this novel technique is very useful for the 3‐D reconstruction of AVM for radiosurgical treatment. The number of views required depends on the complexity of the object. In general, six to eight views appear adequate. The accuracy of the reconstruction can be compromised if the view angles are limited as with the current radiographic frame. A new frame design with practically unlimited view angles is proposed to avoid this potential limitation. However, structures that are always obscured (such as concavity) could not be accurately reconstructed, leading to overestimates of the object size. This “limitation” has a positive side, in that the technique will not underestimate the actual target volume. The ability to delineate both the shape and volume of the lesion should facilitate optimal target coverage while sparing a significant amount of normal tissue.
Comparison of x‐ray cross sections for diagnostic and therapeutic medical physics
Authors: Boone John M. , Chavez Andres E.
Published: March 2003

The purpose of this technical report is to make available an up‐to‐date source of attenuation coefficient data to the medical physics community, and to compare these data with other more familiar sources. Data files from Lawrence Livermore National Laboratory (in Livermore, CA) were truncated to match the needs of the medical physics community, and an interpolation routine was written to calculate a continuous set of cross sections spanning energies from 1 keV to 50 MeV. Coefficient data are available for elements Z=1 through Z=100. Values for mass attenuation coefficients, mass‐energy‐transfer coefficients, and mass‐energy absorption coefficients are produced by a single computer subroutine. In addition to total interaction cross sections, the cross sections for the photoelectric, Rayleigh, Compton, pair, and some triplet interactions are also produced by this single program. The coefficients were compared to the 1970 data of Storm and Israel over the energy interval from 1 to 1000 keV; for elements 10, 20, 30, 40, 50, 60, 70, and 80, the average positive difference between the Storm and Israel coefficients and the coefficients reported here are 1.4%, 2.7%, and 2.6%, for the mass attenuation, mass energy‐transfer, and mass‐energy absorption coefficients, respectively. The 1969 data compilation of mass attenuation coefficients from McMaster et al. were also compared with the newer LLNL data. Over the energy region from 10 keV to 1000 keV, and from elements Z=1 to Z=82 (inclusive), the overall average difference was 1.53% (σ=0.85%). While the overall average difference was small, there was larger variation (>5%) between cross sections for some elements. In addition to coefficient data, other useful data such as the density, atomic weight, K,L1, L2, L3, M, and N edges, and numerous characteristic emission energies are output by the program, depending on a single input variable. The computer source code, written in C, can be accessed and downloaded from the World Wide Web at: http://www.aip.org/epaps/epaps.html [E‐MPHSA‐23‐1997].
Effects of temperatures and extracellular proteins on dewaterability of thermophilically digested biosolids
Authors: Zhou Jianpeng , Mavinic Donald S , Kelly Harlan G , Ramey William D
Published: March 2003

Thermophilic processes digest sludge at high temperatures to produce Class A biosolids. Recent research work revealed that digestion temperature is the predominant factor affecting dewaterability of thermophilic biosolids. This paper presents findings of a laboratory study that investigated how various digestion temperatures affect dewaterability of digested biosolids, studied the phase partition of the substances affecting dewaterability in digested biosolids, and tested the role of extracellular proteins in affecting dewaterability. Secondary sludges were digested at 40°C, 50°C, 60°C, 70°C, or 22°C for up to 12 d. Filtrates from thermophilically digested biosolids were treated with protease and boiling. This study found that, during the first few hours of digestion, higher temperatures resulted in more rapid and more significant deterioration in dewaterability than lower digestion temperatures. Continued digestion resulted in either improved (60°C or 70°C), unchanged (40°C or 50°C), or gradually deteriorated dewaterability (22°C). The substances affecting dewaterability were primarily located in the liquid phase of thermophilically digested biosolids. Boiling treatment did not result in significant changes in dewaterability. Protease treatment of the liquid phase of thermophilic biosolids improved dewaterability by 1319%. Such an improvement confirmed the role of proteins in affecting dewaterability. Key words: dewaterability, thermophilic, mesophilic, digestion, biosolids, protein, protease.
Transport of bacteria in heterogeneous media under leaching conditions
Authors: Lo Kei Wai , Jin Yee-Chung , Viraraghavan T
Published: March 2003

Bacterial mobility under unsaturated soils play an important role in the dispersal of pathogenic microorganisms and enhancing biorestoration of contaminated soil. Experiments were conducted to evaluate the effects of bacterial retention under unsaturated flow conditions in 5% and 10% bentonitesand mixtures. Bacterial transport and retention was investigated under different rainfall events at 22°C and 4°C. Results indicated that bacterial accumulation was predominantly at the surface of the porous media and decreased with depth. Bacterial movement was also retarded relative to the chloride tracer in all fractions of the porous media. Heterogeneity of the porous media enhanced retention through filtration, specific surface area, and reduction in permeability. Recovery of the bacteria was influenced by the airwater interface with greater bacteria recovered at 4°C compared to 22°C. The colloidal filtration model described the distribution through the experimental columns. A linear relationship was observed between the filtration coefficient and the hydraulic conductivity from the different proportions of bentonitesand. This correlation confirms that the colloidal filtration model can be used to determine the transport of bacteria through varying hydraulic conductivities of the porous media. Key words: porous media, hydraulic conductivity, retention, unsaturated flow, bacterial transport, filtration coefficient.
Walkerton: Lessons learned in comparison with waterborne outbreaks in the developed world
Authors: Hrudey S E , Huck P M , Payment P , Gillham R W , Hrudey E J
Published: March 2003

An estimated 2300 people became seriously ill and 7 died from exposure to microbially contaminated drinking water in the town of Walkerton, Ontario, in May of 2000. The severity of this drinking water disaster resulted in the Government of Ontario calling a public inquiry by Mr. Justice Dennis O'Connor to address the cause of the outbreak, the role, if any, of government policies in contributing to this outbreak, and ultimately, the implications of this experience on the safety of drinking water across the province of Ontario. This paper summarizes relevant evidence presented at the inquiry by the expert panel together with Justice O'Connor's findings addressing the circumstances of the outbreak. These findings are reviewed in relation to the published causes of previous waterborne disease outbreaks that have been reported elsewhere in developed countries. The circumstances surrounding the Walkerton tragedy are an important source of knowledge for those concerned with providing safe drinking water to the public. Although some circumstances are obviously specific to this epidemic, others echo common themes in waterborne outbreaks that have occurred before. These common themes suggest the need for attention to broad issues of drinking water safety in addition to the individual specific details that often command attention. Key words: waterborne disease, Escherichia coli O157:H7, Campylobacter jejuni, Cryptosporidium, Giardia, multiple barriers, health risk.
Challenges in using environmental indicators for measuring sustainability practices
Authors: Tam Edwin K.L
Published: March 2003

Many businesses are pursuing sustainability for a variety of reasons, ranging from increased financial competitiveness to meeting upcoming regulatory initiatives. Choosing the appropriate indicators to measure environmental progress, however, is a critical challenge. Using data from the automotive industry, this paper illustrates how indicators can be incorrectly selected, misused, or misinterpreted, resulting in misleading conclusions. Such issues are especially critical when using indicators in emerging tools, such as life cycle analysis, to assess the impacts posed by alternative designs. Furthermore, incorporating the impacts represented by the indicators into the decision-making process can be problematic, since these indicators will be used to assess the success or failure of design changes. The automotive sector is an ideal example because it has implemented a variety of measures to meet its environmental challenges: numerous indicators and decision approaches have been developed for or adapted to the industry and it has had to address important issues, such as the use of normalized metrics and appropriate weighting schemes. Key words: indicators, automotive industry, sustainability, environment, life cycle assessment, decision making.
A mathematical modeling approach to improve the point estimation of landfill gas surface emissions using the flux chamber technique
Authors: Perera M D.N , Hettiaratchi J P.A , Achari G
Published: March 2003

The accurate determination of gas emissions from sanitary landfills is necessary to assess the contribution of landfill gas emissions to global warming and to develop optimum techniques to control emissions from individual landfills. The most popular method available for point measurement of landfill gas, the closed or static flux chamber technique, has inaccuracies associated with the technique itself. A new mathematical modeling approach is presented to estimate the errors caused by changes to the flow pattern of gases within the soil cover when a closed flux chamber is placed on top of the cover to measure gas emissions. The proposed two-dimensional numerical model considers both advective and dispersive processes of gas migration. The model was calibrated and verified using data from controlled laboratory experiments. The model was able to predict the fluxes with 95% accuracy. Based on laboratory experiments and model predictions, our analysis showed that a closed flux chamber technique would underestimate actual gas flux by as much as 65% depending on the configuration of the flux chamber, the actual flux rate, and the characteristics of the soil in the landfill cover. Key words: landfill gas, methane, global warming, mathematical modeling, landfill cover, simulation, environmental monitoring, flux chamber.
Réduction de la concentration des tensioactifs dans une solution aqueuse par électroflotation
Authors: Moulai-Mostefa N , Tir M
Published: March 2003

The purpose of this study was to investigate the use of electroflotation to reduce surfactant concentrations of Tween 20 and Tween 60 present in aqueous streams. A series of experiments was carried out using a reactor of electroflotation. The variables examined included the effects of the current density, the additive concentration, and the initial surfactant concentration. Results showed that the residual surfactant concentration decreases by increasing the current density, the added salt concentrations, or the initial concentration of solution. According to these results, more than 88% of Tween 60 and 75% of Tween 20 are effectively separated from an initial concentration of 200 mg/L. Key words: wastewater, surfactant, electroflotation, reduction.
Evaluation of adsorption and coagulation as membrane pretreatment steps for the removal of organic material and disinfection-by-product precursors
Authors: Bérubé P R , Mavinic D S , Hall E R , Kenway S E , Roett K
Published: March 2003

Adsorption using powdered activated carbon and coagulation using polyaluminium chloride or aluminum sulphate were investigated as pretreatment steps prior to membrane filtration to remove organic material and trihalomethane (THM) precursors contained in a raw drinking water source. Ultrafiltration and microfiltration membrane treatment alone could not effectively and consistently remove organic material, measured as total organic carbon, and THM precursors, measured as chloroform formation potential, contained in the raw water. Coagulation, prior to membrane treatment, significantly improved the removal of organic material and THM precursors contained in the raw water. Microfiltration membrane treatment, with pre-coagulation, consistently removed approximately 75% of the organic material and the THM precursors contained in the raw water. A coagulant concentration of approximately 0.3 mg/L, as Al, was sufficient to achieve this high removal efficiency. Adsorption, prior to membrane treatment, did not significantly improve the removal of organic material or THM precursors. Key words: adsorption, chloroform, coagulation, disinfection-by-products, drinking water treatment, microfiltration, trihalomethanes, ultrafiltration.
A study of aerobic digester performance with the use of methanol for biological nutrient removal in a full-scale sequencing batch reactor
Authors: Koh Jeffrey J.H , Mavinic Donald S , Oldham William K , Meisen Axel , Nuttall Steven J
Published: March 2003

The primary goal of this research was to determine whether the use of methanol in a full-scale sequencing batch reactor (SBR) affected the subsequent aerobic sludge digester performance. The methanol injection into an experimental SBR resulted in a significant increase in the solids level in the SBR, increased wasting into the digesters, and a lower sludge age. When the methanol dosage in the SBR was 81 L/d, the dissolved oxygen level in the subsequent aerobic digesters became inadequate for proper digestion. The net result was a drop in solids reduction efficiency. However, the methanol injection appeared to have no effect on the dewaterability of the digested sludge, as samples from the experimental and control units had very similar capillary suction time (CST) results. It was found that the dewaterability was affected not only by the total suspended solids concentration of the digested sludge, but even more by the temperature of the digested sludge, through a change in filtrate viscosity. Key words: aerobic digestion, biological nutrient removal, denitrification, methanol, sludge dewaterability.
A Study of Value Factors for Adopting Information Technology in Professional Service Industry — A Demonstrative Case of Accounting Firms in Taiwan
Authors: Huang Shi-Ming , Ku Cheng-Yuan , Chu Yuan-Te , Hsueh Hsiang-Yuan
Published: March 2003

With the popular adoption of information technology (IT), business models and types of services in industries are strongly influenced. Consider the professional service industries such as accounting firms, services are the main business activities in their daily job. These firms are now facing the critical issue on how to apply IT effectively and improve their service quality. The purpose of this paper is to provide a demonstrative analysis for the evaluation of valuable activities in professional service firms via "Value Shop" model. And then find the strategic benefits of IT invested with corresponding value activities by the case study of accounting firms in Taiwan. The findings indicate that IT investment is indeed helpful for activities in daily business activities in such firms, whether it is strategy-centric, managerial, or operational activities.
Impacts of Intervention Incorporates with Interest Rate Policy on Taiwan's Economy in E-commerce Environment
Authors: Lo Melody
Published: March 2003

Fully sterilized intervention, an operation that involves a pure swap of foreign and domestic assets which leaves the money supply unchanged, gained it popularity through the experience among developed countries in the early 1980s. Ideally, it provides an independent policy tool that allows monetary authorities to pursue internal and external stabilization objectives simultaneously. In this paper, we employ a vector error correction model (VECM) to examine the dynamic interactions between exchange rate condition and policy reactions by Taiwanese monetary authorities, as Taiwan is ready to join the WTO and to help businesses take full advantages of e-commerce. We found that little efforts were made to sterilize interventions in the short term after an exchange rate shock occurred. The intention of not to sterilize interventions is to alleviate the exchange rate pressure by drastically changing domestic short term interest rates to force private sectors instantaneously adjust shares between domestic and foreign assets in their portfolios where there are speculative positions. Presumably, this official effort to avoid great fluctuations of exchange rates would offer businesses more freedoms in dealing with challenges in e-commerce environment. The result also suggests that, unlike the experience in developed countries, an independent monetary policy may not always be preferred by policy markers in small open economies.
ARCHITECTURAL OR MODULAR INNOVATION? MANAGING DISCONTINUOUS PRODUCT DEVELOPMENT IN RESPONSE TO CHALLENGING ENVIRONMENTAL PERFORMANCE TARGETS
Authors: MAGNUSSON THOMAS , LINDSTRÖM GÖRAN , BERGGREN CHRISTIAN
Published: March 2003

By adopting challenging targets on environmental performance, pro-active industrial firms may push themselves towards discontinuous product innovation. Such innovation can be understood as being either architectural, i.e. arranging components in new ways, or modular, i.e. introducing new technologies in specific components or subsystems. We argue that these two dimensions of discontinuous change call for some specific managerial responses. Architectural innovation challenges the whole engineering organisation, making it necessary to focus development efforts on technological interfaces, whereas modular innovation has a more isolated effect, making specialisation and co-ordination over organisational boundaries particularly important. Altogether, our analysis highlights the importance of adapting the project organisation to the development task and addressing part-whole relationships when managing innovation in established products and systems, something that becomes increasingly important in the strive towards sustainable development.
REGIONAL INNOVATION SYSTEMS IN THE PERIPHERY: THE CASE OF THE BEAUCE IN QUÉBEC (CANADA)
Authors: DOLOREUX DAVID
Published: March 2003

All too often, innovation research emphasizes core regions exemplifying successful innovation systems or "learning regions" such as, Silicon Valley, Route 128, Emilia-Romagna and Baden-Württemberg. However, lessons learned from these regions are seldom applicable elsewhere, in particular to territories where actors strategic to the innovation process are less diversified. The regional innovation system (RIS) in peripheral regions, and the likelihood of their acting as conduits for the innovation system, have seldom been the subjects of discussion. The objective of this paper is to study the way in which innovation occurs, including an investigation of actual innovation activities and capabilities of firms located in a peripheral area, and specific factors affecting their innovation activities. The discussion draws its empirical substance from the case of the Beauce in Québec (Canada). A survey of 45 SMEs was conducted in order to get a better understanding of the key dimensions of innovation activities.
CHOICE OF ENERGY DATA IN ENVIRONMENTAL ASSESSMENT OF THE BUILT ENVIRONMENT
Authors: VON MALMBORG FREDRIK BURSTRÖM , FORSBERG ANNA
Published: March 2003

Life cycle oriented methods are increasingly used for environmental assessments (EAs) of the built environment. However, many assumptions are made in such assessments, potentially influencing the results and making the assessment more ambiguous. To increase the reliability of EAs, consequences of the assumptions made have to be better understood. Since energy use in the operation and maintenance phase is an important factor decisive for the overall environmental performance of a building, the purpose of this study is to investigate how the selection of heat and electricity mix affects the assessed environmental performance of buildings. It also aims to suggest how to choose heat and electricity data in EAs of the built environment in general.

Applying four different modes of electricity production and two different modes of heat production in a case study of three different buildings with different technical solutions for heat and electricity supply, the study show that choices of heat and electricity mix have significant influence on the final results of the EA. Regarding the choice of heat and electricity mix in an EA of buildings and the built environment, it is argued that both average and marginal data on electricity production should be used in general. As for data on district heat production, it is recommended to use data on the average production in the specific, local district heating system in general. Finally, it is argued that consequences of the assumptions made should be explicitly communicated in the EA report, so as to let the decision-makers rather than the analysts make the evaluation.