bluuebunny/crossref_metadata_2025 huggingface dataset:
Intermediate energy photons to improve dose gradient, conformality, and homogeneity: Potential benefits for small field intracranial radiosurgery
Authors: Keller Brian M. , Pignol Jean‐Philippe , Presutti Joe , Beachey David J.
Published: January 2009

A previously conceived and demonstrated principle of reducing penumbra for small radiosurgical dose fields is here now applied to a multiple beam arrangement in a stereotactic head phantom. In this work it is found that the fourfold reduction in radiological penumbra of small, single x‐ray fields translates to a more conformal, homogeneous dose distribution in the more complex beam arrangements. The film dosimetry is conducted with a high resolution digital microscope to quantify the sharp dose gradients. Further, the Gafchromic EBT™ film measurements in phantom are compared to calculations using the Xknife RT3 (Radionics, Burlington, MA) treatment planning software (TPS) with modeled beam data. An orthogonal pair of coplanar beams and an 18‐beam coplanar arc irradiation both yielded agreement between the modeling within the TPS and the film work. Conventional modality is compared alongside throughout. The 90%–50% and 90%–10% dose gradients at the intersection of the orthogonal beam pair were 1.7 and for versus 0.5 and for for an identical setup. The 18‐beam coplanar arc plan yielded 90%–80% and 90%–50% dose gradients of 0.84 and for versus gradients of 0.29 and for for the midaxial slice coplanar with all beamlet axes. Uncertainties in gradient measurements were . The 18‐beam coplanar beam arrangement represented a worst case scenario for penumbra overlap deteriorating the dose distribution. In brief, x‐rays provided superior homogeneity, conformality, and dose fall‐off to for the irradiations examined.
Multiscale registration of planning CT and daily cone beam CT images for adaptive radiation therapy
Authors: Paquin Dana , Levy Doron , Xing Lei
Published: January 2009

Adaptive radiation therapy (ART) is the incorporation of daily images in the radiotherapy treatment process so that the treatment plan can be evaluated and modified to maximize the amount of radiation dose to the tumor while minimizing the amount of radiation delivered to healthy tissue. Registration of planning images with daily images is thus an important component of ART. In this article, the authors report their research on multiscale registration of planning computed tomography (CT) images with daily cone beam CT (CBCT) images. The multiscale algorithm is based on the hierarchical multiscale image decomposition of E. Tadmor, S. Nezzar, and L. Vese [Multiscale Model. Simul. 2(4), pp. 554–579 (2004)]. Registration is achieved by decomposing the images to be registered into a series of scales using the (BV, ) decomposition and initially registering the coarsest scales of the image using a landmark‐based registration algorithm. The resulting transformation is then used as a starting point to deformably register the next coarse scales with one another. This procedure is iterated at each stage using the transformation computed by the previous scale registration as the starting point for the current registration. The authors present the results of studies of rectum, head‐neck, and prostate CT‐CBCT registration, and validate their registration method quantitatively using synthetic results in which the exact transformations our known, and qualitatively using clinical deformations in which the exact results are not known.
Self‐calibration of a cone‐beam micro‐CT system
Authors: Patel V. , Chityala R. N. , Hoffmann K. R. , Ionita C. N. , Bednarek D. R. , Rudin S.
Published: January 2009

Use of cone‐beam computed tomography (CBCT) is becoming more frequent. For proper reconstruction, the geometry of the CBCT systems must be known. While the system can be designed to reduce errors in the geometry, calibration measurements must still be performed and corrections applied. Investigators have proposed techniques using calibration objects for system calibration. In this study, the authors present methods to calibrate a rotary‐stage CB micro‐CT system using only the images acquired of the object to be reconstructed, i.e., without the use of calibration objects. Projection images are acquired using a system constructed in the authors’ laboratories. Dark‐ and flat‐field corrections are performed. Exposure variations are detected and quantified using analysis of image regions with an unobstructed view of the x‐ray source. Translations that occur during the acquisition in the horizontal direction are detected, quantified, and corrected based on sinogram analysis. The axis of rotation is determined using registration of antiposed projection images. These techniques were evaluated using data obtained with calibration objects and phantoms. The physical geometric axis of rotation is determined and aligned with the rotational axis (assumed to be the center of the detector plane) used in the reconstruction process. The parameters describing this axis agree to within and with those determined using other techniques. Blurring due to residual calibration errors has a point‐spread function in the reconstructed planes with a full‐width‐at‐half‐maximum of less than in a tangential direction and essentially zero in the radial direction for the rotating object. The authors have used this approach on over 100 acquisitions over the past and have regularly obtained high‐quality reconstructions, i.e., without artifacts and no detectable blurring of the reconstructed objects. This self‐calibrating approach not only obviates calibration runs, but it also provides quality control data for each data set.
The effective atomic numbers of some biomolecules calculated by two methods: A comparative study
Authors: Manohara S. R. , Hanagodimath S. M. , Gerward L.
Published: January 2009

The effective atomic numbers of some fatty acids and amino acids have been calculated by two numerical methods, a direct method and an interpolation method, in the energy range of 1 keV–20 MeV. The notion of is given a new meaning by using a modern database of photon interaction cross sections (WinXCom). The results of the two methods are compared and discussed. It is shown that for all biomolecules the direct method gives larger values of than the interpolation method, in particular at low energies (1–100 keV) At medium energies (0.1–5 MeV), for both methods is about constant and equal to the mean atomic number of the material. Wherever possible, the calculated values of are compared with experimental data.
Monte Carlo simulation of an x‐ray volume imaging cone beam CT unit
Authors: Spezi Emiliano , Downes Patrick , Radu Emil , Jarvis Richard
Published: January 2009

In this work the authors characterized the radiation field produced by a kilovolt cone beam computed tomography (CBCT) unit integrated in the Elekta Synergy linear accelerator. The x‐ray volume imaging (XVI) radiation unit was modeled in detail using the BEAMNRC Monte Carlo (MC) code system. The simulations of eight collimator cassettes and the neutral filter F0 were successfully carried out. MC calculations from the EGSNRC code DOSXYZNRC were benchmarked against measurements in water. A large set of depth dose and lateral profiles was acquired with the ionization chamber in water, with the x‐ray tube in a stationary position, and with the beam energy set to 120 kV. Measurements for all the available collimator cassettes were compared with calculations, showing very good agreement ( in most cases). Furthermore, half value layer measurements were carried out and used to validate the MC model of the XVI unit. In this case dose calculations were performed with the EGSNRC code cavity and these showed excellent agreement. In this manuscript the authors also report on the optimization work of the relevant parameters that influenced the development of the MC model. The dosimetric part of this work was very useful in characterizing the XVI radiation output for the energy of interest. The detailed simulation part of the work is the first step toward an accurate MC based assessment of the dose delivered to patients during routine CBCT scans for image and dose guided radiotherapy.
Iterative image reconstruction for CBCT using edge‐preserving prior
Authors: Wang Jing , Li Tianfang , Xing Lei
Published: January 2009

On‐board cone‐beam computed tomography (CBCT) is a new imaging technique for radiation therapy guidance, which provides volumetric information of a patient at treatment position. CBCT improves the setup accuracy and may be used for dose reconstruction. However, there is great concern that the repeated use of CBCT during a treatment course delivers too much of an extra dose to the patient. To reduce the CBCT dose, one needs to lower the total mAs of the x‐ray tube current, which usually leads to reduced image quality. Our goal of this work is to develop an effective method that enables one to achieve a clinically acceptable CBCT image with as low as possible mAs without compromising quality. An iterative image reconstruction algorithm based on a penalized weighted least‐squares (PWLS) principle was developed for this purpose. To preserve edges in the reconstructed images, we designed an anisotropic penalty term of a quadratic form. The algorithm was evaluated with a CT quality assurance phantom and an anthropomorphic head phantom. Compared with conventional isotropic penalty, the PWLS image reconstruction algorithm with anisotropic penalty shows better resolution preservation.
Dosimetric equivalence of nonstandard HDR brachytherapy catheter patterns
Authors: Cunha J. A. M. , Hsu I‐C. , Pouliot J.
Published: January 2009

Purpose: To determine whether alternative high dose rate prostate brachytherapy catheter patterns can result in similar or improved dose distributions while providing better access and reducing trauma. Materials and Methods: Standard prostate cancer high dose rate brachytherapy uses a regular grid of parallel needle positions to guide the catheter insertion. This geometry does not easily allow the physician to avoid piercing the critical structures near the penile bulb nor does it provide position flexibility in the case of pubic arch interference. This study used CT datasets with slice spacing from ten previously treated patients and digitized new catheters following three hypothetical catheter patterns: conical, bi‐conical, and fireworks. The conical patterns were used to accommodate a robotic delivery using a single entry point. The bi‐conical and fireworks patterns were specifically designed to avoid the critical structures near the penile bulb. For each catheter distribution, a plan was optimized with the inverse planning algorithm, IPSA™, and compared with the plan used for treatment. Irrelevant of catheter geometry, a plan must fulfill the RTOG‐0321 dose criteria for target dose coverage and organ‐at‐risk dose sparing (, , ). Results: The three nonstandard catheter patterns used 16 nonparallel, straight divergent catheters, with entry points in the perineum. Thirty plans from ten patients with prostate sizes ranging from were optimized. All nonstandard patterns fulfilled the RTOG criteria when the clinical plan did. In some cases, the dose distribution was improved by better sparing the organs‐at‐risk. Conclusion: Alternative catheter patterns can provide the physician with additional ways to treat patients previously considered unsuited for brachytherapy treatment (pubic arch interference) and facilitate robotic guidance of catheter insertion. In addition, alternative catheter patterns may decrease toxicity by avoidance of the critical structures near the penile bulb while still fulfilling the RTOG criteria.
Error analysis of marker‐based object localization using a single‐plane XRII
Authors: Habets Damiaan F. , Pollmann Steven I. , Yuan Xunhua , Peters Terry M. , Holdsworth David W.
Published: January 2009

The role of imaging and image guidance is increasing in surgery and therapy, including treatment planning and follow‐up. Fluoroscopy is used for two‐dimensional (2D) guidance or localization; however, many procedures would benefit from three‐dimensional (3D) guidance or localization. Three‐dimensional computed tomography (CT) using a C‐arm mounted x‐ray image intensifier (XRII) can provide high‐quality 3D images; however, patient dose and the required acquisition time restrict the number of 3D images that can be obtained. C‐arm based 3D CT is therefore limited in applications for x‐ray based image guidance or dynamic evaluations. 2D‐3D model‐based registration, using a single‐plane 2D digital radiographic system, does allow for rapid 3D localization. It is our goal to investigate—over a clinically practical range—the impact of x‐ray exposure on the resulting range of 3D localization precision. In this paper it is assumed that the tracked instrument incorporates a rigidly attached 3D object with a known configuration of markers. A 2D image is obtained by a digital fluoroscopic x‐ray system and corrected for XRII distortions and mechanical C‐arm shift . A least‐square projection‐Procrustes analysis is then used to calculate the 3D position using the measured 2D marker locations. The effect of x‐ray exposure on the precision of 2D marker localization and on 3D object localization was investigated using numerical simulations and x‐ray experiments. The results show a nearly linear relationship between 2D marker localization precision and the 3D localization precision. However, a significant amplification of error, nonuniformly distributed among the three major axes, occurs, and that is demonstrated. To obtain a 3D localization error of less than for an object with marker spacing, the 2D localization precision must be better than . This requirement was met for all investigated nominal x‐ray exposures at FOV, and for all but the lowest two at FOV. However, even for those two nominal exposures, the expected 3D localization error is less than . The tracking precision was for the out‐of‐plane translations, for in‐plane translations, and for the rotations. The root mean square (RMS) difference between the true and projection‐Procrustes calculated location was . It is believed these results show the potential of this technique for dynamic evaluations or real‐time image guidance using a single x‐ray source and XRII detector.
VEGF-A and i-NOS expression are prognostic factors in serous epithelial ovarian carcinomas after complete surgical resection
Authors: Engels K , du Bois A , Harter P , Fisseler-Eckhoff A , Kommoss F , Stauber R , Kaufmann M , Nekljudova V , Loibl S
Published: January 2009

Aims:

Clinical stage at the time of diagnosis and achievement of complete macroscopic resection during initial surgery are key factors determining the outcome of ovarian cancer. However, prediction of outcome lacks accuracy and more reliable prognostic factors are required. Therefore, an analysis and evaluation of key angiogenic factors was carried out to determine their diagnostic and prognostic value in serous ovarian cancer.

Methods:

Expression levels of vascular endothelial growth factor (VEGF)-A, hypoxia-inducible factor (HIF)1-α and inducible nitric oxide synthase (i-NOS) were analysed by immunohistochemistry in a homogenous group of 112 patients with serous adenocarcinoma of the ovary. Vascular density as an indicator of angiogenesis was assessed using the Chalkley eyepiece method after staining for CD34. The correlation of these data with survival and established prognostic factors such as histological grade, Federation of Gynecology and Obstetrics (FIGO) stage, and residual tumour after surgery, was evaluated. Survival analyses, multivariate analyses and correlation tests were performed.

Results:

In the patient group with macroscopic complete tumour resection (R0) there was a significant correlation between VEGF-A and i-NOS expression. Kaplan–Meier analysis further revealed improved progression-free survival for R0 patients with VEGF-A-positive and i-NOS-negative tumours. The predictive relevance of VEGF-A regarding progression-free survival was sustained in multivariate analysis using FIGO stage, grading and resection status as fixed variables.

Conclusion:

VEGF-A and i-NOS are prognostic markers for clinical outcome in serous ovarian cancer patients with macroscopic complete tumour resection (R0). Hence, pre-therapeutic assessment of VEGF-A as predictive factor for an antiangiogenic therapy might be of clinical value.
(Epi)genomics and neurodevelopment in schizophrenia: monozygotic twins discordant for schizophrenia augment the search for disease-related (epi)genomic alterationsBased on a lecture during the joint meeting of the Genetics Society of Canada and the Society of Developmental Biology, 1 March 2008, at Banff Centre, Banff, Alberta, Canada, in recognition of the William F. Grant and Peter B. Moens Award of Excellence (2008) of the Genetics Society of Canada to Professor Shiva M. Singh.
Authors: Singh Shiva M. , O’Reilly Richard
Published: January 2009

Unlike stunning breakthroughs in the identification of genes for Mendelian disorders during the last three decades, gene identification in most complex disorders has been full of twists and turns and little progress. Doing more of the same will not guarantee success. The lessons learned argue for a need to reconsider genetic models that are appropriate for the disorder in question along with an interdisciplinary, systematic approach using genomic methods that have now become possible. We will use schizophrenia as an example to review the genetic progress to date that has been disappointing. We will argue that the causation of this complex disease may involve heterogeneous genomic changes of major effect. We will provide three approaches, retroviral transpositions, methylation, and copy number variations, to test this hypothesis. We will present arguments to suggest that such experiments will be most effective if undertaken on monozygotic twins. It will include our experience with associated experiments on the monozygotic twins discordant for schizophrenia. The results support that (epi)genomic changes of major effect, rather than accumulation of mutations of small effect, underlie the causation of this complex disease. More important, this experimental strategy will be an effective strategy for studies on other complex (behavioural) disorders as well.
Insect mitochondrial genomics 3: the complete mitochondrial genome sequences of representatives from two neuropteroid orders: a dobsonfly (order Megaloptera) and a giant lacewing and an owlfly (order Neuroptera)
Authors: Beckenbach Andrew T. , Stewart James Bruce
Published: January 2009

We describe the complete mitochondrial genomes from representatives of two orders of the Neuropterida: a dobsonfly, Corydalus cornutus (Megaloptera: Corydalidae, GenBank Accession No. FJ171323), a giant lacewing Polystoechotes punctatus (Neuroptera: Polystoechotidae, FJ171325), and an owlfly, Ascaloptynx appendiculatus (Neuroptera: Ascalaphidae, FJ171324). The dobsonfly sequence is 15 687 base pairs with a major noncoding (A+T rich) region of approximately 967 bp. The gene content and organization of the dobsonfly is identical to that of most insects. The giant lacewing sequence is 16 036 bp with a major noncoding region of about 1123 bp, while the owlfly sequence is 15 877 bp with a major noncoding region of about 1066 bp. The two Neuroptera sequences include a transposition of two tRNA genes, tRNATrpand tRNACys. These tRNA genes are coded on opposite strands and overlap by seven residues in the standard insect mitochondrial gene arrangement. Thus, the transposition required a duplication of at least the region of overlap. It is likely that the transposition occurred by a duplication of both genes followed by deletion of one copy of each gene. Examination of this region in two other neuropteroid species, a snakefly, Agulla sp. (Raphidioptera: Raphidiidae), and an antlion, Myrmeleon immaculatus (Neuroptera: Myrmeleontidae), shows that the rearrangement is widespread in the order Neuroptera but not present in either of the other two orders of Neuropterida.
An X chromosome effect responsible for asymmetric reproductive isolation between maleDrosophila virilisand heterospecific females
Authors: Nickel Desirée , Civetta Alberto
Published: January 2009

Reproductive isolation between closely related species is expressed through uncoordinated courtship, failed fertilization, and (or) postzygotic barriers. Behavioural components of mating often form an initial barrier to hybridization between species. In many animals, females are responsible for mating discrimination in both intra- and interspecific crosses; males of Drosophila virilis group represent an exception to this trend. Using overall productivity tests, we show that a lower proportion of D. virilis males sire progeny when paired with a heterospecific female ( Drosophila novamexicana or Drosophila americana texana ) for 2 weeks. This suggests male mate discrimination or some other kind of asymmetrical incompatibility in courtship and mating or early zygote mortality. We used males from D. virilis – D. novamexicana and from D. virilis – D. a. texana backcross populations to map chromosome effects responsible for male reproductive isolation. Results from the analysis of both backcross male populations indicate a major X chromosome effect. Further, we conduct a male behavioural analysis to show that D. virilis males significantly fail to continue courtship after the first step of courtship, when they tap heterospecific females. The combined results of a major X chromosome effect and the observation that D. virilis males walk away from females after tapping suggest that future studies should concentrate on the identification of X-linked genes affecting the ability of males to recognize conspecific females.
Isolation of expressed sequences from a specific chromosome ofThinopyrum intermediuminfected by BYDV
Authors: Jiang Shu-Mei , Yin Wei-Bo , Hu Jun , Shi Rui , Zhou Ruo-Nan , Chen Yu-Hong , Zhou Guang-He , Wang Richard R.-C. , Song Li-Ying , Hu Zan-Min
Published: January 2009

To map important ESTs to specific chromosomes and (or) chromosomal regions is difficult in hexaploid wheat because of its large genome size and serious interference of homoeologous sequences. Large-scale EST sequencing and subsequent chromosome localization are both laborious and time-consuming. The wheat alien addition line TAi-27 contains a pair of chromosomes of Thinopyrum intermedium (Host) Barkworth & D.R. Dewey that carry the resistance gene against barley yellow dwarf virus. In this research, we developed a modified technique based on chromosome microdissection and hybridization-specific amplification to isolate expressed sequences from the alien chromosome of TAi-27 by hybridization between the DNA of the microdissected alien chromosome and cDNA of Th. intermedium infected by barley yellow dwarf virus. Twelve clones were selected, sequenced, and analyzed. Three of them were unknown genes without any hit in the GenBank database and the other nine were highly homologous with ESTs of wheat, barley, and (or) other plants in Gramineae induced by abiotic or biotic stress. The method used in this research to isolate expressed sequences from a specific chromosome has the following advantages: (i) the obtained expressed sequences are larger in size and have 3′ end information and (ii) the operation is less complicated. It would be an efficient improved method for genomics and functional genomics research of polyploid plants, especially for EST development and mapping. The obtained expressed sequence data are also informative in understanding the resistance genes on the alien chromosome of TAi-27.
Reduction of acid generation in mine tailings through the use of moisture-retaining cover layers as oxygen barriers
Authors: Nicholson Ronald V. , Gillham Robert W. , Cherry John A. , Reardon Eric J.
Published: January 2009

Acid production in sulphidic tailings can cause severe degradation of water quality in both subsurface and surface systems. The availability of gaseous oxygen and the rate of diffusion of oxygen through the open pore spaces in the upper zone of the tailings are the critical factors controlling the rate of acid generation. Acid generation can be reduced by applying a fine-grained, nonreactive cover layer to the tailings surface. The key process involves moisture retention by capillary forces so that near-saturated conditions can be maintained even when the cover layer occurs at several metres above the water table. Textured layering of fine over coarse materials improves moisture retention in the fine layer when infiltration exceeds evapotranspiration. The application of such a cover layer can theoretically reduce oxygen diffusion coefficients and rates of acid generation by up to four orders of magnitude. This can represent a substantial difference in the potential treatment costs of tailings seepage. Simplified calculations based on Fick's first law can be applied to preliminary laboratory measurements of diffusion characteristics of potential cover materials to evaluate their effectiveness in decreasing acidification. These concepts and methods provide an initial evaluation before field-scale testing of cover performance. Key words: pyrite oxidation, tailings, remediation, covers, acid generation, oxygen diffusion.
Foundation design for the Skydome Stadium, Toronto
Authors: Lo K. Y. , Cooke B. H.
Published: January 2009

The construction of the Skydome Stadium will provide Toronto with the first multipurpose stadium in the world with a retractable roof. The foundation for the structure, with a diameter of about 210 m and a height of about 86 m, will be supported by several hundred columns, about 100 of which will have loadings up to 50 000 kN. The foundation rock is a shale with numerous highly weathered zones and clay seams. Laboratory tests to investigate the strength and deformation properties of these weak layers were performed. Field plate loading tests at two locations with three different size plates were also carried out to study the size effect on the mass modulus of the rock. This paper presents the results of detailed geological mapping and field and laboratory tests together with design considerations for the foundations. The field acceptance criteria, developed to ensure that the differential settlements between foundations are within specified limits, are also discussed. Key words: Skydome, shale, clay seams, plate loading tests, rock-mass modulus, size effect, layered rocks.
Influence of changes in methanol concentration on clay particle interactions
Authors: Storey John M. E. , Peirce J. Jeffrey
Published: January 2009

The interactions of clay particles with alcohol–water mixtures are investigated with hydraulic conductivity measurements, the electrophoretic mobilities of the suspended particles are measured, particle settling tests are carried out, and Atterberg limits are determined. Organic liquids frequently interact with clay particles in the clay liners of surface impoundments. Such fluids can cause changes in hydraulic conductivity of the liner material. This study looks at the effects of dilution of a liquid hydrocarbon with water on the properties of a clay soil. Tests with 20, 40, 60, 80, and 100% (by volume) methanol concentrations are used to investigate the changes in hydraulic conductivity of water-compacted clay samples. Particle settling tests, Atterberg limits, and electrophoretic mobility studies are used with the same concentrations to determine the effects of changing methanol concentration on clay particle behavior. The results indicate that higher concentrations of methanol cause an increase in the attraction between the clay particles, and the same concentrations also cause an increase in hydraulic conductivity. Key words: Atterberg limits, clay, electrophoresis, hydraulic conductivity, methanol, settling tests, zeta potential.
Setbacks from the crests of slopes along the North Saskatchewan River, Alberta
Authors: Cruden D. M. , Tedder K. H. , Thomson S.
Published: January 2009

Setbacks from the crests of slopes along the North Saskatchewan River valley between Edmonton and Fort Saskatchewan can be estimated from the ultimate angle of the slope and the rate of lateral river erosion. The ultimate slope angle depends on the slope stratigraphy and the position of the water table in the slope. Three slopes, in overburden, with a bedrock base and dominantly in bedrock, typically having groundwater tables at respectively the toe of the slope, halfway up the slope, and at the lower quarter of the slope height, are studied. Theoretical estimates of the ultimate slope angle in each type, from infinite slope analysis and from charts, agree with observations of the inclinations of abandoned slopes along the river valley. The procedure recommended presents a rational estimation of setback distances without extensive site investigations. Key words: setback, slope, ultimate angle, abandoned slopes, river erosion.
Origin and movement of groundwater and major ions in a thick deposit of Champlain Sea clay near Montréal
Authors: Desaulniers Donald E. , Cherry John A.
Published: January 2009

At a site near Montréal, piezometers and core samples were used to assess the origin, age, and rate of groundwater movement in a 28 m thick deposit of Champlain Sea clay. 3H occurs only within the upper 3–4 m, which indicates that groundwater below this surficial weathered zone originated prior to 1952. Concentrations of 18O, Na+, and Cl− in water from the deepest piezometer suggest that the deep clay was deposited in a mixture of about 33% seawater and 67% freshwater. Profiles of several major ions show a gradual increase in concentration with depth. Mathematical simulations of vertical migration of Ca2+, Mg2+, K+, Na+, and Cl− provide close matches to the field profiles when only upward diffusion of these ions into the surficial freshwater zone is included in the model with a diffusion time of approximately 10 000 a. When the downward advection rate of 0.13 cm ∙ a−1 obtained from field measurements of hydraulic gradient and hydraulic conductivity is included in the model, the simulated major-ion profiles deviate markedly from the field profiles. This suggests that the hydraulic gradient in the clay is less than the threshold gradient necessary to cause Darcian flow. This study suggests that, in areas where clayey Champlain Sea deposits are thick, opportunities exist for locating waste disposal facilities that would have no significant potential for causing contamination of groundwater resources beneath the clay. Key words: groundwater, permeability, diffusion, environmental isotopes, threshold gradient, geochemistry, subsurface waste disposal.
The behaviour of very loose sand in the triaxial compression test
Authors: Sladen J. A. , Oswell J. M.
Published: January 2009

Very loose sand is defined as sand whose state is significantly looser than its critical state. The detailed stress-strain behaviour of very loose sand in triaxial compression is described for the first time within the framework of critical state soil mechanics. It is shown that the undrained behaviour of very loose sand under static loading can be rationalized by normalization with respect to the critical state, an approach that has been successful when applied to clays and to sands dense of critical. Strain contours in normalized stress space are presented for several sands and are shown to be remarkably consistent. The observed normalized behaviour is used to develop a simple constitutive model for the behaviour of very loose sands, based on plasticity theory. It is demonstrated that this model can be used successfully to predict the essential features of the behaviour of very loose sands in undrained and drained triaxial compression including cyclic loading conditions. The model includes the strain softening that occurs in very loose sands in conditions of impeded drainage and the cumulative increase in pore pressure that occurs during undrained cyclic loading. It can be used to predict the onset of liquefaction, a phenomenon only exhibited by very loose sands and quick clays. Key words: sand, liquefaction, triaxial test, cyclic loading, steady state testing, collapse surface.
Stability threshold for cyclic loading of saturated clay
Authors: Lefebvre Guy , LeBoeuf Denis , Demers Benoît
Published: January 2009

This paper presents the results of an experimental investigation performed to study the stability threshold under cyclic (repeated) loading, and the postcyclic static strength of a sensitive clay from the Hudson Bay region. The strain rate and structure effects were also studied by carrying out monotonic and cyclic triaxial tests at both slow and rapid strain rates or frequencies, and at confining pressures above and below the apparent preconsolidation pressure. The stability threshold for both structured and normally consolidated Grande Baleine clay is about 60–65% of the original undrained shear strength measured at the same strain rate as that used in the repeated loading test. The undrained shear strength and the failure envelope remain essentially unchanged if the repeated preloading is kept below the threshold. The clay structure remains unaltered by this preloading. Key words: clay, stability threshold, cyclic loading, earthquake, postcyclic strength.
Bearing capacity tests on strip footing resting on reinforced sand subgrades
Authors: Mahmoud M. A. , Abdrabbo F. M.
Published: January 2009

This note presents an experimental study concerning a method of improving the bearing capacity of strip footing resting on sand subgrades utilizing vertical nonextensible reinforcement. The test results indicate that this type of reinforcement increases the bearing capacity of subgrades and modifies the load–displacement behaviour of the footing. Key words: bearing capacity, nonextensible reinforcement, loading tests, strip footing, reinforcing element.
Behavior of Mexico City clay subjected to undrained repeated loading
Authors: Diaz-Rodriguez J. Abraham
Published: January 2009

This note describes a series of cyclic triaxial tests on undisturbed soil samples of Mexico City clay, obtained near the SCT building. The site is a silty clay deposit of a very high water content and soft consistency. The material exhibits elastic behavior in spite of its very high water content. Three empirical relationships describing an equivalent Young's modulus, an equivalent damping ratio, and a cyclic stress level, associated with cyclic strain level, were obtained. Test results define two different patterns of strength loss. Key words: undrained strength, repeated load, clay, modulus, damping, Mexico City.
A reevaluation of using laboratory shear tests
Authors: Mesri G.
Published: January 2009

The expression [Formula: see text] for the average undrained shear strength mobilized on a slip surface in the field resulted from in situ vane [Formula: see text] and oedometer [Formula: see text] data, combined with a correction factor μ obtained from the computed factor of safety of unstable embankments, footings, and excavations. It is shown here that the same expression for mobilized undrained strength of soft clays is also obtained from laboratory shear tests by taking into account anisotropy and time effects. This result is highly significant, since the laboratory undrained shear strength data, as well as the correction factor for the time effect, are completely unrelated to the in situ data that previously resulted in the expression for field mobilized undrained shear strength. Key words: mobilized undrained shear strength, in situ vane test, laboratory shear tests.
COMPUTING AN ADAPTIVE MESH IN FLUID PROBLEMS USING NEURAL NETWORK AND GENETIC ALGORITHM WITH ADAPTIVE RELAXATION
Authors: EMAM NAMEER N. EL. , SHAHEED RASHEED ABDUL
Published: January 2009

A method based on neural network with Back-Propagation Algorithm (BPA) and Adaptive Smoothing Errors (ASE), and a Genetic Algorithm (GA) employing a new concept named Adaptive Relaxation (GAAR) is presented in this paper to construct learning system that can find an Adaptive Mesh points (AM) in fluid problems. AM based on reallocation scheme is implemented on different types of two steps channels by using a three layer neural network with GA. Results of numerical experiments using Finite Element Method (FEM) are discussed. Such discussion is intended to validate the process and to demonstrate the performance of the proposed learning system on three types of two steps channels. It appears that training is fast enough and accurate due to the optimal values of weights by using a few numbers of patterns. Results confirm that the presented neural network with the proposed GA consistently finds better solutions than the conventional neural network.
DISTRIBUTED MINING OF ASSOCIATION RULES BASED ON REDUCING THE SUPPORT THRESHOLD
Authors: BOUTSINAS BASILIS , SIOTOS COSTAS , GEROLIMATOS ANTONIS
Published: January 2009

One of the most important data mining problems is learning association rules of the form "90% of the customers that purchase product x also purchase product y". Discovering association rules from huge volumes of data requires substantial processing power. In this paper we present an efficient distributed algorithm for mining association rules that reduces the time complexity in a magnitude that renders as suitable for scaling up to very large data sets. The proposed algorithm is based on partitioning the initial data set into subsets and processing each subset in parallel. The proposed algorithm can maintain the set of association rules that are extracted when applying an association rule mining algorithm to all the data, by reducing the support threshold during processing the subsets. The above are confirmed by empirical tests that we present and which also demonstrate the utility of the method.
A GRAPH BASED OBJECT DESCRIPTION AND RECOGNITION METHODOLOGY
Authors: BOURBAKIS N. , YUAN P. , KAKUMANU P.
Published: January 2009

This paper presents a methodology for recognizing 3D objects using synthesis of 2D views. In particular, the methodology uses wavelets for rearranging the shape of the perceived 2D view of an object for attaining a desirable size, local-global (LG) graphs for representing the shape, color and location of each image object's region obtained by an image segmentation method and the synthesis of these regions that compose that particular object. The synthesis of the regions is obtained by composing their local graph representations under certain neighborhood criteria. The LG graph representation of the extracted object is compared against a set of LG based object-models stored in a Database (DB). The methodology is accurate for recognizing objects existed in the DB and it has the capability of "learning" the LG patterns of new objects by associating them with attributes from existing LG patterns in the DB. Note that for each object-model stored in the database there are only six views, since all the intermediate views can be generated by appropriately synthesizing these six views. Illustrative examples are also provided.
THE CHALLENGE OF MOTION PLANNING FOR SOCCER PLAYING HUMANOID ROBOTS
Authors: CARPIN STEFANO , KALLMANN MARCELO , PAGELLO ENRICO
Published: January 2009

Motion planning for humanoids faces several challenging issues: high dimensionality of the configuration space, necessity to address balance constraints in single and double support mode, higher levels of planning for coordination of different skills, etc. While the above challenges hold for any humanoid robot, the soccer scenario adds difficulties rarely addressed in humanoid motion planning research, as for example: dynamic environments with active opponents, the requirement to perform short- and long-term plans for performing soccer-relevant actions, and the necessity to plan movements purposely terminating with a collision with the ball. These aspects open a completely new scenario for researchers. This paper surveys state-of-the-art research in motion planning for humanoid robots with a focus on outlining connections, differences, and identifying the key aspects that ought to be addressed when developing effective humanoid soccer players.
LIE GROUP FORMULATION FOR ANALYSIS OF KICKING MOTION IN HUMANOID SOCCER ROBOTS
Authors: ZHANG LIANDONG , ZHOU CHANGJIU
Published: January 2009

In this paper, we develop a general Lie group framework for analysis of kicking motion in humanoid soccer robots which aims to capture the multidimensional kicking information and hence to study how to develop more powerful and skilful kicking motion for humanoid soccer robots. To maintain dynamic stability while kicking is being performed, the zero-moment point (ZMP) is used to evaluate the performance of the humanoid kick. The proposed Lie-group-formulation-based compensation approach for force/torque sensing from the humanoid ankle has been implemented on, Robo-Erectus, our humanoid soccer robot. Humanoid kicking experiments have been conducted to verify the effectiveness of the proposed approach.
Symbiotic adaptive multisimulation
Authors: Mitchell Bradley , Yilmaz Levent
Published: January 2009

Inspired by the compound arthropod eye, Symbiotic Adaptive Multisimulation (SAMS) introduces an autonomic decision support capability for systems in shifting, ill-defined, uncertain environments. Rather than rely on a single authoritative model, SAMS explores an ensemble of plausible models, which are individually flawed but collectively provide more insight than would be possible otherwise. A case study based on a UAV team search and attack model is presented to illustrate the potential of SAMS. Results demonstrate the capability of SAMS to produce a large degree of exploratory behavior, followed by increased exploitative search behavior as the physical system unfolds.
Mathematical programming models of closed tandem queueing networks
Authors: Chan Wai Kin Victor , Schruben Lee W.
Published: January 2009

Closed tandem queueing networks are an important class of queueing models. Common approaches for analyzing these systems include Markov processes, renewal theory, and random walks. This article presents optimization models for sample paths of closed tandem queues. These mathematical models provide a new tool for analyzing these queueing systems using the techniques and algorithms from mathematical programming, and from graph theory in particular. We then apply operators from computer graphics (electronic picture manipulation) to graph theoretic representations of discrete-event system dynamics to establish some fundamental mathematical properties for these queueing systems.
Fidelity of network simulation and emulation
Authors: Chertov Roman , Fahmy Sonia , Shroff Ness B.
Published: January 2009

In this article, we investigate the differences between
simulation
and
emulation
when conducting denial of service (DoS) attack experiments. As a case study, we consider low-rate TCP-targeted DoS attacks. We design constructs and tools for emulation testbeds to achieve a level of control comparable to simulation tools. Through a careful sensitivity analysis, we expose difficulties in obtaining meaningful measurements from the DETER, Emulab, and WAIL testbeds with default system settings. We find dramatic differences between simulation and emulation results for DoS experiments. Our results also reveal that software routers such as Click provide a flexible experimental platform, but require understanding and manipulation of the underlying network device drivers. Our experiments with commercial Cisco routers demonstrate that they are highly susceptible to the TCP-targeted attacks when ingress/egress IP filters are used.
Attack-tolerant localization via iterative verification of locations in sensor networks
Authors: Park Taejoon , Shin Kang G.
Published: January 2009

In sensor networks, secure localization—determining sensors' locations in a hostile, untrusted environment—is a challenging, but very important, problem that has not yet been addressed effectively. This paper presents an attack-tolerant localization protocol, called
Verification for Iterative Localization
(VeIL), under which sensors cooperatively safeguard the localization service. By exploiting the high spatiotemporal correlation existing between adjacent nodes, VeIL realizes (a) adaptive management of a profile for normal localization behavior, and (b) distributed detection of false locations advertised by attackers by comparing them against the profile of normal behavior. Our analysis and simulation results show that VeIL achieves high-level tolerance to many critical attacks, and is computationally feasible on resource-limited sensors.
Verifying average dwell time of hybrid systems
Authors: Mitra Sayan , Liberzon Daniel , Lynch Nancy
Published: January 2009

Average dwell time (ADT) properties characterize the rate at which a hybrid system performs mode switches. In this article, we present a set of techniques for verifying ADT properties. The stability of a hybrid system A can be verified by combining these techniques with standard methods for checking stability of the individual modes of A.

We introduce a new type of simulation relation for hybrid automata—
switching simulation
—for establishing that a given automaton A switches more rapidly than another automaton B. We show that the question of whether a given hybrid automaton has ADT τ

a

can be answered either by checking an invariant or by solving an optimization problem. For classes of hybrid automata for which invariants can be checked automatically, the invariant-based method yields an automatic method for verifying ADT; for automata that are outside this class, the invariant has to be checked using inductive techniques. The optimization-based method is automatic and is applicable to a restricted class of initialized hybrid automata. A solution of the optimization problem either gives a counterexample execution that violates the ADT property, or it confirms that the automaton indeed satisfies the property. The optimization and the invariant-based methods can be used in combination to find the unknown ADT of a given hybrid automaton.
Temporal interaction between an artificial orchestra conductor and human musicians
Authors: Reidsma Dennis , Nijholt Anton , Bos Pieter
Published: January 2009

The Virtual Conductor project concerns the development of the first properly interactive virtual orchestra conductor—a Virtual Human that can conduct a piece of music through interaction with musicians, leading and following them while they are playing. This article describes our motivation for developing such a system; related work in the areas of ambient entertainment and coordinated timing, automatic music processing, virtual humans, and conducting; the design, implementation, and evaluation of the Virtual Conductor, and, finally, contains a discussion of the resulting system and expected developments in the (still ongoing) Virtual Conductor project.