bluuebunny/crossref_metadata_2025 huggingface dataset:
A Model of Neuro–Musculo–Skeletal System for Human Locomotion Under Position Constraint Condition
Authors: Ni Jiangsheng , Hiramatsu Seiji , Kato Atsuo
Published: August 2003

The human locomotion was studied on the basis of the interaction of the musculo–skeletal system, the neural system and the environment. A mathematical model of human locomotion under position constraint condition was established. Besides the neural rhythm generator, the posture controller and the sensory system, the environment feedback controller and the stability controller were taken into account in the model. The environment feedback controller was proposed for two purposes, obstacle avoidance and target position control of the swing foot. The stability controller was proposed to imitate the self-balancing ability of a human body and improve the stability of the model. In the stability controller, the ankle torque was used to control the velocity of the body gravity center. A prediction control algorithm was applied to calculate the torque magnitude of the stability controller. As an example, human stairs climbing movement was simulated and the results were given. The simulation result proved that the mathematical modeling of the task was successful.
Analysis of Body Segment Parameter Differences Between Four Human Populations and the Estimation Errors of Four Popular Mathematical Models
Authors: Durkin Jennifer L. , Dowling James J.
Published: August 2003

Calculating the kinetics of motion using inverse or forward dynamics methods requires the use of accurate body segment inertial parameters. The methods available for calculating these body segment parameters (BSPs) have several limitations and a main concern is the applicability of predictive equations to several different populations. This study examined the differences in BSPs between 4 human populations using dual energy x-ray absorptiometry (DEXA), developed linear regression equations to predict mass, center of mass location (CM) and radius of gyration (K) in the frontal plane on 5 body segments and examined the errors produced by using several BSP sources in the literature. Significant population differences were seen in all segments for all populations and all BSPs except hand mass, indicating that population specific BSP predictors are needed. The linear regression equations developed performed best overall when compared to the other sources, yet no one set of predictors performed best for all segments, populations or BSPs. Large errors were seen with all models which were attributed to large individual differences within groups. Equations which account for these differences, including measurements of limb circumferences and breadths may provide better estimations. Geometric models use these parameters, however the models examined in this study did not perform well, possibly due to the assumption of constant density or the use of an overly simple shape. Creating solids which account for density changes or which mimic the mass distribution characteristics of the segment may solve this problem. Otherwise, regression equations specific for populations according to age, gender, race, and morphology may be required to provide accurate estimations of BSPs for use in kinetic equations of motion.
An Overview of Optimal Control for Central Cooling Plants with Ice Thermal Energy Storage
Authors: Henze Gregor P.
Published: August 2003

This paper surveys past and current research of optimal control for central chilled water plants with ice thermal energy storage. The motivation for thermal energy storage in commercial buildings is provided and common operating strategies for ice storage including their implementation are presented. The concept of optimality serves as the basis for introducing the various approaches to optimal control of thermal energy storage. Optimal strategies minimizing either energy or demand costs, near-optimal rule based control minimizing total cost, comfort-based energy optimal control, and combined optimal sizing and energy cost optimal control are discussed and contrasted with mathematically non-optimal, but heuristically improved operating strategies. Fully optimal control based on perfect knowledge is introduced and subsequent developments of predictive optimal control subject to uncertain weather, load, and utility rate information illustrated. In addition, recent investigations of adaptive optimal reinforcement learning based control are presented.
Actual Unloading Behavior and Its Significance on Residual Stress in Machined Autofrettaged Tubes
Authors: Jahed Hamid , Ghanbari Ghader
Published: August 2003

A simple method for obtaining actual unloading behavior of high strength steels is proposed. Based on this method loading-unloading stress-strain curves for NiCrMoV125 steel is obtained. It is shown that the actual unloading behavior tends to be nonlinear as soon as unloading occurs. Using the variable material properties (VMP) method, residual stresses induced by autofrettage process of a tube made of this type of steel are calculated. Significance of employing actual unloading behavior is demonstrated by comparing the results with ideal models such as isotropic hardening and bilinear models. There is at least 30% over estimation of compressive residual stress at the bore if ideal models are used. Also, the process of material removal is simulated by using commercial FEM software to evaluate the recommended scenarios of removal on redistribution of residual stresses at the bore. Resulting stresses after machining are also calculated by the VMP method using actual behavior. It is shown that the final residual stress field differs significantly if actual unloading behavior is used.
Finite Element Simulation of Crack Compliance Experiments to Measure Residual Stresses in Thick-Walled Cylinders
Authors: de Swardt R. R.
Published: August 2003

A comparative study to map the residual strain/stress states through the walls of autofrettaged thick-walled high-strength steel cylinders has been conducted with neutron diffraction, Sachs boring, and the compliance methods. Test samples with different wall thickness ratios were prepared to have significant amounts of reverse yielding due to the Bauschinger effect. In an effort to explain observed differences in the hoop stress results, the crack compliance experiment was simulated with finite elements. Several residual stress fields were introduced in the finite element models. A theoretical finite element (FE) model, which is capable of accurately modeling the highly nonlinear reverse yielding of the material, was able to accurately predict the crack compliance strain measurements.
Numerical Analysis of the Effect of Machining on the Depth of Yield, Maximum Firing Pressure and Residual Stress Profile in an Autofrettaged Gun Tube
Authors: Hameed Amer , Brown R. D. , Hetherington J. G.
Published: August 2003

A multi-linear kinematic, two dimensional finite element model incorporating Bauschinger effect, developed using ANSYS commercial software is used to determine the effect of machining both at the bore and at the outside diameter, on the depth of yield, maximum firing pressure and final residual stress field present in an autofrettaged gun tube. The model, which is in good agreement with experimental findings, clearly shows that the reduction in maximum compressive circumferential stress is more sensitive to internal machining than to external machining; the depth of yield remains stable and there is no movement of the elastic-plastic interface, relative to its location before material removal. If the internal machining removes material in which reverse yield has occurred, the maximum firing pressure is not affected. The finite element analysis supported by experimental evidence thus leads to an optimization technique for gun tube design.
Application of Laser Pulse Heating to Simulate Thermomechanical Damage at Gun Bore Surfaces*
Authors: Cote Paul J. , Lee Sabrina L. , Todaro Mark E. , Kendall Gay
Published: August 2003

Laser pulse heating (LPH) experiments were performed to provide insights into the thermomechanical damage effects that occur at the surface of coated and uncoated gun steel under cyclic, rapid heating and cooling. These effects include generation of a heat-affected zone (HAZ), severe plastic deformation, crack blunting, cavitation, fracture initiation, and generation of residual stresses. In addition, several of the deformation effects observed in the HAZ indicate superplasticity. The results are compared with data from surfaces exposed to several different firing conditions to provide a basis for analyzing the specific role of the various degradation mechanisms. Supporting information is provided from x-ray diffraction measurement of residual stresses in the steel heat-affected zones produced in a firing environment. The measured compressive stresses are explained using dilatometry data and are shown to be consistent with the observed damage processes.
Failure Studies on Flow Formed High Strength Pressure Vessel: A Case Study
Authors: Rajan K. M. , Narasimhan K.
Published: August 2003

High strength thin walled flow formed tubes are manufactured from AISI 4130 medium carbon low alloy steel. Starting with an ultimate tensile strength of 650 MPa, the material has recorded a tensile strength of 1250–1300 MPa corresponding to a percentage thickness reduction of 88. It has been observed that material with higher impurity levels and inclusion ratings are more vulnerable to development of micro cracks at higher percentage thickness reduction. Deformed inclusions like MnS act as stress raisers leading to initiation of micro cracks. Hard to deform inclusions like silicates create high stress concentration at inclusion-matrix interface, leading to de-cohesion and finally cracking. The presence of dissolved gas contents, particularly hydrogen, are harmful in flow forming. Hydrogen embrittlement is a serious problem which is likely to lead to cracking of the flow formed tube. It could be concluded from this study that clean steel (electro slag refined) processed through hardening and tempering route with a maximum percentage reduction in thickness of 88 or less can give consistently very high strength of the order of 1250–1300 MPa for AISI 4130 steel.
Plasma molding over deep trenches and the resulting ion and energetic neutral distributions
Authors: Kim Doosik , Economou Demetre J.
Published: August 2003

A two-dimensional fluid/Monte Carlo simulation was developed to study plasma molding over deep trenches and the resulting ion and energetic (fast) neutral distributions, with emphasis on neutral beam sources. Plasma molding occurs when the sheath thickness is comparable to or smaller than the trench width. Using the electric field profiles predicted by the self-consistent fluid simulation, ions and energetic neutrals (resulting mainly by ion neutralization on the sidewall) were followed by the Monte Carlo simulation. The dominant energetic species at the bottom of a high aspect ratio trench were neutrals. A thin sheath (compared to the trench width), favored a larger energetic neutral flux at the bottom, at the expense of neutral energy and directionality. A relatively thick sheath produced neutrals of higher directionality at the expense of neutral flux. Neutral energy and directionality both increased by increasing the sheath potential.
Conductance imaging of thermally desorbed silicon oxide
Authors: Young Park Jeong , Phaneuf R. J.
Published: August 2003

We report on the use of scanning tunneling microscopy-conductance mapping to image voids in a thermally decomposed wet-chemical silicon oxide. Prominent contrast is observed between regions of remaining oxide and atomically clean silicon surface regions due to the difference in the local density of electronically active surface states. Differences in measured tunneling spectra within the voids, and in the surrounding oxidized regions, confirm that the origin of the contrast is mainly due to surface Fermi-level pinning at the clean Si(100) surface and metal–insulator–semiconductor junction behavior at the oxidized region. The maps show little sensitivity to pure topographical features, such as steps, and allow selective probing of electronic variations across a device structure with a resolution of 2 nm or better.
Detection of antibody peptide interaction using microcantilevers as surface stress sensors
Authors: Kim B. H. , Mader O. , Weimar U. , Brock R. , Kern D. P.
Published: August 2003

Micromechanical cantilevers were validated for the detection of antibody peptide interactions. For this purpose, gold-coated microcantilevers were chemically functionalized with an analog of the myc-tag decapeptide. Chemoselective covalent coupling of the peptide to the gold surface occurred via the sulfhydryl-group of a C-terminal cystein residue. In order to verify the surface functionalization by epifluorescence microscopy, a carboxyfluorescein reporter group was attached to the N-terminus. Binding of an anti-myc-tag antibody caused a bending of the microcantilever, resulting from a change in surface stress. The bending was recorded optically from the deflection of a laser beam. In order to compensate for bending due to nonspecific interactions, a nonfunctionalized cantilever serving as a reference was measured in parallel. A charge coupled device camera served as a position-sensitive detector, enabling the parallel and simultaneous detection of signals from an array of microcantilevers. The results validate microcantilevers for the label-free detection of antibody peptide interactions at physiological solvent conditions.
Growth of cubic SiC thin films on Si(001) by high vacuum chemical vapor deposition using 1,3-disilabutane and an investigation of the effect of deposition pressure
Authors: Boo J.-H. , Lim D.-C. , Lee S.-B , Lee K.-W. , Sung M. M. , Kim Y. , Yu K.-S.
Published: August 2003

We have deposited cubic SiC thin films on Si(001) substrates by high vacuum chemical vapor deposition (CVD) using a single molecular precursor of 1,3-disilabutane (DSB) at various temperatures (600–1000 °C) and pressures in the range of 1×10−6–1×10−5 Torr. A single-crystalline cubic SiC thin film with stoichiometric composition can be obtained under deposition conditions of 900–1000 °C and 4.0–6.5×10−6 Torr. However, on increasing the deposition pressure and decreasing the growth temperature to 1×10−5 Torr and 600 °C, respectively, the film became polycrystalline. The effect of deposition pressure on the film growth rate and crystallinity was also studied. Based on the experimental results from x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy, and transmission electron diffraction, the best SiC film was grown at 900 °C and 6.5×10−6 Torr of DSB at a maximum growth rate of 0.1 μm/h. The thicknesses of as-grown films were determined by cross-sectional SEM and Rutherford backscattering spectroscopy. Two different activation energies for cubic SiC film formation were obtained from Arrhenius plots. The deposition temperatures and pressures used in this study are lower by as much as 200 °C and a factor of 102, respectively, compared with those grown by conventional CVD methods.
Reflection high-energy electron diffraction pattern of GaN grown on 6H–SiC by metalorganic molecular beam epitaxy using AlGaN template
Authors: Honda Tohru , Kawanishi Hideo
Published: August 2003

Refraction high-energy diffraction (RHEED) patterns of GaN layers during the growth by metalorganic molecular beam epitaxy using (0001)6H–SiC and metalorganic vapor phase epitaxy grown Al0.05Ga0.95N/(0001)6H–SiC as substrates are observed. The patterns in initial growth are different for the GaN layers grown on 6H–SiC substrate and AlGaN template. The in-plane lattice constants of grown GaN layers estimated the duration of RHEED patterns are also discussed.
Reliability retention in in situ pyrolytic-gas passivated ultrathin silicon oxide gate films oxidized at 700 °C
Authors: Yamada Hiroshi
Published: August 2003

The oxidation temperature dependence of the reliability of in situ pyrolytic-gas passivated (PGP) ultrathin silicon oxide gate films was investigated. PGP uses a little pyrolytic N2O gas during ultradry oxidation with pure O2 at less than 1 ppb humidity. The reliability of the PGP films oxidized at 700–900 °C was evaluated by measuring the time-dependent dielectric breakdown (TDDB) lifetime (TTDDB) and interface state density (Dit). It was found that the reliability for the PGP films oxidized at the low temperature of 700 °C is much like the others. That is, TTDDB of the 700 °C PGP films barely decrease in comparison with those of the 800–900 °C PGP ones and their Dit are less than 7×1010 eV−1 cm−2. This indicates that PGP has a potential for application to future low-temperature processes for fabricating nanometer-scale electronic and optoelectronic devices.
Generalized interfaces
Authors: Ferry D. K. , Akis R. A. , Bird J. P. , Elhassan M. , Knezevic I. , Prasad C. , Shailos A.
Published: August 2003

The properties of very small semiconductor devices can be dominated by their environments in a nonperturbative manner. General treatments of the device embedded within its environment must account for the strong interactions between the device and the environment. While perturbative examples include remote phonons, surface roughness scattering, and edge fluctuations, the more general class give new dynamics for the device. This includes superlattice effects in arrays of devices and modified dynamics arising from device induced variations in the environment.
Electron heating measurements in an In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As heterostructure system
Authors: Prasad C. , Ferry D. K. , Vasileska D. , Wieder H. H.
Published: August 2003

Electron heating experiments are carried out on a two-dimensional electron gas fabricated in an In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As heterostructure and the energy loss rates and energy relaxation times are extracted from the Shubnikov–de Haas oscillations to get a better understanding of the electron–phonon interaction in these heterostructures. The exponent of the energy loss rate dependence is used to indicate a dominant unscreened piezoelectric coupling in the temperature range of 4.2–30 K. Simulations of the quantum well band structure verify the presence of two populated subbands in this heterostructure system. The energy relaxation time is observed to be on the order of several tens of nanoseconds and its decay with temperature shows a T−3 behavior at higher temperatures and a T−1 behavior at lower temperatures.
Surface and interface barriers of InxGa1−xAs binary and ternary alloys
Authors: Wieder H. H.
Published: August 2003

The absolute position of the valence band maxima of the semiconducting InxGa1−xAs alloys relative to the vacuum level, a composition-independent energy level, defined as the Fermi level stabilization energy, EFS, located ∼4.95 eV below the vacuum level, and the energy interval between the composition dependent conduction band minima or valence band maxima determine the equilibrium surface barriers and band offsets of these alloys and their heterostructures. Charged, amphoteric defects, located on EFS, compensate deliberately introduced donor or acceptor impurities and determine the maximum achievable electron or hole concentrations. Experimental measurements made on undoped or on donor-doped metal–semiconductor and on metal–insulator–semiconductor structures of these alloys, indicate that the composition dependence of the equilibrium surface potentials and metal semiconductor barrier heights are consistent with this “vacuum pinning rule.”
Soft x-ray photoelectron spectroscopy of (HfO2)x(SiO2)1−x high-k gate-dielectric structures
Authors: Ulrich M. D. , Hong J. G. , Rowe J. E. , Lucovsky G. , Chan A. S.-Y. , Madey T. E.
Published: August 2003

Soft x-ray photoelectron spectroscopy has been used to study several (HfO2)x(SiO2)1−x film compositions. The relationships between composition and Si 2p and Hf 4f core level binding energies were investigated using nominally thick films. Both the Si 2p [Si4+] and Hf 4f features shift to lower binding energy by approximately 1.3 eV as the composition is varied from SiO2 to HfO2. The shift to lower binding energy is consistent with both an electron transfer model of the chemical environment and final-state core-hole screening resulting from differences in material polarizability. In addition, the Gaussian widths of the core levels narrow with increasing HfO2 content. Calculations of phonon broadening indicate that this trend is due instead to inhomogeneous disorder. The dielectric/Si interface was investigated with ultrathin (∼10–20 Å) films. There was virtually no difference in binding energies or Gaussian width among the various compositions, indicating a preferential composition of approximately x=0.5 at the interface. Interface suboxides were also investigated and indicate a quality entropy-driven oxide/silicon interface.
Hybrid deposition of sputtered and evaporated multilayer thin films
Authors: Martin P. M. , Olsen L. C. , Johnston J. W. , Depoy D. M.
Published: August 2003

Si:H/CaF 2 and Si:H/HfF4 high reflectors with as many as 27 layers were deposited by a hybrid process that combined reactive magnetron sputtering and electron beam evaporation. The ultimate goal of this work was to deposit interference filters with low near-infrared (NIR) and LWIR absorption for use in thermophotovoltaic systems. The high index Si:H layers were deposited by reactive magnetron sputtering in mixtures of Ar+H2. Electron beam evaporation was the preferred deposition method for the CaF2 layers. The multilayer hybrid coatings were deposited in the same chamber by sequentially rotating the substrate over the Si sputtering target and the CaF2 evaporation source. The deposition rate of the evaporated CaF2 was 18.3 Å/s, compared to 0.42 Å/s for sputtered CaF2. The deposition rate of the Si:H layers was 1 Å/s. The refractive index of the SiH at NIR wavelengths was 3.45, with extinction coefficient <0.001. The refractive index of the CaF2 in the same wavelength range was 1.34, with an extinction coefficient <0.0001. The refractive index of HfF4 was 1.56 in the same wavelength range, with a comparable extinction coefficient. The resulting multilayer coatings had lower physisorbed water than those with sputtered CaF2 layers. The optical performance of the 9- and 27-layer all-sputtered and hybrid coatings was similar. The major advantage of the hybrid process was in deposition times. The deposition rate of the magnetron sputtered fluoride films was at least an order of magnitude lower than that of the e-beam evaporated films. The times required to deposit a quarter-wave (QW) optical thickness (3.2 μm) for hybrid (Si:H/HfF4) and (Si:H/CaF2) pairs were 34 min. The times to deposit comparable QW pairs by magnetron sputtering were 194 and 534 min, respectively. Advantages of this hybrid deposition method were reduced deposition times, optimum deposition process for each layer material, and improved optical and mechanical properties.
Depth profiling for ultrashallow implants using backside secondary ion mass spectrometry
Authors: Hongo C. , Tomita M. , Takenaka M. , Suzuki M. , Murakoshi A.
Published: August 2003

We studied accurate depth profiling for ultrashallow implants using backside secondary ion mass spectrometry (SIMS). For measuring ultrashallow dopant profiles such as 200 eV B implantation profiles, the effects of surface transient and atomic mixing are not negligible. We applied backside SIMS to analyze ultrashallow doping in order to exclude these effects. Comparing the SIMS profiles of surface side and those of backside, backside SIMS profiles showed a shallower ion implantation tail than surface-side SIMS profiles. Furthermore, backside SIMS profiles showed almost no dependence on primary ion energy. This indicates that backside SIMS provides sharp B profiles suitable for analyzing ultrashallow implants, even in the case where higher primary ion energy is used in comparison with implantation energy. The backside SIMS technique has a good potential to be used for the development of next-generation devices.
Selective sublimation processing of a molybdenum–tungsten mixed oxide thin film
Authors: Ferroni M. , Guidi V. , Comini E. , Sberveglieri G. , Vomiero A. , Della Mea G. , Martinelli G.
Published: August 2003

Thin films of Mo and W mixed oxides were achieved by reactive sputtering, assisted by the selective sublimation processing technique. Deposition of the film resulted in nucleation of Mo oxide in a Mo–W–O amorphous matrix, then the film underwent partial crystallization and oxidation on annealing. A two-phased nanostructure was achieved, featuring substoichiometric MoO3 flakes dispersed over a porous W–Mo–O film. Diffusion of Mo ions toward the film surface and sublimation of MoO3 were observed, the latter resulting in porosity increase of the layers through annealing. This behavior is interesting because it allows one to establish the content of residual Mo in the W–Mo–O film. Moreover, the presence of dispersed Mo and W anions in the WO3 or MoO3 phases inhibited grain coalescence upon annealing. The films were tested as chemo-resistive sensors towards CO at concentration level useful for environmental monitoring.
Temperature cycling and control system for photosensitive materials processing
Authors: El-Awady Khalid , Schaper Charles D. , Kailath Thomas
Published: August 2003

A temperature processing module and control system is presented for the thermal cycling of substrates such as semiconductor wafers and/or quartz photomasks. The module consists of a multizone etched foil heater adhered to the surface of a fluid heat exchanger. The heat exchanger is designed with aluminum foam that enables an angularly uniform temperature distribution on the heat exchanger surface as heat is transferred to it from the fluid. A temperature control algorithm is employed to manipulate the multizone surface heater to compensate for wafer temperature nonuniformities during the thermal cycle. The performance specifications for the thermal technology are: 30 s ramp-up time, 35 s ramp-down time, 3.5 °C peak nonuniformity during ramp up, 1 °C steady-state nonuniformity, and 3 °C peak nonuniformity during ramp down for a 200 mm wafer. The control results are achieved at the expense of significant energy expenditure. The total energy for the thermal cycle exceeded 10 kW compared to a theoretical minimum of a few hundred watts for 200 or 300 mm wafers. The axial temperature gradients in the module plate also induce thermal stresses that lead to a transient mechanical deformation of the heat exchanger that can be as large as 15 mil (380 μm) during the ramp up. We conclude that the proposed technology is more appropriate for operations with low throughput applications, such as photomask or large substrate processing, that benefit from thermal cycling.
Spectroscopic study of chemical phase separation in zirconium silicate alloys
Authors: Rayner G. B. , Kang D. , Lucovsky G.
Published: August 2003

This article presents a comprehensive spectroscopic study of chemical phase separation in zirconium silicate alloys, (ZrO2)x(SiO2)1−x, using Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy, extended x-ray absorption fine structure spectroscopy, and near edge x-ray absorption spectroscopy. These measurements are complemented by measurements of x-ray diffraction and high resolution transmission electronic microscopy imaging. This combination has been applied to Zr silicate alloys, providing the first comprehensive comparisons of the relative sensitivities of these spectroscopic techniques applied to micro- and nanoscale chemical phase separation of high-k dielectric alloys.
Comparisons of three alternative breast modalities in a common phantom imaging experiment
Authors: Li Dun , Meaney Paul M. , Tosteson Tor D. , Jiang Shudong , Kerner Todd E. , McBride Troy O. , Pogue Brian W. , Hartov Alexander , Paulsen Keith D.
Published: August 2003

Four model‐based imaging systems are currently being developed for breast cancer detection at Dartmouth College. A potential advantage of multimodality imaging is the prospect of combining information collected from each system to provide a more complete diagnostic tool that covers the full range of the patient and pathology spectra. In this paper it is shown through common phantom experiments on three of these imaging systems that it was possible to correlate different types of image information to potentially improve the reliability of tumor detection. Imaging experiments were conducted with common phantoms which mimic both dielectric and optical properties of the human breast. Cross modality comparison was investigated through a statistical study based on the repeated data sets of reconstructed parameters for each modality. The system standard error between all methods was generally less than 10% and the correlation coefficient across modalities ranged from 0.68 to 0.91. Future work includes the minimization of bias (artifacts) on the periphery of electrical impedance spectroscopy images to improve cross modality correlation and implementation of the multimodality diagnosis for breast cancer detection.
Computer‐assisted detection of mammographic masses: A template matching scheme based on mutual information
Authors: Tourassi Georgia D. , Vargas‐Voracek Rene , Catarious David M. , Floyd Carey E.
Published: August 2003

The purpose of this study was to develop a knowledge‐based scheme for the detection of masses on digitized screening mammograms. The computer‐assisted detection (CAD) scheme utilizes a knowledge databank of mammographic regions of interest (ROIs) with known ground truth. Each ROI in the databank serves as a template. The CAD system follows a template matching approach with mutual information as the similarity metric to determine if a query mammographic ROI depicts a true mass. Based on their information content, all similar ROIs in the databank are retrieved and rank‐ordered. Then, a decision index is calculated based on the query's best matches. The decision index effectively combines the similarity indices and ground truth of the best‐matched templates into a prediction regarding the presence of a mass in the query mammographic ROI. The system was developed and evaluated using a database of 1465 ROIs extracted from the Digital Database for Screening Mammography. There were 809 ROIs with confirmed masses (455 malignant and 354 benign) and 656 normal ROIs. CAD performance was assessed using a leave‐one‐out sampling scheme and Receiver Operating Characteristics analysis. Depending on the formulation of the decision index, CAD performance as high as was achieved. The CAD detection rate was consistent for both malignant and benign masses. In addition, the impact of certain implementation parameters on the detection accuracy and speed of the proposed CAD scheme was studied in more detail.
Dynamic model of the left ventricle for use in simulation of myocardial perfusion SPECT and gated SPECT
Authors: Bullich S. , Ros D. , Cot A. , Falcón C. , Muxı́ A. , Pavia J.
Published: August 2003

Simulation is a useful tool in cardiac SPECT to assess quantification algorithms. However, simple equation‐based models are limited in their ability to simulate realistic heart motion and perfusion. We present a numerical dynamic model of the left ventricle, which allows us to simulate normal and anomalous cardiac cycles, as well as perfusion defects. Bicubic splines were fitted to a number of control points to represent endocardial and epicardial surfaces of the left ventricle. A transformation from each point on the surface to a template of activity was made to represent the myocardial perfusion. Geometry‐based and patient‐based simulations were performed to illustrate this model. Geometry‐based simulations modeled (1) a normal patient, (2) a well‐perfused patient with abnormal regional function, (3) an ischaemic patient with abnormal regional function, and (4) a patient study including tracer kinetics. Patient‐based simulation consisted of a left ventricle including a realistic shape and motion obtained from a magnetic resonance study. We conclude that this model has the potential to study the influence of several physical parameters and the left ventricle contraction in myocardial perfusion SPECT and gated‐SPECT studies.
Dose linearity and uniformity of a linear accelerator designed for implementation of multileaf collimation system‐based intensity modulated radiation therapy
Authors: Saw Cheng B. , Li Sicong , Ayyangar Komanduri M. , Yoe‐Sein Maung , Pillai Susha , Enke Charles A. , Celi Juan C.
Published: August 2003

The dose linearity and uniformity of a linear accelerator designed for multileaf collimation system‐ (MLC) based IMRT was studied as a part of commissioning and also in response to recently published data. The linear accelerator is equipped with a PRIMEVIEW, a graphical interface and a SIMTEC IM‐MAXX, which is an enhanced autofield sequencer. The SIMTEC IM‐MAXX sequencer permits the radiation beam to be “ON” continuously while delivering intensity modulated radiation therapy subfields at a defined gantry angle. The dose delivery is inhibited when the electron beam in the linear accelerator is forced out of phase with the microwave power while the MLC configures the field shape of a subfield. This beam switching mechanism reduces the overhead time and hence shortens the patient treatment time. The dose linearity, reproducibility, and uniformity were assessed for this type of dose delivery mechanism. The subfields with monitor units ranged from 1 MU to 100 MU were delivered using 6 MV and 23 MV photon beams. The doses were computed and converted to dose per monitor unit. The dose linearity was found to vary within 2% for both 6 MV and 23 MV photon beam using high dose rate setting (300 MU/min) except below 2 MU. The dose uniformity was assessed by delivering 4 subfields to a Kodak X‐OMAT TL film using identical low monitor units. The optical density was converted to dose and found to show small variation within 3%. Our results indicate that this linear accelerator with SIMTEC IM‐MAXX sequencer has better dose linearity, reproducibility, and uniformity than had been reported.
Mitochondrial Abnormalities and Oxidative Imbalance in Neurodegenerative Disease
Authors: Ogawa Osamu , Zhu Xiongwei , Perry George , Smith Mark A.
Published: August 2003

An increasing body of evidence now suggests the involvement of mitochondrial abnormalities in the etiology of neurodegenerative diseases, such as Parkinson's disease (PD) and Alzheimer disease. In this Perspective, we describe a recent study that shows that treatment of human patients with the antioxidant coenzyme Q
10
, which functions in concert with certain mitochondrial enzymes, reduced the worsening of symptoms associated with PD. These findings are consistent with the hypothesis that mitochondrial dysfunction plays a role in the pathogenesis of PD and that treatments that target mitochondrial biochemistry might ameliorate the functional decline observed in patients suffering from PD.
An All-Optical Quantum Gate in a Semiconductor Quantum Dot
Authors: Li Xiaoqin , Wu Yanwen , Steel Duncan , Gammon D. , Stievater T. H. , Katzer D. S. , Park D. , Piermarocchi C. , Sham L. J.
Published: August 2003

We report coherent optical control of a biexciton (two electron-hole pairs), confined in a single quantum dot, that shows coherent oscillations similar to the excited-state Rabi flopping in an isolated atom. The pulse control of the biexciton dynamics, combined with previouslydemonstrated control of the single-exciton Rabi rotation, serves as the physical basis for a two-bit conditional quantum logic gate. The truth table of the gate shows the features of an all-optical quantum gate with interacting yet distinguishable excitons as qubits. Evaluation of the fidelity yields a value of 0.7 for the gate operation. Such experimental capabilityis essential to a scheme for scalable quantum computation bymeans of the optical control of spin qubits in dots.
Amygdalar and Hippocampal Theta Rhythm Synchronization During Fear Memory Retrieval
Authors: Seidenbecher Thomas , Laxmi T. Rao , Stork Oliver , Pape Hans-Christian
Published: August 2003

The amygdalohippocampal circuit plays a pivotal role in Pavlovian fear memory. We simultaneously recorded electrical activity in the lateral amygdala (LA) and the CA1 area of the hippocampus in freely behaving fear-conditioned mice. Patterns of activity were related to fear behavior evoked by conditioned and indifferent sensory stimuli and contexts. Rhythmically synchronized activity at theta frequencies increased between the LA and the CA1 after fear conditioning and became significant during confrontation with conditioned fear stimuli and expression of freezing behavior. Synchronization of theta activities in the amygdalohippocampal network represents a neuronal correlate of conditioned fear, apt to improve neuronal communication during memory retrieval.
Structural Dynamics of Eukaryotic Chromosome Evolution
Authors: Eichler Evan E. , Sankoff David
Published: August 2003

Large-scale genome sequencing is providing a comprehensive view of the complex evolutionary forces that have shaped the structure of eukaryotic chromosomes. Comparative sequence analyses reveal patterns of apparently random rearrangement interspersed with regions of extraordinarily rapid, localized genome evolution. Numerous subtle rearrangements near centromeres, telomeres, duplications, and interspersed repeats suggest hotspots for eukaryotic chromosome evolution. This localized chromosomal instability may play a role in rapidly evolving lineage-specific gene families and in fostering large-scale changes in gene order. Computational algorithms that take into account these dynamic forces along with traditional models of chromosomal rearrangement show promise for reconstructing the natural history of eukaryotic chromosomes.
Retrograde Viral Delivery of IGF-1 Prolongs Survival in a Mouse ALS Model
Authors: Kaspar Brian K. , Lladó Jerònia , Sherkat Nushin , Rothstein Jeffrey D. , Gage Fred H.
Published: August 2003

Amyotrophic lateral sclerosis (ALS) is a progressive, lethal neuromuscular disease that is associated with the degeneration of spinal and brainstem motor neurons, leading to atrophy of limb, axial, and respiratory muscles. The cause of ALS is unknown, and there is no effective therapy. Neurotrophic factors are candidates for therapeutic evaluation in ALS. Although chronic delivery of molecules to the central nervous system has proven difficult, we recently discovered that adeno-associated virus can be retrogradely transported efficiently from muscle to motor neurons of the spinal cord. We report that insulin-like growth factor 1 prolongs life and delays disease progression, even when delivered at the time of overt disease symptoms.
Cave infill and associated biotic remains as indicators of Holocene environment in Gatineau Park (Quebec, Canada)
Authors: Lauriol B , Deschamps E , Carrier L , Grimm W , Morlan R , Talon B
Published: August 2003

A rich sedimentary deposit reaches a depth of more than 4 m in a cave located on the Eardley Escarpment in the Gatineau Park. Analysis shows that the infilling started during the last Ice Age. Following the deglaciation and the Champlain Sea retreat, terrestrial sedimentation began. Radiocarbon dating of wood charcoal indicates that around 9200 ± 110 years BP trees and shrubs were starting to grow on the Eardley Escarpment. A fauna, with boreal affinity, including the Ungava collared lemming (Dicrostonyx hudsonius), was living in vegetation dominated by jack pine. After 8170 ± 60 years BP, the boreal forest was replaced by a mixed forest dominated by white pine, oak, and red maple. The faunal assemblage was enriched at that time by woodland vole (Microtus pinetorum) and Strobilops aenea, a terrestrial mollusk. These two species are presently living in the Carolinian Life Zone south of the Great Lakes. By around 5742 ± 120 years BP these two species had left the site, and the modern fauna was established with mammals, such as the black bear and the white-tailed deer. Holocene infilling of the cave was gravity driven and unassisted, except for an episode just before 8170 ± 60 years BP when a sand layer was deposited by water coming from the surface.
Dike swarms on Seward Peninsula, Alaska, and their implications for the kinematics of Cretaceous extension in the Bering Strait region
Authors: Amato Jeffrey M , Miller Elizabeth L , Wright James E , McIntosh William C
Published: August 2003

Late Cretaceous dike swarms on Seward Peninsula, northwestern Alaska, represent the youngest local manifestation of a ~11575 Ma magmatic event in the Bering Strait region. Magmatism accompanied and followed high-grade metamorphism and ductile deformation. A Late Cretaceous extensional tectonic setting for the region is suggested by the thickness and seismic-reflection characteristics of the crust, regional basin development, formation of high-strain tectonites with subhorizontal foliations, bimodal magmatism, and dike swarms. The orientation of the dike swarms is used to address the kinematics of extension. A diabase dike swarm in the Kigluaik Mountains consists of dikes that strike northeast (040°) and dip steeply. Phenocrysts include plagioclase, clinopyroxene, orthopyroxene, and hornblende. Geochemical data indicate that SiO2 ranges from 48% to 56%, and K2O from 1.2% to 4.0%. The dikes are geochemically similar to the mafic to intermediate root of the 90 Ma Kigluaik pluton. Sr- and Nd-isotope data show that initial 87Sr/86Sr ranges from 0.7070 to 0.7077 and initial εNd ranges from 0.85 to 2.90. Field relations and 40Ar/39Ar geochronology bracket the dike ages between 90 and 84 Ma. Diabase dikes in the York Mountains are associated with normal faults that strike eastwest to east-northeast. Dikes in the Bendeleben Mountains are both mafic and felsic, but their orientations are unknown. Alkalic dikes in the Darby Mountains strike 030°050°, similar to those in the Kigluaik Mountains. Regional relationships including the orientation of dikes, normal faults, mineral stretching lineations, and other shear-sense indicators suggest that between 110 and 90 Ma extension on Seward Peninsula was generally oriented northsouth to north-northwestsouth-southeast.
The distribution of igneous rocks beneath Mont Mégantic (the easternmost Monteregian) as revealed by gravity
Authors: Feininger Tomas , Goodacre Alan K
Published: August 2003

At the surface, Mont Mégantic, the easternmost and most imposing of the Monteregian hills, is composed of 77.5% leucogranite and syenite and 22.5% gabbro. Nonetheless, the intrusion is characterized by a major positive Bouguer anomaly of +20 mGal. A computed three-dimensional gravity adumbration is consonant with the intrusion having the form of a vertical prismatic column with a flat base at a depth of 10 km. The base appears to coincide with the unconformity atop Precambrian basement rocks. Gabbro composes 96% of the adumbration. Leucogranite and syenite make up the remainder and are confined to an uppermost layer no more than about 1 km thick. The subvolcanic texture of the granite and presence of miarolitic cavities at Mégantic show the shallow level of the intrusion, the present surface perhaps having been no deeper than 1 or 2 km. This is the same as the depth of emplacement elucidated at Mont Royal, at the opposite end of the Monteregian chain, which in turn points to uniform uplift and erosion since Early Cretaceous time across the entire area, from the shield and well into the Appalachians. The mechanism of intrusion at Mégantic appears to be the same as that we proposed earlier for the eight classical Monteregians.
The effect of variable-retention riparian buffer zones on water temperatures in small headwater streams in sub-boreal forest ecosystems of British Columbia
Authors: Macdonald J S , MacIsaac E A , Herunter H E
Published: August 2003

Stream temperature impacts resulting from forest harvesting in riparian areas have been documented in a number of locations in North America. As part of the StuartTakla FisheriesForestry Interaction Project, we have investigated the influence of three variable-retention riparian harvesting prescriptions on temperatures in first-order streams in the interior sub-boreal forests of northern British Columbia. Prescriptions were designed to represent a range of possible harvesting options outlined by the Forest Practices Code of B.C., or associated best management practice guidelines. Five years after the completion of harvesting treatments, temperatures remained four to six degrees warmer, and diurnal temperature variation remained higher than in the control streams regardless of treatment. Initially, the high-retention treatment acted to mitigate the temperature effects of the harvesting, but 3 successive years of windthrow was antecedent to reduced canopy density and equivalent temperature impacts. We speculate that late autumn reversals in the impacts of forest harvesting also occur. Temperature impacts in this study remained within the tolerance limits of local biota. However, even modest temperature changes could alter insect production, egg incubation, fish rearing, migration timing, and susceptibility to disease, and the effects of large changes to daily temperature range are not well understood.
Large wood recruitment and redistribution in headwater streams in the southern Oregon Coast Range, U.S.A.
Authors: May Christine L , Gresswell Robert E
Published: August 2003

Large wood recruitment and redistribution mechanisms were investigated in a 3.9 km2 basin with an old-growth Pseudotsuga menziesii (Mirb.) Franco and Tsuga heterophylla (Raf.) Sarg. forest, located in the southern Coast Range of Oregon. Stream size and topographic setting strongly influenced processes that delivered wood to the channel network. In small colluvial channels draining steep hillslopes, processes associated with slope instability dominated large wood recruitment. In the larger alluvial channel, windthrow was the dominant recruitment process from the local riparian area. Consequently, colluvial channels received wood from further upslope than the alluvial channel. Input and redistribution processes influenced piece location relative to the direction of flow and thus, affected the functional role of wood. Wood recruited directly from local hillslopes and riparian areas was typically positioned adjacent to the channel or spanned its full width, and trapped sediment and wood in transport. In contrast, wood that had been fluvially redistributed was commonly located in mid-channel positions and was associated with scouring of the streambed and banks. Debris flows were a unique mechanism for creating large accumulations of wood in small streams that lacked the capacity for abundant fluvial transport of wood, and for transporting wood that was longer than the bank-full width of the channel.