bluuebunny/crossref_metadata_2025 huggingface dataset:
Wind Heat Loss From Corrugated, Transpired Solar Collectors
Authors: Gawlik Keith M. , Kutscher Charles F.
Published: October 2002

Heat transfer from a perforated, sinusoidal plate with suction to air flowing over the plate, perpendicular to the corrugations, has been studied numerically and experimentally. This study used a numerical model, validated by wind tunnel tests and hot wire anemometer/resistance thermometer measurements, to determine the heat loss to the air stream over the plate as a function of wind speed, suction velocity, and plate geometry. Both attached and separated flow regimes were observed, and the criterion for flow attachment was determined to be ReV0,P⩾6.93 ReU∞,A0.5. Correlations were developed for heat transfer to the air stream for each flow regime. For attached flow, the heat transfer can be represented as Nuatt=Nuflat{1+0.81A/P0.5}. For separated flow, the following correlation applies: Nusep=2.05A/P1.40 Re1.63.
A Financial Worksheet for Computing the Cost (¢/kWh) of Solar Electricity Generated at Grid Connected Photovoltaic (PV) Generating Plants
Authors: Stavy Michael
Published: October 2002

This paper discusses the technical, financial, and economic principles underlying the levelized cost method of computing the cost of solar electricity. Topics include the levelized cost method, solar radiation, solar panel efficiency, depreciation, cost of capital, fixed and variable operating and maintenance costs, and taxes. The paper includes the worksheet, “Levelized Cost Worksheet for a 1 kW Solar Electric Generating Plant.” Its benchmark values are for a model solar plant located in Chicago, IL. The paper discusses these benchmark values as it analyzes the worksheet’s constants (capacity-1 kW, 8,760 hr/yr), independent variables (capital cost-$/kW, cost of capital-%, physical life-yr, standard sun hours, fixed and variable O & M expense), and dependent variables (capital amortization expense, capacity factor, cost of solar electricity).
Solar Processing for the Glazing of ZrO2-Y2O3 Thermal Barrier Coatings: Reduction of Crack Initiation
Authors: Ferriere and Alain , Lestrade Laurent
Published: October 2002

The glazing of thermal barrier coatings using concentrated solar energy has already been demonstrated, but crack initiation appeared as a major drawback of this processing. In this paper, the thermo-mechanical effects resulting from the fast heating at high temperature were modeled. Crack initiation was found to result from high temperature gradients in the ceramic coating. Experiments performed on plasma-sprayed ZrO2-Y2O3 layer showed that a significant reduction of crack initiation was achieved when the specimen was preheated at temperatures in the range 500°C-800°C. The potential of the solar processing was improved and this technique becomes competitive with conventional laser processes.
Carbon Particle Cloud Generation for a Solar Particle Receiver
Authors: Bertocchi Rudi
Published: October 2002

The development and performance of a full-scale carbon particle cloud generator together with the evaluation of nine commercial carbon blacks is reported. Large variations were found in the dispersability and settling properties of the investigated powders. Scanning electron microscope analysis of cloud samples from different powders showed unequal state of agglomeration and particle size. The particle population distribution of the most suitable powder was determined, showing that the particle cloud consisted of 99.8% spheroid primary particles (25–570 nm dia) and 0.2% large irregularly shaped agglomerates. Although the numerical fraction of the agglomerates was only 0.2%, they contributed 40% to the cloud’s geometrical cross section. Significant variations in the population distribution were found from different batches of the same particle powder. The developed full-scale particle generator was capable of sustained operation, creating a particle cloud with an extinction coefficient exceeding 40m−1 at a nominal flow rate of 25 SLPM. The dispersal efficiency of the system with the optimal ejection nozzle was 25%, compared to less than 1% for free ejection. The particle dispersal rate was 30 g/hr at 25 SLPM at an evacuation efficiency of 87%. Specific extinction cross-sections of 5.8m2/g were measured for particle mass loading higher than 2g/m3.
Dynamic Shear Fracture at Subsonic and Transonic Speeds in a Compressible Neo-Hookean Material Under Compressive Prestress
Authors: Brock L. M.
Published: October 2002

A crack driven by shear forces translating on its surfaces grows in an isotropic compressible neo-Hookean material that is initially in uniform compression. The material replicates a linear isotropic solid at small deformations, and preserves as a limit case for all deformations the incompressibility that occurs in the linear case when Poisson’s ratio becomes 1/2. A plane-strain steady state is assumed such that the crack and surface forces move at the same constant speed, whether subsonic, transonic, or supersonic. An exact analysis is performed based on superposition of infinitesimal deformations upon large, both for frictionless crack surface slip, and slip resisted by friction. The pre-stress induces anisotropy and increases the Rayleigh, rotational and dilatational wave speeds from their classical values. A positive finite fracture energy release rate arises for crack speeds below the Rayleight value and at two transonic speeds. In contrast, the transonic range in a purely linear analysis exhibits only one speed. It is found that friction enhances fracture energy release rate, and that compressive pre-stress enhances the rates for small crack speeds, but decreases it for speeds near the Rayleigh value.
Nonlinear Internal Solitary Wave on a Pycnocline
Authors: Valentine Daniel T. , Sipcic Radica
Published: October 2002

This paper describes the theory of nonlinear internal-solitary waves of the type observed in coastal seas. It also describes a numerical solution of an initial-value problem that leads to an internal solitary-like wave. The equations solved numerically are the Navier-Stokes, diffusion, and continuity equations. The computer solution illustrates that solitary-like waves are easily generated. A comparison with the theory illustrates that the wave is a KdV-like solitary wave. Hence, the computed wave is caused by a near balance between dispersive and nonlinear effects. However, the shape of the fully-nonlinear solitary wave is fore-aft asymmetric with a relatively long, somewhat elevated tail. This feature is characteristic of the computationally derived wave as compared with the fore-aft symmetry of the theoretical wave. (This work is motivated by the fact that internal solitary-like waves have practical importance in the design of offshore structures and on the acoustic properties of the sea, among other environmental consequences.)
Influence of Non-Proportional Environmental Loading on the Reliability of Production Jack-ups
Authors: Ronalds B. F. , Bjarke T. , Trinh S.
Published: October 2002

Inherent features of jack-up units, including their mobility and their integrated and standardized form, make them well suited for certain field developments. An overview of the configurations and attributes of production jack-ups is presented, including a database of applications to date. The relationship between jack-up configuration and structural reliability under storm overload is then explored. Critical values of the wave height exponent α are presented for a wide range of water depths and jack-up geometries, along with selected pushover analysis results. There is a strong tendency for the structural reliability to decrease in shallower water depths and when the jack-up is elevated in the water column by a storage tank or braced base. The latter is due essentially to the non-proportional increase in environmental loading down the structure with increasing return period.
Bayesian Updating in the Reliability Assessment of Maintained Floating Structures
Authors: Garbatov Y. , Soares C. Guedes
Published: October 2002

The present paper adopts a Bayesian approach to update some of the parameters of the probability distributions governing the reliability assessment of maintained floating structures. It is based on a time dependent fatigue reliability formulation presented earlier but the description of the time to crack initiation, crack growth law and probability of crack detection are updated using the information from the inspections. Its performance is demonstrated with a simulated example.
Micro-Mechanics of Creep-Fatigue Damage in PB-SN Solder Due to Thermal Cycling—Part I: Formulation
Authors: Sharma Pradeep , Dasgupta Abhijit
Published: October 2002

This paper presents a micro-mechanistic approach for modeling fatigue damage initiation due to cyclic creep in eutectic Pb-Sn solder. Damage mechanics due to cyclic creep is modeled with void nucleation, void growth, and void coalescence model based on micro-structural stress fields. Micro-structural stress states are estimated under viscoplastic phenomena like grain boundary sliding, its blocking at second-phase particles, and diffusional creep relaxation. In Part II of this paper, the developed creep-fatigue damage model is quantified and parametric studies are provided to better illustrate the utility of the developed model.
Film Thickness and Wave Velocity Measurements in a Vertical Duct
Authors: Kumar Ranganathan , Gottmann Matthias , Sridhar K. R.
Published: October 2002

This paper describes the experimental investigation of an upward annular air-water flow in a duct with a 6.35 mm by 63.5 mm rectangular cross section. The test section was instrumented to measure the film thickness and the interfacial wave velocity. Flush-wire electrical conductivity probes were used to obtain local film thickness measurement with a spatial resolution of 200 μm or better and a temporal resolution greater than 2 kHz. Measurements of the base films range from 50 μm to ∼325 μm (2% to 10% of half-channel thickness). Statistical analysis shows that the standard deviation of the film thickness is a good measure of the film roughness. The relative roughness and the nondimensional film thickness are correlated as functions of the phasic Reynolds number ratio, R=Rel0.15/Reg0.3. It is found that at R=0.15, the relative roughness is a maximum. A simple model developed by matching the interfacial shear in the two fluids, predicts the wave velocity data very well.
Liquid Film Atomization on Wall Edges—Separation Criterion and Droplets Formation Model
Authors: Maroteaux F. , Llory D. , Le Coz J-F. , Habchi C.
Published: October 2002

In order to predict the fuel mixture preparation inside the cylinder of port fuel injection engines, a model for the aerodynamic stripping of the fuel film deposited on the manifold walls is discussed, and a model for the fuel film separation and atomization near the sharp edges is developed. A separation criterion is set up using an analogy with Rayleigh-Taylor instabilities driven by the inertial forces of the liquid film. To determine the physical parameters of the resulting droplets, a liquid sheet atomization scheme is used. The critical value for the separation criterion is adjusted using experimental data obtained in 2D wind tunnel equipped with different steps shaped as a valve seat, and reproducing the main characteristics of the intake of spark ignition engine. CFD simulations are performed using the KMB code, a modified version of KIVA-2 already including a stochastic Lagrangian description of the spray, and an Eulerian liquid film model. Computations results for different operating conditions are in good agreement with the images of film separation and measured droplet size distributions.
Accurate Evaluation of the Loss Coefficient and the Entrance Length of the Inlet Region of a Channel
Authors: Sadri R. M. , Floryan J. M.
Published: October 2002

Evaluations of loss coefficient and entrance length in the inlet region of a channel are presented. Correlations and numerical values of these quantities are provided for Reynolds number ranging from 0.01 to 2200. The results provide an accurate benchmark for engineering design.
Analysis of Impinging and Countercurrent Stagnating Flows by Reynolds Stress Model
Authors: Im Yong H. , Huh Kang Y. , Kim Kwang-Yong
Published: October 2002

Numerical simulation is performed for stagnating turbulent flows of impinging and countercurrent jets by the Reynolds stress model (RSM). Results are compared with those of the k−ε model and available data to assess the flow characteristics and turbulence models. Three variants of the RSM tested are those of Gibson and Launder (GL), Craft and Launder (GL-CL) and Speziale, Sarkar and Gatski (SSG). As is well known, the k−ε model significantly overestimates turbulent kinetic energy near the wall. Although the RSM is superior to the k−ε model, it shows considerable difference according to how the redistributive pressure-strain term is modeled. Results of the RSM for countercurrent jets are improved with the modified coefficients for the dissipation rate, Cε1 and Cε2, suggested by Champion and Libby. Anisotropic states of the stress near the stagnation region are assessed in terms of an anisotropy invariant map (AIM).
Evaluation of Methylene Blue and Rose Bengal for Dye Sensitized Solar Water Treatment
Authors: Cooper Adrienne T. , Goswami D. Yogi
Published: October 2002

The experimental work described in this paper evaluated the efficacy of dyes as sensitizing agents for solar photochemical detoxification and disinfection of water. Methylene blue and rose bengal were evaluated as photosensitizing agents. While neither dye was effective for detoxification, methylene blue showed some efficacy for photodisinfection over natural sunlight. In all sunlight experiments, methylene blue effected a coliform reduction ranging from 96% at pH 7 and lower methylene blue concentrations, to 99.5% for all concentrations at pH 10 and the 10 mg/L concentration for pH 7. The 99.5% reduction at pH 7 is comparable to 74% reduction at the same pH using sunlight alone. Significant coliform reduction was also observed in dark experiments with 10 mg/L of methylene blue.
Interactions of alkylamines with the silicon (001) surface
Authors: Cao Xiaoping , Hamers Robert J.
Published: October 2002

The interactions of primary, secondary, and tertiary alkylamines with the Si(001) surface have been investigated using x-ray/ultraviolet photoelectron spectroscopy, Fourier transform infrared spectroscopy and scanning tunneling microscopy. Experimental and computational results show that alkylamines bond to the surface through the nitrogen atom. Primary alkylamines such as hexylamine bond to the surface by breaking only one N–H bond. Secondary alkylamines such as dimethylamine and N-methylpentylamine cleave only the N–H bond, leaving the N–C bonds intact. Tertiary alkylamines, such as trimethylamine and N,N-dimethylbutylamine, can form stable dative-bonded adducts on the surface that are characterized by very high N(1s) binding energies of 402.2 eV. The ability to form dative-bonded adducts between tertiary alkylamines and Si(001) stems from the capability of electron transfer from nitrogen to the surface. Our results show that this charge exchange controls the propensity for N–H vs N–C bond cleavage.
Molecular beam epitaxy of IV–VI mid-infrared vertical cavity surface-emitting quantum well laser structures
Authors: Wu H. , Zhao F. , Jayasinghe L. , Shi Z.
Published: October 2002

PbSe/PbSrSe multiple quantum well vertical cavity surface-emitting laser (VCSEL) structures were successfully grown by molecular beam epitaxy on freshly cleaved BaF2(111) substrates. In situ reflection high-energy electron diffraction characterizations demonstrated high quality active layer growth of the VCSEL structure. Three-stack Pb0.97Sr0.03Se/BaF2 distributed Bragg reflector renders reflectivity as high as 99%. Top mirror with 35% Sr/PbSe flux ratio was grown for the first time to allow 1.064 Nd:YAG pumping. The transition energies of PbSe/PbSrSe multiple quantum wells that were employed as active layers were determined by both photoluminescence and differential Fourier transform infrared transmission spectra. The combined measurements of reflectance and photoluminescence show good alignment of the gain peak of PbSe/Pb0.97Sr0.03Se multiple quantum well (MQW) active layers to the cavity resonance. Above-room-temperature pulsed emission at lasing wavelength of λ=4.1 μm was observed.
Control of ZnO film polarity
Authors: Hong Soon-Ku , Ko Hang-Ju , Chen Yefen , Yao Takafumi
Published: October 2002

The polarity of heteroepitaxial ZnO films is controlled by interface engineering. The ZnO films are grown on Ga-polar GaN templates by plasma-assisted molecular beam epitaxy. By forming a ZnO/GaN heterointerface without any interfacial layer through Zn pre-exposure, Zn-polar ZnO films are grown. O-polar ZnO films are obtained by forming a Ga2O3 interfacial layer, with an inversion center, inbetween the ZnO and GaN through O-plasma pre-exposure. A polarity inverted ZnO heterostructure is fabricated, without the formation of inversion domain boundaries, by inserting a MgO layer with an inversion center between the lower and upper ZnO layers. Mosaic tilt and twist angles of Zn- and O-polar ZnO films are, respectively, 0.10° and 0.18° (tilt), and 0.25° and 0.32° (twist). Dislocation densities in Zn-polar ZnO films are lower than those in O-polar ZnO films from both high resolution x-ray diffraction and transmission electron microscopic evaluation. A higher Ga-doping efficiency in the O-polar ZnO films than in the Zn-polar ZnO films was determined by two-layer Hall-effect analyses and photoluminescence intensities of Ga-related donor bound exciton emission. Free exciton emissions are observed from both undoped Zn-and O-polar ZnO films with narrower linewidths of bound exciton emissions from the Zn-polar ZnO films. Relative redshifts of bound exciton emissions from the O-polar ZnO films compared with those from the Zn-polar ZnO films are consistently observed for the undoped and Ga-doped ZnO films.
Low-temperature formation of highly reliable silicon-nitride gate dielectrics with suppressed soft-breakdown phenomena for advanced complementary metal–oxide–semiconductor technology
Authors: Nakajima Anri , Khosru Quazi Deen Mohd , Yoshimoto Takashi , Kidera Toshirou , Yokoyama Shin
Published: October 2002

Thin (equivalent oxide thickness Teq of 2.4 nm) silicon nitride was deposited on Si substrates by atomic-layer deposition (ALD) at low temperatures (<550 °C). Substantial enhancement of reliability was obtained with respect to the conventional SiO2 samples. An exciting feature of suppressed soft breakdown events was observed. Injected-carrier-induced physical damage, which results in the formation of the conductive filaments at the poly-Si/ALD-Si-nitride and ALD-Si-nitride/Si-substrate interfaces, is suppressed due to the higher stability of the Si–N bonds than that of the strained Si–O bonds. This suppression of physical damage leads to enhanced reliability. Therefore, the ALD silicon nitride can be a good choice for a highly reliable ultrathin gate dielectric in deep submicron complementary metal–oxide–semiconductor technology.
Effects of photowashing treatment on electrical properties of an AlGaN/GaN heterostructure field-effect transistor
Authors: Choi Kyoung Jin , Jeon Chang Min , Jang Ho Won , Lee Jong-Lam
Published: October 2002

The effects of photowashing treatment on the electrical properties of an AlGaN/GaN heterostructure field-effect transistor were studied by observing changes in atomic composition and band bending at the surface of AlGaN through synchrotron radiation photoemission spectroscopy. The surface treatment produced group-III oxides on the surface of AlGaN, leaving N vacancies behind. Both the gate leakage current (IGD) and drain current (IDS) simultaneously decreased after the treatment. The decrease of IGD was due to a delay in movement of the electrons, namely, trapping and detrapping. The trapped electrons reduced the effective channel thickness, and led to the reduction of IDS.
Valence band offset at the CdS/CdTe interface
Authors: Boieriu P. , Sporken R. , Sivananthan S.
Published: October 2002

Wurtzite CdS was grown by molecular beam epitaxy on CdTe(1̄1̄1̄)B and CdTe(111)A substrates. CdTe was grown on top of the CdS layers. X-ray photoelectron spectroscopy (XPS) indicates the existence of a thin reacted layer at the interface when CdTe(1̄1̄1̄)B is used as a substrate. No reaction is seen during growth of CdTe on CdS/CdTe(111)A. The valence band offset was measured by XPS and indicates a type-I alignment.
Structure and interface composition of Co layers grown on As-rich GaAs(001) c(4×4) surfaces
Authors: Lüdge K. , Schultz B. D. , Vogt P. , Evans M. M. R. , Braun W. , Palmstrøm C. J. , Richter W. , Esser N.
Published: October 2002

The initial growth of cobalt on the GaAs(001) c(4×4) surface has been studied using scanning tunneling microscopy, soft x-ray photoemission spectroscopy, and low energy electron diffraction. The structure and chemical reactivity of the Co layer are studied as a function of the substrate temperature and Co coverage. At low substrate temperatures (−10 °C), Co grows as small randomly distributed islands that start to coalesce for coverages exceeding 2 monolayers. Larger diameter islands are formed at substrate temperatures above 95 °C. However, higher growth temperatures result in significant interfacial reactions despite an improved surface morphology. Comparisons are made with CoAs and CoGa films grown directly on GaAs(001) and studied in situ with x-ray photoemission spectroscopy and scanning tunneling microscopy.
ErAs interlayers for limiting interfacial reactions in Fe/GaAs(100) heterostructures
Authors: Schultz B. D. , Farrell H. H. , Evans M. M. R. , Lüdge K. , Palmstro/m C. J.
Published: October 2002

In situ scanning tunneling microscopy and x-ray photoelectron spectroscopy were combined to examine the formation of the Fe/GaAs interface for Fe films grown on GaAs(100) As-rich surfaces by molecular beam epitaxy. Scanning tunneling microscopy images acquired following the growth of ultrathin layers of Fe on GaAs (2×4)/c(2×8)β2 surfaces show the initial growth of Fe results in little disruption of the As-dimer rows located directly adjacent to the deposited Fe clusters for growth temperatures between −15 and 175 °C. X-ray photoemission spectra show the interfacial Fe–Ga–As reactions depend on the growth temperature and can be minimized by growing at temperatures below 95 °C. However, approximately 0.7 ML of As was found to segregate to the Fe surface during growth, independent of the growth temperature. Atomic layer-by-layer calculations of the normalized intensity curves obtained from x-ray photoemission were used to quantify the extent of the interfacial reactions as a function of growth temperature. A 5 ML thick (∼14 Å) ErAs interlayer was used as a diffusion barrier to further limit the Fe–Ga–As interfacial reactions. For Fe growth at 225 °C on ErAs interlayers, the extent of the interfacial reactions was found to be comparable with the extent of the reactions resulting from the growth of Fe directly on GaAs at −15 °C. Although the ErAs interlayers suppressed the reactions between Fe and GaAs at the interface, they were unable to significantly alter the amount of As segregating to the Fe surface during growth.
Electronic states at the interface of Ti–Si oxide on Si(100)
Authors: Fulton C. C. , Lucovsky G. , Nemanich R. J.
Published: October 2002

The requirement for high K dielectrics for Si devices includes both a low interface state density and a band alignment that blocks both electrons and holes. Titanium dioxide materials are known to exhibit dielectric constants of 80 or higher depending on the crystal structure and, as such, are prime candidates for gate dielectrics. We employ an ultrathin layer of SiO2 prior to the formation of a Ti oxide to limit the density of defect states. The electronic structure is observed during the stepwise growth of the oxide using x-ray and ultraviolet photoemission spectroscopy. Measurements indicate Ti oxide states at approximately 2 eV below the Si valence band maximum suggesting that the TiO2 conduction band aligns with the Si conduction band. The results indicate nearly flat bands in the silicon consistent with a low interface state density.
Interface electronic structure of Ta2O5–Al2O3 alloys for Si-field-effect transistor gate dielectric applications
Authors: Ulrich M. D. , Johnson R. S. , Hong J. G. , Rowe J. E. , Lucovsky G. , Quinton J. S. , Madey T. E.
Published: October 2002

Interfacial electronic structure is important for a fundamental understanding of the properties of field-effect transistor (FET) device structure systems. Previous studies using soft x-ray photoelectron spectroscopy (SXPS) have demonstrated well-defined interface states that appear at binding energies between the peaks due to the substrate Si and the oxide SiO2. Recently we have shown that significant interface changes with annealing for the SiO2/Si system commonly used for FET gate dielectrics illustrating the effectiveness of SXPS for the current study. The present article presents SXPS studies using synchrotron radiation of the electronic structure at the interface between Ta2O5–Al2O3 alloys and Si(111). This system is typical of FET alternative-gate-oxide films and has an electronic structure characteristic of high-k gate dielectrics. Thin films (<20 Å) of Ta2O5–Al2O3 alloys were carefully prepared using remote plasma enhanced chemical vapor deposition on Si(111). For this study, SXPS spectra were taken for the Si 2p, Al 2p, and Ta 4f core levels. The Si 2p SXPS data confirm that SiO2 is formed at the Si interface during deposition for all alloys (in agreement with previously published results) and that the Si interface is qualitatively similar to SiO2/Si samples. The binding energy of the Si4+ Si 2p3/2 core level varies significantly for our alloy samples and this is interpreted as a screening effect rather than being due to Ta or Al silicate formation. The Al 2p and Ta 4f SXPS core level peak positions reveal screening effects. For these data, line shape analysis also supports alloy homogeneity as independently determined by Auger electron spectroscopy and Fourier transform infrared spectroscopy.
Nonlinear composition dependence of x-ray photoelectron spectroscopy and Auger electron spectroscopy features in plasma-deposited zirconium silicate alloy thin films
Authors: Rayner G. B. , Kang D. , Zhang Y. , Lucovsky G.
Published: October 2002

The local bonding of Zr, Si, and O atoms in plasma-deposited, and post-deposition annealed Zr silicate pseudobinary alloys [(ZrO2)x(SiO2)1−x] was studied by x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). Systematic decreases in XPS binding energies, and increases in AES kinetic energies with alloy composition x are consistent with an empirical chemical bonding model based on electronegativity equalization; however, there are significant departures from the predicted linear composition dependencies of that model. Deviations from linearity in the XPS compositional dependencies are correlated with dipolar network atom fields as determined from ab initio calculations. The nonlinearities in the x dependence of ZrMVV and OKVV AES spectral features are determined primarily by oxygen–atom coordination dependent shifts in valence band offset energies. The energy spread in the compositional dependence of binding energies (∼1.85 eV) for the XPS Zr 3d5/2 and Si 2p features combined with x-ray absorption spectroscopy data indicates that the conduction band offset energies between the Si substrate and Zr silicate dielectrics are alloy composition independent. Changes in O 1s XPS features in alloys with x∼0.3 to 0.6 as function of annealing temperature are consistent with a previously identified chemical phase separation that occurs after 60 s anneals at 900 °C in a nonoxidizing ambient, Ar.
Reduction of etching plasma damage on low dielectric constant fluorinated amorphous carbon films by multiple H2 plasma treatment
Authors: Shieh Jia-Min , Tsai Kou-Chiang , Dai Bau-Tong , Wu Yew-Chung , Wu Yu-Hen
Published: October 2002

Two-step hydrogen plasma treatment on low dielectric constant (low-k) fluorinated amorphous carbon films (a-C:F) was conducted to improve their thermal stability and reduce the damage caused by the patterning processes. First, hydrogen plasma treatment repairs imperfect bonds of as-deposited a-C:F films, stabilizing their chemical structures and increasing their resistance against elevated thermal stresses. After this passivation process, an additional hydrogen plasma treatment was applied to a-C:F films that had been etched using a mixture of N2+O2+CHF3, enabling sub-130 nm damascene trenches to be patterned and repairing the chemical structures destroyed by the etching plasma.
Magneto–photoluminescence study of intermixed self-assembled InAs/GaAs quantum dots
Authors: Ménard S. , Beerens J. , Morris D. , Aimez V. , Beauvais J. , Fafard S.
Published: October 2002

The electronic structure of InAs/GaAs self-assembled quantum dots and the carrier capture dynamics in these dots have been studied by magneto–photoluminescence at low temperature (5 K). We report results obtained on a series of samples processed by rapid thermal annealing. This intermixing procedure led to a significant narrowing of the inhomogeneous photoluminescence emission bands related to the various dot shell states, as compared to results obtained on unprocessed samples, which in turn improved the conditions for the observation of the Fock–Darwin energy levels structure as a function of the magnetic field, up to 15 T. We also observed that the ratio of the wetting layer emission intensity over the integrated intensity of the quantum dot emission bands increases nonlinearly with the magnetic field. This nonlinear behavior, which is more apparent at low photocarrier density, suggests that transport properties contribute to limit the carrier capture by the dots.
Comparison of three high‐resolution digitizers for radiochromic film dosimetry
Authors: Gluckman G. R. , Reinstein L. E.
Published: October 2002

A recently introduced radiographic film scanner from Howtek is evaluated and compared to two other commercially available densitometry systems for its use in radiochromic (RC) film dosimetry in the clinical dose range 0–100 Gy. It has a high‐intensity red LED light‐source centered at 662 nm (near the major absorption peak for RC film), and is coupled to a CCD linear array detector. This new densitometry system is directly compared to two high‐resolution film scanners commonly employed in RC film dosimetry, namely the Lumiscan 75 digitizer (He–Ne laser light source) and the Vidar VXR‐16 digitizer (fluorescent light source). A spot densitometer (Nuclear Associates Radiochromic Densitometer) with a filtered 671 nm laser‐diode light source is also included as a reference for comparison. The response of the spot densitometer and three high‐resolution digitizers is characterized by the dose required to reach a net optical density of 1 (DNOD1), and is 16.0, 37.3, and 46.4 Gy for the Nuclear Associates Radiochromic Densitometer, Howtek MultiRAD 460 and Lumiscan 75 digitizer, respectively. The Vidar VXR‐16 does not reach a net optical density of 1. The minimum usable dose at which a 2% level of uncertainty can be achieved on the three digitizers are 2.6, 6.0, and 38.5 Gy for the Howtek MultiRAD 460, Lumiscan 75, and Vidar VXR‐16, respectively. The Howtek MultiRAD 460 shows the greatest sensitivity, lowest and best signal‐to‐noise ratio in the clinical dose range 0–100 Gy. Furthermore, it has no apparent interference (moiré) artifacts that severely limit the low optical density region of the He–Ne laser digitizer. For high‐resolution radiochromic dosimetry in the clinical dose range 0–100 Gy, the high‐intensity red LED light‐source digitizer proves to be the superior modality.
A preliminary comparative study of two treatment planning systems developed for boron neutron capture therapy: MacNCTPlan and SERA
Authors: Wojnecki C. , Green S.
Published: October 2002

Two treatment planning systems have been specifically developed for BNCT: MacNCTPlan by the Harvard–MIT group and the SERA system developed by the INEEL/Montana State University group. In order to compare the dose components computed by the treatment planning systems, and therefore the clinical results available, it is important to first compare the basic features of the codes. This study investigated the effect of the reconstruction techniques and the form of the cross‐section libraries used by the two treatment planning systems on the thermal neutron fluence distributions. Six mono‐directional neutron sources of 0.0253 eV, 1 keV, 5 keV, 10 keV, 100 keV, and 1 MeV were directed onto simple geometric phantoms filled with water. The general‐purpose Monte Carlo radiation transport code MCNP was used as a reference tool in this study. For the examples studied, it is found that the methods used for geometry representation (in MacNCTPlan) and for cross‐section representation (in SERA) were found to impact directly on the accuracy of the calculated results.
A dosimetric comparison of two multileaf collimator designs
Authors: Killoran J. H. , Giraud J. Y. , Chin L.
Published: October 2002

We present the results of measurements designed to compare two different multileaf collimator (MLC) designs using a novel evaluation technique. The MLC designs evaluated were: a “single‐focused” MLC (SF‐MLC) mounted below the jaws, and a “double‐focused” MLC, which is a complete replacement for the lower jaws. The ability of each MLC to conform isodose lines to a prescribed field edge (PFE) was evaluated using film dosimetry. Circular fields, centered on axis and off axis, were used because they produce a range of “angles of approach” between the MLC leaves and the PFE. They also have the advantage that for an ideal field shaping system the resulting isodoses are concentric perfect circles, a well‐defined basis for evaluation. The amplitude of the oscillations of the 50% isodose line about the PFE and the penumbra width as determined by the 20%, 80%, and 90% isodose lines was examined. We observe that the 50% isodose line oscillates around the PFE with greater amplitude for SF‐MLC. We attribute this, at least in part, to the rounded ends of the SF‐MLC leaves. However, the SF‐MLC has a noticeably sharper penumbra, which we attribute to its position further from the source. We conclude that these results are relevant for accurate dosimetric modeling of these devices.
Spectral reconstruction of high energy photon beams for kernel based dose calculations
Authors: Hinson William H. , Bourland J. Daniel
Published: October 2002

A kernel‐based dose computation method with finite‐size pencil beams (FSPBs) requires knowledge of the photon spectrum. Published methods of indirect spectral measurements using transmission measurements through beam attenuators use mathematical fits with a large number of parameters and constraints. In this study, we examine a simple strategy for fitting transmission data that models important physical characteristics of photon beams produced in clinical linear accelerators. The shape of an unattenuated bremsstrahlung spectrum is known, varying linearly from a maximum at zero energy to a value of zero at a maximum energy. This unattenuated spectrum is altered primarily by absorption of low energy photons by the flattening filter, causing the true spectrum to roll off to zero at low photon energies. A fitting equation models this behavior and has these advantages over previous methods: (1) the equation describes the shape of a bremsstrahlung spectrum based on physical expectations; and (2) only three fit parameters are required with a single constraint. Results for 4 MV and 6 MV accelerators for central axis and off‐axis beams show good agreement with the maximum, average and modal energies for known spectra. Previously published models, representations of beam fluence (energy fluence, experimental methods, and the fitting process are discussed.
Studies on developments of imaging and analytical methods and evaluations of properties mainly on image quality in MRI (in Japanese)
Authors: Miyati Tosiaki
Published: October 2002

The aims of this thesis were to develop imaging and analytical methods in magnetic resonance imaging (MRI) to obtain morphological and functional information of the human body and to evaluate image quality of an MRI system. Various new methods are illustrated. A fast imaging method for obtaining a T1‐weighted image by using the rapid acquisition relaxation enhanced sequence combined with the variable flip angle excitation is described. Next, the thesis describes a method for performing a dynamic contrast‐enhanced T1‐weighted and study simultaneously to evaluate regional hemodynamics in brain tumors. This method can increase the amount of vascular information and reveals the hemodynamics of the brain tumor and surrounding regions in greater detail. The thesis describes a frequency analysis of cerebrospinal fluid (CSF) flow measured with an ECG gated phase contrast cine‐MRI to clarify the flow dynamics of intracranial CSF in normal pressure hydrocephalus (NPH). This frequency analysis can noninvasively provide a picture of the pathophysiology of NPH and of intracranial changes. Developments of the above imaging and analytical methods in MRI make it possible to obtain more detailed information on the human body. In addition, the thesis describes a new method to accurately measure the modulation transfer function and the signal‐to‐noise ratio in the positive and negative frequencies in MRI with a specially designed phantom. This evaluation method makes it possible to obtain more detail on the image quality of MRI, and is useful in various performance assessments such as the evaluation of pulse sequences.
A simple experimental setup to demonstrate the basics of positron emission tomography
Authors: Sonnabend Kerstin , Bayer Wolfgang , Mohr Peter , Zilges Andreas
Published: October 2002

We present a setup of a simplified positron emission tomograph (PET) which can be used in a third-year laboratory course for physics students. The equipment of a standard γ–γ angular correlation experiment was modified using bismuth-germanate crystals instead of NaI. Using this setup it is possible to locate several radioactive sources hidden in a closed box. The problems of two-dimensional imaging tomography using one-dimensional projections are illustrated as well as the problems encountered in medical PET examinations.
An algebraic method for solving central force problems
Authors: Cooke T. H. , Wood J. L.
Published: October 2002

A simple algebraic method, which is as easy to use as the angular momentum algebra, is demonstrated as a pedagogical way to solve certain central force problems exactly. Solutions for the hydrogen atom and the three-dimensional isotropic harmonic oscillator are presented together with a discussion of the limits of the method.
The mid-level hump at 2 kHz
Authors: Nizami Lance , Reimer Jason F. , Jesteadt Walt
Published: October 2002

Shortening the duration of a Gaussian-shaped 2-kHz tone-pip causes the intensity-difference limen (DL) to depart from the “near-miss to Weber’s law” and swell into a mid-level hump [Nizami et al., J. Acoust. Soc. Am. 110, 2505–2515 (2001)]. For some subjects the size of this hump approaches or exceeds the size reported for longer tones under forward masking, suggesting that forward masking might make little difference to the DL for very brief probes. To test this hypothesis, DLs were determined over 30 to 90 dB SPL for a brief Gaussian-shaped 2-kHz tone-pip. DLs were obtained first without forward masking, then with the pip placed 10 or 100 ms after a 200-ms 2-kHz tone of 50 dB SPL, or 100 ms after a 200-ms 2-kHz tone of 70 dB SPL. DLs inflated significantly under all forward-masking conditions. DLs also enlarged under an 80 dB SPL forward masker at pip delays of 4, 10, 40, and 100 ms. The peaks of the humps obtained under forward masking clustered around a sensation level (SL) that was significantly lower than the average SL for the peaks of the humps obtained without forward masking. Overall, the results do not support the neuronal-recovery-rate model of Zeng et al. [Hear. Res. 55, 223–230 (1991)], but are not incompatible with the Carlyon and Beveridge hypothesis [J. Acoust. Soc. Am. 93, 2886–2895 (1993)] that nonsimultaneous maskers corrupt the memory trace evoked by the probe.
A linearized Eulerian sound propagation model for studies of complex meteorological effects
Authors: Blumrich Reinhard , Heimann Dietrich
Published: October 2002

Outdoor sound propagation is significantly affected by the topography (including ground characteristics) and the state of the atmosphere. The atmosphere on its part is also influenced by the topography. A sound propagation model and a flow model based on a numerical integration of the linearized Euler equations have been developed to take these interactions into account. The output of the flow model enables the calculation of the sound propagation in a three-dimensionally inhomogeneous atmosphere. Rigid, partly reflective, or fully absorptive ground can be considered. The linearized Eulerian (LE) sound propagation model has been validated by means of four different scenarios. Calculations of sound fields above rigid and grass-covered ground including a homogeneous atmosphere deviate from analytic solutions by ⩽1 dB in most parts of the computed domain. Calculations of sound propagation including wind and temperature gradients above rigid ground agree well with measured scale model data. Calculations of sound propagation over a screen including ground of finite impedance show little deviations to measured scale model data which are probably caused by an insufficient representation of the complex ground impedance. Further calculations included the effect of wind on shading by a screen. The results agree well with the measured scale model data.
Breaking wind waves as a source of ambient noise
Authors: Tkalich Pavlo , Chan Eng Soon
Published: October 2002

A theoretical model for the prediction of ambient noise level due to collective oscillations of air bubbles under breaking wind waves is presented. The model uses a budget of the energy flux from the breaking waves to quantify acoustic power radiation by a bubble cloud. A shift of the noise spectra to lower frequency due to collective bubble oscillation is assumed. The model derives good estimates of the magnitude, slope, and frequency range of the noise spectra using the wind speed or height of breaking waves.
Analysis of the time-reversal operator for scatterers of finite size
Authors: Chambers D. H.
Published: October 2002

Recently, it was shown that the time-reversal operator for a single, small spherical scatterer could have up to four distinguishable eigenstates [Chambers and Gautesen, J. Acoust. Soc. Am. 109, 2616–2624 (2001)]. In this paper, that analysis is generalized for scatterers of arbitrary shape and larger size. It is shown that the time-reversal operator may have an indefinitely large number of distinguishable eigenstates, with the exact number depending on the nature of the scatterer and the geometry of the time-reversal mirror. In addition, the case of a multiple number of well-separated scatterers is investigated, with the result that the total spectrum is the direct combination of the eigenstates associated with each scatterer. As an example, the singular value spectrum of the time-reversal operator for a linear array is calculated explicitly for bubbles and hard rubber spheres of finite size. Both resonance peaks and apparent crossing points can be observed in the spectrum as the size of the scatterer increases.
A two-way parabolic equation that accounts for multiple scattering
Authors: Lingevitch Joseph F. , Collins Michael D. , Mills Michael J. , Evans Richard B.
Published: October 2002

A two-way parabolic equation that accounts for multiple scattering is derived and tested. A range-dependent medium is divided into a sequence of range-independent regions. The field is decomposed into outgoing and incoming fields in each region. The conditions between vertical interfaces are implemented using rational approximations for the square root of an operator. Rational approximations are also used to relate fields between neighboring interfaces. An iteration scheme is used to solve for the outgoing and incoming fields at the vertical interfaces. The approach is useful for solving problems involving scattering from waveguide features and compact objects.
Normalized amplitude quotient for parametrization of the glottal flow
Authors: Alku Paavo , Bäckström Tom , Vilkman Erkki
Published: October 2002

Normalized amplitude quotient (NAQ) is presented as a method to parametrize the glottal closing phase using two amplitude-domain measurements from waveforms estimated by inverse filtering. In this technique, the ratio between the amplitude of the ac flow and the negative peak amplitude of the flow derivative is first computed using the concept of equivalent rectangular pulse, a hypothetical signal located at the instant of the main excitation of the vocal tract. This ratio is then normalized with respect to the length of the fundamental period. Comparison between NAQ and its counterpart among the conventional time-domain parameters, the closing quotient, shows that the proposed parameter is more robust against distortion such as measurement noise that make the extraction of conventional time-based parameters of the glottal flow problematic. Experiments with breathy, normal, and pressed vowels indicate that NAQ is also able to separate the type of phonation effectively.
A model cochlear partition involving longitudinal elasticity
Authors: Jaffer Taha S. A. , Kunov Hans , Wong Willy
Published: October 2002

This paper addresses the issue of longitudinal stiffness within the cochlea. A one-dimensional model of the cochlear partition is presented in which the resonant sections are coupled by longitudinal elastic elements. These elements functionally represent the aggregate mechanical effect of the connective tissue that spans the length of the organ of Corti. With the plate-like morphology of the cochlear partition in mind, the contribution of longitudinal elasticity to partition dynamics is appreciable, though weak and nonlinear. If the elasticity is considered Hookian then the nonlinearity takes a cubic form. Numerical solutions are presented that demonstrate the compressive nature of the partial differential nonlinear equations and their ability to produce realistic cubic distortion product otoacoustic emissions. Within the framework of this model, some speculations can be made regarding the dynamical function of the phalangeal processes, the sharpness of active cochlear mechanics, and the propogation of pathology along the partition.
Captive dolphins, Tursiops truncatus, develop signature whistles that match acoustic features of human-made model sounds
Authors: Miksis Jennifer L. , Tyack Peter L. , Buck John R.
Published: October 2002

This paper presents a cross-sectional study testing whether dolphins that are born in aquarium pools where they hear trainers’ whistles develop whistles that are less frequency modulated than those of wild dolphins. Ten pairs of captive and wild dolphins were matched for age and sex. Twenty whistles were sampled from each dolphin. Several traditional acoustic features (total duration, duration minus any silent periods, etc.) were measured for each whistle, in addition to newly defined flatness parameters: total flatness ratio (percentage of whistle scored as unmodulated), and contiguous flatness ratio (duration of longest flat segment divided by total duration). The durations of wild dolphin whistles were found to be significantly longer, and the captive dolphins had whistles that were less frequency modulated and more like the trainers’ whistles. Using a standard t-test, the captive dolphin had a significantly higher total flatness ratio in 9/10 matched pairs, and in 8/10 pairs the captive dolphin had significantly higher contiguous flatness ratios. These results suggest that captive-born dolphins can incorporate features of artificial acoustic models made by humans into their signature whistles.