bluuebunny/crossref_metadata_2025 huggingface dataset:
Locally delivered rhBMP‐2 enhances bone ingrowth and gap healing in a canine model
Authors: Sumner D. R. , Turner T. M. , Urban R. M. , Turek T. , Seeherman H. , Wozney J. M.
Published: June 2003

The purpose of the present study was to determine if recombinant human bone morphogenetic protein‐2 (rhBMP‐2) enhances bone ingrowth into porous‐coated implants and gap healing around the implants. In the presence of a 3‐mm gap between the implant and host bone, porous‐coated implants were placed bilaterally for four weeks in the proximal humeri of skeletally mature, adult male dogs. In three treatment groups, the test implant was treated with HA/TCP and rhBMP‐2 in buffer at a dose of 100 μg/implant (n = 5), 400 μg/implant (n = 6), or 800 μg/implant (n = 5) and placed in the left humerus. In these same animals, an internal control implant was treated only with HA/TCP and buffer and placed in the right humerus. These groups were compared with a previously reported external control group of seven animals in which no growth factor was delivered [J. Orthop. Res. 19 (2001) 85]. The BMP treated implants in the two lower dose groups had significantly more bone ingrowth than the external controls with the greatest effect in the 100 g/implant group (a 3.5‐fold increase over the external control, p = 0.008). All three dose groups had significantly more bone formation in the 3‐mm gap surrounding the BMP treated implants than the external controls with the greatest effect in the 800 μg group (2.9‐fold increase, p < 0.001). Thus, application of rhBMP‐2 to a porous‐coated implant stimulated local bone ingrowth and gap healing. The enhancement of bone formation within the implant (bone ingrowth) was inversely related to dose. © 2003 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved.
Evaluation of Ad‐BMP‐2 for enhancing fracture healing in an infected defect fracture rabbit model
Authors: Southwood Louise L. , Frisbie David D. , Kawcak Chris E. , Ghivizzani Steven C. , Evans Chris H. , McIlwraith C. Wayne
Published: June 2003

The objective of this study was to evaluate the use of adenoviral transfer of the BMP‐2 gene (Ad‐BMP‐2) for enhancing healing in an infected defect fracture model. A femoral defect stabilized with plates and screws was surgically created in sixty‐four skeletally mature New Zealand white rabbits. Experimental groups were: (1) non‐infected Ad‐luciferase (Ad‐LUC, NONLUC), (2) non‐infected Ad‐BMP‐2 (NONBMP), (3) infected Ad‐LUC (INFLUC), and (4) infected Ad‐BMP‐2 (INFBMP). A sclerosing agent was applied to the ends of the bone at surgery to facilitate the development of osteomyelitis. Fracture healing was evaluated radio‐graphically and histologically. Data were analyzed using an ANOVA, with statistical significance set as p < 0.05.

Rabbits in the non‐infected and infected groups that were treated with Ad‐BMP‐2 had earlier initial‐ and bridging‐callus formation, and a higher overall external callus grade compared to rabbits in the Ad‐LUC groups. Rabbits in the Ad‐LUC groups had more defect ossification compared to rabbits in the Ad‐BMP‐2 groups. There was a trend for rabbits in the Ad‐BMP‐2 group that were euthanized at 2 and 4 weeks after surgery to have more bone and cartilage compared to rabbits in the Ad‐LUC group. The results of this study suggest that Ad‐BMP‐2 enhances the early stages of healing in an infected defect fracture. The results of our study were not as favorable as those reported in previous studies because animals healed by a large bridging callus and not by defect ossification. This could have been a result of the sclerosing agent, which may have damaged the cells in the defect. © 2003 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved.
Factors and motives associated with drop-out in an ambulatory service for patients with psychotic disorders
Authors: Fuciec M. , Mohr S. , Garin C.
Published: June 2003

The aim is to study motives and factors associated with treatment drop-out in an ambulatory psychiatric service, which integrates medical, social, familial and rehabilitation treatments. Only 9% of the psychotic patients dropped out, whose motives were non-compliance with medication and unawareness of illness, and the associated factors were comorbidity of substance abuse, social isolation and male gender.
An expanded target-strength relationship for herring
Authors: Ona Egil
Published: June 2003

Target-strength (TS) experiments on captive, adult herring have been conducted at intervals over several years to investigate the acoustic effect of pressure and seasonal changes on fish physiology. Experiments in a large, net pen (4500 m3) were done at 18, 38, and 120 kHz frequencies with calibrated, split-beam echosounders. The main ex situ results at 38 kHz, including a vertical-excursion experiment, were combined with in situ TS data collected at 38 kHz with a probing, split-beam transducer lowered into the dense herring layers, recorded during two surveys in the wintering area of the Norwegian spring-spawning stock. Multiple-linear regression analysis was used to investigate the functional relationship between TS and the measured parameters. The mean TS of herring was found to be significantly dependent on the depth (pressure) and the gonadosomatic index. These are the additional parameters included in the new TS relationship.
Diurnal changes in the acoustic-frequency characteristics of Japanese anchovy (Engraulis japonicus) post-larvae “shirasu” inferred from theoretical scattering models
Authors: Miyashita Kazushi
Published: June 2003

Diurnal changes in the acoustic-frequency characteristics of “shirasu”, a post-larval stage of Japanese anchovy (Engraulis japonicus), were analysed based on theoretical scattering models. Since post-larval swimbladders contain gas at night but not during the day, the distorted-wave Born approximation (DWBA), based on the deformed-cylinder model, which assumes there is no gas in the swimbladder, was applied to daytime observations, and the fish-bladder resonance model, which assumes there is gas in the swimbladder, to those taken at night. The two sets of acoustic frequencies employed were 50 and 200 kHz, which are those used for shirasu commercial fishing, and 38 and 120 kHz, which are usually employed for acoustic surveys using a quantitative echosounder. During the daytime, differences in shirasu target strengths between the two frequencies were large, especially between 38 and 120 kHz, but at night there was little difference with frequency, suggesting that acoustic surveys for identifying and estimating the abundance of shirasu should be done during daytime, when differences occur between frequencies and the shirasu form dense schools.
Tissue distribution, intracellular localization and proteolytic processing of rat 4‐hydroxyphenylpyruvate dioxygenase
Authors: Neve Søren , Aarenstrup Lene , Tornehave Ditte , Rahbek‐Nielsen Henrik , Corydon Thomas Juhl , Roepstorff Peter , Kristiansen Karsten
Published: June 2003

4‐hydroxyphenylpyruvate dioxygenase (HPD) is an important enzyme involved in tyrosine catabolism. HPD was shown to be identical to a protein named the F‐antigen, exploited by immunologists because of its unique immunological properties. Congenital HPD deficiency is a rare, relatively benign condition known as hereditary type III tyrosinemia. Decreased expression of HPD is often observed in association with the severe type I tyrosinemia, and interestingly, inhibition of HPD activity seems to ameliorate the clinical symptoms of type I tyrosinemia. In this study we present a comprehensive analysis of tissue specific expression and intracellular localization of HPD in the rat. By combined use of in situ hybridization and immunohistochemistry we confirm previously known sites of expression in liver and kidney. In addition, we show that HPD is abundantly expressed in neurons in the cortex, cerebellum and hippocampus. By using immunoelectron microscopy and confocal laser scanning microscopy, we provide evidence that HPD contrary to earlier assumptions specifically localizes to membranes of the endoplasmic reticulum and the Golgi apparatus. Detailed mass spectrometric analyses of HPD purified from rat liver revealed N‐terminal and C‐terminal processing of HPD, and expression of recombinant HPD suggested that C‐terminal processing enhances the enzymatic activity.
New insights on the tectonics along the New Hebrides subduction zone based on GPS results
Authors: Calmant Stéphane , Pelletier Bernard , Lebellegard Pierre , Bevis Michael , Taylor Frederick W. , Phillips David A.
Published: June 2003

At the New Hebrides (NH) subduction zone, ridges born by the subducting Australia plate enter the trench and collide with the overriding margin. Results from GPS surveys conducted on both sides of the trench and new bathymetry maps of the NH archipelago bring new light on the complex tectonics of this area. Convergence vectors present large variations that are not explained by Australia/Pacific (A/P) poles and that define four segments. Vectors remain mostly perpendicular to the trench and parallel to the earthquake slip vectors. Slow convergence (i.e., 30–40 mm/yr) is found at the central segment facing the D'Entrecasteaux Ridge. The southern segment moves faster than A/P motion predicts (89 to 124 mm/yr). Relatively to a western North Fiji basin (WNFB) reference, the northern and southern segments rotate in opposite directions, consistently with the extension observed in the troughs east of both segments. Both rotations combine in Central Vanuatu into an eastward translation that “bulldozes” the central segment into the WNFB at ∼55 mm/yr. That model suggests that the motion of the central segment, forced by the subduction/collision of the D'Entrecasteaux ridge, influences the motion of the adjoining segments. The New Caledonia archipelago is motionless with respect to the rest of the Australia plate despite the incipient interaction between the Loyalty ridge and the NH margin. Southeast of the interaction area, convergence is partitioned into a ∼50 mm/yr trench‐normal component accommodated at the trench and a ∼90 mm/yr trench‐parallel component, close to the A/P convergence, and presumably accommodated by a transform boundary at the rear of the NH arc.
Composition of altered oceanic crust at ODP Sites 801 and 1149
Authors: Kelley Katherine A. , Plank Terry , Ludden John , Staudigel Hubert
Published: June 2003

We present a comprehensive major and trace element dataset establishing ODP Site 801 as a geochemical reference for altered oceanic crust. The composition of old crustal sequences like those at Sites 801 and 1149 are critical to developing models of crustal aging and seawater chemistry evolution and to understanding the fate of crust consumed at subduction zones. Our estimate of the bulk composition of oceanic crust at Site 801 comprises ICP‐AES and ICP‐MS analyses of 117 discrete samples, 14 mixed composites and 5 glasses from the upper 500 m of Jurassic Pacific crust. Comparing the 801 “super‐composite” with glass reveals enrichment of U (5x), Li (2x), K2O (4x), Rb (9x), and Cs (7x), similar to DSDP Sites 417/418, but little to no enrichment in Ba or Pb. The data also demonstrate good (∼10%) agreement between U measured on discrete samples and natural gamma logs, suggesting logging data is a reliable means of establishing bulk geochemical characteristics of oceanic crust. Data reported here serve to link other geochemical and mineralogical measurements on Site 801 and 1149 samples. We also document Boston University sample preparation procedures and instrument parameters for ICP‐MS and ICP‐AES analyses, and provide comparisons with other laboratories and techniques. We present new techniques for basaltic glass analyses using the Boston University 213 nm Nd‐YAG LA‐ICP‐MS system, and show the data agree well with both solution‐ICP‐MS (5–10%) and ion probe measurements (∼10%).
A backward modeling study of intercontinental pollution transport using aircraft measurements
Authors: Stohl A. , Forster C. , Eckhardt S. , Spichtinger N. , Huntrieser H. , Heland J. , Schlager H. , Wilhelm S. , Arnold F. , Cooper O.
Published: June 2003

In this paper we present simulations with a Lagrangian particle dispersion model to study the intercontinental transport of pollution from North America during an aircraft measurement campaign over Europe. The model was used for both the flight planning and a detailed source analysis after the campaign, which is described here with examples from two episodes. Forward calculations of emission tracers from North America, Europe, and Asia were made in order to understand the transport processes. Both episodes were preceded by stagnant conditions over North America, leading to the accumulation of pollutants in the North American boundary layer. Both anthropogenic sources and, to a lesser extent, forest fire emissions contributed to this pollution, which was then exported by warm conveyor belts to the middle and upper troposphere, where it was transported rapidly to Europe. Concentrations of many trace gases (CO, NOy, CO2, acetone, and several volatile organic compounds; O3 in one case) and of ambient atmospheric ions measured aboard the research aircraft were clearly enhanced in the pollution plumes compared to the conditions outside the plumes. Backward simulations with the particle model were introduced as an indispensable tool for a more detailed analysis of the plume's source region. They make trajectory analyses (which, to date, were mainly used to interpret aircraft measurement data) obsolete. Using an emission inventory, we could decompose the tracer mixing ratios at the receptors (i.e., along the flight tracks) into contributions from every grid cell of the inventory. For both plumes we found that emission sources contributing to the tracer concentrations over Europe were distributed over large areas in North America. In one case, sources in California, Texas, and Florida contributed almost equally, and smaller contributions were also made by other sources located between the Yucatan Peninsula and Canada. In the other case, sources in eastern North America, including moderate contributions from forest fires, were most important. The plume's maximum was mainly caused by anthropogenic emissions from the New York area. To our knowledge, this is the first case reported where a pollution plume from a megacity was reliably detected over another continent.
Pattern of first and last appearance in diatoms: Oceanic circulation and the position of polar fronts during the Cenozoic
Authors: Cervato Cinzia , Burckle Lloyd
Published: June 2003

First and last occurrences of 389 diatom species from the first global Cenozoic record are used to reconstruct the position of major oceanographic boundaries. First appearances and extinctions group in three latitudinal bands: middle to high northern latitudes, equatorial region, and high southern latitudes. Sparse Paleogene occurrences were limited to southern high latitudes along the equivalent of the modern Antarctic polar front. Its late middle Eocene to middle Miocene position varied within 10°, and within a 20° band from middle Miocene to present, suggesting an association with global cooling. First and last occurrence events appear in the two remaining latitudinal regions during the Eocene and increase in a stepwise fashion, mimicking significant cooling events. At about 16 Ma, first and last appearances shift from the North Atlantic to the North Pacific. Low‐latitude data suggest low surface water productivity prior to 40 Ma, while increased abundance from the middle Miocene correlates with expansion of the east Antarctic Ice Sheet.
Investigating the geoelectrical response of hydrocarbon contamination undergoing biodegradation
Authors: Werkema D. Dale , Atekwana Estella A. , Endres Anthony L. , Sauck William A. , Cassidy Daniel P.
Published: June 2003

A newly proposed geoelectrical model for hydrocarbon contaminated sites predicts high conductivities coincident with the contaminated zone as opposed to the traditionally accepted low conductivity. The model attributes the high conductivities to mineral weathering resulting from byproducts of microbial redox processes. To evaluate this conductive model, in situ vertical conductivity measurements were acquired from a light non‐aqueous phase liquid (LNAPL) contaminated site. The results showed high conductivities coincident with the zone of contamination and within the smear zone influenced by seasonal water table fluctuations. We infer this zone as an active zone of biodegradation and suggest significant microbial degradation under partially water saturated conditions. A simple Archie's Law analysis shows large pore water conductivities necessary to reproduce the bulk conductivity measured at the contaminated location. This study supports the conductive layer model and demonstrates the potential of geoelectrical investigations for assessing microbial degradation of LNAPL impacted soils.
Fast Multidimensional Scaling Through Sampling, Springs and Interpolation
Authors: Morrison Alistair , Ross Greg , Chalmers Matthew
Published: June 2003

The term ‘proximity data’ refers to data sets within which it is possible to assess the similarity of pairs of objects. Multidimensional scaling (MDS) is applied to such data and attempts to map high-dimensional objects onto low-dimensional space through the preservation of these similarity relations. Standard MDS techniques have in the past suffered from high computational complexity and, as such, could not feasibly be applied to data sets over a few thousand objects in size. Through a novel hybrid approach based upon stochastic sampling, interpolation and spring models, we have designed an algorithm running in O( N√N). Using Chalmers’ 1996 O( N2) spring model as a benchmark for the evaluation of our technique, we compare layout quality and run times using sets of synthetic and real data. Our algorithm executes significantly faster than Chalmers’ 1996 algorithm, while producing superior layouts. In reducing complexity and run time, we allow the visualisation of data sets of previously infeasible size. Our results indicate that our method is a solid foundation for interactive and visual exploration of data.
Real time technique to measure the electrical resistivity of ultrathin films during growth in plasma environments
Authors: Barnat E. V. , Nagakura D. , Lu T.-M.
Published: June 2003

A technique used to obtain the evolution of the electrical resistivity of ultrathin films during growth in a plasma environment is described. Details are given on the physical construction of the substrate assembly that house specially prepared substrates used for film growth. Discussion on the considerations that were needed for proper design of the circuitry to minimize or eliminate the effects of the plasma and any electrode bias on the measurement of the resistivity is given. Operation of the final design is demonstrated through measurements of the current and induced voltages obtained in real time for ultrathin copper sputter deposited onto silicon dioxide. The measured signals are then used to calculate the resistivity as a function of the thickness of the film.
Intrinsic compressive stress in polycrystalline films with negligible grain boundary diffusion
Authors: Sheldon Brian W. , Ditkowski Adi , Beresford R. , Chason Eric , Rankin Janet
Published: June 2003

The model developed here describes compressive stress evolution during the growth of continuous, polycrystalline films (i.e., beyond the point where individual islands have coalesced into a continuous film). These stresses are attributed to the insertion of excess adatoms at grain boundaries. Steady state occurs when the strain energy at the top of the film is balanced by the local excess chemical potential of surface adatmos. Strain gradients associated with this compressive stress mechanism depend on the kinetics of the process. In the absence of grain boundary diffusion, these strain profiles are determined by the ratio of the atom insertion and growth rates. The steady-state strain and the strain evolution kinetics also depend on the two key length scales, the grain size, and the film thickness. The ratio of these two lengths (i.e., the grain aspect ratio) can also have a significant influence on the thermodynamic driving force for strain evolution if the grain sizes are sufficiently small. The model is fit to existing data for the growth of AlN films. However, more detailed comparisons will require experiments that are specifically designed to test this model.
Effective-medium model for nearly constant loss in ionic conductors
Authors: Macdonald J. Ross
Published: June 2003

A complex quantitative model for nearly constant loss (NCL) is proposed based on an effective-medium approach. Unlike previous NCL response models, it satisfies the Kronig–Kramers transform relations. Here the effective-medium dielectric-level model depends directly on the concentration of mobile charge present and its complex dielectric response is identified as arising from electrical interactions between vibrating and/or hopping ions and the bulk matrix material. The parallel combination of the effective-medium response with dispersive hopping described by the Kohlrausch K1 model, a version of the corrected-modulus-formalism approach, leads to behavior that can represent dominant NCL at low temperatures well and, at higher temperatures, dispersive response followed by NCL. Complex nonlinear-least-squares fitting of experimental data sets that exhibit both types of response leads to excellent fits. Further, the effective-medium NCL model, which involves physically realizable response, can represent a wide range of NCL behavior analytically. Such behavior ranges from either approximate or exact power-law frequency dependence for both parts of the complex dielectric constant or to such response for its real part and very close to constant loss over a wide range of frequency for the associated imaginary part, as sometimes observed.
Ultrafast carrier trapping and recombination in highly resistive ion implanted InP
Authors: Carmody C. , Tan H. H. , Jagadish C. , Gaarder A. , Marcinkevičius S.
Published: June 2003

MeV P+ implanted and annealed p-InP, and Fe+ implanted and annealed semi-insulating InP have both been shown to produce the high resistivity, good mobility, and ultrafast optical response desired for ultrafast photodetectors. Hall effect measurements and time resolved photoluminescence were used to analyze the electrical and optical features of such implanted materials. Low temperature annealing was found to yield the fastest response times—130 fs for Fe+ implanted and 400 fs for P+ implanted InP, as well as resistivities of the order ∼106 Ω/square. It was found that the electrical activation of Fe-related centers, useful for achieving high resistivities in Fe+ implanted semi-insulating InP, was not fully realized at the annealing temperatures chosen to produce the fastest optical response. Implanting p-InP in the dose regime where type conversion occurs, and subsequent annealing at 500 °C, produces high resistivities and ultrafast carrier trapping times that are only marginally dose dependent.
Optical and structural properties of β-FeSi2 precipitate layers in silicon
Authors: Schuller B. , Carius R. , Mantl S.
Published: June 2003

Semiconducting iron disilicide (β-FeSi2) precipitates in silicon were fabricated by ion beam synthesis. The samples were characterized by Raman spectroscopy, transmission electron microscopy, and photoluminescence spectroscopy. By comparison with a β-FeSi2 single crystal, the silicide precipitates are found to be unstrained in all cases, so there is no correlation between strain and photoluminescence efficiency. Our results indicate that carrier recombination at silicon dislocations is sufficient to explain the photoluminescence in our samples.
Electron beam generation in a diode with a gaseous plasma electron source II: Plasma source based on a hollow anode ignited by a hollow-cathode source
Authors: Krokhmal A. , Gleizer J. Z. , Krasik Ya. E. , Felsteiner J. , Gushenets V. I.
Published: June 2003

We describe the operation of a hollow plasma anode (HPA) with a hollow cathode incorporated in it for the production of preliminary plasma. The operation of the hollow anode was studied with a discharge current amplitude up to 1 kA. It was shown that the gaseous discharge is realized without formation of plasma spots at the anode wall and the output grid. The plasma parameters inside the HPA were measured for different N2 gas pressures and discharge current amplitudes. It was found that the plasma acquires a positive potential with respect to the anode and that the plasma density and temperature are ⩽5×1012 cm−3 and ⩽10 eV, respectively. This plasma source was used as a cathode in a diode for the generation of high-current electron beams under an accelerating-voltage ⩽250 kV and 400 ns pulse duration. The characteristics of the diode and the generated electron beam as a function of the HPA parameters are presented. It was found that at the beginning of the accelerating pulse the diode operates in a plasma prefilled mode, and further in the accelerating pulse the diode current is determined by the emission capability of the HPA. It was shown that this source allows reliable generation of a uniform electron beam with a cross-sectional area of 100 cm2 and a current amplitude up to 1 kA without the formation of explosive plasma at the HPA output grid.
Local structure in nematic and isotropic liquid crystals
Authors: Phuong Nguyen Hoang , Schmid Friederike
Published: June 2003

By computer simulations of systems of ellipsoids, we study the influence of the isotropic/nematic phase transition on the direct correlation functions (DCF) in anisotropic fluids. The DCF is determined from the pair distribution function by solving the full Ornstein–Zernike equation, without any approximations. Using a suitable molecular-fixed reference frame, we can distinguish between two qualitatively different contributions to the DCF: One which preserves rotational invariance, and one which breaks it and vanishes in the isotropic phase. We find that the symmetry preserving contribution is barely affected by the phase transition. However, symmetry breaking contributions emerge in the nematic phase and may become quite substantial. Thus the DCF in a nematic fluid is not rotationally invariant. In the isotropic fluid, the DCF is in good agreement with the prediction of the Percus–Yevick theory.
Shift of resonance frequency of long conducting fibers embedded in a composite
Authors: Matitsine S. M. , Hock K. M. , Liu L. , Gan Y. B. , Lagarkov A. N. , Rozanov K. N.
Published: June 2003

An experimental study on the dipole resonance of long high-conducting fibers embedded in an inhomogeneous composite sheet was conducted. The location of the resonance characterizes the effect of the inhomogeneous environment on the electromagnetic response of the fibers. It is shown that the resonance frequency is determined completely by the thickness and permittivity of the composite sheet, in particular, with the anisotropy of the permittivity. No effect due to inhomogeneity of the environment is observed. This is in disagreement with the scale-dependent effective medium theory (SDEMT) that is conventionally exploited to model the permittivity of fiber-filled composites, because this theory shows that the response of the fibers depends on the inhomogeneity scale of the environment. Therefore, although the SDEMT provides qualitative agreement with the observed behavior of fiber-filled composites, it must be further improved to obtain better quantitative agreement with experimental data. The experimental data obtained can also be useful to the development of microwave dielectrics with complex frequency dispersion behavior, which are necessary for many microwave applications.
Surface-plasmon photonic band gaps in dielectric gratings on a flat metal surface
Authors: Yoon Jaewoong , Lee Gwansu , Song Seok Ho , Oh Cha-Hwan , Kim Pill-Soo
Published: June 2003

Photonic band gaps created by Bragg scattering of the surface plasmon polaritons are observed from dielectric grating structures on a flat metal surface. Observation results that directly image the band gaps are confirmed by the well-known numerical calculation method of diffraction, the rigorous coupled-wave analysis method. A numerical model based on the plane wave expansion method is also developed for estimation of the surface-plasmon band-gap characteristics in our dielectric-on-metal system. Consistency among the results of the band structures obtained from the experiment and the two numerical methods is achieved.
Effect of accelerating electrode rotation on ion beam optics
Authors: Surrey Elizabeth
Published: June 2003

The effect of a rotation of the electrode used to accelerate a positive ion beam is treated analytically for the Joint European Torus (JET) Positive Ion Neutral Injector (PINI) tetrode accelerator. The rotation is taken to be about an axis in the plane of the electrode and perpendicular to the beam axis, so the effect is that of a tilt in the alignment of the affected electrode. The effect of such a tilt in either of the two multiaperture accelerating electrodes is to introduce an additional steering of the beam, the magnitude of which depends upon the ratio of the potentials across the first and second accelerating gaps and the position of the beamlet with respect to the tilt axis. The direction of the steering is dependent upon which electrode is displaced. Steering angles of the order 10 mrad can be generated by this effect, which is significant compared to the alignment precision required from high power neutral injectors such as those on JET. The presence of a grid rotation also affects the total perveance of a multiaperture system and this can be used to obtain information on the position of the tilt axis. Typical values are calculated for the JET PINI geometry and compared to observation.
Characterization of a high-density electron-cyclotron resonance plasma source operating in nitrogen
Authors: Toader E. I. , Fredriksen A. , Aanesland A.
Published: June 2003

Parametric characterization of a low-pressure and high-density electron-cyclotron resonance plasma source operating in nitrogen over a range of low-pressure 10−3–10−4 mbar, dissipated power 500 W, and magnetic field intensity 200–400 G, is presented. Internal parameters like electron energy distribution function, plasma density, electron temperature, plasma potential, and floating potential, were measured using a compensated Langmuir probe. The radial variation of internal parameters evidences two discharge modes, that is, a constricted mode for low-magnetic field values and a diffuse mode for high-magnetic field values. The electron energy distribution function is Maxwellian within the energy range of 0–15 eV and presents a structure with two prominent dips around 3.5 and 9.0 eV. The form of the structure and the position of the dips do not change significantly with the radial position or by changing the external parameters.
Design and analysis of two-dimensional zero-reference marks for alignment systems
Authors: Chen Yuhang , Huang Wenhao , Dang Xueming
Published: June 2003

The demand for ultrahigh resolution in positioning and alignment is increasing in the field of precision engineering. By superimposing a pair of specially coded two-dimensional (2D) gratings, the correct alignment position of the two gratings can be detected with high resolution and accuracy. Due to the small dimensions of the grating, the diffraction effect is strong and it cannot be ignored. In this article, design considerations for such 2D zero-reference gratings are presented and the behavior of the diffraction of the zero-reference gratings is analyzed theoretically. The transmission function obtained by diffraction analysis agrees with the result from the autocorrelation method by neglecting the diffraction effect. The alignment is independent of the small variation in the gap between two gratings.
Electric-field-induced anisotropy of excitonic optical properties in semiconductor quantum dots
Authors: Gotoh H. , Kamada H. , Saitoh T. , Ando H. , Temmyo J.
Published: June 2003

We report the anisotropic excitonic optical properties (polarization dependent photoemission and photoabsorption) induced by applying a lateral electric field in a single semiconductor quantum dot. The excitonic optical polarization characteristics are examined using theoretical calculation and optical measurement. The optical properties are numerically analyzed taking into account the quantum dot potential, electric field, and electron–hole Coulomb interaction. We evaluate the polarization properties from calculated exciton wave functions. The polarization properties depend strongly on the size of the quantum dots and the spatial symmetry of the hole part of the wave function. There is large electric-field-induced anisotropy in thin quantum dots to a larger lateral extent even where the polarization properties are completely isotropic without an electric field. We compare the theoretical results with experimental results for InGaAs quantum dots obtained using the microphotoluminescence technique. Qualitative agreement between the theoretical results and experimental ones is obtained.
Polarity determination of a-plane GaN on r-plane sapphire and its effects on lateral overgrowth and heteroepitaxy
Authors: Wu Feng , Craven Michael D. , Lim Sung-Hwan , Speck James S.
Published: June 2003

Achieving nitride-based device structures unaffected by polarization-induced electric fields can be realized with nonpolar GaN, although polarity plays a key role in the growth. (112¯0) a-plane GaN films were grown on (11¯02) r-plane sapphire substrates and subsequently laterally overgrown using metalorganic chemical vapor deposition. Convergent beam electron diffraction analysis was used to determine the a-GaN polarity to explicitly define the film/substrate relationship, and subsequently to identify various growth features and surfaces observed throughout our studies of a-plane GaN. In particular, the effects of polarity on (1) lateral overgrowth from mask stripe openings aligned along [1¯100]GaN and (2) pit formation in heteroepitaxial films grown under nonoptimized conditions were investigated. The fundamental differences between the polar surfaces are clearly observed; analysis of the lateral epitaxial overgrowth stripes revealed that (0001) surfaces grew faster than (0001̄) surfaces by approximately an order of magnitude, and these stable, slow-growing (0001̄) surfaces are a likely cause of pitting in a-GaN films. The growth features under investigation were imaged using scanning and transmission electron microscopy.
Transport coefficients in glassy colloidal fluids
Authors: Saltzman Erica J. , Schweizer Kenneth S.
Published: June 2003

Our microscopic theory of entropic barrier formation and activated hopping for hard-sphere colloidal suspensions [K. S. Schweizer and E. J. Saltzman, J. Chem. Phys. 119, 1181 (2003), preceding paper] is combined with general statistical mechanical relations and a binary-collision-type model for the low-viscosity regime [E. G. D. Cohen, R. Verberg, and I. M. deSchepper, Physica A 251, 251 (1998)] to construct a theory for transport properties applicable for all particle concentrations. Quantitative, no adjustable parameter comparisons with experimental measurements of the self-diffusion constant and shear viscosity over a wide range of volume fractions show that the theory is quite accurate. The ability of model functions which contain dynamic singularities to describe our theoretical results is also established. Critical power laws and free-volume models can fit the theoretical calculations quite well over three to six orders of magnitude variation in the high-concentration regime, but all deviate qualitatively at sufficiently low and high volume fractions.
Effects of high-temperature heat treatment on Nd3+-doped optical fibers for use in fluorescence intensity ratio based temperature sensing
Authors: Sidiroglou F. , Wade S. A. , Dragomir N. M. , Baxter G. W. , Collins S. F.
Published: June 2003

The effect of very high-temperature exposure on the measurement properties of a fluorescence intensity ratio based optical fiber temperature sensor, using Nd3+-doped fiber as the sensing material, has been investigated. The results obtained indicate that exposing the sensor material to 750 °C for 100 h improves the accuracy of the fluorescence intensity ratio versus temperature characteristics from approximately 2.5 to approximately 1.3 °C. Measurements of the refractive index profiles of Nd3+-doped fiber samples prior to and after exposure to 750 °C indicate that such exposure results in small but measurable changes in the refractive index profile.
Growth and physical properties of epitaxial CeN layers on MgO(001)
Authors: Lee T.-Y. , Gall D. , Shin C.-S. , Hellgren N. , Petrov I. , Greene J. E.
Published: June 2003

While NaCl-structure transition-metal nitrides have been widely studied over the past two decades, little is known about the corresponding NaCl-structure rare-earth nitrides. Polycrystalline CeN, for example, has been reported by different groups to be both a wide band-gap semiconductor and a metal. To address this controversy, we have grown epitaxial CeN layers on MgO(001) and measured their physical properties. The films were grown at 700 °C by ultrahigh vacuum reactive magnetron sputter deposition in mixed Ar/N2 discharges maintained at 4 mTorr (0.53 Pa). X-ray diffraction and transmission electron microscopy results establish the film/substrate epitaxial relationship as cube-on-cube, (001)CeN‖(001)MgO with [100]CeN‖[100]MgO, while Rutherford backscattering spectroscopy shows that the layers are stoichiometric with N/Ce=0.99±0.02. CeN is metallic with a positive temperature coefficient of resistivity and a temperature-independent carrier concentration, as determined by Hall effect measurements, of 2.8±0.2×1022 cm−3 with a room temperature mobility of 0.31 cm2 V−1 s−1. At temperatures between 2 and 50 K, the resistivity is limited by defect scattering and remains constant at 29 μΩ cm, while at higher temperatures it increases linearly, limited primarily by phonon scattering, to reach a room-temperature value of 68.5 μΩ cm. The hardness and elastic modulus of CeN(001) were determined from nanoindentation measurements to be 15.0±0.9 and 330±16 GPa.
Modeling random telegraph signals in the gate current of metal–oxide–semiconductor field effect transistors after oxide breakdown
Authors: Avellán A. , Schroeder D. , Krautschneider W.
Published: June 2003

Measurements of random telegraph signals (RTS) in the gate current of n-channel metal–oxide–semiconductor field effect transistors (MOSFETs) after oxide breakdown are presented. Two types of behavior of the time constants and the relative amplitudes of the signals as a function of gate voltage are observed. A theory relating time constants and relative amplitudes of the fluctuations to the energetic and geometric trap location in the oxide is developed. This theory is also applicable to the commonly observed RTS in the drain current of undamaged MOSFETs.
Simulation of tuning of one-dimensional photonic crystals in the presence of free electrons and holes
Authors: Sánchez Adán S. , Halevi P.
Published: June 2003

We simulate the tuning of the optical reflectance in one-dimensional photonic crystals. Two monolithic superlattices are considered: Intrinsic InSb/air and extrinsic n-type Si/air, both with high densities of free-electron plasmas. The tuning is achieved, respectively, by varying the temperature and the donor concentration. In our modeling, we have taken into account both dispersion and absorption for the electrons, the holes, and the phonons. Our realistic simulation demonstrates that very strong sensitivity of the optical response is achievable.
Characterization of low-frequency noise in molecular beam epitaxy-grown GaN epilayers deposited on double buffer layers
Authors: Fong W. K. , Ng S. W. , Leung B. H. , Surya Charles
Published: June 2003

We report the growth of high-mobility Si-doped GaN epilayers utilizing unique double buffer layer (DBL) structures, which consist of a thin buffer layer and a thick GaN intermediate-temperature buffer layer (ITBL). In this study, three types of DBL were investigated: (i) thin GaN low-temperature buffer layer /GaN ITBL (type I); (ii) nitridated Ga metal film/GaN ITBL (type II); and (iii) thin AlN high-temperature buffer layer /GaN ITBL (type III). Systematic measurements were conducted on the electron mobilities and the low-frequency noise over a wide range of temperatures. It is found that the electron mobilities of the GaN films are substantially improved with the use of DBLs, with the sample using type III DBL which exhibits the highest low-temperature mobility. Furthermore, the same sample also demonstrates the elimination of deep levels at 91 and 255 meV below the conduction band. This is believed to result from the relaxation of tensile stress during growth with the use of type III DBLs.
The monolayer structure of CO2 adsorbed on the NaCl(100) single crystal surface: A tensor low-energy electron diffraction analysis
Authors: Vogt J. , Weiss H.
Published: June 2003

For the first time a detailed experimental analysis of all structural parameters of the p(2×1) monolayer phase of CO2 physisorbed at 75 K on a NaCl(100) single crystal substrate has been performed. The system was investigated by means of low-energy electron diffraction (LEED) at primary beam currents in the nA range. Intensities of six beams, including two of fractional order, were recorded at normal incidence in the energy range between 70 and 250 eV. These served as experimental data set for a TLEED-based I(V) analysis, in which the observed glide-plane symmetry as well as the linearity of the physisorbed molecules were fully considered. The substrate was represented by (a) an ideally bulk-terminated surface and (b) the relaxed surface which was reported before for the clean NaCl(100) surface. For both substrate models satisfactory agreement between experimental and theoretical I(V) curves was attained with Pendry R factors RP of 0.23 and 0.22, respectively, and similar molecular best-fit structures. Thereafter, the LEED experiment supports the herringbone adsorbate lattice proposed by theoretical studies as well as earlier experiments, with adsorption sites close to the sodium cations. However, the vertical distance of the molecules to the surface is significantly smaller than predicted by potential calculations, the lower oxygens in the tilted molecules being (a) 2.44±0.05 Å and (b) 2.46±0.04 Å above the geometrical means of the topmost layer in the different surface models, respectively. The corresponding molecular tilt angles are 62±2° and 61±2° with respect to the surface normal, in good agreement with the value resulting from the polarization dependence of infrared spectra of the ν3 monolayer vibration.
Influence of electric artwork on thermomechanical properties and warpage of printed circuit boards
Authors: Grenestedt Joachim L. , Hutapea Parsaoran
Published: June 2003

The electric copper lines in printed circuit boards (PCBs) introduce anisotropy in the various layers in multilayered PCBs. This anisotropy in combination with a general lack of symmetry with respect to the PCB midplane is a cause for thermally induced warpage. An analytical model which can predict the thermomechanical properties and warpage of PCBs with various electric artworks was developed. The model is based on Kirchhoff plate theory. An effective medium assumption was employed for the layers consisting of copper lines and composite side by side. The properties of the effective medium were obtained by a combination of Voigt (constant strain) and Reuss (constant stress) predictions, in conjunction with three-dimensional finite element unit cell calculations to determine a few constants. The prediction of the model conform well to some recent experiments. The model was finally used to “tune” the electric artwork of a PCB to minimize thermally induce warpage by changing trace widths and spacings in a six layered board. The calculations predict that isothermal warpage could be reduced by more than 90% for this board.
Nondestructive characterization of nanopore microstructure: Spatially resolved Brunauer–Emmett–Teller isotherms using nuclear magnetic resonance imaging
Authors: Beyea Steven D. , Caprihan Arvind , Glass S. Jill , DiGiovanni Anthony
Published: June 2003

This article presents the results of nuclear magnetic resonance imaging (MRI) studies of gas adsorption/desorption in nanoporous solids. MR images obtained as a function of the equilibrium pressure, at constant temperature, form a pixel-by-pixel map of adsorption isotherms. Analysis of these isotherms using Brunauer–Emmett–Teller (BET) theory results in spatial maps of the specific surface area, the net energy of adsorption, and the pore morphology. Results obtained using MRI for γ-Al2O3 and ZnO powders and partially sintered ceramics of these materials, as well as Vycor® porous glass, compare well to results for bulk samples obtained using conventional N2 BET adsorption. MRI studies of gas adsorption are shown to provide statistical averages of the pore microstructure parameters, resolved on a macroscopic scale.
Photoacoustics of the stressed state in solids
Authors: Muratikov K. L. , Glazov A. L. , Rose D. N. , Dumar J. E.
Published: June 2003

The modern experimental and theoretical states of the problem of residual stress detection by the photoacoustic method are analyzed. Some experimental results obtained by the photoacoustic method for Vickers indentation zones in silicon nitride and Al2O3–SiC–TiC ceramics are presented. The effect of annealing on the photoacoustic piezoelectric signal for the Al2O3–SiC–TiC ceramic and the influence of the given external loading on the behavior of the photoacoustic signal near the radial crack tips are investigated. It is experimentally shown that both compressive and shear stresses contribute to the photoacoustic signal near the radial crack tips. The theoretical approach based on the nonlinear thermoelastic model of the photoacoustic effect is further developed for explanation of the photoacoustic signal behavior near the radial crack tips. It is demonstrated that this model of the photoacoustic effect agrees qualitatively with the available experimental data.
A computerized Langmuir probe system
Authors: Pilling L. S. , Bydder E. L. , Carnegie D. A.
Published: June 2003

For low pressure plasmas it is important to record entire single or double Langmuir probe characteristics accurately. For plasmas with a depleted high energy tail, the accuracy of the recorded ion current plays a critical role in determining the electron temperature. Even for high density Maxwellian distributions, it is necessary to accurately model the ion current to obtain the correct electron density. Since the electron and ion current saturation values are, at best, orders of magnitude apart, a single current sensing resistor cannot provide the required resolution to accurately record these values. We present an automated, personal computer based data acquisition system for the determination of fundamental plasma properties in low pressure plasmas. The system is designed for single and double Langmuir probes, whose characteristics can be recorded over a bias voltage range of ±70 V with 12 bit resolution. The current flowing through the probes can be recorded within the range of 5 nA–100 mA. The use of a transimpedance amplifier for current sensing eliminates the requirement for traditional current sensing resistors and hence the need to correct the raw data. The large current recording range is realized through the use of a real time gain switching system in the negative feedback loop of the transimpedance amplifier.