bluuebunny/crossref_metadata_2025 huggingface dataset:
A cost model for plumbing and drainage systems
Authors: Wong L.T.
Published: September 2002

The construction cost, yearly maintenance cost and yearly remedial cost of plumbing and drainage systems in buildings were investigated. Occupancy, age, piping material, pipe length and the size of the systems were surveyed in 63 buildings. Correlations for costs of the systems in commercial and residential buildings were made with the surveyed results. Length, material and size of the pipes provide good parameters to determine the system construction costs. Higher maintenance cost and remedial cost for aged systems were reported. Remedial cost for corrosion problems increased significantly for the aged systems.
From traditional inter‐library loan to a new interlending model – the role of the CURL monograph interlending pilot
Authors: Prowse Stephen , Massie Dennis
Published: September 2002

The traditional inter‐library loan of monographs is often seen as the future niche of interlending activity, with journal article supply being catered for by other means, such as full text access through e‐journals. Examines how a monograph interlending pilot project, undertaken by CURL institutions, is part of a move towards a more distributed interlending model for the UK. Describes the project, presents statistical figures, and outlines results from feedback questionnaires. Shows the relationship to SHARES, RLG’s interlending program, and how the pilot has affected international interlending. Calls for other models to support the new interlending paradigm.
Business guests’ accommodation selection: the view from both sides
Authors: Lockyer Tim
Published: September 2002

A comparative study was undertaken analysing what accommodation managers and business guests believed were the factors influencing accommodation selection. It was discovered that business guests rated “bathroom and shower quality”, “standard of bedroom maintenance” and “comfort of mattress and pillow” highly, while accommodation management rated “courteous, polite, well‐mannered staff”, “enthusiasm, and commitment of staff” and “efficiency of front desk” highly. In contrast, both the business guests and accommodation managers indicated that the cleanliness of the hotel was the most significant factor influencing accommodation selection. The research also identified that there was a statistically significant difference in many items in the survey between what management and guests believed were important, which indicates a lack of understanding by management. The ramifications for management who do not provide those items important to guests are lower occupancy rates and guest dissatisfaction. Further, spending time and money on items that are not so important to guests may not be a wise use of resources. Regarding the question of whether managers understand their guests, this research indicates that they do not.
The interface between experiential learning and the Internet
Authors: Fry Gerald W.
Published: September 2002

This paper addresses the persisting problem of stagnant productivity in the education sector and its contribution to escalating costs. An approach to improving learning productivity is proposed which emphasizes the integration of ICT, service learning, experiential learning, and cooperative learning. Thus, the fundamental theme of this paper is to link these four learning domains as a basic strategy to improve the quality and productivity of education and at the same time to reduce costs or limit cost increases. The advances in ICT and the concomitant “death of distance” greatly strengthen the potential for teachers to become facilitators to organize creative autonomous learning in diverse settings. Concrete examples are described from diverse cultural settings such as South Africa, Cambodia, Costa Rica, Chile, Japan, Laos, Vietnam, Thailand and Oregon. The paper concludes by offering a number of specific recommendations to improve learning productivity.
Advancing social justice as a part of educational leadership development
Authors: Cryss Brunner C. , Hitchon W. Nick G. , Brown Rachel
Published: September 2002

We discuss beneficial uses of imaging technologies in higher education that advance social justice. Misuse and ineffectiveness of shared decision making, specifically as related to power relationships and the redistribution of decision‐making authority, are addressed through the development of technologically delivered experiential simulations (ES). We outline ways in which ES can change higher education preparation programs to meet and adapt to the challenges of the future. ES entails using computer technology to modify a person’s appearance and thereby evoking an atypical response from an audience. The key to our proposal, however, is having the person with the modified persona learn lessons pertinent to democratic cultures and social justice from their experience of immersion in that response.
Note on reliabilities of series‐parallel and parallel‐series system
Authors: Nakagawa Toshio , Cun Hua Qian
Published: September 2002

This paper considers a series‐parallel and a parallel‐series system, and investigates theoretically their fundamental characteristics: it is shown that the reliability of the series‐parallel system with the same number of series and parallel tends to one as its number goes to infinity. It would be of great interest that the golden ratio plays a role in analyzing two systems. Further, an optimal number of units for a series‐parallel system with complexity is derived.
Enabling the emergent entrepreneurial organisation to develop new products
Authors: Bamber David , Owens Jon , Davies John , Suleman Amir
Published: September 2002

The research literature concerning the new product development process (NPD) is reviewed and this is placed within the concepts required for effective intrapreneurial learning (IL). A model of IL for emergent entrepreneurial organisations (EO) is presented and the necessity to assess progression towards learning objectives at the individual, job and organisation level is shown. Three aspects of organisational groundwork are identified and discussed. These include developing the NPD process, implementing the NPD strategy and allocating resources for development and IL. Sets of IL objectives are identified and discussed. These are organisational analysis, barrier demolition, team working, flexible problem solving, use of advanced support tools, facilitating communication, maintaining communication, decision making, assessment of the entrepreneurial environment (EE), and NPD risk analysis. These analyses will identify the groundwork that should be undertaken by the emergent EO and the initial learning objectives for the intrapreneurs. It is proposed that EOs will be promoted when the objectives set by both an organisational needs analysis and an individual needs analyses are accomplished and the EE is formed.
Using LTCC for microsystems
Authors: Thelemann Torsten , Thust Heiko , Hintz Michael
Published: September 2002

A characteristic feature of LTCC is good workability. In some cases a LTCC‐based microsystem can be a good alternative to microsystems made in silicon or other technologies. Reasons for choosing LTCC‐Technology may be financial considerations or specific material properties. A main problem is to simplify a mechanical component in such a way, that it is possible to integrate this component in a planar structure with a small height in consideration of the restrictions of the LTCC‐Technology. In contrast to LTCC‐based substrates with only electrical circuits the integration of mechanical components make other demands on the different technological steps of the LTCC‐Process. In this paper some 3D‐structures made in LTCC‐like fluidic channels, membranes usable for micropumps or pressure sensors – and some aspects of required special technological demands are described.
On the zero offset stability of thick film strain gauges
Authors: Zheng Yulan , Atkinson John , Sion Russ
Published: September 2002

This paper presents results of work aimed at characterising the zero offset stability in novel thick film strain gauges. The devices studied arez‐axis (k33) load sensors fabricated on insulated stainless steel substrates and include examples of novel commercially developed force sensors. Devices loaded with compressive strains using a purpose designed test jig were found to exhibit a significant zero offset shift, which is negative up to a certain level (typically 1,000 micro strains) and then increasingly positive when strained beyond this point. Repeated cycles of loading then produced a certain level of stability until the previous maximum value of applied strain was exceeded. Temperature coefficient of resistance (TCR) measurements showed the devices to exhibit characteristics that depend significantly on the device geometry. The TCR was found to increase positively with increasing device thickness and surface area. The effect of overglazing the devices was found to decrease the TCR.
Dosimetry for ocular proton beam therapy at the Harvard Cyclotron Laboratory based on the ICRU Report 59
Authors: Newhauser W. D. , Burns J. , Smith A. R.
Published: September 2002

The Massachusetts General Hospital, the Harvard Cyclotron Laboratory (HCL), and the Massachusetts Eye and Ear Infirmary have treated almost 3000 patients with ocular disease using high‐energy external‐beam proton radiation therapy since 1975. The absorbed dose standard for ocular proton therapy beams at HCL was based on a fluence measurement with a Faraday cup (FC). A majority of proton therapy centers worldwide, however, use an absorbed dose standard that is based on an ionization chamber (IC) technique. The ion chamber calibration is deduced from a measurement in a reference photon field together with a calculated correction factor that takes into account differences in a chamber's response in and proton fields. In this work, we implemented an ionization chamber‐based absolute dosimetry system for the HCL ocular beamline based on the recommendations given in Report 59 by the International Commission on Radiation Units and Measurements. Comparative measurements revealed that the FC system yields an absorbed dose to water value that is 1.1% higher than was obtained with the IC system. That difference is small compared with the experimental uncertainties and is clinically insignificant. In June of 1998, we adopted the IC‐based method as our standard practice for the ocular beam.
Experimental and theoretical determination of dosimetric characteristics of IsoAid ADVANTAGE™ brachytherapy source
Authors: Meigooni Ali S. , Hayes Joshua L. , Zhang Hualin , Sowards Keith
Published: September 2002

brachytherapy sources are being used for interstitial implants in tumor sites such as the prostate. Recently, the ADVANTAGE™ Model IAI‐125, source became commercially available for interstitial brachytherapy treatment. Dosimetric characteristics (dose rate constant, radial dose function, and anisotropy function) of this source were experimentally and theoretically determined, following the AAPM Task Group 43 recommendations. Derivation of the dose rate constant was based on recent NIST WAFAC calibration performed in accordance with their 1999 standard. Measurements were performed in Solid Water™ phantom using LiF thermoluminescent dosimeters. The theoretical calculations were performed in both Solid Water™ and water using the PTRAN Monte Carlo code. The results indicated that a dose rate constant of the new source in water was The radial dose function of the new source was measured in Solid Water™ and calculated both in water and Solid Water™ at distances up to 10.0 cm. The anisotropy function, of the new source was measured and calculated in Solid Water™ at distances of 2 cm, 3 cm, 5 cm, and 7 cm and also was calculated in water at distances ranging from 1 cm to 7 cm from the source. From the anisotropy function, the anisotropy factors and anisotropy constant were derived. The anisotropy constant of the ADVANTAGE™ source in water was found to be The dosimetric characteristics of this new source compared favorably with those from the Amersham Health Model 6711 source. Complete dosimetric parameters of the new source are presented in this paper.
A three‐source model for the calculation of head scatter factors
Authors: Yang Yong , Xing Lei , Boyer Arthur L. , Song Yixin , Hu Yimin
Published: September 2002

Accurate determination of the head scatter factor is an important issue, especially for intensity modulated radiation therapy, where the segmented fields are often very irregular and much less than the collimator jaw settings. In this work, we report an calculation algorithm for symmetric, asymmetric, and irregular open fields shaped by the tertiary collimator (a multileaf collimator or blocks) at different source‐to‐chamber distance. The algorithm was based on a three‐source model, in which the photon radiation to the point of calculation was treated as if it originated from three effective sources: one source for the primary photons from the target and two extra‐focal photon sources for the scattered photons from the primary collimator and the flattening filter, respectively. The field mapping method proposed by Kim et al. [Phys. Med. Biol. 43, 1593–1604 (1998)] was extended to two extra‐focal source planes and the scatter contributions were integrated over the projected areas (determined by the detector's eye view) in the three source planes considering the source intensity distributions. The algorithm was implemented using Microsoft Visual C/C++ in the MS Windows environment. The only input data required were head scatter factors for symmetric square fields, which are normally acquired during machine commissioning. A large number of different fields were used to evaluate the algorithm and the results were compared with measurements. We found that most of the calculated agreed with the measured values to within 0.4%. The algorithm can also be easily applied to deal with irregular fields shaped by a multileaf collimator that replaces the upper or lower collimator jaws.
Precision dosimetry for narrow photon beams used in radiosurgery—Determination of Gamma Knife® output factors
Authors: Mack Andreas , Scheib Stefan G. , Major Jörg , Gianolini Stefano , Pazmandi Gyorgy , Feist Harald , Czempiel Heinz , Kreiner Hans‐Jürg
Published: September 2002

Treatment units for radiosurgery, like Leksell Gamma Knife® and adapted, or dedicated, linear accelerators use small circular beams of ionizing radiation down to 4 mm in diameter at the isocenter. By cross‐firing, these beams generate a high dose region at the isocenter together with steep dose gradients of up to 30% per mm. These units are used to treat small complex shaped lesions, often located close to critical structures within the brain, by superimposing several single high dose regions. In order to commission such treatment units for stereotactic irradiations, to carry out quality assurance and to simulate treatment conditions, as well as to collect input data for treatment planning, a precise dosimetric system is necessary. Commercially available radiation dosimeters only partially meet the requirements for narrow photon beams and small field sizes as used in stereotactic treatment modalities. The aim of this study was the experimental determination of the output factors for the field defining collimators used in Gamma Knife® radiosurgery, in particular for the smallest, the 4 mm collimator helmet. For output factor measurements a pin point air ionization chamber, a liquid ionization chamber, a diode detector, a diamond detector, TLD microcubes and microrods, alanine pellets, and radiochromic films were used. In total, more than 1000 measurements were performed with these different detection systems, at the sites in Munich and Zurich. Our results show a resultant output factor for the 4 mm collimator helmet of 0.8741 ± 0.0202, which is in good agreement with recently published results and demonstrates the feasibility of such measurements. The measured output factors for the 8 mm and 14 mm collimator helmets are 0.9578 ± 0.0057 and 0.9870 ± 0.0086, respectively.
Fast and accurate leaf verification for dynamic multileaf collimation using an electronic portal imaging device
Authors: Vieira Sandra C. , Dirkx Maarten L. P. , Pasma Kasper L. , Heijmen Ben J. M.
Published: September 2002

A prerequisite for accurate dose delivery of IMRT profiles produced with dynamic multileaf collimation (DMLC) is highly accurate leaf positioning. In our institution, leaf verification for DMLC was initially done with film and ionization chamber. To overcome the limitations of these methods, a fast, accurate and two‐dimensional method for daily leaf verification, using our CCD‐camera based electronic portal imaging device (EPID), has been developed. This method is based on a flat field produced with a 0.5 cm wide sliding gap for each leaf pair. Deviations in gap widths are detected as deviations in gray scale value profiles derived from the EPID images, and not by directly assessing leaf positions in the images. Dedicated software was developed to reduce the noise level in the low signal images produced with the narrow gaps. The accuracy of this quality assurance procedure was tested by introducing known leaf position errors. It was shown that errors in leaf gap as small as 0.01–0.02 cm could be detected, which is certainly adequate to guarantee accurate dose delivery of DMLC treatments, even for strongly modulated beam profiles. Using this method, it was demonstrated that both short and long term reproducibility in leaf positioning were within 0.01 cm (1σ) for all gantry angles, and that the effect of gravity was negligible.
Kilovision: Thermal modeling of a kilovoltage x‐ray source integrated into a medical linear accelerator
Authors: Cho Youngbin , Munro P.
Published: September 2002

The thermal and thermo‐mechanical (fatigue) properties of a stationary‐anode kilovoltage x‐ray source that can be integrated into the head of a medical linear accelerator have been modeled. A finite element program has been used to model two new target designs. The first design makes minor modifications to the existing target assembly of a Varian medical linear accelerator, while the second design adds an additional cooling tube, changes the target angle, and uses a tungsten–rhenium alloy rather than tungsten as the kilovoltage target material. The thermal calculations have been used to generate cyclic stress/strain values from which estimates of fatigue in the target designs have been made. Both kilovoltage and megavoltage operation have been studied. Analysis of the megavoltage operation shows that there are only small differences in the thermal and fatigue characteristics after the target assembly is modified to include a kilovoltage target. Thus, megavoltage operation should not be compromised. The first kilovoltage target design can handle a 900 W heat load (e.g., 120 kVp, 7.5 mA, source size); the heat load being limited by the temperature at the surface of the cooling tubes and mechanical fatigue at the surface of the target. The second design can handle a 1250 W heat load (e.g., 120 kVp, ∼10.4 mA, source size). Our calculations show that installation of a kilovoltage x‐ray target is practical from thermal and thermo‐mechanical perspectives.
Proton magnetic resonance spectroscopy in the brain: Report of AAPM MR Task Group #9
Authors: Drost Dick J. , Riddle William R. , Clarke Geoffrey D.
Published: September 2002

AAPM Magnetic Resonance Task Group #9 on proton magnetic resonance spectroscopy (MRS) in the brain was formed to provide a reference document for acquiring and processing proton MRS acquired from brain tissue. MRS is becoming a common adjunct to magnetic resonance imaging (MRI), especially for the differential diagnosis of tumors in the brain. Even though MR imaging is an offshoot of MR spectroscopy, clinical medical physicists familiar with MRI may not be familiar with many of the common practical issues regarding MRS. Numerous research laboratories perform in vivo MRS on other magnetic nuclei, such as and However, most commercial MR scanners are generally only capable of spectroscopy using the signals from protons. Therefore this paper is of limited scope, giving an overview of technical issues that are important to clinical proton MRS, discussing some common clinical MRS problems, and suggesting how they might be resolved. Some fundamental issues covered in this paper are common to many forms of magnetic resonance spectroscopy and are written as an introduction for the reader to these methods. These topics include shimming, eddy currents, spatial localization, solvent saturation, and post‐processing methods. The document also provides an extensive review of the literature to guide the practicing medical physicist to resources that may be useful for dealing with issues not covered in the current article.
A simple medical physics experiment based on a laser pointer
Authors: Delaney Colin , Rodriguez Juan
Published: September 2002

Recent advances in medical physics have led to a proliferation of medical diagnostic instrumentation, particularly in the area of medical imaging. The pervasiveness of this new technology in turn has promoted a growing interest among physics faculty and students in courses covering this material (Ref. 1). However, few physics departments have responded to this interest with the creation of undergraduate courses in medical physics due to staffing limitations or a lack of experience in this area of physics or both. Nevertheless it may be possible for those institutions unable to offer a full course in medical physics to provide at least a substantial hands-on experience in the form of an advanced laboratory experiment on a representative topic, if it can be implemented with relative ease. In this paper we describe such an experiment in medical imaging using readily available hardware that illustrates the concepts behind one of the most successful medical imaging modalities developed to date, namely computed tomography (CT) (Ref. 2).
A dynamical picture of the oceanic tides
Authors: Butikov Eugene I.
Published: September 2002

A detailed treatment of tide-generating forces is given, followed by a simplified dynamic theory of tidal waves. To clarify the underlying physics, we use a simple model of the ocean that consists of a water shell of uniform depth completely covering the globe. The treatment is appropriate for college and university undergraduate students studying introductory geophysics or astronomy, general physics, or intermediate mechanics. A computer simulation is developed to aid in understanding the properties of sun- or moon-induced tide-generating forces and of the stationary tidal waves created by these forces in the open ocean.
Synchronization of metronomes
Authors: Pantaleone James
Published: September 2002

Synchronization is a common phenomenon in physical and biological systems. We examine the synchronization of two (and more) metronomes placed on a freely moving base. The small motion of the base couples the pendulums causing synchronization. The synchronization is generally in-phase, with antiphase synchronization occurring only under special conditions. The metronome system provides a mechanical realization of the popular Kuramoto model for synchronization of biological oscillators, and is excellent for classroom demonstrations and an undergraduate physics lab.
Coordinated Reactivation of Distributed Memory Traces in Primate Neocortex
Authors: Hoffman K. L. , McNaughton B. L.
Published: September 2002

Conversion of new memories into a lasting form may involve the gradual refinement and linking together of neural representations stored widely throughout neocortex. This consolidation process may require coordinated reactivation of distributed components of memory traces while the cortex is “offline,” i.e., not engaged in processing external stimuli. Simultaneous neural ensemble recordings from four sites in the macaque neocortex revealed such coordinated reactivation. In motor, somatosensory, and parietal cortex (but not prefrontal cortex), the behaviorally induced correlation structure and temporal patterning of neural ensembles within and between regions were preserved, confirming a major tenet of the trace-reactivation theory of memory consolidation.
Quantum Solvation of Carbonyl Sulfide with Helium Atoms
Authors: Tang Jian , Xu Yunjie , McKellar A. R. W. , Jäger Wolfgang
Published: September 2002

High-resolution infrared and microwave spectra of He

N

–carbonyl sulfide (He

N

-OCS) clusters with
N
ranging from 2 to 8 have been detected and unambiguously assigned. The spectra show the formation of a solvation layer beginning with an equatorial “donut” of five helium atoms around the OCS molecule. The cluster moment of inertia increases as a function of
N
and overshoots the liquid droplet limit for
N
> 5, implying that even atoms in the first solvation shell are decoupled from the OCS rotation in helium nanodroplets. To the extent that this is due to superfluidity, the results directly explore the microscopic evolution of a phenomenon that is formally macroscopic in nature.
Climate-Driven Bedrock Incision in an Active Mountain Belt
Authors: Hartshorn Karen , Hovius Niels , Dade W. Brian , Slingerland Rudy L.
Published: September 2002

Measurements of fluvial bedrock incision were made with submillimeter precision in the East Central Range of Taiwan, where long-term exhumation rates and precipitation-driven river discharge are independently known. They indicate that valley lowering is driven by relatively frequent flows of moderate intensity, abrasion by suspended sediment is an important fluvial wear process, and channel bed geometry and the presence of widely spaced planes of weakness in the rock mass influence erosion rate and style.
A Star to Sail Her By
Authors: Austin James
Published: September 2002

At the Helm
A Laboratory Navigator. Kathy Barker. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, New York, 2002. 362 pp. $45. ISBN 0-87969-583-8.

The author offers a how-to manual for newly appointed principal investigators and those who wish to run their own labs.
OPTICAL PROPERTIES OF CdTe/ZnTe ULTRATHIN QUANTUM WELLS GROWN BY ATOMIC LAYER EPITAXY
Authors: GARCÍA-ROCHA M. , HERNÁNDEZ-CALDERÓN I.
Published: September 2002

Ultrathin quantum wells (UTQWs) of CdTe within ZnTe barriers were successfully grown by atomic layer epitaxy (ALE) on GaAs(001) substrates. ALE growth of CdTe was performed by alternate exposure of the substrate surface to individual fluxes of Cd and Te. Two different samples with 2-monolayer (ML) (substrate temperature Ts= 270° C ) and 4 ML (Ts = 290° C ) CdTe QWs were grown. Low temperature photoluminescence (PL) experiments exhibited intense and sharp peaks associated to the 2 ML QWs at 2.26 eV. In the case of the nominally 4-ML-thick QW the PL spectrum presented an intense peak around 2.13 eV and two weak features around 2.04 and 1.91 eV. The first peak is attributed to ~ 3 ML QW and the second one to ~ 4 ML QW. The dominance of the 3 ML peak is mainly attributed to Cd loss in the QW due to its substitution by Zn atoms. Due to a high diffusion length of the photogenerated carriers in the barriers, quite weak signals from the ZnTe barriers were observed in both cases. Room temperature (RT) photoreflectance (PR) spectra showed contributions from the CdTe UTQWs, the ZnTe barriers, and the GaAs substrate.
FABRICATION AND CHARACTERIZATION OF CuInSe2 THIN FILMS GROWN BY MEANS OF A TWO-STAGE PROCESS
Authors: GORDILLO G. , LANDAZÁBAL F.
Published: September 2002

CuInSe 2 thin films were deposited on soda lime glass substrates following a two-stage process which includes a chemical reaction between thin films of Cu and In x Se y, followed by thermal annealing in a Se environment. Initially, the Cu layer is deposited on the glass substrate by DC magnetron sputtering in the S-gun configuration, and subsequently the In x Se y layer is deposited by the closed spaced sublimation (CSS) method. The influence of the deposition method and of the main deposition parameters of the precursor layers (Cu and In x Se y) on the phases present in the resulting compound were studied by means of X-ray diffraction (XRD) and optical gap (Eg) measurements. The conditions for growing CuInSe 2 thin films in the chalcopyrite phase were determined through an exhaustive parameter study. The study revealed that the thickness of the precursor layers and the selenization conditions affect the phase in which the CuInSe 2 compound grows.
DETERMINATION OF THE OPTICAL CONSTANTS OF InxSey THIN FILMS DEPOSITED BY EVAPORATION AND COEVAPORATION
Authors: SANDINO J. , GORDILLO G.
Published: September 2002

In x Se y thin films, grown on soda lime glass substrates in the In 6 Se 7 phase by evaporation of the In 2 Se 3 compound and in the In 2 Se 3 phase by coevaporation of In and Se, were optically characterized through spectral transmittance measurements. A special procedure was developed to determine the thickness d and the optical constants (refractive index n, absorption coefficient α, and optical gap Eg). This includes experimental measurements of the spectral transmittance and the use of a model taking into account interference effects induced by internal reflections presented in the interfaces substrate/film and film/air and the fitting of the n vs. λ curve to the Cauchy equation (n = A + B/λ2). The optical constants of the In x Se y thin films were corrected comparing the experimental transmittance spectrum with the theoretical one.

The results revealed that the optical constants of the In x Se y films were significantly affected by the deposition method.
CORROSION STUDY OF A Zn–22Al–2Cu ALLOY WITH THE SURFACE MODIFIED BY AN Y2O3 THIN FILM
Authors: GUERRERO-PENALVA R. , FARIAS M. H. , COTA-ARAIZA L.
Published: September 2002

Samples of Zn–22Al–2Cu (zinalco) alloys with and without a thin film of Y 2 O 3 were submitted to corrosion by potentiodynamic polarization and analyzed by means of Tafel extrapolation. In addition, in-depth profiles by Ar ion sputtering and Auger electron spectroscopy were obtained. Samples with Y 2 O 3-deposited film and subjected to potentiodynamic polarization present an improvement in corrosion resistance up to 75% in pH = 4.5 aerated water as compared to samples without the Y 2 O 3 deposit. The variations in electrochemical parameters are explained by the spectroscopic in-depth profile measurements.
STUDY OF Al0.065Ga0.935Sb AVALANCHE PHOTODETECTORS FOR 1.55 μm OF WAVELENGTH BY LIQUID PHASE EPITAXY AT LOW TEMPERATURE
Authors: MARTÍNEZ-JUÁREZ J. , OLVERA J. , DÍAZ T. , DE ANDA F. , ESCOBOSA A.
Published: September 2002

We report the results of a study of Al 0.065 Ga 0.935 Sb avalanche photodetectors grown on n-GaSb substrates. The devices have been fabricated from layers with the structure p-Al 0.13 Ga 0.87 Sb/n-Al 0.065 Ga 0.935 Sb:Te/n-GaSb (substrate) grown by liquid phase epitaxy (LPE) with a composition matched to detect light of 1.55 μm. The heterostructures were grown from Ga-rich solutions at 400°C. Just after their growth, the structures were subjected to baking processes inside the growth chamber. The baking time was varied and its influence on the breakdown voltages of the junctions was observed. Breakdown voltages up to 12 V, very low net donor concentration in the active layer (1E15 cm -3), and avalanche multiplication factors of around 50 have been obtained. The carrier concentration was determined by the C–V method. Photoluminescence and X-ray diffraction measurements were carried out to investigate the properties of the LPE-grown ternary layers, to determine the band gap and to estimate the quality of epitaxial layers. The photoresponses of the detectors are also presented.
DETERMINATION OF NANOMETER-SCALE SIZES IN n+-TYPE POROUS SILICON BY THE USE OF X-RAY AND RAMAN SPECTROSCOPIES
Authors: RAMÍREZ-PORRAS A.
Published: September 2002

Porous silicon layers were obtained by electrochemical etching on (111) plane surfaces of crystalline phosphorus-doped silicon in the presence of hydrofluoric acid. The photoluminescence of this kind of layers when illuminated with UV light is possibly explained by the quantum confinement model (QCM), which states the presence of nanometer-scale crystallites that enlarge the semiconductor band gap up to optical photon energies when the band-to-band recombination processes take place. In this study, the size determination of those proposed structures was performed by X-ray diffractiometry and by Raman spectroscopy. The obtained results suggest a consistency between the experimental work and the QCM.
Early Signals in Cardiac Development
Authors: Zaffran Stéphane , Frasch Manfred
Published: September 2002

The heart is the first organ to form during embryogenesis and its circulatory function is critical from early on for the viability of the mammalian embryo. Developmental abnormalities of the heart have also been widely recognized as the underlying cause of many congenital heart malformations. Hence, the developmental mechanisms that orchestrate the formation and morphogenesis of this organ have received much attention among classical and molecular embryologists. Due to the evolutionary conservation of many of these processes, major insights have been gained from the studies of a number of vertebrate and invertebrate models, including mouse, chick, amphibians, zebrafish, and
Drosophila
. In all of these systems, the heart precursors are generated within bilateral fields in the lateral mesoderm and then converge toward the midline to form a beating linear heart tube. The specification of heart precursors is a result of multiple tissue and cell-cell interactions that involve temporally and spatially integrated programs of inductive signaling events. In the present review, we focus on the molecular and developmental functions of signaling processes during early cardiogenesis that have been defined in both vertebrate and invertebrate models. We discuss the current knowledge on the mechanisms through which signals induce the expression of cardiogenic transcription factors and the relationships between signaling pathways and transcriptional regulators that cooperate to control cardiac induction and the formation of a linear heart tube.
O
2
Sensing in the Human Ductus Arteriosus
Authors: Michelakis Evangelos D. , Rebeyka Ivan , Wu XiChen , Nsair Ali , Thébaud Bernard , Hashimoto Kyoko , Dyck Jason R.B. , Haromy Al , Harry Gwyneth , Barr Amy , Archer Stephen L.
Published: September 2002

Functional closure of the human ductus arteriosus (DA) is initiated within minutes of birth by O
2
constriction. It occurs by an incompletely understood mechanism that is intrinsic to the DA smooth muscle cell (DASMC). We hypothesized that O
2
alters the function of an O
2
sensor (the mitochondrial electron transport chain, ETC) thereby increasing production of a diffusible redox-mediator (H
2
O
2
), thus triggering an effector mechanism (inhibition of DASMC voltage-gated K
+
channels, Kv). O
2
constriction was evaluated in 26 human DAs (12 female, aged 9±2 days) studied in their normal hypoxic state or after normoxic tissue culture. In fresh, hypoxic DAs, 4-aminopyridine (4-AP), a Kv inhibitor, and O
2
cause similar constriction and K
+
current inhibition (
I
K
). Tissue culture for 72 hours, particularly in normoxia, causes ionic remodeling, characterized by decreased O
2
and 4-AP constriction in DA rings and reduced O
2
- and 4-AP–sensitive
I
K
in DASMCs. Remodeled DAMSCs are depolarized and express less O
2
-sensitive channels (including Kv2.1, Kv1.5, Kv9.3, Kv4.3, and BK
Ca
). Kv2.1 adenoviral gene-transfer significantly reverses ionic remodeling, partially restoring both the electrophysiological and tone responses to 4-AP and O
2
. In fresh DASMCs, ETC inhibitors (rotenone and antimycin) mimic hypoxia, increasing
I
K
and reversing constriction to O
2
, but not phenylephrine. O
2
increases, whereas hypoxia and ETC inhibitors decrease H
2
O
2
production by altering mitochondrial membrane potential (ΔΨm). H
2
O
2
, like O
2
, inhibits
I
K
and depolarizes DASMCs. We conclude that O
2
controls human DA tone by modulating the function of the mitochondrial ETC thereby varying ΔΨm and the production of H
2
O
2
, which regulates DASMC Kv channel activity and DA tone.
Characterization and Enrichment of Cardiomyocytes Derived From Human Embryonic Stem Cells
Authors: Xu Chunhui , Police Shailaja , Rao Namitha , Carpenter Melissa K.
Published: September 2002

Cell replacement therapy is a promising approach for the treatment of cardiac diseases, but is challenged by a limited supply of appropriate cells. We have investigated whether functional cardiomyocytes can be efficiently generated from human embryonic stem (hES) cells. Cardiomyocyte differentiation was evaluated using 3 parent (H1, H7, and H9) hES cell lines and 2 clonal (H9.1 and H9.2) hES cell lines. All cell lines examined differentiated into cardiomyocytes, even after long-term culture (50 passages or ≈260 population doublings). Upon differentiation, beating cells were observed after one week in differentiation conditions, increased in numbers with time, and could retain contractility for over 70 days. The beating cells expressed markers characteristic of cardiomyocytes, such as cardiac α-myosin heavy chain, cardiac troponin I and T, atrial natriuretic factor, and cardiac transcription factors GATA-4, Nkx2.5, and MEF-2. In addition, cardiomyocyte differentiation could be enhanced by treatment of cells with 5-aza-2′-deoxycytidine but not DMSO or retinoic acid. Furthermore, the differentiated cultures could be dissociated and enriched by Percoll density centrifugation to give a population containing 70% cardiomyocytes. The enriched population was proliferative and showed appropriate expression of cardiomyocyte markers. The extended replicative capacity of hES cells and the ability to differentiate and enrich for functional human cardiomyocytes warrant further development of these cells for clinical application in heart diseases.
Seismic anisotropy in sedimentary rocks, part 2: Laboratory data
Authors: Wang Zhijing
Published: September 2002

Part one of this paper presents a method for measuring seismic velocities and transverse isotropy in rocks using a single core plug. This method saves at least two‐thirds of the time for preparing core samples and measuring velocities in transversely isotropic (TI) rocks. Using this method, we have measured velocity and anisotropy of many shale and reservoir rocks from oil and gas fields around the world. We present some of the data in this paper, which include seismic velocity and anisotropy in 17 brine‐saturated shale samples, 1 gas‐ and brine‐saturated coal sample, 8 brine‐saturated sands, 12 gas‐saturated sands, 32 gas‐saturated carbonate samples, and 25 brine‐saturated carbonate samples. The results show that clays and fine layering in sedimentary rocks are the main causes of seismic anisotropy. Very little intrinsic anisotropy exists in unfractured reservoir rocks such as sands, sandstones, and carbonates under reservoir conditions. In contrast, all shales were found seismically anisotropic: anisotropy ranges from 6% to 33% for P‐waves and from 2% to 55% for S‐waves. The magnitude of shale anisotropy seems to decrease exponentially with increasing porosity. At present, the magnitude of shale anisotropy cannot be predicted accurately from other data without laboratory measurements. This paper also presents some best practices for laboratory measurements of shale velocity and anisotropy.
New theoretical and practical aspects of electromagnetic soundings at low induction numbers
Authors: Gómez‐Treviño Enrique , Esparza Francisco J. , Méndez‐Delgado Sóstenes
Published: September 2002

This paper presents a theoretical yet practical study of electromagnetic (EM) soundings at low induction numbers for vertical and horizontal magnetic dipoles. The physical model is a heterogeneous half‐space with arbitrary vertical conductivity variations. The study comprises a novel approach for solving forward problems, analytical formulas for inversion, and a practical algorithm for recovering conductivity variations from field measurements. The basis of the theoretical approach is a series representation of the EM field in terms of ascending powers of frequency. At low induction numbers only two terms are required. When substituted into Maxwell's equations, one term in the series can be obtained in terms of the other. Furthermore, if the electrical conductivity varies only with depth, the imaginary part of the field can be obtained from its real part through a differential equation. The real part, which corresponds to zero frequency, plays the role of a distributed source for the frequency‐dependent imaginary part. In the case of vertical magnetic dipoles, the approach applies directly to the real and imaginary components of the magnetic field, while for horizontal dipoles one must use the Hertz potential, but the procedure is exactly the same.

In each case this leads to a statement of the forward problem as the solution of a real differential equation. The solutions are integral expressions valid for arbitrary conductivity profiles. Assuming that these expressions represent integral equations for conductivity, analytical inverse formulas are derived for both vertical and horizontal dipoles. These formulas ensure a unique recovery of the conductivity profile under ideal conditions.

An algorithm based on linear programming offers a variety of practical advantages for the inversion of field data. Numerical experiments and applications to field data illustrate the performance of the algorithm.
A multiscale radar‐stratigraphic analysis of fluvial aquifer heterogeneity
Authors: Lesmes David P. , Decker Scott M. , Roy David C.
Published: September 2002

The objective of this study is to use an integrated and multiscale exploration approach to quantify the geometrical parameters that are needed to predict block hydraulic conductivity tensors within fluvial deposits. We use 3‐D ground‐penetrating radar (GPR) data, electromagnetic (EM) surveys, resistivity soundings, and hand‐augered borings to characterize the 3‐D architecture of fluvial deposits on a floodplain of the Piscatiquis River, near South Sebec, Maine. Field‐scale surveys made across the entire floodplain were used to map the depth to the glacially eroded bedrock surface and the thickness of the overlying sediments, which consist of glaciomarine clay, fluvial sands and silts, and overbank deposits. An EM conductivity anomaly in the center of the floodplain defines the position of a ridge in the glaciomarine clay deposit. This ridge separates horizontally bedded sand and silt deposits in the northern half of the floodplain from inclined point‐bar sand and silt deposits in the southern half of the floodplain. The orientation and spacing of the lateral accretion surfaces (or bounding layers) within the point‐bar deposits in the southern part of the floodplain were measured in a 3‐D GPR survey conducted over a 50‐m2grid. The geometrical parameters defining the internal architecture of the point‐bar deposits are used to estimate anisotropy ratios for the principal components of the block hydraulic conductivity tensor. This integrated exploration approach establishes a framework for quantifying fluvial aquifer heterogeneity from local to regional scales. Geostatistical methods and geological models can be used to integrate the local‐scale and field‐scale surveys. With the addition of more local‐scale surveys, geophysical logs, and high‐resolution cores, this exploration approach can be used to develop a multiscale flow model for the entire floodplain.
Interface scattering versus body scattering in subbasalt imaging and application of prestack wave equation datuming
Authors: Martini Francesca , Bean Christopher J.
Published: September 2002

The presence of high‐velocity, highly heterogeneous layers such as basalt have a detrimental effect on imaging below those structures. Internal characteristics of the basalt itself can also degrade the subbasalt image quality. In many cases the boundary surfaces of a basalt sequence are not smooth but contain some roughness at a scale similar to the seismic wavelength. Interface scattering resulting from interface roughness can be a serious problem. In this paper, body and interface scattering problems are addressed through acoustic finite‐difference modeling. Interface scattering seems to have the most detrimental effect on imaging at depth. A wave equation prestack datuming procedure is applied to synthetic acoustic data to remove the effects of rough interfaces. This computational process transforms seismic data to a new datum plane in the subsurface, eliminating propagation effects between the surface and the new datum plane. The technique leads to a much improved image of below the basalt, with the great advantage that accurate knowledge of the velocity field for the overburden only is required as opposed to the entire velocity‐depth model (e.g., for prestack depth migration).
Volumetric wavefield recording and wave equation inversion for near‐surface material properties
Authors: Curtis Andrew , Robertsson Johan O. A.
Published: September 2002

“Volumetric recording” of the seismic wavefield implies that the local receiver group or array approximately encloses a volume of the earth. We show how volumetric recording can be used to measure several spatial derivatives of the wavefield. By making use of the full elastic wave equation, the free surface condition on elastic wavefields, and derivative centering techniques analagous to Lax‐Wendroff corrections used in synthetic finite‐difference modeling, these derivative estimates can be inverted for P‐ and S‐velocities in the near surface directly beneath the receiver group.

The quantities estimated are the effective velocities of the P‐ and S‐components experienced by the wavefield at any point in time. Hence, the velocity estimates may vary with both wave type and wavelength. The estimates may be useful to aid statics estimation and are exactly the effective velocities required for separation of the wavefield into P‐ and S‐, and up‐ and down‐going components.
Joint inversion of PP and PS reflection data for VTI media: A North Sea case study
Authors: Grechka Vladimir , Tsvankin Ilya , Bakulin Andrey , Hansen Jan Ove , Signer Claude
Published: September 2002

Despite the significant advantages of combining PP and PS reflection data in anisotropic parameter estimation, application of this approach has been hindered by the inherent complexity of PS‐wave moveout. To overcome this problem, V. Grechka and I. Tsvankin suggested a model‐independent procedure to construct the traveltimes of pure SS‐wave reflections from PP and PS data. Here, we apply their method and anisotropic multicomponent stacking‐velocity tomography to a 2‐D line acquired over the lower Tertiary Siri reservoir in the North Sea.

The computed traveltimes of SS reflections from several horizons are used to estimate the effective SS‐wave normal‐moveout (NMO) velocities, which are combined with the NMO velocities of PP‐waves in the tomographic velocity analysis. Comparison of the vertical and NMO velocities of the PP‐ and SS‐waves provides clear evidence of anisotropy in the section above the reservoir. The interval parameter estimation is performed under the assumption that the section is composed of transversely isotropic layers with a vertical symmetry axis (VTI media). Since the subsurface structure is close to horizontally layered, the reflection data cannot be uniquely inverted for the VTI parameters without additional information (e.g., the vertical velocities found from borehole data).

The parameter‐estimation algorithm produces a family of equivalent VTI models that fit the PP and PS (or SS) traveltimes equally well. Although the range of variations in ε and δ for the equivalent models is rather wide, it does not include isotropic media (ε = δ = 0), which implies that accurate matching of both PP and PS data is impossible without accounting for anisotropy. To overcome the nonuniqueness in the inversion of reflection data and build a VTI depth model, we use P‐wave check shots acquired in the only borehole drilled on the processed line. Throughout the section ε > δ, with the largest values of both anisotropic coefficients observed in the depth range 0.7–1.5 km where ε reaches almost 0.25. Time sections of the original PS data computed using the VTI model have a much higher quality than the conventional isotropic sections.