bluuebunny/crossref_metadata_2025_split huggingface dataset:
CdZnTe and CdTe materials for X‐ray and gamma ray radiation detector applications
Authors: Szeles Csaba 
Published: February 2004

AbstractGood detection efficiency and high energy‐resolution make Cadmium Zinc Telluride (CdZnTe) and Cadmium Telluride (CdTe) detectors attractive in many room temperature X‐ray and gamma‐ray detection applications such as medical and industrial imaging, industrial gauging and non‐destructive testing, security and monitoring, nuclear safeguards and non‐proliferation, and astrophysics. Advancement of the crystal growth and device fabrication technologies and the reduction of bulk, interface and surface defects in the devices are crucial for the widespread practical deployment of Cd1−xZnxTe‐based detector technology. Here we review the effects of bulk, interface and surface defects on charge transport, charge transport uniformity and device performance and the progress in the crystal growth and device fabrication technologies aiming at reducing the concentration of harmful defects and improving Cd1−xZnxTe detector performance. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Self‐assembled quantum dot formation induced by surface energy change of a strained two‐dimensional layer
Authors: Tinjod Frank , Mariette Henri 
Published: February 2004

AbstractTo account for the occurrence (or not) of the Stranski‐Krastanow (SK) transition (two‐dimensional to 3D change of surface morphology) during the epitaxial growth of various lattice‐mismatched semiconductor systems, we present a simple equilibrium model taking into account not only the lattice mismatch, but also the dislocation formation energy and the surface energy. It demonstrates the importance of these parameters especially for II–VI systems such as CdTe/ZnTe and CdSe/ZnSe. For II–VIs indeed, as misfit dislocations are easier to form than in III–Vs (such as InAs/GaAs) or IV systems (Ge/Si), the 3D elastic transition is short‐circuited by the plastic one. Nevertheless, by lowering surface energy, telluride and selenide quantum dots can also be grown as predicted by our model and as evidenced experimentally by reflection high‐energy electron diffraction (RHEED), atomic force microscopy and optical measurements. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth and characterization of ultra‐thin quantum wells of II–VI semiconductors for optoelectronic applications
Authors: Hernández‐Calderón Isaac , García‐Rocha Miguel , Díaz‐Arencibia Pedro 
Published: February 2004

AbstractAtomic layer epitaxy (ALE) was used to grow CdTe and CdSe quantum wells (QWs) with 1 to 4 monolayer thickness. With this ultra‐thin quantum wells (UTQWs) it is possible to cover the red‐blue spectral range. Low temperature photoluminescence spectroscopy reveals that most of these UTQWs present very intense and narrow emission and, depending on growth conditions, no thickness fluctuations are observed over the whole sample area. The heterostructures were grown at different temperatures between 260 and 290 °C. Both CdTe and CdSe UTQWs grown at the higher temperature presented blue‐shifted emission compared to those grown at lower temperatures. This effect is attributed to Cd losses by reevaporation and Cd substitution by Zn. This effect of the temperature can be employed for fine tuning of the UTQW emission. The critical thickness of CdSe/ZnSe grown by ALE is estimated to be 5 ML. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Selected area growth of II–VI nanostructures using shadow masks
Authors: Schallenberg T. , Schumacher C. , Brunner K. , Molenkamp L. W. 
Published: February 2004

AbstractWe investigate molecular beam epitaxy of II–VI materials through GaAs/AlGaAs epitaxial shadow masks on GaAs(001) substrate. Scanning electron and atomic force microscopy are employed to investigate the effects of surface diffusion, faceting, partial shadow (minimized in the experimental set‐up), and material deposition on the mask (closing of apertures) on the selected area growth of ZnSe and CdSe. The results illustrate that selected area growth of II–VI nanostructures is controlled by the growth geometry. In contrast to the case of III–V materials, we found no macroscopic features (>10 nm) which could be attributed to surface diffusion. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spin–lattice relaxation in diluted magnetic (Cd,Mn)Se quantum dots
Authors: Puls J. , Hundt A. , Thomas H. , Henneberger F. 
Published: February 2004

AbstractSpin–lattice relaxation (SLR) is studied in quantum well and quantum dot structures by photo‐carrier induced spin heating. For the SLR time constants no qualitative difference is found between quantum well and quantum dot structures. There is no hint for a specific zero‐dimensional behaviour. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical phonons and resonant Raman scattering in II–VI spheroidal quantum dots
Authors: Trallero‐Giner C. 
Published: February 2004

AbstractFirst order and multiphonon resonant Raman scattering processes from confined and interface polar optical phonons in II–VI nanocrystallites are analyzed. Fröhlich interaction between excitons and optical phonons has been considered and general selection rules for the exciton–phonon matrix elements of the scattering processes in the case of spheroidal quantum dots are given. A comparison is made between the Raman selection rules and non‐linear hyper‐Raman selection rules for spherical dots. It is shown that the relative intensities between phonon overtones in II–VI spherical quantum dots can be correctly described in the framework of excitonic model and the optical polar vibrational continuum model satisfying both the mechanical and electrostatic matching conditions at the interface. Detailed discussions of the surface optical phonons are provided in the case of a spherical Quantum‐Dot/Quantum‐Well (QD/QW) heterostructure. Their frequency dependence on the geometry, material parameters, as well as the electron–phonon interaction Hamiltonian are also reported. In addition, the interface optical phonons and the corresponding electron–phonon interaction in nanostructures with prolate and oblate spheroidal geometries and their contribution to the first order scattering process have been studied. This surface‐optical phonon modes are strongly dependent on the nanocrystal geometry and new Raman selection rules are obtained given a plausible explanation for the observed low frequency shoulders present in the spectrum of several II–VI semiconductor nanostructures. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Saturated absorption and reverse saturated absorption of Cu:SiO2 at λ = 532 nm
Authors: Ganeev R. A. , Ryasnyansky A. I. , Stepanov A. L. , Usmanov T. 
Published: February 2004

AbstractNonlinear absorption in copper‐doped silicate glasses was investigated by the Z‐scan technique using second harmonic radiation of a Nd:YAG laser (λ = 532 nm, τ = 55 ps). The simultaneous influence of saturated and reverse saturated nonlinear absorption processes was analyzed. The nonlinear absorption coefficient and the saturation intensity of copper‐doped glasses at laser intensity of 5.4 × 109 W cm−2 were measured to be 6 × 10−6 cm W−1 and 4.3 × 108 W cm−2, respectively. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Temperature dependence of the energy gap of MgxZnyCd1−x−ySe alloy
Authors: Maksimov O. , Muñoz Martin , Wang W. H. , Tamargo M. C. , Samarth N. 
Published: February 2004

AbstractThe temperature dependence of the energy gap of MgxZnyCd1−x−ySe (x ∼ 0.5) and Zn0.5Cd0.5Se alloys was determined from reflectivity measurements at temperatures between 4.2 and 300 K. The data were fitted to a Bose–Einstein type relationship and temperature dependence of band gaps was compared. A similar temperature dependence of band gap was observed indicating that quantum confinement in the MgxZnyCd1−x−ySe/Zn0.5Cd0.5Se quantum wells did not depend on temperature. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Second order nonlinear susceptibility coefficients of porous semiconducting compounds
Authors: Monecke J. , Bezrukova J. , Cordts W. , Richardson G. 
Published: February 2004

AbstractIt is proven that effective second order nonlinear susceptibility coefficients of porous semiconductors, responsible for second harmonic generation, are not bounded and can be enhanced compared to those of the bulk material. The proof is based on an effective medium theory for a special fractal structure, large electric fields between nearly touching pores resulting in an enhancement of higher order field fluctuations. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Intersubband absorption in n‐type GaAs/AlGaAs (001) quantum wells: A tight‐binding study
Authors: Shtinkov N. , Vlaev S. J. 
Published: February 2004

AbstractWe present theoretical calculations of the intersubband absorption in the conduction band of GaAs/AlGaAs (001) quantum wells (QWs), performed using the sp3d5s* empirical tight‐binding model and a Green’s functions approach. The absorption spectra for both in‐plane (TE) and perpendicular (TM) polarizations are calculated. The obtained TE/TM absorption ratio is in excellent agreement with recent experimental results. We find that the asymmetry of the QW potential has no significant effect on the TE/TM ratio. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Slow mode degradation mechanism of ZnSe based white LEDs
Authors: Adachi Masahiro , Ando Koshi , Abe Tomoki , Tsutsumi Shigeyuki , Inoue Noboru , Kasada Hirofumi , Katayama Koji , Nakamura Takao 
Published: February 2004

AbstractThe cover picture is a photograph showing a row of ZnSe based white LEDs. In this issue's ‘Editor's Choice’ [1], the point defect induced degradation in these high quality diodes is investigated by electroluminescence, deep level transient spectroscopy, and isothermal capacitance transient spectroscopy investigations.The first author, Masahiro Adachi, is member of the Optoelectronics Laboratory at Tattori University, where he is working on microscopic defects in ZnSe based devices, defect induced degradation, and defect behaviour.The paper is an invited presentation from the II–VI '03 Conference held in Niagara Falls, New York, USA, 22–26 September 2003.The full Proceedings of the Eleventh International Conference on II–VI Compounds are published in physica status solidi (c) – conferences and critical reviews 1, No. 4 (March 2004) (ISBN 3‐527‐40510‐0).
Reversing the objective: Adding guinea pig pedagogies
Authors: Weinstein Matthew 
Published: February 2004

AbstractThis article explores objectification in science and science education, i.e., the way material is turned into an object of interest to scientists. Drawing on sociological and anthropological drama theory, it examines how objectification does and does not occur in classrooms and schools. To understand the role and relationship of the object to the scientist, I look at current literature from the social studies of science concerning human and nonhuman objects as well as my own ethnographic work on the activism of politicized human research subjects. The paper concludes by how and why a more self‐conscious focus on the object of science is important for those concerned with equity in science education, suggesting that such guinea pig pedagogies restore missing historical and ethical dimensions to science education. © 2004 Wiley Periodicals, Inc.Sci Ed88:248–262, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/sce.10107
Finding meaning in science: Lifeworld, identity, and self
Authors: Kozoll Richard H. , Osborne Margery D. 
Published: February 2004

AbstractDespite the many hours students spend studying science, only a few relate to these subjects in such a manner that it becomes a part of their essential worldview and advances their education in a larger sense—one in which they make a connection to the subject matter so that it becomes a source of inspiration and occupies a formative position in their life. Using the hermeneutic/phenomenological sense of lifeworld as our “being in the world,” we explore questions of identity in the teaching and learning of science. We suggest that by taking the notion of identity in science to include students' identities in their collective, inclusive of an orientation toward both who the student is and who he wants to become, we can enable this broader educative process. Science's link to lifeworld, identity, and self as well as the literature surrounding each are treated separately in the context of empirical case studies drawn from interviews with young college‐aged migrant agricultural workers. This population of students is living within a distinct culture where ideological systems are spread across lines of ethnicity, class, and vocation that place this population of students at risk of dropping out of school. Given the nature of their circumstances and their desire to leave the life of migration behind, these students show how their perceptions of science are embedded within particular issues of lifeworld, identity, and self while illustrating their interrelationships. © 2004 Wiley Periodicals, Inc.Sci Ed88:157–181, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/sce.10108
Newton's laws beyond the classroom walls
Authors: Pugh Kevin J. 
Published: February 2004

AbstractOne of the most profound qualities of science is its potential to transform and enrich students' experiences with the world. In prior work, I have conceptualized this quality of science in the construct of transformative experience. In order to illustrate the difference between transformative and nontransformative experience, this article presents the contrasting experiences of two students learning Newton's Laws in a seventh‐grade general science class. One student exemplifies engagement in a transformative experience—the learning of Newton's Laws enriches his experience with events of motion in his everyday, out‐of‐school life. The other student exemplifies the “good” student who is engaged in the class and learns the content, but does not undergo a transformative experience. The experiences of these two students are analyzed and discussed. Recommendations include a need to focus on student experience outside the classroom and engagement with content (as opposed to engagement with peripheral things, such as humor or mere activity). © 2004 Wiley Periodicals, Inc. Sci Ed 88:182–196, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/sce.10109
Urban middle‐school students' attitudes toward a defined science
Authors: Zacharia Zacharias , Barton Angela Calabrese 
Published: February 2004

AbstractRecent studies have shown that urban students and students of color have exceptionally negative attitudes toward school science and their futures in that field as compared with white students and nonurban students. In this paper we summarize research findings on students' attitudes toward science. We note that most of the studies of students' attitudes toward science that have been conducted so far have measured students' attitudes against the backdrop of a “generalized science.” Thus, we develop a detailed argument for why science needs to be more clearly defined in attitude instruments. We report on our development of this instrument as well as our initial findings. © 2004 Wiley Periodicals, Inc. Sci Ed 88:197–222, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/sce.10110
Science education as/for participation in the community
Authors: Roth Wolff‐Michael , Lee Stuart 
Published: February 2004

AbstractIn this paper, we take up and advance the project of rethinking “scientific literacy” by Eisenhart, Finkel, and Marion (American Educational Research Journal, 1996, 33, 261–295). As part of a project of rethinking science education, we advance three propositions. First, because society is built on division of labor, not everybody needs to know the same basic sets of concepts; it is more important to allow the emergence of scientific literacy as a collective property. Second, scientific knowledge ought not to be privileged in democratic collective decision making but ought to be one of many resources. Third, rethinking science education as and for participation in community life sets up the potential for lifelong participation in and learning of science‐related issues. To show the viability of these propositions, we provide a case study based on a 3‐year, multisite ethnographic research project as part of which we investigated science in the community. Framing our work in terms of activity theory, we provide descriptions of science in a local middle school, where students learn science while participating in a community effort to contribute to the knowledge base about a local creek. The children's activities are continuous with those of adults concerned about environmental health. In this way, rather than preparing for life after school, science education allows students to participate in legitimate ways in community life and therefore provides a starting point for uninterrupted lifelong learning across the presently existing boundary separating formal schooling from everyday life outside schools. © 2004 Wiley Periodicals, Inc.Sci Ed88:263–291, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/sce.10113
Multiple modes of meaning‐making in a science center
Authors: Rahm Jrene 
Published: February 2004

AbstractIn this paper, I address some of the unique challenges of studies of learning in museums through a microanalytic case study of meaning‐making among a group of youth and a curator. Through an examination of youths' forms of participation in one exhibit, I illustrate local meaning making achieved through multiple modalities—by doing, talking, and the manipulation of the exhibit. In turn, I show how multiple on‐going dialogues come to interact and constitute talk and action at the science exhibit underlining the idiosyncratic nature of meaning‐making. While the dialogue examined in this paper may be considered as a rather unremarkable event in terms of learning, it underlines that the study of meaning‐making entails a focus on more than mere conversations in situ in that verbal and nonverbal interactions need to be considered simultaneously. Furthermore, the analysis suggests that museums may be best seen as one among many resources for science literacy development whose impact can only be understood through an assessment of learning trajectories over time and across space. Suggestions are made for museum design and future studies of learning in consideration of the issues raised. © 2004 Wiley Periodicals Inc. Sci Ed 88: 223–247, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/sce.10117
Modelling HIV‐RNA viral load in vertically infected children
Authors: Gray Linsay , Cortina‐Borja Mario , Newell Marie‐Louise 
Published: February 2004

AbstractHuman immunodeficiency virus (HIV) ribo‐nucleic acid (RNA) viral load is a measure of actively replicating virus and is used as a marker of disease progression. For a thorough understanding of the dynamics of the evolution of the virus in the early life of HIV‐1 vertically infected children, it is important to elucidate the pattern of HIV‐RNA viral load over age.An aspect of assay systems used in the quantification of RNA viral load is that they measure values above particular cut‐off values for detection, below which the assays used are not sufficiently sensitive. In this way, measurements are potentially left‐censored. Recent adult studies suggest that to adequately model RNA pattern over age, it is necessary to account for within‐subject correlation, due to repeated measures, and censoring.The aim of this study, therefore, was to establish whether it is necessary to use complex methods to allow for repeated measures within individuals and censoring of the HIV‐RNA viral load in children enrolled in a cohort study.The approach involved the identification of an appropriate model for the basic pattern of RNA viral load by age and subsequent assessment of various estimation procedures accounting for repeated measures and censoring in different ways. Methods developed by Hughes involving the expectation‐maximization (EM) algorithm and the Gibbs sampler were taken as the benchmark for comparison of simpler alternatives. Other approaches considered involve linear mixed‐effects and ordinary least squares in which censoring is dealt with informally by taking the cut‐off value as absolute or taking the mid‐point between cut‐off and zero.Fractional polynomials provided a substantially superior approach for modelling the dynamics of viral load over age compared to conventional polynomials or change‐point models. Allowing for repeated measures was necessary to improve the power of the likelihood ratio tests required to establish the final model, but methods beyond taking the mid‐point for censored values did not further improve the fit. Although Hughes' methodology is the best approach, its implementation is not necessary for the identification of the optimal model. Copyright © 2004 John Wiley & Sons, Ltd.
A new measure of prognostic separation in survival data
Authors: Royston Patrick , Sauerbrei Willi 
Published: February 2004

AbstractMultivariable prognostic models are widely used in cancer and other disease areas, and have a range of applications in clinical medicine, clinical trials and allocation of health services resources. A well‐founded and reliable measure of the prognostic ability of a model would be valuable to help define the separation between patients or prognostic groups that the model could provide, and to act as a benchmark of model performance in a validation setting. We propose such a measure for models of survival data. Its motivation derives originally from the idea of separation between Kaplan–Meier curves. We define the criteria for a successful measure and discuss them with respect to our approach. Adjustments for ‘optimism’, the tendency for a model to predict better on the data on which it was derived than on new data, are suggested. We study the properties of the measure by simulation and by example in three substantial data sets. We believe that our new measure will prove useful as a tool to evaluate the separation available‐with a prognostic model. Copyright © 2004 John Wiley & Sons, Ltd.
Uncertainty and the value of diagnostic information, with application to axillary lymph node dissection in breast cancer
Authors: Parmigiani Giovanni 
Published: February 2004

AbstractIn clinical decision making, it is common to ask whether, and how much, a diagnostic procedure is contributing to subsequent treatment decisions. Statistically, quantification of the value of the information provided by a diagnostic procedure can be carried out using decision trees with multiple decision points, representing both the diagnostic test and the subsequent treatments that may depend on the test's results. This article investigates probabilistic sensitivity analysis approaches for exploring and communicating parameter uncertainty in such decision trees. Complexities arise because uncertainty about a model's inputs determines uncertainty about optimal decisions at all decision nodes of a tree. We present the expected utility solution strategy for multistage decision problems in the presence of uncertainty on input parameters, propose a set of graphical displays and summarization tools for probabilistic sensitivity analysis in multistage decision trees, and provide an application to axillary lymph node dissection in breast cancer. Copyright © 2004 John Wiley & Sons, Ltd.