bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparative investigation of Stöber silica Langmuir–Blodgett films as optical model structures
Authors: Nagy N. , Deák A. , Hámori A. , Hórvölgyi Z. , Fried M. , Petrik P. , Bársony I. 
Published: March 2008

AbstractMono‐ and multilayered Stöber silica Langmuir–Blodgett (LB) films were investigated by Spectroscopic Ellipsometry (SE) and Optical Waveguide Lightmode Spectroscopy (OWLS) comparatively. The effective refractive index and film thickness were determined from the results of multiparameter fitting of SE and OWLS spectra, and verified by reflectance spectroscopy measurements. LB layers of silica nanospheres are excellent model structures for the experimental verification of the validity of the Effective Medium Approximation (EMA) methods in SE evaluation. Since the structure of the LB films is nearly ideally close‐packed, even single layer Maxwell–Garnett EMA offers a sufficiently adequate description of this structure. Deviation from the ideally calculated porosity in the LB monolayer can be interpreted in terms of an average distance between individual spheres (coverage) in the uniform layer (assuming monodisperse particles). In case of the evaluations of OWLS measurements homogeneous single layer model can not be used because of the exponential form of the sensing evanescent field. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Error analysis of a simple and accurate optical coherent ellipsometer
Authors: Nee Soe‐Mie F. , Yu Chih‐Jen , Wu Jheng‐Syong , Huang Hong‐Sheng , Chou Chien 
Published: March 2008

AbstractThe polarization modulation of optical coherent ellipsometry (OCE) is provided by the coupling between two highly correlated orthogonal polarizations with slightly different frequencies. Error of the sample‐analyzer (SA) OCE is analyzed using the Stokes–Mueller formalism to include samples with roughness. Sample's depolarization will degrade the coherency of the incident two‐frequency laser beam, and the degradation is more serious for smaller sin 2ψ. For the simplest SA OCE with the analyzer angle at 45° from both polarizations, the misalignment of the analyzer affects only the measured dc signal but not the beat signal; and the extinction of the analyzer affects only the beat signal but not the dc signal. This SA OCE is used to measure the polarization properties for a few samples to demonstrate its applicability. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Generation of droplet‐free high‐power pulsed sputtering (HPPS) glow plasma with several tens of kilowatts
Authors: Yukimura K. , Mieda R. , Tamagaki H. , Okimoto T. 
Published: March 2008

AbstractA droplet free metallic plasma source is promising for enhanced adhesion of films with a smooth coating surface. This paper concerns a highly ionized metallic plasma source using a pulsed Penning discharge. A high‐power pulsed sputtering (HPPS) glow discharge plasma is generated using electric‐ and magnetic‐field interactions. The metallic species are sputtered by the energetic argon ion bombardment, followed by their ionization in as short as approximately 3 μs. The plasma source is compact in size (approximately 60 × 60 × 60 mm3) and the plasma is arc‐free. The glow plasma is generated at a gap with a length of 10 mm. The magnetic field at the gap is approximately 0.3 T. A pulsed power source with a rectangular‐shaped voltage‐output is used. Fundamental electrical and optical characteristics are obtained. The glow voltage and current are approximately –0.43 kV and 37 A at 30 μs, respectively, which corresponds to a peak power of approximately 16 kW, where the applied voltage –1.2 kV and a current limiting series resistance is 20 Ω. The consumed energy is approximately 0.41 J, which corresponds to an average power of 250 W at a repetition rate of 625 Hz. The power and energy are changed by circuit conditions. In order to increase the consumed power, the current limiting‐resistance is decreased to be 3 Ω, the peak power is increased to approximately 70 kW with a power density of 2.9 kW/cm2, where a current density is 4.5 A/cm2. The ambient gas is argon at a pressure of 2 Pa. In the emission spectra, singly‐ and doubly‐ionized titanium ions are observed, following the generation of argon ions, which shows the ionization of sputtered titanium species. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Quantum degeneracy of polaritons in a GaAs based Microcavity
Authors: Bajoni Daniele , Senellart Pascale , Lemaître Aristide , Bloch Jacqueline 
Published: March 2008

AbstractPolariton quantum degeneracy is obtained in a GaAs Microcavity by pulsed resonant excitation of the excitonic reservoir. Time resolved emission is monitored in this stimulated regime along the polariton branch.Analyzing the polariton population distribution for different time delays, we conclude that polariton thermalization is not achieved and that the dynamics is governed by the scattering kinetics from the reservoir into the polariton trap. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Current spreading, heat transfer, and light extraction in multi‐pixel LED array
Authors: Bogdanov M. V. , Bulashevich K. A. , Evstratov I. Yu. , Karpov S. Yu. 
Published: March 2008

AbstractUsing simulation, we have investigated into the current spreading, heat transfer, and light emission in a high‐power light‐emitting diode (LED) with an interdigitated multipixel array (IMPA) chip design. The main advantages of such LEDs compared with conventional square‐shaped ones, like a lower series resistance and a higher emission efficiency at high currents, are interpreted in terms of current spreading and local active region overheating originated from the current crowding typical for planar LED dice. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spectral and time resolved scanning near‐field microscopy of broad area 405 nm InGaN laser diode dynamics
Authors: Braun Harald , Meyer Tobias , Scholz Dominik , Schwarz Ulrich T. , Brüninghoff Stefanie , Lell Alfred , Strauß Uwe 
Published: March 2008

AbstractRidge widths of GaN laser diodes (LDs) are typically in the order of few mm. In contrast to GaAs material systems, beam quality of GaN broad area lasers is still a critical point. By time resolved scanning near‐field optical microscopy (SNOM) on pulsed electrically pumped LDs with different ridge widths we observe dynamic features caused by thermal and carrier induced changes of the refractive index like filamentation and lateral mode competition, which strongly influence the far‐field of the LDs. Using a high spectral resolution spectrometer we can additionally resolve the individual longitudinal modes of the laser spectrum both time resolved and correlated to the lateral position in the waveguide. Especially on samples with broad ridges we observe complex spectral and spatial dynamics of the laser mode like different filaments lasing on different longitudinal mode combs. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Beam quality of blue InGaN laser for projection
Authors: Strauss Uwe , Eichler Christoph , Rumbolz Christian , Lell Alfred , Lutgen Stephan , Tautz Sönke , Schillgalies Marc , Brüninghoff Stefanie 
Published: March 2008

AbstractThe blue light sources of choice for laser projection will be long wavelength nitride lasers because of their high wall plug efficiency and their small form factor compared to blue light sources using second harmonic generation. High quality of the far field is required for laser projection. However, optical confinement of GaN/AlGaN structures becomes increasingly difficult when wavelength shifts from 405 nm to the true blue spectrum. We will show excellent far fields by suppression of higher order laser modes and by improved waveguiding, respectively. We present simulations of laser modes as a function of ridge width. The slow axis far field is improved by absorber layers that guarantee in‐plane values of M2 < 1.5. Sufficient vertical confinement of the laser light by thick cladding layers is necessary to suppress laser modes guided within the substrate. We present 440 nm lasers for projection with threshold currents of 20 mA and slope efficiencies more than 0.8 W/A. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structural properties of aluminum nitride bulk single crystals grown by PVT
Authors: Bickermann M. , Epelbaum B. M. , Filip O. , Heimann P. , Nagata S. , Winnacker A. 
Published: March 2008

AbstractDefect analysis is performed on 1‐inch diameter bulk AlN crystals grown on AlN‐on‐SiC templates by physical vapour transport. The mean density of threading dislocations as evaluated by wet chemical etching is about 4 × 104 cm–2; mosaicity of the crystals is mostly inherited from the quality of the SiC and the AlN‐on‐SiC template used as seed. Comparing crystals grown without and with growth optimization, the dislocation topography is significantly different, and in crystals grown under optimized conditions, low angle grain boundaries have a more pronounced tendency to dissolve into dislocation bunches and thus a lower density at the crystal top. This corresponds to a ‘coarser’. mosaic structure as observed in X‐ray rocking curve measurements. In summary, AlN bulk crystals grown on AlN‐on‐SiC templates under optimized conditions show not only significant improvement in cracking mitigation and optical homogeneity, but also in structural quality, within a single growth run. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Piezoelectric actuation of all‐nitride MEMS
Authors: Tonisch K. , Buchheim C. , Niebelschütz F. , Donahue M. , Goldhahn R. , Cimalla V. , Ambacher O. 
Published: March 2008

AbstractWe present a MEMS technology based on (GaN/)AlGaN/GaN–heterostructures. Thereby the lower GaN layer represents the mechanical active layer, while the upper GaN and AlGaN layers supply the piezoelectrically active layers for actuation and the confinement of a 2D electron gas (at the lower interface). The 2DEG serves as back electrode for the piezoelectric actuation and as read–out, since it is modulated by the mechanical oscillation. The upper AlGaN and GaN layer both contribute to the total piezoelectric response, which was determined by piezoelectric force microscopy. The electrical field distribution throughout the heterostructure was determined by means of electroreflectance. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High sensitivity of photoluminescence‐ excitation spectroscopy for probing effects of plasma‐induced surface damages on carrier transport in AlxGa1–xN/GaN heterostructures
Authors: Takeuchi H. , Shirahama T. , Yamamoto Y. , Kamo Y. , Kunii T. , Oku T. , Tanaka H. , Nakayama M. 
Published: March 2008

AbstractWe demonstrate that photoluminescence‐excitation (PLE) spectroscopy is applicable to probe effects of the surface damages on the carrier transport in AlxGa1–xN/GaN heterostructures by systematically characterizing as‐grown and plasma‐exposed samples. The characterization of the surface morphology with atomic force microscopy clarifies that the plasma exposure modifies the atomic steps and pits on the AlxGa1–xN surface. The PLE spectrum of the as‐grown sample measured at the energy of the photoluminescence from the GaN layer shows a step rising from the AlxGa1–xN fundamental transition energy, which reflects the photogenerated‐carrier injection from the AlxGa1–xN layer to the GaN layer, while the rising step disappears in the plasma‐exposed sample. In contrast, the reflectance spectra are the same in the two samples; namely, the excitonic transition is hardly changed. Thus, it is concluded that PLE spectroscopy is highly sensitive to probe the carrier‐transport characteristics in the AlxGa1–xN/GaN heterostructure. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth and characterization of InCrN and (In,Ga,Cr)N
Authors: Kimura S. , Emura S. , Tokuda K. , Hiromura Y. , Hayakawa S. , Zhou Y. K. , Hasegawa S. , Asahi H. 
Published: March 2008

AbstractInCrN and a new quaternary alloy (In,Ga,Cr)N were synthesized by molecular beam epitaxy. Their structural properties were studied with X‐ray diffraction and X‐ray absorption fine structure (XAFS). It was found that low temperature growth enables the growth of InCrN and (In,Ga,Cr)N with higher Cr contents, while they were not crystallized at higher substrate temperature (450 °C). XAFS studies suggest that Cr atoms substitute on cation sites and no trace of locally formed secondary phases, such as Cr cluster, CrN (NaCl type) and Cr2N, in the grown InCrN and (In,Ga,Cr)N layers. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Creativity, inquiry, or accountability? Scientists' and teachers' perceptions of science education
Authors: Taylor Amy R. , Jones M. Gail , Broadwell Bethany , Oppewal Tom 
Published: March 2008

AbstractAlthough there have been numerous studies that indicate the benefits of teachers and students working with scientists, there is little research that documents scientists' views of science education, science teacher preparation, and the goals of science education. Furthermore, little is known about how scientists' views of science education may differ from those held by science teachers. Through the use of semistructured interviews, the perceptions of 37 scientists from diverse science domains and 21 middle and high school science teachers were explored. Participating scientists expressed concerns about the variability in quality of teaching, programs, and resources available for science instruction. Scientists expressed a desire for teachers to have more experience conducting science research and developing their own critical thinking skills. When asked what goals are most important for science education, 40% of the scientists emphasized that teachers should make science fun and exciting for their students. Science teachers' perceptions of science education were compared with the scientists' perceptions. Thirty percent of the teachers agreed with the scientists that too much variability in program or instructional quality exists in science education. Seventy‐six percent of the science teachers also thought there is a need to teach critical thinking skills, but more importantly there is a need to inspire creativity and a desire to learn science in students. Both teachers and scientists expressed concerns about how high‐stakes accountability inhibits efforts to improve science education. © 2008 Wiley Periodicals, Inc. Sci Ed 92:1058–1075, 2008
A varying‐coefficient model for the evaluation of time‐varying concomitant intervention effects in longitudinal studies
Authors: Wu Colin O. , Tian Xin , Bang Heejung 
Published: March 2008

AbstractConcomitant interventions are often introduced during a longitudinal clinical trial to patients who respond undesirably to the pre‐specified treatments. In addition to the main objective of evaluating the pre‐specified treatment effects, an important secondary objective in such a trial is to evaluate whether a concomitant intervention could change a patient's response over time. Because the initiation of a concomitant intervention may depend on the patient's general trend of pre‐intervention outcomes, regression approaches that treat the presence of the intervention as a time‐dependent covariate may lead to biased estimates for the intervention effects. Borrowing the techniques of Follmann and Wu (Biometrics 1995; 51:151–168) for modeling informative missing data, we propose a varying‐coefficient mixed‐effects model to evaluate the patient's longitudinal outcome trends before and after the patient's starting time of the intervention. By allowing the random coefficients to be correlated with the patient's starting time of the intervention, our model leads to less biased estimates of the intervention effects. Nonparametric estimation and inferences of the coefficient curves and intervention effects are developed using B‐splines. Our methods are demonstrated through a longitudinal clinical trial in depression and heart disease and a simulation study. Copyright © 2008 John Wiley & Sons, Ltd.
Bayesian semiparametric regression for longitudinal binary processes with missing data
Authors: Su Li , Hogan Joseph W. 
Published: March 2008

AbstractLongitudinal studies with binary repeated measures are widespread in biomedical research. Marginal regression approaches for balanced binary data are well developed, whereas for binary process data, where measurement times are irregular and may differ by individuals, likelihood‐based methods for marginal regression analysis are less well developed. In this article, we develop a Bayesian regression model for analyzing longitudinal binary process data, with emphasis on dealing with missingness. We focus on the settings where data are missing at random (MAR), which require a correctly specified joint distribution for the repeated measures in order to draw valid likelihood‐based inference about the marginal mean. To provide maximum flexibility, the proposed model specifies both the marginal mean and serial dependence structures using nonparametric smooth functions. Serial dependence is allowed to depend on the time lag between adjacent outcomes as well as other relevant covariates. Inference is fully Bayesian. Using simulations, we show that adequate modeling of the serial dependence structure is necessary for valid inference of the marginal mean when the binary process data are MAR. Longitudinal viral load data from the HIV Epidemiology Research Study are analyzed for illustration. Copyright © 2008 John Wiley & Sons, Ltd.
Factors influencing partner selection in strategic alliances: the moderating role of alliance context
Authors: Shah Reshma H. , Swaminathan Vanitha 
Published: March 2008

AbstractThe growth of alliances has generated considerable interest in this topic among both academics and practitioners. While multiple factors may affect alliance success, partner selection emerges as one of the most influential. Previous studies on alliances present general models that assume the factors (e.g., trust, commitment, complementarity, financial payoff) that drive partner attractiveness and, in turn, the likelihood of selection, are consistent across varying alliance projects and situations. In contrast, the present study proposes a contingency approach grounded in management control theory that suggests the criteria managers use in choosing alliance partners will vary by alliance project type. Specifically, it introduces a framework that addresses when and why managers select partners with certain, specific characteristics. The results of the present study strongly support hypotheses that the critical criteria for assessing alliance partner attractiveness and selection vary depending on the differential levels of process manageability and outcome interpretability inherent in a strategic alliance. Implications for theory and practice are discussed. Copyright © 2008 John Wiley & Sons, Ltd.
Color Control of Natural Fluorescent Proteins by Photonic Crystals
Authors: Blum Christian , Mosk Allard P. , Nikolaev Ivan S. , Subramaniam Vinod , Vos Willem L. 
Published: March 2008

AbstractThe emission of fluorescent proteins inside photonic crystals is studied. It is demonstrated that the apparent emission color of the fluorescent protein can be controlled externally by the photonic crystal. With increasing crystal lattice parameter, the appearance of the proteins turns from orange to red, and suddenly to green. The dramatic color changes agree with the theoretically expected redistribution of light escaping around the stop band of the photonic crystal. Our experiments show the potential of combining biological systems with nanophotonics. This “biophotonic engineering” may be extended to control emission rates and complex Förster energy‐transfer systems obtained by protein engineering.
Direct Syntheses of Bis(tetraphenylphosphonium) and Bis(ethyltriphenylphosphonium) Hexabromo‐diselenates(II), [PPh4]2[Se2Br6] and [PEtPh3]2[Se2Br6]. The Crystal Structure of [PEtPh3]2[Se2Br6]
Authors: Janickis Vitalijus , Herberhold Max , Milius Wolfgang 
Published: March 2008

AbstractBrown crystals of [PPh4]2[Se2Br6] (1) and [PEtPh3]2[Se2Br6] (2) were obtained when selenium and bromine reacted in acetonitrile solution in the presence of tetraphenylphosphonium bromide and ethyltriphenylphosphonium bromide, respectively. The crystal structure of 2 has been determined by X‐ray methods and refined to R = 0.0420 for 4161 reflections. The crystals are monoclinic, space group P21/n with Z = 2 and a = 13.055(3) Å, b = 12.628(3) Å, c = 13.530(3) Å, β = 92.40(3)° (293(2) K). In the solid state structure of 2 the dinuclear hexabromo‐diselenate(II) anion is centrosymmetric and consists of two distorted almost square‐planar SeBr4 units sharing a common edge through two bridging Br atoms. The terminal SeII–Br bond distances are found to be 2.419(1) and 2.445(1) Å, the bridging μBr–SeII bond distances 2.901(1) and 2.802(1) Å.
Synthesis and Crystal Structure of (CH3NH3)2[Cu(NO3)4]: a Rare Example of a Tetranitratocuprate(II) with a Light Cation of the Type M2[Cu(NO3)4]
Authors: Steinhauser Georg , Karaghiosoff Konstantin , Klapötke Thomas M. 
Published: March 2008

AbstractThe reaction of methylammonium nitrate and copper(II) nitrate pentahemihydrate in concentrated nitric acid yields the novel bis(monomethylammonium) tetranitratocuprate(II). By evaporation of the nitric acid at elevated temperatures single crystals suitable for crystal structure analysis by X‐ray diffraction were obtained. The crystal structure shows a clear Jahn‐Teller distortion in the octahedral nitratocuprate anion.
The Influence of Substituents at C2 Carbon Atom of Thiosemicarbazones {R(H)C2=N3‐N2(H)‐C1(=S)‐N1H2} on their Dentacy in PtII/PdII Complexes: Synthesis, Spectroscopy, and Crystal Structures
Authors: Lobana Tarlok S. , Bawa Gagandeep , Hundal Geeta , Zeller M. 
Published: March 2008

AbstractThe coordination chemistry of platinum(II) with a series of thiosemicarbazones {R(H)C2=N3‐N2(H)‐C1(=S)‐N1H2, R = 2‐hydroxyphenyl, H2stsc; pyrrole, H2ptsc; phenyl, Hbtsc} is described. Reactions of trans‐PtCl2(PPh3)2 precursor with H2stsc (or H2ptsc) in 1 : 1 molar ratio in the presence of Et3N base yielded complexes, [Pt(η3‐ O, N3, S‐stsc)(PPh3)] (1) and [Pt(η3‐ N4, N3, S‐ptsc)(PPh3)] (2), respectively. Further, trans‐PtCl2(PPh3)2 and Hbtsc in 1 : 2 (M : L) molar ratio yielded a different compound, [Pt(η2‐ N3, S‐btsc)(η1‐S‐btsc)(PPh3)] (3). Complex 1 involved deprotonation of hydrazinic (‐N2H‐) and hydroxyl (‐OH) groups, and stsc2− is coordinating via O, N3, S donor atoms, while complex 2 involved deprotonation of hydrazinic (‐N2H‐) and ‐N4H groups and ptsc2− is probably coordinating via N4, N3, S donor atoms. Reaction of PdCl2(PPh3)2 with Hbtsc‐Me {C6H5(CH3)C2=N3‐N2(H)‐C1(=S)‐N1H2} yielded a cyclometallated complex [Pd(η3‐C, N3, S‐btsc‐Me)(PPh3)] (4). These complexes have been characterized with the help of analytical data, spectroscopic techniques {IR, NMR (1H, 31P), U.V} and single crystal X‐ray crystallography (1, 3 and 4). The effects of substituents at C2 carbon of thiosemicarbazones on their dentacy and cyclometallation are emphasized.
[PdCl(TeMe2)3](BArF) – The First Structurally Characterized Palladium(II) Complex with TeMe2 Ligands
Authors: Bröring Martin , Kleeberg Christian 
Published: March 2008

Abstract[PdCl(TeMe2)3]BArF (4) forms as the major tellurium containing product from the reaction of [(4‐Mebti)PdCl] with TeMe2 and Na(BArF) and is isolated by crystallization from the reaction mixture. At −20 °C, the compound forms orange columns from toluene/pentane, space group $P{\bar 1}$, with Z = 2. In the solid, the cationic [PdCl(TeMe2)3]+ complex ions show a non‐planar PdClTe3 coordination unit and are associated to dimers via weak Pd···Te interactions.