bluuebunny/crossref_metadata_2025 huggingface dataset:
Economic Cycles in Argentina: 1875–1990
Authors: SANZ-VILLARROYA ISABEL
Published: July 2006

This article analyses the short-run periods that can be derived from the GDP per capita series for Argentina between 1875 and 1990, after extracting its segmented long-run trend using time series techniques and unit root tests. It also studies the economic forces which, from the aggregate demand side, might provide an explanation for this behaviour. This mode of operation makes it possible to identify successive cycles more accurately than in previous studies. A high level of agreement is observed between the results of this study and arguments in the literature regarding the causes shaping these short-run periods: the analysis demonstrates that exports were the key factor until 1932 while after this year consumption and investment came to predominate.
A re-emerging Atlantic forest? Urbanization, industrialization and the forest transition in Santa Catarina, southern Brazil
Authors: BAPTISTA SANDRA R. , RUDEL THOMAS K.
Published: July 2006

During the second half of the twentieth century, southern Brazil underwent rapid industrialization and urbanization. In earlier historical periods in Europe and North America, these trends have contributed to a forest transition in which deforestation gives way to forestation. In a developing country, like Brazil, with a more skewed income distribution and a larger rural underclass, industrialization and urbanization may not give rise to a forest transition. These competing theoretical expectations were tested with data on forest cover change from the Brazilian censuses of 1970 through 1995/1996 for the state of Santa Catarina in southern Brazil. The analyses show forestation replacing deforestation between 1975 and 1980. An increase in the extent of planted forests close to urban areas explains the turnaround in forest cover trends. Because the planted forests contain relatively few native plant species, the expansion of these forests does not ease the biodiversity crisis. The re-emerging second Atlantic forest represents a smaller, less diverse and degraded version of the first Atlantic forest.
Health Policy in Twentieth-Century Europe
Authors: FORSBACH RALF
Published: July 2006

Iris Borowy and Wolf D. Gruner eds., Facing Illness in Troubled Times: Health in Europe in the Interwar Years 1918–1939 (Frankfurt am Main: Peter Lang, 2005), 424 pp., €64.00 (hb), ISBN 363119486.

Horst H. Freyhofer The Nuremberg Medical Trial: The Holocaust and the Origin of the Nuremberg Medical Code, Studies in Modern European History 53 (New York: Peter Lang, 2005), 209 pp., €30.00 (pb), ISBN 0820467979.

Ulrike Lindner Gesundheitspolitik in der Nachkriegszeit. Großbritannien und die Bundesrepublik Deutschland im Vergleich, Veröffentlichungen des Deutschen Historischen Instituts London 57 (Munich: R. Oldenbourg Verlag, 2004), 581 pp., €64.00 (hb), ISBN 3486200143.
Blackening Europe/Europeanising Blackness: Theorising the Black Presence in Europe
Authors: SMITH MICHELLE
Published: July 2006

Tina Campt, Other Germans: Black Germans and the Politics of Race, Gender and Memory in the Third Reich (Ann Arbor: University of Michigan Press, 2003), 256 pp., $22.95 (pb), ISBN 0472113607.

Paul Gilroy, Postcolonial Melancholia (New York: Columbia University Press, 2005), 192 pp., $24.50 (pb), ISBN 0231134541.

Brent Hayes Edwards, The Practice of Diaspora: Literature, Translation, and the Rise of Black Internationalism (Cambridge, MA: Harvard University Press, 2003), 397 pp., $24.95 (pb), ISBN 0674011031.

Heike Raphael-Hernandez, Blackening Europe. The Afro-American Presence (London and New York: Routledge, 2004), 314 pp., £18.99 (pb), ISBN 0-415-94399X.
Zur Bedeutung dimensionaler Aufwärts- und Abwärtsvergleiche
Authors: Pohlmann Britta , Möller Jens , Streblow Lilian
Published: July 2006

Zusammenfassung. Das Internal/External Frame of Reference Model (I/E-Modell) von Marsh (1986) postuliert, dass zur Ausbildung fachspezifischer Selbstkonzepte neben sozialen Vergleichen (externaler Bezugsrahmen) auch dimensionale Vergleiche (internaler Bezugsrahmen) herangezogen werden. Dimensionale Vergleiche sind Vergleiche der eigenen Leistungen in zwei Domänen, die zu einer Kontrastierung der fachbezogenen Selbstkonzepte führen. Ungeklärt ist bisher, ob dieser Kontrasteffekt in erster Linie auf die Aufwertung des Selbstkonzepts in der besseren Domäne zurückzuführen ist oder eher auf die Abwertung des Selbstkonzepts in der schwächeren Domäne. Zur Prüfung dieser Frage wurde ein Untersuchungsdesign gewählt, das es erlaubt, die Effekte dimensionaler Auf- und Abwärtsvergleiche getrennt zu analysieren. Dazu wurde das mathematische (verbale) Selbstkonzept bei Schülern mit durchschnittlichen mathematischen (verbalen) Leistungen in Abhängigkeit von der verbalen (mathematischen) Leistungen (gut vs. durchschnittlich vs. schwach) untersucht. Die Daten einer Feldstudie (N = 1443) zeigten für beide Domänen stärkere positive Effekte dimensionaler Abwärtsvergleiche als negative Effekte dimensionaler Aufwärtsvergleiche.
Zum Zusammenspiel von schulischer Leistung, Selbstkonzept und Interesse in der gymnasialen Oberstufe
Authors: Köller Olaf , Trautwein Ulrich , Lüdtke Oliver , Baumert Jürgen
Published: July 2006

Zusammenfassung. Zwischen schulischen Selbstkonzepten, Interessen, Kurswahlen und Leistungen im Fach Mathematik besteht ein komplexes Beziehungsgefüge. Der vorliegende Beitrag untersucht Vorhersagen des so genannten Fischteich-Effekts ( Marsh, 1987 ), wonach sich eine hohe mittlere Schulleistung der Mitschüler negativ auf motivationale Maße und leistungsthematische Wahlen auswirken sollte. Zudem wird analysiert, ob die mittlere Leistungsstärke einer Schule positive Effekte auf die Lernentwicklung hat. Daten von N = 5.527 Gymnasiasten am Ende der 10. und 12. Jahrgangsstufe wurden ausgewertet. Im Einklang mit dem Fischteich-Effekt wiesen Schülerinnen und Schüler aus besonders leistungsstarken Schulen bei Kontrolle der individuellen Leistung ein niedrigeres mathematisches Selbstkonzept auf, zeigten geringeres Interesse an der Mathematik und wählten seltener einen Mathematik-Leistungskurs in der gymnasialen Oberstufe. Der Wissenszuwachs wurde nur geringfügig positiv durch die Leistungsstärke der Schule beeinflusst. Interesse, Selbstkonzept und Leistung in Mathematik entwickelten sich für Leistungskursschüler zwischen der 10. und 12. Jahrgangsstufe günstiger als für Grundkursschüler. Zudem zeigten sich positive Effekte schulischer Selbstkonzepte und Interessen auf den Wissenszuwachs.
Facetten schulischen Selbstkonzepts
Authors: Schilling Susanne R. , Sparfeldt Jörn R. , Rost Detlef H.
Published: July 2006

Zusammenfassung. Untersucht wurden Geschlechtsunterschiede in sechs schulfachspezifischen Selbstkonzepten (Mathematik, Physik, Deutsch, Englisch, Biologie und Geschichte) bei N = 1496 Gymnasiasten der 7. bis 10. Klassenstufe. Konfirmatorische Analysen belegten, dass die faktorielle Struktur für Mädchen und Jungen praktisch identisch ist. Auch in der Vorhersage des allgemeinen schulischen Selbstkonzepts durch die fachspezifischen Facetten sowie im Zusammenhangsmuster mit Schulzensuren waren keine bedeutsamen Differenzen festzustellen. Im Gegensatz dazu gab es - unabhängig von der besuchten Klassenstufe - praktisch und statistisch relevante Unterschiede im Mittelwertsprofil, die sich nur teilweise durch Geschlechtsunterschiede in den Zensuren erklären lassen. Mädchen hatten höhere Selbstkonzeptwerte in Deutsch und Englisch. Diese waren vollständig durch die besseren Fachnoten der Mädchen erklärbar. Jungen hatten höhere Selbstkonzepte in Biologie, Geschichte, Mathematik und Physik. In diesen Fächern blieben die Effekte bei statistischer Kontrolle der Zensuren konstant.
Stoichiometry of the degradation of dissolved and particulate biogenic organic matter in the NW Iberian upwelling
Authors: Álvarez‐Salgado X. A. , Nieto‐Cid M. , Gago J. , Brea S. , Castro C. G. , Doval M. D. , Pérez F. F.
Published: July 2006

The average composition of the dissolved and particulate products of early degradation of marine phytoplankton has been established for the first time in a coastal upwelling system using a mixing analysis along isopycnal surfaces combined with a stoichiometric model. About 17–18% of the mineralized organic matter is derived from the decomposition of organic particulates, and 16–35% is from the dissolved organic matter. The remaining 50–70% is derived probably from large fast sinking particles. On average, the mineralized material on large particles has the closest composition to the Redfield formula. The ratio of dissolved saccharides to dissolved organic matter respiration is >40% higher than expected from a material of Redfield composition. Finally, the ratio of lipid to particulate organic matter respiration is >80% larger than expected from a material of Redfield composition. Regarding the decomposition of hard structures, biogenic silica dissolves predominantly in the inner shelf, where organic carbon oxidation is more intense, and diatom deposition occurs preferentially.
Central Zagros fold‐thrust belt (Iran): New insights from seismic data, field observation, and sandbox modeling
Authors: Sherkati S. , Letouzey J. , Frizon de Lamotte D.
Published: July 2006

We present five generalized cross sections across the central Zagros fold‐and‐thrust belt (Iran). These sections show that the fold geometry varies significantly both horizontally and vertically. The style is closely related to the changes in the mechanical behavior of the lithostratigraphic horizons and, in particular, to the presence of intermediate décollements within the sedimentary pile. Restoration of the sections shows amounts of shortening of the same order from one section to the other. However, it appears to be unequally distributed, suggesting variations in basal décollement shear strength. Analogue modeling has been performed to systematically investigate the effect of an intermediate décollement level at different depths on the style of folding. The models demonstrate that the position of intermediate décollements is an important factor controlling both structural style and fold wavelength. Models with shallow intermediate décollement show regularly and widely spaced anticlines. In these models, the fold wavelength depends directly on the thickness of the dominant competent layer and short‐wavelength superficial structures mask broad anticlines at depth. Models with deep intermediate décollement are characterized by the rapid propagation of deformation (with small rate of shortening) along this décollement influencing localization of forthcoming anticlines in the upper levels. Such propagation favors the development of duplexes and multiwavelength folds. On this basis, fold kinematics in central Zagros is discussed using the variation of structural style along different folds as an indicator of the sequence of deformation. Detachment folding is the main folding style at least for the initial stages of deformation and thrust faults developed only at later stages. Some of these faults, branched on décollement levels, express the progression of folding, whereas others are linked to late basement faults cutting through early structures. In general, the décollement levels are activated sequentially from deeper horizons to shallower ones. However, in one case (Gachsaran décollement) a shallow décollement is activated during the early stages of folding and then abandoned during the subsequent evolution.
Paleosecular variation and the average geomagnetic field at ±20° latitude
Authors: Lawrence K. P. , Constable C. G. , Johnson C. L.
Published: July 2006

We assembled a new paleomagnetic directional data set from lava flows and thin dikes for four regions centered on ±20° latitude: Hawaii, Mexico, the South Pacific, and Reunion. We investigate geomagnetic field behavior over the past 5 Myr and address whether geographical differences are recorded by our data set. We include inclination data from other globally distributed sites with the ±20° data to determine the best fitting time‐averaged field (TAF) for a two‐parameter longitudinally symmetric (zonal) model. Values for our model parameters, the axial quadrupole and octupole terms, are 4% and 6% of the axial dipole, respectively. Our estimate of the quadrupole term is compatible with most previous studies of deviations from a geocentric axial dipole (GAD) field. Our estimated octupole term is larger than that from normal polarity continental and igneous rocks, and oceanic sediments, but consistent with that from reversed polarity continental and igneous rocks. The variance reduction compared with a GAD field is ∼12%, and the remaining signal is attributed to paleosecular variation (PSV). We examine PSV at ±20° using virtual geomagnetic pole (VGP) dispersion and comparisons of directional distributions with simulations from two statistical models. Regionally, the Hawaii and Reunion data sets lack transitional magnetic directions and have similar inclination anomalies and VGP dispersion. In the Pacific hemisphere, Hawaii has a large inclination anomaly, and the South Pacific exhibits high PSV. The deviation of the TAF from a GAD contradicts earlier ideas of a “Pacific dipole window,” and the strong regional PSV in the South Pacific contrasts with the generally low secular variation found on short timescales. The TAF and PSV at Hawaii and Reunion are distinct from values for the South Pacific and Mexico, demonstrating the need for time‐averaged and paleosecular variation models that can describe nonzonal field structures. Investigations of zonal statistical PSV models reveal that recent models are incompatible with the empirical ±20° directional distributions and cannot fit the data by simply adjusting relative variance contributions to the PSV. The ±20° latitude data set also suggests less PSV and smaller persistent deviations from a geocentric axial dipole field during the Brunhes.
Aircraft validation of clear air absorption models at millimeter wavelengths (89–183 GHz)
Authors: Hewison Tim J.
Published: July 2006

Measurements with an airborne microwave radiometer are used to validate absorption models in clear air at frequencies used in satellite microwave humidity sounders, such as AMSU‐B and MHS. The data set includes 33 profiles of radiometric and in situ observations ranging from the tropics to the high arctic. In cold, dry conditions the MPM and Rosenkranz models were found to underestimate the observed downwelling radiances near the surface in window channels dominated by the water vapor continuum. The models' absorption coefficient is calculated and found to be strongly deficient compared to observations in layers of low specific humidity. For medium humidity, the models' negative bias persists at 89 GHz and becomes statistically significant, but reduces at higher frequencies. Previously, the radiometer calibration had been adjusted to fit modeled radiances during high‐level flight; this approach has been revised in the light of these findings and a tip curve method applied. Possible spectroscopic reasons for the models' deficits are suggested, including the underestimation of continuum terms or the extrapolation of oxygen line coupling coefficients to low temperatures. The impacts for operational use of radiative transfer models are discussed.
Winds on Titan from ground‐based tracking of the Huygens probe
Authors: Folkner W. M. , Asmar S. W. , Border J. S. , Franklin G. W. , Finley S. G. , Gorelik J. , Johnston D. V. , Kerzhanovich V. V. , Lowe S. T. , Preston R. A. , Bird M. K. , Dutta‐Roy R. , Allison M. , Atkinson D. H. , Edenhofer P. , Plettemeier D. , Tyler G. L.
Published: July 2006

Large radio telescopes on Earth tracked the radio signal transmitted by the Huygens probe during its mission at Titan. Frequency measurements were conducted as a part of the Huygens Doppler Wind Experiment (DWE) in order to derive the velocity of the probe in the direction to Earth. The DWE instrumentation on board Huygens consisted of an ultrastable oscillator which maintained the high Doppler stability required for a determination of probe horizontal motion during the atmospheric descent. A vertical profile of the zonal wind velocity in Titan's atmosphere was constructed from the Doppler data under the plausible assumption of generally small meridional wind, as validated by tracked images from the Huygens Descent Imager/Spectral Radiometer (DISR). We report here on improved results based on data with higher temporal resolution than that presented in the preliminary analysis by Bird et al. (2005), corroborating the first in situ measurement of Titan's atmospheric superrotation and a region of strong vertical shear reversal within the lower stratosphere. We also present the first high‐resolution display and interpretation of the winds near the surface and planetary boundary layer.
Reconstruction of sea surface temperature variations in the Arabian Sea over the last 23 kyr using organic proxies (TEX86 and U37K′)
Authors: Huguet Carme , Kim Jung‐Hyun , Sinninghe Damsté Jaap S. , Schouten Stefan
Published: July 2006

Two sediment cores from the western Arabian Sea, NIOP905 and 74KL, were analyzed to determine sea surface temperature (SST) variations over the last 23 kyr. Two organic molecular SST proxies were used, the well‐established U37K′ based on long‐chain unsaturated ketones synthesized by haptophyte algae and the newly proposed TEX86 derived from the membrane lipids of Crenarchaeota. Comparison of NIOP905 and 74KL core top data with present‐day SST (0–10 m) values indicates that both proxies yield temperatures similar to local annual mean SSTs. However, TEX86 and U37K′ SST down‐core records derived from the same cores differ in magnitude and phasing. The alkenone SST record of NIOP905 shows small changes in SST (∼0.5°C) over the last 23 kyr, while that of core 74KL shows a ∼2°C increase from the Last Glacial Maximum (LGM) (23–19 calendar (cal) kyr B.P.) through the Holocene (the last 11.5 cal kyr B.P.) synchronous with changes in the Northern Hemisphere. In contrast, the TEX86 records of both cores show a large increase in SST from 22°–23°C in the LGM to 28°–30°C during Termination I (19–11.5 cal kyr B.P.), decreasing to present‐day annual means of ∼26°C. A cold phase between 14.5 and 12 cal kyr B.P. that may correspond to the Antarctic cold reversal is also observed. This implies a Southern Hemisphere control on tropical SST reconstructed by the TEX86, possibly related to SW monsoon. Our results suggest that the application of both TEX86 and U37K′ give different but complementary information on SST developments in past marine environments.
Aerosol effects on the lifetime of shallow cumulus
Authors: Jiang Hongli , Xue Huiwen , Teller Amit , Feingold Graham , Levin Zev
Published: July 2006

We explore the effects of increases in aerosol concentration on cloud lifetime for warm convective clouds using a two‐dimensional single cloud model and three‐dimensional large eddy simulations (LES). The models include size‐resolved treatment of drop size distributions and warm microphysical processes. It is shown using a variety of soundings representing marine trade cumulus, and continental convective clouds that contrary to expectation, an increase in aerosol concentration from very clean to very polluted does not increase cloud lifetime, even though precipitation is suppressed. Cloud lifetimes are statistically similar although individual clouds may experience decreases in lifetime of 10–40%. An evaporation‐entrainment feedback that tends to dilute polluted clouds more than clean clouds is identified. It is proposed that the small changes in cloud lifetime are due to competing effects of precipitation suppression and enhanced evaporation, with the latter tending to dominate in these shallow clouds.
A statistical model linking Siberian forest fire scars with early summer rainfall anomalies
Authors: Jupp Tim E. , Taylor Christopher M. , Balzter Heiko , George Charles T.
Published: July 2006

Forest fires in Siberia have a significant effect on the global carbon balance. It is therefore of interest to study the environmental factors that may be responsible for their variability. Here we examine variability in the annual number of forest fire scars at a spatial scale of 2.5°. This is decomposed statistically into a spatio–temporal component correlated with low summer rainfall, a spatial component correlated with population density and a temporal component correlated with the Arctic Oscillation. Data come from ten years of satellite–derived data, incorporating both the number of forest fire scars and monthly rainfall. The expected number of fire scars halves for each additional 0.35 mm per day of rainfall in the period April–July. Our findings may prove useful in parameterising both fire models within climate simulations and fire warning systems based on numerical weather predictions of regional dry anomalies.
Formation of a Ge-rich layer during the oxidation of strained Si1−xGex
Authors: Min B.-G. , Pae Y. H. , Jun K. S. , Ko D.-H. , Kim H. , Cho M.-H. , Lee T.-W.
Published: July 2006

The diffusion of Ge in Ge-rich layer (GRL) and the factors affecting on it during the oxidation of strained Si1−xGex layers were examined. Strained Si1−xGex layers, having different initial Ge concentrations (x=0.15 and 0.3), were oxidized at 800 and 900°C in a dry O2 ambient for different oxidation times. The diffusion of Ge into the underlying Si1−xGex layer having an initial constant composition and the resulting transformation to GRL were both enhanced with an increase in oxidation temperature. After complete transformation to GRL, GeO2 started to become incorporated into the resulting oxide layer. The formation of GeO2 was initiated by the Ge saturation of the GRL layer with Ge and by the differences in diffusivity of Ge atoms in Si1−xGex and Si substrate. The relaxation occurred when the Ge concentration in the GRL reached a critical value and was not affected by either oxidation time or temperature.
Influence of the microstructure on the magnetism of Co-doped ZnO thin films
Authors: Fouchet A. , Prellier W. , Mercey B.
Published: July 2006

The prediction of ferromagnetism at room temperature in Co–ZnO thin films has generated a large interest in the community due to the possible applications. However, the results are controversial, going from ferromagnetism to nonferromagnetism, leading to a large debate about its origin (secondary phase, Co clusters or not). By carefully studying the microstructure of various Co–ZnO films, we show that the Co2+ partly substitutes the ZnO wurtzite matrix without forming Co clusters. Surprisingly, the ferromagnetism nature of the films disappears as the Co content increases. In addition, our results suggest that the observed ferromagnetism is likely associated to a large amount of defects—close to the interface and strongly depending on the growth temperature—which may explain the spreading of the results.
Double perovskite Sr2FeMoO6 films: Growth, structure, and magnetic behavior
Authors: Di Trolio A. , Larciprete R. , Testa A. M. , Fiorani D. , Imperatori P. , Turchini S. , Zema N.
Published: July 2006

The structural and magnetic properties of Sr2FeMoO6 thin films prepared by pulsed laser deposition were studied as a function of the laser energy density used to ablate a noncommercial stoichiometric target. Films deposited at a laser fluence as low as 1.6J∕cm2 exhibit a high degree of double perovskite lattice ordering, a ferromagnetic-paramagnetic transition around 355K, and a saturation magnetization of ∼3.4μB∕f.u. On the contrary, films deposited at φ values >3J∕cm2 show a vertically elongated lattice unit cell and the lack of long range ferromagnetic order with a severe decrease of the saturation magnetization (Ms∼1μB∕f.u.). The structural and magnetic properties observed in the latter samples are attributed to lattice disorder and to secondary phases resulting from the ablation process performed at high laser energy density. In these samples the presence of Fe ions not arranged in the Sr2FeMoO6 is confirmed by x-ray absorption measurement at the Fe L2,3 edge.
Mechanical modeling of carbonic anhydrase motion in simple channels
Authors: Yi Y. B. , Lengsfeld C. S.
Published: July 2006

The difference in potential energy generated by molecular confinement arising from molecular length has a potential application to separation technology. However, the design and optimization of an integrated microfluidic device to detect and separate chemically similar molecules will require computational techniques capable of predicting the energy storage (or release) associated with conformational change. To this end we developed midlevel modeling approach for the prediction of macromolecular motion in a confinement channel using finite element analysis and stochastic methods. As a proof of concept, we investigated the mechanical behavior of a carbonic anhydrase molecule where the molecule was modeled as a beam network constructed by the backbone carbon atoms. Each pair of the adjacent atoms form an elastic beam that bears both axial and shear stresses. The molecular conformation and associated dynamic behavior of the reconstructed molecule were investigated via two protocols: (1) compression of the molecule under a pair of parallel plates; and (2) propagation of the molecule through a shrinking channel. The probabilistic simulation results along with the characteristic velocity profiles demonstrate the capability of this approach to capture physically relevant behavior.
Magnetoresistance effects in Zn0.90Co0.10O films
Authors: Xu Qingyu , Hartmann Lars , Schmidt Heidemarie , Hochmuth Holger , Lorenz Michael , Schmidt-Grund Rüdiger , Spemann Daniel , Grundmann Marius
Published: July 2006

Zn 0.90 Co 0.10 O films of different thicknesses (689, 408, 355nm) doped with 0.5 at. % Al were prepared by pulsed laser deposition on a-plane sapphire substrates. At 290K the resistivity increases drastically with decreasing film thickness, while the electron concentration and mobility decrease. Magnetoresistance (MR) effects were measured in the temperature range of 5–290K. At low temperature, the positive MR increases with decreasing film thickness. Positive MR decreases rapidly with increasing temperature. With increasing temperature, the MR of the thicker film changes to negative, while positive MR was still observed for the 355nm thick film at 290K. Anomalous Hall effect was observed in the 355nm thick film at 20K, indicating the possible ferromagnetism in Zn0.90Co0.10O.
Optical and structural properties of Er2O3 films grown by magnetron sputtering
Authors: Miritello M. , Lo Savio R. , Piro A. M. , Franzò G. , Priolo F. , Iacona F. , Bongiorno C.
Published: July 2006

The structural properties and the room temperature luminescence of Er2O3 thin films deposited by magnetron sputtering have been studied. In spite of the well-known high reactivity of rare earth oxides towards silicon, films characterized by good morphological properties have been obtained by using a SiO2 interlayer between the film and the silicon substrate. The evolution of the properties of the Er2O3 films due to thermal annealing processes in oxygen ambient performed at temperatures in the range of 800–1200°C has been investigated in detail. The existence of well defined annealing conditions (rapid treatments at a temperature of 1100°C or higher) allowing to avoid the occurrence of extensive chemical reactions with the oxidized substrate has been demonstrated; under these conditions, the thermal process has a beneficial effect on both structural and optical properties of the film, and an increase of the photoluminescence (PL) intensity by about a factor of 40 with respect to the as-deposited material has been observed. The enhanced efficiency of the photon emission process has been correlated with the longer lifetime of the PL signal. Finally, the conditions leading to a reaction of Er2O3 with the substrate have been also identified, and evidences about the formation of silicate-like phases have been collected.
A constitutive model for a uranium-niobium alloy
Authors: Zubelewicz A. , Addessio F. L. , Cady C. M.
Published: July 2006

A constitutive model that includes the effects of elasticity, crystal reorientation (twinning or detwinning), phase transformations, and plasticity is presented. The model is applied to a uranium-6wt% niobium (U-6Nb) alloy, which is known to exhibit the shape memory effect. The inelastic strains for phase transformation and reorientation are based on the material’s phase diagrams. The model captures the effects of martensitic transformation and reorientation; both of the phenomena are coupled with the alloy’s phase diagrams, which are defined in terms of temperature, hydrostatic pressure, and shear stress. Computational simulations are presented that demonstrate the ability of the model to capture the relevant physical response of the material. Also, we include experimental results that demonstrate the phenomena of phase transformation, reorientation, and plasticity for low- and high-strain rates and for variations in temperature. The model replicates the experimental data for the broad range of strain rates and temperatures. Comparisons between the model and low-strain rate data, which demonstrate the shape memory effect of U-6Nb, are also provided.
Accurate measurement of electrical bulk resistivity and surface leakage of CdZnTe radiation detector crystals
Authors: Prokesch Michael , Szeles Csaba
Published: July 2006

A classical method for the accurate measurement of the bulk resistivity and a quantitative separation of bulk and surface leakage currents in semi-insulating CdZnTe radiation detectors is evaluated. We performed an extensive set of experiments on CdZnTe single-crystal test devices to confirm the reliability and reproducibility of the measurements and the validity of the underlying assumptions for data analysis and parameter extraction. The experiments included temperature dependent dual current-voltage measurements on devices with guard electrodes as a function of device thickness, surface preparation, surface passivation, and electrode deposition conditions. We also evaluated the temperature dependence of the bulk resistivity and implemented a general temperature normalization routine to allow a reliable comparison between various crystal samples.
Brillouin light scattering studies of the mechanical properties of ultrathin low-k dielectric films
Authors: Link A. , Sooryakumar R. , Bandhu R. S. , Antonelli G. A.
Published: July 2006

In an effort to reduce RC time delays that accompany decreasing feature sizes, low-k dielectric films are rapidly emerging as potential replacements for silicon dioxide (SiO2) at the interconnect level in integrated circuits. The main challenge in low-k materials is their substantially weaker mechanical properties that accompany the increasing pore volume content needed to reduce k. We show that Brillouin light scattering is an excellent nondestructive technique to monitor and characterize the mechanical properties of these porous films at thicknesses well below 200nm that are pertinent to present applications. Observation of longitudinal and transverse standing wave acoustic resonances and the dispersion that accompany their transformation into traveling waves with finite in-plane wave vectors provides for a direct measure of the principal elastic constants that completely characterize the mechanical properties of these ultrathin films. The mode amplitudes of the standing waves, their variation within the film, and the calculated Brillouin intensities account for most aspects of the spectra. We further show that the values obtained by this method agree well with other experimental techniques such as nanoindentation and picosecond laser ultrasonics.
Study of pinched loop characteristics of lead zirconate titanate (65∕35)
Authors: Pandey S. K. , Thakur O. P. , Kumar Anand , Prakash Chandra , Chatterjee Ratnamala , Goel T. C.
Published: July 2006

We report the effect of processing parameters such as (1) uniaxial and (2) isostatic pressings on ferroelectric behavior of lead zirconate titanate (PZT) having Zr∕Ti ratio 65∕35. The effect of temperature (−125–250°C) on pinched loop characteristics of uniaxially pressed PZT is also reported. Polycrystalline ceramic samples were synthesized by solid-state reaction technique and sintered at 1250°C. The density was estimated to be 7.63 and 7.58g∕cc for the uniaxially and isostatically pressed samples, respectively, prepared by conventional ball milling. X-ray diffraction analysis confirmed single phase formation with rhombohedral structure. All samples pressed uniaxially and isostatically showed pinched hysteresis loops at room temperature that disappear at higher temperatures. The remnant polarization (Pr) and coercive field (Eo) for the uniaxially pressed samples become well defined in magnitude and shape at higher measurement temperatures below phase transition temperature (Tc), but at low temperatures a distorted-loop-like structure was observed indicating low polarization properties. The effect of ferroelectric switching cycles on the PZT samples with and without annealing in oxygen is also discussed.
Stiff subcircuit islands of diamondlike carbon for stretchable electronics
Authors: Lacour Stéphanie P. , Wagner Sigurd , Narayan Roger J. , Li Teng , Suo Zhigang
Published: July 2006

Stretchable electronics on elastomeric substrates requires fragile and brittle device materials to be placed on stiff, mechanical distinct subcircuit islands. We deposited a diamondlike carbon (DLC) film at room temperature on a silicone substrate by pulsed laser ablation, and patterned the film into an array of 200×200μm2 islands. When the substrate was uniaxially stretched to a strain of 25%, the islands remained adherent to the substrate and only deformed by ∼5%, while the exposed substrate stretched by more than 30%. A row of 11 DLC islands interconnected with gold stretchable metallization maintained end-to-end electrical conduction during a mechanical cycle to 20% tensile strain. This demonstration of electrically interconnected stiff islands on silicone illustrates two important steps toward fully integrated, elastically stretchable electronics.
A model for variation of velocity versus density trends in porous sedimentary rocks
Authors: DeMartini David C. , Glinsky Michael E.
Published: July 2006

A rock physics model appropriate for porous media in which some of the solid material is “floating” or not involved in load support is developed that explains observed variation in compressional wave velocity versus density trends. This same model predicts no significant change in the shear versus compressional wave velocity trend, as is also observed. These floating grains are correlated with poor sorting of the matrix grains as expected. The presence of the floating grains is found to correlate with a decrease in the permeability of the rock and therefore the viability of potential petroleum reservoirs. Shifts in the velocity versus density relationships can be determined by wireline log but not directly by seismic reflectivity measurements. However, the introduction of an additional concept, the capture fraction of smaller grains, adds another constraint to the model which enables remote sensing of the viability of certain petroleum reservoirs by seismic reflectivity measurements alone. Experimental evidence is described that supports this model and additional experiments are suggested to further confirm it.
The role of Si orientation and temperature on the carrier mobility in metal oxide semiconductor field-effect transistors with ultrathin HfO2 gate dielectrics
Authors: Mereu B. , Rossel C. , Gusev E. P. , Yang M.
Published: July 2006

The effective carrier mobility in HfO2-based n- and p-metal oxide semiconductor field-effect transistors and in their control SiO2 devices has been investigated as a function of temperature for three different silicon crystal orientations (100), (111), and (110). For both HfO2 and SiO2, the electron mobility is steadily reduced between these orientations, whereas the hole mobility exhibits the opposite trend. The mobility-temperature dependence follows a power law μ∼μoTα, and the exponent α varies also systematically with Si orientation and carrier type. The main finding is the presence of two temperature ranges with specific exponent values α1 and α2 occurring only for holes and for the (100) and (111) orientations. This crossover with rising temperature is explained by the progressive scattering of Si light holes that form the first excited states above the heavy-hole ground state. The same observation in SiO2∕Si(100) points to scattering by acoustic phonons in bulk Si. In addition to the contribution of acoustic phonons, the systematic reduction of mobility in HfO2 devices as compared to SiO2 is attributed to remote soft optical phonon scattering. A detailed analysis allows us to determine the precise inversion charge density range (or effective electric field) where remote phonon scattering predominates.
Self-diffusion in submonolayer colloidal fluids near a wall
Authors: Anekal Samartha G. , Bevan Michael A.
Published: July 2006

Theoretical expressions are developed to describe self-diffusion in submonolayer colloidal fluids that require only equilibrium structural information as input. Submonolayer colloidal fluids are defined for the purpose of this work to occur when gravity confines colloids near a planar wall surface so that they behave thermodynamically as two dimensional fluids. Expressions for self-diffusion are generalized to consider different colloid and surface interaction potentials and interfacial concentrations from infinite dilution to near fluid-solid coexistence. The accuracy of these expressions is demonstrated by comparing self-diffusion coefficients predicted from Monte Carlo simulated equilibrium particle configurations with standard measures of self-diffusion evaluated from Stokesian Dynamics simulated particle trajectories. It is shown that diffusivities predicted for simulated equilibrium fluid structures via multibody hydrodynamic resistance tensors and particle distribution functions display excellent agreement with values computed from mean squared displacements and autocorrelation functions of simulated tracer particles. Results are obtained for short and long time self-diffusion both parallel and normal to underlying planar wall surfaces in fluids composed of particles having either repulsive electrostatic or attractive van der Waals interactions. The demonstrated accuracy of these expressions for self-diffusion should allow their direct application to experiments involving submonolayer colloidal fluids having a range of interaction potentials and interfacial concentrations.
Spectroscopic and laser cooling results on Yb3+-doped BaY2F8 single crystal
Authors: Bigotta Stefano , Parisi Daniela , Bonelli Lucia , Toncelli Alessandra , Tonelli Mauro , Di Lieto Alberto
Published: July 2006

Anti-Stokes cooling has been observed in an Yb3+-doped BaY2F8 single crystal. Single crystals have been grown by the Czochralski technique. The absorption spectra and the emission properties have been measured at room temperature and at 10K. The energy positions of the Stark sublevels of the ground and the excited state manifolds have been determined and separated from the vibronic substructure. The intrinsic decay time of the F5∕22 level has been measured taking care of avoiding the effect of multiple reabsorption processes. The theoretical and experimental cooling efficiencies of Yb:BaY2F8 are evaluated and compared with respect to those of the most frequently investigated materials for laser cooling. A temperature drop of almost 4K was measured by pumping the crystal with 3W of laser radiation at ∼1025nm in single pass configuration with a cooling efficiency of ∼3%.
Photoluminescence analysis on the indium doped Cd0.9Zn0.1Te crystal
Authors: Li Qiang , Jie Wanqi , Fu Li , Yang Ge , Zha Gangqiang , Wang Tao , Zeng Dongmei
Published: July 2006

Photoluminescence spectra are used to characterize high resistivity of In-doped CdZnTe crystal. Shallow level donor-acceptor pair (DAPs) peak at 1.6014eV is found due to shallow donor and acceptor compensation related defects, which forms the [VCd–InCd]− singly negative complex and the neutral complex [VCd–2InCd]. Cd vacancy acceptors are compensated dominantly due to indium doped [InCd]+ donor and Te antisite [TeCd]4+ donor, which improves the resistivity of CdZnTe:In crystal. Energy level model diagram of CdZnTe:In crystal is discussed. Current-voltage measurement results confirm that Cd vacancy compensation by doped indium improves the resisitivity of CdZnTe crystal.
The defect structure, sintering behavior, and dielectric responses of Cr2O3-doped Sr0.5Ba0.5Nb2O6
Authors: Fang Tsang-Tse , Chen Fung-Yu
Published: July 2006

Sr 0.5 Ba 0.5 Nb 2 O 6 (SBN50) with and without Cr2O3 dopant had been prepared by the solid-state reaction. The structural variations of undoped and Cr2O3-doped SBN were examined by the x-ray diffractometer. As the Cr2O3 content increases, the lattice parameters remain almost unchanged initially but become greatly changed revealing the increase in a axis and the decrease in c axis when the Cr2O3 content is >1mol%, which was mainly influenced by the created oxygen vacancies. Isothermal sintering behavior of undoped and Cr2O3-doped SBN50 has been investigated. It was found that the creation of the charge-compensated oxygen vacancies and the accompanied structural change had a significant influence on the sintering behavior. The direct jumping path through vacant O sites (path 2 in Fig. 9) was further considered as the main reason for the enhancement of the densification rate and slight increase of the activation energy when the Cr2O3 content is ≦1mol% and the decrease of the densification rate but great increase of the activation energy when the Cr2O3 content is >1mol%. Tmax [temperature at the maximum dielectric constant (εmax)] decreased with the increase of Cr doping and is essentially determined by the structural change of the NbO6 units in SBN. εmax is suggested to be determined by the competition between the reduction of the polarization due to the substitution of Cr for Nb and the enhancement of the polar moment arising from the weakening of Nb–O bonds due to the creation of the oxygen vacancies.
Mechanism of charge transport in poly(3-octylthiophene)
Authors: Singh Ramadhar , Kumar Jitendra , Singh Rajiv K. , Chand Suresh , Kumar Vikram , Rastogi R. C.
Published: July 2006

The direct current (dc) conductivity (σdc) of pristine and ferric chloride doped poly(3-octylthiophene) has been measured in the temperature range of 6–300K. Mott’s three-dimensional variable range hopping and thermally activated tunneling are suggested as the dominant mechanisms of dc conduction at high (77–300K) and low (<77K) temperature regions, respectively.
Magnetoresistance of spin valve structures based on the full Heusler alloy Co2MnSi
Authors: Singh L. J. , Leung C. W. , Bell C. , Prieto J. L. , Barber Z. H.
Published: July 2006

Co 2 Mn Si ∕ Cu ∕ Co pseudo-spin-valves (PSVs) have been grown by dc magnetron sputtering from elemental targets onto GaAs(001). The stoichiometric Heusler layer was highly textured, following the [001] orientation of the lattice matched GaAs(001). Hysteresis loops showed independent switching of the magnetization of the two ferromagnetic layers. Transport measurements of the samples were performed in both the current in plane (CIP) and current perpendicular to plane (CPP) geometries. Clear low-field spin valve contributions were observed at 15K for the CIP PSV, a conventionally patterned mesa CPP device and a CPP device fabricated in the focused ion beam microscope. Analysis of the CPP data did not show the half-metallic behavior of Co2MnSi as expected from theory.
Atomic density function theory and modeling of microstructure evolution at the atomic scale
Authors: Jin Yongmei M. , Khachaturyan Armen G.
Published: July 2006

The atomic density function kinetic theory of a spontaneous atomic rearrangement at the atomic scale is developed. In this theory, the evolution of the system is described not by the individual movement of each atom in the same system but by the evolution of the atomic density functions, which are averages over the time-dependent ensemble. The temporal evolution of atomic densities is driven by the free energy relaxation. The thermodynamic aspects of the instability of the homogeneous liquid state and the formation of crystalline and amorphous state are discussed. Examples of self-assembling of atoms in the formation of a three-dimensional nanocrystal, and the two-dimensional diffusionless transformation in the crystalline and amorphous states are considered. The modeling reveals the special features of displacive phase transformations in the crystalline state through a transient stress-accommodating state. It also demonstrates that the thermodynamic relaxation of the liquid below its critical instability point produces a relaxed amorphous state that is practically a metastable phase.
Midwave infrared type-II InAs∕GaSb superlattice detectors with mixed interfaces
Authors: Plis E. , Annamalai S. , Posani K. T. , Krishna S. , Rupani R. A. , Ghosh S.
Published: July 2006

We report the growth and fabrication of midwave infrared InAs∕GaSb strain layer superlattice (SLS) detectors. Growth of alternate interfaces leads to a reduced strain between the GaSb buffer and SLS (Δa‖∕a=−5×10−4), enabling the growth of active regions up to 3μm (625 periods). The structural, optical, and electrical properties of the active region were characterized using x-ray crystallography and photoluminescence, respectively. p-i-n detectors were grown using 625 periods of 8 ML (monolayer) InAs∕8 ML GaSb as the active region. The λcutoff for the detectors was 4.6μm with a conversion efficiency of 32% at Vb=−0.2V. Detectivity was obtained using noise power spectral density measurements under 300K 2π field of view illumination and was equal to 5.2×1010 and 3×1010cmHz1∕2∕W (Vb=−0.02V, T=80K) in the white noise and 1∕f noise limit (at 50Hz).
Orientational order in high density dipolar hard sphere fluids
Authors: Weis J.-J. , Levesque D.
Published: July 2006

Taking advantage of recent estimates, by one of us, of the critical temperature of the isotropic-ferroelectric transition of high density dipolar hard spheres, we performed new Monte Carlo simulations in the close vicinity of these estimates and applied histogram reweighting methods to obtain refined values of the critical temperatures from the crossing of the fourth-order cumulant for different system sizes. The ferroelectric line is determined in the density range ρ*=0.80–0.95, and the onset of columnar ordering is located.