bluuebunny/crossref_metadata_2025 huggingface dataset:
Rapid declines in habitat quality and population size of the Liben (Sidamo) LarkHeteromirafra sidamoensisnecessitate immediate conservation action
Authors: DONALD PAUL F. , BUCHANAN GRAEME M. , COLLAR NIGEL J. , DELLELEGN ABEBE YILMA , GABREMICHAEL MERID N. , MWANGI M. A. KIRAGU , NDANG'ANG'A PAUL KARIUKI , SPOTTISWOODE CLAIRE N. , WONDAFRASH MENGISTU
Published: January 2010

The Critically Endangered Liben Lark (formerly Sidamo Lark) is known only from the Liben Plain of southern Ethiopia, where rapid grassland deterioration is driving the species towards extinction. Fieldwork on the Liben Plain in May 2009 to assess changes in habitat and population since June 2007 recorded a significant deterioration in habitat and decline in numbers. In both 2007 and 2009, birds were associated with areas with greater than average grass cover, and in 2007 with areas of higher grass. However, between 2007 and 2009 there was a significant decline in grass cover and height, a 40% decline in number of birds recorded along repeated transects, and a contraction of 38% in the occupied area of the Liben Plain. Moreover, the cover of bare ground increased more in areas where the species was recorded in 2007 than at random points, suggesting a more rapid degradation of the best sites. There was also a loss to arable agriculture of 8% of the grassland present in 2007. Invading fennel plants increased in number and area on the plain but did not appear to influence the distribution of the lark. An analysis of NDVI showed that grassland deterioration could not be explained by drought, and the most likely explanation is that grassland quality is suffering from overgrazing. Predictive modelling suggests that, apart from a smaller and politically insecure area some 500 km to the north-east near Somalia, there is no suitable habitat for this species elsewhere in the Horn of Africa. As a matter of extreme urgency, cattle exclosures need to be established on the Liben Plain to allow grassland regeneration. This may require the ploughing of land to reduce soil compaction and re-sowing with local grass species. In the longer term, further degradation of the plain should be prevented by, for example, clearing encroaching scrub to increase grassland area and reduce grazing pressure, and by developing sustainable rangeland management practices. These actions have the full and active support of local pastoralists.
Animism as a Means of Exploring Archaeological Fishing Structures on Willapa Bay, Washington, USA
Authors: Losey Robert
Published: January 2010

Remnants of stationary fishing structures on the Northwest Coast of North America are commonly investigated by archaeologists, with most studies focusing on questions of function and chronology. Here it is argued that in Native Northwest Coast ontologies fish and fishing structures were considered animate and part of the social worlds within which humans and fish were engaged. Fish were considered capable of retaliating against those who treated them improperly, and one way of ensuring that no offence would occur was to dismantle fish traps when they were not in use. Using recently documented archaeological fishing structures on Willapa Bay, Washington, USA, as examples, it is argued that these and many other Northwest Coast archaeological fish traps were partially dismantled in the past.
Working with Memory in the Archaeology of Modern Conflict
Authors: Moshenska Gabriel
Published: January 2010

The aim of this article is to situate archaeological approaches to modern conflicts within a framework of conflict memory and commemoration. A critical appreciation of historical archaeology as a commemorative practice requires a firm grounding in memory theory, specifically the formation and contestation of memory narratives. This article offers a detailed analysis of the relevant theories and demonstrates their applicability in the contested archaeology of the Nazi era in Berlin. On the basis of this critique I argue that archaeological work on contested sites offers a unique and powerful forum for socially engaged interdisciplinary research.
Palaeolithic Art as Cultural Memory: a Case Study of the Aurignacian Art of Southwest Germany
Authors: Porr Martin
Published: January 2010

This article examines aspects of social memory in the Aurignacian mobiliary art of southwest Germany. An analytical distinction is introduced between cultural and communicative memory with different characteristics and functions in Palaeolithic social life. It is argued that the statuettes are reflections of cultural memory, but also stood in a complex and unstable relationship with the flexible conditions of everyday life. The figurative objects are not passive reproductions of collective ideas. Rather, they have to be seen as products of an active individual and intense concern with the field of meanings and associations of cultural memory, and consequently represent individual variations of a socially shared meaningful ideology
Differential expression of abscisic acid metabolism and signalling genes induced by seed-covering structures or hypoxia in barley (Hordeum vulgare L.) grains
Authors: Mendiondo Guillermina M. , Leymarie Juliette , Farrant Jill M. , Corbineau Françoise , Benech-Arnold Roberto L.
Published: January 2010

Dormant barley grains cannot germinate at 30°C and this inability to germinate is imposed mostly by the glumellae which have been suggested to limit oxygen supply to the embryo. Hypoxia imposed either artificially or by the glumellae to embryos from dormant grains, increases embryo sensitivity to abscisic acid (ABA) and promotes the accumulation of ABA during the first hours after imbibition. Expression of candidate genes involved in ABA synthesis (HvNCED), catabolism (HvABA8OH1) and signalling (HvABI5, HvVP1 and HvPKABA) was analysed in embryos isolated from dormant whole or de-hulled grains incubated in air or in hypoxia (5% oxygen). The presence of the glumellae enhanced the expression of genes involved in ABA metabolism and signalling with respect to that observed in de-hulled grains incubated in air. These results suggest that at least part of the observed physiological responses to the presence of the glumellae are regulated at the level of gene expression. However, hypoxia imposed on dormant de-hulled grains did not mimic the presence of the glumellae in terms of expression of candidate genes. Hypoxia mimics the presence of the glumellae in terms of dormancy maintenance and ABA accumulation and sensitivity, but its effects appear to operate through different mechanisms.
Effects of age and experience on the production of English word-final stops by Korean speakers
Authors: BAKER WENDY
Published: January 2010

This study examined the effect of second language (L2) age of acquisition and amount of experience on the production of word-final stop consonant voicing by adult native Korean learners of English. Thirty learners, who differed in amount of L2 experience and age of L2 exposure, and 10 native English speakers produced 8 English monosyllabic words ending in voiced and voiceless stops. These productions were presented to 10 English listeners for perceptual judgment and subjected to acoustic analyses to determine how well learners produced vowel duration and closure (stop gap) duration, two cues to stop consonant voicing. Results revealed that even learners with 10 years of L2 experience did not always produce stop consonant voicing accurately, that learners' age of acquisition influenced their production of both cues, that vowel duration was easier to learn than closure duration, and that English listeners used both these cues in their judgments of production accuracy.
Das verbale Kurzzeitgedächtnis als Produkt der Interaktion zwischen Aufmerksamkeitskapazitäten, Sequenzverarbeitung und Aktivierung des Sprachsystems
Authors: Majerus Steve
Published: January 2010

Zusammenfassung. In diesem Beitrag wird ein theoretisches Modell diskutiert, das das verbale Arbeitsgedächtnis als einen Systemverbund auffasst, in dem Aufmerksamkeitskapazitäten, das Sprachsystem und ein Sequenzverarbeitungssystem miteinander verbunden sind. Ausgangspunkt der Überlegungen ist der bekannte Zusammenhang zwischen Kurzzeitgedächtnis und lexikalischer Sprachentwicklung. Mittels Studien aus der Entwicklungspsychologie, der experimentellen Psychologie und der kognitiven Neurowissenschaften wird gezeigt, dass ein großer Teil der Prozesse, die mit Kurzzeitgedächtnistests gemessen werden, durch Aufmerksamkeitskapazitäten und eine Aktivierung des Sprachsystems erklärt werden können. Eine mögliche Ausnahme ist die Verarbeitung zeitlicher Abfolgeinformation. Dies könnte eine spezifische Funktion eines Kurzzeitgedächtnissystems darstellen, die ausschlaggebend ist für das Erlernen verbaler Sequenzen und neuer Wortformen.
Visuell-räumliches Arbeitsgedächtnis
Authors: Zimmer Hubert D.
Published: January 2010

Zusammenfassung. In der Multikomponentenkonzeption des Arbeitsgedächtnisses wird explizit eine separate visuelle Teilkomponente postuliert, die in einen Speicher für statische visuelle Informationen (Visual Cache) und einen dynamischen (räumlichen) Wiederholungsprozess (Inner Scribe) unterteilt wird. In der vorliegenden Arbeit wird argumentiert, dass eine solche Aufteilung begrifflich unscharf und nicht geeignet ist, die empirischen Befunde angemessen zu erklären. Die Unterscheidung statisch versus dynamisch trifft nicht die richtige Dimension. Stattdessen sprechen neurowissenschaftliche Befunde eher für eine Trennung zwischen räumlich und visuell, wobei die räumliche Komponente zum Teil supramodal ist, während die visuelle Komponente eine Binnendifferenzierung entlang den repräsentierten Inhalten aufweist. Es wird die These aufgestellt, dass kein separater Speicher postuliert werden muss, um die in der Literatur dokumentierten Phänomene zu erklären. Die Annahme von temporär im visuellen Wahrnehmungsprozess entstehenden Repräsentationen reicht aus, um kurzzeitiges Erinnern zu erklären. Folglich wird das Arbeitsgedächtnis im gleichen verteilten neuronalen Netzwerk realisiert, das die visuelle Informationsverarbeitung in der Wahrnehmung leistet.
Kindliche Krankheitskonzepte
Authors: Ball Juliane , Lohaus Arnold
Published: January 2010

Zusammenfassung. In diesem Übersichtsbeitrag wird über den Forschungsstand zur Entwicklung von Krankheitskonzepten im Kindes- und Jugendalter berichtet. Es werden zunächst verschiedene theoretische Konzeptionen vorgestellt, die bei der Forschung zur Entwicklung von Krankheitskonzepten eine Rolle spielen. Danach wird auf die Entwicklung von Krankheitskonzepten in verschiedenen Altersabschnitten eingegangen. Es wird dabei nach Vorschule, Grundschule und Jugendalter differenziert. In jedem Entwicklungsabschnitt wird auf die Entwicklung der Konzepte über Krankheitssymptome, Krankheitsursachen sowie Verlauf und Behandlung von Erkrankungen eingegangen. Abschließend erfolgt eine zusammenfassende Diskussion der vorliegenden Befunde.
Die Bedeutung der subjektiven Perspektive auf die Behandlung von HIV
Authors: Gaab Jens
Published: January 2010

Zusammenfassung. Die HIV-Infektion hat sich aufgrund der Fortschritte in der medikamentösen Behandlung von einer tödlichen zu einer chronischen Erkrankung gewandelt. Zur Sicherstellung des langfristigen Erfolgs der sogenannten hochaktiven antiretroviralen Therapie (HAART) ist eine strikte Adhärenz an das individuelle Therapieregime eine notwendige Voraussetzung. Dennoch liegt die Adhärenz im Durchschnitt unter den geforderten 90 Prozent. Bislang wurde eine Vielzahl möglicher Determinanten der Adhärenz identifiziert, die in Abhängigkeit der untersuchten Population unterschiedlich gewichtet und in der Regel deskriptiv sind. Aus einer theoriegeleiteten Perspektive zeigt sich jedoch, dass eine individuelle Perspektive, d.h. die Berücksichtigung subjektiver Annahmen zur Notwendig- und Sinnhaftigkeit sowie zu den Befürchtungen negativer Nebenwirkungen, einen großen Erklärungswert besitzt und wichtige Ansatzpunkte für eine Verbesserung der Adhärenz liefert.
Person Fit for Test Speededness
Authors: Goegebeur Yuri , De Boeck Paul , Molenberghs Geert
Published: January 2010

The local influence diagnostics, proposed by Cook (1986) , provide a flexible way to assess the impact of minor model perturbations on key model parameters’ estimates. In this paper, we apply the local influence idea to the detection of test speededness in a model describing nonresponse in test data, and compare this local influence approach to the optimal person fit index proposed by Drasgow and Levine (1986) , and the empirical Bayes estimate of the test speededness random effect. The performance of the methods is illustrated on the Chilean SIMCE mathematics test data. The data example indicates that the three statistics are promising when it comes to the detection of special profiles, and besides overlap to a considerable extent. Given that the statistics were developed for different purposes, they react of course differentially to the various characteristics of the response profiles, and hence also exhibit some specificity.
Incidence of Missing Item Scores in Personality Measurement, and Simple Item-Score Imputation
Authors: van Ginkel Joost R. , Sijtsma Klaas , van der Ark L. Andries , Vermunt Jeroen K.
Published: January 2010

The focus of this study was the incidence of different kinds of missing-data problems in personality research and the handling of these problems. Missing-data problems were reported in approximately half of more than 800 articles published in three leading personality journals. In these articles, unit nonresponse, attrition, and planned missingness were distinguished but missing item scores in trait measurement were reported most frequently. Listwise deletion was the most frequently used method for handling all missing-data problems. Listwise deletion is known to reduce the accuracy of parameter estimates and the power of statistical tests and often to produce biased statistical analysis results. This study proposes a simple alternative method for handling missing item scores, known as two-way imputation, which leaves the sample size intact and has been shown to produce almost unbiased results based on multi-item questionnaire data.
Diapycnal diffusivities in homogeneous stratified turbulence
Authors: Stretch D. D. , Venayagamoorthy S. K.
Published: January 2010

Quantifying diapycnal mixing in stably stratified turbulence is fundamental to the understanding and modeling of geophysical flows. Data of diapycnal mixing from direct numerical simulations of homogeneous stratified turbulence and from grid turbulence experiments, are analyzed to investigate the scaling of the diapycnal diffusivity. In these homogeneous flows the instantaneous diapycnal diffusivity is given exactly by Kd = ερ/(∂/∂z)2 where ρ is the dissipation rate of density fluctuations, and ∂ is the mean density gradient. The diffusivity Kd may be expressed in terms of the large scale properties of the turbulence as Kd = γLE2/TL, where LE is the Ellison overturning length‐scale, TL is the turbulence decay time‐scale, and γ is half the mechanical to scalar time‐scale ratio. Our results show that LE and TL can explain most of the variations in Kd over a wide range of shear and stratification strengths while γ remains approximately constant.
Shift of peak in summer monsoon rainfall over Korea and its association with El Niño–Southern Oscillation
Authors: Lee Sun‐Seon , Vinayachandran P. N. , Ha Kyung‐Ja , Jhun Jong‐Ghap
Published: January 2010

The annual cycle of rainfall over the Korean Peninsula is marked by two peaks: one during July and the other during August. Since the mid‐1970s, the maximum rainfall over the Korean Peninsula has shifted from July to August. This shift in rainfall peak was caused by a significant increase of August rainfall after the mid‐1970s. The basic reason for this shift has been traced to a change in teleconnection between El Niño–Southern Oscillation (ENSO) and August rainfall. The relationship between August rainfall over Korea and ENSO changed from 1954–1975 (PI) to 1976–2002 (PII). The variability of August rainfall was significantly associated with sea surface temperature (SST) variation over the eastern equatorial Pacific during PI, but this relationship is absent during the PII period. In El Niño years during PI, low‐level westerly and southerly wind anomalies are dominant around the East China Sea, which relates to strong August rainfall. In La Niña years during PI, easterly and northerly wind anomalies are dominant. During the PII period, however, westerly and southerly wind anomalies around the East China Sea were responsible for the high August rainfall over the East Asian region, even though La Niña SST conditions were in effect over the eastern Pacific.
Large‐scale topography of China: A factor for the seasonal progression of the Meiyu rainband?
Authors: Xu Xiangde , Lu Chungu , Shi Xiaohui , Ding Yihui
Published: January 2010

Monsoon rainfall has been the major precipitation source for many East Asian countries, particularly China. This rainfall typically forms as a band with a distinctive northwestward movement from early spring to midsummer and is known as the Meiyu front. Meiyu rainfall constitutes a part of the East Asian monsoon. As spring transitions into summer, the thermal contrast between the land and the ocean drives the monsoon's circulation. The topography of western China's highlands further intensifies this thermal contrast. The present study tries to analyze how Meiyu rainfall responds to the intensification of the monsoon's driving force by China's large‐scale topography. In particular, the cascade of western China's elevated lands toward the northeast seems to act as a “dynamic attractor” that causes the Meiyu rainband to move to the northwest. When this monsoonal rainfall is fully developed along the foot of China's western highlands, the westerly downslope winds stop the convection, resulting in an abrupt cessation of the Meiyu rainband. The general topographic feature of China clearly defines the low‐plain climate as wet versus the plateau climate as arid or semiarid. Analyses of precipitation, water vapor, Earth's surface and near‐surface air temperatures, and atmospheric circulation provide a clear picture of this land‐ocean‐atmosphere interaction.
Quality decay and shelf-life study of fresh celery (Apium graveolens L.) grown under different nitrogen fertilization
Authors: Rizzo Valeria , Muratore Giuseppe , Russo Marco Antonio , Iacona Riccardo , Belligno Adalgisa
Published: January 2010

Nitrogen fertilization is useful and widespread to obtain higher growth and quality of productions. To evaluate the influence of nitrogen-rich fertilizers on the quality characteristics, shelf-life tests of celery grown with two levels (80-120 kg ha-1) of two different nitrogen fertilizers were performed. Celery plants were selected and packed in two plastic films (anti-fog polyolefin and micro-perforated polypropylene). Nitrate contents, weight loss, hardness, changes in colour parameters and total phenols, were studied in both packaging solutions during storage. Results showed that celery fertilized with organic nitrogen and packed in anti-fog polyolefin reached a shelf-life of 37 days. Not treated sample packed in micro-perforated polypropylene was not marketable after 20 days, while the same sample packed in anti-fog polyolefin reached 30 days.
Myosin VI Lever Arm Rotation: Fixed or Variable?
Authors: Sun Yujie , Schroeder III Harry , Beausang John , Homma Kazuaki , Ikebe Mitsuo , Goldman Yale
Published: January 2010

Two recent articles addressed the power-stroke of myosin VI molecules during stepping. Although both groups measured the angles of fluorescent probes attached on the myosin VI molecule lever arm using polarized fluorescence techniques, they differ about whether the myosin VI lever arm rotation is fixed1 or variable2. Here we discuss the causes of the discrepancy between the two studies and the implications for myosin VI processive motility.
Poly(A)-binding protein (PABP): a common viral target
Authors: Smith Richard W. P. , Gray Nicola K.
Published: January 2010

Cytoplasmic PABP [poly(A)-binding protein] is a multifunctional protein with well-studied roles in mRNA translation and stability. In the present review, we examine recent evidence that the activity of PABP is altered during infection with a wide range of viruses, bringing about changes in its stability, complex formation and intracellular localization. Targeting of PABP by both RNA and DNA viruses highlights the role of PABP as a central regulator of gene expression.
Evolution of residual-strain distribution through an overload-induced retardation period during fatigue-crack growth
Authors: Lee S. Y. , Sun Y. , An K. , Choo H. , Hubbard C. R. , Liaw P. K.
Published: January 2010

Neutron diffraction was employed to investigate the crack-growth retardation phenomenon after a single tensile overload by mapping both one-dimensional and two-dimensional residual-strain distributions around the crack tip in a series of compact-tension specimens representing various crack-growth stages through an overload-induced retardation period. The results clearly show a large compressive residual-strain field near the crack tip immediately after the overload. As the fatigue crack propagates through the overload-induced plastic zone, the compressive residual strains are gradually relaxed, and a new compressive residual-strain field is developed around the propagating crack tip, illustrating that the subsequent fatigue-induced plastic zone grows out of the large plastic zone caused by the overloading. The relationship between the overload-induced plastic zone and subsequent fatigue-induced plastic zone, and its influence on the residual-strain distributions in the perturbed plastic zone are discussed.
Electrical transport mechanisms in a-Si:H/c-Si heterojunction solar cells
Authors: Schulze T. F. , Korte L. , Conrad E. , Schmidt M. , Rech B.
Published: January 2010

We present temperature-dependent measurements of I-V curves in the dark and under illumination in order to elucidate the dominant transport mechanisms in amorphous silicon-crystalline silicon (a-Si:H/c-Si) heterojunction solar cells. ZnO:Al/(p)a-Si:H/(n)c-Si/(n+)a-Si:H cells are compared with inversely doped structures and the impact of thin undoped a-Si:H buffer layers on charge carrier transport is explored. The solar cell I-V curves are analyzed employing a generalized two-diode model which allows fitting of the experimental data for a broad range of samples. The results obtained from the fitting are discussed using prevalent transport models under consideration of auxiliary data from constant-final-state-yield photoelectron spectroscopy, surface photovoltage, and minority carrier lifetime measurements. Thus, an in-depth understanding of the device characteristics is developed in terms of the electronic properties of the interfaces and thin films forming the heterojunction. It is shown that dark I-V curve fit parameters can unequivocally be linked to the open circuit voltage under illumination which opens a way to a simplified device assessment.
Enhanced fluorescence by surface plasmon coupling of Au nanoparticles in an organic electroluminescence diode
Authors: Fujiki A. , Uemura T. , Zettsu N. , Akai-Kasaya M. , Saito A. , Kuwahara Y.
Published: January 2010

A significant increase in electroluminescence was achieved through coupling with localized surface plasmons in a single layer of Au nanoparticles. We fabricated a thin-film organic electroluminescence diode, which consists of an indium tin oxide (ITO) anode, a Au nanoparticle array, a Cu phthalocyanine hole transport layer, a tris(8-hydroxylquinolianato) aluminum (III) electron transport layer, a LiF electron injection layer, and an Al cathode. The device structure, with size-controlled Au particles embedded on ITO, can be used to realize the optimum distance for exciton-plasmon interactions by simply adjusting the thickness of the hole transport layer. We observed a 20-fold increase in the molecular fluorescence compared with that of a conventional diode structure.
Optical lattices for atom-based quantum microscopy
Authors: Klinger Andreas , Degenkolb Skyler , Gemelke Nathan , Brickman Soderberg Kathy-Anne , Chin Cheng
Published: January 2010

We describe new techniques in the construction of optical lattices to realize a coherent atom-based microscope, comprised of two atomic species used as target and probe atoms, each in an independently controlled optical lattice. Precise and dynamic translation of the lattices allows atoms to be brought into spatial overlap to induce atomic interactions. For this purpose, we have fabricated two highly stable, hexagonal optical lattices, with widely separated wavelengths but identical lattice constants using diffractive optics. The relative translational stability of 12 nm permits controlled interactions and even entanglement operations with high fidelity. Translation of the lattices is realized through a monolithic electro-optic modulator array, capable of moving the lattice smoothly over one lattice site in 11 μs, or rapidly on the order of 100 ns.
Lithium related deep and shallow acceptors in Li-doped ZnO nanocrystals
Authors: Rauch C. , Gehlhoff W. , Wagner M. R. , Malguth E. , Callsen G. , Kirste R. , Salameh B. , Hoffmann A. , Polarz S. , Aksu Y. , Driess M.
Published: January 2010

We study the existence of Li-related shallow and deep acceptor levels in Li-doped ZnO nanocrystals using electron paramagnetic resonance (EPR) and photoluminescence (PL) spectroscopy. ZnO nanocrystals with adjustable Li concentrations between 0% and 12% have been prepared using organometallic precursors and show a significant lowering of the Fermi energy upon doping. The deep Li acceptor with an acceptor energy of 800 meV could be identified in both EPR and PL measurements and is responsible for the yellow luminescence at 2.2 eV. Additionally, a shallow acceptor state at 150 meV above the valence band maximum is made responsible for the observed donor-acceptor pair and free electron-acceptor transitions at 3.235 and 3.301 eV, possibly stemming from the formation of Li-related defect complexes acting as acceptors.
A model for radiation-induced off-state leakage current in N-channel metal-oxide-semiconductor transistors with shallow trench isolation
Authors: Wang Sihao , Pei Yunpeng , Huang Ru , Wang Wenhua , Liu Wen , Xue Shoubin , An Xia , Tian Jingquan , Wang Yangyuan
Published: January 2010

A radiation-induced leakage current model in deep submicron bulk silicon N-channel metal-oxide-semiconductor field effect transistor (NMOSFET) is proposed in this paper for circuit simulations. The model takes into account the impact of the substrate doping concentration, the angle of shallow trench isolation (STI) region, and the junction depth of source/drain, which can predict the off-state leakage current of the NMOSFET with STI region irradiated at different radiation doses. The model is verified by comparing with the experimental results. The model can be easily implemented into the circuit simulator to evaluate the impact of total ionizing dose effect on the performance of circuit.
Impact of viscous flux flow on the stress in long rectangular slab superconductors
Authors: Yang Yong , Xiao Li-Ye , Li Xiao-Hang
Published: January 2010

We have attempted to resolve the influence of the rate (dBa/dt), at which an external magnetic field Ba is swept down, on the tensile stress in bulk type-II superconductors. The effect of viscous flux velocity (υ0) on the stress is discussed for two magnetization processes: the decreasing field after zero-field cooling (ZFC) and the field cooling (FC). With increasing υ0, the maximum tensile stress increases in ZFC and keeps constant in FC when the position x0, at which the remagnetization front is located, changes. x0 moves away from the center of the superconductor with increasing υ0. The effect of dba/dt, which is a parameter for dBa/dt, on the stress is similar to the effect of υ0. These results imply that dBa/dt must be considered in the magnetization processes in order to avoid cracking in type-II bulk superconductor.
Ni doping of semiconducting boron carbide
Authors: Hong Nina , Langell M. A. , Liu Jing , Kizilkaya Orhan , Adenwalla S.
Published: January 2010

The wide band gap, temperature stability, high resistivity, and robustness of semiconducting boron carbide make it an attractive material for device applications. Undoped boron carbide is p type; Ni acts as a n-type dopant. Here we present the results of controlled doping of boron carbide with Ni on thin film samples grown using plasma enhanced chemical vapor deposition. The change in the dopant concentration within the thin film as a function of the dopant flow rate in the precursor gas mixture was confirmed by x-ray photoelectron spectroscopy measurements; with increasing dopant concentration, current-voltage (I-V) curves clearly establish the trend from p-type to n-type boron carbide.
Raman and Fourier transform infrared study of substitutional carbon incorporation in rapid thermal chemical vapor deposited Si1−x−yGexCy on (1 0 0) Si
Authors: Wasyluk Joanna , Perova Tatiana S. , Meyer Francoise
Published: January 2010

We report on a detailed study of the dependence of the vibrational modes in rapid thermal chemical vapor deposited Si1−x−yGexCy films on the substitutional carbon concentration. Si1−x−yGexCy films were investigated using Raman and infrared spectroscopy with x varying in the range of 10%–16% and y in the range of 0%–1.8%. The introduction of C into thin SiGe layers reduces the average lattice constant. It has been shown that the integrated infrared intensity of the Si–C peak and the ratio of both the Raman integrated and peak intensities of the Si–C peak (at ∼605 cm−1) to the Si–Si peak of SiGeC layer, increase linearly with C content and are independent of the Ge content. This leads to the conclusion that infrared absorption and Raman scattering data can be used to determine the fraction of substitutional carbon content in Si1−x−yGexCy layers with a Ge content of up to 16%. It is also shown that the intensity ratio of the carbon satellite peak to the local carbon mode increases linearly with C content up to a C level of 1.8%. This confirms a conclusion of an increase in the probability of creating third-nearest-neighbor pairs with increasing carbon content, as derived from theoretical calculations.
A metal-to-insulator transition in cut-wire-grid metamaterials in the terahertz region
Authors: Takano Keisuke , Shibuya Kyoji , Akiyama Koichi , Nagashima Takeshi , Miyamaru Fumiaki , Hangyo Masanori
Published: January 2010

Metamaterials with metallic wire-gird structures support extremely low frequency plasmons and their electromagnetic responses exhibit metallic characteristics described by the Drude model. In this paper, we have investigated the electromagnetic responses of the wire-grid structures in the terahertz frequency range when periodic and random cuts are introduced in the wires. It is found experimentally that the wire-grid structures exhibit a transition from a metallic response of negative permittivity to an insulators-like response of large positive permittivity at terahertz frequencies when small cuts are introduced in the wires. It is also revealed from the finite-difference time-domain simulation that such a transition is accompanied by an enhancement of the electric fields in the cuts, which is applicable to practical technologies.
Tunable rectification and giant positive magnetoresistance in Ge1−xMnx/Ge epitaxial heterojunction diodes
Authors: Tian Y. F. , Deng J. X. , Yan S. S. , Dai Y. Y. , Zhao M. W. , Chen Y. X. , Liu G. L. , Mei L. M. , Liu Z. Y. , Sun J. R.
Published: January 2010

Ge 1 − x Mn x / Ge single-crystal heterojunction diodes with p-type Ge1−xMnx ferromagnetic semiconductor were grown, respectively on Ge substrates of p-type, n-type, and intrinsic semiconductors by molecular beam epitaxy. The I-V curve of the p-Ge0.95Mn0.05/intrinsic-Ge diode can be greatly tuned by a magnetic field, which was indicated by a large positive magnetoresistance. The magnetoresistance shows a peak value of 700% under a +2 V bias voltage around the Curie temperature of 225 K of the Ge0.95Mn0.05 magnetic semiconductor, and it remains as high as 440% at room temperature. The origin of the positive magnetoresistance is discussed.
Electrical and optical properties of Fe doped AlGaN grown by molecular beam epitaxy
Authors: Polyakov A. Y. , Smirnov N. B. , Govorkov A. V. , Kozhukhova E. A. , Dabiran A. M. , Chow P. P. , Wowchak A. M. , Pearton S. J.
Published: January 2010

Electrical and optical properties of AlGaN grown by molecular beam epitaxy were studied in the Al composition range 15%–45%. Undoped films were semi-insulating, with the Fermi level pinned near Ec-0.6–0.7 eV. Si doping to (5–7)×1017 cm−3 rendered the 15% Al films conducting n-type, but a large portion of the donors were relatively deep (activation energy 95 meV), with a 0.15 eV barrier for capture of electrons giving rise to strong persistent photoconductivity (PPC) effects. The optical threshold of this effect was ∼1 eV. Doping with Fe to a concentration of ∼1017 cm−3 led to decrease in concentration of uncompensated donors, suggesting compensation by Fe acceptors. Addition of Fe strongly suppressed the formation of PPC-active centers in favor of ordinary shallow donors. For higher Al compositions, Si doping of (5–7)×1017 cm−3 did not lead to n-type conductivity. Fe doping shifted the bandedge luminescence by 25–50 meV depending on Al composition. The dominant defect band in microcathodoluminescence spectra was the blue band near 3 eV, with the energy weakly dependent on composition.
Two-dimensional imaging of thermal diffusivity in metals by scanning photodeflection detection
Authors: Archiopoli Ulises Crossa , Mingolo Nélida , Martínez Oscar E.
Published: January 2010

We present a technique that retrieves the thermal diffusivity of metallic samples in a two-dimensional map with micrometer resolution. The technique uses a photothermal method based on the deflection of a probe beam after heating the surface with a modulated pump. After adequate calibration, the time delay between the pump modulation and the deflection modulation provides direct information on the local thermal diffusivity. The calibration is carried out by measuring the frequency dependence of the deflection signal at several sample locations. The capabilities of the technique are illustrated with the measurement of a cross section of a surface treated steel sample.
Photopolymerization kinetics and volume holographic recording in ZrO2 nanoparticle-polymer composites at 404 nm
Authors: Omura Koji , Tomita Yasuo
Published: January 2010

We investigate volume holographic recording in a ZrO2 nanoparticle-polymer composite film at a wavelength of 404 nm. Dependences of the polymerization kinetics on concentrations of an initiator and ZrO2 nanoparticles doped in acrylate monomer are examined by using a photodifferential scanning calorimeter. It is found that there exists the optimum concentration of ZrO2 nanoparticles to maximize the polymerization rate. The diffraction and scattering properties of transmission volume gratings are also investigated. It is found that the refractive index modulation and the material recording sensitivity are as high as 8×10−3 and 9000 cm/J, respectively, at the optimum ZrO2 nanoparticle concentration of 35 vol % and at a recording intensity of 5 mW/cm2. These material parameters are larger than typical minimum ones of 5×10−3 and 500 cm/J, respectively, for optimized performance in holographic data storage.
Experimental study of the horizontally averaged flow structure in a model wind-turbine array boundary layer
Authors: Cal Raúl Bayoán , Lebrón José , Castillo Luciano , Kang Hyung Suk , Meneveau Charles
Published: January 2010

When wind turbines are deployed in large arrays, their ability to extract kinetic energy from the flow decreases due to complex interactions among them, the terrain topography and the atmospheric boundary layer. In order to improve the understanding of the vertical transport of momentum and kinetic energy across a boundary layer flow with wind turbines, a wind-tunnel experiment is performed. The boundary layer flow includes a 3×3 array of model wind turbines. Particle-image-velocity measurements in a volume surrounding a target wind turbine are used to compute mean velocity and turbulence properties averaged on horizontal planes. Results are compared with simple momentum theory and with expressions for effective roughness length scales used to parametrize wind-turbine arrays in large-scale computer models. The impact of vertical transport of kinetic energy due to turbulence and mean flow correlations is quantified. It is found that the fluxes of kinetic energy associated with the Reynolds shear stresses are of the same order of magnitude as the power extracted by the wind turbines, highlighting the importance of vertical transport in the boundary layer.
Characterization of thin metal films via frequency-domain thermoreflectance
Authors: Schmidt Aaron J. , Cheaito Ramez , Chiesa Matteo
Published: January 2010

Frequency-domain thermoreflectance is extended to the characterization of thin metals films on low thermal diffusivity substrates. We show how a single noncontact measurement can yield both the thickness and thermal conductivity of a thin metal film with high accuracy. Results are presented from measurements of gold and aluminum films 20–100 nm thick on fused silica substrate. The thickness measurements are verified independently with atomic force microscope cross sections, and the thermal conductivity measurements are verified through electrical conductivity measurements via the Wiedemann–Franz law. The thermoreflectance thermal conductivity values are in good agreement with the Wiedemann–Franz results for all the films at least 30 nm thick, indicating that our method can be used to estimate electrical conductivity along with thermal conductivity for sufficiently thick films.
The drift-diffusion interpretation of the electron current within the organic semiconductor characterized by the bulk single energy trap level
Authors: Cvikl B.
Published: January 2010

The closed solution for the internal electric field and the total charge density derived in the drift-diffusion approximation for the model of a single layer organic semiconductor structure characterized by the bulk shallow single trap-charge energy level is presented. The solutions for two examples of electric field boundary conditions are tested on room temperature current density-voltage data of the electron conducting aluminum/tris(8-hydroxyquinoline aluminum/calcium structure [W. Brütting et al., Synth. Met. 122, 99 (2001)] for which jexp∝Va3.4, within the interval of bias 0.4 V≤Va≤7. In each case investigated the apparent electron mobility determined at given bias is distributed within a given, finite interval of values. The bias dependence of the logarithm of their lower limit, i.e., their minimum values, is found to be in each case, to a good approximation, proportional to the square root of the applied electric field. On account of the bias dependence as incorporated in the minimum value of the apparent electron mobility the spatial distribution of the organic bulk electric field as well as the total charge density turn out to be bias independent. The first case investigated is based on the boundary condition of zero electric field at the electron injection interface. It is shown that for minimum valued apparent mobilities, the strong but finite accumulation of electrons close to the anode is obtained, which characterize the inverted space charge limited current (SCLC) effect. The second example refers to the internal electric field allowing for self-adjustment of its boundary values. The total electron charge density is than found typically to be of U shape, which may, depending on the parameters, peak at both or at either Alq3 boundary. It is this example in which the proper SCLC effect is consequently predicted. In each of the above two cases, the calculations predict the minimum values of the electron apparent mobility, which substantially exceed the corresponding published measurements. For this reason the effect of the drift term alone is additionally investigated. On the basis of the published empirical electron mobilities and the diffusion term revoked, it is shown that the steady state electron current density within the Al/Alq3 (97 nm)/Ca single layer organic structure may well be pictured within the drift-only interpretation of the charge carriers within the Alq3 organic characterized by the single (shallow) trap energy level. In order to arrive at this result, it is necessary that the nonzero electric field, calculated to exist at the electron injecting Alq3/Ca boundary, is to be appropriately accounted for in the computation.
Probing Cu doped Ge0.3Se0.7 based resistance switching memory devices with random telegraph noise
Authors: Soni R. , Meuffels P. , Petraru A. , Weides M. , Kügeler C. , Waser R. , Kohlstedt H.
Published: January 2010

The ultimate sensitivity of any solid state device is limited by fluctuations. Fluctuations are manifestations of the thermal motion of matter and the discreteness of its structure which are also inherent ingredients during the resistive switching process of resistance random access memory (RRAM) devices. In quest for the role of fluctuations in different memory states and to develop resistive switching based nonvolatile memory devices, here we present our study on random telegraph noise (RTN) resistance fluctuations in Cu doped Ge0.3Se0.7 based RRAM cells. The influence of temperature and electric field on the RTN fluctuations is studied on different resistance states of the memory cells to reveal the dynamics of the underlying fluctuators. Our analysis indicates that the observed fluctuations could arise from thermally activated transpositions of Cu ions inside ionic or redox “double-site traps” triggering fluctuations in the current transport through a filamentary conducting path. Giant RTN fluctuations characterized by relative resistance variations of up to 50% in almost macroscopic samples clearly point to the existence of weak links with small effective cross-sectional areas along the conducting paths. Such large resistance fluctuations can be an important issue for the industrial applications of RRAM devices because they might lead to huge bit-error rates during reading cycles.
Plasmonic interferences and optical modulations in dark-bright-dark plasmon resonators
Authors: Su Xiong-Rui , Zhang Zong-Suo , Zhang Li-Hui , Li Qun-Qing , Chen Chun-Chong , Yang Zhong-Jian , Wang Qu-Quan
Published: January 2010

We fabricated dark-bright-dark plasmon resonators, investigated enhanced-transmission induced by plasmon transfer from the bright mode to the dark modes. Furthermore, we demonstrated interferences between dark plasmons excited by the near-field bright plasmons and directly excited by slantwise incident light, which leads to selective storage of excited energy in one of the two dark plasmon cells in the resonators by adjusting the phase between signal and control sources. This could find the applications in all-optical modulations.
Molecular dynamics study of congruent melting of the equimolar ionic liquid-benzene inclusion crystal [emim][NTf2]•C6H6
Authors: Kowsari M. H. , Alavi Saman , Ashrafizaadeh Mahmud , Najafi Bijan
Published: January 2010

We use molecular dynamics simulations to study the structure, dynamics, and details of the mechanism of congruent melting of the equimolar mixture of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide with benzene, [emim][NTf2]•C6H6. Changes in the molecular arrangement, radial distribution functions, and the dynamic behavior of species are used to detect the solid to liquid transition, show an indication of the formation of polar islands by aggregating of the ions in the liquid phase, and characterize the melting process. The predicted enthalpy of melting ΔHm=38±2 kJ mol−1 for the equimolar inclusion mixture at 290 K is in good agreement with the differential scanning calorimetry experimental results of 42±2 kJ mol−1. The dynamics of the ions and benzene molecules were studied in the solid and liquid states by calculating the mean-square displacement (MSD) and the orientational autocorrelation function. The MSD plots show strong association between ion pairs of the ionic liquid in the inclusion mixture. Indeed, the presence of a stoichiometric number of benzene molecules does not affect the nearest neighbor ionic association between [emim]+ and [NTf2]−, but increases the MSDs of both cations and anions compared to pure liquid [emim][NTf2], showing that second shell ionic associations are weakened. We monitored the rotational motion of the alkyl chain sides of imidazolium cations and also calculated the activation energy for rotation of benzene molecules about their C6 symmetry axes in their lattice sites prior to melting.
On the Cholesky decomposition for electron propagator methods: General aspects and application on C60
Authors: Vysotskiy Victor P. , Cederbaum Lorenz S.
Published: January 2010

To treat the electronic structure of large molecules by electron propagator methods we developed a parallel computer program called P-RICDΣ. The program exploits the sparsity of the two-electron integral matrix by using Cholesky decomposition techniques. The advantage of these techniques is that the error introduced is controlled only by one parameter, which can be chosen as small as needed. We verify the tolerance of electron propagator methods to the Cholesky decomposition threshold and demonstrate the power of the P-RICDΣ program for a representative example (C60). All decomposition schemes addressed in literature are investigated. Even with moderate thresholds the maximal error encountered in the calculated electron affinities and ionization potentials amount to a few meV only, and the error becomes negligible for small thresholds.
Ewald-type formulas for Gaussian-basis Bloch states in one-dimensionally periodic systems
Authors: Fripiat Joseph G. , Delhalle Joseph , Flamant Isabelle , Harris Frank E.
Published: January 2010

Expressions for integrals involving general Gaussian (s, p, d, …) basis Bloch functions are presented. Applying the Poisson transformation and the Ewald-type partitioning scheme, all lattice sums appearing in these expressions lead to fast convergence in both direct and Fourier spaces. Numerical results produced for selected test cases show that a limited number of terms in the lattice sums are necessary to get convergence in the two spaces.
Strong perpendicular magnetic anisotropy in thick CoFeB films sandwiched by Pd and MgO layers
Authors: Jung J. H. , Lim S. H. , Lee S. R.
Published: January 2010

A strong perpendicular magnetic anisotropy is formed in unit structures containing a thick CoFeB layer (2 nm) that are suitable for an MgO-based magnetic tunnel junction. The value of the coercivity, measured under perpendicular applied magnetic fields, is as high as 1050 Oe after annealing under optimum conditions. The intermixing between the Pd and the CoFeB and a low saturation magnetization of the Co-rich CoFeB layer are considered to be responsible for the strong perpendicular magnetic anisotropy.
Rectifying characteristic of Pt/TiOx/metal/Pt controlled by electronegativity
Authors: Zhong Ni , Shima Hisashi , Akinaga Hiro
Published: January 2010

Current voltage characteristic of the TiOx/metal interface has been studied by the systematic investigation on the top electrode (TE) material dependence of the carrier transport through the TiOx/metal interface. Rather than work function of TE (ϕM), electronegativity (χM) of TE plays a dominant role on current conduction and carrier transport of Pt/TiOx/metal (TE) devices. Pt/TiOx/metal (TE) exhibits rectifying property, if χM of TE is high. On the other hands, a symmetric I-V curves were observed if χM of TE is low. Plots of Schottky barrier at TiOx/metal (TE) interface versus χM of TE provides an index of interface behavior S≈0.55, suggesting partial Fermi-level pinning at TiOx/metal interface.