bluuebunny/crossref_metadata_2025 huggingface dataset:
Secular changes in the solar semidiurnal tide of the western North Atlantic Ocean
Authors: Ray Richard D.
Published: October 2009

An analysis of twentieth century tide gauge records reveals that the solar semidiurnal tide S2 has been decreasing in amplitude along the eastern coast of North America and at the mid‐ocean site Bermuda. In relative terms the observed rates are unusually large, of order 10% per century. Periods of greatest change, however, are inconsistent among the stations, and roughly half the stations show increasing amplitude since the late 1990s. Excepting the Gulf of Maine, lunar tides are either static or slightly increasing in amplitude; a few stations show decreases. Large changes in solar, but not lunar, tides suggest causes related to variable radiational forcing, but the hypothesis is at present unproven.
Three‐dimensional diffusion simulation of outer radiation belt electrons during the 9 October 1990 magnetic storm
Authors: Albert Jay M. , Meredith Nigel P. , Horne Richard B.
Published: September 2009

Relativistic (>1 MeV) electron flux increases in the Earth's radiation belts are significantly underestimated by models that only include transport and loss processes, suggesting that some additional acceleration process is required. Here we use a new, three‐dimensional code that includes radial diffusion and quasi‐linear pitch angle and energy diffusion due to chorus waves, including cross terms, to simulate the 9 October 1990 magnetic storm. The diffusion coefficients are activity dependent, and time‐dependent boundary conditions are imposed on all six boundary faces, taken from fits to CRRES Medium Electrons A electron data. Although the main phase dropout is not fully captured, the persistent phase space density peaks observed during the recovery phase are well explained, but this requires both chorus wave acceleration and radial diffusion.
Real and apparent changes in sediment deposition rates through time
Authors: Schumer Rina , Jerolmack Douglas J.
Published: September 2009

Field measurements show that estimated sediment deposition rate decreases as a power law function of the measurement interval. This apparent decrease in sediment deposition has been attributed to completeness of the sedimentary record; the effect arises because of incorporation of longer hiatuses in deposition as averaging time is increased. We demonstrate that a heavy‐tailed distribution of periods of nondeposition (hiatuses) produces this phenomenon and that observed accumulation rate decreases as tγ−1, over multiple orders of magnitude, where 0 < γ ≤ 1 is the parameter describing the tail of the distribution of quiescent period length. By using continuous time random walks and limit theory, we can estimate the actual average deposition rate from observations of the surface location over time. If geologic and geometric constraints place an upper limit on the length of hiatuses, then average accumulation rates approach a constant value at very long times. Our model suggests an alternative explanation for the apparent increase in global sediment accumulation rates over the last 5 million years.
Gut commensal Lactobacillus reuteri 100‐23 stimulates an immunoregulatory response
Authors: Livingston Megan , Loach Diane , Wilson Michelle , Tannock Gerald W , Baird Margaret
Published: September 2009

Lactobacillus reuteri 100‐23 is a bacterial commensal of the gastrointestinal tract of mice. Previous studies have shown that colonization of the murine gut by this strain stimulates small‐bowel enterocytes to produce proinflammatory cytokines. This is associated with a mild, transitory inflammatory response 6 days after inoculation of formerly Lactobacillus‐free animals. The inflammation subsides by 21 days after colonization, although lactobacilli continue to be present in the bowel. To determine the immunological mechanisms that underpin tolerance to bowel commensals, we investigated cytokine responses of dendritic cells and T cells after exposure to cells of L. reuteri 100‐23. Interleukin‐10 (IL‐10), IL‐2 and transforming growth factor‐β (TGF‐β) concentrations in supernatants of cultured immune cells, as well as the results of proliferative assays of mesenteric lymph node (MLN) cells and quantification of Foxp3‐positive cells in MLN and spleen, indicated that L. reuteri 100‐23 stimulated the development of an increased number of regulatory T cells.
Extracellular redox status regulates Nrf2 activation through mitochondrial reactive oxygen species
Authors: Imhoff Barry R. , Hansen Jason M.
Published: October 2009

The redox status of the extracellular compartment has only just been elucidated as a mechanism controlling intracellular signal transduction and correlates with aging, diabetes, heart disease and lung fibrosis. In the present paper, we describe a mechanism by which oxidizing extracellular environments, as maintained by the cysteine/cystine (Cys/CySS) redox couple, induce mitochondria-derived ROS (reactive oxygen species) generation and cause the activation of Nrf2 (nuclear factor-erythroid 2-related factor 2), inducing an antioxidant response. NIH 3T3 cells were cultured in medium with extracellular Cys/CySS redox potentials (Eh), ranging from 0 to −150 mV. Cellular and mitochondrial ROS production significantly increased in cells incubated under more oxidizing extracellular conditions (0 and −46 mV). Trx2 (thioredoxin-2) is a mitochondrial-specific oxidoreductase and antioxidant and became oxidized in cells incubated at 0 or −46 mV. MEFs (mouse embryonic fibroblasts) from Trx2-overexpressing transgenic (Trx2 Tg) mice produced less intracellular ROS compared with WT (wild-type) MEFs at the more oxidizing extracellular conditions. Nrf2 activity was increased in WT MEFs at the 0 or −46 mV conditions, but was inhibited in Trx2 Tg MEFs under the same conditions. Furthermore, Nrf2-regulated gene expression was significantly increased in the WT MEFs, but not in the Trx2 Tg MEFs. These results show that the Cys/CySS redox status in the extracellular compartment regulates intracellular ROS generated primarily in the mitochondria, which play an important role in the activation of Nrf2 and up-regulation of antioxidant and detoxification systems.
Risk and Protective Factors Associated With Speech and Language Impairment in a Nationally Representative Sample of 4- to 5-Year-Old Children
Authors: Harrison Linda J. , McLeod Sharynne
Published: September 2009

Purpose

To determine risk and protective factors for speech and language impairment in early childhood.

Method

Data are presented for a nationally representative sample of 4,983 children participating in the Longitudinal Study of Australian Children (described in McLeod & Harrison, 2009). Thirty-one child, parent, family, and community factors previously reported as being predictors of speech and language impairment were tested as predictors of (a) parent-rated expressive speech/language concern and (b) receptive language concern, (c) use of speech-language pathology services, and (d) low receptive vocabulary.

Results

Bivariate logistic regression analyses confirmed 29 of the identified factors. However, when tested concurrently with other predictors in multivariate analyses, only 19 remained significant: 9 for 2–4 outcomes and 10 for 1 outcome. Consistent risk factors were being male, having ongoing hearing problems, and having a more reactive temperament. Protective factors were having a more persistent and sociable temperament and higher levels of maternal well-being. Results differed by outcome for having an older sibling, parents speaking a language other than English, and parental support for children’s learning at home.

Conclusion

Identification of children requiring speech and language assessment requires consideration of the context of family life as well as biological and psychosocial factors intrinsic to the child.
Judgments of Omitted BE and DO in Questions as Extended Finiteness Clinical Markers of Specific Language Impairment (SLI) to 15 Years: A Study of Growth and Asymptote
Authors: Rice Mabel L. , Hoffman Lesa , Wexler Ken
Published: September 2009

Purpose

Clinical grammar markers are needed for children with SLI older than 8 years. This study followed children who were previously studied on sentences with omitted finiteness to determine if affected children continue to perform at low levels and to examine possible predictors of low performance. This is the first longitudinal report of grammaticality judgments of questions.

Method

Three groups of children participated: 20 SLI, 20 age controls, and 18 language-matched controls, followed from ages 6–15 years. An experimental grammaticality judgment task was administered with BE copula/auxiliary and DO auxiliary in
wh-
and yes/no questions for 9 times of measurement. Predictors were indices of vocabulary, nonverbal intelligence, and maternal education.

Results

Growth curve analyses show that the affected group performed below the younger controls at each time of measurement, for each variable. Growth analyses show linear and quadratic effects for both groups across variables, with the exception of BE acquisition, which was flat for both groups. The control children reached ceiling levels; the affected children reached a lower asymptote.

Conclusion

The results suggest an ongoing maturational lag in finiteness marking for affected children with promise as a clinical marker for language impairment in school-aged and adolescent children and probably adults as well.
Institutionalisation as a Process of Interplay between Technology and Its Organisational Context of Use
Authors: Baptista (John) João
Published: September 2009

This study contributes to the IS literature with a distinct explanation of the process of institutionalisation of technology in organisations. The research analyses the role of micro-level processes of interplay in embedding an intranet in the formal functioning of an organisation and in the habits and routines of its employees. The findings identify two types of processes of interplay underpinning this process of institutionalisation. The first operates at the level of constitutive expectations and refers to mutual changes to the governance, policy and control mechanisms which foster the perception that the intranet is part of the expected formal functioning of the organisation. The second operates at the level of background expectations and refers to mutual changes that make the intranet look more familiar, functional, easier to use, fostering its embedding in routines and habits of the employees. The study aims to motivate more research on institutionalisation as a bottom-up micro process of gradual development of institutionalised behaviour.
The Diffusion and Use of Institutional Theory: A Cross-Disciplinary Longitudinal Literature Survey
Authors: Weerakkody Vishanth , Dwivedi Yogesh K , Irani Zahir
Published: September 2009

There is a plethora of theories to explore the disciplines of business, management and sociology, with institutional theory being widely used to explore a range of research challenges. In the area of Information Systems (IS), the use of institutional theory remains in its infancy, with much potential for adoption. Much of the rationale underpinning the proposed research is that a systematic review and synthesis of the normative literature may support the direction of further research and the use of institutional theory in exploring pertinent research challenges facing the IS community. This study also serves to signpost cross-disciplinary research, and thus opens up a whole new research paradigm. Therefore, this article seeks to provide a bibliometric analysis and a comprehensive and systematic review of the literature pertaining to institutional theory to ascertain the current ‘state of play’ of the theory. Information on a series of variables was extracted after conducting a review of 511 articles across various disciplines that have utilised institutional theory, published in 210 peer-reviewed journals between 1978 and 2008. The findings suggest that the positivist paradigm, empirical and quantitative research, the survey method and organisation/firm as a unit of analysis was used predominantly in combination with institutional theory. The results of this study may have implications for researchers, journal editors, reviewers and universities.
Molecular arrangement for twisted nematic liquid crystal displays having liquid crystalline materials with opposite chiral structures (reverse twisted nematic liquid crystal displays)
Authors: Takatoh Kohki , Akimoto Mitsuhiro , Kaneko Hiroomi , Kawashima Koji , Kobayashi Shunsuke
Published: September 2009

It was found that in twisted nematic liquid crystal displays (TN-LCDs) in which the chiral direction of the liquid crystalline (LC) material is opposite to the twist direction determined by the rubbing directions, which are referred to as a reverse twisted nematic LCDs, LC molecules tilt largely without the application of an electric field. Reducing the pitch length of LC materials increases the polar angles of the LC molecules. This phenomenon can be explained by assuming that the stress generated by the helical power being in the opposite direction to the twist direction can be released by increasing the polar angle. The resultant molecular arrangement resembles that of TN-LCDs to which a voltage is applied. By using this LC molecular arrangement, a drastic reduction in the driving voltage of TN-LCDs could be realized. We believe that this method is capable of reducing the driving voltage of TN-LCDs more than other methods.
Creation and relaxation of light- and bias-induced metastabilities in Cu(In,Ga)Se2
Authors: Urbaniak A. , Igalson M.
Published: September 2009

Metastabilities in Cu(In,Ga)Se2 based solar cells were investigated. Capacitance and conductance transients were measured in order to analyze carrier trapping and emission processes related to the creation and relaxation of metastable states. Our experimental findings support the theoretical predictions of Lany and Zunger [Lany and Zunger, J. Appl. Phys. 100, 113725 (2006)] for a (VSe-VCu) complex, a defect with negative-U energy that can exist in both the donor and acceptor configurations. We show that two different defect reactions induced by either voltage bias or illumination lead to the same acceptor configuration of the defect. The relaxation process is the same for light- and bias-induced metastabilities in devices and thin films. Time constants and activation energies for all investigated processes have been obtained. The results agree very well with the values calculated for (VSe-VCu) divacancy.
Indirect drive ablative Rayleigh–Taylor experiments with rugby hohlraums on OMEGA
Authors: Casner A. , Galmiche D. , Huser G. , Jadaud J.-P. , Liberatore S. , Vandenboomgaerde M.
Published: September 2009

Results of ablative Rayleigh–Taylor instability growth experiments performed in indirect drive on the OMEGA laser facility [T. R. Boehly, D. L. Brown, S. Craxton et al., Opt. Commun. 133, 495 (1997)] are reported. These experiments aim at benchmarking hydrocodes simulations and ablator instabilities growth in conditions relevant to ignition in the framework of the Laser MégaJoule [C. Cavailler, Plasma Phys. Controlled Fusion 47, 389 (2005)]. The modulated samples under study were made of germanium-doped plastic (CHGe), which is the nominal ablator for future ignition experiments. The incident x-ray drive was provided using rugby-shaped hohlraums [M. Vandenboomgaerde, J. Bastian, A. Casner et al., Phys. Rev. Lett. 99, 065004 (2007)] and was characterized by means of absolute time-resolved soft x-ray power measurements through a dedicated diagnostic hole, shock breakout data and one-dimensional and two-dimensional (2D) side-on radiographies. All these independent x-ray drive diagnostics lead to an actual on-foil flux that is about 50% smaller than laser-entrance-hole measurements. The experimentally inferred flux is used to simulate experimental optical depths obtained from face-on radiographies for an extensive set of initial conditions: front-side single-mode (wavelength λ=35, 50, and 70 μm) and two-mode perturbations (wavelength λ=35 and 70 μm, in phase or in opposite phase). Three-dimensional pattern growth is also compared with the 2D case. Finally the case of the feedthrough mechanism is addressed with rear-side modulated foils.
Identification of the slower secondary relaxation’s nature in maltose by means of theoretical and dielectric studies
Authors: Wlodarczyk P. , Kaminski K. , Adrjanowicz K. , Wojnarowska Z. , Czarnota B. , Paluch M. , Ziolo J. , Pilch J.
Published: September 2009

Dielectric relaxation measurements on maltose were performed at ambient and increasing pressure. The loss spectra collected below glass transition of this disaccharide revealed presence of two well separated secondary relaxations. Activation energies determined for both modes are Ea=73 kJ/mol and 47 kJ/mol for the slower (β) and faster (γ) relaxation, respectively. From high pressure measurements activation volume ΔV=15.6 ml/mol for the slower secondary relaxation was estimated. Both quantities: activation energy and activation volume for α-process derived from dielectric data, were compared to those obtained from the conformational calculations with use of density functional theory (DFT). We found out satisfactory agreement between both quantities for the molecular motion related to the rotation of the two monosaccharide units around glycosidic linkage in this disaccharide.
Graphene growth on polycrystalline Ru thin films
Authors: Sutter E. , Albrecht P. , Sutter P.
Published: September 2009

Monolayer graphene has been grown on polycrystalline Ru thin films on SiO2/Si substrates. The Ru films have columnar structure with strongly aligned grains exposing flat (0001) surface facets. Adjacent grains show small relative tilts of their [0001] axes and variations in in-plane orientation. Graphene layers grown on this template cover the entire surface and have uniform monolayer thickness. Analysis of the graphene/Ru moiré structure shows that monocrystalline graphene domains are coherent across a large number of substrate grains. Hence, the size of monolayer graphene domains is not limited by grain boundaries in the metal template.
Discharge characteristics of He–Ne–Xe gas mixture with varying Xe contents and at varying sustain electrode gap lengths in the plasma display panel
Authors: Kwon Ohyung , Bae Hyun Sook , Whang Ki-Woong
Published: September 2009

The discharge characteristics of He–Ne–Xe gas mixture in the plasma display panel were investigated using a two-dimensional numerical simulation to understand the effects of adding He and varying the Xe contents in the gas mixture, and also varying sustain electrode gap. With 5% Xe content and 60 μm sustain electrode gap, decreased ionization led to the improvement of the vacuum ultraviolet (vuv) efficacy at increasing He mixing ratios. However, at 20% Xe content and 60 μm sustain electrode gap, increased electron heating improved the vuv efficacy until the He mixing ratio reached 0.7, but the efficacy decreased beyond the ratio of 0.7 due to the increased ionization of Xe atoms. At 5% Xe content and 200 μm sustain electrode gap, the vuv efficacy increased as a result of increased electron heating at the gap space at increasing He mixing ratios.
Electron paramagnetic resonance linewidth narrowing of Gd3+ ions in Y-doped ceria nanocrystals with decreasing crystallite size
Authors: Rakhmatullin R. M. , Aminov L. K. , Kurkin I. N. , Böttcher R. , Pöppl A. , Avila-Paredes H. , Kim S. , Sen S.
Published: September 2009

Electron paramagnetic resonance (EPR) spectra of Gd3+ ions in crystalline Ce1−x−yGdxYyO2−[0.5∗(x+y)] (x=0.0025, y=0.10, and 0.25) with crystallite sizes ranging from 600 nm down to 5 nm have been measured at X-band and at Q-band near liquid He and room temperatures. The EPR line shape is controlled by the low-symmetry surrounding of Gd3+ ions in a coordination environment with one oxygen-vacancy and seven oxygen nearest-neighbors forming GdO7 polyhedra. These coordination polyhedra are characterized by a wide distribution of crystal field parameters that primarily controls the EPR linewidth. The EPR linewidth of the central (−12↔+12) transition is observed to decrease systematically with decreasing crystallite size. This observation implies that the size of the crystallites in the nanoregime may have important influence on the energetics of vacancy distribution in crystalline materials.
Stepped light-induced transient measurements of photocurrent and voltage in dye-sensitized solar cells based on ZnO and ZnO:Ga
Authors: Gonçalves Agnaldo de Souza , Davolos Marian R. , Masaki Naruhiko , Yanagida Shozo , Mori Shogo , Nogueira Ana F.
Published: September 2009

In order to explain the higher short-circuit current (Jsc) with comparable open-circuit voltage (Voc) from dye-sensitized solar cells (DSCs) based on gallium-modified ZnO (ZnO:Ga) porous electrodes, the diffusion coefficient (D) and electron lifetime (τ) in DSCs with and without Ga-modified ZnO were studied by stepped light-induced transient measurements of photocurrent and voltage. In comparison to DSCs based on ZnO electrodes, the ZnO:Ga-based solar cells provided lower D and higher τ values. The results were interpreted according to the transport-limited recombination model, where the Ga modification induced a higher density of intraband charge traps. At matched electron densities, a decrease in Voc from DSCs based on ZnO:Ga was observed, suggesting a positive shift of the ZnO:Ga conduction band edge. The higher Jsc can be explained by the positive shift of the ZnO:Ga conduction band edge in addition to the increased roughness factor of the electrode due to the Ga modification.
Symmetries and alignment of biaxial nematic liquid crystals
Authors: Karahaliou Panagiota K. , Vanakaras Alexandros G. , Photinos Demetri J.
Published: September 2009

The possible symmetries of the biaxial nematic phase are examined against the implications of the presently available experimental results. Contrary to the widespread notion that biaxial nematics have orthorhombic symmetry, our study shows that a monoclinic (C2h) symmetry is more likely to be the case for the recently observed phase biaxiality in thermotropic bent-core and calamitic-tetrapode nematic systems. The methodology for differentiating between the possible symmetries of the biaxial nematic phase by NMR and by IR spectroscopy measurements is presented in detail. The manifestations of the different symmetries on the alignment of the biaxial phase are identified and their implications on the measurement and quantification of biaxiality as well as on the potential use of biaxial nematic liquid crystals in electro-optic applications are discussed.
Optical transitions and band gap discontinuities of GaInAsSb/AlGaAsSb quantum wells emitting in the 3 μm range determined by modulation spectroscopy
Authors: Motyka M. , Sęk G. , Ryczko K. , Misiewicz J. , Belahsene S. , Boissier G. , Rouillard Y.
Published: September 2009

Modulation spectroscopy, in a form of photoreflectance (PR), has been used to study the electronic structure properties of Ga0.55In0.45AsxSb1−x/Al0.30Ga0.70AsySb1−y quantum wells (QWs) designed for the 3 μm emission range at room temperature. A number of spectral features related to QW transitions have been revealed. With the support of energy level calculations they could be identified unambiguously for the unstrained (chemical) conduction band offset of 85%, almost independent of a small As/Sb content change in both the well and the barrier. This has been recalculated into the band discontinuities of the realistic (strained) structure, which have been found to be in a good agreement with the values obtained based on the first principles method.
Frequency response of large aperture oxide-confined 850 nm vertical cavity surface emitting lasers
Authors: Mutig A. , Blokhin S. A. , Nadtochiy A. M. , Fiol G. , Lott J. A. , Shchukin V. A. , Ledentsov N. N. , Bimberg D.
Published: September 2009

Small and large signal modulation measurements are carried out for 850 nm vertical cavity surface emitting lasers (VCSELs). The resonance frequency, damping factor, parasitic frequency, and D-factor are extracted. Small signal modulation bandwidths larger than 20 GHz are measured. At larger currents the frequency response becomes partially limited by the parasitics and damping. Our results indicate that by increasing the parasitic frequency, the optical 3 dB bandwidth may be extended to ∼25 GHz. A decrease in the damping should enable VCSEL bandwidths of 30 GHz for current densities not exceeding ∼10 kA/cm2 and ultimately error-free optical links at up to 40 Gbit/s.
Y–O hybridization in the ferroelectric transition of YMnO3
Authors: Kim Jinyoung , Cho Kyung Chul , Koo Yang Mo , Hong Kun Pyo , Shin Namsoo
Published: September 2009

The electron density distribution of paraelectric and ferroelectric YMnO3 are investigated by analyzing high temperature synchrotron radiation powder diffraction data using the maximum entropy method (MEM) and MEM-based pattern fitting combined with the Rietveld method. The results show that chemical bonding by orbital hybridization is established between the Y and in-plane O ions along the polar c-axis below the ferroelectric transition temperature. We suggest that the hybridization observed in the ferroelectric phase is the driving force for ferroelectricity in YMnO3.
Spectral shifts and helium configurations in H4eN–tetracene clusters
Authors: Whitley Heather D. , DuBois Jonathan L. , Whaley K. Birgitta
Published: September 2009

Spectral shifts of electronic transitions of tetracene in helium droplets are investigated in a theoretical study of H4eN–tetracene clusters with 1≤N≤150. Utilizing a pairwise interaction for the S0 state of tetracene with helium that is extended by semiempirical terms to construct a potential for the S1 state of tetracene with helium, the spectral shift is calculated from path integral Monte Carlo calculations of the helium equilibrium properties with tetracene in the S0 and S1 states at T=0 and at T=0.625 K. The calculated spectral shifts are in quantitative agreement with available experimental measurements for small values of N (≤8) at T∼0.4 K and show qualitative agreement for larger N (10–20). The extrapolated value of the spectral shift in large droplets (N∼104) is ∼90% of the experimentally measured value. We find no evidence of multiple configurations of helium for any cluster size for either the S0 or S1 state of tetracene. These results suggest that the observed spectral splitting of electronic transitions of tetracene in large helium droplets is not due to the coexistence of static metastable helium densities, unlike the situation previously analyzed for the phthalocyanine molecule.
Dynamic modifications of polarizability for large metallic spheroidal nanoshells
Authors: Chung H. Y. , Leung P. T. , Tsai D. P.
Published: September 2009

We present an approach alternative to the hybridization model for the treatment of the coupled interfacial plasmon modes in spheroidal metallic nanoshells. Rather than formulating the problem from the Lagrangian dynamics of the free electronic fluid, we adopt an effective medium approach together with the uniqueness of the solutions to electromagnetic boundary value problem, from which the polarizability of the shells can then be systematically and efficiently derived; and the resonance frequencies for the coupled modes can be obtained from the poles in the polarizability. This approach can treat confocal nanoshells with different geometries for the spheroidal cavity and external surface and allow for a natural extension to incorporate corrections from the finiteness of the optical wavelength which are important for nanoparticles of larger sizes. This thus surpasses the hybridization model which is limited to incorporate only the electrostatic Coulomb interaction between the uncoupled plasmons. Numerical results will be provided for different nanoshell systems, and for the illustration of the various geometric and dynamic effects from our model.
Large Rashba splitting in highly asymmetric CdTe/PbTe/PbSrTe quantum well structures
Authors: Jin Shuqiang , Wu Huizhen , Xu Tianning
Published: September 2009

The realization of PbTe/CdTe quantum structures and determination of highly asymmetric energy band make it feasible to construct asymmetric CdTe/PbTe/Pb1−xSrxTe quantum wells (QWs) for the probe of spintronics. Contrary to HgTe/CdTe QWs, the spin-orbit interaction in the CdTe/PbTe/Pb1−xSrxTe QWs is purely Rashba and anisotropic. Rashba splittings in the asymmetric QWs with different growth orientations and electron densities are explored. For the QWs grown along [110] direction the Rashba splitting for the oblique valley is particularly large (13.7 meV). The strong Rashba effect presented in the highly asymmetric QWs provides a potential candidate for spintronic devices.
Near edge x-ray absorption fine structure spectroscopy with x-ray free-electron lasers
Authors: Bernstein D. P. , Acremann Y. , Scherz A. , Burkhardt M. , Stöhr J. , Beye M. , Schlotter W. F. , Beeck T. , Sorgenfrei F. , Pietzsch A. , Wurth W. , Föhlisch A.
Published: September 2009

We demonstrate the feasibility of near edge x-ray absorption fine structure spectroscopy on solids by means of femtosecond soft x-ray pulses from a free-electron laser (FEL). Our experiments, carried out at the FEL at Hamburg used a special sample geometry, spectrographic energy dispersion, single shot position-sensitive detection, and a data normalization procedure that eliminates the severe fluctuations of the incident intensity in space and photon energy. As an example, we recorded the D31 N4,5 edge absorption resonance of La3+ ions in LaMnO3. Our study opens the door for x-ray absorption measurements on future x-ray FEL facilities.
Dynamics of emitting electrons in strong laser fields
Authors: Sokolov Igor V. , Naumova Natalia M. , Nees John A. , Mourou Gérard A. , Yanovsky Victor P.
Published: September 2009

A new derivation of the motion of a radiating electron is given, leading to a formulation that differs from the Lorentz–Abraham–Dirac equation and its published modifications. It satisfies the proper conservation laws. Particularly, it conserves the generalized momentum, eliminating the symmetry-breaking runaway solution. The equation allows a consistent calculation of the electron current, the radiation effect on the electron momentum, and the radiation itself, for a single electron or plasma electrons in strong electromagnetic fields. The equation is then applied to a simulation of a strong laser pulse interaction with a plasma target. Some analytical solutions are also provided.
Photocurrent spectroscopy investigation of deep level defects in Mg-doped GaN and Mg-doped AlxGa1−xN (0.20<x<0.52)
Authors: Batoni P. , Stokes E. B. , LeBoeuf S. F. , Nohava T.
Published: September 2009

Pulsed infrared photocurrent spectroscopy is used to investigate deep levels in highly resistive metal organic chemical vapor deposition-grown, magnesium-doped aluminum gallium nitride metal-semiconductor-metal test structures in the range of aluminum fraction from x=0.0 to x=0.52. Some background level of photocurrent is observed at all infrared pump wavelengths between 1.35 and 4.0 μm. The photocurrent decay time is a decreasing function of aluminum fraction. A peak photocurrent energy is observed for each aluminum fraction. With increasing aluminum fraction, the peak blueshifts and narrows.
Response properties with explicitly correlated coupled-cluster methods using a Slater-type correlation factor and cusp conditions
Authors: Hanauer Matthias , Köhn Andreas
Published: September 2009

The recently proposed extension of the explicitly correlated coupled-cluster ansatz using cusp conditions [A. Köhn, J. Chem. Phys. 130, 104104 (2009)] is tested for suitability in the calculation of response properties. For this purpose, static and dynamic electrical properties up to ESHG hyperpolarizabilities as well as optical rotations have been computed within the CCSD(F12) model. It is shown that effectively converged correlation contributions can reliably be obtained using augmented quadruple zeta basis sets already. The ansatz is optionally equipped with an extension capable of reducing the one-electron basis set error. A further simplification of the method specific Lagrangian aimed at reducing the computational effort has been tested and is shown to be uncritical. Furthermore, we examined the impact of conventional triple and quadruple excitations in explicitly correlated property calculations.
In situ studies of interfacial contact evolution via a two-axis deflecting cantilever microinstrument
Authors: Liu Fang , Laboriante Ian , Bush Brian , Roper Christopher S. , Carraro Carlo , Maboudian Roya
Published: September 2009

The time-dependent assessment of two contacting polycrystalline silicon surfaces is realized using a microinstrument that allows for in situ surface analysis. The evolution in contact resistance, morphology, and chemistry is probed as a function of contact cycle. Initially, the contact resistance is found to decrease and then increase with impact cycle. Upon prolonged cycling, the fracture of Si grains is observed which grow to form a wear crater. The electrical, morphological, and chemical analyses suggest that the wear of rough polysilicon surfaces due to impact proceeds through three distinct phases, namely plastic deformation of asperities, adhesive wear, and grain fracture.
ZnO(0001) surfaces probed by scanning tunneling spectroscopy: Evidence for an inhomogeneous electronic structure
Authors: Dumont J. , Hackens B. , Faniel S. , Mouthuy P.-O. , Sporken R. , Melinte S.
Published: September 2009

The stability of the polar Zn-terminated ZnO surface is probed by low-temperature scanning tunneling microscopy and scanning tunneling spectroscopy (STS). Surface states in the bandgap of ZnO are evidenced by STS and their presence is correlated with the local surface corrugation. Very defective surface regions are characterized by a bulk electronic structure showing a wide bandgap while nanometer-scale defect free regions exhibit a narrower bandgap and surface states. We also image atomically resolved (3×3)R30° reconstructions on the defect-free areas.
Stable ferromagnetism in p-type carbon-doped ZnO nanoneedles
Authors: Herng T. S. , Lau S. P. , Wei C. S. , Wang L. , Zhao B. C. , Tanemura M. , Akaike Y.
Published: September 2009

The authors report the synthesis and magnetic properties of carbon-doped ZnO (ZnO:C) nanoneedles. A saturated magnetic moment of 2.16 emu/cm3 was found in the ZnO:C nanoneedles. The samples showed anomalous Hall effect and p-type conduction with a hole concentration of 1.8×1018 cm−3. The ferromagnetism in the ZnO:C nanoneedles could be attributed to C substitution on the O site which introduces hole, so the p-p interaction leads to the strong spin interaction between the C atoms and carriers. It was found that the ferromagnetism and p-type conduction in the ZnO:C nanoneedles were stable in ambient air over a period of 1 year and annealing temperature of up to 100 °C.
Double aperture focusing transducer for controlling microparticle motions in trapezoidal microchannels with surface acoustic waves
Authors: Tan Ming K. , Tjeung Ricky , Ervin Hannah , Yeo Leslie Y. , Friend James
Published: September 2009

We present a method for controlling the motion of microparticles suspended in an aqueous solution, which fills in a microchannel fabricated into a piezoelectric substrate, using propagating surface acoustic waves. The cross-sectional shape of this microchannel is trapezoidal, preventing the formation of acoustic standing waves across the channel width and therefore allowing the steering of microparticles. The induced acoustic streaming transports these particles to eliminate the use of external pumps for fluid actuation.
Output power enhancement of light-emitting diodes via two-dimensional hole arrays generated by a monolayer of microspheres
Authors: Hou Chia-Hung , Tseng Shao-Ze , Chan Chia-Hua , Chen Tsing-Jen , Chien Hung-Ta , Hsiao Fu-Li , Chiu Hua-Kung , Lee Chien-Chieh , Tsai Yen-Ling , Chen Chii-Chang
Published: September 2009

The output power enhancement of the GaN-based light-emitting diodes (LEDs) featuring two-dimensional (2D) hole arrays is demonstrated. The 2D air hole arrays were first generated in the photoresist by utilizing the focusing nature of microspheres, and then transferred onto the GaN surface through dry etching. The maximum output power of the surface-textured LEDs was enhanced by 45% compared with the LEDs without surface texturing. The finite-difference time-domain calculation was performed and revealed that the light extraction efficiency of the textured LEDs increased with increasing etching depth.
Effects of independent double-gated configuration on polycrystalline-Si nonvolatile memory devices
Authors: Chen Wei-Chen , Lin Horng-Chih , Chang Yu-Chia , Huang Tiao-Yuan
Published: September 2009

A polycrystalline-Si thin-film transistor configured with independent double-gated structure and ultrathin channel film is proposed for use as a Si-oxide-nitride-oxide-Si memory device. Taking advantage of additional control gate bias offered by the independent double-gated scheme in addition to the driving gate, this work demonstrated that the reading window and programming efficiency can be improved by applying a proper control gate bias. It is also found that the relationship between programming/erasing speed and control gate bias is strongly related to channel film thickness. Our results indicate that the independent double-gated device possesses promising potential for future nonvolatile memory applications.
Influence of a static magnetic field on the photoluminescence of an ensemble of nitrogen-vacancy color centers in a diamond single-crystal
Authors: Lai Ngoc Diep , Zheng Dingwei , Jelezko Fedor , Treussart François , Roch Jean-François
Published: September 2009

We investigate the electron spin resonance of an ensemble of nitrogen-vacancy (NV) color centers in a bulk diamond crystal. The four possible orientations of the NV center in the lattice lead to different dependences on the magnitude and the orientation of an external static magnetic field. Experimental results obtained with a continuous microwave excitation are in good agreement with simulations. In addition, we observe that the average radiative lifetime of the NV color center is also modified when the external magnetic field is applied. This variation is explained by the mixing between mS=0 and mS=±1 spin states of the NV center with different radiative lifetimes, due to magnetic coupling. These results are of interest for a broad range of applications, such as spin-resonance-based magnetometry with a high-density ensemble of NV centers.
Polarization justified Fukui functions
Authors: Komorowski Ludwik , Lipiński Józef , Szarek Paweł
Published: September 2009

New Fukui functions have been derived within the conceptual density functional theory by the analysis of the polarization effect of a system in static electric field. Resulting Fukui functions accurately reproduce the global softness and electronic dipolar polarizability; they meet the condition ∫[f(r)/r]dr=−(∂μ/∂Z)N and lead to very reasonable values of the global hardness for atoms for the group of 29 main group elements. Computational clarity makes the new Fukui functions a promising tool in studies of molecular reactivity.
The third-order law for increments in magnetohydrodynamic turbulence with constant shear
Authors: Wan M. , Servidio S. , Oughton S. , Matthaeus W. H.
Published: September 2009

We extend the theory for third-order structure functions in homogeneous incompressible magnetohydrodynamic turbulence to the case in which a constant velocity shear is present. A generalization is found of the usual relation [Politano and Pouquet, Phys. Rev. E 57, 21 (1998)] between third-order structure functions and the dissipation rate in steady inertial range turbulence, in which the shear plays a crucial role. In particular, the presence of shear leads to a third-order law which is not simply proportional to the relative separation. Possible implications for laboratory and space plasmas are discussed.
Programming margin enlargement by material engineering for multilevel storage in phase-change memory
Authors: Yin You , Noguchi Tomoyuki , Ohno Hiroki , Hosaka Sumio
Published: September 2009

In this work, we investigate the effect of the material engineering on programming margin in the double-layered phase-change memory, which is the most important parameter for the stability of multilevel storage. Compared with the TiN/SbTeN cell, the TiSiN/GeSbTe double-layered cell exhibits the resistance ratio of the highest to lowest resistance levels up to two to three orders of magnitude, indicating much larger programming margin and thus higher stability and/or more available levels. Our calculation results show that the resistivities of the top heating layer and the phase-change layer have a significant effect on the programming margin.
Comment on “Equivalence of two approaches for quantum-classical hybrid systems” [J. Chem. Phys. 128, 204104 (2008)]
Authors: Gerasimenko V. I.
Published: September 2009

We discuss the links between consistent and approximate descriptions of the quantum-classical systems, i.e., systems composed of two interacting subsystems, one of which behaves almost classically while the other requires a quantum description.
High temperature excitonic lasing characteristics of randomly assembled SnO2 nanowires
Authors: Yang H. Y. , Yu S. F. , Tsang S. H. , Chen T. P. , Gao J. , Wu T.
Published: September 2009

The lasing characteristics of randomly assembled SnO2 nanowires, whose excitonic gain is attributed to the exciton states bounded to the surface defects, are studied from room temperature up to 500 K. It is found that the amount of excited carriers under the lasing conditions is well below the Mott density of SnO2 so that high pumping intensities have less influence on the radiative recombination mechanism and wavelength of the lasing peaks. Furthermore, the redshift of lasing peaks is mainly due to the reduction of bandgap energy of SnO2 with the increase of temperature.
Structure and photoluminescence of wurtzite/zinc-blende heterostructure GaN nanorods
Authors: Xu H. Y. , Liu Z. , Liang Y. , Rao Y. Y. , Zhang X. T. , Hark S. K.
Published: September 2009

GaN nanorods with a wurtzite/zinc-blende (WZ/ZB) heterostructure are synthesized by chemical vapor deposition. They have a triangular cross section and grow along the WZ [011¯0] direction. The WZ and ZB phases appear alternately along the nanorod’s transverse direction, forming a type-II superlattice structure. Two ultraviolet emission peaks dominate the photoluminescence spectra of the GaN nanorods. One originates from excitonic transitions within the WZ regions. The other shows an anomalous “S-shaped” energy shift with increasing temperature, and is attributed to radiative recombinations of carriers localized at potential fluctuations in ZB regions. The carrier localization also results in high luminescent efficiency of the GaN nanorods.
Orientation-controlled Si thin films on insulating substrates by Al-induced crystallization combined with interfacial-oxide layer modulation
Authors: Kurosawa Masashi , Kawabata Naoyuki , Sadoh Taizoh , Miyao Masanobu
Published: September 2009

Orientation-controlled Si films on transparent insulating substrates are strongly desired to achieve high-efficiency thin-film solar cells. We have developed the interfacial-oxide layer modulated Al-induced low temperature (<450 °C) crystallization technique, which enables dominantly (001) or (111)-oriented Si films with large grains (20–100 μm). These results are qualitatively explained on the basis of a model considering the phase transition of the interfacial Al oxide layers. This process provides the orientation-controlled Si templates on insulating substrates, which enables successive high quality epitaxial growth necessary for advanced Si thin-film solar cells.
Fencing artificial waterpoints failed to influence density and distribution of red kangaroos (Macropus rufus)
Authors: Fukuda Y. , McCallum H. I. , Grigg G. C. , Pople A. R.
Published: September 2009

Provision of artificial waterpoints in Australian rangelands has resulted in an increase in the range and density of kangaroos. At high densities, kangaroos can inhibit vegetation regeneration, particularly in some protected areas where harvesting is prohibited. Fencing off waterpoints has been proposed to limit these impacts. Our aim was to determine whether fencing off waterpoints during a drought (when kangaroos would be especially water-limited) would influence the density and distribution of red kangaroos (Macropus rufus). Two waterpoints were fenced within the first 6 months of the 27-month study and a further two waterpoints were kept unfenced as controls in Idalia National Park, western Queensland. We estimated kangaroo densities around waterpoints from walked line-transect counts, and their grazing distribution from dung-pellet counts. Fencing off waterpoints failed to influence either the density or distribution up to 4 km from the waterpoints. Our results indicate that food availability, rather than the location of waterpoints, determines kangaroo distribution. Few areas in the rangelands are beyond kangaroos’ convenient reach from permanent waterpoints. Therefore, fencing off waterpoints without explicitly considering the spatial context in relation to other available water sources will fail to achieve vegetation regeneration.
Aerial baiting with 1080 to control wild dogs does not affect the populations of two common small mammal species
Authors: Fenner Sally , Körtner Gerhard , Vernes Karl
Published: September 2009

More than most other animal control techniques, toxic baiting is fraught with the potential impact on non-target species. In the present study, we investigated the effect of aerial baiting with 1080 to control wild dogs in north-eastern New South Wales (NSW), Australia, on populations of southern bush rats (Rattus fuscipes assimilis) and brown antechinus (Antechinus stuartii), using a controlled experiment. Six populations, three each within widely spaced baited and unbaited trapping grids, were monitored before and after bait laying. To develop capture–mark–recapture indices, separate 4-day trapping surveys were undertaken twice before and twice after meat baits (250 g containing 6 mg sodium fluoroacetate, 1080) were delivered from a helicopter at 40 baits per kilometre. To assess non-fatal bait consumption, all baits contained rhodamine B (RhB), which gets incorporated into the vibrissae of animals that have ingested this marker. Neither mammal population decreased in size after baiting, nor was there any increase in population turnover rates or changes in the movement patterns of either species. Furthermore, no trapped animal tested positive for RhB, suggesting that these small mammals rarely consume meat baits, and that, at the population level, the impact of baiting on them was likely negligible. It is therefore unlikely that the current practise of aerial baiting in NSW, although effective in reducing dog activity, threatens populations of these two common species and perhaps small mammals in general.