bluuebunny/crossref_metadata_2025 huggingface dataset:
SNOMED CT’s Ontological Commitment
Authors: Schulz Stefan , Cornet Ronald
Published: July 2009

SNOMED CT is a clinical terminology that describes the meaning of terms by logical axioms. This requires an ontological commitment, i.e. precise agreements about the ontological nature of the entities referred to. We provide evidence that SNOMED implicitly supports at least three different kinds of commitments, viz. (i) independently existing entities, (ii) representational artifacts, and (iii) clinical situations. Our analysis shows how the truth-value of a sentence changes according to one of these perspectives. We argue that a clear understanding of to what kind of entities SNOMED CT concepts extend is crucial for the proper use and maintenance of SNOMED CT.
Providing a Realist Perspective on the eyeGENE Database System
Authors: Ceusters Werner
Published: July 2009

One of the achievements of the eyeGENE Network is a repository of DNA samples of patients with inherited eye diseases and an associated database that tracks key elements of phenotype and genotype information for each patient. Although its database structure serves its direct research needs, eyeGENE has set a goal of enhancing this structure to become increasingly well integrated with medical information standards over time. This goal should be achieved by ensuring semantic interoperability with other information systems but without adopting the incoherencies and inconsistencies found in available biomedical standards. Therefore, eyeGENE’s current pragmatic perspective with focus on data and information, rather than what the information is about, should shift to a realism-based perspective that includes also the portion of reality described, and the competing opinions that clinicians may hold about it. An analysis of eyeGENE’s database structure and user interfaces suggests that such a transition is possible indeed.
Computing the inverse of the neurophysiological spike-response transform
Authors: Brezina Vladimir , Stern Estee , Garcia-Crescioni Keyla , Miller Mark , Peskin Charles
Published: July 2009

Consider the transform from a discrete neuronal spike train to a continuous neurophysiological response such as postsynaptic membrane voltage or muscle contraction. Often, we can record only the response. Here we therefore ask about the inverse of this transform: given the response, how can we estimate from it the spike train that produced it? In previous work, we have developed a kernel-based "decoding" method for system identification of the forward transform. Using several variant approaches based on this method, here we demonstrate how to identify the spike train, in the minimal case from just the response, with synthetic as well as real synaptic and neuromuscular data.
Clonal Complexes in Biomedical Ontologies
Authors: Goldfain Albert , Cowell Lindsay , Smith Barry
Published: July 2009

An accurate classification of bacteria is essential for the proper identification of patient infections and subsequent treatment decisions. Multi-Locus Se-quence Typing (MLST) is a genetic technique for bacterial classification. MLST classifications are used to cluster bacteria into clonal complexes. Importantly, clonal complexes can serve as a biological species concept for bacteria, facilitating an otherwise difficult taxonomic classification. In this paper, we argue for the inclusion of terms relating to clonal complexes in biomedical ontologies.
Small regulatory non‐coding RNAs in bacteria: physiology and mechanistic aspects
Authors: Repoila Francis , Darfeuille Fabien
Published: July 2009

Regulatory ncRNAs (non‐coding RNAs) adjust bacterial physiology in response to environmental cues. ncRNAs can base‐pair to mRNAs and change their translation efficiency and/or their stability, or they can bind to proteins and modulate their activity. ncRNAs have been discovered in several species throughout the bacterial kingdom. This review illustrates the diversity of physiological processes and molecular mechanisms where ncRNAs are key regulators.
Social or Academic Language Intervention? You Don’t Have To Choose
Authors: Robinson Lee , Westby Carol
Published: July 2009

Students with a variety of types of language impairments exhibit deficits that affect both social interactions and academic performance. Two types of theory of mind underlie social and academic language skills: interpersonal and intrapersonal. In this article, the authors describe strategies for developing interpersonal and intrapersonal theory of mind abilities with the goal of promoting the inferencing skills essential for comprehension of social and academic language.
Teaching Conversation Skills to Children With High Functioning Autism/Asperger Syndrome
Authors: Breit-Smith Allison , Murray Donna S.
Published: July 2009

This article discusses the conversational abilities of children diagnosed with High functioning autism/Asperger’s syndrome in the context of the broader social deficits associated with the disorder and describes how social skills training groups might address conversation skill difficulties in this population. We present a template for how speech-language pathologists might structure a social skills training group to increase conversational responding in children with high functioning autism/Asperger’s syndrome.
Assessment and Treatment of Pragmatic Disorders: Integrating Linguistic and Neurocognitive Perspectives
Authors: Abdelal Ahmed M.
Published: July 2009

The increasing demand for pragmatic intervention, paucity of standardized diagnostic tools targeting this domain, and the impressive advances in neuroscientific research over the past decade have made it necessary for us to re-examine the way we conduct assessment and treatment of pragmatic disorders. This article uses a case study format to summarize an intervention framework that views pragmatics as an integrative, neurocognitive-linguistic domain.
The Communication Neuroscience Laboratories at the University of Kansas: An Overview
Authors: Barlow Steven M.
Published: July 2009

The Communication Neuroscience Laboratories (CNL) celebrates its 25th anniversary in 2009 with a brief overview of past and current research projects concerned with the sensorimotor development and control of orofacial and laryngeal systems subserving speech, vocalization, suck, oromotor, and aeroingestive behaviors in health and disease across the human life span. A key ingredient in the multidimensional study lines described in this review is the assembly and nurturing of a strong multidisciplinary research team involving students and research faculty from communication sciences, biology, neuroscience, bioengineering, computer science, neurology, radiology and medical physics, neonatology, nursing, pediatrics, and physical therapy. The transfer of technology from bench to bedside (or even cribside) is another important function. An example of an innovation from the CNL is highlighted by a new therapeutic sensorimotor entrainment intervention (NTrainer) that helps premature infants with feeding disorders develop ororhythmic (suck) skills. When possible, project lines are directed toward patient-oriented research and innovative interventions aimed at driving mechanisms of brain plasticity to improve communication/ oromotor function, neurodevelopmental outcomes, or both.
Orofacial Biomechanics and Speech Motor Control
Authors: Chu Shin Ying , Barlow Steven M.
Published: July 2009

The mechanical properties (e.g., mass, stiffness, viscoelasticity) of bone, cartilage, muscle, tendon, ligament, fat, and skin among articulatory subsystems involved in speech and gesture collectively influence all aspects of movement and must be accounted for in the selection and sequencing of motor program elements. Damage or disease processes affecting peripheral or central nervous system function, or both, can affect muscle coordination and alter muscle stiffness. Therefore, the biomechanics of orofacial and vocal tract structures should be taken into account when considering the movement patterns and network signaling in the neuromotor control system in health and disease. The purpose of this report is to summarize our evolving approach to and application of orofacial biomechanics in the context of movement disorders associated with dysarthria and craniofacial anomalies. We describe a new application for mapping stiffness in the lips for clinical application in pediatric and adult populations.
Facilitating or Inhibiting Newcomer Socialisation Outcomes in International Hotels
Authors: Yang Jen-Te
Published: July 2009

The purpose of this study is to explore the effects of social interaction, work group autonomy, information-seeking behaviour, work stress and role conflict on newcomer socialisation outcomes in terms of individual job competences. The research samples have been drawn from all levels of employees in the organisational hierarchy of 61 international tourist hotels in Taiwan. The questionnaires were distributed to 1380 voluntary participants who had worked in the current hotels for between 3 and 6 months. The study of the 428 respondents shows that the newcomers preferred to use observation and reading approaches to seek information. It also shows that socialisation outcomes - in terms of individual job competences - were predicted at a significant level negatively by role conflict and work stress, and positively by social interaction and the monitor approach of information-seeking behaviour. This study suggests that an organisation should develop social activities to strengthen interpersonal relationships and mutual understanding among employees in a workgroup, as this would enable them to feel more open to discuss job-related matters at work.
Enhanced open-circuit voltage in polymer solar cells
Authors: Luo Jie , Wu Hongbin , He Chao , Li Aiyuan , Yang Wei , Cao Yong
Published: July 2009

We reported that the open-circuit voltage (VOC) of polymer solar cells (PSCs) can be enhanced by 0.3 V via inserting a thin layer of alcohol/water-soluble polyelectrolyte between the active layer and metal electrode. The origin of the increase in VOC can be attributed to the superposition of the built-in field with the interfacial dipole of the interlayer, and the existence of the interlayer as a dielectric was confirmed by ac impedance spectroscopy. The significant enhancement in VOC and the simplicity of incorporation of interlayer by solution processing make this method a good candidate for further enhancing the performance of PSCs.
Observation of torsional mode in CdS1−xSex nanoparticles in a borosilicate glass
Authors: Gupta Sanjeev K. , Sahoo Satyaprakash , Jha Prafulla K. , Arora A. K. , Azhniuk Y. M.
Published: July 2009

Phonon modes found in low-frequency Raman scattering from CdS1−xSex nanocrystals embedded in a borosilicate glass arising from confined acoustic phonons are investigated. In addition to the breathing and quadrupolar modes, two additional modes are found in the spectra. In order to assign the new modes, confined acoustic phonon frequencies are calculated using the complex frequency model, the core-shell model, and the Lamb model. Based on the ratio of the frequencies of the new modes to those of the quadrupolar mode, the new modes are assigned to the first overtone of the quadrupolar mode (l=2, n=1) and to the l=1, n=0 torsional mode. To confirm the assignment of the torsional mode, the polarized Raman scattering measurements in parallel-polarized (VV) and perpendicular-polarized (VH) symmetries are performed. The torsional mode is present in both VV and VH symmetries. The appearance of the forbidden torsional mode is attributed to the near-spherical shape of the nanoparticle found from high-resolution transmission electron microscopy and its interaction with the surrounding medium.
Modeling charge transport in graphene nanoribbons and carbon nanotubes using a Schrödinger-Poisson solver
Authors: Odili D. I. , Wu Y. , Childs P. A. , Herbert D. C.
Published: July 2009

Interest in carbon-based electronics has been stimulated in recent years, initially through the discovery of carbon nanotubes, but recently with the formation of graphene layers. In this paper metal-oxide-semiconductor (MOS) systems based on these carbon structures are used to model and compare charge transport within them. Schrödinger’s equation is solved self-consistently with Poisson’s equation, using the scattering matrix method. A tight-binding model is used to determine the energy band structure in graphene. The current-voltage characteristics of MOS devices based on graphene and those based on carbon nanotubes demonstrate significant differences associated with their respective transmission probabilities.
Spin-orbit coupling effects in dihydrides of third-row transition elements. II. Interplay of nonadiabatic coupling in the dissociation path of rhenium dihydride
Authors: Koseki Shiro , Shimakura Noriyuki , Fujimura Yuichi , Asada Toshio , Kono Hirohiko
Published: July 2009

This is the second paper in a series of investigations on spin-orbit coupling (SOC) effects in dihydrides of third-row transition elements. The dissociation path of rhenium dihydride was explored using the multiconfiguration self-consistent-field method followed by diagonalization of SOC matrices, in which the Stevens–Basch–Krauss–Jasien–Cundari (SBKJC) basis sets were employed after adding one set of polarization functions for each atom. The most stable rhenium dihydride has a linear structure and its ground state is Σ6g+. Both C2v and Cs dissociation paths into a Re atom and a hydrogen molecule (Re(S6)+H2(Σ1g+)) were explored on the potential energy curves of low-lying states. A relatively high energy barrier was obtained along the C2v path and two conical intersections were found at the H–Re–H angles of 29.8° and 96.1° along the C2v path. Since it was revealed that the geometrical deformation to Cs symmetry at the H–Re–H angle of 29.8° does not provide explicit lowering of the energy barrier for the dissociation, even after considering nonadiabatic couplings (NACs) in the neighborhood of the conical intersections, it can be concluded that the most feasible path is hopping from the lowest A61 state to the lowest B62 state at the H–Re–H angle of 96.1° followed by hopping from the lowest B62 state back to the lowest A61 state at the H–Re–H angle of 29.8°, where the latter crossing point is the highest in energy along this path. Thus, when the molecular system can reach the areas of these crossing points, the molecular system hops from one of the states to another owing to NAC or SOC effects; especially, SOC effects become important at the crossing point with C2v symmetry.
Zero-quantum frequency-selective recoupling of homonuclear dipole-dipole interactions in solid state nuclear magnetic resonance
Authors: Hu Kan-Nian , Tycko Robert
Published: July 2009

We describe a method for measuring magnetic dipole-dipole interactions, and hence distances, between pairs of like nuclear spins in a many-spin system under magic-angle spinning (MAS). This method employs a homonuclear dipolar recoupling sequence that creates an average dipole-dipole coupling Hamiltonian under MAS with full zero-quantum symmetry, including both secular and flip-flop terms. Flip-flop terms are then attenuated by inserting rotor-synchronized periods of chemical shift evolution between recoupling blocks, leaving an effective Hamiltonian that contains only secular terms to a good approximation. Couplings between specific pairs of nuclear spins can then be selected with frequency-selective π pulses. We demonstrate this technique, which we call zero-quantum shift evolution assisted homonuclear recoupling, in a series of one-dimensional and two-dimensional C13 NMR experiments at 17.6 T and 40.00 kHz MAS frequency on uniformly C13-labeled L-threonine powder and on the helix-forming peptide MB(i+4)EK, synthesized with a pair of uniformly C13-labeled L-alanine residues. Experimental demonstrations include measurements of distances between C13 sites that are separated by three bonds, placing quantitative constraints on both sidechain and backbone torsion angles in polypeptides.
Size-dependent formation enthalpy of nanoclusters
Authors: Yang C. C. , Li S.
Published: July 2009

The size-dependent formation enthalpies of Sn and SnTe nanoclusters are investigated using a nanothermodynamic model based on the liquid-droplet model (LDM) and the modified broken-bond theory. The bulk cohesive energy of SnTe used in the modeling was verified by ab initio density functional theory. The results show that the formation enthalpy increases with decreasing cluster size, which is in good agreement with the experimental data. With considering the size-independent surface energy and surface/volume ratio, the developed model possesses a better applicability than LDM and may provide new insight into the fundamental understanding of the thermal stability of nanoclusters.
Correlation-induced corrections to the band structure of boron nitride: A wave-function-based approach
Authors: Stoyanova A. , Hozoi L. , Fulde P. , Stoll H.
Published: July 2009

We present a systematic study of the correlation-induced corrections to the electronic band structure of zinc-blende BN. Our investigation employs an ab initio wave-function-based local Hamiltonian approach which offers a rigorous theoretical framework for the calculation of the polarization and local charge redistribution effects around an extra electron or hole placed into the conduction or valence bands of semiconducting and insulating materials. Moreover, electron correlations beyond relaxation and polarization can be readily incorporated. The electron correlation treatment is performed on finite clusters. In conducting our study, we make use of localized Wannier functions and embedding potentials derived explicitly from prior periodic Hartree–Fock calculations. The on-site and nearest-neighbor charge relaxations bring corrections of several eV to the Hartree–Fock band gap. Additional corrections are caused by long-range polarization effects. In contrast, the dispersion of the Hartree–Fock bands is marginally affected by electron correlations. Our final result for the fundamental gap of zinc-blende BN compares well with that derived from soft x-ray experiments at the B and N K-edges.
Towards an optimum coupling between Er ions and Si-based sensitizers for integrated active photonics
Authors: Hijazi K. , Rizk R. , Cardin J. , Khomenkova L. , Gourbilleau F.
Published: July 2009

Series of Er-doped Si-rich silicon oxide layers were studied with the aim of optimizing the coupling between Er ions and the Si-based sensitizers. The layers were grown at substrate temperature between 400 and 600°C by the cosputtering of three confocal targets: Si, SiO2, and Er2O3. The influence of Si excess (5–15at.%) and annealing temperature (500–1100°C) was examined for two concentrations of Er ions (3.5×1020 and ∼1021cm−3). We report the first observation of significant Er photoluminescence (PL) from as-grown samples excited by a nonresonant 476nm line, with a lifetime in the range of 1.3–4ms. This suggests the occurrence of an indirect excitation of Er through Si-based entities formed during the deposition. A notable improvement was observed for both Er PL intensity and lifetime after annealing at 600°C. This temperature is lower than that required for phase separation, suggesting the formation of “atomic scale” sensitizers (Si agglomerates, for example) considered in recent work. For high Er doping (∼1021cm−3), an optimum Er PL was obtained for the sample grown at 500°C, annealed at 600°C, and containing ∼13at.% of Si excess. This high PL should correspond to an optimum fraction of coupled Er for this series, which was roughly estimated to about 11% of the total Er content for an excitation photon flux of few 1019phcm−2s−1. For the moderately Er-doped series (3.5×1020cm−3) grown at 500°C, the optimum Er PL was found for the samples containing about 9at.% silicon and annealed in the 600–900°C range. The time decay reached a value as high as 9ms for low Si excess (<6at.%) and 6–7.5ms for high values of Si excess. The fraction of Er ions coupled to sensitizers was similarly estimated for the best sample of this series and found to be as high as 22% of the total Er content.
Removing the discontinuous shifts in emission wavelength of a chiral nematic liquid crystal laser
Authors: Morris S. M. , Ford A. D. , Coles H. J.
Published: July 2009

The laser wavelength of a band-edge liquid crystal laser is known to vary in a stepwise fashion with temperature. This report describes a method for removing the discontinuous shifts in the laser wavelength by doping a nematic sample with two different chiral dopants which exhibit opposing dependences of the natural pitch on temperature. On cooling from the isotropic phase to room temperature the total shift of the laser wavelength is 15 nm with no discontinuities. This is in contrast to that observed for samples consisting of only one chiral dopant whereby the wavelength shift was as large as 75 nm for the same temperature range.
Shock-induced disproportionation of mullite (3Al2O3⋅2SiO2)
Authors: Kawai Nobuaki , Atou Toshiyuki , Nakamura Kazutaka G. , Kondo Ken-ichi , Ito Shun , Yubuta Kunio , Kikuchi Masae
Published: July 2009

Shock-recovery experiments have been performed on high-purity mullite polycrystals in the pressure range up to 72GPa. The recovered samples have been examined by an x-ray diffraction method, nuclear magnetic resonance spectroscopy, and transmission electron microscopy. The samples shocked above 65GPa contain an amorphous SiO2 phase and a γ-Al2O3 phase, indicating that a rapid disproportionation reaction of mullite is induced by shock compression. The recovered amorphous SiO2 has a mean Si–O–Si bond angle roughly 7° narrower than that of the fused SiO2 glass, indicating the formation of the densified amorphous SiO2 phase. The γ-Al2O3 phase is crystallized as very fine particles with grain sizes less than 10nm in the matrix of the desified amorphous SiO2 phase. The crystallization of γ-Al2O3 is expected to occur during a pressure-release process owing to the crystal size effect concerning the phase stability of Al2O3.
Effects of gold patterning on the bending profile and frequency response of a microcantilever
Authors: Lee Dongkyu , Kim Seonghwan , Jung Namchul , Thundat Thomas , Jeon Sangmin
Published: July 2009

We have systematically investigated the effect of various gold patterns on the bending profile and frequency response of a microcantilever. The gold patterns were deposited on the cantilever arrays using four types of shadow mask. The local bending profile, slope, and curvature varied depending on the area and position of the gold pattern. Also, the variations in the first three modes of the flexural resonance frequencies of the gold patterned cantilevers were measured to understand the opposing effects of mass loading and flexural rigidity; both of these parameters are dependent on the position and area of the gold pattern. The experimental results validated the theoretical one-dimensional model introduced by Tamayo et al. [Appl. Phys. Lett. 89, 224104 (2006)] and our calculations using the finite element method. The gold patterns giving the maximum response of the mass loading and flexural rigidity change were determined by examining how the relative resonance frequency shifts as a function of the distance of the gold coating from the free end or clamping region. The results of this study can potentially be applied in the design of a microcantilever sensor in which pattern analysis is utilized to determine the presence of adsorbed biological and chemical molecules.
Antireflective coating using aluminum hydroxide formed by hydrothermal treatment of sputtered aluminum films
Authors: Ishiguro Takashi , Hori Toshiyuki , Qiu Zhiyong
Published: July 2009

Here we have proposed a simple method for forming antireflective coating. By putting a rf sputtered metallic Al film into boiling ultrapure water, the film becomes transparent. Its optical transmittance exceeds the glass substrate itself. In addition, the glass substrate with such coating on both sides shows almost perfect transmittance at specific wavelengths. By electron diffraction, the crystal structure of the transformed film is confirmed to be boehmite. The refractive index of the transparent film is estimated to be one of the median values of the glass and air.
Improving thermoelectric performance of caged compounds through light-element filling
Authors: Pei Y. Z. , Yang Jiong , Chen L. D. , Zhang W. , Salvador J. R. , Yang Jihui
Published: July 2009

Heavy elements filling have been considered the most effective way to improve the thermoelectric performance of caged compounds such as CoSb3 by reducing kL. Here, we show an opposite example of filling a light element, Na, into CoSb3 for obtaining high thermoelectric figure of merit ZT.ZT=1.25 at 850 K for Na0.48Co4Sb12 is one of the highest values among all reported single-element-filled CoSb3. The Na-filling scatters phonons less effectively but it results in relatively high mobility thus large power factor. This most likely comes from the extra electronic states near the Fermi level induced by Na.
Origin of remarkable positive temperature coefficient effect in the modified carbon black and carbon fiber cofillled polymer composites
Authors: Dang Zhi-Min , Li Wei-Kang , Xu Hai-Ping
Published: July 2009

In order to achieve a desired conductivity and further improvement in positive temperature coefficient (PTC) effect, carbon fibers (CFs) are incorporated into the modified nanoscale carbon black (MNCB) filled polymer composites. The CF with high aspect ratio can easily span across insulating regions and further connect the existing conductive pathways. In this work, the total volume fraction of MNCB and CF is set as 8vol%. When the concentration of CF reaches a certain value, we observe remarkably improved PTC intensity (PTCI).The PTCI is nearly two orders of magnitude larger than that in the MNCB filled polymer (same at 8 vol % loading). When compared to the polymer composites only loaded with MNCB, the negative temperature coefficient effect in the (CF-MNCB)/polymer composites was also weakened to some extent. These results can be explained by considering the change in microstructure of the (CF-MNCB)/polymer composites.
Dielectric properties of a-axis-oriented orthorhombic HoMnO3 thin films
Authors: Wang Weitian , Yuan Dehua , Sun Yuming , Sun Yuanping
Published: July 2009

Orthorhombic HoMnO3 films were prepared epitaxially on Nb-doped SrTiO3 (110) single crystal substrates by using pulsed laser deposition technique. The films showed perfectly a-axis crystallographic orientations and were well aligned with the substrates. The complex dielectric properties of HoMnO3 films were measured as functions of temperature (77–250 K) and frequency (100 Hz–100 kHz). Thermally activated dielectric relaxations were found, and the respective peaks shifted to higher temperatures as the measuring frequency increased. The frequency dependence of dielectric properties was ascribed to the universal dielectric response models, and the hopping conductivity and the dipolar effects induced by the charge carriers were used to explain the results.
Effects of the rotational excitation of D2 and of the potential energy surface on the H++D2→HD+D+ reaction
Authors: González-Lezana T. , Honvault P. , Jambrina P. G. , Aoiz F. J. , Launay J.-M.
Published: July 2009

The H++D2→HD+D+ reaction has been theoretically investigated by means of an exact quantum mechanical approach, a quasiclassical trajectory method, and two statistical methods based in the propagation of either wave functions or trajectories. The study addresses the possible changes on the overall dynamics of the title reaction when the D2 diatom is rotationally excited to its v=0, j=1 state. In addition, the reactivity for the ground rotational state on two different potential energy surfaces (PESs), namely, the surface by Aguado et al. [J. Chem. Phys. 112, 1240 (2000)] and the PES by Kamisaka et al. [J. Chem. Phys. 116, 654 (2002)], is examined. Reaction probabilities and cross sections at 0.524 and 0.1 eV collision energies are calculated. The major differences with respect to the reaction initiated with D2 in its ground rovibrational state are observed for the lowest collision energy Ec=0.1 eV. Differential cross sections have been found to depend to some extend on the PES employed. In addition, at Ec=0.1 eV further discrepancies in the total and rotational cross sections are noticeable.
A decentralized adaptive robust method for chaos control
Authors: Kobravi Hamid-Reza , Erfanian Abbas
Published: July 2009

This paper presents a control strategy, which is based on sliding mode control, adaptive control, and fuzzy logic system for controlling the chaotic dynamics. We consider this control paradigm in chaotic systems where the equations of motion are not known. The proposed control strategy is robust against the external noise disturbance and system parameter variations and can be used to convert the chaotic orbits not only to the desired periodic ones but also to any desired chaotic motions. Simulation results of controlling some typical higher order chaotic systems demonstrate the effectiveness of the proposed control method.
Anisotropic thermal expansion of RuCo alloys in carbon nanotube matrix
Authors: Qadri S. B. , Keller T. M. , Laskoski M. , Husz A. M. , Mahadik N. A.
Published: July 2009

Ru 1 − x Co x alloys exhibit hexagonal close packed phase for x≤0.75. The nanocrystalline samples of Ru1−xCox alloys in the presence of carbon nanotubes were prepared by organometallic synthesis and their thermal expansion coefficients were determined using high resolution x-ray diffraction over a temperature range of 25–250 °C. The coefficients of linear thermal expansions (CTE) showed anisotropy along the c- and a-axis. The CTE values showed dependence on the composition and varied between 8.8×10−6/°C to 16.1×10−6/°C for c-axis (α∥) and 5.9×10−6/°C to 12.6×10−6/°C for a-axis (α⊥). These results suggest that RuCo alloys have low thermal expansivity and allow the tailoring of their thermal properties. The radial thermal expansion coefficient (αc) of carbon nanotube was 26×10−6/°C.
Three-dimensional surface profile measurement using a beam scanning chromatic confocal microscope
Authors: Chun Byung Seon , Kim Kwangsoo , Gweon Daegab
Published: July 2009

In this research, chromatic confocal microscopy with transverse point beam scanning is constructed for three-dimensional surface measurement without longitudinal mechanical translation. In beam scanning chromatic confocal microscopy, the wavelength-to-depth relation and the lateral field of view should be determined considering the beam scanning angle. With the experimental results from a sample structure, the three-dimensional profile is reconstructed by relating the wavelength and scanning angle to the axial and the lateral coordinates.
Optical black hole: Broadband omnidirectional light absorber
Authors: Narimanov Evgenii E. , Kildishev Alexander V.
Published: July 2009

We develop an approach to broad-band omnidirectional light absorption, based on light propagation in a metamaterial structure forming an effective “black hole.” The proposed system does not rely on magnetic response, is nonresonant, and can be fabricated from existing materials.
Role of natural length and time scales on shear driven two-dimensional electron magnetohydrodynamic instability
Authors: Gaur Gurudatt , Sundar Sita , Yadav Sharad K. , Das Amita , Kaw Predhiman , Sharma Sarveshwar
Published: July 2009

The electron magnetohydrodynamic (EMHD) model represents an incompressible electron fluid flow against a static neutralizing background ion species. In contrast to hydrodynamic fluid models the EMHD model contains intrinsic length (the electron skin depth) and time scale (the whistler period). The paper discusses the role of skin depth and the existence of whistler waves on a prominent fluid instability, namely, the velocity shear driven Kelvin–Helmholtz instability in the context of two-dimensional EMHD. Numerical simulations are also carried out to understand the role played by the whistler waves in the nonlinear saturated regime of the instability.
Ultrafast absorption recovery dynamics of 1300 nm quantum dot saturable absorber mirrors
Authors: Lumb M. P. , Clarke E. , Harbord E. , Spencer P. , Murray R. , Masia F. , Borri P. , Langbein W. , Leburn C. G. , Jappy C. , Metzger N. K. , Brown C. T. A. , Sibbett W.
Published: July 2009

We compare the performance of two quantum dot saturable absorber mirrors with one device operating at the quantum dot ground state transition whereas the other operates at the first excited state transition. Time-resolved photoluminescence and heterodyne four-wave mixing experiments demonstrate faster recovery of the excited-state device compared to the ground-state device. Femtosecond pulses were achieved with both devices, with the ground-state device producing 91 fs pulses and the excited-state device producing 86 fs pulses in a Cr:forsterite laser. The fast absorption recovery dynamics indicates the potential of devices exploiting excited-state transitions for use in high repetition rate lasers.
Excited state reaction dynamics of Ti(aF5J)+O2→TiO(A,B)+O studied by a crossed-beam technique
Authors: Yamashiro Ryo , Matsumoto Yoshiteru , Honma Kenji
Published: July 2009

Oxidation reactions of the gas-phase titanium atom in its excited state with oxygen molecule, Ti(aF5J)+O2→TiO(A3Φ,B3Π)+O, were studied by a crossed-beam technique. Metastable excited Ti, Ti(aF5J), was generated by an optical pumping method and the reaction products were detected by the chemiluminescence spectroscopy. The chemiluminescence from TiO(A3Φ,B3Π) was analyzed to determine vib-rotational state distributions of both excited states and their branching ratio. The vib-rotational state distribution of TiO(B) was represented by the statistical energy disposal and the branching ratio of TiO(A)/TiO(B) was also consistent with the statistical expectation. These results suggested the presence of long-lived intermediates in the course of the reactions of the excited Ti(aF5J) atom with O2. Also observed was the significant deviation of the vibrational state distribution of TiO(A) from the statistical one and another reaction pathway which may not proceed via the long-lived intermediates was implied.
Dopant distribution in gate electrode of n- and p-type metal-oxide-semiconductor field effect transistor by laser-assisted atom probe
Authors: Inoue K. , Yano F. , Nishida A. , Takamizawa H. , Tsunomura T. , Nagai Y. , Hasegawa M.
Published: July 2009

Three dimensional dopant distributions in polycrystalline Si gate of n-type (n-) and p-type (p-) metal-oxide-semiconductor field effect transistor (MOSFET) structure were investigated by laser-assisted three dimensional atom probe. The remarkable difference in dopant distribution between n-MOSFET and p-MOSFET was clearly observed. In n-MOSFET gate, As and P atoms were segregated at grain boundaries and the interface between gate and gate oxide. No diffusion of As and P atoms into the gate oxide was observed. On the other hand, in p-MOSFET, no segregations of B atoms at grain boundaries or the interface were observed, and diffusion of B atoms into the gate oxide was directly observed.
Quantum Monte Carlo ground state energies for the atoms Li through Ar
Authors: Buendía E. , Gálvez F. J. , Maldonado P. , Sarsa A.
Published: July 2009

All-electron quantum Monte Carlo energies are reported for the ground state of the atoms Li to Ar. The present work is mainly focused on the atoms Na to Ar as well as in those that have a stronger multiconfiguration nature, i.e., Be, B, and C and Mg, Al, and Si. Explicitly correlated wave functions with a single configuration model function times a Jastrow factor are employed for all of the atoms studied. The accuracy obtained for the atoms Na to Ar is similar to that reached for the atoms Li to Ne. In addition, a restricted multiconfiguration expansion has been employed for the atoms Be, B, and C and Mg, Al, and Si obtaining accurate results. Near degeneracy and the effect of other configurations are systematically analyzed for these systems, at both variational and diffusion Monte Carlo levels.
Direct observation of the controlled magnetization reversal processes in Py/Al/Py asymmetric ring stacks
Authors: Huang L. , Schofield M. A. , Zhu Y.
Published: July 2009

Electron holographic experiments were performed to study the magnetization reversal process of patterned Py/Al/Py (20nm/20nm/10nm) asymmetric ring stacks. By changing the in-plane field applied perpendicular to the ring’s symmetric axis, we directly observed the vortex-based magnetization reversal process through controlled domain wall motion and annihilation. The two magnetic layers were found to switch at different critical fields, leading to the existence of various distinct domain state combinations. Quantitative agreement was obtained between measured phase shifts and those derived from micromagnetic calculations, which allows us to resolve the layer-by-layer magnetic behavior as a function of applied external field.
Work flux density measurements in a pulse tube engine
Authors: Yoshida T. , Yazaki T. , Futaki H. , Hamaguchi K. , Biwa T.
Published: July 2009

A heat engine called a pulse tube engine has been recently proposed, which consists of only a few parts, namely, differentially heated stacked metal meshes in a cylinder and one piston, coupled to a flywheel. We built the prototype engine and tested its working mechanism from the standpoint of a thermoacoustic framework. We measured the work flux density distribution over the cross section of the pulse tube to elucidate the work source of the engine. This engine belongs to the standing wave engine group and the work source resides not in the stacked metal meshes but in the pulse tube.
Synchronization of delay-coupled nonlinear oscillators: An approach based on the stability analysis of synchronized equilibria
Authors: Michiels Wim , Nijmeijer Henk
Published: July 2009

We consider the synchronization problem of an arbitrary number of coupled nonlinear oscillators with delays in the interconnections. The network topology is described by a directed graph. Unlike the conventional approach of deriving directly sufficient synchronization conditions, the approach of the paper starts from an exact stability analysis in a (gain, delay) parameter space of a synchronized equilibrium and extracts insights from an analysis of its bifurcations and from the corresponding emerging behavior. Instrumental to this analysis a factorization of the characteristic equation is employed that not only facilitates the analysis and reduces computational cost but also allows to determine the precise role of the individual agents and the topology of the network in the (in)stability mechanisms. The study provides an algorithm to perform a stability and bifurcation analysis of synchronized equilibria. Furthermore, it reveals fundamental limitations to synchronization and it explains under which conditions on the topology of the network and on the characteristics of the coupling the systems are expected to synchronize. In the second part of the paper the results are applied to coupled Lorenz systems. The main results show that for sufficiently large coupling gains, delay-coupled Lorenz systems exhibit a generic behavior that does not depend on the number of systems and the topology of the network, as long as some basic assumptions are satisfied, including the strong connectivity of the graph. Here the linearized stability analysis is strengthened by a nonlinear stability analysis which confirms the predictions based on the linearized stability and bifurcation analysis. This illustrates the usefulness of the exact linearized analysis in a situation where a direct nonlinear stability analysis is not possible or where it yields conservative conditions from which it is hard to get qualitative insights in the synchronization mechanisms and their scaling properties. In the examples several network topologies are considered.
Synchronization of low-frequency oscillations in the human cardiovascular system
Authors: Karavaev A. S. , Prokhorov M. D. , Ponomarenko V. I. , Kiselev A. R. , Gridnev V. I. , Ruban E. I. , Bezruchko B. P.
Published: July 2009

We investigate synchronization between the low-frequency oscillations of heart rate and blood pressure having in humans a basic frequency close to 0.1 Hz. A method is proposed for quantitative estimation of synchronization between these oscillating processes based on calculation of relative time of phase synchronization of oscillations. It is shown that healthy subjects exhibit on average substantially longer epochs of internal synchronization between the low-frequency oscillations in heart rate and blood pressure than patients after acute myocardial infarction.
Magnetron injection gun for a broadband gyrotron backward-wave oscillator
Authors: Yuan C. P. , Chang T. H. , Chen N. C. , Yeh Y. S.
Published: July 2009

The magnetron injection gun is capable of generating relativistic electron beam with high velocity ratio and low velocity spread for a gyrotron backward-wave oscillator (gyro-BWO). However, the velocity ratio (α) varies drastically against both the magnetic field and the beam voltage, which significantly limits the tuning bandwidth of a gyro-BWO. This study remedies this drawback by adding a variable trim field to adjust the magnetic compression ratio when changing the operating conditions. Theoretical results obtained by employing a two-dimensional electron gun code (EGUN) demonstrate a constant velocity ratio of 1.5 with a low axial velocity spread of 6% from 3.4–4.8 Tesla. These results are compared with a three-dimensional particle-tracing code (computer simulation technology, CST). The underlying physics for constant α will be discussed in depth.
The effect of off-axis neutral beam injection on sawtooth stability in ASDEX Upgrade and Mega-Ampere Spherical Tokamak
Authors: Chapman I. T. , de Bock M. F. , Pinches S. D. , Turnyanskiy M. R. ,   MAST Team, Igochine V. G. , Maraschek M. , Tardini G. ,   ASDEX Upgrade Team
Published: July 2009

Sawtooth behavior has been investigated in plasmas heated with off-axis neutral beam injection in ASDEX Upgrade [A. Herrmann and O. Gruber, Fusion Sci. Technol. 44, 569 (2003)] and the Mega-Ampere Spherical Tokamak (MAST) [A. Sykes et al., Nucl. Fusion 41, 1423 (2001)]. Provided that the fast ions are well confined, the sawtooth period is found to decrease as the neutral beam is injected further off-axis. Drift kinetic modeling of such discharges qualitatively shows that the passing fast ions born outside the q=1 rational surface can destabilize the n=1 internal kink mode, thought to be related to the sawtooth instability. This effect can be enhanced by optimizing the deposition of the off-axis beam energetic particle population with respect to the mode location.
Polarization rotation contributions to dielectric nonlinearity in 65Pb(Mg1/3Nb2/3)O3–35PbTiO3 single crystals
Authors: Bernal Ashley , Bassiri-Gharb Nazanin
Published: July 2009

The dielectric response of 65Pb(Mg1/3Nb2/3)O3–35PbTiO3 (PMN-35PT) single crystals is reported for ac field amplitudes up to ∼3.5 kV/cm over a frequency range from 3 Hz to 1 kHz. The nonlinear dielectric response is described by a Rayleigh-like analysis, indicating extrinsic contributions from nonlinear and hysteretic motion of internal interfaces (phase boundaries and domain walls). Furthermore, the extrinsic contributions are more than five times higher in the [110]- and [001]-poled crystals than crystals poled along the [111] axis. This is attributed to the ease of the polarization vector rotation along the MC mirror plane between orthorhombic and tetragonal phases of PMN-35PT.
Local temperature control of photonic crystal devices via micron-scale electrical heaters
Authors: Faraon Andrei , Vučković Jelena
Published: July 2009

We demonstrate a method to locally control the temperature of photonic crystal devices via micron-scale electrical heaters. The method is used to control the resonant frequency of InAs quantum dots strongly coupled to GaAs photonic crystal resonators. This technique enables independent control of large ensembles of photonic devices located on the same chip at tuning speed as high as hundreds of kilohertz.
Energy-level alignment and charge injection at metal/C60/organic interfaces
Authors: Wang Z. B. , Helander M. G. , Greiner M. T. , Qiu J. , Lu Z. H.
Published: July 2009

The energy-level alignment and charge injection at metal/C60/organic interfaces have been studied by ultraviolet photoelectron spectroscopy and temperature dependent current-voltage (IV) measurements. It is found that the Fermi level at the interface is pinned to ∼4.7eV by adsorbed C60 molecules on the metal surface, resulting in more favorable energy level alignment for charge injection. The findings are in excellent agreement with interface dipole theory derived from traditional semiconductor physics.
Single-mode 2.4 μm InGaAsSb/AlGaAsSb distributed feedback lasers for gas sensing
Authors: Gupta J. A. , Barrios P. J. , Lapointe J. , Aers G. C. , Storey C.
Published: July 2009

Single-mode laser diodes on GaSb substrates were developed using InGaAsSb/AlGaAsSb triple quantum well active regions grown by molecular beam epitaxy. The devices were fabricated using lateral Cr gratings, with a grating pitch designed to coincide with a strong absorption feature of HF gas, deposited adjacent to a dry-etched narrow ridge waveguide. High sidemode suppression was achieved, and in 20 °C continuous-wave operation, devices with a 400 μm long cavity provided 9 mW total output power at the 2396 nm target wavelength. High-resolution direct absorption measurements of HF gas agreed with HiTran calculations, yielding an absorption linewidth of 0.030 nm.
A Hirshfeld interpretation of the charge, spin distribution, and polarity of the dipole moment of the open shell (Σ3−) nitrogen halides: NF, NCl, and NBr
Authors: Harrison James F.
Published: July 2009

We calculated the dipole moment function for the ground Σ3−(mS=+1) state of the open shell molecules, NF, NCl, and NBr, and analyzed it in terms of the charge and spin distribution and the induced atomic dipoles using the Hirshfeld partitioning of the electron density. The smallest dipole moment (0.026ea0) obtains with NF, in which the atoms have the largest difference in electronegativity, while the dipole moments in NCl and NBr are 0.441ea0 and 0.506ea0, respectively. All dipoles have the N−X+ polarity. In the σ system α spin electrons flow from N to the halogen while β spin electrons flow in the opposite direction and interestingly from both the σ and the π systems of the halogen to the σ system of N. In NF the number of β spins lost by F is essentially equal to the number of α spins gained and the atomic charges are essentially 0. The small dipole in NF is the result of a slight imbalance in the induced atomic dipoles. For NCl and NBr the halogen loses more β spins than it gains α spins resulting in the polarity N−X+. It is interesting that at equilibrium N gained electrons in the π system while the halogen lost π electrons relative to the separated atoms. This however is not back donation in the usual sense because the electrons gained by N have α spin while those lost by the halogen have β spin. Detailed examination of the spin flow shows that the excess α electrons in the π system of N come from an intra-atomic transfer from the N σ system. The induced atomic dipole moments essentially cancel at all internuclear separations and the polarity of the dipole moment accurately reflects the molecular charge distribution.