bluuebunny/crossref_metadata_2025 huggingface dataset:
The ‘anaphase problem’: how to disable the mitotic checkpoint when sisters split
Authors: Vázquez-Novelle María Dolores , Mirchenko Lesia , Uhlmann Frank , Petronczki Mark
Published: December 2010

Two closely connected mechanisms safeguard the fidelity of chromosome segregation in eukaryotic cells. The mitotic checkpoint monitors the attachment of kinetochores to microtubules and delays anaphase onset until all sister kinetochores have become attached to opposite poles. In addition, an error correction mechanism destabilizes erroneous attachments that do not lead to tension at sister kinetochores. Aurora B kinase, the catalytic subunit of the CPC (chromosomal passenger complex), acts as a sensor and effector in both pathways. In this review we focus on a poorly understood but important aspect of mitotic control: what prevents the mitotic checkpoint from springing into action when sister centromeres are split and tension is suddenly lost at anaphase onset? Recent work has shown that disjunction of sister chromatids, in principle, engages the mitotic checkpoint, and probably also the error correction mechanism, with potentially catastrophic consequences for cell division. Eukaryotic cells have solved this ‘anaphase problem’ by disabling the mitotic checkpoint at the metaphase-to-anaphase transition. Checkpoint inactivation is in part due to the reversal of Cdk1 (cyclin-dependent kinase 1) phosphorylation of the CPC component INCENP (inner centromere protein; Sli15 in budding yeast), which causes the relocation of the CPC from centromeres to the spindle midzone. These findings highlight principles of mitotic checkpoint control: when bipolar chromosome attachment is reached in mitosis, the checkpoint is satisfied, but still active and responsive to loss of tension. Mitotic checkpoint inactivation at anaphase onset is required to prevent checkpoint re-engagement when sister chromatids split.
Driving chromosome segregation: lessons from the human and Drosophila centromere–kinetochore machinery
Authors: Orr Bernardo , Afonso Olga , Feijão Tália , Sunkel Claudio E.
Published: December 2010

The kinetochore is a complex molecular machine that serves as the interface between sister chromatids and the mitotic spindle. The kinetochore assembles at a particular chromosomal locus, the centromere, which is essential to maintain genomic stability during cell division. The kinetochore is a macromolecular puzzle of subcomplexes assembled in a hierarchical manner and fulfils three main functions: microtubule attachment, chromosome and sister chromatid movement, and regulation of mitotic progression though the spindle assembly checkpoint. In the present paper we compare recent results on the assembly, organization and function of the kinetochore in human and Drosophila cells and conclude that, although essential functions are highly conserved, there are important differences that might help define what is a minimal chromosome segregation machinery.
CINister thoughts
Authors: Foijer Floris
Published: December 2010

Chromosome instability (CIN) is the process that leads to aneuploidy, a known hallmark of human tumours for over a century. Nowadays, it is believed that CIN promotes tumorigenesis by shuffling the genome into a malignant order through translocations, amplifications, deletions (structural CIN), and gains and losses of whole chromosomes (numerical CIN or nCIN). The present review focuses on the causes and consequences of nCIN. Several roads can lead to nCIN, including a compromised spindle assembly checkpoint, cohesion defects, p53 deficiency and flawed microtubule–kinetochore attachments. Whereas the link between nCIN and tumorigenesis is becoming more evident, indications have emerged recently that nCIN can suppress tumour formation as well. To understand these paradoxical findings, novel reagents and more sophisticated mouse models are needed. This will provide us with a better understanding of nCIN and eventually with therapies that exploit this characteristic of human tumours.
Undergraduate Elementary Education Majors' Knowledge of Augmentative and Alternative Communication
Authors: Kessel Lindsay , Sickman Linda Sue
Published: December 2010

This study describes survey results measuring the knowledge undergraduate elementary education major students have about augmentative and alternative communication. Those students with experience and course knowledge surrounding AAC were more knowledgeable. Implications for speech-language pathologists (SLPs) will be addressed, including how SLPs can provide classroom teachers with classroom support for general education teachers.
Frailty, Nutrition, and Sarcopenia in the Geriatric Patient With Dysphagia
Authors: Murray Joseph
Published: December 2010

In this review, the interaction of aging and deglutition are discussed with attention to normal changes in bodily systems that occur with aging and the acceleration of decline often observed in frail individuals. The concepts of frailty and sarcopenia are discussed in a way to aid the speech-language pathologist providing services to the elderly with swallowing disorders. It is important for the practicing speech-language pathologist to be able to identify elders who are at risk of poor outcome as the result of the synergy of poor nutrition and frailty as these symptoms appear in daily clinical practice.
Feeding and Swallowing Strategies for the Individual With Dementia
Authors: Voyzey George A.
Published: December 2010

As the 24 million individuals living with some form of dementia follow the course of the disease, they experience deterioration in cognitive and swallowing capabilities. The speech-language pathologist can guide the individual and his/her caregivers and family to support a safe intake and the least restrictive diet. This article will familiarize clinicians with feeding and swallowing techniques, as well environmental and physical recommendations to facilitate assessment and management of individuals with dysphagia and dementia. The goal is to ensure the individual with dementia can experience quality of life on a daily basis by focusing on one of the last remaining skills a person with dementia possesses: The ability to eat and enjoy food with both safety and dignity.
How To Practice “Undefensively”
Authors: Leslie Paula , Krival Kate
Published: December 2010

Speech-language pathologists (SLPs) are increasingly challenged by the medical complexities our patients present and gripped by the fear of litigation, if patients decline physically under our care. One response to these pressures may be to practice defensive medical speech-language pathology. We propose that best practice is ethically achieved by deliberately using specific external and internal resources to practice undefensively. We suggest how consideration of these materials and processes will help SLPs ensure evaluation and clinical decision-making processes are as effective, evidence-based, and transparent to patients, caregivers, administrators, and payers as possible.
Reliability of the Conversational Interaction Coding Form When Applied to Natural Conversation of Individuals With Aphasia
Authors: Coote Ashley Pozzolo , Pimentel Jane
Published: December 2010

Purpose: Development of valid and reliable outcome tools to document social approaches to aphasia therapy and to determine best practice is imperative. The aim of this study is to determine whether the Conversational Interaction Coding Form (CICF; Pimentel & Algeo, 2009) can be applied reliably to the natural conversation of individuals with aphasia in a group setting.

Method: Eleven graduate students participated in this study. During a 90-minute training session, participants reviewed and practiced coding with the CICF. Then participants independently completed the CICF using video recordings of individuals with non-fluent and fluent aphasia participating in an aphasia group. Interobserver reliability was computed using matrices representative of the point-to-point agreement or disagreement between each participant's coding and the authors' coding for each measure. Interobserver reliability was defined as 80% or better agreement for each measure.

Results: On the whole, the CICF was not applied reliably to the natural conversation of individuals with aphasia in a group setting.

Conclusion: In an extensive review of the turns that had high disagreement across participants, the poor reliability was attributed to inadequate rules and definitions and inexperienced coders. Further research is needed to improve the reliability of this potentially useful clinical tool.
The Use of History in is Research An Opportunity Missed?
Authors: Land Frank
Published: December 2010

The article is shaped by two regularly repeated cliches. The first is History is bunk, Henry Ford's well known saying has two Implications: (1) that what purports to be history Is more often than not inaccurate If not a downright lie, and (2) that we have nothing to learn from history as modern innovations make the past Irrelevant. The second cliche is We will heed the lessons we have learned from past disasters, How often do we hear that claim with respect to information systems (IS) failures? Again there are two implications: (1) that history repeats Itself, and that If we learn how prior mistakes were made we can avoid the same mistakes being repeated, and (2) that we have the capability to analyse the past with sufficient accuracy that we can Identify all the problems that led to the mistakes being made. In this article, I will argue that the historiography of IS is Important to understanding IS and Its evolution through time, and that understanding even the most transformative, revolutionary, Innovations benefits from the study of the historical context. Henry Ford's viewpoint Is far too prevalent, and In my view damaging to IS research. The argument will be supported by a number of examples.
Modular system for data acquisition and control of experiments with digital output
Authors: Calabria Mauro F. , Deza Roberto R.
Published: December 2010

In the present work, the design of an efficient, modular, and scalable data acquisition and control system is described. It consists of an array of microcontrollers and memories, which feed a single concentrating unit whose information can be accessed by means of a universal series bus (USB) interface to be processed later on. Signal levels can be controlled through a set of digital potentiometers. This system is ideal for experiments with a large number of digital outputs.
Magnetization pinning in conducting films demonstrated using broadband ferromagnetic resonance
Authors: Kostylev M. , Stashkevich A. A. , Adeyeye A. O. , Shakespeare C. , Kostylev N. , Ross N. , Kennewell K. , Magaraggia R. , Roussigné Y. , Stamps R. L.
Published: December 2010

The broadband microstrip ferromagnetic resonance (FMR), cavity FMR, and Brillouin light scattering spectroscopy techniques have been applied for detection and characterization of a magnetic inhomogeneity in a film sample. In the case of a 100 nm thick permalloy film, an additional magnetically depleted top sublayer has been detected due to pinning effect it produces on the magnetization in the bulk of the film. The pinning results in appearance of an exchange standing spin wave mode in the broadband FMR absorption spectrum, whose amplitudes are different depending on whether the film or the film substrate faces the microstrip transducer. Comparison of the experimental amplitudes for this mode with results of our theory for both film placements revealed that the depleted layer is located at the film surface facing away from the film substrate. Subsequent broadband FMR characterization of a large number of other presumably single-layer films with thicknesses in the range 30–100 nm showed the same result.
Vlasov equation and collisionless hydrodynamics adapted to curved spacetime
Authors: Dodin I. Y. , Fisch N. J.
Published: December 2010

The modification of the Vlasov equation, in its standard form describing a charged particle distribution in the six-dimensional phase space, is derived explicitly within a formal Hamiltonian approach for arbitrarily curved spacetime. The equation accounts simultaneously for the Lorentz force and the effects of general relativity, with the latter appearing as the gravity force and an additional force due to the extrinsic curvature of spatial hypersurfaces. For an arbitrary spatial metric, the equations of collisionless hydrodynamics are also obtained in the usual three-vector form.
Comment on “MEMS-based high speed scanning probe microscopy” [Rev. Sci. Instrum. 81, 043702 (2010)]
Authors: Degertekin F. Levent , Torun Hamdi
Published: December 2010

In a recent article, Disseldorp et al. [Rev. Sci. Instrum. 81, 043702 (2010)] present a micromachined z-scanner for scanning probe microscopy (SPM). The scanner comprises a micromachined electrostatically actuated membrane anchored to its substrate with crab-leg flexures. This structure is used as a fast actuator specifically for atomic force microscope and scanning tunneling microscope. The authors present topographic images acquired using the scanner in this paper and elsewhere [F. C. Tabak et al., Ultramicroscopy 110, 599 (2010)]. Although the work is clearly described, it does not appear to be placed in proper context. For example, the authors claim that previous work on microelectromechanical systems SPM has not been focused on high-speed imaging with feedback, which is not supported by the existing literature. In addition, similar actuator structures, albeit slightly larger scale, have been designed and used for SPM applications. Here, we would like comment briefly on the existing literature to clarify the significance of the work.
An extended macroscopic transport model for rarefied gas flows in long capillaries with circular cross section
Authors: Taheri Peyman , Struchtrup Henning
Published: December 2010

Pressure-driven and thermally driven rarefied gas flows in long capillaries with circular cross sections are investigated. For both Poiseuille and thermal transpiration flows, a unified theoretical approach is presented based on the linear form of regularized 13-moment (R13) equations. The captured nonequilibrium effects in the processes are compared to available kinetic solutions, and the shortcomings of classical hydrodynamics, i.e., the Navier–Stokes–Fourier equations, are highlighted. Breakdown of Onsager’s symmetry is proposed as a criterion to determine the range of applicability of extended macroscopic models. Based on Onsager’s reciprocity relation it is shown that linearized R13 equations provide agreement with kinetic data for moderate Knudsen numbers, Kn≤0.25. Two-way flow pattern and thermomolecular pressure difference in simultaneous pressure-driven and temperature-driven flows are analyzed. Moreover, second-order boundary conditions for velocity slip and temperature jump are derived for the Navier–Stokes–Fourier system. The proposed boundary conditions effectively improve classical hydrodynamics in the transition flow regime.
The formal path integral and quantum mechanics
Authors: Johnson-Freyd Theo
Published: December 2010

Given an arbitrary Lagrangian function on \documentclass[12pt]{minimal}\begin{document}${\mathbb R}^d$\end{document}Rd and a choice of classical path, one can try to define Feynman's path integral supported near the classical path as a formal power series parameterized by “Feynman diagrams,” although these diagrams may diverge. We compute this expansion and show that it is (formally, if there are ultraviolet divergences) invariant under volume-preserving changes of coordinates. We prove that if the ultraviolet divergences cancel at each order, then our formal path integral satisfies a “Fubini theorem” expressing the standard composition law for the time evolution operator in quantum mechanics. Moreover, we show that when the Lagrangian is inhomogeneous quadratic in velocity such that its homogeneous-quadratic part is given by a matrix with constant determinant, then the divergences cancel at each order. Thus, by “cutting and pasting” and choosing volume-compatible local coordinates, our construction defines a Feynman-diagrammatic “formal path integral” for the nonrelativistic quantum mechanics of a charged particle moving in a Riemannian manifold with an external electromagnetic field.
Quantum Monte Carlo simulations of selected ammonia clusters (n = 2–5): Isotope effects on the ground state of typical hydrogen bonded systems
Authors: Curotto E. , Mella Massimo
Published: December 2010

Variational Monte Carlo, diffusion Monte Carlo, and stereographic projection path integral simulations are performed on eight selected species from the (NH3)n, (ND3)n, (NH2D)n, and (NH3)n − 1(ND3) clusters. Each monomer is treated as a rigid body with the rotation spaces mapped by the stereographic projection coordinates. We compare the energy obtained from path integral simulations at several low temperatures with those obtained by diffusion Monte Carlo, for two dimers, and we find that at 4 K, the fully deuterated dimer energy is in excellent agreement with the ground state energy of the same. The ground state wavefunction for the (NH3)2 − 5 clusters is predominantly localized in the global minimum of the potential energy. In all simulations of mixed isotopic substitutions, we find that the heavier isotope is almost exclusively the participant in the hydrogen bond.
Dynamic coupling of a small rigid probe to viscous ortho-terphenyl
Authors: Huang Wei , Richert Ranko
Published: December 2010

We have measured the dielectric relaxation of 2,2,6,6-tetramethyl-piperidine-1-oxyl (TEMPO) as a rotational probe in supercooled ortho-terphenyl (OTP). Due to the significant dipole moment of TEMPO compared with OTP, its contribution to the loss spectra can be identified already at moderate concentrations. For time scales ranging from 10 μs to 1 s, it is found that the tumbling mode of TEMPO is a true replica of the structural relaxation of OTP regarding average time constant, relaxation time dispersion, and the temperature dependence. While the present dielectric results are consistent with a decoupling of a spinning mode (about the nitroxyl dipole axis) of TEMPO from viscosity, they do not agree with the strong decoupling of the tumbling mode derived from electron spin resonance experiments.
Gold adatoms and clusters on PPV: An ab initio investigation
Authors: Brito W. H. , Silva R. A. , Miwa R. H.
Published: December 2010

We have performed an ab initio investigation of the energetic, structural, electronic, and vibrational properties of Au atoms and clusters adsorbed on poly-p-phenylene vinylene (PPV) chains, Aun/PPV (with n = 1, 2, 6, 7, 10, and 12). We find that the Aun/PPV systems are energetically stable by 0.5 eV, compared with the isolated systems, viz., PPV chain and Aun clusters, thus supporting the formation of Aun/PPV nanocomposites. Further support to the formation of Aun/PPV has been provided by examining the vibrational properties of pristine PPV and Aun/PPV systems. In agreement with experimental measurements, we find a reduction on the in-plane vibrational frequency of C–C bonds of Aun/PPV, when compared with the same vibrational modes of pristine PPV. The electronic properties of isolated Aun clusters are modified when adsorbed on PPV. The highest occupied states of Aun/PPV are mostly concentrated on the Aun cluster, while the lowest unoccupied states are mainly localized along the PPV chain. The HOMO–LUMO energy gap of the Aun/PPV systems are smaller than the energy gap of the isolated systems, Aun clusters, and pristime PPV chains.
Development and characterization of high temperature stable Ta–W–Si–C amorphous metal gates
Authors: Grubbs Melody E. , Zhang Xiao , Deal Michael , Nishi Yoshio , Clemens Bruce M.
Published: December 2010

Threshold voltage variability (σVth) due to the polycrystalline nature of current metal gates has been identified as a problem in future generations of complementary metal oxide semiconductor (CMOS) devices. Amorphous metal Ta40W40Si10C10 gates are introduced in this work as a remedy. It was found that Ta–W–Si–C films remain amorphous at temperatures as high as 1120 °C, have n-type work functions, and are stable on HfO2. This alloy is a promising gate-first compatible material that has the potential to significantly reduce σVth.
Gyrokinetic simulations of mesoscale energetic particle-driven Alfvénic turbulent transport embedded in microturbulence
Authors: Bass E. M. , Waltz R. E.
Published: December 2010

Energetic particle (EP) transport from local high-n toroidal Alfvén eigenmodes (TAEs) and energetic particle modes (EPMs) is simulated with a gyrokinetic code. Linear and nonlinear simulations have identified a parameter range where the longwave TAE and EPM are unstable alongside the well-known ion-temperature-gradient (ITG) and trapped-electron-mode (TEM) instabilities. A new eigenvalue solver in GYRO facilitates this mode identification. States of nonlinearly saturated local TAE/EPM turbulent intensity are identified, showing a “soft” transport threshold for enhanced energetic particle transport against the TAE/EPM drive from the EP pressure gradient. The very long-wavelength (mesoscale) TAE/EPM transport is saturated partially by nonlinear interaction with microturbulent ITG/TEM-driven zonal flows. Fixed-gradient-length, nonlinearly saturated states are accessible over a relatively narrow range of EP pressure gradient. Within this range, and in the local limit employed, TAE/EPM-driven transport more closely resembles drift-wave microturbulent transport than “stiff” ideal MHD transport with a clamped critical total pressure gradient. At a higher, critical EP pressure gradient, fixed-gradient nonlinear saturation fails: EP transport increases without limit and background transport decreases. Presumably saturation is then obtained by relaxation of the EP pressure gradient to near this critical EP pressure gradient. If the background plasma gradients driving the ITG/TEM turbulence and zonal flows are weakened, the critical gradient collapses to the TAE/EPM linear stability threshold. Even at the critical EP pressure gradient there is no evidence that TAE/EPM instability significantly increases transport in the background plasma channels.
Piezoelectric InAs (211)B quantum dots grown by molecular beam epitaxy: Structural and optical properties
Authors: Dialynas G. E. , Kalliakos S. , Xenogianni C. , Androulidaki M. , Kehagias T. , Komninou P. , Savvidis P. G. , Hatzopoulos Z. , Pelekanos N. T.
Published: December 2010

The structural and optical properties of piezoelectric (211)B InAs nanostructures grown by molecular beam epitaxy are systematically investigated as a function of the various growth parameters. Depending on the specific growth conditions, we show that the InAs nanostructures take the form of a quantum dot (QD) or a quantum dash, their height ranges between 2 and 20 nm, and their density varies from a few times 108 cm−2 all the way up to a few times 1010 cm−2. The (211)B QDs are characterized by large aspect ratios, which are compatible with a truncated pyramid morphology. By analyzing the QD emission spectrum, we conclude that only small size QDs, with heights less than 3 nm, are optically active. This is consistent with high resolution transmission electron microscopy observations showing that large QDs contain misfit dislocations, whereas small QDs are dislocation-free. The formation of a two-dimensional wetting layer is observed optically, and its thickness is determined to be between 0.30 and 0.39 nm. Finally, the large blueshift in the QD emission observed with increasing excitation power represents a clear evidence of the strong built-in piezoelectric field present in these dots.
All maximally entangled four-qubit states
Authors: Gour Gilad , Wallach Nolan R.
Published: December 2010

We find an operational interpretation for the 4-tangle as a type of residual entanglement, somewhat similar to the interpretation of the 3-tangle. Using this remarkable interpretation, we are able to find the class of maximally entangled four-qubits states which is characterized by four real parameters. The states in the class are maximally entangled in the sense that their average bipartite entanglement with respect to all possible bipartite cuts is maximal. We show that while all the states in the class maximize the average tangle, there are only a few states in the class that maximize the average Tsillas or Renyi α-entropy of entanglement. Quite remarkably, we find that up to local unitaries, there exists two unique states, one maximizing the average α-Tsallis entropy of entanglement for all α ⩾ 2, while the other maximizing it for all 0 < α ⩽ 2 (including the von-Neumann case of α = 1). Furthermore, among the maximally entangled four qubits states, there are only three maximally entangled states that have the property that for two, out of the three bipartite cuts consisting of two-qubits verses two-qubits, the entanglement is 2 ebits and for the remaining bipartite cut the entanglement between the two groups of two qubits is 1 ebit. The unique three maximally entangled states are the three cluster states that are related by a swap operator. We also show that the cluster states are the only states (up to local unitaries) that maximize the average α-Renyi entropy of entanglement for all α ⩾ 2.
Measurement of the thermal conductance of the graphene/SiO2 interface
Authors: Mak Kin Fai , Lui Chun Hung , Heinz Tony F.
Published: December 2010

We have examined the interfacial thermal conductance GK of single and multilayer graphene samples prepared on fused SiO2 substrates by mechanical exfoliation of graphite. By using an ultrafast optical pump pulse and monitoring the transient reflectivity on the picosecond time scale, we obtained an average value of GK of GK=5000 W/cm2 K for the graphene/SiO2 interface at room temperature. We observed significant variation in GK between individual samples, but found no systematic dependence on the thickness of the graphene layers.
Acoustic solitons in inhomogeneous pair-ion plasmas
Authors: Shah Asif , Mahmood S. , Haque Q.
Published: December 2010

The acoustic solitons are investigated in inhomogeneous unmagnetized pair ion plasmas. The Korteweg–de Vries (KdV) like equation with an additional term due to density gradients is deduced by employing reductive perturbation technique. It is noticed that pair-ion plasma system is conducive for the propagation of compressive as well as rarefactive solitons. The increase in the temperature ratio causes the amplitude of the rarefactive soliton to decrease. However, the amplitude of the compressive solitons is found to be increased as the temperature ratio of ions is enhanced. The amplitude of both compressive and rarefactive solitons is found to be increased as the density gradient parameter is increased. The equlibrium density profile is assumed to be exponential. The numerical results are shown for illustration.
A computationally efficient method for calculating the maximum conductance of disordered networks: Application to one-dimensional conductors
Authors: Pereira Luiz F. C. , Rocha C. G. , Latgé A. , Ferreira M. S.
Published: December 2010

Random networks of carbon nanotubes and metallic nanowires have shown to be very useful in the production of transparent, conducting films. The electronic transport on the film depends considerably on the network properties, and on the interwire coupling. Here we present a simple, computationally efficient method for the calculation of conductance on random nanostructured networks. The method is implemented on metallic nanowire networks, which are described within a single-orbital tight binding Hamiltonian, and the conductance is calculated with the Kubo formula. We show how the network conductance depends on the average number of connections per wire, and on the number of wires connected to the electrodes. We also show the effect of the inter/intrawire hopping ratio on the conductance through the network. Furthermore, we argue that this type of calculation is easily extendable to account for the upper conductivity of realistic films spanned by nanowire networks. When compared to experimental measurements, this quantity provides a clear indication of how much room is available for improving the film conductivity.
Detrapping and retrapping of free carriers in nominally pure single crystal GaP, GaAs, and 4H–SiC semiconductors under light illumination at cryogenic temperatures
Authors: Mouneyrac David , Hartnett John G. , Le Floch Jean-Michel , Tobar Michael E. , Cros Dominique , Krupka Jerzy
Published: December 2010

We report on extremely sensitive measurements of changes in the microwave properties of high purity nonintentionally-doped single-crystal semiconductor samples of gallium phosphide, gallium arsenide, and 4H–silicon carbide when illuminated with light of different wavelengths at cryogenic temperatures. Whispering gallery modes were excited in the semiconductors while they were cooled on the coldfinger of a single-stage cryocooler and their frequencies and Q-factors measured under light and dark conditions. With these materials, the whispering gallery mode technique is able to resolve changes of a few parts per million in the permittivity and the microwave losses as compared with those measured in darkness. A phenomenological model is proposed to explain the observed changes, which result not from direct valence to conduction band transitions but from detrapping and retrapping of carriers from impurity/defect sites with ionization energies that lay in the semiconductor band gap. Detrapping and retrapping relaxation times have been evaluated from comparison with measured data.
Spin reorientation transition and phase diagram in an He+ ion irradiated ultrathin Pt/Co(0.5 nm)/Pt film
Authors: Bergeard N. , Jamet J.-P. , Ferré J. , Mougin A. , Fassbender J.
Published: December 2010

A rich thermal magnetic phase diagram has been determined by magneto-optical Kerr magnetometry and microscopy in a He+ ion irradiated ultrathin Pt/Co(0.5 nm)/Pt film. The components of the net magnetization and the evolution and disappearance of the ribbonlike magnetic domain pattern have been studied in the perpendicular to in-plane spin reorientation transition temperature region. As observed in a dipolar frustrated ferromagnet, the ribbon pattern blurs progressively with increasing the temperature as due to efficient spatial fluctuations. We emphasize the limitation of present theories for interpreting such a type of dynamic transition.
Defects at oxygen plasma cleaned ZnO polar surfaces
Authors: Dong Yufeng , Fang Z.-Q. , Look D. C. , Doutt D. R. , Cantwell G. , Zhang J. , Song J. J. , Brillson Leonard J.
Published: December 2010

Depth-resolved cathodoluminescence spectroscopy (DRCLS) reveals the evolution of surface and near surface defects at polar surfaces with remote oxygen plasma (ROP) treatment. Furthermore, this evolution exhibits significant differences that depend on surface polarity. ROP decreased the predominant 2.5 eV defect emission related to oxygen vacancies on the O face, while creating a new 2.1 eV defect emission on the Zn face that increases with ROP time. The surface-located 2.1 eV emission correlates with carrier profiles from capacitance-voltage measurements and a shift of the E3 trap to higher binding energy from deep level transient spectroscopy (DLTS). This result suggests that ROP generates Zn vacancies on the Zn face which act as compensating acceptors at the surface and in the near surface region. Secondary ion mass spectrometry (SIMS) shows no polarity dependence due to impurities. We conclude that the near-surface deep level optical emissions and free carrier densities of ZnO depend strongly on the ROP modulation of native defects related to Zn or O vacancies.
Barrier dependent electron tunneling lifetime in one-dimensional device structures
Authors: Li Hui , Gong Jian , Hu Xing , Zhang Rui-Qin
Published: December 2010

The tunneling times of electrons in one-dimensional potential structures were studied using a projected Green function (PGF) method. The approach was applied to cases with potentials with one barrier, two barriers, and three barriers at the right side of a quantum well where the electron is located at the initial time. Our results include the effects of well width and barrier thickness on the tunneling time, and also show the impact on the tunneling time of splitting a single barrier into more barriers. This study confirms not only the validity of the PGF method but also reveals the impact of the potential structure on the operation speed of resonant tunneling devices.
Atomic structure of interface between monolayer Pd film and Ni(111) determined by low-energy electron diffraction and scanning tunneling microscopy
Authors: An B. , Wen M. , Zhang L. , Imade M. , Iijima T. , Fukuyama S. , Yokogawa K.
Published: December 2010

The atomic structure of Pd ultrathin films grown on Ni(111) at 300 K is investigated by low-energy electron diffraction and scanning tunneling microscopy. It is determined atomically that the growth of monolayer Pd films leads to a periodic arrangement of triangular misfit dislocation loops in the underlying Ni(111) surface, resulting in a triangular superstructure on the monolayer Pd surface. The triangular dislocation loops tend to align at an angle of about 5° from the Ni atom row, owing to a slight rotation of the Pd films with respect to the Ni substrate, and appear as a moirélike superstructure on the multilayer Pd surfaces. Atomistic simulations indicate that the slight rotation of monolayer Pd films and the formation of misfit dislocation loops in the Ni surface minimize the Pd–Ni interface energy.
Effect of microstructure on Au/sapphire interfacial thermal resistance
Authors: Xu Yibin , Kato Ryozo , Goto Masahiro
Published: December 2010

We deposit Au films on single crystal sapphire substrates by sputtering and evaporation methods. The microstructure characteristics such as crystal textures, grain sizes, and fraction of contacted area of the films are examined by x-ray diffraction and transmission electron microscopy. The sputtered films have an average grain size of about 200 nm and perfectly attach to the substrates; the as-evaporated films partially attach to the substrate; the grain size varies from 10 to 30 nm, and after annealing, increases to 50 nm. Au2Al phase is observed in the annealed samples. The interfacial thermal resistance is measured by a frequency domain thermoreflectance method. The thermal resistance of the sputtered Au/sapphire interfaces is 35.5×10−9 m2 K W−1, and those of the evaporated samples are up to three times as large as this value. The change in interfacial thermal resistance is explained by the effect of detachment using a parallel arranged thermal resistance model, the effect of grain size, and the influence of chemical bonding at the interfaces.
Near-infrared Kerr nonlinearity of Pb(PO3)2–WO3 glasses
Authors: Oliveira T. R. , Fedus K. , Manzani D. , Falcão-Filho E. L. , Boudebs G. , de Araújo Cid B. , Messaddeq Y.
Published: December 2010

We report measurements of the nonlinear refractive index, n2, and the nonlinear absorption coefficient, α2, of Pb(PO3)2–WO3 glasses. The measurements were performed using 100 fs (17 ps) laser pulses at 800 nm (1064 nm). Positive values of n2∼10−19 m2/W and negligible α2 were measured. The results show that the nonlinearity is faster than 100 fs and it is observed an increase of n2 with the increasing of the WO3 amount in the samples. The Boling, Glass, and Owyoung model, based on the semiclassical harmonic oscillator model, was used to predict the values of n2, with basis on the values of the linear refractive index of the samples.
Surface effects in the magnetic properties of crystalline 3 nm ferrite nanoparticles chemically synthesized
Authors: Lima E. , De Biasi E. , Mansilla M. Vasquez , Saleta M. E. , Effenberg F. , Rossi L. M. , Cohen R. , Rechenberg H. R. , Zysler R. D.
Published: December 2010

We have systematically studied the magnetic properties of ferrite nanoparticles with 3, 7, and 11 nm of diameter with very narrow grain size distributions. Samples were prepared by the thermal decomposition of Fe(acac)3 in the presence of surfactants giving nanoparticles covered by oleic acid. High resolution transmission electron microscopy (HRTEM) images and XRD diffraction patterns confirms that all samples are composed by crystalline nanoparticles with the spinel structure expected for the iron ferrite. ac and dc magnetization measurements, as well in-field Mössbauer spectroscopy, indicate that the magnetic properties of nanoparticles with 11 and 7 nm are close to those expected for a monodomain, presenting large MS (close to the magnetite bulk). Despite the crystalline structure observed in HRTEM images, the nanoparticles with 3 nm are composed by a magnetically ordered region (core) and a surface region that presents a different magnetic order and it contains about 66% of Fe atoms. The high saturation and irreversibility fields in the M(H) loops of the particles with 3 nm together with the misalignment at 120 kOe in the in-field Mössbauer spectrum of surface component indicate a high surface anisotropy for the surface atoms, which is not observed for the core. For T<10 K, we observe an increase in the susceptibility and of the magnetization for former sample, indicating that surface moments tend to align with applied field increasing the magnetic core size.
Surface plasmon enhanced UV emission in AlGaN/GaN quantum well
Authors: Lin J. , Mohammadizia A. , Neogi A. , Morkoc H. , Ohtsu M.
Published: December 2010

The surface plasmon (SP) energy for resonant enhancement of light has shown to be modified by the epitaxial substrate and the overlying metal thin film. The modification of SP energy in AlGaN/GaN epitaxial layers is studied using spectroscopic ellipsometry for enhanced UV-light emission. Silver induced SP can be extended to the UV wavelength range by increasing the aluminum concentration in AlxGa1−xN epilayer. A threefold increase in the UV-light emission is observed from AlGaN/GaN quantum well due to silver induced SP. Photoluminescence lifetime measurements confirm the resonant plasmon induced increase in Purcell factor as observed from the PL intensity measurements.
18.7% efficient laser-doped solar cell on p-type Czochralski silicon
Authors: Hameiri Z. , Mai L. , Sproul A. , Wenham S. R.
Published: December 2010

The use of laser doping in solar cell fabrication has received increased attention in recent years, especially due to its ability to form a selective emitter without subjecting the wafer to prolonged high-temperature processes. At the University of New South Wales, a laser doping method was developed that combines the formation of the selective emitter with a self-aligned metallization pattern. This letter reports 18.7% efficient laser-doped solar cells, fabricated on large area commercial-grade p-type Czochralski silicon, and analyzes the loss mechanisms.
Effects of the intermediate SiO2 layer on polarized output of a light-emitting diode with surface plasmon coupling
Authors: Shen Kun-Ching , Liao Che-Hao , Yu Zan-Yao , Wang Jyh-Yang , Lin Cheng-Hung , Kiang Yean-Woei , Yang C. C.
Published: December 2010

The variation behaviors of the output intensity and polarization ratio of InGaN/GaN quantum well (QW) light-emitting diodes (LEDs) with surface plasmon (SP) coupling by inserting SiO2 intermediate layers between the p-GaN layers and surface Ag grating structures are demonstrated. The insertion of the SiO2 layer is expected to reduce the metal dissipation of SP energy and extend the near-field distribution range of the induced SP for generating more favored SP-QW coupling effects. The Ag grating period for optimizing SP-QW coupling is increased when a SiO2 layer is added to the device, which is consistent with the simulation results of the momentum matching of SP polariton and the resonance behavior of localized SP. The almost unpolarized outputs from other LED samples fabricated with an epitaxial structure of thicker p-GaN layer, which leads to weak SP-QW coupling, indicate that the observed polarization ratios are due to near-field SP-QW coupling, instead of far-field diffraction.
Nanocomposite electrical generator based on piezoelectric zinc oxide nanowires
Authors: Momeni K. , Odegard G. M. , Yassar R. S.
Published: December 2010

A nanocomposite electrical generator composed of an array of zinc oxide nanowires is considered. The electric potential distribution along zinc oxide nanowires is modeled using continuum mechanics and Maxwell’s equations for the case of axial loading. A perturbation technique is used for decoupling the constitutive equations. The governing differential equations are solved using a finite difference method. It is shown that a gradient of electric potential exists along the axis of the zinc oxide nanowires. Maximum and minimum values of electric potential exist at the extreme ends along the nanowire length and have opposite signs. The positive and negative voltages are separated by a zero-valued electric potential at the middle of the nanowire. It is also shown that the electric potential is a strong function of shear stress at the interface of matrix-nanowire. The proposed system and loading configuration can generate up to 160% more electric potential than the values reported for the nanowire in the bended configuration, which results in a more sustainable energy source.
Schottky and tunneling behavior of Fe/MgO/Ge(100) structures
Authors: Laloë J.-B. , Hickey M. C. , Chang J. , Moodera J. S.
Published: December 2010

We investigated interface and electrical properties of Ge-based Schottky and tunnel diodes with crystalline MgO barriers. Following a simple cleaning procedure not requiring a high-temperature anneal, x-ray data indicated smooth interfaces and that the MgO tunnel barrier was highly textured. Transport characteristics were fitted using a self-consistent field Simmons–Schottky current-voltage model, yielding the Schottky and tunnel barrier heights for the devices and the distribution of tunneling currents. Considering the Fermi-level depinning and the ratio of Schottky to tunneling currents for each barrier thickness, we find that a MgO thickness of 15 Å yields the best transport properties in this system.
Ultrahigh energy proton generation in sequential radiation pressure and bubble regime
Authors: Zhang Xiaomei , Shen Baifei , Ji Liangliang , Wang Fengchao , Wen Meng , Wang Wenpeng , Xu Jiancai , Yu Yahong
Published: December 2010

Protons in a microtarget embedded in an underdense high-mass plasma can be accelerated sequentially by the radiation pressure of a short circularly polarized laser pulse and the induced wake bubble field in the background plasma, which has been shown in detail by two-dimensional particle in cell simulations. It has been found that instead of using transverse Gaussian pulses proton energy can be increased dramatically by using a transverse super-Gaussian laser pulse. With a 2.14×1023 W/cm2 laser pulse in a tritium plasma of density 1.5×1020/cm3, 76 GeV high-quality quasimonoenergetic protons have been obtained. The scaling relations between the obtainable proton energy and the laser amplitude as well as the background plasma density have been shown.
Study of single particle charge and Brownian motions with surface plasmon resonance
Authors: Shan Xiaonan , Wang Shaopeng , Tao Nongjian
Published: December 2010

We demonstrated a method to accurately measure the zeta potentials and surface charges of individual particles by surface plasmon resonance microscopy (SPRM). The principle is based on the sensitive dependence of surface plasmons in a metal surface on the distance between a particle and the surface. By applying a periodic (ac) electric field to the metal surface, the charged particle oscillates, which is measured with SPRM, from which the zeta potential and the surface charge of the particle can be determined. The ac method reduces the electro-osmotic effect and noises induced by Brownian motions and allows for the rapid determination of the zeta potentials of individual particles.
Enhanced laser ion acceleration from mass-limited foils
Authors: Kluge T. , Enghardt W. , Kraft S. D. , Schramm U. , Zeil K. , Cowan T. E. , Bussmann M.
Published: December 2010

This paper reports on simulations of solid mass-limited targets (MLT) via electrodynamic two-dimensional, three velocity component particle-in-cell simulations. The interaction with long (300 fs) high intensity (1020 W/cm2) laser pulses with targets of diameter down to 1 μm is described in detail with respect to electron dynamics and proton and ion acceleration. Depending on the foil diameter, different effects consecutively arise. Electrons laterally recirculate within the target, smoothening the target rear accelerating sheath and increasing the hot electron density and temperature. Our results suggest that the most significant ion energy enhancement should be expected for MLT with diameter below the laser focal spot size. The spread of energetic protons is decreased for medium sized foils while it is greatly increased for foils of size near the focal spot size.
Trapping of electrons in metal oxide-polymer memory diodes in the initial stage of electroforming
Authors: Bory Benjamin F. , Meskers Stefan C. J. , Janssen René A. J. , Gomes Henrique L. , de Leeuw Dago M.
Published: December 2010

Metal oxide-polymer diodes require electroforming before they act as nonvolatile resistive switching memory diodes. Here we investigate the early stages of the electroforming process in Al/Al2O3/poly(spirofluorene)/Ba/Al diodes using quasistatic capacitance-voltage measurements. In the initial stage, electrons are injected into the polymer and then deeply trapped near the poly(spirofluorene)-Al2O3 interface. For bias voltages below 6 V, the number of trapped electrons is found to be CoxideV/q with Coxide as the geometrical capacitance of the oxide layer. This implies a density of traps for the electrons at the polymer-metal oxide interface larger than 3×1017 m−2.
Dual dielectric tunnel barrier in silicon-rich silicon nitride charge-trap nonvolatile memory
Authors: Kim Eunkyeom , Yim Taekyung , An Seungman , Cho Won-Ju , Park Kyoungwan
Published: December 2010

We investigated a tunnel barrier with dual (SiO2 and SiNx) dielectric layers in charge-trap nonvolatile memories to improve the program/erase speed and charge retention characteristics. Threshold voltage shift measurements performed for various stress voltages and time durations revealed that these devices had a large memory window (2–6 V) and long retention time (>10 years). With a decrease in the SiO2 layer thickness, the program speed increased but the erase speed decreased. The change in the program/erase speed and charge retention characteristics with the relative thickness ratio could be attributed to the asymmetric shape of the tunnel barrier. The tunneling currents were explained on the basis of Fowler–Nordheim tunneling and Frenkel–Poole emission in the asymmetric tunnel barrier.
p-n junctions on Ga-face GaN grown by NH3 molecular beam epitaxy with low ideality factors and low reverse currents
Authors: Hurni Christophe A. , Bierwagen Oliver , Lang Jordan R. , McSkimming Brian M. , Gallinat Chad S. , Young Erin C. , Browne David A. , Mishra Umesh K. , Speck James S.
Published: December 2010

A comprehensive analysis of forward and reverse current of Ga-face GaN p-n junctions grown by NH3 molecular beam epitaxy (NH3-MBE) on metal organic chemical vapor deposition (MOCVD) GaN:Fe on sapphire is presented. NH3-MBE has a great potential for growing low leakage vertical devices due to its nitrogen-rich growth. Diodes with the lowest n-doping of n∼3.5×1017 cm−3 exhibit an extremely low reverse current of 2.6×10−7 A/cm2 at −40 V and an ideality factor of 1.3, which is lower than the state-of-the-art Ga-face p-n junctions grown on sapphire by MOCVD. An explanation for the difficulty for observing low ideality factors in GaN is presented.