bluuebunny/crossref_metadata_2025 huggingface dataset:
Search for the global signature of the Martian dynamo
Authors: Milbury C. , Schubert G.
Published: October 2010

We analyze Mars’ global magnetic field observations to gain insight into the evolution of Mars and its paleodynamo. Statistical properties of the magnetic field above Noachian and Hesperian age crust are similar, suggesting that the dynamo persisted past the Noachian. We model crustal magnetization in order to match the large‐scale features of the magnetic field. The model is based on a spherical shell of uniform thickness that was magnetized uniformly by an internal dipole. Crustal magnetization is removed from the northern lowlands, the Tharsis volcanic province, and the Hellas, Argyre, and Isidis impact basins. The magnetic field due to the remaining crustal magnetization is computed and compared with published models of the magnetic field data. The comparison is based on the spherical harmonic coefficients of the radial magnetic field component for the crustal magnetization models and the models of the observations. The correlation coefficients between the magnetization models and the models of the observations are calculated as a function of spherical harmonic degree. The correlations maximize for paleopole positions that are located near the equator in the southeast and northwest quadrants of Mars. The root‐mean‐square differences of the spherical harmonic coefficients are also calculated, and paleopole positions that minimize these differences generally agree with the paleopoles that maximize the correlations. The low‐latitude to midlatitude paleopoles suggest that true polar wander occurred early in Mars’ history, and the polarity of the paleopole positions suggests that at least one reversal of the dynamo magnetic field occurred.
Thermokarst in Siberian ice‐rich permafrost: Comparison to asymmetric scalloped depressions on Mars
Authors: Ulrich M. , Morgenstern A. , Günther F. , Reiss D. , Bauch K. E. , Hauber E. , Rössler S. , Schirrmeister L.
Published: October 2010

On Earth, the thawing of permafrost deposits with high‐ground ice content results in massive surface subsidence and the formation of characteristic large thermokarst depressions. Slope asymmetries within thermokarst depressions suggest lateral growth, which occurs due to thermoerosion and gravimetric mass wasting along these slopes. It has been proposed that rimless, asymmetrically shaped depressions (called scalloped depressions) on Mars were formed by insolation‐driven ground ice sublimation. We investigated a large thermokarst depression in ice complex deposits in the Siberian Arctic as a terrestrial analogue for scalloped depressions in Martian volatile‐rich mantle deposits. Our results from field studies, insolation modeling, and geomorphometric analyses suggest lateral thermokarst development in a northern direction. This conclusion is obvious due to steeper slope angles of the south facing slopes. Insolation and surface temperatures are crucial factors directly influencing thermokarst slope stability and steepness. Comparative analyses of Martian scalloped depressions in Utopia Planitia were conducted using high‐resolution (High‐Resolution Imaging Science Experiment, Context Camera) and thermal infrared (Thermal Emission Imaging System) satellite data. By direct analogy, we propose that the lateral scalloped depression development on Mars was primarily forced on the steep pole‐facing slopes in the equator‐ward direction. Insolation modeling confirms that this must have happened in the last 10 Ma during an orbital configuration of higher obliquity than today. Development would have been maximized if the orbit was both highly oblique and highly eccentric, and/or the Martian summer coincided with perihelion. Relatively short events of increasing sublimation or even thawing of ground ice led to fast slumping processes on the steep pole‐facing slopes.
Quantifying subcellular distribution of fluorescent fusion proteins in cells migrating within tissues
Authors: Melichar Heather J , Li Ou , Herzmark Paul , Padmanabhan Raghav K , Oliaro Jane , Ludford‐Menting Mandy J , Bousso Philippe , Russell Sarah M , Roysam Badrinath , Robey Ellen A
Published: October 2010

The movement of proteins within cells can provide dynamic indications of cell signaling and cell polarity, but methods are needed to track and quantify subcellular protein movement within tissue environments. Here we present a semiautomated approach to quantify subcellular protein location for hundreds of migrating cells within intact living tissue using retrovirally expressed fluorescent fusion proteins and time‐lapse two‐photon microscopy of intact thymic lobes. We have validated the method using GFP‐PKCζ, a marker for cell polarity, and LAT‐GFP, a marker for T‐cell receptor signaling, and have related the asymmetric distribution of these proteins to the direction and speed of cell migration. These approaches could be readily adapted to other fluorescent fusion proteins, tissues and biological questions.
Molecular characterization of the evolution of phagosomes
Authors: Boulais Jonathan , Trost Matthias , Landry Christian R , Dieckmann Régis , Levy Emmanuel D , Soldati Thierry , Michnick Stephen W , Thibault Pierre , Desjardins Michel
Published: October 2010

Amoeba use phagocytosis to internalize bacteria as a source of nutrients, whereas multicellular organisms utilize this process as a defense mechanism to kill microbes and, in vertebrates, initiate a sustained immune response. By using a large‐scale approach to identify and compare the proteome and phosphoproteome of phagosomes isolated from distant organisms, and by comparative analysis over 39 taxa, we identified an ‘ancient’ core of phagosomal proteins around which the immune functions of this organelle have likely organized. Our data indicate that a larger proportion of the phagosome proteome, compared with the whole cell proteome, has been acquired through gene duplication at a period coinciding with the emergence of innate and adaptive immunity. Our study also characterizes in detail the acquisition of novel proteins and the significant remodeling of the phagosome phosphoproteome that contributed to modify the core constituents of this organelle in evolution. Our work thus provides the first thorough analysis of the changes that enabled the transformation of the phagosome from a phagotrophic compartment into an organelle fully competent for antigen presentation.
Integrating Degradation into Fuel Cell Models and Lifetime Prediction
Authors: Gubner Andreas
Published: October 2010

A one dimensional (1D) model for simulating Solid Oxide Fuel Cell (SOFC) isothermal performance with humidified hydrogen and air is introduced. It is based on a set of ordinary differential equations (ODEs) describing the local current density as a function of the flow path for parallel flow SOFCs. Isothermal operation is a reasonable idealisation for laboratory cells placed in comparatively large furnaces, especially when operated at low fuel utilization. Such small scale SOFCs are often used to characterize the electrochemical cell performance.

The electrochemical behaviour is modeled by a single constant Area Specific Resistance (ASR) by taking the slope of an experimentally recorded I-V curve. It will be discussed that suitable operating conditions are found at a steam content (fuel humidity) of approx. 50 Vol-% and low fuel utilizations of less than 10 %. Alternatively, the 1D model can be used to calculate the ASR from I-V data directly which is less strict on operating condition requirements. Using the 1D model also allows to convert endurance test data, usually delivering a Vcell(t) data set, at constant electric current into a corresponding ASR(t) data set. The ODE set is solved numerically. Based on this model, a further step is taken by introducing a simple model for describing SOFC degradation during stationary operation. The simple degradation model can be useful as a first approach to more sophisticated life time prediction models and for deriving accelerated life time tests.
Accelerated Lifetime Testing for Phosphoric Acid Fuel Cells
Authors: Donahue John , Cipollini Ned , Fredley Robert
Published: October 2010

This chapter opens by discussing the the need for accelerated testing and the role of carbon in reducing the cost of PEM and PAFC fuel cells. Equation 11.1 describes the electrochemical conversion of carbon and water to CO2 and points to graphitization of the carbon to reduce the carbon activity. The oxidation potential is defined, reported for selected samples and used in a simplified Butler-Volmer equation (11.2) to quantify the kinetically controlled carbon corrosion rate. This equation also shows the carbon surface area exposed to electrolyte directly proportional to the carbon corrosion rate and the possible use of the water partial pressure as an acceleration factor. Experimental design and three generations of testing are discussed, culminating in out of cell hardware that exposes separator plates to the actual conditions important in degrading the component. “Equivalent stack operation hours” is used as the time scale to present weight loss data as a function of time at potential. 200 KW power plant fleet durability is presented and it documents the utility of this accelerated testing approach.
Unravelling Single Cell Genomics
Authors: Baret Jean-Christophe , Cauli Bruno , Chabert Max , Abecassis-Taly Valerie , Dittrich Petra , Fort Emmanuel , Klein Christoph , Lachuer Joel , Lambolez Bertrand , Le Novere Nicholas , le Gac Severine , Mahmoudian Laili , Marcy Yann , Polzer Bernhard , Vinh Joelle , Vitalis Tania ,   Royal Society of Chemistry
Published: October 2010

This unique introduction to the growing field of microfluidics applied to genomics provides an overview of the latest technologies and emphasizes its potential in answering important biological questions. Written by a physicist and a biologist, it offers a more comprehensive view than the previous literature. The book starts with key ideas in molecular biology, developmental biology and microtechnology before going on to cover the specifics of single cell analysis and microfluidic devices for single cell molecular analysis. Review chapters discuss the state-of-the art and will prove invaluable to all those planning to develop microdevices for molecular analysis of single cells. Methods allowing complete analysis of gene expression in the single cell are stressed - as opposed the more commonly used techniques that allow analysis of only a few genes at a time. As pioneers in the field, the authors understand how critical it is for a physicist to understand the biological issues and questions related to single cell analysis, as well for biologists to understand what microfluidics is all about. Aimed predominantly at graduate students, this book will also be of significant interest to scientists working in or affiliated with this field.
An Introduction to Molecular Biology
Authors: Dauphinot Luce
Published: October 2010

The cell constitutes the basic structure of all living organisms (cellula in latin means small chamber). The typical diameter of a cell is 10–100 micrometers (μm), its volume around 10 picoliters (pl) and its mass around 1 nanogram (ng).

Cells can be divided in two main groups. Prokaryotic cells, such as bacteria, lack nucleus and are unicellular organism, characterized by a relatively simple organization with only one compartment containing a circular DNA molecule. Eukaryotic cells are characterized by a nucleus and a cytoplasm containing many sub-cellular compartments. The nucleus is surrounded by a nuclear envelope with nuclear pores that allow the transport of macromolecules between the nucleus and the cytoplasm. The DNA molecule is localized inside the nucleus and organized in chromosomes. Some eukaryote organisms are unicellular such as yeasts, but the most part are pluricellular, with the most complex organism being human, with more than 10 000 billion cells.
Understanding Cellular Differentiation
Authors: Vitalis Tania
Published: October 2010

Developmental biology is making tremendous progress in describing the mechanisms that coordinate developmental programs and lead to the specification and differentiation of the correct cell at the correct position with appropriate synaptic or cell–cell contacts. In parallel, progress in microscale and nanoscale technologies and microfluidics is revealing new insights into single cell development in a specific environment. With these approaches it becomes possible to pinpoint the master genes that control the specification and differentiation of a single cell. In addition, these new technologies are also providing means to control microenvironments and possibly direct cell differentiation. They could also be valuable in understanding the role of a cell environment versus the genetic determinants. To revue what micro and nano-tools could offer to understand development, we will focus on the development of the nervous system.
Realistic Models of Neurons Require Quantitative Information at the Single-cell Level
Authors: Novère Nicolas Le
Published: October 2010

Detailed modelling of neurons is now a recognised sub-field of neurobiology. Such models rely on accurate and quantitative experimental measurements. For instance, modelling electrophysiology requires morphological reconstructions of identified neurons. Similarly, understanding the biochemical basis of neurotransmission becomes possible if we know about the molecular composition of the connected neurons. In this chapter we will describe the pitfalls of generic models that seek to reproduce common features of groups of neurons, and in particular, the artifacts generated by an excessive abstraction. Instead, we advocate the development of typological models, seeking to describe accurately a given neuron, generic inferences being derived afterwards.
Microfluidics: Basic Concepts and Microchip Fabrication
Authors: Vollrath Conni , Dittrich Petra S.
Published: October 2010

Microfluidic devices are nowadays versatile platforms for analytical applications and chemical syntheses, and are frequently used for cell culturing and cell studies. What are the unique features of a microfluidic device and how do these properties support the development of novel analytical methods for investigations on the single cell level? This chapter introduces to the basic concepts and aspects of microfluidics. It gives newcomers an understanding of the special characteristics such as the laminar flow and segmented flow. Furthermore, a short overview of fabrication methods is given highlighting the most popular approaches, particularly soft lithography. Finally, various materials useful for microchip fabrication are described and discussed with a special emphasis on their applicability for cell analytical devices.
Trace gas detection based on off-beam quartz enhanced photoacoustic spectroscopy: Optimization and performance evaluation
Authors: Liu Kun , Yi Hongming , Kosterev Anatoliy A. , Chen Weidong , Dong Lei , Wang Lei , Tan Tu , Zhang Weijun , Tittel Frank K. , Gao Xiaoming
Published: October 2010

A gas sensor based on off-beam quartz enhanced photoacoustic spectroscopy was developed and optimized. Specifically, the length and diameter of the microresonator tube were optimized, and the outer tube shape is modified for enhancing the trace gas detection sensitivity. The impact of the distance between the quartz tuning fork and an acoustic microresonator on the sensor performance was experimentally investigated. The sensor performance was evaluated by determining the detection sensitivity to H2O vapor in ambient air at normal atmospheric pressure. A normalized noise equivalent absorption coefficient (1σ) of 6.2×10−9 cm−1 W/Hz1/2 was achieved.
Electron relaxation in empty quantum-well states of a Pb island on Cu(111) studied by Z-V (distance-voltage) spectroscopy in scanning tunneling microscopy
Authors: Lu S. M. , Su W. B. , Lin C. L. , Chan W. Y. , Hsiao H. L. , Chang C. S. , Tsong Tien T.
Published: October 2010

We use the Z-V (distance-voltage) spectroscopy in scanning tunneling microscopy to detect the linewidths of empty quantum-well (QW) states acquired from a Pb island grown on the Cu(111) substrate. It is found that the continual broadening of the linewidth can extend to the electronic states near the vacuum level. We apply the Fermi-liquid theory with the Fabry–Pérot mode to analyze the linewidths of the QW states, and obtain the electron-phonon coupling constant, the electron-electron coupling factor, and the product of the electron reflectivities at the surface and interface of the Pb island.
Different approaches for evaluating exponentially weighted nonequilibrium relations
Authors: Reid James C. , Cunning Benjamin V. , Searles Debra J.
Published: October 2010

The Kawasaki identity (KI) and the Jarzynski equality (JE) are important nonequilibrium relations. Both of these relations take the form of an ensemble average of an exponential function and can exhibit convergence problems when the average of the exponent differs greatly from the log of the average of the exponential function. In this work, we re-express these relations so that only selected regions need to be evaluated in an attempt to avoid these convergence issues. In the context of measuring free energies, we compare our method to the JE and the literature standard approach, the maximum likelihood estimator (MLE), and show that in a system with asymmetric work distributions it can perform as well as the MLE. For the KI, we derive an analog to the MLE to compare with our relation and show that these two new relations improve on the KI and are complimentary to each other.
Epoxy-based nanocomposites for electrical energy storage. I: Effects of montmorillonite and barium titanate nanofillers
Authors: Tomer V. , Polizos G. , Manias E. , Randall C. A.
Published: October 2010

Polymer nanocomposites prepared by epoxy reinforced with high permittivity barium titanate (BT) fillers or high aspect ratio montmorillonite (MMT) fillers exhibited marked changes in their high electric field properties and their relaxation dynamics, depending on the nanoparticle type and concentration, the nanoparticle size, and the epoxy matrix conversion. We investigated epoxy resin composites based on organically modified montmorillonite (oMMT) or BT (BaTiO3) nanoparticles in order to delineate the effects of the high aspect ratio of the MMT and the high permittivity of the BT particles. We also explored the potential benefits of the synergy between the two fillers in systems consisting of epoxy and both oMMT and BT particles. It was observed that the nature of the organic–inorganic interfaces dominate the glass transition temperature and the dielectric properties of these composites. Specifically, using dielectric relaxation spectroscopy, we probed the local dynamics of the polymer at the interfaces. The MMT systems had approximately three orders of magnitude slower interfacial dynamics than those at the BT interfaces, indicating more robust interfaces in the MMT composites than in the BT-based composites; the corresponding energy barriers (activation energies) associated with these motions were also doubled for the MMT systems. Furthermore, we investigated the effect of the decreased glass transition, interfacial area, polymer-phase at the organic–inorganic interface, and of the dielectric breakdown on the electrical energy storage capabilities of these composites.
Epoxy-based nanocomposites for electrical energy storage. II: Nanocomposites with nanofillers of reactive montmorillonite covalently-bonded with barium titanate
Authors: Polizos G. , Tomer V. , Manias E. , Randall C. A.
Published: October 2010

Barium titanate (BT) and montmorillonite (MMT) nanoparticles were covalently-bonded by organically modifying the particle surfaces and chemically reacting them in solution. These integrated two-material hybrid inorganic nanofillers were subsequently dispersed in epoxy resin and nanocomposites were obtained at several weight fractions. The inorganic component consisted of well dispersed BT spherical nanoparticles that are surrounded by attached layered MMT nanoplatelets, with the latter having the ability to react with the epoxy matrix. The thermodynamic properties of the glass transition process, the macroscopic mechanical properties of the nanocomposites, and the dynamics of the polymer segments at the inorganic interfaces, all indicate that this filler configuration enhances the polymer-ceramic interfaces. Polarization as a function of electric field and dielectric breakdown show improvements in the electrical properties of these composites, compared to the corresponding unfilled epoxy, despite the expected reduction in crosslinking density. The resulting nanocomposites have a property set which can be utilized in energy storage and power system applications.
Stabilization of sample temperature in a surface-science vacuum chamber to 0.03 K and quartz-crystal microbalance frequency to 0.06 Hz over 0.5 h
Authors: Slavin Alan J.
Published: October 2010

Improvements have been made to a high-stability quartz-crystal microbalance for use in a typical surface-science, ultrahigh vacuum chamber, with a frequency stability of one part in 108 (0.06 Hz) over 0.5 h. This gives a resolution equivalent to 2% of an atomic monolayer of oxygen over 0.5 h. The quartz-crystal microbalance (QCM) crystal can be rotated to different surface-analysis positions in the chamber. These characteristics open up the combination of surface and bulk adsorption studies on the same sample without transferring the sample to another chamber. To accomplish this, it was necessary to stabilize the sample temperature to ±0.03 K over several hours. The oscillator performance is illustrated by the uptake of oxygen by a gold-plated QCM crystal.
First experimental demonstration of a photonic band gap channel-drop filter at 240 GHz
Authors: Simakov Evgenya I. , Earley Lawrence M. , Heath Cynthia E. , Shchegolkov Dmitry Yu. , Schultz Brian D.
Published: October 2010

We have designed, fabricated, and tested a novel photonic band gap (PBG) channel-drop filter (CDF) operating at around 240 GHz. A PBG CDF is a device that allows the channeling of selected frequencies from continuous spectra into separate waveguides through select defects in a PBG structure. It is compact and configurable, and thus, it can be employed for millimeter-wave spectrometry with applications in communications, radio astronomy, and radar receivers for remote sensing and nonproliferation. In this paper we present the design, modeling, and fabrication methods used to produce a silicon-based PBG CDF, and demonstrate its ability to filter the frequency of 240 GHz with a linewidth of approximately 1 GHz and transmission of 25 dB above background.
The nonmonotonic concentration dependence of the mean activity coefficient of electrolytes is a result of a balance between solvation and ion-ion correlations
Authors: Vincze Julianna , Valiskó Mónika , Boda Dezső
Published: October 2010

We propose a simple model to explain the nonmonotonic concentration dependence of the mean activity coefficient of simple electrolytes without using any adjustable parameters. The primitive model of electrolytes is used to describe the interaction between ions computed by the adaptive grand canonical Monte Carlo method. For the dielectric constant of the electrolyte, we use experimental concentration dependent values. This is included through a solvation term in our treatment to describe the interaction between ions and water that changes as the dielectric constant changes with concentration. This term is computed by a Born-treatment fitted to experimental hydration energies. Our results for LiCl, NaCl, KCl, CsCl, NaBr, NaI, MgCl2, CaCl2, SrCl2, and BaCl2 demonstrate that the principal reason of the nonmonotonic behavior of the activity coefficient is a balance between the solvation and ion-ion correlation terms. This conclusion differs from previous studies that assumed that it is the balance of hard sphere repulsion and electrostatic attraction that produces the nonmonotonic behavior. Our results indicate that the earlier assumption that solvation can be taken into account by a larger, “solvated” ionic radius should be reconsidered. To explain second order effects (such as dependence on ionic size), we conclude that explicit water models are needed.
Density measurements using coherence imaging spectroscopy based on Stark broadening
Authors: Lischtschenko O. , Bystrov K. , De Temmerman G. , Howard J. , Jaspers R. J. E. , König R.
Published: October 2010

A coherence imaging camera has been set up at Pilot-PSI. The system is to be used for imaging the plasma density through the Stark effect broadening of the Hγ line. Local density values are then obtained by the Abel inversion of the measured interferometric fringe contrast. This report will present the instrument setup and proof-of-principle demonstration. The inverted spatial electron density profiles obtained near the cascaded arc source of Pilot-PSI in discharges with axial magnetic field of B=0.4 T are compared with an independent measurement of electron density by Thomson scattering and good agreement is found.
Gyrokinetic simulations including the centrifugal force in a rotating tokamak plasma
Authors: Casson F. J. , Peeters A. G. , Angioni C. , Camenen Y. , Hornsby W. A. , Snodin A. P. , Szepesi G.
Published: October 2010

Tokamak experiments operate with a rotating plasma, with toroidal velocity which can be driven externally but can also arise spontaneously. In the frame that corotates with the plasma, the effects of the centrifugal force are felt through a centrifugal drift and an enhanced mirror force [Peeters et al., Phys. Plasmas 16, 042310 (2009)]. These inertial terms become important in the case of strong rotation, as is common in spherical devices, and are also important for heavy impurity ions even at small toroidal velocities. In this work, the first gyrokinetic simulations including the centrifugal force in a strongly rotating plasma are presented. The enhanced mirror force redistributes density over a flux surface and modifies the trapping condition, destabilizing trapped electron modes. At intermediate scales this can result in promotion of the trapped electron mode over the ion temperature gradient (ITG) mode as the dominant instability, which under marginal conditions could result in an enhanced electron heat flux. The centrifugal drift acts to damp the residual zonal flow of the geoacoustic mode, while its frequency is increased. For nonlinear ITG dominated turbulence, increased trapped electron drive and reduced zonal flow lead to an increase in ion heat diffusivity if the increased rotation is not accompanied by rotational shear stabilization. An increased fraction of slow trapped electrons enhances the convective particle pinch, leading to an increase in the steady state density gradient with strong rotation. Linear ITG mode results show an increased pinch of heavy trace impurities due to their strong centrifugal trapping.
Zonal flow modes in a tokamak plasma with dominantly poloidal mean flows
Authors: Zhou Deng
Published: October 2010

The zonal flow eigenmodes in a tokamak plasma with dominantly poloidal mean flows are theoretically investigated. It is found that the frequencies of both the geodesic acoustic mode and the sound wave increase with respect to the poloidal Mach number. In contrast to the pure standing wave form in static plasmas, the density perturbations consist of a standing wave superimposed with a small amplitude traveling wave in the poloidally rotating plasma.
Available information in 2D motional Stark effect imaging
Authors: Creese Mathew , Howard John
Published: October 2010

Recent advances in imaging techniques have allowed the extension of the standard polarimetric 1D motional Stark effect (MSE) diagnostic to 2D imaging of the internal magnetic field of fusion devices [J. Howard, Plasma Phys. Controlled Fusion 50, 125003 (2008)]. This development is met with the challenge of identifying and extracting the new information, which can then be used to increase the accuracy of plasma equilibrium and current density profile determinations. This paper develops a 2D analysis of the projected MSE polarization orientation and Doppler phase shift. It is found that, for a standard viewing position, the 2D MSE imaging system captures sufficient information to allow imaging of the internal vertical magnetic field component BZ(r,z) in a tokamak.
Analysis of thermal properties of GaInN light-emitting diodes and laser diodes
Authors: Shan Qifeng , Dai Qi , Chhajed Sameer , Cho Jaehee , Schubert E. Fred
Published: October 2010

The thermal properties, including thermal time constants, of GaInN light-emitting diodes (LEDs) and laser diodes (LDs) are analyzed. The thermal properties of unpackaged LED chips are described by a single time constant, that is, the thermal time constant associated with the substrate. For unpackaged LD chips, we introduce a heat-spreading volume. The thermal properties of unpackaged LD chips are described by a single time constant, that is, the thermal time constant associated with the heat spreading volume. Furthermore, we develop a multistage RthCth thermal model for packaged LEDs. The model shows that the transient response of the junction temperature of LEDs can be described by a multiexponential function. Each time constant of this function is approximately the product of a thermal resistance, Rth, and a thermal capacitance, Cth. The transient response of the junction temperature is measured for a high-power flip-chip LED, emitting at 395 nm, by the forward-voltage method. A two stage RthCth model is used to analyze the thermal properties of the packaged LED. Two time constants, 2.72 ms and 18.8 ms are extracted from the junction temperature decay measurement and attributed to the thermal time constant of the LED GaInN/sapphire chip and LED Si submount, respectively.
Microwave annealing of Mg-implanted and in situ Be-doped GaN
Authors: Aluri Geetha S. , Gowda Madhu , Mahadik Nadeemullah A. , Sundaresan Siddarth G. , Rao Mulpuri V. , Schreifels John A. , Freitas J. A. , Qadri S. B. , Tian Y.-L.
Published: October 2010

An ultrafast microwave annealing method, different from conventional thermal annealing, is used to activate Mg-implants in GaN layer. The x-ray diffraction measurements indicated complete disappearance of the defect sublattice peak, introduced by the implantation process for single-energy Mg-implantation, when the annealing was performed at ≥1400 °C for 15 s. An increase in the intensity of Mg-acceptor related luminescence peak (at 3.26 eV) in the photoluminescence spectra confirms the Mg-acceptor activation in single-energy Mg-implanted GaN. In case of multiple-energy implantation, the implant generated defects persisted even after 1500 °C/15 s annealing, resulting in no net Mg-acceptor activation of the Mg-implant. The Mg-implant is relatively thermally stable and the sample surface roughness is 6 nm after 1500 °C/15 s annealing, using a 600 nm thick AlN cap. In situ Be-doped GaN films, after 1300 °C/5 s annealing have shown Be out-diffusion into the AlN layer and also in-diffusion toward the GaN/SiC interface. The in-diffusion and out-diffusion of the Be increased with increasing annealing temperature. In fact, after 1500 °C/5 s annealing, only a small fraction of in situ doped Be remained in the GaN layer, revealing the inadequateness of using Be-implantation for forming p-type doped layers in the GaN.
Optical response of small closed-shell sodium clusters
Authors: Pal George , Lefkidis Georgios , Schneider Hans Christian , Hübner Wolfgang
Published: October 2010

Absorption spectra of closed-shell Na2, Na3+, Na4, Na5+, Na6, Na7+, and Na8 clusters are calculated using a complex Bethe–Salpeter equation derived using a conserving linear response method. In the framework of a quasiparticle approach, we determine electron-hole correlations in the presence of an external field. The calculated results are in excellent agreement with experimental spectra, and some possible cluster geometries that occur in experiments are analyzed. The position and the broadening of the resonances in the spectra arise from a consistent treatment of the scattering and dephasing contributions in the linear response calculation. Comparison between the experimental and the theoretical results yields information about the cluster geometry, which is not accessible experimentally.
Influence of ambient gas on the growth kinetics of Si nanocones
Authors: Wan Y. T. , Sha J. , Wang Z. L. , Wang Y. W.
Published: October 2010

Multi-segment silicon nanocones were designed and fabricated to investigate their growth kinetics. We found the ambient gas influenced the growth rates of Si nanocones remarkably. The axial growth rate increased with the total pressure of ambient gas, finally approaching saturation. Meanwhile the radial growth rate also increased with the total pressure but decreased with hydrogen content. A model was developed to study the growth kinetics by combining the effects of Langmuir adsorption, silane decomposition, and hydrogen coverage on the surface of SiNCs, which agreed with the experimental results. This paper also demonstrated the controllable cone angles by the ambient gas.
Ferroelectric BaTiO3/BaZrO3 superlattices: X-ray diffraction, Raman spectroscopy, and polarization hysteresis loops
Authors: El Marssi M. , Gagou Y. , Belhadi J. , De Guerville F. , Yuzyuk Yu. I. , Raevski I. P.
Published: October 2010

Artificial superlattices (SLs) consisting of ferroelectric BaTiO3 (BT) and paraelectric BaZrO3 (BZ) have been growth by a pulsed laser deposition technique. The epitaxial BT and BZ layers with a periodicity from 16 Å to 1056 Å were sequentially deposited on (001) MgO substrate buffered with an oxide conducting layer of La1/2Sr1/2CoO3. The out-of-plane lattice parameters of the SLs constituents were determined by modeling of the x-ray diffractograms. The results indicate that the polar c-axis of the BT layers lies in the plane of the substrate and BZ layers exhibit enhanced tetragonal distortion which is induced by the mismatch between the alternating BZ and BT layers. The Raman data reinforces this interpretation and suggest a monoclinic phase in BT layers and polar phase in BZ layers. The Raman spectra give evidence of coupling between the constituent layers and a narrowing of the Raman peaks is attributed to a reduction in the disorder of the Ti4+ ions due to the epitaxial strain. This strain is responsible for the upward frequency shift in the soft modes, especially, the E(1TO) mode, which is markedly altered with respect to its analogs in BT-bulk crystal and BT thin film. Ferroelectric hysteresis loops measurements, confirmed the x-ray diffraction and Raman results, and revealed a clear ferroelectric behavior for the constrained SLs (32 Å≤Λ≤256 Å) while a weak ferroelectricity is observed for the large periods (Λ=500 Å and 1056 Å). This is attributed to the strain-induced ferroelectricity in BZ layers for the constrained SLs.
Fabrication and characterization of relaxor ferroelectric PbFe1/2Ta1/2O3 thin film: A comparison with ceramics
Authors: Martínez V R. , Kumar Ashok , Sanchez Dilsom A. , Palai R. , Katiyar R. S.
Published: October 2010

Highly oriented Pb(Fe1/2Ta1/2)O3 (PFT) film is fabricated on conducting La0.67Sr0.33CoO3 coated (100) MgO substrate using pulsed laser deposition technique. The x-ray diffraction pattern shows single phase compound having preferential orientation along (100) plane. Surface topography of the film indicates homogeneous distribution of grains with an average grain size ∼55 nm. Broad dielectric dispersion, high dielectric diffusivity, and moderate dielectric loss are observed in the vicinity of wide range of temperatures and frequencies. A reasonably good shift in dielectric maximum temperature (∼30 K) is observed from 1 to 500 kHz suggests relaxor nature of film in this frequency range. At the same time, diffuse dielectric dispersion is seen above 500 kHz indicating diffuse ferroelectric phase transition. Dielectric data fallows the nonlinear Vogel–Fulcher relation below 500 kHz applied frequency which support the relaxor nature of PFT film. The ferroelectric hysteresis loop and butterfly loop show well defined saturated loop below freezing temperature (Tf) (∼150 K). A large shift in dielectric maximum temperature (Tm), i.e., around 75 K is observed compared to bulk counterpart that may be due to misfit strain across substrate-bottom electrode-film interface and in plane compressive strain in the film.
Free energy surfaces for the interaction of D-glucose with planar aromatic groups in aqueous solution
Authors: Wohlert Jakob , Schnupf Udo , Brady John W.
Published: October 2010

Multidimensional potentials of mean force for the interactions in aqueous solution of both anomers of D-glucopyranose with two planar aromatic molecules, indole and para-methyl-phenol, have been calculated using molecular dynamics simulations with umbrella sampling and were subsequently used to estimate binding free energies. Indole and para-methyl-phenol serve as models for the side chains of the amino acids tryptophan and tyrosine, respectively. In all cases, a weak affinity between the glucose molecules and the flat aromatic surfaces was found. The global minimum for these interactions was found to be for the case when the pseudoplanar face of β-D-glucopyranose is stacked against the planar surfaces of the aromatic residues. The calculated binding free energies are in good agreement with both experiment and previous simulations. The multidimensional free energy maps suggest a mechanism that could lend kinetic stability to the complexes formed by sugars bound to sugar-binding proteins.
Impact of network topology on cationic diffusion and hardness of borate glass surfaces
Authors: Smedskjaer Morten M. , Mauro John C. , Sen Sabyasachi , Deubener Joachim , Yue Yuanzheng
Published: October 2010

The connection between bulk glass properties and network topology is now well established. However, there has been little attention paid to the impact of network topology on the surface properties of glass. In this work, we report the impact of the network topology on both the transport properties (such as cationic inward diffusion) and the mechanical properties (such as hardness) of borate glasses with modified surfaces. We choose soda lime borate systems as the object of this study because of their interesting topological features, e.g., boron anomaly. An inward diffusion mechanism is employed to modify the glass surface compositions and hence the surface topology. We show that accurate quantitative predictions of the hardness of the modified surfaces can be made using topological constraint theory with temperature-dependent constraints. Experimental results reveal that Ca2+ diffusion is most intense in glasses with lowest BO4 fraction, whereas Na+ diffusion is only significant when nonbridging oxygens start to form. These phenomena are interpreted in terms of the atomic packing and the local electrostatic environments of the cations.
Spectroscopy of the copper dimer in normal fluid, superfluid, and solid H4e
Authors: Lebedev V. , Moroshkin P. , Toennies J. P. , Weis A.
Published: October 2010

Copper atoms and molecules are laser ablated into bulk liquid and solid helium, and the emission spectra of the laser excited D→X, B→X, and a→X transitions of Cu2 are observed to exhibit clearly resolved vibrational bands. Surprisingly, for the D→X and the B→X transitions, no differences were observed for superfluid He at 1.5 K, for the normal liquid at 2.65 K, or for the 1.5 K solid at higher pressures of about 30 bars. An interpretation based on the bubble model indicates that the interaction with the He matrix is much weaker than in the case of the alkali atoms. Compared to other solid rare gas matrices, the line shifts and line widths in condensed helium are much smaller by nearly an order of magnitude.
On the reverse gate leakage current of AlGaN/GaN high electron mobility transistors
Authors: Yan Dawei , Lu Hai , Cao Dongsheng , Chen Dunjun , Zhang Rong , Zheng Youdou
Published: October 2010

In this work, we include the polarization effect within the AlGaN barrier into calculation of the near-surface electrical field ES underneath the Schottky contact metal which determines the field-dependent characteristics of reverse gate leakage current of AlGaN/GaN high electron mobility transistors. High-frequency capacitance-voltage measurement combined with electrostatic analysis is used to estimate ES as a function of reverse bias voltage. The resultant log(I/ES) versus ES curves over a temperature range from 293 to 453 K agree well with the predicted model of Frenkel–Poole (FP) emission of electrons up to the conductive states of threading dislocations. Around zero bias, the reverse polarization-field-induced FP emission current is balanced by a forward defect-assisted tunneling current, both of which follow the same temperature dependent characteristics.
The origin of the resistance change in GeSbTe films
Authors: Jang Moon Hyung , Park Seung Jong , Park Sung Jin , Cho Mann-Ho , Kurmaev E. Z. , Finkelstein L. D. , Chang Gap Soo
Published: October 2010

Amorphous Ge2Sb2Te5 (a-GST) films were deposited by ion beam sputtering deposition. Extended x-ray absorption fine structure (EXAFS) data confirmed the existence of the Ge–Ge homopolar bonds in the films. Raman spectra also indicated that the Ge tetrahedral coordination in the a-GST film disappeared after an annealing treatment above 220 °C. Resonantly excited Ge L2,3 x-ray emission spectra (which probe occupied Ge 3d4s-electronic states) show that the phase change from the amorphous to crystalline state is accompanied by a reduction in the Ge I(L2)/I(L3) intensity ratio due to a L2L3N Coster–Kronig transition, indicating that the number of carriers is increased in the Ge 4sp valence state. These findings constitute direct evidence for the contribution of the Ge electronic states to the resistivity change.
Diluted manganese on the bond-centered site in germanium
Authors: Decoster S. , Cottenier S. , Wahl U. , Correia J. G. , Pereira L. M. C. , Lacasta C. , Da Silva M. R. , Vantomme A.
Published: October 2010

The functional properties of Mn-doped Ge depend to large extent on the lattice location of the Mn impurities. Here, we present a lattice location study of implanted diluted Mn by means of electron emission channeling. Surprisingly, in addition to the expected substitutional lattice position, a large fraction of the Mn impurities occupies the bond-centered site. Corroborated by ab initio calculations, the bond-centered Mn is related to Mn-vacancy complexes. These unexpected results call for a reassessment of the theoretical studies on the electrical and magnetic behavior of Mn-doped Ge, hereby including the possible role of Mn-vacancy complexes.
Non-melting super-resolution near-field apertures in Sb–Te alloys
Authors: Simpson R. E. , Fons P. , Wang X. , Kolobov A. V. , Fukaya T. , Tominaga J.
Published: October 2010

The super-resolution near-field structure permits the formation of short-lived subdiffraction limit apertures that channel electromagnetic energy at the aperture boundary. This effect is commonly observed when a laser is focused onto a thin film of Sb based material. The aperture formation within Sb, Sb2Te3, Sb2Te, and SbTe is investigated by time resolved optical pump-probe techniques and found to occur without melting. Ab initio modeling has shown a threshold-like change in the optical properties below the melting temperature which leads to the formation of a near-field aperture. This threshold is shown to be a consequence of thermally induced misalignment of p-type bonding.
Carrier-suppressing effect of scandium in InZnO systems for solution-processed thin film transistors
Authors: Choi Yuri , Kim Gun Hee , Jeong Woong Hee , Bae Jung Hyeon , Kim Hyun Jae , Hong Jae-Min , Yu Jae-Woong
Published: October 2010

The carrier-suppressing effect of Sc in InZnO systems was studied using thin-film transistors (TFTs) with a sol-gel processed active channel. As the amount of Sc content increased, the off current decreased, and the threshold voltage shifted to a positive bias region. The Sc effectively controlled the oxygen vacancies and supplied free electrons. X-ray photoelectron spectroscopy (XPS) verified that the vacancy-related oxygen 1s peak decreased with increasing Sc content. The TFT performance with 14% Sc showed that a field-effect mobility and on-off ratio were 2.06 cm2/V s and 8.02×106, respectively.
Shear piezoelectricity in bone at the nanoscale
Authors: Minary-Jolandan Majid , Yu Min-Feng
Published: October 2010

Recent demonstration of shear piezoelectricity in an isolated collagen fibril, which is the origin of piezoelectricity in bone, necessitates investigation of shear piezoelectric behavior in bone at the nanoscale. Using high resolution lateral piezoresponse force microcopy (PFM), shear piezoelectricity in a cortical bone sample was studied at the nanoscale. Subfibrillar structure of individual collagen fibrils with a periodicity of 60–70 nm were revealed in PFM map, indicating the direct contribution of collagen fibrils to the shear piezoelectricity of bone.
Silicon-photonics light source realized by III–V/Si-grating-mirror laser
Authors: Chung Il-Sug , Mørk Jesper
Published: October 2010

A III–V/Si vertical-cavity in-plane-emitting laser structure is suggested and numerically investigated. This hybrid laser consists of a distributed Bragg reflector, a III–V active region, and a high-index-contrast grating (HCG) connected to an in-plane output waveguide. The HCG and the output waveguide are made in the Si layer of a silicon-on-insulator wafer by using Si-electronics-compatible processing. The HCG works as a highly-reflective mirror for vertical resonance and at the same time routes light to the in-plane output waveguide. Numerical simulations show superior performance compared to existing silicon light sources.
Electronic structures and transverse electrical field effects in folded zigzag-edged graphene nanoribbons
Authors: Zheng X. H. , Song L. L. , Wang R. N. , Hao H. , Guo L. J. , Zeng Z.
Published: October 2010

Folded graphene nanoribbons were observed and their unusual transport properties were reported recently. In this work, the electronic structures and the effects of external transverse electrical field in the folded zigzag-edged graphene nanoribbons (ZGNRs) are investigated by first-principles calculations. It is found that, the folding does not break the semiconductivity, the antiferromagnetically coupled edge states and edge magnetism characteristic of ZGNRs. Interestingly, when external electrical field is applied, the ribbons can be turned to metal or half-metal, depending on the direction of the field. The robustness of the half-metallicity and the edge magnetism to the electrical field is also discussed.
Poling-inhibited ridge waveguides in lithium niobate crystals
Authors: Sones C. L. , Ganguly P. , Ying C. Y. J. , Soergel E. , Eason R. W. , Mailis S.
Published: October 2010

Ultraviolet laser irradiation of a lithium niobate +z polar surface enables the production of ridge waveguides. Ultraviolet laser induced inhibition of poling is used to define an inverted domain pattern which transforms into a ridge structure by differential etching in hydrofluoric acid. The laser irradiation step also induces a refractive index change that provides the vertical confinement within the ridge structure. Furthermore, it was observed that poling-inhibition results in a significant enhancement of the refractive index contrast between the bulk crystal and the ultraviolet irradiated tracks.
Surface tensions and surface potentials of acid solutions
Authors: dos Santos Alexandre P. , Levin Yan
Published: October 2010

A theory is presented which allows us to quantitatively calculate the excess surface tension of acid solutions. The H+, in the form of hydronium ion, is found to be strongly adsorbed to the solution-air interface. To account for the electrostatic potential difference measured experimentally, it is necessary to assume that the hydronium ion is oriented with its hydrogens pointing into the bulk water. The theory is quantitatively accurate for surface tensions and is qualitative for electrostatic potential difference across the air-water interface.