bluuebunny/crossref_metadata_2025 huggingface dataset:
Microwave dielectric constant of Titan‐relevant materials
Authors: Paillou Philippe , Lunine Jonathan , Ruffié Gilles , Encrenaz Pierre , Wall Stephen , Lorenz Ralph , Janssen Michael
Published: September 2008

For four years, the Cassini Radar instrument has slowly revealed the surface of Titan. It has discovered cryovolcanic flows, craters, dunes, channels, rivers, lakes and seas. In order to analyze and model the microwave behaviour of Titan's surface, we need to know the dielectric constant of its surface materials. We present here Ku‐band (10 and 13 GHz) measurements of the dielectric constant of various materials that are likely to be present on Titan. Most of the measured values are in the 1.5–4.3 range with a very low loss tangent (less than 10−2), consistent with results obtained from the Radar scatterometer and radiometer modes, indicating that the Cassini Ku‐band Radar should penetrate several meters of Titan's surface.
Contribution of stratospheric ozone to the interannual variability of tropospheric ozone in the northern extratropics
Authors: Terao Yukio , Logan Jennifer A. , Douglass Anne R. , Stolarski Richard S.
Published: September 2008

We examined the role of variability in the input of stratospheric ozone on the interannual variability of tropospheric ozone in the northern extratropics using correlations of monthly ozone anomalies for the lower stratosphere and the troposphere. We used output from a multiyear simulation of the NASA Goddard Space Flight Center (GSFC) Chemistry and Transport Model (CTM), and evaluated model results using ozonesonde data. The GSFC CTM explicitly calculates stratospheric ozone and simulates separate tracers of stratospheric and tropospheric ozone (O3‐strat and O3‐trop, respectively). The climatological seasonal cycle of ozone shows that O3‐strat contributes significantly to the spring maximum of ozone at 500 hPa, ∼40% at high latitudes and ∼30% at midlatitudes. We find large regional differences in the correlation of ozone in the lower stratosphere and troposphere in the model that are supported by the ozonesonde data. Highest correlations are found from the eastern Atlantic to Europe, from the eastern Pacific to the western United States, and over the polar regions, in winter‐spring. This spatial pattern is due to the input of O3‐strat into the troposphere. The distribution and time lag of the correlations (highest with no lag for midlatitudes and a 1–2 month lag for polar regions) are consistent with the dynamical indicators of stratosphere‐troposphere exchange (STE), such as storm tracks in the midlatitudes and slow descending motion in the polar region. Our simple approach can be widely applied to diagnose the effect of STE on tropospheric ozone.
Earth surface reflectance climatology from 3 years of OMI data
Authors: Kleipool Q. L. , Dobber M. R. , de Haan J. F. , Levelt P. F.
Published: September 2008

Global maps of the Earth's surface Lambertian equivalent reflectance (LER) are constructed using 3 years of Ozone Monitoring Instrument (OMI) measurements obtained between October 2004 and October 2007 at 23 wavelengths between 328 and 500 nm. The maps are constructed on a 0.5° by 0.5° longitude‐latitude grid for each calendar month using an algorithm based on temporal histograms of the observed LER values per geophysical location. The algorithm allows seasonal effects related to vegetation, snow, and ice but excludes statistical outliers. The maps show typical features like open ocean regions with high reflectivity indicative of low phytoplankton levels, coastal waters with high reflectance caused by silt, and oceanic regions with low reflectance correlated with chlorophyll. Open oceans in general have a higher reflectivity than does land up to 420 nm. The highest reflectivity values of oceans occur at 380 nm. Good agreement is found with a similar LER map based on data from the Total Ozone Mapping Spectrometer (TOMS) at 331, 340, 360, and 380 nm, which is 0.015 lower on average. The comparison with data from the Global Ozone Monitoring Experiment (GOME) at 335, 380, 440, and 494 nm is also satisfactory, being 0.005 lower on average. The LER derived from OMI data is approximately 0.02 higher than the black sky albedo as derived from the Moderate Resolution Imaging Spectroradiometer at 470 nm, which is partly related to viewing geometry effects of the bidirectional reflectance distribution function of the surface. The data set presented contains residual cloud features over tropical rain forest regions, has a higher spatial resolution than those created using TOMS and GOME data, and includes more wavelengths.
Millennial‐scale surface and subsurface paleothermometry from the northeast Atlantic, 55–8 ka BP
Authors: Peck V. L. , Hall I. R. , Zahn R. , Elderfield H.
Published: September 2008

We present high‐resolution records of upper ocean temperatures derived from Mg/Ca ratios of surface‐dwelling Globigerina bulloides and subsurface‐dwelling Neogloboquadrina pachyderma sinistral and the relative abundance of N. pachyderma sinistral for the period 55–8 ka BP from NE Atlantic sediment core MD01‐2461. Millennial‐scale temporal variability and longer‐term trends in these records enable us to develop a detailed picture of past ocean conditions such as a weakening of thermocline intensity from marine isotope stage 3 (MIS 3) to the last glacial maximum (LGM). The correspondence of all temperature proxies and convergence of paired oxygen isotope (δ18O) records from both planktonic species implies a breakdown in the thermocline and year‐round mixing of the upper water column through the LGM, perhaps related to decreasing insolation and additional cooling in association with the expansion of the circum–North Atlantic ice sheets. Millennial‐scale divergence in surface and subsurface temperatures and δ18O across the last glacial correspond to meltwater release and the development of a strong halocline associated with both Heinrich (H) events and instabilities of the NW European ice sheet. During such episodes, G. bulloides Mg/Ca appears to record ambient, even warming summer sea surface temperatures across H events while the other proxies record maximum cooling.
Mechanism of the elevation in cardiolipin during HeLa cell entry into the S-phase of the human cell cycle
Authors: Hauff Kristin , Linda Dorota , Hatch Grant M.
Published: September 2008

CL (cardiolipin) is a key phospholipid involved in ATP generation. Since progression through the cell cycle requires ATP we examined regulation of CL synthesis during S-phase in human cells and investigated whether CL or CL synthesis was required to support nucleotide synthesis in S-phase. HeLa cells were made quiescent by serum depletion for 24 h. Serum addition resulted in substantial stimulation of [methyl-3H]thymidine incorporation into cells compared with serum-starved cells by 8 h, confirming entry into the S-phase. CL mass was unaltered at 8 h, but increased 2-fold by 16 h post-serum addition compared with serum-starved cells. The reason for the increase in CL mass upon entry into S-phase was an increase in activity and expression of CL de novo biosynthetic and remodelling enzymes and this paralleled the increase in mitochondrial mass. CL de novo biosynthesis from D-[U-14C]glucose was elevated, and from [1,3-3H]glycerol reduced, upon serum addition to quiescent cells compared with controls and this was a result of differences in the selection of precursor pools at the level of uptake. Triascin C treatment inhibited CL synthesis from [1-14C]oleate but did not affect [methyl-3H]thymidine incorporation into HeLa cells upon serum addition to serum-starved cells. Barth Syndrome lymphoblasts, which exhibit reduced CL, showed similar [methyl-3H]thymidine incorporation into cells upon serum addition to serum-starved cells compared with cells from normal aged-matched controls. The results indicate that CL de novo biosynthesis is up-regulated via elevated activity and expression of CL biosynthetic genes and this accounted for the doubling of CL seen during S-phase; however, normal de novo CL biosynthesis or CL itself is not essential to support nucleotide synthesis during entry into S-phase of the human cell cycle.
Modelling the dynamics of signalling pathways
Authors: Sreenath Sree N. , Cho Kwang-Hyun , Wellstead Peter
Published: September 2008

In the present chapter we discuss methodologies for the modelling, calibration and validation of cellular signalling pathway dynamics. The discussion begins with the typical range of techniques for modelling that might be employed to go from the chemical kinetics to a mathematical model of biochemical pathways. In particular, we consider the decision-making processes involved in selecting the right mechanism and level of detail of representation of the biochemical interactions. These include the choice between (i) deterministic and stochastic chemical kinetics representations, (ii) discrete and continuous time models and (iii) representing continuous and discrete state processes. We then discuss the task of calibrating the models using information available in web-based databases. For situations in which the data are not available from existing sources we discuss model calibration based upon measured data and system identification methods. Such methods, together with mathematical modelling databases and computational tools, are often available in standard packages. We therefore make explicit mention of a range of popular and useful sites. As an example of the whole modelling and calibration process, we discuss a study of the cross-talk between the IL-1 (interleukin-1)-stimulated NF-κB (nuclear factor κB) pathway and the TGF-β (transforming growth factor β)-stimulated Smad2 pathway.
The harmony of the cell: the regulatory design of cellular processes
Authors: Hofmeyr Jan-Hendrik S.
Published: September 2008

The living cell is a complex system of interacting processes. The properties of the agents that facilitate these processes, such as enzymes, transporters and receptors, must be tuned to each other if the system is to behave harmoniously. The present chapter describes how the regulatory design of cellular subsystems that makes this harmonious behaviour possible can be visualized on a graph that combines the so-called log–log rate characteristics of these subsystems. The tools that are needed to create and analyse these graphs are metabolic control analysis, supply-demand analysis, enzyme kinetics and computer simulation.
Modelling cellular signalling systems
Authors: Rangamani Padmini , Iyengar Ravi
Published: September 2008

Cell signalling pathways and networks are complex and often non-linear. Signalling pathways can be represented as systems of biochemical reactions that can be modelled using differential equations. Computational modelling of cell signalling pathways is emerging as a tool that facilitates mechanistic understanding of complex biological systems. Mathematical models are also used to generate predictions that may be tested experimentally. In the present chapter, the various steps involved in building models of cell signalling pathways are discussed. Depending on the nature of the process being modelled and the scale of the model, different mathematical formulations, ranging from stochastic representations to ordinary and partial differential equations are discussed. This is followed by a brief summary of some recent modelling successes and the state of future models.
Systems biology of JAK/STAT signalling
Authors: Pfeifer Andrea C. , Timmer Jens , Klingmüller Ursula
Published: September 2008

Signalling in multicellular organisms is mediated by complex networks that integrate extracellular and intracellular signals to generate appropriate responses regulating cell proliferation, differentiation and survival. Downstream of many cytokine and growth hormone receptors, receptor-associated JAKs (Janus kinases) activate transcription factors of the STAT (signal transducer and activator of transcription) protein family and thereby mediate signal transduction from the plasma membrane to the nucleus. The JAK/STAT pathway has been shown to be constitutively activated in a wide array of human malignancies. To elucidate mechanisms contributing to tumour formation and identify system properties of the JAK/STAT signalling pathway, a systems biology approach can be employed. So far the majority of studies available have focused on down-regulation of the signalling pathway based on simulations. However, a data-based model of the core module of the JAK2/STAT5 signalling pathway showed that rapid nucleocytoplasmic cycling of STAT5 is an essential pathway property. In the future, combining assays for quantitative analysis at different levels will be important to gain deeper insight into molecular mechanisms regulating intracellular communication mediated by such complex dynamic systems as signalling pathways and their targets.
Single live-cell imaging for systems biology 9
Authors: Mullassery Dhanya , Horton Caroline A. , Wood Christopher D. , White Michael R.H.
Published: September 2008

Understanding how mammalian cells function requires a dynamic perspective. However, owing to the complexity of signalling networks, these non-linear systems can easily elude human intuition. The central aim of systems biology is to improve our understanding of the temporal complexity of cell signalling pathways, using a combination of experimental and computational approaches. Live-cell imaging and computational modelling are compatible techniques which allow quantitative analysis of cell signalling pathway dynamics. Non-invasive imaging techniques, based on the use of various luciferases and fluorescent proteins, trace cellular events such as gene expression, protein–protein interactions and protein localization in cells. By employing a number of markers in a single assay, multiple parameters can be measured simultaneously in the same cell. Following acquisition using specialized microscopy, analysis of multi-parameter time-lapse images facilitates the identification of important qualitative and quantitative relationships–linking intracellular signalling, gene expression and cell fate.
Short-term volume and turgor regulation in yeast
Authors: Schaber Jörg , Klipp Edda
Published: September 2008

Volume is a highly regulated property of cells, because it critically affects intracellular concentration. In the present chapter, we focus on the short-term volume regulation in yeast as a consequence of a shift in extracellular osmotic conditions. We review a basic thermodynamic framework to model volume and solute flows. In addition, we try to select a model for turgor, which is an important hydrodynamic property, especially in walled cells. Finally, we demonstrate the validity of the presented approach by fitting the dynamic model to a time course of volume change upon osmotic shock in yeast.
Parameter estimation and optimal experimental design
Authors: Banga Julio R. , Balsa-Canto Eva
Published: September 2008

Mathematical models are central in systems biology and provide new ways to understand the function of biological systems, helping in the generation of novel and testable hypotheses, and supporting a rational framework for possible ways of intervention, like in e.g. genetic engineering, drug development or treatment of diseases. Since the amount and quality of experimental ‘omics’ data continue to increase rapidly, there is great need for methods for proper model building which can handle this complexity. In the present chapter we review two key steps of the model building process, namely parameter estimation (model calibration) and optimal experimental design. Parameter estimation aims to find the unknown parameters of the model which give the best fit to a set of experimental data. Optimal experimental design aims to devise the dynamic experiments which provide the maximum information content for subsequent non-linear model identification, estimation and/or discrimination. We place emphasis on the need for robust global optimization methods for proper solution of these problems, and we present a motivating example considering a cell signalling model.
Systems biology model databases and resources
Authors: van Gend Carel , Snoep Jacky L.
Published: September 2008

Systems biology aims at a quantitative understanding of systemic behaviour as a function of its components and their interactions. In systems biology studies computer models play an important role: (i) to integrate the components’ behaviour and (ii) to analyse experimental data sets. With the growing number of kinetic models that are being constructed for parts of biological systems, it has become important to store these models and make them available in a standard form, such that these models can be combined, eventually leading to a model of a complete system. In the present chapter we describe database initiatives that contain kinetic models for biological systems, together with a number of other systems biology resources related to kinetic modelling.
Organic/inorganic nanocomposites for high-dielectric-constant materials
Authors: Sarasqueta Galileo , Roy Choudhury Kaushik , Kim Do Young , So Franky
Published: September 2008

A different approach to fabricate metallic nanostructures in an insulating organic matrix in situ using thermal coevaporation is demonstrated. The method is used to fabricate metal-organic percolative nanocomposite capacitors. Thermal annealing of the nanocomposite films results in a dramatic enhancement (>50 times at 10kHz) of the dielectric constant accompanied by significant lowering (approximately four times) of conductivity and dissipation loss, especially at low frequencies. The improved performance is attributed to structural modifications in the films resulting from enhanced phase segregation of constituents, induced by annealing at optimized temperatures.
Size dependence of core and valence binding energies in Pd nanoparticles: Interplay of quantum confinement and coordination reduction
Authors: Aruna I. , Mehta B. R. , Malhotra L. K. , Shivaprasad S. M.
Published: September 2008

An analysis is given of the electronic structure of Pd nanoparticles synthesized by inert gas evaporation technique. A study of the effect of size on various core and valence electrons in Pd nanoparticles reveals a varied dependence of binding energy of electrons in different electronic levels. The shift in the Pd x-ray photoelectron spectroscopy 4d valence band centroid is more than the core level shift. The results of the present study provide a direct evidence of interplay of quantum confinement (a size effect) and coordination reduction (a surface effect).
Electrotunable band gaps of one- and two-dimensional photonic crystal structures based on silicon and liquid crystals
Authors: Arriaga J. , Dobrzynski L. , Djafari-Rouhani B.
Published: September 2008

One- and two-dimensional photonic crystals based on silicon with infiltrated liquid crystals are investigated in this paper. We show that the photonic band gap can be continuously tuned changing the orientation of the director of the liquid crystal. For the one-dimensional case, we considered arbitrary direction of propagation of the electromagnetic waves, and we show that it is possible to tune the photonic band gap by an adequate orientation of the liquid crystal. For the two-dimensional case and propagation in the plane of periodicity, we show that there exists no complete photonic band gap in the system for both polarizations. We consider two different configurations, square array of solid Si cylinders in liquid crystal background and a triangular array of liquid crystal cylinders surrounded by Si. We show that for the triangular array it is possible to tune the photonic band gap only for the transversal electric modes. We used the plane wave expansion method to solve the Maxwell equations for anisotropic systems.
Theoretical study of the D̃→C̃ emission spectrum of NO2
Authors: Schinke R.
Published: September 2008

The 3 A2′(D̃)→1 A2″(C̃) emission spectrum of NO2 has been calculated by means of exact dynamics calculations and an accurate potential energy surface for the C̃ state. The potential energy surface has been obtained by electronic structure calculations employing the internally contracted multireference configuration interaction method plus Davidson correction and the augmented correlation consistent polarized quadruple zeta basis set. The calculated spectrum, based on energies as well as intensities, agrees well with the measured one. Despite the two asymmetric Cs potential wells of the C̃ potential energy surface, the spectrum is best described by a C2v assignment in terms of symmetric stretch, bending, and antisymmetric stretch quantum numbers. The barrier separating the two wells is merely of the order of 500 cm−1 with the consequence that only the two lowest states, (0,0,0) and (0,0,1), show a tunneling splitting. Essential for the correct assignment of the spectrum is the pronounced negative anharmonicity of the antisymmetric stretch mode. Excitation of the symmetric stretch mode is not directly seen in the main part of the spectrum.
A new crossed molecular beam apparatus using time-sliced ion velocity imaging technique
Authors: Wu Guorong , Zhang Weiqing , Pan Huilin , Shuai Quan , Jiang Bo , Dai Dongxu , Yang Xueming
Published: September 2008

A new crossed molecular beam apparatus has been constructed for investigating polyatomic chemical reactions using the time-sliced ion velocity map imaging technique. A unique design is adopted for one of the two beam sources and allows us to set up the molecular beam source either horizontally or vertically. This can be conveniently used to produce versatile atomic or radical beams from photodissociation and as well as electric discharge. Intensive H-atom beam source with high speed ratio was produced by photodissociation of the HI molecule and was reacted with the CD4 molecule. Vibrational-state resolved HD product distribution was measured by detecting the CD3 product. Preliminary results were also reported on the F+SiH4 reaction using the discharged F atom beam. These results demonstrate that this new instrument is a powerful tool for investigating chemical dynamics of polyatomic reactions.
Damping behavior of carbon nanotube reinforced aluminum oxide coatings by nanomechanical dynamic modulus mapping
Authors: Balani Kantesh , Agarwal Arvind
Published: September 2008

Nanomechanical dynamic analysis has been utilized to evaluate damping behavior of plasma sprayed carbon nanotube (CNT) reinforced Al2O3 ceramic coatings. Addition and dispersion of CNTs in Al2O3 matrix elicited modulus enhancement from 200 to 400 GPa. Tan delta increases from 0.26 for Al2O3 to 0.39 with 8 wt % CNT coating. CNT bending and curling, Al2O3 coating on CNT, interparticle Al2O3 friction, and CNT/splat sliding serve as strong loss mechanisms in imparting enhanced damping to Al2O3 nanocomposites reinforced with CNTs. Damping and fracture toughness of CNT-Al2O3 coating is semiempirically related to the enhancement of storage modulus and tan delta with varying CNT content and degree of dispersion.
Experiment and simulation of the compositional evolution of Ti–B thin films deposited by sputtering of a compound target
Authors: Neidhardt Jörg , Mráz Stanislav , Schneider Jochen M. , Strub Erik , Bohne Wolfgang , Liedke Bartosz , Möller Wolfhard , Mitterer Christian
Published: September 2008

The evolution of the coating stoichiometry with pressure, target-substrate distance, and angle was analyzed for dc sputtering of TixB (x=0.5, 1, 1.6) compound targets by elastic recoil detection analysis. For an investigation of the underlying fundamental processes primarily Ar was used as sputter gas. Additionally, the effect of a reactive gas (N2) as well as bias voltage (floating up to −200 V) was briefly cross-checked. For deposition along the target normal (90°) a pronounced Ti-deficiency of up to 20% is detected. Increasing the pressure or distance from 0.5 to 2 Pa and from 5 to 20 cm, respectively, leads to an almost equivalent linear increase in Ti/B ratio surpassing even the target composition. Off-axis depositions at lower angles (30° and 60°) on the other hand result in a higher Ti/B ratio. This is consistent with results obtained from Monte Carlo simulations combining the respective emission characteristics from the sputter process as well as the gas-phase transport. Hence, the pressure, distance, and sample position induced changes in chemical film composition can be understood by considering gas scattering and the angular distribution of the sputtered flux. The theoretically determined transition from a directional flux to thermal diffusion was experimentally verified by mass-energy analysis of the film-forming atoms.
Effects of triplet energies and transporting properties of carrier transporting materials on blue phosphorescent organic light emitting devices
Authors: Lee Jaewon , Chopra Neetu , Eom Sang-Hyun , Zheng Ying , Xue Jiangeng , So Franky , Shi Jianmin
Published: September 2008

We have studied the effects of the hole transporting layers and electron transporting layers on the device efficiencies of iridium(III) bis[(4,6-di-fluorophenyl)-pyridinato-N,C2′] picolinate (FIrpic) doped 3,5′−N,N′-dicarbazole-benzene (mCP) host blue phosphorescent organic light emitting diodes. We found that the device efficiency is very sensitive to the hole transporting materials used and both the triplet energy and carrier transport properties affect the device efficiency. On the other hand, there is no apparent correlation between the device efficiency and the triplet energy of the electron transporting material used. Instead, the device efficiency is affected by the electron mobility of the electron transporting layer only.
Flux pinning properties of YBCO/DyBCO multilayers
Authors: Develos-Bagarinao K. , Yamasaki H. , Ohki K.
Published: September 2008

Multilayered structures of YBa2Cu3O7−δ (YBCO) interlayered with thin layers of DyBa2Cu3O7-δ (DyBCO) were prepared on CeO2-buffered r-cut sapphire (Al2O3) substrates by pulsed laser deposition. Evaluation of the magnetic-field angular dependence of the critical current density [Jc(H,θ)] revealed that the flux pinning properties of multilayered YBCO/DyBCO films were significantly enhanced in comparison to single-layer YBCO films (monolayers) prepared using the same experimental parameters. The YBCO/DyBCO multilayers are highly anisotropic, i.e., the angular-dependent Jc exhibits a very prominent peak when the applied magnetic field (H) is oriented parallel to the ab-plane direction (H∥ab). Analysis of the Jc(H,θ) data revealed an enhanced random pinning for the multilayers for the entire range of field investigated. In the angular-dependent Jc data, correlated pinning along the c-axis crystallographic direction was also evidenced at low applied fields by a less prominent peak at H∥c. This result was further corroborated by the presence of defect microstructures comprised of linear and planar defects which were considered as strong sources of c-axis-correlated pinning. However, for higher applied fields the contribution of c-axis-correlated pinning is highly diminished and the ratio of Jc(H∥ab) to Jc(H∥c) is significantly enhanced. In addition to enhanced random pinning, it is considered that improved pinning along the H∥ab direction occurs due to ab-correlated pinning, arising from intrinsic pinning and possibly extended planar defects.
Hybrid functionals with local range separation
Authors: Krukau Aliaksandr V. , Scuseria Gustavo E. , Perdew John P. , Savin Andreas
Published: September 2008

Range-separated (screened) hybrid functionals provide a powerful strategy for incorporating nonlocal exact (Hartree–Fock-type) exchange into density functional theory. Existing implementations of range separation use a fixed system-independent screening parameter. Here, we propose a novel method that uses a position-dependent screening function. These locally range-separated hybrids add substantial flexibility for describing diverse electronic structures and satisfy a high-density scaling constraint better than the fixed screening approximation does.
Effectiveness of silicon as a laser shinethrough barrier for 351-nm light
Authors: Edgell D. H. , Seka W. , Bahr R. E. , Boehly T. R. , Bonino M. J.
Published: September 2008

Many laser beams directly illuminate a spherical target in direct-drive inertial confinement fusion experiments, ionizing the outer surface and surrounding the target with a plasma containing an opaque critical surface. In the earliest stages of irradiation, before the plasma forms a critical-density surface, laser light can penetrate into the target. This “shinethrough” light can be sufficiently intense to undergo filamentation and damage the inside of the target, thereby seeding hydrodynamic instabilities. Laser shinethrough can be blocked by a thin coating of opaque material, such as, aluminum (Al). For cryogenic direct-drive targets, the shinethrough barrier material must also be compatible with cryogenic target fabrication procedures, which rules out Al layers since they would interfere with permeation filling and optical characterization of cryogenic targets. Silicon (Si) has been found to be a promising candidate for a direct-drive cryogenic target shinethrough barrier material. Several cryogenic targets have been coated with Si, successfully permeation filled with either deuterium (D2) or deuterium-tritium (DT), and subsequently layered and optically characterized. Various thicknesses of Si coatings have been applied to planar targets and tested under relevant irradiation conditions. Experiments have shown that 200Å of Si is sufficient to protect targets from laser shinethrough.
V/Al/V/Ag contacts to n-GaN and n-AlGaN
Authors: Miller M. A. , Lin S.-K. , Mohney S. E.
Published: September 2008

Low-resistance V/Al/V/Ag contacts have recently been reported to Al0.27Ga0.73N/GaN heterostructures with a thin GaN cap. These contacts had smooth surfaces and good edge definition. In this study, the V/Al/V/Ag metallization was adapted to other compositions of n-AlxGa1−xN, and it was found to provide low specific contact resistances as well as smooth surfaces on both n-GaN and n-Al0.58Ga0.42N. Another advantage of these contacts is that limited changes in specific contact resistance and morphology were observed when changing the metal layer thicknesses and processing conditions of the V/Al/V/Ag metallization on these semiconductors. The V (20)/Al (95)/V (20)/Ag (120 nm) contact provided a specific contact resistance of (2.1±0.9)×10−6 Ω cm2 when annealed at 825 °C for 30 s on n-GaN and a V (20)/Al (95)/V (5)/Ag (120 nm) contact provided a value of (2.4±0.3)×10−4 Ω cm2 when annealed at 875 °C for 60 s on n-Al0.58Ga0.42N. In each case, transmission electron microscopy revealed that the reaction between the semiconductor and metallization was limited and the majority of the interface was contacted by a composite of primarily Ag-bearing grains. Measurements of the specific contact resistance as a function of temperature revealed that field emission is the dominant current transport mechanism in low resistance Ohmic contacts to n-GaN and n-Al0.58Ga0.42N.
Laser induced gratings enhanced by surface-charge mediated electric field in doped nematic liquid crystals
Authors: Xiang Ying , Liu Yi-Kun , Li Tao , Yang Shun-Lin , Jiang Zhi-Jie
Published: September 2008

The optically induced grating enhanced by dc electric field in nematic liquid crystal (LC) doped with copper porphyrin is studied. The reorientational effect of the LC was not observed for the writing beams with the intensity up to 500 mW/mm2, but the threshold of the reorientation was reduced to 1 mW/mm2 with the assistance of an electric pulse applied to the LC. The low threshold for the induced grating can be retained even after switching off the dc pulse, indicating that an induced field inside the LC is present to sustain the low threshold operation for the induced grating. The low threshold operation does not persist by short circuiting of LC electrodes. The underlying mechanism is explained by an optical surface-charge mediated effect.
Characterization of a supersonic microwave discharge in Ar/H2/Air mixtures
Authors: Drake D. J. , Popović S. , Vušković L.
Published: September 2008

Detailed characterization of a microwave cavity discharge in the supersonic flow of Ar/H2/Air mixtures at static pressures of 1–10 Torr and Mach number 2 is mostly based on emission spectroscopy techniques. In the conditions close to real combustion environments, effects of hydrogen and air admixture to plasma parameters and population of excited species in the discharge are demonstrated. The effects resulting in ionization loss are discussed from the aspects of dominant mechanisms and consequences for the plasma assisted hydrogen oxidation.
Fiber textures of titanium nitride and hafnium nitride thin films deposited by off-normal incidence magnetron sputtering
Authors: Deniz D. , Harper J. M. E.
Published: September 2008

We studied the development of crystallographic texture in titanium nitride (TiN) and hafnium nitride (HfN) films deposited by off-normal incidence reactive magnetron sputtering at room temperature. Texture measurements were performed by x-ray pole figure analysis of the (111) and (200) diffraction peaks. For a deposition angle of 40° from substrate normal, we obtained TiN biaxial textures for a range of deposition conditions using radio frequency (rf) sputtering. Typically, we find that the ⟨111⟩ orientation is close to the substrate normal and the ⟨100⟩ orientation is close to the direction of the deposition source, showing substantial in-plane alignment. We also introduced a 150 eV ion beam at 55° with respect to substrate normal during rf sputtering of TiN. Ion beam enhancement caused TiN to align its out-of-plane texture along ⟨100⟩ orientation. In this case, (200) planes are slightly tilted with respect to the substrate normal away from the ion beam source, and (111) planes are tilted 50° toward the ion beam source. For comparison, we found that HfN deposited at 40° without ion bombardment has a strong ⟨100⟩ orientation parallel to the substrate normal. These results are consistent with momentum transfer among adatoms and ions followed by an increase in surface diffusion of the adatoms on (200) surfaces. The type of fiber texture results from a competition among texture mechanisms related to surface mobilities of adatoms, geometrical, and directional effects.
Asymmetric one-dimensional random walks
Authors: Antczak Grazyna , Ehrlich Gert
Published: September 2008

For one-dimensional surface diffusion in the presence of fields, movement of particles has to be considered as a random walk in which jumps to the right occur at a rate different from jumps to the left. Moments of the displacement distribution are worked out for such a one-dimensional walk to nearest-neighbor sites as well as by longer jumps to second nearest neighbors. The actual distribution of displacements, and how it changes as the asymmetry of the jump rates changes, is also examined, as this provides important information about the participating jump processes. We show that deriving the third moment gives a clear indication of the asymmetry in the random walk.
Evaluation of a ln tan integral arising in quantum field theory
Authors: Coffey Mark W.
Published: September 2008

We analytically evaluate a dilogarithmic integral that is prototypical of volumes of ideal tetrahedra in hyperbolic geometry. We additionally obtain new representations of the Clausen function Cl2 and the Catalan constant G=Cl2(π/2), as well as new relations between sine and Clausen function values.
A compact UHV deposition system for in situ study of ultrathin films via hard x-ray scattering and spectroscopy
Authors: Couet Sebastien , Diederich Thomas , Schlage Kai , Röhlsberger Ralf
Published: September 2008

We report on a compact ultrahigh vacuum deposition system developed for in situ experiments using hard x rays. The chamber can be mounted on various synchrotron beamlines for spectroscopic as well as scattering experiments in grazing incidence geometry. The deposition process is completely remotely controlled and an ellipsometer is available for online monitoring of the layer growth process. The unique sample position in the chamber allows one to perform deposition, grazing incidence x-ray experiments, and ellipsometry measurements at the same time, enabling to correlate the x-ray analysis with parameters of the growth process. Additionally, the setup can be used to study in situ chemical and structural changes in an element specific manner by x-ray absorption spectroscopy. The flexibility and versatility of the system brings new possibilities to study the chemistry and structure of surfaces and interfaces in thin films systems during their formation.
Bright spots in 1 MA X pinches as a function of wire number and material
Authors: Sinars D. B. , Pikuz S. A. , Douglass J. D. , McBride R. D. , Ampleford D. J. , Knapp P. , Bell K. , Chalenksi D. , Cuneo M. E. , Greenly J. B. , Hammer D. A. , Kusse B. R. , Mingaleev A. , Shelkovenko T. A. , Wenger D. F.
Published: September 2008

Bright, intense x-ray sources with extreme plasma parameters (micropinch plasmas) have previously been characterized at 0.1–0.4MA, but the scaling of such sources at higher current is poorly understood. The x-ray source size and radiation power of 1MA X pinches were studied as a function of wire material (Al, Ti, Mo, and W) and number (1-, 2-, 8-, 32-, and 64-wire configurations). The smallest bright spots observed were from 32-wire tungsten X pinches, which produced ⩽11–16μm, ∼2J, 1–10GW sources of 3–5keV radiation.
Frequency conversion of propagating surface plasmon polaritons by organic molecules
Authors: Hakala T. K. , Toppari J. J. , Pettersson M. , Kuzyk A. , Tikkanen H. , Kunttu H. , Törmä P.
Published: September 2008

We demonstrate frequency conversion of surface plasmon polaritons (SPP) by utilizing the coupling between organic dye molecules and SPP. Launching of SPPs into a plasmonic waveguide is done in two ways: by optically excited molecules and by quantum dots (QDs). QDs are demonstrated to overcome the major problem of bleaching occurring with molecules. The SPP propagates tens of micrometers and clear frequency conversion is observed in the SPP spectrum after passing an area of converter molecules. The use of molecules and QDs as elements of all-plasmonic devices has the potential for high integration and use of self-assembly in fabrication.
On the efficiency droop in InGaN multiple quantum well blue light emitting diodes and its reduction with p-doped quantum well barriers
Authors: Xie Jinqiao , Ni Xianfeng , Fan Qian , Shimada Ryoko , Özgür Ümit , Morkoç Hadis
Published: September 2008

Multiple quantum well (MQW) InGaN light emitting diodes with and without electron blocking layers, with relatively small and large barriers, with and without p-type doping in the MQW region emitting at ∼420nm were used to determine the genesis of efficiency droop observed at injection levels of approximately ⩾50A∕cm2. Pulsed electroluminescence measurements, to avoid heating effects, revealed that the efficiency peak occurs at ∼900A∕cm2 current density for the Mg-doped barrier, near 550A∕cm2 for the lightly doped n-GaN injection layer, meant to bring the electron injection level closer to that of holes, and below 220A∕cm2 for the undoped InGaN barrier cases. For samples with GaN barriers (larger band discontinuity) or without p-AlGaN electron blocking layers the droop occurred at much lower current densities (⩽110A∕cm2). In contrast, photoluminescence measurements revealed no efficiency droop for optical carrier generation rates corresponding to the maximum current density employed in pulsed injection measurements. All the data are consistent with heavy effective mass of holes, low hole injection efficiency (due to relatively lower p-doping) leading to severe electron leakage being responsible for efficiency droop.
In Vitro picosecond ultrasonics in a single cell
Authors: Rossignol C. , Chigarev N. , Ducousso M. , Audoin B. , Forget G. , Guillemot F. , Durrieu M. C.
Published: September 2008

Ultrasonics signals at frequencies 5.7±0.1 and 6.8±0.1GHz are measured in two organelles of a single vegetal cell in vitro with a picosecond ultrasonic technique. Using standard values for cell optical index, ultrasound velocities of 1.6±0.1 and 2.0±0.1μm∕ns are measured from several signals recorded in the vacuole and in the nucleus of a single Allium cepa cell, respectively. A 1μm lateral and 0.25μm depth resolution is attained.
40.8% efficient inverted triple-junction solar cell with two independently metamorphic junctions
Authors: Geisz J. F. , Friedman D. J. , Ward J. S. , Duda A. , Olavarria W. J. , Moriarty T. E. , Kiehl J. T. , Romero M. J. , Norman A. G. , Jones K. M.
Published: September 2008

A photovoltaic conversion efficiency of 40.8% at 326 suns concentration is demonstrated in a monolithically grown, triple-junction III–V solar cell structure in which each active junction is composed of an alloy with a different lattice constant chosen to maximize the theoretical efficiency. The semiconductor structure was grown by organometallic vapor phase epitaxy in an inverted configuration with a 1.83 eV Ga.51In.49P top junction lattice-matched to the GaAs substrate, a metamorphic 1.34 eV In.04Ga.96As middle junction, and a metamorphic 0.89 eV In.37Ga.63As bottom junction. The two metamorphic junctions contained approximately 1×105 cm−2 and 2–3×106 cm−2 threading dislocations, respectively.
Exchange bias in NiFe/granular-FeMn–MgO bilayers
Authors: Hu H. N. , Qiu X. P. , Shi Z. , Zhou S. M. , Bai X. J. , Du J. , Sun L.
Published: September 2008

A series of polycrystalline NiFe/(FeMn)1−x(MgO)x bilayers with granular antiferromagnetic layers were prepared by magnetron sputtering. For a specific antiferromagnetic layer thickness, the intensity of the fcc (111) x-ray diffraction peaks from Cu, NiFe, and FeMn layers, and the FeMn grain size exhibit maxima at x=0.025. At this composition, significant enhancement in exchange field is observed together with slight change in coercivity. Remarkably, the training effect in exchange bias is greatly suppressed. These observations indicate the possibility of utilizing granular antiferromagnetic layers in magnetoelectronic devices to improve thermal stability.
Reduction in threading dislocation densities in AlN epilayer by introducing a pulsed atomic-layer epitaxial buffer layer
Authors: Sang L. W. , Qin Z. X. , Fang H. , Dai T. , Yang Z. J. , Shen B. , Zhang G. Y. , Zhang X. P. , Xu J. , Yu D. P.
Published: September 2008

A method of reducing threading dislocation (TD) density in AlN epilayers grown on sapphire substrate is reported. By introducing an AlN buffer layer grown by a pulsed atomic-layer epitaxy method, TDs in epitaxial AlN films were greatly decreased. From transmission electron microscopic images, a clear subinterface was observed between the buffer layer and the subsequently continuous grown AlN epilayer. In the vicinity of the subinterface, the redirection, annihilation, and termination of TDs were observed. The increase in lateral growth rate accounted for TD redirection and annihilation in the AlN epilayer. Strain variation between the two regions resulted in the termination of TDs owing to the dislocation line energy minimization.
Percolating oxide film growth during Cu(111) oxidation
Authors: Zhou Guangwen , Chen Xidong , Gallagher David , Yang Judith C.
Published: September 2008

We report in situ transmission electron microscopy dynamic observations of the early stage oxidation of Cu(111) surfaces at ∼450 °C, which show that the Cu2O film morphology evolves with continued oxidation from initially ramified islands to irregularly connected clusters. The geometrical features of these noncompact oxide films are analyzed in terms of the scaling theory of percolation. We show by kinetic Monte Carlo simulations that the percolating oxide film growth is related to a mechanism of neighbor-dependent site percolation.
Calibration of shielded microwave probes using bulk dielectrics
Authors: Lai K. , Kundhikanjana W. , Kelly M. A. , Shen Z. X.
Published: September 2008

A stripline-type near-field microwave probe is microfabricated for microwave impedance microscopy. Unlike the poorly shielded coplanar probe that senses the sample tens of microns away, the stripline structure removes the stray fields from the cantilever body and localizes the interaction only around the focused-ion beam deposited Pt tip. The approaching curve of an oscillating tip toward bulk dielectrics can be quantitatively simulated and fitted to the finite-element analysis result. The peak signal of the approaching curve is a measure of the sample dielectric constant and can be used to study unknown bulk materials.
Air-stable n-type operation of Gd-contacted carbon nanotube field effect transistors
Authors: Kim Hyo-Suk , Jeon Eun-Kyoung , Kim Ju-Jin , So Hye-Mi , Chang Hyunju , Lee Jeong-O , Park Noejung
Published: September 2008

We report air-stable n-type operations of the single-walled carbon nanotube field effect transistors (SWNT-FETs) fabricated with Gd electrodes. Unlike previously reported n-type SWNT-FETs, our devices maintained their n-type operation characteristics in ambient atmosphere for more than two months. The shallow Gd films with a thickness below 20 nm are corroded by environmental oxygen, whereas the well-contacted Gd-SWNT interfaces underneath the thick Gd layers are protected from contaminations by air molecules. Theoretical studies based on the first-principles electronic structure calculations confirm that Gd layers have an excellent binding affinity to the SWNTs.
Shopping-Related Attitudes: A Factor and Cluster Analysis of Northern California Shoppers
Authors: Mokhtarian Patricia L , Ory David T , Cao Xinyu
Published: September 2008

This paper presents an analysis of general shopping and travel-related attitudes collected from a custom-designed Internet-based survey conducted in the spring of 2006, of randomly selected residents of two communities in Northern California. These and other data collected in the survey will eventually lead to models of shopping mode (channel) choice, intention, and frequency among other analyses. In this early examination of the data ( N = 966), exploratory factor analysis is performed to identify the conceptual constructs underlying a group of forty-two general shopping-related attitudinal statements, with which respondents agreed or disagreed on a five-point Likert-type scale. From the nineteen potential constructs identified in the design stage, thirteen dimensions emerged empirically: shopping and store enjoyment, price and time consciousness, impulse buying, materialism, trust, caution, trendsetting, and opinions with respect to credit card usage, technology, exercise, and the environment. Cluster analysis is then conducted to identify seven market segments having different attitudinal profiles: store shopaholics (15%), bichannel shopaholics (14%), time-starved worriers (16%), nonmaterialistic greens (16%), unwired antishoppers (14%), practical and leisure-oriented (13%), and technoconservatives (11%). These segments differ significantly, in logical ways, on a number of sociodemographic and other characteristics, including shopping channel choices. Thus, more detailed investigations of choice behavior using these market segments should prove fruitful.
Trading Schemes, Risks, and Costs: The Cases of the European Union Emissions Trading Scheme and the Renewables Obligation
Authors: Toke David
Published: September 2008

The appropriateness and importance of market-based environmental governance systems vary according to different cases. Although so-called ‘market trading’ regimes can be useful in some circumstances, a false belief in the inevitability of their cost-effectiveness compared with so-called ‘command and control’ systems has allowed policy distortions to occur. So-called ‘command and control’ policies are being underemphasised, despite the fact that they may achieve reductions in carbon emissions that are cheaper than those likely to be achieved through emissions (or ‘certificate’) trading regimes. I address theoretical arguments which I then place in context with analysis of some features of the British Renewables Obligation and the European Union Emissions Trading Scheme.