bluuebunny/crossref_metadata_2025 huggingface dataset:
Geochemical properties of rocks and soils in Gusev Crater, Mars: Results of the Alpha Particle X‐Ray Spectrometer from Cumberland Ridge to Home Plate
Authors: Ming D. W. , Gellert R. , Morris R. V. , Arvidson R. E. , Brückner J. , Clark B. C. , Cohen B. A. , d'Uston C. , Economou T. , Fleischer I. , Klingelhöfer G. , McCoy T. J. , Mittlefehldt D. W. , Schmidt M. E. , Schröder C. , Squyres S. W. , Tréguier E. , Yen A. S. , Zipfel J.
Published: December 2008

Geochemical diversity of rocks and soils has been discovered by the Alpha Particle X‐Ray Spectrometer (APXS) during Spirit's journey over Husband Hill and down into the Inner Basin from sol 470 to 1368. The APXS continues to operate nominally with no changes in calibration or spectral degradation over the course of the mission. Germanium has been added to the Spirit APXS data set with the confirmation that it occurs at elevated levels in many rocks and soils around Home Plate. Twelve new rock classes and two new soil classes have been identified at the Spirit landing site since sol 470 on the basis of the diversity in APXS geochemistry. The new rock classes are Irvine (alkaline basalt), Independence (low Fe outcrop), Descartes (outcrop similar to Independence with higher Fe and Mn), Algonquin (mafic‐ultramafic igneous sequence), Barnhill (volcaniclastic sediments enriched in Zn, Cl, and Ge), Fuzzy Smith (high Si and Ti rock), Elizabeth Mahon (high Si, Ni, and Zn outcrop and rock), Halley (hematite‐rich outcrop and rock), Montalva (high K, hematite‐rich rock), Everett (high Mg, magnetite‐rich rock), Good Question (high Si, low Mn rock), and Torquas (high K, Zn, and Ni magnetite‐rich rock). New soil classes are Gertrude Weise (very high Si soil) and Eileen Dean (high Mg, magnetite‐rich soil). Aqueous processes have played a major role in the formation and alteration of rocks and soils on Husband Hill and in the Inner Basin.
Eustatic variations during the Paleocene‐Eocene greenhouse world
Authors: Sluijs Appy , Brinkhuis Henk , Crouch Erica M. , John Cédric M. , Handley Luke , Munsterman Dirk , Bohaty Steven M. , Zachos James C. , Reichart Gert‐Jan , Schouten Stefan , Pancost Richard D. , Damsté Jaap S. Sinninghe , Welters Natasja L. D. , Lotter André F. , Dickens Gerald R.
Published: December 2008

We reconstruct eustatic variations during the latest Paleocene and earliest Eocene (∼58–52 Ma). Dinoflagellate cysts, grain size fractions, and organic biomarkers in marine sections at four sites from three continents indicate an increased distance to the coast during the Paleocene‐Eocene thermal maximum (PETM). The same trend is recognized in published records from other sites around the world. Together, the data indicate a eustatic rise during the PETM, beginning 20 to 200 ka before the globally recorded negative carbon isotope excursion (CIE) at ∼55.5 Ma. Although correlations are tentative, we recognize other global transgressions during Chrons C25n and C24n. The latter may be associated with Eocene Thermal Maximum 2 (∼53.5 Ma) or the “X”‐event (∼52 Ma). These results suggest a link between global sea level and “hyperthermal” intervals, potentially because of the melting of small alpine ice sheets on Antarctica, thermal expansion of seawater, or both. However, the early onset of sea level rise relative to the CIE of the PETM suggests contributions from other mechanisms, perhaps decreasing ocean basin volume, on sea level rise.
Global mapping of ionospheric HF/VHF radio wave absorption due to solar energetic protons
Authors: Sauer Herbert H. , Wilkinson Daniel C.
Published: December 2008

Simple, one‐parameter algorithms are applied to the observed energetic proton flux as provided by instruments aboard the GOES series of satellites to yield estimates of the high‐latitude HF and VHF radio wave absorption for day and night, respectively. These results are extended to full daily coverage by treating the effects of solar illumination, geomagnetic cutoff variation, and frequency dependence over the entire earth. Validation calculations of the polar cap absorption of HF radio waves have been performed for 11 larger solar energetic particle events during the period from 1992 to 2002 and the results are compared to observations of 30 MHz riometers operated by the Air Force Geophysics Laboratory and located at Thule, Greenland. Prediction of the minimum event duration from current flux level is also obtained, and a specimen presentation of the north and south polar caps illustrates the graphical output of the model for the peak of the 6 December 2006 solar proton event.
Downstream patterns of bed material grain size in a large, lowland alluvial river subject to low sediment supply
Authors: Singer Michael Bliss
Published: December 2008

A new data set of bimodal subaqueous channel bed sediments was analyzed for longitudinal patterns in grain size. It yielded two interesting observations: (1) separate fining trends in d50 exist for gravel and fines that overlap for ∼175 river kilometers, and (2) this overlap in fining trends results in a protracted (nonabrupt) gravel to sand transition. These suggest bed patchiness that is interpreted in the context of inherent grain size bimodality, localized hydraulic sorting due to spatially heterogeneous (and low) sediment supply, and local deviations in channel gradient. The data also show that tributaries have a minor impact on main stem downstream fining due to basin shape and tectonic history. In addition, subaqueous channel sediments were observed to be finer than nearby sediments collected from exposed bars, which may indicate a narrow active zone of transport where bars are disconnected from sediment movement. This research has implications for bed material collection and theories of downstream fining.
Modular proteins at the cell surface
Authors: Campbell I.D.
Published: December 2008

Many proteins, including cell-surface receptors, extracellular matrix (ECM) proteins and intracellular signalling systems, are constructed from a relatively small number of domains or modules. Modularity provides biological systems with a convenient way of presenting binding sites on a stable protein scaffold, in the correct position for function; it also allows regulation by module rearrangement. Knowledge about modular proteins is increasing rapidly because of good databases and more systematic approaches to protein expression and structure determination. There have been a number of important recent structures of modular proteins at the cell surface, including the low-density-lipoprotein receptor, epidermal growth factor receptor and an integrin. These and other studies show how the main task of structural biology has moved from determination of module structures to the task of assessing how modular proteins are regulated and how they bind their various ligands. These aspects are illustrated here by recent studies of modular proteins carried out in our laboratory and elsewhere. Examples will include studies of ECM proteins, such as fibronectin, and proteins associated with focal adhesion complexes that involve fibronectin, integrins and various intracellular modular proteins, such as focal adhesion kinase, Src family kinases, talin and paxillin.
Fatty acid-induced insulin resistance: role of insulin receptor substrate 1 serine phosphorylation in the retroregulation of insulin signalling
Authors: Le Marchand-Brustel Y. , Gual P. , Grémeaux T. , Gonzalez T. , Barrès R. , Tanti J.-F
Published: December 2008

Insulin resistance, when combined with impaired insulin secretion, contributes to the development of type 2 diabetes. Insulin resistance is characterized by a decrease in the insulin effect on glucose transport in muscle and adipose tissue. Tyrosine phosphorylation of IRS-1 (insulin receptor substrate 1) and its binding to PI 3-kinase (phosphoinositide 3-kinase) are critical events in the insulin signalling cascade leading to insulin-stimulated glucose transport. Various studies have implicated lipids as a cause of insulin resistance in muscle. Elevated plasma fatty acid concentrations are associated with reduced insulin-stimulated glucose transport activity as a consequence of altered insulin signalling through PI 3-kinase. Modification of IRS-1 by serine phosphorylation could be one of the mechanisms leading to a decrease in IRS-1 tyrosine phosphorylation, PI 3-kinase activity and glucose transport. Recent findings demonstrate that non-esterified fatty acids, as well as other factors such as tumour necrosis factor α, hyperinsulinaemia and cellular stress, increase the serine phosphorylation of IRS-1 and identified Ser307 as one of the phosphorylated sites. Moreover, several kinases able to phosphorylate this serine residue have been identified. These exciting results suggest that Ser307 phosphorylation is a possible hallmark of insulin resistance in biologically insulin-responsive cells or tissues. Identification of IRS-1 kinases could enable rational drug design in order to selectively inhibit the activity of the relevant enzymes and generate a novel class of therapeutic agents for type 2 diabetes.
Intramembrane proteolysis and post-targeting functions of signal peptides
Authors: Martoglio B.
Published: December 2008

Signal sequences are the addresses of proteins destined for secretion. In eukaryotic cells, they mediate targeting to the endoplasmic reticulum membrane and insertion into the translocon. Thereafter, signal sequences are cleaved from the pre-protein and liberated into the endoplasmic reticulum membrane. We have recently reported that some liberated signal peptides are further processed by the intramembrane-cleaving aspartic protease signal peptide peptidase. Cleavage in the membrane-spanning portion of the signal peptide promotes the release of signal peptide fragments from the lipid bilayer. Typical processes that include intramembrane proteolysis is the regulatory or signalling function of cleavage products. Likewise, signal peptide fragments liberated upon intramembrane cleavage may promote such post-targeting functions in the cell.
Oxidative stress and aging – the use of superoxide dismutase/catalase mimetics to extend lifespan
Authors: Sampayo J.N. , Gill M.S. , Lithgow G.J.
Published: December 2008

To date, more than 40 genes have been identified in the nematode Caenorhabditis elegans, which, when mutated, lead to an increase in lifespan. Of those tested, all confer an increased resistance to oxidative stress. In addition, the lifespan of C. elegans can also be extended by the administration of synthetic superoxide dismutase/catalase mimetics. These compounds also appear to confer resistance to oxidative damage, since they protect against paraquat treatment. The protective effects of these compounds are apparent with treatment during either development or adulthood. These findings have demonstrated that pharmacological intervention in the aging process is possible and that these compounds can provide important information about the underlying mechanisms. To date, such interventions have targeted known processes rather than screening compound libraries because of the limitations of assessing lifespan in nematodes. However, we have recently developed a microplate-based assay that allows for a rapid and objective score of nematode survival at rates many times higher than previously possible. This system now provides the opportunity to perform high-throughput screens for compounds that affect nematode survival in the face of acute oxidative stress and will facilitate the identification of novel drugs that extend nematode lifespan.
The irony of manganese superoxide dismutase
Authors: Whittaker J.W.
Published: December 2008

The manganese and iron SODs (superoxide dismutases) form a superfamily of closely related antioxidant defence metalloenzymes. MnSOD requires Mn (not Fe) for activity. However, when MnSOD is expressed in Escherichia coli grown in medium supplemented with ferrous salts, Fe substitutes for Mn in the active site, reflecting relatively indiscriminate uptake of either Mn or Fe and a surprisingly low selectivity for the identity of the bound metal ion. X-ray crystallographic studies on Fe-substituted MnSOD show that the substrate access channel is blocked by solvent (hydroxide), providing a structural explanation for the observed metal specificity of the catalytic activity. The mechanism of metal binding has been investigated in vitro using recombinant thermophilic SODs. The thermophilic Thermus thermophilus MnSOD expressed in E. coli was isolated as the metal-free apoprotein when heat treatment was eliminated from the purification procedure. While incubation of the purified MnSOD apoprotein with metal salts at ambient temperatures did not restore SOD activity, re-activation could be achieved by heating the protein with Mn salts at elevated temperatures. This in vitro thermally triggered metal uptake is non-specific for the metal ion; both Mn and Fe bind, but only Mn restores catalytic activity. Formation of the metal complex is essentially irreversible under these conditions. The metallation process is strongly temperature-dependent, suggesting that there are substantial activation barriers to metal uptake at ambient temperatures that are overcome by a transition in the apoprotein structure under physiological conditions. Two mechanisms may be proposed for SOD metallation: one involving subunit dissociation and another involving domain separation. Thermally triggered metal binding by thermophilic SODs is providing new insight into the metallation mechanism of the SOD apoprotein, which is likely to be conserved over this family of enzymes.
Rotting by radicals – the role of cellobiose oxidoreductase?
Authors: Mason M.G. , Nicholls P. , Wilson M.T.
Published: December 2008

Cellobiose oxidoreductase is a flavocytochrome secreted by wood-rotting fungi. The structure and functional role of the enzyme are reviewed, and a mechanism through which the enzyme produces superoxide, ferrous iron and hydrogen peroxide is proposed. The reactions of hydroxyl radicals formed by Fenton chemistry are discussed in the context of lignocellulose biodegradation.
Protecting the genome: defence against nucleotide glycation and emerging role of glyoxalase I overexpression in multidrug resistance in cancer chemotherapy
Authors: Thornalley P.J.
Published: December 2008

Glycation of nucleotides in DNA forms AGEs (advanced glycation end-products). Nucleotide AGEs are: the imidazopurinone derivative dG-G {3-(2´-deoxyribosyl)-6,7-dihydro-6,7-dihydroxyimidazo[2,3-b]purin-9(8)one}, CMdG (N2-carboxymethyldeoxyguanosine) and gdC (5-glycolyldeoxycytidine) derived from glyoxal, dG-MG {6,7-dihydro-6,7-dihydroxy-6-methylimidazo-[2,3-b]purine-9(8)one}, dG-MG2 [N2,7-bis-(1-hydroxy-2-oxopropyl)deoxyguanosine] and CEdG [N2-(1-carboxyethyl)deoxyguanosine] derived from methylglyoxal, and dG-3DG [N2-(1-oxo-2,4,5,6-tetrahydroxyhexyl)deoxyguanosine] derived from 3-deoxyglucosone and others. Glyoxal and methylglyoxal induce multi-base deletions, and base-pair substitutions – mostly occurring at G:C sites with G:C→C:G and G:C→T:A transversions. Suppression of nucleotide glycation by glyoxalase I and aldehyde reductases and dehydrogenases, and base excision repair, protects and recovers DNA from damaging glycation. The effects of DNA glycation may be most marked in diabetes and uraemia. Mutations arising from DNA glycation may explain the link of non-dietary carbohydrate intake to incidence of colorectal cancer. Overexpression of glyoxalase I was found in drug-resistant tumour cells and may be an example of an undesirable effect of the enzymatic protection against DNA glycation. Experimental overexpression of glyoxalase I conferred resistance to drug-induced apoptosis. Glyoxalase I-mediated drug resistance was found in human leukaemia and lung carcinoma cells. Methylglyoxal-mediated glycation of DNA may contribute to the cytotoxicity of some antitumour agents as a consequence of depletion of NAD+ by poly(ADP-ribose) polymerase, marked increases in triosephosphate concentration and increased formation of methylglyoxal. S-p-Bromobenzylglutathione cyclopentyl diester is a cell-permeable glyoxalase I inhibitor. It countered drug resistance and was a potent antitumour agent against lung and prostate carcinoma. Glyoxalase I overexpression was also found in invasive ovarian cancer and breast cancer.
Anti-AGEing defences against Alzheimer's disease
Authors: Münch G. , Kuhla B. , Lüth H.-J. , Arendt T. , Robinson S.R.
Published: December 2008

Accumulation of insoluble protein deposits and their cross-linking by AGEs (advanced glycation end products) in the brain is a feature of aging and neurodegeneration, especially in AD (Alzheimer's disease). In AD, two types of fibrillar protein aggregates are present: extracellular deposits (plaques) consisting mainly of Aβ (β-amyloid peptide), and intracellular deposits (tangles) composed predominantly of microtubule-associated protein tau. Both plaques and tangles are modified by AGEs, which occurs particularly at lysine and arginine residues. Interaction of a synthetic amyloid plaque (fibrillar Aβ) with microglia leads to a strong pro-inflammatory response, indicating that priming of immune cells with β-amyloid potentiates their response to secondary stimuli such as AGE and cytokines such as interferon-γ. Formation of hyperphosphorylated and cross-linked microtubule-associated protein tau aggregates, especially tau dimers as the first step in tangle formation, can be induced in vitro by the combination of okadaic acid, a PP2A phosphatase inhibitor, and methylglyoxal. These results suggest that excess production of reactive carbonyl compound (‘carbonyl stress’) and subsequent AGE formation can contribute to cross-linking of protein fibrils and to pathological pro-inflammatory signalling, which all contribute to pathological changes and dementia progression in AD. However, the human brain has developed the glyoxalase system, a most effective defence system to scavenge small dicarbonyl compounds such as glyoxal and methylglyoxal. Very importantly, this system needs GSH as a rate-limiting cofactor. Since GSH is limited under conditions of oxidative stress and inflammation, supplementation with antioxidants such as lipoic acid, vitamin E or flavonoids could indirectly strengthen the anti-glycation defence system in AD. In addition, synthetic carbonyl scavengers and anti-inflammatory drugs could also be valuable drugs for the ‘anti-glycation’ treatment of AD.
Sprouty: a controversial role in receptor tyrosine kinase signalling pathways
Authors: Li X. , Wheldon L. , Heath J.K.
Published: December 2008

Sprouty was first identified in Drosophila as a novel antagonist of the fibroblast growth factor signalling pathway. Sprouty proteins comprise a big family, members of which are characterized by a cysteine-rich domain which confers inhibitory activity, whereas differences in the N-terminal region may be responsible for functional divergence. The role of Sprouty in RTK (receptor tyrosine kinase) signalling pathways is still controversial. Sprouty may negatively or positively regulate RTK signalling via differential interaction with different signalling molecules, and hence exert different mechanism of action.
Modelling the controls of the eukaryotic cell cycle
Authors: Novák B. , Tyson J.J.
Published: December 2008

The eukaryotic cell-division cycle is regulated by three modules that control G1/S, G2/M and meta/anaphase transitions. By using mathematical modelling, we show the dynamic characteristics of these individual modules and we also assemble them together into a comprehensive model of the eukaryotic cell-division cycle. With this comprehensive model, we also discuss the mechanisms by which different checkpoint pathways stabilize different cell-cycle states and inhibit the transitions that drive cell-cycle progression.
Modeling low energy sputtering of hexagonal boron nitride by xenon ions
Authors: Yim John T. , Falk Michael L. , Boyd Iain D.
Published: December 2008

The sputtering of hexagonal boron nitride due to low energy xenon ion bombardments occurs in various applications including fabrication of cubic boron nitride and erosion of Hall thruster channel walls. At low ion energies, accurate experimental characterization of sputtering increases in difficulty due to the low yields involved. A molecular dynamics model is employed to simulate the sputtering process and to calculate sputter yields for ion energies ranging from 10 to 350 eV. The results are compared to experimental data and a semiempirical expression developed by Bohdansky [Nucl. Instrum. Methods Phys. Res. B 2, 587 (1984)] is found to adequately describe the simulation data. Surface temperature effects are also investigated, and the sputter yield at 850 K is approximately twice that at 423 K.
Parametric study of thermal interface resistance using laser-based thermal wave imaging
Authors: Hurley D. H. , Fig M. K.
Published: December 2008

A parametric study of harmonic heat flow in a thin isotropic film on an anisotropic, semi-infinite, transparent substrate is presented using the thermal interface resistance as a parameter. The heat source is provided by an amplitude modulated Gaussian laser beam. This study reveals that the anisotropic nature of the substrate is masked for large values of the interface resistance. Furthermore, for intermediate values of the interface resistance, there are localized regions in which the gradient of the thermal wave amplitude is in a direction away from the source. This anomalous behavior is explained by considering the relative phase relation of the temperature field between the film and the substrate.
Thermodynamic and kinetic approach in density functional theory studies of microscopic structure of GaN(0001) surface in ammonia-rich conditions
Authors: Krukowski Stanisław , Kempisty Paweł , Jalbout Abraham F.
Published: December 2008

GaN (0001) surface in an ammonia-rich vapor ambient, typical for ammonia annealing, metalo-organic vapor phase epitaxy (MOVPE) or hydride vapor phase epitaxy (HVPE) was considered. It was shown that, in these three cases, the stationary state of the surface corresponds to condition far from equilibrium. The chemical potential of nitrogen and hydrogen at the surface was determined using kinetic arguments, i.e., derived form the magnitude of flux of ammonia. For HVPE and MOVPE growth, the chemical potential of gallium depends on the distance from the steps. Thus, only far distance from the step value of the gallium chemical potential at the GaN(0001) surface could be determined in similar way. In the alternative case of GaN annealing in ammonia atmosphere, gallium chemical potential at the surface remains undetermined (the surface is in a metastable state). Additionally, using thermodynamic arguments, the limits for the chemical potential of gallium (upper) and nitrogen (lower) were formulated for the case of vapor growth, and expressed as functions of temperature and pressure. The results, regarding the atomic processes on the GaN(0001) surface, were obtained using the SIESTA, density functional theory based code, and consequently employed in the comparable thermodynamic and kinetic analysis of the state of GaN(0001) surface.
Characterization of magnetic force microscopy probe tip remagnetization for measurements in external in-plane magnetic fields
Authors: Weis Tanja , Krug Ingo , Engel Dieter , Ehresmann Arno , Höink Volker , Schmalhorst Jan , Reiss Günter
Published: December 2008

A quantitative analysis of magnetic force microscopy (MFM) images taken in external in-plane magnetic fields is difficult because of the influence of the magnetic field on the magnetization state of the magnetic probe tip. We prepared calibration samples by ion bombardment induced magnetic patterning with a topographically flat magnetic pattern magnetically stable in a certain external magnetic field range for a quantitative characterization of the MFM probe tip magnetization in point-dipole approximation.
Nonthermal laser-induced formation of crystalline Ge quantum dots on Si(100)
Authors: Hegazy M. S. , Elsayed-Ali H. E.
Published: December 2008

The effects of laser-induced electronic excitations on the self-assembly of Ge quantum dots on Si(100)-(2×1) grown by pulsed laser deposition are studied. Electronic excitations due to laser irradiation of the Si substrate and the Ge film during growth are shown to decrease the roughness of films grown at a substrate temperature of ∼120 °C. At this temperature, the grown films are nonepitaxial. Electronic excitation results in the formation of an epitaxial wetting layer and crystalline Ge quantum dots at ∼260 °C, a temperature at which no crystalline quantum dots form without excitation under the same deposition conditions.
Computation of dust charge and potential on a static spherical dust grain immersed in rf discharges
Authors: Ikkurthi V. R. , Matyash K. , Melzer A. , Schneider R.
Published: December 2008

Dust charge and potential on static spherical dust grains located in an argon rf discharge under typical laboratory experiment conditions have been computed using a three-dimensional particle-particle-particle-mesh code. Elastic and inelastic collisions have been included in the current model to obtain realistic rf discharge plasma conditions. Dust charge, potential, and potential distribution around the dust have been computed for various sizes of dust placed at different locations in the rf discharge. The dust charge is found to be smaller than the values from the simple orbit motion limited model due to ion-neutral collisions. Further, the dust potential has been found to be increasing with dust size. Moreover, the shielding length of the dust has been found between electron and ion Debye lengths.
Stress induced Curie temperature shift in high-aspect ratio PbTiO3 nanotube arrays
Authors: Yang Yang , Wang Xiaohui , Sun Changku , Li Longtu
Published: December 2008

High-aspect ratio PbTiO3 nanotube arrays with a length of 20 μm were synthesized by hydrothermal method. Curie temperature of the specimen (at about 620 °C) was found to be dispersive and much higher than PbTiO3 bulks. Ferroelectric to paraelectric phase transition in the high-aspect ratio PbTiO3 nanotube arrays was studied by Raman scattering and XRD. The nanotubular structure plays an important role in optimizing the stress distribution in the nanotube arrays. It was found that optimized two-dimensional compressive stress was responsible for the shift of Curie temperature in PbTiO3 nanotube arrays.
Modeling of electrical characteristics of midwave type II InAs∕GaSb strain layer superlattice diodes
Authors: Gopal V. , Plis E. , Rodriguez J.-B. , Jones C. E. , Faraone L. , Krishna S.
Published: December 2008

This paper reports the results of modeling of electrical characteristics of midinfrared type II InAs∕GaSb strain layer superlattice (SLS) diode with p-on-n polarity. Bulk based model with the effective band gap of SLS material has been used in modeling of the experimental data. Temperature dependence of zero-bias resistance area product (R0A) and bias dependent dynamic resistance of the diode have been analyzed in detail to investigate dark current contributing mechanisms that are limiting the electrical performance of the diode. R0A of the diode is found to be limited by thermal diffusion currents at higher temperatures and Ohmic shunt resistance contribution limits it at low temperatures ∼82K.
Phonon in BC3 layer and nanotubes
Authors: Dobardžić E.
Published: December 2008

We have found force constants providing excellent agreement to the experimental phonon dispersions along Γ-M direction. Using them we discuss vibrational properties of BC3 layer and nanotubes. Particularly, we analyze Raman and infrared activity singling out the relevant modes by symmetry. The diameter/chiral angle dependence of the active modes is derived, and its application to the sample characterization is emphasized.
Nonvolatile multilevel memory effect by resistive switching in manganite thin films
Authors: Lau H. K. , Leung C. W.
Published: December 2008

A planar multilevel memory structure is proposed and examined based on the resistive switching phenomenon in La0.7Sr0.3MnO3 films with gold electrodes. Through the application of specific voltage pulses, such structures can be driven to well-defined intermediate resistance values. Samples were subjected to repeated switching cycles and prolonged reading processes to examine their durability during operations. Prescribed states of the samples could be retained after 10 000 switching cycles, and such states remained stable upon continuous probing. The proposed structure provides a simple scheme for the implementation of compact and nonvolatile multibit memory devices.
Laser-induced convection nanostructures on SiON/Si interface
Authors: Maksimović A. , Lugomer S. , Geretovszky Zs. , Szörényi T.
Published: December 2008

The homogenized beam of an excimer KrF laser has been used to form rectangular millimeter-scale holes of vertical walls in the ∼1 μm thick silicon-oxynitride (SiON) thin film deposited on Si ⟨111⟩ wafer. The regular rectangular craters in SiON layer have the flat bottom surface reaching the SiON/Si interface. At the same time horizontal thermal gradient causes the formation of the nanoscale Marangoni convection structures at the SiON/Si interface. The inhomogeneous pattern of the roll structures can be divided into domains of regular, irregular, and chaotic organizations. The roll diameter is about 200 nm while their average wavelength, Λ, is, ∼2 μm, i.e., about ten times larger than the laser wavelength, and decreases with increasing number of pulses. Numerical simulation of the Marangoni domain roll structures based on the simple Swift–Hohenberg equation has reproduced all observed types of the roll organization, including those that show the evolution of dislocations from the Eckhause instability.
Dissociation of O2 in low pressure glow discharges in He–O2, Ne–O2, and Ar–O2 gas mixtures
Authors: Khan Mohammad Aslam , Al-Jalal Abdulaziz M.
Published: December 2008

Low-pressure glow discharges in He, Ne, or Ar gases containing small amounts of O2 can produce considerable dissociation of O2 molecules. High-lying metastable states in these noble gases play a predominant role in this process. Due to the difference in energies of metastable states of the noble gas atoms, there is a significant variation in the product states of O atoms created as a result of dissociation. Apparently, for He and Ne, superexcited O2 molecules are formed through collisions with high-lying metastable states of the noble gases. The superexcited O2 molecule could either autoionize to form an O2+ ion that subsequently captures an electron and dissociates or it could directly dissociate through some curve-crossing interactions yielding at least one atom in highly excited state. However, in the case of Ar, the formation of superexcited O2 may be possible through a prior creation of Ar2+ ion. We report some interesting observations on spectral emissions from O atoms in the three gas mixtures covering transition from 5d, 4d D3,5, and 5s S3,5, to 3p 3,5P levels and 4p and 3p P3,5 to 3s S3,5 levels. The emission from the b Σ4g−−a Π4u system of O2+ ions is also reported. In general, populations of the above-stated O and O2+ levels are highest in the case of He–O2 mixture and lowest for the Ar–O2 mixture. However, the Ne–O2 mixture appears to strongly populate the 4p P5 levels, while the Ar–O2 mixture strongly populates the 3p P3 levels. The He–O2 mixture appears to be more efficient among the three gas mixtures considered in dissociating the O2 molecules.
Valence band offset of InN/4H-SiC heterojunction measured by x-ray photoelectron spectroscopy
Authors: Zhang B. L. , Sun G. S. , Guo Y. , Zhang P. F. , Zhang R. Q. , Fan H. B. , Liu X. L. , Yang S. Y. , Zhu Q. S. , Wang Z. G.
Published: December 2008

The valence band offset (VBO) of InN/4H-SiC heterojunction has been directly measured by x-ray photoelectron spectroscopy. The VBO is determined to be 0.55±0.23 eV and the conduction band offset is deduced to be −2.01±0.23 eV, indicating that the heterojunction has a type-I band alignment. The accurate determination of the valence and conduction band offsets is important for applications of InN/SiC optoelectronic devices.
Direct calibration of colloidal probe cantilevers via Derjaguin, Landau, Verwey, and Overbeek surface forces in electrolyte solution
Authors: Hong Xiaoting , Willing Gerold A.
Published: December 2008

The development of colloidal probe microscopy has made it possible to directly measure the interaction forces between two different surfaces in solution. Cantilever calibration is presently a subject of intense experimental and theoretical interest due to the need for accurate force measurement. We developed a novel and direct calibration method for colloidal probe cantilevers to which a silica microsphere has been previously attached based on fitting experimental force curves for the interaction between the silica sphere and a silica flat in dilute KBr solutions to the theoretical Derjaguin, Landau, Verwey, and Overbeek force curves using the measured zeta potential of the silica surfaces.
Microfluidic polymerase chain reaction
Authors: Maltezos George , Gomez Alvaro , Zhong Jiang , Gomez Frank A. , Scherer Axel
Published: December 2008

We implement microfluidic technology to miniaturize a thermal cycling system for amplifying DNA fragments. By using a microfluidic thermal heat exchanger to cool a Peltier junction, we have demonstrated rapid heating and cooling of small volumes of solution. We use a miniature K-type thermocouple to provide a means for in situ sensing of the temperature inside the microrefrigeration system. By combining the thermocouple, two power supplies controlled by a relay system, and computer automation, we reproduce the function of a commercial polymerase chain reaction thermal cycler and demonstrate amplification of a DNA sample of about 1000 base pairs.
A new titration system of a novel split-type superconducting magnet NMR spectrometer
Authors: Kitagawa Isao , Tanaka Hideki , Okada Michiya , Kitaguchi Hitoshi , Kohzuma Takamitsu
Published: December 2008

A new titration system for studying protein-ligand interactions has been developed. In this system, the sample solution is circulated in the route formed by an access path in a split superconducting magnet to maintain a constant protein concentration during the titration experiments. A concentration-control procedure for the ligand/protein ratio is devised, and the ligand/protein ratio is well controlled by this apparatus.
Single-crystal CeCl3(CH3OH)4: A new metal-organic cerium chloride methanol adduct for scintillator applications
Authors: Boatner L. A. , Wisniewski D. , Neal J. S. , Ramey J. O. , Kolopus J. A. , Chakoumakos B. C. , Wisniewska M. , Custelcean R.
Published: December 2008

A new scintillator material consisting of a methanol adduct of cerium trichloride with the composition CeCl3(CH3OH)4 has been discovered and crystallized in the form of large single crystals by solution growth in methanol. The peak emission of the x-ray-excited luminescence spectrum occurs at ∼364 nm. A light yield of up to ∼16 600 photons/MeV and an energy resolution of 11.4% were obtained using 662 keV gamma-ray photons. The scintillator decay time for 662 keV gamma-ray excitation was measured using the time-correlated, single-photon-counting method, and a nominal value of 64.4 ns was obtained. The molecular adduct CeCl3(CH3OH)4 represents the first example of a rare-earth, metal-organic scintillator that is applicable to gamma ray, x ray, and neutron detection.
Effect of transverse ponderomotive nonlinearity on the propagation of ultrashort laser pulses in a plasma channel
Authors: Upadhyay Ajay K. , Singh Ram Gopal , Singh Vijay , Jha Pallavi
Published: December 2008

The present study deals with the propagation of an ultrashort narrow laser beam in a parabolic plasma channel. The effect of transverse ponderomotive nonlinearity on the propagation characteristics of the laser beam is analyzed. Using the variational technique, coupled equations describing the evolution of pulse length and spot size are obtained. The variation of intensity, of mismatched and matched laser pulses, with propagation distance is graphically depicted.
Atomic-layer-deposited Al2O3/GaAs metal-oxide-semiconductor field-effect transistor on Si substrate using aspect ratio trapping technique
Authors: Wu Y. Q. , Xu M. , Ye P. D. , Cheng Z. , Li J. , Park J.-S. , Hydrick J. , Bai J. , Carroll M. , Fiorenza J. G. , Lochtefeld A.
Published: December 2008

High quality GaAs epilayers grown by metal-organic chemical vapor deposition are demonstrated on a SiO2-patterned silicon substrate using aspect ratio trapping technique, whereby threading dislocations from lattice mismatch are largely reduced via trapping in SiO2 trenches during growth. A depletion-mode metal-oxide-semiconductor field-effect transistor (MOSFET) is demonstrated on a n-doped GaAs channel with atomic-layer deposited Al2O3 as the gate oxide. The 10 μm gate length transistor has a maximum drain current of 88 mA/mm and a transconductance of 19 mS/mm. The surface mobility estimated from the accumulation drain current has a peak value of ∼500 cm2/Vs, which is comparable with those from previously reported depletion-mode GaAs MOSFETs epitaxially grown on semi-insulating GaAs substrates.
Multichannel filters via Γ-M and Γ-K waveguide coupling in two-dimensional triangular-lattice photonic crystal slabs
Authors: Liu Ya-Zhao , Liu Rong-Juan , Feng Shuai , Ren Cheng , Yang Hai-Fang , Zhang Dao-Zhong , Li Zhi-Yuan
Published: December 2008

We demonstrate the design, fabrication, and characterization of a multichannel filter in a two-dimensional triangular-lattice photonic crystal slab. The output signal channel, which directs in the Γ-M crystalline direction, is orthogonal to the input signal channel that directs in the Γ-K crystalline direction. In each channel, the filtering function is guaranteed by the indirect resonant coupling between the waveguide and the cavity. Four resonant cavities with different sizes provide the mechanism of finely tuning the output wavelength. Our experimental results are in good agreement with simulations.
Surface and interfacial effect of filler particle on electrical properties of polyvinyledene fluoride/nickel composites
Authors: Panda Maheswar , Srinivas V. , Thakur A. K.
Published: December 2008

The effect of processing conditions and filler particle size/surface area on the dielectric behavior of polyvinyledene fluoride/nickel composites is reported. Large enhancement of low frequency dielectric constant with reduction in metal particle size in a metal-polymer composite is observed. Enhancement in the dielectric constant has been attributed to increase in interfacial area and consequent interfacial polarization with reduction in metal particle size. The increased interparticle contacts from the nearest neighbors result in enhanced tunneling probability leading to lowering of percolation threshold for nanosized nickel/polyvinyledene fluoride composites as compared to micron nickel/polyvinyledene fluoride composites.
A Location Model for Urban Hierarchy Planning with Population Dynamics
Authors: Antunes António , Berman Oded , Bigotte João , Krass Dmitry
Published: December 2008

Spatial development plans often aim at defining the level of hierarchy to assign to the urban centers of a region, each level being characterized by a class of facilities. The services provided at the facilities typically include education, health care, public safety, and justice. In this paper we present a multiperiod, multilevel location model for urban hierarchy planning. The objective of the model is to maximize the aggregate accessibility of population to the different classes of facilities, taking explicitly into account the fact that location decisions influence the spatial distribution of population growth. The model was applied to a problem dealt with in Portugal during the preparation of the Centro Region Development Plan 1994: the redefinition of the regions' urban hierarchy. The results obtained through the model demonstrate its potential usefulness in real-world applications.
Is Green Space in the Living Environment Associated with People's Feelings of Social Safety?
Authors: Maas Jolanda , Spreeuwenberg Peter , van Winsum-Westra Marijke , Verheij Robert A , Vries Sjerp , Groenewegen Peter P
Published: December 2008

The authors investigate whether the percentage of green space in people's living environment affects their feelings of social safety positively or negatively. More specifically they investigate the extent to which this relationship varies between urban and rural areas, between groups in the community that can be identified as more or less vulnerable, and the extent to which different types of green space exert different influences. The study includes 83 736 Dutch citizens who were interviewed about their feelings of social safety. The percentage of green space in the living environment of each respondent was calculated, and data analysed by use of a three-level latent variable model, controlled for individual and environmental background characteristics. The analyses suggest that more green space in people's living environment is associated with enhanced feelings of social safety—except in very strongly urban areas, where enclosed green spaces are associated with reduced feelings of social safety. Contrary to the common image of green space as a dangerous hiding place for criminal activity which causes feelings of insecurity, the results suggest that green space generally enhances feelings of social safety. The results also suggest, however, that green space in the most urban areas is a matter of concern with respect to social safety.
Evidence for marine production of monoterpenes
Authors: Yassaa Noureddine , Peeken Ilka , Zöllner Eckart , Bluhm Katrin , Arnold Steve , Spracklen Dominick , Williams Jonathan
Published: December 2008

Environmental context. Laboratory incubation experiments and shipboard measurements in the Southern Atlantic Ocean have provided the first evidence for marine production of monoterpenes. Nine marine phytoplankton monocultures were investigated using a GC-MS equipped with an enantiomerically-selective column and found to emit monoterpenes including (–)-/(+)-pinene, limonene and p-ocimene, all of which were previously thought to be exclusively of terrestrial origin. Maximum levels of 100–200 pptv total monoterpenes were encountered when the ship crossed an active phytoplankton bloom.
Abstract. Laboratory incubation experiments and shipboard measurements on the Southern Atlantic Ocean have provided the first evidence for marine production of monoterpenes. Nine marine phytoplankton monocultures were investigated using a GC-MS equipped with an enantiomerically-selective column and found to emit at rates, expressed as nmol C10H16 (monoterpene) g [chlorophyll a]–1 day–1, from 0.3 nmol g [chlorophyll a]–1 day–1 for Skeletonema costatum and Emiliania huxleyi to 225.9 nmol g [chlorophyll a]–1 day–1 for Dunaliella tertiolecta. Nine monoterpenes were identified in the sample and not in the control, namely: (–)-/(+)-pinene, myrcene, (+)-camphene, (–)-sabinene, (+)-3-carene, (–)-pinene, (–)-limonene and p-ocimene. In addition, shipboard measurements of monoterpenes in air were made in January–March 2007, over the South Atlantic Ocean. Monoterpenes were detected in marine air sufficiently far from land as to exclude influence from terrestrial sources. Maximum levels of 100–200 pptv total monoterpenes were encountered when the ship crossed an active phytoplankton bloom, whereas in low chlorophyll regions monoterpenes were mostly below detection limit.
Growth and reproductive biology of tarwhine Rhabdosargus sarba (Sparidae) in eastern Australia
Authors: Hughes Julian M. , Stewart John , Kendall Benjamin W. , Gray Charles A.
Published: December 2008

The growth and reproductive biology of the commercially and recreationally important sparid fish, tarwhine (Rhabdosargus sarba), was examined from the coastal waters of New South Wales (NSW), south-eastern Australia. Previous research on this species in other parts of the world has yielded conflicting results concerning its growth and reproductive biology. Age estimates were made by counting opaque zones in otolith sections. The method was validated by marking the otoliths of captive fish with alizarin complexone, and also by marginal increment analyses using otoliths from wild-caught fish. Both sexes grew at a similar rate. Von Bertalanffy growth function parameters were: L∞ = 26.40 ± 0.40 cm fork length (FL), k = 0.39 ± 0.02 year–1 and to = –0.56 ± 0.09 years. The maximum estimated age was 16.5 years. Spawning occurred from May to August with a peak in July. Both sexes matured at a similar size (L50 = 19.44 ± 0.15 cm FL), which was larger than the current minimum legal length in NSW. Ovotestes were identified in adult tarwhine and were confirmed by histological analyses. Results of this study provided evidence that tarwhine are likely to be rudimentary hermaphrodites in eastern Australia and are more similar in growth rate, maximum size/age, and reproductive biology to tarwhine from Western Australia than those from other parts of the world.
Four-dimensional realistic modeling of pancreatic organogenesis
Authors: Setty Yaki , Cohen Irun R. , Dor Yuval , Harel David
Published: December 2008

Organogenesis, the process by which organs develop from individual precursor stem cells, requires that the precursor cells proliferate, differentiate, and aggregate to form a functioning structure. This process progresses through changes in 4 dimensions: time and 3 dimensions of space—4D. Experimental analysis of organogenesis, by its nature, cuts the 4D developmental process into static, 2D histological images or into molecular or cellular markers and interactions with little or no spatial dimensionality and minimal dynamics. Understanding organogenesis requires integration of the piecemeal experimental data into a running, realistic and interactive 4D simulation that allows experimentation and hypothesis testing in silico. Here, we describe a fully executable, interactive, visual model for 4D simulation of organogenic development using the mouse pancreas as a representative case. Execution of the model provided a dynamic description of pancreas development, culminating in a structure that remarkably recapitulated morphologic features seen in the embryonic pancreas. In silico mutations in key signaling molecules resulted in altered patterning of the developing pancreas that were in general agreement with in vivo data. The modeling approach described here thus typifies a useful platform for studying organogenesis as a phenomenon in 4 dimensions.
Volume-selective magnetic resonance imaging using an adjustable, single-sided, portable sensor
Authors: Paulsen Jeffrey L. , Bouchard Louis S. , Graziani Dominic , Blümich Bernhard , Pines Alexander
Published: December 2008

Portable, single-sided NMR sensors can operate under conditions inaccessible to conventional NMR while featuring lower cost, portability, and the ability to analyze arbitrary-sized objects. Such sensors can nondestructively probe the interior of samples by collecting images and measuring relaxation and diffusion constants, and, given careful shimming schemes, even perform chemical analysis. The inherently strong magnetic-field gradients of single-sided sensors developed so far has prevented imaging of materials with high water content, such as biological tissues, over large volumes whereas designs with more homogeneous fields suffer from low field strength and typically cannot probe volumes larger than ≈10 cm3. We present a design with a continuously adjustable sensitive volume, enabling the effective volume to be enlarged several fold. This capability allows for imaging in reasonable times of much bigger objects and opens the door to the possibility of clinical imaging with portable sensors. We demonstrate MRI in axial and sagittal planes, at different depths of the sensitive volume and T1-weighted contrast in a tissue sample.