bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of geomagnetic disturbances and solar wind density on relativistic electrons at geostationary orbit
Authors: Lyatsky Wladislaw , Khazanov George V.
Published: August 2008

It is well known that fluxes of relativistic electrons in the Earth's magnetosphere well correlate with solar wind speed but surprisingly they show a weaker correlation with geomagnetic activity indices. For a long time, this result seemed puzzling since geomagnetic disturbances, measured by geomagnetic activity indices, are associated with strong electric fields and low‐frequency waves, which should significantly affect (directly or indirectly) the particle acceleration to high energies. To understand why the relativistic electron fluxes show the relatively weak correlation with geomagnetic disturbances, we investigated statistically the data of relativistic electrons at geostationary orbit for 6 years (1997–2002) and compared these data with solar wind parameters and geomagnetic activity indices. We found that, for the generation of the strong electron fluxes, the combination of two factors is needed: (1) strong geomagnetic disturbances about two days before the following increases in electron fluxes and (2) low solar wind density within these 2‐day intervals between the geomagnetic disturbances and following increases in the electron fluxes. By these conditions, the correlation between the electron fluxes and geomagnetic indices is improved and becomes higher than the correlation between the electron fluxes and solar wind speed. A large majority of the strongest relativistic electron events occurred just during these conditions. This allows us to suggest that not solar wind speed alone but rather geomagnetic activity combined with low solar wind density conditions may be a primary cause for the generation of relativistic electrons.
Initial condition influence on coronal mass ejection propagation
Authors: Wu P. , Schwadron N. A. , Siscoe G. L. , Riley P.
Published: August 2008

In the melon‐seed‐overpressure‐expansion (MSOE) model described by Siscoe et al. (2006) for the acceleration of coronal mass ejections (CMEs), magnetic repulsion force plays a central role. MSOE is a combination of Pneuman's (1984) melon seed concept with an overpressure expansion analytically formulated by Siscoe et al. (2006). The MSOE model creates a reduced formalism to describe CME acceleration and is highly advantageous for comparative studies. As originally presented, the MSOE model has the drawback of being able to produce only fast CMEs. For the work presented in this paper, we compare the acceleration of a 2.5‐D magnetohydrodynamics (MHD)‐modeled CME with that of a version of the MSOE model. On the basis of the results of the MHD simulations, we divide the acceleration of a CME into two phases: (1) a tethered phase before detachment (when the CME is tethered by external closed loops) and (2) a repulsion phase after detachment (when the tethering force that binds the CME is much smaller than outward magnetic repulsion force). We find that during the repulsion phase, the acceleration can be described well by the standard MSOE model. However, during the tethered phase, the CME acceleration is much slower than MSOE predictions. We therefore refine the MSOE model to include tethering and can account for both fast and slow CMEs with the final CME speed controlled by the CME detachment height.
Wave activity inside hot flow anomaly cavities
Authors: Tjulin A. , Lucek E. A. , Dandouras I.
Published: August 2008

Low‐frequency wave properties inside two hot flow anomalies (HFAs) at different stages of evolution are, for the first time, studied applying the k‐filtering technique on multipoint measurements from the Cluster satellites. The observed wave activity in an HFA cavity in an early stage of its evolution was interpreted as the combination of inherent fluctuation in the solar wind and those of a plasma component specularly reflected at the Earth's bow shock, where the amplitude of the fluctuations had been enhanced by a plasma beam instability. The wave field of a more evolved HFA was found to be less complex but contained a periodicity in the wave number distribution with a period that is suggested to come from the geometry of the HFA cavity.
HAND transcription factors are required for neonatal sympathetic neuron survival
Authors: Doxakis Epaminondas , Howard Laura , Rohrer Hermann , Davies Alun M
Published: August 2008

Expression of the basic helix–loop–helix transcription factor HAND2 begins early in sympathetic neuron development and is essential for the differentiation of noradrenergic neurons. Here, we show that the expression of HAND2 and related HAND1 are maintained in sympathetic neurons throughout fetal and postnatal development when these neurons depend on target‐derived nerve growth factor (NGF) for survival. Short interfering RNA knockdown of endogenous HAND2 and, to a lesser extent, HAND1 in neonatal sympathetic neurons cultured with NGF, reduced the expression of the NGF receptor tyrosine kinase TrkA (tropomyosin‐related kinase A), as well as neuronal survival. Chromatin immunoprecipitation analysis showed that NGF promotes HAND2 binding to the TrkA minimal enhancer and that transfection of sympathetic neurons with a TrkA expression plasmid rescued the neurons from HAND knockdown. These findings show that HAND transcription factors have a crucial function in sustaining the survival of neonatal sympathetic neurons with NGF by a feed‐forward loop that maintains the expression of TrkA.
GabiPD: The GABI Primary Database - a plant integrative ‘omics’ database
Authors: Riaño-Pachón Diego Mauricio , Nagel Axel , Neigenfind Jost , Wagner Robert , Basekow Rico , Weber Elke , Mueller-Roeber Bernd , Diehl Svenja , Kersten Birgit
Published: August 2008

The GABI Primary Database, GabiPD (http://www.gabipd.org/), was established in the frame of the German initiative for Genome Analysis of the Plant Biological System (GABI). The goal of GabiPD is to collect, integrate, analyse and visualise primary information from GABI projects. GabiPD constitutes a repository and analysis platform for a wide array of heterogeneous data from high-throughput experiments in several plant species. Data from different ‘omics’ fronts are incorporated (i.e., genomics, transcriptomics, proteomics and metabolomics), originating from 14 different model or crop species. We have developed the concept of GreenCards for text based retrieval of all data types in GabiPD (e.g., clones, genes, mutant lines). All data types point to a central Gene GreenCard, where gene information is integrated from genome projects or NCBI UniGene sets. The centralised Gene GreenCard allows visualising ESTs aligned to annotated transcripts as well as displaying identified protein domains and gene structure. Moreover GabiPD makes available interactive genetic maps from potato and barley, and 2DE-gels from Arabidopsis thaliana and Brassica napus. Gene expression and metabolic profiling data can be visualised through MapManWeb. By the integration of complex data in a framework of existing knowledge, GabiPD provides new insights and allows for new interpretations of the data.
Potential pathways of indole acetic acid (IAA) biosynthesis in Euphorbia abyssinica
Authors: Aerts Raf , Prinsen Els , Muys Bart
Published: August 2008

Desert candle (Euphorbia abyssinica J.F. Gmel.) (further referred to as EAG) is a succulent tree of dry deciduous and evergreen montane forest, woodland and shrub savanna. It occurs widely throughout dryland Africa, where it is appreciated as a live fence because it is easily propagated from untreated mature branch cuttings.Earlier we argued that the ability of large EAG branches to regenerate with ease in dry soil may be related to the natural plant growth regulator hormone indole acetic acid (IAA) contained in the latex of the plant. EAG latex samples from northern Ethiopia (n = 3) that were chemically analyzed contained on average 0.06 mg/l latex, as well as the IAA metabolites indole lactate (ILA) and indole ethanol (IEt). One sample also contained IAA conjugated to amino-acids and to glucose. Here we present a schematic overview of the potential pathways of IAA biosynthesis in EAG and suggest that auxin biosynthesis in EAG is tryptophane (Trp) dependent.
High efficiency electron spin polarization analyzer based on exchange scattering at Fe∕W(001)
Authors: Winkelmann A. , Hartung D. , Engelhard H. , Chiang C.-T. , Kirschner J.
Published: August 2008

We report on a compact electron spin analyzer based on exchange scattering from a magnetic surface. The heart of the detector is an Fe(001) thin film grown on W(001) with chemisorbed oxygen in the p(1×1) structure. The device is mounted at the exit of an energy dispersive analyzer and works at a scattering energy of about 13.5eV. Its figure of merit is 2×10−3, combined with an excellent stability of more than 2weeks in UHV.
Time-dependent density functional theory study of cobalt corrinoids: Electronically excited states of methylcobalamin
Authors: Andruniów Tadeusz , Jaworska Maria , Lodowski Piotr , Zgierski Marek Z. , Dreos Renata , Randaccio Lucio , Kozlowski Pawel M.
Published: August 2008

Time-dependent density functional theory (TDDFT) has been applied to the analysis of the electronic spectra of methylcobalamin (MeCbl) and its derivative in which the trans axial base was replaced by a water molecule (MeCbiH2O). The latter corresponds to the situation encountered in strongly acidic solutions. The study primarily focuses on the accuracy of two functionals, the hybrid B3LYP and the gradient corrected BP86, in dealing with the electronic excitations. The high resolution crystal structure of MeCbl was the source of the initial coordinates. To generate the initial structures, the full MeCbl was simplified by replacing the corrin side chains by H atoms. The vertical excitation energies, together with the corresponding oscillator strengths, were calculated at the optimized BP86 and B3LYP structures of the ground electronic state of the complexes. The NBO analysis shows that the B3LYP functional gives a bonding description of the ground state as a more polarized covalent bond compared to that given by BP86. The latter functional has more covalent bonding and is thus more appropriate for modeling the axial bonding properties. To validate the accuracy of the present TDDFT analysis, the computed excitations were directly compared to the absorption spectra of MeCbl. In order to obtain a reliable agreement between experiment and theory, the two-parameter scaling technique was introduced, which compensates differently the low-energy and high-energy excitations. Electronic excitations strongly depend on the choice of the functional. Transitions involving corrin π→π* excitations are better described by the B3LYP functional while transitions associated with metal-to-ligand (d∕π→π*∕d) excitations are better described by BP86. These differences can be associated with the different bonding descriptions obtained by B3LYP and BP86.
Spin wave propagation in spatially nonuniform magnetic fields
Authors: Smith Kevin R. , Kabatek Michael J. , Krivosik Pavol , Wu Mingzhong
Published: August 2008

Spin wave pulse propagation in a magnetic thin film under static, spatially nonuniform magnetic fields has been studied. The experiment was carried out with an yttrium iron garnet film strip. The film strip was magnetized with a spatially nonuniform magnetic field parallel to the length of the film strip. Spin wave pulses were excited with a microstrip transducer at one end of the film strip. The spin wave pulse propagation along the film strip was mapped with a high-resolution time- and space-resolved inductive magnetodynamic probe. The wave number for the spin wave pulses was found to increase in a spatially increasing field and decrease in a spatially decreasing field. The wave number change in a static, general spatially varying static field is reversible for this field-film geometry. The phase velocity was found to decrease in a spatially increasing magnetic field and increase in a spatially decreasing field. The carrier frequency of the spin wave pulses remained constant throughout pulse propagation.
Blue and red electroluminescence of Europium-implanted metal-oxide-semiconductor structures as a probe for the dynamics of microstructure
Authors: Rebohle L. , Lehmann J. , Prucnal S. , Kanjilal A. , Nazarov A. , Tyagulskii I. , Skorupa W. , Helm M.
Published: August 2008

The strong blue and red electroluminescence from Eu-implanted SiO2 layers were investigated as a function of implantation and annealing conditions. It is shown that the red electroluminescence assigned to Eu3+ ions is favored by low Eu concentrations, low annealing temperatures, and short annealing times. Based on a more quantitative analysis of the electroluminescence spectra this preference is explained by a shorter supply of oxygen for higher Eu concentrations and the growth of Europium or Europium oxide clusters with increasing annealing temperatures and annealing times. The correlation between electroluminescence and microstructure is supported by transmission electron microscopy investigations and demonstrates that the electroluminescence of Eu-implanted SiO2 layers can serve as a probe for the microstructural development in the active layer of the light emitter.
Investigation of the O+allyl addition/elimination reaction pathways from the OCH2CHCH2 radical intermediate
Authors: FitzPatrick Benjamin L. , Lau Kai-Chung , Butler Laurie J. , Lee Shih-Huang , Lin Jim Jr-Min
Published: August 2008

These experiments study the preparation of and product channels resulting from OCH2CHCH2, a key radical intermediate in the O+allyl bimolecular reaction. The data include velocity map imaging and molecular beam scattering results to probe the photolytic generation of the radical intermediate and the subsequent pathways by which the radicals access the energetically allowed product channels of the bimolecular reaction. The photodissociation of epichlorohydrin at 193.3nm produces chlorine atoms and c-OCH2CHCH2 radicals; these undergo a facile ring opening to the OCH2CHCH2 radical intermediate. State-selective resonance-enhanced multiphoton ionization (REMPI) detection resolves the velocity distributions of ground and spin-orbit excited state chlorine independently, allowing for a more accurate determination of the internal energy distribution of the nascent radicals. We obtain good agreement detecting the velocity distributions of the Cl atoms with REMPI, vacuum ultraviolet (VUV) photoionization at 13.8eV, and electron bombardment ionization; all show a bimodal distribution of recoil kinetic energies. The dominant high recoil kinetic energy feature peaks near 33kcal∕mol. To elucidate the product channels resulting from the OCH2CHCH2 radical intermediate, the crossed laser-molecular beam experiment uses VUV photoionization and detects the velocity distribution of the possible products. The data identify the three dominant product channels as C3H4O(acrolein)+H, C2H4+HCO (formyl radical), and H2CO (formaldehyde)+C2H3. A small signal from C2H2O (ketene) product is also detected. The measured velocity distributions and relative signal intensities at m∕e=27, 28, and 29 at two photoionization energies show that the most exothermic product channel, C2H5+CO, does not contribute significantly to the product branching. The higher internal energy onset of the acrolein+H product channel is consistent with the relative barriers en route to each of these product channels calculated at the CCSD(T)/aug-cc-pVQZ level of theory, although a clean determination of the barrier energy to H+acrolein is precluded by the substantial partitioning into rotational energy during the photolytic production of the nascent radicals. We compare the measured branching fraction to the H+acrolein product channel with a statistical prediction based on the calculated transition states.
Plasmon enhanced performance of organic solar cells using electrodeposited Ag nanoparticles
Authors: Kim Seok-Soon , Na Seok-In , Jo Jang , Kim Dong-Yu , Nah Yoon-Chae
Published: August 2008

To enhance solar harvesting in organic solar cells, uniform-sized metal nanoparticles of ∼13 nm were incorporated to the device via pulse-current electrodeposition, which is a kind of simple and quick solution process that can control the density and size of metal nanoparticles. By incorporating plasmonic Ag nanoparticles on surface modified transparent electrodes, overall power conversion efficiency was increased from 3.05% to 3.69%, mainly resulting from the improved photocurrent density as a result of enhanced absorption of the photoactive conjugate polymer due to the high electromagnetic field strength in the vicinity of the excited surface plasmons.
Tunable interband and intersubband transitions in modulation C-doped InGaAs∕GaAs quantum dot lasers by postgrowth annealing process
Authors: Zhang Z. Y. , Jiang Q. , Hogg R. A.
Published: August 2008

A bandgap and intersublevel spacing tuned laser has been realized by using a modulation C-doped InGaAs∕GaAs quantum dot structure, which utilizes a postgrowth annealing process. The intermixed laser exhibits comparable light-current characteristics, indicating little detrimental change to the quantum dot laser material, and show a ground state bandgap blueshift of ∼13nm and intersublevel energy spacing reduction of ∼30nm compared to the unannealed device. The differences in the samples during annealing are attributed to the suppression of Ga vacancy propagation for samples with modulation C doping.
Effects of UV cure on glass structure and fracture properties of nanoporous carbon-doped oxide thin films
Authors: Gage David M. , Stebbins Jonathan F. , Peng Luming , Cui Zhenjiang , Al-Bayati Amir , MacWilliams Kenneth P. , M’Saad Hichem , Dauskardt Reinhold H.
Published: August 2008

The effects of UV radiation curing on the glass structure and fracture properties were examined for a class of nanoporous organosilicate low dielectric constant films. A detailed characterization by nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy showed significant changes in the glass structure with increasing curing time, marked by the removal of terminal organic groups and increased network-forming bonds following the initial removal of porogen material. The higher degree of film connectivity brought about by an increased cure duration is demonstrated to significantly enhance adhesive fracture properties and to moderately improve cohesive fracture resistance. Explanations for the enhanced fracture behavior are considered in terms of the glass structure. The important role of crack path selection during adhesive and cohesive fracture processes is used to rationalize the observed behavior.
Surface morphological evolution during annealing of epitaxial Cu(001) layers
Authors: Purswani J. M. , Gall D.
Published: August 2008

Single crystal Cu(001) layers were grown on MgO(001) by ultrahigh vacuum magnetron sputtering at Ts=100 °C. Quantitative surface morphological analyses by in situ scanning tunneling microscopy show that the surfaces exhibit self-affine mound structures with a scaling exponent of 0.82±0.03 and a mound radius rc that increases from 31±8 to 39±6 nm for increasing layer thickness t=24–120 nm. In situ annealing at 200 and 300 °C leads to a thermodynamically driven mass transport that minimizes the surface step density, resulting in broader mounds and a smaller root mean square surface roughness σ. This effect is most pronounced for t=24 nm, for which rc increases from 31±8 to 70±20 nm and σ decreases from 1.3±0.1 to 0.74±0.08 nm, resulting in a decrease in the average surface slope from χ=7° to 2° and an increase in the average terrace width wT by more than a factor of 4. In contrast, wT increases by only 20% for t=120 nm. This remarkable difference between “thin” and “thick” layers is attributed to diverging surface morphological pathways during annealing: The strong smoothening for t=24 nm is due to a competitive coalescence process where some mounds grow laterally at the expense of their smaller neighbors, which die out. In contrast, the initially wider mounds of thicker layers (t=120 nm) combine to form a quasistable surface morphology that exhibits anisotropic mound structures, which limit mass transport and stabilize the surface step density.
High-temperature AlN interlayer for crack-free AlGaN growth on GaN
Authors: Sun Qian , Wang Jianfeng , Wang Hui , Jin Ruiqin , Jiang Desheng , Zhu Jianjun , Zhao Degang , Yang Hui , Zhou Shengqiang , Wu Mingfang , Smeets Dries , Vantomme Andre
Published: August 2008

This paper presents a study of the transformation of high-temperature AlN (HT-AlN) interlayer (IL) and its effect on the strain relaxation of Al0.25Ga0.75N/HT-AlN/GaN. The HT-AlN IL capped with Al0.25Ga0.75N transforms into AlGaN IL in which the Al composition increases with the HT-AlN IL thickness while the total Ga content keeps nearly constant. During the HT-AlN IL growth on GaN, the tensile stress is relieved through the formation of V trenches. The filling up of the V trenches by the subsequent Al0.25Ga0.75N growth is identified as the Ga source for the IL transformation, whose effect is very different from a direct growth of HT-AlGaN IL. The a-type dislocations generated during the advancement of V trenches and their filling up propagate into the Al0.25Ga0.75N overlayer. The a-type dislocation density increases dramatically with the IL thickness, which greatly enhances the strain relaxation of Al0.25Ga0.75N.
Self-excited hydrothermal waves in evaporating sessile drops
Authors: Sefiane K. , Moffat J. R. , Matar O. K. , Craster R. V.
Published: August 2008

Pattern formation driven by the spontaneous evaporation of sessile drops of methanol, ethanol, and FC-72 using infrared thermography is observed and, in certain cases, interpreted in terms of hydrothermal waves. Both methanol and ethanol drops exhibit thermal wave trains, whose wave number depends strongly on the liquid volatililty and substrate thermal conductivity. The FC-72 drops develop cellular structures whose size is proportional to the local thickness. Prior to this work, hydrothermal waves have been observed in the absence of evaporation in shallow liquid layers subjected to an imposed temperature gradient. In contrast, here both the temperature gradients and the drop thickness vary spatially and temporally and are a natural consequence of the evaporation process.
High Tm lead-free relaxor ferroelectrics with broad temperature usage range: 0.04BiScO3−0.96(K0.5Na0.5)NbO3
Authors: Du Hongliang , Zhou Wancheng , Luo Fa , Zhu Dongmei , Qu Shaobo , Li Ye , Pei Zhibin
Published: August 2008

In order to develop high temperature lead-free relaxors, xBiScO3−(1−x)(K0.5Na0.5)NbO3[xBS−(1−x)KNN] ceramics were proposed using a tolerance factor approach. To verify this proposal, xBS−(1−x)KNN ceramics were synthesized by conventional solid-state sintering. A stable perovskite phase was obtained when KNN content was greater than 96 mol %. The diffuse phase transition and frequency dispersion of the dielectric constant, which are two typical characteristics of relaxor ferroelectrics, were observed in xBS−(1−x)KNN ceramics. The dielectric relaxor behavior follows a modified Curie–Weiss law relationship. In addition, 0.04BS-0.96KNN ceramics show a broad and stable permittivity maximum near 2500 from 100 to 300 °C and lower dielectric loss (<5%) at broad temperature usage range (100–300 °C). The results indicate that this material may have great potential for high temperature capacitors in automobile applications.
High pressure study on molecular mobility of leucrose
Authors: Kaminski K. , Kaminska E. , Hensel-Bielowka S. , Pawlus S. , Paluch M. , Ziolo J.
Published: August 2008

Broadband dielectric measurements on leucrose were performed under ambient and high pressure. We showed that in this disaccharide, there are two secondary relaxation modes, a slower one sensitive to pressure and a faster one that is not. This finding clearly indicates that the faster secondary relaxation originates from the intramolecular motion. This conclusion contradicted previous interpretations of this mode observed for trehalose and maltitol, systems very closely related to leucrose. In addition, pressure sensitivity of the slower relaxation confirms our recent interpretation about the character of this process. Furthermore, we discovered that unlike the faster relaxation, the slower secondary relaxation is sensitive to the thermodynamic history of measurements. Finally, monitoring the changes in maximum loss of the slower secondary relaxation measured at the same pressure and temperature conditions for glasses obtained via different thermodynamic routes enabled us to draw a conclusion about the density of the formed glasses. Our observations may be helpful in establishing a new method of suppressing crystallization of amorphous drugs.
Direct evidence for abrupt postcrystallization germanium precipitation in thin phase-change films of Sb–15at.% Ge
Authors: Cabral C. , Krusin-Elbaum L. , Bruley J. , Raoux S. , Deline V. , Madan A. , Pinto T.
Published: August 2008

We present evidence for the instability in the crystalline (metallic) state of binary Te-free phase-change Ge–Sb thin films considered for integration into nonvolatile nanosized memory cells. We find that while the amorphous (semiconducting) phase of eutectic Sb–15at.% Ge is very robust until Sb crystallization at 240°C, at about 350°C, germanium rapidly precipitates out. Ge precipitation, visualized directly with transmission electron microscopy, is exothermic and is found to affect the films’ reflectivity, resistance, and stress. It converts melting into a two-step process, which may seriously impact the switching reliability of a device.
Structure formation in layered ferrofluid nanofilms
Authors: Trasca R. A. , Klapp S. H. L.
Published: August 2008

We present Monte Carlo simulation results for strongly coupled dipolar fluids, such as ferrofluids, confined to a narrow slit pore accommodating only a few layers of particles. Our results show that the ferromagnetic ordering observed in dense bulk systems and in thick fluid films persists down to nanoscopic wall separations where the system consists of only 3 monolayers. The ferromagnetic transition density in these systems approaches experimentally accessible values. For even smaller wall separations, we observe stripelike defects and finally the breakdown of orientational ordering for systems close to the two-dimensional limit. Our results for the liquid phase are supported by simulations starting from quasicrystalline soft-sphere configurations.
Time-dependent configuration-interaction calculations of laser-driven dynamics in presence of dissipation
Authors: Tremblay Jean Christophe , Klamroth Tillmann , Saalfrank Peter
Published: August 2008

Correlated, multielectron dynamics of “open” electronic systems within the fixed-nuclei approximation are treated here within explicitly time-dependent configuration-interaction schemes. Specifically, we present simulations of laser-pulse driven excitations of selected electronic states of LiCN in the presence of energy and phase relaxation. The evolution of the system is studied using open-system density matrix theory, which embeds naturally in the time-dependent configuration-interaction singles (doubles) formalism. Different models for dissipation based on the Lindblad semigroup formalism are presented. These models give rise to lifetimes for energy relaxation ranging from a few hundreds of femtoseconds to several nanoseconds. Pure dephasing is treated using a Kossakowski-like Gaussian model, proceeding on similar time scales. The pulse lengths employed range from very short (tens of femtoseconds) to very long (several nanoseconds). To make long-time propagations tractable, the quasiresonant approximation is used. The results show that despite the loss of efficiency, selective dipole switching can still be achieved in the presence of dissipation when using appropriately designed laser pulses.
Strain induced change of bandgap and effective mass in silicon nanowires
Authors: Shiri Daryoush , Kong Yifan , Buin Andrei , Anantram M. P.
Published: August 2008

This work computationally investigates the electromechanical properties of hydrogen passivated silicon nanowires under uniaxial tensile strain. It has been observed that bandgap changes can be as large as 60 and 100 meV per 1% axial strain for [100] and [110] nanowires, respectively. This rate of change in the bandgap is independent of nanowire size and depends only on the growth direction. More importantly, the nature of the bandgap can reversibly change from indirect to direct as a function of strain. It is also observed that for larger diameter nanowires, the indirect-to-direct transition occurs at smaller compressive strain.
Intervalley carrier transfer in short-wavelength InP-based quantum-cascade laser
Authors: Semtsiv M. P. , Wienold M. , Dressler S. , Masselink W. T. , Fedorov G. , Smirnov D.
Published: August 2008

The scattering of electrons out of the upper laser state into indirect valleys in quantum-cascade lasers is demonstrated by investigating the operation of the laser under the influence of magnetic fields up to 45 T. A quantum-cascade laser based on strain-compensated AlAs barriers and In0.73Ga0.27As/InAs wells, emitting with wavelength 3.1 μm, is investigated as a function of magnetic field normal to the surface. Minima in emission power are observed when Landau levels of the upper laser state are brought into resonance with states derived from the indirect valleys, leading to the partial depopulation of the upper laser level. The energy for the indirect valley states is determined to be about 640 meV above the bottom of the In0.73Ga0.27As Γ valley, about 70 meV above the upper laser level.
Characteristics of the interaction of azulene with water and hydrogen sulfide: A computational study
Authors: Cabaleiro-Lago Enrique M. , Rodríguez-Otero Jesús , Peña-Gallego Ángeles
Published: August 2008

A computational study was carried out for studying the characteristics of the interaction between azulene and water or hydrogen sulfide. In azulene ⋯ water complex the water molecule is located with both hydrogen atoms pointing toward the aromatic cloud but displaced to the five-membered ring. Hydrogen sulfide adopts a similar arrangement but located roughly over the central C–C bond of azulene. Calculations show that hydrogen sulfide interacts with azulene more strongly (−4.19 kcal/mol) than water (−3.76 kcal/mol), although this is only revealed at the highest levels of calculation. The nature of the interaction is electrostatic and dispersive in the same percentage for water cluster, whereas for hydrogen sulfide dispersion is the dominant contribution. Clusters containing two water molecules are controlled by the possibility of establishing an O–H⋯O hydrogen bond. As a consequence, the most stable structure corresponds to the interaction between a water dimer and azulene, with an interaction energy amounting to −11.77 kcal/mol. Hydrogen sulfide interaction is stronger with azulene than with itself, so structures with S–H⋯S contact and others, where H2S only interacts with azulene, present similar interaction energies (−8.02 kcal/mol for the most stable one).
Zn- and O-face polarity effects at ZnO surfaces and metal interfaces
Authors: Dong Yufeng , Fang Z-Q. , Look D. C. , Cantwell G. , Zhang J. , Song J. J. , Brillson L. J.
Published: August 2008

Depth-resolved cathodoluminescence spectroscopy, current-voltage, capacitance-voltage, and deep level transient spectroscopy of ZnO (0001) Zn- and (0001¯) O-polar surfaces and metal interfaces show systematically higher Zn-face near band edge emission and lower near-surface defect emission. Even with remote plasma decreases of the 2.5 eV near-surface defect emission, (0001)-Zn face emission quality still exceeds that of (0001¯)-O face. Ultrahigh vacuum-deposited Au and Pd diodes on as-received and O2/He plasma-cleaned surfaces display a strong polarity dependence that correlates with defect emissions, traps, and interface chemistry. A comprehensive model accounts for the polarity-dependent transport properties and their correlations with carrier concentration profiles.
Room temperature hydrogen detection using Pd-coated GaN nanowires
Authors: Lim Wantae , Wright J. S. , Gila B. P. , Johnson Jason L. , Ural Ant , Anderson Travis , Ren F. , Pearton S. J.
Published: August 2008

Multiple GaN nanowires produced by thermal chemical vapor deposition were employed as gas sensors for detection of hydrogen at concentrations from 200–1500 ppm in N2 at 300 K. Palladium coating of the wires improved the sensitivity by a factor of up to 11 at low ppm concentrations relative to uncoated controls. The GaN nanowires showed relative responses of ∼7.4% at 200 ppm and ∼9.1% at 1500 ppm H2 in N2 after a 10 min exposure. Upon removal of hydrogen from the measurement ambient, ∼90% of the initial GaN conductance was recovered within 2 min. Temperature dependent measurements showed a larger relative response and shorter response time at elevated temperature. The adsorption activation energy of the sensor was 2.2 kcal mol−1 at 3000 ppm H2 in N2. These sensors exhibit low power consumption (<0.6 mW) at 300 K.
Optimized orientation of 0.71Pb(Mg1/3Nb2/3)O3–0.29PbTiO3 single crystal for applications in medical ultrasonic arrays
Authors: Zhou Dan , Chen Jing , Luo Laihui , Zhao Xiangyong , Luo Haosu
Published: August 2008

In order to extend the potential applications of medical ultrasonic array transducers, two optimized directions with the maximal electromechanical coefficient k33′ and minimal k31 are determined for [001] and [110] poled 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 single crystals using the experimental method. The maximum values of k33′ can reach 92.8% and 93.3%, respectively, corresponding to [001]W/[110]L and [110]W/[1–11]L cuts. Furthermore, we simulate the performances of three 3.5 MHz linear array transducers based on the determined directions by PIEZOCAD. Results indicate that under the [001]W/[110]L direction, 25% broader bandwidth, 40% shorter pulse length, and 3 dB higher sensitivity can be obtained compared to the traditional Pb(Zr1−xTix)O3 transducers.
Intelligent multiparameter sensing with fiber Bragg gratings
Authors: Men Liqiu , Lu Ping , Chen Qiying
Published: August 2008

An approach to achieve intelligent sensing of multiple environmental parameters with a single-fiber sensor system is demonstrated through the use of multiplexed fiber Bragg gratings (FBGs) with coatings of different polymers and specifications. Using three FBGs of either acrylate or polyimide coating and polyimide coatings of different thicknesses, in situ discrimination of saccharinity, salinity, and temperature from the changes in the optical responses of the Bragg wavelengths of the gratings has been realized with sensitivities of 1.10×10−3 nm/%, 3.80×10−3 nm/% (blueshift), and 1.10×10−2 nm/°C (redshift), respectively.
Relaxation of strained silicon on Si0.5Ge0.5 virtual substrates
Authors: Parsons J. , Morris R. J. H. , Leadley D. R. , Parker E. H. C. , Fulgoni D. J. F. , Nash L. J.
Published: August 2008

Strain relaxation has been studied in tensile strained silicon layers grown on Si0.5Ge0.5 virtual substrates, for layers many times the critical thickness, using high resolution x-ray diffraction. Layers up to 30 nm thick were found to relax less than 2% by the glide of preexisting 60° dislocations. Relaxation is limited because many of these dislocations dissociate into extended stacking faults that impede the dislocation glide. For thicker layers, nucleated microtwins were observed, which significantly increased relaxation to 14%. All these tensile strained layers are found to be much more stable than layers with comparable compressive strain.
Spatially resolved strain measurements in Mo-alloy micropillars by differential aperture x-ray microscopy
Authors: Bei H. , Barabash R. I. , Ice G. E. , Liu W. , Tischler J. , George E. P.
Published: August 2008

Spatially resolved strain distributions in the NiAl matrix and the ∼550–1000 nm Mo fibers of a NiAl–Mo eutectic were investigated by microbeam x-ray diffraction. Position sensitive d-spacings for the individual phases were obtained from spatially resolved and energy-resolved Laue patterns. For embedded Mo fibers, the measured elastic strain is consistent with the predicted thermal mismatch strain between the NiAl and Mo phases. However, when the NiAl matrix is etched back to expose Mo micropillars, the d-spacing increases to that of unconstrained Mo, indicating release of the compressive residual strain in the Mo fibers.
Atomically smooth and single crystalline MnTiO3 thin films with a ferrotoroidic structure
Authors: Toyosaki H. , Kawasaki M. , Tokura Y.
Published: August 2008

We report the epitaxial growth and magnetic properties of MnTiO3 thin films with an ilmenite structure. Although the lattice mismatch with sapphire substrates was as large as 8.0%, highly crystalline films with atomically flat surfaces were grown by using pulsed laser deposition. X-ray diffraction and transmission electron microscopy showed that the optimized film had almost a single crystalline structure with totally relaxed lattice parameters, inducing periodic misfit dislocations at the film/substrate interface. The magnetization curve showed an abrupt increase due to spin flopping when the magnetic field along the c-axis exceeded the critical magnetic field (μ0Hc∼6 T). Due to the spin flopping, we concluded that MnTiO3 had a ferrotoroidic structure and, thus, was magnetoelectrically active.
Effect of carbon codoping on boron diffusion in amorphous silicon
Authors: Edelman L. A. , Jin S. , Jones K. S. , Elliman R. G. , Rubin L. M.
Published: August 2008

The effect of carbon codoping on boron diffusion in amorphous silicon is investigated during low temperature annealing. The diffusivity of boron is unaffected by carbon codoping, but the fraction of mobile boron is observed to increase with increasing carbon concentration. A concomitant reduction in boron clustering is also observed at higher carbon coimplant concentrations, consistent with a change in the local trap concentration. This is consistent with carbon possibly acting as a trap site for boron and thereby changing the size and dynamics of the boron cluster formation.
Artificial crevice habitats to assess the biodiversity of vagile macro-cryptofauna of subtidal rocky reefs
Authors: Baronio Mateus de A. , Bucher Daniel J.
Published: August 2008

Reef cryptofauna (animals inhabiting cracks and crevices) represent much of a reef’s biodiversity yet are seldom studied owing to their inaccessibility. Subtidal rocky reefs off Brunswick Heads and Byron Bay in northern New South Wales, Australia support benthic communities ranging from coral-dominated offshore reefs to kelp beds of Ecklonia radiata on inshore reefs. It was hypothesised that differential exposure to river discharge and the East Australian Current, as well as proximity to other reef habitats, may produce differences in recruitment and persistence of cryptofauna between superficially similar reefs within a small geographical range. Artificial crevice habitats were deployed at similar depths on three inshore reefs supporting similar Ecklonia densities. Although the species richness of crevice fauna was similar at all reefs, the species composition differed significantly along with the assemblages recruited in different seasons and to different crevice sizes. Neither reef faunas nor that of varying crevice sizes changed consistently with the seasons, yet all crevices appeared equally accessible to colonists. These results demonstrate the potential inadequacy of classifying reef communities for management of regional biodiversity based on the visual dominance of a few species that may not be as sensitive to environmental variables as many of the less obvious taxa.
Vertical migration of postlarval penaeid prawns in two Australian estuaries: the effect of tide and day/night
Authors: Vance D. J. , Pendrey R. C.
Published: August 2008

Knowledge of the vertical migration behaviour of postlarval penaeid prawns is important in understanding postlarval migration from offshore spawning grounds to estuarine nursery areas. We sampled throughout several 24-h periods in two estuaries in Australia to assess the distribution of postlarvae in the water column. We used four trawl nets: one net in the top 0.5 m of the water column and three nets one above the other, from the seabed to 0.72 m above the seabed. Penaeus plebejus was abundant in catches in the Nerang River, southern Queensland, while Penaeus semisulcatus, Penaeus esculentus and Penaeus merguiensis were caught in the Embley River, northern Queensland. For all species, the highest catches at the surface were on night flood tides. Many postlarvae in the Embley River were caught in nets above the seabed on ebb tides, suggesting that net migration patterns cannot be determined simply by sampling surface waters. The vertical distribution of penaeid postlarvae is determined primarily by tide and day/night; however, water turbidity and cloud cover, factors that reduce light at the seabed, are also likely to be important. All these aspects of postlarval behaviour should be included in hydrodynamic models of larval advection from spawning grounds to inshore nursery areas.
Can pikeperch colonise new freshwater systems via estuaries? Evidence from behavioural salinity tests
Authors: Scott Dawn M. , Rabineau Johanna , Wilson Rod W. , Hodgson Dave J. , Brown J. Anne
Published: August 2008

Pikeperch (Sander lucioperca) are non-native in the United Kingdom. It is important to understand how environmental factors, such as salinity, influence the behaviour and activity of introduced fish species to identify their dispersal potential. Previous studies have shown that pikeperch, traditionally recognised as a freshwater fish, can tolerate brackish waters and demonstrate physiological acclimation. However, their behavioural responses to brackish waters are unknown. The aim of the present study was therefore to investigate the activity and swimming behaviour of pikeperch obtained from freshwater canals in southern England. In the laboratory, fish were exposed to a 12-h simulated tidal cycle and a 12-day stepped salinity challenge where salinity was increased by 4 every 2 days, up to a salinity of 20. In both regimes, fish showed increased swimming activity in response to increasing salinity, which may represent an avoidance response. The most dramatic changes, including vertical movements, occurred at salinities above ~16. At these higher salinities, head shaking and coughing behaviours were also observed, suggesting significant stress and respiratory impairment. However, during the simulated tidal cycle, normal behaviour was rapidly restored once salinity was reduced. The results of this study may have implications in understanding the dispersal of non-native fish in the wild.
Nucleus accumbens AGS3 expression drives ethanol seeking through Gβγ
Authors: Bowers M. Scott , Hopf F. Woodward , Chou Jonathan K. , Guillory Anitra M. , Chang Shao-Ju , Janak Patricia H. , Bonci Antonello , Diamond Ivan
Published: August 2008

Approximately 90% of alcoholics relapse within 4 years, in part because of an enhanced motivation to seek alcohol (EtOH). A novel G protein modulator (Gpsm1/AGS3) was up-regulated in the rat nucleus accumbens core (NAcore) but not in other limbic nuclei during abstinence from operant EtOH self-administration. Furthermore, NAcore AGS3 knockdown reduced EtOH seeking to pre-abstinence levels in a novel rat model of compulsive, human EtOH seeking. AGS3 can both inhibit G protein Giα-mediated signaling and stimulate Gβγ-mediated signaling. Accordingly, sequestration of Gβγ, but not Giα knockdown, significantly reduced EtOH seeking to pre-abstinence levels. Thus, AGS3 and Gβγ are hypothesized to gate the uncontrolled motivation to seek EtOH during abstinence. AGS3 up-regulation during abstinence may be a key determinant of the transition from social consumption to compulsion-like seeking during relapse.
Engineering graded tissue interfaces
Authors: Phillips Jennifer E. , Burns Kellie L. , Le Doux Joseph M. , Guldberg Robert E. , García Andrés J.
Published: August 2008

Interfacial zones between tissues provide specialized, transitional junctions central to normal tissue function. Regenerative medicine strategies focused on multiple cell types and/or bi/tri-layered scaffolds do not provide continuously graded interfaces, severely limiting the integration and biological performance of engineered tissue substitutes. Inspired by the bone-soft tissue interface, we describe a biomaterial-mediated gene transfer strategy for spatially regulated genetic modification and differentiation of primary dermal fibroblasts within tissue-engineered constructs. We demonstrate that zonal organization of osteoblastic and fibroblastic cellular phenotypes can be engineered by a simple, one-step seeding of fibroblasts onto scaffolds containing a spatial distribution of retrovirus encoding the osteogenic transcription factor Runx2/Cbfa1. Gradients of immobilized retrovirus, achieved via deposition of controlled poly(
l
-lysine) densities, resulted in spatial patterns of transcription factor expression, osteoblastic differentiation, and mineralized matrix deposition. Notably, this graded distribution of mineral deposition and mechanical properties was maintained when implanted
in vivo
in an ectopic site. Development of this facile and robust strategy is significant toward the regeneration of continuous interfacial zones that mimic the cellular and microstructural characteristics of native tissue.
Structure of apolipoprotein A-I in spherical high density lipoproteins of different sizes
Authors: Silva R. A. Gangani D. , Huang Rong , Morris Jamie , Fang Jianwen , Gracheva Elena O. , Ren Gang , Kontush Anatol , Jerome W. Gray , Rye Kerry-Anne , Davidson W. Sean
Published: August 2008

Spherical high density lipoproteins (HDL)
†
predominate in human plasma. However, little information exists on the structure of the most common HDL protein, apolipoprotein (apo) A-I, in spheres vs. better studied discoidal forms. We produced spherical HDL by incubating reconstituted discoidal HDL with physiological plasma-remodeling enzymes and compared apoA-I structure in discs and spheres of comparable diameter (79–80 and 93–96 Å). Using cross-linking chemistry and mass spectrometry, we determined that the general structural organization of apoA-I was overall similar between discs and spheres, regardless of diameter. This was the case despite the fact that the 93 Å spheres contained three molecules of apoA-I per particle compared with only two in the discs. Thus, apoA-I adopts a consistent general structural framework in HDL particles—irrespective of shape, size and the number of apoA-Is present. Furthermore, a similar cross-linking pattern was demonstrated in HDL particles isolated from human serum. We propose the first experiment-based molecular model of apoA-I in spherical HDL particles. This model provides a new foundation for understanding how apoA-I structure modulates HDL function and metabolism.
Brk is coamplified with ErbB2 to promote proliferation in breast cancer
Authors: Xiang Bin , Chatti Kiranam , Qiu Haoqun , Lakshmi B. , Krasnitz Alexander , Hicks Jim , Yu Min , Miller W. Todd , Muthuswamy Senthil K.
Published: August 2008

Amplification of the receptor tyrosine kinase ErbB2 is frequently observed in breast cancer. Amplification of
erbB2
is also associated with multiple genomic gains and losses; however, the importance of these associated changes is largely unknown. We demonstrate that Brk, a cytoplasmic tyrosine kinase, is coamplified and coexpressed with ErbB2 in human breast cancers. ErbB2 interacts with Brk and increases its intrinsic kinase activity. Expression of Brk enhances the ErbB2-induced activation of Ras/MAPK signaling and cyclin E/cdk2 activity to induce cell proliferation of mammary 3-dimensional acini in culture. In a murine model of breast cancer, expression of Brk was found to shorten the latency of ErbB2-induced tumors by promoting cell proliferation, with no effect on protection from apoptosis. Furthermore, overexpression of Brk conferred resistance to the ability of Lapatinib, an ErbB2 kinase inhibitor, to inhibit ErbB2-induced proliferation. Thus, we identified Brk as a drug target for ErbB2-positive cancers.