bluuebunny/crossref_metadata_2025 huggingface dataset:
Photoelectric photometry of Europa and Callisto 1976–1991
Authors: Thompson Don T. , Lockwood G. W.
Published: May 2009

We have used a stable, dedicated telescope and photoelectric photometer to measure the brightnesses of Europa and Callisto near greatest elongation. The measurements, made regularly since 1976, delineate the phase functions of these objects from solar phase angles of about 12° to less than 0.5°. The phase functions of the two faces of Europa are essentially the same over this range, but Callisto's leading and trailing faces are quite different. The phase function of the leading face of Callisto is very similar to that of the Moon over the range of angles we observed. Europa exhibits a very strong opposition spike at phase angles of less than 1°. We compare these observed phase functions to those of some other atmosphereless bodies. These satellites exhibit a slight variation during the Jovian year which we attribute to the change in sub‐Earth latitude exposing alternate polar regions. If this variation and that due to rotation are adjusted for, the satellites are photometrically stable over the span of time covered by our observations.
Anatomy of a Venusian hot spot: Geology, gravity, and mantle dynamics of Eistla Regio
Authors: Grimm Robert E. , Phillips Roger J.
Published: May 2009

Eistla Regio is a series of broad swells, each up to a few thousand kilometers in diameter, in the equatorial highlands of Venus. It is characterized by strong positive free‐air gravity anomalies, shield volcanoes, and rift systems. We present a two‐part study of the western and central portions of this Venusian hot spot. First, Magellan radar images were mapped in order to understand the general geologic history of the region. Radial fracture systems both on the rises and volcanoes indicate uplift and associated faulting accompanied volcanic construction. Prominent fracture zones strike WNW to NW, parallel to the long axis of the highlands. The largest of these, Guor Linea, displays a progressive deformation history that may include minor clockwise rotation in addition to bulk NNE‐SSW extension. Other regional structural patterns also suggest this sense of rotation. The parts of Eistla studied here appear to be structurally distinct from surrounding regions, although volcanic radar‐bright plains and ridge‐and‐groove deformation to the west indicate an earlier, more diffuse thermal uplift. In the second part of our analysis, Pioneer Venus line‐of‐sight accelerations were inverted for vertical gravity which, when combined with topography, were used to solve for mass anomalies on the crust‐mantle boundary and in the upper levels of the mantle convective system. Both western and central Eistla appear to be sites of vigorous mantle upwelling. A linear upwelling appears beneath Guor Linea, indicating that rifting is actively driven by mantle flow. Minor crustal thinning may be present beneath western Eistla and the northern plains, whereas some thickening occurs beneath central Eistla and the southern plains. Heng‐O corona, in particular, may be the site of a small shallow mass anomaly of either compositional (thickened crust) or thermal origin. Mantle return flow is asymmetrically distributed about Eistla, being much stronger to the south than the north, and little flow is inferred at all to the NE in Bereghinya Planitia. These differences introduce a clockwise rotation to finite strain, in agreement with observations.
Core formation in asteroids
Authors: Taylor G. Jeffrey
Published: May 2009

Chemical arguments based on the S concentrations in the metallic magmas that formed magmatic iron meteorites and on the lack of pyroxene in pallasites suggest that core formation in asteroids was accompanied by >40% melting of the associated silicates. The existence of plagioclase‐free residues from partial melting, such as lodranite meteorites, indicates that metal did not segregate from silicates when the amount of partial melting was only 15%. Thus, core formation in asteroids requires substantial melting of an asteroid. High interfacial energies between metallic melts and silicates require that metallic spherules sink through partially molten silicates to form cores in asteroids and planetesimals. The globule‐sinking mechanism is not very efficient because silicate crystal‐liquid mixtures have high yield strengths, making it difficult for the globules to sink. Calculations suggest that the melt fraction must reach >50% before globules can sink. Alternatively, porous flow of molten metal is possible when the amount of metal is high enough to form an interconnected network, about 50%; this can be achieved by high initial abundances of metal or by gradual removal of silicate melt, thereby enriching the residue in the metal‐sulfide assemblage. This also requires removal of 50% silicate partial melt, though not necessarily all at once. Such high amounts of melting were not always attained in asteroids, so many asteroids probably consist of partially differentiated silicates and metallic masses that did not segregate to a core. S asteroids might represent such partially differentiated bodies.
Atmospheric effects on ejecta emplacement and crater formation on Venus from Magellan
Authors: Schultz Peter H.
Published: May 2009

The Venus cratering record provides a unique environment for assessing the effects of both gravity and an atmosphere on impact crater formation. This contribution uses surface signatures of energy partitioning as a framework for testing extrapolations from laboratory experiments and other planetary settings. Seven general conclusions can be drawn. First, the dense lower atmosphere of Venus takes on the role of a low‐density target for bodies smaller than about 4 km in diameter. Air blasts created by cratering in the atmosphere create distinctive surface signatures that allow the derivation of an independent assessment of impactor energy at the limit of break up. Second, dynamic pressures during entry of larger bodies will exceed their strength limit but may not prevent penetration of the atmosphere due to aerodynamic reshaping that minimizes the drag coefficient. Such a process may account for the formation of unusually small craters (1–3 km). Third, the dense atmosphere of Venus preserves signatures of early time cratering processes on the surface that are typically lost on atmosphere free surfaces. Such signatures not only provide another estimate of impactor energy but also include a distinctive record of the impactor (i.e., comet versus asteroid) in distinctive run‐out flows created before the crater has finished formation. Strong winds and turbulence associated with the atmospheric disturbance at later times create wind streaks behind topographic barriers. Fourth, ballistic ejection of excavated debris occurs from craters on Venus just as it does on planets without an atmosphere, thereby underscoring the fundamental mechanical transfer of energy from impactor to target. Fifth, ejecta emplacement is nonballistic due to the large dynamic forces acting on the advancing curtain and its constituent ejecta. The outward moving ejecta curtain induces strong response winds that entrain ejecta and drive a ground‐hugging debris flow outward without returning to the cavity. Flow separation creates an overriding run out ejecta flow further sustained by atmospheric turbulence and identified as radar dark lobate lobes. Sixth, radar‐dark parabolas are proposed to be late time fallout deposits created as the downrange fireball evolves aloft, perhaps analogous to terrestrial tektite strewn fields. And seventh, the response of crater formation to the atmosphere is conversely expressed by a reduction in cratering efficiency as revealed by the unusually large central peak complexes and the unexpected diameter‐depth relations of craters. Hence surface ages may be significantly underestimated.
Geology of the Venera 8 landing site region from Magellan data: Morphological and geochemical considerations
Authors: Basilevsky Alexandre T. , Nikolaeva Olga V. , Weitz Catherine M.
Published: May 2009

A photogeologic analysis of high‐resolution Magellan radar images covering the Venera 8 landing site area has shown that: (1) the majority of the region is characterized by mottled plain; (2) a younger plains complex exists in the western half of the landing circle; and (3) there are steep‐sided domes and a possible collapsed caldera inside the landing circle. A preliminary photogeological analysis of all the geochemically studied Venera/Vega sites has shown that for the Venera 8 and 13 sites, where nontholeiitic compositions were measured for the surface material, steep‐sided domes were found. Meanwhile, for the five sites where geochemical signatures of tholeiitic basalts were identified (Venera 9, 10, and 14 and Vega 1 and 2), steep‐sided domes were not found. Emissivity, reflectivity, altimetry, and rms slope values inside the landing circle are typical for the Venusian plains. A continuation of searching through the literature for terrestrial igneous rocks with similar K2O, U, and Th contents as the Venera 8 material resulted in the finding of another group of rocks which are K2O‐U‐Th analogs of the material (in addition to a previously identified group of evolved intermediate subalkaline rocks). These potential analogs are dike rocks (lamprophyres) with mostly mafic silica contents. Among these analogs is a sample having the same K2O and Th content as the Venera 8 material (no uranium content was measured) and a primitive bulk chemistry close to the Venera 13 material. Both evolved and mafic terrestrial igneous rocks identified as analogs or as potential analogs to the Venera 8 material showed a distinct enrichment of their magma and/or magma source in incompatible elements. This indicates the involvement of continental crust material in the terrestrial analogs, and it suggests that crustal material enriched in incompatible elements may also be present on Venus.
Analysis of volcanic surface morphology on Venus from comparison of Arecibo, Magellan, and terrestrial airborne radar data
Authors: Campbell Bruce A. , Campbell Donald B.
Published: May 2009

Arecibo Observatory and Magellan radar data for Venus are compared to airborne radar images for potential terrestrial analog surfaces. Volcanic deposits in Western Eistla Regio and northern Sedna Planitia are characterized. It is shown that the expected‐sense circularly polarized echoes in the “dark plains” and broad flow aprons of Eistla Regio decrease rapidly with incidence angle. This angular scattering behavior implies surfaces no rougher than terrestrial pahoehoe flows. Polarization ratio (based on the ratio of the “unexpected”‐ to “expected”‐sense circular echoes) comparisons show that the extensive lava flows in Western Eistla Regio and Sedna Planitia are generally consistent with the properties of terrestrial pahoehoe flows, with only limited occurrences of a'a morphology. Blocky textures on scales of several meters are not observed in these regions. This occurs despite the fact that Arecibo images are collected at 12.6‐cm wavelength, while the airborne data are collected at 24‐cm wavelength; shorter illuminating wavelengths tend to increase the perceived roughness of a given surface. Comparison of calibrated backscatter cross section values for Hawaiian lava flows and Magellan synthetic aperture radar data of the study areas supports these interpretations: only three major units of a'a morphology are identified (other radar‐bright surfaces are likely rough pahoehoe flows). These results suggest three scenarios: (1) many of the large flow units in the two study regions were emplaced as complexes of low‐effusion rate (presumably tube‐fed) pahoehoe flows, rather than as higher eruption rate events which might be expected to produce a'a surface textures, (2) the long lava flows were originally emplaced as a'a but have since weathered to a smoother texture, or (3) a combination of atmospheric and magma compositional effects combine to inhibit a'a formation even at high volume eruption rates.
Dike emplacement on Venus and on Earth
Authors: McKenzie Dan , McKenzie James M. , Saunders R. Stephen
Published: May 2009

Many long linear troughs are visible in synthetic aperture radar images of the surface of Venus. Their geometry closely resembles that of dike swarms on Earth. Such troughs will be formed if dikes fail to reach the surface, or if the magma in them is partially drained. Dikes that form closed ellipses in plan view can be produced by intrusions near a depression, and intersecting dikes can result if the stress field changes with time. Because of the absence of erosion and sedimentation, all these effects are better displayed on Venus than they are on Earth. The magnitude of the regional stress on Venus can be estimated from the dike patterns to be about 3 MPa, or similar to that of Earth. Dikes consisting of en echelon segments whose total length is 1500 km or more occur on both Earth and Venus. On Earth their widths are generally greater than 30 m and are sometimes as great as 250 m, and they are likely to be similar on Venus. The melt velocity during their emplacement is predicted to be a few meters per second, and the calculated rate of heat loss is sufficiently slow that they can remain molten as they propagate for distances of more than 1000 km. The same calculations apply to sills, though less is known about their geometry. The results therefore suggest that magma intrusion in thin sheets extending over 1000 km or more could produce regional crustal thickening and uplift on both Earth and Venus.
Impact cratering on Venus: Physical and mechanical models
Authors: Ivanov B. A. , Nemchinov I. V. , Svetsov V. A. , Provalov A. A. , Khazins V. M. , Phillips R. J.
Published: May 2009

Results are presented on laboratory, theoretical and numerical simulations of various phenomena related to impact cratering processes specific to the Venusian environment. Such processes are influenced mainly by two factors: the high atmospheric density and the high surface temperature. Model results are presented for the influence of the atmosphere on high‐velocity meteoroids, the influence of high‐velocity meteoroids on the atmosphere, the influence of atmospheric shock waves on the Venusian surface, and the influence of high crustal temperature on impact melting and melt cooling. New modeling techniques based on the two‐dimensional Free‐Lagrangian method have been employed and show that an icy body of 1‐km radius may reach the bottom of the Venusian atmosphere in a partially dispersed state and form an impact crater approximately 20 km in diameter. A significant amount of energy is transferred to the Venusian atmosphere during meteoroid transit, and the gas dynamic flow will be similar to a strong explosion. Modeling shows that a significant wake of low density will form behind the meteoroid and have an important influence on crater formation and ejecta distribution. According to our estimates, the boundary of the flow of dense gas may correspond to the region of hummocky ejecta deposition observed for Venusian impact craters. The collapse of the gas‐rock debris column on the boundary between the low‐ and high‐density regions may result in a turbiditelike flow outside the hummocky ejecta area. We carried out preliminary laboratory simulations of the interaction of meteoroid shock waves with the surface. Considerable surface disruption is possible, even under the trajectory of an oblique impact. The possibility of “back venting” caused by shock wave pressuring and depressuring in ground pores may provide an explanation for the origin of dark margins. The differences between Venus and Earth for impact melting and melt cooling were examined. Melt generation on Venus should be 20% to 40% greater than on Earth for the same crater diameter. Melt volumes should stay molten about an order of magnitude longer on Venus, leading to substantial melt flows and smooth crater floors.
Mercury's atmospheric bright spots and potassium variations: A possible cause
Authors: Sprague A. L.
Published: May 2009

An explanation is given for time‐variable and spatially discrete enhancements of neutral sodium (Na) and potassium (K) in Mercury's atmosphere. Some locations of increased intensity can be explained in terms of sodium and potassium ion implantation into the surface regolith grains during the long, 88 Earth day, Mercurian night with subsequent diffusion to the atmosphere when the enriched surface of Mercury rotates into the intense sunlight of day. Support for the suggested mechanism is shown by the K data which show a marked morning/afternoon asymmetry and can be explained by time and temperature dependent degassing. The magnetospheric mechanism necessary for ion implantation is discussed as is the diffusion mechanism. Alternative source, recycling, and distribution processes are also discussed.
Mineral equilibria and the high radar reflectivity of Venus mountaintops
Authors: Klose K. B. , Wood J. A. , Hashimoto A.
Published: May 2009

We studied the relationship between altitude and microwave emissivity (the complement of power reflectivity) in 10 highland regions of Venus, using the Magellan data set. Above a critical altitude that ranges from 4.75 km on Maxwell Montes to 2.49 km on Sapas Mons, emissivity undergoes an abrupt decrease to values so low (<0.6) that the surface mineralogy on these mountaintops must differ from that at lower altitudes in such a way as to enhance the bulk dielectric constant of the highland surface material. This emissivity effect probably is produced not by basalt minerals but by a secondary, weathered mineral assemblage. We developed the phase diagrams descriptive of equilibrium secondary mineral assemblages on Venus, as a function of altitude and atmospheric redox state. The mineral responsible for low emissivity on mountaintops appears to be the electrical semiconductor pyrite (FeS2). Variation from one highland area to another in the altitude at which pyrite becomes the stable Fe mineral (as opposed to magnetite at lower altitudes) may be attributable to local modulation by topography of the atmospheric thermal profile. The altitudes at which the magnetite/pyrite phase boundary is encountered vary with the redox slate of the atmosphere, and observed values of this altitude can be used to estimate an oxygen fugacity at plains level of ∼10−21 bars. Maat Mons, a volcanic peak almost as lofty as Maxwell Montes, is the only high mountaintop on Venus that has not weathered to a low‐emissivity mineral assemblage. Presumably, this means flows at the highest altitudes are negligibly weathered and the volcano is relatively young.
A new representation of the absorption by the CO2 15‐μm band for a Martian general circulation model
Authors: Hourdin Frédéric
Published: May 2009

A model for absorption by the CO2 15‐μm band has been adapted from the Morcrette et al. (1986) terrestrial wide‐band model for use in a general circulation model of the Martian atmosphere. The absorption model is validated by comparison with exact line‐by‐line integrations for a set of atmospheric profiles characteristic of Martian conditions. The Doppler effect is included in a simple way with no significant increase of the computational cost. The model gives accurate results up to 80 km. The Doppler effect, in fact, is shown to be significant only above 50 km for mean Martian conditions. The transmissivities of the wide‐band model are fitted to the results of a more accurate statistical narrow‐band model. Various formulations of the statistical band model, including accurate representation of the Doppler effect (Fels, 1979; Zhu, 1989) are validated by comparison with line‐by‐line results.
Europa, Ganymede, and Callisto: New radar results from Arecibo and Goldstone
Authors: Ostro S. J. , Campbell D. B. , Simpson R. A. , Hudson R. S. , Chandler J. F. , Rosema K. D. , Shapiro I. I. , Standish E. M. , Winkler R. , Yeomans D. K. , Velez R. , Goldstein R. M.
Published: May 2009

Observations of the icy Galilean satellites, conducted during 1987–1991 with the Arecibo 13‐cm system and the Goldstone 3.5‐cm system, yield significant improvements in our knowledge of the satellites' radar properties. Hardly any wavelength dependence is seen for either the total power radar albedo
or the circular polarization ratio μc. For Europa, Ganymede, and Callisto our 13‐cm estimates of mean values and rms dispersions are
, 1.39 ± 0.14, and 0.69 ± 0.06; and μc = 1.53 ± 0.03, 1.43 ± 0.06, and 1.17 ± 0.04. Radar albedo features are seen on each satellite. Evidence for μc features is lacking, except for indications of a weak hemispheric asymmetry for Callisto. That intersatellite and intrasatellite fractional variations in albedo greatly exceed variations in μc is consistent with predictions of coherent backscatter theory and implies that albedo might be a crude indicator of relative silicate abundance. The satellites' albedo distributions overlap. The most prominent radar features are tentatively identified with Galileo Regio and the Valhalla basin. Estimates of echo Doppler frequencies show Callisto to be lagging its ephemeris by 200 ± 50 km.
A spectral analysis of ordinary chondrites, S‐type asteroids, and their component minerals: Genetic implications
Authors: Fanale Fraser P. , Clark Beth E. , Bell Jeffrey F.
Published: May 2009

Three salient features of visible and infrared reflectance spectra of ordinary chondrites (OCs) and S‐type asteroids are (1) albedo at 0.56 μm, (2) continuum slope, and (3) depth of the electronic absorption band due to octahedrally coordinated Fe2+ in olivine and pyroxene. These quantities were numerically extracted from the spectra of 23 OCs representing all metamorphic grades and 39 S‐type asteroids to be plotted in a three‐dimensional coordinate system. The spectral characteristics of three OCs which were comminuted, melted, recrystallized, and recomminuted are also presented in the same format. The results show that although laboratory simulation of melt alteration in an asteroidal regolith does alter OC spectra, the spectral parameters of these altered meteorites do not change enough to leave the parametric region defined by “unaltered” OC spectra. When the region containing the 39 S‐asteroid spectra is compared with that of the altered and unaltered OCs, it is found that not one of the OCs falls within the S‐asteroid region. The differences may be largely attributed to spectral differences between the respective metallic components. The range of S‐asteroid parameters is then compared with potential pure “end‐member” components most likely to result from magmatic differentiation of a chondritic protoasteroid: olivine, orthopyroxene, clinopyroxene, and Fe,Ni meteorite metal (alternatively represented by the M‐asteroids). It is found that the S‐asteroid array is consistent with random mixtures of the differentiated components except for a notable dominance of the spectral characteristics of the opaque (metallic) component. These results suggest that the M‐asteroids may form a composition continuum with the S‐asteroids. We discuss a scenario consistent with this analysis and with the Bell et al. theory of the geological structure of the asteroid belt. Ordinary chondritic protoasteroids of all sizes were probably the dominant primary condensates in the inner portion of the main asteroid belt. These were later heated by electromagnetic induction or by 26Al nuclide decay. As a result, the smaller ones were subjected to various degrees of metamorphism, while the larger ones were subjected to large‐scale magmatic differentiation. Petrological domains of the S‐asteroids (beneath a mixed regolith) may be large and supply achondrites, irons, and stony irons to Earth rather than well‐mixed breccias of these components. The (smaller) OC protoasteroids may still be abundant in the asteroid belt but, if small enough to escape differentiation, may also be small enough to escape Earth‐based identification.
First-principles study of native point defects in crystalline indium gallium zinc oxide
Authors: Omura Hideyuki , Kumomi Hideya , Nomura Kenji , Kamiya Toshio , Hirano Masahiro , Hosono Hideo
Published: May 2009

Materials in In–Ga–Zn–O system are promising candidates for channel layers of high-performance thin-film transistors (TFTs). We investigated the atomic arrangements and the electronic structures of crystalline InGaZnO4 containing point defects such as oxygen vacancy (VO), interstitial hydrogen (Hi), and interstitial oxygen (Oi) by density functional theory (DFT) using a plane-wave pseudopotential method. The calculations for the atomic structure relaxation suggest that Hi bonds to a lattice oxygen (OO), and Oi occupies a split interstitial site [Oi(split)] forming a chemical bond with OO which is similar to O2 molecule, or Oi occupies an octahedral interstitial site [Oi(oct)]. The electronic structure calculations reveal that VO forms fully occupied states around the middle of the DFT band gap, while Hi does not form a defect level in the band gap but raises the Fermi level above the conduction band minimum. Oi(split) forms fully occupied states above the valence band maximum of the defect-free model (VBM0), while Oi(oct) forms both occupied and unoccupied states above the VBM0. It is thus suggested that VO and Oi(split) are electrically inactive for electrons but work as hole traps, Hi acts as a donor, and Oi(oct) is electrically active, trapping both electrons and holes. These observations imply that VO and Oi(split) do not but Hi and Oi(oct) influence electrical properties of the n-channel TFTs based on the In–Ga–Zn–O semiconductor materials.
Influence of magnetic interactions on magnetic and magnetoresistive properties of Cu80Fe10Ni10 ribbons
Authors: Cazottes S. , Coïsson M. , Fnidiki A. , Lemarchand D. , Danoix F.
Published: May 2009

Magnetic and magnetotransport properties measurements of Cu80Fe10Ni10 (at. %) melt spun and annealed ribbons were combined to study the magnetic interactions present in this system. Those ribbons are composed of magnetic FeNi rich precipitates embedded in a nonmagnetic Cu rich matrix. When the precipitates are small enough, they have a superparamagnetic behavior. Upon annealing the precipitates get larger and progressively turn ferromagnetic. The relatively high magnetoresistive properties are attributed to the presence of those superparamagnetic precipitates. Using Mössbauer spectrometry, Zero Field Cooled/Field Cooled and magnetization curves, the presence of interactions among the precipitates was evidenced, which degrades the magnetoresistance properties. Using Allia model, the magnetic coherence length Rm between the precipitates was calculated and compared with the mean free path of the electrons λ, with the precipitates size and the mean distance between them. Three different regimes were observed. At high fields, where Rm<λ, meaning that the precipitates are not interacting, at smaller fields, where Rm>λ and the precipitates are in the so called “interacting superparamagnetic regime,” and at low fields, and at 5 K, Rm>10λ, the magnetic interactions among the precipitates are strong and give rise to a hysteresis on the magnetization curves.
Enhancement of current-voltage characteristics of multilayer organic light emitting diodes by using nanostructured composite films
Authors: Dinh Nguyen Nang , Chi Le Ha , Chung Thuy Tran Thi , Trung Tran Quang , Truong Vo-Van
Published: May 2009

With the aim of improving the photonic efficiency of an organic light emitting diode (OLED) and its display duration, both the hole transport layer (HTL) and the emitting layer (EL) were prepared as nanostructured thin films. For the HTL, nanocomposite films were prepared by spin-coating a homogeneous solution of low molecular weight poly(4-styrenesulfonate) (PEDOT-PSS) and surfactant-capped TiO2 nanocrystals onto low resistivity indium tin oxide (ITO) substrates; for the EL, nancrystalline titatium oxide (nc-TiO2)-embedded Poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV+nc-TiO2) conjugate polymers were spin-coated onto the HTL. Also, for a shallow contact of Al/LiF/MEH-PPV instead of Al/MEH-PPV a super LiF thin film was deposited onto the EL by vacuum evaporation. The resulting multilayer OLED had the following structure of Al/LiF/MEH-PPV+nc-TiO2/PEDOT-PSS+nc-TiO2/ITO. Characterization of the nanocomposite films showed that both the current-voltage (I-V) characteristics and the photoluminescent properties of the nanocomposite materials were significantly enhanced in comparison with the standard polymers. OLEDs made from these layers would exhibit a large photonic efficiency.
Short pulse, high power microwave radiation source with a laser-induced sheet plasma mirror
Authors: Higashiguchi Takeshi , Yugami Noboru
Published: May 2009

We have demonstrated the short pulse, high power microwave radiation source using an ultraviolet laser-induced sheet plasma mirror in a gas-filled x-band rectangular waveguide from the conventional microwave sources and components. A laser-induced sheet plasma with an overdense plasma acts as a plasma mirror. The long pulse propagating in the gas-filled waveguide was sliced by the sheet plasma mirror at two different points along the waveguide. We observed about twice the power of the pulse by adding the two sliced microwave pulses produced by this scheme. A maximum peak power of 200 kW with a pulse duration of 10 ns (full width at half maximum) from the long microwave pulse source with a pulse duration of 0.8 μs was observed.
Molecular conductance obtained in terms of orbital densities and response functions
Authors: Rocheleau Philippe , Ernzerhof Matthias
Published: May 2009

Using the source-sink potential (SSP) approach recently developed in our group, we study electron transmission through molecular electronic devices (MEDs). Instead of considering the source-sink potentials exactly, we use a perturbative approach to find an expression for the transmission probability T(E)=1−|r(E)|2 that depends on the properties of the bare molecule. As a consequence, our approach is limited to weak molecule-contact coupling. Provided that the orbitals of the isolated molecule are not degenerate, we show that it is the orbital density, on the atoms that connect the molecule to the contacts, that largely determines the transmission through the device. Corrections to this leading-order contribution involve the second- and higher-order molecular response functions. An explicit expression for T(E) is obtained that is correct up to first order in the molecular response function. Illustrating our approach, a qualitative explanation is provided for why orders of magnitude difference in the transmission probability are obtained [M. Mayor et al., Angew. Chem. Int. Ed. 42, 5834 (2003)] upon modification of the contact position in the molecule. An extension of the formalism to interacting systems is outlined as well.
Coherent infrared multidimensional spectra of the OH stretching band in liquid water simulated by direct nonlinear exciton propagation
Authors: Falvo Cyril , Palmieri Benoit , Mukamel Shaul
Published: May 2009

The two-dimensional vibrational response of the disordered strongly fluctuating OH exciton band in liquid water is investigated using a new simulation protocol. The direct nonlinear exciton propagation generalizes the nonlinear exciton equations to include nonadiabatic time dependent Hamiltonian and transition dipole fluctuations. The excitonic picture is retained and the large cancellation between Liouville pathways is built-in from the outset. The sensitivity of the photon echo and double-quantum-coherence techniques to frequency fluctuations, molecular reorientation, intermolecular coupling, and the two-exciton coherence is investigated. The photon echo is particularly sensitive to the frequency fluctuations and molecular reorientation, whereas the double-quantum coherence provides a unique probe for intermolecular couplings and two-exciton coherence.
A diabatic three-state representation of photoisomerization in the green fluorescent protein chromophore
Authors: Olsen Seth , McKenzie Ross H.
Published: May 2009

We give a quantum chemical description of the photoisomerization reaction of green fluorescent protein (GFP) chromophores using a representation over three diabatic states. Photoisomerization leads to nonradiative decay, and competes with fluorescence in these systems. In the protein, this pathway is suppressed, leading to fluorescence. Understanding the electronic states relevant to photoisomerization is a prerequisite to understanding how the protein suppresses it, and preserves the emitting state of the chromophore. We present a solution to the state-averaged complete active space problem, which is spanned at convergence by three fragment-localized orbitals. We generate the diabatic-state representation by block diagonalization transformation of the Hamiltonian calculated for the anionic chromophore model HBDI with multireference, multistate perturbation theory. The diabatic states are charge localized and admit a natural valence-bond interpretation. At planar geometries, the diabatic picture of the optical excitation reduces to the canonical two-state charge-transfer resonance of the anion. Extension to a three-state model is necessary to describe decay via two possible pathways associated with photoisomerization of the (methine) bridge. Parametric Hamiltonians based on the three-state ansatz can be fit directly to data generated using the underlying active space. We provide an illustrative example of such a parametric Hamiltonian.
Ab initio study of the Br(P2)–HBr van der Waals complex
Authors: Toboła R. , Chałasiński G. , Kłos J. , Szczęśniak M. M.
Published: May 2009

This study reports an ab initio characterization of a prereactive van der Waals complex between an open-shell atom Br(P2) and a closed shell molecule HBr. The three adiabatic potential surfaces 1 A2′, 2 A2′, and 1 A2″, which result from the splitting of degenerate P state of Br are obtained from coupled cluster calculations. The coupling between same-symmetry states is calculated by multireference configuration-interaction method. A transformation to a diabatic representation and inclusion of the spin-orbit coupling effects on the interactions are also discussed. Bound states are calculated using an adiabatic bender model. The global minimum on the lowest adiabatic potential surface corresponds to a T-shaped geometry and has a well depth of De=762.5 cm−1 at Re=3.22 Å. A secondary minimum occurs for a hydrogen-bonded geometry with De=445.3 cm−1 at Re=4.24 Å. Upon inclusion of spin-orbit coupling the hydrogen-bonded minimum remains at the same depth, but the T-shaped minimum washes out to less than half of its spin-free value. The lowest bound state is localized in the linear minimum. The spin-orbit coupling plays a very important role in shaping of the potential energy surfaces of Br–HBr.
Abstract cluster expansion with applications to statistical mechanical systems
Authors: Poghosyan Suren , Ueltschi Daniel
Published: May 2009

We formulate a general setting for the cluster expansion method and we discuss sufficient criteria for its convergence. We apply the results to systems of classical and quantum particles with stable interactions.
An ab initio global potential-energy surface for NH2(A2A′) and vibrational spectrum of the Renner–Teller A2A′-X2A″ system
Authors: Zhou Shulan , Li Zheng , Xie Daiqian , Lin Shi Ying , Guo Hua
Published: May 2009

A global potential-energy surface for the first excited electronic state of NH2(A2A′) has been constructed by three-dimensional cubic spline interpolation of more than 20 000 ab initio points, which were calculated at the multireference configuration-interaction level with the Davidson correction using the augmented correlation-consistent polarized valence quadruple-zeta basis set. The (J=0) vibrational energy levels for the ground (X2A″) and excited (A2A′) electronic states of NH2 were calculated on our potential-energy surfaces with the diagonal Renner–Teller terms. The results show a good agreement with the experimental vibrational frequencies of NH2 and its isotopomers.
Photoacoustic technique to measure beam profile of pulsed laser systems
Authors: Mallidi Srivalleesha , Emelianov Stanislav
Published: May 2009

The beam profiles of pulsed lasers are currently measured using either complementary metal oxide semiconductor (CMOS) or charge coupled device (CCD) cameras. Despite providing high-resolution beam profiles, these devices cannot work with high power lasers. If additional optical attenuators are used, beam distortions may occur. In this paper we demonstrate a high-resolution photoacoustic technique capable of measuring the beam profile of pulsed lasers. The beam profiles of a pulsed neodymium-doped yttrium aluminium garnet (Nd:YAG) laser and a pulsed optical parametric oscillator (OPO) laser system were measured using a polydimethylsiloxane film and a single element high-frequency ultrasonic transducer. The advantages and limitations of the developed photoacoustic technique are discussed.
On the statistical behavior of the O+OH→H+O2 reaction: A comparison between quasiclassical trajectory, quantum scattering, and statistical calculations
Authors: Jorfi Mohamed , Honvault Pascal , Bargueño Pedro , González-Lezana Tomás , Larrégaray Pascal , Bonnet Laurent , Halvick Philippe
Published: May 2009

The dynamics of the O+OH reaction on the ground state potential energy surface (PES) is investigated by means of the quasiclassical trajectory method and two statistical methods: phase space theory and statistical quantum method. Preliminary calculations with an exact quantum method are also reported. The quasiclassical trajectory calculations show evidence for a phase space bottleneck inhibiting the intramolecular energy transfer between the O–H and O–O bonds. As a result, the probability of the intermediate complex dissociating back toward the reactants is high, thereby yielding a reaction probability significantly lower than expected for a barrierless and exothermic reaction. The features of the PES, which are the cause of this dynamical effect, are identified. This is essentially the conservation of the equilibrium distance of the O–H bond, hardly changed by a close encounter with an oxygen atom. The statistical calculations, which do not take into account the PES in the complex region, yield a high reaction probability, much larger than the probability calculated from the dynamical methods, both classical and quantum. If the statistical cross sections are corrected by a scaling factor, which corresponds actually to scaling the capture probability, then a good agreement is observed between dynamical and statistical calculations of the product state distributions. The differential cross sections calculated with all the methods show a backward-forward symmetry, with sharp polarization peaks. The complex lifetime is divided into two parts by the bottleneck. During the first part, the system remains trapped in a small region of the phase space and has a high probability to dissociate back toward the reactants. This is a nonstatistical effect due to the PES shape. During the second part, fast intramolecular vibrational energy redistribution takes place, leading to a statistical distribution of energy on the rovibrational states of the products. These findings indicate that the O+OH reaction has mixed dynamics, both with statistical and nonstatistical aspects.
Dynamics in scheduled networks
Authors: Zanin Massimiliano , Lacasa Lucas , Cea Miguel
Published: May 2009

When studying real or virtual systems through complex networks theories, usually time restrictions are neglected, and a static structure is defined to characterize which node is connected to which other. However, this approach is oversimplified, as real networks are indeed dynamically modified by external mechanisms. In order to bridge the gap, in this work we present a scheduled network formalism, which takes into account such dynamical modifications by including generic time restrictions in the structure of an extended adjacency matrix. We present some of its properties and apply this formalism to the specific case of the air transportation network in order to analyze its efficiency. Real data are used at this point. We finally discuss on the applicability of this formalism to other complex systems.
Symmetry breaking in the ground state of BNB: A high level multireference study
Authors: Liu Yang , Zou Wenli , Bersuker Isaac B. , Boggs James E.
Published: May 2009

A series of multireference approaches based on the SA-CASSCF wave function, i.e., CASPT2, MRCI, MRCI+Q, and MRAQCC with single- or multireference states, have been employed to investigate the symmetry breaking effect in the ground state X̃ Σu+2 of the triatomic BNB radical. We found that the mixing of the reference states contributes significantly to the dynamical correlation energy, which strongly affects the geometry of the ground state. Our results show that BNB in its ground state has a linear noncentrosymmetric structure with two equivalent global minima of the adiabatic potential energy surface and, respectively, two oppositely directed dipole moments of about 2 D. The barrier between the minima is about 20 cm−1. The origin of the double-minimum potential in the ground state of BNB is explained as due to the pseudo-Jahn–Teller effect involving vibronic interaction with the first excited state Ã Σg+2 via the asymmetric stretching vibrations.
Strain-induced Stranski–Krastanov three-dimensional growth mode of GaSb quantum dot on GaAs substrate
Authors: Fu K. , Fu Y.
Published: May 2009

The growth dynamics of self-assembled GaSb quantum dots (QDs) on GaAs substrate was investigated using kinetic Monte Carlo method. The strain induced by the lattice mismatch between the epitaxial material and the substrate was shown to be directly responsible for the three-dimensional QD formation. Different geometries of the initial seeds on the surface which are equally favorable from an energy point of view can result in different GaSb nanostructures (nanostrips and nanoring).
Second harmonic generation χ tensor microscopy for tissue imaging
Authors: Chen Wei-Liang , Li Tsung-Hsian , Su Ping-Jung , Chou Chen-Kuan , Fwu Peter Tramyeon , Lin Sung-Jan , Kim Daekeun , So Peter T. C. , Dong Chen-Yuan
Published: May 2009

Important biological molecules such as collagen and myosin are strong second harmonic generators. The polarization dependence of second-harmonic generation (SHG) is a property of the second order susceptibility elements (χ tensor) of the molecules that produce the signal. In this work, we used polarization SHG microscopy to image and map pixel scale polarization anisotropy information of collagen-muscle junction of chicken wing and the dermis of human skin. We show that the variation in the χ tensor components can be displayed as images to show the contrast between different molecular sources of SHG.
Dependence of surface plasmon lifetimes on the hole size in two-dimensional metallic arrays
Authors: Li J. , Iu H. , Lei D. Y. , Wan J. T. K. , Xu J. B. , Ho H. P. , Waye M. Y. , Ong H. C.
Published: May 2009

Two-dimensional metallic arrays with different hole sizes have been fabricated by using interference lithography and their optical properties have been studied by using angle-dependent reflectivity measurements. The lifetimes of different surface plasmon polariton (SPP) modes have been determined from the linewidths of reflectivity spectra for different resonance wavelengths and hole sizes. It is found that the lifetimes display an λn dependence, where n is strongly dependent on hole radius. In particular, n is found to be ∼4 for small hole, as expected from Rayleigh dipole scattering, and linearly increases to ∼11 when the hole radius is increased to 177 nm. By plotting n with hole radius, the relationship between n and hole radius is found.
Origin of high room temperature ferromagnetic moment of nanocrystalline multiferroic BiFeO3
Authors: Vijayanand S. , Potdar H. S. , Joy P. A.
Published: May 2009

Single phase nanocrystalline BiFeO3 of average crystallite size ∼25 nm with very high magnetization at room temperature is synthesized by an autocombustion method. Magnetic measurements above room temperature show deviation between field cooled and zero field cooled magnetization below 645 K, the Néel temperature (TN) of the bulk material, indicating intrinsic nature of ferromagnetism. However, observation of a broad magnetic transition above TN of BiFeO3 and extended up to 800 K suggests the presence of Fe3O4 as a possible magnetic impurity phase. Evidence for the presence of Fe3O4 is obtained from detailed analysis of the powder x-ray diffraction pattern.
Influence of interfaces and doping on the crystallization temperature of Ge–Sb
Authors: Raoux Simone , Cheng Huai-Yu , Jordan-Sweet Jean L. , Muñoz Becky , Hitzbleck Martina
Published: May 2009

The crystallization temperature Tx of the phase change material Ge–Sb as a function of film thickness and cladding material was measured using time-resolved x-ray diffraction. For films >5 nm, a weak influence of the cladding material on Tx was found (increase for Si, SiN, Pt, SiC, and TiN and decrease for Al and W). For very thin films, however, Tx differed up to 200 °C. Doping of Ge–Sb with these materials led to an increase in Tx in all cases, up to a maximum of 180 °C for SiN. Such a large influence of interfaces and doping on Tx is of great technological importance.
Dagelet and Dawes: Their Meeting, Their Instruments and the First Scientific Experiments on Australian Soil
Authors: Morrison Doug , Barko Ivan
Published: May 2009

At Botany Bay on 2 February 1788, the Lap�rouse expedition's astronomer, Joseph Lepaute Dagelet, met his First Fleet counterpart, William Dawes. Dagelet sent Dawes a three-page letter containing the geographic co-ordinates of his observatory, advice on various aspects of the observatory that Dawes was building at Sydney Cove, a discussion of the main issues of contemporary astronomy and information on his own research. By drawing on the evidence of Dagelet's letter and other surviving documents, instrument inventories, fragments of instruments recovered from the Vanikoro shipwreck sites, private and official correspondence by members of the expedition and others, and importantly a short professional biography of Lepaute Dagelet written in 1803 by his mentor J�r�me Lalande, the scientific experiments made by Dagelet at Botany Bay are identified. Dawes' gravity experiments are also identified.
Intrathymic proliferation wave essential for Vα14
+
natural killer T cell development depends on c-Myc
Authors: Dose Marei , Sleckman Barry P. , Han Jin , Bredemeyer Andrea L. , Bendelac Albert , Gounari Fotini
Published: May 2009

The molecular requirements for invariant Vα14-bearing natural killer T cells (iNKT) in the thymus are poorly understood. A minute population of ≈500 newly selected CD69
+
CD24
+
stage 0 (ST0) iNKT cells gives rise to ≈100 times more CD44
neg/lo
CD24
−
stage 1 (ST1) cells, which then generate similar frequencies of CD44
hi
CD24
−
stage 2 (ST2) and mature iNKT cells. Although the increased number of ST1 compared with ST0 cells indicates the initiation of a proliferation wave in the very early stages of iNKT cell development, details about the controlling mechanism are currently lacking. Here, we show that the transcription factor c-Myc is required for iNKT cell development. Conditional ablation of c-Myc in double-positive thymocytes specifically impacted iNKT but not conventional T cell development. Within the iNKT population, a progressive reduction of iNKT cells was observed starting at ST1 (≈50-fold) and ST2 (≈350-fold), with a complete lack of mature cells in thymus, spleen, and liver. ST0/ST1 c-Myc-deficient iNKT cells showed reduced proliferation. In contrast, annexin V staining did not reveal increased apoptosis, and transgenic overexpression of BCL-2 did not rescue iNKT cell development in c-Myc-deficient mice. Moreover, expression of known iNKT differentiation factors such as Plzf and Gata3 was not dramatically altered. These, findings provide compelling evidence that c-Myc mediates an intrathymic proliferation wave immediately after agonist selection of iNKT cells and illustrate the importance of this expansion for the generation of mature iNKT cells in vivo.