bluuebunny/crossref_metadata_2025 huggingface dataset:
Construction of the Galápagos platform by large submarine volcanic terraces
Authors: Geist Dennis , Diefenbach Bridget A. , Fornari Daniel J. , Kurz Mark D. , Harpp Karen , Blusztajn Jerzy
Published: March 2008

New multibeam bathymetric and side‐scan sonar data from the southwestern edge of the Galápagos platform reveal the presence of ∼60 large, stepped submarine terraces between depths of 800 m and 3500 m. These terraces are unique features, as none are known from any other archipelago that share this geomorphic form or size. The terraces slope seaward at <2° and are surrounded by escarpments that average ∼300 m in height with average slopes of 24°. The stepped morphology, fine‐scale features, and sinuous planform continuity of terrace edges indicate that each terrace results from a sequence of major submarine volcanic eruptions, similar in extent to young deep‐water (>3000 m) lava flow fields west of Fernandina and Isabela Islands. The terraces are formed of thick sequences of lava flows that coalesce to form the foundation of the Galápagos platform, on which the subaerial central volcanoes are built. The compositions of basalts dredged from the submarine terraces indicate that most lavas are chemically similar to subaerial lavas erupted from Sierra Negra volcano on southern Isabela Island. There are no regular major element, trace element, or isotopic variations in the submarine lavas as a function of depth, relative stratigraphic position, or geographic location along the southwest margin of the platform. We hypothesize that magma supply at the western edge of the Galápagos hot spot, which is influenced by both plume and mid‐ocean ridge magmatic processes, leads to episodic eruption of large lava flows. These large lava flows coalesce to form the archipelagic apron upon which the island volcanoes are built.
3D structure of Asian dust transport revealed by CALIPSO lidar and a 4DVAR dust model
Authors: Uno I. , Yumimoto K. , Shimizu A. , Hara Y. , Sugimoto N. , Wang Z. , Liu Z. , Winker D. M.
Published: March 2008

We present detailed 3D structure of Asian dust outflow from a dust source region to the northwestern Pacific ocean retrieved by NASA/CALIOP onboard CALIPSO and results simulated by a four‐dimensional variational (4DVAR) data assimilation version of a dust transport model (RC4) based on the NIES Lidar network. The modeled and CALIOP dust extinction showed good agreement, both for horizontal scale (600–1200 km) and vertical depth (1600–3600 m) near the dust source regions. Cross‐section analyses of CALIOP and RC4 assisted by forward trajectory revealed that dust from the Gobi Desert on 5 May traveled approximately 1000–1500 km/day to the east and passed over Japan on 8 May. The elevated dust subsequently passed to the Pacific Ocean while maintaining the major dust layer height of 2500–4000 m MSL trapped within the potential temperature of 302–306 K. Results of our analyses demonstrate the importance of integration of CALIOP measurement and the dust model for clarifying the overall structure of an Asian dust event.>
Daytime 150‐km echoes observed with the Equatorial Atmosphere Radar in Indonesia: First results
Authors: Patra A. K. , Yokoyama T. , Otsuka Y. , Yamamoto M.
Published: March 2008

Results of the daytime 150‐km echoes from 10.36°S magnetic latitude observed using the Equatorial Atmosphere Radar (EAR), which are first of its kind from magnetic southern hemisphere, are presented. The echoing region of 145–165 km shows forenoon descent and afternoon ascent with signal intensity modulation with time resembling a necklace and the Doppler spectra are narrow, which are quite similar to those reported earlier from other locations. Westward and upward/southward irregularity drifts are found to be consistent with daytime background electric fields, providing a tool to investigate low latitude daytime electrodynamics. Detectability of these echoes suggests the absence of strong latitudinal dependence in contrast to the earlier belief, suggesting a possibility of their detection at mid‐latitudes. Also the echoes show zonal anisotropy that is opposite to that observed over Pohnpei. The implications of these observations are discussed in the light of present understanding of 150‐km echoing phenomenon.
Ionospheric modeling for short‐ and long‐term predictions of F region parameters over Indian zone
Authors: Dabas R. S. , Sharma Kavita , Das Rupesh M. , Sethi N. K. , Pillai K. G. M. , Mishra A. K.
Published: March 2008

The equatorial and low latitudinal F region ionosphere is highly dynamic and unpredictable because of various geophysical mechanisms operating therein. In the present study, two HF prediction models for short and long term are developed for equatorial and low‐latitude F region ionosphere. In the first approach, multiple regression analysis (MRA) for the dependence of F region parameters, namely, foF2 and M(3000)F2, on solar 2800 MHz flux (F10) and geomagnetic index Ap are generated, and in the second one, second‐degree (SD) coefficients are generated, both by fitting monthly median foF2 and M(3000)F2 with corresponding 12 monthly mean sunspot numbers (R12) using data over three solar cycles. For MRA, daily foF2 and M(3000)F2 values for each hour obtained from Delhi (28.6°N, 77.1°E) digital ionosonde for about half a solar cycle are used. MRA coefficients for foF2 and M(3000)F2 are obtained for every month over 2400 UT times using daily F10 and Ap values separately for quiet (Ap < 25) and disturbed (Ap > 25) periods. Similarly, SD coefficients are obtained each month at all local times for all the 14 stations covering a geographic latitude range from about 0°N to 45°N. In this way, once appropriate coefficients for each hour for all the 12 months are obtained, they are used by the computer‐based MRA and SD models to predict ionospheric hourly foF2 and hmF2 values for given inputs such as month, F10, Ap, and R12, as the case may be. Predicted model values of foF2 and hmF2, calculated on short‐ and long‐term basis, are then compared with the observed data over Delhi and also with those obtained using international reference ionosphere (IRI)‐2001 model. From our comparative studies it is observed that MRA and SD models show better agreement with observations compared to the IRI model for both long‐ and short‐term basis and among the two the MRA model provides best agreement with the observed ones, even during the magnetic storm periods. The SD model, on the other hand, which is based on monthly median values, is useful for providing long‐term predictions for HF communication applications.
Validation of a synoptic solar wind model
Authors: Cohen O. , Sokolov I. V. , Roussev I. I. , Gombosi T. I.
Published: March 2008

We present a validation of a three‐dimensional magnetohydrodynamic model for the solar corona and the inner heliosphere. We compare the results of the model with long‐term satellite data at 1 AU for a 1 year period during solar minimum and another year period of solar maximum. Overall, the model predicts rather well the magnitude of the magnetohydrodynamical variables for solar minimum conditions. For solar maximum conditions, the magnitude of the magnetic field predicted by the model is too low. This result is consistent with the assumption that during solar maximum, a significant portion of the heliospheric open magnetic flux is not captured by the magnetogram input and the potential field approximation.
Effects of 2000–2050 global change on ozone air quality in the United States
Authors: Wu Shiliang , Mickley Loretta J. , Leibensperger Eric M. , Jacob Daniel J. , Rind David , Streets David G.
Published: March 2008

We investigate the effects on U.S. ozone air quality from 2000–2050 global changes in climate and anthropogenic emissions of ozone precursors by using a global chemical transport model (GEOS‐Chem) driven by meteorological fields from the NASA Goddard Institute for Space Studies general circulation model (NASA/GISS GCM). We follow the Intergovernmental Panel on Climate Change A1B scenario and separate the effects from changes in climate and anthropogenic emissions through sensitivity simulations. The 2000–2050 changes in anthropogenic emissions reduce the U.S. summer daily maximum 8‐hour ozone by 2–15 ppb, but climate change causes a 2–5 ppb positive offset over the Midwest and northeastern United States, partly driven by decreased ventilation from convection and frontal passages. Ozone pollution episodes are far more affected by climate change than mean values, with effects exceeding 10 ppb in the Midwest and northeast. We find that ozone air quality in the southeast is insensitive to climate change, reflecting compensating effects from changes in isoprene emission and air pollution meteorology. We define a “climate change penalty” as the additional emission controls necessary to meet a given ozone air quality target. We find that a 50% reduction in U.S. NOx emissions is needed in the 2050 climate to reach the same target in the Midwest as a 40% reduction in the 2000 climate. Emission controls reduce the magnitude of this climate change penalty and can even turn it into a climate benefit in some regions.
Universal properties of mechanisms from two-state trajectories
Authors: Flomenbom O. , Silbey R. J.
Published: March 2008

Finding the underlying mechanism from the statistical properties of an experimental two-state trajectory generated from dynamics in a complex on-off multisubstate kinetic scheme (KS) is the aim of many experiments. Since the data explicitly shows only transitions between substates of different states, information about the KS is lost, resulting in equivalence of KSs, i.e., the occurrence of different KSs that lead to the same data, in a statistical sense. In order to deal with this phenomenon, a canonical (unique) form of reduced dimensions (RD) is built from the data. RD forms are on-off networks with connections only between substates of different states, where the connections usually have nonexponential waiting time probability density functions. In this paper, we give a list of (about 50) relationships between properties of the data, the topology of reduced dimension forms, and features of KSs. Many of these relationships involve symmetries in RD forms, KSs, and the data and irreversible transitions in KSs. These relationships are useful both in theoretical analysis of on-off KSs and in the analysis of the data.
Effects of soft underlayer and cap layer thicknesses on the R/W performance of composite perpendicular media
Authors: Das Sarbanoo , Suzuki Hiroyuki
Published: March 2008

The dependence of perpendicular magnetic recording media read/write characteristics on the soft underlayer (SUL) and recording cap layer thicknesses was investigated. Optimal media signal to noise ratio (SNR) was observed at intermediate SUL and cap layer thicknesses. Media noise dominated the SNR. For thin SUL and cap layers, high media noise was due to insufficient writability; whereas for thick layers it was related to transition jitter.
Liquid-solid coexistence via the metadynamics approach
Authors: Prestipino Santi , Giaquinta Paolo V.
Published: March 2008

The metadynamics method, recently proposed by Laio and Parrinello as a general tool to map multidimensional free-energy landscapes [A. Laio and M. Parrinello, Proc. Natl. Acad. Sci. U.S.A. 99, 12562 (2002)], has been exploited with the aim of illustrating the properties of generalized thermodynamic potentials across a discontinuous phase transition. Virtues and limitations of the method are discussed in the exemplifying case of the freezing of a Lennard-Jones fluid in two dimensions.
Core level shifts of undercoordinated Pt atoms
Authors: Bianchettin Laura , Baraldi Alessandro , de Gironcoli Stefano , Vesselli Erik , Lizzit Silvano , Petaccia Luca , Comelli Giovanni , Rosei Renzo
Published: March 2008

We present the results of high-energy resolution core level photoelectron spectroscopy experiments paralleled by density functional theory calculations to investigate the electronic structure of highly undercoordinated Pt atoms adsorbed on Pt(111) and its correlation with chemical activity. Pt4f7∕2 core level binding energies corresponding to atoms in different configurations are shown to be very sensitive not only to the local atomic coordination number but also to the interatomic bond lengths. Our results are rationalized by introducing an indicator, the effective coordination, which includes both contributions. The calculated energy center of the valence 5d-band density of states, which is a well known depicter of the surface chemical reactivity, shows a noteworthy correlation with the Pt4f7∕2 core level shifts and with the effective coordination.
Seed electron production from O− ions under high-power microwave excitation
Authors: Edmiston G. F. , Neuber A. A. , Krompholz H. G. , Krile J. T.
Published: March 2008

Surface and volume breakdown formation during pulsed high-power microwave (HPM) excitation can severely limit the power densities which can be transmitted into an atmospheric medium. Recent studies in this area have focused on developing models which accurately predict flashover formation at either dielectric/air interfaces or in the gas volume directly adjacent to these interfaces. These models are typically validated through comparison with experimentally gathered data. With respect to HPM surface flashover, experiments in the S-band at 5 MW power levels have reported on the contributing factors to flashover development including the effects of gas type, pressure, and relative humidity. A Monte Carlo-type electron motion simulation code, MC, has been developed to calculate the increasing electron density during flashover formation in this case. Results from the MC code have exhibited a quantitative agreement with experimental data over a wide range of atmospheric conditions. A critical parameter to flashover development is the stochastic process involving the appearance of initiatory or “seed” electrons, as seen by the reduction in flashover delay time by approximately 10−20% in the presence of external ultraviolet illumination. While the current version of the MC code seeds the flashover location with electron densities on the order of background ion densities produced by cosmic radiation, it fails to incorporate the field-assisted collisional detachment processes which are often assumed to be the primary origin of these electrons on the time scales of interest. Investigation of these processes and development of more accurate seeding in the MC code is a key step toward predicting HPM flashover over a wide range of parameters, particularly in the presence of highly electronegative gases such as SF6 or O2, in which there is an absence of free electrons with zero applied field.
Metal gate: HfO2 metal-oxide-semiconductor structures on high-indium-content InGaAs substrate using physical vapor deposition
Authors: Ok InJo , Kim H. , Zhang M. , Zhu F. , Park S. , Yum J. , Zhao H. , Garcia Domingo , Majhi Prashant , Goel N. , Tsai W. , Gaspe C. K. , Santos M. B. , Lee Jack C.
Published: March 2008

In this work, we studied the effects of postdeposition anneal (PDA) time on the material and electrical characteristics of the metal-oxide-semiconductor capacitor (MOSCAP) with high-k (HfO2) material on high-indium-content In0.52Ga0.48As. Thin equivalent oxide thickness (EOT∼1nm) with excellent capacitance voltage (C-V) characteristics has been obtained. Indium content in InGaAs with high-k material and PDA time were correlated with C-V characteristics of TaN/physical vapor deposition HfO2∕InGaAs MOSCAPs. It was found that high indium content resulted in improved C-V characteristics, EOT, hysteresis, and especially frequency dispersion (∼5%).
Control of resputtering in biased CoCrPt–SiO2 media to enhance grain decoupling and grain size distribution
Authors: Lee Hwan-Soo , Guo Vickie W. , Zhu Jian-Gang , Laughlin David E.
Published: March 2008

A CoCrPt–SiO2 magnetic layer was investigated as functions of argon pressure and substrate bias voltage. Use of these two parameters provided fine tuning of the average kinetic energy of incoming Ar+, which causes resputtering and, consequently, influences adatom mobility during film growth. Biasing and high Ar pressure resulted in a significant improvement in grain decoupling and grain size distribution in the films. Furthermore, resputtering of the metal and oxide species from the growing CoCrPt–SiO2 film was interpreted in terms of the surface adhesion energy of the species on the metal Ru underlayer.
Mn behavior in Ge0.96Mn0.04 magnetic thin films grown on Si
Authors: Wang Yong , Zou Jin , Zhao Zuoming , Han Xinhai , Zhou Xiaoyu , Wang Kang L.
Published: March 2008

Mn behaviors in the Ge0.96Mn0.04 thin films grown on Si (001) substrates by molecular beam epitaxy were investigated by high resolution transmission electron microscopy, electron energy loss spectroscopy, and energy dispersive spectroscopy. Unlike the previously reported case of GeMn thin films grown on Ge, Mn has been found to be diffused toward to the surface during the thin film growth. When the Mn concentration is sufficiently high, Mn5Ge3 clusters may be formed. Further annealing of the high Mn concentrated thin film promotes the formation of α-Mn metallic clusters. We believe that all these extraordinary phenomena are attributed to Si as the substrate.
Planar laser imaging of differential molecular diffusion in gas-phase turbulent jets
Authors: Brownell C. J. , Su L. K.
Published: March 2008

Planar laser Rayleigh scattering yields quantitative, two-dimensional measurements of differential diffusion in a turbulent propane-helium jet issuing into air. The jet exit Reynolds number ranges from 1000 to 3000, corresponding to estimated outer-scale Reynolds numbers from 4300 to 13 000. Using a technique originally proposed by Bilger and Dibble [Combust. Sci. Technol. 28, 161 (1982)], the imaging measurements allow direct determination of a normalized scalar difference quantity ξ. For the lower Re, significant differential diffusion develops in the pretransitional portion of the flow. Downstream of the turbulent transition, radial profiles of mean ξ take on a characteristic form, with an excess of the less-diffusive propane on the jet boundary. This characteristic form is independent of Reynolds number, and is thus apparently independent of the degree of differential diffusion in the pretransition range. Evolution of the ξ fields in the turbulent part of the flow is surprisingly consistent with the mixing of conventional scalar quantities. Fluctuation profiles of ξ have a self-similar, bimodal shape for each Re, and power spectra of ξ are monotonically decreasing, with a distinct k−5∕3 inertial range. This spectral form is at odds with prior analytical and computational results in isotropic turbulence, which predicted that the spectrum would show a peak intermediate between the diffusive cutoffs of the individual scalars. The discrepancy appears to be due to the forcing applied in the simulations; the differential diffusion in the experiments preferentially develops in the jet near field, so the resulting evolution is more akin to a decay process. This is further emphasized by the observation that the thickness of ξ structures in the jet decreases with downstream distance. The present results indicate that consideration of differential diffusion must account for the details of the flow configuration, particularly the uniformity of turbulence levels. This has important implications for reacting flows, where local laminarization by heat release can be significant.
High resolution and low-temperature photoelectron spectroscopy of an oxygen-linked fullerene dimer dianion: C120O2−
Authors: Wang Xue-Bin , Matheis Katerina , Ioffe Ilya N. , Goryunkov Alexey A. , Yang Jie , Kappes Manfred M. , Wang Lai-Sheng
Published: March 2008

C 120 O comprises two C60 cages linked by a furan ring and is formed by reactions of C60O and C60. We have produced doubly charged anions of this fullerene dimer (C120O2−) and studied its electronic structure and stability using photoelectron spectroscopy and theoretical calculations. High resolution and vibrationally resolved photoelectron spectra were obtained at 70K and at several photon energies. The second electron affinity of C120O was measured to be 1.02±0.03eV and the intramolecular Coulomb repulsion was estimated to be about 0.8eV in C120O2− on the basis of the observed repulsive Coulomb barrier. A low-lying excited state (B12) was also observed for C120O− at 0.09eV above the ground state (A12). The C120O2− dianion can be viewed as a single electron on each C60 ball very weakly coupled. Theoretical calculations showed that the singlet and triplet states of C120O2− are nearly degenerate and can both be present in the experiment. The computed electron binding energies and excitation energies, as well as Franck–Condon factors, are used to help interpret the photoelectron spectra. A C–C bond-cleaved isomer, C60–O–C602−, was also observed with a higher electron binding energy of 1.54eV.
The boundary effects of the shock wave dispersion in discharges
Authors: Markhotok A. , Popovic S. , Vuskovic L.
Published: March 2008

Interaction of shock waves with a weakly ionized gas generated by discharges has been studied. An additional thermal mechanism of the shock wave dispersion on the boundary between a neutral gas and discharge has been proposed [A. Markhotok, S. Popovic, and L. Vuskovic, Proceedings of the 15th International Conference on Atomic Processes in Plasmas, March 19–22, 2007 (NIST, Gaitersburg, MD, 2007)]. This mechanism can explain a whole set of thermal features of the shock wave-plasma interaction, including acceleration of the shock wave, broadening or splitting of the deflection signals and its consecutive restoration. Application has been made in the case of a shock wave interacting with a laser induced plasma. The experimental observations support well the results of calculation based on this model.
Vibrational effects on the reaction of NO2+ with C2H2: Effects of bending and bending angular momentum
Authors: Boyle Jason M. , Uselman Brady W. , Liu Jianbo , Anderson Scott L.
Published: March 2008

N O 2 + in six different vibrational states was reacted with C2H2 over the center-of-mass energy range from 0.03to3.3eV. The reaction, forming NO++C2H2O and NO+C2H2O+, shows a bimodal dependence on collision energy (Ecol). At low Ecol, the reaction is quite inefficient (<2%) despite this being a barrierless, exoergic reaction, and is strongly inhibited by Ecol. For Ecol>∼0.5eV, a second mechanism turns on, with an efficiency reaching ∼27% for Ecol>3eV. The two reaction channels have nearly identical dependence on Ecol and NO2+ vibrational state, and identical recoil dynamics, leading to the conclusion that they represent a single reaction path throughout most of the collision. All modes of NO2+ vibrational excitation enhance both channels at all Ecol, however, the effects of bend (010) and bend overtone (0200) excitation are particularly strong (factor of 4). In contrast, the asymmetric stretch (001), which intuition suggests should be coupled to the reaction coordinate, leads to only a factor of ∼2 enhancement, as does the symmetric stretch (100). Perhaps the most surprising effect is that of the bending angular momentum, which strongly suppress reaction, even though both the energy and angular momentum involved are tiny compared to the collision energy and angular momentum. The results are interpreted in light of ab initio and Rice-Ramsperger-Kassel-Marcus calculations.
A microscopic view of substitution reactions solvated by ionic liquids
Authors: Arantes Guilherme M. , Ribeiro Mauro C. C.
Published: March 2008

The solvation effect of the ionic liquid 1-N-butyl-3-methylimidazolium hexafluorophosphate on nucleophilic substitution reactions of halides toward the aliphatic carbon of methyl p-nitrobenzenesulfonate (pNBS) was investigated by computer simulations. The calculations were performed by using a hybrid quantum-mechanical/molecular-mechanical (QM/MM) methodology. A semiempirical Hamiltonian was first parametrized on the basis of comparison with ab initio calculations for Cl− and Br− reaction with pNBS at gas phase. In condensed phase, free energy profiles were obtained for both reactions. The calculated reaction barriers are in agreement with experiment. The structure of species solvated by the ionic liquid was followed along the reaction progress from the reagents, through the transition state, to the final products. The simulations indicate that this substitution reaction in the ionic liquid is slower than in nonpolar molecular solvents proper to significant stabilization of the halide anion by the ionic liquid in comparison with the transition state with delocalized charge. Solute-solvent interactions in the first solvation shell contain several hydrogen bonds that are formed or broken in response to charge density variation along the reaction coordinate. The detailed structural analysis can be used to rationalize the design of new ionic liquids with tailored solvation properties.
Influence of functional groups on charge transport in molecular junctions
Authors: Mowbray D. J. , Jones G. , Thygesen K. S.
Published: March 2008

Using density functional theory (DFT), we analyze the influence of five classes of functional groups, as exemplified by NO2, OCH3, CH3, CCl3, and I, on the transport properties of a 1,4-benzenedithiolate (BDT) and 1,4-benzenediamine (BDA) molecular junction with gold electrodes. Our analysis demonstrates how ideas from functional group chemistry may be used to engineer a molecule’s transport properties, as was shown experimentally and using a semiempirical model for BDA [Nano Lett. 7, 502 (2007)]. In particular, we show that the qualitative change in conductance due to a given functional group can be predicted from its known electronic effect (whether it is σ∕π donating/withdrawing). However, the influence of functional groups on a molecule’s conductance is very weak, as was also found in the BDA experiments. The calculated DFT conductances for the BDA species are five times larger than the experimental values, but good agreement is obtained after correcting for self-interaction and image charge effects.
Anomalously large ferromagnetic Curie temperature of epitaxial Bi2CoMnO6 thin films
Authors: Singh M. P. , Truong K. D. , Fournier P. , Rauwel P. , Rauwel E. , Carignan L. P. , Ménard D.
Published: March 2008

We present the structural and physical properties of epitaxial Bi2CoMnO6 films grown on SrTiO3 and LaAlO3. They display magnetic hysteresis loop with 170 Oe coercivity and a 3.1μB∕f.u. saturation magnetization which indicates a disordered Co∕Mn state. Nevertheless, these films display an unusually large ferromagnetic Curie temperature of about 800 K. We propose that the large Curie temperature is the result of a strong coupling between the magnetization and the polarization order parameters of Bi2CoMnO6 promoted by substantial structural changes in the films with respect to the bulk. These structural modifications amplify the overlap of the electronic wave functions of the Mn–O–Mn, Mn–O–Co and Co–O–Co bonds and the Bi 6s2 lone pair electrons providing the long-range spin order through the minimization of the magnetoelastic energy.
Ultrahigh growth rate of epitaxial silicon by chemical vapor deposition at low temperature with neopentasilane
Authors: Chung K. H. , Yao N. , Benziger J. , Sturm J. C. , Singh K. K. , Carlson D. , Kuppurao S.
Published: March 2008

A precursor, neopentasilane, is used to produce high-quality silicon epitaxy by chemical vapor deposition under 700°C with very high growth rates. Low background dopant concentration and excellent crystal quality were determined from secondary-ion-mass spectroscopy and cross sectional transmission electron microscopy. Growth rates as high as 130nm∕min at 600°C have been achieved. Growth rates in nitrogen and hydrogen ambients are about equal for neopentasilane, unlike those for growth with low-order silanes. A concerted reaction, where an open site is generated at the same time the adatom is adsorbed, is proposed as a possible mechanism for both the high growth rate with neopentasilane as well as the similar rate with hydrogen and nitrogen carriers.
Restoration of antenna parameters in scattering environments using electromagnetic cloaking
Authors: Kwon Do-Hoon , Werner Douglas H.
Published: March 2008

It is proposed that electromagnetic cloaks be used as effective shielding devices which enable improved antenna performance in highly scattering, multiple-antenna environments. In multiple frequency, multiple-antenna environments, each antenna is enclosed in a dispersive cloak that is designed to operate at the transmitting frequencies of the neighboring antennas. The loading effect of large objects in close proximity to a radiating antenna can be removed by enclosing the scatterer with a cloak. Application of cloaks to microwave antenna shielding only requires narrow band performance, which can be realized using currently available metamaterials technology.
Ordering of Ge islands on hill-patterned Si (001) templates
Authors: Chen Gang , Vastola G. , Lichtenberger H. , Pachinger D. , Bauer G. , Jantsch W. , Schäffler F. , Miglio Leo
Published: March 2008

We studied the nucleation and ordering mechanism of Ge islands on hill-patterned Si (001) templates. Like in the case of pit-patterned substrates, the initial Ge wetting layer decorates the inclined surfaces of the hill pattern with corrugations consisting entirely of {105} faceted prisms and {001} terraces. Upon further Ge deposition, islands nucleate as pairs in the V-shaped troughs between neighboring hills, and subsequently merge into a single island near the center of each trough. Finite element calculations show that island nucleation and the subsequent movement toward the center of the trough are governed by elastic energy minimization.
Temperature dependence of ambipolar diffusion in silicon on insulator
Authors: Zhao Hui
Published: March 2008

Spatiotemporal dynamics of electron-hole pairs locally excited in a silicon-on-insulator structure by indirect interband absorption are studied by measuring differential transmission caused by free-carrier absorption of a probe pulse tuned below the bandgap, with 200fs temporal and 3μm spatial resolution. From sample temperatures of 250–400K, the ambipolar diffusivity decreases, and is similar to reported values of bulk silicon. Cooling the sample from 250to90K, a decrease of ambipolar diffusivity is observed, indicating important influences of defects and residual stress on carrier diffusion. No detectable density dependence of ambipolar diffusivity is observed.
Successive phase transitions of tin under shock compression
Authors: Hu Jianbo , Zhou Xianming , Tan Hua , Li Jiabo , Dai Chengda
Published: March 2008

Longitudinal and bulk sound velocities of tin in the shock pressure range from ∼25to∼80GPa were measured using a direct reverse-impact method. The bct to bcc phase transition along the Hugoniot was identified by the discontinuity of the longitudinal sound velocity against shock pressure. The incipient melting on the Hugoniot was also revealed by the transition from longitudinal to bulk sound velocity. The shock pressure for bct-bcc phase transition and incipient melting were constrained to be ∼35 and ∼45GPa, respectively. It is inferred that the bcc phase possesses higher shear modulus than the bct phase.
Coordination of leaf area, sapwood area and canopy conductance leads to species convergence of tree water use in a remnant evergreen woodland
Authors: Zeppel Melanie , Eamus Derek
Published: March 2008

This paper compares rates of tree water use, Huber value, canopy conductance and canopy decoupling of two disparate, co-occurring tree species, in a stand of remnant native vegetation in temperate Australia in order to compare their relative behaviour seasonally and during and after a drought. The study site was an open woodland dominated by Eucalyptus crebra F.Muell. (a broad-leaved species) and Callitris glaucophylla J.Thompson & L.A.S. Johnson (a needle-leaved tree species). Tree water use was measured with sapflow sensors and leaf area and sapwood area were measured destructively on felled trees. The Huber value was calculated as the ratio of sapwood area to leaf area. Diameter at breast height (DBH) of the stem was used as a measure of tree size. Canopy conductance was calculated with an inversion of the Penman–Monteith equation, whereas canopy decoupling) was calculated as described by Lu et al. (2003). The relationship between DBH and daily total water use varied during the four measurement periods, with largest rates of water use observed in summer 2003–2004, following a large rainfall event and the smallest maximum water use observed in winter 2003 when monthly rainfall was much less than the long-term mean for those months. Despite differences in the relationship between sapwood area and DBH for the two species, the relationship between daily total water use and DBH did not differ between species at any time. The same rates of water use for the two species across sampling periods arose through different mechanisms; the eucalypt underwent significant changes in leaf area whereas the Callitris displayed large changes in canopy conductance, such that tree water use remained the same for both species during the 2-year period. Canopy conductance and the decoupling coefficient were both significantly larger in winter than summer in both years. The generally low decoupling coefficient (0.05–0.34) reflects the low leaf area index of the site. When evaporative demand was small (winter), the degree of stomatal control was small and the decoupling coefficient was large. There was no relationship between tree size and either canopy conductance or the decoupling coefficient. Transpiration rates generally showed little variation between seasons and between species because of the balance between changes in leaf area, canopy conductance and evaporative demand. The occurrence of a significant drought did not appear to prevent these coordinated changes from occurring, with the result that convergence in water use was observed for these two disparate species.
Structural and histochemical characterisation of the colleters of Rodriguezia venusta (Orchidaceae)
Authors: Leitão Carlos André E. , Cortelazzo Angelo L.
Published: March 2008

Colleters are secretory structures present in many dicotyledon families, but they have not yet been reported for the Orchidaceae. However, the orchid Rodriguezia venusta was observed to possess secretory trichomes on the adaxial side of the bracts subtending floral buds that can be interpreted to be colleters. The present work describes the anatomy and histochemistry of these structures. These bracteal trichomes are multicellular, uniseriate, and densely spaced near the region where the bract attaches to the inflorescence. The secretions of these trichomes are mucilaginous and apparently exclusively constituted by carbohydrates, and they appear to act as a lubricant that facilitates the young floral bud to slide over the bract as it grows. In light of these characteristics, it is proposed that these secretory trichomes should be considered to be ‘colleters’.
Corrigendum to: Protection mechanisms in the resurrection plant Xerophyta viscosa: cloning, expression, characterisation and role of XvINO1, a gene coding for a myo-inositol 1-phosphate synthase
Authors: Lehner Arnaud , Chopera Denis R. , Peters Shaun W. , Keller Felix , Mundree Sagadevan G. , Thomson Jennifer A. , Farrant Jill M.
Published: March 2008

We have used reverse transcription-PCR coupled with 52- and 32-RACE to isolate a full length INO1 cDNA (1692�bp with an ORF of 1530) from the resurrection plant Xerophyta viscosa Baker. XvINO1 encodes 510 amino acids, with a predicted MW of 56.7kD and contains four sequence motifs that are highly conserved in plant myo-inositol-1-phosphate synthases (MIPS, EC5.5.1.4), the enzyme that catalyses the first step in the formation of myo-inositol (Ino). Northern and western analyses show that the transcript and protein are constitutively present in leaves but their expression increases, temporarily, in response to both accumulative salt stress (~300�mM NaCl) and desiccation (to 5% relative water content). Leaf Ino concentration increases 40-fold during the first 6�h of salt stress, and levels of this and other carbohydrates (galactinol, sucrose, raffinose, stachyose and hexoses) remain elevated relative to control leaves for the duration of salt stress treatment. The timing and pattern of accumulation of these carbohydrates differ under desiccation stress and we propose that they perform different functions in the respective stresses. These are elaborated in discussion of our data.
The N-terminal presequence from F1-ATPase β-subunit of Nicotiana plumbaginifolia efficiently targets green fluorescent fusion protein to the mitochondria in diverse commercial crops
Authors: Gnanasambandam Annathurai , Anderson David J. , Purnell Matthew P. , Nielsen Lars K. , Brumbley Stevens M.
Published: March 2008

Approximately 10–15% of plant nuclear genes appear to encode mitochondrial proteins that are directed to mitochondria by specific targeting signals. Reports on the heterologous function of these targeting signals are generally limited to one or a few species, with an emphasis on model plants such as tobacco and Arabidopsis. Given their sequence diversity and their insufficient testing in commercially important crops (including monocotyledonous crops), the extent to which these signals can be relied on for biotechnological purposes across species remains to be established. This study provides the experimental verification of a mitochondrial signal that is functional across diverse crop species, including five monocots (sugarcane, wheat, corn, sorghum and onion) and seven dicots (cucumber, cauliflower, tomato, capsicum, pumpkin, coriander and sunflower). In all 12 crops, transient assays following microprojectile bombardment showed that the N-terminal mitochondrial presequence from F1-ATPase β-subunit (ATPase-β) of Nicotiana plumbaginifolia Viv. targeted green fluorescent fusion protein to the mitochondria. The transient assay results in sugarcane were confirmed in stably transformed root cells. The ATPase-β signal should be a useful metabolic engineering tool for directing recombinant proteins to the mitochondrial matrix in diverse plant species of commercial interest.
A New Zealand species of the trans-Tasman centipede order Craterostigmomorpha (Arthropoda : Chilopoda) corroborated by molecular evidence
Authors: Edgecombe Gregory D. , Giribet Gonzalo
Published: March 2008

Craterostigmus tasmanianus Pocock, 1902, is the sole species in the centipede order Craterostigmomorpha and the focus of much phylogenetic research in Chilopoda. Originally named from Tasmania, Craterostigmus from New Zealand was first considered conspecific with Tasmanian samples based on external morphology, though recent anatomical studies have argued for a deep divergence between New Zealand and Tasmanian Craterostigmus, and a high-ranking taxonomic separation has been advocated. Unambiguous diagnostic nucleotide characters in nuclear ribosomal 18S and 28S rRNA genes as well as in the mitochondrial 16S rRNA, together with the significantly smaller size of New Zealand individuals, the arrangement of supernumerary Malpighian tubules, and patterns in leg spinosity, permit distinction of a New Zealand species, Craterostigmus crabilli, sp. nov. In addition, phylogenetic analysis of four markers (the aforementioned markers plus cytochrome c oxidase subunit I) suggests differentiation of C. tasmanianus from the New Zealand specimens. Combination of the nuclear ribosomal genes and mitochondrial 16S rRNA and COI sequences retrieves a geographic pattern within C. crabilli, sp. nov. in which geographic proximity is decoupled from closest affinities, although the 16S rRNA dataset alone shows more geographic structure. The genetic pattern observed, where among species diversity (for both mitochondrial markers) is equivalent to, or greater than, the within species diversity, is not consistent with a recent long-distance dispersal event, and a relictual Gondwanan distribution is the most plausible alternative.
Phylogeny and distribution of the mayfly genus Austrophlebioides Campbell & Suter (Ephemeroptera:Leptophlebiidae)
Authors: Christidis Faye , Dean John C.
Published: March 2008

The mayfly genus Austrophlebioides Campbell & Suter, 1988 is endemic to Australia and is widely distributed in eastern Australia and Tasmania. Here, the phylogenetic relationships among species of Austrophlebioides are investigated using cladistic analyses based on morphological characters of the nymph and adult, and the first phylogenetic hypothesis for the genus is presented. The results from the phylogenetic analyses support the recognition of three monophyletic species-groups: the ‘rieki’, ‘pusillus’ and ‘marchanti’ clades. The ‘pusillus’ clade is the sister-group to the ‘rieki’ clade, and the clade comprising these two groups is sister to the ‘marchanti’ clade. Minimal overlap was observed in the geographic distribution of the three Austrophlebioides clades. The ‘rieki’ clade is confined to the Wet Tropics bioregion of north-eastern Queensland. The ‘pusillus’ clade is distributed from central-eastern Queensland to Victoria. The ‘marchanti’ clade occurs in southern New South Wales, Victoria and Tasmania. Distributional limits of the three clades correspond with the presence of recognised biogeographic barriers (Burdekin Gap, Hunter Valley and Bass Strait) suggesting that vicariance has been important in the differentiation of the group and in determining present-day distributions of species.
Microbial biomass carbon and some soil properties as influenced by long-term sodic-water irrigation, gypsum, and organic amendments
Authors: Kaur Joginder , Choudhary O. P. , Bijay-Singh
Published: March 2008

Long-term sodic-water irrigation may adversely affect the quality of soil organic carbon along with some soil properties. The extent to which the adverse effects can be ameliorated through the use of gypsum and amendments needs to be known. Soil properties and microbial biomass carbon (MBC) were studied after 14 years of sodic water (SW) irrigation and application of different levels of gypsum, farmyard manure (FYM), green manure (GM), and wheat straw (WS) to a sandy loam soil. Irrigation with SW increased pH, electrical conductivity, sodium adsorption ratio, exchangeable sodium percentage (ESP), and bulk density, and decreased final infiltration rate of soil. Application of gypsum and organic amendments reversed these trends. Decrease in MBC due to SW irrigation was from 132.5 to 44.6 mg/kg soil in the 0–75 mm soil layer and from 49.0 to 17.3 mg/kg soil in the 75–150 mm soil layer. Application of gypsum and organic amendments significantly increased MBC; GM and FYM were more effective than WS. Changes in soil ESP explained 85 and 75% variation in MBC in the unamended and organically amended SW treatments, respectively. Soil pH as additional variable improved the predictability of MBC to 96% and 77%. Irrigation with SW reduced yield of rice plus wheat by 5 t/ha. Application of gypsum and organic amendments significantly increased the rice and wheat yield; it was significantly correlated with MBC (r = 0.56**, n = 60). It confirms that MBC rather than organic C is a more sensitive indicator of environmental stresses in soils caused by long-term sodic water irrigation.
PHDs overactivation during chronic hypoxia “desensitizes” HIFα and protects cells from necrosis
Authors: Ginouvès Amandine , Ilc Karine , Macías Nuria , Pouysségur Jacques , Berra Edurne
Published: March 2008

Cell adaptation to changes in oxygen (O2) availability is controlled by two subfamilies of O2-dependent enzymes: the hypoxia inducible factor (HIF)–prolyl and asparaginyl hydroxylases [prolyl hydroxylases domain (PHDs) and factor inhibiting HIF (FIH)]. These oxygen sensors regulate the activity of the HIF, a transcriptional complex central in O2homeostasis. In well oxygenated cells, PHDs hydroxylate the HIFα subunits, thereby targeting them for proteasomal degradation. In contrast, acute hypoxia inhibits PHDs, leading to HIFα stabilisation. However, here we show that chronic hypoxia induces HIF1/2α“desensitization”in celluloand in mice. At the basis of this general adaptative mechanism, we demonstrate that chronic hypoxia not only increases the pool of PHDs but also overactivates the three PHD isoforms. This overactivation appears to be mediated by an increase in intracellular O2availability consequent to the inhibition of mitochondrial respiration. By usingin celluloandin vivosiRNA, we found that the PHDs are the key enzymes triggering HIFα desensitization, a feedback mechanism required to protect cells against necrotic cell death and thus to adapt them across a chronic hypoxia. Hence, PHDs serve as dual enzymes, for which inactivation and later overactivation is necessary for cell survival in acute or chronic hypoxia, respectively.
Increased amphetamine-induced hyperactivity and reward in mice overexpressing the dopamine transporter
Authors: Salahpour Ali , Ramsey Amy J. , Medvedev Ivan O. , Kile Brian , Sotnikova Tatyana D. , Holmstrand Ericka , Ghisi Valentina , Nicholls Peter J. , Wong Ling , Murphy Karen , Sesack Susan R. , Wightman R. Mark , Gainetdinov Raul R. , Caron Marc G.
Published: March 2008

The dopamine transporter (DAT) plays a key role in the regulation of dopaminergic signaling wherein it controls both the spatial and temporal actions of dopamine. Here we evaluated the behavioral and neurochemical consequences of increased DAT function by generating DAT transgenic mice (DAT-tg) that overexpress the transporter. These mice were generated by pronuclear injection of a bacterial artificial chromosome containing the mouse DAT locus, yielding an anatomical expression pattern of DAT-tg identical to WT. In DAT-tg mice there is a 3-fold increase in the levels of total and membrane-expressed DAT, but synaptic plasma membrane fractions of DAT-tg mice show only a 30% increase in transporter levels. Functional studies reveal that in the DAT-tg animals there is a 50% increase in the rate of dopamine (DA) uptake resulting in extracellular levels of DA that are decreased by ≈40%. Behaviorally, DAT-tg animals display similar locomotor stimulation when treated with DAT blockers such as GBR12909, methylphenidate, and cocaine. However, these mice demonstrate markedly increased locomotor responses to amphetamine compared with WT animals. Furthermore, compared with controls, there is a 3-fold greater increase in the amount of DA released by amphetamine in DAT-tg mice that correlates with the 3-fold increase in protein expression. Finally, DAT-tg animals show reduced operant responding for natural reward while displaying preference for amphetamine at much lower doses (0.2 and 0.5 mg/kg) than WT mice (2 mg/kg). These results suggest that overexpression of DAT leads to a marked increase in sensitivity to psychomotor and rewarding properties of amphetamine.