bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulating plant water availability in dry lands under climate change: A generic model of two soil layers
Authors: Tietjen Britta , Zehe Erwin , Jeltsch Florian
Published: January 2009

Dry lands are exposed to a highly variable environment and face a high risk of degradation. The effects of climate change are likely to increase this risk; thus a profound knowledge of the system dynamics is crucial for evaluating management options. This applies particularly for the interactions between water and vegetation, which exhibit strong feedbacks. To evaluate these feedbacks and the effects of climate change on soil moisture dynamics, we developed a generic, process‐based, spatially explicit soil moisture model of two soil layers, which can be coupled with vegetation models. A time scale relevant for ecological processes can be simulated without difficulty, and the model avoids complex parameterization with data that are unavailable for most regions of the world. We applied the model to four sites in Israel along a precipitation and soil type gradient and assessed the effects of climate change by comparing possible climatic changes with present climate conditions. The results show that in addition to temperature, the total amount of precipitation and its intra‐annual variability are an important driver of soil moisture patterns. This indicates that particularly with regard to climate change, the approach of many ecological models that simulate water dynamics on an annual base is far too simple to make reliable predictions. Thus, the introduced model can serve as a valuable tool to improve present ecological models of dry lands because of its focus on the applicability and transferability.
Aerosol black carbon in the European Arctic: Measurements at Zeppelin station, Ny‐Ålesund, Svalbard from 1998–2007
Authors: Eleftheriadis K. , Vratolis S. , Nyeki S.
Published: January 2009

An aerosol black carbon (BC) data set from ongoing measurements at Zeppelin station (474 m asl), near Ny‐Ålesund (10 m asl), Svalbard is reported for the period 1998–2007. Annual average and median BC concentrations were 39 and 27 ng m−3, respectively, while monthly averages ranged from a maximum ∼80 ng m−3 in February/March to a minimum 0–10 ng m−3 from June to September. BC concentrations were calibrated by elemental carbon thermo‐optical analysis. PSCF trajectory analysis indicated that BC concentrations at Zeppelin were mainly influenced by source regions in northern and central Russia. Since 2001, a small decreasing trend in BC concentration (−9.5 ng m−3 per decade) for the period to 2007 has been observed which is, however, similar to the detection limit.
A preliminary estimate of the Stokes dissipation of wave energy in the global ocean
Authors: Kantha Lakshmi , Wittmann Paul , Sclavo Mauro , Carniel Sandro
Published: January 2009

The turbulent Reynolds stresses in the upper layers of the ocean interact with the vertical shear of the Stokes drift velocity of the wave field to extract energy from the surface waves. The resulting rate of dissipation of wind waves in the global ocean is about 2.5 TW on the average but can reach values as high as 3.7 TW, making it as important as the dissipation of wave energy in the surf zones around the ocean margins. More importantly, the effect of Stokes dissipation is felt throughout the mixed layer. It also contributes to Langmuir circulations. Unfortunately, this wave dissipation mechanism has hitherto been largely ignored. In this note, we present a preliminary estimate of the Stokes dissipation rate in the global oceans based on the results of the WAVEWATCH III model for the year 2007 to point out its potential importance. Seasonal and regional variations are also described.
On optical and microphysical characteristics of contrails and cirrus
Authors: Febvre Guy , Gayet Jean‐François , Minikin Andreas , Schlager Hans , Shcherbakov Valéry , Jourdan Olivier , Busen Reinhold , Fiebig Markus , Kärcher Bernd , Schumann Ulrich
Published: January 2009

In situ measurements of light scattering and microphysical characteristics of young and 20‐min‐aged persistent contrails and of frontal cirrus clouds were carried out with the airborne polar nephelometer and microphysical Particle Measuring Systems instruments. Optical and microphysical properties of contrails at different stages of evolution and of cirrus clouds sampled in ice‐supersaturated air masses at ambient temperatures near −60°C are examined. The results show that quasi‐spherical ice particles with diameters smaller than 5μm control the optical properties of the plume shortly after formation. In slightly aged contrails the optical properties are governed by larger nonspherical ice crystals. Very similar optical properties are observed in frontal cirrus but with a different ice particle size distribution. The contrail optical and microphysical ice particle data obtained in this study are representative of the visible persistent contrail created by a midsized airliner after the wake vortices have decayed.
Columnar water vapor retrievals from multifilter rotating shadowband radiometer data
Authors: Alexandrov Mikhail D. , Schmid Beat , Turner David D. , Cairns Brian , Oinas Valdar , Lacis Andrew A. , Gutman Seth I. , Westwater Ed R. , Smirnov Alexander , Eilers James
Published: January 2009

The multifilter rotating shadowband radiometer (MFRSR) measures direct and diffuse irradiances in the visible and near‐infrared spectral range. In addition to characteristics of atmospheric aerosols, MFRSR data also allow retrieval of precipitable water vapor (PWV) column amounts, which are determined from the direct normal irradiances in the 940‐nm spectral channel. The HITRAN 2004 spectral database was used in our retrievals to model the water vapor absorption. We present a detailed error analysis describing the influence of uncertainties in instrument calibration and spectral response, as well as those in available spectral databases, on the retrieval results. The results of our PWV retrievals from the Southern Great Plains (SGP) site operated by the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Program were compared with correlative standard measurements by microwave radiometers (MWRs) and a global positioning system (GPS) water vapor sensor, as well as with retrievals from other solar radiometers (AERONET's CIMEL, AATS‐6). Some of these data are routinely available at the SGP's Central Facility; however, we also used measurements from a wider array of instrumentations deployed at this site during the water vapor intensive observation period (WVIOP2000) in September–October 2000. The WVIOP data show better agreement between different solar radiometers or between different microwave radiometers (both groups showing relative biases within 4%) than between these two groups of instruments, with MWR values being consistently higher (up to 14%) than those from solar instruments (especially in the large PWV column amount range). We also demonstrate the feasibility of using MFRSR network data for creation of 2D data sets comparable with that of the MODIS satellite water vapor product.
Quantifying aerosol direct radiative effect with Multiangle Imaging Spectroradiometer observations: Top‐of‐atmosphere albedo change by aerosols based on land surface types
Authors: Chen Yang , Li Qinbin , Kahn Ralph A. , Randerson James T. , Diner David J.
Published: January 2009

Using internally consistent albedo, aerosol, cloud, and surface data from the Multiangle Imaging Spectroradiometer (MISR) instrument onboard the Terra satellite, top‐of‐atmosphere (TOA) spectral albedo change (dα) in the presence of aerosols over land is estimated and its dependence on aerosol and surface properties is analyzed. Linear regressions between spectral TOA albedo and aerosol optical depth (AOD) for different surface types are examined to derive the aerosol‐free TOA albedo. MISR surface BiHemispherical Reflectance (BHR) values are used to differentiate surface types. We find relatively high correlations between spectral TOA albedo and AOD for BHR‐stratified data in 2° × 2° grid cells. The global mean values of cloud‐free dα over land for June–September 2007 are estimated to be 0.018 ± 0.003 (blue), 0.010 ± 0.003 (green), 0.007 ± 0.003 (red), and 0.008 ± 0.006 (near‐infrared). Individual regions show large variations from these values. Global patterns of dα are determined mainly by AOD and aerosol radiative efficiency. Large positive values of dα are observed over regions with high aerosol loading and large single‐scattering albedo, where the aerosol scattering effect is dominant. The presence of light‐absorbing aerosols reduces aerosol radiative efficiency and dα. Surface reflectance influences both aerosol scattering and absorbing effects. Generally, the aerosol radiative efficiency decreases with increasing BHR. We also examined dα‐AOD correlations over different vegetation types. We find the smallest dα values are over needleleaf forests and shrublands, whereas the largest values are over cropland and barren regions. The aerosol radiative efficiencies are lowest over needleleaf forests and barren regions and highest over grasslands and croplands.
Long‐term precipitation and late‐stage valley network formation: Landform simulations of Parana Basin, Mars
Authors: Barnhart Charles J. , Howard Alan D. , Moore Jeffrey M.
Published: January 2009

We use a computer landform evolution model to show that Noachian‐Hesperian‐aged, late‐stage valley network formation required numerous and repeated moderate flood events rather than one or a few continuous, multiyear, deluge‐style flows. We introduce a technique that generates an estimated “initial conditions” digital elevation model (DEM) of the Parana Valles drainage catchment (PDC) prior to valley network incision. We then explored how variations in three classes of environmental parameters related to fluvial processes, and surface material properties evolve the initial conditions DEM. Specifically, we parameterized discharge scaling, evaporation from ponded water, and the effects of an indurated surface crust. Each simulation run produced a model output DEM that was qualitatively and statistically compared to the actual surface DEM. Simulations with an arid to semiarid climate, moderate evaporation rates, and an indurated surface crust provide the best match to the actual surface. Simulated valley network formation requires periods of fluvial activity that last a minimum of 103–104years under constant deluge‐style conditions. However, craters within the PDC in deluge‐style simulations overflow and generate exit breaches that cut through all crater walls. Longer simulations (105–106years) that modeled repeated, episodic flows with interim evaporation avoid universal crater breaching. The paucity of crater rim exit breaches in the PDC and the southern highlands in general implies both that the precipitation was not continuous and that formation conditions were inconsistent with a few short‐lived extreme climate excursions such as might be induced by large‐scale impacts or other cataclysmic events.
Impact of feedbacks on Chihuahuan desert grasslands: Transience and metastability
Authors: Okin Gregory S. , D'Odorico Paolo , Archer Steven R.
Published: January 2009

A simplistic model of grass‐shrub dynamics was used to investigate the role of grass demographic processes on grassland‐shrubland dynamics when grasses are in competitive advantage over shrubs. The model suggests that a feedback between grass biomass and soil erosion may cause an abrupt transition to a shrubland state. The model explains how a simple change in either grass recruitment or grass mortality, presumably linked to climate change or grazing, could produce changes in Holocene flora and the conversion of grasslands to shrublands, which has been observed throughout the southwestern U.S. in the past 150 years.
RNA pol II subunit RPB7 is required for RNA pol I‐mediated transcription in Trypanosoma brucei
Authors: Peñate Xenia , López‐Farfán Diana , Landeira David , Wentland Amy , Vidal Isabel , Navarro Miguel
Published: January 2009

In the protozoan parasite Trypanosoma brucei, the two main surface glycoprotein genes are transcribed by RNA polymerase I (pol I) instead of RNA pol II, the polymerase committed to the production of mRNA in eukaryotes. This unusual feature might be accomplished by the recruitment of specific subunits or cofactors that allow pol I to transcribe protein‐coding RNAs. Here, we report that transcription mediated by pol I requires TbRPB7, a dissociable subunit of the pol II complex. TbRPB7 was found to interact with two pol I‐specific subunits, TbRPA1 and TbRPB6z. Pol I‐specific transcription was affected on depletion of TbRPB7 in run‐on assays, whereas recombinant TbRPB7 increased transcription driven by a pol I promoter. These results represent a unique example of a functional RNA polymerase chimaera consisting of a core pol I complex that recruits a specific pol II subunit.
Enthalpy of formation and anharmonic force field of diacetylene
Authors: Simmonett Andrew C. , Schaefer Henry F. , Allen Wesley D.
Published: January 2009

The enthalpy of formation of diacetylene (C4H2) is pinpointed using state-of-the-art theoretical methods, accounting for high-order electron correlation, relativistic effects, non-Born–Oppenheimer corrections, and vibrational anharmonicity. Molecular energies are determined from coupled cluster theory with single and double excitations (CCSD), perturbative triples [CCSD(T)], full triples (CCSDT), and perturbative quadruples [CCSDT(Q)], in concert with correlation-consistent basis sets (cc-pVXZ, X=D, T, Q, 5, 6) that facilitate extrapolations to the complete basis set limit. The first full quartic force field of diacetylene is determined at the highly accurate all-electron CCSD(T) level with a cc-pCVQZ basis, which includes tight functions for core correlation. Application of second-order vibrational perturbation theory to our anharmonic force field yields fundamental frequencies with a mean absolute difference of only 3.9 cm−1 relative to the experimental band origins, without the use of any empirical scale factors. By a focal point approach, we converge on an enthalpy change for the isogyric reaction 2H–C≡C–H→H–C≡C–C≡C–H+H2 of (+0.03, +0.81) kcal mol−1 at (0, 298.15) K. With the precisely established ΔfH° of acetylene, we thus obtain ΔfH°(C4H2)=(109.4,109.7)±0.3 kcal mol−1 at (0, 298.15) K. Previous estimates of the diacetylene enthalpy of formation range from 102 to 120 kcal mol−1.
High-pressure Raman scattering and x-ray diffraction of phase transitions in MoO3
Authors: Liu D. , Lei W. W. , Hao J. , Liu D. D. , Liu B. B. , Wang X. , Chen X. H. , Cui Q. L. , Zou G. T. , Liu J. , Jiang S.
Published: January 2009

The high-pressure behavior of molybdenum trioxides (MoO3) has been investigated by angle-dispersive synchrotron x-ray powder diffraction and Raman spectroscopy techniques in a diamond anvil cell up to 43 and 30 GPa, respectively. In the pressure range of up to 43 GPa, structural phase transitions from the orthorhombic α-MoO3 phase (Pbnm) to the monoclinic MoO3-II phase (P21/m), and then to the monoclinic MoO3-III phase (P21/c), occurred at pressures of about 12 and 25 GPa at room temperature, respectively. Our observation of the transition from the orthorhombic α-MoO3 to the monoclinic MoO3-II phase is in disagreement with earlier studies in which the phase transition could not be obtained when only pressure is applied. The changes in the Mo–O distances and O–Mo–O and Mo–O–Mo angles may explain the changes in Raman spectrum. The pressure dependence of the volume of two monoclinic high-pressure phases is described by a third-order Birch–Murnaghan equation of state, which yields a bulk modulus value of B0=143.41(3) GPa with B0′=12, and B0=261.9(3) GPa with B0′=3.5.
Liquid crystal nanodroplets in solution
Authors: Brown W. Michael , Petersen Matt K. , Plimpton Steven J. , Grest Gary S.
Published: January 2009

The aggregation of liquid crystal nanodroplets from a homogeneous solution is studied by molecular dynamics simulations. The liquid crystal particles are modeled as elongated ellipsoidal Gay–Berne particles while the solvent is modeled as spherical Lennard–Jones particles. Extending previous studies of Berardi et al. [J. Chem. Phys. 126, 044905 (2007)], we find that liquid crystal nanodroplets are not stable and that after sufficiently long times the nanodroplets always aggregate into a single large droplet. Results describing the droplet shape and orientation for different temperatures and shear rates are presented. The implementation of the Gay–Berne potential for biaxial ellipsoidal particles in a parallel molecular dynamics code is also briefly discussed.
One-dimensional assemblies of charged nanoparticles in water: A simulation study
Authors: Richardi J.
Published: January 2009

While the template-free one-dimensional assembly of nanoparticles, e.g., in chains, has been widely observed experimentally, the formation mechanism is still not well known. Therefore, the homogeneous nucleation in a model system of charged nanoparticles in water is investigated using Brownian dynamics simulations. The interaction between the particles is described by a sum of steric repulsion, screened Coulomb potential, and van der Waals attraction. A systematic study is carried out by varying the effective charge and the counterion concentration. The accuracy of the Brownian dynamics results is verified by the comparison with Monte Carlo simulations. At low particle charge and low counterion concentrations, a thermodynamically stable phase of clusters with few particles is observed. An increase in the ion concentration at low particle charge leads to anisotropic assemblies of the small clusters. In contrast at high particle charge, large spherical nuclei are observed, which assemble to form larger aggregates. These simulation results are interpreted with the help of recent theoretical work using similar interaction potentials. Only when the rearrangements of the initial clusters are blocked using constraint dynamics are one-dimensional assemblies of particles observed in simulations, in good agreement with the experiments. The experimental conditions of linear nanoparticle assembly in water are discussed. The comparison with the simulation results leads to proposing a mechanism for one-dimensional nanoparticle assemblies: The nanoparticles form chains by a diffusion-limited aggregation at low particle charge and the rearrangement of the chains in compact structures is hindered due to attractive spots at the particle surface created by the desorption of coating molecules.
New infrared spectra of the nitrous oxide trimer
Authors: Dehghany M. , Afshari Mahin , Moazzen-Ahmadi N. , McKellar A. R. W.
Published: January 2009

Infrared spectra of N2O trimers are studied using a tunable diode laser to probe a pulsed supersonic slit-jet expansion. A previous observation by Miller and Pedersen [J. Chem. Phys. 108, 436 (1998)] in the N2O ν1+ν3 combination band region (∼3480 cm−1) showed the trimer structure to be noncyclic, with three inequivalent N2O monomer units which could be thought of as an N2O dimer (slipped antiparallel configuration) plus a third monomer unit lying above the dimer plane. The present observations cover the N2O fundamental band regions ν3 (∼1280 cm−1) and ν1 (∼2230 cm−1). In the ν3 region, two trimer bands are assigned with vibrational shifts and other characteristics similar to those in the ν1+ν3 region, but in the ν1 region all three possible trimer bands are observed. Relationships among the various bands are considered with reference to their rotational intensity patterns, their vibrational shifts, and the properties of the related N2O dimer, with results that generally support the conclusions of Miller and Pedersen. Three trimer bands are also observed for the fully N15-substituted species in the ν1 region, and these results should aid in the detection of the as-yet-unobserved pure rotational microwave spectrum of the trimer.
Vapor-liquid coexistence of fluids with attractive patches: An application of Wertheim’s theory of association
Authors: Liu Hongjun , Kumar Sanat K. , Sciortino Francesco , Evans Glenn T.
Published: January 2009

We compare simulations and theoretical predictions based on Wertheim’s thermodynamic perturbation theory (TPT) for spheres that interact through an isotropic square well interaction coupled to patchy attractions. Following a proposal of Foffi and Sciortino [J. Phys. Chem. B 111, 9702 (2007)], we show that, if we use the second virial coefficient as a scaling parameter, a generalized law of corresponding states holds not only for the critical point but also for the vapor-liquid coexistence curve of patchy hard sphere fluids with the same numbers of single-bonded patches. The predictions for patchy square well fluids from Wertheim’s TPT are in good agreement with Monte Carlo simulation data, although no aspects of universality were found. Instead, we find a crossover from the behavior of isotropically short-ranged attractive fluids to that of patchy hard sphere fluids as the strength of patchy interaction increases.
Theoretical and numerical investigations on shapes of planar lipid monolayer domains
Authors: Wu Hao , Tu Z. C.
Published: January 2009

Shapes of planar lipid monolayer domains at the air-water interface are theoretically and numerically investigated by minimizing the formation energy of the domains, which consist of the surface energy, line tension energy, and dipole electrostatic energy. The shape equation, which describes boundary curves of the domains at equilibrium state, is derived from the first order variation of the formation energy. A relaxation method is proposed to find the numerical solutions of the shape equation. The theoretical and numerical results are in good agreement with previous experimental observation. Some new shapes not observed in previous experiments are also obtained, which awaits experimental confirmation in the future.
Diffusivity of Er3+ into LiNbO3 as a function of stoichiometry
Authors: Zhang De-Long , Hua Ping-Rang , Yang Qing-Zhong , Liu Hong-Li , Cui Yu-Ming , Pun E. Y. B.
Published: January 2009

Diffusivity of Er3+ into LiNbO3 crystal has been studied as a function of Li2O content and crystal orientation. The Li2O content in single-crystal LiNbO3 plates was adjusted by Li-rich vapor transport equilibration (VTE) technique. Five X-cut and five Z-cut congruent substrates were VTE treated at first at 1100 °C for different durations ranging from 6 to 74 h, and then were subjected to a special post-VTE anneal procedure at the same temperature for 60 h to obtain homogeneous Li2O content. The Li2O content was determined from the measured fundamental optical absorption edge. Its homogeneity is verified by measuring the optical absorption edge as a function of the crystal thickness. After the composition characterization, the substrates were coated with 45 nm thick Er film and annealed at 1130 °C for 40 h in argon atmosphere. The Er3+ profile was analyzed by secondary ion mass spectrometry. The results show that the Er3+ diffusivity decreases monoexponentially with the increase in the Li2O content in both cases of X- and Z-cut. As the Li2O content is increased from the congruent point (48.4 mol %) to the near-stoichiometric composition (∼49.9 mol %), the diffusivity decreases from 0.107 (0.072) to 0.017 (0.018) μm2/h for the Z (X)-cut substrate. The diffusion shows considerable anisotropy for the lower Li2O content and the diffusivity in a Z-cut substrate is larger. The anisotropy weakens gradually with the increase in the Li2O content, and the diffusivities in the X- and Z-cut substrates ultimately tend to a same value (∼0.02 μm2/h) at the Li-rich phase boundary. After the Er diffusion procedure, endface coupling experiment was carried out to check if a planar waveguide layer was formed near the Er-diffused surface due to the Li outdiffusion. The results show that the Li outdiffusion did not accompany the Er diffusion procedure.
Determination of phase ratio in polymorphic materials by x-ray absorption spectroscopy: The case of anatase and rutile phase mixture in TiO2
Authors: Smith M. F. , Klysubun W. , Kityakarn S. , Worayingyong A. , Zhang S. B. , Wei S.-H. , Onkaw D. , Songsiriritthigul P. , Rujirawat S. , Limpijumnong S.
Published: January 2009

We demonstrate that x-ray absorption spectroscopy (XAS) can be used as an unconventional characterization technique to determine the proportions of different crystal phases in polymorphic samples. As an example, we show that ratios of anatase and rutile phases contained in the TiO2 samples obtained by XAS are in agreement with conventional x-ray diffraction (XRD) measurements to within a few percent. We suggest that XAS measurement is a useful and reliable technique that can be applied to study the phase composition of highly disordered or nanoparticle polymorphic materials, where traditional XRD technique might be difficult.
Damage induced by electronic excitation in ion-irradiated yttria-stabilized zirconia
Authors: Moll S. , Thomé L. , Vincent L. , Garrido F. , Sattonnay G. , Thomé T. , Jagielski J. , Costantini J. M.
Published: January 2009

This article presents a study of the damage production in yttria-stabilized cubic zirconia single crystals irradiated with swift heavy ions. The combination of techniques which probe the material at different spatial scales (Rutherford backscattering spectrometry in channeling geometry, x-ray diffraction, transmission electron microscopy, and atomic force microscopy) was used in order to gain information about the damage depth distribution, the disordering buildup, the nature of radiation defects, and the occurrence of microstructural modifications. The damage results from the formation of tracks, due to the huge electronic excitations induced in the wake of incident ions. The melting of the material in the core of tracks, via a thermal spike mechanism, leads to the creation of large hillocks at the surface of the crystals. The overlapping of ion tracks at high fluence (above ∼1012 cm−2) induces a severe transformation of the microstructure of the material. Nanodomains slightly disoriented from the main crystallographic direction are formed, with a size decreasing with increasing irradiation fluence. These results may be used to predict the damage evolution in other nonamorphizable ceramics irradiated with swift heavy ions.
Modeling flux pinning in thin undoped and BaZrO3-doped YBCO films
Authors: Paturi P. , Irjala M. , Huhtinen H. , Abrahamsen A. B.
Published: January 2009

A simple model based on distributions of twin boundaries, dislocations, and BaZrO3 nanorods is presented to describe the Jc properties of undoped and BaZrO3 (BZO)-doped YBa2Cu3Ox thin films. The model accurately describes the shape of Jc(B,T) curves of the films, when the pinning site distributions are taken from distributions of twin spacings and BZO nanorods from transmission electron microscope images. Thus, assuming that the model can be used for prediction of the Jc properties, we conclude that for enhancement of undoped films more crystalline defects are needed and for doped films a dopant that would create slightly larger rods would be optimal.
Enhanced capability in a gas aggregation source for magnetic nanoparticles
Authors: Iles Gail N. , Baker S. H. , Thornton S. C. , Binns C.
Published: January 2009

We describe the characterization of a high-temperature (2000K) thermal gas aggregation source that is ultrahigh vacuum compatible and can cleanly deposit transition metal clusters with partial pressures of contaminants in the 10−11mbar range allowing codeposition with highly reactive matrices. In particular, we investigate the effect of varying (i) the bath gas pressure and composition on the size distribution and flux of clusters produced and (ii) the position of the crucible within the source. The mass spectra of Fe clusters produced, recorded using a quadrupole filter, show that changing the operating conditions and configuration of the source allow a wide range of cluster sizes—3000–320000amu (∼50–6000 atoms for Fe or Co) to be produced. We demonstrate the cleanliness of the source by producing uncontaminated Fe clusters in rare-earth matrices.
Application of the anisotropy field distribution method to arrays of magnetic nanowires
Authors: De La Torre Medina J. , Darques M. , Piraux L. , Encinas A.
Published: January 2009

The applicability of the anisotropy field distribution method and the conditions required for an accurate determination of the effective anisotropy field in arrays of magnetic nanowires have been evaluated. In arrays of magnetic nanowires that behave as ideal uniaxial systems having only magnetostatic contributions to the effective anisotropy field, i.e., shape anisotropy and magnetostatic coupling, the method yields accurate values of the average anisotropy field at low-moderate dipolar coupling and accuracy decreases as wire packing increases. When an additional non-negligible magnetocrystalline anisotropy is present, the method is less accurate, as shown for the case of hcp Co nanowires.
Effect of plasma density scale length on the properties of bremsstrahlung x-ray sources created by picosecond laser pulses
Authors: Courtois C. , Compant La Fontaine A. , Landoas O. , Lidove G. , Méot V. , Morel P. , Nuter R. , Lefebvre E. , Boscheron A. , Grenier J. , Aléonard M. M. , Gerbaux M. , Gobet F. , Hannachi F. , Malka G. , Scheurer J. N. , Tarisien M.
Published: January 2009

Results of an experimental study of multi-MeV bremsstrahlung x-ray sources created by picosecond laser pulses are presented. The x-ray source is created by focusing the short pulse in an expanding plasma obtained by heating a solid target with a time-delayed nanosecond laser beam. The high-energy part of the x-ray spectrum and emission lobe are inferred from photonuclear activation techniques. The x-ray dose is measured with silicon diodes. Two-dimensional images of the source are reconstructed from a penumbral imaging technique. These results indicate the creation of a relatively small source, below 200μm diameter, delivering doses up to 12mrad in air at 1m with x-ray temperature up to 2.8MeV. The diagnostics used give access to a whole set of coherent experimental results on the x-ray source properties which are compared to extensive numerical simulations. X-ray intensity and temperature are found to increase with the size of the preplasma.
Electron transport properties of undoped SnO2 monocrystals
Authors: Lanfredi Alexandre J. C. , Geraldes Renan R. , Berengue Olivia M. , Leite Edson R. , Chiquito Adenilson J.
Published: January 2009

Using low-resistance indium contacts, we measured some transport properties of undoped vapor-liquid-solid grown tin oxide monocrystals with a belt shape. From the transport measurements, the two following conduction mechanisms were investigated: thermal activation and variable range hopping. An energy gap of 3.8 eV was found. The energy gap was confirmed by thermally activated measurements in the range between 10 and 300 K. For high temperatures (T>300 K), the influence of the disorder caused by the superficial ions layer is measurable. The electron transport in this case was found to be governed by the well known variable range hopping mechanism and the spatial extension of carrier’s wavelength was calculated to be 4 nm.
Diode junctions between two ZnO nanoparticles: Mechanism of rectification
Authors: Mohanta Kallol , Pal Amlan J.
Published: January 2009

We form junctions between two ZnO nanoparticles. Such junctions are formed by electrostatic adsorption of two different monolayers in sequence. While one of the monolayers contains intrinsically n-type ZnO nanoparticles, concentration of Al dopant in the other monolayer is varied. All the junctions show current rectification. In one of the several control experiments, direction of rectification in a junction reverses when sequence of the components in the junction is inversed. This rules out any effect of interface or metal electrode in the observed current rectification. We study the mechanism of rectification that occurs in such a narrow junction. From the current-voltage characteristics, we evaluate the ideality factor of the diodes and find that a recombination current predominates in these junctions in the voltage range of our studies. Capacitance-voltage measurements show that a depletion layer has indeed formed between the two nanoparticles.
Analysis of UV light photodetectors using slanted finger interdigital surface acoustic wave devices
Authors: Huang Tsai-Ju , Ma Chein-Ching , Yu Jhih-Ming
Published: January 2009

In this study, an ultraviolet array photodetector with lithium-based slanted finger interdigital transducers (SFITs) and ZnO optically active areas is developed. The array photodetector can obtain multiple ultraviolet light intensities within a single measurement and is proven to be capable of measuring a distributed light field. The acoustoelectric effect is introduced in the SFIT coupling-of-mode simulation to evaluate the performance of the array photodetector. The simulated results have good agreement with the experimental responses. An optimum design of the SFIT and ZnO for the performance of the array photodetector is analyzed. To evaluate the performance of a surface acoustic wave photodetector, several design parameters such as working frequency, size of optically active areas, and separation gaps between active areas, are discussed in detail. Important results of design parameters from the detailed analysis are summarized in this study which are useful for the application of the proposed photodector.
In situ real-time monitoring of apoptosis on leukemia cells by surface infrared spectroscopy
Authors: Yamaguchi Ryo-taro , Hirano-Iwata Ayumi , Kimura Yasuo , Niwano Michio , Miyamoto Ko-ichiro , Isoda Hiroko , Miyazaki Hitoshi
Published: January 2009

We have investigated in situ real-time monitoring of apoptosis on human promyelocytic leukemia (HL-60) cells using infrared absorption spectroscopy with the multiple internal reflection (MIR-IRAS) geometry. Actinomycin D (Act D)-induced apoptosis on HL-60 cells was monitored for 24 h. Apoptotic cells showed two strong peaks around the protein amide I and amide II bands probably due to the leakage of cytoplasmic proteins, while growing viable cells showed a peak corresponding to the secretion of metabolites and two downward peaks corresponding to uptake of nutrients from culture media. In addition, IR absorption peak intensity of the amide I and amide II bands was proportional to the extracellular concentration of lactate dehydrogenase, a marker protein for cell damage. These results demonstrate that our MIR-IRAS method is useful for discrimination of apoptotic cells from viable ones and cell apoptotic processes can be monitored in situ by analyzing the amide I and amide II peak intensity.
Microfluidic pumps employing surface acoustic waves generated in ZnO thin films
Authors: Du X. Y. , Fu Y. Q. , Luo J. K. , Flewitt A. J. , Milne W. I.
Published: January 2009

ZnO thin film based surface acoustic wave (SAW) devices have been utilized to fabricate microfluidic pumps. The SAW devices were fabricated on nanocrystalline ZnO piezoelectric thin films deposited on Si substrates using rf magnetron sputtering and use a Sezawa wave mode for effective droplet motion. The as-deposited ZnO surface is hydrophilic, with a water contact angle of ∼75°, which prevents droplet pumping. Therefore, the ZnO surface was coated using a self-assembled monolayer of octadecyltrichlorosilane which forms a hydrophobic surface with a water contact angle of ∼110°. Liquid droplets between 0.5 and 1 μl in volume were successfully pumped on the hydrophobic ZnO surface at velocities up to 1 cm s−1. Under acoustic pressure, the water droplet on an hydrophilic surface becomes deformed, and the asymmetry in the contact angle at the trailing and leading edges allow the force acting upon the droplet to be calculated. These forces, which increase with input voltage above a threshold level, are found to be in the range of ∼100 μN. A pulsed rf signal has also been used to demonstrate precision manipulation of the liquid droplets. Furthermore, a SAW device structure is demonstrated in which the ZnO piezoelectric only exists under the input and output transducers. This structure still permits pumping, while avoiding direct contact between the piezoelectric material and the fluid. This is of particular importance for biological laboratory-on-a-chip applications.
Raman gain in niobium-phosphate glasses
Authors: Sirleto L. , Donato M. G. , Messina G. , Santangelo S. , Lipovskii A. A. , Tagantsev D. K. , Pelli S. , Righini G. C.
Published: January 2009

In this paper, niobium-phosphate glasses doped with rare earths (Er and Sm) are investigated by Raman scattering. The goal of Raman characterization is twofold: (a) to perform a fine structural characterization of the synthesized glasses and (b) to measure the Raman gain coefficient of the samples and to compare it with fused silica. The results reveal the presence of NbO6 octahedra and Nb–O–P–Nb–O mixed chains. A broadening of bandwidth and a significant enhancement (∼24 times) in gain coefficient G with respect to conventional silica glasses are also demonstrated.
Model for spin coupling disorder effects on the susceptibility of antiferromagnetic nanochains
Authors: Chaves C. M. , Paiva Thereza , d’Albuquerque e Castro J. , Koiller Belita
Published: January 2009

The temperature dependence of the static magnetic susceptibility of exchange-disordered antiferromagnetic Heisenberg spin-1/2 finite chains with an odd number of spins is investigated as a function of size and type of disorder in the exchange coupling. Two models for the exchange disorder distribution are considered. At sufficiently low temperatures each chain behaves like an isolated spin-1/2 particle. As the size of the chains increases, this analogy is lost and the chains evolve into the thermodynamic limit behavior. The present study provides a simple criterion, based on susceptibility measurements, to establish when odd-sized chains effectively simulate a single spin-1/2 particle.
rf streak camera based ultrafast relativistic electron diffraction
Authors: Musumeci P. , Moody J. T. , Scoby C. M. , Gutierrez M. S. , Tran T.
Published: January 2009

We theoretically and experimentally investigate the possibility of using a rf streak camera to time resolve in a single shot structural changes at the sub-100 fs time scale via relativistic electron diffraction. We experimentally tested this novel concept at the UCLA Pegasus rf photoinjector. Time-resolved diffraction patterns from thin Al foil are recorded. Averaging over 50 shots is required in order to get statistics sufficient to uncover a variation in time of the diffraction patterns. In the absence of an external pump laser, this is explained as due to the energy chirp on the beam out of the electron gun. With further improvements to the electron source, rf streak camera based ultrafast electron diffraction has the potential to yield truly single shot measurements of ultrafast processes.
Successive antiferromagnetic phase transitions in α-MnS probed by the exchange bias effect
Authors: Chen Xi , Hochstrat Andreas , Borisov Pavel , Kleemann Wolfgang
Published: January 2009

The temperature dependence of the exchange bias of the heterolayer structure α-MnS(111)/Fe(1.5 nm)/Pt(3 nm) is investigated. It arises below Tc1=152 K due to the antiferromagnetic (AF) type-II spin structure of α-MnS and maximizes at Tc2=129 K, below which it vanishes steplike in parallel with a sudden increase in the coercive field of the Fe layer. These features are consistent with a spin reorientation transition at Tc2 probably into an AF multi-k spin order rather than with an activated domain conformation transition.
Controlling energy level offsets in organic/organic heterostructures using intramolecular polar bonds
Authors: Duhm Steffen , Salzmann Ingo , Heimel Georg , Oehzelt Martin , Haase Anja , Johnson Robert L. , Rabe Jürgen P. , Koch Norbert
Published: January 2009

The impact of intramolecular polar bonds (IPBs) on the energy level alignment in layered systems of rodlike conjugated molecules standing on the substrate was investigated for pentacene (PEN) and perfluoropentacene (PFP) on SiO2 using ultraviolet photoelectron spectroscopy. A remarkably large energy offset of 1.75 eV was found between the highest occupied molecular orbital (HOMO) levels of PEN and PFP caused by IPBs at the surface of standing PFP layers. This large HOMO-level offset results in a narrow intermolecular energy gap of approximately 0.4 eV at the interface between PEN and PFP layers. However, the absence of significant spatial overlap of PEN and PFP electron wave functions across the layers suppresses interlayer optical transitions.
Monoclinic MC phase in (001) field cooled BaTiO3 single crystals
Authors: Cao Hu , Devreugd Christopher P. , Ge Wenwei , Li Jiefang , Viehland D. , Luo Haosu , Zhao Xiangyong
Published: January 2009

We report here the finding of a new phase in BaTiO3 single crystals. High precision x-ray diffraction investigations of (001) field cooled crystals have shown the presence of a monoclinic MC phase for temperatures below 300 K. This MC phase is shown to be stable upon removal of the electric field. The results demonstrate the presence of structurally bridging low symmetry phases that lie between tetragonal and rhombohedral ones in this classic perovskite system: indicating a means to achieve high piezoelectricity in Pb-free systems via domain engineering.
Contactless electroreflectance of GaInNAsSb/GaNAs/GaAs quantum wells emitting at 1.5–1.65 μm: Broadening of the fundamental transition
Authors: Kudrawiec R. , Poloczek P. , Misiewicz J. , Bae H. P. , Sarmiento T. , Bank S. R. , Yuen H. B. , Wistey M. A. , Harris James S.
Published: January 2009

Contactless electroreflectance (CER) has been applied to study the broadening of the fundamental transition for GaInNAsSb/GaNAs/GaAs quantum wells (QWs) obtained at various growth and annealing conditions. It has been observed that CER resonances are about 50% narrower for QWs grown at lower group V fluxes and annealed at lower temperatures (660–720 °C) and longer time (30–60 min) than those previously considered optimal (∼760 °C and ∼60 s). The long annealing can be partially realized in situ during (and/or after) the growth of the upper part of the laser structure instead the ex situ short-time annealing, where the laser structure can unintentionally be overannealed very easily.
Real-time near-field imaging of photoinduced matter motion in thin solid films containing azobenzene derivatives
Authors: Garrot D. , Lassailly Y. , Lahlil K. , Boilot J. P. , Peretti J.
Published: January 2009

We present a study of the formation of surface relief gratings in thin solid films containing azobenzene derivatives upon illumination with an interference pattern. This study is based on near-field microscopy techniques that provide real-time imaging of both the photomechanical response of the material and light excitation profile. We demonstrate that the material deformation follows two distinct regimes characterized by different kinetics, a different phase relative to the light intensity pattern, and a specific dependence on light polarization.
Multilayer structure with gradual increasing porosity for dye-sensitized solar cells
Authors: Tian Zhipeng , Tian Hanmin , Wang Xiangyan , Yuan Shikui , Zhang Jiyuan , Zhang Xiaobo , Yu Tao , Zou Zhigang
Published: January 2009

Multilayer structure was prepared in a dye-sensitized solar cell work electrode by enlarging the porosity in each layer being coated on the fluorine-doped tin oxide transparent conducting glass from bottom to top. The multilayer structure exhibits an improved light scattering character, which resulted in better light harvesting of the cell. An obvious improvement in short circuit current is obtained. I-V characteristic measurement indicates an improved efficiency by 13% as compared to homogeneous pore-size samples. Diffuse reflectance spectra, scanning electron microscope images, and porosity measurements demonstrate that larger porosity is the cause of enhanced light scattering.
Colossal resistance switching effect in Pt/spinel-MgZnO/Pt devices for nonvolatile memory applications
Authors: Chen Xinman , Wu Guangheng , Jiang Peng , Liu Weifang , Bao Dinghua
Published: January 2009

We reported the discovery of colossal resistance switching effect in polycrystalline spinel-like structure MgZnO thin films with high Mg contents sandwiched by Pt electrodes. The ultrahigh resistance ratio of high resistance state to low resistance state of about seven to nine orders of magnitude with a low reset voltage of less than 1 V was obtained in this thin film system. The resistance ratio shows an increase of several orders of magnitude compared with those of previously reported resistance switching material systems including metal oxides, semiconductors, and organic molecules. This colossal resistance switching effect will greatly improve the signal-to-noise ratio and simplify the process of reading memory state for nonvolatile memory applications. Our study also provides a material base for studying the origin of resistance switching phenomenon.
In situ characterization of initial growth of HfO2
Authors: Wang L. , Chu Paul K. , Xue K. , Xu J. B.
Published: January 2009

The initial growth of HfO2 on Si (111) is monitored in situ by ultrahigh vacuum (UHV) scanning probe microscopy. UHV scanning tunneling microscopy and UHV atomic force microscopy reveal the topography of HfO2 films in the initial stage. The chemical composition is further confirmed by x-ray photoelectron spectroscopy. Scanning tunneling spectroscopy is utilized to inspect the evolution of the bandgap. When the film thickness is less than 0.6 nm, the bandgap of HfO2 is not completely formed. A continuous usable HfO2 film with thickness of about 1.2 nm is presented in this work.
Rayleigh surface acoustic wave modes of (100) ZnO films on (111) diamond
Authors: Wu Sean , Ro Ruyen , Lin Zhi-Xun
Published: January 2009

(100) zinc oxide (ZnO) films were combined with (111) diamond to be a composite high velocity surface acoustic wave (SAW) substrate. Rayleigh SAW modes of (100) ZnO films on (111) diamond were theoretically analyzed. Those Rayleigh SAW modes have smaller films thickness ratios (h/λ), higher phase velocities, and larger electromechanical coupling coefficients (K2) than the ones of (002) ZnO films on (111) diamond. The research results provide a predictable and theoretical basis for further application on the high velocity SAW devices.
In situ x-ray investigation of freestanding nanoscale Cu–Nb multilayers under tensile load
Authors: Aydıner C. C. , Brown D. W. , Mara N. A. , Almer J. , Misra A.
Published: January 2009

The yield behavior in a freestanding sputter-deposited Cu/Nb multilayer with 30 nm nominal individual layer thickness has been investigated with in situ synchrotron x-ray diffraction during tensile loading. A pronounced elastic-plastic transition is observed with the fraction of plastically yielded grains increasing gradually with strain. Near synchronous yielding is observed in the Cu and Nb grains. The gradual progression in yield behavior is interpreted in terms of residual stresses, and elastic and plastic anisotropy.
The role of the nanospine in the nanocomb arrays for surface enhanced Raman scattering
Authors: Liu Y.-J. , Zhang Z.-Y. , Zhao Q. , Dluhy R. A. , Zhao Y.-P.
Published: January 2009

We have investigated the surface enhanced Raman scattering (SERS) from Au nanocombs and nanorods under different excitation conditions. The SERS intensity from nanocombs is always larger than that from nanorods, but the polarized SERS dependence is similar for the two nanostructures. These results agree quantitatively well with the local E-field calculations, and the nanospine in the nanocomb increases the local E-field over all surfaces of the nanocomb structure. The combination of experimental and numerical results predicts that the Raman enhancement at 633 nm excitation is estimated to be from seven to eight times that at 785 nm excitation.