bluuebunny/crossref_metadata_2025 huggingface dataset:
Statistical fusion of lidar, InSAR, and optical remote sensing data for forest stand height characterization: A regional‐scale method based on LVIS, SRTM, Landsat ETM+, and ancillary data sets
Authors: Kellndorfer J. M. , Walker W. S. , LaPoint E. , Kirsch K. , Bishop J. , Fiske G.
Published: March 2010

A method is presented to characterize forest stand heights in a 110,000 km2 region in the eastern United States surrounding the Chesapeake Bay area, driven by a statistical fusion model solely based on remote sensing data. The predicted map was tested against ground survey data from the Forest Inventory and Analysis (FIA) plot network. Input data to the model were 2003 medium footprint lidar data from the Laser Vegetation Imaging Sensor (LVIS) sensor, interferometric radar data from the 2000 Shuttle Radar Topography Mission (SRTM), 1999–2001 Landsat ETM+ data, and ancillary data sets of land cover and canopy density developed for the 2001 National Land Cover Database. In the presented approach, the interferometric synthetic aperture radar (InSAR), optical, and ancillary data sets were masked to the forested areas of the study region and used to segment the raster data stack. The generated image objects closely represented quasi‐homogenous forest stands. For a small region in the study area covered by an LVIS acquisition, LVIS lidar data were then used within the established segments to extract lidar‐based mean forest stand heights. Subsequently these LVIS mean stand heights were used as the response variable to the statistical prediction model (randomForest) which had segment‐based metrics like mean InSAR height (derived from SRTM minus ground digital elevation model data from the National Elevation Data set), mean optical reflectance (derived from Landsat ETM+ Tassled Cap Data), and ancillary metrics as predictive variables. The model developed over the area where LVIS data were available was then applied to map the entire study region. Independent validation of the model was performed in two ways. First, splitting of the model data stack into training and independent testing populations, i.e., testing on LVIS data. This test was deemed to describe the model performance within the LVIS swath. Second, predicted heights were compared to plot height metrics derived from FIA data in the entire study region, thus testing the validity of the model across the larger study area. Results, which are somewhat tampered by the time disconnect between the various data collections, showed the validity and usefulness of this approach. Independent LVIS testing resulted in a correlation coefficient r = 0.83 with an RMSE of 3.0 m (9% error), independent FIA data tested with r = 0.71 with an RMSE of 4.4 m (13% error).
Spatial and temporal variability of droughts in Portugal
Authors: Santos João Filipe , Pulido‐Calvo Inmaculada , Portela Maria Manuela
Published: March 2010

An analysis of droughts in mainland Portugal based on monthly precipitation data, from September 1910 to October 2004, in 144 rain gages distributed uniformly over the country is presented. The drought events were characterized by means of the Standardized Precipitation Index (SPI) applied to different time scales (1, 6, and 12 consecutive months and 6 months from April to September and 12 months from October to September). To assess spatial and temporal patterns of droughts, a principal component analysis (PCA) and K‐means clustering (KMC) were applied to the SPI series. In this way, three different and spatially well‐defined regions with different temporal evolution of droughts were identified (north, central, and south regions of Portugal). A spectral analysis of the SPI patterns obtained with principal component analysis and clusters analysis, using the fast Fourier transform algorithm (FFT), showed that there is a manifest 3.6‐year cycle in the SPI pattern in the south of Portugal and evident 2.4‐year and 13.4‐year cycles in the north of Portugal. The observation of the drought periods supports the occurrence of more frequent cycles of dry events in the south (droughts from moderate to extreme approximately every 3.6 years) than in the north (droughts from severe to extreme approximately every 13.4 years). These results suggest a much stronger immediate influence of the NAO in the south than in the north of Portugal, although these relations remain a challenging task.
Increased Plasma and Tissue MMP Levels are Associated with BCSFB and BBB Disruption Evident on Post-Contrast FLAIR after Experimental Stroke
Authors: Batra Ayush , Latour Lawrence L , Ruetzler Christl A , Hallenbeck John M , Spatz Maria , Warach Steven , Henning Erica C
Published: March 2010

In this study, we examined the relationship between tissue and blood levels of matrix metalloproteinase (MMP)-2 and MMP-9 through gelatin zymography at multiple time points after experimental stroke. We additionally investigated the association between these levels and the evidence of blood–cerebrospinal fluid (CSF) barrier (BCSFB) and blood–brain barrier (BBB) disruption on post-contrast fluid-attenuated inversion-recovery (FLAIR) imaging. Increased plasma MMP-9 was associated with BCSFB disruption at 1h post-reperfusion. Ventricular enhancement ipsilateral to the stroke was 500±100%, significantly higher than sham, 24, and 48 h groups. Increased tissue MMP-2 and MMP-9 were associated with BBB disruption at 48 h post-reperfusion. Parenchymal enhancement was 60±20% for a volume equivalent to 260±80 mm3. Although the percent enhancement was comparable across groups, the volume of enhancing lesion was significantly higher at 48 h (260±80 mm3, 100%) in comparison to 1 h (8±3 mm3, 3%) and 24 h (51 mm3, 18%). These findings support the use of imaging markers of BCSFB and BBB status as indirect measures of MMP regulation in the blood and brain tissue. The methods presented herein should be useful in understanding the link between MMPs, barrier integrity, and subsequent hemorrhagic transformation.
Activation of PKC Isoform βI at the Blood–Brain Barrier Rapidly Decreases P-Glycoprotein Activity and Enhances Drug Delivery to the Brain
Authors: Rigor Robert R , Hawkins Brian T , Miller David S
Published: March 2010

P-glycoprotein is an ATP (adenosine triphosphate)-driven drug efflux transporter that is highly expressed at the blood–brain barrier (BBB) and is a major obstacle to the pharmacotherapy of central nervous system diseases, including brain tumors, neuro-AIDS, and epilepsy. Previous studies have shown that P-glycoprotein transport activity in rat brain capillaries is rapidly reduced by the proinflammatory cytokine, tumor necrosis factor-α (TNF-α) acting through protein kinase C (PKC)-dependent signaling. In this study, we used isolated rat brain capillaries to show that the TNF-α-induced reduction of P-glycoprotein activity was prevented by a PKCβI/II inhibitor, LY333531, and mimicked by a PKCβI/II activator, 12-deoxyphorbol-13-phenylacetate-20-acetate (dPPA). Western blotting of brain capillary extracts with phospho-specific antibodies showed that dPPA activated PKCβI, but not PKCβII. Moreover, in intact rats, intracarotid infusion of dPPA potently increased brain accumulation of the P-glycoprotein substrate, [3H]-verapamil without compromising tight junction integrity. Thus, PKCβI activation selectively reduced P-glycoprotein activity both in vitro and in vivo. Targeting PKCβI at the BBB may prove to be an effective strategy for enhancing the delivery of small molecule therapeutics to the brain.
A Spectral Analysis Approach for Determination of Regional Rates of Cerebral Protein Synthesis with the L-[1-11C]leucine PET Method
Authors: Veronese Mattia , Bertoldo Alessandra , Bishu Shrinivas , Unterman Aaron , Tomasi Giampaolo , Smith Carolyn Beebe , Schmidt Kathleen C
Published: March 2010

A spectral analysis approach was used to estimate kinetic model parameters of the L-[1-11C]leucine positron emission tomography (PET) method and regional rates of cerebral protein synthesis (rCPS) in predefined regions of interest (ROIs). Unlike analyses based on the assumption that tissue ROIs are kinetically homogeneous, spectral analysis allows for heterogeneity within a region. To improve estimation performance, a new approach was developed—spectral analysis with iterative filter (SAIF). In simulation SAIF produced low bias, low variance estimates of the influx rate constant for leucine ( K1), blood volume fraction ( V b), fraction of unlabeled leucine in the tissue precursor pool for protein synthesis derived from arterial plasma (λ), and rCPS. Simulation of normal count rate studies showed that SAIF applied to ROI time-activity curves (TACs) performed comparably to the basis function method (BFM) applied to voxel TACs when voxelwise estimates were averaged over all voxels in the ROI. At low count rates, however, SAIF performed better. In measured L-[1-11C]leucine PET data, there was good agreement between ROI-based SAIF estimates and average voxelwise BFM estimates of K1, V b, λ, and rCPS. We conclude that SAIF sufficiently addresses the problem of tissue heterogeneity in ROI data and provides a valid tool for estimation of rCPS, even in low count rate studies.
Inhibition of Bradykinin Receptor B1 Protects Mice from Focal Brain Injury by Reducing Blood–Brain Barrier Leakage and Inflammation
Authors: Raslan Furat , Schwarz Tobias , Meuth Sven G , Austinat Madeleine , Bader Michael , Renné Thomas , Roosen Klaus , Stoll Guido , Sirén Anna-Leena , Kleinschnitz Christoph
Published: March 2010

Kinins are proinflammatory and vasoactive peptides that are released during tissue damage and may contribute to neuronal degeneration, inflammation, and edema formation after brain injury by acting on discrete bradykinin receptors, B1R and B2R. We studied the expression of B1R and B2R and the effect of their inhibition on lesion size, blood–brain barrier (BBB) disruption, and inflammatory processes after a focal cryolesion of the right parietal cortex in mice. B1R and B2R gene transcripts were significantly induced in the lesioned hemispheres of wild-type mice ( P<0.05). The volume of the cortical lesions and neuronal damage at 24 h after injury in B1R −/− mice were significantly smaller than in wild-type controls (2.5±2.6 versus 11.5±3.9 mm3, P<0.001). Treatment with the B1R antagonist R-715 1 h after lesion induction likewise reduced lesion volume in wild-type mice (2.6±1.4 versus 12.2±6.1 mm3, P<0.001). This was accompanied by a remarkable reduction of BBB disruption and tissue inflammation. In contrast, genetic deletion or pharmacological inhibition of B2R had no significant impact on lesion formation or the development of brain edema. We conclude that B1R inhibition may offer a novel therapeutic strategy after acute brain injuries.
White-emitting oxidized silicon nanocrystals: Discontinuity in spectral development with reducing size
Authors: Dohnalová K. , Ondič L. , Kůsová K. , Pelant I. , Rehspringer J. L. , Mafouana R.-R.
Published: March 2010

Small oxidized silicon nanocrystals of average sizes below 3.5 nm are prepared using modified electrochemical etching of a silicon wafer. Modifications introduced in the etching procedure together with postetching treatment in H2O2 lead to a decrease in the nanocrystalline core size and also, to some extent, to changes in the surface oxide. The interplay between these two factors allows us to blueshift the photoluminescence (PL) spectrum from 680 down to 590 nm, which is accompanied by changes in PL dynamics. This continual development, however, stops at about 590 nm, below which abrupt switching to fast decaying blue emission band at about 430 nm was observed. Discontinuity of the spectral shift and possible relation between both bands are discussed.
Critical states in thin planar type-II superconductors in a perpendicular or inclined magnetic field (Review)
Authors: Mikitik G. P.
Published: March 2010

The theory of the critical states of a vortex lattice in type-II superconductors is examined without any assumptions about the relative perpendicularity of the local magnetic fields and circulating currents in the sample. Such a theory has made it possible to solve a number of problems for thin films of superconductors in an external magnetic field oriented perpendicular to their surface: a theory of the shaking effect is constructed for rectangular superconducting plates and the critical states in samples with anisotropic pinning of the flux lines as well as in the presence of an order-disorder phase transition in a vortex lattice are studied. In addition, the critical states in a long superconducting strip in an inclined magnetic field are investigated.
Magnetoresistance and 2D-3D crossover in aluminum-doped YBa2Cu3−zAlzO7−δ single crystals with a system of unidirectional twinning boundaries
Authors: Zavgorodniĭ A. A. , Vovk R. V. , Obolenskiĭ M. A. , Samoĭlov A. V.
Published: March 2010

The effect of a constant magnetic field to 12.7kOe on the temperature dependences of the electric conductivity of aluminum-doped YBaCuO single crystals with a system of unidirectional twinning boundaries is investigated. The temperature dependences of the excess paraconductivity and the field dependence of the coherence length ξc(0,H) along the c axis are determined in the basal ab plane. It is determined that the twinning boundaries are effective centers of scattering of fluctuation carriers. The temperature dependences of the excess paraconductivity are interpreted on the basis of the Hikami-Larkin theoretical model of fluctuation conductivity for layered superconducting systems. The reasons for the suppression of three-dimensional superconducting fluctuations and the nonmonotonic dependence of ξc(0,H) in weak magnetic fields with the magnetic field vector oriented along the c axis are discussed.
The role of substrate electrons in the wetting of a metal surface
Authors: Schiros T. , Takahashi O. , Andersson K. J. , Öström H. , Pettersson L. G. M. , Nilsson A. , Ogasawara H.
Published: March 2010

We address how the electronic and geometric structures of metal surfaces determine water-metal bonding by affecting the balance between Pauli repulsion and electrostatic attraction. We show how the rigid d-electrons and the softer s-electrons utilize different mechanisms for the redistribution of charge that enables surface wetting. On open d-shell Pt(111), the ligand field of water alters the distribution of metal d-electrons to reduce the repulsion. The closed-shell Cu d10 configuration of isostructural Cu(111), however, does not afford this mechanism, resulting in a hydrophobic surface and three-dimensional ice cluster formation. On the geometrically corrugated Cu(110) surface, however, charge depletion involving the mobile sp-electrons at atomic rows reduces the exchange repulsion sufficiently such that formation of a two-dimensional wetting layer is still favored in spite of the d10 electronic configuration.
An in situ tensile tester for studying electrochemical repassivation behavior: Fabrication and challenges
Authors: Neelakantan Lakshman , Schönberger Bernd , Eggeler Gunther , Hassel Achim Walter
Published: March 2010

An in situ tensile rig is proposed, which allows performing electrochemical (repassivation) experiments during dynamic mechanical testing of wires. Utilizing the basic components of a conventional tensile tester, a custom-made minitensile rig was designed and fabricated. The maximal force that can be measured by the force sensor is 80 N, with a sensitivity of 0.5 mV/V. The maximum travel range of the crosshead induced by the motor is 10 mm with a minimum step size of 0.5 nm. The functionality of the tensile test rig was validated by investigating Cu and shape memory NiTi wires. Wires of lengths between 40 and 50 mm with varying gauge lengths can be tested. An interface between wire and electrochemical setup (noncontact) with a smart arrangement of electrodes facilitated the electrochemical measurements during tensile loading. Preliminary results on the repassivation behavior of Al wire are reported.
HTSC cuprate films doped with nanoparticles and their electrodynamics, determined by Abrikosov vortices
Authors: Flis V. S. , Kalenyuk A. A. , Kasatkin A. L. , Moskalyuk V. O. , Rebikov A. I. , Svechnikov V. L. , Tret’yachenko K. G. , Pan V. M.
Published: March 2010

This paper presents the results of a comprehensive study of the relationship of the structural and electrodynamic characteristics of quasi-single-crystal films of the HTSC cuprate YBa2Cu3O7−δ (YBCO) with various concentrations (several mass percent) of nanosize inclusions of the perovskitelike phase of BaZrO3 (BZO). High-resolution electron microscopy is used to investigate the nanostructure of the fabricated films and to determine the main types of defects that cause strong pinning of Abrikosov vortices and, accordingly, large critical current densities. The results of theoretically modelling the genesis of the defect nanostructure that appears in such films and its influence on the critical current are presented. The magnetic and transport properties of HTSC films made from YBCO(BZO) have been experimentally studied. The temperature, magnetic-field, and magnetic-orientation dependences of the critical current density of the test films are found. The results of an experimental investigation of the high-frequency properties of YBZO(BZO) films—the surface microwave impedance of the films in the linear and nonlinear regimes—are also given. The experimental results are discussed, and the influence of the nanostructure of the impurity phase on the electrodynamic characteristics of the HTSC films is analyzed.
The Hall effect and microwave absorption by vortices in an anisotropic superconductor with a periodic pinning potential
Authors: Shklovskij V. A. , Hop Dang Thi Bich
Published: March 2010

This paper presents the results of theoretical calculations of the absorbed power, the impedance tensors, and the magnetoresistances of anisotropic superconductors of the second kind in a model of a periodic pinning potential in the presence of the Hall effect.
Ideal and distorted vortex lattice in bulk and film superconductors (Review)
Authors: Brandt Ernst Helmut
Published: March 2010

The solution of the linearized Ginzburg-Landau theory describing a periodic lattice of vortex lines in type-II superconductors with high inductions and first discovered by Abrikosov is generalized to nonperiodic vortex arrangements, e.g. lattices with a vacancy, surrounded by a relaxing vortex lattice, and periodically distorted lattices that are needed in the nonlocal theory of elasticity of a vortex lattice. Generalizations to lower magnetic inductions and three-dimensional arrangements of curved vortex lines are also given. It is shown how a periodic vortex lattice can be computed for bulk superconductors and for thick and thin films in a perpendicular field for all inductions B and all Ginzburg-Landau parameters κ.
Static and dynamic order-disorder transition of a vortex lattice in YBaCuO crystals: The effect of point defects, anisotropy, temperature, and magnetic field
Authors: Petrusenko Yu. T.
Published: March 2010

This paper presents the results of measurements of the field dependence Fp(H) and angle dependence Fp(α) of the pinning force in an YBa2Cu3O7−δ crystal that contains various concentrations of point defects. A comparison of the Fp(H) and Fp(α) dependences gives decisive reasons for assuming that, when the vortices travel at low velocities υ, the minimum on the Fp(α) dependence corresponds to the order-disorder transition in the vortex lattice (VL). It is shown that the minimum on the Fp(α) dependence shifts toward larger angles α at large velocities υ, and this is caused by the partial dynamic ordering of the disordered VL.
The displacement and annihilation of macroscopic regions with hypervortices in ceramic YBa2Cu3O7−x
Authors: Shablo A. A. , Koverya V. P. , Bondarenko S. I.
Published: March 2010

Features of the controllable displacement, annihilation, and transformation of macroscopic regions of a weak frozen magnetic field (FMF) have been experimentally studied in a plate of granulated ceramic YBa2Cu3O7−x under the action of the transport current flowing through it. It is shown that the displacement of regions with an FMF lower than the first critical field of the ceramic granules (Hc1g) is associated with a relatively weak pinning force of the hypervortices that is less than the maximum experimentally attainable Lorenz force. A discussion is presented of the role of the transport current that not only is one of the conditions for the appearance of the Lorenz force but also acts on the internal current structure of the local FMF, which in turn influences its mobility and magnitude. If a local field greater than Hc1g is frozen in, the experimentally produced Lorenz force is less than the pinning force of the Abrikosov vortices in the mixed state of the granules, and there is no displacement of the regions with an FMF.
Manipulation of the crystallinity boundary of pulsed laser deposited high-k HfO2–TiO2–Y2O3 combinatorial thin films
Authors: Klamo J. L. , Schenck P. K. , Burke P. G. , Chang K.-S. , Green M. L.
Published: March 2010

Combinatorial library films of HfO2–TiO2–Y2O3, a high-k dielectric system, grown by pulsed laser deposition, exhibit visible boundary lines separating amorphous and crystalline phases. By changing processing space parameters, specifically substrate temperature during deposition, as well as the composition of the library film, we are able to manipulate the boundary and hence, the microstructural properties of the film. High-throughput x-ray diffraction and spectroscopic reflectometry are effective tools for measuring the properties of the resulting library films altered via these changes in processing. Electrical measurements confirm that the dielectric constant of the library films is composition and microstructure dependent.
Impedance spectroscopy as a probe for the degradation of organic light-emitting diodes
Authors: Nowy Stefan , Ren Wei , Elschner Andreas , Lövenich Wilfried , Brütting Wolfgang
Published: March 2010

Impedance spectroscopy is a powerful method for characterizing the electrical properties of materials and their interfaces. In this study we use capacitance measurements to investigate the degradation of electrically aged bottom-emitting organic light-emitting diodes with different polymeric hole injection layers. The devices comprise a heterojunction between a hole transporting triphenyl-diamine and an electron transporting and green emitting aluminum chelate complex [Alq3, tris-(8-hydroxyquinoline) aluminum]. A detailed analysis of the capacitance as function of frequency and dc bias yields information about trapped and interfacial charges as well as the dynamics of injected charges. We find that the loss of luminance and the increase in drive voltage of stressed devices is accompanied by a deterioration of hole injection and the formation of positively charged quenching centers at or close to the organic heterojunction. Using a new polymeric hole injection layer leads to improved device stability.
Electron beam irradiation of dimethyl-(acetylacetonate) gold(III) adsorbed onto solid substrates
Authors: Wnuk Joshua D. , Gorham Justin M. , Rosenberg Samantha G. , van Dorp Willem F. , Madey Theodore E. , Hagen Cornelis W. , Fairbrother D. Howard
Published: March 2010

Electron beam induced deposition of organometallic precursors has emerged as an effective and versatile method for creating two-dimensional and three-dimensional metal-containing nanostructures. However, to improve the properties and optimize the chemical composition of nanostructures deposited in this way, the electron stimulated decomposition of the organometallic precursors must be better understood. To address this issue, we have employed an ultrahigh vacuum-surface science approach to study the electron induced reactions of dimethyl-(acetylacetonate) gold(III) [AuIII(acac)Me2] adsorbed onto solid substrates. Using thin molecular films adsorbed onto cooled substrates, surface reactions, reaction kinetics, and gas phase products were studied in the incident energy regime between 40 and 1500 eV using a combination of x-ray photoelectron spectroscopy (XPS), reflection absorption infrared spectroscopy (RAIRS), and mass spectrometry (MS). XPS and RAIRS data indicate that electron irradiation of AuIII(acac)Me2 is accompanied by the reduction in AuIII to a metallic Au0 species embedded in a dehydrogenated carbon matrix, while MS reveals the concomitant evolution of methane, ethane, carbon monoxide, and hydrogen. The electron stimulated decomposition of AuIII(acac)Me2 is first-order with respect to the surface coverage of the organometallic precursor, and exhibits a rate constant that is proportional to the electron flux. At an incident electron energy of 520 eV, the total reaction cross section was ≈3.6×10−16 cm2. As a function of the incident electron energy, the maximum deposition yield was observed at ≈175 eV. The structure of discrete Au-containing deposits formed at room temperature by rastering an electron beam across a highly ordered pyrolytic graphite substrate in the presence of a constant partial pressure of AuIII(acac)Me2 was also investigated by atomic force microscopy.
Structural evolution, epitaxy, and sublimation of silver nanoclusters on TiO2 (110)
Authors: Sivaramakrishnan S. , Tedjasaputra A. P. , Sato K. , Zuo J. M.
Published: March 2010

The structural evolution, epitaxy, and sublimation temperature of silver nanoclusters (NCs) on TiO2 (110) surfaces prepared in two different ways are reported here based on a combination of in situ reflection high energy electron diffraction characterization and ex situ electron imaging. It is shown that silver NCs deposited at room temperature on oxidized TiO2 (110) surfaces are unable to form a single epitaxy prior to sublimation. When heated close to sublimation, two particle orientations dominate: (111)Ag∥(110)TiO2, [−110]Ag∥[001]TiO2 and (112)Ag∥(110)TiO2, [−110]Ag∥[001]TiO2. Single twinned silver NCs are found to be stable even at temperatures close to sublimation. On the other hand, silver NCs prepared similarly on reduced TiO2 (110) surfaces behave very differently when heated to higher temperatures. On the reduced surface, the NCs are able to evolve into a single epitaxy-(111)Ag∥(110)TiO2, [−110]Ag∥[001]TiO2. The sublimation temperature for silver NCs on the reduced surface is found to be less than those on the oxidized surface by about 35°. The epitaxy formed by annealing is the same as the one formed by depositing silver onto reduced TiO2 (110) at 350 °C (>0.5 Tm of Ag).
Electron-induced adhesion and patterning of gold nanoparticles
Authors: Torchinsky I. , Amdursky N. , Inberg A. , Rosenman G.
Published: March 2010

Self assembly of ligand-covered gold nanoparticles from water colloid solution on silicon dioxide substrate, modified, and patterned by low energy electron beam, has been observed. High selective adhesion of Au-nanoparticles on hydrophobic regions of wettability patterning was discovered and has been explained within the framework of the classical thermodynamic theory of particle adhesion on a substrate immersed into the colloid solution. The Au-nanoparticles patterns were imaged using confocal microscopy. Our results indicate that the developed technique may be considered as high resolution and environmentally clean technology for nanoparticles adhesion for metal nanoelectrode deposition, development of biosensor arrays, and nanophotonic devices.
An investigation of the thermal sensitivity and stability of the β-NaYF4:Yb,Er upconversion nanophosphors
Authors: Shan Jingning , Kong Wenjun , Wei Robert , Yao Nan , Ju Yiguang
Published: March 2010

The upconversion luminescence (UCL) of the hexagonal (β)-phase NaYF4:Yb,Er nanophosphors as a function of temperature (300–450 K) was examined under 978 nm light excitation. The thermal sensitivity was evaluated based on the UCL intensity ratio between H211/2–I415/2 and S43/2–I415/2 transitions (RHS). Excitation power, particle sizes (37, 65, and 140 nm), ion doping concentrations, and with and without silica coating were studied. It was found that RHS is only dependent on temperature at the low excitation power, and has no direct relation with the particle size and surface effects. Silica coating was found to enhance the thermal stability significantly without altering the thermal sensitivity.
Thermal stability of gas phase magnesium nanoparticles
Authors: Krishnan Gopi , Kooi Bart J. , Palasantzas George , Pivak Yevheniy , Dam Bernard
Published: March 2010

In this work we present a unique transmission electron microscopy study of the thermal stability of gas phase synthesized Mg nanoparticles, which have attracted strong interest as high capacity hydrogen storage materials. Indeed, Mg nanoparticles with a MgO shell (∼3 nm thick) annealed at 300 °C show evaporation, void formation, and void growth in the Mg core both in vacuum and under a high pressure gas environment. This is mainly due to the outward diffusion and evaporation of Mg with the simultaneously inward diffusion of vacancies leading to void growth (Kirkendall effect). The rate of Mg evaporation and void formation depends on the annealing conditions. In vacuum, and at T=300 °C, the complete evaporation of the Mg core takes place (within a few hours) for sizes ∼15–20 nm. Void formation and growth has been observed for particles with sizes ∼20–50 nm, while stable Mg nanoparticles were observed for sizes >50 nm. Furthermore, even at relative low temperature annealing (as low as 60 °C), void formation and growth occurs in 15–20 nm sized Mg nanoparticles, indicating that voiding will be even more dominant for nanoparticles smaller than 10 nm. Our findings confirm that Mg evaporation and void formation in nanoparticles with sizes less than 50 nm present formidable barriers for their applicability in hydrogen storage, but also could inspire future research directions to overcome these obstacles.
Analytical solution for mode-mismatched thermal lens spectroscopy with sample-fluid heat coupling
Authors: Malacarne Luis C. , Astrath Nelson G. C. , Pedreira Paulo R. B. , Mendes Renio S. , Baesso Mauro L. , Joshi Prakash R. , Bialkowski Stephen E.
Published: March 2010

This paper presents an improved theoretical description of the mode-mismatched thermal lens effect using models that account for heat transport both within the sample and out to the surrounding coupling medium. Analytical and numerical finite element analysis (FEA) solutions are compared and subsequently used to model the thermal lens effect that would be observed using continuous laser excitation. FEA model results were found to be in excellent agreement with the analytical solutions. The model results show that heat transfer to the air coupling medium introduces only a minor effect when compared with the solution obtained without considering axial air-sample heat flux for practical examples. On the other hand, the thermal lens created in the air coupling fluid has a relatively more significant effect on the time-dependent photothermal lens signals.
Influences of evaporation temperature on electronic structures and electrical properties of molybdenum oxide in organic light emitting devices
Authors: Lin Chang-Ting , Yeh Cheng-Hung , Chen Mei-Hsin , Hsu Shu-Han , Wu Chih-I , Pi Tun-Wen
Published: March 2010

The influence of evaporation temperatures on the electronic structures of molybdenum oxide (MoOx) films and the electrical properties of organic light emitting diodes were investigated. MoOx films evaporated at a high temperature and a high deposition rate are close to a stoichiometric phase, but become less effective when they are used as a hole injection layer. However, when MoOx is evaporated at a lower temperature and a slower rate, there are large amounts of defect-related states present in the forbidden gap, which make the films behave like a high work function conductor and an effective hole injection layer.
Investigation of osmium carbides with various stoichiometries: First-principles calculations
Authors: Du Xiang Po , Wang Yuan Xu
Published: March 2010

Using first-principles calculations, we have investigated osmium carbides with various stoichiometries (i.e., OsC, Os2C3, and OsC2). It is found that the predicted cubic OsC is of about 0.29 eV/(formula unit) lower in energy than previously proposed NiAs–OsC at ambient conditions. The plot of the computed enthalpy as a function of pressure indicates that cubic OsC is more stable than NiAs–OsC up to about 33 GPa. Moreover, cubic OsC shows a semiconductor character with a narrow gap of about 0.5 eV. The hypothetical P-4c2 and Pbcn Os2C3 show large incompressibility with their bulk moduli being about 360 GPa. P-4c2 Os2C3 exhibits the semiconductor character, while Pbcn Os2C3 metallic. Among the considered osmium carbides, the two hexagonal OsC2 have larger shear moduli, which indicates that they are potential superhard materials, and the total density of states suggest they are metallic. We have also discussed the dependence of shear modulus on carbon content. It was found that the shear modulus increases with the increased carbon content, and that the strong C–C bond in OsC2 is helpful to its high shear modulus. It is also found that a sublinear relationship exists between the Debye temperature and shear modulus.
Terahertz current oscillations assisted by optical phonon emission in GaN n+nn+ diodes: Monte Carlo simulations
Authors: Íñiguez-de-la-Torre A. , Mateos J. , González T.
Published: March 2010

Under certain conditions, plasma instabilities associated with streaming motion of carriers taking place in n+nn+ diodes can lead to current oscillations. The origin of the phenomenon, known as optical phonon transit time resonance, is characterized by a frequency related to the transit time between consecutive optical phonon emissions by electrons along the active region of the diode. By means of Monte Carlo simulations, the possibility to obtaining current oscillations in GaN n+nn+ diodes is analyzed. The optimum conditions for the onset of such mechanism are investigated: applied bias, temperature, doping, and length of the active n region. Simulations show that current oscillations at frequencies in the terahertz range can be obtained at very low temperatures. Moreover, by choosing the appropriate applied voltage and length of the n region, some degree of tunability can be achieved for frequencies close to the plasma frequency of the n region of the n+nn+ diode.
Layer-to-island growth of electrodeposited Cu2O films and filamentary switching in single-channeled grain boundaries
Authors: Kang Sung-Oong , Hong Sahwan , Choi Jinsik , Kim Jin-Soo , Hwang Inrok , Byun Ik-Su , Kim Yeon Soo , Kim Wondong , Park Bae Ho
Published: March 2010

We investigated a growth behavior of highly oriented and columnar grained cuprous oxide (Cu2O) films, which were obtained through a chelate-assisted electrochemical solution approach. It was demonstrated that the electrochemical growth of Cu2O films followed a layer-to-island growth mode with a critical thickness of ∼190 nm. The chelating agent induced the layer-growth of flat-surfaced films consisting of single-crystalline planar grains, and influenced the preferred orientation of films maintained within the island-growth mode. In particular, the single-crystalline columnar grains with stable interfaces and diameters of 100–200 nm provided highly localized areas of linear grain boundaries for filamentary resistive switching. We measured different conduction behaviors of flat-surfaced films showing nonswitching Ohmic conduction and unipolar memory switching in as-deposited and annealed films, respectively. These different conduction behaviors were found to originate from the microstructure changes generated by the annealing process, which may suggest a clue for the origins of filamentary resistive memory switching in single-channeled grain boundaries.
Probing the heat affected zone by chemical modifications in femtosecond pulse laser ablation of titanium nitride films in air
Authors: Bonse Jörn , Krüger Jörg
Published: March 2010

A new approach is presented to quantify the so-called “heat affected zone” (HAZ) during femtosecond laser pulse processing. Ablation of titanium nitride (TiN) thin films (∼3 μm thickness) by multiple femtosecond laser pulses (τ=130 fs, λ=800 nm) in air environment was studied by means of two different surface analytical methods both being sensitive to chemical alterations at the surface. Scanning Auger electron microscopy was applied for a visualization of the spatial distribution of specific elements (Ti, O) within the laser-modified areas. The chemical state of the irradiated surface was revealed by complementary x-ray photoelectron spectroscopy. Both methods were used for a depth-profiling chemical analysis (tracking the elements Ti, N, O, and C) using an Ar-ion beam for surface sputtering. In a narrow laser fluence range slightly below the ablation threshold of TiN significant superficial oxidation can be observed leading to the formation of substoichiometric TiO2−x. At fluences above the ablation threshold, an increased titanium concentration is observed within the entire ablation craters. Following upon sputter removal the elemental distribution into the depth of the nonablated material, the results allow an estimation of the heat-affected zone for femtosecond laser ablation in air environment. According to our analyses, the HAZ extends up to a few hundreds of nanometers into the nonablated material.
The problematic C2H4+F2 reaction barrier
Authors: Feng Hao , Allen Wesley D.
Published: March 2010

The C2H4+F2 reaction is investigated through the most rigorous electronic structure methods currently feasible, using a focal point approach to converge toward the ab initio limit. Explicit computations were executed with basis sets as large as aug-cc-pV5Z and correlation treatments as extensive as coupled cluster through full triples with a perturbative inclusion of quadruple excitations [CCSDT(Q)]. Auxiliary core correlation, diagonal Born–Oppenheimer, and first-order relativistic corrections were included. All optimized geometries and vibrational frequencies were determined completely at the CCSD(T)/aug-cc-pVQZ level. The final C2H4+F2 reaction barrier from theory (8.0 kcal mol−1) is significantly higher than the recently reported experimental barrier (5.5±0.5 kcal mol−1). Our computations also yield a new enthalpy of formation of the fluoroethyl radical, ΔfH298°(C2H4F)=−13.2±0.2 kcal mol−1, whose uncertainty is an order of magnitude less than previous experimental values.
Electronic structures and rovibronically averaged geometries of the X̃ A6i′ and Ã A6i″ states of FeOH
Authors: Hirano Tsuneo , Nagashima Umpei , Winnewisser Gisbert , Jensen Per
Published: March 2010

We have recently reported a theoretical prediction of the rovibronic spectra of the FeOH molecule. These spectra have not been observed experimentally. In the present work, we complement the previously published information by reporting the details of the electronic structure of FeOH together with rovibrationally averaged structural parameters. The electronic ground state is X̃ A6i′, which is Renner-degenerate with the Ã A6i″ state; the two states correlate with a Δ6 state at linearity. We have calculated the three-dimensional potential energy surfaces (PESs) of the X̃ and Ã states, which are close in energy over the range of geometries studied, at the MR-SDCI+Q+Erel/[Roos ANO (Fe), aug-cc-pVQZ (O, H)] level of theory. The equilibrium structure of the X̃ state is bent with re(Fe–O)=1.806 Å, re(O–H)=0.952 Å, and ∠e(Fe–O–H)=134.2°. The barrier to linearity is 273 (266) cm−1 in the X̃ (Ã) state so that FeOH is quasilinear in the X̃ and Ã states. The Fe–O bonds in both states are ionic and the bending potentials are shallow, resulting in large amplitude bending motion. The rovibrationally averaged structures of the X̃ A6′ and Ã A6″ electronic states have been calculated for the average of the X̃ and Ã PESs by the variational MORBID method as expectation values in terms of rotation-vibration wave functions. FeOH is said to be quasilinear, but the rovibrationally averaged structure is bent with ⟨r(Fe–O)⟩0=1.805 Å, ⟨r(O–H)⟩0=0.967 Å, and ⟨∠(Fe–O–H)⟩0=141(14)° (where the quantity in parentheses is the quantum mechanical uncertainty), which is close to the equilibrium structure. We demonstrate that by means of the Yamada–Winnewisser quasilinearity parameter we can distinguish linear and quasilinear molecules.
Hybrid functionals including random phase approximation correlation and second-order screened exchange
Authors: Paier Joachim , Janesko Benjamin G. , Henderson Thomas M. , Scuseria Gustavo E. , Grüneis Andreas , Kresse Georg
Published: March 2010

There has been considerable recent interest in density functionals incorporating random phase approximation (RPA) ground-state correlation. By virtue of its full nonlocality, RPA correlation is compatible with exact Hartree–Fock-type exchange and describes van der Waals interactions exceptionally well [B. G. Janesko et al., J. Chem. Phys. 130, 081105 (2009); J. Chem. Phys. 131, 034110 (2009)]. One caveat is that RPA correlation contains one-electron self-interaction error, which leads to disturbingly large correlation energies in the stretched bond situation of, e.g., H2+, He2+, or Ne2+. In the present work, we show that inclusion of second-order screened exchange rectifies the aforementioned failure of RPA correlation. We present a large number of molecular benchmark results obtained using full-range as well as long-range corrected hybrids incorporating second-order screened exchange correlation. This correction has a generally small, and sometimes undesirable, effect on RPA predictions for chemical properties, but appears to be very beneficial for the dissociation of H2+, He2+, and Ne2+.
Influence of the matrix properties on the performances of Er-doped Si nanoclusters light emitting devices
Authors: Irrera Alessia , Iacona Fabio , Franzò Giorgia , Miritello Maria , Lo Savio Roberto , Castagna Maria Eloisa , Coffa Salvatore , Priolo Francesco
Published: March 2010

We investigated the properties of light emitting devices whose active layer consists of Er-doped Si nanoclusters (nc) generated by thermal annealing of Er-doped SiOx layers prepared by magnetron cosputtering. Differently from a widely used technique such as plasma enhanced chemical vapor deposition, sputtering allows to synthesize Er-doped Si nc embedded in an almost stoichiometric oxide matrix, so as to deeply influence the electroluminescence properties of the devices. Relevant results include the need for an unexpected low Si excess for optimizing the device efficiency and, above all, the strong reduction of the influence of Auger de-excitation, which represents the main nonradiative path which limits the performances of such devices and their application in silicon nanophotonics.
On the applicability of fragmentation methods to conjugated π systems within density functional framework
Authors: Yeole Sachin D. , Gadre Shridhar R.
Published: March 2010

For the accurate ab initio treatment of large molecular systems, linear scaling methods (LSMs) have been devised and successfully applied to covalently bonded systems as well as to those involving weak intra/intermolecular bonds. Very few attempts to apply LSM to highly conjugated molecules, especially to two-dimensional systems, have so far been reported in the literature. The present article examines the applicability of a LSM, viz., molecular tailoring approach (MTA), to π-conjugated systems within density functional theory. A few test cases within second order Møller–Plesset framework are also reported. MTA is applied to some one-dimensional π-conjugated molecules, for which the difference between MTA energy and actual energy is found out to be less than 1 mhartree and also reduced computation time as well as hardware requirements. The method is also extended to some small/medium-sized two-dimensional π-conjugated molecules by developing a systematic algorithm for tailoring such systems. However, for such systems, although the energies are in error by a few millihartrees, gradients are found to match reasonably well their actual counterparts. Hence, geometry optimization of these systems within MTA framework is attempted. The geometries thus generated are found to be in good agreement with their actual counterparts, with the actual single point energies matching within 1 mhartree, along with reduced computational effort. These results point toward the potential applicability of MTA to large two- and three-dimensional π-conjugated systems.
Photodetection around 10 μm wavelength using s-p transitions in InAs/AlAs/AlGaAs self-assembled quantum dots
Authors: Nagashima Mitsuhiro , Kibe Michiya , Doshida Minoru , Uchiyama Yasuhito , Matsukura Yusuke , Nishino Hironori
Published: March 2010

We propose a quantum dot infrared photodetector (QDIP) having distinct sensitivity to mutually orthogonal in-plane polarized infrared radiation, and applicable to practical infrared (IR) imaging applications. Our QDIP has either an InAs/AlAs/AlGaAs or an AlAs/InAs/AlAs/AlGaAs structure in which extra-thin AlAs layers were introduced underneath the AlGaAs buffer layer to strongly confine the carriers and also to enhance the dot density before the Stranski–Krastanov mode growth of InAs quantum dots was carried out. At 80 K, the detector has high sensitivity to in-plane orthogonally polarized infrared light, and photocurrent responsivity peaks of up to 230 mA/W associated with distinct mutually orthogonal polar lights which were observed at a wavelength of around 10.0 μm.
High response deep ultraviolet organic photodetector with spectrum peak focused on 280 nm
Authors: Wu Shuang-hong , Li Wen-lian , Chu Bei , Lee C S , Su Zi-sheng , Wang Jun-bo , Yan Fei , Zhang Guang , Hu Zhi-zhi , Zhang Zhi-qiang
Published: March 2010

A high response organic deep ultraviolet (DUV) photodetector (PD) with 280 nm as the response spectrum peak was demonstrated. A maximum photoresponse of 309 mA/W under 280 nm UV illumination with an intensity of 0.428 mW/cm2 and a detectivity of 1×1012 cmHz1/2/W at −8 V were achieved, respectively. The optimized PD diode has a structure of ITO/m-MTDATA (10 nm)/m-MTDATA:Bphen(1:1, 60 nm)/Bphen (10 nm)/Cs2CO3: Bphen (30 wt %,10 nm)/Al(12 nm)/TPD(40 nm). Under 280 nm constant and shuttered illumination conditions with an intensity of 0.18 mW/cm2 the operational time is longer than 440 min when its response respectively decreases to 50% and 83% of its original value. The realization of the DUV detection is attributed to the stronger absorption of shorter UV wavelengths of Bphen acceptor and covering UV waveband longer than 300 nm by the TPD layer. The more detailed mechanism of harvesting the high PD performance is also discussed.
Communications: Short-range dynamics of a nematic liquid-crystalline phase
Authors: Poulos Andreas S. , Constantin Doru , Davidson Patrick , Pansu Brigitte , Freyssingeas Éric , Madsen Anders , Chanéac Corinne
Published: March 2010

Using x-ray photon correlation spectroscopy, we studied the dynamics in the nematic phase of a nanorod suspension. The collective diffusion coefficient in the plane perpendicular to the director varies sharply with the wave vector. Combining the structure factor and the diffusion coefficient, we find that the hydrodynamic function of the phase decreases by more than a factor of 10 when going from length scales comparable to the interparticle distance toward larger values. Thus, the collective dynamics of the nematic phase experiences strong and scale-dependent slowing down, in contrast with isotropic suspensions of slender rods or of spherical particles.
Mechanism of morphological transition in heteroepitaxial growth of metal films
Authors: Li Cui-Lian , Hu Chin-Kun
Published: March 2010

We investigate the mechanisms of three-dimensional (3D) to two-dimensional (2D) morphological transition in the heteroepitaxial growth of metal films by kinetic Monte Carlo simulations, and find that the difference between two types of neighbor interactions play an important role on the film morphology. The difference will vanishes with the film growing up. Just what the difference vanishes causes the morphological transition from 3D-cluster to 2D-island. Combined with elastic energy, we can predict which layer first occurs morphological transition. Our predicted results are consistent with the experiment reported by Su et al. [Phys. Rev. B 71, 073304 (2005)].