bluuebunny/crossref_metadata_2025 huggingface dataset:
Transmission electron microscopy study of aerosol particles from the brown hazes in northern China
Authors: Li Weijun , Shao Longyi
Published: May 2009

Airborne aerosol collections were performed in urban areas of Beijing that were affected by regional brown haze episodes over northern China from 31 May to 12 June 2007. Morphologies, elemental compositions, and mixing states of 810 individual aerosol particles of different sizes were obtained by transmission electron microscopy coupled with energy‐dispersive X‐ray spectrometry. The phases of some particles were verified using selected‐area electron diffraction. Aerosol particle types less than 10 μm in diameter include mineral, complex secondary (Ca‐S, K‐, and S‐rich), organic, soot, fly ash, and metal (Fe‐rich and Zn‐bearing). Most soot, fly ash, and organic particles are less than 2 μm in diameter. Approximately 84% of the analyzed mineral particles have diameters between 2 and 10 μm, while 81% of the analyzed complex secondary and metal particles are much smaller, from 0.1 to 2 μm. Trajectory analysis with fire maps show that southerly air masses arriving at Beijing have been transported through many agricultural biomass burning sites and heavy industrial areas. Spherical fly ash and Fe‐rich particles were from industrial emissions, and abundant K‐rich and organic particles likely originated from field burning of crop residues. Abundant Zn‐bearing particles are associated with industrial activities and local waste incinerators. On the basis of the detailed analysis of 443 analyzed aerosol particles, about 70% of these particles are internally mixed with two or more aerosol components from different sources. Most mineral particles are covered with visible coatings that contain N, O, Ca (or Mg), minor S, and Cl. K‐ and S‐rich particles tend to be coagulated with fly ash, soot, metal, and fine‐grained mineral particles. Organic materials internally mixed with K‐ and S‐rich particles can be their inclusions and coatings.
Remote sensing of cirrus cloud vertical size profile using MODIS data
Authors: Wang Xingjuan , Liou K. N. , Ou Steve S. C. , Mace G. G. , Deng M.
Published: May 2009

This paper describes an algorithm for inferring cirrus cloud top and cloud base effective particle sizes and cloud optical thickness from the Moderate Resolution Imaging Spectroradiometer (MODIS) 0.645, 1.64 and 2.13, and 3.75 μm band reflectances/radiances. This approach uses a successive minimization method based on a look‐up library of precomputed reflectances/radiances from an adding‐doubling radiative transfer program, subject to corrections for Rayleigh scattering at the 0.645 μm band, above‐cloud water vapor absorption, and 3.75 μm thermal emission. The algorithmic accuracy and limitation of the retrieval method were investigated by synthetic retrievals subject to the instrument noise and the perturbation of input parameters. The retrieval algorithm was applied to three MODIS cirrus scenes over the Atmospheric Radiation Measurement Program's southern Great Plain site, north central China, and northeast Asia. The reliability of retrieved cloud optical thicknesses and mean effective particle sizes was evaluated by comparison with MODIS cloud products and qualitatively good correlations were obtained for all three cases, indicating that the performance of the vertical sizing algorithm is comparable with the MODIS retrieval program. Retrieved cloud top and cloud base ice crystal effective sizes were also compared with those derived from the collocated ground‐based millimeter wavelength cloud radar for the first case and from the Cloud Profiling Radar onboard CloudSat for the other two cases. Differences between retrieved and radar‐derived cloud properties are discussed in light of assumptions made in the collocation process and limitations in radar remote sensing characteristics.
Antenna aperture size reduction using subbeam concept in multiple spot beam cellular satellite systems
Authors: Kilic Ozlem , Zaghloul Amir I.
Published: May 2009

Multiple beam configurations in satellite systems enable the reuse of frequency in beams separated by a sufficient distance to address bandwidth limitation issues. Phased array antennas can simultaneously produce a large number of spot beams directed toward specific areas and therefore are a natural platform for multiple‐beam satellite communications. This paper discusses a method to generate a large number of spot or cellular beams for multiple‐beam satellite systems using smaller apertures. The basic spot beam is divided into a number of smaller subbeams with lower crossover levels that operate within the same bandwidth as the spot beam. The frequency reuse configuration can be maintained, while the overall aperture size is reduced. The aperture reduction is shown to have little or no effect on the cochannel interference. The technique is applicable to all satellite orbits as well as high‐altitude platforms.
Tracer studies of sheet flow in the Florida Everglades
Authors: Ho David T. , Engel Victor C. , Variano Evan A. , Schmieder Paul J. , Condon Madison E.
Published: May 2009

Information on sheet flow patterns in the marsh ridge and slough habitat of the Florida Everglades is scarce, primarily because of difficulty in taking measurements across large enough spatial scales in such a heterogeneous environment. As part of the Everglades Tracer Release Experiment (EverTREx), two SF6 tracer releases were conducted to measure sheet flow in relatively intact ridge and slough habitats. The first was a pilot experiment that allowed the analytical equipment to be tested in the Everglades, and yielded some preliminary, coarse‐scale measurements of advection and dispersion in multiple sloughs. In the second experiment, higher‐resolution measurements of tracer distributions in a single slough showed that the mean advection ranged from 0.08 to 0.15 cm s−1, while longitudinal dispersion ranged from 3.7 × 102 to 2.6 × 103 cm2 s−1.
Estimating site amplification factors from ambient noise
Authors: Taylor Steven R. , Gerstoft Peter , Fehler Michael C.
Published: May 2009

We present a methodology to obtain frequency‐dependent relative site amplification factors using ambient seismic noise. We treat a seismic network or array as a forced damped harmonic oscillator system where each station responds to a forcing function obtained from frequency‐wavenumber beams of the ambient noise field. A network or array beam is necessary to estimate the forcing function. Taken over long time periods, each station responds to the forcing function showing a frequency‐dependent resonance peak whose amplitude and spectral width depends upon the elastic and anelastic properties of the underlying medium. Our results are encouraging in that hard rock sites show little variability and have narrower resonance peaks with reduced amplitudes relative to soft rock sites in sedimentary basins. There is much more variability observed at soft rock sites and a tendency for spectral peaks to shift to higher frequencies and become broader as the site amplification increases. This could be due to due to lower densities and/or small‐strain nonlinearity at stations having high site amplification.
Raman and electron microscopy analysis of carbon nanotubes exposed to high power laser irradiance
Authors: Ramadurai Krishna , Cromer Christopher L. , Dillon Anne C. , Mahajan Roop L. , Lehman John H.
Published: May 2009

High power laser radiometry requires efficient and damage-resistant detectors. The current study explores the evolving nature of carbon nanotube coatings for such detectors upon their exposure to incrementally increasing laser power levels. Electron microscopy images along with the D-band to G-band intensity ratios from the Raman spectra from eight irradiance levels are used to evaluate changes before and after the exposure. Electron microscopy images of the exposed multiwalled carbon nanotubes revealed the formation of intermittent pockets of moundlike structures at high power densities exceeding 11 kW/cm2. Raman spectroscopy measurements also demonstrated higher values for the ratio of the D-band intensity to that of the G-band, suggesting the possible transformation of nanotubes into structurally different forms of carbon. Exposure to a sample of single-walled nanotubes did not demonstrate the evolution of structural changes, which could be due in part to the higher irradiance levels relative to the damage threshold, employed in the experiment.
Scanning Hall probe microscopy of a diluted magnetic semiconductor
Authors: Kweon Seongsoo , Samarth Nitin , de Lozanne Alex
Published: May 2009

We have measured the micromagnetic properties of a diluted magnetic semiconductor as a function of temperature and applied field with a scanning Hall probe microscope built in our laboratory. The design philosophy for this microscope and some details are described. The samples analyzed in this work are Ga0.94Mn0.06As films grown by molecular beam epitaxy. We find that the magnetic domains are 2–4 μm wide and fairly stable with temperature. Magnetic clusters are observed above TC, which we ascribe to MnAs defects too small and sparse to be detected by a superconducting quantum interference device magnetometer.
N
,
N
′
-dimethylperylene-3,4,9,10-bis(dicarboximide) on alkali halide (001) surfaces
Authors: Fendrich Markus , Lange Manfred , Weiss Christian , Kunstmann Tobias , Möller Rolf
Published: May 2009

The growth of N,N′-dimethylperylene-3,4,9,10-bis(dicarboximide) (DiMe-PTCDI) on KBr(001) and NaCl(001) surfaces has been studied. Experimental results have been achieved using frequency modulation atomic force microscopy at room temperature under ultrahigh vacuum conditions. On both substrates, DiMe-PTCDI forms molecular wires with a width of 10nm, typically, and a length of up to 600nm at low coverages. All wires grow along either the [110] direction (or [11¯0] direction, respectively) of the alkali halide (001) substrates. There is no wetting layer of molecules: atomic resolution of the substrates can be achieved between the wires. The wires are mobile on KBr but substantially more stable on NaCl. A p(2×2) superstructure in a brickwall arrangement on the ionic crystal surfaces is proposed based on electrostatic considerations. Calculations and Monte Carlo simulations using empirical potentials reveal possible growth mechanisms for molecules within the first layer for both substrates, also showing a significantly higher binding energy for NaCl(001). For KBr, the p(2×2) superstructure is confirmed by the simulations; for NaCl, a less dense, incommensurate superstructure is predicted.
Deep defects in GaN/AlGaN/SiC heterostructures
Authors: Kindl D. , Hubík P. , Krištofik J. , Mareš J. J. , Výborný Z. , Leys M. R. , Boeykens S.
Published: May 2009

Deep level transient spectroscopy (DLTS) measurements were carried out on GaN/AlGaN/SiC heterostructures prepared by low-pressure metalorganic vapor phase epitaxy. Si-doped n-GaN layers were grown using an n-AlGaN nucleation layer (8% and 30% of aluminum) on two kinds of p-type 4H-SiC substrates. The DLTS spectra of on-axis (0001) grown samples exhibit a dominant peak of a majority carrier trap with apparent activation energy close to 0.80 eV and capture cross section of about 5×10−14 cm2 regardless of the AlGaN composition. The energy of this deep level decreases with increasing electrical field due to Poole–Frenkel effect. Carrier capture kinetics indicates interacting point defects arranged along a line, probably a threading dislocation. Two additional traps (0.52 and 0.83 eV) were found in on-axis samples with 8% AlGaN composition. For 30% Al content, only a 0.83 eV level was detected. Majority carrier trap with activation energy of 0.66 eV was observed in the off-axis grown samples. This level is probably related to an interface defect or to a defect lying near the heterojunction interface.
Quantitative compositional analysis and strain study of InAs quantum wires with InGaAlAs barrier layers
Authors: Cui K. , Robertson M. D. , Robinson B. J. , Andrei C. M. , Thompson D. A. , Botton G. A.
Published: May 2009

Quantitative compositional analysis of InAs quantum wires deposited between In0.53Ga0.37Al0.1As barrier layers grown on InP substrates was performed by electron energy loss spectrometry and energy dispersive x-ray spectrometry. An indium-rich region in the center of the wire, with decreasing indium concentration toward the interface with the barrier layers, was observed from indium concentration maps for individual quantum wires. “Stripelike” contrast modulation was observed in diffraction contrast transmission electron microscope images of the In0.53Ga0.37Al0.1As barrier layer immediately above the quantum wires. The contrast originated from indium compositional modulations in the upper barrier layer as confirmed by electron energy loss spectrometry and the modulation is attributed to the presence of an inhomogeneous elastic strain field generated by the buried quantum wires. These results suggest that quantitative analysis of the composition and strain distributions at very high spatial resolution provides insights necessary to further model the physical properties and to understand the growth of these nanostructures.
Local mapping of interface traps in HfSiO/Si structure by scanning capacitance microscopy using dV/dC signal
Authors: Kuge Shingo , Yoshida Haruhiko
Published: May 2009

Scanning capacitance microscopy (SCM) using a dV/dC signal has been proposed for local mapping of interface traps in an insulator/semiconductor structure. In conventional SCM measurements using a dC/dV signal, it is difficult to accurately analyze the spatial distribution of interface traps from the obtained SCM images because the dC/dV signal is inversely proportional to the interface trap density. In the proposed technique, however, the spatial distribution of the interface traps can be characterized using the dV/dC signal, which is directly proportional to the interface trap density. The effectiveness of the proposed technique has been demonstrated by characterizing the spatial distributions of the interface traps in HfSiO/Si structures before and after H2 annealing. The dV/dC images obtained reveal that the spatial variation in the interface trap density is reduced by H2 annealing. Consequently, SCM measurements using a dV/dC signal have been verified to effectively characterize the spatial distribution of interface traps.
Intermetallic ordering and structure in Fe–Pd alloy nanoparticles
Authors: Sato Kazuhisa , Wen J. G. , Zuo J. M.
Published: May 2009

We report an in situ study of epitaxial island formation and alloying of FePd nanoparticles using reflection high-energy electron diffraction (RHEED) followed by ex situ atomic structure characterization. We used aberration corrected (AC) scanning transmission electron microscopy (STEM) with a high-angle annular dark field (HAADF) detector for the study of chemical ordering. The FePd nanoparticles were formed by sequential deposition of Pd and Fe onto NaCl substrates, which was then followed by heating to high temperatures to promote chemical ordering during a short period of annealing. We show that the epitaxial island growth and subsequent alloying of Fe into Pd can be clearly detected by RHEED. The high resolution and the atomic number (Z) contrast of AC HAADF-STEM allow a clear observation of nanometer-sized local chemical order in very small nanoparticles. The results revealed complex chemical structures at an intermediate stage of the ordering process with ordered regions of both L10 and L12 phases.
Real space first-principles derived semiempirical pseudopotentials applied to tunneling magnetoresistance
Authors: Bevan K. H. , Low Tony , Guo H.
Published: May 2009

We present a real space density functional theory localized basis set semiempirical pseudopotential (SEP) approach. The method is applied to iron and magnesium oxide, where bulk SEP and local spin density approximation band structure calculations are shown to agree within approximately 0.1 eV. Subsequently we investigate the qualitative transferability of bulk derived SEPs to Fe/MgO/Fe tunnel junctions. We find that the SEP method is particularly well suited to address the tight binding transferability problem because the transferability error at the interface can be characterized not only in orbital space (via the interface local density of states) but also in real space (via the system potential). To achieve a quantitative parameterization, we introduce the notion of ghost SEPs extracted from the first-principles calculated Fe/MgO bonding interface. Such interface corrections are shown to be particularly necessary for barrier widths in the range of 1 nm, where interface states on opposite sides of the barrier couple effectively and play an important role in the transmission characteristics. In general the results underscore the need for separate tight binding interface and bulk parameter sets when modeling conduction through thin heterojunctions on the nanoscale.
Small polaron transport and colossal magnetoresistance in La2/3Ca1/3MnO3
Authors: Srivastava C. M. , Srivastava N. B. , Singh L. N. , Bahadur D.
Published: May 2009

Despite numerous attempts to explain the phenomenon of transport and magnetoresistance in manganites based on Jahn–Teller phonon coupling and double exchange mechanisms, satisfactory results could not be reached. The small polaron transport mechanism, based on the valence exchange arising from Madelung energy, is shown to account for the resistivity and magnetoresistance of the doped manganite La2/3Ca1/3MnO3 in the ferromagnetic range. The transport equation for the correlated polaron based on the Holstein Hamiltonian shows the well known transition from the low temperature band to the localized polaron hopping conductivity at high temperature in agreement with experiment. The present attempt is to demonstrate that the complexity of the problem that involves the interplay between the spin and charge order on one hand and itinerant and localized behavior on the other for a simple ferromagnetic metal system of manganites is best described by the correlated small polaron model leaving the more complicated systems for future studies.
High-Q, in-plane modes of nanomechanical resonators operated in air
Authors: Waggoner Philip S. , Tan Christine P. , Bellan Leon , Craighead Harold G.
Published: May 2009

Nanomechanical resonators have traditionally been limited to use in vacuum due to low quality factors that come as a result of viscous damping effects in air or liquid. We have fabricated arrays of 90 nm thick trampoline-shaped resonators, studied their resonant frequency spectrum as a function of pressure, and found that some high frequency modes exhibit quality factors over 2000 at atmospheric pressure. We have excited the in-plane resonances of these devices, verified their identities both experimentally and with finite element modeling, and demonstrated their advantageous characteristics for ambient sensing. Even after deposition of a relatively thick polymer layer, the in-plane resonant modes still boast quality factors on the order of 2000. These results show promise for the use of nanomechanical resonant sensors in real-time atmospheric sensing applications.
The short range anion-H interaction is the driving force for crystal formation of ions in water
Authors: Alejandre José , Chapela Gustavo A. , Bresme Fernando , Hansen Jean-Pierre
Published: May 2009

The crystal formation of NaCl in water is studied by extensive molecular dynamics simulations. Ionic solutions at room temperature and various concentrations are studied using the SPC/E and TIP4P/2005 water models and seven force fields of NaCl. Most force fields of pure NaCl fail to reproduce the experimental density of the crystal, and in solution some favor dissociation at saturated conditions, while others favor crystal formation at low concentration. A new force field of NaCl is proposed, which reproduces the experimental phase diagram in the solid, liquid, and vapor regions. This force field overestimates the solubility of NaCl in water at saturation conditions when used with standard Lorentz–Berthelot combining rules for the ion-water pair potentials. It is shown that precipitation of ions is driven by the short range interaction between Cl–H pairs, a term which is generally missing in the simulation of ionic solutions. The effects of intramolecular flexibility of water on the solubility of NaCl ions are analyzed and is found to be small compared to rigid models. A flexible water model, extending the rigid SPC/E, is proposed, which incorporates Lennard-Jones interactions centered on the hydrogen atoms. This force field gives liquid-vapor coexisting densities and surface tensions in better agreement with experimental data than the rigid SPC/E model. The Cl–H, Na–O, and Cl–O pair distribution functions of the rigid and flexible models agree well with experiment. The predicted concentration dependence of the electric conductivity is in fair agreement with available experimental data.
Microstructural effects on electrical conductivity relaxation in nanoscale ceria thin films
Authors: Tsuchiya Masaru , Bojarczuk Nestor A. , Guha Supratik , Ramanathan Shriram
Published: May 2009

Microstructure evolution and electrical conductivity relaxation kinetics in highly textured and nanocrystalline dense ceria thin films (∼65 nm) are reported in this paper. Highly textured films were grown on sapphire c-plane substrates by molecular beam synthesis (MBS) with orientation relationship (111)CeO2∥(0001)Al2O3 and [11¯0]CeO2∥[12¯10]Al2O3. No significant structural changes were observed in highly textured films even after extensive annealing at high temperature. In contrast to MBS grown films, ceria films grown by electron beam evaporation at room temperature had polycrystalline structure with ∼10 nm grains, which grew to ∼30 nm upon annealing at 1173 K. Grain growth kinetics was self-limiting and the out-of-plane orientation was found to be substrate dependent. From conductivity relaxation measurements, oxygen exchange rate in highly textured thin films was found to be much slower than that in polycrystalline films. The response time for highly textured films to changes in P(O2) from 1.07×10−12 to 5.43×10−10 Pa at 1148 K was 0.65 s, whereas that for polycrystalline films was 0.13 s under identical conditions. From temperature dependent experiments, activation energy for relaxation time was found to be similar, suggesting similar rate-limiting mechanisms in polycrystalline and highly textured films. The results highlight the importance of near-surface defects in controlling kinetics of oxygen incorporation into nanostructured oxides. In a broader context, the results maybe of relevance to designing catalytic surfaces in solid state ionic devices such as fuel cells.
Cold-target recoil-ion momentum spectroscopy for diagnostics of high harmonics of the extreme-ultraviolet free-electron laser light source at SPring-8
Authors: Liu X.-J. , Fukuzawa H. , Prümper G. , Okunishi M. , Shimada K. , Ueda K. , Motomura K. , Saito N. , Iwayama H. , Nagaya K. , Yao M. , Rudenko A. , Ullrich J. , Foucar L. , Czasch A. , Schmidt-Böcking H. , Dörner R. , Nagasono M. , Higashiya A. , Yabashi M. , Ishikawa T. , Ohashi H. , Kimura H.
Published: May 2009

We have developed a cold-target recoil-ion momentum spectroscopy apparatus dedicated to the experiments using the extreme-ultraviolet light pulses at the free-electron laser facility, SPring-8 Compact SASE Source test accelerator, in Japan and used it to measure spatial distributions of fundamental, second, and third harmonics at the end station.
Similarity reduction, nonlocal and master symmetries of sixth order Korteweg–deVries equation
Authors: Sahadevan R. , Nalinidevi L.
Published: May 2009

A systematic investigation to derive the Lie point symmetries, nonlocal and master symmetries of sixth order Korteweg–de Vries equation (KdV6) is presented. Using the obtained point symmetries, similarity reductions are derived and constructed their particular solutions wherever possible. It is shown that KdV6 admits infinitely many nonlocal and master symmetries. The existence of infinitely many master symmetries ensures that KdV6 is completely integrable.
Local structure anomaly around Ge dopants in Mn3Cu0.7Ge0.3N with negative thermal expansion
Authors: Matsuno J. , Takenaka K. , Takagi H. , Matsumura D. , Nishihata Y. , Mizuki J.
Published: May 2009

Local structure analysis of Cu and Ge atoms in the negative thermal expansion material Mn3Cu0.7Ge0.3N was conducted using x-ray absorption fine structure measurements. The temperature dependence of the interatomic distance was found to reflect the macroscopic negative thermal expansion both for Cu–Mn and Ge–Mn shells, although the magnitude of the relative change was much larger for Ge–Mn than Cu–Mn. An enhanced anomaly of the Debye–Waller factor was observed for the Ge–Mn shell in the temperature region of the negative expansion, indicating the presence of static local disorder around Ge impurities. These local structure anomalies strongly suggest that the local and inhomogeneous strain around Ge is essential in broadening the discontinuous volume contraction.
Intermediate valency of Eu in a cubic intermetallic compound Ce0.5Eu0.5Pd3
Authors: Pandey Abhishek , Mazumdar Chandan , Ranganathan R. , Reddy V. Raghavendra , Gupta Ajay
Published: May 2009

We report on a change in the valency of the Eu ions in cubic EuPd3 upon Ce substitution. The resultant compound Ce0.5Eu0.5Pd3 exhibits a mixed-valent state of Eu, where the valency differs from +3 observed in the case of EuPd3. This change in the valency also manifests in significant modifications of magnetic properties of Ce0.5Eu0.5Pd3 in comparison to that of EuPd3 and CePd3. In contrast to the usually observed expansion of the lattice accompanied with such valence transitions, our results suggest that the lattice volume in the present case remains essentially constant with respect to EuPd3.
Electroluminescent measurement of the internal quantum efficiency of light emitting diodes
Authors: Getty Amorette , Matioli Elison , Iza Michael , Weisbuch Claude , Speck James S.
Published: May 2009

An experimental method is demonstrated for the determination of internal quantum efficiency (IQE) in III-nitride-based light-emitting diodes (LEDs). LED devices surrounded with an optically absorbing material have been fabricated to limit collected light to photons emitted directly from the quantum wells across a known fraction of the recombination area. The emission pattern for this device configuration was modeled to estimate the extraction efficiency. IQE can then be calculated from the measured input current and output power. This method was applied to c-plane InxGa1−xN-based LEDs emitting at 445 nm. Initial measurements estimate an IQE of 43%±1% at a current density of 7.9 A/cm2.
Effect of O vacancies on the Young’s modulus of the BaCe1−xYxO3−δ perovskite
Authors: Cordero F. , Trequattrini F. , Deganello F. , La Parola V. , Roncari E. , Sanson A.
Published: May 2009

The effect of oxygen vacancies on the elastic properties of BaCe0.9Y0.1O3−δ is studied by measuring the complex Young’s modulus between 80 and 850 K varying the content of O vacancies from 0 to nearly 0.05. The Young’s modulus measured at a fixed temperature above 300 K may change by more than 20% but this is due to a shift of the rhombohedral-orthorhombic transition by 250 K and to proton and vacancy hopping. Below 100 K these effects are frozen and the filling of the O vacancies with OH ions increases the Young’s modulus by ∼1.3%.
dc superconducting quantum interference device based neodymium magnet displacement sensor for superfluid experiments
Authors: Sato Yuki , Packard Richard
Published: May 2009

A new displacement sensor that uses a rare-earth magnet attached to a flexible diaphragm is demonstrated for superfluid experiments. Its construction, calibration, and performance are described.
Size-dependent photocurrent of photodetectors with silicon nanocrystals
Authors: Kim Sang-Kyun , Kim Baek-Hyun , Cho Chang-Hee , Park Seong-Ju
Published: May 2009

We report on the effect of nanocrystal size on the photocurrent of silicon nanocrystal (Si NC) photodetectors. The photocurrent onset energy was increased with decreasing the size of Si NCs, which agreed with the blueshift in the absorption onset. The increase in the quantum efficiency with increasing the size of Si NCs was much larger than the increase in the absorbance with increasing the size of Si NCs. This was attributed to the differences in charge separation for Si NC of different sizes, which was influenced by the recombination rate and binding energy of photogenerated excitons in Si NCs.
Shape prediction of two-dimensional adatom islands on crystal surfaces during homoepitaxial growth
Authors: Yin Cong , Ning Xi-Jing , Zhuang Jun , Xie Yi-Qun , Gong Xiu-Fang , Ye Xiang-Xi , Ming Chen , Jin Yun-Fei
Published: May 2009

A dynamic model based on surface interaction potentials is established to predict the geometric structure of two-dimensional (2D) adatom islands on surfaces formed at temperatures for general epitaxial growth. The prediction based on the model is independent of the number of atoms in the island and can be implemented easily by ab initio calculations. Predictions of the homoepitaxial 2D islands on Pt(111), Ag(111), and Cu(111) surfaces are in good agreement with relevant experimental observations.
Electrical injection and detection of spin-polarized electrons in silicon through an Fe3Si/Si Schottky tunnel barrier
Authors: Ando Y. , Hamaya K. , Kasahara K. , Kishi Y. , Ueda K. , Sawano K. , Sadoh T. , Miyao M.
Published: May 2009

We demonstrate electrical injection and detection of spin-polarized electrons in silicon (Si) using epitaxially grown Fe3Si/Si Schottky-tunnel-barrier contacts. By an insertion of a δ-doped n+-Si layer (∼1019 cm−3) near the interface between a ferromagnetic Fe3Si contact and a Si channel (∼1015 cm−3), we achieve a marked enhancement in the tunnel conductance for reverse-bias characteristics of the Fe3Si/Si Schottky diodes. Using laterally fabricated four-probe geometries with the modified Fe3Si/Si contacts, we detect nonlocal output signals that originate from the spin accumulation in a Si channel at low temperatures.
Controlling magnetic switching properties of EuS for constructing double spin filter magnetic tunnel junctions
Authors: Miao Guo-Xing , Moodera Jagadeesh S.
Published: May 2009

EuS is a well established spin filter (SF) material and its magnetic properties are shown to be tunable with deposition temperature. In tunnel junctions consisting of double EuS SF barriers, different coercive fields of the two adjacent SFs are achieved by depositing one EuS layer at room temperature and quench condensing the other at liquid nitrogen temperature. A thin Al2O3 spacer layer is introduced in between to prevent direct magnetic coupling. Magnetoresistance with well defined spin-parallel and spin-antiparallel states is obtained this way, and the resistance change originates completely within the SF/I/SF composite tunnel barrier, with no ferromagnetic electrodes involved.
Deep ultraviolet emitting AlGaN quantum wells with high internal quantum efficiency
Authors: Bhattacharyya A. , Moustakas T. D. , Zhou Lin , Smith David. J. , Hug W.
Published: May 2009

We report the development of Al0.7Ga0.3N/AlN quantum wells with high internal quantum efficiency. All samples had identical well and barrier thickness but the III/V flux ratio was varied during growth by increasing the Ga flux. The luminescence spectra show single peaks which vary from 220 nm (III/V∼1) to 250 nm (III/V⪢1) with internal quantum efficiency varying from 5% to 50%, respectively. To account for these results, a growth model was proposed in which at III/V∼1 the growth proceeds via vapor phase epitaxy, while at III/V⪢1 the growth proceeds via liquid phase epitaxy.
First-principles investigation of the electron spin resonance parameters of germanium interfacial dangling bond centers
Authors: Sankaran K. , Pourtois G. , Houssa M. , Stesmans A. , Caymax M. , Heyns M. M.
Published: May 2009

First-principles simulations have been used to investigate the electron spin resonance g-factors of Ge Pb0 and Pb1 dangling-bond centers of germanium rich SixGe(1−x)On alloys. The computed values and the relative orientation of the dangling bond orbital have been compared to experimental results, allowing for the identification of a Ge Pb1 type center at (100)SixGe(1−x)/SiO2 interfaces.
The flowering hormone florigen functions as a general systemic regulator of growth and termination
Authors: Shalit Akiva , Rozman Alexander , Goldshmidt Alexander , Alvarez John P. , Bowman John L. , Eshed Yuval , Lifschitz Eliezer
Published: May 2009

The florigen paradigm implies a universal flowering-inducing hormone that is common to all flowering plants. Recent work identified
FT
orthologues as originators of florigen and their polypeptides as the likely systemic agent. However, the developmental processes targeted by florigen remained unknown. Here we identify local balances between SINGLE FLOWER TRUSS (SFT), the tomato precursor of florigen, and SELF-PRUNING (SP), a potent SFT-dependent SFT inhibitor as prime targets of mobile florigen. The graft-transmissible impacts of florigen on organ-specific traits in perennial tomato show that in addition to import by shoot apical meristems, florigen is imported by organs in which
SFT
is already expressed. By modulating local SFT/SP balances, florigen confers differential flowering responses of primary and secondary apical meristems, regulates the reiterative growth and termination cycles typical of perennial plants, accelerates leaf maturation, and influences the complexity of compound leaves, the growth of stems and the formation of abscission zones. Florigen is thus established as a plant protein functioning as a general growth hormone. Developmental interactions and a phylogenetic analysis suggest that the SFT/SP regulatory hierarchy is a recent evolutionary innovation unique to flowering plants.
Segregating the core computational faculty of human language from working memory
Authors: Makuuchi Michiru , Bahlmann Jörg , Anwander Alfred , Friederici Angela D.
Published: May 2009

In contrast to simple structures in animal vocal behavior, hierarchical structures such as center-embedded sentences manifest the core computational faculty of human language. Previous artificial grammar learning studies found that the left pars opercularis (LPO) subserves the processing of hierarchical structures. However, it is not clear whether this area is activated by the structural complexity per se or by the increased memory load entailed in processing hierarchical structures. To dissociate the effect of structural complexity from the effect of memory cost, we conducted a functional magnetic resonance imaging study of German sentence processing with a 2-way factorial design tapping structural complexity (with/without hierarchical structure, i.e., center-embedding of clauses) and working memory load (long/short distance between syntactically dependent elements; i.e., subject nouns and their respective verbs). Functional imaging data revealed that the processes for structure and memory operate separately but co-operatively in the left inferior frontal gyrus; activities in the LPO increased as a function of structural complexity, whereas activities in the left inferior frontal sulcus (LIFS) were modulated by the distance over which the syntactic information had to be transferred. Diffusion tensor imaging showed that these 2 regions were interconnected through white matter fibers. Moreover, functional coupling between the 2 regions was found to increase during the processing of complex, hierarchically structured sentences. These results suggest a neuroanatomical segregation of syntax-related aspects represented in the LPO from memory-related aspects reflected in the LIFS, which are, however, highly interconnected functionally and anatomically.
Chemical signals associated with life inhibit necrophoresis in Argentine ants
Authors: Choe Dong-Hwan , Millar Jocelyn G. , Rust Michael K.
Published: May 2009

One of the most conspicuous and stereotyped activities of social insects such as ants and honey bees is necrophoresis, the removal of dead colony members from the nest. Previous researchers suggested that decomposition products such as fatty acids trigger necrophoric behavior by ant workers. However, fatty acids elicit both foraging and necrophoric responses, depending on the current nest activities (e.g., feeding or nest maintenance). Furthermore, workers often carry even freshly killed workers (dead for <1 h) to refuse piles before significant decomposition has a chance to occur. Here, we show that the cuticular chemistry of Argentine ant workers,
Linepithema humile
, undergoes rapid changes after death. When the workers are alive or freshly killed, relatively large amounts of 2 characteristic ant-produced compounds, dolichodial and iridomyrmecin, are present on the ants' cuticle. However, these compounds disappear from the cuticle within about 1 h after death. We demonstrate how this phenomenon supports an alternative mechanism of ant necrophoresis in which the precise recognition and rapid removal of dead nestmates are elicited by the disappearance of these chemical signals associated with life.
Language regions of brain are operative in color perception
Authors: Ting Siok Wai , Kay Paul , Wang William S. Y. , Chan Alice H. D. , Chen Lin , Luke Kang-Kwong , Hai Tan Li
Published: May 2009

The effect of language on the categorical perception of color is stronger for stimuli in the right visual field (RVF) than in the left visual field, but the neural correlates of the behavioral RVF advantage are unknown. Here we present brain activation maps revealing how language is differentially engaged in the discrimination of colored stimuli presented in either visual hemifield. In a rapid, event-related functional MRI study, we measured subjects' brain activity while they performed a visual search task. Compared with colors from the same lexical category, discrimination of colors from different linguistic categories provoked stronger and faster responses in the left hemisphere language regions, particularly when the colors were presented in the RVF. In addition, activation of visual areas 2/3, responsible for color perception, was much stronger for RVF stimuli from different linguistic categories than for stimuli from the same linguistic category. Notably, the enhanced activity of visual areas 2/3 coincided with the enhanced activity of the left posterior temporoparietal language region, suggesting that this language region may serve as a top-down control source that modulates the activation of the visual cortex. These findings shed light on the brain mechanisms that underlie the hemifield- dependent effect of language on visual perception.
Role of breast regression protein 39 (BRP-39)/chitinase 3-like-1 in Th2 and IL-13–induced tissue responses and apoptosis
Authors: Lee Chun Geun , Hartl Dominik , Lee Gap Ryol , Koller Barbara , Matsuura Hiroshi , Da Silva Carla A. , Sohn Myung Hyun , Cohn Lauren , Homer Robert J. , Kozhich Alexander A. , Humbles Alison , Kearley Jennifer , Coyle Anthony , Chupp Geoffrey , Reed Jennifer , Flavell Richard A. , Elias Jack A.
Published: May 2009

Mouse breast regression protein 39 (BRP-39; Chi3l1) and its human homologue YKL-40 are chitinase-like proteins that lack chitinase activity. Although YKL-40 is expressed in exaggerated quantities and correlates with disease activity in asthma and many other disorders, the biological properties of BRP-39/YKL-40 have only been rudimentarily defined. We describe the generation and characterization of BRP-39−/− mice, YKL-40 transgenic mice, and mice that lack BRP-39 and produce YKL-40 only in their pulmonary epithelium. Studies of these mice demonstrated that BRP-39−/− animals have markedly diminished antigen-induced Th2 responses and that epithelial YKL-40 rescues the Th2 responses in these animals. The ability of interleukin13 to induce tissue inflammation and fibrosis was also markedly diminished in the absence of BRP-39. Mechanistic investigations demonstrated that BRP-39 and YKL-40 play an essential role in antigen sensitization and immunoglobulin E induction, stimulate dendritic cell accumulation and activation, and induce alternative macrophage activation. These proteins also inhibit inflammatory cell apoptosis/cell death while inhibiting Fas expression, activating protein kinase B/AKT, and inducing Faim 3. These studies establish novel regulatory roles for BRP-39/YKL-40 in the initiation and effector phases of Th2 inflammation and remodeling and suggest that these proteins are therapeutic targets in Th2- and macrophage-mediated disorders.
A 220-nucleotide deletion of the intronic enhancer reveals an epigenetic hierarchy in immunoglobulin heavy chain locus activation
Authors: Chakraborty Tirtha , Perlot Thomas , Subrahmanyam Ramesh , Jani Anant , Goff Peter H. , Zhang Yu , Ivanova Irina , Alt Frederick W. , Sen Ranjan
Published: May 2009

A tissue-specific transcriptional enhancer, Eμ, has been implicated in developmentally regulated recombination and transcription of the immunoglobulin heavy chain (IgH) gene locus. We demonstrate that deleting 220 nucleotides that constitute the core Eμ results in partially active locus, characterized by reduced histone acetylation, chromatin remodeling, transcription, and recombination, whereas other hallmarks of tissue-specific locus activation, such as loss of H3K9 dimethylation or gain of H3K4 dimethylation, are less affected. These observations define Eμ-independent and Eμ-dependent phases of locus activation that reveal an unappreciated epigenetic hierarchy in tissue-specific gene expression.
Identification and characterization of IL-10/IFN-γ–producing effector-like T cells with regulatory function in human blood
Authors: Häringer Barbara , Lozza Laura , Steckel Bodo , Geginat Jens
Published: May 2009

Two subsets of natural and adaptive regulatory T (T reg) cells have been described, but the identity of adaptive type 1 regulatory (Tr1)–like cells in humans is unclear. We analyzed a subset of human blood CD4+ T cells—CD45RA−CD25−interleukin (IL)-7 receptor (R)− cells—that rapidly secreted high levels of IL-10 together with interferon γ, but produced little IL-2. These IL-7R− T cells were rare, anergic, and largely Foxp3−. They expressed low levels of Bcl-2 but high levels of Ki-67 and ICOS, suggesting that they have been recently activated in vivo. Consistently, they responded selectively to persistent foreign and self-antigens under steady-state conditions. Unlike natural CD25+ T reg cells, IL-7R− cells suppressed naive and memory T cell proliferation in an IL-10–dependent fashion, and they required strong T cell receptor stimulation for suppression. To our knowledge, this is the first report that identifies Tr1-like cells in human blood. These IL-10–secreting cells have characteristics of chronically activated Th1 effector cells and are distinct from CD25+ T reg cells.
Ikaros controls isotype selection during immunoglobulin class switch recombination
Authors: Sellars MacLean , Reina-San-Martin Bernardo , Kastner Philippe , Chan Susan
Published: May 2009

Class switch recombination (CSR) allows the humoral immune response to exploit different effector pathways through specific secondary antibody isotypes. However, the molecular mechanisms and factors that control immunoglobulin (Ig) isotype choice for CSR are unclear. We report that deficiency for the Ikaros transcription factor results in increased and ectopic CSR to IgG2b and IgG2a, and reduced CSR to all other isotypes, regardless of stimulation. Ikaros suppresses active chromatin marks, transcription, and activation-induced cytidine deaminase (AID) accessibility at the γ2b and γ2a genes to inhibit class switching to these isotypes. Further, Ikaros directly regulates isotype gene transcription as it directly binds the Igh 3′ enhancer and interacts with isotype gene promoters. Finally, Ikaros-mediated repression of γ2b and γ2a transcription promotes switching to other isotype genes by allowing them to compete for AID-mediated recombination at the single-cell level. Thus, our results reveal transcriptional competition between constant region genes in individual cells to be a critical and general mechanism for isotype specification during CSR. We show that Ikaros is a master regulator of this competition.
Neutropenia with impaired host defense against microbial infection in mice lacking androgen receptor
Authors: Chuang Kuang-Hsiang , Altuwaijri Saleh , Li Gonghui , Lai Jiann-Jyh , Chu Chin-Yi , Lai Kuo-Pao , Lin Hung-Yun , Hsu Jong-Wei , Keng Peter , Wu Ming-Chi , Chang Chawnshang
Published: May 2009

Neutrophils, the major phagocytes that form the first line of cell-mediated defense against microbial infection, are produced in the bone marrow and released into the circulation in response to granulocyte-colony stimulating factor (G-CSF). Here, we report that androgen receptor knockout (ARKO) mice are neutropenic and susceptible to acute bacterial infection, whereas castration only results in moderate neutrophil reduction in mice and humans. Androgen supplement can restore neutrophil counts via stabilizing AR in castrated mice, but not in ARKO and testicular feminization mutant (Tfm) mice. Our results show that deletion of the AR gene does not influence myeloid lineage commitment, but significantly reduces the proliferative activity of neutrophil precursors and retards neutrophil maturation. CXCR2-dependent migration is also decreased in ARKO neutrophils as compared with wild-type controls. G-CSF is unable to delay apoptosis in ARKO neutrophils, and ARKO mice show a poor granulopoietic response to exogenous G-CSF injection. In addition, AR can restore G-CSF–dependent granulocytic differentiation upon transduction into ARKO progenitors. We further found that AR augments G-CSF signaling by activating extracellular signal-regulated kinase 1/2 and also by sustaining Stat3 activity via diminishing the inhibitory binding of PIAS3 to Stat3. Collectively, our findings demonstrate an essential role for AR in granulopoiesis and host defense against microbial infection.
Low-dose rectal inoculation of rhesus macaques by SIVsmE660 or SIVmac251 recapitulates human mucosal infection by HIV-1
Authors: Keele Brandon F. , Li Hui , Learn Gerald H. , Hraber Peter , Giorgi Elena E. , Grayson Truman , Sun Chuanxi , Chen Yalu , Yeh Wendy W. , Letvin Norman L. , Mascola John R. , Nabel Gary J. , Haynes Barton F. , Bhattacharya Tanmoy , Perelson Alan S. , Korber Bette T. , Hahn Beatrice H. , Shaw George M.
Published: May 2009

We recently developed a novel strategy to identify transmitted HIV-1 genomes in acutely infected humans using single-genome amplification and a model of random virus evolution. Here, we used this approach to determine the molecular features of simian immunodeficiency virus (SIV) transmission in 18 experimentally infected Indian rhesus macaques. Animals were inoculated intrarectally (i.r.) or intravenously (i.v.) with stocks of SIVmac251 or SIVsmE660 that exhibited sequence diversity typical of early-chronic HIV-1 infection. 987 full-length SIV env sequences (median of 48 per animal) were determined from plasma virion RNA 1–5 wk after infection. i.r. inoculation was followed by productive infection by one or a few viruses (median 1; range 1–5) that diversified randomly with near starlike phylogeny and a Poisson distribution of mutations. Consensus viral sequences from ramp-up and peak viremia were identical to viruses found in the inocula or differed from them by only one or a few nucleotides, providing direct evidence that early plasma viral sequences coalesce to transmitted/founder viruses. i.v. infection was >2,000-fold more efficient than i.r. infection, and viruses transmitted by either route represented the full genetic spectra of the inocula. These findings identify key similarities in mucosal transmission and early diversification between SIV and HIV-1, and thus validate the SIV–macaque mucosal infection model for HIV-1 vaccine and microbicide research.