bluuebunny/crossref_metadata_2025 huggingface dataset:
Vertical stratification of oribatid (Acari: Oribatida) communities in relation to their morphological and life‐history traits and tree structures in a subtropical forest in Japan
Authors: Karasawa Shigenori , Hijii Naoki
Published: February 2007

To clarify the effect of tree structure on the diversity of oribatid mites (Acari: Oribatida), we collected a total of 16,325 oribatids in 181 morphospecies from the leaves, branches, and trunk bark of trees and from the forest‐floor soil and litter in a subtropical forest, Okinawa, Japan, and tested three predictions: (1) moisture stress in arboreal habitats would lead to larger body size (not supported); (2) morphological traits related to gripping a surface (number and size of claws) would be more developed in arboreal species (supported); and (3) advantages in colonization (no cost for searching mates and doubled population growth) would favor parthenogenesis in the arboreal oribatid communities (not supported). We observed vertical stratification among the five habitats in terms of mite density, species diversity, and species composition, but found no difference in the body length of oribatid species between the arboreal and forest‐floor habitats. However, (homo‐)tridactylous species predominated in the arboreal habitat, suggesting that this claw morphology facilitates adherence to and movement on arboreal substrates. Sexual species were common in the arboreal oribatid communities, whereas about half of the dominant species collected from the forest floor were likely to be parthenogenetic. It is unclear how these different reproductive systems may be advantageous for oribatid mites in arboreal and forest‐floor habitats. Nevertheless, the structural complexity provided by trees appears to enhance and maintain the diversity of oribatid communities through vertical stratification in this subtropical forest.
Oral secretions from herbivorous lepidopteran larvae exhibit ion channel‐forming activities
Authors: Maischak Heiko , Grigoriev Pavel A. , Vogel Heiko , Boland Wilhelm , Mithöfer Axel
Published: February 2007

Feeding insects introduce oral secretions (OS) into the wounded tissue of the attacked plant. Various OS‐derived molecules must be involved in subsequent processes including the induction of plant defence reactions. Using the planar lipid bilayer membrane technique, isolated OS were analyzed with respect to their membrane activities. Transmembrane ion fluxes were generated by OS of eight different lepidopteran larvae, all of which form comparable ion channels in artificial membranes. Currents were characterized by long lasting open times and conductivities from 250 pS up to 1100 pS. Channels formed by Spodoptera exigua secretions showed a preference for cations over anions. OS also induced a transient increase of the cytosolic calcium concentration in soybean cells, determined by the aequorin technique. Known compounds of the OS, fatty‐acid–glutamine conjugates, also interfered with the membrane but were unable to form stable channels. Since ion fluxes and depolarization are early responses upon insect feeding, OS‐derived components may be involved in the elicitation process by direct interaction with the plant membranes.
A field investigation of phreatophyte‐induced fluctuations in the water table
Authors: Butler James J. , Kluitenberg Gerard J. , Whittemore Donald O. , Loheide Steven P. , Jin Wei , Billinger Mark A. , Zhan Xiaoyong
Published: February 2007

Hydrographs from shallow wells in vegetated riparian zones frequently display a distinctive pattern of diurnal water table fluctuations produced by variations in plant water use. A multisite investigation assessed the major controls on these fluctuations and the ecohydrologic insights that can be gleaned from them. Spatial and temporal variations in the amplitude of the fluctuations are primarily a function of variations in (1) the meteorological drivers of plant water use, (2) vegetation density, type, and vitality, and (3) the specific yield of sediments in the vicinity of the water table. Past hydrologic conditions experienced by the riparian zone vegetation, either in previous years or earlier within the same growing season, are also an important control. Diurnal water table fluctuations can be considered a diagnostic indicator of groundwater consumption by phreatophytes at most sites, so the information embedded within these fluctuations should be more widely exploited in ecohydrologic studies.
Large increase of NO2 in the north polar mesosphere in January–February 2004: Evidence of a dynamical origin from GOMOS/ENVISAT and SABER/TIMED data
Authors: Hauchecorne Alain , Bertaux Jean‐Loup , Dalaudier Francis , Russell James M. , Mlynczak Martin G. , Kyrölä Erkki , Fussen Didier
Published: February 2007

Odd nitrogen species play an important role in the stratospheric ozone balance through catalytic ozone destruction. A layer of strongly enhanced NO2 was detected in the north polar mesosphere by the GOMOS/ENVISAT stellar spectrometer in mid‐January 2004. Large NO2 enhancements in the polar winter mesosphere have been previously reported by several authors and have been attributed to NO production by solar proton or by energetic electron precipitations. The simultaneous occurrence of an intense mesospheric warming observed by the SABER/TIMED instrument indicates that a strong air descent occurred in the polar region, transporting a large quantity of NO from the upper mesosphere‐lower thermosphere to the lower mesosphere. The proposed mechanism may have a significant contribution to the budget of polar stratospheric ozone.
Global spatial deconvolution of Lunar Prospector Th abundances
Authors: Lawrence D. J. , Puetter R. C. , Elphic R. C. , Feldman W. C. , Hagerty J. J. , Prettyman T. H. , Spudis P. D.
Published: February 2007

We have completed the first global spatial deconvolution analysis of planetary gamma‐ray data for lunar Th abundances as measured by the Lunar Prospector Gamma‐ray Spectrometer. We tested two different spatial deconvolution techniques – Jansson's method and the Pixon method – and determined that the Pixon method provides superior performance. The final deconvolved map results in a spatial resolution improvement of a factor of 1.5–2. The newly deconvolved data allow us to clearly delineate nearside Th enhancements and depressions, validate enhanced Th abundances associated with specific lunar red spots, and reveal new details of the Th distribution at the Aristarchus plateau.
Sensitivity of pan‐Arctic terrestrial net primary productivity simulations to daily surface meteorology from NCEP‐NCAR and ERA‐40 reanalyses
Authors: Zhang Ke , Kimball John S. , Zhao Maosheng , Oechel Walter C. , Cassano John , Running Steven W.
Published: February 2007

We applied a terrestrial net primary production (NPP) model driven by satellite remote sensing observations of vegetation properties and daily surface meteorology from the 45‐year ECMWF Re‐Analysis (ERA‐40) and the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP‐NCAR) reanalysis (NNR) to assess NPP spatial and temporal variability for the pan‐Arctic basin and Alaska from 1982 to 2000. Sensitivity analysis of the production efficiency model (PEM) to uncertainties in surface meteorological inputs indicate that ERA‐40 solar radiation and NNR solar radiation and surface temperatures are the primary sources of PEM‐based NPP uncertainty for the region. Considerable positive bias in solar radiation inputs relative to surface observation networks resulted in overprediction of annual NPP by approximately 35.2 and 61.6% using ERA‐40 and NNR inputs, respectively. Despite these uncertainties, both reanalysis products captured the major annual anomalies and trends in surface meteorology for the domain. The two reanalysis products also produced similar NPP spatial patterns for 74.7% of the domain, and similar annual anomalies and temporal trends, though there were significant regional differences particularly for Eurasia. A simple correction method based on a sensitivity experiment between reanalysis and surface station meteorological measurements produced generally consistent NPP results that were considerably smaller than PEM simulations derived from uncorrected reanalysis drivers. The results of this study identify major sources of uncertainty in reanalysis‐based surface meteorology, and associated impacts on regional NPP simulations of the northern high latitudes.
Numerical computation of orbits and rigorous verification of existence of snapback repellers
Authors: Peng Chen-Chang
Published: February 2007

In this paper we show how analysis from numerical computation of orbits can be applied to prove the existence of snapback repellers in discrete dynamical systems. That is, we present a computer-assisted method to prove the existence of a snapback repeller of a specific map. The existence of a snapback repeller of a dynamical system implies that it has chaotic behavior [F. R. Marotto, J. Math. Anal. Appl. 63, 199 (1978)]. The method is applied to the logistic map and the discrete predator-prey system.
Quantum-classical description of the amide I vibrational spectrum of trialanine
Authors: Gorbunov Roman D. , Nguyen Phuong H. , Kobus Maja , Stock Gerhard
Published: February 2007

A quantum-classical description of the amide I vibrational spectrum of trialanine cation in D2O is given that combines (i) a classical molecular dynamics simulation of the conformational distribution of the system, (ii) comprehensive density functional theory calculations of the conformation-dependent and solvent-induced frequency fluctuations, and (iii) a semiclassical description of the vibrational line shapes which includes nonadiabatic transitions between vibrational eigenstates. Various assumptions that are usually employed in the calculation of condensed-phase vibrational spectra are tested, including the adiabatic, the Franck-Condon, and the second-order cumulant approximations, respectively. All three parts of the theoretical formulation are shown to have a significant impact on the simulated spectrum, suggesting that the interpretation of peptide amide I spectra may require substantial theoretical support.
Efficient implementation of three-dimensional reference interaction site model self-consistent-field method: Application to solvatochromic shift calculations
Authors: Minezawa Noriyuki , Kato Shigeki
Published: February 2007

The authors present an implementation of the three-dimensional reference interaction site model self-consistent-field (3D-RISM-SCF) method. First, they introduce a robust and efficient algorithm for solving the 3D-RISM equation. The algorithm is a hybrid of the Newton-Raphson and Picard methods. The Jacobian matrix is analytically expressed in a computationally useful form. Second, they discuss the solute-solvent electrostatic interaction. For the solute to solvent route, the electrostatic potential (ESP) map on a 3D grid is constructed directly from the electron density. The charge fitting procedure is not required to determine the ESP. For the solvent to solute route, the ESP acting on the solute molecule is derived from the solvent charge distribution obtained by solving the 3D-RISM equation. Matrix elements of the solute-solvent interaction are evaluated by the direct numerical integration. A remarkable reduction in the computational time is observed in both routes. Finally, the authors implement the first derivatives of the free energy with respect to the solute nuclear coordinates. They apply the present method to “solute” water and formaldehyde in aqueous solvent using the simple point charge model, and the results are compared with those from other methods: the six-dimensional molecular Ornstein-Zernike SCF, the one-dimensional site-site RISM-SCF, and the polarizable continuum model. The authors also calculate the solvatochromic shifts of acetone, benzonitrile, and nitrobenzene using the present method and compare them with the experimental and other theoretical results.
Surface amorphization in conductors by using skin effect: Model and experiment
Authors: Vinogradov A. , Lazarev S. G. , Mozgovoi A. L. , Gornostai-Polskii S. A. , Okumura R. , Hashimoto S.
Published: February 2007

An approach to amorphization and/or nanostructurization of a metal surface layer is proposed utilizing a skin effect induced by a high power electric pulse. Modeling electric and magnetic fields and heat transfer in a metallic cylinder predicts that melting followed by rapid quenching can occur in a thin skin layer if the amplitude of a passing electric pulse is high enough. The quenching rates can reach 108–109K∕s, giving rise to an opportunity of surface amorphization and spectacular surface structure modification in a wide range of metallic systems. Justifying the approach, a glassylike structure has been found experimentally in ordinary stainless steel subjected to the treatment proposed. Furthermore, specific ultradispersed structures containing nanocrystalline particles embedded into amorphous matrix or twin lamellar structures with nanodimensions can be produced in the subsurface layer.
Molecular frame and recoil frame photoelectron angular distributions from dissociative photoionization of NO2
Authors: Toffoli Daniele , Lucchese Robert R. , Lebech M. , Houver J. C. , Dowek D.
Published: February 2007

The authors report measured and computed molecular frame photoelectron angular distributions (MFPADs) and recoil frame photoelectron angular distributions (RFPADs) for the single photon ionization of the nonlinear molecule NO2 leading to the (1a2)−1bA23 and (4a1)−1A13 states of NO2+. Experimentally, the RFPADs were obtained using the vector correlation approach applied to the dissociative photoionization (DPI) involving these molecular ionic states. The polar and azimuthal angle dependences of the photoelectron angular distributions are measured relative to the reference frame provided by the ion recoil axis and direction of polarization of the linearly polarized light. Experimental results are reported for the photon excitation energies hν=14.4 and 22.0eV. Theoretically the authors give expressions for both the MFPAD and the RFPAD. They show that the functional form in the recoil frame, where an average over the azimuthal dependence of the molecular fragments about the recoil direction is made, is identical to that they have earlier found for the DPI experiments performed on linear molecules. MFPADs were then computed using single-center expansion techniques within the fixed-nuclei frozen-core Hartree-Fock approximation. The computed cross sections for ionization to the (1a2)−1bA23 state show a strong propensity for ionization with the polarization of the light perpendicular to the plane of the molecule, whereas the ionization to the (4a1)−1A13 state of the ion is of similar intensity for all orientations of the polarization of the light in the molecular frame. These qualitative features of the MFPAD are also evident in the RFPAD. The RFPAD for ionization leading to the (1a2)−1bA23 state is strongly peaked in the perpendicular orientation, whereas the RFPAD for ionization leading to the (4a2)−1A13 state is much more nearly isotropic. Comparison between experimental and theoretical RFPADs indicates that the recoil angle for NO+ fragments is ∼50° relative to the symmetry axis of the initial C2v symmetry of the NO2 molecule in the ionization leading to the (1a2)−1bA23 state and the recoil angle is ∼120° for the O+ fragment for ionization leading to the (4a1)−1A13 state.
Structural and multiferroic properties of La-modified BiFeO3 ceramics
Authors: Das S. R. , Choudhary R. N. P. , Bhattacharya P. , Katiyar R. S. , Dutta P. , Manivannan A. , Seehra M. S.
Published: February 2007

The coexistence of the magnetic and the electrical properties in lanthanum (La)-modified bismuth ferrite (Bi1−xLaxFeO3, x=0.05, 0.1, 0.15, and 0.2) ceramics was studied and compared with those of bismuth ferrite (BiFeO3). The presence of a small secondary phase of BiFeO3 (arises due to excess Bi2O3) was removed on La substitution at the Bi site, as observed in x-ray diffraction (XRD). The effect of La substitution on dielectric constant, loss tangent, and remnant polarization of the samples was studied in a wide range of temperature (77–400K) and frequency (1kHz–1MHz). The variation of magnetization, coercive field, and exchange bias with temperature (2–300K) and La concentration were investigated. These changes in the magnetic parameters with La doping along with those of the electron magnetic resonance parameters measured at 300K and 9.28GHz are understood in terms of increase in the magnetic anisotropy and magnetization. These results also show that stabilization of crystal structure and nonuniformity in spin cycloid structure by La substitution enhances the multiferroic properties of BiFeO3.
Ceramic liquid droplets stabilized in vacuum
Authors: Takahashi R. , Tsuruta Y. , Yonezawa Y. , Ohsawa T. , Koinuma H. , Matsumoto Y.
Published: February 2007

We have studied the ceramic liquid droplet of CuOx-added BiOx at high temperature in vacuum. CuOx always floated on the BiOx as a surfactant and suppressed the evaporation of volatile BiOx liquid droplets. A clear liquid behavior of the BiOx droplets was directly observed by in situ laser microscope, with numerous liquid droplets growing by the coalescences in accordance with Marangoni’s [Nuovo Cimento Ser. 2, 239 (1872)] effect involved with the precursor film. We have also found a unique absorption of CaO into the BiOx liquid droplets, based on which a reliable process has been established for an atomically flat surface of MgO(001). These results open a broad window of opportunity to tailor not only a chemical interaction on oxide surface but also a liquid droplet dynamics in vacuum.
Dynamics of electro-optical switching processes in surface stabilized biaxial nematic phase found in bent-core liquid crystal
Authors: Lee Ji-Hoon , Lim Tong-Kun , Kim Won-Taeck , Jin Jung-Il
Published: February 2007

The dynamics of electro-optical switching processes in the biaxial nematic phase of an oxadizole-based bent-core liquid crystal (LC) was studied. This LC exhibits optical biaxiality in the lower temperature range of the nematic phase although it exhibits optical uniaxiality in the higher temperature range. In particular, the short axis and the long axis of the LC were independently switched when an electric field was applied in the biaxial nematic phase. The switching time of the short axis was much faster than that of the long axis in response to the applied field as well as in relaxation.
1.84
μ
m
emission of Tm3+ sensitized by Yb3+ ions in monoclinic KGd(WO4)2 single crystals
Authors: Güell F. , Massons J. , Gavaldà Jna. , Pujol M. C. , Aguiló M. , Díaz F.
Published: February 2007

By exciting at 940nm, we have characterized the 1.84μm near infrared emission of trivalent thulium ions in Yb3+, Tm3+:KGd(WO4)2 single crystals as a function of the dopant concentration and temperature, from 10K to room temperature. An overall H63 Stark splitting of ∼470cm−1 for the Tm3+ ions in the Yb3+, Tm3+:KGd(WO4)2 was obtained. We also studied the blue emission at 476nm (Tm3+) and the near infrared emissions at 1.48μm (Tm3+) and 1μm (Yb3+) as a function of the dopant concentration. Experimental decay times of the G41, H43, and F43 (Tm3+) and F5∕22 (Yb3+) excited states have been measured as a function of Yb3+ and Tm3+ ion concentrations. For the F43→H63 transition of Tm3+ ions, we used the reciprocity method to calculate the maximum emission cross section of 3.07×10−20cm2 at 1.84μm for the polarization parallel to the Nm principal optical direction.
Space charge limited electron transport in AlGaN photoconductors
Authors: Lebedev V. , Cherkashinin G. , Ecke G. , Cimalla I. , Ambacher O.
Published: February 2007

Electrical properties and photoresponse of AlGaN based photodetectors were studied demonstrating an adverse effect of the broad-band trap distribution on the spectral, electrical, and time-response characteristics. It was found that n-type conduction mechanism is space charge limited indicating a strong carrier trapping effect. In particular, we show that dark current, photoresponsivity, and response time are determined by the slow-varying energy distribution of traps located above the equilibrium Fermi level. We demonstrate also that both the deep recombination centers and the localized shallow states do not impact the response time of the photodetector, and the persistent photocurrent effect is directly connected to the voltage-induced injection and trapping of the excess carriers.
Effects of barrier growth temperature ramp-up time on the photoluminescence of InGaN∕GaN quantum wells
Authors: Wang Y. , Pei X. J. , Xing Z. G. , Guo L. W. , Jia H. Q. , Chen H. , Zhou J. M.
Published: February 2007

The influence of ramp-up time of barrier growth temperature on optical properties is investigated for InGaN∕GaN quantum wells deposited on sapphire substrate by metal organic chemical vapor deposition. Three ramp-up times are used from the low and high growth temperatures for the well and barrier, respectively. The results indicate that increasing the ramp-up time leads to a blueshift of the photoluminescence (PL) peak position and a broadening of the PL emission linewidth. Similarly, “S-shaped” temperature dependences of the PL peak energy are observed in all the samples. However, very different temperature dependences of PL linewidth, such as the conventional shaped, “U-shaped,” and S-shaped, are observed in the samples with different ramp-up time. These effects are attributed to the redistribution of the In-rich clusters in the wells. Small quantum-dot-like In-rich clusters with high density are considered to be formed in the wells for the sample with a long ramp-up time, leading to the unconventional PL linewidth behavior and enhanced internal quantum efficiency.
Stochastic Liouville equation treatment of the electron paramagnetic resonance line shape of an S-state ion in solution
Authors: Borel Alain , Clarkson R. B. , Belford R. Linn
Published: February 2007

The current approaches used for the analysis of electron paramagnetic resonance spectra of Gd3+ complexes suffer from a number of drawbacks. Even the elaborate model of [Rast et al., J. Chem. Phys. 113, 8724 (2000)] where the electron spin relaxation is explained by the modulation of the zero-field splitting (ZFS), by molecular tumbling (the so called static contribution), and deformations (transient contribution), is only readily applicable within the validity range of the Redfield theory [Advances in Magnetic Resonance, edited by J.-S. Waugh (Academic, New York, 1965), Vol. 1, p. 1], that is, when the ZFS is small compared to the Zeeman energy and the rotational and vibrational modulations are fast compared to the relaxation time. Spin labels (nitroxides and transition metal complexes) have been studied for years in systems that violate these conditions. The theoretical framework commonly used in such studies is the stochastic Liouville equation (SLE). The authors shall show how the physical model of Rast et al. can be cast into the SLE formalism, paying special attention to the specific problems introduced by the [Uhlenbeck and Ornstein, Phys. Rev. 36, 823 (1930)] process used to model the transient ZFS. The resulting equations are very general and valid for arbitrary correlation times, magnetic field strength, electron spin S, or symmetry. The authors demonstrate the equivalence of the SLE approach with the Redfield approximation for two well-known Gd3+ complexes.
High-frequency electrical properties of individual and bundled carbon nanotubes
Authors: Plombon J. J. , O’Brien Kevin P. , Gstrein Florian , Dubin Valery M. , Jiao Yang
Published: February 2007

Bundles of single wall carbon nanotubes have been proposed as an interconnect that could potentially replace copper in state-of-the-art ultralarge-scale-integrated circuits if theoretically predicted inductance, resistance, and capacitance scale with the number of carbon nanotubes within the bundle. The authors report direct measurement of the kinetic inductance of individual single wall carbon nanotubes and measurement of the high-frequency impedance of bundles showing that the bundle inductance scales with the number of individual carbon nanotubes.
Midinfrared metamaterials fabricated by nanoimprint lithography
Authors: Wu Wei , Yu Zhaoning , Wang Shih-Yuan , Williams R. Stanley , Liu Yongmin , Sun Cheng , Zhang Xiang , Kim Evgenia , Shen Y. Ron , Fang Nicholas X.
Published: February 2007

A metamaterial comprising an ordered array of four metallic L-shaped components designed to operate in the mid-IR frequency regime has been fabricated and characterized. The fourfold rotational symmetry of the unit cell should suppress the undesirable bianisotropy observed for split-ring resonators. Nanoimprint lithography was used to demonstrate scalability for mass production. A dipole plasmon resonance with a negative permittivity and a magnetic resonance with a negative permeability were observed at wavelengths of 3.7 and 5.25μm, respectively, in agreement with theoretical predictions.
Comparative study of InAs quantum dots with different InGaAs capping methods
Authors: Lin C. H. , Pai Woei Wu , Chang F. Y. , Lin H. H.
Published: February 2007

The authors have used cross-sectional scanning tunneling microscopy to examine strain relaxation profiles of InAs quantum dots with In0.33Ga0.67As layers overgrown by three distinct capping methods. A statistical analysis of strain relaxation profile allowed them to infer that the long wavelength emission (>1.3μm) of InAs quantum dots capped with sequential GaAs∕InAs binary growth is mainly due to a weaker quantum confinement effect. This particular capping method is better than the traditional molecular beam epitaxy with simultaneous In∕Ga∕As deposition, and much better than a capping method with separated Ga deposition followed by As and InAs growth.
Effect of grain shape on the agglomeration of polycrystalline thin films
Authors: Bouville Mathieu
Published: February 2007

The shape of the grains can dramatically affect the agglomeration of polycrystalline thin films by grain-boundary grooving. Anisotropy plays a central role in the stability against agglomeration of faceted films. Even a small difference between the interface energies of the facets can destabilize faceted grains or, on the contrary, it can make them perfectly stable at any thickness.
Unusual carrier thermalization in a dilute GaAs1−xNx alloy
Authors: Tan P. H. , Xu Z. Y. , Luo X. D. , Ge W. K. , Zhang Y. , Mascarenhas A. , Xin H. P. , Tu C. W.
Published: February 2007

Photoluminescence (PL) properties of the E0, E0+Δ0, and E+ bands in an x=0.62% GaAs1−xNx alloy were investigated in detail, including their peak position, linewidth, and line shape dependences on the excitation energy, excitation power, and temperature, using micro-PL. The hot electrons within the E+ band are found to exhibit highly unusual thermalization, which results in a large blueshift in its PL peak energy by >2kBT, suggesting peculiar density of states and carrier dynamics of the E+ band.
Ambipolar conduction in transistors using solution grown InAs nanowires with Cd doping
Authors: Hang Qingling , Wang Fudong , Buhro William E. , Janes David B.
Published: February 2007

Nanowire field effect transistors have been fabricated using Cd doped InAs nanowires synthesized using a solution-liquid-solid technique. Both n-channel and p-channel characteristics have been observed, which implies that the surface Fermi level is not pinned in the conduction band. The observation of a p channel is attributed to the passivation of surface states by surface ligands introduced during nanowire synthesis and to the effects of heavy acceptor doping. Devices in which the surface ligands are removed by O2 plasma treatment exhibit only n-channel conduction, which would be consistent with surface Fermi level pinning in the conduction band.
Effect of surface energy on the yield strength of nanoporous materials
Authors: Zhang W. X. , Wang T. J.
Published: February 2007

The effect of surface energy on the yield strength of nanoporous materials is investigated in this letter. The conventional micromechanics method is extended to consider the surface effect and an analytical expression of the yield surface of nanoporous materials in a complex stress state is derived. It is seen that surface energy has obvious effect on the overall yield strength of nanoporous materials, and the smaller the nanosized void, the more significant the effect of surface energy. The yield strength of nanoporous materials is size dependent.
Strain-free GaN thick films grown on single crystalline ZnO buffer layer with in situ lift-off technique
Authors: Lee S. W. , Minegishi T. , Lee W. H. , Goto H. , Lee H. J. , Lee S. H. , Lee Hyo-Jong , Ha J. S. , Goto T. , Hanada T. , Cho M. W. , Yao T.
Published: February 2007

Strain-free freestanding GaN layers were prepared by in situ lift-off process using a ZnO buffer as a sacrificing layer. Thin Zn-polar ZnO layers were deposited on c-plane sapphire substrates, which was followed by the growth of Ga-polar GaN layers both by molecular beam epitaxy (MBE). The MBE-grown GaN layer acted as a protecting layer against decomposition of the ZnO layer and as a seeding layer for GaN growth. The ZnO layer was completely in situ etched off during growth of thick GaN layers at low temperature by hydride vapor phase epitaxy. Hence freestanding GaN layers were obtained for the consecutive growth of high-temperature GaN thick layers. The lattice constants of freestanding GaN agree with those of strain-free GaN bulk. Extensive microphotoluminescence study indicates that strain-free states extend throughout the high-temperature grown GaN layers.
Between Longing and Despair: State, Space, and Subjectivity in Turkey
Authors: Secor Anna J
Published: February 2007

This paper begins as an investigation of the spatiality of the state in Turkey. In everyday life the state is experienced and recognized through a multiplicity of sites, agents, institutions, techniques, and regulatory capacities. Given this fragmentation, I ask how it is that the state is conceptualized as having a reality beyond its incoherence. Through a discursive analysis of focus-group discussions with lower-class and lower-middle-class men and women in Istanbul, I trace the spatial–temporal techniques through which state power is enacted. I argue that this power operates through referral and deferral, circulation and arrest; it is the power both to set in motion and to suspend the circulation of people, documents, money, and influence that marks out the space–time of the state. Further, my reading of focus-group texts suggests that it is through the operation of the space–time of the state that individuals both submit to state power and become subjects of rights—that is, citizens. At once establishing the authority of the state and the self-recognition of the subject, the Althusserian turn towards the law is a gesture of conscience or guilt. However, I argue that not all subjects are equally guilty in their imagined relationship to the state, some are more guilty than others, and, in this inequality, difference enters into the process of subjection. Focus-group participants discuss how acts such as showing identity cards or performing labor function both to assert their innocence and to mark them as guilty. By tracing out how spatial techniques of power and processes of subjection are discussed among particular groups of people in Istanbul, I hope to speak in an alternative voice to the usual top-down narration of the Turkish ‘strong state’. Finally, this paper is an attempt to wrap an argument around the secret of the state, around the desire, despair, and guilt that infuse the relational production of citizen and state.
Geographies of Local Life: Marietta Pallis and Friends, Long Gores, Hickling, Norfolk
Authors: Matless David , Cameron Laura
Published: February 2007

This paper concerns a group of educated women of independent means and their relationship to a Norfolk village and its people in the early 20th and mid-20th century. The focal figure is Marietta Pallis (1882–1963), ecologist and artist, who rented and then owned the marshland property of Long Gores, Hickling. In this paper we consider Pallis and friends' engagement with land and its management, their relationship to the locality as residents and employers of servants, and their literary consideration of local culture in terms of architecture and dialect. We emphasise the currencies of the local informing their actions, and reactions to them, and the related geographies of private life. Pallis and friends' relationship to land, their relationship to people, and their commentary on local character and identity make sense through and foster geographies of local life.
X-ray fluorescence microscopy reveals large-scale relocalization and extracellular translocation of cellular copper during angiogenesis
Authors: Finney Lydia , Mandava Suneeta , Ursos Lyann , Zhang Wen , Rodi Diane , Vogt Stefan , Legnini Daniel , Maser Jorg , Ikpatt Francis , Olopade Olufunmilayo I. , Glesne David
Published: February 2007

Although copper has been reported to influence numerous proteins known to be important for angiogenesis, the enhanced sensitivity of this developmental process to copper bioavailability has remained an enigma, because copper metalloproteins are prevalent and essential throughout all cells. Recent developments in x-ray optics at third-generation synchrotron sources have provided a resource for highly sensitive visualization and quantitation of metalloproteins in biological samples. Here, we report the application of x-ray fluorescence microscopy (XFM) to
in vitro
models of angiogenesis and neurogenesis, revealing a surprisingly dramatic spatial relocalization specific to capillary formation of 80–90% of endogenous cellular copper stores from intracellular compartments to the tips of nascent endothelial cell filopodia and across the cell membrane. Although copper chelation had no effect on process formation, an almost complete ablation of network formation was observed. XFM of highly vascularized ductal carcinomas showed copper clustering in putative neoangiogenic areas. This use of XFM for the study of a dynamic developmental process not only sheds light on the copper requirement for endothelial tube formation but highlights the value of synchrotron-based facilities in biological research.
The 3D structure of a periplasm-spanning platform required for assembly of group 1 capsular polysaccharides in
Escherichia coli
Authors: Collins Richard F. , Beis Konstantinos , Dong Changjiang , Botting Catherine H. , McDonnell Catherine , Ford Robert C. , Clarke Bradley R. , Whitfield Chris , Naismith James H.
Published: February 2007

Capsular polysaccharides (CPSs) are essential virulence determinants of many pathogenic bacteria.
Escherichia coli
group 1 CPSs provide paradigms for widespread surface polysaccharide assembly systems in Gram-negative bacteria. In these systems, complex carbohydrate polymers must be exported across the periplasm and outer membrane to the cell surface. Group 1 CPS export requires oligomers of the outer membrane protein, Wza, for translocation across the outer membrane. Assembly also depends on Wzc, an inner membrane tyrosine autokinase known to regulate export and synthesis of group 1 CPS. Here, we provide a structural view of a complex comprising Wzc and Wza that spans the periplasm, connecting the inner and outer membranes. Examination of transmembrane sections of the complex suggests that the periplasm is compressed at the site of complex formation. An important feature of CPS production is the coupling of steps involved in biosynthesis and export. We propose that the Wza–Wzc complex provides the structural and regulatory core of a larger macromolecular machine. We suggest a mechanism by which CPS may move from the periplasm through the outer membrane.
A dominant mutation in
Snap25
causes impaired vesicle trafficking, sensorimotor gating, and ataxia in the blind-drunk mouse
Authors: Jeans Alexander F. , Oliver Peter L. , Johnson Reuben , Capogna Marco , Vikman Jenny , Molnár Zoltán , Babbs Arran , Partridge Christopher J. , Salehi Albert , Bengtsson Martin , Eliasson Lena , Rorsman Patrik , Davies Kay E.
Published: February 2007

The neuronal soluble
N
-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex is essential for synaptic vesicle exocytosis, but its study has been limited by the neonatal lethality of murine SNARE knockouts. Here, we describe a viable mouse line carrying a mutation in the b-isoform of neuronal SNARE synaptosomal-associated protein of 25 kDa (SNAP-25). The causative I67T missense mutation results in increased binding affinities within the SNARE complex, impaired exocytotic vesicle recycling and granule exocytosis in pancreatic β-cells, and a reduction in the amplitude of evoked cortical excitatory postsynaptic potentials. The mice also display ataxia and impaired sensorimotor gating, a phenotype which has been associated with psychiatric disorders in humans. These studies therefore provide insights into the role of the SNARE complex in both diabetes and psychiatric disease.
Targeted cell killing by reconstituted caspases
Authors: Chelur Dattananda S. , Chalfie Martin
Published: February 2007

We have developed a two-component system involving reconstituted caspase (recCaspase) for selective and/or conditional ablation of targeted cells. Caspases, the executioners of programmed cell death, are normally synthesized as inactive zymogens and are activated by proteolytic processing of their subunits. We show here, using two different caspases,
Caenorhabditis elegans
CED-3 and human Caspase-3, that coexpression of the subunits generates constitutively active caspase activity that leads to cell death. This recCaspase activity, however, occurred only when the subunits associated through binding of linked antiparallel leucine-zipper domains. We exploited the dual-component nature of recCaspases by expressing the individual subunits from combinations of promoters either to target selectively the subset of cells for apoptosis or induce cell death in specific cells at specific times during development. The high degree of target specificity and tight regulation of induction of recCaspase would be advantageous in creating animal models that are ablated for specific cells and in other targeted cell killings.
Restoring species-specific posttransfer editing activity to a synthetase with a defunct editing domain
Authors: SternJohn Julius , Hati Sanchita , Siliciano Paul G. , Musier-Forsyth Karin
Published: February 2007

Aminoacyl-tRNA synthetases are multidomain proteins responsible for the attachment of specific amino acids to their tRNA substrates. Prolyl-tRNA synthetases (ProRSs) are notable due to their particularly diverse architectures through evolution. For example,
Saccharomycese cerevisiae
ProRS possesses an N-terminal extension with weak homology to a bacterial-specific domain typically present as an insertion (INS) within the aminoacylation active site. The INS domain has been shown to contain a “posttransfer” editing active site responsible for cleaving the aminoacyl-ester bond of misacylated Ala-tRNA
Pro
species. However, wild-type
S. cerevisiae
ProRS does not perform posttransfer editing
in vitro
. Here, we show that replacement of the N-terminal domain of
S. cerevisiae
ProRS with the
Escherichia coli
INS domain confers posttransfer editing function to this chimeric enzyme, with specificity for yeast Ala-tRNA
Pro
. In contrast, the isolated INS domain displays only weak editing activity and lacks tRNA sequence specificity. These results emphasize the modular nature of synthetase editing active sites and demonstrate how in evolution, a weak editing activity can be converted to a more robust state through fusion to the body of a synthetase. In this manner, a single editing module can be distributed to different synthetases, and simultaneously acquire specificity and enhanced activity.
βIV spectrin is recruited to axon initial segments and nodes of Ranvier by ankyrinG
Authors: Yang Yang , Ogawa Yasuhiro , Hedstrom Kristian L. , Rasband Matthew N.
Published: February 2007

High densities of ion channels at axon initial segments (AISs) and nodes of Ranvier are required for initiation, propagation, and modulation of action potentials in axons. The organization of these membrane domains depends on a specialized cytoskeleton consisting of two submembranous cytoskeletal and scaffolding proteins, ankyrinG (ankG) and βIV spectrin. However, it is not known which of these proteins is the principal organizer, or if the mechanisms governing formation of the cytoskeleton at the AIS also apply to nodes. We identify a distinct protein domain in βIV spectrin required for its localization to the AIS, and show that this domain mediates βIV spectrin's interaction with ankG. Dominant-negative ankG disrupts βIV spectrin localization, but does not alter endogenous ankG or Na+ channel clustering at the AIS. Finally, using adenovirus for transgene delivery into myelinated neurons, we demonstrate that βIV spectrin recruitment to nodes of Ranvier also depends on binding to ankG.
A conserved surface on Toll-like receptor 5 recognizes bacterial flagellin
Authors: Andersen-Nissen Erica , Smith Kelly D. , Bonneau Richard , Strong Roland K. , Aderem Alan
Published: February 2007

The molecular basis for Toll-like receptor (TLR) recognition of microbial ligands is unknown. We demonstrate that mouse and human TLR5 discriminate between different flagellins, and we use this difference to map the flagellin recognition site on TLR5 to 228 amino acids of the extracellular domain. Through molecular modeling of the TLR5 ectodomain, we identify two conserved surface-exposed regions. Mutagenesis studies demonstrate that naturally occurring amino acid variation in TLR5 residue 268 is responsible for human and mouse discrimination between flagellin molecules. Mutations within one conserved surface identify residues D295 and D367 as important for flagellin recognition. These studies localize flagellin recognition to a conserved surface on the modeled TLR5 structure, providing detailed analysis of the interaction of a TLR with its ligand. These findings suggest that ligand binding at the β sheets results in TLR activation and provide a new framework for understanding TLR–agonist interactions.
CD4+CD25−Foxp3− Th1 cells are the source of IL-10–mediated immune suppression in chronic cutaneous leishmaniasis
Authors: Anderson Charles F. , Oukka Mohammed , Kuchroo Vijay J. , Sacks David
Published: February 2007

Nonhealing forms of leishmaniasis in humans are commonly associated with elevated levels of the deactivating cytokine IL-10, and in the mouse, normally chronic infections can be cleared in the absence of IL-10. Using a Leishmania major strain that produces nonhealing dermal lesions in a T helper type 1 (Th1) cell–polarized setting, we have analyzed the cellular sources of IL-10 and their relative contribution to immune suppression. IL-10 was produced by innate cells, as well as CD4+CD25+Foxp3+ and CD4+CD25−Foxp3− T cells in the chronic lesion. Nonetheless, only IL-10 production by antigen-specific CD4+CD25−Foxp3− T cells, the majority of which also produced IFN-γ, was necessary for suppression of acquired immunity in Rag−/− reconstituted mice. Surprisingly, Rag−/− mice reconstituted with naive CD4+ T cells depleted of natural T regulatory cells developed more severe infections, associated with elevated levels of IL-10 and, especially, Th2 cytokines in the site. The data demonstrate that IL-10–producing Th1 cells, activated early in a strong inflammatory setting as a mechanism of feedback control, are the principal mediators of T cell–derived IL-10–dependent immune suppression in a chronic intracellular infection.
A novel approach to ultrasensitive diagnosis using supramolecular protein nanoparticles
Authors: Lee Sung-Hyun , Lee Hyewon , Park Jin-Seung , Choi Hyoung , Han Kyung-Yeon , Seo Hyuk-Seong , Ahn Keum-Young , Han Sung-Sik , Cho Yunjung , Lee Kee-Hyoung , Lee Jeewon
Published: February 2007

We report on the ultrasensitive protein nanoprobe system that specifically captures disease marker (autoantibodies of Type I diabetes in this case) with attomolar sensitivity. The system relies on supramolecular protein nanoparticles that bind a specific antibody [65 kDa glutamate decarboxylase (GAD65)‐specific autoantibody, i.e., the early marker of Type I diabetes]. The ultrasensitive detection of early marker of Type I diabetes during the early phase of pancreatic β‐cell destruction is important because individuals at high risk of developing Type I diabetes can be identified several years before the clinical onset of the ailment. The bacterial expression of chimera genes encoding N‐[human ferritin heavy chain (hFTN‐H)]::[specific antigenic epitope]‐C produces supramolecular nanoparticles with uniform diameters (10‐15 nm), owing to self‐assembly activity of hFTN‐H. Each nanoparticle, formed by intermolecular self‐assembly between the chimera protein molecules, is subjected to carrying a large number (presumably, 24) of epitopes with a homogeneous and stable conformation per autoantibody binding, thereby allowing substantial enhancement of sensitivity. The sensitivity was finally boosted to 3 attomolar concentration of the autoantibodies, 4‐9 orders of magnitude more sensitive than conventional immunoassays. Also, this ultrasensitive protein nanoprobe successfully detected natural autoantibodies in the sera from Type I diabetic patients. The attomolar sensitivity was successfully reproduced on the detection of other antibodies, i.e., monoclonal antibodies against hepatitis B surface antigen. With the two antibody markers above, the feasibility of simultaneous and multiplexing‐mode detection was also demonstrated.—Lee S‐H., Lee, H., Park J‐S., Choi, H., Han K‐Y., Seo H‐S., Ahn K‐Y., Han S‐S., Cho, Y., Lee K‐H., Lee J. A novel approach to ultrasensitive diagnosis using supramolecular protein nano‐particles. FASEB J. 21, 1324–1334 (2007)
Elastic‐plastic fracture mechanics assessment for steam generator tubes with through‐wall cracks
Authors: HUH NAM‐SU , KIM JONG‐MIN , CHANG YOON‐SUK , KIM YOUNG‐JIN , HWANG SEONG‐SIK , KIM JOUNG‐SOO
Published: February 2007

ABSTRACTS

The present work provides an elastic‐plastic fracture mechanics (EPFM) assessment scheme for a steam generator tube with a through‐wall crack under internal pressure. Noting that the geometry and material are rather uniform for steam generator tubes, and furthermore the only loading to be considered is internal pressure, an engineering EPFM analysis method is proposed to assess through‐wall cracks in steam generator tubes. Important outcomes of the present work are closed‐form approximations for J and crack opening displacement (COD). Sufficient confidence in the proposed J and COD estimates is gained from good agreements with the finite element results over a wide range of the crack length and pressure magnitude. Another important element of the EPFM assessment is to determine relevant J‐resistance curve for steam generator tubes. To improve the accuracy of predicting tube failure, the present paper also proposes a new method to determine fracture toughness using an actual tubular specimen instead of using a standard specimen, from which J‐resistance curves of steam generator tubes are obtained. Using the proposed J and toughness estimates, maximum pressures of steam generator tubes with through‐wall crack are estimated based on EPFM analysis, which is compared with experimental results and predicted ones based on limit load approach.