bluuebunny/crossref_metadata_2025 huggingface dataset:
Tunable magneto-optical wavelength filter of long-period fiber grating with magnetic fluids
Authors: Liu Ting , Chen Xianfeng , Di Ziyun , Zhang Junfeng , Li Xinwan , Chen Jianping
Published: September 2007

In this paper, the authors propose a magneto-optical tunable filter based on a long-period fiber grating (LPG) coated with magnetic fluids (MFs) as the ambient media. By applying a tunable magnetic field, the center wavelength shift of the attenuation band of LPG is found as large as 7.4nm. The refractive index dependence of MF on the external magnetic intensity is measured and the simulation results show that it is well agreeable with the experimental observations.
Electromagnetic actuation and microchannel engineering of a polymer micropen array integrated with microchannels and sample reservoirs for biological assay patterning
Authors: Im Maesoon , Cho Il-Joo , Yun Kwang-Seok , Yoon Euisik
Published: September 2007

A polymer (SU-8) micropen array was fabricated for application to biological assay patterning. The micropen, which is integrated with a microchannel and a sample reservoir, can be actuated by Lorentz force induced on an integrated metal actuator. Current to a metal line deflects the micropen up to 1.8μm by electromagnetic force induced from external permanent magnets. Red ink is loaded in the reservoir and is automatically drawn to the end point of the microchannel by capillary force. A red-ink dot with a diameter of 11μm was successfully placed onto paper by the fabricated micropen.
Remarkable enhancement of domain-wall velocity in magnetic nanostripes
Authors: Lee Jun-Young , Lee Ki-Suk , Kim Sang-Koog
Published: September 2007

Remarkable reductions in the velocity of magnetic-field (or electric current)-driven domain-wall (DW) motions in ferromagnetic nanostripes have typically been observed under magnetic fields stronger than the Walker threshold field [N. L. Schryer and L. R. Walker, J. Appl. Phys. 45, 5406 (1974)]. This velocity breakdown is known to be associated with an oscillatory dynamic transformation between transverse- and antivortex (or vortex)-type DWs during their propagations. The authors propose, as the result of numerical calculations, a simple means to suppress the velocity breakdown and rather enhance the DW velocities, using a magnetic underlayer of strong perpendicular magnetic anisotropy. This underlayer plays a crucial role in preventing the nucleation of antivortex (or vortex)-type DWs at the edges of nanostripes, in the process of periodic dynamic transformations from the transverse into antivortex- or vortex-type wall. The present study not only offers a promising means of the speedup of DW propagations to levels required for their technological application to ultrafast information-storage or logic devices, but also provides insight into its underlying mechanism.
Magnetic field driven nanowire rotation in suspension
Authors: Keshoju K. , Xing H. , Sun L.
Published: September 2007

Magnetic field driven nanowire rotation in liquids has been investigated. This approach provides a noncontact, sensitive, cost effective, and easy to scale up scenario to manipulate the motion of magnetized one-dimensional nanostructures for “nanomachine” and anisotropic nanomaterial development. Due to the small dimensions, viscous behavior dominates the nanowire motion. Qualitative analyses considering the competing magnetic field induced torque and resisting fluid drag torque have been conducted for nanowire rotation under different circumstances. The analyses and experimental observations can provide key information for the understanding of hydrodynamics at the nanoscale.
Conductivity spectroscopy in aromatic polyimide from 200to400°C
Authors: Diaham Sombel , Locatelli Marie-Laure , Lebey Thierry
Published: September 2007

Dielectric relaxation spectroscopy experiments have been performed in a polyimide (PI) in order to measure its electrical conductivity from 200to400°C. The high temperature static (dc) conductivity in PI appears as superimposed by electrode polarization due to the building up of thin space-charge capacitor layers at the bulk-electrode interfaces of the metal-insulator-metal structure making the conduction phenomenon difficult to identify in dielectric spectra. However, the dynamic (ac) conductivity plot versus frequency allows for an approximation of the dc conductivity in PI which was reported here up to 400°C with values reaching 10−6Ω−1m−1 at 400°C.
Reversible color switching from blue to red in a polymer stabilized chiral nematic liquid crystals
Authors: Chen Jing , Morris Stephen M. , Wilkinson Timothy D. , Coles Harry J.
Published: September 2007

In this letter, the authors demonstrate reversible color switching from blue to red in polymer stabilized chiral nematic liquid crystals when viewed at oblique angles. A series of unusual colored scattering states, different from those noted in polymer-free samples, was observed in cells that had been prepared using a technique of cooling the sample from the isotropic phase in the presence of a low frequency (80Hz) applied electric field and then photopolymerizing the sample on both sides of the cell. This process “freezes-in” a texture whereby the helix axis lies preferentially in the plane of the cell.
Enhanced spontaneous emission rate from single InAs quantum dots in a photonic crystal nanocavity at telecom wavelengths
Authors: Balet L. , Francardi M. , Gerardino A. , Chauvin N. , Alloing B. , Zinoni C. , Monat C. , Li L. H. , Le Thomas N. , Houdré R. , Fiore A.
Published: September 2007

The authors demonstrate coupling at 1.3μm between single InAs quantum dots (QDs) and a mode of a two dimensional photonic crystal (PhC) defect cavity with a quality factor of 15 000. By spectrally tuning the cavity mode, they induce coupling with excitonic lines. They perform a time integrated and time-resolved photoluminescence and measure an eightfold increase in the spontaneous emission rate inducing a coupling efficiency of 96%. These measurements indicate the potential of single QDs in PhC cavities as efficient single-photon emitters for fiber-based quantum information processing applications.
Determining the defect parameters of the deep aluminum-related defect center in silicon
Authors: Rosenits Philipp , Roth Thomas , Glunz Stefan W. , Beljakowa Svetlana
Published: September 2007

Through a combined application of two characterization methods, deep-level transient spectroscopy and lifetime spectroscopy, the lifetime-limiting defect level in intentionally aluminum-contaminated Czochralski silicon has been analyzed and a complete set of defect parameters could be obtained. This aluminum-related defect center is found to be located at an energy level of Et−EV=0.44±0.02eV and exhibits an asymmetric capture cross section, with σp=3.6×10−13cm2 and σn=3.1×10−10cm2 being the hole and electron capture cross sections, respectively. The investigated defect center is attributed to the aluminum-oxygen complex (Al–O).
Manipulation of in-plane uniaxial anisotropy in Fe∕MgO(001) films by ion sputtering
Authors: Zhan Qing-feng , Vandezande Stijn , Van Haesendonck Chris , Temst Kristiaan
Published: September 2007

Grazing-incidence Ar+ ion sputtering has been used to produce nanoscale ripples on the surface of the Fe∕Mg(001) system. This way, a uniaxial anisotropy with both controllable strength and orientation can be superimposed on top of the cubic anisotropy, resulting in Fe∕MgO(001) films with unusual anisotropy symmetry. By combining longitudinal and transverse Kerr-effect measurements, different switching processes are revealed. Depending on the orientation of the external magnetic field, one-jump, two-jump, and “reverse” two-jump magnetization reversals can be observed. A simple model, which takes into account the relevant anisotropy energies, is developed to explain the experimentally observed switching fields and to evaluate the domain wall pinning energies of the sputtered sample.
Thickness-driven antiferroelectric-to-ferroelectric phase transition of thin PbZrO3 layers in epitaxial PbZrO3∕Pb(Zr0.8Ti0.2)O3 multilayers
Authors: Boldyreva Ksenia , Pintilie Lucian , Lotnyk Andriy , Misirlioglu I. B. , Alexe Marin , Hesse Dietrich
Published: September 2007

Epitaxial antiferroelectric/ferroelectric PbZrO3∕PbZr0.8Ti0.2O3 multilayers were grown on SrRuO3-electroded SrTiO3(100) substrates by pulsed laser deposition. Polarization-field and switching current-voltage curves show a mixed antiferroelectric-ferroelectric behavior of the multilayers with an individual layer thickness above 10nm, whereas below 10nm the multilayers show only ferroelectric behavior. Clearly the PbZrO3 layers thinner than 10nm experienced a transition into the ferroelectric state. X-ray diffraction reciprocal space mapping showed a corresponding orthorhombic-to-rhombohedral transition of the PbZrO3 layers. The observations are discussed in terms of the influence of strain.
Marangoni flow in an evaporating water droplet
Authors: Xu Xuefeng , Luo Jianbin
Published: September 2007

Marangoni effect has been observed in many liquids, but its existence in pure water is still a debated problem. In the present work, the Marangoni flow in evaporating water droplets has been observed by using fluorescent nanoparticles. Flow patterns indicate that a stagnation point where the surface flow, the surface tension gradient, and the surface temperature gradient change their directions exists at the droplet surface. The deduced nonmonotonic variation of the droplet surface temperature, which is different from that in some previous works, is explained by a heat transfer model considering the adsorbed thin film of the evaporating liquid droplet.
Micronanofabrication of assembled three-dimensional microstructures by designable multiple beams multiphoton processing
Authors: Dong Xian-Zi , Zhao Zhen-Sheng , Duan Xuan-Ming
Published: September 2007

The authors proposed a customizable multiple beam multiphoton polymerization micronanofabrication method for parallel processing of assembled structures. The configuration and geometry of multiple beams were designed by changing the parameters of lenses set as well as aperture masks. Various assembled two-dimensional and three-dimensional microstructures including microgears and photonic crystals were demonstrated under nanometer scale resolution and high fabrication efficiency. The proposed micronanofabrication method could be expected to play an important role in the fabrication of micromachines and microdevices.
Thin-film polarizer based on a one-dimensional–three-dimensional–one-dimensional photonic crystal heterostructure
Authors: Thiel M. , Hermatschweiler M. , Wegener M. , von Freymann G.
Published: September 2007

The recent experimental demonstration of polarization stop bands in three-dimensional dielectric circular-spiral photonic crystals is extended in two ways. First, the combination with a one-dimensional set of lamellae on one side allows for “poor-man’s optical isolators” or for thin-film polarizers—depending on from which side light impinges onto the device. Second, a chiral three-dimensional photonic crystal sandwiched between two one-dimensional sets of lamellae acts as a thin-film polarizer from both sides. Corresponding polymeric heterostructures are fabricated by means of direct laser writing. Their performance is compared with theory.
Switching characteristics of Cu2O metal-insulator-metal resistive memory
Authors: Chen A. , Haddad S. , Wu Y. C. , Lan Z. , Fang T. N. , Kaza S.
Published: September 2007

The Cu2O metal-insulator-metal (MIM) resistive switching memory was characterized on a 64kb memory test array. The switching properties are consistent with the proposed switching model of conductivity modulation by a charge trapping process. Retention, programing characteristics, and temperature effects are analyzed based on the switching model. The measured characteristics and the switching model for Cu2O MIM are compared with those of other resistive switching materials. The statistical characteristics provide essential evidence for analysis of the switching mechanism and evaluation of the memory devices.
A direct first principles study on the structure and electronic properties of BexZn1−xO
Authors: Fan X. F. , Zhu Zexuan , Ong Yew-Soon , Lu Y. M. , Shen Z. X. , Kuo Jer-Lai
Published: September 2007

We present a systematic study on the structural and electronic properties of all alloy configurations of BexZn1−xO in a unit cell with 16 cations using density functional theory (DFT) methods. The 216 complexity is reduced by considering the symmetry of the parent structures. The experimental structures and electronic properties of the bulk material are reasonably reproduced by the DFT methods. The lattice constants of the alloy are found to follow Vegard’s law [Z. Phys. 5, 17 (1921)] and are comparable with the experimental values. Examining the formation enthalpy of all alloy configurations suggests the possible existence of three metastable order states. The calculated band gap of the BexZn1−xO is also compared with the experimental measurements and the authors found that some alloy configurations with the same concentration can have band gaps differed by ∼1.5eV.
Measuring the mass, density, and size of particles and cells using a suspended microchannel resonator
Authors: Godin Michel , Bryan Andrea K. , Burg Thomas P. , Babcock Ken , Manalis Scott R.
Published: September 2007

We demonstrate the measurement of mass, density, and size of cells and nanoparticles using suspended microchannel resonators. The masses of individual particles are quantified as transient frequency shifts, while the particles transit a microfluidic channel embedded in the resonating cantilever. Mass histograms resulting from these data reveal the distribution of a population of heterogeneously sized particles. Particle density is inferred from measurements made in different carrier fluids since the frequency shift for a particle is proportional to the mass difference relative to the displaced solution. We have characterized the density of polystyrene particles, Escherichia coli, and human red blood cells with a resolution down to 10−4g∕cm3.
Hole-injection barrier in pentacene field-effect transistor with Au electrodes modified by C16H33SH
Authors: Kawasaki Naoko , Ohta Yohei , Kubozono Yoshihiro , Fujiwara Akihiko
Published: September 2007

Field-effect transistor with thin films of pentacene has been fabricated with Au electrodes modified by 1-hexadecanethiol (C16H33SH), and the hole-injection barriers have been determined from the temperature dependence of output properties on the basis of the thermionic emission model for double Schottky barriers. The large tunneling barriers are formed by the insulating C16H33SH at the interfaces between the Au electrodes and pentacene thin films.
Spatial imaging of modifications to fluorescence lifetime and intensity by individual Ag nanoparticles
Authors: Ritman-Meer T. , Cade N. I. , Richards D.
Published: September 2007

Highly ordered periodic arrays of silver nanoparticles have been fabricated which exhibit surface plasmon resonances in the visible spectrum. We demonstrate the ability of these structures to alter the fluorescence properties of vicinal dye molecules by providing an additional radiative decay channel. Using fluorescence lifetime imaging microscopy, we have created high resolution spatial maps of the molecular lifetime components; these show an order of magnitude increase in decay rate from a localized volume around the nanoparticles, resulting in a commensurate enhancement in the fluorescence emission intensity.
Evidence for strong Fermi-level pinning due to metal-induced gap states at metal/germanium interface
Authors: Nishimura Tomonori , Kita Koji , Toriumi Akira
Published: September 2007

The purpose of this paper is to understand metal/germanium (Ge) junction characteristics. Electrode metals with a wide work function range were deposited on Ge. All metal/p-Ge and metal/n-Ge junctions have shown Ohmic and Schottky characteristics, respectively, with the strong Fermi-level pinning. The charge neutrality level (CNL) at metal/Ge interface is close to the branch point calculated for the bulk Ge. Moreover, the pinning level is hardly modulated by annealing in forming gas, forming metal-germanide/Ge interfaces or changing the substrate orientation. These results suggest that Fermi level at metal/Ge interface is intrinsically pinned at the CNL characterized by the metal-induced gap states model.
Epitaxial growth and electrical spin injection from Fe(1−x)Gax (001) films on AlGaAs∕GaAs (001) heterostructures
Authors: van ‘t Erve O. M. J. , Li C. H. , Kioseoglou G. , Hanbicki A. T. , Osofsky M. , Cheng S.-F. , Jonker B. T.
Published: September 2007

The authors have grown epitaxial films of Fe(1−x)Gax (0<x<0.75), a material noted for its high magnetostriction, on AlGaAs∕GaAs (001) heterostructures and summarize the structure, magnetization, spin polarization, and results for electrical spin injection into AlGaAs∕GaAs. The out-of-plane saturation field and magnetization decrease rapidly with Ga content, but the spin polarization determined by point contact Andreev reflection remains near that of Fe for x⩽0.5 Electrical spin injection from Fe0.5Ga0.5 produces an electron spin polarization >70% in GaAs at 20K, similar to that obtained from Fe contacts but at out-of-plane saturation fields as low as 0.36T rather than 2.2T.
Carrier dynamics in stacked InP∕GaAs quantum dots
Authors: Veloso A. B. , Nakaema M. K. K. , de Godoy M. P. F. , Lopes J. M. J. , Iikawa F. , Brasil M. J. S. P. , Bortoleto J. R. R. , Cotta M. A. , Fichtner P. F. P. , Morschbächer M. , Madureira J. R.
Published: September 2007

We investigated two stacked layers of InP∕GaAs type-II quantum dots by transmission electron microscopy and optical spectroscopy. The results reveal that InP quantum dots formed in two quantum dot layers are more uniform than those from a single layer structure. The thermal activation energies as well as the photoluminescence decays are rather independent of the separation between quantum dot layers and the presence of the second layer. The quantum dot optical emission persists for thermal activation energy larger than the calculated exciton binding energy. The photoluminescence decay is relatively fast for type-II alignment.
Predicting hardness of covalent∕ionic solid solution from first-principles theory
Authors: Hu Q. M. , Kádas K. , Hogmark S. , Yang R. , Johansson B. , Vitos L.
Published: September 2007

We introduce a hardness formula for the multicomponent covalent and ionic solid solutions. This expression is tested on nitride spinel materials A3N4 (A=C,Si,Ge) and applied to titanium nitrogen carbide (TiN1−xCx with 0⩽x⩽1), off-stoichiometric transition-metal nitride (TiN1−x and VN1−x with x⩽0.25), and B-doped semiconductors (C1−xBx, Si1−xBx, and Ge1−xBx with x⩽0.1). In all cases, the theoretical hardness is in good agreement with experiments.
Intrusion-type deformation in epitaxial Ti3SiC2∕TiC0.67 nanolaminates
Authors: Wilhelmsson O. , Eklund P. , Giuliani F. , Högberg H. , Hultman L. , Jansson U.
Published: September 2007

We investigate the deformation of epitaxial Ti3SiC2(0001)∕TiCx(111) (x∼0.67) nanolaminates deposited by magnetron sputtering. Nanoindentation and transmission electron microscopy show that the Ti3SiC2 layers deform via basal plane slip and intrusion into the TiC layers, suppressing kink-band and pile-up deformation behaviors analogous with monolithic Ti3SiC2. This remarkable response to indentation is due to persistent slip in the TiC layers and prevention of gross slip throughout the nanolaminate by the interleaving Ti3SiC2 layers. Hardness and Young’s modulus were measured as ∼15 and ∼240GPa, respectively.
Ultrafast soft x-ray absorption spectroscopy with sub-20-fs resolution
Authors: Seres Enikoe , Spielmann Christian
Published: September 2007

The most challenging application of time-resolved spectroscopy is to watch the motion of atoms directly. In the current experiment, we were able to follow the displacement of atoms in silicon after excitation with an intense near infrared femtosecond laser pulse with time-resolved x-ray absorption spectroscopy. The sub-20-fs x-ray probe pulses in an energy range up to several 100eV were generated by high harmonic generation of intense femtosecond laser pulses at a repetition rate of 1kHz. In a proof of principle experiment, we found an oscillatory motion of the atoms which can be explained by the excitation of coherent phonons. Our setup can be easily extended for studying structural dynamics in many important systems not only in solids but also in gases and liquids.
The significance of denitrification in relation to external loading and nitrogen retention in a mountain reservoir
Authors: Koszelnik Piotr , Tomaszek Janusz A. , Gruca-Rokosz Renata
Published: September 2007

Nitrogen retention (Nret) and denitrification were studied in the mesotrophic Solina reservoir (south-east Poland) between spring and autumn in 2002 and 2003. Nret was calculated on the basis of the input-output mass balance. The rate of denitrification was measured using the 15N isotope pairing technique in two types of areas; in deep areas, where the bottom sediment makes contacts with the hypolimnion (Dprof), and in the unstratified shallows (Dlitt). The calculated daily load of removed nitrogen (Dtot) varied somewhat from 11.0 to 19.1 mg N m–2 day–1 with a standard deviation of 3.0 mg N m–2 day–1. The limited oscillation noted for Dtot results from the major participation of the deep areas of the reservoir, which are characterised by stable Dprof, as distinct from Dlitt, which varied seasonally from 5.8 mg N m–2 day–1 in November to 109.9 mg N m–2 day–1 in August. The primary factor limiting the denitrification rate was temperature, the other being availability of substrates, mainly organic matter. Nitrogen retention ranged seasonally between –25.0 and 175.9 mg N m–2 day–1. The contribution of denitrification to Nret ranged from 9.0% to 49.8% (mean 16.4%). On average, only 4.9% of the nitrogen external load was denitrified (range 2.6–7.9%, s.d. 1.5%). After comparing obtained data with others available in the literature, we concluded that reservoirs, estuaries and highly-loaded lakes in a river system experience a more limited contribution of Dtot to Nload than is the case in natural lakes.
Quantum dynamics and entanglement of spins on a square lattice
Authors: Christensen N. B. , Rønnow H. M. , McMorrow D. F. , Harrison A. , Perring T. G. , Enderle M. , Coldea R. , Regnault L. P. , Aeppli G.
Published: September 2007

Bulk magnetism in solids is fundamentally quantum mechanical in nature. Yet in many situations, including our everyday encounters with magnetic materials, quantum effects are masked, and it often suffices to think of magnetism in terms of the interaction between classical dipole moments. Whereas this intuition generally holds for ferromagnets, even as the size of the magnetic moment is reduced to that of a single electron spin (the quantum limit), it breaks down spectacularly for antiferromagnets, particularly in low dimensions. Considerable theoretical and experimental progress has been made in understanding quantum effects in one-dimensional quantum antiferromagnets, but a complete experimental description of even simple two-dimensional antiferromagnets is lacking. Here we describe a comprehensive set of neutron scattering measurements that reveal a non-spin-wave continuum and strong quantum effects, suggesting entanglement of spins at short distances in the simplest of all two-dimensional quantum antiferromagnets, the square lattice Heisenberg system.
The mouse homeobox gene
Noto
regulates node morphogenesis, notochordal ciliogenesis, and left–right patterning
Authors: Beckers Anja , Alten Leonie , Viebahn Christoph , Andre Philipp , Gossler Achim
Published: September 2007

The mouse homeobox gene
Noto
represents the homologue of zebrafish floating head (
flh
) and is expressed in the organizer node and in the nascent notochord. Previous analyses suggested that
Noto
is required exclusively for the formation of the caudal part of the notochord. Here, we show that
Noto
is also essential for node morphogenesis, controlling ciliogenesis in the posterior notochord, and the establishment of laterality, whereas organizer functions in anterior–posterior patterning are apparently not compromised. In mutant embryos, left–right asymmetry of internal organs and expression of laterality markers was randomized. Mutant posterior notochord regions were variable in size and shape, cilia were shortened with highly irregular axonemal microtubuli, and basal bodies were, in part, located abnormally deep in the cytoplasm. The transcription factor
Foxj1
, which regulates the dynein gene
Dnahc11
and is required for the correct anchoring of basal bodies in lung epithelial cells, was down-regulated in mutant nodes. Likewise, the transcription factor
Rfx3
, which regulates cilia growth, was not expressed in
Noto
mutants, and various other genes important for cilia function or assembly such as
Dnahc5
and
Nphp3
were down-regulated. Our results establish
Noto
as an essential regulator of node morphogenesis and ciliogenesis in the posterior notochord, and suggest
Noto
acts upstream of
Foxj1
and
Rfx3
.
Posttetanic potentiation critically depends on an enhanced Ca
2+
sensitivity of vesicle fusion mediated by presynaptic PKC
Authors: Korogod Natalya , Lou Xuelin , Schneggenburger Ralf
Published: September 2007

Activity-dependent enhancement of transmitter release is a common form of presynaptic plasticity, but the underlying signaling mechanisms have remained largely unknown, perhaps because of the inaccessibility of most CNS nerve terminals. Here we investigated the signaling steps that underlie posttetanic potentiation (PTP), a form of presynaptic plasticity found at many CNS synapses. Direct whole-cell recordings from the large calyx of Held nerve terminals with the perforated patch-clamp technique showed that PTP was not mediated by changes in the presynaptic action potential waveform. Ca
2+
imaging revealed a slight increase of the presynaptic Ca
2+
transient during PTP (≈15%), which, however, was too small to explain a large part of PTP. The presynaptic PKC pathway was critically involved in PTP because (
i
) PTP was occluded by activation of PKC with phorbol esters, and (
ii
) PTP was largely (by approximately two-thirds) blocked by the PKC inhibitors, Ro31-8220 or bisindolylmaleimide. Activation of PKC during PTP most likely acts directly on the presynaptic release machinery, because in presynaptic Ca
2+
uncaging experiments, activation of PKC by phorbol ester greatly increased the Ca
2+
sensitivity of vesicle fusion in a Ro31-8220-sensitive manner (≈300% with small Ca
2+
uncaging stimuli), but only slightly increased presynaptic voltage-gated Ca
2+
currents (≈15%). We conclude that a PKC-dependent increase in the Ca
2+
sensitivity of vesicle fusion is a key step in the enhancement of transmitter release during PTP.
Quantum spin correlations through the superconducting-to-normal phase transition in electron-doped superconducting Pr
0.88
LaCe
0.12
CuO
4-δ
Authors: Wilson Stephen D. , Li Shiliang , Zhao Jun , Mu Gang , Wen Hai-Hu , Lynn Jeffrey W. , Freeman Paul G. , Regnault Louis-Pierre , Habicht Klaus , Dai Pengcheng
Published: September 2007

The quantum spin fluctuations of the S = 1/2 Cu ions are important in determining the physical properties of high-transition-temperature (high
T
c
) copper oxide superconductors, but their possible role in the electron pairing of superconductivity remains an open question. The principal feature of the spin fluctuations in optimally doped high-
T
c
superconductors is a well defined magnetic resonance whose energy (
E
R
) tracks
T
c
(as the composition is varied) and whose intensity develops like an order parameter in the superconducting state. We show that the suppression of superconductivity and its associated condensation energy by a magnetic field in the electron-doped high-
T
c
superconductor Pr
0.88
LaCe
0.12
CuO
4-δ
(
T
c
= 24 K), is accompanied by the complete suppression of the resonance and the concomitant emergence of static antiferromagnetic order. Our results demonstrate that the resonance is intimately related to the superconducting condensation energy, and thus suggest that it plays a role in the electron pairing and superconductivity.
A quantitative trait locus for variation in dopamine metabolism mapped in a primate model using reference sequences from related species
Authors: Freimer Nelson B. , Service Susan K. , Ophoff Roel A. , Jasinska Anna J. , McKee Kevin , Villeneuve Amelie , Belisle Alexandre , Bailey Julia N. , Breidenthal Sherry E. , Jorgensen Matthew J. , Mann J. John , Cantor Rita M. , Dewar Ken , Fairbanks Lynn A.
Published: September 2007

Non-human primates (NHP) provide crucial research models. Their strong similarities to humans make them particularly valuable for understanding complex behavioral traits and brain structure and function. We report here the genetic mapping of an NHP nervous system biologic trait, the cerebrospinal fluid (CSF) concentration of the dopamine metabolite homovanillic acid (HVA), in an extended inbred vervet monkey (
Chlorocebus aethiops sabaeus
) pedigree. CSF HVA is an index of CNS dopamine activity, which is hypothesized to contribute substantially to behavioral variations in NHP and humans. For quantitative trait locus (QTL) mapping, we carried out a two-stage procedure. We first scanned the genome using a first-generation genetic map of short tandem repeat markers. Subsequently, using >100 SNPs within the most promising region identified by the genome scan, we mapped a QTL for CSF HVA at a genome-wide level of significance (peak logarithm of odds score >4) to a narrow well delineated interval (<10 Mb). The SNP discovery exploited conserved segments between human and rhesus macaque reference genome sequences. Our findings demonstrate the potential of using existing primate reference genome sequences for designing high-resolution genetic analyses applicable across a wide range of NHP species, including the many for which full genome sequences are not yet available. Leveraging genomic information from sequenced to nonsequenced species should enable the utilization of the full range of NHP diversity in behavior and disease susceptibility to determine the genetic basis of specific biological and behavioral traits.
Taking account of catchability in groundfish survey trawls: implications for estimating demersal fish biomass
Authors: Fraser Helen M. , Greenstreet Simon P. R. , Piet Gerjan J.
Published: September 2007

Fraser, H. M., Greenstreet, S. P. R., and Piet, G. J. 2007. Taking account of catchability in groundfish survey trawls: implications for estimating demersal fish biomass. – ICES Journal of Marine Science, 64. Groundfish surveys are a key component of current scientific data monitoring and data-collection activities undertaken in support of fisheries management. Recent requirements to develop and implement an ecosystem approach to management are placing increasing and varied demands on such datasets. Successfully incorporating ecosystem and environmental objectives within fisheries management will, for example, require greater understanding of foodweb trophodynamics, which in turn requires detailed information on the abundance and distribution of fish predators and prey species on spatial scales hitherto rarely considered. However, no trawl gear catches all the fish in its path, so density estimates provided by such trawl samples do not reflect true densities of fish. Catchability in a trawl gear is affected by many factors and varies both between species and between different sized conspecifics, and therefore has the capacity to confound our understanding of predator–prey interactions and of the relative abundance of different species and size classes of fish at any point in time or space. To overcome such problems, estimates of the catchability of each size class of each species sampled in a given survey are required for trawl sample densities to be raised to the actual densities of fish present at each location sampled. Here, we present a method for estimating catchability coefficients for 1-cm size classes of fish species sampled by the Grande Overture Vertical trawl during the third quarter ICES International Bottom Trawl Survey. The catchability coefficients obtained are applied to survey data collected between 1998 and 2004 to examine annual variation in actual abundance of the demersal fish assemblage in the North Sea.
A method for evaluating the impacts of fishing mortality and stochastic influences on the demography of two long-lived shark stocks
Authors: McAuley Rory B. , Simpfendorfer Colin A. , Hall Norm G.
Published: September 2007

McAuley, R. B., Simpfendorfer, C. A., and Hall, N. G. 2007. A method for evaluating the impacts of fishing mortality and stochastic influences on the demography of two long-lived shark stocks. — ICES Journal of Marine Science, 64.

Stochastic demographic models were developed for Carcharhinus obscurus and C. plumbeus populations off the west coast of Australia by resampling the input parameters for life tables from empirical biological data collected from commercial target fisheries and fishery-independent surveys. The models were used to examine the effects of multiple scenarios of age-specific survival, derived from the fishing mortality rates estimated from a tagging study on sharks and indirect estimates of natural mortality. In the absence of fishing, median estimates of the rates of intrinsic population increase (r) were 0.025 for both species. Inclusion of the age-specific fishing mortality rates estimated for C. obscurus recruits born in 1994 and 1995 resulted in the median estimates of r declining to 0.007 and 0.012, respectively, suggesting that recent harvest levels of mainly neonates by the target fishery were probably sustainable. However, the model also suggested that the population was more susceptible to exploitation of older sharks than was previously believed. The C. plumbeus model indicated that fishing mortality between 2001 and 2004 was probably unsustainable. The increasingly negative trend in median r estimates (from –0.032 to –0.049), and the population’s apparently limited capacity for density-dependent compensation through changes in fecundity, somatic growth and longevity, suggests that management intervention is necessary to prevent continued stock depletion.
John Michael Hammersley. 21 March 1920 — 2 May 2004
Authors: Grimmett Geoffrey , Welsh Dominic
Published: September 2007

John Hammersley was a pioneer among mathematicians, who defied classification as pure or applied; when introduced to guests at Trinity College, Oxford, he would say he did ‘difficult sums’. He believed passionately in the importance of mathematics with strong links to real–life situations and in a system of mathematical education in which the solution of problems takes precedence over the generation of theory. He will be remembered for his work on percolation theory, subadditive stochastic processes, self–avoiding walks and Monte Carlo methods, and, by those who knew him, for his intellectual integrity and his ability to inspire and to challenge. Quite apart from his extensive research achievements, for which he earned a reputation as an outstanding problem–solver, he was a leader in the movement of the 1950s and 1960s to rethink the content of school mathematics syllabuses.
Reduced Expression of Succinyl-Coenzyme A Ligase Can Be Compensated for by Up-Regulation of theγ-Aminobutyrate Shunt in Illuminated Tomato Leaves
Authors: Studart-Guimarães Claudia , Fait Aaron , Nunes-Nesi Adriano , Carrari Fernando , Usadel Björn , Fernie Alisdair R.
Published: September 2007

Increasing experimental evidence suggests that the tricarboxylic acid cycle in plants is of greater importance in illuminated photosynthetic tissues than previously thought. In this study, transgenic tomato (Solanum lycopersicum) plants expressing a fragment of the β-subunit of succinyl-coenzyme A ligase in either the antisense orientation or using the RNA interference approach, however, revealed little alteration in either photosynthesis or plant growth despite exhibiting dramatic reductions in activity. Moreover, the rate of respiration was only moderately affected in the transformants, suggesting that this enzyme does not catalyze a crucial step in mitochondrial respiration. However, metabolite and transcript profiling of these lines alongside enzyme and label redistribution experiments revealed that, whereas considerable activity of this enzyme appears to be dispensable, the reason for such a mild phenotype in extremely inhibited lines was an up-regulation of an alternative pathway for succinate production—that offered by the γ-aminobutyric acid shunt. When taken together, these data highlight the importance both of succinate production for mitochondrial metabolism and the interplay between various routes of its production. The results are discussed in the context of current models of plant respiration in mitochondrial and cellular metabolism of the illuminated leaf.
A Proteinaceous Elicitor Sm1 from the Beneficial FungusTrichoderma virensIs Required for Induced Systemic Resistance in Maize
Authors: Djonović Slavica , Vargas Walter A. , Kolomiets Michael V. , Horndeski Michelle , Wiest Aric , Kenerley Charles M.
Published: September 2007

We have previously shown that the beneficial filamentous fungus Trichoderma virens secretes the highly effective hydrophobin-like elicitor Sm1 that induces systemic disease resistance in the dicot cotton (Gossypium hirsutum). In this study we tested whether colonization of roots by T. virens can induce systemic protection against a foliar pathogen in the monocot maize (Zea mays), and we further demonstrated the importance of Sm1 during maize-fungal interactions using a functional genomics approach. Maize seedlings were inoculated with T. virens Gv29-8 wild type and transformants in which SM1 was disrupted or constitutively overexpressed in a hydroponic system or in soil-grown maize seedlings challenged with the pathogen Colletotrichum graminicola. We show that similar to dicot plants, colonization of maize roots by T. virens induces systemic protection of the leaves inoculated with C. graminicola. This protection was associated with notable induction of jasmonic acid- and green leaf volatile-biosynthetic genes. Neither deletion nor overexpression of SM1 affected normal growth or development of T. virens, conidial germination, production of gliotoxin, hyphal coiling, hydrophobicity, or the ability to colonize maize roots. Plant bioassays showed that maize grown with SM1-deletion strains exhibited the same levels of systemic protection as non-Trichoderma-treated plants. Moreover, deletion and overexpression of SM1 resulted in significantly reduced and enhanced levels of disease protection, respectively, compared to the wild type. These data together indicate that T. virens is able to effectively activate systemic disease protection in maize and that the functional Sm1 elicitor is required for this activity.
Phage-Type RNA Polymerase RPOTmp Transcribes the rrn Operon from the PC Promoter at Early Developmental Stages in Arabidopsis
Authors: Courtois Florence , Merendino Livia , Demarsy Emilie , Mache Régis , Lerbs-Mache Silva
Published: September 2007

The plastid genome of higher plants is transcribed by two different types of RNA polymerases named nucleus encoded RNA polymerase (NEP) and plastid encoded RNA polymerase. Plastid encoded RNA polymerase is a multimeric enzyme comparable to eubacterial RNA polymerases. NEP enzymes represent a small family of monomeric phage-type RNA polymerases. Dicotyledonous plants harbor three different phage-type enzymes, named RPOTm, RPOTp, and RPOTmp. RPOTm is exclusively targeted to mitochondria, RPOTp is exclusively targeted to plastids, and RPOTmp is targeted to plastids as well as to mitochondria. In this article, we have made use of RPOTp and RPOTmp T-DNA insertion mutants to answer the question of whether both plastid-located phage-type RNA polymerases have overlapping or specific functions in plastid transcription. To this aim, we have analyzed accD and rpoB messenger RNAs (mRNA; transcribed from type I NEP promoters), clpP mRNA (transcribed from the −59 type II NEP promoter), and the 16S rRNA (transcribed from the exceptional PC NEP promoter) by primer extension. Results suggest that RPOTp represents the principal RNA polymerase for transcribing NEP-controlled mRNA genes during early plant development, while RPOTmp transcribes specifically the rrn operon from the PC promoter during seed imbibition.
Alteration of Organic Acid Metabolism in Arabidopsis Overexpressing the Maize C4 NADP-Malic Enzyme Causes Accelerated Senescence during Extended Darkness
Authors: Fahnenstich Holger , Saigo Mariana , Niessen Michaela , Zanor María I. , Andreo Carlos S. , Fernie Alisdair R. , Drincovich María F. , Flügge Ulf-Ingo , Maurino Verónica G.
Published: September 2007

The full-length cDNA encoding the maize (Zea mays) C4 NADP-malic enzyme was expressed in Arabidopsis (Arabidopsis thaliana) under the control of the cauliflower mosaic virus 35S promoter. Homozygous transgenic plants (MEm) were isolated with activities ranging from 6- to 33-fold of those found in the wild type. The transformants did not show any differences in morphology and development when grown in long days; however, dark-induced senescence progressed more rapidly in MEm plants compared to the wild type. Interestingly, senescence could be retarded in the transgenic lines by exogenously supplying glucose, sucrose, or malate, suggesting that the lack of a readily mobilized carbon source is likely to be the initial factor leading to the premature induction of senescence in MEm plants. A comprehensive metabolic profiling on whole rosettes allowed determination of approximately 80 metabolites during a diurnal cycle as well as following dark-induced senescence and during metabolic complementation assays. MEm plants showed no differences in the accumulation and degradation of carbohydrates with respect to the wild type in all conditions tested, but accumulated lower levels of intermediates used as respiratory substrates, prominently malate and fumarate. The data indicated that extremely low levels of malate and fumarate are responsible for the accelerated dark-induced senescence encountered in MEm plants. Thus, in prolonged darkness these metabolites are consumed faster than in the wild type and, as a consequence, MEm plants enter irreversible senescence more rapidly. In addition, the data revealed that both malate and fumarate are important forms of fixed carbon that can be rapidly metabolized under stress conditions in Arabidopsis.
Participation of the Arabidopsis bHLH Factor GL3 in Trichome Initiation Regulatory Events
Authors: Morohashi Kengo , Zhao Mingzhe , Yang Manli , Read Betsy , Lloyd Alan , Lamb Rebecca , Grotewold Erich
Published: September 2007

The development of trichomes (leaf hairs) from pluripotent epidermal cells in Arabidopsis (Arabidopsis thaliana) provides a powerful system to investigate the regulatory motifs involved in plant cell differentiation. We show here that trichome initiation is triggered within 4 h of the induction of the GLABRA3 (GL3) basic helix-loop-helix transcription factor. Within this developmental window, GL3 binds to the promoters of at least three genes previously implicated in the development and patterning of trichomes (GL2, CAPRICE, and ENHANCER OF TRIPTYCHON AND CAPRICE1) and activates their transcription. The in vivo binding of GL3 to the promoters of these genes requires the presence of the R2R3-MYB factor GL1, supporting a model in which a GL3-GL1 complex is part of the trichome initiation enhanceosome. In contrast, GL3 is recruited to its own promoter in a GL1-independent manner, and this results in decreased GL3 expression, suggesting the presence of a GL3 negative autoregulatory loop. In support of genetic analyses indicating that ENHANCER OF GL3 (EGL3) is partially redundant with GL3, we show that EGL3 shares some direct targets with GL3. However, our results suggest that GL3 and EGL3 work independently of each other. Taken together, our results provide a regulatory framework to understand early events of epidermal cell differentiation.
yucca6, a Dominant Mutation in Arabidopsis, Affects Auxin Accumulation and Auxin-Related Phenotypes
Authors: Kim Jeong Im , Sharkhuu Altanbadralt , Jin Jing Bo , Li Pinghua , Jeong Jae Cheol , Baek Dongwon , Lee Sang Yeol , Blakeslee Joshua J. , Murphy Angus S. , Bohnert Hans J. , Hasegawa Paul M. , Yun Dae-Jin , Bressan Ray A.
Published: September 2007

Auxin plays critical roles in many aspects of plant growth and development. Although a number of auxin biosynthetic pathways have been identified, their overlapping nature has prevented a clear elucidation of auxin biosynthesis. Recently, Arabidopsis (Arabidopsis thaliana) mutants with supernormal auxin phenotypes have been reported. These mutants exhibit hyperactivation of genes belonging to the YUCCA family, encoding putative flavin monooxygenase enzymes that result in increased endogenous auxin levels. Here, we report the discovery of fertile dominant Arabidopsis hypertall1-1D and hypertall1-2D (yucca6-1D, -2D) mutants that exhibit typical auxin overproduction phenotypic alterations, such as epinastic cotyledons, increased apical dominance, and curled leaves. However, unlike other auxin overproduction mutants, yucca6 plants do not display short or hairy root phenotypes and lack morphological changes under dark conditions. In addition, yucca6-1D and yucca6-2D have extremely tall (>1 m) inflorescences with extreme apical dominance and twisted cauline leaves. Microarray analyses revealed that expression of several indole-3-acetic acid-inducible genes, including Aux/IAA, SMALL AUXIN-UP RNA, and GH3, is severalfold higher in yucca6 mutants than in the wild type. Tryptophan (Trp) analog feeding experiments and catalytic activity assays with recombinant YUCCA6 indicate that YUCCA6 is involved in a Trp-dependent auxin biosynthesis pathway. YUCCA6:GREEN FLUORESCENT PROTEIN fusion protein indicates YUCCA6 protein exhibits a nonplastidial subcellular localization in an unidentified intracellular compartment. Taken together, our results identify YUCCA6 as a functional member of the YUCCA family with unique roles in growth and development.
Differential Expansion and Expression ofα- andβ-Tubulin Gene Families inPopulus
Authors: Oakley Rodney V. , Wang Yuh-Shuh , Ramakrishna Wusirika , Harding Scott A. , Tsai Chung-Jui
Published: September 2007

Microtubule organization is intimately associated with cellulose microfibril deposition, central to plant secondary cell wall development. We have determined that a relatively large suite of eight α-TUBULIN (TUA) and 20 β-TUBULIN (TUB) genes is expressed in the woody perennial Populus. A number of features, including gene number, α:β gene representation, amino acid changes at the C terminus, and transcript abundance in wood-forming tissue, distinguish the Populus tubulin suite from that of Arabidopsis thaliana. Five of the eight Populus TUAs are unusual in that they contain a C-terminal methionine, glutamic acid, or glutamine, instead of the more typical, and potentially regulatory, C-terminal tyrosine. Both C-terminal Y-type (TUA1) and M-type (TUA5) TUAs were highly expressed in wood-forming tissues and pollen, while the Y-type TUA6 and TUA8 were abundant only in pollen. Transcripts of the disproportionately expanded TUB family were present at comparatively low levels, with phylogenetically distinct classes predominating in xylem and pollen. When tension wood induction was used as a model system to examine changes in tubulin gene expression under conditions of augmented cellulose deposition, xylem-abundant TUA and TUB genes were up-regulated. Immunolocalization of TUA and TUB in xylem and phloem fibers of stems further supported the notion of heavy microtubule involvement during cellulose microfibril deposition in secondary walls. The high degree of sequence diversity, differential expansion, and differential regulation of Populus TUA and TUB families may confer flexibility in cell wall formation that is of adaptive significance to the woody perennial growth habit.