bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental comparison of exchange bias measurement methodologies
Authors: Hovorka Ondrej , Berger Andreas , Friedman Gary
Published: May 2007

Measurements performed on all-ferromagnetic bilayer systems and supported by model calculation results are used to compare different exchange bias characterization methods. We demonstrate that the accuracy of the conventional two-point technique based on measuring the sum of the coercive fields depends on the symmetry properties of hysteresis loops. On the other hand, the recently proposed center of mass method yields results independent of the hysteresis loop type and coincides with the two-point measurement only if the loops are symmetric. Our experimental and simulation results clearly demonstrate a strong correlation between loop asymmetry and the difference between these methods.
Influence of quenching rate on the microstructure and magnetic properties of melt-spun L10-FePt∕Fe2B nanocomposite magnets
Authors: Zhang Wei , Yubuta Kunio , Sharma Parmanand , Makino Akihiro , Inoue Akihisa
Published: May 2007

The quenching rate, which is dependent on the surface velocity (Vs) of Cu wheel during melt spinning, has significant influence on the formation of nanocomposite structure in the Fe52Pt32B18 melt-spun ribbons. The L10-FePt∕Fe2B hard magnetic nanocomposite structure was formed at Vs=20–37m∕s, while the soft magnetic fcc-FePt+amorphous phases were formed at Vs=40–50m∕s. The ribbons melt spun at Vs=37m∕s exhibit in-plane coercivity (Hci)=760kA∕m, remanence (Br)=0.71T, and energy product (BH)max=93.4kJ∕m3. The Br=0.74–0.77T, Hci=681–718kA∕m, and (BH)max=101–108kJ∕m3 were obtained for the ribbons melt spun at Vs=50m∕s and annealed at 748–773K for 900s. The improvement in hard magnetic properties is due to the formation of more finer and homogeneous nanocomposite structure, which results in the enhancement in exchange coupling among the nanosized hard L10-FePt and soft Fe2B magnetic phases.
GeV electron beams from a centimeter-scale channel guided laser wakefield accelerator
Authors: Nakamura K. , Nagler B. , Tóth Cs. , Geddes C. G. R. , Schroeder C. B. , Esarey E. , Leemans W. P. , Gonsalves A. J. , Hooker S. M.
Published: May 2007

Laser wakefield accelerators can produce electric fields of order 10–100GV∕m, suitable for acceleration of electrons to relativistic energies. The wakefields are excited by a relativistically intense laser pulse propagating through a plasma and have a phase velocity determined by the group velocity of the light pulse. Two important effects that can limit the acceleration distance and hence the net energy gain obtained by an electron are diffraction of the drive laser pulse and particle-wake dephasing. Diffraction of a focused ultrashort laser pulse can be overcome by using preformed plasma channels. The dephasing limit can be increased by operating at a lower plasma density, since this results in an increase in the laser group velocity. Here we present detailed results on the generation of GeV-class electron beams using an intense femtosecond laser beam and a 3.3cm long preformed discharge-based plasma channel [W. P. Leemans et al., Nature Physics 2, 696 (2006)]. The use of a discharge-based waveguide permitted operation at an order of magnitude lower density and 15 times longer distance than in previous experiments that relied on laser preformed plasma channels. Laser pulses with peak power ranging from 10–40TW were guided over more than 20 Rayleigh ranges and high quality electron beams with energy up to 1GeV were obtained by channeling a 40TW peak power laser pulse. The dependence of the electron beam characteristics on capillary properties, plasma density, and laser parameters are discussed.
Triarylamine siloxane anode functionalization/hole injection layers in high efficiency/high luminance small-molecule green- and blue-emitting organic light-emitting diodes
Authors: Huang Qinglan , Li Jianfeng , Marks Tobin J. , Evmenenko Guennadi A. , Dutta Pulak
Published: May 2007

High efficiency/high luminance small-molecule organic light-emitting diodes (OLEDs) are fabricated by combining thin, covalently bound triarylamine hole injection/adhesion interlayers with hole- and exciton-blocking/electron transport interlayers in tris(8-hydroxyquinolato)aluminum(III) (Alq) and tetrakis(2-methyl-8-hydroxyquinolinato)borate (BQ4−)-based OLEDs. Green-emitting OLEDs with maximum luminance ∼85000cd∕m2, power and forward external quantum efficiencies as high as 15.2lm∕W and 4.4±0.5%, respectively, and turn-on voltages ∼4.5V are achieved in devices of the structure, ITO∕N,N′-diphenyl-N,N′-bis(p-trichlorosilylpropylphenyl)(1,1′-biphenyl)-4,4′-diamine (TPD-Si2)/1,4-bis(1-naphthylphenylamino)biphenyl (NPB)/Alq doped with N,N′-di(3-heptyl)quinacridone (DIQA)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)∕Li∕AgMg. Also, bright and efficient blue-emitting OLEDs with turn-on voltages ∼5.0V, maximum luminance ∼30000cd∕m2, and ∼5.0lm∕W and 1.6±0.2% power and external forward quantum efficiencies, respectively, are achieved in devices of the structure, ITO∕TPD-Si2∕NPB∕BQ4−∕BCP∕Li∕Al. TPD-Si2 interlayers are fabricated by spin casting N,N′-diphenyl-N,N′-bis(p-trichlorosilylpropylphenyl)(1,1′-biphenyl)-4,4′-diamine onto the ITO surface, while BCP interlayers are introduced by thermal evaporation. The excellent OLED performance is attributed to the differing functions of the above two interlayers: (1) The TPD-Si2 layer has a direct impact on hole injection by reducing the injection barrier and improving interfacial cohesion, and an indirect but strong effect on electron injection by altering internal electric fields. (2) The BCP layer, doped with lithium, directly reduces the electron injection barrier. Incorporation of both interlayers in OLED structures affords synergistically enhanced hole/electron injection and recombination efficiency. The results demonstrate a strategy to enhance OLED performance and an alternative strategy to increase electron density in electron-limited devices.
Mid-infrared high finesse microcavities and vertical-cavity lasers based on IV–VI semiconductor/BaF2 broadband Bragg mirrors
Authors: Schwarzl T. , Eibelhuber M. , Heiss W. , Kaufmann E. , Springholz G. , Winter A. , Pascher H.
Published: May 2007

We report on molecular beam epitaxially grown high-reflectivity broadband Bragg mirrors for mid-infrared devices using IV–VI semiconductors and BaF2. This material combination exhibits a high ratio between the refractive indices of up to 3.5, leading to a broad mirror stop band with a relative width of 75%. To verify the high quality of the PbEuTe/BaF2 Bragg mirrors, we study a half-wavelength microcavity formed by mirrors with only three periods. The resonance of the microcavity has a narrow linewidth of 5.2 nm corresponding to a very high finesse of 750. From this, a mirror reflectivity higher than 99.7% is deduced, in good agreement to transfer matrix simulations. Furthermore, we demonstrate mid-infrared continuous-wave vertical-cavity surface-emitting lasers based on these mirrors. Optical excitation of laser structures with a PbSe active region results in stimulated emission at various cavity modes between 7.3 and 5.9 μm at temperatures between 54 and 135 K. Laser emission is evidenced by a strong linewidth narrowing with respect to the linewidth of the cavity mode and a clear laser threshold at a pump power of 130 mW at 95 K.
Asymmetry in electron and ion charge collection in a drifting plasma bunch
Authors: Belloni F. , Lorusso A. , Nassisi V.
Published: May 2007

We report on the different behavior of electron and ion currents recorded by a Faraday cup in a plasma bunch generated via laser ablation. An excimer laser was employed to irradiate a Ge target. The current signals were recorded equipping the Faraday cup collector by a set of diaphragms. We found that the electron time-of-flight spectra were fairly similar to the ion ones, but the collected charge yield for electrons was up to 200 times larger than the corresponding ion yield. We ascribed such a discrepancy to the different cup collection efficiency for ions and electrons forming the plasma which was heavily influenced by the plume geometry, the energy of the particles, as well as the diaphragm size. Our findings would suggest that the overall electron charge “tended” to be collected, unlike the ion charge which scaled upon the collection solid angle.
Numerical modeling of diffusive heat transport across magnetic islands and highly stochastic layers
Authors: Hölzl M. , Günter S. , Yu Q. , Lackner K.
Published: May 2007

Diffusive heat transport across magnetic islands and highly stochastic layers is studied numerically for realistic values of χ‖∕χ⊥ in cylindrical geometry, where χ‖ denotes the heat diffusion coefficient parallel and χ⊥ the one perpendicular to the magnetic field lines. The computations are performed with a second-order finite difference scheme, for which the numerical errors are independent from the value of χ‖∕χ⊥ [S. Günter et al., J. Comput. Phys. 209, 354 (2005)]. Sufficient spatial resolution is ensured by using an unsheared helical coordinate system. The heat flux around magnetic islands as well as the effective radial heat diffusivity χr are examined and compared to analytical theory. The temperature perturbations caused by magnetic islands and the resulting bootstrap current perturbations essential for the stability of neoclassical tearing modes are analyzed and compared to analytical predictions [R. Fitzpatrick, Phys. Plasmas 2, 825 (1995)]. Agreement is found in the “small” and “large” island limits, but an enhanced NTM drive is observed in between. A correction factor that can reproduce the numerical results very well is presented. For a highly stochastic layer, produced by five strongly overlapping islands, the radial heat diffusivity χr is determined and compared to several analytical theories.
Observation of three-dimensional shell filling in cylindrical silicon nanowire single electron transistors
Authors: Cho K. H. , Jung Y. C. , Hong B. H. , Hwang S. W. , Oh J. H. , Ahn D. , Suk S. D. , Yeo K. H. , Kim D.-W. , Park D. , Lee W.-S.
Published: April 2007

The authors have measured addition energy spectra from gate-all-around twin silicon nanowire single electron transistors (SETs) with the radius of 5nm and with circular cross sections. Nonmonotonically varying addition energies are observed and the authors interpret them as shell fillings of silicon nanowire quantum dots with three-dimensional harmonic confinement potentials. A 45nm long SET shows 2-1-2-1 filling behavior while a 38nm long SET exhibits 1-2-2-1 filling. These filling behaviors match with the calculated degeneracies of nanowires with different confinement strengths.
Epitaxial stabilization of artificial hexagonal GdMnO3 thin films and their magnetic properties
Authors: Lee D. , Lee J.-H. , Murugavel P. , Jang S. Y. , Noh T. W. , Jo Y. , Jung M.-H. , Ko Y.-D. , Chung J.-S.
Published: May 2007

The authors investigated the role of oxygen partial pressure on the epitaxial growth of an artificial hexagonal GdMnO3 phase, which should exist in an orthorhombic structure in bulk. The hexagonal GdMnO3 film showed diverse, but obvious, magnetic phase transitions with highly enhanced ferromagnetic properties. Its remnant magnetization at 4.2K is higher than those of other hexagonal RMnO3 (R=Ho, Er, and Yb) compounds, and the Curie temperature increases by around 25K. The results demonstrate that the epitaxial stabilization technique is a promising method for fabricating an artificial material with enhanced magnetic properties.
Characterization of plasma parameters, first beam results, and status of electron cyclotron resonance source
Authors: Jain S. K. , Jain Akhilesh , Hannurkar P. R. , Kotaiah S.
Published: May 2007

Electron cyclotron resonance (ECR) plasma source at 50keV, 30mA proton current has been designed, fabricated, and assembled. Its plasma study has been done. Plasma chamber was excited with 350W of microwave power at 2450MHz, along with nitrogen and hydrogen gases. Microwave power was fed to the plasma chamber through waveguide. Plasma density and electron temperature were studied under various operating conditions, such as magnetic field, gas pressure, and transversal distance. Langmuir probe was used for plasma characterization using current-voltage variation. The nitrogen plasma density calculated was approximately 4.5×1011cm−3, and electron temperatures of 3–10eV (cold) and 45–85eV (hot) were obtained. The total ion beam current of 2.5mA was extracted, with two-electrode extraction geometry, at 15keV beam energy. The optimization of the source is under progress to extract 30mA proton beam current at 50keV beam energy, using three-electrode extraction geometry. This source will be used as an injector to continuous wave radio frequency quadrupole, a part of 100MeV proton linac. The required root-mean-square normalized beam emittance is less than 0.2πmmmrad. This article presents the study of plasma parameters, first beam results, and status of ECR proton source.
Mechanism of all-optical spin-dependent polarization switching in Bragg-spaced quantum wells
Authors: Nguyen D. T. , Kwong N. H. , Yang Z. S. , Binder R. , Smirl Arthur L.
Published: May 2007

The authors outline a microscopic theory of pump-induced anisotropy in the optical response of Bragg-spaced quantum wells (BSQWs). Their theory explains the manipulation of the band structure of the BSQWs by the pump through the microscopic interactions between excitons in the quantum wells. They apply their theory to understand the mechanism of an all-optical polarization switch implemented on a BSQW structure. They trace the relation between the strongly spin-dependent exciton-exciton interactions and the switching signal. Reasonably good agreement is found between their theoretical results and experimental data.
Effect of arsenic species on the formation of (Ga)InAs nanostructures after partial capping and regrowth
Authors: Suraprapapich S. , Panyakeow S. , Tu C. W.
Published: May 2007

Surface morphologies of self-assembled (Ga)InAs nanostructures grown by partial-capping-and-regrowth technique using gas-source molecular beam epitaxy (GSMBE) and solid-source molecular beam epitaxy (SSMBE) are compared. With SSMBE under an As4 ambient, as-grown quantum dots (QDs) change to a camel-like nanostructure after being partially overgrown with GaAs. When additional InAs is deposited, quantum-dot molecules are created. In comparison, with GSMBE under As2 overpressure, as-grown QDs are transformed into quantum rings after partial capping with GaAs and then, after regrowth, become double QDs. At higher regrowth temperature, QD rings are formed.
Protecting a lens with air
Authors: Liao Tai-Shan , Chou Eyleen , Tsai Ruei-Hung , Huang Ting-Ming
Published: May 2007

A novel design is the concept of preventing the camera lens from contamination of the particles by using “airwall.” An experimental wireless video camera debris deflecting system was realized and performed to verify the concept. Functional tests have been successfully verified.
Surface plasmon enhanced diffraction in cholesteric liquid crystals
Authors: Hung Wen-Chi , Cheng Wood-Hi , Tsai Ming-Shan , Juan Yi-Chung , Jiang I-Min , Yeh Pochi
Published: May 2007

The authors report the observation of an enhanced optical diffraction in cholesteric liquid crystals (CLCs) due to the presence of silver nanoparticles. The silver nanoparticles are deposited on the surface of one of the indium tin oxide electrodes of the CLC cell. With the application of a proper voltage, the liquid crystals assume its cholesteric phase with the helical axis perpendicular to the applied electric field. The CLC grating was probed by a beam of polarized light in the spectral range from 450to750nm. The direction of propagation of the beam is perpendicular to the helical axis of the liquid crystals. The authors report a significant enhancement in the first-order diffraction efficiency at around 543nm. The results of the experimental observation are presented and discussed.
A photonic crystal localizes light in two dimensions
Authors: Wilson Mark
Published: May 2007

An all-optical system offers a flexible experimental approach to observing a new class of localization effect.
Remembering the oil-drop experiment
Authors: Perry Michael F.
Published: May 2007

In their memoirs, Robert Millikan and Harvey Fletcher describe what happened during the months leading up to their now-famous measurements on charged droplets. But intriguing differences in the accounts make it unclear just who made the key contributions.
Coupled influences of topography and wind on wildland fire behaviour
Authors: Linn Rodman , Winterkamp Judith , Edminster Carleton , Colman Jonah J. , Smith William S.
Published: April 2007

Ten simulations were performed with the HIGRAD/FIRETEC wildfire behaviour model in order to explore its utility in studying wildfire behaviour in inhomogeneous topography. The goal of these simulations is to explore the potential extent of the coupling between the fire, atmosphere, and topography. The ten simulations described in this paper include five different topographies, each run with two different ambient wind speeds of 6 and 12 m s–1. The five topologies explored are: an idealised hill (which serves as the base centerline for the other topographies), two variations of the hill with lateral gradients downwind from the ignition line (one sloping up from the ‘hill’ at the centerline to form an upward sloping canyon parallel to the ambient wind, and the other sloping down from the centerline to form a ridge parallel to the ambient flow), one with a second hill upwind of the ignition line such that the fire is ignited in the bottom of a canyon that runs perpendicular to the ambient wind, and finally a flat terrain. The four non-trivial topographies have the same profile along the centerline downwind of the ignition line to help assess the impacts of topographic gradients that are perpendicular to the ambient wind. It is hoped that analysis of these simulations will help reveal where point-functional models are sufficient, where topographically modified wind fields are needed, and where fully coupled fire and transport models are necessary to properly describe wildfire behaviour.
Two molecular pathways initiate mitochondria-dependent dopaminergic neurodegeneration in experimental Parkinson's disease
Authors: Perier Celine , Bové Jordi , Wu Du-Chu , Dehay Benjamin , Choi Dong-Kug , Jackson-Lewis Vernice , Rathke-Hartlieb Silvia , Bouillet Philippe , Strasser Andreas , Schulz Jörg B. , Przedborski Serge , Vila Miquel
Published: May 2007

Dysfunction of mitochondrial complex I is associated with a wide spectrum of neurodegenerative disorders, including Parkinson's disease (PD). In rodents, inhibition of complex I leads to degeneration of dopaminergic neurons of the substantia nigra pars compacta (SNpc), as seen in PD, through activation of mitochondria-dependent apoptotic molecular pathways. In this scenario, complex I blockade increases the soluble pool of cytochrome
c
in the mitochondrial intermembrane space through oxidative mechanisms, whereas activation of pro-cell death protein Bax is actually necessary to trigger neuronal death by permeabilizing the outer mitochondrial membrane and releasing cytochrome
c
into the cytosol. Activation of Bax after complex I inhibition relies on its transcriptional induction and translocation to the mitochondria. How complex I deficiency leads to Bax activation is currently unknown. Using gene-targeted mice, we show that the tumor suppressor p53 mediates Bax transcriptional induction after PD-related complex I blockade
in vivo
, but it does not participate in Bax mitochondrial translocation in this model, either by a transcription-independent mechanism or through the induction of BH3-only proteins Puma or Noxa. Instead, Bax mitochondrial translocation in this model relies mainly on the JNK-dependent activation of the BH3-only protein Bim. Targeting either Bax transcriptional induction or Bax mitochondrial translocation results in a marked attenuation of SNpc dopaminergic cell death caused by complex I inhibition. These results provide further insight into the pathogenesis of PD neurodegeneration and identify molecular targets of potential therapeutic significance for this disabling neurological illness.
Probing a moving target with a plastic unfolding intermediate of an ankyrin-repeat protein
Authors: Werbeck Nicolas D. , Itzhaki Laura S.
Published: May 2007

Repeat proteins are composed of tandem arrays of 30- to 40-residue structural motifs and are characterized by short-range interactions between residues close in sequence. Here we have investigated the equilibrium unfolding of D34, a 426-residue fragment of ankyrinR that comprises 12 ankyrin repeats. We show that D34 unfolds via an intermediate in which the C-terminal half of the protein is structured and the N-terminal half is unstructured. Surprisingly, however, we find that we change the unfolding process when we attempt to probe it. Single-site, moderately destabilizing mutations at the C terminus result in different intermediates dominating. The closer to the C terminus the mutation, the fewer repeats are structured in the intermediate; thus, structure in the intermediate frays from the site of the mutation. This behavior contrasts with the robust unfolding of globular proteins in which mutations can destabilize an intermediate but do not cause a different intermediate to be populated. We suggest that, for large repeat arrays, the energy landscape is very rough, with many different low-energy species containing varying numbers of folded modules so the species that dominates can be altered easily by single, conservative mutations. The multiplicity of partly folded states populated in the equilibrium unfolding of D34 is also mirrored by the kinetic folding mechanism of ankyrin-repeat proteins in which we have observed that parallel pathways are accessible from different initiation sites in the structure.
The
Orientia tsutsugamushi
genome reveals massive proliferation of conjugative type IV secretion system and host–cell interaction genes
Authors: Cho Nam-Hyuk , Kim Hang-Rae , Lee Jung-Hee , Kim Se-Yoon , Kim Jaejong , Cha Sunho , Kim Sang-Yoon , Darby Alistair C. , Fuxelius Hans-Henrik , Yin Jun , Kim Ju Han , Kim Jihun , Lee Sang Joo , Koh Young-Sang , Jang Won-Jong , Park Kyung-Hee , Andersson Siv G. E. , Choi Myung-Sik , Kim Ik-Sang
Published: May 2007

Scrub typhus is caused by the obligate intracellular rickettsia
Orientia tsutsugamushi
(previously called
Rickettsia tsutsugamushi
). The bacterium is maternally inherited in trombicuid mites and transmitted to humans by feeding larvae. We report here the 2,127,051-bp genome of the Boryong strain, which represents the most highly repeated bacterial genome sequenced to date. The repeat density of the scrub typhus pathogen is 200-fold higher than that of its close relative
Rickettsia prowazekii
, the agent of epidemic typhus. A total of 359
tra
genes for components of conjugative type IV secretion systems were identified at 79 sites in the genome. Associated with these are >200 genes for signaling and host–cell interaction proteins, such as histidine kinases, ankyrin-repeat proteins, and tetratrico peptide-repeat proteins. Additionally, the
O. tsutsugamushi
genome contains >400 transposases, 60 phage integrases, and 70 reverse transcriptases. Deletions and rearrangements have yielded unique gene combinations as well as frequent pseudogenization in the
tra
clusters. A comparative analysis of the
tra
clusters within the genome and across strains indicates sequence homogenization by gene conversion, whereas complexity, diversity, and pseudogenization are acquired by duplications, deletions, and transposon integrations into the amplified segments. The results suggest intragenomic duplications or multiple integrations of a massively proliferating conjugative transfer system. Diversifying selection on host–cell interaction genes along with repeated population bottlenecks may drive rare genome variants to fixation, thereby short-circuiting selection for low complexity in bacterial genomes.
Deletion of the phosphoinositide 3-kinase p110γ gene attenuates murine atherosclerosis
Authors: Chang James D. , Sukhova Galina K. , Libby Peter , Schvartz Eugenia , Lichtenstein Alice H. , Field Seth J. , Kennedy Caitlin , Madhavarapu Swetha , Luo Ji , Wu Dianqing , Cantley Lewis C.
Published: May 2007

Inflammatory cell activation by chemokines requires intracellular signaling through phosphoinositide 3-kinase (PI3-kinase) and the PI3-kinase-dependent protein serine/threonine kinase Akt. Atherosclerosis is a chronic inflammatory process driven by oxidatively modified (atherogenic) lipoproteins, chemokines, and other agonists that activate PI3-kinase. Here we show that macrophage PI3-kinase/Akt is activated by oxidized low-density lipoprotein, inflammatory chemokines, and angiotensin II. This activation is markedly reduced or absent in macrophages lacking p110γ, the catalytic subunit of class Ib PI3-kinase. We further demonstrate activation of macrophage/foam cell PI3-kinase/Akt in atherosclerotic plaques from apolipoprotein E (apoE)-null mice, which manifest an aggressive form of atherosclerosis, whereas activation of PI3-kinase/Akt was undetectable in lesions from apoE-null mice lacking p110γ despite the presence of class Ia PI3-kinase. Moreover, plaques were significantly smaller in apoE
−/−
p110γ
−/−
mice than in apoE
−/−
p110γ
+/+
or apoE
−/−
p110γ
+/−
mice at all ages studied. In marked contrast to the embryonic lethality seen in mice lacking class Ia PI3-kinase, germ-line deletion of p110γ results in mice that exhibit normal viability, longevity, and fertility, with relatively well tolerated defects in innate immune and inflammatory responses that may play a role in diseases such as atherosclerosis and multiple sclerosis. Our results not only shed mechanistic light on inflammatory signaling during atherogenesis, but further identify p110γ as a possible target for pharmacological intervention in the primary and secondary prevention of human atherosclerotic cardiovascular disease.
The Molecular Mechanism of Hepcidin-mediated Ferroportin Down-Regulation
Authors: De Domenico Ivana , Ward Diane McVey , Langelier Charles , Vaughn Michael B. , Nemeth Elizabeta , Sundquist Wesley I. , Ganz Tomas , Musci Giovanni , Kaplan Jerry
Published: May 2007

Ferroportin (Fpn) is the only known iron exporter in vertebrates. Hepcidin, a peptide secreted by the liver in response to iron or inflammation, binds to Fpn, inducing its internalization and degradation. We show that after binding of hepcidin, Fpn is tyrosine phosphorylated at the plasma membrane. Mutants of human Fpn that do not get internalized or that are internalized slowly show either absent or impaired phosphorylation. We identify adjacent tyrosines as the phosphorylation sites and show that mutation of both tyrosines prevents hepcidin-mediated Fpn internalization. Once internalized, Fpn is dephosphorylated and subsequently ubiquitinated. An inability to ubiquitinate Fpn does not prevent hepcidin-induced internalization, but it inhibits the degradation of Fpn. Ubiquitinated Fpn is trafficked through the multivesicular body pathway en route to degradation in the late endosome/lysosome. Depletion of proteins involved in multivesicular body trafficking (Endosome Sorting Complex Required for Transport proteins), by small-interfering RNA, reduces the trafficking of Fpn-green fluorescent to the lysosome.
The Role of Trs65 in the Ypt/Rab Guanine Nucleotide Exchange Factor Function of the TRAPP II Complex
Authors: Liang Yongheng , Morozova Nadya , Tokarev Andrei A. , Mulholland Jonathan W. , Segev Nava
Published: May 2007

The conserved modular complex TRAPP is a guanine nucleotide exchanger (GEF) for the yeast Golgi Ypt-GTPase gatekeepers. TRAPP I and TRAPP II share seven subunits and act as GEFs for Ypt1 and Ypt31/32, respectively, which in turn regulate transport into and out of the Golgi. Trs65/Kre11 is one of three TRAPP II-specific subunits. Unlike the other two subunits, Trs120 and Trs130, Trs65 is not essential for viability, is conserved only among some fungi, and its contribution to TRAPP II function is unclear. Here, we provide genetic, biochemical, and cellular evidence for the role of Trs65 in TRAPP II function. First, like Trs130, Trs65 localizes to the trans-Golgi. Second, TRS65 interacts genetically with TRS120 and TRS130. Third, Trs65 interacts physically with Trs120 and Trs130. Finally, trs65 mutant cells have low levels of Trs130 protein, and they are defective in the GEF activity of TRAPP II and the intracellular distribution of Ypt1 and Ypt31/32. Together, these results show that Trs65 plays a role in the Ypt GEF activity of TRAPP II in concert with the two other TRAPP II-specific subunits. Elucidation of the role played by Trs65 in intracellular trafficking is important for understanding how this process is coordinated with two other processes in which Trs65 is implicated: cell wall biogenesis and stress response.
Campylobacter jejuni
colonization and transmission in broiler chickens: a modelling perspective
Authors: Conlan Andrew J.K , Coward Christopher , Grant Andrew J , Maskell Duncan J , Gog Julia R
Published: May 2007

Campylobacter jejuni
is one of the most common causes of acute enteritis in the developed world. The consumption of contaminated poultry, where
C. jejuni
is believed to be a commensal organism, is a major risk factor. However, the dynamics of this colonization process in commercially reared chickens is still poorly understood. Quantification of these dynamics of infection at an individual level is vital to understand transmission within populations and formulate new control strategies. There are multiple potential routes of introduction of
C. jejuni
into a commercial flock. Introduction is followed by a rapid increase in environmental levels of
C. jejuni
and the level of colonization of individual broilers. Recent experimental and epidemiological evidence suggest that the celerity of this process could be masking a complex pattern of colonization and extinction of bacterial strains within individual hosts. Despite the rapidity of colonization, experimental transmission studies exhibit a highly variable and unexplained delay time in the initial stages of the process. We review past models of transmission of
C. jejuni
in broilers and consider simple modifications, motivated by the plausible biological mechanisms of clearance and latency, which could account for this delay. We show how simple mathematical models can be used to guide the focus of experimental studies by providing testable predications based on our hypotheses. We conclude by suggesting that competition experiments could be used to further understand the dynamics and mechanisms underlying the colonization process. The population models for such competition processes have been extensively studied in other ecological and evolutionary contexts. However,
C. jejuni
can potentially adapt phenotypically through phase variation in gene expression, leading to unification of ecological and evolutionary time-scales. For a theoretician, the colonization dynamics of
C. jejuni
offer an experimental system to explore these ‘phylodynamics’, the synthesis of population dynamics and evolutionary biology.
Crystallographic dissolution of high purity aluminium
Authors: Koroleva E.V , Thompson G.E , Skeldon P , Noble B
Published: May 2007

Alkaline etching of high purity aluminium has been examined using the complementary techniques of scanning electron microscopy and atomic force microscopy. Provision of specific grain orientations, generated by zone melting, has revealed dissolution rates of individual grains which decrease in the order {334}>{225}>{119}. Further, the faceting of the {334} grain, which has an orientation close to (111), reveals the crystallographic nature of alkaline etching of high purity aluminium, with the limited presence of discrete cathodic sites. For the {119} grain orientation, distinct faceting is replaced by a cellular texture that is elongated in the 〈120〉 direction. The {225} grain reveals cells elongated in the 〈111〉 direction, with step-like features present across the surface. These step features are explained by dissolution along preferred crystallographic directions to reveal facets of low-energy planes of appropriate separation and associated steps.
Spatial turnover in the global avifauna
Authors: Gaston Kevin J , Davies Richard G , Orme C. David L , Olson Valerie A , Thomas Gavin H , Ding Tzung-Su , Rasmussen Pamela C , Lennon Jack J , Bennett Peter M , Owens Ian P.F , Blackburn Tim M
Published: May 2007

Despite its wide implications for many ecological issues, the global pattern of spatial turnover in the occurrence of species has been little studied, unlike the global pattern of species richness. Here, using a database on the breeding distributions of birds, we present the first global maps of variation in spatial turnover for an entire taxonomic class, a pattern that has to date remained largely a matter of conjecture, based on theoretical expectations and extrapolation of inconsistent patterns from different biogeographic realms. We use these maps to test four predictions from niche theory as to the form that this variation should take, namely that turnover should increase with species richness, towards lower latitudes, and with the steepness of environmental gradients and that variation in turnover is determined principally by rare (restricted) species. Contrary to prediction, we show that turnover is high both in areas of extremely low and high species richness, does not increase strongly towards the tropics, and is related both to average environmental conditions and spatial variation in those conditions. These results are closely associated with a further important and novel finding, namely that global patterns of spatial turnover are driven principally by widespread species rather than the restricted ones. This complements recent demonstrations that spatial patterns of species richness are also driven principally by widespread species, and thus provides an important contribution towards a unified model of how terrestrial biodiversity varies both within and between the Earth's major land masses.
Motility and autotoxicity inKarenia mikimotoi(Dinophyceae)
Authors: Gentien P , Lunven M , Lazure P , Youenou A , Crassous M.P
Published: May 2007

Karenia mikimotoiis one of the most common red-tide dinoflagellates proliferating in the eastern North Atlantic and around Japan. Kills of marine fauna are associated with its blooms. In mixed water columns it migrates vertically, while in stratified water columns, the population remains confined within pycnocline layers. Wind events, increasing mixing and agitation initiate declines in its populations. This paper is focused on the formulation of mortality rate relative to shear rate. Autotoxicity is demonstrated by the use of a synthetic toxin. Bioconvection observed in cultures allows the establishment of a trade-off between phototropism, which leads to the local accumulation of cells, and their autotoxicity, which would prevent cell concentration. The combination of these processes allows diffusion of the toxin into the underlying water, where it subsequently degrades. Confinement of the population in the pycnocline layer results also from another trade-off between growth conditions and shear-rate-modulated mortality. A simplified encounter kernel was introduced into the population dynamics equation to account for a mortality factor. Under realistic forcing conditions with a small number of parameters, this model reproduced the confinement of the population in the pycnocline layer, the proper timing and the duration of the recurrentK. mikimotoibloom on the Ushant front (France).
Copepod flow modes and modulation: a modelling study of the water currents produced by an unsteadily swimming copepod
Authors: Jiang Houshuo , Strickler J. Rudi
Published: May 2007

Video observation has shown that feeding-current-producing calanoid copepods modulate their feeding currents by displaying a sequence of different swimming behaviours during a time period of up to tens of seconds. In order to understand the feeding-current modulation process, we numerically modelled the steady feeding currents for different modes of observed copepod motion behaviours (i.e. free sinking, partial sinking, hovering, vertical swimming upward and horizontal swimming backward or forward). Based on observational data, we also reproduced numerically a modulated feeding current associated with an unsteadily swimming copepod. We found that: (i) by changing its propulsive force, a copepod can switch between different swimming behaviours, leading to completely different flow-field patterns in self-generated surrounding flow; (ii) by exerting a time-varying propulsive force, a copepod can modulate temporally the basic flow modes to create an unsteady feeding current which manipulates precisely the trajectories of entrained food particles over a long time period; (iii) the modulation process may be energetically more efficient than exerting a constant propulsive force onto water to create a constant feeding current of a wider entrainment range. A probable reason is that the modulated unsteady flow entrains those water parcels containing food particles and leaves behind those without valuable food in them.
Linking environmental variability and fish performance: integration through the concept of scope for activity
Authors: Claireaux Guy , Lefrançois Christel
Published: May 2007

Investigating the biological mechanisms linking environmental variability to fish production systems requires the disentangling of the interactions between habitat, environmental adaptation and fitness. Since the number of environmental variables and regulatory processes is large, straightening out the environmental influences on fish performance is intractable unless the mechanistic analysis of the ‘fish-milieu’ system is preceded by an understanding of the properties of that system. While revisiting the key points in our currently poorly integrated understanding of fish ecophysiology, we have highlighted the explanatory potential contained within Fry's (Fry 1947Univ. Toronto Stud. Biol. Ser.55, 1–62) concept of metabolic scope and categorization of environmental factors. These two notions constitute a pair of powerful tools for conducting an external (at the emerging property level) analysis of the environmental influences on fish, as well as an internal (mechanistic) examination of the behavioural, morphological and physiological processes involved. Using examples from our own and others work, we have tried to demonstrate that Fry's framework represents a valuable conceptual basis leading to a broad range of testable ecophysiological hypotheses.
Effects of turbidity on the spontaneous and prey-searching activity of juvenile Atlantic cod (Gadus morhua)
Authors: Meager Justin J , Batty Robert S
Published: May 2007

Increasing turbidity in coastal waters in the North Atlantic and adjacent seas has raised concerns about impacts on Atlantic cod (Gadus morhua) using these areas as nurseries. A previous experiment (Meageret al.2005Can. J. Fish. Aquat. Sci.62, 1978–1984) has shown that turbidity (up to 28 beam attenuation m−1) had little effect on the foraging rate of juvenile cod. Although this was attributed to cod using chemoreception in conjunction with vision to locate prey, foraging rates may also be maintained by increased activity. Higher activity, however, is energetically costly and may offset benefits from increased foraging return.

We examined the effects of turbidity on prey searching and spontaneous activity of juvenile cod in the laboratory, by measuring activity with and without prey cues. Activity of juvenile cod was nonlinearly affected by turbidity and was lower at intermediate turbidity, regardless of the presence of prey odour. Activity increased over time when prey odour was present and decreased when absent, but the effects of prey odour were similar across all turbidity levels. Position in the tank was unaffected by turbidity or prey odour. Reduced activity at intermediate turbidities is likely to offset longer prey-search times. At high turbidity (greater than 17 m−1), both longer prey-search times and higher activity indicate that increased energetic costs are probable.
External Constraints on Monetary Policy and the Financial Accelerator
Authors: GERTLER MARK , GILCHRIST SIMON , NATALUCCI FABIO M.
Published: May 2007

We develop a small open economy macroeconomic model where financial conditions influence aggregate behavior. Our goal is to explore the connection between the exchange rate regime and financial distress. We first show that a calibrated version of the model captures well the behavior of the Korean economy during its financial crisis period of 1997–98. In particular, the model accounts for the sharp increase in lending rates and the large drop in output, employment, investment, and measured productivity. The financial market frictions play an important role, further, explaining roughly half the decline in overall economic activity. We then perform some counterfactual exercises to illustrate how the fixed exchange rate regime likely exacerbated the crisis by tying the hands of monetary policy.
Communication by Central Bank Committee Members: Different Strategies, Same Effectiveness?
Authors: EHRMANN MICHAEL , FRATZSCHER MARCEL
Published: May 2007

The paper assesses the communication strategies of the Federal Reserve, the Bank of England, and the European Central Bank and their effectiveness. We find that the effectiveness of communication is not independent from the decision‐making process. The paper shows that the Federal Reserve has been pursuing a highly individualistic communication strategy amid a collegial approach to decision making, while the Bank of England is using a collegial communication strategy and highly individualistic decision making. The European Central Bank (ECB) has chosen a collegial approach both in its communication and in its decision making. Assessing these strategies, we find that predictability of policy decisions and the responsiveness of financial markets to communication are equally good for the Federal Reserve and the ECB. This suggests that there may not be a single best approach to designing a central bank communication strategy.
The Great Inflation of the 1970s
Authors: COLLARD FABRICE , DELLAS HARRIS
Published: May 2007

The two leading explanations for the poor inflation performance during the 1970s are policy opportunism (Barro and Gordon 1983) and “inadvertently” bad monetary policy (Clarida, Gali, and Gertler 2000, Orphanides 2003). The main models of the latter category are that of Orphanides (loose monetary policy was the outcome of mis‐perceptions about potential output rather than of inflation tolerance) and of Clarida, Gali, and Gertler (weak policy reaction to expected inflation led to indeterminacies). We show that both of these models can account for high and persistent inflation and also have satisfactory overall performance if an exceptionally large decrease in productivity took place at that time.
Blood Pressure Treatment and Cognition in the Elderly
Authors: Paran Esther , Anson Ofra
Published: May 2007

While the health and longevity benefits of antihypertensive treatment have been established in past research, the cognitive consequences of blood pressure control in the elderly are still under debate. In this paper, the authors review the current evidence and the different ways in which cognition is measured. Since research on the cognitive consequences of blood pressure control in the elderly population is characterized by a variety of research questions, designs, and cognitive measurements, the authors conclude that a large‐scale study that compares the cognitive benefits of different methods of blood pressure reduction is urgently needed.
Cardiovascular Risk Factors for Alzheimer's Disease
Authors: Rosendorff Clive , Beeri Michal S. , Silverman Jeremy M.
Published: May 2007

There is now sizable literature on the association between traditional cardiovascular risk factors and Alzheimer's disease (AD). Based on epidemiologic studies, both cross‐sectional and longitudinal, there are statistically significant correlations between the prevalence of AD and diabetes, hypercholesterolemia, hypertension, hyperhomocysteinemia, dietary saturated fats, cholesterol, antioxidants, alcohol consumption, smoking, physical activity, the presence of atrial fibrillation, atherosclerotic disease, and the plasma concentration of some hemostatic factors. Most of the cardiovascular risk factors found to be associated with AD are age‐dependent, and the prevalence of AD increases with age. Therefore, the association could simply be attributed to aging. On the other hand, the common pathogenetic mechanisms for the generation of both atherosclerotic disease and AD, such as inflammation and the generation of free radicals, suggest a causal link. If this is the case, the identification of modifiable risk factors for dementia becomes a research priority and early intervention aimed at reducing those cardiovascular risk factors a therapeutic imperative.
The CXCR4 chemokine receptor in acute and chronic leukaemia: a marrow homing receptor and potential therapeutic target
Authors: Burger Jan A. , Bürkle Andrea
Published: May 2007

Chemokine (C‐X‐C motif) receptor 4 (CXCR4) is essential for homing and maintenance of haematopoietic stem cells in distinct stromal cell niches within the marrow. Chemotactic responsiveness of haematopoietic stem cells is restricted to the ligand for CXCR4, stromal cell‐derived factor‐1 (SDF‐1/CXCL12), which is constitutively secreted by marrow stromal cells. Myeloid and lymphoid leukaemia cells also express CXCR4 that induces leukaemia cell chemotaxis and migration beneath marrow stromal cells. CXCR4 expression levels have a major prognostic impact in acute myeloid leukaemia. There is growing in vitro and in vivo evidence that CXCR4 expression by leukaemia cells allows for homing and their retention within the marrow. As such, leukaemia cells appear to utilise CXCR4 to access niches that are normally restricted to progenitor cells, and thereby reside in a microenvironment that favours their growth and survival. CXCR4‐ and integrin‐mediated contact between leukaemia cells and stromal cells protects leukaemia cells from spontaneous and chemotherapy‐induced cell death and therefore may represent a mechanism to explain minimal residual disease and subsequent relapses commonly seen in the treatment of these diseases. This review summarises our current knowledge regarding the importance of CXCR4 in acute and chronic leukaemia, discusses the importance of CXCR4 detection by flow cytometry in the diagnostic workup of leukaemia patients, and introduces the potential role of CXCR4‐targeting compounds for the treatment of leukaemia patients.
Building resilience and resistance against racism and discrimination among Salvadorian female youth in Canada
Authors: Carranza Mirna E.
Published: May 2007

This paper reports on the findings of a qualitative study (32 in‐depth interviews) with Salvadorian mothers and their daughters. In particular this paper focuses on the strategies that mothers and daughters utilized to resist prejudice and racism in their settlement country, Canada. Findings contribute to the literature specifically by drawing attention to the importance of ethnic pride in helping mothers and their daughters bridge significant strains that arise in their acculturation process.