bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of SrTiO3 capping in La2∕3Ca1∕3MnO3 electrodes of different orientations
Authors: Infante I. C. , Sánchez F. , Fontcuberta J. , Estradé S. , Peiró F. , Arbiol J. , Wojcik M. , Jedryka E.
Published: February 2008

We report on the study of the structural, magnetic, and electronic properties of SrTiO3 capped La2∕3Ca1∕3MnO3 electrodes grown on (001) and (110) SrTiO3 substrates. Magnetic properties of the (001) and (110) capped electrodes evolve differently when the capping layer thickness increases, revealing a reduction of the saturation magnetization for the (001) ones. Electronic properties are studied combining Mn55 nuclear magnetic resonance (NMR) and x-ray photoemission spectroscopy (XPS). NMR experiments highlight that electronic phase separation in the (001) electrodes is enhanced by the presence of the SrTiO3 capping layer and XPS measurements show that the electronic state of interfacial Mn ions from (001) electrode is more sensitive to the capping layer.
The role of orbital products in the optimized effective potential method
Authors: Kollmar Christian , Filatov Michael
Published: February 2008

The orbital products of occupied and virtual orbitals are employed as an expansion basis for the charge density generating the local potential in the optimized effective potential method thus avoiding the use of auxiliary basis sets. The high computational cost arising from the quadratic increase of the dimension of this product basis with system size can be greatly reduced by elimination of the linearly dependent products according to a procedure suggested by Beebe and Linderberg [Int. J. Quantum Chem. 12, 683 (1977)]. Numerical results from this approach show a very good agreement with those obtained from balancing the auxiliary basis for the expansion of the local potential with the orbital basis set.
The cyclic CO2 trimer: Observation of a parallel band and determination of an intermolecular out-of-plane torsional frequency
Authors: Dehghany M. , Afshari Mahin , Moazzen-Ahmadi N. , McKellar A. R. W.
Published: February 2008

A new parallel (ΔK=0) band of the cyclic CO2 trimer is observed at 2364cm−1. The trimers are generated in a pulsed supersonic expansion from a slit-jet nozzle and probed with a tunable infrared diode laser. The band is assigned as a combination of an intramolecular CO2 monomer ν3 stretch and an intermolecular out-of-plane torsion, giving a torsional frequency of 12–13cm−1. The band is surprisingly strong and completely unperturbed, providing a rare and near perfect example for a parallel band of a symmetric top molecule with C3h symmetry and zero nuclear spins.
Multiferroic CoFe2O4–Pb(Zr0.52Ti0.48)O3 nanofibers by electrospinning
Authors: Xie S. H. , Li J. Y. , Qiao Y. , Liu Y. Y. , Lan L. N. , Zhou Y. C. , Tan S. T.
Published: February 2008

Multiferroic materials possess two or more types of orders simultaneously that couple the electric and magnetic fields, and composite multiferroics have been widely explored for their excellent magnetoelectric coupling. In this letter, we report a strategy to hybrid multiferroicity at nanoscale. Multiferroic CoFe2O4–Pb(Zr0.52Ti0.48)O3 nanofibers are synthesized by sol-gel process and electrospinning, the spinel structure of CoFe2O4 (CFO) and perovskite structure of Pb(Zr0.52Ti0.48)O3 (PZT) are verified by x-ray diffraction and high resolution transmission electron microscopy, and the multiferroicity of the nanofibers are confirmed by piezoresponse force microscopy and magnetic hysteresis. Excellent ferroelectric and ferromagnetic properties have been observed, which could enable multiferroic devices at nanoscale.
Activation energies and potentials of mean force for water cluster evaporation
Authors: Kathmann Shawn M. , Palmer Bruce J. , Schenter Gregory K. , Garrett Bruce C.
Published: February 2008

Activation energies for water cluster evaporation are of interest in many areas of chemical physics. We present the first computation of activation energies for monomer evaporation of small water clusters using the formalism of dynamical nucleation theory (DNT). To this end, individual evaporation rate constants are computed for water clusters (H2O)i, where i=2–10 for temperatures ranging from 243to333K. These calculations employ a parallel sampling technique utilizing a Global Arrays toolkit. The resulting evaporation rate constants for each cluster are then fitted to Arrhenius equations to obtain activation energies. We discuss DNT evaporation rate constants and their relation to potentials of mean force, activation energies, and how to account for nonseparability of the reaction coordinate in the reactant state partition function.
Hund’s multiplicity rule: From atoms to quantum dots
Authors: Sajeev Y. , Sindelka M. , Moiseyev N.
Published: February 2008

In 1965, Davidson has shown that the textbook explanation for the Hund’s multiplicity rule in atoms, based on the Pauli principle, is wrong. The reason for the failure of the textbook proof, as has been given later by others and as appears today in modern textbooks, it is based on the need to introduce angular electronic correlation into the calculations. Here, we investigate an applicability of this argumentation for helium and for the case of two-electron spherically symmetric rectangular quantum dots (QDs). We show that, for helium and also for the QD, the differences between the singlet and triplet excited states can be explored by calculations within the framework of the mean-field approximation, and, surprisingly, without the need of introducing the angular electronic correlation. Moreover, our calculations have shown that the triplet state of the QD is lower in energy than the corresponding singlet state due to lower electronic repulsion contribution, exactly as being assumed in the oldest explanation of the Hund’s rule based on the Pauli principle.
Effects of compressibility on the finite Larmor radius stabilized Rayleigh–Taylor instability in Z-pinch implosions
Authors: Huang L. , Jian G. D. , Qiu X. M. , Peng X. D. , Wang S. Q.
Published: February 2008

The effects of compressibility on the Rayleigh–Taylor (RT) instability in a finite Larmor radius (FLR) plasma of magnetic field acceleration are studied by means of FLR magnetohydrodynamic (MHD) theory. FLR effects are introduced in the momentum equation of MHD theory through an anisotropic ion stress tensor. The linear mode equation which includes main equilibrium quantities and their high-order differential terms is derived. The dispersion equation is solved numerically. The main results indicate that in the compressible FLR plasma the growth rate of the RT instability displays faster growing and broader wavenumber range; and a new branch of low-frequency and long-wavelength instability, whose real frequency is positive (opposite from the negative real frequency of the RT instability), is found in the compressible FLR plasma. That is, plasma compressibility is a destabilizing factor for both the FLR stabilized RT instability and the new branch of instability.
Damping of Bernstein–Greene–Kruskal modes in collisional plasmas
Authors: Valentini Francesco
Published: February 2008

In this paper, the effect of Coulomb collisions on the stability of Bernstein–Greene–Kruskal (BGK) modes [I. B. Bernstein, J. M. Greene, and M. D. Krukal, Phys. Rev. 108, 546 (1957)] is analyzed by comparing the numerical results of collisional particle-in-cell (PIC) simulations with the theoretical predictions by Zakharov and Karpman [V. E. Zakharov and V. I. Karpman, Sov. Phys. JETP 16, 351 (1963)], for the collisional damping of nonlinear plasma waves. In the absence of collisions, BGK modes are undamped nonlinear electrostatic oscillations, solutions of the Vlasov–Poisson equations; in these structures nonlinearity manifests as the formation of a plateau in the resonant region of the particle distribution function, due to trapping of resonant particles, thus preventing linear Landau damping. When particle-particle Coulomb collisions are effective, this plateau is smoothed out since collisions drive the velocity distribution towards the Maxwellian shape, thus destroying the BGK structure. As shown by Zakharov and Karpman in 1963, under certain assumptions, an exponential time decay with constant damping rate is predicted for the electric field amplitude and a linear dependence of the damping rate on the collision frequency is found. In this paper, the theory by Zakharov and Karpman is revisited and the effects of collisions on the stability of BGK modes and on the long time evolution of nonlinear Landau damping are numerically investigated. The numerical results are obtained through a collisional PIC code that reproduces a physical phenomenology also observed in recent experiments with trapped pure electron plasmas.
Porosity dependence of electron percolation in nanoporous TiO2 layers
Authors: Ofir Ashi , Dor Snir , Grinis Larisa , Zaban Arie , Dittrich Thomas , Bisquert Juan
Published: February 2008

The electron diffusion coefficient at varying porosity has been determined in a series of nanostructured TiO2 films of different initial thicknesses. The porosity was changed by applying different pressures prior to sintering, thereby modifying the internal morphology of the films though not their chemical and surface conditions. A systematic increase of the effective diffusion coefficient was observed as the porosity was decreased, indicating the improvement of the internal connectivity of the network of nanoparticles. The experimental results have been rationalized using percolation theory. First of all, applying a power law dependence, the diffusion coefficient as a function of porosity from different films collapsed in a single master curve. In addition, application of the models of effective medium approximation (EMA) allows us to compare the experimental results with previous data from Monte Carlo simulation. The different data show a similar dependence in agreement with the EMA predictions, indicating that the geometrical effect of electron transport due to variation of porous morphology in TiO2 nanoparticulate networks is well described by the percolation concept.
Properties of N-polar AlGaN/GaN heterostructures and field effect transistors grown by metalorganic chemical vapor deposition
Authors: Keller S. , Suh C. S. , Chen Z. , Chu R. , Rajan S. , Fichtenbaum N. A. , Furukawa M. , DenBaars S. P. , Speck J. S. , Mishra U. K.
Published: February 2008

Smooth N-polar GaN/AlxGa1−xN/GaN heterostructures with a different Al mole fraction were grown by metalorganic chemical vapor deposition on (0001) sapphire substrates with a misorientation angle of 4° toward the a-sapphire plane. The sheet electron density of the two-dimensional electron gas (2DEG), which formed at the upper GaN/AlxGa1−xN interface increased with an increasing Al-mole fraction in the AlxGa1−xN layer and increasing silicon modulation doping, similar to the observations for Ga-polar heterostructures. The transport properties of the 2DEG, however, were anisotropic. The growth on vicinal substrates led to the formation of well ordered multiatomic steps during AlxGa1−xN growth and the sheet resistance of the 2DEG parallel to the steps was about 25% lower than the resistance measured in the perpendicular direction. The fabricated devices exhibited a drain-source current, IDS, of 0.9 A/mm at a gate-source voltage +1 V. At a drain-source voltage of 10 V and IDS=300 mA/mm, current-gain and maximum oscillation frequencies of 15 and 38 GHz, respectively, were measured.
Sheath and presheath in ion-ion plasmas via particle-in-cell simulation
Authors: Meige A. , Leray G. , Raimbault J.-L. , Chabert P.
Published: February 2008

A full particle-in-cell simulation is developed to investigate electron-free plasmas constituted of positive and negative ions under the influence of a dc bias voltage. It is shown that high-voltage sheaths following the classical Child-law sheaths form within a few microseconds (which corresponds to the ion transit time) after the dc voltage is applied. It is also shown that there exists the equivalent of a Bohm criterion where a presheath accelerates the ions collected at one of the electrodes up to the sound speed before they enter the sheath. From an applied perspective, this leads to smaller sheaths than one would expect.
Anisotropic mobility in large grain size solution processed organic semiconductor thin films
Authors: Headrick R. L. , Wo S. , Sansoz F. , Anthony J. E.
Published: February 2008

The hollow pen method for writing thin films of materials from solution is utilized to deposit films of 6,13-bis(tri-isopropylsilylethynyl) pentacene (TIPS pentacene) onto SiO2 surfaces with pre-patterned source/drain gold contacts. We demonstrate that large domains are obtained for TIPS pentacene films deposited from 0.5–4.0wt% solutions with toluene. Crystalline grains with (001) orientation are observed to grow with sizes that can exceed 1mm along the writing direction. A preferred azimuthal orientation is also selected by the process, resulting in anisotropic field effect transistor mobility in the films.
Electrical and thermal transport in single nickel nanowire
Authors: Ou M. N. , Yang T. J. , Harutyunyan S. R. , Chen Y. Y. , Chen C. D. , Lai S. J.
Published: February 2008

The thermal conductivity and electrical resistivity of a suspended nickel nanowire have been measured for T=15–300K. The temperature dependence of the thermal conductivity and the Lorenz number strongly differ from the bulk. The comparison of the transports in the Ni nanowire shows, that at temperatures 75<T<300K Wiedemann–Franz (WF) law holds, whereas at temperatures T<75K the WF law is violated, indicating that thermal current in this material is suppressed more than electrical current. The results are explained by combined effect of confined dimension, enhanced disorder, and grown contribution of N-processes.
Precipitation analysis on P-implanted silicon by reflectivity spectrum
Authors: Huang Shih-An , Lo Kuang-Yao , Hsu Li-Hsuan , Hung Kuang-Ming
Published: February 2008

Reflectivity measurement is used to investigate the precipitation of low-energy phosphorous (P)-implanted Si(111) followed by rapid thermal annealing (RTA). The electrically activated dopant concentration near the surface broadens the critical point peaks and shifts them toward low-photon energy side. The redshift of the E2 peak in the imaginary part of dielectric function is a function of the annealing condition and is strongly related to the electrically activated dopant concentration. The precipitation of P atoms, which arises from the excess P atoms in silicon at lower RTA temperature, is observed through the reflectivity spectrum and theoretical inference.
Monolithic vertical microcavities based on tetracene single crystals
Authors: Del Carro Pompilio , Camposeo Andrea , Persano Luana , Tavazzi Silvia , Campione Marcello , Papagni Antonio , Raimondo Luisa , Silvestri Leonardo , Spearman Peter , Cingolani Roberto , Pisignano Dario
Published: February 2008

The authors report on monolithic, light-emitting vertical microcavities based on an organic semiconductor single crystal. The devices are realized by reactive electron-beam deposition of dielectric mirrors and growth of tetracene crystals by physical vapor transport. The microcavities exhibit optical cavity modes in the visible range (550–580nm) with full width at half maximum down to 2–3nm, corresponding to a Q factor of about 200, and polarization-induced modal splitting up to 20meV. These results open perspectives for the realization of polarized-emitting optoelectronic devices based on organic crystals.
High-efficiency and solution processible multilayer white polymer light-emitting diodes using neutral conjugated surfactant as an electron injection layer
Authors: Zhang Yong , Huang Fei , Jen Alex K.-Y. , Chi Yun
Published: February 2008

High-efficiency white polymer light-emitting diodes were fabricated by using an yellow-emitting osmium complex Os(fptz)2(dppe) [fptz=3-trifluoromethyl-5-(2-pyridyl)-1,2,4-triazole, dppe=cis-1,2-bis-(dipheneyl-phosphino) ethylene] doped into blue fluorescent copolymer based on an ultraviolet-blue light emitting host poly[2,7-(9,9-dioctylfluorene)-co-1,3-(5-carbazolphenylene)] and a blue light emitting component 4-N,N-diphenylaminostilbene (PFCz-DPS1-OXD5) as the emissive layer and a neutral conjugated surfactant, poly[9,9-bis(6′(diethanolamino)hexyl)-fluorene] (PFN-OH), as the electron injection layer sandwiched between the emissive layer and Al cathode. The device with the configuration of indium tin oxide/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid)/poly(N-vinylcarbazole)/Os(fptz)2(dppe)(1wt%):PFCz-DPS1-OXD5∕PFN-OH∕Al exhibited efficient white light emission at the Commission Internationale de I’Eclairage coordinates of (0.33, 0.34) and a maximum luminance efficiency of 16.9cd∕A and brightness of 22100cd∕m2.
Interfacial potential in La1−xCaxMnO3∕SrTiO3:Nb junctions with different Ca contents
Authors: Lü W. M. , Sun J. R. , Wang D. J. , Xie Y. W. , Liang S. , Chen Y. Z. , Shen B. G.
Published: February 2008

Manganite-based heterojunctions La1−xCaxMnO3∕SrTiO3:Nb (0.05wt%) with x=0.1, 0.2, 0.33, 0.65, 0.75, and 1 have been fabricated, and the effects of Ca content on the interfacial potential are experimentally studied. Rectifying behavior well described by the Shockley equation is observed, and the interfacial potential (VD) is obtained for all of the junctions based on an analysis of the current-voltage characteristics. The most remarkable result of the present work is the strong dependence of the interfacial potential on the carrier content of La1−xCaxMnO3 films: VD increases monotonously from ∼0.6to∼1.1V as x sweeps from 0.1 to 1. Influence on VD of the Fermi energy and Jahn–Teller effect in La1−xCaxMnO3 films are discussed.
Magnetic properties of Heusler compounds Ru2CrGe and Ru2CrSn
Authors: Okada Hironari , Koyama Keiichi , Watanabe Kazuo , Kusakari Yosuke , Kanomata Takeshi , Nishihara Hironori
Published: February 2008

We have succeeded in synthesizing the Heusler compounds Ru2CrGe and Ru2CrSn and performed magnetization measurements in high magnetic fields up to 18T in order to investigate the magnetic properties of Ru2CrGe and Ru2CrSn. We confirmed that the compounds have an ordered Heusler L21 structure. It was found that Ru2CrGe is an antiferromagnet with the Néel temperature TN=13K and Ru2CrSn shows a spin-glass-like behavior below 7K. The Heisenberg exchange constants determined on the basis of the experimental results for Ru2CrGe are different from the values of Mn-based Heusler compounds.
Inhomogeneous magnetoelectric coupling in Pb(Zr,Ti)O3/Terfenol-D laminate composite
Authors: Zhou Jian-ping , Meng Ling , Xia Ze-hu , Liu Peng , Liu Gang
Published: February 2008

Inhomogeneous magnetoelectric coupling in a simple Pb(Zr,Ti)O3/Terfenol-D laminate composite is investigated. Four magnetic-field-induced voltage (MIV) and three electric-field-induced magnetization (EIM) resonance frequencies are caused by magnetomechanical and electromechanical resonances. The different positions in the sample have different contributions to the MIV and EIM, which are mainly related to the resonant behaviors and the corresponding strain distribution. The MIV distribution shows mirror symmetry, while the EIM distribution shows mirror antisymmetry. The EIM with different directions forms close electric-field-induced magnetic loops around Terfonel-D to meet the lowest magnetic energy. These results are helpful for the future design of magnetoelectric devices.
Hiring Difficulties and Manpower Flows: Does Labour Market Density Matter?
Authors: Blanc Michel , Cahuzac Eric , Tahar Gabriel
Published: February 2008

We analyse the impact of density on labour markets when firms and workers are heterogeneous. Using the results of a survey carried out in the French Midi-Pyrénées region, we show that, for comparable sizes and sectors, recruiting firms in low-density areas experience more difficulties in finding workers meeting the requirements of the jobs, especially since being usually located far away from large urban agglomerations, they appear to hold little attractiveness for potential migrants. As a consequence, they recruit less and the competition between firms on the local labour market is reduced. This, in turn, contributes to lessen the hiring difficulties for firms that do post vacancies in low-density areas. The labour market density therefore has opposite effects on the causes of hiring difficulties, but we show that its overall impact on the frequency of those difficulties for firms which hire is negative. Finally, because they are less likely to find a better match than their current job, employees living in low-density local labour markets have a lower tendency to resign than other workers do. As a consequence, turnover increases density.
Local Linear Estimation of Spatially Varying Coefficient Models: An Improvement on the Geographically Weighted Regression Technique
Authors: Wang Ning , Mei Chang-Lin , Yan Xiao-Dong
Published: February 2008

Geographically weighted regression (GWR), as a useful method for exploring spatial non-stationarity of a regression relationship, has been applied to a variety of areas. In this method a spatially varying coefficient model is locally calibrated and the spatial-variation patterns of the locally estimated regression coefficients are taken as the main evidence of spatial nonstationarity for the underlying data-generating processes. Therefore, the validity of the analysis results drawn by GWR is closely dependent on the accuracy between the underlying coefficients and their estimates. Motivated by the local polynomial-modelling technique in statistics, we propose a local linear-based GWR for the spatially varying coefficient models, in which the coefficients are locally expanded as linear functions of the spatial coordinates and then estimated by the weighted least-squares procedure. Some theoretical and numerical comparisons with GWR are conducted and the results demonstrate that the proposed method can significantly improve GWR, not only in goodness-of-fit of the whole regression function but also in reducing bias of the coefficient estimates.
Ethnic-Minority Businesses in the UK: A Review of Research and Policy Developments
Authors: Ram Monder , Jones Trevor
Published: February 2008

In recent years there have been important academic and policy-related developments in the field of ethnic-minority entrepreneurship in the UK. It is a subject that is marked by increasing theoretical sophistication and activity on the part of policy makers and practitioners. We investigate the principal theoretical and policy developments in UK research, and identify issues for future investigation. In relation to theoretical developments, the contribution of a ‘mixed-embeddedness’ perspective is highlighted; this stresses the importance of social, economic, and institutional processes (rather than ‘ethnic culture’). Although the number of initiatives directed at ethnic-minority businesses is growing, their effectiveness in promoting ‘upward mobility’ is still open to question. Further attention needs to be accorded to the rationale and ultimate beneficiaries of such measures. Future research needs to locate ethnic-minority entrepreneurship in its political and economic contexts. Potential new topics for policy and research include: the social contribution of ethnic-minority entrepreneurship, ethnic-minority women in self-employment, and ‘new communities’.
Akt regulates centrosome migration and spindle orientation in the early Drosophila melanogaster embryo
Authors: Buttrick Graham J. , Beaumont Luke M.A. , Leitch Jessica , Yau Christopher , Hughes Julian R. , Wakefield James G.
Published: February 2008

Correct positioning and morphology of the mitotic spindle is achieved through regulating the interaction between microtubules (MTs) and cortical actin. Here we find that, in the Drosophila melanogaster early embryo, reduced levels of the protein kinase Akt result in incomplete centrosome migration around cortical nuclei, bent mitotic spindles, and loss of nuclei into the interior of the embryo. We show that Akt is enriched at the embryonic cortex and is required for phosphorylation of the glycogen synthase kinase-3β homologue Zeste-white 3 kinase (Zw3) and for the cortical localizations of the adenomatosis polyposis coli (APC)–related protein APC2/E-APC and the MT + Tip protein EB1. We also show that reduced levels of Akt result in mislocalization of APC2 in postcellularized embryonic mitoses and misorientation of epithelial mitotic spindles. Together, our results suggest that Akt regulates a complex containing Zw3, Armadillo, APC2, and EB1 and that this complex has a role in stabilizing MT–cortex interactions, facilitating both centrosome separation and mitotic spindle orientation.
Importin-β and the small guanosine triphosphatase Ran mediate chromosome loading of the human chromokinesin Kid
Authors: Tahara Kiyoshi , Takagi Masatoshi , Ohsugi Miho , Sone Takefumi , Nishiumi Fumiko , Maeshima Kazuhiro , Horiuchi Yasuomi , Tokai-Nishizumi Noriko , Imamoto Fumio , Yamamoto Tadashi , Kose Shingo , Imamoto Naoko
Published: February 2008

Nucleocytoplasmic transport factors mediate various cellular processes, including nuclear transport, spindle assembly, and nuclear envelope/pore formation. In this paper, we identify the chromokinesin human kinesin-like DNA binding protein (hKid) as an import cargo of the importin-α/β transport pathway and determine its nuclear localization signals (NLSs). Upon the loss of its functional NLSs, hKid exhibited reduced interactions with the mitotic chromosomes of living cells. In digitonin-permeabilized mitotic cells, hKid was bound only to the spindle and not to the chromosomes themselves. Surprisingly, hKid bound to importin-α/β was efficiently targeted to mitotic chromosomes. The addition of Ran–guanosine diphosphate and an energy source, which generates Ran–guanosine triphosphate (GTP) locally at mitotic chromosomes, enhanced the importin-β–mediated chromosome loading of hKid. Our results indicate that the association of importin-β and -α with hKid triggers the initial targeting of hKid to mitotic chromosomes and that local Ran-GTP–mediated cargo release promotes the accumulation of hKid on chromosomes. Thus, this study demonstrates a novel nucleocytoplasmic transport factor–mediated mechanism for targeting proteins to mitotic chromosomes.
Australin: a chromosomal passenger protein required specifically for Drosophila melanogaster male meiosis
Authors: Gao Shan , Giansanti Maria Grazia , Buttrick Graham J. , Ramasubramanyan Sharada , Auton Adam , Gatti Maurizio , Wakefield James G.
Published: February 2008

The chromosomal passenger complex (CPC), which is composed of conserved proteins aurora B, inner centromere protein (INCENP), survivin, and Borealin/DASRA, localizes to chromatin, kinetochores, microtubules, and the cell cortex in a cell cycle–dependent manner. The CPC is required for multiple aspects of cell division. Here we find that Drosophila melanogaster encodes two Borealin paralogues, Borealin-related (Borr) and Australin (Aust). Although Borr is a passenger in all mitotic tissues studied, it is specifically replaced by Aust for the two male meiotic divisions. We analyzed aust mutant spermatocytes to assess the effects of fully inactivating the Aust-dependent functions of the CPC. Our results indicate that Aust is required for sister chromatid cohesion, recruitment of the CPC to kinetochores, and chromosome alignment and segregation but not for meiotic histone phosphorylation or spindle formation. Furthermore, we show that the CPC is required earlier in cytokinesis than previously thought; cells lacking Aust do not initiate central spindle formation, accumulate anillin or actin at the cell equator, or undergo equatorial constriction.
Molecular chaperone Hsp90 stabilizes Pih1/Nop17 to maintain R2TP complex activity that regulates snoRNA accumulation
Authors: Zhao Rongmin , Kakihara Yoshito , Gribun Anna , Huen Jennifer , Yang Guocheng , Khanna May , Costanzo Michael , Brost Renée L. , Boone Charles , Hughes Timothy R. , Yip Christopher M. , Houry Walid A.
Published: February 2008

Hsp90 is a highly conserved molecular chaperone that is involved in modulating a multitude of cellular processes. In this study, we identify a function for the chaperone in RNA processing and maintenance. This functionality of Hsp90 involves two recently identified interactors of the chaperone: Tah1 and Pih1/Nop17. Tah1 is a small protein containing tetratricopeptide repeats, whereas Pih1 is found to be an unstable protein. Tah1 and Pih1 bind to the essential helicases Rvb1 and Rvb2 to form the R2TP complex, which we demonstrate is required for the correct accumulation of box C/D small nucleolar ribonucleoproteins. Together with the Tah1 cofactor, Hsp90 functions to stabilize Pih1. As a consequence, the chaperone is shown to affect box C/D accumulation and maintenance, especially under stress conditions. Hsp90 and R2TP proteins are also involved in the proper accumulation of box H/ACA small nucleolar RNAs.
First phylogeny of predatory flower flies (Diptera, Syrphidae, Syrphinae) using mitochondrial COI and nuclear 28S rRNA genes: conflict and congruence with the current tribal classification
Authors: Mengual Ximo , Ståhls Gunilla , Rojo Santos
Published: February 2008

The family Syrphidae (Diptera) is traditionally divided into three subfamilies. The aim of this study was to address the monophyly of the tribes within the subfamily Syrphinae (virtually all with predaceous habits), as well as the phylogenetic placement of particular genera using molecular characters. Sequence data from the mitochondrial protein‐coding gene cytochrome c oxidase subunit I (COI) and the nuclear 28S ribosomal RNA gene of 98 Syrphinae taxa were analyzed using optimization alignment to explore phylogenetic relationships among included taxa. Volucella pellucens was used as outgroup, and representatives of the tribe Pipizini (Eristalinae), with similar larval feeding mode, were also included. Congruence of our results with current tribal classification of Syrphinae is discussed. Our results include the tribe Toxomerini resolved as monophyletic but placed in a clade with genera Ocyptamus and Eosalpingogaster. Some genera traditionally placed into Syrphini were resolved outside of this tribe, as the sister groups to other tribes or genera. The tribe Bacchini was resolved into several different clades. We recovered Paragini as a monophyletic group, and sister group of the genus Allobaccha. The present results highlight the need of a reclassification of Syrphinae.

© The Willi Hennig Society 2008.
Probiotics in infancy induce protective immune profiles that are characteristic for chronic low‐grade inflammation
Authors: Marschan E. , Kuitunen M. , Kukkonen K. , Poussa T. , Sarnesto A. , Haahtela T. , Korpela R. , Savilahti E. , Vaarala O.
Published: February 2008

Background
Probiotics are widely studied both in the treatment and prevention of allergic diseases, but their mode of action is poorly known.

Objective
Our aim was to examine the effect of probiotic bacteria on in vivo cytokine, antibody, and inflammatory responses in allergy‐prone infants.

Methods
In a randomized double‐blind study, probiotic bacteria or placebo were given for 1 month before delivery to mothers and for 6 months to infants with a family history of allergy. Plasma samples were analysed for C‐reactive protein (CRP), total IgA and IgE, food‐specific IgA, IgG, and IgE, IL‐2, IL‐4, IL‐6, IL‐10, TNF‐α, and IFN‐γ. We analysed the associations of immunological and inflammatory parameters at age 6 months with probiotic treatment and allergic phenotype at 2 years.

Results
Infants receiving probiotic bacteria had higher plasma levels of CRP (P=0.008), total IgA (P=0.016), total IgE (P=0.047), and IL‐10 (P=0.002) than infants in the placebo group. Increased plasma CRP level at age 6 months was associated with a decreased risk of eczema [odds ratio (OR) 0.41 [95% confidence interval (CI) 0.17–0.99], P=0.046], and with a decreased risk of allergic disease [OR 0.38 (95% CI 0.16–0.87), P=0.023] at age 2 years, when adjusted with probiotic use.

Conclusion
The association of CRP with a decreased risk of eczema at 2 years of age in allergy‐prone children supports the view that chronic, low‐grade inflammation protects from eczema. Probiotic‐induced low‐grade inflammation was characterized by elevation of IgE, IgA, and IL‐10, the changes typically observed in helminth infection‐associated induction of regulatory mechanisms. The findings emphasize the role of chronic microbial exposure as an immune modulator protecting from allergy.
Reproductive potential of a marine ecosystem engineer at the edge of a newly expanded range
Authors: LING SCOTT D. , JOHNSON C. R. , FRUSHER S. , KING C. K.
Published: February 2008

Global climate change is leading to redistribution of marine species and altering ecosystem dynamics. Given recent poleward range extension of the barrens‐forming sea urchin Centrostephanus rodgersii (Diadematidae) from mainland Australia to Tasmania, there is a need to understand the population dynamics of this ecologically important species in the Tasmanian environment. This paper informs possible population dynamics of C. rodgersii in Tasmania by examining its reproductive ecology in this new environment. Reproductive periodicity (gonad index and propensity to spawn) was assessed bimonthly over 18 months at four sites in eastern Tasmania spanning ∼2° in latitude. At all sites, C. rodgersii displayed a strong seasonal cycle in gonad production with major spawning occurring in winter (∼August) at minimum annual water temperature. Gametes from Tasmanian C. rodgersii were viable as determined by fertilization and early development trials. However, development to the two‐arm stage at ∼3 weeks was strongly dependent on water temperature across the 8–20 °C temperature range, with poor development occurring below 12 °C. The range of temperatures tolerated by Tasmanian C. rodgersii larvae was similar to that of larvae from its native New South Wales range, indicating that this species has not undergone an adaptive shift to the cooler Tasmanian environment. There was also no evidence for an adaptive shift in reproductive phenology. Importantly, coastal water temperatures in eastern Tasmania during the peak spawning in August fluctuate about the 12 °C larval development threshold. Recent warming of the eastern Tasmanian coast and further warming predicted by global climate change will result in an environment increasingly favourable for the reproduction and development of C. rodgersii.
Microbial activity and soil respiration under nitrogen addition in Alaskan boreal forest
Authors: ALLISON STEVEN D. , CZIMCZIK CLAUDIA I. , TRESEDER KATHLEEN K.
Published: February 2008

Climate warming could increase rates of soil organic matter turnover and nutrient mineralization, particularly in northern high‐latitude ecosystems. However, the effects of increasing nutrient availability on microbial processes in these ecosystems are poorly understood. To determine how soil microbes respond to nutrient enrichment, we measured microbial biomass, extracellular enzyme activities, soil respiration, and the community composition of active fungi in nitrogen (N) fertilized soils of a boreal forest in central Alaska. We predicted that N addition would suppress fungal activity relative to bacteria, but stimulate carbon (C)‐degrading enzyme activities and soil respiration. Instead, we found no evidence for a suppression of fungal activity, although fungal sporocarp production declined significantly, and the relative abundance of two fungal taxa changed dramatically with N fertilization. Microbial biomass as measured by chloroform fumigation did not respond to fertilization, nor did the ratio of fungi : bacteria as measured by quantitative polymerase chain reaction. However, microbial biomass C : N ratios narrowed significantly from 16.0 ± 1.4 to 5.2 ± 0.3 with fertilization. N fertilization significantly increased the activity of a cellulose‐degrading enzyme and suppressed the activities of protein‐ and chitin‐degrading enzymes but had no effect on soil respiration rates or 14C signatures. These results indicate that N fertilization alters microbial community composition and allocation to extracellular enzyme production without affecting soil respiration. Thus, our results do not provide evidence for strong microbial feedbacks to the boreal C cycle under climate warming or N addition. However, organic N cycling may decline due to a reduction in the activity of enzymes that target nitrogenous compounds.
The effects of stem density of tropical swards and age of grazing cattle on their foraging behaviour
Authors: Benvenutti M. A. , Gordon I. J. , Poppi D. P.
Published: February 2008

The effects of stem density of tropical swards and age of cattle on their foraging behaviour were evaluated using artificial microswards, consisting of leaves of 20 cm in height and high tensile‐resisting stems of 25 cm in height of Panicum maximum. The treatments consisted of a factorial combination of four stem densities of swards (0, 100, 200 and 400 stems m−2) and two ages of cattle (1‐ and 3‐year‐old steers). There was a significant interaction between stem density of sward and age of cattle for bite area (BA), bite mass (BM) and instantaneous intake rate (IIR). Stem density had a significant negative effect on these variables describing ingestive behaviour which was particularly strong for older steers. In leaf‐only swards, mature cattle achieved a much greater BA (106·5 vs. 57·9 cm2), BM (0·88 vs. 0·47 g DM) and IIR (46·9 vs. 17·2 g DM min−1) than did young cattle. However, these variables were very similar across ages of cattle at the highest stem density of sward. These results show the importance of the high tensile‐resisting stems as deterrents of the grazing process in tropical pastures, particularly in older cattle.
Influence of solar radiation on the productivity and nutritive value of herbage of cool‐season species of an understorey sward in a mature conifer woodland
Authors: Neel J. P. S. , Feldhake C. M. , Belesky D. P.
Published: February 2008

Silvopastoral systems in the Appalachian region of the USA could increase the carrying capacity of livestock and contribute to a reliable supply of high‐quality herbage. In 2000, 2001 and 2002, the influence of solar radiation [0·20, 0·50 or 0·80 of maximum solar radiation (MSR); treatments 20‐, 50‐ and 80‐MSR respectively] on the productivity and nutritive value of a mixture of sown grasses and legumes established under a mature stand of conifers was investigated. Yields of dry matter (DM), crude protein (CP), total non‐structural carbohydrates (TNC) and total digestible nutrients (TDN) were greater for the 80‐MSR treatment except in 2000 when DM yield did not differ. As a proportion of the sward, introduced species (Dactylis glomerata L., Trifolium repens L., and Lolium perenne L.) increased over time for the MSR‐80 treatment, corresponding with a decrease in the proportion of bare area and of non‐introduced species. CP concentration of herbage was 207 g kg−1 DM or greater across treatments and years with higher concentrations on the 20‐ and 50‐MSR treatments. Herbage from the 80‐MSR treatment had a greater concentration of TNC than that of the 20‐ and 50‐MSR treatments. Estimated concentration of TDN was similar for all treatments in 2000 and greater for the 80‐MSR treatment than the other two treatments in 2001 and 2002. High CP concentrations in herbage, as a result of appropriate thinning of trees in an Appalachian silvopastoral systems, could be utilized as a protein supplement to herbage with low CP and higher fibre concentrations.
Effect of different grazing management systems on the herbage mass and pasture height of a Nardus stricta grassland in western Scotland, United Kingdom
Authors: Holland J. P. , Waterhouse A. , Robertson D. , Pollock M. L.
Published: February 2008

The aims of this study were to examine the effect of three grazing treatments (year‐round stocking rates of 0·8 ewes ha−1, 0·5 ewes ha−1 and 0·5 ewes ha−1 plus grazing cattle in summer), imposed for 4 years, on the herbage mass and surface height of a Nardus stricta‐dominated grassland in western Scotland and to obtain estimates of annual productivity of this grassland. Nardus stricta‐dominated grassland comprised proportionately 0·20 of the grazing area. Stocking rate of sheep had no significant effect on the herbage mass of the grassland in the first 2 years of the experiment, although mean summer pasture heights were significantly higher under the lower stocking rate of sheep. The pasture on the treatment with cattle grazing in summer had a significantly lower herbage mass and lower surface height than the two sheep‐only grazing treatments. Year‐to‐year variation in the herbage mass and surface height of herbage in summer was greater than the effect of treatments. Despite changes in surface height, the structural diversity of the grasslands was not increased by the treatments. The annual production of vascular plant material ranged from 417 g DM m−2 in 1994 to 628 g DM m−2 in 1996.
Effects of species aggregation, habitat and season on the accuracy of double‐sampling to measure herbage mass in a lowland grassland ecosystem
Authors: Ebrahimi A. , Bossuyt B. , Hoffmann M.
Published: February 2008

Double‐sampling, as a cost‐effective and sufficiently accurate method, is an acknowledged method for estimating herbage mass at the level of the plant species up to the total plant community. It was investigated whether adjusting visual estimations of double‐sampling is applicable at different levels of species aggregation when different seasons and habitats are involved. The method was used in six different habitats of the same ecosystem, a grassland nature reserve in western Belgium, based on eight sampling periods. A general linear model was used to analyse the data at four levels of species aggregation. The correlation between estimated and measured values of herbage mass was significant for the majority of graminoid species at the levels of the sub‐life‐form and total plant community but not at the level of the life‐form. Interaction of habitat type and measured herbage mass, and interaction of date and measured herbage mass, were significant for a minority of species. A significant interaction of both date and habitat with measured herbage mass was found in some cases at the level of the sub‐life‐form and total plant community. Results suggest that the double‐sampling method is reliable for most graminoids and at the sub‐life‐form level, but should be applied more cautiously for forbs species, and when different sampling periods and habitat types are involved at the level of the life‐form. To avoid producing several calibration lines at the level of the species and to overcome deficiency of observations at this level, lumping morphologically similar species from the same vegetation stratum in sub‐life‐form groups is recommended for adjusting estimated herbage mass.
Effect of breed of cattle and season on diet selection and defoliation of competitive plant species in semi‐natural grasslands
Authors: Hessle A. , Wissman J. , Bertilsson J. , Burstedt E.
Published: February 2008

To maintain biodiversity in semi‐natural grasslands, the choice of breed of livestock and season of grazing can be important. The objective was to determine the effects of breed and season on the composition of plant fragments in the faeces of cattle grazing a heterogeneous semi‐natural grassland. Twelve heifers of the traditional Swedish Väneko breed (live weight 309 kg) and twelve heifers of the Charolais breed (live weight 431 kg) were allocated to three pastures per breed. Faeces samples were collected in spring, summer and autumn for micro‐histological examination of plant fragments. On the same occasion, defoliation of four competitive plant species was recorded. Faecal plant fragments mainly consisted of grasses but also herbs, whereas Cyperaceae, despite their abundance on the pastures, only composed a small proportion of fragments. Season affected the composition of plant fragments in the faeces, with a higher proportion of Cyperaceae and herbs in spring than later in the grazing period (P < 0·001), and the heifers ingesting more grasses and woody plants in autumn. In spite of a clear difference in live weight between the two breeds, no effects of breed on the composition of plant fragments in faeces were observed, although Väneko heifers defoliated more Filipendula ulmaria in spring than the Charolais heifers (P < 0·01). In addition, defoliation of Alnus glutinosa increased later in the grazing period (P < 0·05), especially for the Väneko heifers, indicating control of pernicious brushwood by grazing may be more effective in autumn.
Genotype × environment interactions for herbage yield of perennial ryegrass sward plots in Ireland
Authors: Conaghan P. , Casler M. D. , McGilloway D. A. , O’Kiely P. , Dowley L. J.
Published: February 2008

Perennial ryegrass (Lolium perenne L.) is by far the most widely sown grass species in Ireland. Genotype × environment (G × E) interactions are a frequent occurrence in herbage yield evaluations. The objectives were to determine (i) the nature and relative magnitudes of the pertinent G × E interaction variance components for dry matter yield of perennial ryegrass sward plots in Ireland and (ii) the optimal allocation of replicates, locations and years in a testing programme. Sixteen perennial ryegrass cultivars were sown at six locations throughout Ireland between 2000 and 2004. Plots from each sowing were harvested for 2 consecutive years under a simulated mixed grazing and conservation management programme. The largest component of the G × E variance was generally genotype × location × year emphasizing the need for evaluation of genotypes across locations and years to adequately characterize genotypes for differences in yield. Relative differences among genotypes from year to year and location to location were due mainly to changes in genotype rankings. Weather was estimated to have a greater effect on annual variation in herbage yield than age of stand. The optimum allocation of resources for a testing programme was estimated at four replicates per location, and either two locations and 3 sowing years or three locations and 2 sowing years with 2 harvest years for each sowing year. The most appropriate option depends on the relative importance of time vs. financial resources.
Fungal contamination of big‐bale grass silage on Irish farms: predominant mould and yeast species and features of bales and silage
Authors: O’Brien M. , O’Kiely P. , Forristal P. D. , Fuller H. T.
Published: February 2008

The extent of visible fungal growth and the identity of the predominant fungi causing spoilage of baled grass silage were recorded on 180 farms in Ireland. Fungal growth was evident on bales on 174 of the 180 farms visited and on 331 of the 360 bales examined. The mean proportion of surface area of bale, that was affected, was 0·06. Silage‐making method, storage characteristics and geographical location were significantly associated with the level of fungal contamination on bales. Fungal contamination was higher (P < 0·001) in bales where the surrounding polythene stretch‐film was visibly damaged compared with bales where the film appeared intact. A strong positive relationship was found between polythene film damage and dry‐matter content of the silage. The predominant fungus affecting the largest numbers of bales wasPenicillium roqueforti. Other fungi frequently isolated includedSchizophyllum commune,Pichia fermentansandPenicillium paneum. The distribution of individual fungi on bales was associated with geographical location, weather at harvest, and lactic and butyric acid concentrations of the silage.Penicillium roquefortiandP. paneumwere more common on bales harvested in dry weather and with higher concentrations of butyric and propionic acids in the silage. Overall, a high incidence of visible fungal growth was recorded on bales throughout the country and the extent of colonization and fungal species occurring were not random.