bluuebunny/crossref_metadata_2025 huggingface dataset:
Dielectric response of polar liquids in narrow slit pores
Authors: Froltsov Vladimir A. , Klapp Sabine H. L.
Published: March 2007

Based on molecular dynamics (MD) simulations and a simple (Stockmayer) model we investigate the static and dynamic dielectric response of polar liquids confined to narrow slit pores. The MD simulations are used to calculate the time-dependent polarization fluctuations along directions parallel and perpendicular to the walls, from which the components of the frequency-dependent dielectric tensor can be derived via linear response theory. Our numerical results reveal that the system’s response is strongly anisotropic. The parallel dielectric function, ε‖(ω), has Debye-like character very similar to the corresponding isotropic bulk function, εbulk(ω), at the same chemical potential. Indeed, the main confinement effect on ε‖(ω) consists in a shift toward smaller values relative to the bulk function. On the other hand, in the perpendicular direction we observe a characteristic peak in the absorption part of the dielectric function, ε⊥(ω). This peak is absent in the bulk system and reflects strongly pronounced, damped oscillations in the polarization fluctuations normal to the walls. We discuss two possible origins of the oscillations (and the resulting absorption peak), that is collective oscillations of dipoles in clusters formed parallel to the walls, and the existence of a “dipolaron mode” previously observed in MD simulations of bulk polar fluids.
Supersonic jet deposition of silver nanoparticle aerosols: Correlations of impact conditions and film morphologies
Authors: Huang Chong , Nichols William T. , O’Brien Daniel T. , Becker Michael F. , Kovar Desiderio , Keto John W.
Published: March 2007

We describe experiments and modeling for the deposition of silver lines and films via the impaction of a silver nanoparticle aerosol delivered through a supersonic jet. The aerosol gas dynamics of the jet flow field, nanoparticle acceleration in the jet, and deposition by impaction onto the substrate were modeled for both a flat-plate nozzle and for a conical nozzle designed to obtain higher impaction velocities. We modeled nanoparticle dynamics for He, Ar, and N2 gasses, all initially at room temperature and 1 atm pressure, flowing through a 250 μm orifice into vacuum with a pressure ratio of ~5000. Experiments were conducted to deposit silver nanoparticle aerosols under the same conditions as were modeled. The silver nanoparticles were generated by laser ablation of a flowing microparticle aerosol entrained in either He or Ar that produced nanoparticles 5−10 and 15−20 nm in diameter, respectively. Deposition was made onto an unheated substrate in vacuum. The morphology of the deposited films was determined by scanning electron microscope cross-section images and crystallite size was determined by x-ray diffraction analysis. The morphological features and crystallite size were correlated with the nanoparticle impaction velocity and impaction energy derived from the model. We found that, for a given gas type, the size of the grains and morphological features within the impacted films were similar to the size of the nanoparticles from which the films were formed. The density and the degree of consolidation of the films were highly dependent on the nanoparticle impaction velocity/energy and were highest for helium. Control of film morphology, grain size, and film density during supersonic impaction of nanoparticle aerosols are discussed in light of these results.
Intra-atomic photoluminescence at 1.41 eV of substitutional Mn in GaMnN of high optical quality
Authors: Zenneck J. , Niermann T. , Mai D. , Roever M. , Kocan M. , Malindretos J. , Seibt M. , Rizzi A. , Kaluza N. , Hardtdegen H.
Published: March 2007

We report on a characteristic photoluminescence feature of the substitutional Mn in high quality GaMnN layers. The lattice site was identified using atom localization by channeling enhanced microanalysis with a transmission electron microscope. It shows that 96.5%±5.0% of the Mn atoms are incorporated on the substitutional Ga site. In photoluminescence a feature appears at 1.41 eV with a phonon sideband related to the GaN matrix. The temperature evolution is characteristic of an intra-atomic transition and it is assigned to the internal transition E5→T52 of the Mn3+ ion. The assignment is supported by absorption experiments. The persistence of the clear PL signal up to about 1% Mn concentration is proposed to be a fingerprint of high quality diluted GaMnN.
Evidence of nonclassical plasma transport in hollow cathodes for electric propulsion
Authors: Mikellides Ioannis G. , Katz Ira , Goebel Dan M. , Jameson Kristina K.
Published: March 2007

Measurements, simplified analyses, and two-dimensional numerical simulations with a fluid plasma model show that classical resistivity cannot account for the elevated electron temperatures and steep plasma potential gradients measured in a 25–27.5A electric propulsion hollow cathode. The cathode consisted of a 1.5cm hollow tube with an ∼0.28cm diameter orifice and was operated with 5.5SCCM (SCCM denotes cubic centimeter per minute at STP) of xenon flow using two different anode geometries: a segmented cone and a circular flat plate. The numerical simulations show that classical resistivity yields as much as four times colder electron temperatures compared to the measured values in the orifice and near-plume regions of the cathode. Classical transport and Ohm’s law also predict exceedingly high electron-ion relative drift speeds compared to the electron thermal speed (>4). It is found that the addition of anomalous resistivity based on existing growth rate formulas for electron-ion streaming instabilities improves qualitatively the comparison between the numerical results and the time-averaged measurements. Simplified analyses that have been based largely on the axial measurements support the conclusion that additional resistivity is required in Ohm’s law to explain the measurements. The combined results from the two-dimensional simulations and the analyses bound the range of enhanced resistivity to be 3–100 times the classical value.
Sampling enhancement for the quantum mechanical potential based molecular dynamics simulations: A general algorithm and its extension for free energy calculation on rugged energy surface
Authors: Li Hongzhi , Yang Wei
Published: March 2007

An approach is developed in the replica exchange framework to enhance conformational sampling for the quantum mechanical (QM) potential based molecular dynamics simulations. Importantly, with our enhanced sampling treatment, a decent convergence for electronic structure self-consistent-field calculation is robustly guaranteed, which is made possible in our replica exchange design by avoiding direct structure exchanges between the QM-related replicas and the activated (scaled by low scaling parameters or treated with high “effective temperatures”) molecular mechanical (MM) replicas. Although the present approach represents one of the early efforts in the enhanced sampling developments specifically for quantum mechanical potentials, the QM-based simulations treated with the present technique can possess the similar sampling efficiency to the MM based simulations treated with the Hamiltonian replica exchange method (HREM). In the present paper, by combining this sampling method with one of our recent developments (the dual-topology alchemical HREM approach), we also introduce a method for the sampling enhanced QM-based free energy calculations.
In situ synchrotron x-ray photon beam characterization
Authors: Kyele Nicholas R. , van Silfhout Roelof G. , Manolopoulos Spyros , Nikitenko S.
Published: March 2007

We have investigated two in situ methods of measuring x-ray beam parameters such as integrated intensity, position, and intensity distribution. These virtually transparent methods both rely on the collection of scattered radiation from a thin amorphous foil. The scattered radiation is collected by an active pixel sensor placed below the foil, well out of the direction of the beam path. These methods measure a cross-sectional image of the beam as opposed to a profile or beam centroid position provided by existing in situ detection methods. We present the results of measurements taken at a third generation synchrotron radiation source and provide analytical methods of deriving beam profile, position, and absolute intensity.
Equilibrium theory for a particle pulled by a moving optical trap
Authors: Astumian R. Dean
Published: March 2007

The viscous drag on a colloidal particle pulled through solution by an optical trap is large enough that on experimentally relevant time scales the mechanical force exerted by the trap is equal and opposite the viscous drag force. The rapid mechanical equilibration allows the system to be modeled using equilibrium theory where the effects of the energy dissipation (thermodynamic disequilibrium) show up only in the coordinate transformations that map the system from the laboratory frame of reference, relative to which the particle is moving, to a frame of reference in which the particle is, on average, stationary and on which the stochastic dynamics is governed by a canonical equilibrium distribution function. The simple equations in the stationary frame can be analyzed using the Onsager-Machlup theory for stochastic systems and provide generalizations of equilibrium and near equilibrium concepts such as detailed balance and fluctuation-dissipation relations applicable to a wide range of systems including molecular motors, pumps, and other nanoscale machines.
Influence of crystallite size on the thermal conductivity in BaTiO3 nanoceramics
Authors: Jeżowski A. , Mucha J. , Pazik R. , Strek W.
Published: March 2007

The grain size effect on the thermal conductivity in BaTiO3 nanoceramics was investigated. The nanoceramics were produced by the low temperature high pressure technique. The averaged sizes of grain varied from 30to100nm. It was found that the thermal conductivity of BaTiO3 nanoceramics decreased with decreasing the grain sizes. For the smallest grains the thermal conductivity was similar to the glasslike materials, whereas for larger grains it behaved as in crystalline dielectrics.
Fabrication and material properties of submicrometer SrTiO3 films exfoliated using crystal ion slicing
Authors: Roth Ryan M. , Djukic Djordje , Lee Yoo Seung , Osgood Richard M. , Lewis Penelope A. , Bakhru Sasha , Bakhru Hassaram
Published: March 2007

The crystal quality of submicrometer-thick SrTiO3 films that are formed by exfoliation from bulk crystals using deep implantation with H-ion beams is investigated. Nuclear reaction analysis and Rutherford backscattering/channeling are used to measure the implantation depth, crystal-lattice disruption, and surface damage prior to exfoliation. The surface profiles of the exfoliated films are examined with atomic force microscopy; the roughness is shown to be reducible to subnanometer levels with postexfoliation mechanical polishing.
Nanoscale quantitative stress mapping with atomic force microscopy
Authors: Unal Kerem , Wickramasinghe H. Kumar
Published: March 2007

A nanometer scale noninvasive method for quantitatively mapping tensile strain in metals or semiconductors is demonstrated. The technique is based on the Kelvin probe force microscopy detection of changes in the electronic work function of a material resulting from the tensile strain. Measurements are quantified using a simple microlever mechanical system by recording changes in the work function as a function of the applied strain. A linear relationship of the work function on the tensile stress is observed with a stress sensitivity of 1kPa. Finally, the stress distribution in a strained silicon membrane is imaged.
Monodisperse spherical mesoporous Eu-doped TiO2 phosphor particles and the luminescence properties
Authors: Yin Jianbo , Xiang Liqin , Zhao Xiaopeng
Published: March 2007

Monodisperse spherical and mesoporous Eu-doped TiO2 phosphor particles were prepared by nonionic surfactant-assisted soft-chemistry method. It is shown that the phosphor particles possess submicron diameter of about 250nm and narrow size distribution. Under ultraviolet irradiation the particles show characteristic luminescence corresponding to D05-Fj7 of Eu3+. Especially, the calcined particles consisted of mesopores and semicrystalline framework shows the strongest photoluminescence compared to the amorphous particles without annealing and the completely crystalline particles annealed at higher temperature. This is attributed to the energy transfer from titania nanocrystallite to Eu3+ ions dispersed in glassy amorphous titania region.
On the nature of the carriers in ferromagnetic FeSe
Authors: Wu X. J. , Shen D. Z. , Zhang Z. Z. , Zhang J. Y. , Liu K. W. , Li B. H. , Lu Y. M. , Yao B. , Zhao D. X. , Li B. S. , Shan C. X. , Fan X. W. , Liu H. J. , Yang C. L.
Published: March 2007

The optical and electrical properties of FeSe thin films are studied by both optical absorption and Hall measurements, which suggest that ferromagnetic FeSe is a metal instead of a semiconductor. No absorption gap is observed in the whole spectrum range from far infrared to ultraviolet. Temperature dependent transport measurement indicates that FeSe has a resistivity about 10−3Ωcm. It is also found that there is a transition from n-type conductivity at low temperatures to p-type conductivity at higher temperatures in FeSe, which is attributed to the two-carrier transport nature and the thermal activation of localized carriers in the thin film.
Fluorine incorporation at HfO2∕SiO2 interfaces in high-k metal-oxide-semiconductor gate stacks: Local electronic structure
Authors: Ha Jeong-Hee , Seo Kang-ill , McIntyre Paul C. , Sarawat Krishna C. , Cho Kyeongjae
Published: March 2007

Effects of fluorine incorporation on the electrical properties of HfO2∕SiO2 dielectric stacks are investigated through both ab initio simulations and electrical measurements. The results show that F ions are able to remove midgap states resulting from undercoordinated Hf ions at the HfO2∕SiO2 interface. They also indicate that F incorporation increases the leakage current if an excessive amount of F ions are present in the dielectric, beyond that required to passivate the undercoordinated interfacial Hf ions. A possible way to maximize the benefits of F incorporation for high-k gate stack electrical characteristics is discussed.
Characteristics of (Pb,Sr)TiO3∕ZrO2 structures on Si and SiON∕Si substrates
Authors: Chen Hung-Yao , Wu Jenn-Ming , Huang Hsin-Erh , Bor Hui-Yun
Published: March 2007

The ferroelectric (Pb,Sr)TiO3 (PST) thin film with ZrO2 insulating buffer on Si and SiON(3nm)∕Si substrates was fabricated by rf magnetron sputtering. ZrO2 demonstrates excellent insulating properties on either Si or SiON∕Si substrates. The metal-ferroelectric-insulator-semiconductor structure shows low leakage currents and exhibits clockwise capacitance-voltage hysteresis loops which are due to the ferroelectric polarization of the PST films. The maximum memory windows of the hysteresis loops are 0.8 and 1.37V, respectively for PST∕ZrO2 films on Si and SiON∕Si substrates. This is of potential as memory devices. The charge injection effect under large sweeping voltages is discussed.
Low-threshold-switch phototransistor based on Kirk effect and float-zone silicon
Authors: Zhou D. B. , Han D. J. , Sun C. M. , Yang R. , Liang K.
Published: March 2007

Based on the Kirk effect, a n+pn−n+ phototransistor with low optical threshold switching on high purity float-zone silicon was demonstrated. Under a collector-emitter voltage range from 3to15V, the phototransistor can turn on from a lower current state (range from 0.29to0.65mA) to a higher current state (range from 2.47to13.20mA) when it was triggered by illumination with a small critical optical power (range from 2.0to3.6μW). The theoretical calculations on critical collector current density were compared with the experimental results. Negative differential resistance and latch characteristics were observed and discussed.
Observation of temporal behavior of the emission frequency from an ultrashort, high-power, and compact millimeter-wave source
Authors: Higashiguchi Takeshi , Ohata Nobuo , Li Kun , Yugami Noboru
Published: March 2007

The authors demonstrated observation of emission frequency chirping of millimeter-wave emission from a time-varying plasma produced by a nanosecond UV laser pulse. By using a heterodyne interferometer the time-resolved frequency of the emission from a dc to ac radiation converter source was observed to range from 20to32GHz due to the rapid plasma creation. This chirped pulse is suitable for application in various novel dense plasma diagnostics.
Heteroepitaxially enhanced magnetic anisotropy in BaTiO3–CoFe2O4 nanostructures
Authors: Zheng Haimei , Kreisel Jens , Chu Ying-Hao , Ramesh R. , Salamanca-Riba Lourdes
Published: March 2007

The authors have studied the magnetic properties of BaTiO3–CoFe2O4 nanostructures, which were prepared using pulsed laser deposition. Such nanostructures show a large uniaxial magnetic anisotropy with an easy axis along the pillar long direction. As the growth temperature decreases, the magnetic anisotropy increases. Careful analyses reveal that heteroepitaxial strain is the primary contribution to the magnetic anisotropy.
Channel cracks in a hermetic coating consisting of organic and inorganic layers
Authors: Cordero Nicolas , Yoon Juil , Suo Zhigang
Published: March 2007

Flexible electronic devices often require hermetic coatings that can withstand applied strains. This letter calculates the critical strains for various configurations of channel cracks in a coating consisting of organic and inorganic layers. The authors show that the coating can sustain the largest strain when the organic layer is of some intermediate thicknesses.
Formation of stacked Ni silicide nanocrystals for nonvolatile memory application
Authors: Chen Wei-Ren , Chang Ting-Chang , Liu Po-Tsun , Lin Po-Sun , Tu Chun-Hao , Chang Chun-Yen
Published: March 2007

The formation of stacked Ni silicide nanocrystals by using a comixed target is proposed in this letter. High resolution transmission electron microscope analysis clearly shows the stacked nanocrystals embedded in the silicon oxide. The memory window enough to define “1” and “0” states is obviously observed at low voltage programming conditions, and good data retention characteristics are exhibited for the nonvolatile memory application. A physical model is also proposed further to explain the saturation phenomenon of threshold voltage at different programming voltages with operation duration.
Automatic navigation of an untethered device in the artery of a living animal using a conventional clinical magnetic resonance imaging system
Authors: Martel Sylvain , Mathieu Jean-Baptiste , Felfoul Ouajdi , Chanu Arnaud , Aboussouan Eric , Tamaz Samer , Pouponneau Pierre , Yahia L’Hocine , Beaudoin Gilles , Soulez Gilles , Mankiewicz Martin
Published: March 2007

The feasibility for in vivo navigation of untethered devices or robots is demonstrated with the control and tracking of a 1.5mm diameter ferromagnetic bead in the carotid artery of a living swine using a clinical magnetic resonance imaging (MRI) platform. Navigation is achieved by inducing displacement forces from the three orthogonal slice selection and signal encoding gradient coils of a standard MRI system. The proposed method performs automatic tracking, propulsion, and computer control sequences at a sufficient rate to allow navigation along preplanned paths in the blood circulatory system. This technique expands the range of applications in MRI-based interventions.
Integrated waveguide with a microfluidic channel in spiral geometry for spectroscopic applications
Authors: Jiang Linan , Pau Stanley
Published: March 2007

The authors fabricated and tested a compact optical sensor with an integrated waveguide and a microchannel in spiral geometry. The multimode waveguide, consisting of an SU-8 core of 40μm thick and 50μm wide and a fluid cladding layer of 60μm thick, realizes a light-fluid interaction length of 110mm within a device area of 4cm2. The waveguide sensor measures changes in liquid sample concentration and is sensitive to changes in liquid refractive index. Absorbance measurements using the spiral waveguide sensor demonstrate increased sensitivity compared with a linear geometry sensor.
Probing intrinsic polarization properties in bismuth-layered ferroelectric films
Authors: Watanabe Takayuki , Funakubo Hiroshi , Osada Minoru , Uchida Hiroshi , Okada Isao , Rodriguez Brian J. , Gruverman Alexei
Published: March 2007

The authors report on an approach to establish intrinsic polarization properties in bismuth-layered ferroelectric films by piezoelectric coefficient and soft-mode spectroscopy, as well as by a direct polarization–electric field hysteresis. In epitaxially grown (Bi4−xNdx)Ti3O12 (0⩽x⩽0.73) films, they show that these complementary characterizations can phenomenologically and thermodynamically represent the intrinsic polarization states in (Bi4−xNdx)Ti3O12 films, and the intrinsic Ps of 67μC∕cm2 is estimated for pure Bi4Ti3O12, superior to 50μC∕cm2 in bulk single crystal. Their results provide a pathway to draw full potential in ferroelectric thin films.
Criterion for predicting the glass-forming ability of alloys
Authors: Sharma S. , Vaidyanathan R. , Suryanarayana C.
Published: March 2007

Mechanical alloying (MA) of blended elemental powder mixtures of Fe42Zr10X28B20 (X=Al, Co, Ge, Mn, Ni, and Sn) was carried out to determine their glass-forming ability (GFA) (as determined by the time required to form the amorphous phase). During milling, amorphization was achieved in systems with X=Al, Ge, or Ni, but not in the other systems. The GFA could be correlated with the total number of intermetallics present in the constituent binary phase diagrams. Thus, this work offers the equilibrium phase diagram as a predictive tool to determine if amorphization can be achieved by the MA method.
Undoped high mobility two-dimensional hole-channel GaAs∕AlxGa1−xAs heterostructure field-effect transistors with atomic-layer-deposited dielectric
Authors: Lu T. M. , Luhman D. R. , Lai K. , Tsui D. C. , Pfeiffer L. N. , West K. W.
Published: March 2007

The authors have fabricated undoped p-channel GaAs∕AlxGa1−xAs heterostructure field-effect transistors with nearly ideal drain current-voltage characteristics, using atomic-layer-deposited Al2O3 as the dielectric, and measured their transport properties. At 0.3K, the densities and mobilities of the two dimensional holes can be tuned up to 2.9×1011∕cm2 and 6.4×105cm2∕Vs, respectively. The variable density high mobility two-dimensional hole system provides a large parameter space for the study of two-dimensional physics.
In
As
∕
Al
Sb
quantum cascade lasers emitting below 3μm
Authors: Devenson J. , Teissier R. , Cathabard O. , Baranov A. N.
Published: March 2007

Quantum cascade lasers emitting below 3μm are demonstrated. The lasers based on the InAs∕AlSb material system emit at 2.95–2.97μm in pulsed mode with threshold current densities near 3kA∕cm2 at 84K and operate up to room temperature. No degradation has been observed in laser performances compared with InAs∕AlSb quantum cascade lasers emitting at 3.14–3.35μm. The obtained results show no influence of the L valley in InAs on operation of these short wavelength quantum cascade lasers.
FeCoSiN film with ordered FeCo nanoparticles embedded in a Si-rich matrix
Authors: Liu Yan , Tan C. Y. , Liu Z. W. , Ong C. K.
Published: March 2007

FeCoSiN film consisting of ordered arrays of FeCo nanoparticles embedded in a Si-rich matrix was fabricated on silicon substrate by reactive rf magnetron sputtering. These nanoparticles have a face-centered cubic structure and a mean diameter of ∼7nm. The FeCoSiN film has a very high resistivity of up to 1000μΩcm due to the breakup of the metal continuum into isolated metal nanoparticles. The static and dynamic magnetic properties of the film were also investigated. A saturation magnetization of 1.0T, coercivity of less than 5Oe in both easy and hard axes, and anisotropy field of 27Oe were obtained. The microwave permeability measurement showed a permeability of around 400 at low frequency and a ferromagnetic resonance frequency of about 1.1GHz.
Visible submicron microdisk lasers
Authors: Zhang Zhaoyu , Yang Lan , Liu Victor , Hong Ting , Vahala Kerry , Scherer Axel
Published: March 2007

The authors describe the performance of submicron microdisk lasers fabricated within InGaP∕InGaAlP quantum well material working at room temperature. The smallest lasers, with diameters of approximately 600nm, feature ultrasmall mode volumes and exhibit single mode operation at low threshold powers. Their small cavity volumes of approximately 0.03μm3 enable microdisk lasers to be used as spectroscopic sources. Here the authors demonstrate the fabrication and characterization of visible, monolithically fabricated, submicron microdisk lasers.
Ultraviolet-enhanced device properties in pentacene-based thin-film transistors
Authors: Choi Jeong-M. , Hwang D. K. , Hwang Jung Min , Kim Jae Hoon , Im Seongil
Published: March 2007

The authors report on the ultraviolet (UV)-enhanced device properties in pentacene-based thin-film transistors (TFTs). Pentacene TFTs showed a degraded mobility and lowered saturation current after illumination by a high energy UV with 254nm wavelength. However, under 364nm UV these devices surprisingly displayed enhanced saturation current and also showed threshold voltage shift toward lower values, maintaining their mobilities. The saturation current increase and threshold voltage shift were further related to the negative fixed charges excessively formed at the pentacene/dielectric interface by the low energy UV. The authors thus conclude that a low energy UV could rather enhance the pentacene TFT performances and also control the threshold voltage of the device.
Modelling the interception of photosynthetically active radiation by evergreen subtropical hedgerows
Authors: Olesen Trevor , Morris Stephen , McFadyen Lisa
Published: March 2007

Horticultural tree crop yields tend to be linearly correlated with the percentage of photosynthetically active radiation (PAR) intercepted by the canopies, at least for part of the PAR interception range. Models of PAR interception by hedgerows have been used in the design of orchards for temperate tree crops, especially apples, but not for subtropical tree crops, such as lychee and macadamia. Subtropical crops need special consideration because of the latitudes at which they are grown, the specific shapes and dimensions of the hedgerows, and the evergreen habit, which requires an understanding of the entire annual cycle. We present outputs from a PAR interception model for solid rectangular and tapered hedgerows, based on a model of irradiation beneath blue skies. Annual PAR interception tends to decline as row orientation rotates from north–south to east–west, but with some exceptions for particular tree geometries, and declines slightly with decreasing latitude. Daily PAR interception is also affected by row orientation, with little seasonal variation for north–south rows but large fluctuations for east–west rows, including very high interception in winter and low interception in summer. Row orientation and tree shape greatly affect the distribution of PAR over the surface of the canopy. For example, the side faces of evenly spaced, symmetrical, identical north–south hedgerows are equally irradiated throughout the year, but there can be large seasonal differences in the relative irradiance of the north and south faces of the same hedgerows aligned east–west. The solid tapered hedgerow model tended to overestimate measured PAR interception by ~6% overall, but the percent overestimation seemed to vary with PAR interception, being greater at lower levels of PAR interception. A curvilinear relationship was found between the yield of macadamia in the Northern Rivers area of NSW in 1997 and the measured PAR intercepted by the trees, with an explained variance of 50%. Maximum yield occurred at ~86% PAR interception. Using modelled PAR interception the explained variance of the yield was 34%. Model estimates of PAR interception were close to those measured and might be used to address a range of physiological questions concerning the canopy development of subtropical hedgerows.
Seasonal animal production of temperate and Mediterranean tall fescue cultivars under continuous variable stocking with close control of sward state
Authors: Lattanzi Fernando A. , Mazzanti the late Arturo , Wade Michael H.
Published: March 2007

In temperate regions, tall fescue (Festuca arundinacea Schreb.) cultivars derived from Mediterranean germplasm out-perform cultivars of temperate origin during autumn and winter, but the opposite occurs in spring and summer. This study assessed whether such seasonal differences are expressed under grazing and can thus be translated into animal production.
Swards of ‘El Palenque’, a temperate cultivar, and of ‘Maris Kasba’, a cultivar developed from Mediterranean germplasm, were grazed under continuous stocking with frequent adjustment of the stocking rate to maintain similar sward state, in temperate Argentina. Liveweight gain per animal (LWGA) and per unit area was determined over 4 consecutive 1-year-long fattening cycles of Angus steers. Close control of sward state resulted in swards of similar height (82 ± 2.5 v. 83 ± 4.5 mm for El Palenque and Maris Kasba, respectively) and herbage mass (96 ± 13 v. 108 ± 8 g DM/m2). Thus, animals grazed structurally very similar swards in both cultivars, throughout the trial.
Both cultivars showed similar seasonal trends in LWGA, but markedly contrasting seasonal patterns of carrying capacity. During autumn–winter, LWGA was 507 g/animal.day, but the temperate and Mediterranean cultivar supported, on average, 1.9 and 2.9 animals/ha, respectively. In spring, LWGA was 843 g/animal.day, but the temperate and Mediterranean cultivar supported, on average, 4.3 and 2.9 animals/ha, respectively. Thus, the established cultivar × season interaction in primary productivity was confirmed in terms of animal production. Mediterranean germplasm is certainly an option for increasing the carrying capacity of temperate-humid systems based on direct grazing during the critical period of low temperatures, helping to smooth annual forage supply.
Expression and relationships of resistance to white rust (Albugo candida) at cotyledonary, seedling, and flowering stages in Brassica juncea germplasm from Australia, China, and India
Authors: Li C. X. , Sivasithamparam K. , Walton G. , Salisbury P. , Burton W. , Banga Surinder S. , Banga Shashi , Chattopadhyay C. , Kumar A. , Singh R. , Singh D. , Agnohotri A. , Liu S. Y. , Li Y. C. , Fu T. D. , Wang Y. F. , Barbetti M. J.
Published: March 2007

White rust (Albugo candida) is a highly destructive disease of oilseed Brassicas such as Brassica juncea and B. rapa. Most commercial B. juncea or B. rapa varieties are highly susceptible and yield losses from combined infection of leaves and inflorescences can be up to 20% or 60% in Australia and India, respectively. In Australia, canola-quality B. juncea has been developed to extend oilseed Brassica production into lower rainfall areas, with the first commercial B. juncea canola-quality variety planned for release in 2006. It is essential to identify useful sources of host resistance in B. juncea as breeding and/or selection of material for resistance is the most cost-effective method of delivering control for farmers. Three experiments were undertaken under controlled-environmental conditions to identify the best methods of characterising host resistance and to identify sources of resistance in B. juncea germplasm from Australia, China, and India. Forty-four B. juncea genotypes, viz. 22 from India, 12 from Australia, and 10 from China, were tested. Four Chinese genotypes (CBJ-001, CBJ-002, CBJ-003, CBJ-004) and one Australian genotype (JR049) consistently showed high resistance to A. candida across the different plant growth stages against a pathotype prevailing in Australia. Similarly, the most susceptible genotypes (viz. Indian genotypes RH781, RL1359, RH819) were extremely susceptible irrespective of the plant growth stage. Overall, although disease severity on cotyledons and leaves at the different growth stages was significantly and positively correlated, there was, however, no significant correlation between the number of stagheads and any of the other disease parameters measured. Our study demonstrates that controlled-environmental conditions are suitable for rapid identification of resistant genotypes and that genotypes with high levels of resistance can be reliably identified at the cotyledonary, seedling, or flowering stages.
Conifer and cycad distribution in the Miocene of southern New Zealand
Authors: Pole Mike
Published: March 2007

One hundred and nineteen samples were investigated from Early Miocene localities of the St Bathans Paleovalley in the Manuherikia Group in Central Otago and the Gore Lignite Measures of the East Southland Group in Southland for their content of conifer and cycad macrofossils. In total, these contained 16 species of conifer in 12 genera. They include the first New Zealand record of Papuacedrus and a new genus of cycad. A specimen previously described as Podocarpaceae-Taxaceae is now regarded as being in the Taxaceae, and is the first clear record of this family in New Zealand. The ranges of Araucaria taieriensis (known from the Late Cretaceous) and Kakahuia (known from the Paleocene) are extended to the Early Miocene. Retrophyllum vulcanense was the most widespread species in the gravel-dominated braided river environment of the St Bathans Paleovalley, and was dominant in some low-diversity communities. Dacrycarpus dacrydioides was the second most widespread species in the Valley. One sample stands out as being distinctly different, as it contains the only record of Papuacedrus and Dacrydium while Retrophyllum is absent. The taxonomic make-up of the Gore Lignite Measures is different, possibly due to the very different peat and clay-dominated soils with poorer drainage. In contrast to the St Bathans paleovalley, Araucariaceae and Dacrydium appear more important in the Gore Lignite Measures.
Karyotype of Araucaria angustifolia and the decondensation/activation mode of its nucleolus organiser region
Authors: Miranda Manoela , Almeida Cícero Carlos de Souza , Guerra Marcelo
Published: March 2007

The chromosomes of the gymnosperm Araucaria angustifolia (Bertol.) Kuntze were analysed with the fluorochromes chromomycin A3 (CMA) and 4′,6-diamidino-2-phenylindole (DAPI) and with C-banding. This species contains a diploid complement made of 26 chromosomes, with 18 larger metacentric, four smaller metacentric and four submetacentric chromosomes. The only CMA+/DAPI– region observed corresponded to the nucleolus organiser region (NOR) localised at the proximal portion of a large metacentric chromosome pair. C-banding marked the NOR as well as a terminal region of another chromosome pair. In addition, small C-bands were occasionally seen interspersed in many chromosomes. The NOR appeared to condense at approximately the same rate as the rest of the chromosome from prophase throughout metaphase. In interphase nuclei, NOR decondensation and activation was characterised by the formation of CMA+ blocks that resembled a string of beads inside the nucleolus. The number and size of beads was inversely proportional to the size of the nucleolus, suggesting that transcriptional activation of the nucleolar cistrons starts simultaneously at several points of the NOR. The mode of NOR activation in A. angustifolia differs from that observed in most species, providing a unique opportunity to study activation and transcriptional control of rRNA genes.
High-throughput telomere length quantification by FISH and its application to human population studies
Authors: Canela Andrés , Vera Elsa , Klatt Peter , Blasco María A.
Published: March 2007

A major limitation of studies of the relevance of telomere length to cancer and age-related diseases in human populations and to the development of telomere-based therapies has been the lack of suitable high-throughput (HT) assays to measure telomere length. We have developed an automated HT quantitative telomere FISH platform, HT quantitative FISH (Q-FISH), which allows the quantification of telomere length as well as percentage of short telomeres in large human sample sets. We show here that this technique provides the accuracy and sensitivity to uncover associations between telomere length and human disease.
Endoproteolytic processing of C-terminally truncated NF-κB2 precursors at κB-containing promoters
Authors: Qing Guoliang , Qu Zhaoxia , Xiao Gutian
Published: March 2007

The C-terminal, partially truncated forms of the NF-κB2/p52 precursor p100, p100ΔCs, manifest constitutive processing and oncogenic ability, although the responsible mechanisms remain unknown. Here, we report that p100ΔCs are specifically processed in association with binding to promoter DNA-containing κB sites. In the nucleus, p100ΔCs bind to the κB promoter DNA and subsequently recruit the proteasome to form a stable proteasome/p100ΔC/DNA complex, which mediates the processing of p100ΔCs. Notably, the processing at the κB promoter is initiated by a proteasome-mediated endoproteolytic cleavage at amino acid D
415
of p100ΔCs, and the processed p52, but not the precursors themselves, is oncogenic by up-regulating a subset of target genes. Our studies demonstrate a different mechanism of p100 processing and also present evidence showing that the proteasome modulates the action of transcription factors at promoter regions through endoproteolysis.
Activation of trypsinogen in large endocytic vacuoles of pancreatic acinar cells
Authors: Sherwood Mark W. , Prior Ian A. , Voronina Svetlana G. , Barrow Stephanie L. , Woodsmith Jonathan D. , Gerasimenko Oleg V. , Petersen Ole H. , Tepikin Alexei V.
Published: March 2007

The intracellular activation of trypsinogen, which is both pH- and calcium-dependent, is an important early step in the development of acute pancreatitis. The cellular compartment in which trypsinogen activation occurs currently is unknown. We therefore investigated the site of intracellular trypsinogen activation by using an established cellular model of acute pancreatitis: supramaximal stimulation of pancreatic acinar cells with cholecystokinin. We used fluorescent dextrans as fluid phase tracers and observed the cholecystokinin-elicited formation and translocation of large endocytic vacuoles. The fluorescent probe rhodamine 110 bis-(CBZ-
l
-isoleucyl-
l
-prolyl-
l
-arginine amide) dihydrochloride (BZiPAR) was used to detect trypsinogen activation. Fluid phase tracers were colocalized with cleaved BZiPAR, indicating that trypsinogen activation occurred within endocytic vacuoles. The development of BZiPAR fluorescence was inhibited by the trypsin inhibitor benzamidine. Fluorescein dextran and Oregon Green 488 BAPTA-5N were used to measure endosomal pH and calcium, respectively. The pH in endocytic vacuoles was 5.9 ± 0.1, and the calcium ion concentration was 37 ± 11 μM. The caged calcium probe
o
-nitrophenyl EGTA and UV uncaging were used to increase calcium in endocytic vacuoles. This increase of calcium caused by calcium uncaging was followed by recovery to the prestimulated level within ≈100 s. We propose that the initiation of acute pancreatitis depends on endocytic vacuole formation and trypsinogen activation in this compartment.
Evaluation of the Anxiolytic Effect of Nepeta persica Boiss. in Mice
Authors: Rabbani M. , Sajjadi S. E. , Mohammadi A.
Published: March 2007

The aim of the present study was to evaluate the anxiolytic effects of hydroalcoholic extract (HE) of Nepeta persica Boiss. (Lamiaceae) on the elevated plus‐maze (EPM) model of anxiety. The extract of arial parts of the plant was administered intraperitoneally to male NMRI mice, at various doses, 30 min before behavioural evaluation. The HE extract of N. persica at the dose of 50 mg kg−1 significantly increased the percentage of time spent and percentage of arm entries in the open arms of the EPM. This dose of plant extract affected neither animal′s locomotor activity nor ketamine‐induced sleeping time. The 50 mg kg−1 dose of the plant extract seemed to be the optimal dose in producing the anxiolytic effects, lower or higher doses of the plant produce either sedative or stimulant effects. At 100 mg kg−1, the plant extract increased the locomotor activity. These results suggested that the extract of N. persica at dose of 50 mg kg−1 possess anxiolytic effect with less sedative and hypnotic effects than that of diazepam and causes a non‐specific stimulation at 100 mg kg−1.
Classification of all travelling-wave solutions for some nonlinear dispersive equations
Authors: Lenells Jonatan
Published: March 2007

We present a method for the classification of all weak travelling-wave solutions for some dispersive nonlinear wave equations. When applied to the Camassa–Holm or the Degasperis–Procesi equation, the approach shows the existence of not only smooth, peaked and cusped travelling-wave solutions, but also more exotic solutions with fractal-like wave profiles.
Re-evaluating AKT regulation: role of TOR complex 2 in tissue growth
Authors: Hietakangas Ville , Cohen Stephen M.
Published: March 2007

Phosphatidylinositol-3-kinase (PI3K)/AKT signaling is essential for growth and metabolism and is elevated in many cancers. Enzymatic activity of AKT has been shown to depend on phosphorylation of two conserved sites by PDK1 and TOR (target of rapamycin) complex 2 (TORC2) in a PI3K-dependent manner. Here we analyze the role of TORC2-mediated AKT phosphorylation in Drosophila. Mutants removing critical TORC2 components, rictor and sin1, strongly reduced AKT hydrophobic motif (HM) phosphorylation and AKT activity, but showed only minor growth impairment. A mutant form of AKT lacking the HM phosphorylation site displayed comparable activity. In contrast to the mild effects of removing HM site phosphorylation at normal levels of PI3K activity, loss of TORC2 activity strongly inhibited hyperplasia caused by elevated pathway activity, as in mutants of the tumor suppressor PTEN. Thus, TORC2 acts as a rheostat to broaden the range of AKT signaling at the high end of its range.
The revenge of the Patterson methods. II. Substructure applications
Authors: Burla Maria Cristina , Caliandro Rocco , Carrozzini Benedetta , Cascarano Giovanni Luca , De Caro Liberato , Giacovazzo Carmelo , Polidori Giampiero , Siliqi Dritan
Published: March 2007

The Patterson techniques, recently developed by the same authors for theab initiocrystal structure solution of proteins, have been applied to single and multiple anomalous diffraction (SAD and MAD) data to find the substructure of the anomalous scatterers. An automatic procedure has been applied to a large set of test structures, some of which were originally solved with remarkable difficulty. In all cases, the procedure automatically leads to interpretable electron density maps. Patterson techniques have been compared with direct methods; the former seem to be more efficient than the latter, so confirming the results obtained forab initiophasing, and disproving the common belief that they could only be applied to determine large equal-atom substructures with difficulty.
Phasing of resonant anomalous X-ray reflectivity spectra and direct Fourier synthesis of element-specific partial structures at buried interfaces
Authors: Park Changyong , Fenter Paul A.
Published: March 2007

A formalism for model-independent determination of element-specific partial structures at buried interfaces using the phase-dependent behavior of resonant anomalous X-ray reflectivity (RAXR) data is described. Each RAXR spectrum (i.e.reflectivityversusenergy at a fixed momentum transfer near the absorption edge of interest) is uniquely constrained by the amplitude and phase of the resonant partial structure factor with pre-determined non-resonant total structure factor and anomalous dispersion corrections of the resonant species. The element-specific partial density distribution is then imaged by discrete Fourier synthesis with the partial structure factor. The utility of this approach is demonstrated in the comparison of Rb+and Sr2+distributions at muscovite (001)–aqueous solution interfaces derived by model-independent and model-dependent approaches. This imaging method is useful for rapid determination of complex buried interfacial structures where element-specific atomic distributions are poorly constrained by conventional X-ray reflectivity analysis.
Small-angle scattering analysis of the spherical half-shell
Authors: Gille Wilfried
Published: March 2007

For a spherical half-shell (SHS) of diameter D, analytic expressions of the small-angle scattering correlation function \gamma_0(r), the chord length distribution (CLD) and the scattering intensity are analyzed. The spherically averaged pair correlation function p_0(r)\simeq r^2\gamma_0(r) of the SHS is identical to the cap part of the CLD of a solid hemisphere of the same diameter. The surprisingly simple analytic terms in principle allow the determination of the size distribution of an isotropic diluted SHS collection from its scattering intensity.
Small-angle neutron scattering resolution with refractive optics
Authors: Hammouda Boualem , Mildner David F. R.
Published: March 2007

The resolution of small-angle neutron scattering instruments is investigated for the case where refractive optics (lenses or prisms) are used. The appropriate equations are derived to describe the position and the spatial variance of the neutron beam at the detector in the horizontal and vertical directions, and the minimum value of the scattering vector. This is given for the spectrometer without any additional optics, and with the insertion of converging lenses or prisms. The addition of the lenses decreases the sample-aperture contribution to the resolution to enable an increase of neutron current at the sample. They also reduce the size of the penumbra of the beam at the detector, thereby lowering the minimum value of the scattering vector. The prisms correct the effect of gravity on the vertical beam position, and make the beam spot less asymmetric.
Likelihood of crystallization: experimental and computational approaches
Authors: Carugo Oliviero , Djinovic Carugo Kristina , Gorbalenya Alexander E. , Tucker Paul
Published: March 2007

A report on the VIZIER Workshop on the `Definition of protein domains and their likelihood of crystallization', Vienna, Austria, 28–30 June 2006.
High-temperature (1500 K) reciprocal space mapping on a laboratory X-ray diffractometer
Authors: Guinebretière R. , Boulle A. , Bachelet R. , Masson O. , Thomas P.
Published: March 2007

A laboratory X-ray diffractometer devoted to thein situcharacterization of the microstructure of epitaxic thin films at temperatures up to 1500 K has been developed. The sample holder was built using refractory materials, and a high-accuracy translation stage allows correction of the dilatation of both the sample and the sample holder. The samples are oriented with respect to the primary beam with two orthogonal rotations allowing the registration of symmetric as well as asymmetric reciprocal space maps (RSMs). The association of a monochromatic primary beam and a position-sensitive detector allows the measurement of RSMs in a few minutes for single crystals and in a few hours for imperfect epitaxic thin films. A detailed description of the setup is given and its potential is illustrated by high-temperature RSM experiments performed on yttria-doped zirconia epitaxic thin films grown on sapphire substrates.