bluuebunny/crossref_metadata_2025 huggingface dataset:
A scattering and absorption identity for metamaterials: Experimental results and comparison with theory
Authors: Sohl C. , Larsson C. , Gustafsson M. , Kristensson G.
Published: March 2008

A dispersion relation for the combined effect of scattering and absorption of electromagnetic waves is presented for a large class of linear and passive material models. By invoking the optical theorem, the result states that the extinction cross section integrated over all frequencies is equal to the static limit of the extinction volume. The present paper focuses on an attempt to experimentally verify this sum rule by measuring the monostatic radar cross section of a fabricated sample of metamaterial. In particular, the paper utilizes the idea that, for a specific class of targets, the scattered fields in the forward and backward directions are identical. It is concluded that the theoretical findings are in good agreement with measurements performed in the frequency range [3.2,19.5] GHz.
A double substrate “sandwich” structure for fiber surface enhanced Raman scattering detection
Authors: Shi Chao , Yan He , Gu Claire , Ghosh Debraj , Seballos Leo , Chen Shaowei , Zhang Jin Z. , Chen Bin
Published: March 2008

A double substrate “sandwiching” structure has been designed and tested for molecular detection using surface enhanced Raman scattering (SERS). With silver (Ag) nanoparticles as SERS substrates and rhodamine 6G (R6G) as a test molecule, the results show that the “sandwich” configuration exhibits significantly higher SERS enhancement compared to just one of the substrates or a simple sum of the signals from the two separate substrates. The improved SERS sensitivity is attributed to a stronger electromagnetic field enhancement by the double substrate sandwich structure.
Unusual thickness dependence of permittivity and elastic strain in Sc modified epitaxial (Ba,Sr)TiO3 thin films
Authors: Park Woo Young , Hwang Cheol Seong , Baniecki John D. , Ishii Masatoshi , Kurihara Kazuaki , Yamanaka Kazunori
Published: March 2008

Undoped and Sc doped epitaxial (Ba0.6,Sr0.4)Ti1+xO3 (BST and SBST) thin films were grown by sputtering on epitaxial Pt∕SrTiO3 substrates. The in-(a∥) and out-of-(an) lattice parameters of the BST films were relaxed with increasing thickness, but a∥ of the SBST films was independent of thickness. The dielectric constant (k) of the BST films decreased as the thickness decreased, whereas k of the SBST film was markedly larger and a maximum was observed at a certain thickness. This unusual behavior correlated with increased cell volume of the SBST and demonstrates doping can be used to adjust the thickness dependence of k.
Surface plasmon coupled electroluminescent emission
Authors: Koller D. M. , Hohenau A. , Ditlbacher H. , Galler N. , Aussenegg F. R. , Leitner A. , Krenn J. R. , Eder S. , Sax S. , List E. J. W.
Published: March 2008

Besides directly emitting light, electroluminescence in organic light emitting diodes (OLEDs) can excite surface plasmons (SPs) on the metal electrodes of the device. By designing a microcavity OLED with thin film metal electrodes, we can directly probe a SP mode by leaky wave extraction with a high refractive index glass prism coupler. Additional angle and polarization resolved reflection measurements on the OLED multilayer structure together with transfer matrix calculations allow us to unequivocally characterize the electroluminescent-driven SP mode.
Direct structural evidences of Mn11Ge8 and Mn5Ge2 clusters in Ge0.96Mn0.04 thin films
Authors: Wang Yong , Zou Jin , Zhao Zuoming , Han Xinhai , Zhou Xiaoyu , Wang Kang L.
Published: March 2008

Mn-rich clusters in Mn-doped Ge thin films epitaxially grown on Ge (001) have been investigated by various transmission electron microscopy techniques. Both the mysterious Mn11Ge8 and the hexagonal Mn5Ge2 (a=0.72nm and c=1.3nm) clusters were confirmed to coexist in the thicker Ge0.96Mn0.04 film (80nm). Their possible formation mechanism is attributed to the existence of ordered stacking faults. The fact that no Mn-rich clusters found in thinner films (<=40nm) suggests that, for a given Mn concentration and growth/annealing condition, a critical thickness exists for the formation of Mn-rich clusters.
Visible photoluminescence from plasma-synthesized SiO2-buffered SiNx films: Effect of film thickness and annealing temperature
Authors: Xu M. , Xu S. , Chai J. W. , Long J. D. , Cheng Q. J. , Ee Y. C. , Ostrikov K.
Published: March 2008

The effect of the film thickness and postannealing temperature on visible photoluminescence (PL) from SiNx films synthesized by plasma-assisted radio frequency magnetron sputtering on SiO2 buffer layers is investigated. It is shown that strong visible PL is achieved at annealing temperatures above 650°C. The optimum annealing temperature for the maximum PL yield strongly depends on the film thickness and varies from 800to1200°C. A comparative composition-structure-property analysis reveals that the PL intensity is directly related to the content of the Si–O and Si–N bonds in the SiNx films. Therefore, sufficient oxidation and moderate nitridation of SiNx∕SiO2 films during the plasma-based growth process are crucial for a strong PL yield. Excessively high annealing temperatures lead to weakened Si–N bonds in thinner SiNx films, which eventually results in a lower PL intensity.
Ferromagnetic GaMnAs grown on (110) faced GaAs
Authors: Wurstbauer Ursula , Sperl Matthias , Soda Marcello , Neumaier Daniel , Schuh Dieter , Bayreuther Günther , Zweck Josef , Wegscheider Werner
Published: March 2008

Thin Ga0.94Mn0.06As layers have been grown by low temperature molecular beam epitaxy on (110) GaAs substrates and on [110] and [−110] oriented GaAs cleaved edges. The Curie temperatures TC for the as-grown samples ranges from 46to80K. After annealing at low temperatures TC increases up to 115K. In addition, magnetic anisotropies determined by superconducting quantum interference device magnetometry and magnetotransport measurements are reported.
Development of magnetically preloaded air bearings for a linear slide: Active compensation of three degrees of freedom motion errors
Authors: Ro Seung-Kook , Kim Soohyun , Kwak Yoonkeun , Park Chun-Hong
Published: March 2008

This article describes a linear air-bearing stage that uses active control to compensate for its motion errors. The active control is based on preloads generated by magnetic actuators, which were designed to generate nominal preloads for the air bearings using permanent magnets to maintain the desired stiffness while changing the air-bearing clearance by varying the magnetic flux generated by the current in electromagnetic coils. A single-axis linear stage with a linear motor and 240mm of travel range was built to verify this design concept and used to test its performance. The motion of the table in three directions was controlled with four magnetic actuators driven by current amplifiers and a DSP (Digital Signal Processor)-based digital controller. The motion errors were measured using a laser interferometer combined with a two-probe method, and had 0.085μm of repeatability for the straightness error. As a result of feed-forward active compensation, the errors were reduced from 1.09to0.11μm for the vertical motion, from 9.42to0.18arcsec for the pitch motion, and from 2.42to0.18arcsec for the roll motion.
Analyzing the effects of front-surface fields on back-junction silicon solar cells using the charge-collection probability and the reciprocity theorem
Authors: Hermle M. , Granek F. , Schultz O. , Glunz S. W.
Published: March 2008

In this work, a one-dimensional analytical model to calculate the quantum efficiency in back-junction solar cells with and without a high-low junction on the front side is presented. The analytical model, based on the reciprocity theorem for charge collection, is compared with numerical device simulations taking into account the influence of high-injection effects. Using the analytical model, the influence of base doping concentration and surface recombination velocity on the internal quantum efficiency of a n-type back-junction solar cell is analyzed.
Permittivity measurements using adjustable microscale electrode gaps between millimeter-sized spherical electrodes
Authors: Ma Hongshen , Lang Jeffrey H. , Slocum Alexander H.
Published: March 2008

This paper presents a technique for measuring the electrical permittivity of liquids and gases using millimeter-sized spherical electrodes with adjustable microscale separation. This technique eliminates the need for wet calibration by using the precise adjustment of electrode separation to remove the inherent errors of parasitic capacitance and electrode polarization. The spherical electrode geometry also eliminates the need for precise parallel adjustment of electrode separation, and enables small-volume, small-electrode-gap measurements where the applied electric field is constrained in a region of well-defined geometry. By further leveraging the fact that spherical electrodes can be obtained with extremely high diametrical accuracy, absolute permittivity measurement accuracies within 1% of the established values has been demonstrated. Finally, the apparatus also enables the creation of nanometer electrode gaps between macroscopic electrodes with precisely controlled separation, which can be used to study the electrical properties of liquids in highly confined states. The electrode gaps created in this manner can be adjusted from 20nmto50μm, in increments of 0.25nm.
Differentiation to fractional orders and the fractional telegraph equation
Authors: Figueiredo Camargo R. , Chiacchio Ary O. , Capelas de Oliveira E.
Published: March 2008

Using methods of differential and integral calculus, we present and discuss the calculation of a fractional Green function associated with the one-dimensional case of the so-called general fractional telegraph equation with one space variable. This is a fractional partial differential equation with constant coefficients. The equation is solved by means of juxtaposition of transforms, i.e., we introduce the Laplace transform in the time variable and the Fourier transform in the space variable. Several particular cases are discussed in terms of the parameters. Some known results are recovered. As a by-product of our main result, we obtain two new relations involving the two-parameter Mittag–Leffler function.
A simple approach to the formation of ultranarrow metal wires
Authors: Chen Yu , Goldman A. M.
Published: March 2008

We report a simple approach to the formation of unbroken metal nanowires with widths as narrow as 5nm and lengths some tens of thousands of nanometers long. A signature of weak antilocalization was found in the temperature dependence of the resistance of nanowires of Au fabricated using this approach. Measurements of the resistance versus temperature in high and zero applied magnetic field were used to extract the temperature dependence of the phase coherence time τφ(T), which was found to be in fair agreement with theory, especially for multiple-wire samples. This technique of wire formation may be generalized to permit the growth of even narrower metal wires.
Electroluminescence characteristics of n-type matrix materials doped with iridium-based green and red phosphorescent emitters
Authors: Baek Heume-Il , Lee Changhee
Published: March 2008

The electroluminescence characteristics of various n-type matrix materials with various orders of electron mobility doped with the phosphorescent green emitter fac-tris(2-phenylpyridine) iridium(III) [Ir(ppy)3] and the phosphorescent red emitter bis(2-(2′-benzo [4,5-a] thienyl)pyridinato-N,C3′)iridium(acetyl-acetonate) [btp2Ir(acac)] were evaluated and compared to those of the p-type 4,4″-N,N′-dicarbazole-biphenyl (CBP) reference matrix. For Ir(ppy)3, the device with the n-type matrix 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene was found to have the highest efficiency and operational lifetime, whereas for btp2Ir(acac) the device with the p-type matrix CBP was found to have the highest efficiency. Our study of hole- and electron-dominant devices and analyses of electroluminescence spectra show that the main recombination zone position and the electron-hole balance change as the matrix material changes, resulting in changes in the characteristics of the organic light emitting diodes.
Anomalous phenomenon in hydrogen gas sensors based upon pyridylimidazoperylene or pyridylimidazonaphthalene
Authors: Hirao Keita , Tsukada Yuichiro , Suzuki Shigeru , Takahashi Hiroo , Mizuguchi Jin
Published: March 2008

We have been involved in the research and development on H2 gas sensors utilizing a high proton affinity of the pyridyl rings integrated in organic pigments such as diketopyrrolopyrroles, peryleneimides, and copperphthalocyanes. Our sensors exhibit a remarkable increase in electrical conductivity by three orders of magnitude even under 0.01% H2. However, an anomalous phenomenon has been observed in the title compounds (pyridylimidazoperylene and pyridylimidazonaphthalene) that shows an additional increase in conductivity (i.e., reverse of the sensor current) as soon as H2 shuts off. The unusual effect has been investigated in the present investigation on the basis of the crystal structure, molecular orbital calculations, and UV-visible/IR spectra with special attention to the sign of the charge carriers before and after exposure to H2. As a result, the pyridylimidazole ring is found to be responsible for the unusual effect that involves two protonation sites. In addition, the charge carriers have been determined to be solely electrons in the build up of the sensor current; whereas both electrons and protons are involved in the decay process. The contribution of the proton conduction in the decay process prevails over the electron current, ending up with the reverse in sensor current.
Tuning coherent radiative thermal conductance in multilayer photonic crystals
Authors: Lau Wah Tung , Shen Jung-Tsung , Veronis Georgios , Fan Shanhui , Braun Paul V.
Published: March 2008

We consider coherent radiative thermal conductance of a multilayer photonic crystal. The crystal consists of alternating layers of lossless dielectric slabs and vacuum, where heat is conducted only through photons. We show that such a structure can have thermal conductance below vacuum over the entire high temperature range due to the presence of partial band gap in most of the frequency range, as well as the suppression of evanescent tunneling between slabs at higher frequencies. The thermal conductance of this structure is highly tunable by varying the thickness of the vacuum layers.
On-axis microbeam wide- and small-angle scattering experiments of a sectioned poly(p-phenylene terephthalamide) fiber
Authors: Davies Richard J. , Koenig Christian , Burghammer Manfred , Riekel Christian
Published: March 2008

Poly(p-phenylene terephthalamide) fiber sections of ∼15μm length were prepared by a laser microdissection system. On-axis mesh scans by combined small- and wide-angle x-ray scattering using a micron-sized synchrotron radiation beam confirms a radial texture of crystalline domains with orientational order differing for skin, central core and intermediate layers. A skin-core variation in small-angle scattering demonstrates the evolution of fiber structure due to the heat-treatment process.
Monolayer segregation of As atoms at the interface between gate oxide and Si substrate in a metal-oxide-semiconductor field effect transistor by three-dimensional atom-probe technique
Authors: Inoue Koji , Yano Fumiko , Nishida Akio , Tsunomura Takaaki , Toyama Takeshi , Nagai Yasuyoshi , Hasegawa Masayuki
Published: March 2008

Atom-probe technique was applied to analyze three-dimensional dopant distribution in Si substrate of metal-oxide-semiconductor field effect transistor (MOSFET) structure. As a result, three-dimensional As atom distribution implanted in Si was obtained. The quantification of the As atom distribution in a depth direction was confirmed as compared with the one-dimensional distribution measured by secondary ion mass spectroscopy. Moreover, monolayer segregation of As atoms at the interface between gate oxide and Si substrate was clearly observed. This result shows the possibility to clarify discrete dopant distribution in Si substrate related to the characteristic variation of MOSFETs.
Analysis of dispersive electroacoustic coupling configurations for application to gigahertz-band, temperature-compensated AlN-based acoustic devices
Authors: Caliendo Cinzia
Published: March 2008

AlN films, 1.4–6.2μm thick, were sputtered on z-cut Al2O3 substrates and four electroacoustic coupling configurations were realized and characterized for x and y surface acoustic wave (SAW) propagation directions. The temperature-coefficient of delay dispersion curves of the four configurations was experimentally evaluated and eight temperature-compensated points were estimated. The velocity anisotropy of the multilayers was investigated for different AlN film thicknesses, electric excitation conditions, and temperature values. The design trade-offs required for temperature-compensated, 50Ω matched, gigahertz-range, enhanced-coupling, low loss SAW devices are provided for the four dispersive coupling configurations.
Characteristics of long wavelength InGaN quantum well laser diodes
Authors: Kim K. S. , Son J. K. , Lee S. N. , Sung Y. J. , Paek H. S. , Kim H. K. , Kim M. Y. , Ha K. H. , Ryu H. Y. , Nam O. H. , Jang T. , Park Y. J.
Published: March 2008

We demonstrated the long wavelength (485nm) lasing of InGaN laser diodes under continuous wave condition at room temperature over 10mW. Two InGaN laser structures were adapted with different indium composition for InGaN optical confinement layers (OCLs) below quantum wells. The blue shift of electroluminescence (EL) was reduced in InGaN laser diodes grown on 3% In concentration in InGaN OCL compared with 1.5% In concentration in InGaN OCL. The EL peak for laser diode with 3% In concentration in InGaN OCL occurs at longer wavelength for all current levels compared to the laser with 1.5% In concentration in InGaN OCL. In addition, the laterally nonuniform InGaN wells grown on 1.5% In concentration in InGaN OCL was verified by the cross-sectional view of InGaN active layer using high-resolution transmission electron microscopy.
Degradation of carbon nanotube field emitters driven by anode adsorbed water
Authors: Fennimore A. M. , Cheng L. T. , Roach D. H. , Reynolds G. A. M. , Getty R. R. , Krishnan A.
Published: March 2008

The field degradation of carbon nanotube field emitters in diode emission at constant current was demonstrated to be highly dependent upon the presence of water at partial pressures as low as 10−9Torr. The anode surface was also seen to significantly impact the degradation rate, with metallic Al films yielding the worst degradation rates. Coating the anode surface with a carbon or polymer film lowered the degradation rate. It is suggested that a majority of the degradation seen in nanotube field emission devices is due to ionization of water adsorbed at the anode surface.
Directional excitation of surface plasmons with subwavelength slits
Authors: Xu Ting , Zhao Yanhui , Gan Dachun , Wang Changtao , Du Chunlei , Luo Xiangang
Published: March 2008

We propose a method to manipulate the excitation direction of surface plasmons using subwavelength slits fabricated in a metallic film. By designing the specific effective index for each slit, the relative phase of plasmonics generated at the slit exit aperture can be tailored. Therefore, the electromagnetic field intensity along one direction on the metal surface can be enhanced or suppressed by surface plasmon interference. Numerical calculations performed by the finite-difference time-domain method illustrate our theoretical design.
Collecting photoelectrons with a scanning tunneling microscope nanotip
Authors: Chiu Ching-Yuan , Chan Yuet-Loy , Hsu Y. J. , Wei D. H.
Published: March 2008

The collection of photoelectrons excited with a synchrotron via a nanotip placed near the surface of a sample is studied. Simulating the electron trajectory, we found that photoelectrons escaping from the surface are too weak to be the only source of electrons contributing to a photocurrent detected with a scanning tunneling microscope tip, as reported recently. The tunneling of low-energy electrons generated with synchrotron irradiation is suggested as an additional channel contributing to the photocurrent at a small separation between tip and sample. An image based on x-ray absorption is expected to attain a resolution comparable to a topographical image.
A study of Al1−xInxN growth by reflection high-energy electron diffraction—incorporation of cation atoms during molecular-beam epitaxy
Authors: Shi B. M. , Wang Z. Y. , Xie M. H. , Wu H. S.
Published: March 2008

Molecular-beam epitaxy of Al1−xInxN alloys with different indium (In) contents, x, were studied by in situ reflection high-energy electron diffraction (RHEED). Growth rates of the alloys were measured by the RHEED intensity oscillations for different source flux conditions, while the lattice parameters were derived from the diffraction patterns. It was found that under the excess nitrogen growth regime, incorporation of aluminum was complete whereas incorporation of In atoms was incomplete even at temperatures below 400°C.
Sizable room-temperature magnetoresistance in cobalt based magnetic tunnel junctions with out-of-plane anisotropy
Authors: Carvello Baptiste , Ducruet Clarisse , Rodmacq Bernard , Auffret Stéphane , Gautier Eric , Gaudin Gilles , Dieny Bernard
Published: March 2008

Submicron alumina based magnetic tunnel junctions (MTJs) using electrodes with out-of-plane magnetic anisotropy were prepared and characterized. Both electrodes are industry-compatible Co∕Pt multilayers. The magnetic properties of the unpatterned samples have been investigated through superconducting quantum interference device (SQUID) magnetometry and extraordinary Hall effect: both electrodes have fully out-of-plane magnetic moments and nonoverlapping coercive fields. Transport measurements on the submicron MTJs showed a magnetoresistance (MR) ratio reaching 8% at room temperature. Nanopillars with diameters of 800, 400, and 200nm patterned from the same wafer show the expected out-of-plane magnetic properties and similar resistance×area products (RA) and MR ratios. The I(V) characteristics of pillars with diameters of 800 and 400nm could be accounted for with reasonable barrier heights and widths.
Observation of large h∕2e and h∕4e oscillations in a proximity dc superconducting quantum interference device
Authors: Wei J. , Cadden-Zimansky P. , Chandrasekhar V.
Published: March 2008

We have measured the magnetoresistance of a dc superconducting quantum interference device in the form of an interrupted mesoscopic normal metal loop in contact with two superconducting electrodes. Below the transition temperature of the superconducting electrodes, large h∕2e periodic magnetoresistance oscillations are observed. By adding a small dc bias to the ac measurement current, h∕4e oscillations can be produced. Lowering the temperature further leads to even larger oscillations, and eventually to sharp switching from the superconducting state to the normal state. This flux-dependent resistance could be utilized to make a highly sensitive flux detector.
Generating electrically tunable optical vortices by a liquid crystal cell with patterned electrode
Authors: Liu Y. J. , Sun X. W. , Luo D. , Raszewski Z.
Published: March 2008

An electrically tunable optical vortex was generated in an antiparallel liquid crystal cell, where one electrode was patterned by a photomask, which is achieved by transferring a computer-generated hologram onto a transparency with a resolution of about 25μm. When a voltage was applied on the cell, an index modulation was induced due to the realignment of liquid crystal molecules, and then an optical vortex beam was produced. The diffraction efficiency measured was about 27.5%. The device also showed a reasonably fast response time.
High pressure polymorph of MgTe predicted by first principles
Authors: Li Yan , Ma Yanming , Cui Tian , Yan Yumei , Zou Guangtian
Published: March 2008

Ab initio phonon calculations on NiAs-type (B8) MgTe are performed to probe the structural behaviors of MgTe under high pressure. We predicted an unstable transverse acoustic mode and a phase transition of B8→orthorhombic Pnma (B31) driven by this soft mode is thus identified. The polymorph of B31 in MgTe adopts MnP-type structure containing chains of metal atoms and is stable above 42.7GPa through the enthalpy calculations. With the discovery of the B31 phase, the previously theoretical high pressure structures of the tetragonal P4∕nmm (PH4I) and the CsCl (B2) are ruled out.
Experimental study of the output dynamics of intracavity frequency doubled optically pumped semiconductor disk lasers
Authors: Hartke René , Baev Valery , Seger Kai , Back Oliver , Heumann Ernst , Huber Günter , Kühnelt Michael , Steegmüller Ulrich
Published: March 2008

The dynamic behavior of the continuous wave output of an intracavity frequency doubled optically pumped semiconductor disk laser is described. These lasers typically exhibit stable emission. The reasons are found to be the tendency to single-mode operation and the high gain coupling of different modes due to an extremely short gain medium and the resonant periodic gain structure. A dependence of the fluctuation amplitude on gain decoupling of different fundamental modes is demonstrated. With the presented laser setup, more than 80% of conversion efficiency with respect to the available fundamental power has been achieved.
Solar-blind AlGaN-based p-i-n photodetectors with high breakdown voltage and detectivity
Authors: Tut Turgut , Yelboga Tolga , Ulker Erkin , Ozbay Ekmel
Published: March 2008

We report on the high performance solar-blind AlGaN-based p-i-n photodetectors that are grown by metal-organic chemical vapor deposition on c-plane sapphire substrates. The dark current of the 200μm diameter devices was measured to be on the order of 5fA for bias voltages up to 10V. The breakdown voltages were higher than 200V. The responsivities of the photodetectors were 0.052 and 0.093A∕W at 280nm under 0 and 40V reverse biases, respectively. We achieved a detectivity of 7.5×1014cmHz1∕2∕W for 200μm diameter AlGaN p-i-n detectors.
Evidence for erbium-erbium energy migration in erbium(III) bis(perfluoro-p-tolyl)phosphinate
Authors: Tan R. H. C. , Pearson J. M. , Zheng Y. , Wyatt P. B. , Gillin W. P.
Published: March 2008

Photoluminescence lifetime measurements of the erbium decay in samples of erbium(III) bis(perfluoro-p-tolyl)phosphinate, Er[(p-CF3C6F4)2PO2]3, as a function of erbium concentration have been made. It has been found that for concentrations greater than 50%, the lifetime could be fitted with a stretched exponential function, which is indicative of erbium-erbium energy migration to quenching sites, most likely at the surface of the finely divided powder. At concentrations below 50%, the decay was single exponential with a maximum lifetime of ∼700μs.
Ordered bimetallic magnets: Ferromagnetic [Cr(NH3)6][Cr(CN)6] and [Cr(H2O)(NH3)5][Cr(CN)6] (abstract)
Authors: Carlin Richard L. , Carnegie David , Casabo J.
Published: March 2008

The isostructural compounds [Cr(NH3)6][Cr(CN)6] and [Cr(H2O)(NH3)5][Cr(CN)6] [R. L. Carlin, R. Burriel, J. Pons, and J. Casabo Gispert, Inorg. Chem. 21, 2905 (1982)] order ferromagnetically at, respectively, 0.6 and 0.38 K. Their susceptibility curves, which are virtually superimposable when plotted on a reduced temperature scale, behave as expected for powdered samples in which demagnetization effects are important. The exchange interaction is remarkably weak for such concentrated magnetic materials, yet is much stronger than that found in a number of other such Cr/Cr compounds [R. L. Carlin, R. Burriel, J. Pons, and J. Casabo Gispert, Inorg. Chem. 22, 2832 (1983)].
Fertiliser N and P applications on two Vertosols in north-eastern Australia. 1. Comparative grain yield responses for two different cultivation ages
Authors: Lester David W. , Birch Colin J. , Dowling Chris W.
Published: March 2008

Nitrogen (N) and phosphorus (P) are the 2 most limiting nutrients for grain production within the northern grains region of Australia. The response to fertiliser N and P inputs is influenced partly by the age of cultivation for cropping, following a land use change from native pasture. There are few studies that have assessed the effects of both N and P fertiliser inputs on grain yield and soil fertility in the long term on soils with contrasting ages of cultivation with fertility levels that are running down v. those already at the new equilibrium. Two long-term N × P experiments were established in the northern grains region: one in 1985 on an old (>40 years) cultivation soil on the Darling Downs, Qld; the second in 1996 on relatively new (10 years) cultivation on the north-west plains of NSW. Both experiments consisted of fertiliser N rates from nil to 120 kg N/ha.crop in factorial combination with fertiliser P from nil to 20 kg P/ha.crop. Opportunity cropping is practiced at both sites, with winter and summer cereals and legumes sown.
On the old cultivation soil, fertiliser N responses were large and consistent for short-fallow crops, while long fallowing reduced the size and frequency of N response. Short-fallow sorghum in particular has responded up to the highest rate of fertiliser N (120 kg N/ha.crop). Average yield increase with fertiliser N compared with nil for 5 short-fallow sorghum crops was 1440, 2650, and 3010 kg/ha for the 40, 80, and 120 kg N/ha, respectively. Average agronomic efficiency of N for these crops was 36, 33, and 25 kg grain/kg fertiliser N applied. This contrasts with relatively new cultivation soil, where fertiliser N response was generally limited to the first 30 kg N/ha applied during periods of high cropping intensity.
Response to P input was consistent for crop species, VAM sensitivity, and starting soil test P level. At both the old and new cultivation sites, generally all winter cereals responded to a 10 kg P/ha application, and more than half of long-fallow sorghum crops from both sites had increased grain yield with P application. At the old cultivation site, average yield gain for 10 kg P/ha.crop treatment was 480 kg/ha for all winter cereal sowings, and 180 kg/ha for long-fallow sorghum. Short-fallow sorghum did not show yield response to P treatment.
Alien genetic resources for wheat leaf rust resistance, cytogenetic transfer, and molecular analysis
Authors: Gill B. S. , Huang L. , Kuraparthy V. , Raupp W. J. , Wilson D. L. , Friebe B.
Published: March 2008

Wild relatives of wheat are useful sources of alien resistance genes for wheat breeding. The objective of this review is to document research on the evaluation, transfer, and molecular analysis of alien resistance to wheat leaf rust especially in Aegilops tauschii, the diploid D-genome donor of common wheat. Nine named resistance genes (Lr1, Lr2, Lr15, Lr21, Lr22, Lr32, Lr34, Lr39, and Lr42) occur in the D genome. Twelve new leaf rust resistance genes have been documented in Ae. tauschii. The south-west Caspian Sea region is the centre of genetic diversity for seedling resistance. Adult-plant resistance is widespread in all geographic regions and should be exploited more in the future. Lr1 and Lr21 have been cloned and are typical NBS-LRR genes. The recent documentation of cryptic introgressions of Lr57/Yr40 from Ae. geniculata and Lr58 from Ae. triuncialis offers exciting possibilities for transferring alien genes without linkage drag. Both Lr21 and Lr34 presumably arose during or following the origin of common wheat ~8000 years ago. Leaf rust resistance genes often are located towards the physical ends of wheat chromosomes. These regions are known to be high in recombination, and this may explain their rapid rate of evolution.
Spermatozoa from a marsupial, the brushtail possum, contain β1,4-galactosyltransferase
Authors: Braundmeier A. G. , Breed William G. , Miller D. J.
Published: March 2008

β1,4-Galactosyltransferase-I (GalTase-I) is one of the key molecules on the sperm surface of eutherian mammals that is likely to be involved in binding to the egg coat, the zona pellucida, to mediate sperm–egg interaction. In laboratory mice, the species for which most data are available, this protein functions as a receptor for the zona pellucida protein ZP3 of the oocyte and, upon binding, triggers the sperm acrosome reaction. In the present study, we investigated the presence and abundance of GalTase-I in epididymal sperm extracts of a marsupial, the brushtail possum, Trichosurus vulpecula. For this, spermatozoa were collected from cauda epididymides and the amount of β1,4-galactosyltransferase activity in washed sperm extracts was compared with that of porcine spermatozoa. Overall β1,4-galactosyltransferase enzyme activity was found to be more abundant in possum sperm extracts than those from porcine spermatozoa (P < 0.05). Immunoblots with an antibody to mouse GalTase-I revealed that the molecular weight of possum spermatozoa GalTase-I was 66 kDa, which is similar to the molecular weight of GalTase-I in spermatozoa from eutherian mammals. The molecular weight of GalTase-I was the same in sperm extracts collected from the caput and cauda epididymides. These results demonstrate that GalTase-I is indeed present in possum spermatozoa and thus it may be a gamete receptor molecule on the sperm surface of marsupials as well as those of eutherian mammals.
Measurement of rest and activity in newborn lambs using actigraphy: studies in term and preterm lambs
Authors: Rurak D. W. , Fay S. , Gruber N. C.
Published: March 2008

The present study used actigraphy to monitor rest–activity cycles in lambs. We employed an Actiwatch Activity Monitor, which was secured on the lamb’s neck in 13 term lambs and six preterm lambs. Activity measurements began on the day of delivery and lasted for 7.3 ± 0.7 days. All lambs exhibited bouts of activity, lasting from ~2 to 60 min, separated by periods of inactivity of about equal duration. There was a progressive increase in the frequency and intensity of activity bouts with age, and a decrease in duration. In relation to postnatal age, preterm lambs had a significantly lower frequency and intensity of activity bouts compared with term lambs and significantly longer mean active bout duration. However, in relation to post-conceptual age, preterm animals were less active at birth, but thereafter the trajectory for activity development was steeper compared with the term lambs. These differences between term and preterm lambs may be due to several factors including differences in: (1) the lengths of time the two groups spent in utero and as neonates as a proportion of the perinatal period, which could influence the rate of muscle and bone growth; (2) prenatal and postnatal hormonal profiles; and (3) maternal care. We also found differences in postnatal motility in male and female lambs, with the trajectory of activity increasing in males at Days 4–5, which could be due, in part at least, to sex differences in both prenatal and postnatal hormonal profiles.
Variation in virulence among clades of
Escherichia coli
O157:H7 associated with disease outbreaks
Authors: Manning Shannon D. , Motiwala Alifiya S. , Springman A. Cody , Qi Weihong , Lacher David W. , Ouellette Lindsey M. , Mladonicky Janice M. , Somsel Patricia , Rudrik James T. , Dietrich Stephen E. , Zhang Wei , Swaminathan Bala , Alland David , Whittam Thomas S.
Published: March 2008

Escherichia coli
O157:H7, a toxin-producing food and waterborne bacterial pathogen, has been linked to large outbreaks of gastrointestinal illness for more than two decades.
E. coli
O157 causes a wide range of clinical illness that varies by outbreak, although factors that contribute to variation in disease severity are poorly understood. Several recent outbreaks involving O157 contamination of fresh produce (e.g., spinach) were associated with more severe disease, as defined by higher hemolytic uremic syndrome and hospitalization frequencies, suggesting that increased virulence has evolved. To test this hypothesis, we developed a system that detects SNPs in 96 loci and applied it to >500
E. coli
O157 clinical strains. Phylogenetic analyses identified 39 SNP genotypes that differ at 20% of SNP loci and are separated into nine distinct clades. Differences were observed between clades in the frequency and distribution of Shiga toxin genes and in the type of clinical disease reported. Patients with hemolytic uremic syndrome were significantly more likely to be infected with clade 8 strains, which have increased in frequency over the past 5 years. Genome sequencing of a spinach outbreak strain, a member of clade 8, also revealed substantial genomic differences. These findings suggest that an emergent subpopulation of the clade 8 lineage has acquired critical factors that contribute to more severe disease. The ability to detect and rapidly genotype O157 strains belonging to such lineages is important and will have a significant impact on both disease diagnosis and treatment guidelines.
IgG glycan hydrolysis by a bacterial enzyme as a therapy against autoimmune conditions
Authors: Collin Mattias , Shannon Oonagh , Björck Lars
Published: March 2008

EndoS from
Streptococcus pyogenes
efficiently hydrolyzes the functionally important and conserved
N
-linked glycan of IgG in human blood. Repeated i.v. administration of EndoS in rabbits completely hydrolyzes the glycans of the whole IgG pool, despite the generation of anti-EndoS antibodies. EndoS administration had no apparent effects on the health of the animals. EndoS hydrolysis of the IgG glycan has profound effects on IgG effector functions, such as complement activation and Fc receptor binding, suggesting that the enzyme could be used as an immunomodulatory therapeutic agent against IgG-mediated diseases. We demonstrate here that EndoS indeed has a protective effect in a mouse model of lethal IgG-driven immune (or idiopathic) thrombocytopenic purpura. EndoS pretreatment of pathogenic antibodies inhibits the development of disease, and the enzyme also rescues mice from already established disease when severe thrombocytopenia and s.c. bleeding have developed. These results identify EndoS as a potential therapeutic agent against diseases where pathogenic IgG antibodies are important and further emphasize antibody glycans as possible targets in future therapies against antibody-mediated autoimmune conditions.
Enduring effects of early structured noise exposure on temporal modulation in the primary auditory cortex
Authors: Zhou Xiaoming , Merzenich Michael M.
Published: March 2008

Studies have shown that acoustic experiences significantly contribute to the functional shaping of the structural organization and signal processing capacities of the mammalian auditory system during postnatal development. Here, we show how an early epoch of exposure to structured noise influences temporal processing in the rat primary auditory cortex documented immediately after exposure and again in adulthood. Pups were continuously exposed to broadband-pulsed noise across the critical period for auditory system development. Immediately after cessation of exposure at postnatal day ≈35 (P35) or ≈55 days later (i.e., P90) in other rats, the temporal modulation-transfer functions of cortical neurons were documented. We found that pulsed noise exposure at a low modulation rate significantly decreased cortical responses to repetitive stimuli presented across a range of higher modulation rates. The highest temporal rate at which temporal modulation-transfer function was at half of its maximum was reduced when compared with naïve rats. Low-rate pulsed noise exposure also decreased cortical response synchronization at higher stimulus rates, as shown by vector strength and Rayleigh statistic measures. These postexposure changes endured into adulthood. These findings bear significant implications for the role of early sound experiences as contributors to the ontogeny of human auditory and language-related abilities and impairments.
A disulfide-stabilized conformer of methionine synthase reveals an unexpected role for the histidine ligand of the cobalamin cofactor
Authors: Datta Supratim , Koutmos Markos , Pattridge Katherine A. , Ludwig Martha L. , Matthews Rowena G.
Published: March 2008

B
12
-dependent methionine synthase (MetH) from
Escherichia coli
is a large modular protein that is alternately methylated by methyltetrahydrofolate to form methylcobalamin and demethylated by homocysteine to form cob(I)alamin. Major domain rearrangements are required to allow cobalamin to react with three different substrates: homocysteine, methyltetrahydrofolate, and
S
-adenosyl-
l
-methionine (AdoMet). These same rearrangements appear to preclude crystallization of the wild-type enzyme. Disulfide cross-linking was used to lock a C-terminal fragment of the enzyme into a unique conformation. Cysteine point mutations were introduced at Ile-690 and Gly-743. These cysteine residues span the cap and the cobalamin-binding module and form a cross-link that reduces the conformational space accessed by the enzyme, facilitating protein crystallization. Here, we describe an x-ray structure of the mutant fragment in the reactivation conformation; this conformation enables the transfer of a methyl group from AdoMet to the cobalamin cofactor. In the structure, the axial ligand to the cobalamin, His-759, dissociates from the cobalamin and forms intermodular contacts with residues in the AdoMet-binding module. This unanticipated intermodular interaction is expected to play a major role in controlling the distribution of conformers required for the catalytic and the reactivation cycles of the enzyme.
Psychiatry's Problem Child: PTSD in the Forensic Context (Part 2)
Authors: Gaughwin Peter
Published: March 2008

Objective: The aim of this paper was to consider whether the Courts in their application of Criterion A for post-traumatic stress disorder (PTSD) in the civil forensic context are in harmony or in conflict with psychiatry.

Method: Discussed are five cases from the civil forensic jurisdiction that considered plaintiffs' submissions that, as a consequence of some wrong, they suffered PTSD.

Results: The Courts have been quite consistent in their approach to PTSD – where there has been conflicting expert evidence as to whether a plaintiff has PTSD, the stressor which brings about this disorder must be extreme (i.e. objectively life-threatening).

Conclusions: The Courts have been consistent in their application of Criterion A and, as such, are consistent with what the DSM-IV-TR requires before the diagnosis can be made. Such an approach ensures that merely unpleasant events, irrespective of how subjectively upsetting they may be, do not qualify for the diagnosis of PTSD. Psychiatrists, therefore, have an enormous responsibility when they provide expert evidence in relation to psychiatric issues that arise in legal matters.
Are Australian Men With Psychosis Spending More Time Homeless?
Authors: Holmes Alex , Hodge Mark , Hodge Mark , Bradley Gail , Bluhm Alan , Markulev Natasha , North Cameron , Innis Andy
Published: March 2008

Objective: The objective of this study was to determine if homeless men with psychosis using emergency accommodation services are spending more time homeless.

Method: A 12-month accommodation history was collected from all men with psychosis referred to mental health services using two emergency accommodation services in inner Melbourne over a 5-year period.

Results: Of the 241 men referred with psychosis, 200 (81%) were able to provide a full accommodation history. In 2001 the mean total days spent in crisis accommodation was 27.0 days and in 2005 the mean number of days was 60.9. Over the 5 years, increasing time was spent homeless in the 12 months prior to assessment, most commonly in emergency accommodations.

Conclusions: Australian men with psychosis using emergency accommodation are spending an increasing amount of time homeless.
The regulation of SIRT2 function by cyclin-dependent kinases affects cell motility
Authors: Pandithage Ruwin , Lilischkis Richard , Harting Kai , Wolf Alexandra , Jedamzik Britta , Lüscher-Firzlaff Juliane , Vervoorts Jörg , Lasonder Edwin , Kremmer Elisabeth , Knöll Bernd , Lüscher Bernhard
Published: March 2008

Cyclin-dependent kinases (Cdks) fulfill key functions in many cellular processes, including cell cycle progression and cytoskeletal dynamics. A limited number of Cdk substrates have been identified with few demonstrated to be regulated by Cdk-dependent phosphorylation. We identify on protein expression arrays novel cyclin E–Cdk2 substrates, including SIRT2, a member of the Sirtuin family of NAD+-dependent deacetylases that targets α-tubulin. We define Ser-331 as the site phosphorylated by cyclin E–Cdk2, cyclin A–Cdk2, and p35–Cdk5 both in vitro and in cells. Importantly, phosphorylation at Ser-331 inhibits the catalytic activity of SIRT2. Gain- and loss-of-function studies demonstrate that SIRT2 interfered with cell adhesion and cell migration. In postmitotic hippocampal neurons, neurite outgrowth and growth cone collapse are inhibited by SIRT2. The effects provoked by SIRT2, but not those of a nonphosphorylatable mutant, are antagonized by Cdk-dependent phosphorylation. Collectively, our findings identify a posttranslational mechanism that controls SIRT2 function, and they provide evidence for a novel regulatory circuitry involving Cdks, SIRT2, and microtubules.
Essential role of B-Raf in oligodendrocyte maturation and myelination during postnatal central nervous system development
Authors: Galabova-Kovacs Gergana , Catalanotti Federica , Matzen Dana , Reyes Gloria X. , Zezula Jürgen , Herbst Ruth , Silva Alcino , Walter Ingrid , Baccarini Manuela
Published: March 2008

Mutations in the extracellular signal-regulated kinase (ERK) pathway, particularly in the mitogen-activated protein kinase/ERK kinase (MEK) activator B-Raf, are associated with human tumorigenesis and genetic disorders. Hence, B-Raf is a prime target for molecule-based therapies, and understanding its essential biological functions is crucial for their success. B-Raf is expressed preferentially in cells of neuronal origin. Here, we show that in mice, conditional ablation of B-Raf in neuronal precursors leads to severe dysmyelination, defective oligodendrocyte differentiation, and reduced ERK activation in brain. Both B-Raf ablation and chemical inhibition of MEK impair oligodendrocyte differentiation in vitro. In glial cell cultures, we find B-Raf in a complex with MEK, Raf-1, and kinase suppressor of Ras. In B-Raf–deficient cells, more Raf-1 is recruited to MEK, yet MEK/ERK phosphorylation is impaired. These data define B-Raf as the rate-limiting MEK/ERK activator in oligodendrocyte differentiation and myelination and have implications for the design and use of Raf inhibitors.