bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Pt and Fe underlayers on the microstructure and magnetization reversal of epitaxial FePt films for high areal density magnetic recording
Authors: Wei D. H. , Yuan F. T. , Chang H. W. , Yao Y. D.
Published: March 2008

The effects of underlayer on the microstructure and magnetic characterizations of epitaxial FePt films were studied. Enhanced out-of-plane coercivity and ordering were obtained in the Pt-underlayered FePt samples, which may be due to the proper lattice strain from the Pt underlayer. The larger lattice parameter of Pt may enlarge the a axis and reduce the c axis of the L10 FePt phase and result in low-temperature ordering. However, such an effect does not appear in Fe-underlayered samples because of the smaller lattice parameter and the considerable interdiffusion. The angular dependence coercivity revealed that the dominant reversal mechanism of the FePt films changed from domain-wall motion to rotation, which is caused by the formation of L10 island structures induced by the Pt underlayer. On the other hand, the Fe-underlayered FePt films showed a broad peak roughly at 45°, implying the tilt of the easy axis about 45° away from the film normal.
Magnetic domains and annealing-induced magnetic anisotropy in nanocrystalline soft magnetic materials
Authors: Suzuki K. , Ito N. , Saranu S. , Herr U. , Michels A. , Garitaonandia J. S.
Published: March 2008

The magnetic domains of nanocrystalline Fe84Nb6B10 annealed under static and rotating magnetic fields have been investigated by means of magneto-optical Kerr effect (MOKE) microscopy in order to clarify the origin of the dramatic magnetic softening brought about by rotating field annealing. The coercivity (Hc) values after static- and rotating-magnetic field annealings are 5.9 and 3.0A∕m, respectively. The MOKE image after static field annealing implies a highly coherent uniaxial anisotropy (Ku) in the sample whereas no sign of such a strong Ku is evident in the domain configuration after rotating field annealing. Our analytical solution of the random anisotropy model with additional Ku predicts that the fluctuating amplitude of the effective anisotropy (δK) in nanocrystalline Fe84Nb6B10 decreases from 20to11J∕m3 by removing Ku. The observed reduction of Hc may be attributed to this decrease in δK induced by rotating field annealing.
Rovibrationally selected and resolved pulsed field ionization-photoelectron study of propyne: Ionization energy and spin-orbit interaction in propyne cation
Authors: Xing Xi , Bahng Mi-Kyung , Reed Beth , Lam C. S. , Lau Kai-Chung , Ng C. Y.
Published: March 2008

By using a high-resolution infrared (IR) laser to prepare propyne (C3H4) in selected rotational levels of the excited ν1 (acetylenic C–H stretching) vibration mode prior to vacuum ultraviolet (VUV) laser pulsed field ionization-photoelectron (PFI-PE) measurements, we have obtained rotationally resolved VUV-PFI-PE spectra for the C3H4+(X̃E3∕2,1∕22,ν1+=1) band. The analysis of these PFI-PE spectra leads to the determination of the spin-orbit constant of A=−13.0±0.2cm−1 for the C3H4+(X̃E3∕2,1∕22,ν1+=1) state. Using this A constant and the relative rotationally selected and resolved state-to-state photoionization cross sections thus measured, we have obtained an excellent simulation for the VUV-PFI-PE origin band of C3H4+(X̃E3∕2,1∕22), yielding a value of 83619.0±1.0cm−1 (10.36744±0.00012eV) for the adiabatic ionization energy of C3H4 [IE(C3H4)]. The present two-color IR-VUV-PFI-PE study has also made possible the determination of the C–H stretching frequencies ν1+=3217.1±0.2cm−1 for C3H4+(X̃E3∕2,1∕22). The spectral assignment and simulation were guided by high-level ab initio calculations on the IE(C3H4), Franck-Condon factors for photoionization transitions, and rotational constants and vibrational frequencies for C3H4+.
Reduction of superconducting transition temperature and flux pinning in Al and C codoped MgB2 with insight from first-principles calculations
Authors: Li A. H. , Wang X. L. , Dou S. X. , Yao Q. W. , Cheng Z. X. , Soltanian S. , Yoo J. M. , Munroe P.
Published: March 2008

We report for the first time the Al and C codoping effect on the structures and superconductivity in MgB2. It was found that both the lattice parameters and the Tc decreased monotonically with increasing doping level of both Al and C. The Tc dropped to 27.5 and 7K for x=0.2 and for x=0.4, respectively. The reduction of Tc for the codoping was found to be quicker than for individual Al doping and slower than for individual C doping at the same doping levels. First-principles calculations indicated that the observed decrease in Tc for the codoped MgB2 can be understood in terms of a band filling effect due to the electron doping by both Al and C. However, it is suggested that other factors may also play a role in the Tc reduction in the real Mg1−xAlxB2−xCx samples. Furthermore, the Al and C codoping also reduces Jc and weakens flux pinning in MgB2.
The divine clockwork: Bohr’s correspondence principle and Nelson’s stochastic mechanics for the atomic elliptic state
Authors: Durran Richard , Neate Andrew , Truman Aubrey
Published: March 2008

We consider the Bohr correspondence limit of the Schrödinger wave function for an atomic elliptic state. We analyze this limit in the context of Nelson’s stochastic mechanics, exposing an underlying deterministic dynamical system in which trajectories converge to Keplerian motion on an ellipse. This solves the long standing problem of obtaining Kepler’s laws of planetary motion in a quantum mechanical setting. In this quantum mechanical setting, local mild instabilities occur in the Keplerian orbit for eccentricities greater than 12 which do not occur classically.
Spin-polarized currents in exchange spring systems
Authors: Franchin Matteo , Bordignon Giuliano , Fischbacher Thomas , Meier Guido , Zimmermann Jürgen , de Groot Peter , Fangohr Hans
Published: March 2008

We present a computational study of the magnetization dynamics of a trilayer exchange spring system in the form of a cylindrical nanopillar in the presence of an electric current. A three-dimensional micromagnetic model is used, where the interaction between the current and the local magnetization is taken into account following a recent model by Zhang and Li [Phys. Rev. Lett. 93, 127204 (2004)] We obtain a stationary rotation of the magnetization of the system around its axis, accompanied by a compression of the artificial domain wall in the direction of the electron flow.
Enhanced proton production from hydride-coated foils
Authors: Foord M. E. , Mackinnon A. J. , Patel P. K. , MacPhee A. G. , Ping Y. , Tabak M. , Town R. P. J.
Published: March 2008

Proton generation from the interaction of an intense, short pulse laser with a foil target is simulated using the particle-in-cell hybrid code LSP. The efficiencies for proton production are compared for foils having thin coatings of CH, CH2, CH4, and LiH, as well as heavy hydrides such as ErH3. Enhanced efficiencies are found for both light hydrogen-rich compounds and for heavy hydrides, which in the latter case approach the pure H result. A simple model reproduces these results over a wide range of materials.
Polymer hot-carrier transistor with low bandgap emitter
Authors: Chao Yu-Chiang , Xie Ming-Hong , Dai Ming-Zhi , Meng Hsin-Fei , Horng Sheng-Fu , Hsu Chain-Shu
Published: March 2008

Vertical polymer hot-carrier transistor using the low bandgap material poly(3-hexylthiophene) as both the emitter and the collector are studied. The common emitter current gain is shown to depend on the LiF thickness and the emitter thickness, with maximal value at 31. Current density as high as 31mA∕cm2 is achieved when collector voltage is −10V. For the device using blend of poly(3-hexylthiophene) and high bandgap polymer poly(9-vinylcarbazole) as the emitter, the current density rises sharply to 428mA∕cm2. The brightness of 3000cd∕m2 is obtained as a polymer light-emitting diode is driven by the transistor with the same area. The transistor can be operated at 100kHz.
A method to study the cooling effect of the thermal actuator
Authors: Ng Ka Wei , Wong Chee How , Leong Siang Huei , Yuan Zhimin , Liu Bo , Chong Tow-Chong
Published: March 2008

We report a method that can be used to study the cooling effect on the thermal actuator of a flying slider with greater sensitivity than magnetoresistive (MR) sensor measurements. By monitoring the first and second harmonics of the read back signal associated with the ac excited thermal protrusion, the second harmonic signal diverges from the linear first harmonic signal as cooling effect intensifies. This is attributed to distortion of the read back signal envelope with increased cooling. Results also indicate that a bonded lube disk produces a higher cooling effect compared with a bonded+mobile lube disk. These were correlated with MR sensor temperature measurements. An ANSYS simulation model was developed to explain the nonlinearity in the second harmonic.
Electrospray on superhydrophobic nozzles treated with argon and oxygen plasma
Authors: Byun Doyoung , Lee Youngjong , Tran Si Bui Quang , Nugyen Vu Dat , Kim Sanghoon , Park Baeho , Lee Sukhan , Inamdar Niraj , Bau Haim H.
Published: March 2008

We report on a simple process to fabricate electrohydrodynamic spraying devices with superhydrophobic nozzles. These devices are useful, among other things, in mass spectrometry and printing technology. The superhydrophobic nozzle is created by roughening the surface of the polyfluorotetraethylene (PTFE) by argon and oxygen plasma treatment. We have developed a polymer-based electrospray device with a flat, superhydrophobic nozzle capable of maintaining a high contact angle and stable jetting.
A nonlinear controller design for permanent magnet motors using a synchronization-based technique inspired from the Lorenz system
Authors: Zaher Ashraf A.
Published: March 2008

The dynamic behavior of a permanent magnet synchronous machine (PMSM) is analyzed. Nominal and special operating conditions are explored to show that the PMSM can experience chaos. A nonlinear controller is introduced to control these unwanted chaotic oscillations and to bring the PMSM to a stable steady state. The designed controller uses a pole-placement approach to force the closed-loop system to follow the performance of a simple first-order linear system with zero steady-state error to a desired set point. The similarity between the mathematical model of the PMSM and the famous chaotic Lorenz system is utilized to design a synchronization-based state observer using only the angular speed for feedback. Simulation results verify the effectiveness of the proposed controller in eliminating the chaotic oscillations while using a single feedback signal. The superiority of the proposed controller is further demonstrated by comparing it with a conventional PID controller. Finally, a laboratory-based experiment was conducted using the MCK2812 C Pro—MS(BL) motion control kit to confirm the theoretical results and to verify both the causality and versatility of the proposed controller.
Correlation between the energy shell structure and geometry in metallic nanoclusters: Quasiresonance states, isotope effect
Authors: Kresin Vladimir
Published: March 2008

Metallic nanoclusters displaying electronic shell structure exhibit the special feature of a correlation between their geometry and the number of delocalized electrons. Their shape evolution can be described as a quantum oscillation between quasiresonant states (prolate and oblate configurations) whose amplitudes depend on the degree of shell filling. The picture explains the evolution of absorption spectra and predicts a peculiar isotope effect.
Combined low-temperature scanning tunneling/atomic force microscope for atomic resolution imaging and site-specific force spectroscopy
Authors: Albers Boris J. , Liebmann Marcus , Schwendemann Todd C. , Baykara Mehmet Z. , Heyde Markus , Salmeron Miquel , Altman Eric I. , Schwarz Udo D.
Published: March 2008

We present the design and first results of a low-temperature, ultrahigh vacuum scanning probe microscope enabling atomic resolution imaging in both scanning tunneling microscopy (STM) and noncontact atomic force microscopy (NC-AFM) modes. A tuning-fork-based sensor provides flexibility in selecting probe tip materials, which can be either metallic or nonmetallic. When choosing a conducting tip and sample, simultaneous STM/NC-AFM data acquisition is possible. Noticeable characteristics that distinguish this setup from similar systems providing simultaneous STM/NC-AFM capabilities are its combination of relative compactness (on-top bath cryostat needs no pit), in situ exchange of tip and sample at low temperatures, short turnaround times, modest helium consumption, and unrestricted access from dedicated flanges. The latter permits not only the optical surveillance of the tip during approach but also the direct deposition of molecules or atoms on either tip or sample while they remain cold. Atomic corrugations as low as 1pm could successfully be resolved. In addition, lateral drifts rates of below 15pm∕h allow long-term data acquisition series and the recording of site-specific spectroscopy maps. Results obtained on Cu(111) and graphite illustrate the microscope’s performance.
Defect studies of ZnO single crystals electrochemically doped with hydrogen
Authors: Čížek J. , Žaludová N. , Vlach M. , Daniš S. , Kuriplach J. , Procházka I. , Brauer G. , Anwand W. , Grambole D. , Skorupa W. , Gemma R. , Kirchheim R. , Pundt A.
Published: March 2008

Various defect studies of hydrothermally grown (0001) oriented ZnO crystals electrochemically doped with hydrogen are presented. The hydrogen content in the crystals is determined by nuclear reaction analysis and it is found that already 0.3at.% H exists in chemically bound form in the virgin ZnO crystals. A single positron lifetime of 182ps is detected in the virgin crystals and attributed to saturated positron trapping at Zn vacancies surrounded by hydrogen atoms. It is demonstrated that a very high amount of hydrogen (up to ∼30at.%) can be introduced into the crystals by electrochemical doping. More than half of this amount is chemically bound, i.e., incorporated into the ZnO crystal lattice. This drastic increase of the hydrogen concentration is of marginal impact on the measured positron lifetime, whereas a contribution of positrons annihilated by electrons belonging to O–H bonds formed in the hydrogen doped crystal is found in coincidence Doppler broadening spectra. The formation of hexagonal shape pyramids on the surface of the hydrogen doped crystals by optical microscopy is observed and discussed.
Acceptable coupling losses in coated conductors at industrial frequencies without twisting the superconducting stripes
Authors: Takács S.
Published: March 2008

The author calculates precisely the induced currents in striated YBa2Cu3O7 coated conductors covered partially by segmented pieces of normal metal, connecting the individual superconducting stripes. It is shown that the induced current density is below the critical current density of the superconducting stripes and the coupling losses are acceptable low, ensuring in addition sufficient current sharing between the stripes. Thus, the proposed structure can be applicable at ac conditions without twisting procedure. The ratio of the current closed between the normal plates to the current flowing in the superconducting stripes and the losses in the substrate are also discussed. The total current flowing through the whole length of the superconductor, which has to be closed at the ends, is also acceptable low. In addition, the frequency range, in which the magnetic flux can fully penetrate both between the stripes and into the normal segments, is given.
Direct integration of vertical In2O3 nanowire arrays, nanosheet chains, and photoinduced reversible switching of wettability
Authors: Zhong Miao , Zheng Maojun , Zeng Ansheng , Ma L.
Published: March 2008

Large-scale In2O3 nanowire (NW) arrays and nanosheet chains are directly integrated on InP substrates via a simple chemical vapor deposition process, benefiting from the substrate-induced, self-assembly and self-catalyzed vapor-liquid-solid growth mechanism. Such particular structures could be expected to have potential applications such as gas sensors and field emission devices. Equally important, remarkable photoinduced wettability conversion between superhydrophobicity and high hydrophilicity has been observed on In2O3 NW arrays. This reversible behavior is ascribed to the photogenerated surface oxygen vacancies and the special nanostructures. Such reversibly switching surface will widen the applications of In2O3 films.
Leakage current origins and passivation effect of GaN-based light emitting diodes fabricated with Ag p-contacts
Authors: Kim Hyunsoo , Cho Jaehee , Park Yongjo , Seong Tae-Yeon
Published: March 2008

The origins of leakage currents and passivation effects of GaN-based light emitting diodes fabricated with Ag p-contacts have been investigated by electrical measurements. A significant increase in reverse leakage current is attributed to the surface migration of Ag. A passivation of mesa sidewalls by SiO2 is found to be effective in suppressing the reverse leakage. However, the passivation results in a somewhat increase in the forward leakage at moderate voltages. Such forward leakage is explained in terms of the presence of local deep-level states in p-GaN generated during SiO2 deposition, acting as a parasitic diode with a lower barrier height.
On a classification of irreducible almost-commutative geometries IV
Authors: Jureit Jan-Hendrik , Stephan Christoph A.
Published: March 2008

In this paper, we will classify the finite spectral triples with KO-dimension 6, following the classification found in Iochum, B., Schücker, T., and Stephan, C. A., J. Math. Phys. 45, 5003 (2004); Jureit, J.-H. and Stephan, C. A., J. Math. Phys. 46, 043512 (2005); Schücker, T. (unpublished); Jureit, J.-H., Schücker, T., and Stephan, C. A., J. Math. Phys. 46, 072302 (2005). with up to four summands in the matrix algebra. Again, heavy use is made of Krajewski diagrams [Krajewski, T., J. Geom. Phys. 28, 1 (1998).] This work has been inspired by the recent paper by Connes (unpublished) and Barrett (unpublished). In the classification, we find that the standard model of particle physics in its minimal version fits the axioms of noncommutative geometry in the case of KO-dimension 6. By minimal version, it is meant that at least one neutrino has to be massless and mass-terms mixing particles and antiparticles are prohibited.
Fully developed thermocreep-driven gas microflow
Authors: Weng Huei Chu , Chen Cha’o-Kuang
Published: March 2008

In this study, we develop the mathematical model of thermocreep-driven gas flow in an unheated parallel-plate microchannel with discrepant temperatures at both ends. The fully developed solutions for flow and thermal fields as well as the corresponding characteristics are derived analytically and presented for air. Results reveal that the velocity and temperature distributions are uniform. This means that the local flow drag and the local heat transfer rate are zero and that the influence of fluid-wall interaction is negligible. In addition, the velocity slip induced by gas rarefaction is shown to increase the flow rate and the average heat transfer rate. Such effect can be magnified by the decreases of the channel width and the channel length.
dc effect in a single micrometric spin valve sensor under ferromagnetic resonance
Authors: Biziere N. , Fermon C.
Published: March 2008

We report on the observation of an increase in the dc voltage of a micrometric spin valve sensor designed as a yoke shape when the ferromagnetic resonance of the free layer is excited by a microwave magnetic field. We show that this effect is a sum of a heating effect and the coupling between the current induced in the sensor by the microwave magnetic field and the giant magnetoresistance (GMR) effect. By making explicit the expression of the GMR effect when submitted to an ac magnetic excitation, we show how to separate both effects.
Structural effect of junction interface on magnetic properties in a Co/MgO/Co system: First-principles calculations
Authors: Kim Chiho , Chung Yong-Chae
Published: March 2008

The structural and magnetic properties of Co(001)/MgO(001)/Co(001) magnetic tunnel junctions with two types of junction interface, on an O-site adsorption case (Case I) and on a Mg-O twofold hollow site adsorption case (Case II), were investigated using density functional theory. Interfacial spin polarization values of electrodes were calculated to be −81.3% for Case I and −90.5% for Case II, resulting from the adsorption site dependency of electrode atoms on the MgO(001) surface. Interestingly, Mg and O atoms also showed significantly induced spin polarization values due to the 2p−3d hybridization between the Mg/O and Co-interface atoms. The magnetic moments of the electrode atoms were calculated to be 1.67 μB and 1.72 μB on average without significant variation across the electrode, except for the surface layer.
Phase formation in the thin film Fe∕GaAs system
Authors: Schultz B. D. , Adelmann C. , Dong X. Y. , McKernan S. , Palmstrøm C. J.
Published: March 2008

Interfacial reactions between epitaxial films of Fe and GaAs were examined using Rutherford backscattering spectrometry, x-ray diffraction, and transmission electron microscopy as a function of postgrowth annealing conditions. At 450°C, two stable binary phases were observed at the Fe∕GaAs(001) interface with DO3Fe3Ga forming near the Fe interface and Fe2As forming near the GaAs interface. The diffusion rate of Fe in the reacted interface was found to be of similar magnitude to that of Ga and As resulting in a rough and intermixed interfacial region.
Noninvasive respiratory monitoring system based on the piezoceramic transducer’s pyroelectric effect
Authors: Huang Y. P. , Young M. S. , Tai C. C.
Published: March 2008

This paper presents a simple alternative method and system for noninvasive respiratory airflow monitoring. The proposed system uses a piezoceramic transducer to measure respiratory airflow. When a piezoceramic transducer is impacted by respiratory airflow, there is a piezoelectric and a pyroelectric response to pressure and thermal airflow fluctuations. In this study, the selected transducer’s response output is dominated by the pyroelectricity factor. Therefore, the piezoelectric effect is not significant and can be ignored in this study. Using the transducer’s pyroelectricity to measure thermal flow variations, a subject’s respiratory rate and respiratory air volumetric flow rate can be monitored. The proposed system was evaluated for accuracy and response time using quiet and postphysical exertion breathing modes. Using the pneumotach system as a benchmark, the proposed system’s respiratory rate measurement accuracy for the two breathing modes is approximately 98.78%. In addition, the proposed system’s output voltage is highly correlated with the respiratory volumetric flow rate measured by the selected pneumotach (r2=0.9783). The average correlation coefficient between the pneumotach system’s output waveform and the proposed system is approximately 0.9389. Moreover, the proposed system and the selected pneumotach have almost the same rapid response time to respiratory airflow. When compared to a temperature measurement thermistor system, the thermistor on average is approximately 25.3ms slower than the proposed system. Furthermore, compared to the selected screen-type pneumotach system, the proposed system simplifies the respiration monitoring requirements. Instead of sensing the pressure drop across a mesh screen, like the screen-type pneumotach, it measures respiration at one point within the respiratory airflow. The proposed system benefits from simplified processing circuits and a mesh-free design. The advantages of this new respiratory airflow measurement method are fast response time, high accuracy, low cost, and ease of implementation.
Structural evolution of ammonia borane for hydrogen storage
Authors: Yang J. B. , Lamsal J. , Cai Q. , James W. J. , Yelon W. B.
Published: March 2008

We have studied the crystal structure of fully deuterated BH3NH3 using powder neutron diffraction at different temperatures. It is evident that an order-disorder phase transition occurs around 225K. At low temperature, the compound crystallizes in the orthorhombic structure with space group Pnm21 and gradually transforms to a high temperature tetragonal structure with space group I4mm above 225K. At 16K, the BD3–ND3 unit stacks along the c axis with a tilt angle of about 16° between the N–B bond and the c axis. As the temperature is increased, the BD3–ND3 groups start to reorient along the c axis and the deuterium atoms become disordered, leading to the tetragonal phase transition.
Femtosecond laser-induced cell fusion
Authors: Gong Jixian , Zhao Xueming , Xing Qirong , Li Fang , Li Huanyu , Li Yanfeng , Chai Lu , Wang Qingyue , Zheltikov Aleksei
Published: March 2008

Femtosecond laser was employed to induce cell fusion. The interface between two protoplasts of Phaffia rhodozyma in contact was irradiated by femtosecond laser pulses with 1.38×104W for 0.25s. After about 20min, the fusion of cells became visible and finally two cells merged into one larger cell within 160min. Fusion rate at this power level was 80%. The experiments suggested the existence of threshold power for cell fusion induced by femtosecond laser. Regarding femtosecond laser pulses as a trigger, we present a hypothetical model for femtosecond laser-induced cell fusion.
Examining the effects of wall numbers on buckling behavior and mechanical properties of multiwalled carbon nanotubes via molecular dynamics simulations
Authors: Zhang Y. Y. , Wang C. M. , Tan V. B. C.
Published: March 2008

Molecular dynamics simulations are performed on multiwalled carbon nanotubes (MWCNTs) under axial compression to investigate the effects of the number of walls and their van der Waals (vdW) interaction on the buckling behaviors and mechanical properties (Young’s modulus and Poisson’s ratio). The Brenner second-generation reactive empirical bond order and Lennard–Jones 12-6 potential have been adopted to describe the short-range bonding and long-range vdW atomic interaction within the carbon nanotubes, respectively. In the presence of vdW interaction, the buckling strain and Young’s modulus of MWCNTs increase as the number of tubes is increased while keeping the outermost tube diameter constant, whereas Poisson’s ratio was observed to decrease. On the other hand, when the MWCNTs are formed by progressively adding outer tubes while keeping the innermost tube diameter constant, Young’s modulus and buckling strain were observed to decrease, whereas Poisson’s ratio increases. The buckling load increases with increasing the number of walls due to the larger cross-sectional areas. Individual tubes of MWCNTs with a relatively large difference between the diameters of the inner and outer tubes buckle one at a time as opposed to simultaneously for MWCNTs with a relatively small difference in diameters.
Electron transport and full-band electron-phonon interactions in graphene
Authors: Akturk Akin , Goldsman Neil
Published: March 2008

We developed a full-band Monte Carlo simulator to investigate electron transport in a single layer of graphite (graphene). The electron and phonon dispersion curves of graphene are first obtained by applying the tight-binding method to the two inequivalent atoms of the graphene unit cell, considering their nearest four neighbors. The electron-phonon scattering rates for interactions that conserve momentum and energy are then determined using Fermi’s golden rule and the deformation potential approximation. Average electron velocities due to external fields applied in different directions are calculated using these electron-phonon scattering rates and a semiclassical electron and electric field interaction. Graphene transport simulations at room temperature indicate large low-field graphene electron mobilities of approximately 4.0×104, 6.0×104, and 8.0×104 cm2/Vs along the ky (kx=0), kx=ky, and kx (ky=0) momentum directions, respectively. These low-field electron mobilities further suggest graphene field-effect mobilities of 1.3−2.6×104 cm2/Vs, which agree with experiments. Also, a large peak electron velocity of roughly 4.6×107 cm2/Vs at high fields is obtained.
The influence of oxygen deficiency on the thermoelectric properties of strontium titanates
Authors: Yu Choongho , Scullin Matthew L. , Huijben Mark , Ramesh Ramamoorthy , Majumdar Arun
Published: March 2008

We report oxygen reduction in bulk strontium titanate substrates when a thin film was deposited in an oxygen-deficient environment. The oxygen diffusion occurred at moderate temperatures and oxygen pressures, which were not enough to produce detectable oxygen vacancies without the film deposition. In order to identify the reduction, we used a series of different annealing conditions and various substrates and performed comparative studies regarding thermoelectric properties before and after removing the films. Our experimental results suggest that the measurements of material properties of thin films on SrTiO3 single crystal substrates need to be performed carefully due to its strong susceptibility to oxygen deficient conditions.
Solution-based formation of multilayers of small molecules for organic light emitting diodes
Authors: Kim Kyung-Ho , Huh Sung-Yoon , Seo Soon-min , Lee Hong H.
Published: March 2008

We developed an approach for fabricating small molecule organic light emitting diodes by solution-based processing. The approach involves dissolving a small molecule organic in a solvent, spin coating it on a mold, and then transferring the layer onto the existing organic layer on a substrate. This ability to form multilayers of small molecule organics allows one to take advantage of both the efficiency offered by the multilayer structures and the low cost fabrication made possible by the solution processing.
An x-ray probe of laser-aligned molecules
Authors: Peterson E. R. , Buth C. , Arms D. A. , Dunford R. W. , Kanter E. P. , Krässig B. , Landahl E. C. , Pratt S. T. , Santra R. , Southworth S. H. , Young L.
Published: March 2008

We demonstrate a hard x-ray probe of laser-aligned small molecules. To align small molecules with optical lasers, high intensities at nonresonant wavelengths are necessary. We use 95ps pulses focused to 40μm from an 800nm Ti:sapphire laser at a peak intensity of 1012W∕cm2 to create an ensemble of aligned bromotrifluoromethane (CF3Br) molecules. Linearly polarized, 120ps x-ray pulses, focused to 10μm, tuned to the Br 1s→σ* preedge resonance at 13.476keV, probe the ensemble of laser-aligned molecules. The demonstrated methodology has a variety of applications and can enable ultrafast imaging of laser-controlled molecular motions with Ångstrom-level resolution.
Tunable intrinsic phase of a spin torque oscillator
Authors: Zhou Yan , Persson J. , Bonetti S. , Åkerman Johan
Published: March 2008

We show analytically why a spin torque oscillator (STO) locks to an alternating current (Iac), having the same frequency as the STO, at a nontrivial, intrinsic, phase value Δϕ0. We determine both the stability and the exact phase of the locked state and explain the recently observed phase jump by about 180° at the in-plane-to-out-of-plane precession boundary. Δϕ0 depends on the STO material parameters and is tunable through both the applied field and the dc current, which provides an additional control of the exact I-V phase in an STO driven radio frequency circuit.
Rare-earth ion doped lead- and cadmium-free bismuthate glasses
Authors: Lin H. , Pun E. Y. B. , Chen B. J. , Zhang Y. Y.
Published: March 2008

Rare-earth ion doped bismuthate (LZBB) glasses without traditional glass formers, lead and cadmium, have been attempted to prepare. In Er3+ doped LKBB glass system, Judd–Ofelt parameters Ω2, Ω4, and Ω6 have been derived to be 3.48×10−20, 9.47×10−21, and 1.01×10−20cm2, respectively, which shows a medium symmetry of the ligand field in the site occupied by Er3+ and a less covalent environment of Er3+. Effective 1.53μm fluorescence was recorded and the peak emission cross section is proved to be more than 9.0×10−21cm2, which is much higher than those in phosphate, silicate, germanate, and tellurite glasses and beneficial to achieving powerful stimulated emission of Er3+ in LZBB glass system. Pr3+, Tm3+, and Ho3+ doped LZBB glasses with the maximum phonon energy of only ∼600cm−1 are potential candidates for developing O-, S-, and U-band amplifiers and medical lasers.
Propagation of shear bands and accommodation of shear strain in the Fe56Nb4Al40 ultrafine eutectic-dendrite composite
Authors: Park Jin Man , Sohn Sung Woo , Kim Do Hyang , Kim Ki Buem , Kim Won Tae , Eckert Jürgen
Published: March 2008

Microstructural investigations of Fe56Nb4Al40 ultrafine eutectic-dendrite composite reveal that its high room temperature plasticity mainly originates from the evolution of slip in the dendrites and multiple shear banding in the ultrafine eutectic matrix, respectively. Here, we sequentially describe that the shear bands in the ultrafine eutectic matrix are propagated with generation of strain field in the soft alpha-Fe(Al) layers rather than passing through by sharp shear banding in the hard (Fe,Al)2Nb intermetallic layers. Consequently, step morphologies at the interfaces of the alternating lamellae and the dendrite/eutectic matrix strongly support the effective accommodation of shear strain during shear band propagation.
Influence of polar distribution on piezoelectric response of aluminum nitride thin films
Authors: Kamohara Toshihiro , Akiyama Morito , Kuwano Noriyuki
Published: March 2008

The authors have investigated the influence of the crystal orientation and the polar distribution on the piezoelectric response of aluminum nitride (AlN) thin films prepared on Si, Mo∕Si, and Mo∕AlN-interlayer (IL)/Si substrates with increasing sputtering power. The crystal orientation of films prepared on Si improves with increasing sputtering power. On the other hand, the crystal orientation of films prepared on Mo∕Si and Mo∕AlN-IL∕Si hardly changes. However, the piezoelectric response of all the films drastically changes from negative to positive values and the predominant polarity changes from N polarity to Al polarity. We found the proportional relationship between the polar distribution and piezoelectric response.
Photon statistics of V-type three-level system in single quantum dots
Authors: Peng Yonggang , Zheng Yujun
Published: March 2008

Based on the generating function approach developed recently, the theoretical study of the photon emission statistics in single InGaAs∕GaAs quantum dots is presented. We show the X- and Y-polarized photon emission statistics, the joint probabilities and marginal probabilities of V-type three-level system in single quantum dots driven by single pulse and a pair of pulses, respectively. The first moment confirm known experimental results while the Mandel’s Q parameters results display complex behaviors.
Passively mode-locked picosecond Nd:YVO4 self-Raman laser
Authors: Weitz Marco , Theobald Christian , Wallenstein Richard , L’huillier Johannes A.
Published: March 2008

We report on a passively mode-locked Nd:YVO4 self-Raman laser which consists of two coupled resonators and generates pulses at 1176nm with a duration of 4.8ps, a repetition rate of 73MHz, and an average power of 420mW.
M
-plane GaN grown on m-sapphire by metalorganic vapor phase epitaxy
Authors: Armitage R. , Hirayama H.
Published: March 2008

GaN layers have been grown on m-plane sapphire by metal organic vapor phase epitaxy using low-temperature AlN nucleation layers. Depending on substrate nitridation and annealing treatments prior to depositing the nucleation layer, the crystal orientation of the resulting GaN layer may be either (11−22) or (1−100) (m plane). For suitably controlled conditions, GaN epilayers with a single m-plane orientation are reproducibly obtained as confirmed by x-ray diffraction. There is a 90° in-plane rotation of the epilayer such that the GaN a axis is parallel to the sapphire c axis.
Children and ‘African Values’: Zimbabwean Professionals in Britain Reconfiguring Family Life
Authors: McGregor JoAnn
Published: March 2008

This paper examines the ways in which Zimbabwean professionals have reconfigured family life in a transnational context. It argues that issues surrounding family and children have received too little attention in the literature on contemporary African diasporas, despite the central importance of family concerns not only in decisions about mobility, work, and remittances, but also in debates about moral value. The paper focuses on children, both as objects of responsibility around which support networks of different sorts are organized, and as moral markers in diasporic debates about identity and belonging. It examines the ways in which family networks have influenced nurses' and teachers' negotiation of work, before investigating issues at stake in decisions to bring children to the UK and the ways that both of these have shaped ongoing transnational connections and embeddedness in the UK context. Despite the appeal of educational opportunities for children in Britain, problems in securing dependents' entry and the cost and difficulty of supporting and caring for children in Britain can lead parents to keep them in Zimbabwe. In addition, encounters with norms of behaviour in schools, childrights legislation, controls on parental discipline and teenage youth culture (black and white) are unappealing and can encourage a sense of difference among Zimbabwean parents. This is often expressed in terms of African' values of respect for parents, authority and extended family, perhaps more than in terms of racial, national, regional or ethnic identities. The paper places such moral debates provoked by everyday interactions in Britain in the context of the very real strains on family relationships created by the crisis in Zimbabwe, the multiple dimensions of exclusion of migrants in the UK, and further problems created by the feminization of employment, different gender norms, and a high rate of divorce.
A Statistical Examination of Visual Depth in Building Elevations
Authors: Crompton Andrew , Brown Frank
Published: March 2008

Old buildings may be easier to read than modern buildings because they possess visual depth. This is the finding of an experiment that analysed building elevations and newspapers looking for a connection between their character and the size – frequency distribution of their component parts. It was found that drawings of older buildings sometimes displayed 1/ f scaling and thus resembled natural scenes, but that this was rarely the case for modern buildings. The same distribution was also found in newspaper pages. We hypothesise that this distribution allows buildings to appear interesting and changeful when approached from afar in the same way that it makes newspapers easy to read over a range of distances, on a newsstand, over a shoulder, and so forth.
The systematic collection and characterisation of herbaceous forage species for recharge and discharge environments in southern Australia
Authors: Hughes S. J. , Snowball R. , Reed K. F. M. , Cohen B. , Gajda K. , Williams A. R. , Groeneweg S. L.
Published: March 2008

Australian temperate pasture Genetic Resource Centres (GRCs) co-ordinated a major program to introduce and screen herbaceous forage species. This program aims to expand the environments where such species could reduce recharge and manage discharge for the control of dryland salinity in southern Australia. The sustainability of agriculture, in Australia especially, depends on continued access to new germplasm to enable plant breeders to continue crop and forage improvement. The GRCs supported the selection and identification of promising new legume, grass and herb species as part of a national pasture evaluation program. In total, 671 species and 21 non-species-specific genera were identified as having potential to increase water use profitability of recharge lands and to improve the productivity of saline lands across a diverse range of agricultural environments in southern Australia. Through a series of activities, 201 of these species, representing legumes, herbs and grasses were identified as promising. These were then disseminated for evaluation in a range of environments across southern Australia. The progress of selected species was monitored and germplasm of the most promising 11 species and three leguminous genera was targeted for intensive acquisition and characterisation as the basis for selection and breeding. In addition to the identification and dissemination of promising species of immediate potential, a comprehensive collection of 544 native and exotic, wild and cultivated pasture species was conserved and is now available to service future plant improvement programs.
Prospects for three Dorycnium species as forage plants in agricultural systems: a review of their agronomic characteristics
Authors: Bell Lindsay W. , Ryan Megan H. , Ewing Mike A. , Moore Geoff A. , Lane Peter A.
Published: March 2008

Perennial legumes in the Dorycnium genus may have potential as forage plants that could reduce the seasonality of feed production and improve the sustainability of agricultural systems. However, Dorycnium species are not currently used commercially and little is known about their agronomic characteristics. This review covers the current knowledge on Dorycnium distribution, taxonomy and the agronomic performance of Dorycnium hirsutum, Dorycnium rectum and Dorycnium pentaphyllum, including adaptation, establishment, biomass production, water use, grazing management and nitrogen fixation, along with considerations for animal production. Dorycnium originate from temperate Europe and the Mediterranean basin and may be suitable for other regions with similar climatic conditions. Little data exist on the climatic and edaphic conditions to which Dorycnium species are best adapted. Current evidence suggests that D. hirsutum is widely adapted and might be suitable as a forage plant for acid soils in drier and frost-prone agricultural regions. D. hirsutum also persists well in low rainfall environments (down to 300 mm mean annual rainfall), can produce up to 21 t dry matter(DM)/ha in its first 3 years and, by utilising extra water compared with annual pastures, can reduce water leakage below the root zone, thereby slowing development of dryland salinity. The use of D. rectum would be limited to high rainfall or water-accumulating sites. D. pentaphyllum is a diverse species, yet available material appears to be less productive but has better forage quality than D. hirsutum. Currently, establishment reliability and/or forage digestibility are major limitations of the tested Dorycnium species that restrict their potential role and challenge the feasibility of their future use. Breeding may overcome or minimise these limitations and improved agronomic management might also enhance their usefulness. However, current collected genetic resources of Dorycnium are very limited and targeted collections would be needed to yield better adapted germplasm. Breeding to reduce the high levels of condensed tannins (>13% of DM) to moderate concentrations in Dorycnium might improve forage digestibility and could have positive implications for animal performance and health. Despite the poor digestibility of some Dorycnium species (<60% DM digestibility), these plants may still play a significant role as drought forage to provide feed when other forage sources are in limited supply. Further research is required to quantify the potential of Dorycnium species for commercial release and to determine how these plants should be best managed and integrated into livestock and mixed cropping systems.
Waterlogging tolerance and recovery of 10 Lotus species
Authors: Real Daniel , Warden Jonathan , Sandral Graeme A. , Colmer Timothy D.
Published: March 2008

Medicago sativa L. is the most widely sown perennial forage legume in farming systems of southern Australia. However, M. sativa lacks adaptation to winter waterlogged conditions. This constraint has highlighted the need for new perennial forage legumes adapted to winter waterlogged conditions and to locations where the summer is too dry for the survival of Trifolium repens L. and T. fragiferum L. To explore new perennial legume options suitable for these circumstances, 10 species of Lotus were evaluated for waterlogging tolerance including: two accessions of L. corniculatus L., four accessions of L. tenuis Waldst. & Kit., two accessions of L. pedunculatus Cav., two accessions of L. australis Andrew, three accessions of L. creticus L., three accessions of L. glaucus Sol., one accession of L. cruentus Court., one accession of L. argyrodes R.P. Murray, one accession of L. campylocladus Webb & Berthel and one accession of L. latifolius Brand. These were compared with the M. sativa cultivar Sceptre. The ability to grow in waterlogged conditions, and to recover, was assessed in a pot experiment conducted over 19 weeks. The Lotus species most tolerant of waterlogging were L. corniculatus, L. tenuis and L. pedunculatus. Each of these species developed aerenchyma, adventitious roots, surface roots and split stems at the base to improve oxygen transport into the roots. Significant intra-species variation was also found within each of the three tolerant species, highlighting the opportunity for genetic improvement. By comparison, the remaining Lotus species were susceptible to waterlogging and showed poor recovery, whereas M. sativa Sceptre partially recovered after waterlogging.
Field evaluation of perennial grasses and herbs in southern Australia. 1. Establishment and herbage production
Authors: Reed K. F. M. , Nie Z. N. , Miller S. , Hackney B. F. , Boschma S. P. , Mitchell M. L. , Albertsen T. O. , Moore G. A. , Clark S. G. , Craig A. D. , Kearney G. , Li G. D. , Dear B. S.
Published: March 2008

To review pasture species for regions with 465–680 mm average annual rainfall, 22 perennial grasses and herbs were evaluated for pasture establishment and productivity in four states at seven locations where the arrest of groundwater recharge is considered necessary to ameliorate dryland salinity. Species represented introduced and native, temperate and subtropical grasses, chicory (Cichorium intybus L.) and plantain (Plantago lanceolata L.). This report describes establishment and yield; the following paper describes persistence and root characteristics. Yields were measured over 2–3 years except at one site, which suffered severe drought. Perennial ryegrass (Lolium perenne L., cv. Avalon) and tall fescue (Festuca arundinacea Schreb. = syn. Lolium arundinaceum. (Schreb.) Darbysh., cvv. AU Triumph and Resolute MaxP), cocksfoot (Dactylis glomerata L., cv. Porto) and phalaris (Phalaris aquatica L., cv. Holdfast and Australian) were the most productive species, with dry matter (DM) yields of 13.6–15.1 t/ha. For summer growth, Porto and Rhodes grass (Chloris gayana Kunth, cv. Katambora) were the most productive species; relative to Australian in summer, Porto and Katambora produced 41% and 26% more DM, respectively (95% confidence). Perennial ryegrass (cv. Avalon), tall fescue (cv. Resolute MaxP) and chicory (cv. Grouse) were particularly valuable for autumn growth; Avalon was 30% more productive than Australian. Tall fescue (cv. Resolute MaxP) was 32% more productive than Australian in winter. Avalon and AU Triumph were the most productive grasses and herbs in spring. Based on natural rainfall over the 2–3 years of measurement, the mean water use productivity, ignoring any runoff, was 10.5 kg DM/ha.mm for the three most productive species. Apart from kangaroo grass (Themeda triandra Forssk), native grasses gradually established, but over a prolonged period weeping grass (Microlaena stipoides (Labill.) R.Br., cv. Wakefield) was the most rapid. Perennial ryegrass, tall fescue, cocksfoot and phalaris maintained productive yields across a diverse range of soils and climates. Exploration of the diversity within these species in a nationally coordinated program of genetic improvement appears warranted for improving reliability and expanding the zone of adaptation.