bluuebunny/crossref_metadata_2025 huggingface dataset:
A versatile system for ultrahigh resolution, low temperature, and polarization dependent Laser-angle-resolved photoemission spectroscopy
Authors: Kiss T. , Shimojima T. , Ishizaka K. , Chainani A. , Togashi T. , Kanai T. , Wang X.-Y. , Chen C.-T. , Watanabe S. , Shin S.
Published: February 2008

We have developed a low temperature ultrahigh resolution system for polarization dependent angle-resolved photoemission spectroscopy (ARPES) using a vacuum ultraviolet (vuv) laser (hν=6.994eV) as a photon source. With the aim of addressing low energy physics, we show the system performance with angle-integrated PES at the highest energy resolution of 360μeV and the lowest temperature of 2.9K. We describe the importance of a multiple-thermal-shield design for achieving the low temperature, which allows a clear measurement of the superconducting gap of tantalum metal with a Tc=4.5K. The unique specifications and quality of the laser source (narrow linewidth of 260μeV, high photon flux), combined with a half-wave plate, facilitates ultrahigh energy and momentum resolution polarization dependent ARPES. We demonstrate the use of s- and p-polarized laser-ARPESs in studying the superconducting gap on bilayer-split bands of a high Tc cuprate. The unique features of the quasi-continuous-wave vuv laser and low temperature enables ultrahigh-energy and -momentum resolution studies of the spectral function of a solid with large escape depth. We hope the present work helps in defining polarization dependent laser excited angle-resolved photoemission spectroscopy as a frontier tool for the study of electronic structure and properties of materials at the sub-meV energy scale.
Tokamak plasma equilibria with a zero total toroidal current
Authors: Hu Yemin
Published: February 2008

Several tokamak experiments have reported the existence of plasma equilibria with a zero total toroidal current in the AC operations of tokamaks. By taking a toroidal current profile model as a function of a quadratic polynomial of ψ, a variety of equilibrium configurations with a zero total toroidal current have been found by solving the Grad-Shafranov equation numerically in the cylindrical coordinate system for the arbitrary cross section and finite aspect ratio. Results from different parametrizations of the current density (pressure) profile are discussed. Using input parameters consistent with experiments, some of the modeling results have been found to be in good agreement with experiment observations.
Low-noise particle algorithms for extended magnetohydrodynamic closure
Authors: Barnes D. C. , Cheng J. , Parker S. E.
Published: February 2008

Two new low-noise particle closure methods are developed and tested. Closure of a small set of moment equations is accomplished with first or second order moments computed from a delta-f particle in cell (δf PIC) distribution. Conservation laws are developed and in one case apply to the discrete system, showing that squared weights are part of the system energy and therefore bounded for all time. Implicit time differencing and orbit averaging techniques are developed and implemented. Low-order moment constraints are satisfied exactly by a new particle representation. Numerical tests for one dimension, k⊥=0, and two dimension, k∥=0 show the successful application of both methods to damped waves and of the second order closure method to unstable gravitational modes. The methods described here are a natural and efficient way to close extended magnetohydrodynamic (MHD) equations to obtain a full kinetic description.
Energy gaps, electronic structures, and x-ray spectroscopies of finite semiconductor single-walled carbon nanotubes
Authors: Gao Bin , Jiang Jun , Wu ZiYu , Luo Yi
Published: February 2008

We report hybrid density functional theory calculations for electronic structures of hydrogen-terminated finite single-walled carbon nanotubes (6,5) and (8,3) up to 100nm in length. Gap states that are mainly arisen from the hydrogen-terminated edges have been found in (8,3) tubes, but their contributions to the density of states become invisible when the tube is longer than 10nm. The electronic structures of (6,5) and (8,3) tubes are found to be converged around 20nm. The calculated band-gap energies of 100nm long nanotubes are in good agreement with experimental results. The valence band structures of (6,5), (8,3), as well as (5,5) tubes are also investigated by means of ultraviolet photoelectron spectra (UPS), x-ray emission spectroscopy (XES), and the resonant inelastic x-ray scattering (RIXS) spectra theoretically. The UPS, XES and RIXS spectra become converged already at 10nm. The length-dependent oscillation behavior is found in the RIXS spectra of (5,5) tubes, indicating that the RIXS spectra may be used to determine the size and length of metallic nanotubes. Furthermore, the chiral dependence observed in the simulated RIXS spectra suggests that RIXS spectra could be a useful technique for the determination of chirality of carbon nanotubes.
Magnetic Rayleigh–Taylor instability mitigation in large-diameter gas puff Z-pinch implosions
Authors: Qi N. , Sze H. , Failor B. H. , Banister J. , Levine J. S. , Riordan J. C. , Steen P. , Sincerny P. , Lojewski D.
Published: February 2008

Recently, a new approach for efficiently generating K-shell x-rays in large-diameter, long-implosion time, structured argon gas Z-pinches has been demonstrated based on a “pusher-stabilizer-radiator” model. In this paper, direct observations of the Rayleigh–Taylor instability mitigation of a 12-cm diameter, 200-ns implosion time argon Z-pinch using a laser shearing interferometer (LSI) and a laser wavefront analyzer (LWA) are presented. Using a zero-dimensional snowplow model, the imploding plasma trajectories are calculated with the driver current waveforms and the initial mass distributions measured using the planar laser induced fluorescence method. From the LSI and LWA images, the plasma density and trajectory during the implosion are measured. The measured trajectory agrees with the snowplow calculations. The suppression of hydromagnetic instabilities in the “pusher-stabilizer-radiator” structured loads, leading to a high-compression ratio, high-yield Z-pinch, is discussed. For comparison, the LSI and LWA images of an alternative load (without stabilizer) show the evolution of a highly unstable Z-pinch.
Minimizing the linewidth of the flux-flow oscillator
Authors: Pankratov Andrey L.
Published: February 2008

The linewidth of the flux-flow oscillator has been calculated by direct computer simulation of the sine-Gordon equation with noise. Good agreement of the numerical results with the formula derived in Phys. Rev. B 65, 054504 (2002) has been achieved. Depending on the length of the unbiased tail, the power may be maximized and the linewidth may be minimized in a broad range of bias currents. The linewidth can be decreased further by 1.5 times by proper load matching.
Molecular dynamics simulations of beta-SiC using both fixed charge and variable charge models
Authors: Ma Ying , Garofalini S. H.
Published: February 2008

In this paper, molecular dynamics simulations have been performed using both fixed charge and variable charge models. In the fixed charge model, partial charges are introduced to Si and C atoms to model the charge transfer observed in first principles studies. The calculated phonon dispersions, elastic constants, and lattice constants are in good accuracy. Variable charge model is also used to obtain geometry and connectivity dependent atomic charges. Our results show that although the variable charge model may not be advantageous in the study of ordered structures, it is important in describing structural disorders such as vacancies.
Modeling, simulation, and experiments of coating growth on nanofibers
Authors: Clemons C. B. , Hamrick P. , Heminger J. , Kreider K. L. , Young G. W. , Buldum A. , Evans E. , Zhang G.
Published: February 2008

This work is a comparison of modeling and simulation results with experiments for an integrated experimental/modeling investigation of a procedure to coat nanofibers and core-clad nanostructures with thin film materials using plasma enhanced physical vapor deposition. In the experimental effort, electrospun polymer nanofibers are coated with metallic materials under different operating conditions to observe changes in the coating morphology. The modeling effort focuses on linking simple models at the reactor level, nanofiber level and atomic level to form a comprehensive model. The comprehensive model leads to the definition of an evolution equation for the coating free surface around an isolated nanofiber. This evolution equation was previously derived and solved under conditions of a nearly circular coating, with a concentration field that was only radially dependent and that was independent of the location of the coating free surface. These assumptions permitted the development of analytical expressions for the concentration field. The present work does not impose the above-mentioned conditions and considers numerical simulations of the concentration field that couple with level set simulations of the evolution equation for the coating free surface. Further, the cases of coating an isolated fiber as well as a multiple fiber mat are considered. Simulation results are compared with experimental results as the reactor pressure and power, as well as the nanofiber mat porosity, are varied.
Large diameter (45–80mm) nested stainless steel wire arrays at the Z accelerator
Authors: Coverdale C. A. , Deeney C. , LePell P. D. , Jones B. , Davis J. , Clark R. W. , Apruzese J. P. , Thornhill J. W. , Whitney K. G.
Published: February 2008

Experiments have been performed at the Z accelerator to elucidate the effects of initial load diameter on the radiated output of a 7keV wire array x-ray source. Nested wire arrays with initial outer diameters of 45–80mm were fielded, with the masses chosen to maintain a nominally constant coupling to the Z generator. The total radiated output decreased from ∼1.1MJ to <0.5MJ for the largest diameter arrays, while the >1keV and K-shell radiation decreased at both small and large diameters. The >1keV output peaked at ∼340kJ, while the K-shell yield peaked at ∼55kJ. The observed trends in radiated output and stagnated plasma parameters are consistent with a phenomenological K-shell scaling theory, and are reproduced in one-dimensional modeling, although multidimensional effects, such as, growth of the Rayleigh–Taylor instability, are observed in the experiments and appear to impact the stagnated plasma for the larger diameter arrays.
A simple model to describe the lateral oscillations of axisymmetric liquid bridges
Authors: Montanero J. M. , Ferrera C.
Published: February 2008

The axisymmetric dynamics of an isothermal liquid bridge has been analyzed frequently over the past years. The studies have considered different phenomena such as free oscillations, forced vibrations, g-jitter effects, extensional deformation, and the breakup process, among others. Works considering the nonaxisymmetric dynamical behavior of a liquid bridge have been far less common, probably due to the further difficulties associated with its three-dimensional nature. Based on simple physical arguments, a model is proposed in this paper to describe the linear lateral oscillations of an axisymmetric viscous liquid bridge. The accuracy of the model is established from comparison with the Navier–Stokes equations for zero Capillary number and with experimental measurements for viscous liquid bridges. Good agreement is found in both cases for frequencies smaller than or of the order of the first resonance frequency. Potential applications of the model are discussed.
Effect of applied magnetic field on a microwave plasma thruster
Authors: Yang Juan , Xu Yingqiao , Meng Zhiqiang , Yang Tielian
Published: February 2008

Theoretical analysis and calculation show that applying a magnetic field in a microwave plasma thruster operating at 2.45GHz can improve the thruster performance, whereby an electron cyclotron resonant layer at thruster startup state contributes to the increase of microwave energy dissipated in plasma, and a strong magnetic field up to 0.5T can increase the peak temperature of inside plasma when the thruster operates in steady state. Experimental measurements of the thruster with applied field and operating on argon gas show high coupling efficiency. Plasma plume diagnostics deduce a high degree of gas ionization in the thruster cavity. This shows the feasibility of operating a microwave plasma thruster with an applied magnetic field.
A W:B4C multilayer phase retarder for broadband polarization analysis of soft x-ray radiation
Authors: MacDonald Michael A. , Schaefers Franz , Pohl Ralph , Poole Ian B. , Gaupp Andreas , Quinn Frances M.
Published: February 2008

A W:B4C multilayer phase retarder has been designed and characterized which shows a nearly constant phase retardance between 640 and 850eV photon energies when operated near the Bragg condition. This freestanding transmission multilayer was used successfully to determine, for the first time, the full polarization vector at soft x-ray energies above 600eV, which was not possible before due to the lack of suitable optical elements. Thus, quantitative polarimetry is now possible at the 2p edges of the magnetic substances Fe, Co, and Ni for the benefit of magnetic circular dichroism spectroscopy employing circularly polarized synchrotron radiation.
Field-induced shift of morphotropic phase boundary and effect of overpoling in (1−x)Pb(Mg1∕3Nb2∕3)O3–xPbTiO3 piezocrystals
Authors: Bokov A. A. , Ye Z.-G.
Published: February 2008

The domain structure and phase symmetry of the (1−x)Pb(Mg1∕3Nb2∕3)O3–xPbTiO3 piezoelectric crystals with a composition close to the morphotropic phase boundary (MPB) between the rhombohedral R3m and monoclinic Pm phases (x≅0.3) have been studied by polarized light microscopy. It is found that poling by an electric field parallel to the ⟨001⟩ pseudocubic direction shifts the MPB toward the lower x side. This shift is the origin of the overpoling effect which degrades the performance of the materials, e.g., the piezoelectric coefficient (d33) and dielectric constant decrease with increasing poling field. In optimally poled crystals, d33 can reach as high as 3100pC∕N.
Theoretical analysis of magnetic force microscopy contrast in multidomain states of magnetic superlattices with perpendicular anisotropy
Authors: Kiselev N. S. , Dragunov I. E. , Neu V. , Rößler U. K. , Bogdanov A. N.
Published: February 2008

Recently synthesized magnetic multilayers with strong perpendicular anisotropy exhibit unique magnetic properties including the formation of specific multidomain states. In particular, antiferromagnetically coupled multilayers own rich phase diagrams that include various multidomain ground states. Analytical equations have been derived for the stray field components of these multidomain states in perpendicular multilayer systems. In particular, closed expressions for stray fields in the case of ferromagnetic and antiferromagnetic stripes are presented. The theoretical approach provides a basis for the analysis of magnetic force microscopy (MFM) images from this class of nanomagnetic systems. Peculiarities of the MFM contrast have been calculated for realistic tip models. These characteristic features in the MFM signals can be employed for the investigations of the different multidomain modes. The obtained results are applied for the analysis of multidomain modes that have been reported earlier in the literature from experiments on [Co/Cr]Ru superlattices.
Time correlations of pressure in isotropic turbulence
Authors: Yao Hua-Dong , He Guo-Wei , Wang Meng , Zhang Xing
Published: February 2008

The time correlations of pressure modes in stationary isotropic turbulence are investigated under the Kraichnan and Tennekes “random sweeping” hypothesis. A simple model is obtained which predicts a universal form for the time correlations. It implies that the decorrelation process of pressure fluctuations in time is mainly dominated by the sweeping velocity, and the pressure correlations have the same decorrelation time scales as the velocity correlations. These results are verified using direct numerical simulations of isotropic turbulence at two moderate Reynolds numbers; the mode correlations collapse to the universal form when the time separations are scaled by wavenumber times the sweeping velocity, and the ratios of the correlation coefficients of pressure modes to those of velocity modes are approximately unity for the entire range of time separation.
Magnetization processes in ultrathin Au∕Co∕Au films grown on a bifacial Mo(110)/Mo(540) single crystal
Authors: Stupakiewicz A. , Maziewski A. , Ślęzak M. , Ślęzak T. , Zając M. , Matlak K. , Korecki J.
Published: February 2008

We studied magnetization reversal processes and magnetic anisotropy in ultrathin Au∕Co∕Au films deposited on a bifacial Mo(110)/(540) single crystal. The influence of the Co thickness and miscut angle on the spin reorientation from out-of-plane into in-plane magnetization were investigated by means of the magneto-optical Kerr effect (MOKE). In the case of Co grown on a vicinal Au∕Mo(540) substrate, the perpendicular magnetization component was found throughout the 1–8nm Co thickness range. The canted orientation of magnetization was deduced from vectorial MOKE magnetometry. The out-of-plane switching field, which is 160Oe for the perpendicular magnetization, increases to about 960Oe as observed at 8nm Co thickness on the vicinal part. The experimental data are discussed taking into account both uniaxial out-of-plane and in-plane magnetic anisotropy energy terms. The results indicate the possibility of tuning the perpendicular magnetization component with the use of vicinal substrates, and are important from both a surface physics and magnetic memory media point of view.
How long can single-walled carbon nanotube ropes last under static or dynamic fatigue?
Authors: Ma Gang , Ren Yu , Guo Jun , Xiao Tan , Li Feng , Cheng Huiming , Zhou Zongrong , Liao Kin
Published: February 2008

We report a study on the static and dynamic fatigue behavior of unidirectional, aligned single-walled carbon nanotube (SWCNT) ropes. By bench marking against the behavior of graphite fiber, it is found that the static fatigue strength of SWCNT ropes is at least twice that of graphite fiber within 104s and is similar to that of graphite fiber at longer times, while the dynamic fatigue strength is twice that of the graphite fiber to up to 107cycles. Fatigue limit seems to exist for SWCNT ropes within the time scale of the investigation at 4–5GPa. Based on experimental data and results of a molecular life prediction scheme, it is suggested that the fatigue behavior of SWCNT ropes may be controlled by preexisting defects.
An 11cm long atmospheric pressure cold plasma plume for applications of plasma medicine
Authors: Lu XinPei , Jiang ZhongHe , Xiong Qing , Tang ZhiYuan , Hu XiWei , Pan Yuan
Published: February 2008

In this letter, a room temperature atmospheric pressure plasma jet device is reported. The high voltage electrode of the device is covered by a quartz tube with one end closed. The device, which is driven by a kilohertz ac power supply, is capable of generating a plasma plume up to 11cm long in the surrounding room air. The rotational and vibrational temperatures of the plasma plume are 300 and 2300K, respectively. A simple electrical model shows that, when the plasma plume is contacted with a human, the voltage drop on the human is less than 66V for applied voltage of 5kV (rms).
Composition dependence of the phonon strain shift coefficients of SiGe alloys revisited
Authors: Reparaz J. S. , Bernardi A. , Goñi A. R. , Alonso M. I. , Garriga M.
Published: February 2008

By combining Raman scattering from the cleaved edge and under hydrostatic pressure, we have accurately determined the tetragonal phonon deformation potentials of strained Si1−xGex alloys in the entire compositional range for the Ge-like, Si-like, and mixed Si–Ge optical modes. A known biaxial strain is induced on thin alloy layers by pseudomorphic epitaxial growth on silicon and subsequent capping. We also determine the strain shift coefficient of the three modes, which are essentially independent of Ge content between 0.4 and 1. This is key information for an effective use of Raman scattering as strain-characterization tool in SiGe nanostructures.
An algorithm for separating multilevel random telegraph signal from 1∕f noise
Authors: Giusi G. , Crupi F. , Pace C.
Published: February 2008

In this work, we propose a robust algorithm for the separation of two- and multilevel dominant random telegraph signals (RTSs) from 1∕f noise in the time domain. The method does not associate each RTS level to a fixed range of the signal values, as assumed by other methods, but it is based on a efficient recognition of the jumps between the different RTS levels. The proposed algorithm can extract the 1∕f component even in the presence of several dominant RTSs with different corner frequencies. The procedure has been validated by using a two-level and a four-level synthesized signals.
rf plasma system as an atomic oxygen exposure facility
Authors: Shpilman Z. , Gouzman I. , Lempert G. , Grossman E. , Hoffman A.
Published: February 2008

The materials of spacecraft external surfaces in low Earth orbit (LEO) are exposed to the various constituents of the space environment, including atomic oxygen (AO) and solar ultra violet (UV) radiation. Material degradation and erosion by LEO are simulated in ground laboratories using a variety of experimental facilities, each with their respective limitations. rf oxygen plasma is a simulation facility widely used for materials screening for LEO application. However, the complex plasma environment, which contains, in addition to the neutral oxygen atoms, excited species, electrons, and ions as well as vacuum ultraviolet (VUV) radiation, might lead to erroneous determination of materials reactivity with respect to LEO. This paper describes the development of a simple, low cost rf plasma system to produce a well-defined AO and VUV environment. The new system constrained the afterglow flow through two right-angle turns. The afterglow was characterized at three specific locations by (i) optical emission spectroscopy for assessment of electronically excited states, (ii) current measurements, and (iii) UV radiation measurements. Kapton® samples were exposed at the three specific locations in the system and characterized by mass loss for etch rate evaluation, and atomic force microscopy for surface modification. It was found that there is a significant reduction in ionic species, excited species, and UV radiation as the afterglow advances through the right-angle turns. The reduction in charged particle flux is due to recombination within the afterglow as well as neutralization by colliding with the grounded metal chamber walls; similar decrease in UV radiation flux occurs through radiation absorption by the chamber walls. Finally, it is shown that the ground state AO is the dominant reactive specie of the plasma afterglow after passing through the two right-angle turns.
Metal-semiconductor junction of graphene nanoribbons
Authors: Hong Seokmin , Yoon Youngki , Guo Jing
Published: February 2008

Patterned all-graphene circuits, in which semiconducting graphene nanoribbon (GNR) device channels are connected by metallic GNR interconnects, raise possibilities for carbon-based electronics. The properties of GNR metal-semiconductor junctions, which are the key elements in all-graphene circuits, are studied by atomistic simulations. The junction conductance strongly depends on the atomistic features of the access geometry from the metallic GNR to the semiconducting GNR. Highly localized states exist at the junction edges, which can result in sharp metal-induced gap states. A defect of a single lattice vacancy can significantly increase rather than decrease the junction conductance for certain junction geometries.
The preparation and thermoelectric properties of Ti0.5Zr0.25Hf0.25Co1−xNixSb half-Heusler compounds
Authors: Xie Wenjie , Jin Qiao , Tang Xinfeng
Published: February 2008

Ni doping Ti0.5Zr0.25Hf0.25Co1−xNixSb (x=0–0.05) half-Heusler compounds have been fabricated by combining high-frequency induction melting with spark plasma sintering technique, and their thermoelectric transport properties have been investigated in the temperature range of 300–900K. With the increase of Ni doping content, the electrical conductivity increases significantly, and withal the Seebeck coefficient of all doped samples improve to some extent compared with the undoped Ti0.5Zr0.25Hf0.25CoSb compound. These lead to a great improvement in the power factor, and the highest power factor of 1.63×10−3Wm−1K−1 is obtained at 715K for Ti0.5Zr0.25Hf0.25Co0.95Ni0.05Sb compound. Furthermore, thermal conductivity of Ti0.5Zr0.25Hf0.25Co1−xNixSb compounds decrease remarkably due to Zr and Hf substitutions on Ti site and Ni doping on Co site. Compared with ternary TiCoSb compound, the thermal conductivity of Ti0.5Zr0.25Hf0.25Co1−xNixSb compound decreases 415%–430% at room temperature, and compared with undoped Ti0.5Zr0.25Hf0.25CoSb compound, the thermal conductivity of Ti0.5Zr0.25Hf0.25Co0.95Ni0.05Sb decreases 34% at 300K and 21% at 900K, respectively. A maximum dimensionless figure of merit ZT of 0.51 has been achieved for Ti0.5Zr0.25Hf0.25Co0.95Ni0.05Sb compound at 813K.
Fluoride-modified electrical properties of lead borate glasses and electrochemically induced crystallization in the glassy state
Authors: M’Peko Jean-Claude , De Souza José E. , Rojas Seila S. , Hernandes Antonio C.
Published: February 2008

Lead fluoroborate glasses were prepared by the melt-quenching technique and characterized in terms of (micro)structural and electrical properties. The study was conducted on as prepared as well as temperature- and/or electric field–treated glass samples. The results show that, in the as-prepared glassy-state materials, electrical conductivity improved with increasing the PbF2 glass content. This result involves both an increase of the fluoride charge carrier density and, especially, a decrease of the activation energy from a glass structure expansion improving charge carrier mobility. Moreover, for the electric field–treated glass samples, surface crystallization was observed even below the glass transition temperature. As previously proposed in literature, and shown here, the occurrence of this phenomenon arose from an electrochemically induced redox reaction at the electrodes, followed by crystallite nucleation. Once nucleated, growth of β-PbF2 crystallites, with the indication of incorporating reduced lead ions (Pb+), was both (micro)structurally and electrically detectable and analyzed. The overall crystallization-associated features observed here adapt well with the floppy-rigid model that has been proposed to further complete the original continuous-random-network model by Zachariasen for closely addressing not only glasses’ structure but also crystallization mechanism. Finally, the crystallization-modified kinetic picture of the glasses’ electrical properties, through application of polarization/depolarization measurements originally combined with impedance spectroscopy, was extensively explored.
Fiber-based confocal microscope for cryogenic spectroscopy
Authors: Högele Alexander , Seidl Stefan , Kroner Martin , Karrai Khaled , Schulhauser Christian , Sqalli Omar , Scrimgeour Jan , Warburton Richard J.
Published: February 2008

We describe the design and performance of a fiber-based confocal microscope for cryogenic operation. The microscope combines positioning at low temperatures along three space coordinates of millimeter translation and nanometer precision with high stability and optical performance at the diffraction limit. It was successfully tested under ambient conditions as well as at liquid nitrogen (77K) and liquid helium (4K) temperatures. The compact nonmagnetic design provides for long term position stability against helium refilling transfers, temperature sweeps, as well as magnetic field variation between −9 and 9T. As a demonstration of the microscope performance, applications in the spectroscopy of single semiconductor quantum dots are presented.
Monolithic InGaN-based white light-emitting diodes with blue, green, and amber emissions
Authors: Lee Sung-Nam , Paek H. S. , Kim H. , Jang T. , Park Y.
Published: February 2008

We demonstrated a monolithic white light-emitting diodes (LEDs) epitaxial structure with blue, green, and amber emissions by introducing the blue InGaN∕GaN five quantum wells (QWs) and InGaN∕GaN single quantum well (SQW) with In-phase separated green/amber emissions as an active layer. Three wavelength emissions were developed by increasing the thickness of InGaN SQW grown on blue InGaN five QWs. From high resolution transmission electron microscope, In-phase separation was clearly observed in a 3.5-nm-thick InGaN SQW. In-phase separation would be generated by the spinodal decomposition which was promoted by the composition pulling effect related to the increment of well thickness. Therefore, white lighting LEDs with three wavelengths for blue emission from InGaN∕GaN five QWs and green/amber emissions were achieved by the In-phase separation in InGaN SQW.
Control of epitaxy-induced magnetocrystalline anisotropy in a molecular beam epitaxy–grown Co∕MgO∕Fe∕MgO(100) pseudo-spin-valve
Authors: Laloë J.-B. , Ionescu A. , Hayward T. J. , Llandro J. , Bland J. A. C. , Vickers M. E.
Published: February 2008

We show that by obtaining a crystalline structure in a Co∕MgO∕Fe tunnel junction, we are able to control the magnetic anisotropies in the spin valve and therefore, induce independent switching of the two magnetic layers. In situ and ex situ structural characterization confirms that the multilayer is fully epitaxial, with smooth interfaces throughout. In confirmation of the high quality of the insulating barrier, we also present a layer-selective measurement of the magnetization of the top electrode using current-in-plane transport measurements.
Improvement of organic solar cell performances using a zinc oxide anode coated by an ultrathin metallic layer
Authors: Bernède J. C. , Berredjem Y. , Cattin L. , Morsli M.
Published: February 2008

The authors have achieved an efficient organic solar cell based on copper phthalocyanine (CuPc) layer as donor and fullerene (C60) as acceptor. The aluminum doped zinc oxide (ZnO:Al) instead of indium tin oxide (ITO) is used as the anode. An ultrathin gold film is introduced among ZnO:Al, transparent conductor oxide, and the CuPc donor layer. We show that the power conversion efficiency of this cell is enhanced by one order of magnitude compared to that achieved with a ZnO anode without ultrathin gold film. Therefore, the power conversion efficiency of this cell is comparable to that with an ITO anode.
Persistent photoconductivity and carrier transport in AlGaN∕GaN heterostructures treated by fluorine plasma
Authors: Li B. K. , Ge W. K. , Wang J. N. , Chen K. J.
Published: February 2008

Fluorine plasma treatment technique can effectively incorporate fluorine atoms into the AlGaN barrier, depleting the two-dimensional electron gases (2DEGs) in the channel of AlGaN∕GaN high electron mobility transistors and converting the device from depletion mode to enhancement mode. To reveal the underlying physical mechanisms, temperature dependent persistent photoconductivity (PPC) and Hall measurements are conducted in AlGaN∕GaN heterostructures treated by CF4 plasma. Weakly temperature dependent 2DEG mobility and much more pronounced PPC effect are observed in the F-treated sample. An energy barrier of 624meV for electrons recaptured by the F-related centers is extracted from the PPC decay behaviors.
Primary and secondary threshold intensities of ultraviolet-laser-induced domain nucleation in nearly stoichiometric LiTaO3
Authors: Zhi Ya’nan , Liu De’an , Yan Aimin , Sun Jianfeng , Zhou Yu , Luan Zhu , Hang Yin , Liu Liren
Published: February 2008

The primary and secondary threshold intensities of ultraviolet-laser-induced preferential domain nucleation in nearly stoichiometric LiTaO3 is observed. The primary threshold is the minimum intensity to achieve the instantaneous preferential domain nucleation within the focus by the combined action of irradiation and electric fields. The secondary threshold is the minimum intensity to achieve the memory effect without any irradiation within the original focus. The space charge field created by the photoionization carriers is thought to be responsible for the instantaneous effect. The explanation based on the formation and transformation of extrinsic defect is presented for the memory effect.
Fringing field effects on electrical resistivity of semiconductor nanowire-metal contacts
Authors: Hu Jun , Liu Yang , Ning C. Z. , Dutton Robert , Kang Sung-Mo
Published: February 2008

Metal contacts play an important role in nanowire devices and are expected to exhibit qualitatively different properties from those of planar contacts due to small contact cross sections. We numerically investigate certain unique properties of nanowire-metal contacts and demonstrate that contact resistivity increases as nanowire radius shrinks. This increase is more significant for nanowire-three-dimensional metal contacts than for nanowire-one-dimensional metal contacts. The underlying cause for this size effect is identified as the strong fringing field effects, which become more significant as temperature decreases. Our simulation provides a more complete understanding of the size effects on nanowire-metal contacts.
Transcriptome sequencing of malignant pleural mesothelioma tumors
Authors: Sugarbaker David J. , Richards William G. , Gordon Gavin J. , Dong Lingsheng , De Rienzo Assunta , Maulik Gautam , Glickman Jonathan N. , Chirieac Lucian R. , Hartman Mor-Li , Taillon Bruce E. , Du Lei , Bouffard Pascal , Kingsmore Stephen F. , Miller Neil A. , Farmer Andrew D. , Jensen Roderick V. , Gullans Steven R. , Bueno Raphael
Published: February 2008

Cancers arise by the gradual accumulation of mutations in multiple genes. We now use shotgun pyrosequencing to characterize RNA mutations and expression levels unique to malignant pleural mesotheliomas (MPMs) and not present in control tissues. On average, 266 Mb of cDNA were sequenced from each of four MPMs, from a control pulmonary adenocarcinoma (ADCA), and from normal lung tissue. Previously observed differences in MPM RNA expression levels were confirmed. Point mutations were identified by using criteria that require the presence of the mutation in at least four reads and in both cDNA strands and the absence of the mutation from sequence databases, normal adjacent tissues, and other controls. In the four MPMs, 15 nonsynonymous mutations were discovered: 7 were point mutations, 3 were deletions, 4 were exclusively expressed as a consequence of imputed epigenetic silencing, and 1 was putatively expressed as a consequence of RNA editing. Notably, each MPM had a different mutation profile, and no mutated gene was previously implicated in MPM. Of the seven point mutations, three were observed in at least one tumor from 49 other MPM patients. The mutations were in genes that could be causally related to cancer and included
XRCC6
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PDZK1IP1
,
ACTR1A
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AVEN
.
The Nup358-RanGAP Complex Is Required for Efficient Importin α/β-dependent Nuclear Import
Authors: Hutten Saskia , Flotho Annette , Melchior Frauke , Kehlenbach Ralph H.
Published: February 2008

In vertebrate cells, the nucleoporin Nup358/RanBP2 is a major component of the filaments that emanate from the nuclear pore complex into the cytoplasm. Nup358 forms a complex with SUMOylated RanGAP1, the GTPase activating protein for Ran. RanGAP1 plays a pivotal role in the establishment of a RanGTP gradient across the nuclear envelope and, hence, in the majority of nucleocytoplasmic transport pathways. Here, we investigate the roles of the Nup358-RanGAP1 complex and of soluble RanGAP1 in nuclear protein transport, combining in vivo and in vitro approaches. Depletion of Nup358 by RNA interference led to a clear reduction of importin α/β-dependent nuclear import of various reporter proteins. In vitro, transport could be partially restored by the addition of importin β, RanBP1, and/or RanGAP1 to the transport reaction. In intact Nup358-depleted cells, overexpression of importin β strongly stimulated nuclear import, demonstrating that the transport receptor is the most rate-limiting factor at reduced Nup358-concentrations. As an alternative approach, we used antibody-inhibition experiments. Antibodies against RanGAP1 inhibited the enzymatic activity of soluble and nuclear pore–associated RanGAP1, as well as nuclear import and export. Although export could be fully restored by soluble RanGAP, import was only partially rescued. Together, these data suggest a dual function of the Nup358-RanGAP1 complex as a coordinator of importin β recycling and reformation of novel import complexes.
A modelling study of developmental stage and environmental variability effects on copepod foraging
Authors: Wiggert Jerry D. , Hofmann Eileen E. , Paffenhöfer Gustav-Adolf
Published: February 2008

Wiggert, J. D., Hofmann, E. E., and Paffenhöfer, G-A. 2008. A modelling study of developmental stage and environmental variability effects on copepod foraging. – ICES Journal of Marine Science, 65: 379–398. We used a stochastic Lagrangian model to study how behaviour contributes to copepod grazing success. The model simulates distinct foraging behaviours of Clausocalanus furcatus, Paracalanus aculeatus, and Oithona plumifera. Three sets of simulations were performed to investigate the effects of (a) prey-size preference; (b) variation in prey-size spectra; and (c) turbulence intensity on these species’ grazing rates. The size preference simulations demonstrate that, compared with copepodites, mature females have cell ingestion rates that are an order of magnitude lower, while carbon uptake is reduced by 35%. A prey spectrum that is skewed towards cells <6 µm promotes copepodite success because the basal metabolic needs of the adult females require a prey concentration of 850–1000 cells ml−1. Variations in turbulence intensity reveal distinct ecological niches, with stronger mixing favouring O. plumifera and stable conditions favouring C. furcatus. Differences in theoretically derived and simulated prey-encounter rates demonstrate that the hopping behaviour of O. plumifera provides an order of magnitude increase in prey encounter, whereas the feeding behaviour of C. furcatus can result in localized depletion of prey. These simulations highlight the importance of species-specific feeding behaviour in defining oceanic copepod distributions.
Novel BRCA2‐interacting protein BJ‐HCC‐20A inhibits the induction of apoptosis in response to DNA damage
Authors: Tomiyoshi Go , Nakanishi Akira , Takenaka Katsuya , Yoshida Kiyotsugu , Miki Yoshio
Published: February 2008

The major hereditary breast cancer susceptibility gene BRCA2 is associated with familial breast and ovarian cancer. BRCA2 plays a role in DNA repair, transcription, cell cycle regulation, maintenance of genomic stability in response to DNA damage, centrosome regulation, and cytokinesis. To further understand the function of BRCA2, we used a yeast two‐hybrid method and identified a novel BRCA2‐interacting protein, BJ‐HCC‐20A, which is reported to be a potential cancer–testis antigen. We confirmed the interaction between endogenous BJ‐HCC‐20A and BRCA2 in mammalian cells, and showed that BJ‐HCC‐20A interacts with a portion of the highly conserved region of BRCA2 in various mammals, and M phase‐specific phosphorylation of the binding region of BRCA2 modulates BJ‐HCC‐20A binding. Overexpression of BJ‐HCC‐20A increases cell growth, and downregulation of endogenous BJ‐HCC‐20A expression using small interfering RNA suppresses cell growth and leads to the induction of apoptosis. Importantly, the BJ‐HCC‐20A mRNA level is downregulated by adriamycin (ADR)‐induced DNA damage and depletion of BJ‐HCC‐20A expression by small interfering RNA promotes the reduction of BRCA2 expression and enhances cell apoptosis in response to DNA damage. Additionally, the recovery of BJ‐HCC‐20A expression in ADR‐induced DNA damage inhibits ADR‐induced apoptosis. The data suggest that BJ‐HCC‐20A promotes cell growth and may regulate the induction of cell apoptosis in response to DNA damage in cooperation with BRCA2 in an M phase‐dependent manner. Therefore, we speculate that targeting BJ‐HCC‐20A may aid in the treatment of breast tumors. (Cancer Sci 2008; 99: 747–754)
Basin‐wide mass‐wasting complexes as markers of the Oligo‐Miocene foredeep‐accretionary wedge evolution in the Northern Apennines, Italy
Authors: Lucente Claudio Corrado , Pini Gian Andrea
Published: February 2008

Sedimentary bodies emplaced by mass‐wasting processes and exceeding tens of metres of thickness and a hundred of square kilometres in area are widespread in the Cretaceous–Pleistocene marine successions of the Northern Apennines of Italy. At least 10 such bodies are present in the stratigraphic record of the Oligo‐Miocene foredeep during the northeastern, time‐transgressive migration of the accretionary wedge‐foredeep system. The term mass‐wasting complex (MWC) is here adopted for these bodies to emphasize their multistory emplacement mechanism and polymictic composition with variously deformed slabs of different lithology, age and provenance. As one of the more intriguing features, their occurrence was associated with changes in turbidite deposition from basin plain to slope. Wide sectors of the internal margin of the basin (lobe‐fan) and even of the basin plain become a slope at the front of the accretionary wedge for a limited period of time (temporary slope). The temporary slope supplied the intrabasinal components of the MWCs, whereas the diffused extrabasinal components came from the front of the accretionary wedge. Therefore, an enhanced instability of the entire foredeep‐wedge system occurred systematically and cyclically. As a consequence, many variously consolidated sediments were transferred into the foredeep basin invading the depocentre and forcing the turbidite deposition towards the foreland, in a more northeasterly position. The presence of such MWCs therefore conditioned basin size and geometry in an analogous way as that reported for some modern convergent margins, as in the case of Costa Rica. Normal sedimentation was restored on top of the MWC only after the levelling of topographic irregularities.
Thermal modelling of magmatic intrusions in the Gjallar Ridge, Norwegian Sea: implications for vitrinite reflectance and hydrocarbon maturation
Authors: Fjeldskaar W. , Helset H. M. , Johansen H. , Grunnaleite I. , Horstad I.
Published: February 2008

Extensive magmatic activity took place in the Vøring Basin, offshore Norway, related to the Early Cenozoic rifting. The break‐up of the North‐Atlantic at the Palaeocene–Eocene transition induced strong volcanism. There are numerous magmatic sills below 3 km depth in the area. They are predominantly layer parallel and thin compared with their lateral extent. Igneous intrusions, sills and dykes affected the temperature history, and thus need to be taken into account in petroleum prospect analysis. We have calculated the temperature and maturity effects in the sedimentary layers in the Gjallar area associated with the emplacement of single sill and sill complexes. A 120‐m‐thick sill produces a theoretical vitrinite reflectance (%R0) 0.8% higher than normal at a distance of 100 m from the sill. Vitrinite reflectance changes caused by a swarm of seven sills varying from 8 to 80 m in thickness were calculated. It is shown that the calculated thermal profile can account for the observed shift in vitrinite reflectance in the well. A two‐dimensional section crossing the Gjallar Ridge, consisting of numerous magmatic intrusions, is also modelled. The modelled geological development and temperature history over the profile show that there are significant maturation effects in the interval under investigation. Based on this work, the sill swarm observed in the area could more than double the fraction of the kerogen that has been transformed to petroleum at the (present) depth of 4 km.
Expanding forests and changing growth forms of Siberian larch at the Polar Urals treeline during the 20th century
Authors: DEVI NADEZHDA , HAGEDORN FRANK , MOISEEV PAVEL , BUGMANN HARALD , SHIYATOV STEPAN , MAZEPA VALERIE , RIGLING ANDREAS
Published: February 2008

The ongoing climatic changes potentially affect plant growth and the functioning of temperature‐limited high‐altitude and high‐latitude ecosystems; the rate and magnitude of these biotic changes are, however, uncertain. The aim of this study was to reconstruct stand structure and growth forms of Larix sibirica (Ledeb.) in undisturbed forest–tundra ecotones of the remote Polar Urals on a centennial time scale. Comparisons of the current ecotone with historic photographs from the 1960s clearly document that forests have significantly expanded since then. Similarly, the analysis of forest age structure based on more than 300 trees sampled along three altitudinal gradients reaching from forests in the valleys to the tundra indicate that more than 70% of the currently upright‐growing trees are <80 years old. Because thousands of more than 500‐year‐old subfossil trees occur in the same area but tree remnants of the 15–19th century are lacking almost entirely, we conclude that the forest has been expanding upwards into the formerly tree‐free tundra during the last century by about 20–60 m in altitude. This upward shift of forests was accompanied by significant changes in tree growth forms: while 36% of the few trees that are more than 100 years old were multi‐stem tree clusters, 90% of the trees emerging after 1950 were single‐stemmed. Tree‐ring analysis of horizontal and vertical stems of multi‐stemmed larch trees showed that these trees had been growing in a creeping form since the 15th century. In the early 20th century, they started to grow upright with 5–20 stems per tree individual. The incipient vertical growth led to an abrupt tripling in radial growth and thus, in biomass production. Based on above‐ and belowground biomass measurements of 33 trees that were dug out and the mapping of tree height and diameter, we estimated that forest expansion led to a biomass increase by 40–75 t ha−1 and a carbon accumulation of approximately 20–40 g C m−2 yr−1 during the last century. The forest expansion and change in growth forms coincided with significant summer warming by 0.9 °C and a doubling of winter precipitation during the 20th century. In summary, our results indicate that the ongoing climatic changes are already leaving a fingerprint on the appearance, structure, and productivity of the treeline ecotone in the Polar Urals.