bluuebunny/crossref_metadata_2025 huggingface dataset:
Controlled fabrication of Cr∕Si and Cr∕SiGe tubes tethered to insulator substrates
Authors: Cavallo F. , Sigle W. , Schmidt O. G.
Published: June 2008

Ultrathin Si and SiGe films on insulator are used as templates for the fabrication of hybrid metal/semiconductor rolled-up tubes. Structured Cr films are thermally evaporated on SiGe- and Si-on-insulator substrates. The metal/semiconductor bilayers are released from the substrate and formed into rolled-up tubes. The tube diameter is controlled by tuning the metal and the semiconductor layer properties. A cross section of a Cr∕SiGe tube is investigated by transmission electron microscopy and electron energy loss spectroscopy.
Temperature effect of the local structure in liquid Sb studied with x-ray absorption spectroscopy
Authors: Wang Q. , Li C. X. , Wu Z. H. , Wang L. W. , Niu X. J. , Yan W. S. , Xie Y. N. , Wei S. Q. , Lu K. Q.
Published: June 2008

The temperature dependence of the local structure of liquid Sb has been studied by x-ray absorption spectroscopy. It is shown that about 10% of the atoms with coordination of 3 and weak Peierls distortion exist in liquid Sb just above its melting point. The Peierls distortion weakens gradually with increasing temperature and vanishes at about 750°C. This structural variation in liquid Sb is different from the normal liquid-liquid phase transition. This work reveals the relationship between the variation in the local structure and the change in the physical properties, such as the electrical resisitvity of liquid Sb, with temperature. The complete agreement between the measured electrical resistivity values during heating and cooling processes suggests that the structural units with the features of a rhombohedron appear above the melting point of Sb during solidification.
Structure and electronic properties of Li-doped vanadium oxide nanotubes
Authors: Hellmann I. , Täschner Ch. , Klingeler R. , Leonhardt A. , Büchner B. , Knupfer M.
Published: June 2008

The influence of Li-doping on the mixed-valent vanadium oxide nanotubes has been investigated using electron energy loss spectroscopy. In particular, the electron diffraction profiles and the vanadium L excitation edges have been studied. We observe that the structure of the vanadium oxide nanotubes is stable against electron transfer upon Li-doping. Excitations at the vanadium L edges show features which are associated with a reduction of the vanadium valency.
Study of electron behavior in a pulsed ion sheath
Authors: Kar S. , Mukherjee S.
Published: June 2008

In many plasma processing applications, like plasma immersion ion implantation (PIII), the substrate is immersed in low pressure plasma and is biased with negative voltage pulses. In typical PIII, the pulse duration is much larger than the ion response time, and hence the ion matrix sheath expands and ion implantation happens on the biased substrate. It is assumed that for pulse duration shorter than ion response times, the ions remain stationary and electrons are repelled by the negative bias. In the present investigation, the negative pulse duration is varied between ion and electron plasma response times; so as to study the electron behavior assuming ions are stationary. The results indicate that the electrons that are lost to the walls come from the ion matrix sheath and probably from the bulk plasma as well. The pulse duration, when it is less than the ion response time, plays a crucial role in determining the number of electrons lost to the walls.
Development of ion source with a washer gun for pulsed neutral beam injection
Authors: Asai T. , Yamaguchi N. , Kajiya H. , Takahashi T. , Imanaka H. , Takase Y. , Ono Y. , Sato K. N.
Published: June 2008

A new type of economical neutral beam source has been developed by using a single washer gun, pulsed operation, and a simple electrode system. We replaced the conventional hot filaments for arc-discharge-type plasma formation with a single stainless-steel washer gun, eliminating the entire dc power supply for the filaments and the cooling system for the electrodes. Our initial experiments revealed successful beam extraction up to 10kV and 8.6A, based on spatial profile measurements of density and temperature in the plasma source. The system also shows the potential to control the beam profile by controlling the plasma parameters in the ion accumulation chamber.
Terahertz near-field imaging of metallic subwavelength holes and hole arrays
Authors: Bitzer Andreas , Walther Markus
Published: June 2008

Metallic microstructures are investigated by time-resolved terahertz near-field imaging. By our approach, we can directly follow field diffraction from subwavelength structures as well as coupling to the surface. Near-field images of the spectral amplitude and phase of the electric field show the formation, propagation, and attenuation of surface waves and allow us to distinguish between propagating and stationary modes. Our results show that the field enhancement in an individual hole, together with the formation of standing waves on the metal surface between the holes, are key mechanisms for the extraordinary transmission phenomenon through periodic hole arrays.
Kim model of stress induced by flux pinning in type-II superconductors
Authors: Yong Hua-Dong , Zhou You-He
Published: June 2008

Magnetoelastic effects, which are caused by flux pinning in the superconductors, often induce fatal cracking of the bulk high temperature superconductors (HTS). In the present work, the Kim model is considered for the critical state in which the critical current density is assumed to depend on the flux density. Based on the plane strain approach, the analytic expression of the stress under the magnetic field is derived for a specimen having a slab geometry and infinitely along the other two directions. The stress field is obtained in the slab for the Kim model, and the stress behavior is discussed for two magnetization processes: the decreasing field and the field cooling. It is shown that the effects of the parameter p on the stress are related to the magnetization process. Compared to the Bean model, the results for the Kim model show the same trend with respect to the external field Ba during field cooling. Generally speaking, these results are of clear interest to experimentalists and to the successful application of bulk superconductors.
Theoretical investigation of the influence of nozzle diameter variation on the fabrication of thin film transistor liquid crystal display color filters
Authors: Shin Dong-Youn , Smith Patrick J.
Published: June 2008

Printing technologies have gained widespread attention from industry as an alternative to expensive photolithographic processes. Among the various kinds of printing technologies, piezoelectric drop-on-demand (piezo-DOD) inkjet printing is regarded as a promising patterning method because of its inherent simplicity and very low levels of material waste generation, especially for display industries such as thin film transistor liquid crystal displays and polymer light emitting diode displays. However, its key engineering difficulty is the variation of droplet volume across the nozzles in a piezo-DOD inkjet printhead, which causes visible swathe marks on a printed display screen. In this paper, it is suggested that the occurrence of these swathe marks could result from the influence of the mechanical nozzle tolerance, i.e., the variation in nozzle diameter of the piezo-DOD printhead. The effect of the mechanical nozzle tolerance on droplet velocity and volume is investigated using mathematical models. Finally, the future research and development direction of piezo-DOD inkjet printing technology for the large area flat panel display industry are discussed.
Fast capacitive probe for electromagnetic pulse diagnostic
Authors: Lorusso A. , Nassisi V. , Siciliano M. V.
Published: June 2008

In this work, we report the study and the development of a capacitive probe which is suitable for getting fast and high voltage/current measurements. Due to the fact that fast pulses propagate generally in coaxial structures, the probe realized in this work was a capacitive divider with the divider electrode properly designed to assure the same characteristic impedance of the coaxial structure and the recombination time of the split signals during the propagation. It was a folded cylindrical ring of 1.4cm long and 0.8cm thick, which introduce a theoretical delay time of about 100ps. Analyzing the behavior of the probe closed on 520Ω, the voltage amplification resulted to be of (3.6±0.1)×10−4 and, as a consequence, the current attenuation factor of 56±1A∕V. The response rise time was less than 320ps, which was limited by oscilloscope bandwave. The capacitor probe can operate voltage measurements of the order of 100kV.
The use of nanolaminates to obtain structurally stable high-K films with superior electrical properties: HfNO–HfTiO
Authors: Mikhelashvili V. , Eisenstein G. , Thangadurai P. , Kaplan W. D. , Brener R. , Saguy C.
Published: June 2008

We propose and demonstrate a metal-insulator-semiconductor (MIS) structure with a gate insulator based on a HfNO–HfTiO nanolaminate stack that has a total thickness of ∼5 nm. Two types of electrodes, Au and Cr, were used and their corresponding performances were compared. Advanced analytical characterization techniques were used to study the influence of annealing on structural, compositional, and electrical characteristics. Two distinct amorphous layers were observed in cross-sectional high resolution transmission microscopy independent of the annealing temperature. The dependence of dielectric constant on annealing temperature was found to be nonmonotonic with a maximum at 750 °C. Structures using a Cr gate electrode exhibit a 1.25–1.35 times larger dielectric constant than those using a Au contact. The minimum quantum mechanical corrected effective oxide thicknesses are 1.29 and 0.86 nm for structures with Au and Cr electrodes, respectively. Structures annealed at 1000 °C exhibit low leakage current densities of 1.5×10−8 and 2.9×10−7 A cm−2 (at an electric field of 2 MV cm−1) for the Au and Cr electrodes, respectively, and a breakdown electric field of ∼10–12 MV cm−1.
Piezoelectric acoustic boundary waves in the structure of multilayer thin films/electrode/piezoelectric substrates
Authors: Yamanouchi Kazuhiko , Satoh Yusuke
Published: June 2008

The propagation characteristics and temperature coefficients of frequency characteristics of boundary waves, which concentrate the acoustic energy in the interface between the thin film-metal electrode and piezoelectric substrate using the structure of multithin film layers/metal electrode/piezoelectric substrates, are described. The new boundary waves are obtained by using higher velocity thin film as the top surface than internal ones of metal electrode and thin film. The materials with structures of AlN, Al2O3/SiO2/Al, Cu, Ag, Au/rotated Y-X LiNO3, and LiTaO3 are applied. The range of existence of boundary wave for thicknesses of thin films, electrodes on Y-X LiNbO3, LiTaO3, and temperature coefficient of frequency are shown. Experimental results of surface acoustic wave resonators show a good frequency response of admittance at 500 MHz range.
Mode selection and phase locking of sidelobe-emitting semiconductor laser arrays via reflection coupling from an external narrow-bandwidth grating
Authors: Riyopoulos S. , Venus G. , Glebov L.
Published: June 2008

A phase locked array design, utilizing direct reflection feedback between adjacent cavities by an external grating, is analyzed and proposed. The narrow grating reflection bandwidth causes longitudinal mode selection, while the array geometry causes transverse wavenumber selection through the coupling strength. As a result, only one among the free running cavity eigenmodes can couple effectively into a phase locked collective eigenmode. The coupled array mode is experiencing the high reflectivity of the grating and surpasses the low gain of the free running modes, that experience only a much lower reflectivity from the cavity edge antireflective coating. These results suggest that in-phase locking and single mode operation can be achieved simultaneously through the use of an external narrow-bandwidth grating.
Domain wall pinning and potential landscapes created by constrictions and protrusions in ferromagnetic nanowires
Authors: Petit Dorothée , Jausovec Ana-Vanessa , Read Dan , Cowburn Russell P.
Published: June 2008

The potential experienced by transverse domain walls (TDWs) in the vicinity of asymmetric constrictions or protrusions in thin Permalloy nanowires is probed using spatially resolved magneto-optical Kerr effect measurements. Both types of traps are found to act as pinning centers for DWs. The strength of pinning is found to depend on the trap type as well as on the chirality of the incoming DW; both types of traps are seen to act either as potential wells or potential barriers, also depending on the chirality of the DW. Micromagnetic simulations have been performed that are in good qualitative agreement with the experimental results.
The Riemann–Lanczos equations in general relativity and their integrability
Authors: Dolan P. , Gerber A.
Published: June 2008

The aim of this paper is to examine the Riemann-Lanczos equations and how they can be made integrable. They consist of a system of linear first-order partial differential equations that arise in general relativity, whereby the Riemann curvature tensor is generated by an unknown third-order tensor potential field called the Lanczos tensor. Our approach is based on the theory of jet bundles, where all field variables and all their partial derivatives of all relevant orders are treated as independent variables alongside the local manifold coordinates (xa) on the given space-time manifold M. This approach is adopted in (a) Cartan’s method of exterior differential systems, (b) Vessiot’s dual method using vector field systems, and (c) the Janet–Riquier theory of systems of partial differential equations. All three methods allow for the most general situations under which integrability conditions can be found. They give equivalent results, namely, that involutivity is always achieved at all generic points of the jet manifold M after a finite number of prolongations. Two alternative methods that appear in the general relativity literature to find integrability conditions for the Riemann–Lanczos equations generate new partial differential equations for the Lanczos potential that introduce a source term, which is nonlinear in the components of the Riemann tensor. We show that such sources do not occur when either of method (a), (b), or (c) are used.
Homogeneous growth of antidot structures electrodeposited on Si by nanosphere lithography
Authors: Spada Edna R. , da Rocha Alexsandro S. , Jasinski Everton F. , Pereira Guilherme M. C. , Chavero Lucas N. , Oliveira Alexandre B. , Azevedo Antonio , Sartorelli Maria Luisa
Published: June 2008

The characteristics of cobalt antidot structures, electrodeposited on Si by nanosphere lithography, is investigated by analysis of current transients and optical and atomic force microscopy. Polystyrene colloidal masks of 1 ML (monolayer) or a maximum of 2, with sphere diameters ranging between 165 and 600nm were fabricated by spin coating. For masks partially covered with bilayer regions, it is shown that the volume of deposited material in bilayer areas corresponds to only 5% of the cobalt deposited in the monolayer areas. This drastic reduction in the deposition rate affects the quality of the deposit. Therefore, the use of colloidal masks of homogeneous thickness is necessary to guarantee the electrodeposition of nanostructured films of controlled thickness. It will also be shown that the use of high quality colloidal masks yields a reproducible electrodeposition process, enabling the use of the current transient as a reliable tool for assessment of the deposition process.
Enhanced terahertz detection by localized surface plasma oscillations in a nanoscale unipolar diode
Authors: Xu K. Y. , Lu X. F. , Song A. M. , Wang G.
Published: June 2008

By using a two-dimensional ensemble Monte Carlo method, we have studied the terahertz-frequency response of a self-switching device (SSD), which is a semiconductor rectifier consisting of an asymmetric nanochannel. The simulations reveal that the performance can be improved by adjusting the shape and dielectric material filling of the insulating trenches that define the SSD. We show that the rectified current of the SSD has a nonmonotonic frequency dependence with a pronounced peak occurring just below the cutoff frequency. Through optimizations of the geometry, the peak current can reach twice that at low frequencies, enabling not only a higher detection sensitivity but also a degree of frequency selectivity. The effect is discussed in terms of a localized surface plasma oscillation in the asymmetric nanostructure.
Metal-oxide-semiconductor-compatible ultra-long-range surface plasmon modes
Authors: Durfee C. G. , Furtak T. E. , Collins R. T. , Hollingsworth R. E.
Published: June 2008

Long-range surface plasmons traveling on thin metal films have demonstrated promising potential in subwavelength waveguide applications. In work toward device applications that can leverage existing silicon microelectronics technology, it is of interest to explore the propagation of surface plasmons in a metal-oxide-semiconductor geometry. In such a structure, there is a high refractive index contrast between the semiconductor (n≈3.5 for silicon) and the insulating oxide (typically n≈1.5−2.5). However, the introduction of dielectrics with disparate refractive indices is known to strongly affect the guiding properties of surface plasmons. In this paper, we analyze the implications of high index contrast in 1D layered surface plasmon structures. We show that it is possible to introduce a thin dielectric layer with a low refractive index positioned next to the metal without adversely affecting the guiding quality. In fact, such a configuration can dramatically increase the propagation length of the conventional long-range mode. While this study is directed at silicon-compatible waveguides working at telecommunications wavelengths, this configuration has general implications for surface plasmon structure design using other materials and operating at alternative wavelengths.
All-electric detection of the polarization state of terahertz laser radiation
Authors: Ganichev S. D. , Weber W. , Kiermaier J. , Danilov S. N. , Olbrich P. , Schuh D. , Wegscheider W. , Bougeard D. , Abstreiter G. , Prettl W.
Published: June 2008

Two types of room-temperature detectors of terahertz laser radiation have been developed which allow, in an all-electric manner, the determination of the plane of polarization of linearly polarized radiation and the Stokes parameters of elliptically polarized radiation, respectively. The operation of the detectors is based on photogalvanic effects in semiconductor quantum well structures of low symmetry. The photogalvanic effects have nanosecond time constants at room temperature, making a high time resolution of the polarization detectors possible.
Fabrication for multilayered composite thin films by dual-channel vacuum arc deposition
Authors: Dai Hua , Shen Yao , Wang Jing , Xu Ming , Li Liuhe , Li Xiaoling , Cai Xun , Chu Paul K.
Published: June 2008

A flexible dual-channel curvilinear electromagnetic filter has been designed and constructed to fabricate multilayered composite films in vacuum arc ion plating. The filter possesses two guiding channels and one mixing unit. Multilayered TiN∕AlN and TiAlN composite films can be produced by controlling the frequency or interval of the two cathodes. The x-ray photoelectron spectroscopy and low-angle x-ray diffraction results reveal the periodic Ti and Al structures in the TiN∕AlN films. The TiAlN films exhibit a smooth surface morphology confirming effective filtering of macroparticles by the filter. High temperature oxidation conducted at 700°C for an hour indicates that the weight increment in the TiAlN films produced by the dual filter is only half of that of the TiAlN films produced without a filter, thereby showing better resistance against surface oxidation.
Nanocrystallization by current annealing (with and without tensile stress) of Fe73.5−xNixSi13.5B9Nb3Cu1 alloy ribbons (x=5, 10, and 20)
Authors: Iturriza N. , Murillo N. , del Val J. J. , González J. , Vara G. , Pierna A. R.
Published: June 2008

Microstructural (crystalline volume fraction and grain size), magnetization (coercive field), and saturation magnetostriction measurements in Fe73.5−xNixSi13.5B9Nb3Cu1 alloy ribbons (x=5, 10, and 20) treated by current annealing and stress-current annealing are presented. Microstructural analysis of the treated ribbons using x-ray diffraction showed a high content of the amorphous phase in the bulk. In addition, substantial changes in the crystalline state such as grain size of the samples annealed at different conditions were observed. The alloy composition also affects greatly the grain size: increase in Ni content leads to higher values of the average grain size. The evolutions of the coercive field with the two kinds of thermal treatment were analyzed, allowing us to conclude that the addition of Ni tends to reduce the magnetic softness of the original material and that the coercivities are higher in the samples treated by stress annealing than in those treated without tensile stress. On the other hand, the saturation magnetostriction decreases with the thermal treatment, which is in agreement with the microstructural behavior (structural relaxation and nanocrystallization process), although some discrepancies are found for samples with x=5.
Giant dielectric properties of CaCu3Ti4O12∕(Li,Ti)-doped NiO composites subjected to postsintering annealing and compressive stress
Authors: Thongbai Prasit , Maensiri Santi , Yamwong Teerapon , Yimnirun Rattikorn
Published: June 2008

We report the effects of postsintering annealing in argon and compressive prestress on the giant dielectric properties of CaCu3Ti4O12–Li0.3Ti0.02Ni0.68O composites in the frequency range from 100Hzto1MHz. After postsintering annealing, all compounds investigated still display a Debye-like relaxation, which can be interpreted based on the Maxwell–Wagner model. The dielectric behavior and the effect of compressive prestress of CaCu3Ti4O12 and CaCu3Ti4O12–Li0.3Ti0.02Ni0.68O after annealing are closely related to the oxygen vacancies in the grain boundaries.
Effect of surface anisotropy on the magnetic properties of magnetite nanoparticles: A Heisenberg–Monte Carlo study
Authors: Mazo-Zuluaga J. , Restrepo J. , Mejía-López J.
Published: June 2008

In this study, we analyze the effect of surface anisotropy on the magnetic properties of magnetite Fe3O4 nanoparticles on the basis of a core-shell model. Magnetization, magnetic susceptibility, and specific heat are computed over a wide range of temperatures. In our model, we stress on magnetite nanoparticles of 5nm in diameter which consist of 6335 ions. Our theoretical framework is based on a three-dimensional classical Heisenberg Hamiltonian with the nearest magnetic neighbor interactions between iron ions involving tetrahedral (A) and octahedral (B) sites. Terms dealing with cubic magnetocrystalline anisotropy for core ions, a single-ion site surface anisotropy for those Fe ions belonging to the shell, and the interaction with a uniform external magnetic field are considered. To compute the equilibrium averages, a single-spin movement Monte Carlo–Metropolis dynamics was used. Results reveal the occurrence of low-temperature spin configurations different from those expected for a collinear single-domain ferrimagnetic state, depending on the magnitude and sign of the surface anisotropy constant. A transition to a spike state, with magnetization close to zero, is obtained beyond a certain critical positive surface anisotropy value. Such a transition is not observed for negative values. Moreover, a two-pole magnetic state is developed at sufficiently high negative values. Such differences are explained in terms of the interplay between the superexchange couplings and the easy directions imposed by the surface anisotropy vectors. Our results are summarized in a proposal of phase diagram for the different spin structures as a function of the surface-to-core anisotropy ratio. Lastly, hysteretic behavior is evaluated. Nanoparticles become magnetically harder as the surface anisotropy increases in magnitude, and the way in wich the coercive field changes with this quantity is explicitly shown.
Thermoelectric properties of La0.9CoFe3Sb12–CoSb3 skutterudite nanocomposites
Authors: Alboni P. N. , Ji X. , He J. , Gothard N. , Tritt Terry M.
Published: June 2008

A hydrothermal nanoparticle-plating technique has been employed in order to grow a layer of CoSb3 nanoparticles on the surface of La0.9CoFe3Sb12 bulk matrix grains. The nanoparticles have a typical size of 30–40 nm while the nano-layer can be up to several hundreds of nanometer thick. The nanoparticle layer, which resides at the grain boundary after hotpressing, provides an extra scattering channel for phonons, in addition to the “rattler” atoms (La), grain boundary scattering, and mass fluctuation mechanisms found within the bulk matrix grain. The electrical resistivity, thermopower, thermal conductivity, and Hall coefficient have been investigated as a function of temperature and the weight percentage (%) of nanoparticles. Largely due to the reduced lattice thermal conductivity, a ZT value of ∼0.5 is attained at 725 K on the sample with 5 wt % of nanoparticles showing a 15% improvement of the ZT from that of the sample without nanoparticles and comparable to the best value reported at this temperature.
Shock compression of condensed matter using Eulerian multimaterial method: Applications to multidimensional shocks, deflagration, detonation, and laser ablation
Authors: Yoh Jack J. , Kim Ki-hong
Published: June 2008

The reactive flow analysis of high energy material is performed using hydro shock compression of condensed matter (SCCM) tool that is being developed for handling complex multimaterial dynamics involving energetic and inert matters. Typically, the reacting flows of high energy materials such as fires and explosions give rise to strong nonlinear shock waves and high strain rate deformation of metallic confinements at unusually high pressure and temperature. In order to address difficulties associated with analyzing such complex systems, we have developed a suite of modeling capabilities for elegantly handling large gradients and high strain rates in solids as well as reactive shock waves present in gaseous phase. Mathematical formulation of explosive dynamics involving condensed matter is explained with an emphasis on validating and application of hydro-SCCM to a series of problems of high-speed multimaterial dynamics in nature. A detailed numerical description of a level-set based reactive ghost fluid approach is reported in a separate paper.
Magnetization reversal in patterned La0.67Sr0.33MnO3 thin films by magneto-optical Kerr imaging
Authors: Saïb M. , Belmeguenai M. , Méchin L. , Bloyet D. , Flament S.
Published: June 2008

The magnetization reversal process in patterned La0.67Sr0.33MnO3 thin films has been studied at room temperature using the magneto-optical Kerr effect. The 100 and 200nm thick films were patterned into 50μm long rectangles of various widths in the 20–50μm range. In each rectangle, holes with 2 and 5μm diameters were patterned aiming at pinning the domain walls. X-ray diffraction study revealed high structural quality of both films. However, the macroscopic surface properties of both films were different, as shown by optical microscopy, which revealed cracks in the thicker film. For each thickness, both the magnetic domain images and the local magnetic hysteresis loops were recorded. For both films, the magnetization reversal process consists in nucleation and propagation of magnetic domains. In the 100nm thick film, the local hysteresis loops depend on the widths of the patterned rectangles and we observed a significant effect of the hole in pinning domains walls, leading to multiple switching transitions in the hysteresis loops. No such effect was observed inside the 200nm thick film containing cracks.
Site modification in BiFeO3 thin films studied by Raman spectroscopy and piezoelectric force microscopy
Authors: Wang Yao , Nan Ce-Wen
Published: June 2008

Site modification in BiFeO3 films was investigated using Raman spectroscopy and piezoelectric force microscopy to explore effect of A- and B-site modifications on structural evolution and ferroelectric behavior of doped BiFeO3 films. Our Raman results revealed the subtle structural changes in the BiFeO3 films caused by the changes of the short-range force in the crystal lattice induced by ionic radii mismatch. The observation of ferroelectric domain and the control of domain switching through an electric field in these doped BiFeO3 films were realized by piezoelectric force microscopy. Piezoelectric response of these doped BiFeO3 films illustrated dependence of their properties upon the lattice symmetry and film microstructure.
Massless field perturbations of the spinning C metric
Authors: Bini D. , Cherubini C. , Geralico A.
Published: June 2008

A single master equation is given describing spin s≤2 test fields that are gauge- and tetrad-invariant perturbations of the spinning C metric space-time representing a source with mass M, uniformly rotating with angular momentum per unit mass a, and uniformly accelerated with acceleration A. This equation can be separated into its radial and angular parts. The behavior of the radial functions near the black hole (outer) horizon is studied to examine the influence of A on the phenomenon of super-radiance, while the angular equation leads to modified spin-weighted spheroidal harmonic solutions generalizing those of the Kerr space-time. Finally the coupling between the spin of the perturbing field and the acceleration parameter A is discussed.
Deformability of ultrahigh strength 5nm Cu∕Nb nanolayered composites
Authors: Mara N. A. , Bhattacharyya D. , Dickerson P. , Hoagland R. G. , Misra A.
Published: June 2008

In this work, micropillar compression testing has been used to obtain stress-strain curves for sputter-deposited Cu–Nb nanolaminate composites with nominal bilayer thickness of 10nm. In addition to the extremely high flow strength of 2.4GPa, the 5nm Cu∕5nm Nb nanolaminate exhibits significant ductility, in excess of 25% true strain.
Hydrogen diffusion behavior in N doped ZnO: First-principles study
Authors: Hu J. , He H. Y. , Pan B. C.
Published: June 2008

We theoretically study the diffusion behavior of H in N doped ZnO, and find that N can trap the diffusing H nearby, with overcoming activation energies of no more than 0.5eV. Then the trapped H moves around the doped N with overcoming low energy barriers (<0.4eV). Breaking the N–H bond to release the H atom requires an energy of at least 1.25eV, which is significantly higher than that for H diffusion in perfect ZnO (∼0.5eV) [M. G. Wardle et al., Phys. Rev. Lett. 96, 205504 (2006)]. Therefore, the acceptor N in ZnO is favorably passivated by donor H, being, in part, responsible for the experimental phenomenon that high hole concentration in N doped p-type ZnO is difficult to be obtained. Calculations of electronic structures reveal that the location of H around the doped N atom sensitively affects the gap states.
Efficient generation of cross-polarized femtosecond pulses in cubic crystals with holographic cut orientation
Authors: Canova Lorenzo , Kourtev Stoyan , Minkovski Nikolay , Jullien Aurélie , Lopez-Martens Rodrigo , Albert Olivier , Saltiel Solomon M.
Published: June 2008

We report here an alternative and more efficient orientation of cubic crystals for generation of cross-polarized femtosecond laser pulses. We show both theoretically and experimentally that the cross polarized wave generation (XPWG) is more efficient when the fundamental beam propagates along the [011] direction (holographic cut) in the crystal than along the [001] direction previously reported. With the [011]-cut BaF2 crystal we measured the highest XPWG conversion efficiencies. We prove other very important advantages of the [011]-cut approach: weak induced phase mismatch and no need for its compensation.
Temperature stable amorphous-TeO2∕36°–46° Y-X LiTaO3 substrates for surface acoustic wave applications
Authors: Shang Xiaoli , Gong Xun , Xiong Jun , Zhang De , Cheng Jianchun
Published: June 2008

This research investigated the temperature coefficient of delay (TCD) of the surface acoustic wave (SAW) on the amorphous TeO2∕36°–46° Y-X LiTaO3 layered substrates. The TCD can reach zero when the thickness of amorphous TeO2 film is much less than that of conventional SiO2 film, which means SAW devices on such substrates can be fabricated easily. Theoretical calculation showed that they have a very high K2 around 8%, a pure transverse surface wave mode, and a zero TCD simultaneously. They are therefore very appealing for a wide range of SAW applications.
Improved a-plane GaN quality grown with flow modulation epitaxy and epitaxial lateral overgrowth on r-plane sapphire substrate
Authors: Huang Jeng-Jie , Shen Kun-Ching , Shiao Wen-Yu , Chen Yung-Sheng , Liu Tzu-Chi , Tang Tsung-Yi , Huang Chi-Feng , Yang C. C.
Published: June 2008

The authors demonstrate superior crystal quality of a-plane GaN grown on r-plane sapphire substrate based on the flow modulation epitaxy (FME) technique, in which the Ga atom supply is alternatively switched on and off with continuous nitrogen supply. With the FME technique, a high growth rate of 2.3μm∕h can still be achieved. With or without epitaxial lateral overgrowth (ELOG), either c- or m-mosaic condition is significantly improved in the samples of using FME. With ELOG, the surface roughness can be reduced from 1.58to0.647nm in an area of 10×10μm2 microns by using the FME technique. Based on the results of photoluminescence measurement, one can also conclude the better optical property of the FME-grown a-plane GaN thin films. Besides, it is shown that tensile strain is more relaxed in the FME samples.
A microfluidic cell for studying the formation of regenerated silk by synchrotron radiation small- and wide-angle X-ray scattering
Authors: Martel Anne , Burghammer Manfred , Davies Richard , DiCola Emanuela , Panine Pierre , Salmon Jean-Baptiste , Riekel Christian
Published: June 2008

A tube-in-square-pipe microfluidic glass cell has been developed for studying the aggregation and fiber formation from regenerated silk solution by in-situ small-angle X-ray scattering using synchrotron radiation. Acidification-induced aggregation has been observed close to the mixing point of the fibroin and buffer solution. The fibrous, amorphous material is collected in a water bath. Micro-wide-angle X-ray scattering of the dried material confirms its β-sheet nature.
Polish Special Economic Zones: Idea versus Practice
Authors: Gwosdz Krzysztof , Jarczewski Woyciech , Huculak Maciej , Wiederman Krzysztof
Published: June 2008

In 1994 special economic zones (SEZs) were introduced in Poland as an instrument supporting regional development. Initially, the idea was to open just a handful of zones located in single-function industrial regions affected by or exposed to structural unemployment. Investor benefits included a full income-tax holiday for a half of the special zone's life (typically ten years) and exemption from real-estate taxation. Subsequently, the initial conditions were considerably modified under the influence of various pressure groups, including the European Commission, the central government, major international investors, and local authorities. The tax benefits were reduced, but the eligibility was extended to new industries and new company types while the overall number of special zones consistently increased. With more than 150 locations enjoying a special status, the SEZs have lost their nature of regional policy tools, almost becoming standard forms of public aid for companies, regardless of their location. This shift in the approach to the special zones had a fundamental impact on the effects generated by the special zones. The investor appeal of areas where state support was essential to overcome a structural economic crisis was further undermined. Indeed, the bulk of investment and jobs was channeled to the zones comfortably located in southwestern Poland near large urban agglomerations with a labor market that was attractive to the investors (the Katowicka, Legnicka, and Wa-brzyska zones). However, few large and middle-sized investments were acquired by single-function industrial areas in crisis (Starachowicka and Tarnobrzeska SEZs) or by peripheral agricultural regions (Warmińsko-Mazurska i Suwalska SEZs). A notable exception to this rule is the first Polish special zone in Mielec: although peripherally located, it achieved success using the first-comer advantage it had over the subsequent zones.
Evaluating the Effectiveness of Public Participation Efforts by Environmental Agencies: Repermitting a Smelter in El Paso, Texas, USA
Authors: Cunningham Catherine A , Tiefenbacher John P
Published: June 2008

Public participation is central to environmental policy-making processes. Government agencies often scramble to involve the public in legitimizing policy decisions. No single tool exists to assess the effectiveness of public participation. Extending previous research, this paper clarifies a framework for evaluating the effectiveness of public participation and we apply this framework to the efforts of three levels of government in the United States—federal, state, and local—in the case surrounding the repermitting of atmospheric emissions from industrial activity at the American Smelting and Refining Company smelter located in western El Paso, Texas. Results show that the three government agencies assessed in this study did not effectively achieve adequate opportunities for public participation. This failure could lead to several undesired repercussions, including increasing public resentment and hostility and also future resistance to participation.
A Static Geometrical Illusion Contributes Largely to the Footsteps Illusion
Authors: Sunaga Shoji , Sato Masayuki , Arikado Natsuko , Jomoto Hiroshi
Published: June 2008

When a black and a white rectangle drifts across a stationary striped background with constant velocity, the rectangles appear to alternately speed up and slow down. Anstis (2001, Perception30 785–794; 2004, Vision Research44 2171–2178) suggested that this ‘footsteps’ illusion is due to confusion between contrast and velocity signaling in the motion detectors of the human visual system. To test this explanation, three experiments were carried out. In experiment 1, the magnitudes of the footsteps illusion in dynamic and static conditions was compared. If motion detectors play an important role in causing the illusion, it should be reduced in the static condition. Remarkably, however, we found that the illusory misalignment between the black and the white rectangle was even more prominent in the static condition than in the dynamic condition. In experiment 2, we measured the temporal-frequency properties of the footsteps illusion. The results showed that the footsteps illusion was tuned to low temporal frequencies. This suggests that the static illusory misalignment can contribute sufficiently to the dynamic illusory misalignment. In experiment 3, the magnitude of the illusion was measured with the rectangles drifting on a temporally modulated background instead of a spatially modulated background. If contrast affects the apparent velocity of the rectangles, temporal modulation of a uniform background should also cause the footsteps illusion. However, the results showed that the magnitude of the illusion was much reduced in this condition. Taken together, the results indicate that the footsteps illusion can be regarded as a static geometrical illusion induced by the striped background and that motion detectors play a minor role at best.
Resistance to race 1 of Kabatiella caulivora in subterranean clover (Trifolium subterraneum L.) cultivars and breeding lines
Authors: Nichols P. G. H. , You M. P. , Barbetti M. J.
Published: June 2008

Twenty-eight cultivars and 106 F6-derived breeding lines of subterranean clover (Trifolium subterraneum) were screened in the field for their response to clover scorch disease caused by race 1 of Kabatiella caulivora. Eleven of the cultivars, including Denmark and Goulburn, were classified as resistant. Breeding lines with Denmark parentage had 55% of progeny with resistance, while those of Goulburn had only 19% of resistant progeny, suggesting different modes of inheritance. Selection for resistance to race 2 of K. caulivora in the F4 generation markedly increased the probability of selecting F6-derived lines with resistance to race 1, suggesting linkage between genes for resistance to both races.
Genotype×environment interaction for wheat yield in different drought stress conditions and agronomic traits suitable for selection
Authors: Dodig Dejan , Zoric Miroslav , Knezevic Desimir , King Stephen R. , Surlan-Momirovic Gordana
Published: June 2008

Wheat cultivars grown in south-eastern Europe are exposed to variable rainfed environments. Climate change predictions indicate that the frequency of dry years will likely increase in the future. This study examined relationships among agronomic traits and some drought indices with grain yield as influenced by genotype and environment. In a 4-year experiment, 100 cultivars and landraces of bread wheat (Triticum aestivum L.) from different countries were tested under 3 watering regimes: fully irrigated, rainfed, and in a rain-out plot shelter. Three selection indices, mean productivity (MP), tolerance (TOL), and stress susceptibility index (SSI), were calculated based on grain yield in irrigated and drought-stressed conditions. The additive main effects and multiplicative interaction (AMMI) models were used to study the genotype × environment effects. Average yield reduction due to drought in the sheltered plots was 37.5%. High-yielding genotypes in each treatment showed high values of MP and high rank for SSI and, particularly, TOL. Conversely, low-yielding genotypes in each treatment had low values of MP and high drought tolerance according to SSI and TOL (i.e. low ranks). MP values were noted as being particularly well suited for predicting performance in this experiment. Total biomass and early vigour were found to be the most important agronomic traits for selecting high-yielding genotypes in a range of stress and non-stress conditions.
Analyzing population growth curves
Authors: Eberhardt L. L. , Breiwick J. M. , Demaster D. P.
Published: June 2008

Assessing animal population growth curves is an essential feature of field studies in ecology and wildlife management. We used five models to assess population growth rates with a number of sets of population growth rate data. A ‘generalized’ logistic curve provides a better model than do four other popular models. Use of difference equations for fitting was checked by a comparison of that method and direct fitting of the analytical (integrated) solution for three of the models. Fits to field data indicate that estimates of the asymptote, K, from the ‘generalized logistic’ and the ordinary logistic agree well enough to support use of estimates of K from the ordinary logistic on data that cannot be satisfactorily fitted with the generalized logistic. Akaike's information criterion is widely used, often with a small sample version AICc. Our study of five models indicated a bias in the AICccriterion, so we recommend checking results with estimates of variance about regression for fitted models. Fitting growth curves provides a valuable supplement to, and check on computer models of populations.
Tree size distributions in an old‐growth temperate forest
Authors: Wang Xugao , Hao Zhanqing , Zhang Jian , Lian Juyu , Li Buhang , Ye Ji , Yao Xiaolin
Published: June 2008

Despite the wide variation in the structural characteristics in natural forests, tree size distribution show fundamental similarities that suggest general underlying principles. The metabolic ecology theory predicts the number of individual scales as the −2 power of tree diameter. The demographic equilibrium theory predicts tree size distribution starting from the relationship of size distributions with growth and mortality at demographic equilibrium. Several analytic predictions for tree size distributions are derived from the demographic equilibrium theory, based on different growth and mortality functions. In addition, some purely phenomenological functions, such as polynomial function, have been used to describe the tree size distributions. In this paper, we use the metabolic ecology theory, the demographic equilibrium theory and the polynomial function to predict the tree size distribution for both the whole community and each species in an old‐growth temperate forest in northeastern China. The results show that metabolic ecology theory predictions for the scaling of tree abundance with diameter were unequivocally rejected in the studied forest. Although these predictions of demographic theory are the best models for most of the species in the temperate forest, the best models for some species (Tilia amurensis, Quercus mongolica and Fraxinus mandshurica) are compound curves (i.e. rotated sigmoid curves), best predicted by the polynomial function. Hence, the size distributions of natural forests were unlikely to be invariant and the predictive ability of general models was limited. As a result, developing a more sophisticated theory to predict tree size distributions remains a complex, yet tantalizing, challenge.
A parasite‐driven wedge: infectious diseases may explain language and other biodiversity
Authors: Fincher Corey L. , Thornhill Randy
Published: June 2008

Parasite–host coevolutionary races are spatially variable across species’ or human cultural ranges. Assortative sociality, biased toward local conspecifics, and limited dispersal (philopatry) in humans and other organisms can be adaptive through reduced contact with dangerous contagions harbored by distant/non‐local conspecifics. These factors can generate cultural or population divergence. Thus, parasites are like a wedge driving groups apart through their effective creation of anticontagion behaviors. If this proposition is correct, then biological diversity should positively correlate with parasite diversity. Here we show that the worldwide distribution of indigenous human language diversity, a form of biodiversity, is strongly, positively related to human parasite diversity indicative of a legacy of parasite‐mediated diversification. The significant pattern remains when potential confounds are removed. The pattern too is seen in each of the six world regions and is not confounded by regional differences in their history of colonization and conquest. We hypothesize that variation in limited dispersal and assortative sociality with conspecifics in response to the worldwide spatial variation in pathogen diversity provides a fundamental mechanism of population divergence explaining many important aspects of the geographic patterns of biodiversity. This hypothesis has broad implications for a diversity of research topics including language diversity, cultural evolution, speciation, phylogeny and biogeography.