bluuebunny/crossref_metadata_2025 huggingface dataset:
Atomically sharp catalyst-free wurtzite GaAs∕AlGaAs nanoneedles grown on silicon
Authors: Moewe Michael , Chuang Linus C. , Crankshaw Shanna , Chase Chris , Chang-Hasnain Connie
Published: July 2008

We report a catalyst-free, self-assembled growth mode generating single-crystal wurtzite phase ultrasharp GaAs∕AlGaAs nanoneedles on both GaAs and Si substrates via low-temperature metal-organic chemical vapor deposition. The needles exhibit record-narrow tip diameters of 2–4nm wide and sharp 6°–9° taper angles. The length is dependent on growth time and up to 3–4μm nanoneedles are attained. The structures do not exhibit twinning defects, contrary to typical GaAs nanowires grown by vapor-liquid-solid catalyzed growth. AlGaAs layered nanoneedle structures are also demonstrated.
Structural, wetting, and electronic properties of metal clusters adsorbed on carbon nanotubes
Authors: Yuan Shijun , Wang Xueli , Li Pai , Wang Chuanhui , Yuan Songliu
Published: July 2008

Atomic structures of M4(M=Ti and Fe) metal clusters on the surface of single-walled carbon nanotubes (SWNT) are studied by the first principles calculations. The various equilibrium structures and total energies of M4 cluster-SWNT composites are presented, which reveal that the relative energies between the tetrahedral and planar configurations correspond to the wetting properties of metal clusters adsorbed on carbon nanotubes. Electronic properties of the M4+SWNT composites are also presented to show the highly spin polarized behaviors. Our results suggest that the M4+SWNT composite is a simple and typical model to study the interactive effects and architectures of metal clusters absorbed on carbon nanotubes, which can be further exploited for the design of nanoscale electrodes and nanoelectronic devices.
Pressure-induced metallization and resonant Raman scattering in Zn1−xMnxTe
Authors: Lin Y. C. , Fan W. C. , Chiu C. H. , Ke F. K. , Yang S. L. , Chuu D. S. , Lee M. C. , Chen W. K. , Chang W. H. , Chou W. C. , Hsu J. S. , Shen J. L.
Published: July 2008

Pressure-induced resonant Raman scattering is adopted to analyze the zone-center optical phonon modes and crystal characteristics of Zn1−xMnxTe (0≦x≦0.26) thin films. The pressure (Pt) at which the semiconducting undergoes a transition to the metallic phase declines as a function of Mn concentration (x) according to the formula Pt(x)=15.7−25.4x+19.0x2 (GPa). Pressure-dependent longitudinal and transverse optical phonon frequencies and the calculated mode Grüneisen parameters were adopted to investigate the influence of Mn2+ ions on the iconicity. The experimental results indicate that the manganese ions tend to increase the iconicity of ZnTe under ambient conditions, whereas an external hydrostatic pressure tends to reduce the iconicity and the bond length of Zn1−xMnxTe.
Experimental determination for resonance-induced transmission of acoustic waves through subwavelength hole arrays
Authors: Hou Bo , Mei Jun , Ke Manzhu , Liu Zhengyou , Shi Jing , Wen Weijia
Published: July 2008

We measured acoustic transmissions through subwavelength hole arrays fabricated on brass plates at normal and oblique incidence. It is found experimentally that the transmission phenomena for the hole array in thin plate case are analogous to the previously observed enhanced transmission of electromagnetic waves [Ebbesen et al., Nature (London) 391, 667 (1998)]. While for the hole array in thick plate case, the transmission peaks of acoustic wave occur well below Wood’s anomalies, and the spectrum characteristics reveal a Fabry–Pérot-like resonance. An effective fluid approach is conceived and it can well describe the transmission properties of the hole array in thick plates within a range of incidence angle.
Giant wave rotation for small helical structures
Authors: Chui S. T.
Published: July 2008

We calculate the circuit parameters, resonant frequencies, and physical properties of small metallic helixes. We study the propagation of electromagnetic radiation through a collection of these helixes and find that under appropriate conditions, a Faraday rotation at zero field can be manifested that is three orders of magnitude higher than that of terbium gallium garnet under a field of 10 T.
Particle concentration and mixing in microdrops driven by focused surface acoustic waves
Authors: Shilton Richard , Tan Ming K. , Yeo Leslie Y. , Friend James R.
Published: July 2008

We report the use of focused surface acoustic waves (SAWs) generated on 128° rotated Y-cut X-propagating lithium niobate (LiNbO3) for enhancing the actuation of fluids and the manipulation of particle suspensions at microscale dimensions. In particular, we demonstrate increased efficiency and speed in carrying out particle concentration/separation and in generating intense micromixing in microliter drops within which acoustic streaming is induced due to the focused SAW beneath the drop. Concentric circular and elliptical single-phase unidirectional transducers (SPUDTs) were used to focus the SAW. We benchmark our results against a straight SPUDT which does not cause focusing of the SAW. Due to the increased wave intensity and asymmetry of the wave, we found both circular and elliptical SPUDTs concentrate particles in under 1 s, which is one order of magnitude faster than the straight SPUDT and several orders of magnitude faster than conventional microscale devices. The concentric circular SPUDT was found to be most effective at a given input power since it generated the largest azimuthal velocity gradient within the fluid to drive particle shear migration. On the other hand, the concentric elliptical SPUDT generated the highest micromixing intensity due to the more narrowly focused SAW radiation that substantially enhances acoustic streaming in the fluid.
Impedance collapse and beam generation in a high power planar diode
Authors: Roy Amitava , Menon R. , Mitra S. , Kumar D. D. P. , Kumar Senthil , Sharma Archana , Mittal K. C. , Nagesh K. V. , Chakravarthy D. P.
Published: July 2008

Intense relativistic electron beam generation studies were carried out in a planar diode configuration to investigate the effect of the plasma expansion on the impedance characteristics of the diode. The typical electron beam parameter was 280kV, 18kA, 100ns, with a few hundreds of A∕cm2 current density. The diode voltage and current waveforms were analyzed with the bipolar space-charge limited flow model. The anode and cathode plasma expansion velocities were calculated using the perveance data. The plasma expands at 9.5cm∕μs for 31mm anode-cathode gap and the plasma velocity decreases for smaller gap. It was found that the electron emission is more uniform for 25mm anode-cathode gap as compared to 31mm gap. Effect of a nylon sheet on the anode plate has been studied with respect to the impedance characteristic of the diode. It was found that the diode closes at a faster rate in the presence of nylon sheet on anode. Nylon materials are released into the diode region due to the electron beam bombardment and get deposited on the cathode. This deposition affects the subsequent electron beam generation.
Four-leg Ca0.95Sm0.05MnO3 unileg thermoelectric device
Authors: Lemonnier Sébastien , Goupil Christophe , Noudem Jacques , Guilmeau Emmanuel
Published: July 2008

A prototype of oxide thermoelectric module only composed of n-legs Ca0.95Sm0.05MnO3, so-called unileg device, has been fabricated. The electrical and thermal measurements have been investigated at high temperature in air. In this non conventional configuration, the pellets are thermally connected in parallel, electrically in series, and linked by silver strips. The system has been characterized under large temperature difference (ΔT=360K) using a homemade system, allowing to record simultaneously the electrical and thermal parameters of the working device. An open circuit voltage of 260mV was obtained for a four-leg “unileg” module. The module exhibits an internal resistance of 1.09Ω. The maximum power output for this four-leg device reached 16mW in these working conditions. The manufacturing quality is discussed, according to the electric contact resistance values, and the reliability of the thermoelectric device is reported.
Bismuth-induced dielectric relaxation in the (1−x)La(Mg1∕2Ti1∕2)O3–xBi(Mg1∕2Ti1∕2)O3 perovskite system
Authors: Salak Andrei N. , Ferreira Victor M. , Ribeiro José L. , Vieira Luís G. , Pullar Robert C. , Alford Neil McN.
Published: July 2008

The temperature variation of the dielectric permittivity and loss of the solid solutions (1−x)La(Mg1∕2Ti1∕2)O3–xBi(Mg1∕2Ti1∕2)O3 [(1−x)LMT–xBMT] (0⩽x⩽0.3) measured at radio, microwave, and far infrared frequency ranges has been analyzed in comparison with that observed in other bismuth-containing and bismuth-free perovskite ceramics based on LMT. It has been found that the low temperature dielectric response of the (1−x)LMT–xBMT compositions with x⩾0 is frequency dependent over a wide range from radio to microwave frequencies. The considerable compositional growth of the dielectric permittivity and loss associated with the amount of bismuth in the system was revealed to be not contributed by the lattice polar phonon modes. The effect was suggested to be related to the low-temperature dielectric relaxation process due to a hopping movement of charge carriers in crystallographic A-sites of the perovskite lattice. Particular role of local lattice distortions caused by the anisotropic chemical bonds involving bismuth 6s2 electrons in a localization of hopping charge carriers in perovskites and other oxygen-octahedral compositions is considered. The characteristic features of the Bi-induced dielectric relaxation and those typical of the ferroelectric relaxors are compared and discussed.
Effect of cathode diameter on intense relativistic electron beam generation in the presence of prepulse
Authors: Roy Amitava , Menon R. , Mitra S. , Kumar D. D. P. , Kumar Senthil , Sharma V. K. , Patel Ankur , Sharma Archana , Mittal K. C. , Nagesh K. V. , Chakravarthy D. P.
Published: July 2008

Intense gigawatt relativistic electron beam generation studies were carried out in the presence of prepulse. Electron beams were generated using planar and annular graphite cathodes of various diameters at a fixed 25mm anode-cathode gap. For the planar cathode, the beam parameters obtained are 340keV, 24kA, and 100ns at a 680A∕cm2 current density. With an annular cathode, 346keV, 10kA, and 100ns electron beam could be generated at a 3.4kA∕cm2 current density. The peak electric field in the diode varies from 58to138kV∕cm. A bipolar prepulse voltage has been recorded at the diode for both the cathodes. The amplitude of the negative prepulse voltage varies with the Marx generator voltage but the time duration remains same. The positive prepulse voltage varies both in amplitude and time duration with the Marx generator voltage. Some shot to shot variation in the diode voltage and current were recorded for the annular cathode due to the nonreproducibility of the prepulse generated plasma. It was found that the effect of prepulse is more pronounced in the cathode of larger diameter.
Remote ionization by a short pulse laser beam propagating in the atmosphere
Authors: Yedierler Burak
Published: July 2008

Self-focusing of high power, short laser pulses is considered for the purpose of identifying physical parameters that allow a remotely controllable ionization in the atmosphere. The propagation equation including diffraction, group velocity dispersion, Kerr nonlinearity and bound electrons effects is derived. A Lagrange density describing the propagation equation depending on a general pulse amplitude is presented for a propagation regime in the absence of ionization and plasma defocusing. Lagrange equations for beam parameters are determined and solved for a particular ansatz describing a chirped Gaussian beam with a curvature function. It is demonstrated that nonlinear effects not only cause transverse focusing but also temporally enhance the group velocity dispersion. A mutual interrelation between the pulse power, curvature, and chirp parameters is derived explicitly. Moreover, the location where the pulse self-focuses is addressed within the limits on the propagation distance along which the beam shape and the initial symmetry are preserved. Thus, a complete analytical structure of remote ionization is underlined.
Nonlinear dust acoustic waves in a mixed nonthermal high energy-tail electron distribution
Authors: Younsi Smain , Tribeche Mouloud
Published: July 2008

Large amplitude as well as weakly nonlinear dust acoustic waves in a mixed nonthermal high-energy-tail electron distribution are investigated. The effects of charge variation and electron deviation from Boltzmann distribution on the large amplitude dust acoustic soliton are then considered. The dust charge variation leads to an additional enlargement of the dust acoustic soliton, which is more pronounced as the electrons evolve far away from Maxwell-Boltzmann distribution. Under certain conditions, the dust charge fluctuation may provide an alternate physical mechanism causing anomalous dissipation, the strength of which becomes important and may prevail over that of dispersion as the suprathermal character of the plasma becomes important. The results complement and provide new insights into our previously published results on this problem [K. Aoutou, M. Tribeche, and T. H. Zerguini, Phys. Plasmas 15, 013702 (2008)].
Optical third-order nonlinearity by nanosecond and picosecond pulses in Cu nanoparticles in ion-implanted silica
Authors: Torres-Torres C. , Reyes-Esqueda J. A. , Cheang-Wong J. C. , Crespo-Sosa A. , Rodríguez-Fernández L. , Oliver A.
Published: July 2008

We report a study of the Kerr effect and nonlinear optical absorption in a high-purity silica sample containing Cu nanoparticles prepared by ion implantation. With a vectorial self-diffraction experiment, we measured the tensorial components of the third-order nonlinear optical susceptibility response at 532 nm with pulses of 7 ns and 26 ps. We identified thermal effect as the main mechanism responsible for the nonlinear refraction in the nanosecond regime and electronic polarization for the picosecond regime. We observed saturable optical absorption in both regimes studied. We also measured the ablation threshold for this material, finding that the contribution of the linear optical absorption to the ablation threshold in each case can be different due to the presence of hot electrons.
The effect of La addition on optical transmittance spectra of hydrogenated Mg–La thin films
Authors: Ouyang L. Z. , Qin F. X. , Zhu M. , Huang C. K. , Guo J.
Published: July 2008

This paper reported that the transmission of hydrogenated Mg–La films is influenced by the content of La dissolved in Mg. With the increase in La:Mg atomic ratio, the transmission decreases and the short wavelength limit of the transmission spectra shifts toward the long wavelength side. This phenomenon is well explained by using the Lambert–Beer law according to the band gap change, which was calculated using CASTEP module caused by dissolving of La.
Suppression of hole-mediated ferromagnetism in Ga1−xMnxP by hydrogen
Authors: Bihler C. , Kraus M. , Brandt M. S. , Goennenwein S. T. B. , Opel M. , Scarpulla M. A. , Farshchi R. , Estrada D. M. , Dubon O. D.
Published: July 2008

We report the passivation of the Mn acceptors in Ga1−xMnxP upon exposure to a hydrogen plasma. The as-grown films are nonmetallic and ferromagnetic with a Curie temperature of TC=55 K. After hydrogenation the sample resistivity increases by approximately three orders of magnitude at room temperature and six orders of magnitude at 25 K. Furthermore, the hydrogenated samples are paramagnetic, which is evidenced by a magnetization curve at 5 K that is best described by a Brillouin function with g=2 and J=5/2 expected for Mn atoms in the 3d5 configuration. Upon annealing, partial depassivation and a recovery of ferromagnetism are observed. These observations unambiguously demonstrate that the ferromagnetism in Ga1−xMnxP is carrier-mediated similar to Ga1−xMnxAs.
Giant piezomagnetism, piezocapacitance, and piezoimpedance effects in MnZn ferrite device under hydrostatic pressure
Authors: Zhang N. , Fang X. , Wang Z. L.
Published: July 2008

The effects of hydrostatic pressure on the magnetism, capacitance, and impedance of a manganese zinc ferrite device have been investigated. Giant piezomagnetism, piezocapacitance, and piezoimpedance that are independent of skin effects have been observed simultaneously under a pressure of a few megapascals. With increasing frequency of the current applied across the ferrite device, these pressure effects have been found to undergo a maximum at a frequency below 3kHz. Under a pressure of 6MPa, a piezoimpedance over 60% has been observed for the ferrite devices with permeabilities ranging from 5000 to 15 000. Analysis shows that these pressure effects result from the variation of the interior stress in the ferrite.
Studies of electronic distribution in potassium-doped mats of single-walled carbon nanotubes, double-walled carbon nanotubes, and peapods
Authors: Desai Sharvil , Rivera Jose , Jalilian Romaneh , Hewaparakrama Kapila , Sumanasekera G. U.
Published: July 2008

In this work, we have performed a systematic study of the electrical transport properties (both the resistivity and the thermoelectric power) on bundles of single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), and peapods (derived from the same batch of initial SWNTs) during in situ doping with potassium (donor). The charge transfer effects in K-doping are similar in SWNTs and DWNTs, but drastically different in C60 at SWNTs. An impurity level associated with the chain of C60 in the band gap of the tube with the Fermi level pinned near the top of the valence band, leading to the p-type behavior for the peapod. Significant charge transfer is found to occur only in the case of very low coverage of these nanostructures.
Reduction of Mg segregation in a metalorganic vapor phase epitaxial grown GaN layer by a low-temperature AlN interlayer
Authors: Tomita Kazuyoshi , Itoh Kenji , Ishiguro Osamu , Kachi Tetsu , Sawaki Nobuhiko
Published: July 2008

The redistribution behavior of Mg in a sequentially regrown GaN epilayer on a p-type doped GaN template was studied. All samples in this study were regrown by metalorganic vapor phase epitaxy on the sapphire substrates. A high density and a slow tail of Mg concentration were observed in a nominally undoped layer due to the surface segregation. We found that the insertion of a low-temperature (LT) AlN interlayer was effective to suppress the Mg redistribution in the GaN regrown layer. Analyzing the temperature dependence of the surface segregation, the activation energy of the Mg segregation was estimated to be 0.63eV in GaN and 2.47eV in a LT-AlN layer, respectively.
Kinetic effect on low frequency Alfvén continuum in tokamaks
Authors: Elfimov A. G.
Published: July 2008

Using a quasi-toroidal set of coordinates in plasmas with coaxial circular magnetic surfaces, the Vlasov equation is solved, and dielectric tensor is found for large aspect ratio tokamaks in a low frequency band. Taking into account the q-profile and drift effects, Alfvén wave continuum deformation by geodesic effects is analyzed. It is shown that the Alfvén continuum has a minimum defined by the ion thermal velocity at the rational magnetic surfaces qs=−M∕N, where M and N are the poloidal and toroidal mode numbers, respectively, and the parallel wave number is zero. Low frequency global Alfvén waves are found below the continuum minimum. In hot ion plasmas, the geodesic term changes sign, provoking some deformation of Alfvén velocity by a factor (1+q2)−1∕2, and the continuum minimum disappears.
Modeling the electrical impedance response of ionic polymer transducers
Authors: Farinholt Kevin M. , Leo Donald J.
Published: July 2008

An analytical study is presented that investigates the electrical impedance response of the ionic polymer transducer. Experimental studies have shown that the electromechanical response of these active materials is highly dependent upon internal parameters such as neutralizing counterion, diluent, electrode treatment, as well as environmental factors such as ambient temperature. Further examination has shown that these variations are introduced predominantly through the polymer’s ability to convert voltage into charge migration. This relationship can easily be represented by the polymer’s electrical impedance as measured across the outer electrodes of the transducer. In the first half of this study an analytical model is developed which predicts the time and frequency domain characteristics of the electrical response of the ionic polymer transducer. Transport equations serve as the basis for this model, from which a series of relationships are developed to describe internal potential, internal charge density, as well as surface current. In the second half of this study several analytical studies are presented to understand the impact that internal parameters have on the polymer’s electrical response, while providing a conceptual validation of the model. In addition to the analytical studies several experimental comparisons are made to further validate the model by examining how well the model predicts changes in temperature, viscosity and pretention within the ionic polymer transducer.
Fluorescence characteristics of Tm3+ in different local environments
Authors: Zheng Hairong , Gao Dangli , Zhang Xiangyu , He Enjie , Zhang Xisheng
Published: July 2008

Fluorescence from ions in both the crystal and glass phases was investigated by selective excitation of Tm3+ doped transparent oxyfluoride glass ceramics containing LaF3 nanocrystals. The spectroscopic properties of ions in different local environments were studied. It was found that the glass phase favored blue up-conversion of Tm3+ when a pulsed red light was applied. The most efficient up-conversion was obtained when the excited state absorption was resonant with the excitation.
A first-principles survey of the partitioning behaviors of alloying elements on γ/γ′ interface
Authors: Wang Yun-Jiang , Wang Chong-Yu
Published: July 2008

A first-principles approach is proposed to investigate the partitioning behaviors of the alloying elements Re, Co, and Cr, and the influence of Ru and Ir addition on them. The results show that Re, Co, and Cr all partition strongly to the γ matrix. The Ru addition decreases the γ phase partitioning trend of Re, Co, and Cr. The results are consistent with the early experimental work. Besides Ru, Ir results in Re less strongly partitioning to γ. Our study shows that the influence of Ru (or Ir) on the partitioning characteristics of alloying elements originates from the strong interactions between Ru(Ir)-Re-Ni through the d−d orbitals hybridization.
Large low-field magnetostriction in Fe–W and Fe–Mo alloy single crystals
Authors: Thuanboon Swieng , Garside Gavin , Guruswamy Sivaraman
Published: July 2008

Fe–Mo and F–W alloys can exist as a single bcc terminal solid solution phase with appreciable Mo and W contents. In this work, the influence of Mo and W additions on the magnetostriction coefficient (3∕2)λ100, elastic constants (C11, C12, and C44), and the magnetomechanical coefficient (B1) of alpha-Fe is examined using alpha-phase Fe–Mo and Fe–W alloy single crystals. Single crystals of Fe–xat.% Mo (x=15,17.5,20) and Fe–xat.% W (x=4.4,10) were grown using the vertical Bridgman technique. Magnetostriction measurements were performed using [100]-oriented and [110]-oriented single crystals. Single crystal elastic constants were determined using resonant ultrasound spectroscopy and analysis technique and [100]-oriented single crystal samples. It is shown that large enhancements in magnetostriction and magnetoelastic coupling constants can be obtained with Mo and W additions. On a per atom addition basis, W additions to Fe provide a larger increase in magnetostriction compared to any other non-rare-earth addition that has been examined with the exception of Ga.
Why are time-dependent density functional theory excitations in solids equal to band structure energy gaps for semilocal functionals, and how does nonlocal Hartree–Fock-type exchange introduce excitonic effects?
Authors: Izmaylov Artur F. , Scuseria Gustavo E.
Published: July 2008

We examine the time-dependent density functional theory (TD-DFT) equations for calculating excitation energies in solids with Gaussian orbitals and analytically show that for semilocal functionals, their lowest eigenvalue collapses to the minimum band orbital energy difference. With the introduction of nonlocal Hartree–Fock-type exchange (as in hybrid functionals), this result is no longer valid, and the lowest TD-DFT eigenvalue reflects the appearance of excitonic effects. Previously reported “charge-transfer” problems with semilocal TD-DFT excitations in molecules can be deduced from our analysis by taking the limit to infinite lattice constant.
Metastable phase formation and magnetic properties of the Fe–Nb system studied by atomistic modeling and ion beam mixing
Authors: Tai K. P. , Dai Y. , Liu B. X.
Published: July 2008

With the aid of ab initio calculations, an n-body Fe–Nb embedded-atom potential is first constructed and then applied to study the crystal-to-amorphous phase transition through molecular dynamic simulations. The simulations determine that the glass-forming range of the Fe–Nb system is 18–83 at. % of Nb. In ion beam mixing experiments, five Fe–Nb multilayered films with overall compositions of Fe85Nb15, Fe75Nb25, Fe55Nb45, Fe25Nb75, and Fe15Nb85, respectively, are irradiated by 200 keV xenon ions to doses in the range of (1–7)×1015Xe+/cm2. The result shows that the Fe–Nb metallic glasses can be synthesized within a composition range of 25–75 at. % of Nb, matching reasonably well the theoretical prediction. Moreover, in the Fe55Nb45 sample, a fcc-structured alloy phase with a large lattice constant of a≈0.408 nm was obtained at a dose of 3×1015 Xe+/cm2 and the associated magnetic moment per Fe atom was measured to be 2.41μB. The observed magnetic moment is much greater than the initial value of 1.42μB in the bcc-Fe lattice and can thus serve as evidence confirming the high-spin ferromagnetic state of fcc Fe predicted by ab initio calculations. Interestingly, further irradiation induced phase separation in the Fe55Nb45 sample, i.e., irradiation to a dose of 5×1015 Xe+/cm2 results in the growth of a fractal pattern consisting of Fe72Nb28 nanoclusters embedded in Fe35Nb65 matrix. The formation mechanism of the metastable phases as well as that of the fractal pattern observed in the Fe–Nb system was discussed in terms of the atomic collision theory and the well-known cluster-diffusion-limited-aggregation model.
The formation of quasiregular microstructure in highly undercooled Ni70.2Si29.8 eutectic alloy
Authors: Lu Yiping , Lin Xin , Yang Gencang , Li Junjie , Zhou Yaohe
Published: July 2008

High undercooling (about 392 K) was achieved in bulk eutectic Ni70.2Si29.8 alloy melt using glass fluxing combined with cyclic superheating. Surprisingly, the microstructure of eutectic Ni70.2Si29.8 transits from irregular to quasiregular when the undercooling exceeds 340 K. The morphology transition at large undercooling is analyzed based on the solution entropy of eutectic phases. The forming process of quasiregular microstructure is ascribed to a transition from faceted-faceted to nonfaceted-nonfaceted eutectic concurring with increased undercooling.
Modeling of the gain and temperature in high pressure, ejector type chemical oxygen-iodine lasers and comparison to experiments
Authors: Waichman K. , Barmashenko B. D. , Rosenwaks S.
Published: July 2008

The results of three-dimensional computational fluid dynamics model calculations are compared to available experimental results [V. D. Nikolaev et al., IEEE J. Quantum Electron. 38, 421 (2002)]. It is shown that the model is applicable to high pressure, ejector type chemical oxygen-iodine laser (COIL), reasonably reproducing the measured gain, temperature, static pressure, and gas velocity. A previous model, which included I2(A′Π32u), I2(AΠ31u), and O2(aΔ1g,v) as significant intermediates in the dissociation of I2 [K. Waichman et al., J. Appl. Phys. 102, 013108 (2007)], reproduced the measured gain and temperature of a low pressure supersonic COIL. The previous model is complemented here by adding the effects of turbulence, which play an important role in high pressure COILs.
Excitation of a surface plasma wave over a plasma cylinder by a relativistic electron beam
Authors: Kumar Gagan , Tripathi V. K.
Published: July 2008

A relativistic electron beam propagating in a plasma cylinder excites a surface plasma wave (SPW) via the Cerenkov interaction. The wave frequency decreases with beam velocity. The growth rate, however, initially increases with frequency ω, attains a maximum, and then falls off due to the localization of the SPW near the surface. For typical parameters, maximum growth occurs at ω∕ωP≈0.36, where ωP is the plasma frequency. With the increase in the radius of the thin plasma cylinder, the optimum growth rate increases in magnitude. The annular beam propagating outside the plasma cylinder excites the SPW with larger growth rate for the same beam current and the beam radius rb=1.02a, where a is the radius of the thin plasma cylinder.
Response to “Comment on ‘An alternative analysis of some recent diffusion experiments on the large plasma device’ ” [Phys. Plasmas 15, 074701 (2008)]
Authors: Simon Albert
Published: July 2008

We respond to the issues raised in the comment by Maggs and Carter. Our simple model still elucidates the basic physics involved in their experiment. The key point is that, in their geometry, any estimate of the radial ion-diffusion coefficient requires one to evaluate a very small difference of two large quantities, neither of which can be accurately measured or calculated. We stand by our original conclusion that one cannot, with any confidence, state that Bohm diffusion has been observed in the large plasma device experiment.
Phase collapse caused by blue-light irradiation in a cyanobridged coordination polymer
Authors: Tokoro Hiroko , Ohkoshi Shin-ichi
Published: July 2008

In this work, we report a photoinduced phase transition, light-induced phase collapse, using rubidium manganese hexacyanoferrate, RbI0.43MnII[FeIII(CN)6]0.81⋅3H2O, which does not exhibit a phase transition upon changing the temperature. However, when this material is irradiated with blue light at temperature around 100–200K, the MnII–FeIII phase collapses and the valence isomer MnIII–FeII phase appears. The MnII–FeIII phase is perfectly recovered as the temperature increased. Theoretical analysis suggests that the initial MnII–FeIII phase is a thermodynamically metastable phase, trapped at a local free-energy minimum, while the photogenerated MnIII–FeII phase is the true thermodynamically stable phase below 230K.
Highly ordered arrays of macroscopically long Pb nanobelts with atomic-level controlled thickness and width on Si
Authors: Guan Z. L. , Wu R. , Ning Y. X. , Song C. L. , Tang L. , Hao D. , Ma Xu-Cun , Jia J. F. , Chen X. , Xue Q. K. , Liao Z. M. , Yu D. P.
Published: July 2008

We report growth of ordered arrays of superlong Pb nanobelts using Al decorated Si(111) substrates as a template. By depositing Al at substrate temperature of 650–700°C, each original Si(111) terrace is divided into two distinct strips, a γ-phase strip and a mixed √7×√7 and √3×√3 structure strip. In situ scanning tunneling microscopy observation reveals that Pb atoms preferentially nucleate on the γ-phase strips and form uniform array of nanobelts with a width from 10to100nm and a thickness from 2.3to20nm, which can delicately be controlled by Al coverage and Pb coverage.
Switchable magnetic dipole induced guided vortex motion
Authors: Verellen N. , Silhanek A. V. , Gillijns W. , Moshchalkov V. V. , Metlushko V. , Gozzini F. , Ilic B.
Published: July 2008

We present evidence of magnetically controlled vortex motion in an Al film on top of a periodic array of Permalloy square rings. The resulting magnetic template generates a strongly anisotropic pinning potential landscape for vortices in the superconducting layer. Transport measurements show that this anisotropy is able to confine the flux motion along the high symmetry axes of the square lattice of dipoles. This guided vortex motion can be rerouted by 90° simply changing the dipole orientation or even suppressed by inducing a flux-closure magnetic state with very low stray fields in the rings.
Nanophotonic split-ring resonators as dichroics for molecular spectroscopy
Authors: Clark A. W. , Glidle A. , Cumming D. R. S. , Cooper J. M.
Published: July 2008

We describe the design and fabrication of nanostructured silver split-ring resonators and demonstrate their application as dichroic sensors for multipurpose visible wavelength molecular spectroscopy. By producing arrays of these identical nanostructures, with critical dimensions of 30–150nm, we demonstrate the controllable generation of plasmonic resonances at two common visible laser wavelengths, produced as a consequence of the polarization of the light with respect to structural geometry. We show the application of these devices in surface enhanced Raman spectroscopy, using their dichroic properties to perform molecular sensing of a self-assembled monolayer of 2-mercaptopyridine at both 532 and 633nm.
Hardness of covalent compounds: Roles of metallic component and d valence electrons
Authors: Guo Xiaoju , Li Lei , Liu Zhongyuan , Yu Dongli , He Julong , Liu Riping , Xu Bo , Tian Yongjun , Wang Hui-Tian
Published: July 2008

Based on the detailed analysis of chemical bonds, we present a Vickers hardness expression for the covalency-dominant crystals such as transition-metal carbides and nitrides. Hardness is dependent not only on bond length, bond density, and ionicity of bond [F. M. Gao et al., Phys. Rev. Lett. 91, 015502 (2003)] but also on the metallicity of bond and orbital form in the crystal structure of a compound, and all of these parameters can be determined by first-principles calculations. The calculated hardness using our expression has a good agreement with the experimental values for known monocarbides, mononitrides of transition metals, and cubic Zr3N4 with Th3P4 structure. In addition, we have predicted the Vickers hardness of the recently predicted tetragonal BC3 and tetragonal B2CN, and the recently synthesized pyrite PtN2 and marcasite OsN2. Our method offers one useful technique to search for superhard materials in transition-metal carbides and nitrides.
Figure of merit of quaternary (Sb0.75Bi0.25)2−xInxTe3 single crystals
Authors: Drašar Č. , Hovorková A. , Lošťák P. , Kong H. , Li C.-P. , Uher C.
Published: July 2008

Single crystals of a quaternary system based on (Sb0.75Bi0.25)2Te3 doped with In were prepared using the Bridgman technique. Samples with varying contents of In were characterized by the measurements of electrical conductivity σ⊥c, Hall coefficient RH(B∥c), Seebeck coefficient S(ΔT⊥c), and thermal conductivity κ(ΔT⊥c). The measurements indicate that by incorporating In in (Sb0.75Bi0.25)2Te3 one lowers the concentration of free holes. This effect is explained in terms of a point defect model in the crystal lattice. We also discuss the temperature dependence of the thermoelectric figure of merit Z=σS2∕κ of the samples. It is observed that low concentrations of In atoms in the (Sb0.75Bi0.25)2Te3 crystal lattice result in a substantial increase in the parameter Z in the temperature region 100–300K.
Substitution effect on the thermoelectric properties of p-type half-Heusler compounds: ErNi1−xPdxSb
Authors: Kawano Kenta , Kurosaki Ken , Muta Hiroaki , Yamanaka Shinsuke
Published: July 2008

The authors conducted thermoelectric characterizations on polycrystalline samples of ErNi1−xPdxSb (x=0.25, 0.5, and 0.75) to develop p-type half-Heusler thermoelectric materials. All samples prepared here indicated positive Seebeck coefficient (S) values. Variations of the electrical resistivity (ρ) and the S of ErNi1−xPdxSb with x were examined by collecting the carrier concentration, mobility, and density-of-state effective mass. The thermal conductivities (κ) of ErNi1−xPdxSb were approximately one-half of those of ErNiSb and ErPdSb, mainly due to an alloy scattering effect between Ni and Pd. With the alloying of ErNiSb and ErPdSb, the thermoelectric figure of merit ZT (=S2T∕ρκ) was enhanced; the maximum ZT value was 0.29 at 650K, obtained in the composition ErNi0.5Pd0.5Sb.
A new large radius imaging plate camera for high-resolution and high-throughput synchrotron x-ray powder diffraction by multiexposure method
Authors: Tanaka Masahiko , Katsuya Yoshio , Yamamoto Akiji
Published: July 2008

A new large radius imaging plate diffraction camera for high-resolution and high-throughput synchrotron x-ray powder diffraction by means of multiple exposures has been developed for an insertion device beamline of SPring-8, Japan. The new imaging plate camera consists of a large radius cylindrical shape imaging plate cassette that is 400mm in length and 954.9mm in cylinder radius. The cassette is designed to be mounted on the 2θ arm of the diffractometer of BL15XU in SPring-8. One imaging plate covers 24° and several times of exposure changing the 2θ-setting angle is necessary to obtain whole powder diffraction data up to a high angle region. One pixel of the imaging plate corresponds to 0.003° in 2θ when the readout pixel size is 50μm squares. Separately collected data are translated to 2θ-intensity format and are connected by comparing the peak and background intensity included in the overlapped area. The exposure time is less than 120s for most samples and the readout time is about 3min; thus, the total measurement time for one powder diffraction pattern is less than 20min. The measurement time is the same order as the continuous 2θ-scanning method of the third generation synchrotron powder diffractometer. The angular resolution of the new imaging plate camera was evaluated by comparing the full width at half maximum of the 111 reflection of NBS-Si. The observed angular resolution is not so high as a powder diffractometer with a Si or a Ge analyzer monochromator in the third generation synchrotron facility but higher than a powder diffractometer with a Ge analyzer monochromator at a bending magnet beamline of the second generation synchrotron. The Rietveld analysis of NBS-CeO2 was successfully carried out with the data taken by the new imaging plate camera.
Photovoltaic effect and charge storage in single ZnO nanowires
Authors: Liao Zhi-Min , Xu Jun , Zhang Jing-Min , Yu Da-Peng
Published: July 2008

Asymmetric Schottky barriers between ZnO nanowire and metal electrode have been fabricated at the two ends of the nanowire. An obvious photocurrent generated from the device at zero voltage bias can be switched on/off with quick response by controlling the light irradiation. Moreover, the device can still afford a current at zero bias after switching off light illumination, which is ascribed to the charge storage effect in single ZnO nanowires. The underlying mechanisms related to the photovoltaic effect and charge storage were discussed.
Angular dependent luminescence of individual suspended ZnO nanorods
Authors: Li Wenliang , Gao Min , Cheng Rui , Zhang Xiaoxian , Xie Sishen , Peng Lian-Mao
Published: July 2008

We report angular dependent microphotoluminescence measurements on individual suspended ZnO nanorods attached to sharp metal tips. The luminescence measured along and perpendicular to the axis of the same single nanorod indicates quantitatively that >99% of the near band edge emission can be confined effectively in the nanorods and emitted from the end facets. The radially confined luminescence is dominated by P bands and LO phonon replicas of the free exciton emission and P bands. The measurements along the length of the nanorods show that the confinement is evidently influenced by the surface structure.
Emission properties of high-Q silicon nitride photonic crystal heterostructure cavities
Authors: Barth Michael , Nüsse Nils , Stingl Johannes , Löchel Bernd , Benson Oliver
Published: July 2008

We report on the fabrication and optical characterization of photonic crystal (PC) double-heterostructure cavities made from silicon nitride (SiN). The intrinsic luminescence of the SiN membranes was used as an internal light source in the visible wavelength range (600–700nm) to study the quality factor and polarization properties of the cavity modes. Quality factors of up to 3400 were found experimentally, which represents the highest value reported so far in low-index PCs. These results highlight the role of SiN as a promising material system for PC devices in the visible.
Realization of regular arrays of nanoscale resistive switching blocks in thin films of Nb-doped SrTiO3
Authors: Muenstermann Ruth , Dittmann Regina , Szot Krzysztof , Mi Shaobo , Jia Chun-Lin , Meuffels Paul , Waser Rainer
Published: July 2008

We report on the realization of short-range-ordered arrays of nanoscale resistive switching blocks in epitaxial Nb-doped SrTiO3 thin films. These blocks can be individually addressed by the tip of a conductive tip atomic force microscope and reversibly switched between a high and a low resistance state reaching an Roff to Ron ratio of up to 50. Scanning micrometer-scale areas with an appropriately biased tip, all blocks within the scanned area can be switched between the two resistive states. We suggest a connection between these nanoscale switching blocks and defect-rich nanoclusters which were detected with high resolution transmission electron microscopy.
Effect of indium on phase-change characteristics and local chemical states of In–Ge–Sb–Te alloys
Authors: Shin H. J. , Kang Youn-Seon , Benayad Anass , Kim Ki-Hong , Lee Y. M. , Jung M.-C. , Lee Tae-Yon , Suh Dong-Seok , Kim Kijoon H. P. , Kim CheolKyu , Khang Yoonho
Published: July 2008

We introduce single-phase In–Ge–Sb–Te (IGST) quaternary thin film (fcc structure when crystallized) deposited by cosputtering from Ge2Sb2Te5(GST) and In3Sb1Te2 targets. This film, compared with the GST ternary system, provides a significant increase of amorphous-to-crystalline transformation temperature. High-resolution x-ray photoelectron spectroscopy (HRXPS) revealed that, with increasing In amounts, the Sb 4d and Ge 3d core peaks shift toward lower binding energies (BEs), with negligible changes in spectral linewidths, whereas the In 4d and Te 4d core peaks show insignificant changes in BEs. HRXPS interpretation suggests that the Na site in IGST can be occupied by Te, Sb, In, and vacancy, whereas in GST it is occupied only by Te.
Cantilevers with integrated sensor for time-resolved force measurement in tapping-mode atomic force microscopy
Authors: Sarioglu A. F. , Solgaard O.
Published: July 2008

We present a micromachined cantilever with an integrated high-bandwidth resonator for direct measurement of tip-sample interaction forces in tapping-mode atomic force microscopy. Force measurements are achieved by a diffraction grating that serves as a differential displacement sensor for the tip motion relative to the cantilever body. Time-resolved tip-sample interaction force measurement is demonstrated on a silicon sample following calibration of the probe structure. By using lock-in detection, the harmonics of periodic tip-sample interaction have been utilized to obtain high-contrast, material specific images. The harmonic images of patterned silicon/silicon nitride control samples and triblock copolymers are presented.
Circulating blood cells function as a surveillance system for damaged tissue in
Drosophila
larvae
Authors: Babcock Daniel T. , Brock Amanda R. , Fish Greg S. , Wang Yan , Perrin Laurent , Krasnow Mark A. , Galko Michael J.
Published: July 2008

Insects have an open circulatory system in which the heart pumps blood (hemolymph) into the body cavity, where it directly bathes the internal organs and epidermis. The blood contains free and tissue-bound immune cells that function in the inflammatory response. Here, we use live imaging of transgenic
Drosophila
larvae with fluorescently labeled blood cells (hemocytes) to investigate the circulatory dynamics of larval blood cells and their response to tissue injury. We find that, under normal conditions, the free cells rapidly circulate, whereas the tissue-bound cells are sessile. After epidermal wounding, tissue-bound cells around the wound site remain sessile and unresponsive, whereas circulating cells are rapidly recruited to the site of damage by adhesive capture. After capture, these cells distribute across the wound, appear phagocytically active, and are subsequently released back into circulation by the healing epidermis. The results demonstrate that circulating cells function as a surveillance system that monitors larval tissues for damage, and that adhesive capture, an important mechanism of recruitment of circulating cells to inflammatory sites in vertebrates, is shared by insects and vertebrates despite the vastly different architectures of their circulatory systems.
Modular networks and cumulative impact of lateral transfer in prokaryote genome evolution
Authors: Dagan Tal , Artzy-Randrup Yael , Martin William
Published: July 2008

Lateral gene transfer is an important mechanism of natural variation among prokaryotes, but the significance of its quantitative contribution to genome evolution is debated. Here, we report networks that capture both vertical and lateral components of evolutionary history among 539,723 genes distributed across 181 sequenced prokaryotic genomes. Partitioning of these networks by an eigenspectrum analysis identifies community structure in prokaryotic gene-sharing networks, the modules of which do not correspond to a strictly hierarchical prokaryotic classification. Our results indicate that, on average, at least 81 ± 15% of the genes in each genome studied were involved in lateral gene transfer at some point in their history, even though they can be vertically inherited after acquisition, uncovering a substantial cumulative effect of lateral gene transfer on longer evolutionary time scales.
The RNA-binding proteins HYL1 and SE promote accurate
in vitro
processing of pri-miRNA by DCL1
Authors: Dong Zhicheng , Han Meng-Hsuan , Fedoroff Nina
Published: July 2008

The results of genetic studies in
Arabidopsis
indicate that three proteins, the RNase III DICER-Like1 (DCL1), the dsRNA-binding protein HYPONASTIC LEAVES1 (HYL1), and the C2H2 Zn-finger protein SERRATE (SE), are required for the accurate processing of microRNA (miRNA) precursors in the plant cell nucleus. To elucidate the biochemical mechanism of miRNA processing, we developed an
in vitro
miRNA processing assay using purified recombinant proteins. We find that DCL1 alone releases 21-nt short RNAs from dsRNA as well as synthetic miR167b precursor RNAs. However, correctly processed miRNAs constitute a minority of the cleavage products. We show that recombinant HYL1 and SE proteins accelerate the rate of DCL1-mediated cleavage of pre- and pri-miR167b substrates and promote accurate processing.