bluuebunny/crossref_metadata_2025 huggingface dataset:
Ionization potentials of small lithium clusters (Lin) and hydrogenated lithium clusters (LinH)
Authors: Wheeler Steven E. , Schaefer Henry F.
Published: May 2005

We present accurate ionization potentials (IPs) for small lithium clusters and hydrogenated lithium clusters (n=1–4), computed using coupled-cluster singles and doubles theory augmented with a perturbative correction for connected triple excitations [CCSD(T)] with the correlation-consistent weighted core-valence quadruple-ζ basis set (cc-pwCVQZ). In some cases the full CCSDT method has been used. Comparison of computed binding energies with experiment for the pure cationic lithium clusters reveals excellent agreement, demonstrating that previous discrepancies between computed and experimentally derived atomization energies for the corresponding neutral clusters are due to the use of an inaccurate experimental IP for Li4. The experimental IP for Li4 falls 0.43eV below our theoretical adiabatic value of 4.74eV, which should be a lower bound to the measured IP. Our recommended zero-point corrected adiabatic IPs for Li, Li2, Li3, Li4, LiH, Li2H, Li3H, and Li4H are 5.39, 5.14, 4.11, 4.74, 7.69, 3.98, 4.69, and 4.05eV, respectively. Zero-point vibrationally corrected CCSD(T) atomization energies per atom for Li2+, Li3+, Li4+, LiH+, Li2H+, Li3H+, and Li4H+ are 0.64, 0.96, 0.90, 0.056, 1.62, 1.40, and 1.40eV, respectively.
Computer simulation study of metastable ice VII and amorphous phases obtained by its melting
Authors: Slovák Jan , Tanaka Hideki
Published: May 2005

Molecular dynamics simulations of metastable ice VII and cubic ice Ic are carried out in order to examine (1) the ability of commonly used water interaction potentials to reproduce the properties of ices, and (2) the possibility of generating low-density amorphous (LDA) structures by heating ice VII, which is known to transform to LDA at ∼135K at normal pressure [S. Klotz, J. M. Besson, G. Hamel, R. J. Nelmes, J. S. Loveday, and W. G. Marshall, Nature (London) 398, 681 (1999)]. We test four simple empirical interaction potentials of water: TIP4P [W. L. Jorgensen, J. Chandrasekhar, J. D. Madura, R. W. Impey, and M. L. Klein, J. Chem. Phys. 79, 926 (1983)], SPC/E [H. J. C. Berendsen, J. R. Grigera, and T. P. Straatsma, J. Phys. Chem. B 91, 6269 (1987)], TIP5P [M. W. Mahoney and W. L. Jorgensen, J. Chem. Phys. 112, 8910 (2000)], and ST2 [F. H. Stillinger and A. Rahman, J. Chem. Phys. 60, 1545 (1974)]. We have found that TIP5P ice VII melts at 210 K, TIP4P at 90 K, and SPC/E at 70 K. Only TIP5P water after transition has a structure similar to that of LDA. TIP4P and SPC/E have almost identical structures, dissimilar to any known water or amorphous phases, but upon heating both slowly evolve towards LDA-like structure. ST2 ice VII is remarkably stable up to 430 K. TIP4P and SPC/E predict correctly the cubic ice collapse into a high-density amorphous ice (HDA) at ∼1GPa whereas TIP5P remains stable up to ∼5GPa. The densities of the simulated ice phases differ significantly, depending on the potential used, and are generally higher than experimental values. The importance of proper treatment of long-range electrostatic interactions is also discussed.
Gas-induced variation in the dielectric properties of carbon nanotube bundles for selective sensing
Authors: Picaud F. , Langlet R. , Arab M. , Devel M. , Girardet C. , Natarajan S. , Chopra S. , Rao A. M.
Published: May 2005

There is an increasing demand for robust, miniaturized sensors with ppm or parts per 109(ppb) sensing capability, and high selectivity to different chemical or biological species. Here we show that trace amounts (ppb) of gases or organic solvent vapors can be detected with high selectivity and sensitivity using single-walled carbon nanotube bundles in a resonator configuration. The enhanced sensing properties result from a change in the effective dielectric properties of the resonator when exposed to different gas environments. A theoretical model is described which computes resonant frequency shifts that are in remarkable agreement with corresponding experimental shifts exhibited by the resonator when exposed to different gas molecules. This work demonstrates a gas-sensing platform with superior sensitivity and selectivity for gas detection, and presents advantages in terms of portability and recovery time. In particular, the sensing platform does not require functionalized carbon nanotubes to enhance specificity, or wire connection to the nanotubes making it attractive for remote sensor technology.
Onset and saturation of guide-field magnetic reconnection
Authors: Pritchett P. L.
Published: May 2005

The onset and saturation of collisionless magnetic reconnection in the presence of a guide field are investigated using two-dimensional particle-in-cell simulations in which the reconnection evolves out of the initial thermal noise in the current sheet and in which the resolution is sufficient to resolve the electron singular layer. The simulations show that reconnection does not abate when the island width exceeds either the electron singular layer or the initial current sheet width. Instead, reconnection proceeds through an explosive stage which appears to be limited only by the spatial size of the system. The guide-field reconnection dynamics is dominated by the formation of an asymmetric configuration with a deep density cavity along one pair of separatrix arms. In this cavity an electron beam feature is formed which excites the Buneman instability. Near the X line the reconnection electric field is supported by a combination of quasiviscous and bulk inertia effects for the electrons. Around the island perimeter, intense Debye-scale, predominantly perpendicular, electric field structures are formed.
Exact orbital motion theory of the shielding potential around an emitting, spherical body
Authors: Delzanno G. L. , Bruno A. , Sorasio G. , Lapenta G.
Published: May 2005

A kinetic theory for the equilibrium of an unmagnetized plasma consisting of electrons and ions surrounding a spherical body emitting electrons (due to thermionic emission, photoemission, or secondary emission) is presented. The theory is valid for positively charged bodies, neglects collisions of the plasma particles, and is formulated for profiles of the shielding potential presenting an attractive well. Particle-in-cell simulations are shown to be in good agreement with the theory. An approximated criterion is derived to determine the presence of the potential well.
Distorted waves for the study of dispersion
Authors: Pal Barnana , Raychaudhuri Santwana , Kawai Yoshinobu
Published: May 2005

A Fourier transform computational method for the study of dispersion causing distortion of waves in general is presented in this paper. The method is employed for the first time to determine the propagation parameters for ion-acoustic waves produced in a double plasma device. The dispersion characteristics obtained for this system are found to be in good agreement with the theoretically predicted dispersion relation.
Simulations of oscillatory convection in He3–He4 mixtures in moderate aspect ratio containers
Authors: Batiste Oriol , Knobloch Edgar
Published: May 2005

Simulations of He3–He4 mixtures with negative separation ratios in two-dimensional containers with realistic boundary conditions and moderately large aspect ratio Γ are described. The system exhibits a large variety of states with complex time dependence including intermittent wave localization and chaotic “repeated transients.” Steady but localized states are also found. Particular attention is paid to the transitions that occur for (R−Rc)∕Rc≈Γ−2, where R is the Rayleigh number and Rc its critical value for the primary instability, in order to clarify the gradual transition from a small number of active degrees of freedom [(R−Rc)∕Rc⪡Γ−2] to many active degrees of freedom [(R−Rc)∕Rc⪢Γ−2].
Transition from flute modes to drift waves in a magnetized plasma column
Authors: Brochard F. , Gravier E. , Bonhomme G.
Published: May 2005

Recent experiments performed on the low β plasma device Mirabelle [T. Pierre, G. Leclert, and F. Braun, Rev. Sci. Instrum. 58, 6 (1987)] using a limiter have shown that transitions between various gradient driven instabilities occurred on increasing the magnetic field strength. New thorough measurements allow to identify unambiguously three instability regimes. At low magnetic field the strong E×B velocity shear drives a Kelvin–Helmholtz instability, whereas at high magnetic field drift waves are only observed. A centrifugal (Rayleigh–Taylor) instability is also observed in between when the E×B velocity is shearless and strong enough. A close connection is made between the ratio ρs∕L⊥ of the drift parameter to the radial density gradient length and each instability regime.
Plasma sputtering system for deposition of thin film combinatorial libraries
Authors: Cooper James S. , Zhang Guanghai , McGinn Paul J.
Published: May 2005

The design of a plasma sputtering system for the deposition of combinatorial libraries is described. A rotating carousel is used to position shadow masks between the targets and the substrate. Multilayer films are built up by depositing sequentially through various masks. Postdeposition annealing is used to promote interdiffusion of the layered structures. Either discrete or compositional gradient libraries can be deposited in this system. Samples appropriate for characterization with a scanning electrochemical microscope or a multichannel microelectrode array system can be produced. The properties of some deposited Pt–Ru films for fuel cell applications are described.
Fast ignition hot spot break-even scaling
Authors: Slutz S. A. , Vesey R. A.
Published: May 2005

A series of numerical simulations have been performed to determine scaling laws for fast ignition break even of a hot spot formed by energetic particles created by a short pulse laser. Hot spot break even is defined to be when the fusion yield is equal to the total energy deposited in the hot spot through both the initial compression and the subsequent heating. In these simulations, only a small portion of a previously compressed mass of deuterium–tritium fuel is heated on a short time scale, i.e., the hot spot is tamped by the cold dense fuel which surrounds it. The hot spot tamping reduces the miminum energy required to obtain break even as compared to the situation where the entire fuel mass is heated, as was assumed in a previous study [S. A. Slutz, R. A. Vesey, I. Shoemaker, T. A. Mehlhorn, and K. Cochrane, Phys. Plasmas 7, 3483 (2004)]. The minimum energy required to obtain hot spot break even is given approximately by the scaling law ET=7.5(ρ∕100)−1.87kJ for tamped hot spots, as compared to the previously reported scaling of EUT=15.3(ρ∕100)−1.5kJ for untamped hotspots. The size of the compressed fuel mass and the focusability of the particles generated by the short pulse laser determines which scaling law to use for an experiment designed to achieve hot spot break even.
Zirconia-germanium interface photoemission spectroscopy using synchrotron radiation
Authors: Chui Chi On , Lee Dong-Ick , Singh Andy A. , Pianetta Piero A. , Saraswat Krishna C.
Published: May 2005

An ultrathin zirconia gate dielectric had been successfully incorporated into germanium metal-oxide-semiconductor (MOS) devices demonstrating very high-permittivity gate stacks with no apparent interfacial layer. In this study, synchrotron-radiation photoemission spectroscopy has been applied on the same gate stack to identify and quantify the presence of any interfacial germanium suboxide layer. By taking progressive core-level spectra during the layer-by-layer removal of the zirconia film, an oxidized germanium layer with submonolayer thickness was found, possibly arising from an interfacial Zr–O–Ge bonding configuration. In addition, the offsets in the valence-band spectra were also monitored and the energy-band diagram of the zirconia–germanium heterostructure was constructed. Compared to high-κ gate stacks on Si, the thinner interfacial layer and larger conduction-band offset in high-κ gate stacks on Ge suggest better scalability towards an ultimately higher MOS gate capacitance.
D
−
centers in intracenter Si:P lasers
Authors: Zhukavin R. Kh. , Pavlov S. G. , Kovalevsky K. A. , Hübers H.-W. , Riemann H. , Shastin V. N.
Published: May 2005

The terahertz Si:P laser is based on the 2p0→1s(T2) transition of neutral phosphorus donors D0 that are photoionized by radiation from a CO2 laser. The manifestation of negatively charged D− donor centers has been studied. The population of D− centers as well as D0 donor states are calculated and the amplification provided by D0 centers is compared with the absorption by D− centers. The small signal gain and laser threshold have been measured for a set of Si:P lasers with different degrees of compensation (doping by neutron transmutation). It is shown that absorption by D− centers terminates the laser action in Si:P lasers with small compensation (K<1%) for pump intensities less than 1kWcm−2. At higher excitation levels (>10kWcm−2), or for larger compensation, absorption by D− centers becomes negligible.
Response to “Comment on ‘Variational principles for stationary one- and two-fluid equilibria of axisymmetric laboratory and astrophysical plasmas’ ” [Phys. Plasmas 12, 064701 (2005)]
Authors: Goedbloed J. P.
Published: May 2005

Contrary to the Comment by McClements and Thyagaraja that the two-fluid equations for stationary axisymmetric equilibria are easier to deal with numerically than the corresponding ideal magnetohydrodynamics (MHD) equations, since they resolve the Alfvén singularity of the latter whereas transonic transitions do not create substantial numerical difficulties, the opposite proposition is maintained. The numerical solution of the single (MHD) or two (two-fluid) Bernoulli equations already eliminates the Alfvén singularity, but it presents major complications (such as the possible nonexistence, multiplicity, and hyperbolicity of the solutions) in the construction of stationary equilibria that are accurate enough to permit spectral analysis of the waves and instabilities of those equilibria. Furthermore, it is shown that imposing charge neutrality on the two-fluid equations not only obscures the solution procedure of the two independent Bernoulli equations but also eliminates the possibility of a self-consistent description of the charge imbalances that occur in rotating and gravitating astrophysical plasmas, such as Goldreich–Julian charges in magnetospheres of pulsars and massive black holes.
Distribution of defects induced in fused silica by ultraviolet laser pulses before and after treatment with a CO2 laser
Authors: Stevens-Kalceff Marion A. , Wong Joe
Published: May 2005

The depth distribution of ultraviolet laser irradiation-induced defects in fused silica has been determined using cathodoluminescence (CL) microanalysis. CL emissions have been observed at 1.9, 2.2, 2.7, and 4.4 eV. In addition, following a CO2 laser treatment for damage mitigation, an emission at 3.2 eV is also observed. The CL emissions have been identified with the nonbridging oxygen hole center, the self-trapped exciton, the oxygen-deficient center, and the aluminum impurity center. The spatially resolved CL data are consistent with the damage initiation at the exit surface. The concentration of 355-nm laser-induced defects is greatest at the surface and monotonically decays to preirradiation levels at ∼10-μm depth below the surface. The CO2 processing reduces the defect concentration and spatial distribution to a maximum depth of ∼6μm, confirming significant damage mitigation.
Extension of geodesic acoustic mode theory to helical systems
Authors: Watari T. , Hamada Y. , Fujisawa A. , Toi K. , Itoh K.
Published: May 2005

The present paper extends the theory of geodesic acoustic mode (GAM) oscillation, which so far has been applied to tokamaks, to helical systems. By using drift kinetic equations for three-dimensional equilibriums, a generalized dispersion relation is obtained including Landau damping. The oscillation frequency is obtained in terms of the squared sum of Fourier components of the magnetic field intensity expressed by means of magnetic flux coordinates. An analytic form of the collisionless damping rate of GAM is obtained by solving the dispersion relation perturbatively. It is found that the GAM frequency is higher in helical systems than in tokamaks and that damping rate is enhanced in multi-helicity magnetic configurations. However, damping rates are predicted to be small if the temperature of electrons is higher than that of ions.
High-pass filtered eddy-viscosity models for large-eddy simulations of transitional and turbulent flow
Authors: Stolz S. , Schlatter P. , Kleiser L.
Published: May 2005

Classical fixed-coefficient eddy-viscosity models for large-eddy simulations (LES), e.g., the Smagorinsky [Mon. Weather Rev. 93, 99 (1963)] and the structure-function model [Métais and Lesieur, J. Fluid Mech. 239, 157 (1992)], have deficiencies with accurately describing laminar flow regions and the viscous sublayer of near-wall turbulence. This is mainly due to unphysically large model contributions in such flow regions and is one main reason for the difficulty with correctly predicting laminar-turbulent transition using such models. For transitional flows, subgrid-scale (SGS) models must be able to properly deal with at least the two limits of the laminar and the turbulent fluid state. The dynamic Smagorinsky model [Germano et al., Phys. Fluids A 3, 1760 (1991)] alleviates this problem by dynamically computing a small, but not necessarily vanishing, value for the model coefficient in laminar regions and in the vicinity of the wall. In this contribution we analyze high-pass filtered (HPF) eddy-viscosity models which were proposed recently and independently by Vreman [Phys. Fluids 15, L61 (2003)] and Stolz et al. [Direct and Large-Eddy Simulation V (Kluwer, Dordrecht, 2004), pp. 81–88]. We investigate high-pass filtering suitable for such HPF eddy-viscosity models, e.g., the Smagorinsky or the (filtered) structure-function model. Furthermore, we suggest suitable high-pass filters and examine the influence of different high-pass filters on the results of LES of transitional and turbulent incompressible channel flow. Except for the filter shape, the cutoff wavenumber of the high-pass filter is the only parameter besides the eddy-viscosity model coefficient, and its influence can be minimized by a proposed adaptation of the model coefficient. We find that high-pass filtering employed to the computational quantities prior to the calculation of the eddy-viscosity and strain rate in the SGS model significantly improves the quality of the prediction of transitional and turbulent flows without using any ad-hoc adaptation or dynamic procedure. Of particular importance is that the sensitivity of the results to the model coefficient is considerably reduced by the high-pass filtering. Furthermore, the proposed high-pass filters enable the computation of the structure function in the filtered or HPF structure-function models in all spatial directions also for inhomogeneous flows and on non-equidistant grids, removing the arbitrariness of a special treatment of selected (e.g., wall-normal) directions. Simulation results are presented for incompressible turbulent channel flow at Reynolds numbers Reτ (based on the channel half-width and the friction velocity) of 180 and 590 and for forced laminar-turbulent transition in a plane channel, demonstrating the effectiveness of the proposed approach. The results are compared to data of direct numerical simulations and to data obtained using the dynamic Smagorinsky model with different test filters.
Structural trends interpretation of the metal-to-semiconductor transition in deformed carbon nanotubes
Authors: Lu Jun-Qiang , Wu Jian , Duan Wenhui , Gu Bing-Lin , Johnson H. T.
Published: May 2005

Two mechanisms that drive metal-to-semiconductor transitions in single-walled carbon nanotubes are theoretically analyzed with a tight-binding model. By considering the structural trends, the results demonstrate that metal-to-semiconductor transitions can be induced more readily in metallic zigzag nanotubes than in armchair nanotubes. Furthermore, it is shown that both mechanisms have the effect of making the two originally equivalent sublattices physically distinguishable.
Experimental verification of the dielectric constant of a magnetized rotating plasma
Authors: Teodorescu C. , Ellis R. F. , Case A. , Cothran C. , Hassam A. , Lunsford R. , Messer S.
Published: May 2005

Direct measurements confirm that the magnetized plasma perpendicular dielectric constant has a linear dependence on the plasma density for fixed magnetic field, as predicted by magnetohydrodynamic (MHD) theory. In experiments performed on the Maryland Centrifugal Experiment (MCX) [R. F. Ellis, A. B. Hassam, S. Messer, and B. R. Osborn, Phys. Plasmas, 8, 2057 (2001)], line-averaged hydrogen plasma electron density is measured using a Mach–Zehnder interferometer. For small rotational Alfven Mach numbers, the measured size of the perpendicular plasma dielectric constant is also in agreement with MHD theory. Plasma density in the range of (1–8)×1020m−3 and relative perpendicular plasma dielectric constant of the order of 106 are measured.
An exact solution of the Grad–Shafranov–Helmhotz equation with central current density reversal
Authors: Wang Shaojie , Yu Jun
Published: May 2005

With the eigenvalue problem solved in the cylindrical coordinate system with a rectangular cross section, an exact analytical solution of the Grad–Shafranov–Helmhotz equation proposed by S. Wang [Phys. Rev. Lett. 93, 155007 (2004)] is found. The exact solution can describe a variety of equilibrium configurations including the current reversal equilibrium configurations, and it is valid for arbitrary aspect ratio.
A novel feedback algorithm for simulating controlled dynamics and confinement in the advanced reversed-field pinch
Authors: Dahlin J.-E. , Scheffel J.
Published: May 2005

In the advanced reversed-field pinch (RFP), the current density profile is externally controlled to diminish tearing instabilities. Thus the scaling of energy confinement time with plasma current and density is improved substantially as compared to the conventional RFP. This may be numerically simulated by introducing an ad hoc electric field, adjusted to generate a tearing mode stable parallel current density profile. In the present work a current profile control algorithm, based on feedback of the fluctuating electric field in Ohm’s law, is introduced into the resistive magnetohydrodynamic code DEBSP [D. D. Schnack and D. C. Baxter, J. Comput. Phys. 55, 485 (1984); D. D. Schnack, D. C. Barnes, Z. Mikic, D. S. Marneal, E. J. Caramana, and R. A. Nebel, Comput. Phys. Commun. 43, 17 (1986)]. The resulting radial magnetic field is decreased considerably, causing an increase in energy confinement time and poloidal β. It is found that the parallel current density profile spontaneously becomes hollow, and that a formation, being related to persisting resistive g modes, appears close to the reversal surface.
Drag reduction in a flat-plate boundary layer flow by polymer additives
Authors: Yang Shu-Qing , Dou G.
Published: May 2005

This paper presents a theoretical study on the velocity distribution and the friction factor of boundary layer flows with polymer additives starting from the concept of “stress deficit.” A novel method of order of magnitude analysis is developed, which converts the governing equations of boundary layer flow into a solvable ordinary differential equation, thus the total shear stress distribution is obtained, then the formulas for the mean velocity profiles and the friction factor for a boundary layer flow are derived after introducing appropriate expressions for the “effective viscosity” and the thickness of viscous sublayer. The derived velocity equation is able to depict the velocity from a solid wall to the outer edge of boundary layer with or without polymer additives using only one fitted parameter D* that is a function of polymer species, its concentration, and Reynolds number. By integrating the velocity profiles, the friction factor and the thickness of boundary layer development are obtained. Experimental data agree well with the theoretical results.
Phase states of nanocrystalline ferroelectric ceramics and their dielectric properties
Authors: Zembilgotov A. G. , Pertsev N. A. , Waser R.
Published: May 2005

Using a nonlinear thermodynamic theory, we describe equilibrium polarization states and the macroscopic dielectric response of nanocrystalline ferroelectric ceramics with single-domain grains. The elastic clamping of individual crystallites by the surrounding material is explicitly taken into account via the introduction of a specific thermodynamic potential. Aggregate material properties are calculated with the aid of an iterative procedure based on the method of effective medium. The numerical calculations, performed for unpolarized BaTiO3 and Pb(Zr1−xTix)O3 ceramics, demonstrate that the equilibrium phase states of nanocrystalline ceramics may differ drastically from those of single crystals and coarse-grained materials. Remarkably, the theory predicts the coexistence of rhombohedral and tetragonal crystallites in nanocrystalline Pb(Zr1−xTix)O3 ceramics in a wide range of compositions and temperatures. For BaTiO3 ceramics, a mixture of rhombohedral and orthorhombic crystallites is found to be the energetically most favorable state at room temperature. The calculations also show that the dielectric properties of nanocrystalline ferroelectric ceramics may be very different from those of conventional materials due to the elastic clamping of single-domain crystallites.
Investigation of fluidic assembly of nanowires using a droplet inside microchannels
Authors: Salalha Wael , Zussman Eyal
Published: May 2005

Nanowires are common building blocks for the bottom-up assembly of electronic and photonic devices. A significant challenge is to introduce a single nanowire into an oriented assembly in order to express its unique anisotropic properties or to fabricate a nanodevice. In this work we focused on the development of a micrometer length scale approach, based on a fluidic method for alignment and assembling of nanowires. The alignment is achieved by manipulating a droplet composed of a dilute nanowire suspension by creating thermocapillary motion inside a microchannel. Our purpose is to explore the nanowires’ alignment mechanism in the middle region between the droplet’s front and rear menisci, and their interaction with the free surface and the contact lines. Experimental results show that nanowires which are found in the middle region of the droplet are generally aligned with the flow direction. Nanowires which reach the front meniscus move together with the displacing fluid which undergoes a “rolling” type motion, and are finally adsorbed to the surface of the microchannel. The adsorbed nanowires were found in most cases to align with the droplet’s flow direction. However, in certain cases nanowires may become reoriented by the passage of the rear-contact line.
Particle simulations with a generalized gyrokinetic solver
Authors: Mishchenko Alexey , Könies Axel , Hatzky Roman
Published: May 2005

This paper presents a generalized gyrokinetic solver which can be used for all perpendicular wavelengths of interest and allows to include the nonlinear gyrokinetic polarization density in the simulations. The polarization density, being an integral over the phase space is calculated using “numerical particles” (not to be confused with the marker particles which are used in the charge assignment) and finite elements. Integrals over the gyroangle are calculated using an N-point approximation. The accuracy requirements on the number of the gyropoints and numerical particles are discussed. The linear part of the solver has been implemented numerically and benchmarked with the slab dispersion relation for both the ion temperature gradient driven (ITG) mode and the electron temperature gradient driven (ETG) mode. Additionally, linear ITG and ETG modes are considered in a two-dimensional bumpy pinch configuration.
Turbulence and intermittent transport at the boundary of magnetized plasmas
Authors: Garcia O. E. , Naulin V. , Nielsen A. H. , Juul Rasmussen J.
Published: May 2005

Numerical fluid simulations of interchange turbulence for geometry and parameters relevant to the boundary region of magnetically confined plasmas are shown to result in intermittent transport qualitatively similar to recent experimental measurements. The two-dimensional simulation domain features a forcing region with spatially localized sources of particles and heat outside which losses due to the motion along open magnetic-field lines dominate, corresponding to the edge region and the scrape-off layer, respectively. Turbulent states reveal intermittent eruptions of hot plasma from the edge region, propagating radially far into the scrape-off layer in the form of field-aligned filaments, or blobs. This results in positively skewed and flattened single-point probability distribution functions of particle density and temperature, reflecting the frequent appearance of large fluctuations. The conditional fluctuation wave forms and transport statistics are also in a good agreement with those derived from the experiments. Associated with the turbulence bursts are relaxation oscillations in the particle and heat confinements as well as in the kinetic energy of the sheared poloidal flows. The formation of blob structures is thus related to profile variations, which are here triggered in a quasiperiodic manner by a global dynamical regulation due to the self-sustained sheared flows.
Piezoelectric properties of (K0.5Na0.5)(Nb1−xTax)O3−K5.4CuTa10O29 ceramics
Authors: Matsubara M. , Kikuta K. , Hirano S.
Published: May 2005

( K 0.5 Na 0.5 ) ( Nb 1 − x Ta x ) O 3  (KNNT)-based ceramics have been synthesized via a solid-state reaction. In this study, KNNT-based ceramics were sintered at atmospheric pressure by adding small amounts of sintering aid [0.38mol% K5.4Cu1.3Ta10O29]. The (K0.5Na0.5)NbO3 (KNN) ceramics which synthesized by using the K5.4Cu1.3Ta10O29 showed “hard” piezoelectric characteristics such as a high mechanical quality factor (Qm=1300) and low tanδ (0.4%). The quantitative effects of Ta on the electrical properties of (K0.5Na0.5)(Nb1−xTax)O3–K5.4Cu1.3Ta10O29 ceramics were also examined. Ta substitution provides “soft” piezoelectric characteristics and a large electrostrictive effect for KNN, which resulted in an improvement in kp, εr, strain, and d33 of KNNT ceramics depending upon the Ta content. Especially, (K0.5Na0.5)(Nb0.7Ta0.3)O3 showed the maximum strain and d33 values of 0.11% (at 40kV∕cm) and 270pm∕V (at 30–40kV∕cm), respectively. This strain level is comparable to that of hard Pb(Zr,Ti)O3 ceramics.
Development of a measurement system for nitrate radical and dinitrogen pentoxide using a thermal conversion/laser-induced fluorescence technique
Authors: Matsumoto Jun , Kosugi Naohiro , Imai Hidekazu , Kajii Yoshizumi
Published: May 2005

An instrument for measuring atmospheric nitrate radical (NO3) and dinitrogen pentoxide (N2O5) has been developed by a thermal conversion/laser-induced fluorescence (TC/LIF) technique. N2O5 is thermally decomposed and converted to NO3, which is measured by laser-induced fluorescence. In situ, fast-response, sensitive measurement of NO3∕N2O5 is expected by use of LIF. In detecting NO3, dual-wavelength excitation at 622.96 and 618.81nm was adopted to remove potential interference and to guarantee high selectivity. A high-power dye laser system was used as the source of excitation light. To measure ambient air directly, the NO3 detection cell was placed on the rooftop. The laser beam was guided by an optical fiber into the excitation cell. Transmittance of the laser beam was 80% for a 10m long fiber. To calibrate the instrument, the series of thermal decomposition of N2O5 and the gas phase titration of NO3 by NO were conducted. NO3 reduction by adding NO was also applied to determine accurately the zero points of the detector. After optimization of conditions such as gate timing in photon counting and the settings of the N2O5 converter, the present detection limits of NO3 and N2O5 were determined to be 4 and 6pptv, respectively, for the integration time of 10min (signal-to-noise ratio=1). It was confirmed that the interference of NO2 on N2O5 detection is negligible, but can be significant for NO3 measurement when NO2 concentration is extremely high (>100ppbv). Measurement of N2O5 in ambient air was made in the urban area of Tokyo, Japan. Observed data demonstrated the capacity of the TC/LIF instrument with a powerful dye laser and a single-path excitation cell for ambient measurements. In this article, we focus on the instrumentation and characterization.
Niobium titanium nitride-based superconductor-insulator-superconductor mixers for low-noise terahertz receivers
Authors: Jackson B. D. , de Lange G. , Zijlstra T. , Kroug M. , Klapwijk T. M. , Stern J. A.
Published: May 2005

Integrating NbTiN-based microstrip tuning circuits with traditional Nb superconductor-insulator-superconductor (SIS) junctions enables the low-noise operation regime of SIS mixers to be extended from below 0.7to1.15THz. In particular, mixers incorporating a NbTiN∕SiO2∕NbTiN microstrip tuning circuit offer low-noise performance below 0.8–0.85THz, although their sensitivities drop significantly at higher frequencies. Furthermore, a microstrip geometry in which NbTiN is used as the ground plane material only (NbTiN∕SiO2∕Al) yields significant improvements in the sensitivities of SIS mixers operating up to 1.15THz, with an upper operating frequency that depends upon the quality of the NbTiN layer, and thus its deposition process. Films deposited at room temperature have Tc=14.4K and ρn,20K∼60μΩcm, and offer low-noise performance up to 1THz, whereas films deposited at 400°C have Tc=16K and ρn,20K∼110μΩcm, and offer low-noise performance up to 1.15THz. Taken together, these results demonstrate that the high-frequency surface resistance of a NbTiN layer depends upon the film’s structural properties. Most significantly, the drop in performance that is seen at F>1THz in mixers incorporating NbTiN ground planes deposited at room temperature is attributed to nonhomogeneities in the structural and electrical properties of these films, as is the poor performance of mixers that incorporate NbTiN wiring layers at F>0.85THz. The development of these NbTiN-based microstrip tuning circuits will enable the production of low-noise SIS mixers for the 0.8–0.96- and 0.96–1.12-THz frequency bands of the Heterodyne Instrument for the Far Infrared on board the European Space Agency’s Herschel Space Observatory.
Structural characterization of carbon nanosheets via x-ray scattering
Authors: French B. L. , Wang J. J. , Zhu M. Y. , Holloway B. C.
Published: May 2005

The structure of carbon nanosheets deposited by radio frequency plasma-enhanced chemical-vapor deposition at different substrate temperatures is investigated via x-ray scattering. Carbon nanosheets consist of vertically aligned graphene-layer stacks, one to nine layers thick, which can attain micron-scale lengths. Histograms of both molecule length and thickness are generated by fitting the experimental data with a linear combination of x-ray scattering intensities, which are calculated for rhombus-shaped molecules of different dimensions. These histograms show that the average uncorrugated length within a nanosheet decreases from 107Å at a 670°C deposition temperature to 50Å at 950°C. The distribution of nanosheet thickness remains qualitatively similar at each deposition temperature, but decreases from an average of eight graphene layers at 670°C to about six layers at 950°C. With increasing temperature large nestlike structures are observed, but are found to consist of the same nanosheet constituents in a more corrugated and bunched form. These changes are accompanied by the transition from a primarily turbostratic structure with some ordered graphite crystallites at 670°C to a completely turbostratic structure with amorphous content at 950°C. All x-ray scattering results are explained in the context of the nanosheet morphology observed with scanning electron microscopy, and corroborating structural information is provided by Raman spectroscopy.
Nanoelectromechanical systems
Authors: Ekinci K. L. , Roukes M. L.
Published: May 2005

Nanoelectromechanical systems (NEMS) are drawing interest from both technical and scientific communities. These are electromechanical systems, much like microelectromechanical systems, mostly operated in their resonant modes with dimensions in the deep submicron. In this size regime, they come with extremely high fundamental resonance frequencies, diminished active masses,and tolerable force constants; the quality (Q) factors of resonance are in the range Q∼103–105—significantly higher than those of electrical resonant circuits. These attributes collectively make NEMS suitable for a multitude of technological applications such as ultrafast sensors, actuators, and signal processing components. Experimentally, NEMS are expected to open up investigations of phonon mediated mechanical processes and of the quantum behavior of mesoscopic mechanical systems. However, there still exist fundamental and technological challenges to NEMS optimization. In this review we shall provide a balanced introduction to NEMS by discussing the prospects and challenges in this rapidly developing field and outline an exciting emerging application, nanoelectromechanical mass detection.
Viscous coupling based lattice Boltzmann model for binary mixtures
Authors: Asinari Pietro
Published: May 2005

A new lattice Boltzmann model for binary mixtures, which can naturally include both the two-fluid approach and the single-fluid approach, is developed. The model is derived from the continuous kinetic model proposed by Hamel, which independently takes into account self-collisions and cross collisions. The original kinetic model is discussed in order to appreciate that cross collisions realize an internal coupling force, proportional to the diffusion velocity, and an additional coupling effect in the effective stress tensor, proportional to the deformation of the barycentric velocity field. For this reason, Hamel’s model is the natural forerunner of all linearized models based on the two-fluid approach and allows us to describe binary mixtures at different limiting regimes consistently. A discrete lattice Boltzmann model, which recovers the original Hamel’s model with second-order accuracy in both time and space, is proposed. This discrete model can analyze ordinary diffusion, pressure diffusion, and forced diffusion.
Dynamic contact angle of spreading droplets: Experiments and simulations
Authors: Šikalo Š. , Wilhelm H.-D. , Roisman I. V. , Jakirlić S. , Tropea C.
Published: May 2005

This paper presents results of an experimental investigation of a single drop impact onto a dry, partially wettable substrate and its numerical simulation. Particularly, the drop spreading diameter and the dynamic contact angle are measured at different time instants after impact. Two surfaces, wax (low wettability) and glass (high wettability), are used to study the effect of surface wettability (static contact angle) on the impact dynamics. It is shown that existing empirical models for the dynamic contact angle (e.g., Hoffman–Voinov–Tanner law) do not predict well the change of the dynamic contact angle, especially at high capillary numbers. In addition to the experimental investigations, the drop impact was studied numerically, focusing primarily on the contact angle treatment. The singularity in the neighborhood of the moving contact line is removed from the computational domain and replaced by a local force with some dependence on the instantaneous advancing/receding contact-line velocity. The predicted time dependence of the drop spreading diameter and of the dynamic contact angle agrees well with the experimental data for both the advancing and receding phases of the impact process.
Pulsed laser Raman spectroscopy in the laser-heated diamond anvil cell
Authors: Goncharov Alexander F. , Crowhurst Jonathan C.
Published: May 2005

We describe the design and operation of a spatially-filtered Raman/fluorescence spectrometer that incorporates a pulsed 532nm laser excitation source and a synchronized and electronically gated CCD detector. This system permits the suppression of undesired continuous radiation from various sources by a factor of up to 50 000 providing the possibility of acquiring Raman signals at temperatures exceeding 5000K. We present performance comparisons of this system with that of a state-of-the-art conventional CW system using a 458nm excitation source. We also demonstrate that the pulsed system is capable of suppressing an impurity-induced (single nitrogen defects) fluorescence in diamond, and further suggest that this capability can be used to suppress the stress-induced fluorescence in diamond that may appear at pressures near or above 150GPa. This work suggests that Raman spectroscopy under conditions of very high temperatures (to 5000K) and/or ultrahigh pressures (to 300GPa) is entirely viable.
Scanning homodyne interferometer for characterization of piezoelectric films and microelectromechanical systems devices
Authors: Chao Chen , Wang Zhihong , Zhu Weiguang , Tan Ooikiang
Published: May 2005

A scanning homodyne interferometer is developed based on the combination of a modulated Mach–Zehnder interferometer and a high-precision two-dimensional translation stage. Due to its ultrahigh out-of-plane resolution (down to pico meters) and wide bandwidth potential, the scanning interferometer is well suited for characterization of piezoelectric thin films as well as for vibration measurement of microelectromechanical systems devices such as micromachined ultrasonic transducers.
Effect of inclined quantum wells on macroscopic capacitance-voltage response of Schottky contacts: Cubic inclusions in hexagonal SiC
Authors: Park K.-B. , Ding Y. , Pelz J. P. , Mikhov M. K. , Wang Y. , Skromme B. J.
Published: May 2005

Finite-element calculations of Schottky diode capacitance-voltage (C-V) curves show that an array of subsurface inclined quantum wells (QWs) produce negligible change in shape and slope of C-V curves, but significantly reduce the intercept voltage. This is particularly important for hexagonal SiC, in which current- or process-induced cubic inclusions are known to behave as electron QWs. These calculations naturally explain the surprisingly large effect of cubic inclusions on the apparent 4H–SiC Schottky barrier determined by C-V measurements, and together with the measured C-V data indicate the QW subband energy in the inclusions to be ∼0.51eV below the host 4H–SiC conduction band.
Nickel-silicide phase effects on flatband voltage shift and equivalent oxide thickness decrease of hafnium silicon oxynitride metal-silicon-oxide capacitors
Authors: Kang Chang Yong , Lysaght Pat , Choi Rino , Lee Byoung Hun , Rhee Se Jong , Choi Chang Hwan , Akbar M. S. , Lee Jack C.
Published: May 2005

This Letter reports the nickel-silicide phase effects on the electrical characteristics of high-k and silicon dioxide (SiO2) metal-oxide-semiconductor devices. It was found that the silicon-deficient nickel-silicided gate electrode on the hafnium silicon oxynitride (HfSiON) led to a positive flatband voltage (Vfb) shift and a reduction in the equivalent oxide thickness (EOT). However, negligible Vfb shift and EOT decrease were observed in the case of control hafnium oxide and SiO2 structures. It was believed that Si dissociation from the HfSiON layer was the main reason for the positive Vfb shift and the EOT decrease.
Relaxation of induced polar state in relaxor PbMg1∕3Nb2∕3O3 thin films studied by piezoresponse force microscopy
Authors: Shvartsman V. V. , Kholkin A. L. , Tyunina M. , Levoska J.
Published: May 2005

Polarization state in epitaxial thin films of relaxor ferroelectric PbMg1∕3Nb2∕3O3 (PMN) was experimentally studied at the nanoscale using a piezoresponse force microscopy (PFM). In the absence of a dc bias applied to the PFM tip, no piezoelectric activity could be found on most of the surface of the film. Under a moderate voltage (>1.5–2V), a polar state with a nonzero piezoresponse could be induced. Longer poling resulted in a significant reduction of the initial piezoresponse. After removing the bias field, a long-term relaxation of the piezoelectric signal obeying a Kohlrausch-Williams-Watt dependence was observed.
Transmission terahertz waveguide-based imaging below the diffraction limit
Authors: Awad M. M. , Cheville R. A.
Published: May 2005

Using a terahertz line source from a near dispersion-free parallel plate waveguide, we demonstrate broad bandwidth imaging at terahertz frequencies with subwavelength image resolution. Terahertz radiation is coupled into a parallel plate waveguide with a 100μm plate spacing, which serves as the imaging aperture. The image data are collected as projections and the final image is reconstructed using the filtered back-projection algorithm, similar to that in x-ray computed tomography. Images taken using a waveguide-based line source demonstrate higher resolution than can be achieved using a confocal cylindrical lens setup.
Self-assembled monolayer modification of indium tin oxide anode surface for polymer light-emitting diodes with poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene vinylene] for high performance
Authors: Hsiao Chung-Chin , Chang Chih-Hao , Hung Ming-Chin , Yang Neng-Jye , Chen Show-An
Published: May 2005

We demonstrate that introducing a self-assembled monolayer (SAM) derived from 1,1,1,3,3,3-hexamethyldisilazane on an indium tin oxide (ITO) anode surface for the device (ITO/SAM/poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene vinylene]/Ca∕Al), can lead to an improvement in maximum device efficiency from 2.0to3.9cd∕A and maximum brightness from 33000to34400cd∕m2. Such improvement is even better than that with introducing a layer of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (2.6cd∕A and 16000cd∕m2), which is usually used as a hole transport (or injection) layer. The improvement results from a hole blocking effect and better wetting by converting the ITO surface from hydrophilic to hydrophobic provided by the SAM.
Pure-edge dislocation network for strain-relaxed SiGe∕Si(001) systems
Authors: Sakai Akira , Taoka Noriyuki , Nakatsuka Osamu , Zaima Shigeaki , Yasuda Yukio
Published: May 2005

We have grown strain-relaxed SiGe layers on Si(001) substrates with a pure-edge dislocation network buried at the heterointerface and analyzed dislocation morphology depending on growth conditions. The process employed here consists of pure-Ge film growth on Si(001) and subsequent high temperature annealing for solid-phase intermixing of the Ge film and Si deposited on the top to form a SiGe alloy layer. Transmission electron microscopy revealed morphological changes of shorter pure-edge dislocation segments initially formed at the Ge∕Si interface into a network structure consisting of longer and regularly spaced dislocations during post-deposition annealing. The dislocation network was explicitly preserved even after the intermixing of Si and Ge and predominantly contributed to in-plane strain relaxation of the SiGe layer. Applicability of the pure-edge dislocation network to strain-relaxed SiGe buffer layers on Si(001) substrates is discussed.