bluuebunny/crossref_metadata_2025 huggingface dataset:
Fusion-product spectral linewidth in D-D, D-T, and 3He-D plasmas as an ion speed-distribution diagnostic
Authors: Slaughter D. R.
Published: July 2002

A Monte Carlo simulation has been used to study the fusion-product spectral line shape in high-temperature thermonuclear and beam-driven plasmas in order to determine whether line-shape measurements are a viable technique to determine the reacting ion speed distribution and its mean energy. Specific reactions considered include D(d,n), T(d,n), and 3He(d,p). Several speed distributions characteristic of ‘‘mirror-confined’’ and beam-driven plasmas were assumed, including Maxwellian, monoenergetic, three-component Gaussian (characteristic of injected neutrals), and an injected beam reacting with Maxwellian targets. Mean energies in these distributions were varied over the range 1–100 keV. Results indicate that symmetrical Gaussian spectral lines are generated for isotropic plasmas regardless of ion energy or speed-distribution form. However, the location and width of the Gaussian depends not only on the mean ion energy, but also on the form of the ion speed distribution and its angular distribution. Generally, the linewidth is proportional to the square root of the mean ion energy, but the proportionality constant varies significantly among the speed and angular distributions considered. Thus the angular distribution and functional form of the reacting ion speed distribution must be known before measured Doppler width in the product spectrum may be used to infer the mean ion energy of the reacting plasma.
Multichord spectroscopy of the DIII-D divertor region
Authors: Brooks N. H. , Howald A. , Klepper K. , West P.
Published: July 2002

A multichannel spectrometer with high spectral resolution (0.01 nm) and high temporal resolution (0.5 ms) has been configured to collect data simultaneously from eight viewchords spanning the divertor region of DIII-D. Fiber optically coupled to a wide-field lens with a vertical view of the vessel floor, the instrument will be capable of differentiating the behavior of impurity line emission at the inner and outer divertor strike points, on and off the Advanced Divertor Program ring, on the face of the Divertor Material Exposure System probe, and in the region of the lower centerpost. Used with a coarse grating (300 grooves/mm), spectral coverage of each spatial channel is 15 nm with 0.3 nm resolution; used in high order with a 1200 groove/mm grating, the instrument is capable of resolving Doppler profiles. Spatial variation of gas recycling and impurity influx will be studied for both single- and double-null divertor configurations in low and high density operating regimes.
The cooling water calorimetry system at ASDEX upgrade tokamak
Authors: Richter T. , Vernickel H.
Published: July 2002

At the tokamak ASDEX upgrade, an extensive cooling water calorimetry system was installed. This system has measured the toroidal and poloidal distributions of the energy deposition by monitoring the temperature rise of the cooling water in 80 separate cooling units in the divertor plates and the central heat shield.
Recent developments in LIDAR Thomson scattering measurements on JET (invited)
Authors: Gowers C. W. , Brown B. W. , Fajemirokun H. , Nielsen P. , Nizienko Y. , Schunke B.
Published: July 2002

The LIDAR Thomson scattering technique uses the time of flight of a short laser pulse to spatially resolve measurements of electron temperature (Te) and density (ne) in a plasma. The technique was pioneered at JET and the first profiles were obtained in 1986. The initial system used a 3 J, 0.5 Hz, 300 ps ruby laser and microchannel-plate photomultiplier detectors to make Te and ne profile measurements with ∼10 cm spatial resolution. Since then we have sought to improve both the spatial resolution and frequency of measurement during a JET pulse. It has proved possible to develop a 4 Hz version of the ruby laser and to enhance the rate of cycling of detection and digitizing to match. The main LIDAR system has now been upgraded to 4 Hz and first JET profiles obtained with the new system are presented. For a LIDAR system, the spatial resolution δL along the laser path is given by δL=(c/2)(τ2L+τ2D)1/2, where c is the velocity of light, τL the laser pulse width, and τD the detection system response time. Over a limited spatial extent it is possible to improve spatial resolution by using a streak camera detection system. We have successfully improved the spatial resolution by a factor of 2 by setting up a streak camera detection system in parallel with the main photomultiplier system.

The much shorter response time of the streak camera gave ∼5 cm resolution over a 75 cm segment of the ∼2 m plasma diameter. This system was used to examine profile details in the outer part of the JET plasma. Results from this high-resolution LIDAR detection system will be presented. Building on the improved spatial resolution obtained with the streak camera technique, we have now designed and installed a new LIDAR scattering system to diagnose the divertor region of the JET plasma. The laser for the new system is again ruby but uses a different principle to obtain short pulses. We have demonstrated with colleagues from the Troitsk Institute the conversion, using SBS pulse compression, of a standard 25 ns ruby laser into a 300 ps system suitable for LIDAR applications. The main components of the JET Divertor LIDAR system are also described.
Helium I line intensity ratios in a plasma for the diagnostics of fusion edge plasmas
Authors: Sasaki Satoshi , Takamura Shuichi , Watanabe Shinichi , Masuzaki Suguru , Kato Takako , Kadota Kiyoshi
Published: July 2002

Helium I line intensity ratios obtained by a collisional radiative model, including new recommended excitation rate coefficients and the effects of hot electrons, enable us to measure electron density (ne) and temperature (Te) in high density plasma. Measured ne and Te using 492.2 nm (4 1D→2 1P)/471.3 nm (4 3S→2 3P), 504.8 nm (4 1S→2 1P)/471.3 nm, and 492.2 nm/504.8 nm line intensity ratios are in good agreement with the Langmuir probe results in the helium discharge plasma in the NAGDIS-I linear device (Nagoya University Divertor Simulator) for ne and Te regions of 1011–4×1012 cm−3 and 5–20 eV. Hot electrons in the plasma are important for the He I line emissions when Te is below the excitation energy ≊20 eV. A resonance scattering effect included in the calculation accounts for the experimental result of the enhanced 501.6 nm (3 1P→2 1S) line emission.
A tangentially viewing vacuum ultraviolet TV system for the DIII–D divertor
Authors: Nilson D. G. , Fenstermacher M. E. , Ellis R. , Brewis G. , Jalufka N. , Snider R. T.
Published: July 2002

A video camera system capable of imaging vacuum ultraviolet emission in the 120–160 nm wavelength range, from the entire divertor region in the DIII–D tokamak, was designed. The new system has a tangential view of the divertor similar to an existing tangential camera system [M. E. Fenstermacher et al., Rev. Sci. Instrum. 68, 974 (1997)] which has produced two-dimensional maps of visible line emission (400–800 nm) from deuterium and carbon in the divertor region. However, the overwhelming fraction of the power radiated by these elements is emitted by resonance transitions in the ultraviolet, namely the C IV line at 155.0 nm and Ly-α line at 121.6 nm. To image the ultraviolet light with an angular view including the inner wall and outer bias ring in DIII–D, a six-element optical system (f/8.9) was designed using a combination of reflective and refractive optics. This system will provide a spatial resolution of 1.2 cm in the object plane. An intermediate UV image formed in a secondary vacuum is converted to the visible by means of a phosphor plate and detected with a conventional charge injection device (CID) camera (30 ms framing rate). A single MgF2 lens serves as the vacuum interface between the primary and secondary vacuums; a second lens must be inserted in the secondary vacuum to correct the focus at 155 nm. Using the same tomographic inversion method employed for the visible TV, we will reconstruct the poloidal distribution of the UV divertor light. The grain size of the phosphor plate and the optical system aberrations limit the best focus spot size to 60 μm at the CID plane. The optical system is designed to withstand 350 °C vessel bakeout, 2 T magnetic fields, and disruption-induced accelerations of the vessel.
Accurate infrared spectroscopy determination of interstitial and precipitated oxygen in highly doped Czochralski-grown silicon
Authors: De Gryse O. , Clauws P. , Rossou L. , Van Landuyt J. , Vanhellemont J.
Published: July 2002

A method has been developed to determine the interstitial and precipitated oxygen concentration in highly doped n- and p-type silicon. 10–30-μm-thin silicon samples in a mechanical stress-free state and without alteration of the thermal history are prepared and measured with Fourier transform infrared spectroscopy at 5.5–6 K. The measured oxygen contents in the as-grown Si samples agree well with those obtained with gas fusion analysis. In the highly boron-doped samples, the interstitial oxygen can be determined down to 1017 cm−3.
Capacitive position sensor with simultaneous, linear X–Y readout
Authors: Field Stuart B. , Barentine John
Published: July 2002

A design is presented for a compact capacitive position sensor suitable for operation at cryogenic temperatures and high magnetic fields. The four quadrants of a base electrode are excited with phases differing by 90°; from its in- and out-of-phase components, the current injected into the movable electrode yields simultaneous information about the x and y sensor positions. This current is also linear in the position of the sensor. The effects of possible sensor imperfections are analyzed in detail.
Thermal-wave resonator cavity design and measurements of the thermal diffusivity of liquids
Authors: Balderas-López J. A. , Mandelis A. , Garcia J. A.
Published: July 2002

A liquid-ambient-compatible thermal wave resonant cavity (TWRC) has been constructed for the measurement of the thermal diffusivity of liquids. The thermal diffusivities of distilled water, glycerol, ethylene glycol, and olive oil were determined at room temperature (25 °C), with four-significant-figure precision as follows: (0.1445±0.0002)×10−2 cm2/s (distilled water); (0.0922±0.0002)×10−2 cm2/s (glycerol); (0.0918±0.0002)×10−2 cm2/s (ethylene glycol); and (0.0881±0.0004)×10−2 cm2/s (olive oil). The liquid-state TWRC sensor was found to be highly sensitive to various mixtures of methanol and salt in distilled water with sensitivity limits 0.5% (v/v) and 0.03% (w/v), respectively. The use of the TWRC to measure gas evolution from liquids and its potential for environmental applications has also been demonstrated.
Na-induced effects on the electronic structure and composition of Cu(In,Ga)Se2 thin-film surfaces
Authors: Heske C. , Fink R. , Umbach E. , Riedl W. , Karg F.
Published: July 2002

X-ray and UV photoelectron spectroscopy measurements of Cu(InGa)Se2 thin films grown on Mo coated soda-lime glass show segregation from the substrate and formation of two different Na species. One of these species is also identified after deliberate deposition of metallic Na. Moreover, the adsorption (or segregation) of this species reduces the native oxide SeO2, while the other, reacted Na species coexists with SeO2. Small amounts of Na (≤0.05 Å) induce a band bending and reduce the surface dipole. These findings reveal a positive influence of segregated Na on the morphology and electrical characteristics of Na-enriched films, improving the overall performance of the solar cells.
Wavelength conversion by difference frequency generation in AlGaAs waveguides with periodic domain inversion achieved by wafer bonding
Authors: Yoo S. J. B. , Caneau C. , Bhat R. , Koza M. A. , Rajhel A. , Antoniades Neo
Published: July 2002

Wavelength conversion by difference-frequency generation is achieved in a periodically domain reversed AlGaAs waveguide. The AlGaAs waveguide is epitaxially grown on a template substrate where a periodic crystal domain inversion is achieved using wafer bonding, selective etching, and organometallic chemical vapor deposition. Wavelength conversion experiments on a fabricated buried heterowaveguide showed a 90 nm conversion bandwidth, polarization diversified operation, and polarization independent conversion efficiency. The experimental results also showed linearity and spectral inversion, which imply transparency to signal formats including analog and frequency modulation. Simultaneous conversion of multiple input wavelengths with no measurable cross talk is also demonstrated.
Group velocities in coplanar strip transmission lines on Si and Si/SiO2/Si substrates measured using differential electro-optic sampling
Authors: Chen Erli , Chou Stephen Y.
Published: July 2002

The group velocities in coplanar strip transmission lines on Si and Si/SiO2/Si substrates were compared experimentally and theoretically. To ensure the experimental accuracy, a differential electro-optic sampling system with a delay-time resolution of 30 fs and a spatial resolution of 1 μm has been developed. Compared with the group velocity on a Si substrate, the group velocity on a Si/SiO2/Si substrate with a 2.2 μm SiO2 layer was found to be 10% faster, which agrees well with the theoretical prediction.
Charge injection in organic light-emitting diodes: Tunneling into low mobility materials
Authors: Davids P. S. , Kogan Sh. M. , Parker I. D. , Smith D. L.
Published: July 2002

We present device model calculations for the current–voltage (I–V) characteristics of organic diodes and compare them with measurements of structures fabricated using MEH-PPV. The measured I–V characteristics have a Fowler–Nordheim (FN) functional form, but are more than three orders of magnitude smaller than the calculated FN tunneling current. We find that the low mobility of the organic materials leads to a large backflow of injected carriers into the injecting contact. These results account for the experimental observations and also demonstrate how transport layers in multilayer organic light-emitting diodes can be used to improve carrier injection.
Increased critical current density in Nb–Ti wires having Nb artificial pinning centers
Authors: Heussner R. W. , Marquardt J. D. , Lee P. J. , Larbalestier D. C.
Published: July 2002

Artificial pinning center (APC) wires containing Nb 47 wt.% Ti with 24 vol.% of round Nb pins have produced very high critical current densities (Jc) which are attributed to a sharply defined, nanometer-scale Nb-pin array. By reducing both the number of warm extrusion steps from four to three and the temperature of the third extrusion from 650 °C to 250 °C, the degree of pin-matrix interdiffusion has been reduced and Jc values at all applied magnetic fields increased by 25–45% over those for a previous composite of almost identical design. The best wire achieved the very high Jc(5 T, 4.2 K) value of 4600 A/mm2. These results underscore the importance of the thermomechanical treatment in determining the maximum flux pinning properties of APC Nb–Ti wires.
A phase-locked shear-force microscope for distance regulation in near-field optical microscopy
Authors: Atia Walid A. , Davis Christopher C.
Published: July 2002

A nonoptical phase-locked shear-force microscope utilizing a quartz crystal tuning fork acting as a voltage-controlled oscillator in a phase-locked loop has been implemented. A tapered optical fiber is rigidly mounted on one of the prongs of the fork to serve as both a shear-force pickup and a near-field optical probe. The crystal is driven at its resonance frequency through positive feedback of the monitored current through the crystal. This signal is used as the voltage-controlled oscillator in a phase-locked loop. The scheme allows for scan speeds far beyond the Q-limited amplitude sensor bandwidth and exhibits excellent sensitivity for a high-Q resonator. Furthermore, given the small vibration amplitude of the tip (<0.5 nm) and the distance over which it is reduced (> 6 nm), it is unlikely that the tip is making direct contact with the sample surface as has been suggested for the optical shear-force detection scheme.
Ion exchange in potassium titanyl phosphate
Authors: Daneshvar K. , Giess E. A. , Bacon A. M. , Dawes D. G. , Gea L. A. , Boatner L. A.
Published: July 2002

Ion-exchange processes in potassium titanyl phosphate (KTiOPO4 or KTP) single crystal immersed in Rb, Rb–Ba, Rb–Sr nitrate molten solutions have been investigated by using Rutherford backscattering depth-profile analysis. The depth to which Rb-ion exchange occurred in KTP was found to be sensitive to the presence of as little as 0.1% of a Ba impurity in a molten solution of rubidium nitrate. The addition of impurities such as Ba significantly increased the ion-exchange depth of Rb in KTP, and the Rb distribution after ion exchange. Using pure RbNO3, however, the depth of the Rb ion exchange was relatively shallow, and the Rb surface concentration was measurably greater at the minus than at the plus polar-axis faces of the crystal. These findings are relevant to the application of ion-exchange techniques to the fabrication of optical waveguides on KTP substrates.
Optical properties of Si-doped GaN
Authors: Schubert E. F. , Goepfert I. D. , Grieshaber W. , Redwing J. M.
Published: July 2002

The optical properties of n-type GaN are investigated for Si doping concentrations ranging from 5×1016 to 7×1018 cm−3. The photoluminescence linewidth of the near-band gap optical transition increases from 47 to 78 meV as the doping concentration is increased. The broadening is modeled in terms of potential fluctuations caused by the random distribution of donor impurities. Good agreement is found between experimental and theoretical results. The intensity of the near-band-gap transition increases monotonically as the doping concentration is increased indicating that nonradiative transitions dominate at a low doping density. The comparison of absorption, luminescence, reflectance, and photoreflectance measurements reveals the absence of a Stokes shift at room temperature demonstrating the intrinsic nature of the near-band edge transition.
Field emitted electron energy distribution from nitrogen-containing diamondlike carbon
Authors: Gröning O. , Küttel O. M. , Gröning P. , Schlapbach L.
Published: July 2002

We report on energy resolved field emission measurements of 0.3 μm thick nitrogen containing diamondlike carbon (DLC). The film used in this study was deposited by filtered arc deposition onto a highly p-doped Si(100) wafer. The film showed homogeneous field emission over the entire wafer area with an onset field for 1 nA emission current of 20–25 V/μm. The energy resolved field emission measurements were carried out with an applied electric field of 20–22 V/μm. The field emitted electrons originate from the Fermi energy, indicating that no field penetration occurs. The energy distribution has a FWHM of 0.63 eV at an applied field of 21 V/μm. The spectra could be deconvoluted using standard tunneling theory. The results of the deconvolution indicate an electric field strength of 6500 V/μm  at the emission site.
Destruction of ozone-depleting substances in a thermal plasma reactor
Authors: Murphy A. B. , McAllister T.
Published: July 2002

A two-dimensional numerical model of the PLASCON™ plasma reactor is used to investigate the destruction of ozone-depleting substances in the reactor. The model includes electromagnetic, fluid dynamic and chemical kinetic phenomena. Calculated temperature, flow and species concentration fields within the plasma torch, the injection manifold and the reaction tube are presented for the case of the destruction of CFC-12 (CF2Cl2). Conversion of CFC-12 to CFC-13 (CF3Cl), a more stable ozone-depleting substance, is found to occur in the region close to the injection manifold, and to be unaffected by reaction tube geometry. CFC-13 is predicted to be the dominant ozone-depleting substance in the exhaust gas. The predictions of the model are found to be in good agreement with measurements of the exhaust gas composition.
Electron affinity at aluminum nitride surfaces
Authors: Wu C. I. , Kahn A. , Hellman E. S. , Buchanan D. N. E.
Published: July 2002

We investigate the electron affinity of aluminum nitride surfaces prepared by nitrogen sputtering and annealing via x-ray, ultraviolet, and inverse photoemission spectroscopy. The combination of these techniques leads to a precise determination of the relative positions of the Fermi level, valence-band maximum, conduction-band minimum, and vacuum level at the semiconductor surface. We demonstrate that, in spite of the presence of a sharp photoemission onset feature previously associated with negative electron affinity, the electron affinity is clearly positive on these surfaces.
An approach for recording and readout beyond the diffraction limit with an Sb thin film
Authors: Tominaga J. , Nakano T. , Atoda N.
Published: July 2002

A technique for recording and retrieving small marks beyond the optical diffraction limit was proposed. The basic experiment with this technique was also carried out at a constant linear velocity of 2.0 m/s, rotating a disk with a multi-layered structure of Sb and GeSbTe, which were separated by a thin film of SiN. By use of the optically nonlinear property of the Sb thin film, carrier to noise ratio of more than 10 dB was obtained from recorded marks of 90 nm, using an optical system with the laser wavelength of 686 nm and a numerical aperture of 0.6.
Magnetophotoluminescence of stacked self-assembled InP quantum dots
Authors: Provoost R. , Hayne M. , Moshchalkov V. V. , Zundel M. K. , Eberl K.
Published: July 2002

We report magnetophotoluminescence measurements of stacked layers of self-assembled InP quantum dots. With a magnetic field applied in the growth direction we have determined the exciton reduced mass from the field dependence of the photoluminescence energy. By applying a magnetic field perpendicular to the growth direction, we have analyzed the spatial confinement of the dots in the growth direction. We observe a large increase in the shift of the exciton energy between 0 and 50 T when the thickness of the GaInP spacer layer between the dots is reduced from 8 to 4 nm. This indicates a decrease in spatial confinement in the growth direction which we attribute to strong electronic coupling between vertically stacked dots.
Precipitation of icosahedral phase from a supercooled liquid region in Zr65Cu7.5Al7.5Ni10Ag10 metallic glass
Authors: Saida J. , Matsushita M. , Zhang T. , Inoue A. , Chen M. W. , Sakurai T.
Published: July 2002

The formation of an icosahedral phase from the rapidly quenched Zr65Cu7.5Al7.5Ni10Ag10 metallic glass was confirmed and the kinetics of the precipitation upon isothermal annealing in the supercooled liquid region were examined by differential scanning calorimetry. Based on the kinetic analysis, it is clarified that the precipitation in the supercooled liquid region takes place by an interfacial controlled growth with a nearly steady-state nucleation rate. The Arrhenius plot between effective time lag, τ, of nucleation and isothermal annealing temperature yields a single linear relation, in which the activation energy for nucleation is evaluated to be 366 kJ/mol. It is concluded that the transformation of amorphous to quasicrystal proceeds by a homogeneous nucleation mode, which is different from those of Pd–U–Si and Al–Cu–V quasicrystals arising from an inhomogeneous distribution of quenched-in nuclei.
High frequency conductivity of the high-mobility two-dimensional electron gas
Authors: Burke P. J. , Spielman I. B. , Eisenstein J. P. , Pfeiffer L. N. , West K. W.
Published: July 2002

We measure the real and imaginary conductivity σ(k=0,ω) of a high-mobility two-dimensional electron gas (2DEG) system at frequencies below and above the momentum scattering rate. The imaginary part of the 2DEG impedance is observed to be inductive, consistent with the Drude model. Using this kinetic inductance, we construct a transmission line by capacitively coupling the 2DEG to an Al Schottky barrier gate separated by 5000 Å from the 2DEG. The measured wave velocity and temperature-dependent damping of this transmission line are in good agreement with a simple Drude model. Exciting these modes is equivalent to exciting a 2D plasma mode strongly modified by the interaction between the 2DEG and the gate.
Molecular detection based on conductance quantization of nanowires
Authors: Li C. Z. , He H. X. , Bogozi A. , Bunch J. S. , Tao N. J.
Published: July 2002

We have studied molecular adsorption onto stable metallic nanowires fabricated with an electrochemical method. Upon the adsorption, the quantized conductance decreases, typically, to a fractional value, which may be attributed to the scattering of the conduction electrons by the adsorbates. The further conductance change occurs when the nanowire is exposed to another molecule that has stronger adsorption strength. Because the quantized conductance is determined by a few atoms at the narrowest portion of each nanowire, adsorption of a molecule onto the portion is enough to change the conductance, which may be used for chemical sensors.
Steady thermocapillary-buoyant flow in an unbounded liquid layer heated nonuniformly from above
Authors: Higuera F. J.
Published: July 2002

Thermocapillary and buoyant flows induced by nonuniform heating of the free surface of a horizontally unbounded liquid layer over a cold solid bottom are studied numerically and by order of magnitude analyses for large Marangoni and Rayleigh numbers. The Prandtl number of the liquid is assumed to be of order unity or large, which are the cases of most interest in combustion. The asymptotic structures of plane and axisymmetric stationary flows are described qualitatively, showing that they consist of several horizontally spaced regions. Heat conduction and viscous forces are confined to thin boundary layers in a region around the heat source, while viscous forces extend to the whole liquid layer in a longer region where the flow is driven by the momentum imparted to the liquid by thermocapillary stresses around the source, in the case of plane thermocapillary flow; by this momentum and remaining thermocapillary stresses, in the case of axisymmetric thermocapillary flow; and by the horizontal gradient of a hydrostatic pressure distribution, in the case of buoyant flows. For large values of the Prandtl number, this region is followed by a region of viscosity-dominated flow which may be responsible for a large fraction of the heat loss to the bottom. A linear stability analysis of the surface boundary layer in the vicinity of the heat source gives values of the critical Marangoni number for the transition to oscillatory flow that are comparable to known experimental results.
Measurement of mechanical properties for dense and porous polymer films having a low dielectric constant
Authors: Xu Yuhuan , Tsai Yipin , Zheng D. W. , Tu K. N. , Wo Ong Chung , Choy Chung Loong , Zhao Bin , Liu Q.-Z. , Brongo Maureen
Published: July 2002

We measured the mechanical properties of dense and porous polymeric films, the modified polyarylethers, which have a low dielectric constant varying from 2.7 to 1.8, by combining three different methods; membrane bulge test, nanoindentation, and single-substrate bending beam method. The elastic modulus and initial stress measured from these three methods are in good agreement. The substrate effect was observed in the measurements by nanoindentation. Data obtained by nanoindentation show a significant dependence on the film thickness and the displacement depth of the indenter. However, the hardness of the low dielectric constant thin film does not depend on thickness and only slightly depends on the indentation depth. A tentative analysis is proposed to explain the results.
Effect of strong radial variation of the ion diamagnetic frequency on internal ballooning modes
Authors: Hastie R. J. , Catto Peter J. , Ramos J. J.
Published: July 2002

The formalism for internal ballooning modes in a tokamak is extended to retain the strong radial variation of the ion diamagnetic drift frequency characteristic of edge plasmas in the pedestal region. The resulting finite Larmor radius (FLR) stabilization is modified and can be weaker than in the case of constant diamagnetic frequency.
Simulations of energy funneling and time- and frequency-gated fluorescence in dendrimers
Authors: Kirkwood Jason C. , Scheurer Christoph , Chernyak Vladimir , Mukamel Shaul
Published: July 2002

Exciton transport and relaxation in optically excited phenylacetylene dendrimers is simulated using the Redfield equations. The interplay of entropic (periphery-bound) and energetic (center-bound) driving forces is explored. The fluorescence signal computed using the Doorway–Window representation provides a direct probe for exciton dynamics. The propagated exciton density matrix is analyzed and several measures of the time-dependent excitonic coherence sizes are proposed and calculated.
Isotope-edited two-dimensional vibrational spectroscopy of trialanine in aqueous solution
Authors: Woutersen S. , Hamm P.
Published: July 2002

Two-dimensional vibrational spectroscopy is applied to the amide I mode of trialanine and two of its isotopomers dissolved in heavy water. We use site-directed 13C isotope substitution to change the individual frequencies of the coupled oscillators, and hence to modify specific matrix elements of the molecular Hamiltonian. It is found that all of the results can be well described by an excitonic model for the amide I band, using the same coupling strength and dipole–dipole angle for all three isotopomers. This demonstrates that these two spectral parameters are determined by the secondary structure of the peptide, which remains unchanged upon isotope substitution.
High-k cobalt–titanium oxide dielectrics formed by oxidation of sputtered Co/Ti or Ti/Co films
Authors: Pan Tung Ming , Lei Tan Fu , Chao Tien Sheng
Published: July 2002

High-k cobalt–titanium oxide (CoTiO3) film was formed by directly oxidizing sputtered Co/Ti or Ti/Co films. Al/CoTiO3/Si3N4/Si capacitor structures were fabricated and measured. Excellent electrical properties with an effective dielectric constant (i.e., k value) as high as 40 have been achieved for a CoTiO3 gate dielectric with a buffer layer. The metal–oxide thus appears to be a very promising high-k gate dielectric for future ultralarge scale integrated devices.
Hydrophobicity in a simple model of water: Entropy penalty as a sum of competing terms via full, angular expansion
Authors: Silverstein Kevin A. T. , Dill Ken A. , Haymet A. D. J.
Published: July 2002

The entropy penalty of solvation for nonpolar solutes dominates the hydrophobic effect at room temperature. We find that this entropy arises from a competition between a relatively localized “two-body” term, and a contribution arising from non-pairwise-decomposable three-body and higher-order terms. We use a full, angular dependent, expansion of solute–water correlation functions over the full range of fluid temperatures for a two-dimensional model of water. This water model has been shown to capture many of the basic anomalies of water and aqueous solutions of sparingly soluble nonpolar molecules, including the volume anomalies of water and the thermal anomalies of the hydrophobic effect. Our results show that for hot liquid water, the two-body approximation is sufficient to estimate the transfer entropy, but in cold liquid water, which is the main regime for biological hydrophobic interactions, the two-body assumption substantially overestimates the degree of ordering in water.
Model of ferromagnetic resonance in granular magnetic solids
Authors: Verdes C. G. , Ruiz-Diaz B. , Thompson S. M. , Chantrell R. W. , Stancu Al.
Published: July 2002

Micromagnetic simulations of ferromagnetic fine particle systems have been used to study the effect of various parameters on the hysteresis loops and on the ferromagnetic resonance (FMR) curves. Systematic calculations show that the effect of the dipolar interactions on such systems significantly differs from that introduced by the exchange interactions. It is important to note that the anisotropy and damping parameter also contribute to the FMR response.
Recent progress toward high performance above the Greenwald density limit in impurity seeded discharges in limiter and divertor tokamaks
Authors: Ongena J. , Budny R. , Dumortier P. , Jackson G. L. , Kubo H. , Messiaen A. M. , Murakami M. , Strachan J. D. , Sydora R. , Tokar M. , Unterberg B. , Samm U. , Vandenplas P. E. , Weynants R. , Asakura N. , Brix M. , Charlet M. , Coffey I. , Cordey G. , Erents S. K. , Fuchs G. , von Hellermann M. , Hillis D. L. , Hogan J. , Horton L. D. , Ingesson L. C. , Itami K. , Jachmich S. , Kallenbach A. , Koslowski H. R. , Kraemer-Flecken A. , Lawson K. D. , Loarte A. , Maddison G. P. , Mank G. , McKee G. R. , Meigs A. , Milani F. , Monier-Garbet P. , Nave M. F. F. , Puiatti M. E. , Parail V. , Rapp J. , Sakurai S. , Sharapov S. , Sartori F. , Stamp M. , Tamai H. , Telesca G. , Valisa M. , Van Wassenhove G. , Weyssow B. , Zastrow K.-D. ,   EFDA-JET workprogramme contributors
Published: July 2002

An overview is given of recent advances toward the realization of high density, high confinement plasmas with radiating mantles in limiter and divertor tokamaks worldwide. Radiatively improved mode discharges on the Torus Experiment for Technology Oriented Research 94 (TEXTOR-94) [Proceedings of the 16th IEEE Symposium on Fusion Engineering, 1995 (Institute for Electrical and Electronics Engineers, Piscataway, NJ, 1995), p. 470] have recently been obtained at trans-Greenwald densities (up to n̄/nGW=1.4) with high confinement mode free of edge localized modes (ELM-free H-mode) confinement quality. Experiments in DIII-D [J. Luxon et al., Proceedings of the 11th IAEA Conference on Plasma Physics and Controlled Nuclear Fusion Research (International Atomic Energy Association, Vienna, 1987), Vol. 1, p. 159] divertor plasmas with a low confinement mode edge have confirmed the dramatic changes in confinement observed with impurity seeding on TEXTOR-94. Recent experiment with impurity seeding on the Joint European Torus [Rebut et al., Fusion Eng. Des. 22, 7 (1993)], and the Japanese Atomic Energy Research Institute Tokamak 60 Upgrade [Horiike et al., Fusion Eng. Des. 16, 285 (1991); Hosogane et al., Proceedings of the 16th IAEA Conference on Plasma Physics and Controlled Nuclear Fusion Research Montreal, 1987 (International Atomic Energy Association, Vienna, 1987), Vol. 3, p. 555] have extended high confinement in ELMy H-mode plasmas to higher densities. Finally, recent progress in the physical understanding of radiating mantle plasmas is summarized.
Field emission site densities of nanostructured carbon films deposited by a cathodic arc
Authors: Cui J. B. , Robertson J. , Milne W. I.
Published: July 2002

The field emission properties of nanostructured carbon films deposited by cathodic vacuum arc have been investigated by measuring both the emission currents and the emission site density. The films have an onset field of 3 V/μm. The emission site density is viewed on a phosphor anode and it increases rapidly with applied field. It is assumed that the emission occurs from surface regions with a range of field enhancement factors but with a constant work function. The field enhancement factor is found to have an exponential distribution.
Electronic and infrared spectra of H2C3H+ and cyclic C3H3+ in neon matrices
Authors: Wyss Muriel , Riaplov Evgueni , Maier John P.
Published: July 2002

The A 1A′←X 1A1 electronic transition of the propargyl cation H2C3H+ with the origin band at 267.8(2) nm has been identified in a neon matrix at 5 K. The frequencies of the two modes excited in the upper state are 667(50) and 1629(50) cm−1 and imply a reduction of symmetry from C2v in the ground state to Cs in the excited state. The most intense IR mode of the propargyl cation is observed at 2079.9(1.0) cm−1 and for the cyclopropenyl cation at 3130.4(1.0) cm−1. Ab initio calculations on the excited states of the two isomer cations support the assignment and explain why the electronic transition could not be observed for the cyclic species; it lies below 200 nm. The A 2A″←X 2B1 and B 2A′←X 2B1 absorptions of the neutral propargyl radical have also been observed with origin bands at 351.9(2) and 343.0(2) nm, respectively. These results provide the basis for the study of these astrophysically interesting C3H3+ species in the gas phase.
Effect of void shape in Czochralski-Si wafers on the intensity of laser-scattering
Authors: Takahashi J. , Kawakami K. , Nakai K.
Published: July 2002

The shape effect of anisotropic-shaped microvoid defects in Czochralski-grown silicon wafers on the intensity of laser scattering has been investigated. The size and shape of the defects were examined by means of transmission electron microscopy. Octahedral voids in conventional (nitrogen-undoped) wafers showed an almost isotropic scattering property under the incident condition of a p-polarization beam. On the other hand, parallelepiped-plate-shaped voids in nitrogen-doped wafers showed an anisotropic scattering property on both p- and s-polarized components of scattered light, depending strongly on the incident laser direction. The measured results were explained not by scattering calculation using Born approximation but by calculation based on Rayleigh scattering. It was found that the s component is explained by an inclination of a dipole moment induced on a defect from the scattering plane. Furthermore, using numerical electromagnetic analysis it was shown that the asymmetric behavior of the s component on the parallelepiped-plate voids is ascribed to the parallelepiped shape effect. These results suggest that correction of the scattering intensity is necessary to evaluate the size and volume of anisotropic-shaped defects from the scattered intensity.
Staircase-like spectral dependence of ground-state luminescence time constants in high-density InAs/GaAs quantum dots
Authors: Mazur Yu. I. , Tomm J. W. , Petrov V. , Tarasov G. G. , Kissel H. , Walther C. , Zhuchenko Z. Ya. , Masselink W. T.
Published: July 2002

Time-resolved photoluminescence (PL) from InAs/GaAs quantum dots with a bimodal size distribution is used to investigate the dynamic carrier-transfer processes which couple transfer between similarly sized quantum dots and between quantum dots in different size categories. The relationship between the decay time and the emission energy appears staircaselike and the energetic positions of the steps as well as the shape can be correlated to the shape of the steady-state PL emission through a rate-equation theory. These results show how transient PL can be used to investigate the dynamics of carrier transfer in quantum-dot systems.
Z-scan analyses for PbO-containing glass with large optical nonlinearity
Authors: Hashimoto Tadanori , Yamamoto Tsuyoshi , Kato Tomohiro , Nasu Hiroyuki , Kamiya Kanichi
Published: July 2002

In order to evaluate the large third-order optical nonlinearity of materials accurately, the influence of the irradiance (I0) and sample thickness (L) on the Z-scan transmittance of PbO-containing glass as a representative material was investigated using simple and conventional Z-scan experiments and analyses. The transmittance difference between the peak and valley (ΔTp–v) in the Z-scan curve resulting from nonlinear refraction and the difference between the baseline (1.0) and valley (ΔT1−v) due to nonlinear absorption deviated from a linear relationship at increased I0 and L. It was found that an analysis based on the linear relationship at large I0 and L underestimated the third-order optical nonlinearity due to saturation. Taking into consideration the saturation of ΔTp−v and ΔT1−v with L under moderate irradiance, the intrinsic nonlinear refractive index (γ) and nonlinear absorption coefficient (β) of the present glass were calculated to be 1.58×10−17 m2 W−1 and 7.75 cm GW−1, respectively.
Nature and properties of the Johari–Goldstein β-relaxation in the equilibrium liquid state of a class of glass-formers
Authors: Ngai K. L. , Lunkenheimer P. , León C. , Schneider U. , Brand R. , Loidl A.
Published: July 2002

Previous dielectric relaxation measurements of glycerol and propylene carbonate and new results on propylene glycol performed below the conventional glass transition temperatures Tg after long periods of aging all show that the excess wing (a second power law at higher frequencies) in the isothermal dielectric loss spectrum, develops into a shoulder. These results suggest that the excess wing, a characteristic feature of a variety of glass-formers, is the high frequency flank of a Johari–Goldstein β-relaxation loss peak submerged under the α-relaxation loss peak. With this interpretation of the excess wing assured, the dielectric spectra of all three glass-formers measured at temperatures above Tg are analyzed as a sum of a α-relaxation modeled by the Fourier transform of a Kohlrausch–Williams–Watts function and a β-relaxation modeled by a Cole–Cole function. Good fits to the experimental data have been achieved. In addition to the newly resolved β-relaxation on propylene glycol, the important results of this work are the properties of the β-relaxation in this class of glass-formers in the equilibrium liquid state obtained over broad frequency and temperature ranges.
Ignition condition and gain prediction for perturbed inertial confinement fusion targets
Authors: Kishony Roy , Shvarts Dov
Published: July 2002

The effect of perturbations on hot spot ignition is studied using full two-dimensional (2D) numerical simulations of the National Ignition Facility [J. D. Lindl, Phys. Plasmas 2, 3933 (1995)] direct drive Laboratory for Laser Energetics target design and newly derived 2D self-similar solutions for a perturbed burn wave propagation. It is shown that the required implosion velocity needed for ignition increases with the perturbation mode number and final amplitude, reaching an asymptotic value for high enough perturbation mode numbers, when the entire mixing zone no longer contributes to the ignition of the hot spot. Using the new self-similar solutions, ignition conditions for various perturbation mode numbers and amplitudes are obtained. These ignition conditions, which correspond to areal densities higher than needed for ignition in the symmetric case, are translated to a required increase in the implosion velocity needed for ignition, using the 1D Levendahl–Lindl scaling, in good agreement with the full 2D numerical simulation results. Finally, using the above results, a model for predicting the gain of a perturbed targets as a function of the perturbation spectra (single-mode and multi-mode) is presented, in good agreement with full numerical simulations.
Effects of yttrium codoping on photoluminescence of erbium-doped TiO2 films
Authors: Ting Chu-Chi , Chen San-Yuan , Hsieh Wen-Feng , Lee Hsin-Yi
Published: July 2002

Er 3+ – Y 3+ codoped TiO2 films were prepared on a fused silica substrate by the sol–gel process. The effect of Y3+ codoping on the ∼1.54 μm photoluminescence (PL) properties of Er3+-doped TiO2 films are investigated. Enhancement of PL properties due to Y3+ codoping by a factor of 10 for intensity and of 1.5 for the full width at half maximum in comparison with the Er3+–Al3+ codoped SiO2 system has been observed in the film annealed at Er3+:Y3+:Ti4+=5:30(∼50):100. Extended x-ray absorption fine structure measurements show that the local chemical environment of Er3+ ions in the Er3+–Y3+ codoped TiO2 films is similar to that in Er2O3. The average spatial distance between Er3+ ions is enlarged due to the partial substitution of Y3+ for Er3+ ions in the Er2O3-like local structure. It is believed that the more intense PL emission of the Er3+–Y3+ codoped TiO2 films can be attributed to the better dispersion and distorted local structure of Er3+ ions in the TiO2 host matrix by yttrium codoping.
Propagator, tree-level unitarity and effective nonrelativistic potential for higher-derivative gravity theories in D dimensions
Authors: Accioly Antonio , Azeredo Abel , Mukai Hatsumi
Published: July 2002

A prescription for computing the propagator for D-dimensional higher-derivative gravity theories, based on the Barnes–Rivers operators, is presented. A systematic study of the tree-level unitarity of these theories is developed and the agreement of their linearized versions with Newton’s law is investigated by computing the corresponding effective nonrelativistic potential. Three-dimensional quadratic gravity with a gravitational Chern–Simons term is also analyzed. A discussion on the issue of light bending within the framework of both D-dimensional quadratic gravity and three-dimensional quadratic gravity with a Chern–Simons term is provided as well.
Hydrodynamic equations for mixed quantum states. II. Coupled electronic states
Authors: Burghardt I. , Cederbaum L. S.
Published: July 2002

A hydrodynamic approach is developed to describe nonadiabatic nuclear dynamics. We derive a hierarchy of hydrodynamic equations which are equivalent to the exact quantum Liouville equation for coupled electronic states. It is shown how the interplay between electronic populations and coherences translates into the coupled dynamics of the corresponding hydrodynamic fields. For the particular case of pure quantum states, the hydrodynamic hierarchy terminates such that the dynamics may be described in terms of the local densities and momentum fields associated with each of the electronic states.
Analysis of the magnetic coupling in binuclear complexes. I. Physics of the coupling
Authors: Calzado Carmen J. , Cabrero Jesús , Malrieu Jean Paul , Caballol Rosa
Published: July 2002

Accurate estimates of the magnetic coupling in binuclear complexes can be obtained from ab initio configuration interaction (CI) calculations using the difference dedicated CI technique. The present paper shows that the same technique also provides a way to analyze the various physical contributions to the coupling and performs numerical analysis of their respective roles on four binuclear complexes of Cu (d9) ions. The bare valence-only description (including direct and kinetic exchange) does not result in meaningful values. The spin-polarization phenomenon cannot be neglected, its sign and amplitude depend on the system. The two leading dynamical correlation effects have an antiferromagnetic character. The first one goes through the dynamical polarization of the environment in the ionic valence bond forms (i.e., the M+⋯M− structures). The second one is due to the double excitations involving simultaneously single excitations between the bridging ligand and the magnetic orbitals and single excitations of the environment. This dispersive effect results in an increase of the effective hopping integral between the magnetic orbitals. Moreover, it is demonstrated to be responsible for the previously observed larger metal-ligand delocalization occurring in natural orbitals with respect to the Hartree–Fock ones.
Mechanisms for hetero-epitaxial nucleation of YBa2Cu3O∼6.1 at the buried precursor/SrTiO3 interface in the postdeposition reaction process
Authors: Wu L. , Solovyov V. F. , Wiesmann H. J. , Zhu Y. , Suenaga M.
Published: July 2002

The mechanisms have been identified for the hetero-epitaxial nucleation of YBa2Cu3O∼6.1 (YBCO) at the buried interface between a precursor film and SrTiO3 for the so-called BaF2 process which is a postdeposition reaction process for the synthesis of epitaxial YBCO films. It is shown that the preferential nucleation of YBCO at the interface is due to (1) the strong chemical affinity of the (Y, Ba)-oxy-fluoride, an intermediate phase, to SrTiO3 and (2) the epitaxial alignment of its (111) planes with the (001) surface of the SrTiO3 which reduces the activation barrier for the formation of YBCO. In thin films (<2–3 μm) the YBCO nuclei, whose c axes are perpendicular to the SrTiO3 surface, form directly from this aligned oxy-fluoride. In thick films (5 μm), however, this oxy-fluoride decomposes into a disordered transitory cubic phase which then orders to form YBCO nuclei with three orientational variants, one with its c axis perpendicular and two with their c axes parallel to the (001) plane of SrTiO3.