bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamics of high‐energy electrons interacting with whistler mode chorus emissions in the magnetosphere
Authors: Omura Yoshiharu , Summers Danny
Published: September 2006

Close examination of whistler mode chorus emissions reveals that a chorus emission is a coherent monochromatic wave typically with a fast rising tone. The frequency of the emission increases rapidly along with growth of the wave amplitude. We first consider the generation mechanism of whistler mode chorus emissions. The essential mechanism of the frequency change is critically related to the inhomogeneity of the geomagnetic field in the equatorial region. The rising tone emission is only possible when the coherent wave propagates away from the equator interacting with a sufficient flux of counterstreaming resonant electrons. Depletion of the resonant trapped electrons from the wave phase space results in formation of an electromagnetic electron hole, which gives rise to a transverse resonant current causing both wave growth and frequency increase. The wave growth of a rising tone can elongate the nonlinear trapping zone, which works as an effective wave train that guides a fraction of the resonant electrons moving toward the equator. We perform test particle simulations where we solve the relativistic equations of motion for high‐energy electrons under the action of the electromagnetic field of a coherent whistler mode wave and the assumed dipole geomagnetic field. We find that a fraction of weakly relativistic electrons are trapped by a coherent wave and that the trapped electrons are effectively accelerated by the chorus wave with a rising tone.
Magnetospheric current systems during stormtime sawtooth events
Authors: Pulkkinen T. I. , Ganushkina N. Y. , Tanskanen E. I. , Kubyshkina M. , Reeves G. D. , Thomsen M. F. , Russell C. T. , Singer H. J. , Slavin J. A. , Gjerloev J.
Published: September 2006

The sawtooth event period embedded in a storm interval on 2001‐10‐22 is analyzed using magnetic field modeling techniques. The model current systems show that sawtooth injections are associated with strong stretching of both the nightside and dusk‐sector magnetic field prior to the injection and a partial disruption of that current at the time of the injection. The currents are strongest near geosynchronous distance and in the premidnight sector. The strong dusk‐sector field stretching produces very fast proton drift speeds, which can explain the near‐simultaneous occurrence of the injections over a wide local time sector. Comparison of sawtooth periods with nonstorm substorms indicates that the tail field behavior resembles that of nonstorm substorms, but that the consequences of the stretching/dipolarization cycle are different from nonstorm times. As the drifting protons during sawtooth events are mostly on open drift paths, the symmetric ring current is only slightly affected, while large variations are seen in the asymmetric ring current. The three‐spacecraft magnetic field measurements together with the Dst index were sufficient to constrain the magnetic field model to give a reasonably accurate global magnetic field representation, as confirmed by an independent test using measurements not used in the fitting. Thus we conclude that the empirical modeling methods can be quite reliable in predicting the large‐scale fields when suitable observations are available.
Interplanetary hydrogen absolute ionization rates: Retrieving the solar wind mass flux latitude and cycle dependence with SWAN/SOHO maps
Authors: Quémerais Eric , Lallement Rosine , Ferron Stéphane , Koutroumpa Dimitra , Bertaux Jean‐Loup , Kyrölä Erkki , Schmidt Walter
Published: September 2006

We present results of the total hydrogen ionization rate obtained from the inversion of almost 10 years of full‐sky maps of the interplanetary Lyman α background measured by the SWAN instrument on SOHO. Thanks to a new estimate of the absolute calibration of the SWAN instrument and its variation during the 10 years of operation of SOHO, we are able to derive absolute values of the ionization rate as well as its latitudinal dependence. We show how the anisotropy of the ionization rate changes from solar minimum to solar maximum. At solar maximum, the so‐called ionization groove has completely disappeared and the ionizing fluxes are the same at all heliographic latitudes. We find that the hydrogen ionization cavity which surrounds the Sun increases in size with solar activity. This is evidenced by the low IP Lyman α intensities measured during and after the solar maximum. Our model calculation also shows that the increased radiation pressure is not sufficient to explain the larger cavity observed at solar maximum. We find also that ionization rates derived from in situ solar wind measurements do agree with the SWAN results at solar minimum but are significantly smaller at solar maximum. Derived in situ ionization rates do not show the solar cycle dependence we see from the SWAN data. In conclusion, we discuss possible explanations for this discrepancy.
Characteristics of Jovian morning bright FUV aurora from Hubble Space Telescope/Space Telescope Imaging Spectrograph imaging and spectral observations
Authors: Gustin J. , Cowley S. W. H. , Gérard J.‐C. , Gladstone G. R. , Grodent D. , Clarke J. T.
Published: September 2006

Observation of an exceptionally bright (peaking at ∼1.8 MR) Jovian auroral morning arc was obtained with the Space Telescope Imaging Spectrograph (STIS) on 21 September 1999, both in the imaging and spectral modes. The images of the HST orbit are used to describe the variation of the position of the bright arc, while the time‐tagged spectra are examined to derive the properties of the precipitating auroral electrons, such as their mean energy and the electron current density at the top of the atmosphere. The first and the last images of the HST orbit, separated by 37 min, show that the bright morning emission is situated on the reference oval, with a “leading” edge fixed in λIII longitudes (i.e., rotating with the planet), and a “trailing” edge that extends into the nightside. The auroral arc is divided in two branches, as was also observed in some previous analyses. An isolated bright spot is also observed at λIII ∼184°. Its brightness reaches 500 kR and it also approximately corotates with Jupiter. Four regions of the auroral morning arc captured by the STIS aperture were extracted from the spectral observation. The four associated low‐resolution spectra (∼4.8 Å) show very different characteristics. In particular, two spectra reveal unusually high color ratios (18.5 and 45.5), with corresponding mean electron energies of ∼280 and ∼460 keV, respectively. The current densities associated with three of the spectra lie in the range 0.09–0.2 μA m−2, consistent with previous estimates, while the fourth spectrum is characterized by a mean current density of 0.54 μA m−2, outside the range ∼0.04–0.4 μA m−2 obtained in a previous study of G140L spectra of the Jovian main oval. Assuming that main oval aurorae are caused by field‐aligned electric fields, the relationship between the energy flux and the current density derived from the spectra has been compared to the Knight's theory of field‐aligned currents. Because of the very high acceleration potential derived from two of the extracted spectra, a relativistic treatment of the Knight theory was used. Assuming an electron temperature Te = 2.5 keV, it is seen that the two regions corresponding to earlier local times (higher λIII longitudes) reveal an electron source density lower than the values observed in the equatorial plane during the Voyager flybys. On the other hand, the equatorward region (lowest latitude) exhibits an electron source density in the upper range of usual values. Analysis of time‐tag spectra reveals that the variations of the energy flux and the color ratios are large but continuous and generally covary.
Fusion of CERES, MISR, and MODIS measurements for top‐of‐atmosphere radiative flux validation
Authors: Loeb Norman G. , Sun Wenbo , Miller Walter F. , Loukachine Konstantin , Davies Roger
Published: September 2006

The Clouds and the Earth's Radiant Energy System (CERES), Multiangle Imaging Spectroradiometer (MISR), and Moderate‐resolution Imaging Spectroradiometer (MODIS) instruments aboard the Terra satellite make critical measurements of cloud and aerosol properties and their effects on the Earth's radiation budget. In this study, a new multiangle, multichannel data set that combines measurements from all three instruments is created to assess uncertainties in instantaneous shortwave (SW) top‐of‐atmosphere (TOA) radiative fluxes inferred from CERES Angular Distribution Models (ADMs). MISR Level 1B2 ellipsoid‐projected radiances from nine viewing directions in four spectral bands are merged with CERES by convolving the MISR radiances with the CERES Point Spread Function. The merged CERES‐MISR data are then combined with the CERES Single Scanner Footprint TOA/Surface Fluxes and Clouds (SSF) product to produce the first merged CERES‐MISR‐MODIS data set. CERES and MISR data are used to generate narrow‐to‐broadband regression coefficients to convert narrowband MISR radiances to broadband SW radiances as a function of MODIS‐based scene type. The regression uncertainty for all‐sky conditions over ocean is approximately 4%. Up to nine SW TOA fluxes for every CERES footprint are estimated by applying the CERES Terra ADMs to each MISR angle. Assuming that differences along the line‐of‐sight from the different MISR angles are small, the consistency of the TOA fluxes provides an indication of the instantaneous TOA flux uncertainty. The overall relative consistency of all‐sky ocean TOA fluxes is 6% (17 W m−2). When stratified by cloud type, TOA fluxes are consistent to 2–3% (<10 W m−2) for moderately thick overcast clouds, which make up 15% of the total population.
Spectral bidirectional reflectance of Antarctic snow: Measurements and parameterization
Authors: Hudson Stephen R. , Warren Stephen G. , Brandt Richard E. , Grenfell Thomas C. , Six Delphine
Published: September 2006

The bidirectional reflectance distribution function (BRDF) of snow was measured from a 32‐m tower at Dome C, at latitude 75°S on the East Antarctic Plateau. These measurements were made at 96 solar zenith angles between 51° and 87° and cover wavelengths 350–2400 nm, with 3‐ to 30‐nm resolution, over the full range of viewing geometry. The BRDF at 900 nm had previously been measured at the South Pole; the Dome C measurement at that wavelength is similar. At both locations the natural roughness of the snow surface causes the anisotropy of the BRDF to be less than that of flat snow. The inherent BRDF of the snow is nearly constant in the high‐albedo part of the spectrum (350–900 nm), but the angular distribution of reflected radiance becomes more isotropic at the shorter wavelengths because of atmospheric Rayleigh scattering. Parameterizations were developed for the anisotropic reflectance factor using a small number of empirical orthogonal functions. Because the reflectance is more anisotropic at wavelengths at which ice is more absorptive, albedo rather than wavelength is used as a predictor in the near infrared. The parameterizations cover nearly all viewing angles and are applicable to the high parts of the Antarctic Plateau that have small surface roughness and, at viewing zenith angles less than 55°, elsewhere on the plateau, where larger surface roughness affects the BRDF at larger viewing angles. The root‐mean‐squared error of the parameterized reflectances is between 2% and 4% at wavelengths less than 1400 nm and between 5% and 8% at longer wavelengths.
Chromaticity of the Martian sky as observed by the Mars Exploration Rover Pancam instruments
Authors: Bell J. F. , Savransky D. , Wolff Michael J.
Published: September 2006

We have derived quantitative color estimates of the Martian sky from data acquired by the Panoramic Cameras (Pancams) on the Mars Exploration Rovers Spirit and Opportunity. We calculate the perceptual color of the sky directly from the absolute radiometric calibration of the cameras, following similar approaches to those used in previous studies with Viking Lander and Mars Pathfinder data. We further use these measurements to study changes in sky color throughout the MER missions and to compare these to changes in atmospheric opacity determined from direct solar imaging by the Pancams. We have derived a functional relationship between sky color and optical depth and discuss its possible uses and limitations. Finally, we simulate changes in sky color as suspended dust is removed and present visual representations of these based on modeling results, past studies, and observed MER sky brightnesses. The color of the Martian sky as opacity decreases from 1.0 to 0.0 is estimated to change from “dark yellowish brown” at high opacity to “bluish‐black” or “black” if dust‐free.
Effect of meal temperature on the frequency of gastric myoelectrical activity
Authors: Verhagen M. A. M. T. , Luijk H. D. , Samsom M. , Smout A. J. P. M.
Published: September 2006

It was hypothesized that the transient postprandial decrease of the dominant frequency in the electrogastrogram (EGG) is related to the temperature of the meal. In a randomized three‐period cross‐over design, EGG recordings were made in 10 healthy volunteers. A liquid meal (36 kcal, 300 mL) was ingested at either 4, 37 or 55 °C. The changes in the dominant EGG frequency that occurred in the first 25 min postprandial were calculated using running spectrum analysis. After the meal a transient shift in frequency was seen, which was significantly greater after the cold meal than after the other meals (P<0.001), with a greater decrease in the dominant frequency (4 °C:−0.75 [−0.92 ∼ −0.68], 37 °C:−0.34 [−0.51 ∼ −0.18], 55 °C:−0.30 [−0.45 ∼ −0.12] cpm, P = 0.020) and a longer duration (4 °C: 16 [13 ∼ 19], 37 °C: 12 [6 ∼ 14], 55 °C: 5 [3 ∼ 8] min, P = 0.014). No differences were found between the 37 °C and 55 °C meals, the power ratios or the number of dysrhythmias. The magnitude of the postprandial shift in frequency of gastric myoelectrical activity depends on the temperature of the meal. Meal temperature should be taken into account in studies on postprandial gastric motility.
Cooperative stochastic behavior in the onset of localized corrosion
Authors: Mikhailov Alexander S. , Jain Swati , Organ Levent , Hudson John L.
Published: September 2006

Stochastic temporal and spatiotemporal models of metastable pitting on a metal surface are presented. A stochastic reaction-diffusion model accounts for the effects of local changes in concentration, potential drop, and oxide film damage on the nucleation of subsequent events. The cooperative interactions among events can lead to the formation of clusters of metastable pits and to an explosive growth in the total number of pits. Recent progress in the studies of such phenomena is reviewed. New results based on a mean-field analysis of the model and numerical simulations on critical nucleation effects are reported.
Turing patterns beyond hexagons and stripes
Authors: Yang Lingfa , Dolnik Milos , Zhabotinsky Anatol M. , Epstein Irving R.
Published: September 2006

The best known Turing patterns are composed of stripes or simple hexagonal arrangements of spots. Until recently, Turing patterns with other geometries have been observed only rarely. Here we present experimental studies and mathematical modeling of the formation and stability of hexagonal and square Turing superlattice patterns in a photosensitive reaction-diffusion system. The superlattices develop from initial conditions created by illuminating the system through a mask consisting of a simple hexagonal or square lattice with a wavelength close to a multiple of the intrinsic Turing pattern’s wavelength. We show that interaction of the photochemical periodic forcing with the Turing instability generates multiple spatial harmonics of the forcing patterns. The harmonics situated within the Turing instability band survive after the illumination is switched off and form superlattices. The square superlattices are the first examples of time-independent square Turing patterns. We also demonstrate that in a system where the Turing band is slightly below criticality, spatially uniform internal or external oscillations can create oscillating square patterns.
Hard x-ray imaging for measuring laser absorption spatial profiles on the National Ignition Facility
Authors: Dewald E. L. , Jones O. S. , Landen O. L. , Suter L. , Amendt P. , Turner R. E. , Regan S.
Published: September 2006

Hard x-ray (“thin wall”) imaging will be employed on the National Ignition Facility (NIF) to spatially locate laser beam energy deposition regions on the hohlraum walls in indirect drive Inertial Confinement Fusion (ICF) experiments, relevant for ICF symmetry tuning. Based on time resolved imaging of the hard x ray emission of the laser spots, this method will be used to infer hohlraum wall motion due to x ray and laser ablation and any beam refraction caused by plasma density gradients. In optimizing this measurement, issues that have to be addressed are hard x-ray visibility during the entire ignition laser pulse with intensities ranging from 1013to1015W∕cm2, as well as simultaneous visibility of the inner and the outer laser drive cones. In this work we will compare the hard x-ray emission calculated by LASNEX and analytical modeling with thin wall imaging data recorded previously on Omega and during the first hohlraum experiments on NIF. Based on these calculations and comparisons the thin wall imaging will be optimized for ICF/NIF experiments.
Synchronization phenomena for a pair of locally coupled chaotic electrochemical oscillators: A survey
Authors: Rivera M. , Martínez Mekler G. , Parmananda P.
Published: September 2006

Chaotic synchronization of two locally coupled electrochemical oscillators is studied numerically. Both bidirectional and unidirectional couplings are considered. For both these coupling scenarios, varying the characteristics of the coupling terms (functional form and/or strength) reveals a wide variety of synchronization phenomena. Standard diagnostic tests are performed to verify and classify the different types of synchronizations observed.
Modeling fast charge exchange recombination spectroscopy measurements from the Madison Symmetric Torus
Authors: Gangadhara S. , Craig D. , Ennis D. A. , Den Hartog D. J.
Published: September 2006

Charge exchange recombination spectroscopy measurements of impurity ion temperature (Ti) and velocity (vi) on the Madison Symmetric Torus present a unique challenge due to two coupled effects: low temperature—typically 300–500eV, though up to 2keV in high current plasmas—and a dominant contribution from background, i.e., non charge exchange driven, emission. For low Ti, the background emission line shape is significantly asymmetric as a result of spin-orbit coupling effects. Accurate modeling of both the background and beam emission is therefore required to obtain precise values for local ion parameters. A model has been developed to provide robust simulation of the experimental measurements with ∼10μs temporal resolution using atomic data obtained from the Atomic Data and Analysis Structure database. Measurements are made using C VI emission at 343.4nm, with background and beam emissions obtained simultaneously using two fiber bundles with slightly displaced lines of sight. Emission from O VI contributes substantially to the background signal, and is included in the modeling. A complete description of the model will be presented, along with results for Ti measurements during magnetic reconnection.
Spatio-temporal behaviors of a clock reaction in an open gel reactor
Authors: Benyaich Khalid , Erneux Thomas , Métens Stéphane , Villain Sébastien , Borckmans Pierre
Published: September 2006

The concentration profiles along the feeding direction of a one side fed gel reactor are analyzed for the iodate-arsenous acid reaction. Multiplicity of inhomogeneous stationary solutions is derived. It is also shown that such profiles may undergo oscillatory bifurcations under long range activation conditions. The bifurcation diagram is analyzed using a Galerkin approximation, the asymptotic validity of which is discussed.
Hamiltonian formalism for semiflexible molecules in Cartesian coordinates
Authors: Kneller G. R.
Published: September 2006

The article gives a concise description of Hamiltonian dynamics and thermal averages of semiflexible molecules in Cartesian coordinates. Using the concept of constrained inverse matrices introduced by Bott and Duffin [Trans. Am. Math. Soc. 74, 99 (1953)] explicit expressions are derived for the constrained Hamiltonian, the corresponding equations of motion, and the momentum partition function. In this context Fixman-type corrections of constrained configurational averages are derived for different forms of the constraints. It is shown that the use of mass-weighted coordinates leads to a nonbiased sampling of constrained configurational averages in Cartesian coordinates. The formalism allows moreover to define and to calculate effective masses arising in thermal velocity averages of atoms in semiflexible molecules. These effective masses are identical to the corresponding Sachs-Teller recoil masses, which are here generalized to the case of only partially rigid molecules.
Magnetohydrodynamic and turbulence activity analysis in the ISTTOK tokamak using empirical mode decomposition
Authors: Coelho R. , Alves D. , Silva C.
Published: September 2006

The understanding of the nature, driving mechanisms, and dynamics of turbulence activity in tokamak plasmas is a major challenge in fusion research. In the ISTTOK tokamak, edge turbulence activity has been extensively studied using both limiter and electrode biasing to induce local sheared electric fields, thus affecting turbulence and consequently particle confinement. Due to the fast time scales involved plasmas (pulse length of 30ms and particle confinement of the order of 0.3ms) and the turbulent nature of ISTTOK plasmas, not only turbulence but also magnetohydrodynamic (MHD) activity occurs at rapid bursts. Therefore, resolving the modes both spatially and during time (in particular, regarding the energy/frequency spectrum) requires advanced time-frequency analysis tools, capable of tracking short lasting (0.1ms) MHD modes. In this article, we explore the capabilities of the empirical mode decomposition method as a tool for turbulence and MHD instability analysis. The time evolution of the energy content associated with fluctuating potential, edge plasma density (obtained from Langmuir probes), and perturbed magnetic fields (Mirnov coil signals) is obtained, and a comparison is made with other advanced time-frequency signal estimators.
3
ω
transmitted beam diagnostic at the Omega Laser Facility
Authors: Froula D. H. , Rekow V. , Sorce C. , Piston K. , Knight R. , Alvarez S. , Griffith R. , Hargrove D. , Ross J. S. , Dixit S. , Pollock B. , Divol L. , Glenzer S. H. , Armstrong W. , Bahr R. , Thorp K. , Pien G.
Published: September 2006

The laser light from a single beam transmitted through a plasma is collected by a 3ω transmitted beam diagnostic which is now operational on the Omega Laser Facility at the Laboratory for Laser Energetics, University of Rochester [Soures et al., Laser. Part. Beams 11, 317 (1993)]. Transmitted laser light from Beam 30 is collected by a focusing mirror and directed onto a diagnostic platform. The near field of the transmitted light is imaged; the system collects information from twice the original f cone of the beam. Two gated cameras capture the near field image of the transmitted light. The evolution of the beam spray is resolved temporally at 13 spatial positions around the near field. The forward stimulated Raman scattering and forward simulated Brillouin scattering are resolved spectrally and temporally at five independent locations within twice the original f cone. The total transmitted energy is measured in two spectral regions above and below 400nm.
Effect of substrate proximity on luminescence yield from Si nanocrystals
Authors: Sychugov Ilya , Galeckas Augustinas , Elfström Niklas , Wilkinson Andrew R. , Elliman Robert G. , Linnros Jan
Published: September 2006

The influence of the proximity of a high refractive index substrate on the luminescence of Si nanocrystals was investigated by time-integrated and time-resolved photoluminescence. The luminescence yield was found to be ∼2.5 times larger for emitters distanced from the substrate compared to those in proximity with the substrate, while luminescence decay measurements revealed only a slight increase in the luminescence lifetime (∼15%). Results are discussed in terms of local density of optical modes surrounding a pointlike light emitter with important implications for the collection efficiency of luminescence and the estimation of internal quantum efficiency for a quantum dot.
Enhancement of x-ray yield from the Z-Beamlet laser for monochromatic backlighting by using a prepulse
Authors: Sinars D. B. , Bennett G. R. , Herrmann M. C. , Smith I. C. , Speas C. S. , Ruggles L. E. , Porter J. L.
Published: September 2006

The Z-Beamlet Laser (ZBL) is capable of providing on-target energies of up to 1.5kJ at 527nm in up to four separate 0.3–1.5ns pulses during a 20ns window. ZBL is routinely used as a source of x rays for backlighting experiments on the Sandia Z facility, a 20MA, 100ns rise-time, pulsed-power driver for z-pinch plasma radiation sources. Most backlighting experiments use monochromatic crystal imaging diagnostics at 1865 or 6151eV. We present calibration data demonstrating that the use of a 0.3–0.6ns, ∼200J pulse, followed 2ns later by a 1.0ns, ∼1kJ pulse results in more than twice the x-ray yield at 6151eV (a He-like Mn emission line) compared to a single 1.0ns, ∼1kJ pulse. The first pulse creates a plasma (and few x rays) that expands and approaches the critical density for the laser when the second pulse arrives, creating a more efficient coupling of laser light to the plasma. A similar improvement was also noted for He-like Ni emission lines, suggesting that this simple technique scales to higher photon energies.
Propagation failures, breathing pulses, and backfiring in an excitable reaction-diffusion system
Authors: Manz Niklas , Steinbock Oliver
Published: September 2006

We report results from experiments with a pseudo-one-dimensional Belousov-Zhabotinsky reaction that employs 1,4-cyclohexanedione as its organic substrate. This excitable system shows traveling oxidation pulses and pulse trains that can undergo complex sequences of propagation failures. Moreover, we present examples for (i) breathing pulses that undergo periodic changes in speed and size and (ii) backfiring pulses that near their back repeatedly generate new pulses propagating in opposite direction.
Nonlocal electron transport in magnetized plasmas with arbitrary atomic number
Authors: Bennaceur-Doumaz D. , Bendib A.
Published: September 2006

The numerical solution of the steady-state electron Fokker-Planck equation perturbed with respect to a global equilibrium is presented in magnetized plasmas with arbitrary atomic number Z. The magnetic field is assumed to be constant and the electron-electron collisions are described by the Landau collision operator. The solution is derived in the Fourier space and in the framework of the diffusive approximation which captures the spatial nonlocal effects. The transport coefficients are deduced and used to close a complete set of nonlocal electron fluid equations. This work improves the results of A. Bendib et al. [Phys. Plasmas 9, 1555 (2002)] and of A. V. Brantov et al. [Phys. Plasmas 10, 4633 (2003)] restricted to the local and nonlocal high-Z plasma approximations, respectively. The influence of the magnetic field on the nonlocal effects is discussed. We propose also accurate numerical fits of the relevant transport coefficients with respect to the collisionality parameter λei∕L and the atomic number Z, where L is the typical scale length and λei is the electron-ion mean-free-path.
Spatial bistability: A source of complex dynamics. From spatiotemporal reaction-diffusion patterns to chemomechanical structures
Authors: Boissonade J. , De Kepper P. , Gauffre F. , Szalai I.
Published: September 2006

We show experimentally and theoretically that reaction systems characterized by a slow induction period followed by a fast evolution to equilibrium can readily generate “spatial bistability” when operated in thin gel reactors diffusively fed from one side. This phenomenon which corresponds to the coexistence of two different stable steady states, not breaking the symmetry of the boundary conditions, can be at the origin of diverse reaction-diffusion instabilities. Using different chemical reactions, we show how stationary pulses, labyrinthine patterns or spatiotemporal oscillations can be generated. Beyond simple reaction-diffusion instabilities, we also demonstrate that the cross coupling of spatial bistability with the size responsiveness of a chemosensitive gel can give rise to autonomous spatiotemporal shape patterns, referred to as chemomechanical structures.
Optical properties of InGaNP quantum wells grown on GaP (100) substrates by gas-source molecular beam epitaxy
Authors: Odnoblyudov V. A. , Tu C. W.
Published: September 2006

The authors describe optical properties of a GaNP and InGaNP quantum wells grown on a GaP(100) substrate by gas-source molecular beam epitaxy. Temperature-dependent photoluminescence shows that the GaNP quantum wells are well described by the Varshni equation, but the InGaNP quantum wells show a deviation, revealing the existence of localized states in these quantum wells. The electron effective mass of InxGa1−xN0.005P0.995 was determined from quantum wells with different indium compositions. Increasing the indium concentration from 0.05 to 0.2 decreases the electron effective mass from 0.77me to 0.4me.
Multifrequency, repulsive-mode amplitude-modulated atomic force microscopy
Authors: Proksch Roger
Published: September 2006

An imaging method where a cantilever is driven at or near two of its flexural resonant eigenmodes is described. For most cantilevers, these eigenmodes are nonharmonic. The cantilever and imaging parameters are chosen such that the tip-sample interactions are repulsive. The driven second eigenmode amplitude and phase show strikingly different contrasts from those same fundamental eigenmode signals on graphite samples imaged in air and λ-digest deoxyribonucleic acid samples imaged in water.
Spiral wave dynamics in excitable media with spherical geometries
Authors: Rohlf Katrin , Glass Leon , Kapral Raymond
Published: September 2006

We describe the spatial and temporal organization of spiral and scroll waves in spherical shells of different sizes and solid spheres. We present simulation results for the evolution of the dynamics and clustering of spiral waves as a function of the excitability of the medium. The excitability, topology, and size of the domain places restrictions on how single and multiarmed spiral waves are organized in space. The results in spherical geometries are compared with those in planar two-dimensional media. These studies are relevant to the dynamics of spiral waves in a variety of media including the heart, and chemical reactions on spherical surfaces.
Periodic and chaotic oscillations of the electrochemical potential of p-Si in contact with an aqueous (CuSO4+HF) solution, caused by electroless Cu deposition
Authors: Nagai Tomoyuki , Nakanishi Shuji , Mukouyama Yoshiharu , Ogata Yukio H. , Nakato Yoshihiro
Published: September 2006

Periodic and chaotic oscillations were observed for the potential of p-type Si(111) immersed in an aqueous (HF+CuSO4) solution, accompanied by electroless Cu deposition on p-Si. They were, to our knowledge, the first examples of open-circuit potential oscillations observed for semiconductor electrodes. The oscillations appeared only when the Cu deposit formed a continuous porous film composed of mutually connected submicrometer-sized particles. Besides, the Si surface was kept flat within the size less than 50nm even after the prolonged oscillation for a few hours, though the Si surface should be etched considerably with HF for this time. A plausible model is proposed for the periodic oscillation, in which interestingly coupling of autocatalytic shift in the flat-band potential of Si (Ufb) caused by the change in the coverage of the Si oxide and the connection and disconnection of the Cu film with the Si surface plays the key role. The appearance of the chaotic oscillation is also explained by taking into account an oscillation-coupled change in the HF or Cu2+ concentration near the Si surface.
High Tc superconducting quantum interference devices made by ion irradiation
Authors: Bergeal N. , Lesueur J. , Faini G. , Aprili M. , Contour J. P.
Published: September 2006

The authors describe a method to make superconducting quantum interference devices (SQUIDs) formed in a single layer of high Tc superconducting materials. The superconducting loop is patterned using ion beam irradiation through an in situ suitable gold mask. Josephson junctions are defined by a lower fluence irradiation through narrow slits opened in a polymethyl methacrylate resist. The critical current and the resistance of the SQUIDs at a given temperature can be adjusted precisely by choosing the fluence of irradiation to make the device operational at temperatures between 4.2K and the Tc of the superconducting material.
Two-electron distribution functions and short-range electron correlations of atoms and molecules by first principles T-matrix calculations
Authors: Noguchi Yoshifumi , Ishii Soh , Ohno Kaoru
Published: September 2006

The accurate first principles description of the correlations between electrons has been a topic of interest in molecular physics. We have reported in our previous paper [J. Chem. Phys. 123, 144112 (2005)] that the T matrix, which is the ladder diagrams up to the infinite order, can accurately represent the short-range electron correlations while calculating the double ionization energy spectra of atoms and molecules. In this paper, we calculate the two-electron distribution functions of real systems (Ar, CO, CO2, and C2H2) from the eigenvalue equation associated with the Bethe-Salpeter equation for the T matrix by beginning with the local density approximation of the density functional theory and the GW approximation. We found that when the interelectron distance is very small, the Coulomb hole appears between antiparallel spin electrons due to the short-range repulsive Coulomb interaction. The resulting two-electron distribution functions clearly show the Coulomb hole.
A clue to the diffuse structure in ultraviolet spectra of the GeCl2 A-X transition
Authors: Yu Hua-Gen , Sears Trevor J.
Published: September 2006

Geometries, harmonic vibrational frequencies, and relative electronic energies of the two low-lying electronic states of the GeCl2 dimer have been calculated at the CIS(D) method with a cc-pVTZ basis set. Minima corresponding to three isomers on the ground-state potential energy surface have been characterized. The most stable dimer has a dissociation energy of 0.74eV and has a trans-(GeCl2)2 structure. There is also a related, less stable, cis minimum. A third, Ci symmetry, isomer has a binding energy of 0.31eV. It is found that this Ci isomer has substantial dipole transition strength to the first excited singlet state of the dimer with a vertical excitation energy of 3.33eV. The transition energy (T0) between this Ci isomer and the van der Waals complex on the singlet excited state is predicted to be 4.007eV, or a 1104cm−1 blueshift with respect to that of the GeCl2 A-X transition. This finding may explain the diffuse structure which has been observed in the ultraviolet laser-induced fluorescence spectra of GeCl2.
Disseminator for rapid, selectable, and quantitative delivery of low and semivolatile liquid species to the vapor phase
Authors: Johnson Timothy J. , Sharpe Steven W. , Covert Matthew A.
Published: September 2006

Nelson and Griggs [Rev. Sci. Instrum. 39, 927 (1968)] introduced a quantitative method for disseminating liquid samples to the vapor phase using a lead screw to depress the plunger of a syringe whose body was heated and whose ambient tip was placed into the flow of a carrier gas. In order to measure quantitative vapor-phase infrared spectra, we have modified a commercial device to improve the accuracy and precision for quantitative vapor delivery. Design changes have focused on disseminating reactive or low volatility liquids by heating only the syringe tip and dispensed liquid. Performance features include quantitative vapor-phase generation with greater than three orders of magnitude concentration range, including low volatility species, with most equilibration times <40s. The method has been vetted by comparing the derived gas-phase infrared data versus IR spectra taken using both gravimetric (National Institute of Standards Technology) and passive vapor generation (Pacific Northwest National Laboratory) techniques. Quantitative vapor spectra of low volatility samples are reported.
Entropy conservation in simulations of magnetic reconnection
Authors: Birn J. , Hesse M. , Schindler K.
Published: September 2006

Entropy and mass conservation are investigated for the dynamic field evolution associated with fast magnetic reconnection, based on the “Newton Challenge” problem [Birn et al., Geophys. Res. Lett. 32, L06105 (2005)]. In this problem, the formation of a thin current sheet and magnetic reconnection are initiated in a plane Harris-type current sheet by temporally limited, spatially varying, inflow of magnetic flux. Using resistive magnetohydrodynamic (MHD) and particle-in-cell (PIC) simulations, specifically the entropy and mass integrated along the magnetic flux tubes are compared between the simulations. In the MHD simulation these should be exactly conserved quantities, when slippage and Ohmic dissipation are negligible. It is shown that there is very good agreement between the conservation of these quantities in the two simulation approaches, despite the effects of dissipation, provided that the resistivity in the MHD simulation is strongly localized. This demonstrates that dissipation is highly localized in the PIC simulation also, and that heat flux across magnetic flux tubes has negligible effect as well, so that the entropy increase on a full flux tube remains small even during reconnection. The mass conservation also implies that the frozen-in flux condition of ideal MHD is a good integral approximation outside the reconnection site. This result lends support for using the entropy-conserving MHD approach not only before and after reconnection but even as a constraint connecting the two phases.
p
H
tracking of silica hydrogel nanoparticle growth
Authors: Cleary Alison , Karolin Jan , Birch David J. S.
Published: September 2006

The authors show that pH increase, due to removal by condensation of silicic acid, correlates with nanoparticle growth during the initial stages of silica hydrogel formation and becomes constant at a time tpH, the point when other particle growth mechanisms dominate. Absorption of common phthalein indicators is shown to allow effectively instantaneous tracking of the pH and nanoparticle size in alkaline and acidic hydrogels. Particle sizes are calibrated using the hydrodynamic radius determined from the fluorescence anisotropy decay. Tracking pH complements fluorescence anisotropy nanometrology by offering a lower cost, speedier, and simpler method of studying particle growth during silica hydrogel fabrication.
Infrared spectroscopy of hydrated sulfate dianions
Authors: Zhou Jia , Santambrogio Gabriele , Brümmer Mathias , Moore David T. , Wöste Ludger , Meijer Gerard , Neumark Daniel M. , Asmis Knut R.
Published: September 2006

We report the first infrared spectra of multiply-charged anions in the gas phase. The spectra of SO42−∙(H2O)n, with n=3–24, show four main bands assigned to two vibrations of the dianionic core, the water bending mode, and solvent libration. The triply degenerate SO42− antisymmetric stretch vibration probes the local solvent symmetry, while the solvent librational band is sensitive to the hydrogen bonding network. The spectra and accompanying electronic structure calculations indicate a highly symmetric structure for the n=6 cluster and closure of the first solvation shell at n=12.
Molecular dynamics simulation of glycine zwitterion in aqueous solution
Authors: Campo Mario G.
Published: September 2006

A classical molecular dynamics method was used to study the modifications of the solution structure and the properties of glycine zwitterion in aqueous solution due to the increase of glycine zwitterion concentration and the incorporation of Na+ and Cl− ions to the solution. The glycine zwitterion had fundamentally a hydrophilic behavior at infinite dilution, establishing around six hydrogen bonds with the water molecules that surrounded it, which formed a strong hydration layer. Because of the increase of glycine zwitterion concentration, the hydration structure became more compact and the quantity of water molecules bound to this molecule decreased. The Na+ ion bound to the CO2 group of glycine, while the Cl− ion bound mainly to the NH3 group of this molecule. The integration of the ions to the hydration layer of the glycine zwitterion produced modifications in the orientational correlation between atoms of glycine zwitterion and water that surrounded them and an increase of the approaches between the glycine zwitterion molecules. The incorporation of ions to the solution also produced changes in the water-water orientational correlation. Decreases of the water-water hydrogen bonds and diffusion coefficient of all molecules were observed when the glycine zwitterion concentration increased and when the ions were incorporated to the solution.
Experimental evidence and theoretical analysis for the chiral symmetry breaking in the growth front of conglomerate crystal phase of 1,1′-binaphthyl
Authors: Asakura Kouichi , Plasson Raphaël , Kondepudi Dilip K.
Published: September 2006

Chirally asymmetric states, chemical oscillations, propagating chemical waves, and spatial patterns, are examples of far-from-equilibrium self-organization. We have found that the crystal growth front of 1,1′-binaphthyl shows many of the characteristics of an open system in which chiral symmetry breaking has occurred. From its supercooled molten phase, 1,1′-binaphthyl crystallizes as a conglomerate of R and S crystals when the temperature is above 145°C. In addition, 1,1′-binaphthyl in its molten phase is always racemic due to its high racemization rate. Under appropriate conditions, bimodal probability distribution of enantiomeric excess (ee) with maxima around 60% was observed. The ee was mass independent, indicating that the growth front maintains a constant ee. A kinetic model that theoretically analyzes the chiral symmetry breaking transition in the growth front of a conglomerate crystal phase was formulated. Computer simulation of the model reproduced not only the average but also the large variation of the ee observed in crystallization experiments.
Magnetic manipulation of materials in a magnetic ionic liquid
Authors: Okuno Masanari , Hamaguchi Hiro-o , Hayashi Satoshi
Published: September 2006

Nonmagnetic materials in a magnetic ionic liquid, which has a very large magnetic susceptibility, respond to a magnet as if they are strongly diamagnetic. The trajectory of deflected nitrogen gas bubbles in 1-butyl-3-methylimidazolium tetrachloroferrate has been measured. It shows a good agreement with theory. Nonmagnetic materials can be transported and separated in a magnetic ionic liquid, according to their density and magnetic susceptibility by regulating magnetic field and its gradient.
Self-limiting oxidation of SiGe alloy on silicon-on-insulator wafers
Authors: Shimura Takayoshi , Shimizu Michihiro , Horiuchi Shinichiro , Watanabe Heiji , Yasutake Kiyoshi , Umeno Masataka
Published: September 2006

Self-limiting oxidation of SiGe alloy on silicon-on-insulator wafers was investigated. For oxidation at 1000°C, oxidation stops completely after a few hours for the Si1−xGex (x=0.068–0.16) layers. For higher initial Ge concentrations of the SiGe layer, the oxidation saturated in a shorter oxidation time, whereas saturation was not observed for the oxidation at 900 and 1100°C. The authors propose a model for self-limiting oxidation, in which the oxidation saturation is governed by an interfacial Ge-rich layer that depends on the oxidation temperature and the initial Ge concentration.
Approximate first passage time distribution for barrier crossing in a double well under fractional Gaussian noise
Authors: Chaudhury Srabanti , Cherayil Binny J.
Published: September 2006

The distribution of waiting times, f(t), between successive turnovers in the catalytic action of single molecules of the enzyme β-galactosidase has recently been determined in closed form by Chaudhury and Cherayil [J. Chem. Phys. 125, 024904 (2006)] using a one-dimensional generalized Langevin equation (GLE) formalism in combination with Kramers’ flux-over-population approach to barrier crossing dynamics. The present paper provides an alternative derivation of f(t) that eschews this approach, which is strictly applicable only under conditions of local equilibrium. In this alternative derivation, a double well potential is incorporated into the GLE, along with a colored noise term representing protein conformational fluctuations, and the resulting equation transformed approximately to a Smoluchowski-type equation. f(t) is identified with the first passage time distribution for a particle to reach the barrier top starting from an equilibrium distribution of initial points, and is determined from the solution of the above equation using local boundary conditions. The use of such boundary conditions is necessitated by the absence of definite information about the precise nature of the boundary conditions applicable to stochastic processes governed by non-Markovian dynamics. f(t) calculated in this way is found to have the same analytic structure as the distribution calculated by the flux-over-population method.
Effect of clay platelet orientation on spin cast nanocomposite films
Authors: Li J. , Schwarz S. A. , Ji Y. , Rafailovich M. H. , Sokolov J. , Rudomen G. , Feng W. H.
Published: September 2006

The authors show that the thickness of spin cast nanocomposite polystyrene/clay films displays a large radial dependence that is not explained by current models. Transmission electron microscopy and atomic force microscopy reveal a tendency for the high aspect ratio clay particles to align in the direction of shear. Near the center of rotation, particles remain randomly oriented leading to the formation of voids as the film dries. They present a two dimensional numerical model that incorporates both hydrodynamic and orientation effects and accurately fits the thickness data over a wide range of filler concentrations and spin rates.