bluuebunny/crossref_metadata_2025 huggingface dataset:
Relative humidity patterns and fog water precipitation in the Atacama Desert and biological implications
Authors: Cáceres Luis , Gómez‐Silva Benito , Garró Ximena , Rodríguez Violeta , Monardes Vinka , McKay Christopher P.
Published: September 2007

Fog is the most important source of water for native plants and biological soil crusts in the Atacama Desert. Since fog depends upon available moisture, an understanding of climatic patterns is essential to interpret its present‐day occurrence and distribution. In this work, temperature and humidity of ambient air and collected fog water in selected sites were studied across a transect from the coast to inland of the Atacama Desert, by using automated outdoor sensors for temperature and relative humidity, and also fog collectors equipped with automated rain gauges to measure collected fog water flow rates. Field measurements were organized to determine fog and collected fog water patterns at three selected sites, namely, Coloso, Inacesa and Yungay in addition to the relative humidity and temperature variation with altitude at Coloso Mountain located within Coloso site. The results show a decreasing trend in the collected fog water flow rates from the coast toward inland locations. Daily thermal oscillations at each site are closely related to fog water collection. At Coloso Mountain, an adiabatic cooling‐like effect of the wind ascending its slope was observed preferentially during nighttime. At daytime, occasional distortions observed in the temperature profiles are probably produced by a thermal driven‐air convection process along the Coloso Mountain slope heated by solar radiation. The reduction in available water from fog from the coast to the inland site is consistent with the reduction in colonization rate for hypolithic cyanobacteria along this same transect.
Multiple scattering of waves by dense random distributions of sticky particles for applications in microwave scattering by terrestrial snow
Authors: Tse Ka Ki , Tsang Leung , Chan Chi Hou , Ding Kung Hau , Leung Kwok Wa
Published: September 2007

We investigate the multiple scattering of waves by dense random distribution of particles. Maxwell equations are put in the form of Foldy‐Lax multiple‐scattering equations which are solved numerically. The positions of the particles are generated by random shuffling and bonding. Simulations are performed for applications in microwave scattering by terrestrial snow. The results are illustrated for the copolarization and cross‐polarization scattering phase matrices and the extinction coefficients for sticky particles. We consider concentrations of particles up to 40% by volume. Results of dense media simulations depart from the predictions on the basis of classical theory of independent scattering and are applicable for very low concentrations. The simulation results agree with those of quasi‐crystalline approximation (QCA) for concentration up to 20%. However, they start to deviate from those of the QCA for higher concentrations as QCA underestimates the extinction. Simulation results also predict strong cross polarization in the phase matrix of densely packed spheres, a result that is not predicted by classical independent scattering nor by QCA.
Exploitation of high‐density DInSAR data points of the Umbria‐Marche (Italy) 1997 seismic sequence for fault characteristics
Authors: Dalla Via G. , Crippa B. , Toraldo Serra E. M. , Giacomuzzi G. , Sabadini R.
Published: September 2007

High spatial resolution DInSAR data for the Umbria Marche 1997 seismic sequence are exploited by relaxing constraints derived from datasets of different nature, such as seismologically derived fault dimensions. DInSAR data are thus inverted for a realistic slip distribution over the faults, in terms of depth distribution and roughness, which allows us to relocate the main faults and to minimize the misfit between the vertical displacement pattern derived from DInSAR and model predictions. Our analysis reveals that slip affected not only the shallowest part of the fault system but also its deepest part, rupturing the whole seismogenic layer of the crust down to 10 km, reaching slip values up to 30 cm at the base of the seismogenic layer. Misfit is reduced by a factor of two with respect to previous analyses based on a smaller number of digitized fringe points.
Electron pitch angle distributions as indicators of magnetic field topology near Mars
Authors: Brain D. A. , Lillis R. J. , Mitchell D. L. , Halekas J. S. , Lin R. P.
Published: September 2007

We have analyzed electron angular distributions recorded near Mars over a period of 7 years in order to constrain the topology of magnetic field lines near Mars. We used 63 million pitch angle distributions of 115 eV electrons measured at ∼400 km altitudes by the Mars Global Surveyor (MGS) spacecraft and classified them according to their shape. Closed magnetic field lines are associated with the Martian crustal magnetic fields and are identified on the nightside by the presence of plasma voids or two‐sided loss cones (trapped distributions). Trapped distributions on the nightside are most often observed in regions surrounding moderate or strong crustal fields, indicating a source process such as reconnection populates the outer layers of closed magnetic field regions. Open magnetic field lines are identified in regions of strong crustal magnetic field by the absence of field‐aligned electrons returning from the planet (loss cones). In regions far from crustal sources many field lines intersect the collisional atmosphere. On the Martian dayside, closed field lines are identified by the presence of trapped or fully isotropic distributions, and they occur at times when ionospheric photoelectron features are evident in MGS electron energy spectra. Variability of the dominant pitch angle distribution shape in certain regions suggests that Martian magnetic field topology is dynamic and is controlled by external conditions.
Influence of fore‐arc structure on the extent of great subduction zone earthquakes
Authors: Llenos Andrea L. , McGuire Jeffrey J.
Published: September 2007

Structural features associated with fore‐arc basins appear to strongly influence the rupture processes of large subduction zone earthquakes. Recent studies demonstrated that a significant percentage of the global seismic moment release on subduction zone thrust faults is concentrated beneath the gravity lows resulting from fore‐arc basins. To better determine the nature of this correlation and to examine its effect on rupture directivity and termination, we estimated the rupture areas of a set of Mw 7.5–8.7 earthquakes that occurred in circum‐Pacific subduction zones. We compare synthetic and observed seismograms by measuring frequency‐dependent amplitude and arrival time differences of the first orbit Rayleigh waves. At low frequencies, the amplitude anomalies primarily result from the spatial and temporal extent of the rupture. We then invert the amplitude and arrival time measurements to estimate the second moments of the slip distribution which describe the rupture length, width, duration, and propagation velocity of each earthquake. Comparing the rupture areas to the trench‐parallel gravity anomaly (TPGA) above each rupture, we find that in 11 of the 15 events considered in this study the TPGA increases between the centroid and the limits of the rupture. Thus local increases in TPGA appear to be related to the physical conditions along the plate interface that favor rupture termination. Owing to the inherently long timescales required for fore‐arc basin formation, the correlation between the TPGA field and rupture termination regions indicates that long‐lived material heterogeneity rather than short timescale stress heterogeneities are responsible for arresting most great subduction zone ruptures.
Autophagy is Increased after Traumatic Brain Injury in Mice and is Partially Inhibited by the Antioxidant γ-glutamylcysteinyl Ethyl Ester
Authors: Lai Yichen , Hickey Robert W , Chen Yaming , Bayιr Hülya , Sullivan Mara L , Chu Charleen T , Kochanek Patrick M , Dixon C Edward , Jenkins Larry W , Graham Steven H , Watkins Simon C , Clark Robert SB
Published: September 2007

Autophagy is a homeostatic process for recycling of proteins and organelles, induced by nutrient deprivation and regulated by oxygen radicals. Whether autophagy is induced after traumatic brain injury (TBI) is not established. We show that TBI in mice results in increased ultrastructural and biochemical evidence of autophagy. Specifically, autophagosomal vacuoles and secondary lysosomes were frequently observed in cell processes and axons in ipsilateral brain regions by electron microscopy, and lipidated microtubule-associated protein light chain 3, a biochemical footprint of autophagy referred to as LC3 II, was increased at 2 and 24 h after TBI versus controls. Since oxygen radicals are believed to be important in the pathogenesis of TBI and are essential for the process of starvation-induced autophagy in vitro, we also sought to determine if treatment with the antioxidant γ-glutamylcysteinyl ethyl ester (GCEE) reduced autophagy and influenced neurologic outcome after TBI in mice. Treatment with GCEE reduced oxidative stress and partially reduced LC3 II formation in injured brain at 24 h after TBI versus vehicle. Treatment with GCEE also led to partial improvement in behavioral and histologic outcome versus vehicle. Taken together, these data show that autophagy occurs after experimental TBI, and that oxidative stress contributes to overall neuropathology, in part by initiating or influencing autophagy.
The Taylor-Culick profile with arbitrary headwall injection
Authors: Majdalani Joseph , Saad Tony
Published: September 2007

Taylor’s incompressible and rotational profile is extended to a porous cylinder with arbitrary headwall injection. This profile, often referred to as Culick’s mean flow, is now generalized to permit the imposition of reactive headwall conditions. Starting with Euler’s steady equations, the solution that we derive is approximate, being exact only at the sidewall, the centerline, or for similarity-conforming inlet profiles. Furthermore, the approximation is quasiviscous, being observant of the no slip requirement at the sidewall. Based on numerical experiments under inviscid flow conditions, the closed-form approximation that we obtain appears to be well suited to describe the bulk flow field in basic models of solid and hybrid rockets where uniform sidewall injection is imposed at the propellant surface. For similarity-nonconforming profiles, the approximation becomes more accurate as we move away from the headwall. Results are verified using computational fluid dynamics for several headwall injection patterns.
Thermodynamic analysis of the low frequency relaxation time in the smectic A and C phases of a liquid crystal
Authors: Urban S. , Roland C. M. , Czub J. , Skrzypek K.
Published: September 2007

Pressure-temperature-volume (pVT) measurements were carried out on 2-(4-hexyloxyphenyl)-5-octyl-pyrimidine, a substance exhibiting nematic and smectic A and C polymorphism. Analysis of the longitudinal relaxation times obtained recently for elevated pressures [Czub et al., Z. Naturforsch. A: Phys. Sci. 58, 333 (2003)] was performed for isobaric, isothermal, and isochoric conditions within the two smectic phases. Several relationships linking the dynamical and thermodynamical quantities, derived recently for isotropic glass formers [Roland et al. Rep. Prog. Phys. 68, 1405 (2005)], were found to hold for the liquid crystal, revealing a striking similarity of behaviors for these two types of materials. The parameter γ characterizing the steepness of the interaction potential was derived in different ways. It is interesting that the liquid crystal gives relaxation time versus TV−γ plots that are linear, unlike results for glass formers, implying that the dynamics of the former is thermally activated.
Magnetohydrodynamics modelling of H-mode plasma response to external resonant magnetic perturbations
Authors: Nardon E. , Bécoulet M. , Huysmans G. , Czarny O.
Published: September 2007

The response of an H-mode plasma to Resonant Magnetic Perturbations (RMPs) generated by so-called “I-coils” in DIII-D experiments on type I edge localized modes suppression is modelled using the nonlinear reduced magnetohydrodynamics (with zero-β, i.e. zero plasma temperature, in the version used here) code JOREK in X-point geometry. JOREK self-consistently advances in time the magnetic flux, vorticity, and plasma density in the presence of the RMPs. Without any toroidal rotation, the magnetic response from the plasma does not significantly modify the islands widths. A radial convective E⃗×B⃗ plasma transport is observed to occur in the presence of the RMPs. The possibility that this mechanism could explain the enhanced density transport observed experimentally in DIII-D is discussed. Simulations with a rigid-body-like rotation at a fixed velocity shows evidence of a screening of the RMPs. The extension of our results to realistic parameters is discussed.
Spectroscopy of the Ã(B21)-X̃(A11) transition of jet-cooled fluorobenzene: Laser-induced fluorescence, dispersed fluorescence, and pathological Fermi resonances
Authors: Butler Phillip , Moss David B. , Yin Hongming , Schmidt Timothy W. , Kable Scott H.
Published: September 2007

A detailed study of the S1(B21)-S0(A11) electronic transition of jet-cooled fluorobenzene has been carried out using laser-induced fluorescence and dispersed fluorescence (DF) spectroscopies. Analysis of over 40 single vibronic level DF spectra resulted in the assignment of 16 fundamental frequencies in the excited electronic state. Progressions in totally symmetric modes, particularly in the ring-breathing mode ν9, feature in both types of fluorescence spectrum. There is also significant activity in non-totally-symmetric modes, with activity in Franck-Condon (FC)-allowed overtones, FC-forbidden combinations induced by Duschinsky mixing, and symmetry-forbidden transitions induced by the same Herzberg-Teller vibronic coupling mechanism that induces the benzene S1-S0 transition. Fermi resonances (FRs) are extensive throughout the spectrum, especially in the important FC-active a1 modes. A consequence of these extensive FRs is that several important previous assignments are shown to be incorrect and have been reassigned here. Ab initio and density functional theory calculations have also been performed to support the experimental assignments.
Quasielastic neutron scattering experiments including activation energies and mathematical modeling of methyl halide dynamics
Authors: Kirstein O. , Prager M. , Grimm H. , Buchsteiner A. , Wischnewski A.
Published: September 2007

Quasielastic neutron scattering experiments were carried out using the multichopper time-of-flight spectrometer V3 at the Hahn-Meitner Institut, Germany and the backscattering spectrometer at Forschungszentrum Jülich, Germany. Activation energies for CH3X, X=F, Cl, Br, and I, were obtained. In combination with results from previous inelastic neutron scattering experiments the data were taken to describe the dynamics of the halides in terms of two different models, the single particle model and the coupling model. Coupled motions of methyl groups seem to explain the dynamics of the methyl fluoride and chloride; however, the coupling vanishes with the increase of the mass of the halide atom in CH3Br and CH3I.
Hopping time of a hard disk fluid in a narrow channel
Authors: Mon K. K. , Percus J. K.
Published: September 2007

We use Monte Carlo (MC) and molecular dynamics (MD) methods to study the self-diffusion of hard disk fluids, confined within a narrow channel. The channels have a pore radius of Rp, above the passing limit of hard disk diameter (σhd). We focus on the average time (τhop) needed for a hard disk to hop past a nearest neighbor in the longitudinal direction. This parameter plays a key role in a recent theory of the crossover from single-file diffusion to the bulk limit. For narrow channels near the hopping threshold (Rp=1 in units of σhd), both MC and MD results for τhop diverge as ∼(Rp−1)−2. Our results indicate that the scaling law exponent does not appear to be dependent on the differences between the two dynamics. This exponent is consistent with the prediction of an approximate transition state theory.
Box-size dependence and breaking of translational invariance in the velocity statistics computed from three-dimensional turbulent Kolmogorov flows
Authors: Sarris I. E. , Jeanmart H. , Carati D. , Winckelmans G.
Published: September 2007

The Kolmogorov flow generated by a stationary one-dimensional forcing varying sinusoidally in space is studied using direct numerical simulations with periodic boundary conditions. The velocity statistics are considered for various computational domains ranging from the minimal cubic box with size equal to the forcing wavelength to significantly larger domains. For the minimal computational domain, the velocity statistics exhibit symmetries that are directly imposed by the forcing properties. However, for larger domains, the translational invariance in the streamwise direction appears to be broken and the turbulence statistics depend on the computational box aspect ratio.
Dielectric relaxation and crystallization of nanophase separated 1-propanol-isoamylbromide mixture
Authors: Power G. , Vij J. K. , Johari G. P.
Published: September 2007

The effects of liquid-liquid phase separation on molecular relaxation of an apparently homogeneous mixture of 1-propanol and isoamylbromide has been studied by dielectric spectroscopy over a broad frequency and temperature range, and its crystallization kinetics investigated in real time. The mixture shows two widely separated relaxation processes, as before, with the faster relaxation due to the orientational diffusion of isoamylbromide and the slower due to that of 1-propanol. In the mixture, the scaled contribution to permittivity from orientation polarization, Δε, of isoamylbromide is about the same as in the pure state, but that of 1-propanol decreases by a factor of ∼3 at 120K. As the temperature is decreased, this difference remains constant. The relaxation time, τ, of isoamylbromide and its distribution parameter remains the same as for the pure liquid, but that of 1-propanol is longer and increases with decrease in T, becoming ∼130 times the pure liquid’s value at 119K. This is in contrast to the finding for an isomeric heptanol, whose τ had decreased. Extrapolation suggests that at T>151K, τ of 1-propanol in the mixture may become less than that in the pure liquid (the isoamylbromide component crystallizes before this temperature could be reached). This indicates that Tg corresponding to τ of 103s for 1-propanol in the mixture would be higher than in the pure liquid. Crystallization of the two components in the mixture occurs at different rates and 1-propanol remains partially uncrystallized while isoamylbromide completely crystallizes. τ of any remaining liquid isoamylbromide does not change in the presence of crystallized states while τ of residual liquid 1-propanol in the mixture is reduced. The mixture phase separates in submicron or nanosize aggregates of the alcohol in isoamylbromide, without affecting the latter’s relaxation kinetics, while its own εs decreases and τ increases. Consequences of the finding for various relaxation mechanisms are briefly described.
Reflection equation and twisted Yangians
Authors: Mudrov A. I.
Published: September 2007

With any involutive antialgebra and coalgebra automorphism of a quasitriangular bialgebra we associate a reflection equation algebra. A Hopf algebraic treatment of the reflection equation of this type and its universal solution is given. Applications to the twisted Yangians are considered.
Monte Carlo simulation on symmetric ABA/AB copolymer blends in confined thin films
Authors: Song Jianhui , Li Yunqi , Huang Qingrong , Shi Tongfei , An Lijia
Published: September 2007

The effects of blend composition on morphology, order-disorder transition (ODT), and chain conformation of symmetric ABA/AB copolymer blends confined between two neutral hard walls have been investigated by lattice Monte Carlo simulation. Only lamellar structure is observed in all the simulation morphologies under thermodynamic equilibrium state, which is supported by theoretical prediction. When the composition of AB diblock copolymer (ϕ) increases, both lamellar spacing and the corresponding ODT temperature increase, which can be attributed to the variation of conformation distribution of the diblock and the triblock copolymer chains. In addition, both diblock and triblock copolymer, chains with bridge conformation extend dramatically in the direction parallel to the surface when the system is in ordered state. Finally, the copolymer chain conformation depends strongly on both the blend composition and the incompatibility parameter χN.
Magnification of subwavelength field distributions at microwave frequencies using a wire medium slab operating in the canalization regime
Authors: Ikonen Pekka , Simovski Constantin , Tretyakov Sergei , Belov Pavel , Hao Yang
Published: September 2007

Authors demonstrate numerically the magnification of subwavelength field pattern using a wire medium slab operating in the canalization regime. The magnifying slab is implemented by radially enlarging the distance between adjacent wires, and the operational frequency is tuned to coincide with the Fabry-Pérot resonance condition. The near-field pattern of a complex-shaped source is canalized over an electrical distance corresponding roughly to three wavelengths (3λ), and the pattern details are magnified by a factor of 3. The performance is also studied at several frequencies deviating from the one of the Fabry-Pérot resonance.
Theory of instabilities in crossed-field discharges at low pressures
Authors: Abolmasov Sergey N. , Samukawa Seiji , Bizyukov Alexander A.
Published: September 2007

Anode layer thruster, Penning, cylindrical magnetron, and inverted-magnetron discharges all behave, at pressures below about 10−4Torr, as crossed-field discharges. At such low pressures, a crossed-field discharge is pure electron plasma and most of the discharge voltage appears across an electron sheath so that the electric field is orthogonal to the magnetic field. The principal difficulties in the practical use of these discharges in this pressure range arise from instabilities in the discharge, which are commonly attributed to diocotron instabilities in the electron sheath. On the contrary, this paper describes a theory of the electron sheath based on the classical expression for the cross-field mobility of electrons. The theory predicts that the observed instabilities, accompanied by appearance of pulses of excess energy electrons at the cathode(s) and nonlinearity in the discharge characteristics, are simply the result of periodic travel of the electron sheath through the discharge gap.
E
×
B
advection of trace ions in tokamak microturbulence
Authors: Hauff T. , Jenko F.
Published: September 2007

The E×B advection of trace ions in realistic tokamak microturbulence (as described by nonlinear gyrokinetics) is investigated. In order to understand the consequences of effects such as large gyroradii, fluctuation anisotropies, zonal flows, or poloidal drifts, they are first studied in the framework of a model that is based on self-created stochastic potentials. Direct numerical simulations are performed, and a semi-analytical model is presented that provides qualitative as well as quantitative insight into the nature of passive tracer transport. One finds that the resulting diffusivities may be larger than expected as long as the gyroradii do not exceed the turbulence correlation length(s) and the poloidal drift velocities are sufficiently small.
Molecular dynamics simulation of polyethylene on single wall carbon nanotube
Authors: Yang Hua , Chen Yong , Liu Yu , Cai Wen Sheng , Li Ze Sheng
Published: September 2007

Molecular dynamics simulations are carried out on the isothermal crystallization process of single polyethylene chains with different chain lengths on the single wall carbon nanotube. This process is summarized as two steps, i.e., adsorption and orientation, and the bond-orientational order parameter is used to show the details of this process. The results show that the attractive van der Waals interactions control the adsorption and orientation of polyethylene on single wall carbon nanotube, and as the chain length increases, more microstructures appear in the last ordered structure. The stems of the ordered structure align parallel to the single wall carbon nanotube axis.
Synthesis and high pressure induced amorphization of C60 nanosheets
Authors: Wang Lin , Liu Bingbing , Liu Dedi , Yao Mingguang , Yu Shidan , Hou Yuanyuan , Zou Bo , Cui Tian , Zou Guangtian , Sundqvist Bertil , Luo Zongju , Li Hui , Li Yanchun , Liu Jing , Chen Shijian , Wang Guorui , Liu Yichun
Published: September 2007

C 60 nanosheets with thicknesses in the nanometer range were synthesized by a simple method. Compared to bulk C60, the lattice of the nanosheets is expanded by about 0.4%. In situ Raman spectroscopy and energy-dispersive x-ray diffraction under high pressures have been employed to study the structure of the nanosheets. The studies indicate that the bulk modulus of the C60 nanosheets is significantly larger than that of bulk C60. The C60 cages in nanosheets can persist at pressures over 30GPa, 3GPa higher than for bulk C60. These results suggest that C60 crystals in even small size will be a potential candidate of superhard materials.
Influence of random roughness on the adhesion between metal surfaces due to capillary condensation
Authors: van Zwol P. J. , Palasantzas G. , De Hosson J. Th. M.
Published: September 2007

The capillary force was measured by atomic force microscopy between a gold coated sphere mounted on a cantilever and gold surfaces with different roughnesses. For smooth surfaces the capillary adhesive force surpasses in magnitude any dispersion, e.g., van der Waals/Casimir and/or electrostatic forces. A substantial decrease in the capillary force was observed by increasing the roughness ampltitude a few nanometers in the range of 1–10nm. From these measurements two limits can be defined: a smooth limit where a closely macroscopic size contact surface interacts through the capillary force and a rough limit where only a few asperities give a capillary contribution.
Non-Debye response for the structural relaxation in glass-forming liquids: Test of the Avramov model
Authors: Puzenko Alexander , Ishai Paul Ben , Paluch Marian
Published: September 2007

The experimentally observed characteristic features of the α-relaxation process in glass-forming liquids are the non-Arrhenius behavior of the structural relaxation times and the non-Debye character of the macroscopic relaxation function. The Avramov model in which relaxation is considered as an energy activation process of surmounting random barriers in liquid energy landscape was successfully applied to describe the temperature and pressure dependences of the macroscopic relaxation times or viscosity. In this paper, we consider the dielectric spectrum associated with Avramov model. The asymmetrical broadening of the loss spectra was found to be related directly to dispersion of the energy barrier distribution. However, it turns out that temperature dependence of the spectrum broadening as predicted by the Avromov model is at odds to experimental observation in glass-forming liquids.
First principles molecular dynamics of molten NaI: Structure, self-diffusion, polarization effects, and charge transfer
Authors: Galamba N. , Costa Cabral B. J.
Published: September 2007

The structure and self-diffusion of NaI and NaCl at temperatures close to their melting points are studied by first principles Hellmann-Feynman molecular dynamics (HFMD). The results are compared with classical MD using rigid-ion (RI) and shell-model (ShM) interionic potentials. HFMD for NaCl was reported before at a higher temperature [N. Galamba and B. J. Costa Cabral, J. Chem. Phys. 126, 124502 (2007)]. The main differences between the structures predicted by HFMD and RI MD for NaI concern the cation-cation and the anion-cation pair correlation functions. A ShM which allows only for the polarization of I− reproduces the main features of the HFMD structure of NaI. The inclusion of polarization effects for both ionic species leads to a more structured ionic liquid, although a good agreement with HFMD is also observed. HFMD Green-Kubo self-diffusion coefficients are larger than those obtained from RI and ShM simulations. A qualitative study of charge transfer in molten NaI and NaCl was also carried out with the Hirshfeld charge partitioning method. Charge transfer in molten NaI is comparable to that in NaCl, and results for NaCl at two temperatures support the view that the magnitude of charge transfer is weakly state dependent for ionic systems. Finally, Hirshfeld charge distributions indicate that differences between RI and HFMD results are mainly related to polarization effects, while the influence of charge transfer fluctuations is minimal for these systems.
Dominance of second Bessel peak in relativistic electromagnetic ion cyclotron instabilities driven by fusion-produced fast ions
Authors: Chen K. R. , Chen H. K. , Lee S. H.
Published: September 2007

Relativistic electromagnetic ion cyclotron instabilities driven by fusion-produced fast ions in magnetized plasmas can have two peaks in their growth rate spectrum. The wave numbers of these two peaks are close to the first and second peaks, respectively, of the Bessel function that is in the resonance driving term. The driving of the second Bessel and growth rate peak occurring at a higher wave number is weaker than that of the first peak. Surprisingly, as in contrast to conventional wisdom, the second peak can dominate near the instability threshold. For the higher energy of fusion-produced fast ion such as 14.7MeV, the slow ion temperature is required to be higher for overcoming the threshold to drive a cubic instability, which is determined by an Alfvénic condition. This cubic instability is due to the coupling of the first-order slow ion resonance and second-order fast ion resonance. This finite temperature effect is on the slow ion resonance and increases with wave number and thus the threshold is first satisfied near the second peak. Therefore, the second peak appears earlier in the instability spectrum and dominates near the threshold. The cubic instability has a much larger frequency mismatch than a coupled quadratic instability; a larger frequency mismatch indicates more fast ion energy to loss before the nonlinear saturation of the instability. When the slow ion temperature or density is about twice that of the threshold, the second peak has transited from the cubic to the coupled quadratic instability while the first peak remains as the cubic instability, in contrast to the previous 3.02MeV proton case.
A new derivation of the plasma susceptibility tensor for a hot magnetized plasma without infinite sums of products of Bessel functions
Authors: Qin Hong , Phillips Cynthia K. , Davidson Ronald C.
Published: September 2007

The susceptibility tensor of a hot, magnetized plasma is conventionally expressed in terms of infinite sums of products of Bessel functions. For applications where the particle’s gyroradius is larger than the wavelength, such as alpha particle dynamics interacting with lower-hybrid waves, and the focusing of charged particle beams using a solenoidal field, the infinite sums converge slowly. In this paper, a new derivation of the plasma susceptibility tensor is presented which exploits a symmetry in the particle’s orbit to simplify the integration along the unperturbed trajectories. As a consequence, the infinite sums appearing in the conventional expression are replaced by definite double integrals over one gyroperiod, and the cyclotron resonances of all orders are captured by a single term. Furthermore, the double integrals can be carried out and expressed in terms of Bessel functions of complex order, in agreement with expressions deduced previously using the Newburger sum rule. From this new formulation, it is straightforward to derive the asymptotic form of the full hot plasma susceptibility tensor for a gyrotropic but otherwise arbitrary plasma distribution in the large gyroradius limit. These results are of more general importance in the numerical evaluation of the plasma susceptibility tensor. Instead of using the infinite sums occurring in the conventional expression, it is only necessary to evaluate the Bessel functions once according to the new expression, which has significant advantages, especially when the particle’s gyroradius is large and the conventional infinite sums converge slowly. Depending on the size of the gyroradius, the computational saving enabled by this representation can be several orders-of-magnitude.
One-dimensional Vlasov simulation of parallel electric fields in two-electron population plasma
Authors: Saharia K. , Goswami K. S.
Published: September 2007

One-dimensional Vlasov simulation in electron current carrying multicomponent plasma seeded with a density depression is presented. Considering two electron populations [one is sufficiently hot (∼keV) and the other is cold along with cold background ions], the formation of weak double layers is investigated. Simulation results show that in this numerical setting, formation of such double layers needs the majority of the hot electrons.
Hydrogen bonding in liquid water probed by resonant Auger-electron spectroscopy
Authors: Winter Bernd , Hergenhahn Uwe , Faubel Manfred , Björneholm Olle , Hertel Ingolf V.
Published: September 2007

We have measured resonant and off-resonant Auger-electron spectra of liquid water. Continuumlike transitions near and above the O1s vertical ionization energy are identified by the characteristic normal Auger-electron spectra. On the contrary, well-resolved spectator shifts of the main Auger-electron peak are observed at the liquid-water O1s absorption main edge and near the absorption pre-edge. The shifts of 1.4 and 1.9eV arise from the localized nature of the excitation. Excited-state localization/delocalization is also discussed for the analogous vacuum ultraviolet (VUV) transitions, and we point out the similarities between x-ray and VUV absorption spectra of liquid water.
Quantum force molecular dynamics study of the reaction of O atoms with HOCO
Authors: Yu Hua-Gen , Muckerman James T. , Francisco Joseph S.
Published: September 2007

The reaction of HOCO with O atoms has been studied using a direct ab initio dynamics approach based on the scaling all correlation UCCD∕D95(d,p) method. Ab initio calculations point to two possible reaction mechanisms for the O+HOCO→OH+CO2 reaction. They are a direct hydrogen abstraction and an oxygen addition reaction through a short-lived HOC(O)O intermediate. The dynamics results show that only the addition mechanism is important under the conditions considered here. The lifetime of the HOC(O)O complex is predicted to be 172±15fs. This is typical of a direct and fast radical-radical reaction. At room temperature, the calculated thermal rate coefficient is 1.44×10−11cm3mol−1s−1 and its temperature dependence is rather weak. The two kinds of reactive trajectories are illustrated in detail.
Assessment of long-range corrected functionals performance for n→π* transitions in organic dyes
Authors: Jacquemin Denis , Perpète Eric A. , Vydrov Oleg A. , Scuseria Gustavo E. , Adamo Carlo
Published: September 2007

The first n→π* transitions of 18 nitroso and 16 thiocarbonyl dyes have been computed by time-dependent density functional theory (TD-DFT) using pure as well as global and range-separated hybrid functionals. It turns out that the accuracy of all hybrids is relatively similar, i.e., the inclusion of a growing fraction of exact exchange does neither worsen nor improve significantly the raw TD-DFT estimations. However, after a simple linear regression, it appears that the range-separated hybrids provide a better accuracy than global hybrids.
Switching mechanism of photochromic diarylethene derivatives molecular junctions
Authors: Huang Jing , Li Qunxiang , Ren Hao , Su Haibin , Shi Q. W. , Yang Jinlong
Published: September 2007

The electronic transport properties and switching mechanism of single photochromic diarylethene derivatives sandwiched between two gold surfaces with closed and open configurations are investigated by a fully self-consistent nonequilibrium Green’s function method combined with density functional theory. The calculated transmission spectra of two configurations are strikingly distinctive. The open form lacks any significant transmission peak within a wide energy window, while the closed structure has two significant transmission peaks on both sides of the Fermi level. The electronic transport properties of the molecular junction with closed structure under a small bias voltage are mainly determined by the tail of the transmission peak contributed unusually by the perturbed lowest perturbed unoccupied molecular orbital. The calculated on-off ratio of currents between the closed and open configurations is about two orders of magnitude, which reproduces the essential features of the experimental measured results. Moreover, we find that the switching behavior within a wide bias voltage window is extremely robust to both substituting F or S for H or O and varying end anchoring atoms from S to Se and Te.
Cold electron and ion beams generated from trapped atoms
Authors: Claessens B. J. , Reijnders M. P. , Taban G. , Luiten O. J. , Vredenbregt E. J. D.
Published: September 2007

A novel way of creating low-temperature electron and ion beams is demonstrated. The beams are generated by converting a laser-cooled atom cloud to a highly excited Rydberg gas, which subsequently develops into an ultracold plasma. Charged particles are extracted from the Rydberg gas and the plasma by a pulsed electric field. The properties of the resulting electron and ion pulses are experimentally studied. Pulses of a few hundred ns duration containing a few pC of charge were observed. Upper limits for the temperature of such beams (60K for ions and 500K for electrons) are obtained, and the beams are shown to have low emittance. Further development of the method may lead to the generation of high-brightness charged-particle beams from ultracold plasmas.
Direct ice detection based on fiber optic sensor architecture
Authors: Ikiades Aristidis A.
Published: September 2007

Ice growth on the wings of aircraft affects their aerodynamic performance and handling qualities which change depending on the location of the ice accretion. Ice detection technology has changed little over the last 30years relying on indirect atmospheric conditions to determine the existence of icing conditions. This letter reports on a simple optical method to measure directly ice thickness and type accreted on the wing in an icing tunnel, by measuring the scattered and reflected light as a function of ice growth with a fiber optic architecture, obtaining characteristic light intensity growth curves.
From atomistic simulation to the dynamics, structure and helical network formation of dendronized polymers: The Janus chain model
Authors: Ding Y. , Öttinger H. C. , Schlüter A. D. , Kröger M.
Published: September 2007

It is the purpose of this paper to establish a bottom-up multiscale approach for dendronized polymers. Based on our understanding of the phenomenology of an atomistic model for this class of polymers, we introduce a “Janus chain” (JC) model which adds a vectorial degree of freedom (Janus vector)—related to the sectorial amphiphilicity—to each segment of the linear backbone of a (classical) uncharged, semiflexible, and multibead chain representation of a polymer. The JC features induced polymeric curvature and ultimately triggers complexation. JC parameters related to the topology and chemical details are obtained from the atomistic level. Available experimental observations including the formation of superstructures and double helical conformations are well reproduced by the JC model. JC is efficiently solved via Brownian dynamics simulation and can be seen as a member of a universality class which is one (two) level(s) above the magnetic (semiflexible) chain model. It therefore should allow to model not only dendronized polymers but also structures belonging to the same class—exhibiting induced (or spontaneous) curvature—such as single stranded DNA and actin filaments.
Reducing the critical thickness of epitaxial Ag film on the Si(111) substrate by introducing a monolayer Al buffer layer
Authors: Tang Zhe , Teng Jing , Jiang Ying , Jia JinFeng , Guo Jiandong , Wu Kehui
Published: September 2007

We report a method to prepare atomically smooth Ag film, with thickness as small as 2 monolayers (ML) and a well-defined interface on the Si(111) substrate, by introducing a monolayer Al(111) 1×1 buffer layer. Scanning tunneling microscopy, low-energy electron diffraction, and x-ray photoelectron emission diffraction were employed to in situ study the film and interface structures. Compared with the growth of Ag on a clean Si(111) 7×7 surface, the buffer layer lowers the critical thickness from 6 to 2 ML. The effect is explained based on an enhanced charge spillage at the interface.
Microstructure, dielectric, and piezoelectric properties of (Li, Ag, Ta) modified (K0.50Na0.50)NbO3 lead-free ceramics with high Curie temperature
Authors: Wang Yuanyu , Wu Jiagang , Xiao Dingquan , Zhu Jumu , Jin Yong , Zhu Jianguo , Yu Ping , Wu Lang , Li Xiang
Published: September 2007

( 1 − x ) [ ( K 0.4725 Na 0.4725 Li 0.055 ) NbO 3 ] − x AgTaO 3 [ ( 1 − x ) KNNL − x AT ] lead-free ceramics have been prepared by the conventional mixed oxide method. Effect of the AgTaO3 (AT) content on the microstructure and electrical properties of (1−x)KNNL−xAT ceramics were systematically investigated. A morphotropic phase boundary (MPB) between orthorhombic and tetragonal phases was identified in the composition range of 0.015<x<0.025. The materials near the MPB exhibit a strong compositional dependence and enhanced electrical properties along with high Curie temperature. It is found that the samples with 2 mol % AT exhibit relatively good electrical properties along with high Curie temperature: the piezoelectric constant d33 and Curie temperature TC reach 237 pC/N and 470 °C, respectively; the electromechanical coupling coefficient of the planar mode kp reaches 39%; and the remnant polarization (Pr) is 29.4 μC∕cm2 with a coercive field (Ec) of 13.6 kV/cm. These results show that (1−x)KNNL−xAT is a promising candidate material for high temperature lead-free piezoelectric ceramics.
Critical current densities and the structural quality of 3- and 4-μm-thick superconducting YBa2Cu3O7 layers synthesized using the ex situ process
Authors: Solovyov Vyacheslav F. , Wiesmann Harold J. , Suenaga Masaki
Published: September 2007

In this work, we used quantitative x-ray diffraction measurements and optical metallography to investigate the relationship between structural quality and critical current densities Jc for 3- and 4-μm-thick YBa2Cu3O7 (YBCO) films grown on CeO2-buffered Ni–W substrates by the BaF2 process. The Jc of the films was shown to be approximately: (1) proportional to the intensity of the YBCO (006) diffraction line, and (2) inversely proportional to the average grain size of the c-axis oriented YBCO as determined from optical micrographs of polished surface of the films. We conclude that to achieve Jcs well above 106 A/cm2 in self-field and at 77 K, it is critical to suppress the formation of randomly oriented YBCO grains while maintaining high crystallographic quality of the c-axis oriented part of the film. The quality of the c-axis oriented YBCO was found to be strongly dependent on the YBCO grains size—e.g., the grains, which are smaller than 10 μm, are required for high Jc films. The fine-grain high Jc films can be synthesized under processing conditions that promote a high rate of nucleation of c-axis oriented YBCO.
Thickness-dependent retention behaviors and ferroelectric properties of BiFeO3 thin films on BaPbO3 electrodes
Authors: Lee Chia-Ching , Wu Jenn-Ming
Published: September 2007

Bi Fe O 3 (BFO) thin films produced with varied film thicknesses ranging from 100to230nm were fabricated on BaPbO3(BPO)∕Pt∕Ti∕SiOx∕Si substrates by rf-magnetron sputtering. Saturated polarization–electrical field hysteresis loops, polarization response by pulse measurement, and retention properties were obtained for BFO films with various thicknesses on BPO. The retention behaviors of BFO demonstrate logarithmic time dependence and stretched exponential law. When the thicknesses of BFO films increase, the contribution of logarithmic time dependence to retention, the stretched exponential law becomes dominant. BFO films with thinner thickness exhibit better retention properties but possess smaller remnant polarization.
Guided wave propagation in 0.67Pb(Mg1∕3Nb2∕3)O3–0.33PbTiO3 single crystal plate poled along [001]c
Authors: Chen Chuanwen , Zhang Rui , Chen Hui , Cao Wenwu
Published: September 2007

Dispersion relations of Lamb waves and shear horizontal (SH) waves propagating in the [100] and [110] directions of 0.67Pb(Mg1∕3Nb2∕3)O3–0.33PbTiO3 piezoelectric single crystal plate poled along [001]c were calculated. Multiple crossings between symmetric and antisymmetric modes appear due to the moderate anisotropy of these crystals. As frequency increases, the velocities for SH wave modes approach 2.88 and 0.88mm∕μs, respectively, for waves propagating along [100] and [110] directions. These limiting velocities are the corresponding shear velocities of bulk crystals.
Equation of motion of a phonon gas and non-Fourier heat conduction
Authors: Cao Bing-Yang , Guo Zeng-Yuan
Published: September 2007

Heat conduction in solids is due to the motion of the phonon gas. A more general description of the heat transport in solids includes consideration of the mass, pressure, and inertial force of the phonon gas. The mass of the phonon gas refers to the equivalent mass of its energy based on Einstein’s mass-energy relation. The thermal vibration of the lattice creates the phonon gas pressure and the momentum change of the phonon gas results in an inertial force. The phonon gas velocity is directly proportional to the heat flux. These concepts are used to establish an equation of motion for the phonon gas including the driving, inertial, and resistant forces using Newtonian dynamics. This equation reduces to Fourier’s law of heat conduction when the inertial force can be neglected relative to the other terms so that heat conduction becomes pure diffusion. However, Fourier’s law of heat conduction no longer holds if the heat flux is very high, such that the inertial force of the phonon gas is not negligible. In such cases, the heat conduction behavior deviates from Fourier’s law even for steady-state conditions so that the heat conduction is characterized by a nonlinear relationship between the heat flux and the temperature gradient.
Highly efficient solution-processed phosphorescent multilayer organic light-emitting diodes based on small-molecule hosts
Authors: Rehmann Nina , Hertel Dirk , Meerholz Klaus , Becker Heinrich , Heun Susanne
Published: September 2007

The authors report on highly efficient phosphorescent organic light-emitting diodes (OLEDs) based on a low-molecular weight electron-conducting, bis-spirobifluorene host doped with a soluble derivative of the green emitter fac-tris(2-phenylpyridine) iridium (III) [Ir(ppy)3]. All organic layers were spin coated and a strong improvement of performance was achieved by introduction of a hole-transporting double layer based on cross-linkable low-molecular weight molecules. The devices combine the easy fabrication procedure known from polymer-based OLEDs with the higher efficiency of small molecules. Maximum luminous and power efficiencies of 59cd∕A and 58lm∕W, respectively, are obtained, combined with a low driving voltage and high efficiencies even at high brightnesses. At 1000cd∕m2 the efficiencies are as high as 55cd∕A and 49lm∕W.