bluuebunny/crossref_metadata_2025 huggingface dataset:
Superdiffusion in the dissipative standard map
Authors: Zaslavsky G. M. , Edelman M.
Published: August 2008

We consider transport properties of the chaotic (strange) attractor along unfolded trajectories of the dissipative standard map. It is shown that the diffusion process is normal except for the cases when a control parameter is close to some special values that correspond to the ballistic mode dynamics. Diffusion near the related crises is anomalous and nonuniform in time; there are large time intervals during which the transport is normal or ballistic, or even superballistic. The anomalous superdiffusion seems to be caused by stickiness of trajectories to a nonchaotic and nowhere dense invariant Cantor set that plays a similar role as cantori in Hamiltonian chaos. We provide a numerical example of such a sticky set. Distribution function on the sticky set almost coincides with the distribution function (SRB measure) of the chaotic attractor.
Full dimensional time-dependent quantum dynamics study of the H+NH3→H2+NH2 reaction
Authors: Yang Minghui
Published: August 2008

A rigorous full dimensional time-dependent wave packet method has been developed for the reactive scattering between an atom and a tetra-atomic molecule. The method has been applied to the hydrogen abstraction reaction H+NH3→H2+NH2. Initial state-selected total reaction probabilities are investigated for the reactions from the ground vibrational state and from four excited vibrational states of ammonia. The total reaction probabilities from two lowest “tunneling doublets” due to the inversion barrier for the umbrella bending motion of NH3 and from two pairs of doubly degenerate vibrational states of NH3 are also inspected. Integral cross sections and rate constants are calculated for the reaction from the ground state with the centrifugal-sudden approximation. The calculated results are compared with those from the previous seven dimensional calculations [M. Yang and J. C. Corchado, J. Chem. Phys. 126, 214312 (2007)]. This work shows that the full dimensional rate constants are a factor of 3 larger than the corresponding seven dimensional calculated values at T=200 K and are overall smaller than those obtained from the variational transition state theory in the whole temperature region. The work also reveals that nonreactive NH bonds of NH3 cannot be treated as spectators due to the fact that three NH bonds are coupled with each other during the reaction process.
H
2
, HD, and D2 inside C60: Coupled translation-rotation eigenstates of the endohedral molecules from quantum five-dimensional calculations
Authors: Xu Minzhong , Sebastianelli Francesco , Bačić Zlatko , Lawler Ronald , Turro Nicholas J.
Published: August 2008

We have performed rigorous quantum five-dimensional (5D) calculations of the translation-rotation (T-R) energy levels and wave functions of H2, HD, and D2 inside C60. This work is an extension of our earlier investigation of the quantum T-R dynamics of H2@C60 [M. Xu et al., J. Chem. Phys. 128, 011101 (2008)] and uses the same computational methodology. Two 5D intermolecular potential energy surfaces (PESs) were employed, differing considerably in their well depths and the degree of confinement of the hydrogen molecule. Our calculations revealed pronounced sensitivity of the endohedral T-R dynamics to the differences in the interaction potentials, and to the large variations in the masses and the rotational constants of H2, HD, and D2. The T-R levels vary significantly in their energies and ordering on the two PESs, as well as from one isotopomer to another. Nevertheless, they all display the same distinctive patterns of degeneracies, which can be qualitatively understood and assigned in terms the model which combines the isotropic three-dimensional harmonic oscillator, the rigid rotor, and the coupling between the orbital and the rotational angular momenta of H2∕HD∕D2. The quantum number j associated with the rotation of H2, HD, and D2 was found to be a good quantum number for H2 and D2 on both PESs, while most of the T-R levels of HD exhibit strong mixing of two or more rotational basis functions with different j values.
Folding transition of a single semiflexible polyelectrolyte chain through toroidal bundling of loop structures
Authors: Iwaki Takafumi , Makita Naoko , Yoshikawa Kenichi
Published: August 2008

We consider how the DNA coil-globule transition progresses via the formation of a toroidal ring structure. We formulate a theoretical model of this transition as a phenomenon in which an unstable single loop generated as a result of thermal fluctuation is stabilized through association with other loops along a polyelectrolyte chain. An essential property of the chain under consideration is that it follows a wormlike chain model. A toroidal bundle of loop structures is characterized by a radius and a winding number. The statistical properties of such a chain are discussed in terms of the free energy as a function of the fraction of unfolded segments. We also present an actual experimental observation of the coil-globule transition of single giant DNA molecules, T4 DNA (165.5kbp), with spermidine (3+), where intrachain phase segregation appears at a NaCl concentration of more than 10mM. Both the theory and experiments lead to two important points. First, the transition from a partially folded state to a completely folded state has the characteristics of a continuous transition, while the transition from an unfolded state to a folded state has the characteristics of a first-order phase transition. Second, the appearance of a partially folded structure requires a folded structure to be less densely packed than in the fully folded compact state.
Unusual catalyst-free epitaxial growth of silicon nanowires by thermal evaporation
Authors: Qin Y. , Zhang X. N. , Zheng K. , Li H. , Han X. D. , Zhang Z.
Published: August 2008

We report a catalyst-free epitaxial growth of silicon nanowires on polyhedral facets of mother Si nanoparticles by thermal evaporation process. Single silicon nanowires and octopuslike silicon nanowires (OSNWs) were synthesized under different temperatures. The OSNWs have several directions including ⟨112⟩, ⟨110⟩, and the unusual directions of ⟨100⟩ and ⟨111⟩. A catalyst-free temperature-dependent epitaxial growth model was suggested. Using the Wulff theory and first principle calculations, these growth directions can be explained by the preferential selection of temperature-dependent surface energies. It thus revealed an important but simple growth model in which the growth directions could be delicately controlled through only determining temperature and substrate orientation.
X-ray pulse emission from cesium chloride aqueous solutions when irradiated by double-pulsed femtosecond laser pulses
Authors: Hatanaka Koji , Ono Hiroshi , Fukumura Hiroshi
Published: August 2008

The intensity of x-ray emission from the aqueous solutions irradiated with focused femtosecond laser pulses (main pulses and relatively low-intensity prepulses) was measured as a function of the delay time between the main pulses and prepulses. Four different x-ray intensity peaks were observed in the picosecond and nanosecond ranges. The prepulse irradiation caused an increase in the x-ray intensity by a factor of 103–104, as confirmed by x-ray emission spectroscopy. Time-resolved reflectance measurements and imaging revealed that the increase was caused by the solution surface dynamics such as the picosecond plasma formation and decay and the transient (nanoseconds) surface roughness.
Loss of confinement at the density limit due to the suppression of stabilizing zonal flows by magnetic turbulence
Authors: Kleva Robert G. , Guzdar Parvez N.
Published: August 2008

The character of particle and energy transport in numerical simulations of drift-ballooning turbulence changes dramatically as the density exceeds a critical limit. When the density is not too large, then unstable drift-ballooning fluctuations grow and nonlinearly generate a sheared zonal (flux surface averaged) flow that saturates the turbulence. But when diamagnetic drift effects are small and the density increases beyond a critical limit, then the turbulent density flux increases monotonically in time to large values without saturation. This loss of confinement is caused by the suppression of the stabilizing zonal flow by the magnetic component of the turbulence. A Kelvin–Helmholtz-like shear-flow instability does not play any role in reducing the magnitude of the zonal flow. The magnetic turbulence prevents the zonal flow from growing large enough to become shear-flow unstable.
Gyrokinetic verification of the persistence of kinetic ballooning modes in the magnetohydrodynamic second stability regime
Authors: Joiner N. , Hirose A.
Published: August 2008

The kinetic ballooning mode (KBM) has been shown in previous work to be unstable within the magnetohydrodynamic (MHD) region (in ŝ-α space) of second stability [Hirose et al., Phys. Rev. Lett. 72, 3993 (2004)]. In this work we verify this result using the gyrokinetic code GS2 [Kotschenreuther et al., Comput. Phys. Commun. 88, 128 (1996)] treating both ions and electrons as kinetic species and retaining the magnetosonic perturbation B∥. Growth rates calculated using GS2 differ significantly from the previous differential/shooting code analysis. Calculations without B∥ find the stability region is preserved, while the addition of B∥ causes the mode to be more unstable than previously calculated within the region of MHD second stability. The inclusion of parallel ion current and B∥ into the shooting code does not account for the GS2 results. The evidence presented in this paper leads us to the conclusion that the adiabatic electron approximation employed in previous studies is found to be unsuitable for this type of instability. Based on the findings of this work, the KBM becomes an interesting instability in the context of internal transport barriers, where α is often large and magnetic shear is small (positive or negative).
Highly sensitive and broadband carbon nanotube radio-frequency single-electron transistor
Authors: Andresen S. E. S. , Wu F. , Danneau R. , Gunnarsson D. , Hakonen P. J.
Published: August 2008

We have investigated radio-frequency single-electron transistor operation of single-walled carbon nanotube quantum dots in the strong tunneling regime. At a temperature of 4.2 K and with a carrier frequency of 754.2 MHz, we reach a charge sensitivity of 2.3×10−6e/Hz over a bandwidth of 85 MHz. Our results indicate a gain-bandwidth product of 3.7×1013 Hz(3/2)/e, which is by one order of magnitude better than those for typical radio-frequency single-electron transistors.
Finite difference time domain analysis of the light extraction efficiency in organic light-emitting field-effect transistors
Authors: Gehlhaar Robert , Yahiro Masayuki , Adachi Chihaya
Published: August 2008

The authors report on three-dimensional numerical optical simulations of the emission outcoupling efficiency in light-emitting devices with a field-effect carrier transport. The finite difference time domain method is applied to organic thin film structures on a silicon substrate with metal and metal oxide electrodes. Simulations are performed for Au, Ag, and indium tin oxide electrodes in a bottom gate, bottom contact geometry. Additional attention is paid to the dependence on electrode thickness and contact shape. We demonstrate that in unipolar driven devices with Si gate, silicon dioxide insulator, and 40 nm thick organic films, the maximum outcoupling efficiency is below 10%. This value can be increased by the implementation of a metal reflecting layer on the Si substrate. In further studies, the emission efficiency in the ambipolar regime is investigated. The result presents the dependence of light extraction on the light source-electrode distance for rectangular and wedge shaped contacts.
Origin of the liquid-liquid phase transition for trans-1,2-dichloroethylene observed by IR spectroscopy
Authors: Merkel Katarzyna , Kocot Antoni , Wrzalik Roman , Ziolo Jerzy
Published: August 2008

IR vibrational spectroscopy has been employed to study liquid-liquid phase transitions of trans-1,2-dichloroethylene (TDCE). The temperature dependence of the vibrational frequency, band absorbance, and band broadening has been analyzed in the temperature range of 293–237K. All peaks show distinct increases in their absorbancies at the temperature of 246.7K accompanied by a frequency shift and bandwidth changes. Weak H⋯Cl hydrogen bonding has been suggested as the explanation for the overall behavior in a wide temperature range, whereas the significant changes in the spectrum at 246.7K are probably due to molecular ordering originating from electrostatic interactions. The transition is well described by the model of the cooperative formation of locally favored structures.
Closed-shell coupled-cluster theory with spin-orbit coupling
Authors: Wang Fan , Gauss Jürgen , van Wüllen Christoph
Published: August 2008

A two-component closed-shell coupled-cluster (CC) approach using relativistic effective core potentials with spin-orbit coupling included in the post-Hartree–Fock treatment is proposed and implemented at the CC singles and doubles (CCSD) level as well as at the CCSD level augmented by a perturbative treatment of triple excitations [CCSD(T)]. The latter invokes as an additional approximation the neglect of the occupied-occupied and virtual-virtual blocks of the spin-orbit coupling matrix in order to avoid the iterative N7 steps in the treatment of triple excitations. The computational effort of the implemented two-component CC methods is about 10–15 times that of its corresponding nonrelativistic counterpart, which needs to be compared to the by a factor of 32 higher cost for fully relativistic schemes and schemes with spin-orbit coupling included already at the Hartree–Fock self-consistent field (HF-SCF) level. This substantial computational saving is due to the use of real molecular orbitals and real two-electron integrals. Results on 5p-, 6p-, and 7p-block element compounds show that the bond lengths and harmonic frequencies obtained with the present two-component CCSD method agree well with those computed with the CCSD approach including spin-orbit coupling at the HF-SCF level even for the 7p-block element compounds. As for the CCSD(T) approach, high accuracy for 5p- and 6p-block element compounds is retained. However, the difference in bond lengths and harmonic frequencies becomes somewhat more pronounced for the 7p-block element compounds.
A diamond anvil cell with resistive heating for high pressure and high temperature x-ray diffraction and absorption studies
Authors: Pasternak Sebastien , Aquilanti Giuliana , Pascarelli Sakura , Poloni Roberta , Canny Bernard , Coulet Marie-Vanessa , Zhang Lin
Published: August 2008

In this paper we describe a prototype of a diamond anvil cell (DAC) for high pressure/high temperature studies. This DAC combines the use of a resistive oven of 250W power in a very small volume, associated with special conical seats for Boehler-type diamond anvils in order to have a large angular acceptance. To protect the diamond anvils from burning and to avoid the oven oxidation, the heated DAC is enclosed in a vacuum chamber. The assemblage was used to study the melting curve of germanium at high pressure (up to 20GPa) and high temperature (up to 1200K) using x-ray diffraction and x-ray absorption spectroscopy.
Implantation conditions for diamond nanocrystal formation in amorphous silica
Authors: Buljan Maja , Radović Iva Bogdanović , Desnica Uroš V. , Ivanda Mile , Jakšić Milko , Saguy Cecile , Kalish Rafi , Djerdj Igor , Tonejc Anđelka , Gamulin Ozren
Published: August 2008

We present a study of carbon ion implantation in amorphous silica, which, followed by annealing in a hydrogen-rich environment, leads to preferential formation of carbon nanocrystals with cubic diamond (c-diamond), face-centered cubic (n-diamond), or simple cubic (i-carbon) carbon crystal lattices. Two different annealing treatments were used: furnace annealing for 1 h and rapid thermal annealing for a brief period, which enables monitoring of early nucleation events. The influence of implanted dose and annealing type on carbon and hydrogen concentrations, clustering, and bonding were investigated. Rutherford backscattering, elastic recoil detection analysis, infrared spectroscopy, transmission electron microscopy, selected area electron diffraction, ultraviolet-visible absorption measurements, and Raman spectroscopy were used to study these carbon formations. These results, combined with the results of previous investigations on similar systems, show that preferential formation of different carbon phases (diamond, n-diamond, or i-carbon) depends on implantation energy, implantation dose, and annealing conditions. Diamond nanocrystals formed at a relatively low carbon volume density are achieved by deeper implantation and/or lower implanted dose. Higher volume densities led to n-diamond and finally to i-carbon crystal formation. This observed behavior is related to damage sites induced by implantation. The optical properties of different carbon nanocrystal phases were significantly different.
The effect of current crowding on the heat and light pattern in high-power AlGaAs light emitting diodes
Authors: Zinovchuk A. V. , Malyutenko O. Yu. , Malyutenko V. K. , Podoltsev A. D. , Vilisov A. A.
Published: August 2008

The results of the light and temperature micromapping in AlGaAs light emitting diodes grown by liquid phase epitaxy as double heterostructures and emitting at λ∼0.87 μm are presented. At a driving current well above the safe operating limit (>300 mA), the nonuniform light pattern and local self-heating (with temperature gradient of about 950 °C/cm) followed by catastrophic degradation of a device were detected with the charge coupled device and infrared microscopes operating in a pulsed mode. These were shown to result from the current crowding effect in the active and contact areas of a device. Good agreement between the theory and experiment was found.
Influence of the oxidative annealing temperature on the magnetism of (Mn, N)-codoped ZnO thin films
Authors: Lu Z. L. , Yan G. Q. , Wang S. , Zou W. Q. , Mo Z. R. , Lv L. Y. , Zhang F. M. , Du Y. W. , Xu M. X. , Xia Z. H.
Published: August 2008

(Mn, N)-codoped ZnO films have been achieved by oxidative annealing of sputtered Zn2N3:Mn films at different temperatures in flowing O2 ambient. X-ray diffraction measurements and x-ray photoelectron spectroscopy studies indicate that both divalent Mn2+ and trivalent N3− ions are incorporated into ZnO lattice. Ferromagnetism with Curie temperature above 300 K was observed in the (Mn, N)-codoped ZnO films and found to be sensitive to the oxidative annealing temperature due to its strong effect on the carrier type and concentration. The strongest ferromagnetism has been found in the (Mn, N)-codoped ZnO films with the highest hole concentration in this study. The results indicate that holes are favorable for ferromagnetic ordering of doped Mn2+ ions in ZnO in agreement with the recent theoretical studies. The mechanism of ferromagnetic coupling in (Mn, N)-codoped ZnO is discussed.
Mechanics of buckled carbon nanotubes on elastomeric substrates
Authors: Xiao J. , Jiang H. , Khang D.–Y. , Wu J. , Huang Y. , Rogers J. A.
Published: August 2008

The buckling of carbon nanotubes (CNTs) on elastomeric substrates is studied in this paper. Simple expressions of the buckle wavelength and amplitude and the critical strain for buckling are obtained analytically. For single-walled CNTs, the wavelength is proportional to the CNT radius to the 3/4 power, while it increases linearly with the number of walls for multiwalled CNTs. For two parallel CNTs on the surface of the elastomeric substrate, there exists a critical spacing below which the two CNTs interact and buckle together, adopting the same wavelength. This cobuckling wavelength is very close to the wavelength for the larger CNT to buckle independently, i.e., the larger tube dominates the coupled buckling.
Angular-dependent vortex pinning mechanism in YBa2Cu3O7−δ/YSZ quasi-multilayer
Authors: Peng Lin , Cai Chuanbing , Chen Changzhao , Liu Zhiyong , Hühne Ruben , Holzapfel Bernhard
Published: August 2008

The temperature and magnetic field dependences of anisotropic pinning contributions of YBa2Cu3O7−δ/YSZ quasi-multilayer have been investigated by the measurement of angular-dependent critical current density (Jc). With the isotropic and anisotropic pinning contributions in a wide range of temperature, we identify the possible sources of the pinning centers and classify them into the weak and the strong flux pinning model. Angular-dependent Jc(H,T) measurements have demonstrated that the growth control strategy is very effective in preventing the vortex motion at high fields and high temperatures. It is suggested that at high applied fields, such as 7 T, the pinning contribution of the nanostructured quasi-multilayers is dominated by the anisotropic disorders, while at intermediate-low fields (such as 1 T) the pinning contribution is determined by both isotropic and anisotropic disorders, suggesting the coexistence of isotropic and anisotropic pinning.
Far-infrared transmission in GaN, AlN, and AlGaN thin films grown by molecular beam epitaxy
Authors: Ibáñez J. , Hernández S. , Alarcón-Lladó E. , Cuscó R. , Artús L. , Novikov S. V. , Foxon C. T. , Calleja E.
Published: August 2008

We present a far-infrared transmission study on group-III nitride thin films. Cubic GaN and AlN layers and c-oriented wurtzite GaN, AlN, and AlxGa1−xN (x<0.3) layers were grown by molecular beam epitaxy on GaAs and Si(111) substrates, respectively. The Berreman effect allows us to observe simultaneously the transverse optic and the longitudinal optic phonons of both the cubic and the hexagonal films as transmission minima in the infrared spectra acquired with obliquely incident radiation. We discuss our results in terms of the relevant electromagnetic theory of infrared transmission in cubic and wurtzite thin films. We compare the infrared results with visible Raman-scattering measurements. In the case of films with low scattering volumes and/or low Raman efficiencies and also when the Raman signal of the substrate material obscures the weaker peaks from the nitride films, we find that the Berreman technique is particularly useful to complement Raman spectroscopy.
The effect of geometric and electric constraints on the performance of polymer-stabilized cholesteric liquid crystals with a double-handed circularly polarized light reflection band
Authors: Relaix Sabrina , Mitov Michel
Published: August 2008

Polymer-stabilized cholesteric liquid crystals (PSCLCs) with a double-handed circularly polarized reflection band are fabricated. The geometric and electric constraints appear to be relevant parameters in obtaining a single-layer CLC structure with a clear-cut double-handed circularly polarized reflection band since light scattering phenomena can alter the reflection properties when the PSCLC is cooled from the elaboration temperature to the operating one. A compromise needs to be found between the LC molecule populations, which are bound to the polymer network due to strong surface effects or not. Besides, a monodomain texture is preserved if the PSCLC is subjected to an electric field at the same time as the thermal process intrinsic to the elaboration process. As a consequence, the light scattering is reduced and both kinds of circularly polarized reflected light beams are put in evidence. Related potential applications are smart reflective windows for the solar light management or reflective polarizer-free displays with higher brightness.
Improving light harvesting in polymer photodetector devices through nanoindented metal mask films
Authors: Macedo A. G. , Zanetti F. , Mikowski A. , Hummelen J. C. , Lepienski C. M. , da Luz M. G. E. , Roman L. S.
Published: August 2008

To enhance light harvesting in organic photovoltaic devices, we propose the incorporation of a metal (aluminum) mask film in the system’s usual layout. We fabricate devices in a sandwich geometry, where the mask (nanoindented with a periodic array of holes of sizes d and spacing s) is added between the transparent electrode and the active layer formed by a blend of the semiconducting polymer P3HT and substituted fullerene. Its function is to promote trapping of the incident light into the device’s cavity (the region corresponding to the active layer). For d, we set a value that allows light diffraction through the holes in the relevant absorption range of the polymer. To optimize the mask structure, we consider a very simple model to determine the s leading to trapped fields that are relatively intense and homogeneous within the device. From measurements of the action spectra, we show that, indeed, such architecture can considerably improve the resulting photocurrent efficiencies—one order of magnitude in the best situation studied.
Vacuum sublimed α,ω-dihexylsexithiophene thin films: Correlating electronic structure and molecular orientation
Authors: Duhm S. , Salzmann I. , Koch N. , Fukagawa H. , Kataoka T. , Hosoumi S. , Nebashi K. , Kera S. , Ueno N.
Published: August 2008

In order to correlate the molecular orientation of organic thin films with charge injection barriers at organic/metal interfaces, the electronic structure and molecular orientation of vacuum sublimed thin films of α,ω-dihexylsexithiophene (DH6T) on the substrates Ag(111), highly oriented pyrolytic graphite (HOPG), and tetratetracontane (TTC) precovered Ag(111) were investigated. Results from metastable atom electron spectroscopy, ultraviolet photoelectron spectroscopy, and x-ray diffraction were used to derive growth models (including molecular orientation and conformation) of DH6T on the different substrates. On Ag(111), DH6T exhibits a transition from lying molecules in the monolayer/bilayer range to almost standing upright molecules in multilayers. This is accompanied by a shift of the molecular energy levels to a lower binding energy by 0.65 eV with respect to the vacuum level. The unit cell of standing DH6T on lying DH6T on Ag(111) is estimated to be similar to the DH6T bulk phase. On HOPG, DH6T grows in the bulk phase with lying orientation, starting already from the monolayer coverage. DH6T on TTC precovered Ag(111) grows in an almost lying orientation and a conformation that allows a strong overlap of the hexyl chains of DH6T with the alkyl chains of TTC. In all cases, the electronic structure and, particulary, the ionization energy of DH6T is dependent on the orientation of DH6T, i.e., lying DH6T has higher ionization energy than standing DH6T.
Electronic and optical properties of 530 nm strain-compensated hybrid InGaN/InGaN/ZnO quantum well light-emitting diodes
Authors: Park Seoung-Hwan , Lee Yong-Tak , Park Jongwoon
Published: August 2008

Electronic and optical properties of 530 nm strain-compensated hybrid InGaN/InGaN/ZnO quantum well (QW) light-emitting diodes (LEDs) using a ZnO substrate are investigated using the multiband effective mass theory. These results are compared to those of conventional InGaN/GaN QW LEDs using a GaN substrate. A strain-compensated QW structure is found to have much larger spontaneous emission than an InGaN/GaN QW structure. This can be explained by the fact that a strain-compensated QW structure has much larger matrix element than an InGaN/GaN QW structure due to the reduction in the internal field.
Rotating black branes in Brans–Dicke–Born–Infeld theory
Authors: Hendi S. H.
Published: August 2008

In this paper, we present a new class of charged rotating black brane solutions in the higher dimensional Brans–Dicke–Born–Infeld theory and investigate their properties. Solving the field equations directly is a nontrivial task because they include the second derivatives of the scalar field. We remove this difficulty through a conformal transformation. Also, we find that the suitable Lagrangian of Einstein–Born–Infeld–dilaton gravity is not the same as presented by Dehghani et al. [J. Cosmol. Astropart. Phys. 0702, 020 (2007)]. We show that the given solutions can present black brane, with inner and outer event horizons, an extreme black brane, or a naked singularity provided the parameters of the solutions are chosen suitably. These black brane solutions are neither asymptotically flat nor (anti-)de Sitter. Then we calculate finite Euclidean action, the conserved, and thermodynamic quantities through the use of counterterm method. Finally, we argue that these quantities satisfy the first law of thermodynamics, and the entropy does not follow the area law.
Moisture exposure to different layers in organic light-emitting diodes and the effect on electroluminescence characteristics
Authors: Liao L. S. , Tang C. W.
Published: August 2008

Moisture effect on electroluminescence characteristics, including current density versus voltage, luminance versus voltage, luminous efficiency versus current density, dark spot formation, and operational stability of organic light-emitting diodes, has been systematically investigated by exposing each layer of the devices to moisture at room temperature. Moisture has a different effect on each of the interfaces or surfaces, and the influence increases as exposure time increases. There is a slight effect on the electroluminescence characteristics after the anode surface has been exposed to moisture. However, severe luminance decrease, dark spot formation, and operational stability degradation take place after the light-emitting layer or the electron-transporting layer is exposed to moisture. It is also demonstrated that the effect of moisture can be substantially reduced if the exposure to moisture is in a dark environment.
Vortices and Rossby waves in cylinder wakes on a parabolic β-plane observed by altimetric imaging velocimetry
Authors: Afanasyev Y. D. , Rhines P. B. , Lindahl E. G.
Published: August 2008

Intense vortices in the wake of a circular cylinder are investigated in a rotating parabolic (polar) β-plane fluid. This system has a background potential vorticity (PV) field that supports Rossby waves and causes vortices to migrate and radiate. A method for imaging rotating flows, which we call “altimetric imaging velocimetry” is employed. Optical color coding of slopes of the free-surface elevation field yields the pressure, geostrophic and gradient wind velocity, and potential vorticity fields with very high spatial resolution, limited largely by the pixel resolution of the available imaging sensors. Cylinder wakes on the polar β-plane exhibit strikingly different regimes as it is translated azimuthally, eastward or westward. Self-arrangement of vortices after the cylinder was stopped drives an intense eastward jet formed by the rows of anticyclones and cyclones on its flanks. In agreement with the idea of a PV staircase, this jet has a strong PV gradient at its center, while PV is homogenized by the vortices on either side. A slowly translating cylinder generates Rossby waves with phase propagation locked to the cylinder, and intermediate cases show a widespread vortex/wave interaction.
Laser proton acceleration in a water spray target
Authors: Ter-Avetisyan S. , Schnürer M. , Nickles P. V. , Smirnov M. B. , Sandner W. , Andreev A. , Platonov K. , Psikal J. , Tikhonchuk V.
Published: August 2008

Studies of interaction of a cloud of submicrometer water droplets with ultrashort (40fs) and intense (∼2×1019W∕cm2) laser pulses demonstrate an efficient acceleration of protons and oxygen ions. Due to a high ratio of the volume to the enveloping surface of a single droplet and a large number of droplets in a focal volume, efficient laser pulse absorption is enabled, which provides high electron temperatures and ion acceleration to high energies. The generation of ions with energies more than 1MeV per nucleon is demonstrated. The observed quasi-monoenergetic feature in the proton spectrum is discussed with the thermal expansion–Coulomb explosion model and numerical simulations.
Structural and dynamical properties of ionic liquids: The influence of ion size disparity
Authors: Spohr H. V. , Patey G. N.
Published: August 2008

The influence of ion size disparity on structural and dynamical properties of ionic liquids is systematically investigated employing molecular dynamics simulations. Ion size ratios are varied over a realistic range (from 1:1 to 5:1) while holding other important molecular and system parameters fixed. In this way we isolate and identify effects that stem from size disparity alone. In strongly size disparate systems the larger species (cations in our model) tend to dominate the structure; the anion-anion distribution is largely determined by anion-cation correlations. The diffusion coefficients of both species increase, and the shear viscosity decreases with increasing size disparity. The influence of size disparity is strongest up to a size ratio of 3:1, then decreases, and by 5:1 both the diffusion coefficients and viscosity appear to be approaching limiting values. The conventional Stokes–Einstein expression for diffusion coefficients holds reasonably well for the cations but fails for the smaller anions as size disparity increases likely due to the neglect of strong anion-cation correlations. The electrical conductivity is not a simple monotonic function of size disparity; it first increases up to size ratios of 2:1, remains nearly constant until 3:1, then decreases such that the conductivities of the 1:1 and 5:1 systems are similar. This behavior is traced to the competing influences of ion diffusion (enhancing) and ion densities (reducing) on conductivities at constant packing fraction. The temperature dependence of the transport properties is examined for the 1:1 and 3:1 systems. In accord with experiment, the temperature dependence of all transport properties is well represented by the Vogel–Fulcher–Tammann equation. The dependence of the diffusion coefficients on the temperature/viscosity ratio is well described by the fractional Stokes–Einstein relation D∝(T/η)β with β≈0.8, consistent with the exponent observed for many molten inorganic salts.
Dynamics of CN+alkane reactions by crossed-beam dc slice imaging
Authors: Huang Cunshun , Li Wen , Estillore Armando D. , Suits Arthur G.
Published: August 2008

The hydrogen atom abstraction reactions of CN (XΣ+2) with alkanes have been studied using the crossed molecular beam technique with dc slice ion imaging at collision energies of 7.5 and 10.8kcal∕mol. The product alkyl radical images were obtained via single photon ionization at 157nm for the reactions of CN (XΣ+2) with n-butane, n-pentane, n-hexane, and cyclohexane. From analysis of the images, we obtained the center-of-mass frame product angular distributions and translational energy distributions directly. The results indicate that the products are largely backscattered and that most of the available energy (∼80%–85%) goes to the internal energy of the products. The reaction dynamics is discussed in light of recent kinetics data, theoretical calculations, and results for related halogen and oxygen atom reactions.
Comparison of path integral molecular dynamics methods for the infrared absorption spectrum of liquid water
Authors: Habershon Scott , Fanourgakis George S. , Manolopoulos David E.
Published: August 2008

The ring polymer molecular dynamics (RPMD) and partially adiabatic centroid molecular dynamics (PA-CMD) methods are compared and contrasted in an application to the infrared absorption spectrum of a recently parametrized flexible, polarizable, Thole-type potential energy model for liquid water. Both methods predict very similar spectra in the low-frequency librational and intramolecular bending region at wavenumbers below 2500 cm−1. However, the RPMD spectrum is contaminated in the high-frequency O–H stretching region by contributions from the internal vibrational modes of the ring polymer. This problem is avoided in the PA-CMD method, which adjusts the elements of the Parrinello–Rahman mass matrix so as to shift the frequencies of these vibrational modes beyond the spectral range of interest. PA-CMD does not require any more computational effort than RPMD and it is clearly the better of the two methods for simulating vibrational spectra.
Algorithmic dimensionality reduction for molecular structure analysis
Authors: Brown W. Michael , Martin Shawn , Pollock Sara N. , Coutsias Evangelos A. , Watson Jean-Paul
Published: August 2008

Dimensionality reduction approaches have been used to exploit the redundancy in a Cartesian coordinate representation of molecular motion by producing low-dimensional representations of molecular motion. This has been used to help visualize complex energy landscapes, to extend the time scales of simulation, and to improve the efficiency of optimization. Until recently, linear approaches for dimensionality reduction have been employed. Here, we investigate the efficacy of several automated algorithms for nonlinear dimensionality reduction for representation of trans, trans-1,2,4-trifluorocyclo-octane conformation—a molecule whose structure can be described on a 2-manifold in a Cartesian coordinate phase space. We describe an efficient approach for a deterministic enumeration of ring conformations. We demonstrate a drastic improvement in dimensionality reduction with the use of nonlinear methods. We discuss the use of dimensionality reduction algorithms for estimating intrinsic dimensionality and the relationship to the Whitney embedding theorem. Additionally, we investigate the influence of the choice of high-dimensional encoding on the reduction. We show for the case studied that, in terms of reconstruction error root mean square deviation, Cartesian coordinate representations and encodings based on interatom distances provide better performance than encodings based on a dihedral angle representation.
L
-band ultrafast fiber laser mode locked by carbon nanotubes
Authors: Sun Z. , Rozhin A. G. , Wang F. , Scardaci V. , Milne W. I. , White I. H. , Hennrich F. , Ferrari A. C.
Published: August 2008

We fabricate a nanotube-polyvinyl alcohol saturable absorber with a broad absorption at 1.6 μm. We demonstrate a pulsed fiber laser working in the telecommunication L band by using this composite as a mode locker. This gives ∼498±16 fs pulses at 1601 nm with a 26.7 MHz repetition rate.
Automated gas burette system for evolved hydrogen measurements
Authors: Zheng Feng , Rassat Scot D. , Helderandt David J. , Caldwell Dustin D. , Aardahl Christopher L. , Autrey Tom , Linehan John C. , Rappé Kenneth G.
Published: August 2008

This paper reports a simple and efficient gas burette system that allows automated determination of evolved gas volume in real time using only temperature and pressure measurements. The system is reliable and has been used successfully to study the hydrogen release kinetics of ammonia borane thermolysis. The system is especially suitable for bench scale studies involving small batches and potentially rapid reaction kinetics.
Formation and evolution of F nanobubbles in amorphous and crystalline Si
Authors: Boninelli S. , Impellizzeri G. , Mirabella S. , Priolo F. , Napolitani E. , Cherkashin N. , Cristiano F.
Published: August 2008

The formation and evolution of F-induced nanobubbles in Si was investigated. Si samples were preamorphized, implanted with F, and partially regrown by solid phase epitaxy (SPE). It is shown that nanobubbles are formed already in the amorphous side of partially regrown samples and are then incorporated in crystalline Si during SPE. The bubbles are interpreted as the result of the diffusion and coalescence of F atoms and dangling bonds already in the amorphous matrix. During high temperature annealing after SPE, F outdiffuses; correspondingly, the bubbles partially dissolve and transform from spherical- to cylinder-shaped bubbles.
Comment on “On the security of a spatiotemporal chaotic cryptosystem” [Chaos 17, 033117 (2007)]
Authors: Wang Shihong , Hu Gang
Published: August 2008

This paper comments on a recent paper by R. Rhouma and B. Safya [Chaos 17, 033117 (2007)]. They claimed to find some security weakness of the spatiotemporal chaotic cryptosystem suggested by G. Tang et al. [Phys. Lett. A 318, 388 (2003)] and proposed a chosen-plaintext attack to analyze this system. We find that in their analysis, called a “chosen-plaintext attack,” they actually act as a legal receiver (with a machine in their hands during the entire decryption process) rather than an attacker and, therefore, the whole reasoning is not valid.
Detection and characterization of dynamical heterogeneity in an event series using wavelet correlation
Authors: Yang Haw
Published: August 2008

A method that combines wavelet-based multiscale decomposition with correlation statistical analysis to extract, detect, and characterize time-dependent variations in the spectral response of a system has been developed. The approach is independent of the distribution of the observable and does not rely on any presumed kinetic model for the system’s dynamical response. It provides a quantitative and objective framework for studies of complex systems exhibiting dynamics that are nonuniform in time. Applying this method to computer simulated data, it is shown that the wavelet correlation approach is capable of resolving the size fluctuations in a single nanostructure by single-molecule tracking spectroscopy.
Reaction coordinate in electron transfer: What physical quantity should we use for it?
Authors: Tachiya M.
Published: August 2008

In the Marcus theory of electron transfer the reaction coordinate due to solvent motion plays a central role. In 1991,Zhu and Rasaiah [J. Chem. Phys.95, 3325 (1991)] tried to define the reaction coordinate in terms of the solvent orientational polarization function. However, their definition is not consistent with the associated free energy curves as functions of the reaction coordinate. The appropriate definition of the reaction coordinate and the associated free energy curves are presented.
Variational and diffusion Monte Carlo study of post-d group 13–17 elements
Authors: Al-Saidi W. A.
Published: August 2008

We present ab initio calculations of atomic and molecular systems containing the first-, second-, and third-row post-d elements (Ga–Br, In–I, and Tl–At) using several methods including variational and diffusion Monte Carlo. In the quantum Monte Carlo calculations, we used the recent scalar-relativistic energy-consistent Hartree–Fock pseudopotentials [M. Burkatzki et al., J. Chem. Phys. 126, 234105 (2007)], which are nonsingular at the origin. For the first- and second-row elements, the calculated ionization energies and electron affinities are in excellent agreement with those obtained using CCSD(T) with large basis sets and with experiment after correcting approximately for spin-orbit effects. For the third-row elements, where relativistic effects cannot be adequately included by a simple j-averaging, the results are in excellent agreement with CCSD(T) energies obtained with a large (5-zeta) basis set. Benchmark calculations of the dissociation energies, vibration frequencies, and equilibrium bond lengths of several diatomic molecules including As2, Br2, Sb2, and I2 as well as the hydrides XH (X=Ga, Br, In, I, and At) are presented.
Polarization and interactions of colloidal particles in ac electric fields
Authors: Mittal Manish , Lele Pushkar P. , Kaler Eric W. , Furst Eric M.
Published: August 2008

Micrometer-sized polystyrene particles form two-dimensional crystals in alternating current (ac) electric fields. The induced dipole-dipole interaction is the dominant force that drives this assembly. We report measurements of forces between colloidal particles in ac electric fields using optical tweezers and find good agreement with the point dipole model. The magnitude of the pair interaction forces depends strongly on the bulk solution conductivity and decreases as the ionic strength increases. The forces also decrease with increasing field frequency. The salt and frequency dependences are consistent with double layer polarization with a characteristic relaxation frequency ωCD∼a2/D, where a is the particle radius and D is the ion diffusivity. This enables us to reinterpret the order-disorder transition reported for micrometer-sized polystyrene particles [Lumsdon et al., Langmuir 20, 2108 (2004)], including the dependence on particle size, frequency, and ionic strength. These results provide a rational framework for identifying assembly conditions of colloidal particles in ac fields over a wide range of parameters.
Maps of current density using density-functional methods
Authors: Soncini A. , Teale A. M. , Helgaker T. , De Proft F. , Tozer D. J.
Published: August 2008

The performance of several density-functional theory (DFT) methods for the calculation of current densities induced by a uniform magnetic field is examined. Calculations are performed using the BLYP and KT3 generalized-gradient approximations, together with the B3LYP hybrid functional. For the latter, both conventional and optimized effective potential (OEP) approaches are used. Results are also determined from coupled-cluster singles-and-doubles (CCSD) electron densities by a DFT constrained search procedure using the approach of Wu and Yang (WY). The current densities are calculated within the CTOCD-DZ2 distributed origin approach. Comparisons are made with results from Hartree-Fock (HF) theory. Several small molecules for which correlation is known to be especially important in the calculation of magnetic response properties are considered—namely, O3, CO, PN, and H2CO. As examples of aromatic and antiaromatic systems, benzene and planarized cyclooctatetraene molecules are considered, with specific attention paid to the ring current phenomenon and its Kohn-Sham orbital origin. Finally, the o-benzyne molecule is considered as a computationally challenging case. The HF and DFT induced current maps show qualitative differences, while among the DFT methods the maps show a similar qualitative structure. To assess quantitative differences in the calculated current densities with different methods, the maximal moduli of the induced current densities are compared and integration of the current densities to yield shielding constants is performed. In general, the maximal modulus is reduced in moving from HF to B3LYP and BLYP, and further reduced in moving to KT3, OEP(B3LYP), and WY(CCSD). The latter three methods offer the most accurate shielding constants in comparison with both experimental and ab initio data and hence the more reliable route to DFT calculation of induced current density in molecules.
Interaction of a skewed Rankine vortex pair
Authors: Jayavel S. , Patil Pratish P. , Tiwari Shaligram
Published: August 2008

An analytical investigation is carried out to study the kinematics of a fluid particle in an interacting field of a skewed pair of fixed Rankine vortices. A general formulation governing the kinematics of a fluid particle has been presented based on the superposition of the velocity field due to each vortex in the pair. The kinematics of a Lagrangian fluid particle is found to be governed by a nonlinear dynamical system. The fixed or stationary points of the dynamical system have been identified analytically and their existence is confirmed by the nature of particle paths in the neighborhood of fixed points. The nature of the particle path and velocity signal is reported for general as well as special configurations of the vortex pair in the presence and absence of an external uniform flow. As a specific application of the proposed problem, superimposition of the translational velocity on a semi-infinite field of longitudinal vortices generated by vortex generators mounted on fin plates of heat exchangers has also been studied.