bluuebunny/crossref_metadata_2025 huggingface dataset:
Flow strength of highly hydrated Mg‐ and Na‐sulfate hydrate salts, pure and in mixtures with water ice, with application to Europa
Authors: Durham William B. , Stern Laura A. , Kubo Tomoaki , Kirby Stephen H.
Published: December 2005

We selected two Europan‐ice‐shell candidate highly hydrated sulfate salts for a laboratory survey of ductile flow properties: MgSO4·7H2O (epsomite) and Na2SO4·10H2O (mirabilite), called MS7 and NS10, respectively. Polycrystalline samples in pure form and in mixtures with water ice I were tested using our cryogenic high‐pressure creep apparatus at temperatures 232 ≤ T ≤ 294 K, confining pressures P = 50 and 100 MPa, and strain rates 4 × 10−8 ≤ ≤ 7 × 10−5 s−1. Grain size of NS10 samples was >100 μm. The flow strength σ of pure MS7 was over 100 times that of polycrystalline ice I at comparable conditions; that of pure NS10 over 20 times that of ice. In terms of the creep law = Aσn e−Q/RT, where R is the gas constant, we determine parameter values of A = 1012.1 MPa−ns−1, n = 5.4, and Q = 128 kJ/mol for pure NS10. Composites of ice I and NS10 of volume fraction ϕ NS10 have flow strength σc = [ϕNS10σNS10J + (1 − ϕNS10)σiceIJ]1/J where J ≈ −0.5, making the effect on the flow of ice with low volume fractions of NS10 much like that of virtually undeformable hard rock inclusions. Being much stronger and denser than ice, massive sulfate inclusions in the warmer, ductile layer of the Europan ice shell are less likely to be entrained in convective ice flow and more likely to be drawn to the base of the ice shell by gravitational forces and eventually expelled. With only smaller, dispersed sulfate inclusions, at probable sulfate ϕ < 0.2, the shell may be treated rheologically as pure, polycrystalline ice, with boundary conditions perhaps influenced by the high density and low thermal conductivity of the hydrated salts.
An analysis of periodic tracers for subsurface characterization
Authors: Mahinthakumar G. Kumar , Moline Gerrilynn R. , Webb Oren F.
Published: December 2005

This paper investigates the feasibility of periodic tracers (i.e., tracers injected in a periodic waveform) for subsurface characterization using numerical simulations. From a theoretical point of view, periodic tracers offer many advantages over conventional pulse or continuous tracers. For example, periodic tracers are more sensitive to various transport and reaction processes and are less susceptible to corruption by environmental noise. With the recent advances in computer‐controlled injection technologies, time is now ripe for investigating the feasibility of these tracers for laboratory and field tracer tests. A series of numerical sensitivity analyses are performed in this study for assessing the sensitivity of these signals for various transport and reaction phenomena in the subsurface. Sensitivity coefficients are calculated and compared for conventional and periodic tracers for various transport phenomena. An inverse modeling case study is performed to evaluate the potential of periodic tracers for detecting the location and concentration of biological active zones. The results indicate that periodic tracers have the potential to perform significantly better than conventional tracers.
Effect of geometry on stress relaxation in InAs∕GaAs rectangular nanomesas: Multimillion-atom molecular dynamics simulations
Authors: Makeev Maxim A. , Kalia Rajiv K. , Nakano Aiichiro , Vashishta Priya , Madhukar Anupam
Published: December 2005

We report the results of multimillion-atom parallel molecular dynamics simulations performed to investigate the lattice-misfit-induced stress relaxation in nanometer-sized rectangular GaAs mesas covered with InAs overlayers of 12-ML thickness. The morphology of atomic planes in the InAs overlayers and the stress distributions in the mesas are studied for varied linear dimensions and aspect ratios. We find that the lattice-mismatch-induced stress relaxation pathways is strongly dependent on the mesa and InAs overlayer geometry. The lattice-misfit-associated stress is accommodated through both the morphology changes of the InAs overlayer planes and the stress accommodation in the GaAs mesa interior. The effects are quantified by computing the atomic displacements in the InAs overlayer atomic planes and the hydrostatic stress distributions. Simulation results reveal that, as the aspect ratio of the rectangular mesa top increases, the morphology of the atomic planes shows a transition from dimple-type morphology, characteristic for mesas of square geometry, to semiperiodic modulations of displacement fields accompanied by the overall downward relaxation. The conclusions regarding the stress relaxation mechanism are supported by comparing the topography of the displacement field patterns with those of the hydrostatic stress observed in the mesa systems of different geometries. The obtained results are in qualitative agreement with experiments.
Heated quartz microbalance to study thermally deposited calcareous scale
Authors: Gabrielli C. , Perrot H. , Rousseau P. , Belghazi A. , Chevrot T. , Colin J. M. , Simonet C.
Published: December 2005

The scaling effect can affect drastically all equipment where water is used. In general, the phenomenon is amplified with hot fluids or hot pipes as, for example, conditions found in the heat exchangers. Thus, dramatic damages can occur that lead to dangerous economic consequences. The basic idea in this article is to promote the development of tools that can characterize the scaling power under certain conditions. A sophisticated heated quartz crystal microbalance was built and its performance was evaluated. It was shown that the scale must be deposited onto the sensor surface in an identic way compared with current scaling deposition conditions and the kinetics of deposition evaluated thanks to the microbalance response.
Microfabricated continuous-flow, turbulent, microsecond mixer
Authors: Majumdar Zigurts K. , Sutin Jason D. B. , Clegg Robert M.
Published: December 2005

We present a microfabricated, continuous-flow, turbulent mixing device that can mix two or more fluids to complete homogeneity on the molecular scale in the microsecond range. The current design is compact, portable, relatively simple to fabricate, adaptable for various measurement techniques, and consumes small sample volumes. The entire mixing process is observable and we use this feature to characterize the dependence of the progress of mixing on the flow velocity. We present details of the mixer’s construction and optical data acquisition using fluorescence. Because the mixer is constructed using microfabrication technology, it is inexpensive and alterations are easy to explore. We show that the dependence of mixing times and pressure drop on the flow velocity agree well with theoretical expectations for turbulent pipe flow. This provides useful guidelines in predicting performance of this type of mixing device.
Nonadiabatic chemical dynamics in an intense laser field: Electronic wave packet coupled with classical nuclear motions
Authors: Yagi Kiyoshi , Takatsuka Kazuo
Published: December 2005

Dynamics of molecules in an intense laser field is studied in terms of the quantum electronic wave packet coupled with classical nuclear motions. The equations of motion are derived taking a proper account of molecular interactions with the vector potential of a classical electromagnetic field, along with the nonadiabatic interaction due to the breakdown of the Born-Oppenheimer approximation. With the aid of electronic structure calculations, the present method enables us to track, in an ab initio manner, the dynamics of polyatomic molecules in an intense field. Preliminary calculations are carried out for the vibrational state of LiF and a collision of Li+F under an intense laser pulse, which are limited to the domain of no ionization.
1
ω
,
2
ω
, and 3ω methods for measurements of thermal properties
Authors: Dames Chris , Chen Gang
Published: December 2005

3 ω methods are commonly used to measure the thermal conductivity of a substrate adjacent to a strip heater or the thermal conductivity and specific heat of a suspended wire. Here we consider the general case of a line heater that is also used to sense temperature. Analysis of all harmonics is presented in terms of generic thermal and electrical transfer functions and is readily adapted to other experimental configurations. We identify voltage signals at 2ω and 1ω that contain the same information about the thermal properties as the 3ω signal. The 2ω voltage requires a dc offset at the current source. The 1ω voltage requires a very stable current source, but eliminates the need for higher-harmonic detection, and is advantageous for studying the dynamics of systems with very fast thermal response times. The 1ω,2ω, and 3ω methods compare favorably with experiments using a suspended platinum wire and a line heater on a Pyrex substrate. With a modern lock-in amplifier, no common-mode voltage subtraction is necessary, which simplifies the experiment compared to the common practice of balancing a bridge or using a multiplying digital-to-analog converter. We also show that the widespread practice of using a voltage source to approximate a current source is only valid when the sample resistance is small compared to the total electrical resistance of the circuit, and derive and experimentally verify a correction factor to be used otherwise.
Mean-field dynamics with stochastic decoherence (MF-SD): A new algorithm for nonadiabatic mixed quantum/classical molecular-dynamics simulations with nuclear-induced decoherence
Authors: Bedard-Hearn Michael J. , Larsen Ross E. , Schwartz Benjamin J.
Published: December 2005

The key factors that distinguish algorithms for nonadiabatic mixed quantum/classical (MQC) simulations from each other are how they incorporate quantum decoherence—the fact that classical nuclei must eventually cause a quantum superposition state to collapse into a pure state—and how they model the effects of decoherence on the quantum and classical subsystems. Most algorithms use distinct mechanisms for modeling nonadiabatic transitions between pure quantum basis states (“surface hops”) and for calculating the loss of quantum-mechanical phase information (e.g., the decay of the off-diagonal elements of the density matrix). In our view, however, both processes should be unified in a single description of decoherence. In this paper, we start from the density matrix of the total system and use the frozen Gaussian approximation for the nuclear wave function to derive a nuclear-induced decoherence rate for the electronic degrees of freedom. We then use this decoherence rate as the basis for a new nonadiabatic MQC molecular-dynamics (MD) algorithm, which we call mean-field dynamics with stochastic decoherence (MF-SD). MF-SD begins by evolving the quantum subsystem according to the time-dependent Schrödinger equation, leading to mean-field dynamics. MF-SD then uses the nuclear-induced decoherence rate to determine stochastically at each time step whether the system remains in a coherent mixed state or decoheres. Once it is determined that the system should decohere, the quantum subsystem undergoes an instantaneous total wave-function collapse onto one of the adiabatic basis states and the classical velocities are adjusted to conserve energy. Thus, MF-SD combines surface hops and decoherence into a single idea: decoherence in MF-SD does not require the artificial introduction of reference states, auxiliary trajectories, or trajectory swarms, which also makes MF-SD much more computationally efficient than other nonadiabatic MQC MD algorithms. The unified definition of decoherence in MF-SD requires only a single ad hoc parameter, which is not adjustable but instead is determined by the spatial extent of the nonadiabatic coupling. We use MF-SD to solve a series of one-dimensional scattering problems and find that MF-SD is as quantitatively accurate as several existing nonadiabatic MQC MD algorithms and significantly more accurate for some problems.
Fluid structure and transport properties of water inside carbon nanotubes
Authors: Liu Yingchun , Wang Qi , Wu Tao , Zhang Li
Published: December 2005

The fluid structure and transport properties of water confined in single-walled carbon nanotubes (CNTs) with different diameters have been investigated by molecular-dynamics simulation. The effects of CNT diameter, density of water, and temperature on the molecular distributions and transport behaviors of water were analyzed. It is interesting that the water molecules ordered in helix inside the (10, 10) CNT, and the layered distribution was clearly observed. It was found that the axial and radial diffusivities in CNTs were much lower than that of the bulk, and it ever decreased as the diameter of CNT decreases. The axial thermal conductivity and shear viscosity in CNTs are obviously larger than that of the bulk and those in the radial direction, they increase sharply as the diameter of CNT decreases, which is clearly in contrast to the diffusivity. The inner space of CNT and the interactions between water molecules and the confining walls play a key role in the structure and transport properties of water confined in the CNTs.
Invariant noncommutative connections
Authors: Masson Thierry , Serié Emmanuel
Published: December 2005

In this paper we classify invariant noncommutative connections in the framework of the algebra of endomorphisms of a complex vector bundle. It has been proven previously that this noncommutative algebra generalizes in a natural way the ordinary geometry of connections. We use explicitly some geometric constructions usually introduced to classify ordinary invariant connections, and we expand them using algebraic objects coming from the noncommutative setting. The main result is that the classification can be performed using a “reduced” algebra, an associated differential calculus and a module over this algebra.
Anisotropy of selective epitaxy in nanoscale-patterned growth: GaAs nanowires selectively grown on a SiO2-patterned (001) substrate by molecular-beam epitaxy
Authors: Lee S. C. , Dawson L. R. , Brueck S. R. J. , Jiang Y.-B.
Published: December 2005

Anisotropic selective epitaxy in nanoscale-patterned growth (NPG) by molecular-beam epitaxy is investigated on a 355nm period two-dimensional array of circular holes fabricated in a 30-nm-thick SiO2 film on a GaAs(001) substrate. The hole diameter ranged from 70to150nm. The small hole diameter and the very thin masking layer stimulated lateral growth over the SiO2 surface at an early stage of selective epitaxy on this patterned substrate. Lateral overgrowth associated with selective epitaxy, however, did not proceed isotropically along the circular boundary between the open substrate surface and the SiO2 mask. There was preferential growth direction parallel to ⟨111⟩B. This anisotropy in the selective epitaxy resulted in the formation of a nanoscale, nontapered, straight-wire-type epitaxial layer (GaAs nanowires), which had a length of up to 1.8μm for a nominal 200nm deposition. Every GaAs nanowire had a hexagonal prismatic shape directed along ⟨111⟩B and was surrounded by six (110) sidewalls. The anisotropy of selective epitaxy and faceting in NPG were affected by the profile of the SiO2 mask and are interpreted using a minimization of the total surface energy for equilibrium crystal shape.
Experimental investigation on the floating potential of cylindrical Langmuir probes in non-Maxwellian electron distributions
Authors: Chung ChinWook
Published: December 2005

[Chen and Arnush Phys. Plasmas 8, 5051 (2001)] theoretically showed that the floating potential is not constant but a function of electron density and the potential difference between the floating potential and the plasma potential differs significantly from the plane probe approximation. The electron energy distribution functions (EEDFs) in an inductively coupled plasma are measured to investigate the effect of the EEDF on the floating potential at argon pressures of 2 and 10mTorr with respect to rf power. It is found that the measured EEDFs at 2mTorr were bi-Maxwellian EEDFs with a high-energy tail and the potential differences were governed by the high electron temperatures. In the case of 10mTorr, the measured EEDFs were nearly Maxwellian EEDFs at 10mTorr and the potential difference agrees qualitatively with the theory of Chen and Arnush assuming that the electron energy distribution is a Maxwellian EEDF.
IR/UV double resonant spectroscopy of the methyl radical: Determination of ν3 in the 3pz Rydberg state
Authors: Fu H. B. , Hu Y. J. , Bernstein E. R.
Published: December 2005

IR + UV double resonant ion-dip and ion-enhancement spectroscopies are employed to study the ν3 asymmetric CH stretch vibration fundamental of CH3 in the ground and 3pz Rydberg electronic states. CH3 radical is synthesized in the supersonic jet expansion by flash pyrolysis of azomethane (CH3NNCH3) prior to the expansion. The Q band of the 3113pz←X̃ transition of CH3, not detected by conventional UV resonantly enhanced multiphoton ionization (REMPI) spectroscopy, is determined to lie at 59898cm−1 using IR+UV REMPI spectroscopy. Energy of the asymmetric CH stretch of CH3 in the 3pz Rydberg state, ν3(3pz), is 3087cm−1, redshifted by ∼74cm−1 with respect to ground state ν3(X̃).
A molecular-dynamics simulation study on the dependence of Lennard-Jones gas-liquid phase diagram on the long-range part of the interactions
Authors: Ou-Yang Wen-Ze , Lu Zhong-Yuan , Shi Tong-Fei , Sun Zhao-Yan , An Li-Jia
Published: December 2005

The particle-transfer molecular-dynamics technique is adopted to construct the Lennard-Jones fluid gas-liquid phase diagram. Detailed study of the dependence of the simulation results on the system size and the cutoff distance is performed to test the validity of the simulation technique. Both the traditional cutoff plus long-range correction (CPC) and Ewald summation methods are used in the simulations to calculate the interactions. In the intermediate range of temperatures, the results with the Ewald summation method are almost the same as those with the CPC method. However, in the range close to the critical point, the results with the CPC method deviate from those with the Ewald summation. Compared with the results obtained via the Ewald summation in a smaller system, simply increasing the system size in the CPC scheme may not give better results.
Quantum escape kinetics over a fluctuating barrier
Authors: Ghosh Pulak Kumar , Barik Debashis , Bag Bidhan Chandra , Ray Deb Shankar
Published: December 2005

The escape rate of a particle over a fluctuating barrier in a double-well potential exhibits resonance at an optimum value of correlation time of fluctuation. This has been shown to be important in several variants of kinetic model of chemical reactions. We extend the analysis of this phenomenon of resonant activation to quantum domain to show how quantization significantly enhances resonant activation at low temperature due to tunneling.
Extended wedge covariance for wetting and filling transitions
Authors: Parry A. O. , Rascón C. , Morgan L.
Published: December 2005

Fluid adsorption on nonplanar and heterogeneous substrates is studied using a simple interfacial model. For systems with short-ranged forces, we find that, by tuning the local strength of the substrate potential, it is possible to find the exact equilibrium interfacial profile as a functional of the wall shape ψ(x). The tuning of the local substrate potential takes the form of a gauge condition θ̇(x)=±ψ̈(x), where θ(x) can be interpreted as a local effective contact angle. For wedgelike geometries with asymptotic tilt angle α, the midpoint interfacial height and roughness satisfy the same covariance relations previously found for simple linear wedges. For troughlike geometries satisfying the gauge condition, covariance is also found for the two-point correlation function. Predictions for more microscopic Landau and Ising models are also discussed.
Photofragmentation study of hexamethyldisiloxane following core ionization and direct double ionization
Authors: Céolin D. , Miron C. , Le Guen K. , Guillemin R. , Morin P. , Shigemasa E. , Millié P. , Ahmad M. , Lablanquie P. , Penent F. , Simon M.
Published: December 2005

X-ray photoelectron spectroscopy and Auger spectroscopy studies of gas-phase hexamethyldisiloxane (HMDSO) are presented. The photodissociation of this molecule is studied using various experimental coincidence techniques. We compare the fragmentation pathways observed after core ionization followed by Auger decay and after valence double photoionization of the molecule. A strongly selective production of the doubly charged tetramethyldisiloxane ion is observed in the low binding-energy regions. Theoretical calculations are carried out to tentatively explain the stability of the produced dication.
Optical Tamm states for the fabrication of polariton lasers
Authors: Kavokin Alexey , Shelykh Ivan , Malpuech Guillaume
Published: December 2005

We propose to embed the ultrathin layer of an organic or inorganic material at the boundary between two specially designed periodic dielectric structures in order to achieve the strong coupling between Frenkel or Wannier-Mott excitons and optical Tamm states localized at the interface. This would allow the fabrication of polariton lasers without microcavities that could be easier from the technological point of view. Analytical formulas are given for the energies of optical Tamm states and the constant of their coupling to excitons.
Identification and analysis of the perturbed cΠ3(v=1)–XΣ+1 and kΠ3(v=5)–XΣ+1 absorption bands of carbon monoxide
Authors: Baker Jacob , Launay Françoise
Published: December 2005

Two new red-degraded bands in the room-temperature vacuum-ultraviolet absorption spectrum of carbon monoxide have been identified in the 94000–94500cm−1 energy region and analyzed. One of the bands at ≈94225cm−1 (106.1nm) has three observable bandheads and is partially overlapped with the strong CΣ+1–XΣ+1 (1–0) transition at lower energy. It is assigned to the cΠ3–XΣ+1 (1–0) transition. The other band at ≈94437cm−1 (105.9nm) with one clear bandhead is assigned to the kΠ3–XΣ+1 (5–0) transition. A strong homogeneous perturbation was found to exist between the two upper states that strongly influences the line positions and shapes of these bands. A rotational deperturbation analysis was performed and molecular rotational constants for both upper states were determined. These deperturbed molecular constants are entirely consistent with the expected values for the kΠ3 valence and cΠ3 Rydberg states. The Hamiltonian interaction term between these two states is found to be separable into vibrational and electronic factors and the electronic factor is determined to be He=323±40cm−1. A discrepancy in the literature regarding the location of the cΠ3 (v=1) state is identified and discussed.
Self-oscillating rubidium magnetometer using nonlinear magneto-optical rotation
Authors: Schwindt P. D. D. , Hollberg L. , Kitching J.
Published: December 2005

The detection of nonlinear magneto-optical rotation (NMOR) of polarized light through alkali atomic vapor is a highly sensitive technique for measuring magnetic fields. We demonstrate that when using frequency modulated light to excite the NMOR resonance, it is possible to cause the system to self-oscillate. The NMOR signal is not a simple replica of the sine wave modulation of the light, but rather contains many higher harmonics of the modulation frequency, and we implement two ways of processing the signal to recover the fundamental modulation frequency in the feedback loop and induce self-oscillation. Self-oscillation simplifies and reduces the power consumption of the electronics required to operate a magnetometer, making the NMOR technique attractive for commercialized magnetic sensors.
Renormalized coupled-cluster methods exploiting left eigenstates of the similarity-transformed Hamiltonian
Authors: Piecuch Piotr , Włoch Marta
Published: December 2005

Completely renormalized (CR) coupled-cluster (CC) approaches, such as CR-CCSD(T), in which one corrects the standard CC singles and doubles (CCSD) energy for the effects of triply (T) and other higher-than-doubly excited clusters [K. Kowalski and P. Piecuch, J. Chem. Phys. 113, 18 (2000)], are reformulated in terms of the left eigenstates ⟨Φ∣L of the similarity-transformed Hamiltonian of CC theory. The resulting CR-CCSD(T)L or CR-CC(2,3) and other CR-CCL methods are derived from the new biorthogonal form of the method of moments of CC equations (MMCC) in which, in analogy to the original MMCC theory, one focuses on the noniterative corrections to standard CC energies that recover the exact, full configuration-interaction energies. One of the advantages of the biorthogonal MMCC theory, which will be further analyzed and extended to excited states in a separate paper, is a rigorous size extensivity of the basic ground-state CR-CCL approximations that result from it, which was slightly violated by the original CR-CCSD(T) and CR-CCSD(TQ) approaches. This includes the CR-CCSD(T)L or CR-CC(2,3) method discussed in this paper, in which one corrects the CCSD energy by the relatively inexpensive noniterative correction due to triples. Test calculations for bond breaking in HF, F2, and H2O indicate that the noniterative CR-CCSD(T)L or CR-CC(2,3) approximation is very competitive with the standard CCSD(T) theory for nondegenerate closed-shell states, while being practically as accurate as the full CC approach with singles, doubles, and triples in the bond-breaking region. Calculations of the activation enthalpy for the thermal isomerizations of cyclopropane involving the trimethylene biradical as a transition state show that the noniterative CR-CCSD(T)L approximation is capable of providing activation enthalpies which perfectly agree with experiment.
Gibbs free-energy estimates from direct path-sampling computations
Authors: Adjanor G. , Athènes M.
Published: December 2005

We have implemented a path-sampling scheme enabling a direct estimation of Gibbs free energy. This scheme consists of a Monte Carlo sampling of constant-pressure Langevin paths, followed by an ensemble averaging carried out over the Markov chain of paths. In practice, we sample an umbrella path ensemble, which requires to rigorously define a statistical weight for the paths, equivalent of the Boltzmann weight. This statistical weight is a function of an effective work related to the path. The umbrella ensemble is chosen so that its work histogram overlaps with the histograms corresponding to the ensembles of forward and backward paths. We have finally investigated the relations between numerical efficiency and overlapping properties of the various work histograms. This analysis yields a built-in criterion for diagnosing the convergence during a single-run simulation.
Density-functional theory and Monte Carlo simulation study on the electric double layer around DNA in mixed-size counterion systems
Authors: Wang Ke , Yu Yang-Xin , Gao Guang-Hua , Luo Guang-Sheng
Published: December 2005

A density-functional approach and canonical Monte Carlo simulations are presented for describing the ionic microscopic structure around the DNA molecule immersed in mixed-size counterion solutions. In the density-functional approach, the hard-sphere contribution to the Helmholtz energy functional is obtained from the modified fundamental measure theory [Y.-X. Yu and J. Z. Wu, J. Chem. Phys. 117, 10156 (2002)], and the electrostatic contribution is evaluated through a quadratic functional Taylor expansion. The new theory is suitable to the systems containing ions of arbitrary sizes and valences. In the established canonical Monte Carlo simulation, an iterative self-consistent method is used to evaluate the long-range energy, and another iterative algorithm is adopted to obtain desired bulk ionic concentrations. The ion distributions from the density-functional theory (DFT) are in good agreement with those from the corresponding Monte Carlo (MC) simulations. It is found that the ratio of the bulk concentrations of two species of counterions (cations) makes significant contribution to the ion distributions in the vicinity of DNA. Comparisons with the electrostatic potential profiles from the MC simulations show that the accuracy of the DFT becomes low when a small divalent cation exists. Both the DFT and MC simulation results illustrate that the electrostatic potential at the surface of DNA increases as the anion diameter or the total cation concentration is increased and decreases as the diameter of one cation species is increased. The calculation of electrostatic potential using real ion diameters shows that the accuracy of DFT predictions for divalent ions is also acceptable.
Cylinder-gyroid-lamella transitions in diblock copolymer solutions: A simulated annealing study
Authors: Yu Bin , Li Baohui , Sun Pingchuan , Chen Tiehong , Jin Qinghua , Ding Datong , Shi An-Chang
Published: December 2005

The morphological transition of an asymmetric diblock copolymer [A(3)-b-B(9)] in A-selective solvents is investigated using a simulated annealing technique. The study was carried out at high copolymer concentrations. Phase-transitions among hexagonally packed cylinders (C), gyroid (G), and lamellae (L) are observed. The phase transition sequence, C→G→L, was obtained with decreasing copolymer concentration and/or increasing B-solvent interaction. The predicted phase-transition sequence is consistent with experiments of diblock copolymers with similar volume fractions in selective solvents of different selectivity. The morphological transitions were further analyzed in terms of the average contact numbers for A or B monomers with other molecules and the total surface area of the core or matrix in each structure. It is found that these quantities correlate with the structures, providing an understanding of the phase-transition mechanisms.
Vapor-liquid equilibrium and critical behavior of the square-well fluid of variable range: A theoretical study
Authors: Schöll-Paschinger Elisabeth , Benavides Ana Laura , Castañeda-Priego Ramon
Published: December 2005

The vapor-liquid phase behavior and the critical behavior of the square-well (SW) fluid are investigated as a function of the interaction range, λ∊ [1.25, 3], by means of the self-consistent Ornstein-Zernike approximation (SCOZA) and analytical equations of state based on a perturbation theory [A. L. Benavides and F. del Rio, Mol. Phys. 68, 983 (1989); A. Gil-Villegas, F. del Rio, and A. L. Benavides, Fluid Phase Equilib. 119, 97 (1996)]. For this purpose the SCOZA, which has been restricted up to now to a few model systems, has been generalized to hard-core systems with arbitrary interaction potentials requiring a fully numerical solution of an integro-partial differential equation. Both approaches, in general, describe well the liquid-vapor phase diagram of the square-well fluid when compared with simulation data. SCOZA yields very precise predictions for the coexistence curves in the case of long ranged SW interaction (λ>1.5), and the perturbation theory is able to predict the binodal curves and the saturated pressures, for all interaction ranges considered if one stays away from the critical region. In all cases, the SCOZA gives very good predictions for the critical temperatures and the critical pressures, while the perturbation theory approach tends to slightly overestimate these quantities. Furthermore, we propose analytical expressions for the critical temperatures and pressures as a function of the square-well range.
Coarse-grained molecular-dynamics simulations of the self-assembly of pentablock copolymers into micelles
Authors: Chushak Y. , Travesset A.
Published: December 2005

Multiblock polymers in aqueous solution, where one or several blocks are hydrophobic, exhibit a rich variety of phases and states of aggregation. In this paper, we investigate a pentablock system ABCBA, where the B block is always hydrophilic and the A and C blocks have varying degrees of hydrophobicity depending on external conditions. We report coarse-grained molecular-dynamics simulations where the solvent is included explicitly and monomers interact via a 6-9 Lennard Jones potential function. The hydrophobic interaction is modeled by tuning the parameter controlling the strength of the interaction between the hydrophobic monomers and the solvent. We investigate the structure and morphology of the micelles for two concrete situations representing changes in temperature and the pH level. The simulated system is directly relevant to a recently synthesized pentablock system consisting of a triblock Pluronic® with an added pH-sensitive end group [B. C. Anderson et al., Macromolecules 36, 1670 (2003)].
Lifetime and predissociation yield of N214bΠu1(v=1) revisited: Effects of rotation
Authors: Lewis B. R. , Gibson S. T. , Sprengers J. P. , Ubachs W. , Johansson A. , Wahlström C. -G.
Published: December 2005

Coupled-channel Schrödinger-equation calculations of the lifetime of the b(v=1) level of N214 reveal strong rotational effects, with extreme lifetime shortening at high J as a result of rapidly increasing predissociation. Comparison with experiment indicates that the apparent discrepancy between the results of Sprengers et al. [J. Chem. Phys.120, 8973 (2004)] and Oertel et al. [Chem. Phys. Lett.82, 552 (1981)] is an artifact, caused by the significant J dependence of the lifetime, together with differing experimental conditions. This comparison is facilitated by the analysis of further experimental data, not previously reported by Sprengers et al. The strong J dependence of the b(v=1) predissociation yield is likely to lead to significant consequences for the interpretation of N2 fluorescence spectra and aeronomical data.
Ultrathin CoPt-pinned current perpendicular to the plane spin valves
Authors: Maat S. , Checkelsky J. , Carey M. J. , Katine J. A. , Childress J. R.
Published: December 2005

The magnetics and magnetotransport of current perpendicular to the plane (CPP) giant magnetoresistive (GMR) spin valves utilizing thin CoPt hard magnet pinning layers on Cr seed layers are investigated. 50-Å-thick CoPt18 films grown on >20Å Cr seed layers exhibit a coercivity of ∼1.5kOe and a resistivity of 31μΩcm. The low critical thickness of the CoPt hard magnet compared to IrMn or PtMn antiferromagnets makes it an attractive pinning material for small gap CPP sensors required for high magnetic recording densities. Furthermore, CoPt∕Ru∕CoFe trilayers exhibit strong antiparallel coupling and the low CoPt resistivity minimizes parasitic resistance yielding a higher magnetoresistance. Moreover, free layers with coercivities and coupling fields in a range of 5–10 Oe have been measured, demonstrating that free layer softness does not suffer from the proximity to the CoPt hard magnet due to the relatively thick spacer layers compatible with CPP GMR sensors. In particular we deposited CoPt18 pinned antiferromagnetically coupled spin with a variety of reference layers. The films were patterned into pillars with diameters ranging from 50 to 200 nm by using a combination of electron beam lithography and ion milling. The devices exhibit a magnetoresistance up to 3.6% and a resistance area product of only 20mΩμm2.
Diffraction of complex harmonic plane waves and the stimulation of transient leaky Rayleigh waves
Authors: Declercq Nico F. , Degrieck Joris , Leroy Oswald
Published: December 2005

This paper describes the interaction of complex harmonic plane waves on a periodically corrugated surface. It is shown that the ability of complex harmonic plane waves to stimulate leaky Rayleigh waves on a corrugated surface is similar to the ability of harmonic inhomogeneous waves to stimulate leaky Rayleigh waves on a smooth interface. Because the experimental generation of harmonic inhomogeneous waves is more complicated and less flexible than the generation of complex harmonic waves, the combination of complex harmonic plane waves with a diffraction grating therefore offers an excellent alternative. The theoretical model developed here is based on the well-known and experimentally verified complex harmonic wave theory and the famous Rayleigh decomposition of the diffracted field. The numerical examples are given for combinations of frequency and corrugation dimensions that justify the use of the Rayleigh theory. A study of the influence of a complex frequency on the generation of Scholte-Stoneley surface waves is performed as well.
On the sharpness of the zero-entropy-density conjecture
Authors: Farkas S. , Zimborás Z.
Published: December 2005

The zero-entropy-density conjecture states that the entropy density defined as s≔limN→∞SN∕N vanishes for all translation-invariant pure states on the spin chain. Or equivalently, SN, the von Neumann entropy of such a state restricted to N consecutive spins, is sublinear. In this paper it is proved that this conjecture cannot be sharpened, i.e., translation-invariant states give rise to arbitrary fast sublinear entropy growth. The proof is constructive, and is based on a class of states derived from quasifree states on a CAR algebra. The question whether the entropy growth of pure quasifree states can be arbitrary fast sublinear was first raised by Fannes et al. [J. Math. Phys. 44, 6005 (2003)]. In addition to the main theorem it is also shown that the entropy asymptotics of all pure shift-invariant nontrivial quasifree states is at least logarithmic.
Transition from a Bloch-Wilson to a free-electron density of states in Znn− clusters
Authors: Kostko Oleg , Wrigge Gert , Cheshnovsky Ori , Issendorff Bernd v.
Published: December 2005

We present photoelectron spectroscopy studies on Znn− in the size range of n=3–117. We show that zinc clusters exhibit a distinct transition in their electronic structure as a function of size. At small sizes (up to n=18) the clusters follow the Bloch-Wilson picture of the development of a metal from closed-shell atoms, exhibiting a gradual decrease of the gap between the fully occupied s band and the empty p band. For large sizes (n≳32) the band overlap allows the valence electrons to fully delocalize. This leads to an almost perfect free-electron density of states, as is demonstrated by discussing the spectra in the light of standard free-electron models and by comparison to the results obtained on sodium clusters.
Statistical-mechanical theory of rheology: Lennard-Jones fluids
Authors: Laghaei Rozita , Eskandari Nasrabad Afshin , Eu Byung Chan
Published: December 2005

The generalized Boltzmann equation for simple dense fluids gives rise to the stress tensor evolution equation as a constitutive equation of generalized hydrodynamics for fluids far removed from equilibrium. It is possible to derive a formula for the non-Newtonian shear viscosity of the simple fluid from the stress tensor evolution equation in a suitable flow configuration. The non-Newtonian viscosity formula derived is applied to calculate the non-Newtonian viscosity as a function of the shear rate by means of statistical mechanics in the case of the Lennard-Jones fluid. For that purpose we have used the density-fluctuation theory for the Newtonian viscosity, the modified free volume theory for the self-diffusion coefficient, and the generic van der Waals equation of state to compute the mean free volume appearing in the modified free volume theory. Monte Carlo simulations are used to calculate the pair-correlation function appearing in the generic van der Waals equation of state and shear viscosity formula. To validate the Newtonian viscosity formula obtained we first have examined the density and temperature dependences of the shear viscosity in both subcritical and supercritical regions and compared them with molecular-dynamic simulation results. With the Newtonian shear viscosity and thermodynamic quantities so computed we then have calculated the shear rate dependence of the non-Newtonian shear viscosity and compared it with molecular-dynamics simulation results. The non-Newtonian viscosity formula is a universal function of the product of reduced shear rate (γ*) times reduced relaxation time (τe*) that is independent of the material parameters, suggesting a possibility of the existence of rheological corresponding states of reduced density, temperature, and shear rate. When the simulation data are reduced appropriately and plotted against τe*γ* they are found clustered around the reduced (universal) non-Newtonian viscosity formula. Thus we now have a molecular theory of non-Newtonian shear viscosity for the Lennard-Jones fluid, which can be implemented with a Monte Carlo simulation method for the pair-correlation function.
Generating random and nonoverlapping dot patterns for liquid-crystal display backlight light guides using molecular-dynamics method
Authors: Chang Jee-Gong , Su Ming-Horng , Lee Cheng-Tai , Hwang Chi-Chuan
Published: December 2005

This paper employs the molecular-dynamics method to generate random-dot patterns for light guides designed for backlight systems. The proposed approach combines various numerical techniques and is designed to optimize the dot-density distribution in order to satisfy the uniform luminance requirements demanded by liquid-crystal displays. In the proposed algorithm, the total domain is divided into a prescribed number of cells whose dot densities can be individually adjusted in order to fine tune the luminance conditions in accordance with the light source position and type. In addition, a variable truncation distance is implemented in each cell according to the dot density of that cell. This variable r-cut technique localizes the repulsive force effects acting within each cell in order that a high-dot-density gradient can be achieved in the overall dot distribution. Finally, an average force control technique is developed to ensure the uniformity of the dot distribution as it passes across the cell boundaries. Several illustrative examples are provided to demonstrate the robustness of the proposed molecular-dynamics dot-generation algorithm.
Morphology and surface-plasmon resonance of silver nanoparticles sandwiched between Si3N4 and BN layers
Authors: Toudert J. , Camelio S. , Babonneau D. , Denanot M.-F. , Girardeau T. , Espiños J. P. , Yubero F. , Gonzalez-Elipe A. R.
Published: December 2005

Nanocermet trilayered thin films consisting of silver nanoclusters sandwiched between two dielectric layers (the buffer and the cap) have been synthesized by ion-beam sputtering with an alternate deposition of the metal and the dielectric species. The influence of the amount of silver, the nature of the buffer and the cap (BN or Si3N4), and a time delay before the cap deposition on clusters morphology and repartition have been investigated by transmission electron microscopy. It has been observed that the clusters display truncated ellipsoidal shapes in which the height to diameter ratio H∕D decreases as the amount of deposited silver increases. For a given amount of silver, this ratio is lower in the case of a Si3N4 cap, whatever the nature of the buffer. Two explanations are proposed to account for this “cap effect” on clusters morphology: the first one is based on a calculation of the H∕D minimizing the surface free energy of the clusters embedded between the buffer and the cap; the second one holds on the shape relaxation of the coalesced nonequilibrium clusters towards their equilibrium shape with the buffer, this process occurring until clusters are fully covered with the cap. Because of the higher deposition rate of Si3N4 compared to BN, a Si3N4 cap would allow a less efficient reshaping and consequently lead to flatter clusters. This explanation is supported by the temporal evolution of clusters morphology and repartition observed during the time delay before deposition of the cap. The evolution of the spectral position of the surface-plasmon resonance (SPR) of the trilayers as a function of their structure has also been investigated by optical transmittance measurements. The influence of cluster morphology, as well as the nature of the buffer and the cap on the SPR spectral position are discussed.
A study of the failure wave phenomenon in glasses compressed at different levels
Authors: Kanel G. I. , Razorenov S. V. , Savinykh A. S. , Rajendran A. , Chen Zhen
Published: December 2005

Shock-wave experiments are performed with four different kinds of glasses of different hardness compressed at different levels. The experiments with the glass specimens consisting of layered thin plates confirm the appearance of a failure wave in elastically compressed soda lime glass, heavy flint glass, K8 crown glass, and fused quartz, although the relationships between the Hugoniot elastic limits and the failure thresholds of these glasses are different. The failure wave process could occur as the stress grows above the failure threshold up to the stress level at which plastic deformation starts. The propagation speed of the failure wave in soda lime glass depends on the stress above the failure threshold, and does not depend on the propagation distance. The failure process becomes unstable and stops at the stress level near the failure threshold. Evidence of internal friction in glass within the elastic deformation region is observed.
Near-field turbulent simulations of rectangular jets using lattice Boltzmann method
Authors: Yu Huidan , Girimaji Sharath S.
Published: December 2005

We perform large eddy simulation (LES) of the near field of low aspect ratio (AR) rectangular turbulent jets (RTJ) using the lattice Boltzmann method. The computational technique combines a D3Q19 multiple relaxation time (MRT) lattice Boltzmann equation (LBE) with the Smagorinsky model for the subgrid stress. First and foremost, we demonstrate that the MRT-LBE model is more suitable than the widely used single-relaxation-time LBE model for LES of turbulent flows. Then, we proceed to compute four jets with MRT-LBE: AR-1, 1.5, 2, 5; exit velocity u0(m∕s)-60, 39, 60, 23; and Reynolds number Re-184 000, 25 900, 128 000, 14 000. The investigated near-field behavior includes: (1) Decay of mean streamwise velocity (MSV) and inverse MSV; (2) spanwise and lateral profiles of MSV; (3) half-velocity width development and MSV contours; and (4) streamwise turbulence intensity distribution. The simulation results are compared against experimental data. Two unique features of RTJ—the saddle-back MSV spanwise (major axis) profile and axis switching of major axis from spanwise to lateral direction—are investigated. Our simulations show that the jet statistical behavior is more sensitive to inflow velocity and less so to the transverse boundary conditions. Overall, this work demonstrates that the MRT-LBE method is a potentially reliable computational tool for LES of turbulence even at high Reynolds numbers.
An upgraded 32-channel heterodyne electron cyclotron emission radiometer on Tore Supra
Authors: Ségui J. L. , Molina D. , Giruzzi G. , Goniche M. , Huysmans G. , Maget P. , Ottaviani M. ,   The Tore Supra Team
Published: December 2005

A 32-channel, 1GHz spaced heterodyne radiometer is used on the Tore Supra tokamak to measure electron cyclotron emission (ECE) in the frequency range 78–110GHz for the ordinary mode (O:E‖B,k⊥B) and 94–126GHz for the extraordinary mode (X:E⊥B,k⊥B). The radial resolution is essentially limited by ECE relativistic effects, depending on electron temperature and density, and not by the channels’ frequency spacing. The time resolution depends on the acquisition scheme: the system allows for both 1ms and 10μs acquisition. For example, this leads to precise electron temperature mapping during MHD activity. First experimental results obtained with this upgraded 32-channel radiometer are presented.
Measurement of wave scattering by topography in the presence of currents
Authors: Magne Rudy , Rey V. , Ardhuin Fabrice
Published: December 2005

Wave scattering over a sinusoidal bottom in the presence of an ambient current is investigated experimentally. Waves were generated in a flume with and without current and propagated over a patch of four sinusoidal bars before dissipating on a beach. A Doppler shift of the resonant Bragg frequency and an amplification of the wave reflection are observed in the presence of the current. Weak reflections over the beach are found to have a significant influence on the wave reflection over the bars.