bluuebunny/crossref_metadata_2025 huggingface dataset:
Geometry and topology of escape. I. Epistrophes
Authors: Mitchell K. A. , Handley J. P. , Tighe B. , Delos J. B. , Knudson S. K.
Published: August 2003

We consider a dynamical system given by an area-preserving map on a two-dimensional phase plane and consider a one-dimensional line of initial conditions within this plane. We record the number of iterates it takes a trajectory to escape from a bounded region of the plane as a function along the line of initial conditions, forming an “escape-time plot.” For a chaotic system, this plot is in general not a smooth function, but rather has many singularities at which the escape time is infinite; these singularities form a complicated fractal set. In this article we prove the existence of regular repeated sequences, called “epistrophes,” which occur at all levels of resolution within the escape-time plot. (The word “epistrophe” comes from rhetoric and means “a repeated ending following a variable beginning.”) The epistrophes give the escape-time plot a certain self-similarity, called “epistrophic” self-similarity, which need not imply either strict or asymptotic self-similarity.
Kinematics, equilibrium, and shape in Hamiltonian systems: The “LAB” effect
Authors: Bunimovich Leonid
Published: August 2003

We demonstrate that a system of a finite number of particles in a container with a “typical” shape does not get mixed in the sense that in an (asymptotic) steady state distribution the particles are not equally likely to occupy (almost) any position inside the container. Our incomplete mixing result should be contrasted with the complete mixing of noninteracting or elastically colliding particles in a box, which does occur because the box is not a “typical” shape. The effect we describe does not disappear in the limit of infinitely many particles. However, it is unlikely to be observed in nature but rather in laboratory (the “LAB” effect) experiments. Ideal gas in a container, which is a product of billiards, serves as a transparent model to understand the “LAB” (look at billiards) effect.
Self-developing aspherical chalcogenide-glass microlenses for semiconductor lasers
Authors: Saitoh A. , Tanaka K.
Published: August 2003

A principle of self-developing microlenses for semiconductor lasers has been demonstrated using a photosensitive glass, As2S3. The glass film is placed in front of a semiconductor laser, the light from which increases the refractive index and thickness of the film. If its position and thickness are properly selected, the illuminated film operates as an aspherical microlens which can focus an elliptical laser beam to a circular spot.
The dioctadecylamine monolayer: Textures, phase transitions, and dendritic growth
Authors: Flores Ana , Ize Pablo , Ramos Salvador , Castillo Rolando
Published: August 2003

The phase diagram of dioctadecylamine Langmuir monolayer has been determined from pressure–area isotherms and from direct observations of the monolayer using Brewster angle microscopy. We describe the observed domains, textures, and phase boundaries for the mesophases presented by this system between 5 °C and 45 °C, at pH=3. The phases were named as G, LE, S1, and S2 according to their apparent texture. Contrast between domains of condensed phases is quite low, indicating small tilting of the amine tails. The G–S1, G–S2, G–LE, and LE–S1 transitions seem to be of first order; meanwhile, the S1–S2 transition seems to be of second order. We observed how the froths changed when the area density increases at constant pressure, along the G–L, G–S1, and G–S2 phase transitions. In the L–S1 transition, the shape of the domains of the emerging phase is of sixfold dendrites. The phase diagram obtained is very different from those obtained for single chain amphiphiles. In this system, the extent of the phases depends on the acid used to fix the pH. In addition, all our observations indicate that dioctadecylamine does not form a monolayer above pH∼3.9.
Oligoazomethine-doped planar tunnel junctions: Correlating molecular structure with junction electrical characteristics
Authors: Dinglasan J. A. M. , Shivji A. , Dhirani A.-A.
Published: August 2003

We have investigated electrical properties of planar aluminum/aluminum oxide/silver tunnel junctions modified with phenyl-based azomethine oligomers. Normalized differential conductance, NDC (NDC=σV/σV=0, where σ=dI/dV), of the junctions increases with oligomer length. At a bias of 2 V, azomethines with three phenyl rings exhibit NDCs that are on average more than an order of magnitude greater than those of unmodified oxide junctions. Differential conductances of junctions modified with azomethines increase more rapidly with temperature than those of plain oxide junctions. Our results are consistent with a model in which both increased conjugated length of the sandwiched organic layer and a molecule/metal interface lead to a lowering of the barrier profile outside the aluminum oxide tunnel region.
Dissociation of acetaldehyde in intense laser field: Coulomb explosion or field-assisted dissociation?
Authors: Elshakre Mohamed E. , Gao Lirong , Tang Xiaoping , Wang Sufan , Shu Yafei , Kong Fanao
Published: August 2003

Dissociation of acetaldehyde in moderate strong laser field of 1013–1014 W/cm2 was investigated. Singly charged parent ion CH3CHO+ and fragmental ions CH3+, CHO+, C2H4+, O+, CH2CHO+, and H+ were produced by 800 nm laser of 100 fs pulse duration and recorded by time-of-flight mass spectrometer. The CH3+ fragment further dissociated to CH2+, CH+, and C+ ions at higher intensity. Ab initio calculated results show that the singly-, doubly-, and triply charged parent ions are stable. So, the dissociation mechanism was not due to Coulomb explosion of multicharged ion. A field-assisted dissociation (FAD) theory, which assumes that only one bond undergoes dissociation while the rest of the molecular geometry stays unchanged, was employed to treat the dissociation dynamics. Accordingly, the dressed potential energy surfaces of the ground state for the parent and the fragment ions were calculated. Corresponding quasiclassical trajectory calculations show that the bond ruptures take place in the order of C–C, C–O, and C–H, agreeing with the observation. The observed angular dependence and charge distribution of the product ions can also be interpreted by the FAD theory.
Pulsed-field ionization zero electron kinetic energy spectroscopy and theoretical calculations of copper complexes: Cu–X(CH3)3 (X=N,P,As)
Authors: Li Shenggang , Sohnlein Bradford R. , Rothschopf Gretchen K. , Fuller Jason F. , Yang Dong-Sheng
Published: August 2003

The copper complexes were produced in pulsed laser vaporization molecular beams and investigated by pulsed-field ionization zero electron kinetic energy (ZEKE) spectroscopy and second-order Møller–Plesset (MP2) perturbation and hybrid B3LYP density functional theory calculations. The ground electronic states of Cu–X(CH3)3 and Cu+–X(CH3)3 (X=N,P,As) are A12 and A11, respectively, both with C3v symmetry. From the ZEKE spectra, the adiabatic ionization potentials of the neutral molecules are determined to be 44 730, 41 508, and 42 324 cm−1, and the Cu+/Cu–X stretching frequencies are 268/199, 214/187, and 188/155 cm−1 for X=N, P, and As, respectively. The degenerate Cu+/Cu–P–C and Cu+/Cu–As–C bending frequencies are measured to be 146/83 and 118/52 cm−1, while the Cu+/Cu–N–C mode was not observed. In addition, the CH3 wag, X–C stretching, and XC3 umbrella modes are also measured for the phosphine and arsine complexes. From the MP2 theory, the dissociation energies of the Cu+ and Cu complexes are estimated to be 59/12, 70/15, and 65/11 kcal mol−1 down the X group. Both MP2 and B3LYP predictions of ionic vibrational frequencies compare well with the spectroscopic values, but the B3LYP calculations of neutral low frequency modes are less satisfactory. On the other hand, the B3LYP calculations yield better ionization potentials than the MP2 methods for these molecules.
Comparison of different propagators in diffusion Monte Carlo simulations of noble gas clusters
Authors: Chiesa Simone , Mella Massimo , Morosi Gabriele , Bressanini Dario
Published: August 2003

Several short-time approximations of the imaginary-time propagator of the Schrödinger equation are compared working on small helium and neon clusters. A recently discussed fourth order short time approximation of the propagator [Phys. Rev. E 61, 2050 (2000)] allows us to compute several properties practically unaffected by the time step bias. The comparison among simulations of the same length shows that this algorithm permits the use of larger time steps, leading to more accurate statistics than the ones obtained by employing commonly used schemes. Results of the mixed estimator of the potential energy, of the first two momenta of the interparticle distribution, and of the particle-center-of-mass distribution seem to indicate that the new propagator is able to perform unbiased sampling even when very large time steps are used. Also, the relative population of the four Ne7 isomers sampled using the fourth order propagator does not show any time step bias in the 200–1000 hartree−1 time step range. This fact indicates that using the fourth order propagator with large time steps is a viable approach to tackle ergodicity problems in semirigid clusters.
On the convergence scaling laws of Lanczos and Chebyshev recursion methods
Authors: Chen Rongqing , Guo Hua
Published: August 2003

In this Note, we discuss the convergence scaling law of the filter-diagonalization method based on the Chebyshev recursion, as applied to molecular spectroscopic problems. Comparison with the scaling law observed earlier for the Lanczos algorithm indicates that the two recursive methods have very similar convergence behaviors.
Twisted S1 excited state geometries in 4-dimethylaminobenzonitrile and dimethylaniline: New -d6 origin bands
Authors: Saigusa Hiroyuki , Miyakoshi Naoki , Mukai Chisato , Fukagawa Tomoyoshi , Kohtani Shigeru , Nakagaki Ryoichi , Gordon Robert
Published: August 2003

The S1←S0 electronic spectra of 4-dimethylaminobenzonitrile-h6 and -d6 (DMABN) and dimethylaniline-h6 and -d6 have been reexamined, and new electronic origins have been observed for the -d6 species, approximately 65 cm−1 lower in energy than previously reported. The spectra of DMABN-h3d3 and several other isotopomers of DMABN are reported for the first time. A prominent low-frequency progression is assigned to dimethylamino torsion, and the S1 states are found to be twisted by about 26° with a small 190 cm−1 barrier to planarity. Other bands are tentatively assigned to inversion and methyl torsional motions.
High-Tc superconducting quantum interference device observation of heat-affected zone in a spot-welded Fe–Cr–Ni system
Authors: Watanabe Yoshimi , Kang S. H. , Chan J. W. , Morris J. W. , Clarke John
Published: August 2003

A study was carried out to observe a heat-affected zone (HAZ) in a deformed Fe–Cr–Ni system containing α′ martensite using high-Tc superconducting quantum interference device (SQUID) microscopy. Microstructure and remanent magnetization images were studied by an optical microscope and a SQUID microscope, respectively. The HAZ, in which only the face-centered-cubic austenite phase exists, could be visualized by the SQUID microscope. It was also found that the SQUID images were consistent with the results from the microstructural analysis. It was concluded that a simple SQUID measurement may serve as an effective method for a nondestructive evaluation of ferromagnetic steel phases by correlating remanent magnetization images to microstructural characteristics.
Chaotic itinerancy generated by coupling of Milnor attractors
Authors: Tsuda Ichiro , Umemura Toshiya
Published: August 2003

We report the existence of chaotic itinerancy in a coupled Milnor attractor system. The attractor ruins consist of tori or local chaos generated from the original Milnor attractors. The chaotic behavior exhibited by a single orbit can be considered a “nonstationary” state, due to the extremely slow convergence of the Lyapunov exponents, but the behavior averaged over randomly chosen initial conditions is consistent with the limit theorem. We present as a possibly new indication of chaotic itinerancy the presence of slow decay of large fluctuations of the largest Lyapunov exponent.
Noise-driven switching and chaotic itinerancy among dynamic states in a three-mode intracavity second-harmonic generation laser operating on a Λ transition
Authors: Otsuka Kenju , Ohtomo Takayuki , Maniwa Tsuyoshi , Kawasaki Hazumi , Ko Jing-Yuan
Published: August 2003

We studied the antiphase self-pulsation in a globally coupled three-mode laser operating in different optical spectrum configurations. We observed locking of modal pulsation frequencies, quasiperiodicity, clustering behaviors, and chaos, resulting from the nonlinear interaction among modes. The robustness of [p:q:r] three-frequency locking states and quasiperiodic oscillations against residual noise has been examined by using joint time-frequency analysis of long-term experimental time series. Two sharply antithetical types of switching behaviors among different dynamic states were observed during temporal evolutions; noise-driven switching and self-induced switching, which manifests itself in chaotic itinerancy. The modal interplay behind observed behaviors was studied by using the statistical dynamic quantity of the information circulation. Well-organized information flows among modes, which correspond to the number of degeneracies of modal pulsation frequencies, were found to be established in accordance with the inherent antiphase dynamics. Observed locking behaviors, quasiperiodic motions, and chaotic itinerancy were reproduced by numerical simulation of the model equations.
Multiconfigurational system-bath dynamics using Gaussian wave packets: Energy relaxation and decoherence induced by a finite-dimensional bath
Authors: Burghardt Irene , Nest Mathias , Worth Graham A.
Published: August 2003

The quantum dynamics of an anharmonic oscillator coupled to a bath of up to 60 harmonic oscillators is investigated by a new multiconfigurational hybrid method for wave packet propagation. The method, originally proposed in [Burghardt, Meyer, and Cederbaum, J. Chem. Phys. 111, 2927 (1999)], represents a variant of the multiconfiguration time-dependent Hartree method including a moving basis of Gaussian functions. Energy relaxation and quantum decoherence induced by the zero-temperature oscillator bath are shown to be accurately described by the new method. Decoherence rates for a bath with a discretized ohmic spectral density are found to be consistent with golden-rule predictions for T=0.
Polymer dynamics in linear mixed flow
Authors: Dua Arti , Cherayil Binny J.
Published: August 2003

Recent simulations by Chu et al. [Phys. Rev. E 66, 011915 (2002)] on the behavior of bead–spring and bead–rod models of polymers in linear mixed flows (flows with unequal amounts of extension and rotation) are compared with the predictions of a finitely extensible Rouse model that was used earlier [J. Chem. Phys. 112, 8707 (2000)] to describe the behavior of long flexible molecules of λ-phage DNA in simple shear. The model is a generalization of the continuum Rouse model in which the “spring constant” of the bonds connecting near neighbor segments is allowed to become nonlinearly flow-dependent through a term involving the initially unknown mean square size of the chain, 〈R2〉. A self-consistent equation for this quantity is derived by using the flow-modified Hamiltonian to calculate it from its statistical mechanical definition. After solving this equation numerically, the mean fractional extension of the chain x can be obtained as a function of the Weissenberg number Wi and a mixing parameter α. The results compare favorably with data from the simulations of Chu et al., and suggest the existence of a scaling variable Wieff=α Wi in terms of which separate curves of x versus Wi fall more or less on a single universal curve.
A Landau free energy for diblock copolymers with compressibility difference between blocks
Authors: Cho Junhan
Published: August 2003

A new Landau free energy is derived for diblock copolymers of incompatible pairs based on the recently developed compressible random-phase approximation analysis. Finite compressibility of each block is generally allowed. The inhomogeneity of each block density and free volume is analyzed in the weak segregation regime. Free volume inhomogeneity fluctuates in two ways: One represents compressibility difference between blocks and the other stands for the screening of unfavorable cross-contacts. It is shown from the Landau energy that a continuous transition, observed in a symmetric block copolymer either incompressible or with no compressibility difference, disappears provided that one block is more compressible. Microphase transitions and their pressure response of commonly used diblock copolymers are calculated and compared with experimental results. A Flory-type interaction parameter χcRPA, which is suggested from the effective second-order vertex function in the free energy, is shown to be useful, owing to its compressible nature in understanding the phase behavior of various copolymers.
Theory of copolymer micellization
Authors: Duque Daniel
Published: August 2003

We consider the micellization of block copolymers in solution, employing self-consistent field theory with an additional constraint that permits the examination of intermediate structures. From the information for an isolated micelle (structure, binding energy, free energy) we describe how the global thermodynamics of these systems can be obtained, which can be used to build a realistic phase diagram; the role of translational entropy must be addressed in this regard.
Effect of gatekeepers on the early folding kinetics of a model β-barrel protein
Authors: Stoycheva Antitsa D. , Onuchic José N. , Brooks Charles L.
Published: August 2003

Recent exciting experimental observations have suggested the existence of gatekeeper residues in protein folding. These residues may influence only slightly the stabilization of a protein’s final folded state, but have an important kinetic function in the early stages of folding—to avoid nonproductive folding routes. We explore the physical mechanism for the action of such gatekeepers, in the form of salt-bridgelike charged residues, on the early folding behavior of a model 46-mer β-barrel protein. Computer simulations employing Langevin dynamics show that the gatekeepers enhance the kinetics of folding on time scales that are about three orders of magnitude shorter than previously reported folding times for this model system. Analysis of the unfolded ensembles of the wild type (WT) β-barrel and several good and poor salt bridge designs indicates that the proteins with well designed salt-bridge gatekeepers favor productive folding routes when compared to the WT system. The conclusions of our theoretical observations are in agreement with experimental studies of the ribosomal protein S6 and its mutants.
General-model-space state-universal coupled-cluster theory: Connectivity conditions and explicit equations
Authors: Li Xiangzhu , Paldus Josef
Published: August 2003

We present a new version of the state-universal (SU), multireference, coupled-cluster (CC) theory that is capable of handling completely general, incomplete model spaces. This is achieved by exploiting the concept of “locality” for the active molecular spin orbitals and by introducing the constraining conditions (C conditions) on cluster amplitudes that are associated with the internal excitations transforming one reference configuration into another one. These C conditions make it possible to represent the exact (i.e., full configuration interaction) wave function via the SU CC cluster ansatz based on an arbitrary model space. The C conditions are then taken into account together with the standard SU CC equations for the external amplitudes, thus enabling us to reach the exact result in the limit, while preserving the connectivity property and thus the size extensivity. We also present compact expressions for the matrix elements of the effective Hamiltonian as well as the explicit expressions for the most important coupling coefficients that are required at the single and double excitation level. All other expressions are the same as in the single reference CC formalism.
Current density maps, magnetizability, and nuclear magnetic shielding tensors of bis-heteropentalenes. I. Di-hydro-pyrrolo–pyrrole isomers
Authors: Garcı́a Cuesta I. , Soriano Jartı́n R. , Sánchez de Merás A. , Lazzeretti P.
Published: August 2003

Magnetic susceptibility and nuclear magnetic shielding at the nuclei of bis-heteropentalenes formed by two pyrrole units ([2,3−b], [3,2−b], [3,4−b], and [3,4−c] isomers) have been evaluated by a series of different approximations and a large Gaussian basis set. An ab initio model of magnetic field induced current density was obtained for four isomeric systems, showing that strong diamagnetic flow takes place within the π electrons. The π currents are responsible for exalted magnetic anisotropy and proton deshielding. The theoretical findings are used to assess a diatropicity scale for these molecules.
Interpolated potential energy surface and classical dynamics for H3++HD and H3++D2
Authors: Moyano Gloria E. , Collins Michael A.
Published: August 2003

A potential energy surface for H5+ has been constructed by a modified Shepard interpolation on a sparse set of data points, using second order Möller–Plesset perturbation theory. An improved version of the surface was also obtained by substituting the energy values at the data points with values evaluated using a coupled cluster treatment (with single and double excitations, and perturbative treatment of triple excitations). Classical simulations for the collisions between H3++HD and H3++D2 were carried out in order to calculate the total integral cross sections and rate coefficients for these systems. There is good agreement with earlier experimental data for rate coefficients at temperatures between 80 and 300 K, but the predicted rate coefficient for the reaction of H3++HD at 10 K deviates from the most recent experimental measurement, suggesting that quantum rather than classical reaction dynamics are necessary.
Structural and quantum effects from anionic centers in rare gas clusters: The (Ne)nH− and (Ne)n+1 systems
Authors: Sebastianelli F. , Baccarelli I. , Di Paola C. , Gianturco F. A.
Published: August 2003

The structural properties and the energetics of some of the smaller ionic clusters of neon atoms with the atomic impurity H−, NenH− with n from 2 up to 8, are examined using different kinds of modeling for the interactions within each cluster and employing different theoretical dynamical approaches, both classical and quantal. The same calculations are carried out also for the corresponding neutral homogeneous clusters Nen+1. The results of the calculations, the physical reliability of the interaction modeling, and the similarities between different features shown by the negative ions with respect to the neutral complexes are discussed. The emerging picture shows that the dopant atom H− always locates itself outside the Nen moiety for clusters of this size without significantly affecting the overall geometries and that many-body (MB) effects within the clusters are rather negligible in the description of the overall interaction potentials.
Success and failure of polarized-ion models: Bending and atomization energy of groups 2 and 12 dihalides
Authors: Donald Kelling J. , Mulder Willem H. , Szentpály László v.
Published: August 2003

Polarized-ion models—with and without dipole reaction fields and charge-quadrupole interaction—are evaluated in calculating atomization energies, bond angles, and bending force constants of groups 2 and 12 dihalides. A study of the sensitivity to changes in the input parameters reveals a strong dependence on dipole polarizabilities. The charge–quadrupole bending terms of a multipole expansion are important for quasi-linear molecules, where the preceding terms in the expansion tend to cancel each other. They normally stabilize the linear geometry, but enhance bent structures, if a certain criterion for the ratio of quadrupole polarizabilities of metal and halide ions is fulfilled. The models explain the bent alkaline earth halides, but fail spectacularly for the group 12 halides—HgBr2 and HgI2 are even calculated as unstable relative to the constituent atoms. The unexpected weakness of ionic bonds is related to the large increase of the ionization energies by relativistic effects and the lanthanide contraction.
Kinetics of CH radicals with O2: Evidence for CO chemiluminescence in the gas phase reaction
Authors: Vaghjiani Ghanshyam L.
Published: August 2003

The production of CO vis-uv-chemiluminescence has been observed for the first time when a trace amount of CHBr3 vapor was photodecomposed in a pulsed-photolysis reactor using a 248-nm laser under multiphoton-dissociation conditions in an excess of O2 in diluent helium or argon carrier gas at 298 K and in the pressure range 2–95 Torr. The time-resolved chemiluminescent traces due to vibronic emissions at several band positions in the CO(A–X), CO(a–X), and CO(d–a) systems, and in the (1–0) and (0–0) bands of the OH(A–X) system were observed to decay nonexponentially. Their integrated intensities all showed quadratic dependence on the photolysis fluence employed. The OH and CO chemiluminescence data can be best interpreted by postulating the occurrence of O2 reactions with the methylidyne radicals in two different electronic states, CH(X 2Π) and CH(a 4Σ−). The production of CO(A) and CO(d) in these reactions require the methylidyne radicals to be internally (vibrationally) excited. The decay kinetics of the chemiluminescence was investigated in the presence of various added substrates, the buffer gas pressure, and in conditions of excess added CH4, which allowed us to isolate and study the CH(a 4Σ−)+O2 reaction, since the CH(X 2Π) could rapidly be removed from the system. The reactions of highly internally excited brominated radical species such as CBr♯, CHBr♯, and CBr2♯ with O2, in principle, can also produce CO chemiluminescence, but are argued to be of negligible importance in the present CHBr3/O2 photolysis system.
Construction of kinetic domains in energy trapping processes and application to a photosynthetic light harvesting complex
Authors: Yang Mino , Fleming Graham R.
Published: August 2003

We develop a formulation allowing construction of various kinetic domains from a master equation for population transfer dynamics and enabling calculation of the time scales of transition between such domains. In this way, a complicated network of energy transfer steps can be simplified to a series of sequential kinetic transitions over the kinetic domains. We illustrate the advantage of this formulation by applying it to energy trapping in a photosynthetic light harvesting system and as a result we obtain a clear picture of energy transfer dynamics and the various rate determining steps in Photosystem I.
Energy levels and wave functions of weakly bound bosonic trimers using Pekeris coordinates and a symmetry-adapted Lanczos approach
Authors: Roy Pierre-Nicholas
Published: August 2003

An approach is presented for the accurate calculation of the energy levels of weakly bound bosonic rare gas trimers. A Pekeris coordinate system is used in order to avoid the interdependent range problem associated with internuclear distance coordinates. The present choice of coordinates also permits a straightforward treatment of boson symmetry and allows one to assess the importance of linear configurations through the calculation of one-body reduced distribution functions. The discrete variable representation is used and the eigenvalue problem is solved using a Lanczos recursion combined with projection operator techniques in order to extract totally symmetric states. Lennard-Jones systems corresponding to Argon and Neon are studied in order to assess the accuracy of the method by comparing them with those of recent benchmark calculations. The approach allows the accurate calculation of several bound states. Calculations are also performed for the case of a Morse interaction potential and the results are compared to those studies based on the commonly used internuclear distance coordinates. The present approach is found to be more accurate.
Conformational analysis of the jet-cooled peptide mimetic ethylacetamidoacetate from torsion-rotation spectra
Authors: Lavrich R. J. , Hight Walker A. R. , Plusquellic D. F. , Kleiner I. , Suenram R. D. , Hougen J. T. , Fraser G. T.
Published: August 2003

Rotational spectra of two conformers of the peptide mimetic, ethyl-acetamidoacetate, were measured in a molecular beam using a Fourier-transform microwave spectrometer. In each conformer, internal rotation of the acetyl methyl group gives rise to observable splittings in the spectrum. From analysis of the torsion-rotation interactions, the methyl group’s orientation has been determined in the principal axis frame of each conformer and is shown to unambiguously identify its conformational form. One conformer exists in the all-trans configuration and belongs to CS point group and the second, higher-energy conformer has C1 symmetry. Two separate theoretical fitting procedures are applied to assess the reliability of the structural information and are shown to be essentially equivalent. For example, methyl torsional barriers are 63.7(1) cm−1 versus 67.1(1) cm−1 and 64.8(1) cm−1 versus 67.5(1) cm−1 for the CS and C1 conformers, respectively, and principal axis orientations of the methyl groups agree to ±0.1°. The small differences in the torsional barriers and rotor axis angles for the two conformers are a result of a change in the orientation of the ethyl group on the other end of the molecule. The predicted energy ordering of these two conformers at the MP2/6-311G(d,p) level of theory is in disagreement with experimental observations.
Rho-axis-method Hamiltonian for molecules having one methyl rotor and C1 point-group symmetry at equilibrium
Authors: Kleiner Isabelle , Hougen Jon T.
Published: August 2003

Two modifications of the rho-axis-method torsion-rotation Hamiltonian for fitting spectra of methyl top molecules belonging to the Cs point group at equilibrium which are required to treat molecules with C1 equilibrium configurations are described: (i) The permutation-inversion group must be changed from G6 to G3, which causes the A1 and A2 species to coalesce into a single A species, and which also introduces the slight complication of separably degenerate E species. (ii) One term must be added to the second-order contact-transformation-reduced Hamiltonian and seven terms must be added to the fourth-order reduced Hamiltonian. Programming strategies for this Hamiltonian are also discussed. In particular, portions of the C1 computer code requiring complex arithmetic are indicated, and three schemes for checking the internal consistency of the C1 code are suggested. Application of this C1 Hamiltonian to ethylacetamidoacetate is given in the preceding paper.
Intermolecular Hamiltonian for solute–solventn clusters and application to the (1|1) isomer of anthracene–He2
Authors: Felker Peter M. , Neuhauser Daniel
Published: August 2003

Intermolecular kinetic-energy operators are derived (in the rigid monomer approximation) for solute–solventn clusters of the type B–An, where B is a molecule and A is either an atom or a molecule. The operators are obtained for a body-fixed frame embedded in the B moiety and parallel to the principal axes of that species. They are expressed in terms of intermolecular coordinates that represent the projection along the body-fixed axes of position vectors pointing from the center of mass of B to the centers of mass of the A species. The results are particularly useful for calculations on clusters in which A–B interactions dominate over A–A interactions in the intermolecular potential energy surface and/or there is minimal interaction between subsets of the A moieties. This utility is demonstrated in variational calculations of intermolecular states in the (1|1) isomer of anthracene–He2.
Formation of small lanthanum–carbide ions from laser induced fragmentation of La@C82
Authors: Lassesson A. , Gromov A. , Mehlig K. , Taninaka A. , Shinohara H. , Campbell E. E. B.
Published: August 2003

The fragmentation behavior of the endohedral metallofullerene La@C82 was studied using gas phase time-of-flight mass spectrometry. The results were compared with the fragmentation of C60. When the metallofullerene was excited by a 337 nm ns laser, small lanthanum–carbide fragments LaCn+, n=0–6, were detected. A simple statistical maximum entropy model was used to simulate the excitation energy dependence of the loss of the LaCn+ molecules as well as C2 evaporation to form smaller metallofullerenes. By comparing experimental ion intensities with the model, the appearance energies of LaCn+, n=0–6, were found to lie above 65 eV. The lanthanum–carbide fragments ejected from La@C82 decrease in size with increasing internal energy. The ejection of La+ and LaC2+ is preferred at the expense of larger fragments such as LaC4+ and metallofullerenes at the higher excitation.
On the constructive role of noise in stabilizing itinerant trajectories in chaotic dynamical systems
Authors: Kozma Robert
Published: August 2003

This work aims at studying dynamical models of neural networks, which exhibit phase transitions between states of various complexities. We use the biologically motivated KIII model, which has demonstrated excellent performance as a robust dynamical memory device. KIII is a high-dimensional dynamical system with extremely fragmented boundaries between limit cycles, tori, fixed points, and chaotic attractors. We study the role of additive noise in the development of itinerant trajectories. Noise not only stabilizes aperiodic trajectories, but there is an optimum noise level with highly itinerant behavior. We speculate that the previously found optimum classification performance of KIII as a function of the noise level, also identified as chaotic resonance, is related to chaotic itinerant oscillations among various ordered states.
Density fitting for the decomposition of three-electron integrals in explicitly correlated electronic structure theory
Authors: Ten-no Seiichiro , Manby Frederick R.
Published: August 2003

It is shown that the convergence of R12-type explicitly correlated electronic structure theories can be improved by rearranging the three-electron integrals before using a resolution of the identity to decompose them into expressions involving only two-electron integrals. The new scheme is illustrated for some test systems within the explicitly correlated second order many-body perturbation theory.
Ground state potential energy curves for He–Kr, Ne–Kr, Ar–Kr, and Kr2: Coupled-cluster calculations and comparison with experiment
Authors: Haley Terence P. , Cybulski Sławomir M.
Published: August 2003

Ab initio calculations were performed with the coupled-cluster single and double excitations with perturbative triples correction method using the augmented correlation consistent polarized triple, quadruple, and quintuple zeta basis sets [aug-cc-pVnZ (n=T,Q,5)] for four complexes: He–Kr, Ne–Kr, Ar–Kr, Kr2. For each complex and each basis set a fitted potential energy curve is given. The most accurate results were obtained with the aug-cc-pV5Z basis set supplemented with an additional (3s3p2d2 f1g) set of bond functions. Ab initio potentials were compared to experimental data and the best empirical potentials available. The agreement was good although calculated potentials were found to be too shallow. To better reproduce spectroscopic data, ab initio potentials were modified using a nonlinear least-squares procedure. The modified potentials were developed for He–Kr, Ne–Kr, Ar–Kr, and Kr2, as well as Ne–Ar and Ar2. They all compare favorably with the best available empirical potentials.
Partial molar volume and compressibility of a molecule with internal degrees of freedom
Authors: Imai Takashi , Hirata Fumio
Published: August 2003

Statistical mechanical expressions for the partial molar volume (PMV) and the partial molar compressibility (PMC) of a solute molecule with internal degrees of freedom are derived. The equilibrium PMV is expressed simply by the conformational ensemble average of PMV. The equilibrium PMC consists of two terms: the conformational ensemble average of PMC and the mean square fluctuation of PMV along conformational axis. As an illustrative application of the theory, the equilibrium PMV and PMC of butane in aqueous solution are calculated from the relations, in which the thermodynamic quantities of each conformer appearing in the relations are obtained by the reference interaction site model theory. The conformational ensemble average of PMC is the predominant contribution to the equilibrium PMC in this particular example. Possibility of shedding light on the protein conformation in terms of PMV and PMC is discussed.
Infrared spectroscopy of acetone–water liquid mixtures. I. Factor analysis
Authors: Max Jean-Joseph , Chapados Camille
Published: August 2003

Acetone and water mixtures covering the whole solubility range were measured by Fourier transform infrared attenuated total reflectance spectroscopy. In this system, only water can supply the hydrogen atoms necessary for hydrogen bonding. Using spectral windowing with factor analysis (FA), 10 principal factors were retrieved, five water and five acetone. Hydrogen bonding is observed on the carbonyl stretch band as water is introduced in the solution, redshifting the band further from its gas position than that observed in pure liquid acetone. This indicates that the hydrogen bonding is stronger than the acetone dipole–dipole interactions because it overrides them. A water molecule isolated in acetone is twice H bonded through its two H atoms; although both OH groups are H-bond donors, the OH stretch band is less redshifted (∼138 cm−1) than that of pure liquid water (∼401 cm−1). This is attributable to the two lone electron pairs remaining on the oxygen atom that sustain a large part of the OH valence bond strength. Hydrogen bonds on the water oxygen weaken both its OH valence bonds and modify the OH stretch band when water is added to the solution. The oxygen atoms of both water and acetone can accept 0, 1, and 2 H bonds given by water to yield three water and three acetone situations. Since these six situations are far less than the 10 principal factors retrieved by FA, other perturbations must be present to account for the difference. Although acetone and water are intermingled through H bonds, hydrates in the sense of an acetone molecule sequestering a number of water molecules or altering the H-bonding water network are not present because the principal factors evolve independently.
Influence of monomer molecular structure on the glass transition in polymers I. Lattice cluster theory for the configurational entropy
Authors: Freed Karl F.
Published: August 2003

The configurational entropy Sc, which is a basic quantity in theoretical descriptions of the glass transition, is evaluated for a multicomponent polymer system using the lattice cluster theory. This theoretical treatment of Sc represents an extension of the Gibbs–DiMarzio theory to a mixture of semiflexible, interacting polymers composed of structured monomers. The extension provides a theoretical tool for investigating how the glass transition of polymer systems depends on the chemical structure of the constituent polymers. Applications of the new theoretical approach to the computation of glass transition temperatures will be given elsewhere.
Quasistable states in globally coupled tent map systems
Authors: Chawanya Tsuyoshi
Published: August 2003

The characteristics of long lasting but not perpetual chaotic states appear in a wide parameter region in a globally coupled overcritical tent map system are exhibited. The lifetime of the transient state has essential relevance with the system size. In some parameter region, the lifetime saturates at a certain level, while in another region it seems to diverge as the size of the system grows. In order to uncover the dynamical structures in large system size limit, the dynamics of one-body distribution is investigated as an idealized model for the infinitely large coupled map system. Obtained numerical results indicate the correspondence between the characteristics of long transient behavior in finite size system and that of the attractor or the ruin of attractor in the idealized model.
Theoretical studies of the interface between water and Langmuir films of aliphatic alcohols
Authors: Nutt David R. , Stone Anthony J.
Published: August 2003

The interface between water and Langmuir films of long chain aliphatic molecules is investigated using accurate intermolecular potentials. The stabilities of various ice structures which could form at the interface are examined. Antiferroelectric ice is found to be the most stable, but this stability depends crucially on the first layer of water. Ferroelectric structures are found to collapse upon relaxation. Our model was not able to differentiate between the different nucleation properties of C31H63OH and C30H61OH. A better description of the alcohol–water interaction is probably required to account for this difference.
The behavior of mixed-metal oxides: Structural and electronic properties of Ce1−xCaxO2 and Ce1−xCaxO2−x
Authors: Rodriguez José A. , Wang Xianqin , Hanson Jonathan C. , Liu Gang , Iglesias-Juez Ana , Fernández-Garcı́a Marcos
Published: August 2003

Synchrotron-based time-resolved x-ray diffraction (TR-XRD), x-ray absorption near edge spectroscopy (XANES), Raman spectroscopy (RS), and first-principles density functional (DF) calculations were used to study the structural and electronic properties of Ce–Ca mixed-metal oxides. The XRD results and DF calculations show that doping with calcium induces relatively minor variations (<0.05 Å) in the cell dimensions of ceria. However, the presence of Ca leads to slightly distorted tetragonal structures, a substantial strain in the lattice of the oxide and a tendency to form O vacancies in an ideal Ce1−xCaxO2 solid solution. The two latter effects can be a consequence of the large number of oxygen neighbors that Ca is forced to have in Ce1−xCaxO2 and differences in the electronic charges of calcium and cerium cations. The Ce1−xCaxO2−x systems are not fully ionic. Cation charges derived from the DF calculations indicate that these systems obey the Barr model for charge redistribution in mixed-metal oxides. The Ca atoms in Ce1−xCaxO2−x are more electropositive than the cations in CaO, while the Ce cations of Ce1−xCaxO2−x are less electropositive than those of CeO2. These trends are consistent with XANES measurements at the Ca K- and Ce LIII-edges. The cation charge redistributions should be taken into consideration when explaining or predicting the chemical and catalytic properties of Ce1−xCaxO2−x. Ca induces structural and electronic perturbations on ceria quite different from those found after doping with Zr. The behavior of Ce1−xCaxO2−x illustrates the drastic effects that doping with an electropositive element can have on the properties of ceria.
Itinerant memory dynamics and global bifurcations in chaotic neural networks
Authors: Kitajima Hiroyuki , Yoshinaga Tetsuya , Aihara Kazuyuki , Kawakami Hiroshi
Published: August 2003

We have considered itinerant memory dynamics in a chaotic neural network composed of four chaotic neurons with synaptic connections determined by two orthogonal stored patterns as a simple example of a chaotic itinerant phenomenon in dynamical associative memory. We have analyzed a mechanism of generating the itinerant memory dynamics with respect to intersection of a pair of α branches of periodic points and collapse of a periodic in-phase attracting set. The intersection of invariant sets is numerically verified by a novel method proposed in this paper.
Collective vibrations of a lattice of screw dislocations as an example of the dynamics of an acoustic superlattice
Authors: Kosevich A. M.
Published: August 2003

Equations for small oscillations of a dislocation lattice are formulated in a simple one-component model. The lattice is formed by a periodic system of parallel rectilinear screw dislocations. Long-wavelength collective vibrations are described, among which are found vibrations similar to plasma oscillations in a system of electric charges. The possibility of a gap appearing in the frequency spectrum near the analog of the plasma frequency is pointed out.
E-field-induced polarization rotation in Pb(Mg1/3Nb2/3)1−xTixO3 crystal
Authors: Tu Chi-Shun , Shih I.-C. , Schmidt V. Hugo , Chien R.
Published: August 2003

A sequence of field-induced phase transformations was observed by means of a polarizing microscope on a (111)-cut single crystal Pb(Mg1/3Nb2/3)0.67Ti0.33O3 at room temperature with an electric field applied along the [111] direction. As electric field increases, polarizations of the rhombohedral R domains whose polar directions are not along [111] rotate first toward a tetragonal T phase associated with 90° domain walls. Then the crystal gradually reaches total optical extinction for all polarizer angles at 12 kV/cm, indicating a single [111] rhombohedral R111 domain with polarization aligned with the electric field. These field-induced phase transformations are irreversible and proceed most likely through MA-type monoclinic distortions, i.e., R→MA→T→MA→R111.
Controlling transient dynamics to communicate with homoclinic chaos
Authors: Baptista M. S. , Boccaletti S. , Allaria E. , Meucci R. , Arecchi F. T.
Published: August 2003

A control that stabilizes the transient dynamics of a homoclinic chaotic laser is used to encode discrete sources of information. The controlled trajectory is a complex spiking signal that has a constrained interspike interval, and therefore, the ratio of information transmitted is approximately constant. We also show that the controlled signal that encodes the source contains more information than the source. This property is advantageously used to correct possible errors in the transmission, or to increase the ratio of information per transmitted spike.
Chaotic itinerancy in coupled dynamical recognizers
Authors: Ikegami Takashi , Morimoto Gentaro
Published: August 2003

We argue that chaotic itinerancy in interaction between humans originates in the fluctuation of predictions provided by the nonconvergent nature of learning dynamics. A simple simulation model called the coupled dynamical recognizer is proposed to study this phenomenon. Daily cognitive phenomena provide many examples of chaotic itinerancy, such as turn taking in conversation. It is therefore an interesting problem to bridge two chaotic itinerant phenomena. A clue to solving this is the fluctuation of prediction, which can be translated as “hot prediction” in the context of cognitive theory. Hot prediction is simply defined as a prediction based on an unstable model. If this approach is correct, the present simulation will reveal some dynamic characteristics of cognitive interactions.
Piezoelectric, electro-optical, and photoelastic effects in InxGa1−xN/GaN multiple quantum wells
Authors: Chen C. H. , Chen W. H. , Chen Y. F. , Lin T. Y.
Published: August 2003

We present microphotoluminescence (PL) and micro-Raman measurements with varying the applied electric field in InxGa1−xN/GaN multiple quantum wells (MQWs). The InGaN A1(LO) phonon was found to show a redshift in frequency with the increase of applied electric field. And, a blueshift in PL spectra has been observed when the applied electric field was increased. Quite interestingly, the change in the refractive index was also observed, which was determined accurately from the interference pattern shown in the emission spectra. This finding correlates very well with the blueshift of PL spectra and the redshift of the InGaN A1(LO) phonon. Based on the stress change induced by the compensation between piezoelectric and external fields, our results firmly establish that strong electro-optical and photoelastic effects do exist in InxGa1−xN/GaN MQWs, which is important in the design of optoelectronic devices.