bluuebunny/crossref_metadata_2025 huggingface dataset:
Dual-probe scanning tunneling microscope: Measuring a carbon nanotube ring transistor
Authors: Watanabe Hiroyuki , Manabe Chikara , Shigematsu Taishi , Shimizu Masaaki
Published: July 2002

We have constructed a dual-probe scanning tunneling microscope (D-STM). We used multiwall carbon nanotubes [(NT), diameter: ∼10 nm] as STM probes. The D-STM allows us to elucidate the electric property of a sample with a spatial resolution of ∼1 nm. Using this system, we have measured the current–voltage curves of a single NT ring as a transistor. The curves show the possibility of nanometer-scale electronic circuits composed of NT devices.
Symmetry-breaking and near-symmetry-breaking in three-electron-bonded radical cations
Authors: Braı̈da Benoı̂t , Lauvergnat David , Hiberty Philippe C.
Published: July 2002

The manifestations of the symmetry-breaking artifact in three-electron-bonded systems have been investigated at several computational levels including second-order Møller–Plesset perturbation theory (MP2), coupled cluster (CC), and Bruckner-coupled cluster (B-CC) theories. The model systems, [HnX∴XHn]+(X=Ne, F, O, N, Ar, Cl, S, P; n=0–3) cover all types of three-electron bonds that can possibly take place between atoms of the second and third rows of the Periodic Table. The critical interatomic distance beyond which symmetry breaking begins to take place at the Hartree–Fock and Møller–Plesset levels are determined for each model system. Their magnitude are found to obey regular tendencies which are related to the compactness of the orbitals involved in the three-electron bonds. In all model systems, the onsets of symmetry-breaking at the MP2 level are greater or equal to the equilibrium bonding distance between the XHn fragments. The symmetry-breaking artifact results in severe discontinuities in the dissociation curves at the MP2 level. The CC level pushes away the occurrence of the artifact to larger distances but do not remove the discontinuities. The artifact is practically cured at the B-CC level with perturbative treatment of triple excitations. The onset of symmetry-breaking may in some cases be shortened by substituent effects, to the extent that it becomes shorter than the equilibrium bonding distance like in the Me4O2+ and Me2F2+ cation radicals that are found to be symmetry-unstable even in their equilibrium geometries. The artifact carries over to unsymmetrical systems that display close functional resemblance to symmetrical systems, leading to convergence difficulties, erroneous geometries, and unphysical localization of the electronic charge. An economical alternative to the MP2 method, based on the average quadratic coupled-clusters (AQCC), is proposed for such cases, or in cases some stretched three-electron-bonded systems or full dissociation curves are to be investigated.
Synchronization phenomena in nephron–nephron interaction
Authors: Holstein-Rathlou Niels-Henrik , Yip Kay-Pong , Sosnovtseva Olga V. , Mosekilde Erik
Published: July 2002

Experimental data for tubular pressure oscillations in rat kidneys are analyzed in order to examine the different types of synchronization that can arise between neighboring functional units. For rats with normal blood pressure, the individual unit (the nephron) typically exhibits regular oscillations in its tubular pressure and flow variations. For such rats, both in-phase and antiphase synchronization can be demonstrated in the experimental data. For spontaneously hypertensive rats, where the pressure variations in the individual nephrons are highly irregular, signs of chaotic phase and frequency synchronization can be observed. Accounting for a hemodynamic as well as for a vascular coupling between nephrons that share a common interlobular artery, we develop a mathematical model of the pressure and flow regulation in a pair of adjacent nephrons. We show that this model, for appropriate values of the parameters, can reproduce the different types of experimentally observed synchronization.
Domain rearrangement in ferroelectric Bi4Ti3O12 thin films studied by in situ optical second harmonic generation
Authors: Barad Yaniv , Lettieri James , Theis Chris D. , Schlom Darrell G. , Gopalan Venkatraman
Published: July 2002

Electric-field induced rearrangement of domain microstructure in an epitaxial thin film of Bi4Ti3O12 on a SrTiO3 (001) substrate is studied by optical second harmonic generation measurements. The input polarization dependence of the second harmonic signal exhibits spatial symmetries that reflect the presence of eight different domain variants present in the film. Changes in these symmetries with the application of electric field are experimentally studied at 23° C and 60 °C, and theoretically modeled to extract the hysteresis loops that reflect quantitative changes in the fraction of domain variants. A strong correlation is observed between the dc electrical conductance (as distinct from transient currents) and the ferroelectric domain state of the film, which is proposed to arise from the creation and destruction of charged domain walls within the film with applied field.
Multifractal structure of a riddled basin
Authors: Suetani Hiromichi , Horita Takehiko
Published: July 2002

For a two-dimensional piecewise linear map with a riddled basin, a multifractal spectrum f(γ), which characterizes the “skeletons” of the riddled basin, is introduced. With f(γ), the uncertainty exponent is obtained by a variational principle, which enables us to introduce a concept of a “boundary” for the riddled basin. A conjecture on the relation between f(γ) and the “stable sets” of various ergodic measures, which coexist with the natural invariant measure on the chaotic attractor, is also proposed.
Non-Hermitian perturbative effective operators: Connectivity and derivation of diagrammatic representation
Authors: Duan C. K. , Reid M. F.
Published: July 2002

Effective Hamiltonians and effective operators act on a restricted model space to give the same energies and matrix elements as those of the full Hamiltonian and operators between the corresponding true eigenstates. For the effective Hamiltonian there are two “obvious” choices: the simplest non-Hermitian effective Hamiltonian and the canonical Hermitian effective Hamiltonian. In this paper, we derive a perturbative effective operator which works together with the non-Hermitian effective Hamiltonian, prove that it can be expanded with only connected diagrams, and show how to construct the connected diagrams easily from the diagrams of the effective Hamiltonian by substitution of vertices. This effective operator is much simpler than the Hermitian effective operator and therefore is expected to be more suitable for ab initio calculations.
Polymer–polymer interaction parameters for homopolymers and copolymers from light scattering and phase separation experiments in a common solvent
Authors: Posharnowa Natalia , Schneider Anja , Wünsch Matthias , Kuleznew Valerie , Wolf Bernhard Anton
Published: July 2002

The thermodynamic behavior of the quaternary system DMAc/PS/PAN/SAN and of all its solvent containing subsystems [DMAc: dimethylacetamide, PS: polystyrene, PAN: polyacrylonitrile, SAN: P(S–ran–AN)] was studied in terms of second virial coefficients and phase separation in the range of moderate polymer concentrations. The most remarkable finding consists in fundamental discrepancies between the Flory–Huggins parameters obtained for the interaction between the segments of polymer X and polymer Y either straightforwardly from the light scattering experiments (ranging from −0.88 to −0.14) and that resulting from the modeling of the measured phase diagrams (+0.01 to +0.33) or from solubility parameter theory (+0.03 to +1.92). The reasons for the disagreement even in the sign of the parameters are discussed in terms of A2XY, the second osmotic virial coefficients referring to the opening of intermolecular contacts between X and Y by the insertion of solvent and in terms of W2, the normalized excess Gibbs energy of contact formation between the two types of solute in the concentration region of pair interaction according to X–X+Y–Y→2X–Y. The pair interaction coefficient W2 results negative for PS/SAN, but positive for PAN/SAN and for PAN/PS. A theoretical explanation of this unexpected result is offered.
Nanometer spot allocation for Raman spectroscopy on ferroelectrics by polarization and piezoresponse force microscopy
Authors: Tarrach G. , Lagos L. P. , Hermans Z. R. , Schlaphof F. , Loppacher Ch. , Eng L. M.
Published: July 2002

We report the 100% correlation between polarized light microscopy (PLM), piezoresponse force microscopy (PFM), and micro-Raman spectroscopy when investigating domain-rich ferroelectric systems. In order to allocate the desired spot on a submicrometer scale, both PLM and PFM were combined to elucidate the effective three-dimensional ferroelectric domain distribution. With PFM we observe spike-like a and c domains well inside extended a and c-polarized areas, which were not conclusive with PLM. The knowledge on such a domain distribution is essential when addressing quantitative micro-Raman spectroscopy. In addition, we show the unambiguous differentiation between a and c domains on the submicrometer scale using the B2 mode of lattice vibrations.
Vibrational relaxation of the free terminal hydroxyl stretch in methanol oligomers: Indirect pathway to hydrogen bond breaking
Authors: Levinger Nancy E. , Davis Paul H. , Fayer M. D.
Published: July 2002

Vibrational relaxation of methanol-d (MeOD) in carbon tetrachloride has been investigated via ultrafast infrared pump–probe experiments. Exciting at 2690 cm−1, only the free O-D (where the D is not H-bonded) stretching mode is initially populated. For MeOD mole fractions ⩽0.025, a 2.15 ps single exponential decay is observed. At mole fractions ⩾0.0375, the signal decays (2.15 ps decay time) below zero (increased absorption) and then recovers on time scales of 22 ps and ≫300 ps. The increased absorption indicates the formation of additional free ODs caused by the breaking of H-bonds that are not directly coupled to the initially excited vibration. The two-time scale recovery of this signal arises from geminate and nongeminate recombination. The data are fit with a set of kinetic equations that accurately reproduce the data. The results suggest that vibrational relaxation of the initially excited free OD stretch into intramolecular modes of the methanol leads to H-bond breaking. This contrasts studies that suggest direct relaxation of a vibrationally excited OH stretch into an H-bond stretch is responsible for H-bond breaking.
Photoelectron spectroscopy of hybrid interfaces for light emitting diodes: Influence of the substrate work function
Authors: Greczynski G. , Salaneck W. R.
Published: July 2002

Photoelectron spectroscopy results of studies of a conjugated polymer poly(9, 9-dioctylfluorene) thin films embedded between two contacts with different work functions are reported in this work. It is demonstrated that, depending on the work function of contact material involved, the binding energy of the C(1s) core level of the polymer, changes according to the resulting built-in potential in the polymer layer. The deposition of the same metal onto a polymer surface can lead to binding energy shifts of the core-level spectra in either direction, determined by the work function of the underlying substrate.
An improved model for hydrate formation in sulfuric acid–water nucleation
Authors: Noppel M. , Vehkamäki H. , Kulmala M.
Published: July 2002

The formation of sulfuric acid–water hydrates in the vapor phase and nucleation rates of sulfuric acid–water clusters are investigated. The result of ab initio calculations and experimental data related to hydrates are utilized to improve the description of sulfuric acid–water hydration and nucleation in atmospheric conditions. The nucleation rates are obtained using the most rigorous nucleation kinetics and the thermodynamically consistent version of the classical nucleation model. The improvements increase the predicted nucleation rates compared to previous models. The predicted nucleation rates are compared with experimental ones, and they are in most cases within experimental errors. Some experimental evidence suggests that the present model gives a more realistic dependence of nucleation rate on relative humidity and sulfuric acid concentration than the earlier versions of the theory.
Magnetic relaxation of iron nanoparticles
Authors: Chamberlin Ralph V. , Humfeld Keith D. , Farrell Dorothy , Yamamuro Saeki , Ijiri Yumi , Majetich Sara A.
Published: July 2002

The magnetic relaxation of highly diluted monodisperse iron-based particles was measured between 10−5 and 104 s, for different temperatures and particle sizes. The decay over a very broad range of times indicated a distribution of energy barriers remained despite the narrow range of sizes. Many features of this decay could be explained using a percolation model of particles with weak dipolar interactions. However, this model did not predict the abrupt change in the decay rate at long times, which was observed for samples of both 8.0 and 5.5 nm particles below a threshold temperature.
Path integrals for boundaries and topological constraints: A white noise functional approach
Authors: Bernido Christopher C. , Carpio-Bernido M. Victoria
Published: July 2002

Using the Streit–Hida formulation where the Feynman path integral is realized in the framework of white noise analysis, we evaluate the quantum propagator for systems with boundaries and topological constraints. In particular, the Feynman integrand is given as generalized white noise functionals for systems with flat wall boundaries and periodic constraints. Under a suitable Gauss–Fourier transform of these functionals the quantum propagator is obtained for: (a) the infinite wall potential; (b) a particle in a box; (c) a particle constrained to move in a circle; and (d) the Aharonov–Bohm system. The energy spectrum and eigenfunctions are obtained in all four cases.
Thickness dependent wall mobility in thin Permalloy films
Authors: Redjdal M. , Giusti J. , Ruane M. F. , Humphrey F. B.
Published: July 2002

Domain wall mobility in Permalloy films has been calculated as a function of thickness at 10, 80, and 160 nm which reflects the structure change of Néel, symmetric Bloch and C-shaped (asymmetric Bloch) domain walls. The mobility has been derived from the dynamics of a single nonperiodic domain wall using direct integration of the Landau–Lifshitz–Gilbert equation in a Cartesian lattice. This investigation allows for a detailed examination of spin precession, wall motion and overall magnetization distortion as the wall is moved in the presence of fields ranging from 0.5 to 5 Oe applied in the easy axis direction. At 10-nm-thick films, the mobility of a Néel wall is 30 m/s Oe. Wall motion takes place without noticeable distortion in the magnetization distribution in the vicinity of the Néel wall. For 80 nm-thick films, the mobility of a symmetric Bloch wall is 5 m/s Oe, or 20% less than the theoretical prediction for the mobility of a 180° domain wall model. At dynamic equilibrium, the symmetric Bloch wall has been slightly distorted into a C-shaped wall. For 160 nm-thick films, the mobility of a C-shaped wall is 12 m/s Oe, or 29% less than the theoretical predicted value. Shearing-type magnetization distortion is observed in this composite structure of a Bloch component at the center and Néel caps of opposite chirality at the surfaces.
Inverted stick–slip friction: What is the mechanism?
Authors: Filippov A. E. , Klafter J. , Urbakh M.
Published: July 2002

A mechanism is proposed for an observed inverted stick–slip motion and a relationship between the macroscopic mechanical response and the dynamics of the embedded system in this regime is established. It is shown that the requirement for the occurrence of inverted stick–slip is the existence of two sliding regimes in the system. The inverted stick–slip stems from a bifurcation from one sliding regime to another. The mechanism suggests that the inverted stick–slip behavior reflects a transition of the embedded system from nonslip to slip boundary conditions.
A kinetic model for the one-dimensional electromagnetic solitons in an isothermal plasma
Authors: Lontano Maurizio , Bulanov Sergei V. , Koga James , Passoni Matteo , Tajima Toshiki
Published: July 2002

Two nonlinear second order differential equations for the amplitude of the vector potential and for the electrostatic potential are derived, starting from the full Maxwell equations where the field sources are calculated by integrating in the momentum space the particle distribution function, which is an exact solution of the relativistic Vlasov equation. The resulting equations are exact in describing a hot one-dimensional plasma sustaining a relativistically intense, circularly polarized electromagnetic radiation. The case of standing soliton-like structures in an electron–positron plasma is then investigated. It is demonstrated that at ultrarelativistic temperatures extremely large amplitude solitons can be formed in a strongly overdense plasma.
Optimization of resonant two-photon absorption with adaptive quantum control
Authors: Ando Taro , Urakami Tsuneyuki , Itoh Haruyasu , Tsuchiya Yutaka
Published: July 2002

Adaptive quantum control is applied to the resonant two-photon absorption of Rb atoms, which includes an intermediate state between the initial and final states. The phase distribution of incident laser pulses in the frequency domain is decided adaptively free from a priori knowledge on the phase distribution with the help of a simulated annealing algorithm to achieve the maximum luminescence intensity from the state associated with the excited state. The optimized phase pattern acquired in our system matches a theoretical prediction based on the perturbative treatment of the semiclassical model on the absorption of light.
An approach to renormalization on the n-torus
Authors: Rockmore Daniel , Siegel Ralph , Tongring Nils , Tresser Charles
Published: July 2002

The coding theory of rotations (by inspecting closely their relation to flows) and the continued fractions algorithm (by considering even two-coloring of the integers with a given proportion of, say, blue and red) are revisited. Then, even n-coloring of the integers is defined. This allows one to code rotations on the (n−1)-torus by considering linear flows on the n-torus and yields a simple geometric approach to renormalization on tori by first return maps on the coding regions.
Chaotic jets with multifractal space-time random walk
Authors: Afanasiev Valerii V. , Sagdeev Roald Z. , Zaslavsky George M.
Published: July 2002

The problem of normal and anomalous diffusion is examined for the four-dimensional (4-D) map that arises from the problem of particle motion in a constant magnetic field and electrostatic wave packet. This 4-D map consists of two coupled 2-D maps: a standard map and a web map. The case of a weak chaos is considered. It is shown that due to the finite observation time, the particle diffusion possesses strong nonhomogeneous properties. Existence of long-living bundles of orbits with coherent propagation property is checked. These bundles are named ‘‘chaotic jets.’’ The same name is used for a part of the trajectory if this part corresponds to long-living trapping or flight. The existence of chaotic jets depends on the topological properties of the phase space and influences the asymptotic law of transport. The particle transport can be considered as a random walk in the multifractal space-time that is produced by flights and trappings of a test particle in some area of its phase space. Lévy random walk theory and its generalization for the multifractal space-time situation is considered and asymptotic laws for displacements are derived. Different intermediate asymptotics are discussed.
Cheyne–Stokes respiration: Stability of interacting systems in heart failure
Authors: Kryger M. H. , Millar T.
Published: July 2002

Cheyne–Stokes respiration, a breathing pattern found in patients with heart failure, is characterized by periodic changes in ventilation. This pattern of breathing is also associated with oscillations in the arousal state, blood oxygen level, carbon dioxide blood level, and the blood pressure. Although originally described as an irregular breathing pattern or an unstable breathing pattern, Cheyne–Stokes respiration may be quite stable for prolonged periods of time. This breathing pattern may represent a clinical disorder in which disease results in a low-frequency oscillation of the system. Treatment that either reduces or abolishes the oscillation results in clinical improvement because of reduced oscillation of the systems whose function is linked to the changes in ventilation.
Dynamics of topological solitons in models with nonlocal interactions
Authors: Alfimov G. L. , Eleonskiĭ V. M. , Kulagin N. E. , Mitskevich N. V.
Published: July 2002

A nondissipative generalization of the sine-Gordon equation to cases with nonlocal interactions is analyzed. A model of this sort is shown to describe signal propagation in a Josephson transmission line with a nonlocal inductive coupling. The incorporation of nonlocal interactions changes the properties of the model in a qualitative way, leading in particular to the appearance of some new soliton entities: 2kπ kinks, where k≳1. These entities do not arise in a local model. They are evolutionary, they interact with each other in a quasielastic fashion, and they can be generated in a corresponding transmission line.
Chaos in the one-dimensional gravitational three-body problem
Authors: Hietarinta Jarmo , Mikkola Seppo
Published: July 2002

We have investigated the appearance of chaos in the one-dimensional Newtonian gravitational three-body system (three masses on a line with −1/r pairwise potential). In the center of mass coordinates this system has two degrees of freedom and can be conveniently studied using Poincaré sections. We have concentrated in particular on how the behavior changes when the relative masses of the three bodies change. We consider only the physically more interesting case of negative total energy. For two mass choices we have calculated 18 000 full orbits (with initial states on a 100×180 lattice on the Poincaré section) and obtained dwell time distributions. For 105 mass choices we have calculated Poincaré maps for 10×18 starting points. Our results show that the Poincaré section (and hence the phase space) divides into three well defined regions with orbits of different characteristics: (1) There is a region of fast scattering, with a minimum of pairwise collisions. This region consists of ‘scallops’ bordering the E=0 line, within a scallop the orbits vary smoothly. The number of the scallops increases as the mass of the central particle decreases. (2) In the chaotic scattering region the interaction times are longer, and both the interaction time and the final state depend sensitively on the starting point on the Poincaré section. For both (1) and (2) the initial and final states consist of a binary + single particle. (3) The third region consists of quasiperiodic orbits where the three masses are bound together forever. At the center of the quasiperiodic region there is a periodic orbit discovered (numerically) by Schubart in 1956. The stability of the Schubart orbit turns out to correlate strongly with the global behavior.
One-dimensional mappings of the eigenelements of the Schrödinger problem
Authors: Eleonskii V. M. , Korolev V. G. , Kulagin N. E.
Published: July 2002

An approach is proposed for analyzing the inverse spectral problems for the Schrödinger equation based on writing the equation for the analog of the number-of-quanta operator for a harmonic oscillator. This equation makes it possible to determine not only the one-dimensional mapping of the energy eigenvalues but also the linear equation for the point spectrum shift operator of the Schrödinger problem. The solvability conditions of the latter lead to a nonlinear equation that determines the class of allowable potentials. Two classes of potentials regular in R1 and symmetrical are isolated on the basis of the proposed approach. The first of these leads to equidistant spectra with a gap of arbitrary size and location. The spectrum of the second potential class is a combination of three rigorously equidistant spectra with ground states that are shifted by an arbitrary amount. Generalizations to the case of essentially nonequidistant spectra are shown to be possible.
Ω-dimension of chaotic time series
Authors: Gaponov-Grekhov A. V. , Rabinovich M. I. , Starobinets I. M. , Tsimring M. Sh. , Chugurin V. V.
Published: July 2002

New characteristics, Ω-dimension (D(Ω)) and spectral density of dimension (D′(Ω)), of deterministically generated irregular signals are proposed. They are the functions that are calculated employing spectral transformation such as filtering with limit transmission frequency Ω. The Ω-dimension of the time series generated by a dynamical system with a homogeneous strange attractor does not depend on Ω and coincides with the dimension measured using a standard technique. If the time series does not possess the similarity property as the time scale changes (i.e., it is multiscaled in time), the calculation of D(Ω) gives additional information on the properties of the signal. In particular, it allows for the estimation of additional degrees of freedom in the time series on signal transmission through the communication channel and preliminary processing.
Dynamical systems theory for music dynamics
Authors: Boon Jean Pierre , Decroly Olivier
Published: July 2002

We show that, when music pieces are cast in the form of time series of pitch variations, the concepts and tools of dynamical systems theory can be applied to the analysis of temporal dynamics in music. (i) Phase space portraits are constructed from the time series wherefrom the dimensionality is evaluated as a measure of the global dynamics of each piece. (ii) Spectral analysis of the time series yields power spectra (∼f−ν) close to red noise (ν∼2) in the low frequency range. (iii) We define an information entropy which provides a measure of the local dynamics in the musical piece; the entropy can be interpreted as an evaluation of the degree of complexity in the music, but there is no evidence of an analytical relation between local and global dynamics. These findings are based on computations performed on eighty sequences sampled in the music literature from the 18th to the 20th century.
Nonannihilation dynamics in an exothermic reaction-diffusion system with mono-stable excitability
Authors: Mimura Masayasu , Nagayama Masaharu
Published: July 2002

We consider a 2-component excitable and diffusive system which describes a simple exothermic reaction process. In some parameter regime, there are two characteristics of travelling pulses of the system: (i) travelling pulses are planarly unstable; (ii) when two travelling pulses approach closely, they do not annihilate each other and repel like elastic objects. Under this situation, it is shown that ring patterns break down into complex patterns in 2-dimensions, which are totally different from those arising in the well-known excitable and diffusive system with the FitzHugh–Nagumo nonlinearity.
The OPCL control method for entrainment, model-resonance, and migration actions on multiple-attractor systems
Authors: Jackson E. Atlee
Published: July 2002

A survey is given of three different control objectives that can be achieved with the use of the Open-Plus-Closed-Loop (OPCL) control method, developed by Jackson and Grosu. For a system that can be characterized by N first-order ordinary differential equations, these objectives are: (1) the asymptotic entrainment of the system’s dynamics to a prescribed “goal” dynamics, g(t); (2) an experimental-search method to determine an approximate dynamic model; (3) the transferal of the system from one attractor to any “target” attractor. For one class of systems, this may be accomplished without a model, by using only a short-duration record of the natural dynamics in the target attractor, as demonstrated experimentally using the Chua system.
The effect of gap junctional distribution on defibrillation
Authors: Keener James P.
Published: July 2002

We summarize a mathematical theory for direct activation and defibrillation of cardiac tissue. We show that the direct stimulus and defibrillation thresholds are likely to be strongly affected by the gap junctional distribution and density, suggesting an indirect experimental test of the theory.
Compactivity and transmission of stress in granular materials
Authors: Edwards S. F. , Grinev D. V.
Published: July 2002

We outline a statistical-mechanical theory of granular materials. Stress propagation and force fluctuations in static granular media are still poorly understood. We develop the statistical-mechanical theory that delivers the fundamental equations of stress equilibrium. The formalism is based on the assumptions that grains are rigid, cohesionless, and that friction is perfect. Since grains are assumed perfectly rigid, no strain or displacement field can enter the equations for static equilibrium of the stress field. The complete system of equations for the stress tensor is derived from the equations of intergranular force and torque balance, given the geometric specification of the material. These new constitutive equations are indeed fundamental and are based on relations between various components of the stress tensor within the material, and depend on the topology of the granular packing. The problem of incorporating into the formalism the “no tensile forces” constraint is considered. The compactivity concept is reviewed. We discuss the relation between the concept of compactivity and the problem of stress transmission.
Algorithms for normalizing by least squares
Authors: Thompson William J.
Published: July 2002

Algorithms for the overall-best-fit normalization of fitted values to data values, or of data values to fitted values, are described. Various weighting schemes for the data, including the case of Poisson statistics, are described. Concise expressions for the minimum objective function obtained after normalization are derived.
Generalizations of ‘‘universal dielectric response’’ and a general distribution-of-activation-energies model for dielectric and conducting systems
Authors: Macdonald J. Ross
Published: July 2002

Three empirical equations introduced by Jonscher to represent the imaginary part of the small-signal frequency response of dielectric materials and termed ‘‘universal dielectric response’’ by him are generalized in three ways. The equations may be applied in normalized form at the impedance level as well as at the usual complex dielectric constant level, defining the response of conducting rather than dielectric materials. They are generalized to include real as well as imaginary parts where possible. A unified dielectric or conductive distribution-of-activation-energies (DAE) physical model is proposed whose predictions agree remarkably well with those of all the Jonscher universal dielectric response equations as well as with many other common dielectric response equations. The new model, unlike previous small-signal response models, leads to quantitative predictions for the temperature dependence of the power-law frequency exponent appearing in the ubiquitous constant-phase-response frequency region of the total response.
Ionization-drift turbulence in rf magnetron plasmas
Authors: I Lin , Wu Ming-Shing
Published: July 2002

Electron density fluctuations in a rf hollow magnetron system are investigated. The weakly ionized and axially magnetized (B∼80 G) discharge supports nonlinear ionization-drift waves in the presence of the nonuniform rf-induced dc electric field and density gradient along the normal of the hollow electrode surface. The fluctuations have good coherence along B and are turbulent in the transverse plane. The turbulence is inhomogeneous along the density gradient. The power spectrum shows two major bands. The amplitude of the high-frequency oscillation is modulated by the low-frequency oscillation. In the transverse plane, the phase velocity is about the same as the diamagnetic drift velocity. It has one component along the diamagnetic drift direction and the other toward the electrode surface. The turbulence also induces anomalous cross-field electron current which deteriorates the electron confinement in the low-pressure regime. Generally, the system combines the nature of the reaction diffusion and the drift systems. The ionization process, the nonlinear transverse drifts under the nonlinear background, and the nonlinear wave-wave interactions drive the system to turbulence. The parametric dependence of the turbulence is studied and discussed in the paper.
Bending piezoelectricity in monomorph polymer films
Authors: Fukada E. , Sessler G. M. , West J. E. , Berraissoul A. , Günther P.
Published: July 2002

Studies with laser-induced pressure pulses show the existence of a piezoelectric monomorph polarization in 22–25-μm-thick PVDF films after irradiation with a 30-kV electron beam. The bending piezoelectric stress constant β31 and the tensile piezoelectric strain constant d31 were determined for such monomorph samples. Both β31 and d31 increase with increasing irradiation time and a linear relation between them is found. The highest values of β31 and d31 achieved are 90 nC/m and 3 pC/N, respectively. A theory is presented for a film with a step-shaped distribution of polarization along the thickness. A bending piezoelectric strain constant f31 is defined which relates the electric displacement to the stress gradient along the thickness. It is concluded that β31 is determined by the distribution of d31 and f31.
Photolytic decomposition of gold metallopolymer thin films by UV laser direct writing
Authors: Houlding V. H. , Clements N. S. , Beeson K. W.
Published: July 2002

Spin-on films of polymeric Au mercaptoterpene can be photochemically decomposed at 257 nm by frequency-doubled Ar+ laser direct writing techniques at very fast writing speeds. Correlation of the linewidth of the written features with the laser beam power demonstrates that the laser writing process is purely photochemical, and that reciprocity is maintained over the entire range of accessible power density of up to 250 W/cm2. An exposure threshold is observed for the formation of adherent patterns which varies in a roughly logarithmic way with film thickness. After exposure, direct written features are developed by washing away unirradiated film with hexane and baking 15 min at 250 °C to remove all carbonaceous material, leaving behind essentially pure gold lines of high crystallinity and granular structure. Due to inherent limitations of the particular Au resinate used, final Au features have a maximum thickness of 500 Å. Resistivity is substantially higher than smooth Au films of comparable thickness.
The instability of rapidly stretching plastic jets
Authors: Romero L. A.
Published: July 2002

A stability analysis of a rapidly stretching jet satisfying the equations of motion for a perfectly plastic material is presented. It is found that the stability of the jet depends on a dimensionless parameter Γ that measures the importance of the inertial forces relative to the plastic forces. This parameter is a decreasing function of time. It will be shown that jets with Γ initially very large will be stable until Γ decreases to order unity. These jets will then go unstable and break up into drops whose axial dimension is comparable to their radius. Jets with Γ initially small will always be unstable. It will be shown that these jets tend to break up into drops whose axial dimension is Γ−1/5 times their radius.
Permanent magnetic materials based on Nd2Fe14C prepared by melt spinning
Authors: Coehoorn R. , Duchateau J. P. W. B. , Denissen C. J. M.
Published: July 2002

Permanent magnetic materials containing the intermetallic compound Nd2Fe14C were obtained by annealing melt-spun flakes. As quenched flakes with compositions close to the stoichiometric composition consist of α-Fe, Nd2Fe17 with some dissolved carbon, and an amorphous phase. At approximately 700 °C Nd2Fe14C is formed in a solid-state reaction. The amount of Nd2Fe14C formed, the presence of secondary phases, and the magnetic properties depend strongly on the composition. Samples with the composition Nd13.5Fe79.6C6.9 contain only a small fraction of secondary phases. The remanence and intrinsic coercive field are 0.72 T and 800 kA/m, respectively. The kinetics of the phase transformation, as well as the thermodynamics of the phase equilibria in the relevant part of the Nd-Fe-C system are discussed.
Magnetization and anisotropy of Co/Pd multilayer thin films
Authors: Stinson Douglas G. , Shin S.-C.
Published: July 2002

Multilayered Co/Pd thin films were prepared by sequential electron-beam evaporation of Co and Pd onto Si substrates at room temperature. The thicknesses of the Co sublayer and of the Pd sublayer were varied between 2.0–10.3 and 4.5–22.3 Å, respectively. As the Pd sublayer thickness was varied at constant Co thickness, broad maxima in the saturation magnetization Ms and intrinsic perpendicular anisotropy energy Ku were observed at a Pd thickness of about 10 Å. At this maximum, Ms per Co volume is larger than the saturation magnetization of bulk Co. This is believed to be caused by the polarization of the Pd atoms within about 10 Å of the Co layer. Ku and Ms per Co volume both decrease with increasing Co layer thickness.
Dielectric constants of yttrium and rare-earth garnets, the polarizability of gallium oxide, and the oxide additivity rule
Authors: Shannon R. D. , Subramanian M. A. , Allik T. H. , Kimura H. , Kokta M. R. , Randles M. H. , Rossman G. R.
Published: July 2002

The dielectric constants (κ′) and dielectric loss values of 10 rare-earth gallium garnets and 1 rare-earth aluminum garnet were measured at 1 MHz using a two-terminal method with empirically determined edge corrections. The results are: κ′(Dy3Al5O12)=11.07±0.05; κ′(Ho3Ga5O12) =12.38±0.05; κ′(Dy3Ga5O12)=12.36±0.06; κ′(Tb3Ga5O12) =12.40 ±0.03; κ′(Gd3Ga5O12) =12.18±0.10; κ′(Eu3Ga5O12) =12.46±0.05; κ′(Sm3Ga5O12) =12.55±0.03; κ′(Nd3Ga5O12) =12.59±0.12; κ′(Y3Sc2Ga3O12) =12.94±0.03; κ′(Sm3Sc2Ga3O12) =13.67±0.04; and κ′(La2.66Lu2.66Ga2.66O12) =14.40±0.03. The dielectric polarizability of Ga2O3 derived from the dielectric constants of these and other Ga compounds is 8.80±0.14 Å3. The agreement between measured dielectric polarizabilities as determined from the Clausius–Mosotti equation and those calculated from the sum of oxide polarizabilities according to αD(mineral) =ΣαD (oxides) for six aluminum garnets and twelve gallium garnets is ∼1%.
Random mixtures with orientational order, and the anisotropic resistivity tensor of high-T
c superconductors
Authors: Díaz-Guilera A. , Tremblay A.-M. S.
Published: July 2002

By generalizing effective-medium theory to the case of orientationally ordered but positionally disordered two-component mixtures, it is shown that the anisotropic dielectric tensor of oxide superconductors can be extracted from microwave measurements on oriented crystallites of YBa2Cu3O7−x embedded in epoxy. Surprisingly, this technique appears to be the only one which can access the resistivity perpendicular to the copper-oxide planes in crystallites that are too small for depositing electrodes. This possibility arises in part because the real part of the dielectric constant of oxide superconductors has a large magnitude. The validity of the effective-medium approach for orientationally ordered mixtures is corroborated by simulations on two-dimensional anisotropic random resistor networks. Analysis of the experimental data suggests that the zero-temperature limit of the finite-frequency resistivity does not vanish along the c axis, a result which would imply the existence of states at the Fermi surface, even in the superconducting state.
On the influence of wall microdeformations on Bloch line visibility in bubble garnets (invited)
Authors: Thiaville A. , Ben Youssef J. , Nakatani Y. , Miltat J.
Published: July 2002

It is proposed that the main source of contrast of vertical Bloch lines (VBLs) in bubble garnets, when viewed by means of anisotropic dark field optical imaging, is a microdeformation of the wall plane at line location. The motive force for wall tilting is the compensation of the monopolar σ charges borne by VBLs. The tilted wall section acts as a phase object and allows for the formation of line images with well-defined symmetries and independent of the incident-beam polarization. All these features agree fully with experimental evidence. An approximate model of the wall deformation is presented and shown to be consistent for a given thickness and material parameters with the results of an ab initio numerical computation of the 3D structure of a VBL. The implications of the microdeformation model in terms of line observability are analyzed and compared with experimental data.
Optical properties of high-quality InGaAs/InAlAs multiple quantum wells
Authors: Gupta S. , Bhattacharya P. K. , Pamulapati J. , Mourou G.
Published: July 2002

We have measured the narrowest half-width at half-maximum photoluminescence linewidth of 2.8 meV, in 40-period lattice-matched In0.53Ga0.47As/In0.52Al0.48As multiple quantum wells, grown by molecular-beam epitaxy with growth interruption. A simple analysis of the linewidth suggests that the structure has near perfect interfaces. Temperature-dependent photoluminescence linewidth data indicate impurity incorporation due to the growth interruption. However, the high quality of the multiple quantum well is not impaired as is seen in the room-temperature absorption data, where excitonic features up to n=3 sublevel are clearly seen. Carrier lifetime in this multiple-quantum-well system has been measured, we believe for the first time, using the picosecond photoluminescence correlation technique. A lifetime of 860 ps is obtained, which is similar to the value obtained for high-quality GaAs/AlGaAs and In0.53Ga0.47As/InP quantum wells. This further confirms the high quality obtained in this ternary material system using growth interruption.
Growth of CdTe(111)B homoepitaxial layers by hot-wall epitaxy
Authors: Tatsuoka H. , Kuwabara H. , Nakanishi Y. , Fujiyasu H.
Published: July 2002

CdTe layers were grown on oriented CdTe(111)B substrates by hot-wall epitaxy. The crystallinity of the layers was examined by etch-pit observation, x-ray rocking curves, and photoluminescence spectra. High-quality CdTe(111)B homoepitaxial layers without twinned domains are obtained. It is found that the CdTe(111)B homoepitaxial layers are strained. The crystallinity and amount of strain of the layers depend on the preheating temperature of substrates before the growth. For comparison, CdTe(100) homoepitaxial layers were grown and characterized.
Threshold behavior and electro-optical properties of twisted nematic layers with weak anchoring in the tilt and twist angle
Authors: Hirning R. , Funk W. , Trebin H.-R. , Schmidt M. , Schmiedel H.
Published: July 2002

Analytical and numerical calculations of threshold behavior and electro-optical characteristics in twisted chiral nematic layers are presented, when weak anchoring in the tilt and twist angle of the director is assumed. An analytical expression for the effective twist angle and the Fréedericksz threshold voltage is derived. In cells with bistabilities, we investigate the influence of the anchoring parameters and device parameters on the width of the hysteresis. Using the 4×4-matrix formalism of Berreman [J. Opt. Soc. Am. 62, 502 (1972)], we demonstrate the influence of the weak anchoring on the transmission-versus-voltage characteristic.
Investigation of near interface properties in semi-insulating InP substrates with epitaxial grown InGaAs and InAlAs by photoreflectance
Authors: Zhou Weimin , Dutta M. , Shen H. , Pamulapati J. , Bennett Brian R. , Perry Clive H. , Weyburne David W.
Published: July 2002

An extensive photoreflectance (PR) study has been done on a series of undoped and n-type, InGaAs and InAlAs molecular beam epitaxy (MBE) grown layers with different In mole fractions, and epilayer thicknesses on Fe-doped semi-insulating (SI)-InP substrates. Three substrate features were observed in the spectra. From investigations of the temperature dependence, time constant dependence, and an additional cw light beam intensity dependence, they were identified as an excitonic transition from the substrate, a free electron transition near the interface which gives a Franz–Keldysh oscillation, and a transition from the spin–orbit split-off valence band. The Franz–Keldysh effect indicates that a temperature dependent built-in electric field is formed near the interface. The dependence of the field on doping concentration, strain, or epilayer composition (band gap) was insignificant. The PR signal from a SI-InP wafer after a pre-MBE-growth heating was found to be strongly enhanced over that from an untreated wafer. This signal was even more enhanced after an epilayer was grown on top, indicating the formation of a built-in field. These results are indicative of a redistribution of charge near the interface/surface in the process of MBE growth; the associated PR signal (phase) could be used for in situ monitoring of epilayer growth on SI-InP wafers.
Single-crystal Si/NiSi2/Si(100) structures
Authors: Tung R. T. , Eaglesham D. J. , Schrey F. , Sullivan J. P.
Published: July 2002

High-quality, uniform, Si/NiSi2/Si(100) structures were demonstrated by a combination of molecular-beam epitaxy and postgrowth, high-temperature annealing. A Si template technique ensures the epitaxial orientation of the Si overlayer. The unusual inverse Volmer–Weber mode observed during the growth of Si on NiSi2(100) is shown to be a result of interface and surface energetics. The evolution of the interface morphology of the double-heteroepitaxial structures is discussed in terms of thermodynamics.
Hindered transformation of Pd2Ge to PdGe in the Pd/a-Ge:H system
Authors: Edelman F. , Cytermann C. , Brener R. , Eizenberg M. , Weil R. , Beyer W.
Published: July 2002

A comparative study of the interfacial reactions between Pd and a-Ge:H, deposited at TS=150 °C (low temperature, LT) and at TS=200, 300 °C (high temperature, HT), was carried out by x-ray diffraction and Auger electron spectroscopy after sample annealing in the regime of T=200–300 °C and t=1/4–4 h. It was found that the Pd/a-Ge:H(LT) formed a much more stable Pd2Ge interfacial layer, compared to the Pd/a-Ge:H(HT) system in which the Pd2Ge was transformed to PdGe. The main difference between the LT- and the HT-a-Ge:H films is probably the structure of the material. Whereas the HT films are compact, the LT-a-Ge films contain a network of voids which slow down the diffusion of Ge to the interface.
Temporal evolution of the electron energy distribution function in oxygen and chlorine gases under dc and ac fields
Authors: Jiang Ping , Economou Demetre J.
Published: July 2002

An analysis of the temporal evolution of the electron energy distribution function (EEDF) and the electron swarm parameters in oxygen and chlorine gases is presented. The spatially homogeneous time-dependent Boltzmann equation is solved for dc and radio-frequency ac electric fields by a finite-element method. A comparison is made of the swarm parameters obtained for the following three cases: (a) under the actual ac field; (b) assuming that the EEDF follows faithfully the applied ac field [quasi-steady-state (QSS) approximation]; and (c) using an ‘‘effective’’ dc field (effective dc approximation). It is shown that the effective dc approximation is not applicable to either oxygen or chlorine for frequencies <10 MHz; however, the QSS approximation is justified for chlorine discharges at <13.56 MHz. This has important implications for reducing the computation time in modeling the bulk plasma of glow discharge reactors. It is also shown that atomic chlorine resulting from molecular dissociation has a significant effect on the swarm parameters, especially for large degrees of gas dissociation.