bluuebunny/crossref_metadata_2025 huggingface dataset:
Self-organized pore formation and open-loop control in semiconductor etching
Authors: Claussen Jens Christian , Carstensen Jürgen , Christophersen Marc , Langa Sergiu , Föll Helmut
Published: February 2003

Electrochemical etching of semiconductors, apart from many technical applications, provides an interesting experimental setup for self-organized structure formation capable, e.g., of regular, diameter-modulated, and branching pores. The underlying dynamical processes governing current transfer and structure formation are described by the current burst model: all dissolution processes are assumed to occur inhomogeneously in time and space as a current burst (CB); the properties and interactions between CBs are described by a number of material- and chemistry-dependent ingredients, like passivation and aging of surfaces in different crystallographic orientations, giving a qualitative understanding of resulting pore morphologies. These morphologies cannot be influenced only by the current, by chemical, material and other etching conditions, but also by an open-loop control, triggering the time scale given by the oxide dissolution time. With this method, under conditions where only branching pores occur, the additional signal hinders side pore formation resulting in regular pores with modulated diameter.
Stochastic phase synchronization in the crayfish mechanoreceptor/photoreceptor system
Authors: Bahar S. , Moss F.
Published: February 2003

The two light-sensitive neurons in the crayfish’s abdominal sixth ganglion (“caudal photoreceptors,” or CPRs), are both primary light sensors and secondary neurons in a mechanosensory pathway. Pei et al. (1996) demonstrated that light enhances the transduction of weak, periodic hydrodynamic stimuli (measured as an increase in the signal-to-noise ratio at the stimulus frequency in the power spectrum of the recorded neural spikes). This has been interpreted as a stochastic resonance effect, in which added light increases the noise intensity of the input to the photoreceptor (possibly through fluctuations in membrane potential), leading to an enhancement of the signal-to-noise ratio (SNR). Here, we discuss the recent demonstration (Bahar et al., 2002) of the correlation between a stochastic-resonance-like effect and an increase in stochastic phase synchronization between the neural response and a periodic mechanical stimulus. We also discuss a novel effect (Bahar et al., 2002) in which light increases the SNR of the second higher harmonic of a periodic input signal, effectively rectifying the input signal. This “second harmonic effect” can also be interpreted in terms of stochastic phase synchronization (Bahar et al., 2002). We review other recent results on the role of stochastic phase synchronization in mediating sensory responses in the crayfish nervous system.
Experimental investigation of partial synchronization in coupled chaotic oscillators
Authors: Heisler Ismael A. , Braun Thomas , Zhang Ying , Hu Gang , Cerdeira Hilda A.
Published: February 2003

The dynamical behavior of a ring of six diffusively coupled Rössler circuits, with different coupling schemes, is experimentally and numerically investigated using the coupling strength as a control parameter. The ring shows partial synchronization and all the five patterns predicted analyzing the symmetries of the ring are obtained experimentally. To compare with the experiment, the ring has been integrated numerically and the results are in good qualitative agreement with the experimental ones. The results are analyzed through the graphs generated plotting the y variable of the ith circuit versus the variable y of the jth circuit. As an auxiliary tool to identify numerically the behavior of the oscillators, the three largest Lyapunov exponents of the ring are obtained.
Stochastic phase resetting of stimulus-locked responses of two coupled oscillators: Transient response clustering, synchronization, and desynchronization
Authors: Tass Peter A.
Published: February 2003

Transient phase dynamics, synchronization, and desynchronization which are stimulus-locked (i.e., tightly time-locked to a repetitively administered stimulus) are studied in two coupled phase oscillators in the presence of noise. The presented method makes it possible to detect such processes in numerical and experimental signals. The time resolution is enormous, since it is only restricted by the sampling rate. Stochastic stimulus locking of the phases or the n:m phase difference at a particular time t relative to stimulus onset is defined by the presence of one or more prominent peaks in the cross-trial distribution of the phases or the n:m phase difference at time t relative to stimulus onset in an ensemble of poststimulus responses. The oscillators’ coupling may cause a transient cross-trial response clustering of the poststimulus responses. In particular, the mechanism by which intrinsic noise induces symmetric antiphase cross-trial response clustering in coupled detuned oscillators is a stochastic resonance. Unlike the presented approach, both cross-trial averaging (where an ensemble of poststimulus responses is simply averaged) and cross-trial cross correlation (CTCC) lead to severe misinterpretations: Triggered averaging cannot distinguish a cross-trial response clustering or decorrelation from a mean amplitude decrease of the single responses. CTCC not only depends on the oscillators’ phase difference but also on their phases and, thus, inevitably displays “artificial” oscillations that are not related to synchronization or desynchronization.
Spin networks for noncompact groups
Authors: Freidel Laurent , Livine Etera R.
Published: February 2003

Spin networks are a natural generalization of Wilson loop functionals. They have been extensively studied in the case where the gauge group is compact and it has been shown that they naturally form a basis of gauge invariant observables. Physically the restriction to compact gauge groups is enough for the study of Yang–Mills theories, however it is well known that noncompact groups naturally arise as internal gauge groups for Lorentzian gravity models. In this context, a proper construction of gauge invariant observables is needed. The purpose of the present work is to define the notion of spin network states for noncompact groups. We first build, by a careful gauge fixing procedure, a natural measure and a Hilbert space structure on the space of gauge invariant graph connections. Spin networks are then defined as generalized eigenvectors of a complete set of hermitic commuting operators. We show how the delicate issue of taking the quotient of a space by noncompact groups can be address in term of algebraic geometry. We finally construct the full Hilbert space containing all spin network states. Having in mind applications to gravity, we illustrate our results for the groups SL(2,R) and SL(2,C).
Unbraiding the braided tensor product
Authors: Fiore Gaetano , Steinacker Harold , Wess Julius
Published: February 2003

We show that the braided tensor product algebra A1⊗_A2 of two module algebras A1,A2 of a quasitriangular Hopf algebra H is isomorphic to the ordinary tensor product A1⊗A2, provided there exists a realization of H within A1. In other words, under this assumption we construct a transformation of generators which decouples A1,A2 (i.e., makes them commuting). We apply the theorem to the braided tensor product algebras of two or more quantum group covariant quantum spaces, deformed Heisenberg algebras and q-deformed fuzzy spheres.
Experimental study of imperfect phase synchronization in the forced Lorenz system
Authors: Pujol-Peré Antonio , Calvo Oscar , Matı́as Manuel A. , Kurths Jürgen
Published: February 2003

In this work we demonstrate for an experimental system, that exhibits the Lorenz butterfly attractor behavior, that perfect chaotic phase synchronization cannot be achieved in systems with an unbounded distribution of intrinsic time scales. Instead, imperfect phase synchronization is characterized by the occurrence of phase slips, associated to epochs of time during which the chaotic oscillator exhibits a slower time scale. Interestingly, during phase slips the chaotic oscillator keeps in sync with the drive, but with a different locking ratio.
Opening a closed Hamiltonian map
Authors: Sanjuán Miguel A. F. , Horita Takehiko , Aihara Kazuyuki
Published: February 2003

A closed Hamiltonian map is opened by introducing an interaction with the outside of the system. The resulting open Hamiltonian system possesses an exit with escaping orbits through it. For such a system equipped with two or three exits, the exit basin structure of the escaping orbits is observed to have a fractal boundary and a boundary shared by the three basins, i.e., a Wada basin boundary. In the small size limit of the exits, a complete fractalization of the phase space, where the predictability of the future state is almost lost, is also observed.
Twist singularities for symplectic maps
Authors: Dullin H. R. , Meiss J. D.
Published: February 2003

Near a nonresonant, elliptic fixed point, a symplectic map can be transformed into Birkhoff normal form. In these coordinates, the dynamics is represented entirely by the Lagrangian “frequency map” that gives the rotation number as a function of the action. The twist matrix, given by the Jacobian of the rotation number, describes the anharmonicity in the system. When the twist is singular the frequency map need not be locally one-to-one. Here we investigate the occurrence of fold and cusp singularities in the frequency map. We show that folds necessarily occur near third order resonances. We illustrate the results by numerical computations of frequency maps for a quadratic, symplectic map.
Regularities unseen, randomness observed: Levels of entropy convergence
Authors: Crutchfield James P. , Feldman David P.
Published: February 2003

We study how the Shannon entropy of sequences produced by an information source converges to the source’s entropy rate. We synthesize several phenomenological approaches to applying information theoretic measures of randomness and memory to stochastic and deterministic processes by using successive derivatives of the Shannon entropy growth curve. This leads, in turn, to natural measures of apparent memory stored in a source and the amounts of information that must be extracted from observations of a source in order for it to be optimally predicted and for an observer to synchronize to it. To measure the difficulty of synchronization, we define the transient information and prove that, for Markov processes, it is related to the total uncertainty experienced while synchronizing to a process. One consequence of ignoring a process’s structural properties is that the missed regularities are converted to apparent randomness. We demonstrate that this problem arises particularly for settings where one has access only to short measurement sequences. Numerically and analytically, we determine the Shannon entropy growth curve, and related quantities, for a range of stochastic and deterministic processes. We conclude by looking at the relationships between a process’s entropy convergence behavior and its underlying computational structure.
W. Gordon’s integral (1929) and its representations by means of Appell’s functions F2, F1, and F3
Authors: Tarasov V. F.
Published: February 2003

Exact analytical representations for W. Gordon’s integral by means of Appell’s functions are given. It is shown, that they correlate between each other. But representation of this integral by means of Appell’s function F2 is more attractive.
Massive complex scalar field in the Kerr–Sen geometry: Exact solution of wave equation and Hawking radiation
Authors: Wu S. Q. , Cai X.
Published: February 2003

The separated radial part of a massive complex scalar wave equation in the Kerr–Sen geometry is shown to satisfy the generalized spheroidal wave equation which is, in fact, a confluent Heun equation up to a multiplier. The Hawking evaporation of scalar particles in the Kerr–Sen black hole background is investigated by the Damour–Ruffini–Sannan method. It is shown that quantum thermal effect of the Kerr–Sen black hole has the same character as that of the Kerr–Newman black hole.
Twisted super-Yangians and their representations
Authors: Briot C. , Ragoucy E.
Published: February 2003

Starting with the super-Yangian Y(M|N) based on gl(M|N), we define twisted super-Yangians Y(M|N)±. Only Y+(M|2n) and Y−(2m|N) can be defined, and appear to be isomorphic one with each other. We study their finite-dimensional irreducible highest weight representations.
Scalings of mixed-mode regimes in a simple polynomial three-variable model of nonlinear dynamical systems
Authors: Khavrus Vyacheslav O. , Strizhak Peter E. , Kawczyński Andrzej L.
Published: February 2003

We describe scaling laws for a control parameter for various sequences of bifurcations of the LSn mixed-mode regimes consisting of single large amplitude maximum followed by n small amplitude peaks. These regimes are obtained in a normalized version of a simple three-variable polynomial model that contains only one nonlinear cubic term. The period adding bifurcations for LSn patterns scales as 1/n at low n and as 1/n2 at sufficiently large values of n. Similar scaling laws 1/k at low k and 1/k2 at sufficiently high values of k describe the period adding bifurcations for complex k(LSn)(LSn+1) patterns. A finite number of basic LSn patterns and infinite sequences of complex k(LSn)(LSn+1) patterns exist in the model. Each periodic pattern loses its stability by the period doubling bifurcations scaled by the Feigenbaum law. Also an infinite number of the broken Farey trees exists between complex periodic orbits. A family of 1D return maps constructed from appropriate Poincaré sections is a very fruitful tool in studies of the dynamical system. Analysis of this family of maps supports the scaling laws found using the numerical integration of the model.
Effects of molecular rotation on densities in doped He4 clusters
Authors: Patel M. V. , Viel A. , Paesani F. , Huang P. , Whaley K. B.
Published: February 2003

The effects of including rotational degrees of freedom on helium solvation densities in molecule-doped helium clusters are investigated for a variety of molecules. Helium densities and cluster energetics are calculated with diffusion Monte Carlo methods. The rotationally induced changes in the helium density distributions are examined and quantified with a theoretical estimator applicable to molecules of arbitrary symmetry. This analysis leads to a discussion of adiabatic following of molecular rotation in a solvating helium environment. We make a detailed comparative study of the effect of molecular rotation as a function of four impurity molecules with varying mass and symmetry: SF6, OCS, HCN, and benzene (C6H6). We find that even for the heaviest rotors, only a fraction of the solvating helium density adiabatically follows the molecular motion in the quantum ground state. For the lightest molecule, HCN, a negligible degree of adiabatic following is found. A discussion of the various definitions is presented to clarify the meaning of adiabatic following, and its applicability to dynamical models of quantum rotation in helium droplets is evaluated in light of the quantitative findings of incomplete adiabatic following established here.
Calculating energy levels of isomerizing tetra-atomic molecules. I. The rovibrational bound states of Ar2HF
Authors: Kozin Igor N. , Law Mark M. , Hutson Jeremy M. , Tennyson Jonathan
Published: February 2003

A general, six-dimensional computational method for the accurate calculation of rotationally and vibrationally excited states of tetra-atomic molecules is developed. The resulting program is particularly appropriate for molecules executing wide-amplitude motions and isomerizations. An application to the Ar2HF van der Waals trimer is presented in which the HF intramolecular stretching coordinate is separated out adiabatically and is not treated explicitly. Vibrational term values up to about 100 cm−1 with absolute convergence to better than 0.1 cm−1 are reported. These calculations employ more extensive vibrational basis sets and hence consider a much higher density of states than hitherto. States that sample Ar–Ar–HF linear configurations and approach Ar–HF–Ar linear configurations are characterized for the first time. Results for total angular momentum J=0 and 1 provide the first accurate calculations of rotational constants for this system. The rotational constants for the HF bending states of Ar2HF in the ground and first vibrationally excited states of the HF monomer are in good agreement with experiment, confirming the accuracy of the potential used in this work.
Preserving the measure of compatibility between quantum states
Authors: Molnár Lajos , Timmermann Werner
Published: February 2003

In this article after defining the abstract concept of compatibility-like functions on quantum states, we prove that every bijective transformation on the set of all states which preserves such a function is implemented by an either unitary or antiunitary operator.
Limits of a Ginzburg–Landau model with codimension-one defects
Authors: Rubinstein J. , Sternberg P.
Published: February 2003

We derive a nondimensional Ginzburg–Landau energy functional that does not use temperature-dependent scaling quantities. Using the machinery of gamma-convergence, the asymptotic limits of the functional are computed in the presence of thin defects centered around co-dimension 1 manifolds. We classify the defects into three groups depending on the L1-norm of the defect potential. We show that each group has its own distinguished asymptotic limit as the thickness of the defect converges to zero.
Rotationally resolved B̃–X̃ electronic spectra of both conformers of the 1-propoxy radical
Authors: Gopalakrishnan Sandhya , Carter Christopher C. , Zu Lily , Stakhursky Vadim , Tarczay György , Miller Terry A.
Published: February 2003

Five bands of the B̃–X̃ laser induced fluorescence spectrum of jet-cooled 1-propoxy radical have been recorded with a spectral resolution of ≈200 MHz. The resolved rotational and fine structure of these bands has been assigned and analyzed providing rotational constants for both the X̃ and B̃ states as well as components of the electron spin-rotation tensor in the X̃ state. By comparison of these constants with ones obtained from quantum chemistry calculations, two bands have been assigned to the gauche (G) conformer of 1-propoxy and 3 bands to the trans (T) conformer. The spectrum of each conformer abruptly terminates after the excitation of a single C–O stretch.
Negative ion photoelectron spectra simulation of V3O from a density functional study
Authors: Calaminici Patrizia , Köster Andreas M. , Salahub Dennis R.
Published: February 2003

A density functional study of neutral and anionic vanadium trimer monoxides is presented. The calculations were of all-electron type employing a newly developed basis set for the vanadium atom. Different isomers of V3O and V3O− were studied in order to determine the ground state structures. For both systems a planar C2v structure with an edge-bonded oxygen atom was found as the ground state. Equilibrium structure parameters of ground states as well as low-lying excited states, harmonic frequencies, the adiabatic electron affinity, and Kohn–Sham orbital diagrams are reported. The experimental negative ion photoelectron spectra of V3O was simulated by calculating multidimensional Franck–Condon factors, using the geometries and harmonic frequencies of the calculated ground states of V3O− and V3O. The good agreement between the experimental and the theoretical spectra allows the determination of the ground state structure of V3O and V3O−. This represents the first work in which a simulation of a vibrationally resolved negative ion photoelectron spectra of a transition metal oxide is presented.
The origin of soft vibrational modes of alkanes adsorbed on Cu: An experimental and theoretical investigation
Authors: Fosser Kari A. , Nuzzo Ralph G. , Bagus Paul S. , Wöll Christof
Published: February 2003

A detailed experimental and theoretical analysis of the metal-induced softening of C–H vibrational modes has been carried out for highly symmetric cyclic saturated hydrocarbons and short chain linear saturated hydrocarbons. The softening of the C–H stretching modes of cyclopropane, cyclohexane, as well as propane and its deuterated analogs adsorbed on Cu(111) was examined experimentally using reflection absorption infrared spectroscopy and theoretically using ab initio Hartree–Fock and correlated calculations. The investigation showed that molecules are present in two bound orientations for both cyclopropane and propane. The data further reveal that significant mode softening is associated with only some (not all) of the bound states of these molecules. Soft modes with significant intensity were found to be present for cyclohexane and propane bound on Cu(111) in a planar orientation. A theoretical analysis of the various adsorbed forms of these three types of molecules confirms the surprising experimental observation that cyclopropane has no soft mode that attends its binding on Cu(111). The calculations show that the occurrence of soft modes in the vibrational spectra of cyclohexane (where a broad, intense soft C–H mode exists) and propane (where a weaker, more narrow linewidth soft mode is found) correlates with a small, but still significant degree of charge transfer that governs the alkane–metal interaction. No evidence is found to support a previously proposed theory of a weak hydrogen-bonding interaction that mediates the metal/H–C interaction.
Thermodynamic properties and structure of the liquid–vapor interface: A neoclassical Redlich–Kwong model
Authors: Carey V. P.
Published: February 2003

It is well known that the classical mean field theory of van der Waals for liquid–vapor interfacial region properties deviates from real fluid behavior in several important ways. In particular, the variations of the surface tension and interfacial region thickness with temperature near the critical point are not consistent with those for real fluids. This paper presents a modified version of the classical mean field model that incorporates Redlich–Kwong fluid properties. It is shown here that this neoclassical Redlich–Kwong fluid model predicts property variations with temperature that agree better with measured data for real fluids. Predictions of the critical exponents associated with the temperature variation of surface tension and interfacial region thickness are developed from the Redlich–Kwong model. This new model predicts that surface tension varies about proportional to (1−T/Tc)1.33 and that the interfacial region thickness varies about proportional to (1−T/Tc)−0.67, with T and Tc being the system temperature and critical temperature, respectively. Compared to the critical exponents predicted by classical van der Waals theory, the Redlich–Kwong model predictions are found to be in better agreement with values inferred from experimental measurements. Predictions of the Redlich–Kwong model regarding interfacial region structure and property fluctuations are also examined.
Fluctuations in entanglements of polymer liquids
Authors: Schieber Jay D.
Published: February 2003

A method for incorporating reptation ideas in a temporary network model is used to predict the fluctuations of entanglement number and monomer density between entanglements in entangled polymeric liquids. The dynamic variables are chosen to be the number of Kuhn steps and the position of the entanglements. A chain of fixed number of Kuhn steps in a bath that fixes the chemical potential conjugate to the number of entanglements is considered. The static equilibrium statistics of such a model can be calculated analytically. Since the dynamics of the model may also be simulated, these analytic expressions may be used to check the algorithm. Also, the damping function is calculated analytically from these distributions, as well as normal stresses following a step shear.
Nonvolatile electrical bistability of organic/metal-nanocluster/organic system
Authors: Ma Liping , Pyo Seungmoon , Ouyang Jianyong , Xu Qianfei , Yang Yang
Published: February 2003

Two-terminal electrical bistable devices have been fabricated using a sandwich structure of organic/metal/organic as the active medium, sandwiched between two external electrodes. The nonvolatile electrical bistability of these devices can be controlled using a positive and a negative electrical bias alternatively. A forward bias may switch the device to a high-conductance state, while a reverse bias is required to restore it to a low-conductance state. In this letter, a model to explain this electrical bistability is proposed. It is found that the bistability is very sensitive to the nanostructure of the middle metal layer. For obtaining the devices with well-controlled bistability, the middle metal layer is incorporated with metal nanoclusters separated by thin oxide layers. These nanoclusters behave as the charge storage elements, which enable the nonvolatile electrical bistability when biased to a sufficiently high voltage. This mechanism is supported by the experimental data obtained from UV–visible absorption spectra, atomic force microscopy, and impedance spectroscopy.
Design of a channel drop filter by using a donor-type cavity with high-quality factor in a two-dimensional photonic crystal slab
Authors: Akahane Yoshihiro , Mochizuki Masamitsu , Asano Takashi , Tanaka Yoshinori , Noda Susumu
Published: February 2003

We report a design of the surface-emitting-type channel drop filters based on point defect cavities and line defect waveguides in two-dimensional photonic crystal slabs, which aim to improve the filtering resolution and light emission characteristics. Since the filters are passive, the mode volume size of the defects needs not be minimized, but the interaction between the defect cavity and the line defect waveguide must be considered. By adopting a donor-type point defect with three missing holes of linear shape, the quality factor of the filter theoretically increases to values as high as 2900 while it reached only 500 in the previously utilized acceptor-type defect. The results suggest that this donor-type defect is very useful for the development of ultrasmall channel add/drop devices.
Electron spin resonance microscopic surface imaging using a microwave scanning probe
Authors: Sakran F. , Copty A. , Golosovsky M. , Bontemps N. , Davidov D. , Frenkel A.
Published: February 2003

We report on a scanning electron-spin-resonance microscopy based on a microwave near-field probe. The probe consists of an open dielectric resonator with a thin-slit aperture. The spatial resolution in one direction is determined by the slit width and can be varied between 1 and 100 μm, while the spatial resolution in the perpendicular direction is ∼10 times larger. We demonstrate spatially-resolved measurements on diphenyl-picryl-hydrazil samples on a substrate. A sensitivity of 1011 spins could be achieved using a 4-μm-wide slit operating at 8.5 GHz and in a contact mode.
Etching depth dependence of the effective refractive index in two-dimensional photonic-crystal-patterned vertical-cavity surface-emitting laser structures
Authors: Yokouchi Noriyuki , Danner Aaron J. , Choquette Kent D.
Published: February 2003

A vertical-cavity surface-emitting laser (VCSEL) having a two-dimensional (2-D) photonic crystal structure on its surface has been investigated for single-lateral-mode operation. We evaluated the effective index change of a VCSEL cavity introduced by a 2-D pattern. Our experimental results showed good agreement with a theoretical model in which the influence of a finite etching depth was taken into consideration. The etching-depth dependence parameter γ, which can be explained by the optical power distribution inside a VCSEL structure, will be helpful for controlling the lateral mode of VCSEL devices.
Tunable optical properties of nanostructured-gold/ mesoporous-silica assembly
Authors: Li Z. S. , Kan C. X. , Cai W. P.
Published: February 2003

Gold nanowires have been fabricated by heat treatment of HAuCl4-soaked mesoporous silica at 300 °C in air atmosphere. Transmission-electron-microscope images show that, with increase of annealing temperature, Au nanowires gradually grow into nanoparticles. Due to the morphology transformation, the surface plasmon resonance peak of the composite can be continuously tuned from about 1080 to about 530 nm. Adopting the extended Gans’ formula in dipole approximation, simulation also proves that tunable optical properties over a large spectral region can be realized by such morphology transformation.
Microwave absorption on a thin film
Authors: Bosman Herman , Lau Y. Y. , Gilgenbach R. M.
Published: February 2003

With the use of a simple model, it is shown that a thin film of contaminant on a microwave window may absorb up to 50% of the incident power, even if the film thickness is only a small fraction of its resistive skin depth. This unexpectedly large amount of absorption is conjectured to have played a significant role in window failure. The temperature rise in a thin film is estimated.
Linear and nonlinear optical properties of single-walled carbon nanotubes within an ordered array of nanosized silica spheres
Authors: Han H. , Vijayalakshmi S. , Lan A. , Iqbal Z. , Grebel H. , Lalanne E. , Johnson A. M.
Published: February 2003

The linear and nonlinear optical properties of well-separated, single-walled carbon nanotubes were measured. The tubes were grown into the voids of an ordered array of silica spheres. Transmission of light through these tubes increased with the incident laser intensity. The nonlinear decay time of a λ=800-nm probe was measured at 320 fs when the sample was pumped with 400-nm light. Current–voltage characteristics changed upon illumination with a laser beam. Raman scattering decreased as electrical biasing increased.
Solar-blind ultraviolet photodetectors based on superlattices of AlN/AlGa(In)N
Authors: Kuryatkov V. , Chandolu A. , Borisov B. , Kipshidze G. , Zhu K. , Nikishin S. , Temkin H. , Holtz M.
Published: February 2003

We describe solar-blind photodetectors based on superlattices of AlN/AlGa(In)N. The superlattices have a period of 1.4 nm, determined by x-ray diffraction, and an effective band gap of 260 nm measured by optical reflectivity. Using simple mesa diodes, without surface passivation, we obtain low dark leakage currents of 0.2–0.3 pA, corresponding to the leakage current density of ∼0.3 nA/cm2, and high zero-bias resistance of ∼1×1011 Ω. Excellent visible cutoff is obtained for these devices, with six orders of magnitude decrease in responsivity from 260 to 380 nm. These results demonstrate the potential of junctions formed by short-period superlattices in large-band-gap devices.
Electronic excitations and decomposition of 1,1-diamino-2,2-dinitroethylene
Authors: Rashkeev S. N. , Kuklja M. M. , Zerilli F. J.
Published: February 2003

We present first-principles density-functional calculations of the atomic and electronic structure of the molecular crystal 1,1-diamino-2,2-dinitroethylene (FOX-7). Under either an isotropic or uniaxial applied stress, the ideal crystal lattice of this material accumulates elastic energy without any chemical or significant electronic structure changes. The presence of “reversed-orientationmolecule” defects narrows the band gap and lowers the decomposition barrier of the material in the solid phase.
Inverse Fourier transform technique to determine second-order optical nonlinearity spatial profiles
Authors: Ozcan A. , Digonnet M. J. F. , Kino G. S.
Published: February 2003

A technique is described to measure the second-order nonlinearity spatial profile of nonlinear films. It consists of placing two identical samples back-to-back to create a symmetric nonlinearity profile and measuring the Maker fringes of this sample. Because the profile is symmetric, both its shape and location inside the film can be determined uniquely from the Maker fringe data. Applied to a sample of thermally poled silica, this method reveals a nonlinearity profile that is both deeper (∼25 μm) and stronger (peak d33=0.8 pm/V) than previously believed, with spatial features that could not be resolved with previous techniques. This powerful principle is applicable to many other physical problems in which the amplitude, but not the phase, of the Fourier transform can be measured.
GaN-based waveguide devices for long-wavelength optical communications
Authors: Hui R. , Taherion S. , Wan Y. , Li J. , Jin S. X. , Lin J. Y. , Jiang H. X.
Published: February 2003

Refractive indices of AlxGa1−xN with different Al concentrations have been measured in infrared wavelength regions. Single-mode ridged optical waveguide devices using GaN/AlGaN heterostructures have been designed, fabricated, and characterized for operation in 1550 nm wavelength window. The feasibility of developing photonic integrated circuits based on III-nitride wide-band-gap semiconductors for fiber-optical communications has been discussed.
Growth and optical properties of single-crystal tubular ZnO whiskers
Authors: Hu J. Q. , Bando Y.
Published: February 2003

The growth of single-crystal tubular ZnO whiskers was achieved via a process of first reduction and following oxidation of ZnS powders. The products were characterized using x-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, and photoluminescence spectroscopy. The whiskers are tubular single crystals with the [001] growth crystallographic direction, and most have outer diameters of ∼400 nm, lengths of up to 15 μm, and wall thickness range of 100–150 nm. Room-temperature photoluminescence spectrum of the whiskers reveals a strong and sharp UV emission band at 381 nm and a weak and broad green emission band at 583 nm. Possible growth mechanism of the ZnO whiskers was briefly discussed.
The shapes of pair polarizability curves
Authors: Bounds David G. , Hinchliffe Alan
Published: February 2003

The relationship between the shapes of the pair polarizability curves of diatomic systems and chemical bonding is explored by means of molecular orbital calculations. The pair polarizability of a diatomic molecule can be split up into contributions from individual MO’s. This analysis shows that β(2)(R), like chemical bonding, is essentially determined by valence shell orbitals; hence the shapes of β(2)(R) curves for various pairs of interacting atoms can be related to the shapes of their potential curves. The relationship between β(2)(R) and molecular shape is illustrated for the system of a point positive charge and a chloride ion.
High resolution and sub-Doppler Fourier transform spectroscopy: Iodine molecular fluorescence excited by the 514.5 and 501.7 nm Ar+ laser lines
Authors: Bacis R. , Churassy S. , Field R. W. , Koffend J. B. , Vergès J.
Published: February 2003

Fluorescence from the I2 B O+u state, excited by the 514.5 and 501.7 nm cw Ar+ laser lines, is recorded using a high resolution Fourier transform spectrometer. Spectra are obtained with both multimode (6 GHz) and single mode (<100 MHz) Ar+ lasers, the latter spectra exhibiting reduced Doppler width. B O+u−X 1Σ+g fluorescence is recorded at 1 mK precision for v″=10–100, eQq″ quadrupole constants are obtained (±5%) from measured linewidths, broadening of quasibound X 1Σ+g rotational levels above the rotationless X 1Σ+g dissociation limit is observed, and perturbations of X 1Σ+ v″⩾92 by two previously unobserved long range I2 molecular states are detected. These two states, 0+g and 1g, which dissociate into two 2P3/2 I atoms, are also observed directly in the fluorescence spectrum. This paper presents illustrative examples; constants and a complete analysis will appear subsequently.
Time delay for bimolecular collisions: Utility of the spectral theorem in the classical limit
Authors: Brumer Paul , Fitz D. E. , Wardlaw David
Published: February 2003

The recently proven multichannel spectral theorem for time delay is explored with the goal of providing a useful expression for ’’lifetimes’’ of bimolecular collisions. The theorem is reduced to an approximate relationship between the classical time delay and the classical excess density of states. Numerical studies on collinear atom–diatom systems confirm the accuracy of the classical relationship and a simple geometric interpretation of the excess density of states for these systems is provided. Results on the sensitivity of collisional time delays to variations in potential surface well depths and system masses are presented. the time delays being simply obtained from the excess density of states.
A systematic preparation of new contracted Gaussian-type orbital basis sets. II. Test basis set for Cu2 molecule with and without splitting of the outer orbitals
Authors: Tatewaki Hiroshi , Huzinaga Sigeru
Published: February 2003

In the previous paper, the two new minimal contracted Gaussian-type orbitals (CGTO’s) are presented for Sc through Zn. Both sets gave excellent orbital energy values for the valence shell atomic orbitals. In the present paper the valence shell orbitals are split into two parts in order to describe the molecular environment, a step which brings improvements especially for the inner shells, 1s, 2s, and 2p atomic orbitals. The basis sets are tested by use in the SCF calculation on the Cu2 molecule.
A theoretical study of the potential energy surface for O(3P)+H2
Authors: Walch Stephen P. , Dunning Thom. H. , Raffenetti Richard C. , Bobrowicz Frank W.
Published: February 2003

Barrier heights and transition state geometries have been calculated for the reaction O(3P)+H2→OH+H using large scale POL-CI wave functions (based on GVB wave functions using basis sets of up to triple zeta valence plus double zeta polarization quality). A detailed study was made of the effects on the calculated barrier height and saddle point geometry of (i) basis set, (ii) choice of orbitals, and (iii) choice of reference configurations. Calculations using a [4s3p2d/3s2p] basis lead to a collinear saddle point with rHH=0.92 Å and rOH=1.23 Å with a corresponding barrier height of 12.5 kcal/mole. There are two surfaces which connect the reactants with the products: one of 3A′ symmetry and one of 3A″ symmetry (these correspond to the two degenerate components of the 3Π state in collinear geometries). In the transition state region, the 3A′ surface has a steeper bending curve than the 3A″ surface leading to significantly different reaction rates on the two surfaces.
Additional HTFFR observations on chemiluminescent Sn-oxidizer reactions
Authors: Manos D. M. , Fontijn Arthur
Published: February 2003

Product quenching of SnO(a 3Σ) from the Sn/N2O reaction was studied in a high-temperature fast-flow reactor (HTFFR) at 850 K. For Sn as the limiting reagent these studies yield the Stern–Volmer expression Φ0(a–X)/Φ (a–X) =1.0+3.9(±σ=0.2) ×105[Sn]initial /[Ar]. A mechanism is advanced by which the precursor state of SnO(a 3Σ) can either transfer to this emitting state by collisions with the bath gas (Ar) or be quenched by other SnO molecules in unspecified states. At 360 K qualitative observations were made of the Sn/O, Sn/O/O2 and Sn/O2 reactions, which show that these reactions populate SnO(a 3Σ, b 3Π, c, and A 1Π) and that O2 is an efficient quencher of SnO(a 3Σ). It is shown that the c–X and A–X emissions from Sn/N2O at elevated temperatures may be attributed to reaction of Sn with O and/or O2 from N2O decomposition.
Chemiluminescence of argon bromide. I. The emission spectrum of ArBr
Authors: Golde Michael F. , Kvaran Agust
Published: February 2003

In this first systematic study of the ArBr molecule, chemiluminescence spectra are generated by the reactions of metastable argon atoms with bromine-containing compounds. Three continua, due to the B (1/2)−X (1/2), B (1/2)−A (1/2) and C (3/2)−A3/2) transitions are characterized, their pressure dependences examined, and the extent of their overlap discussed in some detail. From the temperture dependence of the spectra, an upper limit for the electronic energy of the B (1/2) state is derived: TeB?61 850 cm−1.
An exactly soluble many channel scattering model
Authors: Rohlfing E. A. , Loeser J. G. , DePristo A. E. , Rabitz H.
Published: February 2003

An exactly soluble model for many channel quantum scattering is presented which is a generalization of elastic scattering from a square radial potential. Through the appropriate choice of channel energies and couplings, as well as total energy and potential strength, this model is readily applicable to a wide variety of scattering problems. The relative simplicity of the calculations allows one to characterize a system easily in terms of the relevant collision parameters (basis set size, coupling strengths, etc.). Moreover,the analytic nature of the solutions enables one to interpret the results of such calculations directly. Two applications are presented which illustrate the capabilities of the model and demonstrate interesting scattering behavior.
Optical investigation of divalent europium in the alkali chlorides and bromides
Authors: Hernandez A. J. , Cory W. K. , Rubio O. J.
Published: February 2003

Detailed optical absorption data are reported for the divalent europium ion in NaCl, KCl, RbCl, KBr, RbBr, and KI single crystals at 300 and 77 K. Values of the oscillator strength are calculated for all the observed bands in the optical spectra at both temperatures. It is established that the optical spectra are well accounted for by a strong crystal field split 5d electron having a Coulomb interaction with the 4f6 core about one-half the free ion value. It is also shown that the measured 10 Dq cubic field splitting of the 4f6 5d configuration into its t2g and eg components is in accord with the expected order of the fields exerted by the different crystal media. In addition, calibration constants are reported for determining the Eu2+ concentration in KBr, RbBr, and KI single crystals by optical techniques, without destroying the sample.
A general theory of the spectroscopic properties of partially ordered ensembles. I. One vector problems
Authors: Friesner Richard , Nairn John A. , Sauer Kenneth
Published: February 2003

We have developed a method for determining the response of a static, partially ordered ensemble of molecules to various types of electromagnetic probes. In our formalism a physical model is constructued for the orientational distribution function, which is represented as a volume integral over a set of weighting functions. Procedures are given for obtaining geometrical and statistical parameters from analysis of the oriented line shapes and intensities. Explicit treatments of linear dichroism, circular dichroism, and magnetic resonance are developed as well as detailed mathematical techniques for calculation of the distribution function.
Hole burning into molecular velocity distribution due to monochromatic radiation and molecular elastic collision
Authors: Koura Katsuhisa
Published: February 2003

The effect of molecular elastic collisions on the hole burning into the molecular velocity distribution due to a monochromatic radiation is studied by solving the Boltzmann equation with the Monte Carlo simulation. A spatially homogeneous gas cell is suddenly irradiated by a unidirectional monochromatic radiation, whose intensity is assumed to be spatially and temporally constant and taken as the square line shape. The molecular model is taken as the hard sphere model. The unsteady hole burning into the velocity distribution is elucidated. It is found that the velocity distribution attains a steady-state distribution because of a balance between radiative hole burning and hole filling due to molecular elastic collisions. The steady-state velocity distribution indicates good agreement with that of the BGK elastic collision model widely used in the analysis of the hole burning process.
The Dufour effect. III. Direct experimental determination of the heat of transport of carbon tetrachloride–cyclohexane liquid mixtures
Authors: Rowley Richard L. , Horne Frederick H.
Published: February 2003

The heat of transport of carbon tetrachloride–cyclohexane liquid mixtures has been determined directly by Dufour effect experiments. The technique employs a withdrawable ’’liquid gate’’ to create a nonturbulent, sharp diffusional interface. The partial differential equations governing the barycentric velocity, composition, and temperature distributions are solved with a Crank–Nicholson implicit numerical scheme. This allows inclusion of the composition and temperature dependence of the thermodynamic and transport parameters. For mean mole fraction of carbon tetrachloride x1 between 0.34 and 0.55 and for mean temperature T between 295.13 and 296.43 °K, the best least squares fit of the data for the heat of transport ?*1 in kJ mol−1 is ?*1=5.82+2.32 (x1−1/2)+0.225 (T−295.82), with a calculated standard error of 0.087. Analysis of the same experiments indicates that the composition dependence of the thermal conductivity κ of the mixture in the specified composition and temperature ranges is best given (in J m−1s−1K−1 ) by (∂κ/∂w1)T,p=0.0252 (w21/2−0.032), where wi is mass fraction.
On the critical point of a Malthus–Verhulst process
Authors: Dekker H.
Published: February 2003

The master equation for the Malthus–Verhulst process including spontaneous generation will be re-examined in the light of an extended version of Van Kampen’s method at the critical point. The Malthus–Verhulst process turns out to be a remarkable special case as the standard scaling property is left untouched at the critical point.
The dynamics of vibrational transitions in molecules: A classical model
Authors: Riehl James P.
Published: February 2003

The absorption of infrared radiation by molecules is examined by comparison with a classical one-dimensional 3-particle model. The equations of motion for this system are solved while it interacts with a classical electromagnetic wave. It is shown that direct ’’electron’’–radiation and nuclei–radiation interactions contribute approximately equally to the absorption process.
Free energy and radial distribution functions for a model of point defects in AgCl doped with CdCl2
Authors: Allnatt A. R. , Allnatt E. Loftus
Published: February 2003

The Helmholtz free energy and radial distribution functions were calculated for impurity and vacancy point defects in AgCl doped with 1–5 mole % CdCl2 at 250 °C. The model assumed a Coulombic interaction except at the nearest-neighbor separation. The method was a variational solution of the hypernetted chain integral equations. The relation of the calculation method and results to liquid electrolyte solution theory is discussed. The degree of association into nearest-neighbor vacancy–impurity complexes is not close to zero, contrary to recent suggestions. The results are consistent with the occurrence of triplet (and possibly larger) nearest-neighbor complexes in addition to the pairs.
An exact relation for the reactivity dependence of the recombination probability
Authors: Pedersen J. Boiden
Published: February 2003

The recombination probability is calculated by solving the Smoluchowski equation with appropriate boundary conditions. (AIP)
Infrared spectrum of the water formaldehyde complex in solid argon and solid nitrogen
Authors: Nelander Bengt
Published: February 2003

Infrared spectra of the water formaldehyde complex in argon and nitrogen matrices have been obtained. The complex shifts of the water fundamentals clearly show that water forms a hydrogen bond with formaldehyde. HDO prefers to form a D bond, but a metastable H-bonded complex is observed in nitrogen matrices below 20 K.
The nearest self-adjoint operator
Authors: Dupré Maurice J. , Goldstein Jerome A. , Levy Mel
Published: February 2003

The construction of self-adjoint matrix Re(μ) =1/2(μ+μ+) from non-Hermitian matrix μ for the purpose of calculational in molecular quantum mechanics is discussed. (AIP)
Population and depopulation of O(3p5P) in a supersonic freejet of an O2-seeded Ar plasma
Authors: Minomo M. , Kimura A. , Nishida M.
Published: February 2003

The electronic energy transfer from metastable Ar to oxygen is studied in a low-density plasma facility operated by the d.c. arc. discharge. The population densities of O(3P3p) and O(3P5p) are measured. (AIP)