bluuebunny/crossref_metadata_2025 huggingface dataset:
Transaction Costs and Information Systems: Does IT Add Up?
Authors: Cordelia Antonio
Published: August 2006

Transaction cost theory has often been used to support the use of information and communication technology (ICT) to reduce imperfection in the economic system. Electronic markets and hierarchies have repeatedly been described as solutions to inefficiencies in the organisation of transactions in complex and uncertain settings. Far from criticising this assumption, this paper highlights the limits associated with this application of transaction cost theory that has been prevalent in IS research. Building on the concepts first proposed by Ciborra, the paper argues that information-related problems represent only some of the elements contributing to transaction costs. These costs also emerge due to the interdependencies among the various factors contributing to their growth. The study of the consequences associated with ICT design and implementation, grounded in transaction cost theory, should consider the overall implication associated with the adoption and use of ICT and not only the direct effect on problems associated with information flow, distribution, and management.
The Hospitality Metaphor as a Theoretical Lens for Understanding the ICT Adoption Process
Authors: Saccol Amarolinda Zanela , Reinhard Nicolau
Published: August 2006

The Hospitality Metaphor proposed by Ciborra represents an alternative view to the traditional models that describe the process of adopting information and communication technologies (ICT). This Metaphor helps us in considering social, behavioral and existential elements related to the adoption process, offering a critical and dialectical view of it. In this paper, we review the philosophical and methodological basis of this Metaphor and its main statements. We also apply it in analyzing a case of mobile ICT adoption. The application of the Hospitality Metaphor enables a clear understanding of this process as an incremental and open one in which social, existential and ‘mundane’ issues play a major role, and where technology reveals its dubious character, leading to unplanned results.
The Validity of the Improvisation Argument in the Implementation of Rigid technology: The Case of ERP systems
Authors: Elbanna Amany R.
Published: August 2006

Claudio Ciborra's improvisation argument provides a realistic dynamic account of how organisational practices address technology. This was developed from the study of malleable open-ended technology, but little research has occurred to investigate the theory's validity within different settings. This paper seeks to address this gap, by examining improvisation in the context of a rigid highly structured technology. It presents findings from the successful implementation of an Enterprise Resource Planning (ERP) system within a large international organisation, which was subsequently defined by the ERP vendor as being an ‘exemplary site’. Through the theoretical lens of Actor Network Theory, the paper reveals the improvisation, enactments and constant work around the plan that took place in dealing with the high contingencies of ERP implementation. The study extends the discussion on improvisation and contributes to an already illuminating argument. It invites practitioners to reflect on ERP implementation practice and review their evaluation methods.
The Vlasov-Poisson model and the validity of a numerical approach
Authors: Califano F. , Galeotti L. , Mangeney A.
Published: August 2006

Our aim in this work is to show that the final macroscopic state of a noncollisional plasma system, computed through numerical simulations, depends on artificial small scale effects induced by the used numerical scheme and/or grid discretization. By using the continuous, Hamiltonian Vlasov-Poisson model, we found significant differences in the nonlinear dynamics when varying the importance of dissipative and/or dispersive (numerical) effects. In particular, such artificial processes are crucial during phase space vortex generation and vortex merging dynamics leading to different irreversible asymptotic states. These results are obtained for numerical grid scale lengths much smaller than any noncollisional physical scale length.
Analysis of tokamak data using a novel Hilbert transform based technique
Authors: Jha R. , Raju D. , Sen A.
Published: August 2006

A novel data analysis technique based on the “empirical mode decomposition” and Hilbert transform is applied to the analysis of edge fluctuation data and Mirnov coil data from the ADITYA tokamak [S. B. Bhatt et al., Ind. J. Pure Appl. Phys. 27, 710 (1989)]. It is shown that the edge fluctuations can be well represented by a finite number of about 10 discrete modes. Their instantaneous energies show intermittent bursts and the high frequency modes are nonstationary. The technique is further developed to study three-mode interactions and employed to show that triplet interactions are statistically significant among high frequency modes of the fluctuation data. A general critique of the method is presented and its utility for the analysis of nonlinear phenomena in complex systems like plasma turbulence is highlighted.
A computationally efficient exact pseudopotential method. I. Analytic reformulation of the Phillips-Kleinman theory
Authors: Smallwood C. Jay , Larsen Ross E. , Glover William J. , Schwartz Benjamin J.
Published: August 2006

Even with modern computers, it is still not possible to solve the Schrödinger equation exactly for systems with more than a handful of electrons. For many systems, the deeply bound core electrons serve merely as placeholders and only a few valence electrons participate in the chemical process of interest. Pseudopotential theory takes advantage of this fact to reduce the dimensionality of a multielectron chemical problem: the Schrödinger equation is solved only for the valence electrons, and the effects of the core electrons are included implicitly via an extra term in the Hamiltonian known as the pseudopotential. Phillips and Kleinman (PK) [Phys. Rev. 116, 287 (1959)]. demonstrated that it is possible to derive a pseudopotential that guarantees that the valence electron wave function is orthogonal to the (implicitly included) core electron wave functions. The PK theory, however, is expensive to implement since the pseudopotential is nonlocal and its computation involves iterative evaluation of the full Hamiltonian. In this paper, we present an analytically exact reformulation of the PK pseudopotential theory. Our reformulation has the advantage that it greatly simplifies the expressions that need to be evaluated during the iterative determination of the pseudopotential, greatly increasing the computational efficiency. We demonstrate our new formalism by calculating the pseudopotential for the 3s valence electron of the Na atom, and in the subsequent paper, we show that pseudopotentials for molecules as complex as tetrahydrofuran can be calculated with our formalism in only a few seconds. Our reformulation also provides a clear geometric interpretation of how the constraint equations in the PK theory, which are required to obtain a unique solution, are themselves sufficient to calculate the pseudopotential.
A computationally efficient exact pseudopotential method. II. Application to the molecular pseudopotential of an excess electron interacting with tetrahydrofuran (THF)
Authors: Smallwood C. Jay , Mejia Cesar N. , Glover William J. , Larsen Ross E. , Schwartz Benjamin J.
Published: August 2006

In the preceding paper, we presented an analytic reformulation of the Phillips-Kleinman (PK) pseudopotential theory. In the PK theory, the number of explicitly treated electronic degrees of freedom in a multielectron problem is reduced by forcing the wave functions of the few electrons of interest (the valence electrons) to be orthogonal to those of the remaining electrons (the core electrons); this results in a new Schrödinger equation for the valence electrons in which the effects of the core electrons are treated implicitly via an extra term known as the pseudopotential. Although this pseudopotential must be evaluated iteratively, our reformulation of the theory allows the exact pseudopotential to be found without ever having to evaluate the potential energy operator, providing enormous computational savings. In this paper, we present a detailed computational procedure for implementing our reformulation of the PK theory, and we illustrate our procedure on the largest system for which an exact pseudopotential has been calculated, that of an excess electron interacting with a tetrahyrdrofuran (THF) molecule. We discuss the numerical stability of several approaches to the iterative solution for the pseudopotential, and find that once the core wave functions are available, the full e−-THF pseudopotential can be calculated in less than 3s on a relatively modest single processor. We also comment on how the choice of basis set affects the calculated pseudopotential, and provide a prescription for correcting unphysical behavior that arises at long distances if a localized Gaussian basis set is used. Finally, we discuss the effective e−-THF potential in detail, and present a multisite analytic fit of the potential that is suitable for use in molecular simulation.
Scaling and the Smoluchowski equations
Authors: Goodisman J. , Chaiken J.
Published: August 2006

The Smoluchowski equations, which describe coalescence growth, take into account combination reactions between a j-mer and a k-mer to form a (j+k)-mer, but not breakup of larger clusters to smaller ones. All combination reactions are assumed to be second order, with rate constants Kjk. The Kjk are said to scale if Kλj,γk=λμγνKjk for j⩽k. It can then be shown that, for large k, the number density or population of k-mers is given by Akae−bk, where A is a normalization constant (a function of a, b, and time), a=−(μ+ν), and bμ+ν−1 depends linearly on time. We prove this in a simple, transparent manner. We also discuss the origin of odd-even population oscillations for small k. A common scaling arises from the ballistic model, which assumes that the velocity of a k-mer is proportional to 1∕√mk (Maxwell distribution), i.e., thermal equilibrium. This does not hold for the nascent distribution of clusters produced from monomers by reactive collisions. By direct calculation, invoking conservation of momentum in collisions, we show that, for this distribution, velocities are proportional to mk−0.577. This leads to μ+ν=0.090, intermediate between the ballistic (0.167) and diffusive (0.000) results. These results are discussed in light of the existence of systems in the experimental literature which apparently correspond to very negative values of μ+ν.
Application of scaling and kinetic equations to helium cluster size distributions: Homogeneous nucleation of a nearly ideal gas
Authors: Chaiken J. , Goodisman J. , Kornilov Oleg , Peter Toennies J.
Published: August 2006

A previously published model of homogeneous nucleation [Villarica et al., J. Chem. Phys. 98, 4610 (1993)] based on the Smoluchowski [Phys. Z. 17, 557 (1916)] equations is used to simulate the experimentally measured size distributions of He4 clusters produced in free jet expansions. The model includes only binary collisions and does not consider evaporative effects, so that binary reactive collisions are rate limiting for formation of all cluster sizes despite the need for stabilization of nascent clusters. The model represents these data very well, accounting in some cases for nearly four orders of magnitude in variation in abundance over cluster sizes ranging up to nearly 100 atoms. The success of the model may be due to particularities of He4 clusters, i.e., their very low coalescence exothermicity, and to the low temperature of 6.7K at which the data were collected.
Detection of protein conformational change by optical second-harmonic generation
Authors: Salafsky Joshua S.
Published: August 2006

An ability to detect and track conformational change in real time is essential to understanding the dynamic relationship between structure and function in biological molecules. Here I show that second-harmonic generation (SHG), a surface-selective technique, offers a new means to probe structural dynamics. A protein, calmodulin, was labeled with a second-harmonic-active dye and immobilized to a surface. Although neither the labeling nor the immobilization was done in a site-specific manner, an overall net orientation of the labels was produced relative to the surface plane. Conformational change of the protein induced by calcium alters the average tilt angle of the labels and causes a change in the intensity of second-harmonic radiation generated by the surface. As SHG is spatially and temporally coherent and depends quantitatively on the structural details of a surface, the method described here should serve as the starting point for more detailed studies of the mechanism of conformational change in molecules, as well as related topics such as protein folding. SHG’s surface selectivity also suggests its use in a range of biological applications which require detection of surface-bound molecules.
Behavior of perturbed plasma displacement near regular and singular
X
-points for compressible ideal magnetohydrodynamic stability analysis
Authors: Alladio F. , Mancuso A. , Micozzi P. , Rogier F.
Published: August 2006

The ideal magnetohydrodynamic (MHD) stability analysis of axisymmetric plasma equilibria is simplified if magnetic coordinates, such as Boozer coordinates (ψT radial, i.e., toroidal flux divided by 2π, θ poloidal angle, ϕ toroidal angle, with Jacobian g∝1∕B2), are used. The perturbed plasma displacement ξ⃗ is Fourier expanded in the poloidal angle, and the normal-mode equation δWp(ξ⃗*,ξ⃗)=ω2δWk(ξ⃗*,ξ⃗) (where δWp and δWk are the perturbed potential and kinetic plasma energies and ω2 is the eigenvalue) is solved through a 1D radial finite-element method. All magnetic coordinates are however plagued by divergent metric coefficients, if magnetic separatrices exist within (or at the boundary of) the plasma. The ideal MHD stability of plasma equilibria in the presence of magnetic separatrices is therefore a disputed problem. We consider the most general case of a simply connected axisymmetric plasma, which embeds an internal magnetic separatrix—ψT=ψTX, with rotational transform ι̷(ψTX)=0 and regular X-points (B⃗≠0)—and is bounded by a second magnetic separatrix at the edge—ψT=ψTmax, with ι̷(ψTmax)≠0—that includes a part of the symmetry axis (R=0) and is limited by two singular X-points (B⃗=0). At the embedded separatrix, the ideal MHD stability analysis requires the continuity of the normal plasma perturbed displacement variable, ξψ=ξ⃗∙∇⃗ψT; the other displacement variables, the binormal ηψ=ξ⃗∙(∇⃗θ−ι̷∇⃗ϕ) and the parallel μ=−gξ⃗∙∇⃗ϕ, can instead be discontinuous everywhere. The permissible asymptotic limits of (ξψ,ηψ,μ) are calculated for the unstable (ω2<0) eigenvectors, imposing the regularity of δWp, δWk, and ξ⃗ at the embedded separatrix and at the edge separatrix. An intensified numerical radial mesh following Boozer magnetic coordinates is set up; it requires a logarithmic fit to the rotational transform near the embedded magnetic separatrix, a minimum distance between the radial mesh and both separatrices, and finally an extended spectrum of poloidal mode numbers in the Boozer angle. The numerical results are compared “a posteriori” with the permissible asymptotic limits for the perturbed displacement: the radial displacement variable ξψ is found to be always near its most unstable asymptotic limit, while the full range of permissible asymptotic behaviors can be obtained for the binormal and the parallel displacement variables.
Influences of the dust size and the dust charge variations to the low-frequency wave modes in a dusty plasma
Authors: Wan Gui-xin , Duan Wen-shan , Chen Quan-hai , Wang Xiao-yun
Published: August 2006

The effects of both the dust size distribution and the adiabatic dust charge variation in unmagnetized dusty plasmas have been studied. Both the analytical and the numerical results are given to compare the differences between the dust plasma with a power-law distribution and the mono-sized dusty plasma. The comparisons are also given between the dusty plasmas with or without charge fluctuations. The present analytical results show that only rarefactive solitary waves exist in this system, which is similar to that without dust charge variation. However, it is shown that the presence of adiabatic dust charge variations and the dust size distribution can significantly influence the characteristic of low-frequency wave modes. This investigation can be relevant to the dust acoustic waves in various space plasma environments, such as Jupiter’s ring and interstellar dusty clouds.
Spectral characterization of hydrogen bond network dynamics in water
Authors: Mudi Anirban , Chakravarty Charusita , Milotti Edoardo
Published: August 2006

Some computational aspects of the characterization of the complex hydrogen bond network dynamics using power spectral analysis are discussed. In the case of hydrogen-bonded liquids, the tagged molecule potential energy is shown to be a useful quantity for capturing the behavior of the networked liquid on different lengths and time scales. The computation of the tagged potential energy for rigid-body effective pair potentials, such as the TIP5P-E and SPC-E models, is discussed. The more structured nature of the TIP5P-E potential, compared to the SPC/E potential, shows up as differences in the high-frequency librational band of the power spectra of the tagged molecule potential energies. The static distributions of the tagged molecule potential energies are also more structured in the case of TIP5P-E, rather than SPC/E, water. The overall behavior of the key power spectral features remains the same in both the models. The possibility of detailed characterization of the power spectrum, and therefore of the underlying dynamics, using a model-based parametric fitting procedure for the power spectra is also discussed. We show that a parametric fitting can allow one to test alternative models of the dynamics underlying the liquid state dynamics.
Control of magnetohydrodynamic modes with a resistive wall above the wall stabilization limit
Authors: Finn John M.
Published: August 2006

Studies are shown of control of magnetohydrodynamic (MHD) modes in the presence of a resistive wall, below and above the regime for which stabilization is possible with a perfectly conducting wall, i.e., in and above the ideal wall limit. The results show that resistive plasma (tearing-like) modes can be feedback stabilized for current profiles which are unstable above the ideal wall limit, both for tokamak-like and reversed field pinch (RFP)-like profiles. However, above the limit for wall stabilization of ideal plasma modes, resonant or nonresonant, the feedback scheme cannot provide stabilization. The control scheme senses both normal and tangential components of the perturbed magnetic field, and the feedback is proportional to a linear combination of the two. Neither plasma rotation nor complex gain is included. A cylindrical reduced MHD model, in resistive or ideal form, is used, with tokamak-like profiles [increasing profile of q(r)] or RFP-like profiles [decreasing q(r)]. The possible relevance to RFPs and tokamaks is discussed.
Waves, particles, and field dynamics
Authors: Strumia Alberto
Published: August 2006

The idea of associating particle trajectories with wave propagation rays is examined in the context of general relativity. The additional assumption that also Hamilton-Jacobi particle equation and wave front equation of motion can be identified in an n>3 coordinate space leads to a Kaluza-Klein type theory involving Klein-Gordon and Dirac equations. Moreover de Broglie and Einstein-Planck quantum relations can be deduced in a natural way.
Physical characterization of high-frequency instabilities in Hall thrusters
Authors: Lazurenko A. , Albaréde L. , Bouchoule A.
Published: August 2006

High-frequency instabilities (5–10MHz) were investigated in two Hall thrusters of different scale and were shown to have the same character. Two diagnostic tools were implemented in this study: capacitive antennas, electrically isolated from plasma, and plasma immersed probes. Their corresponding signals were analyzed in terms of capacitive and charge-collecting effects. The previously suggested physical representation of these high frequency instabilities as azimuthally drifting electron density fluctuations was reinforced and significant deviations from azimuthal symmetry in the thruster plume are evidenced. Finally, data obtained by using positively biased probe evidenced lower frequency components, assigned to “ion transit time” instabilities.
Infrared overtone spectroscopy and vibrational analysis of a Fermi resonance in nitric acid: Experiment and theory
Authors: Konen Ian M. , Li Eunice X. J. , Lester Marsha I. , Vázquez Juana , Stanton John F.
Published: August 2006

High resolution infrared spectra of nitric acid have been recorded in the first OH overtone region under jet-cooled conditions using a sequential IR-UV excitation method. Vibrational bands observed at 6933.39(3), 6938.75(4), and 6951.985(3)cm−1 (origins) with relative intensities of 0.42(1), 0.38(1), and 0.20(1) are attributed to strongly mixed states involved in a Fermi resonance. A vibrational deperturbation analysis suggests that the optically bright OH overtone stretch (2ν1) at 6939.2(1)cm−1 is coupled directly to the ν1+2ν2 state at 6946.4(1)cm−1 and indirectly to the 3ν2+ν3+ν7 state at 6938.5(1)cm−1. Both the identity of the zero-order states and the indirect coupling scheme are deduced from complementary CCSD(T) calculations in conjunction with second-order vibrational perturbation theory. The deperturbation analysis also yields the experimental coupling between 2ν1 and ν1+2ν2 of −6.9(1)cm−1, and that between the two dark states of +5.0(1)cm−1. The calculated vibrational energies and couplings are in near quantitative agreement with experimentally derived values except for a predicted twofold stronger coupling of 2ν1 to ν1+2ν2. Weaker coupling of the strongly mixed states to a dense background of vibrational states via intramolecular vibrational energy redistribution is evident from the experimental linewidths of 0.08 and 0.25cm−1 for the higher energy and two overlapping lower energy bands, respectively. A comprehensive rotational analysis of the higher energy band yields spectroscopic parameters and the direction of the OH overtone transition dipole moment.
Heat-and-pull rig for fiber taper fabrication
Authors: Ward Jonathan M. , O’Shea Danny G. , Shortt Brian J. , Morrissey Michael J. , Deasy Kieran , Nic Chormaic Síle G.
Published: August 2006

We describe a reproducible method of fabricating adiabatic tapers with 3–4μm diameter. The method is based on a heat-and-pull rig, whereby a CO2 laser is continuously scanned across a length of fiber that is being pulled synchronously. Our system relies on a CO2 mirror mounted on a geared stepper motor in order to scan the laser beam across the taper region. We show that this system offers a reliable alternative to more traditional rigs incorporating galvanometer scanners. We have routinely obtained transmission losses between 0.1 and 0.3dB indicating the satisfactory production of adiabatic tapers. The operation of the rig is described in detail and an analysis on the produced tapers is provided. The flexibility of the rig is demonstrated by fabricating prolate dielectric microresonators using a microtapering technique. Such a rig is of interest to a range of fields that require tapered fiber fabrication such as microcavity-taper coupling, atom guiding along a tapered fiber, optical fiber sensing, and the fabrication of fused biconical tapered couplers.
Magnetic insulation at finite temperatures
Authors: Goedecke G. H. , Davis Brian T. , Chen Chiping
Published: August 2006

A finite-temperature non-neutral plasma (FTNNP) theory of magnetically insulated (MI) electron flows in crossed-field vacuum devices is developed and applied in planar geometry. It is shown that, in contrast to the single type of MI flow predicted by traditional cold-plasma treatments, the nonlinear FTNNP equations admit five types of steady flow, of which three types are MI flows, including flows in which the electric field and/or the tangential velocity at the cathode may be zero or nonzero. It is also shown that finite-temperature Vlasov-Poisson treatments yield solutions for electron number densities and electrostatic potentials that are a subset of the FTNNP solutions. The algorithms that are used to solve the FTNNP equations numerically are discussed, and the numerical results are presented for several examples of the three types of MI flow. Results include prediction of the existence, boundaries, number density profiles, and other properties of sheaths of electrons in the anode-cathode gap.
How “sticky” are short-range square-well fluids?
Authors: Malijevský Alexandr , Yuste Santos B. , Santos Andrés
Published: August 2006

The aim of this work is to investigate to what extent the structural properties of a short-range square-well (SW) fluid of range λ at a given packing fraction η and reduced temperature T*=kBT∕ϵ can be represented by those of a sticky-hard-sphere (SHS) fluid at the same packing fraction and an effective stickiness parameter τ(T*,λ). Such an equivalence cannot hold for the radial distribution function g(r) since this function has a delta singularity at contact (r=σ) in the SHS case, while it has a jump discontinuity at r=λσ in the SW case. Therefore, the equivalence is explored with the cavity function y(r), i.e., we assume that ySW(r∣η,T*;λ)≈ySHS(r∣η,τ(T*,λ)). Optimization of the agreement between ySW and ySHS to first order in density suggests the choice τ(T*,λ)=[12(e1∕T*−1)(λ−1)]−1. We have performed Monte Carlo (MC) simulations of the SW fluid for λ=1.05, 1.02, and 1.01 at several densities and temperatures T* such that τ(T*,λ)=0.13, 0.2, and 0.5. The resulting cavity functions have been compared with MC data of SHS fluids obtained by Miller and Frenkel[J. Phys.: Condens. Matter 16, S4901 (2004)]. Although, at given values of η and τ, some local discrepancies between ySW and ySHS exist (especially for λ=1.05), the SW data converge smoothly toward the SHS values as λ−1 decreases. In fact, precursors of the singularities of ySHS at certain distances due to geometrical arrangements are clearly observed in ySW. The approximate mapping ySW→ySHS is exploited to estimate the internal energy and structure factor of the SW fluid from those of the SHS fluid. Taking for ySHS the solution of the Percus-Yevick equation as well as the rational-function approximation, the radial distribution function g(r) of the SW fluid is theoretically estimated and a good agreement with our MC simulations is found. Finally, a similar study is carried out for short-range SW fluid mixtures.
On the performance of the intermediate Hamiltonian Fock-space coupled-cluster method on linear triatomic molecules: The electronic spectra of NpO2+, NpO22+, and PuO22+
Authors: Infante Ivan , Severo Pereira Gomes André , Visscher Lucas
Published: August 2006

In this paper we explore the use of the novel relativistic intermediate Hamiltonian Fock-space coupled-cluster method in the calculation of the electronic spectrum for small actinyl ions (NpO2+, NpO22+, and PuO22+). It is established that the method, in combination with uncontracted double-zeta quality basis sets, yields excitation energies in good agreement with experimental values, and better than those obtained previously with other theoretical methods. We propose the reassignment of some of the peaks that were observed experimentally, and confirm other assignments.
An efficient implementation of the “cluster-in-molecule” approach for local electron correlation calculations
Authors: Li Shuhua , Shen Jun , Li Wei , Jiang Yuansheng
Published: August 2006

An efficient implementation of the “cluster-in-molecule” (CIM) approach is presented for performing local electron correlation calculations in a basis of orthogonal occupied and virtual localized molecular orbitals (LMOs). The main idea of this approach is that significant excitation amplitudes can be approximately obtained by solving the coupled cluster (or Møller-Plesset perturbation theory) equations of a series of “clusters,” each of which contains a subset of occupied and virtual LMOs. In the present implementation, we have proposed a simple approach for constructing virtual LMOs of clusters, and new ways of constructing clusters and extracting the correlation contributions from calculations on clusters, which are more efficient than those suggested in the original work. More importantly, linear scaling of computational time of the CIM approach is achieved by evaluating the transformed two-electron integrals over LMOs using simple truncation techniques in limited operations (independent of the molecular size). With typical thresholds, for a variety of molecules our test calculations demonstrate that more than 99% of the conventional MP2 or coupled cluster with doubles correlation energies can be recovered in the present CIM approach.
Potential energy surface intersections in the C(D1)H2 reactive system
Authors: Liu Xiaojun , Bian Wensheng , Zhao Xian , Tao Xutang
Published: August 2006

Potential energy surface (PES) intersection seams of two or more electronic states from the 1A′1, 2A′1, 3A′1, 1A″1, and 2A″1 states in the C(D1)H2 reactive system are investigated using the internally contracted multireference configuration interaction method and the aug-cc-pVQZ basis set. Intersection seams with energies less than 20kcal∕mol relative to the C(D1)+H2 asymptote are searched systematically, and finally several seam lines (at the linear H–C–H, linear C–H–H, and C2v, geometries, respectively) and a seam surface (at Cs geometries) are discovered and determined. The minimum energy crossing points on these seams are reported and the influences of the PES intersections, in particular, conical intersections, on the CH2 spectroscopy and the C(D1)+H2 reaction dynamics are discussed. In addition, geometries and energies of the 1A21 and 1B21 states of methylene biradical CH2 are reported in detail for the first time.
Plasma shaping effects on the collisionless residual zonal flow level
Authors: Xiao Yong , Catto Peter J.
Published: August 2006

Plasma shaping effects, such as elongation, triangularity, and Shafranov shift have long been considered important ingredients in improving tokamak performance. It is known that the growth rate of ion temperature gradient (ITG) turbulence can be regulated by these shaping effects and that the ITG turbulence level can also be regulated by zonal flow. Moreover, recent numerical simulation shows that the collsionless residual zonal flow level can be influenced by these shaping effects. An analytical approach is used to explicitly evaluate plasma shaping effects on the collisionless residual zonal flow. The results show that the residual zonal flow level increases with elongation, triangularity and the Shafranov shift.
Self-diffusion of supercritical water in extremely low-density region
Authors: Yoshida Ken , Matubayasi Nobuyuki , Nakahara Masaru
Published: August 2006

The self-diffusion coefficient D for super- and subcritical water is determined by using the proton pulsed-field-gradient spin echo method at high temperatures and low densities. The density of water is ranged in the steamlike region from 0.0046to0.0650gcm−3 at a supercritical temperature of 400°C, also at 0.0046–0.0079 and 0.0046–0.0462gcm−3 (the steam-branch densities on the coexistence curve and lower) at 200 and 300°C, respectively. The density is precisely determined on the basis of the PVT dependence of the proton chemical shift. The density-diffusivity products in the zero-density limit divided by the square root of the temperature, (ρD)0∕T, are 1.03, 1.28, and 1.44fgm−1s−1K−1∕2 (f, femto) at 200, 300, and 400°C, respectively. The (ρD)0∕T obtained decreases with decreasing temperature and is significantly smaller than the temperature-independent value from the hard sphere model, 1.95fgm−1s−1K−1∕2. The marked temperature dependence reflects the presence of the strong attractive interaction between a pair of water molecules. The magnitude of the experimental D values and the temperature dependence are well reproduced by the molecular dynamics simulation using TIP4P-FQ model. The initial slope of the product ρD∕T against ρ is almost zero at 400°C and slightly negative at 300°C.
Melt dispersion mechanism for fast reaction of nanothermites
Authors: Levitas Valery I. , Asay Blaine W. , Son Steven F. , Pantoya Michelle
Published: August 2006

An unexpected mechanism for fast oxidation of Al nanoparticles covered by a thin oxide shell (OS) is proposed. The volume change due to melting of Al induces pressures of 0.1–4GPa and causes spallation of the OS. A subsequent unloading wave creates high tensile pressures resulting in dispersion of liquid Al clusters, oxidation of which is not limited by diffusion (in contrast to traditional mechanisms). Physical parameters controlling this process are determined. Methods to promote this melt dispersion mechanism, and consequently, improve efficiency of energetic nanothermites are discussed.
Room temperature polariton luminescence from a GaN∕AlGaN quantum well microcavity
Authors: Feltin E. , Christmann G. , Butté R. , Carlin J.-F. , Mosca M. , Grandjean N.
Published: August 2006

The authors report on the demonstration of strong light-matter coupling at room temperature using a crack-free UV microcavity containing GaN∕AlGaN quantum wells (QWs). Lattice-matched AlInN∕AlGaN distributed Bragg reflectors (DBRs) with a maximum peak reflectivity of 99.5% and SiO2∕Si3N4 DBRs were used to form high finesse hybrid microcavities. State-of-the-art GaN∕Al0.2Ga0.8N QWs emitting at 3.62eV with a linewidth of 45meV at 300K were inserted in these structures. For a 3λ∕2 microcavity containing six QWs, the interaction between cavity photons and QW excitons is sufficiently large to reach the strong coupling regime. A polariton luminescence is observed with a vacuum field Rabi splitting of 30meV at 300K.
Analytical approach to impurity transport studies: Charge state dynamics in tokamak plasmas
Authors: Shurygin V. A.
Published: August 2006

Ionization and recombination of plasma impurities govern their charge state kinetics, which is imposed upon the dynamics of ions that implies a superposition of the appropriate probabilities and causes an impurity charge state dynamics. The latter is considered in terms of a vector field of conditional probabilities and presented by a vector charge state distribution function with coupled equations of the Kolmogorov type. Analytical solutions of a diffusion problem are derived with the basic spatial and temporal dimensionless parameters. Analysis shows that the empirical scaling DA∝ne−1 [K. Krieger, G. Fussmann, and the ASDEX Upgrade Team, Nucl. Fusion 30, 2392 (1990)] can be explained by the ratio of the diffusive and kinetic terms, DA∕(nea2), being used instead of diffusivity, DA. The derived time scales of charge state dynamics are given by a sum of the diffusive and kinetic times. Detailed simulations of charge state dynamics are performed for argon impurity and compared with the reference modeling.
Soliton reflection in a negative ion containing plasma: Effect of magnetic field and ion temperature
Authors: Singh Dhananjay K. , Malik Hitendra K.
Published: August 2006

Considering an inhomogeneous plasma having negative ions, positive ions, and electrons, relevant modified Korteweg-de Vries equations are derived and solved for obtaining the expressions of amplitudes and widths of the incident and reflected solitons together with the reflection coefficient under the combined effect of magnetic field, obliqueness (angle θ between the magnetic field and the direction of wave propagation) and ion temperature. A limit is found on the obliqueness θ for the reflection of incident soliton, which shows a dependence on the density, temperature, and drift velocity of both the ions. The incident solitons are observed to reflect more strongly under the effects of weak magnetic field, higher negative ion density, higher ion temperature, stronger density gradient and smaller angle θ. It is inferred that whereas the incident solitons show faster change in their characteristics with the ion density, the reflected solitons are more sensitive to the ion temperature.
Ab initio study of the electronic structure of the crystalline high-mobility organic semiconductor 1,4-diiodobenzene
Authors: Ellman Brett
Published: August 2006

We use ab initio crystalline calculations to explore the role of iodine in determining the properties of 1,4-diiodobenzene. The results strongly suggest that the large halogen is an important or perhaps the dominant determinant of the ability of diiodobenzene to transport holes. We conjecture that the high mobility of diiodobenzene is due to a combination of electronic and phononic effects, both influenced by the presence of the iodine.
Basis set limit electronic excitation energies, ionization potentials, and electron affinities for the 3d transition metal atoms: Coupled cluster and multireference methods
Authors: Balabanov Nikolai B. , Peterson Kirk A.
Published: August 2006

Recently developed correlation consistent basis sets for the first row transition metal elements Sc–Zn have been utilized to determine complete basis set (CBS) scalar relativistic electron affinities, ionization potentials, and 4s23dn−2–4s1dn−1 electronic excitation energies with single reference coupled cluster methods [CCSD(T), CCSDT, and CCSDTQ] and multireference configuration interaction with three reference spaces: 3d4s, 3d4s4p, and 3d4s4p3d′. The theoretical values calculated with the highest order coupled cluster techniques at the CBS limit, including extrapolations to full configuration interaction, are well within 1kcal∕mol of the corresponding experimental data. For the early transition metal elements (Sc-Mn) the internally contracted multireference averaged coupled pair functional method yielded excellent agreement with experiment; however, the atomic properties for the late transition metals (Mn-Zn) proved to be much more difficult to describe with this level of theory, even with the largest reference function of the present work.
A potential model for methane in water describing correctly the solubility of the gas and the properties of the methane hydrate
Authors: Docherty H. , Galindo A. , Vega C. , Sanz E.
Published: August 2006

We have obtained the excess chemical potential of methane in water, over a broad range of temperatures, from computer simulation. The methane molecules are described as simple Lennard-Jones interaction sites, while water is modeled by the recently proposed TIP4P/2005 model. We have observed that the experimental values of the chemical potential are not reproduced when using the Lorentz-Berthelot combining rules. However, we also noticed that the deviation is systematic, suggesting that this may be corrected. In fact, by introducing positive deviations from the energetic Lorentz-Berthelot rule to account indirectly for the polarization methane-water energy, we are able to describe accurately the excess chemical potential of methane in water. Thus, by using a model capable of describing accurately the density of pure water in a wide range of temperatures and by deviating from the Lorentz-Berthelot combining rules, it is possible to reproduce the properties of methane in water at infinite dilution. In addition, we have applied this methane-water potential to the study of the solid methane hydrate structure, commonly denoted as sI, and find that the model describes the experimental value of the unit cell of the hydrate with an error of about 0.2%. Moreover, we have considered the effect of the amount of methane contained in the hydrate. In doing so, we determine that the presence of methane increases slightly the value of the unit cell and decreases slightly the compressibility of the structure. We also note that the presence of methane increases greatly the range of pressures where the sI hydrate is mechanically stable.
Low-energy states of a semiflexible polymer chain with attraction and the whip-toroid transitions
Authors: Ishimoto Y. , Kikuchi N.
Published: August 2006

We establish a general model for the whip-toroid transitions of a semiflexible homopolymer chain using the path integral method and the O(3) nonlinear sigma model on a line segment with the local inextensibility constraint. We exactly solve the energy levels of classical solutions and show that some of its classical configurations exhibit toroidal forms, and the system has phase transitions from a whip to toroidal states with a conformation parameter c=(W∕2l)(L∕2π)2. We also discuss the stability of the toroid states and propose the low-energy effective Green’s function. Finally, with the finite size effect on the toroid states, predicted toroidal properties are successfully compared to experimental results of DNA condensation.
Tailoring holes for improving the efficiency of single-mode photonic crystal waveguide lasers on InP substrate
Authors: Checoury X. , Boucaud P. , Li X. , Lourtioz J.-M. , Derouin E. , Drisse O. , Poingt F. , Legouezigou L. , Legouezigou O. , Pommereau P. , Duan G.-H.
Published: August 2006

The authors show that the use of triangular lattice photonic crystals (PhCs) with wide holes can significantly improve the lasing performances of PhC waveguides in the InP substrate approach. The study is carried out on W2-3 waveguides made in PhCs whose air filling factor is varied from ∼25% to 55%. Intrinsically single-mode laser emissions with reduced threshold (/2) are obtained when the laser mode folds deeply into the gap. Concurrently, the slope of the light-light characteristic is increased by a factor of 14. The laser spectral behavior and threshold evolution are explained from three-dimensional finite difference time domain calculations.
Complementary thermoreflectance and micro-Raman analysis of facet temperatures of diode lasers
Authors: Ochalski Tomasz J. , Pierścińska Dorota , Pierściński Kamil , Bugajski Maciej , Tomm Jens W. , Grunske Tobias , Kozlowska Anna
Published: August 2006

A methodological approach for advanced facet temperature characterization of operating diode lasers is presented. It relies on the concerted application of micro-Raman spectroscopy and thermoreflectance mapping. The latter technique allows for fast facet mapping, whereas the Raman data provide the temperature calibration. Residual effects, e.g., caused by the different reflectances of the materials involved into the laser structure, are discussed. Since both techniques provide rather complementary information, their concerted application appears as an effective tool for advanced device inspection.
Theoretical studies of molecular scale near-field electron dynamics
Authors: Baer Roi , Neuhauser Daniel
Published: August 2006

Near-field scanning microscopy and nonlinear spectroscopy on a molecular scale involve weakly interacting subsystems that dynamically exchange electrons and electromagnetic energy. The theoretical description of such processes requires unified approach to the electron-near-field dynamics. By considering electronic structure and dynamics of two distant clusters or atoms we show that adiabatic local spin-density approximation (ALSDA) fails to describe (even qualitatively) essential details of electron dynamics in weakly interacting systems. A recently developed functional addresses these ailments within a time-dependent setting. With this method we study the spectroscopy of a composite system, namely, two weakly coupled metallic clusters. The near-field (dipole-dipole) coupling and electron transfer display an interesting interplay, producing exponential sensitivity of emission yield to the intercomponent distance.
Molecular beam measurements and Monte Carlo simulations of the kinetics of N2O decomposition on Rh(111) single-crystal surfaces
Authors: Omar Uñac Rodolfo , Bustos Victor , Wilson Jarod , Zgrablich Giorgio , Zaera Francisco
Published: August 2006

The kinetics of N2O decomposition on Rh(111) single-crystal surfaces were investigated both experimentally by isothermal molecular beam measurements and theoretically using a Monte Carlo algorithm. The present work was directed to the understanding of two unusual observations derived from our previous work on this system, namely, (1) the lower rates for N2O decomposition seen at higher reaction temperatures, and (2) the lower total nitrogen yields and final oxygen surface coverages that accompany that behavior. Experimentally, it was determined here that after the rhodium surface is rendered inactive by N2O decomposition at high (520K) temperatures, significant activity is still possible at lower (350K) temperatures. The Monte Carlo simulations explain these observations by assuming that the surface sites required for the activation of adsorbed N2O increase in size with increasing reaction temperature.
Fabrication of inorganic GeO2:SiO2 channel waveguides by ultraviolet imprinting technique
Authors: Rajni  , Pita K. , Yu S. F. , Tjin S. C. , Kam C. H.
Published: August 2006

The authors demonstrate the effective waveguiding channel formation inside an ∼3μm thick photosensitive GeO2(20%):SiO2(80%) planar slab waveguide film prepared using the sol-gel technique by the direct ultraviolet (UV) imprinting technique. This is possible because of the ability to induce large refractive index change (∼10−3) in the films by the UV radiation. Channel waveguides with various refractive index values have been fabricated. The measured modal profiles of the waveguides match well with the simulation results. The simplicity of the direct UV imprinting technique is also shown by the fabrication of a 1×2 multimode-interference 3dB light splitter in one single processing step.
Rapid self-assembly of Ni nanodots on Si substrate covered by a less-adhesive and heat-accumulated SiO2 layers
Authors: Lin Gong-Ru , Kuo Hao-Chung , Lin Huang-Shen , Kao Chih-Chiang
Published: August 2006

Rapid self-aggregation of Ni nanodots on Si substrate covered with a thin SiO2 buffered layer is investigated. The Ni nanodots can hardly self-aggregate on highly heat-dissipated Si substrate with a thermal conductivity of 148W∕mK. Adding a 200-Å-thick SiO2 buffer with an ultralow thermal conductivity of 1.35W∕mK prevents the formation of NiSi2 compounds, enhances the heat accumulation, and releases the adhesion at Ni∕Si interface, which greatly accelerates the self-assembly of Ni nanodots. Dense Ni nanodots with size and density of 30nm and 7×1010cm−2, respectively, can be formatted after rapid thermal annealing at 850°C for 22s.
Carrier carrying capacity of one-step grown suspended carbon nanotube bridge with carbon nanotube contact electrodes: For practical one-dimensional electronics
Authors: Lee Yun-Hi , Lee Jong-Hee , Chung S. J. , Lee S. , Ju B. K.
Published: August 2006

The authors report the carrier transport and electrical breakdown behaviors of micron-long-channel suspended carbon nanotube (CNT) of carbon-based one-dimensional junction with CNTs as drain and source electrodes. The structure consisted of bundle-type CNT electrode–a CNT channel–bundle-type CNT electrode, produced by one-step in situ direct growth via a unique diluted magnetic nanothick film catalyst at low temperature. The unique suspended all-one-dimensional CNT-based junction provides some insights into recent reports that an electrical breakdown of CNTs can be induced not by the contact problem but by the nonhomogeneously Joule heating along nanotube without release of heat into contacts by the observed breakdown at midlength of a 1–2μm long channel. The high current carrying all-CNT junction with bridging yield of 90% and stable operation at fixed voltage level can contribute into realization of practical integrated nanoelectronics such as interconnector and transistor via junction formation of one-step final process.