Charge Distribution

This paper gives a new insight into the problem of RF MEMS irreversible stiction due to dielectric charging. Previous reported works describing the phenomenon only account for a drift of the actuation characteristics as a whole as they consider uniform charge densities. We demonstrate how the spatial charge distribution in the dielectric layer can result in the failure of the devices. We emphasize the role of the variance of the distribution, a parameter neglected in the literature. Our model can account for a shift of the C-V actuation characteristics but also for a change in its profile. In particular, the pull-out window can be narrowed and even made to disappear as a result of the non-zero variance of the charge distribution. We identify the processing, the contact conditions and the distributed charge depths as variance-and thus failure-enhancer parameters.

The increasing use of Carbon nuclei in cancer therapy centres is motivated by their potential advantages as a very precise high LET radiation. The knowledge of the fragmentation of Carbon nuclei when they interact with the human body is important to evaluate the spatial profile of their energy deposition in the tissues, hence the damage to the tissues neighbouring the tumour. We report here a study of the fragmentation with the nuclear emulsion experimental technique. We have designed, built and exposed to a Carbon nuclei beam a chamber made of Lexan plates alternated with nuclear emulsion films. Lexan plates acted as passive material simulating human body tissues while nuclear emulsion films were used as both tracking devices with micrometric accuracy and ionisation detectors. Such a detector allowed the detection of Carbon interactions produced along their path, the identification of the fragments produced and the measurement of their scattering angle. We have measured the Carbon ion survival probability and studied their interactions. We report on the secondary particle multiplicity and the electrical charge distribution. We give results of the scattering angle of final state fragments as well as the range for H and He. Finally we give the total and partial charge-changing cross-sections for z = 1, 2, 3, 4 which are compared with previous results when available. The present work aims at providing data required as input to Monte Carlo simulations of Carbon ion interactions in the human body and ultimately of their therapeutic effectiveness.

A double-walled carbon nanotube is used to study the radial charge distribution on the positive inner electrode of a cylindrical molecular capacitor. The outer electrode is a shell of bromine anions. Resonant Raman scattering from phonons on each carbon shell reveals the radial charge distribution. A self-consistent tight-binding model confirms the observed molecular Faraday cage effect, i.e., most of the charge resides on the outer wall, even when this wall was originally semiconducting and the inner wall was metallic.

In order to understand the common features of tetrahedral liquids with water-like anomalies, the relationship between local order and anomalies has been studied using molecular dynamics simulations for three categories of such liquids: (a) atomistic rigid-body models for water (TIP4P, TIP4P/2005, mTIP3P, SPC/E), (b) ionic melts, BeF 2 (TRIM model) and SiO 2 (BKS potential) and (c) Stillinger-Weber liquids parametrized to model water (mW) and silicon. Rigid-body, atomistic models for water and the Stillinger-Weber liquids show a strong correlation between tetrahedral and pair correlation order and the temperature for the onset of the density anomaly is close to the melting temperature. In contrast, the ionic melts show weaker and more variable degrees of correlation between tetrahedral and pair correlation metrics, and the onset temperature for the density anomaly is more than twice the melting temperature. In the case of water, the relationship between water-like anomalies and solvation is studied by examining the hydration of spherical solutes (Na + , Cl − , Ar) in water models with different temperature regimes of anomalies (SPC/E, TIP4P and mTIP3P). For both ionic and nonpolar solutes, the local structure and energy of water molecules is essentially the same as in bulk water beyond the second-neighbour shell. The local order and binding energy of water molecules are not perturbed by the presence of a hydrophobic solute. In the case of ionic solutes, the perturbation is largely localized within the first hydration shell. The binding energies for the ions are strongly dependent on the water models and clearly indicate that the geometry of the partial charge distributions, and the associated multipole moments, play an important role. However the anomalous behaviour of the water network has been found to be unimportant for polar solvation.

Surface acoustic waves (SAW) are an ideal tool for the noninvasive detection of conductivity and carrier distributions in otherwise unstructured semiconductor systems. Here we demonstrate a technique that allows for spatially resolved experiments with a resolution of a few acoustic wavelengths. Extremely narrow acoustic paths, excited by tapered interdigital transducers, are employed to probe conductivity proÿles. The method is used to resolve the spatial form of a photogenerated electron-hole plasma and allows for the direct observation of room-temperature drag and transport of electrons and holes in the coherent phonon wind of an intense SAW beam. By the application of a tomographic technique we are able to reconstruct 2D charge distributions.

We present a fully Hamiltonian and computationally efficient scheme to include the electrostatic effects due to the classical environment in a Car-Parrinello mixed quantum Mechanics/molecular mechanics ͑QM/MM͒ method. The polarization due to the MM atoms close to the quantum system is described by a Coulombic potential modified at short range. We show that the functional form of this potential has to be chosen carefully in order to obtain the correct interaction properties and to prevent an unphysical escape of the electronic density to the MM atoms ͑the so-called spill-out effect͒. The interaction between the QM system and the more distant MM atoms is modeled by a Hamiltonian term explicitly coupling the multipole moments of the quantum charge distribution with the classical point charges. Our approach remedies some of the well known deficiencies of current electrostatic coupling schemes in QM/MM methods, allowing molecular dynamics simulations of mixed systems within a fully consistent and energy conserving approach.

We study by means of first-principles pseudopotential method the coordination defects in a-Si and a-Si:H, also in their formation and their evolution upon hydrogen interaction. An accurate analysis of the valence charge distribution and of the "electron localization function" (ELF) allows to resolve possible ambiguities in the bonding configuration, and in particular to identify clearly three-fold (T3) and five-fold (T5) coordinated defects. We found that electronic states in the gap can be associated to both kind of defects, and that in both cases the interaction with hydrogen can reduce the density of states in the gap.

In this (partly review) paper several important situations are analyzed in which molecular systems are distorted, but there are no apparent degeneracies or close in energy states to justify their origin as due to the Jahn-Teller effect (JTE) or pseudo JTE (PJTE). It is shown that in all these cases above the JTE are ''hidden'' in the excited states of the undistorted configuration even when the energy gap to these states is very large, and the involvement of these states in the vibronic coupling explains the JT origin of the distortions. This confirms the general validity of the JTE as the only source of instabilities and distortions of high-symmetry configurations of polyatomic systems. For the example of the ozone molecule, which has no degenerate ground state, neither in the distorted (obtuse-triangular), nor in the undistorted (regular triangular) configurations, and there are no low-lying excited states, the distortion is shown to emerge from the JTE in the excited E state situated at $8.3 eV above the ground state. The JT stabilization energy is more than $9 eV which makes the distorted configuration the lowest in energy.

We present a second-order accurate algorithm for solving the free-space Poisson's equation on a locally-refined nested grid hierarchy in three dimensions. Our approach is based on linear superposition of local convolutions of localized charge distributions, with the nonlocal coupling represented on coarser grids. The representation of the nonlocal coupling on the local solutions is based on Anderson's Method of Local Corrections and does not require iteration between different resolutions. A distributed-memory parallel implementation of this method is observed to have a computational cost per grid point less than three times that of a standard FFT-based method on a uniform grid of the same resolution, and scales well up to 1024 processors.

An analytical threshold voltage model for doublegate MOSFETs with localized charges is developed. From the 2-D Poisson's equation with parabolic potential approximation, a compact threshold voltage model is derived. The proposed model is then verified with a 2-D device simulator. The model can be used to investigate hot-carrier-induced device degradation for various device dimensions and various charge distributions. Index Terms-Double-gate (DG) MOSFETs, hot-carrier effects (HCEs), localized charge, surface potential, threshold voltage.

This paper examines leadership in practice, specifically the interaction of leaders and followers, taking account of context (Spillane, J.P. (2006). Distributed Leadership. San Francisco, CA: Jossey Bass). Employing Gronn's dimensions of concertive action and conjoint agency (Gronn, P. (2002). Distributed leadership as a unit of analysis. Leadership Quarterly, 13, pp. 423-451), different conceptualizations of distributed leadership (DL) are examined, and the influence of a health and social care context on attempts to enact DL is analysed. In so doing, boundary conditions or the limits to distributing leadership in health and social care are identified. The analysis suggests that the collective leadership DL model presented by Denis et al. (Denis, J.-L., Lamothe, L. and Langley, A. (2001). The dynamics of collective leadership and strategic change in pluralistic organizations. Academy of Management Journal, 44, pp. 809-837) is most likely to be enacted in the face of policy and professional pressures towards more concentrated leadership. However, where DL does not encompass conjoint agency, it will tend towards more towards 'nobody in charge' (Buchanan, D.A., Addicott, R., Fitzgerald, L., Ferlie, E. and Baeza, J.I. (2007). Nobody in charge: distributed change agency in healthcare. Human Relations, 60, pp. 1065-1090) or collaborative leadership (Huxham, C. and Vangen, S. (2000). Leadership in the shaping and implementation of collaboration agendas: how things happen in a (not quite) joined-up world. Academy of Management Journal, 43, pp. 1159-1175). Following the analysis, the authors argue that researchers need to move beyond a reified concept of DL, and ask a more straightforward question of how power is distributed.As Gosling et al. suggest (Gosling, J., Bolden, R. and Petrov, G. (2009). Distributed leadership in higher education: what does it accomplish? Leadership, 5, pp. 299-310)

i n t e r n a t i o n a l j o u r n a l o f r e f r i g e r a t i o n 3 1 ( 2 0 0 8 ) 3 5 3 -3 7 0 Charge en frigorigè ne Calcul Conception Circuit frigorifique COP TEWI une approche globale, la ré duction de la charge en frigorigè ne doit conduire à respecter les contraintes environnementales sans affecter les performances é nergé tiques [Montré al 1987, Kyoto 1997]. L'architecture du systè me et la ré partition de la charge sont essentiels; leurs analyses permettent de dé terminer les é lé ments cibles et de dé finir ainsi ceux dans lesquels la charge pourrait ê tre ré duite (é changeurs de chaleur, conduites de liquide, ré servoirs, .). Dans ce travail, nous pré sentons une synthè se des é tudes sur la charge en frigorigè ne dans une installation frigorifique (mé thodes de mesure de charge, corré lations de taux de vide, valeurs caracté ristiques pour les diverses technologies); on é value aussi l'influence de la charge sur le coefficient de performance (COP) et sur la puissance frigorifique. Enfin, on propose un inventaire des diffé rents moyens qui permettent de minimiser la charge d'un systè me frigorifique.

The vertical transition energies for butadiene have been calculated using the CIS/6-3 1 1 (2+)G* theoretical model. The observed energies were satisfactorily reproduced. The charge distribution for each of the excited states was calculated so that the change from the ground-state distribution could be examined. The nature of the Rydberg states are discussed. Quantitative information on the degree of charge-transfer and bond-order changes was obtained for the excited states. The adiabatic geometries of the valence and Rydberg states were examined, and vibrational frequencies for the excited states were calculated, providing agreement with experiment. The triplet states were also studied for both the vertical and adiabatic surfaces. Analysis of the charge density gave information on the charge reorganization that occurs in the excited states. It showed the remarkable similarity of the atomic orbital-like Rydberg states to the corresponding radical cation and, moreover, showed the unique nature of the 1 'B, A -A* valence state. The vertical 2lA, state was examined with the MCSCF method. For a comparison, the 1 'B", 13B,, and 13A, states were studied in the same fashion. The relationship between these states is discussed.

... to as the ellipse and the circle), the latter A THOMAS JAMES HIGGINS, Professor of Electrical Engineering, and DANIEL KINSETH REITAN are of which is a special case of the former. 2. Of such shape that assumption of ... Q_____=_____iA_____i____ tion Esu Esu j=1 ...

Irregularity in charge distribution of an insulator may lead to accelerated aging and electrical breakdown.
However, knowledge of charge distribution on the insulation surface is still insufficient albeit has gained
worldwide attention. The insufficiency is particularly on the charge profile along the string insulator
under AC excitation. Therefore, charges distributions on the surfaces of glass insulators without installed
grading ring are investigated in this paper. Simulation and experimental results were found in good
agreement when studying the charge distribution pattern along glass insulator string where the polarity
of charge swinging occurs at the center of suspension string insulator of I-type.

A new method for calculation of layer charge and charge distribution of smectites is proposed. The method is based on comparisons between X-ray diffraction (XRD) patterns of K-saturated, ethylene glycol-solvated, oriented samples and calculated XRD patterns for three-component, mixed-layer systems. For the calculated patterns it is assumed that the measured patterns can be modeled as random interstratifications of fully expanding 17.1 A Ê layers, partially expanding 13.5 A Ê layers and non-expanding 9.98 A Ê layers. The technique was tested using 29 well characterized smectites. According to their XRD patterns, smectites were classified as group 1 (low-charge smectites) and group 2 (high-charge smectites). The boundary between the two groups is at a layer charge of -0.46 equivalents per half unit-cell. Lowcharge smectites are dominated by 17.1 A Ê layers, whereas high-charge smectites contain only 20% fully expandable layers on average. Smectite properties and industrial applications may be dictated by the proportion of 17.1 A Ê layers present. Non-expanding layers may control the behavior of smectites during weathering, facilitating the formation of illite layers after subsequent cycles of wetting and drying. The precision of the method is better than 3.5% at a layer charge of -0.50; therefore the method should be useful for basic research and for industrial purposes.

Soft matter materials, such as polymers, membranes, proteins, are often electrically charged. This makes them water soluble, which is of great importance in technological application and a prerequisite for biological function. We discuss a few static and dynamic systems that are dominated by charge effects. One class comprises complexation between oppositely charged objects, for example the adsorption of charged ions or charged polymers on oppositely charged substrates of different geometry. Here the main questions are whether adsorption occurs and what the effective charge of the resulting complex is. We explicitly discuss the adsorption behavior of polyelectrolytes on substrates of planar, cylindrical and spherical geometry with specific reference to DNA adsorption on supported charged lipid layers, DNA adsorption on oppositely charged cylindrical dendro-polymers, and DNA binding on globular histone proteins, respectively. In all these systems salt plays an important role, and some of the important features can already be obtained on the linear Debye-Hückel level. The second class comprises effective interactions between similarly charged objects. Here the main theme is to understand the experimental finding that similarly and highly charged bodies attract each other in the presence of multi-valent counterions. This is demonstrated using field-theoretic arguments as well as Monte-Carlo simulations for the case of two homogeneously charged bodies. Realistic surfaces, on the other hand, are corrugated and also exhibit modulated charge distributions, which is important for static properties such as the counterion-density distribution, but has even more pronounced consequences for dynamic properties such as the counterion mobility. More pronounced dynamic effects are obtained with highly condensed charged systems in strong electric fields. Likewise, an electrostatically collapsed highly charged polymer is unfolded and oriented in strong electric fields. All charged systems occur in water, and water by itself is not a very well understood material. At the end of this review, we give a very brief and incomplete account of the behavior of water at planar surfaces. The coupling between water structure and charge effects is largely unexplored, and a few directions for future research are sketched. On an even more nanoscopic level, we demonstrate using ab-initio methods that specific interactions between oppositely charged groups (which occur when their electron orbitals start to overlap) are important and cause ion-specific effects that have recently moved into the focus of interest.

A dipole interaction model (IM) for calculating the molecular second hyperpolarizability, γ, of aliphatic and aromatic molecules has been investigated. The model has been parametrized from quantum chemical calculations of γ at the self-consistent field (SCF) level of theory for 72 molecules. The model consists of three parameters for each element p: an atomic polarizability, an atomic second hyperpolarizability, and an atomic parameter, Φ p , describing the width of the atomic charge distribution. The Φ p parameters are used for modeling the damping of the interatomic interactions. Parameters for elements H, C, N, O, F, and Cl were determined, and typical differences between the molecular γ derived from quantum chemical calculations and from the IM are below 30% and on average around 10%. As a preliminary test, the dipole interaction model was applied to the following molecular systems not included in the training set: the urea molecule, linear chains of urea molecules, and C 60. For these molecules deviations of the IM result for the molecular γ from the corresponding SCF value were at most around 30% for the individual components, which in all cases is a better performance than obtained with semiempirical methods.

The point of departure in this paper is the diagnosis of Hoehn and Szymanski (1999) that the interlocking system of European football creates an unbalanced system. To secure competitive balance at both the European and the national level, they recommend to reform European football into a closed superleague American-style. In this paper I argue for a radically different route. Instead of giving up dominant traditions of European football, like promotion-relegation and the interlocking system, it is possible to maintain the defining characteristics of European football by returning to the state of affairs in the 1950s, before the commercialisation of football through the media started. This requires the free of charge distribution of football matches on TV, which can be justified by standard economic welfare analysis.

Fluctuating-charge models are computationally efficient methods of treating polarization and charge-transfer phenomena in molecular mechanics and classical molecular dynamics simulations. They are also theoretically appealing as they are minimally parameterized, with parameters corresponding to the chemically important concepts of electronegativities and chemical hardness. However, they are known to overestimate charge transfer for widely separated atoms, leading to qualitative errors in the predicted charge distribution and exaggerated electrostatic properties. We present the charge transfer with polarization current equilibration (QTPIE) model, which solves this problem by introducing distance-dependent electronegativities. A graph-theoretic analysis of the topology of charge transfer allows us to relate the fundamental quantities of charge transfer back to the more familiar variables that represent atomic partial charges. This allows us to formulate a unified theoretical framework for fluctuatingcharge models and topological charge descriptors. We also demonstrate the important role of charge screening effects in obtaining correct size extensivity in electrostatic properties. Analyzing the spatial symmetries of these properties allows us to shed light on the role of charge conservation in the electronegativity equalization process. Finally, we develop a water model for use in classical molecular dynamics simulations that is capable of treating both polarization and charge transfer phenomena.

. Molecular electrostatic potentials MEPs are used to investigate the biochemical reactivity of DNA nucleic acid bases Ž . NABs . As a complementary scheme, a Mulliken population analysis is performed to determine internal charge distribution changes when nucleic acids take part in pair complexes and DNA mini-sequences. From the fact that MEPs are capable enough for predicting the formation of different hydrogen bonded pairs among NABs, it is inferred that for these compounds the electrostatic force plays a dominant role. Particular attention is paid to Watson-Crick dimers as they exhibit different preferred sites for an electrophilic attack to these of single nucleic acids. Finally, from the mini-sequences studied here, it is concluded that recognition of DNA segments proceeds at relatively short distances as a result of a poor influence of NABs on sugar and phosphate fragments. All quantum mechanical computations are performed within the density functional formulation. q 1998 Elsevier Science B.V.

Theoretical study of several para-substituted S-Nitroso-thiophenols has been performed using quantum computational ab initio RHF and density functional B3LYP and B3PW91 methods with 6-31G(d,p) basis set. Geometries obtained from DFT calculations were used to perform NBO analysis. It is noted that the weakness in the SAN sigma bond is due to n o1 ! r à S3AN2 delocalisation and is responsible for the longer SAN bond length in para-substituted S-Nitroso-thiophenols. It is also noted that decreased occupancy of the localized r SN orbital in the idealized Lewis structure, or increased occupancy of r à SN of the non-Lewis orbital, and their subsequent impact on molecular stability and geometry (bond lengths) are related with the resulting p character of the corresponding sulfur natural hybrid orbital (NHO) of r SN bond orbital. In addition, the charge transfer energy decreases with the increasing of the Hammett constants of subsitutent groups and the partial charge distribution on the skeletal atoms shows that the electrostatic repulsion or attraction between atoms can give a significant contribution to the intra-and intermolecular interaction.

The vacuum amplitude of the closed membrane theory is investigated using the fact that any three-dimensional manifold has the corresponding Heegaard diagram (splitting) although it is not unique. We concentrate on the topological aspect with the geometry considered only perturbatively. In the simplest case where the action describes the free fields we find that the genus one amplitudes (lens space) are obtained from the S3 amplitude by merely renormalizing the membrane tension. The amplitudes corresponding to the Heegaard diagram of genus two or higher can be calculated as the Coulomb amplitudes with arbitrary charge distributed on a knot or a link which corresponds to the set of branch points of a given regular or an irregular covering space. We also discuss the case of membrane instanton.

We show that the main features of the cuprates superconductors phase diagram can be derived considering the disorder as a key property of these materials. Our basic point is that the high pseudogap line is an onset of phase separation which generates compounds made up of regions with distinct doping levels. We calculate how this continuous temperature dependent phase separation process occurs in high critical temperature superconductors (HTSC) using the Cahn-Hilliard approach, originally applied to study alloys. Since the level of phase separation varies for different cuprates, it is possible that different systems with average doping level pm exhibit different degrees of charge and spin segregation. Calculations on inhomogeneous charge distributions in form of stripes in finite clusters performed by the Bogoliubov-deGennes superconducting approach yield good agreement to the pseudogap temperature T*(pm), the onset of local pairing amplitudes with phase locked and concomitantly, how they develop at low temperatures into the superconducting phase at Tc(pm) by percolation.

A compact analytical model of short-channel AlGaN/ GaN HEMTs in the presence of a current collapse is presented. The model is based on an experimentally established trapping mechanism at the gate edges and relies on significant differences between the characteristic carrier capture-escape times and typical RF signal periods. For the first time, we implement the theory describing electric field distributions in the HEMT gate-to-drain spacing region, with and without trapped charge distributions. By consequently accounting for velocity saturation effects in gated and trapped regions of the device, the presented model shows good agreement with the experimental data. The model uses a minimal number of fitting parameters, most of which are physical parameters describing velocity-field dependence of the carriers.

In this paper, a novel silicon-on-insulator (SOI) metal-semiconductor field-effect transistor (MESFET) with modified charge distribution is presented. Changing charge distribution leads to lower electric field crowding and increased breakdown voltage (V BR ). For modifying charge distribution, a metal region (MR) is utilized in buried oxide of the SOI MESFET. In order to achieve the best results, the MR location and dimensions are optimized carefully. DC and radio frequency characteristics of the SOI MESFET with MR (MR-SOI MESFET) are analyzed by 2-D numerical simulation and compared with conventional SOI MESFET (C-SOI MESFET) characteristics. The simulated results show that the MR has excellent effect on the V BR of the device. The V BR of the MR-SOI MESFET structure improves by 116% compared with that of the C-SOI MESFET structure. Although drain current of the proposed structure reduces slightly, 126% improvement in maximum output power density of the device is achieved due to high enhancement of the V BR . Also, the MR leads to the enhancement of maximum oscillation frequency and maximum available gain of the MR-SOI MESFET structure. As a result, the MR-SOI MESFET structure has superior electrical performances in comparison with the similar device based on the conventional structure.

Curcumin is the main constituent of curry. In its ground state it shows chemo-preventive, chemo-therapeutic, anti-inflammatory and immune stimulating effects, and it is considered as a drug or drug model in the treatment of AIDS and cystic fibrosis. Further biological activity is induced in curcumin by light exposure: cytotoxicity is enhanced and photosensitized antibacterial effects are achieved. For the curcumin cis enol conformer, the fastest deactivation mechanism of the first excited singlet state is an excited-state intra-molecular proton transfer, which brings curcumin back to the ground state. This mechanism, as well as reketonization, interaction with the solvent and photodegradation, compete with the phototherapeutic action. The native compound curcumin carries phenolic hydroxyl and methoxy groups that influence the molecular charge distribution and hence the excited-state intra-molecular proton transfer rate in an unpredictable way. In this work we study static and time-resolved spectroscopic properties of a non-substituted curcuminoid that lacks both the phenolic hydroxyl and the phenolic methoxy groups. The photophysical properties of this compound are compared to those of native curcumin, in order to provide a rationale to the design of curcuminoids with molecular structures optimized for a photosensitizer.

In this work we present a computational approach to the design of nanostructures made of structural motifs taken from left-handed b-helical proteins. Previously, we suggested a structural model based on the self-assembly of motifs taken from Escherichia coli galactoside acetyltransferase (Protein Data Bank 1krr, chain A, residues 131-165, denoted krr1), which produced a very stable nanotube in molecular dynamics simulations. Here we modify this model by changing the charge distribution in the inner core of the system and testing the effect of this change on the structural arrangement of the construct. Our results demonstrate that it is possible to generate the proper conditions for charge transfer inside nanotubes based on assemblies of krr1 segment. The electronic transfer would be achieved by introducing different histidine ionization states in selected positions of the internal core of the construct, in addition to specific mutations with charged amino acids that altogether will allow the formation of coherent networks of aromatic ring stacking, salt-bridges, and hydrogen bonds.

Charge distribution in insulators has received considerable attention but still poses great scientific challenges, largely due to a current lack of firm knowledge about the nature and speciation of charges. Recent studies using analytical microscopies have shown that insulators contain domains with excess fixed ions forming various kinds of potential distribution patterns, which are also imaged by potential mapping using scanning electric probe microscopy. Results from the authors' laboratory show that solid insulators are seldom electroneutral, as opposed to a widespread current assumption. Excess charges can derive from a host of charging mechanisms: excess local ion concentration, radiochemical and tribochemical reactions added to the partition of hydroxonium and hydronium ions derived from atmospheric water. The last factor has been largely overlooked in the literature, but recent experimental evidence suggests that it plays a decisive role in insulator charging. Progress along this line is expected to help solve problems related to unwanted electrostatic discharges, while creating new possibilities for energy storage and handling as well as new electrostatic devices.

This paper presents calculations in charge coupled systems. The method is based upon a finite element approach for solving the Poisson equation and a nonstationary higher-order upstream finite volume scheme on unstructured grids for the transport equation. In contrast to conventional approaches that constrain source distributions to piece-wise constants, a higherorder approximation is obtained by reconstructing the gradient of the charge distribution in the finite volumes. Anisotropy, nonlinearities, and recombination can easily be introduced because conservation is stated in integral form. Interaction with the surrounding neutral gas and the transport phenomena of charged particles are considered in separate turbulent flow models that are described elsewhere (Meroth et al., Int. Symp. Filtration and Separation of Fine Dust, April 1996). . 0304-3886/99/$ -see front matter 1999 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 -3 8 8 6 ( 9 8 ) 0 0 0 4 6 -1

Two simulation packages were used to model the sharing of charge, due to the scattering and diffusion of carriers, between adjacent pixel elements in semiconductors X-ray detectors. The X-ray interaction and the consequent multiple scattering was modelled with the aid of the Monte Carlo package, MCNP. The resultant deposited charge distribution was then used to create the charge cloud profile in the finite element semiconductor simulation code MEDICI. The analysis of the current pulses induced on pixel electrodes for varying photon energies was performed for a GaAs pixel detector. For a pixel pitch of 25 mm, the charge lost to a neighbouring pixel was observed to be constant, at 0.6%, through the energies simulated. Ultimately, a fundamental limit on the pixel element size for imaging and spectroscopic devices may be set due to these key physical principles. r (K. Mathieson).

The solvaton–CS INDO model, previously successfully used to describe the solvatochromic properties of merocyanines, has been extended to the study of the solvent influence on the fluorescence spectra (fluorosolvatochromism) of these dyes. A ketocyanine (M1) and a stilbazolium betaine (M2) were chosen as representatives of positively and negatively solvatochromic behaviours, respectively. The gap of experimental knowledge concerning the emission properties of M2 was filled by a spectrofluorometric analysis in a set of solvents covering a large range of the ET(30) scale. Solvato- and fluorosolvatochromism were described by calculating the S0(eq.)→S1(Franck–Condon) and S1(eq.)→S0(Franck–Condon) transition energies as a function of a polarity factor related to the static dielectric constant of the solvent, and ranging from 0 to 1. The absorbing S0(eq.) and emitting S1(eq.) units (solute molecule + solvent cage) were approximated using the S0 and S1 geometries of the unsolvated molecule and the respective charge distributions fitted to the current value of k(ε). The calculation results fully confirm that S0 and S1 states of merocyanines can be viewed as a mixture of a neutral and a zwitterionic structure whose composition is controlled by the solvent polarity. The plots of the calculated spectral data (absorption and emission maxima and corresponding Stokes shifts) vs k(ε) are in fairly good agreement with those of the experimental data over almost the entire range of the normalized ETN values, thus showing that specific solvent interactions are at least partly simulated within the solvaton–CS INDO scheme. The methodological prerequisites for a correct prediction of solvatochromic shifts are recalled with reference to previous conflicting theoretical interpretations.

Polyaniline (PANI) shows electrical as well as optical property changes when it is in contact with oxidant/reductor gas. In this work, the optical transmittance changes in PANI coatings originated by their exposure to the ammonia gas were detected by a nulling optical transmittance bridge. The adsorption and desorption curves were carefully analysed using Langmuir kinetic theory for the adsorption of ammonia gas on PANI single and PANI±PMMA composite coatings. Because of the inhomogeneous nature of the PANI ®lm surface adsorption isotherms were the best described by Freundlich model. From the numerical ®tting equations it is suggested that there may be two energetically different adsorption sites on the PANI surface for NH 3 molecules, which corroborates with the no-uniform positive charge distribution on the nitrogen atoms of the PANI backbone chains. The activation energy of adsorption and the heat of adsorption were estimated to be about 0.3±0.5 eV at a NH 3 gas concentration of 10±1000 ppm. #

Computational and experimental studies were performed to explore heterogeneous reduction of U 6+ by structural Fe 2+ at magnetite (Fe 3 O 4 ) surfaces. Molecular Fe-Fe-U models representing a uranyl species adsorbed in a biatomic bidentate fashion to an iron surface group were constructed. Various possible charge distributions in this model surface complex were evaluated in terms of their relative stabilities and electron exchange rates using ab initio molecular orbital methods. Freshlycleaved, single crystals of magnetite with different initial Fe 2+ /Fe 3+ ratios were exposed to uranyl-nitrate solution (pH $ 4) for 90 h. X-ray photoelectron spectroscopy and electron microscopy indicated the presence of a mixed U 6+ /U 5+ precipitate heterogeneously nucleated and grown on stoichiometric magnetite surfaces, but only the presence of sorbed U 6+ and no precipitate on sub-stoichiometric magnetite surfaces. Calculated electron transfer rates indicate that sequential multi-electron uranium reduction is not kinetically limited by conductive electron resupply to the adsorption site. Both theory and experiment point to structural Fe 2+ density, taken as a measure of thermodynamic reducing potential, and sterically accessible uranium coordination environments as key controls on uranium reduction extent and rate. Uranium incorporation in solid phases where its coordination is constrained to the uranate type should widen the stability field of U 5+ relative to U 6+ . If uranium cannot acquire 8-fold coordination then reduction may proceed to U 5+ but not necessarily U 4+ .

Using 4-methoxylphenylhydra zine hydrochloride (1a) as starting material, 2-[2-(4-methoxyphenyl) hydrazono] acetic acid (2a) was prepared after treatment with 1 equivalent of 2-oxoacetic acid, and 3-(4-methoxyphenyldiazo) acrylic acid (3a) was obtained with 2 equivalents of 2-oxoacetic acid through a novel reaction. The mechanism of reaction was analyzed with the help of charge distribution computation. This suggests that the novel reaction depends on the electronegativity of C9, which can be mainly affected by the substituents of the benzene ring.

Despite steady progress in the understanding of electrokinetic or seismoelectric processes over the years, further field studies are needed to develop acquisition methodology as well as processing for testing the electrokinetic (EKS) method's viability. Many past studies appear to be opportunistic rather than controlled tests. Very few of the researchers cited have published more than one example of field data, and generally these reports show electrokinetic signals from only one layer (water table or weathered base), e.g., glacial till interface. This may be blamed upon the very weak signals (µV/m to mV/m) that are extremely difficult to measure, and also a lack of predictive theory to design experiments to test hypotheses.

We show that the single quasi-particle Schr\"odinger equation for a certain form of one-body potential yields a stationary one soliton solution. The one-body potential is assumed to arise from the self- interacting charge distribution with the singular kernel of the Calogero-Sutherland model. The quasi-particle has negative or positive charge for negative or positive coupling constant of the interaction. The magnitude of the charge is unity only for the semion. It is also pointed out that for repulsive coupling, our equation is mathematically the same as the steady-state Smoluchowski equation of Dyson's Coulomb gas model.

Molecular dynamics simulations for liquid CaAl 2 Si 2 O 8 have been carried out at 72 state points spanning ranges in density (q: 2398-4327 kg/m 3 ), temperature (T: 3490-6100 K) and pressure (P: 0.84-120 GPa) relevant to geosystems. The atomic scale structure of the melt is determined by analysis of nearest neighbor coordination statistics as a function of T and P. Dramatic structural change occurs as pressure increases especially for 0 < P <20 GPa at all temperatures. Changes in structure are encapsulated by examining the coordination of Si, Al, Ca and O around oxygen and vice versa. Si and Al change from predominantly fourfold at low-P to dominantly sixfold for P >$ 20 GPa. Pentahedrally coordinated Si and Al in distorted trigonal bipyramids attain abundance maxima corresponding to $60% of total (Si, Al)O n at 3-5 GPa and weakly depend on T. The coordination of Ca by oxygen increases from 7 to 10 for 0 < P < 20 GPa and changes slowly for P > 20 GPa at 3500 K. Similar behavior is seen at 6000 K except that the interval of rapid changes occurs at higher pressure. Oxygen with only one nearest Si or Al neighbor (i.e., non-bridging oxygen, NBO) decreases whereas oxygen with two or three nearest neighbors of Si, Al or Ca increases as pressure increases. Changes in melt structure are reflected in the variation of thermodynamic and transport properties of the liquid. Values of the self-diffusivities of Ca, Al, Si and O are fit to a modified Arrhenian expression and compare well to limited laboratory data. Self-diffusivities are best fit using 'low P' and 'high-P' expressions, identical in form but with different parameters, with activation energies and activation volumes in the range 150-200 kJ/mol and +5 to À1 cm 3 /mol, respectively. Green-Kubo calculations for liquid shear viscosity are presented and compare well with limited laboratory results. Application of the Eyring model to determine the characteristic size and number of atoms in the activated cluster based on independently computed D and g suggests that the activated cluster decreases from $8 to $3 atoms from low to high pressure while its characteristic size shrinks from $14 Å to $3 Å providing insight into dynamics of atom mobility and possible cooperative behavior. The equation of state and variation of internal energy with T and V are used in Part II to derive a comprehensive thermodynamic description of liquid CaAl 2 Si 2 O 8 . This is best accomplished by allowing for EOS expressions broken into high and low pressure intervals consistent with coordination statistics and MD-derived transport properties.