Electric Field Gradient

Conversion electron-gamma PAC measurements of the 49–37 keV cascade in 80Br through the intermediate 2− state with T 1/2=7.4 ns were performed with a system of two magnetic lens spectrometers and two BaF2 scintillation detectors. The parent 80mBr activity with a halflife of 4.4 hrs was implanted into Ni, Zn and graphite at the ISOLDE separator at CERN. The observed

Electronic structure calculations of cubic SrTiO3 and SrHfO3 are presented. The full-potential linear augmented-plane-wave method is used and exchange-correlation effects are treated by the local-density approximation. The tendency to ferroelectricity of both compounds is explored and compared by displacing the transition metal atom (Ti or Hf) towards one of the oxygens (001 direction). The calculations show that ferroelectricity is favored in SrTiO3 with respect to SrHfO3 and that this fact may be correlated with the degree of hybridization between transition metal d-O p bands as has been found for other related systems. Also a detailed discussion of the calculated electric field gradients is presented.

An experimental and theoretical study is described concerning the dielectric motion of particles in a suspension subject to high-gradient AC electric fields. The experiments were performed on very dilute suspensions of polystyrene latex heads in DI water.

Real-time holographic interferometry and shadowgraph visualization are used to study convection in the fluid between two concentric spheres when two distinct buoyancy forces are applied to the fluid. The heated inner sphere has a constant temperature that is greater than the constant temperature of the outer sphere by ΔT. In addition to the usual gravitational buoyancy from temperature induced density differences, another radial buoyancy is imposed by applying an a.c. voltage difference, ΔV between the inner and outer spheres. The resulting electric field gradient in this spherical capacitor produces a central polarization force. The temperature dependence of the dielectric constant results in the second buoyancy force that is especially large near the inner sphere. The normal buoyancy is always present and, within the parameter range explored in our experiment, always results in a large-scale cell that is axisymmetric about the vertical. We have found that this flow becomes unstabl...

The dependence of the electric field gradients (EFGs) in the Hf-doped LaNis-hydrogen system, as a function of hydrogen composition ratio (X), has been investigated in the range 0<-X-<5.7 using the Time Differential Perturbed Angular Correlation (TDPAC) technique. The TDPAC spectrum of LaNi~ was fitted with a single EFG, while two EFGs were needed to fit the LaNisH x spectra. The first EFG was similar to the one found in metallic LaNi 5 and the second one was interpreted as related to those probe atoms located in the basal plane next to hydrogen interstitial sites located in the same plane. The relative fraction of the probe atoms experiencing these EFGs is dependent on the relative occupation of hydrogen in these sites.

This paper presents the design, fabrication, and testing of a novel electrohydrodynamic (EHD) ion-drag micropump. In order to maximize the electrical field gradients that are responsible for EHD pumping, we incorporated three-dimensional (3-D) triangular bumps of solder as part of the EHD electrodes. To form these bumps, Niobium was sputter-deposited onto a ceramic substrate, coated with photoresist, optically exposed and etched using a reactive ion etcher to define the electrode pattern. The substrate was then "dipped" into a molten solder pool. Since the solder adheres only to the metallic film, bumps of solder form on the electrodes, giving the electrodes a significant 3-D character. The overall dimensions of the micropump are 19 mm 32 mm 1.05 mm. Four different designs were fabricated and tested. Static pressure tests were performed with a 3M Thermal Fluid (HFE-7100) as the working fluid and the optimum design was identified. The results with the thermal fluid were highly promising and indicated a pumping head of up to 700 Pa at an applied voltage of 300 V. The experimental results for the four different designs show that the presence of the 3-D bump structures significantly improves the pumping performance. Also, a much better pumping performance was obtained with the micropump in which the emitter had a saw-tooth shape.

Cobalt-59 NMR experiments have been carried out on single-crystal and polycrystalline (powder) samples of (7)-tris(ethylenediamine)cobalt(III) chloride trihydrate, (7)-[Co(en) 3 ]Cl 3 Á 3H 2 O, and of its dehydrate. In addition, the X-ray crystal structure of the dehydrated sample has been determined. X-ray diffraction measurements confirm a long-held assumption that dehydration has only minor effects on the structure of the [Co(en) 3 ] 3+ cation. Nevertheless, these small differences have a detectable effect on the 59 Co nuclear magnetic resonance properties of these compounds; in particular, the nuclear quadrupole coupling constant, C Q . Straightforward identification of the c-axis for large single crystals of (7)-[Co(en) 3 ]Cl 3 Á 3H 2 O and of its dehydrate allowed us to obtain single-crystal 59 Co NMR data by orienting the crystals in an MAS rotor. Data collected on single crystals and polycrystalline samples indicate that C Q =À3.0570.05 and À2.8070.05 MHz for the hydrated and dehydrated samples, respectively; the signs have been assigned on the basis of a point charge model. The chemical shift tensor principal components were also determined: for the hydrated sample, d > ¼ 728172 ppm, d jj ¼ 700474 ppm and d iso ¼ 7189 ppm; for the dehydrated ARTICLE IN PRESS sample, d > ¼ 728872 ppm, d jj ¼ 700874 ppm and d iso ¼ 7195 ppm. The electric field gradient and chemical shift tensors are axially symmetric, as required by crystal symmetry. r

A computational study at the level of density functional theory (DFT) was carried out to investigate C-H…O_C and N-H…O_C hydrogenbonding interactions (HBs) in the real crystalline cluster of thymine by O-17, N-14 and H-2 calculated nuclear quadrupole resonance (NQR) parameters. To perform the calculations, a hydrogen-bonded pentameric cluster of thymine was created using X-ray coordinates where the hydrogen atoms positions are optimized and the electric field gradient (EFG) tensors were calculated for the target molecule. Additional EFG calculations were also performed for crystalline monomer and an optimized isolated gas-phase thymine. The calculated EFG tensors at the level of B3LYP and B3PW91 DFT methods and 6-311++G ⁎⁎ and CC-pVTZ basis sets were converted to those experimentally measurable NQR parameters, quadrupole coupling constants and asymmetry parameters. The results reveal that because of strong contribution to N-H…O_C HBs, NQR parameters of O 2 , N 1 and N 3 undergo significant changes from monomer to the target molecule in cluster. Furthermore, the NQR parameters of O 2 also undergo some changes because of non-classical C-H…O_C HBs.

Peek's formula is demonstrated to behave in reality as a mere "fiddle factor". An equation alternative to Peek's law is therefore proposed which allows the definition of a true strand coeficient, whose feature is to be only dependent on the number of outer strands for standard condnctors. The formulae and curves shown in this paper largely cover the range of engineering applications and precision requirements.

Structural disorder at the scale of two to three atomic positions around the probe nucleus results in variations of the EFG and thus in a distribution of the quadrupolar interaction. This distribution is at the origin of the lineshape tailing toward high fields which is often observed in the MAS NMR spectra of quadrupolar nuclei in disordered solids. The Czjzek model provides an analytical expression for the joint distribution of the NMR quadrupolar parameters t Q and g from which a lineshape can be predicted. This model is derived from the Central Limit Theorem and the statistical isotropy inherent to disorder. It is thus applicable to a wide range of materials as we have illustrated for 27 Al spectra on selected examples of glasses (slag), spinels (alumina), and hydrates (cement aluminum hydrates). In particular, when relevant, the use of the Czjzek model allows a quantitative decomposition of the spectra and an accurate extraction of the second moment of the quadrupolar product. In this respect, it is important to realize that only rotational invariants such as the quadrupolar product can make sense to describe the quadrupolar interaction in disordered solids.

The basis set dependence of density functional theory computed electric field gradients (EFG) in 3d transition metal compounds is assessed. Uncontraction of basis sets at the metal atom is crucial for a correct description of its EFG. Original and revised TPSS functionals and their hybrid variants perform best for our test set of experimental gas phase-determined nuclear quadrupole coupling constants. Recent range-separated hybrid functionals that perform well for the difficult case of CuCl, do not perform well for our larger test set. Relativistic effects for the latter, evaluated using the Douglas-Kroll-Hess and zero-order regular approximations, are found to be small. Table 4 Uncontracted basis EFG calculations with the revTPSSh functional and different relativistic approximations: V zz values in au, a compared to gas-phase MW data. Comp. NR b DKH1 DKH1-pc c DKH2 DKH2-pc c ZORA Exp.

We have performed magic-angle-spinning solid-state NMR experiments in which protons are recoupled to oxygen-17 nuclei by applying a symmetry-based recoupling sequence at the proton Larmor frequency. Two-dimensional quadrupole-dipole correlation spectra are produced, in which the second-order quadrupolar shift of the oxygen-17 central transition is correlated with the recoupled heteronuclear dipole-dipole interaction. These spectra are sensitive to the relative orientation of the electric field gradient at the site of the oxygen-17 nucleus and the O-H internuclear vector. We also demonstrate experiments in which polarization is transferred from protons to oxygen-17, and show that oxygen-17 signals may be selected according to the protonation state of the oxygen site. We discuss the small observed value of the heteronuclear dipolar splitting in the central-transition oxygen-17 spectra.

deA combination of experiments and ab initio quantum-mechanical calculations has been applied to examine electronic, structural, and hyperfine interactions in pure and Ta-doped zirconium dioxide in its monoclinic phase (m-ZrO2). From the theoretical point of view, the full-potential linear augmented plane wave plus local orbital (APW + lo) method was applied to treat the electronic structure of the doped system including the atomic relaxations introduced by the impurities in the host in a fully self-consistent way using a supercell approach. Different charge states of the Ta impurity were considered in the study and its effects on the electronic, structural, and hyperfine properties are discussed. Our results suggest that two different charge states coexist in Ta-doped m-ZrO2. Further, ab initio calculations predict that depending on the impurity charge state, a sizeable magnetic moment can be induced at the Ta-probe site. This prediction is confirmed by a new analysis of experimental data.

We report on a 59 Co NMR investigation of the trigonal cobaltate Ca 3 Co 2 O 6 carried out on a single crystal, providing precise determinations of the electric field gradient and chemical shift tensors, and of the internal magnetic fields at the nonmagnetic Co I sites, unavailable from former studies on powders. The magnetic-fieldinduced ferri-and ferromagnetic phases at intermediate temperature (e.g., 10 K) are identified by distinct internal fields, well accounted for by purely dipolar interactions. The vanishing transferred hyperfine field at the Co I site indicates that the Co 3+ (I) orbitals do not participate in the intrachain superexchange, in disagreement with a previous theoretical model. The strong Ising character of the system is confirmed experimentally by the field dependence of the resonance lines, indicating that local moments are saturated even at the phase boundaries. In the vicinity of the critical fields, nuclear spin-spin relaxations detect the spin-reversal dynamics of large magnetic assemblies, either Ising chain fragments or finite-size domains, which drive the metamagnetic transitions. Such collective excitations exhibit a glassy behavior, slowing down to subacoustic frequencies and freezing at low temperature. The relevance of such slow-fluctuation modes for the low-temperature multistep behavior reported in the magnetization is discussed.

A review is presented of the present status of the theory, the developed technology and the current applications of dielectrophoresis ͑DEP͒. Over the past 10 years around 2000 publications have addressed these three aspects, and current trends suggest that the theory and technology have matured sufficiently for most effort to now be directed towards applying DEP to unmet needs in such areas as biosensors, cell therapeutics, drug discovery, medical diagnostics, microfluidics, nanoassembly, and particle filtration. The dipole approximation to describe the DEP force acting on a particle subjected to a nonuniform electric field has evolved to include multipole contributions, the perturbing effects arising from interactions with other cells and boundary surfaces, and the influence of electrical double-layer polarizations that must be considered for nanoparticles. Theoretical modelling of the electric field gradients generated by different electrode designs has also reached an advanced state. Advances in the technology include the development of sophisticated electrode designs, along with the introduction of new materials ͑e.g., silicone polymers, dry film resist͒ and methods for fabricating the electrodes and microfluidics of DEP devices ͑photo and electron beam lithography, laser ablation, thin film techniques, CMOS technology͒. Around three-quarters of the 300 or so scientific publications now being published each year on DEP are directed towards practical applications, and this is matched with an increasing number of patent applications. A summary of the US patents granted since January 2005 is given, along with an outline of the small number of perceived industrial applications ͑e.g., mineral separation, micropolishing, manipulation and dispensing of fluid droplets, manipulation and assembly of micro components͒. The technology has also advanced sufficiently for DEP to be used as a tool to manipulate nanoparticles ͑e.g., carbon nanotubes, nano wires, gold and metal oxide nanoparticles͒ for the fabrication of devices and sensors. Most efforts are now being directed towards biomedical applications, such as the spatial manipulation and selective separation/enrichment of target cells or bacteria, high-throughput molecular screening, biosensors, immunoassays, and the artificial engineering of three-dimensional cell constructs. DEP is able to manipulate and sort cells without the need for biochemical labels or other bioengineered tags, and without contact to any surfaces. This opens up potentially important applications of DEP as a tool to address an unmet need in stem cell research and therapy.

Variable temperature 2 H NMR experiments on the orthorhombic phase of selectively deuterated NH 3 BH 3 spanning the static to fast exchange limits of the borane and amine motions are reported. New values of the electric field gradient (EFG) tensor parameters have been obtained from the static 2 H spectra of V zz ) 1.652 ((0.082) × 10 21 V/m 2 and η ) 0.00 ( 0.05 for the borane hydrogens and V zz ) 2.883 ((0.144) × 10 21 V/m 2 and η ) 0.00 ( 0.05 for the amine hydrogens. The molecular symmetry inferred from the observation of equal EFG tensors for the three borane hydrogens and likewise for the three amine hydrogens is in sharp contrast with the C s symmetry derived from diffraction studies. The origin of the apparent discrepancy has been investigated using molecular dynamics methods in combination with electronic structure calculations of NMR parameters, bond lengths, and bond angles. The computation of parameters from a statistical ensemble rather than from a single set of atomic Cartesian coordinates gives values that are in close quantitative agreement with the 2 H NMR electric field gradient tensor measurements and are more consistent with the molecular symmetry revealed by the NMR spectra.

An ab initio investigation of the quadrupole moment, the polarizability anisotropy and the temperature-independent term Ž . entering the electric-field-gradient-induced birefringence EFGB of CO and CS is presented. For the latter property, the 2 2 y40 2 y14.27 " 0.61 = 10 Cm . q

The extended porous framework of divalent transition metal hexacyanocobaltates(III) was studied from the refined crystal structures and adsorption isotherms of H 2 O, CO 2 and N 2 . From the obtained adsorption data the pore accessibility, pore volume, adsorption potentials and nature of the guest-host interactions were evaluated. The properties of the porous framework are modulated by the metal used to form the 3D framework from the elemental building block, the hexacyanocobaltate(III) ion. From that fact, this family of microporous compounds can be considered as tunable zeolites, with a pore volume and a system of pore windows appropriate for separation and storage of small molecules. The adsorption isotherms also reveal that the electric field gradient at the pore surface and the pore accessibility are determined by the metal linked at the N end of the CN groups. These compounds are usually obtained as hydrates. The dehydration process and the thermal stability were studied from thermo-gravimetry combined with X-ray diffraction. The crystal water is lost below 100°C and then the anhydrous structure remains stable, preserving its porous features, up to 250°C. Upon water removal a progressive cell contraction which amounts 4% of cell volume reduction was observed.

A 59C0 NMR study of a series of mixed-metal tetrahedral clusters prepared from the basic structures MCo, (M = Fe, Ru) by the substitution of one, two or three carbonyl groups by phosphines, phosphites, thioethers or amines is described. The variations of the chemical shifts and the linewidths are discussed according to the nature of M and the type of ligand. Some theoretical considerations show the difficulty of interpreting rough correlations found between NMR parameters and electronic properties of the ligands.

Two kinds of non-linear electrophoresis (ef) that can be detected in strong electric fields (several hundred V/ cm) are considered. The first ("classical" non-linear ef) is due to the interaction of the outer field with fieldinduced ionic charges in the electric double layer (EDL) under conditions, when field-induced variations of electrolyte concentration remain to be small comparatively to its equilibrium value. According to the Shilov theory, the non-linear component of the electrophoretic velocity for dielectric particles is proportional to the cubic power of the applied field strength (cubic electrophoresis) and to the second power of the particles radius; it is independent of the zeta-potential but is determined by the surface conductivity of particles. The second one, the so-called "superfast electrophoresis" is connected with the interaction of a strong outer field with a secondary diffuse layer of counterions (space charge) that is induced outside the primary (classical) diffuse EDL by the external field itself because of concentration polarization. The Dukhin-Mishchuk theory of "superfast electrophoresis" predicts quadratic dependence of the electrophoretic velocity of unipolar (ionically or electronically) conducting particles on the external field gradient and linear dependence on the particle's size in strong electric fields. These are in sharp contrast to the laws of classical electrophoresis (no dependence of V ef on the particle's size and linear dependence on the electric field gradient). A new method to measure the ef velocity of particles in strong electric fields is developed that is based on separation of the effects of sedimentation and electrophoresis using videoimaging and a new flowcell and use of short electric pulses. To test the "classical" non-linear electrophoresis, we have measured the ef velocity of non-conducting polystyrene, aluminium-oxide and (semiconductor) graphite particles as well as Saccharomice cerevisiae yeast cells as a function of the electric field strength, particle size, electrolyte concentration and the adsorbed polymer amount. It has been shown that the electrophoretic velocity of the particles/cells increases with field strength linearly up to about 100 and 200 V/cm (for cells) without and with adsorbed polymers both in pure water and in electrolyte solutions. In line with the theoretical predictions, in stronger fields substantial nonlinear effects were recorded (V ef~E 3 ). The ef velocity of unipolar ion-type conducting (ion-exchanger particles and fibres), electron-type conducting (magnesium and Mg/Al alloy) and semiconductor particles (graphite, activated carbon, pyrite, molybdenite) increases significantly with the electric field (V ef~E 2 ) and the particle's size but is almost independent of the ionic strength. These trends are inconsistent with Smoluchowski's equation for dielectric particles, but are consistent with the Dukhin-Mishchuk theory of superfast electrophoresis.

Paper-oil insulation in power transformers is degraded and gradually damaged due to electrical, chemical, mechanical and moisture factors. It is well established from several studies that moisture is a major source of insulation failure in high voltage power transformers. Measurement and monitoring of moisture is essential to predict life and operation condition for power transformers. This paper presents direct optical measurement of water content at paper insulation immersed in transformer oil inside a test cell, which contains a water source, and a capillary paper bridge to transfer water to the paper inside an oil reservoir. Optical measurement of water content was carried out in the near infrared from 900 to 1500 nm band. Experimental studies of light transmission in transformer oil and water are discussed. The criteria to establish the best optical bands for maximum sensitivities are given. The measurement limitations, calibration procedures and an error analysis are presented. The resulting technique can be used for on-line measurements in electrical apparatus that use oil-paper insulation under large electrical field gradients. The presented method has advantages, since it is a direct and fast technique to measure the water transfer to paper immersed in oil, and it could be applied in compact portable equipment at a low cost.

Efficient and robust particle separation and enrichment techniques are critical for a diverse range of lab-on-a-chip analytical devices including pathogen detection, sample preparation, high-throughput particle sorting, and biomedical diagnostics. Previously, using insulatorbased dielectrophoresis (iDEP) in microfluidic glass devices, we demonstrated simultaneous particle separation and concentration of various biological organisms, polymer microbeads, and viruses. As an alternative to glass, we evaluate the performance of similar iDEP structures produced in polymer-based microfluidic devices. There are numerous processing and operational advantages that motivate our transition to polymers such as the availability of numerous innate chemical compositions for tailoring performance, mechanical robustness, economy of scale, and ease of thermoforming and mass manufacturing. The polymer chips we have evaluated are fabricated through an injection molding process of the commercially available cyclic olefin copolymer Zeonor 1060R. This publication is the first to demonstrate insulator-based dielectrophoretic biological particle differentiation in a polymeric device injection molded from a silicon master. The results demonstrate that the polymer devices achieve the same performance metrics as glass devices. We also demonstrate an effective means of enhancing performance of these microsystems in terms of system power demand through the use of a dynamic surface coating. We demonstrate that the commercially available nonionic block copolymer surfactant, Pluronic F127, has a strong interaction with the cyclic olefin copolymer at very low concentrations, positively impacting performance by decreasing the electric field necessary to achieve particle trapping by an order of magnitude. The presence of this dynamic surface coating, therefore, lowers the power required to operate such devices and minimizes Joule heating. The results of this study demonstrate that iDEP polymeric microfluidic devices with surfactant coatings provide an affordable engineering strategy for selective particle enrichment and sorting.

Most conventional derivative-based color edge detectors have shortcomings such as high computational cost, difficulty in implementation and missing edges. In this paper, we propose a new, simple and effective cubical voxels and virtual electric field model (CVVEFM) for edge detection in color images. The main idea is to model a color image as the network of elementary cubical points (voxels) of virtual electric charges. These charges are uniformly distributed on a cube, in electrostatic balance. In this edge detector, three designed operators which provide approximate gradients of each plane color component are determined. The method is based on the combinations of simple cubical voxels (CV) and virtual electric field (VEF) models. The CV model describes the color pixels as cubical voxels. The VEF model describes the voxels as punctual electric charges by mathematical expressions. Both are used simultaneously to describe the color images including more edges than usually used. Fast, easy to implement and satisfactory edge detection due to its characteristics is accomplished with the CVVEFM. Some color images illustrate the results. r

Linear Stark splitting of the H β Balmer line components and spatially resolved optical emission spectroscopy (OES) measurements were used to estimate the electric field gradient in the cathode sheath region (∼70 μm long) of an atmospheric pressure direct current argon flow-stabilized microplasma jet. Also, plasma parameters in the negative glow region were investigated by both OES and electrical diagnostics. The microplasma jet was operated for current ranging from 10 to 110 mA. OH (A 2 Σ + , v = 0 → X 2 Π, v = 0) rotational bands at 306.357 nm and also the Ar 603.213 nm line were used to determine the gas temperature, which ranges from 600 to 1000 K. Electron number density, ranging from 4.

We discuss some accuracy aspects inherent to ab initio electronic structure calculations in the understanding of nuclear quadrupole interactions. We use the projector augmented wave method to study the electric-field gradient (EFG) at both Sn and O sites in the prototype cases SnO and SnO 2 . The term ab initio is used in the standard context of the also called first principles methods in the framework of the Density Functional Theory. As the main contributions of EFG calculations to problems in condensed matter physics are related to structural characterizations on the atomic scale, we discuss the ''state of the art'' on theoretical EFG calculations and make a brief critical review on the subject, calling attention to some fundamental theoretical aspects. r

We report on low-temperature infrared-absorption spectroscopy studies of compensated p-type Ge͑Ga,As͒ samples with varying doping compensation ratios. Previous difficulties in preparing appropriate samples are overcome by neutron-transmutation doping of high-purity, isotopically controlled germanium composed exclusively of 70 Ge and 74 Ge, viz. 70 Ge x 74 Ge 1Ϫx . With this technique, we have produced a series of crystals with compensation ratios between 0.082 and 0.87, while maintaining the net-acceptor concentration ͓Ga͔-͓As͔ constant at 5ϫ10 14 cm Ϫ3 . The observed excitation lines of Ga acceptors broaden linearly with the ionized impurity concentration due to the quadrupole interactions between Ga bound holes and the electric-field gradient. Experimental linewidths are quantitatively compared with existing theories of electric-field broadening developed in the context of donor transitions. We find excellent agreement with the theory based on the correlated distribution of ionized impurity centers.

The present status of surface electric field gradients measured with perturbed "/T-angular correlations (PAC) is reviewed. Experiments concentrate on well-characterized, free surfaces of metals and applications to detection of probe sites and diffusion phenomena are discussed.

The electric field gradients in perovskite SrHfO3 and BaHfO3 powder samples were investigated by means of Perturbed Angular Correlation spectroscopy, using implanted In-111 hyperfine probes. The measurements cover the temperature ranges from 22 to 893 K for SrHfO3 and from 293 to 875 K for BaHfO3, respectively. In both compounds, three quadrupole interactions were established. The largest fraction showing a pronounced dynamic interaction is assigned to In-111/Cd-111 probe atoms on substitutional Hf sites in both compounds. For SrHfO3, the temperature dependence of the dynamic interaction was associated to the Pnma <-> Imma phase transition for SrHfO3 at about 700 K. We discuss the results in relation to those obtained for In-111/Cd-111-probes in PbZrO3 and BaTiO3, and for Hf-181/Ta-181-probes in AHfO(3) (A = Ca, Sr, Ba).

Myoglobin is one of the premature identifying cardiac markers, whose concentration increases from 90 pg/ml or less to over 250 ng/ml in the blood serum of human beings after minor heart attack. Separation, detection, and quantification of myoglobin play a vital role in revealing the cardiac arrest in advance, which is the challenging part of ongoing research. In the present work, one of the electrokinetic approaches, i.e., dielectrophoresis ͑DEP͒, is chosen to separate the myoglobin. A mathematical model is developed for simulating dielectrophoretic behavior of a myoglobin molecule in a microchannel to provide a theoretical basis for the above application. This model is based on the introduction of a dielectrophoretic force and a dielectric myoglobin model. A dielectric myoglobin model is developed by approximating the shape of the myoglobin molecule as sphere, oblate, and prolate spheroids. A generalized theoretical expression for the dielectrophoretic force acting on respective shapes of the molecule is derived. The microchannel considered for analysis has an array of parallel rectangular electrodes at the bottom surface. The potential and electric field distributions are calculated using Green's theorem method and finite element method. These results also compared to the Fourier series method, closed form solutions by Morgan et al. ͓J. Phys. D: Appl. Phys. 34, 1553 ͑2001͔͒ and Chang et al. ͓J. Phys. D: Appl. Phys. 36, 3073 ͑2003͔͒. It is observed that both Green's theorem based analytical solution and finite element based numerical solution for proposed model are closely matched for electric field and square electric field gradients.

Epitaxially stabilized iron monosilicide films having the CsCl structure (c-FeSi) have been investigated by conversion electron Mössbauer spectroscopy and transmission electron microscopy. The 57 Fe Mössbauer parameters ͑isomer shift ␦, linewidth ⌫, and quadrupole splitting ⌬͒ are reported and discussed in terms of the local surrounding of the Fe nucleus. High statistical accuracy and resolution allowed a detailed investigation of the effects of strain and of the structural phase transformation from the epitaxially stabilized to the bulk stable phase. The phase transformation was found to proceed in a rather surprising layer by layer mechanism with smooth interfaces between the epitaxially stabilized, the bulk stable, and a third phase. Results from a molecular-dynamics simulation at constant pressure and temperature of the structural phase transition are presented and compared with the experimental findings. The isomer shift and the electric-field gradient at the Fe nucleus in the strained c-FeSi and in the third phase have been calculated using the ab initio full potential linear muffin-tin orbital method. The Mössbauer parameters of some relevant point defects in c-FeSi have likewise been calculated within this framework.

Cu NMR has been used to observe the evolution of the precipitate structures in the solution treated and quenched dilute alloy Al-1.7 at%Cu following thermal aging. The distinguishable phases in this alloy form in the following sequence (i) fcc a-phase with Cu in random substitutional sites, (ii) Guinier-Preston zones, (iii) qЉ-phase, (iv) qЈ-phase and finally (v) q-phase, where the last two phases are structural variants of CuAl 2 . The Cu site in all five of these phases has been detected as a resolved line in the 63 Cu FT-NMR spectrum at room temperature, together with a line assigned to surface Cu sites on qЈ-phase platelets. Two additional lines have been observed in spectra from specimens containing the q-phase due to Cu substituting for Al in the CuAl 2 structure, and Cu in the CuAl h 2 -phase. Density functional based ab initio electronic structure calculations have been used to reproduce accurately the observed electric field gradient (V zz ) at the Cu site in q-phase CuAl 2 and to explain the relatively narrow 63 Cu lines observed for GPzones, qЉ-phase and qЈ-phase.

A coupled cluster ͑CC͒ investigation is presented for the ͑generalized͒ Sternheimer shieldings and the electric field gradient ͑EFG͒ polarizabilities which describe the effect of external electric fields and field gradients on the electric field gradient at the nuclei. Calculations are performed for the linear molecules N 2 , CO, HF, C 2 H 2 , HCl, HCN, and HNC. Correlation effects are monitored by employing a hierarchy of CC models consisting of CCS, CC2, CCSD, and CC3. The effect of tight basis functions and core correlation is investigated by carrying out CCSD calculations with core-valence basis sets. Accurate theoretical estimates for EFGs, Sternheimer shieldings, and EFG polarizabilities are given and the effects of vibrational corrections are discussed. Our final estimates for the considered EFG properties can be used, for example, in simulations of electric field effects on the EFG at the nuclei in interacting molecules.

In hexacyanometallates, the involved transition metals are usually found with octahedral coordination. The exception corresponds to the hexagonal zinc phases where this metal appears tetrahedrally coordinated to N ends from the CN ligands. Those zinc hexacyanometallates where such atypical coordination appears were identified and for four of them the crystal structure was refined from X-ray diffraction powder patterns using the Rietveld method. Zinc hexacyanoferrates (III), hexacyanocobaltate (III), hexacyanoiridate (III) and the mixed zinc-cesium hexacyanoferrate (II) were found to be dimorphic, cubic (Fm-3m) and hexagonal (R-3c), related to the zinc atom in octahedral or tetrahedral coordination, respectively. In the absence of an exchangeable cation, the hexagonal phases result anhydrous. This last feature was attributed to a low polar character for the pores surface. The Mo¨ssbauer spectrum of hexagonal zinc hexacyanoferrate (III) is an unresolved quadrupole splitting doublet (D ¼ 0.18 mm/s). The iron nucleus is sensing a weak electric field gradient related to a relatively high symmetry for its ligands and charge environment. The IR spectrum appears to be an excellent sensor to identify the coordination for the zinc atom in a given sample. For the tetrahedral coordination, the CN stretching absorption was found at least 8 cm À1 above the frequency observed for this vibration in the octahedral one. For hydrated phases, the crystal water evolves on heating preserving the material porous framework. The temperature at which the material becomes anhydrous parallels the polarizing power of the charge balancing cation sited within the channels. Hexagonal Zn-Cs ferrocyanide becomes anhydrous at 100 1C, while for the Zn-Na analogue a heating close to 200 1C is required. The stability temperature range for the anhydrous phases depends on the nature of the engaged hexacyanometallate anion; the higher stability was observed for hexacyanoferrates (II). Zinc ferricyanide shows the weaker magnetic interaction for the hexagonal modification due to an unfavourable geometry for the overlapping path between the unpaired electrons on the iron(III) atoms. The open 3D porous network is formed by relatively large ellipsoidal cavities, three per cell, communicated through elliptical openings (windows), six per cavity. For dimorphic zinc hexacyanometallates (III), the most compact structure (higher density) corresponds to the hexagonal modification, however, it has the largest cavity windows and cavity (pore) size, and also the higher thermal stability.

Chemical bonding in UFel Ni Al is interpreted within the framework of nonempirical calculations of charge-density distribution, performed by means of the modified statistical method. Maps of constant density in the principal planes of the crystal structure are presented. It is shown that an electron-density (ED) distribution exhibits a pronounced charge transfer from the [Al-Fe(Ni)] plane towards the [U-Fe(Ni)] plane as the Ni concentration in the alloy changes up to x =0.3. As a result of such a transfer, the ED distribution in the latter plane becomes largely nonuniform. Chemical bonding within the [Al-Fe(Ni)] group of ious shows mostly a covalent character. Thus, such regions determine, to a large extent, the electric-field gradient at the ' Fe nuclei. Results of theoretical investigations of chemical bonding peculiarities in the UFel Ni Al alloys are compared with Mossbauer-e6'ect data. On this basis we have attempted to explain the anomalous behavior of the lattice parameters in the solid solutions UFel Ni Al.

^{27}Al and ^{63,65}Cu NMR measurements are reported for powder samples of stable AlCuFe and AlCuRu icosahedral quasicrystals and their crystalline approximants, and for a AlPdMn single grain quasicrystal. Furthermore, ^{27}Al NQR spectra at 4.2 K have been observed in the AlCuFe and AlCuRu samples. From the quadrupole perturbed NMR spectra at different magnetic fields, and from the zero field NQR spectra, a wide distribution of local electric field gradient (EFG) tensor components and principal axis system orientations was found at the Al site. A model EFG calculation based on a 1/1 AlCuFe approximant was successful in explaining the observed NQR spectra. It is concluded that the average local gradient is largely determined by the p-electron wave function at the Al site, while the width of the distribution is due to the lattice contribution to the EFG. Comparison of ^{63}Cu NMR with ^{27}Al NMR shows that the EFG distribution at the two sites is similar, but that the electronic con...

Behavior of atomic oxygen, O 2 and O 3 molecules adsorbed on external surface of H-capped (5,0) singlewalled carbon nanotube is studied using density functional calculations. Geometry optimizations were carried out at B3LYP/6-31G* level of theory using Gaussian 98 suites of program. Binding energies corresponding to chemical adsorption of atomic oxygen, O 2 and O 3 molecules are obtained to be in the range 65-250 kcal/mol. An oxygen atom is found to bind to the outside surface of the nanotubes to give stable epoxide-like and ether structures. Of these, the most stable is the epoxide, with calculated adsorption energy of 68.014 kcal/mol. Calculated chemical shielding, electric filed gradient tensors and their relative orientation at the sites of carbons reveal that atomic oxygen, O 2 and O 3 adsorptions have a dramatic effect on the electronic structure of single-walled carbon nanotubes (SWCNTs). Moreover, total density of states calculations show a significant difference in the density of states at the Fermi level for the two sites of (O-CNT) system.

Results from a solid-state 139 La NMR spectroscopic investigation of the anhydrous lanthanum(III) halides (LaX 3 ; X ¼ F, Cl, Br, I) at applied magnetic fields of 7. 0, 9.4, 11.7, 14.1, and 17.6 T are presented and highlight the advantages of working at high applied magnetic field strengths. The 139 La quadrupolar coupling constants are found to range from 15.55 to 24.0 MHz for LaCl 3 and LaI 3 , respectively. The lanthanum isotropic chemical shifts exhibit an inverse halogen dependence with values ranging from À135 ppm for LaF 3 to 700 ppm for LaI 3 , which represents nearly half of the total lanthanum chemical shift range. The spans of the magnetic shielding tensors also vary widely, from 35 to 650 ppm for the solid LaF 3 through LaI 3 . DFT calculations of the 139 La electric field gradient and magnetic shielding tensors have been performed and provide a qualitative interpretation of the trends observed experimentally. r 2005 Elsevier Inc. All rights reserved.

The ordinary single channel Kondo model consists of one or more spin 1/2 local moments interacting antiferromagnetically with conduction electrons in a metal. This model has provided a paradigm for understanding many phenomena of strongly correlated electronic materials, ranging from the formation of heavy fermion fermi liquids to the mapping to a one-band model in the cuprate superconductors. The simplest extension of this ordinary Kondo model in metals which yields exotic non-Fermi liquid physics is the multichannel Kondo impurity model in which the conduction electrons are given an extra quantum label known as the channel or flavor index. In the overcompensated regime of this model non-Fermi liquid physics is possible, in contrast to the single channel model. We overview here the multichannel Kondo impurity model candidates most extensively studied for explaining real materials, specifically the two level system Kondo model relevant for metallic glasses, nanoscale devices, and some doped semiconductors, and the quadrupolar and magnetic two-channel Kondo models developed for rare earth and actinide ions with crystal field splittings in metals. We provide an extensive justification for the derivation of the theoretical models, noting that whenever the local impurity degree of freedom is non-magnetic a two-channel Kondo model must follow by virtue of the magnetic spin degeneracy of the conduction electrons. We carefully delineate all energetic and symmetry restrictions on the applicability of these models. We describe the various 1 methods used to study these models along with their results and limitations (multiplicative renormalization group, numerical renormalization group, non-crossing approximation, conformal field theory, and abelian bosonization), all of which provide differing and useful views of the physics. We pay particular attention to the role that scale invariance plays in all of these theoretical approaches. We point out in each case how various perturbing fields (magnetic, crystalline electric, electric field gradients, uniaxial stress) may destabilize the non-Fermi liquid fixed point. We then provide an extensive discussion of the experimental evidence for the relevance of the two-level system Kondo model to metallic glasses, nanoscale devices, and of the quadrupolar/magnetic two-channel models to a number of heavy fermion based alloys and compounds. We close with a discussion of the extension of the single impurity models which comprise the main focus of this review to other sytems (Coulomb blockade), multiple impurities, and lattice models. In the latter case, we provide an overview of the relevance of the two-channel Kondo lattice model to non-fermi liquid behavior and exotic superconductivity in heavy fermion compounds and to the theoretical possibility of odd-frequency superconductivity, which is realized (for the first time) in the limit of infinite spatial dimensions for this model.

Cement is the ubiquitous material upon which modern civilisation is built, providing long-term strength, impermeability and durability for housing and infrastructure. The fundamental chemical interactions which control the structure and performance of cements have been the subject of intense research for decades, but the complex, crystallographically disordered nature of the key phases which form in hardened cements has raised difficulty in obtaining detailed information about local structure, reaction mechanisms and kinetics. Solid-state nuclear magnetic resonance (SS NMR) spectroscopy can resolve key atomic structural details within these materials and has emerged as a crucial tool in characterising cement structure and properties. This review provides a comprehensive overview of the application of multinuclear SS NMR spectroscopy to understand compositionestructureeproperty relationships in cements. This includes anhydrous and hydrated phases in Portland cement, calcium aluminate cements, calcium sulfoaluminate cements, magnesia-based cements, alkali-activated and geopolymer cements and synthetic model systems. Advanced and multidimensional experiments probe 1

The electronic properties of the HfNi-hydrogen system has been investigated, as a function of the hydrogen composition ratio (x), using combined Time Differential Perturbed Angular Correlation (TDPAC) technique and standard full-potential Linearized-Augmented-Plane-Wave method. The experimental TDPAC data confirm the presence of a two-step hydrogenation process in this system, with the octahedral holes filled first. The major part of the electric field gradient at the hafnium site is from pYp contribution, shifted down in energy by hydrogen s-states contribution.

The hyperfine interactions at 181 Ta ions on Fe 3+ sites in -Fe 2 O 3 (hematite) were studied in the temperature range 11Y1100 K by means of the perturbed angular correlation (PAC) technique. The 181 Hf( j ) 181 Ta probe nuclei were introduced chemically into the sample during the preparation. The hyperfine interaction measurements allow to observe the magnetic phase transition and to characterize the supertransferred hyperfine magnetic field B hf and the electric field gradient (EFG) at the impurity sites. The angles between B hf and the principal axes of the EFG were determined. The Morin transition was also observed. The results are compared with those of similar experiments carried out using 111 Cd probe.

Sodium germanate glasses of compositions Na 2 O á 9GeO 2 and 2Na 2 O á 9GeO 2 have been studied using solid-state 17 O nuclear magnetic resonance (NMR). Quartz-type and rutile-type GeO 2 were used as examples of oxygen connected to 4-fold and 6-fold coordinated germanium. The 17 O spectra yielded nuclear quadrupole coupling constants, (e 2 qQ/h), asymmetry parameters, (g), and isotropic chemical shifts, (d i ), from line shape simulations. The chemical shifts of oxygen in [GeO 4 ] and [GeO 6 ] units in germania are 70 5 and 160 5 ppm, respectively, with only a small dierence in the quadrupole coupling constant but a larger dierence in the asymmetry parameter. In the Na 2 O±GeO 2 glasses, the quadrupole coupling constant decreases with addition of Na 2 O to the glass with no evidence for any oxygen with a smaller electric ®eld gradient, indicating that there are very few non-bridging oxygens (NBOs) present. The 17 O chemical shift in Na 2 O á 9GeO 2 is similar to that in [GeO 6 ] while in 2Na 2 O á 9GeO 2 the chemical shift is close to that of [GeO 4 ]. Ó

Hyperfine interactions in perovskite-structure RCoO 3 ͑R=Gd,Tb͒ compounds have been measured by perturbed angular correlation technique using 111 Cd and 181 Ta nuclear probes. The electric quadrupole interactions at 111 Cd show two different sites, assigned to probe substituting Gd or Tb and Co atoms. The temperature dependence of quadrupole frequencies shows discontinuities which have been interpreted as thermally activated spin-state transitions from low-spin ground state configuration to the intermediate-spin ͑IS͒ state and from IS state to high-spin state of Co 3+ ion. For 181 Ta only one major interaction was observed, which was assigned to probe at Co sites. Indication of a Jahn-Teller distortion, which stabilizes the intermediate-spin state with orbital ordering, is also pointed out.

The basis set dependence of density functional theory computed electric field gradients (EFG) in 3d transition metal compounds is assessed. Uncontraction of basis sets at the metal atom is crucial for a correct description of its EFG. Original and revised TPSS functionals and their hybrid variants perform best for our test set of experimental gas phase-determined nuclear quadrupole coupling constants. Recent range-separated hybrid functionals that perform well for the difficult case of CuCl, do not perform well for our larger test set. Relativistic effects for the latter, evaluated using the Douglas-Kroll-Hess and zero-order regular approximations, are found to be small. Table 4 Uncontracted basis EFG calculations with the revTPSSh functional and different relativistic approximations: V zz values in au, a compared to gas-phase MW data. Comp. NR b DKH1 DKH1-pc c DKH2 DKH2-pc c ZORA Exp.