Electric Field Gradient

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.

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.

The magnetic properties of hematite (␣-Fe 2 O 3 ) particles with sizes of about 16 nm have been studied by use of Mössbauer spectroscopy, magnetization measurements, and neutron diffraction. The nanoparticles are weakly ferromagnetic at temperatures at least down to 5 K with a spontaneous magnetization that is only slightly higher than that of weakly ferromagnetic bulk hematite. At Tտ100 K the Mössbauer spectra contain a doublet, which is asymmetric due to magnetic relaxation in the presence of an electric field gradient in accordance with the Blume-Tjon model. Simultaneous fitting of series of Mössbauer spectra obtained at temperatures from 5 K to well above the superparamagnetic blocking temperature allowed the estimation of the pre-exponential factor in Néel's expression for the superparamagnetic relaxation time, 0 ϭ(6Ϯ4)ϫ10 Ϫ11 s and the magnetic anisotropy energy barrier, E bm /kϭ590 Ϫ120 ϩ150 K. A lower value of the pre-exponential factor, 0 ϭ1.8 Ϫ1.3 ϩ3.2 ϫ10 Ϫ11 s, and a significantly lower anisotropy energy barrier E bm magn /kϭ305Ϯ20 K was derived from simultaneous fitting to ac and dc magnetization curves. The difference in the observed energy barriers can be explained by the presence of two different modes of superparamagnetic relaxation which are characteristic of the weakly ferromagnetic phase. One mode involves a rotation of the sublattice magnetization directions in the basal ͑111͒ plane, which gives rise to superparamagnetic behavior in both Mössbauer spectroscopy and magnetization measurements. The other mode involves a fluctuation of the net magnetization direction out of the basal plane, which mainly affects the magnetization measurements.

The local electronic structure of YBa2Cu3O7 has been calculated using first-principles cluster methods. Several clusters embedded in an appropriate background potential have been investigated. The electric field gradients at the copper and oxygen sites are determined and compared to previous theoretical calculations and experiments. Spin polarized calculations with different spin multiplicities have enabled a detailed study of the spin density distribution to be made and a simultaneous determination of magnetic hyperfine coupling parameters. The contributions from on-site and transferred hyperfine fields have been disentangled with the conclusion that the transferred spin densities essentially are due to nearest neighbour copper ions only with marginal influence of ions further away. This implies that the variant temperature dependencies of the planar copper and oxygen NMR spin-lattice relaxation rates are only compatible with commensurate antiferromagnetic correlations. The theoretical hyperfine parameters are compared with those derived from experimental data.

Dielectrophoresis (DEP), the motion of a particle caused by an applied electric field gradient, can concentrate microorganisms non-destructively. In insulator-based dielectrophoresis (iDEP) insulating microstructures produce non-uniform electric fields to drive DEP in microsystems. This article describes the performance of an iDEP device in removing and concentrating bacterial cells, spores and viruses while operated with a DC applied electric field and pressure gradient. Such a device can selectively trap particles when dielectrophoresis overcomes electrokinesis or advection. The dielectrophoretic trapping behavior of labeled microorganisms in a glass-etched iDEP device was observed over a wide range of DC applied electric fields. When fields higher than a particle-specific threshold are applied, particles are reversibly trapped in the device. Experiments with Bacillus subtilis spores and the Tobacco Mosaic Virus (TMV) exhibited higher trapping thresholds than those of bacterial cells. The iDEP device was characterized in terms of concentration factor and removal efficiency. Under the experimental conditions used in this study with an initial dilution of 1 Â105 cells/ml, concentration factors of the order of 3000Â and removal efficiencies approaching 100% were observed with Escherichia coli cells. These results are the first characterization of an iDEP device for the concentration and removal of microbes in water. D

We demonstrate photon echoes in Eu3+:Y2SiO5 by controlling the inhomogeneous broadening of the Eu3+ 7F0<-->5D0 optical transition. This transition has a linear Stark shift, and we induce inhomogeneous broadening by applying an external electric field gradient. After optical excitation, reversing the polarity of the field rephases the ensemble, resulting in a photon echo. This is the first demonstration of such a photon echo, and its application as a quantum memory is discussed.

T he past decade has witnessed an explosion of techniques used to pattern polymers on the nano (1-100 nm) and submicrometre (100-1,000 nm) scale, driven by the extensive versatility of polymers for diverse applications, such as molecular electronics 1,2 , data storage 3 , optoelectronics 4 , displays 5 , sacrificial templates 6,7 and all forms of sensors. Conceptually, most of the patterning techniques, including microcontact printing (soft lithography) 8 , photolithography 9,10 , electron-beam lithography 11 , block-copolymer templating 12,13 and dip-pen lithography 14 , are based on the spatially selective removal or formation/deposition of polymer. Here, we demonstrate an alternative and novel lithography techniqueelectrostatic nanolithography using atomic force microscopy-that generates features by mass transport of polymer within an initially uniform, planar film without chemical crosslinking, substantial polymer degradation or ablation. The combination of localized softening of attolitres (10 2 -10 5 nm 3 ) of polymer by Joule heating, extremely non-uniform electric field gradients to polarize and manipulate the soften polymer, and single-step process methodology using conventional atomic force microscopy (AFM) equipment, establishes a new paradigm for polymer nanolithography, allowing rapid (of the order of milliseconds) creation of raised (or depressed) features without external heating of a polymer film or AFM tip-film contact.

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.

Five distinctly resolved I7O solid-state NMR resonances in room temperature coesite, an Si02 polymorph, have been observed and assigned using dynamic-angle spinning (DAS) at 11.7 T along with magic-angle spinning (MAS) spectra at 9.4 and 11.7 T. The I7O quadrupolar parameters for each of the five oxygen environments in coesite are correlated with the Si-0-Si bridging bond angles determined by diffraction experiments. The sign of e2qQ/h along with the orientation of the electric field gradient for oxygen in the Si-0-Si linkage were determined from a Townes-Dailey analysis of the data.

An integral-direct implementation of first-order one-electron properties in the coupled cluster singles and doubles ͑CCSD͒ model is presented. The implementation increases the range of applicability of CCSD first-order one-electron property calculations significantly compared to nondirect approaches. As an application a thorough basis set investigation is performed on five diatomic molecules at the Hartree-Fock and CCSD levels for the molecular electric dipole moment, the molecular electric quadrupole moment, and the electric field gradient at the nuclei. In general, basis sets of polarized triple-zeta quality are the smallest to be recommended, and the convergence towards the basis set limit is faster at the Hartree-Fock level than at the CCSD level. Among the properties considered, the electric dipole moment is the easiest to converge. The electric dipole and especially the electric quadrupole moment require diffuse functions for high accuracy. With standard basis sets, it is not possible to calculate electric field gradients consistently within three thousandths of an atomic unit of the basis set limit-for this purpose, elaborate nonstandard basis sets are required. The electric field gradients at the nuclei in HCN and the electric dipole moment of the furan molecule are calculated at the CCSD level employing up to 417 basis functions, further demonstrating the large-scale applicability of the implementation.

An attempt is made to improve the currently accepted muonic value for the 197 Au nuclear quadrupole moment ͓+0.547͑16͒ ϫ 10 −28 m 2 ͔ for the 3 / 2 + nuclear ground state obtained by Powers et al. ͓Nucl. Phys. A230, 413 ͑1974͔͒. From both measured Mössbauer electric quadrupole splittings and solid-state density-functional calculations for a large number of gold compounds a nuclear quadrupole moment of +0.60ϫ 10 −28 m 2 is obtained. Recent Fourier transform microwave measurements for gas-phase AuF, AuCl, AuBr, and AuI give accurate bond distances and nuclear quadrupole coupling constants for the 197 Au isotope. However, four-component relativistic density-functional calculations for these molecules yield unreliable results for the 197 Au nuclear quadrupole moment. Relativistic singles-doubles coupled cluster calculations including perturbative triples ͓CCSD͑T͒ level of theory͔ for these diatomic systems are also inaccurate because of large cancellation effects between different field gradient contributions subsequently leading to very small field gradients. Here one needs very large basis sets and has to go beyond the standard CCSD͑T͒ procedure to obtain any reliable field gradients for gold. From recent microwave experiments by Gerry and co-workers ͓Inorg. Chem. 40, 6123 ͑2001͔͒ a significantly enhanced 197 Au nuclear quadrupole coupling constant in ͑CO͒AuF compared to free AuF is observed. Here, these cancellation effects are less important, and relativistic CCSD͑T͒ calculations finally give a nuclear quadrupole moment of +0.64ϫ 10 −28 m 2 for 197 Au. It is argued that it is currently very difficult to improve on the already published muonic value for the 197 Au nuclear quadrupole moment.

Accurate, yet simple and efficient, formulae are presented for calculation of the electrostatic potential (ESP), electric field (EF) and electric field gradient (EFG) from the aspherical Hansen-Coppens pseudoatom model of electron density . Acta Cryst. A34, 909-921]. They are based on the expansion of |r 0 À r| À1 in spherical harmonics and the incomplete gamma function for a Slater-type function of the form R l (r) = r n exp(Àr). The formulae are valid for 0 r 1 and are easily extended to higher values of l. Special treatment of integrals is needed only for functions with n = l and n = l + 1 at r = 0. The method is tested using theoretical pseudoatom parameters of the formamide molecule obtained via reciprocal-space fitting of PBE/6-31G** densities and experimental X-ray data of Fe(CO) 5 . The ESP, EF and EFG values at the nuclear positions in formamide are in very good agreement with those directly evaluated from density-functional PBE calculations with 6-31G**, aug-cc-pVDZ and aug-cc-pVTZ basis sets. The small observed discrepancies are attributed to the different behavior of Gaussian-and Slater-type functions near the nuclei and to imperfections of the reciprocal-space fit. An EF map is displayed which allows useful visualization of the lattice EF effects in the crystal structure of formamide. Analysis of experimental 100 K X-ray data of Fe(CO) 5 yields the value of the nuclear quadrupole moment Q( 57 Fe m ) = 0.12 Â 10 À28 m 2 after taking into account Sternheimer shielding/antishielding effects of the core. This value is in excellent agreement with that reported by Su & Coppens [Acta Cryst. (1996), A52, 748-756] but slightly smaller than the generally accepted value of 0.16 AE 5% Â 10 À28 m 2 obtained from combined theoretical/spectroscopic studies ). Phys. Rev. Lett. 25, 3545-3548]. Acta Cryst. (2006). A62, 400-408 Anatoliy Volkov et al. Aspherical pseudoatom model 401 research papers research papers 408 Anatoliy Volkov et al. Aspherical pseudoatom model Acta Cryst. (2006). A62, 400-408 letters to the editor 198

We demonstrate an easily-implemented, edge-plate geometry for electrospinning and produce high quality nanofibers from unconfined polymer fluids. We show that for electrospinning in general, the electric field gradient, not just the electric field amplitude, is a critical parameter for successful selfinitiated jetting. Considering a single spinning site, the edge-plate configuration resulted in the same or a higher fabrication rate as traditional needle electrospinning, while producing nanofibers similar in quality (diameter, diameter distribution, and collected mat porosity); moreover, this novel configuration operates without the possibility of clogging and has high potential for scale-up. We analyze the fundamental physical processes which underlie edge-plate electrospinning, including electric field, working distance, and feed rate dependence and the resultant changes to the linear and whipping regions, and thus to the fiber diameter. We conclude that the edge-plate configuration functions in a remarkably similar manner to traditional needle electrospinning.

The molecular geometry and vibrational frequencies of TeF have been calculated using different quantum chemical 6 Ž . Hartree-Fock, MP2, DFT theories in conjunction with various basis set combinations including relativistic effective core potentials supplemented with polarised double-and triple-zeta valence basis sets for Te and with a 6-31 q G U , 6-311q G U and Dunning's correlation consistent bases for F. The results demonstrate that the errors of the individual theories and basis sets are fairly systematic. Investigating the basis set convergence for the molecular geometry, an increase of the valence basis of tellurium resulted in negligible alteration of the calculated bond length. On the other hand, the results were sensitive to the basis set of fluorine. An augmented correlation consistent triple-zeta basis was required to provide theoretical results in agreement with experiment. q 1999 Elsevier Science B.V. All rights reserved.

We present the first relativistic study of the electric-field-gradient induced birefringence (Buckingham birefringence), with application to the series of molecules CX 2 (X = O, S, Se, Te). A recently developed atomicorbital-driven scheme for the calculation of time-dependent molecular properties using one-, two-and four-component relativistic wave functions (Bast et al. in Chem Phys 356:177, 2009) is extended to first-order frequencydependent magnetic-field perturbations, using London atomic orbitals to ensure gauge-origin independent results and to improve basis-set convergence. Calculations are presented at the Hartree-Fock and Kohn-Sham levels of theory and results for CO 2 and CS 2 are compared with previous high-level coupled-cluster calculations. Except for the heaviest member of the series, relativistic effects are small-in particular for the temperature-independent contribution to the birefringence. By contrast, the effects of electron correlation are significant. However, the reliability of standard exchange-correlation functionals in describing Buckingham birefringence remains unclear based on the comparison with high-level coupled-cluster singles-anddoubles calculations.

A microchannel device is presented which separates and focuses charged proteins based on electric field gradient focusing. Separation is achieved by setting a constant electroosmotic flow velocity against step changes in electrophoretic velocity. Where these two velocities are balanced for a given analyte, the analyte focuses at that point because it is driven to it from all points within the channel. We demonstrate the separation and focusing of a binary mixture of bovine serum albumin and phycoerythrin. The device is constructed of intersecting microchannels in poly(dimethylsiloxane)(PDMS) inlaid with hollow dialysis fibers. The device uses no exotic chemicals such as antibodies or synthetic ampholytes, but operates instead by purely physical means involving the independent manipulation of electrophoretic and electroosmotic velocities. One important difference between this apparatus and most other devices designed for field-gradient focusing is the injection of current at discrete intersections in the channel rather than continuously along the length of a membrane-bound separation channel.

A new technique is demonstrated for the simultaneous concentration and high-resolution separation of chiral compounds. With temperature gradient focusing, a combination of a temperature gradient, an applied electric field, and a buffer with a temperature-dependent ionic strength is used to cause analytes to move to equilibrium, zero-velocity points along a microchannel or capillary. Different analytes are thus separated spatially and concentrated in a manner that resembles isoelectric focusing but that is applicable to a greater variety of analytes including small chiral drug molecules. Chiral separations are accomplished by the addition of a chiral selector, which causes the different enantiomers of an analyte to focus at different positions along a microchannel or capillary. This new technique is demonstrated to provide high performance in a number of areas desirable for chiral separations including rapid separation optimization and method development, facile reversal of peak order (desirable for analysis of trace enantiomeric impurities), and high resolving power (comparable to capillary electrophoresis) in combination with greater than 1000-fold concentration enhancement enabling improved detection limits. In addition, chiral temperature gradient focusing allows for real-time monitoring of the interaction of chiral analyte molecules with chiral selectors that could potentially be applied to the study of other molecular interactions. Finally, unlike CE, which requires long channels or capillaries for high-resolution separations, separations of equivalent resolution can be performed with TGF in very short microchannels (mm); thus, TGF is inherently much more suited to miniaturization and integration into lab-on-a-chip-devices. (41) Chankvetadze, B.; Schulte, G.; Blaschke, G. Enantiomer 1997, 2, 157-179. (42) Balss, K. M.; Ross, D.; Begley, H.; Olsen, K. G.; Tarlov, M.

Recently, the structure of the Shaker channel Kv1.2 has been determined at a 2.9-Å resolution. This opens new possibilities in deciphering the mechanism underlying the function of voltage-gated potassium (Kv) channels. Molecular dynamics simulations of the channel, embedded in a membrane environment show that the channel is in its open state and that the gating charges carried by S4 are exposed to the solvent. The hydrated environment of S4 favors a local collapse of the electrostatic potential, which generates high electric-field gradients around the arginine gating charges. Comparison to experiments suggests furthermore that activation of the channel requires mainly a lateral displacement of S4. Overall, the results agree with the transporter model devised for Kv channels from electrophysiology experiments, and provide a possible pathway for the mechanistic response to membrane depolarization.

This article presents results of first-principles calculations of quadrupolar parameters measured by solidstate nuclear magnetic measurement (NMR) spectroscopy. Different computational methods based on density functional theory were used to calculate the quadrupolar parameters. Through a series of illustrations from different areas of solid state inorganic chemistry, it is shown how quadrupolar solid-state NMR properties can be tackled by a theoretical approach and can yield structural information.

Solid-state 27A1, 29Si and 23Na MAS NMR spectra have been obtained for an A1,Si ordered low albite to low microcline ion exchange series for which unit-cell parameters and 298i NMR data have previously been reported. 27A1 t~i vary continuously with composition from 63.4 (_+0.5) ppm for albite to 58.9 (_+0.5) ppm for microdine, and parallel the 29Si chemical shifts assigned to the T2m-site. The 27A1 and 295i chemical shifts for this series correlate well with composition-dependent lattice parameters, most notably cell volume and the angle [201]^b. The linewidths of the 29Si and 27A1 resonances indicate a significant amount of structural disorder in the intem]ediate compositions due to Na, K substitution. The 1 o-width of the distribution of average Si-O-T angles for each T-site is estimated to be about 1 ~ for the Or33 sample. The average 23Na t~i varies monotonically from -8.5 (+ 1)ppm for albite to -24.3 (+ 1)ppm for Or83. Similarly, the average 23Na nuclear quadrupole coupling constant decreases from 2.60 to 1.15 (-+0.05) MHz and the asymmetry parameter of the electric field gradient increases from 0.25 to 0.6 with increasing K-content from albite to Or83. The observed variations in the quadrupole coupling parameters are consistent with simple electrostatic calculations. Higher resolution 23Na spectra of the intermediate compositions obtained at 11.7 T indicate the presence of an inhomogeneous linebroadening which is related to the distribution of Naenvironments. A model based on a random distribution of local compositions does not simulate the spectra, suggesting that the distribution of Na is skewed toward Na-rich clusters. Observation of the ZaNa NMR lineshape of Or49 after short periods of heat treatment indicate that 23Na NMR is very sensitive to the changes in the Na, K distribution accompanying the early stages of exsolution. Reversible changes occur after heating at 530 ~ C for 3 h, whereas heating at 600 ~ C produces no changes, possibly bracketing the position of the coherent spinodal for A1, Si ordered alkali feldspars at this composition.

Prior theoretical studies indicate that the negative spatial derivative of the electric field induced by magnetic stimulation may be one of the main factors contributing to depolarization of the nerve fiber. This paper studies this parameter for peripheral nerve stimulation (PNS) induced by time-varying gradient fields during MRI scans. The numerical calculations are based on an efficient, quasi-static, finite-difference scheme and an anatomically realistic human, full-body model. Whole-body cylindrical and planar gradient sets in MRI systems and various input signals have been explored. The spatial distributions of the induced electric field and their gradients are calculated and attempts are made to correlate these areas with reported experimental stimulation data. The induced electrical field pattern is similar for both the planar coils and cylindrical coils. This study provides some insight into the spatial characteristics of the induced field gradients for PNS in MRI, which may be used to further evaluate the sites where magnetic stimulation is likely to occur and to optimize gradient coil design.

The high-resolution pure rotational spectrum of GaF has been measured using a Balle-Flygare-type Fourier transform spectrometer. Improved nuclear quadrupolar coupling constants and rotational constants have been obtained along with the first reported fluorine spin-rotation constant for gallium fluoride, C I ( 69 Ga 19 F, v ϭ 0) ϭ ϩ32.0(21) kHz. Accurate spin-rotation tensors from microwave or molecular beam spectroscopy are particularly important to NMR spectroscopists and theoreticians because these data provide information about anisotropic nuclear magnetic shielding in the absence of intermolecular effects. For quadrupolar nuclei such as gallium, the quadrupolar interaction is sufficiently large that it is very difficult to characterize shielding tensors directly via NMR spectroscopy. The experimentally determined nuclear quadrupolar coupling constants and spin-rotation constants for GaF are compared with the results of a series of high-level ab initio calculations carried out at various levels of theory with a range of basis sets. Further calculations on BF and AlF, supplemented with available experimental data for InF and TlF, allow for the investigation of trends in nuclear magnetic shielding, spin-rotation, and electric field gradient tensors in the group-13 fluorides. Calculations at the MP2/6-311ϩϩG** and MP2/6-311G(2df, 2pd) levels provide the most consistently satisfactory results in comparison with the experimental data.

Magnetic stimulation of neural tissue is an attractive technology because neural excitation may be affected without requiring implantation of electrodes. Pulsed discharge circuits are typically implemented for clinical magnetic stimulation systems. However, pulsed discharge systems can confound in-vitro experimentation. As an alternative to pulsed discharge circuits, we present a circuit to deliver asymmetric current pulses for generation of the magnetic field. We scaled the system down by using ferrite cores for the excitation coil. The scaled system allows observation using electrophysiological techniques and preparations not commonly used for investigation of magnetic stimulation. The design was refined using a comprehensive set of design equations. Circuit modeling and simulation demonstrate that the proposed system is effective for stimulating neural tissue with electric-field gradients generated by time-varying magnetic fields. System performance is verified through electrical test.

The perturbed angular correlation ͑PAC͒ technique was used to study the hyperfine interactions in the antiferromagnetic and paramagnetic regions of the distorted perovskites LaCrO 3 and LaFeO 3 . The dilute 111 In→ 111 Cd nuclear probes were introduced into the samples through a chemical process. The present measurements cover the temperature ranges from 15 to 848 K for LaCrO 3 and 77 to 1324 K for LaFeO 3 . Two distinct electric-quadrupole interactions were observed in each compound. The lower quadrupole frequency was assigned to the transition-metal atom site while the higher frequency was attributed to the lanthanum site in both cases. Temperature dependence of the electric-quadrupole interaction parameters indicated structural phase transitions at around 512 and 1223 K, respectively, in LaCrO 3 and LaFeO 3 . The phase transitions were associated with the change from an orthorhombic to rhombohedral structure and characterized by a sudden increase in the electric field gradient V zz and a decrease in the asymmetry parameter for both sites. PAC spectra measured below the Néel temperature revealed that at 0 K the supertransferred magnetic hyperfine field on 111 Cd at the Cr site in LaCrO 3 ͑2.4 T͒ is much smaller than at the Fe site in LaFeO 3 ͑19.4 T͒. The magnetic field on 111 Cd at La sites in both compounds is of the order of 0.3 T. Additional measurements were made to determine the magnetic hyperfine field using the probe nucleus 140 La→ 140 Ce. The result reconfirmed that a relatively weak hyperfine field is supertransferred to the probe atoms at La sites.

In this paper, we successfully separated malignant human breast cancer epithelial cells (MCF 7) from healthy breast cells (MCF 10A) and analyzed the main parameters that influence the separation efficiency with an advanced dielectrophoresis (DEP)-activated cell sorter (DACS). Using the efficient DACS, the malignant cancer cells (MCF 7) were isolated successfully by noninvasive methods from normal cells with similar cell size distributions (MCF 10A), depending on differences between their material properties such as conductivity and permittivity, because our system was able to discern the subtle differences in the properties by generating continuously changed electrical field gradients. In order to evaluate the separation performance without considering size variations, the cells collected from each outlet were divided into size-dependent groups and counted statistically. Following that, the quantitative relative ratio of numbers between MCF 7 and MCF 10A cells in each size-dependent group separated by the DEP were compared according to applied frequencies in the range 48, 51, and 53 MHz with an applied amplitude of 8 V pp. Finally, under the applied voltage of 48 MHz-8 V pp and a flow rate of 290μm/s, MCF 7 and MCF 10A cells were separated with a maximum efficiency of 86.67% and 98.73% respectively. Therefore, our suggested system shows it can be used for detection and separation of cancerous epithelial cells from noncancerous cells in clinical applications.

Ž . The structure of the electrical double layer EDL of colloidal systems is discussed. The methods of determination of the most important parameters of the EDL, i.e. the value of the surface-potential , the Stern-potential and the electrokinetic-potential , the U Ž . P I I S 0 0 0 1 -8 6 8 6 9 7 0 0 0 4 3 -2 ( ) ( ) S. Barany A.A. Baran r Ad¨. Colloid Interface Sci. 75 1998 45᎐78 46 field with the space charge near the surface of unipolar conducting particles. This space charge is induced by the strong external field because of the concentration polarisation. ᮊ 1998 Elsevier Science B.V.

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

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.

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.

The elements of the electric field gradient tensor at Li position in the intercalation compound Li x TiS 2 (with x = 0.25, 0.33, 0.67, and 1.0) were calculated with first-principles methods and periodic supercell models. The theoretical results obtained with density functional and Hartree-Fock hybrid methods were compared with experimental field gradients extracted from 7 Li NMR spectra from the literature and from our measurements presented here. The dependence of calculated field gradients on the basis set and the explicit form of the exchange-correlation density functional was investigated. In agreement with earlier studies a pronounced effect of polarization functions at the Li site was observed. After optimization of internal degrees of freedom in LiTiS 2 all methods under consideration give quadrupole coupling constants in close agreement with experiment. For x Ͻ 1 the calculated quadrupole coupling constants were found to depend more sensitively on the method which was attributed to differences in the description of spin localization. The calculations allow one to distinguish between Li atoms placed at octahedral and tetrahedral interstitial sites of the host lattice TiS 2 .

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.

The Mossbauer effect in Te single-crystal absorbers was studied along different crystal axes. Area ratios of the quadrupole doublet were used as an experimental parameter to extract the electric field gradient and mean-square displacement tensors. Experimental data, taken at the temperature of liquid helium, are well fitted by collinear principal axes for the electric field gradient and mean-square displacement tensors. The quadrupole splitting, asymmetry parameter, and mean-square displacement parameters are 4E =7.74+ 0. 10 mm/sec, g = 0.64+0. 04,

It is shown that the anisotropic NMR parameters for half-integer quadrupolar nuclei can be determined using double rotation (DOR) NMR at a single magnetic field with comparable accuracy to multi-field static and MAS experiments. The 17 O nuclei in isotopically enriched L-alanine and OPPh 3 are used as illustrations. The anisotropic NMR parameters are obtained from spectral simulation of the DOR spinning sideband intensities using a computer program written with the GAMMA spin-simulation libraries. Contributions due to the quadrupolar interaction, chemical shift anisotropy, dipolar coupling and J coupling are included in the simulations. In L-alanine the oxygen chemical shift span is 455 ± 20 ppm and 350 ± 20 ppm for the O1 and O2 sites, respectively, and the Euler angles are determined to an accuracy of ±5-10°. For cases where effects due to heteronuclear J and dipolar coupling are observed, it is possible to determine the angle between the internuclear vector and the principal axis of the electric field gradient (EFG). Thus, the orientation of the major components of both the EFG and chemical shift tensors (i.e., V 33 and d 33 ) in the molecular frame may be obtained from the relative intensity of the split DOR peaks. For OPPh 3 the principal axis of the 17 O EFG is found to be close to the O-P bond, and the 17 O-31 P one-bond J coupling ( 1 J OP = 161 ± 2 Hz) is determined to a much higher accuracy than previously.

Elasmobranch ®shes localize weak electric sources at ®eld intensities of <5 gV cm A1 , but the response dynamics of electrosensory primary aerent neurons to near threshold stimuli in situ are not well characterized. Electrosensory primary aerents in the round stingray, Urolophus halleri, have a relatively high discharge rate, a regular discharge pattern and entrain to 1-Hz sinusoidal peak electric ®eld gradients of £20 gV cm A1. Peak neural discharge for units increases as a non-linear function of stimulus intensity, and unit sensitivity (gain) decreases as stimulus intensity increases. Average peak rate-intensity encoding is commonly lost when peak spike rate approximately doubles that of resting, and for many units occurs at intensities <1 lV cm A1. Best neural sensitivity for nearly all units is at 1±2 Hz with a low-frequency slope of 8 dB/decade and a high-frequency slope of A23 dB/decade. The response characteristics of stingray electrosensory primary aerents indicate sensory adaptations for detection of extremely weak phasic ®elds near 1±2 Hz. We argue that these properties re¯ect evolutionary adaptations in elasmobranch ®shes to enhance detection of prey, communication and social interactions, and possibly electric-mediated geomagnetic orientation. Key words Electroreception á Elasmobranch á Neural sensitivity á Response dynamics á Sensory biology Abbreviations AEN ascending eerent neuron á CV coecient of variation á DC resting discharge á EOD electric organ discharge á PTP peak-to-peak

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.

Single-crystal samples of the peptide N-acetyl-D,L-valine (NAV) with the exchangeable amide and carboxyl hydrogens replaced by deuterons were investigated by deuterium NMR spectroscopy. The electric field gradient (EFG) and chemical shift (CS) tensors for the amide and the carboxyl hydrogens, both of which are involved in intermolecular hydrogen bonds, were determined. The relationship of these tensors to the structure of NAV is discussed. The orientations of the EFG and the CS tensors of the amide hydrogen in a protein can provide information about thexlypeptide backbone structure. For NAV the eigenvector of the largest eigenvalue of the EFG tensor coincides with the NH bond direction, as found by X-ray crystallography, within 2 O , and the eigenvector of the intermediate eigenvalue with the normal (Epptidc) to the peptide plane within 1'. The directions of largest and smallest shielding are similarly aligned with =and Epcp,idc, respectively. However, the deviations are considerably larger, namely 9O and 1 1 ", respectively. The anisotropy of the CS tensor is determined to be 13.4 * 2.7 ppm, confirming that the amide hydrogen is involved in a weak hydrogen bond.

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.

Three vanadium complexes of chlorodipicolinic acid (4-chloro-2,6-dipicolinic acid) in oxidation states III, IV, and V were prepared and their properties characterized across the oxidation states. In addition, the series of hydroxylamido, methylhydroxylamido, dimethylhydroxylamido, and diethylhydroxylamido complexes were prepared from the chlorodipicolinato dioxovanadium(V) complex. The vanadium(V) compounds were characterized in solution by 51 V and 1 H NMR and in the solid-state by X-ray diffraction and 51 V NMR. Density Functional Theory (DFT) calculations were performed to evaluate the experimental parameters and further describes the electronic structure of the complex. The small structural changes that do occur in bond lengths and angles and partial charges on different atoms are minor compared to the charge features that are responsible for the majority of the electric field gradient tensor. The EPR parameters of the vanadium(IV) complex were characterized and compared to the corresponding dipicolinate complex. The chemical properties of the chlorodipicolinate compounds are discussed and correlated with their insulin-enhancing activity in streptozoticin (STZ) induced diabetic Wistar rats. The effect of the chloro-substitution on lowering diabetic hyperglycemia was evaluated and differences were found depending on the compounds oxidation state similar as was observed for the vanadium III, IV and V dipicolinate complexes (III, G.R. Willsky, Inorg. Chem. 44 (2005) 5416-5427). However, a linear correlation of oxidation states with efficacy was not observed, which suggests that the differences in mode of action are not simply an issue of redox equivalents. Importantly, our results contrast the previous observation with the vanadium-picolinate complexes, where the halogen substituents increased the insulin-enhancing properties of the complex

We have carried out a theoretical study of the effect of coupling between rotational and translational degrees of freedom first proposed by Michel and Naudts on the elastic constants and phonon frequencies of ionic molecular solids. We have applied our theory to the high-temperature plastic phase of alkali cyanides NaCN, KCN, and RbCN. We find that the competition between short-range repulsion and the interaction of the electric quadrupole moment of the CN ion with the fluctuating electric field gradient strongly influences the elastic softening and ferroelastic instabilities in these systems. The effect of direct intermolecular interaction and anharmonicity is found to be significant in some cases. The ferroelastic transition temperatures for the above three compounds are found to be 337.5, 190, and 179 K which compare favorably with the experimental values 255.4, 156, and 130 K if we note the mean-field nature of our theory. Within our model we can understand the qualitative differences between the cyanides and the superoxides, a similar class of compounds showing drastically different ferroelastic behavior. Our calculations provide a microscopic justification for the use of certain phenomenological parameters by Strauch et al. in their calculation of phonon frequencies in NaCN and KCN at 300 K.

Fully relativistic four-component self-consistent field and correlated calculations at the Mo "ller-Plesset second-order perturbation theory level ͑MP2͒ have been performed for the monofluorides and mono-and trihydrides of lanthanum, lutetium, actinium, and lawrencium. The calculated spectroscopic constants are in good agreement with available experimental data. The calculated bond lengths have been compared with values from nonrelativistic calculations to give an estimate of the effect of relativity on the molecular lanthanide and actinide contraction. The calculated lanthanide contraction at the relativistic MP2 level is 0.12, 0.12, and 0.19 Å for the monohydrides, monofluorides, and trihydrides, respectively. The corresponding results for the actinides are 0.20, 0.15, and 0.28 Å, and we demonstrate that the larger size of the actinide contraction is a consequence of relativistic effects. Between 10% and 30% of the lanthanide contraction and between 40% and 50% of the actinide contraction is caused by relativity in these compounds.

We investigated geometry, energy, ν N-H harmonic frequencies, 14 N nuclear quadrupole coupling tensors, and n O → σ * N-H charge transfer properties of (acetamide) n clusters, with n = 1−7, by means of second-order Møller-Plesset perturbation theory (MP2) and DFT method. Dependency of dimer stabilization energies and equilibrium geometries on various levels of theory was examined. B3LYP/6-311++G** calculations revealed that for acetamide clusters, the average hydrogen-bonding energy per monomer increases from −26.85 kJ mol −1 in dimer to −35.12 kJ mol −1 in heptamer; i.e., 31% cooperativity enhancement. The n-dependent trend of ν N-H and 14 N nuclear quadrupole coupling values were reasonably correlated with cooperative effects in r N-H bond distance. It was also found that intermolecular n O → σ *

Relativistic coupled cluster theory is used to determine accurate electric field gradients in order to provide a theoretical value for the nuclear quadrupole moment of (139)La. Here we used the diatomic lanthanum monohalides LaF, LaCl, LaBr, and LaI as accurate nuclear quadrupole coupling constants are available from rotational spectroscopy by Rubinoff et al. [J. Mol. Spectrosc. 218, 169 (2003)]. The resulting nuclear quadrupole moment for (139)La (0.200+/-0.006 barn) is in excellent agreement with earlier work using atomic hyperfine spectroscopy [0.20(1) barn].

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.

The electric field gradient ͑EFG͒ at the nuclei, the generalized Sternheimer shielding constants and the EFG electric dipole polarizabilities are computed for eight small molecules employing multiconfigurational self-consistent field wave functions and the corresponding linear and quadratic response functions. The molecules studied are H 2 , N 2 , CO, HF, C 2 H 2 , HCl, HCN, and HNC, all of which are linear. For the hydrogen molecule, full configuration-interaction results for the properties are also reported. The dependence of the computed quantities on the basis set and the electron-correlation treatment is analyzed.

The imaginary part of the dielectric function of CuAlO 2 has been calculated including the electron-hole correlation effects within Bethe-Salpeter formalism ͑BSE͒. In the initial step of the BSE solver the band structure was calculated within density-functional theory plus an orbital field ͑LDA/ GGA+ U͒ acting on Cu atoms. We discuss the influence of the strength of the additional orbital field on the band structure, electric field gradients, and the dielectric function. The calculated dielectric function shows very strong electron-hole correlation effects manifested with large binding energies of the lowest excitons. The electron-hole pair for the lowest excitations are very strongly localized at a single Cu plane and confined within only a few neighboring shells.