Dipole Moment Method Research Articles

Polarizability of red blood cells with an anisotropic membrane

We predict the complex polarizability of a realistic model of a red blood cell (RBC), with an inhomogeneous dispersive and anisotropic membrane. In this model, the frequency-dependent complex electrical parameters of the individual cell layers are described by the Debye equation while the dielectric anisotropy of the cell membrane is taken into account by the different permittivities along directions normal and tangential to the membrane surface. The realistic shape of the RBC is described in terms of the Jacobi elliptic functions. To calculate the polarizability, we evoke the effective dipole moment method to determine the cell internal electric field distribution, employing an adaptive finite-element numerical approach. We have furthermore investigated the influence of the anisotropic membrane and dispersive electrical parameters of each individual cell layer on the total complex polarizability. Our findings suggest that the individual layer contribution depends on two factors: the volume of the layer and the associated induced electric field, which in turn is influenced by other layers of the cell. These results further show that the average polarizability spectra of the cell are significantly impacted by the anisotropy and associated dispersion of the cellular compartments.

A hybrid equivalent dipole moment and adaptive modified characteristic basis function method for electromagnetic scattering by multilayered dielectric bodies

In this article, the equivalent dipole moment (EDM) method is extended and applied to analyze the electromagnetic scattering of multilayered dielectric bodies. Besides the advantage of reducing the computation time, the proposed EDM method makes it unnecessary to treat the boundary condition on the surface or the interface of the multilayered dielectric body. However, the EDM method is incapable of saving memory. In this case, the adaptive modified characteristic basis function (AMCBF) method is introduced and combined with the EDM method. Numerical results are given to demonstrate the merits of this EDM-AMCBF method. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.

Process parameters and their relations for the dielectrophoretic assembly of carbon nanotubes

The selection of process parameters, which include the concentration of the carbon nanotube (CNT) suspension, the magnitude of the applied voltage, and the duration of the electric field, is significant in the assembly of a small number of CNTs across an electrode gap by dielectrophoresis (DEP). This paper investigates by simulation and experimentation these parameter relations. The simulation is based on the effective dipole moment method and considers the DEP force and viscous force on the CNT by the liquid medium. The method can be used to predict the assembly of a CNT originally located at any position within the electric field. The results demonstrate that the assembly time depends on the distance between the CNT and the electrode gap, as well as the magnitude of the applied voltage. Experiments confirm assembly times after recognizing the differences between the simulation and the experimental conditions. The results can help analyze the assembly of CNTs between electric conductors and help select DEP process parameters.

Numerical calculation of the dielectrophoretic force on a slender body

In this paper, a model is proposed to numerically calculate the dielectrophoretic (DEP) force acting on a straight slender body in a non-uniform electric field. The induced charges are assumed to be located along the centerline of the slender body. By enforcing the boundary conditions at the interfaces of the two dielectrics, an integral equations system is obtained with the induced charge densities as unknowns. Based on the calculated induced charge densities, expressions to calculate the DEP force and torque are obtained. The calculated induced charge density of a prolate ellipsoid under a uniform electric field is compared with the analytic solution and an excellent agreement is achieved. The smaller the slenderness (the ratio of maximum radius to length of the slender body), the smaller the error is. The DEP force that a prolate ellipsoid experiences in a general electric field is numerically calculated and compared with the results obtained by the commonly accepted effective dipole moment method. The current model is expected to possess higher accuracy than the effective dipole moment method and to demand less calculation work than the Maxwell stress tensor method.

Dipole moments and structure of ortho-diphenyl(diethyl)phosphinoyl-substituted benzyl alcohols, phenols, and their derivatives

The method of dipole moments and DFT B3LYP/6-31G* quantum-chemical calculations were used to study the structures of ortho-substituted aryl-and arylmethyldiphenyl(diethyl)phosphine oxides. It was established that methyl ethers of phosphorus-containing benzyl alcohols and phenols exist as equilibrium mixtures of several conformers with prevalence of forms with the weakest steric interactions. Preferred conformers of o-[(diethylphosphinoyl)methyl]benzyl alcohol and i-[(diphenylphosphinoyl)methyl]phenol contain an intramolecular hydrogen bond between the hydroxyl hydrogen atom and phosphinoyl oxygen atom.

Dipole moments, structure, and transannular interactions in silatranes containing planar fragments

The method of dipole moments and theoretical calculations (DFT B3LYP/6-31G*) were used for structural assessment of silatranes N[CH2(RMeC6H2)O]3SiR1 containing planar fragments in the six-membered semirings. They are endo structures with transannular N→Si interaction which involves, along with nitrogen and silicon, oxygen atoms adjacent to silicon.

Structure of 16-hydroxyisosteviol-derived dicarboxylic acid esters

Dielcometry, method of dipole moments, IR spectroscopy, and computer simulation were used to show that dicarboxylic acid esters derived from 16-hydroxyisosteviol (ent-16-hydroxybeyeran-19-oic acid) exist in CCl4 solutions as tweezer-like or open-chain structures, or dimers with various steric structures, depending on the degree of dilution. Concentrations at which both the esters and parent dicarboxylic acids undergo structural rearrangement were established. The structure of three esters was confirmed by X-ray diffraction.

Conformational analysis of 2-substituted 1-nitro-and 1-bromo-1-nitroethenes

Conformational analysis of 2-trichloromethyl(ethoxycarbonyl)-1-nitro-and 2-trichloromethyl-(ethoxycarbonyl)-1-bromo-1-nitroethenes was performed using the dipole moment method, IR spectroscopy, and DFT quantum-chemical calculations (B3LYP/6-31G*). The nitro and ester (or trichloromethyl) groups in the molecules of these compounds were found to occupy trans positions with respect to the double C=C bond, i.e., the nitroalkenes have E, and their bromine-containing analogs, Z configuration; the compounds having an ethoxycarbonyl group are characterized by s-cis orientation of the C=C and C=O bonds.

Conformational analysis of 1,4-heterophosphinanes

Conformational analysis of 1,4-heterophosphinanes in solution, based on a combination of the dipole moment and Kerr effect methods, molecular mechanics, and quantum-chemical calculations (B3LYP/6-31G*) was performed. It was established that, regardless the second heteroatom in the six-membered phosphorus-containing heterocycle (oxygen, sulfur, or silicon) and phosphorus coordination, these compounds prefer a chair conformation with an equatorial exocyclic phenyl substituent.

First-principles calculations of dielectric constants for ultrathin SiO2 films

We studied the dielectric properties of ultrathin SiO2 films using two methods, internal field method and dipole moment method, based on first-principles calculations of the ground state in a finite electric field. We evaluated the optical and static dielectric constants, ε∞ and ε0, of H-terminated β-quartz (0001) films through calculations without and with the lattice relaxation in the electric field applied, respectively. The calculated values of ε∞ and ε0 with these two methods are in good agreement with each other, and they reproduce well the experimental values. Both the optical and static dielectric constants hardly depend on the film thickness, and the spatial variation of the local dielectric constant is also very small. These results indicate that both the surface effect and the quantum confinement effect are small for the ultrathin H-terminated β-quartz (0001) films.

Conformational analysis of mono-and bis(dimethoxyphosphoryl)benzenes

Conformational analysis of mono-and bis(dimethoxyphosphoryl)benzenes with substituents in the benzene ring was performed by the method of dipole moments, IR spectroscopy, and quantum-chemical calculations (DFT B3LYP/6-31G*). Comparison of all calculated and experimental data shows that the compounds studied exist as equilibrium mixtures of conformers with preferred gg orientation of the phosphoryl and methoxy groups.

Dielectric Properties of Ultra-thin Semiconducting Films

We have explored dielectric properties of ultra-thin Si(111) films using two different evaluation methods based on the first-principles calculations, the internal field (IF) method and the dipole moment (DM) method. As the thickness of the film increases, the dielectric constant evaluated at the innermost region of the film approaches a value near to the experimental bulk dielectric constant at a thickness of only 8 bi-layers. The theoretical value of the electronic dielectric constant for the Si(111) film is 12.85, which is only 6.2% higher than the experimental one. Furthermore, we have shown that the IF method is applicable to microscopic analysis of dielectric properties. The spatial variation in dielectric constant near the surface reveals that depolarized charges at the surface penetrate into the film up to the thickness of 3 bi-layers, resulting in an effective reduction of the dielectric constant near the surface. We have also discussed a microscopic picture of polarization on atomic scale.

Equivalent Dipole Moment Method to Characterize Magnetic Fields Generated by Electric Appliances: Extension to Intermediate Frequencies of Up to 100 kHz

A previously proposed simple method to characterize magnetic fields near electric appliances was extended to intermediate frequencies of up to 100 kHz. The method consists of identification of the magnetic dipole moment that is equivalent to a magnetic field source of an electric appliance and simple estimation of the magnetic field distribution around the appliance. In addition, frequency characteristics of the magnetic field were taken into account by considering the harmonic components in the magnetic-field waveform for both power frequency and intermediate frequency ranges. For the application of the method, a wide-frequency range (from power frequency to 100 kHz) magnetic-field measuring instrument was developed and applied to appliances that generate intermediate frequency magnetic fields, i.e., an induction heating cooker, a TV set, and a metal detector. The results revealed that the method is adequate to quantify the magnetic field near the electric appliances at frequencies of up to 100 kHz.

Discrete dipole moment method for calculation of the T matrix for nonspherical particles.

A computational method, based on a moment solution to the discrete dipole approximation (DDA) interaction equations, is proposed for calculation of the T matrix of arbitrary-shaped particles. It is shown that the method will automatically provide the conservation-of-energy and origin-invariance properties required of the T matrix. Furthermore, the method is significantly faster than a T-matrix calculation by direct inversion of the DDA equations. Because the method retains the dipole lattice representation of the particle, it can be applied with relative ease to particles with irregular shapes-although in the same respect it will not automatically simplify for axisymmetric particles. Calculations of scattering matrix distributions, in fixed and random orientations, are made for tetrahedron, cylindrical, and prolate spheroid particle shapes and compared with DDA and extended boundary condition method results.

Conformational analysis and regioisomerism of mono- and diadducts of O, O-diisopropyl isoxazolinophosphonate with C60

Theoretically, cycloaddition of two molecules of phosphorylated nitrile oxide to C60 can give rise to 22 regioisomers. A simple convenient nomenclature was proposed for their classification based on the well-known Hirsh nomenclature. A combination of HPLC, semiempirical quantum-chemical PM3 calculations, and the dipole moment method demonstrated that the equatorial, trans-4(tt), and trans-3(tt) adducts are most probable.

Resonant optical orientation and alignment of excitons in superlattices

Exciton states in short-period GaAs/AlGaAs superlattices have been studied by optical orientation and optical dipole-moment alignment methods. The effect of magnetic field in the Faraday and Voigt geometries on the degree of linear and circular polarization of photoluminescence have been studied under resonant and nonresonant excitation. The constants of electron-hole exchange interaction in the exciton have been determined.

The method of dipole moments in the calculation of current system fields

Abstract The method of dipole moments used to assess the stationary magnetic field of current systems is presented. The possibilities of this method and essential features of its realization are demonstrated by the example of the particular problems solved analytically. Attention is drawn to the efficiency of the method used when analyzing the field disturbances associated with coil parameter deviations from specific values, as well as with deformations in the form.

ChemInform Abstract: Conformational Investigations of Benzophenones (I)‐(III) by Means of the Kerr Effect and Dipole Moment Methods.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Conformational investigations of benzophenones by means of the Kerr effect and dipole moment methods

Molar Kerr constants and electric dipole moments are reported for differently substituted benzophenones (such as (4-FC6H4)2CO, (4-ClC6H4)(C6H5)CO, (4-MeC6H4)(C6H5)CO, (4-MeOC6H4)(C6H5)CO, (2-ClC6H4)(C6H5)CO, (2-MeC6H4)(C6H5)CO, (4-ClC6H4)(2′,4′,6′-Me3C6H2)CO, (2-ClC6H4)(2′,4′,6′-Me3C6H2)CO, and (C4H3S)(4′-MeOC6H4)CO) as solutes in dioxane solution at 298 K. The data are analysed in terms of the preferred conformations adopted in solution. In most cases these data are consistent with the presence in dioxane of asymmetric (gauche) conformers which both aromatic rings are twisted in the same direction with respect to the CAr-C(0)-CAr molecular reference plane, although by different torsional angles for each ring. The rings bearing or the substituents adopt orthogonal positions to the reference plane. The (4-FC6H4)2CO molecule prefers a helical (both torsional angles equal) rather than a gauche conformation.

Conformational investigation of 1,8-disubstituted naphthalenes as solutes by Kerr effect and dipole moment methods

Abstract Molar Kerr constants and electric dipole moments are reported for 1-methoxycarbonylnaphthalene, 1-bromo-5-methoxycarbonylnaphthalene, 1-bromo-5-nitronaphthalene, 1-amino-8-bromonaphthalene, 1-dimethylamino-8-methoxycarbonylnaphthalene and 1-dimethylamino-8-dimethylthiocarbamoylnaphthalene as solutes in dioxane at 298 K. The data are analyzed in terms of the preferred conformations in solution. These data are consistent with acoplanar orientations of 1- and 1,8-substituents relative to the naphthalene plane. The preferred conformers of the last two molecules are stabilized by a Me 2 N ⋯ C  O(S) through-space interaction.