Dipole Moment Constant Research Articles

Applicability of the single equivalent point dipole model to represent a spatially distributed bio-electrical source.

Although the single equivalent point dipole model has been used to represent well-localised bio-electrical sources, in realistic situations the source is distributed. Consequently, position estimates of point dipoles determined by inverse algorithms suffer from systematic error due to the non-exact applicability of the inverse model. In realistic situations, this systematic error cannot be avoided, a limitation that is independent of the complexity of the torso model used. This study quantitatively investigates the intrinsic limitations in the assignment of a location to the equivalent dipole due to distributed electrical source. To simulate arrhythmic activity in the heart, a model of a wave of depolarisation spreading from a focal source over the surface of a spherical shell is used. The activity is represented by a sequence of concentric belt sources (obtained by slicing the shell with a sequence of parallel plane pairs), with constant dipole moment per unit length (circumferentially) directed parallel to the propagation direction. The distributed source is represented by N dipoles at equal arc lengths along the belt. The sum of the dipole potentials is calculated at predefined electrode locations. The inverse problem involves finding a single equivalent point dipole that best reproduces the electrode potentials due to the distributed source. The inverse problem is implemented by minimising the chi2 per degree of freedom. It is found that the trajectory traced by the equivalent dipole is sensitive to the location of the spherical shell relative to the fixed electrodes. It is shown that this trajectory does not coincide with the sequence of geometrical centres of the consecutive belt sources. For distributed sources within a bounded spherical medium, displaced from the sphere's centre by 40% of the sphere's radius, it is found that the error in the equivalent dipole location varies from 3 to 20% for sources with size between 5 and 50% of the sphere's radius. Finally, a method is devised to obtain the size of the distributed source during the cardiac cycle.

Squeezed harmonic generation in cooperative resonance scattering of intense radiation by dipole molecules

We examine the processes of resonance Raman scattering of intense electromagnetic radiation by a lumped system of two-level atoms with a constant dipole moment. We calculate the intensity of the sth generated harmonic in a saturating electromagnetic field and the statistical characteristics of this harmonic. Finally, we show that the sth harmonic is squeezed at saturating field intensities.

Interacting induced dipoles polarization model for molecular polarizabilities: application to benzothiazole (A)-benzobisthiazole (B) oligomers AB 13A

We have outlined a method for the calculation of atomic net charges and molecular dipole-dipole,  α , dipole-quadrupole,  A , and quadrupole-quadrupole,  C , polarizabilities which we have successfully applied to benzothiazole (A)-benzobisthiazole (B) oligomers in the series AB 1A to AB 13A, and the results have been extrapolated to give predictions for polybenzobisthiazole. The calculation of  α ,  A and  C has been carried out by the interacting induced dipoles polarization model that calculates tensor effective anisotropic point polarizabilities (method of Applequist). The mean effective atomic α effpolarizabilities for the monomeric unit are of the same order of magnitude as reference calculations (PAPID program). The value of the dipole moment drops sharply from the monomeric unit to the dimeric unit. The high dipole moment of the monomeric unit forces a charge redistribution in the molecule, that reverses the sign of the mean quadrupole moment with respect to the remaining oligomers. The values of  α and  C for the oligomers are much larger than the sum of their component parts, as would be expected owing to the larger length of π conjugation. However, the values of  A are also sensitive to the molecular dipole moment. This fact explains a relative maximum in ¦ A x, xx ¦ for the polar monomeric unit. The remaining oligomers show a constant dipole moment, and a non-linear increase in ¦ A x, xx ¦ with the number of units is observed. The fractal dimension of the solvent accessible surface and the 1-octanol-water partition coefficient, P, increase with the number of units in the oligomer. Functions of N (the total number of units either A or B) have been fitted to α (mean value), α xx , ¦ A x ¦ ( x vector component), ¦ A x, xx ¦ and C xx, xx , and these may be used to predict the values for longer oligomers. The finite oligomer results have been extrapolated to predict optical properties of polybenzobisthiazole.

Laser dual-wavelength interferometric measurement of the structure and refractive parameters of carbon tetrachloride

The dual-wavelength laser Mach-Zehnder interferometric technique was used for measuring the refractive index and its gradient with temperature for the important laser dye solvent carbon tetrachloride (CTC). The Argon and HeNe laser, at wavelengths 514.5 nm and 632.8 nm respectively, are used. Applying Maxwell's and Lorentz-Lorenz equations, the structure parameters (optical permittivity, thermal coefficient of permittivity, specific and molar refraction, polarizability, molecular radius, constant dipole moment, relaxation time, impedance, … etc), of the solvent are calculated at the two wavelengths. The calculations are carried out using the measured data for the refractive index and its gradient with temperature. On the other hand the refractive index gradient with density was determined. Accordingly the optical permittivity, density and molar polarization of CTC at different temperatures were calculated. Using Caushy's equation the refractive index and permittivity as a function of wavelength were deduced. The gradient of refractive index (d n/d T) and hence the gradient of permittivity (d ϵ/d T) versus wavelength are calculated using Murphy-Alpert's equation. In addition the constants A and B of Cauchy equation are plotted as a function of temperature. Accuracy, sensitivity and discussions are treated in details.

Electrorheological Effect of Reducing the Suspension Viscosity in Laminar Flows below the Viscosity of Anisotropic Dispersive Medium

Electrorheological features of a dilute suspension in Ericksen anisotropic fluid are analyzed on the basis of rheological constitutive equations obtained in the present paper. It is assumed that suspended particles possess a zero bouyancy and constant dipole moment, the anisotropic dispersive medium of suspension is electrically neutral. As a hydrodynamic model of suspended particles, the uniaxial dumbbell is used. The sizes of suspended particles are assumed to be much more than elements of microstructure which are responsible for anisotropy of dispersive medium. The rheological equations of suspension under consideration are obtained on the basis of the structure-phenomenological approach. The rheological behavior is suspension is investigated in a simple shear flow in the presence of external electric field. It is shown that the suspension behaves itself as anisotropic non-Newtonian fluid. The possibility of reducing the effective viscosity of suspension of laminar shear flows below the value of effective viscosity of anisotropic dispersive medium is predicted theoretically. It takes place at certain orientation of suspension particles of suspension under action of the external stationary electric field and the hydrodynamic forces. The result obtained can be used for studying the suspension in liquid crystals.

The Dynamics of Benzene Molecules in Liquid Carbon Tetrachloride Solution

It is well-known that the dynamics of molecules depends both on temperature and the environment. When a molecule is in liquid solution, the above mentioned factors can influence strongly the changes of the intermolecular forces. Molecules which have neither charge nor constant dipole moment interact mainly by Lennard—Jones forces which strongly depend on the shape of molecules and their interdistances. Benzene solution in carbon tetrachloride is a typical model of such a system. The aim of our measurements was to obtain information on the influence of CCl4 spherical molecules on the dynamics and orientation of plane C6H6 molecules.

The influence of external electric field on f−f absorption spectrum of lithium niobate crystals doped by rare earth ions

The influence of an external electric field on the absorption spectra of LiNbO3 crystals doped by Ho3+, Er3+, Tm3+ was studied by means of sensitive modulation technique at 77 K. The linear Stark effect has been observed in spectra of these crystals. The properties of Stark effect reveal orientation of constant dipole moments of rare earth centres along the trigonal axis of crystals, which confirms their trigonalc 3-symmetry. Moreover, the linear Stark effect connected with the removal of orbital level degeneracy has been observed in spectra of crystals with impurities Ho3+ and Tm3+ in the field ɛ⊥c 3.

Laser-induced order–disorder phase transition and second harmonic generation with a threshold in fiber waveguides

A mechanism is proposed of optical second harmonic generation in centrosymmetric media, which has a threshold and is an efficient process. It is assumed that a light-induced phase transition occurs in a system of centers with constant dipole moments interacting via a strong effective Lorentz field and a lattice displacement field, as well as a field representing reemission at the second harmonic frequency. The proposed mechanism accounts for the main results of experimental investigations of second harmonic generation in centrosymmetric fiber waveguides.

Optical detection and inverse Kerr effect in a gas of free atoms

The constant dipole moment induced in an atom by a static electric field is changed by monochromatic radiation which produces an additional optical-detection type constant moment. The latter is determined by the Kerr effect susceptibility χ ijkl (0; 0, ω,- ω) and has some properties characteristics of this effect.

Thermodynamic properties and waves in a dipole plasma

A low-temperature plasma containing polar molecules with constant electric dipole moment as the neutral component is considered. The thermodynamic functions and the dispersion properties of such a plasma are investigated.

Adsorption of oxygen on electrolytic silver by UPS and work function measurement

The adsorption of oxygen on an electrolytic silver surface has been investigated by ultra-violet photoelectron spectroscopy (UPS), and by the measurements of work function change and kinetics. UPS difference spectra show three positive peaks at about 3.0, 5.3 and 9.0 eV below the Fermi level, which are due to the adsorbate resonances of atomic and molecular oxygen on the silver surface. The peak at 5.3 eV indicates that the orbitals derived from the π g ∗ orbital of molecular oxygen are electronically filled in the adsorbed dioxygen complex and the peak at 9.0 eV corresponds to electron feedback from the π u orbital of adsorbed dioxygen species to valence orbitals of silver. The bonding configuration is also supported by the changes of work function. Owing to the transfer of electrons from metal to adsorbate, this adsorption of the atomic oxygen increases the work function ( Δφ sat = +0.5 eV), and O − (ads) species are formed; with the saturated surface the constant dipole moment per adsorbed oxygen is 0.24 Debye. The kinetic results show the presence of a maximum ( S max = 9.3 × 10 −3) in the sticking coefficient curve at room temperature. The relation, S = k exp(550/ T), has been obtained by measurement of the kinetics, and the results are discussed in terms of precursor adsorption models.

A Tight-Seal Whole Cell Study of the Voltage-Dependent Gating Mechanism of K+-Channels of Protoplasmic Droplets of Chara corallina

The biophysical properties of voltage-dependent K(+)-channels of protoplasmic droplets of Chara corallina Klein ex Willd., em, R.D.W. were investigated using the tight-seal whole cell method. Two potassium currents were observed in voltage-clamp mode and they can be used to explain the transient membrane potential time course observed in current-clamp mode. The K(+)-channels are identified by the effect of tetraethylammonium chloride which blocks both currents. A two-state, constant dipole moment model is used to fit the voltage-conductance curve. From this model the minimum equivalent gating charge involved in the gating mechanism of K(+)-channels of Chara can be estimated.

Temperature dependence of the electric dipole moment of paraelectric Ag + and OH - centers in rubidium halide crystals

Sensitive dielectric measurements were performed in diluted substitutional impurity dipole systems (10 17 – 10 18 cm -3) in rubidium halides. Both, molecular OH - and monatomic Ag + off-center dipole systems were studied at low frequencies (up to 100 KHz) and at temperatures between 1.5 and 300 K. A best fit to the experiment yields for all the above systems a constant dipole moment over a wide temperature range. Even for the shallow Ag + off-center systems no indication for an off-center to on-center transition was found.

Structure and energetics of potassium overlayers on ruthenium (101̄0)

The chemisorption and desorption of K at the (101̄0) surface of Ru has been investigated by LEED, Auger spectroscopy, Δφ, neutral atom and ion desorption measurements. The results reveal that substantial K-enrichment of the immediate subsurface region occurs for small potassium coverages at 430 K. Desorption of neutral K atoms is characterised by a monotonic fall in activation energy from 280 kJ mol −1 at zero potassium coverage to 180 kJ mol −1 near the monolayer coverage point. Analysis of the K + desorption data yields a value for the activation energy to atomic K desorption which agrees well with that determined directly from the neutral atom desorption spectra. Work function measurements indicate a constant adatom dipole moment of ~ 3.9 D over the coverage regime of 0 ⩽ θ(K) ⩽ 0.18. At higher coverages, the alkali overlayer depolarises (α = 30 Å 3), a near metallic overlayer being formed at completion of the first monolayer (θ(K) = 0.67). LEED shows the existence of a series of ordered phases for 0.36 ⩽ θ(K.) ⩽ 0.67. An examination of the splitting of the fractional-order beams indicates that the Ru(101̄0) surface can accommodate increasing K coverage by two distinct mechanisms: growth of c(2 × 2) domains when θ(K) ⩽ 0.5 and uni-axial compression along [1̄21̄0] when θ(K) ⩾ 0.5.

Magneto- and electro-optic constants of some nitrobenzenes and anisotropy of the magnetic susceptibility of the nitro group

1. The magnetic-susceptibility ellipsoids of a nitro group attached to an aromatic ring and of a nitrate anion have been determined by measuring the Cotton-Mouton effect. The axis of maximal diamagnetism of the ellipsoids obtained coincides with the normal to the plane in which the bonds are located. 2. The significant acoplanarity of the trinitrotoluene molecule in solution has been established by measuring the magnetic and electric birefringences. 3. The molecule of p-dinitrobenzene in solution has an anomalously high atomic polarization and a small constant dipole moment.

Computer simulation and theoretical results for a polar-polarizable fluid

In this paper we present molecular dynamics (MD) results for a fluid of polarizable Lennard-Jones particles with permanent dipole and quadrupole moments. Detailed comparisons are made with theoretical results obtained using a previously developed self-consistent mean field (SCMF) approximation together with the LHNC and QHNC integral equation theories. The SCMF approximation is found to give a reasonably accurate description of the polarizable system. The SCMF/QHNC and SCMF/LHNC calculations both give values for the dielectric constant and average dipole moment which are in good agreement with the MD simulations. The SCMF/QHNC theory gives better results for the pair correlation function and for some thermodynamic properties.

Physical properties of homoionic montmorillonite and kaolinite complexed with amino acids and peptides

X-ray diffractometry was used to investigate whether various amino acids and peptides expanded montmorillonite (M) homoionic to different cations, and the electrophoretic mobility (EPM) was measured to determine whether the binding of these amino acids and peptides influenced the net surface charge of M and kaolinite (K). Neither aspartic acid, adsorbed at equilibrium at concentrations of 20–250 nM mg −1 M homoionic to Ca or Zn, nor cysteine, at 50–830 nM mg −1 M homoionic to Zn or Al, caused expansion, whereas proline, at 90–870 nM mg −1 clay, caused expansion of M homoionic to Ca or Zn, and both proline and arginine, at 60–1150 nM mg −1 clay, caused expansion of M homoionic to H or Al. The extent of expansion caused by proline and arginine was related to the concentration of the amino acids and the exchangeable cation on the homoionic M. Only M-A1 complexed with arginine remained expanded after extensive washing of the clay-amino acid complexes. The expansion of M was apparently dependent on both the type of exchangeable cation on the clay and the characteristics of the amino acid (i.e. the functional groups, dielectric constant increment, dipole moment and concentration). M homoionic to H, Na, Zn, Al or La was not expanded by a series of di- to tetrapeptides bound on these clays and none of the homoionic K-amino acid or peptide complexes was expanded. The EPM of the homoionic M and K and of the corresponding clay-amino acid or peptide complexes was identical, indicating that the concentration of the amino acids or peptides bound was not sufficient to cover enough of the surface of the clays to alter significantly their net charge. The lack of differences in the bulk pH of the clays after binding with amino acids or peptides (with the exception of complexes with arginine) also indicated limited coverage of the clays by these organics.

Physical basis for piezoelectricity in PVDF

Abstract Consideration of the molecular and bulk structures of PVDF and related semicrystalline polymers, and the effects of processing to make transducer films, leads to a novel way of analysing the elastic and piezoelectric constant data. The results of this analysis support the conclusion that thickness changes contribute about 2/3 of the piezoelectric activity. An increase in thickness decreases the charge on the electrodes. The probable mechanism is simply the displacement of the electrodes in the fields of the constant dipole moments of the crystals. The remaining 1/3 of the activity is attributed to changes in the film's dipole moment at constant thickness. Strains in the orientation direction of the film increase the charge on the surface while strains in the plane of the film normal to the orientation direction decrease it. Eight separate possible contributions to the change in moment are discussed, and qualitative evaluations of their importance are given.

Electric properties and structure of DNA-restriction fragments from measurements of the electric dichroism.

The electric dichroism of 17 homogeneous DNA fragments, ranging in size from 43 to 4362 base-pairs, has been analyzed in high electric fields. The orientation of the small fragments can be described in terms of an induced dipole moment, whereas the large fragments are oriented according to a constant dipole mechanism. In the intermediate size range, DNA orients according to an induced dipole mechanism at low field strengths and according to a constant dipole mechanism at high field strengths. From these observations we propose an orientation mechanism with a saturating induced dipole. The induced dipole observed at low field strengths is saturated at a field strength Eo within a transition range Em to give a constant dipole moment at high field strengths. These parameters together with the polarizability and the limit reduced dichroism are evaluated by a least-squares analysis of the experimental data. Eo and Em are found to decrease with increasing chain length from Eo approximately 40 kV/cm (Em approximately 14 kV/cm) at 65 base-pairs to 10 kV/cm (6 kV/cm) at 194 base-pairs. The polarizability is found to increase with the square of the chain length, whereas the saturated dipole increases with chain length N at low N and goes to a limit value at high N. The temperature dependence of the orientation parameters is found to be very small. The values obtained for the limit dichroism are between -1.0 and -1.3 for chain lengths between 60 and 1000 base-pairs, whereas values around -1.4 are observed at chain lengths greater than 1000 base-pairs. These data indicate that electric fields extend the contour of DNA strands at high chain lengths from a weakly bent to a more linear form. The variations of the limit dichroism observed for short fragments suggest sequence-dependent differences in the secondary structure of the helix. The experimental results are compared with numerical calculations based on simple polyelectrolyte models. For short fragments the magnitude of several electrochemical parameters can be adequately explained by a polarization of the ion cloud around the DNA molecules. However, these polyelectrolyte models do not adequately describe the observed chain length dependence of the orientation phenomena.

The solvent effect on the dimerization constant and electric dipole moment of ϵ-caprolactam

Abstract The dimerization constant, and electric dipole moments of both monomeric and dimeric species, have been deduced for ϵ-caprolactam from dielectric polarization studies on dilute solutions in cyclohexane, carbon tetrachloride, benzene and dioxan. Results in carbon tetrachloride are consistent with a stereospecific interaction between the solute (as monomeric) and solvent, possibly leading to a charge-transfer complex. Part of monomeric ϵ-caprolactam interacts with n -basic dioxan, and at a lesser extent with π-basic benzene, giving a hydrogen-bonded complex, whose dipole moment contains a large term due to increase in the (NHCO) mesomeric moment. Incidentally, the dipole moments of 1-tetralone and NN -dimethylformamide have been measured and interpreted.