Effect Of Static Electric Field Research Articles

Static electric field effects at the surface of a metallic cluster

A jellium/free-electron model is used to estimate the static electric field at the surface of a metal cluster. The electric field near a cluster with a radius of 10–50 au is found to deviate significantly from the field at the same distance from an infinite metallic plane. This will influence several adsorbate properties, including bonding. At a smooth planar surface the field is sufficiently strong to cause significant contributions to the dipole and transition moments of an admolecule. These contributions become even more important at the surface of a cluster. It is postulated that microscopic roughness may enhance the electron-transfer contribution to surface-enhanced Raman scattering, since the Fermi energy of electrons in a protuberance is increased relative to the bulk. Moreover, for the same reason, the molecule-metal interaction is increased when the molecule is adsorbed at a protuberance. Finally, by means of a WKB formula derived from the model, an accurate prediction can be made of the “magic numbers” which refer to the enhanced abundances of certain clusters when formed in an atomic beam. Therefore these numbers are likely to be determined by the symmetry of the problem and not by the detailed nature of the one-electron potential.

Collisional ionization of Na by HBr in weak to strong electric fields

We report the effect of static electric fields on the collisional ionization of highly excited sodium atoms by HBr. The binding energy dependence of the collisional ionization cross section is measured at zero field and in static electric fields up to that point at which the atom field ionizes. The applied electric field lowers the ionization threshold of the atom from its zero field value. Therefore an atom near the ionization threshold in an electric field is of smaller size than a free field atom with the same binding energy. Thus measuring the binding energy dependence of the cross section at different values of the electric field allows us to study the effects of the physical size of the atom on the cross section. The effect of the electric field was to lower the measured ionization cross section. However, the binding energy dependence of the cross section remains unchanged at the level of our measurement accuracy. The measured cross sections are larger for larger atoms, exhibit a drop with increasing binding energy characteristic of rotational to electronic excitation transfer, and are of order 10−12–10−11 cm2. A simple calculation based on dipole (J→ J−1) excitation transfer from the molecule to the atom predicts, with good agreement, the binding energy dependence of the cross section. The electric field dependence of the data however, is not shown in the theory.

Effect of static electric fields on phase conjugation in silicon

The effect of an electric field applied transversely to a transient grating on the phase-conjugated response of silicon is modeled theoretically. The field is shown to reduce the intensity of the phase-conjugate output, providing a mechanism for modulating optical phase conjugation.

Perturbational calculation of the electric field effect on the conductivity of two-dimensional disordered systems

A perturbational proof is given about the existence of the effect of static electric field on the quantum correction of conductivity of disordered systems. The term “static” means the static limit. A brief discussion is presented about a recent experiment.

Bi‐directional electron pitch angle anisotropy in the plasma sheet

Analysis of low‐energy particle measurement on Imp 6 satellite have revealed the occurrence of bi‐directional electron pitch angle anisotropy (enhanced flux in field‐aligned directions) in the magnetotail at the energy range of several hundreds to several keV. The bi‐directional anisotropy was observed most commonly near the neutral sheet, with a parallel and perpendicular temperature ratio of 2–3, and they appeared also just inside of the magnetopause and in the boundary layer. The anisotropy of this extent was not an unusual phenomenon in the plasma sheet; in about 10% of the total of ∼200‐hour interval that we examined electrons had bi‐directional anisotropy. On the other hand, more sharply field‐aligned electron flux enhancements, which cannot be represented by a Maxwellian distribution, are sometimes observed at radial distances of ∼10 RE, near the inner edge of the plasma sheet. The small pitch angle (less than ∼10°) observed in such cases suggests coupling of the enhanced field‐aligned component with the ionosphere. In this paper we describe the observed characteristics of these anisotropic distributions and attempt to explain their formation by Fermi acceleration process in the plasma sheet. Owing to this process, electrons are more accelerated in parallel than perpendicular directions to the magnetic field as they traverse the neutral sheet. The effect of static electric field along the field line caused by the difference in pitch angle anisotropy of protons and electrons is also discussed.

Temporal variation of the static electric field inside an animal cage.

The temporal variation of a static electric field inside an animal cage was investigated with a newly developed small, simple field meter. The field inside the cage was found to be highly dependent on the surface conductivity of the dielectric material. As the surface of the cage became dirty because of animal occupancy, the static electric field inside it became considerably smaller from the moment the field was turned on. Clean cages also modified the static electric field inside them, the field decaying from an initial to a much lower value over several hours. The mechanism of field attenuation for both cases is surface leakage. Surface leakage for a clean cage takes place much more slowly than for a dirty cage. This was confirmed by measuring DC insulation resistance. To examine this phenomenon further, the field in a metal cage width high electrical conductivity was measured. The static electric field inside the metal cage was also found to be reduced. An improved cage design that avoids these problems, is suggested for the study of the biologic effects of static electric fields.

Effects of electric fields on doubly excited autoionizing Rydberg states of barium

We report the effects of static electric fields on the doubly excited $6{p}_{\frac{1}{2}}\mathrm{nl}$ states of barium in the region ${n}^{*}=12$. Using a three-step laser excitation scheme we have measured the electric-field dependence of the positions and autoionization widths of the $6{p}_{\frac{1}{2}}\ensuremath{-}17s,16p,15d,12l (l=4\ensuremath{-}10),12f, \mathrm{and} 16s$ states at field values of up to 4.92 kV/cm. The photoexcitation spectra of the autoionizing states exhibit interference effects which are well understood and provide a better understanding of the character of these states in electric fields. The systematic study of the spectra and positions allows us to explain the field dependence of the autoionization widths in terms of electric-field mixing of the discrete portions of the auoionizing states. The relationship of these effects to dielectronic recombination rates of ions and electrons in plasma microfields is discussed.

Electric-field effect on positronium formation and decay in some polymers and fused quartz

The effect of static electric field on the formation and annihilation of positronium in polyethylene, polystyrene, teflon, quartz, nylon and perspex has been investigated employing a fast timing spectrometer with prompt resolution (fwhm) ∼200 ps at the positron experimental settings. No significant variation in the lifetime of the long lived pick-off component with electric field has been observed. The intensity of the long-lived pick-off component decreases with increase of the field in all the cases investigated except in nylon and perspex where the intensity remains constant with the field. The results have been discussed in the frame work of the spur reaction model proposed by Mogensen and also in the light of the Ore gap model, as discussed by Brandt and Wilkenfeld. Another interesting correlation seems to exist between positronium formation and dielectric loss factor; in case of increasing loss factor there is a decrease in the effect of electric field.

Effect of static electric field on neutron diffraction by lattice planes of KH2PO4

Effect of static electric field on neutron diffraction by lattice planes of KH2PO4

Effect of a Static Electric Field on the Propagation of Electromagnetic Waves in Indium Antimonide

The effect of a weak longitudinal static electric field on the propagation of transverse circularly polarized electromagnetic waves traveling along the magnetostatic field in indium antimonide plasma has been studied theoretically. Using the dispersion relationship, the variation of the amplitude constant $\ensuremath{\alpha}$, the phase constant $\ensuremath{\beta}$ of both the left- and right-hand circularly polarized waves with the wave frequency $f$, the static magnetic field ${\stackrel{\ensuremath{\rightarrow}}{\mathrm{B}}}_{0}$, and the static electric field ${\stackrel{\ensuremath{\rightarrow}}{\mathrm{E}}}_{0}$ are examined in detail for three cases: case (i), intrinsic indium antimonide at room temperature; case (ii), $n$-type indium antimonide at liquid-nitrogen temperature; and case (iii), $p$-type indium antimonide at liquid-nitrogen temperature. The amplitude constant $\ensuremath{\alpha}$ may be either negative or positive for a positive $\ensuremath{\beta}$ depending upon the particular combination of the system parameters $f$, ${\stackrel{\ensuremath{\rightarrow}}{\mathrm{B}}}_{0}$, and ${\stackrel{\ensuremath{\rightarrow}}{\mathrm{E}}}_{0}$. When $\ensuremath{\alpha}$ is negative, the wave decays spatially and the decay rate $|\ensuremath{\alpha}|$ tends to decrease while $\ensuremath{\beta}g0$ tends to increase with $|{\stackrel{\ensuremath{\rightarrow}}{\mathrm{E}}}_{0}|$ in general. In the presence of carrier drift, i.e., $|{E}_{0}|\ensuremath{\ne}0$, it is possible for the transverse wave to grow spatially ($\ensuremath{\alpha}\ensuremath{\beta}g0$) in indium antimonide for all three cases considered, provided the combination of parameters is proper. For example, in case (i) the product (${\ensuremath{\alpha}}_{l}{\ensuremath{\beta}}_{l}$) for the left-hand wave is positive when ${B}_{0}=13$ kG, $fl0.04$ GHz, ${E}_{0}=80$ V/cm or ${B}_{0}=13$ kG, $f=0.1$ GHz, and ${E}_{0}g120$ V/cm. In case (ii) the product (${\ensuremath{\alpha}}_{l}{\ensuremath{\beta}}_{l}$) for the left-hand wave is positive when ${B}_{0}=10$ kG, $fl0.7$ GHz, ${E}_{0}=36$ V/cm or ${B}_{0}=10$ kG, $f=0.5$ GHz, and ${E}_{0}g30$ V/cm. In case (iii), (${\ensuremath{\alpha}}_{l}{\ensuremath{\beta}}_{l}$) is positive when $2.4l{B}_{0}l54$ kG, $f=0.1$ GHz, ${E}_{0}=120$ V/cm or ${B}_{0}=5$ kG, $fl0.2$ GHz, and ${E}_{0}=120$ V/cm. The influence of the presence of ${E}_{0}$ on the propagation of the helicon wave in case (ii) and the microwave Faraday rotation at $f=35$ GHz in the range $130\ensuremath{\le}{B}_{0}\ensuremath{\le}150$ kG is also considered.

Effect of longitudinal electrostatic field on the whistler mode propagation in a warm magneto-ionic medium

The dispersion equation for a whistler mode propagation in a warm plasma, subjected to parallel static electric and magnetic fields, is derived by using a linearized coupled Vlasov-Maxwell equation. From the derived dispersion equation, the amplitude constant a and phase constant β of the whistler mode are expressed in terms of static electric field E 0, static magnetic field B 0, the electron number density N 0, the electron temperature and the wave angular frequency ω. The effect of a weak static electric field on the propagation of a whistler mode is investigated in detail; the whistler mode may be amplified or attenuated according to whether E 0 and B 0 are in the same direction or in the opposite direction. The spatial rate of change of the wave amplitude and phase velocity of the whistler mode increase with ¦ E 0¦ in general. For a low-frequency wave propagation, a is directly proportional to E 0, ω, and N 0, and inversely proportional to B 0 3. A whistler mode propagation in the magnetosphere is also considered. The results of study show that the effects of a static electric field on the propagation characteristic of a whistler mode are likely to be more important in the region of low geomagnetic latitude and high altitude rather than in the high latitude region.

Use of Morphic Effects for the Study of Vibrational and Optical Properties of Impurity Atoms in Crystals

Morphic effects are effects induced in a crystal by the lowering of its symmetry through the application of a generalized external force. In this paper we study the effects of static electric fields and of strains on the frequencies of localized vibration modes associated with substitutional impurity atoms in homo-polar crystals. It is shown that the splitting of the triple degeneracy of such modes when the impurity is at a site of cubic symmetry by the application of these generalized forces can yield information about the anharmonic forces, electric dipole moment, and electronic polarizability associated with the impurity atom.

The hypochromism of helical polynucleotides

The hypochromism of the 260 mμ. absorption band of helical DNA is its lower absorbance, per base group, compared to the absorbance of the mononucleotides. The hypochromism of DNA has been calculated as a function pf the base composition and sequence. The oscillator strengths, transition monopoles and transition moments for the π→π* transitions of the bases with wavelengths of 187 to 276 mμ have been calculated from molecular orbital theory and u.v. spectra. The effect of transitions with wavelengths close to 200 mμ, is to make the calculated hypochromism increase with increasing guanine + cytosine content. Experimental measurements of hypochromism, while they seem to show the opposite dependence on base composition, are not yet detailed enough for definite conclusions to be made. The effect of transitions in the vacuum u.v. has been approximated by base polarizabilities and solvent refractive index. The vacuum u.v. transitions inside the helix cause hypochromism; those in the sugar and phosphate groups and the solvent cause hyperchromism. The net hypochromism cannot be accurately calculated but should have little dependence on base composition. The effect of static electric fields is negligible.