On the Cherenkov radiation from extended charge distributions

2000 ◽  
Vol 77 (10) ◽  
pp. 775-784 ◽  
Author(s):  
M Villavicencio ◽  
J L Jiménez ◽  
JAE Roa-Neri
Keyword(s):  
Explicit Expression ◽  
Charge Distribution ◽  
Constant Velocity ◽  
Cherenkov Radiation ◽  
Poynting Vector ◽  
Time Dependent ◽  
Spherically Symmetric ◽  
Charge Distributions ◽  
Extended Charge ◽  
A Charge

In this work the Cherenkov effect for extended charge distributions is analyzed using two different methods. In the first method, the Poynting vector is employed to determine the energy radiated, whereas in the second one, we apply the idea of generating time-dependent elemental dipoles, induced by a charge distribution moving with constant velocity, inside a material medium. An explicit expression for the Cherenkov radiation generated by some different kinds of spherically symmetric charge, travelling inside a medium, is obtained.PACS Nos.: 03.50.De, 41.20.Bt, 41.60.-m, 41.60.Bq

On the Cherenkov radiation from extended charge distributions

1999 ◽  
Vol 77 (10) ◽  
pp. 775-784
Author(s):  
M. Villavicencio ◽  
J.L. Jiménez ◽  
J.A.E. Roa-Neri
Keyword(s):  
Cherenkov Radiation ◽  
Charge Distributions ◽  
Extended Charge

Polarizations of atomic and molecular charge distributions

1969 ◽  
Vol 47 (12) ◽  
pp. 2308-2311 ◽  
Author(s):  
R. F. W. Bader ◽  
I. Keaveny ◽  
G. Runtz
Keyword(s):  
Electric Field ◽  
Charge Distribution ◽  
Primary Response ◽  
Fundamental Nature ◽  
Charge Distributions ◽  
Molecular Charge ◽  
A Charge

It is shown that the dominant polarization of a molecular charge distribution in the region of a nucleus of an atom which employs p orbitals in its bonding (Be → F, Mg → Cl) is quadrupolar in nature, and dipolar for an atom which employs s orbitals (H, He, Li, Na). That these polarizations are of a fundamental nature is demonstrated by showing that they represent the primary response of a charge distribution to an electric field, whether it be internal or external, static or dynamic.

scholarly journals Water-Mediated Electronic Structure of Oligopeptides Probed by Their UV Circular Dichroism, Absorption Spectra, and Time-Dependent DFT Calculations

2020 ◽  
Author(s):  
Anshuman Kumar ◽  
Siobhan E. Toal ◽  
David DiGuiseppi ◽  
Reinhard Schweitzer-Stenner ◽  
Bryan Wong
Keyword(s):  
Circular Dichroism ◽  
Absorption Spectra ◽  
Density Functional ◽  
Time Dependent ◽  
Water Model ◽  
Cd Spectra ◽  
Influence Of Water ◽  
Explicit Consideration ◽  
A Charge ◽  
Circular Dichroïsm

<p>We investigate the UV absorption spectra of a series of cationic GxG (where x denotes a guest residue) peptides in aqueous solution and find that the spectra of a subset of peptides with x = A, L, I, K, N, and R (and, to a lesser extent, peptides with x = D and V) vary as a function of temperature. To explore whether or not this observation reflects conformational dependencies, we carry out time-dependent density functional calculations for the polyproline II (pPII) and β-strand conformations of a limited set of tripeptides (x = A, V, I, L, and R) in implicit and explicit water. We find that the calculated CD spectra for pPII can qualitatively account for the experimental spectra irrespective of the water model. The reproduction of the <i>β</i>-strand UV-CD spectra, however, requires the explicit consideration of water. Based on the calculated absorption spectra, we explain the observed temperature dependence of the experimental spectra as being caused by a reduced dispersion (larger spectral density) of the overlapping NV<sub>2</sub> band and the influence of water on electronic transitions in the β-strand conformation. Contrary to conventional wisdom, we find that both the NV<sub>1</sub> and NV<sub>2</sub> band are the envelopes of contributions from multiple transitions that involve more than just the HOMOs and LUMOs of the peptide groups. A natural transition orbital analysis reveals that some of the transitions with significant oscillator strength have a charge-transfer character. The overall manifold of transitions, in conjunction with their strengths and characters, depends on the peptide’s backbone conformation, peptide hydration, and also on the side chain of the guest residue. It is particularly noteworthy that molecular orbitals of water contribute significantly to transitions in <i>β</i>-strand conformations. Our results reveal that peptide groups, side chains, and hydration shells must be considered as an entity for a physically valid characterization of UV absorbance and circular dichroism. </p>

The Electrostatic Moments of a Charge Distribution

1997 ◽  
Author(s):  
Philip Coppens
Keyword(s):  
Dipole Moment ◽  
Charge Distribution ◽  
Dipole Moments ◽  
Practical Importance ◽  
Diffraction Method ◽  
Quadrupole Moments ◽  
Charge Densities ◽  
Moment Vector ◽  
Experimental Values ◽  
A Charge

The moments of a charge distribution provide a concise summary of the nature of that distribution. They are suitable for quantitative comparison of experimental charge densities with theoretical results. As many of the moments can be obtained by spectroscopic and dielectric methods, the comparison between techniques can serve as a calibration of experimental and theoretical charge densities. Conversely, since the full charge density is not accessible by the other experimental methods, the comparison provides an interpretation of the results of the complementary physical techniques. The electrostatic moments are of practical importance, as they occur in the expressions for intermolecular interactions and the lattice energies of crystals. The first electrostatic moment from X-rays was obtained by Stewart (1970), who calculated the dipole moment of uracil from the least-squares valence-shell populations of each of the constituent atoms of the molecule. Stewart’s value of 4.0 ± 1.3 D had a large experimental uncertainty, but is nevertheless close to the later result of 4.16 ± 0.4 D (Kulakowska et al. 1974), obtained from capacitance measurements of a solution in dioxane. The diffraction method has the advantage that it gives not only the magnitude but also the direction of the dipole moment. Gas-phase microwave measurements are also capable of providing all three components of the dipole moment, but only the magnitude is obtained from dielectric solution measurements. We will use an example as illustration. The dipole moment vector for formamide has been determined both by diffraction and microwave spectroscopy. As the diffraction experiment measures a continuous charge distribution, the moments derived are defined in terms of the method used for space partitioning, and are not necessarily equal. Nevertheless, the results from different techniques agree quite well. A comprehensive review on molecular electric moments from X-ray diffraction data has been published by Spackman (1992). Spackman points out that despite a large number of determinations of molecular dipole moments and a few determinations of molecular quadrupole moments, it is not yet widely accepted that diffraction methods lead to valid experimental values of the electrostatic moments.

scholarly journals Relativistic extension of a charge-conservative finite element solver for time-dependent Maxwell-Vlasov equations

2018 ◽  
Vol 25 (1) ◽  
pp. 013109 ◽  
Author(s):  
D.-Y. Na ◽  
H. Moon ◽  
Y. A. Omelchenko ◽  
F. L. Teixeira
Keyword(s):  
Finite Element ◽  
Time Dependent ◽  
Vlasov Equations ◽  
Relativistic Extension ◽  
A Charge
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