Search NASA⌕ Search

SEARCH · Search NASA

Results for “DIPOLES”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,333 records · Page 74
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Influence of the polarization effect on the donor properties of 1-phenylsilatrane

A new mechanism of the dipole—induced dipole polarization interaction was considered to explain an anomalous increase in the +I effect in a 1-phenylsilatrane molecule with the pentacoordinated Si atom. The interaction through the space between the silatrane cage having a high dipole moment and easily polarizable aromatic phenyl substituent induces dipole that adds the influence of the inductive effect along the bonds, which is characteristic of usual silatranes. The high inductive constant σ{sub I} calculated for 1-phenylsilatrane on the basis of chemical shifts δ{sub C} of aromatic carbon atoms was interpreted as a superelectronodonor effect in silatranes. However, the polarization effect through the space leads to a substantial change in the chemical shifts δ{sub C} for the phenyl group in the direction that formally corresponds to the enhancement of the +I effect transmitted via the bonds. It is shown for the first time that the inductive effect in silatranes is not constant and varies according to the polarizability of the substituent at the Si atom.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Charge-signal multiplication mediated by urea wires inside Y-shaped carbon nanotubes

In previous studies, we reported molecular dynamics (MD) simulations showing that single-file water wires confined inside Y-shaped single-walled carbon nanotubes (Y-SWNTs) held strong and robust capability to convert and multiply charge signals [Y. S. Tu, P. Xiu, R. Z. Wan, J. Hu, R. H. Zhou, and H. P. Fang, Proc. Natl. Acad. Sci. U.S.A. 106, 18120 (2009); Y. Tu, H. Lu, Y. Zhang, T. Huynh, and R. Zhou, J. Chem. Phys. 138, 015104 (2013)]. It is fascinating to see whether the signal multiplication can be realized by other kinds of polar molecules with larger dipole moments (which make the experimental realization easier). In this article, we use MD simulations to study the urea-mediated signal conversion and multiplication with Y-SWNTs. We observe that when a Y-SWNT with an external charge of magnitude 1.0 e (the model of a signal at the single-electron level) is solvated in 1 M urea solutions, urea can induce drying of the Y-SWNT and fill its interiors in single-file, forming Y-shaped urea wires. The external charge can effectively control the dipole orientation of the urea wire inside the main channel (i.e., the signal can be readily converted), and this signal can further be multiplied into 2 (or more) output signals by modulating dipole orientations of urea wires in bifurcated branch channels of the Y-SWNT. This remarkable signal transduction capability arises from the strong dipole-induced ordering of urea wires under extreme confinement. We also discuss the advantage of urea as compared with water in the signal multiplication, as well as the robustness and biological implications of our findings. This study provides the possibility for multiplying signals by using urea molecules (or other polar organic molecules) with Y-shaped nanochannels and might also help understand the mechanism behind signal conduction in both physical and biological systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Critical binding and electron scattering by symmetric-top polar molecules

Quantum treatments of electron interactions with polar symmetric-top rotor molecules show features not present in the treatment of the linear-polar-rotor model. For symmetric tops possessing non-zero angular momentum about the symmetry axis, a new critical dipole can be defined that guarantees an infinite set of dipole-bound states independent of the values of the components of the inertial tensor. Additionally, for this same class, the scattering cross section diverges for all nonzero values of dipole moments and inertial moments, similar to solutions for the fixed linear dipole. Additional predictions are presented for electron affinities and rotational resonances of these systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Induced photoemission from driven nonadiabatic dynamics in an avoided crossing system

When vibrational dynamics on an ionic state (large dipole moment) is coupled to that on a neutral state (small dipole moment) such as at an avoided crossing in the alkali halide system, the population transfer between the states cause oscillation of the molecular dipole, leading to dipole emission. Such dynamics may be driven by an external field. We study how the coupled wavepacket dynamics is affected by the parameters (intensity, frequency) of the driving field with the aim of making use of the photoemission as an alternative detection scheme of femtosecond and subfemtosecond vibrational and electronic dynamics or as a characteristic optical source.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Contemporary research with nuclear resonance fluorescence at the S-DALINAC

In the last decades many nuclear resonance fluorescence experiments aiming for low-lying dipole excitations were performed at the Darmstadt High Intensity Photon Setup at S-DALINAC facility. On the electric dipole side, quadrupole-octupole coupled states and the Pygmy Dipole Resonance are of particular interest. On the magnetic dipole side, the so-called scissors mode is in the focus of interest. Furthermore, using the method of resonant self absorption, the decay behavior of J{sup π} = 1{sup −} states was investigated in {sup 140}Ce.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Reactive intermediates in {sup 4}He nanodroplets: Infrared laser Stark spectroscopy of dihydroxycarbene

Singlet dihydroxycarbene (HOC{sup ¨}OH) is produced via pyrolytic decomposition of oxalic acid, captured by helium nanodroplets, and probed with infrared laser Stark spectroscopy. Rovibrational bands in the OH stretch region are assigned to either trans,trans- or trans,cis-rotamers on the basis of symmetry type, nuclear spin statistical weights, and comparisons to electronic structure theory calculations. Stark spectroscopy provides the inertial components of the permanent electric dipole moments for these rotamers. The dipole components for trans, trans- and trans, cis-rotamers are (μ{sub a}, μ{sub b}) = (0.00, 0.68(6)) and (1.63(3), 1.50(5)), respectively. The infrared spectra lack evidence for the higher energy cis,cis-rotamer, which is consistent with a previously proposed pyrolytic decomposition mechanism of oxalic acid and computations of HOC{sup ¨}OH torsional interconversion and tautomerization barriers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Multi-resolution anisotropy studies of ultrahigh-energy cosmic rays detected at the Pierre Auger Observatory

Here, we report a multi-resolution search for anisotropies in the arrival directions of cosmic rays detected at the Pierre Auger Observatory with local zenith angles up to 80(o) and energies in excess of 4 EeV (4 × 10 18 eV). This search is conducted by measuring the angular power spectrum and performing a needlet wavelet analysis in two independent energy ranges. Both analyses are complementary since the angular power spectrum achieves a better performance in identifying large-scale patterns while the needlet wavelet analysis, considering the parameters used in this work, presents a higher efficiency in detecting smaller-scale anisotropies, potentially providing directional information on any observed anisotropies. No deviation from isotropy is observed on any angular scale in the energy range between 4 and 8 EeV. Above 8 EeV, an indication for a dipole moment is captured, while no other deviation from isotropy is observed for moments beyond the dipole one. The corresponding p-values obtained after accounting for searches blindly performed at several angular scales, are 1.3 × 10 -5 in the case of the angular power spectrum, and 2.5 × 10 -3 in the case of the needlet analysis. While these results are consistent with previous reports making use of the same data set, they provide extensions of the previous works through the thorough scans of the angular scales.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Photoluminescence and thermal stability of yellow-emitting Na{sub 2}Ba{sub 2}Si{sub 2}O{sub 7}:Sm{sup 3+} phosphor for light-emitting diodes

Highlights: • Na{sub 2}Ba{sub 2}Si{sub 2}O{sub 7}:Sm{sup 3+} phosphors are obtained via a solid-state reaction method. • Excitation at 402 nm, the yellow color purity is close to 100%. • The mechanism of concentration quenching is dipole–dipole interaction. • The temperature-dependent luminescence property exceed that of YAG:Ce{sup 3+}. - Abstract: A series of yellow-emitting Na{sub 2}(Ba{sub 2−x}Sm{sub x})Si{sub 2}O{sub 7} phosphors have been prepared via solid-state reaction technique. X-ray diffraction (XRD), photoluminescence (PL) spectra, temperature-dependent luminescence property, concentration quenching mechanism and luminescence lifetime are applied to characterize the obtained samples. Under 402 nm near ultraviolent excitation, the samples emit yellow light and the color purity is close to 100%. The critical quenching concentration of Sm{sup 3+} in the Na{sub 2}Ba{sub 2}Si{sub 2}O{sub 7} host is about 3.6 mol% and corresponding quenching behavior is ascribed to be electric dipole–dipole interaction. Furthermore, the phosphor has good thermal stability property, superior to the commercial yellow Y{sub 3}Al{sub 5}O{sub 12}:Ce{sup 3+} phosphor and the activation energy for thermal quenching is calculated as 0.18 eV.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Concentration quenching of Eu{sup 2+} doped Ca{sub 2}BO{sub 3}Cl

Highlights: • Ca{sub 2}BO{sub 3}Cl doped with Eu{sup 2+} prepared by solid state reaction. • Concentration quenching studied by intensity and lifetime measurements. • Accurate determination of the critical transfer distance. • Interaction mechanism verified to be dipole–dipole interactions. - Abstract: With the aim of determining the concentration quenching mechanism of Eu{sup 2+} doped Ca{sub 2}BO{sub 3}Cl, a series of phosphors with a varied Eu{sup 2+} concentration (Ca{sub 2−x}BO{sub 3}Cl:xEu{sup 2+}) was synthesized by the solid state reaction method. The phase structure was determined by X-ray diffraction. Photoluminescence (PL) measurements showed broad excitation and emission signatures of the allowed f–d transition of Eu{sup 2+} ions. The PL emission intensity was found to be increased by increasing the concentration of Eu{sup 2+} ions up to x = 0.03 and then decreased as a result of the concentration quenching effect. The lifetime of the emission from the Eu{sup 2+} ions was measured and the decrease in the lifetime with increasing Eu{sup 2+} concentration confirmed that non-radiative energy transfer occurred between Eu{sup 2+} ions. From the luminescence data, the value of the critical transfer distance was calculated as 1.5 nm and the corresponding concentration quenching mechanism was verified to be a dipole–dipole interaction.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Photoluminescence investigations on Sm3+ ions doped borate glasses for tricolor w-LEDs and lasers

Highlights: • Borate glasses with Sm3+ ions were synthesized by melt quenching technique. • Under 402 nm excitation Borate glasses show reddish orange luminescence. • Energy transfer through cross-relaxation leads to fall in decay time of Sm3+ ions. • I-H model confirms energy transfer between Sm3+ ions as dipole-dipole in nature. • 1 mol% Sm3+ ions in these glasses are apt for red photonic device applications. - Abstract: This work describes mainly the optical absorption, photoluminescence (PL) and decay spectral properties of Sm{sup 3+} ions doped borate glasses to understand their possible usage in tricolor w-LEDs and lasers.The XRD spectrum recorded for an un-doped glass confirms glassy nature of the as prepared glass. The Judd-Ofelt (J-O) intensity parameters evaluated from experimental oscillator strengths were used in estimating the various radiative parameters. Under 402 nm excitation, the PL spectra exhibit intense emission at 600 nm for which the decay spectral profiles were recorded.The decay profiles are converting from single exponential to non-exponential with increase in Sm{sup 3+} ion concentration ensuing decrease in experimental lifetimes which may be attributed to the efficient energy transfer through cross-relaxation process. The non-exponential decay curves fitted to I-H model reveals the interaction between the Sm{sup 3+} ions as dipole-dipole in nature. From the evaluated emission cross-sections, quantum efficiency, branching ratios and CIE co-ordinates, it is concluded that 1 mol% Sm{sup 3+} ions in these glasses are aptly suitable to fabricate reddish-orange luminescent devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Photoluminescence properties and efficient energy transfer of Ce3+/Eu2+ activated K2Ba7Si16O40 phosphors

Highlights: • K{sub 2}Ba{sub 7}Si{sub 16}O{sub 40}:Ce{sup 3+}/Eu{sup 2+} phosphors have been synthesized by a high temperature solid-state method with CO atmosphere. • The resonance-type energy transfer by dipole-dipole interaction from Ce{sup 3+} to Eu{sup 2+} in K{sub 2}Ba{sub 7}Si{sub 16}O{sub 40} is demonstrated. • The critical distance between Ce{sup 3+} and Eu{sup 2+} ions is calculated to be 25.06 Å. • The thermal activation energy of K{sub 2}Ba{sub 7}Si{sub 16}O{sub 40} is calculated to be 0.26 eV. - Abstract: Ce{sup 3+}/Eu{sup 2+} activated K{sub 2}Ba{sub 7}Si{sub 16}O{sub 40} phosphors have been synthesized via a high-temperature solid-state method with CO atmosphere. Under ultraviolet (UV) light pump, the photoluminescence (PL) spectra of K{sub 2}Ba{sub 7}Si{sub 16}O{sub 40}: Ce{sup 3+} is composed of a broadband from 300 nm to 500 nm ascribed to the spin-allowed 5d–4f transition of Ce{sup 3+} ions. The optimal concentration is 8% for Ce{sup 3+} single doped K{sub 2}Ba{sub 7}Si{sub 16}O{sub 40} due to the ernergy dispersion between Ce{sup 3+} ions and the critical distance between Ce{sup 3+} ions is 15.05 Å. K{sub 2}Ba{sub 7}Si{sub 16}O{sub 40}: Eu{sup 2+} emits a broad green emission peaking at 498 nm. The spectral overlap between the emission of Ce{sup 3+} and the excitation of Eu{sup 2+} suggests the resonance-type energy transfer from Ce{sup 3+} to Eu{sup 2+}, which is further demonstrated by the decay curves of K{sub 2}Ba{sub 7}Si{sub 16}O{sub 40}: 8 mol% Ce{sup 3+}, m Eu{sup 2+}. The critical distance between Ce{sup 3+} and Eu{sup 2+} ions is calculated to be 25.06 Å by Dexter’s theory. Furthermore, the energy transfer mechanism is dipole-dipole interaction. In addition, the thermal activation energy is calculated to be 0.26 eV. The CIE coordinates can be tuned from blue to green by increasing Eu{sup 2+} ions. All results suggest that K{sub 2}Ba{sub 7}Si{sub 16}O{sub 40}: Ce{sup 3+}, Eu{sup 2+} is potentially useful for near-UV pumped white LEDs.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Most spin-1/2 transition-metal ions do have single ion anisotropy

The cause for the preferred spin orientation in magnetic systems containing spin-1/2 transition-metal ions was explored by studying the origin of the easy-plane anisotropy of the spin-1/2 Cu{sup 2+} ions in CuCl{sub 2}·2H{sub 2}O, LiCuVO{sub 4}, CuCl{sub 2}, and CuBr{sub 2} on the basis of density functional theory and magnetic dipole-dipole energy calculations as well as a perturbation theory treatment of the spin-orbit coupling. We find that the spin orientation observed for these spin-1/2 ions is not caused by their anisotropic spin exchange interactions, nor by their magnetic dipole-dipole interactions, but by the spin-orbit coupling associated with their crystal-field split d-states. Our study also predicts in-plane anisotropy for the Cu{sup 2+} ions of Bi{sub 2}CuO{sub 4} and Li{sub 2}CuO{sub 2}. The results of our investigations dispel the mistaken belief that magnetic systems with spin-1/2 ions have no magnetic anisotropy induced by spin-orbit coupling.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Far field emission profile of pure wurtzite InP nanowires

We report on the far field emission profile of pure wurtzite InP nanowires in comparison to InP nanowires with predominantly zincblende crystal structure. The emission profile is measured on individual nanowires using Fourier microscopy. The most intense photoluminescence of wurtzite nanowires is collected at small angles with respect to the nanowire growth axis. In contrast, zincblende nanowires present a minimum of the collected light intensity in the direction of the nanowire growth. Results are explained by the orientation of electric dipoles responsible for the photoluminescence, which is different from wurtzite to zincblende. Wurtzite nanowires have dipoles oriented perpendicular to the nanowire growth direction, whereas zincblende nanowires have dipoles oriented along the nanowire axis. This interpretation is confirmed by both numerical simulations and polarization dependent photoluminescence spectroscopy. Knowledge of the dipole orientation in nanostructures is crucial for developing a wide range of photonic devices such as light-emitting diodes, photodetectors, and solar cells.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Order and correlation contributions to the entropy of hydrophobic solvation

The entropy of hydrophobic solvation has been explained as the result of ordered solvation structures, of hydrogen bonds, of the small size of the water molecule, of dispersion forces, and of solvent density fluctuations. We report a new approach to the calculation of the entropy of hydrophobic solvation, along with tests of and comparisons to several other methods. The methods are assessed in the light of the available thermodynamic and spectroscopic information on the effects of temperature on hydrophobic solvation. Five model hydrophobes in SPC/E water give benchmark solvation entropies via Widom’s test-particle insertion method, and other methods and models are tested against these particle-insertion results. Entropies associated with distributions of tetrahedral order, of electric field, and of solvent dipole orientations are examined. We find these contributions are small compared to the benchmark particle-insertion entropy. Competitive with or better than other theories in accuracy, but with no free parameters, is the new estimate of the entropy contributed by correlations between dipole moments. Dipole correlations account for most of the hydrophobic solvation entropy for all models studied and capture the distinctive temperature dependence seen in thermodynamic and spectroscopic experiments. Entropies based on pair and many-body correlations in number density approach the correct magnitudes but fail to describe temperature and size dependences, respectively. Hydrogen-bond definitions and free energies that best reproduce entropies from simulations are reported, but it is difficult to choose one hydrogen bond model that fits a variety of experiments. The use of information theory, scaled-particle theory, and related methods is discussed briefly. Our results provide a test of the Frank-Evans hypothesis that the negative solvation entropy is due to structured water near the solute, complement the spectroscopic detection of that solvation structure by identifying the structural feature responsible for the entropy change, and point to a possible explanation for the observed dependence on length scale. Our key results are that the hydrophobic effect, i.e. the signature, temperature-dependent, solvation entropy of nonpolar molecules in water, is largely due to a dispersion force arising from correlations between rotating permanent dipole moments, that the strength of this force depends on the Kirkwood g-factor, and that the strength of this force may be obtained exactly without simulation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Ion aggregation in high salt solutions. III. Computational vibrational spectroscopy of HDO in aqueous salt solutions

The vibrational frequency, frequency fluctuation dynamics, and transition dipole moment of the O—D stretch mode of HDO molecule in aqueous solutions are strongly dependent on its local electrostatic environment and hydrogen-bond network structure. Therefore, the time-resolved vibrational spectroscopy the O—D stretch mode has been particularly used to investigate specific ion effects on water structure. Despite prolonged efforts to understand the interplay of O—D vibrational dynamics with local water hydrogen-bond network and ion aggregate structures in high salt solutions, still there exists a gap between theory and experiment due to a lack of quantitative model for accurately describing O—D stretch frequency in high salt solutions. To fill this gap, we have performed numerical simulations of Raman scattering and IR absorption spectra of the O—D stretch mode of HDO in highly concentrated NaCl and KSCN solutions and compared them with experimental results. Carrying out extensive quantum chemistry calculations on not only water clusters but also ion-water clusters, we first developed a distributed vibrational solvatochromic charge model for the O—D stretch mode in aqueous salt solutions. Furthermore, the non-Condon effect on the vibrational transition dipole moment of the O—D stretch mode was fully taken into consideration with the charge response kernel that is non-local polarizability density. From the fluctuating O—D stretch mode frequencies and transition dipole vectors obtained from the molecular dynamics simulations, the O—D stretch Raman scattering and IR absorption spectra of HDO in salt solutions could be calculated. The polarization effect on the transition dipole vector of the O—D stretch mode is shown to be important and the asymmetric line shapes of the O—D stretch Raman scattering and IR absorption spectra of HDO especially in highly concentrated NaCl and KSCN solutions are in quantitative agreement with experimental results. We anticipate that this computational approach will be of critical use in interpreting linear and nonlinear vibrational spectroscopies of HDO molecule that is considered as an excellent local probe for monitoring local electrostatic and hydrogen-bonding environment in not just salt but also other confined and crowded solutions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Spin polarization transfer by the radical pair mechanism

In a three-site representation, we study a spin polarization transfer from radical pair spins to a nearby electron or nuclear spin. The quantum dynamics of the radical pair spins is governed by a constant exchange interaction between the radical pair spins which have different Zeeman frequencies. Radical pair spins can recombine to the singlet ground state or to lower energy triplet states. It is then shown that the coherent dynamics of the radical pair induces spin polarization on the nearby third spin in the presence of a magnetic field. The spin polarization transfer depends on the difference between Zeeman frequencies, the singlet and triplet recombination rates, and on the exchange and dipole-dipole interactions between the different spins. In particular, the sign of the polarization depends on the exchange coupling between radical pair spins and also on the difference between singlet and triplet recombination rate constants.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Electronic structure investigation of atomic layer deposition ruthenium(oxide) thin films using photoemission spectroscopy

Analyzing and manipulating the electronic band line-up of interfaces in novel micro- and nanoelectronic devices is important to achieve further advancement in this field. Such band alignment modifications can be achieved by introducing thin conformal interfacial dipole layers. Atomic layer deposition (ALD), enabling angstrom-precise control over thin film thickness, is an ideal technique for this challenge. Ruthenium (Ru{sup 0}) and its oxide (RuO{sub 2}) have gained interest in the past decade as interfacial dipole layers because of their favorable properties like metal-equivalent work functions, conductivity, etc. In this study, initial results of the electronic structure investigation of ALD Ru{sup 0} and RuO{sub 2} films via photoemission spectroscopy are presented. These experiments give insight into the band alignment, growth behavior, surface structure termination, and dipole formation. The experiments were performed in an integrated vacuum system attached to a home-built, stop-flow type ALD reactor without exposing the samples to the ambient in between deposition and analysis. Bis(ethylcyclopentadienyl)ruthenium(II) was used as precursor and oxygen as reactant. The analysis chamber was outfitted with X-ray photoemission spectroscopy (LIXPS, XPS). The determined growth modes are consistent with a strong growth inhibition situation with a maximum average growth rate of 0.21 Å/cycle for RuO{sub 2} and 0.04 Å/cycle for Ru.{sup 0} An interface dipole of up to −0.93 eV was observed, supporting the assumption of a strongly physisorbed interface. A separate experiment where the surface of a RuO film was sputtered suggests that the surface is terminated by an intermediate, stable, non-stoichiometric RuO{sub 2}/OH compound whose surface is saturated with hydroxyl groups.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Sub- and super-luminar propagation of structures satisfying Poynting-like theorem for incompressible generalized hydrodynamic fluid model depicting strongly coupled dusty plasma medium

The strongly coupled dusty plasma has often been modelled by the Generalized Hydrodynamic (GHD) model used for representing visco-elastic fluid systems. The incompressible limit of the model which supports transverse shear wave mode is studied in detail. In particular, dipole structures are observed to emit transverse shear waves in both the limits of sub- and super-luminar propagation, where the structures move slower and faster than the phase velocity of the shear waves, respectively. In the sub-luminar limit the dipole gets engulfed within the shear waves emitted by itself, which then backreacts on it and ultimately the identity of the structure is lost. However, in the super-luminar limit the emission appears like a wake from the tail region of the dipole. The dipole, however, keeps propagating forward with little damping but minimal distortion in its form. A Poynting-like conservation law with radiative, convective, and dissipative terms being responsible for the evolution of W, which is similar to “enstrophy” like quantity in normal hydrodynamic fluid systems, has also been constructed for the incompressible GHD equations. The conservation law is shown to be satisfied in all the cases of evolution and collision amidst the nonlinear structures to a great accuracy. It is shown that monopole structures which do not move at all but merely radiate shear waves, the radiative term, and dissipative losses solely contribute to the evolution of W. The dipolar structures, on the other hand, propagate in the medium and hence convection also plays an important role in the evolution of W.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗