Hard-shell Model Research Articles

Electrical percolation threshold of magnetostrictive inclusions in a piezoelectric matrix under simulated sintering conditions

Magnetoelectric (ME) composites can be produced by embedding magnetostrictive H particles in a piezoelectric E matrix derived from a piezoelectric powder precursor. Previously, using a bi-disperse hard-shell model (Barbero and Bedard in Comput Part Mech, 2018. https://doi.org/10.1007/s40571-017-0165-4 ), it has been shown that the electrical percolation threshold of the conductive H phase can be increased by decreasing the piezoelectric E particle size, relative to the H phase particle size, and by increasing short-range affinity between the E and H particles. This study builds on our previous study by exploring what happens during sintering of the ME composite when either the H or E particles undergo deformation. It was found that deformation of the H particles reduces the percolation threshold, and that deformation of E particles increases inter-phase H–E mechanical coupling, thus contributing to enhancing of ME coupling.

Evolution of the energy-loss-spectrum profile with the projectile mass in impulsive ion-molecule collisions

Systematic analysis is made for illuminating the mechanism of rotational and vibrational excitations in an impulsive ion-molecule collision from the viewpoint of its sudden nature. Variation of the energy-loss spectrum with the projectile mass is examined in the collision system of an alkali-metal ion with a nitrogen molecule at a hyperthermal energy of 27 eV using a common interaction potential. The spectra are obtained by the classical trajectory calculation and compared with two sudden-limit models---the hard-shell model for rigid-rotor molecules and the hard-potential model for vibrating-rotor molecules [A. Ichimura and M. Nakamura, Phys. Rev. A 69, 022716 (2004)]. For a projectile much lighter than the target, the vibrational and rotational excitation occurs in such a way that the hard-potential model predicts, producing a spectral profile with double peaks. As the projectile mass increases, the vibrational suddenness is degraded so that the vibrational excitation becomes quenched, while the spectral profile still shows a double-peak structure explainable with the hard-shell model. Subsequently, as the projectile mass further increases, the rotational suddenness is also degraded so that the spectrum indicates a profile departing far from the prediction of the hard-shell model; the deeply inelastic peak is suppressed and the nearly elastic peak is enhanced. Such spectral deformation actually occurs in an experimental result reported for ${\mathrm{Na}}^{+}--{\mathrm{N}}_{2}$ collisions [M. Nakamura, S. Kita, and T. Hasegawa, J. Phys. Soc. Jpn. 56, 3161 (1987)]. Eventually, the deeply inelastic peak disappears due to temporary excitation during a collision.

Double impulse effects in ion-molecule collisions at hyperthemal energies

SynopsisThe possibility of double impulse phenomenon in a single collision event is studied by the hard-shell model. Such an effect would be observed if the projectile is as heavy as target and the interaction potential has a strong anisotropy.

Rotational Alignment of NO (A2Σ+) from Collisions with Ne

We report the direct angle-resolved measurement of collision-induced alignment of short-lived electronically excited molecules using crossed atomic and molecular beams. Utilizing velocity-mapped ion imaging, we measure the alignment of NO in its first electronically excited state (A(2)Σ(+)) following single collisions with Ne atoms. We prepare A(2)Σ(+) (v = 0, N = 0, j = 0.5) and by comparing images obtained using orthogonal linear probe laser polarizations, we experimentally determine the degree of alignment induced by collisional rotational excitation for the final rotational states N' = 4, 5, 7, and 9. The experimental results are compared to theoretical predictions using both a simple classical hard-shell model and quantum scattering calculations on an ab initio potential energy surface (PES). The experimental results show overall trends in the scattering-angle dependent polarization sensitivity that are accounted for by the simple classical model, but structure in the scattering-angle dependence that is not. The quantum scattering calculations qualitatively reproduce this structure, and we demonstrate that the experimental measurements have the sensitivity to critique the best available potential surfaces. This sensitivity to the PES is in contrast to that predicted for ground-state NO(X) alignment.

Analysis of gross vibrational-rotational energy-loss spectra inLi+−N2collisions with the hard-potential model

The energy-loss spectra in large-angle ${\mathrm{Li}}^{+}+{\mathrm{N}}_{2}$ scatterings are analyzed with the hard-potential model recently proposed, along with the previous hard-shell model. The respective roles of rotational and vibrational excitations are revealed through systematic comparisons of experimental spectra with the models in a wide range of energies $(8--100\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$ and angles (40\ifmmode^\circ\else\textdegree\fi{}--120\ifmmode^\circ\else\textdegree\fi{}). The effect of vibrational excitation is found to manifest itself in the shifts of double peaks. Their energy dependence is accounted for by the shape of the equipotential surface as well as by the vibrational suddenness in a collision. The peak position is shown to be sensitive to the curvature of the surface at the orientation angle of 90\ifmmode^\circ\else\textdegree\fi{}, hence to the three-body potential. The unacceptable result of a previous semiclassical calculation is suggested to come from the inappropriate potential taken.

De-Perimeterisation: Benefits and limitations

De-Perimeterisation is a new term to describe phenomena becoming common in modern ICT environments. It refers to the erosion of the hard-shell model used to describe the structure of traditional information security implementations while capturing the growing requirement for perimeters to be breached in order to facilitate commerce and collaboration. The Jericho Forum, formed by a group of leading information security managers, has started an exploration of De-Perimeterisation concentrating on identifying its scope and creating working groups to study and specify requirements. This paper, after a review, discusses the benefits and the limitations of this approach.

Rotational rainbows in high energy H+CO scattering

Large-scale coupled-channel scattering calculations are reported for collisions of H with CO for zero total angular momentum and total energies between 0.60 and 1.00 eV, where two to three vibrational states of CO and many rotational states are open. An ab initio global potential surface is used in these calculations. Rotational rainbows are observed in the final rotational distributions, thermally averaged over initial rotational states for 300 K, for the ground and first excited final vibrational states of CO. The energy dependence of these rainbows is determined and shown to be well described by a simple hard-shell model. In addition, classical trajectory calculations are reported at 1.0 eV total energy and compared to the quantum results.

Rotational Excitation in Moderate-Energy Na+–N2 and Na+–CO Collisions

Rotational and vibrational excitations in Na + –N 2 , Na + –CO collisions at the center-of-mass energies of 27 eV≤ E ≤192 eV were studied both experimentally and theoretically. A rotational rainbow-like structure was observed in the energy loss spectra. Theoretical analyses of the collisions were carried out by a simple hard-shell model, and by the scattering calculation with the infinite-order-sudden approximation as well as by the classical trajectory method. These analyses confirmed that the characteristic structure observed in these experiments was due to the rotational excitation, which played an important role in a large energy transfer. This study is an extension of the previous paper of Hasegawa et at. (J. Phys. B (At. Mol. Phys.) 18 (1985) 3775). The experimental results of the previous work are summarized and their theoretical analyses are described in detail.

Rotational rainbows: An IOS study of rotational excitation of hard-shell molecules

The hard-shell model for rotationally inelastic scattering is studied within the infinite-order-sudden (IOS) approximation. In addition to the rotational rainbow oscillations of the differential cross sections for j = 0→j′ transitions, a pronounced diffraction structure for small j′ (j′≊0, 2, 4, and 6) and small scattering angles is observed. A classical and semiclassical IOS approximation developed recently is compared with the quantal results for hard-shell He–Na2 collisions at 0.1 eV. The semiclassical IOS approximation leads to a simple (almost closed form) formula for the inelastic differential cross sections. Very good agreement with the quantal results is obtained with the exception of the small angle region for low Δj transitions, which is dominated by diffraction structures. The validity of the IOS approximation for hard-shell molecules is discussed. The model results for He–Na2 are compared with IOS calculations using a soft ab initio potential surface. The results differ drastically with the exception of the region of backward scattering, where the rotational rainbow oscillations are in good agreement. The integral cross sections show the same disagreement—again with the exception of high j′ excitation, which is dominated by wide-angle scattering.

Differential cross sections for Δ m transitions in sudden atom-molecule collisions

Differential ( jm j ) → ( j'm j' ) cross sections in repulsive He-Na 2 collisions are calculated within the IOS approximation probing various choices for the effective angular momentum quantum number l̄. Oscillatory structures in Δ m distributions almost independent of the collisional dynamics are explained by a classical hard-shell model.