Academic literature on the topic 'Ballistic bombardment'

We present results from an atomistic computer simulation model of the sputtering of gold crystal surfaces under 500 eV ion bombardment by Au and Ar ions for doses up to 10 14 ions cm −2 . The multi time-scale technique uses molecular dynamics to calculate the fast ballistic collision processes in the early stages of the cascade, whereas an on-the fly kinetic Monte Carlo technique is used to model the relaxation and diffusion processes between successive ion impacts when the defect motion has begun to be dominated by rare events. The results indicate a large amount of crystalline recovery between impacts, some facetting of the crystal surfaces but no large sub-surface defect accumulation. Because of this recovery process, sputtering yields and energy distributions are in good agreement with those obtained assuming a perfect crystal surface and also with those experimentally measured.

Very low energy electrons in a solid should behave like Bloch electrons and will interact with perturbations of the atomic lattice, that is, with phonons. So we use the acoustic phonon scattering for replacing the elastic binary encounter approximation of the Mott scattering for electrons with low energies E < 100 eV. For ballistic electrons (1 eV < E < Eg) and higher energies up to 1 keV we determined the acoustic phonon scattering and the impact ionization rate by means of the “backscattering-versus-range” proof and respective η(E0) − R(E0) diagrams. Electron trajectories demonstrate the relatively short range of primary electrons (PE) with energies E > 50 eV due to strong impact ionization losses (cascading) and the much greater range of secondary electrons (SE) with E < 50 eV, finally as a consequence of less effective phonon losses. The field-dependent transport parameters allow us to model the self-consistent charge transport and charging-up of insulating SiO2 layers during electron bombardment maintained by the current components of primary electrons jPE, secondary electrons jSE, and associated ballistic holes jBH, as well as by Fowler–Nordheim field injection jFN from the substrate. The resulting distributions of currents j(x,t), charges ρ(x,t), electric fields F(x,t), and the potential V(x,t) across the dielectric layer explain the phenomena of field-enhanced and field-blocked secondary electron emission with rates δ [gel ] 1.

ABSTRACTWe studied the irradiation effects on Ti and Zr surfaces in slightly oxidizing environment (rarefied dry air, 500°C) using multi-charged argon ions in the low MeV range (1 – 9 MeV) to the aim of determining the respective role of the electronic and nuclear stopping power in the operating oxidation process under irradiation. We have shown that ballistic collisions contribute significantly to the enhanced Ti and Zr oxidation under MeV argon bombardment. We have also shown that the projectile energy plays a significant role in the overall process.A significant oxide film thickening is visible on titanium under irradiation, taking the form of a well-defined oxidation peak between 1 and 4 MeV, as a result of the Nuclear Backscattering Spectroscopy and Spectroscopic Ellipsometry studies.A significant oxide film thickening is also visible on zirconium under same irradiation conditions, at 4 and 9 MeV, as a result of the NBS study. Work is in progress in order to determine how the modified oxidation process depends in this case on the projectile energy.

Extended AbstractSaturn’s ring particles and airless moons are exposed to a large flux of interplanetary debris, principally comets and comet dust. Collisions with this debris are responsible for both physical and dynamical changes in objects orbiting about Saturn. Physical changes include cratering of large bodies and catastrophic disruption of small bodies. Dynamical changes, which are analyzed in this paper, include orbital alteration (principally of ring particles) and changes in spin state (which are only important for moons, as ring particle spins are continually altered by mutual collisions).Saturn’s rings are rapidly being eroded by impacts of hypervelocity meteoroids in cometary orbits. Ejecta from these impacts will, in most cases, remain in orbit about Saturn and eventually be reaccreted by the rings, possibly at a different radial location. The resulting mass transport has been suggested as the cause of some of the features observed in Saturn’s rings (see Durisen 1984 for a review). Previous attempts to model this transport have used numerical simulations which have not included effects of angular momentum transport coincident with this mass transport. I have developed an analytic model for ballistic mass transport in Saturn’s rings. The model includes the effects of angular momentum advection and shows that the net material movement due to the combined effects of mass and angular momentum transport is roughly half that calculated when angular momentum advection is ignored. See Lissauer (1984) for further details.All of Saturn’s mid-sized moons are rotating synchronously with their orbital period; thus, the same hemisphere of these moons always faces the planet, and the same point is always at the center of the satellite’s leading hemisphere (the apex). The satellites orbit Saturn with velocities ranging from 14 km/sec for Mimas to 8.5 km/sec for Rhea and 3.3 km/sec for Iapetus. These speeds are a significant fraction of the encounter velocities between comets and the Saturn system (~ 10−25 km/sec); thus, due to a type of “windshield effect” (more raindrops hit the windshield of a moving car than hit the rear window), more comets will collide with the moons’ leading hemispheres than with their trailing hemispheres; also, higher relative velocities between comets and the moons will lead to larger craters for impacts by comets of a given mass on the leading hemispheres. The combination of these effects suggests that regions of the satellites’ surfaces near the apex should be much more heavily cratered than regions near the antapex (Shoemaker and Wolfe 1982). Such a major cratering asymmetry has not been observed (Plescia and Boyce 1983). A similar situation exists for Jupiter’s moons Ganymede and Callisto (Passey and Shoemaker 1982).McKinnon (1981) suggested that stochastic reorientation of the moons by impact-induced “spinup” during the establishment of the cratering record tended to equilibrate the crater densities between hemispheres. I have re-examined the dynamics of this problem, and I conclude that most impacts large enough to have caused “spinup” would have catastrophically disrupted the moons in question (Lissauer 1985).

This paper reports the characterization of the velocity (energy) dependencies of the Al + secondary ion emission produced by 0.5 keV and 5 keV Ne + and Ar + bombardment of polycrystalline pure aluminium. The distributions of secondary Al + ions over their kinetic energy were measured for emission energies of 1–1000 eV without applying electric fields to force the ions into the mass–energy analyzer. To extract the ionization probability, the measured energy distributions of emitted ions were normalized with respect to reference energy distributions of neutral atoms. The reference distributions were obtained by original numerical simulations, as well as analytically, through a sophisticated normalization of the Thompson distribution. It was shown that for both extraction methods, the logarithmic plots of the normalized secondary ion fraction versus the normal component of the reciprocal ion velocity (the reciprocal or inverse velocity plots) are nonmonotonic, with two peaks and two linear portions situated at a low emission energy (Ek=5–25 eV ) and at a high emission energy (Ek=80–280 eV ). The linear portions were fit by exponential dependency P+∝ exp (-v0/vn) with two different values of the characteristic velocity v0. For the low emission energy, the value v01~(3.3±0.2)×106 cm / s was independent of the mass and energy of the projectiles. However, for the high emission energy, the characteristic velocity depended on the projectile's mass, M, namely v02~(5.3±0.3)×106 cm / s for Ne + and v02~(8.1±0.3)×106 cm / s for Ar +; the ratio v02( Ne +)/v02( Ar +) is close to the value [Formula: see text]. This indicates that ballistic mechanisms might contribute to affect the high-energy part of the reciprocal velocity plots along with nonballistic ionization processes, which are generally believed to be the only significant factor for the plots.

The method of biological ballistics (biolistic transformation, genetic bombardment) of plants is one of the most modern methods used for direct gene transfer into plant cells. The main advantages of this method include the ability to simultaneously incorporate several target genes into the plant genome, carry out transfer without unnecessary agrobacterial parts and plasmid DNA sequences, and the short time needed to produce transgenic cells. For different plant objects, the efficiency of obtaining transgenic plants by the ballistic method varies from 1 to 3 %. For potato plants, the transformation efficiency is quite low at the moment and the selection of optimal conditions for biolistics is one of the pressing issues of practical biotechnology. This article presents a successful experience of introducing two genes of interest into two potato varieties using the biolistic approach. The results of biolistic transformation experiments are presented for two types of explants: potato internodes and calli of the varieties Aksor and Nevskiy. Of the 862 explants used for transformation, 56 regenerated plants were obtained. PCR screening of transformants revealed one plant with the insertion of the chitinase gene, one with the insertion of the endo-β-1,3-glucanase gene, and co-transformation by both genes was confirmed in four regenerants. The average transformation efficiency for potato explants was 0.7 %. A high number of regenerants (56) as opposed to a low number of transformants (6) reflects an attempt to increase the number of regenerants by using a lower concentration of the selective agent (kanamycin). Although this approach requires more effort, it can be used to produce potato lines with integrated genes of interest for further use in crop breeding. The lines of potato obtained in the current study by introducing two genes associated with the plant response to fungal pathogens will be further assessed for their resistance to fungal diseases and, if successful, will be used in potato crop breeding.

The law of naval warfare as it existed in 1899 and as it is understood in 1999 exhibits a few similarities but many differences. The fundamental similarity is that the law of naval warfare can be seen, then as now, as consisting primarily of customary international law. The many differences in this law have been caused by the major changes in war at sea and the law of the sea. In 1899 war at sea meant combat primarily by gunfire between surface warships, control of maritime commerce, and shore bombardment. Today, war at sea also involves nuclear-powered aircraft carriers; supersonic aircraft, helicopters and tilt-rotor aircraft; submarines; high-speed patrol craft; ballistic, cruise, and other guided missiles; long-range secure communications for command, control, computers, intelligence, surveillance, and reconnaissance; radar; underwater sound technology; electronic and information warfare; satellites in space; unmanned aerial and undersea vehicles; and stealth and computer technology; as well as expeditionary and amphibious capabilities. Nevertheless, the fundamental role of navies continues to be to establish control at sea or to deny it to the enemy, linking that control to broad political and economic issues ashore. In view of these constants and changes, this article reviews the state of the law of naval warfare at the end of the nineteenth and twentieth centuries and assesses its future prospects.

The initial development of large rockets was driven by military rivalry. The von Braun programs of military space expansionism are a ladder of projects starting with bombardment and culminating in planetary dominance, each considered in detail in this chapter. Ballistic missiles hurling nuclear weapons at intercontinental distances are commonly not considered space weapons but inherently are because they employ the frictionless vacuum of space to achieve their distinctive high speed. This means humanity’s largest and most consequential space program is hiding in plain sight, an unknown known. Information satellite force multipliers increase the potency of other weapons. There are many ways to destroy satellites, and an antisatellite race is starting. Shooting down ballistic missiles remains largely impossible, despite vast expenditures. Wrapping orbital space with hundreds of satellite battle stations, an “Earth Net,” might roll back the nuclear revolution and establish planetary hegemony. Visionary astro-Archimedeans propose stationing nuclear weapons in deep space, and using asteroids as planetoid bombs.