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Jets of highly energized plasma with relativistic velocities are associated with black holes ranging in mass from a few times that of the Sun to the billion-solar-mass black holes at the centres of galaxies (1). A popular but unconfirmed hypothesis to explain how the plasma is energized is the 'internal shock model', in which the relativistic flow is unsteady (2). Faster components in the jet catch up to and collide with slower ones, leading to internal shocks that accelerate particles and generate magnetic fields (3). This mechanism can explain the variable, high-energy emission from a diverse set of objects (4-7), with the best indirect evidence being the unseen fast relativistic flow inferred to energize slower components in X-ray binary jets (8,9). Mapping of the kinematic profiles in resolved jets has revealed precessing and helical patterns in X-ray binaries (10,11), apparent superluminal motions (12,13), and the ejection of knots (bright components) from standing shocks in the jets of active galaxies (14,15). Observations revealing the structure and evolution of an internal shock in action have, however, remained elusive, hindering measurement of the physical parameters and ultimate efficiency of the mechanism. Here we report observations of a collision between two knots in the jet of nearby radio galaxy 3C 264. A bright knot with an apparent speed of (7.0 ± 0.8)c, where cis the speed of light in a vacuum, is in the incipient stages of a collision with a slower-moving knot of speed (1.8 ± 0.5) c just downstream, resulting in brightening of both knots--as seen in the most recent epoch of imaging., We obtained deep V-band imaging of 3C 264, a radio galaxy 91 megaparsecs (Mpc) from Earth with the Advanced Camera for Surveys (ACS) on board the Hubble Space Telescope (HST) [...]

This paper is devoted to study the acceleration and collision of charged particles in a general regular space-time. Using angular momentum, energy, and components of four-velocity, we explore the effect of charged particles on the center of mass energy. It is found that the collision energy of charged particles (independent of both singularity as well as horizon) is greater than that of uncharged particles. This depends not only on the mass to charge ratio of the black hole but also on the charge of the particle. Finally, we evaluate the collision energy of charged particles for a regular black hole, a particular example. PACS Nos.: 95.30.Sf, 04.70.-s. Nous etudions ici l'acceleration et les collisions de particules chargees dans un espace-temps regulier general. Utilisant le moment angulaire, l'energie et les composantes de la quatre-vitesse, nous explorons l'effet de particules chargees sur l'energie du centre de masse. Nous trouvons que l'energie de collision des particules chargees (independante d'une singularite et d'un horizon) est plus grande que celle des particules non chargees. Ceci depend non seulement du rapport masse sur charge du trou noir mais egalement de la charge de la particule. Finalement, nous evaluons l'energie de collision de particules chargees pour un trou noir regulier, un cas particulier., 1. Introduction That black hole (BH) could serve as a particle accelerator is an interesting fact favored by recent work. The collision of charged particles near a BH can produce [...]

Crustal deformation along the present-day northern margin of the Tibetan Plateau has occurred since mid to late Eocene time, soon after India collided with Eurasia. Assuming that on these distance and time scales the lithosphere can be approximated using a thin viscous sheet, we show that far-field lithospheric deformation caused by an indenting boundary is expected to start shortly after collision begins. When a strong region analogous to cratonic lithosphere like that of the Tarim Basin is included in the calculations, shear and vertical strain rates concentrate along the southern edge of the strong region, resulting in enhanced deformation there. In calculations scaled to the dimensions of India and the Tibetan Plateau, shear and vertical strain rates on the northern edge of the plateau increase soon after collision begins. Crustal thickening accelerates later in the calculations. We propose that the apparent increased exhumation (and perhaps surface uplift) around 10 Ma may signal the arrival of the thickening front. Citation: Dayem, K. E., P. Molnar, M. K. Clark, and G. A. Houseman (2009), Far-field lithospheric deformation in Tibet during continental collision, Tectonics, 28, TC6005, doi: 10.1029/2008TC002344.

In continuation of our series of works on the phenomenological studies on production of particles in various high-energy collisions, we attempt here to deal exclusively with some very crucial aspects of Au-Au collisions at RHIC-BNL. With emphasis on understanding the qualitative and quantitative properties of several important observables related to Au-Au interactions at RHIC, we have also endeavored to analyze and assess, if possible, the limits to the successes and failures of such absolutely phenomenological approaches. As all the models in the domain of high-energy physics are invariably and essentially phenomenological in nature, we have also tried to pinpoint the main and major constrictions of and constraints on these approaches-cum-models. By this yardstick, even the so-called Standard Model (SM), which is too greatly lauded and taken for granted ,cannot escape our critical remarks that are cast on the general framework of what is termed 'phenomenology', in the realm of physics in particular and of science in general. PACS Nos.: 25.75.-q, 13.60.Hb, 13.60.Le, 13.85.Ni Pour continuer notre serie d'articles qui etudient la production de particules dans differentes collisions de haute energie, nous nous penchons ici sur des aspects cruciaux des collisions Au-Au observees au RHIC-BNL. Insistant sur la comprehension des proprietes qualitatives et quantitatives de plusieurs observables relies aux interactions Au-Au au RHIC, nous nous sommes employes a analyser et a evaluer, si possible, les limites des succes et des echecs de telles approches totalement phenomenologiques. Comme tous les modeles en physique des hautes energies sont essentiellement phenomenologiques en nature, nous avons aussi essaye de circonscrire les contraintes et restrictions les plus importantes et centrales de ces approches et modeles. Selon ce point de vue, meme le celebre Modele Standard qui est loue au dela de toute proportion et pris comme acquis ne peut echapper a ce type de critique dans un cadre general des theories phenomenologiques en physique en particulier et en sciences en general. [Traduit par la Redaction], It's not what you don't know that gets you in trouble, it's what you think you know.--Mark Twain. 1. Introduction This study is set in the context of a controversy [...]

A ball can be hit faster if it is projected without spin, but it can be hit farther if it is projected with backspin. Measurements of the tradeoff between the speed and spin for a baseball impacting a baseball bat are presented. The results are inconsistent with a collision model in which the ball rolls off the bat and instead imply tangential compliance in the ball, the bat, or both. If the results are extrapolated to the higher speeds that are typical of the game of baseball, they suggest that a curveball can be hit with greater backspin than a fastball, but by an amount that is less than would be the case in the absence of tangential compliance. [DOI: 10.1119/1.2209246]

O'Brien and Greenberg [O'Brien, D.P., Greenberg. R., 2005. Icarus 178, 179-212] developed a self-consistent numerical model of the collisional and dynamical evolution of the main-belt and NEA populations that was tested against a diverse range of observational and theoretical constraints. In this paper, we use those results to update the asteroid cratering model of Greenberg et al. [Greenberg, R., Nolan, M.C., Bottke, W.F., Kolvoord, R.A., Veverka, J., 1994. Icarus 107, 84-97: Greenberg, R., Bottke, W.F, Nolan, M., Geissler, P., Petit, J., Durda, D.D., Asphaug, E., Head, J., 1996. Icarus 120, 106-118], and show that the main-belt asteroid population from the O'Brien and Greenberg collisional/dynamical evolution modeling is consistent with the crater records on Gaspra, Ida, Mathilde, and Eros, the four asteroids that have been observed by spacecraft. Keywords: Asteroids; Cratering; Collisional physics

The lobula giant movement detector (LGMD) is an identified neuron in the locust brain that responds most strongly to the images of an approaching object such as a predator. Its computational model can cope with unpredictable environments without using specific object recognition algorithms. In this paper, an LGMD-based neural network is proposed with a new feature enhancement mechanism to enhance the expanded edges of colliding objects via grouped excitation for collision detection with complex backgrounds. The isolated excitation caused by background detail will be filtered out by the new mechanism. Offline tests demonstrated the advantages of the presented LGMD-based neural network in complex backgrounds. Real time robotics experiments using the LGMD-based neural network as the only sensory system showed that the system worked reliably in a wide range of conditions; in particular, the robot was able to navigate in arenas with structured surrounds and complex backgrounds. Index Terms--Collision detection, complex environment, dynamic visual scene, mobile robot, visual neural network.

A fast, efficient, real-time method for the quantitative analysis of the peroxide explosive, TATP, is described. The method utilizes rapid ion-molecule reactions of chemical reagent ions with the vapor above solid TATP. The reactions of three reagent ions ([H.sub.3][O.sup.+], [O.sub.2.sup.-]-, N[O.sup.+]) were examined. Although all three ions exhibited a near-collision-rate reaction with TATP, only N[O.sup.+] showed product ions that provide unequivocal evidence for a TATP-based explosive. The limit of detection of TATP in the gas phase is 10 ppb (4 x [10.sup.10] mol [L.sup.-1]).

The key issues associated with fluid modeling of a low temperature plasma discharge and charged-particle swarms called colloquium, in both hydrodynamic and nonhydrodynamic circumstances, at the level of momentum and energy balance are identified. The result suggests that assumption and approximation concerning closure of fluid equation in general, and heat flux term in particular are pivotal for nonhydrodynamic situation.

Collision induced processes (CIP) are important and play a central role in the mechanism governing heterogeneous catalytic processes at pressures and elevated temperatures. A number of different CIPs are discussed with a strong emphasis on the utilization of molecular dynamics (MD) simulations.

We study the ballistic pendulum in a situation that is not usually considered where the bullet shot into a hanging block requires a finite time (the collision time) to come to rest relative to the block. During this time the block undergoes a non-negligible displacement. A slow collision is one for which the block's displacement during the collision time is an appreciable fraction of its maximum displacement. For slow collisions, the quantitative results of our model differ significantly from the standard ballistic pendulum treatment. Suitably generalized momentum and energy relations are evaluated and provide a check on the numerical solutions. This work extends the treatment of a familiar problem and demonstrates the utility of computational tools accessible to undergraduates. [DOI: 10.1119/1.1538572]

It is well known that asteroid families have steeper absolute magnitude (H) distributions for H < 12-13 values than the background population. Beyond this threshold, the shapes of the absolute magnitude distributions in the family/background populations are difficult to determine, primarily because both populations are not yet observationally complete. Using a recently generated catalog containing the proper elements of 106,284 main belt asteroids and an innovative approach, we debiased the absolute magnitude distribution of the major asteroid families relative to the local background populations. Our results indicate that the magnitude distributions of asteroid families are generally not steeper than those of the local background populations for H > 13 (i.e., roughly for diameters smaller than 10 km). In particular, most families have shallower magnitude distributions than the background in the range 15-17 mag. Thus, we conclude that, contrary to previous speculations, the population of kilometer-size asteroids in the main belt is dominated by background bodies rather than by members of the most prominent asteroid families. We believe this result explains why the Spacewatch, Sloan Digital Sky Survey, and Subaru asteroid surveys all derived a shallow magnitude distribution for the dimmer members of the main belt population. We speculate on a few dynamical and collisional scenarios that can explain this shallow distribution. One possibility is that the original magnitude distributions of the families (i.e., at the moment of the formation event) were very shallow for H larger than ~ 13, and that most families have not yet had the time to collisionally evolve to the equilibrium magnitude distribution that presumably characterizes the background population. A second possibility is that family members smaller than about 10 km, eroded over time by collisional and dynamical processes, have not yet been repopulated by the break-up of larger family members. For this same reason, the older (and possibly characterized by a weaker impact strength) background population shows a shallow distribution in the range 15-60 km. Keywords: Asteroids; Collisional physics

The motion of a stone skimming over a water surface is considered. A simplified description of the collisional process of the stone with water is proposed. The maximum number of bounces is estimated by considering both the slowing down of the stone and its angular stability. The conditions for a successful throw are discussed.

The characterization of the performance of baseball bats is presented from a physics point of view. The goal is to define a set of laboratory measurements that can be used to predict performance in the field. The concept of a model-independent collision efficiency, which relates the post-collision ball speed to the initial ball and bat speeds, is introduced and its properties are investigated. It is shown to provide a convenient link between laboratory and field measurements. Other performance metrics are presented, related to the collision efficiency, and evaluated according to their predictive power. Using a computational model, it is shown that bat performance depends on the interplay of the elasticity of the ball-bat collision, the inertial properties of the ball and bat, and the bat swing speed. It is argued that any method of determining performance needs to take all of these factors into account. A new method is proposed and compared with commonly used existing methods.

By studying the diffusion operator in Grover's quantum search algorithm, we find an analogy between quantum searching and classical, elastic two-body collisions. We exploit this mathematical analogy using a thought experiment involving multiple collisions between two bodies to help illuminate why Grover's quantum search algorithm works. Related issues are discussed. [DOI: 10.1119/1.1514231]

The rate coefficients of collisional transfer between lambda-doublet levels of OH[X(super 2)Pi(3/2), epsilon = 1, j = 3.5, and 6.5] in collisions with He, Ar, N2, and HNO3 are measured. An infrared-ultraviolet double resonance method is used for this purpose.

This paper reports the results of experiments on projectile impact into regolith targets at various impact angles. Copper projectiles of 240 mg are accelerated to 197 to 272 m [s.sup.-1] using an electromagnetic gun. The ejecta are detected by thin Al foil targets as secondary targets, and the resulting holes on the foil are measured to derive the spatial distribution of the ejecta. The ejecta that penetrated the foil are concentrated toward the downrange azimuths of impacting projectiles in oblique impacts. In order to investigate the ejecta velocity distribution, the nondimensional volume of ejecta with velocities higher than a given value is calculated from the spatial distribution. In the case of the vertical impact of the projectile, most ejecta have velocities lower than 24% of the projectile speed (~50 m [s.sup.-1]), and there are only several ejecta with velocities higher than 72 m [s.sup.-1]. This result confirms the existence of an upper limit to the ejection velocity in the ejecta velocity distribution (Hartmann cutoff velocity) (W. K. Hartmann, 1985, Icarus 63, 69-98). On the other hand, it is found that, in the oblique impacts, there are a large number of ejecta with velocities higher than the Hartmann cutoff velocity. The relative quantity of ejecta above the Hartmann cutoff velocity increases as the projectile impact angle decreases. Taking these results with the results of S. Yamamoto and A. M. Nakamura (1997, Icarus 128, 160-170) from impact experiments using an impact angle of 30[degrees], it can be concluded that the ejecta from these regolith targets exhibit a bimodal velocity distribution. Below a few tens of m [s.sup.-1], we see the expected velocity distribution of ejecta, but above this velocity we see a separate group of high-velocity ejecta. Key Words: impact processes; regoliths; cratering; collisional physics.

A dynamical description of estuarial fine sediment aggregation has been developed. The spectrum of fine particle or agglomerate size is represented by a discrete number of classes based on particle mass. Aggregation and disaggregation, respectively, move mass up and down through the classes. The frequency of two- and three-body particle collisions due to Brownian motion, shearing and differential settling is expressed by simple statistical relationships, using a new form of the collision efficiency parameter. This parameter is defined by nondimensional terms accounting for the physical and chemical forces that determine whether close encounters result in collisions. Calculations of the rate of change of sediment mass for each class as the aggregation process approaches equilibrium, when compared with previously obtained data in a Couette chamber, highlight the need to characterize the sediment as to particle density and strength. Near equilibrium, three-body collisions seem to play a major role by disaggregating particles that have been aggregated by the more numerous but less forceful two-body collisions.

The results of a detailed study of the influence of rotational angular momentum on vibrational transfer in the system Li(sub 2)(super *) (vi.ji) + Ne -> Li(sub 2)(super *) (vf.jf) + Ne, where vi,f and ji,f indicate initial and final vibrational and rotational levels and Li(sub 2)(super *) is in its first electronically exited (super 1)(sigma)(sub u)(super +) state are presented. Level-to level in elastic rate constants for ji up to 76 were measured.

The article discusses the cause of dual compression that occurs in elastic collision. The Routh's model is used to analyze conditions for compression.

The collision of Comet Shoemaker-Levy 9 (SL 9) with Jupiter created crescent-shaped ejecta patterns around impact sites. Although the observed impact plumes rose through a similar height of [approximately]3000 km, the radii of the created ejecta patterns differ from impact to impact and generally are larger for larger impacts. The azimuthal angle of the symmetry axis of the ejecta pattern is larger than that predicted by the models of oblique impacts, due to the action of the Coriolis force that rotates ejecta patterns counterclockwise from the south. We study the formation of ejecta patterns using a simple model of ballistic plume above a rotating plane. The ejected particles follow ballistic trajectories and slide horizontally for about an hour after reentry into the jovian atmosphere. The lateral expansion of the plume is stopped by the friction force, which is assumed to be proportional to the square of the horizontal velocity. Two different mass-velocity distributions used in the simulations produce qualitatively similar results. The simulated ejecta patterns fit very well the 'crescents' observed at the impact sites. The sizes and azimuthal angles of symmetry axis of ejecta patterns depend on a parameter L, which has dimension of length and is related to the mass of the fragment. Thus more massive impacts produce larger ejecta patterns that are rotated through a wider angle. Key Words: comets, S-L9; Jupiter; impact processes.

This article presents molecular dynamics of the nonadiabatic phenomenon. The dynamics of atomic and molecular collision and the effects of nonadiabatic state in scattering excited atoms and formation and decomposition of molecular complexes are explained.

The problem of determining the direction in which to hit a perfectly inelastic billiard ball on a circular billiard table such that it bounces off the cushion once and then hits the other ball is analyzed. A new and intuitively interesting geometric derivation of the solution is presented. An analytical equation for a separatrix between areas with two and four solutions is found after examining the solution with respect to the number of allowable paths for any given scenario.

Christiaan Huygens was probably the first person to solve the problem of elastic collisions. He did this in the 1650s when he was only in his early twenties. The first formal publication of his general rule for the outcome of a head-on hard collision was in March 1669 in the Journal des Scavans. Our present paper describes in detail Huygens' work on elastic collisions. We focus particularly on how Huygens' instinct for symmetry led him to a solution in the center-of-gravity reference frame. He readily transformed this solution to other frames using what we now call the Galilean velocity transformation. Huygens' symmetry approach is quite different from the modern description of collisions using Newtonian action and reaction forces.

The significance of the influence of turbulence on collisions and coalescence of small cloud droplets is still an outstanding problem. In particular, the growth of droplets in the radius range from 10 to 15 [[micro]meter] is not well understood. The present research examines whether or not turbulence affects the growth rate of such small drops by simulating trajectories of two hydrodynamically interacting droplets in a turbulent field. The trajectories were calculated with a model based on linear Stokes hydrodynamics. Turbulence was modeled in the form of random Fourier modes with both the space and time spectra prescribed. Both spectra were characterized by Kolmogorov scaling. The space spectrum was modeled in the inertial and dissipation subranges. On the basis of scale analysis, only small-scale time variations were allowed, and the so-called Eulerian-Lagrangian time spectrum was applied. The results show that most collision rates increase moderately in a turbulent flow characterized by rates of energy dissipation of the order of 1, 10, and 100 [cm.sup.2] [s.sup.-3].

A front-tracking finite difference method analyzes the surface tension and deformable fluid interface during three-dimensional simulations of the off-axis collisions of two drops. The bouncing or coalescing of drops depends upon rupturing of the interface between the drops. For coalescing drops, the effect is permanent for small impact parameters but results in a grazing collision for large impact parameters. In the grazing collision, drops coalesce and then separate. The numerical limits for coalescing and grazing collisions are presented.

The Ida/Dactyl system is the first confirmed asteroid/satellite pair as well as the first family asteroid to be studied in detail by a spacecraft. We explore consequences for Ida of formation by disruption of the Koronis parent body. A significant flux of projectiles onto Ida in a few years following the formation of the family is found, based on models of the disruption of the Koronis parent body by Marzari et al. (Marzari, F., D. Davis, and V. Vanzani 1995. Icarus 113, 168-187). This flux generated craters at a rate much higher than the current crater production rate; however, the flux decreases rapidly as fragment orbits become randomized. Also, we compare the figure of Ida with figures of equilibrium fluid bodies and find that the interior of Ida is nearly stress-free and that Ida could be a rubble pile. Finally, collisional models predict that Dactyl would have been shattered several times in the past 2 billion years, the lower bound on Ida's age derived from its cratered surface. However, some of the ejecta from such disruptions would be trapped in orbit about Ida, subsequently reaccumulating into a satellite. This process could explain the rather regular shape of Dactyl as well as explaining how Dactyl now exists, given its short (compared with Ida's age) collisional disruption lifetime.

Numerical simulations of the initial stages of the expanding debris field resulting from the disruption of a parent asteroid show that the formation of co-orbiting fragments and even contact binaries is a natural outcome of catastrophic collisions between asteroids. The formation of contact structures is favored over the formation of true orbiting pairs. A wide range of primary-to-secondary size ratios is produced, from Ida/Dactyl-like pairs to small binaries with equal-sized components. Composite configurations with satellites orbiting around contact structures are also possible.

The history of Ida is constrained by its membership in the Koronis family, its satellite Dactyl, the record of impacts left on its surface, and other dynamical, morphological, and spectral properties. Models of crater production and comparably effective erasure processes, combined with the current size-frequency distribution of craters, suggest that the age of the surface is either about 50 myr or >1 byr. The younger age may be inconsistent with the degraded appearance of many craters, while the older age conflicts with the collisional life expectancy of Dactyl. Consideration of Dactyl's evolution may resolve this issue as well as shed light on the formation of Dactyl, the density of Ida, and possible source regions for Ida and Dactyl within the Koronis parent body.

The results of the determination of collisionless explosion plasma expansion into an ionized magnetized medium using kinetic expansions are consistent with those obtained by using the magnetohydrodynamic (MHD) equation. Shifting the ions around the magnetic field lines is a major contributory factor of particle collision. The disorder created by reduced ion free path and ion Larmor radius is necessary for the validity of the gas dynamics equation. The MHD model is suitable to determine explosions in the upper atmosphere.

As Comet Shoemaker-Levy 9 races toward its mid-July collision with the planet Jupiter, considerable public attention is being focused on catastrophic impacts with the Earth--in the past and in the […]

General formulas are given for the masses and spring constants of one-dimensional finite chains with linear dispersion relations, examples of which were given by Herrmann and Schmalzle in 1981 in their discussion of a well-known collision apparatus. The mathematical similarity to the problem of a Boson in a constant magnetic field is shown. The explicit formulas make a study of the continuum limit possible. This is shown to be related to the system of uniform rods studied by Bayman in 1976. Examples are given of chains with quadratic dispersion relations. Resonances that give singularities in the interaction time are discovered in certain chains of elastic spheres.

The attempts to understand the macroscopic behavior of fluids, in particular their nonequilibrium properties, in terms of the dynamics of the many particles, out of which they consist, are sketched from Clausius, in the middle of the 19th century, to the present day. The fundamental role that collisions play for dilute as well as dense gaseous or liquid systems is emphasized. The main difficulty is to identify the relevant collision sequences in the myriads of collisions that go on in a macroscopic system. While for dilute gases uncorrelated binary collisions dominate, as was already known in the 19th century, relevant correlated collision sequences for dense gases and liquids have only been identified in the last 25 years, leading to vortex and cage diffusion. Applications to transport coefficients are discussed.

Canonical equations are used as differential equations of motion to analyze collision or impact for multibody systems. Discontinuity during impact can also be calculated through piecewise analysis by repeatedly integrating these equations to derive momentum balance-impulse equations. The advantages of canonical equations include computation accuracy, compliance with velocity constraints and suitability for impact analysis.

A study is conducted on the swarm parameters in carbon tetrafluoride (CF4) using the Monte Carlo method. Results show that swarm parameter errors caused by the isotropic scattering assumption are high for low and middle values of electric field to gas density ratios. This is attributed to the fact that collisions with excitation of vibrational states exceed the elastic collisions in the vicinity of the Ramsauer minimum.

An analysis of the third corollary to the Laws of Motion in Newton's 'Principia,' reveals that Newton concentrated only on satisfying the corollary mathematically and hence ignored the physical aspects of collision. The collisions described by Newton are physically not possible. Newton describes three types of collisions between two bodies, one of which is three times heavier and larger than the other body. In one of these collisions the total kinetic energy is found to be enhanced which is not possible practically.

The collision cross section of a charged finite cylinder with a beam of ions and electrons in collisionless plasma is calculated. The corresponding charging currents are calculated and have shown that the charging behavior of the nanowire in Maxwellian plasma is described by an equivalent sphere whose radius has depended only on the aspect ratio of the nanowire.