Collision effects

Caldin E F, de Forest L and Queen A 1990 Steric and repeated collision effects in diffusion-controlled reactions in solution J. Chem. See. Faraday Trans. 86 1549-54... 

Natural linewidths are broadened by several mechanisms. Those effective in the gas phase include collisional and Doppler broadening. Collisional broadening results when an optically active system experiences perturbations by other species. Collisions effectively reduce the natural lifetime, so the broadening depends on a characteristic impact time, that is typically 1 ps at atmospheric pressure ... 

Characterizing the radiation dose to persons as a result of exposure to radiation is a complex issue. It is difficult to (1) measure internally the amount of energy actually transferred to an organic material and to correlate any observed effects with this energy deposition and (2) account for and predict secondary processes, such as collision effects or biologically triggered effects, that are an indirect consequence of the primary interaction event. 

Note that the lubrication effect due to particle collisions in liquid is significant. The liquid layer dynamics pertaining to the lubrication effect was examined by Zenit and Hunt (1999). Zhang et al. (1999) used a Lattice-Boltzmann (LB) simulation to account for a close-range particle collision effect and developed a correction factor for the drag force for close-range collisions, or the lubrication effect. Such a term has been incorporated in a 2-D simulation based on the VOF method (Li et al., 1999). Equation (36) does not consider the lubrication effect. Clearly, this is a crude assumption. However, in the three-phase flow simulation, this study is intended to simulate only the dilute solids suspension condition (ep = 0.42-3.4%) with the bubble flow time of less than 1 s starting when bubbles are introduced to the solids suspension at a prescribed ep. 

The particle collision effect under this simulation condition, therefore, would be small. 

The dynamic behavior of liquid-crystalline polymers in concentrated solution is strongly affected by the collision of polymer chains. We treat the interchain collision effect by modelling the stiff polymer chain by what we refer to as the fuzzy cylinder [19]. This model allows the translational and rotational (self-)diffusion coefficients as well as the stress of the solution to be formulated without resort to the hypothetical tube model (Sect. 6). The results of formulation are compared with experimental data in Sects. 7-9. 

Particles migrate to the wall region by means of particle-particle collisions and diffusion, and through particle-wall collision effects which tend to widen the particle velocity distribution in the radial direction. 

In these considerations, it must be kept in mind that there is a stellar spike around the black hole at the Galactic Center. The steepness of this stellar spike is however not very well know. With large uncertainties, Genzel et al.(2003) estimate the slope of the stellar spike to be 7stars 1.3-1.4. This means that the current stellar spike is probably shallow. We may think that the stellar spike is our best proxy for the dark matter spike. If so, also the dark matter spike would also be shallow, and thus inconsequential for neutralino signals. However, the dark matter and stellar spikes follow very different evolution histories, because contrary to the dark matter, binary collisions of stars and coalescence of two stars into one at collisions effectively relax the stellar system to a shallower spike. 

Finally we note that studies of control in solution [186, 187] indicate that control in the presence of collisional effects is indeed possible. For example, coherent control of the dynamics of I3 in ethanol and acetonitrile has been demonstrated. Specifically, I3 was excited with a 30-fs ultraviolet (UV) laser pulse to the first excited state, The resultant wave function was comprised of a localized wave function on the ground electronic state and a corresponding depletion of wave function density, that is, a hole, on the ground electronic state. In this instance the target of the control was the nature of the spectrum associated with the coherences associated with the symmetric stretch. By manipulating various attributes of the exciting pulse (intensity, frequency, and chirp of the excitation pulse), aspects of the spectrum were controlled, despite the decoherence associated with collision effects. 

Despite such successes, it was obvious that only a continuous wave laser source can do justice to the extremely sharp 1S-2S transition. Production of intense cw radiation near 243 nm remained long an elusive goal. Satisfactory power levels of several mW were first achieved by B. COUILLAUD et al. [19] by summing the frequency of a 351 nm argon laser and a 790 nm dye laser in a crystal of KDP. In the first cw experiment with this source [11], the power in the observation cell was further enhanced with a standing wave build-up cavity. Fig. 3 shows two-photon spectra recorded in this way. Although the resolution is much superior to the earlier pulsed spectra, it remains limited to a few MHz by laser frequency jitter, collision effects, and transit-time broadening. A further at least millionfold improvement in resolution should ultimately be achievable. 

It is an experimental fact that cross field transport in fusion edge plasmas cannot be realistically described by the classical Coulomb collision effects. Strictly then a term — q,a/maV (((f (f/Q)) resulting from turbulent fluctuations in the electric field SE and in the phase space density Sfa must be included on the right-hand side of (2.1), see [3]. 

M. Sommerfeld and J. Kussin. Analysis of collision effects for turbulent gas-particle flow in a horizontal channel, part ii. integral properties and validation. Int. J. Multiphase Flow, 29(4) 701-718, 2003. 

Figure 2. Diagram of the existence of thresholds for N and I in QRLPP. Key A, ground state atom As, ground state molecule and L, laser excitation, a At low N, radiative decay of A dominates, b At high N but low I, A collisionally produces an electron which causes no further excitation, c At high N and high I, the electron produced can undergo superelastic and inelastic collisions, effectively completing a self-propagating loop.

A current limitation of the model is the omission of hyperthermal collision effects, particularly with respect to the formation of ions. Another serious disadvantage is the exclusion of winds, with the result that the... 

The most important practical consequence of the failure of the strong collision approximation is that the faU-off curve is shifted to higher pressures, and broadened a little. There are two main approaches to dealing with this situation. It is possible to find parametric corrections for the weak collision effect, which will be introduced below. Alternatively the energy transfer may be treated as a random process with transitions between states occurring on collision. This latter type of approach is called the Master Equation, and is the main subject of Part 3 of this work. 

In reality, more complicated expressions apply because of the multi-step character of the reaction ki and k i depend on the energy E and the angular momentum (quantum number J), and the colhsional energy transfer is a multi-step process with activations and deactivations, to be characterized by a master equation. It has become customary to consider "strong collisions" first and to introduce "weak collision effects" afterwards. For strong collisions, equation (6) takes the form... 

Qxk has a constant value for E > Exk such that every electron-molecule collision effects a reaction of type Rl,... 

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