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Results for “COLLISION RATE”

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.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2021

Expected Collision Rates for Tracked Satellites

This analysis estimates collision risks between tracked satellites based on the statistically expected collision rate _Nc and number of collisions Nc, which are closely related to the collision probability Pc. For isolated encounters, Nc equals Pc. For multi-encounter interactions, Nc can exceed Pc and is significantly easier to approximate semi-analytically. Estimating Nc requires integrating the collision rate over time throughout an interaction, with each required _Nc value calculated as a statistical expectation value based on the uncertainty distributions of initial orbital states. The uncertainty distributions are estimated from orbit determination analyses of satellite trajectory measurements. The formulation accounts for the nonlinear orbital motion of the satellites, and derives Nc and _Nc expressions for Monte Carlo simulations as well as semi-analytical approximations for single- and multi-encounter interactions.

Collision Rates↗
DOE OSTI2014

OH{sup +} in astrophysical media: state-to-state formation rates, Einstein coefficients and inelastic collision rates with He

The rate constants required to model the OH{sup +} observations in different regions of the interstellar medium have been determined using state of the art quantum methods. First, state-to-state rate constants for the H{sub 2}(v = 0, J = 0, 1) + O{sup +}({sup 4} S) → H + OH{sup +}(X {sup 3}Σ{sup –}, v', N) reaction have been obtained using a quantum wave packet method. The calculations have been compared with time-independent results to assess the accuracy of reaction probabilities at collision energies of about 1 meV. The good agreement between the simulations and the existing experimental cross sections in the 0.01-1 eV energy range shows the quality of the results. The calculated state-to-state rate constants have been fitted to an analytical form. Second, the Einstein coefficients of OH{sup +} have been obtained for all astronomically significant rovibrational bands involving the X {sup 3}Σ{sup –} and/or A {sup 3}Π electronic states. For this purpose, the potential energy curves and electric dipole transition moments for seven electronic states of OH{sup +} are calculated with ab initio methods at the highest level, including spin-orbit terms, and the rovibrational levels have been calculated including the empirical spin-rotation and spin-spin terms. Third, the state-to-state rate constants for inelastic collisions between He and OH{sup +}(X {sup 3}Σ{sup –}) have been calculated using a time-independent close coupling method on a new potential energy surface. All these rates have been implemented in detailed chemical and radiative transfer models. Applications of these models to various astronomical sources show that inelastic collisions dominate the excitation of the rotational levels of OH{sup +}. In the models considered, the excitation resulting from the chemical formation of OH{sup +} increases the line fluxes by about 10% or less depending on the density of the gas.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Measurements of correlations enhanced collision rates in the mildly correlated regime (Γ~1)

We measure the perpendicular-to-parallel collision rate ν ⊥|| in laser cooled, magnetized ion plasmas in the mildly correlated regime of Γ~1 and find collision rates enhanced by exp(Γ). This ν⊥|| enhancement due to correlations is directly analogous to the enhancement of fusion collisions in hot dense stellar plasmas, as first analyzed by Salpeter [Aust. J. Phys. 7, 373 (1954)]. The enhancement is caused by screening of the repulsive Coulomb potential between charges, allowing closer collisions for a given relative energy. The measurements indicate that the screening is done by thermal particles and allows us to rule out dynamical screening theories, which predict no enhancement to the collisions rate for Γ≲ 1.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Behaviour related flight speeds of Sandwich Terns and their implications for wind farm collision rate modelling and impact assessment

Highlights: • Flight speeds of Sandwich Terns vary with behavioural states. • Flight speed is a vital part of wind turbine collision rate models (CRM) for birds. • The variation in flight speed has major consequences for CRM output. • CRM output is vital for adequate Environmental Impact Assessments. - Abstract: Accurate quantification of flight speeds is a prerequisite to accurately predict the numbers of collision victims of proposed wind farms using collision rate models that are a vital part of Environmental Impact Assessments. We used GPS-loggers on Sandwich Terns to collect novel data on instantaneous flight speeds during foraging trips, separated for different behavioural stages, and applied these estimates in a widely used collision rate model. Average flight speed during a foraging trip corrected for individual variation and flight type was 36.9 ± 12.3 SD km h{sup −1} and flight speed was highest during inbound commuting (44.4 ± 12.0 km h{sup −1}) and lowest during foraging (29.9 ± 10.7 km h{sup −1}). Our results show significant differences in flight speeds of Sandwich Terns between behaviour stages during foraging trips, which resulted in divergent estimates of collision victims due to wind turbines depending on the function of the area in which wind farms are proposed. Since these conclusions are likely to hold for many other bird species, we conclude that behaviour of birds in a proposed wind farm is a factor to take into account when modelling collision rates as part of the Environmental Impact Assessment.

17 WIND ENERGY↗
NASA NTRS1981

Low-temperature He-Na collision rate measurements

The foreign-gas collision broadening of the Na D2 line by He at a temperature of 8 K is measured. These data combined with those of other investigators provide an empirical scaling of the collision rates and cross sections over a wide range of temperatures and relative velocities, respectively.

Zimmermann, M.↗
NASA NTRS1985

Binary collision rates of relativistic thermal plasmas. I Theoretical framework

Binary collision rates for arbitrary scattering cross sections are derived in the case of a beam of particles interacting with a Maxwell-Boltzmann (MB) plasma, or in the case of two MB plasmas interacting at generally different temperatures. The expressions are valid for all beam energies and plasma temperatures, from the nonrelativistic to the extreme relativistic limits. The calculated quantities include the reaction rate, the energy exchange rate, and the average rate of change of the squared transverse momentum component of a monoenergetic particle beam as a result of scatterings with particles of a MB plasma. Results are specialized to elastic scattering processes, two-temperature reaction rates, or the cold plasma limit, reproducing previous work.

Dermer, C. D.↗
NASA NTRS1979

Earth-crossing asteroids - Orbital classes, collision rates with earth, and origin

Asteroids that can intersect the orbit of the earth are discussed, which include Aten asteroids (semimajor axis (a) less than 1 AU, aphelion greater than 0.983 AU), Apollo asteroids (a greater than 1 AU, perihelion less than 1.017 AU), and Amor asteroids (perihelion distance between 1.017 and 1.3 AU). The principal sources of earth-crossing asteroids appear to be extinct comet nuclei and collision fragments from regions in the main asteroid belt. The total population of earth-crossers is estimated at 13,000, of which approximately 8% are Atens, 50% are Apollos, and 40% are Amors,and the present collision rate of such asteroids with the earth is estimated at about 3.5 objects, to absolute magnitude 18, per million years.

Shoemaker, E. M.↗
DOE OSTI2011

Enhanced light-assisted-collision rate via excitation to the long-lived 5S{sub 1/2}-5D{sub 5/2} molecular potential in an {sup 85}Rb magneto-optical trap

We report measurements of a significant increase in the two-body loss rate in an {sup 85}Rb magneto-optic trap (MOT) caused by the addition of light resonant with the 5P{sub 3/2}-to-5D{sub 5/2} transition (776 nm) in Rb. Exposure to the additional light resulted in up to a factor of 5 decrease in the steady-state number of atoms in the MOT. This loss is attributed to more than an order of magnitude increase in the light-assisted collision rate brought about by the 776-nm light. By measuring the intensity dependence of the loss rate, the loss channel was identified to be the relatively long-lived 5S{sub 1/2}-5D{sub 5/2} molecular potential.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS1991

The rate of collisions due to Brownian or gravitational motion of small drops

Quantitative predictions of the collision rate of two spherical drops undergoing Brownian diffusion or gravitational sedimentation are presented. The diffusion equation for relative Brownian motion of two drops is derived, and the relative motion of pairs of drops in gravitational sedimentation is traced via a trajectory analysis in order to develop theoretical models to determine the collision efficiencies, both with and without interparticle forces applied between the drops. It is concluded that finite collision rates between nondeforming fluid drops are possible for Brownian diffusion or gravitational sedimentation in the absence of attractive forces, in stark contrast to the prediction that lubrication forces prevent rigid spheres from contacting each other unless an attractive force that becomes infinite as the separation approaches zero is applied. Collision rates are shown to increase as the viscosity of the drop-phase decreases. In general, hydrodynamic interactions reduce the collision rates more for gravitational collisions than for Brownian collisions.

Zhang, Xiaoguang↗
DOE OSTI2021

Tutorial: Langevin Dynamics methods for aerosol particle trajectory simulations and collision rate constant modeling

The Langevin Dynamics (LD) method (also known in the literature as Brownian Dynamics) is routinely used to simulate aerosol particle trajectories for transport rate constant calculations as well as to understand aerosol particle transport in internal and external fluid flows. This tutorial intends to explain the methodological details of setting up a LD simulation of a population of aerosol particles and to deduce rate constants from an ensemble of classical trajectories. We discuss the applicability and limitations of the translational Langevin equation to model the combined stochastic and deterministic motion of particles in fields of force or fluid flow. The drag force and stochastic “diffusion” force terms that appear in the Langevin equation are discussed elaborately, along with a summary of common forces relevant to aerosol systems (electrostatic, gravity, van der Waals, …); a commonly used first order and a fourth order Runge-Kutta time stepping schemes for linear stochastic ordinary differential equations are presented. A MATLAB® implementation of a LD code for simulating particle settling under gravity using the first order scheme is included for illustration. Scaling analysis of aerosol transport processes and the selection of timestep and domain size for trajectory simulations are demonstrated through two specific aerosol processes: particle diffusion charging and coagulation. Fortran® implementations of the first order and fourth order time-stepping schemes are included for simulating the 3D motion of a particle in a periodic domain. Lastly, potential applications and caveats to the usage of LD are included as a summary.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1993

Raman linewidths and rotationally inelastic collision rates in nitrogen

Using the N2-N2 interaction potential of van der Avoird et al. (1986) rotationally inelastic collision cross sections have been computed within the infinite order sudden (IOS) approximation, assuming the molecules are distinguishable. Methods for enforcing detailed balance and correcting for effects of inelasticity, which are ignored in the IOS approximation, are considered, including the energy corrected sudden (ECS) method. Suitably averaged cross sections are compared with experimental Raman Q-branch linewidths for temperatures from 295 to 1500 K and with recently measured room temperature state-to-state rates. Agreement is rather good, especially if ECS corrections are applied.

Green, Sheldon↗
NASA NTRS1992

Collision rates and impact velocities in the Main Asteroid Belt

Wetherill's (1967) algorithm is presently used to compute the mutual collision probabilities and impact velocities of a set of 682 asteroids with large-than-50-km radius representative of a bias-free sample of asteroid orbits. While collision probabilities are nearly independent of eccentricities, a significant decrease is associated with larger inclinations. Collisional velocities grow steeply with orbital eccentricity and inclination, but with curiously small variation across the asteroid belt. Family asteroids are noted to undergo collisions with other family members 2-3 times more often than with nonmembers.

Farinella, Paolo↗
NASA NTRS1974

ICR study of nonreactive ion-molecule collision rate constants for Cl/-/ and Cr/CO/5/-/

Determination of experimental momentum transfer rate constants for systems of Cl(-) and Cr(CO)5(-) ions by means of an ion cyclotron resonance (ICR) line-broadening technique. It is found that in the pure polarization limit of small ion/large neutral collisions the Langevin ion mobility theory gives good agreement with experimental results. A comparison of isotropic and anisotropic neutral systems suggests that a correction for the anisotropic systems is necessary. Beyond the pure polarization limit the Langevin theory gives poor predictions for ion mobilities. The adjustable parameter, gamma, of the Mason-Schamp (12-6-4) potential function permits unique solution of the ion mobility for Cr(CO)5(-) in a wide range of neutral gases. The large values of gamma obtained for most of these systems imply, in terms of the Mason-Schamp theory, that the r to the minus 6th power contribution to the potential function is significant.

Dymerski, P. P.↗
NASA NTRS1986

Binary collision rates of relativistic thermal plasmas. II - Spectra

Spectra of importance for the analysis of relativistic thermal plasmas are numerically calculated assuming a thermal form for the particle distribution functions. Complete sets of optically thin thermal electron-proton, electron-electron, and electron-positron bremsstrahlung spectra are calculated throughout the transrelativistic regime of electron temperatures and compared with approximate expressions for the spectra in the nonrelativistic and extreme relativistic regimes of temperature. A method for calculating accurate secondary particle production spectra in proton-proton collisions from threshold to the highest energies is presented based on an isobaric model near threshold and scaling representations at high energies. The production spectra of charged and neutral pions resulting from proton-proton collisions in relativistic proton plasmas are calculated, and the resultant electron, positron, and gamma-ray spectra from the decay of secondary pions are presented.

Dermer, C. D.↗