Post-impact Conditions Research Articles

Simulations of Prebiotic Chemistry under Post-Impact Conditions on Titan.

The problem of how life began can be considered as a matter of basic chemistry. How did the molecules of life arise from non-biological chemistry? Stanley Miller’s famous experiment in 1953, in which he produced amino acids under simulated early Earth conditions, was a huge leap forward in our understanding of this problem. Our research first simulated early Earth conditions based on Miller’s experiment and we then repeated the experiment using Titan post-impact conditions. We simulated conditions that could have existed on Titan after an asteroid strike. Specifically, we simulated conditions after a potential strike in the subpolar regions of Titan that exhibit vast methane-ethane lakes. If the asteroid or comet was of sufficient size, it would also puncture the icy crust and bring up some of the subsurface liquid ammonia-water mixture. Since, O’Brian, Lorenz and Lunine showed that a liquid water-ammonia body could exist between about 102–104 years on Titan after an asteroid impact we modified our experimental conditions to include an ammonia-water mixture in the reaction medium. Here we report on the resulting amino acids found using the Titan post-impact conditions in a classical Miller experimental reaction set-up and how they differ from the simulated early Earth conditions.

A theoretical exercise in the modeling of ground-level ozone resulting from the K–T asteroid impact: Its possible link with the extinction selectivity of terrestrial vertebrates

The extinction pattern of the Maastrichtian indicates that long-term and short-term events contributed to the Cretaceous–Tertiary (K–T) mass extinction at 65 Ma. However, it is not clear how the impact events are linked with the extinction selectivity; e.g. non-avian dinosaurs became extinct, whereas birds survived. The post-impact air quality is discussed, and attention is focused on the then land vertebrates. Although ground-level (tropospheric) O 3 is a powerful irritant on the order of 0.1 ppm toxicity, the presence of ground-level O 3 has hardly been considered since the K–T impact theory was reported about 30 years ago. Under the post-impact conditions reconstructed by simulating the carbon cycle (including isotope balance) and impact chemistry, a trajectory model suggests that the then photochemical reactions formed ground-level O 3 whose concentration was apparently low at ∼ 1.0 ppm, but it is much greater than the current level of ∼ 0.04 ppm: that is, an O 3 concentration above the health-threatening level persisted on the ground after the K–T impact. All land vertebrates must have suffered from respiratory O 3 irritation at the time. However, analysis suggests that variables of O 3 characteristics – hourly variation, short half-life in water and decomposition due to catalytic effects in soil – were randomly combined with variables of lifestyle features such as habitat, torpor, etc. to form new variables (i.e. survival rates): a high survival probability for amphibians; middle/high probabilities for semi-aquatic reptiles, mammals and birds; low/middle probabilities for marsupials and terrestrial reptiles; and a zero probability for non-avian dinosaurs.

How to hit home runs: Optimum baseball bat swing parameters for maximum range trajectories

Improved models for the pitch, batting, and post-impact flight phases of a baseball are used in an optimal control context to find bat swing parameters that produce maximum range. The improved batted flight model incorporates experimental lift and drag profiles (including the drag crisis). An improved model for bat–ball impact includes the dependence of the coefficient of restitution on the approach relative velocity and the dependence of the incoming pitched ball angle on speed. The undercut distance and bat swing angle are chosen to maximize the range of the batted ball. The sensitivity of the maximum range is calculated for all model parameters including bat and ball speed, bat and ball spin, and wind speed. Post-impact conditions are found to be independent of the ball–bat coefficient of friction. The lift is enhanced by backspin produced by undercutting the ball during batting. An optimally hit curve ball will travel farther than an optimally hit fastball or knuckleball due to increased lift during flight.

Hydrodynamical simulations of the stream–core interaction in the slow merger of massive stars

We present detailed simulations of the interaction of a stream emanating from a mass-losing secondary with the core of a massive supergiant in the slow merger of two stars inside a common envelope. The dynamics of the stream can be divided into a ballistic phase, starting at the L1 point, and a hydrodynamical phase, where the stream interacts strongly with the core. Considering the merger of a 1- and 5-M⊙ star with a 20-M⊙ evolved supergiant, we present two-dimensional hydrodynamical simulations using the prometheus code to demonstrate how the penetration depth and post-impact conditions depend on the initial properties of the stream material (e.g. entropy, angular momentum, stream width) and the properties of the core (e.g. density structure and rotation rate). Using these results, we present a fitting formula for the entropy generated in the stream–core interaction and a recipe for the determination of the penetration depth based on a modified Bernoulli integral.

Optimization of the clubface shape of a golf driver to minimize dispersion of off-center shots

The objective was to optimize the post-impact conditions of a golf driver and golf ball in order to minimize dispersion of a drive for off-center hits. When a golf ball is struct by a clubhead at a point away from the “sweetspot” on the clubface, spin is induced on the ball which makes it curve during flight. Over the years, clubmakers have made the clubface slightly convex in shape in order make off-center hits land as close to the fairway as possible. A general, three-dimensional impact model using principles of momentum conservation on rigid bodies was used to extract the spin and velocity vectors of the ball after impact. An aerodynamic model including drag, lift and skin friction was then used to obtain the landing position of the ball. An optimization routine was used to calculate the optimum clubface shape to minimize golf ball dispersion from the middle of the fairway, for off-center hits. In order to have an accurate simulation of impact on a computer, the mass and inertia tensor of the clubhead was experimentally measured. The clubface shape relative to the center of gravity of the clubhead was also measured. The impact computer program and golf ball trajectory computer programs were verified by using the golfing robot “Iron Byron” to hit various shots on the clubface of a particular driver. The computer simulation yielded results of ball landing positions from the middle of the fairway that fell within the standard deviations of those experimentally measured. The optimization routine was used to find the optimum clubface shape to minimize golf ball dispersion for off-center hits, for a particular driver swung at a certain initial velocity in a certain direction. The clubface shape was modeled in the impact program as an ellipsoid. After running the optimization program, the average dispersion from the middle of the fairway for the worst possible off-center hit locations was reduced on the average from 8.075 to 2.198 yards. The optimization program demonstrated its effectiveness in determining the optimum clubface to minimize dispersion of off-center hits.