Kevin R. Grazier

Imaging of Titan from the Cassini spacecraft

Titan, the largest moon of Saturn, is the only satellite in the Solar System with a substantial atmosphere. The atmosphere is poorly understood and obscures the surface, leading to intense speculation about Titans nature. Here we present observations of Titan from the imaging science experiment onboard the Cassini spacecraft that address some of these issues. The images reveal intricate surface albedo features that suggest aeolian, tectonic and fluvial processes; they also show a few circular features that could be impact structures. These observations imply that substantial surface modification has occurred over Titans history. We have not directly detected liquids on the surface to date. Convective clouds are found to be common near the south pole, and the motion of mid-latitude clouds consistently indicates eastward winds, from which we infer that the troposphere is rotating faster than the surface. A detached haze at an altitude of 500 km is 150–200 km higher than that observed by Voyager, and more tenuous haze layers are also resolved.

A Multirate Störmer Algorithm for Close Encounters

We present, analyze, and test a multirate Stormer-based algorithm for integrating close encounters when performing N-body simulations of the Sun, planets, and a large number of test particles. The algorithm is intended primarily for accurate simulations of the outer solar system. The algorithm uses stepsizes H and hi , i = 1, ⋯, Np , where h i ≪ H and Np is the number of planets. The stepsize H is used for the integration of the orbital motion of the Sun and planets at all times. H is also used as the stepsize for the integration of the orbital motion of test particles when they are not undergoing a close encounter. The stepsize hi is used to integrate the orbital motion of test particles during a close encounter with the ith planet. The position of the Sun and planets during a close encounter is calculated using Hermite interpolation. We tested the algorithm on two contrasting problems, and compared its performance with the existing method which uses the same stepsize for all bodies (this stepsize must be significantly smaller than H to ensure the close encounters are integrated accurately). Our tests show that the integration error for the new and existing methods are comparable when the stepsizes are chosen to minimize the error, and that for this choice of stepsizes the new method requires considerably less CPU time than the existing method.

High order explicit Runge---Kutta Nyström pairs

Explicit Runge–Kutta Nyström pairs provide an efficient way to find numerical solutions to second-order initial value problems when the derivative is cheap to evaluate. We present new optimal pairs of orders ten and twelve from existing families of pairs that are intended for accurate integrations in double precision arithmetic. We also present a summary of numerical comparisons between the new pairs on a set of eight problems which includes realistic models of the Solar System. Our searching for new order twelve pairs shows that there is often not quantitative agreement between the size of the principal error coefficients and the efficiency of the pairs for the tolerances we are interested in. Our numerical comparisons, as well as establishing the efficiency of the new pairs, show that the order ten pairs are more efficient than the order twelve pairs on some problems, even at limiting precision in double precision.

The performance of phase-lag enhanced explicit Runge-Kutta Nyström pairs on N-body problems

Explicit Runge-Kutta Nystrom methods with enhanced phase-lag order are intended for long integrations of initial value ordinary differential equations describing free oscillations or free oscillations of high frequency and forced oscillations of low frequency. Numerical comparisons by others of RKN4(3), RKN6(4) and RKN8(6) pairs has established that the pairs with enhanced phase-lag order are more efficient on the intended problems than general purpose pairs. We investigate if these gains in efficiency extend to N-body problems used to model the orbital dynamics of the Solar System. The emphasis in our comparisons is on the RKN8(6) pairs because we are interested in long, accurate integrations. We have included the RKN4(3) and RKN6(4) pairs principally to gain insight about how the gains in efficiency depend on the order. Our main finding is that the gains for the RKN8(6) pair extend to the system of major planets except at severe accuracy requirements, and to the system of regular satellites of these planets. In addition, we found for Keplers two-body problem that the gains can be sensitive to small changes in eccentricity.

Heavy Metal: AIs and Robots in Cinema

“Would you like fries with that?” is not only how students with technical majors mock their liberal arts peers, it is an example of the suggestive marketing that has long been commonplace in fast food restaurants. Now, the concept of suggestive marketing has exploded into a whole new dimension. Shop on a cloud-based marketing site like Amazon.com and purchase composer Bear McCreary’s Caprica soundtrack (see our discussion with Bear in Chap. 9), and the site will also offer you links to every CD he’s ever released, CDs that other shoppers who have purchased his material have purchased, and, oh, here’s a book about Caprica, and one about Battlestar Galactica as well.

The Gravity of the Situation: Orbits

“Mr. Sulu, assume standard orbit.” How often have we heard Captain Kirk utter those words? The sheer number of scenes to entire screenplays set on either a space station or a spaceship means that a surprising amount of sci-fi drama occurs while the heroes are simply going around and around and around. Recent examples include The 100 (2014–), Elysium (2013), and Gravity (2013).

Prologue: For Sake of Argument

We argue. A lot. With the Internet now a mainstay in most of our lives, arguments that were once conflagrations confined to the local pub, barbershop, or sports arena, now spread like wildfire to the desktops of tens of thousands of complete strangers. While, traditionally, watercooler debates have taken the form of, “Drew Brees is at least as good as Aaron Rodgers! Did you even watch the game?” or “Did you see what that jackass in the White House did this time?”, cyberspace infernos ignited by scientific topics like climate change, vaccinations, evolution, and genetically modified organisms have assumed a much larger role in the realm of public debate.

Let’s Get Digital: Computers in Cinema

Today is a typical day. Waking up is difficult because you had a very long day yesterday, and worked well into the evening. At least you have a beautiful view this morning, as the rising sun glints off the Jemez Mountains. Drinking your government-issued coffee with your breakfast, you decided that this will be a two-cup morning, because today is going to be a long one, too. Walking from your home to work means a stop at the security checkpoint. After showing the guard your credentials, you walk to your building in the secure area, then to your desk, where you will sit, along with row after row after row of other women with similar desks, spending the day doing mathematical calculations.

The Many-Body Problem: The Culture of Science

To a physicist, a “body” is any object with mass. Depending upon the problem at hand, it can be an atom, a block of wood, a person, a plane, a train, an automobile, a comet, a planet, a star, a black hole, even an entire galaxy. If we want to calculate the trajectories of two bodies moving under their mutual influence—for example, a single planet orbiting a star—that is referred to as a two-body problem. There are reasonably simple equations that can define the state—the positions and velocities of both bodies—of that system at any time.

Putting Science In, Not Taking Drama Out: The Culture of Hollywood

This book, along with its predecessor, has examined and explained science concepts and phenomena that have appeared on the big and little screen, the issues and complexities relating to science accuracy, how the depiction of screen scientists meshes with real life scientists, and how the depiction of the culture of science is at least as important as the depiction of individual researchers. Now it is time to flip the script, and put the culture of Hollywood under the microscope.