Mark Lewis

Trinity University, Texas, Computer Science, Faculty Member

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Papers by Mark Lewis

Introduction to scala and its use in CS education

Journal of Computing Sciences in Colleges, 2014

Scala is one of a new generation of hybrid languages that merge the functional and object-oriente... more Scala is one of a new generation of hybrid languages that merge the functional and object-oriented paradigms. Thanks to its concise and expressive syntax, paired with JVM support and Java integration capabilities, Scala has been adopted by many companies and currently leads the pack of second-tier languages in the RedMonk ranking.

Scala for introductory CS

Journal of Computing Sciences in Colleges, Apr 1, 2014

ABSTRACT With adoption by notable companies like Twitter, FourSquare, and Linked in and a positio... more ABSTRACT With adoption by notable companies like Twitter, FourSquare, and Linked in and a position at the top of the second tier of languages in the RedMonk rankings, it is clear that Scala has become the leader among next-generation programming languages. Can the benefits of this hybrid functional/object-oriented language that have attracted many startups and cutting edge developers carry over into the classroom? In this workshop I will introduce participants to the Scala programming language and run them through the benefits that the language can bring to CS1 and CS2. We will start with the REPL and basic scripting environment for coding in the small and see how static typing with type inference can help you out early on. We then progress to look at the basic constructs of the language and show how the uniform syntax fixes many of those trouble spots that you often get with other languages, such as Java. We will spend time on the power and expressivity that the collections library brings to play through the functional aspects of the language and show how you can bring in GUIs and Graphics to keep things visual and more interesting. Some time will also be spent looking at parallelism in Scala.

Modified Huffman Code for Bandwidth Optimization Through Lossless Compression

Advances in Intelligent Systems and Computing, 2018

In the interest of minimizing bandwidth usage, a modified Huffman code structure is proposed, wit... more In the interest of minimizing bandwidth usage, a modified Huffman code structure is proposed, with an accompanying algorithm, to achieve excellent lossless compression ratios while maintaining a quick compression and decompression process. This is important as the usage of internet bandwidth increases greatly with each passing year, and other existing compression models are either too slow, or not efficient enough. We then implement this data structure and algorithm using English text compression as the data and discuss its application to other data types. We conclude that if this algorithm were to be adopted by browsers and web servers, bandwidth usage could be reduced significantly, resulting in cut costs and a faster internet.

The Value of Video Quizzes in a Computer Science Flipped Classroom: An Empirical Study

ABSTRACT

Collisional Simulations of Wakes at the Encke Gap

ABSTRACTS 1045 17P.08 Vertical Distribution of Temperature and Density in a Planetary Ring J. Sch... more ABSTRACTS 1045 17P.08 Vertical Distribution of Temperature and Density in a Planetary Ring J. Schmidt, F. Spahn, 0. Petzschmarm (Universitaet Postsdam, Germany), Heikki Salo (University of Oulu, Fiiiland) We model temperature and density profiles for a dilute planetary ring, based on the hydrodynamic balance equations for momentum and energy of granular flows. Within our approximation the ring consists of inelastic smooth spheres of unique size and mass, while the fluxes of mass, momenturn and energy are linear functions of the gradients of density, ...

Analysis of Ring Wake Simulations

indent= 20pt Collisional N-body simulations at the edge of a perturbed planetary ring are used to... more indent= 20pt Collisional N-body simulations at the edge of a perturbed planetary ring are used to model the edges of the Encke gap in Saturn's rings. A small satellite, Pan, orbits inside the Encke gap and excites forced eccentricities and density wakes on both edges of the gap. The simulations use a local cell method to model a narrow ring using particles of the appropriate size for the A-ring at the proper optical depth. In the simulations we see evidence for shear reversal at the wake peaks. Our results imply that the most ...

Effects of Particle Size on Wakes at the Encke Gap

We will look at the effects caused by particle size distributions on the behavior of the wakes fo... more We will look at the effects caused by particle size distributions on the behavior of the wakes formed at the Encke Gap. The results of simulations using power-law size distributions and bi-modal distributions will be compared to simulations using a single particle size and, where possible, observations. The simulations are performed with a code that uses guiding center coordinates to evolve up to 1,000,000 smooth, inelastic particles and ignores the self gravity of the particles. Included in the results will be damping rates ...

The Effect of Perturbation Magnitude on Narrow Ring Formation

We have previously shown how the perturbations of a nearby moon can cause a broadly distributed s... more We have previously shown how the perturbations of a nearby moon can cause a broadly distributed sparse population of ring particles to become concentrated into narrow rings that not only form, but can also be maintained outside of resonance. We speculated that the separation between the final ringlets was largely determined by the magnitude of the forced eccentricities induced by the moon at closest approach. Here we present simulations where a variety of different moon masses are used to vary the magnitude of the forced ...

Collisional Formation Of Ringlets In High M Resonances

Numerical, N-body simulations were run of ring particles in various mean motion resonances with a... more Numerical, N-body simulations were run of ring particles in various mean motion resonances with a single moon to observe the formation of ringlets. In these simulations the M value of the resonances, moon mass, particle size, and optical depth were varied. The simulations include particle collisions using a velocity dependent normal coefficient of restitution. Transverse friction, spin, and particle self-gravity were ignored. The simulations were run for ten synotic periods and many clearly showed formation of ringlets in ...

A Proactive Load Balancing Policy for Spatial Multi-Agent Simulations

As multi-agent researchers seek to scale their simulations of complex systems towards more realis... more As multi-agent researchers seek to scale their simulations of complex systems towards more realistic levels of agents they are posed with the challenge of balancing the integrity of the system's underlying model against their ability to harness the extra computational power that comes from utilizing multiple interconnected machines. An increased number of agents generates larger workloads on each machine and ensuring that the load of each reflects the resources available to the machine at the time becomes integral in minimizing the ...

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Wakes Magnitudes and Locations on the Edge of the Encke Gap

Results from numerical, N-body simulations of the edge of the Encke Gap to explore Pan wake dynam... more Results from numerical, N-body simulations of the edge of the Encke Gap to explore Pan wake dynamics are presented. The simulations were run from the gap edge out to 260km beyond the gap. In these simulations, optical depth and particle size were varied. The simulations included particle collisions using a velocity dependent normal coefficient of restitution while transverse friction, spin, and particle self-gravity were ignored. The simulations were run for one synodic period, this gives enough time to observe the ...

Why Saturn's F Ring Breaks up into Multiple Ringlets

The conventional explanation for the maintenance of narrow planetary rings against radial spreadi... more The conventional explanation for the maintenance of narrow planetary rings against radial spreading by inter-particle collisions is the confining torques exerted by nearby``shepherd satellites." We offer an alternative explanation that is in better agreement with our N-body simulations of Saturn's F ring. The key observation is that inter-particle collisions cause particles to migrate up eccentricity gradients. This happens for two reasons:(1) Strong eccentricity gradients and strongly correlated orbital phases in a ...

Negative Diffusion in Simulations of Planetary Rings With Near by Moons

Results from simulations of planetary rings with a nearby moon are presented. The setup most clos... more Results from simulations of planetary rings with a nearby moon are presented. The setup most closely resembles the Encke gap, but the results can be extended to the Keeler gap, the F ring, or other narrow rings with nearby shepherd moons. The simulations were done with varying particle distribution, optical depth, perturbation strength (moon mass), and particle size. The simulations clearly show a process we referred to as negative diffusion because the orbits of the ring particles seems to migrate to areas of high density. Only a ...

Self-gravity wakes in saturnian rings: effects of varying location, particle density, and introducing a particle size distribution

We have completed 200 local N-body simulations of the A (130 Mm), B (100 Mm), and C (85 Mm) rings... more We have completed 200 local N-body simulations of the A (130 Mm), B (100 Mm), and C (85 Mm) rings in order to identify systematic differences in the degree of particle clumping into self-gravity wakes as a function of orbital distance from Saturn, classical optical depth (which is proportional to surface density of particles), internal particle density, and dependence on particles of a single size vs. a size distribution. The purpose of exploring such a large parameter space is to constrain each parameter by comparing the ...

Effects of Self-Gravity on Wakes at the Encke Gap

Previous non-self-gravitating simulations of the region around the Encke gap have shown extensive... more Previous non-self-gravitating simulations of the region around the Encke gap have shown extensive complex dynamics in the region due to the perturbation caused by the moon Pan when dissipative particle collisions are considered. While the behavior of the wakes in those simulations shows features seen in Voyager observations, not all the observations are properly modeled. Adding self-gravity increases the realism of the simulated system and could potentially resolve the discrepancies with observations. The ...

Narrow Rings Outside of Resonance

We present the results of high resolution, fully collisional simulations of a narrow ring perturb... more We present the results of high resolution, fully collisional simulations of a narrow ring perturbed by a small nearby satellite over multiple synodic periods. In these simulations we see the formation of ringlets at the first order Lindblad resonance locations. The resonances are so closely spaced that these ringlets begin to interact in only a few synodic periods and merge. Ringlets are maintained outside of the resonance locations by a negative diffusion process like that seen in some of our previous simulations of the edge ...

Collisional formation of arcs in narrow rings

We present the results of simulations showing that the formation of stable arcs in narrow rings p... more We present the results of simulations showing that the formation of stable arcs in narrow rings perturbed by a single eccentric perturber is to be expected. We have been performing simulations of a system resembling Saturn's F ring with a Prometheus like perturber. The ring is circular, but the moon is on an eccentric orbit. We find that in some of these simulations the ring material begins to group in azimuthally confined regions that resemble arcs. This type of behavior had been seen by Showalter and Burns (Icarus 1982 ...

SwiftVis: Data Analysis and Visualization for Planetary Science

Proceedings of the 2007 International Conference on Modeling, Simulation & Visualization Methods, Las Vegas, NV, USA, 2007

ABSTRACT SwiftVis is a tool originally developed as part of a rewrite of Swift to be used for ana... more ABSTRACT SwiftVis is a tool originally developed as part of a rewrite of Swift to be used for analysis and plotting of simulations performed with Swift and Swifter. The extensibility built into the design has allowed us to make SwiftVis a general purpose analysis and plotting package customized to be usable by the planetary science community at large. SwiftVis is written in Java and has been tested on Windows, Linux, and Mac platforms. Its graphical interface allows users to do complex analysis and plotting without having to write custom code.

Computer Simulations of Planetary Rings

Planetary Ring Systems

The local dynamics of planetary rings is governed by the orbital motion, the frequent impacts bet... more The local dynamics of planetary rings is governed by the orbital motion, the frequent impacts between ring particles, their mutual self-gravity, and the perturbations exerted by external satellites and embedded moonlets. In Saturn\u27s dense A and B rings the particles collide ~100 times per orbital revolution. Although the orbital velocities are ~20 km/s, the random velocities related to orbital eccentricities and inclinations are small, of the order of few mm/s (this corresponds to a ring vertical thickness of few tens of meters, excluding strongly perturbed regions). Such gentle impacts do not lead to fragmentation, but still dissipate a significant fraction of random kinetic energy in each collision. This loss is balanced by the viscous gain of energy from the orbital motion around the planet, resulting in a local steady-state in a timescale of few tens of impacts per particle. Characteristics of this energy balance (such as velocity dispersion, geometric thickness, and viscosity) are determined by the frequency and elasticity of impacts, and by the internal density and size distribution of particles. In much longer timescales the ring radial evolution is governed by viscous evolution. Depending on the viscosity–density relation following from the energy balance, the ring can be either stable or unstable against the viscous growth of local perturbations. For example, dense rings composed of quite inelastic particles can become viscously overstable, while less dissipative particles may be prone to viscous instability