# Completed VERUM Projects

**On Copoint Graphs**

Professor Jon Beagley

**Technical Report: On Copoint Graphs**

A convex geometry is a discrete abstraction of convexity defined by a meet-distributive lattice on a finite set. In particular, we study a graph formed from the copoints of a convex geometry. A graph that can be realized in this way from some

convex geometry is called a copoint graph. We demonstrate existence and non-existence for several infinite families of graphs as copoint graphs. We show that the graph join of any non-copoint graph with an arbitrary graph is not a copoint graph. Further, we provide a construction to show that the complement of a copoint graph need not be a copoint graph. We conclude that not all trees are copoint graphs and argue that the Hasse diagram of a convex geometry has a ‘rhomboidal’ structure if and only if its copoint graph is a tree.

**An Agent-based Model of Pollen Competition in ***Arabidopsis thaliana*

Professor Alex Capaldi

*Arabidopsis thaliana*

**Technical Report: An Agent-based Model of Pollen Competition in Arabidopsis thaliana**

In 2016, Swanson et al. showed that when an *Arabidopsis thaliana* stigma is pollinated with equal amounts of pollen by two accessions, Columbia and Landsberg, Columbia pollen sire disproportionately more seeds. This phenomenon is known as nonrandom mating. Previous experiments have investigated nonrandom mating by examining how pollen performance traits such as proportion of pollen germinated, time to germination, and pollen tube growth rates differ between these two accessions. In addition, bioenergetics, such as the energy supplied to pollen tubes from the pistil during fertilization, likely also magnify competition. While plant fertilization is well-studied, the exact mechanics of pollen competition remain unknown. Using an agent-based model, we aim to identify the traits that cause pollen from one accession to sire more offspring than pollen from another accession and to what extent these traits contribute to this process. We calibrate our model against a number of parameters from empirical data to observe the output of seed siring proportions from mixed pollinations; we compare these values to those found in the literature. Our model can also be extended to predict seed siring proportions for other accessions of *Arabidopsis thaliana* given data on their pollen performance traits.

**Colored Motzkin Paths of Higher Order**

Professor Paul Drube

**Technical Report: Colored Motzkin Paths of Higher Order**

Motzkin paths are integer lattice paths that use the steps U = (1, 1), L = (1, 0), and D = (1, −1) and stay weakly above the line y = 0. We generalize Motzkin paths to allow for down steps with multiple slopes and for various coloring schemes on the edges of the resulting paths. These colored, higher-order Motzkin paths provide a general setting where specific coloring schemes yield sets that are in bijection with many well-studied combinatorial objects. We develop bijections between various classes of colored, higher-order Motzkin paths and certain subclasses of l-ary paths, including a generalization of Fine paths, as well as certain subclasses of l-ary trees. All of this utilizes the language of proper Riordan arrays, and we also include a series of results about the Riordan arrays whose entries enumerate sets of generalized Motzkin paths.

**Stabilization of Hamiltonian Systems ****with Multiplicative Noise**

Professor Tiffany Kolba

**Technical Report: Stabilization of Hamiltonian Systems with Multiplicative Noise**

Noise-induced stabilization is the phenomenon where a system of ordinary differential equations is unstable, but by adding randomness, its corresponding system of stochastic differential equations is stable. It has been proven that unstable Hamiltonian systems cannot be stabilized by adding constant noise, where global stochastic boundedness is our notion of stability. In this study, we investigate adding nonconstant noise to two classes of Hamiltonian systems to achieve noise-induced stabilization. Our method for proving noise-induced stabilization consists of constructing local Lyapunov functions on various subsets of the plane, and then smoothing them together to form a global Lyapunov function defined on the entire plane. We also pursue the minimum noise necessary for stabilization of these systems.

**Constructing Copoint Graphs of Convex Geometries**

Professor Jon Beagley

**Technical Report: Constructing Copoint Graphs of Convex Geometries**

We work with copoint graphs of convex geometries. Copoint graphs can be used to study the complex and fairly recent eld of convex geometries. Comparing copoint graphs and their convex geometries helps identify properties. We demonstrate that multiple convex geometries have the same underlying copoint graph. All graphs on one to ve vertices can be represented as possible copoint graphs of some convex geometry. Furthermore, we construct several innite classes of copoint graphs including the complete k-partite graph, path graph, centipede graph, ladder graph, comb graph, pom-pom graph, sharkteeth graph, and broken wheel graph.

**Optimizing the Creditworthiness Threshold of a Bivariate Distribution**

Professor Hui Gong

**Technical Report: Optimizing the Creditworthiness Threshold of a Bivariate Distribution**

Financial institutions must evaluate credit applications when deciding to issue credit. Creditworthiness varies amongst the applicants. Creditors must decide which applications to accept in order to maximize profit. For this paper, we assume applicants are divided into Good and Bad populations. We found optimal threshold values that maximized the creditor’s profit under varying assumptions of Normal, Chi-squared, and Γ-distributions. To do so, we optimized the profit function with respect to the threshold value and we ran simulations to find the threshold value that maximizes the profit.

**Asymmetric Two-Sex Models with a Mate-Finding Allee Effect**

Professor Daniel Maxin

**Technical Report: Asymmetric Two-Sex Models with a Mate-Finding Allee Effect**

In a two-sex demographic model, the most challenging mathematical components are the couple-formation functions. These functions link the number of pairs with the number of available singles. They are usually not detailed enough to include important aspects of social behavior such as: motivation for pairing which may be gender specific, scarcity or abundance of the opposite gender or social/economic factors.

In this research we analyze several two-sex models to better describe asymmetric demographic situations. In particular we focus on a mate-finding Allee effect which models the difficulty of pairing at low population densities and investigate whether this effect is sensitive to changes in sex ratios and/or overall female/male densities. We also compute the Allee threshold which separates population extinction from persistence and test these results against real demographic data from world populations.

**Publication: **Elizabeth Anderson, Daniel Maxin, Jared Ott and Gwyneth Terrett, A logistic two-sex model with mate-finding Allee effect, *Involve, a Journal of Mathematics* 12.8 (2019), 1343–1355. (https://doi.org/10.2140/involve.2019.12.1343)

**Packing Patterns into ππ and ππ^r words**

Professor Lara Pudwell

**Technical Report: Packing Patterns into ππ and ππ^r words**

In this paper we will discuss packing permutation patterns into words of the form ππ, i.e., a permutation followed by itself, and ππ^r, i.e., a permutation followed by its reverse. We consider the optimal packing of patterns of lengths 3 and 4 for the former words and 3, 4, and 5 for the latter. We also discuss the methods by which these packings are obtained and characteristics of patterns which follow a strict upper bound.

**Mathematical Modeling in Ecology: White-nose Syndrome in North American Bats**

Professor Alex Capaldi

**Technical Report: Mathematical Modeling in Ecology: White-nose Syndrome in North American Bats**

White-nose syndrome (WNS) is an infectious disease that affects hibernating bats in North America. First discovered in New York in 2006, it has spread across much of the eastern United States and has also been found in Washington. In a mere ten years, it has wiped out approximately 80% of bats in North America. This summer, we will use mathematical models incorporating difference and/or differential equations to study the spread of WNS, the population dynamics of bats, and to evaluate potential control measures.

**Publication: **Eva Cornwell, David C. Elzinga, Shelby Stowe, and Alex Capaldi, Modeling vaccination strategies to control white-nose syndrome in little brown bat colonies, *Ecological Modelling** 407* (2019), 108724. (https://doi.org/10.1016/j.ecolmodel.2019.108724)

**Set-Valued Young Tableaux and Lattice Paths**

Professor Paul Drube

**Technical Report: Set-Valued Young Tableaux and Lattice Paths**

Standard Young tableaux are two dimensional arrays of positive integers arranged so that the numbers used increase from left to right across each row and increase from top to bottom down each column. Standard Young tableaux of a fixed shape are quickly enumerated via the famous Hook Length Formula, and there are numerous well-studied bijections between standard Young tableaux and other combinatorial objects such as integer lattice paths. In this project, we study a generalization of standard Young tableaux known as standard set-valued Young tableaux, whereby the entries are disjoint sets of integers as opposed to a single integer. The primary focus of our investigation will be the enumeration of these tableaux for a variety of basic shapes, as well as the development of new maps between standard set-valued Young tableaux and integer lattice paths satisfying specific properties.

**Publication: **Paul Drube, Ashley Skalsky, Maxwell Krueger and Meghan Wren, Set-valued Young tableaux and product-coproduct prographs, *Australasian Journal of Combinatorics ***72(1)** (2018), pp.29-54. (https://ajc.maths.uq.edu.au/pdf/72/ajc_v72_p029.pdf)

**Noise-Induced Stabilization of Hamiltonian Systems**

Professor Tiffany Kolba

**Technical Report: Noise-Induced Stabilization of Hamiltonian Systems**

The phenomenon of noise-induced stabilization occurs when an unstable deterministic system of ordinary differential equations is stabilized by the addition of randomness into the system. This is quite a surprising and intriguing phenomenon because one’s first intuition is often that noise will destabilize, rather than stabilize, a system.

Hamiltonian systems are characterized by a Hamiltonian function that is constant along each solution curve. Due to their structure, Hamiltonian systems can never be stabilized by noise that is constant in space. This project will investigate how to deterministically perturb a certain class of unstable Hamiltonian systems in order to retain the instability and essential behavior of the systems, but allow for noise-induced stabilization to occur with constant noise.

**Publication:**T.N. Kolba, A. Coniglio, S. Sparks, and D. Weithers, Noise-Induced Stabilization of Perturbed Hamiltonian Systems, *The American Mathematical Monthly *126(6) (2019), pp. 505-518.(https://www.tandfonline.com/doi/abs/10.1080/00029890.2019.1586502)

**Classification and Characterization of Networks**

Professor Karl Schmitt

**Technical Report: Classification and Characterization of Networks**

Networks and graphs have become an ubiquitous way of describing systems in science, ranging from protein-protein interaction networks to power grids to the internet. The networks generated from different disciplines often exhibit attributes that are very similar within a discipline (e.g. biological:protein networks) but different between disciplines. Many graph models have been proposed to capture important traits and it can often be difficult for researchers to pick the correct model *a priori*.

In this summer project we will work with data mining techniques on network data (such as the www.NetworkRepository.com) and generate graphs to develop, validate, and deploy a learner/predictor for graph classification and most likely theoretical model. This will build on previous student work which created graph ‘fingerprints’ for most of the repository.

An additional direction of research is to investigate comparing graphs (and theoretical models) by developing and comparing regression models that predict the rate of graph discovery or inference.

**Mathematical Modeling in Ecology: Simulating the Reintroduction of the Extinct Passenger Pigeon (Ectopistes migratorius)**

Professor Alex Capaldi

**Technical Report: Mathematical Modeling in Ecology: Simulating the Reintroduction of the Extinct Passenger Pigeon (Ectopistes migratorius)**

The Passenger Pigeon (Ectopistes migratorius) was an iconic species of bird in eastern North America that comprised 25-40% of North American avifauna. Passenger Pigeons went extinct in 1914 due to excessive hunting over the previous 50 years. Current research aims to de-extinct the Passenger Pigeon and someday release the species into its historic range. To determine under which conditions a Passenger Pigeon could survive a reintroduction into a natural habitat, we used two types of models. First, we used a system of delay differential equations to explore the relationship between the young pigeon, adult pigeon, nest predator, and raptor populations. The model incorporates logistic population growth, an Allee effect, and a Holling Type III functional response. Next, we developed a spatially explicit, agent-based model to simulate the population dynamics of the Passenger Pigeon in a number of present-day forest environments. The model incorporates the following stochastic processes: varying availability of food sources, reproduction, and natural death of the Passenger Pigeon. Bio-energetics, tree distributions, and other ecological values were obtained from literature. Results from our simulations suggest that the Passenger Pigeon could survive a reintroduction into a natural environment.

**Publication: **DC Elzinga, E Boggess, J Collignon, A Riederer, A Capaldi, Natural Resource Modeling 33 (4), e12292

(https://onlinelibrary.wiley.com/doi/10.1111/nrm.12292)

**Noise-Induced Stabilization of Stochastic Differential Equations**

Professor Tiffany Kolba

**Technical Report: Noise-Induced Stabilization of Stochastic Differential Equations**

The phenomenon of noise-induced stabilization occurs when an unstable deterministic system of ordinary differential equations is stabilized by the addition of randomness into the system. Noise-induced stabilization is quite an intriguing and surprising phenomenon as one’s first intuition is often that noise will only serve to further destabilize the system. In this paper, we investigate under what conditions one-dimensional, autonomous stochastic differential equations are stable, where we take the notion of stability to be that of global stochastic boundedness. Specifically, we find the minimum amount of noise necessary for noise-induced stabilization to occur when the drift and noise coefficients are power, exponential, or logarithmic functions.

**Publication:** T. Allen, E. Gebhardt, A. Kluball, and T.N. Kolba. Minimal Noise-Induced Stabilization of One-Dimensional Diffusions. Minnesota Journal of Undergraduate Mathematics, Vol 3(1), July 2017. (https://mjum.math.umn.edu/index.php/mjum/article/view/37/30)

**Pattern Avoidance in Reverse Double Lists**

Professor Lara Pudwell

**Technical Report: Pattern Avoidance in Reverse Double Lists**

Pattern avoidance is a branch of combinatorics that arose in 1968 when Donald Knuth began studying stack sorting. One central problem in pattern avoidance is finding the number of permutations of length n that avoid a specific pattern . We expanded this problem to reverse double lists, or lists built by combining a permutation with its reverse. We computed the number of reverse double lists of each length that avoid patterns of up to length four and then conjectured and proved formulas to explain these sequences.

**Publication: **Monica Anderson, Marika Diepenbroek, Lara Pudwell, and Alex Stoll, Pattern avoidance in reverse double lists, *Discrete Mathematics and Theoretical Computer Science* 19.2 (2018), #13. (https://dmtcs.episciences.org/4919)

**Pattern Avoidance in Double Lists**

Professor Lara Pudwell

**Technical Report: Pattern Avoidance in Double Lists**

The motivation for this paper is to continue combinatorics research in the area of pattern avoidance. We have constructed a subset of words to study called “double lists” which are based on the standard permutations used in counting pattern avoiding lists. We will begin this paper with an introduction to pattern avoidance for those unfamiliar. However, the majority of this paper will focus on our own research of pattern avoidance within double lists.

**Publication: **Charles Cratty, Samuel Erickson, Frehiwet Negassi, and Lara Pudwell, Pattern avoidance in double lists, *Involve, a Journal of Mathematics* 10.3 (2017), 379-398. (https://doi.org/10.2140/involve.2017.10.379)

**The Influence of Risk-Taking Behavior on The Evolution of Infectious Diseases**

Professor Daniel Maxin

**Technical Report: ****The Influence of Risk-Taking Behavior on The Evolution of Infectious Diseases**

Individuals facing an infectious disease, consciously or not, evaluate the contamination risk and engage in or avoid risky situations or behaviors. The risk-taking behavior of any individual is probably a very complex functional response that depends on many factors such as: morbidity of the disease, infectiousness, mode of transmission, existence and eﬃcacy of treatment, etc. There are multiple studies that show that individuals have dynamic responses to transmission risks that change with varying circumstances. For example, the advent of antibiotics makes all of us less concerned with exposure risks to common pathogens. Nobody is worried about getting tick bites in the woods, since a course of penicillin would cure a possible exposure to Lyme disease. To the contrary, knowledge about the severity of disease (measured by number of infectious people, virrulence, lack of eﬀective treatment) may cause susceptible individuals to be more cautious and reduce their exposure risk. From these remarks we can talk about two general ways in which behavioral attitudes inﬂuence the spread of a disease:

**Publication: **Sega, L., D. Maxin, L. Eaton, A. Latham, A. Moose, and S. Stenslie. “The effect of risk-taking behaviour in epidemic models.” Journal of biological dynamics 9, no. 1 (2015): 229-246. (https://doi.org/10.1080/17513758.2015.1065351)

**Estimating Option Prices with Heston’s Stochastic Volatility Model**

Professor Hui Gong

**Technical Report: Estimating Option Prices with Heston’s Stochastic Volatility Model**

Options are a type of financial derivative. This means that their price is not based directly on an asset’s price. Instead, the value of an option is based on the likelihood of change in an underlying asset’s price. More specifically, an option is a contract between a buyer and a seller. This contract gives the holder the right but not the obligation to buy or sell an underlying asset for a specific price (strike price) within a specific amount of time. The date at which the option expires is called the date of expiration.

**Mathematical Modeling in Ecology – What Killed the Mammoth?**

Professor Alex Capaldi

**Technical Report: Mathematical Modeling in Ecology – What Killed the Mammoth?**

During the Paleolithic Period, mammoths, as well as other mega mammals, went extinct. The exact reasons for this have been debated for some time, and current hypotheses point to causes such as disease, climate change, over hunting by humans, or some combination thereof. However, recent developments in mathematical ecology may be able to elucidate the matter. A recent study has given strong evidence in support of the hypothesis that the Neanderthals’ extinction was due to strong competition from modern humans. The goal of this project is to follow in the footsteps of the Neanderthal study and consider the similar question as to whether the mammoth’s extinction was anthropogenic.

**Publication: **M. Frank, A. Slaton, T. Tinta, and A. Capaldi, “Investigating Anthropogenic Mammoth Extinction with Mathematical Models,” Spora – A Journal of Biomathematics 1 (2015), 8-16. (https://doi.org/10.30707/SPORA1.1Frank)

**Estimating the Volatility in the Black-Scholes Formula**

Professor Hui Gong

**Technical Report: ****Estimating the Volatility in the Black-Scholes Formula**

Black-Scholes formula has been a huge success since its introduction. However, the formula has a component of the volatility, which is not deterministic and available immediately for application of this formula. We can estimate this volatility via multiple models or methods, such as parametric approaches with different probabilistic models, nonparametric approaches and time series models approaches, such as smoothing techniques. We will derive these estimates and incorporate into the Black-Scholes formula.

**Graph Labelings**

Professor Zsuzsanna Szaniszlo

**Technical Report: 4−Equitable Tree Labelings**

In this project we will look at edge-vertex graphs and investigate a certain assignment of numbers to the edges and vertices. These so-called labeling problems were introduced in the 1960s as possible tools for solving graph decomposition problems. Since then different labelings were studied for their own sake and for other applications as well. In the summer project, we will investigate when we can distribute labels (numbers) equally in a graph. Answering this question for trees would settle the famous graceful tree conjecture.

**Publication: **Z. Coles, A. Huszar, J. Miller, Z. Szaniszlo, 4-equitable tree labelings, Congressus Numernatium 228 (2017), 51-63.

**Quandles and Generalized Colorings of Knots**

Professor Paul Drube

**Technical Report: A Partial Ordering Of Knots**

Knot theory is a branch of topology that studies how one may embed a circle within three-dimensional space. Since knots may become quite complicated, much of modern knot theory involves the development of invariants that can distinguish between different equivalence classes of knots. One basic class of knot invariants is the Fox n-colorings of knots, which count the ways that one may appropriately “decorate” the strands of a knot diagram with elements of a cyclic abelian group. In recent years, the mathematical structure underlying these Fox n-colorings has been greatly generalized utilizing abstract binary operations known as quandles. After a brief introduction to knot theory, this project will explore basic properties about quandles and their associated knot invariants, hopefully developing interesting results about the generalized colorability invariants of specific classes of knots.

**Publication: **Arazelle Mendoza, Tara Sargent, John Travis Shrontz and Paul Drube, A New Partial Ordering of Knots, Involve, Vol. 8, No. 3 (2015), 447-466. (https://dx.doi.org/10.2140/involve.2015.8.447)

**Vertical transmission in two-sex epidemic models with isolation from reproduction**

Professor Daniel Maxin

**Technical Report: Vertical transmission in two-sex epidemic models with isolation from reproduction**

Vertical transmission is the transmission of an infection from mother to child at birth. During the academic year 2008-2009, Tim Olson and Adam Shull (students at Valparaiso University) worked on a project with me to study the influence of isolation from reproduction on sexually transmitted infections with vertical transmission. One of the questions addressed in their project was the behavior of the disease in the case of 100% vertical transmission (i.e. all newborns from infected mothers acquire the disease). A surprising result showed that, under several conditions on the vital parameters, the isolation from reproduction may prevent a Susceptible Extinction situation (a case when the disease eliminates the entire healthy population) even when the infection rate is large. For simplicity the model did not separate the individuals by gender (to keep the number of equations low). Our project consists of establishing a two-sex version of this model that follows the dynamics of females and males. The main objective is to investigate if the result described above holds in the more realistic framework of gender structured models and whether the result is independent from various types of mating functions commonly used in the literature. A secondary objective is to improve the original model with features that were not included so far such as diseases with recovery or temporary isolation from reproduction.

**Publication: **Daniel Maxin, Ludec Berec, Adrienna Bingham, Denali Molitor and Julie Pattyson, Is more better? Higher sterilization of infected hosts need not result in reduced pest population, J. Math. Biol., Vol. 70, No. 6 (2015), 1381-1409. (https://doi.org/10.1007/s00285-014-0800-0)

**Generalized Pattern Avoidance in Trees**

Professor Lara Pudwell

**Technical Report: Non-Consecutive Pattern Avoidance in Binary Trees**

A current hot topic in combinatorics is enumerating structures that avoid certain patterns. In the 2010 VERUM program, Gabriel, Peske, and Tay studied contiguous pattern avoidance in ternary trees. In the 2011 VERUM program, Dairyko, Tyner, and Wynn studied non-contiguous pattern avoidance in binary trees. There are a number of variations on tree-pattern avoidance that remain to be explored by modifying what types of trees or what types of patterns are considered. We will consider a new type of tree pattern that is a hybrid of contiguous patterns and non-contiguous patterns. In particular, counting problems in the 2010 project always resulted in algebraic generating functions, while counting problems in the 2011 project always resulted in rational generating functions. We will try to characterize whether hybrid patterns fall under the algebraic or rational paradigm and extend our work from there.

**Publication: **Lara Pudwell, Connor Scholten, Tyler Schrock, and Alexa Serrato, Non-contiguous pattern containment in binary trees, ISRN Combinatorics vol. 2014, Article ID 316535, 8 pages, 2014. (https://dx.doi.org/10.1155/2014/316535)

**Mathematical Models of Infectious Disease**

Professor Alex Capaldi

**Technical Report: Mathematical Models of Infectious Diseases**

In a world where infectious diseases, such as the H1N1 flu, bird flu or SARS, pose a tangible public health risk, it is vital to understand the dynamics of outbreaks. We will see how to gain information about epidemics by using an array of mathematical tools including differential equation models, stochastic models, and network models. Different control strategies for containing diseases such as vaccination and quarantine and how they can be optimized using mathematics will be introduced. An infectious disease topic from current events (such as the swine flu pandemic, the whooping cough outbreaks in California, or even the mythology of the spread of vampires in a human population) will be chosen to be studied in depth.

**Publication:** Sydney Garmer, Rachel Lynn, D. Rossi, and A. Capaldi, “Multistrain Infections in Metapopulations,” Spora – A Journal of Biomathematics 1 (2015), 17-27. (https://doi.org/10.30707/SPORA1.1Garmer)

**Pattern Avoidance in Trees**

Professor Lara Pudwell

**Technical Report: Non-Consecutive Pattern Avoidance in Binary Trees**

A current hot topic in combinatorics is enumerating structures that avoid certain patterns. In 2008, Rowland defined contiguous pattern avoidance in binary trees. In the 2010 VERUM program, Gabriel, Peske, and Tay extended Rowland’s results to ternary trees. For all this previous work, the trees were rooted and ordered, and the tree patterns were contiguous. Any of these three conditions can be relaxed to produce a related, but new and as-yet-unstudied counting problem. We will begin by considering trees that contain non-contiguous tree patterns and work to generalize our results from there.

**Publication: **Michael Dairyko, Lara Pudwell, Samantha Tyner, Casey Wynn, “Non-contiguous pattern avoidance in binary trees”, Electronic Journal of Combinatorics 19 (3) (2012), P22. (https://www.combinatorics.org/ojs/index.php/eljc/article/view/v19i3p22)

**Computer Monitored Problem Solving Dialogues**

Professor Michael Glass

**Technical Report: Computer Monitored Problem Solving Dialogues**

Is it possible to monitor small groups of students solving a problem online? A common instructional method in mathematics classrooms is to have students work together exploring some phenomenon while the teacher walks around the room monitoring progress and assisting as needed. As instruction moves online, two issues are how to adequately replace the manipulatives-and-worksheet physical problem-solving environment and how to get the computer to “see” what the teacher sees by looking over shoulders, using clickstream data and the students’ conversation. Research questions include sensing student affective states (e.g. bored, engaged, confused), student cognitive states (e.g. what aspects of the math do they understand), and degree and quality of collaboration.

**The logistic two-sex model without pair-formation**

Professor Daniel Maxin

**Technical Report: The Impact of Sexually Abstaining Groups on Persistence of Sexually Transmitted Infections in Populations with Ephemeral Pair Bonds**

It has been shown that the isolation from reproduction may induce a locally asymptotically stable disease-free equilibrium in an endemic situation. For human populations, a gender-structured model includes single individuals (females and males) and couples. In animal populations however, various species do not form stable pairs, and the mating is a consequence of direct encounter among individuals of different genders. The main objective of this project is to develop and analyze a two-sex logistic model without pairs and to extend this model to an epidemic model and verify if and under what conditions previous results are still valid. A second objective is to analyze in more detail the mathematical and biological properties of various fertility functions both theoretical and against real data.

**Publication: **Ludek Berec, Michael Covello, Jill Jessee, Daniel Maxin, and Matthew Zimmer, “The impact of sexually abstaining groups on persistence of sexually transmitted infections in populations with ephemeral pair bonds”, Journal of Theoretical Biology, 292 (2012), 1-10. (https://doi.org/10.1016/j.jtbi.2011.09.023)

**Generalized primes on the Mosaic of an Integer**

Professor Rick Gillman

**Technical Report: Mosaic Arithmetic**

The mosaic of an integer is the configuration of primes obtained by repeated applications of the Fundamental Theorem of Arithmetic to a positive integer *n* and any composite exponents. The concept of the mosaic was introduced by Mullin, in a series of papers in the early 1960s. Various arithmetic functions dependent only on the primes in the mosaic were investigated by Girse and Gillman. During the summer of 2007, a team of undergraduate research students investigated this same structure and developed several potential concepts of divisors, allowing the set of arithmetic functions defined on mosaics to be expanded greatly. This team will continue to develop these notions of divisibility, eventually leading to more fully developed theory of mosaics.

**Pattern Avoidance in Ternary Trees**

Professor Lara Pudwell

**Technical Report: Pattern Avoidance in Ternary Trees**

For this project we will consider rooted ordered trees avoiding other trees. In 2008, Rowland defined pattern avoidance in binary trees (i.e. trees where each vertex has either 0 or 2 children). The standard combinatorial sequences appear when enumerating such trees, and there exist bijections between these trees and other common combinatorial objects. There is also a method to determine equivalence classes of binary trees based on the number of trees that avoid them. This team will extend these known results about pattern avoidance to ternary trees (i.e. trees in which each vertex has 0 or 3 children).

**Publication:** Nathan Gabriel, Katherine Peske, Lara Pudwell, and Sam Tay, “Pattern Avoidance in Ternary Trees”, Journal of Integer Sequences, Vol. 15, No. 1, (2012) 12.1.5., 20pp. (https://cs.uwaterloo.ca/journals/JIS/VOL15/Pudwell/pudwell.html)

**Groundwater Flow**

Director: Ken Luther

**Technical Report: Self-Influencing Interpolation in Groundwater Flow**

In this project we will investigate analytic (closed form) solutions to three dimensional steady state groundwater flow problems. While numerical solutions to groundwater flow problems are more commonly used in practice, especially in the three-dimensional realm where analytic solutions are cumbersome or even nonexistent, the construction of some analytic solutions is essential so that numerical models can be validated. The specific problem at hand will involve flow to a well in a stratified aquifer, and/or interaction between a horizontal well and a surface water body.

**Functions on the Mosaic of n**

Director: Rick Gillman

**Technical Report: Mosaics: A Prime-al Art**

Any integer n can be uniquely factored into a product of prime powers. Each of the resulting exponents greater than 1 can, in turn, be factored into a product of prime powers. Iterating this process until there are no composite exponents results in an array of numbers called the mosaic of n. In this project we will define new arithmetic functions on the mosaic of n and investigate their arithmetic and algebraic properties.

**Publication:**

Kristen Bildhauser, Jared Erickson, Rick Gillman, and Cara Tacoma, “More Functions on the Mosaic of n”, Involve, Vol. 2, No. 1, (2009), 65-78. (https://dx.doi.org/10.2140/involve.2009.2.65)

**Understanding Mathematics Tutoring Dialogue (Computer Science project)**

Director: Michael Glass

**Technical Report: Computerized Tutoring**

As part of building dialogue-based computer tutors for mathematics, this project works on developing the techniques for computer understanding of student utterances. During the course of a tutoring conversation students can perform discourse actions such as checking whether some idea is true, asking a question, expressing confusion, and so on. Examining transcripts of tutoring sessions, this project will work on software methods for guessing the intentions behind a student’s utterance. This summer’s experiments may involve both numerical and symbolic methods, such as statistical models, latent semantic analysis, and finite-state machines.

**Distributions of Interest Disfor Quantifying Reasonable Doubt and their Applications**

Director: Professor James Caristi

**Technical Report: Distributions of Interest for Quantifying Reasonable Doubt and Their Applications**

The concept of reasonable doubt is a standard of our legal system; however, it is a standard that is not well defined. Differences in the way reasonable doubt is applied in different courts and states, as well as ambiguities in its different definitions, suggest that the standard puts pressure on due process and equal protection concerns. This paper explores probability distributions that will aid in the understanding of the American legal system as it is today, what reasonable doubt means under this system, and how reasonable doubt should be defined.

**Systems of Matrix Equations**

Director: Professor Patrick Sullivan

**Technical Report: On the Properties A _{m,n} for Subspaces of C^{kk}**

his project will study properties of complex matrices. The students will explore what subsets of matrices have certain properties related to rank one matrices. We will be studying when arrays of matrices can be solved simultaneously as rank one matrices up to a certain equivalence.

**Graph Labelings**

Director: Professor Zsuzsanna Szaniszlo

**Technical Report: L(3, 2, 1)-Labeling of Simple Graphs**

An L(3,2,1)-labeling is a simplified model for the channel assignment problem. It is a natural generalization of the widely studied L(2,1)-labeling. An L(3,2,1)-labeling of a graph G is a function f from the vertex set of the graph to the set of positive integers such that for any two vertices x,y, if d(x,y)=1 then | f(x)-f(y) | ≥3; if d(x,y)=2, then | f(x)-f(y) | ≥2; and if d(x,y)=3, then | f(x)-f(y) | ≥1. The L(3,2,1)-labeling number k(G) of G is the smallest positive integer k such that G has an L(3,2,1)-labeling number for paths, cycles, caterpillars, n-ary trees, complete graphs and complete bipartite graphs. We also present an upper bound for k(G) in terms of the maximum degree of G.

**Publication:
**Jean Clipperton, “L(d,2,1)-labeling of simple graphs”, Rose-Hulman Undergraduate Mathematics Journal, Vol 9, No. 2 (2009), #2, 11pp. (https://scholar.rose-hulman.edu/rhumj/vol9/iss2/2/)

**Mathematical Models in Traffic Assignment and Congestion Pricing**

Director: Professor Lihui Bai

**Technical report: A Genetic Algorithm For The Minimum Tollbooth Problem **

This project uses rigorous mathematical models to study traffic assignment in urban transportation networks. Traffic assignment distributes vehicles in a transportation network so that certain criterion are satisfied. The study of traffic assignment models can be used in traffic congestion management, where traffic planners want to minimize the total travel delay for a given transportation network.

**Publications:
**Lihui Bai, Corby Harwood, Chris Kollman, and Matthew Stamps, “An Evolutionary Method for the Minimum Toll Booth Problem: the Methodology”, Academy of Information and Management Sciences Journal, Vol. 11, No. 2, (2008), 33-51.

**Lihui Bai, Corby Harwood, Chris Kollman, and Matthew Stamps, “A Genetic Algorithm for the Minimum Toll Booth Problem”, Annual Proceedings of Decision Science Institute (2006), 30411-30416.**

**Crystallographic Groups**

Director: Professor Kimberly Pearson

**Technical report: Virtually Cyclic Subgroups of Three-Dimensional Crystallographic Groups**

An enumeration of the virtually cyclic subgroups of the three-dimensional crystallographic groups is given. Additionally, we offer explanations of the underlying group theory and develop several exclusion theorems which simplify our calculations.

**Power Distributions in Weighted Voting Systems**

Director: Professor Rick Gillman

**Technical report: Using Sets of Winning Coalitions to Generate Feasible Banzhaf Power Distributions**

Given a weighted voting system, the Banzhaf Power Index can be used to determine the power distribution of the individual voters. We are interested in the converse of this problem: given a collection of voters, can a weighted voting system be constructed which has a prescribed power distribution? This problem has been solved for a system with four voters, but still open in more general settings.