Research Publications (Mathematical and Statistical Sciences)

2011

Newton, Fraser, Kouritzin, Michael

A CAPTCHA is an automatically generated test designed to distinguish between humans and computer programs; specifically, they are designed to be easy for humans but difficult for computer programs to pass in order to prevent the abuse of resources by automated bots. They are commonly seen...

2013

Kouritzin, Michael, Wu, B., Newton, F.

Herein, we propose generating CAPTCHAs through random field simulation and give a novel, effective and efficient algorithm to do so. Indeed, we demonstrate that sufficient information about word tests for easy human recognition is contained in the site marginal probabilities and the...

2005

Kouritzin, Michael, Kim, H., Hu, Y., Ballantyne, D.

This paper addresses the problem of detecting and tracking an unknown number of submarines in a body of water using a known number of moving sonobuoys. Indeed, we suppose there are N submarines collectively maneuvering as a weakly interacting stochastic dynamical system, where N is a random...

2015-01-01

Peacock, Stephanie J., Krkošek, Martin, Bateman, Andrew W., Lewis, Mark A.

There is an increasing realization of the diverse mechanisms by which parasites and pathogens influence the dynamics of host populations and communities. In multi‐host systems, parasites may mediate food web dynamics with unexpected outcomes for host populations. Models have been used to explore...

2001

Chan, Hubert, Kouritzin, Michael

Filtering is a method of estimating the conditional probability distribution of a signal based upon a noisy, partial, corrupted sequence of observations of the signal. Particle filters are a method of filtering in which the conditional distribution of the signal state is approximated by the...

2019-01-01

Yu Jin, Qihua Huang, Julia Blackburn, Mark A. Lewis

The study of population persistence in river ecosystems is key for understanding population dynamics, invasions, and instream flow needs. In this paper, we extend theories of persistence measures for population models in one-dimensional rivers to a benthic-drift model in two-dimensional...

2001

Ballantyne, David, Hoffman, John, Kouritzin, Michael

Particle-based nonlinear filters provide a mathematically optimal (in the limit) and sound method for solving a number of difficult filtering problems. However, there are a number of practical difficulties that can occur when applying particle-based filtering techniques to real world problems....

2011-01-01

Molnár, Péter K., Derocher, Andrew E., Klanjscek, Tin, Lewis, Mark A.

Predicting the ecological impacts of climate warming is critical for species conservation. Incorporating future warming into population models, however, is challenging because reproduction and survival cannot be measured for yet unobserved environmental conditions. In this study, we use...

2021-01-01

Pouria Ramazi, Mélodie Kunegel-Lion, Russell Greiner, Mark A. Lewis

2015

Kouritzin, Michael A., Newton, Fraser, Wu, Biao

A real-time algorithm to produce correlated random fields on general undirected graphs has been used in CAPTCHA generation and optical character recognition. This algorithm can not simulate all possible joint graph distributions but does match all marginal vertex distributions as well as...