SIAM News Blog

Obituary: Mary Ann Horn

Mary Ann Horn, 1965-2024. Photo courtesy of the contributors.
The mathematical biology community is mourning the loss of Mary Ann Horn, who passed away on February 7, 2024, at the age of 58. Throughout her impressive career, Mary Ann made significant contributions to both academia and government; she is especially remembered for her successful efforts to establish mathematical biology as a powerful area of study in its own right.

Mary Ann graduated from Penn State University in 1987 with a B.S. in mathematics and received a National Science Foundation (NSF) Graduate Research Fellowship for her continuing studies at the University of Virginia, where she earned her Ph.D. in applied mathematics in 1992. During this time, she coauthored numerous research papers in control theory for partial differential equations (PDEs) with her doctoral advisor, Irena Lasiecka. Mary Ann then continued this course of inquiry from 1992 to 1995 while completing an NSF Mathematical Sciences Postdoctoral Research Fellowship at the University of Minnesota under the direction of her postdoctoral mentor, Walter Littman. She was also rewarded a Humboldt Research Fellowship to conduct postdoctoral research with Günter Leugering’s group at the University of Erlangen-Nuremberg in Germany.

In 1994, Mary Ann became an associate professor in the Department of Mathematics at Vanderbilt University, where she continued her high-quality research on the control of PDEs and began to explore the subject of in mathematical biology. In the early stages of her career, she also helped to organize several mathematical conferences at Vanderbilt and the University of Minnesota.

In 2004, Mary Ann’s expertise in mathematical biology compelled her to join the NSF’s Division of Mathematical Sciences as a lead program officer in applied mathematics and mathematical biology. She was enthusiastic and committed to her role at NSF for more than a dozen years, and her service to the new Mathematical Biology Program played a major role in establishing mathematical biology as a thriving subdiscipline of applied mathematics in the U.S. Mary Ann’s contributions inspired the creation of funding opportunities that sponsored a variety of mathematical biology projects and supported the early careers of many current leaders in the field. She spearheaded several collaborative programs at NSF, including the Initiative to Support Research at the Interface of the Biological and Mathematical Sciences — jointly with the National Institute of General Medical Sciences at the National Institutes of Health (NIH). This and other programs emphasize the collaborative nature of mathematical biology that unites clinicians and experimentalists with mathematicians and computational scientists. 

Mary Ann also played a significant role in the Interdisciplinary Training for Undergraduates in Biological and Mathematical Sciences program, which enabled the early support of future experts in mathematical biology. Over the years, she was a strong supporter of the Mathematical Biosciences Institute at The Ohio State University and the Institute for Mathematics and its Applications at the University of Minnesota — both of which provided numerous opportunities to further national and international research at the forefront of mathematical biology. Mary Ann’s leadership in fostering interdisciplinary collaborations inside NSF and through joint programs with other federal funding agencies positively impacted on mathematical scientists who were seeking support for their research endeavors.

In 2017, Mary Ann became a professor and chair of the Department of Mathematics, Applied Mathematics, and Statistics at Case Western Reserve University in Cleveland, Ohio. She continued to conduct research in this role, including her inspiring work that built upon clinical data to develop population-level models of antibiotic-resistant bacteria. As chair, she mentored other faculty members and remained dedicated to the mathematical sciences community as a whole.

Mary Ann was an active contributor to SIAM and other like-minded societies throughout her career. She served as the SIAM News liaison for the SIAM Activity Group (SIAG) on Life Sciences and chaired the SIAG in 2017 and 2018. She also sat on the AWM-SIAM subcommittee for the Association for Women in Mathematics (AWM) and was a member of the SIAM Board of Trustees from 2009 to 2017. Early in her career, Mary Ann’s interest in control theory inspired her appointment as vice chair of the SIAG on Control and Systems Theory, as well as her later participation in the SIAG’s prize and nomination committees. Additionally, she was treasurer of AWM in the early 2000s. 

Mary Ann’s outgoing and supportive yet professional attitude was much appreciated by her colleagues, coworkers, and students. She had a wonderful ability to remember people’s names and faces—as well as their research fields and a host of other details— and often helped to connect individuals in mutually beneficial ways.

Those of us who worked with Mary Ann at NSF recall her dedication and enthusiasm for her job, as well as her generous mentorship for anyone who took on the role of program director. She enlightened us to the wide scope for mathematical biology opportunities in both NSF and NIH, energetically met with colleagues across the scientific disciplines at these institutions, and continually searched for ways to increase funding for mathematical biology research.

Mary Ann was adept at flying small planes, and her uncle helped build a two-seater experimental RV aircraft for her in the 1980s. She loved animals and always shared her life with one or two favorite cats. She will be greatly missed by friends, family, colleagues, and the entire mathematical community.

In honor of Mary Ann’s inspiring career, SIAM has established the Mary Ann Horn Memorial Fund to provide financial support for students and early-career SIAM members to attend the SIAM Conference on the Life Sciences. To contribute to this fund, please visit, log in or click “donate as guest,” and select the fund’s name from the drop-down menu. 

SIAM extends its appreciation to Rosemary Renaut, Deborah Lockhart, Fariba Fahroo, and Lisa Fauci for organizing the fundraising campaign for the Mary Ann Horn Memorial Fund.

Special thanks to Fariba Fahroo (Air Force Office of Scientific Research), Lisa Fauci (Tulane University), Suzanne Lenhart (University of Tennessee, Knoxville), Deborah Lockhart (retired), and Rosemary Renaut (Arizona State University) for their contributions to this article.

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