About

Sidney R. Nagel, Ph.D. from Princeton in 1974, is the Stein-Freiler Distinguished Service Professor affiliated with the Department of Physics, James Franck Institute, Enrico Fermi Institute, and the College at the University of Chicago. The page lists him as the head of the Nagel Group, which includes postdoctoral researchers, graduate students, recent visitors, and alumni. The group appears to focus on various topics in physics, as indicated by the diverse affiliations and research interests of its members, but the page does not provide specific details about Professor Nagel's personal research focus, background, or key contributions. The information primarily consists of names and affiliations of current and former group members, without a narrative biography or description of Professor Nagel's work.

Research topics

• Materials science
• Physics
• Mechanics
• Condensed matter physics
• Statistical physics

Selected publications

• Evolutionary pathways in epistatic mechanical networks

  Proceedings of the National Academy of Sciences · 2026-01-30

  articleOpen accessSenior author

  An elastic spring network is an example of evolvable matter. It can be pruned to couple separated pairs of nodes so that when a strain is applied to one of them, the other responds either in-phase or out-of-phase. This produces two pruned networks, with incompatible functions, that are nearly identical but differ from each other by a set of “mutations” each of which removes or adds a single bond in the network. We generate ensembles of network pairs that differ by a fixed number, M , of discrete mutations and evaluate all M ! mutational paths between the in- and out-of-phase behaviors up to M <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mo>=</mml:mo> </mml:math> 14. With a threshold response for the network to be considered sufficiently fit for either function, so that nonfunctional networks are disallowed, only some mutational pathways are viable. We find that there is a surprisingly high critical response threshold above which no evolutionarily viable path exists between the two networks. The few remaining pathways at this critical value dictate much of the behavior along the evolutionary trajectory. The effect of multiple mutations is epistatic, that is, the impact of a mutation is not invariant but depends on what other mutations have already occurred. In most cases, the mutations break up into two distinct classes based on epistasis. The analysis clarifies how the number of mutations and the position of a mutation along the pathway affect the evolutionary outcome.

  PublisherDOI

• Data to accompany "Effect of translational shear on interfacial structure in the viscous fingering instability"

  Open MIND · 2026-02-03

  articleSenior author

  This archive contains the numerical values in the plots and a COMSOL simulation file in Science Advances. See the paper for the figures corresponding to these files, and explanations of how they were generated. - **Plot data** Data files used directly to generate the figures in the main text and Supplementary Materials. These files are sufficient to reproduce all plots in the paper. - **COMSOL simulation** `linear_Vs12_U4_A3_cluster_ri5.zip` This zip file contains the COMSOL Multiphysics model used to run the linear simulation described in the manuscript. To run the simulation, unzip the file and open the model in COMSOL Multiphysics.

  DOI

• Data to accompany "Effect of translational shear on interfacial structure in the viscous fingering instability"

  Zenodo (CERN European Organization for Nuclear Research) · 2026-02-03

  articleOpen accessSenior author

  This archive contains the numerical values in the plots and a COMSOL simulation file in Science Advances. See the paper for the figures corresponding to these files, and explanations of how they were generated. - **Plot data** Data files used directly to generate the figures in the main text and Supplementary Materials. These files are sufficient to reproduce all plots in the paper. - **COMSOL simulation** `linear_Vs12_U4_A3_cluster_ri5.zip` This zip file contains the COMSOL Multiphysics model used to run the linear simulation described in the manuscript. To run the simulation, unzip the file and open the model in COMSOL Multiphysics.

  PublisherDOI

• Effect of translational shear on interfacial structure in the viscous fingering instability

  Science Advances · 2026-04-03

  articleOpen accessSenior author

  We introduce applied shear as a method to control viscous fingering by smoothing the interface between miscible fluids. In the viscous fingering instability, a less viscous fluid displaces a more viscous one through the formation of fingers. The instability, which requires a confined geometry, is often studied in the thin gap of a quasi–two-dimensional Hele-Shaw cell. When the two fluids are miscible, the structures that form in the dimension traversing the gap are important for determining the instability onset. We demonstrate with experiments and simulations that oscillatory translational shear of the confining plates changes the gap-averaged viscosity profile so that it becomes less abrupt at the fingertips. Increasing the amplitude or velocity of the shear delays the instability onset and decreases the finger growth rate. Shear can thus be used to stabilize a pair of miscible fluids against fingering. The results show a direct correlation between a smoother viscosity profile and delayed instability.

  PublisherDOI

• Studies of granular compaction

  2026-02-19

  book-chapter

  The work reported here is an overview of several studies of the compaction of granular material that we have conducted in our laboratories. We show that external vibrations lead to a slow, essentially logarithmic, approach of the packing density to a final steady-state value. Depending on the initial conditions and the magnitude of the vibration acceleration, the system can either reversibly move between steady-state densities or can become irreversibly trapped into metastable states. We find that the highest packing densities are obtained along the reversible branch. Finally, measurements of the spectrum of density fluctuations around the steady-state values provide a probe of the internal relaxation dynamics of the system and a link to recent thermodynamic theories for the settling of granular material.

  PublisherDOI

• Evolutionary pathways in epistatic mechanical networks

  Proceedings of the National Academy of Sciences · 2026-01-30 · 1 citations

  preprintOpen accessSenior author

  An elastic spring network is an example of evolvable matter. It can be pruned to couple separated pairs of nodes so that when a strain is applied to one of them, the other responds either in-phase or out-of-phase. This produces two pruned networks, with incompatible functions, that are nearly identical but differ from each other by a set of “mutations” each of which removes or adds a single bond in the network. We generate ensembles of network pairs that differ by a fixed number, M , of discrete mutations and evaluate all M ! mutational paths between the in- and out-of-phase behaviors up to M <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mo>=</mml:mo> </mml:math> 14. With a threshold response for the network to be considered sufficiently fit for either function, so that nonfunctional networks are disallowed, only some mutational pathways are viable. We find that there is a surprisingly high critical response threshold above which no evolutionarily viable path exists between the two networks. The few remaining pathways at this critical value dictate much of the behavior along the evolutionary trajectory. The effect of multiple mutations is epistatic, that is, the impact of a mutation is not invariant but depends on what other mutations have already occurred. In most cases, the mutations break up into two distinct classes based on epistasis. The analysis clarifies how the number of mutations and the position of a mutation along the pathway affect the evolutionary outcome.

  PublisherDOI

• Training and retraining liquid crystal elastomer metamaterials for pluripotent functionality

  Proceedings of the National Academy of Sciences · 2025-07-16 · 4 citations

  articleOpen accessSenior author

  Training has emerged as a promising materials design technique in which function can be achieved through repeated physical modification of an existing material rather than by direct chemical functionalization, cutting, or reprocessing. This work investigates both the ability to train for function and then to erase that function on-demand in macroscopic metamaterials made from liquid crystal elastomers. We first show that the Poisson's ratio of these disordered arrays can be tuned via directed aging to induce an auxetic response. We then show that the arrays can be reset and retrained for another local mechanical function, allostery, thus demonstrating pluripotent functionality.

  PublisherDOI

• Minimal cyclic behavior in sheared amorphous solids

  New Journal of Physics · 2025-08-01 · 1 citations

  articleOpen accessSenior authorCorresponding

  Abstract Although jammed packings of soft spheres exist in potential energy landscapes with a vast number of minima, when subjected to cyclic shear they may revisit the same configurations repeatedly. Simple hysteretic spin models, in which particle rearrangements are represented by interacting spin flips called hysterons, capture many features of this periodic behavior. Yet it has been unclear to what extent individual rearrangements can be described by such binary objects and how such objects interact with one another. Using a particularly sensitive algorithm, we identify rearrangements in simulated jammed packings and select pairs of rearrangements that undo one another to create periodic cyclic behavior. We find that the rearrangement pairs surprisingly persist down to the smallest increments in strain, even in the smallest systems we can study. We explore the statistics of these rearrangement pairs and find that there is a relation between the amount of hysteresis and the energy drop and mean-square displacement of the particles; these results are inconsistent with the scaling found in models that treat rearrangements as localized buckling events. Finally, our analysis shows that there is no clean distinction between the particle motions that represent the identity of a single, individual rearrangement and the particle motions that lead to interactions between separated rearrangements or hysterons. These results offer insight into how complex systems such as amorphous solids can reach a limit cycle.

  PublisherDOI

• Cooperative Function with Thermal Fluctuations in Mechanical Networks

  ArXiv.org · 2025-09-24

  preprintOpen accessSenior author

  Elastic networks can be tuned to exhibit complex mechanical responses and have been extensively used to study protein allosteric functionality, where a localized strain regulates the conformation at a distant site. We show that cooperative binding, where two sites each enhance the other's ability to function, can be trained via a symmetric application of the training previously employed for creating network allostery. We identify a crossover temperature above which cooperative functionality breaks down due to thermal fluctuations. We develop a modified training protocol to increase this crossover temperature, enabling function to remain robust at biologically relevant temperatures.

  PublisherOA PDFDOI

• Training and re-training liquid crystal elastomer metamaterials for pluripotent functionality

  ArXiv.org · 2025-02-24

  preprintOpen accessSenior author

  Training has emerged as a promising materials design technique in which function can be acheived through repeated physical modification of an existing material rather than by direct chemical functionalization, cutting or reprocessing. This work investigates both the ability to train for function and then to erase that function on-demand in macroscopic metamaterials made from liquid crystal elastomers (LCEs). We first show that the Poisson's ratio of these disordered arrays can be tuned via directed aging to induce an auxetic response. We then show that the arrays can be reset and re-trained for another local mechanical function, allostery, thus demonstrating pluripotent functionality.

  PublisherOA PDFDOI

Recent grants

• Workshop to identify and explore the grand challenges in experimental soft condensed matter science; Arlington, VA; January 2016

  NSF · $50k · 2015–2016

• REU Site: Summer Research Projects in Contemporary Physics for Women and Minorities

  NSF · $388k · 2008–2011

• Studies in Fluids: Splashing, Singularities and Memory Formation

  NSF · $391k · 2011–2014

• REU Site: Summer Research Projects in Contemporary Physics for Women and Minorities

  NSF · $390k · 2012–2016

• REU Site: Summer Research Projects in Contemporary Physics for Women and Minorities

  NSF · $105k · 2007–2008

Frequent coauthors

• Andrea J. Liu

  105 shared

• Heinrich M. Jaeger

  University of Chicago

  77 shared

• Daniel Hexner

  Technion – Israel Institute of Technology

  41 shared

• Irmgard Bischofberger

  Massachusetts Institute of Technology

  34 shared

• Taehun Lee

  City College of New York

  32 shared

• Nidhi Pashine

  31 shared

• J. Tauc

  John Brown University

  29 shared

• Jeffrey F. Morris

  City College of New York

  27 shared

Labs

• Nagel GroupPI

Awards & honors

• 2023 APS Medal for Exceptional Achievement in Research
• American Philosophical Society (elected, 2020)
• Alfred P. Sloan Research Fellowship (1979)
• Fellow, American Physical Society (1988)
• Fellow, American Association for the Advancement of Science…