Marek Cieplak

Marek Cieplak, the head of the Laboratory of Biological Physics at the Polish Academy of Sciences’ Institute of Physics, passed away on 31 December 2021, after a heroic battle with multiple myeloma.

Born in Warsaw on 8 December 1950, Marek received his MSc degree from the University of Warsaw in 1973 and his PhD in 1977 from the University of Pittsburgh with Frederic Keffer. Poland was then behind an iron curtain, and going to the US for a PhD was not an easy feat. Marek was able to accomplish this with help of the faculty of both universities and his dogged perseverance. Subsequently, he returned to the US almost every year, primarily to Rutgers and Johns Hopkins. In 1998 he was elected a fellow of the American Physical Society.

Marek was a man of many interests, both within and outside science. He made substantive and creative contributions to many areas in condensed-matter physics, statistical physics, and biological physics. With the late Mark Robbins, Marek analyzed the capillary invasion of a fluid into a porous medium and predicted a dynamical phase transition, confirmed by experiment and now known as the Cieplak–Robbins transition, as the wettability of the invading fluid increases. In another study, published in Science with Mark and Elisabeth Smith, he explored the microscopic origins of friction, showing that—in contrast to the macroscale—there is no static friction between the atomic monolayers and that their relative velocity depends linearly on the applied force.

Marek, with Joel Koplik, carried out several studies of molecular dynamics simulations of fluids in nanochannels. The bounding walls dominate the physics of such fluids. The nature of the boundary conditions cannot easily be determined experimentally because of the small scales involved. Continuum fluid mechanics cannot help here, because the boundary conditions typically need to be fed into the differential equations. Molecular dynamics can be used to bridge the gap between molecular scales and continuum scales. In a series of calculations, with different types of walls and simple and complex fluids, Marek presented a compelling picture of how the surface affects flows in its vicinity and away from it. His studies of patterned walls along with the self-cleaning lotus effect are important for understanding molecular fluids and are guiding applications in nanotechnology with fluids. In addition, he showed how cellular automata could be utilized to mimic surface tension in hydrodynamics. He, along with Amos Maritan, presented exact results for exponents for optimal channel networks using scaling ideas and simple mathematics. The interesting lesson, published in Science, is that the shape of a river basin, whether it is rounded like a blueberry leaf or elongated like a banana leaf, determines all other exponents.

During the last 25 years, Marek’s focus was on biological physics, including computer models of protein folding, interpretation of genetic microarray data, and knots and entanglements in biomolecules. Marek was one of the leaders of coarse-grained modeling of proteins and generalized the approach to a large and important class called intrinsically disordered proteins, which offers new opportunities for studying the properties of cellular liquids comprising proteins. He also contributed greatly to our understanding of protein stretching and the nano-indentation of large virus capsids. Marek used all-atom simulations in the context of biosensors and in studies of conformational biases of alpha-synuclein (implicated in Parkinson’s disease). He worked with European colleagues on sophisticated theoretical studies of cellulose to improve ways to convert biomass into biofuels.

Marek created a large and productive laboratory at the Institute of Physics, specializing in biological physics and successfully combining experimental, computational, and theoretical approaches to the subject. He trained and mentored many young people. Marek was the initiator and one of the exuberant hosts of a series of conferences, Biomolecules and Nanostructures, which was held seven times between 2004 and 2019. These meetings were a vibrant platform for biologists, physicists, and applied mathematicians to exchange ideas and nucleate new scientific projects.

Marek was an active participant of the cultural life of Poland, he was a vivid reader of contemporary literature, and he loved music. He was an avid tennis enthusiast and traveled extensively with his family exploring the world. Marek embodied joy, enthusiasm, and optimism. He was a true son of Poland and a citizen of the world. He is greatly missed by his wife, Marta, a condensed-matter experimentalist working on superconductivity at the Institute of Physics; his daughters, Magda and Maja; his grandchildren, Mikolaj and Milena; and by us and the large number of people whose life he touched.

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