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- Amir Haji-Akbari, Michael Engel, +4 authors Sharon C. Glotzer
- Nature
- 2009

All hard, convex shapes are conjectured by Ulam to pack more densely than spheres, which have a maximum packing fraction of phi = pi/ radical18 approximately 0.7405. Simple lattice packings of many shapes easily surpass this packing fraction. For regular tetrahedra, this conjecture was shown to be true only very recently; an ordered arrangement was obtained… (More)

- Miguel Camacho-Lopez, Heino Finkelmann, Peter Palffy-Muhoray, Michael J. Shelley
- Nature materials
- 2004

Liquid-crystal elastomers (LCEs) are rubbers whose constituent molecules are orientationally ordered. Their salient feature is strong coupling between the orientational order and mechanical strain. For example, changing the orientational order gives rise to internal stresses, which lead to strains and change the shape of a sample. Orientational order can be… (More)

- Xiaoyu Zheng, Peter Palffy-Muhoray
- Physical review. E, Statistical, nonlinear, and…
- 2007

The distance of closest approach of hard particles is a key parameter of their interaction and plays an important role in the resulting phase behavior. For nonspherical particles, the distance of closest approach depends on orientation, and its calculation is surprisingly difficult. Although overlap criteria have been developed for use in computer… (More)

We study the Saffman-Taylor instability of a non-Newtonian fluid in a Hele-Shaw cell. Using a fluid model with shear-rate dependent viscosity, we derive a Darcy’s law whose viscosity depends upon the squared pressure gradient. This yields a natural, nonlinear boundary value problem for the pressure. A model proposed recently by Bonn et al. @Phys. Rev. Lett.… (More)

- Wenyi Cao, Antonio Munoz, Peter Palffy-Muhoray, Bahman Taheri
- Nature materials
- 2002

Photonic-bandgap materials, with periodicity in one, two or three dimensions, offer control of spontaneous emission and photon localization. Low-threshold lasing has been demonstrated in two-dimensional photonic-bandgap materials, both with distributed feedback and defect modes. Liquid crystals with chiral constituents exhibit mesophases with modulated… (More)

Liquid crystals are all around us: in high-strength plastics, snail slime, laundry detergent, textile fibers such as silk and Kevlar, crude oil, insect wings, mineral slurries, lipstick, Bose-Einstein condensates, and the mantles of neutron stars. We eat them as aligned molecules in gluten and drink them as phospholipids in milk, where they stabilize fat… (More)

Structured surfaces give rise to novel and potentially useful properties such as controllable wettability and structural colour. Here, we demonstrate structured surfaces via reversible surface wrinkling in liquid crystal elastomers (LCEs). A thin polymer film deposited on top of a shape-responsive LCE exhibits a reversible, periodic surface wrinkling… (More)

- Shuwang Li, John S. Lowengrub, Jake Fontana, Peter Palffy-Muhoray
- Physical review letters
- 2009

We study numerically and experimentally the dynamics and control of viscous fingering patterns in a circular Hele-Shaw cell. The nonlocality and nonlinearity of the system, especially interactions among developing fingers, make the emergent pattern difficult to predict and control. By controlling the injection rate of the less viscous fluid, we can… (More)

We explore the Saffman-Taylor instability of a gas bubble expanding into a shear thinning liquid in a radial Hele-Shaw cell. Using Darcy’s law generalized for non-Newtonian fluids, we perform simulations of the full dynamical problem. The simulations show that shear thinning significantly influences the developing interfacial patterns. Shear thinning can… (More)