Analysis of homoepitaxial growth on Ir~111! by scanning tunneling microscopy ~STM! reveals that two different phases nucleate. We find islands in the regular face-centered cubic ~fcc! stacking as well as in the hexagonal close-packed ~hcp! stacking. Performing STM measurements on fcc and hcp areas shows an apparent, voltage dependent height difference of up to 6% of the regular layer distance. ...

We have studied the dynamics of large vortex lattices in a dilute-gas Bose-Einstein condensate. While undisturbed lattices have a regular hexagonal structure, large-amplitude quadrupolar shape oscillations of the condensate are shown to induce a wealth of nonequilibrium lattice dynamics. When exciting an m=-2 mode, we observe shifting of lattice planes, changes of lattice structure, and sheetli...

The recent discovery of a distorted hexagonal phase in 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine/1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPE/DOPC) mixtures raised the intriguing question as to whether lipid mixtures demix in a bent monolayer. We performed neutron diffraction on a mixture of headgroup deuterated DOPC-d(13) and nondeuterated DOPE to study the lipid distribution i...

The round and arc-shaped formations are known in some galaxies, the Bubble complex (the Hodge object) in NGC 6946 being the most remarkable. The rim of the complex has a form of a regular arc in which a part of a hexagonal structure is embedded. A similar morphology is recognized in NGC 7421 galaxy, in that part of its rim which is leading in the galaxy motion through the intergalactic gas, as ...

We consider hexagonal systems embedded into the 3-dimensional space R3. We define the fundamental group π1(G) of such a system G and show that in case G is a finite hexagonal system with boundary, then π1(G) is a (non-abelian) free group. In this case, the rank of π1(G) equals m(G) − h(G) − n(G) + 1 where n(G) (resp. m(G), h(G)) denotes the number of vertices (resp. edges, hexagons) in G. A hex...

Monodisperse emulsion droplets with a high volume fraction form crystalline phases that can potentially serve as adjustable photomasks in photolithography. Such photomasks were prepared using a microfluidic device in which a flow-focusing junction, side channels, and a reservoir were connected in series. Transparent oil droplets were generated in a dye-containing continuous water phase at the f...

Physics and chemistry of ice surfaces are not only of fundamental interest but also have important impacts on biological and environmental processes. As ice surfaces-particularly the two prism faces-come under greater scrutiny, it is increasingly important to connect the macroscopic faces with the molecular-level structure. The microscopic structure of the ubiquitous ice Ih crystal is well-know...

We show a simple method to generate polyominoes and polyiamonds that produce isohedral tilings with p3, p4 or p6 rotational symmetry by using n line segments between lattice points on a regular hexagonal, square and triangular lattice, respectively. We exhibit all possible tiles generated by this algorithm up to n = 9 for p3, n = 8 for p4, and n = 13 for p6. In particular, we determine for n ≤ ...

A regular hexagonal array of morphological units is observed in negatively stained preparations of a membrane from the surface of the spherical bacterium Micrococcus radiodwans. Fragments of this membrane are frequently folded so that structural details from two or more layers are superimposed. The appearance of the resulting moiri patterns is illustrated and the need to be aware of the possibi...

A formation process for semiconductor quantum dots based on a surface instability induced by ion sputtering under normal incidence is presented. Crystalline dots 35 nanometers in diameter and arranged in a regular hexagonal lattice were produced on gallium antimonide surfaces. The formation mechanism relies on a natural self-organization mechanism that occurs during the erosion of surfaces, whi...