Achiral symmetry breaking and positive Gaussian modulus lead to scalloped colloidal membranes

In the presence of a non-adsorbing polymer, monodisperse rod-like particles assemble into colloidal membranes, which are one rod-length thick liquid-like monolayers of aligned rods. Unlike 3D edgeless bilayer vesicles, colloidal monolayer membranes form open structures with an exposed edge, thus presenting an opportunity to study physics of thin elastic sheets. Membranes assembled from single-component chiral rods form flat disks with uniform edge twist. In comparison, membranes comprised of mixture of rods with opposite chiralities can have the edge twist of either handedness. In this limit disk-shaped membranes become unstable, instead forming structures with scalloped edges, where two adjacent lobes with opposite handedness are separated by a cusp-shaped point defect. Such membranes adopt a 3D configuration, with cusp defects alternatively located above and below the membrane plane. In the achiral regime the cusp defects have repulsive interactions, but away from this limit we measure effective long-ranged attractive binding. A phenomenological model shows that the increase in the edge energy of scalloped membranes is compensated by concomitant decrease in the deformation energy due to Gaussian curvature associated with scalloped edges, demonstrating that colloidal membranes have positive Gaussian modulus. A simple excluded volume argument predicts the sign and magnitude of the Gaussian curvature modulus that is in agreement with experimental measurements. Our results provide insight into how the interplay between membrane elasticity, geometrical frustration and achiral symmetry breaking can be used to fold colloidal membranes into 3D shapes.Comment: Main text: 25 pages, 6 figures. Supplementary information: 6 pages, 6 figure

ALBACORE OBS recovery cruise report

The primary goal of the 2011 ALBACORE (Asthenosphere and Lithosphere Broadband Architecture from the California Offshore Region Experiment) cruise was to recover 34 ocean bottom seismometers (OBSs) in a 150 km (north-south) by 400 km (east-west) region off the coast of Southern California (Fig. 1). The cruise took place on R/V New Horizon, departing out of San Diego on Sept 7, 2011 and arriving back in San Diego on Sept 16, 2011 with no port stops in between

Data integration in eHealth: a domain/disease specific roadmap

The paper documents a series of data integration workshops held in 2006 at the UK National e-Science Centre, summarizing a range of the problem/solution scenarios in multi-site and multi-scale data integration with six HealthGrid projects using schizophrenia as a domain-specific test case. It outlines emerging strategies, recommendations and objectives for collaboration on shared ontology-building and harmonization of data for multi-site trials in this domain

ALBACORE OBS deployment cruise report

The primary goal of the 2010 ALBACORE (Asthenospheric and Lithospheric Broadband Architecture from the California Offshore Region Experiment) cruise was to deploy 34 ocean bottom seismometers (OBSs) in a 150 km (north-south) by 400 km (east-west) region off the coast of Southern California (Fig. 1). The cruise took place on R/V Melville, departing out of San Diego on August 14, 2010 and arriving back in San Diego on August 27, 2001 with no port stops in between

Reconfigurable self-assembly through chiral control of interfacial tension

Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature 481 (2012): 348–351, doi:10.1038/nature10769.From determining optical properties of simple molecular crystals to establishing preferred handedness in highly complex vertebrates, molecular chirality profoundly influences the structural, mechanical, and optical properties of both synthetic and biological matter at macroscopic lengthscales1,2. In soft materials such as amphiphilic lipids and liquid crystals, the competition between local chiral interactions and global constraints imposed by the geometry of the self-assembled structures leads to frustration and the assembly of unique materials3-6. An example of particular interest is smectic liquid crystals, where the 2D layered geometry cannot support twist, expelling chirality to the edges in a manner analogous to the expulsion of a magnetic field from superconductors7-10. Here, we demonstrate a previously unexplored consequence of this geometric frustration which leads to a new design principle for the assembly of chiral molecules. Using a model system of colloidal membranes11, we show that molecular chirality can control the interfacial tension, an important property of multi-component mixtures. This finding suggests an analogy between chiral twist which is expelled to the edge of 2D membranes, and amphiphilic surfactants which are expelled to oil-water interfaces12. Similar to surfactants, chiral control of interfacial tension drives the assembly of myriad polymorphic assemblages such as twisted ribbons with linear and circular topologies, starfish membranes, and double and triple helices. Tuning molecular chirality in situ enables dynamical control of line tension that powers polymorphic transitions between various chiral structures. These findings outline a general strategy for the assembly of reconfigurable chiral materials which can easily be moved, stretched, attached to one another, and transformed between multiple conformational states, thus enabling precise assembly and nano-sculpting of highly dynamical and designable materials with complex topologies.This work was supported by the National Science Foundation (NSF-MRSEC-0820492, NSF-DMR-0955776, NSF-MRI 0923057) and Petroleum Research Fund (ACS-PRF 50558-DNI7).2012-07-0

Using Semantic Dependencies for Consistency Management of an Ontology of Brain-Cortex Anatomy

In the context of the Semantic Web, ontologies have to be usable by software agents as well as by humans. Therefore, they must meet explicit representation and consistency requirements. This article describes a method for managing the semantic consistency of an ontology of brain-cortex anatomy. The methodology relies on the explicit identification of the relationship properties and of the dependencies that might exist among concepts or relationships. These dependencies have to be respected for insuring the semantic consistency of the model. We propose a method for automatically generating all the dependent items. As a consequence, knowledge base updates are easier and safer

An X-ray reflectivity study of evaporation-induced self-assembled titania-based films

X-Ray reflectivity was used to monitor the structural development of a titania-based film at the solid/air interface by evaporation-induced self-assembly (EISA). A nonionic poly(ethylene oxide)-based surfactant, Brij 58, was used as the template and titanium chloride as the inorganic precursor. The reflectivity pattern, film thickness and refractive index were shown to be dependent on film deposition method, whether by casting or by dip-coating onto a silicon wafer, the Brij 58 TiO2 ratio and the relative humidity. At Brij 58 contents of 40 wt%, the reflectivity profile displayed only a single diffraction peak. At 70 wt% Bragg diffraction indicated a lamellar ordering of film components. Modelled reflectivity data suggested a 1060 Å thick film that comprised 17 layers of alternating surfactant and titania with a d spacing of about 60 Å. The effect of relative humidity on film structure was explored

A zirconium oxide film self-assembled at the air-water interface

A self-assembled zirconia-based film, produced at the air-water interface using sodium dodecyl sulphate (SDS) as the template, has been characterised by energy-dispersive X-ray reflectometry, X-ray diffraction, and X-ray fluorescence analysis. Long-rang

Force-Induced Formation of Twisted Chiral Ribbons

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