Disclination-mediated thermo-optical response in nematic glass sheets

Nematic solids respond strongly to changes in ambient heat or light, significantly differently parallel and perpendicular to the director. This phenomenon is well characterized for uniform director fields, but not for defect textures. We analyze the elastic ground states of a nematic glass in the membrane approximation as a function of temperature for some disclination defects with an eye towards reversibly inducing three-dimensional shapes from flat sheets of material, at the nano-scale all the way to macroscopic objects, including non-developable surfaces. The latter offers a new paradigm to actuation via switchable stretch in thin systems.Comment: Specific results for spiral defects now added. References to Witten, Mahadevan and Ben Amar now added

Geometrical Frustration in Two Dimensions: Idealizations and Realizations of a Hard-Disk Fluid in Negative Curvature

We examine a simple hard-disk fluid with no long-range interactions on the two-dimensional space of constant negative Gaussian curvature, the hyperbolic plane. This geometry provides a natural mechanism by which global crystalline order is frustrated, allowing us to construct a tractable, one-parameter model of disordered monodisperse hard disks. We extend free-area theory and the virial expansion to this regime, deriving the equation of state for the system, and compare its predictions with simulations near an isostatic packing in the curved space. Additionally, we investigate packing and dynamics on triply periodic, negatively curved surfaces with an eye toward real biological and polymeric systems

2.5d/3d models for the enhancement of architectural-urban heritage. An virtual tour of design of the fascist headquarters in Littoria

Enhancement of cultural heritage is not simply a matter of preserving material objects but comes full circle only when the heritage can be enjoyed and used by the community. This is the rationale behind this presentation: an urban Virtual Tour to explore the 1937 design of the Fascist Headquarters in Littoria, now part of Latina, by the architect Oriolo Frezzotti. Although the application is deliberately “simple”, it was part of a much broader framework of goals. One such goal was to create “friendly and perceptively meaningful” interfaces by integrating different “3D models” and so enriching. In fact, by exploiting the activation of natural mechanisms of visual perception and the ensuing emotional emphasis associated with vision, the illusionistic simulation of the scene facilitates access to the data even for “amateur” users. A second goal was to “contextualise the information” on which the concept of cultural heritage is based. In the application, communication of the heritage is linked to its physical and linguistic context; the latter is then used as a basis from which to set out to explore and understand the historical evidence. A third goal was to foster the widespread dissemination and sharing of this heritage of knowledge. On the one hand we worked to make the application usable from the Web, on the other, we established a reliable, rapid operational procedure with high quality processed data and ensuing contents. The procedure was also repeatable on a large scale

How to Pare a Pair: Topology Control and Pruning in Intertwined Complex Networks

Recent work on self-organized remodeling of vasculature in slime-mold, leaf venation systems and vessel systems in vertebrates has put forward a plethora of potential adaptation mechanisms. All these share the underlying hypothesis of a flow-driven machinery, meant to alter rudimentary vessel networks in order to optimize the system's dissipation, flow uniformity, or more, with different versions of constraints. Nevertheless, the influence of environmental factors on the long-term adaptation dynamics as well as the networks structure and function have not been fully understood. Therefore, interwoven capillary systems such as found in the liver, kidney and pancreas, present a novel challenge and key opportunity regarding the field of coupled distribution networks. We here present an advanced version of the discrete Hu--Cai model, coupling two spatial networks in 3D. We show that spatial coupling of two flow-adapting networks can control the onset of topological complexity in concert with short-term flow fluctuations. We find that both fluctuation-induced and spatial coupling induced topology transitions undergo curve collapse obeying simple functional rescaling. Further, our approach results in an alternative form of Murray's law, which incorporates local vessel interactions and flow interactions. This geometric law allows for the estimation of the model parameters in ideal Kirchhoff networks and respective experimentally acquired network skeletons

Calibration of Concentric Tube Continuum Robots: Automatic Alignment of Precurved Elastic Tubes

Joint level calibration is an integral part of robotics as it directly influences the achievable accuracy. As opposed to serial robotic arms, continuum robots are not composed of any rigid links or joints, but of elastic materials that undergo bending and torsion. The jointless composition requires dedicated calibration procedures. In this letter, we introduce an automatic method for aligning precurved elastic tubes for joint level calibration of concentric tube continuum robots. The robot tip is equipped with a sensor in order to track its position during calibration such that subsequent data processing can extract the rotational zero position automatically. While we present a general framework independent of the utilized sensor technology, we evaluate our approach using three different sensing methodologies, i.e. magnetic, inductive, and electromagnetic. Furthermore, we advise on properties for appropriate sensors. Our experimental results show, that the rotational home position can be found reproducibly with a minimal dispersion of 0.011°

Spherical Foams in Flat Space

Regular tesselations of space are characterized through their Schlafli symbols {p,q,r}, where each cell has regular p-gonal sides, q meeting at each vertex, and r meeting on each edge. Regular tesselations with symbols {p,3,3} all satisfy Plateau's laws for equilibrium foams. For general p, however, these regular tesselations do not embed in Euclidean space, but require a uniform background curvature. We study a class of regular foams on S^3 which, through conformal, stereographic projection to R^3 define irregular cells consistent with Plateau's laws. We analytically characterize a broad classes of bulk foam bubbles, and extend and explain recent observations on foam structure and shape distribution. Our approach also allows us to comment on foam stability by identifying a weak local maximum of A^(3/2)/V at the maximally symmetric tetrahedral bubble that participates in T2 rearrangements.Comment: 4 pages, 4 included figures, RevTe

The gift of gab: probing the limits of dynamic concentration-sensing across a network of communicating cells

Many systems in biology and beyond employ collaborative, collective communication strategies for improved efficiency and adaptive benefit. One such paradigm of particular interest is the community estimation of a dynamic signal, when, for example, an epithelial tissue of cells must decide whether to react to a given dynamic external concentration of stress signaling molecules. At the level of dynamic cellular communication, however, it remains unknown what effect, if any, arises from communication beyond the mean field level. What are the limits and benefits to communication across a network of neighbor interactions? What is the role of Poissonian vs. super Poissonian dynamics in such a setting? How does the particular topology of connections impact the collective estimation and that of the individual participating cells? In this letter we construct a robust and general framework of signal estimation over continuous time Markov chains in order to address and answer these questions. Our results show that in the case of Possonian estimators, the communication solely enhances convergence speed of the Mean Squared Error (MSE) of the estimators to their steady-state values while leaving these values unchanged. However, in the super-Poissonian regime, MSE of estimators significantly decreases by increasing the number of neighbors. Surprisingly, in this case, the clustering coefficient of an estimator does not enhance its MSE while reducing total MSE of the population