Better tired than lost: Turtle ant trail networks favor coherence over short edges

Creating a routing backbone is a fundamental problem in both biology and engineering. The routing backbone of the trail networks of arboreal turtle ants (Cephalotes goniodontus) connects many nests and food sources using trail pheromone deposited by ants as they walk. Unlike species that forage on the ground, the trail networks of arboreal ants are constrained by the vegetation. We examined what objectives the trail networks meet by comparing the observed ant trail networks with networks of random, hypothetical trail networks in the same surrounding vegetation and with trails optimized for four objectives: minimizing path length, minimizing average edge length, minimizing number of nodes, and minimizing opportunities to get lost. The ants’ trails minimized path length by minimizing the number of nodes traversed rather than choosing short edges. In addition, the ants’ trails reduced the opportunity for ants to get lost at each node, favoring nodes with 3D configurations most likely to be reinforced by pheromone. Thus, rather than finding the shortest edges, turtle ant trail networks take advantage of natural variation in the environment to favor coherence, keeping the ants together on the trails.

A fast quadrature-based gravity model for the homogeneous polyhedron

ABSTRACT To date several probes have been sent to explore the Solar system’s asteroids and comets. These bodies are often irregular in shape and to safely navigate probes in their vicinity accurate gravity models are required. For an arbitrarily shaped constant-density body, the gravitational field can be determined from the surface topology and bulk properties. This is achieved by replacing the body’s true geometry with a polyhedron that closely resembles it and for which analytic equations for the gravitational field exist. For some applications however, these equations are too computationally expensive and it can be beneficial to replace them with numerically amenable approximations. In this work, a numerical-quadrature-based model for the gravitational field of a polyhedron consisting of triangular facets is derived. The proposed approximate model is found to be faster than its analytic counterpart. The error of the approximation is found to be negligible for the potential and Laplacian calculations. The approximate model introduces singularities to the surface of the acceleration calculation degrading the solution at altitudes less than the average edge length of the polyhedron.

Conditions for numerically accurate TMS electric field simulation

Background: Computational simulations of the E-field induced by transcranial magnetic stimulation (TMS) are increasingly used to understand its mechanisms and to inform its administration. However, characterization of the accuracy of the simulation methods and the factors that affect it is lacking. Objective: To ensure the accuracy of TMS E-field simulations, we systematically quantify their numerical error and provide guidelines for their setup. Method: We benchmark the accuracy of computational approaches that are commonly used for TMS E-field simulations, including the finite element method (FEM), boundary element method (BEM), finite difference method (FDM), and coil modeling methods. Results: To achieve cortical E-field error levels below 2%, the commonly used FDM and 1st order FEM require meshes with an average edge length below 0.4 mm, whereas BEM and 2nd (or higher) order FEM require edge lengths below 1.5 mm, which is more practical. Coil models employing magnetic and current dipoles require at least 200 and 3,000 dipoles, respectively. For thick solid-conductor coils and frequencies above 3 kHz, winding eddy currents may have to be modeled. Conclusion: BEM, FDM, and FEM methods converge to the same solution. However, FDM and 1st order FEM converge slowly with increasing mesh resolution; therefore, the use of BEM or 2nd (or higher) order FEM is recommended. In some cases, coil eddy currents must be modeled. Both electric current dipole and magnetic dipole models of the coil current can be accurate with sufficiently fine discretization.

Collection of Sixteen High-Quality Human Head CAD Models Generated with SimNIBS 2.1 Using Connectome Subject Data within MATLAB® Platform

The goal of this study is to introduce a collection of sixteen high-resolution, 2-manifold CAD compatible head models within the MATLAB platform available to all interested parties for electromagnetic and acoustic simulations. Each model contains skin, skull, CSF, GM, cerebellum, WM, and ventricles head compartments and possesses an “onion” topology: the grey matter shell is a container for white matter, ventricles, and cerebellum objects, the CSF shell contains the grey matter shell, the skull shell contains the CSF shell, and finally the skin or scalp shell contains the skull shell. The models are fully compatible with ANSYS ED FEM software, CST Studio Suite, Sim4Life/SEMCAD software, and other electromagnetic software packages.The collection is based on MRI data from the Human Connectome Project (HCP) segmented using the SimNIBS 2.1/2.1.1 processing pipeline. The average number of triangular surface facets in a model is 866,000, the average triangle quality is 0.25, the average edge length is 1.48 mm, and the average surface mesh density or resolution is 0.57 points per mm2. If necessary, a finer model mesh can be created for every head using available MATLAB tools.

Co2+xTi1−xO4 nano-octahedra as high performance anodes for lithium-ion batteries

Single crystal Co2+xTi1−xO4 nano-octahedra enclosed by {111} planes with an average edge length of 200 nm were synthesized via a one-step hydrothermal approach using economical TiO2 as a titanium source.

Synthesis of Hollow Ba0.7Sr0.3TiO3 Nanocubes by Using Molten Hydrated Salt as a Solvent

Perovskite Ba0.7Sr0.3TiO3nanocubes with a hollow structure were prepared by molten hydrated salt method at 180 °C for 15 h, using Ba (OH)2·8H2O, Sr (OH)2·8H2O and anatase-TiO2as raw materials without any additive or template. The phase composition, morphology and microstructure of the products were characterized by XRD, SEM, TEM and HRTEM. The XRD result indicates that the products are phase pure cubic Ba0.7Sr0.3TiO3, with the calculated unit cella=0.3965 nm. The SEM, TEM and HRTEM results show that the products with polycrystalline structure are composed of the hollow nanocubes whose average edge length is about 180 nm, and their morphologies are greatly influenced by reaction temperature and reaction time. In addition, the formation mechanism of the hollow nanocubes also was discussed.

Microstructure Characterization of Low Density EPS

This paper presents a procedure to determine the geometry of a representative unit cell for low density expandable polystyrene foams (EPS), specifically, 8.5 kg/m3, 12 kg/m3and 23 kg/m3. Several researches used different geometries to describe a unit cell, but none indicate neither how they established the shape of it nor how they determinate its dimensions. The foam specimens preparation is described in order to be observed in a scanning electron microscope (SEM) and the average edge length and average face thickness are calculated, based on SEM images. A mathematical procedure to calculate the size that the edge geometry would present is described and is based on an analytic model available in literature. With the obtained values, a theoretical geometry adjusted to a tetrakaidecahedron was built in CAD software. Thereupon, this geometry is compared with the SEM observations, from this comparison it is concluded that said model is not applicable to these low density EPS foams. Finally, the geometry is readjusted to obtain a representative unit cell able to be used in future research.

Electrochemical Deposition and Formation Mechanism of Single-Crystalline Cu2O Octahedra on Aluminum

A simple electrochemical deposition was developed to synthesize the cuprous oxide (Cu2O) octahedra on aluminum foils. The average edge length of the octahedra is about 300 nm. The chemical composition of the octahedra was determined using energy dispersive X-ray spectroscopy and electron energy-loss spectroscopy. The microstructure of the octahedra was investigated using transmission electron microscopy. The formation mechanism of the octahedra is proposed.

Synthesis of perfect silver nanocubes by a simple polyol process

In this work, we report on silver nanocubes with perfect shape prepared by a simple poly(vinyl pyrrolidone)-directed polyol synthesis process. The effects of poly(vinyl pyrrolidone)/AgNO3ratio Rand reaction temperature Ton the morphology and size of the products were investigated. Ag nanocubes with an average edge length of 230 nm were obtained successfully with sharp edges and corners under a precise synthesis condition of R= 1 and T= 150 °C. The optical properties of Ag nanocubes show an attractive plasma resonance red-shift with size in a wide spectra region. The growth mechanism of the Ag nanocubes is proposed to be thermodynamically and kinetically controlled.

Facile Synthesis of Cu2O Nanocubes in Triblock Copolymer Solutions

Cuprous oxide and related materials in nanosizes are of much interest and investigated extensively recently. It is reported here that cubic Cu2O nanocubes were synthesized successfully in aqueous solutions at room temperature in air condition. Copper (II) salts in water were reduced with ascorbate acid in air, using the nonionic pluronic amphiphilic triblock copolymer EO20PO70EO20 (P123) as the template-directing and protecting agent. The average edge length of the cubes varied from 50 to 100 nm. Transmission electron microscopy (TEM) has been used for the shape and structural characterization of the obtained Cu2O nanocubes. The UV-Vis spectra showed an obvious blue-shift (0.53 eV), compared to the band gap of the bulk Cu2O crystal, which makes it a promising candidate in solar energy conversion since this sample can make use of higher energy visible rays of solar spectrum. In the FT-IR spectra the peak of Cu-O bond for the Cu2O is clearly distinguished and several weak peaks of the C-H, C-C and C=O bonds for the organic species can also be detectable, implying a little P123 residua in the products. The effect of the triblock copolymer P123 on the growth of the Cu2O nanocubes is discussed.