Frustration of freezing in a two dimensional hard-core fluid due to particle shape anisotropy

The freezing mechanism suggested for a fluid composed of hard disks [Huerta et al., Phys. Rev. E, 2006, 74, 061106] is used here to probe the fluid-to-solid transition in a hard-dumbbell fluid composed of overlapping hard disks with a variable length between disk centers. Analyzing the trends in the shape of second maximum of the radial distribution function of the planar hard-dumbbell fluid it has been found that the type of transition could be sensitive to the length of hard-dumbbell molecules. From the ${NpT}$ Monte Carlo simulations data we show that if a hard-dumbbell length does not exceed 15% of the disk diameter, the fluid-to-solid transition scenario follows the case of a hard-disk fluid, i.e., the isotropic hard-dumbbell fluid experiences freezing. However, for a hard-dumbbell length larger than 15% of disk diameter, there is evidence that fluid-to-solid transition may change to continuous transition, i.e., such an isotropic hard-dumbbell fluid will avoid freezing.Comment: 9 pages, 7 figure

Revisiting the optical PTPT-symmetric dimer

Optics has proved a fertile ground for the experimental simulation of quantum mechanics. Most recently, optical realizations of $\mathcal{PT}$-symmetric quantum mechanics have been shown, both theoretically and experimentally, opening the door to international efforts aiming at the design of practical optical devices exploiting this symmetry. Here, we focus on the optical $\mathcal{PT}$-symmetric dimer, a two-waveguide coupler were the materials show symmetric effective gain and loss, and provide a review of the linear and nonlinear optical realizations from a symmetry based point of view. We go beyond a simple review of the literature and show that the dimer is just the smallest of a class of planar $N$-waveguide couplers that are the optical realization of Lorentz group in 2+1 dimensions. Furthermore, we provide a formulation to describe light propagation through waveguide couplers described by non-Hermitian mode coupling matrices based on a non-Hermitian generalization of Ehrenfest theorem.Comment: 25 pages, 12 figure

A Young Planet Search in Visible and IR Light: DN Tau, V836 Tau, and V827 Tau

In searches for low-mass companions to late-type stars, correlation between radial velocity variations and line bisector slope changes indicates contamination by large starspots. Two young stars demonstrate that this test is not sufficient to rule out starspots as a cause of radial velocity variations. As part of our survey for substellar companions to T Tauri stars, we identified the ~2 Myr old planet host candidates DN Tau and V836 Tau. In both cases, visible light radial velocity modulation appears periodic and is uncorrelated with line bisector span variations, suggesting close companions of several M_Jup in these systems. However, high-resolution, infrared spectroscopy shows that starspots cause the radial velocity variations. We also report unambiguous results for V827 Tau, identified as a spotted star on the basis of both visible light and infrared spectroscopy. Our results suggest that infrared follow up observations are critical for determining the source of radial velocity modulation in young, spotted stars.Comment: Accepted for publication in the Astrophysical Journal Letter

Oxygen isotope equilibrium in brachiopod shell fibres in the context of biological control

No abstract available

Dynamical Encoding by Networks of Competing Neuron Groups: Winnerless Competition

Following studies of olfactory processing in insects and fish, we investigate neural networks whose dynamics in phase space is represented by orbits near the heteroclinic connections between saddle regions (fixed points or limit cycles). These networks encode input information as trajectories along the heteroclinic connections. If there are N neurons in the network, the capacity is approximately e(N-1)!, i.e., much larger than that of most traditional network structures. We show that a small winnerless competition network composed of FitzHugh-Nagumo spiking neurons efficiently transforms input information into a spatiotemporal output

Evaluación foliar de aceites esenciales de especies de Eucalytus sp. susceptibles al daño de Gonipterus scutellatus (coleoptera: curculionidae)

- Huerta, A.; García, D. Departamento de Silvicultura, Facultad de Ciencias Forestales, Universidad de Chile. Casilla 9206, Santiago, Chile. - Chiffelle, I . Departamento de Agroindustria y Enología, Facultad de Ciencias Agronómicas, Universidad de Chile. Casilla 1004, Santiago, Chile.Dada la presencia en Chile desde 1998 del insecto defoliador Gonipterus scutellatus (Coleoptera: Curculionidae), el cual está causando serios daños en las plantaciones de Eucalipto desde las regiones IV a la VIII, se evaluó la composición de los principales aceites esenciales volátiles entre tres especies de eucalipto cultivadas en Chile (E. globulus, E. nitens y E. camaldulensis) por su rol en la resistencia al ataque de este insecto. La identificación de los aceites esenciales se hizo por cromatografía de gases. El gas de arrastre fue vapor de agua y las muestras se diluyeron 20 veces en n-hexano y se compararon con patrones preestablecidos. Se hicieron tres repeticiones por especie de eucalipto de 20 minutos a 100ºC. Como resultado se obtuvo que el componente esencial de las hojas de eucalipto más abundante fue el eucalyptol, destacándose en las hojas de E. nitens, donde tuvo una participación superior al 50%, seguido de E. globulus, con un 25% de presencia y finalmente, en E. camaldulensis con cerca del 2%. Este aceite esencial se asocia a un papel defensivo. El aceite esencial proveniente de las hojas de E. camaldulensis tuvo una mayor participación de ciclo azuleno (20%), presentándose únicamente en esta especie. También se encontraron otros aceites esenciales en menor proporción, tales como: alfa-pineno, camphino, entre otros. Por último, se recomienda proseguir con estudios conducentes a profundizar sobre el comportamiento de los aceites esenciales como factor de resistencia/susceptibilidad al daño causado por insectos

Aryl Hydrocarbon Receptor-Dependent inductions of omega-3 and omega-6 polyunsaturated fatty acid metabolism act inversely on tumor progression.

The Western diet contains a high ratio of omega-6 (ω6) to omega-3 (ω3) polyunsaturated fatty acids (PUFA). The prototypical aryl hydrocarbon receptor (AHR) ligand, 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), induces CYP1 family enzymes, which can metabolize PUFA to epoxides. Mice fed ω3-rich or ω6-rich diets were treated with TCDD and injected subcutaneously with AHR-competent Hepa1-GFP hepatoma cells or AHR-deficient LLC lung cancer cells. TCDD reduced the growth rates of the resulting tumors in ω3-fed mice and inhibited their metastasis to the liver and/or lung, but had the opposite effects in mice fed ω6 PUFA. These responses were likely attributable to the corresponding PUFA epoxides generated in tumor cells and/or host, since many depended upon co-administration of a soluble epoxide hydrolase (EPHX2) inhibitor in males, and/or were associated with increases in epoxide levels in tumors and sites of metastasis. Equivalent effects occurred in females in the absence of EPHX2 inhibition, probably because this sex expressed reduced levels of EPHX2. The responses elicited by TCDD were associated with effects on tumor vascularity, tumor cell proliferation and/or apoptosis. Thus environmental AHR agonists, and potentially also endogenous, nutritional, and microbiome-derived agonists, may reduce or enhance cancer progression depending on the composition of dietary PUFA, particularly in females