Neurally Implementable Semantic Networks

We propose general principles for semantic networks allowing them to be implemented as dynamical neural networks. Major features of our scheme include: (a) the interpretation that each node in a network stands for a bound integration of the meanings of all nodes and external events the node links with; (b) the systematic use of nodes that stand for categories or types, with separate nodes for instances of these types; (c) an implementation of relationships that does not use intrinsically typed links between nodes.Comment: 32 pages, 12 figure

Label-free imaging of fatty acid content within yeast samples

Fungi have been found to be an underlying cause of 70% of all plant and animal extinctions caused by infectious diseases. Fungal infections are a growing problem affecting global health, food production and ecosystems. Lipid metabolism is a promising target for antifungal drugs and since effective treatment of fungal infections requires a better understanding of the effects of antifungal agents at the cellular level, new techniques are needed to investigate this problem. Recent advances in nonlinear microscopy allow chemically-specific contrast to be obtained non-invasively from intrinsic chemical bonds within live samples using advanced spectroscopy techniques probing Raman-active resonances. We present preliminary data using Stimulated Raman Scattering (SRS) microscopy as a means to visualise lipid droplets within individual living fungi by probing Raman resonances of the CH stretching region between 2825cm-1 and 3030cm-1. © 2013 Copyright SPIE

Design guidelines for assessing and controlling spacecraft charging effects

The need for uniform criteria, or guidelines, to be used in all phases of spacecraft design is discussed. Guidelines were developed for the control of absolute and differential charging of spacecraft surfaces by the lower energy space charged particle environment. Interior charging due to higher energy particles is not considered. A guide to good design practices for assessing and controlling charging effects is presented. Uniform design practices for all space vehicles are outlined

Bound states of magnons in the S=1/2 quantum spin ladder

We study the excitation spectrum of the two-leg antiferromagnetic S=1/2 Heisenberg ladder. Our approach is based on the description of the excitations as triplets above a strong-coupling singlet ground state. The quasiparticle spectrum is calculated by treating the excitations as a dilute Bose gas with infinite on-site repulsion. We find singlet (S=0) and triplet (S=1) two-particle bound states of the elementary triplets. We argue that bound states generally exist in any dimerized quantum spin model.Comment: 4 REVTeX pages, 4 Postscript figure

Biological Invasions: The Case of Soybean Aphid Infestation

Soybeans, the second highest cash crop following corn in the U.S., have come under attack by invasive species, the soybean aphid from the North and soybean rust from the South. We estimated the economic losses resulting from soybean aphid infestation by using a dynamic equilibrium model. Results indicate that, first, the reduction of soybean production resulting from soybean aphid infestation is largely absorbed by reducing soybean exports, due to the higher price elasticity of export demand compared to the domestic demand. Second, the economic losses to U.S. soybean producers would grow on average annually between $12.8 million and$23.4 million during the first five years of infestation. In the longer-run, soybean producers would suffer greater economic losses as the dispersion rate of infested soybean acreage with soybean aphids rises. However, the successful discovery of the soybean aphid gene (TF04048) Rag-1 (which confers resistance) does not at this time warrant soybean growers and policy-makers becoming too seriously alarmed. Even so, time is an important factor in the eventual control of the soybean aphid.Crop Production/Industries,

An implicit finite-difference solution to the viscous shock layer, including the effects of radiation and strong blowing

An implicit finite-difference scheme is developed for the fully coupled solution of the viscous, radiating stagnation-streamline equations, including strong blowing. Solutions are presented for both air injection and injection of carbon-phenolic ablation products into air at conditions near the peak radiative heating point in an earth entry trajectory from interplanetary return missions. A detailed radiative-transport code that accounts for the important radiative exchange processes for gaseous mixtures in local thermodynamic and chemical equilibrium is utilized in the study. With minimum number of assumptions for the initially unknown parameters and profile distributions, convergent solutions to the full stagnation-line equations are rapidly obtained by a method of successive approximations. Damping of selected profiles is required to aid convergence of the solutions for massive blowing. It is shown that certain finite-difference approximations to the governing differential equations stabilize and improve the solutions. Detailed comparisons are made with the numerical results of previous investigations. Results of the present study indicate lower radiative heat fluxes at the wall for carbonphenolic ablation than previously predicted

High-z radio starbursts host obscured X-ray AGN

We use Virtual Observatory methods to investigate the association between radio and X-ray emission at high redshifts. Fifty-five of the 92 HDF(N) sources resolved by combining MERLIN+VLA data were detected by Chandra, of which 18 are hard enough and bright enough to be obscured AGN. The high-z population of microJy radio sources is dominated by starbursts an order of magnitude more active and more extended than any found at z<1 and at least a quarter of these simultaneously host highly X-ray-luminous obscured AGN.Comment: 4 pages, 2 figures, To appear in the proceedings of 'At the Edge of the Universe' (9-13 October 2006, Sintra, Portugal