AGE STRUCTURE OR FUNCTIONAL RESPONSE? RECONCILING THE ENERGETICS OF SURPLUS PRODUCTION BETWEEN SINGLE-SPECIES MODELS AND ECOSIM

Whole-ecosystem foodweb models, specifically the dynamic model ECOSIM, contain specific hypotheses for surplus production that differ from traditional single-species management models. Specifically, ECOSIM begins with an assumption that all species are tightly connected and energetic surplus does not arise through fishing, whereas single-species fishing theory implies that fishing leads to surplus by removing larger, older, less-productive fish from populations. Although ECOPATH production ratios and single-species estimated production levels are both derived from the dynamics of von Bertalanffy consumption and growth equations, the dynamics of ECOSIM differ from the implied bioenergetics of fishing as applied to age-structured populations. Specifically, while the ECOSIM “Arena” functional response and the von Bertalanffy equations both lead to the appearance of densitydependence in predator consumption per unit biomass, the difference in starting assumptions between the models leads ECOSIM to “fix production energetics” while age-structured models capture changes in within-population energetics between populations of younger versus older fish. This may cause ECOSIM to greatly overestimate the amount of biomass supportable in “pristine” systems of large, mature fish, especially when projections are based on models of currently exploited ecosystems. However, if the ECOSIM Arena is seen as a proxy for age structure rather than as a function of predator/prey behaviour, the original derivation of von Bertalanffy growth equations, applied as a modification of ECOSIM, may allow the predictions made by biomass dynamics ecosystem models to incorporate critical life-history characteristics of modelled populations. Afr. J. mar. Sci. 26: 289–30

Role of Alpha Oscillations During Short Time Memory Task Investigated by Graph Based Partitioning

In this study, we investigate the clustering pattern of alpha band (8 Hz - 12 Hz) electroencephalogram (EEG) oscillations obtained from healthy individuals during a short time memory task with 3 different memory loads. The retention period during which subjects were asked to memorize a pattern in a square matrix is analyzed with a graph theoretical approach. The functional coupling among EEG electrodes are quantified via mutual information in the time-frequency plane. A spectral clustering algorithm followed by bootstrapping is used to parcellate memory related circuits and for identifying significant clusters in the brain. The main outcome of the study is that the size of the significant clusters formed by alpha oscillations decreases as the memory load increases. This finding corroborates the active inhibition hypothesis about alpha oscillations

Negative refraction through an impedance-matched left-handed metamaterial slab

Cataloged from PDF version of article.We report the transmission and reflection characteristics of a two-dimensional (2D) left-handed metamaterial (LHM). A well-defined left-handed (LH) transmission band with a peak value of −9.9 dB is obtained at frequencies where both effective permittivity and permeability are negative. A very sharp dip −38 dB at the reflection spectrum due to impedance matching at the surface of a 2D LHM is observed. Gaussian beam shifting experiments are performed to study the LH properties of a LHM structure. The structure has a negative refraction of electromagnetic waves in a certain frequency range. The negative refractive index values obtained for four different incident angles are in good agreement. © 2006 Optical Society of Americ

A new approach to dynamic finite-size scaling

In this work we have considered the Taylor series expansion of the dynamic scaling relation of the magnetization with respect to small initial magnetization values in order to study the dynamic scaling behaviour of 2- and 3-dimensional Ising models. We have used the literature values of the critical exponents and of the new dynamic exponent $x_0$ to observe the dynamic finite-size scaling behaviour of the time evolution of the magnetization during early stages of the Monte Carlo simulation. For 3-dimensional Ising Model we have also presented that this method opens the possibility of calculating $z$ and $x_0$ separately. Our results show good agreement with the literature values. Measurements done on lattices with different sizes seem to give very good scaling.Comment: Latex file with six figures. Accepted for publication in IJM

Isotropic three-dimensional left-handed meta-materials

We investigate three-dimensional left-handed and related meta-materials based on a fully symmetric multi-gap single-ring SRR design and crossing continuous wires. We demonstrate isotropic transmission properties of a SRR-only meta-material and the corresponding left-handed material which possesses a negative effective index of refraction due to simultaneously negative effective permeability and permittivity. Minor deviations from complete isotropy are due to the finite thickness of the meta-material.Comment: 4 pages, 6 figure

AdS/CFT Correspondence with a 3D Black Hole Simulator

The AdS/CFT correspondence has been insightful for high-energy and condensed matter physics alike. An application of this correspondence is the duality between the entanglement entropy of Anti-de Sitter (AdS) black holes and lower-dimensional conformal field theories (CFT). To explicitly demonstrate this correspondence we simulate the effect a 3D black hole geometry has on Dirac fields by employing a square lattice of fermions with inhomogeneous tunnelling couplings. Simulating a 3D BTZ black hole horizon, we numerically obtain an area law behaviour that is in agreement with the corresponding 2D CFT with a central charge that depends on the cosmological constant of the AdS space. A systematic numerical investigation of various 3D black hole profiles suggests that all 3D black holes give an entropic behaviour that can be represented by the same CFT.Comment: 6 pages, 4 figure

Highly directional emission from photonic crystals with a wide bandwidth

Cataloged from PDF version of article.The authors numerically and experimentally demonstrated highly directional emission from photonic crystals. This was achieved by first splitting the incident electromagnetic wave into multiple beams using photonic crystal waveguide structures. The beams were then emitted out of the surface of a photonic crystal with the same phase, which resulted in a highly directional radiation pattern. The measured half power beam width was 4.8 degrees, which was in good agreement with the calculated value of 4.1 degrees. In contrast to the traditional beaming structures, their design did not involve gratinglike structures, which resulted in a wider operation bandwidth. (c) 2007 American Institute of Physics

Subwavelength resolution with a negative-index metamaterial superlens

Cataloged from PDF version of article.Negative-index metamaterials are candidates for imaging objects with sizes smaller than a half-wavelength. The authors report an impedance-matched, low loss negative-index metamaterial superlens that is capable of resolving subwavelength features of a point source with a 0.13 lambda resolution, which is the highest resolution achieved by a negative-index metamaterial. By separating two point sources with a distance of lambda/8, they were able to detect two distinct peaks on the image plane. They also showed that the metamaterial based structure has a flat lens behavior. (c) 2007 American Institute of Physics