Emerging Network-Based Tools in Movement Ecology

New technologies have vastly increased the available data on animal movement and behaviour. Consequently, new methods deciphering the spatial and temporal interactions between individuals and their environments are vital. Network analyses offer a powerful suite of tools to disentangle the complexity within these dynamic systems, and we review these tools, their application, and how they have generated new ecological and behavioural insights. We suggest that network theory can be used to model and predict the influence of ecological and environmental parameters on animal movement, focusing on spatial and social connectivity, with fundamental implications for conservation. Refining how we construct and randomise spatial networks at different temporal scales will help to establish network theory as a prominent, hypothesis-generating tool in movement ecology

The Local Group Census: planetary nebulae in Sextans B

Five planetary nebulae (PNe) have been discovered in the nearby dwarf irregular galaxy. Emission line images were obtained using the Wide Field Camera of the 2.5m Isaac Newton Telescope (INT) at La Palma (Spain). The candidate PNe were identified by their point-like appearance and relatively strong [OIII] emission-line fluxes. They are located within a galactocentric distance of 2.8 arcmin, corresponding to 1.1 kpc at the distance of Sextans B. Luminosities are in the range 1800--5600Lsolar. Sextans B is one of the smallest dwarf irregular galaxies with a PN population. The number of PNe detected suggest an enhanced star formation rate between 1 and 5 Gyr ago.Comment: 7 pages, 2 figure

Chemical Abundances of Planetary Nebulae in M33

Using spectroscopic data presented in Magrini et al. (2003), we have analyzed with the photoionization code CLOUDY 94.00 (Ferland et al. 1998) 11 Planetary Nebulae belonging to the spiral galaxy M 33. Central star temperatures and nebular parameters have been determined. In particular the chemical abundances of He/H, O/H, N/H, Ar/H, and S/H have been measured and compared with values obtained via the Ionization Correction Factors (ICFs) method, when available. Chemical abundance relationships have been investigated; in particular, a correlation between N/H and N/O similar to the Galactic one (Henry 1989), and a feeble anti-correlation between O/H and N/O have been found. A gradient in O/H across the disc of M~33 is indicatively consistent with the one found from HII regions in this galaxy (Vilchez et al 1988). Further studies in the more external parts of M~33 are however needed to ascertain this point. The present result shows that oxygen and helium abundances (with lower accuracy also nitrogen, argon and sulphur) can be actually estimated from the brightest PNe of a galaxy, even if the electron temperature cannot be measured. We also found that the oxygen abundance is quite independent of the absolute magnitude of the PN and consequently the brightest PNe are representative of the whole PN population. This represents an important tool to measure the metallicity of galaxies at the time of the formation of PNe progenitors.Comment: 17 pages, 6 figures, A&A accepte

The Rapidly Fading Afterglow from the Gamma-Ray Burst of 1999 May 6

We report on the discovery of the radio afterglow from the gamma-ray burst (GRB) of 1999 May 6 (GRB 990506) using the Very Large Array (VLA). The radio afterglow was detected at early times (1.5 days), but began to fade rapidly sometime between 1 and 5 days after the burst. If we attribute the radio emission to the forward shock from an expanding fireball, then this rapid onset of the decay in the radio predicts that the corresponding optical transient began to decay between 1 and 5 minutes after the burst. This could explain why no optical transient for GRB 990506 was detected in spite of numerous searches. The cause of the unusually rapid onset of the decay for the afterglow is probably the result of an isotropically energetic fireball expanding into a low density circumburst environment. At the location of the radio afterglow we find a faint (R ~ 24 mag) host galaxy with a double morphology.Comment: in press at ApJ Letters, 13 page LaTeX document includes 2 postscript figure

Analysis of the Coal Sector under Carbon Constraints

Abstract in HTML and technical report in PDF available on the MIT Joint Program on the Science and Policy of Global Change website (http://mit.edu/globalchange/www/).Application of the MIT Emissions Prediction and Policy Analysis (EPPA) model to assessment of the future of coal under climate policy revealed the need for an improved representation of load dispatch in the representation of the electric sector. A new dispatching algorithm is described and the revised model is applied to an analysis of the future of coal use to 2050 and 2100 under alternative assumptions about CO2 prices, nuclear expansion and prices of natural gas. Particular attention is devoted to the potential role of coal-electric generation with CO2 capture and storage. An appendix provides a comparison of a subset of these results with and without the more detailed model of electric dispatch.Development of the analysis model used in this research was supported by the U.S. Department of Energy, Office of Biological and Environmental Research [BER] (DE-FG02-94ER61937), by the U.S. Environmental Protection Agency (XA-83042801-0), the Electric Power Institute, and by a consortium of industry and foundation sponsors

Is the whole really more than the sum of its parts? Estimates of average size and orientation are susceptible to object substitution masking

We have a remarkable ability to accurately estimate average featural information across groups of objects, such as their average size or orientation. It has been suggested that, unlike individual object processing, this process of feature averaging occurs automatically and relatively early in the course of perceptual processing, without the need for objects to be processed to the same extent as is required for individual object identification. Here, we probed the processing stages involved in feature averaging by examining whether feature averaging is resistant to object substitution masking (OSM). Participants estimated the average size (Experiment 1) or average orientation (Experiment 2) of groups of briefly presented objects. Masking a subset of the objects using OSM reduced the extent to which these objects contributed to estimates of both average size and average orientation. Contrary to previous findings, these results suggest that feature averaging benefits from late stages of processing, subsequent to the initial registration of featural information