On the redshift cut-off for steep-spectrum radio sources

We use three samples (3CRR, 6CE and 6C*) selected at low radio frequency to constrain the cosmic evolution in the radio luminosity function (RLF) for the 'most luminous' steep-spectrum radio sources. Though intrinsically rare, such sources give the largest possible baseline in redshift for the complete flux-density-limited samples currently available. Using parametric models to describe the RLF, incorporating distributions in radio spectral shape and linear size, as well as the usual luminosity and redshift, we find that the data are consistent with a constant comoving space density between     and     . We find that this model is favoured over a model with similar evolutionary behaviour to that of optically selected quasars (i.e., a roughly Gaussian distribution in redshift) with probability ratios of     and     for spatially flat cosmologies with     and     respectively. Within the uncertainties, this evolutionary behaviour may be reconciled with the shallow decline preferred for the comoving space density of flat-spectrum sources by Dunlop & Peacock and Jarvis & Rawlings, in line with the expectations of unified schemes.     

Seasonal global mean sea level change from satellite altimeter, GRACE, and geophysical models

We estimate seasonal global mean sea level changes using different data resources, including sea level anomalies from satellite radar altimetry, ocean temperature and salinity from the World Ocean Atlas 2001, time-variable gravity observations from the Gravity Recovery and Climate Experiment (GRACE) mission, and terrestrial water storage and atmospheric water vapor changes from the NASA global land data assimilation system and National Centers for Environmental Prediction reanalysis atmospheric model. The results from all estimates are consistent in amplitude and phase at the annual period, in some cases with remarkably good agreement. The results provide a good measure of average annual variation of water stored within atmospheric, land, and ocean reservoirs. We examine how varied treatments of degree-2 and degree-1 spherical harmonics from GRACE, laser ranging, and Earth rotation variations affect GRACE mean sea level change estimates. We also show that correcting the standard equilibrium ocean pole tide correction for mass conservation is needed when using satellite altimeter data in global mean sea level studies. These encouraging results indicate that is reasonable to consider estimating longer-term time series of water storage in these reservoirs, as a way of tracking climate change.     

Lava effusion rates from hand-held thermal infrared imagery: an example from the June 2003 effusive activity at Stromboli

A safe, easy and rapid method to calculate lava effusion rates using hand-held thermal image data was developed during June 2003 at Stromboli Volcano (Italy). We used a Forward Looking Infrared Radiometer (FLIR) to obtain images of the active lava flow field on a daily basis between May 31 and June 16, 2003. During this time the flow field geometry and size (where flows typically a few hundred meters long were emplaced on a steep slope) meant that near-vertical images of the whole flow field could be captured in a single image obtained from a helicopter hovering, at an altitude of 750 m and ∼1 km off shore. We used these images to adapt a thermally based effusion rate method, previously applied to low and high spatial resolution satellite data, to allow automated extraction of effusion rates from the hand-held thermal infrared imagery. A comparison between a thermally-derived (0.23–0.87 m³ s⁻¹) and dimensionally-derived effusion rate (0.56 m³ s⁻¹) showed that the thermally-derived range was centered on the expected value. Over the measurement period, the mean effusion rate was 0.38±0.25 m³ s⁻¹, which is similar to that obtained during the 1985–86 effusive eruption and the time-averaged supply rate calculated for normal (non-effusive) Strombolian activity. A short effusive pulse, reaching a peak of ∼1.2 m³ s⁻¹, was recorded on June 3, 2003. One explanation of such a peak would be an increase in driving pressure due to an increase in the height of the magma contained in the central column. We estimate that this pulse would require the magma column to attain a height of ∼190 m above the effusive vent, which is approximately the elevation difference between the vent and the floor of the NE crater. Our approach gives an easy-to-apply method that has the potential to provide effusion rate time series with a high temporal resolution.Editorial responsibility: M. Carroll     

ELGYGYTGYN CRATER,SIBERIA: PROBABLE SOURCE OF AUSTRALASIAN TEKTITE FIELD (and Bediasites from Popigai)

Elgygytgyn crater (lat. 67–30 N, long. 172–00 E) in remote northeastern Siberia is proposed as the meteorite impact site from which the Australasian tektite strewnfield was splashed. The following points support this interpretation: 1, Elgygytgyn very likely is an impact crater and is of adequate size, 18 km across, to generate tektites; 2, the apex of the strewnfield points towards this crater; 3, the terrane is Mesozoic which fits the age of the tektite parental material from Sr/Rb data; 4, compositional and specific gravity lineations within the strewnfield are directed, in part, toward this crater; 5, the high velocity tektites, australites, are distal with respect to this crater while the low velocity tektites, splash forms and Muong Nong tektites, are proximal; 6, the loess deposits and mixed acid/basic rocks of the impact site provide a suitable subgraywacke-type source material; 7, the erosional state of Elgygytgyn suggests that its age may well be in accordance with that of the Australasian tektite event, i.e., 700,000 years.     

An efficient incremental algorithm for generating the characteristic shape of a dynamic set of points in the plane

Several algorithms have been proposed to generate a polygonal ‘footprint’ to characterize the shape of a set of points in the plane. One widely used type of footprint is the χ-shape. Based on the Delaunay triangulation (DT), χ-shapes guaranteed to be simple (Jordan) polygons. This paper presents for the first time an incremental χ-shape algorithm, capable of processing point data streams. Our incremental χ-shape algorithm allows both insertion and deletion operations, and can handle streaming individual points and multiple point sets. The experimental results demonstrated that the incremental algorithm is significantly more efficient than the existing, batch χ-shape algorithm for processing a wide variety of point data streams.     

The X-ray spectrum and variability of the Seyfert 2 galaxy NGC 7172

We present evidence of flux variability, on both short (hours) and long (months) time-scales, of the Seyfert 2 galaxy NGC 7172. These results are based on the ASCA observation of NGC 7172 performed in 1996 May. The source was detected at a rather low flux level, about 3 times fainter than its usual state (including 1 yr before, when it was also observed by ASCA ).   The source also varied by about 30 per cent during the observation, confirming the presence of a type 1 nucleus in its centre. However, its spectrum appears to be flatter than the typical Seyfert 1 spectrum (in agreement with findings on other Seyfert 2s), posing problems for the unification model unless complex absorption is invoked.     

A spectroscopic study of IRAS F10214 + 4724

The z  = 2.286  IRAS galaxy F10214 + 4724 remains one of the most luminous galaxies in the Universe, despite its gravitational lens magnification. We present optical and near-infrared spectra of F10214 + 4724, with clear evidence for three distinct components: lines of width ∼ 1000 km s⁻¹ from a Seyfert 2 nucleus; ≲ 200 km s⁻¹ lines which are likely to be associated with star formation; and a broad (∼ 4000 km s⁻¹) C  III ] 1909-Å emission line which is blueshifted by ∼ 1000 km s⁻¹ with respect to the Seyfert 2 lines. Our study of the Seyfert 2 component leads to several new results. (i) From the double-peaked structure in the Lyα line, and the lack of Lyβ, we argue that the Lyα photons have emerged through a neutral column of N _H ∼ 2.5 × 10²⁵ m⁻², possibly located within the AGN narrow-line region, as proposed for several high-redshift radio galaxies. (ii) The resonant O  VI 1032, 1036-Å doublet (previously identified as Lyβ) is in an optically thick (1:1) ratio. At face value this implies an extreme density ( n _e ∼ 10¹⁷ m⁻³) more typical of broad-line region clouds. However, we attribute this instead to the damping wings of Lyβ from the resonant absorption. (iii) A tentative detection of He  II 1086 suggests little extinction in the rest frame ultraviolet.     

Cracking the Code: a legal geography and political ecological perspective on vegetation clearing regulations

ABSTRACT

In 2014, the New South Wales (NSW) state parliament passed legislation implementing a new Code of Practice (‘Code 10/50’) granting property owners in bushfire-prone areas the right to clear all trees within 10 m, and all vegetation within 50 m, of residences without prior approval from authorities. The Code is a significant departure from previous regimes which often required permits for vegetation clearance. The Code was introduced in direct response to bushfire threat in the wake of the 2013–14 bushfires in NSW. However, the Code has been plagued by controversy, with accusations of abuse in areas with little or no bushfire history, and a lack of any substantial environmental protections, particularly prior to a review in August 2015. In this paper we examine the debates surrounding the enactment of the Code and consider the way in which particular justifications for the Code permeated parliamentary deliberations. Our investigation relies on unpacking how the Code emerged in order to shed light on how a very controversial policy came into being. We adopt a legal geography approach, together with insights from political ecology, to demonstrate that changes in regulatory processes have the potential to fundamentally alter our landscapes.     

Linking Spatial and Temporal Variation at Multiple Scales in a Heterogeneous Landscape*

Anthropogenic, ecological, and land‐surface processes interact in landscapes at multiple spatial and temporal scales to create characteristic patterns. The relationships between temporally and spatially varying processes and patterns are poorly understood because of the lack of spatiotemporal observations of real landscapes over significant stretches of time. We report a new method for observing joint spatiotemporal landscape variation over large areas by analyzing multitemporal Landsat data. We calculate the spatiotemporal variation of the Normalized Difference Vegetation Index (NDVI) in the area covered by one Landsat scene footprint in north central Florida, over spatial windows of 10⁴–10⁸ m² and time steps of two to sixteen years. The correlations, slopes, and intercepts of spatial versus temporal regressions in the real landscape all differ significantly from results obtained using a null model of a randomized landscape. Spatial variances calculated within windows of 10⁵–10⁷ m² had the strongest relationships with temporal variances (regressions with both larger and smaller windows had lower coefficients of determination), and the relationships were stronger with longer time steps. Slopes and y‐intercepts increased with window size and decreased with increased time step. The spatial and temporal scales at which NDVI signals are most strongly related may be the characteristic scales of the processes that most strongly determine landscape patterns. For example, the important time and space windows correspond with areas and timing of fires and tree plantation harvests. Observations of landscape dynamics will be most effective if conducted at the characteristic scales of the processes, and our approach may provide a tool for determining those scales.