An improved method for 21-cm foreground removal

21-cm tomography is expected to be difficult in part because of serious foreground contamination. Previous studies have found that line-of-sight approaches are capable of cleaning foregrounds to an acceptable level on large spatial scales, but not on small spatial scales. In this paper, we introduce a Fourier space formalism for describing the line-of-sight methods, and use it to introduce an improved new method for 21-cm foreground cleaning. Heuristically, this method involves fitting foregrounds in Fourier space using weighted polynomial fits, with each pixel weighted according to its information content. We show that the new method reproduces the old one on large angular scales, and gives marked improvements on small scales at essentially no extra computational cost.     

Prediction of salinity intrusion in the sheltered estuary of Terengganu River in Malaysia using 1-D empirical intrusion model

Generally one dimensional(1-D) empirical salinity intrusion model is limited to natural alluvial estuary. However,this study attempts to investigate its ability to model a sheltered alluvial estuary of the Terengganu River in Malaysia. The constructed breakwater at the mouth of the river shelters the estuary from direct influence of the open sea. The salinity density along the estuary was collected during the wet and dry seasons for scenarios before and after the constructed breakwater. Moreover, the freshwater discharges, tidal elevations and bathymetry data were also measured as model inputs. A good fit was demonstrated between simulated and observed variables,namely salinity distribution and intrusion length for both scenarios. Thus, the results show that 1-D empirical salinity model can be utilized for sheltered estuarine condition at the Terengganu Estuary, but with an appropriate determination of an initial point. Furthermore, it was observed that the salinity intrusion in the study area is largely dependent on the freshwater discharge rather than tidal elevation fluctuations. The scale of the salinity intrusion length in the study area is proportional to the river discharge of the –1/2 power. It was appeared that the two lines of the 1-D empirical salinity model and discharge power based equation fitted well to each other, with the average predicted minimum freshwater discharge of 150 m3/s is going to be required to maintain acceptable salinity levels during high water slack(HWS) near the water intake station, which is located at 10.63 km from river mouth.     

The Planetary Nebula A 79 Revisited: Discovery of a Large Emission Nebula

New observations of the planetary nebula A 79 using selective interference filters (Δ λ ≤ 10 Å) are reported. Thanks to the large field of view (< 11″5) offered by the Observatoire de Haute Provence 120-cm telescope we were able to discover a new extended feature close to A 79.     

Towards quantitative ecological risk assessment of elevated carbon dioxide levels in the marine environment

The environmental impact of elevated carbon dioxide (CO₂) levels has become of more interest in recent years. This, in relation to globally rising CO₂ levels and related considerations of geological CO₂ storage as a mitigating measure. In the present study effect data from literature were collected in order to conduct a marine ecological risk assessment of elevated CO₂ levels, using a Species Sensitivity Distribution (SSD). It became evident that information currently available from the literature is mostly insufficient for such a quantitative approach. Most studies focus on effects of expected future CO₂ levels, testing only one or two elevated concentrations. A full dose-response relationship, a uniform measure of exposure, and standardized test protocols are essential for conducting a proper quantitative risk assessment of elevated CO₂ levels. Improvements are proposed to make future tests more valuable and usable for quantitative risk assessment.     

A comparison of statistical downscaling and climate change factor methods: impacts on low flows in the River Thames, United Kingdom

Strategic-scale assessments of climate change impacts are often undertaken using the change factor (CF) methodology whereby future changes in climate projected by General Circulation Models (GCMs) are applied to a baseline climatology. Alternatively, statistical downscaling (SD) methods apply climate variables from GCMs to statistical transfer functions to estimate point-scale meteorological series. This paper explores the relative merits of the CF and SD methods using a case study of low flows in the River Thames under baseline (1961–1990) and climate change conditions (centred on the 2020s, 2050s and 2080s). Archived model outputs for the UK Climate Impacts Programme (UKCIP02) scenarios are used to generate daily precipitation and potential evaporation (PE) for two climate change scenarios via the CF and SD methods. Both signal substantial reductions in summer precipitation accompanied by increased PE throughout the year, leading to reduced flows in the Thames in late summer and autumn. However, changes in flow associated with the SD scenarios are generally more conservative and complex than that arising from CFs. These departures are explained in terms of the different treatment of multidecadal natural variability, temporal structuring of daily climate variables and large-scale forcing of local precipitation and PE by the two downscaling methods.     

Suspended-Sediment Impacts on Light-Limited Productivity in the Delaware Estuary

The Delaware Estuary has a history of high anthropogenic nutrient loadings but has been classified as a high-nutrient, low-growth system due to persistent light limitation caused by turbidity. While the biogeochemical implications of light limitation in turbid estuaries have been well-studied, there has been minimal effort focused on the connectivity between hydrodynamics, sediment dynamics, and light limitation. Our understanding of sediment dynamics in the Delaware Estuary has advanced significantly in the last decade, and this study describes the impact of spatiotemporal variability of the estuarine turbidity maximum (ETM) on light-limited productivity. This analysis uses data from eight along-estuary cruises from March, June, September, and December 2010 and 2011 to evaluate the impact of the turbidity maximum on production. Whereas the movement of the ETM is controlled primarily by river discharge, the structure of the ETM is modulated by stratification, which varies with both river discharge and spring-neap conditions. We observe that the ETM’s location and structure control spatial patterns of light availability. To evaluate the relative contributions of river discharge and spring-neap variability to the location of phytoplankton blooms, we develop an idealized two-dimensional Regional Ocean Modeling System (ROMS) numerical model. We conclude that high river flows and neap tides can drive stratification that is strong enough to prevent sediment from being resuspended into the surface layer, thus providing light conditions favorable for primary production. This study sheds light on the role of stratification in controlling sediment resuspension and promoting production, highlighting the potential limitations of biogeochemical models that neglect sediment processes.     

18O16O ratios in Luna 16 fines

Partial fluorination experiments developed on a 26 mg sample of Luna 16 fines show a big ¹⁸O enrichment in the first oxygen evolved similar to those observed by Epstein and Taylor on Apollo samples and probably related to the high solar wind content of this sample.     

On the parameterization of biological influences on offshore sand wave dynamics

The bed of the North Sea is covered by sand waves and houses a great number of macrobenthic animals. These bio-engineers are known to have a significant influence on the stability of the bed and thereby on the geomorphology of the seabed. This paper proposes a parameterization of these bio-geomorphological interactions. Given the abundance of three dominant bio-engineers on the Dutch Continental Shelf, the predicted occurrence of sand waves, in which the parameterization is included, shows significantly better results, compared to the prediction for the default case without biology. Therefore, the inclusion of biological activity could be important to predict the occurrence of sand waves.     

EXPERIMENTS ON THE STABILITY OF FeOOH ON THE SURFACE OF THE MOON

The FeOOH phase in Apollo 16 rocks is akaganéite. Other polymorphs of FeOOH, i.e. geothite and lepidocrocite, may exist but have not been identified by X-ray diffraction. Experiments performed during this study using akaganéite, geothite, and lepidocrocite placed at 135°C and under a pumping vacuum of 10^?2 torr, demonstrate that these forms of FeOOH are not stable on the surface of the Moon, where daytime temperatures are about 140°C and pressures are about 10^?7 torr. The effect of the vacuum is to strip off the water, and the temperature speeds up this dehydration process. These data lend support to the contention of Taylor et al. (1973) that the FeOOH in lunar rocks formed by the oxyhydration of lawrencite, FeCl₂, due to contamination by terrestrial water vapor.