Charge coupled devices (CCDs) in X-ray astronomy

The application of CCDs to X-ray imaging and spectroscopy for astronomy is described. The requirements which differ markedly from those of traditional optical applications are highlighted. Results of recent research programs to optimize CCD X-ray response are presented. It is shown that very high quantum efficiencies and Fano noise limited energy resolutions can be obtained. A number of issues related to the practical implementation of future instruments are reviewed.     

Use of chemical tracers in assessing the diet and foraging regions of eastern North Pacific killer whales

Top predators in the marine environment integrate chemical signals acquired from their prey that reflect both the species consumed and the regions from which the prey were taken. These chemical tracers-stable isotope ratios of carbon and nitrogen; persistent organic pollutant (POP) concentrations, patterns and ratios; and fatty acid profiles-were measured in blubber biopsy samples from North Pacific killer whales (Orcinus orca) (n=84) and were used to provide further insight into their diet, particularly for the offshore group, about which little dietary information is available. The offshore killer whales were shown to consume prey species that were distinctly different from those of sympatric resident and transient killer whales. In addition, it was confirmed that the offshores forage as far south as California. Thus, these results provide evidence that the offshores belong to a third killer whale ecotype. Resident killer whale populations showed a gradient in stable isotope profiles from west (central Aleutians) to east (Gulf of Alaska) that, in part, can be attributed to a shift from off-shelf to continental shelf-based prey. Finally, stable isotope ratio results, supported by field observations, showed that the diet in spring and summer of eastern Aleutian Island transient killer whales is apparently not composed exclusively of Steller sea lions.     

Evidence for chromatic X-ray light-curve breaks in Swift gamma-ray burst afterglows and their theoretical implications

The power-law decay of the X-ray emission of gamma-ray burst (GRB) afterglows 050319, 050401, 050607, 050713A, 050802 and 050922C exhibits a steepening at about 1–4 h after the burst which, surprisingly, is not accompanied by a break in the optical emission. If it is assumed that both the optical and X-ray afterglows arise from the same outflow then, in the framework of the standard forward shock model, the chromaticity of the X-ray light-curve breaks indicates that they do not arise solely from a mechanism related to the outflow dynamics (e.g. energy injection) or the angular distribution of the blast-wave kinetic energy (structured outflows or jets). The lack of a spectral evolution accompanying the X-ray light-curve break shows that these breaks do not arise from the passage of a spectral break (e.g. the cooling frequency) either. Under these circumstances, the decoupling of the X-ray and optical decays requires that the microphysical parameters for the electron and magnetic energies in the forward shock evolve in time, whether the X-ray afterglow is synchrotron or inverse-Compton emission. For a steady evolution of these parameters with the Lorentz factor of the forward shock and an X-ray light curve arising cessation of energy injection into the blast wave, the optical and X-ray properties of the above six Swift afterglows require a circumburst medium with a r ⁻² radial stratification, as expected for a massive star origin for long GRBs. Alternatively, the chromatic X-ray light-curve breaks may indicate that the optical and X-ray emissions arise from different outflows. Neither feature (evolution of microphysical parameters or the different origin of the optical and X-ray emissions) was clearly required by pre-Swift afterglows.     

Regional Air Quality Modelling in Canada – Applications for Policy and Real-Time Prediction

Acid rain and photochemical smog are two regionalair-quality issues that have received considerableattention in the last two decades due to their harmfuleffects. Health impacts of particulate matter (PM) inthe atmosphere is another issue of concern.Sulphur dioxide emission controls were introducedin both Canada and the U.S.A. to reduceacid-deposition-related damage. While these emissionreductions have already resulted in reduced sulphatedeposition, based on results from modelling studiesmuch of southeastern Canada is still expected toexperience damaging levels of acid deposition evenafter all currently legislated emission controls arefully implemented. Moreover, there has not been acorresponding reduction in the acidity ofprecipitation. This may be attributable to aconcurrent reduction in base-cation concentration inprecipitation.Models were also developed to understand theformation, transport and diffusion of troposphericozone. The models have been used to provide policyguidance for emission control options to reduceground-level ozone to acceptable limits. In thesummer of 1997 a Canadian pilot project was initiatedto provide real-time forecasts of ground-level ozonein the southeastern part of the province of NewBrunswick in eastern Canada.With the emergence of fine Particulate Matter(PM_2.5) as a health concern, efforts are underwayin Canada to develop a unified' regional air-qualitymodel that will address the combined impacts ofvarious pollutants in the atmosphere. In this effortthe atmosphere is viewed as a single entity where theimpacts of multiple pollutants are considered at thesame time.     

The Intercomparison of Top-of-Atmosphere Reflectivity Measured by MERIS and SCIAMACHY in the Spectral Range of 443–865 nm

This letter is aimed at better understanding of Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) reflectance radiometric calibration errors using the Medium Resolution Imaging Spectrometer (MERIS) onboard ENVISAT. Earlier investigations showed that the SCIAMACHY calibration error can reach 20% in the visible bands, which prevents aerosol retrievals using the SCIAMACHY data. Recent improvements of the SCIAMACHY calibration are discussed. It is found that the differences in reflectances for the wavelengths 443, 560, 665, 754, and 865 nm between MERIS and improved Processor 6 SCIAMACHY data are close to the MERIS radiometric calibration error, which is below 4%     

Improved dissolved oxygen status following removal of exotic weed mats in important fish habitat lagoons of the tropical Burdekin River floodplain, Australia

The Burdekin delta floodplain, north Queensland, is highly modified for agricultural purposes. Riparian condition is very poor and exotic aquatic weeds dominate waterways. Historically, most streams and lagoons were highly seasonal, but those now used for the delivery of irrigation water maintain elevated flows and increased turbidity and nutrient loading. These factors have aided exotic weed growth and many major lagoons are covered by dense water hyacinth (Eichhornia crassipes) mats which greatly reduce dissolved oxygen levels, one of the most important water quality variables for aquatic fauna. Mechanical harvesting of water hyacinth from several of these lagoons resulted in rapid and substantial increases in dissolved oxygen saturation, and improved suitability of the habitat to support fish species. Decrease in dissolved oxygen as water passes sequentially through weed-infested lagoons, justified the approach of harvesting upstream lagoons first, however, the channels that connect these lagoons remain weed-infested and are still impacting upon downstream oxygen levels.