The extreme, red afterglow of GRB 060923A: distance or dust?

Gamma-ray bursts (GRBs) are powerful probes of the early Universe, but locating and identifying very distant GRBs remain challenging. We report here the discovery of the K -band afterglow of Swift GRB 060923A, imaged within the first hour post-burst, and the faintest so far found. It was not detected in any bluer bands to deep limits, making it a candidate very high- z burst  ( z ≳ 11)  . However, our later-time optical imaging and spectroscopy reveal a faint galaxy coincident with the GRB position which, if it is the host, implies a more moderate redshift (most likely   z ≲ 2.8  ) and therefore that dust is the likely cause of the very red-afterglow colour. This being the case, it is one of the few instances so far found of a GRB afterglow with high-dust extinction.     

Geoeffectiveness of interplanetary shocks during solar minimum (1995–1996) and solar maximum (2000)

Plasma and magnetic field parameter variations across fast forward interplanetary shocks are analyzed during the last solar cycle minimum (1995–1996, 15 shocks), and maximum year 2000 (50 shocks). It was observed that the solar wind velocity and magnetic field strength variation across the shocks were the parameters better correlated with Dst. Superposed epoch analysis centered on the shock showed that, during solar minimum, B _z profiles had a southward, long-duration variation superposed with fluctuations, whereas in solar maximum the B _z profile presented 2 peaks. The first peak occurred 4 hr after the shock, and seems to be associated with the magnetic field disturbed by the shock in the sheath region. The second peak occurred 19 hr after the shock, and seems to be associated with the ejecta fields. The difference in shape and peak in solar maximum (Dst peak =−50 nT, moderate activity) and minimum (Dst peak =−30 nT, weak activity) in average Dst profiles after shocks are, probably, a consequence of the energy injection in the magnetosphere being driven by different interplanetary southward magnetic structures. A statistical distribution of geomagnetic activity levels following interplanetary shocks was also obtained. It was observed that during solar maximum, 36% of interplanetary shocks were followed by intense (Dst≤−100 nT) and 28% by moderate (−50≤Dst <−100 nT) geomagnetic activity. During solar minimum, 13% and 33% of the shocks were followed by intense and moderate geomagnetic activity, respectively. Thus, during solar maximum a higher relative number of interplanetary shocks might be followed by intense geomagnetic activity than during solar minimum. One can extrapolate, for forecasting goals, that during a whole solar cycle a shock has a probability of around 50–60% to be followed by intense/moderate geomagnetic activity.     

The conditionality of status: Experience-based reflections on the insider/outsider issue

When a researcher undertakes research into his/her own ethnic group, issues of positionality abound. These issues relate not only to the impact of inherent insider positionality when interacting with study participants but also in the interpretation and presentation of study findings. My research with contemporary Irish immigrants not only reinforced the advantages of being an insider but also highlighted the incomplete and unstable nature of insiderness. Heterogeneity within the study group, in terms of their geo-political, regional and religious origins, meant that presumptions of insiderness and outsiderness were frequently challenged. A new awareness of the conditionality of each positionality was forged from these experiences.     

Multiwavelength study of the nuclei of a volume-limited sample of galaxies – II. Optical, infrared and radio observations

We present optical and infrared broad-band images, radio maps, and optical spectroscopy for the nuclear region of a sample of nearby galaxies. The galaxies have been drawn from a complete volume-limited sample for which we have already presented X-ray imaging. We modelled the stellar component of the spectroscopic observations to determine the star formation history of our targets. Diagnostic diagrams were used to classify the emission-line spectra and determine the ionizing mechanism driving the nuclear regions. All those sources classified as active galactic nuclei present small Eddington ratios  (∼10⁻³–10⁻⁶)  , implying a very slow growth rate of their black holes. We finally investigate the relative numbers of active and normal nuclei as a function of host galaxy luminosity and find that the fraction of active galaxies slowly rises as a function of host absolute magnitude in the   M _B ∼−12  to −22 range.     

The Landscape of Diversity in U.S. Higher Education Geography

Palynological analyses were completed for the A and B horizons of a forested Mollic Hapludalf to determine type, amount, and distribution of pollen and spores within the soil solum. Hypotheses regarding the origin of pollen and the mechanisms of its movement within soil bodies are also advanced. Pollen downwash within the mineral soil seems to be very slow and confined to the uppermost porous and most homogenized part of the solum. The predominance of non-arboreal pollen at depth was believed to be a result of deposition with the loess parent material. High arboreal pollen frequencies in the upper horizons coupled with increases in non-arboreal types at depth indicate gradual ongoing mixing from the present vegetation into the soil.     

Harmful algal blooms and eutrophication: ��strategies�� for nutrient uptake and growth outside the Redfield comfort zone

While many harmful algal blooms have been associated with increasing eutrophication, not all species respond similarly and the increasing challenge, especially for resource managers, is to determine which blooms are related to eutrophication and to understand why particular species proliferate under specific nutrient conditions. The overall goal of this brief review is to describe why nutrient loads are not changing in stoichiometric proportion to the "Redfield ratio", and why this has important consequences for algal growth. Many types of harmful algae appear to be able to thrive, and/or increase their production of toxins, when nutrient loads are not in proportion classically identified as Redfield ratios. Here we also describe some of the physiological mechanisms of different species to take up nutrients and to thrive under conditions of nutrient imbalance.     

Estimation of bioavailability of polycyclic aromatic hydrocarbons in river sediments

This study aimed to evaluate the total concentration of polycyclic aromatic hydrocarbons in sediments of Iguassu River in Southern Brazil. Alongside the concentration, the amount of such compounds bioavailable was also evaluated. This is accomplished by comparing its total amount present in sediments and the amount extracted by n-butanol. The results showed that the total concentration of polycyclic aromatic hydrocarbons presented in sediment ranged from 4.49 to 58.75???g/g. The total amount of polycyclic aromatic hydrocarbons extracted by n-butanol ranged from 1.22 to 17.07???g/g. The use of n-butanol represents the mimetic conditions that hydrocarbons, derived from oil, could be taken up by organisms. Most of the hydrocarbons extracted by n-butanol were those with lower octanol?Cwater partition constant, usually those with three and four rings. Compounds with more than four rings were extracted in lower or insignificant amounts. Even the hydrocarbons with lower molecular weight available may be degraded or eliminated by organisms, when accumulated. Estimating bioavailability of hydrocarbons represents what specific hydrocarbons could be available to be taken up by organisms.     

Perceptive of the pyroxene-bearing micrometeorites and their relation to chondrites

We studied 149 pyroxenes from 69 pyroxene-bearing micrometeorites collected from deep-sea sediments of the Indian Ocean and South Pole Water Well at Antarctica, Amundsen-Scott South Pole station. The minor elements in pyroxenes from micrometeorites are present in the ranges as follows: MnO ~0.0–0.4 wt%, Al₂O₃ ~0.0–1.5 wt%, CaO ~0.0–1.0 wt%, Cr₂O₃ ~0.3–0.9 wt%, and FeO ~0.5–4 wt%. Their chemical compositions suggest that pyroxene-bearing micrometeorites are mostly related to precursors from carbonaceous chondrites rather than ordinary chondrites. The Fe/(Fe+Mg) ratio of the pyroxenes and olivines in micrometeorites shows similarities to carbonaceous chondrites with values lying between 0 and 0.2, and those with values beyond this range are dominated by ordinary chondrites. Atmospheric entry of the pyroxene-bearing micrometeorites is expected to have a relatively low entry velocity of <16 km s⁻¹ and high zenith angle (70–90°) to preserve their chemical compositions. In addition, similarities in the pyroxene and olivine mineralogical compositions between carbonaceous chondrites and cometary particles suggest that dust in the solar system is populated by materials from different sources that are chemically similar to each other. Our results on pyroxene chemical compositions reveal significant differences with those from ordinary chondrites. The narrow range in olivine and pyroxene chemical compositions are similar to those from carbonaceous chondrites, and a small proportion to ordinary chondrites indicates that dust is largely sourced from carbonaceous chondrite-type bodies.