Modeling atmospheric effects of the September 1859 Solar Flare

We have modeled atmospheric effects, especially ozone depletion, due to a solar proton event which probably accompanied the extreme magnetic storm of 1-2 September 1859. We use an inferred proton fluence for this event as estimated from nitrate levels in Greenland ice cores. We present results showing production of odd nitrogen compounds and their impact on ozone. We also compute rainout of nitrate in our model and compare to values from ice core data.Comment: Revised version including improved figures; Accepted for publication in Geophys. Res. Lett, chosen to be highlighted by AG

Discussion quality diffuses in the digital public square

Studies of online social influence have demonstrated that friends have important effects on many types of behavior in a wide variety of settings. However, we know much less about how influence works among relative strangers in digital public squares, despite important conversations happening in such spaces. We present the results of a study on large public Facebook pages where we randomly used two different methods--most recent and social feedback--to order comments on posts. We find that the social feedback condition results in higher quality viewed comments and response comments. After measuring the average quality of comments written by users before the study, we find that social feedback has a positive effect on response quality for both low and high quality commenters. We draw on a theoretical framework of social norms to explain this empirical result. In order to examine the influence mechanism further, we measure the similarity between comments viewed and written during the study, finding that similarity increases for the highest quality contributors under the social feedback condition. This suggests that, in addition to norms, some individuals may respond with increased relevance to high-quality comments.Comment: 10 pages, 6 figures, 2 table

Ethical and compliance-competence evaluation: a key element of sound corporate governance

Motivated by the ongoing post-Enron refocusing on corporate governance and the shift by the Financial Services Authority (FSA) in the UK to promoting compliance- competence within the financial services sector, this paper demonstrates how template analysis can be used as a tool for evaluating compliance-competence. Focusing on the ethical dimension of compliance-competence, we illustrate how this can be subjectively appraised. We propose that this evaluation technique could be utilised as a starting point in informing senior management of corporate governance issues and be used to monitor and demonstrate key compliance and ethical aspects of an institution to external stakeholders and regulators

A Cytotoxic, Co-operative Interaction Between Energy Deprivation and Glutamate Release From System x\u3csub\u3ec\u3c/sub\u3e\u3csup\u3e−\u3c/sup\u3e Mediates Aglycemic Neuronal Cell Death

The astrocyte cystine/glutamate antiporter (system xc−) contributes substantially to the excitotoxic neuronal cell death facilitated by glucose deprivation. The purpose of this study was to determine the mechanism by which this occurred. Using pure astrocyte cultures, as well as, mixed cortical cell cultures containing both neurons and astrocytes, we found that neither an enhancement in system xc− expression nor activity underlies the excitotoxic effects of aglycemia. In addition, using three separate bioassays, we demonstrate no change in the ability of glucose-deprived astrocytes—either cultured alone or with neurons—to remove glutamate from the extracellular space. Instead, we demonstrate that glucose-deprived cultures are 2 to 3 times more sensitive to the killing effects of glutamate or N-methyl-D-aspartate when compared with their glucose-containing controls. Hence, our results are consistent with the weak excitotoxic hypothesis such that a bioenergetic deficiency, which is measureable in our mixed but not astrocyte cultures, allows normally innocuous concentrations of glutamate to become excitotoxic. Adding to the burgeoning literature detailing the contribution of astrocytes to neuronal injury, we conclude that under our experimental paradigm, a cytotoxic, co-operative interaction between energy deprivation and glutamate release from astrocyte system xc− mediates aglycemic neuronal cell death

Climatic and Biogeochemical Effects of a Galactic Gamma-Ray Burst

It is likely that one or more gamma-ray bursts within our galaxy have strongly irradiated the Earth in the last Gy. This produces significant atmospheric ionization and dissociation, resulting in ozone depletion and DNA-damaging ultraviolet solar flux reaching the surface for up to a decade. Here we show the first detailed computation of two other significant effects. Visible opacity of NO2 is sufficient to reduce solar energy at the surface up to a few percent, with the greatest effect at the poles, which may be sufficient to initiate glaciation. Rainout of dilute nitric acid is could have been important for a burst nearer than our conservative nearest burst. These results support the hypothesis that the characteristics of the late Ordovician mass extinction are consistent with GRB initiation.Comment: 12 pages, 2 figures, in press at Geophysical Research Letters. Minor revisions, including details on falsifying the hypothesi

Stratospheric Ozone Variations Caused by Solar Proton Events between 1963 and 2005

Solar proton fluxes have been measured by satellites for over forty years (1963-2005). Several satellites, including the NASA Interplanetary Monitoring Platforms (1963-1993) and the NOAA Geostationary Operational Environmental Satellites (1994-2005), have been used to compile this long-term dataset. Some solar eruptions lead to solar proton events (SPEs) at the Earth, which typically last a few days. High energy solar protons associated with SPEs precipitate on the Earth's atmosphere and cause increases in odd hydrogen (HOx) and odd nitrogen (NOy) in the polar cap regions (greater than 60 degrees geomagnetic). The enhanced HOx leads to short-lived ozone depletion (~days) due to the short lifetime of HOx constituents. The enhanced NOy leads to long-lived ozone changes because of the long lifetime of the NOy family in the stratosphere and lower mesosphere. Very large SPEs occurred in 1972, 1989, 2000, 2001, and 2003 and were predicted to cause maximum total ozone depletions of 1-3%, which lasted for several months to years past the events. These long-term ozone changes caused by SPES are discussed

Alternative Models of Dynamics in Binary Time-Series-Cross-Section Models: The Example of State Failure

This paper investigates a variety of dynamic probit models for time-series-cross-section data in the context of explaining state failure. It shows that ordinary probit, which ignores dynamics, is misleading. Alternatives that seem to produce sensible results are the transition model and a model which includes a lagged latent dependent variable. It is argued that the use of a lagged latent variable is often superior to the use of a lagged realized dependent variable. It is also shown that the latter is a special case of the transition model. The relationship between the transition model and event history methods is also considered: the transition model estimates an event history model for both values of the dependent variable, yielding estimates that are identical to those produced by the two event history models. Furthermore, one can incorporate the insights gleaned from the event history models into the transition analysis, so that researchers do not have to assume duration independence. The conclusion notes that investigations of the various models have been limited to data sets which contain long sequences of zeros; models may perform differently in data sets with shorter bursts of zeros and ones

Diamond Etching Beyond 10 μm with Near-Zero Micromasking

To exploit the exceptional properties of diamond, new high quality fabrication techniques are needed to produce high performing devices. Etching and patterning diamond to depths beyond one micron has proven challenging due to the hardness and chemical resistance of diamond. A new cyclic Ar/O2 - Ar/Cl2 ICP RIE process has been developed to address micromasking issues from the aluminium mask by optimising the proportion of O2 in the plasma and introducing a preferential “cleaning” step. High quality smooth features up to, but not limited to, 10.6 μm were produced with an average etched surface roughness of 0.47 nm at a diamond etch rate of 45 nm/min and 16.9:1 selectivity

Experimental X-ray Stress Analysis Procedures for Ultra High Strength Materials

X-ray stress analysis procedures for accurate measurement of elastic strain in high strength steel