Ultra High Energy Cosmic Rays

Cosmic rays with energies above $10^{18}$ eV are currently of considerable interest in astrophysics and are to be further studied in a number of projects which are either currently under construction or the subject of well-developed proposals. This paper aims to discuss some of the physics of such particles in terms of current knowledge and information from particle astrophysics at other energies.Comment: 44 pages, 17 figures. Invited review, PASA, in pres

Observation of gamma-rays from LMC X-4 above 10(16) eV

Data from the University of Adelaide air shower array at Buckland Park taken over a three year period have been analyzed to search for evidence of ultra high energy gamma-ray emission from neutron star binary X-ray sources having known orbital periods. The detection of UHE gamma-rays from LMC X-4 above 10 to the 16th power eV, is reported; the first extragalactic object to be positively detected at these energies

When is an error not a prediction error? An electrophysiological investigation

A recent theory holds that the anterior cingulate cortex (ACC) uses reinforcement learning signals conveyed by the midbrain dopamine system to facilitate flexible action selection. According to this position, the impact of reward prediction error signals on ACC modulates the amplitude of a component of the event-related brain potential called the error-related negativity (ERN). The theory predicts that ERN amplitude is monotonically related to the expectedness of the event: It is larger for unexpected outcomes than for expected outcomes. However, a recent failure to confirm this prediction has called the theory into question. In the present article, we investigated this discrepancy in three trial-and-error learning experiments. All three experiments provided support for the theory, but the effect sizes were largest when an optimal response strategy could actually be learned. This observation suggests that ACC utilizes dopamine reward prediction error signals for adaptive decision making when the optimal behavior is, in fact, learnable

The longitudinal thickness of air-shower fronts

Linsely (1983) has proposed a technique for the detection and analysis of air showers at large distances from the shower axis based on a measurement of the shower front thickness and the assumption that this thickness is closely related to the core distance. Some of the problems involved with realizing such a technique were investigated, and some related observations are reported. The practical problems of how consistent the measurements of the shower front would be, how one would use the measurement, and how the rate of triggered events would depend on the minimum pulse width required are studied

Phase diagram of the one dimensional Hubbard-Holstein Model at 1/2 and 1/4 filling

The Hubbard-Holstein model is one of the simplest to incorporate both electron-electron and electron-phonon interactions. In one dimension at half filling the Holstein electron-phonon coupling promotes onsite pairs of electrons and a Peierls charge density wave while the Hubbard onsite Coulomb repulsion U promotes antiferromagnetic correlations and a Mott insulating state. Recent numerical studies have found a possible third intermediate phase between Peierls and Mott states. From direct calculations of charge and spin susceptibilities, we show that (i) As the electron-phonon coupling is increased, first a spin gap opens, followed by the Peierls transition. Between these two transitions the metallic intermediate phase has a spin gap, no charge gap, and properties similar to the negative-U Hubbard model. (ii) The transitions between Mott/intermediate and intermediate/Peierls states are of the Kosterlitz-Thouless form. (iii) For larger U the two transitions merge at a tritical point into a single first order Mott/Peierls transition. In addition we show that an intermediate phase also occurs in the quarter-filled model.Comment: 10 pages, 10 eps figure

Some considerations on coastal processes relevant to sea level rise

The effects of potential sea level rise on the shoreline and shore environment have been briefly examined by considering the interactions between sea level rise and relevant coastal processes. These interactions have been reviewed beginning with a discussion of the need to reanalyze previous estimates of eustatic sea level rise and compaction effects in water level measurement. This is followed by considerations on sea level effects on coastal and estuarine tidal ranges, storm surge and water level response, and interaction with natural and constructed shoreline features. The desirability to reevaluate the well known Bruun Rule for estimating shoreline recession has been noted. The mechanics of ground and surface water intrusion with reference to sea level rise are then reviewed. This is followed by sedimentary processes in the estuaries including wetland response. Finally comments are included on some probable effects of sea level rise on coastal ecosystems. These interactions are complex and lead to shoreline evolution (under a sea level rise) which is highly site-specific. Models which determine shoreline change on the basis of inundation of terrestrial topography without considering relevant coastal processes are likely to lead to erroneous shoreline scenarios, particularly where the shoreline is composed of erodible sedimentary material. With some exceptions, present day knowledge of shoreline response to hydrodynamic forcing is inadequate for long-term quantitative predictions. A series of interrelated basic and applied research issues must be addressed in the coming decades to determine shoreline response to sea level change with an acceptable degree of confidence. (PDF contains 189 pages.

Muon Capture on Deuteron and 3He: A Personal Review

The present status of theoretical and experimental studies of muon capture reactions on light nuclei is reviewed. In particular, the recent results for the two reactions 2H(\mu^-,\nu_\mu)nn and 3He(\mu^-,\nu_\mu)3H are presented, and the unresolved discrepancies among different measurements and calculations, open problems, and future developments are discussed.Comment: 19 pages, submitted to International Journal of Modern Physics

Water Scarcity and Water Markets: A Comparison of Institutions and Practices in the Murray-Darling Basin of Australia and the Western US

Water markets in Australia’s Murray-Darling Basin (MDB) and the US west are compared in terms of their ability to allocate scarce water resources among competing uses. Both locations have been in the forefront of the development of water markets with defined water rights and conveyance structures to assist in the reallocation of water across competing demands. They also share the challenge of managing water with climate variability and climate change. As these two markets occur in developed, wealthy countries, their experiences in water markets with different water rights (appropriative, riparian and statutory rights) provide ‘best-case’ scenarios of what institutional arrangements work best, indicate which are less effective, and demonstrate what might be possible for greater use of water markets elsewhere in the world. The paper finds that the gains from trade in the MDB is worth hundreds of millions of dollars in per year, total turnover in water rights exceeds $2 billion per year and the volume of trade accounts for over 20$4.3 billion (2008 $) spent or committed by urban buyers between 1987 and 2008. Despite the clear benefits of water markets in both locations, there are on-going restrictions to trade that limit the potential gains and also third-party effects from use that require resolution.

A Comparative Assessment of Water Markets: Insights from the Murray-Darling Basin of Australia and the Western US

Water markets in Australia’s Murray-Darling Basin (MDB) and the US west are compared in terms of their ability to allocate scarce water resources. The study finds that the gains from trade in the MDB are worth hundreds of millions of dollars per year. Total market turnover in water rights exceeds $2 billion per year while the volume of trade exceeds over 20$4.3 billion (2008 $) spent or committed by urban buyers between 1987 and 2008. The two-market comparison suggests that policy attention should be directed towards ways to promote water trade while simultaneously mitigating the legitimate thirdparty concerns about how and where water is used, especially conflicts between consumptive and in situ uses of water. The study finds that institutional innovation is feasible in both countries and that further understanding about the size, duration, and distribution of third-party effects from water trade, and how these effects might be regulated, can improve water markets to better manage water scarcity.water markets, US west, Murray-Darling Basin, gains from trade