Simulation Study of TenTen: A new Multi-TeV IACT array

TenTen is a proposed array of Imaging Atmospheric Cherenkov Telescopes (IACT) optimized for the gamma ray energy regime of 10 TeV to 100 TeV, but with a threshold of ~1 to a few TeV. It will offer a collecting area of 10 km2 above energies of 10 TeV. In the initial phase, a cell of 3 to 5 modest-sized telescopes, each with 10-30 m2 mirror area, is suggested for an Australian site. A possible expansion of the array could comprise many such cells. Here we present work on configuration and technical issues from our simulation studies of the array. Working topics include array layout, telescope size and optics, camera field of view, telescope trigger system, electronics, and site surveys.Comment: 4 pages, 7 figures, submitted to Proceedings of the ICRC 2007, pdf forma

TenTen: A New Array of Multi-TeV Imaging Cherenkov Telescopes

The exciting results from H.E.S.S. point to a new population of gamma-ray sources at energies E > 10 TeV, paving the way for future studies and new discoveries in the multi-TeV energy range. Connected with these energies is the search for sources of PeV cosmic-rays (CRs) and the study of multi-TeV gamma-ray production in a growing number of astrophysical environments. TenTen is a proposed stereoscopic array (with a suggested site in Australia) of modest-sized (10 to 30m^2) Cherenkov imaging telescopes with a wide field of view (8 to 10deg diameter) optimised for the E~10 to 100 TeV range. TenTen will achieve an effective area of ~10 km^2 at energies above 10 TeV. We outline here the motivation for TenTen and summarise key performance parameters.Comment: 4 pages, 2 figures, proceedings of the 30th ICRC, Merida, Mexico, 200

Timing analysis techniques at large core distances for multi-TeV gamma ray astronomy

We present an analysis technique that uses the timing information of Cherenkov images from extensive air showers (EAS). Our emphasis is on distant, or large core distance gamma-ray induced showers at multi-TeV energies. Specifically, combining pixel timing information with an improved direction reconstruction algorithm, leads to improvements in angular and core resolution as large as ~40% and ~30%, respectively, when compared with the same algorithm without the use of timing. Above 10 TeV, this results in an angular resolution approaching 0.05 degrees, together with a core resolution better than ~15 m. The off-axis post-cut gamma-ray acceptance is energy dependent and its full width at half maximum ranges from 4 degrees to 8 degrees. For shower directions that are up to ~6 degrees off-axis, the angular resolution achieved by using timing information is comparable, around 100 TeV, to the on-axis angular resolution. The telescope specifications and layout we describe here are geared towards energies above 10 TeV. However, the methods can in principle be applied to other energies, given suitable telescope parameters. The 5-telescope cell investigated in this study could initially pave the way for a larger array of sparsely spaced telescopes in an effort to push the collection area to >10 km2. These results highlight the potential of a `sparse array' approach in effectively opening up the energy range above 10 TeV.Comment: Published in Astroparticle Physic

Advanced engine study program

A design and analysis study was conducted to provide advanced engine descriptions and parametric data for space transfer vehicles. The study was based on an advanced oxygen/hydrogen engine in the 7,500 to 50,000 lbf thrust range. Emphasis was placed on defining requirements for high-performance engines capable of achieving reliable and versatile operation in a space environment. Four variations on the expander cycle were compared, and the advantages and disadvantages of each were assessed. Parametric weight, envelope, and performance data were generated over a range of 7,500 to 50,000 lb thrust and a wide range of chamber pressure and nozzle expansion ratio

Sinking particle fluxes from the euphotic zone over the continental slope of an eastern boundary current region

We analyze data from sediment traps and current meters moored at two locations 100 km apart over the Vancouver Island continental slope during the spring and summer of 1990. Time-series of sinking particle fluxes, major biogenic components (biogenic silica, calcium carbonate, and particulate organic carbon and nitrogen), and stable isotopic composition (δ13Corganic and δ15Ntotal) were determined on samples obtained with sequential sediment traps moored at 200–250 m depth. Associated water property data were obtained from CTD/Rosette profiles taken during trap service periods and from current meters positioned in the surface layer and near the sediment trap. These data indicate that the two locations (a southern site J and a northern site NJ) were hydrographically distinct during the investigation. At site J, we found evidence for frequent upwelling events and more variability in the upper layer water properties. The main difference in the sinking fluxes of particles between the two sites was the occurrence of a one-week event at the end of May at J that contributed about one third of the total particle flux during the sampling period. Otherwise, the total flux collected during the study and the flux of major biogenic particles were similar at both sites. Silica shells dominated the flux of particles, particularly during the spring and early summer period. At both sites, particulate organic carbon rather than calcium carbonate was the main contributor to particulate carbon fluxes. The δ13Corganic showed marked variations during the sampling period at both sites likely due to variations in the growth rate of phytoplankton and in species composition. In comparison, variations in nitrate availability appear to dominate the changes in δ15Ntotal

Influence of turbulent advection on a phytoplankton ecosystem with nonuniform carrying capacity

In this work we study a plankton ecosystem model in a turbulent flow. The plankton model we consider contains logistic growth with a spatially varying background carrying capacity and the flow dynamics are generated using the two-dimensional (2D) Navier-Stokes equations. We characterize the system in terms of a dimensionless parameter, γ TB / TF, which is the ratio of the ecosystem biological time scales TB and the flow time scales TF. We integrate this system numerically for different values of γ until the mean plankton reaches a statistically stationary state and examine how the steady-state mean and variance of plankton depends on γ. Overall we find that advection in the presence of a nonuniform background carrying capacity can lead to very different plankton distributions depending on the time scale ratio γ. For small γ the plankton distribution is very similar to the background carrying capacity field and has a mean concentration close to the mean carrying capacity. As γ increases the plankton concentration is more influenced by the advection processes. In the largest γ cases there is a homogenization of the plankton concentration and the mean plankton concentration approaches the harmonic mean, 1/K -1. We derive asymptotic approximations for the cases of small and large γ. We also look at the dependence of the power spectra exponent, β, on γ where the power spectrum of plankton is k-β. We find that the power spectra exponent closely obeys β=1+2/γ as predicted by earlier studies using simple models of chaotic advection

The social security rights of older international migrants in the European Union

Europe is now home to a significant and diverse population of older international migrants. Social and demographic changes have forced the issue of social security in old age onto the European social policy agenda in the last decade. In spite of an increased interest in the financial well-being of older people, many retired international migrants who are legally resident in the European Union face structured disadvantages. Four linked factors are of particular importance in shaping the pension rights and levels of financial provision available to individual older migrants: migration history, socio-legal status, past relationship to the paid labour market, and location within a particular EU Member State. Building on a typology of older migrants, the paper outlines the ways in which policy at both the European Union and Member State levels serves to diminish rather than enhance the social security rights of certain older international migrants

An experimental design approach to the chemical characterisation of pectin polysaccharides extracted from Cucumis melo Inodorus

Extracted pectins have been utilised in a number of applications in both the food and pharmaceutical industries where they are generally used as gelling agents, thickeners and stabilisers, although a number of pectins have been shown to be bioactive. These functional properties will depend upon extraction conditions. A statistical experimental design approach was used to study the effects of extraction conditions pH, time and temperature on pectins extracted from Cucumis melo Inodorus. The results show that the chemical composition is very sensitive to these conditions and that this has a great influence on for example the degree of branching. Higher temperatures, lower pHs and longer extraction times lead to a loss of the more acid labile arabinofuranose residues present on the pectin side chain. The fitting of regression equations relating yield and composition to extraction conditions can therefore lead to tailor-made pectins for specific properties and/ or applications