A Model of Habitability Within the Milky Way Galaxy

We present a model of the Galactic Habitable Zone (GHZ), described in terms of the spatial and temporal dimensions of the Galaxy that may favour the development of complex life. The Milky Way galaxy is modelled using a computational approach by populating stars and their planetary systems on an individual basis using Monte-Carlo methods. We begin with well-established properties of the disk of the Milky Way, such as the stellar number density distribution, the initial mass function, the star formation history, and the metallicity gradient as a function of radial position and time. We vary some of these properties, creating four models to test the sensitivity of our assumptions. To assess habitability on the Galactic scale, we model supernova rates, planet formation, and the time required for complex life to evolve. Our study improves on other literature on the GHZ by populating stars on an individual basis and by modelling SNII and SNIa sterilizations by selecting their progenitors from within this preexisting stellar population. Furthermore, we consider habitability on tidally locked and non-tidally locked planets separately, and study habitability as a function of height above and below the Galactic midplane. In the model that most accurately reproduces the properties of the Galaxy, the results indicate that an individual SNIa is ~5.6 \times more lethal than an individual SNII on average. In addition, we predict that ~1.2% of all stars host a planet that may have been capable of supporting complex life at some point in the history of the Galaxy. Of those stars with a habitable planet, ~75% of planets are predicted to be in a tidally locked configuration with their host star. The majority of these planets that may support complex life are found towards the inner Galaxy, distributed within, and significantly above and below, the Galactic midplane.Comment: Accepted for publication in Astrobiology. 40 pages, 12 figures, 3 table

A systematic search for anomaly-free supergravities in six dimensions

We conduct a systematic search for anomaly-free six-dimensional N=1 chiral supergravity theories. Under a certain set of restrictions on the allowed gauge groups and the representations of the hypermultiplets, we enumerate all possible Poincare and gauged supergravities with one tensor multiplet satisfying the 6D anomaly cancellation criteria.Comment: 39 pages, JHEP3 class, references added, minor typos correcte

Mars climate engineering using orbiting solar reflectors

The manned mission is seen as a first step towards a Mars surface exploration base-station and, later, establishing permanent settlement. The location and use of Mars's natural resources is vital to enable cost-effective long-duration human exploration and exploitation missions as well as subsequent human colonization. Planet resources include various crust-lodged materials, a low-pressure natural atmosphere, assorted forms of utilizable energy, lower gravity than Earth's, and ground placement advantages relative to human operability and living standards. Power resources may include using solar and wind energy, importation of nuclear reactors and the harvesting of geothermal potential. In fact, a new branch of human civilization could be established permanently on Mars in the next century. But, meantime, an inventory and proper social assessment of Mars's prospective energy and material resources is required. This book investigates the possibilities and limitations of various systems supplying manned bases on Mars with energy and other vital resources. The book collects together recent proposals and innovative options and solutions. It is a useful source of condensed information for specialists involved in current and impending Mars-related activities and a good starting point for young researchers

A-D-E Quivers and Baryonic Operators

We study baryonic operators of the gauge theory on multiple D3-branes at the tip of the conifold orbifolded by a discrete subgroup Gamma of SU(2). The string theory analysis predicts that the number and the order of the fixed points of Gamma acting on S^2 are directly reflected in the spectrum of baryonic operators on the corresponding quiver gauge theory constructed from two Dynkin diagrams of the corresponding type. We confirm the prediction by developing techniques to enumerate baryonic operators of the quiver gauge theory which includes the gauge groups with different ranks. We also find that the Seiberg dualities act on the baryonic operators in a non-Abelian fashion.Comment: 46 pages, 17 figures; v2: minor corrections, note added in section 1, references adde

Split-domain calibration of an ecosystem model using satellite ocean colour data

The application of satellite ocean colour data to the calibration of plankton ecosystem models for large geographic domains, over which their ideal parameters cannot be assumed to be invariant, is investigated. A method is presented for seeking the number and geographic scope of parameter sets which allows the best fit to validation data to be achieved. These are independent data not used in the parameter estimation process. The goodness-of-fit of the optimally calibrated model to the validation data is an objective measure of merit for the model, together with its external forcing data. Importantly, this is a statistic which can be used for comparative evaluation of different models. The method makes use of observations from multiple locations, referred to as stations, distributed across the geographic domain. It relies on a technique for finding groups of stations which can be aggregated for parameter estimation purposes with minimal increase in the resulting misfit between model and observations.The results of testing this split-domain calibration method for a simple zero dimensional model, using observations from 30 stations in the North Atlantic, are presented. The stations are divided into separate calibration and validation sets. One year of ocean colour data from each station were used in conjunction with a climatological estimate of the station’s annual nitrate maximum. The results demonstrate the practical utility of the method and imply that an optimal fit of the model to the validation data would be given by two parameter sets. The corresponding division of the North Atlantic domain into two provinces allows a misfit-based cost to be achieved which is 25% lower than that for the single parameter set obtained using all of the calibration stations. In general, parameters are poorly constrained, contributing to a high degree of uncertainty in model output for unobserved variables. This suggests that limited progress towards a definitive model calibration can be made without including other types of observations

Self-gravitating branes of codimension 4 in Lovelock gravity

We construct a familly of exact solutions of Lovelock equations describing codimension four branes with discrete symmetry in the transverse space. Unlike what is known from pure Einstein gravity, where such brane solutions of higher codimension are singular, the solutions we find, for the complete Lovelock theory, only present removable singularities. The latter account for a localised tension-like energy-momentum tensor on the brane, in analogy with the case of a codimension two self-gravitating cosmic string in pure Einstein gravity. However, the solutions we discuss present two main distinctive features : the tension of the brane receives corrections from the induced curvature of the brane's worldsheet and, in a given Lovelock theory, the spectrum of possible values of the tension is discrete. These solutions provide a new framework for the study of higher codimension braneworlds.Comment: 22 page

Perchlorate on Mars - Overview and Implications

Perchlorate was first detected on Mars by the Wet Chemistry Laboratory (WCL) instrument on the Phoenix lander at a concentration of ~0.5 wt% in northern plains soils. Since that initial detection, perchlorate (and likely chlorate) have been detected on Mars by both surface and orbital instruments. Perchlorate (ClO4-) is an oxidized chlorine compound and salts of perchlorate are kinetically stable (though very reactive at high temperature), very soluble, deliquescent, and have low eutectic temperature (which decreases the temperature for stable liquids on Mars). Chlorate (ClO3-) salts are similar, though they are less kinetically stable than perchlorates. Because many of the analytical signatures of perchlorate and chlorate are similar to the instruments we have used on Mars, we cannot always determine which species is present, so we will use the more generic term oxychlorine when referring to perchlorate and/or chlorate

Mucolipidosis II presenting as severe neonatal hyperparathyroidism.

UNLABELLED: Mucolipidosis II (ML II or I-cell disease ) (OMIM 252500) is an autosomal recessive lysosomal enzyme targeting disorder that usually presents between 6 and 12 months of age with a clinical phenotype resembling Hurler syndrome and a radiological picture of dysostosis multiplex. When ML II is severe enough to be detected in the newborn period, the radiological changes have been described as similar to hyperparathyroidism or rickets. The biological basis of these findings has not been explored and few biochemical measurements have been recorded. We describe three unrelated infants with ML II who had radiological features of intrauterine hyperparathyroidism and biochemical findings consistent with severe secondary neonatal hyperparathyroidism (marked elevation of serum parathyroid hormone and alkaline phosphatase levels). The vitamin D metabolites were not substantially different from normal and repeatedly normal calcium concentrations excluded vitamin D deficiency rickets and neonatal severe hyperparathyroidism secondary to calcium-sensing receptor gene mutations (OMIM 239200). The pathogenesis of severe hyperparathyroidism in the fetus and newborn with ML II is unexplained. We hypothesize that the enzyme targeting defect of ML II interferes with transplacental calcium transport leading to a calcium starved fetus and activation of the parathyroid response to maintain extracellular calcium concentrations within the normal range. CONCLUSION: Newborns with mucolipidosis II can present with radiological and biochemical signs of hyperparathyroidism. Awareness of this phenomenon may help in avoiding diagnostic pitfalls and establishing a proper diagnosis and therapy

Counting BPS Operators in Gauge Theories: Quivers, Syzygies and Plethystics

We develop a systematic and efficient method of counting single-trace and multi-trace BPS operators with two supercharges, for world-volume gauge theories of $N$ D-brane probes for both $N \to \infty$ and finite $N$. The techniques are applicable to generic singularities, orbifold, toric, non-toric, complete intersections, et cetera, even to geometries whose precise field theory duals are not yet known. The so-called ``Plethystic Exponential'' provides a simple bridge between (1) the defining equation of the Calabi-Yau, (2) the generating function of single-trace BPS operators and (3) the generating function of multi-trace operators. Mathematically, fascinating and intricate inter-relations between gauge theory, algebraic geometry, combinatorics and number theory exhibit themselves in the form of plethystics and syzygies.Comment: 59+1 pages, 7 Figure

Supersymmetric Gauge Theories, Intersecting Branes and Free Fermions

We show that various holomorphic quantities in supersymmetric gauge theories can be conveniently computed by configurations of D4-branes and D6-branes. These D-branes intersect along a Riemann surface that is described by a holomorphic curve in a complex surface. The resulting I-brane carries two-dimensional chiral fermions on its world-volume. This system can be mapped directly to the topological string on a large class of non-compact Calabi-Yau manifolds. Inclusion of the string coupling constant corresponds to turning on a constant B-field on the complex surface, which makes this space non-commutative. Including all string loop corrections the free fermion theory is elegantly formulated in terms of holonomic D-modules that replace the classical holomorphic curve in the quantum case.Comment: 67 pages, 6 figure