Variables in Globular Cluster NGC 5024

We present the results of a commissioning campaign to observe Galactic globular clusters for the search of microlensing events. The central 10' X 10' region of the globular cluster NGC 5024 was monitored using the 2-m Himalayan Chandra Telescope in R-band for a period of about 8 hours on 24 March 2010. Light curves were obtained for nearly 10,000 stars, using a modified Difference Image Analysis (DIA) technique. We identified all known variables within our field of view and revised periods and status of some previously reported short-period variables. We report about eighty new variable sources and present their equatorial coordinates, periods, light curves and possible types. Out of these, 16 are SX Phe stars, 10 are W UMa-type stars, 14 are probable RR Lyrae stars and 2 are detached eclipsing binaries. Nine of the newly discovered SX Phe stars and two eclipsing binaries belong to the Blue Straggler Star (BSS) population.Comment: 29 pages, 22 figures, replaced with rewritten data reduction par

Interaction of Hydrogen with Graphitic Surfaces, Clean and Doped with Metal Clusters

Producción CientíficaHydrogen is viewed as a possible alternative to the fossil fuels in transportation. The technology of fuel-cell engines is fully developed, and the outstanding remaining problem is the storage of hydrogen in the vehicle. Porous materials, in which hydrogen is adsorbed on the pore walls, and in particular nanoporous carbons, have been investigated as potential onboard containers. Furthermore, metallic nanoparticles embedded in porous carbons catalyze the dissociation of hydrogen in the anode of the fuel cells. For these reasons the interaction of hydrogen with the surfaces of carbon materials is a topic of high technological interest. Computational modeling and the density functional formalism (DFT) are helping in the task of discovering the basic mechanisms of the interaction of hydrogen with clean and doped carbon surfaces. Planar and curved graphene provide good models for the walls of porous carbons. We first review work on the interaction of molecular and atomic hydrogen with graphene and graphene nanoribbons, and next we address the effects due to the presence of metal clusters on the surface because of the evidence of their role in enhancing hydrogen storage.Ministerio de Economía, Industria y Competitividad (Grant MAT2014-54378-R

Perfusion-weighted software written in Python for DSC-MRI analysis

IntroductionDynamic susceptibility-weighted contrast-enhanced (DSC) perfusion studies in magnetic resonance imaging (MRI) provide valuable data for studying vascular cerebral pathophysiology in different rodent models of brain diseases (stroke, tumor grading, and neurodegenerative models). The extraction of these hemodynamic parameters via DSC-MRI is based on tracer kinetic modeling, which can be solved using deconvolution-based methods, among others. Most of the post-processing software used in preclinical studies is home-built and custom-designed. Its use being, in most cases, limited to the institution responsible for the development. In this study, we designed a tool that performs the hemodynamic quantification process quickly and in a reliable way for research purposes.MethodsThe DSC-MRI quantification tool, developed as a Python project, performs the basic mathematical steps to generate the parametric maps: cerebral blood flow (CBF), cerebral blood volume (CBV), mean transit time (MTT), signal recovery (SR), and percentage signal recovery (PSR). For the validation process, a data set composed of MRI rat brain scans was evaluated: i) healthy animals, ii) temporal blood–brain barrier (BBB) dysfunction, iii) cerebral chronic hypoperfusion (CCH), iv) ischemic stroke, and v) glioblastoma multiforme (GBM) models. The resulting perfusion parameters were then compared with data retrieved from the literature.ResultsA total of 30 animals were evaluated with our DSC-MRI quantification tool. In all the models, the hemodynamic parameters reported from the literature are reproduced and they are in the same range as our results. The Bland–Altman plot used to describe the agreement between our perfusion quantitative analyses and literature data regarding healthy rats, stroke, and GBM models, determined that the agreement for CBV and MTT is higher than for CBF.ConclusionAn open-source, Python-based DSC post-processing software package that performs key quantitative perfusion parameters has been developed. Regarding the different animal models used, the results obtained are consistent and in good agreement with the physiological patterns and values reported in the literature. Our development has been built in a modular framework to allow code customization or the addition of alternative algorithms not yet implemented

Ecología reproductiva y pesquerías en el contexto iberoamericano

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The Socio-Economic Value of Natural Riverbanks in the Netherlands

Ecologists and economists both use a different approach to determine the value of nature. Its ecological value can be measured using criteria like rarity and diversity of species in an ecosystem. The economic value can be determined using non-market valuation techniques. This paper focuses on an empirical application of the Contingent Valuation Method (CVM) to find out whether this valuation method is a suitable method to estimate the economic value of natural riverbanks in the Netherlands. Natural riverbanks will provide habitat for species that particularly depend on the land water transit area. Since common riverbanks do not provide this habitat, natural river banks increase biodiversity in the Netherlands. On the basis of technical and ecological characteristics nine different types of natural riverbanks were distinguished. For each type a laymen description was made. This description served as a basis for economic valuation by means of CVM. The results of the CVM study shows that the average willingness to pay for non-use of a natural riverbank varied between 16 and 25 Dutch guilders per household year. The willingness to pay for recreational use ranged from 1,07 to 2,50 guilders per visit. The generated outcomes proved to be consistent with results from other studies. At first sight, the economic value of natural riverbanks seemed to be higher than their construction and maintenance cost

Optimal Afforestation Contracts with Asymmetric Information on Private Environmental Benefits

We investigate the problem of subsidising afforestation when private information exists with respect to the level of private utility derived from the project. We develop a simple model that allows for an intelligent design of contracts when information is asymmetric. The model involves the Principal and two groups of agents (landowners): a green' group deriving high private utility from the projects and a conventional' group deriving lower utility. Afforestation projects may be produced in different environmental quality, and we distinguish between two cases, a high quality and a low quality project. We find that the optimal set of contracts under asymmetric information involves two different contracts. One in which green landowners are somewhat overcompensated for projects of high quality, and one where conventional landowners are offered contracts including lower quality projects, compared to the symmetric case, but with compensation equal to his indifference payment. It is the ability to reduce quality requirements along with subsidies offered that allows for revelation of the private information. Finally, we discus how the results obtained may be used in the implementation of incentive schemes

On Coalition Formation with Heterogeneous Agents

We propose a framework to analyze coalition formation with heterogeneous agents. Existing literature defines stability conditions that do not ensure that, once an agent decides to sign an agreement, the enlarged coalition is feasible. Defining the concepts of refraction and exchanging, we set up conditions of existence and enlargement of a coalition with heterogeneous agents. We use the concept of exchanging agents to give necessary conditions for internal stability and show that refraction is a sufficient condition for the failure of an enlargement of the coalition. With heterogeneous agents we can get a situation where a group of members of an unstable coalition does not deviate, neither within the coalition nor within the extended coalition. Hence, the possibilities of agreement are richer than in the standard analysis with homogeneous agents. Examples of industrial economics are used for illustration, and an application to climate change negotiations is discussed in more detail

Modelling Dynamic Conditional Correlations in WTI Oil Forward and Futures Returns

This paper estimates the dynamic conditional correlations in the returns on WTI oil one-month forward prices, and one-, three-, six-, and twelve-month futures prices, using recently developed multivariate conditional volatility models. The dynamic correlations enable a determination of whether the forward and various futures returns are substitutes or complements, which are crucial for deciding whether or not to hedge against unforeseen circumstances. The models are estimated using daily data on WTI oil forward and futures prices, and their associated returns, from 3 January 1985 to 16 January 2004. At the univariate level, the estimates are statistically significant, with the occasional asymmetric effect in which negative shocks have a greater impact on volatility than positive shocks. In all cases, both the short- and long-run persistence of shocks are statistically significant. Among the five returns, there are ten conditional correlations, with the highest estimate of constant conditional correlation being 0.975 between the volatilities of the three-month and six-month futures returns, and the lowest being 0.656 between the volatilities of the forward and twelve-month futures returns. The dynamic conditional correlations can vary dramatically, being negative in four of ten cases and being close to zero in another five cases. Only in the case of the dynamic volatilities of the three-month and six-month futures returns is the range of variation relatively narrow, namely (0.832, 0.996). Thus, in general, the dynamic volatilities in the returns in the WTI oil forward and future prices can be either independent or interdependent over time

Investments in Gas Pipelines and Liquefied Natural Gas Infrastructure. What is the Impact on the Security of Supply?

This paper addresses the question of the infrastructure investment required for gas pipeline and liquefied natural gas (LNG) connections to meet growing gas demand in an enlarged EU over the next 20 years. Several issues are presented, bearing in mind the major objective of the security of supply for EU countries. First, to set the scene, recent projections of gas demand in an enlarged EU are presented along with the corresponding need for additional imports. Then a scenario is developed showing possible supply routes to meet the import gap, relying on increasingly remote routes. An impressive bill of $150 to 200 billion will have to be paid for extending and building the required infrastructure in pipeline links and LNG-receiving facilities. The expected major development of LNG markets is subject to a particular discussion, as far as the progressive globalisation of this market and its inherent flexibility provide major advantages in terms of the security of supply, despite more costly infrastructure than pipeline links. The impact of technological progress is expected to reduce both capital investment and unit transport costs, offering access to new supply opportunities. Finally, the question of major obstacles to the realisation of the required huge investments in gas infrastructure over the next 20 years is addressed, opening hot debate on the subjects of future gas price, market liberalisation and financing issues