4,192 research outputs found


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    After a historical sketch of the evolution of land tenure systems in the Eritrean highlands, this paper describes the main features of the new Eritrean land law and its operative assumption that the legislation is meant to extend state control over land. The legal devices employed by the law are widely used in sub-Saharan Africa (and were largely inspired by colonial policies). The State of Eritrea frequently asserts that its recent independence gives it the opportunity to learn from other developing countries' mistakes and to avoid them. The basic patterns of the new land law, however, are common to the rest of Africa, notwithstanding the evident poor results. The central government wants its control to be widespread and pervasive. The fight against traditional social groups controlling land, at least in the highlands, is severe. Apart from a formal repeal of customary law, the state's acquisition of the power to modify village boundaries according to a scheme already completed at higher administrative levels and to introduce equal rights on land for women entails a disruption of the villages' social identity. Mandatory state control over landed property in Eritrea is, as usual, motivated by the necessity to address higher social needs. The ultimate intent, of course, is that the evolution from communal property to state property will eventually result in the widespread introduction of individual property once a sufficient level of economic development is achieved. This unfavorable attitude toward communal property is not supported by the evidence, which shows that, in fact, efficient land management can be obtained through renovation of traditional institutions.Land tenure -- Eritrea, Land tenure -- Government policy -- Eritrea, Land tenure -- Law and legislation -- Eritrea, Customary law -- Eritrea, Tenure types, Traditional -- Eritrea, Land reform -- Eritrea, Land Economics/Use,

    Which radius for the Sun?

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    The high accuracy reached by solar limb observations, by helioseismic measurements and by Standard Solar Models (SSMs) calculations suggests that general relativity corrections are included when discussing the solar radius. The Allen value (R⊙_{\odot} = 695.99 ±\pm 0.07 Mm) has to be reduced by 1.5 Km. This correction, which is small as compared with present accuracy, should be kept in mind for future more precise measurements and/or calculations.Comment: Latex, 3 page

    On the application of Mattis-Bardeen theory in strongly disordered superconductors

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    The low energy optical conductivity of conventional superconductors is usually well described by Mattis-Bardeen (MB) theory which predicts the onset of absorption above an energy corresponding to twice the superconducing (SC) gap parameter Delta. Recent experiments on strongly disordered superconductors have challenged the application of the MB formulas due to the occurrence of additional spectral weight at low energies below 2Delta. Here we identify three crucial items which have to be included in the analysis of optical-conductivity data for these systems: (a) the correct identification of the optical threshold in the Mattis-Bardeen theory, and its relation with the gap value extracted from the measured density of states, (b) the gauge-invariant evaluation of the current-current response function, needed to account for the optical absorption by SC collective modes, and (c) the inclusion into the MB formula of the energy dependence of the density of states present already above Tc. By computing the optical conductvity in the disordered attractive Hubbard model we analyze the relevance of all these items, and we provide a compelling scheme for the analysis and interpretation of the optical data in real materials.Comment: 11 pages, 6 figure

    Stellar Evolutionary Models for Magellanic Clouds

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    We supplement current evolutionary computations concerning Magellanic Cloud stars by exploring the evolutionary behavior of canonical stellar models (i.e.,with inefficient core overshooting) with metallicities suitable for stars in the Clouds. After discussing the adequacy of the adopted evolutionary scenario, we present evolutionary sequences as computed following a selected sample of stellar models in the mass range 0.8-8 Mo from the Main Sequence till the C ignition or the onset of thermal pulses in the advanced Asymptotic Giant Branch phase. On this basis, cluster isochrones covering the range of ages from 100 Myr to 15 Gyr are presented and discussed. To allow a comparison with evolutionary investigations appeared in the recent literature, we computed additional sets of models which take into account moderate core overshooting during the H burning phase, discussing the comparison in terms of current uncertainties in the stellar evolutionary models. Selected predictions constraining the cluster ages are finally discussed, presenting a calibration of the difference in magnitude between the luminous MS termination and the He burning giants in terms of cluster age. Both evolutionary tracks and isochrones have been made available at the node http://gipsy.cjb.net as a first step of a planned ``Pisa Evolutionary Library''.Comment: 11 pages, 9 eps figures, A&A accepted, evolutionary tracks and isochrones available at http://gipsy.cjb.net at the link ``Pisa Evolutionary Library'

    Surviving on Mars: test with LISA simulator

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    We present the biological results of some experiments performed in the Padua simulators of planetary environments, named LISA, used to study the limit of bacterial life on the planet Mars. The survival of Bacillus strains for some hours in Martian environment is shortly discussed.Comment: To be published on Highlights of Astronomy, Volume 15 XXVIIth IAU General Assembly, August 2009 Ian F Corbett, ed. 2 pages, 1 figur

    Predicted HST FOC and broad band colours for young and intermediate Simple Stellar Populations

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    This paper presents theoretical HST and broad band colours from population synthesis models based on an homogeneous set of stellar evolutionary tracks as computed under canonical (no overshooting) assumptions, covering the range of cluster ages from t=8 Myr to t=5 Gyr for three different metallicities (Z=0.02, 0.006, and 0.001). Statistical fluctuations in the cluster population have been investigated, assessing the predicted fluctuations of the various colours as a function of the cluster integrated absolute magnitude. We show that the red leak in HST UV filters deeply affects the predicted fluxes and colours. However, we find that for F152M-F307M < 0.5 and for F170M-F278M < 0.5 (which means ages lower than 1 Gyr) the HST UV colours can still be used to infer reliable indications on the age of distant clusters. Moreover, one finds that the age calibration of these colours is scarcely affected by the amount of original helium or by the assumed IMF. On this basis, we present a calibration of the HST UV two-colours (F152M-F307M vs F170M-F278M) in terms of cluster ages for the three above quoted metallicities. We suggest the combined use of HST UV colours and IR colours (V-K in particular) to disentangle the metallicity-age effect in integrated colours of young stellar populations (t< 1 Gyr).Comment: Latex 18 pages, 16 encapsulated figures, 6 tables, A&ASS accepte

    On the observational properties of He-burning stars: some clues on the tilt of the HB in metal rich clusters

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    We investigate the predicted Color-Magnitude distribution of metal-rich Horizontal Branch (HB) stars, discussing selected theoretical models computed under various assumptions about the star metallicity and the efficiency of super-adiabatic convection. We find that canonical Zero Age Horizontal Branches with metallicity larger or of the order of Z=0.002 should be all affected by a tilt, by an amount which increases when the metallicity is increased and/or the mixing length is decreased, reaching a tilt of ΔV∌\Delta V \sim0.2 mag in the case of solar metallicity when a mixing length value α\alpha=1.6 is assumed (ΔV\Delta V is the magnitude difference between the top of the blue HB and the fainter magnitude reached by the red HB). Uncertainties in the luminosity of the red HB due to uncertainty in the mixing length value are discussed. We finally discuss the much larger tilt observed in the clusters NGC 6441 and NGC 6388, reporting additional evidence against suggested non-canonical evolutionary scenarios. Numerical experiments show that differential reddening could produce such sloped HBs. Further, HST-PC imaging of NGC 6441 gives clear indications about the occurrence of differential reddening across the cluster. However, the same imaging shows that the observed slope of the red HB {\em is not} an artifact of differential reddening. We finally show that sloping red HBs in metal rich clusters are a common occurrence not necessarily correlated with the appearance of extended blue HB.Comment: 14 pages, 9 figures, Accepted by Ap

    Synthetic Stellar Clusters for Pop III

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    We present preliminary results of an incoming theoretical work concerning the integrated properties of the Population III clusters of stars. On the basis of synthetic Color-Magnitude Diagrams, we provide a grid of optical and near-IR colors of Simple Stellar Populations with very low metallicity (Z=10−10^{-10} and Z=10−6^{-6}) and age which spans from 10 Myr to 15 Gyr. A comparison with higher metallicities up to 0.006 is also shown, disclosing sizable differences in the CMD morphology, integrated colors and Spectral Energy Distribution (SED).Comment: 2 pages, incl. 2 figures, "The First Stars", Proceedings of the second MPA/ESO workshop, Eds.: Weiss, Abel, Hill, Springer, Heidelberg, 200