Reply to Comment on "A dynamic rating curve approach to indirect discharge measurement by Dottori et al. (2009)" by Koussis (2009)

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A Search for Old Star Clusters in the Large Magellanic Cloud

We report the first results of a color-magnitude diagram survey of 25 candidate old LMC clusters. For almost all of the sample, it was possible to reach the turnoff region, and in many clusters we have several magnitudes of the main sequence. Age estimates based on the magnitude difference $\delta T_1$ between the giant branch clump and the turnoff revealed that no new old clusters were found. The candidates turned out to be of intermediate age (1-3 Gyr) We show that the apparently old ages as inferred from integrated UBV colors can be explained by a combination of stochastic effects produced by bright stars and by photometric errors for faint clusters lying in crowded fields. The relatively metal poor candidates from the CaII triplet spectroscopy also turned out to be of intermediate age. This, combined with the fact that they lie far out in the disk, yields interesting constraints regarding the formation and evolution of the LMC disk. We also study the age distribution of intermediate age and old clusters This homogeneous set of accurate relative ages allows us to make an improved study of the history of cluster formation/destruction for ages $>1$Gyr. We confirm previous indications that there was apparently no cluster formation in the LMC during the period from 3-8 Gyr ago, and that there was a pronounced epoch of cluster formation beginning 3 Gyrs ago that peaked at about 1.5 Gyrs ago. Our results suggest that there are few, if any, genuine old clusters in the LMC left to be found.Comment: LaTeX, to be published in Nov. 1997 Astronomical Journa

A dynamic rating curve approach to indirect discharge measurement

Abstract. The operational measurement of discharge in medium and large rivers is mostly based on indirect approaches by converting water stages into discharge on the basis of steady-flow rating curves. Unfortunately, under unsteady flow conditions, this approach does not guarantee accurate estimation of the discharge due, on the one hand, to the underlying steady state assumptions and, on the other hand, to the required extrapolation of the rating curve beyond the range of actual measurements used for its derivation. Historically, several formulae were proposed to correct the steady-state discharge value and to approximate the unsteady-flow stage-discharge relationship. In the majority of these methods, the correction is made on the basis of water level measurements taken at a single cross section where a steady state rating curve is available, while other methods explicitly account for the water surface slope using stage measurements in two reference sections. However, most of the formulae available in literature are either over-simplified or based on approximations that prevent their generalisation. Moreover they have been rarely tested on cases where their use becomes essential, namely under unsteady-flow conditions characterised by wide loop rating curves. In the present work, an original approach, based on simultaneous stage measurements at two adjacent cross sections, is introduced and compared to the approaches described in the literature. The most relevant feature is that the proposed procedure allows for the application of the full dynamic flow equations without restrictive hypotheses. The comparison has been carried out on channels with constant or spatially variable geometry under a wide range of flood wave and river bed slope conditions. The results clearly show the improvement in the discharge estimation and the reduction of estimation errors obtainable using the proposed approach

A New Giant Branch Clump Structure In the Large Magellanic Cloud

We present Washington C, T1 CCD photometry of 21 fields located in the northern part of the Large Magellanic Cloud (LMC), and spread over a region of more than 2.52 degrees approximately 6 degrees from the bar. The surveyed areas were chosen on the basis of their proximity to SL 388 and SL 509, whose fields showed the presence of a secondary giant clump, observationally detected by Bica et al. (1998, AJ, 116, 723). From the collected data we found that most of the observed field CMDs do not show a separate secondary clump, but rather a continuous vertical structure (VS), which is clearly seen for the first time. Its position and size are nearly the same throughout the surveyed regions: it lies below the Red Giant Clump (RGC) and extends from the bottom of the RGC to approximately 0.45 mag fainter, spanning the bluest color range of the RGC. The more numerous the VS stars in a field, the larger the number of LMC giants in the same zone. Our analysis demonstrate that VS stars belong to the LMC and are most likely the consequence of some kind of evolutionary process in the LMC, particularly in those LMC regions with a noticeable large giant population. Our results suggest that in order to trigger the formation of VS stars, there should be other conditions besides the appropriate age, metallicity, and the necessary red giant star density. Indeed, stars satisfying the requisites mentioned above are commonly found throughout the LMC, but the VS phenomenon is only clearly seen in some isolated regions. Finally, the fact that clump stars have an intrinsic luminosity dispersion further constrains the use of the clump magnitude as a reliable distance indicator.Comment: 25 pages, 9 figures, 3 tables; to be published in AJ, Dec. issu

Analysis of flash flood scenarios in an urbanized catchment using a two-dimensional hydraulic model

Abstract. In Italy, growing urbanization is leading to a higher risk of flooding of small water courses, especially in steep catchments of limited area, where severe flash flood events can occur. The assessment of flash flood hazard requires new modelling tools that can reproduce both the rainfall–runoff processes in the catchment, and the flow processes in the drainage network. In this paper we propose the use of a simple two-dimensional hydraulic model for analysing a flood scenario in a small valley within the urban area of the city of Bologna, Italy. Historically this area has been prone to severe flood events, the most recent of which occurred in 1955 and 1932. Since then there has been a significant increase in urbanization of the lower portion of the catchment, while the natural stream bed has been partially replaced by a culvert. The two-dimensional hydraulic model was therefore applied at catchment scale, in order to simulate the possible effects of historical scenarios in the present catchment configuration. Rainfall and runoff data measured during recent rainfall events were used to calibrate model parameters. Model results show that the current culvert section would be insufficient to drain the runoff produced by intense rainfall events, with potential inundation of surrounding urban areas

Properties of young star cluster systems: the age signature from near-infrared integrated colours

A recent JHKs study of several grand-design spiral galaxies shows a bimodal distribution of their system of star clusters and star forming complexes in colour-magnitude and colour-colour diagrams. In a comparison with stellar population models including gas, the (J-H) vs (H-Ks) diagram reveals that embedded clusters, still immersed in their parental clouds of gas and dust, generally have a redder (H-Ks) colour than older clusters, whose gas and dust have already been ejected. This bimodal behaviour is also evident in the colour-magnitude diagram MK vs (J-Ks), where the brightest clusters split into two sequences separating younger from older clusters. In addition, the reddening-free index Qd = (H-Ks) - 0.884 (J-H) has been shown to correlate with age for the young clusters and thus provided an effective way to differentiate the embedded clusters from the older ones. We aim to study the behaviour of these photometric indices for star cluster systems in the Local Group. We investigate the effectiveness of the Qd index in sorting out clusters of different ages at their early evolutionary stages. Surface photometry was carried out for 2MASS images of populous clusters younger than ~100Myr whose ages were available. Some clusters, particularly the embedded ones, were studied for the first time using this method. The integrated magnitudes and colours extracted from the surface photometry of the most populous clusters/complexes in the Local Group shows the expected bimodal distribution in the colour-colour and colour-magnitude diagrams. In particular, we confirm the index Qd as a powerful tool for distinguishing clusters younger than about 7Myr from older clusters. (abridged)Comment: 10 pages, 11 figures; accepted for publication in A&

High performance liquid chromatography of long-chain acylcarnitine and phospholipids in fatty acid turnover studies.

In this paper we describe a rapid, isocratic high performance liquid chromatography (HPLC) method for the study of radioactive fatty acid incorporation into complex lipids of human erythrocytes, which allows the simultaneous separation of the major phospholipid classes and long-chain acylcarnitines. The lipid extract of erythrocytes pulsed with radioactive fatty acids was injected into an HPLC system equipped with a silica column. The individual components eluted were monitored by ultraviolet absorption and radioactive emission. With respect to the UV profile, the radioactive profile showed an additional peak between phosphatidyl-choline and phosphatidylethanolamine, which was identified as long-chain acylcarnitine by different experimental approaches. The radioactivity recovered in the long-chain acylcarnitines contains essential information enabling definition of acyl trafficking in red cells