The visible spectra of three B stars: π Cet, 36 Lyn 134 Tau

We present an identification list for the visible spectra of three B stars: π Cet (B7V), 36 Lyn B8 IIIp (?)),and 134 Tau (B9 IV). Equivalent widths have been measured on medium dispersion plates (7.0 and 12.4 Å mm^?1) taken with the 152 cm coudé reflector at the Observatoire de Haute Provence (France). These results are also presented. The photographic plates were digitized by using a PDS 1010A microdensitometer. The spectroscopic data were reduced by means of a dedicated software package and an attempt was made to compute equivalent widths in a homogeneous way. T _eff and logg parameters were estimated by using the computer to compare automatically the spectroscopic data with the value of theoretical models.     

POLARIX: a pathfinder mission of X-ray polarimetry

Since the birth of X-ray astronomy, spectral, spatial and timing observation improved dramatically, procuring a wealth of information on the majority of the classes of the celestial sources. Polarimetry, instead, remained basically unprobed. X-ray polarimetry promises to provide additional information procuring two new observable quantities, the degree and the angle of polarization. Polarization from celestial X-ray sources may derive from emission mechanisms themselves such as cyclotron, synchrotron and non-thermal bremsstrahlung, from scattering in aspheric accreting plasmas, such as disks, blobs and columns and from the presence of extreme magnetic field by means of vacuum polarization and birefringence. Matter in strong gravity fields and Quantum Gravity effects can be studied by X-ray polarimetry, too. POLARIX is a mission dedicated to X-ray polarimetry. It exploits the polarimetric response of a Gas Pixel Detector, combined with position sensitivity, that, at the focus of a telescope, results in a huge increase of sensitivity. The heart of the detector is an Application-Specific Integrated Circuit (ASIC) chip with 105,600 pixels each one containing a full complete electronic chain to image the track produced by the photoelectron. Three Gas Pixel Detectors are coupled with three X-ray optics which are the heritage of JET-X mission. A filter wheel hosting calibration sources unpolarized and polarized is dedicated to each detector for periodic on-ground and in-flight calibration. POLARIX will measure time resolved X-ray polarization with an angular resolution of about 20 arcsec in a field of view of 15 × 15 arcmin and with an energy resolution of 20% at 6 keV. The Minimum Detectable Polarization is 12% for a source having a flux of 1 mCrab and 10⁵ s of observing time. The satellite will be placed in an equatorial orbit of 505 km of altitude by a Vega launcher. The telemetry down-link station will be Malindi. The pointing of POLARIX satellite will be gyroless and it will perform a double pointing during the earth occultation of one source, so maximizing the scientific return. POLARIX data are for 75% open to the community while 25% + SVP (Science Verification Phase, 1 month of operation) is dedicated to a core program activity open to the contribution of associated scientists. The planned duration of the mission is one year plus three months of commissioning and SVP, suitable to perform most of the basic science within the reach of this instrument. A nice to have idea is to use the same existing mandrels to build two additional telescopes of iridium with carbon coating plus two more detectors. The effective area in this case would be almost doubled.     

Estimate of the optimum measuring time in the synchronous photometry of optical sources

The note shows how to estimate accurately the optimum measuring time in the measurement of a periodical optical source by means of a synchronous photometer affected by phase-tracking error. The procedure used can be easily generalized to sources or signal patterns not considered here. The optimum number of scans to be averaged results to be typicallyN _opt≈0.5r/ɛ for an optical source of Lorentzian signal pattern, wherer is the duty cycle of the pulsed component and ɛ the relative truncation error of the local sync to the source period. Work supported by Consiglio Nazionale delle Ricerche, Gruppo Nazionale di Astronomia, Settore Tecnologie Astronomiche. Trieste Observatory — Instruments and Data Processing Group (4/76).     

A comparison among olive flowering trends in different Mediterranean areas (south-central Italy) in relation to meteorological variations

Phenological observations of the anthesic phases of olive flowering in a central Mediterranean area were recorded over a 9-year period. The aim of this research was to compare the flowering dates in relationship to the meteorological changes. Pollen emission from anthers was monitored by remote instrumentation placed directly in olive groves and phenological data regarding daily pollen concentrations (pollen/m³) were recorded using a pollen monitoring methodology. The rhythm of the phenological phases emerged as dependent on the meteorological trend of the spring forcing temperature. Generally, the phenomenon of pollen emission occurred progressively earlier prior to 2001, while in the following 5 years, the trend seemed to be inverted, showing a progressive delay of flowering. The spring quarterly mean temperature trends registered by GISS data in Europe confirmed the presence of diverse meteorological behavior during the study period, probably causing the biological divergences that were monitored. The principal result of the present contribution is to evidence the relativity of empirical investigations and observations considering different time intervals. This is due to the partial, brief series (9 years) of flowering dates which have to be considered as part of a longer series (26 years) in order to have a complete vision of the true phenomenon.     

The seventh facet of uncertainty: wrong assumptions,unknowns and surprises in the dynamics of human–water systems

ABSTRACT

The scientific literature has focused on uncertainty as randomness, while limited credit has been given to what we call here the “seventh facet of uncertainty”, i.e. lack of knowledge. This paper identifies three types of lack of understanding: (i) known unknowns, which are things we know we don’t know; (ii) unknown unknowns, which are things we don’t know we don’t know; and (iii) wrong assumptions, things we think we know, but we actually don’t know. Here we discuss each of these with reference to the study of the dynamics of human–water systems, which is one of the main topics of Panta Rhei, the current scientific decade of the International Association of Hydrological Sciences (IAHS), focusing on changes in hydrology and society. In the paper, we argue that interdisciplinary studies of socio-hydrological dynamics leading to a better understanding of human–water interactions can help in coping with wrong assumptions and known unknowns. Also, being aware of the existence of unknown unknowns, and their potential capability to generate surprises or black swans, suggests the need to complement top-down approaches, based on quantitative predictions of water-related hazards, with bottom-up approaches, based on societal vulnerabilities and possibilities of failure.

Editor D. Koutsoyiannis; Associate editor S. Weijs     

Timely Low Resolution SAR Imagery To Support Floodplain Modelling: a Case Study Review

It is widely recognised that remote sensing can support flood monitoring, modelling and management. In particular, satellites carrying Synthetic Aperture Radar (SAR) sensors are valuable as radar wavelengths can penetrate cloud cover and are insensitive to daylight. However, given the strong inverse relationship between spatial resolution and revisit time, monitoring floods from space in near real time is currently only possible through low resolution (about 100 m pixel size) SAR imagery. For instance, ENVISAT-ASAR (Advanced Synthetic Aperture Radar) in WSM (wide swath mode) revisit times are of the order of 3 days and the data can be obtained within 24 h at no (or low) cost. Hence, this type of space-borne data can be used for monitoring major floods on medium-to-large rivers. This paper aims to discuss the potential for, and uncertainties of, coarse resolution SAR imagery to monitor floods and support hydraulic modelling. The paper first describes the potential of globally and freely available space-borne data to support flood inundation modelling in near real time. Then, the uncertainty of SAR-derived flood extent maps is discussed and the need to move from deterministic binary maps (wet/dry) of flood extent to uncertain flood inundation maps is highlighted.     

Model averaging versus model selection: estimating design floods with uncertain river flow data

ABSTRACT

This study compares model averaging and model selection methods to estimate design floods, while accounting for the observation error that is typically associated with annual maximum flow data. Model selection refers to methods where a single distribution function is chosen based on prior knowledge or by means of selection criteria. Model averaging refers to methods where the results of multiple distribution functions are combined. Numerical experiments were carried out by generating synthetic data using the Wakeby distribution function as the parent distribution. For this study, comparisons were made in terms of relative error and root mean square error (RMSE) referring to the 1-in-100 year flood. The experiments show that model averaging and model selection methods lead to similar results, especially when short samples are drawn from a highly asymmetric parent. Also, taking an arithmetic average of all design flood estimates gives estimated variances similar to those obtained with more complex weighted model averaging.     

Investigating the influence of minor hydraulic structures on modeling flood events in lowland areas

Flood inundation models have been recognized to be a valuable tool to reproduce flow dynamics in a given area and support decision‐making processes on flood management measures. In many cases, in the simulation of flood events, only the main river channel and the associated structures are represented within the model. However, during flood events involving lowland areas, the minor drainage network – and the associated hydraulic structures – may have an important role in conveying flow and determining which areas will be flooded. The objective of this study is to investigate whether – and to what extent – small hydraulic structures in drainage networks have an influence in flooding on lowland areas. The case study for this research is the 1990 flood event which occurred in the lowland plain of the Reno River, in Northern Italy. The study area is mainly used for agricultural purposes and has a drainage system with several small bridges and culverts. The influence of the minor hydraulic structures on flood dynamics was analyzed through a combined use of one‐dimensional (1D) and two‐dimensional (2D) hydraulic models. First, a number of detailed and simplified approaches to represent hydraulic structures in the computational grids were analyzed by means of the HECRAS 1D model. Second, these approaches were implemented and tested in several 2D simulations of the flood event. The simulated inundation extents and flood levels were then compared with the observed data and with each other. The analysis of results showed that simplified schematizations were sufficient to obtain good model predictions of peak inundation extent and flood levels, at least for the present case study. Moreover, the influence of the structures on the peak flood inundation extent and flood levels was found to be limited, whereas it showed to be more significant during the drainage phase of the flood. Copyright © 2013 John Wiley & Sons, Ltd.     

Multiple cosmogenic nuclides document complex Pleistocene exposure history of glacial drifts in Terra Nova Bay (northern Victoria Land, Antarctica)

Geomorphological and glacial geological surveys and multiple cosmogenic nuclide analyses (¹⁰Be, ²⁶Al, and ²¹Ne) allowed us to reconstruct the chronology of variations prior to the last glacial maximum of the East Antarctic Ice Sheet (EAIS) and valley glaciers in the Terra Nova Bay region. Glacially scoured coastal piedmonts with round-topped mountains occur below the highest local erosional trimline. They represent relict landscape features eroded by extensive ice overriding the whole coastal area before at least 6 Ma (pre-dating the build-up of the Mt. Melbourne volcanic field). Since then, summit surfaces were continuously exposed and well preserved under polar condition with negligible erosion rates on the order of 17 cm/Ma. Complex older drifts rest on deglaciated areas above the younger late-Pleistocene glacial drift and below the previously overridden summits. The combination of stable and radionuclide isotopes documents complex exposure histories with substantial periods of burial combined with minimal erosion. The areas below rounded summits were repeatedly exposed and buried by ice from local and outlet glaciers. The exposure ages of the older drift(s) indicate multiple Pleistocene glacial cycles, which did not significantly modify the pre-existing landscape.