Total-to-selective extinction ratio in nearby and distant objects

In an area of nearly 23.1 square degrees centered at α(1950) = 23^h57^m and δ(1950) = + 59δ48' magnitudes, colors, and spectral classes were determined for 1419 stars brighter than m_pg = 13^m.00. Star counts were made in this area for all objects brighter than m_pg = m_pv = 15^m.5. Altogether 50585 stars were included in the pv counts. The original photographic data have been transformed to the B, V system. From star counts the ratio of total-to-selective extinction was derived to be R ≉ 4.0 ± 0.2. It depends on the distance to the stars under consideration as well as on the surface density of the objects inside the considered region. In einem Gebiet von annähernd 23.1 Quadratgrad mit den Mittelpunktskoordinaten α(1950) = 23^h57^m und δ(1950) = 59°48' werden für 1419 Sterne heller als m_pg = 13^m.00 Helligkeiten, Farben und Spektraltypen bestimmt. Sternzählungen in Helligkeitsintervallen m_pg und m_pv wurden für alle Objekte heller als m_pg = m_pv = 15^m.5 durchgeführt. Für diese 50585 Sterne wurden die gemessenen photographischen und photovisuellen Helligkeiten in das B, V-System transformiert. Im Ergebnis dieser Sternzählungen wurde ein Wert von R ≉ 4.0 ± 0.2 abgeleitet. Er hängt sowohl von der Entfernung der betrachteten Objektgruppen als auch von der Flächendichte der Sterne innerhalb der Region ab.     

Understanding hydrological processes in glacierized catchments: Evidence and implications of highly variable isotopic and electrical conductivity data

The spatial and temporal characterization of geochemical tracers over Alpine glacierized catchments is particularly difficult, but fundamental to quantify groundwater, glacier melt, and rain water contribution to stream runoff. In this study, we analysed the spatial and temporal variability of δ²H and electrical conductivity (EC) in various water sources during three ablation seasons in an 8.4‐km² glacierized catchment in the Italian Alps, in relation to snow cover and hydro‐meteorological conditions. Variations in the daily streamflow range due to melt‐induced runoff events were controlled by maximum daily air temperature and snow covered area in the catchment. Maximum daily streamflow decreased with increasing snow cover, and a threshold relation was found between maximum daily temperature and daily streamflow range. During melt‐induced runoff events, stream water EC decreased due to the contribution of glacier melt water to stream runoff. In this catchment, EC could be used to distinguish the contribution of subglacial flow (identified as an end member, enriched in EC) from glacier melt water to stream runoff, whereas spring water in the study area could not be considered as an end member. The isotopic composition of snow, glacier ice, and melt water was not significantly correlated with the sampling point elevation, and the spatial variability was more likely affected by postdepositional processes. The high spatial and temporal variability in the tracer signature of the end members (subglacial flow, rain water, glacier melt water, and residual winter snow), together with small daily variability in stream water δ²H dynamics, are problematic for the quantification of the contribution of the identified end members to stream runoff, and call for further research, possibly integrated with other natural or artificial tracers.     

Optical Frequency Comb as a general-purpose and wide-band calibration source for astronomical high resolution infrared spectrographs

A spectrally filtered Optical Frequency Comb (OFC) laser is proposed as a versatile calibration source for astronomical spectrometers in the 1?C2 ??m spectral range. Such a source overcomes the limitations of current calibration lamps providing a uniform spectrum of equally spaced lines with similar intensity and extremely high long-term frequency stability. We present preliminary studies and results of a system which filters the OFC from a 100 MHz comb spacing to 16 GHz one, an adequate spacing for spectrometers with resolving power ????/???>30000. The first approach employs two Fabry-Perot cavities in series, made of dielectric coated mirrors, followed by a non-linear optical broadening system. The limitations of such a filtering process are discussed. These can be overcome by the second approach, based on filtering cavities with metallic coated mirrors.     

Alternative conceptual models and the robustness of groundwater management scenarios in the multi-aquifer system of the Central Veneto Basin, Italy

A three-dimensional (3D) groundwater flow model of the deep multi-aquifer Quaternary deposits of the Po plain sedimentary basin, within a 3,300-km² area (Veneto, Italy), is developed, tested and applied to aid sustainable large-scale water-resources management. Integrated mathematical modelling proves significantly successful, owing to an unusual wealth of available geological, geophysical, and hydrologic data and to state-of-the-art numerical tools. Of particular interest is the evaluation of the influence of alternative conceptual models; that is, of reconstructed representations of the 3D geological model of the structure of the aquifers. The reference conceptual model is set up by means of extended geological sections and stratigraphic records, and is used to create a large, unstructured 3D finite element grid. By analyzing the effects on piezometric surfaces and on the overall water budget of geometrical perturbations from the reference structure, alternative geo-structural models, obtained by systematically shifting the pinch-out of the aquitards, are compared. Interestingly, the impacts of aquitard pinch-out prove far from negligible. The results suggest the critical importance of reliable geological models even for large, complex 3D models. The good practice of iteratively testing numerically the impact of surprises on the conceptual model, as more field information is collected, is thus supported.     

Field study on drainage densities and rescaled width functions in a high‐altitude alpine catchment

This paper addresses the effect of accurately mapping spatially heterogeneous drainage densities in high‐altitude alpine basins on Rescaled Width Functions (RWFs), used in some applications as a minimalist model of the hydrologic response. The channel network and 373 of its channel heads were mapped in the field in a high mountain catchment in the Swiss Alps. The mapped channel network is characterized by highly uneven drainage density, here described by the distribution of the length to the first channelized site computed along steepest descent from any unchannelled site. Various channel networks were extracted from a 1 m lidar‐derived digital terrain model and compared with the field‐mapped channel network using geomorphologic parameters, hillslope‐to‐channel distance and RWFs. Our results show that the channel network derived by statistical analysis of surface morphology is consistent with the field‐mapped network. Larger discrepancies were observed when the channel network was obtained with classical threshold‐based approaches relying on cumulative drainage area and local slope. The actual arrangement of the drainage densities has a significant impact on the RWFs. The discrepancy was largest between RWFs derived from classical extraction methods and RWFs derived with the field‐mapped network, indicating an inappropriate extraction of the channelled portion of the high‐altitude catchment that is a reflection of the variety of channel initiation processes. Our results suggest that spatial heterogeneity of the drainage density might play an important role in modelling streamflow generation. Copyright © 2016 John Wiley & Sons, Ltd.     

Dam-break Modeling in Alpine Valleys

Dam-break analysis is of great importance in mountain environment,especially where reservoirs are located upstream of densely populated areas and hydraulic hazard should be assessed for land planning purposes.Accordingly,there is a need to identify suitable operative tools which may differ from the ones used in flat flood-prone areas.This paper shows the results provided by a 1D and a 2D model based on the Shallow Water Equations（SWE） for dam-break wave propagation in alpine regions.The 1D model takes advantage of a topographic toolkit that includes an algorithm for pre-processing the Digital Elevation Model（DEM） and of a novel criterion for the automatic cross-section space refinement.The 2D model is FLO-2D,a commercial software widely used for flood routing in mountain areas.In order to verify the predictive effectiveness of these numerical models,the test case of the Cancano dam-break has been recovered from the historical study of De Marchi（1945）,which provides a unique laboratory data set concerning the consequences of the potential collapse of the former Cancano dam（Northern Italy）.The measured discharge hydrograph at the dam also provides the data to test a simplified method recently proposed for the characterization of the hydrograph following a sudden dam-break.     

Invasion genetics of Pacific oyster Crassostrea gigas shaped by aquaculture stocking practices

As a result of aquaculture activities Pacific oysters Crassostrea gigas (Thunberg, 1793) have invaded the European Wadden Sea. Using a variable noncoding mitochondrial marker, we show that the invaded range is the result of two independent invasions. Haplotype frequencies point towards two separate groups, one in the southern and the other in the northern Wadden Sea. We found virtually no genetic differentiation throughout the southern range and the putative source from British Columbia, Canada, suggesting that the Southern region can be considered as a closed population. In the North, mismatch distributions, haplotype ordination and isolation-by-distance analysis suggest a stronger, persistent impact of aquaculture on invasive populations. Due to the ongoing supply of new genetic material from hatchery production the northern invasive populations can therefore be considered as an open population highlighting the importance of aquaculture practice on the genetics of this keystone invader in the Wadden Sea.     

Deep Hubble Space Telescope imaging surveys and the formation of spheroidal galaxies

We have extended our previous analysis of morphologically selected elliptical and S0 galaxies in the Hubble Deep Field (HDF) North to include Hubble Space Telescope ( HST ) data in the HDF South and the HDFS–NICMOS areas. Our final sample amounts to 69 E/S0 galaxies with K <20.15 over an area of 11 arcmin². Although a moderately small number over a modest sky area, this sample benefits from the best imaging and photometric data available on high-redshift galaxies. Multi-waveband photometry allows us to estimate with good accuracy the redshifts for the majority of these galaxies, which lack a spectroscopic measure. We confirm our previous findings that massive E/S0s tend to disappear from flux-limited samples at z >1.4. This adds to the evidence that the rest-frame colours and spectral energy distributions (SEDs) of the numerous objects found at 0.8< z <1.2 are inconsistent with a very high redshift of formation for the bulk of stars, while they are more consistent with protracted (either continuous or episodic) star formation down to z ≤1. These results based on high-quality imaging on a small field can be complemented with data from colour-selected extremely red objects (EROs) on much larger sky areas: our claimed demise of E/S0s going from z =1 to z =1.5 is paralleled by a similarly fast decrease in the areal density of EROs when the colour limit is changed from ( R − K )=5 to ( R − K )=6 (corresponding to z ≃1 and z ≃1.3 respectively). Altogether, the redshift interval from 1 to 2 seems to correspond to a very active phase for the assembly of massive E/S0 galaxies in the field, and also probably one where a substantial fraction of their stars are formed.     

Comparison of the ENEAR peculiar velocities with the PSCz gravity field

We present a comparison between the peculiar velocity field measured from the ENEAR all-sky D _n– σ catalogue and that derived from the galaxy distribution of the IRAS Point Source Catalog Redshift Survey (PSC z ). The analysis is based on a modal expansion of these data in redshift space by means of spherical harmonics and Bessel functions. The effective smoothing scale of the expansion is almost linear with redshift reaching 1500 km s⁻¹ at 3000 km s⁻¹. The general flow patterns in the filtered ENEAR and PSC z velocity fields agree well within 6000 km s⁻¹, assuming a linear biasing relation between the mass and the PSC z galaxies. The comparison allows us to determine the parameter     where Ω is the cosmological density parameter and b is the linear biasing factor. A likelihood analysis of the ENEAR and PSC z modes yields     in good agreement with values obtained from Tully–Fisher surveys.