Assessing the effect of a catchment-scale restoration project in Wallonia (Belgium)

peer reviewedIn the context of fulfilling the Water Framework Directive requirements, the LIFE+ project Walphy allowed experimental restoration projects to be undertaken on two medium-size catchments of the Meuse basin in Wallonia (Belgium) between 2009 and 2014. Before undertaking sustainable rehabilitation measures, a multi-scale assessment of hydromorphological conditions (catchment, stream and site) was conducted. It was based on a variety of variables characterizing the river system and its geomorphic processes (e.g. sediment transport), along with human-induced disturbances (e.g. barriers to river continuity). The Bocq catchment has been subject to a large-scale restoration project through the removal or modification of 20 barriers (mainly old weirs), reconnecting the Bocq with the Meuse. In addition, 2.6 km of straightened courses were improved by restoring meanders or diversifying habitats through a wide range of rehabilitation techniques. The success of the restoration projects was evaluated on the basis of a multi-disciplinary monitoring. We compared hydromorphological parameters and biological diversity of benthic invertebrates, fish and macrophytes. 2-3 years post-rehabilitation, hydromorphology was significantly improved. Depending on the rehabilitation measures, the restoration effects observed for invertebrates and fish differ. Weir removal and restored meanders have resulted in the most positive effects, while habitat diversification has led to more contrasted results, depending on the level of ambition. The geomorphological monitoring has focused on the effectiveness of spawning gravel rehabilitation and the effect of barriers on sediment transport. Topographic surveys and the use of pebble tracers have highlighted a natural bedload transport following a weir removal.Walph

Canonical lossless state-space systems: Staircase forms and the Schur algorithm

A new finite atlas of overlapping balanced canonical forms for multivariate discrete-time lossless systems is presented. The canonical forms have the property that the controllability matrix is positive upper triangular up to a suitable permutation of its columns. This is a generalization of a similar balanced canonical form for continuous-time lossless systems. It is shown that this atlas is in fact a finite sub-atlas of the infinite atlas of overlapping balanced canonical forms for lossless systems that is associated with the tangential Schur algorithm; such canonical forms satisfy certain interpolation conditions on a corresponding sequence of lossless transfer matrices. The connection between these balanced canonical forms for lossless systems and the tangential Schur algorithm for lossless systems is a generalization of the same connection in the SISO case that was noted before. The results are directly applicable to obtain a finite sub-atlas of multivariate input-normal canonical forms for stable linear systems of given fixed order, which is minimal in the sense that no chart can be left out of the atlas without losing the property that the atlas covers the manifold

On the Excitation and Formation of Circumstellar Fullerenes

We compare and analyze the Spitzer mid-infrared spectrum of three fullerene-rich planetary nebulae in the Milky Way and the Magellanic Clouds; Tc1, SMP SMC16, and SMP LMC56. The three planetary nebulae share many spectroscopic similarities. The strongest circumstellar emission bands correspond to the infrared active vibrational modes of the fullerene species C60 and little or no emission is present from Polycyclic Aromatic Hydrocarbons (PAHs). The strength of the fullerene bands in the three planetary nebulae is very similar, while the ratio of the [NeIII]15.5um/[NeII]12.8um fine structure lines, an indicator of the strength of the radiation field, is markedly different. This raises questions about their excitation mechanism and we compare the fullerene emission to fluorescent and thermal models. In addition, the spectra show other interesting and common features, most notably in the 6-9um region, where a broad plateau with substructure dominates the emission. These features have previously been associated with mixtures of aromatic/aliphatic hydrocarbon solids. We hypothesize on the origin of this band, which is likely related to the fullerene formation mechanism, and compare it with modeled Hydrogenated Amorphous Carbon that present emission in this region.Comment: 13 pages, 2 tables, 7 figures, Accepted for publication in Ap

The Formation of Fullerenes in Planetary Nebulae

In the last decade, fullerenes have been detected in a variety of astrophysical environments, with the majority being found in planetary nebulae. Laboratory experiments have provided us with insights into the conditions and pathways that can lead to fullerene formation, but it is not clear precisely what led to the formation of astrophysical fullerenes in planetary nebulae. We review some of the available evidence, and propose a mechanism where fullerene formation in planetary nebulae is the result of a two-step process where carbonaceous dust is first formed under unusual conditions; then, the fullerenes form when this dust is being destroyed

Physical properties of fullerene-containing Galactic planetary nebulae

We searched the Spitzer Space Telescope data archive for Galactic planetary nebulae (PNe), which show the characteristic 17.4 and 18.9 µm features due to C60, also known as buckminsterfullerene. Out of 338 objects with Spitzer/Infrared Spectrograph data, we found eleven C60-containing PNe, six of which (Hen2-68, IC2501, K3-62, M1-6, M1-9 and SaSt2-3) are new detections, not known to contain C60 prior to this work. The strongest 17.4 and 18.9 µm C60 features are seen in Tc1 and SaSt2-3, and these two sources also prominently show the C60 resonances at 7.0 and 8.5 µm. In the other nine sources, the 7.0 and 8.5 µm features due to C60 are much weaker. We analysed the spectra, along with ancillary data, using the photoionization code CLOUDY to establish the atomic line fluxes, and determine the properties of the radiation field, as set by the effective temperature of the central star. In addition, we measured the infrared spectral features due to dust grains. We find that the polycyclic aromatic hydrocarbon (PAH) profile over 6–9 µm in these C60-bearing carbon-rich PNe is of the more chemically processed class A. The intensity ratio of 3.3 to 11.3 µm PAH indicates that the number of C-atoms per PAH in C60-containing PNe is small compared to that in non-C60 PNe. The Spitzer spectra also show broad dust features around 11 and 30 µm. Analysis of the 30 µm feature shows that it is strongly correlated with the continuum, and we propose that a single carbon-based carrier is responsible for both the continuum and the feature. The strength of the 11 µm feature is correlated to the temperature of the dust, suggesting that it is at least partially due to a solid-state carrier. The chemical abundances of C60-containing PNe can be explained by asymptotic giant branch nucleosynthesis models for initially 1.5–2.5 M⊙ stars with Z = 0.004. We plotted the locations of C60-containing PNe on a face-on map of the Milky Way and we found that most of these PNe are outside the solar circle, consistent with low metallicity values. Their metallicity suggests that the progenitors are an older population

Актуальность и основные аспекты антикризисного менеджмента предприятием

Целью данной статьи является выявление значимости и основных аспектов антикризисного менеджмента

Balanced realizations of discrete-time stable all-pass systems and the tangential Schur algorithm

In this report, the connections are investigated between two different approaches towards the parametrization of multivariable stable all-pass systems in discrete-time. The first approach involves the tangential Schur algorithm, which employs linear fractional transformations. It stems from the theory of reproducing kernel Hilbert spaces and enables the direct construction of overlapping local parametrizations using Schur parameters and interpolation points. The second approach proceeds in terms of state-space realizations. In the scalar case, a balanced canonical form exists that can also be parametrized by Schur parameters. This canonical form can be constructed recursively, using unitary matrix operations. Here, this procedure is generalized to the multivariable case by establishing the connections with the first approach. It gives rise to balanced realizations and overlapping canonical forms directly in terms of the parameters used in the tangential Schur algorithm

Lossless scalar functions: boundary interpolation, Schur algorithm and Ober's canonical form

International audienceIn Ober (1987) a balanced canonical form for continuous-time lossless systems was presented. This form has a tridiagonal dynamical matrix A and the useful property that the corresponding controllability matrix K is upper triangular. In this paper, a connection is established between Ober's canonical form and a Schur algorithm builts from angular derivative interpolation conditions. It provides a new interpretation of the parameters in Ober's form, as interpolation values at infinity, and a recursive construction of the balanced realization

Parametrization of matrix-valued lossless functions based on boundary interpolation

International audienceThis paper is concerned with parametrization issues for rational lossless matrix valued functions. In the same vein as previous works, interpolation theory with metric constraints is used to ensure the lossless property. We consider here boundary interpolation and provide a new parametrization of balanced canonical forms in which the parameters are angular derivatives. We finally investigate the possibility to parametrize orthogonal wavelets with vanishing moments using these results

Spitzer Characterization of Dust in the Ionized Medium of the Large Magellanic Cloud

A systematic investigation of dust emission associated with the ionized gas has so far been performed only in our Galaxy and for wavelengths longer than 60 {\mu}m. Newly available Spitzer data now offer the opportunity to carry out a similar analysis in the Large Magellanic Cloud (LMC). By cross-correlating Spitzer SAGE (Surveying the Agents of a Galaxy's Evolution) data with the ATCA/Parkes HI 21-cm data, the NANTEN 12CO (J=1-0) data, and both the SHASSA H{\alpha} and the Parkes 6-cm data, we investigate the physical properties of dust associated with the different phases of the gas (atomic, molecular and ionized). In particular, we study the presence and nature of dust from 3.6 to 160 {\mu}m and for various regimes of the ionized gas, spanning emission measures (EM) from \sim 1 pc cm-6 (diffuse component) to \sim 10^3 pc cm-6 (HII regions). Using a dust emission model, and testing our results with several radiation field spectra, we show that dust in the ionized gas is warmer than dust associated with other phases (atomic and molecular). We also find a decrease of the polycyclic aromatic hydrocarbons (PAH) relative abundance with respect to big grains (BGs), as well as an increase of the near infrared (NIR) continuum. These three results (e.g. warmer temperature, decrease of PAH abundance and increase of the NIR continuum) are found consistently for all regimes of the ionized gas. On the contrary, the molecular phase appears to provide favorable conditions for the survival of PAHs. Furthermore, the very small grain (VSG) relative abundance tends to increase in the ionized phase, especially in bright HII regions. Last but not least, our analysis shows that the emissivity of dust associated with the ionized gas is lower in the LMC than in our Galaxy, and that this difference is not accounted for by the lower metallicity of the LMC.Comment: Accepted for publication in ApJ, 15 pages, 5 figures, 3 table