Acacia auriculiformis production in the Mampu agroforestry zone on the Batéké plateau, Democratic Republic of Congo

peer reviewedThe Mampu agroforestry zone on the Batéké plateau in the Democratic Republic of Congo, which has been managed with Acacia auriculiformis shade trees for over twenty years by local communities, supplies subsistence products and fuel wood to Kinshasa. Thanks to international grant funding, this agroforestry system, which integrates traditional slashand- burn cultivation, has been replicated in many places across the RDC, but its performance has never been assessed. The aim of this study was to estimate Acacia auriculiformis production in terms of total biomass and usable biomass for charcoal (stems and branches more than 4 cm in diameter) as part of the agroforestry system. To do so, two local allometric equations for total and usable biomass were adjusted from destructive testing data. Using existing inventory data (n = 112 plots), we identified significant structural heterogeneity throughout the rotation period (8-10 years) but also among plots of the same age. Despite this heterogeneity, which may be accounted for by environmental conditions on site and/or by differences in the handling of plot management techniques, production is comparable to that observed at other sites, averaging 145 tonnes per hectare over 10 years. The Mampu agroforestry system has many advantages, including direct services creating rural employment and combined production of subsistence goods and charcoal, but also indirect services such as avoided deforestation and carbon sequestration. The system's sustainability and dissemination should nevertheless be discussed

The Role of Oxidation Compounds in Biofilm Growth on Polyethylene Geomembrane Barriers Used in Landfill

In a model study, polyethylene was preoxidized and incubated for a period of 7 months at 40°C in two different municipal solid waste leachates. During the postexperimental analyses, specific attention was paid to the carbonyl species and carboxylic acid depletion during the environmental exposure because it is well known that carboxylic acids are believed to be a potential substrate for the development of microorganisms. The results showed that the carbonyl as well as the carboxylic acid depletion observed follows first-order kinetics. The biofilm formation was characterized using a suite of analytical techniques, and its formation was compared with the carboxylic acid and carbonyl depletion profil

The compensation approach for walks with small steps in the quarter plane

This paper is the first application of the compensation approach to counting problems. We discuss how this method can be applied to a general class of walks in the quarter plane $Z_{+}^{2}$ with a step set that is a subset of $\{(-1,1),(-1,0),(-1,-1),(0,-1),(1,-1)\}$ in the interior of $Z_{+}^{2}$. We derive an explicit expression for the counting generating function, which turns out to be meromorphic and nonholonomic, can be easily inverted, and can be used to obtain asymptotic expressions for the counting coefficients.Comment: 22 pages, 5 figure

Long range correlations and phase transition in non-equilibrium diffusive systems

We obtain explicit expressions for the long range correlations in the ABC model and in diffusive models conditioned to produce an atypical current of particles.In both cases, the two-point correlation functions allow to detect the occurrence of a phase transition as they become singular when the system approaches the transition

Polyethylene loss of ductility during oxidation: Effect of initial molar mass distribution

This paper reports a study of thermal oxidation induced embrittlement in several polyethylene grades differing mainly by the broadness of the molar mass distribution (ranging for lower than 3 to more than 30). Thermal oxidation was monitored at macromolecular scale (Gel Permeation Chromatography, Differential Scanning Calorimetry) and macroscopic scale (tensile tests). As expected, the samples undergo predominant chain scission and plastic deformation is suppressed below a critical molar mass value (M’C). Even though this latter was previously reported to be independent of the initial weight average molar mass, it is shown here that it depends on initial polydispersity index. Samples were also shown to undergo chemicrystallization, i.e. that segments released by chain scissions migrate into the crystalline phase with a yield increasing with initial polydispersity index. Finally, the main novelty of this work is to evidence that the previously proposed end-of-life criteria at macromolecular level linked to loss of ductility (critical molar mass, crystallization yield) depend on the initial polydispersity index

Quantification of segregation dynamics in ice mixtures

(Abridged) The observed presence of pure CO2 ice in protostellar envelopes is attributed to thermally induced ice segregation, but a lack of quantitative experimental data has prevented its use as a temperature probe. Quantitative segregation studies are also needed to characterize diffusion in ices, which underpins all ice dynamics and ice chemistry. This study aims to quantify the segregation mechanism and barriers in different H2O:CO2 and H2O:CO ice mixtures covering a range of astrophysically relevant ice thicknesses and mixture ratios. The ices are deposited at 16-50 K under (ultra-)high vacuum conditions. Segregation is then monitored at 23-70 K as a function of time, through infrared spectroscopy. Thin (8-37 ML) H2O:CO2/CO ice mixtures segregate sequentially through surface processes, followed by an order of magnitude slower bulk diffusion. Thicker ices (>100 ML) segregate through a fast bulk process. The thick ices must therefore be either more porous or segregate through a different mechanism, e.g. a phase transition. The segregation dynamics of thin ices are reproduced qualitatively in Monte Carlo simulations of surface hopping and pair swapping. The experimentally determined surface-segregation rates for all mixture ratios follow the Ahrrenius law with a barrier of 1080[190] K for H2O:CO2 and 300[100] K for H2O:CO mixtures. During low-mass star formation H2O:CO2 segregation will be important already at 30[5] K. Both surface and bulk segregation is proposed to be a general feature of ice mixtures when the average bond strengths of the mixture constituents in pure ice exceeds the average bond strength in the ice mixture.Comment: Accepted for publication in A&A. 25 pages, including 13 figure

The abundance of C18O and HDO in the envelope and hot core of the intermediate mass protostar NGC 7129 FIRS 2

NGC 7129 FIRS 2 is a young intermediate-mass (IM) protostar, which is associated with two energetic bipolar outflows and displays clear signs of the presence of a hot core. It has been extensively observed with ground based telescopes and within the WISH Guaranteed Time Herschel Key Program. We present new observations of the C18O 3-2 and the HDO 3_{12}-2_{21} lines towards NGC 7129 FIRS 2. Combining these observations with Herschel data and modeling their emissions, we constrain the C18O and HDO abundance profiles across the protostellar envelope. In particular, we derive the abundance of C18O and HDO in the hot core. The intensities of the C18O lines are well reproduced assuming that the C18O abundance decreases through the protostellar envelope from the outer edge towards the centre until the point where the gas and dust reach the CO evaporation temperature (~20-25 K) where the C18O is released back to the gas phase. Once the C18O is released to the gas phase, the modelled C18O abundance is found to be ~1.6x10^{-8}, which is a factor of 10 lower than the reference abundance. This result is supported by the non-detection of C18O 9-8, which proves that even in the hot core (T_k>100 K) the CO abundance must be 10 times lower than the reference value. Several scenarios are discussed to explain this C18O deficiency. One possible explanation is that during the pre-stellar and protostellar phase, the CO is removed from the grain mantles by reactions to form more complex molecules. Our HDO modeling shows that the emission of HDO 3_{12}-2_{21} line is maser and comes from the hot core (T_k>100 K). Assuming the physical structure derived by Crimier et al. (2010), we determine a HDO abundance of ~0.4 - 1x10^{-7} in the hot core of this IM protostar, similar to that found in the hot corinos NGC 1333 IRAS 2A and IRAS 16293-2422.Comment: 10 pages, 7 figure

The nonlinear time-dependent response of isotactic polypropylene

Tensile creep tests, tensile relaxation tests and a tensile test with a constant rate of strain are performed on injection-molded isotactic polypropylene at room temperature in the vicinity of the yield point. A constitutive model is derived for the time-dependent behavior of semi-crystalline polymers. A polymer is treated as an equivalent network of chains bridged by permanent junctions. The network is modelled as an ensemble of passive meso-regions (with affine nodes) and active meso-domains (where junctions slip with respect to their positions in the bulk medium with various rates). The distribution of activation energies for sliding in active meso-regions is described by a random energy model. Adjustable parameters in the stress--strain relations are found by fitting experimental data. It is demonstrated that the concentration of active meso-domains monotonically grows with strain, whereas the average potential energy for sliding of junctions and the standard deviation of activation energies suffer substantial drops at the yield point. With reference to the concept of dual population of crystalline lamellae, these changes in material parameters are attributed to transition from breakage of subsidiary (thin) lamellae in the sub-yield region to fragmentation of primary (thick) lamellae in the post-yield region of deformation.Comment: 29 pages, 12 figure