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

Mise en oeuvre de la séparation de sources sur un ensemble d'antennes colocalisées : application à l'augmentation du débit numérique en transmission H.F. ( 3-30 MHz)

Cet article décrit un système opérationnel de transmission numérique en gamme H.F. visant à augmenter le débit binaire de façon significative par rapport au standard actuel. Pour cela, un traitement d'antenne est mis en oeuvre sur un ensemble de quatre capteurs colocalisés présentant une diversité de réponses spatiales. Les techniques utilisées tant pour la synchronisation ( Zéro Crossing Detector) que pour la séparation de sources ( algorithme LMS) sont des solutions classiques et éprouvées faisant appel à des séquences d'apprentissage. Les résultats obtenus sont conformes à l'objectif fixé puisque le débit binaire atteint 15 kbits/s dans une bande de 3 kHz

Variability of Black Carbon Deposition to the East Antarctic Plateau, 1800-2000 AD

Refractory black carbon aerosols (rBC) from biomass burning and fossil fuel combustion are deposited to the Antarctic ice sheet and preserve a history of emissions and long-range transport from low- and mid-latitudes. Antarctic ice core rBC records may thus provide information with respect to past combustion aerosol emissions and atmospheric circulation. Here, we present six East Antarctic ice core records of rBC concentrations and fluxes covering the last two centuries with approximately annual resolution (cal. yr. 1800 to 2000). The ice cores were drilled in disparate regions of the high East Antarctic ice sheet, at different elevations and net snow accumulation rates. Annual rBC concentrations were log-normally distributed and geometric means of annual concentrations ranged from 0.10 to 0.18 m cro-g/kg. Average rBC fluxes were determined over the time periods 1800 to 2000 and 1963 to 2000 and ranged from 3.4 to 15.5 m /a and 3.6 to 21.8 micro-g/sq m/a, respectively. Geometric mean concentrations spanning 1800 to 2000 increased linearly with elevation at a rate of 0.025 micro-g/kg/500 m. Spectral analysis of the records revealed significant decadal-scale variability, which at several sites was comparable to decadal ENSO variability

Variation of Accumulation Rates Over the Last Eight Centuries on the East Antarctic Plateau Derived from Volcanic Signals in Ice Cores

Volcanic signatures in ice-core records provide an excellent means to date the cores and obtain information about accumulation rates. From several ice cores it is thus possible to extract a spatio-temporal accumulation pattern. We show records of electrical conductivity and sulfur from firn cores from the Norwegian-USA scientific traverse during the International Polar Year 2007-2009 (IPY) through East Antarctica. Major volcanic eruptions are identified and used to assess century-scale accumulation changes. The largest changes seem to occur in the most recent decades with accumulation over the period 1963- 2007/08 being up to 25 % different from the long-term record. There is no clear overall trend, some sites show an increase in accumulation over the period 1963 to present while others show a decrease. Almost all of the sites above 3200 m above sea level (asl) suggest a decrease. These sites also show a significantly lower accumulation value than large-scale assessments both for the period 1963 to present and for the long-term mean at the respective drill sites. The spatial accumulation distribution is influenced mainly by elevation and distance to the ocean (continentality), as expected. Ground-penetrating radar data around the drill sites show a spatial variability within 10-20 % over several tens of kilometers, indicating that our drill sites are well representative for the area around them. Our results are important for large-scale assessments of Antarctic mass balance and model validation

Changes in Black Carbon Deposition to Antarctica from Two Ice Core Records, A.D. 1850-2000

Continuous flow analysis was based on a steady sample flow and in-line detection of BC and other chemical substances as described in McConnell et al. (2007). In the cold room, previously cut one meter ice core sticks of 3x3cm, are melted continuously on a heated melter head specifically designed to eliminate contamination from the atmosphere or by the external parts of the ice. The melted ice from the most inner part of the ice stick is continuously pumped by a peristaltic pump and carried to a clean lab by Teflon lines. The recorded signal is continuous, integrating a sample volume of about 0.05 mL, for which the temporal resolution depends on the speed of melting, ice density and snow accumulation rate at the ice core drilling site. For annual accumulation derived from the WAIS and Law Dome ice cores, we assumed ~3.1 cm water equivalent uncertainty in each year's accumulation from short scale spatial variability (glaciological noise) which was determined from several measurements of annual accumulation in multiple parallel ice cores notably from the WAIS Divide ice core site (Banta et al., 2008) and from South Pole site (McConnell et al., 1997; McConnell et al., 2000). Refractory black carbon (rBC) concentrations were determined using the same method as in (Bisiaux et al., 2011) and adapted to continuous flow measurements as described by (McConnell et al., 2007). The technique uses a single particle intracavity laser induced incandescence photometer (SP2, Droplet Measurement Technologies, Boulder, Colorado) coupled to an ultrasonic nebulizer/desolvation (CETAC UT5000) Flow Injection Analysis (FIA). All analyses, sample preparation etc, were performed in a class 100 cleanroom using anti contamination "clean techniques". The samples were not acidified

Inborn errors of OAS-RNase L in SARS-CoV-2-related multisystem inflammatory syndrome in children

Multisystem inflammatory syndrome in children (MIS-C) is a rare and severe condition that follows benign COVID-19. We report autosomal recessive deficiencies of OAS1, OAS2, or RNASEL in five unrelated children with MIS-C. The cytosolic double-stranded RNA (dsRNA)-sensing OAS1 and OAS2 generate 2'-5'-linked oligoadenylates (2-5A) that activate the single-stranded RNA-degrading ribonuclease L (RNase L). Monocytic cell lines and primary myeloid cells with OAS1, OAS2, or RNase L deficiencies produce excessive amounts of inflammatory cytokines upon dsRNA or severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) stimulation. Exogenous 2-5A suppresses cytokine production in OAS1-deficient but not RNase L-deficient cells. Cytokine production in RNase L-deficient cells is impaired by MDA5 or RIG-I deficiency and abolished by mitochondrial antiviral-signaling protein (MAVS) deficiency. Recessive OAS-RNase L deficiencies in these patients unleash the production of SARS-CoV-2-triggered, MAVS-mediated inflammatory cytokines by mononuclear phagocytes, thereby underlying MIS-C

The WAIS Divide deep ice core WD2014 chronology - Part 2: Annual-layer counting (0-31 ka BP)

We present the WD2014 chronology for the upper part (0–2850 m; 31.2 ka BP) of the West Antarctic Ice Sheet (WAIS) Divide (WD) ice core. The chronology is based on counting of annual layers observed in the chemical, dust and electrical conductivity records. These layers are caused by seasonal changes in the source, transport, and deposition of aerosols. The measurements were interpreted manually and with the aid of two automated methods. We validated the chronology by comparing to two high-accuracy, absolutely dated chronologies. For the Holocene, the cosmogenic isotope records of ¹⁰Be from WAIS Divide and ¹⁴C for IntCal13 demonstrated that WD2014 was consistently accurate to better than 0.5% of the age. For the glacial period, comparisons to the Hulu Cave chronology demonstrated that WD2014 had an accuracy of better than 1% of the age at three abrupt climate change events between 27 and 31 ka. WD2014 has consistently younger ages than Greenland ice core chronologies during most of the Holocene. For the Younger Dryas–Preboreal transition (11.595 ka; 24 years younger) and the Bølling–Allerød Warming (14.621 ka; 7 years younger), WD2014 ages are within the combined uncertainties of the timescales. Given its high accuracy, WD2014 can become a reference chronology for the Southern Hemisphere, with synchronization to other chronologies feasible using high-quality proxies of volcanism, solar activity, atmospheric mineral dust, and atmospheric methane concentrations

Black Carbon Nanoparticles in Paleo-Records: A Combustion Proxy

Emitted to the atmosphere through fire and fossil fuel combustion, refractory black carbon nanoparticles (rBC) impact the global climate, atmospheric chemistry, human health, and the carbon cycle. In the Southern Hemisphere (SH), rBC is transported in the atmosphere from low latitudes to Antarctica and deposited to the polar ice sheet, preserving a history of the variability of emissions and atmospheric transport. Here we present a total of eight records of rBC over the polar continent, covering a period ranging from the pre-industrial era to the modern era. These new records represent one of the first surveys of rBC deposition variability over Antarctica for that period of time. Firstly, two high-resolution rBC records from the West Antarctic Ice Sheet divide (WAIS) and Law Dome, on the periphery of the East Antarctic ice sheet, spanning calendar years 1850-2001, are investigated. Highly correlated over the past 60 years, the records show that coherent large-scale changes in rBC deposition to Antarctica occurred at decadal to inter-annual time scales, notably in ENSO-like periodicities. Since about 1940, the records show decadal trends similar to the inventories of SH rBC emissions from grass fires and biofuels. The two records suggest a large-scale reduction in rBC deposition from 1950 to 1990 to WAIS and Law Dome. In order to better understand the spatial and temporal variability in rBC deposition to the polar continent, those high resolution records are compared to six other rBC ice core records from the East-Antarctic Plateau. Located on the Dronning Maud Land, those additional records are characterized by a lower accumulation and thereby lower temporal resolution compared to the WAIS and Law Dome sites. Temporal and spatial analysis of rBC concentrations and fluxes in the East-Antarctic ice cores for the period 1800-2000 reveals high variability of concentrations, and a slightly increasing general trend. Some of the variability recorded at those sites is similar to the high resolution records and suggests a link with short and long-term variability of ENSO.Once emitted to the atmosphere, rBC particles also enter aquatic environments, where they may affect the fate of other pollutants. However, measurements of very low rBC-concentrated waters have almost never been investigated for that purpose. Here, a study determining rBC in waters of the Lake Tahoe watershed in the western United States from 2007 to 2009 are presented. The study period spanned a large fire within the Tahoe basin, seasonal snow-melt, and a number of storm events, which injected urban runoff into the Lake with rBC concentrations up to four orders of magnitude higher than background concentrations. The results show that rBC pulses from both the wildfire and urban runoff were rapidly attenuated within the lake, suggesting unexpected removal from the water column or aggregation to sizes outside of analysis detection capability. Those processes prevent rBC concentrations from building up in the clear and oligotrophic Lake Tahoe. Results obtained for the Tahoe study are compared to similar measurements performed in other oligotrophic lakes, and interpreted to characterize rBC transfer to sediments. Additionally, we measure rBC concentrations in a sediment core from Lake Tahoe, to evaluate the potential of this archive as a combustion record. Despite loss of rBC particles observed in the water column, rBC is transferred to sediments which preserve a local-to-regional scale history of its emissions as revealed by comparison with other pollutant records

Étude de la restauration des caractéristiques de tubes de four de vapocraquage en Manaurite 36 XS

Le vieillissement de tubes de four en Manaurite 36XS d'une unité de vapocraquage se traduit par une précipitation et une coalescence de carbures aux joints de grains, une évolution locale de la composition chimique et une forte diminution de la ductilité. Des traitements thermiques appropriés, dont l'efficacité est suivie par microanalyse et par l'évolution des propriétés mécaniques, permettent de restaurer en quasi totalité les caractéristiques de l'acier. Après détermination des conditions en laboratoire, un essai très positif a été réalisé sur tube de four avec des moyens utilisables sur chantier