bluuebunny/crossref_metadata_2025 huggingface dataset:
Estudo de ataque de cloreto em Betões Autocompactantes de alto desempenho com adjuvantes mitigadores de retração e diferentes relações água/aglomerante
Authors: Dors Sakata Rafael , Longuini Repette Wellington , Gómez Luis Alberto , Onghero Lucas
Published: March 2018

O concreto autoadensável de alto desempenho (CAAAD) é um concreto autoadensável desenvolvido para aumentar o desempenho das estruturas de concreto através do aumento da sua durabilidade. O CAAAD possui, portanto uma alta durabilidade, principalmente pelo fato de ter uma estrutura de poros mais refinada, porém se mostra vulnerável aos efeitos da retração autógena, que é majorada com a diminuição de tamanho dos poros do concreto. Esta retração pode gerar fissuras no concreto diminuindo sua durabilidade, para diminuir ou eliminar a retração do concreto são utilizados aditivos mitigadores de retração. Esta pesquisa tem como objetivo mostrar o comportamento de CAAAD que foram produzidos com aditivos mitigadores de retração e com diferentes relações água/aglomerantes, em relação à resistência ao ataque de cloretos. Para tanto foram realizados nesta pesquisa os seguintes ensaios: ensaio acelerado de penetração de cloretos, análise do teor de cloretos e análise da corrente passante nos primeiros minutos do ensaio acelerado de penetração de cloretos. Para comparação da influência do uso de aditivos mitigadores de retração em relação à resistência ao ataque de cloretos dos CAAAD, foram produzidos concretos com relações água/aglomerante (a/agl) 0,25 e 0,32 nos quais se utilizou aditivo redutor de retração (ARR) nos teores de 0,5%, 1% e 2%, em relação à massa de cimento, além de aditivo compensador de retração (ACR) nos teores de 5% e 10%, em substituição ao cimento, apenas para o concreto com relação água/aglomerante 0,25 utilizou-se o teor de 15%. Além destes para o concreto com relação a/agl de 0,378 foi utilizado um polímero superabsorvente (SAP) no teor de 0,04%, em relação a massa de cimento. Para se verificar a influência da relação água/aglomerante na penetração de cloretos dos CAAAD foram ensaiados concretos produzidos sem aditivos mitigadores de retração, com os seguintes valores de relação água/aglomerante: 0,25; 0,295; 0,32 e 0,378. Concluiu-se que, excluindo o traço com 15% de ACR e relação a/agl 0,25, que demostrou ser uma dosagem excessiva, os concretos produzidos com os aditivos mitigadores de retração não alteraram significativamente as propriedades de resistência ao ataque de cloretos dos concretos estudados, portanto, podem ser utilizados em estruturas de CAAAD sem prejudicar sua durabilidade. Em relação aos concretos produzidos com diferentes relações a/agl, sem aditivo, os resultados demonstraram que quanto menor a relação a/agl melhor é o desempenho do concreto frente ao ingresso de agentes agressivos.DOI: http://dx.doi.org/10.4995/HAC2018.2018.6326
Influencia de la fracción mixta y de hormigón en las prestaciones mecánicas de los hormigones reciclados
Authors: Medina C. , Plaza P. , Velardo P. , Matías A. , Sánchez de Rojas M.I. , Sáez del Bosque I.F.
Published: March 2018

La utilización de áridos reciclados en el ámbito de la ingeniería civil ha incrementado en los últimos años, representando en 2014 un 8% de la producción total de áridos a nivel europeo. A nivel nacional el empleo de los mismos se ha visto estimulado en la última década por el desarrollo de un marco normativo que permite su empleo en aplicaciones, tales como mezclas bituminosas, base de carreteras, hormigones estructurales y no estructurales …. La actual Instrucción Española de Hormigón Estructural (EHE-08) permite la incorporación parcial (< 20% peso) de áridos reciclados gruesos de hormigón como sustitutos de los áridos convencionales. El presente trabajo de investigación persigue analizar el efecto de utilizar simultáneamente la incorporación parcial (20%) de arena reciclada (hormigón o mixta) con árido grueso reciclado de hormigón (50%) en las prestaciones finales de los hormigones reciclados con fines estructurales. Para alcanzar este ítem, se caracterizó primeramente los áridos empleados, para posteriormente proceder al diseño y fabricación de las mezclas objeto de estudio. A continuación, se llevó a cabo la caracterización física (densidad y consistencia) y mecánicas (compresión, tracción y flexión) de los nuevos hormigones.  Resultado de este estudio se observa que la incorporación de la fracción fina y gruesa reciclada no afecta nocivamente en las prestaciones finales de los mismos pudiendo ser empleados en el sector de la construcción y contribuyendo al actual modelo de economía circular. Finalmente, indicar que este trabajo contribuye a aportar un mayor conocimiento a la laguna científica y técnica que tiene la reutilización integral (fracción fina y gruesa) de los residuos de la construcción y demolición en el campo de los hormigones.DOI: http://dx.doi.org/10.4995/HAC2018.2018.6447
Desempeño de compuestos con fibras de alcohol polivinílico y nano-fibras/tubos de carbono
Authors: Flores Vivian Ismael , Hoheneder Joshua , Vergara Alvarez Lourdes , Sobolev Konstantin
Published: March 2018

La adición de fibras en compuestos a base de cemento portland es una práctica común para la prevención de la formación de grietas y para incrementan la resistencia a la flexión. En esta investigación, se estudiaran los compuestos fibro-reforzados (CFR) con fibras de polivinilo alcohol (PVA), reforzadas con nanofibras de carbono (NFC) o nanotubos de carbono (NTC). Los especímenes fabricados fueron ensayados a la resistencia a la flexión y a la conductividad eléctrica en agua o en solución con NaCl. Los resultados demostraron una dependencia de los especímenes al tipo de solución a la cual fueron expuestos. Se demostró que la sensitivdad a la deformación y a la solución de NaCl puede ser incrementada por la adición de los NTC. Los resultados en el incremento de la conductividad con los compuestos de NTC pueden ser escalables para las aplicaciones de monitoreo no-destructivo en estructuras de concreto que requieran una mejora integral bajo las cargas aplicadas y estabilidad en ambientes deletéreos.DOI: http://dx.doi.org/10.4995/HAC2018.2018.6473
El uso de hormigones reciclados en el sector agroganadero
Authors: García González Julia , Juan Valdés Andrés , Rodríguez Robles Desirée , Morán del Pozo Julia Mª , Guerra Romero Manuel Ignacio , De Belie Nele
Published: March 2018

El impacto medioambiental ocasionado durante las últimas décadas por el sector de la construcción, teniendo en cuenta tanto la elevada utilización de recursos naturales como la generación de grandes volúmenes de residuos, ha fomentado el interés de dicho sector por el conocimiento y uso de los hormigones reciclados. Este tipo de material proporciona una alternativa capaz de solventar los dos costes ecológicos mencionados anteriormente, ya que el uso de residuos de construcción y demolición en la elaboración de nuevos hormigones disminuye las necesidades de deposición en el medio de dicho flujo residual, así como también reduce la demanda de nuevas extracciones. En el presente estudio se muestran las diferencias de comportamiento existentes entre un hormigón convencional (realizado con árido 100% natural) y un hormigón reciclado (50% del árido grueso natural se ha sustituido por árido reciclado mixto) cuando estos son utilizados en el sector agroganadero. Este tipo de ambientes son muy exigentes con los materiales constructivos, ya que la presencia de ácidos orgánicos generados por los efluentes del material ensilado y las excreciones de los animales junto con la abrasión mecánica ejercida por los animales y la maquinaria, ocasionan un alto nivel de degradación. Para este ensayo, se ha utilizado un equipo de ensayo de degradación acelerada implementado en la Universidad de Gante (Bélgica), el cual somete las probetas cilíndricas de hormigón (230mm de diámetro y 70mm de alto) a ciclos de degradación. En cada ciclo, las probetas están rotando durante 7 días, alternando de este modo su contacto con la solución ácida y con el aire. La solución ácida es una mezcla de base acuosa donde se incorporan ácido láctico y ácido acético, con una concentración de 30g/l. Tras este periodo, se aplica un barrido sobre la superficie de las probetas, el cual simula el desgaste mecánico. Un sistema de medición laser, permite posteriormente cuantificar la disminución de radio experimentada por las probetas, y de este modo la resistencia de los distintos materiales frente a este tipo de degradación.Los resultados alcanzados muestran como el hormigón reciclado presenta una mayor resistencia a los ataques ácidos y mecánicos que pueden darse en un ambiente ganadero. La justificación de este comportamiento se encuentra en el efecto que ejerce el material cerámico sobre la red porosa del hormigón, modificando la cantidad de agua libre presente en la pasta de hormigón durante el amasado.DOI: http://dx.doi.org/10.4995/HAC2018.2018.6557
Influência de agregados reciclados de concreto na reologia do concreto
Authors: Pepe Marco , Amario Mayara , Toledo Filho Romildo D.
Published: March 2018

O presente estudo avalia a influência de agregados de resíduo de concreto (ARC) no comportamento reológico de concretos reciclados no estado fresco. De fato, a elevada porosidade dos agregados e sua angularidade modificam a trabalhabilidade dos concretos contendo ARC. Portanto, esse é um estudo preliminar que tem como objetivo estender ferramentas conceituais para concretos contendo agregados reciclados, como por exemplo, o modelo de Bingham simplificado, cuja aplicação para concretos convencionais já está bem consolidada. Para isso, diferentes ensaios experimentais foram realizados a fim de investigar os efeitos das propriedades dos ARCs no comportamento no estado fresco de concretos reciclados. Os resultados obtidos demonstram que, de fato, os ARCs modificam as propriedades reológicas dos concretos, aumentando a sua trabalhabilidade e diminuindo sua tensão de escoamento. Além disso, suas propriedades são altamente relacionadas com a condição de umidade inicial dos agregados.DOI: http://dx.doi.org/10.4995/HAC2018.2018.7237
Nighttime wind and scalar variability within and above an Amazonian canopy
Authors: Oliveira Pablo E. S. , Acevedo Otávio C. , Sörgel Matthias , Tsokankunku Anywhere , Wolff Stefan , Araújo Alessandro C. , Souza Rodrigo A. F. , Sá Marta O. , Manzi Antônio O. , Andreae Meinrat O.
Published: March 2018

Abstract. Nocturnal turbulent kinetic energy (TKE) and fluxes of energy, CO2 and O3 between the Amazon forest and
the atmosphere are evaluated for a 20-day campaign at the Amazon Tall Tower Observatory (ATTO) site. The distinction of
these quantities between fully turbulent (weakly stable) and intermittent (very stable) nights is discussed. Spectral
analysis indicates that low-frequency, nonturbulent fluctuations are responsible for a large portion of the variability
observed on intermittent nights. In these conditions, the low-frequency exchange may dominate over the turbulent
transfer. In particular, we show that within the canopy most of the exchange of CO2 and H2O happens on
temporal scales longer than 100 s. At 80 m, on the other hand, the turbulent fluxes are almost absent in
such very stable conditions, suggesting a boundary layer shallower than 80 m. The relationship between TKE and
mean winds shows that the stable boundary layer switches from the very stable to the weakly stable regime during
intermittent bursts of turbulence. In general, fluxes estimated with long temporal windows that account for low-frequency effects are more dependent on the stability over a deeper layer above the forest than they are on the
stability between the top of the canopy and its interior, suggesting that low-frequency processes are controlled over
a deeper layer above the forest.
Ozone impacts of gas–aerosol uptake in global chemistry transport models
Authors: Stadtler Scarlet , Simpson David , Schröder Sabine , Taraborrelli Domenico , Bott Andreas , Schultz Martin
Published: March 2018

Abstract. The impact of six heterogeneous gas–aerosol uptake reactions on tropospheric ozone and nitrogen species was studied using two chemical transport models, the Meteorological Synthesizing Centre-West of the European Monitoring and Evaluation Programme (EMEP MSC-W) and the European Centre Hamburg general circulation model combined with versions of the Hamburg Aerosol Model and Model for Ozone and Related chemical Tracers (ECHAM-HAMMOZ). Species undergoing heterogeneous reactions in both models include N2O5, NO3, NO2, O3, HNO3, and HO2. Since heterogeneous reactions take place at the aerosol surface area, the modelled surface area density (Sa) of both models was compared to a satellite product retrieving the surface area. This comparison shows a good agreement in global pattern and especially the capability of both models to capture the extreme aerosol loadings in east Asia. The impact of the heterogeneous reactions was evaluated by the simulation of a reference run containing all heterogeneous reactions and several sensitivity runs. One reaction was turned off in each sensitivity run to compare it with the reference run. The analysis of the sensitivity runs confirms that the globally most important heterogeneous reaction is the one of N2O5. Nevertheless, NO2, HNO3, and HO2 heterogeneous reactions gain relevance particularly in east Asia due to the presence of high NOx concentrations and high Sa in the same region. The heterogeneous reaction of O3 itself on dust is of minor relevance compared to the other heterogeneous reactions. The impacts of the N2O5 reactions show strong seasonal variations, with the biggest impacts on O3 in springtime when photochemical reactions are active and N2O5 levels still high. Evaluation of the models with northern hemispheric ozone surface observations yields a better agreement of the models with observations in terms of concentration levels, variability, and temporal correlations at most sites when the heterogeneous reactions are incorporated. Our results are loosely consistent with results from earlier studies, although the magnitude of changes induced by N2O5 reaction is at the low end of estimates, which seems to fit a trend, whereby the more recent the study the lower the impacts of these reactions.
Aerosol optical properties over Europe: an evaluation of the
AQMEII Phase 3 simulations against satellite observations
Authors: Palacios-Peña Laura , Jiménez-Guerrero Pedro , Baró Rocío , Balzarini Alessandra , Bianconi Roberto , Curci Gabriele , Landi Tony Christian , Pirovano Guido , Prank Marje , Riccio Angelo , Tuccella Paolo , Galmarini Stefano
Published: March 2018

Abstract. The main uncertainties in estimates of changes in the Earth's energy budget are related to the role of atmospheric aerosols. These changes are caused mainly by aerosol-radiation (ARI) and aerosol-cloud interactions (ACI), which heavily depend on aerosol properties. From the 1980s, many international modelling initiatives have studied atmospheric aerosols and their climate effects. Phase 3 of the Air Quality Model Evaluation International Initiative (AQMEII) focuses on evaluating and intercomparing regional and linked global/regional modelling systems by collaborating with the Task Force on the Hemispheric Transport of Air Pollution Phase 2 (HTAP2) initiative. Within this framework, the main aim of this work was to evaluate the representation of aerosol optical depth (AOD) and the Ångström exponent (AE) by the AQMEII Phase 3 simulations over Europe. The evaluation was made using satellite data from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensors on board the Terra and Aqua platforms. The results indicated that the skills of AQMEII simulations in the AOD representation produced fewer errors than in the AE. Regardless of the models and emissions used, models were skilful at representing the low and medium AOD values observed (below 0.5). However, high values (close to 1.0) were underestimated for biomass burning episodes, and were overestimated for desert dust contributions, related mainly to emission and boundary conditions. Despite this behaviour, the spatial and temporal variability of this variable was well-represented by all the models. Generally, the AE evaluation showed more serious errors than the AOD evaluation. Moreover, the observed variability of this parameter was strongly underestimated in all the simulations.
Regional uncertainty of GOSAT XCO2 retrievals in China: quantification and attribution
Authors: Bie Nian , Lei Liping , Zeng ZhaoCheng , Cai Bofeng , Yang Shaoyuan , He Zhonghua , Wu Changjiang , Nassar Ray
Published: March 2018

Abstract. The regional uncertainty of the column-averaged dry air mole fraction of CO2 (XCO2) retrieved using different algorithms from the Greenhouse gases Observing SATellite (GOSAT) and its attribution are still not well understood. This paper investigates the regional performance of XCO2 within a latitude band of 37–42° N segmented into 8 cells in a grid of 5° from west to east (80–120° E) in China, where typical land surface types and geographic conditions exist. The former includes desert, grassland and built-up areas mixed with cropland; and the latter includes anthropogenic emissions that change from small to large from west to east, including those from the megacity of Beijing. For these specific cells, we evaluate the regional uncertainty of GOSAT XCO2 retrievals by quantifying and attributing the consistency of XCO2 retrievals from four algorithms (ACOS, NIES, OCFP and SRFP) by intercomparison. These retrievals are then specifically compared with simulated XCO2 from the high-resolution nested model in East Asia of the Goddard Earth Observing System 3-D chemical transport model (GEOS-Chem). We also introduce the anthropogenic CO2 emissions data generated from the investigation of surface emitting point sources that was conducted by the Ministry of Environmental Protection of China to GEOS-Chem simulations of XCO2 over the Chinese mainland. The results indicate that (1) regionally, the four algorithms demonstrate smaller absolute biases of 0.7–1.1 ppm in eastern cells, which are covered by built-up areas mixed with cropland with intensive anthropogenic emissions, than those in the western desert cells (1.0–1.6 ppm) with a high-brightness surface from the pairwise comparison results of XCO2 retrievals. (2) Compared with XCO2 simulated by GEOS-Chem (GEOS-XCO2), the XCO2 values from ACOS and SRFP have better agreement, while values from OCFP are the least consistent with GEOS-XCO2. (3) Viewing attributions of XCO2 in the spatio-temporal pattern, ACOS and SRFP demonstrate similar patterns, while OCFP is largely different from the others. In conclusion, the discrepancy in the four algorithms is the smallest in eastern cells in the study area, where the megacity of Beijing is located and where there are strong anthropogenic CO2 emissions, which implies that XCO2 from satellite observations could be reliably applied in the assessment of atmospheric CO2 enhancements induced by anthropogenic CO2 emissions. The large inconsistency among the four algorithms presented in western deserts which displays a high albedo and dust aerosols, moreover, demonstrates that further improvement is still necessary in such regions, even though many algorithms have endeavored to minimize the effects of aerosols scattering and surface albedo.
An initial ULF wave index derived from 2 years of Swarm observations
Authors: Papadimitriou Constantinos , Balasis Georgios , Daglis Ioannis A. , Giannakis Omiros
Published: March 2018

Abstract. The ongoing Swarm satellite mission provides an opportunity for better knowledge of the near-Earth electromagnetic environment. Herein, we use a new methodological approach for the detection and classification of ultra low-frequency (ULF) wave events observed by Swarm based on an existing time-frequency analysis (TFA) tool and utilizing a state-of-the-art high-resolution magnetic field model and Swarm Level 2 products (i.e., field-aligned currents – FACs – and the Ionospheric Bubble Index – IBI). We present maps of the dependence of ULF wave power with magnetic latitude and magnetic local time (MLT) as well as geographic latitude and longitude from the three satellites at their different locations in low-Earth orbit (LEO) for a period spanning 2 years after the constellation's final configuration. We show that the inclusion of the Swarm single-spacecraft FAC product in our analysis eliminates all the wave activity at high altitudes, which is physically unrealistic. Moreover, we derive a Swarm orbit-by-orbit Pc3 wave (20–100 MHz) index for the topside ionosphere and compare its values with the corresponding variations of solar wind variables and geomagnetic activity indices. This is the first attempt, to our knowledge, to derive a ULF wave index from LEO satellite data. The technique can be potentially used to define a new Level 2 product from the mission, the Swarm ULF wave index, which would be suitable for space weather applications. Keywords. Space plasma physics (waves and instabilities)
The pyrogeography of eastern boreal Canada from 1901 to 2012 simulated with the LPJ-LMfire model
Authors: Chaste Emeline , Girardin Martin P. , Kaplan Jed O. , Portier Jeanne , Bergeron Yves , Hély Christelle
Published: March 2018

Abstract. Wildland fires are the main natural disturbance shaping forest
structure and composition in eastern boreal Canada. On average, more than
700 000 ha of forest burns annually and causes as much as CAD 2.9 million
worth of damage. Although we know that occurrence of fires depends upon the
coincidence of favourable conditions for fire ignition, propagation, and fuel
availability, the interplay between these three drivers in shaping
spatiotemporal patterns of fires in eastern Canada remains to be evaluated.
The goal of this study was to reconstruct the spatiotemporal patterns of fire
activity during the last century in eastern Canada's boreal forest as a
function of changes in lightning ignition, climate, and vegetation. We
addressed this objective using the dynamic global vegetation model
LPJ-LMfire, which we parametrized for four plant functional types (PFTs) that
correspond to the prevalent tree genera in eastern boreal Canada
(Picea, Abies, Pinus, Populus).
LPJ-LMfire was run with a monthly time step from 1901 to 2012 on a
10 km2 resolution grid covering the boreal forest from Manitoba to
Newfoundland. Outputs of LPJ-LMfire were analyzed in terms of fire frequency,
net primary productivity (NPP), and aboveground biomass. The predictive
skills of LPJ-LMfire were examined by comparing our simulations of annual
burn rates and biomass with independent data sets. The simulation adequately
reproduced the latitudinal gradient in fire frequency in Manitoba and the
longitudinal gradient from Manitoba towards southern Ontario, as well as the
temporal patterns present in independent fire histories. However, the
simulation led to the underestimation and overestimation of fire frequency at
both the northern and southern limits of the boreal forest in Québec. The
general pattern of simulated total tree biomass also agreed well with
observations, with the notable exception of overestimated biomass at the
northern treeline, mainly for PFT Picea. In these northern areas,
the predictive ability of LPJ-LMfire is likely being affected by the low
density of weather stations, which leads to underestimation of the strength
of fire–weather interactions and, therefore, vegetation consumption during
extreme fire years. Agreement between the spatiotemporal patterns of fire
frequency and the observed data across a vast portion of the study area
confirmed that fire therein is strongly ignition limited. A drier climate
coupled with an increase in lightning frequency during the second half of the
20th century notably led to an increase in fire activity. Finally, our
simulations highlighted the importance of both climate and fire in
vegetation: despite an overarching CO2-induced enhancement of NPP in
LPJ-LMfire, forest biomass was relatively stable because of the compensatory
effects of increasing fire activity.
Modelling biogeochemical processes in sediments from the north-western Adriatic Sea: response to enhanced particulate organic carbon fluxes
Authors: Brigolin Daniele , Rabouille Christophe , Bombled Bruno , Colla Silvia , Vizzini Salvatrice , Pastres Roberto , Pranovi Fabio
Published: March 2018

Abstract. This work presents the result of a study carried out in the north-western Adriatic Sea, by combining two different types of biogeochemical models with field sampling efforts. A longline mussel farm was taken as a local source of perturbation to the natural particulate organic carbon (POC) downward flux. This flux was first quantified by means of a pelagic model of POC deposition coupled to sediment trap data, and its effects on sediment bioirrigation capacity and organic matter (OM) degradation pathways were investigated constraining an early diagenesis model by using original data collected in sediment porewater. The measurements were performed at stations located inside and outside the area affected by mussel farm deposition. Model-predicted POC fluxes showed marked spatial and temporal variability, which was mostly associated with the dynamics of the farming cycle. Sediment trap data at the two sampled stations (inside and outside of the mussel farm) showed average POC background flux of 20.0–24.2 mmol C m−2 d−1. The difference of organic carbon (OC) fluxes between the two stations was in agreement with model results, ranging between 3.3 and 14.2 mmol C m−2 d−1, and was primarily associated with mussel physiological conditions. Although restricted, these changes in POC fluxes induced visible effects on sediment biogeochemistry. Observed oxygen microprofiles presented a 50 % decrease in oxygen penetration depth (from 2.3 to 1.4 mm), accompanied by an increase in the O2 influx at the station below the mussel farm (19–31 versus 10–12 mmol O2 m−2 d−1) characterised by higher POC flux. Dissolved inorganic carbon (DIC) and NH4+ concentrations showed similar behaviour, with a more evident effect of bioirrigation underneath the farm. This was confirmed through constraining the early diagenesis model, of which calibration leads to an estimation of enhanced and shallower bioirrigation underneath the farm: bioirrigation rates of 40 yr−1 and irrigation depth of 15 cm were estimated inside the shellfish deposition footprint versus 20 yr−1 and 20 cm outside. These findings were confirmed by independent data on macrofauna composition collected at the study site. Early diagenesis model results indicated a larger organic matter mineralisation below the mussel farm (11.1 versus 18.7 mmol m−2 d−1), characterised by similar proportions between oxic and anoxic degradation rates at the two stations, with an increase in the absolute values of oxygen consumed by OM degradation and reduced substances re-oxidation underneath the mussel farm.
Patterns and controls of soil respiration and its temperature
sensitivity in grassland ecosystems across China
Authors: Feng Jiguang , Wang Jingsheng , Song Yanjun , Zhu Biao
Published: March 2018

Abstract. Soil respiration (Rs), a key process in the terrestrial carbon cycle, is very sensitive to climate change. In this study, we synthesized 54 measurements of annual Rs and 171 estimates of Q10 value (the temperature sensitivity of soil respiration) in grasslands across China. We quantitatively analyzed their spatial patterns and controlling factors in five grassland types, including temperate typical steppe, temperate meadow steppe, temperate desert steppe, alpine grassland, and warm-tropical grassland. Results showed that the mean (± SE) annual Rs was 582.0 ± 57.9 g C m−2 yr−1 across Chinese grasslands. Annual Rs significantly differed among grassland types, and positively correlated with mean annual temperature, mean annual precipitation, soil organic carbon content and aboveground biomass, but negatively correlated with latitude and soil pH (P < 0.05). Among these factors, mean annual precipitation was the primary factor controlling the spatial variation of annual Rs in Chinese grasslands. The mean contributions of growing season Rs and heterotrophic respiration to annual Rs were 78.7 % and 72.8 %, respectively. Moreover, the mean (± SE) of Q10 across Chinese grasslands was 2.60 ± 0.08, ranging from 1.03 to 8.13, and varied largely within and among grassland types, and among soil temperature measurement depths. Generally, the seasonal variation of soil respiration in Chinese grasslands cannot be well explained by soil temperature using the van't Hoff equation. Longitude and altitude were the dominant driving factors and accounted for 26.0 % of the variation in Q10 derived by soil temperature at the depth of 5 cm. Overall, our findings advance our understanding of the spatial variation and environmental control of soil respiration and Q10 across Chinese grasslands, and also improve our ability to predict soil carbon efflux under climate change on the regional scale.
Coastal primary productivity changes over the last millennium: a case study from the Skagerrak (North Sea)
Authors: Binczewska Anna , Risebrobakken Bjørg , Polovodova Asteman Irina , Moros Matthias , Tisserand Amandine , Jansen Eystein , Witkowski Andrzej
Published: March 2018

Abstract. A comprehensive multi-proxy study on two sediment cores from western and central Skagerrak was performed in order to detect the variability and causes of marine primary productivity changes in the investigated region over the last 1100 years. The cores were dated by Hg pollution records and AMS 14C dating and analysed for palaeoproductivity proxies such as total organic carbon, δ13C, total planktonic foraminifera, benthic foraminifera (total as well as abundance of Brizalina skagerrakensis and other palaeoproductivity taxa) and palaeothermometers such as Mg / Ca and δ18O. Our results reveal three periods with changes in productivity in the Skagerrak region: (i) moderate productivity at ~ CE 900–1200; (ii) low to moderate productivity at ~ CE 1200–1600 and (iii) high productivity at ~ CE 1600–present. During ~ CE 900–1200, moderate productivity was likely driven by the nutrients transported with the warm Atlantic water inflow associated with a tendency for a persistent positive NAO phase during the warm climate of the Medieval Climate Anomaly. The following low productivity period at ~ CE 1200–1600 was likely caused by a lower contribution of nutrient-rich Atlantic water due to a generally more negative NAO phase and a shift to the more variable and generally cooler climate conditions of the Little Ice Age. At that time the nutrient supply was largely sustained by the Baltic Sea outflow and river runoff associated with land-use changes. Since ~ CE 1600 towards present day our data point to an increased nutrient content in the Skagerrak waters. This increased nutrient content was likely caused by enhanced inflow of warm Atlantic water, increased Baltic outflow, intensified river runoff and enhanced human impact through agriculture expansion and industrial development. Intensified human impact likely increased nutrient transport to the Skagerrak and caused changes in the oceanic carbon isotope budget, known as the Suess effect, which is clearly visible in our records as a negative shift in δ13C values from ~ CE 1750. In addition, a higher benthic foraminiferal Mn / Ca suggests slightly decreased bottom water oxygen conditions between ~ CE 1050 and 1400 in the central Skagerrak and in the last 70 years at both studied locations.
Quantification of the impacts of climate change and human agricultural activities on oasis water requirements in an arid region: a case study of the Heihe River basin, China
Authors: Liu Xingran , Shen Yanjun
Published: March 2018

Abstract. Ecological
deterioration in arid regions caused by agricultural
development has become a global issue. Understanding water requirements of
the oasis ecosystems and the influences of human agricultural activities and
climate change is important for the sustainable development of oasis
ecosystems and water resource management in arid regions. In this study,
water requirements of the main oasis in Heihe River basin during 1986–2013
were analyzed and the amount showed a sharp increase from 10.8 × 108 m3
in 1986 to 19.0 × 108 m3 in 2013. Both
human agricultural activities and climate change could lead to the increase
in water requirement. To quantify the contributions of agricultural
activities and climate change to the increase in water requirements, partial
derivative and slope method were used. Results showed that climate change and
human agricultural activities, such as oasis expansion and changes in land
cropping structure, has contributed to the increase in water requirement at
rates of 6.9, 58.1, and 25.3 %, respectively. Overall, human
agricultural activities were the dominant forces driving the increase in
water requirement. In addition, the contribution of oasis expanding to the
increased water requirement was significantly greater than that of
other concerned variables. This reveals that controlling the oasis scale is
extremely important and effective for balancing water for agriculture and
ecosystems and to achieving a sustainable oasis development in arid regions.
A 20-year record (1998–2017) of permafrost, active layer and meteorological conditions at a high Arctic permafrost research site (Bayelva, Spitsbergen)
Authors: Boike Julia , Juszak Inge , Lange Stephan , Chadburn Sarah , Burke Eleanor , Overduin Pier Paul , Roth Kurt , Ippisch Olaf , Bornemann Niko , Stern Lielle , Gouttevin Isabelle , Hauber Ernst , Westermann Sebastian
Published: March 2018

Abstract. Most permafrost is located in the Arctic, where frozen organic carbon makes it an important component of the global climate system. Despite the fact that the Arctic climate changes more rapidly than the rest of the globe, observational data density in the region is low. Permafrost thaw and carbon release to the atmosphere are a positive feedback mechanism that can exacerbate global warming. This positive feedback functions via changing land–atmosphere energy and mass exchanges. There is thus a great need to understand links between the energy balance, which can vary rapidly over hourly to annual timescales, and permafrost, which changes slowly over long time periods. This understanding thus mandates long-term observational data sets. Such a data set is available from the Bayelva site at Ny-Ålesund, Svalbard, where meteorology, energy balance components and subsurface observations have been made for the last 20 years. Additional data include a high-resolution digital elevation model (DEM) that can be used together with the snow physical information for snowpack modeling and a panchromatic image. This paper presents the data set produced so far, explains instrumentation, calibration, processing and data quality control, as well as the sources for various resulting data sets. The resulting data set is unique in the Arctic and serves as a baseline for future studies. The mean permafrost temperature is −2.8 °C, with a zero-amplitude depth at 5.5 m (2009–2017). Since the data provide observations of temporally variable parameters that mitigate energy fluxes between permafrost and atmosphere, such as snow depth and soil moisture content, they are suitable for use in integrating, calibrating and testing permafrost as a component in earth system models.The presented data are available in the Supplement for this paper (time series) and through the PANGAEA and Zenodo data portals: time series (https://doi.org/10.1594/PANGAEA.880120, https://zenodo.org/record/1139714) and HRSC-AX data products (https://doi.org/10.1594/PANGAEA.884730, https://zenodo.org/record/1145373).
Changing seasonality of moderate and extreme precipitation events in the Alps
Authors: Brönnimann Stefan , Rajczak Jan , Fischer Erich , Raible Christoph C. , Rohrer Marco , Schär Christoph
Published: March 2018

Abstract. The intensity of precipitation events is expected to increase in the future. The rate of increase depends on the strength or rarity of the events; very strong and rare events tend to follow the Clausius-Clapeyron relation, whereas weaker events or precipitation averages do not. An often overlooked aspect is seasonal occurrence of such events, which might change in the future. To address the impact of seasonality, we use a large ensemble of regional and global climate model simulations, comprising tens of thousands of model years of daily temperature and precipitation for the past, present and future. In order to make the data comparable, they are quantile-mapped to observation-based time series representative of the Aare catchment in Switzerland. Model simulations show no increase in annual maximum 1-day precipitation events (Rx1day) over the last 400 yrs and an increase of 10–20 % until the end of the century for a strong (RCP8.5) forcing scenario. This fits with a Clausius-Clapeyron scaling of temperature at the event day, which increases less than annual mean temperature. An important reason for this is a shift in seasonality. Rx1day events become less frequent in late summer and more frequent in early summer and early fall, when it is cooler. The seasonality shift is shown to be related to summer drying. Models with decreasing annual mean or summer mean precipitation show this behavior more strongly. The highest Rx1day per decade, in contrast, shows no change in seasonality in the future. This discrepancy implies that decadal-scale extremes are thermodynamically limited; conditions conducive to strong events still occur during hottest time of the year on a decadal scale. In contrast, Rx1day events are also limited by other factors. Conducive conditions are not reached every summer in the present, and even less so in the future. Results suggest that changes in the seasonal cycle need to be accounted for when preparing for moderately extreme precipitation events and assessing their socio-economic impacts.
A general theory on frequency and time–frequency analysis of irregularly sampled time series based on projection methods – Part 2: Extension to time–frequency analysis
Authors: Lenoir Guillaume , Crucifix Michel
Published: March 2018

Abstract. Geophysical time series are sometimes sampled irregularly along the time axis. The situation is particularly frequent in palaeoclimatology. Yet, there is so far no general framework for handling the continuous wavelet transform when the time sampling is irregular. Here we provide such a framework. To this end, we define the scalogram as the continuous-wavelet-transform equivalent of the extended Lomb–Scargle periodogram defined in Part 1 of this study (Lenoir and Crucifix, 2018). The signal being analysed is modelled as the sum of a locally periodic component in the time–frequency plane, a polynomial trend, and a background noise. The mother wavelet adopted here is the Morlet wavelet classically used in geophysical applications. The background noise model is a stationary Gaussian continuous autoregressive-moving-average (CARMA) process, which is more general than the traditional Gaussian white and red noise processes. The scalogram is smoothed by averaging over neighbouring times in order to reduce its variance. The Shannon–Nyquist exclusion zone is however defined as the area corrupted by local aliasing issues. The local amplitude in the time–frequency plane is then estimated with least-squares methods. We also derive an approximate formula linking the squared amplitude and the scalogram. Based on this property, we define a new analysis tool: the weighted smoothed scalogram, which we recommend for most analyses. The estimated signal amplitude also gives access to band and ridge filtering. Finally, we design a test of significance for the weighted smoothed scalogram against the stationary Gaussian CARMA background noise, and provide algorithms for computing confidence levels, either analytically or with Monte Carlo Markov chain methods. All the analysis tools presented in this article are available to the reader in the Python package WAVEPAL.
Permeability and seismic velocity anisotropy across a ductile-brittle
fault zone in crystalline rock
Authors: Wenning Quinn C. , Madonna Claudio , de Haller Antoine , Burg Jean-Pierre
Published: March 2018

Abstract. This study characterizes the elastic and fluid flow properties systematically across a ductile-brittle fault zone in crystalline rock at the Grimsel Test Site underground research laboratory. Anisotropic seismic velocities and permeability measured every 0.1 m in the 0.7 m across the transition zone from the host Grimsel granodiorite to the fault core show that foliation-parallel p- and s- wave velocities systematically increase from the host rock towards the fault core, while permeability is reduced nearest to the fault core. The results suggest that although brittle deformation has persisted in the recent evolution, antecedent ductile fabric continues to control the matrix elastic and fluid flow properties outside the fault core. The juxtaposition of the ductile strain zone next to the brittle zone, which is bounded inside the two mylonitic fault cores, causes a significant elastic, mechanical, and fluid flow heterogeneity, which has important implications for crustal deformation and fluid flow, and exploitation and use of geothermal energy and geologic waste storage. The results illustrate how physical characteristics of faults in crystalline rocks change in fault zones during the ductile to brittle transitions.
Home inspection: Mina Rees and national computing infrastructure
Authors: Losh Elizabeth
Published: March 2018

This essay seeks to undermine the primacy of Vannevar Bush as an architect of digital culture by reimagining the story of national computing infrastructure through the framework of feminized care work. It argues that early forms of networked computational media were situated in collaborative spaces in which labor oriented around utilization, maintenance, and other forms of labor associated with domesticity were understood to be essential duties. This essay also tries not to focus exclusively on programmers, engineers, or designers as potential “mothers of invention.” Using theoretical frameworks from global feminists working on contemporary information and communication technologies, this essay argues that those who engage with the messiness of networks of relationships that constitute infrastructure should be acknowledged as critical in the history of computing, particularly to question myths of disintermediation that are so dominant in technological discourses. In considering recovered histories of women in computing, this essay examines the career of Mina Rees, who headed the mathematics department of the U. S. Office of Naval Research, as a way to rethink the origin stories of computer history.
Comparison of vapour pressure deficit patterns during cucumber cultivation in a traditional high PE tunnel greenhouse and a tunnel greenhouse equipped with a heat accumulator
Authors: Konopacki Paweł J. , Treder Waldemar , Klamkowski Krzysztof
Published: March 2018

Plant productivity in protected cultivation is highly influenced by air temperature and humidity. The conditions relating to the moisture content of the air in protected plant cultivation are preferably defined by vapour pressure deficit (VPD), which describes the difference between the maximal and actual water vapour pressure (kPa). VPD is widely used as the parameter describing the climate conditions favourable for the development of fungal diseases and for highlighting conditions unfavourable for plant development. In protected cultivation, both the air temperature and the humidity are influenced by heating systems, and one such system is a heat accumulator, which may store the excessive heat produced during the day by converting the solar energy inside the plastic tunnel, and using it when plant heating is required. The tunnel equipped with a heat accumulator maintained an optimal level of humidity for a longer period, and significantly reduced the time of excessive air humidity. The longest time with an optimal VPD was recorded in August in a tunnel with an accumulator – 30.5% of total time vs. 22.3% of time for control tunnel. The highest difference of total time where the VPD was too low (below 0.2 kPa) was recorded in July – 12.4% of time in a tunnel with an accumulator vs. 39.1% of time for control tunnel. The highest difference of total time with an excessive VPD (over 1.4 kPa) was recorded in May – 12.1% of time in a tunnel with an accumulator vs. 17.9% of time for control tunnel. However, a situation beneficial for plant growth occurred every month during the investigated season.
Presencia del neofascismo en las democracias europeas contemporáneas
Authors: Omar García Olascoaga
Published: March 2018

Este artículo se propone constatar la presencia del neofascismo en las democracias europeas. El neofascismo no es un fenómeno estático y se manifiesta en diversas etapas: como escuelas de pensamiento, movimientos sociales, partidos políticos y regímenes políticos. Sin una ideología propia, el fascismo del periodo de entreguerras fue un fenómeno pragmático que evolucionó según sus circunstancias, por tal motivo, el neofascismo debe abordarse bajo esta misma dinámica, es decir, desde sus orígenes como movimiento hasta su última manifestación como régimen. En la actualidad, el neofascismo está presente como una opción política en el mercado electoral y su presencia en los recintos parlamentarios ha crecido en los últimos años, como lo atestigua el caso griego de Amanecer Dorado.
Speed of Reversion to PPP with Structural Breaks for Brazilian Cities
Authors: Bastos Felipe S. , Arruda Elano F. , Barbosa Rafael B. , Ferreira Roberto T.
Published: March 2018

This article analyzes the effect of introducing structural breaks in calculating the convergence speed of relative prices for Brazilian cities in the period from 1991.01 to 2016.11. Three structural break dates were endogenously chosen (1996.02, 2001.12 and 2010.10) and they represent different situations of the Brazilian economy, with impacts on intra-national relative prices. The convergence speed, measured by the half-life, declined by approximately 77% after controlling for these structural changes. The result was robust to changes in numeraire both for calculation of the half-life and estimation of the structural break dates, and indicates the importance of considering structural breaks in calculating intra-national purchasing power parity, as found in other studies.
Implementation of Silvopastoral Systems under Nutrient Cycling in Secondary Vegetation in the Amazon
Authors: Santos Perlon Maia dos , Santos Antonio Clementino dos , Neves Neto Durval Nolasco das , Oliveira Wallace Henrique de , Sousa Luciano Fernandes , Oliveira Leonardo Bernardes Taverny de
Published: March 2018

Silvopastoral systems can be implemented in idle secondary forests; however, they may affect nutrient cycling in these ecosystems. This farming practice using babassu palms (Attalea speciosa Mart.) and Mombasa grass (Panicum maximum Jacq.) has been little studied, and the nutrient cycling occurred during this practice is yet unknown. The goal of this paper was to detect the leaf litter accumulation, decomposition, and nutrient release occurring in silvopastoral systems in a babassu secondary forest, and compared the results with those of a native forest and of a pasture grown under full sunlight. The data relating to deposition, chemical composition, decomposition, and macronutrient release of leaf litter and pasture litter were evaluated by multivariate analyses. The results showed that forest thinning reduced leaf litter deposition and overall nutrient cycling but had no effect on decomposition rates. Conversely, the presence of grass in the understory promoted increased overall nutrient cycling rates. The cycling in integrated systems occurs more similar to that of forests than that of monocultures. The greater the thinning intensity the more similar the cycling will be relative to that occurring in pastures and in monocultures. The nutrients Ca, Mg, and N were the most affected by thinning. Moreover, the presence of grass in integrated systems provided an increased N and Mg cycling, whereas the thinning reduced Ca cycling. K showed the highest release and return ratio to the soil. Lastly, leaf litter from pasture areas showed higher contents of nutrients, decomposition rates, as well as an enhanced nutrient cycling capacity.