bluuebunny/crossref_metadata_2025 huggingface dataset:
Concreto autocompactante con materiales cementicios suplementarios de Colombia
Authors: Delvasto Arjona Silvio , Silva Urrego Yimmy Fernando
Published: March 2018

Una de las limitaciones para un uso más extenso del concreto autocompactante (CAC) es su costo elevado. Sin embargo, lo anterior puede ser obviado si se recurre a dosificarlo con adiciones o con fillers más económicos, que estén disponibles localmente. En este trabajo se presentan resultados de investigaciones realizadas por el Grupo de Investigación Materiales Compuestos de la Universidad del Valle (Colombia) sobre concretos autocompactantes (CACs) obtenidos a partir del empleo de algunas adiciones, tales como una ceniza volante (FA), una escoria de carbón (E), un lodo calcáreo de la industria papelera (LC), residuos de construcción y demolición como el residuo de mampostería (RM). También, algunos materiales de origen volcánico (MVP y MVT) y fillers como harina calcárea (LP). La evaluación en estado fresco de estos concretos, hecha de acuerdo a los estándares de European Federation of National Associations Representing for Concrete, EFNARC. mediante técnicas como el embudo en V, caja en L y flujo de asentamiento con cono de Abrams, mostró que cumplían las especificaciones de EFNARC para ser considerados CACs. El Índice de Actividad Puzolánica (ASTM C311) fue superior al 75%, que es un indicio positivo de la actividad del material. El mejor resultado en resistencia a la compresión fue de 43,4 MPa para un CAC conteniendo 35 % en peso de FA con respecto al cemento y un contenido total de 550 Kg de cementante. El cemento portland utilizado presentaba ya una adición (35% en peso), por lo tanto, la relación de material total suplementario (318 Kg por metro cúbico de CAC fue significativamente superior al equivalente de cemento sin adición (232 Kg por metro cúbico de CAC) para un total de material cementante de 550 Kg/metro cúbico de CAC. Las resistencias a la tracción indirecta fueron correlativas con las de compresión. Los resultados obtenidos indican que la elevada demanda de finos de los CACs puede abordarse mediante el empleo de subproductos industriales o residuos de construcción y demolición. Este empleo no solo disminuye los costos, también reduce la huella de carbono y ofrece una alternativa de valorización por uso de los materiales estudiados. DOI: http://dx.doi.org/10.4995/HAC2018.2018.6090
Comportamiento diferido en estado fisurado de elementos de UHPFRC a flexotracción
Authors: Llano-Torre Aitor , López Juan Ángel , Martí-Vargas José R. , Serna Pedro
Published: March 2018

Se pretende estudiar y evaluar el comportamiento a largo plazo de los Hormigones de Ultra Alta Resistencia Reforzados con Fibras (UHPFRC). Para ello se ha diseñado una campaña experimental que cubre todos los aspectos del comportamiento del UHPFRC en estados de carga mantenida en el tiempo. Una primera fase comprende la caracterización tanto a compresión como a flexotracción de las características de la dosificación estudiada. En una segunda fase de larga duración se realizarán ensayos de fluencia a compresión, retracción y fluencia a flexotracción en dos tamaños de probetas diferentes para evaluar la influencia de la escala y esbeltez en los resultados. En total se han fabricado tres tipos diferentes de probetas de una misma dosificación de hormigón UHPFRC. Las probetas cilíndricas (Ø100x200mm) se utilizarán para los ensayos de compresión, control de retracción y fluencia a compresión siguiendo la metodología ASTM C512. Dos tamaños diferentes de probetas prismáticas fueron fabricadas: una con dimensiones estándar de 150x150x600mm y otras de mayor esbeltez de 150x40x600mm. Estas probetas fueron prefisuradas y posteriormente colocadas en los bastidores de fluencia para los ensayos de flexotracción de larga duración. En función de las dimensiones de las probetas, se han utilizado dos criterios de fisuración diferentes: una abertura de fisura CMOD de 0.35 mm en el caso de las probetas de dimensiones estándar y una pérdida de rigidez del 50% en el caso de las probetas esbeltas. La duración de los ensayos de fluencia está prevista que sea de un mínimo de 9 meses.DOI: http://dx.doi.org/10.4995/HAC2018.2018.6144
Avaliação da durabilidade do concreto autoadensável com diferentes teores de fíler calcário em substituição ao cimento Portland
Authors: Miranda Luiza Rodrigues Meira de , Resende Fabrício Gonzales de , Capuzzo Valdirene Maria Silva
Published: March 2018

O concreto autoadensável (CAA) é uma mistura que está inclusa em um grupo de concretos que possuem tecnologias inovadoras para a sua utilização, os denominados Concretos Especiais. Para que um concreto possa receber a denominação de autoadensável é imprescindível que ele possua, simultaneamente, três características: fluidez, habilidade passante e coesão. Quando comparado ao concreto convencional, o CAA exige um maior cuidado na sua dosagem e produção, sendo necessário um controle rígido na escolha dos materiais e na sua variabilidade durante o processo. Por ser um material relativamente novo no meio técnico, poucas foram as pesquisas que trataram da durabilidade do CAA. Sabe-se que um dos principais mecanismos de deterioração do concreto é a carbonatação, que ocorre pela reação entre o dióxido de carbono da atmosfera e compostos hidratados do cimento, e está diretamente ligada à facilidade que o CO2 tem para difundir-se no interior do concreto, às condições ambientais e às propriedades de permeabilidade. A dosagem do concreto foi realizada utilizando o conceito da composição do esqueleto granular através do ensaio de massa unitária no estado compactado e os critérios do ACI 237R-07. Optou-se por fixar a relação água/aglomerante em 0,55, a fim de representar o cenário de maior vulnerabilidade do material. Foram realizados três traços de concreto, sendo o referência com 0% de fíler calcário e outros dois traços com 10% e 20% de fíler calcário em substituição ao cimento Portland. No estado fresco foram realizados os ensaios de espalhamento, caixa L, funil V, índice de estabilidade visual e massa específica. Para determinação das propriedades mecânicas foram executados os ensaios de resistência à compressão simples axial, resistência à tração por compressão diametral e módulo de elasticidade. O ensaio de carbonatação acelerada seguiu as recomendações da ISO 1920-12:2015. Com os resultados obtidos, tanto foi possível classificar esse CAA conforme os critérios da NBR 15823:2010, quanto também avaliar o comportamento da carbonatação acelerada no concreto autoadensável com diferentes consumos de cimento Portland.DOI: http://dx.doi.org/10.4995/HAC2018.2018.6242
Estudo da microcelulose em compósitos cimentícios
Authors: Vanderlei Romel Dias , Silva Lívia Fernanda , Parveen Shama , Gomes Filho Aloysio , Fangueiro Raul , Sardeiro Paula
Published: March 2018

Materiais em escala nano e micro oferecem novas possibilidades para compósitos cimentícios com melhor desempenho mecânico. Os tamanhos reduzidos permitem interações entre a celulose e o sistema de cimento, contribuindo de forma potencial para o combate das microfissuras e aumento da resistência do concreto.  A metodologia da pesquisa seguiu um roteiro em que foram realizados ensaios com argamassas confeccionadas contendo diferentes dosagens de MCC em relação à massa de cimento, em que foram feitos os ensaios de índice de consistência, resistência à compressão, resistência aflexão e absorção. Em ensaio de índice de consistência observou-se que à medida que se aumentam as taxas de MCC nos compósitos cimentícios há um decaimento progressivo da consistência (mm). Em relação às resistências à compressão observou-se aumento de resistência em todas as idades, com inserção da MCC em 0,2% de adição. Em relação à resistência à flexão há um aumento progressivo até a porcentagem de 0,6% de MCC, sendo esta que deteve o pico máximo de resistência de 7,67 MPa.Em ensaio de absorção observou-se que quanto maiores foram às taxas de MCC nos compósitos cimentícios maiores foram os índices de absorção, tendo um suave declínio da taxa de 0,8% de MCC a 1% de MMC.DOI: http://dx.doi.org/10.4995/HAC2018.2018.6275
Tiempos de fraguado, consistencia y propiedades mecánicas de hormigón de ultra alta resistencia con fibras (UHPRC)
Authors: Giménez Carbo Ester , Torres Remon Raquel , Serna Ros Pedro
Published: March 2018

El objetivo del trabajo es el desarrollo de dosificaciones de hormigón de ultra alta resistencia con fibras, que pueda ser utilizado con la técnica de puesta en obra de la proyección. En este estudio se analizan una serie de mezclas de UHPFRC con diferente cantidad, tipo de aditivos (plastificantes y acelerantes de fraguado) y diferentes tiempos de mezclado para conseguir hormigones que se puedan colocar en obra proyectados, con tiempos de fraguado ultrarápido y altas resistencias mecánicas iniciales. Se estudia la trabajabilidad, la consistencia, los tiempos de fraguado y las resistencias mecánicas (flexión y compresión) de las distintas mezclas. Los resultados mostraron dosificaciones con tiempos de inicio de fraguado inferior a 1 minutos y  muy buenas propiedades mecánicas a las 24horas, sin reducir la alta resistencia a compresión a los 28 días. A partir de los resultados obtenidos, se proponen diferentes utilizaciones de estas mezclas, teniendo en cuenta el nuevo contexto en el campo de la construcción, con la aparición de nuevas técnicas de puesta en obra del hormigón.DOI: http://dx.doi.org/10.4995/HAC2018.2018.6380
Nuevos hormigones celulares geopoliméricos aireados con agua oxigenada: síntesis y propiedades
Authors: Payá Bernabeu Jordi , Font Pérez Alba , Monzó Balbuena José María , Soriano Martínez Lourdes , Borrachero Rosado María Victoria
Published: March 2018

Los hormigones ligeros representan, hoy en día, una alternativa interesante en la industria de la construcción. Caracterizados por su baja densidad y moderada resistencia mecánica, son excelentes aislantes térmicos y acústicos. Dentro de este tipo de materiales, se clasifica el hormigón celular. Se trata de una pasta o mortero de cemento Portland con un sistema cerrado de microburbujas de aire que ocupa hasta el 85% del material.  Este sistema se puede generar mediante la adición de: i) agentes tensoactivos; o ii) agentes generadores de gas. Entre estos últimos se encuentran el polvo de aluminio metálico (por generación de hidrógeno molecular) y el agua oxigenada (por generación de oxígeno molecular). Una forma de obtener este tipo de hormigones celulares con menor impacto medioambiental es por medio del uso de matrices geopoliméricas, de modo que el cemento portland es sustituido por un precursor y una disolución activadora alcalina. En este trabajo se estudia el efecto que produce el agua oxigenada en sistemas geopoliméricos basados en residuo de catalizador de craqueo catalítico (FCC). El activador es una mezcla de hidróxido sódico y de silicato sódico, el cual produce la formación de geles N-A-S-H. Dicho medio altamente alcalino también activa la descomposición del agua oxigenada, que evoluciona originando oxígeno molecular. Este gas es atrapado por la matriz del material en estado fresco y da lugar a un material celular con poros que van desde unas pocas micras hasta millares de micras. Los materiales resultantes se han caracterizado a nivel microestructural (químico y físico) y a nivel mecánico, y se ha medido sus propiedades térmicas. Así, se ha analizado el tipo de productos cementantes generados por medio de la termogravimetría, FESEM/EDS y de la difracción de rayos X. Se ha caracterizado la distribución de la estructura porosa por medio de las microscopías óptica y electrónica con el objeto de evaluar el tamaño de los poros. Se ha determinado la resistencia mecánica a compresión y, finalmente, se ha evaluado la conductividad térmica asociada a este tipo de materiales, comparando con los valores obtenidos en otros hormigones celulares tanto de cemento portland como otros sistemas geopoliméricos.DOI: http://dx.doi.org/10.4995/HAC2018.2018.6453
Resistencia de los hormigones elaborados con árido reciclado frente a ciclos de hielo-deshielo
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 sector de los pavimentos es una de las aplicaciones del hormigón donde mejor aceptación ha experimentado la utilización de áridos reciclados. Centrándose principalmente en la incorporación de áridos reciclados procedentes hormigón en su totalidad, debido a que se trata de un material inerte y con un gran potencial de reutilización. Los prometedores resultados alcanzados por esta aplicación, ya que satisfacen los criterios de construcción sostenible en lo referente a medio ambiente, economía y sociedad, han fomentado el interés por aumentar el espectro de materiales susceptibles de ser reciclados. Teniendo en cuenta el significativo volumen que supone en países como España y Portugal la fracción cerámica del total de los residuos de construcción y demolición, este estudio persigue analizar el comportamiento de los hormigones que incorporan áridos reciclados frente a ciclos de hielo-deshielo, prestando especial atención a los distintos porcentajes de cerámica existente. Para llevar a cabo este estudio se elaboran 3 tipos de hormigón: un hormigón convencional con árido 100% natural, un hormigón reciclado donde el 50% del árido grueso natural es sustituido por árido reciclado mixto, el cual posee un 33% de contenido cerámico (suministrado por la empresa madrileña Tecnología y Reciclado S.L.), y un segundo hormigón reciclado, donde el porcentaje de sustitución se mantiene en 50%, pero en este caso el árido reciclado procede de material cerámico en su totalidad (suministrado por la empresa leonesa Bierzo Recicla S.L.).  En base a la norma EN 1339 (2004), las muestras se someten a 28 ciclos de hielo-deshielo en presencia de cloruros (solución con NaCl al 3%). La incorporación de sales descongelantes en el ensayo permite una mayor similitud entre las pruebas experimentales y la aplicación real en carreteras. Los resultados alcanzados demuestran que las caras moldeadas de los hormigones reciclados mantienen los niveles de resistencia a hielo-deshielo experimentados por el hormigón convencional cuando el porcentaje de material cerámico es bajo, y superan dichos niveles de resistencia cuando el porcentaje de cerámica aumenta. Para el caso de las superficies enrasadas, la presencia de árido reciclado supone una pérdida de resistencia a los ciclos de hielo-deshielo, siendo menos intensa esta pérdida cuanto mayor es el contenido cerámico existente en los áridos.DOI: http://dx.doi.org/10.4995/HAC2018.2018.6559
Estudio de las reacciones de hidratación temprana en el hormigón proyectado
Authors: Galan Garcia Isabel , Stauffacher Anina , Mittermayr Florian , Thumann Maria , Kusterle Wolfgang , Juilland Patrick , Stenger Christian , Lindlar Benedikt
Published: March 2018

El hormigón proyectado es un tipo de hormigón especial utilizado como soporte de rocas durante la construcción de túneles y excavación de minas, entre otras aplicaciones. Las principales características de este tipo de hormigón son el fraguado rápido y el desarrollo de una muy alta resistencia mecánica a edades tempranas, lo cual permite que el hormigón se fije a la base sin necesidad de un soporte extra, endureciéndose en pocos minutos. Las reacciones de hidratación que ocurren en las primeras horas en el hormigón proyectado determinan el desarrollo de las propiedades mecánicas y su estudio es de crucial importancia para entender y optimizar el comportamiento de este tipo de hormigones. El estudio de estas reacciones, sin embargo, resulta relativamente complicado por varias razones: (i) el hormigón proyectado endurece muy rápido, lo cual dificulta su manejo durante los ensayos experimentales, y (ii) composiciones similares mezcladas en el laboratorio no se comportan de forma similar a las proyectadas. En este trabajo se presenta una metodología experimental desarrollada para el estudio de las reacciones de hidratación que ocurren en el hormigón proyectado durante las primeras horas y su correlación con la resistencia mecánica.DOI: http://dx.doi.org/10.4995/HAC2018.2018.6907
Influencia de aditivos orgánicos en las propiedades reológicas de pastas de cemento de aluminato de calcio
Authors: Roig-Flores Marta , Palacios Marta , Martínez-Urbanos María , Alonso María Cruz
Published: March 2018

El cemento de aluminato de calcio (CAC) es un tipo de cemento utilizado en elementos constructivos que necesitan propiedades refractarias, debido a su resistencia a elevadas temperaturas. Sin embargo, este tipo de cemento presenta diversas dificultades para su puesta en obra debido a su fraguado rápido y la dificultad para obtener trabajabilidades elevadas con relaciones agua/cemento bajas. Este trabajo realiza un análisis de la reología obtenida al utilizar distintas familias de aditivos con CAC, incluyendo superplastificantes basados en policarboxilato, vinílicos, naftalenos o lignosulfonatos, así como aditivos retardadores como ácido cítrico y gluconato. Además, se estudia la influencia de la presencia de cenizas volantes y escorias de alto horno como adiciones minerales. Para ello se ha calculado el esfuerzo de cizalla umbral de pastas con aditivos a partir de los valores de escurrimiento a lo largo del tiempo. Los resultados muestran la elevada compatibilidad de los aditivos tipo lignosulfonato y de los retardadores manteniéndose la fluidez hasta 90 minutos tras el inicio de la hidratación. Finalmente, la adición conjunta de aditivos basados en lignosulfonato y policarboxilato ha permitido obtener una fluidez óptima de los sistemas de CAC.DOI: http://dx.doi.org/10.4995/HAC2018.2018.7226
Ultra high Performance Concrete - Materials Formulations and Serviceability based Design
Authors: Mobasher Barzin , Yao Yiming , Arora Aashay , Neithalath Narayanan
Published: March 2018

Materials and mechanical design procedures for ultra-high performance cement composites (UHPC) members based on analytical models are addressed. A procedure for the design of blended components of UHPC is proposed using quaternary cementitious materials. The blending procedures are used using a packing and rheology optimization approach to blend high performance mixtures using non-proprietary formulations. Closed-form solutions of moment-curvature responses of UHPC are derived based on elastic-plastic compressive model and trilinear strain hardening tension stress strain responses. Tension stiffening behavior of UHPC due to fiber toughening and distributed cracking is then incorporated in the cross-sectional analysis. Load-deflection responses for beam members are obtained using moment-area, and direct integration approach. The proposed models provide insights in the design of SHCC to utilize the hardening properties after cracking. Using proper parameters, generalized materials model developed are applicable to both SHCC and strain softening cement composites such as steel fiber reinforced concrete (SFRC), textile reinforced concrete (TRC) and ultra-high performance concrete (UHPC).DOI: http://dx.doi.org/10.4995/HAC2018.2018.8263
Lower tropospheric ozone over India and its linkage to the South Asian monsoon
Authors: Lu Xiao , Zhang Lin , Liu Xiong , Gao Meng , Zhao Yuanhong , Shao Jingyuan
Published: March 2018

Abstract. Lower tropospheric (surface to 600 hPa) ozone over India poses serious risks
to both human health and crops, and potentially affects global ozone distribution
through frequent deep convection in tropical regions. Our current
understanding of the processes controlling seasonal and long-term variations in
lower tropospheric ozone over this region is rather limited due to spatially
and temporally sparse observations. Here we present an integrated process
analysis of the seasonal cycle, interannual variability, and long-term trends
of lower tropospheric ozone over India and its linkage to the South Asian
monsoon using the Ozone Monitoring Instrument (OMI) satellite observations
for years 2006–2014 interpreted with a global chemical transport model
(GEOS-Chem) simulation for 1990–2010. OMI observed lower tropospheric ozone
over India averaged for 2006–2010, showing the highest concentrations
(54.1 ppbv) in the pre-summer monsoon season (May) and the lowest
concentrations (40.5 ppbv) in the summer monsoon season (August). Process
analyses in GEOS-Chem show that hot and dry meteorological conditions and
active biomass burning together contribute to 5.8 Tg more ozone being produced in
the lower troposphere in India in May than January. The onset of the summer
monsoon brings ozone-unfavorable meteorological conditions and strong upward
transport, which all lead to large decreases in the lower tropospheric ozone
burden. Interannually, we find that both OMI and GEOS-Chem indicate strong positive correlations (r=0.55–0.58) between ozone and
surface temperature in pre-summer monsoon seasons, with larger correlations
found in high NOx emission regions reflecting NOx-limited
production conditions. Summer monsoon seasonal mean ozone levels are strongly
controlled by monsoon strengths. Lower ozone concentrations are found in
stronger monsoon seasons mainly due to less ozone net chemical production.
Furthermore, model simulations over 1990–2010 estimate a mean annual trend
of 0.19 ± 0.07 (p value < 0.01) ppbv yr−1 in Indian lower
tropospheric ozone over this period, which are mainly driven by increases in
anthropogenic emissions with a small contribution (about 7 %) from global
methane concentration increases.
Aerosol–cloud interactions in mixed-phase convective clouds – Part 1: Aerosol perturbations
Authors: Miltenberger Annette K. , Field Paul R. , Hill Adrian A. , Rosenberg Phil , Shipway Ben J. , Wilkinson Jonathan M. , Scovell Robert , Blyth Alan M.
Published: March 2018

Abstract. Changes induced by perturbed aerosol conditions in moderately deep mixed-phase convective clouds
(cloud top height ∼ 5 km)
developing along sea-breeze convergence
lines are investigated with high-resolution numerical model simulations. The
simulations utilise the newly developed Cloud–AeroSol Interacting Microphysics (CASIM) module for
the Unified Model (UM), which allows for the representation of the two-way interaction between cloud and
aerosol fields. Simulations are evaluated against observations collected during the COnvective
Precipitation Experiment (COPE) field campaign over the southwestern peninsula of the UK in 2013.
The simulations compare favourably with observed thermodynamic profiles, cloud base cloud droplet
number concentrations (CDNC), cloud depth, and radar reflectivity statistics. Including the
modification of aerosol fields by cloud microphysical processes improves the correspondence with
observed CDNC values and spatial variability, but reduces the agreement with observations for
average cloud size and cloud top height. Accumulated precipitation is suppressed for higher-aerosol conditions before clouds become organised
along the sea-breeze convergence lines. Changes in precipitation are smaller in simulations with
aerosol processing. The precipitation suppression is due to less efficient precipitation production
by warm-phase microphysics, consistent with parcel model predictions. In contrast, after convective cells organise along the sea-breeze convergence zone, accumulated
precipitation increases with aerosol concentrations. Condensate production increases with the
aerosol concentrations due to higher vertical velocities in the convective cores and higher cloud
top heights. However, for the highest-aerosol scenarios, no further increase in the condensate
production occurs, as clouds grow into an upper-level stable layer. In these cases, the reduced
precipitation efficiency (PE) dominates the precipitation response and no further precipitation
enhancement occurs. Previous studies of deep convective clouds have related larger vertical
velocities under high-aerosol conditions to enhanced latent heating from freezing.
In the presented simulations changes in latent heating above the 0∘C are negligible, but latent
heating from condensation increases with aerosol concentrations. It is hypothesised that this
increase is related to changes in the cloud field structure reducing the mixing of environmental air
into the convective core. The precipitation response of the deeper mixed-phase clouds along well-established convergence lines
can be the opposite of predictions from parcel models. This occurs when clouds interact with a
pre-existing thermodynamic environment and cloud field structural changes occur that are not
captured by simple parcel model approaches.
Investigating the yield of H2O and H2 from methane oxidation in the stratosphere
Authors: Frank Franziska , Jöckel Patrick , Gromov Sergey , Dameris Martin
Published: March 2018

Abstract. An important driver of climate change is stratospheric water vapour (SWV), which in turn is influenced by the oxidation of atmospheric methane (CH4). In order to parameterize the production of water vapour (H2O) from CH4 oxidation, it is often assumed that the oxidation of one CH4 molecule yields exactly two molecules of H2O. However, this assumption is based on an early study, which also gives evidence, that this is not true at all altitudes. In the current study we re-evaluate this assumption with a comprehensive systematic analysis using a state-of-the art Chemistry-Climate model (CCM), namely the ECHAM/MESSy Atmospheric Chemistry (EMAC) model, and present three approaches to investigate the yield of H2O and hydrogen gas (H2) from CH4 oxidation. We thereby make use of Module Efficiently Calculating the Chemistry of the Atmosphere (MECCA) in a box model and global model configuration. Furthermore, we use the kinetic chemistry tagging technique (MECCA-TAG) to investigate the chemical pathways between CH4, H2O and H2, by being able to distinguish hydrogen atoms stemming from CH4 and other sources. We apply three approaches, which all agree that assuming a yield of 2 overestimates the production of H2O in the lower stratosphere (calculated as 1.5–1.7). Additionally, transport and subsequent photochemical processing of longer-lived intermediates raise the local yield values in the upper stratosphere and lower mesosphere above 2 (maximum > 2.2). In the middle and upper mesosphere, the influence of loss and recycling of H2O increases, making it a crucial factor in the parameterization of the yield of H2O from CH4 oxidation. An additional sensitivity study with the Chemistry As A Boxmodel Application (CAABA) shows a dependence of the yield on the hydroxyl radical (OH) abundance. No significant temperature dependence is found. We focus representatively on the tropical zone between 23° S–23° N, where seasonal variations are negligible. It is found in the global approach that presented results are mostly valid for mid latitudes as well. Our conclusions question the use of a constant yield of H2O from CH4 oxidation in climate modeling and encourage to apply comprehensive parameterizations that follow the vertical profiles of the H2O yield derived here and take the chemical H2O loss into account.
Ice-nucleating efficiency of aerosol particles and possible sources at
three coastal marine sites
Authors: Si Meng , Irish Victoria E. , Mason Ryan H. , Vergara-Temprado Jesús , Hanna Sarah , Ladino Luis A. , Yakobi-Hancock Jacqueline D. , Schiller Corinne L. , Wentzell Jeremy J. B. , Abbatt Jonathan P. D. , Carslaw Ken S. , Murray Benjamin J. , Bertram Allan K.
Published: March 2018

Abstract. Despite the importance of ice-nucleating particles (INPs) for climate and precipitation, our understanding of these particles is far from complete. Here, we investigated INPs at three coastal marine sites in Canada, two at mid-latitude (Amphitrite Point and Labrador Sea), and one in the Arctic (Lancaster Sound). At all three sites, the ice-nucleating efficiency on a per number basis (expressed as the fraction of aerosol particles acting as an INP) was strongly dependent on the size. For example, at diameters of around 0.2 µm, approximately 1 in 106 particles acted as an INP at −25 ºC, while at diameters of around 8 µm, approximately 1 in 10 particles acted as an INP at −25 ºC. The ice-nucleating efficiency on a per surface area basis (expressed as the surface active site density, ns) was also dependent on the size, with larger particles being more efficient at nucleating ice. The ns values of supermicron particles at Amphitrite Point and Labrador Sea were larger than previously measured ns values of sea spray aerosol, suggesting that sea spray aerosol was not a major contributor to the supermicron INP population at these two sites. Consistent with this observation, a global model of INP concentrations under-predicted the INP concentrations when assuming only marine organics as INPs. On the other hand, assuming only K-feldspar as INPs, the same model was able to reproduce the measurements at a freezing temperature of −25 ºC, but under-predicted INP concentrations at −15 ºC, suggesting that the model is missing a source of INPs active at a freezing temperature of −15 ºC.
Mesopause region temperature variability and its trend in southern Brazil
Authors: Venturini Mateus S. , Bageston José V. , Caetano Nattan R. , Peres Lucas V. , Bencherif Hassan , Schuch Nelson J.
Published: March 2018

Abstract. Nowadays, the study of the upper atmosphere is increasing, mostly because of
the need to understand the patterns of Earth's atmosphere. Since studies on
global warming have become very important for the development of new
technologies, understanding all regions of the atmosphere becomes an
unavoidable task. In this paper, we aim to analyze the temperature
variability and its trend in the mesosphere and lower thermosphere (MLT)
region during a period of 12 years (from 2003 to 2014). For this purpose,
three different heights, i.e., 85, 90 and 95 km, were focused on in order to
investigate the upper atmosphere, and a geographic region different to other
studies was chosen, in the southern region of Brazil, centered in the city of
Santa Maria, RS (29∘41′02′′ S; 53∘48′25′′ W). In
order to reach the objectives of this work, temperature data from the SABER
instrument (Sounding of the Atmosphere using Broadband Emission Radiometry),
aboard NASA's Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED)
satellite, were used. Finally, two cases were studied related to distinct
grids of latitude/longitude used to obtain the mean temperature profiles. The
first case considered a grid of 20∘ × 20∘ lat/long,
centered in Santa Maria, RS, Brazil. In the second case, the region was
reduced to a size of 15∘ × 15∘ in order to compare
the results and discuss the two cases in terms of differences or similarities
in temperature trends. Observations show that the size of the geographical
area used for the average temperature profiles can influence the results of
variability and trend of the temperature. In addition, reducing the time
duration of analyses from 24 to 12 h a day also influences the trend
significantly. For the smaller geographical region
(15∘ × 15∘) and the 12 h daily time window
(09:00–21:00 UT) it was found that the main contributions for the
temperature variability at the three heights were the annual and semi-annual
cycles and the solar flux influence. A smaller trend
(−0.02 ± 0.16 % decade−1) was found at 90 km height and
small positive trends (0.58 ± 0.26 % and
0.41 ± 0.19 % decade−1) were found at altitudes of 85 and
95 km, respectively.. Keywords. Atmospheric composition and structure (middle atmosphere – composition and chemistry; pressure, density, and temperature) – meteorology and atmospheric dynamics (climatology)
Case study of mesospheric front dissipation observed over the northeast of Brazil
Authors: Medeiros Amauri Fragoso , Paulino Igo , Wrasse Cristiano Max , Fechine Joaquim , Takahashi Hisao , Bageston José Valentin , Paulino Ana Roberta , Buriti Ricardo Arlen
Published: March 2018

Abstract. On 3 October 2005 a mesospheric front was observed over São João
do Cariri (7.4∘ S, 36.5∘ W).
This front propagated
to the northeast and appeared in the airglow images on the west side
of the observatory. By about 1.5 h later, it
dissipated completely when the front crossed the local zenith.
Ahead of the front, several ripple structures appeared during the
dissipative process of the front. Using coincident temperature
profile from the TIMED/SABER satellite and wind profiles from a meteor
radar at São João do Cariri, the background of the atmosphere
was investigated in detail. On the one hand, it was noted that a strong vertical wind
shear in the propagation direction of the front produced by
a semidiunal thermal tide was mainly responsible for the
formation of duct (Doppler duct), in which the front propagated up to
the zenith of the images. On the other hand, the evolution of the
Richardson number as well as the appearance of ripples ahead of
the main front suggested that a presence of instability in the
airglow layer that did not allow the propagation of the front to the
other side of the local zenith. Keywords. Atmospheric composition and structure (airglow and aurora) – meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides)
Manganese incorporation in living (stained) benthic foraminiferal shells: A bathymetric and in-sediment study in the Gulf of Lions (NW Mediterranean)
Authors: Ní Fhlaithearta Shauna , Fontanier Christophe , Jorissen Frans , Mouret Aurélia , Dueñas-Bohórquez Adriana , Anschutz Pierre , Fricker Mattias B. , Günther Detlef , de Lange Gert J. , Reichart Gert-Jan
Published: March 2018

Abstract. Manganese geochemistry in deep-sea sediments is known to vary greatly over the first few centimeters, which overlaps with the in-sediment depth habitats of several benthic foraminiferal species. Here we investigated manganese incorporation in benthic foraminiferal shell carbonate across a 6-station depth transect in the Gulf of Lions, NW Mediterranean to unravel the impacts of foraminiferal ecology and Mn pore water geochemistry. Over this transect water depth increases from 350 to 1987 m, while temperature (~ 13 °C) and salinity (~ 38.5) remained relatively constant. Manganese concentrations in the tests of living (Rose Bengal stained) benthic foraminiferal specimens of Hoeglundina elegans, Melonis barleeanus, Uvigerina mediterranea, Uvigerina peregrina were measured using laser ablation inductively coupled mass spectrometry (laser ablation ICP-MS). Pore water manganese concentrations show a decrease from shallow to deeper waters, which corresponds to a generally decreasing organic matter flux with water depth. Differences in organic matter loading at the sediment water interface affects oxygen penetration depth into the sediment and hence Mn pore water profiles. Mn / Ca values for the investigated foraminiferal species reflect pore water geochemistry and species-specific microhabitat in the sediment. The observed degree of variability within a single species is in–line with know ranges in depth habitat and gradients in redox conditions. Both Mn / Ca ratio and inter-specific variability hence reflect past Mn cycling and related early diagenetic processes within the sediment, making this a potential tool for bottom-water oxygenation and organic-matter fluxes. Dynamics of both in-sediment foraminiferal depth habitats and Mn cycling, however, limit the application of such a proxy to settings with relatively stable environmental conditions.
U–Th and 10Be constraints on sediment recycling in proglacial settings, Lago Buenos Aires, Patagonia
Authors: Cogez Antoine , Herman Frédéric , Pelt Éric , Reuschlé Thierry , Morvan Gilles , Darvill Christopher M. , Norton Kevin P. , Christl Marcus , Märki Lena , Chabaux François
Published: March 2018

Abstract. The estimation of sediment transfer times remains a challenge to our
understanding of sediment budgets and the relationships between
erosion and climate. Uranium (U) and thorium (Th) isotope
disequilibria offer a means of more robustly constraining sediment
transfer times. Here, we present new uranium and thorium
disequilibrium data for a series of nested moraines around Lago
Buenos Aires in Argentine Patagonia. The glacial chronology for the
area is constrained using in situ cosmogenic 10Be analysis
of glacial outwash. Sediment transfer times within the periglacial
domain were estimated by comparing the deposition ages of moraines
to the theoretical age of sediment production, i.e., the comminution
age inferred from U disequilibrium data and recoil loss factor
estimates. Our data show first that the classical comminution age
approach must include weathering processes accounted for by
measuring Th disequilibrium. Second, our combined data suggest that
the pre-deposition history of the moraine sediments is not
negligible, as evidenced by the large disequilibrium of the youngest
moraines despite the equilibrium of the corresponding glacial
flour. Monte Carlo simulations suggest that weathering was more
intense before the deposition of the moraines and that the transfer
time of the fine sediments to the moraines was on the order of
100–200 kyr. Long transfer times could result from a combination of
long sediment residence times in the proglacial lake (recurrence
time of a glacial cycle) and the remobilization of sediments from
moraines deposited during previous glacial cycles. 10Be
data suggest that some glacial cycles are absent from the preserved
moraine record (seemingly every second cycle), supporting a model of
reworking moraines and/or fluctuations in the extent of glacial
advances. The chronological pattern is consistent with the U–Th
disequilibrium data and the 100–200 kyr transfer time. This long
transfer time raises the question of the proportion of freshly
eroded sediments that escape (or not) the proglacial environments
during glacial periods.
The influence of intraocular pressure on the damping of a coupled speaker–air–eye system
Authors: Osmers Jan , Patzkó Ágnes , Hoppe Oskar , Sorg Michael , von Freyberg Axel , Fischer Andreas
Published: March 2018

Abstract. Although glaucoma is currently the world's most common cause of irreversible blindness, there is no curative therapy available to date. The major risk factor that can be influenced in order to stop disease progression is the eye pressure (IOP). Therefore early diagnosis of an altered IOP is essential for the goal of preserving vision. A novel IOP measurement principle for a handheld noncontact self-tonometer shall be validated. The measurement principle uses a pressure pulse generated by a loudspeaker to cause vibrations of the eye. In order to reach the required sound pressure, a closed pressure chamber is placed on the human orbit. With a microphone and a displacement sensor the dynamic behavior of the entire system is detected. In this article the abovementioned principle is being analyzed on porcine eyes under laboratory conditions. The combination of the loudspeaker, the pressure chamber, and the eye to be measured can be described as a coupled spring–mass–damper system. It is demonstrated for enucleated porcine eyes that a defined IOP variation leads to a change in the system's damping ratio. Considering only stochastic deviations, the derived standard uncertainty for the determination of the IOP amounts to < 1 mmHg in the physiological range. The in vitro measurements on porcine eyes help the understanding of the underlying physics and demand for further research on the influence of biometric parameters on eye vibrations. However, the laboratory results provide the basis for a gentle noncontact tonometry method with great applicational prospects. Data is currently being collected on human subjects in a clinical trial, to corroborate the measurement principle in vivo.
Geomorphological evolution of landslides near an active normal fault in northern Taiwan, as revealed by lidar and unmanned aircraft system data
Authors: Chang Kuo-Jen , Chan Yu-Chang , Chen Rou-Fei , Hsieh Yu-Chung
Published: March 2018

Abstract. Several remote sensing techniques, namely traditional aerial photographs, an unmanned aircraft system (UAS), and airborne lidar, were used in this study to decipher the morphological features of obscure landslides in volcanic regions and how the observed features may be used for understanding landslide occurrence and potential hazard. A morphological reconstruction method was proposed to assess landslide morphology based on the dome-shaped topography of the volcanic edifice and the nature of its morphological evolution. Two large-scale landslides in the Tatun volcano group in northern Taiwan were targeted to more accurately characterize the landslide morphology through airborne lidar and UAS-derived digital terrain models and images. With the proposed reconstruction method, the depleted volume of the two landslides was estimated to be at least 820 ± 20  ×  106 m3. Normal faulting in the region likely played a role in triggering the two landslides, because there are extensive geological and historical records of an active normal fault in this region. The subsequent geomorphological evolution of the two landslides is thus inferred to account for the observed morphological and tectonic features that are indicative of resulting in large and life-threatening landslides, as characterized using the recent remote sensing techniques.
Phase-dependent dynamics of breather collisions in the compact
Zakharov equation for envelope
Authors: Kachulin Dmitry , Gelash Andrey
Published: March 2018

Abstract. We study collisions of the solitary type coherent wave structures – breathers in the nonintegrable Zakharov equation for envelope describing gravity waves on the surface of deep water. The numerical simulations of breather interactions revealed several fundamentally different effects when compared to analytical two-soliton solutions of the nonlinear Schrodinger equation. The relative phase of the breathers is shown to be the key parameter determining the dynamics of the interaction. We show that the maximum of the amplitude amplification can significantly exceed the sum of the breather amplitudes. The breathers lose up to a few percent of their energy during the collisions due to radiation of incoherent waves and in addition exchange energy with each other. The level of the energy loss increases with large values of the wave steepness, and also with certain synchronisation of breather phases. Each of the breathers can gain or lose the energy after collision resulting in the increase or decrease of the amplitude. The magnitude of the space shifts that breathers acquire after collisions depends on the relative phase and can be either positive or negative.
Review article: Comparison of local particle filters and new implementations
Authors: Farchi Alban , Bocquet Marc
Published: March 2018

Abstract. Particle filtering is a generic weighted ensemble data assimilation method based on sequential importance sampling, suited for nonlinear and non-Gaussian filtering problems. Unless the number of ensemble members scales exponentially with the problem size, particle filter (PF) algorithms lead to weight degeneracy. This phenomenon is a consequence of the curse of dimensionality that prevents one from using PF methods for high-dimensional data assimilation. The use of local analyses to counteract the curse of dimensionality was suggested early on. However, implementing localisation in the PF is a challenge because there is no simple and yet consistent way of gluing locally updated particles together across domains. In this article, we review the ideas related to localisation and the PF in the geosciences. We introduce a generic and theoretical classification of local particle filter (LPF) algorithms, with an emphasis on the advantages and drawbacks of each category. Alongside with the classification, we suggest practical solutions to the difficulties of local particle filtering, that lead to new implementations and improvements in the design of LPF algorithms. The LPF algorithms are systematically tested and compared using twin experiments with the one-dimensional Lorenz 40-variables model and with a two-dimensional barotropic vorticity model. The results illustrate the advantages of using the optimal transport theory to design the local analysis. With reasonable ensemble sizes, the best LPF algorithms yield data assimilation scores comparable to those of typical ensemble Kalman filter algorithms.
Digital detritus: 'Error' and the logic of opacity in social media content moderation
Authors: Roberts Sarah T.
Published: March 2018

The late 2016 case of the Facebook content moderation controversy over the infamous Vietnam-era photo, “The Terror of War,” is examined in this paper for both its specifics, as well as a mechanism to engage in a larger discussion of the politics and economics of the content moderation of user-generated content. In the context of mainstream commercial social media platforms, obfuscation and secrecy work together to form an operating logic of opacity, a term and concept introduced in this paper. The lack of clarity around platform policies, procedures and the values that inform them lead users to wildly different interpretations of the user experience on the same site, resulting in confusion in no small part by the platforms’ own design. Platforms operationalize their content moderation practices under a complex web of nebulous rules and procedural opacity, while governments and other actors clamor for tighter controls on some material, and other members of civil society demand greater freedoms for online expression. Few parties acknowledge the fact that mainstream social media platforms are already highly regulated, albeit rarely in such a way that can be satisfactory to all. The final turn in the paper connects the functions of the commercial content moderation process on social media platforms like Facebook to their output, being either the content that appears on a site, or content that is rescinded: digital detritus. While meaning and intent of user-generated content may often be imagined to be the most important factors by which content is evaluated for a site, this paper argues that its value to the platform as a potentially revenue-generating commodity is actually the key criterion and the one to which all moderation decisions are ultimately reduced. The result is commercialized online spaces that have far less to offer in terms of political and democratic challenge to the status quo and which, in fact, may serve to reify and consolidate power rather than confront it.
No longer an orphan: evidence for appositive attachment from sentence comprehension
Authors: Dillon Brian , Frazier Lyn , Clifton Charles
Published: March 2018

In this paper, we investigate the comprehension of appositive relative clauses and nominal appositives. First, we present experimental evidence that suggests that nominal appositives and appositive relative clauses behave like other adjunct phrases with respect to ambiguity resolution (Experiment 1). Second, we show that an ambiguous nominal appositive can modify a distant syntactic head as easily across an appositive relative clause as across a restrictive relative clause (Experiment 2). Last, we show that syntactic repair is as successful across an appositive relative clause or parenthetical as it is across an at-issue restrictive relative clause (Experiment 3). Taken together, our results suggest that i) appositive relative clauses and nominal appositives are syntactically sited in a fashion comparable to restrictive relative clauses and ii) appositive phrases do not substantially reduce the availability of the syntactic material that precedes the appositive phrase as might have been expected if processing an appositive involved shifting attention to a higher structure, away from local preceding constituents. These results constitute an argument from sentence comprehension for a local syntactic attachment of appositive relative clauses and nominal appositives (cf. Jackendoff 1977; Potts 2005; de Vries 2006), and against so-called orphan analyses of appositive content (e.g. Ross 1967; Haegeman 1988).