443 research outputs found
Predicción de las propiedades mecánicas del cemento en la micro-escala
Prediction of the mechanical properties of cement paste at microscale has been done in this contribution by making use of 3D lattice fracture model.
The microstructure of cement paste is simulated by HYMOSTRUC3D first, which is represented in terms of sphere particles. Then the microstructure is converted into a voxel-based image, and a lattice system is constructed based on the image of the microstructure through ImgLat (Image to Lattice). A virtual uni-axial tensile test is configured and the fracture process is simulated by GLAK (Generalized Lattice Analysis Kernel). The outputs of fracture process simulation are the load-displacement diagram and micro-cracks propagation. The load-displacement diagram reveals the tensile behavior of cement paste at microscale, from which the elastic modulus and tensile strength can be obtained.
A numerical experiment is carried out to show how the model works, and the final results also demonstrate the feasibility of the above modeling procedure.En el presente trabajo se ha realizado una predicción de las propiedades mecánicas del cemento en la micro-escala, empleando un modelo de fractura reticular 3D.
En primer lugar se simula la micro-estructura del cemento mediante el código HYMOSTRUC3D, representando dicha micro-estructura mediante partículas esféricas. A continuación, la micro-estructura generada se convierte en una imagen basada en “vóxeles”, y se construye un sistema reticular basado en esa imagen mediante el código ImgLat (Image to Lattice). Se define un ensayo de tensión uniaxial virtual, y se simula el proceso de fractura usando el código GLAK (Generalized Lattice Análisis Kernel). Los resultados obtenidos de esta simulación del proceso de fractura son diagramas de carga-desplazamiento y propagación de micro-roturas. El diagrama de carga-desplazamiento caracteriza el comportamiento a fractura de la pasta de cemento en la micro-escala, y a partir de éste se puede obtener la resistencia a fractura y el módulo de elasticidad del material.
Con el objetivo de mostrar el funcionamiento de la simulación, se ha realizado un experimento teórico, cuyos resultados sirven para validar el modelo empleado
Measurement of advancing and receding contact angles between mercury and cement-based materials
The selection of the incorrect value of contact angles is one of the important error sources in calculating the pore size in mercury porosimetry studies. However, from literature, it is difficult to find out an appropriate technique, which can be used to measure both advancing and receding contact angles. In this paper, a new method is proposed to measure the advancing and receding contact angles between mercury and cement-based materials. This method is demonstrated with a measurement on Portland cement paste with the water-to-cement ratio of 0.3. This method can give very consistent results with the standard deviation lower than 1 %. The measured advancing and receding contact angles range from 131.7° to 138.6° and from 123.3° to 128.2°, respectively, as curing age increases from 3 days to 28 days
Rapid Liana Colonization along a Secondary Forest Chronosequence
Lianas (woody vines) can have profound effects on tree recruitment, growth, survival, and diversity in tropical forests. However, the dynamics of liana colonization soon after land abandonment are poorly understood, and thus it is unknown whether lianas alter tree regeneration early in succession. We examined the liana community in 43 forests that ranged from 1 to 31 yr old in central Panama to determine how fast lianas colonize young forests and how the liana community changes with forest succession. We found that lianas reached high densities early in succession, commonly exceeding 1000 stems/ha within the first 5 yr of forest regeneration. Lianas also increased rapidly during early succession in terms of basal area but did not show evidence of saturation within the 30 yr of our chronosequence. The relative contribution of lianas to total woody plant community in terms of basal area and density increased rapidly and reached a saturation point within 5 yr (basal area) to 15 yr (density) after land abandonment. Our data demonstrate that lianas recruit early and in high density in tropical forest regeneration, and thus lianas may have a large effect on the way in which secondary forests develop both early and throughout succession
Micro-costing study of rituximab subcutaneous injection versus intravenous infusion in dutch setting
Micro-costing study of rituximab subcutaneous injection versus intravenous infusion in dutch setting
Annual survey air quality 2001
The air quality for 2001 is found to strongly resemble that for 2000. The decreasing trend in concentrations seen in the nineties, is still valid on the whole. Concerning the meteorological influences, 2001 can be considered as a normal year. Widespread exceedances occurred for ozone and PM10, and in the deposition of potential acid and total nitrogen. In the urban environment, exceedances of the annual mean limit value for NO2 occurred along road length of about 2000 km. Calculations for benzene and benzo[a]pyrene showed that exceedances were incidental. This annual air quality survey provides an overview of the air quality and the load placed on soils and surface water by atmospheric deposition in the Netherlands, on the basis of measurements and model calculations. The report describes global, photochemical, acidifying, particulate and local air pollution. Special attention has been paid to the Dutch air quality in relation to the new European legislation on air quality.Als we de luchtkwaliteit over 2001 vergelijken met die van 2000 blijken deze in grote lijnen met elkaar overeen te komen. De trendmatige daling van concentraties heeft zich in grote lijnen doorgezet. 2001 was wat meteorologische invloed betreft een normaal jaar. Normoverschrijdingen op landelijke schaal hebben zich voorgedaan van ozon, zwevende deeltjes (PM10), depositie van potentieel zuur en stikstof. In de stedelijke omgeving is de jaargemiddelde norm NO2 overschreden langs een weglengte van circa 2000 km. Voor benzeen en benzo[a]pyreen geven berekeningen aan dat incidenteel overschrijdingen van grenswaarden kunnen zijn voorgekomen. In het jaaroverzicht luchtkwaliteit 2001 wordt op basis van metingen en modelberekeningen een samenvattend beeld gegeven van de luchtkwaliteit en de belasting van bodem en oppervlaktewater door atmosferische depositie in Nederland over 2001. Het rapport beschrijft de onderwerpen: mondiale, fotochemische, verzurende, deeltjesvormige en lokale luchtverontreiniging. Als extra onderwerp is een hoofdstuk opgenomen over de Nederlandse luchtkwaliteit in relatie tot de nieuwe Europese wetgeving voor luchtkwaliteit
Minkowski's Object: A Starburst Triggered by a Radio Jet, Revisited
We present neutral hydrogen, ultraviolet, optical and near-infrared imaging,
and optical spectroscopy, of Minkowski's Object (MO), a star forming peculiar
galaxy near NGC 541. The observations strengthen evidence that star formation
in MO was triggered by the radio jet from NGC 541. Key new results are the
discovery of a 4.9E8 solar mass double HI cloud straddling the radio jet
downstream from MO, where the jet changes direction and decollimates; strong
detections of MO, also showing double structure, in UV and H-alpha; and
numerous HII regions and associated clusters in MO. In UV, MO resembles the
radio-aligned, rest-frame UV morphologies in many high redshift radio galaxies
(HzRGs), also thought to be caused by jet-induced star formation. MO's stellar
population is dominated by a 7.5 Myr-old, 1.9E7 solar mass instantaneous burst,
with current star formation rate 0.52 solar masses per year (concentrated
upstream from where the HI column density is high). This is unlike the
jet-induced star formation in Centaurus A, where the jet interacts with
pre-existing cold gas; in MO the HI may have cooled out of a warmer, clumpy
intergalactic or interstellar medium as a result of jet interaction, followed
by collapse of the cooling clouds and subsequent star formation (consistent
with numerical simulations). Since the radio source that triggered star
formation in MO is much less luminous, and therefore more common, than powerful
HzRGs, and because the environment around MO is not particularly special in
terms of abundant dense, cold gas, jet-induced star formation in the early
universe might be even more prevalent than previously thought.Comment: 52 pages, 15 figures, accepted for publication in Ap
The Extended Line Region of 3C 299
We present results of HST observations of the radio galaxy 3C 299. The
broad-band F702W (R) and F555W (V) images (WFPC2/PC) show an elliptical galaxy,
with a comet-like structure extending to the NE in the radio jet direction. The
[OIII]5007 emission line map, shows a bi-conical structure centered on
the nucleus, that overlaps the structure found in the broad-band filters. The
radio core coincides with the center of the bi-conical structure and the radio
axes are aligned with the direction of the cones. These data show clear
evidence of a strong interaction between the radio jet and the NE morphology of
the galaxy. We show evidence that this NE region is an ENLR; the line-ratio
diagnostics show that models involving gas shocked by the radio-jet plus
ionization from a precursor HII region, produced itself by the ionizing photons
of the postshocked gas on the preshocked gas provide a good match to the
observations. We investigate the spatial behavior of the ionizing parameter
, by determining the [OIII]/[OII] line ratio which is sensitive to the
change of the ionization parameter, and trace its behavior over the ENLR along
the radio jet direction. We find that [OIII]/[OII] does not follow a simple
dilution model, but rather that it is approximately constant over a large range
of distance from the nucleus thus requiring a local source of ionization which
seems to be compatible with the shock models driven by the radio jet.Comment: 17 pages, 9 Postscript figures, ApJ accepted, uses aaspp.st
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