INFLUENCIA DEL MUCÍLAGO DE NOPAL Y EXTRACTO DE ALGAS CAFÉS EN EL GRADO DE HIDRATACIÓN DE PASTAS DE CEMENTO PORTLAND ORDINARIO

This paper presents the effect produced by the addition of aqueous dispersions of cactus mucilage and brown seaweed extract on the degree of hydration of ordinary Portland cement pastes. Cement pastes with water/cement ratios of 0.30 and 0.60 were prepared containing the natural additives at three concentrations. The curing conditions were moist cured and sealed. The degree of hydration was determined by ignition and thermo-gravimetric analysis at 14, 28 and 56 days of age. The results indicate a higher degree of hydration in pastes with a water/cement ratio of 0.60 containing the natural additives with respect to control specimens. This effect could be explained by a better dispersion of cement particles in the presence of the natural additives and their capacity to retain water, thereby providing internal curing.Este trabajo presenta el efecto que produce la adición de dispersión acuosa de mucílago de nopal y el extracto de algas marinas cafés en el grado de hidratación de pastas de cemento Portland ordinario. Se elaboraron pastas de cemento con relaciones agua/cemento de 0.30 y 0.60, conteniendo los aditivos naturales en tres concentraciones. Las pastas se curaron en húmedo y selladas. Se determinó el grado de hidratación de las pastas ignición y análisis termo-gravimétrico a los 14, 28 y 56 días de edad. Los resultados indican un mayor grado de hidratación en las pastas de cemento con relación agua/cemento de 0.60 conteniendo los aditivos naturales en comparación con el control. Se sugiere que esto es debido a una mejor dispersión de las partículas de cemento en la presencia de estos aditivos y a la capacidad de estos para retener agua, con lo cual se produce curado interno

INFLUENCIA DEL MUCÍLAGO DE NOPAL Y EXTRACTO DE ALGAS CAFÉS EN EL GRADO DE HIDRATACIÓN DE PASTAS DE CEMENTO PORTLAND ORDINARIO

This paper presents the effect produced by the addition of aqueous dispersions of cactus mucilage and brown seaweed extract on the degree of hydration of ordinary Portland cement pastes. Cement pastes with water/cement ratios of 0.30 and 0.60 were prepared containing the natural additives at three concentrations. The curing conditions were moist cured and sealed. The degree of hydration was determined by ignition and thermo-gravimetric analysis at 14, 28 and 56 days of age. The results indicate a higher degree of hydration in pastes with a water/cement ratio of 0.60 containing the natural additives with respect to control specimens. This effect could be explained by a better dispersion of cement particles in the presence of the natural additives and their capacity to retain water, thereby providing internal curing.Este trabajo presenta el efecto que produce la adición de dispersión acuosa de mucílago de nopal y el extracto de algas marinas cafés en el grado de hidratación de pastas de cemento Portland ordinario. Se elaboraron pastas de cemento con relaciones agua/cemento de 0.30 y 0.60, conteniendo los aditivos naturales en tres concentraciones. Las pastas se curaron en húmedo y selladas. Se determinó el grado de hidratación de las pastas ignición y análisis termo-gravimétrico a los 14, 28 y 56 días de edad. Los resultados indican un mayor grado de hidratación en las pastas de cemento con relación agua/cemento de 0.60 conteniendo los aditivos naturales en comparación con el control. Se sugiere que esto es debido a una mejor dispersión de las partículas de cemento en la presencia de estos aditivos y a la capacidad de estos para retener agua, con lo cual se produce curado interno

Quasi-free photoproduction of η-mesons off 3He nuclei

Quasi-free photoproduction of η-mesons has been measured off nucleons bound in 3He nuclei for incident photon energies from the threshold region up to 1.4 GeV. The experiment was performed at the tagged photon facility of the Mainz MAMI accelerator with an almost 4π covering electromagnetic calorimeter, combining the TAPS and Crystal Ball detectors. The η-mesons were detected in coincidence with the recoil nucleons. This allowed a comparison of the production cross section off quasi-free protons and quasi-free neutrons and a full kinematic reconstruction of the final state, eliminating effects from nuclear Fermi motion. In the S11(1535) resonance peak, the data agree with the neutron/proton cross section ratio extracted from measurements with deuteron targets. More importantly, the prominent structure observed in photoproduction off quasi-free neutrons bound in the deuteron is also clearly observed. Its parameters (width, strength) are consistent with the expectations from the deuteron results. On an absolute scale the cross sections for both quasi-free protons and neutrons are suppressed with respect to the deuteron target pointing to significant nuclear final-state interaction effects

Photoproduction of mesons off nuclei

Recent results for the photoproduction of mesons off nuclei are reviewed. These experiments have been performed for two major lines of research related to the properties of the strong interaction. The investigation of nucleon resonances requires light nuclei as targets for the extraction of the isospin composition of the electromagnetic excitations. This is done with quasi-free meson photoproduction off the bound neutron and supplemented with the measurement of coherent photoproduction reactions, serving as spin and/or isospin filters. Furthermore, photoproduction from light and heavy nuclei is a very efficient tool for the study of the interactions of mesons with nuclear matter and the in-medium properties of hadrons. Experiments are currently rapidly developing due to the combination of high quality tagged (and polarized) photon beams with state-of-the-art 4pi detectors and polarized targets

Quasi-free photoproduction of eta-mesons off the deuteron

Precise data for quasi-free photoproduction of $\eta$ mesons off the deuteron have been measured at the Bonn ELSA accelerator with the combined Crystal Barrel/TAPS detector for incident photon energies up to 2.5 GeV. The $\eta$-mesons have been detected in coincidence with recoil protons and neutrons. Possible nuclear effects like Fermi motion and re-scattering can be studied via a comparison of the quasi-free reaction off the bound proton to $\eta$-production off the free proton. No significant effects beyond the folding of the free cross section with the momentum distribution of the bound protons have been found. These Fermi motion effects can be removed by an analysis using the invariant mass of the $\eta$-nucleon pairs reconstructed from the final state four-momenta of the particles. The total cross section for quasi-free $\eta$-photoproduction off the neutron reveals even without correction for Fermi motion a pronounced bump-like structure around 1 GeV of incident photon energy, which is not observed for the proton. This structure is even narrower in the invariant mass spectrum of the $\eta$-neutron pairs. Position and width of the peak in the invariant mass spectrum are $W\approx 1665$ MeV and FWHM $\Gamma\approx 25$ MeV. The data are compared to the results of different models.Comment: accepted for publication in Eur. Phys. J.

Taxis in archaea

Microorganisms can move towards favorable growth conditions as a response to environmental stimuli. This process requires a motility structure and a system to direct the movement. For swimming motility, archaea employ a rotating filament, the archaellum. This archaea-specific structure is functionally equivalent, but structurally different, from the bacterial flagellum. To control the directionality of movement, some archaea make use of the chemotaxis system, which is used for the same purpose by bacteria. Over the past decades, chemotaxis has been studied in detail in several model bacteria. In contrast, archaeal chemotaxis is much less explored and largely restricted to analyses in halophilic archaea. In this review, we summarize the available information on archaeal taxis. We conclude that archaeal chemotaxis proteins function similarly as their bacterial counterparts. However, because the motility structures are fundamentally different, an archaeaspecific docking mechanism is required, for which initial experimental data have only recently been obtained

Computing transformation semigroups

AbstractThis paper describes algorithms for computing the structure of finite transformation semigroups. The algorithms depend crucially on a new data structure for an R -class in terms of a group and an action. They provide for local computations, concerning a single R -class, without computing the whole semigroup, as well as for computing the global structure of the semigroup. The algorithms have been implemented in the share package MONOID within theGAP system for computational algebra