147 research outputs found
Structureāfunction relationship during the early and long-term hydration of one-part alkali-activated slag
Understanding the mechanisms controlling the early (fresh) and long-term (hardened) hydration of one-part alkali-activated slags (AAS) is key to extend their use as low CO2 substitutes for ordinary Portland cement (OPC). Their ājust add waterā use makes them easier and less hazardous to manipulate than the more studied two-part ones. This is due to the absence of liquid alkaline activators, which are environmentally and energy demanding. In this work, numerous experimental techniques have been linked to obtain a comprehensive physico-chemical characterization of a one-part AAS activated with Na2CO3 and Ca(OH)2 powders at several water to solid ratios (w/s). Calorimetry and pH/conductivity measurements describe the functioning of the activators immediately after contact with water. Early reactivity is characterized through in situ X-ray powder diffraction (XRPD) and small amplitude oscillatory shear (SAOS) rheology, which reveal a rapid precipitation of nanometric hydration products (nano-C-A-S-H), which results in a continuous increase in the paste cohesivity until setting. Moreover, SAOS shows that rejuvenating the paste by means of shearing (performed externally to the rheometer in this study) is enough to restore the initial cohesion (i.e., workability) for long time spans until setting occurs. The long-term hydration is characterized by ex situ XRPD on aged AAS pastes, in parallel with mechanical testing on AAS mortar. A correlation can be observed between the amount of nano-C-A-S-H and the increase in compressive strength. Overall, this formulation shows satisfactory fresh and solid properties, demonstrating suitability for low- and normal-strength applications
Semiaquatic adaptations in a giant predatory dinosaur
Mysterious dinosaur a swimmer?
Dinosaurs are often appreciated for their size and oddity. In this regard, the North African carnivorous theropod
Spinosaurus
, with its huge dorsal sail and a body larger than
Tyrannosaurus rex
, has long stood out. This species also stands out because of its history. The unfortunate loss of the type specimen during World War II left much of what we know about
Spinosaurus
to be divined through speculation and reconstruction. Ibrahim
et al.
now describe new fossils of this unusual species. They conclude it was, at least partly, aquatic, a first for dinosaurs.
Science
, this issue p.
1613
</jats:p
Reducing Nitrogen Dosage in Triticum durum Plants with Urea-Doped Nanofertilizers
Nanotechnology is emerging as a very promising tool towards more efficient and sustainable
practices in agriculture. In this work, we propose the use of non-toxic calcium phosphate nanoparticles
doped with urea (U-ACP) for the fertilization of Triticum durum plants. U-ACP nanoparticles present
very similar morphology, structure, and composition than the amorphous precursor of bone mineral,
but contain a considerable amount of nitrogen as adsorbed urea (up to ca. 6 wt % urea). Tests on
Triticum durum plants indicated that yields and quality of the crops treated with the nanoparticles at
reduced nitrogen dosages (by 40%) were unaltered in comparison to positive control plants, which
were given the minimum N dosages to obtain the highest values of yield and quality in fields. In
addition, optical microscopy inspections showed that Alizarin Red S stained nanoparticles were
able to penetrate through the epidermis of the roots or the stomata of the leaves. We observed that
the uptake through the roots occurs much faster than through the leaves (1 h vs. 2 days, respectively).
Our results highlight the potential of engineering nanoparticles to provide a considerable efficiency
of nitrogen uptake by durum wheat and open the door to design more sustainable practices for
the fertilization of wheat in fields.This research was funded by Fondazione CARIPLO (project no. 2016-0648: Romancing the stone:
size-controlled HYdroxyaPATItes for sustainable AgricultureāHYPATIA) and the Spanish Ministerio de Ciencia,
InnovaciĆ³n y Universidades (MCIU/AEI/FEDER) with the Projects NanoSmart (RYC-2016-21042) and NanoVIT
(RTI-2018-095794-A-C22). GBRR also acknowledges the Spanish MICINN for her postdoctoral contract within
the Juan de la Cierva Program (JdC-2017)
Processo de enfermagem conforme a classificaĆ§Ć£o internacional para as prĆ”ticas de enfermagem: uma revisĆ£o integrativa
Short-Snouted Toothless Ichthyosaur from China Suggests Late Triassic Diversification of Suction Feeding Ichthyosaurs
Ichthyosaurs were an important group of Mesozoic marine reptiles and existed
from the Early Triassic to the early Late Cretaceous. Despite a great
diversity in body shapes and feeding adaptations, all share greatly enlarged
eyes, an elongated rostrum with numerous conical teeth, and a streamlined
body.. may be linked to the Late
Triassic minimum in atmospheric oxygen
A New Pterosaur (Pterodactyloidea: Azhdarchidae) from the Upper Cretaceous of Morocco
The Kem Kem beds in South Eastern Morocco contain a rich early Upper (or possibly late Lower) Cretaceous vertebrate assemblage. Fragmentary remains, predominantly teeth and jaw tips, represent several kinds of pterosaur although only one species, the ornithocheirid Coloborhynchus moroccensis, has been named. Here, we describe a new azhdarchid pterosaur, Alanqa saharica nov. gen. nov. sp., based on an almost complete well preserved mandibular symphysis from Aferdou N'Chaft. We assign additional fragmentary jaw remains, some of which have been tentatively identified as azhdarchid and pteranodontid, to this new taxon which is distinguished from other azhdarchids by a remarkably straight, elongate, lance-shaped mandibular symphysis that bears a pronounced dorsal eminence near the posterior end of its dorsal (occlusal) surface. Most remains, including the holotype, represent individuals of approximately three to four meters in wingspan, but a fragment of a large cervical vertebra, that probably also belongs to A. saharica, suggests that wingspans of six meters were achieved in this species. The Kem Kem beds have yielded the most diverse pterosaur assemblage yet reported from Africa and provide the first clear evidence for the presence of azhdarchids in Gondwana at the start of the Late Cretaceous. This, the relatively large size achieved by Alanqa, and the additional evidence of variable jaw morphology in azhdarchids provided by this taxon, indicates a longer and more complex history for this clade than previously suspected
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