Investigation of autoclaved cement systems with reactive MgO and Al <inf>2</inf>O<inf>3</inf>-SiO<inf>2</inf> rich fired clay brick

Portland cement (PC) is one of the world's most important building materials, as it is a fundamental component of concrete. However, the manufacture of PC is highly energy intensive and leads to the emission of carbon dioxide (CO2). One promising control measure is the use of industrial wastes and by-products as supplementary cementing materials (SCMs) in order to minimise PC consumption, thereby producing greener cement-based products. This study investigates mechanical properties and phase development of hydrothermally treated cement-ground quartz sand blends with the incorporation of fired clay-brick (CB) waste and reactive magnesia (MgO). The addition of CB waste in autoclaved PC-quartz mortar mixes showed that the alumina-silica rich CB waste was pozzolanic when the Al2O3 accelerated formation and increased crystallinity of Al substituted 1.1 nm tobermorite, resulting in the observed strength gain. Autoclaved mortar specimens incorporating reactive MgO showed a reduction in strength with increasing MgO addition. This was a result of dilution when the relative proportion of PC available for the formation of the strength contributing hydration products including tobermorite is decreased

The thermophysical properties of australian opal

The characterisation of the surface area and porosity of opals derived from Tintenbar, a volcanic environment, and Lightning Ridge, a sedimentary environment, using nitrogen gas adsorption at -196°C is reported. Both opal types were found to have relatively low surface areas and displayed little porosity. The low surface areas observed is indicative of the ability of silica to infill voids and interstices. Thermogravimetric analysis of the samples before and after degassing was carried out to determine the amount of water removed by the degassing process. Negligible difference was found in the water content before and after degassing in the case of the Lightning Ridge sedimentary opal, while the Tintenbar volcanic opal was found to have lost more that 60 per cent of its water during the degassing process. These differences were ascribed to the differences in the silica structure of the opals with the Lightning Ridge opal having a denser cage structure, which traps the molecular water, while a more open structure is postulated for the Tintenbar opal, allowing the water to be relatively easily removed

A spectroscopic investigation of the weathering of a heritage Sydney sandstone

Infrared spectroscopy has been employed in a study of the degradation of heritage Sydney sandstone used in St. Mary's Cathedral in Sydney, Australia. Spectra were used to characterise the clay components taken from weathered and unweathered sandstone blocks removed from the Cathedral as part of a restoration programme. Two types of kaolin clays - kaolinite and its polymorph, dickite - have been identified. A higher amount of dickite present in the clay of weathered sandstone indicated that a kaolinite-to-dickite transformation occurs upon weathering. X-ray photoelectron spectroscopy was also used to confirm the presence of a more thermally stable polymorph of the kaolinite in the sandstone. © 2008 Elsevier B.V. All rights reserved

Development of shrinkage resistant cement-based materials using fibers

Copyright © 2011 by Research Publishing Services. Drying shrinkage is themajor contributor to volume changes in normal strength concrete. Several classes of shrinkage compensating admixtures are known to the concrete industry. This study deals with the literature review and categorization of different classes of shrinkage reducing fibers, especially polyethylene fibers, with the objective of introducing new types of shrinkage reducing fiber. In this investigation a special type of hydrophobic polyethylene minifibers has been used in different dosages in mortar samples. The experimental results on drying shrinkage aswellasonseveralotherpropertiesarereported.Thehydrophobicminifibersshowedremarkable improvement in shrinkage reduction even at very lowconcentrations (0.1%of cementweight)

Characterisation of Portland cement blended with pitchstone fines aiding carbon dioxide emission reduction

Climate change and global wanning present a significant challenge as unsustainable levels of greenhouse gas emissions arising from human activities continue to be emitted. The cement industry is responsible for between five and ten per cent of annual world carbon dioxide emissions; most arising from the manufacture of Portland cement (PC). An effective way of reducing emissions is by incorporating supplementary cementitious materials (SCMs) as partial PC replacements. SCMs are silicate or aluminosilicate based pozzolanic materials which, in finely divided form, combine with water and calcium hydroxide (lime), liberated by cement hydration, to form compounds exhibiting cementitious properties. Pitchstone is such an aluminosilicate and has the potential to act as an effective pozzolan for partial replacement of PC. In North Queensland, Australia, a vast deposit of pitchstone is mined and processed for expandable perlite aggregate. During the classification stage of the excavated natural material, waste pitchstone fines (PF) less than 0.5 mm in size are generated. This study evaluates the waste PF as a viable, eco-friendly pozzolan for the partial replacement of PC. The reactivity of the PF is compared to fly ash (FA), using the pozzolanic compressive strength activity index (SAI) after seven, 28, and 91 days ageing at 20 per cent and 40 per cent PC substitutions. PF was found to be comparable to FA as a pozzolan at 20 per cent PC substitution at all ages tested. However, for the 40 per cent substitution blends significant strength was only achieved at 91 days ageing for the FA blend. The pozzolanic reactivity was also investigated using thermogravimetric analysis to determine the degree of free lime present after 91 days. In all cases where an SCM was added, the free lime was observed to be consumed with increasing age

Semantic closure demonstrated by the evolution of a universal constructor architecture in an artificial chemistry

We present a novel stringmol-based artificial chemistry system modelled on the universal constructor architecture (UCA) first explored by von Neumann. In a UCA, machines interact with an abstract description of themselves to replicate by copying the abstract description and constructing the machines that the abstract description encodes. DNA-based replication follows this architecture, with DNA being the abstract description, the polymerase being the copier, and the ribosome being the principal machine in expressing what is encoded on the DNA. This architecture is semantically closed as the machine that defines what the abstract description means is itself encoded on that abstract description. We present a series of experiments with the stringmol UCA that show the evolution of the meaning of genomic material, allowing the concept of semantic closure and transitions between semantically closed states to be elucidated in the light of concrete examples. We present results where, for the first time in an in silico system, simultaneous evolution of the genomic material, copier and constructor of a UCA, giving rise to viable offspring

The MRN complex is transcriptionally regulated by MYCN during neural cell proliferation to control replication stress

The MRE11/RAD50/NBS1 (MRN) complex is a major sensor of DNA double strand breaks, whose role in controlling faithful DNA replication and preventing replication stress is also emerging. Inactivation of the MRN complex invariably leads to developmental and/or degenerative neuronal defects, the pathogenesis of which still remains poorly understood. In particular, NBS1 gene mutations are associated with microcephaly and strongly impaired cerebellar development, both in humans and in the mouse model. These phenotypes strikingly overlap those induced by inactivation of MYCN, an essential promoter of the expansion of neuronal stem and progenitor cells, suggesting that MYCN and the MRN complex might be connected on a unique pathway essential for the safe expansion of neuronal cells. Here, we show that MYCN transcriptionally controls the expression of each component of the MRN complex. By genetic and pharmacological inhibition of the MRN complex in a MYCN overexpression model and in the more physiological context of the Hedgehog-dependent expansion of primary cerebellar granule progenitor cells, we also show that the MRN complex is required for MYCN-dependent proliferation. Indeed, its inhibition resulted in DNA damage, activation of a DNA damage response, and cell death in a MYCN- and replication-dependent manner. Our data indicate the MRN complex is essential to restrain MYCN-induced replication stress during neural cell proliferation and support the hypothesis that replication-born DNA damage is responsible for the neuronal defects associated with MRN dysfunctions.Cell Death and Differentiation advance online publication, 12 June 2015; doi:10.1038/cdd.2015.81

Structural analysis of MDM2 RING separates degradation from regulation of p53 transcription activity

MDM2–MDMX complexes bind the p53 tumor-suppressor protein, inhibiting p53's transcriptional activity and targeting p53 for proteasomal degradation. Inhibitors that disrupt binding between p53 and MDM2 efficiently activate a p53 response, but their use in the treatment of cancers that retain wild-type p53 may be limited by on-target toxicities due to p53 activation in normal tissue. Guided by a novel crystal structure of the MDM2–MDMX–E2(UbcH5B)–ubiquitin complex, we designed MDM2 mutants that prevent E2–ubiquitin binding without altering the RING-domain structure. These mutants lack MDM2's E3 activity but retain the ability to limit p53′s transcriptional activity and allow cell proliferation. Cells expressing these mutants respond more quickly to cellular stress than cells expressing wild-type MDM2, but basal p53 control is maintained. Targeting the MDM2 E3-ligase activity could therefore widen the therapeutic window of p53 activation in tumors

Myxoid Neurothekeoma: A Rare Soft Tissue Tumor of Hand in a Male Toddler

Neurothekeomas are rare benign neoplasms, typically occurring in young patients with a remarkable predilection for the female population. Patients usually present with a small nodule in different anatomical sites, commonly  involving the face and the upper limb. We report a case of a three.year.old  boy, who presented with a nontender nodule on the left thumb. Surgical biopsy and immunostaining confirmed the diagnosis as myxoid neurothekeoma. The rarity of this unusual skin tumor in a toddler prompted the following report.Keywords: Neurothekeoma, soft tissue tumor, toddle

Massive stars as thermonuclear reactors and their explosions following core collapse

Nuclear reactions transform atomic nuclei inside stars. This is the process of stellar nucleosynthesis. The basic concepts of determining nuclear reaction rates inside stars are reviewed. How stars manage to burn their fuel so slowly most of the time are also considered. Stellar thermonuclear reactions involving protons in hydrostatic burning are discussed first. Then I discuss triple alpha reactions in the helium burning stage. Carbon and oxygen survive in red giant stars because of the nuclear structure of oxygen and neon. Further nuclear burning of carbon, neon, oxygen and silicon in quiescent conditions are discussed next. In the subsequent core-collapse phase, neutronization due to electron capture from the top of the Fermi sea in a degenerate core takes place. The expected signal of neutrinos from a nearby supernova is calculated. The supernova often explodes inside a dense circumstellar medium, which is established due to the progenitor star losing its outermost envelope in a stellar wind or mass transfer in a binary system. The nature of the circumstellar medium and the ejecta of the supernova and their dynamics are revealed by observations in the optical, IR, radio, and X-ray bands, and I discuss some of these observations and their interpretations.Comment: To be published in " Principles and Perspectives in Cosmochemistry" Lecture Notes on Kodai School on Synthesis of Elements in Stars; ed. by Aruna Goswami & Eswar Reddy, Springer Verlag, 2009. Contains 21 figure