Microstructure and bonding behavior of fiber-mortar interface in fiber-reinforced concrete

The interfacial properties between fiber and matrix play a critical role in the overall mechanical responses of composite materials. In this paper, the glass fiber-mortar interfacial microstructure in fiber reinforced concrete (FRC) is visualized and characterized using X-ray microscopy. Additionally, three types of fiber-mortar interface (glass fiber, high modulus polyvinyl alcohol (PVA) fiber, and basalt fiber) are analyzed by scanning electron microscopy and energy dispersive X-ray spectroscopy. The results revealed a lot of microcracks along with the glass fiber-mortar interface; moreover, the hydration product of the glass/PVA/basalt fiber-mortar interface was much lower than that of the mortar matrix. Because microcracks or lower hydration product have such a negative effect on the interfacial bonding between fiber and mortar, the objective of this paper was to provide an analysis of this problem through extensive testing of their bonding properties. Specimens made of three types of fiber were tested along with three different mortar types under tensile stress and a combined stress state to investigate the interfacial bond properties between fiber and mortar. Results show that both of the tensile and shear bond strength of the interface were not only improved by stronger mortar matrix, but also significantly affected by fiber type. Furthermore, when the interface failed by slipping along the interfacial area, the interface showed an increasing shear bond strength with the increase of compressive stress. This was not the case when failure was due to the crushing of mortar. Finally, the FRC splitting tensile strength was tested to demonstrate the bonding mechanism effects on the FRC mechanical properties

Indoor Mould Testing of a Historic University Building: UCL Chadwick Building

Indoor mould is one of the most important determinants of indoor air quality, with serious implications not only on human health, but also on the building envelope itself. This study is based on the Chadwick building, which is a late 19th century building, currently under the ownership of UCL as a workplace and school. Therefore it brings together different functions which are conventionally discussed separately in the relevant literature. This study aims to measure airborne and surface mould concentrations within the Chadwick Building, and to find out the correlations between these and the physical characteristics of the tested spaces. To this end, 3 classrooms, 3 offices, 3 laboratories, and 1 activity room were sampled to examine the airborne (active or aggressive) and surface mould concentrations. Samples were analysed for the β-N-acetylhexosaminidase (NAHA) activity to determine the fungal cell biomass at the laboratories of Mycometer in Denmark. The testing protocol also involved active particle counting, and temperature and relative humidity measurements. Offices were found to be the least mould intensive spaces, while laboratories were found to have the highest level of mould and particle intensity among all tested spaces. Based on the benchmarks previously established for residential indoor environments (currently in use by the Danish Building Institute), the results showed that most of the tested spaces did not have no mould and with a good/normal cleaning standard. Only one space and a few surfaces indicated either a minor (most likely non-building-related) mould, or a poor cleaning standard. The validity of these categories for a workplace/school should be further investigated by future research

Polistes olivaceous decreases biotic surface colonization

The objective of this investigation was to evaluate the anti-bacterial efficacy of the honeycomb of Polistes olivaceous on oral biotic surface (biofilm) model by means of pH response, population of oral bacteria and enamel mineralization. Three copies of a three-organism-bacterial consortium was grown on hydroxyapatite (HA) surfaces in a continuous culture system and exposed to repeated solution pulses of sucrose solution every 12 h to construct a cariogenic biofilm on the HA discs in the flow cells. One flow cell was only pulsed with 500 μmol/ml of sucrose (S group). The second flow cell was pulsed with 500 μmol/ml sucrose and 2.5 mg/ml P. olivaceous extract (P group). The third flow cell was pulsed with 500 μmol/ml sucrose, 230 mg/L sodium fluoride and 0.2% chlorohexidine digluconate (C group). During the course of carbohydrate supplement, the pH of the S group dropped sharply compared with the others. The P group demonstrated pH recovery to baseline more easily than the S group (p < 0.05). The C group demonstrated very little pH drop. The P group displayed a lower level of colonization than the S group, which was reflected by a lower cariogenic bacterial count and a less compact biofilm especially after the third pulse. P. olivaceous suppresses bacteria growth and accelerates pH recovery. P. olivaceous may have stabilizing effect against cariogenic shift on the oral biofilm, preventing tooth decay. © 2009 Academic Journals.published_or_final_versio

Optimal density of radial major roads in a two-dimensional monocentric city with endogenous residential distribution and housing prices

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Climate and soil moisture content during development ofthe frst palaeosol in the southern Loess Plateau

The scientific problems concerning Quaternary soil water content and the water cycle have not been researched. This study examined the soil water content and depth of distribution of gravitational water in the south Loess Plateau during development of the first palaeosol layer (S1) by methods such as field investigation, electron microscopy, energy spectrum analysis, chemical analysis, and so on. The purpose was to reveal the climate, water balance and vegetation type at the time when S1 developed. The depth of migration of CaCO3 and Sr were 4.2&thinsp;m below the upper boundary of the S1 palaeosol, and the depth of weathered loess beneath the argillic horizon was 4.0&thinsp;m. Ferri‐argillans developed well in the argillic horizon and their depth of migration was 1&thinsp;m below the argillic horizon. These findings suggest that the climate during the last interglacial was subtropical and humid, and the soil‐water balance was positive. Gravitational water was present to a depth of least 4.2&thinsp;m from the top of S1, and the water content was adequate for tree growth. The chemical weathering index showed that this palaeosol has been moderately weathered

Evolution of superconductivity in K2-xFe4+ySe5: Spectroscopic studies of X-ray absorption and emission.

This study investigates the evolution of superconductivity in K2-xFe4+ySe5 using temperature-dependent X-ray absorption and resonant inelastic X-ray scattering techniques. Magnetization measurements show that polycrystalline superconducting (SC) K1.9Fe4.2Se5 has a critical temperature (T c) of ∼31 K with a varying superconducting volume fraction, which strongly depends on its synthesis temperature. An increase in Fe-structural/vacancy disorder in SC samples with more Fe atoms occupying vacant 4d sites is found to be closely related to the decrease in the spin magnetic moment of Fe. Moreover, the nearest-neighbor Fe-Se bond length in SC samples exceeds that in the non-SC (NS) sample, K2Fe4Se5, which indicates a weaker hybridization between the Fe 3d and Se 4p states in SC samples. These results clearly demonstrate the correlations among the local electronic and atomic structures and the magnetic properties of K2-xFe4+ySe5 superconductors, providing deeper insight into the electron pairing mechanisms of superconductivity

Erratum: Vital Signs During the COVID-19 Outbreak: A Retrospective Analysis of 19,960 Participants in Wuhan and Four Nearby Capital Cities in China (Global Heart (2021) 16: 1 (47) DOI: 10.5334/gh.913)

This article details a correction to: Li J-W, Guo Y-T, Di Tanna GL, Neal B, Chen Y-D, Schutte AE. Vital Signs During the COVID-19 Outbreak: A Retrospective Analysis of 19,960 Participants in Wuhan and Four Nearby Capital Cities in China. Global Heart. 2021;16(1):47. DOI: http://doi.org/10.5334/gh.913. CORRECTION The original article was published without complete funding details. It listed one funder, the National Natural Science Foundation of China (H2501), National Key Research and Development Project of China (2018YFC2001200). There was another funder missing from the original article, the Chinese Military Health Care (20BJZ26). The originally listed funder covered expenses for enrolment and follow-up of patients, and the purchase and maintenance of necessary equipment. The second funder covered the costs of publication. COMPETING INTERESTS J.L. held an International Postdoctoral Exchange Fellowship Program China (20170103) during the course of this work. G. Tao has no disclosures. A.E. Schutte received speaker honoraria from Omron Healthcare, Takeda Pharmaceuticals, Novartis, Servier, and serves on research advisory board for Abbott. She is President of the International Society of Hypertension, 2018-2020. G.L. Di Tanna has no disclosures. B. Neal is supported by an Australian National Health and Medical Research Council Principal Research Fellowship; holds a research grant for this study from Janssen; and has held research grants for other large-scale cardiovascular outcome trials from Roche, Servier, and Merck Schering Plough; and his institution has received consultancy, honoraria, or travel support for contributions he has made to advisory boards and/or the continuing medical education programs of Abbott, Janssen, Novartis, Pfizer, Roche, and Servier. Y. Chen has no disclosures

Atomically dispersed Ni in cadmium-zinc sulfide quantum dots for high-performance visible-light photocatalytic hydrogen production.

Catalysts with a single atom site allow highly tuning of the activity, stability, and reactivity of heterogeneous catalysts. Therefore, atomistic understanding of the pertinent mechanism is essential to simultaneously boost the intrinsic activity, site density, electron transport, and stability. Here, we report that atomically dispersed nickel (Ni) in zincblende cadmium-zinc sulfide quantum dots (ZCS QDs) delivers an efficient and durable photocatalytic performance for water splitting under sunlight. The finely tuned Ni atoms dispersed in ZCS QDs exhibit an ultrahigh photocatalytic H2 production activity of 18.87 mmol hour-1 g-1. It could be ascribed to the favorable surface engineering to achieve highly active sites of monovalent Ni(I) and the surface heterojunctions to reinforce the carrier separation owing to the suitable energy band structures, built-in electric field, and optimized surface H2 adsorption thermodynamics. This work demonstrates a synergistic regulation of the physicochemical properties of QDs for high-efficiency photocatalytic H2 production

On the Successful Encapsulation of Water Droplets into Oil Droplets

Compound water-in-oil microdroplets can serve as microreactors in chemical and biological analyses. The inkjet printing is a useful technique to generate compound microdroplets by droplet impact. To understand the underlying physics during the droplet impact, a combined experimental and numerical study is carried out. The effect of spreading condition, impact velocity, and oil viscosity are investigated. The balance of the tripe-line among the three interfaces dominates primarily the stable morphology of the compound droplet. Reducing oil viscosity can reduce the required impact velocity. High impact velocity is necessary to reduce the side-slipping of the water droplet