Structural behavior of recycled aggregates concrete filled steel tubular columns

This paper presents an experimental and numerical investigation to determine the behavior of steel tubular columns filled with recycled aggregates concrete up to failure under constant axial compression loads. The experimental program included two steel tube columns, four recycled concrete columns and eight composite columns filled with different types of recycled coarse aggregates (granite and ceramic). Different percentages of recycled coarse aggregates: 0, 25 and 50 of the percentage of the coarse aggregates (dolomite) were used. The results of the numerical model that was employed by the finite element program, ANSYS, were compared with the experimental results. The results of the experimental study and the finite element analysis were compared with the design equations using different national building codes: AISC1999, AISC2005 and EC4. The results indicated that the recycled aggregates concrete infill columns have slightly lower but comparable ultimate capacities compared with the specimens filled with normal concrete

Unveiling the role of carbon defects in the exceptional narrowing of m-ZrO2 bandgap for enhanced photoelectrochemical water splitting performance

The development of efficient photoelectrodes via defect engineering of wide-band gap metal oxides has been the prime focus for many years. Specifically, the effect of carbon defects in wide-band gap metal oxides on their performance in photoelectrochemical (PEC) applications raised numerous controversies and still elusive. Herein, the effect of various carbon defects in m-ZrO2 was investigated using the density functional theory to probe the thermodynamic, electronic, and optical properties of the defective structures against pristine m-ZrO2. The defect formation energies revealed that elevating the temperature promotes and facilitates the formation of carbon defects. Moreover, the binding energies confirmed the stability of all studied complex carbon defects. Furthermore, the band edge positions against the redox potentials of water species revealed that all the studied defective structures can serve as photoanodes for water splitting. Additionally, CO3c (carbon atom substituted O3c site) was the only defective structure that exhibited slight straddling of the redox potentials of water. Importantly, all investigated defective structures enhanced light absorption with different optical activities. Finally, CO3cVO3c (carbon atom substituted O3c associated with O3c vacancy) defective m-ZrO2 enjoyed low direct band gap (1.9 eV), low defect formation energy, low exciton binding energy, high mobility of charge carriers, fast charge transfer, and low recombination rate. Concurrently, its optical properties were exceptional in terms of high absorption, low reflectivity and improved static dielectric constant. Hence, the study recommends CO3cVO3c defective m-ZrO2 as the leading candidate to serve as a photoanode for PEC applications

Recontextualising the determinants of external CSR in the services industry: A cross-cultural study

Although the relationship between institutional pressures and corporate social responsibility (CSR) has been well studied, its underlying mechanisms and boundary conditions are not well understood. To remedy these gaps, we draw on institutional theory and the literature on organisational sensemaking, stakeholder salience and the resource-based view of the firm. We test our conceptual model using survey data from 442 managers of hospitality and tourism enterprises based in Egypt and the United Kingdom. SEM-based results show that both stakeholder issue salience and discretionary slack mediate the link between institutional pressures and external CSR. National culture moderates the effects of institutional pressures on both stakeholder issue salience and external CSR. Multi-group analyses reveal noticeable differences between Egyptian and British managers regarding their interpretations of CSR issues and the institutional environment. This study contributes to the emerging micro-institutional stream and cross-cultural CSR research, providing important insights for managers, policymakers and researchers.Egyptian Ministry of Higher Education and Scientific Research MM27/19info:eu-repo/semantics/publishedVersio

Comparative study on the using of PEG and PAM as curing agents for self-curing concrete

There are many factors, which may affect on concrete quality. One of those is concrete curing. Self-curing concrete is the solution. It may produce by using chemical curing agents. The concept of those agents is to reduce the water evaporation from concrete. This research aims to study the effect of chemical curing agents on the behavior of self-curing concrete. Two different chemical curing agents were used to study the main mechanical properties of concrete. The main variables are; the type of curing agent (Polyethylene glycol "PEG400"–Poly Acrylamide "PAM") and its dosages. The results obtained in terms of compressive, tensile and flexure strength values. Test results showed that the self-curing concrete cured by each agent performed better in hardened properties compared to none cured concrete. Also, curing using the both agents together perform better than using each one individually

TiO2 nanotubes with ultrathin walls for enhanced water splitting

We demonstrate, for the first time, the synthesis of titania nanotubes with ultrathin (3–5 nm) wall thickness. As revealed by the incident photon-to-current collection efficiency (IPCE) and electrochemical impedance spectroscopy measurements, the ultrathin walls, less than the charge carrier diffusion length, were essential to ensure fast and efficient charge carrier collection.Qatar National Research Fund, a member of Qatar Foundation NPRP Grant no. 6-569-1-11

Computational and experimental elucidation of the boosted stability and antibacterial activity of ZIF-67 upon optimized encapsulation with polyoxometalates

Water microbial purification is one of the hottest topics that threats human morbidity and mortality. It is indispensable to purify water using antimicrobial agents combined with several technologies and systems. Herein, we introduce a class of nanosized metal organic framework; Zeolitic imidazolate framework (ZIF-67) cages encapsulated with polyoxometalates synthesized via facile one-step co-precipitation method. We employed two types of polyoxometalates bioactive agents; phosphotungstic acid (PTA) and phosphomolybdic acid (PMA) that act as novel antibacterial purification agents. Several characterization techniques were utilized to investigate the morphological, structural, chemical, and physical properties such as FESEM, EDS, FTIR, XRD, and N₂ adsorption/desorption isotherms techniques. The antibacterial assessment was evaluated using colony forming unit (CFU) against both Escherichia coli and Staphylococcus aureus as models of Gram-negative and Gram-positive bacteria, respectively. The PTA@ZIF-67 showed higher microbial inhibition against both Gram-positive and Gram-negative bacteria by 98.8% and 84.6%, respectively. Furthermore, computational modeling using density functional theory was conducted to evaluate the antibacterial efficacy of PTA when compared to PMA. The computational and experimental findings demonstrate that the fabricated POM@ZIF-67 materials exhibited outstanding bactericidal effect against both Gram-negative and Gram-positive bacteria and effectively purify contaminated water

Rapid and controlled electrochemical synthesis of crystalline niobium oxide microcones

We demonstrate the fabrication by anodization of niobium oxide microcones, several microns long, from aqueous solutions of 1 wt% hydrogen fluoride (HF) with varied sodium fluoride (NaF) concentration (0–1 M). Raman spectroscopy and x-ray diffractometer analysis revealed the as-grown microcones to be crystalline Nb_2O_(5−x) with preferred (1 0 0) and (0 1 0) orientations. The overall Nb_2O_(5−x) formation rate increased with the increasing NaF concentration, and structures as tall as 20 μm were achieved in just 20 min of anodization at 1 M NaF. Rapid formation of niobia microcones was even observed in the absence of HF at this NaF concentration. Photocatalytic activity for water oxidation was highest for microcones grown under the highest NaF concentration

Intense intrafamilial transmission of HBV in a rural area in Egypt is a probable cause of non-response to vaccination: A cross-sectional-seroprevalence-community-study.

Background: Worldwide, the prevalence of hepatitis B virus (HBV) infection is decreasing particularly in the vaccinated population. However, there are foci of increased transmission particularly in localized communities and within families. Objective: This study aimed at identifying HBV infection status among family members (FMs) of a cohort of HBsAg positive index cases (ICs) living in a village near Ismailia City, North-East Egypt. Design and participants: The study targeted ICs with chronic hepatitis B and their FMs. All were inquired for socio-demographic data, previous vaccination, kinship, and risk factors. All were tested for hepatitis markers and in HBcAb positive sera, HBV DNA and ALT were added. Results: The study included 96 participants including 14 ICs, 51 (53.1%) were females and 73 (76%) self-reported receiving hepatitis B vaccine after birth. Among 82 FMs, HBcAb was found in 49 (59.76%) of whom overt and occult HBV were diagnosed in 24 (49%) and 18 (36.7%). HBs Ag and HBcAb were more frequent in unvaccinated compared to vaccinated FMs; being 60.9% vs. 32.9% for HBsAg (p < /em>=0.017) and 91.3% vs. 57.5% for HBcAb (p < /em>=0.003). Among the FMs, active HBV were more related to male than female ICs (54.9% vs. 45.2%, p < /em>=0.73) while among children, it is more related to females more than male ICs (38.9% vs. 25%, p < /em>=0.33). In all HBsAg positive participants, HBeAg was negative and HBV DNA load was higher among female than male ICs (median 3500 vs. 2594.5 IU/mL, p < /em>=0.82). Conclusion: The study shows a high rate of HBV transmission among FMs of HBsAg carriers living in a remote area in North-East Egypt. Both overt and occult HBV infections were frequent despite previous vaccinatio

The DFT+U: Approaches, Accuracy, and Applications

This chapter introduces the Hubbard model and its applicability as a corrective tool for accurate modeling of the electronic properties of various classes of systems. The attainment of a correct description of electronic structure is critical for predicting further electronic-related properties, including intermolecular interactions and formation energies. The chapter begins with an introduction to the formulation of density functional theory (DFT) functionals, while addressing the origin of bandgap problem with correlated materials. Then, the corrective approaches proposed to solve the DFT bandgap problem are reviewed, while comparing them in terms of accuracy and computational cost. The Hubbard model will then offer a simple approach to correctly describe the behavior of highly correlated materials, known as the Mott insulators. Based on Hubbard model, DFT+U scheme is built, which is computationally convenient for accurate calculations of electronic structures. Later in this chapter, the computational and semiempirical methods of optimizing the value of the Coulomb interaction potential (U) are discussed, while evaluating the conditions under which it can be most predictive. The chapter focuses on highlighting the use of U to correct the description of the physical properties, by reviewing the results of case studies presented in literature for various classes of materials

TOLERANCE OF HONEY BEE COLONIES TO VARROA DESTRUCTOR (ANDERSON AND TRUEMAN) AND THE ECONOMIC THRESHOLD OF THE PARASITE IN THE CENTRAL REGION OF KINGDOM OF SAUDI ARABIA

Experiments were carried out on honey bee colonies (Apis mellifera) during the winter of 2008 and spring of 2009 using colonies wintered with five levels of varroa infestation (0.0, 3.8, 9.0, 13.1 and 22.9%) in the Central Region of the kingdom of Saudi Arabia. The goal of the present work is to determine varroa treatment thresholds and colony collapse level. Response variables examined included varroa mite infestation level (%), cm2 of brood number of frames of brood, number of frames covered with adult honey bees and mites recovered on sticky boards. The data obtained reveled that no significant differences were noticed in cm2 of brood, number of frames of brood, and number of frames of bees in colonies (range of 0.0 to 9.0% varroa infestation or 0.0 – 0.9 mites/bee). Colonies with 13.1% infestation (0.13 mites/bee) exhibited a significant reduction in all measures of performance. The present results suggested that honey bee colonies can tolerate a level of 9.0% varroa infestation (0.9 mites/bee) during the winter without evidence of colony injury. It also suggested that 13.1% infestation (0.13 mites/bee) is the colony collapse or economic injury threshold in the Central Region of the Kingdom of Saudi Arabia. Also colonies with 12.3 or more mites falling on sticky boards after 48-hour period were likely to have lower populations of bees and brood the following spring