Effect of mix parameters on strength of geopolymer mortars - experimental study

Abstract: In this article, an investigation is reported on development of strength in South African fly ash (FA) – based geopolymer mixtures. Locally available Class F, FA from one of the coal power stations was used in the investigation. The alkali-activator used consisted of sodium silicate (SS) and sodium hydroxide (SH) mixed in varied ratios of 1.0, 1.5, 2.0, 2.5 and 3.0 SS to SH. The SS of silicate modulus = 2.5 was used but the SH concentration in the activator was varied to 10, 12, 14M NaOH. Mortars of 2.25 aggregate/binder ratio were used to prepare 50 mm cubes. In preparing mortar mixtures, the liquid to solids (L/S) ratios were varied to L/S = 0.3, 0.4, 0.5 and 0.6. Mortar cubes were cast and cured at 80oC for 7 days then tested for compressive strength. It was found that all three parameters consisting of SS/SH ratio of the activator, concentration of NaOH used in the activator and the L/S ratio, showed significant influence upon compressive strength development. The optimum strength of the geopolymer mortar mixtures was obtained at SS/SH = 2.0, 12M NaOH concentration ad L/S = 0.5

Placing Confidence Limits on Polarization Measurements

The determination of the true source polarization given a set of measurements is complicated by the requirement that the polarization always be positive. This positive bias also hinders construction of upper limits, uncertainties, and confidence regions, especially at low signal-to-noise levels. We generate the likelihood function for linear polarization measurements and use it to create confidence regions and upper limits. This is accomplished by integrating the likelihood function over the true polarization (parameter space), rather than the measured polarization (data space). These regions are valid for both low and high signal-to-noise measurements.Comment: 8 pages, 3 figures, 1 table, submitted to PAS

The Nehari Manifold for p-Laplacian Equation with Dirichlet Boundary Condition

The Nehari manifold for the equation −∆pu(x) = λu(x)|u(x)|p−2 + b(x)|u(x)|γ−2u(x) for x ∈ Ω together with Dirichlet boundary condition is investigated in the case where 0 < γ < p. Exploiting the relationship between the Nehari manifold and fibrering maps (i.e., maps of the form of t → J(tu) where J is the Euler functional associated with the equation), we discuss how the Nehari manifold changes as λ changes, and show how existence results for positive solutions of the equation are linked to the properties of Nehari manifold

Pozzolanic materials and waste products for formulation of geopolymer cements in developing countries : a review

Abstract: Potential use of Geopolymers as binders in concrete instead of ordinary Portland cement (OPC) has attracted worldwide attention in recent years, due to its advantages such as environmental benefits, better durability and acceptable mechanical properties. In this paper, it is shown that the large resources of aluminosilicate waste materials in developing countries present a great opportunity for their use to make geopolymer concretes towards building of local physical infrastructure. This paper reviewed research on characteristics and properties of geopolymer binders and concretes. The effects of different raw materials, various activators, mixture formation and curing are discussed

Polarization of Broad Absorption Line QSOs I. A Spectropolarimetric Atlas

We present a spectropolarimetric survey of 36 broad absorption line quasi-stellar objects (BAL QSOs). The continuum, absorption trough, and emission line polarization of BAL QSOs yield clues about their structure. We confirm that BAL QSOs are in general more highly polarized than non-BAL QSOs, consistent with a more equatorial viewing direction for the former than the latter. We have identified two new highly-polarized QSOs in our sample (1232+1325 and 1333+2840). The polarization rises weakly to the blue in most objects, perhaps due to scattering and absorption by dust particles. We find that a polarization increase in the BAL troughs is a general property of polarized BAL QSOs, indicating an excess of scattered light relative to direct light, and consistent with the unification of BAL QSOs and non-BAL QSOs. We have also discovered evidence of resonantly scattered photons in the red wing of the C IV broad emission lines of a few objects. In most cases, the broad emission lines have lower polarization and a different position angle than the continuum. The polarization characteristics of low-ionization BAL QSOs are similar to those of high-ionization BAL QSOs, suggesting a similar BAL wind geometry.Comment: 39 pages, 6 figures (20 .gif files), accepted for publication in The Astrophysical Journal Supplement

Superior UVC light-mediated catalytic activity of a novel NiFe₂O₄@ TiO₂ magnetic nanocomposite synthesized with green route using Pulicaria Gnaphalodes plant extract for enhanced photocatalytic degradation of an antibiotic in water solution

In this study, the NiFe₂O₄@TiO₂ magnetic nanocomposite was synthesized by the green synthesis method, which is an efficient and economical method. Pulicaria Gnaphalodes plant extract was used for nanocomposite synthesis because this method is suitable for the biosynthesis of nanocomposites on a large scale, and the nanocomposite produced by plants is more stable. The efficiency of the synthesized nanocomposite was investigated for the photocatalytic degradation of Penicillin G (PNG) under UVC light irradiation in aqueous solutions. The structural characteristics of this nanocomposite were determined by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, vibrating sample magnetometer, and dynamic light scattering. The effect of different parameters including pH, nanocomposite dose, penicillin G concentration and time were studied to reach optimum conditions. About 71% of PNG in optimal conditions (pH = 9, nanocomposite dose = 0.6 g/L, and penicillin G concentration = 10 mg/L) was decomposed. Generally, the NiFe₂O₄@TiO₂ nanocomposite can be used as an efficient catalyst for the degradation of PNG in aqueous solutions

Pulicaria gnaphalodes-assisted green synthesis of NiFe₂O₄@ZnO nanocomposites for sustainable remediation of an antibiotic from aqueous solution

In this study, the NiFe₂O₄@ZnO nanocomposite was synthesized in a simple, accessible and affordable method using Pulicaria gnaphalodes plant extract as a reducing agent. The structural characteristics of this nanocomposite were determined by transmission electron microscopy (TEM), X-ray diffraction, Fourier transform infrared spectroscopy, vibrating sample magnetometer, X-ray energy diffraction spectroscopy and dynamic light scattering. TEM micrograph confirmed the formation of spherical and cubic spinel ferrite with average dimensions of 75–85 nm. Some parameters such as pH, dose of NiFe₂O₄@ZnO nanocomposite, concentration of penicillin G and reaction time to reach optimal conditions were investigated. According to the results of the present research, the photocatalyst process along with the use of NiFe₂O₄@ZnO nanocomposite as an oxidizing agent is an effective method in degradation of the penicillin G antibiotic from aqueous solutions

Effects of Chlamydia trachomatis Infection on Fertility; A Case-Control Study.

BACKGROUND: Nowadays, Chlamydia trachomatis is known as a causative agent of infertility. Because of, asymptomatic nature of infection, many may suffer from its lasting complications such as infertility. This study was performed in Tehran during April 2007 to April 2008 to compare the prevalence of Chlamydia trachomatis infection in fertile and infertile women using ELISA and PCR methods. METHODS: Overall, 234 infertile and 223 pregnant women, as the fertile group, participated in this hospital-based case-control study. After completing an informed consent form and the questionnaire, first catch urine and blood sample were obtained for PCR and ELISA (IgG, IgM) tests, respectively. Logistic regression analysis was used to control possible confounding factors, and determine adjusted odds ratio of infertility due to the infection. RESULTS: PCR results revealed that 29 (12.4%) of the infertile and 19 (8.5%) of the fertile women were positive for C. trachomatis infection (p = 0.440). IgG was positive in 21 (9.0%) of the infertile and 11 (5.0%) in the fertile group (p = 0.093). IgM assays identified that 2 (0.9%) of the infertile and 4 (1.8%) of the fertile women were positive for the micro-organism (p = 0.375). CONCLUSION: We found no significant differences among fertile and infertile women for Chlamydia trachomatis infection. Nevertheless, molecular techniques which are more sensitive, more specific and non-invasive can be used to detect C. trachomatis infection

To explore identifying the influencing factors of divorce in Tehran

Background & Objectives: The aim of this explorative study was to identify influencing factors as main causes of divorce among couples in Tehran Methods: Three hundred persons from family court of Justice participated from March 2006 to March 2007 in this study. Structured interviews in addition a standard questionnaire were employed. Results: The results indicated that the most causes were psychological factors (96.3), socio-cultural factors (87.3), sex problems (88), economic factors (80.3) and violence (84.3) in participatnts. Conclusion: Premarital counseling suggested for couples to prevent divorce in Iranian community

Exploring efficient photocatalytic degradation of humic acid from aqueous solution with plant-based ZnFe₂O₄@TiO₂ magnetic nanocomposite using Elaeagnus angustifolia tree bark methanolic extract

In the process of sanitizing drinking water, humic acid present in drinking water sources reacts with chlorine disinfectant and forms mutagenic defective, and carcinogenic disinfection byproducts such as trihalomethanes and haloacetic acids. In the present study, the methanolic extract of Elaeagnus angustifolia tree bark was used for the synthesis of ZnFe₂O₄@TiO₂ nanocomposite and then properties and structural elements and diagnostic features of nanoparticles were analyzed. According to the results, the ZnFe₂O₄@TiO₂ nanocomposites have an average crystalline size of ∼65-250 nm. Also, the effects of pH (3-11), nanoparticle dose (0.005-0.1 g/L), and humic acid concentration (2-15 mg/L) were examined up to 120 min of time. From the results, the highest removal percentages achieved about 100% at optimal conditions (pH = 3, nanocomposite dose= 0.05 g/L and humic acid initial concentration = 2 mg/L). The results of this research showed that the efficiency of nanocomposite at the highest concentration of humic acid that was investigated in this research (15 mg/L) was about 95.67%. Therefore, it can be concluded that this nanocomposite, while being cost-effective and environmentally friendly, is also very effective in removing humic acid from an aqueous solution