Behaviour of fly ash geopolymer binders under exposure to alkaline media

Abstract: Alkaline agents are primary binder components of geopolymer systems. In the converse, however, the hardened geopolymer binders can be adversely affected under exposure to strong alkalis. This paper presents an investigation conducted to evaluate the effects of highly alkaline exposure environment on fly ash geopolymer binders. In the study, a combination of sodium silicate and 12M NaOH solution was used as the alkali activator to prepare a low calcium (Class F) fly ash - based geopolymer binder. Fly ash geopolymer pastes or mortars were cast into 50 mm cubes and 25 x 25 x 285 mm prisms, then immersed in different media consisting of water or 1M to 3M NaOH solutions maintained at varied temperatures of 23, 38 and 80⁰C. The tests done include compressive strength, expansion, weight changes. Analytical studies were done using X - ray diffraction, X - ray fluorescence, Fourier transform infrared spectroscopy, scanning electron microscopy. Leaching analysis of storage solutions was also conducted

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

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

Infrared and optical polarimetry around the low-mass star-forming region NGC 1333 IRAS 4A

We performed J- and R-band linear polarimetry with the 4.2 m William Herschel Telescope at the Observatorio del Roque de los Muchachos and with the 1.6 m telescope at the Observat\'orio do Pico dos Dias, respectively, to derive the magnetic field geometry of the diffuse molecular cloud surrounding the embedded protostellar system NGC 1333 IRAS 4A. We obtained interstellar polarization data for about two dozen stars. The distribution of polarization position angles has low dispersion and suggests the existence of an ordered magnetic field component at physical scales larger than the protostar. Some of the observed stars present intrinsic polarization and evidence of being young stellar objects. The estimated mean orientation of the interstellar magnetic field as derived from these data is almost perpendicular to the main direction of the magnetic field associated with the dense molecular envelope around IRAS 4A. Since the distribution of the CO emission in NGC 1333 indicates that the diffuse molecular gas has a multi-layered structure, we suggest that the observed polarization position angles are caused by the superposed projection along the line of sight of different magnetic field components.Comment: 37 pages, 9 figures, 5 tables, accepted for publication in A

Analyzing food patterns and preferences of urban population of FasA (Phase I of studying the nutritional healthy city in Fasa)

Background: Proper and healthy eating is one of the key steps for developing a healthy population. The risk of disease and mortality decreases with a good nutrition. The access level, quality and choice of food consumed among people are affected by the economic, social, race and cultural status. It means that people with various culture and social system consume various types of food in various amounts. Methods: In a cross-sectional study, 1000 adults living in the Fasa were selected by cluster sampling. Demographic, socioeconomic status, dietary habits, consumption of some important food items such as fruit and vegetables, oils, cereals, dairy, and salt were questioned in a 26 item questionnaire. Results: The results show that there are significant problems in people lifestyle and dietary patterns in Fasa. A significant proportion of population had not regularly consumed breakfast and snack or significant consumption in fruits and vegetables. Hydrogenated vegetable oil and fried oil considerably used, and the most common method to prepare meat products was frying in oil. The refined grains are the major source of energy in people, and whole grains and cereals did not significantly used. Sugar and sweeteners were consumed significantly. Albeit, there were some positive points in the diet of region, including low consumption of carbonated beverages and processed foods, as well as high consumption of dairy products. Conclusion: Significant drawbacks in the dietary pattern of the region exists that need to be planned to improve them to minimize the risk factors of noncommunicable diseases. © Copyright 2019 by Gazi University Medical Facult

Solidification enhancement in a multi-tube latent heat storage system for efficient and economical production: Effect of number, position and temperature of the tubes

Copyright: © 2021 by the authors. Thermal energy storage is an important component in energy units to decrease the gap between energy supply and demand. Free convection and the locations of the tubes carrying the heat-transfer fluid (HTF) have a significant influence on both the energy discharging potential and the buoyancy effect during the solidification mode. In the present study, the impact of the tube position was examined during the discharging process. Liquid-fraction evolution and energy removal rate with thermo-fluid contour profiles were used to examine the performance of the unit. Heat exchanger tubes are proposed with different numbers and positions in the unit for various cases including uniform and non-uniform tubes distribution. The results show that moving the HTF tubes to medium positions along the vertical direction is relatively better for enhancing the solidification of PCM with multiple HTF tubes. Repositioning of the HTF tubes on the left side of the unit can slightly improve the heat removal rate by about 0.2 in the case of p5-u-1 and decreases by 1.6% in the case of p5-u-2. It was found also that increasing the distance between the tubes in the vertical direction has a detrimental effect on the PCM solidification mode. Replacing the HTF tubes on the left side of the unit negatively reduces the heat removal rate by about 1.2 and 4.4%, respectively. Further, decreasing the HTF temperature from 15◦C to 10 and 5◦C can increase the heat removal rate by around 7 and 16%, respectively. This paper indicates that the specific concern to the HTF tube arrangement should be made to improve the discharging process attending free convection impact in phase change heat storage

Assessment of Nutritional Status in Post Menopausal Women of Ardebil, Iran

The aim of the present study is to describe socio-demographic and anthropometric factors, energy, nutrient intake and food habit of menopause women. In the descriptive cross-sectional study, 924 females (386 urban and 538 rural) aged more than 50 years from different areas of Ardebil province were selected by a multi stage sampling method. Variables including age, anthropometric factors, calorie and nutrients intake as well as the food habit were recorded for each case. In order to determine dietary intake, information of 24 h dietary food recall was recorded for three successive days. The educational levels and some socio-demographic variables were evaluated using an appropriate questionnaire. Statistical comparison of means among different groups was performed using ANOVA and t-test. The general proportions of overweight for rural and urban women were 37.9 and 44.6%, respectively. There was significant differences in anthropometric factors including height, weight and BMI among literacy levels (p< 0.05). No statistically differences were between job levels and anthropometric indicators. The mean of daily iron and vitamins (B1, B3 and C) intakes of post menopausal women were adequate. However the mean of folate, vitamins B2 and B6, calcium, zinc, selenium and calorie intake were less than dietary reference intakes. We concluded that percentage of overweight, obesity among post menopausal women in urban area were more than rural area

Optimum placement of heating tubes in a multi‐tube latent heat thermal energy storage

Data Availability Statement: Data is contained within the article.Utilizing phase change materials in thermal energy storage systems is commonly considered as an alternative solution for the effective use of energy. This study presents numerical simulations of the charging process for a multitube latent heat thermal energy storage system. A thermal energy storage model, consisting of five tubes of heat transfer fluids, was investigated using Rubitherm phase change material (RT35) as the. The locations of the tubes were optimized by applying the Taguchi method. The thermal behavior of the unit was evaluated by considering the liquid fraction graphs, streamlines, and isotherm contours. The numerical model was first verified compared with existed experimental data from the literature. The outcomes revealed that based on the Taguchi method, the first row of the heat transfer fluid tubes should be located at the lowest possible area while the other tubes should be spread consistently in the enclosure. The charging rate changed by 76% when varying the locations of the tubes in the enclosure to the optimum point. The development of streamlines and free-convection flow circulation was found to impact the system design significantly. The Taguchi method could efficiently assign the optimum design of the system with few simulations. Accordingly, this approach gives the impression of the future design of energy storage systems.Funding: This research received no external funding