Mechanical Properties and Microstructure of a Metakaolin-Based Inorganic Polymer Mortar Reinforced with Quartz Sand

Silicon - The synthesis, mechanical behaviour, and microstructure of metakaolin-based geopolymer mortar reinforced with quartz sand are presented in this investigation. Fine sand (quartz sand)...     

An integrated technique using solar and evaporation ponds for effective brine disposal management

Desalination is a process that involves the removal of salts and non-ionic minerals from seawater to produce freshwater that is fit for human consumption. This process produces brine, which is typically redisposed into the sea. The relatively high salt concentration in the disposed brine increases the salinity of water and soil, which adversely affects the environment. However, brine is found to be rich in economically valuable minerals. In order to effectively manage the disposed brine, this study proposes an integrated technique using solar and evaporation ponds to filter valuable minerals from concentrated brine. The results of this study demonstrate that the proposed technique can be effectively employed for this purpose. Furthermore, this helps reduce desalination costs and complies with the notion of renewable energy production and eco-friendliness.     

Hydrous iron oxide for removal of inorganic contaminants in simulated stormwater: A batch sorption kinetics study

Urban stormwater runoff, which consists of inorganic and organic contaminants, is a major source of pollutants to receiving waters and therefore they need to be removed. Simultaneous removal of contaminants, Cd²⁺, Cu²⁺, Ni²⁺, Zn²⁺ (heavy metal cations), and SeO₄²⁻ (oxyanion) from a simulated stormwater by a hydrous ferric oxide (HFO) was studied in batch and column sorption experiments. In the batch experiment the rate of sorption of the ions was rapid at the beginning and reached equilibrium in approximately 300 min. The amounts of ions sorbed were proportionate to the respective initial concentration of the ions added to the HFO. Cluster analysis showed that all heavy metals had similar sorption behavior, whereas Se had a distinctly different sorption process. Of the three different kinetic models tested the pseudo-first order kinetic model fitted the data the best. The column experimental results beyond 180 min were consistent with those of the batch experiment that the removal efficiencies of the ions were in proportion to the ion concentration in the feed. Below 180 min, Cu appeared to be preferentially removed than Zn.     

Radiation modelling and performance evaluations of fixed,single- and double-axis tracking surfaces: a case study for Dhahran city,Saudi Arabia

This work overviews the solar radiation basics and insolation of different surfaces is presented. A complete solar radiation modelling and investigation on the effect of horizontal plate, yearly tilt, monthly tilt, and single-axis and double-axis tracking surface on the insolation are carried out to conduct performance evaluation using the case study in Dhahran city of Saudi Arabia. The increments received by insolation for the yearly tilt, monthly tilt, and single-axis and dual-axis tracking surface with respect to traditional flat-plate collector is estimated. The results show that the yearly optimal tilt angle due to the south is close to the 0.913 time latitude of Dhahran. It is found that the yearly irradiation gains using yearly and monthly optimal tilts relative to flat panel installation are 7% and 14%, respectively. The yearly insulation gains made by single-axis and dual-axis continuous tracking surfaces are 33% and 48%, respectively.     

The impact of Soft handoff on the uplink capacity in WCDMA systems

Soft handoff has improved the performance of user communications during the crossing from one cell to another. However, it influences from other side on the aggregate availability of resources. Each mobile station in soft handoff uses multiple resources in both directions (uplink and downlink) to transmit/receive same data to/from each cell the mobile station connects with. Furthermore, these connections themselves will increase the interference in those cells. This paper suggests a mechanism to reduce the handoff failure and call blocking by reducing the interference arising from multiple connections of a user in soft handoff. Simulation results show that the handoff failure and call blocking can be reduced if we integrated this mechanism in the scheme of resource allocation.     

Epidemiolgical significance of HBs-antigen subtypes D and Y in the Heidelberg area

We have had a positive experience using a modified approach to behavior modification of eating patterns, exercise, and activity, along with nutrition and health education. During the first year, forty-four adult patients completed the program, which was conducted in the out-patient clinic of a large hospital by a dietitian and a nurse practitioner. A cross-section of the patient population was admitted. The program had a pre-determined number of sessions, each of which was partially structured. When compared with the patients in individual therapy in our Nutrition Clinic, a more consistent weight loss in a shorter time was observed in the group participants. Whether the techniques described here will lead to sustained weight loss over time bears further study.     

Clear-water scour at long skewed bridge piers

Abstract

The results of an experimental study on clear-water scour at long skewed rectangular piers under steady flows at threshold velocity are presented. The scour mechanisms due to skewness effects with a wide range of angle of attack, α, and two sizes of uniform cohesionless bed sediment (d₅₀ = 0.23 and d₅₀ = 0.80 mm) have been investigated in a 50-m-long, 1.5-m-wide, and 2.0-m-deep flume. Empirical relation to demonstrate the effects of skewness in terms of dimensionless variables, such as aspect ratio (L/b), the angle of attack (α), flow shallowness (y/B_α), sediment coarseness (B_α/d₅₀), the sediment gradation coefficient (σ_g), on scour depth is presented. The empirical relation is focused on predicting the angle of attack factor, K_α. The experimental data obtained in this study and data available from the literature were used to validate the predictions of existing methods and the accuracy of the proposed method. The proposed method gives reasonable scour depth predictions and was verified with statistical methods where the mean error was reduced from 53.6 to 18.1%.     

Functionalized multi-walled carbon nanotubes for oil spill cleanup from water

The growing global economy resulted in an incessant increase in transportation and exploitation of oil. Hence, the oil spillage has been considered a serious threat to aquatic and terrestrial ecosystems. Therefore, water purification has been considered a major challenge around the world. There are numerous classical methods available for oil removal from water, but owing to multiple defects and disadvantages, research efforts have focused to find such adsorbents which can improve oil adsorption capability. Traditional adsorbent material typically applied in oil removal includes activated carbon, organoclays, wool, zeolites, etc. These materials suffer from several drawbacks such as low absorption capacity, non-selective absorption, and complicated reusability, whereas nano-adsorbents offer multiple advantages such as having multiple sorption sites, large surface area, short intra-particle diffusion distance, tuneable pore size, and ease of low-temperature modification. Multi-walled carbon nanotubes (MWCNTs) are extensively used adsorbent materials with a strong affinity for the removal of organic pollutants. The functionalization MWCNTs further increase the sorption capacity of adsorbents manifolds to remove organic materials. These nanocomposites are also compatible with green materials and considered environmentally friendly adsorbents. This review paper aims at providing an insight to understand the properties of the MWCNTs and their potential use to adsorb hydrocarbons from water. Moreover, the synthesis methods of those materials, their modification procedures including the functionalization with metal oxide nanoparticles, and applications are also discussed in detail.

Graphic abstract

     

Development and Background of Shells Theories-A Review Study

Thin shells are one of the structural elements that have versatile contributions in different engineering sectors,specifically in architectural,civil,mechanical,aeronautical,and marine engineering industries.Liquid-retaining structures,wide-span roofs,water tanks,arch dooms,and shells used in building nuclear power plants are recognized application examples of shell structures in architectural and civil engineering.This variety in using shells in different engineering sectors is due to the productivity of load-carrying behavior,excellent reservation in strength and structural integrity,shell structures are preferable in comparison to structural systems having the same span and dimensions;high stiffness,and covering a large areas.Besides the above distinguishing mechanical pros,it is widely accepted that structures and building containing shells are usually preferred by architectures and designers for aesthetic purposes.The analysis of shells has gone through many stages until the arrival of modern theories.In this study the different theories of shells were discussed,the background and development of shell theories were illustrated in this investigation.