Two years of aerosol pollution monitoring in Singapore: a review

An aerosol sampling campaign was initiated more than two years ago in Singapore. The aim was to determine the average elemental concentrations in fine and coarse aerosol fractions as well as to identify major pollution sources and their impact. For that purpose, two air samplers were employed at two different sampling locations; one sampler was a fine particulate aerosol sampler (PM2.5) located at the vicinity of a major industrial area. The other was a stacked filter unit (SFU) sampler designed for collection of fine and coarse fractions (PM2.5 and PM10) and installed in the residential area. Samples were taken typically twice a week and in several occasions daily. During the period of two years more than 700 aerosol samples were collected and analyzed using PIXE and RBS techniques. All samples were analyzed for 18 elements ranging between Na, Mg, Al, etc. up to As and Pb. Large daily and seasonal variations were found for most of the elements. These variations are attributed mainly to meteorological changes, in particular changes in wind speed and direction. On several occasions, short term sampling was performed to identify fingerprints of major pollution sources such as road traffic, refineries, as well as the rain-forest fires in neighboring countries. A summary of our findings is presented and discussed.     

Review of Nanocellulose Polymer Composite Characteristics and Challenges

The nanosize cellulose has emerged in the last two decades as an efficient strategy to improve the structural and functional properties of polymer composite. This review focuses to explore the unique mechanical–thermal properties of cellulose-based nanocomposites particularly on the various reinforcing mechanisms of nanocellulose. The promising reinforcing capabilities of nanocellulose mainly lie in their intrinsic chemical natures, aspect ratio, and degree of crystallinity. In this article, the potential factors deteriorating the aspect ratio and crystallinity have been systematically reviewed. Some relevant suggestions/solutions were also widely exploited toward tailoring the generating problems.     

Domain patterns in free-standing nanoferroelectrics

A real space three-dimensional (3-D) Ginzburg–Landau framework is used to investigate the domain patterns in free-standing ferroelectric nanostructures undergoing cubic to tetragonal transitions. The study is motivated by the recent progress in fabricating free-standing single crystalline ferroelectric nanostructures which exhibit complex ferroelastic domain patterns. We demonstrate that for nanostructures with uncompensated surface charges internal stresses generated due to the coupling between electrostatic and elastic interactions can induce bulk-like ferroelastic domain patterns in free-standing ferroelectrics, without invoking any extrinsic mechanisms such as non-transforming surface layers. Further, we show that for very small structures the interplay between electrostatics and elasticity leads to a large diversity of domain patterns that can be observed in 3-D free-standing nanostructures.     

Benefits and Biosafety of Use of 3D-Printing Technology for Titanium Biomedical Implants: A Pilot Study in the Rabbit Model

Background: Titanium has been used in osteosynthesis for decades and its compatibility and safety is unquestioned. Studies have shown that there is release and collection of titanium in the organ systems with little note of toxicity. The gold standard is considered to be titanium osteosynthesis plate produced by milling methods. The use of customized titanium plates produced with 3D printing, specifically direct metal laser sintering, have found increasing use in recent years. It is unknown how much titanium is released in these printed titanium implants, which is known to be potentially porous, depending on the heat settings of the printer. We hypothesize that the amount of titanium released in printed titanium implants may be potentially more or equal compared to the gold standard, which is the implant produced by milling. Methods: We studied the biosafety of this technology and its products by measuring serum and organ titanium levels after implantation of 3D-printed versus traditionally fabrication titanium plates and screws in a pilot study using the rabbit model. A total of nine rabbits were used, with three each in the control, milled and printed titanium group. The animals were euthanized after six months. Serum and organs of the reticuloendothelial system were harvested, digested and assayed for titanium levels. Results: Organ and serum titanium levels were significantly higher in rabbit subjects implanted with titanium implants (milled and printed) compared to the control group. However, there was no significant difference in organ and serum titanium levels of subjects implanted with milled and traditionally fabricated titanium implants. Conclusions: The biosafety of use of 3D-printed titanium implants and traditionally fabricated titanium implants are comparable. With this in mind, 3D-printed custom implants can not only replace, but will very possibly surpass traditionally fabricated titanium implants in the mode and extent of use.     

Modeling peirce-smith converter operating costs

A cost model for the operation of copper converters is developed in this study, allowing an evaluation of the economic impact of changes to operating procedures and/or injection technologies. The model uses material and enthalpybalances for the slag and copper blows in a Peirce-Smith converter. The length of the converting cycle is calculated from the capacity of the blowers and the required blast along with the times required for other operations such as charging and skimming and idle time. Downtime, labor, and materials for converter lining repair as well as other costs such as oxygen enrichment are also considered in the cost calculations. The model is formulated in a spreadsheet using common programming language and is easily extended to examine the costs of alternative operating strategies or injection technologies such as high-pressure, shrouded injection. Example calculations showing the cost benefits of changing operating procedures and technology are presented.     

Finite element modeling of erosive wear

Material damage caused by the attack of particles entrained in a fluid system impacting a surface at high speed is called ‘Erosion’. Erosion is a phenomenon that takes place in several engineering applications. It also can be used in several manufacturing process such as abrasive waterjet machining. Erosion is a complex process dependent on particle speed, size, angle of attack as well as the behavior of the eroded material. Extensive experimental results have been reported in the literature on the erosion of different materials. Simulating the erosion process through finite element enables the prediction of erosion behavior of materials under different conditions, which will substitute the need of experimentation, and will enable the identification of constants required for existing analytical models.In this paper, an elasto-plastic finite element (FE) model is presented to simulate the erosion process in 3D configuration. The FE model takes into account numerical and material damping, thermal elastic–plastic material behavior and the effect of multiple particle impacts as well as material removal. The workpiece material modeled was Ti–6Al–4V. The effects of strain hardening, strain rate and temperature were considered in the non-linear material model. Comparison against results reported in literature and erosion models by Finnie, Bitter and Hashish are made. It is shown that the predicted results are in agreement with published results obtained experimentally and from analytical erosion models.     

Phononic and magnonic dispersions of surface waves on a permalloy/BARC nanostructured array

Phononic and magnonic dispersions of a linear array of periodic alternating Ni₈₀Fe₂₀ and bottom anti-reflective coating nanostripes on a Si substrate have been measured using Brillouin light scattering. The observed phononic gaps are considerably larger than those of laterally patterned multi-component crystals previously reported, mainly a consequence of the high elastic and density contrasts between the stripe materials. Additionally, the phonon hybridization bandgap has an unusual origin in the hybridization and avoided crossing of the zone-folded Rayleigh and pseudo-Sezawa waves. The magnonic band structure features near-dispersionless branches, with unusual vortex-like dynamic magnetization profiles, some of which lie below the highly-dispersive fundamental mode branch. Finite element calculations of the phononic and magnonic dispersions of the magphonic crystal accord well with experimental data.     

Effect of porogenic solvent on the porous properties of polymer monoliths

Polymer monoliths with open pores and median pore size of about 15 nm–3 μm have been successfully synthesized by photoinitiated polymerization of butyl methacrylate and ethylene glycol dimethacrylate monomers. The solubility of the monomers in a porogenic solvent is determined by Hildebrand solubility parameter, and it is found that it has great effect on the pore size of the polymers synthesized. Polymers with larger pores are usually generated with poorer solvents for the monomers. However, polymers with different pore sizes and porosities have been obtained using porogenic solvents with similar Hildebrand solubility parameters. The evaporation rate of the porogenic solvents might be another critical factor affecting the properties of the polymer monoliths. Moreover, the effect of water as a cosolvent on the pore size and porosity of the polymers have also been investigated. Polymers with larger pore size have been prepared with the presence of water due to the occurrence of earlier phase separation in the polymerization. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Drying Characteristics of Malaysian Paddy: Kinetics & Grain Cracking Quality

Abstract

Drying kinetics of Malaysian paddy dried in a laboratory scale batch rapid bin dryer was studied. Quality of paddy after drying at temperatures of 60 and 80°C, bed heights of 2 and 4 cm, and at different drying stages was presented in terms of cracking percentage. Moisture content of paddy reduced exponentially with time and became stable at equilibrium moisture content. Characteristic drying rate curves exhibited mainly falling rate period, with an induction period in deep beds, but without the constant rate period. A custom-made light box was built to visually analyze the cracking in paddy kernel. The extent of breakage is directly related to the crack percentage. The percentage of cracks increased with drying and tempering temperatures and was higher after 2 weeks of storage before milling. Bed heights did not significantly affect the head rice yield as much as tempering between two drying stages. Temperatures above 80°C caused severe cracking in paddy kernel and produced miserable yield of head rice after milling, which could be slightly improved by tempering. The use of a proper miller is also important in ensuring good head yield results and whiteness quality.     

Electro-Kinetic Technology as a Low-Cost Method for Dewatering Food By-Product

Increasing volumes of food waste, intense environmental awareness, and stringent legislation have imposed increased demands upon conventional food waste management. Food by-products that were once considered to be without value are now being utilized as reusable materials, fuels, and energy in order to reduce waste. One major barrier to the valorization of food by-products is their high moisture content. This has brought about the necessity of dewatering food waste for any potential re-use for certain disposal options. A laboratory system for experimentally characterizing electro-kinetic dewatering of food by-products was evaluated. The bench scale system, which is an augmented filter press, was used to investigate the dewatering at constant voltage. Five food by-products (brewer's spent grain, cauliflower trimmings, mango peel, orange peel, and melon peel) were studied. The results indicated that electro-kinetic dewatering combined with mechanical dewatering can reduce the percentage of moisture from 78% to 71% for brewer's spent grain, from 77% to 68% for orange peel, from 80% to 73% for mango peel, from 91% to 74% for melon peel, and from 92% to 80% for cauliflower trimmings. The total moisture reduction showed a correlation with electrical conductivity (R² = 0.89). The energy consumption of every sample was evaluated and was found to be up to 60 times more economical compared to thermal processing.