Electronically tunable voltage-mode quadrature oscillator based on high performance CCCDBA

This paper presents a new electronically tunable voltage-mode quadrature oscillator using two high performance current controlled current differencing buffered amplifiers (CCCDBA), two capacitors and single resistor, all of them are grounded which is advantageous for monolithic integration. The condition of oscillation and the frequency of oscillation are independent and can be controlled by two separate bias currents. The output voltages are obtained at the terminals with almost zero internal impedances, thus there is no need to use any buffering devices. The MOS structure of the CCCDBA presented in this paper is of a high performance and ensures precision, large dynamic range, wide bandwidth and has the capability to drive a load with very low resistance. Non-ideal analysis of the proposed oscillator is provided and PSpice simulation results using the 0.18 μm n-well CMOS technology from TSMC are included to verify the correct functionality of the proposed circuit.     

Optimal sizing of building integrated hybrid PV/diesel generator system for zero load rejection for Malaysia

In this research, an optimisation for building integrated hybrid PV/diesel generator system for zero load rejection for Malaysia is performed. The optimisation is performed considering a loss-of-load probability (LLP) less than 0.01. However, the daily averages of solar energy for Malaysia and a mathematical model of a hybrid PV/diesel generator system are used in this optimisation. The optimisation presented in this paper aims to calculate the optimum capacities of a PV array and diesel generator, which investigate the minimum system cost. An optimisation problem in terms of system units’ cost is solved graphically in this study. Moreover, the optimised system is compared to other energy source choices to highlight its feasibility. The recommended configuration of a PV/diesel system located in Malaysia is C_A = 1.2, C_DG = 0.3, while the optimum C_B is 0.1. The results of the optimisation show that a PV/diesel generator choice is more feasible compared to a standalone PV system or diesel generator system because it reduces the system cost by 35%.     

Direct Oxidation of Propylene to Propylene Oxide with Molecular Oxygen: A Review

The direct oxidation of propylene to propylene oxide (PO) using molecular oxygen has many advantages over existing chlorohydrin and hydroperoxide process, which produce side products and require complex purification schemes. Recent advances in liquid-phase and gas-phase catalytic oxidation of propylene in the presence of only molecular oxygen as oxidant and in absence of reducing agents are summarized. Liquid-phase PO processes involving soluble or insoluble Mo, W, or V catalysts have been reported which provide moderate conversions and selectivities, but these likely involve autoxidation by homogeneous chain reactions. Gas-phase PO catalysts have been mostly Ag-, Cu-, or TiO₂-based substances, although other compositions such as Au-, MoO₃-, Bi-based catalysts and photocatalysts have also been suggested as possibilities. The Ag catalysts differ from those used for ethylene oxide production in having high Ag contents and numerous additives. The additives are solid-phase alkali metals, alkaline earth metals, and halogens, with the most common substances being NaCl and CaCO₃. Nitrogen oxides in the form of gas-phase species or nitrates have also been found to be effective in enhancing PO production. Direct epoxidation by surface nitrates is a possibility. Titania catalysts supported on silicates have also been reported. These have higher PO selectivities at high conversion than silver catalysts.     

Sample preparation optimization for the simultaneous determination of mycotoxins in cereals

The efficiency of three extraction solvents and three clean-up procedures was compared for simultaneous extraction and purification of aflatoxins (AFB1, AFB2, AFG1 and AFG2), ochratoxin A (OTA), and zearalenone (ZEA) from spiked cereal samples. The best recovery rates for all mycotoxins were achieved using methanol: water (80:20) as the extraction solvent and AOZ multi-functional immunoaffinity column (IAC), as clean up method with recovery values of 61–89%, while that of Oasis HLB and MycoSep 226 were 37–67% and 44–78%, respectively. Then, five variables in the IAC clean-up conditions, including primary conditioning with phosphate buffer saline (PBS) (0–10 mL) (X1), extract load up volume (10–20 mL) (X2), washing volume with PBS (10–20 mL) (X3), and eluting solution volumes with methanol (1–3 mL) (X4) and acetic acid (0–1.5 mL) (X5), were optimized for the specific purification and enrichment of the mycotoxins. Results showed that primary conditioning and PBS washing did not have a significant effect on the recovery responses of mycotoxins. Optimized conditions were selected as 0, 15, 10, 1.3, and 1.5 mL for X1–X5, respectively. The recovery rates of AFB1, AFB2, AFG1, AFG2, OTA and ZEA were within 93–104% in spiked rice, under optimal conditions. LOD and LOQ were 0.0125 and 0.05 ng/g for AFB1 and AFG1, 0.0037 and 0.015 ng/g for AFB2 and AFG2, 0.05 and 0.2 ng/g for OTA, and 0.5 and 2 ng/g for ZEA, respectively. Extraction of spiked cereal samples with methanol: water (80:20) and clean up using AOZ IAC column in optimal condition provided recovery range of 77–104% for all targeted mycotoxins.     

Abrasion resistance and mechanical properties of high-volume fly ash concrete

The abrasion resistance and mechanical properties of concrete containing high-volume fly ash (HVFA) were investigated. Sand (fine aggregate) was replaced with 35, 45, and 55% of Class F fly ash by mass. The water to cement ratio and the workability of mixtures were maintained constant at 0.46 and 55 ± 5 mm respectively. Properties examined were compressive strength, splitting tensile strength, flexural strength, modulus of elasticity and abrasion resistance expressed as depth of wear. Test results indicated that replacement of sand with fly ash enhanced the 28-day compressive strength by 25–41%, splitting tensile strength by 12–21%, flexural strength by 14–17%, and modulus of elasticity by 18–23% depending upon the fly ash content, and showed continuous improvement in mechanical properties up to the ages of 365 days. Replacing fly ash with sand significantly improved the abrasion resistance of concrete at all ages. Strong correlation exists between the abrasion resistance and each of the mechanical properties investigated.     

Influence of superplasticizer and curing on porosity and pore structure of cement paste

Most concrete produced today contains admixtures. Superplasticizers (SP) are used for the purpose of improving workability and reducing the water to cement ratio; therefore producing more durable concrete. SP cause better dispersion even at high water to cement ratio. Although SP improves the dispersion of particles, it is not quite clear how the addition of SP affect the porosity and pore size distribution of cement paste. The purpose of this study was to examine the influence of one type of SP on porosity and pore size distribution under different curing regimes. Paste specimens with and without SP were prepared at constant water to cement ratio of 0.45. Specimens were cured for 28 days and some for six months. Specimens were exposed to high temperature (45°C) and normal temperature curing (20°C) and also subjected to different relative humidities (100%, 55% and 25%). Curing at high temperature was carried out to simulate temperature in hot climates. Tests on porosity and pore size distribution were conducted using mercury intrusion porosimetry. The results show that the inclusion of SP decreases the total intruded pore volume of paste. The dominant pore diameter, however, does not seem to be affected and the percentage of pores smaller than 100 nm increases in the presence of SP.     

Petrographic,mechanical and chemical properties of sand resources in Lebanon,eastern mediterranean

In a previous study, the results of extensive surveys and investigations covering 80 percent of the Lebanese territory to locate the major sand resources, were reported. Forty-one samples representing major operating sand quarries or sand excavation sites were located, described, and sampled. The research program reported in this paper was designed to evaluate the 41 sand samples based on petrographic analysis, mechanical and chemical acceptance tests, and results of tests conducted on fresh and hardened concrete samples identical except for the type of sand. Conclusions are presented concerning each sand source. In general, Lebanese sands were found to be fine, poorly graded, and rich with material finer than #200 sieve (0.075 mm). The gradation of the sands used was found to have the most significant effect on concrete compressive strength. Because of the scarcity of construction material resources, techniques are presented to improve the gradation of Lebanese sands and to clean them from excessive deleterious substances.     

Development of Bi-polar plate design of PEM fuel cell using CFD techniques

This paper reviews the common existing designs of flow plates of fuel cells and suggests modifications to some of them to help reduce the pressure drop in the flow channels. Pressure drop is one of the factors that influence the overall performance of the cell both directly and indirectly through interaction with other factors including water management in the cell.The work uses computational fluid dynamics (CFD) to examine different design and study the effect of varying the flow rate (i.e. velocity) on the pressure drop for each of the designs modelled. Again, the designs are optimized by changing different parameters using ANSYS CFX. Results showing the effects of the modifications on pressure drop in the various plates are presented in this paper.From the study of the various designs, a conclusion was drawn that a modification of fuel cell designs in existence using a system similar to the diesel injection system design approach reduced the pressure drop in the fuel cell as shown by the simulation results.This reduction in pressure drop will contribute to the improvement of performance but it must be stressed that other factors also contribute to the overall performance of the cell and reduction in pressure drop alone is not a guarantee of better performance of a certain fuel cell design.     

Invited review: Genetic contributions underlying the development of preimplantation bovine embryos

In recent years, it has become evident that genetic selection to improve milk production has resulted in a decline in dairy cattle fertility. Growing evidence suggests that the greatest loss occurs early in pregnancy around the time of embryo implantation. As a means to make genetic improvements and to assist in reproductive performance, use of artificial reproductive technologies such as artificial insemination and in vitro production of embryos have been widely used. Both of these technologies rely on the competence and quality of gametes for successful development of embryos. Often, selection of animals is based on the genetic merit of the animal, although specific fertility markers are relatively underdeveloped compared with markers for production traits. Similarly, current in vitro fertilization systems could benefit from a uniform method for selection of the best quality embryos to transfer into recipients for successful implantation and delivery of healthy offspring. As genetics underlie biological processes such as fertility, the need exists to further identify and characterize genes that affect fertility and development within both the parental gametes and the embryo. Furthermore, the magnitude of the contribution of each parental genome to the success of embryo development and pregnancy is not clear. As such, the objective of this review is to provide an overview of studies relating to genetic markers at the DNA level, parental and embryonic gene expression, and the effects of epigenetics on embryonic development. Future studies should exploit advances in molecular technologies to identify and classify genes underlying fertility and development to establish biomarkers and predictors for improved genetic selection.