A study of the weathering of the bukit timah granite part a: Review,field observations and geophysical survey

The Bukit Timah granite exhibits a full range of weathering grades. Examination of these exposures shows that the weathering has been rapid. Field observations and geophysical surveys show that the rock has been weathered up to 70 meters depth, and that the main mechanisms of weathering is chemical decomposition. The humid tropical condition in Singapore with high annual precipitation has produced secondary weathering of the residual soil. The weathering profiles suggest that the weathering of the Bukit Timah granite is stratified with weathered layers and a sharp boundary between the residual soil and the slightly to moderately weathered granite. This paper (Part A) is a review of current weathering classification systems for weathered rock. Some results from field observations and geophysical surveys are also presented in the paper. A weathering classification and determination method is proposed for the Bukit Timah granite. Results from field and laboratory investigations of the weathering of the granite and material properties will be presented in Part B.     

A study of the weathering of the Bukit Timah granite Part B: Field and laboratory investigations

Field investigations consisting of surface seismic refraction and electrical resistivity surveys, drilling and downhole geophysical logging of the rock mass and of the residual soil indicate that the weathering of the Bukit Timah granite has been rapid and is primarily caused by chemical decomposition due to the tropical climate in Singapore. The granite is usually overlain by a thick layer of residual soil. Laboratory tests indicated a large reductions of the material strength, the modulus of elasticity, the rock mass quality and other mechanical properties of the weathered granite. Apart from the mechanical properties of the residual material and/or of the weathered granite rock, physical properties including density, water content, Atterberg's limits, grain size distribution, permeability, sonic velocity and electrical resistivity were also studied in order to assess the weathering grade and the weathering processes.     

Simple-structure integrated coherent transceiver with novelcounter-receiving heterodyne detection scheme

A novel counter-receiving heterodyne detection (CRHD) scheme for a four-section integrated coherent transceiver for access networks is proposed. Error free detection at 100 Mbit/s is achieved with the CRHD scheme. This scheme leads to the relaxation of the design requirements of integrated coherent transceivers and facilitates duplex transmissions with coherent transceivers. A novel full-duplex transmission approach is also proposed and experimentally demonstrated     

Strengthening and Toughening Mechanisms of Ceramic Nanocomposites

Crack-tip bridging by particles is considered to be one of the primary strengthening mechanisms of ceramic nanocomposites. Small, brittle particulate inclusions have been shown to cause crack-tip bridging at short distances behind the crack tip. This mechanism leads to modest toughness but a very steep R -curve, and it is the latter that produces the very high fracture strength of the ceramic nanocomposite. Localized high residual stress around the particles (particularly in the case of silicon carbide-alumina material) causes the strengthening mechanism to operate effectively, even at a small volume fraction of 5%. The present study predicts the magnitude of the toughness increase and the extent of R -curve behavior for the nanocomposite.     

Synthesis and electrical properties of (Bi(1/2)Na(1/2))TiO3 (BNT) ferroelectric thin films by liquid sprayed mist chemical vapor deposition technique

This study aims to synthesize lead-free ferroelectric material, (Bi(1/2)Na(1/2))TiO3 using the Liquid Sprayed Mist Chemical Vapor Deposition (LSMCVD) technique. The mist of precursor solution was vaporized and deposited on two different substrates of Si(100) and (111)Pt/TiO2/SiO2/Si(100) in an oxygen atmosphere. The deposition temperature and time were varied in the range of 400-600 degrees C and 30-90 min. (Bi(1/2)Na(1/2))TiO3 thin film had preferred orientations of (110). The thickness of the thin film deposited was 35-162 nm. The remnant polarization (2Pr) and the dielectric constant were 4.6-16.8 microC/cm2, 325-350, respectively.     

Fabrication and magnetic characteristics of vertical feco nanowire arrayed in Al2O3 insulator of honeycomb bulkhead structure

High-density and uniform-sized FeCo alloy nanowires were prepared by electro deposition of Fe2+ and Co2+ into Anodic aluminum oxide (AAO) templates with two different diameters. These templates were fabricated with three-step anodization method. The additional anodization after the 2nd anodization step resulted in the decrease of the thickness of bottom barrier layer. It found an optimum condition to obtain a successful electrodeposition of Fe2+ and Co2+ into AAO templates. The nanowires with the diameters of 25 nm and 80 nm were homogeneously embedded in the AAO templates and their magnetic properties were strongly affected by diameters of nanowire.     

Characteristics of nano-sized (Pb, La)TiO3 powder synthesized at room temperature

We synthesized nano-sized (Pb, La)TiO3 powder using a high energy mechano-chemical technique at room temperature. By the results, nano-sized (Pb, La)TiO3 powder with perovskite structure was successfully synthesized from an oxide mixture using a high energy mechano-chemical technique without any post-annealing. The mechanically-synthesized (Pb, La)TiO3 powder consisted of nanometer sized particles and had very high homogeneity. According to increase of milling time, source phases such as Pb oxides and TiO2 disappeared and the perovskite PLT phase was formed by chemical reaction and the release of OH group.     

Mechanical flexibility of transparent PEDOT:PSS electrodes prepared by gravure printing for flexible organic solar cells

The mechanical flexibility of transparent poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films printed onto a flexible PET substrate using a gravure printing method was investigated using a lab-made bending test system. Gravure-printed PEDOT:PSS electrodes with a sheet resistance of 359 Ω/square and a transparency of 88.92% showed outstanding flexibility in several types of flexibility tests, including outer/inner bending, twisting and stretching. Notably, the PEDOT:PSS electrode had a constant resistance change (ΔR/R₀) within an outer and inner bending radius of 10 mm. In addition the stretched PEDOT:PSS electrode showed a fairly constant resistance change (ΔR/R₀) up to 4%, which is more stable than the resistance change of conventional amorphous ITO electrode. The twisting test revealed that the resistance of the PEDOT:PSS electrode began to increase at an angle of 36° due to delamination of the film from the PET substrate. Despite the high sheet resistance of the PEDOT:PSS electrode the flexible organic solar cells fabricated on the PEDOT:PSS electrode showed a power conversion efficiency of ∼2% (FF: 44.9%, V_o: 0.495 V and J_sc: 9.1 mA/cm²), indicating the possibility of using gravure printed PEDOT:PSS as a flexible and transparent electrode for printing-based flexible organic solar cells.     

Role of Si on the Diffusional Interactions Between U-Mo and Al-Si Alloys at 823?K (550?��C)

U-Mo dispersions in Al-alloy matrix and monolithic fuels encased in Al-alloy are under development to fulfill the requirements for research and test reactors to use low-enriched molybdenum stabilized uranium alloy fuels. Significant interaction takes place between the U-Mo fuel and Al during manufacturing and in-reactor irradiation. The interaction products are Al-rich phases with physical and thermal characteristics that adversely affect fuel performance and result in premature failure. Detailed analysis of the interdiffusion and microstructural development of this system was carried through diffusion couples consisting of U-7 wt pct Mo, U-10 wt pct Mo and U-12 wt pct Mo in contact with pure Al, Al-2 wt pct Si, and Al-5 wt pct Si, annealed at 823 K (550 °C) for 1, 5 and 20 hours. Scanning electron microscopy and transmission electron microscopy were employed for the analysis. Diffusion couples consisting of U-Mo in contact with pure Al contained UAl₃, UAl₄, U₆Mo₄Al₄₃, and UMo₂Al₂₀ phases. Additions of Si to the Al significantly reduced the thickness of the interdiffusion zone. The interdiffusion zones developed Al- and Si-enriched regions, whose locations and size depended on the Si and Mo concentrations in the terminal alloys. In these couples, the (U,Mo)(Al,Si)₃ phase was observed throughout the interdiffusion zone, and the U₆Mo₄Al₄₃ and UMo₂Al₂₀ phases were observed only where the Si concentrations were low.     

Antimicrobial resistance observed in Escherichia coli strains isolated from fecal samples of cattle and pigs in Korea during 2003-2004

A total of 744 Escherichia coli strains isolated from 830 fecal samples of healthy cattle and pigs in all provinces of Korea were examined for resistance to 16 antimicrobials. The most frequently observed resistance in cattle isolates was to tetracycline (30.5%), followed by resistance to streptomycin (20.4%), ampicillin (12.0%) and chlorampenicol (6.9%). Prevalences of resistance to the same four antimicrobials in swine isolates were 96.3%, 66.8%, 66.1%, and 47.6%, respectively. The prevalence of resistance in pigs was much higher than that in cattle, with 98.3% of pig isolates and 37.1% of cattle isolates showing resistance to one or more of the antimicrobial agents tested.