In situ formation of leak-free polyethylene glycol (PEG) membranes in microfluidic fuel cells.

Membraneless microfluidic fuel cells operated under two co-laminar flows often face serious fuel cross-over problems, especially when flow rates are close to zero. In this study, we show that polyethylene glycol (PEG) monomers can be cross-linked inside microfluidic channels to form leak-free PEG membranes, which prevent mixing of two incompatible electrolyte solutions while allowing diffusion of certain molecules (e.g. glucose) and ions. By using PEG monomers of different molecular weights and cross-linking conditions, we are able to tailor selectivity of the membrane to allow passage of glucose while blocking larger molecules such as trypan blue. As a proof of principle, a microfluidic fuel cell with a PEG membrane and two incompatible electrolytes (acid and base) is demonstrated. Thanks to the leak-free nature of the PEG membrane, these two electrolytes do not mix together even at very slow flow rates. This microfluidic fuel cell is able to generate a voltage up to ∼450 mV from 10 mM of glucose with a flow rate of 20 µL min-1. This microfluidic fuel cell is potentially useful as a miniature power source for many applications.

Phase transitions of silver and silver-palladium alloys immersed in mercury.

A series of Ag-Hg and Ag-Pd-Hg phases have been prepared by immersion in mercury and subsequent heat treatment of pure Ag and a series of Ag-Pd alloys. Phase transitions, along with the changes involved in morphology and chemistry, are investigated. Experimental results indicate that when mercury-immersed Ag discs are heat-treated at 90 degrees C for 12 h, large (>50 microm) crystals with Ag/Hg atomic ratios close to those of stoichiometric AgHg(2) form on the Ag surface. Heat treatment for 36 h causes these crystals to disintegrate into smaller (majority <10 microm) Ag(2)Hg(3) (gamma(1)) crystals. After 60 h, the stoichiometric gamma(1) crystals further breakdown into even smaller stoichiometric AgHg(beta(1)) crystals. The oft-referenced beta(1) phase Ag(1.1)Hg(0.9) is not supported in the present study. Addition of Pd to Ag has a dramatic effect on the morphology of the gamma(1) phase. With more addition of Pd, large-faceted and elongated gamma(1) crystals tend to grow in the midst of smaller matrix gamma(1) crystals. All three different Pd-containing crystals have (Ag + Pd)/Hg ratios very close to those of the stoichiometric gamma(1) phase, indicating that added Pd tends to replace Ag, rather than Hg, in the gamma(1) phase.

Distribution of the FcgammaRIIIa 176 F/V polymorphism amongst healthy Chinese, Malays and Asian Indians in Singapore.

AIMS: To determine and compare the distribution of the FcgammaRIIIa 176 F/V polymorphism across three ethnically distinct populations (Chinese, Asian Indians and Malays) in Singapore. METHODS: The FcgammaRIIIa 176 F/V polymorphism was genotyped by direct sequencing from genomic DNA samples obtained from normal healthy Chinese, Asian Indians and Malays (n = 192 from each population). RESULTS: The allelic frequencies of the high binding affinity FcgammaRIIIa 176 V allele for Chinese, Asian Indians and Malays were 35%, 33% and 46%, respectively (F allele frequencies were 65%, 67% and 54%, respectively). Genotype distributions were found to conform to the Hardy-Weinberg law (P > 0.05) in each group. chi(2) comparisons revealed significant differences in the genotype distributions of the FcgammaRIIIa 176 V/F polymorphism of Malays from the other two populations (Chinese and Asian Indians). However, no significant difference in the genotype distributions of the FcgammaRIIIa 176 V/F polymorphism was observed between Chinese and Asian Indian populations. CONCLUSIONS: The genotype distributions of the FcgammaRIIIa 176 V/F polymorphism in healthy Malays are significantly different from both Chinese and Indians. These observations provide the fundamentals on which future disease associations may be built and also present important implications for the design of therapeutic regimens amongst various ethnic groups.

Structure and properties of Titanium-25 Niobium-x iron alloys.

The present work studies the effect of iron on microstructure, mechanical properties and corrosion behavior of Ti-25Nb based system with emphasis on improving strength/modulus ratio. Experimental data shows that cast Ti-25Nb-3Fe has a beta phase with a entirely of dendrite morphology. The bending strength/modulus ratio is 24.6 higher than Ti-6Al-4V (17.4) by 41.4% and than c.p. Ti (9.3) by 165%. The critical anodic current density of the metal in 37 degrees C Hank's solutions is lower than approximately 100 microA/cm(2). Ti-25Nb-3Fe alloy has a great potential for use as an implant material.

Structure and properties of cast binary Ti-Mo alloys.

Structure and properties of a series of binary Ti-Mo alloys with molybdenum contents ranging from 6 to 20 wt% have been investigated. Experimental results indicated that crystal structure and morphology of the cast alloys were sensitive to their molybdenum contents. The hexagonal alpha' phase c.p. Ti exhibited a feather-like morphology. When Mo content was 6 wt%, a fine, acicular martensitic structure of orthorhombic alpha" phase was observed. When Mo content was 7.5 wt%, the entire alloy was dominated by the martensitic alpha" structure. When Mo content was increased to 10 wt% or higher, the retained beta phase became the only dominant phase. Among all Ti-Mo alloys, the alpha" phase Ti-7.5Mo alloy had the lowest hardness. The bending strength of Ti-7.5Mo was similar to that of Ti-15Mo and Ti-13Nb-13Zr, and higher than c.p. Ti by nearly 60%. The bending modulus of the alpha"-dominated Ti-7.5Mo alloy was lower than that of Ti-15Mo by 22%, of Ti-6A1-4V by 47%, of Ti-13Nb-13Zr by 17%, and of c.p. Ti by 40%.