A simple HPLC-UVD method for detection of etofenprox in green tea using sample hydration

Residue levels were estimated using HPLC-UV detection. Samples were hydrated and extracted using acetonitrile. Analytical linearity in the range of 0.02 to 2.0 mg/kg was excellent with a determination coefficient (R ²) of 1.0. Recovery at levels of 0.2 and 1.0 mg/kg ranged from 89.9 to 94.6% with a relative standard deviation <5%. Sufficient sensitivity was achieved. The limits of detection and quantification were 0.006 and 0.02 mg/kg, respectively. The method was successfully applied to analysis of field samples. This method was effective and can be used for routine analysis of etofenprox in tea samples at low concentrations.     

Direct reproduction of 3D microstructures using a hybrid approach; by creation of master-patterns and metallic molds for embossing

The fabrication of a three-dimensional (3D) metallic mold for multi-production of microstructures was studied to settle the problem of long processing time and efforts in 3D fabrication based on the accumulation of layer-by-layer. Even though two-photon induced polymerization (TPP) has been considered as a unique way for fabrication of precise real 3D microstructures such as 3D filters, 3D photonic crystals, microlens arrays, it required considerable effort and much processing time inevitably for these fabrications. Therefore, a simple and effective method was proposed using a metallic mold in this work. 3D micro-master patterns were prepared using TPP, and then counter-shaped Ni molds were created using an electroforming process. With this hybrid approach, 3D microstructures were much more easily and quickly reproduced by hot-forming compared to the TPP approach was used only. In this work, we report on the processing parameters used to fabricate a metallic mold and reproduce 3D microstructures using the mold.     

A review of the internal forced convective heat transfer characteristics of nanofluids: Experimental features,mechanisms and thermal performance criteria

In this review paper, we summarize important milestones in experimental studies that indicate the effects of volume fraction, nanoparticle size, operating temperature and pH on the internal forced convective heat transfer characteristics of nanofluids. In addition, many mechanisms for the enhancement of the convective heat transfer coefficient of nanofluids proposed by investigators are categorized into two dominant mechanisms. The first dominant mechanism is properties’ change of nanofluids such as thermal conductivity and viscosity. The other is the motion of nanoparticles in nanofluid flow due to Brownian motion, thermal dispersion and migration. Finally, the thermal performance criteria which can estimate whether nanofluids are useful in actual engineering systems, are summarized. Authors expect that the understanding of the convective heat transfer characteristics of nanofluids could help many thermal engineers to develop nanofluids which can be used in industrial applications.     

Fabrication of nickel micromesh sheets and evaluation of their water-repellent and water-proof abilities

Nickel micromesh sheets were designed and fabricated and their water-repellent and water-proof abilities were characterized. The network-type microstructures of the micromesh sheets functioned as micro-protrusions of lotus leaves, which allowed the sheets to superhydrophobic. The micromesh enabled the material waves, including sound and light waves, to pass through the microholes, but repelled water. Because of the effects of the micromesh and plasma polymerized fluorocarbon (PPFC) coating, the contact angle of the micromesh sheets was drastically jumped up from 63° of the non-coated nickel flat film to 140° of the PPFC-coated nickel micromesh, which modified the nickel sheet from hydrophilic to superhydrophobic. The narrower lattice width in the micromesh was more effective at enhancing the water-repellency. On the other hand, the narrow lattice width weakened the water-proof ability. Reducing the hole size and increasing the lattice width of the micromesh are necessary to improve the water-proof ability.     

Formation of nanosized martensite particles in stainless steels

Martensitic transformations occur in steels and other metals when the material is quenched or cooled. During the transformation, a metastable phase transforms in an autocatalytic way into a thermodynamically stable phase. Thus, it has been considered to be impossible to control the size of martensite in the order of nanometers. Here, we report the formation and dispersion of nanosized martensite in stainless steels by controlling the dislocation density and temperature. Electron microscopy revealed that martensite particles of approximately 5 nm in diameter were dispersed. Since both work hardening and precipitation hardening are effective in this material, this would be an additional, newly discovered strengthening mechanism for steels.     

High-shock silicon accelerometer with suspended piezoresistive sensing bridges

A high-shock 2000 g accelerometer with suspended piezoresistive sensing bridges has been designed, fabricated, and tested. Structural size of the accelerometer has been obtained through an optimal design process. Four resistors are electrically connected to form a Wheatstone bridge circuit. A sensitivity of 25.5 μV/g has been measured from the fabricated accelerometer with a nonlinearity of 0.2% in an acceleration range within 2000 g. The real-time response of the fabricated accelerometers accurately follows the reference accelerometer. The newly fabricated accelerometer has survived an over-shock condition of 4667 g.     

Wild and hatchery populations of Korean starry flounder (Platichthys stellatus) compared using microsatellite DNA markers

Starry flounder (Platichthys stellatus) is an important sport and food fish found around the margins of the North Pacific. Aquaculture production of this species in Korea has increased because of its commercial value. Microsatellite DNA markers are a useful DNA-based tool for monitoring the genetic variation of starry flounder populations. In this study, 12 polymorphic microsatellite DNA markers were identified from a partial genomic starry flounder DNA library enriched in CA repeats, and used to compare allelic variation between wild and hatchery starry flounder populations in Korea. All loci were readily amplified and demonstrated high allelic diversity, with the number of alleles ranging from 6 to 18 in the wild population and from 2 to 12 in the farmed population. A total of 136 alleles were detected at the 12 microsatellite loci in the two populations. The mean observed and expected heterozygosities were 0.62 and 0.68, respectively, in the hatchery samples and 0.67 and 0.75, respectively, in the wild samples. These results indicate lower genetic variability in the hatchery population as compared to the wild population. Significant shifts in allelic frequencies were detected at eight loci, which resulted in a small but significant genetic differences between the wild and hatchery populations (F(ST) = 0.043, P < 0.05). Further studies with additional starry flounder sample collections are needed for comprehensive determinations of the genetic varieties between the wild and hatchery populations. These microsatellite loci may be valuable for future population genetic studies, monitoring the genetic variation for successful aquaculture management and the preservation of aquatic biodiversity.     

Engineering of the catalytic site of xylose isomerase to enhance bioconversion of a non-preferential substrate

Mutation in active site would either completely eliminate enzyme activity or may result in an active site with altered substrate-binding properties. The enzyme xylose isomerase (XI) is sterospecific for the α-pyranose and α-fructofuranose anomers and metal ions (M1 and M2) play a pivotal role in the catalytic action of this enzyme. Mutations were created at the M2 site of XI of Thermus thermophilus by replacing D254 and D256 with arginine. Mutants D254R and a double mutant (D254R/D256R) showed complete loss of activity while D256R showed an increase in the specificity on D-lyxose, L-arabinose and D-mannose which are non-preferential substrates for XI. Both wild type (WT) and D256R showed higher activity at pH 7.0 and 85°C with an increase in metal requirement. The catalytic efficiency Kcat/Km (S(-1) mM(-1)) of D256R for D-lyxose, L-arabinose and D-mannose were 0.17, 0.09 and 0.15 which are higher than WT XI of T.thermophilus. The altered catalytic activity for D256R could be explained by the possible role of arginine in catalytic reaction or the changes in a substrate orientation site. However, both the theories are only assumptions and have to be addressed with crystal study of D256R.     

Synthesis of an active and stable Ptshell–Pdcore/C catalyst for the electro-oxidation of methanol

A Pt_shell–Pd_core/C catalyst is prepared via electroless deposition and galvanic displacement. The catalyst is active toward the electro-oxidation of methanol and is more stable against CO_ad-poisoning than a commercial Pt/C catalyst. The stable activity of Pt_shell–Pd_core/C is ascribed to the tuned electronic property of the Pt over-layer in the Pt_shell–Pd_core/C, which leads to weak binding with CO_ad and increases the kinetics of OH_ad formation. The weakened binding property of the surface Pt with CO_ad and the facile oxidation of CO_ad by OH_ad were confirmed by a spectroscopic analysis and in a CO_ad-stripping experiment, respectively. The electro-oxidation of CO_ad by OH_ad is the rate-determining step of methanol oxidation. Therefore, the accelerated formation of OH_ad contributes to the overall oxidation reaction, preventing CO_ad-poisoning. In addition, Pt_shell–Pd_core/C maintains its activity longer than Pt/C does during a prolonged cycle experiment.