Nested PCR in magnetically actuated circular closed-loop PCR microchip system

We demonstrate a new and sensitive amplification technique (referred to as Nested Polymerase Chain Reaction; nPCR). It based on a magnetically actuated circular closed-loop PCR microchip system. nPCR involves the use of two sets of primers in two successive PCR runs, and allows the amplification of a single locus from a minute quantity of template DNA. Two sets of primers are specially designed to a target 500-bp region of the bacteriophage lambda template DNA in the first PCR run, and a 247-bp region of the targeted 500-bp first PCR product in the second PCR run. PCR is run on the microchip system and concurrently in regular thermocycler for comparison. The products are analyzed by conventional agarose gel electrophoresis. The detection limit for the initial template DNA is 1.63?×?10⁵ copies per μL (or 8.67?pg) for the first PCR run, and 1.63 copies per μL (or 0.0867?fg) for the second run. The results are comparable to a regular thermocycler. This preliminary study opens a new gateway to future development of specialized nPCR on chip.

Endoepitaxial growth of hexagonal-Fe13Ge8 islands on Cubic-Ge(001)

The growth and shape evolution of epitaxial Fe₁₃Ge₈ (hexagonal lattice) islands on single crystal Ge(001) (cubic lattice) substrate was observed in real time using an in situ ultra-high vacuum transmission electron microscope (TEM). Post-deposition high-resolution TEM in conjunction with stereographic projection enabled the identification of the interface structure between the Fe₁₃Ge₈ islands and the Ge substrate. Only one low-energy coherent interface formed via Fe₁₃Ge₈ islands growing into the substrate along the inclined Ge(11?1) plane. This indicates that minimization of net interfacial energy is the driving force for hexagonal Fe₁₃Ge₈ islands formation on Ge(001).     

Alkali metal ion conductors based on sulfonated poly(p-phenylene terephthalamide)

To obtain thermally stable and mechanically strong sodium and lithium conducting polymers, we prepared Na⁺ and Li⁺ poly(phenylene terephthalamide sulfonate salts) (MW ～ 5500). We also synthesized oligo(ethylene oxide) (3, 5, or 7 units of ethylene oxide) substituted ethylene carbonate and poly[oxymethylene-oligo(oxyethylene)]. These are high boiling point liquids with high dielectric constants as well as metal chelating properties. Polyelectrolyte systems were prepared by mixing Na⁺ or Li⁺ poly(phenylene terephthalamide sulfonate) salts with various amounts of modified ethylene carbonate and/or poly[oxymethylene-oligo(oxyethylene)]. Films (0.1–0.5 mm thick) obtained from the blends were found to have considerable mechanical strength; forming free standing films. The ionic conductivities of the Na⁺ and Li⁺ polyelectrolyte systems were 10^?6?10^?5 S/cm at 25°C. Thermal properties of these blend systems were investigated in detail. © 1994 John Wiley & Sons, Inc.     

Interstitial and substitutional light elements in transition metals for heterogeneous catalysis

The addition of foreign element dopants to monometallic nanoparticle catalysts is of great importance in industrial applications. Both substitutional and interstitial doping of pure metallic phases can give profound effects such as altering electronic and transport properties, lattice parameters, phase transitions, and consequently various physicochemical properties. For transition metal catalysts, this often leads to changes in catalytic activity and selectivity. This article provides an overview of the recent developments regarding the catalytic properties and characterisation of such systems. In particular, the structure–activity relationship for a number of important chemical reactions is summarised and the future prospects of this area are also explored.

TOC summarises some recent developments in synthesis, characterisation and catalytic applications of light elements doped to transition metals presented in this article.     

Photonic microring resonator modulated resonance response analysis

This paper presents the resonance response analysis of a photonic microring resonator. It covers the mathematical as well as simulation analysis on the modulated signals. The mathematical formulation provides a relation of several microring resonator parameters that could potentially affect the ring resonator performances. The simulation shows a graphical representation of the ring resonator full-width at half-max, quality factor (Q-factor) as well as the depth of the resonance at different modulation voltages applied to the ring. Several parameters have also been altered which is the ring radius, the coupling coefficient of the waveguides as well as the waveguide material group index. With this investigation, we determine the possible cause of the change in Q factor of a silicon microring resonator when the resonance is modulated and the possible solution to minimize the problem.     

Green's-function theory for disordered anisotropic Heisenberg ferromagnets

The Green's function theory for disordered Heisenberg Ferromagnets developed by Montgomery et al. has been extended for anisotropic systems. The densities of spin-wave states for such systems exhibit split-bands. This behavior differs qualitatively from that of the isotropic case and offers a partial explanation for the neutron scattering experiment of Buyers et al. in which they observe two well defined branches of magnetic excitations in disordered substitutional anti-ferromagnetic alloys.     

Dietary Vitamin B6 and Enzymes of Methionine Metabolism in Rat Liver

Hepatic cystathionase activity, but not methionine adenosyl-transterase and cystathionine synthetase, was markedly decreased in weanling female rats fed a vitamin B₆-deficient diet, compared to that of the control animals fed ad libitum or pair-fed. The depressed enzyme activity was restored rapidly to normal by administering pyridoxine to the deficient rats. Excess pyridoxal phosphate added to enzyme reaction mixtures stimulated cystathionase in liver extracts from both control and deficient animals, but it did not raise activity of deficients to normal level. The data indicate that the amount of apocystathionase in rat liver is regulated by the availability of its coenzyme vitamin.     

Charge ordering, commensurability, and metallicity in the phase diagram of the layered NaxCoO2

The phase diagram of nonhydrated NaxCoO2 has been determined by changing the Na content x using a series of chemical reactions. As x increases from 0.3, the ground state goes from a paramagnetic metal to a charge-ordered insulator (at x=1/2), then to a "Curie-Weiss metal" (around 0.70), and finally to a weak-moment magnetically ordered state (x>0.75). The unusual properties of the state at 1/2 (including particle-hole symmetry at low T and enhanced thermal conductivity) are described. The strong coupling between the Na ions and the holes is emphasized.     

Characteristics of driven polymer surfaces: growth and roughness

Using a Monte Carlo simulation, the growth and roughness characteristics of polymer surfaces are studied in 2+1 dimensions. Kink-jump and reptation dynamics are used to move polymer chains under a driving field where they deposit onto an impenetrable attractive wall. Effects of field (E), chain length (L(c)), and the substrate size (L) on the growing surfaces are studied. In low field, the interface width (W) shows a crossover from one power-law growth in time (W approximately t(beta(1))) to another (W approximately t(beta(2))), before reaching its asymptotic value (W(s)), with beta(1)( approximately 0.5+/-0.1)相似文献   

Mimicking both petal and lotus effects on a single silicon substrate by tuning the wettability of nanostructured surfaces

We describe a new method of fabricating large-area, highly scalable, "hybrid" superhydrophobic surfaces on silicon (Si) substrates with tunable, spatially selective adhesion behavior by controlling the morphologies of Si nanowire arrays. Gold (Au) nanoparticles were deposited on Si by glancing-angle deposition, followed by metal-assisted chemical etching of Si to form Si nanowire arrays. These surfaces were chemically modified and rendered hydrophobic by fluorosilane deposition. Au nanoparticles with different size distributions resulted in the synthesis of Si nanowires with very different morphologies (i.e., clumped and straight nanowire surfaces). The difference in nanowire morphology is attributed to capillary force-induced nanocohesion, which is due to the difference in nanowire porosity. The clumped nanowire surface demonstrated the lotus effect, and the straighter nanowires demonstrated the ability to pin water droplets while maintaining large contact angles (i.e., the petal effect). The high contact angles in both cases are explained by invoking the Cassie-Baxter wetting state. The high adhesion behavior of the straight nanowire surface may be explained by a combination of attractive van der Waals forces and capillary adhesion. We demonstrate the spatial patterning of both low- and high-adhesion superhydrophobicity on the same substrate by the simultaneous synthesis of clumped and straight silicon nanowires. The demonstration of hybrid superhydrophobic surfaces with spatially selective, tunable adhesion behavior on single substrates paves the way for future applications in microfluidic channels, substrates for biologically and chemically based analysis and detection where it is necessary to analyze a particular droplet in a defined location on a surface, and as a platform to study in situ chemical mixing and interfacial reactions of liquid pearls.