Rapid synthesis and consolidation of nanostructured Mg<Subscript>2</Subscript>SiO<Subscript>4</Subscript>–MgSiO<Subscript>3</Subscript> composites by high frequency induction heated sintering

Rapid synthesis and sintering of nanostructured MgSiO₃–Mg₂SiO₄ composites was investigated via a high-frequency induction heating sintering process. The advantage of this process is that it enables very quick densification to near theoretical density and prohibition of grain growth in nanostructured materials. High-density nanostructured MgSiO₃–Mg₂SiO₄ composites were produced by simultaneous application of 80 MPa pressure under an induced output power of 15 kW within 2 min. The grain sizes and hardness of MgSiO₃–Mg₂SiO₄ composites were investigated.     

Novel route to a finite center-of-mass momentum pairing state for superconductors: A current-driven Fulde-Ferrell-Larkin-Ovchinnikov state

The previously studied Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state is stabilized by a magnetic field via the Zeeman coupling in spin-singlet superconductors. Here we suggest a novel route to achieve nonzero center-of-mass momentum pairing states in superconductors with Fermi surface nesting. We investigate two-dimensional superconductors under a uniform external current, proportional to a finite pair momentum of q(e). We find that an FFLO state with a spontaneous pair momentum of q(s) is stabilized above a certain critical current that depends on the direction of the external current. A finite q(s) arises in order to make the total pair-momentum of q(t)(=q(s) + q(e)) perpendicular to the nesting vector, which is independent of spin states of Cooper pairs. We also discuss experimental signatures of the FFLO state.     

Synthesis and magnetic properties of silica-coated FePt nanocrystals

Colloidal FePt nanocrystals, 6 nm in diameter, were synthesized and then coated with silica (SiO2) shells. The silica shell thickness could be varied from 10 to 25 nm. As-made FePt@SiO2 nanocrystals have low magnetocrystalline anisotropy due to a compositionally disordered FePt core. When films of FePt@SiO2 particles are annealed under hydrogen at 650 degrees C or above, the FePt core transforms to the compositionally ordered L1(0) phase, and superparamagnetic blocking temperatures exceeding room temperature are obtained. The SiO2 shell prevents FePt coalescence at annealing temperatures up to approximately 850 degrees C. Annealing under air or nitrogen does not induce the FePt phase transition. The silica shell limits magnetic dipole coupling between the FePt nanocrystals; however, low temperature (5 K) and room temperature magnetization scans show slightly constricted hysteresis loops with coercivities that decrease systematically with decreased shell thickness, possibly resulting from differences in magnetic dipole coupling between particles.     

Effect of Heat Generation on Forced Convection Through a Porous Saturated Duct

The effect of heat generation on the flow characteristics of the fully developed forced convection through a porous duct is investigated analytically on the basis of Brinkman?CForchheimer model. The duct is bounded by two isoflux plates. For solving momentum equation a regular asymptotic expansion method is used for hyper-porous materials and a matched asymptotic expansion method is used for low-porous materials. This solution permits a uniform solution for the energy equation to find the temperature distribution as well as Nusselt number. A numerical solution is found here to check the accuracy of the asymptotic one.     

Rotational and translational diffusivities of germanium nanowires

Understanding the rheological behavior of dilute dispersions of cylindrical nanomaterials in fluids is the first step towards the development of rheological models for these materials. Individual particle tracking was used to quantify the rotational and translational diffusivities of high-aspect-ratio germanium nanowires in alcohol solvents at room temperature. In spite of their long lengths and high aspect ratios, the rods were found to undergo Brownian motion. This work represents the first time that the effects of solvent viscosity and confinement have been directly measured and the results compared to proposed theoretical models. Using viscosity as a single adjustable parameter in the Kirkwood model for Brownian rods was found to be a facile and versatile way of predicting the diffusivities of nanowires across a broad range of length scales.     

Influence of the side chain protecting group on the stereoselectivity of the 1,3-dipolar cycloaddition of d-talo-configured nitrones

Two new five-membered cyclic d-talo-configured nitrones were synthesized from d-mannose, and examined in 1,3-dipolar cycloadditions with vinyl acetate and vinylene carbonate. The stereoselectivity of the cycloadditions depends greatly on the protecting group of the vicinal diol attached to the nitrone C-5 carbon atom. Methyl protection resulted in limited syn/anti-selectivity, giving mixtures of the two isomeric exo-syn and exo-anti isoxazolidines in comparable amounts. On the other hand, the cyclohexylidene-substituted nitrone reacted more selectively in favour of the syn isomer. The difference in the diastereoselectivity was attributed to the specific spatial orientation of the nitrone C-5 substituent.     

Interaction of hydrogen with ZnO: surface adsorption versus bulk diffusion

The interaction of hydrogen (H) and a ZnO(0001)-O surface has been investigated using a temperature programmed desorption (TPD) technique. When the surface is exposed to atomic hydrogen below 400 K, hydrogen is adsorbed on the surface. As the hydrogen exposure increases, bulk diffusion of hydrogen takes place. The existence of surface and bulk hydrogen has been confirmed using X-ray photoelectron spectroscopy (XPS). When the ZnO surface dosed with hydrogen is heated, surface hydrogen is desorbed at 432 K and bulk hydrogen is evolved at ～539 K. Diffusion of hydrogen into the ZnO bulk is an activated process, and the activation energy is estimated to be 0.19 eV.     

A novel pathogen detection system based on high‐resolution CE‐SSCP using a triblock copolymer matrix

Although CE‐SSCP analysis combined with 16S ribosomal RNA gene‐specific PCR has enormous potential as a simple and versatile pathogen detection technique, low resolution of CE‐SSCP causes the limited application. Among the experimental conditions affecting the resolution, the polymer matrix is considered to be most critical to improve the resolution of CE‐SSCP analysis. However, due to the peak broadening caused by the interaction between hydrophobic moiety of polymer matrices and DNA, conventional polymer matrices are not ideal for CE‐SSCP analysis. A poly(ethyleneoxide)‐poly(propyleneoxide)‐poly(ethyleneoxide) (PEO‐PPO‐PEO) triblock copolymer, with dynamic coating ability and a propensity to form micelles to minimize exposure of hydrophobic PPO block to DNA, can be an alternative matrix. In this study, we examined the resolution of CE‐SSCP analysis using the PEO‐PPO‐PEO triblock copolymer as the polymer matrix and four same‐sized DNA fragments of similar sequence content. Among 48 commercially available PEO‐PPO‐PEO triblock copolymers, three were selected due to their transparency in the operable range of viscosity and PEO₁₃₇PPO₄₃PEO₁₃₇ exhibited the most effective separation. Significant improvement in resolution allowed discrimination of the similar sequences, thus greatly facilitated CE‐SSCP analysis compared to the conventional polymer matrix. The results indicate that PEO‐PPO‐PEO triblock copolymer may serve as an ideal matrix for high‐resolution CE‐SSCP analysis.