Synthesis of 2,4-disubstituted 5-aminoimidazoles using microwave irradiation

A microwave-assisted parallel synthesis of 2,4-disubstituted 5-aminoimidazoles has been developed. Significant rate enhancement was observed for all steps in the three-step protocol. The overall reaction time was shortened to 25 min, as compared to 53 h for the conventional procedures. A representative set of 2,4-disubstituted 5-aminoimidazoles was prepared using commercially available parallel reactors.     

An ideal spline-wavelet family for curve design and editing

Subdivision schemes provide the most efficient and effective way to design and render smooth spatial curves. It is well known that among the most popular schemes are the de Rham–Chaikin and Lane–Riesenfeld subdivision schemes, that can be readily formulated by direct applications of the two-scale (or refinement) sequences of the quadratic and cubic cardinal B-splines, respectively. In more recent works, semi-orthogonal and bi-orthogonal spline-wavelets have been integrated to curve subdivision schemes to add such powerful tools as automatic level-of-detail control algorithm for curve editing and rendering, and efficient simulation processing scheme for global graphic illumination and animation. The objective of this paper is to introduce and construct a family of spline-wavelets to overcome the limitations of semi-orthogonal and bi-orthogonal spline-wavelets for these and other applications, by adding flexibility to the enhancement of desirable characters without changing the sweep of the subdivision spline curve, by providing the shortest lowpass and highpass filter pairs without decreasing the discrete vanishing moments, and by assuring robust stability.     

Development of an Analytical <Emphasis Type="Italic">β</Emphasis>-Function PDF Integration Algorithm for Simulation of Non-premixed Turbulent Combustion

Among many presumed-shape pdf approaches for modeling non-premixed turbulent combustion, the presumed β-function pdf is widely used in the literature. However, numerical integration of the β-function pdf may encounter singularity difficulties at mixture fraction values of Z = 0 or 1. To date, this issue has been addressed by few publications. The present study proposes the Piecewise Integration Method (PIM), an efficient, robust and accurate algorithm to overcome these numerical difficulties with the added benefit of improving computational efficiency. Comparison of this method to the existing numerical integration methods shows that the PIM exhibits better accuracy and greatly increases computational efficiency. The PIM treatment of the β-function pdf integration is first applied to the Burke–Schumann solution in conjunction with the k − ε turbulence model to simulate a CH₄/H₂ bluff-body turbulent flame. The proposed new method is then applied to the same flow using a more complex combustion model, the laminar flamelet model. Numerical predictions obtained by using the proposed β-function pdf integration method are compared to experimental values of the velocity field, temperature and species mass fractions to illustrate the efficiency and accuracy of the present method.     

Effect of surface nanocrystallization induced by fast multiple rotation rolling on hardness and corrosion behavior of 316L stainless steel

A nanostructured layer was fabricated by using fast multiple rotation rolling (FMRR) on the surface of 316L stainless steel. The microstructure in the surface was characterized by transmission electron microscopy and X-ray diffraction. The effects of FMRR on the microhardness, surface roughness and corrosion behavior of the stainless steel were investigated by microhardness measurements, surface roughness measurements, potentiodynamic polarization curves and pitting corrosion tests. The surface morphologies of pitting corrosion specimens were characterized by scanning electron microscopy. The results show that FMRR can cause surface nanocrystallization with the grain size ranges from 6 to 24 nm in the top surface layer of the sample. The microhardness of FMRR specimen in the top surface layer remarkably increases from 190 to 530 HV. However, the surface roughness slightly rises after FMRR treatment. The potentiodynamic polarization curves and pitting corrosion tests indicated that the FMRR treated 316L stainless steel with a surface nanocrystallized layer reduced the corrosion resistance in a 3.5% NaCl solution and enhanced the pitting corrosion rate in a FeCl₃ solution. Possible reasons leading to the decrease in corrosion resistance were discussed.     

Magnetic surface plasmon-induced tunable photonic bandgaps in two-dimensional magnetic photonic crystals

We experimentally studied magnetically controllable photonic band gaps (PBGs) in two-dimensional magnetic photonic crystals consisting of ferrite rods. Besides the conventional PBG that relates to Bragg scattering, two other types of PBG, resulting from magnetic surface plasmon (MSP) resonance and spin-wave resonance, respectively, are observed. The PBG due to MSP resonance is particularly interesting because of its analogy to surface plasmon in metal; furthermore, it is shown to be completely tunable by an external static magnetic field from both an experimental and a theoretical point of view.     

Applications of optimally local interpolation to interpolatory approximants and compactly supported wavelets

The objective of this paper is to introduce a general scheme for the construction of interpolatory approximation formulas and compactly supported wavelets by using spline functions with arbitrary (nonuniform) knots. Both construction procedures are based on certain ``optimally local' interpolatory fundamental spline functions which are not required to possess any approximation property.

     

Absolute frequency measurement of rubidium 5S-7S two-photon transitions with a femtosecond laser comb

The absolute frequencies of rubidium 5S-7S two-photon transitions at 760 nm are measured to an accuracy of 20 kHz with an optical frequency comb based on a mode-locked femtosecond Ti:sapphire laser. The rubidium 5S-7S two-photon transitions are potential candidates for frequency standards and serve as important optical frequency standards for telecommunication applications. The accuracy of the hyperfine constant of the 7S1/2 state is improved by a factor of 5 in comparison with previous results.