Synthesis of novel 2,4,6,8,10-pentaaza[3.3.3]propellane derivatives

Propellanes and azapropellanes are attractive compounds for their unique structure and valuable applications but there are few synthetic studies for highly N-substituted azapropellanes. Several novel derivatives of 2,4,6,8,10-pentaaza[3.3.3]propellane, such as 3, 4, and 5 were successfully synthesized from readily available diethyl tartrate. Most of the synthetic steps were efficient. Their propellane structures were established by spectroscopic data and confirmed with single crystal X-ray analyses.     

An optimal service rate in a Poisson arrival queue with two-stage service policy*

We consider a two-stage service policy for a Poisson arrival queueing system. The idle server starts to work with ordinary service rate when a customer arrives. If the number of customers in the system reaches N, the service rate gets faster and continues until the system becomes empty. Otherwise, the server finishes the busy period with ordinary service rate. After assigning various operating costs to the system, we show that there exists a unique fast service rate minimizing the long-run average cost per unit time.This work was supported by Korea Research Foundation Grant(KRF-2002-070-C00021).     

Sources of spurious force oscillations from an immersed boundary method for moving-body problems

When a discrete-forcing immersed boundary method is applied to moving-body problems, it produces spurious force oscillations on a solid body. In the present study, we identify two sources of these force oscillations. One source is from the spatial discontinuity in the pressure across the immersed boundary when a grid point located inside a solid body becomes that of fluid with a body motion. The addition of mass source/sink together with momentum forcing proposed by Kim et al. [J. Kim, D. Kim, H. Choi, An immersed-boundary finite volume method for simulations of flow in complex geometries, Journal of Computational Physics 171 (2001) 132–150] reduces the spurious force oscillations by alleviating this pressure discontinuity. The other source is from the temporal discontinuity in the velocity at the grid points where fluid becomes solid with a body motion. The magnitude of velocity discontinuity decreases with decreasing the grid spacing near the immersed boundary. Four moving-body problems are simulated by varying the grid spacing at a fixed computational time step and at a constant CFL number, respectively. It is found that the spurious force oscillations decrease with decreasing the grid spacing and increasing the computational time step size, but they depend more on the grid spacing than on the computational time step size.     

Full‐Color Emissive Poly(Ethylene Oxide) Electrospun Nanofibers Containing a Single Hyperbranched Conjugated Polymer for Large‐Scale,Flexible Light‐Emitting Sheets

White‐light‐emitting protocols based on organic materials have received much attention in the academic and industrial fields because of their potential applications in full‐color displays and back‐lighting units for liquid crystal displays. Here, the attempt is made to fabricate white‐light‐emitting, electrospun poly(ethylene oxide) (PEO) sheets containing controlled concentrations of a single light‐emitting material composed of a type of hyperbranched conjugated polymer (HCP). The HCPs used here have the unique property of exhibiting a variety of fluorescence colors in the electrospun matrix that is caused by the different distances between HCP chains depending on their concentrations, leading to different degrees of intermolecular energy transfer. Therefore, the emission colors of the PEO sheets can be easily manipulated by simply varying the HCP concentrations in the PEO matrix. The resulting method for fabricating nanofibers comprising light‐emitting materials in the polymer matrix has great potential for easy fabrication of cost‐effective, flexible light‐emitting system.

     

Erratum to Formation and control of Au and Ag nanoparticles inside borate glasses using femtosecond laser and heat treatment

We report the spectroscopic properties of femtosecond laser-irradiated sodium-alumino-borate glass doped with silver and gold ions. We precipitated gold and silver nanoparticles by laser irradiation and annealing at 400°C for 30 min. The irradiation and annealing treatment produced different absorption and emission characteristics in Au³⁺ doped and Au³⁺, Ag⁺ codoped glasses, and the possible mechanisms of the observed results are discussed. The size of the nanoparticles was estimated by TEM and absorption band analysis.     

Partially positively charged silver nanoparticles prepared by p-benzoquinone

Partially positively charged silver nanoparticles were successfully prepared by interaction between p-benzoquinone and the surface of the nanoparticles. This result was primarily due to electron affinity of the carbonyl group in p-benzoquinone, as confirmed by FT-IR and X-ray photoelectron spectroscopy (XPS). In this study, p-benzoquinone acted as both a stabilizer and a reducing agent for silver nanoparticles. UV–vis spectra showed the formation of silver nanoparticles. TEM micrographs confirmed that most of silver nanoparticles exist in sizes less than 7 nm, and the average size of particle aggregates is approximately 20 nm.     

Water sorption and activation energy in polyimide thin films

The water sorption behavior and the activation energy were investigated for various chemical structure polyimide thin films; BPDA‐PDA, BPDA‐ODA, PMDA‐ODA, and 6FDA‐ODA. The activation energy for the water diffusion varied in the range of 5.53 to 9.27kcal/mol, and was in the increasing order: BPDA‐PDA < BPDA‐ODA < PMDA‐ODA < 6FDA‐ODA. BPDA‐PDA and BPDA‐ODA polyimide films showed relatively well‐ordered morphological structure, which results in relatively low diffusion coefficient and high activation energy. It was found that the diffusion coefficient and the activation energy are significantly related to the in‐plane orientation, crystallinity, and packing order in the polyimide thin films. The morphological structure was predominant factors for the water diffusion coefficient and activation energy in the polyimide thin films. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2714–2720, 2000     

Improving precursor adsorption characteristics in ATR-FTIR spectroscopy with a ZrO2 nanoparticle coating

Journal of Nanoparticle Research - Transparent superhydrophobic coatings, which are highly desired for the protection of material surfaces, have been limited to particular kinds of materials, e.g....     

Cobalt Ion‐Mediated Cysteine Detection With a Hyperbranched Conjugated Polyelectrolyte as a New Sensing Platform

A highly efficient colorimetric and fluorescence turn‐off probe for the sensitive and selective detection of the biologically important amino acid, cysteine (Cys), is demonstrated using a newly synthesized water‐soluble hyperbranched polymer (HP) containing sulfonic acid groups. The detection mechanism involves two steps: (i) the slight quenching of HP in the presence of Co²⁺ in advance; and (ii) the gradual quenching of the HP–Co²⁺ complex according to the concentration of Cys due to the absorption screening effect of the formation of the Cys‐Co²⁺ complex, which prevents HP from absorbing excitation energy.