Spontaneous formation of mesoporous silica films using non-surfactant template, and optimization with Doehlert designs, for adsorbent for polycyclic aromatic hydrocarbons

To prepare mesoporous silica thin-films by a simple and environmentally friendly pathway, spontaneous formation of silica thin-films in a sol–gel solution without surfactants was studied. The silica thin-films were prepared by immersing a glass substrate, such as a cylindrical test-tube, into a sol–gel solution containing tetraethoxysilane, water, acetic acid, 2-propanol, and triethylene glycol as a pore-forming agent. The resulting thin-films were transparent. The presence of mesopores was confirmed by field-emission scanning electron microscopy, atomic-force microscopy and nitrogen adsorption–desorption isotherms. The Barrett–Joyner–Halenda plot from the adsorption branch of the isotherms indicated that the pore diameter was 2.6 nm. To illustrate the potential use of the film as an adsorbent, the extraction of polycyclic aromatic hydrocarbons was conducted using the chemically modified silica thin-film coated on a test-tube. The composition of the sol–gel solution was optimized using experimental design, i.e., Doehlert design, and recovery of polycyclic aromatic hydrocarbons.     

On the Cauchy problem for second order strictly hyperbolic equations with non–regular coefficients

In this paper we shall consider some necessary and sufficient conditions for well–posedness of second order hyperbolic equations with non–regular coefficients with respect to time. We will derive some optimal regularities for well–posedness from the intensity of singularity to the coefficients by WKB representation of the solution and some counter examples which are constructed by using ideas of Floquet theory.     

Homogeneous SiGe crystals grown by using the traveling liquidus-zone method

It is indispensable to estimate a diffusion coefficient in a solution zone in order to grow a homogeneous crystal by using the traveling liquidus-zone (TLZ) method. To estimate the diffusion coefficient of Ge in the SiGe solution zone, result of a two-dimensional numerical simulation is compared with an experimental result. From the comparison, the diffusion coefficient is estimated to be 9.5×10⁻⁵ cm²/s. By using this coefficient, a sample translation rate for obtaining a homogeneous SiGe crystal is determined. By translating samples with appropriate rates, homogeneous Si_0.5Ge_0.5 crystals are successfully grown. The typical Ge composition is 0.496±0.006 for more than 13 mm long. The experimental result shows the homogeneity of ±1.2% in the mole fraction. This deviation corresponds to the variation of less than ±0.03% in the lattice constant. Since this variation is negligibly small, the homogeneity is excellent. Thus it is found that the TLZ method is the universal growth technique, which is applicable to the crystal growth of not only the III–V compounds but also the IV–IV compounds.     

Fundamental studies on electrokinetic chromatography with PEGylated phospholipid micelles.

In this study, micelles prepared from distearoylphosphatidylethanolamine with covalently attached poly(ethylene) glycol) (PEG) of molecular weight 2000 (DSPE-PEG-2000) were employed in micellar electrokinetic chromatography (MEKC) as pseudostationary phases. Since DSPE-PEG-2000 contains long hydrophobic alkyl chains, an anionic phosphate group, and hydrophilic PEG chains, the prepared micelles are expected to provide a characteristic retention behavior for both neutral and ionic compounds. As a typical example, a baseline separation of phenol and 2-naphthol was successfully achieved by using the DSPE-PEG-2000 micelles as a background electrolyte for MEKC; such success clearly shows that the micelles can retain electrically neutral compounds. The MEKC separations of anionic and cationic compounds with a DSPE-PEG-2000 micellar solution and the enantioseparation of binaphthyl compounds with mixed micelles containing bile salt are also discussed.     

Influence of Polarization and Pulse Shape of Femtosecond Initial Laser Pulses on Spectral Broadening in Microstructure Fibers

We theoretically studied the influence of initial parameters of laser pulses, such as polarization, pulse shape and frequency chirp, on the broadening of spectrum during pulse propagation through microstructure fibers (MSFs). We utilized two coupled-mode equations based on the nonlinear Schrödinger equation using an intermediate-broadening model for a Raman response function, and the dispersion coefficients from 2nd to 7th orders for the slow and fast axes, respectively, of highly birefringent MSFs.     

New insights into the effects of molecular weight and end group on the temperature-induced phase transition of poly(N-isopropylacrylamide) in water

In an attempt to clarify issues related to the molecular weight dependence of the phase transition of poly(N-isopropylacrylamide) (PNIPAM) in water,we prepared a library of PNIPAM samples of well-controlled molecular weight (7000 to 45000 g/mol) bearing identical groups on each chain end.The polymers were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization of N-isopropylacrylamide (NIPAM) with a bifunctional chain tranfer agent and further end group modification.The effects of the end group chemical structure,hydroxyethyl (HE),propargyl (Pr),chloroethyl (CE),n-butyl (nBu),n-hexyl (nHe),and isobutylsulfanylthiosulfanyl (IBS) on the phase transition temperature of aqueous PNIPAM solutions were investigated by high-sensitivity differential scanning calorimetry (HS-DSC),yielding the enthalpy ΔH and the endotherm maximum temperature (T M),and turbidimetry,providing the cloud point (T CP) of each solution.The T CP and T M of the PNIPAM sample of lowest molar mass (M n 7,000 g/mol,0.5 g/L) ranged,respectively,from 38.8 to 22.5 °C and 42.2 to 26.0 °C,depending on the structure of the end-group,whereas H showed no strong end-group dependence.The phase transition of all polymers,except,-di(n-butyl-PNIPAM),exhibited a marked dependence on the polymer molar mass.     

Label-free detection of amino acids using gold nanoparticles in electrokinetic chromatography-thermal lens microscopy

To achieve label-free detection of amino acids in capillary-based electrokinetic chromatography-thermal lens microscopy (EKC-TLM), gold nanoparticles (GNPs), which possess the absorption around 500nm attributed to surface plasmon resonance (SPR), were added to the background solution (BGS). Since the SPR absorption of the GNPs exhibits a sensitive response toward environmental changes and the degree of aggregation, the sensitive detection of non-absorbing species is expected by using the GNPs in EKC-TLM (GNP-EKC-TLM). In the GNP-EKC-TLM analysis of glutamic acid (Glu), a sharp peak was observed when the GNPs were added to the BGS. The plot of the peak area of Glu against its concentration gave a good linear relationship and the limit of detection was estimated to be 25mug/mL. Furthermore, a baseline separation of lysine and Glu was successfully achieved. Thus, the EKC separation and label-free TLM detection of the amino acids can be realized only by adding the GNPs into the BGSs.     

Thermoreversible gelation with hydrogen‐bonded zipper‐like crosslink junctions

Thermoreversible gelation of polymer chains bearing hydrogen‐bonding functional groups is studied by off‐lattice Monte Carlo simulation with semiflexible bead‐and‐spring model chains. To see the formation of zipper‐like sequential crosslink junctions (domino effect), we introduce stabilization energy ?Δε between the nearest neighboring hydrogen‐bonded beads along a chain in addition to the ordinary pairwise hydrogen‐bond energy ?ε. It is found that the condition nθ/ = 2 is fulfilled at the sol/gel transition point, where is the average zipper length, θ the zipper content per chain, and n the total number of beads on a chain. It is also shown that, at low temperature, zipper growth dominates the nucleation of new zippers, and as a result, there is another transition from a three‐dimensional network to a pairwisely bound state (network/pair transition). © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3331–3336, 2005     

Global solvability for Kirchhoff equation in special classes of non-analytic functions

In this paper we derive the following two properties: the first one is a precise representation of WKB solution to the Cauchy problem of a linear wave equation with a variable coefficient with respect to time, and the second one is the global solvability for Kirchhoff equation in some special classes of nonreal-analytic functions, which is proved by grace of the first property.