Transport property characterization of sparse CNT networks via AFM images

A simulation method for correlating the resistivity and resistance of sparse carbon nanotube (CNT) networks via atomic force microscopy images was proposed. For the demonstration, resistance values simulated by this method were compared with values obtained by directory measuring the resistance of sparse CNT networks. Results were also compared with those obtained by a thin-film approximation in which CNT networks are approximated as thin rectangles. Simulated resistance values were closer to the experimental values of the same samples than those estimated on the basis of the thin-film approximation. The use of atomic force microscopy (AFM) images enabled the implementation of inhomogeneity to numerical models, as well as one-to-one comparison between real samples and numerical models.     

Thermosensitive, soft glassy and structural colored colloidal array in ionic liquid: colloidal glass to gel transition

A novel soft material comprising thermosensitive poly(benzyl methacrylate)-grafted silica nanoparticles (PBnMA-g-NPs) and the ionic liquid (IL), 1-ethyl-3-methylimidazolium bis(trifluoromethane sulfonyl)amide ([C(2)mim][NTf(2)]), was fabricated. The thermosensitive properties were studied over a wide range of particle concentrations and temperatures. PBnMA-g-NPs in the IL underwent the lower critical solution temperature (LCST) phase transition at lower temperatures with a broader transition temperature range as compared to the free PBnMA solution. Highly concentrated suspensions formed soft glassy colloidal arrays (SGCAs) exhibiting a soft-solid behavior and angle-independent structural color. For the first time, we report a discrete change in the angle-independent structural color of SGCAs with temperature because of a temperature-induced colloidal glass-to-gel transition. The interparticle interaction changed from repulsive to attractive at the LCST temperature, and it was characterized by a V-shaped rheological response and a direct electron microscope observation of the colloidal suspension in the IL. With unique rheological and optical properties as well as properties derived from the IL itself, the thermosensitive SGCAs may be of interest as a new material for a wide range of applications such as electrochemical devices and color displays.     

A class number formula for the p-cyclotomic field

Let p be an odd prime number and . Let be the classical Stickelberger ideal of the group ring . Iwasawa [6] proved that the index equals the relative class number of . In [2], [4] we defined for each subgroup H of G a Stickelberger ideal of , and studied some of its properties. In this note, we prove that when mod 4 and [G : H] = 2, the index equals the quotient . Received: 13 January 2006     

On the 2-part of the ideal class group of the cyclotomic <Emphasis Type="BoldItalic">Z</Emphasis><Subscript><Emphasis Type="Italic">p</Emphasis></Subscript>-extension over the rationals

Let p be an odd prime number, and $\mbox {\boldmath $\mbox {\boldmath the cyclotomic $\mbox {\boldmath $\mbox {\boldmath -extension over the rationals. We show that the 2-part of the ideal class group of $\mbox {\boldmath $\mbox {\boldmath is trivial for p<500.     

The crystalline structures of carboxylic acid monolayers adsorbed on graphite

X-ray and neutron diffraction have been used to investigate the formation of solid crystalline monolayers of all of the linear carboxylic acids from C(6) to C(14) at submonolayer coverage and from C(8) to C(14) at multilayer coverages, and to characterize their structures. X-rays and neutrons highlight different aspects of the monolayer structures, and their combination is therefore important in structural determination. For all of the acids with an odd number of carbon atoms, the unit cell is rectangular of plane group pgg containing four molecules. The members of the homologous series with an even number of carbon atoms have an oblique unit cell with two molecules per unit cell and plane group p2. This odd-even variation in crystal structure provides an explanation for the odd-even variation observed in monolayer melting points and mixing behavior. In all cases, the molecules are arranged in strongly hydrogen-bonded dimers with their extended axes parallel to the surface and the plane of the carbon skeleton essentially parallel to the graphite surface. The monolayer crystal structures have unit cell dimensions similar to certain close-packed planes of the bulk crystals, but the molecular arrangements are different. There is a 1-3% compression on increasing the coverage over a monolayer.     

Estimation of Fatigue Limits from Temperature Data Measured by IR Thermography

To determine the fatigue limits of materials, fatigue testing, which is time-consuming and very expensive, is required. In order to overcome these shortcomings, estimating methods for fatigue limits based on temperature changes measured by IR camera have been proposed, and research and development of such methods have been widely conducted. In the current paper, a non-lock-in type, inexpensive IR camera was used for rotational bending fatigue testing to estimate the fatigue limit from temperature changes independent from loading signals. The results indicated that it is possible to estimate the fatigue limit from the time-temperature change curves measured under various stress conditions and converted stress amplitude-temperature change curves. The estimated results were sufficiently accurate and thus we confirmed that it is promising to estimate the fatigue limit by a non-lock-in type, inexpensive IR camera. The inflection point of a stress amplitude-temperature change curve can be determined by approximating a curve by two straight lines and finding the combination of the lines for which the sum of the residuals between the curve and the lines is the smallest. Although the temperature changes depended on the loading history (the number of loading cycles), the results of fatigue limit estimation changed little. Therefore, the proposed method is practically accurate as a simple estimation method. We also measured the behavior of stress-stroke for each loading history (the number of loading cycles) in tension-compression fatigue testing and confirmed that temperature changes during fatigue testing are associated with plastic strain energy.     

On a Theorem of Childs on Normal Bases of Rings of Integers

Let p be a prime number, F a number field, and the set of all unramified cyclic extensions overF of degree p having a relative normal integral basis. When_p F^x, Childs determined the set in terms of Kummer generators. When p=3 and F is an imaginaryquadratic field, Brinkhuis determined this set in a form whichis, in a sense, analogous to Childs's result. The paper determinesthis set for all p 3 and F with _p F^x (and satisfying an additionalcondition), using the result of Childs and a technique developedby Brinkhuis. Two applications are also given.     

A note on Greenberg's conjecture and the abc conjecture

For any totally real number field and any prime number , Greenberg's conjecture for asserts that the Iwasawa invariants and are both zero. For a fixed real abelian field , we prove that the conjecture is ``affirmative' for infinitely many (which split in if we assume the abc conjecture for .

     

Polymerization of surface-active monomers. I. Micellization and polymerization of higher alkyl salts of dimethylaminoethyl methacrylate

Micellization of cationic salts of dimethylaminoethyl methacrylate (DMAEMA) quaternized with n-alkyl bromides such as octyl, lauryl, myristyl, and stearyl bromide and their polymerizations were investigated. The critical micelle concentration (cmc) in water at 25°C was determined by electrical conductivity and dye(azobenzene) solubilization methods and the relation log(cmc) = 1.46–0.31N was obtained, where cmc is in mmol L^?1 and N corresponds to carbon number of alkyl bromides used for the monomer preparations. All of these monomeric salts exhibited a high radical polymerizability in water and benzene. The polymerizations in water appeared to proceed with a higher rate with increasing a chain length of the alkyl moiety of the monomers and those in benzene gave the polymers with a remarkably high viscosity. The rate of polymerization of lauryl bromide salt in anisotropic solutions (in water and benzene) was exceedingly fast as compared with that in isotropic solution(in acetonitrile). All of the polymers obtained here were insoluble in water. Solubility characteristics of these monomers and polymers in other solvents were also presented. The reduced viscosity, in dimethylformamide and methanol, of poly(lauryl bromide salt) prepared in water increased with dilution but that for the polymer obtained in benzene exhibited an inverse concentration dependence. Some discussions were made on the peculiarities of the polymerizations of these monomers and the resulting polymers.     

Synthesis of a complementary dimer from mono(imidazolyl)-substituted cobalt(II) porphyrin as a new artificial T-form hemoglobin

Mono(imidazolyl)-substituted Co(II) porphyrin dimer with a ‘picket fence’ structure was synthesized as a new artificial hemoglobin model containing two binding sites. The dimer was confirmed by UV-vis, resonance Raman and ESR spectral measurements to bind two dioxygen molecules reversibly. The dioxygen binding affinity of the dimer was lower than that of the corresponding monomer. The decrease in this affinity is discussed in terms of steric hindrance and orientational effect of the axial ligand.