Magnetic anisotropic properties in Fe3O4 and CoFe2O4 ferrite epitaxy thin films

Epitaxial thin films of Fe₃O₄ and CoFe₂O₄ on MgO (0 0 1) substrates were grown by molecular beam epitaxy at low temperature growth process. Magnetization and hysteresis loop of both films were measured to investigate magnetic anisotropic properties at various temperatures. Anomalous magnetic properties are found to be correlated with crystalline, shape, and stress anisotropies. The Fe₃O₄ film below Verwey structural transition has a change in crystal structure, thus causing many anomalous magnetic properties. Crystalline anisotropy and anomalous magnetic properties are affected substantially by Co ions. The saturation magnetization of Co–ferrite film becomes much lower than that of Fe₃O₄ film, being very different from the bulks. It indicates that the low temperature growth process could not provide enough energy to have the lowest energy state.     

Selective permeation of CO2 and CH4 through kapton polyimide: Effects of penetrant competition and gas-phase nonideality

Sorption isotherms for pure CO₂ and pure CH₄ in Kapton H® polymide films at 60°C are reported for pressures up to 20 atm and are analyzed in terms of the dual-mode sorption model. An experimental scheme for the measurement of steady-state permeabilities of both pure and mixed gas feeds is described. Permeabilities of Kapton to the individual components at 60°C are presented for a mixture comprised of 32.2% CO₂ in CH₄ as functions of feed pressure up to 590 psi (absolute). The permeabilities for the individual penetrants in the mixed feed are lower than the respective purecomponent values at the corresponding partial pressures. Furthermore, the permeabilities of both penetrants drop as the feed pressure is increased at constant composition. The dual-mobility transport model used to analyze the data postulates that the observed pressure and composition dependence of the permeabilities is due to competition between penetrants for a limited microvoid sorption capacity in the glassy polymer. It is demonstrated that in addition to flux depressions due to dual-mode effects, nonideality of the gas phase must be accounted for to explain the substantial flux depressions observed for the CO₂/CH₄ mixtured used in this study.     

On the dynamics of a tethered satellite system

The Hamiltonian structure for a fundamental model of a tethered satellite system is constructed. The model is composed of two point masses connected by a string with no restrictions on the motions of the two masses. A certain symmetry with respect to the special orthogonal group SO(3) for such a system is observed. The classical station-keeping mode for the tethered system is found to be nothing more than the relative equilibrium corresponding to the reduction of the system by the symmetry. The microgravity forces on the two point masses are responsible for the possible configurations of the string at the so-called radial relative equilibrium. A stability analysis is performed on the basis of the reduced energy-momentum method. Criteria for stability are derived, which could find potential applications in space technology.     

Transport of carbon dioxide and methane in glassy aromatic polyesters

Solubilities and diffusivities of CO₂ and CH₄ in two aromatic polyesters [Ardel® poly(bisphenol A phthalate) (PAr) and poly(phenolphthalein phthalate) (PPha)] and one polycarbonate [Lexan® (PC)], generated from independent sorption and permeation measurements at 35°C and up to 25 atm, are compared. The permeability ratio for CO₂ over CH₄, at 20 atm and 35°C, ranges from 24 for PC, to 21 for PAr, and 27 for PPha. However, the permeability of PPha and PAr are 40 and 120% higher, respectively, than that of PC. Less than 21% change in the gas diffusivity was observed; therefore, a major portion of the observed higher permeability of PPha and PAr is attributed to an increase in the gas solubility. These data are interpreted qualitatively in terms of changes in the calculated packing density, chain torsional mobility of the polymer, and gas-polymer attraction.     

The effect of aryl nitration on gas sorption and permeation in polysulfone

CO_2, CH_4, O_2, and N₂ permeability and solubility of unmodified and aryl-nitrated polysulfone were determined at 35°C and pressures up to 20 atm. The degree of nitration was varied from 0 to 2 nitro groups per repeat unit. The permeability and diffusion coefficients for all gases decreased with increasing degree of nitro substitution. The decrease in gas diffusivity is attributed to a combination of decreased fractional free volume and decreased torsional mobility with increasing degree of substitution. The solubilities of N_2, O_2, and CH₄ do not show a systematic dependence on degree of substitution. However, CO₂ solubility apparently goes through a minimum as the degree of substitution is increased. CO₂ solubility may be influenced by a competition between increases in polymer polarity (favoring higher solubility) and lower free volume (favoring lower solubility) that accompanies increases in the polar nitro substituent concentration. CO₂/CH₄ solubility selectivity increases monotonically as the degree of substitution increases. CO₂/CH₄ permselectivity and diffusivity selectivity increased with increasing degree of substitution. © 1995 John Wiley & Sons, Inc.     

A novel and efficient synthesis of the naturally occurring nucleoside doridosine

1-Methylisoguanosine was synthesized by a one-pot reaction involving a condensation of 5-amino-1-(β-$\text{D}$-ribofuranosyl)imidazole-4-carboxamide (1) with methyl isothiocyanate, treatment of the resulting thiourea derivative with DCC furnished 5-(3-methyl-1-ureido)-1-(β-$\text{D}$-ribofuranosyl)imidazole-4-carbonitrile (4) which was then annulated with ethanolic ammonia to furnish doridosine in a 68% yield from 1.     

Experimental suppression of chaos in a modulated multimode laser

Suppressing chaotic behavior by addition of a weak second periodic perturbation signal, which is nearly resonant to a subharmonic of the fundamental system frequency, is observed in a modulated microchip LiNdP(4)O(12) multimode laser by a highly sensitive self-mixing modulation technique. The stabilization of the unstable period-2 orbit embedded in a chaotic attractor is demonstrated in a wide parameter region. The chaos-suppressing experiments are well reproduced by simulations of globally coupled modulated Tang-Statz-deMars [J. Appl. Phys. 34 8289 (1963)] multimode laser equations, including a spatial hole-burning effect.     

Reactions of 2-aminothiobenzamide with isocyanates: A new synthesis of 2, 3-dihydroimidazo[1, 2-c]quinazolin-5(6H)-one and 3, 4-Dihydro-2H-pyrimido[1, 2-c]quinazolin-6(7H)-one

2-(2-Chloroethylureido)- and 2-(3-chloropropylureido)thiobenzamides 5a, b were prepared in good yields by treating 2-aminothiobenzamide with 2-chloroethyl and 3-chloropropyl isocyanates respectively. Subsequent treatment of compound 5a and 5b either with alkali or mineral acid led to the formation of 2, 3-dihydro-imidazo[1, 2-c]quinazolin-5(6H)-one 7a and 3, 4-Dihydro-2H-pyrimido[1, 2-c]quinazolin-6(7H)-one 7b .