Recognition of subgroups of direct products of hyperbolic groups

We give examples of direct products of three hyperbolic groups in which there cannot exist an algorithm to decide which finitely presented subgroups are isomorphic.

     

Synthesis of poly(arylene disulfide)-vermiculite nanocomposites via in situ ring-opening reaction of cyclic oligomers

An exfoliated poly(4,4^′-oxybis(benzene)disulfide) (POBDS)/vermiculite (VMT) nanocomposite was prepared by using cyclo(4,4^′-oxybis(benzene)disulfide) (COBDS) oligomers and cetyltrimethyl ammonium bromide exchanged VMT. The POBDS/VMT nanocomposites were fabricated in two steps. First, the COBDS oligomers were used to swell and exfoliate organo VMT to afford COBDS-VMT nanocomposite precursor. Subsequently, the exfoliated POBDS-VMT nanocomposite can be made via in situ and instant melt ring-opening polymerization of the COBDS-VMT nanocomposite precursor. High molecular weight POBDS polymer can be formed in a few minutes. The nano scale dispersion of VMT layers within POBDS polymer was confirmed by both the X-ray diffraction patterns and TEM examinations. This methodology provides a potential approach to synthesize high performance polymer nanocomposite.     

Effect of aeration on lignin peroxidase production by Streptomyces viridosporus T7A

The effect of aeration on lignin peroxidase production by Streptomyces viridosporus T7A was studied in a bench-scale bioreactor using a previously optimized growth medium (0.65% yeast extract and 0.1% corn oil, pH7.0) at 37°C and natural pH. Airflow rates of 0.3, 1.0, and 1.5 vvm and a fixed agitation of 200 rpm were initially studied followed by 1.0 vvm and 200, 300, 400, and 500 rpm. The use of 1.0 vvm and 400 rpm increased enzyme concentration 1.8-fold (100–180 U/L) and process productivity 4.8-fold (1.4–6.7 U/[L·h]) in comparison with the use of 200 rpm and 0.3 vvm. The inexpensive corn oil, used as carbon source, besides its antifoam properties, proved to be nonrepressive for enzyme production.     

Ill-posedness for the Zakharov system with generalized nonlinearity

We study the ill-posedness question for the one-dimensional Zakharov system and a generalization of it in one and higher dimensions. Our point of reference is the criticality criteria introduced by Ginibre, Tsutsumi and Velo (1997) to establish local well-posedness.

     

Photostimulated phenomena in relaxors

The action of illumination on the conducting and dielectric properties of lead magnoniobate was investigated. The photostimulated currents were examined and the spectral dependence of photoconductivity in the region of diffuse phase transition was obtained. It was found that the illumination affects the dielectric properties and that its action is memorized at temperatures below room temperature. The role of defect states in the formation of relaxor properties is discussed on the basis of the obtained data.     

Role of vitreous matrix on the optical activity of Ge-doped silica

We report an experimental study on the relationship between the optical activity of Ge-oxygen deficient centers and dynamic properties and conformational heterogeneity of vitreous matrix in silica. We focus our attention on the absorption band at ∼5.2 eV (B_2β) and on the two related emissions at ∼4.2 eV (α_E) and at ∼3.1 eV (β). From the temperature dependence of B_2β band we estimate a mean energy value of 26 meV for local vibrational modes coupled to the electronic transition, suggesting that the chromophore and its surrounding have access to low frequency dynamics. From the thermal behavior of the two emissions we distinguish the two competitive relaxation processes from the first singlet excited state S₁: the radiative one, giving rise the α_E band, and the thermally activated intersystem-crossing process between S₁ and the triplet state T₁, originating the β band. The intersystem-crossing rate increases on increasing the temperature, determining an opposite thermal behavior of the intensity of the two emissions. However, this temperature dependence cannot be rationalized by a simple Arrhenius law and the α_E decay kinetics at high temperatures do not follow a single exponential law, suggesting a complex landscape of configurational energies of the process.     

Effect of External Acidity of Mordenite-Supported Catalysts on the 2,2-Dimethylbutane Content in Hydroisomerization Products of n-Hexane

We have used potentiometric titration with tetrabutylammonium hydroxide to determine the acid center content on the outer surface of dealuminated natural and synthetic mordenites. We have established a symbatic relationship between the 2,2-dimethylbutane content in the hydroisomerization products of n-hexane on dealuminated palladium-containing mordenites and the number of their external acid centers. We have studied the possibility of partial deactivation of such centers during ion-exchange deposition of palladium on the catalysts, using a tetraammine palladium solution.     

Role of water vapor and CO2 in the paleoclimatic fluctuations along northwestern and southern Syria, and the adjacent Mediterranean Sea

Microscopic petrified grains were collected from a mafic–ultramafic pipe, NE of Dreikeesh, NW Syria. The grains were identified as anthers/gynoecia in herb/grass flowers. Three of the grains showed evidence of magnetism, two slowly dissolved in concentrated HCl, and three microprobed grains showed a montmorillonitic composition. Iron originating from pyroxene was oxidized to magnetite. Released silica formed the mineral suite agate–chalcedony–opal. Warm/cold paleoclimatic fluctuations, occurring during late Pliocene–Holocene, depended on water vapor, CO₂ production, and cinders in the atmosphere. Most of these were associated with changing volcanic/tectonic events. Fluctuations were controlled by heat reflected from the Earth's surface being absorbed by water vapor and CO₂, which both re-reflected the heat back to the surface, thus, raising the temperature. This cycle was repeated several times during late Pliocene–Holocene.