Metastable chaos in the ammonia ring laser

We report experimental studies of metastable chaos in the far-infrared ammonia ring: laser. When the laser pump power is switched from above chaos threshold to slightly below, chaotic intensity pulsations continue for a varying time afterward before decaying to either periodic or cw emission. The behavior is in good qualitative agreement with that predicted by the Lorenz equations, previously used to describe this laser. The statistical distribution of the duration of the chaotic transient is measured and shown to be in excellent agreement with the Lorenz equations in showing a modified exponential distribution. We also give a brief numerical analysis and graphical visualization of the Lorenz equations in phase space illustrating the boundary between the metastable chaotic and the stable fixed point basins of attraction. This provides an intuitive understanding of the metastable dynamics of the Lorenz equations and the experimental system.

Bi-directional reflectance of corals

An assessment of the bi-directional reflectance distribution function (BRDF) of corals with different morphologies was undertaken using hyperspectral reflectance measurements. The highest variance in reflectance obtained at different viewing angles was found for the open branching Acropora colony, possibly attributed to branch orientation and internal shadow distribution. Spectral separation within and between features at the nominated sensor-viewing angles was greatest in the near infrared portion of the spectrum. The analysis of coral reef bi-directional reflectance properties and degree of internal shadowing holds potential for future assessment and information extraction relating to coral structural characteristics.

Copolymerization of methyl methacrylate and allyl acetate Part I. Rate of reaction

Free radical bulk copolymerization of methyl methacrylate (MMA) and allyl acetate (AAc) has been investigated using electron spin resonance (ESR) and FT-near infrared (FTNIR) spectroscopy. Data are used to evaluate the rate constants. The mole fraction of AAc plays an important role in the copolymerization of these two monomers. AAc not only delays the Trommsdorff effect but also increases the onset of percentage total conversion at which the Trommsdorff region begins. With AAc fraction 0.5 and higher, no Trommsdorff effect was observed. Inclusion of AAc into copolymer structure mainly occurs in the Trommsdorf region or when the AAc fraction in the comonomer feed is dominant. This is associated with a drop in the concentration of propagating radicals. However, ESR spectra indicate that the MMA propagating radical is predominant during the reaction. In the comonomer mixtures where a Trommsdorff region can be observed, the addition of AAc does not produce any significant change in k(p) and k(t) in the steady state region. Major changes in k(p) and k(t) are observed after the gel point and glassy state, respectively. (C) 2001 Society of Chemical Industry.

A systematic study of the microwave and thermal cure kinetics of the TGDDM/DDS and TGDDM/DDM epoxy-amine resin systems

The microwave and thermal cure processes for the epoxy-amine systems N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenyl methane (TGDDM) with diaminodiphenyl sulfone (DDS) and diaminodiphenyl methane (DDM) have been investigated. The DDS system was studied at a single cure temperature of 433 K and a single stoichiometry of 27 wt% and the DDM system was studied at two stoichiometries, 19 and 32 wt%, and a range temperatures between 373 and 413 K. The best values the kinetic rate parameters for the consumption of amines have been determined by a least squares curve Ft to a model for epoxy-amine cure. The activation energies for the rate parameters for the MY721/DDM system were determined as was the overall activation energy for the cure reaction which was found to be 62 kJ mol(-1). No evidence was found for any specific effect of the microwave radiation on the rate parameters, and the systems were both found to be characterized by a negative substitution effect. Copyright (C) 2001 John Wiley & Sons, Ltd.

Chemistry, properties, and phylogenetic implications of the methylated carrageenans from red algae of the genus Areschougia (Areschougiaceae, Gigartinales, Rhodophyta)

The three Australian-endemic species comprising the genus Aresehougia have been examined to determine the structure of their nonfibrillar wall components. The polysaccharide extracted from the most widely distributed species, A. congesta (Turner) J. Agardh, was shown by compositional analyses, Fourier transform infrared (FTIR) spectroscopy, linkage analysis, and C-13-NMR spectroscopy to be a carrageenan composed predominantly of the repeating disaccharides 6'-O-methylcarrabiose 2,4'-disulfate, carrabiose 2,4-disulfate (the repeating unit of L-carrageenan), 4',6'-O-(1-carboxyethylidene)carrabiose 2-sulfate, and 6'-O-methylcarrabiose 2-sulfate. The carrageenan also contained small amounts of 4-linked Galp residues, some bearing methyl ether substitution at O-3 and some possibly bearing sulfate ester and/or glycosyl substitutions at O-3. The A. congesta carrageenan had unique rheological properties, its gels having some similarities to those of commercial iota -carrageenan but with the viscosity of commercial lambda -carrageenan. Polysaccharides from A. ligulata Harvey ex J. Agardh and A. stuartii Harvey were shown by constituent sugar and FTIR analyses to be sulfated galactans rich in mono-O-methylgalactose. The carrageenan structures of Areschougia spp. were consistent with those of the genera Rhabdonia, Erythroclonium, and Austroclonium, the other genera constituting the family Areschougiaceae.

Controlling the complex Lorenz equations by modulation

We demonstrate that a system obeying the complex Lorenz equations in the deep chaotic regime can be controlled to periodic behavior by applying a modulation to the pump parameter. For arbitrary modulation frequency and amplitude there is no obvious simplification of the dynamics. However, we find that there are numerous windows where the chaotic system has been controlled to different periodic behaviors. The widths of these windows in parameter space are narrow, and the positions are related to the ratio of the modulation frequency of the pump to the average pulsation frequency of the output variable. These results are in good agreement with observations previously made in a far-infrared laser system.

Carbene and nitrene rearrangements: A theoretical study of cyclic allenes and carbenes, carbodiimides, and azirines

B3LYP/6-31G(d) calculations of structures, energies, and infrared spectra of several rearrangement products of (hetero)aromatic nitrenes and carbenes are reported. 3-Isoquinolylnitrene 36 ring closes to the azirine 37 prior to ring expansion to the potentially stable but unobserved seven-membered-ring carbodiimide 38 and diazacycloheptatrienylidene C-s-39S. A new, stable cycloheptatrienylidene, C-s-19S, is located on the naphthylcarbene energy surface. 4-Quinolylnitrene undergoes reaction via the azirine 50 in solution, but ring expansion to the stable seven-membered-ring ketenimine 47 under Ar matrix photolysis conditions. There is excellent agreement between calculated infrared spectra of 1,5-diazacyclohepta-1,2,4,6-tetraene 54 (obtained by photolysis of 4-pyridyl azide), 1-azacyclohepta-1,2,4,6-tetraene 5, 1-azacyclohepta-1,3,5,6-tetraene 55, and 1-azacyclohepta-1,3,4,6-tetraene 56 and the available experimental data.

2-cyano(2-pyridyl)ketene

Flash vacuum thermolysis of quinolizinones is a new way of generating ketenes. The title ketene is obtained from 1-cyano-2-hydroxyquinolizine-4-one and characterized by its Ar matrix infrared spectrum. (C) Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany 2002.

Quinolizine-2,4-diones by reversible dimerisation 2-pyridylketenes

Quinolizine-2,4-diones 11 are obtained by ash vacuum thermolysis (FVT) of 3-acyl-1,2,3-triazolo[1,5-a]pyridines 7. The reaction takes place via methyl- and phenyl(2-pyridyl)ketenes 10, which are directly observable by infrared spectroscopy in low temperature matrices. FVT of 11 regenerates the ketenes 10.

Synthesis of polymer-montmorillonite nanocomposites by in situ intercalative polymerization

Two polymer-montmorillonite (MMT) nanocomposites have been synthesized by in situ intercalative polymerization. The styrene monomer is intercalated into the interlayer space of organically modified MMT, a layered clay mineral. Upon the intercalation, the complex is subsequently polymerized in the confinement environment of the interlayer space with a free radical initiator, 2,2-azobis isobutyronitrile. The aniline monomer is also intercalated and then polymerized within the interlayer space of sodium- and copper-MMT initiated by ammonium peroxodisulphate and interlayer copper cations respectively. X-ray diffraction indicates that the MMT layers are completely dispersed in the polystyrene matrix and an exfoliated structure has been obtained. The resulting polyaniline-MMT nanocomposites show a highly ordered structure of a single polyaniline layer stacked with the MMT layers. Fourier transform infrared spectra further confirm the intercalation and formation of both polymer-MMT nanocomposites.

Hydrofluoric acid pre-treatment for improving 13C CPMAS NMR spectral quality of forest soils in south-east Queensland, Australia

Hydrofluoric acid (HF) was used to pre-treat forest soils of south-east Queensland for assessing the effectiveness of iron (Fe) removal, carbon (C) composition using C-13 cross-polarisation (CP) with magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) before and after the HF pre-treatment, and the improvement of C-13 CPMAS NMR spectra. Soil samples were collected from 4 experimental sites of different soil types, harvest residue management or prescribed burning, and tree species. More than 86% of Fe was in all soil types removed by the HF treatment. The C-13 NMR spectral quality was improved with increased resolution, especially in the alkyl C and O-alkyl C regions, and reduced NMR run-time (1-5 h per sample compared with >20 h per sample without the pre-treatment). The C composition appeared to alter slightly after the pre-treatment, but this might be largely due to improved spectrometer conditions and increased resolution leading to more accurate NMR spectral integration. Organic C recovery after HF pre-treatment varied with soil types and forest management, and soluble soil organic matter (SOM) could be lost during the pre-treatment. The Fourier Transform-Infrared (FT-IR) spectra of HF extracts indicated the preferential removal of carboxylic C groups during the pre-treatment, but this could also be due to adsorbed water on the mineral matter. The NMR spectra revealed some changes in C composition and quality due to residue management and decomposition. Overall, the HF treatment was a useful pre-treatment for obtaining semi-quantitative C-13 CPMAS NMR spectra of subtropical Australian forest soils.

Genotypic variation in proanthocyanidin status in the Leucaena genus

The proanthocyanidin (PA) status of 116 accessions from the Leucaena genus representing 21 species, 6 subspecies, 3 varieties and 4 interspecific hybrids was evaluated under uniform environmental and experimental conditions at Redland Bay, Queensland, Australia in October 1997. The PA content of lyophilized youngest fully expanded leaves was measured spectrophotometrically by the butanol/HCl assay referenced to L. leucocephala ssp. glabrata standard PA and expressed as L. leucocephala ssp. glabrata PA equivalents (LLPAE). Considerable interspecific variation in PA concentration existed within the genus, ranging from 0-339 g LLPAE/kg dry matter (DM). Taxa including L. confertiflora, L. cuspidata, L. esculenta and L. greggii contained very high (> 180 g LLPAE/kg DM) PA concentrations. Similarly, many agronomically superior accessions from L. diversifolia, L. pallida and L. trichandra contained extremely high (up to 250 g LLPAE/kg DM) PA concentrations, although these taxa exhibited wide intraspecific variation in PA content offering the potential to select accessions with lower (120-160 g LLPAE/kg DM) PA content. Commercial cultivars of L. leucocephala ssp. glabrata, known to produce forage of superior quality, contained low amounts of PA (33-39 g LLPAE/kg DM). Artificial interspecific hybrids had PA contents intermediate to those of both parents, Lesser-known taxa. including L. collinsii, L. lanceolata, L. lempirana, L. macrophylla, L. magnifica, L. multicapitula, L. salvadorensis and L. trichodes, contained undetectable to low (0-36 g LLPAE/kg DM) quantities of PA and have potential as parents to breed interspecific hybrids of low PA status and superior forage quality. Extractable PA was the dominant PA component, accounting for 91% of total PA within the genus. Regression analysis of accession ranks from different experiments compared to these results indicated that genetic regulation of Leucaena spp. PA content was consistent (P < 0.01) under different edapho-climatic environments. The distribution of PA within the Leucaena genus did not concur with the predictions of various evolutionary and phylogenetic plant defence theories.

Radio frequency plasma-induced hydrogen bonding on kaolinite

The radio frequency (RF) plasma-modified surfaces of kaolinite were investigated by diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) and deuteration techniques to determine the nature of RF plasma-induced surface functional groups, the altered sites in the lattice, and interaction mechanism between RF plasma and the surface of the kaolinite. It has been concluded that the RF plasma-induced infrared (IR) vibration absorption bands at 2805, 3010, and 3100 cm(-1) are attributable to the stretching vibration of hydrogen-bonded hydroxyl groups, and the band at 1407 cm(-1) is attributable to the bending vibration of (HO-)Al-O or (HO-)Si-O groupings with hydrogen-bonded hydroxyl groups. Structural alteration occurred on both the surface and subsurface region of the kaolinite during RF plasma treatment. Further structural alteration or adjustment was also observed on well-modified and well-deuterated kaolinite. There are two types of OD bands visible in the DRIFT spectra of this kaolinite, one type which decreased rapidly as a function of time in moist air, and the other which remained unchanged during the measurement. Furthermore, the appearance of broad IR bands at 3500-3100 cm(-1) as a result of deuteration is evidence of structural disturbance by RF plasma treatment lattice deuteration. An RF plasma-induced hydrogen bonding model on the surface of the kaolinite is proposed.