Late Quaternary cycles of mangrove development and decline on the north Australian continental shelf

Mangrove communities in the Australian tropics presently occur as narrow belts of vegetation in estuaries and on sheltered, muddy coasts. Palynological data from continental shelf and deep-sea cores indicate a long-term cyclical component of mangrove development and decline at a regional scale, which can be linked to specific phases of late Quaternary sealevel change. Extensive mangrove development, relative to today, occurs during periods of marine transgression, whereas very diminished mangrove occurs during marine regressions and during rarer periods of relative sea-level stability. Episodes of flourishing mangrove cannot be linked to phases of humid climate, as has been suggested in studies elsewhere. Rather, the cycle of expansion and decline of mangrove communities on a grand scale is explained in terms of contrasting physiographic settings characteristic of continental-shelf coasts during transgressive and regressive phases, in particular by the existence, or lack, of well-developed tidal estuaries. Copyright (C) 1999 John Wiley & Sons, Ltd.

A comparative study of the effects of UV- and gamma-radiation on copolymers of acrylonitrile/butadiene

The radiolysis of nitrile rubbers with different acrylonitrile/butadiene composition and the homopolymers, poly(butadiene) (PBD) and poly(acrylonitrile) (PAN) has been investigated and compared with the photolysis of the same polymers. A significantly different mechanism of degradation was found for the two types of radiation. The results obtained by ESR, FTIR and measurements of soluble fractions of irradiated samples, indicated that the acrylonitrile units of the nitrile rubbers are more sensitive units to gamma-radiation, with the effects of irradiation increasing with the acrylonitrile content. The reactions observed were consumption of double bonds, crosslinking, and cyclization with the formation of conjugated double bonds. No chain-scission reactions were detected. In contrast to gamma-irradiation, the effects of photolysis were centred at the butadiene units, and increases in the acrylonitrile content resulted in a proportional decrease in the sensitivity of the copolymers. Crosslinking and chain scission were identified as the main effects of photolysis of NBR rubbers. (C) 1999 Society of Chemical Industry.

Effect of temperature and a crosslinking promoter on the gamma-radiolysis of a perfluoroelastomer

Methods of promoting the radiation-induced cross linking of poly(tetrafluoro-ethylene-co-perfluoromethyl vinyl ether) (TFE/PMVE) have been investigated. Greater control of the crosslinking and chain-scission reactions was achieved by varying the radiolysis temperature. This was attributed to temperature affecting the mobilities of reactive species such as polymeric free radicals. These reactive species are precursors to radiation-induced cross links and chain-ends. Analysis of the sol/gel behaviour, tensile properties and FTIR indicated that the optimum temperature for the radiation crosslinking of TFE/PMVE, at a dose of 150 kGy, was 263 K. This temperature was 10 K below the glass transition temperature. Incorporation of 1 wt% triallyl isocyanurate (TAIC) greatly amplified the radiation crosslinking of TFE/PMVE, The dose for gelation was decreased by 70%, and the additive imparted superior mechanical properties compared to the neat irradiated TFE/PMVE. Electron spin resonance (ESR) measurements showed higher radical yields at 77 K with the 1 wt% TAIC, indicating that the crosslinking promoter was acting as a radical trap. (C) 1999 Society of Chemical Industry.

Water diffusion in hydroxyethyl methacrylate (HEMA)-based hydrogels formed by gamma-radiolysis

Polymer hydrogels based upon methacrylates are used extensively in the pharmaceutical industry, particularly as controlled release drug delivery systems. These materials are generally prepared by chemically initiated polymerization, but this can lead to the presence of unwanted initiator fragments in the polymer matrix. In the present work, initiation of polymerization by gamma-irradiation of hydroxyethyl methacrylate, with and without added crosslinkers, has been investigated, and the diffusion coefficients for water in the resulting polymers have been measured through mass uptake by the polymers. The diffusion of water in poly(hydroxyethyl methacrylate) at 310 K was found to be Fickian, with a diffusion coefficient of 1.96 +/- 0.1 x 10(11) m(2) s(-1) and an equilibrium water content of 58%, NMR imaging analyses confirmed the adherance to a Fickian model of the diffusion of water into polymer cylinders. The incorporation of small amounts (0.2-0.5 wt%) of added ethyleneglycol-dimethacrylate-based crosslinkers was found to have only a small effect on the diffusion coefficient and the equilibrium water content for the copolymers. (C) 1999 Society of Chemical Industry.

The moderating role of task characteristics in determining responses to a stressful work simulation

Two experimental studies were conducted to examine whether the stress-buffering effects of behavioral control on work task responses varied as a function of procedural information. Study 1 manipulated low and high levels of task demands, behavioral control, and procedural information for 128 introductory psychology students completing an in-basket activity. ANOVA procedures revealed a significant three-way interaction among these variables in the prediction of subjective task performance and task satisfaction. It was found that procedural information buffered the negative effects of task demands on ratings of performance and satisfaction only under conditions of low behavioral control. This pattern of results suggests that procedural information may have a compensatory effect when the work environment is characterized by a combination of high task demands and low behavioral control. Study 2 (N = 256) utilized simple and complex versions of the in-basket activity to examine the extent to which the interactive relationship among task demands, behavioral control, and procedural information varied as a function of task complexity. There was further support for the stress-buffering role of procedural information on work task responses under conditions of low behavioral control. This effect was, however, only present when the in-basket activity was characterized by high task complexity, suggesting that the interactive relationship among these variables may depend on the type of tasks performed at work. Copyright (C) 1999 John Wiley & Sons, Ltd.

Contemporary sexism - The relationships among hostility, benevolence, and neosexism

Previous research has examined the relationship between the Modern Sexism Scale (Swim, Aikin, Hall & Hunter, 1995) and the Ambivalent Sexism Inventory (ASI; Glick & Fiske, 1996) or the relationship between the Modern Sexism Scale and the Neosexism Scale (Campbell, Schellenberg, & Senn, 1997; Tougas, Brown, Beaten, & Joly, 1995). The present study examined the relationship between the ASI and the Neosexism Scale. Across three samples (N = 907), neosexism was found to be associated primarily with the hostile rather than the benevolent component of ambivalent sexism. Hostile sexism, benevolent sexism, and neosexism were all significantly associated with attitudes toward lesbians' and gay men's rights, and both hostile sexism and neosexism were significantly associated with attitudes toward women's rights. Neosexism and hostile sexism were negatively associated with a humanitarian-egalitarian orientation, whereas benevolent sexism was positively associated with a Protestant-ethic orientation. It is concluded that, although both the Neosexism Scale and ASI measure contemporary sexism, only the Benevolent Sexism subscale of the ASI taps the subjectively positive side of contemporary sexism.

Protein sequence threading, the alignment problem, and a two-step strategy

Conventionally, protein structure prediction via threading relies on some nonoptimal method to align a protein sequence to each member of a library of known structures. We show how a score function (force field) can be modified so as to allow the direct application of a dynamic programming algorithm to the problem. This involves an approximation whose damage can be minimized by an optimization process during score function parameter determination. The method is compared to sequence to structure alignments using a more conventional pair-wise score function and the frozen approximation. The new method produces results comparable to the frozen approximation, but is faster and has fewer adjustable parameters. It is also free of memory of the template's original amino acid sequence, and does not suffer from a problem of nonconvergence, which can be shown to occur with the frozen approximation. Alignments generated by the simplified score function can then be ranked using a second score function with the approximations removed. (C) 1999 John Wiley & Sons, Inc.

Polymerization of diglycidyl ether of bisphenol A/diaminodiphenyl sulfone epoxy resins using radio frequency fields

Curing of diglycidyl ether of bisphenol A/diaminodiphenyl sulfone (DGEBA/DDS) epoxy resin has been effected by heating with radio frequency (RF) radiation at frequencies of 30-99 MHz. The epoxy resins can be cured rapidly at low RF power levels. Comparison of the kinetics of the RF curing with thermal curing while maintaining the same curing temperature revealed no differences. Previous differences in rates of thermal and microwave curing are believed to be due to lack of temperature control during microwave curing. For RF curing,the rate of cure, at constant power level, increases at lower RF frequency, thus emphasizing one of the principal advantages of RF curing over microwave curing. (C) 1999 John Wiley & Sons, Inc.

High level of aspartic acid-bond isomerization during the synthesis of an N-linked tau glycopeptide

An increased degree of utilization of the potential N-glycosylation site In the fourth repeat unit of the human tau protein may be involved in the inability of tau to bind to the corresponding tubulin sequence(s) and in the subsequent development of the paired helical filaments of Alzheimer's disease. To model these processes, we synthesized the octadecapeptide spanning this region without sugar, and with the addition of an N-acetyl-glucosamine moiety. The carbohydrate-protected, glycosylated asparagine was incorporated as a building block during conventional Fmoc-solid phase peptide synthesis. While the crude non-glycosylated analog was obtained as a single peptide, two peptides with, the identical, expected masses, in approximately equal amounts, were detected after the cleavage of the peracetylated glycopeptide. Surprisingly, the two glycopeptides switched positions on the reversed-phase high performance liquid chromatogram after removal of the sugar-protecting acetyl groups. Nuclear magnetic resonance spectroscopy and peptide sequencing identified the more hydrophobic deprotected peak as the target peptide, and the more hydrophilic deprotected peak as a peptide analog in which the aspartic acid-bond just preceding the glycosylated asparagine residue was isomerized resulting in the formation of a beta-peptide. The anomalous chromatographic behavior of the acetylated beta-isomer could be explained on the basis of the generation of an extended hydrophobic surface which is not present in any of the other three glycopeptide variants. Repetition of the syntheses, with altered conditions and reagents, revealed reproducibly high levels of aspartic acid-bond isomerization of the glycopeptide as well as lack of isomerization for the non-glycosylated parent analog. If similar increased aspartic acid-bond isomerization occurs in vivo, a protein modification well known to take place for both the amyloid deposits and the neurofibrillary tangles in Alzheimer's disease, this process may explain the aggregation of glycosylated tau into the paired helical filaments in the affected brains. Copyright (C) 1999 European Peptide Society and John Wiley & Sons, Ltd.

Maximal sets of Hamilton cycles in Kn,n

In this article, we prove that there exists a maximal set of m Hamilton cycles in K-n,K-n if and only if n/4 < m less than or equal to n/2. (C) 2000 John Wiley & Sons, Inc.

Expression of EphA5 during development of the olfactory nerve pathway in rat

The olfactory neuroepithelium is a highly plastic region of the nervous system that undergoes continual turnover of primary olfactory neurons throughout life. The mechanisms responsible for persistent growth and guidance of primary olfactory axons along the olfactory nerve are unknown. In the present study, we used antibodies against the Eph-related receptor, EphA5, to localise EphA5, and recombinant EDhA5-IgG fusion protein to localise its ligands. We found that although both EphA5 and its ligands were both expressed by primary olfactory neurons within the embryonic olfactory nerve pathway, there was no graded or complementary expression pattern. In contrast, the expression patterns altered postnatally such that primary olfactory neurons expressed the ligands, whereas the second-order olfactory neurons, the mitral cells, expressed EphA5. The role of EphA5 was analysed by blocking EphA5-ligand interactions in explant cultures of olfactory neuroepithelium using anti-EphA5 antibodies and recombinant EphA5. These perturbations reduced neurite outgrowth from explant cultures and suggest that intrafascicular axon repulsion may serve to limit adhesion and optimise conditions for axon growth. (C) 2000 Wiley-Liss, Inc.

Approach to designing rotating drum bioreactors for solid-state fermentation on the basis of dimensionless design factors

The development of large-scale solid-stale fermentation (SSF) processes is hampered by the lack of simple tools for the design of SSF bioreactors. The use of semifundamental mathematical models to design and operate SSF bioreactors can be complex. In this work, dimensionless design factors are used to predict the effects of scale and of operational variables on the performance of rotating drum bioreactors. The dimensionless design factor (DDF) is a ratio of the rate of heat generation to the rate of heat removal at the time of peak heat production. It can be used to predict maximum temperatures reached within the substrate bed for given operational variables. Alternatively, given the maximum temperature that can be tolerated during the fermentation, it can be used to explore the combinations of operating variables that prevent that temperature from being exceeded. Comparison of the predictions of the DDF approach with literature data for operation of rotating drums suggests that the DDF is a useful tool. The DDF approach was used to explore the consequences of three scale-up strategies on the required air flow rates and maximum temperatures achieved in the substrate bed as the bioreactor size was increased on the basis of geometric similarity. The first of these strategies was to maintain the superficial flow rate of the process air through the drum constant. The second was to maintain the ratio of volumes of air per volume of bioreactor constant. The third strategy was to adjust the air flow rate with increase in scale in such a manner as to maintain constant the maximum temperature attained in the substrate bed during the fermentation. (C) 2000 John Wiley & Sons, Inc.

Implications of specimen preparation and of surface contamination for the measurement of the grain boundary carbon concentration of steels using x-ray microanalysis in an UHVFESTEM

The purpose of the present investigation was to gain an understanding of the nature of the carbon contamination on the surface of standard steel transmission electron spectroscopy (TEM) specimens, the effect of exposure of a clean specimen to normal laboratory air, and the efficacy of plasma-cleaning treatments. This knowledge is a necessary prerequisite to the development of appropriate specimen preparation and/or specimen cleaning methods. X-ray photoelectron spectroscopy in combination with argon ion beam profiling was used to characterize the specimen surfaces of X65 steel and 316 stainless steel. The only clean carbon-free surface obtained was that during argon etching of the sample in the surface analysis chamber. Any exposure of a previously cleaned sample to laboratory air resulted in a rapid carbon (hydrocarbon) contamination of the sample surface and the development of surface oxidation, Plasma cleaning with subsequent exposure of the specimen to the laboratory air also resulted in a carbon-contaminated surface. This suggests that procedures of preparation of TEM specimens of steels outside an ultrahigh vacuum chamber are unlikely to result in the lowering of contamination rates on specimens to levels where measurements for carbon in the grain boundaries are possible. What is needed is a cleaning system as an integral part of the specimen insertion system into the field-emission scanning transmission electron microscope. This cleaning could be carried out by argon ion etching. Copyright (C) 2000 John Wiley & Sons, Ltd.

Chemical synthesis, characterization and activity of RK-1, a novel alpha-defensin-related peptide

The 32-residue peptide, RK-1, a novel kidney-derived three disulfide-bonded member of the antimicrobial alpha-defensin family, was synthesized by the continuous now Fmoc-solid phase method. The crude, cleaved and S-reduced Linear peptide was both efficiently folded and oxidized in an acidic solution of aqueous dimethyl sulfoxide. Following purification of the resulting product, it was shown by a variety of analytical techniques, including matrix assisted laser desorption time of flight mass spectrometry, to possess a very high degree of purity. The disulfide bond pairing of the synthetic peptide was determined by H-1-NMR spectroscopy and confirmed to be a Cys(1)-Cys(6), Cys(2)-Cys(4), Cys(3)-Cys(5) arrangement similar to other mammalian alpha-defensin peptides. The synthetic RK-1 was also shown to inhibit the growth of Escherichia coli type strain NCTC 10418, Copyright (C) 2000 European Peptide Society and John Wiley & Sons, Ltd.