Numerical modelling of the stress regime at subduction zones

The stress regime at subduction zones has been modelled using a visco-elastic, quadratic isoparametric finite element model. An isoparametric model is used because it performs more accurately than constant strain triangular elements (CST) and also allows curved sided elements to be introduced.A method for modelling the frictional sliding on Isoparametric fault elements has been developed by extending Mithen's (1980) CST model. The resulting method is suitable for modelling the deformation on both plane and listric, normal and thrust faults. Graben widths predicted by normal fault models agree with analytic solutions and this implies than Mithen's CST models failed to do so because they were too stiff. Application of this model to subduction zones demonstrates that the slab pull force induces tension in the subducting plate and compression in the overlying plate. Part of the lateral variation in stress which is observed at all subduction zones is therefore inferred to arise from the slab pull force. Differences in the magnitude of these stresses at different subduction zones may therefore be accounted for by local variations in the magnitude or dip of the slab pull force, and also by the extent of the coupling across the plate boundary. Various forces account for the stress regime in back arc regions. Tensional stress is generated by lateral density variations, and the heating and shearing caused by slab induced convection. Compressive stress, arising from the slab pull force, is superimposed upon this. The magnitude of the compression, however, is dependent upon the dip and size of the slab pull force and also the degree of mechanical coupling between the plates at the subduction zone fault. Local variations in the magnitude of the compressive stress may therefore explain why the stress regime is observed to be so variable in back arc regions, and is more commonly tension than compression

Methane emission by alpaca and sheep fed on lucerne hay or grazed on pastures of perennial ryegrass/white clover or birdsfoot trefoil

Based on the knowledge that alpaca (Lama pacos) have a lower fractional outflow rate of feed particles (particulate FOR) from their forestomach than sheep (San Martin 1987), the current study measured methane (CH4) production and other digestion parameters in these species in three successive experiments (1, 2 and 3): Experiment 1, lucerne hay fed indoors; Experiment 2, grazed on perennial ryegrass/white clover pasture (PRG/WC); and Experiment 3, grazed on birdsfoot trefoil (Lotus corniculatits) pasture (Lotus). Six male alpaca and six castrated Romney sheep were simultaneously and successively fed on the forages either ad libitium or at generous herbage allowances (grazing). CH4 production (g/day) (using the sulphur hexafluoride tracer technique), voluntary feed intake (VFI), diet quality, and protozoa counts and volatile fatty acid concentrations in samples of forestomach contents were determined. In addition, feed digestibility, energy and nitrogen (N) balances and microbial N supply from the forestomach (using purine derivatives excretion) were measured in Experiment 1. Diets selected by alpaca were of lower quality than those selected by sheep, and the voluntary gross energy intakes (GEI, MJ) per kg of liveweight(0.75) were consistently lower (P0.05) in their CH4 yields (% GEI) when fed on lucerne hay (5.1 v. 4.7), but alpaca had a higher CH4 yield when fed on PRG/WC (9.4 v. 7.5, P0.05) in diet N partition or microbial N yield, but alpaca had higher (P<0.05) neutral detergent fibre digestibility (0.478 v. 0.461) and lower (P<0.01) urinary energy losses (5.2 v. 5.8 % GEI) than sheep. It is suggested that differences between these species in forestomach particulate FOR might have been the underlying physiological mechanism responsible for the differences in CH4 yield, although the between-species differences in VFI and diet quality also had a major effect on it

The Effect of Cow-Diet on the Fermentation of Forages

In vitro fermentation of fresh forages minced to resemble chewed material have enabled net proteolysis and volatile fatty acid (VFA) production to be measured using rumen inocula from a cow fed lucerne hay (Burke et al., 2000). However both cow and diet affect the rumen cellulolytic bacterial populations (Weimer et al., 1999) and are able to influence in vitro digestion kinetics (Mertens et al., 1998). The objective of this study was to measure cow-diet effects on in vitro digestion and fermentation of perennial ryegrass (P; Lolium perenne), sulla (S; Hedysarum coronarium), maize (M; Zea maize) silage and mixtures

Effect of Condensed Tannin in Lotus Corniculatus and Lotus Pedunculatus on Digestion of Rubisco in the Rumen

The in vitro precipitation of ribulose-1,5-bisphosphate carboxylase (Rubisco) by condensed tannin (CT) extracted from Lotus corniculatus and Lotus pedunculatus and the effect of these CT on the in vitro rumen degradation of Rubisco was used to compare the reactivity of these CT. The chemical structure of CT from Lotus corniculatus was homogenous with epicatechin stereochemistry and mostly procyanidin units. The CT from Lotus pedunculatus was heterogenous with mostly prodelphinidin units. The amount of CT required to precipitate all the Rubisco when total soluble leaf protein was incubated with CT from Lotus corniculatus and Lotus pedunculatus was similar. Although CT from both species were able to reduce the in vitro degradation of Rubisco, CT from Lotus corniculatus was less effective than CT from Lotus pedunculatus at reducing this degradation

High Floral Tannin White Clover Reduces Rumen Ammonia Concentrations in Dairy Cows

White clover produces high quality forage for ruminant production, but it results in high rumen ammonia concentrations, indicating extensive protein degradation. The excess ammonia is absorbed through the rumen and excreted as urea in urine, at a cost to the animal and the environment. Condensed tannins (CT) contained in some forages reduce proteolysis in the rumen, which can lead to increased amino acid absorption and therefore improved animal performance. White clover produces CT in its flower heads, but concentrations are normally too low to benefit animals. This paper reports on comparisons of rumen ammonia concentrations in dairy cows grazing HT (high tannin) white clover (an experimental line of white clover with increased flowering) or Grasslands Huia white clover

Condensed Tannin Concentration and Herbage Accumulation of a White Clover Bred for Increased Floral Condensed Tannin

White clover is a high quality feed for ruminants, however, its high protein content results in excessive urea excretion in urine and can cause bloat, reducing its potential value for animal production. The condensed tannins (CT) in some forages can reduce these problems, but plants may have poor agronomic performance. White clover produces CT in its flower heads, but herbage CT concentrations are normally too low to benefit animals. This paper reports CT concentrations and herbage accumulation over 2 years of an experimental line of white clover (HT) selected for increased flowering and floral CT concentrations

Animal management and feed intake.

Methane (CH4) is the most abundant hydrocarbon in the atmosphere.Disponivel em : http://www.globalresearchalliance.or

Late Miocene to early Pliocene stratigraphic record in northern Taranaki Basin: Condensed sedimentation ahead of Northern Graben extension and progradation of the modern continental margin

The middle Pliocene-Pleistocene progradation of the Giant Foresets Formation in Taranaki Basin built up the modern continental margin offshore from western North Island. The late Miocene to early Pliocene interval preceding this progradation was characterised in northern Taranaki Basin by the accumulation of hemipelagic mudstone (Manganui Formation), volcaniclastic sediments (Mohakatino Formation), and marl (Ariki Formation), all at bathyal depths. The Manganui Formation has generally featureless wireline log signatures and moderate to low amplitude seismic reflection characteristics. Mohakatino Formation is characterised by a sharp decrease in the GR log value at its base, a blocky GR log motif reflecting sandstone packets, and erratic resistivity logs. Seismic profiles show bold laterally continuous reflectors. The Ariki Formation has a distinctive barrel-shaped to blocky GR log motif. This signature is mirrored by the SP log and often by an increase in resistivity values through this interval. The Ariki Formation comprises (calcareous) marl made up of abundant planktic foraminifera, is 109 m thick in Ariki-1, and accumulated over parts of the Western Stable Platform and beneath the fill of the Northern Graben. It indicates condensed sedimentation reflecting the distance of the northern region from the contemporary continental margin to the south