ALBERT

Description: A solidification boundary layer, where vorticity is concentrated, is shown to scale as δ ∼ (v / V) sin χ where χ is the angle that the solidification front makes with the oncoming flow, v is the kinematic viscosity of the melt, and V is the solidification rate. Key similarities with the suction boundary layer are outlined. Transport of vorticity, by diffusion and advection, in flows that solidify is discussed in the context of the planar-flow spin casting process, with special attention paid to how vorticity leaves the flow. Direct experimental evidence for a solidification layer in that application is reported.

Description: Motion of a single fluid sphere is described by two theories, each characterized by different levels of Hill's vortex circulation within the sphere. An existing experimental data set giving measurements of vertical velocity along the major axis of the sphere is re-examined. Contrary to published discussions of that experiment, we find that the theory of Parlange agrees better with the laboratory data than that of Harper and Moore. This agreement supports the key difference between the two theories, i.e. that the fluid within the sphere is unlikely to have a singular (infinite) velocity as it moves upwards towards the stagnation region at the top of the sphere.

Description: Stratigraphic relationships, radiocarbon dating, sediment and peat characteristics, and rates of peat and carbon accumulation from a soligenous peatland, or “bofedal,” in the Chilean Altiplano shows the peatland to be unusually young, dynamic, and sensitive to environmental changes. The site lies in the National Park Nevado de Tres Cruces in the puna desert grassland at an elevation of 4300 m a.s.l. Eight peat cores were extracted from a 1.75-km transect yielding a maximum of 3.6 m of organic sediment. Organic matter began to accumulate 1700–1100 cal yr B.P. under a progressively arid local climate, after a period when regional climate is believed to have been more humid than at present. Areas of greater relief and better drainage in the valley bottom eventually fostered the growth of a riparian cushion plant community after water flowing down the valley began to diminish. This led to rapid lateral expansion of the riparian peatland communities over open water in topographic depressions at a rate heretofore unprecedented in the peatland literature. It appears that development of the peatland has been encouraged by autoregulation of internal hydrology. The drainage impediment created by organic mass accumulation in lower-relief areas probably reduced the amount of water arriving at the lower reaches of the peatland. These areas have become progressively drier and have since died and oxidized. Through endogenous peat accumulation and a concomitant drainage impediment, the ecosystem has been migrating upstream over the past 50 years.

Description: Lake-water oxygen-isotope histories for three lakes in northern Russia, derived from the cellulose oxygen-isotope stratigraphies of sediment cores, provide the basis for preliminary reconstruction of Holocene paleohydrology in two regions along the boreal treeline. Deconvolution of shifting precipitation δ18O from secondary evaporative isotopic enrichment is aided by knowledge of the distribution of isotopes in modern precipitation, the isotopic composition of paleo-waters preserved in frozen peat deposits, as well as other supporting paleoclimatic information. These data indicate that during the early Holocene, when the boreal treeline advanced to the current arctic coastline, conditions in the lower Yenisey River region were moist compared to the present, whereas greater aridity prevailed to the east near the lower Lena River. This longitudinal moisture gradient is consistent with the suggestion that oceanic forcing (increased sea-surface temperatures in the Nordic Seas and reduced sea-ice cover) was a major contributor to the development of a more maritime climate in western Eurasia, in addition to increased summer insolation. East of the Taimyr Peninsula, large tracts of the continental shelf exposed by glacial sea-level drawdown may have suppressed maritime climatic influence in what are now coastal areas. In contrast, during the late Holocene the two regions have apparently experienced coherent shifts in effective moisture. The similarity of the records may primarily reflect reduced North Atlantic influence in the Nordic Seas and southward retreat of coastline in eastern Siberia, coupled with declining summer insolation.

Description: Linearly statified salt solutions of different Prandtl number were subjected to turbulent stirring by a horizontally oscillating vertical grid in a closed laboratory system. The experiment set-up allowed independent direct measurements of a root mean square turbulent lengthscale Lt, turbulent diffusivity for mass Kp, rate of dissipation of turbulent Kinetic energy ε, buoyancy N and viscosity v, as time and volume averaged quantities. The behaviour of both Lt and Kp was characterized over a wide range of the turbulence intensity measures, ε / v N2, and two regimes were identified. In the more energetic of these regimes (Regime E, where 300 〈 ε / v N2 〈 105), Lt was found to be a function of v, K and N, whilst Kp was a function of v, K and (ε / v N2)1/3. From these expressions for Lt and Kp, a scaling relation for the root mean square turbulent velocity scale Ut was derived, and this relationship showed good agreement with direct measurements from other data sets. In the weaker turbulence regime (Regime W, where 10 〈 ε / v N2 〈 300) Kp was a function of v, K and ε / v N2. For 10 〈 ε / v N2 〈 1000, our directly measured diffusivities, Kp, are approximately a factor of 2 different to the diffusivity predicted by the model of Osborn (1980). For ε / v N2 〉 1000, our measured diffusivities diverge from the model prediction. For example, at ε / v N2 ≈ 104 there is at least an order of magnitude difference between the measured and predicted diffusivities.

Description: Four low and four high methane (CH4) emitters were selected from a flock of 20 Romney sheep on the basis of CH4 production rates per unit of intake, measured at grazing using the sulphur hexafluoride (SF6) tracer technique. Methane emissions from these sheep were monitored at grazing for four periods (P): October, November, January and February 1999/2000. All measurements were carried out on perennial ryegrass/white clover pasture under generous herbage allowance, and the sheep were maintained on similar pastures during non-measurement periods. The tracer technique was used for all the CH4 measurements and feed DM intake was calculated from total faecal collection and estimated DM digestibility. Data for liveweight (LW), gross energy intake (GEI) and CH4 emission were analysed using split-plot analysis of variance. In addition, a between-period rank order correlation analysis was carried out for CH4 emission data.Low CH4 emitters were heavier (P

Description: In situ and in vitro rumen incubations were used to determine the effect of condensed tannins (CT) on the solubilization and degradation of the plant protein from white clover (Trifolium repens) and Lotus corniculatus. These forages contained, respectively 0·3 and 22·1 g CT/kg dry matter (DM). The sheep used for the experiments were also fed either white clover or L. corniculatus. Effects of CT were determined by making measurements in the presence and absence of polyethylene glycol (PEG; molecular weight 3500), which binds and inactivates CT. The loss of DM, neutral detergent fibre (NDF), total nitrogen (N) and Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase; EC 4.1.1.39; fraction I leaf protein) from polyester bags suspended in the rumen of sheep was measured. The loss of these constituents from polyester bags suspended in the rumen was used as a measurement of their solubilization. Degradation was defined as the disappearance of Rubisco from white clover and L. corniculatus added to in vitro incubations with rumen fluid obtained from the same fistulated sheep fed either white clover or L. corniculatus.In the absence of PEG, the in situ loss of Rubisco from L. corniculatus was less rapid than the loss of this protein from white clover when each forage was incubated in the rumen of sheep fed the same diet. Addition of PEG tended to increase the loss of Rubisco from L. corniculatus, suggesting that CT slowed the rates of solubilization of Rubisco from this forage. Effects of rumen fluid were small, but there was some evidence that the rumen fluid in sheep fed L. corniculatus reduced the solubilization of Rubisco from white clover. The action of CT did not inhibit the in situ loss of NDF from either white clover or L. corniculatus.In the absence of PEG, the in vitro degradation of Rubisco from L. corniculatus was slower when compared to the degradation of this protein from white clover; PEG addition increased the degradation of Rubisco from L. corniculatus, but not from white clover, showing that CT was the causal agent. The addition of CT extracted from L. corniculatus markedly depressed the degradation of Rubisco from white clover, with the effect being completely reversible by PEG. The large subunit (LSU) of Rubisco was consistently degraded at a faster rate than the small subunit (SSU) and added CT had a greater effect in slowing the degradation of the LSU compared to the SSU. There was little difference in the degradation of Rubisco when rumen fluid from sheep fed either white clover or L. corniculatus was used for in vitro incubations.It was concluded that the action of CT from L. corniculatus reduces the digestion of protein in the rumen of sheep. This effect is predominantly due to the action of CT reducing the degradation of plant protein, although CT also reduced the solubilization of plant protein. The main effects of CT on protein solubilization and degradation seemed to be produced locally by CT present in plant tissue; transfer of these effects through rumen fluid was small in magnitude.