ALBERT

Description: The Mackenzie River is the seventh longest river in the world and with its tributaries drains a million sq. miles of northern Canada. Its drainage basin includes almost all of that portion of the District of Mackenzie lying south of the so-called “tree line”, two large sections of Yukon Territory and portions of the provinces of Saskatchewan, Alberta, and British Columbia. When flying from Fort Smith, lat. 60° N., to Inuvik near the Arctic Ocean it seems to be an endless expanse of swamp and tundra with almost no possibilities for logging, either now or in the future. Closer inspection, however, shows that there are forested areas capable of supplying timbers suitable for lumber and heavy construction, as well as poles for piling and mining timbers. It is with these forests that this article is primarily concerned.

Description: The problem of the stability of a fluid with time-dependent heating has been investigated by Morton (1957), Lick (1965) and Foster (1965). Morton and Lick assumed that the rate of change of the temperature profile is small compared with the growth rate of the disturbances (quasi-static assumption). This assumption is invalid near the onset of instability (as defined by ∂/∂t = 0), and Foster has therefore used an initial-value approach.In this paper the range of validity of the quasi-static assumption is discussed, and results of a time-scaled analysis and calculations based on this are compared with the work of Foster; the agreement is found to be good. We restrict our attention to a semi-infinite fluid initially at a constant temperature; at time t = 0 a temperature difference ΔT is applied at the (lower) horizontal boundary (case (A) of Foster).

Description: In this paper we consider two-dimensional steady cellular motion in a fluid heated from below at large Rayleigh number and Prandtl number of order unity. This is a boundary-layer problem and has been considered by Weinbaum (1964) for the case of rigid boundaries and circular cross-section. Here we consider cells of rectangular cross-section with three sets of velocity boundary conditions: all boundaries free, rigid horizontal boundaries and free vertical boundaries (referred to here as periodic rigid boundary conditions), and all boundaries rigid; the vertical boundaries of the cells are insulated. It is shown that the geometry of the cell cross-section is important, such steady motion being not possible in the case of free boundaries and circular cross-section; also that the dependence of the variables of the problem on the Rayleigh number is determined by the balances in the vertical boundary layers.We assume only those boundary layers necessary to satisfy the boundary conditions and obtain a Nusselt number dependence $N sim R^{frac{1}{3}}$ for free vertical boundaries. For the periodic rigid case, Pillow (1952) has assumed that the buoyancy torque is balanced by the shear stress on the horizontal boundaries; this is equivalent to assuming velocity boundary layers beside the vertical boundaries (rather than the vorticity boundary layers demanded by the boundary conditions) and leads to a Nusselt number dependence N ∼ R¼. If it is assumed that the flow will adjust itself to give the maximum heat flux possible the two models are found to be appropriate for different ranges of the Rayleigh number and there is good agreement with experiment.An error in the application of Rayleigh's method in this paper is noted and the correct method for carrying the boundary-layer solutions round the corners is given. Estimates of the Nusselt numbers for the various boundary conditions are obtained, and these are compared with the computed results of Fromm (1965). The relevance of the present work to the theory of turbulent convection is discussed and it is suggested that neglect of the momentum convection term, as in the mean field equations, leads to a decrease in the heat flux at very high Rayleigh numbers. A physical argument is given to derive Gill's model for convection in a vertical slot from the Batchelor model, which is appropriate in the present work.

Description: SUMMARYEwo milk yield data obtained by the lamb suckling technique from nutritional experiments were analysed statistically to obtain estimates of the several components of variation. Diurnal variation was studied. The fitting of a sinusoidal curve removed a significant amount of variation.There was a highly significant correlation between successive milk yields obtained at 4 h intervals. Number of lambs suckled and body weight of ewe at parturition had a significant effect on total daily milk yield.The variation within ewes after the removal of diurnal variation and between ewes after the removal of the effects of number of lambs suckled and body weight at parturition were computed. These sources of variation were combined in a general equation which enabled the prediction of the standard errors associated with daily milk production for a given sampling technique. The practical application of the predicted standard errors is discussed.

Description: SUMMARYThirty-six mature Finnish Landrace × Dorset Horn ewes, each suckling two lambs, were used in a comparative slaughter experiment to measure changes in body tissues during early lactation. Two levels of body fatness at lambing were established by giving ewes a complete diet containing 10 MJ metabolizable energy (ME) and 139 g crude protein (CP)/kg d.m. either close to requirements or ad libitum during the second half of pregnancy. In lactation half the ewes in each group were given a complete diet containing either 90 (diet A) or 60 (diet B) % milled hay ad libitum. These diets contained 7·9 and 9·2 MJ ME and 121 and 132 g CP/kg d.m. respectively.Ewes fed at the two levels in pregnancy contained 8·4 and 19·6 kg chemically determined fat 5 days after lambing but had similar amounts of body protein, ash and water. Over 6 weeks of lactation ewes given diet A lost 60 and 69% of these weights of fat respectively, while ewes given diet B gained 5% and lost 30% respectively. Up to 26 g of body protein was lost daily from ewes given diet A but none from ewes on diet B. During early lactation the weight of the empty digestive tract increased while the weights of most other body components, particularly the carcass, decreased. The ratio of body energy change to live-weight change varied from 24 to 90 MJ/kg. Thus live-weight change did not accurately reflect relative or absolute changes in body energy.Voluntary food intake was greater for ewes given the high-energy diet (B) than for those given diet A and was depressed in the fatter ewes. Differences in intake could be explained by the effects of body fatness and diet on the weight of gut contents. Milk yield was not significantly affected by body fat reserves but was higher on diet B than A. Fat content of milk was higher and protein content lower for ewes with the higher fat reserves at lambing.As the contribution of fat loss to energy available for milk synthesis increased there appeared to be a reduction in the energetic efficiency of milk synthesis. A number of possible reasons for this are discussed.

Description: SUMMARYThe efficacy of estimates of gut contents and total body water in increasing the precision with which the chemical composition of the body could be estimated in early lactation was evaluated in 36 Finnish Landrace × Dorset Horn ewes. The ewes were fed at two levels in pregnancy, and, in lactation, given diets of two metabolizable energy concentrations.The allometric relationships relating weight of chemical fat and protein to emptybody weight were not affected by treatment or stage of lactation. Inclusion of an index of gut contents, based on dry-matter intake, indigestibility and retention time of food residues, together with live weight in a regression equation predicting weight of body fat, only slightly increased the precision of estimate compared with equations using live weight alone.There was a close negative relationship between the proportions of water and fat in live weight. Inclusion of weight of body water with live weight in a regression equation predicting weight of body fat markedly increased the precision of estimate and the residual error (0·81 kg) was similar at different stages of lactation. However, when deuterium oxide space was used instead of body water there was only a small increase in precision of estimate and the residual error varied from 5·3 kg in early lactation to 2·1 kg in mid-lactation. The relationship between deuterium oxide space and body water was shown to be variable and altered by stage of lactation, and these differences were associated with differences in rate of water turnover in the animal's body.It is concluded that estimates of body water are unsuitable for estimating weight of body fat in early lactation.

Description: The work reported in two previous papers, Robinson (1960a, b) led to certain conclusions which required evaluation in terms of coffee yields (Coffee arabica Linn). The work describes changes in nitrate and ammonia-N in the Kikuyu red loam coffee topsoil, both natural and fertilizer derived, in the presence and absence of mulches.This paper presents early coffee yield results which have been obtained from field trials laid down on the Coffee Research Station, Ruiru, Kenya, to measure the effect of treatments based on the conclusions drawn from the soil studies.

Description: 1. Evidence is presented to show that compared with an unmulched soil, a surface mulch reduces the nitrate-N levels significantly following an application of a nitrogen fertilizer during the rains.2. Natural nitrate-X values in the top-soil were lower under a gravel mulch than a Napier grass mulch. It is concluded that the effect of a Napier grass-mulch cover in lowering natural soil nitrogen-N is offset in part by nitrates formed from the nitrogen it contains.

Description: 1. The general seasonal trends of top-soil nitrate and ammonia-N, and growth of the coffee tree are described for conditions of both soil and climate which are representative of a large proportion of the coffee-producing area in Kenya.2. When rainfall is heavy and persistent at the beginning of a rains period soil nitrate-N levels decrease rapidly, partly because of leaching losses and partly through uptake by the crop. Under conditions of rainfall and cropping similar to those described for the first half of 1954, the flush of nitrate-N in the early part of the rains will not be detected under field conditions. When the onset of the rainfall season is more gentle and substantial water movement through the upper part of the soil profile does not take place, for example, Short Rains, 1954, nitrate-N values do not decrease rapidly and there is indirect evidence of the stimulatory effect of this type of rainfall on nitrate-N formation in a remoistened field soil.3. Rapid and substantial build-up of nitrate-N is shown to take place during intervening dry weather between the rainfall periods. This is particularly marked in the top 6 in. of the soil profile and is attributed to nitrate-N formation in the absence of leaching losses; to a decreased rate of uptake by the coffee tree in the absence of vigorous growth and to the physical movement of nitrate-N upwards into the top-soil.It may be inferred from the results that alternate periods of rain and sunshine, rather than continuous heavy rain, will favour high soil nitrate-N levels and a more satisfactory nitrogen nutrition of the coffee tree.4. During periods of very low soil moisture ammonia-N builds up in the dry top-soil.5. The sharp peak and rapid decline in the rate of coffee growth during the Long Rains period coincides with very low soil nitrate-N values although climatologically conditions for continued growth are still excellent. This suggests that low available soil nitrate -N may be at least partially responsible for this early and rapid decline in the growth rate.6. In the light of observed trends in nitrate-N and coffee growth the timing of fertilizer nitrogen application to mature coffee has been altered. During the Long Rains split applications are recommended with the particular object of maintaining a supply of readily available nitrate-N in the soil. An additional and supplementary fertilizer nitrogen application is also suggested in the Short Rains period.

Description: SUMMARYMilk yield data obtained by the lamb-suckling technique on twenty-four ewes over a period of 5 consecutive days in the second and third week of their lactation have been related to lamb body weights and lamb body-weight changes over the same period. The regression equation obtained wasThe equation was used to estimate the milk consumption of lambs over the range of lamb body weights and lamb body-weight changes studied. The standard errors of these estimates have been computed for comparison with those obtained directly from the lamb suckling technique.The role of the prediction equation in estimating daily milk consumption of lambs is discussed.