ALBERT

Description: The important role of viscosity in producing second-order Eulerian drift currents in the presence of small-amplitude water waves was first recognized by Longuet-Higgins (1953). The theoretical and experimental background is first reviewed. It is then shown that, contrary to previous belief, the presence of surface contamination must greatly enhance the drift velocity of short waves. We then solve an initial-value problem for the drift current associated with temporally decaying waves, thereby resolving questions raised by the work of Liu & Davis (1977), whose solution exhibits anomalous singularities. Next, the steady drift velocity of spatially decaying waves is calculated and shown to bear a close resemblance to Longuet-Higgins’ ‘ conduction solution ‘ for unattenuated waves. Finally, we establish that unidirectional drift currents of both surface and interfacial waves are sure to be unstable to span wise-periodic disturbances; the instability mechanism being identical to that first proposed by Craik (1977), and recently developed by Leibovich & Paolucci (1981), to explain the generation of Langmuir circulations. © 1982, Cambridge University Press. All rights reserved.

Description: The steady, laminar, incompressible flow over a periodic wavy surface with a prescribed surface-velocity distribution is found from the solution (via Newton's method) of the two-dimensional Navier-Stokes equations. Validation runs have shown excellent agreement with known analytical (Benjamin 1959) and analytico-numerical (Bordner 1978) solutions for small-amplitude wavy surfaces. For steeper waves, significant changes are observed in the computed surface-pressure distribution(and consequently in the nature of the momentum flux across the interface) when a surface orbital velocity distribution, of the type found in water waves, is included. © 1982, Cambridge University Press. All rights reserved.

Description: The generalized Lagrangian-mean (GLM) formulation of Andrews & Mclntyre (1978a, b) offers alternative physical concepts and possible saving of effort in calculation, as compared with the more conventional Eulerian-mean approach. Though mostexisting applications of this theory concern waves on weakly sheared mean flows, it is also suitable for study of waves in strong shear flows. The hydrodynamic stability of parallel shear flows is examined from this point of view. An appreciation is gained of the roles of Stokes drift, pseudomomentum, energy and pseudoenergy in this context, such understanding being a necessary prerequisite for future developments. Several known results of linear stability theory, including the inflexion-point and semicircle theorems, are concisely rederived from the GLM conservation laws. © 1982, Cambridge University Press. All rights reserved.

Description: The instability of two-dimensional periodic flows to spanwise-periodic ‘longitudinal-vortex ‘ modes is examined. The undisturbed state comprises a parallel shear flow and a two-dimensional 0(e) wave field as encountered in, say, water-wave or hydrodynamic-stability theories.When the mean shear is weak, of order Ɛ2, the present theory reduces to that of Craik (1977) and Leibovich (1977b, 1980). For stronger but still weak shear, of order Ɛ, it is established that the Craik-Leibovieh instability mechanism is essentially unchanged, apart from scaling factors. For strong O(1) shear flows, the governing equations are derived by using, in part, a generalized Lagrangian-mean formulation. The resultant eigenvalue problem for the longitudinal-vortex instability is then more complex, but simplifies in the case of small spanwise spacing of the vortices, in the inviscid limit. An example is given of flows that exhibit instability in this limiting case. Such instability seems likely to occur for a wide class of periodic shear flows. Complementary physical interpretations of the instability mechanism are discussed. © 1982, Cambridge University Press. All rights reserved.

Description: SUMMARYHalo blight resistance was transferred in a backcrossing programme from PI 150414 to a Michigan-type bean. The resistant selections obtained gave yields that were up to 10% higher than that of cv. Seafarer and had seed of good quality that was suitable for baking in tomato sauce. These selections were also resistant to the common strains of bean common mosaic virus (BCMV) and to the lambda race of anthracnose.In addition, selections with white seed of similar size to Seafarer were obtained from crosses between Seafarer and cold-tolerant lines with large, coloured seeds. In trials over 4 years these selections gave 20% higher yields than Seafarer and were less sensitive to environmental changes. Like Seafarer, they were homozygous for the I gene for resistance to BCMV but were susceptible to halo blight and anthracnose. Although not as suitable for canning in tomato sauce as other material in the National Vegetable Research Station programme, they offer useful parental material for further cycles of breeding.

Description: SUMMARYThe benefits to establishment and growth of white clover cvs Aberystwyth S.184 and Grasslands Huia of inoculation with three strains of Rhizobium trifolii, using the peat or liquid inoculum techniques, were investigated during 1975–8 on improved hill soils ranging from brown earth through dry and wet peaty podzol to deep peat.Inoculation induced positive response in either number of seedlings, plant cover or dry-matter production in 18 out of 139 comparisons, had no effect in 118 and produced a negative response in three. Most of the positive responses to inoculation were at sites with wet peaty podzol or deep peat soils but of the five sites where increase in clover D.M. production was found in the first harvest year one was a brown earth. The positive agronomic responses occurred only when the proportion of plants with nodules was high and where a substantial proportion ( 〉 50%) of the latter contained introduced Rhizobium strains at least in the year of sowing. The three negative responses were in numbers of seedlings on one brown earth and two dry peaty podzol soils and with the Huia cultivar only. Despite lack of statistical significance at individual sites the dominant overall trend was for inoculation to enhance seedling establishment and the early growtli of white clover in all soil types.On one brown earth and one dry peaty podzol soil there was some evidence that spraying the Rhizobium on to emerging white clover seedlings was more beneficial, atleast in microbiological terms, than the customary peat inoculum procedure.The incorporation of even a small amount of nitrogen (30 kg/ha) into the seed bed at the time of sowing adversely affected germination, establishment and growth of white clover in some soils. Sometimes the effects of this nitrogen persisted into the first harvest year.

Description: SUMMARYThe digestible energy (DE) and metabolizable energy (ME) content of eight samples of barley, eight of wheat, four of maize and two each of oats and rye were determined using growing gilts. The DE content of barley ranged from 15·35 to 15·89 MJ/kg D.M., from 15·15 to 16·42 MJ/kg D.M. for wheat and from 16·05 to 16·47 MJ/kg D.M. for maize. DE values for the two oat samples were 12·48 and 12·74 MJ/kg D.M. and 15–04 and 15–47 MJ/kg D.M. for the two rye samples. There was a significant correlation between DE and ME:ME (MJ/kg D.M.) = 0·050 + 0·965 DE: r = 0·99; P 〈 0·001.The ratio ME/DE was significantly influenced by crude-protein content:ME/DE = 100–0·254 CP%: r = –0·77; P 〈 0·001.ME values were also corrected to zero nitrogen retention (MEno) and to 30% nitrogen retention (MEN30). The effect of such corrections was expressed as MEN0/ME and MEN30/ME. Values thus obtained were 0·98 and 1·00 respectively for the pooled values for all cereals.The data indicated that there was unlikely to be significant variation in the DE content of samples of the same cereal species, selected from commercial sources within the U.K. when evaluated under standardized experimental conditions.

Description: SUMMARYThe net energy values for growth and fattening of two artificially dried tropical grasses-, pangola (Digitaria decumbens) and setaria (S. sphacelata var. sericea cv. Nandi), of similar estimated metabolizable energy content (8·07 and 7·96 MJ/kg D.M.) were determined with cattle using a slaughter technique. Growing cattle with a mean initial weight of 175 kg were given equal quantities of dry matter of the two grasses at each of three planes of nutrition above maintenance for a period of 152 days.The initial energy, fat and protein content of the total body of the 24 test animals was estimated from regressions relating fasted live weight to theśe components, derived from 12 similar cattle slaughtered at the beginning of the feeding period. The final energy, fat and protein content of the test animals was determined directly by chemical analysis. The metabolizable energy (ME) content of the grasses was estimated from the level of digestible energy (DE) determined with eight cattle, assuming that ME = 0·815 DE.The cattle fed pangola gained more live weight, empty-body weight, fat, protein and energy than animals fed similar quantities of setaria. The net energy value for growth and fattening (NEf) was determined using regressions relating energy retention to the quantity of dry matter eaten. NEf in MJ/kg dry matter was 2·27 for pangola and 1·31 for setaria.Efficiency of utilization of ME for growth and fattening (kf) was.27·7% for pangola and 16·9% for setaria. These values for tropical grasses are lower than any values reported for temperate pasture species. Thus the lower efficiency of utilization of ME may cause the lower production of cattle which graze tropical grasses.It was concluded that as the kf values of different tropical grasses are not constant, kf values should be measured on a wider range of tropical grasses so that this factor can be taken into account when evaluating grasses in animal production systems.

Description: SUMMARYThree experiments examined the effects on seedling emergence and seedling weight of covering pelleted, natural and pre-germinated seeds of the variety Pennlake with soil and other media.Covering seeds with a peat-vermiculite mix gave significantly greater, earlier and more uniform emergence and seedlings with a lower coefficient of variation (c.v.) of weight than covering with soil.Seedlings from pre-germinated seeds emerged more rapidly than those from natural and pelleted seeds and tended to be heavier when harvested 24 or 41 days after emergence. However, natural seeds consistently gave more uniform emergence than the other seed treatments and the lowest c.v. of seedling weight.

Description: A formalism that accounts for inertial and diffusive effects in the dynamics of a dilute gas-particle suspension is introduced. The treatment is purely deterministic away from a very thin Brownian diffusion sublayer, while, within the sublayer, inertial effects are small, permitting a near-equilibrium expansion in powers of the Stokes number (particle relaxation time divided by flow characteristic residence time). This expansion provides phenomenological expressions for theparticle velocity including two terms: the standard Brownian diffusion, and an additional inertial drift velocity which is closely related to the pressure diffusion term of the Chapman-Enskog expansion. As an example, the general formalism is applied in detail to the case of Stokes flow about a sphere, and sketched for the similar case of a cylinder. Two competing mechanisms are seen to affect the total rate of particle capture by the sphere: (i) the stagnation-point region is considerably enriched in particles owing to the high compressibility of the particle phase, which leads to locally enhanced deposition; (ii) centrifugal forces tend to deplete the Brownian diffusion sublayer of particles, reducing diffusion rates away from the stagnation point to the surface. The first effect is seen to dominate over the second except in a very narrow zone of small Stokes numbers. Our method bridges the gap between Levich's solution for the ‘pure-diffusion’ limit and Michael's treatment in the ‘pure-inertia’ limit. © 1982, Cambridge University Press. All rights reserved.