85,766 research outputs found
Oscillatory processes in the theory of particulate formation in supersaturated chemical solutions
We study a nonlinear problem which occurs in the theory of particulate formation in supersaturated chemical solutions. Mathematically, the problem involves the bifurcation of time-periodic solutions in an initial-boundary value problem involving a nonlinear integro-differential equation. The mechanism controlling the oscillatory states is revealed by combining the theory of characteristics for first order partial differential equations with the multi-time scale perturbation analysis of a certain third order system of nonlinear ordinary differential equations
Effects of extended grazing during mid, late or throughout pregnancy, and winter shearing of housed ewes, on ewe and lamb performance
peer-reviewedA flock of March-lambing ewes was used to evaluate the effects of (i) extended (deferred, winter) grazing of pasture during mid, late or throughout pregnancy, and (ii) winter shearing of ewes housed during mid and late pregnancy, on lamb birth weight and subsequent growth to weaning. Ewes (n = 265) were allocated at random to five treatments for the period from 7 December (~ day 47 of pregnancy) to lambing. The treatments were: housed shorn (HS), housed unshorn (HU), grazing throughout
(EG), grazing to 20 January followed by housing (EGH), housed to 20 January followed by grazing (HEG). From 1 March to lambing the HEG and EG ewes were dispersed on the paddocks intended for grazing post lambing. All ewes were offered a concentrate supplement during the final 6 weeks of pregnancy. Housed ewes were offered grass silage while ewes on extended grazing were allocated 1.3 kg herbage dry matter per head per day from swards that had been closed for approximately 10 weeks. Ewes plus lambs (except triplet-rearing ewes which were grazed separately) from all treatments were grazed together post lambing, grouped according to lambing date. For treatments HS, HU, EGH, HEG and EG gestation lengths were 147.0, 145.6, 146.3, 146.6 and 146.9 (s.e. 0.34, P < 0.001) days, lamb birth weights were 4.9, 4.3, 4.4, 4.6 and 5.0 (s.e. 0.10, P < 0.001) kg, and lamb weaning weights were 34.6, 32.1, 33.3, 33.8 and 34.9 (s.e. 0.66, P < 0.001) kg, respectively. Extended grazing in mid and late pregnancy resulted in 35% and 65%, respectively, of the increase in lamb birth weight associated with extended grazing throughout. Treatment effects on lamb birth weight were associated with those on weaning weight (P < 0.01, R2 = 0.93). It is concluded that extended grazing or shearing of housed ewes increased lamb birth weight and subsequent weaning weight. The increased lamb birth weight from deferred grazing in mid pregnancy was probably due to improved protein utilisation from the grazed herbage. Meanwhile, the increase
An evaluation of two grassland-based systems of mid-season prime lamb production using prolific ewes of two genotypes
peer-reviewedA 4-year study was undertaken to evaluate the effects of two contrasting management
systems [year-round grazing (YRG) and normal seasonal grazing followed by indoor
feeding during winter (GWF)] on performance of mid-season lambing ewes. On the
GWF system, the annual stocking rate was 14.4 ewes/ha, grass silage was conserved
for winter feeding indoors, and the ewes were lambed indoors and were then turned
out to pasture. The YRG system was stocked at 10.5 ewes/ha, was grazed during the
winter, had outdoor lambing and the animals had access to all the farmlet for summer
grazing. The ewes were Belclare and Cheviot × Belclare which were balanced
across systems. Mean lambing dates and fertiliser N application rates were 20 and 30
March, and 85 and 92 kg/ha, for the GWF and YRG systems, respectively. Concentrate
supplementation during late pregnancy was similar on both systems. For the GWF and
YRG systems, litter size, lamb mortality, number of lambs reared, birth weight (kg),
weaning weight (kg) and lamb carcass output (kg/ha) were 2.17 and 2.24 (s.e. 0.038),
10.1 and 13.8% (P = 0.05), 1.77 and 1.78 (s.e. 0.042), 4.0 and 4.7 (s.e. 0.05, P < 0.001),
27.9 and 30.8 (s.e. 0.25, P < 0.001) and 469 and 348, respectively. Belclare ewes had a
higher litter size (2.34 v 2.07; s.e. 0.038, P < 0.001) and number of lambs reared per
ewe joined (1.86 v 1.69; s.e. 0.048, P < 0.01) than the Cheviot × Belclare ewes. There
were no significant interactions between system and ewe breed type. It is concluded that
the YRG system of prime lamb production was sustainable using prolific ewes but at
a reduced stocking rate (−26%) and with greater lamb mortality relative to the GWF
system. Ewe genotypes with a mean litter size of up to 2.34 lambs are suitable for both
systems. Lamb carcass output of 501 kg/ha was achieved from a primarily grass-based
system of mid-season prime lamb production using prolific ewes (Belclare)
Resilience of Hierarchical Critical Infrastructure Networks
Concern over the resilience of critical infrastructure networks has increased dramatically over the last decade due to a
number of well documented failures and the significant disruption associated with these. This has led to a large body of
research that has adopted graph-theoretic based analysis in order to try and improve our understanding of infrastructure
network resilience. Many studies have asserted that infrastructure networks possess a scale-free topology which is
robust to random failures but sensitive to targeted attacks at highly connected hubs. However, many studies have
ignored that many networks in addition to their topological connectivity may be organised either logically or spatially
in a hierarchical system which may significantly change their response to perturbations. In this paper we explore if
hierarchical network models exhibit significantly different higher-order topological characteristics compared to other
network structures and how this impacts on their resilience to a number of different failure types. This is achieved by
investigating a suite of synthetic networks as well as a suite of ‘real world’ spatial infrastructure networks
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