1,720,962 research outputs found
The vibration of rolling discs
No full textThe study presented is a fundamental investigation into the vibration of a rolling disc and an analysis of the sound which is then produced by the disc response. In order to characterise the disc's behaviour the free and forced vibration of a thin disc is analysed with the additional conditions which occur in rolling. These conditions include the geometric boundary conditions, the effect of the in-plane load, the change due to rotation of the disc and the effect of contact on the disc which in the first instance is modelled as a simple pinning constraint. Further in depth analysis is described for a more realistic model of the rolling contact including the effect of the contact stiffness and the creepage forces which may be present and simple contact models are proposed and corresponding responses predicted. Possible various sources of excitation are examined which cover the Rigid Body dynamics of the rolling disc, the effect of the contact model as a source of excitation and a preliminary consideration of the forces generated by contact of rough surfaces. An elementary representation is presented for the sound radiated by the rolling disc, assuming it is baffled, and its efficiency evaluated and the unbaffled disc radiation is also presented for a particular case
A perturbation method for locally damped dynamic systems
No full textIn the field of stochastic structural dynamics, perturbation methods are widely used to estimatethe response statistics of uncertain systems. When large built up systems are to be modelled inthe mid-frequency range, perturbation methods are often combined with finite element modelreduction techniques in order to considerably reduce the computation time of the response.Existing methods based on Component Mode Synthesis (CMS) allow the uncertainties in thesystem parameters to be treated independently in each of the substructures and the perturbationin the local parameters to be propagated to the full system global parameters. However, localtreatment of damping uncertainty is usually avoided by assuming proportional damping. Here,a perturbation method that includes local modal damping uncertainty and its propagation tothe global response is proposed. Local damping is accounted for in the CMS model by useof complex modes. A perturbation relationship between local and global modal properties isstated for non-classically damped systems
Farmer-related threats to cheetah (Acinonyx jubatus) survival in Namibia.
No full textThesis (M.Sc.)-University of Natal, Pietermaritzburg, 2002.This mini-dissertation is a comparison, by repeat survey, of farmer-related threats to
cheetah (Acinonyx jubatus) survival on specific commercial farms in central Namibia.
The research was conducted, to investigate if there had been changes in these threats to
cheetah survival over a ten-year period (June 1991 to October 2001). A sub-sample of 31
farmers who were originally interviewed by the Cheetah Conservation Fund in June 1991,
were re-interviewed between July and October 2001. These farmers were exposed to the
Cheetah Conservation Fund awareness-raising programme. The results of this survey
were compared to the results of the original survey of these farmers.
This study showed that changes in farmer-related threats to cheetah survival have taken
place. These include changes in land use, the attitude and behaviour of farmers towards
cheetah, and cattle management practices. The land use changes include an increase in
game farming, as a major source of income, by 19% of the farmers, since 1991. This
increase in game farming was associated with an increase in game proof fencing and the
introduction of alien antelope species into game fenced areas. The attitude of farmers
towards the presence of cheetah on their farms was found to have changed significantly (p
= 0.024), with 13% more farmers than before 1991 favouring cheetah presence on their
farms. The behaviour of farmers towards cheetah has also changed in favour of cheetah
survival. During the ten-year period from 1991 to 2001, 23% of the farmers removed no
cheetah, compared to 10% for the ten-year period before 1991. Thirteen percent of the
farmers were found to remove cheetah by trophy hunting only, as opposed to none prior
to 1991. During the ten-year period from 1991 to 2001, the number of cheetah removed
by the same farmers had declined by 243 (55%) cheetah when compared to the previous
ten-year period. Game farmers were found to remove on average 3.75 times more cheetah
than livestock farmers. Five game farmers were responsible for removing 92 cheetah,
representing 47% of the total number of cheetahs removed.
The majority (88%) of cattle farmers experienced calf losses to cheetah predation. In
contrast to this, only 44% of smallstock farmers experienced losses to cheetah predation.
The mean loss of livestock to predation by cheetah was found to be low, less than one
animal per year for both calves and smallstock. The majority (73%) of cattle farmers implement only one livestock management strategy to prevent predation on calves by
cheetah. The majority (88%) of smallstock farmers implemented more than one strategy
to prevent predation. Changes in management practices to protect calves from cheetah
predation since 1991 included a 14% decline in farmers using a technique known as
'calving camps' and an increase of 42% in the number of farmers monitoring their cows
during the calving season.
In conclusion, during the ten-year period from 1991 to 2001, both positive and negative
changes in farmer-related threats to cheetah survival were recorded amongst the farmers
interviewed. The positive changes include changes in the attitude and behaviour of
farmers in favour of cheetah survival. However, this progress was tempered by change in
land use from livestock to game farming, since game farmers pose a greater threat to
cheetah survival than livestock farmers
The evaluation of the growth parameters of six South African commercial crossbred pig genotypes.
No full textThesis (M.Sc.)-University of Natal, Pietermaritzburg, 2002.Simulation modeling is an active part of animal nutrition. These complex programs rely on mathematical functions to predict the performance of an animal. The Gompertz equation is a simple, but accurate function that fits animal growth data well. In conjunction with allometry, the growth of a specific genotype can be predicted. Only three parameters are needed to sufficiently describe a genotype, viz. protein weight at maturity (Pm), the Gompertz growth rate parameter (B) and the lipid to protein ratio at
maturity (LPRm), These descriptors are lacking for commercial pig genotypes in South Africa, and this hinders the use of models in simulating nutrient requirements. It is the aim of this thesis to estimate these parameters in six South African pig genotypes. Thirty pigs from each of six commercial genotypes were analysed using a serial slaughter method in which pigs were slaughtered at 4 and 14 days of age, and at 30, 40, 70, 80, 90 and 100kg live weight. The animals were choice fed and were housed in conventional housing facilities. Analyses for protein, lipid, water, and ash contents of the empty body at the respective weights were performed. The results indicated that there were no
significant differences between the six genotypes in terms of mature weights or B of the various body chemical components, or between the B values estimated for all components across genotypes. The mean of the estimated values for Pm, B and LPRm were 38,8 ± 2.1 kg, 0.012 ± 0.004 day(-1), and 1.16 kg/kg respectively and can therefore be used to adequately describe all six genotypes. The assumption made that all body
components have a similar B value is supported. To investigate the possible effects of the environment on growth, a comparative trial was
performed on 20 pigs each from genotypes 4, 5 and 6 using chambers in which the temperature could be controlled to within 1 degree C of the setting. All other experimental methodologies were similar to those adopted in the first experiment. No significant differences were found between the two housing facilities, in terms of the genetic parameters, within the respective genotypes supporting the findings of the previous trial. It may therefore be possible to estimate B using the live weight and estimating Pm and lipid at maturity using allometry, instead of going to the expense of a full serial slaughter trial. The allometric coefficients relating lipid, water and ash to protein were 1.18, 0.88 and 0.97 respectively
Farm environmental factors and cow physiological traits affecting the gender ratio of newborn dairy calves.
No full textThesis (M.Sc.Agric.)-University of Natal, Pietermaritzburg, 2002.Farm environmental factors in the KwaZulu-Natal Midlands were investigated to
determine whether any of them had an influence on the calf gender ratio in dairy
herds in this area. Heat detection score (P<0.001), number of inseminators
(P<0.001), geographical location (P<0.001), bull .presence on the farm
(P<0.001), and timing of insemination (P<0.001), had a highly significant effect
on the calf gender ratio. The probability of female calves increased when heat
detection included visual observation and two aids, three inseminators,
geographical location around Boston, Kamberg, Umzimkulu or Underberg,
when a bull was present on the farm and when timing of insemination was
according to an assessment of oestrous behaviour of each cow (where
insemination was immediate if a cow was thought to have been on standing
heat for a period before being observed, or delayed until the next milking if this
was not the case). These factors could be manipulated, where possible, in an
attempt to skew the gender ratio of newborn dairy calves in favour of females,
as this would lead to economic gain in a dairy enterprise due to the comparative
worth of heifer calves compared to bull calves.
An additional experiment was conducted to examine the relationship between
rectal and vaginal temperature with oestrus and ovulation in the cow. Rectal
temperature was found to be the best predictor of both oestrus (P<0.001) and
ovulation (P<0.001), when measured within 24 hours of the start of oestrus.
Rectal temperature should, therefore, only be used to predict the onset of
oestrus if the approximate time of oestrus was known from heat expectancy
records. Rectal temperature could also be used to determine when to
inseminate relative to estimated time of ovulation to increase the probability of
male or female calves, if used in conjunction with the observation of oestrous
behaviour
Movements, nesting and the effects of pollution on the Nile crocodile (Crocodylus niloticus) in the Olifants River, Kruger National Park.
Get PDFThesis (M.Sc.)-University of Natal, Pietermaritzburg, 1999.A pilot study was launched in 1993 to determine the movements of crocodiles in the Olifants River in
Kruger National Park (KNP). This turned into a research project in 1994 and lasted for five years until
1998. The objectives of the study were to determine movement, study nesting preferences and to
investigate the possible effects of metal pollution in crocodiles.
The movements of the total population were studied by doing regular foot counts, four times per annum.
The basis for movement was found on the principle that a change in numbers signified movement. Foot
counts were supported by spot counts at three different locations in the study area at 14 day intervals.
The foot counts were done along a pre-determined route, followed with every count, and this resulted in
data indicating a definite change in numbers at certain times of the year. A comparison was made
between the movements of crocodiles in large bodies of open water (lakes & estuaries), a so called
"closed" system and the Olifants River or "open" system. There was a movement of the population
during August of every year, followed by another one in December/Jan and yet another in May. The
largest movement, in August, co-coincided with the prelude to mating and ultimately nesting.
The spot counts indicated that there was a smaller and probably localized movement during May and
December of each year. This corresponds to nesting behaviour and the flood status of the river. All
indications are that major movements took place during periods of high flow and thus during the rain
season (Sept - Feb). A major flood was experienced during February 1996 which changed the geomorphology of the river.
In addition to the foot and spot counts, eleven large adult crocodiles were fitted with radio transmitters to
monitor their movements for a period of one year (1997 -1998). The results indicated that movements
over large distances occurred. The longest distance covered was in access of 36 km. Some individuals
returned to the location of origin, thus completing a round trip from their point of departure. The majority
of crocodiles fitted with transmitters left the protection of KNP, spent time in neighbouring Mozambique and some returned to Kruger after an average period of three months. Indications are that there is a lack
of territorial dominance amongst large individuals at certain times of the year, allowing for less restricted
movement up and down the river. A difference was found between the movements of crocodiles in the
Olifants River as opposed to a large body of water eg. a lake or estuary.
The second objective was to collect data on nesting preference, nest content and egg dimensions. A
total of seven parameters were measured including slope, distance to water, height above water, soil
type, vegetation, exposure to direct sunlight and the size of the female. Besides these parameters, a
comparison was made between egg size, mass and length and the correlation with female size. The
results indicated that egg mass and length increased with an increase in female size. The average
clutch size was 34 eggs. A difference was found between two nesting years (1997 and 1998) with the
larger females nesting in 1998 (egg mass 122.7g). A higher rainfall was measured for 1998, leading to
the conclusion that smaller females nested during dryer years. The larger females, because of physical
abilities, dug deeper nests ,36 cm in 1998 as opposed to 25 cm in 1997. No difference was found
between nesting habits elsewhere in Africa and that in the Olifants River.
Twelve individuals of varying sizes ranging from 1.4 m to 4.1 m, were collected from three locations and
various tissue samples were analysed for metal content. Tissue from muscle, liver, kidney and fat were
analysed for Al, Cu, Cr, Fe, Mn, Ni, Pb, Section ranger and Zn. As this was the first data of its kind to be
collected, no meaningful conclusions could be reached, except to offer the data as base line data and for
future comparisons. There was however a correlation between Fe concentration in muscle tissue and
body size, total length (TL). An increase in TL resulted in an increase in Fe concentration. The opposite
were found with Fe in fat tissue. Smaller crocodiles (TL) had higher concentrations of Fe in their fat
tissues.
Besides the large amount of base line data that resulted from this study, it also highlighted the shortage of knowledge on this species, particularly in Kruger, to enable us to manage and protect them successfully
Modeling the spatial ecology of lions (Panthera leo) in Hluhluwe - Umfolozi park.
Get PDFThesis (M.Sc.)-University of Natal, Pietermaritzburg, 2002.While many studies have been done on Lions, relatively little work has been conducted on how they interact with local habitats and the factors of importance in determining home ranges and territories. The interactions between predators and patchily distributed resources and the basic
tenets of Ideal Free Distribution theory have been used in this study as the basis in explaining how lions distribute themselves in space and why they choose particular areas above others in regards territory location. The study was conducted in the Hluhluwe-Umfolozi Park, South Africa and involved the use of historical lion sightings data recorded between the years 1973 and 1999 inclusive. A variety of potential explanatory variables including vegetation, topography, rainfall, main river distribution, roads, hyaena den locations and prey were used in developing logistic models which were then used to predict areas most likely to be colonised by lion. Model predictions were tested against independently collected validation data from an introduced pride . Modelling was conducted at a 1km² grid cell size. In total, seventeen models were formulated for four lion variables, namely cubs, adult females in groups of two or more, adult males seen with adult females and adult males only. All models accounted for a significant amount of deviance (p<0.001) except for one cub model
(p=0.003). Models which performed best in correlations with validation data were those formulated for adult females in groups of two or more and cubs (p<0.05). Variables of importance in these models included distance from main rivers and presence/absence of public roads. Preferences for travelling on roads were influenced by vegetation type, with thicket promoting travel on roads and the opposite being true of open woodland, however this was only true for females in groups of two or more. Main rivers represent high quality resource areas for lions in the reserve since they provide water, shelter, cover (hence ease of prey capture) and travel lines
Responses in growing pigs to lysine and threonine limiting feeds and environmental temperature.
No full textThesis (M.Sc. Agric.)-University of Natal, Pietermaritzburg, 1996.In this thesis two experiments were conducted. The objective of the first experiment was to
measure the response of a range of dietary threonine concentrations and environmental
temperatures on the performance of young pigs. Large White x Landrace entire male pigs (n=48) at 12 kg live weight were assigned to one of six dietary threonine treatments (n=2) and one
of four temperature treatments. Dietary threonine concentrations were formulated as 8.9 g
Threonine/kg food (T1); 6.7 g/kg (T2); 6.2 g/kg (T3); 4.9 g/kg (T4); 3.6 g/kg (T5); 4.9 g/kg
(T6). To check that threonine was limiting the most diluted diet (T5) was supplemented with
synthetic threonine. The animals were fed ad libitum and housed in environmentally-controlled
facilities. The experiment was conducted using four different temperature regimes; 18.1
(±0.38)°C, 21.9 (±0.19)°C, 26.1 (±0.50)°C and 29.9 (±0.34)°C. On reaching 25 kg live weight
the pigs were slaughtered and the carcasses prepared to obtain samples for carcass analysis.
There were significant differences (P < 0.001) in the rate of growth (ADG) between dietary
treatments with the highest gains on T1 (0.571 kg/d). There were significant differences (P <
0.01) in ADG between temperature treatments with the highest growth rate at 22°C (0.527 kg/d)
and the lowest at 30°C (0.428 kg/d). Food intakes were significantly affected by temperature (P
< 0.001) and unaffected by dietary threonine concentrations. There was a 26.1 % increase in feed
intake at 18°C when compared to the feed intake at 26°C. The highest FCE was recorded at
26°C (449 g gain/kg food) and the lowest at 18°C (386 g gain/kg food). There was an 18.4%
reduction in body protein content at 25 kg live weight between pigs fed on Tl as opposed to
those fed on T5. Dietary treatment had a significant effect (P < 0.001) on the fat composition of
the empty carcass. The highest fat content was on T5 (4.898 kg) and the lowest on T1 (2.041
kg). Temperature had a significant effect (P < 0.001) on lipid growth rates. Threonine accretion
rates were higher (P < 0.001) for pigs fed on T1 (3.52 g/d) than those fed on T2 to T5. The
lowest threonine retention was on T5 at 1.49 g/d. Linear regression of daily carcass threonine
accretion on daily threonine intake resulted in an efficiency of threonine utilization for pigs
between 12 kg and 25 kg live weight of 38%.
The objective of the second experiment was to measure the response of dietary lysine
concentrations and environmental temperature on the performance of young pigs. Large White
x Landrace entire male pigs (n=48) were assigned to one of six dietary lysine treatments (n=2)
and one of four temperature treatments. Dietary lysine concentrations were formulated as 12.7
g Lysine/kg food (T1); 10.8 g/kg (T2); 8.9 g/kg (T3); 7.0 g/kg (T4); 5.1 g/kg (T5); 7.0 g/kg (T6).
To check that lysine was limiting, the most diluted diet (T5) was supplemented with synthetic
lysine. The animals were fed ad libitum and housed in environmentally controlled facilities. The
experiment was conducted using four different temperature regimes; 18.1 (±0.19)°C,
22.0(±O.17)°C, 25.7 (±O.32)°C and 29.6 (±O.40)°C. On reaching 25 kg live weight the pigs were
slaughtered and the carcasses prepared for chemical analysis. There were significant differences
(P < 0.001) in ADG between dietary lysine treatments, with the highest gains on T1 (0.621 kg/d)
and the lowest on T5 (0.395 kg/d). There were significant differences (P < 0.001) in ADG
between temperature treatments, with the highest growth rate at 22°C (0.588 kg/d) and the lowest
at 30°C (0.466 kg/d). Food intakes were significantly affected by dietary treatment (P < 0.05)
and environmental temperature (P < 0.001). The highest feed intake was on T4 (1.284 kg/d) and
the lowest on T1 (1.080 kg/d). There was a 21.4% increase in feed intake at 18°C (1.394 kg/d)
when compared to the feed intake at 30°C (1.096 kg/d). The highest FCE was recorded at 22°C
(491 g gain/kg food) and the lowest at 18°C (417 g gain/kg food). There was an 19.9% reduction
in body protein of pigs at 25 kg live weight fed on T1 (3 .715 kg) as opposed to those fed on T5
(2.976 kg). Dietary treatment had a significant effect (p < 0.001) on the fat content of the empty
carcass. There was an increase of 134% in the fat content of the empty carcass between those
pigs fed on T5 as opposed to those fed on T5. The highest fat content was on T5 (4.926 kg) and
the lowest on T1 (2.103 kg). There were significant differences in protein accretion rates (p <
0.001) between the dietary and temperature treatments. The highest PR was on T1 (91.85 g/day)
and at 18°C (77.08 g/day). The highest THL (P < 0.05) was at 18°C (12.84 MJ/d). Lysine
accretion rates were highest on T1 (6.475 g/d) and lowest on T5 (2.726 g/d). Linear regression
of daily carcass lysine accretion on daily lysine intake showed that the efficiency of lysine
utilization for pigs between 12 kg and 25 kg live weight was 37%
The biological and economic responses of growing pigs to nutrient density.
No full textThesis (M.Sc.Agric.)-University of Natal, Pietermaritzburg, 1999.No abstract available
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