167 research outputs found
Escapement of the Cape rock lobster (Jasus lalandii ) through the mesh and entrance of commercial traps
Metal-framed traps covered with polyethylene mesh used in the fishery for the South African Cape rock lobster (Jasus lalandii) incidentally capture large numbers of undersize (<75 mm CL) specimens. Air-exposure, handling, and release
procedures affect captured rock lobsters and reduce the productivity of the stock, which is heavily fished.
Optimally, traps should retain legalsize rock lobsters and allow sublegal animals to escape before traps are hauled. Escapement, based on lobster morphometric measurements, through meshes of 62 mm, 75 mm, and 100 mm was investigated theoretically under controlled conditions in an aquarium, and during field trials. SELECT models were used to model
escapement, wherever appropriate. Size-selectivity curves based on the logistic model fitted the aquarium and field data better than asymmetrical Richards curves. The lobster length at 50% retention (L50) on the escapement curve for 100-mm mesh in the aquarium (75.5 mm CL) approximated the minimum legal size (75 mm CL); however estimates of L50 increased to 77.4 mm in field trials where trapentrances
were sealed, and to 82.2 mm where trap-entrances were open.
Therfore, rock lobsters that cannot escape through the mesh of sealed field traps do so through the trap entrance of open traps. By contrast, the wider selection range and lower
L25 of field, compared to aquarium, trials (SR = 8.2 mm vs. 2.6 mm; L25 =73.4 mm vs. 74.1 mm), indicate that small lobsters that should be able to escape from 100-mm mesh
traps do not always do so. Escapement from 62-mm mesh traps with open entrance funnels increased by 40−60% over sealed traps. The findings of this study with a known size
distribution, are related to those of a recent indirect (comparative) study for the same species, and implications for trap surveys, commercial catch rates, and ghost fishing are discussed
Comparative response of blood cortisol levels to two different doses of intravenous acth (tetracosactrin) in overweight cats
Fifteen middle-aged to older, overweight cats were investigated to rule out hyperadrenocorticism as a cause of their weight problem, using two different protocols for the adrenocorticotrophic hormone (ACTH) stimulation test. The cats received intravenous synthetic ACTH (tetracosactrin) at a dose of 125 µg initially and then, between 2 and 3 weeks later, a second test was performed using a dose of 250 µg intravenously. The peak of the mean serum cortisol concentrations taken at all time points, occurred at 60 minutes following the 125 µg dose and at 120 minutes following the 250 µg dose. There was no statistically significant difference between the cortisol peaks attained using either dose of tetracosactrin. There was, however, a significantly higher serum cortisol concentration attained after the higher dose at the 180 minutes time point, indicating a more prolonged response, when compared with the lower dose. The mean basal cortisol concentration was 203 nmol/l (range 81 – 354 nmol/l). The cats were followed up for one year after the initial investigations. Urine obtained one year later in the cats’ home environment, showed a mean urinary cortisol/creatinine ratio (UCCR) of 3.3 x 10 -6 (range 0.85 - 8.67 x 10 -6). A mean weight loss of 6 per cent was achieved over the period of the study. The weight loss, lack of development of clinical signs and the normal UCCR’s confirm that none of these cats had gone on to develop hyperadrenocorticism.Dissertation (MMedVet (Med))--University of Pretoria, 2001.Companion Animal Clinical Studiesunrestricte
An optimised QPSK-based receiver structure for possibly sparse data transmission over narrowband and wideband communication systems
In this dissertation an in-depth study was conducted into the design, implementation and evaluation of a QPSK-based receiver structure for application in a UMTS WCDMA environment. The novelty of this work lies with the specific receiver architecture aimed to optimise the BER performance when possibly sparse data streams are transmitted. This scenario is a real possibility according to Verd´u et al [1] and Hagenauer et al [2–6]. A novel receiver structure was conceptualised, developed and evaluated in both narrowband and wideband scenarios, where it was found to outperform conventional receivers when a sparse data stream is transmitted. In order to reach the main conclusions of this study, it was necessary to develop a realistic simulation platform. The developed platform is capable of simulating a communication system meeting the physical layer requirements of the UMTS WCDMA standard. The platform can also perform narrowband simulations. A flexible channel emulator was developed that may be configured to simulate AWGN channel conditions, frequency non-selective fading (either Rayleigh or Rician with a configurable LOS component and Doppler spread), or a full multipath scenario where each path has a configurable LOS component, Doppler spread, path gain and path delay. It is therefore possible to even simulate a complex, yet realistic, COST207-TU channel model. The platform is also capable of simulating MUI. Each interfering user has a unique and independent multipath fading channel, while sharing the same bandwidth. Finally, the entire platform executes all simulations in baseband for improved simulation times. The research outputs of this work are summarised below: A parameter, the sparseness measure, was defined in order to quantify the level by which a data stream differs from an equiprobable data stream. A novel source model was proposed and developed to simulate data streams with a specified amount of sparseness. An introductory investigation was undertaken to determine the effect of simple FEC techniques on the sparseness of an encoded data stream. Novel receiver structures for both narrowband and wideband systems were proposed, developed and evaluated for systems where possibly sparse data streams may be transmitted. Analytic expressions were derived to take the effect of sparseness into account in communication systems, including expressions for the joint PDF of a BPSK branch, the optimal decision region of a detector in AWGN conditions as well as the BER performance of a communication system employing the proposed optimal receiver in both AWGN channel conditions as well as in flat fading channel conditions. Numerous BER performance curves were obtained comparing the proposed receiver structure with conventional receivers in a variety of channel conditions, including AWGN, frequency non-selective fading and a multipath COST207-TU channel environment, as well as the effect of MUI. AFRIKAANS : In hierdie verhandeling word ’n in-diepte studie gedoen rakende die ontwerp, implementasie en evaluasie van ’n KPSK-gebaseerde ontvanger struktuur wat in ’n UMTS WKVVT omgewing gebruik kan word. Die bydrae van hierdie werk lˆe in die spesifieke ontvanger argitektuur wat daarop mik om die BFT werksverrigting te optimeer wanneer yl data strome versend word. Hierdie is ’n realistiese moontlikheid volgens Verd´u et al [1] en Hagenauer et al [2–6]. ’n Nuwe ontvanger struktuur is gekonsepsualiseer, ontwikkel en evalueer vir beide noueband en wyeband stelsels, waar dit gevind is dat dit beter werksverrigting lewer as tradisionele ontvangers wanneer yl data strome versend word. Dit was nodig om ’n realistiese simulasie platform te ontwikkel om die belangrikste gevolgtrekkings van hierdie studie te kan maak. Die ontwikkelde platform is in staat om ’n kommunikasie stelsel te simuleer wat aan die fisiese laag vereistes van die UMTS WKVVT standaard voldoen. Die platform kan ook noueband stelsels simuleer. ’n Aanpasbare kanaal simulator is ontwikkel wat opgestel kan word om SWGR kanaal toestande, plat duining (beide Rayleigh of Ricies met ’n verstelbare siglyn komponent en Doppler verspreiding), sowel as ’n veelvuldige pad omgewing (waar elke unieke pad ’n verstelbare siglyn komponent, Doppler verspreiding, pad wins en pad vertraging het) te emuleer. Dit is selfs moontlik om ’n komplekse, maar steeds realistiese COST207-TU kanaal model te simuleer. Die platform het ook die vermo¨e om VGS te simuleer. Elke steurende gebruiker het ’n unieke en onafhanklike veelvuldige pad deinende kanaal, terwyl dieselfde bandwydte gedeel word. Laastens, alle simulasies van die platvorm word in basisband uitgevoer wat verkorte simulasie periodes verseker. Die navorsingsuitsette van hierdie werk kan as volg opgesom word: ’n Parameter, die ylheidsmaatstaf, is gedefin¨ýeer om dit moontlik te maak om die vlak waarmee die ylheid van ’n datastroom verskil van ’n ewekansige stroom te versyfer. ’n Nuwe bronmodel is voorgestel en ontwikkel om datastrome met ’n spesifieke ylheid te emuleer. ’n Inleidende ondersoek is onderneem om vas te stel wat die effek van VFK tegnieke op die ylheid van ’n enkodeerde datastroom is. Nuwe ontvanger strukture is voorgestel, ontwikkel en evalueer vir beide noueband en wyeband stelsels waar yl datastrome moontlik versend kan word. Analitiese uitdrukkings is afgelei om die effek van ylheid in ag te neem in kommunikasie stelsels. Uitdrukkings vir onder andere die gedeelte WDF van ’n BFVK tak, die optimale beslissingspunt van ’n detektor in SWGR toestande, sowel as die BFT werksverrigting van ’n kommunikasie stelsel wat van die voorgestelde optimale ontvangers gebruik maak, hetsy in SWGR of in plat duinende kanaal toestande. Talryke BFT werksverrigting krommes is verkry wat die voorgestelde ontvanger struktuur vergelyk met die konvensionele ontvangers in ’n verskeidenheid kanaal toestande, insluitend SWGR, plat duinende kanale en ’n veelvuldige pad COST207-TU kanaal omgewing, sowel as in die teenwoordigheid van VGS.</p CopyrightDissertation (MEng)--University of Pretoria, 2010.Electrical, Electronic and Computer Engineeringunrestricte
Prevalence of canine Babesia and Ehrlichia co-infection and the predictive value of haematology
Canine babesiosis and ehrlichiosis are important tick-borne infections in South Africa. Many South African general veterinary practitioners perceive co-infection with Ehrlichia spp. as a common occurrence in dogs with babesiosis. Studies about the prevalence of co-infection in South African dogs are lacking. This retrospective study aimed to determine the prevalence of Ehrlichia co-infection in dogs with babesiosis. Additionally, the predicative value of specific haematological variables for co-infection was evaluated. The study population consisted of 205 dogs diagnosed with canine babesiosis presented to the Onderstepoort Veterinary Academic Hospital (OVAH) in 2006 and between 2011 and 2013. The Babesia-infected dogs were grouped based on presence or absence of an Ehrlichia spp. co-infection. Ehrlichia spp. co-infection was confirmed using polymerase chain reaction. Positive and negative predictive values (PPVs and NPVs) of leukopenia or thrombocytopenia for co-infection were also calculated. The prevalence of Babesiaspp. and Ehrlichia spp. co-infection in this cohort of dogs was 2%. In the babesiosis dogs, the PPV of leukopenia for co-infection with Ehrlichia spp. was 1.3%, and the NPV 97.4%. Similarly, the PPV and NPVs of thrombocytopenia for co-infection were 2.1% and 100%, respectively. Co-infection with Ehrlichia spp. was a rare occurrence in dogs with babesiosis presented to the OVAH. Normal leukocyte or platelet counts confidently ruled out the presence of concurrent ehrlichiosis in this cohort of dogs. However, the diagnosis of Ehrlichia co-infection based on the presence of thrombocytopenia or leukopenia would have been associated with false positive results in more than 97.4% of cases
Medical management of myxomatous mitral valve disease : an evidence-based veterinary medicine approach
Myxomatous mitral valve disease (MMVD) is the most common heart disease of dogs. The
current management of MMVD in dogs is mostly pharmacological, and the recommendations
for treatment are based on a number of veterinary studies. Notwithstanding the current
consensus regarding the medical management of MMVD, there remains active debate
as to which drugs are the most effective. In order to understand how recommendations
are constructed in the pharmacological management of diseases, the veterinarian needs to
understand the concept of evidence-based veterinary medicine, and how the findings of these
studies can be applied in their own practices. This review summarises the current veterinary
literature and explains how the consensus regarding the management of MMVD has been
reached. This review highlights the limitations of veterinary studies in order to provide
veterinary practitioners with a sense of the difficulty there is in establishing the benefit of one
treatment over the other. Veterinarians should therefore apply treatment recommendations
based on the best evidence, integrated with a pathomechanistic understanding of the disease
process and clinical experience.http://www.jsava.co.zaam201
Advances in the understanding of the pathogenesis, progression and diagnosis of myxomatous mitral valve disease in dogs
A number of key questions remain unanswered in the pathogenesis of myxomatous mitral
valve disease (MMVD). As MMVD typically afflicts small-breed dogs, a genetic basis has
been implied. In addition, the fact that not all dogs within a risk group develop MMVD
is still unexplained. Research into the pathogenesis of MMVD typically falls under three
categorical divisions, namely genetic factors, mechanical factors of the valve and systemic
factors. Genetic studies have implicated certain loci in the pathogenesis of MMVD. Of
particular interest is the insulin-like growth factor (IGF)-1 locus, as IGF-1 is also associated
with growth. The mechanical structure and function of the mitral valve have also received
much attention in recent years. What has emerged is the notion of a highly complex dynamic
structure, which has an uneven distribution of stress and strain according to the flow of
blood. Research efforts have also identified a number of systemic factors such as cytokines
and signalling pathways that may contribute to the failure of the valve. Serotonin remains
an area of interest in this field. Taken together, the amalgamation of research efforts in
these three areas will go a long way towards resolving the understanding of this disease.
Another area of focus in MMVD has been the development of clinical tests to diagnose the
onset of congestive heart failure. To this end, echocardiographic indices and biochemical
markers have been investigated. Echocardiographic indices such as left atrial to aortic ratio
and the N-terminal of the prohormone brain natriuretic peptide (NT-proBNP) have been
identified as specific risk factors to predict progression. Advanced imaging studies such as
cardiac magnetic resonance imaging have enabled investigators to determine the earliest
remodelling changes that occur in MMVD.http://www.jsava.co.zaam201
Early enteral nutrition in puppies with parvovirus enteritis
Canine parvovirus (CPV) enteritis is an important cause of severe, often fatal enteritis
in dogs. Survival rates can be as high as 90% when puppies receive intensive
treatment at tertiary veterinary facilities. No disease-specific therapies exist
and treatment consists of supportive therapies. These therapies include intensive
fluid therapy, antibiotic therapy, antiemetic therapy and analgesic therapy. Anthelminthic
therapy is added to eliminate possible concurrent verminosis. One
supportive measure which was found to be associated with more rapid clinical
improvement in canine parvovirus enteritis is the early implementation of enteral
nutrition. This article reviews the research findings in various aspects of early
enteral nutrition in both human and animal critical care. Different naso-enteric
feeding devices are compared and various feeding methods for the various clinical
scenarios encountered with canine parvovirus enteritis are briefly discussed. The
concept of gastric residual volume and its potential role in early enteral nutrition
is evaluated. The authors’ view on how these research findings can be practically
applied to treat puppies with canine parvovirus enteritis is presented. A detailed
description is given on the decision-making process in early enteral nutrition in a
tertiary facility treating puppies with canine parvovirus enteritis.http://www.theveterinarynurse.com/copyright.shtmlhb201
Influence of high-protein and high-carbohydrate diets on serum lipid and fructosamine concentrations in healthy cats
Objectives: The aim of this study was to determine whether high-protein and high-carbohydrate diets exert differential effects on serum cholesterol, triglyceride and fructosamine concentrations in healthy cats. Methods A randomised, crossover diet trial was performed in 35 healthy shelter cats. Following baseline health assessments, cats were randomised into groups receiving either a high-protein or high-carbohydrate diet for 4 weeks. The cats were then fed a washout diet for 4 weeks before being transitioned to whichever of the two studied diets they had not yet received. Fasting serum cholesterol, triglyceride and fructosamine concentrations were determined at the end of each 4-week diet period. Results Cats on the high-carbohydrate diet had significantly lower serum cholesterol ( P 5) had lower cholesterol ( P = 0.007) and triglyceride ( P = 0.032) concentrations on the high-protein diet than cats within other BCS groups. Conclusions and relevance Diets higher in protein and lower in carbohydrates appear beneficial for short-term glucose control in healthy cats. A high-protein diet was associated with significantly elevated cholesterol and triglyceride concentrations in healthy cats, even though the increase was significantly less pronounced in cats with a BCS >5. This finding suggests that overweight cats process high-protein diets, cholesterol and triglycerides differently than leaner cats
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