• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 2
  • 1
  • 1
  • 1
  • Tagged with
  • 5
  • 5
  • 2
  • 2
  • 2
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Feasibility studies on the friction stir welding of the multi-laminated silicon steel sheets

Lin, Jia-Shiang 22 August 2011 (has links)
A friction stir welding equipment with high rotation speed and constant load is successfully developed in this study to weld the multi-laminated silicon steel sheets widely used on regular transformers. This equipment consists of a spinning unit, a loading unit, and a feeding unit. A WC round rod with 3 mm diameter is used as welding tool. Under different operating conditions, such as the normal load(140~480 N), the spindle speed (12000~24000rpm), the feeding rate (0~1.58 mm/s), the welding characteristics and the welding mechanism of multi-laminated silicon steel sheets, and the welding feasibility of the transformer are investigated. Firstly, the contour map of welding depth in terms of spindle speed,normal load, and depth of point welding is established for dwell welding time 15 seconds. Secondly, based on this contour map, two experimental conditions of the long-pass welding tests are selected to investigate the effect of normal load (Fd), the spindle speed (Ns), and the feeding rate (f) on the failure load of weld under the shear. According to the experimental results, the empirical formula is obtained as Ff =40.6(Fd¡DNs)1.123(f)-0.791. In this formula,(Fd¡DNs)1.123(f)-0.791 is proportional to the frictional work per unit moving distance. With the larger frictional work, this represents the heat generation of the workpiece material is higher with more uniform friction stir, so that the bonding strength of the material increases and the failure load of weld is larger. According to the micrograph observations, the thermo-mechanically affected zone is significantly influenced by high heat action generated from the friction between the tool and the weld surface region, so that the plastic flow of the workpiece material occurs to cause the multi-laminated silicon steel sheets bonding together. Finally, the transformer is successfully welded under the experimental conditions of the long-pass welding tests with the smaller welding depth and the better failure load.
2

Závislost predace a rychlosti metabolismu na teplotě z pohledu kořisti i predátora

MODRÁ, Denisa January 2017 (has links)
Climate changes affect species interactions which can have cascading effect up to the ecosystem level. This work investigates the effects of temperature and predator size on predator prey interactions by measuring the feeding rates of predators and metabolic rates of both predator and prey, using dragonfly larvae Aeshna cyanea and toad tadpoles Bufo bufo as a model system. Possible consequences of the findings for the impacts of climate change and predation on amphibian populations are discussed.
3

Efeito da taxa arraçoamento e da freqüência alimentar no crescimento de juvenis do pampo Trachinotus marginatus

Cunha, Viviana Lisboa da January 2008 (has links)
Dissertação(mestrado)-Universidade Federal do Rio Grande, Programa de Pós-Graduação em Aqüicultura, Instituto de Oceanografia, 2008. / Submitted by Cristiane Silva (cristiane_gomides@hotmail.com) on 2012-08-10T12:32:21Z No. of bitstreams: 1 Viviana.pdf: 145507 bytes, checksum: 5b6588d4650811ce2cf7155c7f9e6830 (MD5) / Approved for entry into archive by Bruna Vieira(bruninha_vieira@ibest.com.br) on 2012-08-21T18:04:33Z (GMT) No. of bitstreams: 1 Viviana.pdf: 145507 bytes, checksum: 5b6588d4650811ce2cf7155c7f9e6830 (MD5) / Made available in DSpace on 2012-08-21T18:04:33Z (GMT). No. of bitstreams: 1 Viviana.pdf: 145507 bytes, checksum: 5b6588d4650811ce2cf7155c7f9e6830 (MD5) Previous issue date: 2008 / A família Carangidae engloba uma série de peixes economicamente importantes, abundantes em águas tropicais e sub-tropicais. O pampo Trachinotus marginatus apresenta fácil adaptação a sistemas intensivos de criação, comprovado pela rápida aceitação de dieta artificiais. Entretanto, para determinar a viabilidade do cultivo de uma espécie é necessário o conhecimento dos fatores limitantes para sua produção. A taxa de arraçoamento e a freqüência alimentar apropriada são importantes para o correto manejo alimentar de uma espécie cultivada. O conhecimento da “Specific dynamic action” (SDA) também é importante e pode auxiliar na determinação da capacidade suporte do sistema de produção. O objetivo deste trabalho foi estabelecer a taxa ótima de arraçoamento, a freqüência alimentar adequada e estudar a taxa de consumo de oxigênio pós-prandial para juvenis do pampo. Os experimentos foram realizados com juvenis (4,8±0,6g) coletados na natureza e aclimatados ao laboratório. Foram testadas diferentes taxas de arraçoamento (4, 8, 12, 16 e 20% da biomassa total por dia) e freqüência alimentar (2, 4, 6, 8 e 10 vezes por dia). O consumo de oxigênio foi avaliado com peixes alimentados com 12% da biomassa por dia. É sugerido o uso de uma taxa de arraçoamento de 8% da biomassa por dia e a freqüência alimentar de 6 a 8x/dia para juvenis de pampo, de modo a otimizar o crescimento e a taxa de conversão alimentar aparente. Foi observado um pico de consumo de oxigênio aos 30 min após a alimentação e decorridos 150 min da alimentação, o consumo de oxigênio retornou ao nível basal. / Carangidae fish are economically important fish, abundant in tropical and subtropical environments. Pompano Trachinotus marginatus easily adapts to captivity, since wild caught fish accept dry diets soon after being captured. However, in order to determine the viability of a new species for aquaculture, it is important to know the limiting factors for its production. Daily ration and feeding frequency are important parameters to control regarding feeding management for juvenile rearing. Specific dynamic action is also important and can help to determine carrying capacity of a given rearing system. The objective of this work was to determine optimum daily ration and feeding frequency, and to study post-pandrial oxygen consumption. Wild caught juvenile pompano (4.8±0.6g) captured in the surf zone at Cassino beach (Brazil). Two independent feeding trials were carried in laboratory. In trial I pompano were fed 4, 8, 12, 16 and 20% total biomass daily (% B.D-1). In trial II, juveniles were fed 2, 4, 6, 8 and 10 times per day. The postprandial metabolic changes were measured with juvenile pompano fed 12%B.D-1. The best feeding ration was 8% B.D-1, while optimum feeding frequency was between 6 and 8 meals per day to maximize growth and feed conversion rate. Postprandial increase in oxygen consumption was observed 30 min after feeding and after 150 min it decreased to the standard metabolic rate.
4

A comparison between the effects of polylactic acid and polystyrene microplastics on Daphnia magna

Puranen Vasilakis, Mikaela January 2017 (has links)
The effects of microplastics on zooplankton are an increasing environmental concern. Both primary microplastics that are produced as constituents of cosmetic products, as well as secondary microplastics that are formed by degradation of larger plastic debris, are ubiquitous in aquatic environments. Today, primary microplastics are being phased out and replaced by plant-derived bioplastics. Whether these new materials have similar effects as oil-based microplastics on animals is currently unknown. Here, we compare the effects of secondary microplastic exposure to Daphnia magna, using polylactic acid (PLA) as a representative for bioplastics and polystyrene (PS) for oil-based plastics. To increase the ecological relevance of our tests, we also provided treatments where the particles were coated with bovine serum albumin (BSA) as a means to simulate the coating of biofilms which readily form on particles under natural conditions. Furthermore, to be able to differentiate the effects of general particles from those specific to microplastics, kaolin clay was used as a control treatments, as well as one treatment containing only algae. The objectives were to test the influence of particles on feeding rates, reproduction and growth. PS caused a higher mortality, decreased feeding rate and reproductive output, while PLA and kaolin did not produce any negative effects. BSA did not have a significant effect on reproduction or growth. However, a decrease in reproduction was observed in the plastic treatments. Degradation of PS into styrene monomers is suggested as a possible explanation for the observed toxicity and effects on life history parameters.
5

Seletividade alimentar e produção secundária de alevinos de peixes neotropicais alimentados com Dendrocephalus brasiliensis (Pesta, 1921) e outras espécies zooplanctônicas

Silva, Ricardo Augusto Custodio da 01 July 2011 (has links)
Made available in DSpace on 2016-06-02T19:31:57Z (GMT). No. of bitstreams: 1 3764.pdf: 1429773 bytes, checksum: 4073170af6df253bf6cb50f4e03c4a19 (MD5) Previous issue date: 2011-07-01 / Universidade Federal de Sao Carlos / The hatchery is now the main obstacle of aquaculture. The live food, especially zooplankton, is essential in early life stages of fish. However, there are difficulties in obtaining enough biomass. The Anostraca Dendrocephalus brasiliensis, known as branconeta, has great potential of use in national aquaculture. In this study, it was performed experiments of food selectivity and secondary production with fingerlings of matrinxã (Brycon cephalus) and pintado-da-amazônia, a hybrid between Pseudoplatystoma corruscans and Leiarius marmoratus, using D. brasiliensis and other species of zooplankton as food. Food selectivity results were evaluated using the Ivlev selectivity index and the coefficient of food Paloheimo. For both species, the indexes of the juveniles indicated a preference by D. brasiliensis in comparison to zooplankton. Secondary production values were better when matrinxã was fed with Artemia plus artificial food; there was no significant difference to fish fed with branconeta. For pintado-da-amazônia, the highest production was obtained from branconeta treatment. So, the selectivity for D. brasiliensis is positive, once it was accepted by both species, without rejection. The results allow us to assert that the use of D. brasiliensis is suitable for the cultivation of both species. / A larvicultura é hoje o principal entrave da aqüicultura. O alimento vivo, em especial zooplanctônico, é essencial nas fases jovens de peixes. No entanto, há dificuldades em se obter biomassa suficiente. O Anostraca Dendrocephalus brasiliensis, conhecido como branconeta, tem grande potencial de utilização na aqüicultura nacional. No presente estudo, foram realizados estudos de seletividade alimentar e produção secundária com alevinos de matrinxã, Brycon cephalus, e pintado-da-amazônia, um híbrido entre Pseudoplatystoma corruscans e Leiarius marmoratus, utilizando-se D. brasiliensis e outras espécies zooplanctônicas como alimento. Os resultados de seletividade alimentar foram avaliados utilizando-se o índice de seletividade de Ivlev e o coeficiente alimentar de Paloheimo. Para as duas espécies, os índices apontaram preferência dos alevinos por D. brasiliensis frente ao zooplâncton. Os ensaios de produção secundária com matrinxã resultaram em melhor rendimento com ração e Artemia, sem diferença significativa com branconeta. Para o pintado-da-amazônia, a maior produção foi obtida com branconeta. Podemos dizer que a seletividade para D. brasiliensis é positiva, aceita por ambas as espécies, sem rejeição. Os resultados nos permitem afirmar que o uso de D. brasiliensis é apropriado no cultivo de ambas as espécies.

Page generated in 0.0755 seconds