• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 134
  • 61
  • 16
  • 13
  • 8
  • 6
  • 5
  • 5
  • 5
  • 4
  • 4
  • 3
  • 1
  • 1
  • 1
  • Tagged with
  • 317
  • 317
  • 45
  • 40
  • 27
  • 26
  • 26
  • 21
  • 20
  • 20
  • 20
  • 19
  • 19
  • 16
  • 15
  • 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.
91

Genetic studies for aquaculture and stock-enhancement of red drum (Sciaenops ocellatus)

Ma, Liang 17 September 2007 (has links)
Hypervariable, nuclear-encoded microsatellites were used to (i) estimate genetic effective size (Ne) of red drum spawning over a two-week period in nine brood tanks at a TPWD hatchery; (ii) estimate heritability of early-larval growth and of growth rate and cold tolerance of juveniles; and (iii) test Mendelian segregation and independent assortment of 31 nuclear-encoded microsatellites. Assuming all tanks contributed equally to an offspring population, the maximum (expected) and observed Ne over the nine brood tanks was 43.2 and 27.0, respectively. The estimate of Ne based on observed variation in family size was 19.4. Simulations indicated that over a limited time period the simplest approach to maximizing Ne for a release population would be to utilize equal numbers of progeny from each brood tank. A family (genetic) effect was found to contribute significantly to the variance in early larval growth, juvenile growth rate, and cold tolerance. Estimates of narrow-sense heritability for these three traits were 0.07 +- 0.03, 0.52 +- 0.21 and 0.20 +- 0.10 (two growth intervals measured), and 0.30 +- 0.11, respectively, under the genetic models employed. The relatively low estimate of heritability for early larval growth suggests that genetic improvement for this trait likely would be slow. The heritability estimates for juvenile growth rate and cold tolerance, alternatively, suggest that genetic selection for these traits could be effective. Segregation at all 31 microsatellites fit Mendelian expectations for autosomal loci; a null allele was inferred at two of the microsatellites. Results from pairwise tests of independent assortment demonstrated that 20 of the 31 microsatellites could be placed into seven linkage groups. Additional linkage groups inferred from a prior study increased the number of inferred linkage groups in red drum to nine, with a range of two - five (avg. = 2.78) microsatellites in each linkage group. The remaining 11 microsatellites tested in this study assorted independently from all other microsatellites, suggesting the possibility of 11 additional linkage groups.
92

Utvärdering av osäkerhet i sprickfortplantningsmodeller / Evaluation of uncertainty of crack propagation models

Tuyishimire, Gabriel January 2015 (has links)
In aerospace industry and other major mechanical industry systems, engineering components that are subjected to cyclic loads often lead to progressive crack growth that eventually results in struc-tural fracture. The damage tolerance design which is based on the assumption of pre-existed flaws in a structure is an important approach in aircraft industry since it is impossible to have flaw-free manufactured components.In this thesis work, an evaluation of crack propagation models was carried out. Fatigue crack growth threshold and fatigue crack growth rate models were evaluated. A method to present ex-perimental data available was developed to evaluate uncertainties in fatigue life models for more accurate predictions. Currently, a software that is used for predicting crack propagation life is NASGRO. The study has been made for two types of materials: a nickel-iron-based alloy (Inconel 718 forging) and titanium alloys (Ti 6-4 both forging and casting).A threshold model is in the normal case developed for each temperature. A method to model fatigue threshold (ΔKth) has been suggested by assuming temperature independence of ΔKth. In this method, a new threshold model was created by making use of an A/P (Actual/Predicted) plot so that all measured threshold values are on the conservative side of the minimum model. With this method, an understanding of fatigue threshold model was improved over the other method due to the possibilities to model ΔKth with average and minimum threshold values for each load ratio (ΔKth, R).Moreover, a method to investigate which set of parameters that best represent the crack growth behaviour has been suggested. In this method the best set of parameters were chosen to be the set of parameters giving the best fit to the available (da/dN, ΔK) points. The comparison between this method and the method with the set of parameters that give minimum scatter in the A/P values was done.Crack growth rate da/dN log curves were plotted as function of stress intensity range ΔK for R-ratio values ranging from -2 to 0.9 for the two different methods. A distinctive difference between the two methods was observed in Paris region at high temperatures (5500C-6500C) which becomes more obvious at lower R-ratios. Predicting crack propagation rate model with set of parameters giving minimum standard deviation in da/dN points was shown to be less conservative than that of parameter sets giving lowest scatter in A/P. Using both evaluation methods, da/dN versus ΔK plots of Inconel718forging were compared to da/dN (ΔK) plots for the pre-existing data at 5500C for R-ratios ranging from 0 to 0.8. An overall R-ratio influence was observed throughout for both ΔKth and da/dN.
93

A STUDY ON THE GROWTH AND METABOLIC ACTIVITY OF STREPTOMYCES VENEZUELAE

MacIntosh, Andrew John 19 August 2010 (has links)
The bacteria Streptomyces venezuelae produce the novel antibiotic jadomycin. The study of growth characteristics and metabolic behavior of the bacteria are necessary to scale up antibiotic production and facilitate further research. In this study, a method for producing consistent inoculum was developed that showed good repeatability when used in growth trials. The rod shaped spores of Streptomyces venezuelae were determined to be approximately 0.8 x 0.2 ?m with a smooth surface type. The effects of temperature and pH on bacterial growth and substrate consumption were examined in a 7 L bioreactor. Of the range of parameters tested (28, 32, 36 °C, and media pH of 5, 7 and 9), 32 °C with a media pH of 7 yielded the highest rate of growth (µmax of 1.43 hours-1 with a lag time of 7.7 hours). The results of all trials showed that free glucose was consumed before the maltose, which was the major sugar substrate in the media. The initiation of exponential bacterial growth occurred after rapid consumption of free glucose. A heat balance analysis was also performed over the bioreactor to identify the heat generated through agitation, losses over the vessel and the heat of metabolism from Streptomyces venezuelae. Under normal operating parameters 33 - 24 % of the heat generated through mixing was lost with the exhaust gas, while 56 - 64 % was lost through the bioreactor wall. The heat of mixing was calculated to be 1.62 J•s-1 while the maximum amount of heat generated by Streptomyces venezuelae metabolism and activity during a growth trial was 2.28 J•s-1 for 60 x 109 CFU?mL-1.
94

Periodic Coefficients and Random Fibonacci Sequences

McLellan, Karyn Anne 20 August 2012 (has links)
The random Fibonacci sequence is defined by t_1 = t_2 = 1 and t_n = ± t_{n–1} + t_{n–2} , for n ? 3, where each ± sign is chosen at random with P(+) = P(–) = 1/2. We can think of all possible such sequences as forming a binary tree T. Viswanath has shown that almost all random Fibonacci sequences grow exponentially at the rate 1.13198824.... He was only able to find 8 decimal places of this constant through the use of random matrix theory and a fractal measure, although Bai has extended the constant by 5 decimal places. Numerical experimentation is inefficient because the convergence is so slow. We will discuss a new computation of Viswanath's constant which is based on a formula due to Kalmár-Nagy, and uses an interesting reduction R of the tree T developed by Rittaud. Also, we will focus on the growth rate of the expected value of a random Fibonacci sequence, which was studied by Rittaud. This differs from the almost sure growth rate in that we first find an expression for the average of the n^th term in a sequence, and then calculate its growth. We will derive this growth rate using a slightly different and more simplified method than Rittaud, using the tree R and a Pascal-like array of numbers, for which we can further give an explicit formula. We will also consider what happens to random Fibonacci sequences when we remove the randomness. Specifically, we will choose coefficients which belong to the set {1, –1} and form periodic cycles. By rewriting our recurrences using matrix products, we will analyze sequence growth and develop criteria based on eigenvalue, trace and order, for determining whether a given sequence is bounded, grows linearly or grows exponentially. Further, we will introduce an equivalence relation on the coefficient cycles such that each equivalence class has a common growth rate, and consider the number of such classes for a given cycle length. Lastly we will look at two ways to completely characterize the trace, given the coefficient cycle, by breaking the matrix product up into blocks.
95

Našiausių baltalksnynų augimo eiga Biržų miškų urėdijoje / The growth process of the most productive gray alder stands in Birzai State Forest Enterprise

Šuminas, Andrius 01 June 2011 (has links)
Detalesnių tyrimų Lietuvos baltalksnynuose niekas neatliko. Šiame darbe siekiama ištirti aukštos bonitetinės klasės baltalksnynų taksacinius parametrus ir įvertinti jų auginimo ekonominę vertę. Darbo objektas – Biržų miškų urėdijos baltalksnynai. Darbo tikslas – Įvertinti našiausių baltalksnynų augimo eigą Biržų miškų urėdijoje, bei atrinkti geriausius medynus ir rinktinius medžius Lietuvos miško sėklinės bazės sąvadui. Darbo metodai – Apibūdinant medyną buvo nustatyta: vidutinis aukštis, skersmuo ir amžius, aukštis iki žalių šakų, stiebo išreikštumas lajos dalyje, stiebo forma, skerspločių suma m2/ha, bonitetas, skalsumas, tūris m3/ha, medžių skaičius 1 ha, metinis tūrio prieaugis m3/ha. Iš viso buvo matuotas 21 sklypas. Kiekviename sklype buvo išskiriama po 3 barelius būdingose sklypo vietose. Darbo rezultatai – Intensyvus baltalksnynų retinimasis vyksta iki 35 metų amžiaus (nuo 3500 vnt/ha – 15 metų amžiaus, iki 1080 vnt/ha – 35 metų amžiaus), o vėliau amžiaus didėjimas medžių skaičiui vnt/ha esminės įtakos nebedaro. Didžiausią tūrio prieaugį m3/ha medynai pasiekia sulaukę 20 metų amžiaus. Vidutinį Lietuvos brandžių baltalksnynų tūrį 1 ha (191 m3/ha) (Lietuvos ..., 2010), našiausi Biržų miškų urėdijos baltalksnynai sukaupia sulaukę 17 metų amžiaus. Sparčiausiai baltalksnynai auga iki 15 metų amžiaus ir per metus į aukštį priauga vidutiniškai po 0,8 m, o nuo 30 iki 45 metų amžiaus per metus į aukštį priauga tik po 0,3 m. Įvertinant baltalksnynų kokybinius rodiklius... [toliau žr. visą tekstą] / Gray alder stands are not studied detailed in Lithuania. The goal of our work is to investigate the main taxation parameters of the most productive gray alder stands and assess the financial benefit of them. Object of the investigation: Gray alder stands in Biržai State Forest Enterprise. The aim of our investigation: to sort out the best gray alder stands in teritory of Biržai State Forest Enterprise and propose to include them in to the base of forests reproductive material. Methods: it was determined middle height, diameter, age, the distance to the vital branches, stem shape, radius (m2/ha), bonitet, stocking level, volume (m3/ha) , the density of trees (units per hectare), the annual growth rate (m3/ha) in order to characterize the gray alder stands. Results: it was determined that the most intensive decline process of gray alder stands continues to 35 years (from 3500 units per hectare in 15 years till 1080 units per hectare – 35 years) after that, increasing age has no significant effect on density. The greatest volume m3/ha is in 20 years. Middle volume of gray alder stands in Lithuania is 191 m3/ha. The most productive gray alder stands in Biržai State Forest Enterprise is in age of 17 years. The most rapidly growth continues to 15 years. Annual growth rate in height reaches 0.8 meter, whereas 30 – 45 years gray alder stands reaches only 0.3 meter annual growth in height. For the qualitative indicators, it was determined that the distance to the crown is 38 % in 15... [to full text]
96

Capital Goods for the Common Good : The Capital-to-income Ratio's connection to Income Inequality in Sweden

Ryberg, Peter January 2015 (has links)
This thesis utilises the second fundamental law of capitalism in order to study the development of income inequality in Sweden, from the start of the 19th century to the beginning of the 21stcentury. The law is studied from a historical perspective (examination of national accounts as time series), and empirically analysed (regression analysis). The results retrieved indicate that the income diverging force of savings exceed the income converging force of growth (via income, innovation, and education). This means that income inequality is predicted to increase. The main conclusion drawn is that choosing whether to save or not on behalf of every individual affects the capital stock of the aggregate economy. When individual savings pile up the aggregate capital stock increases, and if this increase surpasses the growth in national income the capital-to-income ratio increases. This ratio is in a sense a measure of how capitalistic the country is. More income inequality is expected to be found the higher this ratio gets.
97

Convergence properties of a continuum damage mechanics model for fatigue of adhesive joints

Josefsson, Axel, Wedin, Johan January 2014 (has links)
The effect of the element length is examined in modelling crack growth in fatigue loading of an adhesive joint. This is done for a cohesive element using an expression for the damage evolution developed at the University of Skövde which is implemented using the UMAT subroutine in the FE-solver Abaqus. These analyses are done for pure mode I loading by analysing a DCB-specimen loaded by a pure moment. An expression is developed in which the critical element length is dependent on the geometry of the specimen (in the form of the wave number of the adhesive joint), the element length, the material properties of the adhesive (in form of the material parameters , , ), the load applied (in form of the stress in the crack tip), the time step used in the analysis and the crack growth rate. It is shown that the results converge by decreasing the element length and the time step used. Therefore an expression for the crack growth rate as a function of the remaining parameters can be determined. Another expression is thereafter developed for the element length needed in order to get a crack growth rate within a certain range of the critical element length. The results show a regular pattern but are not monotone. Therefor two different definitions of the critical element length are tested, either by defining the critical element length as the point where the error is greater than an arbitrary boundary of 1 % of a converged result or where a least square approximation of the error is within 1 % of the converged results. The first method shows a highly irregular result which makes it difficult to develop an expression out of these results. The second method on the other hand gives results that are predictable enough to develop a function out of them. This is done using a regression analysis with all parameters of a third order expression in order to get an expression.
98

Genetic aspects of calving, growth, and carcass traits in beef cattle /

Eriksson, Susanne, January 2003 (has links) (PDF)
Diss. (sammanfattning). Uppsala : Sveriges lantbruksuniv., 2003. / Härtill 5 uppsatser.
99

Housing, management and health in Swedish dairy calves /

Lundborg, Karin, January 2004 (has links) (PDF)
Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2004. / Härtill 4 uppsatser.
100

Food competition and its relation to aquaculture in Juvenile Perca fluviatilis /

Staffan, Fia, January 2004 (has links) (PDF)
Diss. (sammanfattning). Umeå : Sveriges lantbruksuniv. / Härtill 6 uppsatser.

Page generated in 0.053 seconds