• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 1033
  • 758
  • 181
  • 102
  • 58
  • 55
  • 35
  • 28
  • 24
  • 19
  • 16
  • 15
  • 14
  • 14
  • 13
  • Tagged with
  • 2822
  • 846
  • 335
  • 302
  • 297
  • 244
  • 239
  • 204
  • 197
  • 172
  • 157
  • 156
  • 150
  • 147
  • 146
  • 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.
291

Survival strategies of poor households in Boitumelo township /|cKabelo Michael Mbele

Mbele, Kabelo January 2012 (has links)
The aim of the study was to analyse the survival strategies of the poor households in Boitumelo township. The research methodology used herein was two fold: Firstly, a literature research based on economic journals, previous research projects, books and internet was done in order to develop a better understanding of poverty. Secondly, an empirical research survey using questionnaires was undertaken. Over the years there have been competing theories which provide an understanding of poverty. Each approach has its strengths and weaknesses. Poverty captures a wide range of meanings, depending on who is defining it. Although various technical solutions have been suggested for differentiating the poor and non-poor using the monetary approach, there is no theory of poverty that clearly differentiate the poor from the non-poor. The survey results showed that 41% of all households in Boitumelo are poor and on average have an income shortage of 63% to the poverty line. Poverty within the area has a gender bias as 76% of the poor are females. The large number of households below the poverty line provided ample opportunity for further analysis to find out about the activities that they use to sustain themselves. Being unemployed in government or manufacturing industries, the urban poor are compelled to create some sort of jobs for themselves. Street vending, odd jobs, gambling, seeking credit on exploitative terms, income from state welfare, begging for survival are just a few of the activities urban poor adopt to survive / Thesis (MCom (Economics))--North-West University, Vaal Triangle Campus, 2013
292

Breeding Ecology of Noethern Pintails in Prairie Landscapes: Tests of Habitat Selection and Reproductive Trade-Off Models

2011 November 1900 (has links)
Ecologists and conservation biologists are interested in explaining why animal abundance and reproductive success vary among habitats. Initial motivation for this research arose from concerns for Northern Pintail (Anas acuta) populations in North America. Unlike many prairie-nesting dabbling duck populations, pintails failed to increase during periods of excellent wetland conditions, and remained below conservation goals. Low pintail populations have been linked to degraded landscape conditions on the Canadian prairies. Current habitat management for pintails aims to protect and create larger areas of perennial cover either by encouraging better management of grazing lands, by converting cropland to grassland, or by promoting adoption of fall-seeded crops like winter wheat. The central premise is that larger areas of natural grassland cover will attract breeding pintails to nest earlier in the season in low-predation-risk habitat. I studied pintail nesting ecology near the Milk River Ridge, Alberta, 2004-2006, in terms of a life-cycle perspective, from spring arrival and settling on breeding areas, to assess age and quality of nesting females, to determine timing and investment in reproduction, and finally to measure nesting success. A gradient in presumed high (grassland) to low (agriculture) habitat quality provided a landscape template for testing habitat selection models. Pintail breeding pair densities were 1.5-3 times higher in grassland than agricultural landscapes in all three years, regardless of regional population size, with pairs occupying grassland landscapes at higher densities immediately upon arrival in early spring. Northern Shoveler (A. clypeata), gadwall (A. strepera) and blue-wing teal (A. discors) had similar settlement patterns as pintails, but mallard (A. platyrhynchos) pair density was higher in agricultural areas. Relatively more, older female pintails were captured at nests in grassland landscapes whereas yearling females were encountered more often in agricultural areas, a pattern that was not detected in female shovelers. This response suggests that older female pintails may be better able to recognize and settle in higher quality grassland habitats. Body mass of pintail females did not vary among years, decreased seasonally, and was positively related to body size index and incubation stage. Furthermore, pintail body mass did not differ between grassland (650 ± 24 g), ecotone (678 ± 27 g) and agriculture (672 ± 33 g). In female shovelers, body mass varied among years (555 ± 29 g in 2004, 481 ± 18 g in 2005, 508 ± 21 g in 2006), and increased with nesting date. Shoveler body mass did not differ between grassland (519 ± 32 g), ecotone (519 ± 44 g), or agriculture (507 ± 35 g). Nest initiation dates did not vary by landscape for pintail, shoveler or mallard, but all species nested earlier in 2006 versus 2004. In pintail, shoveler and mallard, clutch size was negatively related to nest initiation date. Pintail and shoveler clutch sizes were generally larger in a wet year with abundant wetlands (2006) when compared with a dry year (2004), but no landscape differences were detected. Mallard clutch size did not vary by year or landscape. Female reproductive timing and investment (in terms of clutch size) were unrelated to upland habitat characteristics, counter to a hypothesis that predicts larger pintail clutch sizes in agricultural landscapes. However, pintail and shoveler invested in larger clutches in 2006, a wet year with abundant wetlands, possibly due to greater abundance of aquatic foods. Finally, nest survival rates of duck species, except mallard, tended to be higher in grassland landscapes and lower in agricultural landscapes. Pintail nest survival was consistently higher in grassland than in agricultural landscapes and was highest in 2006 when wetland conditions were excellent. Shoveler and blue-winged teal nest survival rates did not vary strongly with landscape, but were also higher in 2006, whereas mallard and gadwall nest survival estimates did not vary with landscape or year. Overall, pintails settled at higher densities in grassland landscapes where breeding success was higher (indexed by nesting success). This suggests that pintails respond appropriately to cues that enable them to recognize suitable habitat, at least in regions where large contiguous areas of grassland habitat remain. Furthermore, assuming that findings for pintails reflect those of other grassland bird species, large remnant areas of intact natural grassland seem particularly in need of protection or restoration, and management regimes that maintain their habitat integrity. By integrating applied and theoretical aspects of pintail reproductive ecology, I attempted to provide deeper insights into the processes that could shape behavioral decisions by breeding pintails and other duck species. Older pintails may occupy wetlands in higher quality grassland habitat early in spring, forcing subordinate or later-arriving individuals into poorer quality habitat (i.e., where nesting success is lower); however, mechanisms involved in this putative process are unknown. Overall, results suggest that grassland restoration or enhancement (e.g., managing grazing intensity) could improve reproductive success of pintails and possibly other grassland bird species.
293

Duration Data Analysis in Longitudinal Survey

Boudreau, Christian January 2003 (has links)
Considerable amounts of event history data are collected through longitudinal surveys. These surveys have many particularities or features that are the results of the dynamic nature of the population under study and of the fact that data collected through longitudinal surveys involve the use of complex survey designs, with clustering and stratification. These particularities include: attrition, seam-effect, censoring, left-truncation and complications in the variance estimation due to the use of complex survey designs. This thesis focuses on the last two points. Statistical methods based on the stratified Cox proportional hazards model that account for intra-cluster dependence, when the sampling design is uninformative, are proposed. This is achieved using the theory of estimating equations in conjunction with empirical process theory. Issues concerning analytic inference from survey data and the use of weighted versus unweighted procedures are also discussed. The proposed methodology is applied to data from the U. S. Survey of Income and Program Participation (SIPP) and data from the Canadian Survey of Labour and Income Dynamics (SLID). Finally, different statistical methods for handling left-truncated sojourns are explored and compared. These include the conditional partial likelihood and other methods, based on the Exponential or the Weibull distributions.
294

Alternative profit scorecards for revolving credit

Sanchez Barrios, Luis Javier January 2013 (has links)
The aim of this PhD project is to design profit scorecards for a revolving credit using alternative measures of profit that have not been considered in previous research. The data set consists of customers from a lending institution that grants credit to those that are usually financially excluded due to the lack of previous credit records. The study presents for the first time a relative profit measure (i.e.: returns) for scoring purposes and compares results with those obtained from usual monetary profit scores both in cumulative and average terms. Such relative measure can be interpreted as the productivity per customer in generating cash flows per monetary unit invested in receivables. Alternatively, it is the coverage against default if the lender discontinues operations at time t. At an exploratory level, results show that granting credit to financially excluded customers is a profitable business. Moreover, defaulters are not necessarily unprofitable; in average the profits generated by profitable defaulters exceed the losses generated by certain non-defaulters. Therefore, it makes sense to design profit (return) scorecards. It is shown through different methods that it makes a difference to use alternative profit measures for scoring purposes. At a customer level, using either profits or returns alters the chances of being accepted for credit. At a portfolio level, in the long term, productivity (coverage against default) is traded off if profits are used instead of returns. Additionally, using cumulative or average measures implies a trade off between the scope of the credit programme and customer productivity (coverage against default). The study also contributes to the ongoing debate of using direct and indirect prediction methods to produce not only profit but also return scorecards. Direct scores were obtained from borrower attributes, whilst indirect scores were predicted using the estimated probabilities of default and repurchase; OLS was used in both cases. Direct models outperformed indirect models. Results show that it is possible to identify customers that are profitable both in monetary and relative terms. The best performing indirect model used the probabilities of default at t=12 months and of repurchase in t=12, 30 months as predictors. This agrees with banking practices and confirms the significance of the long term perspective for revolving credit. Return scores would be preferred under more conservative standpoints towards default because of unstable conditions and if the aim is to penetrate relatively unknown segments. Further ethical considerations justify their use in an inclusive lending context. Qualitative data was used to contextualise results from quantitative models, where appropriate. This is particularly important in the microlending industry, where analysts’ market knowledge is important to complement results from scorecards for credit granting purposes. Finally, this is the first study that formally defines time-to-profit and uses it for scoring purposes. Such event occurs when the cumulative return exceeds one. It is the point in time when customers are exceedingly productive or alternatively when they are completely covered against default, regardless of future payments. A generic time-to-profit application scorecard was obtained by applying the discrete version of Cox model to borrowers’ attributes. Compared with OLS results, portfolio coverage against default was improved. A set of segmented models predicted time-to-profit for different loan durations. Results show that loan duration has a major effect on time-to-profit. Furthermore, inclusive lending programmes can generate internal funds to foster their growth. This provides useful insight for investment planning objectives in inclusive lending programmes such as the one under analysis.
295

Integration of quantitative and molecular genetic approaches to improve characteristics associated with pig welfare

Kapell, Dagmar Nicoline Reinhildis Gertrud January 2011 (has links)
The aims of this thesis were to investigate whether characteristics associated with animal welfare are genetically and genomically determined by using quantitative and molecular genetic approaches and to develop strategies indicating how these traits could be used in breeding programmes. Two traits that are closely related to animal welfare and associated with high socio-economic values are piglet survival at birth and aggressive behaviour in pigs. Piglet survival traits were analysed based on quantitative Bayesian approaches using phenotypic and pedigree information only, while aggressive behaviour was analysed based on molecular genetic approaches such as genome-wide association studies and genomic selection using additionally a dense panel of single nucleotide polymorphisms (SNP). The latter approach was validated using behavioural traits related to welfare characteristics in a welldocumented mouse data set. Selection for piglet survival at birth is expected to be effective, because all lines and breeds in this thesis showed considerable variation for this trait and relatively high heritabilities, particularly in lines with low average birth weight. Maternal heritabilities of individual birth weight were mostly at moderate magnitude and thus of great interest for selection. The genetic correlations between piglet survival and birth weight indicated that selection for either individual or average birth weight or variation of birth weight within litter would indirectly increase survival. The genetic associations of piglet survival with economically important (re)production traits are of great importance for breeding organisations. Undesirable genetic correlations between piglet survival and (re)production traits were generally of low magnitude, so that simultaneous improvement of all traits could be achieved. A comparison of five breeds and lines showed that differences in genetic parameters between breeds and lines can be substantial and no single selection strategy would be optimal for all. A unique study of a sire and a dam line originating from one breed but selected for more than 25 years with different breeding goals demonstrated how selection pressure can alter the genetic parameters over years. Breeding organisations should therefore consider selection strategies per breed or line individually to achieve maximum overall improvement. This study gives new insight into the use of genomic selection for traits associated with animal welfare. It is one of the first to present estimates for linkage disequilibrium in the pig using a new 60K SNP panel and the first to evaluate the efficiency of genomic selection against aggressive behaviour in pigs. Genomic selection showed a high predictive ability in comparison to traditional polygenic selection. It was especially advantageous for traits with lower heritabilities. In particular in situations where little family information was available, the performance of polygenic selection was low and genomic selection increased the performance considerably. Reducing the number of SNPs did not significantly change the performance of genomic selection. The consistently high performance across models indicates that low-density SNP panels may be sufficient to ensure a high efficiency of genomic selection, thus reducing the high costs associated with genotyping in pig breeding with its short generation interval. To summarize, this thesis has shown how to optimise quantitative and genomic approaches to improve animal welfare related characteristics efficiently in pig breeding programmes.
296

The use of democratic institutions as a strategy to legitimize authoritarian rule.

Michalik, Susanne 05 1900 (has links)
Numerous authoritarian states use institutions usually associated with democratic regimes like a constitution, elections, and a legislature. This seems to be counterintuitive. Authoritarian regimes should rather shrink away from democratic institutions. Elections can be won by the opposition and legislatures can make decisions against the interests of the ruler. So, why do autocratic regimes install institutions which limit their power and threaten their survival in office? Assuming actors behave rationally, one should expect authoritarian rulers only to introduce procedures working in their favor. This study looks at the effect of institutions in authoritarian regimes. The findings suggest that legislatures significantly lower the chances of regime breakdown in the long run. However, particularly in election years, authoritarian regimes are facing a higher likelihood of failure.
297

THE ROLE OF CANNABINOIDS AND CANNABINOID RECEPTORS IN ENTERIC NEURONAL SURVIVAL

Li, Yan 23 November 2009 (has links)
The Endocannabinoid system has been found in the gastrointestinal tract, where it plays an important role in gut under both physiological and pathological conditions. Although the major effects of cannabinoids in the gut are mediated through effects on enteric neurons, the role of cannabinoids in the enteric nervous system is poorly understood. In the present study, we have used the primary cultures of myenteric ganglia and a newly developed fetal enteric neuronal cell line to identify whether the endocannabinoid, anandamide, affects ganglionic and neuronal survival and the pathways involved. Anandamide had a biphasic effect on ganglionic survival, increasing survival at low concentrations (1nM-0.1uM) and decreasing survival at high concentrations (1-10uM). Maximal survival (68% increase in number of ganglia surviving) occurred at 0.1uM and the ED50 was 3nM. This effect on promoting survival was inhibited by the CB1 antagonist AM251 (1uM) and by AraC (10uM), but not the CB2 antagonist AM630 (1uM). AM630 (1uM) significantly blocked the decreased survival induced by high concentration anandamide (10uM). The enteric glia was involved in anandamide-induced ganglion survival. Anandamide had no effect on the number of neurons/ganglion in the presence of enteric glia, but decreased the number of neurons/ganglion by 15-20% in absence of enteric glia. This effect was partially reversed by CB1 antagonist, AM251 (1uM) (20%-145% at 1nM-10uM) and by CB2 antagonist AM630 (1uM) (40%-185% at 1nM-10uM). In the fetal enteric neural cell line (IM-FEN), anandamide decreased enteric neuronal survival in a concentration-dependent manner at both 39 and 33 degree (11-45% and 10-22%decrease in survival at 1nM-10uM, respectively). Coculture of astrocytes with the enteric neuronal cells was not able to reverse anandamide-mediated neuronal death. Immunocytochemistry and western blot confirmed that the presence of both CB1 and CB2 receptors in enteric neurons (primary cultures and IM-FEN) and glia (primary cultures). In addition, the PLC-beta inhibitor U73122 (1uM) inhibited anandamide induced ganglia survival significantly. Anandamide also induced increased expression of phospho-P44/42MAPK (13-48% at 1nM-10uM) and phospho-AKT (1-28% at 1 nM-10uM) in IM-FEN. We conclude that anandamide has a differential effect on survival of enteric ganglia and neurons. It promotes ganglionic and neuronal survival by CB1 receptors in the presence of glia and this involves the PLC-beta pathway. Conversely, anandamide promotes neuron death in absence of glia as a result of effects on both the MAPK and PI-3K/AKT pathways. Since the endocannabinoid system is upregulated in inflammatory bowel diseases, these effects may play a role in the pathogenesis of the response to inflammation as well as the recovery and reinnervation of the gut following the acute phase of inflammation. The further significance of this work could contribute to developing new therapeutic methods for treatment of inflammatory bowel disease and related symptoms in clinic practice.
298

A Voice from the Dust

Pierotti, Gian 11 May 2011 (has links)
We shall not starve. We shall not lack shelter. We shall have a hearth. Awake self reliance! Our art is for feeding, warmth, protection. Ceramics– our temporal salvation. Clay– our material life-force. Transformed by fire we arise with the skills of the ancients! No longer will we live in obscurity. To the deskilled, your fate is at hand! You have chosen alienation, distraction, banality, and sloth. Embrace your digital false Gods and die or be reborn to the natural physical world. Now, together we complete our reason for being. We create a new world of kinship. A hope for the utopia not of rigid modernism but one of a new world, a rediscovery of the natural order.
299

Finding the Cutpoint of a Continuous Covariate in a Parametric Survival Analysis Model

Joshi, Kabita 01 January 2016 (has links)
In many clinical studies, continuous variables such as age, blood pressure and cholesterol are measured and analyzed. Often clinicians prefer to categorize these continuous variables into different groups, such as low and high risk groups. The goal of this work is to find the cutpoint of a continuous variable where the transition occurs from low to high risk group. Different methods have been published in literature to find such a cutpoint. We extended the methods of Contal and O’Quigley (1999) which was based on the log-rank test and the methods of Klein and Wu (2004) which was based on the Score test to find the cutpoint of a continuous covariate. Since the log-rank test is a nonparametric method and the Score test is a parametric method, we are interested to see if an extension of the parametric procedure performs better when the distribution of a population is known. We have developed a method that uses the parametric score residuals to find the cutpoint. The performance of the proposed method will be compared with the existing methods developed by Contal and O’Quigley and Klein and Wu by estimating the bias and mean square error of the estimated cutpoints for different scenarios in simulated data.
300

Contributions à l'analyse de survie / Contributions to survival analysis

Bousquet, Damien 04 October 2012 (has links)
Dans ce travail, nous présentons de nouveaux modèles pour l'analyse de survie. Nous généralisons l'approche de Marshall et Olkin (A New Method for Adding a Parameter to a Family of Distributions with Application to the Exponential and Weibull Families, Biometrika, 1997). Partant d'une distribution de probabilité de base arbitraire, nous lui ajoutons des paramètres extérieurs au sens qu'il ne s'agit pas directement de paramètres d'échelle ou de forme. Nous obtenons des courbes de risque plus riches, garanties de la souplesse de ces nouvelles distributions de probabilité. Des méthodes d'estimation de ces paramètres sont présentées. Nous montrons l'adéquation de notre modèle sur des données réelles. Dans un second temps, nous nous intéressons aussi au problème de l'estimation sans biais dans les échantillons censurés. Nous apportons des résultats nouveaux. En particulier, nous généralisons un résultat de Rubin et Van der Laan (A Doubly Robust Censoring Unbiased Transformation, The International Journal of Biostatistics, 2007). / In this work, we propose new models for survival analysis. We generalise the approach from Marshall and Olkin (A New Method for Adding a Parameter to a Family of Distributions with Application to the Exponential and Weibull Families, Biometrika, 1997). Given an arbitrary baseline probability distribution, we add some external parameters that are not scale or shape parameters. In this way, we obtain more flexible hazard rate curves. Some methods to estimate these parameters are presented. We show the goodness of fit of our model with a real data set. In a second part, we are also interesting by unbiased estimation in a censored sample. We give new results. We generalise a result from Rubin and Van der Laan (A Doubly Robust Censoring Unbiased Transformation, The International Journal of Biostatistics, 2007).

Page generated in 0.0419 seconds