Browsing by Subject "Growth"
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Item Assessing the impacts of forest disturbances on stand and individual tree growth in the Lake States(2016-06) Glasby, MackForest disturbances cause changes in site conditions and forest structure which in turn influences the species composition of the site. This study utilized Forest Inventory and Analysis (FIA) annual plot data collected between 1999 and 2014, in Michigan, Minnesota, and Wisconsin to analyze the impacts of disturbance across the region. The study also analyzed the accuracy of the Forest Vegetation Simulator- Lake States (FVS-LS) diameter growth equation in disturbed and non-disturbed forests. Results showed that animal and weather disturbances were the most common disturbance agents in the region, while human-caused disturbance (excluding timber harvesting) resulted in the largest losses in live and standing dead tree basal area. Results indicated that the FVS-LS diameter growth equations performed well on average, but when the data were grouped by species or disturbance, the model equation was rarely validated using equivalence tests. Findings highlight the importance of incorporating forest disturbance into tree and stand growth and yield projections.Item Chondroitin Sulfate And Keratan Sulfate Proteoglycans In Retinal Axon Growth And Guidance(2018-08) McAdams, BrianAxons of retinal ganglion cells grow from the eye to the visual centers of the brain during development. Evidence suggests that adhesive and anti-adhesive interactions between growing axons and the cells and extracellular matrix in their environment guide retinal axons to their central targets. Proteoglycans are a family of extracellular glycoproteins that could contribute to these interactions. The present study investigated the potential interaction and influence of glycosaminoglycans with retinal axons in situ and in vitro. Immunostaining showed both chondroitin sulfate and keratan sulfate proteoglycans throughout the retinotectal pathway during the period of axon growth. Retinal neurites extending from explants in culture were immunopositive for chondroitin sulfate indicating that retinal axons may contribute proteoglycans to the pathway. Retinal neurite behavior was examined in the presence of soluble glycosaminoglycans. High concentrations of chondroitin sulfate promoted retinal neurite growth on normally less adhesive substrates, which suggests that this glycosaminoglycan may promote neurite outgrowth in some conditions. Retinal axon growth was also examined in nanomelic chicks, mutants which do not secrete a large chondroitin sulfate proteoglycan, aggrecan. Aggrecan immunostaining was colocalized with retinal axons in normal embryos. For the parameters studied, retinal axon growth and guidance appeared unaffected in nanomelic mutants, which suggested that aggrecan was not essential for retinal axon growth or guidance. Its spatiotemporal distribution, however, suggests that aggrecan has other developmental roles in this system. Collectively, the data are ambiguous regarding the role of chondroitin sulfate and keratan sulfate proteoglycans relative to retinal axon growth during development. Proteoglycans are capable of influencing retinal axon growth in vitro, but whether they influence growth in vivo and the nature of this influence will require future investigations.Item Dietary evaluation of low-oligosaccharide soybean meal in pigs(2012-10) Pangeni, Devi P.To evaluate the potential benefit of low oligosaccharide soybean meal (LOSBM) in the diets of early-weaned pigs, three experiments were performed by replacing conventional soybean meal (cSBM) with LOSBM. Low oligosaccharide soybean meal has a higher CP content than SBM. The interaction between LOSBM and the use of fishmeal and spray dried porcine plasma (FM/SDPP) was also evaluated during the nursery phase of the study. The objective of study 1 was to evaluate the effect of LOSBM on growth performance, viscosity of intestinal content, intestinal morphology, organ weights and blood urea nitrogen (BUN) in early-weaned pigs during 14 d post weaning. Four phase 1 diets used were corn-SBM or corn-LOSBM with or without supplementation of FM/SDPP in a 2 × 2 factorial arrangement. There was no interaction between FM/SDPP and the sources of soybean meal for the parameters studied. Treatments had no effect on growth performance, organ weight and intestinal length. No effect of treatment was observed for ileal crypt depth, jejunal crypt depth and ileal villi height. However, jejunal villi height was greater (P = 0.01) in pigs with cSBM diet. Levels of BUN were higher (P = 0.01) in pigs fed LOSBM diet and replacing cSBM with LOSBM reduced (P = 0.01) the viscosity of intestinal content. The objective of study 2 was to determine the apparent total tract digestibility (ATTD) and apparent ileal digestibility (AID) of DM, energy, N, ADF and NDF by grower pigs fed corn-LOSBM and corn-SBM diets in two different adaptation periods (5d and 7d). Grower pigs cannulated at ileo-cecal junction were randomly allotted to one of two dietary treatments. Treatment 1 consisted of conventional corn-SBM diet and treatment 2 consisted of corn-LOSBM. Replacing SBM with LOSBM improved percent AID of DM (P < 0.01), energy (P < 0.01) and ADF (P < 0.01). Similarly pigs fed LOSBM had improved ATTD of DM (P < 0.01), energy (P < 0.01) and ADF (P < 0.01). Study 3 was conducted to determine the effect of replacing cSBM with LOSBM on growth performance and carcass characteristics of pigs from wean to finish. Dietary treatments were fed in 6 phases based on a 2 × 3 factorial arrangement with 2 levels of FM/SDPP (none or phases 1 to 3) and 3 levels of LOSBM inclusion (none, phases 1 to 3, or phases 1 to 6). There was no interaction between FM/SDPP in nursery and LOSBM in any phase for ADG, ADFI or G:F. Replacing SBM with LOSBM resulted in gains in piglets feed efficiency (phase 1 and 2, P< 0.01) and piglets fed FM/SDPP had improved ADG (P < 0.01) and feed efficiency (P < 0.05) only in phase 2. Neither treatment factor affected live weight, carcass weight, fat or loin depth, percent lean, percent yield, grade or value. The early improvements did not affect overall performance from wean to finish, nor did they affect the final carcass characteristics. In summary, replacing cSBM with LOSBM did not affect the performance of the pigs. It seems that young pigs can better tolerate LOSBM as it decreased the viscosity of intestinal content. Improved ileal digestibility of nutrients in LOSBM in compared to cSBM may be beneficial for pigs. Key words:Item Does public capital spur private investment in developing economies?(2014-10) Zoff, Mark StevenWhat drives private investment in a country is a question of paramount importance to both researchers and policy makers. Additions to a country's private capital stock help drive both faster growth and faster wealth creation, which often creates many positive spillover effects for a country's populace. In a study of twenty-two developing countries over a total of 660 country-year observations utilizing vector error correction models, this report found preliminary evidence that public capital stock growth positively caused growth in future values of the private capital stock in a country. Additionally, this study found that changes in the level of the population and changes in the strength of political institutions also caused changes in the level of the stock of private capital in a developing country. Tentative causal evidence also existed for changes in the domestic credit to the private sector as a share of GDP, financial openness, and the size of the economy causing changes in the stock of private capital in a country. Policy makers in developing countries should focus future efforts on improving the quality of their institutions and providing high quality infrastructure, both traditional and social, if they want to help increase their country's private capital formation and, consequently, growth.Item Ecology and ecosystem impacts of common buckthorn (Rhamnus cathartica): a review(2007) Knight, Kathleen S; Kurylo, Jessica S; Endress, Anton G; Stewart, J. Ryan; Reich, Peter BIn this review, we synthesize the current knowledge of the ecology and impacts of Rhamnus cathartica L., a shrub from Europe and Asia that is a successful invader in North America. Physiological studies have uncovered traits including shade tolerance, rapid growth, high photosynthetic rates, a wide tolerance of moisture and drought, and an unusual phenology that may give R. cathartica an advantage in the environments it invades. Its high fecundity, bird-dispersed fruit, high germination rates, seedling success in disturbed conditions, and secondary metabolite production may also contribute to its ability to rapidly increase in abundance and impact ecosystems. R. cathartica impacts ecosystems through changes in soil N, elimination of the leaf litter layer, possible facilitation of earthworm invasions, unsubstantiated effects on native plants through allelopathy or competition, and effects on animals that may or may not be able to use it for food or habitat.Item Essays in international macroeconomics(2013-08) Steinberg, Joseph BowlinThis thesis is composed of two separate essays. In the first essay, I study the hypothesis that real exchange rate undervaluation can alleviate the economic symptoms of financial underdevelopment, acting as a temporary substitute for institutional reform. This hypothesis is motivated by recent empirical studies that document a link between real exchange rate undervaluation and increased growth in GDP per capita in developing countries. As further motivation I present new evidence that this effect is driven by an interaction between undervaluation and financial frictions. Using panel data on value added in manufacturing sectors at the 3-digit ISIC level for 103 countries, I find that for countries with low levels of financial development, real exchange rate undervaluation is associated with stronger growth in sectors that depend more heavily on external financing. To establish a causal relationship between undervaluation, financial development and growth and evaluate its quantitative implications I build a multi-sector semi-small open economy model with limited enforcement of financial contracts. Qualitative partial equilibrium results indicate that a government policy of subsidizing the purchase of tradeable goods undervalues the real exchange rate and loosens enforcement constraints, leading to temporary increased growth on the transition to a new steady state with higher output. The magnitude of this effect is increasing in the severity of the enforcement problem. For economies with severe enforcement problems this policy increases consumption although the quantitative effect is quite small. Misallocation of resources can cause large reductions in total factor productivity (TFP). The literature emphasizes financial frictions driven by limited contract enforcement that restrict productive firms' access to credit. Evidence suggests that information frictions also reduce access to credit, particularly in countries with weak contract enforcement. In the second essay, I study how the interaction between information frictions and limited enforcement affects resource allocation and TFP. I build a model in which lenders have imperfect information about borrowers' default risk and enforcing repayment is costly. I use the model to illustrate i) how imperfect information of this type causes misallocation, and ii) how limited enforcement exacerbates this effect. I calibrate the model and find that imperfect information causes TFP to fall by up to 23% when I take contract enforcement parameter values from U.S. data, and by up to 32% when I set them to values common in low-income countries.Item Essays in Macroeconomics(2024-05) Perez Perez, LuisOver the course of the past five decades, several puzzling macroeconomic trends have caught the eye of economists and policymakers alike. The rise of market power, the decline of the labor share, and the decline of productivity growth are simply some prominent examples. Given their importance, much has been written and discussed about these topics, yet little is still known about their underlying causes. In addition to these phenomena, in recent years economists have turned their attention to the Covid-19 pandemic, grappling with understanding its economic ramifications and with formulating optimal policy interventions. My doctoral dissertation, titled "Essays in Macroeconomics," consists of four distinct yet interconnected chapters. These chapters delve into the topics outlined above, with Economic Growth and Public Finance serving as unifying themes. The first two chapters fall within the scope of Economic Growth, while the last two center on Public Finance. Methodologically, each chapter combines economic theory with empirical or quantitative analysis, if not both, to shed light on important macroeconomic questions.Item Fish growth and degree-days: Advice for selecting base temperatures in both within- and among-lake studies(2013-08) Chezik, Kyle AugustEctotherm growth and development are largely a function of temperature. Within the range of thermal tolerance, growth and development increases linearly over a mid-range of temperatures. Degree-days (DD; °C;days) are a method of quantifying the thermal experience of an organism over the linear range and are an increasingly popular method for describing growth and development in fish. To limit degree-day calculations to temperatures within the linear range, a lower temperature threshold (To) is incorporated that defines the onset of growth. However, there is currently no convention for choosing To and the implications of choosing an inappropriate To are largely unknown. This uncertainty has resulted in a wide range of To values currently in use both among- and within-species. In this thesis I explore i) how To affects the ability of DD to explain within-population variation in fish growth, and ii) the effect of To on apparent growth among populations in thermally dissimilar environments. To address these objectives, I first use simulated data to determine the theoretical relationship between To and growth. I then demonstrate these theoretical relationships using immature length-at-age data from 8 species and 85 waterbodies in Minnesota USA and Ontario Canada. My results show that DD at low To are highly correlated and that these highly correlated low To values explain variation in growth equally well within a single population. Furthermore, growth rates among populations of thermally dissimilar habitat become increasingly dissimilar as To deviates from the To that minimizes the variation in growth rate among populations. This effect is especially apparent when the among-population range in thermal habitats is large. These findings suggest that, although To matters little when accounting for variation in growth within a single population, an inappropriate To can lead to the appearance of among-population differences in growth. When choosing To, I recommend estimating To using the Charnov and Gillooly (2003) “10°C rule” and then rounding to the nearest To standard (0, 5, 10 and 15°C). Choosing a To standard in this way will minimize the effect of To error on growth bias in among-population studies. In general, standardization i) simplifies To identification, ii) facilitates comparative studies, and ii) promotes the use of DD in future studies.Item Growth dynamics of the canine proximal tibial physis(2010-06) McBrien Jr., Charles S.Objective- To determine growth of the proximal tibial physis in the Labrador Retriever, a breed of dog at risk for rupture of the cranial cruciate ligament (RCCL). Animals- 6 male Labrador Retriever dogs Methods- 0.5 mm tantalum markers were implanted in the right proximal tibial epiphysis and metaphysis of each dog at sixteen weeks of age. Lateral and cranio-caudal radiographs of the tibia were made monthly and longitudinal growth was assessed from the radiographs. A growth curve was generated from the data. Data from previous patients that had undergone proximal tibial epiphysiodesis (PTE) was compared to the growth curve to demonstrate if the growth curve accurately predicted changes in growth associated with this procedure. Results- Growth rate decreased slowly and non-linearly over the first year of age. Growth from the proximal tibial physis is described. Conclusions- The growth curve generated here follows the model of saltation and stasis. The growth curve generated here predicted the change in tibial plateau angle (TPA) for two Labrador Retrievers that underwent PTE (+/- 1°). Clinical relevance- The growth curve generated in the present study may be considered for use for the surgical planning of PTE in Labrador Retrievers. Key Words- Proximal tibial epiphysiodesis, growth, saltation and stasis, Labrador RetrieverItem Hydrocortisone Suspension Provides Similar Growth Outcomes as Hydrocortisone Tablets in Young Children with Congenital Adrenal Hyperplasia: A Cross Sectional Study.(2021-08) Al-Rayess, HebaBACKGROUND. Young children with CAH require small doses (0.1-1.25 mg) of hydrocortisone (HC) to control excess androgen production and to avoid the negative effects of overtreatment. The smallest commercially available HC formulation, before the recent FDA approval of HC granules, was a scored 5 mg tablet. The options to achieve small doses were limited to using a pharmacy-compounded suspension, which the CAH Clinical PracticeGuidelines recommends against, or splitting tablets into quarters or eighths, or dissolving tablets into water. METHODS. Cross sectional chart review of 130 children with classic CAH treated with tablets versus a pharmacy-compounded alcohol-free hydrocortisone suspension to compare growth, weight, skeletal maturation, total daily HC dose, and total HC exposure over the first four years of life. RESULTS. No significant differences were found in height, weight, or BMI z-scores at 4 years, and in predicted adult height, before or after adjusting for age at diagnosis and sex. Bone age z- scores averaged 2.78 SDs lower for patients treated with HC suspension compared to HC tablets after adjusting for sex and age at diagnosis (p<0.001). The suspension group received 30.4% lower (p<0.001) average cumulative HC doses by their 4th birthday. CONCLUSIONS. Our data indicates that treatment with alcohol-free HC suspension decreased androgen exposure as shown by lower bone age z-scores, allowed lower average and cumulative daily HC dose compared to HC tablets, and generated no significant differences in SDS in growth parameters in children with CAH at 4 years of age. Long-term outcomes of treating children with CAH with smaller HC doses during childhood need to be studied.Item Identification and characterization of novel positive regulators of the Target of Rapamycin (TOR) pathway in Drosophila melanogaster(2008-12) Goraksha-Hicks, PankuriTarget of Rapamycin (TOR) is an evolutionary conserved pathway in eukaryotes for growth and proliferation. TOR pathway plays an important role for growth homeostasis by coupling nutritional and growth factor availability and cellular stress levels to both temporal and spatial aspects of growth. Aberrant TOR signaling results in dysregulation of growth leading to a number of human pathologies such as Tuberous Sclerosis, Peutz-Jegher's syndrome, cancers and neurological diseases such as Alzeihmer's. Inspite of the importance of TOR-mediated growth, there are a number of unanswered questions in the pathway such as unknown regulators and effectors of TOR and how exactly amino acids are sensed by TOR pathway. In order to understand the complexity of the TOR pathway and gain answers to some of the questions in the pathway, we undertook forward and reverse genetic approaches to identify novel positive regulators in the TOR pathway using Drosophila as a model. Our studies identify Rag GTPases to be important for amino acid sensing and upregulating TOR activity. We also present a possible mechanistic model for how Rag-GTPase mediated amino acid sensing may activate TOR pathway. The positive regulators identified in this study have aided our understanding of the important process of amino acid sensing at a cellular level and have contributed to furthering our knowledge of the TOR pathway.Item Prevalence of Clostridium difficile in retail meats from Minnesota and comparison of growth and survival of human and animal isolates(2013-08) Sepulveda Diaz, Rocio VeronicaClostridium difficile is a Gram positive, anaerobic, spore-forming, rod-shaped bacterium that causes antibiotic-associated diarrhea in hospitalized and community-dwelling patients. Recent findings have suggested that this organism may be transmitted from animals to humans through the consumption of contaminated foods. Genotypic similarities have been found among C. difficile strains isolated from animals and humans. However, comparisons of the behavior of these two groups of strains at the physiological level have not been conducted in detail. This study sought to determine the prevalence of C. difficile in retail meats from Minnesota and to compare human and animal isolates by measuring the growth rate and their survival in meats during cold storage. Meat samples were obtained from retail stores from Minnesota and consisted mainly of raw beef, pork, and poultry. These samples were analyzed for the presence of C. difficile by initial enrichment in Clostridium difficile moxalactam-norfloxacin (CDMN) broth, followed by ethanol shock, plating onto CDMN agar, and anaerobic incubation for 48 h at 37°C. Suspicious colonies were subjected to confirmation by colony morphology, Gram staining, and production of L-proline aminopeptidase. Growth rate parameters were determined for a total of 35 C. difficile strains isolated from humans and animals. Optical density was measured during exponential growth on brain hearth infusion broth at 37°C anoxically. The average growth rates of the two groups were then compared. A subgroup of 5 human and 5 animal strains was selected to assess the survival of C. difficile in meats during cold storage. C. difficile strains were inoculated onto ground meats to a level of approximately 105 CFU/g. Inoculated meats were stored at 4°C and -15°C for 5 and 20 days, respectively. C. difficile counts were determined at different times during storage by plating onto CDMN agar. A total of 342 raw meat and poultry samples were collected from 5 different counties in central Minnesota from 25 retail stores. Twenty nine samples had CDMN-presumptive colonies, but none of them were confirmed as C. difficile C.I. 0-0.013% of meats positive for C. difficile at a 95% level. The average growth rate of 22 human strains at 37°C was 0.52± 0.25 h-1, which was not significantly different from the value for 13 animal strains (0.62± 0.15 h-1) (p>0.05). Counts of C. difficile strains inoculated on ground beef and chicken diminished during storage at 4°C and -15°C. Overall reduction in bacterial counts was not significantly different between human and animal strains. These findings suggested that C. difficile was not commonly present in retail meats from Minnesota. C. difficile strains isolated from animals had similar growth rates at 37°C as the strains from human origin. C. difficile viable counts diminished over time during refrigeration and freezing of inoculated meats. Additionally, the methodology used in the present study was effective in recovering C. difficile from artificially inoculated meats.Item Seasonal patterns in growth, diet, and prey availability of Brown Trout Salmo Trutta in groundwater-dominated streams in the Driftless Ecoregion of southeastern Minnesota(2015-11) Biederman, JenniferGroundwater-dominated streams of southeastern Minnesota support highly productive populations of Brown Trout and aquatic macroinvertebrate fauna, but past research has shown that fish growth varies on spatial and temporal scales. As the diet of Brown Trout depends on the availability and abundance of aquatic macroinvertebrates, it is possible that spatial and temporal variations in macroinvertebrate assemblages (e.g. abundance, diversity, distribution) shape patterns in the growth, distribution, fitness, and abundance of Brown Trout populations. In particular, there is evidence that suggests spatial and seasonal variation in winter conditions (including water temperature and prey assemblages) may influence broader patterns of Brown Trout growth in this region. Although studies related to Brown Trout growth, diet, prey availability, and selectivity have been conducted in southeastern Minnesota, no research has addressed all of these factors simultaneously over multiple streams, seasons, and years. The overall goal of this dissertation was to examine seasonal and spatial patterns in Brown Trout growth, diet, and prey selection, and in the availability of macroinvertebrate prey in six streams that demonstrate a gradient in fish growth. Chapter 1 examines temporal and spatial differences in the growth and diet of Brown Trout, and identifies associations between diet and physical stream characteristics, including groundwater input, stream drainage area, and channel slope. Although stomach contents were dominated by relatively few taxa, including Chironomidae and Brachycentrus, there were significant differences in diet composition among streams and seasons. Overall, fish in most streams demonstrated positive growth during summer, winter, and spring; and winter growth was significantly associated with groundwater input. Chapter 2 addresses seasonal patterns in Brown Trout prey assemblages, including the abundance, diversity, and overlap of macroinvertebrate benthos and drift. Benthic and drift assemblages differed among streams and seasons, with most pronounced differences among streams. Abundances of drift and benthos varied significantly, with highest availability in spring and summer, and lowest availability during winter in most streams. Non-metric multidimensional scaling indicated associations between assemblage composition and groundwater input. The goal of the third and final chapter was to identify seasonal and spatial patterns in the availability and selection of macroinvertebrate prey by Brown Trout. Overall electivity of benthos and drift varied spatially and temporally with a negative relationship between the total proportion of prey available and prey electivity. In general, Brown Trout consistently favored one or two taxa, including Physella and Gammarus while displaying negative selection for all other prey types. Foraging patterns suggested a preference of benthic feeding. Ultimately, the results of this dissertation will help managers take effective actions in mitigating the effects of climate change on stream communities. In addition to a better understanding of the influence of groundwater control on patterns in Brown Trout growth, foraging, and prey communities, this dissertation identifies key prey taxa associated with the growth of Brown Trout on seasonal and spatial scales. With this knowledge, managers can more accurately predict how climate-induced changes to water temperature and prey communities will alter fish productivity on a stream-by-stream basis. Considering the substantial economic and cultural importance of groundwater-dominated streams in southeastern Minnesota, conserving the integrity and health of stream communities through the development and implementation of science-based management plans should be a priority among natural resource managers, scientists, and policymakers.