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  • 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.
251

Studies of magnesium metabolism in ruminants : a comparison of sheep and cattle

Laporte Uribe, José Alberto January 2005 (has links)
Transactions of magnesium (Mg) along the gastrointestinal tract and the effect of change in potassium (K) intake were recorded in two in vivo experiments in sheep and cattle. Additional information on the sensitivity to K intake was obtained by comparing Mg transport and electrochemical properties of isolated rumen epithelia of sheep and cattle in 4 additional in vitro experiments. The experiment described in Chapter 2, and performed in sheep housed indoors in metabolic crates, investigated the compensatory capacity of the intestine to respond to the reduction in Mg absorption from the stomach as a consequence of increase in K intake. The animals were equipped with a ruminal cannula and two intestinal cannulae (duodenum and ileum) and flow of digesta was measured by the addition of two indigestible markers, chromium ethylenediaminetetra-acetic acid (Cr-EDTA) and ytterbium acetate (Yb). The animals were infused in a Latin square design for periods of 10 days with a solution of K bicarbonate that provided between 15 and 47 g of K/day. The diet consisted of a 50:50 combination of concentrates plus lucerne hay that provided around 3.7 g of Mg per day and 15 g of K per day. After 5 days of infusion samples of feed, faeces, urine and plasma were collected and analysed for Mg and K content. After 6 days of infusion, samples of duodenal and ileal flow were obtained. The treatments reproduced the detrimental effect of K on Mg absorption, especially in the rumen; a rise in K intake from 15 to 23 g/day reduced total Mg absorption from the gastrointestinal tract from 1.36 to 1.23 g/day, further increase in K intake to 38 and 47 g/day reduced absorption to 1.12 and 1.05 g/day, an overall reduction of around 50% in Mg apparent availability. Magnesium was mainly absorbed in the stomachs and large intestine with the small intestine a site of net secretion. Most of the reduction in Mg absorption with increase in K intake occurred in the stomachs, reducing from 1.86 to 1.11 g/day. A compensatory reduction in the net secretion of Mg from the intestines (small and large) was observed. This compensation was largely due to reduction in net secretion from the small intestine, from 0.85 to 0.22 g/day, rather than an increase in net absorption from the large intestine, although both segments acted synergistically. Results also suggested significant individual variation in plasma Mg concentration, urinary Mg excretion and in the flow and absorption of Mg along the gastrointestinal tract. It was suggested that most of that variability was due to genetic factors. Differences between species (cattle and sheep) were pursued during the course of the experiment described in Chapter three. Four triple cannulated rams and 3 triple cannulated dry cows were placed in metabolic crates, fed daily fresh-cut pasture and infused, in a total randomised design that provided the equivalent of an intake of 30,40 and 50 g of K per kg dry matter intake (DMI) per day. Solutions of K (as K bicarbonate) and markers (CrEDT A and Yb acetate) were infused continuously for a period of 10 days; after 5 days of infusion samples of pasture, faeces, urine and plasma were collected and analysed for Mg and K content. After 6 days of infusion, samples of duodenal and ileal flow were obtained. Total feed offered, refusals and water consumption were recorded daily. Results showed a greater sensitivity of cattle to the increase in K supply. A rise in K supply from 30 to 40 g per kg DMI/day reduced Mg absorption by almost 50% from 0.32 to 0.16 g per kg DMI/day, whereas only the highest treatment dose (50 g of K per kg DMI/day) produced the same deleterious effect in sheep. The absorption of Mg occurred mainly in the stomachs and large intestine; in contrast the small intestine was a site of net secretion in both species. The addition of K slightly reduced the rate of Mg absorption from the rumen, especially in cattle. Similarly, net Mg secretion within the intestines increased with increasing K intake in both species, only to be counterbalanced by a greater Mg absorption from the large intestine. The large intestine in both species (sheep and cattle) reduced faecal losses of Mg but was unable to fully compensate for the reduction in Mg absorption from the stomach or the greater net Mg secretion observed at the small intestine. Differences between species in water content of the faeces were observed to be mainly related to the moisture content of the digesta that reached the ileum rather than a result of differences in absorption in the large intestine. More evidence of species differences in Mg transport and of sensitivity to K intake were obtained by using isolated rumen epithelia and the Ussing chamber technique. Transport and electrophysiological properties of the tissues were observed in standard conditions and by adding different K concentrations to the mucosal side. Under standard conditions and open-circuit voltage, sheep isolated rumen epithelia had greater transmural potential difference (PDt), and lower conductance (Gt) but similar short-circuit current (Isc) than those from cattle. These results suggested that the rumen epithelium of cattle is leakier than that of sheep. Measurement of the transport of Mg showed that isolated rumen epithelia of cattle transported more Mg and was saturated at higher Mg concentrations (12 vs 4 mM) than sheep epithelia. These differences in Mg influx (transport from mucosa to serosa) were also observed in studies of Mg transport using stable isotopes. Magnesium influx (transport from mucosa to serosa) from the isolated rumen of cattle was greater than in sheep (57.5 ± 12.72 vs. 17.3 ± 12.72 nmol.cm⁻².h⁻¹); however this was counterbalanced by a greater Mg efflux (transport from serosa to mucosa) of 48.1 ± 12.72 vs. 9.9 ± 12.72 nmol.cm⁻².h⁻¹, for cattle and sheep respectively, when mucosal K concentrations were around 25 mM. A increase in K concentration on the mucosal side enhanced transmural potential difference (PDt) and short-circuit current (Isc) to a greater extent in sheep than in cattle, suggesting a greater effect of K on sheep than on cattle epithelia. On the other hand, the transport of Mg measured by stable isotopes suggested that net absorption of Mg (7.4 ± 12.72 vs. 11.1 ± 12.72 nmol.cm⁻².h⁻¹) in sheep epithelia was similar at 25 and 50 mM of K on the mucosal side, whereas net Mg influx in cattle was largely depressed as a consequence of a reduction in Mg influx (mucosa to serosa) from 57.7 ± 12.72 to 2.9 ± 12.72 nmol.cm⁻² h⁻¹ together with a constant Mg efflux (serosa to mucosa) 48.1 ± 12.72 and 41.2 ± 12.72 nmol.cm⁻².h⁻¹, presumably leaving through a paracellular shunt. However, this finding was based on date from a small size and caution should be applied to this conclusion. In conclusion, data collected from several comparative studies suggest differences in Mg apparent availability between sheep and cattle and also a greater sensitivity of cattle to an increase in K intake. This high sensitivity to K represents a great risk of hypomagnesaemia in dairy cattle in New Zealand where high K concentration is endemic in pastures. Most importantly, these results suggest that models for Mg metabolism in cattle should be based on measurements from cattle nutritional and physiological studies rather than on extrapolation from sheep studies.
252

Quantification of mineral weathering rates in sulfidic mine tailings under water-saturated conditions

Gleisner, Magdalena January 2005 (has links)
<p>Tailings are a fine-grained waste product produced during the metal recovery process. Tailings consist mostly of different silicates but also sulfides (e.g. pyrite), since 100 % metal recovery is not possible. Freshly processed tailings are deposited in large impoundments. If the mine tailings in the impoundments are exposed to water and oxygen, the sulfides will oxidize and release acidity and metals such as Fe, Cu, Zn, and Pb. The sulfide mineral oxidation reactions are catalyzed by sulfur and iron oxidizing bacteria (principally <i>Acidithiobacillus ferrooxidans</i>) that oxidize ferrous iron to ferric iron, which then oxidizes pyrite. When the leachate produced by this process discharges from the impoundment, it is called acid mine drainage, which may lead to the pollution of adjacent streams and lakes.</p><p>The intention with this thesis is to investigate and quantify mineral weathering processes and element release rates occurring in water-saturated and soil-covered sulfidic mine tailings. The study was performed in different batch and column experiments in room temperature and in the laboratory. The batch experiments were conducted for ca. three months and investigated: a) microbial and abiotic sulfide oxidation in freshly processed tailings under oxic conditions at pH 2-3 and pH 8, b) microbial oxidation of pure pyrite grains at pH 2-3 under different oxygen concentrations ranging from anoxic to oxic conditions. The column experiments, consisting of unoxidized tailings in water-saturated columns, were conducted for up to three years. In these experiments, an oxygen-saturated solution was continually pumped into the column inlet, and investigated: a) differences in oxidation rates between tailings of two different grain sizes, b) factors affecting element discharge rates, acid neutralization, and sulfide oxidation, c) the effect of ions released in a soil cover on release rates in the tailings.</p><p>Sulfide oxidation processes within the batch experiments were limited by surface kinetics. The microbial oxidation of pure pyrite at atmospheric conditions produced the most rapid rate, while the microbial oxidation of pure pyrite at anoxic conditions was slower by 1.8 orders of magnitude. Microbial and abiotic oxidation of pyrite in freshly-processed tailings resulted in pyrite oxidation rates that were intermediate between these two extremes. The results from the microbial experiments with pure pyrite indicated a positive correlation between the concentration of dissolved oxygen, ferric iron and bacterial cells (at a total cell concentration > 10<sup>6</sup> cells/mL and a dissolved oxygen concentration ≥ 13.2 µM), which implies an interdependence of these factors. The results from these batch experiments support the indirect mechanism for microbial oxidation by the ferric oxidation pathway. Pyrite oxidation rates estimated from the batch experiments may be comparable with oxidation rates in the unsaturated zone and at the groundwater table in a tailings impoundment.</p><p>Acid neutralization reactions in the column experiments resulted in the release of base cations to the column leachate. Calcite was the most important neutralizing mineral despite that it was only present in minor amounts in the tailings. It was confirmed that acidity forced the calcite dissolution. Element release rates in the column experiments were controlled by the availability of dissolved oxygen, which was a function of the water flow rate into the column. These column experiments also showed that the results are comparable with results from field studies, justifying the use of column experiments to study processes within tailings impoundments.</p>
253

The effects on cotton production due to climate change : an assessment on water availability and pesticide use in two different cotton growing regions in India

Flores Araya, Jesserina January 2008 (has links)
<p>According to several scientific reports, climate change will have an impact on water provision and thus agriculture, which depends on soil moisture for plant survival. India is a country that is heavily dependent on agriculture as a source of income. One of the country’s future challenges is securing water for irrigation. Cotton in India is an important cash crop which is grown under high evapotranspirative demand, using about 15% of the national water resources, making the crop vulnerable to changes in water availability.</p><p>The purpose of this study is to evaluate the resilience of cotton production with regards to water availability and pesticide use in Punjab and Andhra Pradesh. Three aspects of resilience: latitude, resistance and precariousness has been used to analyse three variables, precipitation, irrigation and pesticide in order to understand how these cotton growing systems are going to be affected by climate change. By bringing together existing data from several scientific reports and governmental websites, assumptions could be made whether these systems are resilient or if they are reaching a threshold. The results show that the cotton growing regions of Punjab are highly vulnerable when it comes to water provision in the region and that they might be reaching a threshold. Changes in climate are predicted to affect precipitation and temperature in the area, which in time might ultimately affect water resources in the region. Groundwater depletion and water logging are already prevailing problems in the area where almost all cotton production is irrigated. Cotton farmers in Andhra Pradesh are struggling with pest infestation which induces them to overconsume pesticides, affecting not only water quality in the area, but also farmers’ livelihood. It is likely that climate change will not minimize the outbreaks; on the contrary it might benefit some pests, which might increase the consumption of pesticide in the region. Coastal districts are more exposed to extreme weather which can harm cotton cultivation.</p>
254

Forensic Computing from a Computer Security perspective / Forensisk granskning av datorer ur ett datasäkerhetsperspektiv

Lázaro, Pablo García-Crovetto January 2004 (has links)
<p>This work contains a brief study about Forensic Computing problems done from a Computer Security perspective. </p><p>Based on the description and investigation methods of Forensic Computing, a list of common difficulties that forensic examiners have to deal with has been created. After making an analysis about each difficulty in the Forensic Computing field, it can be said that the main reasons are related to the legal restrictions and an incorrect security management. </p><p>Using a Computer Security perspective for analysing why the incorrect security management generates problems in the forensic computing field, we have made a risk analysis of a possible distribution for a correct security management. Later, based on own results, a list on priorities in prevention methods in t he Forensic Computing field has been created. </p><p>Finally it can be said that the difficulties in the Forensic Computing field could be avoided by creating awareness among users about the importance of taking prevention methods for protecting data and consequently for decreasing the number of e-crimes.</p>
255

Speech recognition availability / Tillgängligheten i taligenkänning

Eriksson, Mattias January 2004 (has links)
<p>This project investigates the importance of availability in the scope of dictation programs. Using speech recognition technology for dictating has not reached the public, and that may very well be a result of poor availability in today’s technical solutions. </p><p>I have constructed a persona character, Johanna, who personalizes the target user. I have also developed a solution that streams audio into a speech recognition server and sends back interpreted text. Johanna affirmed that the solution was successful in theory. </p><p>I then incorporated test users that tried out the solution in practice. Half of them do indeed claim that their usage has been and will continue to be increased thanks to the new level of availability.</p>
256

Hur blir en stad konkurrenskraftig på den internationella kongressmarknaden? : En analys av Stockholm som mötesdestination / How to become a competitive city in the international congress market? : An analysis of Stockholm as a meeting destination

Kostic, Vladica, Mikael, Sjöberg January 2010 (has links)
<p><strong>Background: </strong>The increasing globalization of business and research has led to an increased demand for international meetings. This is a market that a number of countries wish to access and the competition is fierce to get the chance to host major conferences. Stockholm has a pronounced good position in the international meeting market and this essay will examine what it takes to be a successful meeting destination for international congresses.</p><p><strong>Purpose: </strong>The purpose of this thesis is to examine the fundamental factors that must be met for a meeting destination to be successful in the international market for conventions.</p><p><strong>Question at issue:</strong> How can a city develop into a more attractive meeting destination for international congresses?</p><p><strong>Method: </strong>Persons with key positions in the Stockholm meeting industry have been approached by qualitative interviews by the authors.</p><p><strong>Theory: </strong>As a theoretical framework the authors used the value of the physical meeting, generally on the congresses, the planning process for site selection for the meeting, the meeting platform and image.</p><p><strong>Conclusion: </strong>The authors' findings are based on the empirical material gathered during the study interviews. The results from these interviews show the importance of facilities and hotels, availability, and the image.</p> / <p><strong>Bakgrund: </strong>Den ökade globaliseringen av företag och forskning har lett till en ökad efterfrågan av internationella möten. Detta är en marknad som många länder vill ta del av och konkurrensen är hård om att få chansen att arrangera större kongresser. Stockholm har idag en uttalad god position på den internationella mötesmarknaden och denna uppsats ämnar undersöka vad som krävs för att bli en framgångsrik mötesdestination för internationella kongresser.</p><p><strong>Syfte: </strong>Uppsatsens syfte är att undersöka vilka grundläggande faktorer som måste uppfyllas för att en mötesdestination ska bli framgångsrik på den internationella marknaden för kongresser.</p><p><strong>Frågeställning: </strong>Hur kan en stad utvecklas till att bli en mer attraktiv mötesdestination för internationella kongresser?</p><p><strong>Metod: </strong>Författarna har använt sig av kvalitativa intervjuer med några av Stockholms mötesindustris nyckelpersoner.</p><p><strong>Teori: </strong>Som teoretisk referensram har författarna använt sig av värdet av det fysiska mötet, allmänt om kongresser, planeringsprocessen för val av plats för möte, mötesplattformen samt image.</p><p><strong>Slutsats: </strong>Författarnas slutsatser baseras på det empiriska material som insamlats under studiens intervjuer. Resultaten från dessa intervjuer visar på vikten av faciliteter och hotell, tillgänglighet samt image.</p>
257

Facebook, E-post, SMS & Mobiltelefoni : en explorativ studie om hur unga vuxna upplever den ständiga tillgängligheten

Hofmann, Åsa January 2008 (has links)
<p>Purpose/Aim: In the information and communication technology society (ICT) we live in today it is easy to feel that we are constantly expected to be available. The daily contact with the Internet and the use of cell phones has changed our way to communicate. With this in mind in combination with the increased stress among young adults my aim is to investigate how young adults, aged 23-26 years, experience to be constantly connected and available through the Internet and the cell phone. What are their opinions, attitudes and feelings about what this entails in their lives?</p><p>Material/Method: The essay is based on four focus group interviews with sixteen students from Uppsala University aged 23-26, two groups consisting of women and two groups consisting of men. The ICT & Internet research is developing rapidly which led me to do an exploratory study that is hypothesis-generating and which I hope can be used for forthcoming research of the consequences of the ICT society. The empiric result has been analyzed from a behavioural science perspective.</p><p>Main results: The results have been interesting from several perspectives. The focus groups seem to think that the Internet and cell phone use is the best thing that has happened. They are so-called "Multitaskers" and have no problems to do several things simultaneously. The relationship between ICT and stress becomes slightly more noticeable among the girls. I dare to say that the constant availability do result in a certain stress, which I based on the clear statements about stress that came up between the lines. The focus groups are highly dependent on both their cell phone and access to Internet. They have also developed new cell phone behaviours that are customized to different situations and people.</p>
258

Fulfillment of Rush Customer Orders under Limited Capacity

Xiong, M.H., Tor, Shu Beng, Khoo, L.P., Bhatnagar, Rohit 01 1900 (has links)
Customer demand fulfillment is the business process within a company that determines how the customer demand is fulfilled. A rush order is the last minute customer order after the production plan of a company has been concluded. For these rush orders, appropriate and reasonable response is imperative as it could put strain on customer relationship and services. A good and positive response could help the company to build and retain its market share in today’s highly competitive markets. A model aims at decreasing the product inventory cost is proposed in this paper. In this model, the prioritized fulfillment sequence of rush customer demands can be searched in terms of the product inventory cost. The paper focuses on two main issues: the available-to-promise (ATP) based fulfillment ability and the prioritized fulfillment of customer demands. For ATP based fulfillment, a dynamic bill-of-material (BOM) is proposed to handle the complicated issues of BOM, BOM explosion and production capacity. By means of dynamic BOM, material availability as well as production capacity can be taken into consideration simultaneously and efficiently. Two methods, mathematical optimization and heuristic algorithm, are constructed and elaborated on in the second issue. The proposed model allows companies to prioritize customer rush orders in terms of product inventory cost. / Singapore-MIT Alliance (SMA)
259

The Use of Demand-wise Shared Protection in Creating Topology Optimized High Availability Networks

Todd, Brody 11 1900 (has links)
In order to meet the availability requirements of modern communication networks, a number of survivability techniques were developed that adapt the demand-wise shared protection design model to incorporate strategies increasing network availability. The survivability methodologies developed took two approaches. The first incorporated availability directly into the network design model. The second ensured minimum dual failure restorability was set within the model. These methodologies were developed for predetermined topologies, as well as to have topology optimization incorporated into the model. All methodologies were implemented and analyzed on a set of samples. The analysis examined cost, topology and actual availability of the network designs. Availability design was effective but computationally intensive and difficult to design. Minimum dual failure restorability was also effective in increasing availability with a significant caveat, dual failure restorability increased exposure to possible failures, and without sufficient levels of dual failure restorability could have a negative impact on availability. / Engineering Management
260

Effect of Maternal Borderline Personality Disorder on Emotional Availability in Mother-Child Interactions

Trupe, Rebecca Devan 01 December 2010 (has links)
Individuals with borderline personality disorder (BPD) experience severe and pervasive disturbances in the development of attachment relationships, identity, and emotion regulation. Given these deficits, mothers diagnosed with BPD are likely to experience significant difficulties in parenting their children. The present study examined the effect of maternal BPD and borderline personality features on emotional availability in interactions between mothers with BPD and their 4- to 7-year-old children. In a low socioeconomic status (SES) sample of n = 35 children of mothers diagnosed with BPD and n = 35 normative comparisons, groups were compared on maternal and child emotional availability, and self-reported maternal borderline personality features were assessed across the sample as a whole. No significant differences in emotional availability were found between groups. Across the sample as whole, however, maternal borderline personality features of affective instability, identity disturbance, negative relationships, and self-harm were significantly correlated with maternal intrusiveness and maternal hostility. Maternal borderline personality features of affective instability and negative relationships were significantly associated with maternal sensitivity, child responsiveness, and child involvement. Results are discussed in terms of putative precursors to BPD and preventive interventions.

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