The corrosion of steel reinforcement is probably the most frequent type of degradation of reinforced concrete structures. Reinforcing bars are protected from corrosion by a thin iron oxide layer which is formed on their surface due to a high alkalinity of the surrounding concrete. Corrosion may start when this layer is destroyed (i) either by chloride ion penetration (when the concentration of dissolved chloride at the depth of the reinforcing steel exceeds a critical value) or (ii) by a reduction in the pH value of pore solution to values below 9.5. Such a reduction in alkalinity is the result of carbonation of the Ca(OH)2 in the concrete mass, i.e. of its reaction with the atmospheric CO2. The main aim of this work is an experimental investigation and modelling of carbonation process. The effect of relative humidity, curing period and replacement of Portland cement by supplementary cementing materials (SCM - fly ash, blast furnace slag and metakaolin) on carbonation process has been studied. Calcium hydroxide content in the presence of SCM and their pozzolanic activities have been also determined. Furthermore, lots of parametric studies and comparison of carbonation models have been provided. The software tools based on the introduced models and considering the input data to be statistically independent random variables have been described and used for other parametric studies.

EU Sustainable Development Strategy planned to achieve improvement of life-quality by promoting sustainable production and consumption of raw materials. On November 2018, EU Commission presented a long-term strategy, aiming among others a climate-neutral economy by 2050. Cement production is contributing to 6-10% of the anthropogenic CO2 emissions. Thus, several strategies for total or partial replacement of Portland cement in concrete production have been developed. The use of supplementary cementitious materials (SCM) and alkali-activated materials (AAM) is considered the most efficient countermeasure to diminish CO2 emissions. The broadening of knowledge with particular attention to the sustainable goals is the primary requirement to be fulfilled when novel materials are investigated. This study aims to develop a novel clay-based binder that can be used as a sustainable alternative to produce SCM as well as AAM. Clay is a commonly occurring material, with large deposits worldwide. However, natural clay has a low reactivity and various compositions, depending, e.g. on the weathering conditions. The present research aims exactly at enhancing the reactivity of natural clays occurring in Sweden subjecting them to mechanical activation in a planetary ball mill. Ball milling (BM) is considered a clean technology able to enhance the reactivity of crystalline materials without resorting to high processing temperatures or additional chemicals. BM was able to induce amorphization in clay minerals and to transform the layered platy morphology to spherical shape particles. The efficiency of the process was strictly related to the used process parameters. Higher ball to processed powder (B/P) ratio, longer time of grinding and higher grinding speeds increased the degree of the obtained amorphization. However, an undesired extensive caking and agglomeration occurred in certain setups. The potential of activated clay as a SCM was investigated in specific case studies. The measured compressive strength results showed a direct correlation between the enhanced amorphization degree of the mechanically activated clay and the increased strength values. The pozzolanic activity was induced and enhanced after the mechanical activation of the clay. The reactivity was assessed by the strength activity index (SAI). Furthermore, preliminary tests have shown that the alkali activation of the processed clays produced solidified matrixes with considerable strength.

Concrete is essential for the construction industry with characteristic properties that make it irreplaceable in some aspects. However, due to the large volumes consumed and the energy intense cement clinker production it also has a notable climate impact. In order to reach the international and national sustainability goals it is therefore important to reduce the climate impact of concrete structures. There are many ways to influence the environmental impact of concrete and a detailed analysis is one of the actions that could push the industry and the society towards a sustainable development. The purpose of this research is to evaluate the environmental impact of concrete structures and the built environment and to highlight the possibilities to reduce that impact with choice of concrete mix and innovative design solutions. A life cycle assessment (LCA) was carried out to analyze the environmental impact of two thin façade solutions with innovative materials and to evaluate influences of different greenhouse gas reducing measures on concrete bridges. The influence of supplementary cementitious materials (SCM) in terms of climate impact and durability was also analyzed. The results indicate that SCMs have a twofold effect on the climate impact of reinforced concrete structures. Not only do they reduce the greenhouse gases through cement clinker replacement but also by an improvement of durability regarding chloride ingress. Currently, this is not considered in the regulations, which makes it difficult to foresee in LCA at early design stages. The results also show great possibilities to reduce the climate impact through different measures and design alternatives and the need for further development of products and solutions. / <p>QC 20171002</p>

Indiana University-Purdue University Indianapolis (IUPUI) / Purpose: The primary objective of this laboratory study was to investigate whether the ability of SDF to remineralize caries lesion is modulated by their baseline mineral distribution. The exploratory objective was to determine whether the staining caused by SDF is modulated by lesion mineral distribution. Materials and methods: This in vitro study utilized bovine permanent enamel specimens. SDF was compared to the clinical reference standard, 5% sodium fluoride varnish (FV), and deionized water (DIW) was the negative control. By utilizing three lesion creation protocols (methylcellulose [MeC], hydroxyethylcellulose [HEC], Carbopol [C907]), artificial caries lesions with different mineral distributions (n=20 per subgroup) were created in the enamel specimens Interventions were applied and the lesions remineralized using artificial saliva. Changes in mineral loss, lesion depth, mineral density of the surface zone, and lesion mineral distribution were determined using transverse microradiography. Throughout the study, color of the lesion and changes thereof were measured using a spectrophotometer. Data were analyzed by using two-way ANOVA. Pair-wise comparisons were performed using Fisher’s Protected Least Significant Differences to control the overall significance level at 5%. Results: For changes in mineral loss, DIW in MeC showed significantly greater change (more remineralization) than both SDF (p<0.01) and FV (p=0.01), which were not different from one another (p=0.13). There were no statistically significant differences between SDF and FV in the other lesions (C907 – p=0.18; HEC – p=0.56). For changes in lesion depth, there was no statistically significant interaction between study factors lesion protocol and treatments (p=0.23) as well as the individual factors lesion protocols (p=0.08) and treatments (p=0.82). For changes in surface zone mineral density, SDF showed significant change in mineral density compared to FV (p=0.02); however, SDF was not different from with DIW (p=0.25). For lesion mineral distribution, MeC exhibited the greater mineral loss in the lesion body and lowest mineral density at the surface zone. HEC lesions were the deepest but exhibited modest differences in mineral loss between the lesion body and the surface zone. C907 lesions were somewhat between MeC and HEC. SDF in MeC had the highest mineral gain in the surface zone, while DIW resulted in the highest mineral gain in the lesion body. SDF in HEC showed the highest mineral gain in the surface area compared to FV and DIW, with all treatments resulting in the largest mineral gain to a similar extent in the lesion body. In C907, SDF showed the most mineral gain in the lesion body compared to DIW and FV, while differences in the surface zone between treatments were less pronounced. For color changes post intervention, SDF showed more darkening in C907 and HEC lesions compared to MeC (p<0.01) and compared to FV and DIW. For post remineralization, SDF treated C907 lesions became significantly whiter (p<0.01) compared to SDF in MeC and HEC which continued to get darker. Conclusion: SDF did exhibit different remineralization abilities and behaviors and the modulation was based on lesion baseline mineral distribution. Staining resulting from SDF treatment varied significantly based on lesion mineral distribution.

Idag visar allt fler forskningsresultat på de språkutvecklande vinsterna hos samtliga barn när verksamheter bedrivs med AKK som komplement. AKK är ett paraplybegrepp som innefattar bland annat bildstöd och tecken som stöd, där olika AKK-system visualiserar språket. Syftet med denna studie har varit att undersöka förskollärares inställningar till användande av AKK, samt vilka förutsättningar de anser sig ha för att naturligt kunna använda sig av AKK i undervisningen. Genom kvalitativa intervjuer har vi kunnat se likheter och olikheter i förskollärarnas kunskaper och sätt att använda AKK, likväl som vi delgetts deras tankar kring ämnet. Studiens resultat visar att förskollärare generellt har en god inställning till AKK och dess arbetsformer, men att verksamhetens arbete oftast endast innefattar arbete med bildstöd. Dagens förskollärare har väldigt olika förutsättningar för att kunna bedriva undervisning med AKK inkluderat, vilket kan ge konsekvenser. Studien påtalar vikten av kompetenshöjande fortbildningsmöjligheter för våra pedagoger, och tidigare forskning visar att pedagoger som är duktiga på AKK har lättare att uppmärksamma behov och anpassa lärmiljöerna på ett sätt som inkluderar alla barn. I studien framkommer också hur både barngruppens och arbetslagets konstellation påverkar hur arbetet med AKK tar vid, samtidigt som resultatet visar på förskollärarnas insikt om fördelarna med AKK oavsett vilka uttalade behov som finns. / Today, more and more research results show the language development gains of all children when activities are conducted with ACC as a supplement. ACC is an umbrella concept that includes image support and signs as support, where different ACC systems visualize the language. The purpose of this study has been to examine preschool teachers' attitudes towards using ACC, as well as what conditions they consider to have to be able to naturally use ACC in teaching. Through qualitative interviews, we have been able to see similarities and differences in the preschool teachers' knowledge and ways of using AKK, as well as their thoughts on the subject. The results of the study show that preschool teachers generally have a good attitude towards ACC and its working methods, but that the organization's work usually only includes work with image support. Today's preschool teachers have very different conditions for being able to teach with ACC included, which can have consequences. The study points to the importance of competence-enhancing continuing education opportunities for our pedagogues, and previous research shows that pedagogues who are good at ACC have an easier time paying attention to needs and adapting learning environments in a way that includes all children. The study also shows how the constellation of both the children's group and the work team affects how the work with AKK takes place, while the results show the preschool teachers' insight into the advantages of ACC regardless of the stated needs.

Магистерская диссертация содержит теоретическую и эмпирическую часть. В теоретической части исследуются теоретические аспекты изучения психологических особенностей участников проекта «Уральская инженерная школа», изучаются вопросы развития личности одарённого ребенка в системе дополнительного образования. В эмпирической части диссертации описываются результаты исследования психологических особенностей детей, занимающихся по направлениям Робототехника и 3Д-моделирвоание. В заключении диссертации сделаны соответствующие выводы по изучаемой проблеме. / This Master thesis contains a theoretical and empirical parts. The theoretical part is devoted to the psychological characteristics of the pupil who participated in the project "Ural School of Engineering' and discusses development of gifted children in the system of supplementary education. The empirical part of the thesis describes the results of the study of the children involved in such fields as 'Robotics' and '3D-Modelling'.

<p>The study focused on examining the effects of using nanoadditives (nano-TiO2 and colloidal silica) on the hydration kinetics, microstructure, mechanical properties, and durability of concretes, especially those containing fly ash and slag and cured at low (4°C) temperature. </p> <p>The results of the Vicat and isothermal calorimetery (IC) tests suggest that the addition of nano-TiO2 accelerates the hydration process of pastes. In addition, the results of the thermogravimetric analysis (TGA) indicated that the addition of nano-TiO2 increased the amount of hydration products in the pastes, with more notable increases observed in fly ash pastes. Moreover, X-ray diffraction (XRD) results revealed that the addition of nano-TiO2 reduced the mean size of calcium hydroxide (CH) crystals.  </p> <p>The interfacial transition zone (ITZ) of concretes with nano-TiO2 was found to be less cracked and less porous when compared to that of concrete without nano-TiO2. Furthermore, the energy dispersive X-ray (EDX) analyses of the outer hydration products around partially hydrated cement particles in fly ash concretes with nano-TiO2 revealed reduction in the values of Ca/Si atomic ratios when compared to the reference fly ash concrete. The image analysis results of the concrete air void system indicated slightly reduced air content, increased specific surface area (SSA), and decreased spacing factor (SF) in concretes with added nano-TiO2. </p> <p>The addition of nano-TiO2 was also found to enhance the compressive and flexural strengths of mortars and concretes. Nano-TiO2 also improved the resistivity and formation factor values of concretes containing fly ash. Moreover, the total volume of pores, as well as the values of water absorption, were also reduced as a result of addition of nano-TiO2. This was true for all types of concretes (i.e., with or without SCMs). Finally, the use of nano-TiO2 seemed to be more beneficial with respect to improving the scaling and freeze-thaw resistance of fly ash concretes compared to cement-only and slag concretes. </p> <p>Concretes with added nanosilica (colloidal silica) also developed higher compressive and flexural strengths when compared to reference concrete. Moreover, the total pores and permeability of concretes decreased due to the addition of nanosilica while the improvement in scaling resistance of these concretes was only slight. Furthermore, concretes with nanosilica were found to have higher percentage of finer air voids compared to reference concretes. Finally, the ITZ of concretes with nanosilica was found to have fewer defects and cracks compared to the reference concrete. </p> <p>In summary, this dissertation presents the results of a study on the multi-scale behavior of nanomodified concretes with and without SCMs cured at both room and low temperatures. Knowledge gained from this study would be helpful in developing concretes with denser and less porous microstructure, a more refined and better-distributed air void system, improved strength, reduced permeability, and enhanced scaling and freeze-thaw resistance, especially in cases when involving the use of SCMs and exposure to low early-age temperatures.</p>

This study explored and evaluated the prevalence of supplementary tuition in the teaching and learning of Mathematics/Mathematical Literacy in some high-performing schools of the East London district in the Eastern Cape. The study followed a descriptive survey design to address the research problem. Data were gathered using questionnaires for grade 11 learners and high school Mathematics/Mathematical Literacy teachers. The learners were the first group to be taught the Mathematics/Mathematical Literacy learning programme of the new National Curriculum Statement (NCS). The results showed that a fair number of learners (about 48%) were not satisfied with their performance in Mathematics/Mathematical Literacy and a large number of the learners (about 90%) considered a good pass in Mathematics/Mathematical Literacy as important, particularly for their future careers. A substantial proportion of learners (42%) expressed concern about the amount of school time allocated to Mathematics/Mathematical Literacy, and thought that this factor hampered the successful completion of the syllabus. Teachers who happened to be adequately qualified and experienced enough, struggled to complete the Grade 11 Mathematics syllabus in time and were concerned about misconceptions carried from lower classes. Teachers also expressed some concern about learners' lack of commitment to Mathematics/Mathematical Literacy. Learners seemingly took supplementary tuition as a way of overcoming their learning challenges. Of the three forms of supplementary tuition (i.e. private tuition, vacation classes and revising model/former examination papers) commonly available in the district, revising examination papers was preferred (about 83%) followed by private tuition at 81% and lastly vacation school. Learners spent 1.67 hours per week on average on supplementary tuition. More Mathematics learners (about 34%) than Mathematical Literacy learners (about 6%) make use of supplementary tuition. Based on these findings, it was concluded that supplementary tuition is not unique to schools that perform poorly, and even at high performing schools, factors exist which influence learners to take supplementary tuition. / MATH, SCIENCE & TECH EDU / MSC (MATHS,SCIENCE OR T/EDU)

Thesis (MScAgric (Animal Sciences))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The purpose of this study was to evaluate the production of slaughter ostriches in a grazing environment at different levels of supplementary feed. Two grazing trials were conducted. In the first trial, one group of finisher ostriches (six months old) was put into a feedlot and received a complete finisher diet. The other four groups were allowed to graze lucerne pasture (stocking rate of 15 birds/ha) with 1500, 1000, 500, and 0g supplementary feed/bird/day. Pasture production and intake were measured. There was no difference (P >0.05) between the end mean live weights of the feedlot ostriches and those two grazing groups receiving 1500 or 1000g supplementation. The average daily gain (ADG) of the group receiving 1000g supplementation was lower (P <0.05) than the ADG of the group receiving 1500g supplementation, but all three groups reached a mean target slaughter weight of 95kg within the 154 days of the study. Therefore, pastures together with the correct supplementation (at least 1000g/bird/day) can replace complete feeds in the finishing phase of slaughter ostriches and can play an important role in the production of these birds. For lucerne intake, a quadratic relationship (P <0.01) was found between pasture dry matter (DM) intake (g/bird/day) and supplementary feed intake (g/bird/day). The maximum lucerne intake level (1692.8g/bird/day) was achieved at 619.6g supplementary feed/bird/day. In the second grazing trial, finisher ostriches were allowed to graze lucerne pastures at two different stocking rates (10 and 15 birds/ha) while receiving either 0 or 800g supplementary feed/bird/day. Ostriches receiving supplementation had higher (P <0.05) mean end live weights than ostriches receiving no supplementation. Ostriches receiving supplementation reached a mean target slaughter weight of 95kg within the timespan of the trial, but ostriches receiving no supplementation did not. Stocking rate had no influence on mean end live weight of the birds. An interaction (P <0.05) was found between the level of supplementation and stocking rate for ADG of the birds. Stocking rate influenced ADG only for birds receiving no supplementation. As stocking rate increased, ADG of birds receiving no supplementation declined. Results of the pasture data indicated an increasing level of replacement of grazed lucerne DM by supplementary feed as the trial progressed and this was more pronounced at the higher stocking rate of 15 birds per hectare. A high stocking rate seems to have had a gradual depressing effect on lucerne DM production, while the less severe levels of defoliation at a lower stocking rate promoted lucerne DM production. A digestibility trial was conducted with mature ostriches (12 months old) to investigate the effect of supplementation on intake and digestibility of nutrients, as well as to investigate the substitution effect that ostriches may display when they receive supplementary feed in addition to grazing. The same dietary treatments as in the first grazing study were given to ostriches while they were kept in metabolism crates. These diets were also fed to 20-week old roosters to obtain energy values for these diets for roosters. These energy values would be used to predict ostrich energy values for the same diets by means of a regression equation. For the roosters, each diet treatment was mixed with 50% maize to prevent digestive disorders and ensure maximum feed intake. Ostriches started to substitute supplementary feed for pasture when supplementation was supplied at levels higher than 62% (i.e. 1000g supplementary feed/bird/day) of total feed intake. For each increase of 100g in supplementary feed intake, pasture was replaced at a rate of 4.9%. Higher (P <0.05) total feed intakes were reached by ostriches if they grazed lucerne pastures and received supplementation than if they grazed pasture alone. Pasture grazing alone had lower (P <0.05) dry matter digestibility (DMD) and apparent metabolizable energy (AME) values for both ostriches and roosters than if pastures were supplied with a supplement. A significant stepwise regression could not be computed for the prediction of ostrich AME values from rooster AME values. The economics of different feeding systems (extensive versus intensive) were evaluated with an economic analysis, which was based on the same materials and methods and results of the first grazing trial. A margin above feed cost (MAFC) analysis was performed to evaluate the economic viability of the different feeding systems. The present value (PV) of the MAFC for the pasture-based system with 1000g/bird/day supplementation was only 8.3% lower than that of the feedlot system over a period of six years, while the PV of the cost of the same pasture-based system was 78.4% lower than that of the feedlot system. Birds finished on lucerne pasture with 1000g supplementation led to a saving of 57% in feeding costs if compared to a feedlot system. A sensitivity analysis of the MAFC revealed that the pasture-based system was less sensitive to changes in feeding costs than the feedlot system. Therefore, the unique circumstances of each ostrich producer will play a role in the decision whether to raise ostriches in a feedlot or on pastures. / AFRIKAANSE OPSOMMING: Die produksie van slagvolstruise in ‘n ekstensiewe weidingsstelsel met verskillende vlakke van aanvullende voeding is gedurende hierdie studie ge-evalueer. Twee weidingsstudies is uitgevoer. In die eerste studie is een groep afrondingsvolstruise (ses maande oud) in ‘n voerkraal geplaas en ‘n volledige afrondingsdieet gevoer. Die ander vier groepe is op besproeide lusernweiding geplaas (teen ‘n weidigtheid van 15 voëls/ha) en het onderskeidelik 1500, 1000, 500 en 0g aanvullende voeding/voël/dag ontvang. Weidingproduksie en -inname is gemeet. Daar was geen verskil (P >0.05) tussen die eindgewigte van die voerkraal volstruise en dié van die weidende voëls wat onderskeidelik 1500 en 1000g aanvullende voeding ontvang het nie. Die gemiddelde daaglikse toename (GDT) van die groep weidende voëls wat 1000g aanvullende voeding ontvang het was laer (P <0.05) as die GDT van die groep weidende voëls wat 1500g aanvullende voeding ontvang het, maar al drie hierdie groepe het ‘n gemiddelde teiken slaggewig van 95kg bereik binne die 154 dae van die studie. Weiding, tesame met die korrekte aanvullende voeding (van ten minste 1000g/voël/dag) kan volvoer rantsoene in die afrondingsfase van slagvolstruise vervang en kan dus ‘n belangrike rol speel ten opsigte van die produksie van hierdie voëls. Vir lusern inname is ‘n kwadratiese passing (P <0.01) tussen weiding droë materiaal (DM) inname (g/voël/dag) en aanvullende voeding inname (g/voël/dag) gevind. Die maksimum lusern inname (1692.8g/voël/dag) is bereik wanneer voëls 619.6g aanvullende voeding/voël/dag ingeneem het. In die tweede weidingsstudie, is afrondingsvolstruise (6 maande oud) toegelaat om lusern te bewei teen twee verskillende weidigthede (10 en 15 voëls/ha) en het ook 0 of 800g aanvullende voeding/voël/dag ontvang. Volstruise wat aanvullende voeding ontvang het, het hoër (P <0.05) gemiddelde eindgewigte bereik as volstruise wat geen aanvullende voeding ontvang het nie. Volstruise wat aanvullende voeding ontvang het, het ook die teiken slaggewig van 95kg bereik binne die tydsduur van die studie, terwyl die volstruise wat geen aanvullende voeding ontvang het nie, nie daarin kon slag nie. Weidigtheid het nie ‘n invloed (P >0.05) gehad op die eindgewigte van die voëls nie, maar ‘n interaksie (P <0.05) is gevind tussen vlak van aanvullende voeding en weidigtheid wat GDT van die voëls betref. Weidigtheid het GDT beïnvloed slegs vir volstruise wat geen aanvullende voeding ontvang het nie. Soos die weidigtheid van die voëls wat geen aanvullende voeding ontvang het nie, toegeneem het, het die GDT van hierdie voëls afgeneem. Ontleding van die weidingsdata het ‘n toenemende vlak van verplasing van die weiding met aanvullende voeding getoon soos die studie gevorder het en dit was meer merkbaar by die hoër weidigtheid. Die hoër weidighteid het ook gelei tot ‘n geleidelike afname in lusern DM produksie, terwyl die minder aggressiewe vlakke van ontblaring by die laer weidigtheid lusern DM produksie bevorder het. ‘n Verteringsstudie is gedoen met volwasse volstruise (12 maande oud) om die invloed van aanvullende voeding op inname en verteerbaarheid van nutriente te toets, asook om die substitusie effek wat volstruise mag toon wanneer hulle aanvullende voeding ontvang op weiding, te ondersoek. Dieselfde dieet behandelings as in die eerste weidingsstudie is vir die volstruise gegee terwyl hulle in metabolisme kratte aangehou is. Hierdie diëte is ook aan 20-week oue hane gevoer om die energie waardes van die diete vir hane te verkry. Hierdie energiewaardes sal dan gebruik word om volstruis energiewaardes te voorspel vir dieselfde diëte met behulp van ‘n regressie vergelyking. Vir die hane is elke dieet gemeng met 50% mielies om inname te handhaaf en spysverteringsstoornisse te voorkom. Volstruise het weiding begin verplaas met aanvullende voeding sodra die vlak van aanvullende voeding hoër as 62% (d.i. meer as 1000g aanvullende voeding/voël/dag) van die totale inname van die voëls was. Vir elke 100g toename in aanvullende voeding, word weiding verplaas teen ‘n tempo van 4.9%. Weiding, tesame met aanvullende voeding, het gelei tot hoër totale droë material (DM) voerinnames by volstruise as wanneer weiding alleen beskikbaar was. Wanneer weiding alleen voorsien was, was daar laer (P <0.05) verteerbaarhede van DM en waarskynlike metaboliseerbare energie (WME) waardes vir beide volstruise en hane as wanneer die weiding voorsien word met aanvullende voeding. Geen betekenisvolle stapsgewyse regressie kon gevind word om volstruis energie waardes uit hoender energie waardes te voorspel nie. Die ekonomie van verskillende sisteme (ekstensief versus intensief) is in hierdie studie vergelyk en is gebaseer op dieselfde materiaal en metodes en resultate van die eerste weidingsstudie. ‘n Marge bo voerkoste analise is gebruik om die ekonomiese lewensvatbaarheid van die sisteme met mekaar te vergelyk. Die huidige waarde van die marge bo voerkoste van die weidingssisteem waar 1000g aanvullende voeding gevoer word was 8.3% laer as dié van die voerkraal sisteem oor ‘n periode van ses jaar. Daarteenoor was die huidige waarde van die koste van dieselfde weidingssisteem 78.4% laer as dié van die voerkraal sisteem. Die weidingssisteem waar volstruise 1000g aanvullende voeding ontvang het, het ‘n besparing van 57% in voerkoste getoon wanneer dit met die voerkraal volstruise vergelyk is. ‘n Sensitiwiteitsanalise van die marge bo voerkoste het getoon dat die weidingssisteem minder sensitief is vir wisselende voerkoste as die voerkraal sisteem. Die unieke omstandighede van elke produsent sal ‘n rol speel in sy keuse om volstruise op weiding of in ‘n voerkraal af te rond.

Financial stress in agriculture has been a concern over the past century. Agrarian values and "love of the land" seem to yield public conclusions for the support of the industry. Much of this support is in the interest of preserving a viable food producing sector in an volatile world climate. High interest rates, declining land values and highly competitive export markets have spurred renewed concern for farm survival in the past ten years. One alternative to traditional price supports and tariffs for farm household support is off-farm income. This may take many forms including off-farm wages and salaries, rental income, interest and dividend income and, retirement or pension funds. Central to the analysis of nonfarm income generation is the allocation of time by farm households. For farmers who place a high value on the farm lifestyle, occupational choice is embedded in the time decision to such an extent that the resource allocations based on economic efficiency criteria may be altered. Tobit techniques offer a new approach to the analysis of farm household decisions on time allocation. The procedure allows the investigator to estimate and evaluate parameters that may affect the amount of off-farm work by farm household members. The Tobit analysis is designed for censored data sets. The data in this study were censored because there were missing observations on the quantity of off-farm work for those individuals who did not work off-farm in 1986. Results of Tobit analyses of off-farm work by farm operators and spouses in three Oregon counties indicated that high levels of gross farm income reduce the likelihood and extent of off-farm work. Middle-aged operators worked off-farm more while the presence of small children and elderly dependents in the farm household inhibited off-farm work. The allocation decisions of the spouse and the operator appeared to be independent; this supports a nonsimultaneous Tobit specification like the one used in this research. / Graduation date: 1988