The costal populations of perch (Perca fluviatilis) in some parts of the Baltic Sea have been in decline for about two decades. Recruitment failure in the early larval stages has been put forward as a possible cause and the decline has also been suggested to coincide with increases in three-pined stickleback (Gasterosteus aculeatus) densities. The aim of this study was to study the effects of growth and survival of newly hatched perch larvae in the presence of the three-pined stickleback, and if possible determine the main mechanism behind any negative effects the perch may suffer under such conditions. Using large scale experimental ponds as a controlled habitat, an experiment was conducted where perch larvae were being exposed to sticklebacks under four different stages of their development. Results showed that the three- spine stickleback can have a strong negative effect on the survival of young perch. This effect was strongest in the earliest stage of perch development and decreased as they grew bigger. The zooplankton densities didn't differ between the controls and stickleback treatments, suggesting that the young perch didn't suffer from food limitation. Instead predation was identified as the main mechanism behind the high mortality. The results of this study highlight the potential danger of the observed patterns of decreasing predator populations in conjunction with increasing populations of smaller prey species in the Baltic Sea.

International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, Nevada / The turbo code is a block code even though a convolutional encoder is used to construct codewords. Its performance depends on the code word length. Since the invention of the turbo code in 1993, most of the bit error rate (BER) evaluations have been performed using large block sizes, i.e., sizes greater than 1000, or even 10,000. However, for telemetry and command, a relatively short message (<500 bits) may be used. This paper investigates the turbo-coded BER performance for short packets. Fading channel is also considered. In addition, biased channel side information is adopted to improve the performance.

The focus of my PhD research has been on the acquisition of computational modeling and simulation methods used in both theoretical and applied Economics. My first chapter provides an interactive review of finite-difference methods for solving systems of ordinary differential equations (ODEs) commonly encountered in economic applications using Python. The methods surveyed in this chapter, as well as the accompanying code and IPython lab notebooks should be of interest to any researcher interested in applying finite-difference methods for solving ODEs to economic problems. My second chapter is an empirical analysis of the evolution of the distribution of bank size in the U.S. This paper assesses the statistical support for Zipf's Law (i.e., a power law, or Pareto, distribution with a scaling exponent of α = 2) as an appropriate model for the upper tail of the distribution of U.S. banks. Using detailed balance sheet data for all FDIC regulated banks for the years 1992 through 2011, I find significant departures from Zipf's Law for most measures of bank size inmost years. Although Zipf's Law can be statistically rejected, a power law distribution with α of roughly 1.9 statistically outperforms other plausible heavy-tailed alternative distributions. In my final chapter, which is based on joint work with Dr. David Comerford, I apply computational methods to model the relationship between per capita income and city size. A well-known result from the urban economics literature is that a monopolistically competitive market structure combined with internal increasing returns to scale can be used to generate log-linear relations between income and population. I extend this theoretical framework to allow for a variable elasticity of substitution between factors of production in a manner similar to Zhelobodko et al. (2012). Using data on Metropolitan Statistical Areas (MSAs) in the U.S. I find evidence that supports what Zhelobodko et al. (2012) refer to as "increasing relative love for variety (RLV)." Increasing RLV generates procompetitive effects as market size increases which means that IRS, whilst important for small to medium sized cities, are exhausted as cities become large. This has important policy implications as it suggests that focusing intervention on creating scale for small populations is potentially much more valuable than further investments to increase market size in the largest population centers.

Bakgrund: Sjukfrånvaron är ett fenomen som snabbt ökar i Sverige idag. Detta är något som kostar stora summor pengar varje år men trots detta finns relativt lite forskning på området. Den forskning som finns i området undersöker till stor del endast den långvariga sjukfrånvaron. Författarna av denna studie har tydligt identifierat en lucka i forskningen vad gäller kortvarig sjukfrånvaro. Syfte: Denna studie syftar därmed att undersöka storleken på avdelningen samt chefens kommunikation och interaktions påverkan på kortvarig sjukfrånvaro. Resultat: Undersökningen resultat är sammanställt ur dels en enkät som de anställda på tre avdelningar inom ett internationellt produktionsföretag fått besvara och dels tre intervjuer genomförda med en HR-chef och två chefer över avdelningarna. Resultatet blev att fem kategorikoder identifierades; Avdelningens storlek, Chefens kommunikation och interaktion, Frånvarokultur, Arbetsuppgifter och Hälsoarbete. Slutsats: Den främsta slutsats som denna undersökning resulterat i är att storleken på avdelningen påverkar de anställdas möjlighet snarare än deras tendens till att vara kortvarigt sjukfrånvarande. Den faktor som istället anses påverka den kortvariga sjukfrånvaron är hur chefen kommunicerar och integrerar med de anställda. Fokus bör därmed läggas vid denna faktor i försök att antingen minska eller kontrollera den kortvariga sjukfrånvaron på avdelningen / Background: Sickness absence is a phenomenon on a rise in todays Sweden. This is costing large sums of money every year, but despite this, there is relatively little research in the field. The current research has its focus, for the most part, on long-term sickness absence. The authors behind this study have therefore identified a clear gap of research regarding the shortterm sickness absence. Aim: With this study, the aim is therefore to examine the size of the workplace along with the managers communication and interactions effect on the short-term sickness absence. Results: The results of the study are produced through a survey to the employees of three departments within a international production company and through three interviews performed with a HR-manager and two managers over the departments. The study resulted in the identification of five category codes; The size of the department, The managers communication and interaction, Absence culture, Assignments and Health. Conclusion: The primary conclusion that this study result in is that the size of the workplace affect the employees possibilities rather than affecting their tendency to have short-term sickness absence. The factor which instead is considered to affect the short-term sickness absence is how the manager communicates and integrates with the employees. Therefore, the focus should be aimed at this factor in attempts to either decrease or control the short-term sickness absence at the workplace.

Studiens övergripande syfte var att undersöka och diskutera vilka som är de viktigaste egenskapernai en förskolas utemiljö och om dess kvalitet är mätbar. Studien har besvarat frågeställningarnagenom att applicera en analys- och bedömningsmodell från tidigare forskning (OPEC) på sexförskolors utemiljöer i Gävle kommun. Modellens bakgrund och kriterier har jämförts mednuvarande svenska styrdokument för planering av förskolor. Experter inom området har använtssom en del i att undersöka vilka egenskaper som utgör en god utemiljö. Resultatet visade att detfinns en diskrepans mellan modellens kriterier och aktuella styrdokument samt sakkunnigas åsikter.Resultatet visar också hur hög kvalitet de studerade förskolornas utemiljöer uppnår enligt OPEC. / The overall aim of this study was to explore and discuss which ones are the most importantcharacteristics of a preschools outdoor environment and if its quality is measurable. The study hasanswered the research questions by applying an analysis and assessment model from previousresearch (OPEC) on six preschools outdoor environments in the city of Gävle. The model'sbackground and criteria was compared with current Swedish policy documents for planningpreschools. Experts in the field has been used to study what characteristics that make a goodoutdoor environment for preschool children. The results showed that there is a discrepancybetween the model’s criteria and both the relevant policy documents and the experts’ opinions.The result also shows the quality of the studied preschools outdoor environments according toOPEC.

Over the years there has been significant research around the misspecification of the Capital Asset Pricing Model (CAPM), which challenges the linear relationship between beta and market returns. One of the biggest challenges relates to the “small-firm effect,” which states there are two classifications of stocks (large and small) and that the companies with small-market capitalizations have higher returns. However, the definition of a small-cap is vague and there has been little focus in academia on the stocks in the middle-market capitalization deciles. Despite this, institutional and retail investors created the “mid-cap” category in the early 1990s and, since then, the risk-adjusted returns have been exceptional, relative to small- and large-cap stocks. This study examined mid-cap stocks from an academic perspective and delves into the “mid-cap myth” by evaluating the category over the past 85 years to answer the question around whether mid-caps are superior to other asset class. The results revealed that the highly touted and advertised mid-cap stock performance premium during the 1980-2013 time period was statistically insignificant. Moreover, mid-caps did have superior risk-adjusted returns over the extended time period studied (1928 to 2014); however, these superior returns relative to small-caps were not driven by the uniqueness of the mid-sized companies, but by the underperformance of small-cap stocks, specifically small-cap growth stocks. When studying the behavior or migration of mid-size companies, they do not appear to exhibit unusual behavior relative to companies with smaller market capitalizations, especially in the area of mergers and acquisitions. Thus, the question becomes why small-cap companies underperform relative to their risk level. The answer lies in the inclusion of the NASDAQ stocks to the CRSP database after 1972. This change not only doubled the number of stocks deemed small-caps, but also added a significant number of unprofitable fast-growing companies to the small-cap growth category, specifically in the technology and healthcare industries. The study benefits practitioners by providing insight into the omnipresent claim of mid-cap outperformance from 1980-2014, while also benefiting academia by providing more insight into small-caps’ underperformance during this period and how investigating small-cap growth companies further could add insight into the viability or magnitude of the size and value premium going forward.

Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The nite size of nucleons should play an important role in the description of high density nuclear matter as found in astro-physical objects. Yet we see that the Walecka model, which is generally used to describe these systems, treats the nucleons as point particles. Here we argue that a non-commutative version of the Walecka model may be a consistent and appropriate framework to describe nite nucleon size e ects. In this framework the length scale introduced through the non-commutative parameter plays the role of the nite nucleon size. To investigate the consequences of this description, the equations of motion and energy-momentum tensor for the non-commutative Walecka model are derived. We also derived an expression for the total energy of the system, as a function of the non-commutative parameter, in a spatially non-uniform matter approximation. The non-commutative parameter, as a variable dependent on the dynamics of the system, remains to be solved self-consistently. / AFRIKAANSE OPSOMMING: Die eindige grootte van nukleone moet 'n belangrike rol speel in die beskrywing van ho e-digtheid kern materie soos gevind in astro- siese voorwerpe. Tog sien ons dat die Walecka model, wat in die algemeen gebruik word om hierdie stelsels te beskryf, die nukleone as punt deeltjies hanteer. Ons redeneer dus dat 'n nie-kommutatiewe weergawe van die Walecka model 'n konsistente en gepaste raamwerk is om die e ekte van eindige nukleon grootte te beskryf. In hierdie raamwerk speel die lengte-skaal wat ingevoer word deur die nie-kommutatiewe parameter die rol van eindige grootte vir nukleone. Om die gevolge van hierdie beskrywing te ondersoek, word die vergelykings van beweging en die energie-momentum tensor afgelei vir die nie-kommutatiewe Walecka model. Ons het ook 'n uitdrukking vir die totale energie van die stelsel, as 'n funksie van die niekommutatiewe parameter, afgelei in 'n ruimtelik nie-uniforme materie benadering. Die niekommutatiewe parameter, as 'n veranderlike afhanklik van die dinamika van die stelsel, bly steeds om self-konsistent opgelos te word.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2006. / As easy to mine high grade ore bodies are being depleted, many mining industries are experiencing an increasing need to process lower grade ores, and thus the high costs involved in the mineral recovery from these ores (of which comminution energy costs are a large component) are of major concern. It has been estimated that up to 70% of the total energy consumption in mineral processing is used up by comminution processes, which characteristically may have efficiencies of less than 0.1% in terms of the transfer of electrical energy into particle breakage. In many cases, very fine grinding is required to liberate the valuable inclusions in such low grade ores, which also leads to slimes losses of valuable minerals due to the inefficiencies of recovery methods in the ultra-fine size ranges. For many years the use of thermal pretreatment has been suggested as a way to decrease the costs of size reduction, and improve the liberation of valuable minerals in ores to aid later beneficiation technologies, but it was not until exploration into the use of microwaves to selectively heat only some of the minerals in ores, that this form of treatment became economically viable. A low grade copper ore from Palabora was subjected to microwave treatment and then tested for ore strength in a laboratory rod mill, using the developing cumulative size distributions of the rod mill products with time to quantitatively determine the effects of microwave treatment on ore strength. It was seen that after microwave treatment the ore responded more readily to milling, producing a finer grind than for untreated ore at every measured time interval of milling. From this data, comminution models were created to describe the grinding of this ore in various flowsheet simulations. An investigation was also performed to determine the effect of the application of microwave treatment on the liberation of minerals, due to the preferential breakage induced along grain boundaries during the selective thermal expansion of certain mineral inclusions in ores during microwave treatment. To ensure consistency between results for microwave treated and untreated material, it was decided to use the same grinding time for both when preparing ore for the next stage of testing. A grinding time was chosen which would produce an 80% passing size of 800 μm for the microwave treated ore. This time was determined from the previous grinding tests and was found to be approximately 16 minutes. After particle size classification of the mill products through sieving, a size range suitable for gravity separation processes was chosen for sink-float testing, with the aim of investigating whether microwave treatment had liberated enough gangue material at large particle sizes to offer the possibility of removing this hard gangue material early on in the process, before costly fine grinding is required. XRF analysis of the products showed little difference in recoveries of gangue material to the floats between treated and untreated material, and that while most of the copper reported to the sinks, that some of the copper was always entrained in the floats. These losses of valuable minerals to the gravity tailings will lead to overall losses in copper mineral recovery from the plant. QEMSCAN® analysis showed that there was a significant increase in mineral liberation in the size ranges associated with flotation as a result of the microwave treatment. An increase in liberation of the copper minerals which are easily recovered by flotation (i.e. chalcopyrite, cubanite, bornite, chalcocite and digenite) of 8.4% over that of the untreated ore was seen. This indicates that significant increases in copper recovery are possible after microwave treatment, and also that less fine grinding is then required to extract the valuable minerals from the ore, which leads to a reduction in loss of these valuable minerals to slimes. Palabora Mining Company supplied enough data on their plant operations from 1989 to enable models to be built to describe the operation of the mills and classifiers used in their comminution circuit. This data, together with the work performed to compare the performance of microwave treated and untreated Palabora ore in both milling and liberation (which allowed for basic recovery models to be built), allowed flowsheet simulations of the plant operations. Simulations of the plant after the addition of microwave pretreatment of the ore showed that the total energy used in comminuting the ore (including that of the microwave treatment) to the correct size distribution for mineral recovery by flotation were reduced by 19% from that required for untreated ore, and was mainly due to reductions in the circulating loads over the mills. By exploiting the greater milling capacity allowed for by these lower circulating loads, it was shown that it was theoretically possible to obtain increases of up to 46% in maximum throughput after microwave treatment, while retaining the same final grind size in the feed sent to flotation as is required for untreated ore. The addition of gravity separation processes to remove liberated gangue material from the comminution circuit early on, led to further savings in energy and also grinding media, and also decreased the requirements for flotation reagents and smelter fuel later on in the flowsheet. Unfortunately, the losses of entrained copper to the gravity separation tailings were such that overall economic losses were incurred by the operation. It was concluded that when dealing with low grade ores, only the implementation of very efficient and mineral specific separation technologies could make the removal of gangue material at large particle sizes (i.e. > 1 mm) viable. Economic analyses based on the simulations of the plant under various operating conditions showed potential increases in plant profitability after the addition of microwave pretreatment of the ore before milling, and were reported using net present value (NPV) calculations for the plant over a 10 year period with monetary values discounted at 20%. When operating under the same conditions and throughput as in the 1989 data provided by Palabora Mining Company, an increase in the NPV of the plant of 23% over that for the reported operation was seen after the addition of microwave pretreatment, and an increase of 72% in NPV given a 10% increase in throughput which is made possible by microwave pretreatment of the ore. In real money terms, after 10 years of operation the increase in NPV of the plant with the addition of microwave pretreatment of the ore was seen to be around R259 million (under the conditions reported for the plant operation in 1989), and around R795 million if the 10% increase in throughput which is only made possible by microwave pretreatment is realized. Current conditions at Palabora are very different from those supplied by the plant for the operation in 1989, however, as the mining operation has since been moved underground resulting in the throughput of the plant being greatly reduced, with the consequence that the plant is currently operating at a loss. Palabora mining company posted a net loss of R158 million over the 6 months leading up to June 2004, while an economic analysis of the proposed addition of microwave pretreatment of the ore at an increased throughput of 10% made possible by this treatment, indicated that a loss of only R138 million would have been incurred over the same 6 month period had this been implemented. Thus, while benefits from the introduction of microwave pretreatment of the ore before milling can still be seen under the operating conditions of the plant during the time period investigated, these alone would not have be able to bring the plant to profitable operation.

Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The challenge of conserving biodiversity is daunting. Despite some local conservation gains, most indicators of the condition of global biodiversity show declines since the 1970’s, while indicators of the threats to biodiversity all show increases. Humanity has in part responded to the global biodiversity extinction crisis by establishing protected areas (PA) and they are widely considered cornerstones of conservation. However, their efficacy in maintaining biodiversity is much debated. Previous studies have been unable to provide a general answer because of their typically restricted geographic and/or taxonomic focus, or qualitative approach. Using a global meta-analysis with 861 pairwise comparisons inside and outside PAs from 86 studies across five major taxon groups, I tested the hypothesis that PAs achieve significant conservation outcomes measured as higher biodiversity values compared with alternative land covers. I found that globally, PAs typically contain higher abundances of individual species, higher assemblage abundances and higher species richness. Variation in effect sizes among taxa nonetheless underscores that PA efficacy can be context specific. To examine factors driving the context specific nature of PA efficacy, an exact distance, timed point count methodology was used to assess PAs ecological effectiveness in terms of bird assemblages of the Kruger National Park (KNP), South Africa, in the Phalaborwa section. Bird assemblages inside the KNP were compared to matched sites in rural and urban land cover, as well as the connecting habitat matrix outside the KNP. Species richness and abundance were significantly lower inside the KNP compared to other land covers. However, the species assemblages are markedly different. The artificial addition of resources in an otherwise resources poor area, mainly in terms of gardening, provide suitable habitat for a range of species, consistent with the more individuals hypothesis. Large-bodied and ground nesting species are virtually absent outside the KNP. Thus species richness and abundance differences between land cover regions mask insidious changes in species traits. Nonetheless, not formally protected land can contribute positively to the regional biodiversity portfolio. Since an understanding of the mechanisms that structure species assemblages can aid in the consequences of anthropogenic drivers disentangling them, I describe and analyse the body size frequency distributions (BSFDs) of avian assemblages at several spatial scales in the Afrotropical biogeographic realm. I found that the African avifaunal continental BSFD is unimodal and right-skewed. African avifaunal BSFDs are quantitatively dissimilar to the African mammal BSFDs, which are bimodal at all spatial scales. Much of the change in median body size with spatial scale can be captured by a range-weighted null model, suggesting that differential turnover between smaller- and larger-bodied species might explain the shift in the central tendency of the BSFD. My results for the first time quantitatively demonstrate that PAs are a vital component of a global biodiversity conservation strategy. However, I also show that PA ecological effectiveness can be context specific, and understanding which species traits are at risk outside of PAs is critical to predicting their efficacy. / AFRIKAANSE OPSOMMING: Dit is ‘n uitnemende uitdaging om biodiversiteit te bewaar. Ten spyte van sommige sukses op ‘n lokale skaal, dui die meeste indikators aan dat die toestand van globale biodiveristeit afgeneem het vanaf die 1970’s, terwyl bedreigings daartoe toegeneem het. Die mensdom het gedeeltelik reageer op die biodiversiteits uitsterfings krisis deur die uiteensetting en instandhouding van bewaringsgebiede (BG). Hierdie metodiek word wêreldwyd geag as ‘n hoeksteen van bewaring. Die ekologiese doeltreffendheid van BG word egter baie debateer. Vorige studies was geografies beperk of het net op sekere takson groepe gefokus. Vorige studies is ook tipies statisties kwalitatief van aard. As gevolg daarvan het ek ‘n globale meta-analiese gebruik, wat bestaan het uit 861 gepaarde meetings vanaf 86 studies, oor vyf verskillende taksonomiese groepe. Ek het die hipotese getoets dat BG statisties beduidende bewaring laat gekiet in terme van hoër biodiveristeits waardes binnekant hul grense, in kontras met areas buite BG. Ek het gevind dat BG juis hoër waardes van hoër indivuduele spesies hoeveelhede, gemeenskaps hoeveelhede en spesiesrykheid bevat. Tog dui die variasie in effek grootte onder takson groepe aan dat BG effektiwiteit konteks spesifiek is. Aangesien BG effektiwiteit konteks spesifiek is, het ek verder ‘n tydstip, eksakte-afstand punttelling metodiek gevolg om die Kruger Nationale Park (KNP) in Suid Afrika, se ekologiese doeltreffendheid te bepaal. Ek het voëlgemeenskappe binne KNP vergelyk met voëlgemeenskappe buite KNP. Metings is buite die KNP gedoen in tuislande, die stadsgebied van Phalaborwa, asook in die habitat matriks wat die areas verbind. Beide spesiesrykheid en hoeveelheid is hoër buite KNP, maar die voëlgemeenskap struktuur tussen gebiede verskil noemenswaardig. Die uitbreiding van bronne ten opstigte van nesmaak en voeding (meestal deur tuinmaak), bied vir voëls goeie habitat in die stadsgebied, soos verwag kan word uit die meer individue hipotese. Hierdie veranderinge in spesiesrykheid tussen die verskillende areas versteek veranderinge in die spesies einskappe. Voëls met groot liggaamsmassa, veral die wat op die grond nes maak, kom in baie minder getalle voor buite KNP. Tog bied onbewaarde areas ‘n positiewe inpak tot die omgewing se biodiversiteit. ‘n Holistiese begrip van die meganismes wat spesies gemeenskappe struktureer kan help om die menslike invloed daarop uit te lig. Daarvolgens beskryf ek die liggaamsmassa frekwensie verspreiding (LMFV) oor verkillende skale in die Afrotropies biografiese streek. Ek het bevind dat Afrika se voëlgemeenskappe op die kontinentale skaal unimodaal en regs-geskewe is. Afrika se voël LMFV is beduidend verskillend van Afrika soogdier LMFV, wat bimodaal is op verskeie skale. Baie van die verandering in mediaan liggaams massa oor verskillende skale kan verduidelik word met ‘n verspreidings-aangepaste nul-model, wat voorstel dat die verskille in omset van voëls met of klein, of groot liggaamsmassa in die landskap die veranderings in LMFV verduidelik. My studie is die eerste van sy soort wat kwantitatief bepaal dat die gebruik van BG krities is tot ‘n globale bewaringsstrategie. Verder het ek bewys dat BG se ekologiese doeltreffendheid afhang van die kontkes op ‘n lokale skaal, en dat spesies eienskappe geïnkorporeer moet word om BG se doeltreffendheid te bepaal.

The North Polar Layered Deposits (NPLD) of Mars contain a complex stratigraphy that has been suggested to retain a record of past eccentricity- and obliquity-forced climate changes. The surface accumulation rate in the current climate can be constrained by the crater retention age. We scale NPLD crater diameters to account for icy target strength and compare surface age using a new production function for recent small impacts on Mars to the previously used model of Hartmann (2005). Our results indicate that ice is accumulating in these craters several times faster than previously thought, with a 100m diameter crater being completely infilled within centuries. Craters appear to have a diameter-dependent lifetime, but the data also permit a complete resurfacing of the NPLD at similar to 1.5 ka.