Many relational databases exhibit complex dependencies between data attributes, caused either by the nature of the underlying data or by explicitly denormalized schemas. In data warehouse scenarios, calculated key figures may be materialized or hierarchy levels may be held within a single dimension table. Such column correlations and the resulting data redundancy may result in additional storage requirements. They may also result in bad query performance if inappropriate independence assumptions are made during query compilation. In this paper, we tackle the specific problem of detecting functional dependencies between columns to improve the compression rate for column-based database systems, which both reduces main memory consumption and improves query performance. Although a huge variety of algorithms have been proposed for detecting column dependencies in databases, we maintain that increased data volumes and recent developments in hardware architectures demand novel algorithms with much lower runtime overhead and smaller memory footprint. Our novel approach is based on entropy estimations and exploits a combination of sampling and multiple heuristics to render it applicable for a wide range of use cases. We demonstrate the quality of our approach by means of an implementation within the SAP NetWeaver Business Warehouse Accelerator. Our experiments indicate that our approach scales well with the number of columns and produces reliable dependence structure information. This both reduces memory consumption and improves performance for nontrivial queries.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2010.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Higher grade steels are being rolled in South Africa by suppliers and results in structural members having an increased axial and bending moment capacity due to an increased yield stress. Structural elements used in designs are stronger and therefore lighter sections with sufficient axial and bending moment capacity are used. Displacements of structural elements are calculated using the stiffness and Young’s modulus of a profile. These values are not affected by the increased yield stress in higher steel grades and therefore have a negative effect on the displacements of the structure. The potential of these higher grade structural elements are not utilized through serviceability limit state criteria, since the displacement determination does not account for the increased capacities of higher grade steels, but only stiffness and elasticity of the members. Structural analysis of portal frames does not account for the real behaviour of steel connections and column bases. It is assumed that connections and bases are either fully rigid or perfectly pinned. This assumption is used in the analysis and design of the structure. Although it is assumed that connections and bases are either rigid or pinned, the real behaviour is in between these two extremes. Rigid connections exhibit a certain flexibility under loading whereas pinned bases provide a certain restraint under loading. The real behaviour of connections and bases are referred to as the moment-rotation behaviour of the connection. For a certain applied moment to the connection or base, the connection exhibits a certain rotation. The focus of this study is placed on the accuracy and feasibility of modelling the real behaviour of connections and bases in a structural analysis of a portal frame. A connection stiffness is determined from the connection’s moment-rotation behaviour, and is assigned to a rotational spring of zero length in a structural analysis. An experimental investigation was conducted to obtain the real displacement data of a portal frame subject to loads for two different support conditions, i.e. a perfect hinge and grouted-support. A perfect hinge support was used to isolate the moment-rotation response of the ridge and eaves connection. The experimental results were used to compared to the results obtained from a structural analysis to determine the accuracy of the numerical results. A real design case was investigated with load combinations imposed on the frame in accordance with SANS 10160:2011. Three methods of modelling connections and bases in an analysis were considered. Firstly modelling connections as rigid and bases as pinned, secondly modelling connections as linear rotational springs and bases as pinned. Lastly was to model connections as linear rotational springs and bases as non-linear rotational springs. The outcome of the research was that more accurate displacements of a portal frame could be obtained by modelling the real behaviour of rigid connections as rotational springs, but this is not the case with grouted column bases. It is thus not feasible to model the real behaviour of connections and bases in a structural analysis as the current method of modelling connections as rigid and bases as pinned provides reliable and accurate displacement results. / AFRIKAANSE OPSOMMING: Hoë graad staal word tans in Suid Afrika gerol deur verskaffers en lei daartoe dat strukturele elemente oor ’n groter aksiale- en buigmomentkapasiteit het as gevolg van ’n groter vloeispanning. Strukturele elemente in ontwerpe is sterker en gevolglik het ligter elemente die benodigde aksiale- en buigmoment-kapasiteit. Verplasings van strukturele elemente word bepaal vanaf die styfheid en Young modulus van die element. Hierdie waardes word nie beïnvloed deur die groter vloeispanning van hoë graad staal nie, en het dus ’n negatiewe uitwerking op die verplasings van die struktuur. Die potensiaal van die gebruik van hoë graad staal word nie benut in die geval van voldoening aan diensbaarheids kriterium nie, aangesien verplasings bepaal word vanaf die styfheid en elastisiteit van die elemente, en nie vloeispanning nie. Strukturele analise van portaalrame neem nie die ware gedrag van konneksies en kolomvoetstukke in ag nie. Die aanname word gemaak in analises en ontwerpe dat konneksies en voetstukke óf rigied óf geskarnierd is. Hierdie is slegs ’n aanname en in die werklikheid lê die ware gedrag van konneksies en voetstukke tussen hierdie grense. Rigiede konneksies toon ’n sekere buigbaarheid tydens belasting en geskarnierde voetstukke toon ’n sekere beperking teen rotasies. Die ware gedrag van konneksies en voetstukke word gedefinieer as moment-rotasie gedrag. Vir ’n spesifieke aangewende moment, ondergaan die konneksie of voetstuk ’n sekere rotasie. Hierdie studie fokus op die akkuraatheid en uitvoerbaarheid van die modellering van die ware gedrag van konneksies en voetstukke in ’n strukturele analise van portaalrame. Die styfheid van ’n konneksie word bepaal vanaf sy unieke moment-rotasie gedrag, en word ingevoer as ’n styfheid van ’n rotasieveer in ’n strukturele analise. ’n Eksperimentele ondersoek was gedoen om verplasingswaardes van ’n portaalraam onder belastings te bepaal. Twee ondersteunings is ondersoek in die eksperimentele program, naamlik ’n geskarnierde ondersteuning asook ’n breivul ondersteuning. Die gebruik van die geskarnierde ondersteuning isoleer die moment-rotasie gedrag van die nok en dakrand konneksies. Die eksperimentele resultate was gebruik om die akkuraatheid van die resultate vanaf die strukturele analise te ondersoek. Laastens was ’n ontwerpsprobleem ondersoek deur laskombinasies, soos bepaal volgens die riglyne van SANS 10160:2011, op ’n portaalraam aan te wend. Drie gevalle van modellering van konneksies in ’n strukturele analise is ondersoek. Eerstens om konneksies as rigied en voetstukke as geskarnierd te beskou. Tweedens was die konneksies as linieêre rotasievere gemodelleer en voetstukke as geskarnierd te beskou. Laastens was om konneksies as linieêre rotasievere te modeleer en voetstukke as nie-linieêre rotasievere. Die navorsing het getoon dat meer akkurate verplasings van portaalrame bepaal kan word deur rigiede konneksies te modelleer as rotasievere, maar dit is nie die geval met breivul ondersteunings nie. Die gevolg is dat die uitvoerbaarheid van die modellering van konneksies en voetstukke as rotasievere nie effektief is nie, aangesien die huidige metode van die modellering van konneksies as rigied en voetstukke as geskarnierd akkurate en betroubare resultate lewer.

<p>Mine waste from Ljusnarsbergsfältet in Kopparberg, Sweden, is considered to constitute a great risk for human health and the surrounding environment. Some of the waste rock consists of sulphide minerals. When sulphide minerals come into contact with dissolved oxygen and precipitation, oxidation may occur resulting in acid mine drainage (AMD) and the release of heavy metals. The purpose of this study has been to characterise the waste material and try to chemically stabilize the waste rock with a mixture of sewage sludge and calcium carbonate. The drawback of using organic matter is the risk that dissolved organic matter can act as a complexing agent for heavy metals and in this way increase their mobility. An additional study to examine this risk has therefore also been performed.</p><p>The project started with a pilot study in order to identify the material fraction that was suitable for the experiment. When suitable material had been chosen, a column test was carried out for the purpose of studying the slurry’s influence on the mobility of metals along with the production of acidity. To clarify the organic material’s potential for complexation a pH-stat batch test was used. Drainage water samples, from the columns, were regularly taken during the experiment. These samples were analysed for pH, electrical conductivity, alkalinity, redox potential, dissolved organic carbon (DOC), sulphate and leaching metals. The effluent from the pH-stat-test were only analysed on a few occasions and only for metal content and change in DOC concentration.</p><p>The results from the laboratory experiments showed that the waste rock from Ljusnarsberg easily leached large amounts of metals. The stabilization of the waste rock succeeded in maintaining a near neutral pH in the rock waste leachate, compared to a pH 3 leachate from untreated rock waste The average concentration of copper and zinc in the leachate from untreated waste rock exceeded 100 and 1000 mg/l respectively, while these metals were detected at concentrations around 0.1 and 1 mg/l, respectively, in the leachate from the treated wastes. Examined metals had concentrations between 40 to 4000 times lower in the leachate from treated waste rock, which implies that the stabilisation with reactive amendments succeeded. The long term effects are, however, not determined. The added sludge contributed to immobilise metals at neutral pH despite a small increase in DOC concentration. The problem with adding sludge is that if pH decreases with time there is a risk of increased metal leaching.</p> / <p>Gruvavfallet från Ljusnarsbergsfältet i Kopparberg anses utgöra en stor risk för människors hälsa och den omgivande miljön. En del av varpmaterialet, ofyndigt berg som blir över vid malmbrytning, utgörs av sulfidhaltigt mineral. Då varpen exponeras för luft och nederbörd sker en oxidation av sulfiderna, vilket kan ge upphov till surt lakvatten och läckage av tungmetaller. Syftet med arbetet har varit att karaktärisera varpen och försöka stabilisera den med en blandning bestående av mesakalk och avloppsslam, samt att undersöka risken med det lösta organiska materialets förmåga att komplexbinda metaller och på så vis öka deras rörlighet.</p><p>Efter insamling av varpmaterial utfördes först en förstudie för att avgöra vilken fraktion av varpen som var lämplig för försöket. När lämpligt material valts ut utfördes kolonntest för att studera slam/kalk-blandningens inverkan på lakning av metaller, samt pH-statiskt skaktest för att bedöma komplexbildningspotentialen hos det organiska materialet vid olika pH värden. Från kolonnerna togs lakvattenprover kontinuerligt ut under försökets gång för analys med avseende på pH, konduktivitet, alkalinitet, redoxpotential, löst organiskt kol (DOC), sulfat och utlakade metaller. Lakvattnet från pH-stat-testet provtogs vid ett fåtal tillfällen och analyserades endast med avseende på metallhalter och förändring i DOC-halt.</p><p>Resultatet från den laborativa studien visade att varpmaterialet från Ljusnarsberg lätt lakades på stora mängder metaller. Den reaktiva tillsatsen lyckades uppbringa ett neutralt pH i lakvattnet från avfallet, vilket kan jämföras med lakvattnet från den obehandlade kolonnen som låg på ett pH kring 3. Medelhalten av koppar och zink översteg under försöksperioden 100 respektive 1000 mg/l i lakvattnet från det obehandlade avfallet, medan halterna i det behandlade materialets lakvatten låg kring 0,1 respektive 1 mg/l. Av de studerade metallerna låg halterna 40-4000 gånger lägre i lakvattnet från den behandlade kolonnen, vilket innebär att slam/kalk-blandningen har haft verkan. Stabiliseringens långtidseffekt är dock okänd. Det tillsatta slammet resulterade inte i någon större ökning av DOC-halten i det pH-intervall som åstadkoms med mesakalken. Utifrån pH-stat-försöket kunde det konstateras att det tillsatta slammet bidrog till metallernas immobilisering vid neutralt pH, trots en liten ökning av DOC-halten. Om en sänkning av pH skulle ske med tidens gång föreligger dock risk för ökat metalläckage.</p>

This research introduces and develops a counter-intuitive seismic retrofit strategy, referred to as “Selective Weakening” (SW), for pre-1970s reinforced concrete (RC) frames with a particular emphasis on the upgrading of exterior beam-column joints. By focusing on increasing the displacement and ductility capacities of the beam-column joints, simple retrofit interventions such as selective weakening of the beam and external post-tensioning of the joint can change the local inelastic mechanism and result in improved global lateral and energy dissipation capacities. The thesis first presents an extensive review of the seismic vulnerability and assessment of pre-1970s RC frames. Following a review of the concepts of performance-based seismic retrofit and existing seismic retrofit solutions, a thorough conceptual development of the SW retrofit strategy and techniques is presented. A “local-to-global” design procedure for the design of SW retrofit is proposed. Based on the evaluation of the hierarchy of strength at a subassembly level, a capacity-design retrofit outcome can be achieved using various combinations of levels of beam-weakening and joint post-tensioning. Analytical tools for the assessment and design of the SW-retrofitted beam-column joints are developed and compared with the test results. Nine 2/3-scaled exterior joint subassemblies were tested under quasi-static cyclic loading to demonstrate the feasibility and effectiveness of SW retrofit for non-ductile unreinforced beam-column connections. Parameters considered in the tests included the presence of column lap-splice, slab and transverse beams, levels of post-tensioning forces and location of beam weakening. Extensive instrumentation and a rigorous testing regime allowed for a detailed experimental insight into the seismic behaviour of these as-built and retrofitted joints. Experimental-analytical comparisons highlighted some limitations of existing seismic assessment procedures and helped in developing and validating the SW retrofit design expressions. Interesting insights into the bond behaviour of the plain-round bars, joint shear cracking and post-tensioned joints were made based on the experimental results. To complement the experimental investigation, refined fracture-mechanic finite-element (FE) modelling of the beam-column joint subassemblies and non-linear dynamic time-history analyses of RC frames were carried out. Both the experimental and numerical results have shown the potential of SW retrofit to be a simple and structurally efficient structural rehabilitation strategy for non-ductile RC frames.

Kate Valley is a municipal waste landfill situated in Waipara, Northern Canterbury. It is a joint venture between the 6 local regional councils and Transwaste Canterbury Ltd to help dispose of waste quantities generated in the wider Canterbury region. Landfill waste disposal also generates waste streams. Major waste streams can include methane gas production and liquid leachate. One practice which can turn liquid leachate waste streams into a nutrient source for plants is land irrigation. It is important to have a thorough understanding of the interactions involved with leachate, soil structure, soil microbiology, flora. This thesis investigates the sorption mechanisms between Kate Valley soil and leachates, through batch and column experiments. Sorption mechanisms between leachate and soil were investigated through batch and column tests. Ex-situ soil samples were extracted from Kate Valley, along with raw leachate samples for batch tests at a soil to liquid ratio of 30 g vs. 70 ml respectively. Tested dilution leachate strengths ranged from raw to 50x raw leachate dilution; meanwhile soil samples were categorized into 3 groups based on soil depth: 0-20 cm, 20-40 cm, and 40-60 cm. Column tests were conducted on 3 extracted in-situ soil column monoliths. Column test irrigation conditions included: control case, 2x and 10x raw leachate dilution, and 200 mg/L KBr (bromide column), where the same soil column was used for bromine testing after control testing had ceased. Batch results suggest deeper soils are less effective at sorption of ammonia, where partitioning coefficient ranged from 9.5x*10-7 to 6.4*10-7 L/mg for 0-20 cm soil to 40-60 cm soil respectively. Column results generally showed lower partitioning capacity than batch results, at 4*10-8 and 5*10-8 L/mg for 10x and 2x dilution leachate irrigation respectively. Discrepancies in experimental data have been attributed to: different dilution leachates tested between batch and column tests, making it difficult for direct comparison; extreme soil to liquid ratios employed in experiments; direct data comparison between the “full-contact” experimental data (between leachate and soil), obtained from batch tests with column results, where not all soil may have been fully exposed for shrinkage of boundary layers of soil particles; and oxygen exposure of samples during testing and sampling, possibly encouraging nitrification.

Evermore, novel and traditional business applications leverage the advantages of a graph data model, such as the offered schema flexibility and an explicit representation of relationships between entities. As a consequence, companies are confronted with the challenge of storing, manipulating, and querying terabytes of graph data for enterprise-critical applications. Although these business applications operate on graph-structured data, they still require direct access to the relational data and typically rely on an RDBMS to keep a single source of truth and access. Existing solutions performing graph operations on business-critical data either use a combination of SQL and application logic or employ a graph data management system. For the first approach, relying solely on SQL results in poor execution performance caused by the functional mismatch between typical graph operations and the relational algebra. To the worse, graph algorithms expose a tremendous variety in structure and functionality caused by their often domain-specific implementations and therefore can be hardly integrated into a database management system other than with custom coding. Since the majority of these enterprise-critical applications exclusively run on relational DBMSs, employing a specialized system for storing and processing graph data is typically not sensible. Besides the maintenance overhead for keeping the systems in sync, combining graph and relational operations is hard to realize as it requires data transfer across system boundaries. A basic ingredient of graph queries and algorithms are traversal operations and are a fundamental component of any database management system that aims at storing, manipulating, and querying graph data. Well-established graph traversal algorithms are standalone implementations relying on optimized data structures. The integration of graph traversals as an operator into a database management system requires a tight integration into the existing database environment and a development of new components, such as a graph topology-aware optimizer and accompanying graph statistics, graph-specific secondary index structures to speedup traversals, and an accompanying graph query language. In this thesis, we introduce and describe GRAPHITE, a hybrid graph-relational data management system. GRAPHITE is a performance-oriented graph data management system as part of an RDBMS allowing to seamlessly combine processing of graph data with relational data in the same system. We propose a columnar storage representation for graph data to leverage the already existing and mature data management and query processing infrastructure of relational database management systems. At the core of GRAPHITE we propose an execution engine solely based on set operations and graph traversals. Our design is driven by the observation that different graph topologies expose different algorithmic requirements to the design of a graph traversal operator. We derive two graph traversal implementations targeting the most common graph topologies and demonstrate how graph-specific statistics can be leveraged to select the optimal physical traversal operator. To accelerate graph traversals, we devise a set of graph-specific, updateable secondary index structures to improve the performance of vertex neighborhood expansion. Finally, we introduce a domain-specific language with an intuitive programming model to extend graph traversals with custom application logic at runtime. We use the LLVM compiler framework to generate efficient code that tightly integrates the user-specified application logic with our highly optimized built-in graph traversal operators. Our experimental evaluation shows that GRAPHITE can outperform native graph management systems by several orders of magnitude while providing all the features of an RDBMS, such as transaction support, backup and recovery, security and user management, effectively providing a promising alternative to specialized graph management systems that lack many of these features and require expensive data replication and maintenance processes.

Although gas and liquid chromatography have emerged as dominant separation techniques in environmental analytical chemistry, these methods do not allow for the concurrent analysis of chemically diverse groups of persistent organic pollutants (POPs). There are also a small number of compounds which are not easily amenable to either of these traditional separation techniques. The main objective of this thesis was to address these issues by demonstrating the applicability of packed column supercritical fluid chromatography (pSFC) coupled to mass spectrometry (MS) in various aspects of environmental chemistry. First, pSFC/MS analytical methods were developed for legacy POPs (PCDDs, PCDFs, and PCBs) as well as the emerging environmental contaminant Dechlorane Plus (DP), and issues relating to the ionization of target analytes when pSFC was coupled to MS were explored. Novel APPI and APCI reagents (fluorobenzene and triethylamine) were optimized and real samples (water and soil) were analyzed to demonstrate environmental applicability. The possibility of chiral and preparative scale pSFC separations was then demonstrated through the isolation and characterization of thermally labile hexabromocyclododecane (HBCDD) stereoisomers. The analytical pSFC separation of the α-, β-, and γ-HBCDD enantiomers as well as the δ and ε meso forms was shown to be superior to results obtained using a published LC method. Finally, technical mixtures of phosphorus flame retardants (RBDPP, BPA-BDPP, and DOPO; a group of related compounds which are challenging to analyze concurrently) were examined using multiple analytical techniques and pSFC was found to be the only method which facilitated the accurate determination of the components of all 3 mixtures. This thesis confirms the potential of pSFC/MS as a fast, green, and cost effective means of separating and analyzing environmental contaminants.

Bubbly flows can be found in many applications in chemical, biological and power engineering. Reliable simulation tools of such flows that allow the design of new processes and optimization of existing one are therefore highly desirable. CFD-simulations applying the multi-fluid approach are very promising to provide such a design tool for complete facilities. In the multi-fluid approach, however, closure models have to be formulated to model the interaction between the continuous and dispersed phase. Due to the complex nature of bubbly flows, different phenomena have to be taken into account and for every phenomenon different closure models exist. Therefore, reliable predictions of unknown bubbly flows are not yet possible with the multi-fluid approach. A strategy to overcome this problem is to define a baseline model in which the closure models including the model constants are fixed so that the limitations of the modeling can be evaluated by validating it on different experiments. Afterwards, the shortcomings are identified so that the baseline model can be stepwise improved without losing the validity for the already validated cases. This development of a baseline model is done in the present work by validating the baseline model developed at the Helmholtz-Zentrum Dresden-Rossendorf mainly basing on experimental data for bubbly pipe flows to bubble columns, bubble plumes and airlift reactors that are relevant in chemical and biological engineering applications. In the present work, a large variety of such setups is used for validation. The buoyancy driven bubbly flows showed thereby a transient behavior on the scale of the facility. Since such large scales are characterized by the geometry of the facility, turbulence models cannot describe them. Therefore, the transient simulation of bubbly flows with two equation models based on the unsteady Reynolds-averaged Navier–Stokes equations is investigated. In combination with the before mentioned baseline model these transient simulations can reproduce many experimental setups without fitting any model. Nevertheless, shortcomings are identified that need to be further investigated to improve the baseline model. For a validation of models, experiments that describe as far as possible all relevant phenomena of bubbly flows are needed. Since such data are rare in the literature, CFD-grade experiments in an airlift reactor were conducted in the present work. Concepts to measure the bubble size distribution and liquid velocities are developed for this purpose. In particular, the liquid velocity measurements are difficult; a sampling bias that was not yet described in the literature is identified. To overcome this error, a hold processor is developed. The closure models are usually formulated based on single bubble experiments in simplified conditions. In particular, the lift force was not yet measured in low Morton number systems under turbulent conditions. A new experimental method is developed in the present work to determine the lift force coefficient in such flow conditions without the aid of moving parts so that the lift force can be measured in any chemical system easily.

The goal of this thesis is to investigate the functional role of the cortical column architecture within some of the existing brain coding theories. Here I focus on the hierarchical models of predictive coding and the 'phase of firing' coding hypothesis. Using an oddball paradigm consisting of a sequence of identical sounds interspersed with rare, unexpected sounds, one can observe a difference between the scalp potentials evoked by oddball and common sounds. This difference has been linked to predictive coding and novelty detection, and Stimulus Specific Adaptation (SSA) has been suggested as a likely substrate at the single neuron level. In order to simultaneously constrain hierarchical models of predictive coding, and so as to investigate the contributions that neural processing within the different cytoarchitectonic layers of the primary auditory cortex (A1) may make to SSA, I simultaneously recorded multi-unit activity and current source density (CSD) profiles across all layers in A1 of the rat in response to standard and oddball tones. Our results suggest that SSA arises at the level of the thalamocortical synapse and is further enhanced in the supragranular layers. The phase of low-frequency Local Field Potentials (LFPs) in primary sensory cortices carries stimulus related information and disambiguates the information about different stimuli evoking similar spike rates. However, it is yet unclear how these informative LFP phase values arise within the laminar organization of cortical columns. To address this issue, I performed CSD recordings in the area A1 of anaesthetized rats during the presentation of complex naturalistic sounds. Information theoretic analysis revealed that most LFP phase information originates from discrete CSD events consisting of strong granular-superficial-layer dipoles, likely triggered by bursts of thalamocortical activation. These events, which occur at rates of 2-4 Hz, reliably reset LFP phases at times of strong network excitation. They therefore provide a useful reference frame to measure neural activity with respect to salient times of stimulus history. CSD events display a diverse, stimulus-dependent morphology: these reflect the outcomes of cortical computations which result in varying extents of activation of infragranular output layers.