Upland peat catchments are usually assumed to function as carbon sinks, however, there have been extensive studies witnessing increasing trends in concentrations and fluxes of organic carbon in UK rivers over the last few decades. A number of controls on dissolved organic carbon (DOC) release from peatlands, such as climatic changes and landuse management, have been proposed. This study examines the effects of land use and management on organic carbon exports in the Dyke catchment of the River Halladale (northern Scotland) with a nested catchment approach. This study provides insight into the processes controlling the DOC dynamics in the Dyke catchment, and the impact of disturbance caused by landuse changes such as afforestation and tree felling for restoration. The results from factor analysis, end-member mixing, absorbance (E4/E6), and hysteresis analyses on stream water chemistry from individual sub-catchments identified the major hydrological pathways during storm events, and based on these results, conceptual models were developed to explain DOC evolution during storm events. At all the sites studied, nearsurface soil water was identified as the major controlling end-member for stream DOC concentrations. The calculated annual flux of DOC from the Dyke catchment, up-scaled from the results of the individual sub-catchments, is 521.6 kg C ha-1 yr-1, which is significantly (~5 times) higher than the previously published value (103.4 kg C ha-1 yr-1) for the River Halladale catchment (Hope et al., 1997). In this study, it is shown that about 57 - 95% of the DOC export occur during 5 - 10% of the high flows, therefore, it is crucial that quantitative records of DOC export are developed using high frequency storm event measurements, as well as lower frequency low flow sampling. Climatic changes related to precipitation, temperature, coupled with water yield capacity of the sub-catchments, are identified as significant controls on DOC fluxes, rather than landuse change, as the intact site releases more organic carbon per unit area compared to the disturbed and re-wetted site undergoing restoration. In addition, the results from this study provide landowners, policy makers and organisations with the evidence they require for initiating future peatland restoration works, as felling of forestry coupled with drain-blocking is shown to be an effective restoration technique that may help a catchment to eventually return to a near-pristine state.

Die in der vorliegenden Arbeit untersuchten Metall-Keramik-Verbunde wurden mittels Pulverspritzgießen hergestellt. Unter Anwendung der teilautomatisierten Verfahrensoptionen Mehrkomponentenspritzgießen und Inmould-Labelling, welches u. a. die Verwendung tiefgezogener Grünfolien beinhaltete, wurden hierzu 2K-Prüfkörpergeometrien (Zugstab, Biegebruchstab, Ringverbund) und 2K-Demonstratoren (Innenzahnrad, Fadenführer, Greifer) jeweils bestehend aus Stahl 17-4PH und ZrO2 (3%Y2O3), im Co-Sinterverfahren unter H2-Atmosphäre bei 1350°C, entwickelt. Schlüssel zur Darstellung schwindungskonformer ZrO2- und Stahl 17-4PH-Formgebungsmassen war der Angleich der Pulverpackungsdichte. Untersucht wurde neben der Werkstoff- und Gefügeausbildung das sich während dem Formgebungs- und Sinterprozess ausbildende Metall-Keramik-Interface sowie die sich bevorzugt in diesem Bereich manifestierenden Verbundeigenspannungen. Neben der stoffschlüssigen Versinterung beider Partner konnte eine Steigerung der Verbundfestigkeit durch Legierungsmodifikation unter Ausschluss technologischer Fehlerquellen erreicht und spezifiziert werden.:1 Einleitung und Zielstellung .................................................................................................5 2 Stand der Technik ..............................................................................................................6 2.1 Metall-Keramische-Verbundwerkstoffe und Werkstoffverbunde.....................................6 2.2 Werkstoffsystem ............................................................................................................6 2.2.1 Oxidkeramische Metall-Keramik-Verbunde.................................................................9 2.2.2 Nichtoxidkeramische Metall-Keramik-Verbunde........................................................15 2.3 Metall-Keramik-Interface..............................................................................................17 2.3.1 Stahl-Keramik-Komposite.........................................................................................21 2.3.2 Stahl-Keramik-Schichtverbunde................................................................................25 2.4 Konventionelle Verbindungs- und Fügetechnik.............................................................27 2.4.1 Kraft- und Formschluss.............................................................................................28 2.4.2 Lösbare Verbindungen .............................................................................................28 2.4.3 Nicht lösbare Verbindungen .....................................................................................29 2.4.4 Stoffschlüssige Verbindungen ..................................................................................30 2.5 Pulvertechnologische Verbindungs- und Fügetechnik ...................................................32 2.5.1 Co-Shaping..............................................................................................................34 2.5.2 Co-Firing..................................................................................................................38 2.6 Pulverspritzgießen........................................................................................................42 2.6.1 Prozesskette.............................................................................................................43 2.6.2 Werkstoffe...............................................................................................................45 2.6.3 Verfahrenscharakteristik...........................................................................................46 2.6.4 PIM in der industriellen Praxis ...................................................................................48 2.6.5 Mehrkomponentenspritzguss...................................................................................49 2.7 Prüfung und Spezifikation für spritzgegossene Metall-Keramik-Verbunde.....................52 2.7.1 zerstörende Prüfverfahren........................................................................................52 2.7.2 zerstörungsfreie Prüfverfahren .................................................................................55 2.7.3 Prädikative Methoden ..............................................................................................55 3 Experimenteller Teil..........................................................................................................57 3.1 Pulveranmusterung ......................................................................................................57 3.1.1 Feedstockherstellung und Charakterisierung ............................................................58 3.1.2 Grünfolienherstellung und Charakterisierung ...........................................................60 3.1.3 Thermische Analyse..................................................................................................62 3.2 Fertigungstechnologie..................................................................................................62 3.2.1 2-Komponentenpulverspritzgießen...........................................................................64 3.2.2 Folienhinterspritzen..................................................................................................64 3.2.3 Entbinderung und Sinterung ....................................................................................65 3.3 Werkstoff- und Verbundspezifikation...........................................................................66 3.3.1 Bestimmung der Dichte............................................................................................66 3.3.2 Dilatometrie.............................................................................................................66 3.5.2 Optische Interfaceanalyse.........................................................................................67 3.5.3 Mechanische Festigkeit ............................................................................................67 3.5.4 Röntgenographische Eigenspannungsanalyse ...........................................................68 4 Ergebnisdiskussion ...........................................................................................................70 4.1 Werkstoff- und Pulverauswahl .....................................................................................70 4.1.1 Untersuchungen zum Co-Sinterverhalten von Metall- und Keramikpulvern........................................................................................................78 4.1.2 Werkstoff- und Gefügeausbildung während der Co-Sinterung .................................85 4.2 Feedstock- und Bindersystem .......................................................................................92 4.2.1 Rheologische Eigenschaften .....................................................................................95 4.2.2 Thermisches Verhalten und Entbinderung ................................................................99 4.2.3 Verarbeitung von Feedstock und Grünfolie.............................................................101 4.3 Prüfkörperentwicklung...............................................................................................105 4.3.1 Gestaltungsoptionen..............................................................................................105 4.3.2 Verfahrensverifizierung ..........................................................................................106 4.3.3 Qualitative Bewertung der Verfahrensoption Inmould-Labelling..............................109 4.4 Werkstoffverbund.........................................................................................................112 4.4.1 Metall-Keramik-Interface........................................................................................112 4.4.2 Zugfestigkeit..........................................................................................................119 4.4.3 Verbundeigenspannungen .....................................................................................122 5 Zusammenfassung.........................................................................................................126 6 Literaturverzeichnis ........................................................................................................130 7 Abkürzungsverzeichnis...................................................................................................140 Anhang ................................................................................................................................141 A1 Spezifikation ZrO2-Feedstock Z1 .................................................................................142 A2 Spezifikation Stahl-17-4PH-Feedstock M1 ..................................................................143 A3 Rezeptur ZrO2-Folien ..................................................................................................144 A4 Rezeptur Stahl 17-4PH-Folien.....................................................................................145 A5 Prozessparameter – Spritzgießen (Bsp. Biegebruchstab 7x7x70mm)............................146 A6 Folienkonfektionierung – Bsp.- Demonstrator Greifer .................................................147 A7 Prozessautomatisierung – Bsp. Demonstrator Fadenführer..........................................148 A8 Spritzgegossene Demonstratoren – 2K-Spritzgießen...................................................149 A9 Spritzgegossene Demonstratoren – Inmould-Labelling................................................150 A10 Dilatometerschaubilder ..............................................................................................151 A11 Mikrozugproben ........................................................................................................152 A12 studentische Arbeiten ................................................................................................153

Multiphase flows abound in nature and enterprises. Our daily interactions with fluids - washing, drinking, and cooking, for example - occur at a free surface and within the realm of multiphase flows. The applications of multiphase flows within the context of emulsions, which are caused by mixing two immiscible fluids, have been of interest since the nineteenth century: compartmentalizing one fluid in another is particularly of interest in applications in pharmaceutical, materials, microfluidics, chemical, and biological engineering. Even more control in compartmentalization and delivery can be obtained through the usage of double emulsions, which are emulsions of smaller drops (i.e., inner drop) within larger drops (i.e., outer drop). The goal of this work is to understand the dynamic behavior of compound drops in confined flow at low Reynolds numbers. These behaviors include the migration patterns, limit cycles, and equilibrium locations in confined flows such as channel flows.<br> <br>Firstly, we look at non-concentric compound drops that are subject to simple shear flows. The eccentricity in the inner drop is either within the place of shear, normal to the plane of shear, or mixed. We show unreported motions that persist throughout time regardless of the initial eccentricity, given that the deformations of the inner and outer drops are small. Understanding the temporal dynamics of compound drops within the simple shear flow, one of the simplest background flows that may be imposed, allows us to probe at the dynamics of more complicated background flows.<br> <br>Secondly, we look at the lateral migration of compound drops in a Poiseuille flow. Depending on the initial condition, we show that there are multiple equilibria. We also show that the majority of initial configurations results in the compound drop with symmetry about the short wall direction. We then show the time it takes for the interfaces to merge if a given initial configuration does not reach the aforementioned symmetry.<br> <br>Thirdly, while the different equilibria of compound drops offer some positional differences at different radii ratio, we show that the lift force profiles at non-equilibrium locations offer distinctly different results for compound drops with different radii ratio. We then look at how this effect is greater than changes that arise due to viscosity ratio changes, and offer insights on what may create such a change in the lift force profile.

Indiana University-Purdue University Indianapolis (IUPUI) / In this research thesis, copper indium gallium selenium (CIGS) nanoparticles were synthesized from metal chlorides, functionalized to disperse in water, and further used in layer by layer (LbL) nanoassembly of CIGS films. CIGS nanoparticles were synthesized through the colloidal precipitation in an organic solvent. The peak and average sizes of the synthesized particles were measured to be 68 nm and 75 nm in chloroform, and 30 nm and 115 nm in water, respectively. Two methods were used to disperse the particle in water. In the first method the stabilizing agent oleylamine (OLA) was removed through multiple cleaning processes, and in the second method ligand exchange was performed with polystyrene sulfonate (PSS). Zeta potential of CIGS nanoparticles dispersed in water was measured to be +61 mV. The surface charge of the nanoparticles was reversed by raising the pH of the solution, which was measured to be −43.3 mV at 10.5 pH. In a separate process, the CIGS nanoparticles dispersed in water were coated with PSS. The resulting dispersion was observed to be stable and the surface charge was measured to be −56.9 mV. The LbL deposition process of CIGS nanoparticles was characterized by depositing thin films on quartz crystal microbalance (QCM). LbL depositions was conducted using (i) oppositely charged CIGS nanoparticles, (ii) positively charged CIGS nanoparticles and PSS, and (iii) PSS-coated CIGS (CIGS-PSS) and polyethyleneimine (PEI). The average thickness of each bi-layer of the above mentioned depositions were measured to be 2.2 nm, 1.37 nm, and 10.12 nm, respectively. The results from the QCM have been observed to be consistent with the film thickness results obtained from atomic force microscopy (AFM). Various immersion times versus thickness of the film were also studied. For electrical characterization, the CIGS films were deposited on indium tindioxide (ITO)-coated glass substrates. Current versus voltage (I/V) measurements were carried out for each of the films using the Keithley semiconductor characterization instruments and micromanipulator probing station. It was observed that the conductivity of the films was increased with the deposition of each additional layer. The I/V characteristics were also measured under the light illumination and after annealing to study the photovoltaic and annealing effects. It was observed that under light illumination, the resistivity of a 12-layer CIGS film decreased by 93% to 0.54 MΩ.m, and that of the same number of layers of PSS-coated CIGS and PEI film decreased by 60% to 0.97 MΩ.m under illumination. The resistivity of an 8-layer CIGS and PSS film decreased by 76.4% to 0.1 MΩ.m, and that of the same layers of PSS-coated CIGS and PEI decreased by 87% to 0.07 MΩ.m after annealing. The functionalized nanoparticles and the LbL CIGS films were implemented in the solar cell devices. Several configurations of CIGS films (p-type), and ZnO and CdS films (n-type) were considered. Poly(3,4-ethylenedioxythiophene) (PEDOT), molybdenum (Mo), and ITO were used as back contacts and ITO was used as front contact for all the devices. The devices were characterized the Keithley semiconductor characterization instruments and micromanipulator probing station. For a CIGS and n-ZnO films device with PEDOT as back contact and ITO as front contact, the current density at 0 V and under light illumination was measured to be 60 nA/cm2 and the power density was measured to be 0.018 nW/cm2. For a CIGS and CdS films device with ITO as both back and front contact, the current density at 0 V and under light illumination was measured to be 50 nA/cm2 and the power density was measured to be 0.01 nW/cm2. For a drop-casted CIGS and CdS films device with Mo as back contact and ITO as front contact, the current density of 50 nA/cm2 at 0 V and power density of 0.5 nW/cm2 under light illumination was measured. For the LbL CIGS and chemical bath deposited CdS films device with ITO as both back and front contact, the current density of 0.04 mA/cm2 at 0 V and power density of 1.6 μW/cm2 under light illumination was measured. Comparing to Device-III, an increase by 99% in the power density was observed by using the CIGS LbL film in the device structure. The novel aspects of this research include, (i) functionalization of the CIGS nanoparticles to disperse in water including coating with PSS, (ii) electrostatic LbL deposition of CIGS films using oppositely charged nanoparticles and polymers, and (iii) the utilization of the fabricated LbL CIGS films to develop solar cells. In addition, the n-type cadmium sulfide film (CdS) and zinc oxide (ZnO) buffer layer were also deposited through LbL process after the respective particles were functionalized with PSS coating in separate experiments.

M. Tech. (Department of Mechanical Engineering, Faculty of Engineering and Technology), Vaal University of Technology. / The purpose of this research was to develop optimal numerical solutions that can be employed during the design of cross bored thick-walled compound cylinders. The geometric design parameters of a cross bored compound cylinder that were optimized include shrinkage pressure, cross bore size, shape, location, and obliquity. Finite Element Analysis (FEA) modeling software called Abaqus version 2019 was used to generate numerical solutions. A total of 48 different part models were created and analyzed in this work. The generated FEA results from these models were validated using analytical solutions developed from Lame’s theory. The effects of shrinkage pressure on hoop stresses and Stress Concentration Factor (SCF) were studied to determine the optimal conditions. The optimum shrinkage pressure obtained was henceforth used for further analysis in this work. In addition, using one factor at time optimization technique, an optimization process was carried out to determine the optimal combination of the cross bore configuration geometry that gives minimum SCF. These parameters of cross bore configuration geometry include different sizes of either circular or elliptical-shaped cross bore, positioned at radial, offset, and/or inclined. The analyses of the effects of shrinkage pressure ranging from 4.4733 to 223.662 MPa on 11 different part models, established that the shrinkage pressure of 89.464 MPa generated the minimum SCF magnitude of 3.02. After analyzing 8 different circular cross bore size ratios ranging from 0.1 to 0.8, at the radial position, it was established that the hoop stress increases with an increase in a cross bore size. The smallest cross bore size ratio of 0.1 gave the lowest hoop stress and minimum SCF of 3.02. Whereas the highest stress was developed at the cross-size ratio of 0.8 with an SCF magnitude of 6.75. The minimum magnitude of SCF translates to a reduction of the pressure carrying capacity of the compound cylinder by 67% than a similar plain compound cylinder. Generally, offsetting of the circularly shaped cross bore from the radial position, led to a reduction of the magnitude of SCFs. For instance, from the 8 offset positions analyzed, the minimum SCF occurred at the offset position of 0.006 m with a magnitude of 2.50. This SCF magnitude indicated a reduction of pressure carrying capacity of 60% in comparison to a similar plain compound cylinder. Evaluation of 12 different diameter ratios of elliptical-shaped cross bore ranging from 0.5 to 10, at the radial position, established the lowest SCF magnitude of 1.33 that occurred at a diameter ratio of 5. Henceforth, this optimum diameter ratio was used for further analysis. This aforesaid SCF magnitude translated to a reduction of the pressure carrying capacity of the compound cylinder by 24.81% when compared to a similar plain compound cylinder. Besides, offsetting of elliptically shaped cross bore generally decreased the magnitudes of SCFs. Therefore, for elliptically shaped cross bore, the lowest SCF occurred at radial position with magnitude of 1.33. A general comparison between the effects of circular and elliptical cross bore, established that the elliptical-shaped cross bores generated both lower hoop stresses and SCFs than those of circularly shaped cross bores. On the other hand, oblique elliptical offset cross bores along the Z-axis of the compound cylinder led to an increase in SCFs. As the oblique angle increased from 0 0 to 75 0, the SCFs also increased progressively, however, there was a significant increase in SCF when the inclination angle increased from 60 0 to 75 0. The lowest and highest SCF magnitude was 1.52 and 1.92 at 15 0 and 6.19 at 75 0, respectively. Overall, the optimum geometric configuration of a cross bore in a thick compound cylinder was found to be elliptically shaped, offset at radial position which is an obliquity angle of 0 0 having a diameter ratio a/b of 5.

Thesis (M.A. (Translation Studies and Linguistics)) -- University of Limpopo, 2022 / The prime goal of this study is to explore, form and analyse the semantic content of compound words in Sepedi. The study used the qualitative method. Data were collected using participant observations from various written sources and it was analysed through Content Analysis. The Theory of Construction Morphology was tested on endocentric, exocentric, and copulative compound words to locate the headedness of Sepedi compound words. The study revealed that the head of compound words can be located on the nominal prefix, left-hand side, right-hand side, on both nominal prefixes and it can be determined outside of the compound word for metaphoric exocentric nominal compounds. Furthermore, because of the role noun class prefixes play on determining the head of compound words, the study found that Sepedi compound words are nominals. The formation of Sepedi compound words involves the combination of different word aspects such as objects concords, deverbatives, verbal roots, stems, suffixal endings, and lexical categories such as nouns, Adjectives, and verbs. The resultant compound word of these combinations always results in a compound noun. It was recommended that future researchers should investigate the semantic content of exocentric compound words in African languages, especially the Sepedi language. The study further highlighted that there is still a need for a study that looks at the influences of nominal prefixes on the headedness of compound words in Sepedi. Furthermore, the study recommended that to alleviate the gap of shortage of literature in Sepedi, future studies should focus on word formation processes in Sepedi. / Feenix Crowdfunding and C Track Fleet Management Solutions Pty Ltd

Doctor of Philosophy / Department of Physics / Jingyu Lin / Time-resolved deep ultraviolet (DUV) Photoluminescence (PL) spectroscopy system has been employed to systematically monitor crystalline quality, identify the defects and impurities, and investigate the light emission mechanism in III-nitride semiconducting materials and photonic structures. A time correlated single photon counting system and streak camera with corresponding time resolutions of 20 and 2 ps, respectively, were utilized to study the carrier excitation and recombination dynamics. A closed cycle He-flow cryogenic system was employed for temperature dependent measurements. This system is able to handle sample temperatures in a wide range (from 10 to 900 K). Structural, electrical, and morphological properties of the material were monitored by x-ray diffraction (XRD), Hall-effect measurement, and atomic force microscopy (AFM), respectively. Most of the samples studied here were synthesized in our laboratory by metal organic chemical vapor deposition (MOCVD). Some samples were bulk AlN synthesized by our collaborators, which were also employed as substrates for homoepilayer growth. High quality AlN epilayers with (0002) XRD linewidth as narrow as 50 arcsec and screw type dislocation density as low as 5x10[superscript]6 cm[superscript]-2 were grown on sapphire substrates. Free exciton transitions related to all valence bands (A, B, and C) were observed in AlN directly by PL, which allowed the evaluation of crystal field (Δ[subscript]CF) and spin-orbit (Δ[subscript]SO) splitting parameters exerimentally. Large negative Δ[subscript]CF and, consequently, the difficulties of light extraction from AlN and Al-rich AlGaN based emitters due to their unique optical polarization properties have been further confirmed with these new experimental data. Due to the ionic nature of III-nitrides, exciton-LO phonon Frohlich interaction is strong in these materials, which is manifested by the appearance of phonon replicas accompanying the excitonic emission lines in their PL spectra. The strength of the exciton-phonon interactions in AlN has been investigated by measuring the Huang-Rhys factor. It compares the intensity of the zero phonon (exciton emission) line relative to its phonon replica. AlN bulk single crystals, being promising native substrate for growing nitride based high quality device structures with much lower dislocation densities (<10[superscript]4 cm[superscript]-2), are also expected to be transparent in visible to UV region. However, available bulk AlN crystals always appear with an undesirable yellow or dark color. The mechanism of such undesired coloration has been investigated. MOCVD was utilized to deposit ~0.5 μm thick AlN layer on top of bulk crystal. The band gap of strain free AlN homoepilayers was 6.100 eV, which is ~30 meV lower compared to hetero-epitaxial layers on sapphire possessing compressive strain. Impurity incorporation was much lower in non-polar m-plane growth mode and the detected PL signal at 10 K was about an order of magnitude higher from a-plane homo-epilayers compared to that from polar c-plane epilayers. The feasibility of using Be as an alternate p-type dopant in AlN has been studied. Preliminary studies indicate that the Be acceptor level in AlN is ~330 meV, which is about 200 meV shallower than the Mg level in AlN. Understanding the optical and electronic properties of native point defects is the key to achieving good quality material and improving overall device performance. A more complete picture of optical transitions in AlN and GaN has been reported, which supplements the understanding of impurity transitions in AlGaN alloys described in previous reports.

Recent genomic data indicate that RNA polymerase II (Pol II) function extends beyond conventional transcription of primarily protein-coding genes. Among the five snRNAs required for pre-mRNA splicing, only the U6 snRNA is synthesized by RNA polymerase III (Pol III). Here we address the question of how Pol II coordinates the expression of spliceosome components, including U6. We used chromatin immunoprecipitation (ChIP) and high-resolution mapping by PCR to localize both Pol II and Pol III to snRNA gene regions. We report the surprising finding that Pol II is highly concentrated ∼300 bp upstream of all five active human U6 genes in vivo. The U6 snRNA, an essential component of the spliceosome, is synthesized by Pol III, whereas all other spliceosomal snRNAs are Pol II transcripts. Accordingly, U6 transcripts were terminated in a Pol III-specific manner, and Pol III localized to the transcribed gene regions. However, synthesis of both U6 and U2 snRNAs was α-amanitin-sensitive, indicating a requirement for Pol II activity in the expression of both snRNAs. Moreover, both Pol II and histone tail acetylation marks were lost from U6 promoters upon α-amanitin treatment. The results indicate that Pol II is concentrated at specific genomic regions from which it can regulate Pol III activity by a general mechanism. Consequently, Pol II coordinates expression of all RNA and protein components of the spliceosome.

Wheat-based thin stillage (W-TS) is liquid by-product of wheat ethanol production and contains valuable chemical intermediates such as 1,3-propanediol (1,3-PD), acetic acid, and glycerophosphorylcholine. Unfortunately, these compounds cannot be recovered/extracted easily due to the presence of high boiling point and hygroscopic solutes and unfermented particles from ethanol fermentation. Fermentation improvement study using endemic bacteria augmented with Lactobacillus panis PM1B discovered that glucose, incubation temperature, micronutrients, and pH adjustment affected two-stage fermentation (TSF). Importantly, fermentation could be scaled to a 210 L fermenter where 2% (w/v) 1,3-PD was produced. Unfermented particles should be removed prior to compound recovery. TSF was effective in producing solutions that were virtually free of colloids. Bacteria present in TSF system produced anoxic gas and exopolysaccharides and the combined action produced substantially clear solution. On the other hand, recovered particles, rich in lactobacilli, had a high protein content (50%, w/w, dry basis), which might be useful as an animal feed ingredient. Washing processes could lower moisture content and recover a high protein slurry (60% w/w, dry basis). Practical processes that incorporated fermentation using Lactobacilli could add substantial value to thin stillage and increase the value of products from ethanol production. These processes are scalable and readily implemented.

Thesis (MSc)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: See full text for abstract / AFRIKAANSE OPSOMMING: Sien volteks vir opsomming