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Μια βάση 621 πειραμάτων τοιχωμάτων οπλισμένου σκυροδέματος χρησιμοποιήθηκαν να ελεγχθούν παλαιά προσομοιώματα για τον υπολογισμό της αντοχής και της ικανότητας παραμόρφωσης του τοιχώματος υπό ανακυκλιζόμενη φόρτιση, και να αναπτυχθούν νέα. Βάσει του τρόπου αστοχίας που παρατηρήθηκε στο πείραμα, τα τοιχώματα κατηγοριοποιήθηκαν σε αυτά που αστόχησαν σε κάμψη, σε λοξό εφελκυσμό και σε λοξή θλίψη, ή σε ολίσθηση στη βάση. Τα παλαιότερα προσομοιώματα που ελέχθηκαν περιλαμβάνουν προσομοιώματα των Biskinis and Fardis [2010] και έχουν υιοθετηθεί στον Eurocode 8-Part 3 και/ή στον MC2010 για τον υπολογισμό της (α) καμπτικής αντοχής, (β) της διατμητικής αντοχής υπό ανακυκλιζόμενη φόρτιση μετά την καμπτική διαρροή (με εξάρτηση από τις ανελαστικές παραμορφώσεις) και (γ) την ικανότητα παραμόρφωσης (γωνία στροφής χορδής) στην καμπτική αστοχία. Τοιχώματα με λόγο διάτμησης μικρότερο του 1.2 εξετάζονται ξεχωριστά, καθώς η διατμητική τους αστοχία απαιτεί διαφορετικά προσομοιώματα: σχολιάζονται παλαιά προσομοιώματα και προτείνεται ένα νέο προσαρμοσμένο στα 130 τοιχώματα χαμηλού λόγου διάτμησης που δοκιμάστηκαν υπό ανακυκλιζόμενη φόρτιση. Ελέγχονται παλαιά προσομοιώματα για τον υπολογισμό της διατμητικής αντοχής σε ολίσθηση και προτείνεται ένα νέο προσαρμοσμένο στα 29 πειράματα τοιχωμάτων με αυτόν τον τρόπο αστοχίας: ένα νέο προσομοίωμα προτείνεται για την πιθανότητα μη-ελεγχόμενης ολίσθησης σε ένα κύκλο φόρτισης-αποφόρτισης όταν η ρωγμή είναι “διαμπερώς” ανοιχτή και μόνον η δράση βλήτρου του ακόμα ελαστικού διαμήκους οπλισμού παραλαμβάνει την τέμνουσα στη διατομή. Εκτός από την καλή συμφωνία της προβλεπόμενης διατμητικής αντοχής και/ή την ικανότητα παραμόρφωσης υπό ανακυκλιζόμενη φόρτιση, η πρόβλεψη του πιθανότερου τρόπου αστοχίας της βάσης είναι επίσης ικανοποιητική. / A database of 621 cyclic tests of RC walls is utilized to evaluate past models for the cyclic strength and deformation capacity of the wall and to develop/calibrate new ones. From the observed damage the failure mode is classified as in flexure, diagonal tension or compression before or after flexural yielding, or in sliding shear. Past models which are evaluated based on the test results include models proposed Biskinis and Fardis [2010] and adopted in Eurocode 8-Part 3 and/or MC2010 for the (a) flexural strength, (b) the cyclic shear strength after flexural yielding (as affected by the imposed ductility demand) and (c) the cyclic chord rotation capacity in flexure. Walls with height-to-length ratio less than 1.2 are considered separately, as their shear failure requires different models: past models are commented and a new one proposed and calibrated on the basis of 130 cyclic tests of squat walls. Past models for sliding shear strength are evaluated and modified on the basis of 29 cyclic tests with that failure mode: a new model is proposed for the possibility of uncontrolled sliding during a load reversal at a point in time when the flexural crack at the base is open throughout the section and only dowel action of the still elastic vertical bars is available to resist the shear force. Besides the good agreement of the predicted cyclic strength and/or deformation capacity per failure mode, the prediction of the most likely mode in the tests of the database is also satisfactory.

This thesis studies two particular bacterial outer membrane proteins called OmpC and Wzi, focusing on their expression, purification, crystallization and X-ray structure determination. A series of four naturally occurring OmpC mutants were isolated from a single patient with an E. coli infection of liver cysts. The isolated E. coli strains progressively exhibited increasing breadth of antibiotic resistance in which OmpC was predicted to take a partial role. We carried out an assay in which a strain of E. coli lacking OmpC was used to express the first (antibiotic sensitive) and the last (antibiotic resistant) of the clinical OmpC mutants and drug permeation assessed. Single channel conductance measurements were carried out and the X-ray structures for all the isolates were determined. Protein stability was assessed. With these data we propose that changes in the transverse electric field, not the pore size, underlie the clinically observed resistance to the antibiotics. This is the first demonstration of this strategy for antibiotic resistance. Wzi is a novel outer membrane protein involved in the biosynthesis and translocation mechanism of the K30 antigen from E. coli. The mechanism is a complicated process that requires several proteins including outer and inner membrane proteins. The protein Wzi was expressed, purified and crystallized. Initial crystals were tested and diffracted to 15Å. After optimization, a crystal diffracting to 2.4Å has been obtained.

This thesis discusses the results of experimental tests on two post-tensioned timber core-walls, tested under bi-directional quasi-static seismic loading. The half-scale two-storey test specimens included a stair with half-flight landings. Multi-storey timber structures are becoming increasingly desirable for architects and building owners due to their aesthetic and environmental benefits. In addition, there is increasing public pressure to have low damage structural systems with minimal business interruption after a moderate to severe seismic event. Timber has been used extensively for low-rise residential structures in the past, but has been utilised much less for multi-storey structures, traditionally limited to residential type building layouts which use light timber framing and include many walls to form a lateral load resisting system. This is undesirable for multi-storey commercial buildings which need large open spaces providing building owners with versatility in their desired floor plan. The use of Cross-Laminated Timber (CLT) panels for multi-storey timber buildings is gaining popularity throughout the world, especially for residential construction. Previous experimental testing has been done on the in-plane behaviour of single and coupled post-tensioned timber walls at the University of Canterbury and elsewhere. However, there has been very little research done on the 3D behaviour of timber walls that are orthogonal to each other and no research to date into post-tensioned CLT walls. The “high seismic option” consisted of full height post-tensioned CLT walls coupled with energy dissipating U-shaped Flexural Plates (UFPs) attached at the vertical joints between coupled wall panels and between wall panels and the steel corner columns. An alternative “low seismic option” consisted of post-tensioned CLT panels connected by screws, to provide a semi-rigid connection, allowing relative movement between the panels, producing some level of frictional energy dissipation.

The linear receptivity and stability of plane idealized detonation with one-step Arrhenius type reaction kinetics is explored in the case of three-dimensional perturbations to a Zel'dovich-von Neumann-Doering base flow. This is explored in both overdriven and explicitly Chapman-Jouguet detonation. Additionally, the use of a multi-domain spectral collocation method for solving the conventional stability problem is explored within the context of normal-mode detonation. An extension of the stability analysis to confined detonations in a slightly porous walled tube is also carried out. Finally, an asymptotic analysis of a detonation with two-step reaction kinetics in the limit of large activation energy and for general overdrive and reaction order is performed yielding a nonlinear evolution equation for perturbations that produce stable limit cycle solutions.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, in fulfilment of the requirements for the degree of Master of Science Johannesburg 2017. / Pre-colonial Stone Walled Structures (SWS) in southern Africa have been studied since the 17th Century. Studies focused on establishing the origins of SWS, classification and other socio-economic components associated with these settlements. The physical environment played a significant role in shaping these communities, therefore making it important to establish the correlation between these pre-colonial cultures and the physical environment. Using Google Earth and GIS Sadr and Rodier (2012) undertook a settlement analysis of a 350 area near the Suikerbosrand nature reserve in southern Gauteng. They observed that settlement patterns revealed a shift from small and dispersed egalitarian societies to more stratified communities between the 15th and 19th century. Using the same techniques that Sadr and Rodier (2012) employed, a settlement pattern analysis was conducted on the rest of the research area in southern Gauteng which is slightly under 9000. Results from an exploratory and a statistical analysis from the research area revealed observations made by Sadr and Rodier 2012 from a 350 concur with the observations made from the rest of the study area. / LG2018

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Integral membrane enzymes contribute a unique repertoire to the cell, as they are capable of synthesizing products from substrates of different chemical character at the membrane-water interface. Membrane-embedded enzymes are often responsible for the synthesis of important components of the cellular membrane and contribute to the structural integrity of the cell, maintenance of cellular homeostasis and signal transduction. One of the main focuses of Dr. Filippo Mancia’s laboratory is understanding how enzymes complete these functions by investigating, at an atomic level, the determinants of substrate binding and catalysis within the membrane and at the membrane surface. Here I will present my investigation of two such integral membrane enzyme systems, which are responsible for the synthesis and processing of membrane-embedded molecules in bacteria. Phosphatidylinositol-phosphate Synthase (PIPS) Phosphaitylinositol (PI) is an essential lipid component in mycobacteria, demonstrated by loss of viability when PI is reduced to 50% of wild-type levels. Phosphatidylinositol (PI) is required for the biosynthesis of key components of the cell wall, such as the glycolipids phosphatidylinositol-mannosides, lipomannan and lipoarabinomannan. For these molecules, PI serves as a common lipid anchor to the membrane. In Mycobacterium tuberculosis, the disease causing pathogen of tuberculosis, these glycolipids function as important virulence factors and modulators of the host immune response. Therefore, the enzyme responsible for PI synthesis in this organism is a potential target for the development of anti-tuberculosis drugs. The defining step in phosphatidylinositol biosynthesis is catalyzed by a member of the CDP-alcohol phosphotransferase enzyme family. The enzyme uses CDP-diacylglycerol as the donor substrate, and either inositol in eukaryotes or inositol-phosphate in prokaryotes as the acceptor alcohol of the synthesis reaction. In prokaryotes, phosphatidylinositol-phosphate synthase (PIPS; a member of the CDP-alcohol phosphotransferase family) catalyzes this reaction to yield phosphatidylinositol-phosphate, which is then dephosphorylated to PI by an uncharacterized enzyme. Structures of PIPS from Renibacterium salmoninarum (RsPIPS), with and without bound CDP-diacylglycerol, have revealed the location of the acceptor site as well as molecular determinants of substrate specificity and catalysis of the enzyme. However, RsPIPS has low activity relative to PIPS from Mycobacterium tuberculosis (MtPIPS) and the two share only 40% protein sequence identity. Therefore, these initial structures have limited potential for meaningful homology modeling and drug design. Presented here are the structures of PIPS from Mycobacterium kansasii (MkPIPS), which is 86% identical to MtPIPS, in an apo state to 3.1 Å resolution, in a nucleotide-bound state to 3.5 Å resolution, and in a novel ligand-bound state to 2.6 Å resolution. This work provides a structural and functional framework to understand the mechanism of phosphatidylinositol-phosphate biosynthesis in the context of mycobacterial pathogens. RodA-PBP2 Complex The cell wall of most gram-negative and gram-positive bacteria (excluding atypical bacteria such as members of Mycoplasmataceae) is composed of peptidoglycan, a mesh of repeating carbohydrates (N-acetylmuramic acid, MurNAc, and N-acetylglucosamine, GlcNAc) cross-linked by small peptides. Peptidoglycan is essential for growth, division and viability of the organism. Any disruption of the biosynthesis of peptidoglycan, whether by genetic mutation, inhibition with antibiotics or degradation by lysozyme, results in bacterial cell lysis. Peptidoglycan helps maintain cell shape and serves as an anchor for accessory proteins and other cell wall components. As essential components of the cell wall, enzymes contributing to the peptidoglycan biosynthetic pathway can be exploited as antibiotic targets. After a hydrophilic peptidoglycan precursor (UDP-MurNAc-pentapeptide) is synthesized in the cytosol, it is attached to the lipid carrier undecaprenyl phosphate (UndP). The lipid-linked precursor (undecaprenyl-pyrophosphoryl-MurNAc-pentapeptide or Lipid I) is modified further to undecaprenyl-pyrophosphoryl-MurNAc-(pentapeptide)-GlcNAc (Lipid II) by addition of a GlcNAc moiety. Lipid II is then flipped across the membrane to the periplasm where its sugars are polymerized to form the glycan strands of the peptidoglycan mesh. SEDS proteins, essential for maintaining bacterial processes that determine shape, elongation, cell division and sporulation, are integral membrane enzyme that have been implicated in this process as either Lipid II flippases, glycosyltransferases responsible for sugar polymerization, or both. SEDS proteins are also known to form a functional complex with type b penicillin-binding proteins (PBPs), which are known as transpeptidase enzymes, responsible for the crosslinking of peptides in the formation of the peptidoglycan mesh. Though structures of both RodA (a SEDS protein involved in bacterial growth and elongation) and type b PBPs are available, the interaction between the two proteins and their joint enzymatic activity is poorly characterized. Here, I present the preliminary structural characterization of a RodA-PBP2 protein complex by single-particle cryo-electron microscopy (cryo-EM). We hope this ongoing work will contribute to the understanding of these enzymes and to the development of antibiotics to combat antibiotic resistance.

No description available.

Construction practices are constantly evolving in order to adapt to physical locations and economic conditions. These adaptations may result in more cost-effective designs, but may also come at a cost of strength. In masonry shear walls, it is becoming more common to reduce the amount of grouting from every cell to only those with reinforcement, a practice known as partial-grouting. Partially-grouted masonry responds differently and in a more complex matter to lateral loads as compared to fully-grouted masonry. The response is made even more complex by wall discontinuities in the form of openings. The main objective of this study is to validate the strut-and-tie procedure for the in-plane lateral strength prediction of partially-grouted, multistory, reinforced concrete masonry walls with openings. The research included testing six three story, half-scale masonry shear walls. Half of the walls had door openings while the other half had window openings. The configurations were selected to represent typical walls in multi-story buildings. The measured lateral strength was compared to estimations from the equations in the US masonry code and to those from an equivalent truss model and a strut-and-tie model. The results show that the U.S. masonry code equations over predicts while the equivalent truss model under predicts the lateral strength of the walls. The results further show that the strut-and-tie model is the most accurate method for lateral strength prediction and is able to account for wall openings and partial-grouting.