Zur Beantwortung der Frage, wie sich die festigkeitssteigernden Effekte aus mehraxialer und dynamischer Druckbelastung in Beton überlagern wurde ein weltweit einzigartiger zweiaxialer Split-Hopkinson-Bar entwickelt. Es wurden umfangreiche Versuchsserien mit insgesamt mehr als 2500 Einzelversuchen durchgeführt. Ermittelt wurden dabei die ein- und zweiaxialen statischen und dynamischen Betondruckfestigkeiten zweier Betone der Druckfestigkeitsklassen C20/25 und C40/50. Die Versuchsergebnisse wurden hinsichtlich der Festigkeitsentwicklung in Abhängigkeit vom Spannungsverhältnis und der Dehnrate ausgewertet. Die Ergebnisse aus den zweiaxialen dynamischen Betondruckversuchen konnten als dreidimensionale Abhängigkeit der Spannungen in beiden Belastungsachsen von der Dehnrate für jede der beiden Betonsorten abgebildet werden. Aus den Ergebnissen wurde ein Ingenieurmodell für jede Betonsorte entwickelt, welches die Betondruckfestigkeitsentwicklung in Abhängigkeit vom Spannungsverhältnis und der Dehnrate beschreibt. Mit zunehmender Dehnrate wird die zweiaxiale Ergebniskurve um einen zusätzlichen, dynamischen Anteil der Festigkeitssteigerung vergrößert. Dabei kommt es aber nur zu einer teilweisen Überlagerung der beiden betrachteten festigkeitssteigernden Einflüsse. Eine Abschätzung der Größenordnung der jeweiligen Einflüsse aus Mehraxialität und hoher Belastungsgeschwindigkeit konnte durch eine entsprechend differenzierte Auswertung vorgenommen werden. Die Untersuchung der Bruchstücke der zerstörten Probekörper zeigte, dass die Verteilung der Partikelgröße stark von der Dehnrate abhängig ist. Im Gegensatz dazu hängt die Partikelgeometrie und die Form und Masse der entstehenden Kernbruchstücke vom Spannungsverhältnis ab.

The box corer is a relatively new tool used in the geotechnical community for collection of soft seabed sediments. Miniature full flow and model pipeline probes were developed as tools to characterize and obtain soil parameters of soft seabed sediments collected in the box core for design of offshore pipelines and analysis of shallow debris flows. Probes specifically developed for this study include the miniature t-bar, ball, motorized vane (MV), and toroid. The t-bar, ball, and MV were developed to measure intact and remolded undrained shear strengths (su and sur). The t-bar and ball can obtain continuous strength profiles and measure sur at discrete depths in the box corer while the MV measures su and sur at discrete depths. The toroid is a form of model pipeline testing which was developed to investigate pipe-soil interaction during axial pipeline movement. Vertical loading and displacement rates can be selected for the toroid to mimic axial pipeline displacement for a variety of pipe weights. A load frame for both miniature penetrometer and toroid testing was developed for testing directly on box core samples offshore. This research presents results from offshore and laboratory testing of the box core and recommended testing procedures for full flow and toroid probes on box core samples.

The current state of the research about dolia in roman bar counters suggest that they were used as wine storage. This exposition has been prevalent within the field for a long time and is based on untried 19-century research. Ardle MacMahon is one of the few who have questioned this interpretation, and who thinks that dolia are unsuitable for wine storage. It is from this premise that this study aims to reconsider the thesis that dolia in bar counters were used for wine. The main material for this study is dolia and as a point of reference amphorae. The other material is the bars in Pompeii and Ostia. These are two fundamental different towns, and the bars have their own characteristics that separate them, Ostia has no dolia in its bar counters. The secondary material is the ancient sources from which a contextualization of both the bars and the dolia can be made. The analysis is done through close reading and a spatial analysis. The result of this study is that dolia are not suitable for wine storage in bar counters. Dolia are better suited for storage of dry foodstuffs like legumes, nuts and dried fruit. The wine were more likely kept in amphorae on wooden racks behind the bar counter. / Den rådande forskningen kring dolia i romerska bardiskar menar att de använts till vinförvaring. Denna tolkning har varit framträdande inom området under en lång tid och grundar sig i oprövad forskning från 1800-talet. Det finns dock några såsom Ardle MacMahon som menar att dolia inte lämpar sig till vinförvaring i bardiskar. Med denna utgångspunkt ämnar denna uppsats ompröva den rådande tesen att dolia i barer var för vin. Det huvudsakliga materialet som analyseras är dolia i största allmänhet och en jämförelse med amforor. Det andra materialet är krogar i Pompeji och Ostia som är fundamentalt olika i det faktum att Ostia saknar dolia i bardiskar. Det sekundära materialet är antika texter som kontextualiserar både krogar och dolia för att sedan diskutera dess signifikans. Materialet nås genom en rumslig analys och närläsning. Resultatet av denna uppsats konstaterar att dolia i bardiskar inte lämpar sig för vinförvaring utan snarare för torra varor såsom legymer, nötter och torkad frukt. Vinet förvarades mer troligtvis i amforor på hyllor bakom baren.

The need for efficient, lightweight armour solutions has never been so great as it is today. Increasing numbers of personnel, both military and civilian are being placed in an expanding variety of life-threatening situations, and we must recognise the responsibility to maximise their combat survivability. One way to help protect these people is to provide them with some form of armour. Advanced polymeric materials are finding an increasing range of industrial and defence applications. These materials have the potential to improve the performance of current armour systems, whilst also reducing their cost and weight. Polymers may be reinforced with the addition of nanofillers such as carbon nanotubes or graphene, to produce nanocomposites, an exciting emerging polymer technology. Nanomaterials have been shown to exhibit extraordinary strength, far higher than that of traditional armour materials. Nanocomposites have the possibility of being remarkable materials, with high strength and light weight. The work detailed in this report is an investigation into the mechanical properties of nanocomposites along with some novel blended polymer composites. Two compressive testing techniques have been used to carry out this investigation. The intermediate strain-rate Optical Drop-Weight, and the high strain-rate Split-Hopkinson Pressure Bar. The latter required some significant modifications in order to optimise it for use with low-density polymers. Ultimately, nanocomposites were found to behave virtually indistinguishably from the monolithic polymer matrices. Yield strengths and energy absorption characteristics remained inside the ordinary experimental scatter. Blended composites, in which a long chain length polymer is combined with a chemically similar polymer with a shorter chain length, proved to be more interesting. Yield strengths of these novel materials were increased over that of either constituent material, although energy absorption remained low.

<p>Rho GTPase signaling regulates a wide variety of cellular functions in the developing and adult central nervous system. These molecular switches are in turn spatially and temporally regulated by an over abundance of positive and negative regulatory proteins: the activating guanine nucleotide exchange factors (GEFs) and the deactivating GTPase activating proteins (GAPs). The WAVE-associated Rac GAP (WRP) is thought to regulate key aspects of synapse development and function, and has been implicated in a form of mental retardation in humans called 3p- Syndrome. WRP is a member of the srGAP family of Rho GAP domain containing proteins, which share a characteristic domain organization and are expressed throughout the brain. Recently, one of the members of this family was found to contain a newly described inverse F-BAR (IF-BAR) domain of unknown function and to regulate cortical migration in developing neurons. This study focuses on the regulatory capacity of WRP during the development of neuronal connections in the central nervous system, and what role its loss may have on cognitive functions.</p><p>To assess these roles, biochemical studies were performed to characterize the way in which WRP's novel IF-BAR domain interacted with lipid membranes. Additionally, WRP's role in regulating neuronal function was assessed both in vitro and in vivo through the use of mouse model systems for critical genes in the WAVE complex pathway, including a conditional WRP KO mouse developed in our lab. Finally, because WRP is implicated in mental retardation, behaviors of WRP heterozygous and null mice have been evaluated.</p><p>This study shows that WRP's IF-BAR domain senses, or facilitates, outward membrane protrusions through a convex lipid-binding surface of the dimerized WRP IF-BAR domain. WRP localizes to the membranes of dendritic shafts via its IF-BAR domain where it is enriched in filopodia like projections. During dendritic filopodia formation, WRP functions to regulate the WAVE-1 complex and its downstream effectors, including the Arp2/3 complex. Loss of WRP in vivo and in vitro results in a reduction of dendritic spines, and that this is a function of WRP's role in the initiation of dendritic filopodia, not during the maturation of dendritic filopodia into mature dendritic spines. Finally, this study demonstrates that the loss of WRP results in deficits in learning and memory, linking WRP to the cognitive deficits seen in 3p- syndrome.</p> / Dissertation

More and more, advanced polymer and composite materials are being applied in engineering situations where a high resistance to loading at high rates of strain, such as by impact or blast deformation, are a vital requirement. Specific examples exist in the fields of defence and sport research and development for personal, and in the case of the former, vehicular, protection. There are obvious advantages to the use of polymer materials for these applications in augmenting the more widely used metals and ceramics, most notably the evident reduction in weight, and it is believed that with suitable nano-reinforcement these materials may exhibit improved combat survivability. The current study concerns the effect that nano-reinforcements in the form of Carbon Black, Titanium Dioxide, Exfoliated Hectorite Nanoclay and Carbon Nanotubes; have upon the high strain rate mechanical properties of structural variants of Polyethylene (Linear Low Density Polyethylene, LLDPE; High Density Polyethylene, HDPE; Ultra-High Molecular Weight Polyethylene, UHMWPE) and blends of UHMWPE and HDPE. The testing samples were manufactured using a novel process developed in the Loughborough University Materials Department, which has produced well-dispersed specimens. The formed nanocomposite samples were studied using an in-house four-bar Split Hopkinson Pressure Bar (SHPB) system for high strain rate performance, instrumented dropweight for intermediate strain rates and a conventional commercial Hounsfield H50KM universal testing machine for quasi-static strain rate compressive tests. The experimental results recorded for un-reinforced materials are used as a reference to allow comparative analysis of any effect the nano-reinforcements or the blending process have upon the structure, performance and properties of the composite material. From the mechanical testing, it was seen that the stress-strain behaviour of Polyethylene is highly strain-rate-dependent, as plots of the average representative yield stress as a function of strain rate show a bilinear relationship when plotted on a logarithmic strain rate scale, with the gradient of the curve rising sharply at around 103s-1. Concerning the addition of the nanofiller materials, it was seen that there was an increase in the flow and yield stresses and the energy absorption characteristics of the resulting composite with the magnitude dependent upon whether it was a pure or blended polymer that was reinforced. Of the aforementioned fillers it was seen that the addition of Carbon Nanotubes in the small concentrations studied resulted in the greatest increase in properties compared to the pure polymers, closely followed by the Carbon Black fillers. Also of note, the un-reinforced blended samples showed significant increases in flow stress, yield stress and energy absorption when compared to the constituent UHMWPE and HDPE polymers. Additionally, a complete set of Differential Scanning Calorimetry and density measurements were made before testing to assess any changes in the properties after reinforcement or blending, and to help in the interpretation of the results from the different mechanical tests.

Denna studie handlar om den matematiska strategin bar modeling som är tagen från undervisingen i Singapores skolor. Syftet med studien är undersöka om bar modeling fungerar som matematisk strategi och hur eleverna upplever arbetssättet. Utöver att studera metoden i praktiken studeras också hur lärarna uppfattar bar modeling.        För att studera bar modeling och vad lärare har att säga om arbetssättet har två metoder använts; fem observationer av elevgrupper och fem intervjuer med lärare. Detta för att ta reda på elevernas respektive lärarnas uppfattning om metoden.     Resultatet i studien visar att lärarna är överrens om att bar modeling mycket väl kan hjälpa många elever vid problemlösningar. Alla lärare ser det simpla sättet att förenkla svåra och komplicerade matematiska problem som metodens största fördel. Observationerna av elevgrupperna visade att metoden underlättade processen av att lösa problemet när uppgifter var matematiskt utmanande. Något lärarna såg som en nackdel är att det kan vara svårt att få med en hel skola eller i alla fall sitt arbetslag att börja arbeta med den nya metoden. Vidare visade också resultatet från observationerna att metoden gav ett bra stöd vid problemlösningar som är mer utmanande rent kunskapsmässigt.

Call number: LD2668 .T4 1986 S53 / Master of Science / Civil Engineering

Call number: LD2668 .T4 1986 Y362 / Master of Science / Civil Engineering

In this study the patterns of sediment transport and deposition in the channels and receiving basin of a crevasse splay in the modern Mississippi River delta are examined, with emphasis on the development of a distributary mouth bar. Simultaneous hydroacoustic and optical measurements on the mouth bar show that the bar conforms to the progradational stage of an existing conceptual model of mouth bar development. This is confirmed by cores dated using Beryllium-7, which provides a record of the deposition on the bar over a 90-day period. Stratigraphic data from cores obtained on the bar are used to extend the conceptual model to account for variable riverine inputs. A numerical model, developed and validated using field data is capable of representing the fundamental sedimentary processes responsible for mouth bar progradation. These results will be of interest to coastal geologists, engineers and coastal managers alike.