A multiphysics finite element model of the wood cell wall

Timber is a highly complex naturally occurring material, with properties adapted to its local environment. These properties, on its many length scales, determine its strength and stiffness and also how it interacts with moisture in the environment, causing dimensional instability both during drying and its lifetime as a construction material. Of particular importance is how the cell wall polymers interact with moisture in the environment and how this effects the properties, due to their strong dependence on intra-molecular hydrogen bonds. To model the dimensional behaviour of a wood cell under varying moisture conditions, the cell wall polymer matrix is modelled using a formulation of coupled deformation and moisture transport. These governing equations of mass and linear momentum conservation are strongly coupled and nonlinear, and solved using the Finite Element Method. The associated constitutive equations are complex. The free energy is described through the deformation of the polymer matrix and the mixing with solvent (in this case, water). It is assumed that the polymer chains and water molecules are incompressible so that a change in volume of the polymer matrix corresponds to a change in the number of solvent molecules. The viscoelastic behaviour is resolved using a Zener spring-dashpot model, capturing both creep and relaxation phenomena, and the moisture transport is resolved using Fick’s 2nd Law. The effects of wetting on the stiffness and relaxation characteristics of the polymer matrix is taken into account through the chemical kinetics of hydrogen bond dissociation. The implementation using the finite element method is discussed in detail and comprehensively verified using a series of numerical tests. Finally, the model is applied to wood cells and the behaviour of the polymers is compared to experimental findings. The resulting model is capable of predicting the interaction between viscoelastic material effects and diffusion and has the ability to predict viscoelastically limited diffusion within wood cell polymers. The model can also predict sorption hysteresis in wood cell wall polymers and therefore could be a valuable tool in future research into wood-water interactions

Development of advanced technologies for the fabrication of III-V high electron mobility transistors

Over the past 5 years there has been an increase in the number of applications that require devices that operate in the millimetre range (30-300GHz). This demand has driven research into " devices that will operate at frequencies above 100GHz. This performance has been achieved using two main technologies, the Heterojunction Bipolar Transistor (HBT) and the High Electron Mobility Transistor (HEMT). At present it is a HEMT device that holds the record for the highest operating frequency of any transistor. It is this technology that this project concentrates on. In order to fabricate devices that operate at these frequencies two methods are commonly employed. The first is to vary the material of the device, in particular, increasing the indium content of the channel. The second method is to reduce the physical dimensions of the transistors, including reducing the gate length of the device therefore reducing transit time and gate capacitance. Reducing the separation of the source-drain ohmic contacts or employing a self-aligned ohmic strategy reduces the associated parasitic resistances. This project will concentrate on the scaling of the gate length in addition to the reduction of parasitic resistances with the use of self-aligned ohmic contacts.This work includes the realisation of the first self-aligned 120nm T -Gate. GaAs pHEMT fabricated at the University of Glasgow. These devices required the development of two key technologies, the non-annealed ohmic contact and the succinic acid based selective wet etch. The self-aligned devices showed good RF performance with a ft of 150 GHz and a fmax of 180 GHz which compares favourable with results o~ 120nm GaAs pHEMTs previously fabricated at Glasgow. The investigation of gate length scaling to device performance included the development of two lithographic process capable of producing HEMT with a gate length of 50nm and 30nm respectively in addition to a method ~f sample preparation that allows these devices to be analysed using TEM techniques. This work has lead to the realisation of SOnm T -gate metamorphic HEMTs using a PMMAIcopolymer resist stack, these devices displayed an excellent yield, with over 95% of devices working. The uniformity of the gate process was also high with a threshold voltage of - 0.44SV with a standard deviation of O.OOSV. The devices demonstrated an .it of 330GHz and a fmax of 260GHz making these devices some of the fastest transistors that have ever been fabricated on a GaAs substrate. The second lithography process was developed to realise T -gates with a gate length of less than SOnm. This processed used a two stage "bi-lithography" process to minimise the effect of forward s7attering through the resist. The gate footprint was transferred into a Si02 gate by a dry etch process. This lithography process was integrated into a full process flow for lattice matched InP HEMTs Using this process, HEMTs were fabricated with a T-gate of 2Snm. This is the smallest T -gate device that has been fabricated at the University of Glasgow and is comparable with the smallest HEMT devices in the world

Abdominal functional electrical stimulation to improve respiratory function in acute and sub-acute tetraplegia

An injury to the cervical region of the spinal cord can cause paralysis affecting all four limbs, termed tetraplegia. People with tetraplegia also have paralysis or impaired function of the major respiratory muscles, namely the diaphragm and intercostal and abdominal muscles. This often reduces respiratory function, with associated respiratory complications a leading cause of morbidity and mortality for this population. Abdominal Functional Electrical Stimulation (AFES), the application of electrical pulses to the abdominal muscles causing them to contract, has been shown to improve respiratory function in tetraplegia. Despite these positive results, further work is needed to establish AFES as a standard clinical treatment. The aim of this thesis is to support the clinical introduction of AFES. This was achieved by addressing two primary objectives. Firstly, the development of new technologies and protocols to optimise AFES for use in a clinical setting. Secondly, the clinical evaluation of these technologies and protocols with tetraplegic patients. For research purposes, AFES has typically been applied manually, requiring an operator to synchronise stimulation with respiratory activity. One important step necessary for the clinical introduction of AFES is the development of an automated AFES device that can apply stimulation in synchrony with the users respiratory activity, with different stimulation parameters applied for different breath types such as a quiet breath and a cough. In this thesis, the signal from a non-intrusive respiratory effort belt, worn around the chest, was used to develop a statistical classifcation algorithm capable of classifying respiratory activity in real-time, and applying AFES in synchrony with the user's respiratory activity. The effectiveness of AFES can also be enhanced by stimulating at the abdominal muscle motor points. In this thesis the positions of the abdominal motor points were located systematically for the frst time, in ten able bodied and five tetraplegic participants. To aid the clinical introduction of AFES it is necessary to establish the patient groups who would benefit most from this intervention, and to develop appropriate clinical protocols. This is addressed in two clinical studies, where the feasibility and effectiveness of AFES to improve the respiratory function of the acute ventilator dependant and sub-acute tetraplegic populations was demonstrated. In the first study, conducted with 10 acute ventilator dependant tetraplegics, AFES was applied on alternate weeks for a total duration of eight weeks. This resulted in acute improvements in breathing and led to a longitudinal increase in respiratory function over the study duration. It was found that participants weaned from mechanical ventilation on average 11 days faster than matched historic controls. Previous work, which investigated the effect of a three week AFES training programme on the respiratory function of people with sub-acute tetraplegia, suggested that an extended AFES training programme may be more effective. In the second clinical study in this thesis, a continuous eight week AFES training protocol (combined with a six week control period) was evaluated with three sub-acute tetraplegic participants. The application of AFES led to an acute increase in respiratory function, with a longitudinal improvement in respiratory function observed throughout the study. In a single participant case study, the feasibility of combining AFES with assisted coughing delivered by mechanical insufflation-exsufflation was demonstrated for the first time. This was shown to lead to an acute improvement in respiratory function at six of the eight assessment sessions, indicating that this technique could be used to aid secretion removal. This thesis highlights the feasibility and effectiveness of AFES to improve the respiratory function of the acute ventilator dependant and sub-acute tetraplegic populations. The clinical protocols that enable AFES to be used with these patient groups, and the technological developments detailed throughout this thesis, are an important step towards the introduction of AFES as a regular treatment modality

Nitrogen-Fixing Symbiotic Paraburkholderia Species: Current Knowledge and Future Perspectives

A century after the discovery of rhizobia, the first Beta-proteobacteria species (beta-rhizobia) were isolated from legume nodules in South Africa and South America. Since then, numerous species belonging to the Burkholderiaceae family have been isolated. The presence of a highly branching lineage of nodulation genes in beta-rhizobia suggests a long symbiotic history. In this review, we focus on the beta-rhizobial genus Paraburkholderia, which includes two main groups: the South American mimosoid-nodulating Paraburkholderia and the South African predominantly papilionoid-nodulating Paraburkholderia. Here, we discuss the latest knowledge on Paraburkholderia nitrogen-fixing symbionts in each step of the symbiosis, from their survival in the soil, through the first contact with the legumes until the formation of an efficient nitrogen-fixing symbiosis in root nodules. Special attention is given to the strain P. phymatum STM815T that exhibits extraordinary features, such as the ability to: (i) enter into symbiosis with more than 50 legume species, including the agriculturally important common bean, (ii) outcompete other rhizobial species for nodulation of several legumes, and (iii) endure stressful soil conditions (e.g., high salt concentration and low pH) and high temperatures

Arylboronic Acid Catalyzed C-Alkylation and Allylation Reactions Using Benzylic Alcohols

: The arylboronic acid catalyzed dehydrative Calkylation of 1,3-diketones and 1,3-ketoesters using secondary benzylic alcohols as the electrophile is reported, forming new C−C bonds (19 examples, up to 98% yield) with the release of water as the only byproduct. The process is also applicable to the allylation of benzylic alcohols using allyltrimethylsilane as the nucleophile (12 examples, up to 96% yield)

Investigating biogeographic patterns of Rhizobium leguminosarum symbiovar viciae within the tribe Fabeae

Presentación en diapositivasNodulation is the symbiotic association of plants and diazotrophic bacteria that results in the formation of specialized organs (nodules) and allows fixation of atmospheric nitrogen. Rhizobial nodulation is widespread in Fabaceae with both promiscuous or exclusive hosts and/or rhizobia existing. An ideal group to explore these patterns is tribe Fabeae. Fabeae includes four genera: Ervilia Link, Ervum L., Vicia L., and Lathyrus L., and around 380 species distributed almost globally. They largely nodulate with Rhizobium leguminosarum symbiovar viciae. With the aim of evaluating the biogeographic patterns of rhizobia that colonize Fabeae species using a broader sampling, the genome of 68 strains of R. leguminosarum symbiovar viciae was sequenced. The nodules were collected from Lathyrus and Vicia hosts growing in Argentina, Canada, Chile, Greece (Crete), Japan, Spain, United Kingdom and United States and cultured to single strains. The DNA was extracted and then sent to MicrobesNG for library preparation and sequencing. Reads were trimmed and draft genomes were assembled. From the contigs, three sets of genes were extracted: (1) 120 non-mobile core genes from the chromosome (2) the 16S rRNA sequence, and (3) the nodulation genes nodA, nodC and nodD. The 16S was highly conserved across the accessions and was not informative to distinguish strains or geographical patterns. However, the set of 120 core genes gave a much more resolved picture allowing genospecies identification and revealing geographical patterns. The preliminary results using the core genes indicate a trend for geographical grouping over large areas. Our analysis consistently retrieved a Japanese clade and a South American clade with the remainder (over 50 accessions) belonging to a very widespread group from Europe and North America. Host plants were generally promiscuous and there was no apparent correlation with the evolutionary phylogeny of the hosts and their choice of rhizobial partners.Instituto de Recursos BiológicosFil: Trad, Rafaela. Royal Botanic Garden Edinburgh, Edinburgo, EscociaFil: Roberts, Sarah. University of California at San Francisco; Estados UnidosFil: Morales, Matias. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Recursos Biológicos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Morón. Facultad de Agronomía y Ciencias Agroalimentarias; ArgentinaFil: James , Euan. Hutton Institute; Reino UnidoFil: Kenicer, Gregory. Royal Botanic Garden Edinburgh; Escoci

Microwave response of hole and patch arrays

Copyright © 2010 American Physical SocietyThe electromagnetic response of two-dimensional square arrays of perfectly conducting square patches, and their complementary structures, is modeled utilizing a modal matching technique and employing Babinet’s principle. This method allows for the introduction of progressively higher diffracted orders and waveguide modes to be included in the calculation, hence aiding understanding of the underlying causal mechanism for the observed response. At frequencies close to, but below, the onset of diffraction, a near-complete reflection condition is predicted, even for low filling fractions: conversely, for high filling fractions a near-complete transmission condition results. These resonance phenomena are associated with evanescent diffraction, which is sufficiently strong to reverse the step change in transmission upon establishment of electrical continuity; i.e., the connected structure demonstrates increased transmission with increasing filling fraction.BAE Systems Ltd.Engineering and Physical Sciences Research Council (EPSRC

FDIR for a Biologically Inspired Trenchless Drilling Device

Failure Detection, Isolation and Recovery (FDIR) of autonomous systems working in hazardous conditions is essential. Methods of detection and recovery without intervention are required. This work describes the failure modes currently identified with an autonomous biologically inspired trenchless drilling robotic system. Inverse Simulation is used for detecting failures and is demonstrated on a simulation model of the robotic system. Results from the experiments, show that Inverse Simulation can be used to detect and identify system failures